A capacity-contributing conductive polyimide binder and its application in silicon-carbon anodes of lithium-ion batteries

Abstract

This invention discloses a capacity-contributing conductive polyimide binder and its application in silicon-carbon anodes of lithium-ion batteries. Through molecular structure design, this invention combines a rigid aromatic structure with flexible segments to construct a rigid-flexible coupled polymer network, thereby endowing the binder with good mechanical strength and toughness. Simultaneously, the introduction of conductive fillers via in-situ polymerization helps to build continuous electron transport channels within the electrode, reducing electrode polarization and improving rate performance. Furthermore, the polyimide molecular chain contains abundant imide carbonyl groups, which can undergo reversible coordination with lithium ions, enabling rapid lithium ion storage and release to a certain extent, thus contributing to the electrode's capacity. While maintaining a high reversible specific capacity, it can significantly improve the electrode's rate performance and long-cycle stability at high current densities.

Description

Technical Field

[0001] This invention belongs to the technical field of silicon-based anode binder materials for lithium-ion batteries, specifically relating to a conductive polyimide binder that can contribute to capacity and its application in silicon-carbon anodes of lithium-ion batteries. Background Technology

[0002] Silicon is considered an ideal candidate material for next-generation high-energy-density lithium-ion battery anodes due to its extremely high theoretical specific capacity (approximately 4200 mAh / g, far exceeding the 372 mAh / g of commercial graphite anodes), low lithium intercalation potential, and ability to form alloys with multiple lithium atoms. However, silicon undergoes drastic volume changes during charge and discharge, with volume expansion exceeding 300% during full lithium intercalation. This can easily lead to pulverization of active materials, damage to the conductive network, and repeated rupture and regeneration of the solid electrolyte interphase (SEI), resulting in rapid capacity decay and reduced cycle life. Combining silicon with carbon materials is an effective strategy to alleviate these problems. The carbon phase can not only construct a continuous electron transport network, improving electrode conductivity, but also provide mechanical support and volume buffering for silicon particles to a certain extent, while also contributing some capacity itself. Therefore, silicon-carbon composite materials can improve electrode cycle stability while maintaining a high specific capacity. However, relying solely on silicon-carbon composites is still insufficient to completely solve the structural instability problem of silicon-based anodes during cycling. Although the binder has a low content in the electrode, it plays a key role in maintaining a stable connection between the active material, conductive agent and current collector, as well as maintaining the integrity of the electrode structure.

[0003] Traditional binders such as polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and polyacrylic acid (PAA), while widely used, have relatively simple molecular structures, limited functional tunability, and typically exist primarily as inert binders, making it difficult to play a significant role in electrode capacity contribution and functionalization. Furthermore, traditional binders still suffer from insufficient bonding strength and limited mechanical buffering capacity when dealing with the massive volume expansion of silicon particles. In contrast, polyimide (PI) possesses excellent mechanical strength, good thermal and chemical stability, and its molecular structure offers strong designability. Its mechanical properties, interfacial interactions, and ion / electron transport behavior can be regulated by introducing rigid aromatic structures, flexible segments, and polar functional groups. Therefore, polyimide, as a novel functional binder, shows great application potential in silicon-based anodes for lithium-ion batteries. As a binder for silicon-based anodes, polyimide can provide effective structural support and stress buffering during repeated lithiation / delithiation of silicon materials, thereby inhibiting electrode cracking, pulverization, and active material shedding. More importantly, unlike traditional inert adhesives, polyimide contains abundant imide carbonyl groups in its molecular chain. These polar carbonyl groups can react with Li +Reversible coordination occurs, enabling the storage and release of lithium ions to a certain extent, thus providing additional capacity to the electrode. This characteristic allows polyimide binders not only to maintain the stability of the electrode structure, but also to participate in the lithium storage process as an electrochemically active functional component, reducing the "dilution effect" of traditional inert binders on electrode capacity.

[0004] Therefore, by fully utilizing the designability of the polyimide molecular structure, high-performance binders with high bonding strength, good flexibility, interfacial stability, and reversible lithium storage function can be constructed, achieving synergistic optimization of "structural stability, interfacial regulation, and capacity contribution." This is of great significance for improving the reversible specific capacity, rate performance, and cycle stability of silicon-based anodes, as well as promoting the development of high-energy-density lithium-ion batteries. Summary of the Invention

[0005] This invention addresses the shortcomings of existing silicon-based anode binders in terms of bonding strength, mechanical buffering capacity, conductivity, and functionalized lithium storage by providing a conductive polyimide binder that can contribute to capacity and its application in silicon-carbon anodes of lithium-ion batteries.

[0006] This invention combines rigid structural units with flexible segments through a rational molecular structure design, giving it both high mechanical strength and good viscoelasticity. This effectively adapts to the significant volume changes of silicon particles during cycling, thus maintaining the integrity of the electrode structure. Simultaneously, the polar functional groups such as carboxyl groups introduced into the polymer molecular chain can form strong hydrogen bonds or chemical interactions with the silicon particle surface, significantly enhancing the interfacial adhesion between the binder and the active material, and inhibiting the shedding of active material and electrode pulverization. Furthermore, the abundant imide carbonyl groups in the polyimide molecular chain can undergo reversible coordination with lithium ions, promoting the rapid storage and release of lithium ions to a certain extent, thereby contributing to the electrode's capacity. This transforms the binder from a traditional inert connecting component into an active functional component with both structural stability and lithium storage capabilities.

[0007] Furthermore, introducing conductive fillers via in-situ polymerization allows for the construction of continuous electron transport channels within the binder network, improving overall electrode conductivity, reducing electrode polarization, and thus enhancing the rate performance of the silicon-based anode. This conductive polyimide binder also exhibits excellent structural stability, alleviating electrode volume stress during repeated charge-discharge cycles, promoting the formation of a stable SEI film, reducing interfacial side reactions, and ultimately comprehensively improving the reversible capacity, rate performance, and cycle stability of the silicon-based anode. This preparation method is simple, has a high yield, and low cost, demonstrating promising prospects for large-scale application.

[0008] The conductive polyimide binder of the present invention, which can contribute capacity, is prepared by polymerization and thermal imidization of diamine monomers and dianhydride monomers, and conductive fillers are introduced in situ during the polymerization process;

[0009] The diamine monomers are 3,5-diaminobenzoic acid and 1,3-bis(3-aminopropyl)tetramethyldisiloxane; the molar ratio of the two is controlled at 4:1.

[0010] The dianhydride monomer is 4,4′-oxobisphthalic anhydride.

[0011] The molar ratio of the diamine monomer to the dianhydride monomer is controlled at 1:1.

[0012] The conductive filler is one or more of Super P, acetylene black, Ketjen black, carbon nanotubes, graphene, or conductive carbon fibers.

[0013] The amount of conductive filler added is controlled to be 1-5% of the total mass of diamine monomer and dianhydride monomer, and more preferably 2%.

[0014] The present invention provides a method for preparing a capacity-contributing conductive polyimide adhesive, comprising the following steps:

[0015] Step 1: In a nitrogen atmosphere, add the diamine monomer to anhydrous N-methylpyrrolidone (NMP), stir and mix to dissolve, then add the conductive filler and disperse evenly to obtain solution A.

[0016] Step 2: Divide the dianhydride monomer into three equal parts and add them to solution A in three portions at 0.5-hour intervals under ice-water bath conditions. After stirring in the ice-water bath for 4 hours, continue stirring at room temperature. Control the total reaction time to 12-16 hours and stir thoroughly for 12 hours to obtain solution B, which is the polyimide binder precursor solution. In subsequent applications, imidization is completed by staged heating.

[0017] The solid content of the polyimide binder precursor solution is 5-20 wt%.

[0018] This invention relates to the application of a capacity-contributing conductive polyimide binder in the silicon-carbon anode of lithium-ion batteries.

[0019] include:

[0020] Step 3: Add the Si / C anode material, conductive agent Super P, and polyimide binder precursor solution to a mortar in proportion, mix evenly, then add N-methylpyrrolidone (NMP) as a solvent, and continue grinding for 15-30 minutes to mix into a uniform viscous slurry.

[0021] Step 4: The slurry obtained in Step 3 is evenly coated onto copper foil with a scraper and vacuum dried at 60-80 ℃ for 6-8 h to remove most of the liquid solvent. Then it is transferred into a tube furnace and subjected to staged heating treatment under a nitrogen-protected atmosphere to obtain a fully imidized negative electrode sheet.

[0022] Step 5: Cut the negative electrode obtained in Step 4 into a circular electrode with a diameter of 12 mm, and use a lithium sheet with a diameter of 16 mm as the counter electrode. Use Celgard 2325 microporous three-layer membrane as the separator, and assemble it into a CR2032 button cell in a glove box filled with argon gas. The oxygen concentration is not higher than 1 ppm and the water vapor concentration is not higher than 0.5 ppm.

[0023] In step 3, the mass of SiC anode material, conductive agent Super P and polyimide binder precursor solution is calculated as 100 parts, with SiC anode material accounting for 70 parts, conductive agent Super P accounting for 20 parts and polyimide binder precursor solution accounting for 10 parts.

[0024] In step 4, the procedure for the staged heating process is set as follows: first, heat to 200℃ and hold for 1 hour, then heat to 250℃ and hold for 2 hours, and finally heat to 300℃ and hold for 1 hour, and then cool naturally to room temperature.

[0025] In step 5, the electrolyte used when assembling the battery is a solvent in which lithium hexafluorophosphate (LiPF6) is dissolved in diethyl carbonate (DEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC), with 5% fluoroethylene carbonate (FEC) added. The volume ratio of diethyl carbonate (DEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) is DEC:EC:EMC = 1:1:1 vol% with 5% FEC, and the concentration of lithium hexafluorophosphate (LiPF6) is 1 mol / L.

[0026] This invention addresses the shortcomings of existing silicon-based anode binders in terms of mechanical buffering, conductivity, and functionalized lithium storage by proposing a simple and low-cost method for preparing a conductive polyimide binder. This binder, through a rationally designed molecular structure, possesses both high mechanical strength and good viscoelasticity, effectively accommodating the significant volume changes of silicon materials during cycling, thereby maintaining the integrity of the electrode structure. Simultaneously, the introduction of conductive fillers and the construction of a continuous conductive network in the binder improves the overall conductivity of the electrode, reduces electrode polarization, and enhances the rate performance of the silicon-based anode. Furthermore, the imide carbonyl groups in its molecular chain can undergo reversible coordination with lithium ions, contributing to the electrode's capacity to a certain extent. In summary, this conductive polyimide binder synergistically improves the overall electrochemical performance of silicon-based anodes in terms of structural stability, electron transport, and capacity contribution, demonstrating promising prospects for large-scale application. Attached Figure Description

[0027] Figure 1 The diagram shows the synthesis circuit of the conductive polyimide binder precursor solution in Examples 1 and 2.

[0028] Figure 2The images show the FT-IR spectra of the conductive polyimide adhesives in Examples 1 and 2.

[0029] Figure 3 The images show SEM images of the cross-sections of the polyimide films after high-temperature imidization of the polyimide precursor solution in Examples 1 and 2.

[0030] Figure 4 Broadband dielectric impedance diagrams of the electrode sheets in Example 1, Comparative Example 1, and Comparative Example 2.

[0031] Figure 5 These are images of the electrode sheets from Example 1, Comparative Example 1, and Comparative Example 2, showing a 180° peel test.

[0032] Figure 6 The graph shows the cycling performance of Example 1, Comparative Example 1, and Comparative Example 2 at a current density of 2A / g.

[0033] Figure 7 The diagram shows the cycle ratio performance of Example 1, Comparative Example 1, and Comparative Example 2.

[0034] Figure 8 The graphs show the cycling performance of Example 2 and Comparative Example 3 at current densities of 0.1 A / g and 2 A / g, respectively.

[0035] Figure 9 Example 2 and Comparative Example 3 were prepared at 0.4mVS. -1 Cyclic voltammetry curves at different scan rates. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0037] Example 1:

[0038] 3,5-Diaminobenzoic acid (DABA, 0.3676 g, 0.0024 mol) and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (DS-NH2, 0.149 g, 0.0006 mol) were weighed separately and added to a dry three-necked flask. Under nitrogen protection, 13 mL of anhydrous N-methylpyrrolidone (NMP) was added as a solvent, and a magnetic stir bar was added. The mixture was stirred until the diamine monomer dissolved. Subsequently, 0.029 g of superconducting carbon black (Super P) was added as a conductive filler in the binder. The mixture was stirred and sonicated for 10 min to ensure that Super P was uniformly dispersed in the system, resulting in a diamine monomer solution containing the conductive filler.

[0039] Separately weigh 0.93 g of 4,4′-oxydiphthalic anhydride (ODPA, 0.003 mol) and divide it into three equal portions. Under ice-water bath conditions, slowly add ODPA to the above diamine monomer solution in three portions, with each addition spaced 0.5 h apart. After the additions are complete, stir in an ice-water bath for 4 hours, then continue stirring at room temperature for 12 hours to obtain a polyamic acid precursor solution for conductive polyimide binders.

[0040] Si / C650 anode material, conductive agent Super P, and polyimide binder precursor solution were added to a mortar in a mass ratio of 7:2:1 and thoroughly ground and mixed. Then, an appropriate amount of NMP was added as a solvent, and grinding continued for 15-30 minutes until a uniform and viscous electrode slurry was formed. The resulting slurry was evenly coated onto the surface of a copper foil using a scraper and dried under vacuum at 60-80 °C for 6-8 hours to remove most of the liquid solvent. The dried electrode sheet was then transferred to a tube furnace and subjected to staged thermal imidization treatment under a nitrogen atmosphere: first, the temperature was raised to 200 °C and held for 1 hour; then, it was raised to 250 °C and held for 2 hours; finally, it was raised to 300 °C and held for 1 hour. After natural cooling to room temperature, a fully imidized silicon-carbon anode sheet was obtained.

[0041] The obtained negative electrode sheet was cut into circular electrode sheets with a diameter of 12 mm. A lithium sheet with a diameter of 16 mm was used as the counter electrode. The separator was a Celgard 2325 microporous three-layer membrane. The electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte, with the solvents being DEC, ethylene carbonate (EC), and ethyl methyl carbonate (EMC), and 5% fluoroethylene carbonate (FEC) was added. The DEC:EC:EMC ratio was 1:1:1 vol% with 5% FEC. The CR2032 button cell was assembled in an argon-filled glove box.

[0042] Example 2:

[0043] 3,5-Diaminobenzoic acid (DABA, 0.3676 g, 0.0024 mol) and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (DS-NH2, 0.149 g, 0.0006 mol) were weighed separately and added to a dry three-necked flask. Under nitrogen protection, 13 mL of anhydrous N-methylpyrrolidone (NMP) was added as a solvent, and a magnetic stir bar was added. The mixture was stirred until the diamine monomer dissolved. Subsequently, 0.029 g of superconducting carbon black (Super P) was added as a conductive filler in the binder. The mixture was stirred and sonicated for 10 min to ensure that Super P was uniformly dispersed in the system, resulting in a diamine monomer solution containing the conductive filler.

[0044] Separately weigh 0.93 g of 4,4′-oxydiphthalic anhydride (ODPA, 0.003 mol) and divide it into three equal portions. Under ice-water bath conditions, slowly add ODPA to the above diamine monomer solution in three portions, with each addition spaced 0.5 h apart. After the additions are complete, stir in an ice-water bath for 4 hours, then continue stirring at room temperature for 12 hours to obtain a polyamic acid precursor solution for conductive polyimide binders.

[0045] The conductive agent Super P and the polyimide binder precursor solution were added to a mortar at a mass ratio of 2:1 and thoroughly ground to mix evenly. Then, an appropriate amount of NMP was added as a solvent, and grinding continued for 15-30 minutes until a uniform and viscous electrode slurry was formed. The resulting slurry was evenly coated onto the surface of a copper foil using a scraper and dried under vacuum at 60-80 °C for 6-8 hours to remove most of the liquid solvent. The dried electrode sheet was then transferred to a tube furnace and subjected to a staged thermal imidization treatment under a nitrogen protective atmosphere: first, the temperature was raised to 200 °C and held for 1 hour; then, it was raised to 250 °C and held for 2 hours; finally, it was raised to 300 °C and held for 1 hour. After naturally cooling to room temperature, a fully imidized negative electrode sheet containing only the conductive agent Super P and the polyimide binder was obtained.

[0046] The obtained negative electrode sheet was cut into circular electrode sheets with a diameter of 12 mm. A lithium sheet with a diameter of 16 mm was used as the counter electrode. The separator was a Celgard 2325 microporous three-layer membrane. The electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte, with the solvents being DEC, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) with the addition of 5% fluoroethylene carbonate (FEC). The DEC:EC:EMC ratio was 1:1:1 vol% with 5% FEC. The CR2032 button cell was assembled in an argon-filled glove box.

[0047] Comparative Example 1:

[0048] The Si / C650 negative electrode material, conductive agent Super P, and water-based polyacrylic acid (PAA) binder (molecular weight 1,250,000) were added to a mortar at a mass ratio of 7:2:1 and mixed evenly. An appropriate amount of deionized water was added as a solvent, and the mixture was ground and stirred for 15-30 minutes to form a uniform and viscous slurry. The slurry was coated onto copper foil with a scraper and vacuum dried at 80℃ for 8-12 hours to obtain a negative electrode sheet. The negative electrode sheet was then cut into circular sheets with a diameter of 12 mm. A lithium sheet with a diameter of 16 mm was used as the counter electrode, and Celgard 2325 was used as the separator. The electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte with DEC, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) as solvents, and 5% fluoroethylene carbonate (FEC) was added. The DEC:EC:EMC ratio was 1:1:1 vol% with 5% FEC. The CR2032 button cell was assembled in an argon-filled glove box.

[0049] Comparative Example 2:

[0050] The Si / C650 anode material, conductive agent Super P, and aqueous sodium carboxymethyl cellulose (CMCNa) binder (viscosity 800-1200 mPa·s) were added to a mortar at a mass ratio of 7:2:1 and mixed evenly. An appropriate amount of deionized water was added as a solvent, and the mixture was ground and stirred for 15-30 minutes to form a uniform and viscous slurry. The slurry was coated onto copper foil with a scraper and vacuum dried at 80℃ for 8-12 hours to obtain the anode sheet. The anode sheet was then cut into circular sheets with a diameter of 12 mm. A lithium sheet with a diameter of 16 mm was used as the counter electrode, and Celgard 2325 was used as the separator. The electrolyte was 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte, with DEC, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) as solvents and 5% fluoroethylene carbonate (FEC) added. The DEC:EC:EMC ratio was 1:1:1 vol% with 5% FEC. The CR2032 button cell was assembled in an argon-filled glove box.

[0051] Comparative Example 3:

[0052] Conductive agent Super P and polyvinylidene fluoride (PVDF, HSV900) binder were added to a mortar at a mass ratio of 2:1 and mixed evenly. An appropriate amount of NMP was added as a solvent, and the mixture was further ground and stirred for 15-30 minutes to form a uniform, viscous slurry. The slurry was then coated onto copper foil using a scraper and vacuum dried at 80°C for 8-12 hours to obtain the negative electrode. This negative electrode was then cut into circular electrodes with a diameter of 12 mm. A 16 mm diameter lithium sheet was used as the counter electrode, and Celgard 2325 was used as the separator. The electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte, with DEC, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) as solvents, and 5% fluoroethylene carbonate (FEC) was added. The DEC:EC:EMC ratio was 1:1:1 vol% with 5% FEC. The CR2032 type button cell was assembled in an argon-filled glove box.

[0053] Figure 1 The diagram shows the synthesis circuit of the conductive polyimide binder precursor solution in Examples 1 and 2. It is synthesized by low-temperature polycondensation reaction of diamine and dianhydride. The process is mature and the reaction conditions are simple.

[0054] Figure 2 The images show the FT-IR spectra of the conductive polyimide adhesives used in Examples 1 and 2. The spectra show that at 1780 cm⁻¹... -1 and 1720 cm -1 A distinct absorption peak appears nearby, corresponding to the asymmetric and symmetric stretching vibrations of the carbonyl group in the imide ring, respectively; simultaneously, at 1360 cm⁻¹... -1 The nearby absorption peaks are attributed to the stretching vibrations of the CN bonds in the imide ring, indicating that the polyamic acid precursor has been successfully converted into a polyimide structure. (1600 cm⁻¹ in the spectrum) -1 and 1500 cm -1 The nearby absorption peak corresponds to the vibration of the aromatic ring skeleton, 1240 cm⁻¹ -1 The nearby absorption peaks are attributed to the COC stretching vibration of the ether bond, while the 1100-1050 cm⁻¹ peaks... -1 The nearby absorption peaks originate from the stretching vibrations of the Si-O-Si bonds, indicating that the flexible siloxane segments have been successfully introduced into the polymer backbone. These results demonstrate that the conductive polyimide binder has been successfully prepared.

[0055] Figure 3The images show SEM images of the cross-sections of the polyimide films after high-temperature imidization of the polyimide precursor solutions in Examples 1 and 2. The relatively smooth and uniform sheet-like structures in the images represent the polyimide matrix, which serves as an insulating continuous phase, providing load-bearing and structural support. The bright white, spherical particles in the images are Super P conductive carbon black, approximately 50 nm in size, dispersed within the polyimide matrix as conductive fillers. The Super P particles are close to each other, even in direct contact, forming particle chains that penetrate the polyimide matrix. Within the insulating polyimide matrix, these interconnected particles achieve electron transport through contact conductivity or tunneling effects, ultimately constructing a three-dimensional conductive network, giving the originally insulating polyimide excellent conductivity.

[0056] Figure 4 Broadband dielectric impedance diagrams for the electrode sheets in Example 1, Comparative Example 1, and Comparative Example 2 are shown. The results indicate that, under the same ratio (Si / C650:Super P: binder = 7:2:1), silicon-carbon anode sheets prepared with different binders exhibit different conductivities. The conductivity of the three groups of samples shows relatively stable changes with frequency, indicating a relatively stable internal conductive network of the electrode sheets. Among them, the electrode sheet using the synthesized polyimide binder exhibits the highest conductivity, significantly higher than that of Comparative Example 1 and Comparative Example 2, which use traditional aqueous binders PAA and CMCNa. This suggests that the conductive polyimide binder system helps improve the dispersion and interfacial connection of the Si / C650 active material and the Super P conductive agent in the electrode, promoting the construction of a continuous conductive network, thereby significantly improving the overall conductivity of the electrode sheet. This result may be attributed to the introduction of Super P conductive filler into the polyimide binder, enhancing the electron transport capability of the binder phase and improving the connectivity of the internal conductive network of the electrode.

[0057] Figure 5Figure 1 shows the 180° peel test results of the electrode sheets in Example 1, Comparative Example 1, and Comparative Example 2. The 180° peel test further evaluated the interfacial adhesion ability of different binders to the silicon-carbon anode electrode sheets. The electrode in Example 1 using a conductive polyimide binder exhibited significantly higher peel force than Comparative Example 1 and Comparative Example 2, indicating that the polyimide binder can significantly enhance the interfacial bonding between active materials. Its superior adhesion performance is mainly attributed to the strong interaction between the polar structures such as carboxyl groups, imide carbonyl groups, and ether bonds in the polyimide binder molecular chain and the Si / C particles and current collector surface. Simultaneously, the rigid aromatic polyimide backbone provides high mechanical strength, while the flexible Si-O-Si segments help alleviate stress concentration during the peeling process. In contrast, the peel forces of PAA and CMCNa binders were lower, indicating that traditional binders have certain shortcomings in maintaining a stable bond between the silicon-carbon anode active layer and the current collector. The above results demonstrate that polyimide binders have stronger interfacial adhesion capabilities, which helps to suppress the shedding of active materials and electrode structure failure during the cycling process of silicon-carbon anodes, thereby improving battery cycle stability.

[0058] Figure 6 The graphs show the cycling performance of Examples 1, 1, and 2 at a current density of 2 A / g. The cycling performance curves show that different binders have a significant impact on the electrochemical performance of the silicon-carbon anode. Example 1, using a conductive polyimide binder, exhibits a higher reversible specific capacity and better capacity retention, significantly exceeding that of Comparative Examples 1 and 2, which use polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMCNa) binders.

[0059] It is noteworthy that the electrode in Example 1 exhibited a significant increase in capacity during the initial cycling phase. This may be related to the gradual wetting of the electrode, the gradual activation of the active material, and the gradual formation of a stable SEI film. Furthermore, the polyimide molecular chain contains abundant imide carbonyl groups, which are polar carbonyl groups that can react with Li... + Reversible coordination occurs, which to some extent promotes the storage and release of lithium ions, thus contributing additional capacity to the electrode. Therefore, polyimide binders not only maintain the stability of the electrode structure but may also participate in the partially reversible lithium storage process.

[0060] In contrast, Comparative Examples 1 and 2 showed lower reversible capacities and relatively poor capacity retention during cycling, indicating that although traditional PAA and CMCNa binders have a certain adhesive effect, they are unable to fully maintain the stability of the electrode structure during repeated lithium insertion / extraction processes in silicon-carbon anodes.

[0061] Figure 7The cycle rate performance graphs for Example 1, Comparative Example 1, and Comparative Example 2 show that the discharge specific capacity of Example 1 is significantly better than that of Comparative Example 1 and Comparative Example 2 at all current densities. Traditional polyimide is an insulator. By introducing a special super-conductive carbon black filler, a three-dimensional continuous high-speed electron transport channel can be formed throughout the electrode. Thanks to the special conductive filler design, the conductive polyimide binder in these examples exhibits faster charge transport capability and better electrochemical reactivity, thus demonstrating excellent rate performance.

[0062] Figure 8 Examples 2 and 3 are shown in the cycling performance graphs at current densities of 0.1 A / g and 2 A / g, respectively. These tests can be used to evaluate the electrochemical activity and capacity contribution of the binder itself. Since the coating contains only conductive carbon black Super P and the binder, and the mass ratio of Super P:binder is 2:1, the conductive component content in both electrodes is consistent. The capacity difference mainly stems from the differences in the structure and electrochemical behavior of the binder itself. As can be seen from the graphs, Example 2, using a conductive polyimide binder, exhibits a significantly higher reversible specific capacity than Comparative Example 3, which uses a PVDF binder. PVDF exhibits electrochemical inertness within the 0.01-3 V voltage window and lacks the ability to react with Li. + The active functional groups involved in reversible reactions mean that the capacity of Super P mainly comes from surface lithium storage or contributions from the electric double layer, resulting in a relatively low overall capacity. In contrast, the polyimide molecular chain contains abundant imide carbonyl groups, carboxyl groups, ether bonds, and polar structures such as Si-O-Si. The imide carbonyl group can react with Li... + A reversible coordination / redox reaction occurs, forming a structure similar to C=O / CO-Li. + The reversible process allows the polyimide binder to exhibit certain electrochemical activity within this voltage range, contributing additional capacity to the electrode. Furthermore, the capacity of Example 2 gradually increases in the early stages of cycling, possibly related to the gradual wetting of the electrode, the gradual activation of the polyimide active sites, and the gradual stabilization of the interfacial film. As cycling progresses, the capacity tends to stabilize, indicating that the polyimide binder possesses good electrochemical reversibility and structural stability. In contrast, the PVDF electrode exhibits lower capacity and less significant change, further demonstrating that traditional PVDF binders primarily function as inert binder components and are unlikely to participate in lithium storage reactions.

[0063] In summary, these results indicate that conductive polyimide binders can not only maintain the integrity of the electrode structure, but also participate in a certain reversible lithium storage process through polar active sites such as imide carbonyl groups, demonstrating a synergistic "binding-conductivity-lithium storage" function that is different from traditional PVDF binders.

[0064] Figure 9Example 2 and Comparative Example 3 were performed at 0.4 mV / s. -1 The cyclic voltammetry curves at the specified scan rate show that the polyimide binder in Example 2 exhibits a certain electrochemical response within the voltage range of 0.01-3 V, indicating that it is not a completely inert binder component. Since the electrode film is composed of Super P and binder in a mass ratio of 2:1, and the Super P content in the comparative samples remains consistent, the difference in electrochemical behavior between the two groups of electrodes mainly stems from the structural differences in the binder itself.

[0065] During the initial scan, the electrode in Example 2 exhibited a significant reduction current response. This may be related to the formation of the SEI film from electrolyte decomposition, surface activation of conductive carbon black, and the initial lithiation process of polar functional groups in the polyimide molecular chain. The polyimide molecular chain contains abundant imide carbonyl groups, carboxyl groups, ether bonds, and Si-O-Si structures, among which the imide carbonyl groups have strong Li-linked properties. + Coordination ability may be similar to C=O / CO-Li + The reversible activation process allows it to participate in the storage and release of lithium ions, contributing to the electrode's capacity. As cycling progresses, the CV curves of the electrode in Example 2 gradually converge, indicating good electrochemical reversibility and structural stability after initial activation. In contrast, the PVDF molecular structure in Comparative Example 3 is more stable and lacks the ability to react with Li. + The active functional groups that undergo reversible coordination or redox reactions are essentially electrochemically inert in the voltage range of 0.01-3 V. Their electrochemical response mainly comes from the surface lithium storage and capacitive behavior of Super P.

[0066] In summary, polyimide binders differ from traditional inert PVDF binders. The polar active sites, such as the imide carbonyl groups in their molecular chains, can participate to some extent in the reversible lithium-ion storage process, giving them the functions of bonding, conductive network construction, and capacity contribution. This functionalized binder design helps reduce the dilution effect of traditional inert binders on electrode capacity and further improves the overall electrochemical performance of silicon-carbon anodes.

Claims

1. A conductive polyimide adhesive that contributes capacity, characterized in that: It is prepared by polymerization and thermal imidization of diamine monomers and dianhydride monomers, and conductive fillers are introduced in situ during the polymerization process; The diamine monomer is 3,5-diaminobenzoic acid and 1,3-bis(3-aminopropyl)tetramethyldisiloxane; The dianhydride monomer is 4,4′-oxobisphthalic anhydride.

2. The conductive polyimide adhesive according to claim 1, characterized in that: In the diamine monomer, the molar ratio of 3,5-diaminobenzoic acid and 1,3-bis(3-aminopropyl)tetramethyldisiloxane is 4:

1.

3. The conductive polyimide adhesive according to claim 1, characterized in that: The conductive filler is one or more of Super P, acetylene black, Ketjen black, carbon nanotubes, graphene, and conductive carbon fibers.

4. The conductive polyimide adhesive according to claim 3, characterized in that: The amount of conductive filler added is controlled to be 1-5% of the total mass of diamine monomer and dianhydride monomer.

5. A method for preparing the conductive polyimide adhesive according to any one of claims 1-4, characterized in that... Includes the following steps: Step 1: In a nitrogen atmosphere, add the diamine monomer to anhydrous N-methylpyrrolidone, stir and mix to dissolve, then add the conductive filler and disperse evenly to obtain solution A; Step 2: Under ice-water bath conditions, the dianhydride monomer is added to solution A in batches. After stirring in the ice-water bath for 4 hours, the reaction is continued at room temperature. The total reaction time is controlled at 12-16 hours to obtain solution B, which is the polyimide binder precursor solution. Subsequently, imidization is completed by staged heating during application.

6. The preparation method according to claim 5, characterized in that: In step 2, the dianhydride monomer is divided into three equal parts and added to solution A in three separate additions under ice-water bath conditions, with each addition spaced 0.5 h apart.

7. The preparation method according to claim 5, characterized in that: The solid content of the polyimide binder precursor solution is 5-20 wt%.

8. The application of the conductive polyimide binder according to any one of claims 1-4 in the silicon-carbon anode of a lithium-ion battery.

9. The application according to claim 8, characterized in that: Si / C anode material, conductive agent Super P, and polyimide binder precursor solution were added to a mortar in proportion and mixed evenly. Then, N-methylpyrrolidone was added as a solvent, and the mixture was further ground and mixed into a uniform viscous slurry. The slurry was coated onto copper foil, vacuum dried, and then transferred to a tube furnace for staged heating treatment under a nitrogen-protected atmosphere to obtain a fully imidized anode sheet, which was then assembled to obtain a battery.

10. The application according to claim 9, characterized in that: The procedure for the staged heating process is as follows: first, heat to 200℃ and hold for 1 hour, then heat to 250℃ and hold for 2 hours, and finally heat to 300℃ and hold for 1 hour, and then cool naturally to room temperature.

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