Cross-linked polyimide binder for silicon-based negative electrode of lithium ion battery and preparation method of cross-linked polyimide binder

Abstract

The invention discloses a cross-linked polyimide binder for a silicon-based negative electrode of a lithium ion battery and a preparation method of the cross-linked polyimide binder, and the preparation method comprises the following steps: in a nitrogen atmosphere, preparing diamine into a solution A; adding dianhydride into the solution A in batches to obtain a solution B; and adding epoxy resin into the solution B, and carrying out prepolymer end-capping cross-linking, thereby obtaining the three-dimensional cross-linked netted binder. In the preparation process, the process of removing a solvent at a high temperature and then dissolving and applying is not carried out, so that the operation flow is simplified, and the energy loss and the solvent waste are reduced; in addition, the phenomena that the molecular weight is reduced and the viscosity becomes poor after a conventional PVDF binder absorbs water are avoided, and fluorine-containing gas is not generated. The binder disclosed by the invention has relatively good adhesive power, can effectively enhance the bonding strength between the active components and the copper foil current collector and between the active components, and has thermal stability. And when the material is applied to a silicon-based negative electrode of a lithium ion battery, the material has relatively good specific capacity after 100 cycles.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a polyimide binder for a silicon-based negative electrode of a lithium ion battery and a preparation method thereof. Background Art

[0002] With the rapid development of portable electronic products, electric vehicles and smart grids, research on high-performance energy storage systems has received widespread attention. Among the various battery systems, lithium-ion batteries have become the dominant choice due to their high energy density, long cycle life and environmental friendliness. Currently, the main negative electrode material for commercial lithium batteries is graphite, mainly due to their relatively low operating voltage (<0.5V vs Li / Li + ), easy to produce and relatively low cost, and then its performance is affected by 372mAhg -1 As one of the many alloy anode materials, silicon-based anode has an ultra-high theoretical specific capacity (~4200mAhg -1 ), lower operating voltage (~0.2V vs Li / Li + ), its rich reserves and environmental friendliness have attracted widespread attention from scientific researchers.

[0003] However, its commercial application faces two major challenges: significant volume changes during cycling, leading to electrode structural deactivation and poor electronic / ionic conductivity. Common solutions currently include structural design of active materials, such as silicon nanowires, nanotubes, and silicon-carbon core-shell structures, to mitigate the expansion stress of silicon-based materials. Furthermore, well-designed binders can enhance the commercial application of silicon-based materials. Binders are an essential component of lithium-ion batteries, bonding the active materials to the conductive current collector. Ideal binders must exhibit resilient mechanical properties, form a stable solid electrolyte interface (SEI) during the initial cycling phase to prevent excessive electrolyte consumption, and overcome the material's low electronic / ionic conductivity by promoting interfacial electron / ion transfer. Currently, commercially available binders primarily use polyvinylidene fluoride (PVDF). However, relying solely on weak van der Waals forces, PVDF cannot effectively mitigate the volume expansion effect, resulting in rapid capacity decay and poor cycling durability in lithium-ion batteries, limiting their further application.

[0004] Polyimide (PI), a polymer material widely used in aerospace, microelectronics, and structural materials, can be prepared through the polycondensation of dianhydrides and diamines. The polyimides obtained from the polycondensation of different types of dianhydrides and diamines have different structures and significant differences in their mechanical and adhesive properties. While the physical properties of polyimide can meet the requirements of silicon-based anode binders, its poor toughness and brittleness make it difficult to adapt well to the huge expansion stress of silicon-based anodes.

[0005] Therefore, it is very necessary to modify and cross-link polyimide to improve its flexibility, further enhance the adhesion between the active material and the copper foil current collector, reduce the shedding of the electrode material during the cycle, and improve the electrochemical performance of the battery.

[0006] Chinese patent CN 119463793 A discloses a method for preparing a fluorine-soluble polyimide binder specifically for lithium batteries. The binder comprises 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. Although the battery exhibits good rate performance and bonding properties, the battery's cycling performance is not described.

[0007] Chinese patent CN 119391360 A discloses a method for preparing a polyimide binder for lithium-ion battery positive electrodes. The method employs cyclodextrin, a sulfonated diamine, triethylamine, and a dibasic acid anhydride in the presence of a catalyst to produce the polyimide binder. However, this method has not been applied to silicon-based materials, which experience significant volume expansion.

[0008] Chinese patent CN115975190 B invented a method for preparing a modified polyimide binder and its application. A series of binders were obtained by prepolymerization of dianhydride and diisocyanate, followed by polymerization with a difunctional monomer. Their bond strength was tested for peeling, but their electrochemical performance in batteries was not tested. Summary of the Invention

[0009] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a cross-linked polyimide binder for a silicon-based negative electrode of a lithium ion battery.

[0010] The second object of the present invention is to provide a method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery.

[0011] The third object of the present invention is to provide an application of a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery.

[0012] The technical solution of the present invention is summarized as follows:

[0013] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0014] (1) Under a nitrogen atmosphere, diamine and an organic solvent are stirred uniformly at room temperature to obtain solution A;

[0015] (2) adding dianhydride to the solution A in batches, stirring until dissolved, and reacting to obtain solution B;

[0016] (3) adding epoxy resin to solution B, reacting at a constant temperature of 80-150° C., performing end-capping and cross-linking of the prepolymer, and obtaining a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery.

[0017] The molar ratio of diamine to dianhydride is preferably 1:1-2.

[0018] The molar ratio of the epoxy resin to the diamine is preferably 0.05 to 1:1.

[0019] The diamine is selected from at least one of ethylenediamine, 2,2-oxybisethylamine, 1,8-octanediamine, 1,8-diamino-3,6-dioxaoctane, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether and isophoronediamine.

[0020] The organic solvent is preferably: N,N-dimethylformamide or N,N-dimethylacetamide.

[0021] The dianhydride is selected from the group consisting of ethylenediaminetetraacetic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, hexafluorodianhydride, 4,4'-biphenyl ether dianhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 3,3,4,4-diphenylsulfonetetracarboxylic dianhydride or perylene-3,4,9,10-tetracarboxylic dianhydride.

[0022] The epoxy resin is at least one of trimethylolpropane triglycidyl ether, 1,2-cyclohexanedicarboxylic acid diglycidyl ester, isocyanuric acid triglycidyl ester and 4,5-epoxytetrahydrophthalic acid diglycidyl ester.

[0023] The cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries is prepared by the above preparation method.

[0024] The cross-linked polyimide binder for silicon-based negative electrode of lithium-ion battery is used for bonding negative electrode of lithium-ion battery.

[0025] Advantages of the present invention:

[0026] The adhesive of the present invention is a three-dimensional cross-linked network adhesive. It is easy to operate and does not require high-temperature solvent removal and subsequent dissolution during preparation, simplifying the process and reducing energy consumption and solvent waste. Furthermore, it avoids the molecular weight loss and poor viscosity of conventional PVDF adhesives after water absorption, and does not produce toxic fluorine-containing gases.

[0027] The adhesive of the present invention has good adhesion, can effectively enhance the bonding strength between the active component and the copper foil current collector and between the active components, and furthermore, the adhesive itself has excellent thermal stability.

[0028] The binder of the present invention is applied to the silicon-based negative electrode of lithium-ion batteries. Compared with the comparative example, the binder prepared in the example has better specific capacity after 100 cycles. In particular, in Example 2, the 100-cycle capacity retention rate of the electrode reaches 95.7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of the silicon-based negative electrode plate to which the binder of the present invention is added in Example 1.

[0030] Figure 2 180° peel test force and displacement relationship diagram of Example 1, Example 3, Comparative Example 1, and Comparative Example 2 of the present invention.

[0031] Figure 3 It is the average peeling force of Example 1, Example 3, Comparative Example 1, and Comparative Example 2 of the present invention.

[0032] Figure 4 This is an electrochemical performance diagram of the silicon-based electrode charge specific capacity and cycle number of Examples 1-7 and Comparative Examples 1-3 in the present invention. DETAILED DESCRIPTION

[0033] Unless otherwise specified, the methods described are all routine test methods, and the drugs described can be obtained from formal and open commercial channels unless otherwise specified.

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Example 1

[0036] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0037] (1) Under nitrogen atmosphere, 1480 mg (10 mmol) of diamine (1,8-diamino-3,6-dioxaoctane) and 20 mL of organic solvent (N,N-dimethylacetamide) were stirred at room temperature to obtain solution A.

[0038] (2) adding 2180 mg (10 mmol) of dianhydride (pyromellitic dianhydride) to the solution A in four batches (once added every 10 minutes), stirring until dissolved, and reacting to obtain solution B;

[0039] (3) 148 mg (0.5 mmol) of epoxy resin (triglycidyl isocyanurate) was added to solution B, and the mixture was reacted at a constant temperature of 150° C. for 2 h to perform end-capping and cross-linking of the prepolymer to obtain a cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries (abbreviated as PI-1).

[0040] Example 2

[0041] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0042] (1) Under nitrogen atmosphere, 1480 mg (10 mmol) of diamine (1,8-diamino-3,6-dioxaoctane) and 20 mL of organic solvent (N,N-dimethylacetamide) were stirred at room temperature to obtain solution A.

[0043] (2) Add 2616 mg (12 mmol) of dianhydride (pyromellitic dianhydride) to the solution A in four batches (once added every 10 minutes), stir until dissolved, and react to obtain solution B;

[0044] (3) 148 mg (0.5 mmol) of epoxy resin (triglycidyl isocyanurate) was added to solution B, and the mixture was reacted at a constant temperature of 150° C. for 2 h to perform end-capping and cross-linking of the prepolymer to obtain a cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries (abbreviated as PI-2).

[0045] Example 3

[0046] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0047] (1) Under nitrogen atmosphere, 1480 mg (10 mmol) of diamine (1,8-diamino-3,6-dioxaoctane) and 20 mL of organic solvent (N,N-dimethylacetamide) were stirred at room temperature to obtain solution A.

[0048] (2) adding 2180 mg (10 mmol) of dianhydride (pyromellitic dianhydride) to the solution A in four batches (once added every 10 minutes), stirring until dissolved, and reacting to obtain solution B;

[0049] (3) 297 mg (1.0 mmol) of epoxy resin (triglycidyl isocyanurate) was added to solution B, and the mixture was reacted at 150° C. for 2 h to perform end-capping and cross-linking of the prepolymer to obtain a cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries (abbreviated as PI-3).

[0050] Example 4

[0051] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0052] (1) Under nitrogen atmosphere, 1480 mg (10 mmol) of diamine (1,8-diamino-3,6-dioxaoctane) and 20 mL of organic solvent (N,N-dimethylacetamide) were stirred at room temperature to obtain solution A.

[0053] (2) Add 2616 mg (12 mmol) of dianhydride (pyromellitic dianhydride) to the solution A in four batches (once added every 10 minutes), stir until dissolved, and react to obtain solution B;

[0054] (3) 297 mg (1.0 mmol) of epoxy resin (triglycidyl isocyanurate) was added to solution B, and the mixture was reacted at 150° C. for 2 h to perform end-capping and cross-linking of the prepolymer to obtain a cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries (abbreviated as PI-4).

[0055] Example 5

[0056] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0057] (1) Under nitrogen atmosphere, 1440 mg (10 mmol) of diamine (1,8-octanediamine) and 20 mL of organic solvent (N,N-dimethylformamide) were stirred at room temperature to obtain solution A.

[0058] (2) adding 2180 mg (10 mmol) of dianhydride (pyromellitic dianhydride) to the solution A in four batches (once added every 10 minutes), stirring until dissolved, and reacting to obtain solution B;

[0059] (3) 296 mg (1 mmol) of epoxy resin (trimethylolpropane triglycidyl ether) was added to solution B, and the mixture was reacted at 80°C for 12 h to perform end-capping and cross-linking of the prepolymer to obtain a cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries (abbreviated as PI-5).

[0060] Example 6

[0061] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0062] (1) Under nitrogen atmosphere, 520 mg (5 mmol) of 2,2-oxobisethylamine, 1000 mg (5 mmol) of 4,4'-diaminodiphenyl ether, and 50 mL of organic solvent (N,N-dimethylacetamide) were stirred at room temperature to obtain solution A.

[0063] (2) adding 6200 mg (20 mmol) of dianhydride (4,4′-biphenyl ether dianhydride) to the solution A in four batches (once added every 10 minutes), stirring until dissolved, and reacting to obtain solution B;

[0064] (3) 2960 mg (10 mmol) of epoxy resin (trimethylolpropane triglycidyl ether) was added to solution B, and the mixture was reacted at a constant temperature of 120° C. for 6 h to perform end-capping and cross-linking of the prepolymer to obtain a cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries (abbreviated as PI-6).

[0065] Example 7

[0066] A method for preparing a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery comprises the following steps:

[0067] (1) Under nitrogen atmosphere, 1040 mg (10 mmol) of diamine (2,2-oxobisethylamine) and 30 mL of organic solvent (N,N-dimethylformamide) were stirred at room temperature to obtain solution A.

[0068] (2) adding 2940 mg (10 mmol) of dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride) to the solution A in four batches (once added every 10 minutes), stirring until dissolved, and reacting to obtain solution B;

[0069] (3) 705 mg (2.5 mmol) of epoxy resin (diglycidyl 1,2-cyclohexanedicarboxylate) and 727 mg (2.5 mmol) of epoxy resin (triglycidylamino-m-cresol) were added to solution B, and the mixture was reacted at 120°C for 6 h to perform end-capping and cross-linking of the prepolymer to obtain a cross-linked polyimide binder for silicon-based negative electrodes of lithium-ion batteries (abbreviated as PI-7).

[0070] Comparative Example 1

[0071] Weigh 0.5g of polyvinylidene fluoride (PVDF, average molecular weight ≈400,000) and dissolve it in 12ml of N-methylpyrrolidone. Stir thoroughly at room temperature to prepare a binder (abbreviated as PVDF) with a mass fraction of 4wt%. Prepare freshly before use.

[0072] Comparative Example 2

[0073] Compared with Example 1, the difference is that no epoxy resin (triglycidyl isocyanurate) is added, and the other components and processes are the same, thereby obtaining a polyimide adhesive (PDAC for short).

[0074] Comparative Example 3

[0075] Weigh 0.5 g of sodium carboxymethyl cellulose (NaCMC, chemically pure CP 300-800 mPa·s) and dissolve it in 12 ml of deionized water. Stir thoroughly at room temperature to prepare a binder (NaCMC) with a mass fraction of 4 wt%. Prepare it fresh before use.

[0076] Experimental example

[0077] Preparation of silicon-based negative electrode sheets:

[0078] Preparation of diluted adhesive: The adhesive of the present invention is used to adjust the mass content of the adhesive to 10% with N,N-dimethylacetamide (N,N-dimethylformamide may also be used) to obtain a diluted adhesive.

[0079] Silicon carbon powder (theoretical specific capacity ~ 600mAhg -1 ), conductive carbon black and diluted binder were mixed in a mass ratio of 80:10:10, homogenized, and the viscosity of the slurry was adjusted with solvent N,N-dimethylacetamide. The slurry was then evenly coated on the copper foil with a 150μm scraper, and the active material loading was controlled to be 1.0-1.5mg / cm 2 , the coated silicon-based electrode piece was obtained, which was transferred to a blast drying oven at 45°C for 2h, and then the electrode piece was cut and weighed, vacuum dried at 80°C for 12h, and then transferred to a vacuum glove box filled with argon (O2, H2O <0.1ppm) to obtain a silicon-based negative electrode piece. The schematic diagram of the negative electrode piece structure in which the binder of the present invention is added in Example 1 is shown in FIG. Figure 1 .

[0080] CR2032 button-type half-cells were assembled using silicon-based negative electrode sheets and metal lithium sheets.

[0081] The prepared adhesive was tested for bonding performance through a 180° peel test:

[0082] The coated silicon-based electrode was subjected to a 180° peeling test on a universal tensile testing machine to characterize the bonding performance of the adhesive, see Table 1. Figure 2 and Figure 3 .

[0083] The electrochemical performance of silicon-based negative electrode sheets with different binders was measured by a Newwell 160CH test system. The test conditions were a voltage range of 0.005 to 2.0 V and a charge and discharge current density of 0.1 C (1 C = 1000 mAh g -1 ) under long cycle test, see Table 1 and Figure 4 .

[0084] Table 1

[0085]

[0086] The 1,8-diamino-3,6-dioxaoctane in Example 3 was replaced with ethylenediamine, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, or isophoronediamine, respectively. The adhesive obtained was tested for bonding performance through a 180° peel test, and the test results obtained were similar to those in Example 3. The battery long cycle test also showed similar test results to those in Example 3.

[0087] The adhesive obtained was tested for bonding performance through a 180° peel test, and the test results were similar to those in Example 3. The battery long cycle test also showed similar test results to those in Example 3.

[0088] The triglycidyl isocyanurate in Example 3 was replaced with diglycidyl 4,5-epoxytetrahydrophthalate, and the other aspects were the same as in Example 3. The adhesive obtained was tested for bonding performance by a 180° peel test, and the test results obtained were similar to those in Example 3. The battery long cycle test also showed similar test results to those in Example 3.

Claims

1. A method for preparing a cross-linked polyimide binder for a lithium-ion battery silicon-based negative electrode, comprising the following steps: (1) Under a nitrogen atmosphere, diamine and an organic solvent are stirred uniformly at room temperature to obtain solution A; (2) adding dianhydride to the solution A in batches, stirring until dissolved, and reacting to obtain solution B; (3) adding epoxy resin to solution B, reacting at a constant temperature of 80-150° C., performing end-capping and cross-linking of the prepolymer, and obtaining a cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery.

2. The preparation method according to claim 1, wherein The molar ratio of diamine to dianhydride is 1:1-2.

3. The preparation method according to claim 1, wherein The molar ratio of the epoxy resin to the diamine is 0.05 to 1:

1.

4. The preparation method according to claim 1, 2 or 3, characterized in that The diamine is at least one of ethylenediamine, 2,2-oxybisethylamine, 1,8-octanediamine, 1,8-diamino-3,6-dioxaoctane, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether and isophoronediamine.

5. The preparation method according to claim 1, wherein The organic solvent is: N,N-dimethylformamide or N,N-dimethylacetamide.

6. The preparation method according to claim 1, wherein The dianhydride is: ethylenediaminetetraacetic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, hexafluorodianhydride, 4,4'-biphenyl ether dianhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 3,3,4,4-diphenylsulfonetetracarboxylic dianhydride or perylene-3,4,9,10-tetracarboxylic dianhydride.

7. The preparation method according to claim 1 or 3, characterized in that The epoxy resin is at least one of trimethylolpropane triglycidyl ether, 1,2-cyclohexanedicarboxylic acid diglycidyl ester, isocyanuric acid triglycidyl ester and 4,5-epoxytetrahydrophthalic acid diglycidyl ester.

8. A cross-linked polyimide binder for a silicon-based negative electrode of a lithium-ion battery prepared by the preparation method according to any one of claims 1 to 7.

9. The cross-linked polyimide binder for a lithium ion battery silicon-based negative electrode according to claim 8 is used for bonding a lithium ion battery negative electrode.

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