Method for manufacturing a negative electrode mixture slurry

Abstract

The present invention provides a method for producing a negative electrode mixture slurry capable of manufacturing a negative electrode active material layer having high ionic conductivity. [Solution] A method for producing a negative electrode mixture slurry is provided, comprising contacting a pre-treated sulfide solid electrolyte with a first organic solvent and drying it to obtain a treated sulfide solid electrolyte, and dispersing the treated sulfide solid electrolyte and a silicon-based electrode active material in a second organic solvent.

Description

Technical Field

[0001] The present disclosure relates to a method for producing a negative electrode composite material slurry.

Background Art

[0002] The negative electrode composite material slurry is a slurry containing an electrode active material, a solid electrolyte and the like, and the negative electrode composite material slurry is applied to the surface of a base material, dried, and optionally pressed, whereby an electrode active material layer is formed.

[0003] As shown in Patent Document 1, such a negative electrode composite material slurry is also used for producing a negative electrode active material layer containing a sulfide solid electrolyte and a silicon-based electrode active material, and in the negative electrode composite material slurry used in this case, the sulfide solid electrolyte and the silicon-based electrode active material are dispersed in an organic solvent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a negative electrode active material layer is produced using a negative electrode composite material slurry, the obtained negative electrode active material layer may not exhibit the ionic conductivity expected from the sulfide solid electrolyte used.

[0006] In view of the above, the present disclosure provides a method for producing a negative electrode composite material slurry that suppresses the above problems, that is, a method for producing a negative electrode composite material slurry that enables production of a negative electrode active material layer having relatively high ionic conductivity.

Means for Solving the Problems

[0007] After careful consideration, the Disclosing Parties have found that the above-mentioned problems can be solved by the following means, and have completed this disclosure. Specifically, this disclosure is as follows:

[0008] <Aspect 1> The sulfide solid electrolyte before treatment is brought into contact with a first organic solvent and dried to obtain a treated sulfide solid electrolyte, and Disperse the treated sulfide solid electrolyte and silicon-based electrode active material in a second organic solvent. A method for producing a negative electrode mixture slurry, including the following: [Effects of the Invention]

[0009] The negative electrode mixture slurry produced by the method of this disclosure makes it possible to produce a negative electrode active material layer having relatively high ionic conductivity. [Modes for carrying out the invention]

[0010] <<Negative electrode mixture slurry>> A method for producing a negative electrode mixture slurry according to this disclosure includes the following steps: The sulfide solid electrolyte before treatment is brought into contact with a first organic solvent and dried to obtain a treated sulfide solid electrolyte, and Disperse the treated sulfide solid electrolyte and silicon-based electrode active material in a second organic solvent.

[0011] The negative electrode mixture slurry produced by the method of this disclosure makes it possible to produce a negative electrode active material layer having relatively high ionic conductivity. In this disclosure, "negative electrode mixture slurry" means a slurry that includes a dispersion medium in addition to the constituent components of the negative electrode active material layer, and which can form a negative electrode active material layer by coating and drying.

[0012] This is not limited to theory, but this is, - The treated sulfide solid electrolyte, obtained by contacting the untreated sulfide solid electrolyte with a first organic solvent and then drying it, is to be relatively homogeneous with the silicon-based electrode active material in the negative electrode mixture slurry, and • In the negative electrode active material layer obtained from such a negative electrode mixture slurry, the treated sulfide solid electrolyte and the silicon-based electrode active material are dispersed relatively homogeneously. This is thought to be the case.

[0013] Furthermore, although not limited to theory, the reason why the treated sulfide solid electrolyte mixes relatively homogeneously with the silicon-based electrode active material in the negative electrode mixture slurry is thought to be because the treated sulfide solid electrolyte retains the first organic solvent on its surface or within it, which cannot be completely removed by drying.

[0014] <Process for obtaining treated sulfide solid electrolyte> The method of the present disclosure includes contacting a pre-treatment sulfide solid electrolyte with a first organic solvent and drying it to obtain a treated sulfide solid electrolyte.

[0015] (Sulfide solid electrolyte before treatment) Any sulfide solid electrolyte can be used as the sulfide solid electrolyte before treatment. Examples of sulfide solid electrolytes having lithium ion conductivity include solid electrolytes containing Li, X (where X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of halogen elements include F, Cl, Br, and I. Specific examples of sulfide solid electrolytes include Li2S-P2S5 glass ceramics.

[0016] (First organic solvent) The first organic solvent used in the method of the present disclosure is not particularly limited. However, as the first organic solvent, it is preferable to use an organic solvent that has no or low reactivity with the untreated sulfide solid electrolyte and the silicon-based electrode active material.

[0017] Specifically, examples of the first organic solvent may include tetralin (1,2,3,4-tetrahydronaphthalene), anisole, xylene, octane, hexane, decalin, butyl acetate, butyl butyrate, ethyl propionate, tripropylamine, N-methyl-2-pyrrolidone (NMP), etc., but are not limited to these cases. The first organic solvent may be a mixture of a plurality of organic solvents or a single organic solvent.

[0018] (Contacting) In the method of the present disclosure, the untreated sulfide solid electrolyte is brought into contact with the first organic solvent. This contacting can be performed by any method, for example, the untreated sulfide solid electrolyte can be dispersed in the first organic solvent, and this contacting can be performed optionally with stirring.

[0019] This contacting can be performed, for example, for 10 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, or 3 hours or more, and this contacting can be performed for a time of 24 hours or less, 12 hours or less, 10 hours or less, or 8 hours or less. In addition, this contacting can be performed under heating conditions, for example, at a temperature of 30°C or higher, 40°C or higher, or 60°C or higher, and can be performed at a temperature of 150°C or lower, 120°C or lower, 100°C or lower, or 80°C or lower.

[0020] (Drying) In the method of the present disclosure, the untreated sulfide solid electrolyte after being brought into contact with the first organic solvent is dried to obtain a treated sulfide solid electrolyte. This drying can be performed by any method, for example, under normal pressure conditions or reduced pressure conditions.

[0021] This drying can be carried out for, for example, 10 minutes or more, 30 minutes or more, 1 hour or more, 3 hours or more, 5 hours or more, 7 hours or more, 9 hours or more, or 10 hours or more, and this drying can be carried out for 24 hours or less, 18 hours or less, 16 hours or less, or 14 hours or less. This contact can be carried out under heating conditions, for example, at temperatures of 50°C or higher, 80°C or higher, 100°C or higher, or 110°C or higher, and at temperatures of 200°C or lower, 180°C or lower, 160°C or lower, or 140°C or lower.

[0022] (Processed sulfide solid electrolyte) In the method of this disclosure, a treated sulfide solid electrolyte is obtained by contacting the untreated sulfide solid electrolyte with a first organic solvent and drying it.

[0023] The ionic conductivity of the treated sulfide solid electrolyte obtained in this way may be lower than the ionic conductivity of the untreated sulfide solid electrolyte. For example, the ionic conductivity of the treated sulfide solid electrolyte may be 90% or less, 80% or less, 70% or less, or 60% or less of the ionic conductivity of the untreated sulfide solid electrolyte, or it may be 20% or more, 30% or more, 40% or more, 50% or more, or 60% or more of the ionic conductivity of the untreated sulfide solid electrolyte.

[0024] Furthermore, the ionic conductivity of the sulfide solid electrolyte before treatment may be 1.0 mS / cm or higher, 1.5 mS / cm or higher, or 2.0 mS / cm or higher, and may also be 3.0 mS / cm or lower, 2.7 mS / cm or lower, or 2.5 mS / cm or lower. The ionic conductivity of the treated sulfide solid electrolyte may be 0.5 mS / cm or higher, 1.0 mS / cm or higher, or 1.5 mS / cm or higher, and may also be 2.5 mS / cm or lower, 2.2 mS / cm or lower, or 2.0 mS / cm or lower.

[0025] In relation to this disclosure, the ionic conductivity can be measured as follows: Without adding anything to the Machor cell, the Machor cell is restrained at 6 N·m, and the resulting thickness is used as the thickness blank. Then, the restraint is released, the pin is removed, and 100 mg of solid electrolyte powder is placed in the Machor cell, with a conductivity of 1 ton / cm². 2 Press with a tweezers, hold for 30 seconds, remove the pins, insert aluminum foil with carbon coating on both sides, and press at 6 tons / cm². 2 Press the cell and hold for 30 seconds. Then, restrain the cell with 6 N·m, measure the thickness, and seal it in a desiccator with molecular sieves. After that, the fabricated Macol cell is heated in a solar tron ​​at 25°C, 0.1-10°C. 6 Ionic conductivity is measured by evaluating it at Hz and 10mV.

[0026] The treated sulfide solid electrolyte may contain, for example, a residual solvent in an amount of 10 ppm or more, 100 ppm or more, or 500 ppm or more, and this amount may be 5000 ppm or less, 3000 ppm or less, 1000 ppm or less, or 1000 ppm or less.

[0027] <Dispersion process> The method of this disclosure includes dispersing a treated sulfide solid electrolyte and a silicon-based electrode active material in a second organic solvent. In addition, the method of this disclosure may further contain other components, such as a binder or a conductive additive, in the second organic solvent.

[0028] (Processed sulfide solid electrolyte) The negative electrode slurry produced by the method of this disclosure contains a treated sulfide solid electrolyte.

[0029] (Silicon-based electrode active material) Examples of silicon-based electrode active materials include any electrode active material containing silicon that acts as an active material. For example, the silicon-based electrode active material may be silicon or a silicon alloy.

[0030] (Second organic solvent) For the second organic solvent, refer to the above description regarding the first organic solvent. The first and second organic solvents may be the same or different.

[0031] (binder) The binder is not particularly limited and examples include polyvinylidene fluoride (PVdF) and butadiene rubber-based binders. These binders may be used individually or in combination of two or more types.

[0032] (Conductive additive) The conductive additives are not particularly limited and include, for example, graphites such as natural graphite and artificial graphite; and carbon blacks such as acetylene black. These conductive additives may be used individually or in combination of two or more.

[0033] (dispersion) The dispersion of the treated sulfide solid electrolyte and the silicon-based electrode active material in the second organic solvent can be carried out by any method.

[0034] For example, this dispersion can be achieved by adding the treated sulfide solid electrolyte and silicon-based electrode active material to a second organic solvent and then stirring.

[0035] <<Method for manufacturing the negative electrode active material layer>> A negative electrode active material layer can be manufactured using the negative electrode mixture slurry produced by the method of this disclosure. Specifically, the negative electrode active material layer can be obtained by coating the negative electrode mixture slurry of this disclosure onto the surface of a substrate, drying it, and pressing it as necessary.

[0036] The ionic conductivity of the negative electrode active material layer obtained in this manner may be, for example, 0.40 mS / cm or higher, 0.50 mS / cm or higher, 0.60 mS / cm or higher, or 0.70 mS / cm or higher, and may also be 1.00 mS / cm or lower, 0.90 mS / cm or lower, or 0.80 mS / cm or lower. [Examples]

[0037] The negative electrode mixture slurries for Comparative Example 1 and Examples 1 and 2 were prepared and evaluated as follows.

[0038] <Comparative Example 1> In a polypropylene container, butyl butyrate as a dispersion medium, a 5% by mass solution of butyl butyrate (a butadiene rubber-based binder), vapor-phase carbon fiber (VGCF) as a conductive additive, silicon particles as a negative electrode active material, and Li2S-P2S5-based glass ceramic as a sulfide solid electrolyte were added and stirred for 30 seconds using an ultrasonic dispersion device (SMT UH-50). Next, the container was shaken for 30 minutes using a shaker (Shibata Scientific Co., Ltd., TTM-1) to obtain the negative electrode mixture slurry of Comparative Example 1.

[0039] The obtained negative electrode mixture slurry was coated onto copper foil (manufactured by UACJ) using an applicator and the blade method. The copper foil coated with the negative electrode mixture slurry was dried on a hot plate at 100°C for 30 minutes to form the negative electrode active material layer of Comparative Example 1 on the copper foil.

[0040] <Example 1> 500 mg of the sulfide solid electrolyte used in Comparative Example 1 (untreated sulfide solid electrolyte) and 2500 mg of butyl butyrate as the first organic solvent were placed in a 20 cc screw bottle and mixed by inversion. The mixture was kept in a constant temperature bath at 25°C for 5 hours. The mixture was then removed and dried in a vacuum dryer at 120°C for 12 hours to obtain the treated sulfide solid electrolyte of Example 1.

[0041] The negative electrode active material layer of Example 1 was formed on a copper foil in the same manner as in Comparative Example 1, except that the obtained treated sulfide solid electrolyte was used as the sulfide solid electrolyte.

[0042] <Example 2> The negative electrode active material layer of Example 2 was formed on the copper foil in the same manner as in Example 1, except that the mixture mixed by inversion was held in a constant temperature bath at 60°C instead of 25°C.

[0043] <Rating> The ionic conductivity of the sulfide solid electrolyte used to produce the negative electrode slurry in the comparative example and the example was measured. Furthermore, the ionic conductivity of the negative electrode active material layer obtained in the comparative example and the example was evaluated. A summary of the experimental conditions and evaluation results for the comparative example and the example is shown in Table 1 below.

[0044] [Table 1]

[0045] As is clear from Table 1, in Examples 1 and 2, when the sulfide solid electrolyte was brought into contact with the first organic solvent to produce a treated sulfide solid electrolyte, the ionic conductivity of the solid electrolyte decreased. However, in Examples 1 and 2, when the treated sulfide solid electrolyte was used to prepare the negative electrode mixture slurry, the ionic conductivity of the resulting negative electrode active material layer was improved.

[0046] This is thought to be because, in Examples 1 and 2, in which a negative electrode mixture slurry was prepared using a treated sulfide solid electrolyte, the treated sulfide solid electrolyte was mixed relatively homogeneously with the silicon-based electrode active material in the negative electrode mixture slurry, and / or the treated sulfide solid electrolyte and the silicon-based electrode active material were relatively homogeneously dispersed in the negative electrode active material layer obtained from such a negative electrode mixture slurry.

Claims

[Claim 1] The sulfide solid electrolyte before treatment is brought into contact with a first organic solvent and dried to obtain a treated sulfide solid electrolyte, and Disperse the treated sulfide solid electrolyte and silicon-based electrode active material in a second organic solvent. A method for producing a negative electrode mixture slurry, including the following:

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