Composite lithium supplement agent, composite diaphragm and preparation method of composite diaphragm

Abstract

The invention belongs to the technical field of lithium supplement materials, and discloses a composite lithium supplement agent, a composite diaphragm and a preparation method of the composite lithium supplement agent, the composite lithium supplement agent comprises hollow mesoporous silica microspheres and a lithium supplement agent, mesopores are distributed in shells of the hollow mesoporous silica microspheres, and the pore diameter is 2-30 nm; cavities of the hollow silicon dioxide microspheres are filled with the lithium supplement agent and / or the surfaces of the hollow silicon dioxide microspheres are coated with the lithium supplement agent, so that the problems that in an existing lithium supplement technology, stability is poor, process compatibility is low, uniformity is difficult to control, and safety risks are high are solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium replenishment materials technology, and specifically relates to a composite lithium replenishing agent, a composite separator, and a method for preparing the same. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] During the charging and discharging process of lithium-ion batteries, the initial charge and discharge permanently consume active lithium, forming a solid electrolyte interphase (SEI) film, resulting in capacity loss, energy density degradation, and lifespan decline. To address these issues, pre-treatment techniques are used to provide additional active lithium to compensate for the irreversible lithium loss in the LIB. Pre-treatment techniques are generally divided into two categories: negative electrode pre-treatment and positive electrode pre-treatment. Negative electrode lithium replenishment techniques include lithium-rich additives, chemical pre-treatment, and electrochemical pre-lithiation, among other lithium replenishment methods.

[0004] Existing lithium supplements mainly have the following problems: Lithium replenishing agents are chemically active, such as lithium powder, and are prone to failure during electrode slurry preparation and coating. This requires the entire process to be carried out under extremely harsh conditions, which significantly increases production costs and process complexity. Lithium supplements may react with slurry solvents and binders, which not only consumes the effective lithium source, but may also deteriorate the electrode structure, increase interfacial impedance, and affect the battery rate and cycle performance. Differences in density and particle size between lithium replenishing agents and electrode active materials can easily lead to sedimentation or agglomeration in the slurry, resulting in uneven lithium replenishment. Local over-lithiation can cause lithium plating, posing a serious safety hazard; local under-lithiation will result in poor performance; when the electrode is dry or in the early stages of battery electrolyte filling, contact between highly active lithium replenishing agents and the electrolyte may trigger a violent exothermic reaction, posing a risk of combustion and explosion. In addition, lithium replenishment agents may release a large amount of oxygen during delithiation, causing severe gas generation during battery cycling or storage. The dissolution of metals (Ni and Fe) can also increase safety risks. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite lithium replenishing agent, a composite separator, and a method for preparing the same. This addresses the problems of poor stability, low process compatibility, difficulty in controlling uniformity, and high safety risks inherent in existing lithium replenishment technologies.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a composite lithium replenishing agent, comprising hollow mesoporous silica microspheres and a lithium replenishing agent, wherein the hollow mesoporous silica microspheres have mesopores distributed on their outer shell, with a pore size of 2-30 nm; The lithium replenishing agent fills the cavity of the hollow silica microspheres and / or coats the surface of the hollow silica microspheres.

[0007] Secondly, the present invention provides a method for preparing the composite lithium supplement, comprising the following steps: Preparation of hollow mesoporous silica microspheres; Lithium replenishing agent is filled into hollow mesoporous silica microspheres using solution impregnation or vapor deposition methods; The filling process was carried out in an inert atmosphere with both water and oxygen content below 0.1 ppm.

[0008] Thirdly, the present invention provides a composite diaphragm, comprising a diaphragm substrate and a coating applied to the surface of the diaphragm substrate, wherein the coating comprises the composite lithium supplement, dispersant and binder, and the composite lithium supplement accounts for 85%-95% of the mass percentage of the coating.

[0009] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: The lithium replenishing agent is pre-encapsulated in a microscale silica "capsule". The hollow mesoporous silica shell acts as a physical barrier, which can effectively isolate the lithium replenishing agent from direct contact with the external environment (air, slurry solvent, binder), greatly improving the stability of the lithium replenishing agent in storage and process, and fundamentally reducing safety risks.

[0010] Achieving a macroscopically uniform distribution of the composite lithium replenishing agent on the separator ensures the uniformity of lithium replenishment throughout the battery. By adjusting the shell thickness, mesopore size, and sealing degree, controllable release of lithium ions can be achieved, avoiding localized over-lithiation.

[0011] Integrating the lithium replenishment function into the separator coating does not require changes to the existing mature electrode manufacturing process, making it easy to achieve industrial application on existing battery production lines and significantly reducing the cost of technology upgrades.

[0012] The hollow mesoporous silica coating enhances the mechanical strength, thermal stability, and electrolyte wettability of the separator, improving battery safety while achieving lithium replenishment. By precisely and uniformly compensating for the initial irreversible capacity loss, it can significantly improve the battery's initial coulombic efficiency, reversible capacity, energy density, and cycle life.

[0013] By utilizing the ion-conducting / electronic-insulating properties of silicon dioxide, the conductivity of the coating layer is prevented from interfering with the conductive network and structural stability of the positive electrode. The lithium replenisher is located in the region between the positive and negative electrodes, operating in a relatively mild electrochemical environment. During the initial charging phase, the lithium replenisher releases lithium ions at a lower potential relative to the negative electrode, resulting in a gentler process. Furthermore, the technical solution of this invention is not only fully compatible with existing electrode formulations and processes, exhibiting good process compatibility, but also solves the problem of the universal stability of the lithium replenisher throughout the entire battery manufacturing and storage process. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0015] Figure 1 This is a schematic diagram of the structure of hollow mesoporous silica microspheres loaded with lithium replenishing agent and the lithium replenishing functional membrane according to an embodiment of the present invention. Detailed Implementation

[0016] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0017] To address the technical problems mentioned in the background art, the present invention provides a composite lithium replenishing agent, comprising hollow mesoporous silica microspheres and a lithium replenishing agent, wherein the hollow mesoporous silica microspheres have mesopores distributed on their outer shell with a pore size of 2-30 nm; The lithium replenishing agent fills the cavity of the hollow silica microspheres and / or coats the surface of the hollow silica microspheres.

[0018] The hollow mesoporous silica microspheres have a core-shell structure, in which the hollow region is used to contain the lithium replenishing agent, and the mesoporous shell (pore size 2-30 nm) serves as an ion transport channel and release control barrier.

[0019] In the composite lithium replenisher of this invention, the lithium replenisher is encapsulated within the cavity of hollow mesoporous silica microspheres. The silica shell acts as a physical barrier, effectively isolating the lithium replenisher from direct contact with the external environment (air, slurry solvent, binder, electrolyte). This addresses the problems of existing lithium replenishers (such as lithium powder) being chemically reactive, easily reacting with solvents / binders, and causing violent exothermic reactions with the electrolyte during injection, leading to failure, safety hazards, and increased process complexity. Encapsulation avoids these side reactions, fundamentally improving stability during storage and manufacturing, and reducing the risk of combustion and explosion.

[0020] The mesopores (pore size 2-30nm) of hollow mesoporous silica microspheres provide channels for lithium-ion transport, and the controllable release of lithium-ions can be achieved by adjusting the shell thickness, mesopore size and sealing degree. At the same time, the composite lithium replenishing agent can achieve macroscopic uniform distribution in the membrane coating, so as to solve the problem that existing lithium replenishing agents are prone to sedimentation / agglomeration due to density and particle size differences, resulting in local over-lithiation (lithium deposition) or under-lithiation.

[0021] The lithium replenishment function is integrated into the separator coating, without the need to modify the existing electrode manufacturing process (such as positive / negative electrode slurry preparation and coating), thus solving the problem that traditional lithium replenishment agents need to be prepared in harsh environments (anhydrous and oxygen-free) to increase production costs and process complexity.

[0022] The hollow mesoporous silica coating itself can enhance the mechanical strength, thermal stability and electrolyte wettability of the separator; at the same time, the lithium replenishment agent is located in the middle region between the positive and negative electrodes, and works in a mild electrochemical environment. Lithium ions can be released at a low potential in the early stage of charging, making the process more gentle and avoiding a large amount of gas production and metal dissolution during delithiation.

[0023] In some embodiments, the lithium replenishing agent includes, but is not limited to, one or more of lithium metal powder, lithium silicon alloy powder, lithium aluminum alloy powder, lithium oxide, lithium peroxide, or lithium sulfide.

[0024] In some embodiments, the hollow mesoporous silica microspheres have a particle size of 200-800 nm.

[0025] Preferably, the hollow mesoporous silica microspheres have a particle size of 300-600 nm.

[0026] If the particle size is too small, the loading capacity will be insufficient; if it is too large, it will affect the thickness of the diaphragm coating and its mechanical properties.

[0027] Preferably, the shell thickness of the hollow mesoporous silica microspheres is 20-100 nm, more preferably 30-60 nm. If the shell is too thin, the mechanical strength is insufficient and it is prone to breakage; if it is too thick, the ion transport resistance is too high.

[0028] Preferably, the pore size of the mesoporous silica microspheres is 3-10 nm in the shell. This pore size range is sufficient to ensure electrolyte wetting and free lithium ion transport, while effectively limiting the escape of lithium replenishment particles.

[0029] The specific surface area of ​​the hollow mesoporous silica microspheres is between 600 and 1000 m². 2 / g; pore volume between 1.0-1.8cm 3 / g.

[0030] In some embodiments, the composite lithium replenishing agent further includes an encapsulation layer, which is deposited and encapsulated on the outside of the hollow mesoporous silica microspheres and the composite lithium replenishing agent.

[0031] Preferably, the encapsulation layer is made of Al2O3, TiO2, SiO2, or an amorphous carbon layer.

[0032] Preferably, the thickness of the encapsulation layer is 1-10 nm, and more preferably 2-5 nm.

[0033] Secondly, the present invention provides a method for preparing the composite lithium supplement, comprising the following steps: Preparation of hollow mesoporous silica microspheres; Lithium replenishing agent is filled into hollow mesoporous silica microspheres using solution impregnation or vapor deposition methods; The filling process was carried out in an inert atmosphere with both water and oxygen content below 0.1 ppm.

[0034] During the filling process, the water and oxygen content are strictly controlled to avoid side reactions between the lithium supplement and water and oxygen, thus ensuring the chemical stability and activity of the lithium supplement.

[0035] In some embodiments, the hollow mesoporous silica microspheres are prepared by a hard template method or a soft template method.

[0036] The hard template method uses monodisperse SiO2 or PS microspheres as templates; the soft template method is synthesized via emulsion synthesis. The hard template method is preferred because its particle size and shell thickness are easier to control.

[0037] In some embodiments, when the lithium replenishing agent is filled by solution impregnation, the solvent used is an aprotic, high-boiling-point organic solvent.

[0038] Preferably, when filling the lithium replenishing agent using the solution impregnation method, the solvent used is ethylene glycol dimethyl ether, sulfolane, or N-methylpyrrolidone.

[0039] In some embodiments, when filling the lithium replenishing agent using the solution impregnation method, hollow mesoporous silica microspheres are immersed in the solution and vacuum impregnated.

[0040] Preferably, the vacuum impregnation temperature is 25-60℃, the vacuum degree of vacuum impregnation is -0.05 MPa to -0.1 MPa, and the vacuum impregnation time is 1-4h.

[0041] In a further preferred embodiment, after impregnation, the solvent is removed by vacuum drying at a temperature of 60-100℃ for 6-24 hours to obtain a composite lithium supplement.

[0042] In some embodiments, when lithium metal is used as the lithium replenishing agent, the lithium replenishing agent is filled using a vapor deposition method. The lithium metal powder may undergo surface coating treatment to improve stability.

[0043] Preferably, the specific method is as follows: a hollow mesoporous silica support is placed in a vacuum reactor, and a lithium metal source is heated and vaporized at the other end. The lithium source heating temperature is 500-800 ℃, and the temperature of the hollow mesoporous silica support substrate is 100-300 ℃; the vacuum degree is less than 10. -3 Pa; deposition 0.5-3 h.

[0044] The lithium load can be precisely controlled by controlling the time.

[0045] In some embodiments, the method further includes an encapsulation step of the prepared composite lithium replenishing agent, wherein the encapsulation material is Al2O3, TiO2, SiO2, or an amorphous carbon layer. After filling with the lithium replenishing agent, the mesopore openings are slightly sealed by atomic layer deposition to further regulate the lithium-ion release kinetics and prevent the lithium replenishing agent from reacting violently with the electrolyte in the initial stage of electrolyte injection.

[0046] Preferably, the encapsulation method is atomic layer deposition or chemical vapor deposition.

[0047] Thirdly, the present invention provides a composite diaphragm, comprising a diaphragm substrate and a coating applied to the surface of the diaphragm substrate, wherein the coating comprises the composite lithium supplement, dispersant and binder, and the composite lithium supplement accounts for 85%-95% of the mass percentage of the coating.

[0048] In some embodiments, the dispersant is fatty alcohol polyoxyethylene ether (AEO), fluoroalkyl ethers, esters (polyoxyethylene dioleate, polytetraethylene glycol monostearate), and modified polyether polyacrylate, APAM, CPAM, or NPAM, and the dispersant has a mass percentage of 3%-8% in the coating.

[0049] In some embodiments, the adhesive is PVDF, CMC / SBR or polyacrylate, and the adhesive accounts for 3%-8% of the coating by mass.

[0050] The present invention will be further described below with reference to the embodiments.

[0051] Example 1: Standard Scheme (Li2O, solution method, unsealed) (1) The preparation method of the composite lithium supplement is as follows: 1) The hollow mesoporous silica microsphere carrier was prepared by the hard template method: the template was polystyrene microspheres (PS) with a particle size of 400 nm. PS microspheres were dispersed in 100 mL of 0.1 M CTAB solution (pH=2) and stirred continuously at 30 °C for 30 min to allow CTAB to adsorb onto the surface of the PS microspheres and form a micelle layer. Tetraethyl orthosilicate (TEOS) (0.15 M) and 0.02 MHCl were added to the above solution, and the temperature was maintained at 30 °C. TEOS was then slowly added dropwise at a rate of 0.5 mL / min. -1 The reaction was carried out for 90 min. After the reaction, the product was collected by centrifugation and washed three times with ethanol to obtain SiO2-coated particles. The particles were then calcined at 600 °C for 4 h under inert gas (N2, Ar) to remove the PS microspheres, yielding hollow mesoporous silica microspheres.

[0052] The parameters of the prepared hollow mesoporous silica microsphere carrier are: average particle size of about 400 nm, average shell thickness of 50 nm, and average pore size of 8 nm.

[0053] 2) The lithium replenishing agent is filled using a solution method. The specific operation is as follows: Prepare a lithium-containing dispersion of ethylene glycol dimethyl ether with a mass concentration of 20% for Li2O; The hollow mesoporous silica microspheres prepared in step 1) were immersed in a lithium replenishment solution and vacuum-impregnated at 30°C for 2 hours under a vacuum of -0.05 MPa. After vacuum impregnation, the solvent is removed by vacuum drying at 70°C for 10 hours, allowing the lithium replenishing agent to crystallize and precipitate and be fixed inside the hollow mesoporous silica cavity.

[0054] In the prepared composite lithium supplement, the lithium supplement loading is 20 wt%.

[0055] 3) The composite lithium supplement, dispersant fatty alcohol polyoxyethylene ether (AEO), and binder aqueous PVDF obtained in step 2) are mixed in a mass ratio of 90:5:5, and then mixed with N-methylpyrrolidone to make the solid content 40% to obtain a slurry. The prepared slurry was coated onto a PE membrane using a microgravure coating method, with a coating areal density of 2.0 mg / cm³. 2 ; After coating, it is dried in an oven at 70°C to obtain the composite diaphragm.

[0056] Example 2: High-performance solution (lithium metal, CVD method, ALD sealing) (1) The preparation method of the composite lithium supplement is as follows: 1) The hollow mesoporous silica microsphere carrier was prepared by the hard template method: the template was polystyrene microspheres (PS) with a particle size of 400 nm. PS microspheres were dispersed in 100 mL of 0.1 M CTAB solution (pH=2) and stirred continuously at 30 °C for 30 min to allow CTAB to adsorb onto the surface of the PS microspheres and form a micelle layer. Tetraethyl orthosilicate (TEOS) (0.15 M) and 0.02 MHCl were added to the above solution, and the temperature was maintained at 30 °C. TEOS was then slowly added dropwise at a rate of 0.5 mL / min. -1 The reaction was carried out for 90 min. After the reaction, the product was collected by centrifugation and washed three times with ethanol to obtain SiO2-coated particles. Hollow mesoporous silica microspheres were prepared by high-temperature calcination at 600 °C for 4 h under inert gas (N2, Ar) protection to remove PS microspheres.

[0057] The parameters of the prepared hollow mesoporous silica microsphere carrier are: average particle size of about 400 nm, average shell thickness of 50 nm, and average pore size of 8 nm.

[0058] 2) The lithium replenishing agent is filled using the CVD method. The specific operation is as follows: Hollow mesoporous silica microspheres were placed in a vacuum reactor. Lithium metal powder coated with Li2CO3 was heated and vaporized at the other end. The heating temperature was 600 ℃, and the substrate temperature of the hollow mesoporous silica carrier was 200 ℃. The vacuum level of the vacuum reactor is less than 10. -3 Pa, deposition time 1 h, to achieve a lithium loading of 30 wt% on the hollow mesoporous silica microspheres; The prepared composite lithium supplement was sealed using atomic layer deposition (ALD) to obtain a 3 nm Al2O3 sealing layer.

[0059] 3) The composite lithium supplement, dispersant AEO and binder PVDF obtained in step 2) are mixed in a mass ratio of 90:5:5, and then combined with N-methylpyrrolidone to make the solid content 40% to obtain a slurry; The prepared slurry was coated onto a PE membrane using a microgravure coating method, resulting in a coating surface density of 1.5 mg / cm². 2 .

[0060] Example 3: Low-cost solution (Li2S, solution method, CVD sealing) (1) The preparation method of the composite lithium supplement is as follows: 1) The preparation method of the hollow mesoporous silica microsphere carrier is the same as that in Example 1. The parameters of the prepared hollow mesoporous silica microsphere carrier are: average particle size of 400 nm, average shell thickness of 50 nm, and average pore size of 8 nm.

[0061] 2) The lithium replenishing agent was filled using a solution method, with the specific operation being the same as in Example 1. The lithium replenishing agent loading in the prepared composite lithium replenishing agent was 25 wt%. The prepared composite lithium supplement was sealed using CVD, resulting in a 3nm carbon coating layer.

[0062] 3) Mix the composite lithium supplement, dispersant AEO and binder PVDF obtained in step 2) at a mass ratio of 90:5:5, and then mix with N-methylpyrrolidone to make the solid content 40% to obtain a slurry; The prepared slurry was coated onto a PE membrane using a microgravure coating method, resulting in a coating areal density of 2.5 mg / cm². 2 .

[0063] Example 4: Application in graphite systems The difference from Example 1 is that the coating surface density is 1.0 mg / cm³. 2 (Because graphite has a low irreversible capacity), everything else is the same as in Example 1.

[0064] Negative electrode system: artificial graphite.

[0065] Example 5: Low areal density scheme The difference from Example 1 is that the coating surface density is 0.8 mg / cm³. 2 Everything else is the same as in Example 1.

[0066] Example 6: High Areal Density Scheme The difference from Example 1 is that the coating surface density is 3.5 mg / cm³. 2 Everything else is the same as in Example 1.

[0067] Comparative Example 1: No lithium replenishment measures Separator: Ordinary PE diaphragm, without any coating.

[0068] Purpose: To serve as a baseline performance reference.

[0069] Comparative Example 2: Lithium supplementation added to conventional cathodes Lithium replenishment method: 0.3% by mass of Li2O powder is directly mixed with NCM811 cathode material to form a slurry.

[0070] Diaphragm: Ordinary PE diaphragm.

[0071] Negative electrode system: silicon-carbon negative electrode.

[0072] Objective: To simulate the most common existing lithium replenishment technology.

[0073] Comparative Example 3: Non-hollow mesoporous SiO2 coating The difference from Example 1 is that the coating material used is solid mesoporous silica microspheres (specific surface area 300 m²). 2 / g (without hollow cavity), after being physically mixed with Li2O, is coated onto the diaphragm, and everything else is the same as in Example 1.

[0074] Coating areal density: 2.0 mg / cm³ 2 .

[0075] Negative electrode system: silicon-carbon negative electrode.

[0076] Objective: To verify the crucial role of hollow structures in high load and stability.

[0077] Comparative Example 4: Lithium supplement agent directly coated on the separator Coating material: Li2O powder, dispersant AEO and binder PVDF are directly mixed in a mass ratio of 90:5:5 to form a slurry, which is then coated onto the diaphragm.

[0078] Coating surface density: The mass of Li2O is the same as the effective mass of Li2O in the coating of Example 1.

[0079] Negative electrode system: silicon-carbon negative electrode.

[0080] Objective: To verify the processing stability and effectiveness of lithium supplementation agent when encapsulated and protected without a hollow mesoporous silica carrier.

[0081] Comparative Example 5: The parameters of the hollow mesoporous silica carrier are outside the preferred range (shell layer is too thick). Hollow mesoporous silica carrier parameters: average particle size 400 nm, average shell thickness 120 nm, pore size 5 nm.

[0082] Lithium supplement and filler: Same as in Example 1.

[0083] Coating areal density: 2.0 mg / cm³ 2 .

[0084] Negative electrode system: silicon-carbon negative electrode.

[0085] Objective: To verify the effect of shell thickness on ion transport dynamics and demonstrate the importance of the optimal parameter range.

[0086] Fabrication of pouch cells: The separators / lithium supplements prepared in the examples and comparative examples were applied to pouch cells for electrochemical performance testing. The cell assembly process is as follows: 1) Ternary material (NMC811) was mixed with Super P, CNT, and PVDF at a mass ratio of 97:1:0.5:1.5, and N-methylpyrrolidone (NMP) was added, with a solid content of 65%. The mixture was homogenized to form a positive electrode slurry free of particles. The slurry was then evenly coated onto aluminum foil using a coating machine, with a coating amount of 390 g / m². 2 To produce a positive electrode roll; Silicon carbide / graphite was added to deionized water at a mass ratio of 97.2:0.6:1:1.2, with a solid content of 55%. A negative electrode slurry was prepared using a homogenization process to ensure the slurry was free of particles. The slurry was then uniformly coated onto copper foil using a coating machine. The coating amount of silicon carbide was 140 g / m³. 2 Graphite: 180 g / m 2 The negative electrode was fabricated into silicon-carbon negative electrode (Si-C, 450 mAh / g) and graphite negative electrode (350 mAh / g).

[0087] 2) The electrode rolls are rolled and die-cut into suitable electrode sheets. Using the coated separators prepared in the examples and comparative examples, dry cells are fabricated through processes such as stacking, welding, and encapsulation. The cells are then placed in a vacuum drying oven at 80 ℃ for 48 hours for vacuum drying. After processes such as electrolyte injection, activation, formation, aging, and secondary sealing, the cells are fabricated. The electrolyte composition is as follows: solvent system: EC / DEC volume ratio of 1:1, LiPF6:1M.

[0088] 3) The charge / discharge voltage range is 2.75-4.35V, the initial discharge rate is 0.5C, and the cycle performance test charge / discharge rate is 1C for 300 cycles.

[0089] Table 1

[0090] Lithium replenishment effectiveness (vs Comparative Example 1): The initial coulombic efficiency of all embodiments (1-6) of the present invention was significantly higher than that of Comparative Example 1 (84.9%) without lithium replenishment, which fully demonstrates the effectiveness of the present invention.

[0091] The crucial role of hollow structures (vs. Comparative Example 3): Example 1 outperforms Comparative Example 3, which uses solid mesoporous SiO2, in almost all performance metrics. This demonstrates that hollow cavities are essential for achieving high lithium loading and maintaining long-term cycling stability.

[0092] Advantages of encapsulation protection (vs. Comparative Examples 2 & 4): Compared to cathode addition (Comparative Example 2) and direct coating (Comparative Example 4), the gas production in each embodiment of the present invention is significantly reduced, demonstrating the superior effect of hollow mesoporous silica encapsulation in suppressing side reactions and improving safety. The initial efficiency of Comparative Example 4 is actually lower than the baseline, indicating that a large amount of lithium replenishment has failed before film formation and has damaged the electrode / separator interface.

[0093] Parameter optimization window: ① Areal density: Examples 5, 1, and 6 demonstrate the effects from low to high. Example 1 (2.0 mg / cm³) 2 Achieving an optimal balance between lithium replenishment, recycling, and gas production. Example 6 (3.5 mg / cm³) 2 Although it has the highest capacity, the gas production increases and the retention rate decreases.

[0094] ② Shell thickness: The initial efficiency and cycling performance of Comparative Example 5 (shell thickness 120 nm) were significantly worse than those of Example 1 (shell thickness 50 nm), which proves that an excessively thick shell will hinder ion transport and the necessity of a preferred range (30-60 nm).

[0095] ③ Application System: Example 4 demonstrates that the present invention is also effective for graphite systems and can achieve extremely high first-time efficiency.

[0096] Technical integration advantages: Example 2 (ALD seal) demonstrates the best overall performance, especially in cycle life and minimum gas production, representing the high-performance direction of the present invention.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 composite lithium supplement, characterized in that: It includes hollow mesoporous silica microspheres and a lithium supplement, wherein the outer shell of the hollow mesoporous silica microspheres is distributed with mesopores with a pore size of 2-30 nm; The lithium replenishing agent fills the cavity of the hollow silica microspheres and / or coats the surface of the hollow silica microspheres.

2. The composite lithium supplement agent according to claim 1, characterized in that: The lithium replenishing agent includes, but is not limited to, one or more of the following: lithium metal powder, lithium silicon alloy powder, lithium aluminum alloy powder, lithium oxide, lithium peroxide, or lithium sulfide.

3. The composite lithium supplement agent according to claim 1, characterized in that: The hollow mesoporous silica microspheres have a particle size of 200-800 nm; Preferably, the hollow mesoporous silica microspheres have a particle size of 300-600 nm; Preferably, the shell thickness of the hollow mesoporous silica microspheres is 20-100 nm, and more preferably 30-60 nm; Preferably, the pore size of the mesopores on the shell of the hollow mesoporous silica microspheres is 3-10 nm.

4. The composite lithium supplement agent according to claim 1, characterized in that: The composite lithium replenishing agent also includes an encapsulation layer, which is deposited and encapsulated on the outside of the hollow mesoporous silica microspheres and the composite lithium replenishing agent; Preferably, the encapsulation layer is made of Al2O3, TiO2, SiO2, or an amorphous carbon layer; Preferably, the thickness of the encapsulation layer is 1-10 nm, and more preferably 2-5 nm.

5. The method for preparing the composite lithium supplement according to any one of claims 1-4, characterized in that: Includes the following steps: Preparation of hollow mesoporous silica microspheres; Lithium replenishing agent is filled into hollow mesoporous silica microspheres using solution impregnation or vapor deposition methods; The filling process was carried out in an inert atmosphere with both water and oxygen content below 0.1 ppm.

6. The method for preparing the composite lithium supplement according to claim 5, characterized in that: When filling lithium replenishing agent using the solution impregnation method, the solvent used is an aprotic, high-boiling-point organic solvent; Preferably, when filling the lithium replenishing agent using the solution impregnation method, the solvent used is ethylene glycol dimethyl ether, sulfolane, or N-methylpyrrolidone.

7. The method for preparing the composite lithium supplement according to claim 5, characterized in that: When filling lithium replenishing agent using the solution impregnation method, hollow mesoporous silica microspheres are immersed in the lithium replenishing agent solution and then impregnated under vacuum. Preferably, the vacuum impregnation temperature is 25-60℃, the vacuum degree of vacuum impregnation is -0.05 MPa to -0.1 MPa, and the vacuum impregnation time is 1-4 hours; Preferably, after impregnation, the solvent is removed by vacuum drying to obtain a composite lithium supplement; Preferably, when the lithium replenishing agent is metallic lithium, the lithium replenishing agent is filled by vapor deposition.

8. The method for preparing the composite lithium supplement according to claim 5, characterized in that: It also includes a step of encapsulating the prepared composite lithium supplement, wherein the encapsulating material is Al2O3, TiO2, SiO2 or an amorphous carbon layer; Preferably, the encapsulation method is atomic layer deposition or chemical vapor deposition.

9. A composite diaphragm, characterized in that: The coating comprises a membrane substrate and a coating applied to the surface of the membrane substrate, wherein the coating comprises the composite lithium supplement agent, dispersant and binder as described in any one of claims 1-4, and the composite lithium supplement agent accounts for 85%-95% of the mass percentage of the coating.

10. The composite diaphragm according to claim 9, characterized in that: The dispersant is fatty alcohol polyoxyethylene ether (AEO), fluoroalkyl ethers, polyoxyethylene dioleate, polytetraethylene glycol monostearate, modified polyether polyacrylate, APAM, CPAM, or NPAM, and the mass percentage of the dispersant in the coating is 3%-8%. Preferably, the adhesive is PVDF, CMC / SBR or polyacrylate, and the adhesive accounts for 3%-8% of the coating by mass.

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