JP6916045B2 - Active material complex - Google Patents

Description

The present disclosure relates to an active material complex used for a negative electrode active material layer of an all-solid-state battery and having good charge / discharge efficiency.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones, and communication devices in recent years, the development of batteries used as their power sources has been emphasized. In addition, the automobile industry and the like are also developing high-output and high-capacity batteries for electric vehicles or hybrid vehicles. Currently, among various batteries, lithium batteries are attracting attention from the viewpoint of high energy density.

As a negative electrode active material of a lithium ion battery, for example, tin or an oxide of tin is drawing attention. For example, Patent Document 1 describes a Li ion rechargeable battery composed of a spherical carbon porous body and a composite composed of Sn and / or Sn oxide microcrystals filled in the pores of the spherical carbon porous body. The negative electrode material of the next battery is disclosed. Patent Document 1 discloses that the pore size of the spherical carbon porous body is about 1 nm to 20 nm. Further, Patent Document 1 discloses that the above-mentioned negative electrode material is used for a liquid-based battery. Further, for example, Patent Document 2 is characterized by including plate-like particles of tin monoxide, conductive carbon particles having a nano size, and spherical particles of tin dioxide supported on the surface of the carbon particles. A negative electrode active material capable of occluding and releasing lithium is disclosed. Further, Patent Document 3 is a metal powder composed of a sulfide-based solid electrolyte composed of lithium, phosphorus and sulfur and at least one element of tin, aluminum, silicon and indium and having a volume average particle diameter of 100 μm or less. A negative electrode mixture containing a negative electrode active material is disclosed.

Japanese Unexamined Patent Publication No. 2014-165023 Japanese Unexamined Patent Publication No. 2013-073816 Special Table 2010-003679

As the performance of batteries increases, it is required to further improve the charge / discharge efficiency of active materials. The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an active material complex having good charge / discharge efficiency.

In order to solve the above problems, in the present disclosure, the active material composite used for the negative electrode active material layer of the all-solid-state battery, the porous carbon having an average pore diameter of 45 nm or more, and the pores of the porous carbon. Provided is an active material composite having a supported tin dioxide and having a volume of the supported tin dioxide per 1 g of the porous carbon of 0.225 cc / g or more.

According to the present disclosure, when the volume of tin dioxide supported per 1 g of porous carbon is a predetermined value or more, an active material complex having good charge / discharge efficiency can be obtained.

The active material complex of the present disclosure has an effect of good charge / discharge efficiency.

It is a schematic cross-sectional view which shows an example of the active material complex of this disclosure. It is the schematic sectional drawing which shows an example of the all-solid-state battery using the active material complex of this disclosure. It is a measurement result of charge / discharge efficiency (%) of Examples 1 to 4 and Comparative Examples 1 to 3. It is a measurement result of the Li insertion amount ratio (%) of Examples 1 and 2 and Comparative Example 2, and Examples 3 and 4 and Comparative Example 3. It is a measurement result of the Li insertion amount ratio (%) of Examples 1 and 2 and Comparative Example 2, and Examples 3 and 4 and Comparative Example 3.

Hereinafter, the active material complex of the present disclosure will be described.
FIG. 1 is a schematic cross-sectional view showing an example of the active material complex of the present disclosure. The active material complex 10 shown in FIG. 1 has a porous carbon 1 having an average pore diameter of 45 nm or more, and tin dioxide 2 supported on the pores 1a of the porous carbon 1. Further, in the present disclosure, the volume of tin dioxide supported per 1 g of porous carbon is 0.225 cc / g or more. The active material complex 10 of the present disclosure is usually used for the negative electrode active material layer of an all-solid-state battery.

According to the present disclosure, an active material complex having good charge / discharge efficiency can be obtained by having the average pore diameter of the porous carbon and the volume (cc / g) of tin dioxide described above being equal to or more than a predetermined value. ..
The reason is presumed as follows.
In the present disclosure, the volume of tin dioxide supported per 1 g of porous carbon is large. In other words, the amount of tin dioxide supported on the porous carbon is large. When the amount of tin dioxide supported on the porous carbon is increased, for example, when the pore volume of the porous carbon is small (for example, when it is 20 nm or less), the stress due to the volume expansion and contraction of tin dioxide, which is an active material component, is applied. It is presumed that the charge / discharge efficiency is low because it cannot be sufficiently relaxed. For example, if the stress is not sufficiently relieved, it is presumed that the lithium ion path or electron path of the active material tin dioxide is interrupted due to the volume expansion of tin dioxide due to the insertion of lithium ions. As a result, it is presumed that it becomes difficult to extract lithium ions from the negative electrode active material after inserting lithium ions into the negative electrode active material in the initial state.
On the other hand, in the present disclosure, since the average pore diameter of the porous carbon is 45 nm or more and the pore diameter is large, the stress due to the volume expansion and contraction of tin dioxide can be sufficiently relaxed, and the charge / discharge efficiency is improved. It is speculated that it can be done.

For example, in the examples of Patent Document 1, the composition of the negative electrode material in which tin dioxide is supported in the pores of the spherical carbon porous body is disclosed, but the change in the amount of tin dioxide supported is disclosed. Not. In the present disclosure, it is important to pay attention to both the average pore size of the porous carbon and the amount of tin dioxide supported.

Hereinafter, the active material complex of the present disclosure will be described for each configuration.

1. 1. Porous carbon The porous carbon in the present disclosure has a predetermined average pore diameter. The porous carbon has an average pore diameter of 45 nm or more. The average pore diameter of the porous carbon may be, for example, 50 nm or more, or 60 nm or more. Further, the average pore diameter of the porous carbon may be, for example, 120 nm or less. The average pore diameter of the porous carbon can be measured, for example, by pore distribution analysis by gas adsorption / desorption isotherm measurement.

The pore volume of the porous carbon is, for example, 1.0 cc / g or more, may be 2.0 cc / g or more, or may be 3.0 cc / g or more. The pore volume of the porous carbon is, for example, 5.0 cc / g or less.
The method for measuring the pore volume of the porous carbon can be obtained by the same measuring method as the measuring method described in Examples described later.

The porous carbon preferably has, for example, connecting holes. This is because it is easy to relieve the stress of volume expansion and contraction of tin dioxide supported on the porous carbon. The porous carbon may or may not have further closed holes, but the latter is more preferable. The ratio of the closed pores to the entire pores of the porous carbon is preferably 20% or less, more preferably 10% or less, and particularly preferably 5% or less.

The shape of the porous carbon is not particularly limited, and examples thereof include a particulate shape. The average particle size (D ₅₀ ) of the porous carbon may be, for example, in the range of 0.5 μm to 10 μm. The average particle size of the porous carbon can be obtained as, for example, an average value obtained by measuring the particle size of 100 particles in a photograph taken by an SEM (scanning electron microscope). The method for forming the porous carbon is not particularly limited as long as the porous carbon having the above-mentioned average pore diameter can be obtained.

2. Tin dioxide The tin dioxide in the present disclosure is supported on porous carbon. Tin dioxide functions, for example, as an active material that reacts with lithium ions. Tin dioxide undergoes, for example, a conversion reaction represented by the following formula (I) and an alloying dealloying reaction represented by the following (II) with lithium ions.
SnO ₂ + 4Li ++ 4e ⁻ ⇔ 2Li ₂ O + Sn (I)
Sn + 4.4e ⁻ ⇔ Li _4.4 Sn (II)

In the active material complex, tin dioxide is dispersed in porous carbon at the nano level (highly dispersed state), so that the reversibility of the conversion reaction of (I) can be improved.

In the present disclosure, the volume (cc / g) of tin dioxide supported per 1 g of porous carbon is usually 0.225 cc / g or more, and may be, for example, 0.230 cc / g or more. It may be 300 cc / g or more. The volume of tin dioxide (cc / g) may be, for example, 0.400 cc / g or less, 0.370 cc / g or less, or 0.350 cc / g or less. good.

In the present disclosure, the weight (g / g) of tin dioxide supported per 1 g of porous carbon is usually 1.56 g / g or more, for example, 1.60 g / g (g / g) or more. It may be 2.00 g / g or more. The weight (g / g) of the tin dioxide may be, for example, 2.60 g / g or less, or 2.40 g / g or less.

The support ratio (% by weight) of tin dioxide in the active material complex may be, for example, in the range of 60% by weight to 75% by weight, or in the range of 60% by weight to 72% by weight.

The support ratio (% by weight) of tin dioxide in the active material composite can be measured by, for example, thermogravimetric analysis (TG-DTA). Further, the volume (cc / g) and weight (g / g) of tin dioxide supported per 1 g of the above-mentioned porous carbon can be calculated from the support ratio (% by weight) of tin dioxide in the active material composite. .. A specific calculation method will be described in Examples.

The shape of tin dioxide is preferably particulate, for example. The average particle size (D ₅₀ ) of tin dioxide is not particularly limited as long as it can be supported in the porous carbon, and may be, for example, 1 nm or more, or 5 nm or more. The average particle size of tin dioxide may be, for example, 10 nm or less.

3. 3. Active Material Complex The active material complex of the present disclosure has the above-mentioned porous carbon and tin dioxide.
In the active material complex of the present disclosure, the ratio of the volume of tin dioxide (vol.%) To the pore volume of the porous carbon is, for example, 8.26 vol. % Or more, 10.00 vol. It may be% or more. The ratio of the volume of tin dioxide (vol.%) To the pore volume of the porous carbon is, for example, 16.79 vol. It may be less than or equal to%.
The above ratio (vol.%) Is a percentage of the value obtained by dividing the volume of tin dioxide per 1 g of the porous carbon (cc / g) by the pore volume (cc / g) of the porous carbon.

The method for producing the active material complex of the present disclosure is not particularly limited as long as the active material complex having the above-mentioned constitution can be obtained. As an example, the following manufacturing method can be mentioned. By introducing SnCl ₂ gas into the porous carbon, the porous carbon and SnCl ₂ are mixed to obtain a mixture. Next, the obtained mixture is heat-treated in a container such as a suspension tube. _{Next, the unreacted SnCl 2} is removed by dispersing the heat-treated mixture in water. Next, the mixture is dried and then heat-treated in an oxygen atmosphere to obtain an active material complex. In the present disclosure, it is preferable to perform the heat treatment in a container such as a suspension tube at a temperature of about 320 ° C. for about 25 hours. Further, it is preferable that the heat treatment in an oxygen atmosphere is performed at a temperature of, for example, about 500 ° C. for about 2 hours.

4. All-solid-state battery The active material complex of the present disclosure is used for the negative electrode active material layer of an all-solid-state battery.
FIG. 2 is a schematic cross-sectional view showing an example of an all-solid-state battery using the active material complex of the present disclosure. The all-solid-state battery 20 shown in FIG. 2 has a positive electrode active material layer 11, a negative electrode active material layer 12, a solid electrolyte layer 13 formed between the positive electrode active material layer 11 and the negative electrode active material layer 12, and a positive electrode active material. It has a positive electrode current collector 14 that collects electricity from the material layer 11 and a negative electrode current collector 15 that collects electricity from the negative electrode active material layer 12. The negative electrode active material layer 12 contains at least the active material complex of the present disclosure. Further, the all-solid-state battery 20 may further have a battery case 16.

The active material complex of the present disclosure is used for the negative electrode active material layer of an all-solid-state battery.
The negative electrode active material layer may contain at least the above-mentioned active material complex, and may further contain a solid electrolyte material, a binder, and a conductive auxiliary material.
The content of the active material complex in the negative electrode active material layer may be in the range of, for example, 40% by volume to 99% by volume.

Examples of the solid electrolyte material used for the negative electrode active material layer include a sulfide solid electrolyte material and an oxide solid electrolyte material. Further, the solid electrolyte material may contain, for example, a halogen (for example, I, Cl, Br). Further, the solid electrolyte material may be a crystalline material or an amorphous material. The solid electrolyte material may be glass or crystallized glass (glass ceramics). Examples of the shape of the solid electrolyte material include particulate matter.

The conductive auxiliary material and the binder can be the same as the materials used for a general solid-state battery. The thickness of the negative electrode active material layer is, for example, preferably in the range of 1 μm to 100 μm, and preferably in the range of 30 μm to 100 μm.

The active material complex is used in all-solid-state batteries. The all-solid-state battery in which the active material composite is used is preferably, for example, an all-solid-state lithium-ion battery.
The all-solid-state battery may be a primary battery or a secondary battery, but a secondary battery is preferable. This is because it can be charged and discharged repeatedly and is useful as an in-vehicle battery, for example. The primary battery also includes the use of a secondary battery as a primary battery (use for the purpose of discharging only once after charging).

The present disclosure is not limited to the above embodiment. The above embodiment is an example, and any object having substantially the same structure as the technical idea described in the claims of the present disclosure and exhibiting the same effect and effect is the present invention. Included in the technical scope of the disclosure.

The present disclosure will be described in more detail with reference to Examples below.

(Synthesis of porous carbon)
Porous carbons having average pore diameters of 18 nm, 45 nm and 140 nm were synthesized by the synthesis method described in S.Oro, K. Urita, I. Moriguchi, Chem. Comm., 50 (54), 7143 (2014).

[Example 1]
( _{Synthesis of SnO 2-} supported porous carbon)
Porous carbon (C45) having an average pore diameter of 45 nm was prepared.
C45 was vacuum dried at 120 ° C. for 2 hours in advance to remove adsorbed moisture. _{Next, SnCl 2} gas was introduced into C45 from which the adsorbed water was removed. C45 and SnCl ₂ were mixed in a weight ratio of C45: SnCl ₂ = 20: 80, and heated in a suspension tube (stainless steel tube) at 320 ° C. for 25 hours. The resulting sample was dispersed in water, unreacted SnCl ₂ was removed and dried in vacuo for 12 hours. The dried sample was heated in air at 500 ° C. for 2 hours _{to obtain SnO 2-} containing porous carbon (SnO ₂ / C45).

[Example 2]
Using porous carbon (C45) having an average pore diameter of 45 nm, _{the weight ratio of porous carbon to SnCl 2} was set to C45: SnCl _{2 = 10: 90, but the SnO 2-} containing porous method was the same as in Example 1. Carbon was made.

[Example 3]
Using porous carbon (C140) having an average pore diameter of 140 nm _{, the SnO 2-} containing porous carbon was prepared in the same manner as in Example 1 except that the weight ratio of _{the porous carbon to SnCl 2 was C140: SnCl 2 = 20: 80.} Was produced.

[Example 4]
Using porous carbon (C140) having an average pore diameter of 140 nm _{, the SnO 2-} containing porous method is the same as in Example 1 except that the weight ratio of _{the porous carbon and SnCl 2 is C140: SnCl 2 = 10: 90.} Carbon was made.

[Comparative Example 1]
Using porous carbon (C18) having an average pore diameter of 18 nm, _{the weight ratio of porous carbon to SnCl 2} was set to C18: SnCl _{2 = 10: 90, but the SnO 2-} containing porous method was the same as in Example 1. Carbon was made.

[Comparative Example 2]
Using porous carbon (C45) having an average pore diameter of 45 nm, _{the weight ratio of porous carbon to SnCl 2} was set to C45: SnCl _{2 = 30: 70, but the SnO 2-} containing porous method was the same as in Example 1. Carbon was made.

[Comparative Example 3]
Using porous carbon (C140) having an average pore diameter of 140 nm, _{the weight ratio of porous carbon to SnCl 2} was set to C140: SnCl _{2 = 30: 70, but the SnO 2-} containing porous method was the same as in Example 1. Carbon was made.

[Evaluation 1]
(Volume of _{SnO 2} supported per 1 g of porous carbon (C))
_{The supported ratio A (% by weight) of SnO 2} in the SnO _2- containing porous carbon was measured by thermogravimetric analysis (TG-DTA). From SnO ₂ of bearing ratio A (% by weight), it was calculated on the weight of SnO ₂ carried per porous carbon 1g B (g / g). The calculation formula was B (g / g) = 100 (g) × A (weight%) ÷ (100 (g) − (100 (g) × A (weight%)).
A porous carbon by weight of SnO ₂ carried per 1g B (g / g), was calculated for SnO ₂ carried per porous carbon 1g volume C (cc / g). The calculation formula was C (cc / g) = B (g / g) ÷ 6.95 (g / cc). Note that 6.95 g / cc is the density (theoretical value) of _{SnO 2.} The results are shown in Table 1.

(Ratio of the volume of _{SnO 2 to} the volume of pores of porous carbon (C))
The pore volume (cc / g) per 1 g of porous carbon before supporting SnO _{2 was determined from the adsorption isotherm by the BET method.} A high-precision gas / vapor adsorption amount measuring device (Microtrac Bell Co., Ltd. product name: Belsolp-Max) was used as the device. The pore volume was calculated by linearly interpolating the obtained adsorption data of the adsorption isotherm up to the relative pressure for calculating the pore diameter, and converting the adsorption amount into the volume of the adsorbent in the liquid state by the following formula. ..
Pore volume V = (n / 22414) × (M / ρ)
(In the formula, n is the adsorbed amount of the adsorbent at the relative pressure, M is the molecular weight of the adsorbent, and ρ is the density of the adsorbent.)
Nitrogen was used as the adsorbent, and the relative pressure was set to 0.98.
From the pore volume of the obtained porous carbon and the volume C (cc / g) of _{SnO 2} described above, the ratio D (vol.%) Of the volume of _{SnO 2 to the pore volume of the porous carbon was calculated.} The calculation formula was D (vol.%) = C (cc / g) / (pore volume of porous carbon (cc / g)) × 100.

[Evaluation 2]
(Sulfide-fixed electrolyte synthesis)
Li ₂ S (Nippon Chemical Industrial Co., Ltd., 99.9%) and P ₂ S ₅ (Aldrich, 99%) were used as starting materials. Each raw material was weighed so as to have a composition of 75Li ₂ S-25P ₂ S _5. Each of the weighed raw materials was treated with a planetary ball mill to prepare a glassy sulfide solid electrolyte (sulfide glass). As the planetary ball mill, P-7 manufactured by FRITCH was used, and processing was performed at a rotation speed of 370 rpm for 40 hours using a medium having a diameter of 5 mm.
The obtained sulfide glass was placed in a quartz tube and vacuum-sealed at 30 Pa or less. The quartz tube was heat-treated in a firing furnace at 310 ° C. for 2 hours. Through the above steps, a sulfide solid electrolyte was obtained.
The heat treatment was carried out at a high temperature of about 10 ° C. to 20 ° C. from the exothermic peak of the sulfide glass obtained from TG-DTA.

Further, in the sulfide solid electrolyte used in the following measurements, the starting materials were Li ₂ S and P ₂ S ₅ , but the starting materials are not limited to this, and for example, Li ₂ S and P ₂ S ₅ are used in the composition ratio. , Li ₂ S: P ₂ S ₅ = 75: 25 may be used, or the raw material weighed at Li ₂ S: P ₂ S ₅ = 70: 30 may be used. Further, as the raw material, for example, P alone or S alone can be used. Further, the ball mill treatment may be, for example, a dry type or a wet type. From the viewpoint of uniform treatment, it is preferably wet. In the case of wet type, the solvent may be appropriately selected. Further, a reaction for advancing the chemical reaction by applying mechanical energy other than the ball mill treatment may be used.

(Preparation of working electrode mixture for electrochemical measurement)
The above-mentioned sulfide solid electrolyte and SnO _2- containing porous carbon are weighed in a volume ratio so that sulfide solid electrolyte: SnO _2- containing porous carbon = 50:50, and an ultrasonic homogenizer is used in heptane. Distributed. The dispersion was evaporated to dryness on a hot plate to give a mixed powder material. All operations were performed in an inert atmosphere.

(Preparation of cell for electrochemical measurement)
The obtained mixed powder material was weighed at 16.8 mg, placed in a cylinder made of Macol (cross-sectional area 1.0 cm ² ), 1 ton pressed with a hydraulic press scale, 100 mg of solid electrolyte was added, and 4 ton pressed with a scale reading. A half cell containing Li foil as a counter electrode was formed and constrained with 2N to obtain a cell for evaluation.

(Electrochemical measurement)
A charge / discharge test was conducted using a charge / discharge device manufactured by Toyo System. Li was inserted and removed at 0.1 C in the range of 0.01 V to 2.5 V based on metallic lithium. The test environment was 25 ° C. The charge / discharge efficiency (efficiency of 1 cyc) was calculated by dividing the capacity at the time of Li insertion by the capacity at the time of Li removal. The results are shown in Table 2. The Li insertion amount ratio refers to the ratio of the capacity at the time of Li insertion to the theoretical capacity. In Examples 1, 2 and 4, the reason why the Li insertion amount ratio exceeds 100% is presumed to be that the metal Sn is slightly mixed.

Examples 1 to 4 and SnO ₂ volumes C per porous carbon 1g in Comparative Example 1 to 3 (cc / g) and Figure the relationship between charge-discharge efficiency (%) 3, of the SnO ₂ volume C (cc / The relationship between g) and the Li insertion amount ratio (%) is shown in FIG. 4, and the relationship between the SnO ₂ volume ratio (vol.%) To the pore volume of the porous carbon and the Li insertion amount ratio (%) is shown in FIG. Shown in.

From the results of Examples 1 to 4 and Comparative Examples 1 to 3, the pore volume of the porous carbon was set to 45 nm or more, and the volume of tin dioxide supported per 1 g of the porous carbon was set to 0.225 cc / g or more. It was confirmed that the charge / discharge efficiency was improved.

Further, from the results of Examples 1 and 2 and Comparative Example 2, and the results of Examples 3 and 4 and Comparative Example 3, when the average pore diameter is constant, the volume of tin dioxide supported per 1 g of porous carbon It was confirmed that the Li insertion amount ratio was improved by increasing the amount. Since the Li insertion amount ratio was improved, it was suggested that the amount of Li that reacts with tin dioxide supported on the porous carbon increases, in other words, the utilization rate of the active material increases.
The reason is presumed as follows. When the volume of tin dioxide supported per 1 g of porous carbon is small, it is presumed that there is a portion where the solid electrolyte (SE) and tin dioxide, which is an active material, do not come into contact with each other and a lithium ion path is not formed. Therefore, it is presumed that the utilization rate of the active material (ratio of lithium ion insertion amount) will be low.
On the other hand, by increasing the volume of tin dioxide supported per 1 g of porous carbon, the tin dioxide in contact with the solid electrolyte (SE) expands during charging of the all-solid-state battery, thereby causing the above. It is speculated that a lithium ion path is formed by contact with tin dioxide, which is adjacent to tin dioxide and is not in contact with the solid electrolyte (SE). That is, even when there is a portion of the all-solid-state battery in which the solid electrolyte and tin dioxide are not in contact with each other, the lithium ion path is formed by the contact of the expanded tin dioxide during charging with the adjacent solid electrolyte (SE) and tin dioxide. It is presumed to be formed. Therefore, it is presumed that the utilization rate of the active material can be improved.

1 ... Porous carbon 1a ... Pore 10 ... Active material complex

Claims (1)

An active material complex used for the negative electrode active material layer of an all-solid-state battery.
It has porous carbon having an average pore diameter of 45 nm or more and tin dioxide supported on the pores of the porous carbon.
An active material complex in which the volume of the tin dioxide supported per 1 g of the porous carbon is 0.225 cc / g or more and 0.370 cc / g or less.

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