JP7271482B2 - cathode material - Google Patents

Description

The present invention relates to a positive electrode material and a lithium ion secondary battery comprising the positive electrode material. More specifically, it relates to a positive electrode material comprising a lithium-transition metal composite oxide and titanium oxide coating the surface of the lithium-transition metal composite oxide.

In recent years, lithium-ion secondary batteries have been suitably used not only as so-called portable power sources for personal computers, mobile terminals, and the like, but also as power sources for driving vehicles. Lithium-ion secondary batteries for such applications are required to have high durability (for example, excellent cycle characteristics) so as to maintain a desired output over a long period of time when mounted in a vehicle.

A positive electrode active material made of a lithium transition metal composite oxide capable of intercalating and deintercalating lithium ions, which are charge carriers, is generally used for the positive electrode of a lithium ion secondary battery. In recent years, techniques for forming a coating on the surface of such a positive electrode active material have been extensively studied. Specifically, for example, Patent Literature 1 describes disposing a compound containing titanium on the surface layer of a positive electrode active material made of a lithium-transition metal composite oxide.

Japanese Patent Application Laid-Open No. 2020-80332

It is said that when a titanium compound is placed on the surface of the positive electrode active material, the dielectric effect of the titanium compound makes it easier for lithium ions to move in and out of the positive electrode active material during charging and discharging of the lithium ion secondary battery. Therefore, it is said that a lithium ion secondary battery containing a positive electrode material having a titanium compound on the surface of the positive electrode active material can improve battery performance.
However, lithium ion secondary batteries containing conventional positive electrode materials such as those described above still have room for improvement in resistance to capacity deterioration (that is, cycle performance) when charging and discharging are repeated.

Accordingly, the present invention has been made in view of the circumstances described above, and an object thereof is to provide a positive electrode material capable of improving the cycle performance of a lithium ion secondary battery.

The present inventors paid attention to the existence state of titanium arranged on the surface of the lithium-transition metal composite oxide (positive electrode active material). Further, the inventors have found that the cycle performance of lithium-ion secondary batteries can be significantly improved by arranging a specific amount of titanium on the surface of such a lithium-transition metal composite oxide in a more finely scattered manner than in the past. I have perfected my invention.
That is, according to the technology disclosed herein, a lithium-transition metal composite oxide containing at least one element selected from the group consisting of nickel, manganese, and cobalt, and a lithium-transition metal composite oxide disposed on the surface of the lithium-transition metal composite oxide A cathode material is provided comprising: titanium.
The molar ratio (Ti/Ni+Mn+Co) of the titanium element to the total of the nickel element, the manganese element and the cobalt element in the lithium-transition metal composite oxide is 0.03 or more and 0.7 or less. The lithium-transition metal composite oxide measured based on an elemental mapping image of the titanium element and the constituent elements of the lithium-transition metal composite oxide obtained using a scanning electron microscope and energy dispersive X-ray analysis. The area (A50 _Ti ) at which the cumulative frequency is 50% in the area distribution of each titanium element- existing portion on the surface of is in the range of 0.028 μm ² or more and 44.3 μm ² or less.
A positive electrode material having such a configuration can significantly improve the cycle performance of a lithium ion secondary battery.

Preferably, the titanium has an average particle size of 0.2 μm or more and 7.5 μm or less.
According to this configuration, the surface of the lithium-transition metal composite oxide can be more finely dotted with titanium, and the cycle performance of the lithium-ion secondary battery can be improved more efficiently.
In the present specification, unless otherwise specified, the "average particle size" refers to a volume-based cumulative frequency of 50% in a particle size distribution measured based on a particle size distribution measuring device based on a laser scattering/diffraction method. It means the particle size, that is, the 50% volume average particle size ( _D50 size).

Moreover, preferably, the molar ratio (Ti/Ni+Mn+Co) is 0.2 or more.
With such a configuration, the cycle performance of the lithium-ion secondary battery can be significantly improved.

Also preferably, the area (A50 _Ti ) is 1.5 μm ² or more.
With such a configuration, the cycle performance of the lithium-ion secondary battery can be significantly improved.

In one preferred embodiment, the titanium is present as titanium dioxide.
Titanium dioxide can be stably arranged on the surface of the core particles.

Furthermore, according to the technology disclosed herein, there is provided a lithium-ion secondary battery that includes an electrode body having a positive electrode and a negative electrode.
The positive electrode comprises the positive electrode material described above.
Such a configuration provides a lithium ion secondary battery with significantly improved cycle performance.

It is a schematic cross section explaining the structure of the positive electrode material which concerns on one Embodiment. It is a schematic diagram explaining the behavior of the lithium ion in the positive electrode material which concerns on one Embodiment. 1 is a cross-sectional view schematically showing the configuration of a lithium-ion secondary battery constructed using a positive electrode material according to one embodiment; FIG. 1 is a schematic exploded view schematically showing the configuration of a lithium-ion secondary battery constructed using a positive electrode material according to one embodiment; FIG.

Preferred embodiments of the technology disclosed herein will be described below with reference to the drawings. Matters other than those specifically mentioned in this specification, which are necessary for carrying out the present invention, can be grasped as design matters by those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Moreover, in the following drawings, members and parts having the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

In this specification, the term “secondary battery” is a general term that refers to an electricity storage device that can be repeatedly charged and discharged. It is a concept that includes a capacitor (physical battery) such as a double layer capacitor. In this specification, the term "lithium ion secondary battery" refers to a secondary battery that utilizes lithium ions as charge carriers and that charges and discharges by the movement of charge associated with the movement of lithium ions between the positive and negative electrodes. .
Further, in the present specification, "A to B" means "A or more and B or less", and includes those exceeding A and below B.

As shown in FIG. 1, the positive electrode material 10 disclosed herein comprises a lithium-transition metal composite oxide 12 as a positive electrode active material, and titanium 14 arranged on the surface thereof.
The lithium-transition metal composite oxide can be a known lithium-transition metal composite oxide typically used as a positive electrode active material in lithium ion secondary batteries.
Such a lithium transition metal composite oxide contains at least one element selected from the group consisting of nickel (Ni), manganese (Mn) and cobalt (Co). For example, lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium iron-nickel-manganese composite oxides, and the like.
Although its crystal structure is not particularly limited, it preferably has a layered structure. As the lithium-transition metal composite oxide, a lithium-nickel-cobalt-manganese-based composite oxide having a layered structure can be preferably used.

As used herein, the term "lithium-nickel-cobalt-manganese-based composite oxide" refers to an oxide containing lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and oxygen (O) as constituent elements. In addition, the term also includes oxides containing one or more additional elements. Examples of such additional elements include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), silicon (Si), yttrium (Y), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Sodium (Na), Iron (Fe), Zinc (Zn), Tin (Sn), etc. transition metal elements, typical metal elements, and the like. Further, the additive elements include metalloid elements such as boron (B), carbon (C), silicon (Si), phosphorus (P), sulfur (S), fluorine (F), chlorine (Cl), bromine Non-metallic elements such as (Br) and iodine (I) may also be used. This also applies to other lithium-transition metal composite oxides described above.

The shape of the lithium-transition metal composite oxide is not particularly limited, and may be spherical, plate-like, needle-like, or the like. The lithium-transition metal composite oxide may be in the form of secondary particles in which primary particles are aggregated, or may be in the form of hollow particles.
The average particle size of the lithium-transition metal composite oxide 12 is not particularly limited, but can be, for example, 0.05 μm to 20 μm.

In the positive electrode material 10 , titanium 14 is arranged like islands on the surface of the lithium-transition metal composite oxide 12 as illustrated. That is, the titanium 14 is scattered on the surface of the lithium-transition metal composite oxide 12 . By finely scattering the titanium 14 on the surface of the lithium-transition metal composite oxide 12, the efficiency of lithium ions entering and exiting the lithium-transition metal composite oxide 12 during charging and discharging can be improved.
The existing area of titanium on the surface of the lithium-transition metal composite oxide can be measured by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). That is, the existence state of titanium on the surface can be grasped by SEM-EDX observation.
Since the specific measuring method is as described in the following examples, detailed description is omitted here.

A50 _Ti can be one of the indicators for grasping the state of existence of titanium on the surface of the lithium-transition metal composite oxide. Specifically, it can be said that the larger the A50 _Ti , the larger the area of one region of titanium arranged on the surface of the lithium-transition metal composite oxide, and the smaller the A50 _Ti , the smaller the area. That is, it can be said that the smaller the A50 _Ti , the finer the titanium is scattered on the surface of the lithium-transition metal composite oxide. For example, for two positive electrode materials having the same total amount of titanium on the surface of the lithium-transition metal composite oxide, when comparing a positive electrode material with a relatively large A50 _Ti and a positive electrode material with a relatively small A50 _Ti , In the latter case, it can be said that titanium is more finely scattered on the surface of the lithium-transition metal composite oxide.
In the cathode material disclosed herein, A50 _Ti is preferably in the range of 0.028 μm ² or more and 44.3 μm ² or less. When A50 _Ti satisfies such a range, the cycle performance of the lithium ion secondary battery can be significantly improved. From the viewpoint of further improving cycle performance, A50 _Ti is preferably 1.5 μm ² or more.

Titanium can be present as titanium materials (eg, lithium titanate, various titanium oxides, etc.). Titanium oxide can be at least one compound selected from the group consisting of titanium dioxide (TiO ₂ ) and Ti _n O _2n-1 . Here, for Ti _n O _2n−1 , n is an integer of 3 or more, for example, an integer of 3 or more and 9 or less. Ti _n O _2n-1 can be, for example, Ti ₃ O ₅ , Ti ₄ O ₇ and Ti ₅ O ₉ . From the viewpoint of further improving cycle performance, titanium dioxide is preferred.

The shape of titanium is not particularly limited, and may be spherical, plate-like, acicular, or the like. Further, titanium may be in the form of primary particles or in the form of secondary particles in which primary particles are agglomerated. From the viewpoint of improving the cycle performance of the lithium ion secondary battery, the average particle size of titanium is preferably 0.2 μm or more and 7.5 μm or less. When the average particle size of titanium satisfies such a range, A50 _Ti suitable for improving cycle performance can be realized.
Note that the average particle size of titanium arranged on the surface of the lithium-transition metal composite oxide is substantially the same as the average particle size of titanium as a raw material.

Regarding the amount of titanium 14 arranged on the surface of the lithium-transition metal composite oxide 12, from the viewpoint of realizing good performance of the lithium-ion secondary battery, the nickel element, the manganese element, and the cobalt element of the lithium-transition metal composite oxide The molar ratio (Ti/Ni+Mn+Co) [atm %] of the titanium element to the total of is preferably 0.03 or more and 0.7 or less. When the molar ratio satisfies this range, the cycle characteristics of the lithium ion secondary battery can be improved. Moreover, from the viewpoint of improving cycle characteristics, the molar ratio is preferably 0.2 or more.
Since the specific measuring method is as described in the following examples, detailed description is omitted here.

For the positive electrode material disclosed herein, for example, a lithium transition metal composite oxide and titanium (e.g., titanium substance) as raw materials are prepared, mixed, and mixed in an inert atmosphere (argon gas atmosphere, nitrogen gas atmosphere, etc.). It can be prepared by firing in
Titanium as a raw material is preferably pulverized in advance so as to have the above average particle size. This makes it possible to achieve the desired A50 _Ti in the positive electrode material. The pulverization method is not particularly limited, and for example, a bead mill or the like can be used.
As a method for mixing the raw materials, a conventionally known stirring/mixing method can be used without particular limitation.

As for the temperature conditions for firing, the maximum firing temperature can be in the range of 200° C. to 900° C. (eg, 300° C. to 800° C.). By setting the sintering temperature condition within this range, it is possible to achieve the desired arrangement amount of titanium and A50 _Ti . The firing time is not particularly limited, but can be 6 hours to 20 hours.

Although not particularly limited, the mechanism by which the cycle performance of the lithium ion secondary battery is improved by using the positive electrode material disclosed herein is as follows, taking the case where titanium exists as titanium oxide as an example. That's right.
As shown in FIG. 2, when the lithium-ion secondary battery is charged and discharged, the dielectric titanium 14 (here, titanium oxide) is dielectrically polarized due to such charging and discharging. When this dielectric polarization causes the titanium 14 to be positive and negative, lithium ions (Li ⁺ ) are attracted to the surroundings of titanium. Solvent molecules 2 are attracted to the lithium ions (Li ⁺ ) coming out of the lithium-transition metal composite oxide 12 , and the lithium ions (Li ⁺ ) are solvated. The presence of titanium 14 promotes desorption/insertion of lithium ions (Li ⁺ ) into the lithium-transition metal composite oxide 12 . At this time, as the titanium 14 is scattered more finely on the surface of the lithium-transition metal composite oxide 12, the number of lithium ion desorption/insertion points increases. Therefore, the cycle performance of a lithium ion secondary battery comprising such a positive electrode material is improved.

The positive electrode material disclosed here can be suitably used as a positive electrode material for lithium ion secondary batteries. As an example of such a lithium ion secondary battery, the lithium ion secondary battery shown in FIGS. 3 and 4 will be described below in detail. Note that the lithium ion secondary battery is not limited to the illustrated example.
As shown, the lithium-ion secondary battery 100 includes a flat wound electrode body 20 and a non-aqueous electrolyte (not shown) housed in a flat rectangular battery case (that is, an outer container) 30. It is a sealed battery constructed. The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 that is set to release the internal pressure of the battery case 30 when it rises above a predetermined level. It is The positive and negative terminals 42 and 44 are electrically connected to the positive and negative current collecting plates 42a and 44a, respectively. As the material of the battery case 30, for example, a metal material such as aluminum that is lightweight and has good thermal conductivity is used.

As shown in the figure, the wound electrode body 20 has a form in which a positive electrode sheet 50 and a negative electrode sheet 60 are superimposed with two long separator sheets 70 interposed therebetween and wound in the longitudinal direction. . The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one side or both sides (here, both sides) of a long positive electrode current collector 52 . The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of a long negative electrode current collector 62 . The positive electrode active material layer non-formed portion 52a (that is, the portion where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed) and the negative electrode active material layer non-formed portion 62a (that is, the negative electrode active material layer 64 is formed). The portion where the negative electrode current collector 62 is exposed without being wound) is formed so as to protrude outward from both ends of the wound electrode body 20 in the winding axial direction (that is, the sheet width direction orthogonal to the longitudinal direction). there is A positive collector plate 42a and a negative collector plate 44a are joined to the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a, respectively.

Examples of the positive electrode current collector 52 forming the positive electrode sheet 50 include aluminum foil. The positive electrode active material layer 54 contains the positive electrode material according to the present embodiment, which contains the positive electrode active material. Also, the positive electrode active material layer 54 may further include a conductive material, a binder, and the like. As the conductive material, for example, carbon black such as acetylene black (AB) and other carbon materials (such as graphite) can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.

Examples of the negative electrode current collector 62 forming the negative electrode sheet 60 include copper foil. The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, for example, a carbon material such as graphite can be used. The negative electrode active material layer 64 may further contain binders, thickeners, and the like. As the binder, for example, styrene-butadiene rubber (SBR) or the like can be used. As a thickening agent, for example, carboxymethyl cellulose (CMC) or the like can be used.

As the separator 70, various porous sheets similar to those conventionally used in lithium ion secondary batteries can be used. A resin sheet is mentioned.

The same non-aqueous electrolyte as used in conventional lithium secondary batteries can be used, and typically an organic solvent (non-aqueous solvent) containing a supporting electrolyte can be used. As the non-aqueous solvent, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and the like can be preferably used. The non-aqueous solvent can be used singly or in combination of two or more. As the supporting salt, for example, a lithium salt such as LiPF ₆ can be suitably used. The concentration of the supporting salt is preferably 0.7 mol/L or more and 1.3 mol/L or less.
The non-aqueous electrolytic solution contains components other than the non-aqueous solvent and the supporting salt, such as a gas generating agent, a film forming agent, a dispersing agent, and a thickening agent, as long as they do not significantly impair the effects of the present invention. Various additives may be included.

The lithium ion secondary battery 100 can be used for various purposes. Suitable applications include drive power supplies mounted in vehicles such as plug-in hybrid vehicles (PHV), hybrid vehicles (HV), and electric vehicles (EV). The lithium ion secondary battery 100 can also be used in the form of an assembled battery in which a plurality of batteries are electrically connected.

The prismatic lithium ion secondary battery including the flattened wound electrode assembly has been described above as an example. However, the positive electrode material according to this embodiment can also be used in other types of lithium ion secondary batteries according to known methods. For example, the positive electrode material according to this embodiment can be used to construct a lithium ion secondary battery including a laminated electrode body. Moreover, a cylindrical lithium ion secondary battery, a laminated lithium ion secondary battery, or the like can be constructed using the positive electrode material according to the present embodiment.

EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

[Example 1]
<Preparation of titanium oxide>
Titanium oxide (IV) (TiO ₂ ) (Fujifilm Wako Pure Chemical Industries, Ltd.) was pulverized with a bead mill (trade name: Easy Nano RMB, marketed by Imex Co., Ltd.). At this time, the beads used were zirconia (φ0.03 mm), and the disk peripheral speed of the bead mill was 3.1 m/s. Pulverization by a bead mill was performed until the particle size of TiO2 reached 0.2 μm.
<Preparation of positive electrode material>
Next, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) particles having a layered structure were prepared as a lithium transition metal composite oxide. The NCM particles and the above TiO ₂ were mixed in a mortar for 30 minutes so that NCM:TiO 2 =99:1 (molar ratio).
The resulting mixture was calcined at 500° C. for 12 hours to obtain a positive electrode material in which a coating of TiO ₂ was formed on the surfaces of NMC particles.

<Production of lithium-ion secondary battery for evaluation>
The positive electrode material prepared above, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were combined with N-methylpyrrolidone at a mass ratio of positive electrode material: AB: PVDF = 87: 10: 3. (NMP) using a planetary mixer to prepare a slurry for forming a positive electrode active material layer. This slurry was applied to both surfaces of an aluminum foil using a film applicator with a film thickness adjustment function (manufactured by All Good Co., Ltd.). After that, it was dried in a dryer at 80° C. for 5 minutes to obtain a positive electrode sheet.
Natural graphite (C) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed at a mass ratio of C: SBR: CMC = 96: 2: 2. were mixed in ion-exchanged water to prepare a slurry for forming a negative electrode active material layer. This slurry was applied to both surfaces of the copper foil using a film applicator with a film thickness adjustment function (manufactured by All Good Co., Ltd.). After that, it was dried in a dryer at 80° C. for 5 minutes to obtain a negative electrode sheet.
Two separator sheets (porous polyolefin sheets) were prepared.
The prepared positive electrode sheet, the negative electrode sheet, and the prepared two separator sheets were superimposed and wound to prepare a cylindrical wound electrode body. Electrode terminals were respectively attached by welding to the positive electrode sheet and the negative electrode sheet of the wound electrode body thus produced, and this was housed in a battery case having a liquid inlet.
Next, a non-aqueous electrolyte was injected from the liquid inlet of the battery case, and the liquid inlet was airtightly sealed. The non-aqueous electrolyte was a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, and LiPF ₆ as a supporting electrolyte. A solution dissolved at a concentration of 0 mol/L was used.
As described above, a lithium-ion secondary battery for evaluation of Example 1 was obtained.

[Comparative Example 1]
A lithium-ion secondary battery for evaluation of Comparative Example 1 was produced in the same manner as in Example 1, except that the NCM particles having a layered structure prepared in Example 1 were used as they were as the positive electrode material.

[Examples 2 to 8, Comparative Examples 2 to 4]
In the preparation of titanium oxide, pulverization by a bead mill was carried out until the particle size of TiO ₂ reached the size shown in the corresponding column of Table 1. In addition, firing was performed while changing the temperature conditions as appropriate so that the amount of titanium oxide and A50 _Ti reached the target values. Lithium ion secondary batteries for evaluation of Examples 2 to 8 and Comparative Examples 2 to 4 were produced in the same manner as in Example 1 except for the above.

<Measurement of molar ratio>
For the positive electrode materials of the above Examples and Comparative Examples, the molar ratio (Ti/Ni+Mn+Co) [atm%] of the titanium element to the sum of the nickel element, manganese element and cobalt element in the NCM particles was obtained using the following method. .
Specifically, the spectrum of XPS (X-ray photoelectron spectroscopy) is measured for the positive electrode material produced, and based on the integrated intensity (peak intensity) of each element, the composition fraction of the surface (i.e., the molar ratio of the titanium element ) was calculated. For the measurement sample, pellets were produced in a glove box using a commercially available tableting machine. This measurement sample was attached to a holder and measured according to the manual of an XPS device (trade name: PHI5000 VersaProbeII, vendor: ULVAC-PHI).
The molar ratio in each positive electrode material obtained here is shown in the corresponding column of Table 1.

<Measurement of A50 _Ti >
For the positive electrode materials of the above Examples and Comparative Examples, the area of the titanium-existing portion on the surface of the NCM particles was measured by SEM-EDX measurement.
Specifically, a carbon tape was attached to the holder in a dry room, and several mg of each observation sample was attached. After removing the unbonded sample with a blower, the surface of the observation sample was coated with platinum using a platinum sputtering device. Using SU8200 series manufactured by Hitachi High-Tech Co., Ltd., SEM-EDX measurement of the observation sample was performed according to the manual of the apparatus. The EDX elemental mapping image obtained here was binarized using image analysis software ImageJ. Here, the existing area of titanium (titanium-coated portion) was obtained, and the ratio of the area was calculated according to the manual of the software.
The measurement results are shown in the corresponding columns of Table 1.

<Activation and initial capacity measurement>
Each lithium-ion secondary battery for evaluation produced as described above was placed in an environment of 25°C. In the activation (initial charge), a constant current-constant voltage method is used, and after performing constant current charging to 4.1 V at a current value of 1/3 C for each lithium ion secondary battery for evaluation, the current value is 1/50 C. Constant-voltage charging was performed until the battery became fully charged. After that, each lithium ion secondary battery for evaluation was subjected to constant current discharge to 3.0 V at a current value of 1/3C. Then, the discharge capacity at this time was measured to obtain the initial capacity.

<Cycle performance evaluation>
Place each activated lithium ion secondary battery for evaluation in an environment of 60 ° C., and repeat 200 cycles of charging and discharging with constant current charging to 4.1 V at 2 C and constant current discharging to 3.0 V at 2 C as one cycle. rice field. The discharge capacity after 200 cycles was determined in the same manner as the initial capacity.
As an indicator of the cycle performance of each lithium-ion secondary battery for evaluation, the capacity retention rate (%) is
Formula (1) below:
Capacity retention rate (%) = (discharge capacity after 200 charge/discharge cycles/initial capacity) (1)
sought based on
The results are shown in the corresponding columns of Table 1.

As shown in Table 1, from the results of Examples 1 to 8 and Comparative Examples 1 to 4, the molar ratio of titanium element to the total of nickel element, manganese element, and cobalt element in NCM (in the table, the amount of Ti ( atm %) is 0.03 or more and 0.7 or less.
From the results of Examples 1 to 8 and Comparative Examples 1 to 3, the lithium ion secondary battery for evaluation containing a positive electrode material having an area (A50 _Ti ) within the range of 0.028 μm ² or more and 44.3 μm ^{2 or} less was charged. It can be seen that the capacity retention rate (%) after discharge cycles is higher.

As described above, a positive electrode material comprising a lithium-transition metal composite oxide containing at least one element selected from the group consisting of nickel, manganese, and cobalt, and titanium disposed on the surface of the lithium-transition metal composite oxide wherein the molar ratio of the titanium element to the total of the nickel element, the manganese element, and the cobalt element in the lithium-transition metal composite oxide is 0.03 or more and 0.7 or less, and the titanium element obtained using SEM and EDX and the constituent elements of the lithium-transition metal composite oxide, the cumulative frequency of 50% and When the area (A50 _Ti ) is in the range of 0.028 μm ² or more and 44.3 μm ² or less, the capacity retention rate is high when the lithium ion secondary battery containing such a positive electrode material is repeatedly charged and discharged. Recognize. It can be seen that the positive electrode material according to the present embodiment can impart excellent cycle performance to a lithium ion secondary battery.

Although specific examples of the present invention have been described in detail above, the above embodiments are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

2 Solvent molecule 10 Positive electrode material 12 Lithium transition metal composite oxide 14 Titanium 20 Wound electrode body 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector 44 Negative electrode terminal 44a Negative electrode current collector 50 Positive electrode sheet 52 Positive electrode current collector 52a Positive electrode active material layer non-formed portion 54 Positive electrode active material layer 60 Negative electrode sheet 62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator sheet 100 Lithium ion secondary battery

Claims (6)

a lithium-transition metal composite oxide containing at least one element selected from the group consisting of nickel, manganese, and cobalt;
a titanium oxide disposed on the surface of the lithium-transition metal composite oxide;
A positive electrode material comprising
The titanium oxide is at least one compound selected from the group consisting of titanium dioxide and Ti _n O _2n-1 , wherein n in Ti _n O _2n-1 is an integer of 3 or more and 9 or less,
The titanium oxide is scattered on the surface of the lithium-transition metal composite oxide,
the molar ratio (Ti/Ni+Mn+Co) of the titanium element contained in the titanium oxide to the sum of the nickel element, the manganese element, and the cobalt element in the lithium-transition metal composite oxide is 0.03 or more and 0.7 or less;
The lithium-transition metal composite oxide measured based on an elemental mapping image of the titanium element and the constituent elements of the lithium-transition metal composite oxide obtained using a scanning electron microscope and energy dispersive X-ray analysis. A positive electrode material in which an area (A50 _Ti ) at which the cumulative frequency is 50% in the area distribution of each titanium element -present portion on the surface of the positive electrode material is in the range of 0.028 μm ² or more and 44.3 μm ² or less. 2. The positive electrode material according to claim 1, wherein said titanium oxide has an average particle size of 0.2 [mu]m or more and 7.5 [mu]m or less. 3. The positive electrode material according to claim 1, wherein said molar ratio (Ti/Ni+Mn+Co) is 0.2 or more. The positive electrode material according to any one of claims 1 to 3, wherein said area (A50 _Ti ) is 1.5 µm ² or more. Cathode material according to any one of claims 1 to 4, wherein the titanium oxide is titanium dioxide. A lithium ion secondary battery comprising an electrode body having a positive electrode and a negative electrode,
A lithium ion secondary battery, wherein the positive electrode comprises the positive electrode material according to any one of claims 1 to 5.

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