JP7748138B2 - In situ electrochemical passivation and repair method for solid-state lithium batteries - Google Patents

Description

The present invention belongs to the field of solid-state lithium batteries, and specifically relates to an in situ electrochemical reduction method for passivating and repairing the positive electrode interface of sulfide-based solid-state batteries.

With the rapid development of 3C electronic products, new energy vehicles, and large-scale energy storage systems, higher energy density and safety are required of lithium-ion batteries. Sulfide solid electrolytes have the advantages of high ionic conductivity, excellent thermal stability, processability, and good ductility. Sulfide-based solid-state lithium batteries manufactured using them instead of conventional flammable organic liquid electrolytes are expected to offer significant improvements in energy density and safety.

However, theoretical calculations and experimental results indicate that the electrochemical stability window of sulfide solid electrolytes is only approximately 1.7 to 2.1 V (vs. Li ⁺ /Li), which is much lower than the operating voltage range (typically 2.0 to 5.0 V) and platform voltage (3.3 to 3.8 V) of currently mainstream commercial layered oxide cathodes (e.g., lithium nickel-cobalt manganese oxide cathodes), polyanion oxide cathodes (e.g., lithium iron phosphate cathodes), and next-generation high-voltage lithium-rich cathodes (e.g., lithium-rich manganese-based solid solutions) (see Figure 14). Therefore, when sulfide solid electrolytes are combined with oxide cathodes for operation, the sulfides oxidize and decompose, producing electronic-ionic insulating products such as phosphorus polysulfides and elemental sulfur, which cover the interface and prevent efficient carrier transport. This results in a sudden increase in interfacial impedance, making it difficult for the capacity of the cathode material to be fully utilized and causing rapid decay. Furthermore, many oxide cathode materials themselves have low electronic conductivity, necessitating their surface coating with conductive carbon, exacerbating the oxidative decomposition of sulfide electrolytes at the cathode interface. Current approaches to coating cathode materials or modifying sulfide electrolytes by doping them are not only insufficient to fundamentally resolve these issues, but also involve high costs and complex processes in large-scale industrial production. Therefore, to achieve stable operation of sulfide solid electrolytes in oxide cathode systems with high operating voltages, it is urgent to develop a simple and effective method for passivating and ultimately repairing the cathode interface of sulfide-based solid-state batteries.

The object of the present invention is to provide an in situ electrochemical reduction method for passivating and repairing the positive electrode interface of a sulfide-based solid-state battery, which, by controlling the charge-discharge procedure, achieves passivation of the sulfide electrolyte and oxide positive electrode interface, thereby repairing the interface after expiration, and ensures full capacity utilization and stable cycling of the positive electrode active material.

To achieve the above objectives, the technical solutions adopted by this invention are as follows:

This method for in-situ electrochemical passivation and repair of solid-state lithium batteries involves discharging a sulfide-based solid-state battery to a specific degree of lithiation at a low current density and in a specific discharge mode, thereby achieving in-situ electrochemical passivation and/or repair of the battery. By controlling the charge/discharge sequence, a passivating interface is formed between the sulfide solid electrolyte and the positive electrode material, or a deactivated interface is repaired and activated.

Preferably, the sulfide-based solid state battery is a sulfide-based solid state battery assembled using a sulfide solid electrolyte as the electrolyte and an ionic conductive agent in the positive electrode, and a layered oxide or polyanion oxide as the positive electrode active material, and the electrolyte and ionic conductive agent in the same battery are not necessarily the same.

More preferably, the sulfide solid electrolyte is selected from _{the group} consisting _of argyrodite-type electrolytes such _{as Li6PS5Cl} , _Li6PS5Br , _{Li6PS5Cl0.5Br0.5} , _{Li5.5PS4.5Cl1.5 , Li5.4PS4.4Cl1.6 ,} lithium fast ion conductors such as _{Li10GeP2S12 , Li10SnP2S12} , _{Li6.75Si0.75As0.25S5I , Li3PS4 , Li7P3S11} , _{xLi2S- ( 100} - _{x ) P2S} , _{and Li2S- ( 100} -x) _{P2S . 5} , and other electrolytes based on the above electrolytes by doping with anions and cations or by complexing with polymers.
More preferably, the layered oxide or polyanion oxide positive electrode is selected from the group consisting of lithium cobalt oxide (LiCoO ₂ ), lithium nickel manganese oxide (LiNi _0.5 Mn _1.5 O ₄ ), lithium nickel cobalt manganese oxide (LiNi _x Co _y Mn _1-x-y O ₂ ), lithium nickel cobalt aluminate (LiNi _x Co _y Al _1-x-y O ₂ ), lithium rich manganese based solid solutions (xLi ₂ MnO _3. (1-x)LiMO ₂ , where M is one or more of Ni, Co, and Mn), lithium iron phosphate (LiFePO ₄ ), lithium manganese iron phosphate (LiMn _x Fe _1-x PO ₄ ), lithium vanadium phosphate (LiVPO ₄ ), positive electrode materials obtained by surface coating modification or doping modification of the above materials, and combinations of one or more of the above positive electrode materials, but are not limited to these.
More preferably, the negative electrode material of the sulfide-based solid state battery includes, but is not limited to, negative electrode materials such as metallic lithium, lithium-indium alloy, graphite, hard carbon, silicon carbon, lithium titanate, niobium titanium oxide, and the like, and negative electrode materials obtained by modifying the above materials, and combinations of one or more of the above positive electrode materials.
More preferably, the ionic conductive agent accounts for 1% to 60% of the total mass of the positive electrode.

Preferably, discharging to a specific lithiation degree in the specific discharge mode includes at least one of discharging to a specific potential in a constant current discharge mode, discharging to a specific current in a constant current-constant voltage discharge mode, and discharging to a specific specific capacity in a constant current discharge mode, and more preferably, the low current density is 0.1 to 50 mA g ⁻¹ (calculated in terms of the mass of the ionic conductive agent in the composite positive electrode of the battery), the specific potential to be discharged is 0.5 to 2.2 V (vs. Li ⁺ /Li), the constant current-constant voltage discharge mode is discharging to a specific potential at a constant current and then discharging to a specific current at a constant voltage, and the cutoff condition is that the constant voltage discharge current is 0.1 to 20 mA g ⁻¹ (calculated in terms of the mass of the ionic conductive agent in the composite positive electrode), and the specific specific capacity is 15 to 500 mAh g ⁻¹ (calculated in terms of the mass of the ion conductive electrode agent in the composite positive electrode).

Preferably, the charge-discharge procedure for passivating a solid-state lithium battery comprises:
(1.1) Passivating the positive electrode interface of a sulfide-based solid state battery, i.e., discharging to a specific lithiation degree at a low current density and a specific discharge mode, so that the sulfide electrolyte at the interface undergoes appropriate reductive decomposition, generating lithium-rich decomposition products to cover the highly reactive sites at the interface, thereby achieving the purpose of passivating the interface and maintaining the lithium ion transport pathway;
(1.2) performing a normal charge-discharge cycle on the sulfide-based solid state battery.
More preferably, in step (1.1), the passivation measures of the positive electrode interface are not limited to the first direct discharge passivation, but can also be carried out 1 to 10 times, i.e., the discharge passivation process can be selectively included within 1 to 10 cycles of the battery to further ensure sufficient passivation of the interface.
More preferably, the normal charge/discharge cycle current is 0.05 to 20 C (calculated by the mass of the positive electrode active material), and the charge/discharge voltage range is the normal charge/discharge voltage range for this positive electrode material.

Preferably, the charge-discharge procedure for repairing the solid-state lithium battery comprises:
(2.1) Repairing the sulfide-based solid-state battery, i.e., repairing the expired battery by discharging it to a specific lithiation degree at a low current density and in a specific discharge mode, and performing an interface passivation operation to re-reduce the reduction products accumulated at the interface to lithium-rich products with lithium ion transport properties, allowing the battery to undergo normal charge-discharge cycles.
More preferably, the sulfide-based solid state battery is a battery that has been cycled until its capacity has significantly decreased, and more preferably, the significant decrease in capacity includes a case where the discharge capacity has decreased to 1% to 70% of the rated discharge capacity, and more preferably, the repair may be performed on a solid state lithium battery that has not undergone the interface passivation step of the present invention, or that has adopted another formation or activation process, or that has directly undergone charge-discharge cycling.
More preferably, the sulfide-based solid state battery may undergo the aforementioned interface passivation treatment, in which case the specific discharge mode, current, cut-off voltage, rated capacity, etc. of the interface repair operation are not necessarily completely the same as those of the passivation step.
More preferably, the normal charge/discharge cycle current is 0.05 to 20 C (calculated by the mass of the positive electrode active material), and the charge/discharge voltage range is the normal charge/discharge voltage range for this positive electrode material.

In the present invention, the sulfide electrolyte undergoes appropriate reductive decomposition by passivating the battery, forming a passivated interface of lithium-rich products at the interface between the sulfide electrolyte and the positive electrode, which has consistent lithium-ion conductivity properties to ensure normal subsequent cycling of the battery. This effectively resolves the problem of the operating voltage range of oxide positive electrode materials exceeding the electrochemical stability window of sulfide solid electrolytes. If the capacity significantly decays during battery cycling, an in-situ electrochemical reduction method is used to reconvert the electronically-ionically insulating oxidation products accumulated at the interface into lithium-rich reduction products, thus repairing the battery. This electrochemical reduction method passivates and stabilizes the interface of sulfide-based solid-state batteries, preventing the sulfide electrolyte from continuing to decompose during the charge/discharge process and making the sulfide solid electrolyte compatible with oxide positive electrode materials with high operating voltages. Furthermore, the oxidation products generated by decomposition during cycling are reconverted into ionically conductive lithium-rich reduction products, which serve as activation and repair functions, thereby providing the battery with better cycle stability.

Compared to conventional technology, the advantageous effects of the present invention are as follows:

The present invention utilizes a simple charge-discharge procedure to control the reversible redox reaction of a sulfide solid electrolyte and achieve passivation of the interface between the sulfide electrolyte and the oxide positive electrode. This allows sulfide electrolytes, which have a narrow electrochemical stability window, to be directly compatible with mainstream oxide positive electrode materials with high operating voltages, avoiding the need for complex interface modification, doping, and other processes. Because discharge of a lithium battery's positive electrode corresponds to the lithiation process, the sulfide electrolyte undergoes reductive decomposition during the first discharge, resulting in the formation of lithium-rich decomposition products such as lithium chloride (or lithium bromide or lithium iodide), lithium sulfide, and lithium phosphide. Unlike the ionically and electronically insulating lithium-poor products produced by oxidative decomposition during charging, these lithium-rich decomposition products possess electronic insulating and ion transport properties. Once formed, they are highly inert and resistant to reoxidation. This not only maintains lithium ion transport at the interface and passivates the interface to a metastable state, but is also expected to suppress inherent problems in the positive electrode material, such as lattice oxygen precipitation, structural collapse, and irreversible phase transition, thereby contributing to maintaining the battery's subsequent cycling stability. Furthermore, the in-situ electrochemical passivation and repair method proposed by this invention is expected to be directly incorporated into the formation process of conventional lithium batteries, and has great application value and potential in the mass production and commercial application of batteries.

1 shows charge-discharge curves for the first and 50th cycles of the cycle process when the lithium iron phosphate positive electrode in Example 1 of the present invention is discharged to 1.0 V to be passivated and then charged and discharged. 1 shows charge-discharge curves at the 1st and 50th cycles when a charge-discharge test was directly carried out on a lithium iron phosphate positive electrode in Comparative Example 1 of the present invention without discharging and passivating it, and this is used as a comparative experiment. FIG. 1 is a graph showing the cycle performance of the 50th cycle of the cycle process at 0.1 C when the lithium iron phosphate positive electrode in Example 1 of the present invention is discharged and passivated, and when direct charge and discharge is performed in Comparative Example 1. 1 shows charge-discharge curves for the first and 60th cycles of a cycle process in which a lithium iron phosphate positive electrode in Example 2 of the present invention is discharged to 0.8 V to be passivated, and then charged and discharged. 1 shows the charge-discharge curves for the first and twentieth cycles in Comparative Example 2 of the present invention, in which the lithium iron phosphate positive electrode was not discharged to passivate it, but was directly subjected to a normal charge-discharge test. This is the comparative experiment. FIG. 10 is a graph showing the cycle performance of the 600th cycle of the cycle process at 1C when the lithium iron phosphate positive electrode in Example 3 of the present invention is passivated. 10 shows charge-discharge curves for the first and tenth cycles of a cycle process in which a lithium-rich manganese-based positive electrode in Example 4 of the present invention is discharged to 1.5 V to be passivated, and then charged and discharged. 10 shows the charge-discharge curves of the first and tenth cycles when the lithium-rich manganese-based positive electrode in Comparative Example 4 of the present invention is not discharged to passivate it, but is directly subjected to normal charge-discharge, and this is used as a comparative experiment. 10 shows charge-discharge curves for the first and tenth cycles of a cycle process in Example 5 of the present invention, in which a lithium manganese iron phosphate positive electrode is discharged to 1.0 V to passivate it, and then charged and discharged. FIG. 10 shows charge-discharge curves for the first and tenth cycles of a comparative example 5 of the present invention, in which the lithium manganese iron phosphate positive electrode was not discharged for passivation but was directly subjected to normal charge-discharge. This is used as a comparative experiment. 10 shows charge-discharge curves for the first and tenth cycles of a mixed positive electrode of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in Example 8 of the present invention, which was discharged to 1.0 V to passivate the positive electrode, and then charged and discharged. FIG. 10 shows charge-discharge curves for the first and tenth cycles of a comparative example 8 of the present invention, in which a mixed positive electrode of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide was directly subjected to normal charge-discharge without being discharged and passivated. This is used as a comparative experiment. 1 is a schematic diagram of the implementation steps and principles of the present invention; 1 is a comparison of the oxidative decomposition potential (2.1 V (vs. Li ⁺ /Li)) of the sulfide solid electrolyte of the present invention with the charge/discharge interval of a typical oxide positive electrode material. 1 shows X-ray photoelectron spectroscopy (XPS) spectra of the positive electrode when charging is performed after passivating the interface in Example 1 of the present invention, and when normal charging is performed directly (i.e., Comparative Example 1).

For ease of understanding, the technical solutions and embodiments of the present invention will be described more clearly, completely, and in detail through specific examples in conjunction with the drawings. It should be noted that the examples described in the present invention are implemented based on the technical solutions of the present invention, and detailed embodiments and specific operation processes are provided. However, these are only a portion of the examples of the present invention, not all of the examples. The described specific embodiments are limited to illustration and explanation of the present invention only, and do not limit the present invention. All other embodiments that can be obtained by those skilled in the art without creative efforts based on the examples of the present invention are within the scope of protection of the present invention.

Unless otherwise noted, the experimental methods used in the following examples are conventional, and the materials, reagents, etc. used in the examples are commercially available unless otherwise noted.

Example 1 (lithium iron phosphate cathode, passivated by discharging to 1.0 V)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: Lithium iron phosphate ( _LiFePO4 , with a carbon coating on the surface), _{Li5.5PS4.5Cl1.5} (ionic conductor), vapor _- grown carbon fiber (electronic conductor), and ethyl cellulose (binder) were mixed in a mass ratio _of 70:24:3:3 and applied to carbon-coated aluminum foil using absolute ethanol as a solvent to produce a positive electrode with a positive electrode active material loading of 1 to 3 _mg cm ^-2 . A solid-state battery was fabricated by press-molding 100 _mg of _{Li5.5PS4.5Cl1.5} as the solid electrolyte and metallic lithium with a diameter of 10 mm as the negative electrode at 360 MPa.
Step 2: First, the fabricated solid-state battery was discharged to 1.0 V at a current density of 20 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interface was charged to 4.0 V and discharged to 2.5 V, and then subjected to normal charge-discharge cycling at a current density of 17 mA g ⁻¹ (0.1 C). The charge-discharge curves at the 1st and 50th cycles are shown in Figure 1.
As Comparative Example 1, the same battery was fabricated and directly subjected to normal charging and discharging at a 0.1 C rate within the range of 2.5 to 4.0 V. From the discharge curves at the first and 50th cycles shown in Figure 2, it can be seen that the battery was unable to operate normally, with the charge/discharge curve significantly deviating from that of a typical lithium iron phosphate battery, and almost completely failing after 10 cycles. A comparison of the performance of the batteries of Example 1 and Comparative Example in the 50-cycle process is shown in Figure 3.
The positive electrodes of Example 1 (passivated state and charged state after passivation) and Comparative Example 1 were characterized by X-ray photoelectron spectroscopy. As shown in FIG. 15 , both the S2p and P2p spectra showed that the in situ electrochemical passivation method used in Example 1 formed a passivated interface with lithium sulfide (Li ₂ S), effectively reducing the accumulation of oxidation products (elemental sulfur (—S _n —), phosphorus polysulfide (P ₂ S _x )) during the charged state, thereby avoiding interface fading due to the continued decomposition of the Li _5.5 PS _4.5 Cl _1.5 electrolyte.

Example 2 (High Loading Lithium Iron Phosphate Cathode, Passivated by Discharging to 0.8 V)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A composite positive electrode _was prepared by mixing lithium iron phosphate ( _LiFePO4 , _with a carbon coating on the surface), _{Li5.5PS4.5Cl1.5} (ionic conductor), vapor-grown carbon fiber (electronic conductor), and polytetrafluoroethylene (binder) in a mass ratio of 60:34:3:3. This was pressed onto the surface of carbon-coated aluminum foil to achieve a positive electrode active material loading of 5 mg cm ^-2. A solid-state battery was fabricated by press-molding 100 _{mg of Li5.5PS4.5Cl1.5} as the solid electrolyte and metallic lithium with a diameter of 10 mm as the negative electrode at 360 MPa.
Step 2: First, the fabricated solid-state battery was discharged to 0.8 V at a current density of 15 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interface was charged to 3.8 V and discharged to 2.5 V, and then subjected to normal charge-discharge cycling at a current density of 17 mA g ⁻¹ (0.1 C). The charge-discharge curves at the 1st and 60th cycles are shown in Figure 4.
As Comparative Example 2, the same battery was directly charged and discharged in the normal manner at a rate of 0.1 C within the range of 2.5 to 3.8 V. The charge-discharge curves for the first and 20th cycles are shown in Figure 5. The capacity was significantly reduced within 20 cycles.

Example 3 (High-Rate Lithium Iron Phosphate Cathode, Passivated by Discharging to 1.0 V)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: Lithium iron phosphate ( _LiFePO4 , _with a carbon coating layer on the surface), _{Li5.5PS4.5Cl1.5} (ionic conductor), vapor-grown carbon fiber (electronic conductor), and ethyl cellulose (binder) were mixed in a mass ratio _of 70:24:3:3, and applied to carbon-coated aluminum foil using absolute ethanol as a solvent to prepare a positive electrode, with the loading amount referencing Example 1. 100 mg _{of Li5.5PS4.5Cl1.5} was used as the solid electrolyte, and metallic lithium _with a diameter of 10 mm was used as the negative electrode, and the mixture was press-molded at 360 MPa to prepare a solid-state battery.
Step 2: First, the fabricated solid-state battery was discharged to 1.0 V at a current density of 20 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interface was subjected to normal charge-discharge cycling by charging to 4.0 V and discharging to 2.5 V at a current density of 170 mA g ^-1 (1 C). The cycle performance in a 600-cycle process is shown in Figure 6. The capacity was almost unchanged within 600 cycles, indicating that a kinetically very stable interface was formed by the in situ electrochemical passivation.

Example 4 (Lithium-Rich Manganese-Based Positive Electrode, Passivated by Discharging to 1.5 V)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A _lithium -rich manganese-based ( _{Li1.2Mn0.54Ni0.13Co0.13O4} ) cathode coated _{with lithium} niobate ( _LiNbO3 ) was used as the active material, _{and Li5.5PS4.5Cl1.5} (ionic conductor), vapor _- grown carbon fiber (electronic conductor), and ethyl cellulose (binder) were _mixed in a mass ratio of 60:30:7:3. The mixture was applied to carbon-coated aluminum foil using anhydrous ethanol as a solvent to prepare a cathode. The loading amounts were the same as in Example 1. 100 mg _{of Li5.5PS4.5Cl1.5} was used as the solid electrolyte, and a 10 mm diameter metallic lithium _anode was press-molded at 360 MPa to prepare a solid-state battery.
Step 2: First, the fabricated solid-state battery was discharged to 1.5 V at a current density of 25 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interface was charged to 4.8 V and discharged to 2.0 V, and then cycled at a current density of 25 mA g ^-1 (0.1 C). The charge-discharge curves for the first and tenth cycles are shown in Figure 7. After the interface was passivated, the interface tended to stabilize, and after 10 cycles, the capacity showed no obvious decay and could stably deliver a capacity of about 220 mAh g ^-1 .
As Comparative Example 4, the same battery was directly subjected to a charge-discharge test at a 0.1 C rate within the range of 2.0 to 4.8 V without passivation. The charge-discharge curves for the first and tenth cycles are shown in Figure 8. For the lithium-rich manganese-based positive electrode without passivation at the interface, the initial discharge capacity was only 70 mAh g ⁻¹ , and due to severe decomposition of the sulfide electrolyte, the capacity after 10 cycles had decayed to 40 mAh g ⁻¹ .
When a lithium-rich manganese-based solid solution (xLi ₂ MnO ₃ ·(1−x)LiMO ₂ , where M is one or more of Ni, Co, and Mn, and 0<x<1) is used as the positive electrode active material, corresponding passivation and/or repair operations are possible and have considerable effects, but due to space limitations, they will not be described in detail here.

Example 5 (Lithium Iron Manganese Phosphate Positive Electrode, Passivated by Discharging to 1.0 V)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A lithium manganese iron phosphate ( _{LiFe0.5Mn0.5PO4} ) cathode, _{Li5.5PS4.5Cl1.5} , _{vapor -} grown carbon fiber, and ethyl cellulose were mixed in a mass ratio of 50 _: 40:7:3 and applied to _a carbon-coated aluminum foil using absolute ethanol as a solvent to prepare a cathode, with the loading amounts referencing Example 1. 100 _mg of _{Li5.5PS4.5Cl1.5} was used as the solid electrolyte, _and a 10 mm diameter metallic lithium anode was pressed at 360 MPa to form a solid-state battery.
Step 2: First, the fabricated solid-state battery was discharged to 1.0 V at a current density of 15 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interfaces was charged to 4.3 V and discharged to 2.5 V, undergoing normal charge-discharge cycling at a current density of 17 mA g ^-1 (0.1 C). The charge-discharge curves for the first and tenth cycles are shown in Figure 9. After the interface was passivated, the initial discharge capacity was approximately 150 mAh g ^-1 , and the capacity did not obviously decay within 10 cycles.
As Comparative Example 5, the same battery was directly subjected to a charge-discharge test at a 0.1 C rate within the range of 2.5 to 4.3 V without passivation. The charge-discharge curves for the first and tenth cycles are shown in Figure 10. This battery had a charge-discharge capacity of less than 30 mAh g ^-1 and exhibited significant polarization due to severe oxidation and decomposition of the electrolyte, which made the battery difficult to operate.
When lithium manganese iron phosphate (LiFe _x Mn _1-x PO ₄ , 0<x<1) is used as the positive electrode active material, corresponding passivation and/or repair operations are possible and have considerable effects, but will not be described in detail here due to space limitations.

Example 6 (Repair of Nickel Cobalt Lithium Manganese Oxide Ternary Positive Electrode)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A lithium nickel cobalt manganese oxide ( _{LiNi0.8Co0.1Mn0.1O2} ) cathode, _{Li5.5PS4.5Cl1.5} (ionic conductor), vapor _- grown carbon fiber (electronic conductor), and ethyl cellulose (binder) were mixed in _a mass ratio _of 60: ₃₀ :7: ₃ and applied to carbon-coated aluminum foil using absolute ethanol as a solvent to prepare a cathode, with the loading amounts referencing Example 1. 100 mg of _{Li5.5PS4.5Cl1.5} was used as the _solid electrolyte, and a ₁₀ mm diameter metallic lithium anode was pressed at 360 MPa to form a solid-state battery.
Step 2: This solid-state battery is cycled 100 times at a current density of 250 mA g ⁻¹ (1C, calculated based on the amount of lithium nickel cobalt manganese oxide carried) within the range of 2.5 to 4.3 V, and the initial discharge capacity is 122 mAh g ⁻¹ .
Step 3: After 100 cycles of the solid-state battery, the capacity significantly decreased to 52 mAh ^g . It was discharged to 1.8 V at a small current of ^{20 mA} g (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to reduce the oxidation products accumulated at the interface to lithium-rich products with a certain ionic conductivity, thereby completing the restoration of the ternary positive electrode.
Step 4: After 1C high-rate cycling, the capacity returned to a high level of 98 mAh g ^-1 after restoration. After that, normal charge-discharge cycling could be performed. After 300 more cycles, the capacity was higher than 80 mAh g ^-1 . Thus, the battery performance was effectively restored and more stable than the previous performance.
When lithium nickel cobalt manganese oxide (LiNi _x Co _y Mn _1-x-y O ₂ , 0<x<1, 0<y<1, 0<1-x-y<1) is used as the positive electrode active material, corresponding passivation and/or repair operations are possible and have considerable effects, but due to space limitations, they will not be described in detail here.

Example 7 (Repairing a High-Voltage Lithium Cobalt Oxide Positive Electrode)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A lithium cobalt oxide ( _LiCoO2 ) cathode, _{Li5.5PS4.5Cl1.5} (ionic conductor), vapor-grown carbon fiber (electronic conductor), and ethyl cellulose (binder) _were mixed in a mass ratio of 60: ₃₀ :7:3 and applied to a carbon-coated aluminum foil using absolute ethanol as a solvent to prepare a cathode, with the loading amount referencing Example 1. 100 mg _{of Li5.5PS4.5Cl1.5} was used as the solid electrolyte, and a 10 mm diameter metallic lithium _anode was pressed at 360 MPa to form a solid-state battery.
Step 2: This solid-state battery is cycled 100 times at a current density of 270 mA g ⁻¹ (1C, calculated based on the amount of lithium cobalt oxide carried) within the range of 2.5 to 4.7 V, and the initial discharge capacity is 85 mAh g ⁻¹ .
Step 3: After 100 cycles of the solid-state battery, the capacity significantly decreased to 30 mAh ^g . The battery was discharged to 1.8 V at a small current of ^{20 mA} g (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to reduce the oxidation products accumulated at the interface to lithium-rich products with a certain ionic conductivity, thereby completing the restoration of the high-voltage lithium cobalt oxide positive electrode.
Step 4: After 1C high-rate cycling, the capacity returned to a high level of 78 mAh g ^-1 . After that, normal charge-discharge cycling could be performed. After 300 cycles, the capacity was higher than 60 mAh g ^-1 . Thus, the battery performance was effectively restored and more stable than the previous performance.

Example 8 (Lithium Iron Manganese Phosphate and Ternary Positive Electrode Blend, Passivated by Discharge to 1.0 V)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1 _: A ternary cathode consisting of lithium manganese iron phosphate ( _{LiFe0.5Mn0.5PO4} ) _and lithium nickel cobalt manganese oxide ( _{LiNi0.8Co0.1Mn0.1O2} ) was mixed in a 1: ₁ mass ratio to _form a cathode. A composite cathode _consisting of _{Li5.5PS4.5Cl1.5} , vapor- _grown carbon fiber, and polytetrafluoroethylene was mixed in a 50:40:7:3 mass ratio to form a cathode. This composite cathode was pressed onto the surface of a carbon _- coated aluminum foil current collector to achieve a positive electrode active material loading of 5 mg cm ^-2 _. 100 _mg of _{Li5.5PS4.5Cl1.5} was used as the solid electrolyte. A 10 mm diameter lithium metal anode was pressed at 360 MPa to form a solid-state battery.
Step 2: First, the fabricated solid-state battery was discharged to 1.0 V at a current density of 15 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interfaces was charged to 4.3 V and discharged to 2.5 V, undergoing normal charge-discharge cycling with a current density of 18.5 mA g ^-1 (0.1 C). The charge-discharge curves for the first and tenth cycles are shown in Figure 11. After the interface was passivated, the initial discharge capacity was approximately 110 mAh g ^-1 , and the capacity did not obviously decay within 10 cycles.
As Comparative Example 8, the same battery was directly subjected to a charge-discharge test at a 0.1C rate within the range of 2.5 to 4.3V. The charge-discharge curves for the first and tenth cycles are shown in Figure 12. The charge-discharge capacities were all low, with the initial specific discharge capacity being 62 mAh g ^-1 and the specific discharge capacity after 10 cycles being 38 mAh g ^-1 , indicating significant polarization. The carbon layer on the surface of the lithium manganese iron phosphate caused intense oxidative decomposition of the electrolyte, making it difficult for the lithium manganese iron phosphate to exert its capacity. The low capacity exerted was solely due to the nickel-cobalt-lithium manganese oxide ternary positive electrode (because there was no carbon coating layer on the surface of the nickel-cobalt-lithium manganese oxide).
When a blend of lithium manganese iron phosphate (LiFe _x Mn _1-x PO ₄ , 0<x<1) and lithium nickel cobalt manganese oxide (LiNi _x Co _y Mn _1-x-y O ₂ , 0<x<1, 0<y<1, 0<1-x-y<1) (including blends in other mass ratios) is used as the positive electrode active material, corresponding passivation and/or repair operations are possible and have considerable effects, but due to space limitations, they will not be described in detail here.

Example 9 (Lithium iron phosphate cathode, passivated in constant current-constant voltage discharge mode)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A composite positive electrode was prepared by mixing lithium iron phosphate ( _LiFePO4 , with _{a carbon} coating on the surface), _Li10GeP2S12 (ionic conductor), vapor-grown carbon fiber (electronic conductor), and polytetrafluoroethylene (binder) in a mass ratio of 60:34:3:3. This composite positive electrode was pressed onto the surface of a carbon-coated aluminum foil current collector so that the positive electrode active material loading was 5 mg cm ^-2 . A solid-state battery was fabricated by press-molding 100 _{mg of Li10GeP2S12} as the solid electrolyte and a 10 mm diameter lithium-indium alloy as the negative electrode at 360 MPa.
Step 2: First, the fabricated solid-state battery was discharged to 1.5 V (vs. lithium potential) at a current density of 10 mA g ⁻¹ (calculated based on the amount of ionic conductive agent supported in the composite positive electrode), and then discharged at a constant voltage of 1.5 V to passivate the interface under a cutoff condition of a current of less than 2 mA g ⁻¹ (calculated based on the amount of ionic conductive agent supported in the composite positive electrode).
Step 3: The solid-state battery with passivated interfaces was subjected to normal charge-discharge cycling by charging to 4.0 V (vs. lithium potential) and discharging to 2.5 V (vs. lithium potential) at a current density of 17 mA g ^-1 (0.1 C). The interface passivation procedure described in Step 2 was also performed after each of the first five charge-discharge cycles. After discharge passivation was completed, the initial discharge capacity was 154 mAh g ^-1 , and the capacity after 50 cycles was 133 mAh g ^-1 .
In Comparative Example 9, the same battery was directly charged and discharged according to the normal procedure without passivation, and the initial discharge capacity was 50 mAh g ⁻¹ , and the capacity after 50 cycles was less than 10 mAh g ⁻¹ .

Example 10 (Lithium-rich manganese-based positive electrode, passivated by discharging at 130 mAh ^g in constant capacity mode)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: _A composite positive electrode was prepared by mixing a _lithium - _rich manganese ( _{Li1.2Mn0.54Ni0.13Co0.13O4} ) cathode active material coated _{with lithium niobate} ( _LiNbO3 ), _Li7P3S11 (ionic conductor), vapor-grown carbon fiber (electronic conductor), and polytetrafluoroethylene (binder) in a mass ratio of 60:34:3:3. This composite positive electrode was pressed onto the surface of an aluminum foil current collector to achieve a positive electrode active material loading of 5 mg _cm ^-2. _A solid-state battery was fabricated by press-molding 100 mg of _Li7P3S11 as the solid electrolyte and a 10 mm diameter lithium sheet as the negative electrode at 360 MPa.
Step 2: First, the fabricated solid-state battery was discharged at a current density of 10 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) for 13 hours, i.e., discharged to a rated capacity of 130 mAh g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interface was charged to 4.8 V and discharged to 2.0 V, and then cycled at a current density of 25 mA ^g (0.1 C). The initial discharge capacity was 194 mAh ^g , and the capacity after 50 cycles was 160 mAh ^g .
As a comparative example, the same battery was directly charged and discharged according to the normal procedure without passivation. The sulfide electrolyte was severely decomposed in the high operating voltage range, and the battery could not operate normally.

Example 11 (High-Voltage Lithium Nickel Manganese Oxide Positive Electrode, Passivated in Constant Current-Constant Voltage Discharge Mode)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A composite positive electrode was prepared _by mixing lithium nickel manganese oxide ( _{LiNi0.5Mn1.5O4} ) positive _electrode , _Li3PS4 (ionic conductor), vapor-grown carbon fiber (electronic conductor), and polytetrafluoroethylene (binder) in _a mass ratio of 60:34:3: ₃ . This composite positive electrode was pressed onto the surface of an aluminum foil current collector so that the positive electrode active material loading was 5 mg cm ^-2 . A solid-state battery was produced by press-molding 100 mg of _Li3PS4 as the solid electrolyte and a 10 mm diameter lithium sheet as the negative electrode at 360 MPa.
Step 2: First, the fabricated solid-state battery was discharged to 1.3 V at a current density of 10 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode), and then discharged at a constant voltage of 1.3 V to passivate the interface under a cutoff condition of a current of less than 2 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode).
Step 3: The solid-state battery with passivated interface was charged to 5.2 V and discharged to 3.0 V, and then cycled at a current density of 14.6 mA ^g (0.1 C). The initial discharge capacity was 113 mAh ^g , and the capacity after 50 cycles was 90 mAh ^g .
As a comparative example, the same battery was directly charged and discharged according to the normal procedure without passivation. The sulfide electrolyte was severely decomposed in the high operating voltage range, and the battery could not operate normally.

Example 12 (High-Voltage Lithium Nickel Manganese Oxide Positive Electrode, Passivated by Discharging at 130 mAh ^g in Constant Capacity Mode)
An in-situ electrochemical passivation and repair method for solid-state lithium batteries, the steps of which are as follows:
Step 1: A lithium nickel manganese oxide positive electrode ( _{LiNi0.5Mn1.5O4} ), _Li7P3S11 ( _ionic conductor ₎ , vapor-grown _carbon fiber (electronic conductor), and polytetrafluoroethylene (binder) were mixed in a mass ratio _of 60:34:3:3 to form a composite positive electrode. This was pressed onto the surface of an aluminum foil current collector so that the positive electrode active material loading was 5 mg cm ^-2 . 100 _mg of _Li7P3S11 was used as the solid electrolyte, and a 10 _mm diameter lithium sheet was used as the negative electrode. This was then press-molded at 360 MPa to produce a solid-state battery.
Step 2: First, the fabricated solid-state battery was discharged at a current density of 10 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) for 13 hours, i.e., discharged to a rated capacity of 130 mA h g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interface was charged to 5.2 V and discharged to 3.0 V, undergoing a conventional charge-discharge cycle with a current density of 14.6 mA g ^-1 (0.1 C). The initial discharge capacity was 105 mAh g ^-1 , and the capacity after 50 cycles was 84 mAh g ^-1 . As a comparative example, the same battery was directly charged and discharged according to the conventional procedure. The sulfide electrolyte was severely decomposed due to the high operating voltage range, and the battery could not operate normally.

Example 13 (Lithium Iron Phosphate Positive Electrode, Combined Interface Passivation and Repair Strategy)
Step 1: Lithium iron phosphate ( _LiFePO4 , with a carbon coating on the surface), _{Li5.5PS4.5Cl1.5} (ionic conductor), vapor _- grown carbon fiber (electronic conductor), and polytetrafluoroethylene (binder) were mixed in a mass ratio _of 60:34:3:3 and pressed onto carbon-coated aluminum foil to a loading of 5 _mg cm ^-2 to produce a positive electrode. 100 mg of _{Li5.5PS4.5Cl1.5} was used as the solid electrolyte, and a ₁₀ mm diameter metallic lithium was used as the negative electrode. These were then press-molded at 360 MPa to produce a solid-state battery.
Step 2: First, the fabricated solid-state battery was discharged to 1.0 V at a current density of 20 mA g ⁻¹ (calculated based on the mass of the ionic conductive agent in the composite positive electrode) to passivate the interface.
Step 3: The solid-state battery with passivated interfaces was charged to 4.0 V and discharged to 2.5 V, undergoing normal charge-discharge cycling at a current density of 170 mA ^g (1 C). The initial discharge capacity was 105 mAh ^g , and within 200 cycles, the capacity was 94 mAh ^g with no obvious decay. After 1000 cycles, the capacity decayed to 53 mAh ^g due to the long-term cycling process, which destroyed the passivation layer, decomposed the electrolyte, and generated oxidation products that re-accumulated at the interfaces.
Step 4: Discharge to 1.5 V at a small current of 20 mA g ⁻¹ to reduce the oxidation products accumulated at the interface to lithium-rich products with the desired ionic conductivity, thus completing the restoration of the lithium iron phosphate positive electrode (after passivation).
Step 5: After 1C high-rate cycling, the capacity returned to a high level of 85 mAh ^g . After that, normal charging and discharging was possible. Even after 500 cycles, the discharge specific capacity remained at >77 mAh ^g .
To further compare the advantages of the technical solution of the present invention, the performance of the batteries manufactured in each example and comparative example are compared as follows (Table 1).

As is clear from the comparison results, the technical solution of the present invention exhibits significantly better performance than the comparative example in terms of discharge specific capacity and cycle stability, and by implementing the technical solution of the present invention, the unstable interface between the sulfide electrolyte and the oxide can be effectively passivated or repaired. This allows the sulfide electrolyte to be well compatible with more high-voltage oxide positive electrode materials, and the passivated/repaired interface exhibits excellent dynamic stability even during long-term cycling processes.

The above is merely a preferred embodiment of the present invention, and those skilled in the art may make some improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims (7)

1. A method for in situ electrochemical passivation and repair of solid-state lithium batteries, comprising:
Discharging the sulfide-based solid-state battery to a specific degree of lithiation at a low current density and in a specific discharge mode to achieve in situ electrochemical passivation and/or repair of the battery;
Discharging to a specific degree of lithiation in the discharge mode
the specific potential is 0.5 to 2.2 V (vs. Li + /Li), the specific current is 0.1 to 20 mA g ⁻¹ , the current is converted into the mass of the ionic conductive agent in the battery positive electrode, and the specific ^specific capacity is 15 to 500 mAh g ⁻¹ , the specific capacity is converted into the mass of the ionic conductive agent in the battery positive electrode ^;
The sulfide-based solid state battery is a sulfide-based solid state battery assembled with a sulfide solid electrolyte as an electrolyte and an ion conductive agent in a positive electrode, and a layered oxide or a polyanion oxide as a positive electrode active material. 2. The in-situ electrochemical passivation and repair method for solid-state lithium batteries according to claim 1, wherein the sulfide solid electrolyte is at least one of an argyrodite-type electrolyte, a lithium ion conductor, a glass-ceramic phase solid electrolyte, and other electrolytes prepared by doping anions and cations or by compounding with a polymer based on the above-mentioned electrolytes. The method for in-situ electrochemical passivation and repair of solid-state lithium batteries described in claim 1, characterized in that the layered oxide or polyanion oxide positive electrode comprises a combination of one or more positive electrode materials selected from the group consisting of lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese-based solid solutions, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and positive electrode materials obtained by surface coating and/or doping modification of the above materials. The charge-discharge procedure for passivating solid-state lithium batteries is as follows:
(1.1) Passivating the cathode interface of a sulfide-based solid state battery, i.e., discharging it to a specific degree of lithiation at a low current density and in a specific discharge mode;
(1.2) subjecting the sulfide-based solid-state battery to a normal charge-discharge cycle. The in-situ electrochemical passivation and repair method for solid-state lithium batteries described in claim 4, characterized in that in step (1.1), the passivation is performed 1 to 10 times. The charging and discharging procedure to repair a solid-state lithium battery is as follows:
(2.1) The in-situ electrochemical passivation and repair method for a solid-state lithium battery according to claim 1, characterized in that it comprises the step of repairing the sulfide-based solid-state battery, i.e., discharging it to a specific degree of lithiation at a low current density and in a specific discharge mode, and then re-cycling the battery through a normal charge-discharge cycle. The method for in-situ electrochemical passivation and repair of a solid-state lithium battery according to claim 6, wherein the sulfide-based solid-state battery is a battery that has been cycled until its capacity decays to 1% to 70% of its rated discharge capacity.