A high-pressure-resistant composite positive electrode sheet for inhibiting battery cycle gas production and a preparation method thereof

Abstract

This invention belongs to the field of electrochemical technology and relates to a high-voltage resistant composite positive electrode sheet and its preparation method for suppressing gas generation during battery cycling. The composite positive electrode sheet includes a positive electrode sheet and a polymer coating on the active material layer of the positive electrode sheet. The polymer coating is a composite polymer coating formed by in-situ copolymerization of phosphorus-containing monomers and fluorinated acrylate monomers in the presence of polyethylene glycol borate under ultraviolet light. The mass ratio of the phosphorus-containing monomers, fluorinated acrylate monomers, and polyethylene glycol borate is (3~4):1:(0.15~0.4). The composite positive electrode sheet of this invention can suppress gas generation during battery cycling and improve its high-voltage resistance (≥4.3V vs Li). + / Li) stability.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a high-voltage resistant composite cathode sheet for suppressing gas generation during battery cycling and its preparation method. Background Technology

[0002] In recent years, with the rapid development of large-scale energy storage devices and new energy electric vehicles, the demand for high-energy-density and high-safety secondary batteries has become increasingly urgent. Alkali metal ion secondary batteries have become a focus of widespread attention, especially lithium-ion batteries, which have been applied in people's production and daily life due to their high energy density and long cycle stability. Improving the energy density of lithium-ion batteries is the core of current technological development, and increasing the charging cut-off voltage of the cathode material is one of the most efficient ways to achieve this. High-nickel layered oxides such as LiNi... x Co γ Mn 1-x-γ O2 (NCM) is a representative cathode material, and under high cutoff voltage (≥4.3V vs Li), + / Li) can achieve more than 200 mAh g -1 Specific capacity.

[0003] However, high cutoff voltages exacerbate the structural and interfacial degradation of cathode materials. Under high voltage, cathode materials are prone to irreversible phase transitions, leading to lattice contraction and microcracks. Simultaneously, the activity of lattice oxygen increases, making oxidation reactions (i.e., lattice oxygen evolution) more likely. The released active oxygen reacts violently with the electrolyte, generating large amounts of gas (such as O2, CO2, CO, etc.) and forming an unstable cathode-electrolyte interface (CEI) film on the electrode surface. These problems not only lead to rapid degradation of battery cycle performance, but the generated gas can also cause battery swelling, posing safety hazards. Traditional bulk doping or powder coating modification methods, while stabilizing the material structure to some extent, are pre-synthetic solutions that require powder preparation and are therefore difficult to apply directly to pre-prepared electrode sheets. Furthermore, they cannot effectively repair microscopic defects generated during electrode processing (slurry casting, drying, rolling), which further promote oxygen release during cycling. Conventional post-assembly methods, such as electrolyte additives, can remove some released oxygen species, but cannot suppress lattice oxygen release at its source.

[0004] Therefore, there is an urgent need to develop a modification technology that can directly act on the positive electrode to effectively suppress lattice oxygen evolution and battery cycle gas generation under high voltage, and improve the stability of the electrode interface and high voltage resistance. Summary of the Invention

[0005] This invention aims to solve the technical problems of gas generation, interface degradation, and poor cycle stability of secondary batteries under high-voltage cycling in the prior art, and provides a high-voltage resistant composite positive electrode sheet that suppresses gas generation during battery cycling and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling includes a positive electrode sheet and a polymer coating on the active material layer of the positive electrode sheet; the polymer coating is a composite polymer coating formed by in-situ copolymerization of phosphorus-containing monomers and fluorinated acrylate monomers in the presence of polyethylene glycol borate under ultraviolet light; the mass ratio of the phosphorus-containing monomers, fluorinated acrylate monomers to polyethylene glycol borate is (3~4):1:(0.15~0.4).

[0008] Preferably, the mass ratio of the phosphorus-containing monomer, the fluorinated acrylate monomer, and the polyethylene glycol borate is (3~3.5):1:(0.2~0.3). The phosphorus-containing monomer and the fluorinated acrylate monomer copolymerize to form a cross-linked polymer network, and the polyethylene glycol borate, as a branched polymer, is interwoven into this network, forming an interpenetrating network structure through non-covalent interactions. In this invention, the proportions of each component need to be controlled; only under appropriate proportions can excellent effects on suppressing gas generation during battery cycling and high-voltage stability be obtained simultaneously.

[0009] Furthermore, the thickness of the polymer coating is 1~2 μm.

[0010] Furthermore, the phosphorus-containing monomer is a phosphate ester compound containing at least two carbon-carbon double bonds (C=C), specifically selected from at least one of triallyl phosphate, diallyl phosphate, triallyl phosphite, and diallyl phosphite, preferably triallyl phosphate. The unsaturated functional groups of the phosphorus-containing monomer enable it to form a cross-linked network during copolymerization. The phosphate ester groups can form strong coordination bonds with the transition metal on the surface of the cathode material, thermodynamically anchoring lattice oxygen and effectively suppressing the precipitation of lattice oxygen under high voltage.

[0011] Furthermore, the fluorinated acrylate monomer is selected from at least one of 2,2,2-trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, and 2-(perfluorooctyl)ethyl methacrylate, preferably 1,1,1,3,3,3-hexafluoroisopropyl acrylate. The double bonds of the fluorinated acrylate monomers are highly reactive, which can improve their copolymerization conversion rate with phosphorus-containing monomers and optimize the crosslinking network structure. In addition, the high electrochemical stability of fluorine can increase the oxidation potential of the coating, prevent the decomposition of the crosslinking structure under high voltage, and induce the formation of a fluorinated positive electrode electrolyte interface film, thereby improving the high-voltage, long-cycle performance of the battery.

[0012] Further, the polyethylene glycol segment (PEG) number-average molecular weight of the polyethylene glycol ester (PEG-BAE) is 400-800, preferably 600-800. The polyethylene glycol ester (PEG-BAE) of this invention refers to an esterification product generated by the esterification reaction of polyethylene glycol and boric acid, with the structural formula B(O-PEG)3, i.e., having three PEG arms. PEG-BAE plays multiple roles in the coating. On the one hand, the PEG arms of PEG-BAE have excellent flexibility, which can effectively buffer the volume expansion effect of the positive electrode active material during cyclic charging and discharging. On the other hand, the three PEG arms of PEG-BAE can efficiently intercalate into the cross-linked network formed by the copolymerization of phosphorus-containing monomers and fluorinated acrylate monomers, forming a stable physical entanglement; simultaneously, its borate groups can generate dynamic and reversible hydrogen bond interactions with the phosphate ester groups [(RO)3-P=O] in the copolymer, which is equivalent to introducing multiple physical cross-linking points into the cross-linked network, making the network structure more compact and stable. This dense network structure, combined with the high electrochemical stability of the fluorinated acrylate component, can more effectively trap O2 and CO2 gases that may escape from the positive electrode region, further enhancing the overall antioxidant capacity of the coating and ensuring its stability under high voltage. Thirdly, when microcracks develop in the coating due to electrode processing or long-cycle fatigue, the aforementioned dynamic hydrogen bonds can undergo reversible breakage and recombination, endowing the coating with self-healing capabilities and preventing electrolyte from penetrating along the cracks and damaging the positive electrode electrolyte interface (CEI), ensuring the long-term integrity of the interface. Furthermore, the empty p orbitals of the borate ester groups can interact with active oxygen species escaping from the positive electrode surface, synergistically enhancing the effect of the phosphate ester groups anchoring lattice oxygen, thus more effectively suppressing gas generation at the source and improving the high-voltage cycle performance of the battery.

[0013] It should be noted that the appropriate molecular weight of polyethylene glycol segments allows polyethylene glycol borate esters to effectively interpenetrate in the cross-linked network to form a stable interpenetrating structure, maintaining sufficient functional group density, while also maintaining good solubility and processing performance.

[0014] Furthermore, the positive electrode is a commercially available layered oxide positive electrode, comprising a current collector and an active material layer formed on one side surface of the current collector. The active material is selected from high-nickel ternary positive electrode materials, lithium-rich manganese-based positive electrode materials, and lithium cobalt oxide positive electrode materials. Preferably, the areal density of the positive electrode active material layer is 10~40 mg / cm³. 2 .

[0015] The high voltage resistance of the composite positive electrode sheet described in this invention refers to its charging cut-off voltage ≥ 4.3V vs Li. + / Li.

[0016] This invention also provides a method for preparing the above-mentioned high-voltage resistant composite positive electrode sheet for suppressing battery cycle gas generation, comprising the following steps:

[0017] (S1) Dissolve the phosphorus-containing monomer, fluorinated acrylate monomer, polyethylene glycol borate and photoinitiator in a polar organic solvent to obtain a precursor solution;

[0018] (S2) The precursor solution is coated on the surface of the positive active material layer of the positive electrode sheet, and polymerized in situ under ultraviolet light irradiation. After irradiation, the electrode is washed and dried to obtain a high-voltage resistant composite positive electrode sheet that suppresses gas generation during battery cycling.

[0019] Further, in step (S1), the ratio of the total mass of the phosphorus-containing monomer, the fluoroacrylate monomer and the polyethylene glycol borate ester to the amount of the polar organic solvent is 10g:10~30mL, preferably 10g:10~20mL.

[0020] Further, in step (S1), the photoinitiator is selected from at least one of 2-hydroxy-2-methylphenylacetone, 1-hydroxy-cyclohexylbenzophenone, isopropylthioxanthraphenone, triarylthioonium salt, and benzophenone; the amount of photoinitiator is 0.5 to 1 wt% of the total mass of phosphorus-containing monomers and fluoroacrylate monomers.

[0021] Further, in step (S1), the polar organic solvent is at least one of dimethyl sulfoxide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0022] Further, in step (S2), the conditions for ultraviolet irradiation are: ultraviolet wavelength 300~450nm, power 15~25W, time 3~10 min; the washing is rinsing with dimethyl carbonate (DMC) or diethyl carbonate (DEC) 2~3 times; the drying is drying at 60~90℃ for 3~8h.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. Suppressing Gas Generation During Battery Cycles: This invention constructs a polymer coating on the surface of the positive electrode. This polymer coating is formed by copolymerizing phosphorus-containing monomers and fluorinated acrylate monomers, and then interacting with polyethylene glycol borate ester through physical entanglement and dynamic hydrogen bonding to form an interpenetrating network structure. The phosphate groups anchor lattice oxygen on the positive electrode surface, while the borate ester groups, through their empty p orbitals, synergistically capture active oxygen, thus suppressing oxygen evolution at its source. Simultaneously, the dense interpenetrating network acts as a physical barrier, effectively trapping trace amounts of O2 and CO2 gases, reducing crosstalk between gases and the negative electrode.

[0025] 2. Improved high voltage stability: The fluorinated acrylate component in the coating has extremely high electrochemical stability. Combined with the dense interpenetrating network structure, the oxidation potential of the coating can reach more than 5.4V, which is suitable for high voltage cathode systems and can induce the formation of a stable CEI film.

[0026] 3. Imparting interface flexibility and self-healing ability: The PEG arms in polyethylene glycol borate can effectively buffer the volume expansion of the cathode material during cycling; the dynamic hydrogen bond network between borate and phosphate esters endows the coating with self-healing ability, timely repairing microcracks generated during cycling, ensuring long-term interface integrity, and significantly improving the cycle life of the battery.

[0027] 4. This invention uses in-situ photocuring technology to directly coat and modify the surface of the prepared commercial positive electrode sheet. The process is simple, does not change the existing battery electrode production process, and is suitable for large-scale industrial production applications. Attached Figure Description

[0028] Figure 1 This is a SEM image of the side surface of the composite positive electrode sheet prepared in Example 1.

[0029] Figure 2 The image shows the Fourier Transform Infrared (FTIR) spectrum of the polymer coating in Example 1.

[0030] Figure 3 This is a comparison graph of the electrochemical window (LSV) test results for Example 1 and Comparative Example 3.

[0031] Figure 4 This is a comparison of the gas generation behavior of the composite cathode and NCM811 cathode in Example 1 during the first charge and discharge process, tested using in-situ differential electrochemical mass spectrometry (DEMS).

[0032] Figure 5 This is a comparison chart of the cycling performance of Example 1 and the NCM811 positive electrode at a cutoff voltage of 4.6V.

[0033] Figure 6 The image shows the cross-sectional SEM images of the composite positive electrode sheets of Examples 1 and 3 after 200 cycles. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that the specific embodiments of this invention are only for explaining the invention and are not intended to limit the scope of protection of this invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents and materials used are commercially available.

[0036] The polyethylene glycol borate esters PEG400-BAE, PEG600-BAE, and PEG800-BAE were purchased from Shandong Aokai Chemical Co., Ltd., and their polyethylene glycol segments (PEG) had number-average molecular weights of 400, 600, and 800, respectively.

[0037] Example 1

[0038] (S1) Dissolve 3g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.2g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 3:1:0.2), and 32mg of 2-hydroxy-2-methylphenylacetone in 5mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0039] (S2) The precursor solution was uniformly coated onto a commercial NCM811 positive electrode (area density approximately 25 mg / cm³). 2 The surface of the positive electrode active material layer (the thickness of the polymer coating in the product is controlled to be 1 μm by controlling the coating amount) is then placed under ultraviolet light (wavelength 365 nm, power 20 W) for 5 min to copolymerize. After irradiation, the surface of the electrode is rinsed with dimethyl carbonate (DMC) to remove unreacted monomers. Finally, it is vacuum dried at 80 °C for 4 h to obtain a high-voltage resistant composite positive electrode that suppresses gas generation during battery cycling.

[0040] Example 2

[0041] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different, specifically:

[0042] (S1) Dissolve 3g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.15g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 3:1:0.15), and 32mg of 2-hydroxy-2-methylphenylacetone in 5mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0043] (S2) Same as Example 1.

[0044] Example 3

[0045] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different, specifically:

[0046] (S1) Dissolve 3.5g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.25g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 3.5:1:0.25), and 36mg of 2-hydroxy-2-methylphenylacetone in 5mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0047] (S2) Same as Example 1.

[0048] Example 4

[0049] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different, specifically:

[0050] (S1) Dissolve 3.5g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.3g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 3.5:1:0.3), and 36mg of 2-hydroxy-2-methylphenylacetone in 5.5mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0051] (S2) Same as Example 1.

[0052] Example 5

[0053] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different, specifically:

[0054] (S1) Dissolve 4g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.35g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 4:1:0.35), and 40mg of 2-hydroxy-2-methylphenylacetone in 6mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0055] (S2) Same as Example 1.

[0056] Example 6

[0057] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different, specifically:

[0058] (S1) Dissolve 4g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.4g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 4:1:0.4), and 40mg of 2-hydroxy-2-methylphenylacetone in 6mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0059] (S2) Same as Example 1.

[0060] Example 7

[0061] The rest is the same as in Example 1, except that in step (S1), polyethylene glycol borate PEG400-BAE is used to replace polyethylene glycol borate PEG600-BAE by mass.

[0062] Example 8

[0063] The rest is the same as in Example 1, except that in step (S1), polyethylene glycol borate PEG800-BAE is used to replace polyethylene glycol borate PEG600-BAE by mass.

[0064] Example 9

[0065] The rest is the same as in Example 1, except that: in step (S1), diallyl phosphite is used to replace triallyl phosphate by mass, and 2,2,2-trifluoroethyl methacrylate is used to replace 1,1,1,3,3,3-hexafluoroisopropyl acrylate by mass, and the thickness of the polymer coating in the product is controlled to be 2 μm by controlling the coating amount.

[0066] Comparative Example 1

[0067] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different (the amount of phosphorus-containing monomers is less), specifically:

[0068] (S1) Dissolve 1g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.2g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 1:1:0.2), and 16mg of 2-hydroxy-2-methylphenylacetone in 3mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0069] (S2) The preparation method is the same as in Example 1, and the composite positive electrode is finally obtained.

[0070] Comparative Example 2

[0071] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different (the amount of phosphorus-containing monomers is larger), specifically:

[0072] (S1) Dissolve 5g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.2g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 5:1:0.2), and 48mg of 2-hydroxy-2-methylphenylacetone in 7mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0073] (S2) The preparation method is the same as in Example 1, and the composite positive electrode is finally obtained.

[0074] Comparative Example 3

[0075] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different (the amount of polyethylene glycol borate is less), specifically:

[0076] (S1) Dissolve 3g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.05g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 3:1:0.05), and 32mg of 2-hydroxy-2-methylphenylacetone in 5mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0077] (S2) The preparation method is the same as in Example 1, and the composite positive electrode is finally obtained.

[0078] Comparative Example 4

[0079] The rest is the same as in Example 1, except that the amount of raw materials used in step (S1) is different (more polyethylene glycol borate is used), specifically:

[0080] (S1) Dissolve 3g of triallyl phosphate, 1g of 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 0.6g of polyethylene glycol borate PEG600-BAE (i.e., the mass ratio of phosphorus-containing monomer, fluorinated acrylate monomer and polyethylene glycol borate is 3:1:0.6), and 32mg of 2-hydroxy-2-methylphenylacetone in 5mL of dimethyl sulfoxide (DMSO), stir well, and obtain the precursor solution;

[0081] (S2) The preparation method is the same as in Example 1, and the composite positive electrode is finally obtained.

[0082] Performance Testing and Analysis

[0083] 1. Structural Characterization and Analysis

[0084] The scanning electron microscope (SEM) image of the side surface of the composite positive electrode sheet prepared in Example 1 of this invention is shown below. Figure 1 As shown, a uniform coating with a thickness of approximately 1 μm can be clearly observed formed on the NCM811 surface. The coating was characterized by Fourier Transform Infrared Spectroscopy (FTIR) (e.g., ...). Figure 2 As shown in the figure), the results indicate that at approximately 1163 cm -1 The characteristic stretching vibration shoulder of the P=O bond appeared at 986 cm. -1 and 927 cm -1 A characteristic peak of the POC bond appeared at [location missing], while a peak of C=C vibration (1649 cm⁻¹) was observed in triallyl phosphate (TAP). -1 The absorption peak (near) basically disappeared, and the C=O absorption peak (1722 cm⁻¹) disappeared. -1 The monomers (nearby) are derived from fluoroacrylate monomers. The above results indicate that the copolymerization reaction occurred successfully.

[0085] 2. Electrochemical window test

[0086] According to the formulations of the examples and comparative examples, the precursor solutions obtained in step (S1) were coated onto stainless steel sheets (SS), and cured under the same ultraviolet light irradiation conditions as in step (S2). Using these as the working electrode and lithium metal as the counter electrode, SS|Li half-cells were assembled, and then linear sweep voltammetry (LSV) tests were performed. A comparison of the electrochemical window (LSV) tests of Example 1 and Comparative Example 3 is shown in the figure. Figure 3 As shown, the oxidation initiation potential of the polymer coating in Example 1 reaches 5.6 V vs. Li. + / Li, higher than Comparative Example 3's 4.6 V vs. Li + / Li. The oxidation initiation potentials of the polymer coatings in the remaining embodiments and comparative examples are summarized in Table 1.

[0087] Table 1 shows that the oxidation initiation potential of the polymer coatings in the examples is all around 5.4 V vs. Li. + The concentration of P / Li is significantly higher than that of Comparative Example 2 (which uses more phosphorus monomers and relatively less fluoroacrylate) and Comparative Example 3 (which uses less polyethylene glycol borate). This indicates that the introduction of polyethylene glycol borate, due to non-covalent cross-linking, results in a denser and more stable coating structure. Combined with fluoroacrylate, it greatly enhances its resistance to high-pressure oxidation.

[0088] 3. Battery cycle gas generation test

[0089] The composite cathode sheets prepared in each embodiment and comparative example were assembled into coin cells with lithium metal as the negative electrode. The cells were first charged at a 0.1 C rate (constant current charging from open-circuit voltage to 4.5 V). In-situ differential electrochemical mass spectrometry (DEMS) was used to monitor the O2 and CO2 gases generated on the positive electrode side during this charging process in real time. Using the NCM811 cathode sheet as a reference, the percentage reduction in cumulative gas release for each embodiment and comparative example is shown in Table 1. A comparison of the gas generation behavior during the first charging process between the composite cathode sheet of Example 1 and the NCM811 cathode sheet is shown in the figure below. Figure 4 As shown.

[0090] As shown in Table 1, compared with the unmodified NCM811 cathode sheet, the composite cathode sheet of the embodiments reduced the cumulative release of O2 by approximately 90-95% and the cumulative release of CO2 by approximately 82-86% during the first charge, which is significantly higher than Comparative Example 1 (with less phosphorus monomer) and also better than Comparative Example 4 (with more polyethylene glycol borate). Although the cumulative release of O2 and CO2 in Comparative Examples 2 and 3 was significantly reduced, their high-voltage resistance was significantly insufficient. This result indicates that the polymer coating of the present invention can effectively suppress the evolution of lattice oxygen under high voltage and the electrolyte side reactions it triggers, thereby suppressing battery gas generation at the source. Since gas generation during the first charge is one of the main sources of gas generation during cycling, and the coating has already shown a significant suppression effect during the first charge, combined with the coating's self-healing ability to maintain interface integrity, it can be expected that it will also effectively suppress gas generation during long-term cycling. In subsequent battery cycle performance tests, the capacity retention rate of the embodiments was significantly higher than that of the comparative examples, which also indirectly confirms that interface degradation and gas generation side reactions were effectively suppressed.

[0091] 4. Electrochemical performance testing

[0092] The composite positive electrode sheets prepared in each example and comparative example were used as working electrodes, lithium metal as counter electrodes, and polypropylene microporous membranes (Celgard 2400) as separators. Half-cells were assembled using 1 M LiPF6 electrolyte (solvent prepared with a volume ratio of ethylene carbonate: dimethyl carbonate: diethyl carbonate = 1:1:1, containing 2% vinylene carbonate and 5% fluorinated vinyl ester additives). The assembled half-cells were subjected to electrochemical performance testing on a Blue Battery Tester. After activation at 0.1 C for 3 cycles, long-term cycling tests were conducted at 1C rate, with a charge / discharge voltage range of 2.8–4.6 V. The initial coulombic efficiency and capacity retention after 200 cycles were tested, and the results are shown in Table 1. A comparison of the cycling performance of Example 1 and the NCM811 positive electrode sheet at a cutoff voltage of 4.6 V is shown in the figure below. Figure 5 As shown.

[0093] Table 1 Performance Tests

[0094]

[0095] The electrochemical performance test data in Table 1 show that the composite cathode prepared in the embodiments of the present invention can maintain a capacity retention of 52-58% after 200 cycles at a high voltage of 4.6V, which is better than the 36-42% of the comparative example, indicating that it has excellent high voltage cycling stability.

[0096] Furthermore, after the batteries assembled with the composite positive electrode sheets of Example 1 and Comparative Example 3 underwent the above-mentioned cycle test (200 cycles at 4.6V under 1C), they were disassembled in a glove box, the positive electrode sheets were removed, and they were washed three times with dimethyl carbonate to remove residual electrolyte. They were then dried in a vacuum oven at 60°C for 12 hours, and the cross-sectional morphology of the electrode sheets was observed using a scanning electron microscope (SEM). Figure 6 (As shown). Figure 6 The results show that after 200 cycles, the composite positive electrode sheet of Example 1 has almost no cracks on its cross-section, and its overall structure is dense; while the electrode sheet of Comparative Example 3 shows obvious cracks on its cross-section. This indicates that the polymer coating of the present invention can effectively suppress the strain of the positive electrode active material particles during long-term cycling, maintain structural integrity, and thus effectively suppress gas generation.

[0097] In summary, combined with the aforementioned gas generation test and oxidation initiation potential, it is shown that the composite cathode with a specific polymer coating prepared in the examples has excellent high-voltage cycling stability and the characteristic of suppressing gas generation during cycling, and does not have a negative impact on the initial coulombic efficiency.

Claims

1. A high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling, characterized in that, The coating includes a positive electrode sheet and a polymer coating on the active material layer of the positive electrode sheet; the polymer coating is a composite polymer coating formed by in-situ copolymerization of phosphorus-containing monomers and fluorinated acrylate monomers in the presence of polyethylene glycol borate under ultraviolet light; the mass ratio of the phosphorus-containing monomers, fluorinated acrylate monomers to polyethylene glycol borate is (3~4):1:(0.15~0.4).

2. The high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling according to claim 1, characterized in that, The mass ratio of the phosphorus-containing monomer, the fluorinated acrylate monomer and the polyethylene glycol borate is (3~3.5):1:(0.2~0.3).

3. The high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling according to claim 1, characterized in that, The thickness of the polymer coating is 1~2 μm.

4. The high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling according to claim 1, characterized in that, The phosphorus-containing monomer is a phosphate ester compound containing at least two carbon-carbon double bonds, specifically selected from at least one of triallyl phosphate, diallyl phosphate, triallyl phosphite, and diallyl phosphite, preferably triallyl phosphate.

5. The high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling according to claim 1, characterized in that, The fluoroacrylate monomer is selected from at least one of 2,2,2-trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, and 2-(perfluorooctyl)ethyl methacrylate, preferably 1,1,1,3,3,3-hexafluoroisopropyl acrylate.

6. The high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling according to claim 1, characterized in that, The polyethylene glycol borate has a number-average molecular weight of 400-800 segments, preferably 600-800.

7. The high-voltage resistant composite positive electrode sheet for suppressing gas generation during battery cycling according to claim 1, characterized in that, The positive electrode is a commercially available layered oxide positive electrode, comprising a current collector and an active material layer formed on one side surface of the current collector. The active material is selected from one of high-nickel ternary positive electrode materials, lithium-rich manganese-based positive electrode materials, and lithium cobalt oxide positive electrode materials.

8. The method for preparing the high-voltage resistant composite positive electrode sheet for suppressing battery cycle gas generation according to any one of claims 1-7, characterized in that, Includes the following steps: (S1) Dissolve the phosphorus-containing monomer, fluorinated acrylate monomer, polyethylene glycol borate and photoinitiator in a polar organic solvent to obtain a precursor solution; (S2) The precursor solution is coated on the surface of the positive active material layer of the positive electrode sheet, and polymerized in situ under ultraviolet light irradiation. After irradiation, the electrode is washed and dried to obtain a high-voltage resistant composite positive electrode sheet that suppresses gas generation during battery cycling.

9. The preparation method according to claim 8, characterized in that, In step (S1), the ratio of the total mass of the phosphorus-containing monomer, the fluorinated acrylate monomer, and the polyethylene glycol borate ester to the amount of the polar organic solvent is 10g:10~30mL, preferably 10g:10~20mL; the photoinitiator is selected from at least one of 2-hydroxy-2-methylphenylacetone, 1-hydroxy-cyclohexylbenzophenone, isopropylthioxanthraphenone, triarylthionium salt, and benzophenone; the amount of photoinitiator is 0.5~1wt% of the total mass of the phosphorus-containing monomer and the fluorinated acrylate monomer; the polar organic solvent is at least one of dimethyl sulfoxide, N,N-dimethylacetamide, and N-methylpyrrolidone.

10. The preparation method according to claim 8, characterized in that, In step (S2), the conditions for ultraviolet irradiation are: ultraviolet wavelength 300~450nm, power 15~25W, time 3~10 min; the washing is rinsing with dimethyl carbonate or diethyl carbonate 2~3 times; the drying is drying at 60~90℃ for 3~8h.

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