Lithium battery and method for restoring capacity of lithium battery

Abstract

This application discloses a lithium battery and a method for restoring its capacity. The method includes the following steps: placing the lithium battery at room temperature for multiple rounds of constant current charge-discharge cycles, stopping the cycles when the battery's state of charge (SOC) reaches 0%; and subjecting the lithium battery to heat treatment after each round of constant current charge-discharge cycles, wherein the heat treatment time is 0.5 h to 5 h, and the heat treatment temperature is 35 °C to 65 °C. This application effectively improves the cycle stability and cycle life of the lithium battery by heating the lithium battery after a certain number of cycles and controlling the heating temperature and time within a certain range.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, and more particularly to a lithium battery and a method for restoring the capacity of a lithium battery. Background Technology

[0002] With technological advancements, the demand for high-performance lithium batteries continues to rise, but capacity decay during battery cycling is an unavoidable problem. Capacity decay primarily stems from side reactions at the electrode-electrolyte interface. Another key reason for capacity decay is the formation of isolated active materials (IAMs), which lose electrical connection with the current collector, causing capacity decay. During cycling, side reactions between the electrolyte and the lithium metal anode lead to the formation of lithium dendrites. Incomplete stripping of lithium dendrites results in the formation of inactive lithium that loses electrical connection with the current collector, leading to a significant decrease in battery cycle performance. Similarly, near the lithium metal deposition potential (~0.2 V vs. Li), the capacity decay also increases. + Graphite anodes operating under ( / Li) conditions undergo numerous side reactions, generating a large amount of isolated active material, including inactive lithium. The continuous accumulation of these isolated active materials is a significant factor limiting the lifespan of lithium-ion batteries. Therefore, restoring the isolated active materials generated during lithium battery cycling and thus restoring battery capacity has become a key research focus. Summary of the Invention

[0003] To address the aforementioned technical problems, this application proposes a method for restoring the isolated active material on the negative electrode side of a lithium battery through a gentle heating process, thereby restoring the lithium battery capacity. For ease of understanding, taking a lithium-ion battery with a graphite negative electrode as an example, this restoration process consists of two stages: thermally driven diffusion and reactivation. First, thermally driven diffusion occurs. The isolated active material on the negative electrode side of the battery can be considered as tiny particles that have lost electrical connection with the current collector but possess electrochemical activity. These particles undergo Brownian motion in the electrolyte. Their distribution follows Gaussian statistical laws, as shown in formula (1): Where x represents the diffusion distance of the microparticles, t represents the diffusion time, D represents the diffusion coefficient, and n represents the total number of microparticles. The relationship between the diffusion coefficient D and the temperature T is expressed by the Einstein-Stokes equations, as shown in formula (2): Where D represents the diffusion coefficient, T represents the temperature, η represents the viscosity, and r represents the radius of the microparticle.

[0004] As the temperature increases, the diffusion coefficient increases, which in turn increases the diffusion range of microparticles. Thermally driven diffusion improves the diffusion range of isolated active materials in the battery and enhances the reactivity of isolated materials in the battery through heating. Lithification of the graphite anode enables the reconnection of active isolated materials on the anode side of the battery, thereby promoting battery capacity recovery.

[0005] In view of this, the first aspect of this application provides a method for restoring the capacity of a lithium battery, comprising the following steps: placing the lithium battery at room temperature for multiple rounds of constant current charge-discharge cycles, stopping the cycles when the state of charge (SOC) of the lithium battery reaches 0%; and subjecting the lithium battery to a heat treatment after each round of constant current charge-discharge cycles, wherein the heat treatment time is 0.5 h to 5 h, and the heat treatment temperature is 35 °C to 65 °C. Please note that the state of charge (SOC) refers to the percentage of usable charge remaining in the battery, i.e., the ratio of the remaining capacity to the total capacity. The SOC is 100% when the battery is fully charged and 0% when the battery is fully discharged.

[0006] Based on the first aspect, in some possible implementations, the temperature of the heat treatment is 40°C to 60°C.

[0007] Based on the first aspect, in some possible implementations, the temperature of the heat treatment is 45°C.

[0008] Based on the first aspect, in some possible implementations, the heat treatment time is 1 hour to 4 hours.

[0009] Based on the first aspect, in some possible implementations, the heat treatment time is 3 hours.

[0010] Based on the first aspect, in some possible implementations, the lithium battery includes any one of lithium-sulfur batteries, lithium-air batteries, lithium metal batteries, and lithium-ion batteries.

[0011] Based on the first aspect, in some possible implementations, the lithium battery is a lithium-ion battery containing a graphite negative electrode, the heating treatment time is 3 hours, and the heating treatment temperature is 45°C.

[0012] Based on the first aspect, in some possible implementations, the lithium battery is a lithium metal battery, the heating treatment time is 0.5 hours, and the heating treatment temperature is 45°C.

[0013] A second aspect of this application provides a lithium battery, which is prepared using the above-described method for restoring lithium battery capacity.

[0014] The above-mentioned method for restoring lithium battery capacity is simple to operate. After a certain number of cycles, the lithium battery is heated. During the heating process, the diffusion range of isolated active materials generated on the negative electrode side of the lithium battery is expanded. The lithiation rate of the negative electrode active material (such as graphite) can be increased by increasing the temperature during the heating process. This allows these isolated active materials to diffuse rapidly and stably to the active material on the graphite negative electrode surface. Through the combination of thermally activated diffusion and interface reactivation, the decayed capacity of the lithium battery is effectively restored, and the cycle stability and cycle life of the lithium battery are improved.

[0015] Furthermore, the aforementioned method for restoring lithium battery capacity is highly versatile, adaptable to various types of lithium batteries (such as lithium-sulfur batteries, lithium-air batteries, lithium-metal batteries, and lithium-ion batteries), and simple to operate. It only requires adjusting the temperature and time during the heating process, without the need for additional equipment or complex processes, making it easy to implement on a large scale for industrial applications. In addition, this method not only achieves good results but also has relatively low costs. Attached Figure Description

[0016] Figure 1 The graph shows the change in discharge capacity of lithium batteries (taking lithium-ion batteries containing graphite negative electrodes as an example) in Examples 1, Comparative Examples 1 and 2 during cycling at 1C charging rate and 1C discharging rate.

[0017] Figure 2 The graph shows the change in discharge capacity of the lithium batteries (taking a lithium-ion battery containing a graphite negative electrode as an example) in Example 7 and Comparative Example 7 during cycling at 2C charging rate and 2C discharging rate. Detailed Implementation

[0018] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0019] One embodiment of this application provides a method for restoring the capacity of a lithium battery, comprising the following steps: Step 1: Assemble the lithium battery and place it at room temperature for multiple rounds of constant current charge-discharge cycles. Stop the cycle when the lithium battery's SOC reaches 0%.

[0020] In some embodiments, the assembly method of the lithium battery (taking a lithium-ion battery with a graphite negative electrode as an example) includes: first cutting the negative electrode sheet into a circular piece with a diameter of Φ = 12 mm, cutting the positive electrode sheet into a circular piece with a diameter of Φ = 12 mm, and cutting the separator into a circular piece with a diameter of Φ = 19 mm; in a glove box filled with high-purity argon gas, assembling the negative electrode sheet, separator and positive electrode sheet into an electrode assembly in sequence, placing the electrode assembly in a button-type shell and adding an appropriate amount of electrolyte, thereby assembling a 2032 type button lithium-ion battery.

[0021] The negative electrode sheet is prepared by uniformly mixing negative electrode active material, conductive agent and binder and coating it onto negative electrode fluid. This application does not limit the types of conductive agent and binder, as long as they meet the requirements of this application.

[0022] In some implementations, the negative electrode active material includes natural graphite and / or artificial graphite.

[0023] In some embodiments, the negative current collector includes at least one of copper foil, copper mesh, copper foam, nickel foil, iron foil, carbon paper, or carbon cloth.

[0024] The positive electrode sheet is prepared by uniformly mixing positive electrode active material, conductive agent and binder and coating it onto an aluminum current collector. This application does not limit the types of conductive agent and binder, as long as they meet the requirements of this application.

[0025] In some embodiments, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide (NCM811) and / or lithium iron phosphate (LiFePO4).

[0026] The electrolyte comprises an organic solvent, a lithium salt, and optional additives. The organic solvent in the electrolyte of this application can be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it can be any electrolyte known in the prior art. The additives in the electrolyte according to this application can be any additives known in the prior art that can be used as electrolyte additives.

[0027] This application does not impose any particular restrictions on the material and shape of the separator used, which can be any technology disclosed in the prior art.

[0028] Step 2: After each constant current charge-discharge cycle, the lithium battery is subjected to a heating treatment, the heating time is 0.5h to 5h, and the heating temperature is 35℃ to 65℃.

[0029] This application heats a lithium battery after it has undergone a certain number of cycles. During the heating process, the diffusion range of isolated active materials generated on the negative electrode side of the lithium battery is expanded. The lithiation rate of the negative electrode active material (e.g., graphite) can be increased by raising the temperature during the heating process. This allows these isolated active materials to diffuse rapidly and stably to the active material on the graphite negative electrode surface. Through the combination of thermally activated diffusion and interface reactivation, the decayed capacity of the lithium battery is effectively restored, and the cycle stability and cycle life of the lithium battery are improved.

[0030] Furthermore, the researchers of this application also discovered that when the heating temperature is too low, for example below the lower limit of this application, the diffusion distance is short, fewer inactive particles can diffuse to the negative electrode side, and the low temperature easily leads to low reactivation activity of inactive lithium, which is not conducive to capacity recovery. When the heating temperature is too high, for example above the upper limit of this application, it will cause electrolyte decomposition, which is not conducive to improving the cycle stability and cycle life of lithium batteries. Therefore, by further limiting the heating temperature and time to meet the above range, this application is beneficial to further improve the cycle stability and cycle life of lithium batteries.

[0031] For example, the temperature for heat treatment can be 35℃, 37℃, 39℃, 40℃, 42℃, 44℃, 46℃, 48℃, 40℃, 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 65℃, or a range of any two of these values. Similarly, the heat treatment time can be 0.5h, 0.7h, 0.9h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h, 4h, 4.2h, 4.4h, 4.6h, 4.8h, 5h, or a range of any two of these values.

[0032] In some embodiments, the heat treatment temperature is preferably 40°C to 60°C, more preferably 45°C, which can help to further improve the cycle stability and cycle life of the lithium battery.

[0033] In some embodiments, the heat treatment time is preferably 1 hour to 4 hours, more preferably 3 hours, which can help to further improve the cycle stability and cycle life of lithium batteries.

[0034] In some embodiments, the lithium battery includes any one of lithium-sulfur batteries, lithium-air batteries, lithium metal batteries, lithium-ion batteries with graphite anodes, and lithium-ion batteries with silicon-carbon anodes.

[0035] In some embodiments, when the lithium battery is a lithium-ion battery with a graphite negative electrode, the heat treatment time is preferably 3 hours, and the heat treatment temperature is preferably 45°C.

[0036] In some embodiments, when the lithium battery is a lithium metal battery, the heating treatment time is preferably 0.5 hours, and the heating treatment temperature is preferably 45°C.

[0037] One embodiment of this application also provides a lithium battery, which is prepared using the above-described method for restoring lithium battery capacity. The lithium battery of this application has good cycle stability (high cycle capacity retention) and a long cycle life.

[0038] The method for restoring lithium battery capacity according to this application is described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0039] Example 1 The method for restoring the capacity of a lithium battery includes the following steps: Step S1: Assembly of lithium batteries (taking a lithium-ion battery containing a graphite negative electrode as an example); First, the negative electrode sheet coated with negative electrode active material is cut into a circular sheet with a diameter of 12 mm. The positive electrode sheet coated with positive electrode active material is cut into a circular sheet with a diameter of 12 mm. The separator is cut into a circular sheet with a diameter of 19 mm. In a glove box filled with high-purity argon gas, the negative electrode sheet, separator and positive electrode sheet are assembled into an electrode assembly in sequence. The electrode assembly is placed in a button shell and an appropriate amount of electrolyte is added to obtain a 2032 type button lithium-ion battery.

[0040] Among them, artificial graphite is selected as the negative electrode active material, and lithium nickel cobalt manganese oxide (NCM811) is selected as the positive electrode active material.

[0041] Step S2: First, activate the 2032 coin cell lithium-ion battery by charging at 0.1C current density and discharging at 0.1C current density (1C=188mAh / g) for one cycle. Then, perform the first constant current charge-discharge cycle of charging at 1C current density and discharging at 1C current density. After 100 cycles, the battery SOC is 0 (fully discharged), and the battery capacity retention rate is 75.54%. Stop the cycle.

[0042] Step S3: After 100 cycles, the 2032 coin cell lithium-ion battery is placed in a 45°C incubator for 3 hours for the first heating treatment.

[0043] Step S4: Remove the 2032 coin cell lithium-ion battery after the first heating and perform a second round of constant current charge-discharge cycle. After 30 cycles, repeat step S3 above for a second heating treatment.

[0044] Repeat the above steps until the 2032 coin cell lithium-ion battery has completed 200 cycles.

[0045] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4416 mAh to 1.6343 mAh, recovering 46.6% of the lost capacity, and the coulombic efficiency increased from 99.9% to 102.98%. Furthermore, the discharge capacity of the 2032 coin cell lithium-ion battery increased with each subsequent heat treatment every 30 cycles. After 200 cycles, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.5226 mAh, with a capacity retention of 81.5%, demonstrating better cycle stability than Comparative Examples 1 to 6.

[0046] Example 2 The method for restoring the capacity of a lithium battery includes the following steps: Step S1: Assembly of lithium batteries (taking a negative electrode-free lithium metal battery as an example); Assembly of a negative electrode-less lithium metal battery: First, cut a copper current collector into a circular piece with a diameter of 12 mm as the negative electrode. Cut a positive electrode plate coated with positive electrode active material into a circular piece with a diameter of 12 mm. Cut a separator into a circular piece with a diameter of 19 mm. In a glove box filled with high-purity argon, assemble the negative electrode plate, separator, and positive electrode plate into an electrode assembly in sequence. Place the electrode assembly in a button-type casing and add an appropriate amount of electrolyte to obtain a 2032 type button lithium-ion battery.

[0047] The negative electrode active material is copper foil, and the positive electrode active material is lithium nickel cobalt manganese oxide (NCM811).

[0048] Step S2: Activate the 2032 coin cell lithium-ion battery by charging at a current density of 0.1C and discharging at a current density of 0.1C (1C=188mAh / g), and then perform the first round of constant current charge-discharge cycle by charging at a current density of 1C and discharging at a current density of 1C. After 15 cycles, the battery capacity retention rate is 68.6%, and the cycle is stopped.

[0049] Step S3: After 15 cycles, the 2032 coin cell lithium-ion battery is placed in a 45°C oven for 0.5 hours for the first heating treatment.

[0050] Step S4: Remove the 2032 coin cell lithium-ion battery after the first heating and perform the second round of constant current charge-discharge cycle.

[0051] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.3356 mAh to 1.6385 mAh, recovering 49.7% of the lost capacity, and the coulombic efficiency increased from 98.5% to 112.2%. After 30 cycles, the heat-treated lithium metal battery retained a discharge capacity of 0.9069 mAh, higher than the remaining discharge capacity of 0.4692 mAh of the untreated lithium metal battery after normal cycling.

[0052] Example 3 The difference from Example 1 is that in step S3, the temperature of the first heat treatment is adjusted from 45°C to 35°C, while the other preparation conditions remain unchanged.

[0053] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4256 mAh to 1.4532 mAh, recovering only 6.7% of the lost capacity, significantly lower than the capacity recovered after heating at 45°C. This is because the recovery temperature was low, the diffusion range of inactive lithium was small, and the reactivity of graphite relithiation was low, resulting in insignificant capacity recovery. After 200 cycles, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.3576 mAh, with a capacity retention of 73.6%, significantly lower than that of Example 1.

[0054] Example 4 The difference from Example 1 is that in step S3, the temperature of the first heat treatment is adjusted from 45°C to 65°C, while the other preparation conditions remain unchanged.

[0055] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4320 mAh to 1.6836 mAh, recovering 69.1% of the lost capacity. This was significantly higher than the capacity recovered after heating at 45°C. This is because the higher recovery temperature allowed for a wider diffusion range of inactive lithium and enhanced the reactivity of graphite relithiation, resulting in a more significant capacity recovery. However, excessively high temperatures can cause electrolyte decomposition, affecting subsequent battery cycling. After 200 cycles, the discharge capacity of the 2032 coin cell lithium-ion battery was only 0.9763 mAh, with a capacity retention of 54.3%, significantly lower than in Example 1.

[0056] Example 5 The difference from Example 1 is that in step S3, the time for the first heating treatment is adjusted from 3 hours to 0.5 hours, while the other preparation conditions remain unchanged.

[0057] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4415 mAh to 1.4878 mAh, recovering 12.1% of the lost capacity. This was significantly lower than the capacity recovered after heating at 45°C for 3 hours. This is because the recovery time was short, and the thermal diffusion distance of inactive lithium was short, leading to a reduced recovered capacity. After 200 cycles of testing, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.3627 mAh, with a capacity retention of 74.7%, significantly lower than that of Example 1.

[0058] Example 6 The difference from Example 1 is that in step S3, the time for the first heat treatment is adjusted from 3 hours to 5 hours, while the other preparation conditions remain unchanged.

[0059] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4280 mAh to 1.6163 mAh, recovering 45.4% of the lost capacity. This is essentially the same as the recovered capacity in Example 1, indicating that adding two hours of heat treatment time did not significantly improve capacity recovery. This is because the capacity loss in lithium-ion batteries is not only caused by inactive lithium, but also by the formation of the SEI (Sediment Injection) layer in the negative electrode. Heating can only recover part of the capacity loss caused by inactive lithium. After 3 hours of heating, the capacity loss was essentially complete; further extending the heating time did not significantly improve capacity recovery and instead wasted energy. After 200 cycles of testing, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.4868 mAh, with a capacity retention rate of 80.6%, essentially the same as in Example 1. This indicates that extending the heating time to 5 hours did not significantly improve capacity recovery compared to 3 hours.

[0060] Example 7 The method for restoring the capacity of a lithium battery includes the following steps: Step S1: Assembly of lithium batteries (taking a lithium-ion battery containing a graphite negative electrode as an example); First, the negative electrode sheet coated with negative electrode active material is cut into a circular sheet with a diameter of 12 mm. The positive electrode sheet coated with positive electrode active material is cut into a circular sheet with a diameter of 12 mm. The separator is cut into a circular sheet with a diameter of 19 mm. In a glove box filled with high-purity argon gas, the negative electrode sheet, separator and positive electrode sheet are assembled into an electrode assembly in sequence. The electrode assembly is placed in a button shell and an appropriate amount of electrolyte is added to obtain a 2032 type button lithium-ion battery.

[0061] Among them, artificial graphite is selected as the negative electrode active material, and lithium nickel cobalt manganese oxide (NCM811) is selected as the positive electrode active material.

[0062] Step S2: First, activate the 2032 coin cell lithium-ion battery by charging at 0.1C current density and discharging at 0.1C current density (1C=188mAh / g) for one cycle. Then, perform the first constant current charge-discharge cycle by charging at 2C current density and discharging at 2C current density. After 60 cycles, the battery SOC is 0 (fully discharged), and the battery capacity retention rate is 83.60%. Stop the cycle.

[0063] Step S3: After 60 cycles, the 2032 coin cell lithium-ion battery is placed in a 45°C incubator for 3 hours for the first heat treatment.

[0064] Step S4: Remove the 2032 coin cell lithium-ion battery after the first heating and perform a second round of constant current charge-discharge cycle to 100 cycles.

[0065] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.458 mAh to 1.650 mAh, recovering 67.1% of the lost capacity, and the coulombic efficiency increased from 99.7% to 102.67%. After 100 cycles, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.599 mAh, with a capacity retention rate of 91.6%.

[0066] Comparative Example 1 The method for restoring the capacity of a lithium battery includes the following steps: Step S1: Assembly of lithium batteries (taking a lithium-ion battery with a graphite negative electrode as an example); First, the negative electrode sheet coated with negative electrode active material is cut into a circular sheet with a diameter of 12 mm. The positive electrode sheet coated with positive electrode active material is cut into a circular sheet with a diameter of 12 mm. The separator is cut into a circular sheet with a diameter of 19 mm. In a glove box filled with high-purity argon gas, the negative electrode sheet, separator and positive electrode sheet are assembled into an electrode assembly in sequence. The electrode assembly is placed in a button shell and an appropriate amount of electrolyte is added to obtain a 2032 type button lithium-ion battery.

[0067] Among them, artificial graphite is selected as the negative electrode active material, and lithium nickel cobalt manganese oxide (NCM811) is selected as the positive electrode active material.

[0068] Step S2: Charge the 2032 coin cell lithium-ion battery at a current density of 1C and discharge it at a current density of 1C (1C=188mAh / g) for 200 consecutive cycles.

[0069] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The test results showed that the discharge capacity was 1.4267 mAh after 101 cycles and 1.3464 mAh after 200 cycles, with a capacity retention rate of 75.2%. The cycle capacity retention rate was significantly lower than that of Example 1, indicating poorer cycle stability compared to Example 1.

[0070] Comparative Example 2 The method for restoring the capacity of a lithium battery includes the following steps: Step S1: Assembly of lithium batteries (taking a lithium-ion battery with a graphite negative electrode as an example); First, the negative electrode sheet coated with negative electrode active material is cut into a circular sheet with a diameter of 12 mm. The positive electrode sheet coated with positive electrode active material is cut into a circular sheet with a diameter of 12 mm. The separator is cut into a circular sheet with a diameter of 19 mm. In a glove box filled with high-purity argon gas, the negative electrode sheet, separator and positive electrode sheet are assembled into an electrode assembly in sequence. The electrode assembly is placed in a button shell and an appropriate amount of electrolyte is added to obtain a 2032 type button lithium-ion battery.

[0071] Among them, artificial graphite is selected as the negative electrode active material, and lithium nickel cobalt manganese oxide (NCM811) is selected as the positive electrode active material.

[0072] Step S2: First, activate the 2032 coin cell lithium-ion battery by charging at 0.1C current density and discharging at 0.1C current density (1C=188mAh / g) for one cycle. Then, perform the first constant current charge-discharge cycle of charging at 1C current density and discharging at 1C current density. After 100 cycles, let it stand for 12 hours for the first time.

[0073] Step S3: After the 2032 coin cell lithium-ion battery has been left to stand for 12 hours for the first time, perform a second constant current charge-discharge cycle. After 30 cycles, repeat step S2 above and leave it to stand for 12 hours for the second time.

[0074] Repeat the above steps until the 2032 coin cell lithium-ion battery has completed 200 cycles.

[0075] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first settling period, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4549 mAh to 1.4853 mAh, recovering 8.1% of the lost capacity. After 200 cycle tests, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.3588 mAh, with a capacity retention rate of 76.3%. This cycle capacity retention rate was significantly lower than that of Example 1, indicating poorer cycle stability compared to Example 1.

[0076] Comparative Example 3 The difference from Example 1 is that in step S3, the temperature of the first heat treatment is adjusted from 45°C to 30°C, while the other preparation conditions remain unchanged.

[0077] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery changed from 1.4116 mAh at cycle 100 to 1.4113 mAh at cycle 101, with no capacity recovery observed. This was attributed to the low recovery temperature, the small diffusion range of inactive lithium, and the low reactivity of graphite relithiation, resulting in no capacity recovery. After 200 cycles, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.2852 mAh, with a capacity retention of 68.7%, significantly lower than that of Example 1.

[0078] Comparative Example 4 The difference from Example 1 is that in step S3, the temperature of the first heat treatment is adjusted from 45°C to 80°C, while the other preparation conditions remain unchanged.

[0079] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4320 mAh to 1.6584 mAh, recovering 57.5% of the lost capacity. This was significantly higher than the capacity recovered after heating at 45°C. This is because the higher recovery temperature allowed for a wider diffusion range of inactive lithium and enhanced the reactivity of graphite relithiation, leading to a more significant capacity recovery. However, excessively high temperatures can cause electrolyte decomposition, affecting subsequent battery cycling. After 200 cycles, the discharge capacity of the 2032 coin cell lithium-ion battery was only 0.1353 mAh, with a capacity retention of 7.3%, significantly lower than in Example 1.

[0080] Comparative Example 5 The difference from Example 1 is that in step S3, the time for the first heating treatment is adjusted from 3h to 0.1h, while the other preparation conditions remain unchanged.

[0081] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery changed from 1.4498 mAh at cycle 100 to 1.4489 mAh at cycle 101, with no capacity recovery observed. This was attributed to the short recovery time and the short thermal diffusion distance of the inactive lithium, which prevented capacity recovery. After 200 cycles, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.2544 mAh, with a capacity retention of 73.4%, significantly lower than that of Example 1.

[0082] Comparative Example 6 The difference from Example 1 is that in step S3, the time for the first heat treatment is adjusted from 3 hours to 12 hours, while the other preparation conditions remain unchanged.

[0083] The electrochemical performance of the assembled 2032 coin cell lithium-ion battery was tested using the Land battery testing system. The test results showed that after the first heat treatment, the discharge capacity of the 2032 coin cell lithium-ion battery recovered from 1.4364 mAh to 1.6123 mAh, recovering 43.2% of the lost capacity. This is basically consistent with the recovered capacity in Example 1, further illustrating that increasing the heat treatment time does not significantly improve capacity recovery. This is because the capacity loss of lithium-ion batteries is not only caused by inactive lithium, but also by the formation of the SEI layer in the negative electrode layer. Heating can only recover part of the capacity loss caused by inactive lithium. After heating for 3 hours, the recovery was basically complete. Extending the heating time further does not significantly improve capacity recovery and instead wastes energy. After 200 cycles of testing, the discharge capacity of the 2032 coin cell lithium-ion battery was 1.3795 mAh, with a capacity retention rate of 74.8%, which was lower than that of Example 1. This indicates that extending the heating time to 12 hours, compared to heating for 3 hours, not only did not significantly improve capacity recovery, but also had a negative effect on the subsequent cycling of the battery.

[0084] Comparative Example 7 The method for restoring the capacity of a lithium battery includes the following steps: Step S1: Assembly of lithium batteries (taking a lithium-ion battery with a graphite negative electrode as an example); First, the negative electrode sheet coated with negative electrode active material is cut into a circular sheet with a diameter of 12 mm. The positive electrode sheet coated with positive electrode active material is cut into a circular sheet with a diameter of 12 mm. The separator is cut into a circular sheet with a diameter of 19 mm. In a glove box filled with high-purity argon gas, the negative electrode sheet, separator and positive electrode sheet are assembled into an electrode assembly in sequence. The electrode assembly is placed in a button shell and an appropriate amount of electrolyte is added to obtain a 2032 type button lithium-ion battery.

[0085] Among them, artificial graphite is selected as the negative electrode active material, and lithium nickel cobalt manganese oxide (NCM811) is selected as the positive electrode active material.

[0086] Step S2: Charge the 2032 coin cell lithium-ion battery at a current density of 0.1C and discharge it at a current density of 0.1C for one cycle of activation. Then charge it at a current density of 2C and discharge it at a current density of 2C (1C=188mAh / g) for 100 cycles.

[0087] The assembled 2032 coin cell lithium-ion battery was tested for electrochemical performance using the Land battery testing system. The test results showed that the discharge capacity was 1.529 mAh after 60 cycles and 1.497 mAh after 100 cycles, with a capacity retention rate of 83.58%. The cycle capacity retention rate was significantly lower than that of Example 7, indicating poorer cycle stability compared to Example 7.

[0088] Test methods State of charge (SOC) test of lithium batteries The state of charge (SOC) of a lithium battery is estimated by measuring the open-circuit voltage. Generally, for lithium-ion batteries with NCM811 material as the positive electrode and graphite material as the negative electrode, when the open-circuit voltage is less than or equal to 3.2V, the SOC is considered to be below 20%, and heating can be used to restore capacity.

[0089] Figure 1 The graph shows the discharge capacity change of lithium batteries (taking lithium-ion batteries with graphite anodes as examples) in Examples 1, 1, and 2 during cycling at 1C charge and 1C discharge rates. Figure 1 As can be seen, the discharge capacity of Comparative Example 1 and Comparative Example 2 gradually decreased with the increase of the number of cycles. This indicates that during long-term cycling, active materials inevitably appear on the graphite negative electrode side of the lithium battery, losing electrical connection with the current collector. The continuous accumulation of such isolated active materials leads to a decrease in battery capacity and limits the lifespan of the lithium battery. Example 1, to a certain extent, slowed down the decay of discharge capacity, especially under conditions of a relatively high number of cycles. After 100 cycles, the method for restoring lithium battery capacity proposed in this application was used to perform a first heat treatment on the lithium battery. Figure 1 As can be clearly seen, the discharge capacity of the lithium battery at this time is higher than that of Comparative Example 1 and Comparative Example 2. This shows that the method for restoring the capacity of lithium batteries in this application helps to expand the diffusion range of isolated active materials generated on the negative electrode side, and can increase the lithiation rate of the negative electrode active material (e.g., graphite) by increasing the temperature during the heating process. This allows these isolated active materials to diffuse rapidly and stably to the active material on the graphite negative electrode surface. Through the combination of thermally activated diffusion and interface reactivation, the decayed capacity of the lithium battery is effectively restored, and the cycle stability and cycle life of the lithium battery are improved.

[0090] Figure 2The graph shows the discharge capacity changes of the lithium batteries (taking a lithium-ion battery containing a graphite negative electrode as an example) in Example 7 and Comparative Example 7 during 2C charge and discharge rate cycling. The solid line represents the battery sample with an initial discharge capacity of 1.744 mAh. It can be seen that after 60 normal cycles, heat treatment restored the battery's discharge capacity from 1.458 mAh to 1.65 mAh, recovering 67.1% of the lost capacity, and the discharge capacity remained at 1.587 mAh after 100 cycles. In contrast, the normally cycled battery had an initial discharge capacity of 1.791 mAh, a 60-cycle discharge capacity of 1.529 mAh, a 61-cycle discharge capacity of 1.532 mAh, and a 100-cycle discharge capacity of 1.497 mAh, significantly lower than the heat-treated battery sample.

[0091] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A method for restoring the capacity of a lithium battery, characterized in that, Includes the following steps: The lithium battery was subjected to multiple constant current charge-discharge cycles at room temperature. The cycle was stopped when the SOC of the lithium battery was 0%. The lithium battery is subjected to a heating treatment after each constant current charge-discharge cycle, wherein the heating treatment time is 0.5h to 5h and the heating treatment temperature is 35℃ to 65℃.

2. The method for restoring lithium battery capacity according to claim 1, characterized in that, The temperature of the heat treatment is 40°C to 60°C.

3. The method for restoring lithium battery capacity according to claim 1, characterized in that, The temperature for the heat treatment is 45°C.

4. The method for restoring lithium battery capacity according to claim 1, characterized in that, The heat treatment time is 1 hour to 4 hours.

5. The method for restoring lithium battery capacity according to claim 1, characterized in that, The heat treatment time is 3 hours.

6. The method for restoring the capacity of a lithium battery according to any one of claims 1 to 5, characterized in that, The lithium battery includes any one of lithium-sulfur batteries, lithium-air batteries, lithium metal batteries, and lithium-ion batteries.

7. The method for restoring lithium battery capacity according to claim 1, characterized in that, The lithium battery is a lithium-ion battery containing a graphite negative electrode, the heating treatment time is 3 hours, and the heating treatment temperature is 45°C.

8. The method for restoring lithium battery capacity according to claim 1, characterized in that, The lithium battery is a lithium metal battery, the heating treatment time is 0.5 hours, and the heating treatment temperature is 45°C.

9. A lithium battery, characterized in that, The lithium battery is prepared using the method for restoring lithium battery capacity as described in any one of claims 1 to 8.

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