JP6927110B2 - Negative electrode mixture manufacturing method - Google Patents

Description

The present invention relates to a method for producing a negative electrode mixture for a battery.

In recent years, it has been proposed to use an alloy-based negative electrode active material having a larger capacity instead of the conventional carbon-based negative electrode active material as the negative electrode active material of a lithium ion secondary battery. The alloy-based negative electrode active material particles occlude lithium ions by reacting with lithium ions to form an alloy with lithium, and release lithium ions by the reverse reaction. Examples of the alloy-based negative electrode active material include silicon, tin, germanium, aluminum and the like. Among these, silicon particles are attracting particular attention because of their particularly large capacity.

A battery using an alloy-based negative electrode active material as the negative electrode active material has a problem of low cycle characteristics as compared with a battery using a conventional carbon-based negative electrode active material as the negative electrode active material. As an attempt to improve the cycle characteristics of an all-solid-state battery using an alloy-based negative electrode active material as the negative electrode active material, for example, Patent Document 1 includes a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer. An all-solid-state battery system having an all-solid-state battery and a control device for controlling a charge / discharge voltage when the all-solid-state battery is used, and having alloy-based negative electrode active material particles in the negative electrode active material layer. , An all-solid-state battery system has been proposed in which the amorphization rate of the alloy-based negative electrode active material particles is 27.8 to 82.8% and the following conditions are satisfied:
0.32 ≤ Z / W ≤ 0.60
(In the formula, Z represents the controlled discharge capacity (mAh) of the all-solid-state battery, and W is the theoretical capacity (mAh / g) of the alloy-based negative electrode active material particles × the weight (g) of the entire alloy-based negative electrode active material particles. × Represents the amorphization rate (%).

Japanese Unexamined Patent Publication No. 2017-059534 Japanese Unexamined Patent Publication No. 2013-222530 Japanese Unexamined Patent Publication No. 2014-192093 Japanese Unexamined Patent Publication No. 2013-06916

According to Patent Document 1, it is possible to improve the cycle characteristics of an all-solid-state battery. However, according to the research of the present inventor, it has been found that when a silicon-based negative electrode active material is used as the alloy-based negative electrode active material, there is room for further improvement in resistance increase after the charge / discharge cycle.

A high-capacity negative electrode active material such as silicon expands (increases in volume) as Li ions are inserted during charging. Due to this volume increase, the solid electrolyte and the conductive auxiliary agent around the negative electrode active material are pushed and deformed. On the contrary, during discharge, the active material shrinks (volume decreases) with the release of Li ions, but the solid electrolyte and conductive aid around the negative electrode active material do not spontaneously deform to follow the shrinkage of the active material. .. Therefore, after the charge / discharge cycle, the electron conduction path and the ion conduction path on the surface of the negative electrode active material are impaired, which is considered to increase the internal resistance of the battery.

Increasing the content of the conductive auxiliary agent in the negative electrode mixture is effective in ensuring the conductivity of the negative electrode after the charge / discharge cycle, but on the other hand, the internal resistance (diffusion) of the battery after the charge / discharge cycle. Resistance) tends to increase rather. It is considered that this is because the ion conduction path between the solid electrolyte and the solid electrolyte is impaired due to the increase in the content of the conductive auxiliary agent.

An object of the present invention is to provide a method for producing a negative electrode mixture capable of suppressing an increase in internal resistance of a battery after a charge / discharge cycle.

One embodiment of the present invention prepares a composite by combining a negative electrode active material containing silicon, a solid electrolyte containing a sulfide solid electrolyte, and a conductive auxiliary agent containing a spherical carbon material. Combining step; and, after the compositing step, a mixing step of mixing the composite, a solid electrolyte containing a sulfide solid electrolyte, and a conductive auxiliary agent containing a fibrous carbon material is included. This is a method for producing a negative electrode mixture.

According to the present invention, it is possible to provide a method for producing a negative electrode mixture capable of suppressing an increase in internal resistance of a battery after a charge / discharge cycle.

It is a flowchart explaining the manufacturing method S10 of the negative electrode mixture which concerns on one Embodiment of this invention. It is a figure explaining the substance flow in the manufacturing method S10 of a negative electrode mixture. It is a figure which schematically explains the complex produced in the compounding step S1. It is a graph which shows the comparison result of the internal resistance increase amount after the charge / discharge cycle in Example 1 and Comparative Example 1. It is a figure explaining the substance flow in the manufacturing method of the negative electrode mixture adopted in the comparative example 1. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these forms. The drawings do not necessarily reflect the exact dimensions. Further, in the figure, some reference numerals may be omitted. In the present specification, unless otherwise specified, the notation "A to B" for the numerical values A and B means "A or more and B or less". When a unit is attached only to the numerical value B in such a notation, the unit shall be applied to the numerical value A as well. The words "or" and "or" shall mean OR unless otherwise specified.

<Manufacturing method of negative electrode mixture S10>
FIG. 1 is a flowchart illustrating a method S10 for manufacturing a negative electrode mixture according to an embodiment of the present invention (hereinafter, may be simply referred to as “manufacturing method S10”). The manufacturing method S10 is a method for manufacturing a negative electrode mixture for a lithium ion secondary battery. FIG. 2 is a diagram illustrating a substance flow in the method S10 for producing a negative electrode mixture. As shown in FIG. 1, the manufacturing method S10 includes a compounding step S1 and a mixing step S2 in this order. Hereinafter, each step will be described in order.

(Composite step S1)
The compounding step S1 (hereinafter, may be simply referred to as “step S1”) is a first solid electrolyte containing a silicon-containing negative electrode active material, a sulfide solid electrolyte, and a spherical carbon material. This is a step of producing a composite by combining with a conductive auxiliary agent.

As the silicon-containing negative electrode active material, a silicon-containing alloy-based negative electrode active material can be preferably used, and for example, silicon particles can be particularly preferably used.

The first solid electrolyte contains one or more sulfide solid electrolytes. The sulfide solid electrolyte is not particularly limited to the conventional sulfide solid electrolyte having lithium ion conductivity as long as it has an affinity with the particle surface of the negative electrode active material to the extent that it can be composited with the particles of the negative electrode active material. Can be used. Examples of preferred solid sulfide electrolytes are Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Si ₂ S-P ₂ S ₅ , LiI-Li _2. Examples thereof include sulfide solid electrolytes such as _{SP 2} O ₅ , LiBr-Li _{2 SP 2} S ₅ , LiI-Li ₃ PO _4- P ₂ S _5. Among these _{, a sulfide solid electrolyte containing Li 2} SP ₂ S ₅ in its composition can be particularly preferably used. The first solid electrolyte may contain two or more kinds of sulfide solid electrolytes.

The first conductive auxiliary agent contains one or more spherical carbon materials. As the spherical carbon material, conductive carbon black such as acetylene black, furnace black, channel black, thermal black, and ketjen black can be preferably used, and among these, ketjen black can be particularly preferably used. The first conductive auxiliary agent may contain two or more kinds of spherical carbon materials.

The blending ratio of the negative electrode active material, the first solid electrolyte, and the first conductive auxiliary agent to be compounded in step S1 is, for example, that the first solid electrolyte is preferably 0 with respect to 100 parts by mass of the negative electrode active material. It can be 1 to 5 parts by mass, more preferably 0.5 to 2 parts by mass, and the first conductive auxiliary agent is preferably 5 to 40 parts by mass with respect to 100 parts by mass of the first solid electrolyte. , More preferably 10 to 30 parts by mass. When the blending ratio of the first solid electrolyte to the negative electrode active material is not more than the above lower limit value and the blending ratio of the first conductive auxiliary agent to the first solid electrolyte is not more than the above upper limit value, the negative electrode active material particles It becomes easy to maintain the ion conduction path on the surface even after the charge / discharge cycle. Further, when the mixing ratio of the first solid electrolyte to the negative electrode active material is not more than the above upper limit value and the mixing ratio of the first conductive auxiliary agent to the first solid electrolyte is not more than the above lower limit value, the negative electrode active material It becomes easy to maintain the electron conduction path on the particle surface even after the charge / discharge cycle. Therefore, when the blending ratio of the negative electrode active material, the first solid electrolyte, and the first conductive auxiliary agent is within the above range, it becomes easy to suppress the decrease in internal resistance after the charge / discharge cycle.
From the same viewpoint, the particle size of the negative electrode active material before being subjected to compounding in step S1 is defined as the median diameter D50 (median value of the equivalent sphere diameter) in the volume-based particle size distribution measured by the laser diffraction / scattering method. It can be preferably 0.1 to 20 μm, more preferably 0.5 to 10 μm. The volume-based particle size distribution can be measured by the laser diffraction / scattering method using, for example, a laser diffraction / scattering particle size distribution measuring device Microtrack MT3000II (manufactured by Microtrack Bell Co., Ltd.).

A preferred example of a method of combining a negative electrode active material, a first solid electrolyte, and a first conductive auxiliary agent is a mechanically driven rotor and a mixing container provided in the mixing container. Examples thereof include a mechanical kneading method in which friction and shear energy are applied to the mixture with the inner wall, preferably in a dry manner. As an apparatus capable of achieving such a mechanical kneading method, a mechanical kneading apparatus that does not use media can be preferably used, and among them, a dry mechanical kneading apparatus can be particularly preferably used. As such a mechanical kneading device, commercially available general mechanical kneading device, for example, Nobilta (trade name: manufactured by Hosokawa Micron Co., Ltd.), mechanofusion, hybridization, COMPOSI (trade name: Nippon Coke Industries). (Manufactured) and the like can be used without particular limitation. By adopting a mechanical kneading device that does not use media, it is possible to reduce thermal and mechanical damage to the active material particles as compared with the case of using a kneading device that uses media such as a planetary ball mill.

(Mixing step S2)
In the mixing step S2 (hereinafter, may be simply referred to as “step S2”), after the step S1, the composite produced in the step S1, the second solid electrolyte containing the sulfide solid electrolyte, and the fibrous carbon This is a step of mixing with a second conductive auxiliary agent containing a material. By going through step S2, a negative electrode mixture is obtained.

FIG. 3 is a diagram schematically illustrating the particles 10 of the complex produced in step S1 (hereinafter, may be referred to as “complex particles 10”). The composite particle 10 includes a negative electrode active material particle 1, a first solid electrolyte 2, and spherical carbon material particles 3, 3, ... (Hereinafter referred to as “spherical carbon material particle 3”). However, at least a part of the surface of the relatively hard negative electrode active material particles 1 is covered with the first solid electrolyte 2 which is relatively soft because it contains a sulfide solid electrolyte, and the surface of the negative electrode active material particles 1 is covered. It is considered that the spherical carbon material particles 3, 3, ... Are retained in the layer of the first solid electrolyte 2 to be coated. That is, in the complex particles 10, it is considered that the negative electrode active material particles 1 and the spherical carbon material particles 3, 3, ... Are integrated by the first solid electrolyte 2.

The second solid electrolyte contains one or more sulfide solid electrolytes. As the second solid electrolyte, the same solid electrolyte as described above can be used in relation to the first solid electrolyte, and the preferred embodiment thereof is also the same as described above. The composition of the second solid electrolyte may be the same as or different from that of the first solid electrolyte. However, from the viewpoint of reducing the ionic conduction resistance at the interface between the second solid electrolyte and the first solid electrolyte present on the particle surface of the composite in the negative electrode mixture, the second solid electrolyte is the first. It is preferable to have the same composition as the solid electrolyte of.

The second conductive auxiliary agent contains one or more fibrous carbon materials. Fibrous carbon materials include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon nanofibers (CNFs), vapor-grown carbon fibers (VGCF), electrospun carbon fibers, and polyacrylonitrile (PAN). Fibrous carbon materials having conductivity such as carbon fibers and pitch-based carbon fibers can be preferably used, and among these, VGCF can be particularly preferably used. The second conductive auxiliary agent may contain two or more kinds of fibrous carbon materials.

In the mixing step S2, in addition to the complex, the second solid electrolyte, and the second conductive auxiliary agent, a binder may be further mixed optionally. Preferred examples of the binder include acrylonitrile-butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR) and the like.

The mixing in the mixing step S2 may be performed by a dry method or a wet method. When the mixing is carried out in a dry manner, the complex produced in step S1, the second solid electrolyte, the second conductive auxiliary agent, and optionally the binder are mixed with a known mixing device or kneading device using a known mixing device or kneading device. Can be mixed. When the mixing is performed wet, the composite prepared in step S1, the second solid electrolyte, the second conductive auxiliary agent, the dispersion medium, and optionally the binder are mixed, and the negative electrode mixture is prepared. A slurry is obtained. A known wet mixing device (for example, a homogenizer or the like) can be used for wet mixing.

In the case of wet mixing, the dispersion medium includes a negative electrode active material, a first solid electrolyte, a first conductive auxiliary agent, a second solid electrolyte, and a second conductive auxiliary agent (and optionally a binder). As long as there is no reaction, a polar solvent, a non-polar solvent, or a combination thereof can be used without particular limitation. Examples of non-polar solvents include heptane, toluene, xylene and the like. Examples of polar solvents include ethanol, N-methylpyrrolidone, butyl acetate, butyl butyrate and the like. As the dispersion medium, a mixture of two or more kinds of solvents may be used.

The mixing ratio in the mixing step S2 can be, for example, preferably 20 to 100 parts by mass, more preferably 50 to 80 parts by mass, and the second solid electrolyte with respect to 100 parts by mass of the composite. The second conductive auxiliary agent can be preferably 1 to 20 parts by mass, more preferably 5 to 15 parts by mass with respect to 100 parts by mass of the solid electrolyte. When the blending ratio of the second solid electrolyte to the composite is not more than the above lower limit value and the blending ratio of the second conductive auxiliary agent to the second solid electrolyte is not more than the above upper limit value, the ions on the surface of the composite are formed. It is easy to maintain the conduction path after the charge / discharge cycle. Further, when the blending ratio of the second solid electrolyte to the composite is not more than the above upper limit value and the blending ratio of the second conductive auxiliary agent to the second solid electrolyte is not more than the above lower limit value, the surface of the composite is surfaced. It becomes easy to maintain the electron conduction path even after the charge / discharge cycle. Therefore, when the compounding ratio of the complex, the second solid electrolyte, and the second conductive auxiliary agent is within the above range, it becomes easy to suppress the decrease in internal resistance after the charge / discharge cycle.

In the mixing step S2, when the binder is further mixed in addition to the composite, the second solid electrolyte, and the second conductive auxiliary agent, the blending ratio of the binder can be the same as before, for example, the composite, the first. The binder may be preferably 0.5 to 5 parts by mass, more preferably 1.0 to 2.5 parts by mass, based on 100 parts by mass of the total amount of the solid electrolyte 2 and the second conductive auxiliary agent. can.

When the mixing in the mixing step S2 is performed without using either the dispersion medium or the binder, a powdery negative electrode mixture is obtained. A negative electrode mixture layer of an all-solid-state battery can be produced by powder molding the powdery negative electrode mixture.
When the mixing in the mixing step S2 is carried out using a binder but not using a dispersion medium, a massive negative electrode mixture can be obtained by kneading. By molding the massive negative electrode mixture, the negative electrode mixture layer of the all-solid-state battery can be produced. In forming the bulk negative electrode mixture, conventional methods such as heating or pressurization or a combination thereof can be used.
When the mixing in the mixing step S2 is carried out using a dispersion medium, a slurry-like negative electrode mixture is obtained by the mixing. A negative electrode mixture layer of an all-solid-state battery can be produced by applying the slurry-like negative electrode mixture on a base material (for example, a negative electrode current collector) and then evaporating and removing the dispersion medium. In applying the slurry-like negative electrode mixture onto the substrate, a conventional method such as the doctor blade method can be used.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the following Examples are examples of the present invention, and the present invention is not limited to the following Examples.

<Example 1>
The following 1. ~ 4. A negative electrode mixture and an all-solid-state battery using the negative electrode mixture were produced according to the above procedure.
(1. Production of sulfide solid electrolyte)
Weigh Li ₂ S (Furuuchi Chemistry) 0.550 g, P ₂ S ₅ (Aldrich) 0.887 g, LiI (Nippoh Chemicals) 0.285 g, and LiBr (High Purity Chemistry) 0.277 g, and weigh 5 in an agate mortar. Mix for minutes. A sulfide solid electrolyte was produced by adding 4 g of dehydrated heptane (Kanto Kagaku Kogyo) to the obtained mixture and performing mechanical milling for 40 hours using a planetary ball mill.

(2. Manufacture of negative electrode mixture)
A negative electrode mixture was produced according to the procedures of 2.1 and 2.2 below.

(2.1 Composite process)
10 g of silicon powder (high-purity chemistry) as the negative electrode active material, and the above 1. as the first solid electrolyte. Weigh 0.1 g of the sulfide solid electrolyte produced in 1 and 0.02 g of Ketjen Black (Lion) as the first conductive auxiliary agent, and use a dry particle composite device (Nobilta (registered trademark) mini manufactured by Hosokawa Micron). The composite was prepared by mixing the mixture at a rotation speed of 6000 rpm for 10 minutes.

(2.2 Mixing process)
1.012 g of the complex prepared in 2.1 above, as the second solid electrolyte, 1. 0.766 g of the sulfide solid electrolyte produced in the above, 0.08 g of VGCF (Showa Denko) as the second conductive auxiliary agent, 0.02 g of PVdF (Kureha) as the binder, and butyl butyrate (Nacalai Tesque) as the dispersion medium. 4 g was weighed and mixed using an ultrasonic homogenizer (UH-50 manufactured by SMT), and then the obtained mixture was dried at 100 ° C. for 30 minutes to produce a negative electrode mixture.

(3. Manufacture of positive electrode mixture)
_{LiNi 1/3} Co _1/3 Mn _1/3 O ₂ (Nichia Corporation) was used as the positive electrode active material, and the surface of the positive electrode active material was surface-treated with _{LiNbO 3.} 1.5 g of the surface-treated positive electrode active material, as a solid electrolyte, described in 1. above. Weigh 0.239 g of the sulfide solid electrolyte produced in the above, 0.023 g of VGCF (Showa Denko) as a conductive auxiliary agent, 0.023 g of PVdF (Kureha) as a binder, and 0.8 g of butyl butyrate (Nacalai Tesque), and ultrasonically. After mixing with a homogenizer (UH-50 manufactured by SMT), the obtained mixture was dried at 100 ° C. for 30 minutes to produce a positive electrode mixture.

(4. Preparation of all-solid-state battery)
In a ceramic mold with a cross-sectional area of 1 cm ^{2, the above 1.} 0.065 g of the sulfide solid electrolyte produced in the above was weighed and pressed at a pressure of 1 ton / cm ² to prepare a solid electrolyte layer. Between one side of the solid electrolyte layer and the positive electrode current collector (aluminum foil). 0.018 g of the positive electrode mixture produced in the above 2. ^{After adding 0.0027 g of the negative electrode mixture produced in 1} and pressing at a pressure of 1 ton / cm 2, the above 2. An all-solid-state battery was prepared by adding 0.0027 g of the negative electrode mixture prepared in ^{1 and pressing at a pressure of 4 ton / cm 2.}

<Comparative example 1>
As a negative electrode mixture, the above 2. An all-solid-state battery was produced in the same manner as in Example 1 except that another negative electrode mixture was used instead of the negative electrode mixture produced in 1. The negative electrode mixture was produced by the following procedure: 1.0 g of silicon powder (high-purity chemistry) as the negative electrode active material, 1. 0.776 g of the sulfide solid electrolyte produced in Japan, 0.08 g of VGCF (Showa Denko) as a conductive auxiliary agent, 0.02 g of PVdF (Kureha) as a binder, and 2.4 g of butyl butyrate (Nacalai Tesque) as a dispersion medium. After weighing and mixing using an ultrasonic homogenizer (UH-50 manufactured by SMT), the obtained mixture was dried at 100 ° C. for 30 minutes to obtain a negative electrode mixture. FIG. 5 shows the substance flow in the method for producing the negative electrode mixture adopted in Comparative Example 1.

<Evaluation method>
For each of the all-solid-state batteries manufactured in Example 1 and Comparative Example 1, the following 5. ~ 8. Performance was evaluated according to the procedure of.
(5. Charging / discharging)
The battery was charged with a constant current constant voltage up to 4.35 V with a charging current of 0.24 mA, and then discharged with a constant current constant voltage up to 3.0 V with a discharge current of 0.245 mA.

(6. Measurement of internal resistance)
After charging at a charging current 0.245mA the battery until voltage 3.7V, discharging current 7.35mA in discharged for 5 seconds, and measuring the internal resistance _{r 1} of the battery from the change in voltage.

(7. Charge / discharge cycle)
6. Above. The battery that had undergone the internal resistance measurement was placed in a constant temperature bath at a temperature of 60 ° C., and 300 cycles of charge / discharge cycles were performed by constant current charge / discharge with a voltage range of 3.2 to 4.2 V and a current value of 4.9 mA.

(8. Measurement of internal resistance after charge / discharge cycle)
7. Above. For the battery after the charge / discharge cycle of the above 5. And 6. By measuring the charge and discharge and internal resistance in the same manner as to measure the internal resistance r ₂ of the battery after the charge and discharge cycles. The measured internal resistance value r ₂ is shown in 6. above. The amount of increase in internal resistance Δr = r ₂ −r ₁ was calculated by _{comparing with the value r 1 of the} internal resistance first measured in.

<Evaluation result>
8. Of the batteries produced in Example 1 and Comparative Example 1. The comparison result of the internal resistance increase amount Δr after the charge / discharge cycle calculated in FIG. 4 is shown in FIG. The battery of Example 1 using the negative electrode mixture produced by the production method of the present invention has a charge / discharge cycle with respect to the battery of Comparative Example 1 using the negative electrode mixture produced by a production method outside the scope of the present invention. The amount of increase in internal resistance later was reduced. From this result, it was shown that according to the present invention, it is possible to provide a method for producing a negative electrode mixture capable of suppressing an increase in the internal resistance of the battery after the charge / discharge cycle.

The method for producing a negative electrode mixture of the present invention can be preferably used for producing a negative electrode mixture for a battery such as a lithium ion secondary battery.

1 Negative electrode active material particles 2 First solid electrolyte 3 Spherical carbon material particles 10 Complex particles

Claims (1)

A compositing step of producing a composite by compositing a negative electrode active material containing silicon, a first solid electrolyte containing a sulfide solid electrolyte, and a first conductive auxiliary agent containing a spherical carbon material. ,as well as,
After the compounding step, a mixing step of mixing the composite, a second solid electrolyte containing a sulfide solid electrolyte, and a second conductive auxiliary agent containing a fibrous carbon material is included. A method for manufacturing a negative electrode mixture.

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