JP7615537B2 - Raw material for negative electrode material for non-aqueous secondary battery, negative electrode material for non-aqueous secondary battery, negative electrode for non-aqueous secondary battery, and non-aqueous secondary battery - Google Patents

Description

The present invention relates to a raw material for a negative electrode material for a non-aqueous secondary battery and a negative electrode material for a non-aqueous secondary battery. The present invention also relates to a negative electrode for a non-aqueous secondary battery and a non-aqueous secondary battery that contain this negative electrode material for a non-aqueous secondary battery.

In recent years, the demand for high-capacity secondary batteries has been increasing with the miniaturization of electronic devices. In particular, non-aqueous secondary batteries, especially lithium ion secondary batteries, have attracted attention because they have higher energy density and superior rapid charge/discharge characteristics than nickel-cadmium batteries and nickel-metal hydride batteries. In particular, non-aqueous lithium secondary batteries consisting of positive and negative electrodes capable of absorbing and releasing lithium ions, and a non-aqueous electrolyte solution in which lithium salts such as _LiPF6 and _LiBF4 are dissolved, have been developed and put to practical use.

Various materials have been proposed as negative electrode materials for non-aqueous lithium secondary batteries, but graphitic carbon materials such as artificial graphite obtained by graphitizing natural graphite or coke, graphitized mesophase pitch, and graphitized carbon fiber are used because of their high capacity and excellent flatness of discharge potential. Amorphous carbon materials are also used because they are relatively stable against some electrolytes. Furthermore, carbon materials are used in which amorphous carbon is coated or attached to the surface of graphite particles, combining the two properties of high capacity and small irreversible capacity due to graphite and excellent stability with electrolytes due to amorphous carbon.

Recently, in the field of electric vehicles and the like, characteristics such as high capacity and excellent low-temperature input/output characteristics are emphasized, and from these viewpoints, among the negative electrode materials of the above-mentioned nonaqueous lithium secondary batteries, materials in which amorphous carbon is coated or attached to the surface of graphite particles are used. Among such materials, Patent Document 1 discloses a negative electrode material in which the rapid charging characteristics are improved by coating the graphite with amorphous carbon under specific conditions and performing an isotropic pressure treatment on the graphite. Patent Document 2 discloses a negative electrode material with high capacity and improved charge/discharge characteristics by controlling the atomic concentrations of sulfur and nitrogen elements present on the surface using coal tar pitch with a high quinoline content as a raw material for the amorphous carbon coated on the graphite particles. Patent Document 3 discloses a negative electrode material with low press load and improved low-temperature output characteristics due to a carbon material with specific thermal characteristics. Furthermore, Patent Document 4 discloses a negative electrode material with improved low-temperature input/output characteristics and high-temperature storage characteristics by being coated with specific amorphous carbon and having a specific pore volume.

WO2011/052452 WO2012/157590 JP 2017-045574 A JP 2018-163868 A

According to the studies of the present inventors, it has been found that the negative electrode materials for nonaqueous secondary batteries described in Patent Documents 1 to 4 cause plate swelling after charge/discharge cycles. That is, an object of the present invention is to provide a raw material for a negative electrode material for nonaqueous secondary batteries and a negative electrode material for nonaqueous secondary batteries that can provide a nonaqueous secondary battery having a high capacity, excellent rapid charging characteristics, and small plate swelling after charge/discharge cycles, as well as a negative electrode for a nonaqueous secondary battery and a nonaqueous secondary battery that contain the same.

As a result of intensive research by the inventors to solve the above problems, they discovered that the above problems can be solved by a negative electrode material for non-aqueous secondary batteries using graphite raw materials, in which the amount of mercury discharged/the amount of mercury injected (B/A) measured by mercury intrusion porosimetry is controlled to a specific range. That is, the gist of the present invention is as follows.

[1] A raw material for a negative electrode material for a non-aqueous secondary battery, comprising graphite, and having a value of the following formula (1) of 45% or more, where A is the amount of mercury injected and B is the amount of mercury released, as determined by mercury intrusion porosimetry:
Formula (1) B/A×100(%)
[2] The raw material for a negative electrode material for a non-aqueous secondary battery according to [1], wherein the amount of mercury intrusion A is 0.001 mL/g or more and 0.5 mL/g or less.
[3] The raw material for a negative electrode material for a non-aqueous secondary battery according to [1] or [2], wherein the amount of mercury discharged B is 0.0005 mL/g or more and 0.5 mL/g or less.
[4] The raw material for a negative electrode material for a non-aqueous secondary battery according to any one of [1] to [3], having a tap density of 0.7 g/cm ³ or more and 1.4 g/cm ³ or less.
[5] A negative electrode material for a non-aqueous secondary battery, comprising the negative electrode material raw material for a non-aqueous secondary battery according to any one of [1] to [4].
[6] The nonaqueous secondary battery negative electrode material according to [5], wherein the interplanar spacing (d002) obtained by X-ray diffraction is 0.34 nm or less, and the crystallite size (Lc) in the c-axis direction is 90 nm or more.
[7] The nonaqueous secondary battery negative electrode material according to [5] or [6], wherein the Raman _R1 value calculated from the following formula α is 0.15 or more and 1.00 or less.
Formula α:
[Raman R ₁ value]=[Intensity I _B of peak P _B at about 1360 cm ⁻¹ in Raman spectrum analysis]/[Intensity I _A of peak P _A at about 1580 cm ⁻¹ ]
[8] A non-aqueous secondary battery using the negative electrode material according to any one of [5] to [7].

The present invention provides a raw material for a negative electrode material for a non-aqueous secondary battery, a negative electrode material for a non-aqueous secondary battery, and a negative electrode for a non-aqueous secondary battery and a non-aqueous secondary battery that contain the same, which can provide a non-aqueous secondary battery that has a high capacity, excellent rapid charging characteristics, and small plate swelling after cycling.

FIG. 1 is a graph showing the relationship between the amount of mercury discharged/the amount of mercury injected (B/A) and cycle swelling in Examples 1 and 2 and Comparative Examples 1 to 3.

The present invention will be described in detail below, but the present invention is not limited to the following description, and can be modified as desired without departing from the gist of the present invention. In the present invention, when "~" is used to express a numerical value or physical property value before and after the value, the value before and after the value is included.

[Raw material for negative electrode material for non-aqueous secondary batteries]
The negative electrode material for a non-aqueous secondary battery according to one embodiment of the present invention (hereinafter, sometimes referred to as the "negative electrode material of the present invention") contains graphite and has a mercury intrusion porosimetry measured. If the amount of mercury (mL/g) is A and the amount of mercury discharged (mL/g) is B, then the ratio of the amount of mercury discharged/the amount of mercury injected (B/
A) × 100 is 45% or more.
The ratio of the amount of mercury discharged/the amount of mercury intrusion (B/A) is an index of the complexity of the structure within the particles of the raw material for the negative electrode material. The complexity of the structure within the particles leads to the magnitude of the residual stress within the particles. The magnitude of the residual stress may lead to the tendency of particle expansion occurring during charge-discharge cycles of the negative electrode material using this raw material. Therefore, the amount of mercury discharged/the amount of mercury injected (B/A) × 100 is , is usually 45% or more, more preferably 50% or more, even more preferably 55% or more, particularly preferably 60% or more, and most preferably 63% or more. The upper limit of the amount of mercury discharged/the amount of mercury intrusion (B/A)×100 is not particularly limited, but the lower the complexity of the intraparticle structure (i.e., the simpler the intraparticle structure), the higher the sphericity of the particles. The sphericity of the particles tends to decrease, and when the sphericity of the particles decreases, the lithium ion diffusion in the negative electrode using the negative electrode material made from this raw material decreases, and there is a risk that the adverse effects on load characteristics such as quick charging performance will become significant. Therefore, it is preferably 95% or less, more preferably 90% or less, even more preferably 85% or less, and most preferably 80% or less.
The amount of mercury intrusion (mL/g) A is not particularly limited, but a small A means that the amount of pores in the particles is small. This may lead to a deterioration in load characteristics such as input/output characteristics. Therefore, the amount of mercury injected (mL/g) A is preferably 0.001 mL/g or more, and more preferably 0.003 mL/g or more. The amount of mercury intrusion (mL/g) A is preferably 0.005 mL/g or more, more preferably 0.01 mL/g or more, and most preferably 0.03 mL/g or more. As for the upper limit of A, a large A means a large amount of pores in the particles, and a large amount of pores in the particles reduces the bulk density of the negative electrode material using this raw material, which leads to poor slurry preparation efficiency and electrode drying. Since this may lead to a decrease in efficiency, it is preferably 1.0 mL/g or less, more preferably 0.8 mL/g or less, even more preferably 0.6 mL/g or less, and more preferably 0. It is particularly preferably 4 mL/g or less, and most preferably 0.3 mL/g or less.
The amount of mercury discharged (mL/g) B is not particularly limited, but a small B reflects a small amount of intraparticle pores or a complex intraparticle structure. This may lead to a decrease in the load characteristics, such as the input/output characteristics, of the anode material using this raw material, and the latter is a reflection of the large residual stress in the particles. This may lead to concerns about particle expansion that occurs with charge/discharge cycles of the negative electrode material. Therefore, the amount of mercury discharged (mL/g) B is preferably 0.001 mL/g or more, and more preferably 0.005 mL/g or more. It is more preferable that the viscosity is 0.010 mL/g or more, even more preferable that the viscosity is 0.040 mL/g or more, and most preferable that the viscosity is 0.065 mL/g or more. The upper limit of the amount of mercury discharged (mL/g) B is set because a large B means that the amount of mercury injected (mL/g) A immediately before the measurement of B is large, and if A is too large, there are concerns as mentioned above. , preferably 1.0 mL/g or less, more preferably 0.6 mL/g or less, even more preferably 0.4 mL/g or less, and particularly preferably 0.2 mL/g or less. It is preferable that the concentration is 0.1 mL/g or less, and most preferable that the concentration is 0.1 mL/g or less.
The above-mentioned raw materials for the negative electrode material are preferable because, when contained in the negative electrode material, swelling of the electrode plate after cycles (cycle swelling) accompanying the charge and discharge of the secondary battery can be suppressed.

The negative electrode material for non-aqueous secondary batteries and the negative electrode material for non-aqueous secondary batteries of this embodiment have the effect of providing a non-aqueous secondary battery that has high capacity, excellent suppression of cycle swelling, and excellent rapid charging performance. The reason why the present invention has such an effect is unclear, but the following reasons are thought to be the cause.

In the negative electrode material of this embodiment, the amount of mercury discharged/the amount of mercury intrusion (B/A) is an index of the complexity of the intra-particle structure, and the smaller the B/A value, the more complex the intra-particle structure. The complexity of the intra-particle structure leads to the magnitude of the residual stress in the particles, and the magnitude of the residual stress in the particles is thought to lead to the tendency of particle expansion to occur during the charge-discharge cycle of the negative electrode material using this negative electrode material raw material. By making the value of B/A×100 45% or more, the complexity of the intra-particle structure is suppressed to a certain level, and the residual stress in the particles is suppressed, making it possible to suppress particle expansion during the charge-discharge cycle of the negative electrode material using this negative electrode material raw material, and it is thought to be excellent in suppressing cycle swelling of the negative electrode.

Furthermore, by maintaining the value of B/A x 100 at 63% or more, it is possible to further improve the rapid charging performance while effectively suppressing cycle swelling of the negative electrode. This is thought to be because the diffusion of lithium ions in the negative electrode is promoted, the lithium ion concentration gradient in the negative electrode becomes gentler, and concentration overvoltage is suppressed under conditions of use where material diffusion is rate-limiting, such as rapid charging.

[Physical Properties]
The negative electrode material according to one embodiment of the present invention satisfies (B/A)×100 described below. <Amount of mercury injected and amount of mercury discharged>
In the negative electrode raw material of the present invention, when the amount of mercury injected (mL/g) measured by mercury intrusion porosimetry is A and the amount of mercury released (mL/g) is B, the amount of mercury released/the amount of mercury injected (B/A)×100 is 45% or more.

As the device for the mercury porosimetry, a mercury porosimeter (Autopore 9520: manufactured by Micromeritics) can be used. A sample (negative electrode raw material) is weighed to a value of about 0.2 g, sealed in a powder cell, and degassed at room temperature under vacuum (50 μmHg or less) for 10 minutes to perform pretreatment. Subsequently, the pressure is reduced to 4 psia (about 28 kPa) and mercury is introduced into the cell, and the pressure is increased in steps from 4 psia (about 28 kPa) to 40,000 psia (about 280 MPa), and then decreased to 25 psia (about 170 kPa). The number of steps during pressure increase is 42 or more, and the number of steps during pressure decrease is 39 or more, and after a 10-second equilibration time in each step, the amount of mercury intrusion is measured. The pore distribution is calculated from the mercury intrusion curve obtained in this way using the Washburn formula. The calculation is based on the assumption that the surface tension (γ) of mercury is 485 dyne/cm and the contact angle (ψ) is 140°. The average pore diameter is defined as the pore diameter when the cumulative pore volume is 50%. From the thus obtained mercury intrusion behavior and mercury exit behavior, the amount of mercury intrusion (A) and the amount of mercury exit (B) were calculated as follows.
Mercury intrusion amount (A) = cumulative pore volume of 0.01 μm or more and 0.6 μm or less on the intrusion side (mL/g) Mercury escape amount (B) = mercury escape amount up to 25 psia (about 170 kPa) on the escape side (mL/g)

In addition, it is preferable that the negative electrode material according to one embodiment of the present invention satisfies the following physical properties:

(Circularity)
In the negative electrode material according to one embodiment of the present invention, the circularity determined by flow-type particle image analysis is preferably 0.88 or more, more preferably 0.90 or more, even more preferably 0.91 or more, particularly preferably 0.92 or more, and most preferably 0.93 or more. Such graphite with a high circularity is preferable because the degree of tortuosity of Li ion diffusion in the negative electrode material produced using it is reduced, the movement of the electrolyte in the interparticle voids becomes smooth, and the rapid charging characteristics can be improved. On the other hand, since the theoretical upper limit of this circularity is 1, it is usually less than 1, preferably 0.99 or less, more preferably 0.98 or less, and even more preferably 0.97 or less. From the viewpoint of ensuring the contact between the obtained negative electrode materials and improving the cycle characteristics, it is preferable that it is below the above upper limit.

The circularity was measured using a flow particle image analyzer (FPIA-2000, manufactured by Toa Medical Electronics Co., Ltd.).
The circularity is determined by measuring the particle size distribution based on the circle-equivalent diameter and calculating the average circularity. The circularity is defined by the following formula, where a circularity of 1 is a theoretical perfect sphere.
[Circularity] = [Perimeter of a circle having the same area as the projected shape of a particle] / [Actual perimeter of the projected shape of a particle]

In measuring this circularity, ion-exchanged water is used as the dispersion medium, and polyoxyethylene (20) monolaurate is used as the surfactant. The equivalent circle diameter is the diameter of a circle (equivalent circle) that has the same projected area as the photographed particle image, and the circularity is the ratio of the perimeter of the equivalent circle as the numerator to the perimeter of the photographed particle projected image as the denominator. The circularity is calculated by averaging the circularities of particles with measured equivalent diameters in the range of 1.5 to 40 μm.

(Tap Density)
The tap density of the negative electrode material raw material is preferably 0.60 g/ ^cm3 or more, more preferably 0.70 g/ ^cm3 or more, even more preferably 0.80 g/ ^cm3 or more, particularly preferably 0.855 g/ ^cm3 or more, and most preferably 0.90 g/ ^cm3 or more, while it is usually 1.40 g/cm3 ^or less, preferably 1.30 g/cm3 or ^less , and more preferably 1.20 g/cm3 or ^less .
The tap density is measured using a powder density measuring instrument, Tap Denser KYT-3000 (manufactured by Seishin Enterprise Co., Ltd.) Specifically, a sample is dropped into a 20 cc tap cell, the cell is filled to capacity, and then tapping is performed 1000 times with a stroke length of 10 mm, and the density at that time is defined as the tap density.

(Volume-based average particle size)
The volume-based average particle size (D50) of the negative electrode raw material is not particularly limited, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, even more preferably 8 μm or more, and particularly preferably 10 μm or more, and is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, even more preferably 20 μm or less, particularly preferably 16 μm or less, and most preferably 14 μm or less.
The average particle diameter (d50) is defined as a value measured by suspending 0.01 g of the composite particles in 10 mL of a 0.2 wt % aqueous solution of polyoxyethylene sorbitan monolaurate (an example of which is Tween 20 (registered trademark)) which is a surfactant, introducing the resulting suspension as a measurement sample into a commercially available laser diffraction/scattering type particle size distribution measurement device (for example, LA-920 manufactured by HORIBA), irradiating the measurement sample with 28 kHz ultrasonic waves at an output of 60 W for 1 minute, and then measuring the volume-based median diameter in the measurement device.

(BET specific surface area)
The BET specific surface area of the negative electrode material raw material is not particularly limited, but is usually 1.0 m ² /g or more, preferably 1.5 m ² /g or more, more preferably 2.0 m ² /g or more, even more preferably 3.0 m ² /g or more, particularly preferably 4.5 m ² /g or more, and most preferably 5.0 m ² /g or more. Also, it is usually 30.0 m ² /g or less, preferably 25.0 m ² /g or less, more preferably 20.0 m ² /g or less, even more preferably 16.0 m ² /g or less, particularly preferably 13.0 m ² /g or less, and particularly preferably 12.0 m ² /g or less.
The BET specific surface area (SA) can be measured using a Maxorb manufactured by Mountec Co., Ltd. Specifically, the sample is pre-dried under reduced pressure at 100° C. for 3 hours under nitrogen flow, then cooled to liquid nitrogen temperature, and the SA can be measured by a nitrogen adsorption BET single point method using a gas flow method, using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[Non-aqueous secondary battery negative electrode material]
The negative electrode material for a non-aqueous secondary battery of the present invention contains the above-mentioned raw material for the negative electrode material for a non-aqueous secondary battery of the present invention.
[Physical Properties]
(Raman _R1 value)
The Raman _R1 value in this specification is, as shown in the following formula α, the intensity I _A of the peak P _A at about 1580 cm ⁻¹ and the intensity P B of the peak P _B at about 1360 cm ⁻¹ in the Raman spectrum obtained by Raman spectroscopy for the negative electrode material. The intensity ratio I B /I _A is defined as the intensity ratio (I _B /I _A ) when the intensity I B of the peak at 1580 cm −1 is measured. Note that, “near 1580 cm ⁻¹ ” refers to the range of 1580 to 1620 cm ⁻¹ , and “near 1360 cm ⁻¹ ” refers to the range of 1580 to 1620 cm −1 . It refers to the range of 1350 to 1370 cm ⁻¹ .
The Raman _R1 value of the negative electrode material, represented by the following formula α, is not particularly limited, but is preferably 0.10 or more and 1.00 or less. The Raman R1 value is more preferably 0.15 or more. It is more preferably 0.20 or more, and particularly preferably 0.25 or more, while it is more preferably 0.80 or less, and further preferably 0.60 or less.
Formula α:
Raman R ₁ value=(Intensity I _B of peak P _B at about 1360 cm ⁻¹ in Raman spectrum analysis)/(Intensity I _A of peak P _A at about 1580 cm ⁻¹ )

<Raman characteristics of negative electrode material (Raman _R1 value, Raman full width at half maximum Δν _B (cm ⁻¹ ), Raman _R2 value, Raman _R3 value)>
(Raman _R1 value)
As described above, the Raman _R1 value in this specification is defined as the intensity ratio (I B /I A ) when measuring the intensity I _A of peak P _A near 1580 cm ^-1 and the intensity I _B of peak P _B near 1360 cm ^-1 in the Raman spectrum obtained by Raman spectroscopy for the negative electrode material, as shown in the following _{formula α .} Note that "near 1580 cm ^-1 " refers to the range of 1580 to 1620 cm ^-1 , and "near 1360 cm ^-1 " refers to the range of 1350 to 1370 cm ^-1 .
Formula α:
[Raman R ₁ value]=[Intensity I _B of peak P _B at about 1360 cm ⁻¹ in Raman spectrum analysis]/[Intensity I _A of peak P _A at about 1580 cm ⁻¹ ]

In this specification, the Raman full width at half maximum Δν _B (cm ⁻¹ ) is defined as the full width at half maximum of the peak P _B at about 1360 cm ⁻¹ in the Raman spectrum obtained by Raman spectroscopy for the negative electrode material. Note that "about 1360 cm ⁻¹ " refers to the range of 1350 to 1370 cm ⁻¹ .

The Raman _R2 value in this specification is defined as the intensity ratio (I C /I A ) when measuring the intensity I _A of the peak P _A near 1580 cm ^-1 in the Raman spectrum obtained by Raman spectroscopy for the negative electrode material, and the intensity I _C of the valley (minimum value) between the peak P _A near 1580 cm ^-1 and the peak P _B near 1360 cm ^-1 , as shown in the following _{formula β} . Note that "near 1580 cm ^-1 " refers to the range of 1580 to 1620 cm ^-1 , and "near 1360 cm ^-1 " refers to the range of 1350 to 1370 cm ^-1 .
Formula β:
[Raman _R2 value]=[Intensity I _C of the valley (minimum value) between peak P _A near 1580 cm ⁻¹ and peak P _B near 1360 cm ⁻¹ in Raman spectrum analysis]/[Intensity I _A of peak P _A near 1580 cm ⁻¹ ]

In one embodiment of the present invention, the Raman _R3 value is defined as the intensity ratio (I C /I B ) when measuring the intensity I _B of the peak P _B near 1360 cm ^-1 in the Raman spectrum obtained by Raman spectroscopy for the negative electrode material, and the intensity I _C of the valley (minimum value) between the peak P _A near 1580 cm ^-1 and the peak P _B near 1360 cm ^-1 , as shown in the following _{formula γ} . Note that "near 1580 cm ^-1 " refers to the range of 1580 to 1620 cm ^-1 , and "near 1360 cm ^-1 " refers to the range of 1350 to 1370 cm ^-1 .
Formula γ:
[Raman _R3 value]=[Intensity I _C of the valley (minimum value) between peak P _A at about 1580 cm ⁻¹ and peak P _B at about 1360 cm ⁻¹ in Raman spectrum analysis]/[Intensity I _B of peak P _B at about 1360 cm ⁻¹ ]

The Raman _R1 value of the negative electrode material according to one embodiment of the present invention is usually 0.15 or more, preferably 0.20 or more, more preferably 0.25 or more, even more preferably 0.30 or more, particularly preferably 0.32 or more, and most preferably 0.35 or more. Also, it is usually 1.00 or less, preferably 0.80 or less, more preferably 0.70 or less, even more preferably 0.65 or less, and particularly preferably 0.50 or less.

The Raman full width at half maximum (Δν _B ) of the negative electrode material according to one embodiment of the present invention is usually 65 cm ⁻¹ or more, preferably 70 cm ⁻¹ or more, more preferably 80 cm ⁻¹ or more, even more preferably 85 cm ⁻¹ or more, particularly preferably 90 cm ⁻¹ or more, and most preferably 100 cm ⁻¹ or more. Also, it is usually 400 cm ⁻¹ or less, preferably 300 cm ⁻¹ or less, more preferably 250 cm ⁻¹ or less, even more preferably 200 cm ⁻¹ or less, particularly preferably 170 cm ⁻¹ or less, and most preferably 145 cm ⁻¹ or less.

The Raman _R2 value of the negative electrode material according to one embodiment of the present invention is preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.07 or more, particularly preferably 0.09 or more, and most preferably 0.11 or more. Also, it is usually 0.60 or less, preferably 0.40 or less, more preferably 0.30 or less, even more preferably 0.25 or less, and particularly preferably 0.22 or less.

These Raman characteristics are indices of the graphite crystallinity of the negative electrode material surface, and the larger these values are, the lower the graphite crystallinity of the negative electrode material surface (the higher the amorphousness). The Raman _R1 value (I _B /I _A ) is influenced not only by the degree of graphitization (perfection of the graphite structure) but also by the ratio of edges and crystal boundaries of the graphite crystal surface, and the larger the Raman _R1 value is, the lower the degree of graphitization and the higher the ratio of edges and crystal boundaries tends to be. For this reason, the Raman R1 value may be large not only when a part of the negative electrode material surface has amorphous carbonaceous matter, but also when the edge ratio is increased due to graphite being crushed in a fractured manner. On the other hand, the Raman full width at half _maximum (Δν _B ) is relatively less influenced by the ratio of edges and crystal boundaries of the graphite crystal surface, and tends to be more influenced by the degree of graphitization (perfection of the graphite structure). For this reason, the Raman full width at half maximum (Δν _B ) tends to increase due to the presence of amorphous carbonaceous matter on a portion of the surface of the negative electrode material, but the change tends to be relatively small when the edge ratio is increased by pulverization or the like. In addition, the intensity I _C of the valley (minimum value) between the peak P _A near 1580 cm ^-1 and the peak P _B near 1360 cm ^-1 is said to be derived from graphite crystal structure defects and SP3 nature in the amorphous carbon structure, and the Raman R ₂ value (I _C /I _A ) and the Raman R ₃ value (I _C /I _B ) tend to reflect the influence of the degree of graphitization (perfection of the local graphite structure). For this reason, the Raman R ₂ value (I _C /I _A ) and the Raman R ₃ value (I _C /I _B ) tend to increase due to the presence of amorphous carbonaceous matter on a portion of the surface of the negative electrode material, but the change tends to be relatively small when the edge ratio is increased by pulverization or the like.

The parameter values of these Raman characteristics being equal to or greater than the lower limit values indicates that the amorphousness of the negative electrode material surface is within an appropriate range, and Li ions are easily inserted and removed, which tends to improve low-temperature input/output characteristics. On the other hand, when the parameter values of these Raman characteristics are equal to or less than the upper limit values, the increase in the effect of irreversible capacity of highly amorphous carbon and the increase in side reactions with the electrolyte are suppressed, and the decrease in the initial charge/discharge efficiency of the lithium-ion secondary battery and the increase in the amount of gas generated are prevented, which tends to improve the battery capacity.

The Raman spectrum is measured by a Raman spectrometer. Specifically, the particles to be measured are loaded into a measurement cell by gravity, and the measurement cell is irradiated with argon ion laser light while the measurement cell is rotated in a plane perpendicular to the laser light.
Wavelength of argon ion laser light: 514.5 nm
Laser power on sample: 25 mW
Resolution: 4 cm ^-1
Measurement range: 1100 cm ^-1 to 1730 cm ^-1 Peak intensity measurement, peak full width at half maximum measurement: background processing, smoothing processing (convolution 5 points by simple average)

<BET specific surface area (SA)>
The negative electrode material according to one embodiment of the present invention has a specific surface area (SA) measured by the BET method of preferably 0.5 m ² /g or more, more preferably 1.0 m ² /g or more, and further preferably It is preferably 1.2 m ² /g or more, particularly preferably 1.5 m ² /g or more, and most preferably 1.8 m ² /g or more, while it is preferably 10.0 m ² /g or less, and more preferably is preferably 6.5 m ² /g or less, more preferably 5.0 m ² /g or less, particularly preferably 4.0 m ² /g or less, and most preferably 3.0 m ² /g or less. When the SA is equal to or greater than this upper limit, sites for the ingress and egress of Li ions are secured, and the rapid charge/discharge characteristics of the lithium ion secondary battery tend to be good. Since the activity against the electrolyte does not become excessive, side reactions with the electrolyte are suppressed, a decrease in the initial charge/discharge efficiency of the battery and an increase in the amount of gas generated are prevented, and the battery capacity tends to be improved. The BET specific surface area (SA) is measured by the same method as that described for the raw material of the negative electrode material.

<Tap density>
The tap density (g/cm ³ ) of the negative electrode material according to one embodiment of the present invention is preferably 0.60 g/cm ³ or more, more preferably 0.80 g/cm ³ or more, even more preferably 1.00 g/cm ³ or more, particularly preferably 1.10 g/cm ³ or more, and most preferably 1.15 g/cm 3 or more, and is preferably 1.40 g/cm ³ or less, more preferably 1.35 g/cm ³ or less, even more preferably 1.30 g/cm ³ or less, and particularly preferably 1.24 g/cm ³ or less. If the tap density is equal to or greater than the lower limit, the processability such as streaking during electrode plate preparation is improved, the packing of the negative electrode material layer is improved, so that the rolling property is good and a high-density negative electrode sheet can be easily formed, and high density is possible. When the electrode body is formed, the curvature of the Li ion migration path is reduced, and the shape of the interparticle voids is regular, so that the movement of the electrolyte is smooth and the rapid charge/discharge characteristics are improved. Also, if the tap density is equal to or less than the upper limit, the particles have a moderate space on the surface and inside, so that the particles do not become too hard, and the electrode pressability is excellent, and the rapid charge/discharge characteristics are excellent. The tap density is measured by the same method as described for the negative electrode material raw material.

<Interplanar spacing (d002) and crystallite size (Lc)>
In the negative electrode material according to one embodiment of the present invention, the crystallinity (degree of graphitization) is preferably such that the interplanar spacing (d002) of the (002) plane determined by the wide-angle X-ray diffraction method according to the Gakushin method is 0.340 nm or less, and the size of the crystallite in the c-axis direction (Lc) is 90 nm or more. The d002 value is more preferably 0.338 nm or less, and even more preferably 0.337 nm or less. Furthermore, Lc is more preferably 95 nm or more, and even more preferably 100 nm or more. When d002 and Lc are in the above ranges, the discharge capacity is increased, which is preferable from the viewpoint of increasing the capacity of the battery.

<Circularity>
In the negative electrode material according to one embodiment of the present invention, the circularity determined by flow-type particle image analysis is preferably 0.88 or more, more preferably 0.90 or more, even more preferably 0.91 or more, particularly preferably 0.92 or more, and most preferably 0.93 or more. In such a negative electrode material with a high circularity, the degree of tortuosity of Li ion diffusion is reduced, the movement of the electrolyte in the interparticle voids is smooth, and rapid charge and discharge characteristics can be improved, which is preferable. On the other hand, since the theoretical upper limit of this circularity is 1, it is usually less than 1, preferably 0.99 or less, more preferably 0.98 or less, and even more preferably 0.97 or less. From the viewpoint of ensuring contact between the obtained negative electrode materials and improving cycle characteristics, it is preferable that it is below the above upper limit. The circularity is determined by the same method as that described in the negative electrode material raw material.

<Volume-based average particle diameter (average particle diameter d50)>
In the negative electrode material according to one embodiment of the present invention, the volume-based average particle diameter (also referred to as "average particle diameter d50") is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, particularly preferably 5 μm or more, and most preferably 8 μm or more. Also, it is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, particularly preferably 20 μm or less, and most preferably 14 μm or less. When the value of d50 is equal to or greater than the lower limit, there is a tendency to easily prevent an increase in irreversible capacity and a loss of initial battery capacity, while when the value of d50 is equal to or less than the upper limit, there is a tendency to prevent process inconveniences such as streaking during slurry application, and to improve rapid charge/discharge characteristics and low-temperature input/output characteristics. The volume-based average particle diameter is determined by the same method as that described for the negative electrode material raw material.

[Production method]
The method for producing a raw material for a negative electrode material for a non-aqueous secondary battery according to one embodiment of the present invention is not particularly limited as long as it contains graphite and can produce a graphite such that the mercury elution amount/mercury elution amount (B/A) x 100 satisfies 45% or more when the mercury elution amount (mL/g) measured by mercury porosimetry is A and the mercury elution amount (mL/g) is B. For example, the graphite can be produced by pressurizing spherical graphite that has been subjected to a spheroidizing treatment. Examples of the pressurizing treatment include anisotropic and isotropic pressurizing treatments, but isotropic pressurizing treatment is preferred from the viewpoint of controlling the mercury elution amount/mercury elution amount (B/A) within a specific range. In addition, the conditions for the pressurizing treatment are not particularly limited, but by treating at 50 MPa or more and 300 MPa or less, the mercury elution amount/mercury elution amount (B/A) can be controlled within a specific range. The conditions of the pressure treatment are preferably 100 MPa or more, more preferably 120 MPa or more, even more preferably 140 MPa or more, particularly preferably 160 MPa or more, most preferably 180 MPa or more, and also preferably 280 MPa or less, more preferably 260 MPa or less, even more preferably 240 MPa or less, particularly preferably 230 MPa or less, and most preferably 220 MPa or less, from the viewpoint of controlling the mercury discharge amount/mercury intrusion amount (B/A) within a specific range. Specifically, the above-mentioned production method is, for example, pulverizing natural graphite, mixing the pulverized natural graphite with a granulating agent to perform a spheroidizing treatment, and further removing the granulating agent by heat treatment to obtain spheroidized graphite. The obtained spheroidized graphite is pressurized, and the obtained molded product is crushed and classified, thereby making it possible to produce a raw material for a negative electrode material for a non-aqueous secondary battery in which the mercury discharge amount/mercury intrusion amount (B/A) is controlled within a specific range.
In addition, the manufacturing method of the negative electrode material for non-aqueous secondary batteries according to one embodiment of the present invention is not particularly limited, but it can be manufactured by mixing the raw material for the negative electrode material for non-aqueous secondary batteries according to one embodiment of the present invention with an amorphous carbon precursor (raw material of amorphous carbon) and firing it. Specifically, it is possible to adjust the pore volume by pressure treatment as spherical graphite, achieve a specific range of mercury withdrawal amount/mercury intrusion amount, and also, it is preferable to use an amorphous carbon precursor with low ash content, metal impurity amount, quinoline insoluble content (Qi), etc., suitable for the development of carbon structure, and to fire it in an inert atmosphere at a moderate firing temperature.

<Graphite>
The negative electrode material according to one embodiment of the present invention includes graphite. The graphite used to manufacture the negative electrode material according to one embodiment of the present invention preferably has the following types and physical properties. The measurement conditions and definitions of the physical properties of graphite are the same as those described for the negative electrode material described above, unless otherwise specified.

The type of graphite is not particularly limited as long as it is capable of absorbing and releasing lithium ions, and may be either natural graphite or artificial graphite. Natural graphite may be any of flake graphite, lump graphite, and earthy graphite, but graphite with few impurities is preferable, and it is preferable to use it after performing a known purification process as necessary. Examples of artificial graphite include coal tar pitch, coal-based heavy oil, atmospheric residual oil, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene silicide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin, which are graphitized by baking at a temperature usually in the range of 2500°C or higher and usually 3200°C or lower. In this case, silicon-containing compounds and boron-containing compounds can also be used as graphitization catalysts.

The crystallinity (degree of graphitization) of graphite is usually such that the interplanar spacing (d002) of the (002) plane measured by wide-angle X-ray diffraction is 0.335 nm or more and less than 0.340 nm. The d002 value is preferably 0.338 nm or less, more preferably 0.337 nm or less, and even more preferably 0.336 nm or less.

From the viewpoint of rapid charge and discharge characteristics, the shape of the graphite is preferably spherical graphite (spheroidized graphite). As a method for spheroidizing graphite particles, spherical graphite particles can be manufactured by performing a spheroidization process using a known technique. For example, the spheroidization process can be performed using an apparatus that repeatedly applies mechanical actions such as compression, friction, shear force, etc., including particle interactions, mainly impact force, to the particles. Specifically, the apparatus used for the spheroidization process is preferably an apparatus that has a rotor with many blades installed inside a casing, and that rotates at high speed to apply mechanical actions such as impact compression, friction, shear force, etc. to the carbon material introduced inside, thereby performing surface treatment. In addition, it is preferable that the apparatus has a mechanism for repeatedly applying mechanical actions by circulating graphite particles. Specific examples of the apparatus include a hybridization system (manufactured by Nara Machinery Works), a Cryptron (manufactured by EarthTechnica), a CF mill (manufactured by Ube Industries, Ltd.), a Mechanofusion system (manufactured by Hosokawa Micron Corporation), and a Theta Composer (manufactured by Tokuju Kogyosho Co., Ltd.). Among these, the hybridization system manufactured by Nara Machinery Works is preferred. For example, when the above-mentioned apparatus is used for the treatment, the peripheral speed of the rotating rotor is not particularly limited, but is preferably 30 m/sec to 100 m/sec, more preferably 40 m/sec to 100 m/sec, and even more preferably 50 m/sec to 100 m/sec. In addition, the treatment can be performed by simply passing the carbonaceous material through the apparatus, but it is preferable to circulate or retain the carbonaceous material in the apparatus for 30 seconds or more, and more preferably to circulate or retain the carbonaceous material in the apparatus for 1 minute or more. In addition, spherical graphite obtained by granulating multiple pieces of scaly or flaky graphite, graphite such as ground graphite fine powder, and a granulating agent using the method described in Patent Document 4 may be used.

(Circularity)
The graphite used in the negative electrode material raw material according to one embodiment of the present invention has a circularity of 0.88 or more, more preferably 0.90 or more, even more preferably 0.91 or more, particularly preferably 0.92 or more, and most preferably 0.93 or more, as determined by flow-type particle image analysis. Graphite with such a high circularity is preferable because the degree of tortuosity of Li ion diffusion in the negative electrode material produced using it is reduced, and the movement of the electrolyte in the interparticle voids becomes smooth, thereby improving the rapid charge and discharge characteristics. On the other hand, since the theoretical upper limit of this circularity is 1, it is usually less than 1, preferably 0.99 or less, more preferably 0.98 or less, and even more preferably 0.97 or less. From the viewpoint of ensuring contact between the obtained negative electrode materials and improving cycle characteristics, it is preferable that it is below the above upper limit.

(Tap Density)
The tap density of graphite is preferably 0.60 g/ ^cm3 or more, more preferably 0.70 g/ ^cm3 or more, even more preferably 0.80 g/cm3 or ^more , particularly preferably 0.855 g/cm3 or ^more , and most preferably 0.90 g/cm3 or ^more , while it is usually 1.40 g/cm3 ^or less, preferably 1.30 g/ ^cm3 or less, and more preferably 1.20 g/cm3 or ^less .

(Volume-based average particle size)
The volume-based average particle diameter (D50) of graphite is not particularly limited, but is usually 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more, and is usually 50 μm or less, preferably 40 μm or less, and more preferably 30 μm or less.

(BET specific surface area)
The BET specific surface area of the graphite is not particularly limited, but is usually 1.0 m ² /g or more, preferably 1.5 m ² /g or more, more preferably 2.0 m ² /g or more, even more preferably 3.0 m ² /g or more, particularly preferably 4.5 m ² /g or more, and most preferably 5.0 m ² /g or more. Also, it is usually 30.0 m ² /g or less, preferably 25.0 m ² /g or less, and more preferably 20.0 m ² /g or less.

(Raman _R1 value)
The Raman _R1 value of graphite, represented by the following formula α, is not particularly limited, but is preferably 0.10 or more and 1.00 or less. The Raman R1 value is more preferably 0.15 or more, even more preferably 0.20 or more, and particularly preferably 0.25 or more, while more preferably 0.80 or less, and even more preferably 0.60 or less.
Formula α:
Raman R ₁ value=(Intensity I _B of peak P _B at about 1360 cm ⁻¹ in Raman spectrum analysis)/(Intensity I _A of peak P _A at about 1580 cm ⁻¹ )

<Graphite pressure treatment>
The manufacturing method of the negative electrode material according to one embodiment of the present invention preferably includes a step of pressurizing graphite. The method of pressurizing graphite is not particularly limited as long as it is a method capable of applying pressure, and examples of the method include placing the graphite as a raw material in a container such as a rubber mold, and performing hydrostatic isotropic pressurizing treatment using water as a pressurizing medium, and air pressure isotropic pressurizing treatment using a gas such as air as a pressurizing medium. Alternatively, the graphite as a raw material may be filled in a mold, and pressurized in a certain direction by a uniaxial press.

The pressure of the pressure medium for the graphite pressure treatment is preferably in the range of 5 to 400 MPa, more preferably in the range of 30 to 350 MPa, and even more preferably in the range of 50 to 300 MPa. If the pressure is equal to or higher than the lower limit, the pore volume can be made smaller. Furthermore, if the pressure is equal to or lower than the upper limit, there is a tendency for the increase in the specific surface area of the resulting negative electrode material to be more easily suppressed.

<Compositing of anode raw materials with amorphous carbon>
The negative electrode material according to one embodiment of the present invention preferably contains graphite having amorphous carbon on at least a part of its surface. The amorphous carbon composite treatment is carried out by mixing the graphite-containing negative electrode material raw material and an amorphous carbon precursor (amorphous carbon raw material) and baking the mixture. By carrying out the amorphous carbon composite treatment of the graphite-containing negative electrode material raw material under appropriate conditions, it becomes easier to control the cumulative pore volume to within the above-mentioned range.

Amorphous carbon precursors include, but are not limited to, organic substances such as tar, pitch, aromatic hydrocarbons such as naphthalene, anthracene and their derivatives, and thermoplastic polymers such as phenolic resins and polyvinyl alcohol. These organic precursors may be used alone or in combination of two or more. Among these, tar, pitch and aromatic hydrocarbons are preferred from the viewpoint of the ease with which the carbon structure can be developed.

The ash content of the amorphous carbon precursor is preferably 1 wt % or less, more preferably 0.5 wt % or less, and even more preferably 0.1 wt % or less, based on the total weight of the amorphous carbon precursor. The lower limit of the ash content is usually 0.1 ppm by weight or more. When the ash content of the amorphous carbon precursor is within the above range, the thermal properties are good.

The amount of metal impurities contained in the amorphous carbon precursor in the present invention is defined as the total content of Fe, Al, Si, and Ca relative to the total weight of the amorphous carbon precursor divided by the carbon residue ratio. It is preferably 1000 ppm by weight or less, more preferably 400 ppm by weight or less, even more preferably 100 ppm by weight or less, particularly preferably 50 ppm by weight or less, and usually 0.1 ppm by weight or more, relative to the total weight of the amorphous carbon precursor. When the amount of metal impurities contained in the amorphous carbon precursor is within the above range, the thermal properties are good.

The quinoline insoluble matter (Qi) contained in the amorphous carbon precursor is preferably 5 wt% or less, more preferably 2 wt% or less, even more preferably 1 wt% or less, particularly preferably 0.5 wt% or less, and most preferably 0.1 wt% or less, based on the total weight of the amorphous carbon precursor. When the quinoline insoluble matter (Qi) contained in the amorphous carbon precursor is within the above range, the thermal properties are good.

After the graphite and the amorphous carbon precursor are mixed, the mixture is fired. The firing temperature is preferably 950°C or higher, more preferably 1000°C or higher, even more preferably 1050°C or higher, particularly preferably 1100°C or higher, and most preferably 1150°C or higher. On the other hand, it is preferably 2000°C or lower, more preferably 1800°C or lower, even more preferably 1600°C or lower, and especially preferably 1500°C or lower. The firing time is preferably 0.5 hours or higher, more preferably 1 hour or higher, while on the other hand, it is preferably 1000 hours or lower, more preferably 500 hours or lower, and even more preferably 100 hours or lower. When the firing temperature and time are within the above ranges, the thermal properties are good.

The atmosphere during firing is preferably an inert atmosphere. Specifically, there are methods for reducing the oxygen concentration by circulating an inert gas such as nitrogen or argon, methods for discharging oxygen from the system by decompression and restoring the pressure with nitrogen or argon, and methods for reducing the oxygen contained in the furnace atmosphere by filling the product with a sacrificial material such as coke breeze. The oxygen concentration in the system can be controlled by the amount and time of inert gas flow, the degree of decompression, and the filling conditions of the sacrificial material. The oxygen concentration (volume concentration) is preferably 3% or less, more preferably 1% or less, even more preferably 1000 ppm or less, particularly preferably 500 ppm or less, and most preferably 100 ppm or less. If the oxygen concentration exceeds the above range, the development of the carbon structure of the amorphous carbonaceous material is inhibited, and favorable thermal properties tend not to be obtained.

The mixing ratio of the amorphous carbon precursor when the amorphous carbon precursor is mixed with the graphite should be appropriately selected based on the composition of the target composite particle, and the amount of the amorphous carbon precursor relative to the graphite as the carbon residue (amorphous carbon) is usually 0.01% or more, preferably 0.1% or more, more preferably 0.5% or more, even more preferably 1% or more, particularly preferably 2% or more, and most preferably 3% or more, in terms of weight ratio ([weight of amorphous carbon]/[weight of graphite]×100). On the other hand, it is preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. When this weight ratio is in the above range, it is preferable in terms of high capacity and easy insertion and desorption of Li ions, and therefore excellent low-temperature input/output characteristics, rapid charge/discharge characteristics, and cycle characteristics.

<Other Processing>
In order to produce the negative electrode material according to one embodiment of the present invention, the composite particles obtained by the above-mentioned production method may be subjected to a separate pulverization process.

Examples of coarse crushers used in the crushing process include jaw crushers, impact crushers, and cone crushers. Examples of intermediate crushers include roll crushers and hammer mills. Examples of fine crushers include ball mills, vibration mills, pin mills, stirring mills, and jet mills. Among these, ball mills and vibration mills are preferred from the viewpoint of short crushing time and processing speed.

The grinding speed is set appropriately depending on the type and size of the equipment. For example, in the case of a ball mill, it is usually 50 rpm or more, preferably 100 rpm or more, more preferably 150 rpm or more, and even more preferably 200 rpm or more. It is also usually 2500 rpm or less, preferably 2300 rpm or less, and more preferably 2000 rpm or less. If the speed is too fast, it tends to be difficult to control the particle size, and if the speed is too slow, the processing speed tends to be slow.

The grinding time is usually 30 seconds or more, preferably 1 minute or more, more preferably 1 minute 30 seconds or more, and even more preferably 2 minutes or more. Also, it is usually 3 hours or less, preferably 2.5 hours or less, and more preferably 2 hours or less. If the grinding time is too short, it tends to be difficult to control the particle size, and if the grinding time is too long, productivity tends to decrease.

In the case of a vibration mill, the grinding speed is usually 50 rpm or more, preferably 100 rpm or more, more preferably 150 rpm or more, and even more preferably 200 rpm or more. Also, it is usually 2500 rpm or less, preferably 2300 rpm or less, and more preferably 2000 rpm or less. If the speed is too fast, it tends to be difficult to control the particle size, and if the speed is too slow, the processing speed tends to be slow.

The grinding time is usually 30 seconds or more, preferably 1 minute or more, more preferably 1 minute 30 seconds or more, and even more preferably 2 minutes or more. Also, it is usually 3 hours or less, preferably 2.5 hours or less, and more preferably 2 hours or less. If the grinding time is too short, it tends to be difficult to control the particle size, and if the grinding time is too long, productivity tends to decrease.

To produce the negative electrode material according to one embodiment of the present invention, the composite particles obtained by the above-mentioned production method may be subjected to a particle size classification process. The classification process is carried out under conditions in which the mesh size is usually 53 μm or less, preferably 45 μm or less, and more preferably 38 μm or less.

There are no particular limitations on the equipment used for classification, but for example, in the case of dry sieving, a rotary sieve, a shaking sieve, a swirling sieve, a vibrating sieve, etc. can be used; in the case of dry airflow classification, a gravity classifier, an inertia classifier, a centrifugal classifier (classifier, cyclone, etc.), etc. can be used; in the case of wet sieving, a mechanical wet classifier, a hydraulic classifier, a sedimentation classifier, a centrifugal wet classifier, etc. can be used.

[Non-aqueous secondary battery negative electrode]
The negative electrode for a non-aqueous secondary battery according to one embodiment of the present invention (hereinafter, sometimes referred to as the "negative electrode of the present invention") comprises a current collector and an active material layer formed on the current collector. and the active material layer contains the negative electrode material according to one embodiment of the present invention.

To make a negative electrode using the above negative electrode material, the negative electrode material is mixed with a binder resin to form a slurry in an aqueous or organic medium, and a thickener is added if necessary, and the slurry is applied to a current collector and dried.

As the binder resin, it is preferable to use one that is stable against non-aqueous electrolyte and is water-insoluble. For example, rubber-like polymers such as styrene-butadiene rubber, isoprene rubber, and ethylene-propylene rubber; synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyacrylic acid, and aromatic polyamide; thermoplastic elastomers such as styrene-butadiene-styrene block copolymers and their hydrogenated products, styrene-ethylene-butadiene, styrene copolymers, styrene-isoprene and styrene block copolymers and their hydrogenated products; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, ethylene-vinyl acetate copolymers, and copolymers of ethylene and α-olefins having 3 to 12 carbon atoms; fluorinated polymers such as tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride, polypentafluoropropylene, and polyhexafluoropropylene. As the organic medium, for example, N-methylpyrrolidone and dimethylformamide can be used.

The binder resin is usually used in an amount of 0.1 part by weight or more, preferably 0.2 part by weight or more, per 100 parts by weight of the negative electrode material. By using 0.1 parts by weight or more of the binder resin per 100 parts by weight of the negative electrode material, the binding strength between the negative electrode materials and between the negative electrode material and the current collector becomes sufficient, and it is possible to prevent a decrease in battery capacity and a deterioration in recyclability due to the negative electrode material peeling off from the negative electrode.

The amount of binder resin used is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, per 100 parts by weight of the negative electrode material. By using 10 parts by weight or less of the binder resin per 100 parts by weight of the negative electrode material, it is possible to prevent a decrease in the capacity of the negative electrode and to prevent problems such as the impediment of the entry and exit of alkaline ions such as lithium ions into the negative electrode material.

Examples of thickeners to be added to the slurry include water-soluble celluloses such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, polyvinyl alcohol, and polyethylene glycol. Among these, carboxymethyl cellulose is preferred. The thickener is preferably used in an amount of usually 0.1 to 10 parts by weight, and particularly 0.2 to 7 parts by weight, per 100 parts by weight of the negative electrode material.

As the negative electrode current collector, any material that has been known to be usable for this purpose, such as copper, copper alloy, stainless steel, nickel, titanium, and carbon, may be used. The current collector is usually in the form of a sheet, and it is also preferable to use one with an uneven surface, a net, a punched metal, etc.

After the slurry of the negative electrode material and the binder resin is applied to the current collector and dried, it is preferable to increase the density of the active material layer formed on the current collector by pressing it to increase the battery capacity per unit volume of the negative electrode active material layer. The density of the active material layer is preferably in the range of 1.2 g/cm ³ to 1.8 g/cm ³ , and more preferably 1.3 g/cm ³ to 1.6 g/cm ^3. By making the density of the active material layer equal to or greater than the lower limit, it is possible to prevent a decrease in the battery capacity due to an increase in the thickness of the electrode. In addition, by making the density of the active material layer equal to or less than the upper limit, the amount of electrolyte held in the voids decreases as the interparticle voids in the electrode decrease, and the mobility of alkaline ions such as lithium ions decreases, which prevents a decrease in rapid charge/discharge characteristics.

[Non-aqueous secondary battery]
The nonaqueous secondary battery according to one embodiment of the present invention is a nonaqueous secondary battery including a positive electrode, a negative electrode, and an electrolyte, and uses the negative electrode according to one embodiment of the present invention as the negative electrode. In particular, the positive electrode and the negative electrode used in the nonaqueous secondary battery according to one embodiment of the present invention are preferably positive electrodes and negative electrodes capable of absorbing and releasing Li ions, and the nonaqueous secondary battery according to one embodiment of the present invention is preferably a lithium ion secondary battery.

A nonaqueous secondary battery according to one embodiment of the present invention can be manufactured according to a conventional method, except that the negative electrode according to one embodiment of the present invention is used. In particular, the nonaqueous secondary battery according to one embodiment of the present invention is preferably designed to have a value of [negative electrode capacity]/[positive electrode capacity] of 1.01 to 1.5, and more preferably 1.2 to 1.4.

[Positive electrode]
As the positive electrode material serving as the positive electrode active material of the nonaqueous secondary battery according to one embodiment of the present invention, for example, lithium cobalt composite oxides having a basic composition represented by _LiCoO2 , lithium nickel composite oxides represented by _LiNiO2 , lithium transition metal composite oxides such as lithium manganese composite oxides represented by _LiMnO2 and _LiMn2O4 , transition metal oxides such as manganese dioxide, and _{mixtures of} these composite oxides may be used. Furthermore, _TiS2 , _FeS2 , _{Nb3S4 , Mo3S4} , _CoS2 , _V2O5 , _CrO3 , _{V3O3 , FeO2 , GeO2 , LiNi0.33Mn0.33Co0.33O2 , LiFePO4 ,} and the like may be used.

The positive electrode can be manufactured by mixing the positive electrode material with a binder resin, forming a slurry in an appropriate solvent, applying it to a current collector, and drying it. It is preferable to include a conductive material such as acetylene black or ketjen black in the slurry. If necessary, a thickener may also be included. The binder and thickener may be any of those well known for this purpose, such as those exemplified as those used in the manufacture of negative electrodes.

The amount of conductive material is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, per 100 parts by weight of the positive electrode material. The amount of thickener is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 7 parts by weight, per 100 parts by weight of the positive electrode material. Furthermore, the amount of binder resin to be mixed with 100 parts by weight of the positive electrode material is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 7 parts by weight, when the binder resin is slurried with water, whereas the amount of binder resin to be mixed with 100 parts by weight of the positive electrode material is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, when the binder resin is slurried with an organic solvent that dissolves the binder resin, such as N-methylpyrrolidone.

Examples of the positive electrode current collector include aluminum, titanium, zirconium, hafnium, niobium, tantalum, and alloys thereof. Among these, aluminum, titanium, tantalum, and alloys thereof are preferred, and aluminum and alloys thereof are most preferred.

[Electrolyte]
The electrolyte may be prepared by dissolving various lithium salts in a conventionally known non-aqueous solvent.

Examples of non-aqueous solvents that can be used include cyclic carbonates such as ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic esters such as γ-butyrolactone; cyclic ethers such as crown ether, 2-methyltetrahydrofuran, tetrahydrofuran, 1,2-dimethyltetrahydrofuran, and 1,3-dioxolane; and chain ethers such as 1,2-dimethoxyethane. Usually, two or more of these are used in combination. It is particularly preferable to use a cyclic carbonate and a chain carbonate, or to mix this with another solvent.

The electrolyte may contain compounds such as vinylene carbonate, vinyl ethylene carbonate, succinic anhydride, maleic anhydride, propane sultone, and diethyl sulfone, and difluorophosphates such as lithium difluorophosphate. In addition, an overcharge inhibitor such as diphenyl ether and cyclohexylbenzene may be added.

Examples of the electrolyte to be dissolved in the non-aqueous solvent include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(CF ₃ CF ₂ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ ) and LiC(CF ₃ SO ₂ ) _3. The concentration of the electrolyte in the electrolytic solution is usually 0.5 mol/L to 2 mol/L, and preferably 0.6 mol/L to 1.5 mol/L.

[Separator]
In the nonaqueous secondary battery according to one embodiment of the present invention, a separator is preferably used between the positive electrode and the negative electrode, and as such a separator, a porous sheet or nonwoven fabric made of polyolefin such as polyethylene or polypropylene is preferably used.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not exceed the gist of the invention. Note that the various manufacturing conditions and evaluation result values in the following examples are meant as preferred upper or lower limit values in the embodiments of the present invention, and the preferred range may be a range defined by a combination of the above-mentioned upper or lower limit values and the values of the following examples or values between the examples.

<Preparation of negative electrode sheet>
A negative electrode material prepared under the conditions described below was used as a negative electrode active material to prepare an electrode plate having an active material layer with an active material layer density of 1.5±0.03 g/cm ^3. Specifically, 50.00±0.02 g of the negative electrode material, 50.00±0.02 g of a 1 wt% carboxymethylcellulose sodium salt aqueous solution (0.500 g in terms of solid content), and 1.00±0.05 g of a styrene-butadiene rubber aqueous dispersion with a weight average molecular weight of 270,000 (0.5 g in terms of solid content) were mixed with 50.00±0.02 g of the negative electrode material, and the mixture was stirred for 5 minutes in a Keyence hybrid mixer and degassed for 30 seconds to obtain a slurry.

This slurry was applied to a width of 10 cm using a die coater on a copper foil with a thickness of 10 μm, which was used as a current collector, so that the negative electrode material adhered to 10.00±0.2 mg/ ^cm2. After drying, the slurry was cut to a width of 5 cm and roll-pressed using a roller with a diameter of 20 cm to adjust the density of the active material layer to 1.5±0.03 g/ ^cm3, thereby obtaining an electrode sheet.

<Preparation of Positive Electrode Sheet>
The positive electrode was prepared as follows. First, 85% by weight of lithium nickel-manganese-cobalt oxide (LiNiMnCoO ₂ ) as a positive electrode active material, 10% by weight of acetylene black as a conductive material, and 5% by weight of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone solvent to obtain a slurry. This slurry was applied to a 15 μm thick aluminum foil current collector using a blade coater so that the positive electrode material adhered to 22.5±0.2 mg/cm ² , and dried at 130° C. Further, roll pressing was performed to adjust the positive electrode density to 2.60±0.05 g/cm ³ to obtain an electrode sheet.

<Method of manufacturing non-aqueous secondary battery (laminated type battery)>
The negative electrode sheet and positive electrode sheet, which had a density of 1.5±0.03 g/cm ³ and had a negative electrode material of 10.0±0.3 mg/cm ² and a polyethylene separator, were laminated in the order of negative electrode, separator, and positive electrode. The battery element thus obtained was wrapped in a cylindrical aluminum laminate film, and an electrolyte solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio = 3:3:4) to a concentration of 1 mol/L was injected, followed by vacuum sealing to prepare sheet-shaped non-aqueous secondary batteries. Furthermore, in order to increase the adhesion between the electrodes, the sheet-shaped battery was sandwiched between glass plates and pressurized.

<Method of manufacturing non-aqueous secondary battery (coin battery)>
The electrode sheet prepared by the above method, with 10.0±0.3 mg/ ^cm2 of negative electrode material attached and an active material layer density of 1.5±0.03 g/ ^cm3, was punched into a disk shape with a diameter of 12.5 mm to form a negative electrode, and lithium metal foil was punched into a disk shape with a diameter of 14 mm to form a counter electrode. Between the two electrodes, a separator (made of a porous polyethylene film) impregnated with an electrolyte solution in which _LiPF6 was dissolved to 1 mol/L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3:7) was placed, and a 2016 coin-type battery was prepared.

<Discharge capacity (mAh/g)>
Using the nonaqueous secondary battery (2016 coin type battery) prepared by the above method, the capacity during battery charge and discharge was measured by the following measurement method.

The battery was charged at a current density of 0.05 C to 5 mV against the lithium counter electrode, and then further charged at a constant voltage of 5 mV until the current density reached 0.005 C. After doping lithium into the negative electrode, the battery was discharged at a current density of 0.1 C to 1.5 V against the lithium counter electrode. The discharge capacity per weight of the negative electrode active material at this time was taken as the discharge capacity (mAh/g) of this material.

<Cycle swelling>
For non-aqueous secondary batteries that had not undergone charge-discharge cycles, three cycles were performed at 25°C with a voltage range of 4.1V to 3.0V and a current value of 0.2C (the current value at which the rated capacity based on the discharge capacity at one-hour rate is discharged in one hour is 1C, the same applies below), and two cycles were performed with a voltage range of 4.2V to 3.0V and a current value of 0.2C (constant voltage charging at 4.2V for an additional 2.5 hours during charging). At this point, the glass plate for fixing was removed, and the thickness was measured at nine points for one battery using a contact thickness meter manufactured by Mitutoyo Corporation, and the average was taken as the "thickness before cycling". After that, the battery was sandwiched between glass plates again, and a cycle test was performed by charging and discharging 25 times in a thermostatic chamber at 45°C under the conditions of 0.8C-CCCV charging, 0.8CCC discharging, and 1.5V cut. Thereafter, the battery in a state of 0% SOC was measured at the same nine locations as before the cycling, and the average was calculated as the "thickness after cycling", and cycle swelling = {(thickness after cycling)/(thickness before cycling)-1} x 100 (%).

<Quick charging characteristics>
For the coin type battery that had not undergone the charge/discharge cycle, three cycles were performed at 25°C with a voltage range of 4.1V to 3.0V and a current value of 0.2C (the current value at which the rated capacity based on the discharge capacity at one hour rate is discharged in one hour is 1C, the same applies below), and two cycles were performed with a voltage range of 4.2V to 3.0V and a current value of 0.2C (constant voltage charging at 4.2V for an additional 2.5 hours during charging). Thereafter, the battery was CC-charged from a state of SOC 0% to SOC 100% at a current value of 3C. The dV/dQ value was calculated from the differential of the obtained voltage (V)-capacity (Q) curve, and the capacity value when dV/dQ=0, where the dV/dQ value goes from the negative region to the positive region, was obtained, and the rapid charge characteristic was calculated as {capacity value (mAh) when dV/dQ=0}/{capacity value (mAh) at SOC 100%}×100(%).

Example 1
Scaly natural graphite with an average particle size (d50) of 100 μm was pulverized to obtain scaly natural graphite with a d50 of 11.1 μm. 100 parts by weight of the obtained scaly natural graphite was mixed with 12 parts by weight of liquid oil as a granulating agent, and then spheroidized treatment was performed, and the granulating agent was removed by heat treatment to obtain spheroidized natural graphite. The obtained spheroidized graphite was filled and sealed in a rubber container and subjected to isotropic pressure treatment at 200 MPa to control the amount of mercury discharged/the amount of mercury injected (B/A). The obtained molded product was crushed and classified. Various physical properties of the obtained spheroidized graphite powder (negative electrode material raw material) are shown in Table 1. The amount of mercury discharged/the amount of mercury injected (B/A)×100(%) in the mercury porosimetry was 61.5%. The spheroidized graphite powder was mixed with pitch adjusted to 0.02% by weight ash, 20 ppm by weight metal impurities, and 1% by weight Qi as an amorphous carbon precursor, and the pressure in the furnace was reduced to 10 torr or less, and the pressure was returned to atmospheric pressure with nitrogen. Nitrogen was then circulated to make the oxygen concentration in the furnace <100 ppm, and a heat treatment was performed at 1300 ° C. in an inert gas. The obtained fired product was crushed and classified to obtain a composite carbon material containing an amorphous carbonaceous material on the surface of the graphite particles. From the firing yield, it was confirmed that the weight ratio of the spheroidized graphite particles to the amorphous carbon (spheroidized graphite particles: amorphous carbon) in the obtained composite carbon material was 1:0.08. Various physical properties of the negative electrode material obtained in this manner are shown in Table 1. In addition, the above-mentioned discharge capacity, cycle swelling, and rapid charging characteristics were measured using the obtained negative electrode material. The results are shown in Table 1. In addition, A and B in Table 1 indicate values rounded off to the fourth decimal place.

Example 2
Scaly natural graphite with an average particle size (d50) of 100 μm was pulverized to obtain scaly natural graphite with a d50 of 8.5 μm. The obtained scaly natural graphite was mixed with 12 parts by weight of liquid oil as a granulating agent, and then subjected to a spheroidizing treatment, and the granulating agent was removed by heat treatment to obtain spheroidized natural graphite. The obtained spheroidized graphite was filled and sealed in a rubber container and subjected to an isotropic pressurizing treatment at 200 MPa to control the amount of mercury discharged/the amount of mercury injected (B/A). The obtained molded product was crushed and classified. Various physical properties of the obtained spheroidized graphite powder (negative electrode material raw material) are shown in Table 1. The amount of mercury discharged/the amount of mercury injected (B/A)×100(%) in the mercury porosimetry was 69.9%. The spheroidized graphite powder was mixed with pitch adjusted to 0.02% by weight ash, 20 ppm by weight metal impurities, and 1% by weight Qi as an amorphous carbon precursor, and the pressure in the furnace was reduced to 10 torr or less, and the pressure was returned to atmospheric pressure with nitrogen. Nitrogen was then circulated to make the oxygen concentration in the furnace <100 ppm, and a heat treatment was performed at 1300 ° C. in an inert gas. The obtained fired product was crushed and classified to obtain a composite carbon material containing an amorphous carbonaceous material on the surface of the graphite particles. From the firing yield, it was confirmed that the weight ratio of the spheroidized graphite particles to the amorphous carbon (spheroidized graphite particles: amorphous carbon) in the obtained composite carbon material was 1:0.06. Various physical properties of the negative electrode material obtained in this manner are shown in Table 1. In addition, the above-mentioned discharge capacity, cycle swelling, and rapid charging characteristics were measured using the obtained negative electrode material. The results are shown in Table 1.

(Comparative Example 1)
Spherical natural graphite (average particle size (d50) 16.2 μm, BET specific surface area (SA) 6.9 m ² /g, tap density 1.00 g/cm ³ ) was obtained by spheroidizing flake natural graphite with an average particle size (d50) of 100 μm. The mercury outflow amount/mercury intrusion amount (B/A)×100(%) of the obtained spherical graphite powder (negative electrode material raw material) was 27.5% in the mercury porosimetry. This spherical graphite powder and an amorphous carbon precursor with an ash content of <0.01% and a metal impurity content of 6.0% were mixed.
After mixing the tar adjusted to 0 ppm and Qi<0.1%, the pressure in the furnace was reduced to 10 torr or less, and the pressure was returned to atmospheric pressure with nitrogen. Nitrogen was then circulated to set the oxygen concentration in the furnace to <100 ppm, and a heat treatment was performed at 1300 ° C. The obtained fired product was crushed and classified to obtain a negative electrode material, which is a composite carbon material containing amorphous carbonaceous material on the surface of graphite particles. From the firing yield, it was confirmed that the weight ratio of the spherical graphite particles to the amorphous carbon (spheroidal graphite particles: amorphous carbon) in the obtained negative electrode material (composite carbon material) was 1:0.03. Using the negative electrode material obtained in this way, the discharge capacity, cycle swelling, and rapid charging characteristics described above were measured. The results are shown in Table 1.

(Comparative Example 2)
Spheroidal natural graphite (average particle size (d50) 10.9 μm, BET specific surface area (SA) 8.1 m ² /g, tap density 0.90 g/cm ³ ) was obtained by spheroidizing flake natural graphite. The mercury outflow/mercury intrusion (B/A)×100(%) of the obtained spheroidal graphite powder was 28.3% in the mercury porosimetry. This spheroidal graphite powder was mixed with tar as an amorphous carbon precursor, which had been adjusted to an ash content of <0.01%, metal impurity content of 60 ppm, and Qi of <0.1%, and then the pressure in the furnace was reduced to 10 torr or less and returned to atmospheric pressure with nitrogen. Nitrogen was then circulated to adjust the oxygen concentration in the furnace to <100 ppm, and heat treatment was performed at 1300° C. The obtained fired material was crushed and classified to obtain a composite carbon material containing amorphous carbonaceous material on the surface of graphite particles. From the firing yield, it was confirmed that the weight ratio of the spheroidized graphite particles to the amorphous carbon (spheroidized graphite particles: amorphous carbon) in the obtained negative electrode material (composite carbon material) was 1:0.04. The above-mentioned discharge capacity, cycle swelling, and rapid charging characteristics were measured using the negative electrode material obtained in this manner. The results are shown in Table 1.

(Comparative Example 3)
Spheroidal natural graphite (average particle size (d50) 7.2 μm, BET specific surface area (SA) 11.1 m ² /g, tap density 0.81 g/cm ³ ) was obtained by spheroidizing flake natural graphite with an average particle size (d50) of 100 μm. The mercury outflow/mercury intrusion (B/A)×100(%) of the obtained spherical graphite powder was 41.2% in the mercury porosimetry. This spherical graphite powder was mixed with tar as an amorphous carbon precursor, which had been adjusted to an ash content of <0.01%, metal impurity content of 60 ppm, and Qi of <0.1%, and then the pressure in the furnace was reduced to 10 torr or less and returned to atmospheric pressure with nitrogen. Nitrogen was then circulated to adjust the oxygen concentration in the furnace to <100 ppm, and heat treatment was performed at 1300° C. The obtained fired material was crushed and classified to obtain a composite carbon material containing amorphous carbonaceous material on the surface of graphite particles. From the firing yield, it was confirmed that the weight ratio of the spheroidized graphite particles to the amorphous carbon (spheroidized graphite particles: amorphous carbon) in the obtained negative electrode material (composite carbon material) was 1:0.03. Using the negative electrode material thus obtained, the discharge capacity, cycle swelling, and rapid charging characteristics described above were measured. The results are shown in Table 1.

(Comparative Example 4)
The above-mentioned discharge capacity, cycle swelling, and rapid charging characteristics were measured using artificial graphite containing amorphous carbon on the surface. The results are shown in Table 1.

The relationship between the amount of mercury discharged/the amount of mercury injected (B/A) and the cycle swelling in Examples 1 and 2 and Comparative Examples 1 to 3 is shown in Figure 1. It can be seen from Table 1 and Figure 1 that by using the negative electrode material and the negative electrode material of the present invention, a lithium ion secondary battery having a high discharge capacity, suppressed cycle swelling, and excellent quick charge characteristics can be obtained.

The negative electrode material for non-aqueous secondary batteries and the negative electrode material for non-aqueous secondary batteries of the present invention, as well as the negative electrodes for non-aqueous secondary batteries and non-aqueous secondary batteries containing the same, have high capacity, small cycle swelling, and excellent rapid charge/discharge characteristics, and therefore can be suitably used for in-vehicle applications, power tool applications, and portable device applications such as mobile phones and personal computers.

Claims (6)

A negative electrode material for a non-aqueous secondary battery, comprising a raw material for a negative electrode material for a non-aqueous secondary battery, which contains graphite, and in which the following formula (1) is 50 % or more, where A is the amount of mercury injected and B is the amount of mercury released, obtained by mercury injection porosimetry:
A negative electrode material for a non-aqueous secondary battery, having a Raman _R1 value calculated from the following formula α of 0.15 or more and 1.00 or less.
Formula (1) B/A×100(%)
Formula α:
[Raman R ₁ value]=[Intensity I _B of peak P _B at about 1360 cm ⁻¹ in Raman spectrum analysis]/[Intensity I _A of peak P _A at about 1580 cm ⁻¹ ] The negative electrode material for a non-aqueous secondary battery according to claim 1, wherein the amount of mercury intrusion A is 0.001 mL/g or more and 0.5 mL/g or less. The negative electrode material for a non-aqueous secondary battery according to claim 1 or 2, wherein the amount of mercury discharged B is 0.0005 mL/g or more and 0.5 mL/g or less. The negative electrode material for non-aqueous secondary batteries according to any one of claims 1 to 3, wherein the tap density of the raw material for non-aqueous secondary batteries is 0.7 g/cm ³ or more and 1.4 g/cm ³ or less. A non-aqueous secondary battery negative electrode material according to any one of claims 1 to 4, in which the interplanar spacing (d002) obtained by X-ray diffraction is 0.34 nm or less, and the size of the crystallite in the c-axis direction (Lc) is 90 nm or more. A non-aqueous secondary battery using the negative electrode material according to any one of claims 1 to 5.

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