A method for restoring the health status of lithium battery electrodes using helium-4 superfluid

Abstract

The present invention aims to provide a method for restoring the health state of lithium battery electrodes by using helium-4 superfluid to assist, so as to achieve efficient, safe and environmentally friendly SOH effective recovery of lithium-ion battery electrodes in an ultra-low temperature helium-4 superfluid environment, thereby improving the battery recycling efficiency and extending the battery life. The method of the present invention comprises the following steps: S1, pre-operation preparation; S2, battery pack disassembly and electrode pretreatment; S3, lithium battery electrodes are moved into a superfluid electrode processing chamber; S4, helium-4 superfluid acts on lithium battery electrodes; S5, lithium battery electrode post-treatment. The present invention can be applied to the field of battery quality management technology.

Description

Technical Field

[0001] The present invention relates to the technical field of battery quality management, and in particular to a method for utilizing helium-4 superfluid to assist in restoring the health status of lithium battery electrodes. Background Art

[0002] With the development of new energy technologies, especially the rapid rise of the electric vehicle industry, lithium-ion batteries have become increasingly prominent as mainstream energy storage devices. However, during the service life of the battery, the performance degradation of the electrode materials (such as the positive electrode and the negative electrode) leads to the attenuation of the battery capacity and the increase of the internal resistance, that is, the decrease of SOH (State of Health), which seriously affects the overall performance and service life of the battery. Specifically, during the multiple charge and discharge cycles of the battery, the electrode active material will undergo repeated lithium insertion and extraction processes, resulting in volume changes. The binder is the main component to maintain the electrode structure, and its main function is to connect the electrode active material, the conductive agent and the current collector to form a complete conductive network. This not only ensures that the electrode sheet has good mechanical properties and processability, but also meets the needs of actual production. Commonly used polymer binders have good flexibility and high peel strength at room temperature, which can effectively maintain the stability and integrity of the electrode structure. These volume changes will cause stress to the electrode structure, causing the binder to gradually lose its original flexibility and strength. When the temperature drops below the glass transition temperature (Tg) of the binder, the binder will change from a flexible rubber state to a hard and brittle glass state. This glass transition causes a significant decrease in the elasticity of the electrode, making it difficult to buffer the volume change of the active material during lithium insertion and extraction. As a result, the mechanical strength of the electrode decreases, making it more prone to cracks, destroying the conductive network of the electrode, and thus affecting the overall performance of the battery.

[0003] Existing electrode repair or regeneration technologies mostly focus on heat treatment, chemical treatment, electrochemical regeneration and other means. However, existing electrode repair or regeneration technologies generally have the following technical problems:

[0004] 1. Although existing methods such as heat treatment, chemical treatment, and electrochemical regeneration can improve electrode performance to a certain extent, it is often difficult to achieve deep structural repair or optimization, resulting in limited electrode SOH recovery. These existing methods may not be able to completely eliminate problems such as microcracks inside the electrode material, poor contact between particles, and SEI film aging, and the treatment process may cause new side reactions or structural damage, further limiting the recovery effect.

[0005] 2. In addition, the existing electrode repair technology process is complicated and requires precise control of multiple processing parameters, which increases the difficulty of operation and process cost. In addition, the use of some chemical reagents or special equipment may lead to higher economic investment and environmental burden, which is not conducive to large-scale commercial application.

[0006] 3. Some electrode repair technologies involve the use of harmful chemicals or produce harmful by-products, which do not meet the requirements of green manufacturing and sustainable development. In addition, wastewater and waste gas that may be generated during the treatment process will have a negative impact on the environment if not properly handled.

[0007] In recent years, ultra-low temperature technology and helium-4 superfluid have attracted the attention of researchers due to their unique physical properties. As early as 1995, Yamada et al. found through low-temperature XRD testing that the spinel-structured LiMn2O4 cathode material underwent partial first-order Jahn-Teller distortion when cooled to 283.5 K, transforming from cubic phase (Fd-3m) to tetragonal phase (I41 / amd), and completely transformed into orthorhombic phase (Fd3d) at 250 K. Later, Piszora et al. further confirmed this through synchrotron radiation testing. The potential of ultra-low temperature technology and helium-4 superfluid in exploring new battery electrode repair strategies has also been valued by researchers. Research on the thermodynamic state of cathode materials at low temperatures is mainly divided into two aspects: one is whether low temperature causes changes in the material structure, and the other is whether low temperature causes changes in its lithium insertion and extraction process. Among them, superfluids, especially helium-4 superfluids, exhibit zero viscosity, no turbulent dissipation, superconductivity and other characteristics at extremely low temperatures (such as below the lambda point, about 2.17 K, usually called lambda phase transition). And it can flow through ceramic materials with zero resistance. These characteristics provide new possibilities for microstructural reforming, defect repair, and interface optimization of electrode materials. Studies have shown that treatment in a helium-4 superfluid environment may help improve the ion diffusion path of electrode materials, reduce interface impedance, and even eliminate certain structural defects, thereby achieving effective recovery of electrode SOH.

[0008] Although helium-4 superfluid has been widely used in basic scientific research and some high-end applications (such as dilution refrigeration, quantum computing, etc.), its application in electrode repair, especially in the field of SOH recovery of lithium-ion battery electrodes, is still in its infancy. How to safely and accurately deliver electrode samples to the ultra-low temperature target area and effectively contact with the helium-4 superfluid, how to transport, fix, monitor samples in low-temperature environments, and how to design the interaction mode with the helium-4 superfluid, etc., all have technical difficulties. At the same time, there is also a lack of mature and reliable experimental equipment support. At present, there is a lack of dedicated experimental equipment for helium-4 superfluid processing electrode SOH recovery technology on the market or in literature reports. Existing devices may not meet the requirements of stable low-temperature operation, integrated electrode processing and performance testing, and convenient operation, which limits the research progress and practical application of helium-4 superfluid technology in the field of electrode repair.

[0009] Therefore, designing a special experimental device that can stably operate on a low-temperature platform manufactured by a dilution refrigerator and adapt to the needs of electrode processing is crucial to the practical application of helium-4 superfluid processing technology for electrode SOH recovery. Summary of the invention

[0010] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for using helium-4 superfluid to assist in the recovery of the healthy state of lithium battery electrodes, so as to achieve efficient, safe and environmentally friendly SOH effective recovery of lithium-ion battery electrodes in an ultra-low temperature helium-4 superfluid environment, thereby improving the battery recycling efficiency and extending the battery life.

[0011] The technical solution adopted by the present invention is a method for using helium-4 superfluid to assist in restoring the health status of lithium battery electrodes. In the method, the helium-4 superfluid state is maintained in a dilution refrigerator, the dilution refrigerator is connected to a superfluid electrode processing chamber, the dilution refrigerator and the superfluid electrode processing chamber are both arranged in a vacuum chamber, the lithium battery electrode is placed in the superfluid electrode processing chamber, the temperature in the superfluid electrode processing chamber is stabilized at a set value by a temperature control system, the internal pressure of the vacuum chamber is monitored and adjusted by a vacuum system arranged outside the vacuum chamber, ensuring that the helium-4 is in a stable state of superfluid, a circulation pump group and a liquid nitrogen cold trap are also arranged outside the vacuum chamber, the dilution refrigerator, the superfluid electrode processing chamber, the circulation pump group and the liquid nitrogen cold trap are sequentially connected to form a low-temperature circulation loop, a mixture of helium-3 and helium-4 is pre-injected into the low-temperature circulation loop, and the helium-4 superfluid flows between the dilution refrigerator and the superfluid electrode processing chamber,

[0012] The method comprises the following steps:

[0013] S1. Preparation before operation: The operator wears protective equipment to ensure the safety of the operator and the environment, starts the dilution refrigerator, and starts the mixed dilution process of helium-3 and helium-4, and finally makes the temperature of the superfluid electrode processing chamber reach and stabilize at the target low temperature;

[0014] S2. Battery pack disassembly and electrode pretreatment: Use battery disassembly tools to separate the electrode group, and clean and dry the lithium battery electrodes that need to be restored;

[0015] S3, moving the lithium battery electrode into the superfluid electrode processing chamber: moving the processed lithium battery electrode into the superfluid electrode processing chamber and completely immersing the lithium battery electrode in the helium-4 superfluid;

[0016] S4, Helium-4 superfluid acts on lithium battery electrodes: Helium-4 superfluid enters the lithium battery electrodes to act, and the whole process is monitored;

[0017] S5. Post-processing of lithium battery electrodes: After the processing is completed in step S4, the processed lithium battery electrodes are moved out of the superfluid electrode processing chamber into a low-temperature environment, and the temperature is slowly increased until it reaches room temperature, thereby completing the recovery of the health status of the lithium battery electrodes.

[0018] In step S1, the dilution refrigerator is precooled. After the precooling is completed, the dilution refrigerator is started, a mixture of helium-3 and helium-4 is injected, a dilution cycle is started, and a mixed dilution process of helium-3 and helium-4 begins. The entropy of the mixture is gradually reduced by controlling the ratio of helium-3 and helium-4 in the mixer and the mixing rate, and the temperature of the superfluid electrode processing chamber is continuously monitored to ensure that it reaches and stabilizes at a target low temperature.

[0019] In step S4, when the helium-4 superfluid acts on the lithium battery electrode, the temperature is set to be within 10 millikelvin and the time is 10 minutes to 5 hours.

[0020] An electrode transfer device is also provided outside the vacuum chamber for moving lithium battery electrode samples into or out of the superfluid electrode processing chamber in a low-temperature environment. The electrode transfer device includes a low-temperature glove box and a low-temperature guide rail. A sample delivery window is provided on the vacuum chamber. The sample delivery window is equipped with a closed door. The low-temperature glove box is connected to the sample delivery window. The low-temperature guide rail extends from the low-temperature glove box through the sample delivery window into the vacuum chamber.

[0021] The superfluid electrode processing chamber is made of low-temperature material, and the outer surface of the superfluid electrode processing chamber is coated with several layers of heat radiation shielding layers. The interior of the superfluid electrode processing chamber is designed to be a space adapted to the shape and size of the lithium battery electrode, and a low-temperature resistant observation window is arranged on the wall of the superfluid electrode processing chamber.

[0022] The temperature control system includes a temperature controller and a plurality of low-temperature temperature sensors arranged at various links of the low-temperature circulation loop. The plurality of low-temperature temperature sensors are connected to the temperature controller via electrical signals, and the temperature controller is communicatively connected to a peripheral control console.

[0023] The vacuum system includes a mechanical pump, a first solenoid valve, a second solenoid valve, a molecular pump and a gate valve connected in sequence. The gate valve is connected to the interior of the vacuum chamber. Two branches are connected between the first solenoid valve and the second solenoid valve, one of which is connected to the vacuum chamber through a bypass valve, and the other is connected to the electrode transfer device through a sample valve.

[0024] The superfluid electrode processing chamber is made of copper, stainless steel or oxygen-free copper, and the low-temperature resistant observation window is made of a sapphire sheet or a quartz sheet.

[0025] The beneficial effects of the present invention are as follows: the present invention can ensure that the electrode is safely and accurately delivered to the target area under ultra-low temperature environment and fully and evenly contacts with the helium-4 superfluid. This design solves the difficulty of the interaction technology between the electrode and the helium-4 superfluid in the prior art, and lays a foundation for realizing the effective treatment of the electrode by the helium-4 superfluid. The present invention can not only stably operate on the low-temperature platform of the dilution refrigerator, but also integrate the electrode pretreatment and sample delivery functions, and is easy to operate and compact in structure, which greatly promotes the research progress and practical application transformation of the helium-4 superfluid technology in the field of electrode repair. In the present invention, in order to restore the healthy state of the electrode, the electrode sample is fully immersed in the ultra-low temperature helium-4 superfluid. The helium-4 in the superfluid state has zero viscosity and extremely high thermal conductivity, and can easily penetrate the tiny pores and cracks of the electrode material. Specifically, it is divided into two processes:

[0026] Phase transition process: The low temperature environment of superfluid helium-4 will cause the cathode material (such as lithium-based cathode materials such as LiMn2O4) to undergo a phase transition process and restore its initial stable structure. For example, LiMn2O4 may transform from the orthorhombic phase at low temperature to the cubic phase and restore its original crystal structure;

[0027] Binder recovery: Superfluid helium-4 will rearrange the binder phase in the battery electrode, restoring it from a hard and brittle glass state to a more flexible state. This process helps restore the binder's elasticity and enhances its ability to connect the electrode active material, conductive agent and current collector;

[0028] Through the treatment of superfluid helium-4, the conductive network of the electrode was repaired, which was manifested as follows:

[0029] Reconnection of the conductive network: The permeation of superfluid helium-4 can reconnect the conductive network that was broken during multiple charge-discharge cycles, restoring the conductive properties of the electrode;

[0030] Improvement of mechanical properties: The restored binder can better buffer the volume change of the active material during the lithium insertion and extraction process, reduce the generation of cracks, and improve the mechanical strength of the electrode;

[0031] Finally, after being treated with ultra-low temperature helium-4 superfluid, the health of the electrode was significantly restored. The electrochemical performance (such as capacity, rate performance and cycle stability) was significantly improved, extending the service life of the battery. This process not only restored the mechanical properties of the electrode, but also improved its conductive network, ensuring the stability and reliability of the battery in multiple charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a simplified structural diagram of the dilution refrigerator and the peripheral structure of the present invention;

[0033] Figure 2 It is a simplified flow chart of the method of the present invention;

[0034] Figure 3 These are the non-in-situ XRD test results of 0.3 lithium-intercalated LiMn2O4 at different temperatures;

[0035] Figure 4 It is the morphology of lithium battery electrodes at different cycle periods;

[0036] Figure 5 These are the battery 1 / 3C rate discharge capacity-voltage curves of three samples (E1, E2, E3) after being treated at different temperatures. DETAILED DESCRIPTION

[0037] like Figures 1 to 5 As shown, in the present invention, the helium-4 superfluid state is maintained in the dilution refrigerator 1. The dilution refrigerator 1 comprises a mixing chamber 22 (mK zone), a silver powder sintering heat exchanger 23, a continuous heat exchanger 24, a distillation chamber 25, a 4K cold plate 26, a 50K cold plate 27 and a pulse tube cold head 28 which are arranged in sequence from one side of the superfluid electrode processing chamber 3. The circulation pump group 7 is connected to the superfluid electrode processing chamber 3, and a low-temperature circulation loop is formed from the liquid nitrogen cold trap 8 → the pulse tube cold head 28 → the 50K cold plate 27 → the 4K cold plate 26 → the distillation chamber 25 → the continuous heat exchanger 24 → the silver powder sintering heat exchanger 23 → the mixing chamber 22 (mK zone) → the superfluid electrode processing chamber 3 → the circulation pump group 7 → the liquid nitrogen cold trap 8. The superfluid electrode processing chamber 3 is also connected with a charging valve 29. The dilution refrigerator is used as a core low-temperature generating device to provide an ultra-low temperature environment for liquid helium-4 to reach a superfluid transition temperature (about 2.17K) or below. The dilution refrigerator 1 is connected to a superfluid electrode processing chamber 3. The dilution refrigerator 1 and the superfluid electrode processing chamber 3 are both arranged in a vacuum chamber 2. The lithium battery electrode is placed in the superfluid electrode processing chamber 3. The temperature in the superfluid electrode processing chamber 3 is stabilized at a set value by a temperature control system 5. The internal pressure of the vacuum chamber 2 is monitored and adjusted by a vacuum system 6 arranged outside the vacuum chamber 2 to ensure that helium-4 is in a stable state of superfluid. A circulation pump group 7 and a liquid nitrogen cold trap 8 are also arranged outside the vacuum chamber 2. The dilution refrigerator 1, the superfluid electrode processing chamber 3, the circulation pump group 7 and the liquid nitrogen cold trap 8 are sequentially connected to form a low-temperature circulation loop. A mixture of helium-3 and helium-4 is pre-injected into the low-temperature circulation loop, and the helium-4 superfluid flows between the dilution refrigerator 1 and the superfluid electrode processing chamber 3. The dilution refrigerator 1 provides a continuous ultra-low temperature environment for the superfluid electrode processing chamber 3.

[0038] An electrode transfer device 4 for moving lithium battery electrode samples into or out of the superfluid electrode processing chamber 3 in a low-temperature environment is also provided outside the vacuum chamber 2. The electrode transfer device 4 includes a low-temperature glove box 9 and a low-temperature guide rail 10. A sample delivery window 11 is provided on the vacuum chamber 2. The sample delivery window 11 is equipped with a closed door. The low-temperature glove box 9 is connected to the sample delivery window 11. The low-temperature guide rail 10 extends from the low-temperature glove box 9 through the sample delivery window 11 to the vacuum chamber 2.

[0039] The superfluid electrode processing chamber 3 is made of low-temperature material, and the outer surface of the superfluid electrode processing chamber 3 is coated with several layers of heat radiation shielding layers. The interior of the superfluid electrode processing chamber 3 is designed to be a space adapted to the shape and size of the lithium battery electrode, and a low-temperature resistant observation window 12 is arranged on the wall of the superfluid electrode processing chamber 3.

[0040] The temperature control system 5 includes a temperature controller 13 and a plurality of low-temperature temperature sensors 14 arranged at various links of the low-temperature circulation loop. The plurality of low-temperature temperature sensors 14 are electrically connected to the temperature controller 13, and the temperature controller 13 is communicatively connected to an external control console.

[0041] The vacuum system 6 includes a mechanical pump 15, a first solenoid valve 16, a second solenoid valve 17, a molecular pump 18 and a gate valve 19 connected in sequence. The gate valve 19 is connected to the interior of the vacuum chamber 2. Two branches are also connected between the first solenoid valve 16 and the second solenoid valve 17, one of which is connected to the vacuum chamber 2 through a bypass valve 20, and the other is connected to the electrode transfer device 4 through a sample valve 21.

[0042] The superfluid electrode processing chamber 3 is made of copper, stainless steel or oxygen-free copper, and the low-temperature resistant observation window 12 is made of sapphire or quartz to facilitate observation of the state of the electrode in the helium-4 superfluid.

[0043] The present invention provides a method for restoring the health status of a lithium battery electrode by using a helium-4 superfluid, comprising the following steps:

[0044] S1. Preparation before operation: The operator wears protective equipment to ensure the safety of the operator and the environment, starts the dilution refrigerator, and starts the mixed dilution process of helium-3 and helium-4, and finally makes the temperature of the superfluid electrode processing chamber 3 reach and stabilize at the target low temperature. Specifically,

[0045] (1) Safety protection:

[0046] Personal protective equipment: Wear protective clothing, chemical-resistant gloves, safety glasses, masks, etc. to ensure the safety of operators.

[0047] Laboratory safety: Ensure that the laboratory is well ventilated, equipped with necessary firefighting equipment, and understand emergency response procedures.

[0048] (2) Dilution refrigerator startup steps:

[0049] A "dilution refrigerator" is a device that uses superfluid helium-4 to dilute helium-3 to achieve extremely low temperature refrigeration. This refrigerator is mainly used in scientific research, especially in experiments that need to reach and maintain ultra-low temperature environments (far below the boiling point of liquid helium, even close to absolute zero). Here are the steps to start a dilution refrigerator:

[0050] Preliminary preparation:

[0051] Safety check: Confirm that all electrical connections are correct and secure, there are no leaks in the pipes, there is no debris around the equipment, and ensure that the work area meets laboratory safety regulations.

[0052] System inspection: Check that all parts of the refrigerator (such as mixer, heat exchanger, distiller, liquid pool condenser, pre-cooling system, etc.) are in good condition, valves are in the correct position, and the interior is clean and free of pollution.

[0053] Precooling stage:

[0054] Liquid nitrogen precooling: Precool the primary cooling section of the refrigerator with liquid nitrogen to reduce the initial temperature of the system.

[0055] Liquid helium precooling: Liquid helium is further used to deeply precool key components, usually including distillers and heat exchangers.

[0056] Boot sequence:

[0057] Turn on the power: Turn on the main power of the dilution refrigerator and start the control system.

[0058] To start a precooling cycle:

[0059] Start the liquid helium circulation pump: ensure that the liquid helium can flow along the designed path and continuously cool the key parts.

[0060] Monitor temperature: Use temperature sensors to monitor the temperature drop at key points of the system to ensure pre-cooling effect.

[0061] To start a dilution cycle:

[0062] Injection of Helium-3 and Helium-4 mixture: After reaching the appropriate pre-cooling temperature, a mixture of Helium-3 and Helium-4 is precisely injected into the system.

[0063] Start the dilution unit: Start the mixer and related control valves to start the mixing and dilution process of helium-3 and helium-4. Here, helium-3 and helium-4 are pre-injected into the cryogenic circulation loop. In fact, the dilution refrigerator uses two isotopes of helium, namely helium-3 and helium-4. Helium-4 will become a superfluid at low temperatures, while helium-3 will remain a normal liquid under the same conditions. By dissolving helium-3 into the superfluid phase of helium-4, a highly ordered mixture can be formed. As the solubility of helium-3 in helium-4 increases, the system will release heat, thereby reducing the temperature. During the dilution process, helium-3 migrates from the high temperature area to the low temperature area, taking away heat, thereby further reducing the temperature of the system. In simple terms, the two substances are mixed together. They will continue to circulate between different temperature areas in the cryogenic circulation loop to maintain a continuous cooling effect.

[0064] Adjusting the dilution ratio: By precisely controlling the ratio of helium-3 and helium-4 in the mixer and the mixing rate, the entropy of the mixture is gradually reduced, thereby achieving refrigeration.

[0065] Monitor the temperature of the cryogenic zone: Continuously monitor the temperature of the final cryogenic platform (i.e., the superfluid electrode processing chamber) to ensure that it reaches and stabilizes at the target low temperature.

[0066] (3) Operation adjustment and monitoring:

[0067] Optimize operating parameters: According to the actual temperature curve and experimental requirements, fine-tune the dilution ratio, mixing rate, pressure and other parameters to optimize the cooling efficiency and stability.

[0068] Monitor system status: Continuously monitor the pressure, flow, liquid level and other parameters of each part to ensure the normal operation of the system and handle abnormal situations in time.

[0069] Record data: Record key parameters during the startup process and stable operation to provide a basis for subsequent operations and fault diagnosis.

[0070] (4) Closure and recovery:

[0071] Stop the dilution cycle: Follow the instructions in the equipment manual to shut down the dilution unit in an orderly manner and stop the mixing of helium-3 and helium-4.

[0072] Return to the pre-cooling state: Keep the liquid helium circulating and gradually increase the system temperature to the stable temperature of the pre-cooling stage.

[0073] Shut down the precooling cycle: According to the operating procedures of the precooling equipment, shut down the supply of liquid helium and liquid nitrogen, and stop the precooling circulation pump.

[0074] Disconnect power: After all cooling processes are completed, disconnect the main power supply of the dilution refrigerator.

[0075] S2. Disassembly of battery pack and pretreatment of electrodes: Use battery disassembly tools to separate the electrode group, and clean and dry the lithium battery electrodes that need to be restored.

[0076] Battery discharge: Use professional equipment to fully discharge the battery pack to a safe voltage level (generally less than 3V) to eliminate potential charge risks.

[0077] •Protective measures: Operate on an explosion-proof box or fire blanket to prevent accidents such as battery short circuit and thermal runaway.

[0078] •Battery disassembly: Use a dedicated battery disassembly tool to open the battery pack casing to avoid damaging the internal structure.

[0079] •Electrode extraction: Carefully separate the electrode group (positive electrode, negative electrode and separator), identify the lithium electrode with low SOH, and minimize physical damage to the electrode material.

[0080] •Electrode cleaning: Use a suitable solvent (e.g., deionized water, organic solvents, such as acetone) to gently clean the lithium electrode to remove surface impurities and electrolyte residues.

[0081] •Electrode drying: Dry the lithium electrode under inert gas protection or in a vacuum oven to ensure that it is free of moisture.

[0082] •Electrode packaging: The pre-treated lithium electrode is placed in a special sample box or sample bag to ensure that it remains clean and easy to transfer during subsequent operations.

[0083] S3, moving the lithium battery electrode into the superfluid electrode processing chamber: moving the processed lithium battery electrode into the superfluid electrode processing chamber 3 and completely immersing the lithium battery electrode in the helium-4 superfluid. Specifically,

[0084] •Cryogenic transfer equipment: Use dedicated cryogenic glove boxes, cryogenic rails or Dewar flasks and other equipment to safely control the packaged lithium electrode samples in an ultra-low temperature environment.

[0085] •Pre-transfer pressure reduction: Use the first-level solenoid valve of the vacuum system to connect the vacuum pump to reduce the air pressure of the electrode transfer device to a low vacuum state in advance.

[0086] • Chamber loading: In an ultra-low temperature environment, open the sample delivery window to connect the cryogenic rail to the superfluid-electrode processing chamber. After the pressure and temperature are balanced and stabilized. Use a clamp to place the lithium electrode sample into the superfluid-electrode processing chamber and fix the position to ensure uniform cooling. Monitor whether the helium-4 in the final cryogenic platform (i.e., the superfluid electrode processing chamber) is the physical phase of helium-4 superfluid and ensure that the electrode sample is fully immersed in the helium-4 superfluid.

[0087] S4, Helium-4 superfluid acts on lithium battery electrodes: Helium-4 superfluid enters lithium battery electrodes to act, and the whole process is monitored. Specifically,

[0088] • Set temperature: Set the temperature of the processing chamber according to the experimental requirements, which may need to reach extremely low temperatures (such as within 10 millikelvin).

[0089] • Treatment time: The time the electrode stays at ultra-low temperature is set according to the experimental protocol, which may vary from a few minutes to several hours.

[0090] • Monitoring and recording: During the entire processing process, the chamber temperature, pressure and other parameters are continuously monitored and the experimental data are recorded.

[0091] S5, lithium battery electrode post-processing: After the processing is completed according to step S4, the processed lithium battery electrode is moved out of the superfluid electrode processing chamber 3 to a low temperature environment, and the temperature is slowly increased until it reaches room temperature, thereby completing the recovery of the health status of the lithium battery electrode. Specifically,

[0092] •Temperature transfer: After processing, use the low-temperature transfer equipment in the reverse order to safely move the lithium electrode sample out of the ultra-low temperature environment.

[0093] •Reheating: Reheat slowly under appropriate conditions to avoid excessive temperature gradients that may cause sample damage or stress.

[0094] Subsequent characterization and analysis:

[0095] The performance of the treated lithium battery electrodes was tested.

[0096] Physical characterization: Use SEM, TEM, XRD, EDS and other equipment to analyze the micromorphology, crystal structure, element distribution and other aspects of the treated lithium electrode.

[0097] In the present invention, the helium-4 superfluid completely immerses the lithium battery electrode and the helium-4 superfluid flows. When helium atoms pass through the positive electrode material (such as lithium-based positive electrode materials such as LiMn2O4), the helium atoms travel through the lattice and transfer kinetic energy to defective positions in the lattice (such as dislocations, vacancies or impurities). These defects are usually the main reason for the degradation of material performance, and the presence of helium-4 superfluid allows these defects to be restored to a more stable structure. Taking LiMn2O4 as an example, the original crystal structure of this material is a cubic phase during the battery life cycle. However, as the number of cycles increases, its state of health (SOH) gradually decreases, and LiMn2O4 will gradually transform from a cubic phase to an orthorhombic phase. This phase change not only reduces the conductivity and ion mobility of the material, but also may cause structural instability, further exacerbating performance degradation. Through the ultra-low temperature environment and the travel of helium-4 atoms in the positive electrode material lattice, the entire positive electrode material lattice is continuously perturbed and kinetic energy is transferred, which can not only repair the lattice defects, but also cause the orthorhombic phase to be transformed back into a cubic phase (see Figure 3 This transition is only possible in the helium-4 superfluid state, as its unique zero-viscosity phase gives it the ability to wet and penetrate the cathode material.

[0098] In addition to the impact on the cathode material itself, superfluid helium-4 also repairs the binder between lithium-based materials in the cathode. Binders play a vital role in batteries. They not only connect active materials, conductive agents, and current collectors, but also affect the mechanical strength and electrochemical properties of the overall electrode. However, as the battery ages, the binder may become hard and brittle, losing its original elasticity and flexibility, thus affecting the overall performance of the battery.

[0099] The role of superfluid helium-4 is to reactivate the binder, restoring it from a hard and brittle glass state to a more flexible state. This process helps to restore the elasticity of the binder and enhance its ability to connect electrode active materials, conductive agents and current collectors. Specifically, the zero viscosity of helium-4 superfluid allows it to penetrate into the microstructure of the binder, and through kinetic energy transfer and perturbation, it changes the interaction force between the binder molecules and restores it to a more ideal state.

[0100] Experimental studies have shown that electrodes treated with helium-4 superfluids exhibit better mechanical strength and electrochemical stability. In particular, under high-rate charge and discharge conditions, the structural integrity of the electrodes has been significantly improved, reducing performance losses due to binder failure. These findings further demonstrate the broad application prospects of helium-4 superfluids in the field of battery electrode repair.

[0101] XRD test

[0102] In order to more intuitively obtain the relationship between the structural information and temperature of the LiMn2O4 cathode material, a low-temperature non-in-situ XRD test was performed on it. The LiMn2O4 | Li button half-cell was charged and discharged at a rate of 0.01C, disassembled at 0.3 and 0.8 lithium-intercalated states, cleaned, and subjected to ultra-low temperature treatment in superfluid helium-4, and then a non-in-situ XRD test was performed. The 0.3 lithium-intercalated state corresponds to the H3 / H2 phase region in the LiMn2O4 cathode material, and the 0.8 lithium-intercalated state corresponds to the M / H1 phase region. According to Figure 3 From the X-ray powder diffraction pattern, it can be seen that at room temperature, a clear peak split is observed in the double peaks of (108) / (110) and (006) / (102), indicating that the disassembled LiMn2O4 cathode is a highly crystalline layered structure material. When the temperature drops to ultra-low temperature (about 2 K), the peak separation of the double peaks of (108) / (110) and (006) / (102) is still clear, but an obvious phase change process is observed. The specific performance is:

[0103] At room temperature, the unit cell parameters a and c of the LiMn2O4 cathode material are 2.86Šand 14.25Šrespectively, and the unit cell volume is 101.1ų.

[0104] After ultra-low temperature treatment, the unit cell parameters a and c become 2.84 Å and 14.20 Å, respectively, and the unit cell volume is 100.5 ų, which indicates that at ultra-low temperatures, the material transforms from a cubic phase (Fd-3m) to a tetragonal phase (I41 / amd).

[0105] The differences in unit cell parameters between the two different lithium-intercalation states Figure 3 The in-situ XRD calculation results are consistent with those of the samples, proving that the controlled voltage decomposition to obtain electrodes of different lithium-intercalation states is accurate. As the temperature drops from room temperature (25°C) to ultra-low temperature (about 2 K), the unit cell parameters of the two lithium-intercalation states fluctuate within a small error range, but the phase change process is significant. Combined with the OCV test results, it can be concluded that the material structure of the LiMn2O4 positive electrode material undergoes a significant phase change in the range from room temperature to ultra-low temperature, but the overall highly crystalline layered structure is maintained, which does not lead to significant changes in the electrode reaction equilibrium.

[0106] The experimental results show that after being treated with helium-4 superfluid, the XRD spectrum of LiMn2O4 shows a significant increase in the intensity of the cubic phase peak, while the orthorhombic phase peak weakens, indicating the successful reversal of the phase change. In addition, electrochemical tests also demonstrated a significant improvement in battery performance, including higher capacity retention and lower internal resistance. These results strongly support the effectiveness of helium-4 superfluid in repairing and optimizing electrode materials.

[0107] SEM and TEM testing

[0108] Figure 4 The small figures are: SEM images of the LiMn2O4 positive electrode surface (ac) 3-cycle electrode, (a) basic electrolyte, (b) 1wt.% PTI electrolyte, (c) 1 wt.% 4-FI electrolyte, (df) 100-cycle electrode ((d) basic electrolyte, (e) 1 wt.% PTI electrolyte 100-cycle electrode, (f) 1wt.% 4-FI electrolyte. Compared with the morphology of the uncycled LiMn2O4 positive electrode ( Figure 4 (a) After cycling, the electrode surface can be observed to be covered with film. This is because the electrolyte decomposes during the charge and discharge process, and its insoluble products are deposited on the electrode surface to form a SEI film. However, in the presence of additives, the SEI film formed is smoother and more uniform ( Figure 4 (b), (c)), especially the SEI film on the electrode surface with 1 wt.% 4-FI added is more uniform and dense, which may be related to the increase of LiF content in the SEI film due to the introduction of fluorinated additives. The presence of LiF is conducive to the formation of a more uniform SEI film. A more dense and uniform protective film can inhibit the decomposition of the electrolyte and protect the electrode material from corrosion. This will be beneficial to Li + The migration in the SEI film has a smaller SEI film impedance. The above phenomenon is consistent with the results of cycle performance and impedance.

[0109] In order to further study the structural changes of electrode materials under ultra-low temperature conditions, we treated the LiMn2O4 cathode with helium-4 superfluid at ultra-low temperature (about 2 K). Superfluid helium-4 molecules can penetrate the tiny pores and phase gaps of the electrode material and penetrate deep into the material. According to the SEM image of the LiMn2O4 cathode after 100 cycles of ultra-low temperature cycling ( Figure 4 (df) It can be seen that compared with the negative electrode after 3 weeks of cycling at room temperature, the surface film-like material is thicker and more evenly wrapped on the particle surface. This indicates that during the ultra-low temperature cycling process, the decomposition reaction of the electrolyte still exists, and the product is deposited on the surface of the negative electrode to further form the SEI film. However, the treatment of superfluid helium-4 helps to repair and optimize the structure of the SEI film, making it more uniform and dense.

[0110] The treatment of superfluid helium-4 not only helps to repair and optimize the structure of the SEI film, but also improves the mechanical properties of the electrode material. The low temperature environment of superfluid helium-4 can restore the binder in the electrode material to its original flexibility and elasticity, and reconnect the conductive network that was broken during multiple charge and discharge cycles. This helps to improve the overall stability and conductivity of the electrode, thereby improving the cycle life and electrochemical performance of the battery.

[0111] Electrochemical testing:

[0112] The battery is reassembled under laboratory conditions, and charge and discharge tests, internal resistance measurements, etc. are performed to evaluate changes in electrode performance. This is basically the same as the normal electrochemical testing process.

[0113] like Figure 5 As shown, by comparing the 1 / 3 C rate discharge capacity-voltage curves after treatment under different temperature conditions, it can be clearly seen that ultra-low temperature treatment has a significant effect on the recovery of battery performance. Figure 5 In the figure, the temperature of each small figure is: (a) 2K, (b) 4K, (c) 50K, (d) -25°C, (e) 0°C, (f), 25°C. In the superfluid helium-4 immersion at ultra-low temperature (2K), the discharge capacity of the treated battery will gradually increase, the voltage platform will become more gentle, and the voltage drop will gradually decrease. The capacity-voltage curve of the battery samples treated at 4K and 50K temperatures also tends to improve. In the samples that have not been treated near 25°C, the discharge capacity of the battery is significantly reduced, the voltage platform becomes less obvious, and the voltage drop is rapid. This shows that at such a low temperature, the diffusion rate of lithium ions is extremely low and the electrochemical reaction rate is greatly reduced. Compared with 25°C, the discharge capacity treated with 0°C helium mixed gas (because helium is in gaseous state at this time) is improved, the voltage platform is slightly gentle, but there is still a significant voltage drop. This shows that after the temperature is slightly increased, the diffusion rate of lithium ions and the electrochemical reaction rate are improved. It may be related to some effects of helium atoms.

[0114] In addition, the infiltration treatment of helium-4 superfluid significantly optimized the structure and performance of the electrode materials, improved the conductivity, mechanical properties and uniformity of the electrochemical reactions of the electrode materials, thereby significantly improving the overall performance of the battery.

[0115] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for restoring the health status of lithium battery electrodes using helium-4 superfluid, characterized in that: In the method, a helium-4 superfluid state is maintained in a dilution refrigerator (1), the dilution refrigerator (1) is connected to a superfluid electrode processing chamber (3), the dilution refrigerator (1) and the superfluid electrode processing chamber (3) are both arranged in a vacuum chamber (2), a lithium battery electrode is placed in the superfluid electrode processing chamber (3), the temperature in the superfluid electrode processing chamber (3) is stabilized at a set value by a temperature control system (5), and is monitored and adjusted by a vacuum system (6) arranged outside the vacuum chamber (2). The internal pressure of the vacuum cavity (2) ensures that the helium-4 is in a stable state of superfluid. A circulation pump group (7) and a liquid nitrogen cold trap (8) are also arranged outside the vacuum cavity (2). The dilution refrigerator (1), the superfluid electrode processing chamber (3), the circulation pump group (7) and the liquid nitrogen cold trap (8) are sequentially connected to form a low-temperature circulation loop. A mixture of helium-3 and helium-4 is pre-injected into the low-temperature circulation loop. The helium-4 superfluid flows between the dilution refrigerator (1) and the superfluid electrode processing chamber (3). The method comprises the following steps: S1. Preparation before operation: the operator wears protective equipment to ensure the safety of the operator and the environment, starts the dilution refrigerator, and starts the mixed dilution process of helium-3 and helium-4, and finally makes the temperature of the superfluid electrode processing chamber (3) reach and stabilize at a target low temperature, which is set within 10 millikelvin; S2. Battery pack disassembly and electrode pretreatment: Use battery disassembly tools to separate the electrode group, and clean and dry the lithium battery electrodes that need to be restored; S3, moving the lithium battery electrode into the superfluid electrode processing chamber: moving the processed lithium battery electrode into the superfluid electrode processing chamber (3) and completely immersing the lithium battery electrode in the helium-4 superfluid; S4. Helium-4 superfluid acts on lithium battery electrodes: Helium-4 superfluid enters lithium battery electrodes to act, and the whole process is monitored. Specifically, the helium-4 superfluid completely immerses the lithium battery electrodes and the helium-4 superfluid flows. When helium atoms pass through the positive electrode material, they travel in the lattice and transfer kinetic energy to the defective positions in the lattice. The existence of helium-4 superfluid allows these defects to be restored to a more stable structure. The zero viscosity property of helium-4 superfluid allows helium-4 superfluid to penetrate into the microstructure of the binder. Through kinetic energy transfer and perturbation, the interaction force between the binder molecules is changed, so that it is restored to a more ideal state. S5, lithium battery electrode post-processing: After the processing is completed according to step S4, the processed lithium battery electrode is moved out of the superfluid electrode processing chamber (3) into a low-temperature environment, and the temperature is slowly increased until it reaches room temperature, thereby completing the recovery of the health status of the lithium battery electrode.

2. The method of claim 1, wherein the method comprises: In step S1, the dilution refrigerator is precooled. After the precooling is completed, the dilution refrigerator is started, a mixture of helium-3 and helium-4 is injected, a dilution cycle is started, and a mixed dilution process of helium-3 and helium-4 begins. By controlling the ratio of helium-3 and helium-4 in the mixer and the mixing rate, the entropy of the mixture is gradually reduced, and the temperature of the superfluid electrode processing chamber (3) is continuously monitored to ensure that it reaches and stabilizes at a target low temperature.

3. The method of claim 1, wherein the method comprises: In the step S4, when the helium-4 superfluid acts on the lithium battery electrode, the temperature is set within 10 millikelvin and the time is 10 minutes to 5 hours.

4. The method of claim 1, wherein the method comprises: An electrode transfer device (4) for moving lithium battery electrode samples into or out of the superfluid electrode processing chamber (3) in a low-temperature environment is also provided outside the vacuum chamber (2). The electrode transfer device (4) comprises a low-temperature glove box (9) and a low-temperature guide rail (10). A sample delivery window (11) is provided on the vacuum chamber (2). The sample delivery window (11) is equipped with a closed door. The low-temperature glove box (9) is connected to the sample delivery window (11). The low-temperature guide rail (10) extends from the low-temperature glove box (9) through the sample delivery window (11) into the vacuum chamber (2).

5. The method of claim 1, wherein the method comprises: The superfluid electrode processing chamber (3) is made of a low-temperature material, and the outer surface of the superfluid electrode processing chamber (3) is coated with a plurality of layers of heat radiation shielding layers. The interior of the superfluid electrode processing chamber (3) is designed to be a space adapted to the shape and size of a lithium battery electrode, and a low-temperature resistant observation window (12) is provided on the wall of the superfluid electrode processing chamber (3).

6. The method of claim 1, wherein: The temperature control system (5) comprises a temperature controller (13) and a plurality of low-temperature temperature sensors (14) arranged at various links of the low-temperature circulation loop, the plurality of low-temperature temperature sensors (14) being electrically connected to the temperature controller (13), and the temperature controller (13) being communicatively connected to a peripheral control console.

7. The method of claim 4, wherein: The vacuum system (6) comprises a mechanical pump (15), a first solenoid valve (16), a second solenoid valve (17), a molecular pump (18) and a gate valve (19) which are connected in sequence, wherein the gate valve (19) is connected to the interior of the vacuum chamber (2), and two branches are connected between the first solenoid valve (16) and the second solenoid valve (17), one of which is connected to the interior of the vacuum chamber (2) via a bypass valve (20), and the other is connected to the electrode transfer device (4) via a sample valve (21).

8. The method of claim 5, wherein: The superfluid electrode processing chamber (3) is made of copper, stainless steel or oxygen-free copper, and the low-temperature resistant observation window (12) is made of a sapphire sheet or a quartz sheet.

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