WO2023185743A1 - 电极极片、二次电池与终端设备 - Google Patents

电极极片、二次电池与终端设备 Download PDF

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Publication number
WO2023185743A1
WO2023185743A1 PCT/CN2023/084116 CN2023084116W WO2023185743A1 WO 2023185743 A1 WO2023185743 A1 WO 2023185743A1 CN 2023084116 W CN2023084116 W CN 2023084116W WO 2023185743 A1 WO2023185743 A1 WO 2023185743A1
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Prior art keywords
layer
sub
active
active particles
particles
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PCT/CN2023/084116
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English (en)
French (fr)
Inventor
田雷雷
宋晓娜
吴仪岚
昝永祥
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华为技术有限公司
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Priority claimed from CN202211641999.9A external-priority patent/CN116895741A/zh
Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Publication of WO2023185743A1 publication Critical patent/WO2023185743A1/zh

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    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids

Definitions

  • This application relates to the field of batteries, and specifically to an electrode pole piece, a secondary battery and a terminal device.
  • the electrode plates of lithium-ion batteries are usually composed of a current collector and an active material layer coated on the surface of the current collector.
  • the stacking structure, compaction density, thickness impedance, etc. of the electrode plates are carefully designed to improve the energy density, charge and discharge rate, cycle life and safety performance of the battery. Achieve balance and comprehensive optimization.
  • the energy density of a battery can be increased by increasing the thickness of the active material layer in the electrode plates.
  • the battery energy density can be increased by 2.8%.
  • the roller pressure required in the process of preparing the active material layer will be increased to obtain a sufficiently dense active material layer.
  • the pressure on the surface of the active material layer away from the current collector will increase significantly. Therefore, the surface particles of the active material layer are easily cracked due to the stress concentration in the surface micro-areas. The increased side reactions between the ruptured active material particles and the electrolyte will significantly reduce the overcharge resistance of the electrode plates and reduce the safety performance of the electrode plates and the battery.
  • This application provides an electrode plate, a secondary battery and a terminal device to improve the anti-fracturing performance of the active material layer in the electrode plate.
  • the present application provides an electrode piece, which includes a current collector and an active material layer coated on at least one side surface of the current collector.
  • the active material layer includes a first sub-layer and a second sub-layer arranged in a stack, and the second sub-layer is provided between the first sub-layer and the current collector.
  • the first sub-layer contains first active particles
  • the second sub-layer contains second active particles
  • the anti-fracturing performance of the first active particles is better than the anti-fracturing performance of the second active particles.
  • the active material layer of the electrode pole piece of the present application includes two stacked sub-layers, a first sub-layer and a second sub-layer.
  • the second sub-layer is located between the first sub-layer and the current collector.
  • the first sub-layer contains first active particles
  • the second sub-layer contains second active particles
  • the anti-fracturing performance of the first active particles is better than the anti-fracturing performance of the second active particles.
  • the compressive stress exerted on the particles of the second sub-layer due to the anti-fracturing protection of the first sub-layer and the pressure transmitted from the first sub-layer to the second sub-layer is dispersed by the inter-particle transmission of the first sub-layer will become smaller, so the second active particles can also be protected during the rolling process. Therefore, using the electrode pole piece with the structure of the present application, that is, the thickness of the active material layer Thickening can also effectively protect the active particles of the active material layer from being crushed during the rolling process, thereby maintaining high safety and overcharge resistance for the electrode plates and secondary batteries.
  • the anti-fracturing performance of the first active particles is better than the anti-fracturing performance of the second active particles, including: before and after 200 MPa pressure, the ratio of the first active particles The change value of the surface area is less than or equal to 15%; before and after the pressure of 200 MPa, the change value of the specific surface area of the second active particles is greater than 15%.
  • the change value of the specific surface area of the first active particles before and after 200MPa pressure is less than or equal to 15%. Therefore, the first active particles can have higher anti-fracturing strength, and thus can avoid fracturing during the rolling process. Reduce the probability of side reactions occurring during the charging and discharging process of the first active particles. Due to the anti-fracturing protection of the first sub-layer, and the pressure transmitted from the first sub-layer to the second sub-layer is dispersed by the inter-particle transmission of the first sub-layer, the compressive stress borne on the particles of the second sub-layer will become smaller. Therefore, the second active particles are allowed to have relatively low anti-fracturing strength.
  • the change in the specific surface area of the second active particles can be greater than 15%.
  • the second active particles can obtain lower impedance while having lower anti-fracturing strength to increase the lithium removal/insertion reaction rate of the second sub-layer and reduce the difference in reaction rates between the inside and outside of the active material layer due to the increase in thickness. , balancing the reaction rates throughout the active material layer, thereby avoiding safety risks such as reduced charge and discharge rate performance of the electrode piece and overcharge/overdischarge of the surface layer due to excessive differences in reaction rates between the inner and outer layers of the active material layer.
  • the anti-fracturing performance of the first active particles is better than the anti-fracturing performance of the second active particles, including: the first active particles and the second active particles.
  • the number of cracks appearing in the first active particles is less than the number of cracks appearing in the second active particles.
  • the magnification of the SEM image is 2000 to 10000 times.
  • the median particle diameter D50 of the second active particles is greater than the median particle diameter D50 of the first active particles.
  • the lithium removal/insertion reaction is active Different active material layers. Since among the active materials, the impedance of the active material with large particles is relatively low, and the impedance of the active material with small particles is relatively high, therefore, by arranging the second sub-layer with relatively larger particle size in the second sub-layer arranged close to the current collector, Two active particles, and arranging first active particles with relatively small particle sizes in the first sub-layer located away from the current collector can reduce the impedance difference of the active material layer in its thickness direction and balance the delithiation of the entire active material layer. / The chemical reaction of lithium embedding can further avoid the safety problems of reduced charge and discharge rate performance of the electrode pole piece and overcharge/overdischarge of the surface layer due to the excessive difference in reaction speed between the inner and outer layers of the active material layer.
  • the median particle diameter D50 of the first active particles is ⁇ 5 ⁇ m.
  • the first active particles can have higher anti-fracturing strength.
  • the first active particles are single crystal particles or single crystal-like particles.
  • the first sub-layer can have higher impedance, reduce the polarization between the first sub-layer and the second sub-layer, and slow down the degeneration of the first sub-layer. /Lithium insertion reaction rate, balancing the reaction rate difference between the first sub-layer and the second sub-layer.
  • At least one of the first sub-layer and the second sub-layer contains a thermal dispersion material.
  • the thermal dispersion material can be provided separately in the first sub-layer or separately in the third sub-layer. Among the two sub-layers, it can also be provided in the first sub-layer and the second sub-layer at the same time.
  • the first sub-layer contains the heat dispersion material.
  • the heat dispersion material includes one of a heat-absorbing material and a heat-conducting material.
  • Thermal dispersion materials are heat-absorbing materials or heat-conducting materials set in some areas of the electrode plates to quickly disperse the heat generated by the electrode plates, eliminate local overheating in micro-areas on the surface of the electrode plates, and avoid local overheating. Heat causes heat accumulation and thermal runaway inside the battery.
  • the heat-absorbing material may be a material that undergoes phase change or chemical reaction in a temperature range of 100 to 350°C to absorb heat.
  • the heat-absorbing material includes at least one of boehmite, magnesium oxyhydroxide, aluminum oxyhydroxide, aluminum hydroxide, magnesium hydroxide or silicon oxyhydroxide.
  • the thermally conductive material may be a material with a thermal conductivity >15W/mK.
  • the thermally conductive material includes at least one of aluminum oxide, aluminum nitride, boron nitride, diamond or silicon carbide.
  • the mass proportion of the heat-absorbing material or the heat-conducting material in the first sub-layer is 0.1% to 25%. Since the endothermic material or thermally conductive material is an inactive material that does not participate in the lithium deintercalation reaction, its mass proportion in the first sublayer and its mass proportion in the electrode pole piece need to be controlled to avoid causing The electrode plates and battery capacity density are reduced.
  • the thickness of the first sub-layer is greater than 5 ⁇ m and less than 50% of the thickness of the active material layer.
  • the thickness of the first sub-layer is too small, and the roller pressure cannot be dispersed through the inter-particle transmission and dispersion of the first sub-layer. This in turn cannot effectively improve the overall pressure resistance of the active material layer, and cannot effectively balance the internal and external reactions of the active material layer. rate. If the thickness of the first sub-layer is too large, it will affect the overall impedance of the active material layer, reduce the reactivity of the active material layer, and is not conducive to the improvement of the energy density of the electrode plate.
  • the thickness of the first sub-layer and the proportion of the thickness of the active material layer it is possible to further ensure the electrode polarity on the basis of effectively balancing the internal and external reaction rates in the thickness direction of the active material layer and improving the pressure resistance of the active material layer. achieve higher energy density.
  • the second active particles include polycrystalline particles or secondary agglomerated particles.
  • Polycrystalline particles or secondary agglomerated particles can have lower impedance, so that the second sub-layer can obtain a faster lithium removal/insertion reaction rate, reduce the impedance difference between the first sub-layer and the second sub-layer, and avoid electrode
  • the active material layer of the pole piece is overcharged or overdischarged.
  • the median particle diameter D50 of the second active particles is >10 ⁇ m.
  • the second sub-layer can have lower impedance.
  • the second sub-layer contains the first active particles.
  • the packing density of the active particles in the second sub-layer can be increased and the anti-fracturing performance can be improved.
  • the difference between the thermal decomposition temperatures of the first sub-layer and the second sub-layer is >5°C.
  • the thermal decomposition temperature of the first sub-layer is greater than the thermal decomposition temperature of the second sub-layer.
  • the first sub-layer is used to achieve thermal protection of the entire active material layer and improve the thermal stability of the active material layer.
  • the thickness of the active material layer is 50-5000 ⁇ m. Compared with the traditional single-layer uniform active material layer, in the implementation of the present application, the thickness of the active material layer can be set relatively thick, which can improve the energy density of the secondary battery.
  • the active material layers are provided on both sides of the current collector, and the structures of the two active material layers on both sides of the current collector are the same or different.
  • the data in each of the above possible implementation methods of this application such as the change value of the specific surface area, the median particle size of the first active particles, the median particle size of the second active particles, the thermal conductivity, the mass proportion, etc., are in When measuring, any value within the engineering measurement error range should be understood to be within the range limited by this application.
  • the present application provides a secondary battery.
  • the secondary battery includes a positive electrode sheet, a separator, and a negative electrode sheet. At least one of the positive electrode sheet and the negative electrode sheet is the first aspect of the present application. of electrode pole pieces.
  • the electrode plate of the first aspect of the present application can be used as a positive electrode plate of a secondary battery or as a negative electrode plate of a secondary battery.
  • both the first active particles and the second active particles in the electrode sheet are selected from the group consisting of positive active particles.
  • both the first active particles and the second active particles in the electrode pole piece are selected from the negative electrode active particles.
  • the secondary battery of the present application can be a lithium ion secondary battery, or a sodium ion secondary battery, a potassium ion secondary battery, a magnesium ion secondary battery, a zinc ion secondary battery or an aluminum ion secondary battery. .
  • the specific types of different secondary batteries are limited here, and can be selected according to the type of active material.
  • the present application provides a terminal device, which includes the secondary battery of the second aspect of the present application.
  • Terminal equipment includes but is not limited to digital equipment, electric vehicles, power storage systems, etc.
  • Figure 1 is a schematic structural diagram of an electrode pole piece according to an embodiment of the present application.
  • Figure 2 is a schematic structural diagram of an active material layer according to an embodiment
  • FIG. 3 is a schematic structural diagram of an electrode pole piece according to another embodiment of the present application.
  • Figure 4 is a schematic structural diagram of an active material layer according to another embodiment
  • Figure 5 is a schematic structural diagram of an active material layer according to another embodiment
  • Figure 6 is a schematic structural diagram of an electrode pole piece according to an embodiment
  • Figure 7 is a schematic structural diagram of an electrode pole piece according to another embodiment
  • Figure 8 is a characteristic SEM image of the first active particles of an embodiment
  • Figure 9 is a characteristic SEM image of the second active particles of an embodiment.
  • 21-First active particles 22-Second active particles; 23-Thermal dispersion material.
  • the electrode plates are mainly composed of a current collector and an active material layer coated on the surface of the current collector.
  • a certain roller pressure needs to be applied to the formed active material slurry layer to increase the compaction density of the active material layer.
  • the roller pressure applied on the surface of the active material layer is not enough to crush the active particles in the active material layer.
  • the required roller pressure also gradually increases to obtain the required compaction density.
  • the pressure exerted on the outer surface of the active material layer is much greater than the pressure on the inner surface of the active material layer. Therefore, during the rolling process, the active particles on the outer surface of the active material layer are easily ruptured under high pressure. After the active particles rupture, the passivation layer on the surface will crack.
  • the internal active material is in direct contact with the electrolyte, thereby aggravating the side reactions between the active material layer and the electrolyte, and reducing the safety of the electrode plates and secondary batteries.
  • the surface layer of the active material layer of the electrode plate reacts first, when the thickness of the active material layer is thicker, there will be a certain difference in the degree of reaction between the surface layer and the inner layer close to the current collector.
  • the inner layer of the active material layer reacts sufficiently, its surface layer is often in an overcharge state. Therefore, the surface layer of the active material layer often needs to withstand greater overcharge resistance.
  • the overcharge resistance of the electrode plate will be reduced, thereby reducing the safety performance of the secondary battery.
  • FIG. 1 is a schematic structural diagram of an electrode pole piece according to an embodiment of the present application.
  • the electrode plate 10 includes a current collector 11 and an active material layer 12 coated on at least one side surface of the current collector 11 .
  • the current collector 11 can be a metal foil, such as copper foil, aluminum foil, alloy foil, etc., or it can also be a polymer metal composite foil, or carbon fiber cloth, etc. The selection can be made according to the potential of the specific electrode pole piece 10 .
  • the active material layer 12 can be provided on one side surface of the current collector 11 , or can also be provided on both sides of the current collector 11 . In this embodiment of the present application, active material layers 12 may be provided on both sides of the current collector 11 .
  • FIG. 2 is a schematic structural diagram of the active material layer 12 according to an embodiment.
  • the active material layer 12 on either side of the current collector 11 may include a first sub-layer 121 and a second sub-layer 122 .
  • the first sub-layer 121 and the second sub-layer 122 are stacked.
  • the second sub-layer 122 is provided between the first sub-layer 121 and the current collector 11 .
  • electrons are connected between the first sub-layer 121 and the second sub-layer 122
  • electrons are connected between the second sub-layer 122 and the current collector 11 .
  • the first sub-layer 121 contains first active particles 21 .
  • the second sub-layer 122 contains second active particles 22 .
  • the anti-fracturing performance of the first active particles 21 is better than the anti-fracturing performance of the second active particles 22 .
  • the anti-fracturing performance can refer to the occurrence of cracks under the same pressure, the pressure endured when the same cracks occur, the pressure endured when rupture occurs, etc.
  • the situation where cracks are generated under the same pressure may include, for example, the number of cracks generated under the same pressure, the size of the cracks generated, the depth of the cracks generated, etc.
  • “better” means that the first active particles have better anti-fracturing properties than the second active particles. For example, fewer cracks will occur under the same pressure, and the pressure will be higher when the same rupture occurs.
  • the anti-fracturing performance of the first active particle is better than the anti-fracturing performance of the second active particle, including: the first active particle and the second active particle.
  • the number of cracks appearing in the first active particles is less than the number of cracks appearing in the second active particles.
  • the magnification of the SEM image is 2000 to 10000 times.
  • the first sub-layer, the first active particles, the second sub-layer and the second active particles will be described in further detail below.
  • the first active particles 21 may be positive active materials or negative active materials.
  • the first active particles 21 are positive active materials.
  • the electrode piece 10 is a negative electrode piece, the first active particles 21 are negative active materials.
  • the first active particles 21 can be, for example, lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickel cobalt manganate aluminate, lithium iron phosphate, lithium manganate, lithium nickelate, One or more of lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, and lithium-rich manganese; it can also be lithium cobalt oxide, lithium nickel cobalt manganate, and nickel modified by doping or coating with different elements.
  • lithium cobalt aluminate lithium nickel cobalt manganese aluminate, lithium iron phosphate, lithium manganate, lithium nickelate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, and lithium-rich manganese.
  • the first active particles 21 may be single crystal particles.
  • the change in the specific surface area of the first active particles 21 before and after the pressure of 200 MPa is less than or equal to 15%.
  • the change value of the specific surface area of the first active particle 21 may be 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6 %, 5%, 4% or lower, or any other value in between.
  • adding the first active particles 21 with high compressive strength can prevent the active material particles in the first sub-layer 121 from being Fracturing or crushing to improve the integrity of each active material particle in the active material layer 12, thereby improving the overcharge resistance of the active material layer 12, and the interface thermal stability of the active material layer 12, thereby improving the electrode piece 10 And the safety performance of the corresponding secondary battery.
  • the first active particles 21 when the change value of the specific surface area of the first active particles 21 before and after 200MPa pressure is less than or equal to 15%, the first active particles 21 can have higher anti-crack strength, and thus can avoid splitting during the rolling process. , reducing the probability of side reactions occurring during the charging and discharging process of the first active particles 21 .
  • the median particle diameter D50 of the first active particles 21 may be ⁇ 5 ⁇ m.
  • the median diameter of the first active particles 21 may be, for example, 4.5 ⁇ m, 4 ⁇ m, 3 ⁇ m, 2 ⁇ m, 1 ⁇ m, 0.5 ⁇ m, and any value between any two of the above values.
  • the first active particles 21 with the median diameter may have higher impedance
  • the first active particles 21 with the median diameter may have a higher impedance.
  • the first sub-layer 121 can have a high compressive strength, preventing the first active particles 21 from cracking during the rolling process, and thus preventing the first active particles 21 from cracking. occurrence of side effects.
  • the first active particles 21 are small particles with high impedance and high anti-fracturing strength.
  • the chemical reaction on the surface can be slowed down and the rolling process can be avoided.
  • Medium pressure cracks the particles on the surface of the active material layer 12, thereby avoiding side reactions of the active material layer 12 caused by exposure of the active material, and improving the safety of the electrode pole piece 10.
  • Figure 3 is a schematic structural diagram of an electrode pole piece according to another embodiment of the present application.
  • the first sub-layer 121 may also include a thermal dispersion material 23 in addition to the first active particles 21 .
  • the mass proportion of the heat dispersion material 23 in the first sub-layer 121 may be, for example, 0.1% to 25%.
  • the mass proportion of the heat dispersion material 23 in the first sub-layer 121 includes but is not limited to 0.1%, 1%, 2%, 5%, 7%, 8%, 10%, 12%, 15%, 17%, 19%, 20%, 21%, 23% or 25%, or any value between the above two values.
  • the heat dispersion material 23 may include, for example, one of a heat absorbing material and a heat conducting material.
  • the endothermic material may be a material that absorbs heat through phase change or chemical reaction within a temperature range of 100 to 350°C.
  • the endothermic material includes, but is not limited to, at least one of boehmite, magnesium oxyhydroxide, aluminum oxyhydroxide, aluminum hydroxide, magnesium hydroxide, or silicon oxyhydroxide.
  • the thermally conductive material can be a material with a thermal conductivity >15W/mK.
  • the thermally conductive material includes, but is not limited to, at least one of aluminum oxide, aluminum nitride, boron nitride, diamond or silicon carbide.
  • the heat dispersion material 23 does not participate in chemical and electrochemical reactions during the internal charging and discharging process of the battery.
  • the heat dispersion material 23 can absorb heat when the local temperature of the first sub-layer 121 rises, or dissipate the heat, quickly transfer and disperse the heat from the local heating point to the surrounding area, and reduce the temperature of the heating point of the first sub-layer 121 , eliminate local hot spots on the surface of the electrode plate 10, avoid causing heat accumulation and further thermal runaway inside the secondary battery, and improve the thermal safety performance of the electrode plate 10 and the secondary battery.
  • the second active particles 22 may be polycrystalline particles or secondary agglomerated particles formed by agglomeration of primary particles.
  • Polycrystalline particles or secondary agglomerated particles may have lower resistance to improve the reactivity of the second sub-layer 122 during charging and discharging.
  • the active material layer 12 generally includes a first surface and a second surface.
  • the first surface is disposed in close contact with the current collector 11
  • the second surface is a surface away from the current collector 11 and used for contact with the electrolyte.
  • the electrolyte or the active ions in the electrolyte are transported from the second surface of the active material layer 12 to the first surface, or from the first surface to the second surface.
  • the distance difference between the first surface and the second surface there are differences in the active materials in different parts of the active material layer 12 during the lithium removal/insertion reaction. When the thickness of the active material layer 12 is thin, this difference is not obvious.
  • the median particle diameter D50 of the second active particles 22 may be greater than the median particle diameter D50 of the first active particles 21 , and the median particle diameter D50 of the second active particles 22 may be, for example, >10 ⁇ m.
  • the median diameter D50 of the second active particles 22 may be, for example, 10 ⁇ m, 12 ⁇ m, 15 ⁇ m, 17 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m or higher, or any two values within the above range. .
  • Selecting the second active particles 22 with large particle sizes can reduce the impedance of the second sub-layer 122 and increase the reaction rate of the second sub-layer 122 .
  • this application can reduce the impedance difference of the active material layer 12 in its thickness direction and balance the chemistry of delithiation/lithium insertion of the entire active material layer 12 reaction to avoid safety issues such as reduced charge and discharge rate performance of the electrode piece 10 and overcharging/overdischarging of the surface layer due to the excessive difference in reaction speed between the inner and outer layers of the active material layer 12 .
  • the second sub-layer 122 may also include a small amount of heat dispersion material.
  • the selection range of the heat dispersion material in the second sub-layer 122 may be the same as the heat dispersion material added in the first sub-layer 121 . Since the calorific value of the first sub-layer 121 is generally higher than the calorific value of the second sub-layer 122, in a preferred embodiment, the heat dispersion material is disposed in the first sub-layer 121. When the first sub-layer 121 and the second sub-layer 122 both contain heat-dispersing materials, the content of the heat-dispersing materials in the first sub-layer 121 may be higher than that of the second sub-layer 122 .
  • the second active particles 22 may be positive active materials or negative active materials. When the electrode piece 10 is a positive electrode piece, the second active particles 22 are positive active materials. When the electrode piece 10 is a negative electrode piece, the second active particles 22 are negative active materials.
  • the second active particles 22 can be, for example, lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickel cobalt manganate aluminate, lithium iron phosphate, lithium manganate, lithium nickelate, One or more of lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, and lithium-rich manganese; it can also be lithium cobalt oxide, lithium nickel cobalt manganate, and nickel modified by doping or coating with different elements.
  • lithium cobalt aluminate lithium nickel cobalt manganese aluminate, lithium iron phosphate, lithium manganate, lithium nickelate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, and lithium-rich manganese.
  • the active materials of the first active particles 21 and the second active particles 22 may have the same component. The difference between the two is that the doping elements and coating modification forms may be different, thereby forming different median values. particle size and fracturing strength of the particles.
  • the change value of the specific surface area of the second active particles 22 may be greater than 15%. Due to the anti-fracturing protection effect of the first sub-layer 121, the compressive stress transmitted from the first sub-layer 121 to the second sub-layer 122 becomes smaller. Therefore, the second active particles 22 may have relatively low anti-fracturing strength. At the same time, the second active particles 22 have lower impedance, which can help to increase the lithium removal/insertion reaction activity of the second sub-layer 122 to increase the lithium removal/insertion reaction rate of the second sub-layer 122 .
  • the second sub-layer 122 may include first active particles 21 in addition to the second active particles 22 .
  • the mass proportion of the first active particles 21 in the second sub-layer 122 may be, for example, 1% to 50%, and the preferred mass proportion is 10% to 35%. %.
  • the difference between Figure 4 and Figure 5 is that the thermal dispersion material 23 is not provided in the first sub-layer 121 of the embodiment shown in Figure 4, while the first sub-layer 121 of the embodiment shown in Figure 5 contains a thermal dispersion material. twenty three.
  • the second sub-layer 122 contains both large-sized second active particles 22 and small-sized first active particles 21,
  • the smaller first active particles 21 can fill the interstitial space between the accumulation of the second active particles 22, eliminate the space for the second active particles 22 to be deformed under pressure, and disperse the internal pressure of the second sub-layer 122 during the rolling process, so as to This effectively prevents the second active particles 22 from being cracked or broken during the rolling process.
  • the second sub-layer 122 containing the first active particles 21 and the second active particles 22 can form a multi-polar stress-dispersed stacking structure, and has a high surface activity that does not cause cracking and breakage during the rolling process of the electrode pole piece 10 . particles, so that the electrode pole piece 10 has higher thermal safety performance.
  • the difference between the thermal decomposition temperatures of the first sub-layer 121 and the second sub-layer 122 is >5°C.
  • the thermal decomposition temperature of the first sub-layer 121 can be greater than the thermal decomposition temperature of the second sub-layer 122. Therefore, the first sub-layer 121 can be used to protect the second sub-layer 122 and improve the thermal stability of the entire active material layer 12. .
  • the active material layers 12 on both sides of the current collector 11 may be the same or different.
  • 6 and 7 are respectively a schematic structural diagram of the electrode pole piece 10 according to an embodiment.
  • the active material layers 12 on both sides of the current collector 11 can be respectively denoted as a first active material layer 12 and a second active material layer 12 .
  • the second sub-layer 122 in the first active material layer 12 may contain first active particles 21 and second active particles 22 .
  • the second sub-layer 122 in the second active material layer 12 does not contain the first active particles 21 .
  • the first sub-layer 121 of the first active material layer 12 on the surface of the current collector 11 does not contain the thermal dispersion material 23
  • the first sub-layer 121 of the second active material layer 12 contains the thermal dispersion material. twenty three.
  • the thickness of the active material layer 12 on either side of the current collector 11 may be 50 to 5000 ⁇ m.
  • the thickness of the active material layer 12 may be, for example, 50 ⁇ m, 100 ⁇ m, 150 ⁇ m, 200 ⁇ m, 250 ⁇ m, 300 ⁇ m, 400 ⁇ m, 500 ⁇ m, 600 ⁇ m, 700 ⁇ m, 800 ⁇ m, 1000 ⁇ m, 1500 ⁇ m, 2000 ⁇ m, 2500 ⁇ m, 3000 ⁇ m, 3500 ⁇ m, 4000 ⁇ m, 4500 ⁇ m Or 5000 ⁇ m, or other values between any two of the above values, are within the range of the thickness of the active material layer 12 defined in the embodiments of the present application.
  • the thickness of the active material layer 12 in the embodiment of the present application can be 50 ⁇ m or more, which can greatly increase the thickness of the active material layer 12 to increase the energy density of the entire electrode plate 10 .
  • the first sub-layer 121 and the second sub-layer 122 in the embodiment of the present application also include conductive agents, binders and other additives. wait.
  • the conductive agent, binder and other additives can be determined according to the specific type of secondary battery and the content of the active material of the electrode plate 10 .
  • the electrode pole piece 10 of the present application will be further described in detail below with reference to specific examples and comparative examples.
  • the electrode plate 10 of this embodiment includes a current collector 11 and active material layers 12 provided on both sides of the current collector 11 .
  • the two active material layers 12 have the same structure and composition.
  • One layer of the active material layer 12 is taken as an example for description.
  • the active material layer 12 includes a first sub-layer 121 and a second sub-layer 122 , wherein the second sub-layer 122 is provided between the first sub-layer 121 and the current collector 11 .
  • the thickness of the active material layer 12 on either side surface of the current collector 11 is 55 ⁇ m.
  • the first sub-layer 121 contains first active particles 21, conductive agent and adhesive.
  • the second sub-layer 122 contains second active particles 22, a conductive agent and a binder.
  • the first active particles 21 and the second active particles 22 are both lithium nickel cobalt manganate particles.
  • the median particle diameter D50 of the first active particles 21 is 3.5 ⁇ m.
  • the change value of the specific surface area of the first active particles 21 before and after 200 MPa pressure is 11%, and there are no visible cracks under 5K times SEM.
  • the median particle diameter D50 of the second active particles 22 is 15 ⁇ m, and the change value of the specific surface area of the second active particles 22 before and after the pressure of 200 MPa is 20%.
  • the first sub-layer 121 is located on the surface layer of the electrode piece 10.
  • the first active particles with high resistance to fracturing in the first sub-layer 121 21 will not crack or break, and has high thermal safety performance.
  • the second sub-layer 122 containing the second active particles 22 is disposed close to the current collector 11.
  • the pressure of the pressure roller is dispersed through the first sub-layer 121 and transmitted to each part of the second sub-layer 122.
  • the stress on the second active particles 22 becomes smaller, which will not cause the second active particles 22 to be cracked and broken. Therefore, the entire electrode piece 10 of this embodiment has a stacked structure based on a stress dispersion design, and no highly surface-active particles will be cracked and broken during the rolling process of the electrode piece 10. Has high thermal safety resistance.
  • the difference between this embodiment and Embodiment 1 is that in addition to the second active particles 22 , the second sub-layer 122 of this embodiment also contains the first active particles 21 .
  • the mass proportion of the first active particles 21 in the second sub-layer 122 is 20%.
  • the electrode piece 10 of Embodiment 2 can fill the second sub-layer 122 with smaller first active particles 21 through the first active particles 21 disposed in the second sub-layer 122 .
  • the gap between the accumulation of active particles 22 reduces and eliminates the deformation space of the large-sized second active particles 22 under pressure, and again disperses the internal stress of the electrode pole piece 10 during the rolling process, preventing the second active particles 22 from cracking and shattering under pressure.
  • the difference between this embodiment and Embodiment 2 is that in addition to the first active particles 21 , the first sub-layer 121 of this embodiment also contains a thermal dispersion material 23 .
  • the mass proportion of the heat dispersion material 23 in the first sub-layer 121 is 3%.
  • the electrode piece 10 of Embodiment 3 by adding the heat dispersion material 23 in the first sub-layer 121, can absorb when the local temperature of the surface layer of the electrode piece 10 rises. Or the heat can be dispersed to lower the temperature of the active material layer 12, thereby eliminating local hot spots on the surface of the electrode piece 10, avoiding heat accumulation and further heat diffusion inside the secondary battery, and improving the thermal safety performance of the electrode piece 10 and the secondary battery.
  • the difference between this embodiment and Embodiment 2 is that the active material layers 12 on both sides of the current collector 11 are different.
  • the active material layers 12 on both sides of the current collector 11 are respectively designated as the first active material layer 12 and the second active material layer 12 .
  • the second sub-layer 122 in the first active material layer 12 contains the first active particles 21 and the second active particles 22
  • the second sub-layer 122 in the second active material layer 12 only contains the second active particles 22 .
  • the difference between this embodiment and Embodiment 2 is that the active material layers 12 on both sides of the current collector 11 are different.
  • the active material layers 12 on both sides of the current collector 11 are respectively designated as the first active material layer 12 and the second active material layer 12 .
  • the first sub-layer 121 in the first active material layer 12 does not contain the heat dispersion material 23
  • the first sub-layer 121 in the second active material layer 12 contains the heat dispersion material 23 .
  • Example 3 takes the structure of Example 3 as an example to describe the preparation process in detail.
  • the specific preparation process of the electrode pole piece 10 of Embodiment 3 is as follows:
  • the change value of the specific surface area of the first active particle 21 is 9.5%, and there are no visible cracks under 5K times SEM.
  • FIG. 8 is a characteristic scanning electron microscope (SEM) picture of the first active particle according to an embodiment.
  • a button half cell (model CR2032) was assembled using the electrode pole piece 10 of Example 3, and a metal lithium foil (thickness 200um) was used as the counter electrode.
  • the charge/discharge current of the button battery is set to 48mA, and the charge/discharge cut-off voltage is 4.3/3.0V. After constant current charge and discharge of the prepared button battery three times, it is fully charged to 4.3V.
  • the battery was disassembled in an argon protective atmosphere, and the active material layer 12 of the taken-out electrode plate 10 was subjected to a DSC test to determine the thermal stability of the active material layer 12 .
  • This comparative example is an electrode piece.
  • the preparation process of the electrode piece of this comparative example is as follows:
  • Electrode pole pieces Preparation of electrode pole pieces: first coat the positive electrode slurry on the surface of the metal aluminum foil current collector (thickness 12 ⁇ m). The coating thickness of the positive electrode slurry is 65 ⁇ m and the surface density is 180g/m 2 . After drying, the active material is formed. layer. Use 180MPa pressure to roll, and the thickness of the active material layer in the electrode pole piece obtained after rolling is 55 ⁇ m.
  • a button half cell (model CR2032) was assembled using the electrode plates of Comparative Example 1, and a metal lithium foil (thickness 200um) was used as the counter electrode.
  • the charge/discharge current of the button battery is set to 47.8mA, and the charge/discharge cut-off voltage is 4.3/3.0V. After constant current charge and discharge of the prepared button battery three times, it is fully charged to 4.3V.
  • the battery was disassembled in an argon protective atmosphere, and the active material layer of the removed electrode piece was subjected to DSC testing to determine the thermal stability of the active material layer.
  • Example 3 The difference between this comparative example and Example 3 is that the components of the first sub-layer and the second sub-layer are interchanged. That is, the first sub-layer in this comparative example is formed from the second slurry in Example 3, and the second sub-layer in this comparative example is formed from the first slurry in Example 3. The thicknesses of the first sub-layer and the second sub-layer in this comparative example are respectively the same as the thicknesses of the first sub-layer and the second sub-layer in Example 3.
  • the measurement method of the specific surface area of the first active particle and the second active particle is tested using the nitrogen adsorption BET specific surface area test method.
  • the particle diameters of the first active particles and the second active particles are measured using a laser particle sizer measurement method.
  • thermal stability performance includes thermal decomposition starting temperature and thermal decomposition peak temperature.
  • the thermal decomposition onset temperature of the active material corresponding to Example 3 of the present application is higher than that of Comparative Examples 1 and 2. This is because when the active particles in the active material layer are ruptured under pressure, the side reactions between the cracked and exposed fresh surface and the electrolyte increase, and more active particles undergo side reactions. The active particles after the side reactions occur The thermal stability of the electrode interface will become worse. Therefore, compared with the active material layers of the structures of Comparative Example 1 and Comparative Example 2, the active material layer of Example 3 of the present application can maintain the integrity of the structure of the active particles in the active material layer, and the electrode interface of the active material layer is more stable. The corresponding thermal decomposition starting temperature and thermal decomposition peak temperature will be relatively high.

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Abstract

本申请提供了一种电极极片、二次电池与终端设备。该电极极片包括集流体和涂覆于所述集流体至少一侧表面的活性材料层。活性材料层包括叠层设置的第一子层和第二子层，第二子层设于第一子层和集流体之间。第一子层中含有第一活性颗粒，第二子层中含有第二活性颗粒，第一活性颗粒的抗压裂性能优于第二活性颗粒的抗压裂性能。该电极极片具有较好的抗压裂性能，可用于改善高辊压压力下的电极极片和二次电池的安全性能。

Description

电极极片、二次电池与终端设备
本申请要求在2022年03月30日提交中国专利局、申请号为202210333750.5、申请名称为“一种复合电极，电池及终端设备”的中国专利申请的优先权，要求在2022年12月20日提交中国专利局、申请号为202211641999.9、申请名称为“电极极片、二次电池与终端设备”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电池领域，具体涉及一种电极极片、二次电池与终端设备。
背景技术
随着移动终端设备和电动汽车应用的快速增长，锂离子电池的能量密度、充放电倍率和安全性能的要求都日趋提升。锂离子电池的电极极片通常是由集流体和涂布在集流体表面的活性材料层构成。在电池设计中，根据性能要求和活性材料特征，对电极极片的堆积结构、压实密度、厚度阻抗等进行精细化的设计，可以使电池的能量密度、充放电倍率、循环寿命和安全性能达到平衡和综合优化。在一种现有方法中，可通过增加电极极片中活性材料层的厚度提高电池的能量密度。以4000mAh的LCO/石墨软包电池测算，相同材料化学体系，正极材料层的厚度增加10um，电池能量密度可以提升2.8％。但是，当活性材料层的厚度提高后，在制备活性材料层的过程中所需要的辊压力就会提高，以获得足够致密的活性材料层。当辊压力提高后，活性材料层的远离集流体的一侧表面，其所受的压力会显著增大，因此，活性材料层的表面颗粒极易因表面微区的应力集中而产生破裂。破裂后的活性材料颗粒与电解液之间的副反应增大，会显著降低电极极片的抗过充能力，并降低电极极片与电池的安全性能。
发明内容
本申请提供了一种电极极片、二次电池与终端设备，以提高电极极片中活性材料层的抗压裂性能。
第一方面，本申请提供一种电极极片，该电极极片包括集流体和涂覆于所述集流体至少一侧表面的活性材料层。所述活性材料层包括叠层设置的第一子层和第二子层，所述第二子层设于所述第一子层和所述集流体之间。所述第一子层中含有第一活性颗粒，所述第二子层中含有第二活性颗粒，所述第一活性颗粒的抗压裂性能优于所述第二活性颗粒的抗压裂性能。
本申请的电极极片，其活性材料层包括两个叠层设置的子层，第一子层和第二子层。第二子层设于第一子层和集流体之间。其中，第一子层中含有第一活性颗粒，第二子层中含有第二活性颗粒，第一活性颗粒的抗压裂性能优于第二活性颗粒的抗压裂性能。这样，当在活性材料层施加大的辊压力后，由于第一活性颗粒具有较高的抗压裂性能，因此，在辊压过程中可尽可能地避免第一活性颗粒被压裂，进而可减少第一活性颗粒在充放电过程中副反应的发生几率。由于第一子层的抗压裂保护作用，并且由第一子层传递至第二子层的压力经第一子层的颗粒间传递分散后，在第二子层的颗粒上施加的压应力会变小，因此，第二活性颗粒在辊压过程中也可以得到保护。由此，采用本申请结构的电极极片，即使活性材料层的厚度 加厚，在辊压过程中也可有效保护活性材料层的活性颗粒不被压裂，进而使电极极片以及二次电池保持较高的安全性和抗过充性能。
在一种可选的实现方式中，所述第一活性颗粒的抗压裂性能优于所述第二活性颗粒的抗压裂性能，包括：在200MPa压力前后，所述第一活性颗粒的比表面积的变化值小于等于15％；在200MPa压力前后，所述第二活性颗粒的比表面积的变化值大于15％。
其中，第一活性颗粒在200MPa压力前后的比表面积的变化值小于等于15％，由此，第一活性颗粒可具有较高的抗压裂强度，进而在辊压过程中可避免发生压裂，减少第一活性颗粒在充放电过程中副反应的发生几率。由于第一子层的抗压裂保护作用，并且由第一子层传递至第二子层的压力经第一子层的颗粒间传递分散后，在第二子层的颗粒上承受的压应力会变小，因此，第二活性颗粒许可具有相对较低的抗压裂强度，在200MPa压力前后，第二活性颗粒的比表面积的变化值可大于15％。第二活性颗粒在具有较低抗压裂强度的同时可获得较低的阻抗，以提高第二子层的脱/嵌锂反应速率，降低由于厚度增大造成的活性材料层的内外反应速率差异，平衡活性材料层的各处的反应速率，进而可避免活性材料层因内外层反应速率差异过大导致电极极片出现充放电倍率性能降低和表面层过充电/过放电的安全风险问题。
在另一种可选实现方式中，所述第一活性颗粒的抗压裂性能优于所述第二活性颗粒的抗压裂性能，包括：所述第一活性颗粒和所述第二活性颗粒在承受相同压力且至少所述第二活性颗粒中出现裂纹后，在相同放大倍数的SEM图中，所述第一活性颗粒出现的裂纹的数量少于所述第二活性颗粒出现的裂纹的数量；其中，所述SEM图的放大倍数为2000～10000倍。
通过在相同压力以及相同倍数下比较第一活性颗粒的裂纹数量以及第二活性颗粒的裂纹数量，可便于选择抗压裂性能更优的第一活性颗粒作为第一子层的活性颗粒，以增加第一子层的抗压裂性能。
在一种可选的实现方式中，所述第二活性颗粒的中值粒径D50大于所述第一活性颗粒的中值粒径D50。
通过利用中值粒径较小的第一活性颗粒形成第一子层，并利用中值粒径较大的第二活性颗粒形成第二子层，从而形成分层设置且脱/嵌锂反应活性不同的活性材料层。由于活性材料中，大颗粒的活性材料的阻抗相对较低，小颗粒的活性材料的阻抗相对较高，因此，通过在靠近集流体设置的第二子层中设置颗粒粒径相对较大的第二活性颗粒，并在远离集流体设置的第一子层中设置颗粒粒径相对较小的第一活性颗粒，可降低活性材料层在其厚度方向的阻抗差异，平衡整个活性材料层的脱锂/嵌锂的化学反应，可进一步避免活性材料层因内外层反应速度差异过大导致电极极片出现充放电倍率性能降低和表面层过充电/过放电的安全问题。
在一种可选实现方式中，所述第一活性颗粒的中值粒径D50＜5μm。第一活性颗粒的中值粒径D50＜5μm时，可使第一活性颗粒具有更高的抗压裂强度。
在一种可选实现方式中，所述第一活性颗粒为单晶颗粒或类单晶颗粒。第一活性颗粒为单晶颗粒或类单晶颗粒时，可使第一子层具有更高的阻抗，降低第一子层和第二子层之间的极化，减缓第一子层的脱/嵌锂反应速率，平衡第一子层和第二子层之间的反应速率差。
在一种可选实现方式中，所述第一子层和第二子层中的至少一个含有热分散材料，如，热分散材料可单独设于第一子层中，也可单独设于第二子层中，还可同时设于第一子层和第二子层中。在一种可选实现方式中，第一子层中含有所述热分散材料。所述热分散材料包括吸热材料和导热材料中的一种。热分散材料是在电极极片部分区域中设置的吸热材料或导热材料，以快速分散电极极片产生的热量，消除电极极片表面微区的局部过热，避免因局部过 热引发电池内部发生热聚集和热失控。
其中，所述吸热材料可为在100～350℃温度范围内发生相变或者化学反应而吸收热量的材料。示例性地，所述吸热材料包括勃姆石、羟基氧化镁、羟基氧化铝、氢氧化铝、氢氧化镁或羟基氧化硅中的至少一种。
所述导热材料可为导热系数>15W/mK的材料。示例性地，所述导热材料包括氧化铝、氮化铝、氮化硼、金刚石或碳化硅中至少一种。
在一种可选实现方式中，所述吸热材料或所述导热材料在所述第一子层中的质量占比为0.1％～25％。由于吸热材料或导热材料为不参与脱嵌锂反应的非活性材料，因此，需要控制其在第一子层中的质量占比，以及其在电极极片中的质量占比，以避免造成电极极片以及电池能力密度的降低。
在一种可选实现方式中，所述第一子层的厚度大于5μm，且小于所述活性材料层厚度的50％。第一子层的厚度过小，无法通过第一子层的颗粒间传递分散实现对辊压力的分散，进而无法有效提升活性材料层整体的抗压能力，也无法有效实现平衡活性材料层内外反应速率。第一子层的厚度过大，会影响活性材料层整体的阻抗，降低活性材料层的反应活性，也不利于电极极片能量密度的提升。因此，通过限定第一子层的厚度，以及在活性材料层的厚度占比，可在有效平衡活性材料层厚度方向的内外反应速率以及提高活性材料层抗压能力的基础上，进一步保证电极极片获得较高的能量密度。
在一种可选实现方式中，所述第二活性颗粒包括多晶颗粒或二次团聚颗粒。多晶颗粒或二次团聚颗粒可具有较低的阻抗，以使第二子层获得更快的脱/嵌锂反应速率，降低第一子层和第二子层之间的阻抗差异，避免电极极片部分活性材料层出现过充电或过放电的问题。
在一种可选实现方式中，所述第二活性颗粒的中值粒径D50＞10μm。第二活性颗粒的中值粒径D50＞10μm时，可使第二子层具有更低的阻抗。
在一种可选实现方式中，所述第二子层中含有所述第一活性颗粒。通过在第二子层中添加第一活性颗粒，可提高第二子层的活性颗粒的堆积密度，提升抗压裂性能。
在一种可选实现方式中，所述第一子层和所述第二子层的热分解温度的差值＞5℃。第一子层的热分解温度大于第二子层的热分解温度，利用第一子层实现对整个活性材料层的热保护，提高活性材料层的热稳定性。
在一种可选实现方式中，所述活性材料层的厚度为50～5000μm。相比传统单层均一性的活性材料层，本申请实现方式中，活性材料层的厚度可设置的相对较厚，可提高二次电池的能量密度。
在一种可选实现方式中，所述集流体的两侧表面均设有所述活性材料层，所述集流体两侧的两个所述活性材料层的结构相同或不同。
其中，本申请上述各可能实现方式中的数据，例如比表面积的变化值、第一活性颗粒的中值粒径、第二活性颗粒的中值粒径、导热系数、质量占比等数据，在测量时，工程测量误差范围内的数值均应理解为在本申请所限定的范围内。
第二方面，本申请提供了一种二次电池，该二次电池包括正极极片、隔膜和负极极片，所述正极极片和所述负极极片中的至少一个为本申请第一方面的电极极片。
本申请第一方面的电极极片可作为二次电池正极极片，也可作为二次电池的负极极片。当将正极极片用作二次电池的正极极片时，电极极片中的第一活性颗粒和第二活性颗粒均选自正极活性颗粒。当将电极极片用作二次电池的负极极片时，电极极片中的第一活性颗粒和第二活性颗粒均选自负极活性颗粒。
本申请的二次电池可为锂离子二次电池，也可为钠离子二次电池、钾离子二次电池、镁离子二次电池、锌离子二次电池或铝离子二次电池等二次电池。在此不同二次电池的具体类型做出限定，可根据活性物质的种类进行选择。
第三方面，本申请提供了一种终端设备，该终端设备包括本申请第二方面的二次电池。终端设备包括但不限于数码设备、电动车辆、电力储存系统等。
上述第二方面和第三方面可以达到的技术效果，可以参照上述第一方面中的相应效果描述，这里不再重复赘述。
附图说明
图1为本申请一种实施例电极极片的结构示意图；
图2为一种实施例的活性材料层的结构示意图；
图3为本申请另一种实施例的电极极片的结构示意图；
图4为另一种实施例的活性材料层的结构示意图；
图5为另一种实施例的活性材料层的结构示意图；
图6为一种实施例的电极极片的结构示意图；
图7为另一种实施例的电极极片的结构示意图；
图8为一种实施例的第一活性颗粒的特征SEM图；
图9为一种实施例的第二活性颗粒的特征SEM图。
附图标记：
10-电极极片；11-集流体；12-活性材料层；121-第一子层；122-第二子层；
21-第一活性颗粒；22-第二活性颗粒；23-热分散材料。
具体实施方式
为了使本申请的目的、技术方案和优点更加清楚，下面将结合附图对本申请作进一步地详细描述。
以下实施例中所使用的术语只是为了描述特定实施例的目的，而并非旨在作为对本申请的限制。如在本申请的说明书和所附权利要求书中所使用的那样，单数表达形式“一个”、“一种”、“上述”、“该”和“这一”旨在也包括例如“一个或多个”这种表达形式，除非其上下文中明确地有相反指示。
在本说明书中描述的参考“一个实施例”或“一些实施例”等意味着在本申请的一个或多个实施例中包括结合该实施例描述的特定特征、结构或特点。由此，在本说明书中的不同之处出现的语句“在一个实施例中”、“在一些实施例中”、“在其他一些实施例中”、“在另外一些实施例中”等不是必然都参考相同的实施例，而是意味着“一个或多个但不是所有的实施例”，除非是以其他方式另外特别强调。术语“包括”、“包含”、“具有”及它们的变形都意味着“包括但不限于”，除非是以其他方式另外特别强调。
现有的二次电池中，其电极极片(包括正极极片和负极极片)主要由集流体和涂覆在集流体表面的活性材料层构成。在电极极片的制备过程中，将活性材料浆料涂覆在集流体表面后，需要对形成的活性材料浆料层施加一定的辊压力，以用于提高活性材料层的压实密度。当活性材料层的厚度较薄时，由于所需的辊压力较小，此时施加在活性材料层表面的辊压力不足以将活性材料层中的活性颗粒压裂。而当活性材料层的厚度逐步提高后，所需的辊压力也逐步提高，才能获得所需的压实密度。当辊压力提高后，施加在活性材料层外表面的压力 要远大于活性材料层内表面的压力，因此，在辊压过程中，活性材料层外表面的活性颗粒极易在大压力下而产生破裂，活性颗粒破裂后，其表层的钝化层开裂，内部的活性物质直接与电解液接触，从而加重活性材料层与电解液之间的副反应，降低电极极片和二次电池的安全性。另外，由于电极极片的活性材料层的表层最先反应，当活性材料层的厚度较厚时，其表层与靠近集流体一侧的内层反应程度会存在一定的差异。当活性材料层的内层反应充分时，其表层往往处于过充状态，因此，活性材料层的表层往往需要承受的更大的抗过充能力。但是当活性材料层外表面的活性颗粒发生破裂后，会降低电极极片的抗过充能力，从而降低二次电池的安全性能。
有鉴于此，本申请实施例提供一种电极极片。图1为本申请一种实施例电极极片的结构示意图。如图1所示，电极极片10包括集流体11和涂覆于所述集流体11至少一侧表面的活性材料层12。其中，集流体11可为金属箔片，例如铜箔、铝箔、合金箔片等，也可为聚合物金属复合箔，或者碳纤维布等。可根据具体的电极极片10的电位进行选择。如图1所示，活性材料层12可设于集流体11的一侧表面，还可设置于集流体11的两侧表面。在本申请实施例中，集流体11的两侧均可设置活性材料层12。
图2为一种实施例的活性材料层12的结构示意图。如图2所示，集流体11任一侧的活性材料层12可包括第一子层121和第二子层122。第一子层121和第二子层122叠层设置。第二子层122设于第一子层121和集流体11之间。其中，第一子层121和第二子层122之间电子导通，第二子层122和集流体11之间电子导通。
参照图1和图2，在一种实施例中，第一子层121中含有第一活性颗粒21。第二子层122中含有第二活性颗粒22。其中，第一活性颗粒21的抗压裂性能要优于第二活性颗粒22的抗压裂性能。
可以理解的是，抗压裂性能可以指在相同压力下产生裂纹的情况、在产生相同裂纹的情况下所承受的压力、以及发生破裂时所承受的压力等。示例性地，在相同压力下产生裂纹的情况例如可包括，在相同压力下产生的裂纹的条数、产生的裂纹的大小以及产生的裂纹的深度等。另外，优于指，相对于第二活性颗粒，第一活性颗粒的抗压裂性格更好。例如，在相同压力下产生的裂纹更少，在产生相同破裂时，所承受压力更高等。
在一种可选的实施例中，所述第一活性颗粒的抗压裂性能优于所述第二活性颗粒的抗压裂性能，包括：所述第一活性颗粒和所述第二活性颗粒在承受相同压力且至少所述第二活性颗粒中出现裂纹后，在相同放大倍数的SEM图中，所述第一活性颗粒出现的裂纹的数量少于所述第二活性颗粒出现的裂纹的数量；其中，所述SEM图的放大倍数为2000～10000倍。
以下将对第一子层、第一活性颗粒、第二子层和第二活性颗粒做进一步详细说明。
参照图1和图2，第一活性颗粒21可为正极活性材料，也可为负极活性材料。当电极极片10为正极极片时，第一活性颗粒21为正极活性材料。当电极极片10为负极极片时，第一活性颗粒21为负极活性材料。
以正极极片为例，第一活性颗粒21例如可为钴酸锂、镍钴锰酸锂、镍钴铝酸锂、镍钴锰铝酸锂、磷酸铁锂、锰酸锂、镍酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、富锂锰中的一种或多种；还可为通过不同元素掺杂或包覆改性的钴酸锂、镍钴锰酸锂、镍钴铝酸锂、镍钴锰铝酸锂、磷酸铁锂、锰酸锂、镍酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、富锂锰中的一种或多种。
在一种可选实施例中，第一活性颗粒21可为单晶颗粒。在一种可选实施例中，在200MPa压力前后，所述第一活性颗粒21的比表面积的变化值小于等于15％。其中，在200MPa压力 前后，第一活性颗粒21在5000倍扫描电子显微镜(scanning electron microscope，SEM)下未产生可见裂纹。示例性地，在200MPa压力前后，第一活性颗粒21的比表面积的变化值可为15％、14％、13％、12％、11％、10％、9％、8％、7％、6％、5％、4％或更低值，或以上任意两数值间的其他数值均可。
在辊压过程中，由于第一子层121需要承受更大的辊压压应力，因此，通过添加抗压强度高的第一活性颗粒21，可避免第一子层121中的活性材料颗粒被压裂或压碎，以提高活性材料层12中各活性材料颗粒的完整性，从而提高活性材料层12的抗过充能力，以及活性材料层12的界面热稳定性，进而提高电极极片10以及相对应二次电池的安全性能。
其中，当第一活性颗粒21在200MPa压力前后的比表面积的变化值小于等于15％时，第一活性颗粒21可具有较高的抗压裂强度，进而在辊压过程中可避免发生劈裂，减少第一活性颗粒21在充放电过程中副反应的发生几率。
另外，第一活性颗粒21的中值粒径D50可＜5μm。示例性地，第一活性颗粒21的中值粒径例如可为4.5μm、4μm、3μm、2μm、1μm、0.5μm，以及上述任意两数值间的数值。第一活性颗粒21的中值粒径小于5μm时，该中值粒径的第一活性颗粒21可具有较高的阻抗，并且，当第一活性颗粒21的中值粒径小于5μm时，其在电极极片10的辊压过程中，可使第一子层121具有较高的抗压强度，避免第一活性颗粒21在辊压过程中发生破裂，进而可避免第一活性颗粒21破裂后副反应的发生。
本申请实施例中，第一活性颗粒21为小颗粒、高阻抗以及高抗压裂强度的颗粒，在脱/嵌锂的反应过程中，可减缓表面的化学反应，并可避免在辊压过程中压裂活性材料层12表面的颗粒，进而可避免因活性物质裸露造成的活性材料层12的副反应发生，提高电极极片10的安全性。
图3为本申请另一种实施例的电极极片的结构示意图。如图3所示，在一种实施例电极极片10中，第一子层121中除包括第一活性颗粒21外，还可包括热分散材料23。热分散材料23在第一子层121中的质量占比例如可为0.1％～25％。示例性地，热分散材料23在第一子层121中的质量占比包括但不限于0.1％、1％、2％、5％、7％、8％、10％、12％、15％、17％、19％、20％、21％、23％或25％、或以上任意两数值间的数值均可。
热分散材料23例如可包括吸热材料和导热材料中的一种。所述吸热材料可为在100～350℃温度范围内发生相变或者化学反应而吸收热量的材料。示例性地，吸热材料包括但不限于勃姆石、羟基氧化镁、羟基氧化铝、氢氧化铝、氢氧化镁或羟基氧化硅中的至少一种。
导热材料可为导热系数>15W/mK的材料。示例性地，所述导热材料包括但不限于氧化铝、氮化铝、氮化硼、金刚石或碳化硅中至少一种。
其中，热分散材料23在电池内部充放电过程中不参与化学和电化学反应。热分散材料23能够在第一子层121的局部温度升高时吸收热量，或者分散热量，把局部发热点的热量快速地传递分散到周围区域，使第一子层121的发热点的温度降低，消除电极极片10表面的局部热点，避免引发二次电池内部热聚集和进一步的热失控，提升电极极片10和二次电池的热安全性能。
一并参照图2和图3，在一种实施例中，第二活性颗粒22可为多晶颗粒或由一次颗粒团聚形成的二次团聚颗粒。多晶颗粒或二次团聚颗粒可具有更低的阻抗，以提高第二子层122在充放电过程中的反应活性。
活性材料层12通常包括第一表面和第二表面，第一表面与集流体11贴合设置，第二表面为远离集流体11且用于和电解液接触的表面。其中，在活性材料层12的充放电循环过程 中，电解液或电解质中的活性离子自活性材料层12的第二表面向第一表面传输，或，自第一表面向第二表面传输。该过程中，由于第一表面和第二表面之间存在距离差，导致活性材料层12不同部位的活性物质在脱/嵌锂反应过程中存在差异。当活性材料层12的厚度较薄时，该差异性不明显。但当为了提高电极极片10的能量密度，逐渐提高活性材料层12的厚度后，活性材料层12内层和外层的反应速率差异较大，反应不均衡问题较为突出，导致电极极片10的充放电倍率性能下降，另外，活性材料层12的外表面容易出现过充电和过放电的问题，也容易导致二次电池出现安全风险。由此，第二活性颗粒22的中值粒径D50可大于第一活性颗粒21的中值粒径D50，第二活性颗粒22的中值粒径D50例如可＞10μm。示例性地，第二活性颗粒22的中值粒径D50例如可为10μm、12μm、15μm、17μm、20μm、25μm、30μm、35μm、40μm或更高，或以上任意两数值范围内的数值均可。
选用大粒径的第二活性颗粒22，可降低第二子层122的阻抗，提高第二子层122的反应速率。本申请通过采用不同中值粒径的第一活性颗粒21和第二活性颗粒22，可降低活性材料层12在其厚度方向的阻抗差异，平衡整个活性材料层12的脱锂/嵌锂的化学反应，避免活性材料层12因内外层反应速度差异过大导致电极极片10出现充放电倍率性能降低和表面层过充电/过放电的安全问题。
其中，可以理解的是，第二子层122中除可包括第二活性颗粒22外，还可包括少量的热分散材料。第二子层122中的热分散材料的选取范围可与第一子层121中添加的热分散材料相同。由于第一子层121的发热量一般高于第二子层122的发热量，因此，在一种优选实施例中，热分散材料设置于第一子层121中。当第一子层121和第二子层122中同时含有热分散材料时，第一子层121中的热分散材料的含量可高于第二子层122。
第二活性颗粒22可为正极活性材料，也可为负极活性材料。当电极极片10为正极极片时，第二活性颗粒22为正极活性材料。当电极极片10为负极极片时，第二活性颗粒22为负极活性材料。
以正极极片为例，第二活性颗粒22例如可为钴酸锂、镍钴锰酸锂、镍钴铝酸锂、镍钴锰铝酸锂、磷酸铁锂、锰酸锂、镍酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、富锂锰中的一种或多种；还可为通过不同元素掺杂或包覆改性的钴酸锂、镍钴锰酸锂、镍钴铝酸锂、镍钴锰铝酸锂、磷酸铁锂、锰酸锂、镍酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、富锂锰中的一种或多种。
第一活性颗粒21和第二活性颗粒22，两者的活性物质可为相同的组分，两者的不同之处在于掺杂元素、包覆改性的形式可不同，从而可形成不同中值粒径以及抗压裂强度的颗粒。
其中，在200MPa压力前后，所述第二活性颗粒22的比表面积的变化值可大于15％。由于第一子层121的抗压裂保护作用，由第一子层121传递至第二子层122的压应力变小，因此，第二活性颗粒22可具有相对较低的抗压裂强度，同时第二活性颗粒22具有较低的阻抗，可有助于提高第二子层122的脱/嵌锂的反应活性，以提高第二子层122的脱/嵌锂反应速率。
图4和图5分别为另一种实施例的活性材料层12的结构示意图。如图4和图5所示，在一种可选实施例中，第二子层122中除可包括第二活性颗粒22外，还可包括第一活性颗粒21。当第二子层122中含有第一活性颗粒21时，第一活性颗粒21在第二子层122中的质量占比例如可为1％～50％，优选的质量占比为10％～35％。其中，图4和图5的区别之处在于，图4所示实施例的第一子层121中未设置热分散材料23，图5所示实施例的第一子层121中含有热分散材料23。
当第二子层122中既含有大尺寸的第二活性颗粒22又含有小尺寸的第一活性颗粒21时， 较小的第一活性颗粒21可填充在第二活性颗粒22的堆积间隙空间，消除第二活性颗粒22受压变形的空间，并分散在辊压过程中第二子层122的内部压力，以有效阻止第二活性颗粒22在辊压过程中发生破裂或破碎。包含第一活性颗粒21和第二活性颗粒22的第二子层122，可形成多极应力分散的堆积结构，在电极极片10的辊压过程中不产生压裂和破碎的高表面活性的颗粒，从而使电极极片10具有较高的热安全性能。
在本申请一种可选实施例中，所述第一子层121和所述第二子层122的热分解温度的差值＞5℃。第一子层121的热分解温度可大于第二子层122的热分解温度，由此，可利用第一子层121对第二子层122形成保护，提高整个活性材料层12的热稳定性。
可以理解的是，集流体11两侧的活性材料层12可相同也可不同。图6和图7分别为一种实施例的电极极片10的结构示意图。如图6和图7所示，在一种可选实施例中，集流体11两侧的活性材料层12可分别记为第一活性材料层12和第二活性材料层12。如图6所示，第一活性材料层12中的第二子层122中可含有第一活性颗粒21和第二活性颗粒22。第二活性材料层12中的第二子层122中未含有第一活性颗粒21。如图7所示，集流体11表面的第一活性材料层12中的第一子层121中未含有热分散材料23，而第二活性材料层12的第一子层121中含有热分散材料23。
参照图1，集流体11任意一侧活性材料层12的厚度可为50～5000μm。示例性地，活性材料层12的厚度例如可为50μm、100μm、150μm、200μm、250μm、300μm、400μm、500μm、600μm、700μm、800μm、1000μm、1500μm、2000μm、2500μm、3000μm、3500μm、4000μm、4500μm或5000μm，或以上任意两数值间的其他数值均在本申请实施例所限定的活性材料层12厚度的范围内。如上，本申请实施例的活性材料层12的厚度可做到50μm及以上，可大幅提高活性材料层12的厚度，以提高整个电极极片10的能量密度。
需要说明的是，本申请实施例的第一子层121和第二子层122中，除包括第一活性颗粒21和第二活性颗粒22外，还包括有导电剂、粘结剂和其他添加剂等。其中，导电剂、粘结剂和其他添加剂可根据具体的二次电池的种类以及电极极片10的活性物质的含量进行确定。
以下将结合具体实施例和对比例对本申请的电极极片10做进一步详细说明。
实施例1
参照图1和图2，该实施例的电极极片10包括集流体11和设于集流体11两侧表面的活性材料层12。其中，两层活性材料层12的结构和成分相同。以其中一层活性材料层12为例进行说明。如图2所示，该活性材料层12包括第一子层121和第二子层122，其中第二子层122设于第一子层121和集流体11之间。集流体11任一侧表面的活性材料层12的厚度为55μm。其中，第一子层121中含有第一活性颗粒21、导电剂和粘结剂。第二子层122中含有第二活性颗粒22、导电剂和粘结剂。其中，第一活性颗粒21和第二活性颗粒22均为镍钴锰酸锂颗粒。第一活性颗粒21的中值粒径D50为3.5μm，在200MPa压力前后，第一活性颗粒21的比表面积的变化值为11％，且5K倍SEM无可见裂纹。第二活性颗粒22的中值粒径D50为15μm，在200MPa压力前后，第二活性颗粒22的比表面积的变化值为20％。
实施例1的电极极片10，第一子层121位于电极极片10的表面层，在电极极片10的辊压过程中，第一子层121中的高抗压裂的第一活性颗粒21不发生破裂和破碎，具有高的热安全性能。含有第二活性颗粒22的第二子层122靠近集流体11设置，在电极极片10的辊压过程中，压辊的压力经第一子层121分散，传递到第二子层122的每个第二活性颗粒22上的应力变小，不会导致第二活性颗粒22压裂和破碎。由此，该实施例的整个电极极片10基于应力分散设计的堆积结构，在电极极片10的辊压过程中不产生压裂和破碎的高表面活性的颗粒， 具有高的热安全抵抗能力。
实施例2
参照图1和图4，该实施例与实施例1的区别在于，本实施例的第二子层122中除含有第二活性颗粒22外，还含有第一活性颗粒21。第二子层122中第一活性颗粒21的质量占比为20％。
相比于实施例1的电极极片10，实施例2的电极极片10，通过在第二子层122中设置的第一活性颗粒21，可使较小的第一活性颗粒21填充第二活性颗粒22堆积的间隙，降低消除大尺寸的第二活性颗粒22受压的变形空间，并再次分散辊压过程的电极极片10的内部应力，阻止第二活性颗粒22受压破裂和破碎。
实施例3
参照图1和图5，该实施例与实施例2的区别在于，该实施例的第一子层121中除含有第一活性颗粒21外，还添加有热分散材料23。其中，热分散材料23在第一子层121中的质量占比为3％。
相比于实施例2的电极极片10，实施例3的电极极片10，通过在第一子层121中添加热分散材料23，可在电极极片10的表面层局部温度升高时吸收或者分散热量使活性材料层12的温度降低，消除电极极片10表面的局部热点，避免二次电池内部热聚集和进一步的热扩散，提升电极极片10和二次电池的热安全性能。
实施例4
参照图1和图6，该实施例和实施例2的区别在于，集流体11两侧的活性材料层12不同。集流体11两侧活性材料层12分别记为第一活性材料层12和第二活性材料层12。第一活性材料层12中的第二子层122中含有第一活性颗粒21和第二活性颗粒22，而第二活性材料层12中的第二子层122中仅含有第二活性颗粒22。
实施例5
参照图1和图7，该实施例和实施例2的区别在于，集流体11两侧的活性材料层12不同。集流体11两侧活性材料层12分别记为第一活性材料层12和第二活性材料层12。第一活性材料层12中的第一子层121中不含热分散材料23，而第二活性材料层12中的第一子层121中含有热分散材料23。
下面以实施例3的结构为例，具体说明其制备过程。实施例3的电极极片10的具体制备过程如下：
S11)提供第一活性颗粒21：化学组成LiNi0.9Co0.07Mn0.03O2，为单晶颗粒，粒径分布D50＝3.5μm，D10＝1.8μm。在200MPa压力前后，第一活性颗粒21的比表面积的变化值为9.5％，且5K倍SEM无可见裂纹。其中，图8为一种实施例的第一活性颗粒的特征扫描电子显微镜(scanning electron microscope，SEM)图。
S12)提供第二活性颗粒22：化学组成LiNi0.85Co0.09Mn0.06O2，为多晶二次团聚颗粒，粒径分布D50＝15μm，D10＝9μm。在200MPa压力前后，第二活性颗粒22的比表面积的变化值为43％。其中，图9为一种实施例的第二活性颗粒的特征SEM图。
S13)制备第一浆料：将第一活性颗粒21、勃姆石、导电剂和粘结剂混合形成第一浆料，其中，以第一浆料的质量为基准计算，第一活性颗粒21的质量占比为90.2％，勃姆石的质量占比为5％、粘结剂聚偏二氟乙烯(polyvinylidene difluoride，PDVF)的质量占比为3％，导电剂乙炔黑的质量占比为1.8％。
S14)制备第二浆料：将第一活性颗粒21、第二活性颗粒22、导电剂和粘结剂混合形成 第二浆料。其中，第二浆料的质量为基准计算，第一活性颗粒21的质量占比为19％、第二活性颗粒22的质量占比为76.3％，粘结剂PDVF的质量占比为2.9％，导电剂乙炔黑的质量占比为1.8％。
S15)制备电极极片10：先将第二浆料涂布在金属铝箔集流体11(厚度12μm)的表面，第二浆料的涂布厚度为50μm，面密度为139g/m2，经干燥后形成第二子层122。在第二子层122的表面涂布第一浆料，第一浆料的涂布厚度为15μm，面密度为41g/m2，经干燥后形成第一子层121。使用180MPa压力辊压，辊压后获得的电极极片10中活性材料层12的厚度55μm。
使用实施例3的电极极片10组装纽扣半电池(型号CR2032)，对电极使用金属锂箔(厚度200um)。纽扣电池的充/放电的电流设置为48mA，充/放电截止电压为4.3/3.0V，对制备的纽扣电池进行3次恒流充放电之后，再满充电至4.3V。在氩气保护气氛中拆解电池，取出的电极极片10的活性材料层12进行DSC测试，确定活性材料层12的热稳定性能。
对比例1
该对比例为一种电极极片，该对比例的电极极片的制备过程如下：
S21)制备正极浆料：将活性颗粒、粘结剂和导电剂混合形成正极浆料。其中，活性颗粒的化学组成为LiNi0.85Co0.09Mn0.06O2，为多晶二次团聚颗粒，粒径分布D50＝15μm，D10＝9μm。其中，以正极浆料的质量为基准计算，活性颗粒的质量占比为95％，粘结剂PVDF的质量占比为3％，导电剂乙炔黑的质量占比为2％。
S22)制备电极极片：先将正极浆料涂布在金属铝箔集流体(厚度12μm)的表面，正极浆料的涂布厚度为65μm，面密度为180g/m2，经干燥后形成活性材料层。使用180MPa压力辊压，辊压后获得的电极极片中活性材料层的厚度55μm。
使用对比例1的电极极片组装纽扣半电池(型号CR2032)，对电极使用金属锂箔(厚度200um)。纽扣电池的充/放电的电流设置为47.8mA，充/放电截止电压为4.3/3.0V，对制备的纽扣电池进行3次恒流充放电之后，再满充电至4.3V。在氩气保护气氛中拆解电池，取出的电极极片的活性材料层的进行DSC测试，确定活性材料层的热稳定性能。
对比例2
该对比例和实施例3的区别在于，第一子层和第二子层的成分互换。即，该对比例中的第一子层包括由实施例3中的第二浆料形成，该对比例中的第二子层由实施例3中的第一浆料形成。该对比例中的第一子层和第二子层的厚度分别与实施例3中的第一子层和第二子层的厚度相同。
其中，第一活性颗粒和第二活性颗粒的比表面积的测量方法使用氮吸附BET比表面积测试法测试。第一活性颗粒和第二活性颗粒的粒径使用激光粒度仪测量法测量。
实施例3与对比例1和对比例2的活性材料层的热稳定性能以及循环性能测试结果列于表1。其中，热稳定性能包括热分解起始温度和热分解峰值温度。
表1

由表1中的数据可知，本申请实施例3对应的活性材料的热分解起始温度要高于对比例1和对比例2。这是因为，当活性材料层的活性颗粒受压发生破裂后，开裂裸露的新鲜表面与电解液之间的副反应增多，并且也有更多的活性颗粒发生副反应，发生副反应后的活性颗粒的电极界面热稳定性会变差。因此，相对于对比例1和对比例2的结构的活性材料层，本申请实施例3的活性材料层，由于活性材料层中活性颗粒的结构能够保持完整，活性材料层的电极界面更稳定，其对应的热分解起始温度以及热分解峰值温度都会相对较高。另外，从实施例3以及对比例1-2的扣电在45℃下的循环容量保持率可以看出，实施例3所对应的扣电池在45℃下60圈后的容量循环保持率会更高。这说明，采用本申请的技术方案获得的电极极片，其活性材料层的稳定性会更高。
以上，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (17)

  1. 一种电极极片，其特征在于，包括集流体和涂覆于所述集流体至少一侧表面的活性材料层，所述活性材料层包括叠层设置的第一子层和第二子层，所述第二子层设于所述第一子层和所述集流体之间；
    所述第一子层中含有第一活性颗粒，所述第二子层中含有第二活性颗粒，所述第一活性颗粒的抗压裂性能优于所述第二活性颗粒的抗压裂性能。
  2. 根据权利要求1所述的电极极片，其特征在于，所述第一活性颗粒的抗压裂性能优于所述第二活性颗粒的抗压裂性能，包括：在200MPa压力前后，所述第一活性颗粒的比表面积的变化值小于等于15％；在200MPa压力前后，所述第二活性颗粒的比表面积的变化值大于15％。
  3. 根据权利要求1或2所述的电极极片，其特征在于，所述第一活性颗粒的抗压裂性能优于所述第二活性颗粒的抗压裂性能，包括：所述第一活性颗粒和所述第二活性颗粒在承受相同压力且至少所述第二活性颗粒中出现裂纹后，在相同放大倍数的SEM图中，所述第一活性颗粒出现的裂纹的数量少于所述第二活性颗粒出现的裂纹的数量；其中，所述SEM图的放大倍数为2000～10000倍。
  4. 根据权利要求1-3任一项所述的电极极片，其特征在于，所述第二活性颗粒的中值粒径大于所述第一活性颗粒的中值粒径。
  5. 根据权利要求1-4任一项所述的电极极片，其特征在于，所述第一活性颗粒的中值粒径D50＜5μm。
  6. 根据权利要求1-5任一项所述的电极极片，其特征在于，所述第一活性颗粒为单晶颗粒或类单晶颗粒。
  7. 根据权利要求1-6任一项所述的电极极片，其特征在于，所述第一子层和所述第二子层中的至少一个含有热分散材料，所述热分散材料包括吸热材料和导热材料中的至少一种；
    所述吸热材料为在100～350℃温度范围内发生相变或者化学反应而吸收热量的材料；
    所述导热材料为导热系数>15W/mK的材料。
  8. 根据权利要求7所述电极极片，其特征在于，所述吸热材料或所述导热材料在所述第一子层中的质量占比为0.1％～25％。
  9. 根据权利要求7所述的电极极片，其特征在于，所述吸热材料包括勃姆石、羟基氧化镁、羟基氧化铝、氢氧化铝、氢氧化镁或羟基氧化硅中的至少一种；
    所述导热材料包括氧化铝、氮化铝、氮化硼、金刚石或碳化硅中至少一种。
  10. 根据权利要求1-9任一项所述的电极极片，其特征在于，所述第一子层的厚度大于5μm，且小于所述活性材料层厚度的50％。
  11. 根据权利要求1-10任一项所述的电极极片，其特征在于，所述第二活性颗粒包括多晶颗粒或二次团聚颗粒。
  12. 根据权利要求1-11所述的电极极片，其特征在于，所述第二活性颗粒的中值粒径D50＞10μm。
  13. 根据权利要求1-12任一项所述的电极极片，其特征在于，所述第二子层中含有所述第一活性颗粒。
  14. 根据权利要求1-13任一项所述的电极极片，其特征在于，所述第一子层和所述第二子层的热分解温度的差值＞5℃。
  15. 根据权利要求1-14任一项所述的电极极片，其特征在于，所述活性材料层的厚度为 50～5000μm。
  16. 一种二次电池，其特征在于，包括正极极片、隔膜和负极极片，所述正极极片和所述负极极片中的至少一个为如权利要求1-15任一项所述的电极极片。
  17. 一种终端设备，其特征在于，包括如权利要求16所述的二次电池。
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WO2015045719A1 (ja) * 2013-09-26 2015-04-02 Ｎｅｃエナジーデバイス株式会社 積層型リチウムイオン二次電池用正極
CN108630945A (zh) * 2017-03-25 2018-10-09 华为技术有限公司 一种电池电极及其制备方法和电池
JP2019140054A (ja) * 2018-02-15 2019-08-22 Tdk株式会社 正極及び非水電解液二次電池
CN110660961A (zh) * 2018-06-28 2020-01-07 宁德时代新能源科技股份有限公司 正极片及锂离子电池
CN113193168A (zh) * 2021-04-30 2021-07-30 珠海冠宇电池股份有限公司 一种正极片及电池
CN115498150A (zh) * 2022-09-08 2022-12-20 盐城工学院 一种正极极片及其应用

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