All-solid-state battery and method for manufacturing all-solid-state battery

Abstract

To increase the carrying amount, enable charging and discharging at room temperature, and improve the cycle characteristics in an all-solid battery using a garnet-type solid electrolyte.SOLUTION: An all-solid battery 1A includes a mixture electrode layer 2A in which a mixed material of a powdered electrode active material and a powdered electrolyte material is sintered, and an electrolyte layer 3A in which the powdered electrolyte material is sintered, the mixture electrode layer 2A and the electrolyte layer 3A are in contact with each other on one side, and the electrolyte material is a compound containing Li and having a garnet-type crystal structure containing La, Zr or other elements, and the mixture electrode layer 2A is a sintered body of a mixed material of a powdered electrode active material and a powdered electrolyte material coated with a low-melting-point Li salt having a melting point of less than 900°C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an all-solid-state battery using a garnet-type solid electrolyte and a method for manufacturing the all-solid-state battery.

Background Art

[0002] All-solid-state batteries using ceramic solid electrolytes are expected to be batteries with excellent safety and reliability because they have no risk of liquid leakage, combustion, or explosion. Furthermore, since it is possible to increase the energy density of the battery by lamination or the like, research and development are underway as candidates for next-generation rechargeable batteries for large-scale applications and power sources for IoT devices.

[0003] As ceramic solid electrolytes, sulfide-based and oxide-based compounds have been widely studied. Sulfide-based solid electrolytes have high ionic conductivity, plasticity, and relatively easy interfacial bonding with active materials, so development towards practical use is underway. However, since they react with water vapor to produce hydrogen sulfide, there are problems in the manufacturing environment and product safety.

[0004] Oxide-based solid electrolytes are superior in chemical stability compared to sulfide-based ones, but are inferior in ionic conductivity and mechanical properties. Since they do not undergo plastic deformation, it is difficult to form an interface with active materials. If the process temperature for battery manufacturing is high, sintering progresses and bonding also occurs with active material particles, but at the same time, each constituent element diffuses mutually and a reaction phase is formed at the interface, resulting in a decrease in electrochemical properties and the battery not functioning. Conversely, if the process temperature is low, no heterogeneous phase is formed, but the interface is not bonded and the particles are in a state of point contact with each other, and an electrochemical reaction field is not formed.

[0005] Regarding oxide-based solid electrolytes, applications to all-solid-state batteries have been attempted mainly with compounds having a garnet-type crystal structure and compounds having a NASICON-type crystal structure.

[0006] The garnet-type solid electrolyte is 5 to 8×10 -4It has a relatively high ionic conductivity of S / cm and excellent reduction resistance that is stable even against metallic lithium.

[0007] Several reports have been made on joining at the interface between the active material and the solid electrolyte without reducing the electrochemical reaction.

[0008] As an all-solid-state battery using a garnet-type solid electrolyte, Non-Patent Document 1 uses LiCoO2 and lithium borate as the active material and electrolyte, respectively, to form a composite electrode. An electrode layer is formed by screen printing using an ink obtained by mixing both powders, and annealing is performed at 700 °C. Lithium borate melts to join the active material / electrolyte interface in the composite electrode layer and also constructs an ionic conduction path. In Non-Patent Document 1, the loading amount of the active material is 1.7 mg / cm 2 and an initial discharge capacity of 85 mAh / g is obtained under the conditions of a temperature of 25 °C and a current density of 10 μA / cm 2 (5.75 mA / g, 0.05C).

[0009] Non-Patent Document 2 uses LiCoO2 (LCO) as the active material constituting the composite electrode and a garnet-type solid electrolyte (LLZO) and lithium carbonate borate (Li 2.3 C 0.7 B 0.3 O3, LCBO) as the electrolyte. To enhance the sinterability, the surface of LCO is coated with a thin layer of Li2CO3. It is also explained that the surface of the LLZO particles is coated with Li2CO3 generated by reacting with moisture and carbon dioxide in the air. A composite electrode composed of LCO, LLZO, and LCBO is fabricated by screen printing and fired at 700 °C. In Non-Patent Document 2, the loading amount of the active material is 1.0 mg / cm 2 and an initial discharge capacity of 92 mAh / g is obtained under the conditions of a temperature of 25 °C and a current density of 5.75 μA / cm 2 (5.75 mA / g, 0.05C).

[0010] Non-Patent Document 3 uses LiCoO2 (LCO) as the active material constituting the composite electrode and garnet-type solid electrolyte (LLZ:Ta) as the electrolyte. Ink containing LCO and LLZ:Ta is applied with a brush and fired at 1050°C for 30 minutes. In Non-Patent Document 3, the loading amount of the active material is 12 - 16 mg / cm 2 and at a temperature of 50°C and a current density of 50 μA / cm 2 (3 - 4 mA / g, 0.02 - 0.03 C), it is said to have obtained an initial discharge capacity of 113 mAh / g.

[0011] Non-Patent Document 4 uses Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2 (NCM) as the active material constituting the composite electrode and garnet-type solid electrolyte (LLZ) as the electrolyte. LLZ-H in which a part of Li ions is ion-exchanged with protons, LiOH, LiNO3, and NCM of the active material are mixed and hot-pressed under the conditions of 400°C, 98 MPa, and 6 hours. In Non-Patent Document 4, the loading amount of the active material is 13.4 mg / cm 2 and at a temperature of 25°C and a current density of 40 μA / cm 2 , it is said to have obtained an initial discharge capacity of 130 mAh / g.

Prior Art Documents

Non-Patent Documents

[0012]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0013] In a solid battery using a garnet-type solid electrolyte, Non-Patent Document 1 and Non-Patent Document 2 disclose interface bonding using lithium borate and lithium borate carbonate. However, since their ionic conductivity is poor, when the composite electrode layer is thickened, the resistance within the composite electrode layer increases and the utilization rate of the active material decreases. For this reason, it is difficult to increase the loading amount of the active material. To realize a battery with a high energy density, it is necessary to increase the capacity (initial discharge capacity) per unit area of the battery. However, the initial discharge capacities per unit area in Non-Patent Document 1 and Non-Patent Document 2 are 0.14~0.17 mAh / cm 2 , 0.094 mAh / cm 2 respectively.

[0014] In addition, in the case of Non-Patent Document 3 in which the active material and the electrolyte are directly sintered, the loading amount is increased compared to Non-Patent Documents 1 and 2, and the initial discharge capacity per unit area is 1.6 to 2.0 mAh / cm 2 However, the temperature of the charge-discharge test is measured at a high temperature of 50°C.

[0015] In the case of Non-Patent Document 4, by mixing the ion-exchanged electrolyte with LiOH and LiNO3, while LiOH and LiNO3 are melting, they react with the electrolyte to promote sintering. There is an advantage that sintering proceeds at a low temperature of 400°C, and the initial discharge capacity per unit area at room temperature is 1.7 mAh / cm 2 is obtained. On the other hand, since a long-time pressure sintering process is required, the cost of the manufacturing apparatus becomes high. Also, due to the low-temperature process, a part of LiNO3 etc. remains, and side reactions occur during charging, so the difference between the charge capacity and the discharge capacity is relatively large.

[0016] Therefore, an object of the present invention is to increase the loading amount, enable charge and discharge at normal temperature, and further improve the cycle characteristics in an all-solid-state battery using a garnet-type solid electrolyte.

Means for Solving the Problems

[0017] To achieve the above object, the present invention includes a composite electrode layer obtained by sintering a mixed material of a powdery electrode active material and a powdery electrolyte material, and an electrolyte layer obtained by sintering a powdery electrolyte material, and the composite electrode layer and the electrolyte layer are in contact with each other on one surface, The electrode active material has a flat particle shape, and in the composite electrode layer, the flat particles of the electrode active material are laminated and in contact with the electrolyte layer. The electrolyte material is a compound having a garnet-type crystal structure containing Li and containing La, Zr or other elements That is, the powdered electrolyte material is a powdered electrolyte material coated with a low melting point Li salt having a melting point of less than 900°C. and the composite electrode layer is a sintered body of a mixed material of a powdery electrode active material and a powdery electrolyte material coated with a low-melting-point Li salt having a melting point of less than 900°C It is a sintered body of a sintered body in which an electrode active material and an electrolyte material are joined, and LiNO 3 The re-sintered body of the sintered body to which the solution was dropped. which is an all-solid-state battery. Further, the present invention includes an electrolyte layer forming step of pressure-molding a powdered electrolyte material to form an electrolyte layer, and a mixed material of a powdered electrode active material and a powdered electrolyte material is deposited on the upper surface of the pressure-molded electrolyte layer and pressure-molded to form a composite electrode layer. A composite electrode layer forming step, and a sintering step of sintering the electrolyte layer and the composite electrode layer at a sintering temperature of 900°C or higher and 1200°C or lower to form an integral composite. The electrode active material has a flat particle shape, and in the composite electrode layer, the flat particles of the electrode active material are laminated and in contact with the electrolyte layer. The electrolyte material is a compound containing Li and having a garnet-type crystal structure containing La, Zr, or other elements. The powdered electrolyte material is a powdered electrolyte material coated with a low melting point Li salt having a melting point of less than 900°C. The composite electrode layer is formed by depositing a mixed material of a powdered electrode active material and a powdered electrolyte material coated with a low melting point Li salt having a melting point of less than 900°C on the upper surface of the electrolyte layer and pressure-molding it in the composite electrode layer forming step, and sintering the electrolyte layer and the composite electrode layer in the sintering step. After the sintering step, the composite electrode layer is further dropped with LiNO 3 This is a method for manufacturing an all-solid-state battery that is re-sintered at a temperature lower than the sintering temperature in the sintering step.

Advantages of the Invention

[0018] According to the present invention, charge and discharge can be performed at room temperature, and a predetermined charge and discharge capacity can be obtained. In addition, an increase in the interfacial resistance within the composite electrode layer can be suppressed.

Brief Description of the Drawings

[0019]

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Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the all-solid-state battery and the method for manufacturing the all-solid-state battery of the present invention will be described with reference to the drawings.

[0021] <Configuration Example of the All-Solid-State Battery of the Present Embodiment> The all-solid-state battery 1A of this embodiment includes a composite electrode layer 2A formed by sintering a mixed material (C) of a powdered electrode active material (A) and a powdered electrolyte material (B), and an electrolyte layer 3A formed by sintering the powdered electrolyte material (B).

[0022] In the all-solid-state battery 1A, the composite electrode layer 2A is formed on one surface of the electrolyte layer 3A. Also, an electrode 4A such as a Li negative electrode is formed on the other surface of the electrolyte layer 3A.

[0023] The electrolyte material (B) constituting the composite electrode layer 2A and the electrolyte layer 3A is a compound containing Li and having a garnet-type crystal structure containing La, Zr, or other elements.

[0024] Further, the electrolyte material (B) constituting the composite electrode layer 2A is coated with a low-melting-point Li salt having a melting point of less than 900°C.

[0025] And the composite electrode layer 2A is a sintered body of the above-described mixed material (C) of the powdered electrode active material (A) and the above-described powdered electrolyte material (B) coated with a low-melting-point Li salt having a melting point of less than 900°C.

[0026] The composite electrode layer 2A is preferably a sintered body formed by pressurizing and heating the above-described mixed material (C) at a predetermined pressure and temperature.

[0027] The electrode active material (A) is represented by the following compositional formula (1). LiM 1-x-y M’ x M” y O z ···(1)

[0028] In the compositional formula (1), M, M’, and M” are any of Co, Ni, Mn, Ti, Al, Cu, and Fe, x and y are 0 to 1, and z is 1.5 to 4.0. Examples of the electrode active material (A) include LiCoO2 and the like.

[0029] The electrolyte material (B) is represented by the following compositional formula (2). Lix M I x’ M II 3M III 2O 12 ···(2)

[0030] In the compositional formula (2), M I is either Al or Mg, or does not contain M I and M II is either an alkaline earth metal, a lanthanoid, or both, and M III is either Zr, Hf, Y, Sb, Sn, Nb, Ta, or two or more thereof, and x + x’ ≦ 7. The electrolyte material (B) is, for example, Li 6,5 La3Zr 1.5 Ta 0.5 O 12 and the like.

[0031] The electrolyte material (B) may be one in which a part of La of M contained in the compositional formula (2) is replaced by an alkaline earth metal, and a part of La may be replaced by any of Ca, Sr, and Ba as the alkaline earth metal. In the compositional formula (2), the electrolyte material (B) in which a part of La of M is replaced by an alkaline earth metal is, for example, Li x M I x’ M II 3M III 2O 12 and Li II La II Ca 6,5 Zr 2.5 Ta 0.5 Zr 1.5 Ta 0.5 O 12 、Li 6,5 La 2.5 Sr 0.5 Zr 1.5 Ta 0.5 O 12 、Li 6,5 La 2.5 Ba 0.5 Zr 1.5 Ta 0.5 O 12 and the like.

[0032] In addition, the low-melting-point Li salt with a melting point of less than 900 °C that coats the electrolyte material (B) in the composite electrode layer 2A is any one of Li hydroxides, salts of Li and oxyacids, Li halides, or a combination of multiple ones.

[0033] Specifically, the low-melting-point Li salt with a melting point of less than 900 °C is preferably any one of LiOH, LiNO3, Li2CO3, Li2SO4, Li3BO3, LiBO2, Li3PO4, LiPO3, LiCl, LiBr, LiI, or a combination of multiple ones.

[0034] In the all-solid-state battery 1A in which the electrolyte material (B) constituting the composite electrode layer 2A is coated with a low-melting-point Li salt, in the region near the interface with the electrolyte layer 3A in the composite electrode layer 2A, it does not contain Co, La, and C, and there is a layer with more oxygen atoms around the particles of the electrode active material (A) and the electrolyte material (B) compared to the surface layer side of the composite electrode layer 2A. Further, the all-solid-state battery 1A contains La4LiCoO8 in the composite electrode layer 2A.

[0035] For the composite electrode layer 2A, it is preferable that the average thickness of the pre-sintering coating layer by the low-melting-point Li salt with a melting point of less than 900 °C that coats the surface of the electrolyte material (B) is 10 nm or more and 100 nm or less.

[0036] In addition, the composite electrode layer 2A is preferably a re-sintered body obtained by further dropping LiNO3 onto a sintered body of a mixed material (C) of a powdery electrode active material (A) and a powdery electrolyte material (B) coated with a low-melting-point Li salt with a melting point of less than 900 °C. Further, in the composite electrode layer 2A, part or all between the powdery electrode active material (A) and the powdery electrolyte material (B) are joined by a reaction phase, and the reaction phase is La4Li x” M y” represented by O8, where x + y = 1, and M is preferably any one of Co, Ni, Mn, Ti, Al, Cu, Fe, or a combination of multiple ones.

[0037] <Example of the manufacturing method of the all-solid-state battery of the present embodiment> In the electrolyte layer forming step (a), the powdery electrolyte material (B) is molded to form the electrolyte layer 3A.

[0038] Next, in the composite electrode layer forming step (b), a mixed material (C) of the powdery electrode active material (A) and the powdery electrolyte material (B) is applied onto the upper surface of the molded electrolyte layer 3A to form the composite electrode layer 2A.

[0039] Specifically, a mixed material (C) of a powdery electrode active material (A) and a powdery electrolyte material (B) coated with a low melting point Li salt having a melting point of less than 900°C is mixed with a dispersion medium to produce an ink having a predetermined viscosity, and the ink made of this mixed material (C) is applied onto the upper surface of the electrolyte layer 3A by screen printing. After applying the ink made of the mixed material (C) onto the upper surface of the electrolyte layer 3A, it is dried in an atmosphere of 80°C. The application and drying of the ink made of the mixed material (C) are repeated until a predetermined thickness is obtained.

[0040] After repeating the application and drying of the ink made of the mixed material (C), the deposited layer made of the mixed material (C) is pressed by hot pressing or cold pressing to densify the deposited layer made of the mixed material (C).

[0041] Next, in the sintering step (c), the electrolyte layer 3A and the composite electrode layer 2A are sintered to form an integral composite body. Specifically, using an electric furnace, the electrolyte layer 3A and the composite electrode layer 2A are sintered under the conditions that the temperature is 900 o °C and the atmosphere is air circulation. Sintering In step (c) Sintering The temperature shall be 900°C or higher and 1200°C or lower.

[0042] Next, in the re-sintering step (d), a LiNO3 solution is further dropped onto the composite electrode layer 2A, Sintering In step (c) Sintering and re-sintered at a temperature lower than that in step (c), for example, 500°C.

[0043] Next, in the counter electrode forming step (e), molten metallic lithium is applied onto the lower surface of the electrolyte layer 3A and cooled.

Example

[0044] [Example 1] In Example 1, LiCoO₂ with a flat particle shape was used as the electrode active material (A), and Li coated with LiOH was used as the electrolyte material (B). 6,5 La 2.9 Ca 0.1 Zr 1.4 Ta 0.6 O 12 After the above-mentioned electrolyte layer forming step (a) and the mixed electrode layer forming step (b), step (c) was carried out at 900 °C. Furthermore, a sintering step (d) and a counter electrode forming step (e) were carried out to manufacture an all-solid-state battery. Sintering In Example 1, in the mixed electrode layer forming step (b), the step of applying and drying the ink with the mixed material (C) was repeated, and the thickness of the mixed electrode layer 2A was set to 50 μm by pressure molding.

[0045] In this all-solid-state battery of Example 1, the loading amount of the active material in the mixed electrode layer 2A was 8.0 mg / cm

[0046] In addition, under the conditions of a temperature of 25 °C and a current density of 11.2 μA / cm 2 the initial charge capacity per unit volume was 1.1 mAh / cm 2 and the initial discharge capacity was 0.81 mAh / cm 2 2

[0047] [Example 2] In Example 2, Sintering an all-solid-state battery was manufactured in the same manner as in Example 1 except that step (c) was carried out at 950 °C. In this all-solid-state battery of Example 2, the loading amount of the active material in the mixed electrode layer 2A was 7.5 mg / cm 2 In addition, under the conditions of a temperature of 25 °C and a current density of 11.2 μA / cm 2 the initial charge capacity per unit volume was 0.91 mAh / cm 2 and the initial discharge capacity was 0.70 mAh / cm 2

[0048] ​​​[Comparative Example 1] In Comparative Example 1, an all-solid-state battery was manufactured in the same manner as in the Example, except that the re-sintering step (d) of further dropping a LiNO3 solution onto the composite electrode layer 2A was not performed.

[0049] [Comparative Example 2] In Comparative Example 2, in the composite electrode layer forming step (b), an all-solid-state battery was manufactured in the same manner as in the Example, except that Li 6,5 La 2.9 Ca 0.1 Zr 1.4 Ta 0.6 O 12 not coated with LiOH was used as the electrolyte material (B).

[0050] [Comparative Example 3] In Comparative Example 3, Sintering an all-solid-state battery was manufactured in the same manner as in the Example, except that step (c) was performed at 800°C.

[0051] [Comparative Example 4] In Comparative Example 4, Sintering an all-solid-state battery was manufactured in the same manner as in the Example, except that step (c) was performed at 850°C.

[0052] [Comparative Example 5] In Comparative Example 5, in the composite electrode layer forming step (b), an all-solid-state battery was manufactured in the same manner as in the Example, except that spherical particle-shaped LiCoO2 was used as the electrode active material (A).

[0053] [Electron Microscope Observation] The composite electrode layer of the all-solid-state battery of Example 1 was embedded in resin, subjected to cross-section processing, and then SEM observation and EDS analysis were performed. The SEM image and EDS mapping image of Example 1 are shown in Fig. 2.

[0054] As shown in Fig. 2, in the EDS mapping, the distributions of Co and La correspond to the electrode active material and the electrolyte material, respectively. The distribution of O was such that, in addition to the regions of the electrode active material and the electrolyte material, it was distributed so as to cover these particles. It is considered that these are LiOH formed by the reaction of Li2O or lithium oxide, which was generated by the melting and thermal decomposition of LiOH and LiNO3 added in the composite electrode layer forming step (b) and the re-sintering step (d), with the atmosphere.

[0055] The composite electrode layer of the all-solid-state battery of Example 1 was thinned and then subjected to STEM observation and EDS analysis. Fig. 3 shows the STEM image and the EDS mapping image of Example 1.

[0056] As shown in Fig. 3, in the EDS mapping, it was found that there were particles consisting only of Co, particles consisting only of La, and particles containing both Co and La, and the particles were closely joined to each other. From the results of electron beam diffraction, each particle was the electrode active material, the electrolyte material, and La4LiCoO8. Sintering In step (c), it is considered that the electrode active material and the electrolyte material dissolved in the molten LiOH, and in the cooling process, a part of the dissolved components became La4LiCoO8, joining the electrode active material and the electrolyte material.

[0057] The composite electrode layer formed on the alumina substrate in the same manner as the composite electrode layer of the all-solid-state battery of Example 1 and Comparative Example 5 was subjected to cross-section processing and then SEM observation was performed. Fig. 4 shows the SEM image of the composite electrode layer of Example 1 formed on the alumina substrate, and Fig. 5 shows the SEM image of the composite electrode layer of Comparative Example 5 formed on the alumina substrate.

[0058] As shown in Fig. 4, in the composite electrode layer formed on the alumina substrate by the same method as in Example 1, it was observed that the electrode active material particles with a flat shape were stacked flatly. From the results of X-ray diffraction, it was found that they were stacked in the c-axis direction of the crystal structure (hexagonal system R-3m) of LiCoO2. On the other hand, as shown in Fig. 5, in the composite electrode layer formed on the alumina substrate by the same method as in Comparative Example 5, it was observed that spherical electrode active material particles were stacked. From the results of X-ray diffraction, it was found that the crystals of the electrode active material were stacked without being oriented in a specific direction.

[0059] [Charge and Discharge Test] For all-solid-state batteries of Example 1, Example 2, and Comparative Examples 1 to 5, after charging to 4.2 V at a current density of 1.40 mA / g (0.01 C) per gram of LiCoO2, it was further charged while maintaining at 4.2 V for 10 hours. Then, it was discharged to 2.5 V at a current density of 1.40 mA / g, and the battery capacity was measured. The charge and discharge measurements were performed at 25°C.

[0060] The first charge-discharge curves of the all-solid-state batteries of Example 1 are shown in Fig. 6, those of the all-solid-state batteries of Comparative Example 1 are shown in Fig. 7, those of the all-solid-state batteries of Comparative Example 2 are shown in Fig. 8, the first charge-discharge curves of the all-solid-state batteries of Example 2 and Comparative Examples 3 to 4 are shown in Fig. 9, and the first charge-discharge curves of the all-solid-state batteries of Comparative Example 5 are shown in Fig. 10. Also, the first charge capacity density (first charge capacity per unit volume), first discharge capacity density (first discharge capacity per unit volume), and first charge efficiency of the all-solid-state batteries of Example 1, Example 2, and Comparative Examples 1 to 5 are shown in Table 1. In Table 1, the first charge capacity density, first discharge capacity density, and first charge efficiency of Non-Patent Document 4 are also shown.

[0061]

Table 1

[0062] As shown in Fig. 6, the all-solid-state battery of Example 1 showed high values for both the initial charge capacity and the initial discharge capacity. In particular, the initial charge capacity per unit weight was almost equal to the theoretical capacity of LiCoO2, the electrode active material, which is 140 mAh / g. On the other hand, as shown in Figs. 7 and 8, the all-solid-state batteries of Comparative Example 1 and Comparative Example 2 had low initial charge capacities and low initial discharge capacities. As shown in Table 1, the initial charge-discharge efficiency was 74% for the all-solid-state battery of Example 1, whereas it was 24% and 47% for the all-solid-state batteries of Comparative Example 1 and Comparative Example 2, respectively. This indicates that Sintering in step (c) and the re-sintering step (d), the dissolved LiOH and LiNO3 function to firmly bond the electrode active material and the electrolyte material.

[0063] Also, as shown in Figs. 6, 9 and Table 1, when comparing the initial charge capacities and the initial discharge capacities of the all-solid-state batteries of Example 1, Example 2 and Comparative Examples 3 to 4, Sintering in step (c) Sintering a sufficient capacity was obtained at 900 °C or higher, but not at less than 900 °C. From this, Sintering it can be seen that a temperature of 900 °C or higher is required for the dissolved LiOH in the step to bond the electrode active material and the electrolyte material.

[0064] As shown in FIGS. 6 and 10 and Table 1, the initial charge capacity per unit weight of the all-solid-state batteries of Example 1 and Comparative Example 5 both showed values close to 140 mAh / g, which is the theoretical capacity of the electrode active material. On the other hand, the initial discharge capacity per unit weight was 100 mAh / g for the all-solid-state battery of Example 1, while it was 69 mAh / g for Comparative Example 5. This difference is due to the strain generated at the interface between the composite electrode layer 2A and the electrolyte layer 3A caused by the volume change of the electrode active material during charge and discharge. As shown in the SEM image of FIG. 4, the electrode active material used in Example 1 is composed of flat LiCoO2 particles stacked and oriented in the c-axis direction. However, during charge and discharge, the volume change mainly occurs along the c-axis direction. During charge and discharge, the composite electrode layer undergoes a large volume change in the film thickness direction, but the volume change in the in-plane direction of the film is small. Therefore, the strain generated at the interface between the composite electrode layer and the electrolyte layer is relatively small. On the other hand, as shown in the SEM image of FIG. 5, the electrode active material used in Comparative Example 5 is composed of spherical LiCoO2 particles stacked, and the crystals are oriented in random directions. With charge and discharge, the composite electrode layer also undergoes a volume change in the in-plane direction of the film, so a large strain is generated at the interface between the composite electrode layer and the electrolyte layer. When the strain exceeds the strength limit of the interface, the interface between the composite electrode layer and the electrolyte layer peels off, losing electrochemical activity and reducing the battery capacity.

[0065] [Output and cycle test] For the all-solid-state battery of Example 1, charge-discharge tests were repeated while changing the current density. For the 1st to 3rd cycles, charging was performed at 0.01C in the CC-CV mode, and discharging was performed at 0.01C in the CC mode. For the 4th to 9th cycles, charging was performed at 0.02C (CC-CV mode), and discharging was performed at 0.02C (CC mode). For the 10th to 12th cycles, charging was performed at 0.05C (CC-CV mode), and discharging was performed at 0.05C (CC mode). For the 13th to 15th cycles, charging was performed at 0.01C (CC-CV mode), and discharging was performed at 0.1C (CC mode). For the 16th to 18th cycles, charging was performed at 0.01C (CC-CV mode), and discharging was performed at 0.01C (CC mode). For the 19th to 48th cycles, charging was performed at 0.05C (CC-CV mode), and discharging was performed at 0.05C (CC mode). For the 49th to 50th cycles, charging was performed at 0.01C (CC-CV mode), and discharging was performed at 0.01C (CC mode). The changes in the initial charge capacity and initial discharge capacity and the ratio of the discharge capacity to the charge capacity (Coulomb efficiency) accompanying the output and cycle tests are shown in FIG. 11 and Table 1.

[0066] As shown in FIG. 11 and Table 1, the all-solid-state battery fabricated in Example 1 showed a relatively large decrease in capacity in the initial stage, but then showed a stable capacity. The discharge capacity at the 18th cycle when the charge-discharge rate was returned to 0.01C again after the output test maintained 77% of the initial discharge capacity. The discharge capacity at the 50th cycle maintained 67% of the initial discharge capacity. Also, the Coulomb efficiency after the 25th cycle was 99.8%.

[0067] [Loading amount of active material and initial discharge capacity] Table 2 shows the loading amount of the active material and the initial discharge capacity density (initial discharge capacity per unit volume) in Example 1, and the loading amount of the active material and the initial discharge capacity density (initial discharge capacity per unit volume) described in Non-Patent Documents 1 to 4.

[0068]

Table 2

[0069] In Example 1, the loading amount of the active material in the composite electrode layer 2A was 8.0 mg / cm2 It was. Also, at a temperature of 25°C and a current density of 11.2 μA / cm 2 , the initial discharge capacity per unit area was 0.81 mAh / cm 2 .

[0070] In contrast, in Non-Patent Document 1, the loading amount of the active material is 1.7 mg / cm 2 , at a temperature of 25°C and a current density of 10 μA / cm 2 (5.75 mA / g, 0.05 C), it is said to have obtained an initial discharge capacity of 0.15 mAh / cm 2 . Also, in Non-Patent Document 2, the loading amount of the active material is 1.0 mg / cm 2 , at a temperature of 25°C and a current density of 5.75 μA / cm 2 (5.75 mA / g, 0.05 C), it is said to have obtained an initial discharge capacity of 0.094 mAh / cm 2 . It can be seen that both in Non-Patent Documents 1 and 2, the loading amount of the active material is small and the initial discharge capacity per unit area is also low.

[0071] In Non-Patent Document 3, the loading amount of the active material is 12 - 16 mg / cm 2 , at a temperature of 50°C and a current density of 50 μA / cm 2 (3 - 4 mA / g, 0.02 - 0.03 C), it is said to have obtained an initial discharge capacity of 1.4 mAh / cm 2 . In the case of Non-Patent Document 3, compared with Non-Patent Documents 1 and 2, the loading amount is increased, and the initial discharge capacity per unit area is also higher. However, the temperature of the charge-discharge test is 50°C, and the above performance cannot be obtained in charge-discharge at room temperature.

[0072] In Non-Patent Document 4, the loading amount of the active material is 13.4 mg / cm 2 , at a temperature of 25°C and a current density of 40 μA / cm 2 , the condition is 1.7 mAh / cm 2It is said that the initial discharge capacity has been obtained. As shown in Table 1, the initial charge-discharge efficiency is 74% in the all-solid-state battery of Example 1 and 75% in the case of Non-Patent Document 4, while the charge-discharge efficiency after 30 cycles is 99.8% in the all-solid-state battery of Example 1 and 80 - 90% in the case of Non-Patent Document 4. Also, the capacity retention rate is 77% in the all-solid-state battery of Example 1 under the conditions of a temperature of 25°C and after 18 cycles, while in Non-Patent Document 4, it was 50% or less under the conditions of a temperature of 100°C and after 20 cycles.

[0073] From the above, in the above-mentioned Example 1 and Example 2, the loading amount of the active material in the composite electrode layer is 7 mg / cm 2 As described above, charge and discharge at room temperature are possible, and the re-sintering step (d) of dropping the LiNO3 solution onto the composite electrode layer is not performed. For Comparative Example 1 outside the scope of the present invention, a garnet-type solid electrolyte (LLZO) not coated with LiOH is used as the electrolyte material (B), and for Comparative Example 2 outside the scope of the present invention, the initial discharge capacity per unit volume becomes high. Also, lithium borate is used for the interface bonding, and for Non-Patent Document 1 outside the scope of the present invention and lithium borate carbonate used in Non-Patent Document 2 outside the scope of the present invention, the initial discharge capacity per unit volume also becomes high.

[0074] Furthermore, Sintering in step (c) Sintering the temperature is less than 900°C, and for Comparative Examples 3 and 4 outside the scope of the present invention, the initial discharge capacity per unit volume also becomes high.

[0075] Also, in the composite electrode layer forming step (b), the electrode active material material (A) has a spherical particle shape, and for Comparative Example 5 outside the scope of the present invention, the initial discharge capacity per unit weight becomes high.

Explanation of Reference Numerals

[0076] 1A ··· All-solid-state battery, 2A ··· Composite electrode layer, 3A ··· Electrolyte layer, 4A ··· Electrode

Claims

1. A composite electrode layer obtained by sintering a mixture of a powdered electrode active material and a powdered electrolyte material, and an electrolyte layer obtained by sintering the powdered electrolyte material, wherein the composite electrode layer and the electrolyte layer are in contact with each other on one surface, the electrode active material has a flat particle shape, in the composite electrode layer, the flat particles of the electrode active material are laminated and in contact with the electrolyte layer, the electrolyte material is a compound having a garnet-type crystal structure containing Li and containing La, Zr or other elements, and the powdered electrolyte material is the powdered electrolyte material coated with a low-melting-point Li salt having a melting point of less than 900°C, the composite electrode layer is a re-sintered body of a sintered body in which the electrode active material and the electrolyte material are joined in a sintered body of the mixture of the powdered electrode active material and the powdered electrolyte material coated with the low-melting-point Li salt having a melting point of less than 900°C, and is the re-sintered body of the sintered body on which a LiNO3 solution has been dropped All-solid-state battery.

2. The composite electrode layer is a sintered body of the mixture material heated and pressurized The all-solid-state battery according to Claim 1.

3. The electrode active material is represented by the composition formula LiM1-x-yM’xM”yOz, where x and y are 0 to 1, z is 1.5 to 4.0, and M, M’, M” are any of Co, Ni, Mn, Ti, Al, Cu, Fe, the electrolyte material is represented by the composition formula LixMIx’MII3MIII2O12, where x + x’ ≤ 7, MI is either Al or Mg or does not contain MI, MII is either an alkaline earth metal, a lanthanoid or both, and MIII is any of Zr, Hf, Y, Sb, Sn, Nb, Ta or two or more of them The all-solid-state battery according to Claim 1 or Claim 2.

4. The electrolyte material is one in which a part of La of MII contained in the composition formula LixMIx’MII3MIII2O12 is substituted with an alkaline earth metal The all-solid-state battery according to Claim 3.

5. The low-melting-point Li salt having a melting point of less than 900°C is any one of a hydroxide of Li, a salt of Li and an oxyacid, a halide of Li, or a combination of a plurality of them The all-solid-state battery according to any one of Claims 1 to 4. **Claim 6**: The low melting point Li salt with a melting point of less than 900 °C is any one of LiOH, LiNO₃, Li₂CO₃, Li₂SO₄, Li₃BO₃, LiBO₂, Li₃PO₄, LiPO₃, LiCl, LiBr, LiI, or a combination of a plurality thereof. The all-solid-state battery according to claim 5. **Claim 7**: The thickness of the coating layer before sintering of the binder electrode layer, which is coated on the surface of the electrolyte material with the low melting point Li salt having a melting point of less than 900 °C, is on average 10 nm or more and 100 nm or less. The all-solid-state battery according to any one of claims 1 to 6. **Claim 8**: In the binder electrode layer, part or all of the space between the powdery electrode active material and the powdery electrolyte material is joined by a reaction phase. The reaction phase is represented by La₄Liₓ”Mᵧ”O₈, where x” + y” = 1, and M is any one of Co, Ni, Mn, Ti, Al, Cu, Fe, or a combination of a plurality thereof. The all-solid-state battery according to any one of claims 1 to 7. **Claim 9**: An electrolyte layer forming step of forming an electrolyte layer by pressure molding a powdery electrolyte material, A binder electrode layer forming step of depositing a mixed material of a powdery electrode active material and the powdery electrolyte material on the upper surface of the pressure-molded electrolyte layer and pressure molding to form a binder electrode layer, A sintering step of sintering the electrolyte layer and the binder electrode layer at a sintering temperature of 900 °C or more and 1200 °C or less to form an integral composite body, The electrode active material has a flat particle shape. In the binder electrode layer, the flat particles of the electrode active material are laminated and in contact with the electrolyte layer. The electrolyte material is a compound having a garnet-type crystal structure containing Li and containing La, Zr, or other elements, and the powdery electrolyte material is the powdery electrolyte material coated with a low melting point Li salt having a melting point of less than 900 °C. In the binder electrode layer, the mixed material of the powdery electrode active material and the powdery electrolyte material coated with the low melting point Li salt having a melting point of less than 900 °C is deposited on the upper surface of the electrolyte layer and pressure molded in the binder electrode layer forming step. In the sintering step, the electrolyte layer and the binder electrode layer are sintered. After the sintering process, LiNO3 is further dropped onto the sintered body of the mixed material of the powdery electrode active material and the powdery electrolyte material coated with a low melting point Li salt having a melting point of less than 900 °C, and re-sintered at a temperature lower than the sintering temperature in the sintering process. Method for manufacturing an all-solid-state battery.

10. In the process of forming the composite electrode layer, the mixed material is deposited on the upper surface of the electrolyte layer and formed by heating and pressing. The method for manufacturing an all-solid-state battery according to claim 9.

11. The electrode active material is represented by the composition formula LiM1-x-yM'xM"yOz, where x and y are from 0 to 1, z is from 1.5 to 4.0, and M, M', and M" are any of Co, Ni, Mn, Ti, Al, Cu, and Fe. The electrolyte material is represented by the composition formula LixMIx'MII3MIII2O12, where x + x' ≤ 7, MI is either Al or Mg, or does not contain MI, MII is either an alkaline earth metal, a lanthanoid, or both, and MIII is any one or two or more of Zr, Hf, Y, Sb, Sn, Nb, and Ta. The method for manufacturing an all-solid-state battery according to any one of claims 9 to 10.

12. The electrolyte material is one in which a part of La of MII contained in the composition formula LixMIx'MII3MIII2O12 is replaced with an alkaline earth metal. The method for manufacturing an all-solid-state battery according to claim 11.

13. The low melting point Li salt having a melting point of less than 900 °C is any one of Li hydroxides, salts of Li and oxyacids, halides of Li, or a combination of a plurality thereof. The method for manufacturing an all-solid-state battery according to any one of claims 9 to 12.

14. The low melting point Li salt having a melting point of less than 900 °C is any one of LiOH, LiNO3, Li2CO3, Li2SO4, Li3BO3, LiBO2, Li3PO4, LiPO3, LiCl, LiBr, LiI, or a combination of a plurality thereof. The method for manufacturing an all-solid-state battery according to claim 13.

15. The thickness of the pre-sintering coating layer of the composite electrode layer by the low melting point Li salt having a melting point of less than 900 °C that covers the surface of the electrolyte material is on average 10 nm or more and 100 nm or less. The manufacturing method of the all-solid-state battery according to any one of claims 9 to 14.

16. In the composite electrode layer, part or all between the powdery electrode active material and the powdery electrolyte material is joined by a reaction phase, The reaction phase is represented by La 4 Li x” M y”, where x” + y” = 1, and M is any one of Co, Ni, Mn, Ti, Al, Cu, Fe, or a combination of a plurality thereof The manufacturing method of the all-solid-state battery according to any one of claims 9 to 15.

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