Manufacturing method for negative electrode material

Abstract

To provide a manufacturing method for a negative electrode material that can improve manufacturing efficiency.SOLUTION: The manufacturing method for a negative electrode material including an alloy containing silicon includes an alloying step for manufacturing silicon-lithium alloy particles by mechanically milling the silicon and lithium, and a step for compositing the silicon and lithium prior to the mechanical milling.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Various techniques have been proposed for producing negative electrode materials as disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-032602 [Patent Document 2] Patent Publication No. 2021-158004 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a method for manufacturing an alloy-based negative electrode material, which includes a mechanical milling process for alloying silicon and lithium. Lithium is highly malleable, and when compressed or rolled by itself, it adheres not only to the metal to be alloyed but also to the container used during mechanical milling, resulting in reduced manufacturing efficiency with conventional techniques.

[0005] The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a method for producing a negative electrode material that can improve production efficiency. [Means for solving the problem]

[0006] <1> A method for producing a negative electrode material comprising an alloy containing silicon, comprising: an alloying step of producing silicon-lithium alloy particles by mechanical milling the silicon and lithium; A method for producing a negative electrode material, comprising the step of forming a composite of the silicon and the lithium prior to the mechanical milling. [Effects of the Invention]

[0007] The method for producing the negative electrode material of the present disclosure can improve production efficiency. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a flowchart showing an example of a method for producing a negative electrode material according to the present disclosure. [Figure 2] FIG. 2 shows the XRD patterns of the alloys obtained in Example 1 (bottom) and Comparative Example 2 (top). DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of negative electrode materials that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. In the present disclosure, unless otherwise specified, the average particle size of particles is the median diameter (D50) value, which is the particle size at 50% of the cumulative value in the volume-based particle size distribution measured by laser diffraction / scattering particle size distribution measurement.

[0010] The present disclosure provides a method for producing a negative electrode material comprising an alloy containing silicon, the method comprising: an alloying step of producing silicon-lithium alloy particles by mechanical milling the silicon and lithium; The present invention provides a method for producing a negative electrode material, which comprises a step of forming a composite of the silicon and the lithium prior to the mechanical milling.

[0011] In conventional technology, the alloy of Si and Li in the negative electrode active material synthesis process is synthesized by dry mechanical mixing of Si and Li in a mortar. The alloy compound obtained by alloying Si and Li has the malleability and ductility inherent in Li, and adheres to the mortar. Therefore, dry methods require scraping work from the walls of the mortar, making automation difficult. Furthermore, mixing in a mortar is done in a batch process, and the equipment needs to be enlarged for batch-up, making continuous, automated equipment necessary. In the present disclosure, the yield of silicon-lithium alloy is increased by providing a step of compounding silicon and lithium before the mechanical milling step, and as a result, the production efficiency of silicon alloy-based negative electrode materials is increased. In this disclosure, Si and Li are alloyed using a bead mill capable of continuous wet processing. In this process, a composite of Si and Li (pre-mixed product with a size of 2 mm or less) that has been cut by pre-mixing is used. Because it is a wet process, processing is possible without adhesion, and transportation (liquid delivery) can be automated using only a liquid delivery pump, making it possible to synthesize alloy compounds equivalent to those obtained by mixing in a mortar.By using a pre-mixed product of Si and Li, clogging of the bead mill piping when adding materials can be prevented.

[0012] FIG. 1 is a flowchart showing an example of a method for producing a negative electrode material according to the present disclosure. In the example shown in Figure 1, a base material of Si is prepared, the base material of Si is alloyed with Li, Li is made porous (Li is removed), clathrate is formed, the obtained clathrate is evaluated, and the confining pressure fluctuation is measured.

[0013] The method for producing the negative electrode material of the present disclosure includes at least an alloying step and a composite step.

[0014] [Alloying process] The alloying step is a step of producing silicon-lithium alloy particles by mechanical milling the silicon and lithium. The mechanical milling may be performed using a bead mill or the like. The conditions for mechanical milling are not particularly limited, and may be 16,000 rpm, 30 seconds x 4 to 10 times. The molar ratio of silicon to lithium in the alloying step may be 1:4 to 4:1. The silicon-lithium alloy particles may have an average particle size of 2 mm or less.

[0015] [Combining process] The composite step is a step of composite-forming the silicon and the lithium prior to the mechanical milling. The silicon used for the composite may be in the form of a powder. The lithium used in the composite may be a lithium foil having a diameter of 2 mm or less. If Si powder is not added when compounding, the Li foil will clump together and the Li foil will not be able to be miniaturized.

[0016] The method for producing the negative electrode material of the present disclosure may include a Li porosity (Li removal) step, a clathration step, and the like, after the alloying step.

[0017] [Li porous formation process] In the Li-porosity process, the alloyed product is added to a dispersion medium, and a Li extractant such as ethanol is added dropwise under an Ar gas atmosphere to remove Li from the alloy, yielding porous Si. The dispersion medium is preferably one that does not react with the alloy and is compatible with the Li extractant. By using the same dispersion medium as in the porosity formation process when alloying LiSi in a bead mill, the liquid can be pumped directly.

[0018] [Clatration process] In the clathration step, voided Si is clathrated by a conventionally known method. The silicon clathrate may be silicon clathrate I, silicon clathrate II, or the like. Silicon clathrate I is a compound formed by a dodecahedron in which one Na atom is enclosed by 20 Si atoms and a tetradecahedron in which one Na atom is enclosed by 24 Si atoms, sharing a face. 46Its composition is expressed by the formula: Na exists in all polyhedral cages that make up silicon clathrate I. Silicon clathrate II is a compound in which a dodecahedron of Si and a hexahedron of Si share a face. x Si 136 Here, x satisfies 0≦x≦24. In other words, Na may or may not be present in the polyhedral cages that make up silicon clathrate II.

[0019] The negative electrode material of the present disclosure comprises an alloy containing silicon. The alloy containing silicon may be a silicon-lithium alloy, or may be an alloy with an element other than lithium, such as sodium. The negative electrode material of the present disclosure is used as a negative electrode active material in a battery. The battery of the present disclosure comprises a positive electrode, an electrolyte layer, and a negative electrode comprising the negative electrode material of the present disclosure. The type of battery is not particularly limited, but examples include lithium ion batteries. The battery may be a primary battery or a secondary battery. The battery may be a liquid battery using an electrolytic solution as an electrolyte, or may be a solid battery. In the present disclosure, a solid-state battery refers to a battery containing a solid electrolyte. The solid-state battery may be a semi-solid-state battery that contains a solid electrolyte and a liquid-based material, or an all-solid-state battery that does not contain a liquid-based material. Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery may be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and as a power source for electrical appliances such as information processing devices. [Example]

[0020] (Comparative Example 1) Mesitylene was added to the bead mill as a dispersion medium, and the tube pump and bead mill were operated at 60 rpm and 12 m / s, respectively, to circulate the liquid. Li foil was cut into 2 mm squares with scissors, and this Li foil and crystalline Si powder (Kojundo Chemical, SIE23PB) were added to the bead mill's slurry tank in a molar ratio of 4:1. At the same time, the mixer attached to the slurry tank was also operated at 150 rpm. The material (Li foil) clogged the pipes, making it impossible to alloy.

[0021] (Comparative Example 2) The alloying step was carried out in the same manner as in Comparative Example 1, except that spherical Li powder with a diameter of 50 μm was used instead of the Li foil. After processing for 60 minutes, the recovered slurry was filtered by suction, and the filtered material was dried at 150°C for 3 hours to obtain silicon-lithium alloy particles. The silicon-lithium alloy particles were analyzed using an XRD device.

[0022] Example 1 [Combining process] Si powder and Li foil were placed in a cutter mill in a molar ratio of 4:1, and pre-mixed at 16,000 rpm for 30 seconds four times to obtain a spherical Li composite (pre-mixed product) with Si attached to the surface. [Alloying process] Mesitylene was added to the bead mill as a dispersion medium, and the tube pump and bead mill body were operated at 60 rpm and 12 m / s, respectively, to circulate the liquid. The composite (pre-mixed product) was added to the bead mill's slurry tank. At the same time, the mixer attached to the slurry tank was also operated at 150 rpm. No pipe clogging occurred, and after 60 minutes of processing, the collected slurry was suction filtered, and the resulting residue was dried at 150°C for 3 hours to obtain silicon-lithium alloy particles. The silicon-lithium alloy particles were analyzed using an XRD device.

[0023] Example 2 Silicon-lithium alloy particles were obtained in the same manner as in Example 1, except that in the compounding step, pre-kneading was carried out at 16,000 rpm for 30 seconds × 10 times.

[0024] [Table 1]

[0025] Table 1 shows the results of Examples 1 and 2 and Comparative Examples 1 and 2. In comparison with Comparative Example 1, it is clear that in Examples 1 and 2, the use of a pre-kneaded product of Si and Li can suppress the occurrence of clogging in the bead mill piping when the material is fed. The factors that are believed to have prevented pipe clogging by pre-mixing are the Li size, Li shape (spherical), and the presence or absence of Si adhesion.

[0026] FIG. 2 shows the XRD patterns of the alloys obtained in Example 1 (bottom) and Comparative Example 2 (top). Li3N is presumed to be a contamination during measurement. As shown in FIG. 2, in both Example 1 and Comparative Example 2, the raw material dSi hardly remains, and the LiSi alloy is present as the main phase. In comparison with Comparative Example 2, Example 1 can reduce the manufacturing cost by using inexpensive Li foil instead of Li powder.

Claims

[Claim 1] A method for producing a negative electrode material comprising an alloy containing silicon, comprising: an alloying step of producing silicon-lithium alloy particles by mechanical milling the silicon and lithium; A method for producing a negative electrode material, comprising the step of forming a composite of the silicon and the lithium prior to the mechanical milling.

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