Positive plate and preparation method thereof, battery, battery pack and electric equipment

Abstract

The invention provides a positive plate and a preparation method thereof, a battery, a battery pack and electric equipment, the positive plate comprises a positive active layer, and the positive active layer comprises a first active layer and a second active layer located on one side, deviating from a positive current collector, of the first active layer; the first active layer comprises a first phosphate positive electrode material and a single crystal ternary positive electrode material; and the second active layer comprises a second phosphate positive electrode material and a polycrystalline ternary positive electrode material. According to the invention, the internal resistance of the battery can be reduced, and the discharge capacity, power performance, high-temperature cycle life and other electrochemical properties of the battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a positive electrode sheet, a preparation method thereof, a battery, a battery pack and an electric device. BACKGROUND

[0002] A battery is a common electrochemical device, which is widely used. For example, a lithium ion battery has the advantages of high voltage, long service life, environmental friendliness, etc., and is widely used in the fields of electronic devices, automobiles, aerospace, etc. A positive electrode sheet is an important component of a battery, which directly affects the performance of the battery. However, due to the defects such as poor ion and electron conductivity of the positive electrode sheet, and the difficulty in balancing the ion and electron conductivity and energy density, the battery generally has problems of low discharge capacity, large internal resistance, poor power performance and high-temperature cycle performance, which need to be solved urgently. SUMMARY

[0003] The embodiments of the present application provide a positive electrode sheet, a preparation method thereof, a battery, a battery pack and an electric device, which can balance the reduction of the internal resistance of the battery and the improvement of the electrochemical performance of the battery such as the discharge capacity, the power performance and the high-temperature cycle life of the battery.

[0004] In one aspect of the present application, a positive electrode sheet is provided, which comprises a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector, the positive electrode active layer comprising a first active layer and a second active layer located on a side of the first active layer away from the positive electrode current collector; the first active layer comprises a first phosphate-based positive electrode material and a single-crystal ternary positive electrode material; and the second active layer comprises a second phosphate-based positive electrode material and a polycrystal ternary positive electrode material.

[0005] According to an embodiment of the present application, the second active layer comprises a first sub-layer and a second sub-layer located on a side of the first sub-layer away from the positive electrode current collector; the particle size D v 50 of the first phosphate-based positive electrode material in the first sub-layer is greater than the particle size D v 50 of the second phosphate-based positive electrode material in the second sub-layer; preferably, the ratio of the particle size D v 50 of the first phosphate-based positive electrode material to the particle size D v 50 of the second phosphate-based positive electrode material in the second sub-layer is 2-10; the particle size D v 50 of the second phosphate-based positive electrode material in the first sub-layer is greater than the particle size D v 50 of the second phosphate-based positive electrode material in the second sub-layer; preferably, the ratio of the particle size D v 50 of the second phosphate-based positive electrode material in the first sub-layer to the particle size D v 50 of the second phosphate-based positive electrode material in the second sub-layer is 2-8.

[0006] According to an embodiment of the present application, the particle size D50 of the first phosphate-based cathode material is 85 nm to 400 nm. v 50 is 85 nm to 400 nm; and / or, the particle size D50 of the second phosphate-based cathode material in the second sub-layer is 85 nm to 400 nm. v 50 is 85 nm to 400 nm; and / or, the particle size D50 of the second phosphate-based cathode material in the second sub-layer is 85 nm to 400 nm. v 50 is 10 nm to 85 nm.

[0007] According to an embodiment of the present application, the first phosphate-based cathode material and the second phosphate-based cathode material are each independently primary particles.

[0008] According to an embodiment of the present application, the first phosphate-based cathode material comprises lithium iron manganese phosphate; and / or, the second phosphate-based cathode material comprises lithium iron manganese phosphate.

[0009] According to an embodiment of the present application, the lithium iron manganese phosphate comprises LiMn x Fe 1-x-y M y PO4, M comprises one or more of Mg, Ca, Al, Sc, Ti, V, Cr, Co, Ni, Cu, Y, Nb, Mo, Zr and Nd, 0.55≤x≤0.85, 0≤y≤0.02.

[0010] According to an embodiment of the present application, the first active layer comprises a first active material, the first active material comprising the first phosphate-based cathode material and the single-crystal ternary cathode material; the mass ratio of the first phosphate-based cathode material in the first active layer to the first active material is 10% to 90%; the second active layer comprises a second active material, the second active material comprising the second phosphate-based cathode material and the polycrystal ternary cathode material; the mass ratio of the second phosphate-based cathode material in the second active layer to the second active material is 10% to 90%.

[0011] According to an embodiment of the present application, the particle size D50 of the single-crystal ternary cathode material is 2 μm to 20 μm. v 50 is 2 μm to 20 μm; and / or, the particle size D50 of the polycrystal ternary cathode material is 0.5 μm to 8 μm. v 50 is 0.5 μm to 8 μm.

[0012] According to an embodiment of the present application, the single-crystal ternary cathode material and the polycrystal ternary cathode material each independently comprise LiNi m Co n Mn 1-m-n O2, 0.5≤m≤0.8, 0.05≤n≤0.3.

[0013] In one aspect of the present application, a method for preparing a positive electrode sheet is provided, comprising the following steps: sequentially forming the first active layer and the second active layer on at least one side of the positive electrode current collector to obtain the positive electrode sheet.

[0014] In one aspect of the present application, a battery is provided, comprising the above-mentioned positive electrode sheet or the positive electrode sheet prepared according to the above-mentioned method for preparing a positive electrode sheet.

[0015] In one aspect of the present application, a battery pack is provided, comprising at least two of the above-mentioned batteries.

[0016] In one aspect of the present application, an electric device is provided, comprising the above-mentioned battery pack.

[0017] The positive electrode sheet and the preparation method thereof, the battery, the battery pack and the electric device provided by the embodiments of the present application have the advantages that the single-crystal ternary material and the first phosphate-based positive electrode material are compounded in the first active layer close to the positive electrode current collector, and the polycrystal ternary material and the second phosphate-based positive electrode material are compounded in the second active layer away from the positive electrode current collector, which helps to give full play to the capacity of the phosphate-based positive electrode material and the ternary positive electrode material, improves the ion and electron transport characteristics of the positive electrode sheet, improves the kinetic performance of the battery, reduces the internal resistance of the battery, and improves the discharge capacity, the power performance and the high-temperature cycle life of the battery. DETAILED DESCRIPTION

[0018] In order for those skilled in the art to better understand the solutions of the present application, the present application will be further described in detail below. The following specific embodiments are only used to describe the principles and characteristics of the present application, and the examples are used to explain the present application, but not to limit the scope of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0019] The defects of poor ion and electron conductivity of the positive electrode sheet, and the difficulty in balancing the ion and electron conductivity and the energy density make the battery have the problems of low discharge capacity, large internal resistance, poor power performance and high-temperature cycle performance, which need to be solved urgently.

[0020] The commonly used positive electrode materials mainly include phosphate-based positive electrode materials and ternary positive electrode materials, each of which has advantages and defects, and it is often difficult to balance, which affects the cycle performance of the battery. For example, the ternary positive electrode material has a high energy density, but its safety performance is poor. Although the iron lithium phosphate has advantages in cost and safety performance, its upper limit of energy density is low. The manganese iron lithium phosphate has the same olivine structure as the iron lithium phosphate, and its safety performance is similar to that of the iron lithium phosphate. At the same time, the higher platform voltage of the manganese iron lithium phosphate can improve the energy density to a certain extent. The electrical conductivity of the nitrogen manganese iron lithium phosphate is lower than that of the iron lithium phosphate, and the kinetic characteristics are poor. Although the nanocrystallization of the manganese iron lithium phosphate can improve the kinetic performance to a certain extent, on the one hand, the improvement effect of the kinetic performance is limited, and on the other hand, it also causes problems such as the decline of the processing process capability. Even if the manganese iron lithium phosphate and the ternary positive electrode material are mixed, due to the difference between the electronic and ionic conductivities of the two materials and other factors, the performance advantages of the two materials cannot be fully utilized, and the battery performance cannot be effectively improved.

[0021] Therefore, the embodiment of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector, the positive electrode active layer comprising a first active layer and a second active layer located on the side of the first active layer away from the positive electrode current collector; the first active layer comprises a first phosphate-based positive electrode material and a single-crystal ternary positive electrode material; and the second active layer comprises a second phosphate-based positive electrode material and a polycrystalline ternary positive electrode material.

[0022] According to the research of the inventor, the present application simultaneously uses phosphate-based positive electrode materials and ternary positive electrode materials, and adjusts the structure of the positive electrode active layer, so as to compound the phosphate-based positive electrode materials and the ternary positive electrode materials with different crystal structures in the different positive electrode active layers, which helps to exert the advantages of the phosphate-based positive electrode materials and the ternary positive electrode materials, improve the ionic and electronic conductivities of the whole positive electrode sheet, improve the kinetic performance of the positive electrode sheet, reduce the internal resistance of the battery, and improve the discharge capacity, power performance and high-temperature cycle life of the battery.

[0023] The reason for this is that the positive electrode uses a multilayer blend of phosphate-based and ternary positive electrode materials. In the first active layer near the positive electrode current collector, a combination of monocrystalline ternary material and a first phosphate-based positive electrode material is used. In the second active layer on the side of the first active layer away from the positive electrode current collector, a combination of polycrystalline ternary material and a second phosphate-based positive electrode material is used. This helps to maximize the capacity of both phosphate-based and ternary positive electrode materials. Furthermore, the voltage windows of the two materials are matched, allowing for precise control of the porosity and conductivity of different active layers and their gradients. This improves the ion and electron transport characteristics of the positive electrode, thereby improving the battery's kinetic performance, reducing internal resistance, and simultaneously enhancing the battery's discharge capacity, energy density, power performance, safety performance, and high-temperature cycle life.

[0024] Furthermore, according to the inventors' research, during short-term charge and discharge of lithium-ion batteries, regions with faster ion and electron transport and better lithium insertion / extraction kinetics tend to undergo electrochemical reactions more preferentially. Therefore, regions in the positive electrode sheet farther from the positive electrode current collector react more preferentially than regions closer to the positive electrode current collector, and polycrystalline material particles react more preferentially than single-crystal materials. Thus, the second phosphate-based positive electrode material and the polycrystalline ternary positive electrode material in the second active layer can improve kinetic performance because the polycrystalline ternary positive electrode material is polycrystalline and reacts more preferentially. At the same time, the first phosphate-based positive electrode material and the single-crystal ternary positive electrode material in the first active layer can ensure the battery's lifespan performance under continuous charge and discharge conditions because the single-crystal ternary positive electrode material is single-crystal and reacts slowly. Under continuous charge and discharge conditions, the structure of the first phosphate-based positive electrode material and the single-crystal ternary positive electrode material is more stable, which can improve the battery's kinetic characteristics, reduce the battery's internal resistance, and improve the battery's cycle stability.

[0025] In this embodiment of the invention, the particle size D v 50 refers to the particle size that accounts for 50% of the total volume distribution of particles; that is, particles with a volume percentage of 50% have a diameter less than or equal to D. v 50. Particles accounting for 50% of the remaining volume have a diameter greater than or equal to D. v50. The testing method is as follows: First, the positive electrode sheet is cut into sections using ion milling (CP), and then the morphology of the section is characterized using scanning electron microscopy (SEM). At least five different regions are selected and SEM images are taken at different magnifications (e.g., 100000, 50000, 20000, 10000, 5000, 2000, 1000, etc., including but not limited to the above magnifications). The obtained images are processed for brightness and contrast to make the particle boundaries clearer. Then, the particle size is statistically analyzed manually or using image analysis software. Since the particle size ranges of phosphate-based positive electrode materials and ternary positive electrode materials do not overlap, the output results can be processed to obtain detailed particle size distribution results for the two materials, thereby obtaining the particle size D of the two materials. v 50.

[0026] In some embodiments, the second active layer includes a first sublayer and a second sublayer located on the side of the first sublayer facing away from the positive electrode current collector, wherein the particle size D of the first phosphate-based positive electrode material is... v The particle size D of the second phosphate-based cathode material (i.e., second phosphate-based cathode material B) is greater than 50. v 50 is beneficial for further balancing the reduction of battery internal resistance and the improvement of battery cycle stability. The reason is that during short-term charge and discharge of lithium-ion batteries, regions with faster ion and electron transport and better lithium insertion / extraction kinetics will preferentially undergo electrochemical reactions. Therefore, the particle size D in the positive electrode sheet is important. v Materials smaller than 50 will be more compact than those with a particle size D. v If the material with a larger 50% phosphate content reacts more preferentially, then the second phosphate-based cathode material B can react more preferentially, which can further reduce the internal resistance of the battery. On the other hand, the first phosphate-based cathode material has a slower electrochemical reaction and a more stable structure, which can further improve the cycle stability of the battery.

[0027] In some preferred embodiments, the particle size D of the first phosphate-based cathode material v 50 and the particle size D of the second phosphate-based cathode material B v The ratio of 50 can be 2 to 10, for example, it can be 2, 4, 6, 8, 10 or any two of them, where the particle size D of the first phosphate-based cathode material is... v 50 and the particle size D of the second phosphate-based cathode material B v If the ratio of 50 is not less than 2, then the particle size D of the first phosphate-based cathode material is... v 50 will not be too small and the particle size D of the second phosphate-based cathode material B is... v A particle size of 50 is not too large, which is beneficial for further improving the battery's dynamic performance and cycle stability. The particle size D of the primary phosphate-based cathode material... v 50 and the particle size D of the second phosphate-based cathode material B vIf the ratio of 50 is not greater than 10, then the particle size D of the first phosphate-based cathode material is... v 50 will not be too large and the particle size D of the second phosphate-based cathode material B is... v A particle size of 50 is not too small, which is beneficial for further improving the stability of the positive electrode active layer structure. Therefore, the particle size D of the first phosphate-based positive electrode material is... v 50 and the particle size D of the second phosphate-based cathode material B v A ratio of 50 to 2-10 can further improve the ionic conductivity and electronic conductivity of the positive electrode, as well as enhance the stability of the positive electrode active layer structure.

[0028] In some embodiments, the particle size D of the second phosphate-based cathode material (i.e., the second phosphate-based cathode material A) in the first sublayer v 50 is greater than the particle size D of the second phosphate-based cathode material B. v 50. The second sublayer includes the second phosphate-based cathode material A and the polycrystalline ternary cathode material, which acts as a transition layer. The polycrystalline ternary cathode material reacts faster than the single-crystal ternary cathode material, while the second phosphate-based cathode material A reacts slower than the second phosphate-based cathode material B. This results in a gradient distribution of conductivity and porosity among the first active layer, the first sublayer, and the second sublayer. Compared to directly using two active cathode layers (the first active layer and the second sublayer), this is more conducive to long-range electron and ion electron transport, thus further improving the conductivity and ion conduction performance of the electrode sheet and further reducing the internal resistance of the battery.

[0029] In some preferred embodiments, the particle size D of the second phosphate-based cathode material A v 50 and the particle size D of the second phosphate-based cathode material B v The ratio of 50 can be 2 to 8, for example, it can be 2, 4, 6, 8 or any range between two of them, and the particle size D of the second phosphate-based cathode material A. v 50 and the particle size D of the second phosphate-based cathode material B v A ratio of 50 to 2 is more conducive to long-range ion-electron transport in the cathode, improving battery kinetic performance. The particle size D of the second phosphate-based cathode material A... v 50 and the particle size D of the second phosphate-based cathode material B v A ratio of 50 to 8 can further improve the structural stability of the positive electrode and enhance the cycle stability of the battery. Therefore, the particle size D of the second phosphate-based positive electrode material A is... v 50 and the particle size D of the second phosphate-based cathode material B v A ratio of 2 to 8 for 50 can further improve battery dynamics and cycle stability.

[0030] In some embodiments, the particle size D of the first phosphate-based cathode material v50 can be 85nm~400nm, for example, it can be 85nm, 125nm, 165nm, 205nm, 245nm, 285nm, 365nm, 400nm or any two of them.

[0031] In some embodiments, the particle size D of the second phosphate-based cathode material A v 50 can be 85nm~400nm, for example, it can be 85nm, 125nm, 165nm, 205nm, 245nm, 285nm, 365nm, 400nm or any two of them.

[0032] In some embodiments, the particle size D of the second phosphate-based cathode material B v 50 can be 10nm to 85nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 85nm or any two of them.

[0033] According to the inventor's research, the particle size D of the first phosphate-based cathode material... v 50 and the particle size D of the second phosphate-based cathode material A v 50 can be equal or unequal, that is, the particle size D of the first phosphate-based cathode material. v 50 can be greater than, equal to or less than the particle size D of the second phosphate-based cathode material A. v 50, which simultaneously meets the particle size D of the first phosphate-based cathode material. v 50 is greater than the particle size D of the second phosphate-based cathode material B. v 50. The particle size D of the second phosphate-based cathode material A v 50 is greater than the particle size D of the second phosphate-based cathode material B. v 50. The large-size first phosphate-based positive electrode active material in the first active layer can ensure the cycle stability of the battery, while the small-size second phosphate-based positive electrode material B in the second active layer can react more preferentially, which can further improve the kinetic performance and cycle stability of the battery.

[0034] In some embodiments, the first phosphate-based cathode material and the second phosphate-based cathode material are each independently a primary particle. Specifically, the first phosphate-based cathode material, the second phosphate-based cathode material A, and the second phosphate-based cathode material B in the cathode sheet are each independently a primary particle. The particle size of the primary particles of the phosphate-based cathode material is 10 nm to 400 nm, for example, it can be 10 nm, 50 nm, 90 nm, 130 nm, 170 nm, 210 nm, 250 nm, 290 nm, 330 nm, 370 nm, 400 nm, or any range between two of these. According to the inventors' research, during the formation of the cathode sheet, the secondary particles in the first phosphate-based cathode material, the second phosphate-based cathode material A, and the second phosphate-based cathode material B break down and dissociate into primary particles. This not only improves the battery's dynamic performance and reduces its internal resistance, but also further enhances the structural stability of the cathode active layer.

[0035] In some embodiments, the first phosphate-based cathode material may include lithium manganese iron phosphate, and the second phosphate-based cathode material may include lithium manganese iron phosphate. That is, the second phosphate-based cathode material A may include lithium manganese iron phosphate, and the second phosphate-based cathode material B may include lithium manganese iron phosphate. According to the inventors' research, on the one hand, lithium manganese iron phosphate has an olivine structure and excellent safety performance, and the higher plateau voltage of lithium manganese iron phosphate can bring about an increase in energy density; on the other hand, the voltage windows of lithium manganese iron phosphate and ternary cathode materials are matched, and the two materials can be blended to improve the conductivity of lithium manganese iron phosphate, which is beneficial to the preparation of cathode sheets. Therefore, the first phosphate-based cathode material may include lithium manganese iron phosphate, and the second phosphate-based cathode material may include lithium manganese iron phosphate. On the basis of reducing the internal resistance of the battery and improving the dynamic performance of the battery, the energy density, power and safety performance of the battery can be further improved, and it is also beneficial to the preparation of cathode sheets.

[0036] Accordingly, the positive electrode active layer includes a positive electrode active material, which includes lithium manganese iron phosphate and a ternary positive electrode material. The lithium manganese iron phosphate includes a first lithium manganese iron phosphate present in the first active layer, a second lithium manganese iron phosphate (i.e., second lithium manganese iron phosphate A) present in the first sublayer, and a second lithium manganese iron phosphate (i.e., second lithium manganese iron phosphate B) present in the second sublayer. The particle size D of the first lithium manganese iron phosphate is... v 50 is greater than the particle size D of lithium manganese iron phosphate B. v 50. Particle size D of lithium manganese iron phosphate A v 50 is greater than the particle size D of lithium manganese iron phosphate B. v50; Ternary cathode materials include monocrystalline ternary cathode materials and polycrystalline ternary cathode materials, namely monocrystalline ternary cathode materials existing in the first active layer, polycrystalline ternary cathode materials existing in the first sub-layer (i.e., the first polycrystalline ternary material), and polycrystalline ternary cathode materials existing in the second sub-layer (i.e., the second polycrystalline ternary material).

[0037] In some embodiments, lithium manganese iron phosphate includes LiMn x Fe 1-x-y M y PO4, wherein M includes one or more of Mg, Ca, Al, Sc, Ti, V, Cr, Co, Ni, Cu, Y, Nb, Mo, Zr and Nd, 0.55≤x≤0.85, 0≤y≤0.02. For example, x can be 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85 or any two of these, and y can be 0, 0.01, 0.02 or any two of these. Based on improving the ionic conductivity and electronic conductivity of the positive electrode, it can further improve the energy density, power and safety performance of the battery.

[0038] Accordingly, lithium manganese iron phosphate can be LiMn x Fe 1-x-y M y PO4, wherein M includes one or more of Mg, Ca, Al, Sc, Ti, V, Cr, Co, Ni, Cu, Y, Nb, Mo, Zr, and Nd, 0.55≤x≤0.85, 0≤y≤0.02; lithium manganese iron phosphate A can be LiMn x Fe 1-x-y M y PO4, wherein M includes one or more of Mg, Ca, Al, Sc, Ti, V, Cr, Co, Ni, Cu, Y, Nb, Mo, Zr, and Nd, 0.55≤x≤0.85, 0≤y≤0.02; lithium manganese iron phosphate B can be LiMn x Fe 1-x- y M y PO4, wherein M includes one or more of Mg, Ca, Al, Sc, Ti, V, Cr, Co, Ni, Cu, Y, Nb, Mo, Zr and Nd, and 0.55≤x≤0.85, 0≤y≤0.02.

[0039] In some embodiments, the positive electrode active layer includes a positive electrode active material, which includes lithium manganese iron phosphate and ternary positive electrode materials. The phosphate-based positive electrode material in the positive electrode active layer accounts for 10% to 90% of the total mass of the positive electrode active material. For example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any range between two of these. If the phosphate-based positive electrode material in the positive electrode active layer accounts for no less than 10% of the total mass of the positive electrode active material, it is beneficial to further improve the energy density and power of the battery and improve the safety performance of the battery. If the phosphate-based positive electrode material in the positive electrode active layer accounts for no more than 90% of the total mass of the positive electrode active material, it is beneficial to further improve the kinetic characteristics of the battery. Therefore, if the phosphate-based positive electrode material in the positive electrode active layer accounts for 10% to 90% of the total mass of the positive electrode active material, it can further improve the kinetic performance of the battery and improve the energy density, power, and safety performance of the battery.

[0040] Accordingly, the first active layer includes a first active material, which includes a first phosphate-based cathode material and a single-crystal ternary cathode material; the first phosphate-based cathode material in the first active layer accounts for 10% to 90% of the mass of the first active material, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or any range between two of them, which can further reduce the internal resistance of the battery and improve the energy density, power and safety performance of the battery.

[0041] Accordingly, the second active layer includes a second active material, which includes a second phosphate-based cathode material and a polycrystalline ternary cathode material. The second phosphate-based cathode material in the second active layer accounts for 10% to 90% of the mass of the second active material. For example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any range between two of these. The second phosphate-based cathode material A accounts for 10% to 90% of the mass of the second active material in the first sublayer, and the second phosphate-based cathode material B accounts for 10% to 90% of the mass of the second active material in the second sublayer. This can further improve the dynamic performance of the battery and enhance its energy density, power, and safety performance.

[0042] In some embodiments, the particle size D of the ternary cathode material v 50 can be 0.5μm to 20μm, for example, it can be 0.5μm, 2μm, 6μm, 10μm, 14μm, 18μm, 20μm or any range between two of them.

[0043] Specifically, the particle size D of the single-crystal ternary cathode material v50 is 2μm~20μm, for example, it can be 2μm, 6μm, 10μm, 14μm, 18μm, 20μm or any range between two of them; the particle size D of the first polycrystalline ternary cathode material v 50 is 0.5μm~8μm, for example, it can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or any range between two of them; the particle size D of the second polycrystalline ternary cathode material v 50 is 0.5μm~8μm, for example, it can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or any two of these ranges. According to the inventor's research, by controlling the structural parameters of the single-crystal ternary cathode material, the first polycrystalline ternary cathode material and the second polycrystalline ternary cathode material, the ion and electron transport characteristics of the cathode sheet can be improved. While ensuring the performance advantages of the mixed electrode, the internal resistance of the battery is further reduced and the battery dynamic performance is improved. Specifically, the particle size D of the second polycrystalline ternary cathode material in the second sublayer... v The particle size of the 50-layer monocrystalline ternary cathode material ranges from 0.5μm to 8μm, which can further improve the dynamic performance of the battery. v The particle size of 50 ranges from 2μm to 20μm, which can improve the cycle stability of the battery. Furthermore, the particle size distribution of the ternary cathode material allows the first, second, and third active layers to form a gradient distribution in terms of conductivity and porosity, which is more conducive to long-range ion and electron transport and reduces the internal resistance of the battery.

[0044] In some embodiments, the single-crystal ternary cathode material, the first polycrystalline ternary cathode material, and the second polycrystalline ternary cathode material each independently include LiNi. m Co n Mn 1-m-n O2, where 0.5≤m≤0.8, 0.05≤n≤0.3, for example, m can be a range of 0.5, 0.6, 0.7, 0.8 or any two of them, and n can be a range of 0.05, 0.1, 0.15, 0.2, 0.25, 0.3 or any two of them, which is beneficial to further improve the electronic conductivity of the positive electrode and reduce the internal resistance of the battery.

[0045] This invention also provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps:

[0046] A first active layer and a second active layer are sequentially formed on at least one side of the positive electrode current collector to obtain the above-mentioned positive electrode sheet.

[0047] Specifically, a first active layer, a first sublayer, and a second sublayer can be sequentially formed on at least one side of the positive electrode current collector to obtain the aforementioned positive electrode sheet.

[0048] In some embodiments, a first active layer and a second active layer are sequentially formed on at least one side of the positive current collector. Specifically, the first active layer and the second active layer can be sequentially disposed on one side of the positive current collector, or the first active layer and the second active layer can be disposed on opposite sides (i.e., the positive and negative surfaces of the positive current collector) in the thickness direction of the positive current collector.

[0049] In some embodiments, the positive electrode sheet can be prepared by conventional methods in the art, such as by a multilayer coating method. Specifically, the first active material, the second active material of the first sublayer, and the second active material of the second sublayer can be mixed uniformly with components used to form the positive electrode active layer, such as conductive agents, binders, and dispersants, and a solvent. The solvent may include, for example, N-methylpyrrolidone (NMP). This mixture is then used to prepare a first positive electrode slurry, a second positive electrode slurry of the first sublayer, and a second positive electrode slurry of the second sublayer. The viscosity is controlled to ensure good slurry flowability. These slurries are then sequentially coated onto the surface of the positive electrode current collector. After drying, rolling, and cutting, the positive electrode sheet is obtained. The coating, drying, rolling, and cutting processes involved are conventional operations for preparing positive electrode sheets using the coating method and are not particularly limited.

[0050] Specifically, the first active material includes a first lithium manganese iron phosphate and a single-crystal ternary cathode material; the second active material of the first sublayer includes a second lithium manganese iron phosphate A and a polycrystalline ternary cathode material; the second active material of the second sublayer includes a second lithium manganese iron phosphate B and a second polycrystalline ternary cathode material.

[0051] In some embodiments, the mixing method may include wet or semi-dry kneading.

[0052] Generally, the conductive agent and binder mentioned above can be conventional materials in the art. For example, the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0053] Generally, in the positive electrode active layer, the mass percentage of the positive electrode active material (i.e., the ratio of the mass of the positive electrode active material to the total mass of the positive electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass percentage of the conductive agent can be 0.5% to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any combination thereof; and the mass percentage of the binder can be 1% to 4%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or any combination thereof.

[0054] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0055] This invention also provides a battery comprising the above-described positive electrode sheet or a positive electrode sheet prepared according to the above-described method for preparing the positive electrode sheet. This battery has advantages corresponding to the above-described positive electrode sheet, which will not be elaborated further.

[0056] Generally, a battery includes a cell and a casing that encapsulates the cell. Electrolyte is injected into the cell within the casing. The cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of positive electrode, separator, and negative electrode layers stacked sequentially and then wound together.

[0057] In this embodiment of the invention, conventional negative electrode sheets in the art can be used, and there are no particular limitations. For example, the negative electrode sheet may include a negative current collector and a negative active layer located on at least one side surface of the negative current collector. Specifically, the negative active layer may be provided on one side surface of the negative current collector, or negative active layers may be provided on both opposite sides of the negative current collector in the thickness direction.

[0058] Specifically, the negative electrode active layer may include a negative electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the negative electrode active material may include graphite, which may include artificial graphite and / or natural graphite; the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0059] Generally, in the negative electrode active layer, the mass percentage of the negative electrode active material (i.e., the ratio of the mass of the negative electrode active material to the total mass of the negative electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass percentage of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof; and the mass percentage of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0060] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0061] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0062] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment of the invention, and there are no special limitations on this.

[0063] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0064] The electrolyte in this embodiment of the invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0065] In this embodiment of the invention, the processes involved in the battery manufacturing process, such as encapsulation, electrolyte injection (i.e., injecting electrolyte into the casing), formation, venting, capacity testing, and aging, are all conventional operations in the field and are not particularly limited.

[0066] This invention also provides a battery pack comprising at least two of the above-described batteries, which has advantages corresponding to the above-described positive electrode, and will not be described in detail hereafter.

[0067] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0068] This invention also provides an electrical device including the battery pack described above. This electrical device has advantages corresponding to the positive electrode plate described above, which will not be elaborated further.

[0069] The electrical equipment used in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0070] The present invention will be further described below through specific embodiments.

[0071] Example 1

[0072] 1. Preparation of positive electrode sheet

[0073] The first active material, the second active material of the first sublayer, and the second active material of the second sublayer were mixed with carbon black and PVDF at a weight ratio of 96:2.4:1.6, respectively, and then mixed with NMP to prepare the first positive electrode slurry, the second positive electrode slurry of the first sublayer, and the second positive electrode slurry of the second sublayer. These were then sequentially coated onto the front and back surfaces of an aluminum foil to obtain a single-sided surface density of 210 g / m². 2 The positive electrode active layer is dried, rolled, and cut to obtain the positive electrode sheet.

[0074] Specifically, the first active material has a particle size D v 50 represents 150nm of lithium manganese iron phosphate, with a particle size D v 50 is a 10μm single-crystal ternary cathode material, in which lithium manganese iron phosphate accounts for 80% of the mass of the first active material; the second active material in the first sublayer has a particle size D v 50 represents 120nm lithium manganese iron phosphate A, particle size D vThe first polycrystalline ternary cathode material has a particle size of 6 μm, wherein the second active material, lithium manganese iron phosphate (LiFePO4), accounts for 60% of the mass of the second active material in the first sublayer; the second active material in the second sublayer has a particle size of D. v 50 is 60nm of lithium manganese iron phosphate B, particle size D v The second polycrystalline ternary cathode material is 4μm thick, wherein the second lithium iron phosphate B accounts for 40% of the mass of the second active material in the second sublayer.

[0075] 2. Preparation of negative electrode sheet

[0076] The negative electrode slurry is prepared by mixing graphite, carbon black conductive agent, and CMC binder in a weight ratio of 97:1:2. It is then coated on both sides of the copper foil. After drying, rolling, and cutting, the negative electrode sheet is obtained.

[0077] 3. Battery assembly

[0078] The positive electrode, separator (polypropylene separator), negative electrode, and separator (polypropylene separator) are stacked in sequence to assemble a battery cell. After conventional processes such as electrolyte injection and formation, a battery is produced.

[0079] The electrolyte is composed of lithium hexafluorophosphate, ethylene carbonate, diethyl carbonate, and vinylene carbonate in a mass ratio of 12.93:43.54:43.54:4.

[0080] Examples 2 to 21: The difference from Example 1 is that the particle size D of the first phosphate-based cathode material is... v 50. The particle size D of the second phosphate-based cathode material A v 50. The particle size D of the second phosphate-based cathode material B v 50. Particle size D of the first phosphate-based cathode material v 50 and the particle size D of the second phosphate-based cathode material B v The ratio of 50, the particle size D of the second phosphate-based cathode material A v 50 and the particle size D of the second phosphate-based cathode material B v The ratio of 50, the particle size D of the single-crystal ternary cathode material v 50. Particle size D of the first polycrystalline ternary cathode material v 50. Particle size D of the second polycrystalline ternary cathode material v 50. The mass ratio of the first lithium manganese iron phosphate to the first active material, the mass ratio of the second lithium manganese iron phosphate A to the second active material of the second sublayer, and the mass ratio of the second lithium manganese iron phosphate B to the second active material of the second sublayer are different, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1.

[0081] Comparative Example 1: The difference from Example 1 is that in the preparation of the positive electrode sheet in step 1, only a single-layer positive electrode active layer is prepared, and the positive electrode active material has a particle size D. v 50 represents 120nm of lithium manganese iron phosphate, with a particle size D v 50 is a 6μm single-crystal ternary cathode material, with lithium manganese iron phosphate accounting for 60% of the mass of the active material. The remaining steps and conditions are the same as in Example 1.

[0082] Comparative Example 2: The difference from Example 1 is that in the preparation of the positive electrode sheet in step 1, a double-layer positive electrode active layer is prepared, and the active material in the active layer near the current collector has a particle size D. v 50 represents 150nm of lithium manganese iron phosphate, with a particle size D v 50 is a 10μm single-crystal ternary cathode material, in which lithium manganese iron phosphate accounts for 80% of the mass of the active material; the active material in the active layer near the electrolyte side has a particle size of D. v 50 is 60nm of lithium manganese iron phosphate A, particle size D v The first polycrystalline ternary cathode material with a diameter of 4 μm is 50, wherein the second lithium manganese iron phosphate A accounts for 40% of the mass of the active material, and the remaining steps and conditions are the same as in Example 1.

[0083] Comparative Examples 3-4: The difference from Example 1 is that in the preparation of the positive electrode sheet in step 1, a double-layer positive electrode active layer is prepared, but each layer has only a single active material, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1.

[0084] Following the procedure below, the discharge specific capacity, energy density, DC internal resistance (DCIR), 80% SOC discharge peak power, and capacity retention rate after 100 high-temperature cycles of the batteries in each embodiment and comparative example were tested respectively. The results are shown in Table 2.

[0085] (1) Test conditions for the discharge specific capacity and energy density of the battery (room temperature): Take the battery prepared above, charge it at room temperature (25℃±5℃) with constant current and constant voltage at 1 / 3C to 4.3V, cut off current at 0.05C, discharge it at 1 / 3C with constant current to 2.5V, cycle three times, record the discharge capacity of the last discharge as Q, and the mass of the positive electrode active material as M, then the discharge specific capacity of the battery = Q / M (unit: mAh / g), the discharge specific capacity results are shown in Table 1; record the energy of the last discharge as E, then the energy density = E / M (unit: Wh / kg), the energy density results are shown in Table 2.

[0086] (2) DC internal resistance (DCIR) test conditions (room temperature): Take the battery prepared above and charge it to 4.3V at 1 / 3C constant current and constant voltage at room temperature (25℃±5℃). Cut off current 0.05C and discharge at 1 / 3C constant current for 90min. At this time, the state of charge (SOC) of the battery is 50%. The termination voltage after standing for 1h is recorded as V0 and the termination voltage after discharging at 1.5C for 30s is recorded as V1. Calculate the DC internal resistance R. The calculation formula is: R = (V1-V0) / 1.5 (unit mΩ Ah). The DCIR results are shown in Table 2.

[0087] (3) Test conditions for peak discharge power of battery at 80% SOC (room temperature): At 25℃±5℃, charge to 4.3V with constant current and constant voltage at 1 / 3C current, cut off current at 0.05C, and let stand for 30min; discharge with constant current at 1 / 3C current for 36min (adjust battery SOC to 80%, i.e., battery state of charge is 80%), and let stand for 1h; pulse discharge with constant current at 1C current for 30s, record cut-off voltage. If cut-off voltage is higher than 2.5V, let stand for 30min, repeat the above steps, set the constant current discharge rate of the pulse discharge step to 2 / 3 / 4 / 5 / ...C in sequence, until the cut-off voltage is lower than 2.5V under a certain constant current discharge rate, take the current I and discharge termination voltage V used in the penultimate pulse discharge, and the battery discharge energy E obtained in the above test, calculate the peak discharge power of battery at 80% SOC P=IV / E (unit: W / Wh), the results are shown in Table 2.

[0088] (4) High-temperature cycling capacity retention test conditions for the battery: Take the battery prepared above and in a 45°C environment: 1) Let the battery stand for 2 hours; 2) Charge it to 2.5V with constant current and constant voltage at 0.5C and cutoff current at 0.05C, and let it stand for 10 minutes; 3) Discharge it to 2.5V with constant current at 0.5C, record the discharge capacity as C1, and let it stand for 10 minutes; 4) Repeat steps 2)-3) 100 times, and record the discharge capacity as C1 at the 100th cycle. 100 The ratio C of the discharge capacity in the 100th cycle to the discharge capacity in the first cycle is... 100 / C1 is the battery's capacity retention rate after 100 high-temperature cycles.

[0089] Table 1. Preparation parameters of positive electrode sheet

[0090]

[0091] Table 2. Cathode preparation parameters and battery performance

[0092]

[0093] Compared to Comparative Examples 1-4, the cathode sheets in Examples 1-21 employ a multilayer blending of phosphate-based cathode materials and ternary cathode materials. In the first active layer near the cathode current collector, a combination of monocrystalline ternary materials and a first phosphate-based cathode material is used. In the second active layer on the side of the first active layer away from the cathode current collector, a combination of polycrystalline ternary materials and a second phosphate-based cathode material is used. This approach helps to maximize the capacity of both phosphate-based and ternary cathode materials, improves the ion and electron transport characteristics of the cathode sheet, enhances the battery's kinetic performance, reduces internal resistance, and simultaneously improves the battery's discharge capacity, power performance, and high-temperature cycle life, among other electrochemical properties.

[0094] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to what has been described above. Various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active layer located on at least one side of the positive current collector, the positive active layer including a first active layer and a second active layer located on the side of the first active layer opposite to the positive current collector; The first active layer comprises a first phosphate-based cathode material and a single-crystal ternary cathode material; The second active layer comprises a second phosphate-based cathode material and a polycrystalline ternary cathode material.

2. The positive electrode sheet according to claim 1, characterized in that, The second active layer includes a first sublayer and a second sublayer located on the side of the first sublayer facing away from the positive current collector; The particle size D of the first phosphate-based cathode material v 50 is greater than the particle size D of the second phosphate-based cathode material in the second sublayer. v 50; Preferably, the particle size D of the first phosphate-based cathode material v 50 and the particle size D of the second phosphate-based cathode material in the second sublayer v The ratio of 50 is 2 to 10; The particle size D of the second phosphate-based cathode material in the first sublayer v 50 is greater than the particle size D of the second phosphate-based cathode material in the second sublayer. v 50; Preferably, the particle size D of the second phosphate-based cathode material in the first sublayer is... v 50 and the particle size D of the second phosphate-based cathode material in the second sublayer v The ratio of 50 is 2 to 8.

3. The positive electrode sheet according to claim 2, characterized in that, The particle size D of the first phosphate-based cathode material v 50 is 85nm~400nm; And / or, the particle size D of the second phosphate-based cathode material in the first sublayer v 50 is 85nm~400nm; And / or, the particle size D of the second phosphate-based cathode material in the second sublayer v 50 refers to the range of 10nm to 85nm.

4. The positive electrode sheet according to any one of claims 1-3, characterized in that, The first phosphate-based cathode material and the second phosphate-based cathode material are each independently primary particles.

5. The positive electrode sheet according to any one of claims 1-4, characterized in that, The first phosphate-based cathode material includes lithium manganese iron phosphate; And / or, the second phosphate-based cathode material includes lithium manganese iron phosphate.

6. The positive electrode sheet according to claim 5, characterized in that, The lithium manganese iron phosphate includes LiMn. x Fe 1-x-y M y PO4, M includes one or more of Mg, Ca, Al, Sc, Ti, V, Cr, Co, Ni, Cu, Y, Nb, Mo, Zr and Nd, 0.55≤x≤0.85, 0≤y≤0.

02.

7. The positive electrode sheet according to any one of claims 1-6, characterized in that, The first active layer includes a first active material, which comprises a first phosphate-based cathode material and the single-crystal ternary cathode material; the first phosphate-based cathode material in the first active layer accounts for 10% to 90% of the mass of the first active material. The second active layer includes a second active material, which includes the second phosphate-based cathode material and the polycrystalline ternary cathode material; the second phosphate-based cathode material in the second active layer accounts for 10% to 90% of the mass of the second active material.

8. The positive electrode sheet according to any one of claims 1-7, characterized in that, The particle size D of the single-crystal ternary cathode material v 50 represents 2μm~20μm; And / or, the particle size D of the polycrystalline ternary cathode material v 50 ranges from 0.5μm to 8μm.

9. The positive electrode sheet according to any one of claims 1-8, characterized in that, The single-crystal ternary cathode material and the polycrystalline ternary cathode material each independently include LiNi. m Co n Mn 1-m-n O2, 0.5≤m≤0.8, 0.05≤n≤0.

3.

10. A method for preparing a positive electrode sheet according to any one of claims 1-9, characterized in that, Includes the following steps: The first active layer and the second active layer are sequentially formed on at least one side of the positive current collector to obtain the positive electrode sheet.

11. A battery, characterized in that, This includes the positive electrode sheet as described in any one of claims 1-9 or the positive electrode sheet prepared according to the method for preparing the positive electrode sheet as described in claim 10.

12. A battery pack, characterized in that, It includes at least two batteries as described in claim 11.

13. An electrical appliance, characterized in that, Includes the battery pack as described in claim 12.

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