Battery lithium supplementing and positive electrode self-repairing method and device based on ultrasonic cavitation effect

Abstract

The invention belongs to the related technical field of lithium ion battery monomers, and discloses a battery lithium supplementing and positive electrode self-repairing method based on an ultrasonic cavitation effect, and the method comprises the following steps: carrying out pretreatment on a lithium iron phosphate system lithium ion battery to be treated; performing ultrasonic cavitation treatment on the lithium ion battery, electrolyzing an electrolyte organic solvent by utilizing an ultrasonic cavitation effect to generate free electrons, and driving lithium salt and the like to release active Li < + >; and free electrons migrate to the surface of the positive electrode of the battery and trigger an interface reduction reaction with active Li < + > in situ, so that active lithium compensation and positive electrode material microstructure repair of the lithium ion battery are synchronously realized. The invention further discloses a corresponding device. Through the method, non-intrusive whole process treatment can be achieved at normal temperature, compared with the prior art, the repairing effect is remarkably improved, the lattice integrity can be recovered while nanoscale local repairing is achieved, and meanwhile the method has the advantages of being convenient to control, low in cost, free of secondary pollution, optimized in safety and environmental protection performance and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery cells, and more particularly relates to a battery lithium supplementing and positive electrode self-repairing method and device based on ultrasonic cavitation effect. BACKGROUND

[0002] Lithium ion batteries, as the current mainstream energy storage technology, have been widely used in electric vehicles, consumer electronics and renewable energy storage. However, one of its core materials, such as lithium iron phosphate positive electrode, faces two bottleneck problems of irreversible capacity loss and structural degradation in long-term cycling, which greatly limits the life and performance of lithium ion batteries.

[0003] More specifically, taking lithium iron phosphate (LiFePO4) battery as an example, it will consume part of lithium due to the formation of solid electrolyte interface (SEI) film during the first charging process, resulting in the loss of lithium in the positive electrode material, and the overall irreversible capacity loss of the battery can reach 10-20%. During the cycling process of lithium ion batteries, the SEI film is consumed and repaired, the internal dead lithium of the positive and negative electrodes increases, and the active lithium decreases, which causes the capacity of the battery to continuously decrease, and also leads to the reduction of the cycle life of the battery.

[0004] In addition, lithium iron phosphate (LiFePO4) battery will undergo a mutual reverse reaction phase change between FePO4 and LiFePO4 during charging and discharging. With the long-term charging and discharging cycle of the battery, the structural loss of the positive electrode mainly manifests as lattice distortion, particle cracking and active material failure, etc. These degradation mechanisms will directly affect the cycle life and rate performance of the battery.

[0005] Although some repair schemes for lithium ion batteries have been proposed in the prior art, there are still three major defects of complex process, high cost and incomplete repair, and the simultaneous supplement of lithium and structural repair cannot be achieved. Accordingly, there is an urgent need in the art to develop a new type of in-situ lithium supplementing technology for batteries in order to better solve the problem of non-destructive repair of lithium iron phosphate positive electrode material. SUMMARY

[0006] In view of one or more of the above defects or needs of the prior art, the present application provides a battery lithium supplementing and positive electrode self-repairing method and device based on ultrasonic cavitation effect, wherein the process route and reaction mechanism of lithium supplementing and positive electrode repair of the entire lithium ion battery are redesigned, and accordingly the entire process treatment can be realized in a non-invasive manner at room temperature without disassembling the battery, and the repair effect is significantly improved compared with the prior art, the lattice integrity can be restored while realizing nanoscale local repair, and the device has the advantages of easy operation, low cost, no secondary pollution, optimized safety and environmental protection, etc.

[0007] To achieve the above object, according to one aspect of the present application, a battery lithium supplementing and positive electrode self-repairing method based on ultrasonic cavitation effect is provided, which comprises the following steps: Step one: battery pretreatment For the lithium iron phosphate system battery to be treated, fresh electrolyte with the same formula as the original battery is supplemented and injected, and a catalyst capable of adsorbing electrons to make them stably exist is added in the electrolyte; after the fresh electrolyte uniformly wets the battery electrode, the battery is charged and discharged to restore the integrity of the solid electrolyte film on the electrode surface, and the electrode is activated; Step two: ultrasonic cavitation treatment The pretreated battery is placed in an ultrasonic reaction tank, ultrasonic waves are applied to the entire battery, and ultrasonic cavitation treatment is performed using the electrolyte inside the battery as the reaction medium; During this process, the organic solvent of the electrolyte is dissociated to generate new free electrons under the cavitation effect and stably exists under the action of the catalyst, the lithium salt and lithium-rich compounds are activated and release active Li + and diffuse to the positive electrode surface of the battery; Step three: lithium supplementing and positive electrode self-repairing reaction The new free electrons migrate to the positive electrode surface of the battery under the driving of the local electric field generated by the cavitation effect, and trigger the interface reduction reaction with the active Li + in situ, thereby generating new positive electrode materials to complete the lithium supplementing of the battery, and repairing the positive electrode lattice defects and adjusting the lattice distortion to realize nanoscale positive electrode self-repairing.

[0008] As a further preferred embodiment of the present application, in step one, the lithium salt and lithium-rich compounds of the fresh electrolyte are preferably at least one of LiPF6, LiFSI, LiTFSI or LiClO4, and the concentration is 0.5M-2M; the organic solvent of the fresh electrolyte is preferably at least two of ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene glycol dimethyl ether (DME), and tetrahydrofuran (THF); in addition, the fresh electrolyte preferably further comprises an additive, which is at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and lithium bis(oxalato)borate (LiBOB), and the addition amount is preferably 0.1wt%-2wt%.

[0009] As a further preference of the present invention, in step 1, the catalyst is preferably a nitrogen-doped carbon material such as nitrogen-doped carbon nanotubes (N-CNTs) and mesoporous carbon spheres (CMK-3); or a metal organic framework derivative such as ZIF-8-derived nitrogen-doped carbon and MIL-101(Cr)-loaded single-atom iron (Fe-SA@MIL); or a wide-bandgap metal oxide such as MgO nanosheets and Al2O3-coated LiFePO4; in addition, the added amount of the catalyst is preferably set to 0.1% to 5% by mass of the battery positive electrode active material.

[0010] As a further preference of the present invention, in step 1, the battery to be treated is preferably a lithium iron phosphate system battery whose positive electrode material is LiFePO4.

[0011] As a further preferred embodiment of the present invention, in step 2, the ultrasonic working parameters are set as follows: frequency is 20kHz to 100kHz, more preferably 40kHz to 60kHz; power density is 0.5W / cm 2 ~3W / cm 2 , more preferably 1W / cm 2 ~2W / cm 2 .

[0012] As a further preferred embodiment of the present invention, in step 2, the ultrasonic wave preferably adopts a pulse mode, and its duty cycle is preferably set to 30% to 80%.

[0013] As a further preferred embodiment of the present invention, in step 2, the temperature in the ultrasonic reaction tank is preferably controlled to be 25°C to 60°C, and is achieved by any of the following methods: constant temperature water bath circulation, and a built-in thermoelectric cooling module in the ultrasonic reaction tank.

[0014] As a further preference of the present invention, the above-mentioned battery to be treated is preferably a new lithium iron phosphate system battery, and the above treatment is used to achieve pre-lithium replenishment in the battery manufacturing process; or it is a retired lithium iron phosphate system battery, and the above treatment is used to achieve cascade utilization and regeneration of retired batteries; or it is a lithium iron phosphate system battery in use, and the above treatment is used to achieve ultrasonic-assisted stable lithium replenishment in extreme environments.

[0015] According to another aspect of the present invention, a corresponding battery lithium replenishment and positive electrode self-repairing device is also provided, the device comprising: A sealed reaction tank, which is used to place the batteries to be processed and is equipped with a temperature sensor for sensing the internal temperature; An ultrasonic processing unit, comprising a frequency-adjustable piezoelectric transducer and a power controller, and configured to perform ultrasonic cavitation treatment on the battery to be processed according to preset working parameters; A control unit is configured to acquire real-time impedance data and dynamically adjust the ultrasonic parameters of the ultrasonic processing unit accordingly.

[0016] As a further preferred embodiment of the present application, the piezoelectric transducer preferably adopts an external coupling structure to transmit ultrasonic waves, which presents a pressure plate type or a ring array type structure that is adapted to the shape of the battery and is in contact with the surface of the battery through an acoustic coupling agent.

[0017] As a further preferred embodiment of the present application, the pressure plate type structure comprises two parallel metal pressure plates, and the transducer array is embedded in the inner side of the pressure plates, and the distance between the pressure plates can be adjusted to adapt to batteries of different thicknesses; the ring array type structure is arranged in a ring shape at equal intervals, the distance between adjacent transducers is 1-5 cm, and the frequency and power of each transducer can be independently adjusted.

[0018] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages: 1. The present application re-designs the process route and reaction mechanism of lithium supplementing and positive electrode repair of the entire lithium ion battery, and accordingly realizes non-invasive process treatment at room temperature without disassembling the battery, and the repair effect is significantly improved compared with the prior art, which can realize nanoscale non-destructive repair of the positive electrode of the battery and restore the integrity of the crystal lattice. 2. The process method of the present application does not need to add expensive lithium supplementing agent, only uses conventional lithium salt electrolyte, saves material cost, and has the advantages of easy operation, closed loop processing, no secondary pollution, optimized safety and environmental protection, etc. 3. The present application further optimizes the design of key conditions such as the frequency, power density and duty cycle of ultrasonic waves, the composition and key ratio of electrolyte and catalyst in the entire process method, and optimizes the overall structure and specific setting mode of the corresponding specific device, which can ensure the smooth progress of ultrasonic cavitation and achieve satisfactory lithium supplementing agent positive self-repairing effect. 4. The process method of the present application is not only suitable for realizing gradient utilization regeneration of retired batteries, but also suitable for providing pre-lithium supplementing for new battery manufacturing links, or realizing ultrasonic assisted stable lithium supplementing in extreme environments for batteries in use, thus having a broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is the overall process flow chart of the battery lithium supplementing and positive self-repairing method based on ultrasonic cavitation effect according to the present application. DETAILED DESCRIPTION

[0020] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0021] Figure 1 is the overall process flow chart of the battery lithium supplementing and positive electrode self-repairing method based on ultrasonic cavitation effect according to the present application. The present application will be explained more specifically below with reference to Figure 1 .

[0022] Step one, battery pretreatment.

[0023] In this step, the lithium iron phosphate system battery to be treated is supplemented with fresh electrolyte with the same formula as the original battery, and the electrolyte is added with a catalyst capable of adsorbing electrons to make them stably exist. After the fresh electrolyte uniformly wets the battery electrode, the battery is charged and discharged to restore the integrity of the solid electrolyte film on the electrode surface, and the electrode is activated.

[0024] More specifically, taking a retired battery with long cycle and dry electrolyte as an example, 0.1-0.5 mL / Ah electrolyte is first supplemented, with the same formula as the original battery, and an appropriate amount of catalyst capable of adsorbing electrons to make them stably exist, such as ZIF-8 derivative, is added into the electrolyte, which is ground to D50=500 nm and dispersed in the electrolyte at a concentration of 1 mg / mL, and the catalyst is synchronously injected into the battery through the electrolyte. After vacuum sealing, it is placed at 25°C to ensure that the fresh electrolyte uniformly wets the electrode. 0.1C small current charging and discharging is performed for 1-2 times to restore the integrity of the SEI film on the electrode surface and complete the electrode activation.

[0025] Step two, ultrasonic cavitation treatment.

[0026] In this step, the pretreated battery is placed in an ultrasonic reaction tank, ultrasonic waves are applied to the entire battery, and ultrasonic cavitation treatment is performed using the electrolyte inside the battery as the reaction medium. In this process, the organic solvent of the electrolyte is dissociated to generate new free electrons under the cavitation effect and stably exists under the action of the catalyst, and the lithium salt and lithium-rich compounds are activated and release active Li + which diffuses to the positive electrode surface of the battery.

[0027] More specifically, the battery to be treated is placed in an ultrasonic reaction tank, 20-50 kHz ultrasonic waves are applied, and the power density is 0.5-3 W / cm 2for 5-30 minutes. The ultrasound cavitation process that occurs can be summarized as follows: the liquid locally forms a negative pressure zone, generating microbubbles (cavitation bubbles) that grow rapidly and collapse violently in the compression-expansion cycle of the acoustic wave. The moment of bubble collapse ( 1 μs) is accompanied by a series of reactions that generate local ultrahigh temperatures (~ 5000 K), high pressures (> 1000 atm), and high-speed microjets (~ 100 m / s).

[0028] Correspondingly, in this high-energy environment, the organic solvent dissociates. Carbonate solvents such as EC, DEC, DMC, etc. undergo C-O bond rupture to generate free radicals such as CH3, RO-CO-OR', and free electrons, and the dissociated electrons can exist stably through catalyst adsorption. At the same time, the lithium salt (such as LiPF6, LiTFSI) in the electrolyte and the lithium-rich compound (such as Li2O, Li5FeO4) are activated under the action of ultrasound cavitation, and the degree of dissociation is improved under the impact of cavitation, fully releasing active Li + . Microjet-enhanced electrolyte convection accelerates the diffusion of active Li + to the positive electrode surface.

[0029] More specifically, the ultrasonic device is configured to select a piezoelectric ceramic transducer, and the resonance frequency is set to 40 ± 2 kHz, taking into account the cavitation intensity and the penetration depth; the power density is calculated by the sound intensity formula I = P / A (A is the bottom area of the reaction tank) to be 1.5 W / cm2, and if the power is too high (> 3 W / cm2), it will cause the aluminum foil current collector to be perforated and the electrolyte to be decomposed. The ultrasonic pulse mode is selected to be intermittent ultrasound with a working time of 6 seconds and a stopping time of 4 seconds, i.e. a duty cycle of 60%, so that the cavitation bubbles can fully grow and collapse, while controlling the temperature rise to be ≤ 5 ℃ / min and reducing the accumulation of thermal effects. Continuous ultrasound will cause the local temperature of the electrolyte to be > 80 ℃, which will trigger the decomposition of DMC. The battery is placed between the ultrasonic pressure plates, the surface of the pressure plate is coated with an acoustic coupling agent such as silicone grease, and the ultrasonic treatment is performed for 10-20 minutes. If the time is too short, the reaction will not be sufficient, and if the time is too long, the electrode structure may be damaged. An infrared thermal imager is used to monitor the surface temperature of the battery in real time, and when the temperature exceeds 45 ℃, the power is automatically reduced or the treatment is paused.

[0030] Step three, lithium supplementing and positive electrode self-repairing reaction.

[0031] In this step, the new free electrons migrate to the positive electrode surface of the battery under the driving of the local electric field generated by the cavitation effect, and trigger the interface reduction reaction in situ with active Li + , thereby generating new positive electrode materials to complete the lithium supplementing of the battery, while repairing the positive electrode lattice defects and adjusting the lattice distortion to achieve nanoscale positive electrode self-repairing.

[0032] More specifically, the free electrons migrate to the positive electrode surface of the battery under the driving of the local electric field generated by the cavitation effect, and trigger the interface reduction reaction in situ: FePO4+ Li + + e- → LiFePO4, the newly generated LiFePO4 is used as a supplement to the cathode material of retired lithium-ion batteries, while repairing FePO4 lattice defects, such as Fe 3+ Vacancies adjust the lattice distortion and form a nanoscale repair layer.

[0033] This invention has thus achieved an integrated process for in-situ lithium deposition and self-repair of lithium iron phosphate cathodes in lithium-ion batteries using ultrasonic cavitation technology. Furthermore, the mechanical vibrations of the ultrasound waves during the ultrasonic cavitation process can alleviate cyclic stress in the electrode material, relieving stress and inhibiting particle pulverization, thereby increasing the battery's cycle life.

[0034] The specific principles of the above-mentioned ultrasonic cavitation and self-repair reaction are explained again below.

[0035] The cavitation effect triggers ionization. Ultrasonic waves produce periodic pressure changes in the electrolyte, forming micron-sized cavitation bubbles. The bubble radius R(t) obeys the Rayleigh-Plesset equation:

[0036] in is the internal pressure of the bubble, is the static pressure, is the surface tension, For viscosity.

[0037] When the bubble collapses, the internal temperature ( =1.4 is the gas adiabatic index). The measured local temperature reaches 4000-5000K. The high temperature and high pressure released at the moment of bubble collapse causes solvent molecules, such as EC, to break the CO bond at high temperature: EC CH2OCH2 - + CH 3 + e - The generated electrons are stably present through the adsorption of the catalyst.

[0038] The dissociation degree of battery cathode materials such as LiPF6 in the cavitation field is increased to α≈0.95, dissociating into Li + and PF6 - , Li was determined by the Bruce-Vincent method + Migration number (t + ) increased from 0.3 to 0.45. Electrons migrate to the cathode surface driven by cavitation microjets.

[0039] The electrons that migrate to the positive electrode interact with Li + Reduction reaction occurs directly at FePO4: FePO4 + Li + + e- → LiFePO4, thus completing the LFP battery anode lithium supplement, while repairing the Fe of FePO4 3+ Vacancies and lattice distortion. The microjet velocity generated by ultrasonic cavitation is about 100 m / s, which can penetrate into the electrode pores and nanoscale cracks (<100 nm), repairing the microscopic defects that cannot be reached by traditional chemical methods.

[0040] The application will be further described in detail below with specific examples, so that those skilled in the art can more clearly understand the application.

[0041] Example 1 Battery pretreatment: Select the same batch of retired LFP||Gr soft pack batteries, the nominal capacity is 2 Ah, and the capacity attenuates to about 1.5 Ah (retention rate is 75%) after 500 cycles, puncture φ=0.1 mm micropores at the corner of the battery, inject 0.75 mL of the same electrolyte selected for the battery in this batch, and select MOFs material, ZIF-8 derivative, as the catalyst, grind to D50=500 nm and disperse in the electrolyte with a concentration of 1 mg / mL, i.e. 7.5 mg. After vacuum sealing, stand for 30 minutes at 25°C, and wait for the electrolyte to be completely soaked.

[0042] Ultrasonic cavitation treatment: ultrasonic equipment selects piezoelectric ceramic transducer, randomly divides the batteries into three groups and labels them as Example 1-1, Example 1-2, and Example 1-3 for treatment. The ultrasonic frequencies of the three groups of batteries are set to 20 kHz, 40 kHz, and 60 kHz respectively, the fixed power density is 1.5 W / cm², the pulse mode is working for 6 seconds and stopping for 4 seconds, and the battery is treated in a 45°C constant temperature water bath for 20 minutes.

[0043] Repair effect verification: the three groups of batteries treated by ultrasonic are tested on the battery test system (Xinwei BTS4000) for complete charge and discharge cycles: 0.5C constant current charge and discharge, voltage range 2.5-3.65 V, stand for 10 hours to stabilize the SEI film formation. Discharge at 0.5C constant current to the cut-off voltage (2.5 V), record the released capacity C after treatment, capacity recovery rate=(C after treatment / C initial) x 100%, used to quantify the recovery degree of battery capacity after ultrasonic treatment.

[0044] Example 2 Battery pretreatment: Select the same batch of LFP||Gr soft pack batteries without cycling, design capacity 5.0 Ah, electrolyte is 1M LiPF6 in EC:EMC(3:7) + 0.5% FEC, and 3 wt% N-CNTs (D50=80 nm) are added as catalyst, vacuum sealing, stand for 30 minutes at 25°C, and wait for the electrolyte to be completely soaked.

[0045] Ultrasonic cavitation treatment: The batteries were placed in the ultrasonic reaction device tank, the ultrasonic frequency was set to 50 kHz, the power density was 2.0 W / cm2, the pulse mode was 6 seconds of work / 4 seconds of stop, and the battery was treated by ultrasonic at 45 °C constant temperature water bath for 20 minutes.

[0046] Repair effect verification: The batteries treated by ultrasonic were tested by complete charge-discharge cycle test on the battery test system (Xinwei BTS4000): the voltage range was 2.8-3.65V, the first charge-discharge rate was 0.1C, and the SEI film was formed by standing for 10 hours to stabilize. The cycle life test was carried out at 1C rate, constant current constant voltage charging to 3.65V, standing for 10 minutes, 1C constant current discharging to 2.8V, standing for 10 minutes, and cycle test for 500 cycles. The first coulombic efficiency, 1C cycle capacity retention rate for 500 times, and cycle charge transfer impedance for 100 cycles of the test battery were tested.

[0047] Comparative Example 1 The same batch of retired LFP||Gr pouch batteries were selected, the nominal capacity was 2Ah, the capacity decayed to about 1.5Ah (retention rate was 75%) after 500 cycles, the electrolyte was 1M LiPF6in EC:EMC(3:7) + 0.5% FEC. No ultrasonic treatment was done. The battery was subjected to complete charge-discharge cycle, and the capacity retention rate was calculated by recording the released capacity. Comparative Example 2 The same batch of uncycled LFP||Gr pouch batteries were selected, the designed capacity was 5.0Ah, the electrolyte was 1M LiPF6in EC:EMC(3:7) + 0.5% FEC, and 3wt% N-CNTs (D50=80 nm) were incorporated as catalyst. After vacuum sealing, the electrolyte was completely soaked at 25°C for 30 minutes. No ultrasonic treatment was done. The battery was subjected to complete charge-discharge cycle test on the battery test system (Xinwei BTS4000): the voltage range was 2.8-3.65V, the first charge-discharge rate was 0.1C, and the SEI film was formed by standing for 10 hours to stabilize. The cycle life test was carried out at 1C rate, constant current constant voltage charging to 3.65V, standing for 10 minutes, 1C constant current discharging to 2.8V, standing for 10 minutes, and cycle test for 500 cycles. The first coulombic efficiency, 1C cycle capacity retention rate for 500 times, and cycle charge transfer impedance for 100 cycles of the test battery were tested.

[0048] The treated capacity, capacity recovery rate, and charge transfer impedance of the three groups of batteries in Example 1 and the battery in Comparative Example 1 were summarized in Table 1, as shown in the following table.

[0049]

[0050] Table 1 From Table 1, it can be seen that after the retired LFP battery is subjected to ultrasonic cavitation treatment, compared with the battery without ultrasonic cavitation treatment, the battery capacity is increased, the Li content is increased, and the battery impedance is reduced. The lithium supplement efficiency and repair effect are optimal at a frequency of 40 kHz. At a high frequency (60 kHz), the penetration is insufficient due to the collapse of the cavitation bubble with too small size and the dispersion of energy. At a low frequency (20 kHz), the cavitation bubble has a large diameter, and the energy is concentrated when the cavitation bubble collapses, which is easy to damage the electrode. It can be inferred that the optimal balance point of the ultrasonic frequency in the ultrasonic cavitation treatment process is 40-50 kHz, which takes into account the lithium supplement efficiency and the safety of the electrode structure.

[0051] The first coulomb efficiency, 1C cycle capacity retention rate after 500 cycles, and charge transfer impedance after 100 cycles of the battery in Example 2 and the battery in Comparative Example 2 are summarized in Table 2, as shown in the following table.

[0052]

[0053] Table 2 From Table 2, it can be seen that after the retired LFP battery is subjected to ultrasonic cavitation treatment, compared with the battery without ultrasonic cavitation treatment, the battery capacity is increased, the Li content is increased, and the battery impedance is reduced. The lithium supplement efficiency and repair effect are optimal at a frequency of 40 kHz. At a high frequency (60 kHz), the penetration is insufficient due to the collapse of the cavitation bubble with too small size and the dispersion of energy. At a low frequency (20 kHz), the cavitation bubble has a large diameter, and the energy is concentrated when the cavitation bubble collapses, which is easy to damage the electrode. It can be inferred that the optimal balance point of the ultrasonic frequency in the ultrasonic cavitation treatment process is 40-50 kHz, which takes into account the lithium supplement efficiency and the safety of the electrode structure.

[0054] In summary, compared with the prior art, the positive electrode self-repairing scheme of the battery lithium supplement agent according to the present application has a simplified process route and is easy to operate. The ultrasonic cavitation technology can realize non-invasive treatment and normal temperature operation without the need for additional addition of expensive lithium supplement agents to achieve in-situ deposition of lithium supplement and self-repairing of lithium iron phosphate positive electrode. The scheme has the advantages of easy operation, low cost, no secondary pollution, optimized safety and environmental protection, and thus has good practical value and application prospect.

[0055] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A battery lithium replenishment and positive electrode self-repair method based on ultrasonic cavitation effect, characterized in that: The method comprises the following steps: Step 1: Battery pretreatment The lithium iron phosphate battery to be treated is supplemented with a fresh electrolyte with the same formula as the original battery, and a catalyst that can absorb electrons and stabilize the electrolyte is added to the electrolyte; after the fresh electrolyte is allowed to evenly infiltrate the battery electrodes, the battery is charged and discharged to restore the integrity of the solid electrolyte membrane on the electrode surface and achieve electrode activation; Step 2: Ultrasonic cavitation treatment The pretreated battery is placed in an ultrasonic reaction tank, ultrasonic waves are applied to the entire battery, and ultrasonic cavitation treatment is performed using the electrolyte inside the battery as a reaction medium; In this process, the organic solvent of the electrolyte dissociates under the cavitation effect to generate new free electrons and exists stably under the action of the catalyst, and the lithium salt and lithium-rich compound are activated and release active Li + And diffuse to the surface of the battery positive electrode; Step 3: Lithium replenishment and positive electrode self-repair reaction The new free electrons migrate to the surface of the battery positive electrode under the driving force of the local electric field generated by the cavitation effect, and in situ react with the active Li + Triggering the interfacial reduction reaction, new positive electrode materials are generated to complete the battery lithium replenishment, while repairing the positive electrode lattice defects and adjusting the lattice distortion to achieve nanoscale positive electrode self-repair.

2. The method according to claim 1, wherein In step 1, the lithium salt and lithium-rich compound of the fresh electrolyte are preferably at least one of LiPF6, LiFSI, LiTFSI or LiClO4, and the concentration thereof is 0.5M to 2M; the organic solvent of the fresh electrolyte is preferably at least two of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene glycol dimethyl ether (DME), and tetrahydrofuran (THF); in addition, the fresh electrolyte preferably further comprises an additive, which is at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and lithium bis(oxalatoborate) (LiBOB), and the addition amount thereof is preferably 0.1wt% to 2wt%.

3. The method according to claim 1 or 2, wherein: In step one, the catalyst is preferably a nitrogen-doped carbon material such as nitrogen-doped carbon nanotubes (N-CNTs) and mesoporous carbon spheres (CMK-3); or a metal organic framework derivative such as ZIF-8-derived nitrogen-doped carbon and MIL-101(Cr)-loaded single-atom iron (Fe-SA@MIL); or a wide-bandgap metal oxide such as MgO nanosheets and Al2O3-coated LiFePO4; in addition, the added amount of the catalyst is preferably set to 0.1% to 5% of the battery positive electrode active material by mass.

4. The method according to any one of claims 1 to 3, wherein: In step 1, the battery to be treated is preferably a lithium iron phosphate system battery whose positive electrode material is LiFePO4.

5. The method according to any one of claims 1 to 4, wherein: In step 2, the ultrasonic working parameters are set as follows: frequency is 20kHz to 100kHz, more preferably 40kHz to 60kHz; power density is 0.5W / cm 2 ~3W / cm 2 , more preferably 1W / cm 2 ~2W / cm 2 .

6. The method according to any one of claims 1 to 5, wherein in step 2, the ultrasonic wave preferably adopts a pulse mode, and its duty cycle is preferably set to 30% to 80%.

7. The method according to any one of claims 1 to 6, wherein in step 2, the temperature in the ultrasonic reaction tank is preferably controlled to be 25°C to 60°C, and is achieved by any one of the following methods: constant temperature water bath circulation, or a built-in thermoelectric cooling module in the ultrasonic reaction tank.

8. According to the method described in any one of claims 1 to 7, the battery to be treated is preferably a new lithium iron phosphate system battery, and the above treatment is used to achieve pre-lithium replenishment in the battery manufacturing process; or it is a retired lithium iron phosphate system battery, and the above treatment is used to achieve cascade utilization and regeneration of the retired battery; or it is a lithium iron phosphate system battery in use, and the above treatment is used to achieve ultrasound-assisted stable lithium replenishment in extreme environments.

9. A battery lithium replenishment and positive electrode self-repairing device for executing the method according to any one of claims 1 to 8, characterized in that: The device includes: A sealed reaction tank, which is used to place the batteries to be processed and is equipped with a temperature sensor for sensing the internal temperature; An ultrasonic processing unit, comprising a frequency-adjustable piezoelectric transducer and a power controller, and configured to perform ultrasonic cavitation treatment on the battery to be processed according to preset working parameters; A control unit is used to obtain real-time impedance data and dynamically adjust the ultrasonic parameters of the ultrasonic processing unit accordingly.

10. The device according to claim 9, wherein The piezoelectric transducer preferably adopts an external coupling structure to transmit ultrasonic waves. It has a pressure plate or annular array structure that is compatible with the battery shape and contacts the battery surface through an acoustic coupling agent. The pressure plate structure includes two parallel metal pressure plates, and a transducer array is embedded on the inner side of the pressure plates. The spacing between the pressure plates is adjustable to accommodate batteries of different thicknesses. The annular array structure is arranged in a circular pattern with equal spacing, and the spacing between adjacent transducers is 1 cm to 5 cm. The frequency and power of each transducer can be adjusted independently.

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