A composite adhesive, its preparation method and application

Abstract

This invention belongs to the field of electrode material technology, specifically relating to a composite binder, its preparation method, and its application. The preparation method of the composite binder of this invention includes the following steps: (1) mixing and stirring acrylamide, ammonium persulfate, and water at 60-80°C for 30-45 min to obtain a mixed solution; (2) adding sodium dextran sulfate and sodium chondroitin sulfate to the mixed solution obtained in step (1), and stirring at 60-80°C for 20-40 min; (3) cooling to room temperature to obtain the composite binder solution. The composite binder of this invention has high bonding strength, good structural stability, and good electrolyte wettability; compared with binders in the prior art, it helps to improve the electrochemical performance of the battery cathode (especially the battery cathode with NCM811 as the active material).

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a composite binder, its preparation method, and its application. Background Technology

[0002] Against the backdrop of the global push for dual-carbon goals and the rapid upgrading of the new energy industry, ternary cathode material NCM811, with its high specific capacity, has become a key component in promoting the high-performance development of power batteries and energy storage devices. However, problems such as lattice distortion, volume changes, particle cracking, and interfacial side reactions that occur during long-cycle operation remain major bottlenecks restricting its commercial application. The binder, acting as the "skeleton" of the electrode structure, plays a decisive role in the structural stability, interfacial compatibility, and ion transport efficiency of the electrode, becoming a core entry point for solving these problems.

[0003] Existing binders have limitations in interfacial stabilization, are difficult to effectively alleviate structural stress and interfacial side reactions during cycling, and rely on organic solvents such as N-methylpyrrolidone (NMP), resulting in poor environmental performance. Therefore, they cannot fully meet the stringent requirements of NCM811 cathodes.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a composite adhesive, its preparation method, and its application, in order to help solve or improve at least one of the following problems of existing adhesives: limited bonding and interfacial stabilization effects, difficulty in effectively alleviating structural stress and interfacial side reactions during cycling, and poor environmental performance due to reliance on organic solvents during use.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a composite adhesive, the method comprising the following steps: (1) mixing and stirring acrylamide, ammonium persulfate and water at 60-80°C for 30-45 min to obtain a mixed solution; (2) adding sodium dextran sulfate and sodium chondroitin sulfate to the mixed solution obtained in step (1), and stirring and reacting at 60-80°C for 20-40 min; (3) cooling to room temperature to obtain a composite adhesive solution.

[0007] Preferably, the ratio of the sum of the masses of sodium dextran sulfate and sodium chondroitin sulfate to the mass of acrylamide is 1:(0.8-1.2); the mass ratio of sodium dextran sulfate to sodium chondroitin sulfate is 1:2-2:1.

[0008] Preferably, the mass ratio of sodium dextran sulfate and sodium chondroitin sulfate is 1:1.

[0009] Preferably, in step (1), the mass ratio of acrylamide to ammonium persulfate is (20-50):1.

[0010] The present invention also provides a composite adhesive, which adopts the following technical solution: a composite adhesive, wherein the composite adhesive is prepared by the method described above.

[0011] The present invention also provides a battery positive electrode, which adopts the following technical solution: a battery positive electrode, wherein the battery positive electrode adopts the composite binder as described above.

[0012] Preferably, the active material of the positive electrode of the battery is NCM811; the conductive agent of the positive electrode of the battery is acetylene black.

[0013] The present invention also provides a battery that adopts the following technical solution: a battery that uses the composite binder as described above; or, the battery that uses the positive electrode as described above.

[0014] Beneficial effects: The composite binder of the present invention has high bonding strength, good structural stability and good electrolyte wettability; compared with the binders in the prior art, it helps to improve the electrochemical performance of the battery cathode (especially the battery cathode with NCM811 as the active material). Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 The figures show the test results of the effects of composite binders PSCS1:1, PSCS2:1 and PSCS1:2 on the cycle stability of the electrode; where (a) is the cycle performance curve at 0.5C and (b) is the rate performance test result.

[0016] Figure 2 Comparison of Fourier transform infrared spectra of PAM, SCS, DSS and the composite adhesive of Example 1 (denoted as PSCS in the figure).

[0017] Figure 3 Figures show the test results of the mechanical and rheological properties of different adhesives; where (a) is the 180° peel curve, (b) is the test result of the average peel force, and (c) is the test result of the rotational viscosity.

[0018] Figure 4The diagram shows the contact angle test structure of different electrodes and electrolytes; where (a) is a PVDF electrode, (b) is a DSS electrode, (c) is a PAMCS electrode, and (d) is a PSCS electrode.

[0019] Figure 5 The figures show the test results of the cycle performance, rate performance and first-cycle charge-discharge curves of different electrodes; where (a) is the cycle performance curve at 0.5C, (b) is the cycle performance curve at 2C, (c) is the rate performance test result figure, and (d) is the first-cycle charge-discharge curve at 0.5C.

[0020] Figure 6 Figure 1 shows the test results of the charge-discharge performance of the PSCS electrode; where (a) is the charge-discharge curve at different cycle numbers under 0.5C, and (b) is the charge-discharge curve of the first cycle under different rates.

[0021] Figure 7 The figures show the cyclic voltammetry results of the PSCS electrode; (a) shows the cyclic voltammetry curves for cycles 1-3 at a scan rate of 0.1 mV / s; (b) shows the cyclic voltammetry curves at different scan rates; and (c) shows the peak currents of peaks 1 and 2 in (b) in relation to the scan rate. The linear fitting curve.

[0022] Figure 8 The figures show the electrochemical impedance spectroscopy and low-frequency kinetic fitting curves for different electrodes; where (a) is the Nyquist curve, and (b) is the real part impedance (…). ) and the square root of angular frequency ( The linear fitting relationship of ).

[0023] Figure 9 The images are SEM images of the PSCS electrode before and after cycling; where (a) is the SEM image before cycling, (b) is a magnified view of (a), (c) is the SEM image after 100 cycles, and (d) is a magnified view of (c).

[0024] Figure 10 The images show cross-sectional SEM images of the PSCS electrode before and after cycling; where (a) is the cross-sectional SEM image before cycling and (b) is the cross-sectional SEM image after 100 cycles.

[0025] Figure 11 The images are TEM images of the PSCS electrode after 100 cycles. (a) is a TEM image of the CEI film on the surface of the PSCS electrode, and (b) is a magnified view of (a).

[0026] Figure 12The images show SEM images and cross-sectional SEM images of the PAMCS electrode before and after cycling; where (a) is the SEM image before cycling, (b) is an enlarged view of (a), (c) is the SEM image after 100 cycles, (d) is an enlarged view of (c), (e) is the cross-sectional SEM image before cycling, and (f) is the cross-sectional SEM image after 100 cycles.

[0027] Figure 13 The images are TEM images of the PAMCS electrode after 100 cycles. (a) is a TEM image of the CEI film on the surface of the PAMCS electrode, and (b) is a magnified view of (a).

[0028] Figure 14 XPS spectra after cycling with different electrodes.

[0029] Figure 15 Figure 1 shows the three-dimensional morphology characterization of different electrode surfaces and the corresponding arithmetic mean roughness Ra obtained by atomic force microscopy (AFM); where (a) is a PVDF electrode, (b) is a DSS electrode, (c) is a PAMCS electrode, and (d) is a PSCS electrode.

[0030] Figure 16 Cyclic performance curves at 0.5C for DSS electrode, PAMDSS1:2 electrode, PAMDSS electrode, and PAMDSS2:1 electrode.

[0031] Figure 17 The figures show the cyclic voltammetry results of the DSS and PVDF electrodes. (a) shows the cyclic voltammetry curves of the PVDF electrode at a scan rate of 0.1 mV / s for cycles 1-3; (b) shows the cyclic voltammetry curves of the DSS electrode at a scan rate of 0.1 mV / s for cycles 1-3; (c) shows the cyclic voltammetry curves of the PVDF electrode at different scan rates; (d) shows the cyclic voltammetry curves of the DSS electrode at different scan rates; and (e) shows the peak currents of peaks 1 and 2 in (c) as a function of the scan rate V. 1 / 2 The linear fitting curves, (f) are the peak currents of peaks 1 and 2 and the sweep rate V in (d). 1 / 2 The linear fitting curve.

[0032] Figure 18 The images show cross-sectional SEM images of the PVDF electrode before and after cycling; where (a) is the cross-sectional SEM image before cycling, and (b) is the cross-sectional SEM image after 100 cycles. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0034] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0035] This invention addresses at least one of the problems of existing adhesives, namely, limited bonding and interfacial stabilization effects, difficulty in effectively alleviating structural stress and interfacial side reactions during cycling, and poor environmental performance due to reliance on organic solvents during use. The invention provides a method for preparing a composite adhesive.

[0036] The preparation method of the composite adhesive in this embodiment of the invention includes the following steps: (1) mixing and stirring acrylamide (AM), ammonium persulfate and water at 60-80°C (e.g., 60°C, 65°C, 70°C, 75°C or 80°C) for 30-45 min (e.g., 35 min, 40 min or 45 min) to obtain a mixed solution; (2) adding sodium dextran sulfate and sodium chondroitin sulfate to the mixed solution obtained in step (1), and stirring and reacting at 60-80°C (e.g., 60°C, 65°C, 70°C, 75°C or 80°C) for 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min or 40 min); (3) cooling to room temperature to obtain the composite adhesive solution. If the temperature in step (1) is too low, the initiation efficiency will be low, the acrylamide polymerization will be incomplete, and a large amount of monomer will remain. If the temperature is too high, the polymerization reaction will be violent and the heat release will be concentrated, which will easily lead to explosive polymerization. The system will thicken rapidly and gel into clumps in a short period of time. If the stirring time in step (1) is too short, the acrylamide polymerization will also be incomplete, and a large amount of monomer will remain. If the stirring time in step (1) is too long and the system is in a high-temperature environment for a long time, the polyacrylamide (PAM) molecular chains that have been generated will be easily thermally degraded. If the stirring reaction time in step (2) is too short, the sodium dextran sulfate (DSS) and sodium chondroitin sulfate (SCS) will not be in complete contact with the polyacrylamide molecules and will not be fully combined, making it difficult to form a uniform network inside. If the stirring reaction time in step (2) is too long, the hydrogen bonds generated will be easily destroyed, the composite network that has been formed will easily loosen slowly, and DSS and SCS will be degraded due to prolonged high-temperature heating.

[0037] The composite binder of this invention constructs a three-dimensional continuous network structure through multiple hydrogen bond crosslinking, which can systematically affect the interface characteristics and structure of NCM811 cathode. The sulfonic acid groups, carboxyl groups, and hydroxyl groups on the molecular chain of the composite binder of this invention can form strong coordination with transition metal ions on the NCM811 surface, effectively inhibiting the dissolution of transition metals during cycling and blocking the occurrence of interfacial side reactions; the three-dimensional network structure of the composite binder of this invention can be Li + Providing an efficient migration path improves the kinetic response of the electrode and helps to enhance rate performance. The crosslinked network of the composite binder of this invention has good resistance to deformation, which can absorb the volume deformation generated during the lithium insertion / extraction process of the electrode, maintain the integrity of the electrode structure, induce the formation of a uniform and stable CEI film, and achieve structural protection of NCM811 particles. The composite binder of this invention can synergistically improve the cycle stability and rate performance of the NCM811 cathode through multiple mechanisms.

[0038] If acrylamide monomer (AM) is mixed with DSS and SCS and reacted simultaneously, the PAM synthetic chain formed by the polymerization of acrylamide monomer will be broken by the active groups on DSS and SCS, resulting in a disordered network with large viscosity fluctuations. At the same time, it consumes the surface active groups on DSS and SCS, making it difficult to prepare the composite binder of the present invention.

[0039] In a preferred embodiment of the preparation method of the composite binder of the present invention, the mass ratio of the sum of sodium dextran sulfate and sodium chondroitin sulfate to the mass of acrylamide is 1:(0.8-1.2) (e.g., 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2); the mass ratio of sodium dextran sulfate to sodium chondroitin sulfate is 1:2-2:1 (e.g., 1:2, 1:1.5, 1:1, 1.5:1, or 2:1). In the composite binder of the present invention, acrylamide forms the framework. If the proportion of acrylamide is too high, the overall viscosity and consistency of the solution increase significantly, and the fluidity deteriorates; if the proportion of acrylamide is too low, the overall viscosity of the system is significantly low, and a continuous and dense network cannot be formed.

[0040] In a preferred embodiment of the preparation method of the composite adhesive of the present invention, the mass ratio of sodium dextran sulfate and sodium chondroitin sulfate is 1:1.

[0041] In a preferred embodiment of the method for preparing the composite adhesive of the present invention, in step (1), the mass ratio of acrylamide to ammonium persulfate is (20-50):1 (e.g., 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1).

[0042] The present invention also proposes a composite adhesive, which is prepared by the method described above in the embodiments of the present invention.

[0043] The present invention also proposes a battery positive electrode, wherein the battery positive electrode of the present invention adopts the composite binder as described above.

[0044] In a preferred embodiment of the positive electrode of the present invention, the active material of the positive electrode is NCM811; the conductive agent of the positive electrode is acetylene black.

[0045] The present invention also proposes a battery in which the composite binder described above is used in the battery of the present invention embodiment; or, the battery in the present invention embodiment uses the battery positive electrode described above.

[0046] The composite adhesive of the present invention, its preparation method, and its application are described in detail below through specific embodiments.

[0047] Unless otherwise specified, all raw materials used in the following examples are commercially available; the sources of the main raw materials are as follows: Table 1. Sources of Main Chemical Reagents

[0048] Example 1 The method for preparing the composite adhesive in this embodiment includes the following steps: (1) Acrylamide and ammonium persulfate were added to hot water at 80°C at a mass ratio of 20:1 and stirred at a constant temperature for 45 minutes to obtain a mixed solution; (2) Add a mixture of sodium dextran sulfate (DSS) and sodium chondroitin sulfate (SCS) to the above mixed solution (wherein, the total mass of DSS and SCS is equal to the mass of acrylamide, and the mass ratio of DSS to SCS is 1:1; in the mixed solution after adding DSS and SCS, the sum of the masses of DSS, SCS and acrylamide is 5% of the mass of the mixed solution), and stir the reaction at 80°C for 20 min; (3) After cooling to room temperature, the composite adhesive (solution) of this embodiment is obtained; denoted as PSCS1:1 (abbreviated as: PSCS).

[0049] The positive electrode of this embodiment uses NCM811 as the active material, acetylene black as the conductive agent, and the composite binder of this embodiment as the binder. The positive electrode of this embodiment is prepared using a method comprising the following steps: The active material NCM811, the conductive agent acetylene black, and the composite binder (solution) prepared in step (3) were mixed in a mass ratio of 85:15:5 and ground in an agate mortar for more than 20 minutes to form a uniformly mixed slurry. Then, the slurry was uniformly coated on the surface of the aluminum foil current collector using a coating doctor blade with a gap of 100µm. The coated current collector was placed in a vacuum drying oven and dried and shaped at a low temperature of 40℃ for 10 minutes. Then, it was transferred to a vacuum drying oven and dried overnight at 80℃ under vacuum. The resulting electrode sheet was first rolled and then cut into a circular electrode sheet with a diameter of 11mm using a slicing machine.

[0050] The electrode obtained in this embodiment is denoted as the PSCS electrode.

[0051] Example 2 The only difference between this embodiment and embodiment 1 is that the mass ratio of DSS to SCS in step (2) is 1:2; the rest are the same as in embodiment 1.

[0052] The composite adhesive in this embodiment is denoted as PSCS1:2.

[0053] The electrode in this embodiment is designated as PSCS1:2 electrode.

[0054] Example 3 The only difference between this embodiment and embodiment 1 is that the mass ratio of DSS to SCS in step (2) is 2:1; the rest are the same as in embodiment 1.

[0055] The composite adhesive in this embodiment is denoted as PSCS2:1.

[0056] The electrode in this embodiment is designated as PSCS2:1 electrode.

[0057] Comparative Example 1 The only difference between this comparative example and Example 1 is that PVDF is used instead of the composite binder in Example 1 to prepare the electrode (the active material NCM811, the conductive agent acetylene black and the PVDF solution are mixed; wherein the solvent of the PVDF solution is NMP, the concentration of PVDF in the PVDF solution is 5wt%; the mass ratio of the active material NCM811, the conductive agent acetylene black and the PVDF is 85:15:5); all other aspects are the same as in Example 1.

[0058] The electrode in this comparative example is denoted as the PVDF electrode.

[0059] Comparative Example 2 The only difference between this comparative example and Example 1 is that DSS is used instead of the composite binder in Example 1 to prepare the electrode (the active material NCM811, the conductive agent acetylene black and the DSS solution are mixed; wherein the solvent of the DSS solution is water, the concentration of DSS in the DSS solution is 5wt%; the mass ratio of the active material NCM811, the conductive agent acetylene black and the DSS is 85:15:5); all other aspects are the same as in Example 1.

[0060] The electrode in this comparative example is denoted as the DSS electrode.

[0061] Comparative Example 3 The only difference between this comparative example and Example 1 is that PAMDSS binder is used instead of the composite binder in Example 1 to prepare the electrode; all other aspects are the same as in Example 1.

[0062] PAMDSS is prepared using a method comprising the following steps: First, acrylamide and ammonium persulfate were added to hot water at 80°C at a mass ratio of 20:1 and stirred at a constant temperature for 45 minutes to obtain a mixed solution. Then, sodium dextran sulfate was added to the mixed solution in different proportions (sodium dextran sulfate to acrylamide mass ratios of 1:2, 1:1, and 2:1, respectively; the sum of the masses of sodium dextran sulfate and acrylamide in the mixed solution after adding sodium dextran sulfate was 5% of the mass of the mixed solution), and the mixture was stirred at 80°C for 20 minutes. After the reaction was completed and cooled to room temperature, the PAMDSS adhesive of this comparative example was obtained (when the mass ratio of sodium dextran sulfate to acrylamide was 1:2, 1:1, and 2:1, the PAMDSS adhesives prepared were respectively denoted as PAMDSS1:2, PAMDSS1:1, and PAMDSS2:1; the PAMDSS adhesive of this comparative example was in solution form).

[0063] The electrodes in this comparative example are identical to those in Example 1, except for the binder; the electrodes in this comparative example are referred to as PAMDSS1:2 electrode, PAMDSS electrode, and PAMDSS2:1 electrode, respectively.

[0064] Comparative Example 4 The only difference between this comparative example and Example 1 is that PAMCS binder is used instead of the composite binder in Example 1 to prepare the electrode; all other aspects are the same as in Example 1.

[0065] PAMCS is prepared using a method comprising the following steps: First, acrylamide (AM) and ammonium persulfate were added to hot water at 80°C at a mass ratio of 20:1 and stirred at a constant temperature for 45 minutes to obtain a mixed solution. Then, sodium chondroitin sulfate in different proportions was added to the mixed solution (so that the mass ratio of sodium chondroitin sulfate to acrylamide was 1:2, 1:1, and 2:1, respectively; in the mixed solution with added sodium chondroitin sulfate, the sum of the mass of sodium chondroitin sulfate and acrylamide was 5% of the mass of the mixed solution), and the mixture was stirred at 80°C for 20 minutes. After the reaction was completed and cooled to room temperature, the PAMCS binder of this comparative example was obtained (when the mass ratio of chondroitin sulfate to acrylamide was 1:2, 1:1, and 2:1, the PAMCS binders prepared were respectively denoted as PAMCS1:2, PAMCS1:1 (abbreviated as: PAMCS), and PAMCS2:1; the PAMCS binder of this comparative example was in solution form).

[0066] The electrodes in this comparative example are identical to those in Example 1, except for the binder; the electrodes obtained in this comparative example are referred to as PAMCS1:2 electrode, PAMCS electrode, and PAMCS2:1 electrode, respectively.

[0067] Experimental Example 1. Under test conditions of 25℃ and 0.5C, the effects of composite binders PSCS1:1, PSCS2:1 and PSCS1:2 on the cyclic stability of the electrode were evaluated by constant current charge-discharge test.

[0068] Test Method: The battery was tested using a CT-4008 Xinwei multi-channel test system, with constant current charge-discharge mode based on the mass of the electrode active materials. The test system operated within a voltage window of 3.0-4.3V, with a current density of 1C = 200mA / g set based on the specific capacity. The ambient test temperature was 26℃.

[0069] Test results are as follows Figure 1 (Among them, (a) is the cycle performance curve at 0.5C, and (b) is the rate performance test result graph) and Table 2; Table 2. Charge / discharge data for the first and 200th weeks at 0.5C.

[0070] Figure 1The test results in (a) show that the PSCS (Example 1) electrode exhibits a high specific capacity in the initial stage of cycling, reaching a discharge specific capacity of 194.82 mAh / g at 0.5C. It also demonstrates good stability under long-term cycling, retaining a discharge specific capacity of 166.80 mAh / g after 200 cycles. The capacity decay rate is significantly lower than that of the PSCS1:2 electrode (Example 2) and PSCS2:1 electrode (Example 3). This indicates that an appropriate DSS and SCS ratio can better leverage the interfacial regulation effect of each component and improve the cycling stability of the composite binder.

[0071] Figure 1 (b) shows the results of the rate performance test. The discharge specific capacity of the PSCS electrode (Example 1) at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C were 199.01 mAh / g, 196.53 mAh / g, 192.71 mAh / g, 177.55 mAh / g, 160.99 mAh / g, and 132.52 mAh / g, respectively, exhibiting the highest specific capacity at all rates.

[0072] The PSCS electrode exhibits superior electrochemical performance, significantly outperforming both the PSCS1:2 electrode (Example 2) and the PSCS2:1 electrode (Example 3) in both long-cycle stability and high-rate charge-discharge capability. When the rate drops from 5C to 0.1C, the PSCS electrode shows the highest capacity recovery, indicating that its electrode structure remains intact under the stress of high-rate charge-discharge. This demonstrates that the composite binder of this invention (especially PSCS1:1) effectively enhances the deformation resistance of the bonding network, achieving a synergy between high-rate kinetics and structural stability.

[0073] 2. Infrared spectroscopy test: Test method: The selected adhesive was analyzed using a Thermo Fisher S50 ATR-FTIR infrared spectrometer to determine its functional groups, with a wavenumber coverage range of 500-4000 cm⁻¹. -1 .

[0074] Test results are as follows Figure 2 As shown ( Figure 2 (Comparison of Fourier transform infrared spectra of PAM, SCS, DSS and the composite adhesive (PSCS) of Example 1). PAM was prepared by adding acrylamide and ammonium persulfate in a mass ratio of 20:1 to hot water at 80°C and stirring at a constant temperature for 45 minutes to obtain PAM.

[0075] As shown in the figure: at 1642 cm -1 The corresponding NH stretching vibration in PAM is at 1230 cm⁻¹.-1 and 1014 cm -1 The two peaks at 1226 cm⁻¹ correspond to the S=O stretching vibration in the DSS. -1 The peak at 1606 cm⁻¹ is typical, corresponding to the S=O stretching vibration in the SCS. The PSCS shows a peak at 1606 cm⁻¹ in the infrared. -1 1203 cm -1 1006 cm -1 The peaks at each point correspond to the peaks and show significant shifts and broadening, indicating that PAM, SCS, and DSS form a uniform three-dimensional cross-linked network through multiple hydrogen bonds.

[0076] 3. The mechanical and rheological properties of different binder systems were characterized by electrode tensile testing and rotational viscosity testing: Test method: 180° Peel Test: The peel strength of the electrodes was tested using an INSTRON 5967 universal testing machine (USA). The samples were cut into specimens 30 mm wide and 120 mm long, fixed to a stainless steel substrate with 3M tape, and subjected to 180° stretching at a rate of 50 mm / min, while the peel force value was recorded.

[0077] Viscosity test: The viscosity of the prepared binder solution was tested at 100 rpm using a Brookfield DV3T rotational viscometer.

[0078] The test results of the mechanical and rheological properties of different binders are as follows: Figure 3 As shown; (a) is the 180° peel curve, (b) is the peel average force test result, and (c) is the rotational viscosity test result.

[0079] Depend on Figure 3 (a) It can be seen that the average peel force of PSCS (Example 1, PSCS1:1) is significantly higher than that of PAMCS (PAMCS1:1 in Comparative Example 4), and far exceeds that of DSS adhesive alone (Comparative Example 2) and conventional PVDF adhesive (Comparative Example 1). Figure 3 (b) This result was specifically quantified, with PSCS (PSCS 1:1) achieving an average peel force of 2.91 N, the highest among the four adhesives. This was confirmed by rotational viscosity testing results ( Figure 3 (c) Further, it can be seen that the viscosity of PSCS (PSCS1:1) is further increased to 512.5 cP. Higher viscosity means a denser and more continuous bonding network, which not only helps to improve the structural integrity of the electrode, but also makes it more conducive to electrolyte wetting, providing direct support for the excellent electrochemical performance of PSCS electrode.

[0080] The above test results show that the three-dimensional network constructed by the PSCS composite binder (PSCS1:1) through the synergistic cross-linking of DSS, SCS and PAM via hydrogen bonds can more effectively buffer the volume change of NCM811 particles, prevent electrode cracking and structural deterioration, and thus break through the bottleneck of high capacity and high stability of binary systems (e.g., PAMCS) in terms of electrochemical performance, demonstrating superior long-cycle stability and rate-matching characteristics.

[0081] 4. Contact angle test between different electrodes and electrolyte: Test method: The wettability of the electrolyte was tested on the sample using a Chengde Dingsheng JY-82C video contact angle meter, and the contact angle between the electrolyte and the electrode was measured.

[0082] The test results of the contact angle test between different electrodes and electrolyte are as follows: Figure 4 As shown; where (a) is the PVDF electrode, (b) is the DSS electrode, (c) is the PAMCS electrode, and (d) is the PSCS electrode.

[0083] As shown in the figure, the contact angles between the PVDF electrode (Comparative Example 1), DSS electrode (Comparative Example 2), PAMCS electrode, and PSCS electrode and the electrolyte are 33.18°, 28.63°, 15.64°, and 12.41°, respectively. This indicates that through the synergistic effect of DSS, SCS, and PAM, PSCS1:1 further reduces the contact angle of the electrode surface and improves the wetting ability of the electrolyte. Better wettability can promote the full penetration of the electrolyte into the electrode, optimize the uniformity of the CEI film, reduce interfacial impedance, and provide key interfacial chemical support for the rate performance and cycle stability of the electrode.

[0084] 5. Electrochemical performance characterization: (1) The cycle performance, cycle performance, rate performance, and first-cycle charge-discharge curve of different electrodes at 0.5C were tested: Test Method: The battery was tested using a CT-4008 Xinwei multi-channel test system, with constant current charge-discharge mode based on the mass of the electrode active materials. The test system operated within a voltage window of 3.0-4.3V, with a current density of 1C = 200mA / g set based on the specific capacity. The ambient test temperature was 26℃.

[0085] Test results are as follows Figure 5 As shown; Figure 5 In the figure, (a) is the cycle performance curve at 0.5C, (b) is the cycle performance curve at 2C, (c) is the rate performance test result graph, and (d) is the first charge-discharge curve at 0.5C.

[0086] Depend on Figure 5 (a) It can be seen that in the long cycle test at 0.5C, the PSCS electrode exhibits very good cycle stability, and its capacity after 200 cycles is much higher than that of electrodes using other binders. The PVDF electrode is prone to degradation during the cycling process, resulting in structural deterioration and the most severe capacity decay. The DSS and PAMCS electrodes perform slightly better than the PVDF electrode, but they still lag behind the PSCS electrode.

[0087] Depend on Figure 5 (b) It can be seen that when conducting long-cycle tests at a high rate of 2C, the PSCS electrode has a more prominent advantage. Its discharge specific capacity in the first cycle is 160.65 mAh / g, and after 200 cycles, the discharge specific capacity is 103.42 mAh / g, with a capacity retention rate of 66.5%. Its capacity decay rate is much lower than that of the DSS electrode and PAMCS electrode, highlighting its better high-rate performance. In contrast, the performance of the PVDF electrode deteriorates significantly at high rates.

[0088] Figure 5 (c) Performance test results at different rates further illustrate the kinetic advantages of the PSCS electrode. Throughout the full rate range from 0.1C to 5C, the PSCS electrode consistently maintained the highest discharge specific capacity. The discharge specific capacities of the PSCS electrode at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C rates were 198.39 mAh / g, 196.53 mAh / g, 192.71 mAh / g, 178.95 mAh / g, 161.69 mAh / g, and 131.82 mAh / g, respectively. Its capacity advantage was particularly pronounced at the high rate conditions of 2C and 5C. When the rate recovered from 5C to 0.1C, the PSCS electrode also exhibited the highest capacity recovery, indicating that its electrode structure remained intact under the stress caused by high-rate charging and discharging.

[0089] Figure 5 The charge-discharge curves of (d) show that the PSCS electrode exhibits the least polarization and the most stable voltage plateau when charged and discharged at a rate of 0.5C, indicating that it has reduced interfacial impedance and more advantageous electrochemical reaction kinetics.

[0090] In summary, the PSCS electrode of Example 1 exhibits excellent electrochemical performance in terms of cycling rate.

[0091] The cycling performance of other electrodes at 0.5C was also tested using the same method, and the test results are shown in Table 3 below: Table 3

[0092] Among them, the PAMDSS1:2 electrode, PAMDSS electrode, and PAMDSS2:1 electrode underwent only 150 cycles in the cycle performance test; the discharge specific capacity of the PAMDSS1:2 electrode, PAMDSS electrode, and PAMDSS2:1 electrode after 150 cycles was 86.16 mAh / g, 125.82 mAh / g, and 87.84 mAh / g, respectively; the discharge specific capacity of the DSS electrode after 150 cycles was 159.13 mAh / g (the cycle performance curves of the DSS electrode, PAMDSS1:2 electrode, PAMDSS electrode, and PAMDSS2:1 electrode at 0.5C are shown in Figure 1). Figure 16 (As shown).

[0093] (2) Charge-discharge performance test of PSCS electrode: Test results are as follows Figure 6 As shown; where (a) is the charge-discharge curve at 0.5C with different number of cycles, and (b) is the first charge-discharge curve at different rates.

[0094] Test results show that the charge-discharge curves of the PSCS electrode highly overlap in the 1st, 25th, 50th, 75th, and 100th cycles, with a stable voltage plateau and no significant shift, and the polarization degree remains within a low range (e.g., ...). Figure 6 (a) shows that the charge-discharge curves of the PSCS electrode exhibit a clear voltage plateau in the 0.1C to 5C rate range. Although polarization increases slightly with increasing current density, the curves maintain good symmetry even at the high rate of 5C, without any noticeable plateau collapse (as shown in (a)). Figure 6 (b) This result fully verifies that the composite binder of Example 1 has good ion transport capabilities.

[0095] (3) Cyclic voltammetry curve test of PSCS electrode: Test results are as follows Figure 7 As shown; (a) are the cyclic voltammograms of the first 3 cycles at a scan rate of 0.1 mV / s; (b) are the cyclic voltammograms at different scan rates; (c) are the peak currents of peaks 1 and 2 in (b) versus scan rate. The linear fitting curve.

[0096] Depend on Figure 7 (a) It can be seen that: in the first scan, the oxidation peak at 3.8V corresponds to Ni. 2+ / Ni 3+The oxidation process corresponds to a reduction peak at 3.70 V, and these two peaks constitute the main redox characteristics of NCM811. Starting from the second cycle, the peak shape, position, and current of both the oxidation and reduction peaks gradually stabilize, and the curves of the second and third cycles almost completely overlap, with the peak potential difference remaining relatively small. This phenomenon indicates that the ternary crosslinking network in PSCS1:1 can induce the formation of a stable CEI film at the cathode and electrolyte interface, effectively suppressing irreversible side reactions in the first cycle and significantly improving the reversibility and cycle stability of the NCM811 electrode electrochemical reaction.

[0097] Depend on Figure 7 (b) It can be seen that as the scan rate gradually increases, the redox peak current increases regularly, the peak potential shifts slightly, but the peak shape remains sharp and symmetrical, without obvious peak broadening or distortion, which shows that the electrode still has good structural stability and ion transport capability in a wide scan rate range.

[0098] Peak current varies with sweep rate The slope of the change reflects the diffusion ability of lithium ions in the electrode, from Figure 7 (c) It can be seen that the oxidation peak fitting slope is 5.02, and the reduction peak slope is -2.71. The absolute values ​​of the slopes of the double peaks of the PSCS electrode are greater than those of the DSS and PVDF electrodes (the oxidation peak fitting slope of the DSS electrode is 2.73, and the reduction peak slope is 1.45; the oxidation peak fitting slope of the PVDF electrode is 2.15, and the reduction peak slope is 1.29), further indicating that the PSCS electrode has superior kinetic performance and Li + Diffusion behavior.

[0099] The test results of the cyclic voltammetry curves of the DSS electrode and the PVDF electrode are as follows: Figure 17 As shown; (a) is the cyclic voltammogram of the PVDF electrode at a scan rate of 0.1 mV / s for the first 3 cycles, (b) is the cyclic voltammogram of the DSS electrode at a scan rate of 0.1 mV / s for the first 3 cycles, (c) is the cyclic voltammogram of the PVDF electrode at different scan rates, (d) is the cyclic voltammogram of the DSS electrode at different scan rates, and (e) is the peak current of peaks 1 and 2 in (c) versus scan rate. The linear fitting curves, (f) are the peak currents and sweep rates of peaks 1 and 2 in (d). The linear fitting curve.

[0100] (4) Electrochemical impedance spectroscopy and kinetic fitting curve tests of different electrodes (the semicircles in the high-frequency region of all curves correspond to the interfacial charge transfer impedance, and the oblique lines in the low-frequency region correspond to the lithium-ion diffusion process): Test results are as follows Figure 8As shown; where (a) is the Nyquist curve, and (b) is the real part of the impedance ( ) and the square root of angular frequency ( The linear fitting relationship of ); The test results of Warburg slope and lithium-ion diffusion coefficient for different electrodes are shown in the table below: Table 4. Warburg slope and lithium-ion diffusion coefficient for different electrodes

[0101] As shown in 8(a), the PSCS electrode has the smallest semicircular diameter, indicating that its interfacial charge transfer impedance is the smallest. This result corresponds to the optimal electrolyte wettability of the PSCS electrode in the contact angle test, indicating that the composite binder in Example 1 can form a stable CEI film to reduce interfacial impedance, providing more favorable conditions for charge transfer. By analyzing the Warburg impedance in the low-frequency region of the Nyquist curve, the lithium-ion diffusion coefficient can be quantitatively calculated. .

[0102] Figure 8 (b) The slope σ of the linear fit relationship is shown. Directly related. The calculation results are as follows, for the PSCS electrode. Reached The difference is significantly greater than that of the PAMCS electrode. This result directly confirms that PSCS1:1 significantly enhances the diffusion ability of lithium ions inside the electrode by constructing a continuous and unobstructed ion transport channel, exhibiting excellent electrochemical performance.

[0103] 6. Morphological and structural characterization: (1) SEM images of the PSCS electrode before and after cycling are shown below. Figure 9 As shown; where (a) is the SEM image before the cycle, (b) is a magnified view of (a), (c) is the SEM image after 100 cycles, and (d) is a magnified view of (c).

[0104] Figure 9 In (a) and (b): In the PSCS electrode before cycling, NCM811 particles are evenly distributed and tightly wrapped by PSCS1:1. The electrode surface is flat and dense, with no obvious particle agglomeration or exposure. Figure 9Compared to before cycling, (c) and (d) show that the overall electrode structure maintained good integrity, and the particles remained tightly bonded together. Only a very small number of microcracks were observed in localized areas (e.g., marked by red circles), and no large-scale particle breakage, detachment, or electrode pulverization occurred. This phenomenon strongly demonstrates that the three-dimensional network structure constructed by the composite binder of the present invention possesses good mechanical toughness and structural constraint capabilities, effectively reducing the volume deformation of NCM811 particles during the charging and discharging process, preventing particle cracking and structural deterioration, thereby maintaining the integrity of the electrode structure.

[0105] (2) Cross-sectional SEM images of the PSCS electrode before and after cycling are shown below. Figure 10 As shown; where (a) is the cross-sectional SEM image before 100 cycles, and (b) is the cross-sectional SEM image after 100 cycles.

[0106] The thickness changes of the electrode before and after cycling were compared using SEM cross-sectional characterization. Figure 10 (a) It can be seen that before cycling, the initial thickness of the PSCS electrode is 25 μm, and the internal particles are arranged relatively tightly, without any prominent pores or delamination. Figure 10 (b) It can be seen that after multiple cycles, the electrode thickness increased to 30.6 μm, and its volume expansion rate was 22.4%. Compared with PAMCS electrodes and traditional PVDF electrodes, the expansion rate of PSCS electrodes decreased. This result indicates that the three-dimensional network structure formed by PSCS1:1 has superior mechanical properties, which can reduce the volume deformation of NCM811 particles during charge and discharge, suppress electrode expansion and structural deterioration, and thus maintain the integrity of the electrode structure, providing structural support for its good long-term cycling stability.

[0107] SEM images and cross-sectional SEM images of the PAMCS electrode before and after cycling are shown below. Figure 12 As shown; where (a) is the SEM image before cycling, (b) is a magnified view of (a), (c) is the SEM image after 100 cycles, (d) is a magnified view of (c), (e) is the cross-sectional SEM image before cycling, and (f) is the cross-sectional SEM image after 100 cycles. Figure 12 As can be seen from (a) and (b), the electrode surface was smooth and dense before cycling, with no obvious microcracks or pores observed. The NCM811 active particles were uniformly dispersed in the PAMCS binder, with no obvious agglomeration and clear particle boundaries. This indicates that PAMCS can effectively disperse the active material in the initial state, constructing a uniform electrode structure, which lays the foundation for its excellent initial capacity and rate performance. Figure 12(c) and (d) show that after 100 cycles, the red dashed lines in the figures indicate the presence of obvious microcracks inside the electrode, and some NCM811 particles have cracked. Figure 12 As can be seen from (e) and (f), the initial thickness of the PAMCS electrode is 25 μm, and after 100 cycles, the electrode thickness increases to 33.4 μm, with a volume expansion rate of 33.6%.

[0108] Cross-sectional SEM images of the PVDF electrode before and after cycling are shown below. Figure 18 As shown in the figure; (a) is a cross-sectional SEM image before cycling, and (b) is a cross-sectional SEM image after 100 cycles; it can be seen from the figure that the initial thickness of the PVDF electrode is 25 μm, and after 100 cycles the electrode thickness increases to 41.4 μm, and its volume expansion rate is 65.6%.

[0109] (3) The CEI film on the surface of NCM811 particles was characterized by transmission electron microscopy under high resolution: Figure 11 The images are TEM images of the PSCS electrode after 100 cycles. (a) is a TEM image of the CEI film on the surface of the PSCS electrode, and (b) is a magnified view of (a).

[0110] Depend on Figure 11 It can be seen that a uniform and continuous CEI film is formed on the surface of NCM811 particles. Measured using a scale, the thickness of this CEI film is approximately 4.8 nm. Lithium-ion migration requires passing through the CEI film; if the film is too thick, the lithium-ion transport path becomes longer and the resistance increases. If the CEI film is too thin or incomplete, it cannot completely cover the cathode surface, and the electrolyte will continue to undergo oxidative decomposition under the high voltage of the cathode, consuming the active lithium and electrolyte in the battery, and also corroding the cathode material. Compared with the binary PAMCS system and the traditional PVDF system, the CEI film thickness of the PSCS electrode is suitable and uniform. This result directly confirms that the PSCS composite binder, by optimizing the interfacial chemical environment, induces the formation of a more stable and efficient CEI film, providing key interfacial structural support for its excellent electrochemical performance.

[0111] TEM image of the PAMCS electrode after 100 cycles as shown below Figure 13 As shown; where (a) is a TEM image of the CEI film on the surface of the PAMCS electrode, and (b) is a magnified view of a portion of (a). Figure 13 It can be seen that the microstructure of the CEI film formed on the surface of NCM811 particles at the positive electrode electrolyte interface is as follows: the thickness of the CEI film is measured to be about 2.9 nm under high magnification. This can effectively isolate NCM811 particles from the electrolyte, inhibit the dissolution of transition metal ions and the continuous decomposition of the electrolyte, thereby reducing interfacial side reactions.

[0112] (4) To further analyze the chemical composition and evolution of the CEI film at the positive electrode electrolyte interface induced by different binders, the surface elements of the electrode after cycling were analyzed by XPS: XPS spectra after 100 cycles with different electrodes are shown below. Figure 14 As shown.

[0113] Depend on Figure 14 It can be seen that in the C 1s and O 1s spectra, the characteristic peak intensity of Li2CO3 byproducts of the PVDF electrode is consistently the highest among the four materials, while that of the DSS, PAMCS, and PSCS electrodes is significantly higher. , The proportion of oxygen-containing functional group peaks increased significantly, while the intensity of the Li2CO3 peak decreased significantly; in the PSCS electrode, its byproducts Li2CO3 and The peak intensity was the lowest among the four electrodes. This confirms that PSCS1:1 can enhance the electrode interface interaction through abundant polar functional groups, effectively inhibiting electrolyte decomposition and the formation of harmful byproducts. This is even more evident in the F 1s spectrum, where the PVDF electrode exhibited the strongest peak intensity among the four electrodes. The characteristic peaks confirm that it is prone to defluorination degradation and violent reactions with electrolyte lithium salts. The intensity of this peak is significantly weakened in the other three electrodes, and the Li-F peak gradually strengthens, with the Li-F peak being the strongest in PSCS. This result indicates that, compared with the traditional PVDF electrode, DSS, PAMCS and PSCS electrodes can all enhance the interaction between the electrode and the interface through abundant polar functional groups, effectively inhibiting electrolyte decomposition and the generation of harmful byproducts. Among them, the PSCS electrode exhibits the best interfacial chemical stability due to its three-dimensional framework composed of hydrogen bonds.

[0114] (5) The three-dimensional morphology of different electrode surfaces was characterized by atomic force microscopy (AFM), and the arithmetic mean roughness Ra was calculated: Test results are as follows Figure 15 As shown; where (a) is the PVDF electrode, (b) is the DSS electrode, (c) is the PAMCS electrode, and (d) is the PSCS electrode.

[0115] Test results show that the PVDF electrode surface exhibits severe undulations, with the largest peak-to-valley difference and the highest average roughness Ra value, which is 216 nm. Figure 15 (a) indicates that the PVDF electrode surface is extremely uneven, with severe particle agglomeration, which easily leads to poor electrolyte wetting and exacerbates interfacial side reactions. The surface roughness of the DSS electrode is reduced, with an Ra value of 162 nm. Figure 15 (b) However, significant undulations still exist, and uniformity needs improvement. The surface smoothness of the PAMCS electrode has been further improved, with the Ra value decreasing to 150 nm ( Figure 15(c) The particle distribution is more uniform. The PSCS electrode surface is the smoothest and has the lowest Ra value, only 135 nm. Figure 15 (d) Lower surface roughness means more uniform particle distribution inside the electrode, more thorough electrolyte wetting, and better interfacial contact.

[0116] In summary, the PSCS1:1 composite binder, through multiple hydrogen bond crosslinking, constructs a three-dimensional continuous network structure, which systematically affects the interface characteristics and structure of the NCM811 cathode. The sulfonic acid groups, carboxyl groups, and hydroxyl groups on its molecular chain form strong coordination with transition metal ions on the NCM811 surface, effectively inhibiting the dissolution of transition metals during cycling and blocking interfacial side reactions. The three-dimensional network structure is Li + It provides an efficient migration path, improves the kinetic response of the electrode, and enhances rate performance. The cross-linked network of PSCS1:1 composite binder has good resistance to deformation, which can absorb the volume deformation generated during the lithium insertion / extraction process of the electrode, maintain the integrity of the electrode structure, induce the formation of a uniform and stable CEI film, and achieve structural protection of NCM811 particles. Ultimately, it improves the cycle stability and rate performance of the NCM811 cathode through multiple synergistic mechanisms.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite adhesive, characterized in that, The method for preparing the composite adhesive includes the following steps: (1) Mix acrylamide, ammonium persulfate and water at 60-80℃ and stir for 30-45 min to obtain a mixed solution; (2) Add sodium dextran sulfate and sodium chondroitin sulfate to the mixed solution obtained by step (1), and stir at 60-80℃ for 20-40 min. (3) Cool to room temperature to obtain the composite adhesive.

2. The method for preparing the composite adhesive as described in claim 1, characterized in that, The ratio of the sum of the masses of sodium dextran sulfate and sodium chondroitin sulfate to the mass of the acrylamide is 1:(0.8-1.2); The mass ratio of sodium dextran sulfate and sodium chondroitin sulfate is 1:2-2:

1.

3. The method for preparing the composite adhesive as described in claim 2, characterized in that, The mass ratio of sodium dextran sulfate and sodium chondroitin sulfate is 1:

1.

4. The method for preparing the composite adhesive as described in claim 1, characterized in that, In step (1), the mass ratio of acrylamide to ammonium persulfate is (20-50):

1.

5. A composite adhesive, characterized in that, The composite adhesive is prepared by the method described in any one of claims 1-4.

6. A battery positive electrode, characterized in that, The positive electrode of the battery uses the composite binder as described in claim 5.

7. The positive electrode of the battery as described in claim 6, characterized in that, The active material of the positive electrode of the battery is NCM811; The conductive agent at the positive electrode of the battery is acetylene black.

8. A battery, characterized in that, The battery uses the composite binder as described in claim 5; or, the battery uses the positive electrode as described in claim 6 or 7.

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