Method for removing dead lithium of negative electrode of lithium metal battery

Abstract

The invention relates to the field of lithium metal batteries, and particularly provides a method for removing dead lithium of a negative electrode of a lithium metal battery, and the method comprises the following steps: step 1, preparing a modified electrolyte; step 2, adding the modified electrolyte into the lithium metal battery; and step 3, alternately performing high-rate charging and low-rate charging on the lithium metal battery. Dead lithium is eliminated by adopting the modified electrolyte, and high-rate charging and low-rate charging are combined. The overall charging rate of the lithium metal battery can meet daily use requirements, meanwhile, it is ensured that the redox medium has sufficient time to remove accumulated dead lithium, and the lithium metal battery is restored. In addition, accumulation of dead lithium can be controlled by adjusting the number of turns of high-rate circulation, finally, dead lithium accumulated in the cycle is removed in time through low-rate circulation, the situation that excessive dead lithium is accumulated in the follow-up process and influences the battery performance is prevented, and the dead lithium removing efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of lithium metal batteries, and more specifically, to a method for removing dead lithium from the negative electrode of a lithium metal battery. Background Technology

[0002] Lithium metal batteries have promising market prospects due to their high theoretical specific capacity and low electrochemical potential. During charging, lithium ions deposit at the negative electrode. Uneven deposition on the negative electrode surface leads to the formation of dendritic or moss-like lithium dendrites. Continuously growing dendrites can pierce the separator, causing internal short circuits, thermal runaway, and even fire or explosion. The "dead lithium" (isolated lithium that has lost electrical contact with the electrode) formed after dendrites break off causes irreversible consumption of active lithium and electrolyte, severely reducing the battery's coulombic efficiency and capacity. In other words, unstable interfacial reactions, lithium dendrite growth, and the accumulation of dead lithium hinder the further application of these batteries. Dead lithium accumulates continuously with cycling, leading to severe capacity loss and safety hazards, becoming one of the key obstacles limiting the practical application of lithium metal batteries.

[0003] Recent strategies for restoring dead lithium involve using redox media soluble in electrolytes to react with and remove dead lithium, thus converting it back into recyclable Li. + This allows for the restoration of lithium metal batteries. For removing dead lithium, the charging rate is a crucial factor. At daily high charging rates (typically 1-2C, or even higher), the redox medium and dead lithium often don't have enough time to react before the charging process ends, resulting in ineffective removal of dead lithium and significantly limiting the efficiency of battery restoration. The continuous accumulation of dead lithium leads to a rapid decline in battery performance; see the paper "Rejuvenating dead lithium supply in lithium metal anodes by iodine redox" (Nature Energy 6, 378-387 (2021)). While consistently charging at low rates can effectively remove dead lithium, the excessively long charging time severely impacts daily battery use and fails to meet user needs. Therefore, existing methods for removing dead lithium are inefficient and cannot meet user requirements. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a method for removing dead lithium from the negative electrode of a lithium metal battery. The method includes the following steps: Step 1, preparing a modified electrolyte; Step 2, adding the modified electrolyte to the lithium metal battery; Step 3, alternating between high-rate charging and low-rate charging of the lithium metal battery to remove dead lithium from the negative electrode of the lithium metal battery.

[0005] By preparing a modified electrolyte and adding it to a lithium metal battery, combined with alternating high-rate and low-rate charging, dead lithium is removed during battery cycling. The functional component (DDB) in the modified electrolyte participates in interfacial reactions, enhancing the interface's reactivity with deactivated lithium, making it easier to reconstitute dead lithium, which was previously unable to participate in electrochemical reactions due to electron isolation, into usable lithium ions. Simultaneously, the high-rate charging stage accelerates the formation of interfacial defects, dendrite fracture, and dead lithium, causing deactivated lithium to concentrate in more easily accessible shallow layers. The subsequent low-rate charging stage, with its lower current density and less polarization, provides a milder and more stable interfacial environment, allowing the active components in the modified electrolyte to fully exert their effects and selectively react with dead lithium, thereby effectively removing it. This invention effectively inhibits the continuous accumulation of dead lithium, improves the interfacial uniformity and stability of the lithium metal anode, and fundamentally solves the technical problems of capacity decay and cycling instability caused by dead lithium.

[0006] Furthermore, the modified electrolyte is a carbonate system electrolyte with added 1,4-bis(tert-butyl)-2,5-dimethoxybenzene.

[0007] Furthermore, the concentration of 1,4-bis(tert-butyl)-2,5-dimethoxybenzene is 10 mmol / L.

[0008] Furthermore, the electrolyte for the carbonate system is 1 M LiPF6 dissolved in ethylene carbonate and diethyl carbonate in a volume ratio of 1:1.

[0009] Furthermore, the high-rate charging speed is 1-5C.

[0010] Furthermore, the low-rate charging is 0.1C.

[0011] Furthermore, in a high-low rate switching cycle, the number of cycles for high-rate charging is greater than the number of cycles for low-rate charging.

[0012] Furthermore, the number of cycles for high-rate charging is greater than or equal to 20 times the number of cycles for low-rate charging.

[0013] Furthermore, the modified electrolyte fills the space between the positive and negative electrodes and the pores of the separator.

[0014] Furthermore, step 2 is carried out in a glove box filled with nitrogen or argon.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This application employs a modified electrolyte to eliminate dead lithium, combining high-rate charging with low-rate charging. This ensures the overall charging rate of the lithium metal battery meets daily usage needs while guaranteeing sufficient time for the redox medium to remove accumulated dead lithium, thus restoring the lithium metal battery. Furthermore, by adjusting the number of high-rate cycles, the accumulation of dead lithium is controlled, and finally, low-rate cycling is used to promptly remove the dead lithium accumulated during the cycle, preventing excessive dead lithium accumulation from subsequently affecting battery performance and improving the efficiency of dead lithium removal.

[0016] The strategy of periodic high and low rate charging in this application can also be applied to other redox media for the reduction of metallic lithium. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a method for removing dead lithium from the negative electrode of a lithium metal battery provided by the present invention; Figure 2 A schematic diagram of the reversible redox reaction of DDB introduced in a method for removing dead lithium from the negative electrode of a lithium metal battery provided by the present invention; Figure 3 This is a time-voltage diagram of the cycle within Example 1; Figure 4 The charge-discharge curves of Example 1 under high-rate and low-rate cycling are shown below. Figure 5 The capacity recovery diagram after the cycle provided in Example 1; Figure 6 Here is a SEM image of the lithium metal anode obtained in Example 1; Figure 7 The image shows the SEM image of the lithium metal anode obtained in Comparative Example 1. Figure 8 The image shows the SEM image of the lithium metal anode obtained in Comparative Example 2. Figure 9 The image shows the SEM image of the lithium metal anode obtained in Comparative Example 3. Figure 10 Electrochemical impedance spectroscopy diagrams of lithium metal batteries after cycling, provided in Example 1 and Comparative Examples 1, 2, and 3; Figure 11 Long-cycle performance graphs of lithium metal batteries provided in Example 1 and Comparative Examples 1, 2, and 3. Detailed Implementation

[0018] To make the implementation process of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings.

[0019] Example 1: This invention provides a method for removing dead lithium from the negative electrode of a lithium metal battery, such as... Figure 1 As shown, it includes the following steps: Step 1: Prepare the modified electrolyte.

[0020] A modified electrolyte was prepared by adding 1,4-di(tert-butyl)-2,5-dimethoxybenzene (DDB) to a carbonate electrolyte system. The carbonate electrolyte system consisted of 1 M LiPF6 dissolved in ethylene carbonate and diethyl carbonate at a volume ratio of 1:1. Specifically, DDB was added to 1 M LiPF6-ethylene carbonate (EC)-diethyl carbonate (DEC) (volume ratio 1:1) at a concentration of 10 mmol / L, and stirred for 6 h to obtain the modified electrolyte. The entire process was carried out in an argon-filled glove box. At room temperature, 25 mg of DDB was weighed into an empty bottle, and then 10 mL of the lipid electrolyte was pipetted into the bottle. The mixture was then stirred with a magnetic stirrer for 6 h to prepare a modified electrolyte containing 10 mmol / L DDB. In other words, the DDB concentration is 10 mmol / L. Too low a concentration will prevent DDB from functioning properly in the battery; even at a low rate of 0.1C, trace amounts of DDB will have difficulty reacting with dead lithium. Too high a concentration, on the other hand, will result in a large amount of DDB constantly present inside the battery. + Because of DDB, even under normal high-rate charging (1C-5C), the lithium metal deposited during charging will continuously react with DDB. + An overcharge reaction occurs, preventing the battery from fully charging. Prolonged overcharging leads to irreversible capacity decay and battery failure. A concentration of 10 mmol / L ensures that the DDB and dead lithium reaction fully occur at 0.1C, while preventing overcharging at high rates of 1C-5C in daily use, thus avoiding impact on battery performance.

[0021] The addition of DDB in this application can effectively eliminate "dead lithium" and reduce the formation of "lithium dendrites"; DDB cation (DDB + It will react with elemental Li to produce DDB and Li ions (Li + The shuttle effect allows this process to occur cyclically. Specifically, during charging, DDB loses electrons at the positive electrode and is oxidized into DDB. + Subsequently, the DDB cations shuttle to the negative electrode due to the shuttle effect. + It will react with the "dead lithium" on the negative electrode surface to regenerate DDB and Li. + The reduced DDB continues to shuttle to the positive electrode and is oxidized into DDB cations. This process cycles during charging. During discharging, DDB cannot lose electrons at the electrode and is oxidized into DDB. + Therefore, a cycle cannot be achieved, and the electrode cannot be restored. In other words, the charging process is mainly responsible for removing dead lithium, while the discharging process can proceed with normal discharge.

[0022] This allows "dead lithium" to be continuously reduced to active Li ions, which then re-participate in electrode reactions, such as... Figure 2 As shown. Because DDB cations continuously react with metallic Li on the negative electrode surface, they can effectively inhibit the continuous growth of lithium dendrites on the negative electrode, reacting them into Li ions that then participate in the deposition again. Without a redox medium, the negative electrode of the battery will experience uneven deposition, leading to the continuous growth of lithium dendrites and the continuous generation and accumulation of dead lithium, severely affecting the battery's performance and safety.

[0023] DDB exhibits excellent reversibility and does not cause side effects to the battery, such as inducing self-discharge. After charging, it discharges internally without electrons passing through the external circuitry and performing no external work. Due to its excellent reversibility, it can continuously undergo cyclic reactions at a low rate of 0.1C, thus continuously reacting with lithium metal. Therefore, it can effectively suppress the continuous growth of lithium dendrites and promptly remove dead lithium.

[0024] The DDB molecular structure of this application exhibits high electrolyte solubility and a small molecular size, enabling rapid and uniform diffusion in the electrolyte and penetration into the porous and highly irregular interface region of the negative electrode surface. The DDB is oxidized to an oxidized state with stronger electron affinity. + DDB⁺ possesses a high oxidation potential and operates in a free-diffusion state, enabling it to penetrate locally damaged, loose, or excessively thick SEI films. It overcomes the SEI layer's limitation on electron and ion isolation, reaching deep dead lithium particles that are either SEI-coated or completely electron-isolated. This allows for in-situ repair of deep-layer dead lithium at the interface, resulting in better removal. Simultaneously, as the redox reaction of DDB becomes reversible at the interface, the local SEI structure undergoes slight redox regulation, leading to a moderate reconstruction of the originally uneven, fragile, or inorganically polluted SEI. This removes excessively thick or highly resistive SEI components, resulting in a thinner, denser, and more uniform SEI film. The generated SEI is richer in organic components with better ionic conductivity and stable phases such as LiF, thereby optimizing the Li... + The transmission channel is established. As dead lithium is gradually dissolved and removed, the distribution of interfacial current density tends to be more uniform, which can effectively reduce the dendrite effect caused by the initial nucleation deviation, making the subsequent lithium deposition process smoother and more continuous, inhibiting dendrite formation and reducing interfacial polarization from the source. In other words, DDB can not only remove existing dead lithium, but also improve the interfacial chemical environment, enhance interfacial stability, and achieve continuous, self-healing protection for the lithium metal anode.

[0025] Step 2: Add the modified electrolyte to the lithium metal battery.

[0026] A modified electrolyte is used to configure a lithium metal battery, and the structure of the lithium metal battery is existing. The positive electrode of the lithium metal battery uses lithium iron phosphate, and the negative electrode uses a lithium metal sheet. They are assembled in the following order: negative electrode shell - stainless steel gasket - negative electrode - separator - positive electrode - stainless steel gasket - spring sheet - positive electrode shell. A modified electrolyte is added to both sides of the separator to obtain the lithium metal battery. The modified electrolyte fills the space between the positive and negative electrode sheets and the pores of the separator. Specifically, in a glove box, the negative electrode shell is first placed horizontally with its opening facing upwards, and a stainless steel gasket is placed inside. The stainless steel gasket serves as a current collector and support. Then, a lithium sheet is placed on the gasket as the negative electrode of the battery, acting as the active material and energy carrier, participating in the battery reaction. Next, 30 μL of modified electrolyte is added to the negative electrode. The electrolyte, acting as an ion-conducting medium, undergoes an irreversible chemical reaction with the highly active lithium metal, forming a solid electrolyte interphase (SEI) film covering the lithium surface. This film significantly reduces lithium corrosion and electrolyte consumption. The modified electrolyte also provides targeted improvements to the battery, such as improving the SEI film, suppressing dendrites, and removing dead lithium. A separator is then placed on the negative electrode. The separator separates the positive and negative electrodes, preventing internal short circuits and blocking direct electron flow, forcing electrons to flow only through the external circuitry. Simultaneously, the separator's micropores create ion channels, allowing lithium ions to shuttle between the positive and negative electrodes, a necessary condition for the battery's charging reaction. The separator used is typically a polyolefin separator, made of materials such as polyethylene (PE) or polypropylene (PP). In this embodiment, a Celgard 2500 separator (polypropylene PP) is used, which possesses better high-temperature stability and high-pressure resistance, resulting in better removal of dead lithium when combined with the modified electrolyte.

[0027] Add 30 μL of modified electrolyte to the separator again to fully wet it. Next, place lithium iron phosphate (LFP) on the separator as the positive electrode to participate in the battery reaction. The LFP positive electrode, as the reversible storage host for lithium ions, is crucial for energy storage and release. Then, place a stainless steel gasket on the positive electrode. Place a spring clip on the stainless steel gasket; the spring clip ensures tight contact between the internal components, forming a reliable current path, and also buffers mechanical shock and deformation. Finally, place the positive electrode shell on the spring clip. The positive and negative electrode shells form a robust, sealed metal container, protecting the internal structure while also serving as a current path. During the configuration process, the glove box is filled with nitrogen or argon to prevent moisture and oxygen from contacting the electrolyte. Contact with moisture will cause LiPF6 to decompose and produce HF, while the surface of the metallic lithium will be rapidly oxidized by water and oxygen, leading to increased interfacial impedance, accelerated formation of dead lithium, and safety hazards.

[0028] Step 3: Alternately charge the lithium metal battery at high and low rates to remove dead lithium on the negative electrode of the lithium metal battery.

[0029] High-rate charging operates at 1-5C; low-rate charging at 0.1C. Within a high-rate / low-rate switching cycle, the number of cycles at high rate charging is greater than the number of cycles at low rate charging. The number of cycles at high rate charging is greater than or equal to 20 times the number of cycles at low rate charging. Specifically, the cycle rate of the lithium metal battery is set as follows: 20-60 cycles at a high rate of 1C-5C to maintain the cycle rate and accumulate some dead lithium; then one cycle at a low rate of 0.1C to fully eliminate dead lithium. This is defined as one cycle, and the cycle is repeated periodically. The 0.1C phase within the cycle is the process of fully removing dead lithium; that is, within a single complete cycle, dead lithium is considered to have been largely removed. With an increase in the number of cycles, more dead lithium can be removed. Dead lithium is eliminated by controlling the charging cutoff time at 0.1C, i.e., controlling the time for DDB to participate in the reaction. In this application, characterization was performed when the reaction time of DDB was increased to 20 hours, and it was found that dead lithium had been basically eliminated. Specifically, the elimination of dead lithium was observed at each reaction time by disassembling the battery and performing SEM characterization.

[0030] Set the cycle rate of the lithium metal battery as follows: "20-60 cycles at high rate + 1 cycle at low rate" constitutes one cycle, and repeat the cycle periodically. Figure 3 As shown. At 1C rate, the accumulation rate of dead lithium is relatively slow, thus allowing for a longer cycle length at 1C rate, such as 60 cycles. 5C rate charging is extremely fast, meeting the fast charging needs of some users while also resolving the dead lithium issue. The high rate range is 1C-5C, and the low rate is 0.1C. The 1C-5C range was set for flexibility; the inventors found that within this range, both high and low rates function effectively, meeting users' fast charging needs while removing dead lithium. Furthermore, as the rate increases, the number of cycles decreases. At high rates, the lithium dendrite problem becomes more severe; fast charging and discharging easily lead to uncontrolled lithium dendrite growth and a large accumulation of dead lithium.

[0031] In this application, during high-rate charging, the high current density, strong polarization, and rapid lithium deposition rate lead to localized oversaturation deposition, increased dendrite tip growth, and periodic SEI fracture on the negative electrode surface. This causes some dendrites to break and transform into dead lithium during subsequent stripping. These newly generated dead lithium particles are typically distributed in the shallow interfacial layer or SEI-dammed areas, providing a clear target for targeted removal in the low-rate stage. In other words, the high-rate stage actively exposes interfacial defects, making the removal process more targeted and efficient. Upon entering the low-rate stage, the current density significantly decreases, interfacial polarization diminishes, and the battery voltage can slowly and steadily rise to the characteristic oxidation plateau of the DDB (Denial Diode) and remain stable within this potential range, ensuring sufficient oxidation of the DDB. The more uniform ion flux at the interface under low-rate conditions further enhances the oxidation of the DDB. +It can successfully penetrate into the SEI damage area or deep porous structure formed during high-rate charging and react with dead lithium. At the same time, after removing dead lithium at low rates, a smoother and more uniform interface is obtained, which can effectively reduce the phenomenon of local current density concentration in subsequent high-rate charging, thereby reducing the risk of accelerated dendrite growth and secondary dead lithium generation.

[0032] Furthermore, different number of cycles are set for different magnification rates; the higher the magnification, the fewer the number of cycles. For example, at 1C, 60 cycles at 1C are allowed, followed by a 0.1C cycle for dead lithium activation. At 2C, 40 cycles at 2C are followed by a 0.1C cycle for dead lithium activation. At 5C, 20 cycles at 5C are followed by a 0.1C cycle for dead lithium activation. Higher magnification rates result in faster dendrite growth and dead lithium formation. Too many cycles at high magnification rates will lead to larger and deeper dead lithium clusters. + It is difficult to achieve complete coverage; limiting the number of high-rate cycles can control the dead lithium within each cycle to within the DDB (Distributed Dead Lithium) limit. + Within manageable limits, reduce deep-seated, difficult-to-remove dead lithium. Ensure timely removal of dead lithium to prevent excessive accumulation and irreversible battery damage. Furthermore, the high-rate phase is configured with short pulses, inserting 1-2 medium-rate (0.5C) pulses as a buffer after every 5-10 high-rate pulses. The high-rate pulses quickly expose interface defects, while the buffer provides a lower polarization environment, improving DDB (Damage Per Dimension). + This allows for timely diffusion and processing of newly formed dead lithium. Experiments have shown that at a rate of 0.1C-0.2C, DDB... + There are obvious traces of reaction. No traces of DDB reaction were found at 0.5C, which prevents dead lithium from accumulating for a long time and being secondary coated by SEI to form deep and difficult-to-remove defects.

[0033] For ease of comparison, in this embodiment, a modified electrolyte is added, and a periodic charging method is used: a 30-cycle 1C cycle and a 1-cycle 0.1C cycle are set, and this cycle is repeated continuously.

[0034] The charging cutoff voltage for lithium iron phosphate batteries is 4.2V, while the reaction potential of DDB is around 3.95V. During charging, lithium metal continuously deposits on the negative electrode, and the battery voltage gradually increases from the initial voltage to the cutoff voltage of 4.2V before charging ends. Under high-rate charging, the rate of lithium metal deposition on the negative electrode accelerates, causing the DDB cations to not have enough time to eliminate the lithium metal before the deposition process on the negative electrode is complete. This results in (DDB--DDB)... + The cyclic reaction of --DDB cannot occur. Figure 4 The voltage curve shown indicates that when the voltage rises to the DDB reaction potential of 3.95V, it almost stops and continues to rise to the cutoff voltage of 4.2V, ending the charging process, as follows. Figure 4 As shown in (a). Under low-rate charging, the rate of lithium metal deposition on the negative electrode slows down, DDB + Sufficient time is available to remove lithium metal, thus ensuring (DDB--DDB) + The cyclic reaction of (-DDB) occurs, achieving the goal of continuously eliminating lithium metal. This is reflected in the voltage curve: when the voltage rises to the reaction potential of DDB (3.95V), the voltage stops rising and remains near 3.95V, forming a clear voltage plateau. This indicates the continuous occurrence of the (DDB--DDB+--DDB) cyclic reaction, as follows: Figure 4 As shown in (b). Figure 4 The charge-discharge curves for Example 1 are shown at high and low rate cycles, respectively. Only at the low rate does a significant voltage plateau (3.95V) appear, corresponding to the DDB / DDB ratio. + The presence of a voltage plateau in the redox reaction indicates that this reaction is ongoing. This suggests that only at low rates can the redox medium fully participate in the battery reaction, thus restoring the battery. Figure 5 The capacity recovery diagram after cycle provided in Example 1 shows that cycled operation can effectively restore battery capacity and regenerate the battery.

[0035] This invention introduces a high-rate + low-rate charging method based on the addition of DDB (Dielectric-Reduction Charge). The battery charges quickly, meeting usage requirements while delaying the accumulation of dead lithium metal. After adding redox additives, the long charging time facilitates the reaction of the redox additives, effectively eliminating dead lithium. After several high-rate cycles accumulating some dead lithium, a single low-rate cycle is used to completely eliminate the accumulated dead lithium, and this cycle is repeated. This application utilizes the characteristic of high reaction intensity of the redox medium at low rates to control the number of high-rate and low-rate cycles within a period, thereby controlling the reaction of the redox medium inside the battery. Furthermore, the charging cutoff time at low rates can be controlled to manage the (DDB--DDB) charging process. + The duration of the cyclic reaction of --DDB to eliminate dead lithium is controlled, thereby controlling the degree of dead lithium elimination.

[0036] Comparative Example 1: Unlike Example 1, Comparative Example 1 uses an electrolyte without DDB and a conventional charging method: a cycle method with a full 1C charge.

[0037] Comparative Example 2: Unlike Example 1, a modified electrolyte was added, and the traditional charging method was a cycle method with a full 1C charge.

[0038] Comparative Example 3: Unlike Example 1, an electrolyte without DDB was used, and a periodic charging method was employed: a 30-cycle 1C cycle and a 1-cycle 0.1C cycle were set up and the cycle was repeated continuously.

[0039] Figure 6 , Figure 7 , Figure 8 , Figure 9 SEM images of the lithium metal anodes obtained in Example 1 and Comparative Examples 1, 2, and 3 are shown. In Comparative Examples 1, 2, and 3 all showed uneven dendritic deposits on their surfaces, while the surface of Example 1 was smooth. Comparative Example 1, lacking a redox medium in its blank electrolyte, could not react with dead lithium and therefore could not remove it. Comparative Example 2, even with a redox medium, suffered from continuous accumulation because the conventional charging method prevented the medium from reacting with the dead lithium. Comparative Example 3 used a periodic charging method but lacked a redox medium; even slowing down the charging process did not eliminate the dead lithium. In contrast, Example 1, using a periodic method, contained a redox medium, ensuring a sufficient reaction between the medium and the dead lithium, promptly removing the accumulated dead lithium during the cycle, resulting in almost no visible residue on the surface.

[0040] Figure 10 Electrochemical impedance spectroscopy (EIS) plots of lithium metal batteries after cycling for Examples 1 and Comparative Examples 1, 2, and 3 are shown. Dead lithium affects the performance of lithium metal batteries, and the impedance of Example 1 is significantly lower than that of Comparative Examples 1, 2, and 3. The semicircle diameter of Example 1 in the high-frequency region is smaller than that of the others, indicating that Example 1 has lower charge transfer resistance. This is attributed to the elimination of accumulated dead lithium, which clears ion transport pathways and reshapes stable interfaces and uniform deposition.

[0041] Figure 11 The graph shows the long-cycle performance of the lithium metal batteries provided in Example 1 and Comparative Examples 1, 2, and 3. The long-cycle life of Example 1 is significantly greater than that of Comparative Examples 1, 2, and 3. This is attributed to the fact that the cyclic cycling can promptly restore the battery, and by continuously repeating the cyclic cycle, the overall performance of the lithium metal battery is continuously improved.

[0042] This scheme fully activates the redox medium DDB during the low-rate charging phase, bringing its oxidized DDB to its oxidized state. + It undergoes a reversible chemical reaction with dead lithium on the surface of the negative electrode, thereby effectively removing dead lithium; and through the periodic combination of high and low rates, it meets the fast charging requirements of actual use on the one hand, and ensures that dead lithium does not continue to accumulate on the other hand, thereby achieving dynamic recovery and life extension of lithium metal batteries.

[0043] Furthermore, the applicant discovered that introducing a discharge stage between high-rate charging and low-rate charging—that is, performing a short pre-discharge treatment before low-rate charging to release 5-10% of the capacity—can further improve the efficiency of dead lithium removal. The pre-discharge process consumes newly formed lithium on the surface, causing the negative electrode interface potential to shift moderately and tend towards a more uniform distribution, thereby reducing the local electron enrichment and overpotential peak at the interface. This weakens the high-energy region at the interface that is prone to triggering solvent oxidation, allowing subsequent DDB oxidation to occur in a more stable potential environment. Simultaneously, pre-discharge can make the charge distribution around dead lithium more balanced, improving DDB efficiency. + The driving force of the reaction with dead lithium causes the formation of DDB + It tends to selectively attack dead lithium, further improving the efficiency of dead lithium removal.

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for removing dead lithium from the negative electrode of a lithium metal battery, characterized in that, The method includes the following steps: Step 1: Prepare the modified electrolyte; Step 2: Add the modified electrolyte to the lithium metal battery; Step 3: Alternately charge the lithium metal battery at high rate and low rate.

2. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 1, characterized in that: The modified electrolyte is a carbonate system electrolyte with added 1,4-bis(tert-butyl)-2,5-dimethoxybenzene.

3. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 2, characterized in that: The concentration of 1,4-bis(tert-butyl)-2,5-dimethoxybenzene is 10 mmol / L.

4. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 3, characterized in that: The electrolyte for the carbonate system is 1 M LiPF6 dissolved in ethylene carbonate and diethyl carbonate in a volume ratio of 1:

1.

5. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 4, characterized in that: The high-rate charging speed is 1-5C.

6. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 5, characterized in that: The low-rate charging is 0.1C.

7. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 6, characterized in that: In a high-low rate switching cycle, the number of cycles of high-rate charging is greater than the number of cycles of low-rate charging.

8. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 7, characterized in that: The number of cycles for high-rate charging is greater than or equal to 20 times the number of cycles for low-rate charging.

9. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 8, characterized in that: The modified electrolyte fills the space between the positive and negative electrode plates and the pores of the separator.

10. The method for removing dead lithium from the negative electrode of a lithium metal battery according to claim 9, characterized in that: Step 2 is performed in a glove box filled with nitrogen or argon.

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