Battery pole piece, lithium ion battery and preparation method of lithium ion battery

Abstract

The invention provides a battery pole piece, a lithium ion battery and a preparation method of the lithium ion battery. Specifically, a coating is arranged on one side, far away from a current collector, of an active material layer of the battery pole piece; the coating is formed by crosslinking a first monomer, a second monomer, a binder and a photoinitiator; the first monomer is prepared from at least one of diethyl allyl phosphonate, triethyl phosphate, diphenyl phosphate, dimethyl methylphosphonate or melamine cyanurate; and the second monomer is prepared from at least one of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, tripropylene glycol diacrylate or trimethylolpropane trimethacrylate. The single and uniform coating not only helps to alleviate the problems of thermal runaway and cycle attenuation of the high-nickel ternary battery, but also does not need precise equipment in the preparation process, can be compatible with the existing lithium battery production line, and realizes collaborative optimization of thermal safety-cycle performance-mass production cost.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and in particular to a battery electrode, a lithium-ion battery, and a method for preparing the same. Background Technology

[0002] The rapid expansion of the new energy vehicle and energy storage industries has driven high-nickel ternary cathode materials (such as NCM811 and NCM911, where Ni ≥ 80%) to become mainstream, with energy densities exceeding 280 mAh / g, meeting the demand for long driving range. However, high-nickel ternary batteries still have two major shortcomings in practical applications: the risk of thermal runaway and poor interface and cycle performance. Summary of the Invention

[0003] In view of this, the purpose of this disclosure is to provide a battery electrode, a lithium-ion battery, and a method for preparing the same.

[0004] To achieve the above objectives, a first aspect of this disclosure provides a battery electrode, the battery electrode comprising a current collector, an active material layer, and a coating layer located on the side of the active material layer away from the current collector; wherein, The coating is formed by crosslinking a first monomer, a second monomer, a binder, and a photoinitiator; The first monomer includes at least one of diethylallylphosphonate, triethyl phosphate, diphenyl phosphate, dimethyl methylphosphonate, or melamine cyanurate; The second monomer includes at least one of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipropylene glycol diacrylate, or trimethylolpropane trimethacrylate.

[0005] In some embodiments, the total mass fraction of the first monomer and the second monomer is 70% to 75% based on the total mass of the coating; and / or The degree of crosslinking of the coating is 80%~90%; and / or The mass ratio of the first monomer to the second monomer is 0.75 to 0.875.

[0006] In some embodiments, the adhesive comprises at least one selected from polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyethylene oxide, polyimide, and polyethylene glycol dimethyl ether; and / or Based on the total mass of the coating, the mass fraction of the adhesive is 24% to 29%.

[0007] In some embodiments, the battery electrode is a positive electrode.

[0008] In some embodiments, the thickness of the coating is 1 μm to 12 μm.

[0009] In some embodiments, the thickness of the coating is 7 μm to 9 μm.

[0010] In some embodiments, the mass fraction of the first monomer is 30% to 35% based on the total mass of the coating; and / or Based on the total mass of the coating, the mass fraction of the second monomer is 40%.

[0011] In some embodiments, the first monomer is diethylallylphosphonate; and / or The second monomer is ethoxylated trimethylolpropane triacrylate; and / or The adhesive is a polyvinylidene fluoride-hexafluoropropylene copolymer.

[0012] Based on the same inventive concept, the second aspect of this disclosure also provides a method for preparing any of the aforementioned battery electrode sheets, comprising: Provide a fluid collection; The active material layer is formed on the current collector; A precursor solution comprising the first monomer, the second monomer, the binder, and the photoinitiator is coated onto the active material layer, and the coating is formed by crosslinking and drying.

[0013] Based on the same inventive concept, a third aspect of this disclosure also provides a lithium-ion battery, including any of the aforementioned battery electrodes.

[0014] As can be seen from the above, the battery electrode, lithium-ion battery, and preparation method disclosed herein provide a coating on the side of the active material layer of the battery electrode away from the current collector. The coating is formed by crosslinking a first monomer, a second monomer, a binder, and a photoinitiator. The first monomer includes at least one of diethylallyl phosphonate, triethyl phosphate, diphenyl phosphate, dimethyl methylphosphonate, or melamine cyanurate. The second monomer includes at least one of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipropylene glycol diacrylate, or trimethylolpropane trimethacrylate. This single, uniform coating not only helps alleviate the thermal runaway and cycle degradation problems of high-nickel ternary batteries, but its preparation process also does not require precision equipment, is compatible with existing lithium battery production lines, and achieves synergistic optimization of "thermal safety, cycle performance, and mass production cost." Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0016] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains.

[0017] In this disclosure, the term "range" is used to define a range in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~130 and 70~120 are listed for a specific parameter, it is expected that ranges of 60~120 and 70~130 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this disclosure, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0018] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0019] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0020] Unless otherwise specified, the terms "comprising" and "including" as used in this disclosure can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0021] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B".

[0022] Terminology Explanation A solid electrolyte interface (SEI) is a passivation layer formed on the surface of a lithium-ion battery during charging and discharging, resulting from the reaction between the electrode material and the electrolyte at the solid-liquid interface. This passivation layer is an interface layer, exhibiting characteristics of a solid electrolyte; it is an electronic insulator, yet it is a Li-ion electrolyte. + Li is an excellent conductor. + It can freely embed and extract through this passivation layer.

[0023] Direct Current Resistance (DCR) is measured at a specified temperature when a battery is discharged at 1C to 50% SOC (State of Charge, reflecting the battery's remaining capacity). The current is then increased to 4C and held for 30 seconds. The difference between the updated stable voltage and the original plateau voltage is measured, and the ratio of this difference to the 4C current value is the battery's DC resistance. The DCR test result performed after the battery's first full charge is the battery's initial DCR.

[0024] High-nickel ternary materials refer to ternary cathode materials with a nickel content of ≥80%, such as NCM811 (Ni:Co:Mn=8:1:1).

[0025] Adhesives refer to those that are resistant to electrolyte corrosion and possess Li + Polymers with conductive properties that combine adhesion and ion conduction.

[0026] An accelerating rate calorimeter (ARC) is a high-precision adiabatic thermal analysis instrument specifically designed to assess the thermal stability and thermal runaway risk of materials such as chemicals and batteries. ARC quantifies thermal safety using temperature parameters including the self-exothermic initiation temperature T1, the thermal runaway trigger temperature T2, and the thermal runaway peak temperature T3.

[0027] Atomic layer deposition (ALD) is a vapor-phase thin film preparation technique that achieves precise thin film growth at the single-atom-layer level through self-limiting surface chemical reactions.

[0028] As described in the background section, high-nickel ternary batteries still suffer from two major shortcomings in practical applications: thermal runaway risk and poor interface and cycle performance. The thermal runaway risk may be due to the fact that high-nickel materials are prone to Ni³⁺ oxidation at high temperatures. + →Ni² +The reduction reaction releases O2, which reacts violently with the electrolyte, causing exothermic reactions. Accelerated calorimetry (ARC) testing shows that the self-exothermic initiation temperature (T1) of a traditional uncoated cathode is ≤65℃, the thermal runaway trigger temperature (T2) is only 135℃, and the peak thermal runaway temperature (T3) exceeds 900℃, making it prone to combustion and explosion in extreme scenarios. Poor interface and cycle performance may be due to the generation of byproducts such as Li2CO3 and LiF in direct contact between the cathode and electrolyte. This results in a capacity retention rate generally below 80% after 1000 cycles, with a cumulative DCR increase of over 30%, severely impacting battery lifespan.

[0029] In related technologies, bulk doping is used to improve thermal runaway performance. For example, Mg²⁺ + F - Equal doping can stabilize the crystal lattice and suppress Ni² + Migration increases the thermal decomposition initiation temperature by 20°C to 30°C, but reduces the specific capacity by 5% to 8% (e.g., NCM811 drops from 285mAh / g to 265mAh / g).

[0030] In other related technologies, a single coating is used to improve battery performance. However, the function of a single coating is isolated, making it difficult to simultaneously achieve the synergistic effects of flame retardancy, O2 barrier, and ion conduction. For example, while polyimide (PI) coatings can improve electrolyte wettability, they are prone to melting at high temperatures and cannot suppress the increase in T3. For example, oxide coatings (such as Al2O3 or ZrO2 prepared by ALD) can slightly increase the thermal decomposition temperature, but they hinder ion conduction. Based on this, using gradient coatings to improve battery performance has become an optional technical solution. However, gradient coatings require precise control of the gradual change in composition, involve many process steps, and have high equipment dependence, resulting in insufficient cost and mass production adaptability.

[0031] It is evident that although the relevant technologies have made some progress, they still cannot achieve an effective balance between thermal safety, cycle performance, and mass production cost.

[0032] In view of this, the present disclosure provides a battery electrode, a lithium-ion battery, and a method for preparing the same, wherein a coating is provided on the side of the active material layer of the battery electrode away from the current collector; the coating is formed by crosslinking a first monomer, a second monomer, a binder, and a photoinitiator; the first monomer includes at least one selected from diethylallyl phosphonate, triethyl phosphate, diphenyl phosphate, dimethyl methylphosphonate, or melamine cyanurate; the second monomer includes at least one selected from ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipropylene glycol diacrylate, or trimethylolpropane trimethacrylate; the mass ratio of the first monomer to the second monomer is 0.75~0.875. Such a single uniform coating not only helps to alleviate the thermal runaway and cycle degradation problems of high-nickel ternary batteries, but its preparation process does not require precision equipment, is compatible with existing lithium battery production lines, and achieves synergistic optimization of "thermal safety-cycle performance-mass production cost".

[0033] To make the technical solutions of this disclosure clearer and easier to understand, the battery electrode sheets, lithium-ion batteries and their preparation methods provided in this disclosure will be described in detail below with reference to specific embodiments.

[0034] Battery electrode The first aspect of this disclosure is to provide a battery electrode.

[0035] In some embodiments, the battery electrode includes a current collector, an active material layer, and a coating. The coating is disposed on the side of the active material layer away from the current collector, and is used to mitigate thermal runaway and interfacial side reactions caused by direct contact between the battery electrode and the electrolyte. Optionally, the battery electrode can be a positive electrode.

[0036] In some embodiments, the coating is formed by crosslinking a first monomer, a second monomer, a binder, and a photoinitiator; wherein the first monomer comprises at least one of diethylallylphosphonate (DEAP), triethyl phosphate (TEP), diphenyl phosphate (DPP), dimethyl methylphosphonate (DMMP), or melamine cyanurate (MCA); and the second monomer comprises at least one of ethoxylated trimethylolpropane triacrylate (ETPTA), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), tripropylene glycol diacrylate (TPGDA), or trimethylolpropane trimethacrylate (TMPTMA).

[0037] It should be noted that, after cross-linking under light conditions, the first monomer, the second monomer, the binder, and the photoinitiator form a homogeneous coating system without the need for gradual component changes. This coating not only exhibits excellent density and thermal stability but also blocks O2 release, balancing adhesion and Li. + Conductivity (conductivity ≥ 8 × 10⁻⁶)-5 (S / cm), working together to resolve the contradiction between "flame retardancy-barrier-conduction", achieving the technical effect of reducing the risk of thermal runaway and reducing cycle decay.

[0038] Furthermore, the mass ratio of the first monomer to the second monomer is 0.75 to 0.875, for example, 0.75, 0.8, 0.81, 0.85, 0.875, etc. Such a mass fraction ratio helps to ensure that the coating achieves a good balance between density, thermal stability and O2 release barrier.

[0039] In some embodiments, the degree of crosslinking of the coating is 80% to 90%, such as 80%, 82%, 85%, 87%, 90%, etc.

[0040] In some embodiments, the total mass fraction of the first monomer and the second monomer is 70% to 75% based on the total mass of the coating, for example, 70%, 72%, 75%, etc. Here, limiting the total mass fraction of the first monomer and the second monomer to 70% to 75% helps the coating to have good conductivity.

[0041] Optionally, based on the total mass of the coating, the mass fraction of the first monomer is 30%-35%, such as 30%, 32%, 35%, etc. In some embodiments, based on the total mass of the coating, the mass fraction of the second monomer is 40%. Such a combination of mass fractions can significantly reduce the peak thermal runaway temperature T3 and improve cycling stability.

[0042] In some embodiments, the binder comprises at least one selected from polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polyethylene oxide (PEO), polyimide (PI), and polyethylene glycol dimethyl ether (PEGDME). Such a binder not only resists electrolyte corrosion but also possesses superior Li... + Conductivity.

[0043] In some embodiments, the mass fraction of the adhesive is 24% to 29% based on the total mass of the coating, for example, 24%, 25%, 28%, 29%, etc.

[0044] In some embodiments, the coating thickness is 1μm to 12μm, for example, 1μm, 2μm, 4μm, 6μm, 8μm, or 12μm. Such a thickness helps ensure that the battery cell meets performance standards.

[0045] Optionally, the thickness of the coating is 7μm to 9μm.

[0046] In some embodiments, the photoinitiator includes at least one selected from 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), 1-hydroxycyclohexylphenyl ketone (HCPK), bisacylphosphine oxide (BAPO), and 1-benzoylcyclohexanol. It should be noted that the crosslinking wavelength can vary depending on the type of photoinitiator, and this disclosure does not limit this.

[0047] Optionally, the photoinitiator has a mass fraction of 0.5% to 1.5% based on the total mass of the coating.

[0048] In some embodiments, the first monomer is diethylallyl phosphonate (DEAP). Here, diethylallyl phosphonate can generate polyphosphoric acid under high temperature conditions, which covers the surface of the battery electrode to block O2 release.

[0049] In some embodiments, the second monomer is ethoxylated trimethylolpropane triacrylate (ETPTA). Here, ETPTA crosslinks to form a three-dimensional network, which helps to improve the density and thermal stability of the coating.

[0050] Preparation method The second aspect of this disclosure provides a method for preparing the aforementioned battery electrode.

[0051] Exemplarily, the preparation method includes: First, a current collector is provided; here, the current collector can be a positive current collector, and can be a metal foil or a composite current collector, which is not limited in this disclosure.

[0052] Next, the active material layer is formed on the current collector; here, the active material layer may include active materials, conductive agents, binders, etc. It should be noted that the fabrication of the active material layer can be referred to the following specific embodiments, and will not be repeated here.

[0053] Finally, a precursor solution comprising the first monomer, the second monomer, the binder, and the photoinitiator is coated onto the active material layer, and the coating is formed by crosslinking and drying.

[0054] Therefore, the coating preparation process provided in this embodiment is not only simple and easy to operate, but also only requires the addition of a crosslinking module without the need for ALD equipment. It is compatible with existing lithium-ion battery production lines, which helps to reduce equipment modification costs and achieve large-scale application, providing an important guarantee for achieving synergistic optimization of "safety-cycle-cost".

[0055] In some embodiments, the first monomer, the second monomer, the binder, and the photoinitiator are weighed in proportion, added to a solvent, and ultrasonically dispersed to obtain the precursor solution. Here, the particle size of the particles present in the precursor solution is ≤500nm to ensure that the first monomer, the second monomer, the binder, and the photoinitiator do not agglomerate.

[0056] For example, the solvent may be N,N-dimethylformamide (DMF).

[0057] It should be noted that, based on the total mass of the precursor solution, the mass percentage of the first monomer, the second monomer, the binder, and the photoinitiator is 7% to 9%, for example, 8%.

[0058] For example, the conditions for ultrasonic dispersion include ultrasonic dispersion at 250W to 350W for 25 to 35 minutes.

[0059] In some embodiments, the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), which accounts for 1% by mass in the coating, the crosslinking wavelength is 365 nm, and the crosslinking time is 40-45 s.

[0060] In some embodiments, the drying conditions may be 110°C to 120°C, with vacuum drying for 1.5h to 2.5h. Here, the vacuum degree may be ≤-0.09MPa.

[0061] Lithium-ion batteries A third aspect of this disclosure provides a lithium-ion battery, including the battery electrode provided above. Here, the lithium-ion battery can be a primary lithium-ion battery or a secondary lithium-ion battery; this disclosure does not limit it in this regard.

[0062] In some embodiments, a lithium-ion battery includes a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0063] Positive electrode sheet The positive electrode includes a positive current collector and an active material layer disposed on at least one surface of the positive current collector, the active material layer comprising a positive active material. Optionally, the aforementioned coating may be disposed on the side of the active material layer away from the positive current collector.

[0064] For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0065] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (e.g., polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0066] In some embodiments, the positive electrode active material includes Li x Ni y Mn z M m O 0.5x+1.5y+1.5z+1.5m Wherein, 0.9≤x≤1.1, 0.8≤y≤1, 0≤z≤0.2, 0≤m≤0.2; and M is selected from one or more of Fe, Ti, Co, Cr, V, Cu, Zn, Zr, Al, and Nb. Optionally, 0.9≤y≤1.

[0067] In some embodiments, the active material layer may optionally include an adhesive. As an example, the adhesive may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0068] In some embodiments, the active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0069] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone, NMP) to form a positive electrode slurry; coating the positive electrode slurry onto the positive current collector, and after drying, cold pressing and other processes, obtaining an active material layer, and then forming a coating according to the aforementioned preparation method to obtain the positive electrode sheet.

[0070] Negative electrode sheet The negative electrode includes a negative current collector and a film layer optionally disposed on at least one surface of the negative current collector.

[0071] For example, the film layer may include a negative electrode active material (e.g., artificial graphite), a conductive agent, a thickener, and a binder.

[0072] In some embodiments, the negative electrode active material includes any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbide, or lithium titanate.

[0073] Optionally, the negative electrode active material is a mixture of silicon carbide and graphite; wherein, based on the total mass of the negative electrode active material, the mass fraction of the silicon carbide is 5% to 35%, for example 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%.

[0074] For example, carbon-based active materials include any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, and natural graphite.

[0075] In some embodiments, the negative electrode sheet can be prepared by dispersing the negative electrode active material, conductive agent, thickener, binder and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0076] Separating membrane In some embodiments, the secondary battery further includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0077] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0078] Example The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0079] The specific preparation method of the secondary lithium-ion battery of Embodiment 1 of this disclosure is as follows: (I) Preparation of positive electrode sheet 1. Mixing of active material layer: Mix high-nickel ternary material (NCM811, 90%~95%), conductive agent (2%~5%), PVDF (2%~3%) and NMP solvent, stir at low speed for 30 minutes, and stir at high speed for 2h~4h.

[0080] 2. Precursor solution: Weigh DEAP:ETPTA:PVDF-HFP:HMPP in the ratio of 30:40:29:1, add it to DMF solvent to make the solid content in the solution 8%, and sonicate at 300W for 30 minutes to ensure no agglomeration; 3. Forming an active material layer: The active material layer is coated onto the positive electrode current collector, and after drying, cold pressing and other processes, a positive electrode with a double-sided active material layer is obtained.

[0081] 4. Coating and Curing: A microgravure coating process (speed 8m / min, doctor blade pressure 0.4MPa) is used to coat the precursor solution onto the surface of the active material layer; 365nm ultraviolet crosslinking is performed, with an ultraviolet irradiance of 100mW / cm². 2 The curing time was 45 seconds, followed by vacuum drying at 120℃ for 2 hours (vacuum degree ≤ -0.09MPa), and the compacted density was 3.5~3.6 g / cm³. 3 This yields a positive electrode sheet with a coating.

[0082] The coating components and crosslinking conditions in other embodiments and comparative examples are prepared in the same manner as in this embodiment, except as specified in Table 1.

[0083] (II) Preparation of negative electrode sheet Ingredients mixture: graphite (95%~97%), Ketjen Black (1%~2%), styrene-butadiene rubber (SBR) (1.5%~2%), sodium carboxymethyl cellulose (CMC) (1%~1.5%), deionized water. Coated onto 8μm-10μm copper foil. Hot air dried at 60℃~80℃, then vacuum dried at 100℃ for 2 hours, moisture content ≤50ppm.

[0084] (III) Diaphragm Treatment The PE or PP / PE / PP separator has a thickness of 20μm~25μm, a porosity of 30%~50%, and is 2mm~3mm wider than the negative electrode sheet.

[0085] (iv) Assembly and Formulation The positive electrode, negative electrode, and separator are stacked to form a 2Ah soft-pack cell. After the cell is placed in the packaging shell, electrolyte is injected, and then the shell is sealed in sequence. After processes such as standing, hot and cold pressing, formation, venting, and capacity testing, a lithium-ion battery is obtained.

[0086] For example, the electrolyte can be prepared by using ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:7 as the base solvent, adding 1M LiPF6, and adding 5% fluoroethylene carbonate (FEC) according to the total mass of the electrolyte.

[0087] Test methods The secondary batteries prepared in the above embodiments and comparative examples can be tested using the following methods: 1. Thermal runaway temperature (°C) Take a fully charged battery cell and place it in an ARC high-pressure reactor under inert gas protection (e.g., Ar atmosphere). Use the "thermal runaway search mode" with an initial temperature of 50℃ and a step temperature increase (5℃ / step). Equilibrium for 30 minutes at each step. When the self-heating rate is ≥0.02℃ / min, enter the adiabatic tracking mode. Record the starting temperature when the battery cell temperature rises sharply (≥10℃ / s) and define it as the thermal runaway temperature.

[0088] 2. Cyclic capacity retention rate (%) The battery cell was charged to 4.25V at a constant current of 0.5C at 25℃, and then charged to 0.05C at a constant voltage. After resting for 30 minutes, it was discharged to 2.5V at a constant current of 1C, and the initial capacity (C0) was recorded. This charge-discharge cycle was repeated 1000 times, and the discharge capacity (C0) of the 1000th cycle was recorded. 1000 ); Calculate retention rate = (C 1000 / C0)×100%.

[0089] 3. DCR growth rate (%) Set the temperature of the constant temperature chamber to 25℃ and let it stand for 10 minutes; charge at a constant current of 0.33C to 4.25V, then charge at a constant current of 4.25V to 0.05C, and let it stand for 30 minutes; discharge at a constant current of 0.33C to 2.5V, and let it stand for 10 minutes. Repeat this cycle twice, and record the discharge capacity of the last discharge as C. Charge at a constant current of 0.33C to 4.25V, then charge at a constant voltage of 0.05C, and let it stand for 30 minutes; then discharge at a constant current of 0.33C to 50%C, and let it stand for 1 hour. Record the voltage V0 at the end of the standing period; discharge at a constant current of 4C for 30 seconds, and record the voltage V1. The initial DCR before the cycle is then = (V0 - V1) / 4C, denoted as R0.

[0090] The battery was discharged at 1C constant current and stabilized in a constant temperature chamber for 30 minutes. It was then charged at 1C constant current to 4.25V, followed by constant voltage charging to 0.05C. After resting for 10 minutes, it was discharged at 1C constant current to 2.5V. This charge-discharge cycle was repeated 1000 times before testing the DCR again. The battery was then charged at 0.33C constant current to 4.25V, followed by constant current charging at 4.25V to 0.05C, and allowed to rest for 30 minutes. It was then discharged at 0.33C constant current to 2.5V, allowed to rest for 10 minutes, and this cycle was repeated twice. The capacity of the last discharge was recorded as C1. The battery was then charged at 0.33C constant current to 4.25V, followed by constant voltage charging to 0.05C, allowed to rest for 30 minutes, and then discharged at 0.33C constant current to 50% of C1. After resting for 1 hour, the voltage V2 at the end of the resting period was recorded. Finally, a 4C constant current discharge was performed for 30 seconds, and the voltage V3 was recorded. Then, after 1000 cycles, DCR = (V2 - V3) / 4C1, denoted as R. 1000 The DCR growth rate after 1000 cycles at 25℃ is: DCR growth rate = (R 1000 -R0) / R0×100%.

[0091] 4. Polymer crosslinking degree test method (swelling method) Peel off the coating with a blade and accurately weigh the initial mass (m0); place the sample in a stoppered test tube, add 20 mL of DMF solvent (at a constant temperature of 25°C), seal and soak for 24 h (to ensure that the uncrosslinked parts are completely dissolved and the swelling reaches equilibrium). Remove the swollen sample, blot the surface solvent with filter paper, and immediately place it in a vacuum oven (120℃, -0.09MPa) to dry for 4 hours. After cooling to room temperature, weigh the residual mass (m1); degree of crosslinking (%) = (m1 / m0)×100%.

[0092] Table 1. Coating composition, crosslinking conditions, and lithium-ion battery performance test results of different groups of examples and comparative examples.

[0093] Comparing Comparative Example 1 with Examples 1 to 15, it can be found that adding a coating to the positive electrode sheet can effectively reduce the risk of thermal runaway of the battery while improving the cycle capacity retention rate.

[0094] Comparing Examples 1 and 3-6, it was found that a coating thickness of 1 μm can reduce the risk of thermal runaway. However, the insufficient thermal barrier capacity due to the smaller thickness results in a less effective improvement compared to coatings with a thickness of 7 μm or more. When the coating thickness reaches 7 μm or more, the risk of thermal runaway in the battery is significantly reduced. Compared to coating thicknesses of 7 μm to 9 μm, the DCR growth rate increases when the thickness reaches 12 μm. This may be because a larger coating thickness leads to a longer ion conduction path, thus increasing the DCR growth rate.

[0095] Comparing Comparative Example 2, Example 1, Example 7, and Example 8, it can be found that increasing the proportion of the first monomer can significantly improve the cycle capacity retention and DCR growth rate of the battery while reducing the risk of thermal runaway. Comparing Example 1, Example 7, and Example 8 shows that when the proportion of the first monomer significantly reduces the proportion of the binder, the cycle capacity retention of the battery decreases to some extent. This may be because insufficient binder reduces the stability of the battery electrodes.

[0096] Comparing Comparative Example 3, Example 1, and Examples 9-10, it can be found that adding a second monomer can effectively reduce the risk of thermal runaway in the battery, while improving the cycle capacity retention rate. As the content of the second monomer increases, the degree of crosslinking improves, effectively reducing the risk of thermal runaway. However, as the content of the second monomer continues to increase, for example, above 50%, the binder content is relatively small, resulting in a decrease in cycle performance. This may be because insufficient binder content reduces the stability of the battery electrode. Optionally, when the second monomer content is 40%, the overall battery performance is better. Furthermore, compared to a crosslinking degree in the range of 80%-90%, a crosslinking degree deviating from 80%-90% leads to a decrease in overall battery performance. Therefore, "crosslinking degree 80%-90%" can be used as a rapid standard for judging coating quality during mass production, replacing complex battery performance testing.

[0097] Comparing Comparative Example 4, Example 1, Example 2, and Examples 11-12, it was found that batteries with a binder concentration in the range of 24% to 29% exhibited better cycle capacity retention and DCR growth rate. Deviations from this range may lead to a decrease in the single function of "ion conduction" or "adhesion," thereby affecting battery cycle performance.

[0098] Comparing Examples 1, 13, and 14, it can be found that the crosslinking time affects the degree of crosslinking. Increasing the degree of crosslinking can improve the density of the coating and help reduce the risk of thermal runaway. However, excessive crosslinking can lead to coating embrittlement, which is not conducive to improving cycle capacity retention. Optionally, a crosslinking time of 40-45 seconds results in better overall battery performance. Optionally, a crosslinking degree of 80%-90% also results in better overall battery performance.

[0099] As can be seen from Examples 1 and 15-17, using a first monomer, a second monomer, and a binder with multiple components to prepare the coating can improve the overall performance of the battery. In other words, the first monomer, the second monomer, and the binder in the embodiments of this disclosure can be selected from multiple sources.

[0100] Comparing Examples 1 to 14, it can be found that when the mass percentage of DEAP is 30% to 35%, the mass percentage of ETPTA is 40%, the mass ratio of PVDF-HFP is 24% to 29%, the coating thickness is 7nm to 9nm, and the degree of crosslinking is 80% to 90%, the overall battery performance is better. Specifically, the thermal runaway related temperatures meet the following conditions: T1≥82℃, T2≥167℃, T3≤82℃, cycle capacity retention rate≥86%, and DCR growth rate≤16%.

[0101] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0102] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A battery electrode, characterized in that, The battery electrode includes a current collector, an active material layer, and a coating layer located on the side of the active material layer away from the current collector; wherein, The coating is formed by crosslinking a first monomer, a second monomer, a binder, and a photoinitiator; The first monomer includes at least one of diethylallylphosphonate, triethyl phosphate, diphenyl phosphate, dimethyl methylphosphonate, or melamine cyanurate; The second monomer includes at least one of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipropylene glycol diacrylate, or trimethylolpropane trimethacrylate.

2. The battery electrode according to claim 1, characterized in that, Based on the total mass of the coating, the total mass fraction of the first monomer and the second monomer is 70%~75%; and / or The degree of crosslinking of the coating is 80%~90%; and / or The mass ratio of the first monomer to the second monomer is 0.75 to 0.

875.

3. The battery electrode according to claim 1, characterized in that, The adhesive comprises at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyethylene oxide, polyimide, and polyethylene glycol dimethyl ether; and / or Based on the total mass of the coating, the mass fraction of the adhesive is 24% to 29%.

4. The battery electrode according to claim 1, characterized in that, The battery electrode is a positive electrode.

5. The battery electrode according to claim 1, characterized in that, The thickness of the coating is 1μm to 12μm.

6. The battery electrode according to claim 1, characterized in that, The coating thickness is 7μm~9μm.

7. The battery electrode according to claim 1, characterized in that, Based on the total mass of the coating, the mass fraction of the first monomer is 30%~35%; and / or Based on the total mass of the coating, the mass fraction of the second monomer is 40%.

8. The battery electrode according to claim 1, characterized in that, The first monomer is diethylallyl phosphonate; and / or The second monomer is ethoxylated trimethylolpropane triacrylate; and / or The adhesive is a polyvinylidene fluoride-hexafluoropropylene copolymer.

9. The method for preparing a battery electrode according to any one of claims 1 to 8, characterized in that, include: Provide a fluid collection; The active material layer is formed on the current collector; A precursor solution comprising the first monomer, the second monomer, the binder, and the photoinitiator is coated onto the active material layer, and the coating is formed by crosslinking and drying.

10. A lithium-ion battery, characterized in that, Includes the battery electrode according to any one of claims 1 to 8.

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