All-solid-state thin-film lithium battery and preparation method thereof

Abstract

The present invention provides an all-solid-state thin-film lithium battery and a preparation method thereof, relating to the field of lithium battery technology. The all-solid-state thin-film lithium battery comprises the following components by weight: 100-120 parts of a lithium metal negative electrode material, 150-250 parts of an oxide solid electrolyte, 100-200 parts of a layered oxide positive electrode material, 10-50 parts of cobalt disulfide, 5-30 parts of a polyionic liquid auxiliary layer material, and 5-20 parts of a PET-PEG block copolymer. The present invention uses lithium metal as the negative electrode material to effectively increase the overall energy density of the battery; introduces an oxide solid electrolyte, and by selecting yttrium-stabilized zirconium oxide, enhances the ionic conductivity and thermal stability of the electrolyte, ensuring reliable operation in high-temperature environments. Layered oxide positive electrodes, such as lithium cobalt oxide, excel in structural stability and discharge platform, and can maintain a high specific capacity and improve cycle life.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to an all-solid-state thin-film lithium battery and a preparation method thereof. Background Art

[0002] The field of lithium battery technology covers a type of electrochemical energy storage system based on lithium as the main energy carrier. Its core lies in the advantages of high energy density, long life and lightweight. It is widely used in consumer electronics, electric vehicles, energy storage systems, aerospace and other fields.

[0003] Existing technologies still have limitations in terms of interface treatment and electrolyte performance control. The use of liquid electrolytes in lithium batteries can easily lead to safety hazards such as electrolyte leakage, high-temperature volatilization, and thermal runaway. In addition, the problem of lithium dendrite penetration in the liquid system can easily cause battery short circuits, affecting the stability of use. At the same time, traditional solid-state electrolyte systems have insufficient interface contact and poor wettability, resulting in low ion migration efficiency at the solid-solid interface, which limits the performance of the battery in high-rate and wide-temperature working environments. Therefore, improvements are needed. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose an all-solid-state thin-film lithium battery and a preparation method thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: an all-solid-state thin-film lithium battery, the all-solid-state thin-film lithium battery comprising the following components in parts by weight:

[0006] 100-120 parts of lithium metal negative electrode material, 150-250 parts of oxide solid electrolyte, 100-200 parts of layered oxide positive electrode material, 10-50 parts of cobalt disulfide, 5-30 parts of polyionic liquid auxiliary layer material, and 5-20 parts of PET-PEG block copolymer.

[0007] Preferably, the oxide solid electrolyte is yttrium-stabilized zirconia.

[0008] Preferably, the layered oxide positive electrode material is lithium cobalt oxide.

[0009] Preferably, the polyionic liquid auxiliary layer material is a mixture of 50-60% 1-ethyl-3-methylimidazolium hexafluorophosphate, 25-30% 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 25-30% bis(fluorosulfonyl)imide by weight.

[0010] The present invention also provides a method for preparing an all-solid-state thin-film lithium battery, comprising the following steps:

[0011] S1, assembling the lithium negative electrode and fixing it on the substrate: inside an inert gas protection glove box, cut the lithium metal negative electrode material into a specified size; take a clean and dry polymer support substrate; use a mechanical rolling device, set the rolling pressure to 10-50 MPa, and the rolling speed to 0.1-1.0 m / min, and at room temperature of 20-30 degrees Celsius, uniformly press the lithium metal negative electrode material onto one or both sides of the polymer support substrate to obtain a polymer substrate-fixed lithium metal negative electrode;

[0012] S2, low-temperature plasma surface activation treatment, transferring the polymer substrate-fixed lithium metal negative electrode from the glove box to a vacuum chamber of a low-temperature plasma treatment equipment; closing the chamber and evacuating the chamber to a basic vacuum of 0.001 to 0.00001 Pascal; then introducing a mixed gas of argon and nitrogen as a working gas, with the argon flow rate controlled at 50-200 sccm and the nitrogen flow rate controlled at 10-50 sccm; setting the plasma glow discharge power to 50-300 watts and the working gas pressure to 10-100 Pascal through a radio frequency power supply; performing plasma bombardment treatment on the lithium metal surface for 30-300 seconds to obtain a surface-activated polymer substrate lithium metal negative electrode;

[0013] S3, coating and thermally curing the polyionic liquid auxiliary layer, coating the surface-activated polymer-based lithium metal negative electrode with a polyionic liquid auxiliary layer material to obtain a lithium metal negative electrode coated with a polyionic liquid auxiliary layer;

[0014] S4, PA-ALD atomic layer deposition to construct an ultra-thin electrolyte layer, constructing an oxide solid electrolyte layer on the surface of the lithium metal negative electrode coated with the polyionic liquid auxiliary layer, to obtain a lithium metal negative electrode assembly deposited with a YSZ solid electrolyte ultra-thin film;

[0015] S5, auxiliary layer composite treatment, for the lithium metal negative electrode assembly deposited with the YSZ solid electrolyte ultra-thin film, preparing a composite auxiliary layer on the surface of the YSZ electrolyte layer to obtain a lithium metal negative electrode assembly modified with the composite auxiliary layer;

[0016] S6, deposition and lamination of positive electrode materials, using the lithium metal negative electrode assembly modified with the composite auxiliary layer as a substrate, depositing positive electrode materials on the outermost layer to obtain a preliminary structure of a multi-layered overall battery cell comprising a positive electrode, an electrolyte, and a negative electrode;

[0017] S7, packaging processing and performance stabilization, packaging the preliminary structure of the multi-layer structure integral battery cell including the positive electrode, electrolyte and negative electrode to obtain a packaged new type of all-solid-state thin-film lithium battery.

[0018] Preferably, the S4 step is specifically as follows: on the surface of the lithium metal negative electrode coated with the polyionic liquid auxiliary layer, using plasma enhanced atomic layer deposition to construct an oxide solid electrolyte layer; selecting yttrium stabilized zirconia as the solid electrolyte material; loading the sample into the PA-ALD reaction chamber, and setting the deposition temperature to 80-200 degrees Celsius; each ALD cycle includes a precursor pulse of 0.1-2 seconds, an inert gas purge of 5-30 seconds, a plasma activation gas pulse of 0.5-5 seconds, and another inert gas purge of 5-30 seconds; controlling the number of ALD cycles to 50-500 cycles to obtain a lithium metal negative electrode assembly deposited with a YSZ solid electrolyte ultra-thin film;

[0019] The S5 step is specifically as follows: for the lithium metal negative electrode assembly deposited with the YSZ solid electrolyte ultra-thin film, a composite auxiliary layer is prepared on the surface of the YSZ electrolyte layer; the PET-PEG block copolymer is dissolved in tetrahydrofuran to form a solution with a concentration of 5-15 weight percent; the polyionic liquid auxiliary layer material is added to the solution, and mechanically stirred for 1-2 hours to form a composite coating slurry; the composite coating slurry is evenly coated on the surface of the YSZ electrolyte layer by a doctor blade method, and the wet film thickness is controlled to be 10-50 microns; thereafter, the composite auxiliary layer is dried in a vacuum oven at 60-100 degrees Celsius for 2-4 hours to solidify the coating to obtain a lithium metal negative electrode assembly modified with a composite auxiliary layer.

[0020] Preferably, the S6 step is specifically as follows: using the composite auxiliary layer modified lithium metal negative electrode assembly as a substrate, depositing a positive electrode material on the outermost layer; using multi-target physical vapor deposition, using a layered oxide positive electrode material, setting the sputtering power to 200-1000 watts, the working pressure to 0.1-1.0 Pascal, and controlling the substrate temperature at room temperature to 200 degrees Celsius; then using cobalt disulfide as a conductive enhancer for the positive electrode, setting the sputtering power to 100-500 watts; after the deposition is completed, a preliminary structure of a multilayer structure integral battery cell comprising a positive electrode, an electrolyte, and a negative electrode is obtained;

[0021] The S7 step is specifically as follows: encapsulating the preliminary structure of the multi-layer structure battery cell comprising the positive electrode, electrolyte and negative electrode; placing the preliminary structure of the battery cell between aluminum-plastic film sheets, and heat-sealing the edges using a hot pressing packaging machine at a temperature of 150-200 degrees Celsius and a pressure of 0.5-1.5 MPa for 2-5 seconds; extracting the internal residual gas during the packaging process to form a vacuum internal environment; after the packaging is completed, placing the battery in a vacuum annealing furnace, keeping it warm in the temperature range of 80-150 degrees Celsius for 1-12 hours, and controlling the heating and cooling rate at 1 to 5 degrees Celsius per minute to obtain a packaged new all-solid-state thin-film lithium battery.

[0022] Preferably, the S3 step is specifically as follows: coating the surface-activated polymer-based lithium metal negative electrode with a polyionic liquid auxiliary layer material in an inert atmosphere glove box; using a spin coating method for coating, the spin coating speed is set at 500-3000RPM, the spin coating time is 30-120 seconds, and a uniform wet film with a thickness of 0.5-5 microns is obtained; after coating is completed, the sample is placed on a heating platform and subjected to heat treatment and curing at a temperature of 60-120 degrees Celsius for 1-3 hours to obtain a lithium metal negative electrode coated with a polyionic liquid auxiliary layer.

[0023] 1. Compared to existing technologies, the present invention utilizes lithium metal as the negative electrode material, effectively increasing the overall energy density of the battery. The introduction of an oxide solid electrolyte and the selection of yttrium-stabilized zirconia enhance the electrolyte's ionic conductivity and thermal stability, ensuring reliable operation in high-temperature environments. Layered oxide positive electrodes, such as lithium cobalt oxide, exhibit excellent structural stability and discharge platform, maintaining high specific capacity and improving cycle life. A polyionic liquid auxiliary layer, formed by mixing 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bistrifluoromethanesulfonyl imide, and bisfluorosulfonyl imide, improves wettability and adhesion at the electrode-electrolyte interface, preventing interfacial delamination and side reactions. Block copolymers, such as PET-PEG, enhance structural adaptability and interfacial stability through their flexibility and polarity. The synergistic effect of various functional materials within the overall structure creates an all-solid-state system with low impedance, high interfacial stability, and high energy density. This enhances the continuity of ion migration channels and interfacial compatibility, resulting in higher battery safety, longer cycle life, and adaptability to smaller applications.

[0024] 2. Compared to existing technologies, the present invention utilizes cut lithium metal and combines it with a polymer support substrate under controlled mechanical rolling conditions at a constant pressure, achieving uniform electrode morphology and stable mechanical coupling. The lithium surface structure is activated through the discharge of a mixed gas plasma under high vacuum, enhancing interfacial reaction activity without destroying the bulk structure and providing a high surface energy state for subsequent coating. A spin coating process is used in an inert environment to achieve uniform adhesion of the polyionic liquid coating, control the film thickness, and solidify it to form a tightly adhered structure, effectively suppressing lithium surface unevenness and the generation of side reactions. A stable and dense YSZ oxide electrolyte layer is constructed using a low-temperature plasma-enhanced atomic layer deposition process. Combined with multiple deposition cycles to control the film thickness, the ion channel thickness can be adjusted to improve conduction efficiency. A composite auxiliary layer is prepared on the electrolyte surface, using a coordinated design of copolymer and liquid components to enhance interfacial flexibility and wettability, effectively mitigating cyclic stress and the risk of interfacial delamination. Multi-target physical vapor deposition is used to construct the positive electrode layer, and multi-material deposition is achieved by regulating power and operating pressure, enhancing conductivity and structural stability. High-temperature hot pressing packaging combined with vacuum annealing process enables the internal interface to reach a low-stress, densified state, improving sealing reliability and electrochemical cycle consistency.

[0025] 3. Compared to existing technologies, the present invention first coats the lithium anode with a polyionic liquid auxiliary layer as a protective layer, and then directly deposits the YSZ solid electrolyte layer via PA-ALD. This "protect first, deposit later" strategy has significant advantages: First, the polyionic liquid protective layer effectively isolates and protects the highly active lithium metal, preventing it from being directly exposed, subject to side reactions, or damaged in the high vacuum or plasma environment of the subsequent YSZ deposition. This inhibits the formation of interfacial impurities and improves the lithium surface state, providing an ideal substrate for the uniform and dense growth of the subsequent YSZ electrolyte layer. Second, directly depositing YSZ on the surface of this optimized protective layer not only ensures the high quality of the YSZ electrolyte film itself (e.g., dense, pinhole-free, and controllable thickness), but also promotes the formation of a solid-solid interface between the protective layer and the YSZ electrolyte layer that exhibits stable physicochemical properties, smooth ion transport, and low impedance. This design enhances the compatibility and structural stability of the overall interface between the lithium anode and solid electrolyte, playing a key role in inhibiting lithium dendrite growth, reducing interfacial resistance, and improving the battery's cycle life and safety.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 The present invention provides a preparation step diagram of a method for preparing an all-solid-state thin-film lithium battery. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] Example 1, an all-solid-state thin-film lithium battery, the all-solid-state thin-film lithium battery comprises the following components by weight: 120 parts of lithium metal negative electrode material, 250 parts of oxide solid electrolyte, 200 parts of layered oxide positive electrode material, 10 parts of cobalt disulfide, 30 parts of polyionic liquid auxiliary layer material, and 20 parts of PET-PEG block copolymer.

[0031] In this embodiment, the oxide solid electrolyte is yttrium-stabilized zirconia.

[0032] In this embodiment, the layered oxide positive electrode material is lithium cobalt oxide.

[0033] In this embodiment, the polyionic liquid auxiliary layer material is a mixture of 50% 1-ethyl-3-methylimidazolium hexafluorophosphate, 25% 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 25% bis(fluorosulfonyl)imide in a weight ratio.

[0034] This embodiment provides a method for preparing an all-solid-state thin-film lithium battery, comprising the following steps:

[0035] S1, lithium negative electrode assembly and substrate fixation: inside an inert gas protection glove box, cut the lithium metal negative electrode material into a specified size; take a clean and dry polymer support substrate; use a mechanical rolling device, set the rolling pressure to 50 MPa and the rolling speed to 0.1 m / min, and at room temperature of 30 degrees Celsius, uniformly press the lithium metal negative electrode material onto one or both sides of the polymer support substrate to obtain a polymer substrate-fixed lithium metal negative electrode;

[0036] S2, low-temperature plasma surface activation treatment, transferring the polymer-based lithium metal anode from the glove box to the vacuum chamber of the low-temperature plasma treatment equipment; closing the chamber and evacuating the chamber to a basic vacuum of 0.00001 Pascal; then introducing a mixed gas of argon and nitrogen as the working gas, with the argon flow rate controlled at 200 sccm and the nitrogen flow rate controlled at 50 sccm; setting the plasma glow discharge power to 50 watts through a radio frequency power supply, and maintaining the working gas pressure at 100 Pascal; performing plasma bombardment treatment on the lithium metal surface for 30 seconds to obtain a surface-activated polymer-based lithium metal anode;

[0037] S3, coating and thermal curing of a polyionic liquid auxiliary layer, coating the surface-activated polymer-based lithium metal negative electrode with a polyionic liquid auxiliary layer material to obtain a lithium metal negative electrode coated with a polyionic liquid auxiliary layer;

[0038] S4, PA-ALD atomic layer deposition to construct an ultra-thin electrolyte layer, and to construct an oxide solid electrolyte layer on the surface of the lithium metal anode coated with a polyionic liquid auxiliary layer, thereby obtaining a lithium metal anode assembly deposited with an ultra-thin YSZ solid electrolyte film;

[0039] S5, auxiliary layer composite treatment, for the lithium metal negative electrode assembly deposited with the YSZ solid electrolyte ultra-thin film, preparing a composite auxiliary layer on the surface of the YSZ electrolyte layer to obtain a lithium metal negative electrode assembly modified with the composite auxiliary layer;

[0040] S6, deposition and lamination of cathode materials, using the composite auxiliary layer-modified lithium metal anode assembly as a substrate, depositing cathode materials on the outermost layer to obtain a preliminary structure of a multilayered battery cell comprising a cathode, electrolyte, and anode;

[0041] S7, packaging processing and performance stabilization, encapsulates the preliminary structure of the multi-layer structure of the overall battery cell including the positive electrode, electrolyte and negative electrode to obtain a new type of encapsulated all-solid-state thin-film lithium battery.

[0042] In this embodiment, step S4 is specifically as follows: on the surface of the lithium metal negative electrode coated with the polyionic liquid auxiliary layer, an oxide solid electrolyte layer is constructed by plasma enhanced atomic layer deposition; yttrium stabilized zirconia is selected as the solid electrolyte material; the sample is loaded into the PA-ALD reaction chamber, and the deposition temperature is set to 200 degrees Celsius; each ALD cycle includes a precursor pulse of 2 seconds, an inert gas purge of 30 seconds, a plasma activation gas pulse of 0.5 seconds, and an inert gas purge of 30 seconds again; the number of ALD cycles is controlled to 50 cycles to obtain a lithium metal negative electrode assembly deposited with a YSZ solid electrolyte ultra-thin film;

[0043] The S5 step is specifically as follows: for a lithium metal negative electrode assembly deposited with a YSZ solid electrolyte ultra-thin film, a composite auxiliary layer is prepared on the surface of the YSZ electrolyte layer; a PET-PEG block copolymer is dissolved in tetrahydrofuran to form a solution with a concentration of 15 weight percent; a polyionic liquid auxiliary layer material is added to the solution, and a composite coating slurry is formed by mechanical stirring for 2 hours; the composite coating slurry is evenly coated on the surface of the YSZ electrolyte layer by a doctor blade method, and the wet film thickness is controlled to be 50 microns; thereafter, the composite coating slurry is dried in a vacuum oven at 100 degrees Celsius for 2 hours to solidify the coating to obtain a lithium metal negative electrode assembly modified with a composite auxiliary layer.

[0044] In this embodiment, step S6 is specifically as follows: using the lithium metal negative electrode assembly modified with the composite auxiliary layer as the substrate, depositing the positive electrode material on the outermost layer; using multi-target physical vapor deposition, using a layered oxide positive electrode material, setting the sputtering power to 1000 watts, the working pressure to 1.0 Pascal, and controlling the substrate temperature between room temperature and 200 degrees Celsius; then using cobalt disulfide as a conductive enhancer for the positive electrode, setting the sputtering power to 500 watts; after the deposition is completed, a preliminary structure of a multilayer structure integral battery cell including a positive electrode, an electrolyte, and a negative electrode is obtained;

[0045] The specific steps of step S7 are as follows: encapsulating the preliminary structure of the multi-layer structure battery cell including the positive electrode, electrolyte and negative electrode; placing the preliminary structure of the battery cell between the aluminum-plastic film cut sheets, and heat-sealing the edges by a hot pressing packaging machine at a temperature of 150 degrees Celsius and a pressure of 1.5 MPa for 5 seconds; extracting the internal residual gas during the packaging process to form a vacuum internal environment; after the packaging is completed, placing the battery in a vacuum annealing furnace, keeping it warm within a temperature range of 150 degrees Celsius for 12 hours, and controlling the heating and cooling rate at 1 degree Celsius per minute to obtain a new type of all-solid-state thin-film lithium battery that has been packaged.

[0046] In this embodiment, step S3 is specifically as follows: coating the surface-activated polymer-based lithium metal negative electrode with a polyionic liquid auxiliary layer material in an inert atmosphere glove box; using a spin coating method for coating, the spin coating speed is set at 3000RPM, the spin coating time is 30 seconds, and a uniform wet film with a thickness of 5 microns is obtained; after the coating is completed, the sample is placed on a heating platform and subjected to a heat treatment and curing at a temperature of 120 degrees Celsius for 3 hours to obtain a lithium metal negative electrode coated with a polyionic liquid auxiliary layer.

[0047] Example 2 is otherwise the same as Example 1, except that the all-solid-state thin-film lithium battery comprises the following components by weight: 110 parts of lithium metal negative electrode material, 180 parts of oxide solid electrolyte, 150 parts of layered oxide positive electrode material, 33 parts of cobalt disulfide, 10 parts of polyionic liquid auxiliary layer material, and 10 parts of PET-PEG block copolymer.

[0048] Experimental methods:

[0049] 1. First discharge specific capacity and average coulombic efficiency test method

[0050] Experimental Equipment Preparation: Place the all-solid-state thin-film lithium battery to be tested (comparative example or example) in the test fixture of a high-precision battery testing system (such as the LAND series, Neware, or Arbin test system). Ensure good contact between the electrodes and the fixture to reduce contact resistance. The test environment is set at a constant temperature of 25°C (±1°C) in a temperature-controlled chamber or laboratory.

[0051] Initial Activation and Charging Process: The first cycle typically includes an activation process. First, charge the battery at a constant current of 0.1C (C represents the current required for a full charge or discharge in one hour, calculated based on the theoretical or design capacity) to the set upper cutoff voltage (for example, 4.2V or 4.35V for common cathode materials). After reaching the cutoff voltage, switch to constant voltage charging mode until the charge current drops to 0.02C or less to ensure the battery is fully charged. Record the total charge capacity during this process.

[0052] First discharge process: After charging is completed, let the battery stand for 30 minutes to allow the electrochemical system to reach equilibrium. Then, discharge at a constant current of 0.1C until the set lower cut-off voltage (for example, 3.0V or 2.8V) is reached. Completely record the voltage, current, and time data during the discharge process. The calculation method for the first discharge specific capacity is: the total amount of electricity released during the first constant current discharge (obtained by integrating the current over time) is divided by the active area of ​​the battery's negative electrode, and the unit is usually mAh / cm 2 .

[0053] Average Coulombic Efficiency Calculation: After completing the initial discharge, continue the charge and discharge test for at least 10 or more cycles. Each cycle uses parameters similar to the initial charge and discharge, such as charging at a constant current of 0.1C to the cut-off voltage, then charging at a constant voltage, and then discharging at a constant current of 0.1C to the cut-off voltage. For the second to tenth cycles (or more specified number of cycles), calculate the Coulombic efficiency of each cycle. The calculation method is: the total discharge capacity of the cycle divided by the total charge capacity of the cycle, and then multiply by 100%. The average Coulombic efficiency is obtained by adding the Coulombic efficiency values ​​of these selected cycles and dividing by the number of cycles. All capacity data is automatically collected and calculated by the battery test system.

[0054] 2. Cycle life and capacity retention test method

[0055] Test Preparation and Environment: The all-solid-state thin-film lithium battery sample to be tested (comparative example or example) was secured to a dedicated test fixture in a multi-channel battery testing system to ensure good electrical contact. The entire test process was conducted at a constant temperature of 25°C (±1°C) to eliminate the effects of temperature fluctuations on battery performance.

[0056] Cycle parameter setting: Set the charge and discharge cycle rate. Cycle life testing typically uses a medium rate. For example, charge at a constant current of 0.5C. After reaching the upper cutoff voltage (e.g., 4.2V), switch to constant voltage charging mode until the current drops to 0.05C. After charging, allow the battery to rest for 10-30 minutes. Then, discharge at a constant current of 0.5C until reaching the lower cutoff voltage (e.g., 3.0V). After discharging, allow the battery to rest for another 10-30 minutes to complete a full charge and discharge cycle.

[0057] Cycling Process and Data Recording: Continuously repeat the above charge and discharge cycles. The battery testing system automatically records key data such as the charge and discharge capacity, charge and discharge cutoff voltage, and cycle count for each cycle. Pay particular attention to the discharge capacity of each cycle.

[0058] Cycle life determination: The end point of cycle life is defined as the number of cycles at which the battery's discharge capacity decays to 80% of its initial stable discharge capacity (usually the average of the stable discharge capacity in the first few cycles, or the discharge capacity of the second and third cycles). When the discharge capacity in a cycle falls below this threshold for the first time, the number of cycles is recorded as the battery's cycle life.

[0059] Capacity retention calculation: The capacity retention after 200 cycles is calculated by recording the discharge capacity at the end of the 200th cycle. Divide this 200th cycle discharge capacity by the initial stable discharge capacity (usually the discharge capacity of the second or third cycle to eliminate the influence of possible irreversible losses in the first cycle), and then multiply the result by 100% to obtain the capacity retention after 200 cycles.

[0060] 3. Rate performance test method

[0061] Battery Preparation and Initial Cycling: Connect the all-solid-state thin-film lithium battery sample (Comparative Example or Example) to the battery testing system and place it in a constant temperature environment at 25°C. First, perform 2-3 complete charge-discharge cycles at a low rate (e.g., 0.1C or 0.2C) to stabilize battery performance and obtain its baseline discharge capacity at low rates. Record the discharge capacity at the last low-rate cycle as the reference capacity (Cref).

[0062] Charging Phase: Before each discharge test at different rates, the battery is charged using a uniform charging schedule. Typically, the battery is charged at a low constant current (e.g., 0.2C or 0.5C) to the upper cutoff voltage. This is followed by constant voltage charging until the current decreases to 0.02C or 0.05C. This ensures that the battery is nearly fully charged before each discharge. After charging, the battery is allowed to rest for 20-30 minutes to allow the battery to reach equilibrium.

[0063] Discharge phase and rate setting: The battery is discharged at different rates in sequence. A typical discharge rate sequence may include 0.2C, 0.5C, 1C, 2C, 5C, and sometimes even higher rates such as 10C, depending on the battery design and application goals. For this test, we will focus specifically on discharge at 0.2C and 5C. At each set rate, discharge at a constant current to the lower cutoff voltage, and record the discharge capacity at that rate. For example, first discharge at 0.2C and record the capacity (C0.2C), then fully charge the battery, and then discharge at 5C and record the capacity (C5C). Ensure that the battery is fully recharged between changes in discharge rate.

[0064] Rate Performance Calculation: Rate performance is typically expressed as the percentage of high-rate discharge capacity relative to low-rate (baseline) discharge capacity. In this example, the 5C / 0.2C discharge capacity ratio is calculated by dividing the battery's capacity at a 5C discharge rate (C5C) by its capacity at a 0.2C discharge rate (C0.2C), and then multiplying the result by 100%. This percentage reflects the battery's capacity retention under high-current discharge conditions. All charge and discharge processes and data acquisition are automatically controlled and recorded by the battery testing system.

[0065] 4. Electrochemical interface impedance test method

[0066] Sample preparation and connection: Remove the all-solid-state thin-film lithium battery to be tested (comparative example or embodiment) from the battery testing system (if other tests are being performed), or directly use a battery in a specific state. Make sure that the battery is in an open circuit state or a specific state of charge (SOC), such as 50% SOC or 100% SOC. This is usually achieved by first accurately charging and discharging the battery to the target state. Connect the battery to the electrode fixture of an electrochemical workstation with electrochemical impedance spectroscopy (EIS) function (such as Solartron, BioLogic, Autolab, etc.), using a four-electrode or two-electrode configuration. For thin-film batteries, a two-electrode configuration is more common, but attention should be paid to the influence of wires and contact resistance. The test is carried out at a constant temperature of 25 degrees Celsius.

[0067] EIS parameter settings: Set the EIS test parameters in the electrochemical workstation software. These typically include: frequency range, for example, sweeping from a high frequency of 1 MHz or 100 kHz to a low frequency of 10 MHz or 1 Hz; perturbation signal amplitude, typically a sinusoidal AC voltage of 5 mV or 10 mV to ensure a linear response; DC bias voltage, typically set to the current open circuit voltage (OCV) of the cell or a specific DC voltage point; and data point density, for example, recording 10 points per decade.

[0068] Impedance Spectroscopy: Start the EIS test. The electrochemical workstation applies an AC signal of the specified frequency and amplitude to the battery and measures the corresponding current response (or applies AC current and measures the voltage response). By analyzing the phase difference and amplitude ratio between the voltage and current, the complex impedance (real part Z' and imaginary part Z'') of the battery at different frequencies is calculated. The entire scan process can take several minutes to tens of minutes, depending on the specified frequency range and low-frequency cutoff.

[0069] Data Analysis and Interfacial Impedance Extraction: After testing, the data is typically presented as a Nyquist plot (-Z' vs. Z'). The Nyquist plot typically contains various features: a capacitive tail or x-axis intercept in the high-frequency region (representing ohmic resistance, including electrolyte resistance, electrode material resistance, and contact resistance); one or more semicircles (representing interfacial charge transfer resistance and resistance and capacitance associated with the solid electrolyte interface (SEI) film or solid electrolyte interface); and a diagonal line in the low-frequency region (representing diffusion processes, also known as Warburg impedance). Electrochemical interfacial impedance primarily focuses on the semicircles associated with the electrode / electrolyte interface. Fitting the Nyquist plot with an equivalent circuit model (ECM) allows quantitative analysis of the various impedance components. Select an appropriate equivalent circuit, such as one that includes a series resistance (Rs), a parallel charge transfer resistance (Rct), and an electric double-layer capacitance (Cdl) (Randles circuit or its variant). The Rct value obtained from the fitting results (or the sum of the resistance values ​​representing the interface process) is divided by the active electrode area of ​​the battery to obtain the area specific interface impedance in Ω·cm 2 This value reflects the difficulty of lithium ions migrating between the electrode and electrolyte interface.

[0070] 5. Energy density test method

[0071] Battery preparation and parameter measurement: Select a packaged all-solid-state thin-film lithium battery sample (comparative example or example). First, accurately measure the physical dimensions of the battery, including length, width, and thickness. Use a caliper or micrometer with an accuracy of not less than 0.01 mm to measure at multiple points and take the average value to calculate the overall volume of the battery (V_cell) in cubic centimeters (cm 3) or convert to liters (L). At the same time, record the battery's designed operating voltage range, that is, the upper limit charge cut-off voltage (U_max) and the lower limit discharge cut-off voltage (U_min).

[0072] Discharge capacity determination: Connect the battery to a high-precision battery testing system. Perform standard charge and discharge tests at a constant temperature of 25°C to determine the actual discharge capacity. Typically, charge the battery at a constant current of 0.1C or 0.2C to U_max, then charge at a constant voltage until the current drops below 0.02C. After 30 minutes of rest, discharge the battery at the same constant current of 0.1C or 0.2C to U_min. Record the discharge capacity (Q_discharge) in ampere-hours (Ah) or milliampere-hours (mAh). To ensure data accuracy, perform 2-3 cycles and take the average discharge capacity.

[0073] Average discharge voltage calculation: During the standard discharge process described above, the battery test system records the voltage variation over time (or capacity). The average discharge voltage (U_avg) can be calculated by integrating the voltage on the discharge curve over the discharge capacity and then dividing by the total discharge capacity. The calculation principle is: the total discharge energy (E_discharge, in Wh) is equal to the integral of the discharge voltage (U(q)) over the discharge charge (q) from 0 to Q_discharge. Therefore, the average discharge voltage U_avg = E_discharge / Q_discharge. Many modern battery test systems can directly provide or calculate the average discharge voltage.

[0074] Energy density calculation: The energy of the battery (E_cell) can be obtained by multiplying the actual discharge capacity (Q_discharge, converted to Ah) by the average discharge voltage (U_avg, unit V), that is, E_cell=Q_discharge×U_avg, in watt-hours (Wh). The volumetric energy density (ρ_E, volume) is calculated by dividing the energy of the battery (E_cell) by the total volume of the battery (V_cell, converted to L). That is, energy density = E_cell / V_cell. The final result is expressed in watt-hours per liter (Wh / L). Ensure that all units are consistent to obtain the correct results. For example, if the capacity is mAh and the volume is cm 3 , then the unit conversion is required: Wh / L=(mAh×V) / (cm 3 ×1000).

[0075] Experiments were conducted on the finished materials prepared in Examples 1-2, where Comparative Example 1 was a lithium battery prepared according to Chinese Invention Publication No. CN118165540A. The experimental results are as follows:

[0076] Table 1 Performance test data

[0077]

[0078] As can be seen from Table 1, Example 1-2 has a higher first discharge specific capacity than Comparative Example 1, which means that it can store and release more charge; Example 1-2 shows a better cycle life and a higher capacity retention rate after cycling, indicating that it has better durability and can withstand more charge and discharge cycles with less performance degradation; Example 1-2 also has a higher average coulombic efficiency, indicating that it has less charge loss during the charge and discharge process and higher energy conversion efficiency; in addition, Example 1-2 is also better in rate performance and can maintain a higher capacity output under high current conditions; and the electrochemical interface impedance of Example 1-2 is lower, which is conducive to improving the transmission rate of lithium ions and reducing polarization, thereby bringing higher energy density.

Claims

1. A method for preparing an all-solid-state thin-film lithium battery, characterized in that: The following steps are involved: S1, assembling the lithium negative electrode and fixing it on the substrate: inside an inert gas protection glove box, cut the lithium metal negative electrode material into a specified size; take a clean and dry polymer support substrate; use a mechanical rolling device, set the rolling pressure to 10-50 MPa, and the rolling speed to 0.1-1.0 m / min, and at room temperature of 20-30 degrees Celsius, uniformly press the lithium metal negative electrode material onto one or both sides of the polymer support substrate to obtain a polymer substrate-fixed lithium metal negative electrode; S2, low-temperature plasma surface activation treatment, transferring the polymer substrate-fixed lithium metal negative electrode from the glove box to a vacuum chamber of a low-temperature plasma treatment equipment; closing the chamber and evacuating the chamber to a basic vacuum of 0.001 to 0.00001 Pascal; then introducing a mixed gas of argon and nitrogen as a working gas, with the argon flow rate controlled at 50-200 sccm and the nitrogen flow rate controlled at 10-50 sccm; setting the plasma glow discharge power to 50-300 watts and the working gas pressure to 10-100 Pascal through a radio frequency power supply; performing plasma bombardment treatment on the lithium metal surface for 30-300 seconds to obtain a surface-activated polymer substrate lithium metal negative electrode; S3, polyionic liquid auxiliary layer coating and thermal curing, coating the surface-activated polymer-based lithium metal negative electrode with a polyionic liquid auxiliary layer material to obtain a lithium metal negative electrode coated with a polyionic liquid auxiliary layer, wherein the polyionic liquid auxiliary layer material is a mixture of 50-60% 1-ethyl-3-methylimidazolium hexafluorophosphate, 25-30% 1-butyl-3-methylimidazolium bistrifluoromethanesulfonyl imide salt, and 25-30% bisfluorosulfonyl imide in a weight ratio; S4, PA-ALD atomic layer deposition to construct an ultra-thin electrolyte layer, constructing an oxide solid electrolyte layer on the surface of the lithium metal negative electrode coated with the polyionic liquid auxiliary layer, wherein the oxide solid electrolyte is yttrium-stabilized zirconia, to obtain a lithium metal negative electrode assembly deposited with an ultra-thin YSZ solid electrolyte film; S5, auxiliary layer composite treatment, for the lithium metal negative electrode assembly deposited with the YSZ solid electrolyte ultra-thin film, preparing a composite auxiliary layer on the surface of the YSZ electrolyte layer; dissolving the PET-PEG block copolymer in tetrahydrofuran to form a solution with a concentration of 5-15 weight percent; adding the polyionic liquid auxiliary layer material to the solution, and mechanically stirring for 1-2 hours to form a composite coating slurry; using a doctor blade method to evenly apply the composite coating slurry on the surface of the YSZ electrolyte layer, with the wet film thickness controlled to be 10-50 microns; then drying in a vacuum oven at 60-100 degrees Celsius for 2-4 hours to cure the coating, thereby obtaining a lithium metal negative electrode assembly modified with the composite auxiliary layer; S6, positive electrode material deposition and lamination assembly, using the composite auxiliary layer modified lithium metal negative electrode assembly as a substrate, depositing a positive electrode material on the outermost layer, the positive electrode material is a layered oxide positive electrode material, the layered oxide positive electrode material is lithium cobalt oxide, and cobalt disulfide is used as a conductive enhancer for the positive electrode, to obtain a preliminary structure of a multi-layer structure integral battery cell including a positive electrode, an electrolyte and a negative electrode; S7, packaging processing and performance stabilization, packaging the preliminary structure of the multi-layer structure integral battery cell including the positive electrode, electrolyte and negative electrode to obtain a packaged new type of all-solid-state thin-film lithium battery.

2. The method for preparing an all-solid-state thin-film lithium battery according to claim 1, wherein: The S4 step is specifically as follows: on the surface of the lithium metal negative electrode coated with the polyionic liquid auxiliary layer, an oxide solid electrolyte layer is constructed by plasma enhanced atomic layer deposition; the sample is loaded into the PA-ALD reaction chamber, and the deposition temperature is set to 80-200 degrees Celsius; each ALD cycle includes a precursor pulse of 0.1-2 seconds, an inert gas purge of 5-30 seconds, a plasma activation gas pulse of 0.5-5 seconds, and an inert gas purge of 5-30 seconds again; the number of ALD cycles is controlled to 50-500 cycles to obtain a lithium metal negative electrode assembly deposited with a YSZ solid electrolyte ultra-thin film.

3. The method for preparing an all-solid-state thin-film lithium battery according to claim 1, wherein: The S6 step is specifically as follows: using the lithium metal negative electrode assembly modified with the composite auxiliary layer as a substrate, depositing a positive electrode material on the outermost layer; using multi-target physical vapor deposition, using a layered oxide positive electrode material, setting the sputtering power to 200-1000 watts, the working pressure to 0.1-1.0 Pascal, and controlling the substrate temperature between room temperature and 200 degrees Celsius; then using a positive electrode conductivity enhancer, setting the sputtering power to 100-500 watts; after the deposition is completed, a preliminary structure of a multi-layered integral battery cell including a positive electrode, an electrolyte, and a negative electrode is obtained; The S7 step is specifically as follows: encapsulating the preliminary structure of the multi-layer structure battery cell comprising the positive electrode, electrolyte and negative electrode; placing the preliminary structure of the battery cell between aluminum-plastic film sheets, and heat-sealing the edges using a hot pressing packaging machine at a temperature of 150-200 degrees Celsius and a pressure of 0.5-1.5 MPa for 2-5 seconds; extracting the internal residual gas during the packaging process to form a vacuum internal environment; after the packaging is completed, placing the battery in a vacuum annealing furnace, keeping it warm in the temperature range of 80-150 degrees Celsius for 1-12 hours, and controlling the heating and cooling rate at 1 to 5 degrees Celsius per minute to obtain a packaged new all-solid-state thin-film lithium battery.

4. The method for preparing an all-solid-state thin-film lithium battery according to claim 1, wherein: The S3 step is specifically as follows: coating the surface-activated polymer-based lithium metal negative electrode with a polyionic liquid auxiliary layer material in an inert atmosphere glove box; using a spin coating method for coating, with the spin coating speed set at 500-3000RPM and the spin coating time being 30-120 seconds to obtain a uniform wet film with a thickness of 0.5-5 microns; after coating is completed, placing the sample on a heating platform and performing a heat treatment and curing at a temperature of 60-120 degrees Celsius for 1-3 hours to obtain a lithium metal negative electrode coated with a polyionic liquid auxiliary layer.

5. The method for preparing an all-solid-state thin-film lithium battery according to claim 1, wherein: The weight proportions of the lithium metal negative electrode material, the oxide solid electrolyte, the layered oxide positive electrode material, cobalt disulfide, the polyionic liquid auxiliary layer material and the PET-PEG block copolymer are respectively: 100-120 parts of the lithium metal negative electrode material, 150-250 parts of the oxide solid electrolyte, 100-200 parts of the layered oxide positive electrode material, 10-50 parts of cobalt disulfide, 5-30 parts of the polyionic liquid auxiliary layer material and 5-20 parts of the PET-PEG block copolymer.

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