Formation method of all-solid-state lithium secondary battery

Abstract

Provided is a formation method capable of improving the cycle characteristics of a full solid-state lithium secondary battery, which is configured to cause lithium to deposit on the surface of a metal film of a negative electrode layer during charging. A formation method for a full solid-state lithium secondary battery, characterized by comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the positive electrode layer having a positive electrode current collector and a positive electrode active material layer, the negative electrode layer having a metal film, the metal film being disposed in a position facing the positive electrode active material layer, lithium being deposited on the surface of the metal film during charging, and the formation method for the full solid-state lithium secondary battery, wherein at least one charging is performed, the average charge current density of the first charging being in the range of 3.0 mA / cm 2 to 14.0 mA / cm 2 2 to 20 mA / cm2, based on the area of the portion of the metal film facing the positive electrode active material layer.

Description

Technical Field

[0001] This invention relates to a formation method for an all-solid-state lithium secondary battery. Background Technology

[0002] In recent years, research and development has been underway on secondary batteries that help improve energy efficiency, aiming to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. All-solid-state lithium secondary batteries are known as such batteries. An all-solid-state lithium secondary battery comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive and negative electrode layers. As an all-solid-state lithium secondary battery, research is underway on batteries that use a metal material that does not alloy with lithium as the negative electrode layer material, and that allow metallic lithium to deposit from the negative electrode layer during charging (see, for example, Patent Documents 1 and 2). In particular, all-solid-state lithium secondary batteries that use a metal film made of a metal material that does not alloy with lithium as the negative electrode current collector, and allow metallic lithium to deposit from the negative electrode current collector, are also called anode-free batteries (see, for example, Patent Document 1). In all-solid-state lithium secondary batteries, the battery is typically charged and discharged immediately after manufacture to perform a formation process that stabilizes the positive and negative electrode layers.

[0003] [Existing technical documents]

[0004] (Patent Documents)

[0005] Patent Document 1: International Publication No. 2022 / 070326

[0006] Patent Document 2: U.S. Patent Application Publication No. 2022 / 0115640 Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] However, in the technology of all-solid-state lithium secondary batteries, achieving high capacity and improving cycle performance remain challenges. Anode-free batteries, compared to batteries using negative electrode active materials that absorb and release lithium as the negative electrode layer material, tend to have higher capacity per unit capacity. Therefore, improving cycle performance is desired in anode-free batteries.

[0009] The purpose of this invention is to provide a formation method that improves the cycle characteristics of an all-solid-state lithium secondary battery, wherein the all-solid-state lithium secondary battery has a structure in which lithium is deposited on the surface of the negative electrode layer metal film during charging. Furthermore, this method contributes to improving energy efficiency.

[0010] [Technical means to solve the problem]

[0011] The inventors discovered that setting the first charging current density within a specified range during the formation process of an all-solid-state lithium secondary battery is effective in solving the aforementioned problems, thus completing this invention. Therefore, this invention provides the following solution.

[0012] (1) A method for forming an all-solid-state lithium secondary battery, characterized in that it comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer has a positive current collector and a positive active material layer, the negative electrode layer has a metal film disposed at a position opposite to the positive active material layer, and lithium is deposited on the surface of the metal film during charging, and in the method for forming the all-solid-state lithium secondary battery, at least one charging is performed, and the average charging current density of the first charging is 3.0 mA / cm², based on the area of ​​the portion of the metal film opposite to the positive active material layer. 2 Above and 14.0 mA / cm 2 Within the following range.

[0013] According to the formation method of the all-solid-state lithium secondary battery in (1), a uniformly thick lithium metal layer is formed on the surface of the negative electrode metal film through the first charge, thereby uniformly activating the surface of the metal film. Therefore, the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment are improved.

[0014] (2) According to the formation method of the all-solid-state lithium secondary battery described in (1), the first charging is carried out until the charging rate of the all-solid-state lithium secondary battery reaches at least 30%.

[0015] According to the formation method of the all-solid-state lithium secondary battery in (2), the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment are further improved because the surface of the metal film is more reliably and uniformly activated.

[0016] (3) According to the formation method of the all-solid-state lithium secondary battery described in (1) or (2), after the first charging, the all-solid-state lithium secondary battery is discharged, and then, based on the area of ​​the portion of the metal film facing the positive electrode active material layer, the average charging current density is 3.0 mA / cm². 2 Above and 14.0 mA / cm 2 Under the following conditions, the aforementioned all-solid-state lithium secondary battery is charged a second time.

[0017] According to the formation method of the all-solid-state lithium secondary battery in (3), the surface of the metal film is further uniformly activated by the second charge, thus the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment are further improved.

[0018] (4) In the formation method of the all-solid-state lithium secondary battery according to any one of (1) to (3), the aforementioned metal film is a film of metal that does not form an alloy with lithium.

[0019] According to the formation method of the all-solid-state lithium secondary battery in (4), since lithium is more likely to be deposited on the surface of the metal film during charging, the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment are further improved.

[0020] (5) According to the formation method of the all-solid-state lithium secondary battery described in (4), the aforementioned metal film is a copper film.

[0021] According to the formation method of the all-solid-state lithium secondary battery in (5), since lithium is more likely to be deposited on the surface of the metal film during charging, the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment are further improved.

[0022] (6) The formation method of the all-solid-state lithium secondary battery according to any one of (1) to (5), wherein the all-solid-state lithium secondary battery has a negative electrode tab connected to the metal film.

[0023] According to the formation method of the all-solid-state lithium secondary battery in (6), since the all-solid-state lithium secondary battery is an anode-free battery in which the metal film acts as the negative electrode current collector, it is easy to increase the capacity per unit capacity.

[0024] (The effect of the invention)

[0025] According to the present invention, a formation method is provided that can improve the cycle characteristics of an all-solid-state lithium secondary battery, wherein the all-solid-state lithium secondary battery has a structure in which lithium is deposited on the surface of the negative electrode layer metal film during charging. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view illustrating an all-solid-state lithium secondary battery that can be used in the formation method of an all-solid-state lithium secondary battery according to an embodiment of the present invention.

[0027] Figure 2A This is a cross-sectional view illustrating an example of the initial state during the first charge in the formation method of an all-solid-state lithium secondary battery according to an embodiment of the present invention.

[0028] Figure 2B This is a cross-sectional view illustrating an example of the state during the first charging stage in the formation method of an all-solid-state lithium secondary battery according to an embodiment of the present invention.

[0029] Figure 2C This is a cross-sectional view illustrating an example of the state at the end of the first charge in the formation method of an all-solid-state lithium secondary battery according to an embodiment of the present invention.

[0030] Figure 3 This is a diagram illustrating an example of the charge and discharge modes in the formation method of an all-solid-state lithium secondary battery according to an embodiment of the present invention.

[0031] Figure 4 The graphs illustrate the relationship between the number of cycles and the discharge capacity retention of the all-solid-state lithium secondary batteries of Examples 1-3 and Comparative Examples 1 and 2. Detailed Implementation

[0032] Hereinafter, a method for forming an all-solid-state lithium secondary battery according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0033] First, the structure of the all-solid-state battery targeted by the formation method of this embodiment will be explained.

[0034] Figure 1 This is a cross-sectional view illustrating an all-solid-state lithium secondary battery that can be used in the formation method of an all-solid-state lithium secondary battery according to an embodiment of the present invention.

[0035] The all-solid-state lithium secondary battery 1 has an electrode stack 10. The electrode stack 10 is configured to include a positive electrode layer 11, a negative electrode layer 12, a solid electrolyte layer 13 disposed between the positive electrode layer 11 and the negative electrode layer 12, and an intermediate layer 14 disposed between the solid electrolyte layer 13 and the negative electrode layer 12. The electrode stack 10 is housed in an outer packaging (not shown) having positive electrode tabs and negative electrode tabs.

[0036] The positive electrode layer 11 has a positive current collector 111 and a positive active material layer 112 disposed on the surface of the positive current collector 111. The positive current collector 111 is connected to a positive electrode tab (not shown).

[0037] Examples of the shapes of the positive current collector 111 include foil, plate, mesh, non-woven fabric, and foam. Examples of materials for the positive current collector 111 include aluminum, aluminum alloy, stainless steel, nickel, iron, and titanium.

[0038] The positive electrode active material layer 112 contains a positive electrode active material. The positive electrode active material can be a lithium compound that releases lithium ions during charging and absorbs lithium ions during discharging. As the lithium compound, layered active materials, spinel-type active materials, and olivine-type active materials can be used, for example. Specific examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel manganese cobalt oxide (NMC:LiNiO2). p Mn q Co r O2(p+q+r=1)), LiNi p Al q Co rO2(p+q+r=1), lithium manganese oxide (LiMn2O4), Li 1+x Mn 2-x-y MO4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni and Zn) represents heteroelement-substituted Li-Mn spinel, lithium titanate (an oxide containing Li and Ti), lithium metal phosphate (LiMPO4, M=at least one selected from Fe, Mn, Co and Ni), etc. The positive electrode active material layer 112 may further include conductive additives, binders and solid electrolytes, etc.

[0039] The negative electrode layer 12 is configured as a metal film (including a metal foil) deposited on the surface of lithium during charging. The negative electrode layer 12 also functions as a negative current collector. The negative electrode layer 12 is connected to a negative electrode tab (not shown).

[0040] Examples of shapes for the negative electrode layer 12 include foil, plate, mesh, non-woven fabric, and foam. Examples of materials for the negative electrode layer 12 include copper, copper alloys, stainless steel, and nickel.

[0041] The negative electrode layer 12 can be a film of a metal that does not alloy with lithium. Examples of metal films that can be used as the negative electrode layer 12 include films of Cu, Ti, Fe, Co, Ni, W, and alloys containing these metals. The metal film can have a layer of a metal that alloys with lithium and an alloy layer, provided it does not hinder lithium deposition. Examples of metals that alloy with lithium include Mg, Zn, Al, In, Si, Ge, Sn, Ag, Au, Pt, Pd, Pb, Sb, Bi, and alloys containing these metals. A carbon coating film may also be used.

[0042] The solid electrolyte layer 13 contains a solid electrolyte. The solid electrolyte is not particularly limited to any dielectric material that has lithium-ion conductivity. Examples of solid electrolytes that can be used include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

[0043] Examples of sulfide solid electrolytes include Li₂S-P₂S₅ and Li₂S-P₂S₅-LiI. Sulfide solid electrolytes can have a pyroxene-type crystal structure.

[0044] Examples of oxide solid electrolytes include NASICON-type oxides, garnet-type oxides, and perovskite-type oxides. Examples of NASICON-type oxides include oxides containing Li, Al, Ti, P, and O (e.g., Li). 1.5 Al 0.5 Ti 1.5(PO4)3). Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., Li7La3Zr2O). 12 Examples of perovskite oxides include oxides containing Li, La, Ti, and O (e.g., LiLaTiO3).

[0045] The intermediate layer 14 functions to uniformly deposit metallic lithium on the surface of the negative electrode layer 12 during charging. The intermediate layer 14 comprises a metal alloyed with lithium and amorphous carbon, and may further comprise a binder, etc. Examples of the metal alloyed with lithium are as described above. Examples of amorphous carbon include, for example, carbon blacks such as acetylene black, furnace black, and Ketjen black, coke, and activated carbon. The amorphous carbon can be easily graphitized carbon (soft carbon), or difficult-to-graphitize carbon (hard carbon), CNTs (carbon nanotubes), fullerenes, and graphene. The binder is not particularly limited as long as it improves adhesion; for example, polyvinylidene fluoride (PVDF) can be included.

[0046] The formation method of the all-solid-state lithium secondary battery in this embodiment involves charging the all-solid-state lithium secondary battery 1 at least once.

[0047] The first charge uses high-speed charging, with the average charging current density being 3.0 mA / cm², calculated based on the area of ​​the opposing portions of the negative electrode layer 12 (metal film) and the positive electrode active material layer 112. 2 Above and 14.0 mA / cm 2 Within the following range, the average charging current density can also be set to 7.5 mA / cm². 2 Above and 11.5 mA / cm 2 Within the following range, the average charging current density can be within a C-rate range of 1.0 C to 3.5 C, or within a C-rate range of 2.0 C to 3.0 C.

[0048] In the all-solid-state lithium secondary battery formation method of this embodiment, since the first charge is a high-speed charge and the average charging current density is within the aforementioned range and relatively high, a uniformly thick lithium metal layer can be formed on the surface of the negative electrode layer 12 after charging. Figures 2A to 2C This describes the state of the negative electrode layer 12 during charging. Figure 2A This is a cross-sectional view illustrating an example of the initial state during the first charge. Figure 2B This is a cross-sectional view illustrating an example of the state during the middle of the first charge. Figure 2C This is a cross-sectional view illustrating an example of the state at the end of the first charge.

[0049] like Figure 2AAs shown, in the initial state of charging, fine lithium metal particles 20 are generated on the surface of the negative electrode layer 12. In the formation method of the all-solid-state lithium secondary battery of this embodiment, since the average current density of the first charge is high, a large number of fine lithium metal particles 20 are generated on the surface of the negative electrode layer 12 simultaneously.

[0050] In the middle of the charging process, such as Figure 2B As shown, new lithium metal particles 20 are generated, and lithium metal is deposited on the surface of the generated lithium metal particles 20 as the nucleus, thereby coarsening the lithium metal particles 20. Since an intermediate layer 14 is disposed on the negative electrode layer 12, the lithium metal particles 20 are difficult to coarsen in the stacking direction of the electrode stack 10, but instead coarsen in a direction perpendicular to the stacking direction of the electrode stack 10.

[0051] In the final stage of charging, such as Figure 2C As shown, coarse lithium metal particles 20 are interconnected to form a lithium metal layer 21.

[0052] In the formation process of an all-solid-state lithium secondary battery, the all-solid-state lithium secondary battery 1 can be pressurized in the stacking direction of the electrode stack 10. By pressurizing the all-solid-state lithium secondary battery 1, during the middle of charging, the lithium metal particles 20 become more coarse in the direction perpendicular to the stacking direction of the electrode stack 10, thereby making it easier to form a more uniform lithium metal layer 21.

[0053] The first charge is preferably performed until the state of charge (SOC) of the all-solid-state lithium secondary battery 1 reaches at least 50%. SOC is defined as the fully charged state of the solid-state lithium secondary battery 1, with 100% as the value. The first charge can be performed until the state of charge of the all-solid-state lithium secondary battery 1 reaches 100%. Alternatively, the first charge can be stopped when the state of charge of the all-solid-state lithium secondary battery 1 reaches 30%, and thereafter, the charging current density can be kept below 3.0 mA / cm². 2 The device charges slowly at a low speed until it reaches 100% charge. The first charge can be performed at a constant current or a constant voltage.

[0054] The all-solid-state lithium secondary battery 1 can be discharged after the first charge. The average discharge current during the first discharge can be in the range of more than 1 / 40 and less than 1 / 5 of the average charging current during the first charge. By discharging under conditions that are slower than charging, the thickness of the lithium metal layer 21 is reduced uniformly, thus making it easier for the surface of the negative electrode layer 12 to become uniform. The first discharge can be performed with constant current or constant voltage.

[0055] The all-solid-state lithium secondary battery 1 can be recharged after the first discharge. The conditions for the second charge and discharge can be set to the same conditions as the first charge and discharge.

[0056] Secondly, use Figure 3 This describes an example of the charge / discharge mode in the formation method of the all-solid-state lithium secondary battery of this embodiment. Figure 3 This is a diagram illustrating an example of a charging / discharging mode. Figure 3 In the charge / discharge modes shown, the horizontal axis represents time, and the vertical axis represents the charging rate of the all-solid-state lithium secondary battery 1.

[0057] exist Figure 3 In the charging and discharging mode, the first charge is performed at high speed until the charge rate reaches 100%. After the first charge, the first discharge is performed until the charge rate drops to 0%. After the first discharge, the second charge is performed at high speed until the charge rate reaches 100%. After the second charge, the second discharge is performed until the charge rate drops to 0%. After the second discharge, the third charge is performed until the charge rate reaches 50%, and then the charged all-solid-state lithium secondary battery 1 is left to rest. The third charge can be performed using an average charging current density of less than 3.0 mA / cm². 2 Low-speed charging. There are no particular restrictions on the ambient temperature during charging and discharging; for example, it can be carried out in a range of above 20°C and below 60°C.

[0058] According to the all-solid-state lithium secondary battery formation method of this embodiment with the above-described structure, a uniformly thick lithium metal layer 21 is formed on the surface of the metal film of the negative electrode layer 12 by a first high-speed charge, thus the surface of the negative electrode layer 12 (metal film) is uniformly activated. Therefore, the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment are improved.

[0059] In the formation method of the all-solid-state lithium secondary battery of this embodiment, by performing a first charge until the charge rate of the all-solid-state lithium secondary battery 1 reaches at least 50%, the surface of the negative electrode layer 12 is more reliably and uniformly activated, thereby further improving the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment. Furthermore, after the first charge, the all-solid-state lithium secondary battery is discharged, followed by a second high-speed charge, thereby further uniformly activating the surface of the negative electrode layer 12, thus further improving the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment.

[0060] In the formation method of the all-solid-state lithium secondary battery of this embodiment, when the negative electrode layer 12 is a film of a metal that does not form an alloy with lithium, lithium is more easily deposited on the surface of the negative electrode layer 12 during charging, thus further improving the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment. In particular, when the metal film is a copper film, lithium is more reliably deposited on the surface of the negative electrode layer 12 during charging, thus further improving the cycle characteristics of the all-solid-state lithium secondary battery after formation treatment. Furthermore, the negative electrode layer 12 is connected to the negative electrode tab (not shown) and functions as a negative electrode current collector, making the all-solid-state lithium secondary battery 1 an anode-free battery, thus making it easier to increase the capacity per unit capacity.

[0061] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. For example, in this embodiment, the negative electrode layer 12 is connected to the negative electrode tab (not shown) and functions as a negative electrode current collector, but the shape of the negative electrode layer is not limited to this. The negative electrode layer may also be a stack of a negative electrode current collector and a metal film for lithium deposition, and the metal film may be positioned opposite to the positive electrode active material layer. Furthermore, in this embodiment, the electrode stack 10 of the all-solid-state lithium secondary battery 1 has a structure containing an intermediate layer 14, but it is not limited to this structure. If the solid electrolyte layer 13 alone can uniformly deposit metallic lithium onto the surface of the negative electrode layer during charging, the intermediate layer 14 may not be included.

[0062]

Example

[0063] The present invention will be described below with reference to embodiments, but the present invention is not limited to these embodiments.

[0064] [All-solid-state lithium rechargeable battery]

[0065] The all-solid-state lithium secondary battery used in this embodiment is fabricated as follows.

[0066] (1) Fabrication of the positive electrode layer

[0067] A 15 μm thick aluminum foil was prepared as the positive electrode current collector. 80 parts by mass of lithium nickel cobalt manganese composite oxide (NCM622) was used as the positive electrode active material, 17 parts by mass of sulfide-germanium sulfide solid electrolyte was used as the solid electrolyte material, 2 parts by mass of carbon black was used as a conductive additive, and 1 part by mass of SBR (styrene-butadiene rubber) binder was used as a binder. The resulting mixture was dispersed in 43 parts by mass of butyl butyrate to prepare a positive electrode active material slurry. The obtained positive electrode active material slurry was coated onto both sides of the positive electrode current collector using a doctor blade, achieving a dry area weight of 27 mg / cm². 2 After drying, a positive electrode active material layer with a thickness of 80 μm is formed, thus obtaining the positive electrode layer.

[0068] (2) Fabrication of solid electrolyte layer transfer sheet

[0069] 97 parts by mass of a sulfide solid electrolyte of silver-germanium sulfide type (median particle size 3.0 μm) were mixed with 3 parts by mass of an SBR (styrene-butadiene rubber) binder as a binder. The resulting mixture was dispersed in a solvent to prepare a solid electrolyte slurry. The obtained solid electrolyte slurry was coated onto a support sheet and dried to obtain a solid electrolyte layer transfer sheet (solid electrolyte layer thickness: 100 μm).

[0070] (3) Fabrication of intermediate layer transfer sheet

[0071] Sn particles (average particle size: 0.07 μm) were used as metal particles, and acetylene black (average particle size: 0.05 μm) were used as amorphous carbon particles. A total of 95 parts by mass of both were mixed with 5 parts by mass of PVDF-based binder as a binder. The resulting mixture was dispersed in 1000 parts by mass of NMP (N-methyl-2-pyrrolidone) to prepare an intermediate layer slurry. The obtained intermediate layer slurry was coated onto a support sheet, and after drying, an intermediate layer transfer sheet (intermediate layer thickness: 3.0 μm) was obtained.

[0072] (4) Negative electrode layer

[0073] As the negative current collector, a copper foil with a thickness of 8 μm (NC-WS, Furukawa Electric Industry Co., Ltd.) is prepared.

[0074] (5) Fabrication of all-solid-state lithium secondary batteries

[0075] On the surface of the positive electrode active material layer of the positive electrode layer, a solid electrolyte layer transfer sheet is laminated, and the solid electrolyte layer is bonded using a uniaxial forming press under bonding conditions of 70 MPa, 3 minutes, and room temperature. Subsequently, the support sheet of the solid electrolyte layer transfer sheet is peeled off to obtain a positive electrode layer-solid electrolyte layer composite. Next, on the surface of the solid electrolyte layer of the positive electrode layer-solid electrolyte layer composite, an intermediate layer transfer sheet is laminated, and the intermediate layer is bonded using a uniaxial forming press under bonding conditions of 110 MPa, 5 minutes, and room temperature. Subsequently, the support sheet of the intermediate layer transfer sheet is peeled off to obtain a positive electrode layer-solid electrolyte layer-intermediate layer composite. Finally, the positive electrode layer-solid electrolyte layer-intermediate layer composite is densified using an isotropic pressing press under bonding conditions of 980 MPa, 5 minutes, and 120°C. Next, on the surface of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer composite, the negative electrode current collector of the negative electrode layer is superimposed to obtain the electrode stack.

[0076] The obtained electrode stack is housed in an aluminum-plastic film outer packaging to form an all-solid-state lithium secondary battery. A buffer material is placed on the negative electrode layer side and constrained with a constraint pressure of 3 MPa.

[0077] [Example 1]

[0078] The above-mentioned all-solid-state lithium secondary battery was subjected to the following formation process. First, the all-solid-state lithium secondary battery was placed in a constant temperature bath at 60°C and left to stand for 4 hours. Then, the all-solid-state lithium secondary battery was charged and discharged in the constant temperature bath under the following conditions.

[0079] (Charging and discharging conditions)

[0080] First charge: 3.80 mA / cm 2 (1 C) Constant current charging is applied until the battery voltage reaches 4.3V, then constant voltage charging is applied at 4.3V until the charging current density drops to 0.19 mA / cm². 2 (0.05C or below) (SOC: 100%).

[0081] First discharge: After charging is complete, let stand for 15 minutes. Then, discharge at a constant current density of 0.38 mA / cm² (0.1 C) until the battery voltage drops to 2.65 V (SOC: 0%).

[0082] Second charge: After discharging, let stand for 30 minutes. Then, charge at a constant current density of 3.80 mA / cm² (1 C) until the battery voltage reaches 4.3 V, and then charge at a constant voltage of 4.3 V until the charging current density drops below 0.19 mA / cm² (0.05 C) (SOC: 100%).

[0083] [Examples 2-3 and Comparative Examples 1 and 2]

[0084] Except for changing the current density of the first and second charges to the current density shown in Table 1 below, the solid-state lithium secondary battery was formed in the same manner as in Example 1.

[0085] Table 1

[0086]

[0087] [evaluate]

[0088] The DC resistance (DCR) and cycle characteristics of the all-solid-state lithium secondary battery after formation treatment were measured by the following method.

[0089] (DC resistance)

[0090] The all-solid-state lithium secondary battery was tested at a temperature of 60℃ and a current density of 0.38 mA / cm². 2 Under conditions of (0.1 C) and voltage corresponding to 50% SOC, the battery was charged to 50% SOC using constant current and constant voltage (CC·CV). The charging was carried out at a temperature of 25°C and a current density of 15.1 mA / cm². 2 Discharge is performed based on the voltage drop ΔV (V), current I (A), and positive electrode area Ac (cm²) during discharge. 2 The initial DC resistance of the all-solid-state lithium secondary battery after charging is calculated using the following formula. The results are shown in Table 2 below.

[0091] Initial DC resistance (Ω·cm) 2 = Voltage drop ΔV (V) / Current value I (A) × Positive electrode area Ac (cm²) 2 )

[0092] Table 2

[0093]

[0094] (Cyclic characteristics)

[0095] At a temperature of 45℃ and a current density of 1.3 mA / cm² 2 A charge-discharge cycle test was conducted under the following conditions: (1 / 3 C), voltage range of upper limit 4.3 V, lower limit 2.65 V, constant current and constant voltage (CCCV) charging, and constant current (CC) discharging. The discharge capacity retention rate for each cycle is as follows: Figure 4 As shown.

[0096] From Table 2 and Figure 4 The results show that the all-solid-state lithium secondary batteries of Examples 1-3, which underwent formation treatment according to the charging rate of the present invention, exhibit low DC resistance, high discharge capacity retention during repeated charge-discharge cycles, and improved cycle characteristics, achieving a balance between reducing DC resistance and improving cycle characteristics. In contrast, the charging current density during formation treatment was lower than that of the all-solid-state lithium secondary battery of Comparative Example 1 of the present invention, resulting in higher DC resistance. This is because during charging under formation treatment, fewer lithium particles were deposited on the surface of the negative electrode layer (copper film), leading to insufficient activation of the negative electrode layer surface. Furthermore, the charging current density during formation treatment was higher than that of the all-solid-state lithium secondary battery of Comparative Example 2 of the present invention, resulting in decreased cycle characteristics. This may be because the excessively high charging current density led to a prolonged constant-voltage charging time, accelerating the oxidation and degradation of the solid electrolyte in the positive electrode layer, and simultaneously exacerbating the reaction inhomogeneity within the positive electrode active material layer, resulting in accelerated local degradation.

[0097] [Figure Labels]

[0098] 1: All-solid-state lithium secondary battery

[0099] 10: Electrode laminate

[0100] 11: Positive electrode layer

[0101] 111: Positive current collector

[0102] 112: Positive electrode active material layer

[0103] 12: Negative electrode layer

[0104] 13: Solid electrolyte layer

[0105] 14: Intermediate layer

[0106] 20: Lithium metal particles

[0107] 21: Lithium metal layer

Claims

1. A method for forming an all-solid-state lithium secondary battery, characterized in that, The battery comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer has a positive current collector and a positive active material layer. The negative electrode layer has a metal film disposed opposite to the positive active material layer. During charging, lithium is deposited on the surface of the metal film. In the formation method of the all-solid-state lithium secondary battery... Charge at least once. Based on the area of ​​the portion of the aforementioned metal film facing the aforementioned positive electrode active material layer, the average charging current density during the first charging cycle is 3.0 mA / cm². 2 Above and 14.0 mA / cm 2 Within the following range.

2. The formation method of the all-solid-state lithium secondary battery according to claim 1, wherein, The first charging operation was carried out until the charge rate of the aforementioned all-solid-state lithium secondary battery reached at least 30%.

3. The formation method of the all-solid-state lithium secondary battery according to claim 1 or 2, wherein, After the first charge, the all-solid-state lithium secondary battery was discharged. Then, based on the area of ​​the portion of the metal film facing the positive electrode active material layer, the average charging current density was 3.0 mA / cm². 2 Above and 14.0 mA / cm 2 Under the following conditions, the aforementioned all-solid-state lithium secondary battery is charged a second time.

4. The formation method of the all-solid-state lithium secondary battery according to claim 1 or 2, wherein, The aforementioned metal film is a film of a metal that does not form an alloy with lithium.

5. The formation method of the all-solid-state lithium secondary battery according to claim 4, wherein, The aforementioned metal film is a copper film.

6. The formation method of the all-solid-state lithium secondary battery according to claim 1 or 2, wherein, The aforementioned all-solid-state lithium secondary battery has a negative electrode tab, which is connected to the aforementioned metal film.

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