Method for manufacturing silicon clathrate electrode active material and method for manufacturing lithium ion battery

Abstract

To provide a method for manufacturing a silicon clathrate electrode active material capable of increasing the throughput of a sodium-containing silicon clathrate in a sodium removal step and capable of reducing the amount of sodium remaining in the obtained silicon clathrate electrode active material, and a method for manufacturing a lithium-ion battery comprising manufacturing such a silicon clathrate electrode active material.SOLUTION: The method of the present disclosure for manufacturing a silicon clathrate electrode active material comprises (a) providing a sodium-containing silicon clathrate; and (b) contacting the sodium-containing silicon clathrate with a hydrogen fluoride solution to remove at least a portion of sodium from the sodium-containing silicon clathrate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a silicon clathrate electrode active material and a method for producing a lithium ion battery. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles or hybrid vehicles is progressing. Silicon is known as an electrode active material for batteries, particularly lithium-ion batteries.

[0003] Silicon electrode active materials have a large theoretical capacity and are effective in increasing the energy density of batteries. However, they suffer from the problem of large expansion during charging. It is known that the use of silicon clathrate electrode active materials as silicon electrode active materials can suppress expansion during charging.

[0004] For example, Patent Document 1 discloses a silicon clathrate electrode active material having a silicon clathrate type II crystalline phase, voids inside the primary particles, and a void volume of voids having a pore diameter of 100 nm or less of 0.05 cc / g or more and 0.15 cc / g or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-158004 Summary of the Invention [Problem to be solved by the invention]

[0006] Silicon clathrate electrode active materials can be produced by removing sodium from sodium-containing silicon clathrates, but there is a need to improve the processing efficiency of sodium-containing silicon clathrates in this process and to reduce the amount of sodium remaining in the resulting silicon clathrate electrode active materials.

[0007] An object of the present disclosure is to provide a method for producing a silicon clathrate electrode active material that can improve the treatment efficiency of sodium-containing silicon clathrate in a sodium removal step and reduce the amount of sodium remaining in the resulting silicon clathrate electrode active material, and a method for producing a lithium-ion battery that includes producing such a silicon clathrate electrode active material. [Means for solving the problem]

[0008] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A method for producing a silicon clathrate electrode active material, comprising the steps of: (a) providing a sodium-containing silicon clathrate; and (b) contacting the sodium-containing silicon clathrate with a hydrogen fluoride solution to remove at least a portion of the sodium from the sodium-containing silicon clathrate. <Aspect 2> 2. The method of claim 1, wherein the solvent for the hydrogen fluoride solution is a mixed solvent of water and an organic solvent. <Aspect 3> 3. The method of any one of claims 1 to 2, wherein the sodium-containing silicon clathrate has a porous structure. <Aspect 4> Aspect 4. The method of any one of Aspects 1 to 3, wherein the silicon clathrate electrode active material is for use as a negative electrode active material in a lithium ion battery. <Aspect 5> Producing a silicon clathrate electrode active material by the method according to any one of aspects 1 to 4; and forming an electrode active material layer containing the silicon clathrate electrode active material; A method for manufacturing a lithium-ion battery, comprising: [Effects of the Invention]

[0009] According to the method for producing a silicon clathrate electrode active material disclosed herein, it is possible to improve the efficiency of treating the sodium-containing silicon clathrate in the sodium removal step and reduce the amount of sodium remaining in the resulting silicon clathrate electrode active material. The present disclosure also provides a method for producing a lithium-ion battery, which includes producing a silicon clathrate electrode active material. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0011] <<Method for producing silicon clathrate electrode active material>> The disclosed method of making a silicon clathrate electrode active material includes (a) providing a sodium-containing silicon clathrate, and (b) contacting the sodium-containing silicon clathrate with a hydrogen fluoride solution to remove at least a portion of the sodium from the sodium-containing silicon clathrate.

[0012] As a method for producing a silicon clathrate electrode active material, for example, a sodium-containing silicon clathrate (e.g., Na 20 Si 136 ) with zinc chloride and calcined to remove sodium (Na) from the sodium-containing silicon clathrate, resulting in a silicon clathrate with a reduced amount of sodium (e.g., NaSi 136 ) is one method.

[0013] However, since the reaction in this method is a solid-state reaction, it requires a relatively long reaction time. The present inventors have found that, instead of or in addition to this reaction, Na can be efficiently removed from the sodium-containing silicon clathrate by contacting the sodium-containing silicon clathrate with a hydrogen fluoride (HF) solution.

[0014] In the present disclosure, the "electrode active material" can be used as either a "positive electrode active material" or a "negative electrode active material", and is particularly used as a "negative electrode active material".

[0015] <Provision of sodium-containing silicon clathrate> The method of the present disclosure includes providing a sodium-containing silicon clathrate.

[0016] Sodium-containing silicon clathrates can be prepared by removing sodium from sodium silicon (NaSi) alloys.

[0017] Specifically, a silicon source is first reacted with a sodium source such as sodium hydride to prepare a NaSi alloy. The NaSi alloy thus prepared is then heated to remove sodium from the NaSi alloy and form a clathrate, thereby preparing a silicon clathrate. Alternatively, the NaSi alloy thus prepared is reacted with aluminum fluoride as a sodium trapping agent to remove sodium from the NaSi alloy and form a clathrate, thereby preparing a silicon clathrate.

[0018] The sodium-containing silicon clathrate may have a porous structure, which is preferable in that the contact area between the sodium-containing silicon clathrate and the hydrogen fluoride (HF) solution is large, improving the efficiency of removing Na.

[0019] <Sodium removal> The disclosed method includes contacting a sodium-containing silicon clathrate with a hydrogen fluoride solution to remove at least a portion of the sodium from the sodium-containing silicon clathrate.

[0020] The solvent for the hydrogen fluoride solution may be water, an organic solvent, or a mixed solvent of water and an organic solvent. When this solvent contains water, i.e., water or a mixed solvent of water and an organic solvent, and particularly when the mixed solvent is water and an organic solvent, it is preferable in that the generation of by-products such as sodium silicofluoride (NaSiF) can be suppressed.

[0021] The solvent preferably contains an organic solvent, which can reduce the amount of water remaining in the silicon clathrate electrode active material. The proportion of the organic solvent in the solution may be 80% by mass or more, 90% by mass or more, or 95% by mass or more.

[0022] The organic solvent may be any organic solvent capable of dissolving hydrogen fluoride, and when used in combination with water, any organic solvent capable of dissolving hydrogen fluoride and compatible with water may be used. The organic solvent is preferably an alcohol, more preferably a lower alcohol, and even more preferably ethanol.

[0023] In the method of the present disclosure, the ratio of the amount (mol) of hydrogen fluoride to the mass (g) of silicon clathrate (HF [mol] / Si [g]) may be 0.01 mol / g or more, 0.02 mol / g or more, 0.03 mol / g or more, or 0.04 mol / g or more, and may be 0.20 mol / g or less. When this ratio is within the above range, sodium can be efficiently removed from the sodium-containing silicon clathrate to Na.

[0024] The method for contacting the sodium-containing silicon clathrate with the hydrogen fluoride solution includes, but is not limited to, a mixing operation such as stirring.

[0025] The time for contacting the sodium-containing silicon clathrate with the hydrogen fluoride solution may be 0.5 hours or more, 1 hour or more, or 2 hours or more, and may be 6 hours or less, 5 hours or less, or 4 hours or less.

[0026] In the silicon clathrate electrode active material produced by the method of the present disclosure, the amount of sodium in the silicon clathrate electrode active material may be 6.5% by mass or less, 6.0% by mass or less, 5.5% by mass or less, 5.2% by mass or less, 5.0% by mass or less, 4.8% by mass or less, or 4.6% by mass or less.

[0027] The amount of sodium in the silicon clathrate electrode active material can be measured, for example, by inductively coupled plasma (ICP) analysis.

[0028] <Application> The silicon clathrate electrode active material obtained by the method of the present disclosure can be used as a negative electrode active material for lithium ion batteries.

[0029] <<Lithium-ion battery manufacturing method>> The disclosed method of making a lithium ion battery includes making a silicon clathrate electrode active material by the disclosed method and forming an electrode active material layer containing the silicon clathrate electrode active material.

[0030] For the method for producing the silicon clathrate electrode active material, reference can be made to the above description regarding the method for producing the silicon clathrate electrode active material of the present disclosure.

[0031] The method for forming the electrode active material layer is not particularly limited, and any known method can be used. For example, when the negative electrode active material layer contains the silicon clathrate electrode active material of the present disclosure, a slurry containing the silicon clathrate electrode active material can be applied to a negative electrode current collector and dried to obtain an electrode active material layer formed on the negative electrode current collector layer, i.e., a negative electrode active material layer.

[0032] The method for forming the battery is not particularly limited, and any known method can be used. Hereinafter, a method for manufacturing a battery in which the negative electrode active material layer contains the silicon clathrate electrode active material of the present disclosure will be described.

[0033] The method for manufacturing a battery according to the present disclosure may include, in addition to manufacturing a silicon clathrate electrode active material and forming a negative electrode active material layer containing the silicon clathrate electrode active material, arranging a negative electrode current collector layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

[0034] <Negative electrode current collector layer> The material used for the negative electrode current collector layer is not particularly limited, and any material that can be used as a negative electrode current collector for a battery can be appropriately adopted. For example, copper, a copper alloy, and copper plated or vapor-deposited with nickel, chromium, carbon, or the like may be used, but is not limited to these.

[0035] The shape of the negative electrode current collector layer is not particularly limited, and examples thereof include foil, plate, mesh, etc. Among these, foil is preferred.

[0036] <Negative electrode active material layer> The negative electrode active material layer of the present disclosure is a layer containing a negative electrode active material, and optionally an electrolyte, a conductive additive, and a binder.

[0037] (Negative electrode active material) The negative electrode active material comprises a silicon clathrate electrode active material of the present disclosure.

[0038] (electrolyte) The material of the solid electrolyte is not particularly limited, and any material that can be used as a solid electrolyte for a lithium ion battery can be used. For example, the solid electrolyte may be a sulfide solid electrolyte.

[0039] Examples of sulfide solid electrolytes include, but are not limited to, amorphous sulfide solid electrolytes, crystalline sulfide solid electrolytes, and argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li2S-P2S5-based (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2(Li 13 GeP3S 16 , Li 10 GeP2S 12 ), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x etc.; or combinations thereof, but are not limited to these.

[0040] The sulfide solid electrolyte may be glass or crystallized glass (glass ceramic).

[0041] When the negative electrode active material layer contains a solid electrolyte, the mass ratio of the silicon clathrate electrode active material to the solid electrolyte in the negative electrode active material layer (mass of silicon clathrate electrode active material: mass of solid electrolyte) is preferably 85:15 to 30:70, and more preferably 80:20 to 40:60.

[0042] The electrolyte preferably contains a supporting salt and a solvent.

[0043] Examples of supporting salts (lithium salts) for the electrolyte solution having lithium ion conductivity include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0044] Examples of solvents used in the electrolytic solution include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).The electrolytic solution preferably contains two or more solvents.

[0045] (Conductive additive) The conductive additive is not particularly limited, and may be, for example, VGCF (Vapor Grown Carbon Fiber), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), carbon nanofibers (CNF), or the like, but is not limited thereto.

[0046] (binder) The binder is not particularly limited, and may be, for example, but not limited to, a material such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), or styrene butadiene rubber (SBR), or a combination thereof.

[0047] The thickness of the negative electrode active material layer may be, for example, 0.1 to 1000 μm.

[0048] <Electrolyte layer> The electrolyte layer contains at least an electrolyte. In addition to the electrolyte, the electrolyte layer may contain a binder, etc., as necessary. For the electrolyte and the binder, reference can be made to the above description of the negative electrode active material layer of the present disclosure.

[0049] The thickness of the electrolyte layer is, for example, 0.1 to 300 μm, and preferably 0.1 to 100 μm.

[0050] <Cathode active material layer> The positive electrode active material layer is a layer containing a positive electrode active material, and optionally an electrolyte, a conductive additive, a binder, and the like.

[0051] The material of the positive electrode active material is not particularly limited. For example, the positive electrode active material may be lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese oxide (LiMnO), LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, Li 1+x Mn 2-x-y Lithium-Mn spinel substituted with different elements, which has a composition represented by MyO4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), and lithium titanate (Li x TiO y ), lithium metal phosphate (LiMPO4, M is one or more metals selected from Fe, Mn, Co, and Ni), etc., but are not limited to these.

[0052] The positive electrode active material may have a coating layer. The coating layer is a layer containing a substance that has lithium ion conductivity, low reactivity with the positive electrode active material and solid electrolyte, and can maintain the shape of the coating layer without flowing even when in contact with the active material and solid electrolyte. Specific examples of materials that constitute the coating layer include LiNbO3 and Li4Ti5O 12 , Li3PO4, etc., but are not limited to these.

[0053] The positive electrode active material may be, for example, particulate. The average particle size (D50) of the positive electrode active material is not particularly limited, but may be, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size (D50) of the positive electrode active material is, for example, 50 μm or less, or may be 20 μm or less. The average particle size (D50) can be calculated, for example, from measurements using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM).

[0054] For the electrolyte, the conductive additive, and the binder, reference can be made to the above descriptions regarding the negative electrode active material layer of the present disclosure.

[0055] When the positive electrode active material layer contains a solid electrolyte, the mass ratio of the positive electrode active material to the solid electrolyte in the positive electrode active material layer (mass of the positive electrode active material: mass of the solid electrolyte) is preferably 85:15 to 30:70, and more preferably 80:20 to 50:50.

[0056] The thickness of the positive electrode active material layer is, for example, 0.1 μm to 1000 μm, preferably 1 μm to 100 μm, and more preferably 30 μm to 100 μm.

[0057] <Positive electrode current collector layer> The material used for the positive electrode current collector layer is not particularly limited, and any material that can be used as a positive electrode current collector for a battery can be appropriately adopted. Examples of the material include, but are not limited to, SUS, nickel, chromium, gold, platinum, aluminum, iron, titanium, zinc, and the like, as well as these metals plated or vapor-deposited with nickel, chromium, carbon, and the like.

[0058] The shape of the positive electrode current collector layer is not particularly limited, and examples thereof include foil, plate, mesh, etc. Among these, foil is preferred.

[0059] The lithium ion battery produced by the method of the present disclosure may be a liquid-based battery containing an electrolytic solution as the electrolyte layer, or may be a solid-state battery having a solid electrolyte layer as the electrolyte layer. In the context of the present disclosure, the term "solid-state battery" refers to a battery that uses at least a solid electrolyte as the electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. The solid-state battery of the present disclosure may also be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as the electrolyte.

[0060] The lithium ion battery produced by the method of the present disclosure may be a primary battery or a secondary battery.

[0061] Examples of the shape of the lithium ion battery include coin type, laminate type, cylindrical type, and square type. [Example]

[0062] <Synthesis of silicon clathrate electrode active material> <Alloying> A sodium-silicon (NaSi) alloy was produced using Si powder and sodium hydride (NaH) as a sodium (Na) source. The NaH used was previously washed with hexane. NaH and Si powder were weighed out to a molar ratio of 1.05:1, and the weighed NaH and Si powders were mixed using a cutter mill. The resulting mixture was heated in a heating furnace under an argon atmosphere at 500°C for 40 hours to obtain a powdered NaSi alloy.

[0063] <Clathrate> The obtained NaSi alloy and aluminum fluoride (AlF3) were weighed out so that the molar ratio was 1:0.35, and the weighed NaSi alloy and AlF3 were mixed in a cutter mill to obtain a reaction raw material. The obtained powdered reaction raw material was placed in a stainless steel reaction vessel and heated in a heating furnace under an argon atmosphere at 310 °C for 60 hours to obtain a sodium-containing silicon clathrate (Na 20 Si 136 ) was obtained.

[0064] <Sodium removal> Example 1 The obtained Na 20 Si 136 100 ml of ethanol and 3.71 ml of 46% by mass aqueous hydrogen fluoride (HF) solution were added to the mixture and stirred. The solution was filtered, and the filtered solid was washed eight times with 25 ml of ethanol and dried overnight at 60°C under reduced pressure. 20 Si 136 The silicon clathrate electrode active material of Example 1 was obtained from which at least a portion of the sodium had been removed.

[0065] (Comparative Example 1) Na 20 Si 136 and zinc chloride (ZnCl2) were weighed out to a molar ratio of 1:0.75, and the weighed Na20 Si 136 and ZnCl2 were mixed to obtain a powdered reaction raw material. The powdered reaction raw material was placed in a stainless steel reaction vessel and fired in a heating furnace under an Ar atmosphere at 430°C to cause a reaction. The reaction product was washed with a mixed solvent of HNO3 and H2O in a volume ratio of 10:90. This removed by-products from the reaction product. After washing, the mixture was filtered, and the filtered solid was dried at 120°C for 3 hours or more to obtain a silicon clathrate electrode active material of Comparative Example 1.

[0066] (Comparative Example 2) A silicon clathrate electrode active material of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that the firing temperature was set to 450°C.

[0067] "evaluation" <Na 20 Si 136 Processing capacity In the sodium removal process, Na 20 Si 136 The amount that can be treated per day was calculated and expressed as a relative value with the value of Comparative Example 1 being set to 1.

[0068] <Sodium content after sodium removal process> The amount of sodium remaining in the silicon clathrate electrode active material after the sodium removal step was measured by inductively coupled plasma (ICP) analysis.

[0069] "result" The evaluation results are shown in Table 1.

[0070] [Table 1]

[0071] As shown in Table 1, Na 20 Si 136 In the method of Example 1, sodium removal from 20 Si 136The amount of sodium that could be treated was large, and the amount of sodium remaining in the silicon clathrate electrode active material was small.

Claims

1. A method for producing a silicon clathrate electrode active material, comprising the steps of: (a) providing a sodium-containing silicon clathrate; and (b) contacting the sodium-containing silicon clathrate with a hydrogen fluoride solution to remove at least a portion of sodium from the sodium-containing silicon clathrate, wherein the solvent of the hydrogen fluoride solution is a mixed solvent of water and an organic solvent.

2. The method described in claim 1, wherein the proportion of the organic solvent in the hydrogen fluoride solution is 95 mass% or more.

3. The method described in claim 2, wherein the organic solvent is ethanol.

4. The method described in claim 1, wherein in step (b), the sodium-containing silicon clathrate and the hydrogen fluoride solution are stirred and mixed for at least 1 hour and not more than 5 hours to remove at least a portion of the sodium from the sodium-containing silicon clathrate.

5. The method described in claim 4, wherein the amount of sodium in the silicon clathrate electrode active material is 5.0 mass% or less.

6. The method of claim 1 , wherein the sodium-containing silicon clathrate has a porous structure.

7. 10. The method of claim 1, wherein the silicon clathrate electrode active material is for use as an anode active material in a lithium ion battery.

8. Producing a silicon clathrate electrode active material by the method according to any one of claims 1 to 7; and forming an electrode active material layer containing the silicon clathrate electrode active material; A method for manufacturing a lithium-ion battery, comprising:

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