WO2025237306A1 - 一种负极片和电池 - Google Patents

一种负极片和电池

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Publication number
WO2025237306A1
WO2025237306A1 PCT/CN2025/094652 CN2025094652W WO2025237306A1 WO 2025237306 A1 WO2025237306 A1 WO 2025237306A1 CN 2025094652 W CN2025094652 W CN 2025094652W WO 2025237306 A1 WO2025237306 A1 WO 2025237306A1
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WIPO (PCT)
Prior art keywords
negative electrode
electrode sheet
silicon
battery
current collector
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Pending
Application number
PCT/CN2025/094652
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English (en)
French (fr)
Inventor
曹萌
舒梨
方嘉琳
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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Application filed by Zhuhai Cosmx Battery Co Ltd filed Critical Zhuhai Cosmx Battery Co Ltd
Publication of WO2025237306A1 publication Critical patent/WO2025237306A1/zh
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This disclosure relates to the technical field of wound battery, specifically to a negative electrode sheet and a battery.
  • lithium-ion batteries are undergoing rapid iteration and upgrading. Improving the energy density of individual lithium batteries is one of the directions for the development of lithium battery technology.
  • widely used methods to improve battery energy density include optimizing the battery structure and improving the performance of active materials.
  • silicon anode materials are being used in lithium batteries to further improve their energy density, among which silicon anode materials have attracted widespread attention due to their high theoretical specific capacity.
  • silicon anode materials are limited by their inherent characteristics, such as low electrical conductivity, volume expansion during cycling, and the risk of breakage under stress.
  • the expansion of the silicon anode paste occurs both perpendicular and parallel to the electrode plane, increasing the battery thickness and electrode width. This leads to a reduction in the gap between the core and the casing, and the casing may even be damaged due to compression caused by the core expansion, ultimately resulting in battery failure.
  • Adding silicon to the negative electrode to improve the energy density of the battery can increase the energy density, but due to the inherent properties of silicon, the performance of the electrode and some structural dimensions of the battery may deteriorate. For example, the resistivity of the electrode may increase, the cell thickness may expand, and the electrode may become more elongated, ultimately affecting the electrochemical performance of the battery.
  • the purpose of this disclosure is to overcome the aforementioned problems in the prior art and to provide a negative electrode sheet and a battery including the negative electrode sheet.
  • the stability of the negative electrode sheet can be improved, enabling the battery containing the negative electrode sheet to have good cycle performance.
  • a first aspect of this disclosure provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material comprising a negative electrode active material; wherein, the tensile strength of the current collector is denoted as ⁇ , the Dv50 of the negative electrode active material is denoted as T, the areal density of the negative electrode sheet is denoted as cw, and the open-cell thickness of the negative electrode sheet when the battery is discharged to 0% SOC is denoted as H, and ⁇ , T, cw, and H satisfy the following relationship: ⁇ >(H/T+1.8*cw)*10,
  • the unit of ⁇ is MPa
  • the unit of T is ⁇ m
  • the unit of cw is mg/ cm2
  • the unit of H is ⁇ m.
  • a second aspect of this disclosure provides a battery comprising the negative electrode, positive electrode, and electrolyte described in the first aspect of this disclosure.
  • the battery provided in this disclosure has the advantages of good cycle performance, good charge and discharge performance, and high energy density.
  • Figure 1 shows a SEM image of the negative electrode sheet of Example 1-1.
  • Figure 2 shows the volumetric particle size distribution of the silicon-based material in Example 3-1.
  • the first aspect of this disclosure provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material comprising a negative electrode active material; wherein, the tensile strength of the current collector is denoted as ⁇ , the Dv50 of the negative electrode active material is denoted as T, the areal density of the negative electrode sheet is denoted as cw, and the open-cell thickness of the negative electrode sheet when the battery is discharged to 0% SOC is denoted as H, and ⁇ , T, cw, and H satisfy the following relationship: ⁇ >(H/T+1.8*cw)*10,
  • the unit of ⁇ is MPa
  • the unit of T is ⁇ m
  • the unit of cw is mg/ cm2
  • the unit of H is ⁇ m.
  • 0% SOC refers to the state of the battery after a 0.5C constant current discharge, reaching a discharge cutoff voltage of 2.75V; or "0% SOC” refers to the state of the battery after completing the 0.5C constant current discharge step, and the cutoff voltage of the constant current discharge step is 2.75V.
  • ⁇ , T, cw, and H satisfy the following relationship: ⁇ > (H/T + 1.8 * cw) * 15. Further optimizing the relationship between the tensile strength of the current collector, the empty electrode thickness, the coating density, and the particle size of the negative electrode active material can result in higher tensile strength of the current collector, more effective mitigation of current collector elongation, better improvement of the stability of the negative electrode, and better maintenance of the battery in a better working state.
  • the tensile strength ⁇ of the current collector is greater than 300 MPa, preferably ⁇ ⁇ 400 MPa, and more preferably ⁇ is between 400 MPa and 800 MPa.
  • the tensile strength ⁇ of the current collector can be 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, or any value within the range of the above two values.
  • the negative electrode active material is coated onto the current collector, and the tensile strength of the current collector also has a certain impact on the performance of the negative electrode sheet and the battery.
  • the negative electrode paste i.e., the negative electrode active material
  • the negative electrode active material expands due to lithium insertion.
  • the gaps between the negative electrode active materials are small, making it difficult for the expansion to be released. This expansion is eventually transferred to the current collector, causing it to extend along with the current collector.
  • the negative electrode active material delithiates, the expansion recedes, and the negative electrode active material returns to its original position.
  • the current collector cannot recover its extension, causing relative displacement between the material and the current collector.
  • the current collector slowly extends along with the electrode sheet, not only compressing the outermost membrane of the cell but also causing relative displacement between the active material and the current collector, resulting in poor contact and ultimately affecting the cell's performance. Therefore, when the tensile strength of the current collector in this disclosure is within the aforementioned range, it can avoid excessive stretching of the current collector, which could cause compression of the cell casing corners and edges, as well as contact problems between the active material and the current collector.
  • the relative displacement between the active material and the current collector is reduced, thereby reducing the risk of the active material loosening or falling off the current collector.
  • it also ensures close contact between the negative electrode and the current collector, reducing the battery's impedance and polarization during cycling. This allows the battery electrodes to have high capacity and energy density while effectively mitigating the stretching of the current collector, keeping the battery in good operating condition.
  • the Dv50(T) of the negative electrode active material is 5 ⁇ m-20 ⁇ m, preferably 6 ⁇ m-15 ⁇ m.
  • the Dv50 of the negative electrode active material can be 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, or any value within the range of the above-mentioned values.
  • the negative electrode sheet is formed by stacking negative electrode active material on a current collector, with gaps between the materials.
  • the particle size of the active material is within the above-defined suitable range, ensuring good liquid retention of the electrode sheet, reducing charge transfer impedance, and maintaining good electronic conductivity between the materials, resulting in better overall electrical performance of the battery, including cycle performance and charge-discharge performance.
  • the air-electric thickness H is 50 ⁇ m-200 ⁇ m, preferably 70 ⁇ m-110 ⁇ m.
  • the air-electric thickness H can be 50 ⁇ m, 60 ⁇ m, 70 ⁇ m, 80 ⁇ m, 90 ⁇ m, 100 ⁇ m, 110 ⁇ m, 120 ⁇ m, 130 ⁇ m, 140 ⁇ m, 150 ⁇ m, 160 ⁇ m, 170 ⁇ m, 180 ⁇ m, 190 ⁇ m, 200 ⁇ m, or any value within the range of the above values.
  • the areal density cw of the negative electrode is 3 mg/ cm2 - 18 mg/ cm2 , preferably 5 mg/ cm2 - 15 mg/ cm2 .
  • the areal density of the negative electrode can be, for example, 3 mg/ cm2 , 5 mg/ cm2 , 6 mg/ cm2 , 7 mg/ cm2 , 8 mg/ cm2 , 9 mg/ cm2 , 10 mg/ cm2 , 11 mg/ cm2 , 12 mg/ cm2 , 13 mg/ cm2 , 15 mg/ cm2 , 16 mg/ cm2 , 18 mg/ cm2 , or any value within the range of the aforementioned values.
  • the capacity and energy density of the battery cell can be improved, the risk of electrode brittleness and easy breakage can be reduced, the wettability of the negative electrode with the electrolyte can be improved, and problems such as increased ion migration impedance and increased polarization can be reduced.
  • further limiting the surface density, open-cell thickness, and particle size of the negative electrode active material within the above-mentioned range can further improve the capacity and energy density of the cell, enhance the stability of the negative electrode sheet, and improve the cycle stability of the battery.
  • the negative electrode active material includes silicon-based material and carbon-based material; the Dv50 of the silicon-based material is denoted as A, and the Dv50 of the carbon-based material is denoted as B; A, B, ⁇ , and H satisfy the following relationship: ⁇ >0.1*H*(1.5A+B), where the unit of A is ⁇ m and the unit of B is ⁇ m.
  • Silicon-based and carbon-based materials are graded and coated onto the current collector. Different particle sizes affect the compactness of the packing, thus influencing the physical properties of the electrode, such as porosity and resistivity. Simultaneously, the size and gradation of the negative electrode active material, along with its compatibility with the current collector, also affect the electrode's elongation, flexibility, and surface appearance.
  • the particle sizes of the silicon-based and carbon-based materials, the tensile strength of the current collector, and the open-cell thickness of the negative electrode satisfy the relationship ⁇ >0.1*H*(1.5A+B), the electrode possesses suitable particle size, compaction density, and a suitable current collector combination. At this point, the negative electrode exhibits better performance, and the active material coated on the current collector has minimal impact on the electrode's elongation.
  • the Dv50(A) of the silicon-based material is 5 ⁇ m to 14 ⁇ m, preferably 7 ⁇ m to 10 ⁇ m.
  • the Dv50 of the silicon-based material can be 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, or any value within the range of any pair of values mentioned above.
  • Silicon-based materials undergo volume changes during charge and discharge. Silicon-based materials with excessively large Dv50 may result in excessively large gaps between materials, affecting battery stability.
  • the particle size of the silicon-based material is within the above range, the impact of volume changes on the battery structure can be reduced, and more of the negative electrode active material surface can participate in the electrochemical reaction, improving the utilization rate of the negative electrode active material and thus increasing the energy density of the battery.
  • the Dv50(B) of the carbon-based material is 7 ⁇ m to 20 ⁇ m, preferably 8 ⁇ m to 12 ⁇ m.
  • the Dv50 of the carbon-based material can be 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, or any value within the range of the above pairs.
  • the particle size of the carbon-based material is within the above range, the diffusion path of lithium ions within the negative electrode active material can be shortened, the diffusion rate of lithium ions can be increased, thereby improving the charge/discharge speed and cycle performance of the battery.
  • the particle size distribution of the above-mentioned negative electrode active material, silicon-based material, and carbon-based material was obtained by measuring the particle size distribution using a Malvern laser particle size analyzer.
  • the ratio A/B of the Dv50 of the silicon-based material to the Dv50 of the carbon-based material is 0.3 to 1, preferably A/B is 0.5 to 0.9.
  • the A/B ratio can be 0.3, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.88, 0.92, 1, or any value within the range of the above pairs.
  • the silicon-based materials and carbon-based materials can be stacked more tightly.
  • the silicon-based materials fill the larger gaps between the carbon-based materials, improving space utilization.
  • the carbon-based materials can better wrap around the silicon-based materials, forming a good conductive network together with the conductive agent, effectively reducing the sheet resistance of the electrode.
  • some smaller pores are retained for electrolyte filling, ensuring lithium ion insertion and extraction, and also reserving appropriate space for the expansion of silicon-based materials during the lithium insertion and extraction process, thus improving the cycle performance and charge-discharge performance of the battery.
  • the silicon-based material comprises 1% to 50% by mass in the negative electrode active material, preferably 3% to 20%, for example, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range of any two of the above values.
  • adding an appropriate amount of silicon-based material can increase the specific capacity of the active material and improve the energy density of the battery; on the other hand, combining silicon-based and carbon-based materials can reduce the expansion of the electrode during cycling, while an appropriate amount of carbon-based material can improve the electronic conductivity of the electrode and reduce the battery impedance.
  • the mass ratio of silicon-based material is further limited. This can reduce the expansion of the electrode during cycling, slow down the extension of the current collector, improve the stability of the negative electrode, and increase the energy density of the battery.
  • the silicon-based material contains 40-100% silicon by mass, preferably 40-60%, more preferably 45-55%, for example, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any value within the range of any two of these values.
  • the main function of silicon-based materials is to increase energy density, but direct use can cause excessive battery expansion and battery cycle capacity decay, while also exhibiting low conductivity and high impedance. Therefore, modification is necessary to maintain the silicon content within the range of 40-100%, ensuring both high specific capacity and stability and improved conductivity through modification methods such as vapor deposition, coating, alloying, and nano-sizing.
  • the resistivity of the silicon-based material powder is 5 ⁇ *cm to 100 ⁇ *cm, preferably 6 ⁇ *cm to 50 ⁇ *cm, and more preferably 10 ⁇ *cm to 30 ⁇ *cm.
  • it can be 5 ⁇ *cm, 10 ⁇ *cm, 20 ⁇ *cm, 30 ⁇ *cm, 40 ⁇ *cm, 50 ⁇ *cm, 60 ⁇ *cm, 70 ⁇ *cm, 80 ⁇ *cm, 90 ⁇ *cm, 100 ⁇ *cm, or any value within the range of any two of the above values.
  • the resistivity of the silicon-based material powder is measured using a powder resistance tester at a powder pressure of 16 kN. When the resistivity of the silicon-based material powder is within the above range, it can improve the conductivity inside the negative electrode, thereby improving the overall performance of the battery, including charge/discharge speed and cycle performance.
  • the current collector can form a good interface between the silicon-based material and the electrolyte, which helps to improve the charge transport efficiency and electrochemical performance of the battery, and further optimize the battery performance.
  • the silicon-based material is a silicon-containing material suitable for the negative electrode of a battery, such as at least one of silicon-carbon, silicon-oxygen, nano-silicon, and silicon alloy.
  • the silicon phase material is distributed within the carbon framework of the silicon-carbon material.
  • the carbon framework provides good electrical conductivity, structural stability, and elasticity, helping to alleviate the expansion problem of silicon materials and improving the cycling stability and electrochemical performance of the material.
  • the carbon-based material is a carbon-containing material suitable for the negative electrode of a battery, such as at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.
  • the current collector comprises copper foil.
  • the thickness of the current collector is 3 ⁇ m to 20 ⁇ m, for example, it can be 3 ⁇ m, 5 ⁇ m, 8 ⁇ m, 10 ⁇ m, 12 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 18 ⁇ m, 20 ⁇ m, or any value within the range of any pair of values mentioned above.
  • the thickness of the negative electrode current collector directly affects the weight and volume of the battery. Limiting the thickness of the current collector within the above range can reduce the battery weight and volume, thereby increasing the battery's energy density.
  • the porosity of the negative electrode sheet is 15%–50%, preferably 18%–35%, and more preferably 19%–28%.
  • the porosity can be 15%, 18%, 20%, 23%, 25%, 30%, 35%, 38%, 40%, 42%, 45%, 49%, 50%, or any value within the range of the above values.
  • the porosity of the negative electrode sheet refers to the gap between materials when the negative electrode active material is stacked in the negative electrode sheet. It reflects the tightness of the material stacking and thus affects the battery performance.
  • the compaction density of the negative electrode sheet is 1 mg/ cm3 to 2.5 mg/ cm3 , for example, it can be 1 mg/ cm3 , 1.1 mg/ cm3 , 1.2 mg/ cm3 , 1.3 mg/ cm3 , 1.4 mg/ cm3 , 1.5 mg/ cm3 , 1.6 mg/ cm3 , 1.7 mg/ cm3 , 1.8 mg/ cm3 , 1.9 mg/ cm3 , 2 mg/ cm3 , 2.3 mg/ cm3 , 2.5 mg/ cm3 , or any value within the range of the above two-to-one values.
  • the compaction density is closely related to its performance.
  • a higher compaction density results in a thinner electrode, ensuring better conductivity and higher energy density in the battery.
  • excessive compaction density can cause a series of problems during the manufacturing process, such as sticking to the rollers, poor appearance, and reduced electrode flexibility. In terms of battery performance, it can lead to difficulties in electrolyte wetting and reduced battery capacity. Therefore, a negative electrode compaction density within the aforementioned range can increase the battery's energy density, reduce internal resistance, minimize polarization loss, and extend the battery's cycle life.
  • the energy density or rate performance of the battery can be improved, while also allowing for some space to release the expansion of the silicon-based material.
  • the elongation of the negative electrode sheet is 1 ⁇ to 6.5 ⁇ , for example, it can be 1 ⁇ , 2 ⁇ , 2.5 ⁇ , 3 ⁇ , 3.5 ⁇ , 4 ⁇ , 4.5 ⁇ , 5 ⁇ , 5.5 ⁇ , 6 ⁇ , 6.5 ⁇ , or any value within the range of the above pairs, preferably 2 ⁇ to 6 ⁇ .
  • the structural stability of the negative electrode sheet during charge and discharge processes can be guaranteed, the contact between the negative electrode active materials can be optimized, and the cracking and pulverization of the negative electrode active materials can be reduced, thereby improving the cycle life of the battery.
  • the negative electrode active material layer further includes a thickener, a binder, and a conductive agent.
  • the thickener includes at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium alginate, guar gum, xanthan gum, and chitosan
  • the binder includes at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, polyimide, polyamide-imide, styrene-butadiene rubber, and polyvinylidene fluoride
  • the conductive agent includes at least one of conductive carbon black, carbon nanotubes, carbon fibers, and Ketjen black.
  • a second aspect of this disclosure provides a battery comprising the negative electrode, positive electrode, and electrolyte described in the first aspect of this disclosure.
  • the battery disclosed herein due to including the aforementioned negative electrode, has advantages such as good cycle performance, good charge-discharge performance, and high energy density.
  • the electrolyte includes a non-aqueous organic solvent, an electrolyte lithium salt, and additives.
  • non-aqueous organic solvent organic solvents conventionally used in the art, such as carbonates and/or carboxylic esters, can be selected.
  • organic solvent is a mixture of multiple solvents, the solvents can be mixed in any proportion.
  • the non-aqueous organic solvent includes a carboxylic acid ester.
  • the mass percentage of the carboxylic acid ester is 5% to 50%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range of any pair of values mentioned above.
  • Adding a carboxylic acid ester to the organic solvent and limiting the mass percentage of the carboxylic acid ester within the above range can reduce the viscosity of the electrolyte, improve the ion transport efficiency of the electrolyte, and enhance the kinetic performance of the battery.
  • An electrolyte with higher kinetics can ensure greater compaction and areal density of the silicon-based negative electrode, and the electrolyte filling the smaller voids in the negative electrode material can also maintain the stability of the electrochemical system in the battery.
  • the high tensile strength current collector suppresses the electrode stretching caused by the expansion of negative electrode active material particles during cycling. When combined with a high-kinetic electrolyte, it can better maintain the normal insertion and extraction of lithium ions and improve the cycle stability of the battery.
  • the carboxylic acid ester includes at least one selected from methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decanoic acid lactone, valerate lactone, ethyl butyrate, or caprolactone.
  • Lithium salts commonly used in the art can be selected, such as lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorobis(oxalate phosphate), lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethylsulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethylsulfonyl)methyl, and lithium di(trifluoromethylsulfonyl)imide.
  • negative electrode film-forming additives and/or positive electrode film-forming additives in the art can be selected.
  • negative electrode film-forming additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.
  • positive electrode film-forming additives include vinyl sulfate (DTD), 1,3-propane sulfonyl lactone (PS), 1,3-propene sulfonyl lactone (PST), etc.
  • the additive includes fluoroethylene carbonate (FEC).
  • FEC fluoroethylene carbonate
  • the mass percentage of fluoroethylene carbonate in the electrolyte is 1-20%, for example, it can be 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, or any value within the range of any pair of values mentioned above.
  • FEC can form a solid electrolyte interface of appropriate thickness on the surface of the silicon-based material, ensuring the stability of the silicon-based material.
  • the FEC additive when used in combination with a high tensile strength current collector, it can ensure that the relative position of the silicon-based material will not easily change, thus ensuring the stability of the silicon-based material and the surrounding environment. This helps to reduce the impact of silicon expansion on the current collector, improve the stability of the electrode, and enhance the cycle performance of the battery.
  • the positive electrode includes a positive electrode material, said positive electrode material including lithium cobalt oxide.
  • the battery is a pouch cell battery.
  • the battery is a lithium-ion secondary battery.
  • the battery cells of the examples and comparative examples were prepared according to the following preparation method, and the specific differences are shown in Table 1.
  • Lithium cobalt oxide, conductive carbon black, carbon nanotubes and PVDF are stirred in NMP in a mass ratio of 95:1:1.5:2.5 to form a slurry.
  • the slurry is coated on aluminum foil (thickness of 9 ⁇ m), dried, rolled, cut, and the tabs are soldered and adhesive paper is applied to prepare the positive electrode sheet.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • Example 7-1 Methyl acetate accounts for 5% by mass
  • Example 7-2 Methyl acetate accounts for 20% by mass
  • Example 7-3 Methyl acetate accounts for 40% of the total mass
  • Example 7-4 Methyl acetate not added.
  • Example 8-1 The mass percentage of FEC is 6%
  • Example 8-2 The mass percentage of FEC is 13%
  • Example 8-3 The mass percentage of FEC is 20%;
  • Strength of negative electrode copper foil Cut the foil into strips of 15mm ⁇ 0.2mm. Use a WD-D3 electronic universal testing machine with a 50mm gap between the upper and lower clamps. Clamp both ends of the foil in the clamps and start testing at a speed of 100mm/min until the equipment stops testing. Record the breaking strength ⁇ . The error of 3 tests should not exceed 10%, and take the average value.
  • Electrode surface density test Cut the electrode into an area of 15.0425 cm2 , weigh it, remove the coating layer and weigh the current collector again, subtract the two weights and divide by the cut area.
  • Electrode blank thickness H A cross-sectional sample of blank electrode sheet (battery discharged to 2.75V at 0.5C, left to stand for 1min, discharged to 2.75V at 100mA, and the electrode sheet was taken after disassembling the battery) was prepared using an ion milling device. The thickness of the electrode sheet was measured under SEM with an accuracy of 0.1 ⁇ m.
  • Silicon content test in silicon-based materials A cross-section of the negative electrode was cut using an ion mill. A scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) was used to locate the cross-section of the silicon-based material. The element content information was collected at the midpoint of the cross-section. Ten samples were collected, and the average value was taken after excluding samples with large deviations.
  • SEM scanning electron microscope
  • EDS energy dispersive spectroscopy
  • Powder resistivity of silicon-based materials Powder resistance tester was used with a powder pressure of 16 kN.
  • Electrode elongation test The battery was cycled at 25°C, charged at 1C constant current to 4.5V, charged at 4.5V constant voltage to 0.2C, and discharged at 0.7C to 3V. After 500 cycles, the battery was discharged to 3V. The battery was dissected, and the electrode width was measured using a 2.5D microscope. The width of the electrode furthest from the paste coating in the double-sided empty foil area was recorded as S1, and the width of the paste coating area was recorded as S2. The electrode elongation rate was (S2-S1)/S1. The average of the five measured values was taken.
  • Battery Energy Density Battery Energy Test: Using a Newway battery tester, charge at 0.2C to the upper limit voltage (cutoff at 0.02C) / discharge at 0.2C to the lower limit voltage, repeat 3 times, and take the discharge energy of the 3rd discharge as the cell energy Q. Use a 2.5D microscope to test the width W and height H of the cell, and use a PPG thickness tester to test the full-charge thickness L of the cell. Then the energy density is Q/(W*H*L).
  • Constant current charge ratio The battery is charged at a constant current of 1C to 4.5V, and the charging capacity at this time is recorded as Q1. Then it is charged at a constant voltage of 4.5V to the cutoff current of 0.05C, and the charging capacity at this time is recorded as Q2.
  • the constant current charge ratio is Q1/(Q1+Q2)*100%.
  • Figure 1 shows the SEM image of the negative electrode sheet of Example 1-1, illustrating the morphology of the negative electrode sheet after roll forming.
  • the brighter particles are silicon-based materials, and the darker particles are carbon-based materials.
  • the silicon-based materials are dispersed within the carbon-based materials. After roll forming, fine voids exist between the particles.
  • Figure 2 shows the volumetric particle size distribution of the silicon-based material in Example 3-1, indicating that the Dv50 of the silicon-based material is approximately 7.6 ⁇ m.

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Abstract

本公开涉及卷芯电池的技术领域，提供了一种负极片和电池。该负极片包括集流体和设置于所述集流体至少一侧表面的负极活性物质层，负极活性物质包括负极活性材料；其中，集流体的拉伸强度记为σ，负极活性材料的Dv50记为T，负极片的面密度记为cw，电池放电至0％SOC时负极片的空电厚度记为H，σ、T、cw和H满足关系式：σ>(H/T+1.8*cw)*10。该负极片中，集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述特定的关系式时，能保证负极片的能量密度能最大程度的发挥，提升负极片的稳定性，使含有负极片的电池具有循环性能良好、充放电性能良好，以及较高的能量密度等优点。

Description

一种负极片和电池 技术领域
本公开涉及卷芯电池的技术领域，具体涉及一种负极片和电池。
背景技术
随着人类社会对新能源的迫切需求，锂离子电池正在飞速的迭代更新，提升单个锂电池的能量密度是锂电池技术发展的方向之一。目前广泛使用到的提升电池能量密度的方法包括优化电池的结构以及提升活性材料的性能。
各种新型的活性材料应用在锂电池中，只为进一步提升其能量密度，其中硅负极材料由于较高的理论克容量而被广泛关注。但是在实际使用过程中，硅负极材料又会受到其自身特性的限制，比如硅负极材料的低电导率，循环过程中体积膨胀以及受到应力而粉碎等。除此之外，硅负极涂膏膨胀会沿垂直极片平面的方向以及平行极片平面的方向，造成电池厚度增加以及极片宽度增加，进而引起卷芯和膜壳的间隙缩小，甚至膜壳会因卷芯膨胀而受到挤压而出现破损，最终导致电池失效。
为了提升电池的能量密度而在负极中添加硅材料，虽然电池的能量密度得到了提升，但是由于硅材料的自身特性会导致极片的性能、电池的一些结构尺寸变差，比如极片的电阻率上升，电芯厚度膨胀增大，极片延展变大等，最终影响电池的电化学性能。
发明内容
本公开的目的在于克服现有技术存在的上述问题，提供一种负极片和包括该负极片的电池。通过调控负极片中集流体强度、负极片空电厚度、涂布面密度以及负极活性材料的粒径，能提升负极片的稳定性，使含有负极片的电池具有良好的循环性能。
为了实现上述目的，本公开第一方面提供了一种负极片，所述负极片包括集流体和设置于所述集流体至少一侧表面的负极活性物质层，所述负极活性物质包括负极活性材料；其中，所述集流体的拉伸强度记为σ，所述负极活性材料的Dv50记为T，所述负极片的面密度记为cw，电池放电至0％ SOC时负极片的空电厚度记为H，σ、T、cw和H满足如下关系式：
σ>(H/T+1.8*cw)*10，
σ的单位为Mpa，T的单位为μm，cw的单位为mg/cm2，H的单位为μm。
本公开第二方面提供了一种电池，所述电池包括本公开第一方面所述的负极片，正极片和电解液。
本公开采用上述技术方案具有以下有益效果：
(1)本公开提供的负极片，集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足特定的关系式时，能保证负极片的能量密度能最大程度的发挥，同时也能保证负极片的尺寸不会在工作中出现较大的变化，提升负极片的稳定性。
(2)本公开提供的电池具有循环性能良好、充放电性能良好，以及较高的能量密度等优点。
在本文中所披露的范围的端点和任何值都不限于该精确的范围或值，这些范围或值应当理解为包含接近这些范围或值的值。对于数值范围来说，各个范围的端点值之间、各个范围的端点值和单独的点值之间，以及单独的点值之间可以彼此组合而得到一个或多个新的数值范围，这些数值范围应被视为在本文中具体公开。本文中，在没有特别说明的情况下，数据范围均包括端点。
附图说明
图1所示为实施例1-1的负极片的SEM图。
图2所示为实施例3-1中硅基材料的体积粒径分布图。
具体实施方式
以下对本公开的具体实施方式进行详细说明。应当理解的是，此处所描述的具体实施方式仅用于说明和解释本公开，并不用于限制本公开。
除非另有定义，本公开中所使用的所有科学和技术术语具有与本公开涉及技术领域的技术人员通常理解的相同的含义。
本公开第一方面提供了一种负极片，所述负极片包括集流体和设置于所述集流体至少一侧表面的负极活性物质层，所述负极活性物质包括负极活性材料；其中，所述集流体的拉伸强度记为σ，所述负极活性材料的Dv50记为T，所述负极片的面密度记为cw，电池放电至0％ SOC时负极片的空电厚度记为H，σ、T、cw和H满足如下关系式：
σ>(H/T+1.8*cw)*10，
σ的单位为Mpa，T的单位为μm，cw的单位为mg/cm2，H的单位为μm。
σ>(H/T+1.8*cw)*10中，计算该关系式时不考虑单位，例如σ为350Mpa，T为11.2μm，cw为6.45mg/cm2，H为101μm时，(H/T+1.8*cw)*10＝(101/11.2+1.8*6.45)*10＝206，满足350>206，即σ>(H/T+1.8*cw)*10。
本公开研究发现负极片中，集流体拉伸强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式时，即优化负极材料的粒径与集流体的选择，能保证负极片的能量密度能最大程度的发挥，同时也能保证负极片的尺寸不会在工作中出现较大的变化，提升负极片的稳定性。
在一些实施方式中，“0％SOC”指的是电池0.5C恒流放电，达到放电截止电压2.75V的状态；或者“0％SOC”指的是电池完成0.5C恒流放电步骤后的状态，且恒流放电步骤的截止电压为2.75V。
优选地，σ、T、cw和H满足如下关系式：σ>(H/T+1.8*cw)*15。进一优化集流体拉伸强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足的关系式，可以使集流体拉伸强度更高，更有效减缓集流体的延展，更好地提高负极片的稳定性，使电池保持在更好的工作状态。
在一些实施方式中，所述集流体的拉伸强度σ>300Mpa，优选σ≥400Mpa，更优选σ为400Mpa-800Mpa。例如，集流体的拉伸强度σ可以为400Mpa、500Mpa、600Mpa、700Mpa、800Mpa或上述两两点值组成范围中的任意点值。
负极活性物质涂布在集流体上，集流体的拉伸强度对负极片和电池的性能也有一定的影响。负极涂膏(即负极活性物质)，尤其是含有硅基材料时，在脱嵌锂的过程中会产生较大的膨胀，也是制约硅基材料在负极活性物质中大比例使用的主要原因。充电过程中，负极活性材料嵌锂膨胀，在高压实，高面密度的极片中，负极活性材料之间的间隙较小，膨胀难以释放，最终传递到集流体，带着集流体一起延展；放电过程中，负极活性材料脱锂，膨胀退去，负极活性材料位置回到原位，但是集流体延展无法恢复，造成了材料和集流体之间的相对位移，在反复的充放电过程中，集流体带着极片慢慢延展，不仅会挤压电芯最外层的膜壳，还会造成活性物质与集流体的相对位移，接触变差，最终影响电芯的性能。因此，本公开中集流体的拉伸强度在上述范围时，能够避免集流体的过度延展造成对电芯外壳角位和边缘的挤压以及活性物质与集流体接触问题，即活性物质材料与集流体的相对位移减少，从而减少活性物质从集流体上松动、脱落的风险，在长期循环过程中也能保证负极与集流体紧密接触，降低电池在循环过程中的阻抗和极化。使电池极片有较高的容量和能量密度的同时，也能有效减缓集流体的延展，使电池保持在良好的工作状态。
进一步地，在负极片中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式的基础上，进一步限定集流体的拉伸强度在上述范围时，能够更有效的减缓集流体的延展，降低电池在循环过程中的阻抗和极化，提高电池的循环稳定性能。
在一些实施方式中，所述负极活性材料的Dv50(T)为5μm-20μm，优选为6μm～15μm。例如，负极活性材料的Dv50可以为5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm或上述两两点值组成范围中的任意点值。负极片是由负极活性物质材料在集流体上堆积而成，材料与材料之间存在间隙，为了使负极片有较高的面密度和压实密度，活性物质材料的粒径在上述限定合适的范围内，保证极片有良好的保液性，降低了电荷转移阻抗，同时材料之间保持良好的电子电导，电池的整体电性能包括循环性能和充放电性能更优。
进一步地，在负极片中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式的基础上，进一步限定负极活性材料的Dv50在上述范围时，使负极片具有更好地保液性，能够更好地提升电池的循环性能和充放电性能。
在一些实施方式中，所述空电厚度H为50μm-200μm，优选为70μm-110μm。例如空电厚度H可以为50μm、60μm、70μm、80μm、90μm、100μm、110μm、120μm、130μm、140μm、150μm、160μm、170μm、180μm、190μm、200μm或上述两两点值组成范围中的任意点值。
在一些实施方式中，所述负极片的面密度cw为3mg/cm2-18 mg/cm2，优选为5mg/cm2-15mg/cm2。负极片的面密度例如可以为3mg/cm2、5mg/cm2、6mg/cm2、7mg/cm2、8mg/cm2、9mg/cm2、10mg/cm2、11mg/cm2、12mg/cm2、13mg/cm2、15mg/cm2、16mg/cm2、18mg/cm2或上述两两点值组成范围中的任意点值。
进一步地，负极片的面密度、空电厚度和负极活性材料的粒径在上述范围时，能够提高电芯的容量和能量密度，减少极片变脆和易断裂的风险，提升负极片与电解液浸润性，减少离子迁移阻抗变大和极化变大等问题。
进一步地，在负极片中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式的基础上，进一步限定负极片的面密度、空电厚度和负极活性材料的粒径在上述范围时，能够进一步提高电芯的容量和能量密度，提升负极片的稳定性，提升电池的循环稳定性。
在一些实施方式中，所述负极活性材料包括硅基材料和碳基材料；所述硅基材料的Dv50记为A，所述碳基材料的Dv50记为B；A、B、σ和H满足如下关系式：σ＞0.1*H*(1.5A+B)，A的单位为μm，B的单位为μm。
σ＞0.1*H*(1.5A+B)中，计算该关系式时不考虑单位，例如σ为350Mpa，H为101μm时，A为7.6μm，B为12.3μm时，0.1*H*(1.5A+B)＝0.1*101*(1.5*7.6+12.3)＝239。350＞239，即满足σ＞0.1*H*(1.5A+B)。
硅基材料和碳基材料级配，涂布在集流体上，不同的粒径影响堆积的紧密程度，从而影响极片的孔隙率、电阻率等物理性能，同时负极活性材料的大小与级配和集流体的相互配合也影响了极片的延展、柔韧性、表面外观等。当硅基材料的粒径、碳基材料的粒径、集流体的拉伸强度和负极片的空电厚度满足关系式σ＞0.1*H*(1.5A+B)时，极片具备了合适的粒径、压实密度以及合适强调的集流体搭配，此时负极片的性能更好，集流体上涂布的活性物质对极片的延展影响最小。
在一些实施方式中，硅基材料的Dv50(A)为5μm～14μm，优选为7μm～10μm。例如硅基材料的Dv50可以为5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm或上述两两点值组成范围中的任意点值。硅基材料在充放电过程中会经历体积变化，Dv50过大的硅基材料可能会导致材料之间的间隙过大，影响电池的稳定性。硅基材料的粒径在上述范围时可以减小体积变化对电池结构的影响，而且可以使更多的负极活性材料表面参与电化学反应，提高负极活性材料的利用率，从而提高电池的能量密度。
在一些实施方式中，碳基材料的Dv50(B)为7μm～20μm，优选为8μm～12μm。例如碳基材料的Dv50可以为7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm或上述两两点值组成范围中的任意点值。碳基材料的粒径在上述范围时，可以缩短锂离子在负极活性材料内部的扩散路径，提高锂离子的扩散速率，从而提高电池的充放电速度和循环性能。
上述负极活性物质材料的粒径、硅基材料的粒径和碳基材料的粒径均使用马尔文激光粒度测试仪测试粒径分布获得。
在一些实施方式中，硅基材料的Dv50与碳基材料的Dv50的比值A/B＝0.3～1，优选为A/B＝0.5～0.9。例如A/B的比值可以为0.3、0.4、0.45、0.5、0.55、0.6、0.65、0.7、0.75、0.8、0.88、0.92、1或上述两两点值组成范围中的任意点值。
硅基材料的Dv50、碳基材料的Dv50二者的比值在上述范围时，能够使硅基材料与碳基材料堆积的更加紧密，硅基材料填补在碳基材料间较大的空隙中，提升空间的使用率，同时碳基材料能够更好的包裹在硅基材料的四周，和导电剂一起形成良好的导电网络，有效降低极片的面电阻；同时保留一些较小的孔隙，供电解液填充，保证锂离子的脱嵌，也给硅基材料在脱嵌锂过程的膨胀预留适当的空间，提升了电池的循环性能和充放电性能。
进一步地，在负极片中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式的基础上，进一步限定A/B的比值在上述范围时，能够使在长期循环过程中负极材料与集流体紧密接触，既可以更有效地提高极片的稳定性，又能提升电池的循环性能和充放电性能。
在一些实施方式中，所述负极活性物质中，所述硅基材料的质量占比为1％～50％，优选为3％-20％，例如可以为1％、5％、10％、15％、20％、25％、30％、35％、40％、45％、50％或上述两两点值组成范围中的任意点值。硅基材料的质量占比在上述范围内的负极片，一方面，添加适量的硅基材料能提升活性物质的克容量，提升电池的能量密度，另一方面和硅基材料和碳基材料搭配能降低极片循环过程中的膨胀，同时适量的碳基材料能提升极片的电子电导率，降低电池的阻抗。
进一步地，在负极片中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式的基础上，进一步限定硅基材料的质量占比，既可以降低极片循环过程中的膨胀，减缓集流体的延展，提高负极片的稳定性，又能提升电池的能量密度。
在一些实施方式中，所述硅基材料中，硅元素的质量占比为40～100％，优选为40-60％，更优选为45-55％，例如可以为40％、50％、60％、70％、80％、90％、100％或上述两两点值组成范围中的任意点值。硅基材料主要作用是提升能量密度，但是直接使用会造成电池膨胀过大，电池循环容量衰减等问题，同时其电导率较低，阻抗较大。因此需要改性，硅元素含量维持在40～100％范围内，既能保证硅基材料具有较高的克容量，又能通过一些改性手段例如气相沉积、包覆、合金化、纳米化等保证硅基材料的稳定性和提升电导率。
进一步地，在负极片中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式的基础上，进一步限定硅基材料中，硅元素的质量占比在上述范围时，能够进一步提升极片的稳定性，以及提升电池的能量密度。
在一些实施方式中，所述硅基材料的粉末电阻率为5Ω*cm～100Ω*cm，优选为6Ω*cm～50Ω*cm，更优选为10Ω*cm～30Ω*cm，例如可以为5Ω*cm、10Ω*cm、20Ω*cm、30Ω*cm、40Ω*cm、50Ω*cm、60Ω*cm、70Ω*cm、80Ω*cm、90Ω*cm、100Ω*cm或上述两两点值组成范围中的任意点值。硅基材料的粉末电阻率使用粉末电阻测试仪，粉末压力16kN。硅基材料的粉末电阻率在上述范围时，可以提高负极片内部的电导率，从而提高电池的整体性能，包括充放电速度和循环性能。
进一步地，在负极片中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足上述关系式的基础上，进一步限定硅基材料的粉末电阻率在上述范围时，集流体可以在硅基材料与电解质之间形成良好的界面，有助于提高电池的电荷传输效率和电化学性能，进一步优化电池的性能。
在一些实施方式中，硅基材料为适用于电池负极的含硅元素的材料，例如所述硅基材料包括硅碳、硅氧、纳米硅、硅合金中的至少一种。
在一些实施方式中，所述硅碳材料中，硅相材料分布在碳骨架中。碳骨架可以提供良好的导电性、结构稳定性和弹性，有助于缓解硅材料的膨胀问题，并提高材料的循环稳定性和电化学性能。
在一些实施方式中，碳基材料为适用于电池负极的含碳元素的材料，例如所述碳基材料包括人造石墨、天然石墨、中间相炭微球、硬炭、软炭中的至少一种。
在一些实施方式中，所述集流体包括铜箔。在一些实施方式中，所述集流体的厚度为3μm～20μm，例如可以为3μm、5μm、8μm、10μm、12μm、14μm、15μm、16μm、18μm、20μm或上述两两点值组成范围中的任意点值。负极集流体的厚度直接影响电池的重量和体积，集流体的厚度限定在上述范围内可以减轻电池重量，减小电池体积，从而提高电池的能量密度。
在一些实施方式中，所述负极片的孔隙率为15％～50％，优选为18％～35％，更优选为19％～28％，例如孔隙率可以为15％、18％、20％、23％、25％、30％、35％、38％、40％、42％、45％、49％、50％或上述两两点值组成范围中的任意点值。负极片的孔隙率是指负极片中负极活性材料堆积时材料之间的间隙，反应了材料之间堆积的紧密程度，从而对电池性能造成影响。负极片的孔隙率越小，极片的吸收电解液的性能就会越差，电解液越难以浸润，材料的比容量发挥较低，电池的保液能力较差，同时会造成锂离子迁移的阻抗增大，电池循环过程中极化就大，衰减就会较大，内阻增加也尤为明显。相反负极片的孔隙率过大，材料之间的空隙太大，负极活性材料连接不够紧密，会降低活性材料物之间的电子电导，导致极片面电阻变大，提升电池的欧姆内阻，增大电池的阻抗。负极片的孔隙率在上述范围时，极片孔隙率适当，有良好的保液性，降低了电荷转移阻抗，同时负极活性材料之间保持良好的电子电导，电池的整体电性能包括循环性能和充放电性能更优。
在一些实施方式中，所述负极片的压实密度为1mg/cm3～2.5mg/cm3，例如可以为1mg/cm3、1.1mg/cm3、1.2mg/cm3、1.3mg/cm3、1.4mg/cm3、1.5mg/cm3、1.6mg/cm3、1.7mg/cm3、1.8mg/cm3、1.9mg/cm3、2mg/cm3、2.3mg/cm3、2.5mg/cm3或上述两两点值组成范围中的任意点值。极片经过辊压后，其压实密度与极片的性能息息相关，压实密度越大的极片具有越小的厚度，能保证极片有更好的导电性以及电池有更高的能量密度，但是过大的压实密度，在制程上会造成粘辊，外观不良，极片柔韧性下降等一系列问题，在电池性能上会导致极片电解液浸润困难，电池容量下降等问题。因此负极压实密度在上述范围时可以增大电池的能量密度，减小内阻，减小极化损失，延长电池的循环寿命。
进一步第，同时满足负极片的压实密度和孔隙率在上述范围时，能提升电池的能量密度或者倍率性能，同时又能有一定的空间释放硅基材料的膨胀。
在一些实施方式中，所述负极片的延展率为1‰～6.5‰，例如可以为1‰、2‰、2.5‰、3‰、3.5‰、4‰、4.5‰、5‰、5.5‰、6‰、6.5‰或上述两两点值组成范围中的任意点值，优选2‰～6‰。负极片的延展率在上述范围时，可以保证负极片在充放电过程中的结构稳定性，优化负极活性材料间的接触，减少负极活性材料破裂和粉化，从而提高电池的循环寿命。
在一些实施方式中，所述负极活性物质层还包括增稠剂、粘结剂和导电剂。例如所述增稠剂包含羧甲基纤维素、羧甲基纤维素钠、海藻酸钠、瓜尔胶、黄原胶、壳聚糖中的至少一种；所述粘结剂包含聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶和聚偏氟乙烯中的至少一种；所述导电剂包含导电炭黑、碳纳米管、碳纤维和科琴黑中的至少一种。
本公开第二方面提供了一种电池，所述电池包括本公开第一方面所述的负极片，正极片和电解液。
本公开提供的电池，由于包含上述的负极片，该电池具有循环性能良好、充放电性能良好，以及较高的能量密度等优点。
在一些实施方式中，所述电解液包括非水性有机溶剂、电解质锂盐和添加剂。
对非水性有机溶剂不做特别的限定，可以选择本领域常规的使用的有机溶剂，例如碳酸酯和/或羧酸酯。在有机溶剂为多种溶剂的混合物时，各个溶剂之间可以任意比例混合。
在一些实施方式中，所述非水性有机溶剂包括羧酸酯，优选地，羧酸酯的质量占比为5～50％，例如可以为5％、10％、15％、20％、25％、30％、35％、40％、45％、50％或上述两两点值组成范围中的任意点值。有机溶剂中加入羧酸酯，并限定羧酸酯的质量占比在上述范围时，能降低电解液的粘度，提升电解液的离子传输效率，提升了电池的动力学性能，动力学较高的电解液能确保含硅基材料的负极片有更大的压实和面密度，在负极材料较小的空隙间填充的电解液也能维持电池中的电化学系统的稳定。
进一步地，高拉伸强度的集流体抑制了循环过程中负极活性材料颗粒膨胀导致的极片延展，维持负极活性材料颗粒间较小的间隙时，与高动力学的电解液组合时，可以更好地维持锂离子的正常脱嵌，提高电池循环稳定性。
在一些实施方式中，所述羧酸脂包括甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、丁酸乙酯或己内酯中的至少一种。
对电解质锂盐不做特别的限定，可以选择本领域常规的使用的锂盐，例如电解质盐包括但不限于六氟磷酸锂、二氟磷酸锂、二氟草酸硼酸锂、双氟磺酰亚胺锂、双三氟甲基磺酰亚胺锂、二氟双草酸磷酸锂、四氟硼酸锂、双草酸硼酸锂、六氟锑酸锂、六氟砷酸锂、二(三氟甲基磺酰)亚胺锂、二(五氟乙基磺酰)亚胺锂、三(三氟甲基磺酰)甲基锂、二(三氟甲基磺酰)亚胺锂中的至少一种。
对添加剂不做特别的限定，可以选择本领域中的负极成膜添加剂和/或正极成膜添加剂。例如，负极成膜添加剂包括碳酸亚乙烯酯(VC)、乙烯基碳酸乙烯酯(VEC)等；正极成膜添加剂包括硫酸乙烯酯(DTD)，1,3-丙烷磺内酯(PS)、1,3-丙烯磺酸内酯(PST)等。
在一些实施方式中，所述添加剂包括氟代碳酸乙烯酯(FEC)。优选地，所述电解液中，氟代碳酸乙烯酯的质量占比为1～20％，例如可以为1％、3％、5％、8％、10％、12％、15％、18％、20％或上述两两点值组成范围中的任意点值。在电解液中加入成膜添加剂FEC，并限定FEC的质量占比在上述范围时，FEC能在硅基材料表面形成厚度适当的固态电解质界面，保证硅基材料的稳定。
进一步地，的FEC添加剂在上述范围时能确保硅基材料不会在脱嵌锂的过程中不停的消耗电解液，与高拉伸强度的集流体组合使用时，可以保证硅基材料相对位置不会轻易改变，保证了硅基材料和邻近周边环境的稳定，有利于降低硅膨胀对于集流体的影响，提升极片的稳定性，提高电池的循环性能。
在一些实施方式中，正极片包括正极材料，所述正极材料包括钴酸锂。
在一些实施方式中，所述的电池为软包电池，
在一些实施方式中，所述电池为锂离子二次电池
下面将结合本公开实施例，对本公开实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅是本公开一部分实施例，而不是全部的实施例。基于本公开中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本公开保护的范围。
下述实施例中所用的材料、试剂等，如无特殊说明，均可从商业途径得到。
下面结合具体实施例详细描述本公开，这些实施例用于理解而不是限制本公开。
实施例和对比例的电芯均按照下述制备方法进行制备，具体区别如表1所示。
实施例1-1
(1)正极片制备：将钴酸锂、导电炭黑、碳纳米管、PVDF以质量比95:1:1.5:2.5的比例在NMP中搅拌成浆料，在铝箔(厚度为9μm)上涂布、干燥、辊压、裁切、焊极耳、贴胶纸制备成正极片。
(2)负极片制备：将硅碳材料和石墨按照质量比1:9混合获得负极活性材料(硅基材料的Dv50记为A，碳基材料的Dv50记为B，负极活性材料的Dv50记为T)，导电炭黑、CMC、SBR按照质量比96:1:1.5:1.5混合，加入去离子水制备成浆料，涂布在高强度铜箔(拉伸强度记为σ，厚度为6μm)上，面密度记为cw，干燥、辊压、裁切、焊极耳、贴胶纸制备成负极片。
(3)电解液制备：配制碳酸酯类溶剂：碳酸乙烯酯(EC)：碳酸二乙酯(DEC)＝3:7(重量比)，再加入乙酸甲酯与碳酸酯溶剂的比例为2:8，乙酸甲酯(羧酸酯)的质量占比为20％，添加1mol/L的六氟磷酸锂，添加占总质量5％的FEC和其他添加剂PS占总质量2％。
(4)隔膜：使用PP基膜，厚度15μm。
(5)将正负极片用隔膜隔开，卷绕成卷芯，再封装在铝塑膜壳中，经过烘烤、注液、化成、二封制备成电芯。
实施例1组-实施例6组，以及对比例1-5中，具体不同特征如表1所示。
表1


注：“*”表示该实施例或对比例中的对应参数与实施例1-2中的相同。
实施例7组
参照实施例1-2进行，不同之处在于调整电解液中羧酸酯的质量占比，且FEC质量占比为10％，具体如下：
实施例7-1：乙酸甲酯的质量占比为5％；
实施例7-2：乙酸甲酯的质量占比为20％；
实施例7-3：乙酸甲酯的质量占比为40％；
实施例7-4：不加乙酸甲酯。
实施例8组
参照实施例1-2进行，不同之处在于调整电解液中中FEC的质量占比，且乙酸甲酯的质量占比为20％，具体如下：
实施例8-1：FEC的质量占比为6％；
实施例8-2：FEC的质量占比为13％；
实施例8-3：FEC的质量占比为20％；
实施例8-4：不加FEC。
上述实施例和对比例中负极片和电池通过如下测试方法进行电化学性能测试：
(1)负极片铜箔强度：将箔材裁切成15mm±0.2mm的小条，使用WD-D3型电子万能试验机，上下夹具间隙50mm，将箔材两端分别夹在夹具中，使用100mm/min的速度开始测试，直到设备停止测试，并记录断裂强度σ。测试3次误差不超过10％，取平均值。
(2)粒径Dv50测试：使用马尔文激光粒度测试仪测试粒径分布。
(3)极片面密度测试，将极片裁切出15.0425cm2的面积，称量重量，去除涂覆层后再称量集流体的重量，两次重量相减，再除以裁切面积。
(4)极片空电厚度H：使用离子研磨设备制备空电极片(电池0.5C放电到2.75V，静置1min，100mA放电到2.75V,拆解电池后取极片)的截面样品，在SEM下测试极片的厚度，精度0.1μm。
(5)硅基材料中硅元素含量测试：使用离子研磨机截取负极片的截面，使用扫描电子显微镜能谱仪，放大倍率选择5kx～10kx(根据材料大小选择)，找到硅基材料的截面位置，在截面中间点扫收集元素含量信息。取10个样品，排除偏差较大的样品后取平均值。
(5)硅基材料的粉末电阻率：使用粉末电阻测试仪，粉末压力16kN。
(6)电解液成分使用气象色谱仪测试，测试其中羧酸酯和FEC的含量。
(7)极片延展测试：25℃恒温循环，1C恒流充电至4.5V，4.5V恒压充电至0.2C，0.7C放电至3V。循环测试500圈后将电池电量放电至3V，解剖电池，使用2.5D显微测试仪测试极片的宽度，双面空箔区离涂膏最远的极片宽度记为S1，极片涂膏区宽度记为S2。极片延展率为(S2-S1)/S1。测试5个值取平均值。
(8)电池能量密度：电池能量测试：使用新威电池测试仪，0.2C充电至上限电压(截止0.02C)/0.2C放电至下限电压，重复3次，取第3次的放电能量为电芯能量Q。使用2.5D显微测试仪测试电芯的宽度W和高度H，使用PPG厚度测试仪测试电芯的满电厚度L，则能量密度为Q/(W*H*L)。
(9)膨胀率：测试初始电芯满电厚度记为H1，1C/1C充放电测试200T，记录电芯循环后满电的厚度为H2。膨胀率＝(H2-H1)/H1*100％。
(10)恒流充入比:电池的充电制度为1C恒流充电至4.5V，此时充电容量记为Q1，然后4.5V恒压充电至截止电流0.05C，此时充电容量记为Q2。恒流充入比为Q1/(Q1+Q2)*100％。
(11)200圈循环容量保持率：1C/1C充放电测试200T，第一圈的放电容量记为Qa，第200圈的放电容量记为Qb，容量保持率为Qb/Qa。
(12)孔隙率测试方法：裁切极片，面积大于0.1㎡或者重量大于3g，测量裁切极片的厚度，并记录厚度数据。折叠后将极片放入样品杯中，使用真密度仪测试极片真实体积V0，计算极片的表观体积V1＝实测极片厚度*极片长度*极片宽度，样品孔隙率＝(V1-V0)/V1*100％。
上述极片或电池的性能测试后的结果记录于表2。
表2

由表2可以看出，本公开中集流体强度、极片空电厚度、涂布面密度以及负极活性材料的粒径满足σ>(H/T+1.8*cw)*15关系式时，能保证极片的能量密度能最大程度的发挥，同时也能保证极片的尺寸不会在工作中出现较大的变化，提升极片的稳定性。
实施例1-1的负极片的SEM图如图1所示，显示了辊压后负极片的形貌。其中较亮的颗粒为硅基材料，较暗的颗粒为碳基材料，硅基材料分散在碳基材料中，极片经过辊压后，颗粒之间存在细微的空隙。实施例3-1中，硅基材料的体积粒径分布图如图2所示，其中显示硅基材料的Dv50约为7.6μm。
需要说明的是，在本文中，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法、物品或者装置不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法、物品或者装置所固有的要素。在没有更多限制的情况下，由语句“包括一个……”限定的要素，并不排除在包括该要素的过程、方法、物品或者装置中还存在另外的相同要素。此外，需要指出的是，本申请实施方式中的方法和装置的范围不限按示出或讨论的顺序来执行功能，还可包括根据所涉及的功能按基本同时的方式或按相反的顺序来执行功能，例如，可以按不同于所描述的次序来执行所描述的方法，并且还可以添加、省去、或组合各种步骤。另外，参照某些示例所描述的特征可在其他示例中被组合。
以上所述仅为本公开的较佳实施例而已，并不用以限制本公开，凡在本公开的精神和原则之内，所作的任何修改、等同替换等，均应包含在本公开的保护范围之内。

Claims (15)

  1. 一种负极片，其特征在于，所述负极片包括集流体和设置于所述集流体至少一侧表面的负极活性物质层，所述负极活性物质包括负极活性材料；其中，所述集流体的拉伸强度记为σ，所述负极活性材料的Dv50记为T，所述负极片的面密度记为cw，电池放电至0％SOC时负极片的空电厚度记为H，σ、T、cw和H满足如下关系式：
    σ>(H/T+1.8*cw)*10，
    σ的单位为Mpa，T的单位为μm，cw的单位为mg/cm2，H的单位为μm。
  2. 根据权利要求1所述的负极片，其特征在于，H，σ、T、cw和H满足如下关系式：σ>(H/T+1.8*cw)*15。
  3. 根据权利要求1或2所述的负极片，其特征在于，σ>300Mpa，优选σ≥400Mpa，更优选σ为400Mpa～800Mpa；
    和/或，H为50μm～200μm；
    和/或，T为5μm～20μm，优选为6μm～15μm；
    和/或，cw为3mg/cm2～18mg/cm2，优选为5mg/cm2～15mg/cm2。
  4. 根据权利要求1-3任一项所述的负极片，其特征在于，所述负极活性材料包括硅基材料和碳基材料；所述硅基材料的Dv50记为A，所述碳基材料的Dv50记为B；A、B、σ和H满足如下关系式：
    σ＞0.1*H*(1.5A+B)，
    A的单位为μm，B的单位为μm。
  5. 根据权利要求4所述的负极片，其特征在于，A为5μm～14μm；
    和/或，B为7μm～20μm。
  6. 根据权利要求4或5所述的负极片，其特征在于，A和B满足：A/B＝0.3～1，更优选A/B＝0.5～0.9。
  7. 根据权利要求4-6任一项所述的负极片，其特征在于，所述负极活性物质中，所述硅基材料的质量占比为1％～50％。
  8. 根据权利要求4-6任一项所述的负极片，其特征在于，所述硅基材料中，硅元素的质量占比为40～100％。
  9. 根据权利要求4-6任一项所述的负极片，其特征在于，所述硅基材料的粉末电阻率为5Ω*cm～100Ω*cm。
  10. 根据权利要求1-9任一项所述的负极片，其特征在于，所述硅基材料包括硅碳、硅氧、纳米硅、硅合金的至少一种；
    优选地，所述硅碳材料中，硅相材料分布在碳骨架中；
    和/或，所述碳基材料包括人造石墨、天然石墨、中间相炭微球、硬炭、软炭中的至少一种。
  11. 根据权利要求1-10任一项所述的负极片，其特征在于，所述负极片的孔隙率为15％～50％；
    和/或，所述负极片的压实密度为1mg/cm3～2.5mg/cm3；
    和/或，所述负极片的延展率为1‰～6.5‰。
  12. 一种电池，其特征在于，所述电池包括权利要求1-11任一项所述的负极片。
  13. 根据权利要求12所述的电池，其特征在于，所述的电池还包括电解液，所述电解液包括非水性有机溶剂；
    优选地，所述非水性有机溶剂包括羧酸酯类；
    优选地，所述非水性有机溶剂中，羧酸酯的质量占比为5～50％。
  14. 根据权利要求13所述的电池，其特征在于，所述羧酸脂包括甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、丁酸乙酯或己内酯中的至少一种。
  15. 根据权利要求12-14任一项所述的电池，其特征在于，所述的电池还包括电解液，所述电解液包括添加剂；
    优选地，所述添加剂包括氟代碳酸乙烯酯；
    优选地，所述电解液中，氟代碳酸乙烯酯的质量占比为1～20％。
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