JP6886822B2 - Manufacturing method of all-solid-state battery - Google Patents

Description

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

Lithium secondary batteries are known to have the highest energy density among various secondary batteries. However, widely used lithium secondary batteries use a flammable organic electrolyte as an electrolyte. Therefore, in lithium secondary batteries, safety measures against liquid leakage, short circuit, overcharge, etc. are required more strictly than other batteries. Therefore, in recent years, research and development on an all-solid-state battery using an oxide-based or sulfide-based solid electrolyte as an electrolyte has been actively carried out. The solid electrolyte is a material composed mainly of an ionic conductor capable of ionic conduction in a solid, and in principle, various problems caused by a flammable organic electrolyte solution like a conventional lithium secondary battery occur. do not. An all-solid-state battery is an integral sintered body (hereinafter referred to as a laminated electrode body) in which a layered solid electrolyte (electrolyte layer) is sandwiched between a layered positive electrode (positive electrode layer) and a layered negative electrode (negative electrode layer). It also has a structure in which a current collector is formed. The solid electrolyte exhibits ionic conductivity by crystallizing by firing, and is contained not only in the solid electrolyte layer but also in the positive electrode layer and the negative electrode layer (hereinafter, also collectively referred to as an electrode layer). That is, the electrode layer exhibits ionic conductivity by interposing the solid electrolyte crystallized by firing between the particles of the positive electrode active material and the negative electrode active material (hereinafter, also collectively referred to as the electrode active material).

As a method for manufacturing the laminated electrode body which is the main body of the all-solid-state battery, a method using a well-known green sheet is common. Since the green sheet method is an already established technology as a method for manufacturing laminated chip components such as multilayer ceramic chip capacitors and multilayer chip inductors, the green sheet method is also used to reliably and inexpensively manufacture all-solid-state batteries. It is preferable to manufacture by.

In order to prepare a laminated electrode body using the green sheet method, a slurry-like positive electrode layer material containing a positive electrode active material and a solid electrolyte, a slurry-like negative electrode layer material containing a negative electrode active material and a solid electrolyte, and a solid electrolyte are used. Each of the slurry-like solid electrolyte layer materials contained therein is formed into a sheet-like green sheet, and the green sheet made of the solid electrolyte layer material (hereinafter, also referred to as the electrolyte layer sheet) is the green sheet made of the positive electrode layer material (hereinafter, the positive electrode layer sheet). The laminate obtained by sandwiching it between a green sheet made of a negative electrode layer material (hereinafter, also referred to as a negative electrode layer sheet) is pressure-bonded, and the pressure-bonded laminate is fired. As a result, a laminated electrode body which is a sintered body is completed.

As a method for producing a green sheet, there is a well-known doctor blade method. In the doctor blade method, a binder (polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylidene fluoride (PVDF), acrylic, ethyl methyl cellulose, etc.) and a solvent (anhydrous alcohol, etc.) are mixed with ceramic powder such as an inorganic oxide. The slurry thus obtained is formed into a thin plate by a coating step or a printing step to prepare a green sheet. Then, in the all-solid-state battery, each powder of the positive electrode active material, the solid electrolyte, and the negative electrode active material is used as the ceramic powder to be contained in the slurry.

As the electrode active material, a material used in a conventional lithium secondary battery can be used. In addition, since the all-solid-state battery does not use a flammable electrolyte, an electrode active material capable of obtaining a higher potential difference is also being studied. The solid electrolyte has the formula _{Li a X b Y c P d} O NASICON type oxide-based solid electrolyte represented by _e, as the solid electrolyte of the NASICON type oxide, Patent Document 1 below The described Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (hereinafter, also referred to as LAGP) is well known. Further, in Non-Patent Document 1 below, in relation to the embodiment of the present invention, lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ , which is well known as a positive electrode active material for a lithium secondary battery, The manufacturing method of (hereinafter also referred to as LVP) is described. As a method for producing LAGP, there is a sol-gel method using a metal alkoxide as a raw material, and Non-Patent Document 2 describes a method for producing LAGP by the sol-gel method. In addition, Non-Patent Document 3 describes an outline of an all-solid-state battery.

International Publication No. 2016/157751

GS Yuasa Co., Ltd., "Development of Lithium Ion Battery Using Vanadium Lithium Phosphate Synthesized by Liquid Phase Method", [online], [Search on December 21, 2016], Internet <URL: http: // www .gs-yuasa.com/jp/technic/vol8/pdf/008_01_016.pdf ＞ Masashi Kotobuki, Keigo Hoshina, Yasuhiro Isshiki, Kiyoshi Kanamura, "PREPARATION OF Li1.5Al0.5Ge1.5 (PO4) 3 SOLID ELECTROLYTE BY SOL-GEL METHOD", Phosphorus Research Bulletin, Vol.25 (2011), pp.061- 063 Osaka Prefecture University Inorganic Chemistry Research Group, "Overview of All Solid-State Batteries", [online], [Searched on December 21, 2016], Internet <URL: http://www.chem.osakafu-u.ac.jp /ohka/ohka2/research/battery_li.pdf ＞

Not limited to all-solid-state batteries, when ceramic parts are manufactured by the green sheet method, when the green sheet is fired to obtain ceramic parts that are sintered bodies, if the binder contained in the green sheet remains, it is baked. There is a problem that the binding density is lowered and the binder component is carbonized to cause an internal short circuit. Therefore, in the green sheet method, a debinder step of heat-treating the green sheet to remove the binder is performed prior to firing.

However, in the case of an all-solid-state battery, there is a problem that some electrode active materials such as LVP are oxidized in the debindering step and the valence changes. When the valence changes, the number of electrons contributing to the charge / discharge reaction decreases, and the characteristics of the battery deteriorate. If the debinder step is performed in an inert gas atmosphere in order to prevent oxidation of the electrode active material, the binder is not completely decomposed and a residue is generated. The residue also causes an internal short circuit. Therefore, when manufacturing an all-solid-state battery using the green sheet method, it is necessary to reliably remove the binder while suppressing the oxidation of the electrode active material in the debinder step.

Therefore, an object of the present invention is to provide a method for producing an all-solid-state battery capable of reliably removing the binder in the green sheet while suppressing the oxidation of the electrode active material in the debinder step.

The present invention for achieving the above object is an integral sintered body, which is a positive electrode layer containing an electrode active material and a solid electrolyte for a positive electrode, a solid electrolyte layer containing a solid electrolyte, and an electrode active material and a solid for a negative electrode. A method for manufacturing an all-solid-state battery that operates as a lithium secondary battery by providing a laminated electrode body in which negative electrode layers containing an electrolyte are laminated in this order.
An electrode active material whose valence changes due to oxidation is used for at least one of the positive electrode active material and the negative electrode active material.
A slurry-like positive electrode layer material and a slurry-like negative electrode layer material are prepared by mixing the amorphous solid electrolyte and the binder with each of the powdery electrode active material for the positive electrode and the electrode active material for the negative electrode. The electrode layer material preparation step to be manufactured and
A solid electrolyte layer material preparation step for producing a slurry-like solid electrolyte layer material containing the powder-like solid electrolyte and a binder, and a solid electrolyte layer material preparation step.
A green sheet preparation step of producing the solid electrolyte layer material, the positive electrode layer material, and the negative electrode layer material into a sheet-shaped green sheet, respectively.
A laminate obtained by laminating a green sheet made of the positive electrode layer material, a green sheet made of the solid electrolyte layer material, and a green sheet made of the negative electrode layer material in this order is heat-treated in an atmospheric atmosphere to form the green sheet. A debinder step for removing the binder and
A firing step of calcining the laminated body that has undergone the debinder step in a non-oxygen atmosphere to prepare the laminated electrode body, and a firing step.
Including
For the electrode active material whose valence changes due to oxidation, an electrolyte film forming step of forming an amorphous film of the solid electrolyte on the particle surface of the electrode active material by the solgel method is executed, and the electrode layer is formed. In the material preparation step, the electrode active material on which the film of the solid electrolyte was formed was used.
In the electrolyte film forming step, the electrode active material in powder form is mixed with a mixed solution of an aqueous stock solution and an organic stock solution prepared as a raw material of the solid electrolyte, and the electrode active material is contained. The crushed product obtained by drying and crushing the mixed solution is heat-treated to vitrify the solid electrolyte.
This is a method for manufacturing an all-solid-state battery.

_{Lithium vanadium phosphate (Li 3} V ₂ (PO ₄ ) ₃ ) is used as the electrode active material of the positive electrode, and in the electrolyte film forming step, the amorphous particle surface of the lithium vanadium phosphate in powder form is used. It can also be used as a method for manufacturing an all-solid-state battery that forms a solid electrolyte film. The solid electrolyte may be used as a method for producing an all-solid-state battery which is a compound represented by the general formula Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) _3.

According to the method for manufacturing an all-solid-state battery according to the present invention, when a laminated electrode body constituting an all-solid-state battery is produced by using the green sheet method, a binder is used while suppressing oxidation of the electrode active material in the debinder step. It can be reliably removed. Thereby, an all-solid-state battery having excellent battery characteristics can be obtained. Other effects will be clarified in the following description.

It is a figure which shows the outline of the manufacturing method of the all-solid-state battery which concerns on Example of this invention. It is a figure which shows the procedure of coating a solid electrolyte on a positive electrode active material in the manufacturing method of the all-solid-state battery which concerns on the said Example. It is a figure which shows the thermogravimetric characteristic of the positive electrode active material which formed the film of the solid electrolyte. It is a figure which shows the oxidation temperature of the positive electrode active material which formed the film of a solid electrolyte. It is a figure which shows the shape and size of the all-solid-state battery produced by the method of the said Example. It is a figure which shows the charge / discharge characteristic of the all-solid-state battery produced by the method of the said Example.

In order to produce a practical all-solid-state battery using the green sheet method, it is necessary to suppress the oxidation of the electrode active material and surely remove the binder during the debinder step. In response to such a requirement, in the method for producing an all-solid-state battery according to the embodiment of the present invention, an amorphous solid electrolyte film is formed on the particle surface of the electrode active material to be contained as ceramic powder in the green sheet. ing. As a result, the coating film prevents contact between the electrode active material and oxygen, and suppresses oxidation of the electrode active material. Then, in the method for producing an all-solid-state battery according to the embodiment of the present invention, the coating film can be formed reliably and effectively.

=== Manufacturing method of all-solid-state battery ===
As an example of the present invention, a method for manufacturing an all-solid-state battery using LAGP as a solid electrolyte, LVP as a positive electrode active material, and anatase-type titanium oxide (TiO _{2) as a negative electrode active material will be mentioned.} Then, in this embodiment, a LAGP film is formed on the surface of the LVP particles by the sol-gel method.

FIG. 1 shows an outline of the manufacturing method of the all-solid-state battery of this example. First, green sheets corresponding to each of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer constituting the laminated electrode body are individually produced. Regarding the positive electrode layer sheet, an amorphous LAGP film was formed on the particle surface of the LVP by the solgel method (s1a), and the amorphous LAGP film was formed on the particle surface with the powdery LVP. , A slurry-like positive electrode layer material containing a powdery LAGP made of amorphous material (hereinafter, also referred to as LAGP powder) and a binder is produced (s2a). Then, the slurry-shaped positive electrode layer material is formed into a sheet to prepare a positive electrode layer sheet (s3a).

Regarding the negative electrode layer sheet, a slurry-like negative electrode layer material containing the above-mentioned LAGP powder made of amorphous material, powdery titanium oxide, and a binder was prepared (s2b), and the negative electrode layer material was molded into a sheet shape. To prepare a negative electrode layer sheet (s3b). For the electrolyte layer sheet, a slurry-like solid electrolyte layer material containing LAGP powder and a binder is prepared (s1c, s2c). Then, the solid electrolyte layer material is formed into a sheet to prepare an electrolyte layer sheet (s3c).

After the green sheet of each layer is produced by the above procedure, the laminated body obtained by laminating the positive electrode layer sheet, the electrolyte layer sheet, and the negative electrode layer sheet in this order is crimped (s4). Then, or if necessary, the crimped laminate is cut to an appropriate size (s5) to obtain a laminate having a predetermined planar shape and planar size.

Then, a debinder step is performed on the laminate having a predetermined plane shape and plane size to remove the binder in the green sheet of each layer constituting the laminate (s6), and the laminate after the debinder step is fired. (S7). As a result, LAGP in the green sheet constituting the laminated body is crystallized, and a laminated electrode body which is a sintered body is obtained. An all-solid-state battery is completed by forming a current collector made of a metal foil on the uppermost layer and the lowermost layer of the laminated electrode body thus obtained by sputtering or the like (s8).

=== LAGP coating ===
<Procedure for forming LAGP film>
Next, a procedure for forming a film made of amorphous LAGP on the particle surface of LVP, which is a positive electrode active material, using the sol-gel method will be described. The procedure is shown in FIG. First, an aqueous stock solution and an organic stock solution are prepared as raw materials for LAGP. Here, along with making the aqueous stock solution were blended water _(H 2 O) as a raw material and a solvent comprising a phosphorus LAGP (P) and the origin of lithium (Li), and aluminum LAGP (Al) Germanium ( A metal alkoxide which is the origin of Ge) and an alcohol as a solvent are mixed to prepare an organic stock solution (s11a, s11b). In the example shown in FIG. 1, the aqueous stock solution contains lithium acetate (CH ₃ COOLi), which is the origin of _{lithium in LAGP, and ammonium dihydrogen phosphate (NH 4} H ₂ PO ₄ ), which is the origin of phosphorus. The organic stock solution consists of aluminum tri-s-butoxide (Al (OBt) ₃ ), which is the origin of aluminum, germanium (IV) ethoxydo (Ge (OEt) ₄ ), which is the origin of germanium, and butanol (BtOH), which is a solvent. Includes. For the aqueous stock solution and the organic stock solution, the next step (s12) is carried out after the raw materials are mixed and left for one day so that the respective raw materials are sufficiently mixed.

Table 1 below shows an example of raw materials and their compounding ratios in aqueous stock solutions and organic stock solutions. The raw materials shown in Table 1 are provided as products by chemical manufacturers. The Table 2 shows the molar ratio concentration of each metal in the starting material (mmol), is the molar ratio of the metal alkoxide of water (H 2 _O) and an organic stock solution is an aqueous solvent stock solution in Table 3 It _{shows H 2} O / Al (OBt) ₃ and H ₂ O / Ge (OEt) _{4 , and H 2} O / BtOH which is a ratio of water and butanol (BtOH) which is a solvent of an organic stock solution. The various conditions related to the aqueous and organic stock solutions shown in Tables 1 to 3 are also described in Non-Patent Document 2 above.

上記表１〜表３に示した水系と有機系のストック溶液を調合して１日間放置したならば、その放置後の水系と有機系のストック溶液を混合する（ｓ１２）。そして本実施例の全固体電池の製造方法では、水系と有機系のストック溶液の混合溶液に粉体状のＬＶＰを混合する（ｓ１３）。すなわち、非晶質のＬＡＧＰをゾルゲル法によって生成する前にＬＡＧＰの原料と正極活物質とを混合する。なお、この手順ｓ１３において正極活物質として混合するＬＶＰは、セラミック材料を扱うメーカーがサンプルあるいは製品として提供しているものを使用することができる。もちろん、上記非特許文献１に記載の方法で作製することもできる。負極活物質として用いる酸化チタンについては製品として提供されている。

After the water-based and organic stock solutions shown in Tables 1 to 3 above are mixed and left to stand for 1 day, the water-based and organic stock solutions after the standing are mixed (s12). Then, in the method for manufacturing an all-solid-state battery of this example, powdery LVP is mixed with a mixed solution of an aqueous-based and organic-based stock solution (s13). That is, the raw material of LAGP and the positive electrode active material are mixed before the amorphous LAGP is produced by the sol-gel method. As the LVP to be mixed as the positive electrode active material in this procedure s13, those provided as samples or products by manufacturers handling ceramic materials can be used. Of course, it can also be produced by the method described in Non-Patent Document 1. Titanium oxide used as a negative electrode active material is provided as a product.

Next, the mixed solution of the aqueous stock solution to which the powdery LVP is added and the organic stock solution is dried. Here, first, the container containing the mixed solution is heated on a hot plate at a temperature of, for example, 100 ° C. and stirred until the solvent evaporates (s14). This gives a gelled compound. Gelation proceeds immediately after mixing the aqueous and organic stock solutions. Further, in order to reliably remove the solvent of the gelled compound, the compound is placed in a vacuum dryer at a temperature of 110 ° C. and dried (s15). Here, it was dried for about one night (for example, 8h to 12h).

Then, the dried agglutinated powder of the compound is crushed using an agate mortar (s16), and the crushed product is heat-treated (s17). As a result, LAGP is vitrified, and an amorphous LAGP film is formed on the particle surface of LVP. Here, using an electric furnace, the mixture was heated to 500 ° C. at a heating rate of 100 ° C./h in a nitrogen atmosphere, and the temperature of 500 ° C. was maintained for 2 hours for vitrification. In addition to the amorphous LAGP film formed on the surface of the LVP particles, the LAGP film to be contained in the solid electrolyte layer material and the negative electrode layer material, and the LAGP film are formed when the positive electrode layer material is produced. The LAGP powder to be mixed with the positive electrode active material can be separately produced by a procedure omitting the LVP mixing step s13 in FIG. Of course, the LAGP powder may be produced by another method, for example, the method described in Patent Document 1 above.

In any case, in the method for producing a solid electrolyte according to the present embodiment, LAGP is mixed with powdered LVP at the stage where it is in the state of a sufficiently fluid raw material solution. Therefore, the raw material solution can be vitrified with the surface of the LVP particles uniformly covered. That is, an amorphous LAGP film is surely and effectively formed on the surface of the LVP particles.

<About oxidation of LVP>
Before manufacturing an all-solid-state battery using an LVP coated with LAGP by the above procedure, a powdery LVP (hereinafter, also referred to as a coated LVP) having a LAGP film formed by the procedure shown in FIG. 2 The characteristics were investigated. Here, in the LVP mixing procedure s13 in FIG. 2, a powdery LVP having an average particle diameter of 0.76 μm is used, and the ratio of LAGP formed as a film to the powdery LVP (wt%:: LVPs with various coatings having different coating amounts) were prepared as samples. The amount of the coating film can be adjusted by the amount of the mixed solution obtained by the procedure s12 in FIG. 2 and the amount of the LVP mixed in the procedure s13. Then, the thermogravimetric (TG) characteristics of each sample were examined using a thermogravimetric analyzer.

Table 4 below shows the percentage of LAGP in each sample.

図３は、表４に示したサンプル１〜３のＴＧ特性を示す図であり、各サンプルのＴＧ特性を示す曲線１０１〜１０３は、温度を高くするのに伴ってＴＧが徐々に減少し、ＬＶＰの酸化が始まる温度でＴＧが極小値となり、その極小値となる温度を超えるとＴＧが急激に上昇に転じる。そして、ＬＡＧＰを含まないサンプル１に対し、ＬＡＧＰの被膜を形成したサンプル２、３では、酸化温度が高温側にシフトしていることが分かる。図４に、図３の結果に基づくＬＡＧＰの被膜量とＬＶＰの酸化開始温度との関係を示した。ＬＡＧＰの被膜量とＬＶＰの酸化開始温度は、ほぼ比例関係にあり、被膜量が多いほど酸化温度が高くなっている。したがって、ＬＶＰにＬＡＧＰの被膜を形成することで、脱バインダー工程において、バインダーを確実除去するためにより高い温度で熱処理を行ってもＬＶＰの酸化が発生し難い。

FIG. 3 is a diagram showing the TG characteristics of the samples 1 to 3 shown in Table 4, and in the curves 101 to 103 showing the TG characteristics of each sample, the TG gradually decreases as the temperature is raised. The TG reaches a minimum value at the temperature at which the oxidation of LVP begins, and when the temperature exceeds the minimum value, the TG suddenly starts to rise. Then, it can be seen that the oxidation temperature of Samples 2 and 3 in which the LAGP film is formed shifts to the high temperature side with respect to Sample 1 which does not contain LAGP. FIG. 4 shows the relationship between the coating amount of LAGP and the oxidation start temperature of LVP based on the result of FIG. The coating amount of LAGP and the oxidation start temperature of LVP are in a substantially proportional relationship, and the larger the coating amount, the higher the oxidation temperature. Therefore, by forming the LAGP film on the LVP, oxidation of the LVP is unlikely to occur even if the heat treatment is performed at a higher temperature in order to reliably remove the binder in the debinder step.

<Charging / discharging characteristics of all-solid-state batteries>
Considering the oxidation start temperature of LVP shown in FIGS. 3 and 4, an all-solid-state battery was actually manufactured by a procedure based on the procedure shown in FIG. 1, and the charge / discharge characteristics of the all-solid-state battery were examined. The positive electrode layer material used in producing the all-solid-state battery contained an electrolyte coating LVP having a coating amount of 30 wt%. Then, in the steps (s1a to s1c and s2b, s3b) for producing the green sheets of the positive electrode layer and the negative electrode layer in the procedure shown in FIG. 2, a conductive aid and a binder are applied to the powdery electrolyte coating LVP and titanium oxide, respectively. , Plasticizer, dispersant, and alcohol were added and mixed to prepare a slurry positive electrode layer material and a negative electrode layer material.

Specifically, a binder is added at, for example, 20 wt% to 30 wt% to a powder material obtained by mixing LVP with a powdery coating or titanium oxide and LAGP powder at a mass ratio of, for example, 50:50. .. Further, anhydrous alcohol such as ethanol is added to the powder material as a solvent in an amount of, for example, 30 wt% to 50 wt%. Then, the mixture of the powder material, the binder and the solvent is mixed in a ball mill for a predetermined time (for example, 20 hours). As a result, a slurry-like positive electrode layer material and a negative electrode layer material can be obtained. The solid electrolyte layer material can be obtained by mixing amorphous LAGP powder, a binder, a plasticizer, and alcohol in the above proportions.

Next, the slurry-like positive electrode layer material, negative electrode layer material, and solid electrolyte layer material obtained in the above procedure were each coated on a PET film and formed into a sheet, which was formed into a sheet at a temperature of 100 ° C. for 30 minutes. By drying over time, a positive electrode layer sheet, a negative electrode layer sheet, and an electrolyte layer sheet can be obtained. The green sheet of each layer is adjusted to a predetermined thickness. If the desired thickness cannot be obtained by one coating, the desired thickness is adjusted by applying the coating multiple times.

Next, the laminate obtained by laminating the green sheets of each layer is pressure-bonded so that the solid electrolyte layer is sandwiched between the positive electrode layer and the negative electrode layer. Here, since an all-solid-state battery is produced as a sample for examining the discharge characteristics, the green sheet of each layer is cut to a predetermined size before laminating the green sheet of each layer, and the cut green sheet of each layer is cut. The laminated product was pressure-bonded under the conditions of a pressure of 100 kg / cm ² , a temperature of 60 ° C., and a time of 30 min. Then, the laminated body after the pressure bonding is heat-treated in an air atmosphere at 400 ° C. for 10 hours by a debindering step, and the laminated body obtained by the debindering step is heat-treated in a nitrogen atmosphere containing no oxygen at 600 ° C. By firing under the conditions of (1), a laminated electrode body which is a sintered body was obtained. Then, a current collector was formed by forming a thin gold film on the surfaces of the uppermost layer and the lowermost layer of the laminated electrode body by sputtering or thin film deposition, and an all-solid-state battery was completed.

FIG. 5 is a diagram showing the shape and size of the laminated electrode body 1 in the manufactured all-solid-state battery, and FIG. 5 (A) is a plan view when each layer (2 to 4) in the laminated electrode body 1 is viewed from the stacking direction. FIG. 5B is a side view of the laminated electrode body 1 when viewed from a direction orthogonal to the stacking direction. As shown in FIG. 5 (A), the planar shape of the laminated electrode body 1 is rectangular, and as shown in FIG. 5 (B), between the positive electrode layer 2 and the negative electrode layer 3 of the same size facing each other. A solid electrolyte layer 4 having a plane size larger than that of the positive electrode layer 2 and the negative electrode layer 3 is sandwiched therein. Further, the solid electrolyte layer 4 is arranged so as to include the plane regions of the positive electrode layer 2 and the negative electrode layer 3. The positive electrode layer 2 and the negative electrode layer 3 have a square planar shape with a side width w1 of 13.5 mm, and the solid electrolyte layer 4 has a square shape with a side width w2 of 15.0 mm. .. The thickness t1 of the positive electrode layer 2 and the negative electrode layer 3 is 0.04 mm, and the thickness t2 of the solid electrolyte layer 4 is 0.09 mm. The positive electrode layer sheet and the negative electrode layer sheet in the laminated body before sintering generally had a mass of 2 to 5 mg, although there was a slight difference depending on the opportunity to manufacture the all-solid-state battery.

<Charging / discharging characteristics>
The charge / discharge characteristics of the all-solid-state battery (hereinafter, also referred to as the implementation battery) produced by the above procedure were investigated. In addition, as a comparative example with respect to the implementation battery, the charge / discharge characteristics of an all-solid-state battery (hereinafter, also referred to as a comparison battery) using LVP in which the positive electrode layer is not coated with LAGP while having the same shape and size as the implementation battery are also investigated. It was. Here, regarding the implementation battery and the comparison battery, the charge capacity and the discharge capacity are determined from the relationship between the charge time and the current during charge when charged and discharged under predetermined conditions, and the relationship between the discharge time and the current during discharge. I asked. Then, the relationship between the capacity per unit mass (mAh / g) obtained by dividing the charge capacity and the discharge capacity by the mass of the all-solid-state battery and the battery voltage was defined as the charge characteristic and the discharge characteristic.

Regarding the charging procedure, the battery was charged at a constant current of 8 μA until the battery voltage reached 2.8 V, and then charged at a constant voltage from 2.8 V. Regarding the discharge procedure, the implementation battery and the comparison battery charged in the previous procedure were discharged at a constant current of 8 μA until the battery voltage changed from 2.8 V to 0.5 V.

FIG. 6 shows the charge / discharge characteristics of the implementation battery and the comparative battery. Here, a plurality of (for example, 10) batteries for implementation and comparison batteries were prepared, and the characteristics when the charge / discharge characteristics of each individual were averaged were shown. Then, FIG. 6A shows the charge / discharge characteristics of the comparative battery, and FIG. 6B shows the charge / discharge characteristics of the implementation battery. As shown in FIG. 6, the discharge capacity of the implementation battery is about 1.5 times larger than that of the comparative battery. It can be considered that this is because in the implementation battery, the oxidation of LVP in the debindering step was effectively suppressed and the valence of LVP did not decrease, so that more Li ions contributed to the charge / discharge reaction.

In the method for manufacturing an all-solid-state battery according to the embodiment of the present invention, when a laminated body of green sheets is fired to produce a laminated electrode body which is a sintered body, it is formed on the particle surface of powdery LVP. The coating of LAGP and the powdery LAGP interposed between the particles of LVP are crystallized in contact with each other. Therefore, it can be expected that an ionic conduction path is surely formed between the LVP particles and the ionic conductivity of the electrode layer is enhanced.

=== Other Examples ===
In the above embodiment, butanol was used as the solvent of the organic stock solution, but of course, other alcohols may be used as long as they function as the solvent of the metal alkoxide.

The positive electrode active material is not limited to LVP. The negative electrode active material is not limited to titanium oxide. Of course, the solid electrolyte is not limited to LAGP. In any case, the sol-gel method may be applied to the electrode active material which may be oxidized during the debindering step to change the valence to form a film of a solid electrolyte.

In the above embodiment, LAGP was vitrified at a temperature of 500 ° C., but of course, the temperature is not limited to this. Generally, when LAGP is produced by the sol-gel method, it is known that LAGP becomes amorphous by heat treatment at a temperature of 400 ° C. or higher and 600 ° C. or lower. In any case, the temperature may be any temperature at which amorphous LAGP is produced at a temperature lower than the firing temperature.

When LVP is fired on an electrode active material at a temperature of 700 ° C. or higher of a solid electrolyte, it may react with LAGP and deteriorate ionic conductivity in the positive electrode layer. Therefore, in the above embodiment, the firing temperature is 600 ° C. Was supposed to be. Of course, if an electrode active material having a higher reaction temperature with LAGP is used, firing can be performed at a temperature higher than 600 ° C.

1 laminated electrode body, 2 positive electrode layer, 3 negative electrode layer, 4 solid electrolyte layer,
s1a Step of forming an amorphous LAGP film on LVP,
s1c Amorphous LAGP manufacturing process, s2a Positive electrode layer material manufacturing process,
s2b Negative electrode layer material manufacturing process, s2c solid electrolyte layer manufacturing process,
s3a to s3c green sheet manufacturing process, s4 laminating / crimping process, s5 cutting process,
s6 debinder step, s7 firing step, s8 current collector forming step,
s11a Aqueous stock solution preparation step, s11b Organic stock solution preparation step,
s12 Water-based stock solution and organic stock solution mixing step, s13 LVP mixing step, s14 drying (gelling) step, s15 vacuum drying step, s16 crushing step,
s17 Heat treatment (vitrification) process

Claims (3)

In an integral sintered body, a positive electrode layer containing an electrode active material for a positive electrode and a solid electrolyte, a solid electrolyte layer containing a solid electrolyte, and a negative electrode layer containing an electrode active material for a negative electrode and a solid electrolyte are laminated in this order. It is a method of manufacturing an all-solid-state battery that operates as a lithium secondary battery by having a laminated electrode body.
An electrode active material whose valence changes due to oxidation is used for at least one of the positive electrode active material and the negative electrode active material.
A slurry-like positive electrode layer material and a slurry-like negative electrode layer material are prepared by mixing the amorphous solid electrolyte and the binder with each of the powdery electrode active material for the positive electrode and the electrode active material for the negative electrode. The electrode layer material preparation step to be manufactured and
A solid electrolyte layer material preparation step for producing a slurry-like solid electrolyte layer material containing the powder-like solid electrolyte and a binder, and a solid electrolyte layer material preparation step.
A green sheet preparation step of producing the solid electrolyte layer material, the positive electrode layer material, and the negative electrode layer material into a sheet-shaped green sheet, respectively.
A laminate obtained by laminating a green sheet made of the positive electrode layer material, a green sheet made of the solid electrolyte layer material, and a green sheet made of the negative electrode layer material in this order is heat-treated in an atmospheric atmosphere to form the green sheet. A debinder step for removing the binder and
A firing step of calcining the laminated body that has undergone the debinder step in a non-oxygen atmosphere to prepare the laminated electrode body, and a firing step.
Including
For the electrode active material whose valence changes due to oxidation, an electrolyte film forming step of forming an amorphous film of the solid electrolyte on the particle surface of the electrode active material by the solgel method is executed, and the electrode layer is formed. In the material preparation step, the electrode active material on which the film of the solid electrolyte was formed was used.
In the electrolyte film forming step, the electrode active material in powder form is mixed with a mixed solution of an aqueous stock solution and an organic stock solution prepared as a raw material of the solid electrolyte, and the electrode active material is contained. The crushed product obtained by drying and crushing the mixed solution is heat-treated to vitrify the solid electrolyte.
A method for manufacturing an all-solid-state battery. In claim 1,
_{Lithium vanadium phosphate (Li 3} V ₂ (PO ₄ ) ₃ ) was used as the electrode active material for the positive electrode.
In the electrolyte membrane forming step, the amorphous solid electrolyte membrane is formed on the surface of the powdery lithium vanadium phosphate particles.
A method for manufacturing an all-solid-state battery. The method for producing an all-solid-state battery according to claim 1 or 2, wherein the solid electrolyte is _{a compound represented by the general formula Li 1.5} Al _0.5 Ge _1.5 (PO ₄ ) _3.

Images