Composite material as well as preparation method and application thereof

Abstract

The invention provides a composite material as well as a preparation method and application thereof. The composite material comprises mesoporous silica particles, a conductive polymer, a cross-linking agent and dopamine, the cross-linking agent is polyethylene glycol. The composite material can be used for preparing a multi-layer positive pole piece of a lithium battery, and the modified mesoporous silica particles are combined with the conductive polymer to construct a flexible three-dimensional conductive network between different active material levels, so that the metal dissolution phenomenon in the circulation process is inhibited, and the compression resilience of the pole piece is improved. And for active materials with different expansion coefficients, the conductive network has good interface compatibility, the interface contact problem of different active material layers is effectively improved, the layer stripping phenomenon in the charging and discharging process is relieved, and the electric cycle performance is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery materials technology, particularly the field of lithium battery cathode materials technology, and specifically relates to a composite material, its preparation method, and its application. Background Technology

[0002] Single-material (monolayer) cathodes are currently the mainstream in the manufacturing industry due to their simplicity, low cost, and mature technology. However, in terms of performance limits, there is a significant gap between them and the ideal high-performance battery. Therefore, multilayer cathodes have become a new research direction for high-performance batteries. The fundamental advantage of multilayer structures lies in breaking the performance limitations of single-material systems. Through the synergistic effect of each material performing its specific function, they achieve comprehensive performance that is difficult to achieve with a single material. However, the complexity of multilayer structures also brings many challenges, which are the main reasons why they have not yet been widely adopted.

[0003] Currently, the following problems exist with multilayer electrodes for lithium-ion batteries: (1) poor interface contact. For example, due to the difference in the expansion coefficient of active materials (e.g., the volume change rate difference between LFP and ternary materials > 8%), the interface delamination during cycling leads to the breakage of electron / ion transport channels, and the interface resistance exceeds 100 Ω·cm. 2 , 5C discharge capacity decay > 20%. (2) Byproduct shuttle, such as high-nickel ternary (NMC811) transitioning metal ions (Ni) in high-voltage cycling. 2+ / Co 2+ (3) Dissolution rate > 10%, shuttle to the negative electrode to cause lithium metal deposition and electrolyte decomposition, capacity retention rate < 80% after 500 cycles. (4) Conductive network breakage, such as uneven distribution of traditional carbon black / CNT conductive agent, breakage of conductive path under high rate, electrode resistance increases by more than 30%, and rate performance decreases significantly. Summary of the Invention

[0004] To address the problems and shortcomings of existing technologies, this invention provides a composite material, its preparation method, and its applications. This composite material can be used to prepare multilayer positive electrode sheets for lithium batteries. By combining modified mesoporous silica particles with conductive polymers, a flexible three-dimensional conductive network is constructed between different active material layers, suppressing metal dissolution during cycling and improving electrode compression resilience. Furthermore, this conductive network exhibits good interfacial compatibility for active materials with different coefficients of thermal expansion, effectively improving interfacial contact problems between different active material layers, alleviating layer delamination during charge and discharge, and enhancing electrical cycle performance.

[0005] According to a first aspect of the present invention, a composite material is provided, comprising mesoporous silica particles, a conductive polymer, a crosslinking agent, and dopamine; the crosslinking agent is polyethylene glycol.

[0006] The composite material provided by this invention includes the aforementioned substances. Dopamine contains active functional groups such as catechol and amino groups, which not only modify the surface of mesoporous silica particles and improve their dispersibility in the conductive polymer, but also allow the active groups such as catechol and amino groups in dopamine to form strong interfacial interactions with the conductive polymer, such as hydrogen bonds or potential covalent bonds, which is beneficial for the strong bonding between the inorganic and organic phases. Furthermore, choosing mesoporous silica allows for deeper interpenetration and stronger interfacial bonding with the conductive polymer, resulting in a more significant synergistic effect and improving the deformation properties of the conductive polymer. Moreover, the hydroxyl groups at the ends of the crosslinking agent polyethylene glycol can react and bind with dopamine, and the long chains of polyethylene glycol can undergo physical bonding and crosslinking with the conductive polymer. Therefore, the crosslinking agent polyethylene glycol can further participate in the formation of the crosslinking network, further improving the density of the polymer matrix and the mechanical flexibility of the overall crosslinking network.

[0007] Therefore, applying the above-mentioned composite material to the modification of multilayer cathode sheets for lithium batteries yields several advantages. First, the composite material can construct a three-dimensional network with excellent conductivity and mechanical flexibility between different active material layers. This network can effectively adapt to the internal stress generated by the difference in expansion coefficients of different active materials during charging and discharging, greatly improving the compression rebound rate of the electrode sheet. This significantly alleviates interlayer delamination during cycling and improves the physical contact within the electrode sheet and between its layers, significantly reducing the overall resistance of the electrode sheet and optimizing the battery's cycle performance. Second, the mesoporous silica particles are uniformly dispersed in the conductive polymer, which can more comprehensively and effectively block the erosion of the cathode active material by HF, thereby inhibiting the dissolution of transition metal ions and further improving the cycle stability of the battery. Moreover, the large specific surface area of ​​mesoporous silica can retain a certain amount of electrolyte, increasing the wettability of the electrolyte in the later stages of cycling, and further improving the interfacial delamination phenomenon caused by material deformation during cycling.

[0008] Preferably, dopamine is modified on the surface of the mesoporous silica particles.

[0009] Preferably, the conductive polymer includes at least one of polyaniline, polypyrrole, polyacrylonitrile, and polythiophene.

[0010] Preferably, the mass ratio of mesoporous silica particles to conductive polymer is 1:3-6; the mass ratio of crosslinking agent to conductive polymer is 0.2-1:100; and the average molecular weight (number average molecular weight) of the crosslinking agent is 300-1000.

[0011] Preferably, the mesoporous silica particles have a diameter of 100-500 nm and a specific surface area of ​​800-1300 m². 2 / g, with a pore size of 15-150 nm.

[0012] Preferably, the mesoporous silica particles are spherical or near-spherical particles.

[0013] According to a second aspect of the present invention, a method for preparing any of the above-mentioned composite materials is provided, comprising the following steps: S1. Dispersing mesoporous silica particles in Tris-HCl buffer, adding dopamine hydrochloride, and continuously stirring the mixture under light-shielding conditions for 12-24 hours. After the reaction is completed, washing, centrifuging, and drying the product to obtain modified mesoporous silica particles; S2. Preparing a modified mesoporous silica particle dispersion using the product obtained in S1, and preparing a conductive polymer solution using a conductive polymer. Mixing the modified mesoporous silica particle dispersion and the conductive polymer solution uniformly to obtain mixture A; S3. Adding a crosslinking agent to mixture A, mixing uniformly, and polymerizing for 1-2 hours to form a composite material.

[0014] Preferably, in S1, the reaction temperature is 25-30°C.

[0015] Preferably, in S1, the pH of the Tris-HCl buffer solution is 7.5-8.8; more preferably 8.5.

[0016] Preferably, in S1, when the mesoporous silica particles are dispersed in the Tris-HCl buffer solution, the mass fraction of the mesoporous silica particles in the resulting dispersion is 2-8%.

[0017] Preferably, in S1, the mass ratio of mesoporous silica particles to dopamine hydrochloride is 1:0.5-2.

[0018] Preferably, in S2, the specific washing and centrifugation operations are as follows: wash with ethanol and water alternately 3-4 times, and the centrifugation speed is 7500-8500 rpm and the centrifugation time is 6-10 min; preferably, the centrifugation speed is 8000 rpm and the centrifugation time is 8 min.

[0019] Preferably, in step S2, the drying is vacuum drying at a temperature of 55-65°C for 12-24 hours.

[0020] Preferably, in step S2, the mass fraction of modified mesoporous silica particles in the modified mesoporous silica particle dispersion is 3-8%. Preferably, the organic solvent used to prepare the modified mesoporous silica particle dispersion includes N,N-dimethylformamide (DMF). Preferably, the specific operation for preparing the modified mesoporous silica particle dispersion is to disperse the modified mesoporous silica particles in N,N-dimethylformamide and sonicate for 30-60 min. The resulting dispersion is a milky white suspension.

[0021] Preferably, in step S2, the conductive polymer solution contains 10-20% by mass of the conductive polymer. Preferably, the organic solvent used to prepare the conductive polymer solution includes N,N-dimethylformamide. Preferably, the specific steps for preparing the conductive polymer solution are as follows: dispersing the conductive polymer in N,N-dimethylformamide, heating the solution to 45-55°C, and stirring until the solution becomes transparent.

[0022] Preferably, in S2, mixing the modified mesoporous silica particle dispersion with the conductive polymer solution uniformly means that the modified mesoporous silica particles are uniformly dispersed inside the conductive polymer.

[0023] Preferably, in step S2, the specific operation of uniformly mixing the modified mesoporous silica particle dispersion with the conductive polymer solution is as follows: the modified mesoporous silica particle dispersion is added to the conductive polymer solution at a rate of 50-60 mL / h, and stirred for 2-4 h to uniformly disperse the modified mesoporous silica particles inside the conductive polymer.

[0024] Preferably, in S2, the mass ratio of modified mesoporous silica particles to conductive polymer is 1:3-6.

[0025] Preferably, in S3, the reaction temperature during the polymerization process is 0-80°C. Preferably, the viscosity of the composite material is 2000-10000 mPa·s.

[0026] Preferably, in step S1, the method for preparing mesoporous silica particles specifically includes the following steps: S11. Dissolve the main template agent in deionized water, add the auxiliary template agent while continuously stirring, stir for 1-2 hours, add a pH adjuster to adjust the pH of the solution to 8-9, and continue stirring for 1-2 hours to obtain a pretreatment solution; S12. Add a silicon source to the pretreatment solution while continuously stirring, and continue stirring for 18-30 hours; S13. After the reaction is completed, wash and dry the product, and then calcine it at 450-650℃ for 3-6 hours.

[0027] Preferably, in step S11 of the method for preparing mesoporous silica particles, the main template agent includes hexadecyltrimethylammonium bromide. Preferably, in step S11, the auxiliary template agent includes styrene-butadiene rubber (SBR) emulsion. Preferably, the mass fraction of SBR is 0.5-1%. Preferably, in step S11, the pH adjuster includes triethanolamine. Preferably, in step S11, the main template agent is dissolved in deionized water, and the mass fraction of the main template agent in the resulting solution is 3-8%. Preferably, the auxiliary template agent is added dropwise at a rate of 50-100 mL / h. Preferably, in step S11, the mass ratio of the main template agent to the auxiliary template agent is 3-15:1.

[0028] Preferably, in step S12 of the method for preparing mesoporous silica particles, a silicon source is added dropwise at a rate of 50-60 mL / h. Preferably, in step S12, the silicon source comprises tetraethyl orthosilicate (TEOS). Preferably, in step S12, the amount of silicon source added is 5-12 wt% of the pretreatment solution. Preferably, in step S12, the reaction temperature is 25 ± 2 °C.

[0029] Preferably, in step S13 of the method for preparing mesoporous silica particles, the particles are cleaned by repeated alternating washing and centrifugation with deionized water and anhydrous ethanol. During centrifugation, the centrifugation rate is 7500-8500 rpm for 3-7 minutes. Preferably, in step S13, the drying temperature is 55-65°C for 10-16 hours. Preferably, in step S13, during calcination, the temperature is programmed to rise to 450-650°C at a rate of 1-5°C / min. Preferably, in step S13, the calcination process is conducted in an air atmosphere.

[0030] According to a third aspect of the present invention, an electrode for a lithium battery is provided, comprising a current collector and at least a first active material layer, a first functional layer, a second active material layer, and a second functional layer sequentially disposed on one side of the current collector; the first functional layer and the second functional layer comprise any of the aforementioned composite materials or composite materials prepared by any of the aforementioned preparation methods. Preferably, the second functional layer is disposed on the side away from the current collector.

[0031] Preferably, the electrode is a positive electrode; the first active material layer includes a first active material; the second active material layer includes a second active material; the first active material and the second active material independently include at least one of lithium manganese iron phosphate (LMFP), lithium iron phosphate (LFP), ternary nickel cobalt manganese (NCM), lithium cobalt oxide (LCO), and lithium manganese oxide (LMO).

[0032] Preferably, the first active material and the second active material have different compositions.

[0033] Preferably, the thickness of the first active material layer is 40-70 μm, the thickness of the first functional interlayer is 3-6 μm, the thickness of the second active material layer is 20-40 μm, the thickness of the second functional interlayer is 3-5 μm, and the total coating weight on one side is 200-300 g / m². 2 The compaction density of the electrode sheet is 2.5-3.5 g / cm³. 3 Preferably, the thickness of the first functional interlayer is greater than the thickness of the second functional interlayer.

[0034] Preferably, the first active material layer comprises a first active material, a polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs, wherein the mass ratio of the first active material, the polyvinylidene fluoride binder, the conductive carbon black, and the conductive CNTs is 95.5-98:1-3:0.5-1.5:0.5-1.5.

[0035] Preferably, the second active material layer comprises a second active material, a polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs, and the mass ratio of the first active material, polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs is 95.5-98:1-3:0.5-1.5:0.5-1.5.

[0036] According to a fourth aspect of the present invention, a lithium battery is provided, comprising any of the aforementioned lithium battery electrodes. The lithium battery prepared from the aforementioned electrodes exhibits high energy density, high rate performance, and long cycle life.

[0037] Preferably, the lithium battery includes a negative electrode sheet, and the total coating weight on one side of the negative electrode sheet is 90-130 g / m². 2 The compaction density is controlled at 1.5-1.7 g / cm³. 3 Preferably, the negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode active material. The negative electrode active material includes at least one of natural graphite, artificial graphite, modified graphite materials, and soft carbon / hard carbon composite materials. Natural graphite includes flake graphite, spherical graphite, etc. Artificial graphite includes mesophase carbon microspheres, needle-like coke-based graphite, pitch-based graphite, etc. Modified graphite materials include carbon-coated graphite, oxide-coated graphite, element-doped graphite, graphite / silicon composite materials, and soft carbon / hard carbon / graphite composite materials. Soft carbon / hard carbon composite materials include hard carbon coated with soft carbon material; soft carbon includes carbon fibers, carbon microspheres, graphitized mesophase carbon microspheres, petroleum coke, needle-like coke, etc., and hard carbon includes resin carbon, organic polymer pyrolysis carbon, carbon black, etc. Preferably, the negative electrode active material is hard carbon coated with soft carbon material.

[0038] Preferably, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder, wherein the mass ratio of the negative electrode active material, the conductive agent, and the binder is 93.5-96.5:1-4:1-3.

[0039] Preferably, the lithium battery further includes a separator, which comprises a base film and a PVDF layer and an alumina layer sequentially disposed on at least one side. The thickness of the base film is 5-10 μm, the thickness of the PVDF layer is 1.5-5 μm, and the thickness of the alumina layer is 1.5-5 μm. Preferably, the base film comprises at least one of PP (polypropylene), PE (polyethylene), PET (polyethylene terephthalate), and PA (polyamide).

[0040] Preferably, the lithium battery further includes an electrolyte in which the lithium salt is LiPF6, the solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1, and the lithium salt concentration is 1.2 mol / L.

[0041] Compared with the prior art, the above-described technical solutions conceived in this invention have the following technical effects: The composite material provided by this invention contains mesoporous silica particles, a conductive polymer, polyethylene glycol, and dopamine. Dopamine can modify the surface of the mesoporous silica particles, and the active groups such as catechol and amino groups in dopamine can form strong interfacial interactions with the conductive polymer, thus allowing the inorganic and organic phases to be firmly bonded. Furthermore, polyethylene glycol can further participate in the formation of the cross-linked network, further improving the density of the polymer matrix and the mechanical flexibility of the overall cross-linked network.

[0042] Therefore, the composite material provided by this invention serves as a functional layer between different active material layers. Its constructed three-dimensional network, possessing both excellent conductivity and mechanical flexibility, effectively adapts to the internal stress generated by the differences in expansion coefficients of different active materials during charging and discharging. This significantly improves the compression resilience of the electrode, thereby greatly alleviating interlayer delamination during cycling and improving the physical contact within the electrode and between its layers. This significantly reduces the overall resistance of the electrode and optimizes the battery's cycle performance. Furthermore, the mesoporous silica particles are uniformly dispersed in the conductive polymer, which can more comprehensively and effectively block the erosion of the positive electrode active material by HF, thereby inhibiting the dissolution of transition metal ions and further improving the battery's cycle stability. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the positive electrode sheet in Example 1.

[0044] The reference numerals in the attached figures are as follows: 1-current collector, 2-first active material layer, 3-first functional layer, 4-second active material layer, 5-second functional layer. Detailed Implementation

[0045] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] According to a first aspect of the present invention, a composite material is provided, comprising mesoporous silica particles, a conductive polymer, a crosslinking agent, and dopamine; the crosslinking agent is polyethylene glycol.

[0047] The composite material provided by this invention includes the aforementioned substances. Dopamine contains active functional groups such as catechol and amino groups, which not only modify the surface of mesoporous silica particles and improve their dispersibility in the conductive polymer, but also allow the active groups in dopamine, such as catechol and amino groups, to form strong interfacial interactions with the conductive polymer, such as hydrogen bonds or potential covalent bonds, which is beneficial for the strong bonding between the inorganic and organic phases. Furthermore, choosing mesoporous silica allows for deeper interpenetration and stronger interfacial bonding with the conductive polymer, resulting in a more significant synergistic effect and improving the deformation properties of the conductive polymer. Moreover, the hydroxyl groups at the ends of the crosslinking agent polyethylene glycol can react and bind with dopamine, and the long chains of polyethylene glycol can undergo physical bonding and crosslinking with the conductive polymer. Therefore, the crosslinking agent polyethylene glycol can further participate in the formation of the crosslinking network, further improving the density of the polymer matrix and the mechanical flexibility of the overall crosslinking network.

[0048] Therefore, applying the above-mentioned composite material to the modification of multilayer cathode sheets for lithium batteries yields several advantages. First, the composite material can construct a three-dimensional network with excellent conductivity and mechanical flexibility between different active material layers. This network can effectively adapt to the internal stress generated by the difference in expansion coefficients of different active materials during charging and discharging, greatly improving the compression rebound rate of the electrode sheet. This significantly alleviates interlayer delamination during cycling and improves the physical contact within the electrode sheet and between its layers, significantly reducing the overall resistance of the electrode sheet and optimizing the battery's cycle performance. Second, the mesoporous silica particles are uniformly dispersed in the conductive polymer, which can more comprehensively and effectively block the erosion of the cathode active material by HF, thereby inhibiting the dissolution of transition metal ions and further improving the cycle stability of the battery. Moreover, the large specific surface area of ​​mesoporous silica can retain a certain amount of electrolyte, increasing the wettability of the electrolyte in the later stages of cycling, and further improving the interfacial delamination phenomenon caused by material deformation during cycling.

[0049] Preferably, dopamine is modified on the surface of the mesoporous silica particles.

[0050] Preferably, the conductive polymer includes at least one of polyaniline, polypyrrole, polyacrylonitrile, and polythiophene.

[0051] Preferably, the mass ratio of mesoporous silica particles to conductive polymer is 1:3-6; the mass ratio of crosslinking agent to conductive polymer is 0.2-1:100; and the average molecular weight (number average molecular weight) of the crosslinking agent is 300-1000. Firstly, when the mass ratio of mesoporous silica to conductive polymer is 1:3 to 1:6, this ratio ensures that the composite material can form a complete three-dimensional conductive network with the conductive polymer as the continuous phase. If the ratio is too low, i.e., the amount of mesoporous silica particles is too small, it cannot effectively suppress the excessive swelling and deformation of the polymer chains, weakening the material's mechanical support and its inhibitory effect on the expansion of the active material. If the ratio is too high, i.e., the amount of mesoporous silica particles is too large, it will disrupt the continuity of the conductive polymer phase, leading to the blockage of conductive pathways, increased electrode resistance, and reduced battery cycle performance; simultaneously, the particles are prone to agglomeration, generating stress concentration points, reducing the material's flexibility and processing performance, and decreasing the electrode resilience. Secondly, a mass ratio of crosslinking agent to conductive polymer within the range of 0.2-1:100 can form moderately dense crosslinking points. If the amount of crosslinking agent is too low, the crosslinking network will be too sparse, failing to effectively improve the mechanical strength and solvent swelling resistance of the composite material. If the amount is too high, the network will become too rigid, increasing brittleness and hindering its ability to adapt to volume changes during cycling, thus negatively impacting electrode stability and battery cycle performance. Furthermore, using a crosslinking agent with a molecular weight of 300-1000 is beneficial for constructing a stable crosslinking network structure. If the molecular weight is too high, the polymerization reaction will be slower, which is detrimental to the stability of the internal polymerization of the resulting composite material. Conversely, if the molecular weight is too low, the resulting composite material structure will lack sufficient strength, also affecting its performance. Simultaneously, this stable crosslinking network structure allows for rapid lithium-ion transport while effectively blocking the free penetration of large molecular solvated ion clusters and harmful substances such as HF in the electrolyte, thereby enhancing the protection of the positive electrode active material at the molecular scale. The average molecular weight of the crosslinking agent mentioned above refers to the number-average molecular weight.

[0052] Preferably, the mesoporous silica particles have a diameter of 100-500 nm and a specific surface area of ​​800-1300 m². 2 / g, with a pore size of 15-150 nm. A diameter of 100-500 nm effectively prevents particle agglomeration and sedimentation, ensuring uniform dispersion within the conductive polymer matrix and laying the foundation for the formation of a homogeneous and stable composite material. 800-1300 nm 2The ultra-high specific surface area of ​​ / g provides a huge surface area for dopamine modification, greatly enhancing the interfacial bonding with conductive polymers. Furthermore, it endows the material with extremely high loading and capture capabilities for harmful substances (such as HF), effectively protecting the positive electrode. The pore size of 15-150nm allows polymer chains to penetrate into the pores, forming a strong "nanocomposite" interface to enhance the material's toughness. Simultaneously, it ensures that electrolyte ions and small molecules such as HF can rapidly enter the pores, without affecting ion transport, while fully utilizing the protective function of the internal surface.

[0053] Preferably, the mesoporous silica particles are spherical or near-spherical particles.

[0054] According to a second aspect of the present invention, a method for preparing any of the above-mentioned composite materials is provided, comprising the following steps: S1. Dispersing mesoporous silica particles in Tris-HCl buffer, adding dopamine hydrochloride, and continuously stirring the mixture under light-shielding conditions for 12-24 hours. After the reaction is completed, washing, centrifuging, and drying the product to obtain modified mesoporous silica particles; S2. Preparing a modified mesoporous silica particle dispersion using the product obtained in S1, and preparing a conductive polymer solution using a conductive polymer. Mixing the modified mesoporous silica particle dispersion and the conductive polymer solution uniformly to obtain mixture A; S3. Adding a crosslinking agent to mixture A, mixing uniformly, and polymerizing for 1-2 hours to form a composite material.

[0055] In the preparation method of the composite material of the present invention, firstly, in S1, the entire reaction process requires light-shielding treatment to prevent dopamine from self-polymerizing, allowing dopamine to more comprehensively and fully modify the surface of the mesoporous silica particles and improve the compatibility between the mesoporous silica particles and the conductive polymer. Next, in S2, a process of first dispersing separately and then slowly mixing is adopted, effectively preventing the agglomeration of the modified mesoporous silica particles and ensuring their uniform dispersion at the nanoscale in the conductive polymer matrix, providing a guarantee for constructing a continuous and stable three-dimensional conductive network. Finally, in S3, a crosslinking agent is added, that is, after obtaining the uniformly dispersed system formed by the modified mesoporous silica and the conductive polymer, the crosslinking agent is added, which is beneficial for the three-dimensional network structure formed by the crosslinking agent to be more uniform, dense, and stable, significantly improving the mechanical strength and toughness of the composite material, effectively inhibiting electrolyte swelling, and enhancing the overall chemical stability. Therefore, applying this composite material to multilayer cathode sheets of lithium batteries can significantly alleviate interlayer delamination during cycling, improve the physical contact within the electrode and between layers, and thus optimize the cycle performance of the battery.

[0056] Preferably, in S1, the reaction temperature is 25-30°C.

[0057] Preferably, in S1, the pH of the Tris-HCl buffer solution is 7.5-8.8; more preferably 8.5.

[0058] Preferably, in S1, when the mesoporous silica particles are dispersed in the Tris-HCl buffer solution, the mass fraction of the mesoporous silica particles in the resulting dispersion is 2-8%.

[0059] Preferably, in S1, the mass ratio of mesoporous silica particles to dopamine hydrochloride is 1:0.5-2.

[0060] Preferably, in S2, the specific washing and centrifugation operations are as follows: wash with ethanol and water alternately 3-4 times, and the centrifugation speed is 7500-8500 rpm and the centrifugation time is 6-10 min; preferably, the centrifugation speed is 8000 rpm and the centrifugation time is 8 min.

[0061] Preferably, in step S2, the drying is vacuum drying at a temperature of 55-65°C for 12-24 hours.

[0062] Preferably, in step S2, the mass fraction of modified mesoporous silica particles in the modified mesoporous silica particle dispersion is 3-8%. Preferably, the organic solvent used to prepare the modified mesoporous silica particle dispersion includes N,N-dimethylformamide (DMF). Preferably, the specific operation for preparing the modified mesoporous silica particle dispersion is to disperse the modified mesoporous silica particles in N,N-dimethylformamide and sonicate for 30-60 min. The resulting dispersion is a milky white suspension.

[0063] Preferably, in step S2, the conductive polymer solution contains 10-20% by mass of the conductive polymer. Preferably, the organic solvent used to prepare the conductive polymer solution includes N,N-dimethylformamide. Preferably, the specific steps for preparing the conductive polymer solution are as follows: dispersing the conductive polymer in N,N-dimethylformamide, heating the solution to 45-55°C, and stirring until the solution becomes transparent.

[0064] Preferably, in S2, mixing the modified mesoporous silica particle dispersion with the conductive polymer solution uniformly means that the modified mesoporous silica particles are uniformly dispersed inside the conductive polymer.

[0065] Preferably, in step S2, the specific operation of uniformly mixing the modified mesoporous silica particle dispersion with the conductive polymer solution is as follows: the modified mesoporous silica particle dispersion is added to the conductive polymer solution at a rate of 50-60 mL / h, and stirred for 2-4 h to uniformly disperse the modified mesoporous silica particles inside the conductive polymer.

[0066] Preferably, in S2, the mass ratio of modified mesoporous silica particles to conductive polymer is 1:3-6.

[0067] Preferably, in S3, the reaction temperature during the polymerization process is 0-80°C. Preferably, the viscosity of the composite material is 2000-10000 mPa·s.

[0068] Preferably, in step S1, the method for preparing mesoporous silica particles specifically includes the following steps: S11. Dissolve the main template agent in deionized water, add the auxiliary template agent while continuously stirring, stir for 1-2 hours, add a pH adjuster to adjust the pH of the solution to 8-9, and continue stirring for 1-2 hours to obtain a pretreatment solution; S12. Add a silicon source to the pretreatment solution while continuously stirring, and continue stirring for 18-30 hours; S13. After the reaction is completed, wash and dry the product, and then calcine it at 450-650℃ for 3-6 hours.

[0069] Preferably, in step S11 of the method for preparing mesoporous silica particles, the main template agent includes hexadecyltrimethylammonium bromide. Hexadecyltrimethylammonium bromide is a cationic surfactant whose hydrophilic head group and hydrophobic long chain can form micelles in water, guiding the hydrolysis and condensation of silica on its surface, ultimately forming a mesoporous structure. Preferably, in step S11, the auxiliary template agent includes styrene-butadiene rubber latex (SBR latex). SBR latex is a polymer latex in which nanoparticles in its polymer chain segments can act as auxiliary templates or pore-forming agents, embedding themselves in the silica framework. After high-temperature calcination, they decompose, leaving larger or secondary pores, which helps to form a hierarchical pore structure and regulate particle size. Preferably, the mass fraction of styrene-butadiene rubber latex is 0.5-1%. Preferably, in step S11, the pH adjuster includes triethanolamine. Triethanolamine acts as a flocculant (or mineralizer) here, adjusting the pH value of the reaction system, promoting the hydrolysis and condensation of the silicon source, and may affect the pelleting rate and particle uniformity through complexation. Preferably, in step S11, the main template agent is dissolved in deionized water, and the mass fraction of the main template agent in the resulting solution is 3-8%. Preferably, the auxiliary template agent is added dropwise at a rate of 50-100 mL / h. This step requires controlling the dropping rate to ensure uniform mixing, followed by further stirring for 1-2 hours to allow the emulsion to fully disperse and initially interact with the cationic surfactant. Preferably, in step S11, the mass ratio of the main template agent to the auxiliary template agent is 3-15:1.

[0070] Preferably, in step S12 of the method for preparing mesoporous silica particles, the silicon source is added dropwise at a rate of 50-60 mL / h. The dropping rate is controlled to avoid excessively rapid local hydrolysis leading to agglomeration. Preferably, in step S12, the silicon source includes tetraethyl orthosilicate (TEOS). TEOS is the most commonly used silicon source; its hydrolysis products (silicic acid monomers) condense under template guidance to form a silica framework. Preferably, in step S12, the amount of silicon source added is 5-12 wt% of the pretreatment solution. Preferably, in step S12, the reaction temperature is 25 ± 2 °C.

[0071] Preferably, in step S13 of the method for preparing mesoporous silica particles, the particles are cleaned by repeated alternating washing and centrifugation with deionized water and anhydrous ethanol. During centrifugation, the centrifugation rate is 7500-8500 rpm for 3-7 minutes. Preferably, in step S13, the drying temperature is 55-65°C for 10-16 hours. Preferably, in step S13, during calcination, the temperature is programmed to rise to 450-650°C at a rate of 1-5°C / min. Preferably, in step S13, the calcination process is conducted in an air atmosphere. Calcination effectively removes template agents such as hexadecyltrimethylammonium bromide and styrene-butadiene rubber latex, retaining the mesoporous structure formed by their guidance, and further condensing and stabilizing the silica framework.

[0072] According to a third aspect of the present invention, an electrode for a lithium battery is provided, comprising a current collector and a first active material layer, a first functional layer, a second active material layer, and a second functional layer sequentially disposed on at least one side of the current collector; the first functional layer and the second functional layer comprise any of the aforementioned composite materials or composite materials prepared by any of the aforementioned preparation methods. Preferably, the second functional layer is disposed on the side away from the current collector. A first functional layer is disposed between the first active material layer and the second active material layer, which acts as a flexible mechanical buffer zone, effectively absorbing and dispersing stress, preventing stress concentration at the rigid interface from causing coating cracking or peeling from the current collector. This ensures the structural integrity of the electrode after long-term cycling. Furthermore, a second functional layer is disposed on the outermost side of the electrode, which constructs a physicochemical barrier between the active material and the electrolyte. It selectively allows lithium ions to pass through while blocking the cross-migration of harmful molecules such as HF and dissolved metal ions between different active layers. This significantly reduces side reactions at the cathode / electrolyte interface, effectively suppresses the dissolution of transition metal ions, and thus greatly improves the cycle performance of the battery.

[0073] Preferably, the electrode is a positive electrode; the first active material layer includes a first active material; the second active material layer includes a second active material; the first and second active materials independently include at least one of lithium manganese iron phosphate (LMFP), lithium iron phosphate (LFP), ternary nickel cobalt manganese (NCM), lithium cobalt oxide (LCO), and lithium manganese oxide (LMO). The composite material prepared by this invention is more suitable for modifying multilayer positive electrode sheets for lithium batteries. Theoretically, the composite material of this invention is not limited to the modification of multilayer negative electrode sheets, but when the functional layer prepared by the composite material is placed between the film and the negative electrode, it will lead to unevenness of the SEI film of the negative electrode, and the lithium intercalation process during charging will be hindered, thus causing a certain degree of degradation in cycle performance.

[0074] Preferably, the first active material and the second active material have different compositions.

[0075] Preferably, the thickness of the first active material layer is 40-70 μm, the thickness of the first functional interlayer is 3-6 μm, the thickness of the second active material layer is 20-40 μm, the thickness of the second functional interlayer is 3-5 μm, and the total coating weight on one side is 200-300 g / m². 2 The compaction density of the electrode sheet is 2.5-3.5 g / cm³. 3 Preferably, the thickness of the first functional interlayer is greater than the thickness of the second functional interlayer. The thickness design of the aforementioned layers, especially the relatively thinner design of the first and second functional layers, allows for the formation of a continuous and dense protective layer without significantly sacrificing the overall energy density of the battery, while simultaneously maximizing its stress buffering and interface isolation functions. The single-sided coating weight (200-300 g / m²) 2 ) and compaction density (2.5-3.5 g / cm³) 3 The aforementioned range ensures that the electrode has high areal capacity and volumetric energy density, while avoiding excessively low porosity and hindered ion transport due to over-compaction. Therefore, the combination of these parameters achieves an optimal balance between high energy density, high rate performance, and long cycle life.

[0076] Preferably, the first active material layer comprises a first active material, a polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs, wherein the mass ratio of the first active material, the polyvinylidene fluoride binder, the conductive carbon black, and the conductive CNTs is 95.5-98:1-3:0.5-1.5:0.5-1.5.

[0077] Preferably, the second active material layer comprises a second active material, a polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs, and the mass ratio of the first active material, polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs is 95.5-98:1-3:0.5-1.5:0.5-1.5.

[0078] According to a fourth aspect of the present invention, a lithium battery is provided, comprising any of the aforementioned lithium battery electrodes. The lithium battery prepared from the aforementioned electrodes exhibits high energy density, high rate performance, and long cycle life.

[0079] Preferably, the lithium battery includes a negative electrode sheet, and the total coating weight on one side of the negative electrode sheet is 90-130 g / m². 2 The compaction density is controlled at 1.5-1.7 g / cm³. 3 Preferably, the negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode active material. The negative electrode active material includes at least one of natural graphite, artificial graphite, modified graphite materials, and soft carbon / hard carbon composite materials. Natural graphite includes flake graphite, spherical graphite, etc. Artificial graphite includes mesophase carbon microspheres, needle-like coke-based graphite, pitch-based graphite, etc. Modified graphite materials include carbon-coated graphite, oxide-coated graphite, element-doped graphite, graphite / silicon composite materials, and soft carbon / hard carbon / graphite composite materials. Soft carbon / hard carbon composite materials include hard carbon coated with soft carbon material; soft carbon includes carbon fibers, carbon microspheres, graphitized mesophase carbon microspheres, petroleum coke, needle-like coke, etc., and hard carbon includes resin carbon, organic polymer pyrolysis carbon, carbon black, etc. Preferably, the negative electrode active material is hard carbon coated with soft carbon material.

[0080] Preferably, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder, wherein the mass ratio of the negative electrode active material, the conductive agent, and the binder is 93.5-96.5:1-4:1-3.

[0081] Preferably, the lithium battery further includes a separator, which comprises a base film and a PVDF layer and an alumina layer sequentially disposed on at least one side. The thickness of the base film is 5-10 μm, the thickness of the PVDF layer is 1.5-5 μm, and the thickness of the alumina layer is 1.5-5 μm. Preferably, the base film comprises at least one of PP (polypropylene), PE (polyethylene), PET (polyethylene terephthalate), and PA (polyamide).

[0082] Preferably, the lithium battery further includes an electrolyte in which the lithium salt is LiPF6, the solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1, and the lithium salt concentration is 1.2 mol / L.

[0083] To further illustrate the present invention, the following embodiments will be described in detail.

[0084] Example 1 1. Preparation of mesoporous silica particles The mesoporous silica particles of this embodiment were prepared according to the following steps: S11. Dissolve hexadecyltrimethylammonium bromide (the main template agent) in deionized water and stir magnetically until completely dissolved to obtain a clear aqueous solution with a mass fraction of 6%. Then, under continuous stirring, slowly (60 ml / h) add styrene-butadiene rubber latex (auxiliary template agent, mass fraction of 0.8%), and stir for 1 hour. Next, add the prepared triethanolamine solution (mass fraction of 3.5%), adjust the pH of the solution to 8-9, and continue stirring for 1-2 hours to obtain the pretreatment solution. In this step, the mass ratio of hexadecyltrimethylammonium bromide to styrene-butadiene rubber (the effective component of styrene-butadiene rubber latex) is 10:1. S12. In the pre-solution under continuous stirring, tetraethyl orthosilicate was slowly added dropwise (60 ml / h) using a constant-pressure dropping funnel. The reaction was carried out under constant stirring at a constant reaction temperature of 25°C for 24 hours. The amount of tetraethyl orthosilicate added was 8 wt% of the pre-solution. S13. After the reaction, the resulting white suspension was washed three times alternately with deionized water and anhydrous ethanol by centrifugation (8000 rpm, 5 minutes). The washed precipitate was transferred to a petri dish and dried in a 60°C oven for 12 hours to obtain a white powder. The white powder was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min under air atmosphere, and calcined at this temperature for 4 hours to obtain a powder with a diameter of 120 nm and a specific surface area of ​​960 m². 2 / g, mesoporous silica particles with a pore size of 35-90 nm.

[0085] 2. Preparation of composite materials The composite material of this embodiment was prepared according to the following steps: S1. The prepared mesoporous silica particles were dispersed in Tris-HCl buffer (pH 8.5) with a solid mass fraction of 5%. Dopamine hydrochloride at a mass of 1.5 times that of the mesoporous silica particles was added. The mixture was stirred continuously at room temperature (25°C) in the dark for 12-24 hours. After the reaction was completed, the product was washed 3-4 times with alternating ethanol and water. During the washing process, the product was centrifuged at 8000 rpm for 8 minutes. The product was collected and dried in a vacuum oven at 60°C for 12 hours to obtain dopamine-modified mesoporous silica particles (i.e., modified mesoporous silica particles). S2. The modified mesoporous silica particles were dispersed in N,N-dimethylformamide (DMF) at a mass fraction of 5%, and ultrasonically dispersed for 30 min to form a milky white suspension, i.e., the modified mesoporous silica particle dispersion; polyacrylonitrile (conductive polymer) powder was dispersed in DMF at a mass fraction of 10-20%, the solution was heated to 50°C, and stirred until the solution was transparent to obtain a polyacrylonitrile dispersion (conductive polymer solution); the modified mesoporous silica particle dispersion was slowly added (mL / h) to the polyacrylonitrile dispersion, maintaining the mass ratio of modified mesoporous silica particles / polyacrylonitrile at 1 / 4.5, and then stirred for 3 h to uniformly disperse the modified mesoporous silica particles inside the conductive polymer to obtain mixture A; S3. Add crosslinking agent polyethylene glycol (average molecular weight 600) to mixture A, accounting for 0.6% of the mass of the conductive polymer. After stirring for 2 h, heat the reaction system to 70℃ and polymerize for 1 h to obtain the composite material.

[0086] 3. Preparation of positive electrode sheet The positive electrode sheet of this embodiment is prepared according to the following steps: (1) The active material, polyvinylidene fluoride binder, conductive carbon black, and conductive CNT were stirred in a weight ratio of 96:2:1:1 to prepare a positive electrode slurry. In this embodiment, two positive electrode slurries were prepared, which are referred to as the first positive electrode slurry and the second positive electrode slurry, respectively. The active materials of the first positive electrode slurry are LFP and NCM, and the mass ratio of LFP to NCM is 1:1. The active materials of the second positive electrode slurry are LMFP and NCM, and the mass ratio of LMFP to NCM is 1:1.

[0087] (2) On one side of the aluminum foil coated with a 0.5 μm conductive carbon layer, a first positive electrode slurry and a composite material are simultaneously coated using an extrusion double-layer coating process to form a first active material layer and a first functional layer, respectively. The thickness of the first active material layer is controlled to be 60 μm and the thickness of the first functional layer is 5 μm. The other side is kept consistent. The dried semi-finished product is then rolled. Subsequently, on one side of the rolled semi-finished product, a second positive electrode slurry and a composite material are simultaneously coated using an extrusion double-layer coating process to form a second active material layer and a second functional layer, respectively. The thickness of the second active material layer is controlled to be 30 μm and the thickness of the second functional layer is 3 μm. The other side is kept consistent. The total coating weight on one side is controlled to be 240 g / m². 2 The dried positive electrode sheet is rolled and pressed, and the compaction density of the positive electrode sheet is controlled to be 3.4 g / cm³. 3 .

[0088] 4. Battery manufacturing (1) Preparation of negative electrode The negative electrode active material (hard carbon surface coated with soft carbon material), conductive agent, and binder are mixed at a mass ratio of 95.5:2.5:2. After stirring evenly, deionized water is added and stirred to form a uniform and stable negative electrode slurry. The negative electrode slurry is coated onto the negative electrode current collector by extrusion coating. After drying, a negative electrode roll is obtained, with the single-sided coating weight controlled at 110 g / m. 2 After rolling, a negative electrode sheet is obtained, with the compaction density controlled at 1.6 g / cm³. 3 .

[0089] (2) Assembly of lithium batteries The diaphragm is made of polypropylene with a thickness of 7 μm, coated with a 3 μm thick PVDF layer on both sides, and then gravure-coated with a 3 μm thick alumina layer. The electrolyte is LiPF6 dissolved in a solvent of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, with a LiPF6 concentration of 1.2 mol / L.

[0090] The positive electrode, separator, and negative electrode prepared above are assembled, injected with electrolyte, formed, and volume-adjusted to obtain a lithium battery.

[0091] Example 2 The difference between this embodiment and Embodiment 1 is that, in the preparation of the positive electrode sheet, in (1) the mass ratio of LFP to NCM in the active material of the first positive electrode slurry (corresponding to the first active material layer) is 1:3; and in the active material of the second positive electrode slurry (corresponding to the second active material layer), the mass ratio of LMFP to NCM is 1:3. The rest is the same as in Embodiment 1.

[0092] Example 3 The difference between this embodiment and Embodiment 1 is that, in the preparation of the positive electrode sheet, the active material of the first positive electrode slurry (corresponding to the first active material layer) in (1) is NCM; and the active material of the second positive electrode slurry (corresponding to the second active material layer) is LFP. The rest is the same as in Embodiment 1.

[0093] Example 4 The difference between this embodiment and Embodiment 1 is that, in the preparation of the positive electrode sheet, the active material of the first positive electrode slurry (corresponding to the first active material layer) in (1) is LFP; and the active material of the second positive electrode slurry (corresponding to the second active material layer) is NCM. The rest is the same as in Embodiment 1.

[0094] Example 5 The difference between this embodiment and Embodiment 1 is that, in the preparation of the positive electrode sheet, the active material of the first positive electrode slurry (corresponding to the first active material layer) in (1) is LCO; and the active material of the second positive electrode slurry (corresponding to the second active material layer) is NCM. The rest is the same as in Embodiment 1.

[0095] Example 6 The difference between this embodiment and Embodiment 1 is that, in the preparation of the positive electrode sheet, the active material of the first positive electrode slurry (corresponding to the first active material layer) in (1) is LMFP; and the active material of the second positive electrode slurry (corresponding to the second active material layer) is NCM. The rest is the same as in Embodiment 1.

[0096] Example 7 The difference between this embodiment and Embodiment 1 is that in the preparation of the positive electrode, the thickness of the first functional layer is controlled to be 3 μm and the thickness of the second functional layer is controlled to be 5 μm in step (2). The rest is the same as in Embodiment 1.

[0097] Example 8 The difference between this embodiment and Embodiment 1 is that in the preparation of the positive electrode, the thickness of the first functional layer is controlled to be 2 μm and the thickness of the second functional layer is controlled to be 6 μm in step (2). The rest is the same as in Embodiment 1.

[0098] Example 9 The difference between this embodiment and Example 1 is that polyaniline is used as the conductive polymer in the preparation of the composite material. Everything else is the same as in Example 1.

[0099] Example 10 The difference between this embodiment and Example 1 is that polypyrrole is used as the conductive polymer in the preparation of the composite material. Everything else is the same as in Example 1.

[0100] Example 11 The difference between this embodiment and Example 1 is that polythiophene is used as the conductive polymer in the preparation of the composite material. Everything else is the same as in Example 1.

[0101] Example 12 The difference between this embodiment and Example 1 is that, in the preparation of the composite material, the mass ratio of modified mesoporous silica particles to conductive polymer (polyacrylonitrile) is 1:2. Everything else is the same as in Example 1.

[0102] Example 13 The difference between this embodiment and Example 1 is that, in the preparation of the composite material, the crosslinking agent (polyethylene glycol) accounts for 0.15% of the mass of the conductive polymer (polyacrylonitrile). The rest is the same as in Example 1.

[0103] Example 14 The difference between this embodiment and Example 1 is that a crosslinking agent (polyethylene glycol) with an average molecular weight of 1200 was used in the preparation of the composite material. Everything else is the same as in Example 1.

[0104] Example 15 The difference between this embodiment and Example 1 is that a crosslinking agent (polyethylene glycol) with an average molecular weight of 250 was used in the preparation of the composite material. Everything else is the same as in Example 1.

[0105] Comparative Example 1 The difference between this embodiment and Embodiment 1 is that no composite material is prepared in the preparation of the positive electrode sheet; therefore, the positive electrode sheet does not have a first functional layer and a second functional layer. Everything else is the same as in Embodiment 1.

[0106] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that, in the preparation of the positive electrode sheet, the first positive electrode slurry is coated and the first active material layer is formed by a single-layer coating method, without preparing the first functional layer. The rest is the same as in Embodiment 1.

[0107] Comparative Example 3 The difference between this embodiment and Embodiment 1 is that, in the preparation of the positive electrode sheet, the second positive electrode slurry is coated and the second active material layer is formed by a single-layer coating method, without preparing the second functional layer. The rest is the same as in Embodiment 1.

[0108] Comparative Example 4 The difference between this embodiment and Example 1 is that step S3 is omitted in the preparation of the composite material, i.e., no crosslinking agent (polyethylene glycol) is added. The rest is the same as in Example 1.

[0109] Comparative Example 5 The difference between this embodiment and Example 1 is that, in the preparation of the composite material, the crosslinking agent polyethylene glycol is changed to polypropylene glycol. Everything else is the same as in Example 1.

[0110] Comparative Example 6 The difference between this embodiment and Embodiment 1 is that unmodified mesoporous silica particles are directly composited with a conductive polymer (polyacrylonitrile). Everything else is the same as in Embodiment 1.

[0111] Comparative Example 7 The difference between this embodiment and Embodiment 1 is that a conductive polymer (polyacrylonitrile) dispersion is directly used as the first and second positive electrode slurries. Everything else is the same as in Embodiment 1.

[0112] Test case 1. Experimental Construction Method The following tests were performed on all the batteries prepared in the above embodiments and comparative examples: (1) Cyclic test: The lithium battery was charged to 3.65 V at a constant current rate of 0.33 C in a 25℃ chamber, and then charged to 0.05 C at a constant voltage rate of 3.65 V. After standing for 30 minutes, it was discharged to 2.5 V at a constant current rate of 0.33 C. After standing, the lithium battery was cycled for three cycles, and the capacity of the last cycle was taken as the actual capacity C0 of the battery. The battery was charged and discharged at 1C / 1C. The capacity of each cycle was compared with that of the first cycle to obtain the cycle capacity retention rate. The cycle was stopped when the capacity reached 0.8*C0, and the number of cycles was recorded.

[0113] (2) Compression and rebound test: For lithium batteries at the end of the cycle, the corresponding positive electrode sheet is disassembled and tested. Rebound test: A pressure of 0.5 MPa is applied to the positive electrode sheet with a thickness of L1, and the thickness of the positive electrode sheet under the pressure of 0.5 MPa is measured to be L2; the pressure is removed, and the sheet is left to stand for 30 min. After the thickness of the positive electrode sheet stabilizes, the thickness L3 of the positive electrode sheet is measured. The thickness rebound rate of the positive electrode sheet is α=(L3-L2) / L1, and the thickness compression rate is β=(L1-L2) / L1.

[0114] 2. Experimental Results The performance test results of the lithium batteries prepared in all the above embodiments and comparative examples are shown in Table 1.

[0115] Table 1. Performance test results of lithium batteries prepared in the examples and comparative examples.

[0116] As can be seen from Table 1, compared with Comparative Example 1, for multiple active material layers, the deformation during the cycling process is increased. Adding the composite material provided by the present invention as a functional layer can suppress interlayer delamination, improve the contact interface, significantly improve cycle life, and the positive electrode sheet has better compression and rebound ability after cycling.

[0117] In Comparative Example 2, the positive electrode lacks a first functional layer, resulting in low compression recovery and a low number of cycles. This is because the absence of a functional layer makes interlayer delamination between the two active material layers more likely, leading to poor interfacial contact and consequently, poor cycle life and compression recovery.

[0118] In Comparative Example 3, the positive electrode does not have a second functional layer. The second active material layer deforms more during cycling, resulting in poor contact with the separator and a significant reduction in cycle performance.

[0119] In Comparative Example 4, without the addition of crosslinking agent polyethylene glycol, the functional layer could not fully polymerize, resulting in a significant decrease in resilience. Irreversible deformation of the functional layer could not be mitigated, thus reducing the impact of deformation between the upper and lower layers during cycling and lowering cycling performance.

[0120] In Comparative Example 5, the crosslinking agent polyethylene glycol was changed to polypropylene glycol. The crosslinking reaction rate was slower, the polymer stability was relatively poor, the compression rebound rate was reduced, and the cycle performance deteriorated.

[0121] In Comparative Example 6, unmodified mesoporous silica particles were directly combined with a conductive polymer (polyacrylonitrile). The unmodified inorganic matter on the surface was difficult to disperse in the organic polymer and tended to agglomerate, resulting in poor electrode film surface condition, local stress concentration, and exacerbating the cyclic water drop phenomenon.

[0122] In Comparative Example 7, a conductive polymer (polyacrylonitrile) dispersion was directly used as the first and second positive electrode slurries. That is, the functional layer only contained conductive polymer and no silica support. The deformation capacity of the functional interlayer was greatly reduced, the rebound rate was significantly reduced, and the electrode interface was significantly deteriorated during cycling, resulting in poor cycle performance.

[0123] Further observation of Examples 1-6 shows that for two active materials with different expansion coefficients, the addition of a functional layer formed by the composite material can stably improve the cycle performance, and the positive electrode sheet also has good compression and rebound ability after cycling.

[0124] As can be seen from Examples 1 and 7-8, the thickness of the functional layer has a certain impact on ion conduction, which leads to a decrease in the number of cycles and the compression resilience of the electrode after cycling. In particular, the functional layer between the two active material layers plays a connecting role and should have a certain thickness to ensure that the impact of interlayer delamination is minimized.

[0125] As can be seen from Examples 1 and 12-13, the ratio of modified mesoporous silica particles (or mesoporous silica particles with negligible mass increase due to modification) to conductive polymers, and the ratio of crosslinking agents to conductive polymers, also affect the final cycle performance and the rebound performance of the electrode after cycling. This is because silica surface modification can significantly improve its compatibility with organic materials, and a suitable polymerization ratio can improve the dispersion of silica in the functional coating, increase the compression rebound rate of the electrode, and provide sufficient buffer for electrode deformation in the later stages of cycling.

[0126] As can be seen from Examples 1 and 14-15, the molecular weight of the crosslinking agent also affects the final cycle performance and the resilience of the electrode after cycling. This is because the larger the molecular weight, the slower the polymerization reaction rate, which affects the integrity of the polymerization inside the functional interlayer. The smaller the molecular weight, the less stable the polymerization structure, and both show a certain degree of deterioration.

[0127] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A composite material, characterized in that: The composite material comprises mesoporous silica particles, a conductive polymer, a crosslinking agent, and dopamine; the crosslinking agent is polyethylene glycol.

2. The composite material as described in claim 1, characterized in that: The conductive polymer includes at least one of polyaniline, polypyrrole, polyacrylonitrile, and polythiophene.

3. The composite material as described in claim 1, characterized in that: The mass ratio of the mesoporous silica particles to the conductive polymer is 1:3-6; The mass ratio of the crosslinking agent to the conductive polymer is 0.2-1:100; the average molecular weight of the crosslinking agent is 300-1000.

4. The composite material as described in claim 1, characterized in that: The mesoporous silica particles have a diameter of 100-500 nm and a specific surface area of ​​800-1300 m². 2 / g, with a pore size of 15-150 nm.

5. A method for preparing the composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Disperse the mesoporous silica particles in Tris-HCl buffer, add dopamine hydrochloride, and stir continuously for 12-24 h under light-shielding conditions. After the reaction is completed, wash, centrifuge and dry the product to obtain modified mesoporous silica particles. S2. Prepare a modified mesoporous silica particle dispersion using the product obtained in S1, and prepare a conductive polymer solution using the conductive polymer. Mix the modified mesoporous silica particle dispersion and the conductive polymer solution evenly to obtain mixture A. S3. Add the crosslinking agent to the mixture A, mix evenly, and polymerize for 1-2 hours to form the composite material.

6. The preparation method according to claim 5, characterized in that: In step S1, the method for preparing the mesoporous silica particles specifically includes the following steps: S11. Dissolve the main template agent in deionized water, add the auxiliary template agent while stirring continuously, stir for 1-2 hours, add pH adjuster to adjust the pH of the solution to 8-9, continue stirring for 1-2 hours to obtain the pretreatment solution; S12. Add a silicon source to the pretreatment solution while stirring continuously, and continue stirring for 18-30 hours. S13. After the reaction is complete, the product is washed, dried, and then calcined at 450-650℃ for 3-6 hours.

7. An electrode for lithium batteries, characterized in that: It includes a current collector and a first active material layer, a first functional layer, a second active material layer, and a second functional layer sequentially disposed on at least one side of the current collector; The first functional layer and the second functional layer comprise the composite material according to any one of claims 1 to 4 or the composite material prepared by the preparation method according to any one of claims 5 to 6.

8. The electrode for a lithium battery as described in claim 7, characterized in that: The electrode is a positive electrode; The first active material layer includes a first active material; the second active material layer includes a second active material. The first active material and the second active material independently include at least one of lithium manganese iron phosphate (LMFP), lithium iron phosphate (LFP), ternary nickel cobalt manganese (NCM), lithium cobalt oxide (LCO), and lithium manganese oxide (LMO).

9. The electrode for a lithium battery as described in any one of claims 7-8, characterized in that: The thickness of the first active material layer is 40-70 μm, the thickness of the first functional interlayer is 3-6 μm, the thickness of the second active material layer is 20-40 μm, the thickness of the second functional interlayer is 3-5 μm, and the total coating weight on one side is 200-300 g / m². 2 The compaction density of the electrode sheet is 2.5-3.5 g / cm³. 3 .

10. A lithium battery, characterized in that: The lithium battery includes the lithium battery electrode as described in any one of claims 7-9.

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