JP2017059342A - Manufacturing method of all solid state battery - Google Patents

Abstract

An object of the present invention is to provide a method for manufacturing an all-solid-state battery having an improved capacity retention rate. According to the present invention, a negative electrode active material layer (2) is laminated on a negative electrode current collector (1), and a solid electrolyte layer (3) is laminated on a negative electrode active material layer (2). Producing an electrode laminated body (4), laminating an electrode terminal (5) on the solid electrolyte layer (3) of the electrode laminated body (4), a negative electrode current collector (1) and an electrode terminal (5) During this period, an electrochemical treatment of applying a voltage of 4.5 V or more (10) is performed, and the electrode terminals (5) laminated on the electrode laminate (4) are removed to remove the electrode laminate (4). ) A positive electrode active material layer and a positive electrode current collector are laminated on the above, and a method for manufacturing an all-solid-state battery. [Selection diagram] Figure 1

Description

The present invention relates to a method for manufacturing an all-solid battery.

  Currently, among various batteries, lithium ion batteries are attracting attention from the viewpoint of high energy density. Among them, all-solid-state batteries in which the electrolytic solution is replaced with a solid electrolyte are particularly attracting attention. This is because an all-solid battery does not use an electrolyte, unlike a battery that uses an electrolyte, so that it does not cause decomposition of the electrolyte due to overcharging, and has high cycle durability and energy density. It is because of having it.

  By the way, in a liquid lithium ion secondary battery using a non-aqueous electrolyte, it is an important issue to reduce the water in the battery container in order to improve the output characteristics of the battery and the capacity retention rate. Recognized. A plurality of inventions for reducing water in the battery container have been disclosed.

  For example, in Patent Document 1, water is removed by immersing the electrode body in a non-aqueous electrolyte and applying a voltage of 1.2 to 4V. In Patent Document 2, a liquid lithium ion secondary battery is applied by applying a voltage not lower than the voltage at which water is electrolyzed (1.23 V) and not higher than the voltage at which a negative electrode film forming reaction occurs. Water contained in the lithium ion secondary battery is removed by electrolysis, and specifically, a voltage of 1.3 V to 3.5 V is applied. In Patent Document 3, an external power source is connected between a negative electrode of a liquid lithium ion secondary battery and a container, and the potential of the container is 1.23 V or higher and the negative electrode is approximately 0 V or lower. By applying a voltage, water inside the battery is removed by electrolysis.

  In Patent Document 4, in order to reduce the organic acid contained in the non-aqueous electrolyte of the liquid lithium ion secondary battery, an electrode active material, an electrode active material, a binder, In addition, after injecting the non-aqueous electrolyte solution into the exterior body of the film-clad battery having an electrode containing the organic acid, the battery is charged to a voltage higher than the voltage at which the organic acid decomposes, thereby reducing the organic acid in the non-aqueous electrolyte solution. The gas generated by the decomposition is discharged from the cut portion of the exterior body.

JP 2009-099285 A JP 2014-056835 A JP 2005-56609 A Japanese Patent Laying-Open No. 2015-69951

  One cause of the decrease in the capacity retention rate of the all-solid battery is a reaction between water and lithium contained in the all-solid battery material. Therefore, in the manufacturing process of an all-solid battery, it is conceivable to suppress a decrease in capacity maintenance rate of the all-solid battery by removing water from the all-solid battery material.

  As a method of removing water from the all-solid battery material, a method of applying a predetermined voltage to the all-solid battery and electrolyzing and removing water can be considered.

  The present inventor theoretically estimates that water electrolysis occurs near 1.2 V, but water electrolysis occurs at a higher voltage in all solid state batteries. It was found that water could not be completely removed even when the same voltage as that described in the method was applied to the all-solid-state battery.

  Therefore, an object of the present invention is to provide a method for producing an all-solid battery in which a decrease in capacity retention rate is suppressed.

  The present inventor has found that the above problem can be solved by the following method.

  The method of the present invention for producing an all-solid battery includes laminating a negative electrode active material layer on a negative electrode current collector, and laminating a solid electrolyte layer on the negative electrode active material layer to produce an electrode laminate, Laminating electrode terminals on the solid electrolyte layer of the electrode laminate, performing an electrochemical treatment of applying a voltage of 4.5 V or more between the negative electrode current collector and the electrode terminals, and on the electrode laminate This includes removing the laminated electrode terminal and laminating a positive electrode active material layer and a positive electrode current collector on the electrode laminate.

  According to the method of the present invention, it is possible to provide a method for producing an all-solid battery in which a decrease in capacity retention rate is suppressed.

FIG. 1 illustrates a specific example of a laminate to which a voltage is applied in the method of the present invention. FIG. 2 (a) illustrates the process steps of the method of Example 1, and FIG. 2 (b) illustrates the process steps of the comparative example 1. FIG. 3 is a diagram comparing the initial charge and discharge efficiencies of the all solid state battery manufactured by the method of Example 1 and the all solid state battery manufactured by the method of Comparative Example 1. FIG. 4 shows the results of cyclic voltammetry measurement in the electrochemical treatment of Example 1.

  Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist of the present invention.

  In the method of the present invention, a negative electrode active material layer is laminated on a negative electrode current collector, and a solid electrolyte layer is laminated on the negative electrode active material layer to produce an electrode laminate, and a solid electrolyte of the electrode laminate Laminating electrode terminals on the layers, performing an electrochemical treatment of applying a voltage of 4.5 V or more between the negative electrode current collector and the electrode terminals, and electrode terminals stacked on the electrode stack And a positive electrode active material layer and a positive electrode current collector are laminated on the electrode laminate.

  Although not limited by the principle, it is considered that the operation principle of the present invention is as follows.

  In an all-solid-state battery, one of the causes of a decrease in the capacity retention rate of the battery is that the negative electrode active material such as graphite, lithium, and water react in the battery to deactivate lithium.

  Therefore, it is important to reduce the amount of water in the battery material in order to suppress a decrease in the capacity retention rate of the all-solid battery.

  As a method for reducing the amount of moisture in the battery material, a method is conceivable in which a voltage is applied to the all solid state battery to electrolyze the water in the battery. However, in this method, lithium ions released from the positive electrode active material by application of voltage chemically react with water before electrolysis on the negative electrode side to become lithium compounds such as lithium hydroxide. For this reason, a decrease in battery capacity cannot be sufficiently suppressed.

  The present inventor performs an electrochemical treatment on the negative electrode active material layer and the solid electrolyte layer before laminating the positive electrode active material layer in the manufacturing process of the all solid state battery, and electrolyzes the water. The present inventors have found a method of reducing the amount of moisture in the material and suppressing the capacity decrease of the all solid state battery.

  In the case of a liquid lithium ion secondary battery, when a negative electrode active material layer is immersed in an electrolytic solution and then moisture is removed by applying a voltage, the negative electrode active material layer is taken out after the moisture is removed. Since the process to perform is needed, a manufacturing process becomes complicated. Moreover, since there exists a possibility of decomposition | disassembly of electrolyte solution and elution of the copper foil used as a collector, sufficient voltage cannot be applied.

<Lamination method>
In the method of the present invention, a negative electrode active material layer is laminated on a negative electrode current collector, and a solid electrolyte layer is laminated on the negative electrode active material layer to produce an electrode laminate, and a solid electrolyte of the electrode laminate The electrode terminal is laminated on the layer. Here, the negative electrode current collector, the negative electrode active material layer, and the solid electrolyte layer can be stacked by a stacking method in a known all-solid battery manufacturing method.

  The method for laminating the electrode terminal on the solid electrolyte layer is not particularly limited, and for example, the electrode terminal can be stacked and pressed on the electrode laminate.

<Electrochemical treatment>
The electrochemical treatment is a treatment in which a voltage of 4.5 V or higher is applied between the negative electrode current collector and the electrode terminal.

  According to this electrochemical treatment, the water contained in the electrode laminate can be reduced by electrolysis. Theoretically, in order to electrolyze water, it is sufficient to apply a voltage at which water begins to electrolyze (1.23 V (standard hydrogen electrode potential)). However, in the present invention, in order to sufficiently remove water, a voltage of 4.5 V or higher, which is higher than the voltage at which water begins to electrolyze, is applied.

  The upper limit of the applied voltage is preferably a voltage at which the material used for the all solid state battery is not denatured. For example, 10.0 V or less, 9.0 V or less, 8.0 V or less, 7.0 V or less, 6.0 V or less, or 5 0.0 V or less is preferable.

  For example, as shown in FIG. 1, the electrochemical treatment is performed on the negative electrode current collector (1), the negative electrode active material layer (2), and the electrode laminate (4) composed of the solid electrolyte layer (3). This can be done by applying (10) a voltage between the electric body (1) and the electrode terminal (5) on the electrode laminate (4).

In addition, the electrolysis of water can be represented by the following chemical reaction formula, for example:
Oxidation reaction: H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e ⁻
Reduction reaction: H ₂ O + e ⁻ → 1 / 2H ₂ + OH ⁻

  Whether the oxidation reaction and the reduction reaction in the electrolysis of water occur on the negative electrode collector side or the electrode terminal side depends on the voltage application direction.

<Removal of electrode terminal>
The method for removing the electrode terminal laminated on the electrode laminate is not particularly limited. For example, if it is a metal foil-shaped electrode terminal, it can be removed by peeling from the electrode laminate.

<Negative electrode current collector>
The raw material of the negative electrode current collector is not particularly limited, and various metals, for example, Ag, Cu, Au, Al, Ni, Fe, SUS, Ti, etc., or current collectors of these alloys are used. Can do. From the viewpoint of chemical stability, the negative electrode current collector is preferably a copper current collector.

<Negative electrode active material layer>
The negative electrode active material layer includes a negative electrode active material, and optionally a solid electrolyte, a conductive aid, and a binder.

  The negative electrode active material is not particularly limited as long as it is a known negative electrode active material. Examples thereof include a carbon-based negative electrode active material such as graphite, soft carbon, or hard carbon, a known alloy active material such as silicon, a silicon alloy, or tin, or a combination thereof.

The solid electrolyte is not particularly limited as long as it is a solid electrolyte used as a solid electrolyte of an all-solid lithium secondary battery. For example, an oxide-based amorphous solid electrolyte such as Li ₂ O—B ₂ O ₃ —P ₂ O ₅ and Li ₂ O—Si ₂ O, Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , _{LiI-Li 2 S-P 2} S 5, LiI-Li 2 S-P 2 O 5, LiI-LiPO 4 -P 2 S 5, and _Li 2 _S-P 2 _{S 5} sulfide solid electrolyte such as, and LiI _{, Li 3 N, Li 5 La} 3 Ta 2 O 12, Li 7 La 3 Zr 2 O 12, Li 6 BaLa 2 Ta 2 O 12, Li3PO (4-3 / 2w) N w (w <1), and Li _Examples thereof include crystalline oxides and oxynitrides such as _3.6 Si _0.6 P _0.4 O ₄ .

  As a conductive aid, in addition to a carbon material such as VGCF, acetylene black, ketjen black, carbon nanotube (CNT), or carbon nanofiber (CNF), a metal such as nickel, aluminum, or SUS, or a combination thereof. Can be raised.

  The binder is not particularly limited, but a polymer resin such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide (PA), polyamideimide (PAI), butadiene rubber (BR) Styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), styrene-ethylene-butylene-styrene block copolymer (SEBS), carboxymethyl cellulose (CMC), or a combination thereof. From the viewpoint of high temperature durability, the binder is preferably polyimide, polyamide, polyamideimide, polyacryl, carboxymethylcellulose, or a combination thereof.

<Solid electrolyte layer>
The solid electrolyte layer has a solid electrolyte. As the solid electrolyte, those similar to those described in the negative electrode active material layer can be used.

<Electrode laminate>
The electrode laminate includes the negative electrode current collector, the negative electrode active material layer, and the solid electrolyte layer in this order.

<Electrode terminal>
The electrode terminal is not particularly limited as long as it has conductivity, and various metals can be used. For example, Ag, Cu, Au, Al, Ni, Fe, SUS, Ti, or an alloy thereof can be used. Can be used. Moreover, alloy tool steel (SKD11) can also be used.

<Positive electrode active material layer>
The positive electrode active material layer includes a positive electrode active material, and optionally a solid electrolyte, a conductive additive, and a binder.

The positive electrode active material is not particularly limited as long as it is a material used as a positive electrode active material for a lithium secondary battery. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), nickel cobalt lithium manganate (Li _{1 + x} Ni _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganate (LiMn ₂ O ₄₎ ), Li _{1 + x} Mn _2−xy M _y O ₄ (M is one or more selected from Al, Mg, Co, Fe, Ni, Zn) And lithium metal phosphate (Li _x TiO _y ) or LiMPO ₄ (wherein M is one or more selected from Fe, Mn, Co, Ni), or a combination thereof. .

  As the solid electrolyte, the conductive additive, and the binder, the same materials as those described in the negative electrode active material layer can be used.

<Positive electrode current collector>
The raw material of the positive electrode current collector is not particularly limited, and various metals, for example, Ag, Cu, Au, Al, Ni, Fe, SUS, Ti or the like, or a current collector of these alloys is used. Can do. From the viewpoint of chemical stability, the positive electrode current collector is preferably an aluminum current collector.

<Example 1>
By the following method, the all-solid-state battery of Example 1 was produced and the initial charge / discharge efficiency was evaluated. FIG. 2A illustrates the method of the first embodiment.

  In the method of Example 1, a negative electrode active material layer is laminated on a negative electrode current collector, and a solid electrolyte layer is laminated on the negative electrode active material layer to produce an electrode laminate. The electrode terminal is laminated on the electrolyte layer, and the water in the battery material is electrolyzed and removed by electrochemical treatment, the electrode terminal on the electrode laminate is removed, and the positive electrode active material layer and the positive electrode collector are disposed on the electrode laminate. The all-solid-state battery is completed by stacking electric bodies and the battery characteristics are evaluated.

  Details of each step of Example 1 are as follows.

1. Preparation of Solid Electrolyte 0.766 g of Li ₂ S (Nippon Chemical Industry) and 1.23 g of P ₂ S ₅ (Aldrich) were weighed and mixed for 5 minutes in an agate mortar. Thereafter, 4 g of heptane as a dispersion medium was put into an agate mortar, and a solid electrolyte was obtained by mechanical milling for 40 hours using a planetary ball mill.

2. Preparation of positive electrode active material layer 12 g of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (Nichia Chemical) as a positive electrode active material, gas-phase carbon fiber (VGCF) as a conductive additive (Showa Denko) 0 0.5 g and 6 g of the above solid electrolyte were mixed and dispersed in heptane (Kanto Chemical) as a dispersion medium to obtain a positive electrode active material layer material. The positive electrode active material was coated on an aluminum foil as a positive electrode current collector to obtain a positive electrode active material layer.

3. Preparation of Negative Electrode Active Material Layer 9 g of graphite (Mitsubishi Chemical) as the negative electrode active material and 9 g of the above solid electrolyte were mixed and dispersed in heptane (Kanto Chemical) to obtain a negative electrode active material layer material. The negative electrode active material layer material was coated on a copper foil as a negative electrode current collector to obtain a negative electrode active material layer (11 mg) on the negative electrode current collector.

4). Electrochemical treatment A solid electrolyte layer (80 mg) was laminated on the negative electrode active material layer (11 mg) to prepare an electrode laminate. Thereafter, an alloy tool steel (SKD11) as an electrode terminal is laminated on the solid electrolyte layer of the electrode laminate, and is pressed and molded at 1 ton / cm ^2. An electrode laminate in which 1 cm ² of electrode terminals are laminated. The body was made.

  A cyclic voltammetry measurement device was connected between the negative electrode current collector and the electrode terminal, and cyclic voltammetry measurement was performed from −4.5 V to +4.5 V. The sweep speed in CV measurement was 2 mV / s.

5. Assembly of all-solid-state battery The electrode terminal laminated on the electrode laminate is removed, the positive electrode active material layer and the positive electrode current collector are laminated on the solid electrolyte layer of the electrode laminate, and pressed at 6 ton / cm ^2. The all-solid battery of Example 1 was produced.

6). Evaluation of all-solid-state battery The all-solid-state battery of Example 1 was charged to 4.4 V with a constant current and a constant voltage, and the charge capacity of the all-solid-state battery was measured. Then, it discharged to 3.0V with constant current and constant voltage, and measured the discharge capacity of the all-solid-state battery. The current value at this time was set to 0.52 mA to 0.016 mA.

  The initial charge / discharge efficiency was measured from the measured charge capacity and discharge capacity.

<Comparative Example 1>
An all-solid-state battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the electrochemical treatment in 4 above was not performed. Further, in the same manner as in Example 1, the all solid state battery of Comparative Example 1 was evaluated.

  FIG. 2B illustrates the method of Comparative Example 1. Unlike the method of Example 1 illustrated in FIG. 2A, the method of Comparative Example 1 did not perform the step of performing electrochemical treatment to remove water in the battery material by electrolysis.

<Result>
The initial charge / discharge efficiency of the all solid state battery of Example 1 was larger than the initial charge / discharge efficiency of the all solid state battery of Comparative Example 1 (see FIG. 3). In the all-solid-state battery of Example 1, it was considered that the water in the battery material was electrolyzed and decreased by electrochemical treatment, so that the reaction between lithium and water inside the battery was reduced and the capacity reduction was suppressed. . On the other hand, since the all-solid-state battery of Comparative Example 1 did not perform electrochemical treatment, it was considered that the reaction between lithium and water inside the battery could not be reduced and the capacity reduction could not be suppressed. .

<Reference example>
4 shows the results of cyclic voltammetry measurement in the electrochemical treatment of Example 1. FIG. In FIG. 4, (i) to (Vii) represent the order of changes in current and voltage in cyclic voltammetry measurement.

  As a result of the cyclic voltammetry measurement in the electrochemical treatment of Example 1, in the all solid state battery of Example 1, it was considered that the water was electrolyzed in the vicinity of 4V, which is higher than the voltage at which water is electrolyzed (1.23V). A current peak was observed, and a current believed to be due to water electrolysis up to around 4.5V was observed.

  From this, when applying a voltage to the negative electrode active material layer of the all-solid battery and the laminate of the solid electrolyte layer to electrolyze the water inside the battery, it is higher than the voltage at which the water is electrolyzed, 4.5 V or more It is considered that water can be electrolyzed more efficiently when a voltage of 1 is applied.

DESCRIPTION OF SYMBOLS 1 Negative electrode collector 2 Negative electrode active material layer 3 Solid electrolyte layer 4 Electrode laminated body 5 Electrode terminal 10 Voltage is applied

Claims (1)

Laminating a negative electrode active material layer on a negative electrode current collector, and laminating a solid electrolyte layer on the negative electrode active material layer to produce an electrode laminate,
Laminating electrode terminals on the solid electrolyte layer of the electrode laminate,
Performing an electrochemical treatment of applying a voltage of 4.5 V or more between the negative electrode current collector and the electrode terminal; and removing the electrode terminal laminated on the electrode laminate; Including laminating a positive electrode active material layer and a positive electrode current collector on the laminate,
Manufacturing method of all solid state battery.

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