Positive electrode sheet and lithium-ion battery

Abstract

This invention relates to the field of battery technology, specifically to a positive electrode sheet and a lithium-ion battery. The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the surface of the positive current collector. The positive active layer includes a positive active material, which includes a first type of particle and a second type of particle. The first type of particle is a polycrystalline high-nickel ternary material; the second type of particle is a monocrystalline high-nickel ternary material. Compared with the prior art, this invention optimizes the complementary electrochemical performance by synergistically designing the parameters of the polycrystalline and monocrystalline materials: nickel content gradient, cobalt-manganese ratio gradient, particle size ratio, and the proportion of the second type of particle, thereby helping to improve the energy density, cycle stability, and rate performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to positive electrode sheets and lithium-ion batteries. Background Technology

[0002] With the rapid development of electric vehicles, large-scale energy storage, and other fields, the market has placed higher demands on the energy density, power density, and cycle life of lithium-ion batteries. High-nickel layered oxide cathode materials (such as LiNi) are becoming increasingly important. x Co y Mn z O2, NCM, x>0.8) are considered key to improving battery energy density due to their high specific capacity.

[0003] However, the industrialization of high-nickel materials faces two major contradictions: first, the contradiction between the increased capacity due to high nickel content and the decreased structural / interface stability; and second, the contradiction between the material's microstructure (single-crystal / polycrystalline) and its kinetic and mechanical properties. Polycrystalline materials are composed of agglomerated nanoparticles, resulting in short lithium-ion diffusion paths and good rate performance. However, during long-term cycling, microcracks easily form at grain boundaries, leading to cycle degradation. Single-crystal materials have a complete structure, high mechanical strength, and good cycle stability, but lithium ions must traverse the entire grain, resulting in poor intrinsic kinetics and limited rate performance.

[0004] Therefore, how to develop a lithium-ion battery that can simultaneously achieve high energy density, high rate performance, and long cycle life through careful material design and system integration has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a positive electrode sheet and a lithium-ion battery. By introducing a coordination factor S, four key design variables—nickel content gradient, cobalt-manganese ratio gradient, particle size ratio, and the proportion of second-type particles—are integrated into a quantitative mathematical model, and a threshold of S≥2.0 is set. This systematically ensures the maximization of the complementary effect of polycrystalline and monocrystalline components in electrochemical performance, achieving synergistic optimization of energy density, rate performance, and cycle life.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a positive electrode sheet is provided, comprising a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector, wherein the positive active layer comprises a positive active material, and the positive active material comprises a first type of particle and a second type of particle; The first type of particles is a polycrystalline high-nickel ternary material. The general chemical formula of the first type of particles is LiNia1Cob1Mnc1O2, where a1+b1+c1=1, 0.85≤a1≤0.94; the average particle size of the first type of particles is D1. The second type of particles is a single-crystal high-nickel ternary material; the general chemical formula of the second type of particles is LiNia2Cob2Mnc2O2, where a2+b2+c2=1, 0.88≤a2≤0.96; the average particle size of the second type of particles is D2; Wherein, the volume ratio of the second type of particles to the positive electrode active material is x, 0 <x<1; The coordination factor S of the positive electrode active material is calculated using the following formula, where S≥2: .

[0007] In some of these implementations, 0.88 ≤ a1 ≤ 0.92, and a2 ≥ a1 + 0.02.

[0008] In some of these implementations, b2 / c2 ≥ 1.5 × (b1 / c1).

[0009] In some of these implementations, D1 is 8µm to 20µm.

[0010] In some of these implementations, D2 is 1µm to 5µm.

[0011] In some of these embodiments, D1 is 10µm to 15µm.

[0012] In some of these implementations, D2 is 2µm to 4µm.

[0013] In some of these implementations, 0.2 ≤ x ≤ 0.8.

[0014] In some of these implementations, 0.3 ≤ x ≤ 0.5.

[0015] In some embodiments, the compaction density of the positive electrode sheet is 3.2 g / cm³. 3 ~3.8g / cm 3 .

[0016] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode comprises the positive electrode described in the above-described technical solution.

[0017] In some embodiments, the lithium-ion battery is a full-tab cylindrical battery, wherein the current collector edge of the electrode of the lithium-ion battery extends to form a full-tab structure, and the width L2 of the full-tab structure and the width L1 of the positive electrode satisfy: L2≥L1×95%.

[0018] Implementing the technical solution of the present invention has at least the following beneficial effects: (1) This invention creatively integrates the nickel content, cobalt-manganese ratio, particle size ratio and mixing ratio of polycrystalline and monocrystalline high-nickel ternary material particles in the positive electrode active material, and performs quantitative characterization through the coordination factor S. When S≥2, it overcomes the limitations of single material or simple mixing, and effectively takes into account the rate performance and cycle life while improving the energy density of lithium-ion batteries, thus achieving the optimization of comprehensive electrochemical performance.

[0019] (2) The present invention optimizes the particle packing state in the positive electrode active material through the gradation effect of large and small particles, thereby improving the compaction density; by making the nickel content of single crystal particles higher than that of polycrystalline particles, the overall specific capacity is improved under the premise of ensuring stability, thereby achieving high energy density in both volume and mass dimensions.

[0020] (3) The grain boundary-free structure of single crystal particles provides excellent skeletal stability. This invention greatly delays the cycle life of the battery by confining the unstable high-nickel phase in a stable single crystal structure, while maintaining a relatively low nickel content in polycrystalline particles to maintain structural stability and reduce stress.

[0021] (4) By increasing the cobalt-manganese ratio of single crystal particles to polycrystalline particles, this invention specifically enhances the lithium-ion diffusion kinetics within the single crystal component, effectively compensating for its intrinsic kinetic shortcomings, making the overall rate performance of the positive electrode active material even better than that of high-quality polycrystalline materials, thus ensuring the high power output and fast charging capability of the battery.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the full tab structure of the lithium-ion battery obtained in Example 1 of the present invention.

[0025] Reference numerals: 1. Positive electrode plate; 2. Electrode tab. Detailed Implementation

[0026] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0029] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0030] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] With the rapid development of electric vehicles, large-scale energy storage, and other fields, the market has placed higher demands on the energy density, power density, and cycle life of lithium-ion batteries. High-nickel layered oxide cathode materials (such as LiNi) are becoming increasingly important. x Co y Mn z O2, NCM, x>0.8) are considered key to improving battery energy density due to their high specific capacity.

[0035] However, the industrialization of high-nickel materials faces two major contradictions: first, the contradiction between the increased capacity due to high nickel content and the decreased structural / interface stability; and second, the contradiction between the material's microstructure (single-crystal / polycrystalline) and its kinetic and mechanical properties. Polycrystalline materials are composed of agglomerated nanoparticles, resulting in short lithium-ion diffusion paths and good rate performance. However, during long-term cycling, microcracks easily form at grain boundaries, leading to cycle degradation. Single-crystal materials have a complete structure, high mechanical strength, and good cycle stability, but lithium ions must traverse the entire grain, resulting in poor intrinsic kinetics and limited rate performance.

[0036] In existing technologies, either a single polycrystalline or monocrystalline material is used and modified through doping or coating, or two materials are simply mixed in an attempt to balance performance. However, the former is difficult to fundamentally solve the inherent performance shortcomings of the material itself; the latter often lacks systematic design principles, the mixing effect is uncertain, and usually only one performance can be improved at the expense of another, failing to achieve synergistic optimization of energy, power, and lifetime.

[0037] Therefore, in the high-nickel cathode material system, how to develop a lithium-ion battery that can simultaneously achieve high energy density, high rate performance and long cycle life through careful material design and system integration has become a technical problem that urgently needs to be solved in this field.

[0038] Based on this, the present invention mixes polycrystalline high-nickel ternary materials and monocrystalline high-nickel ternary materials. By adjusting the nickel content, cobalt-manganese ratio, particle size ratio, and mixing ratio of the first and second types of particles, the coordination factor S range of the positive electrode active material is adjusted and S≥2 is limited, which effectively improves the energy density, rate performance and cycle life of lithium-ion batteries.

[0039] Specifically, the present invention adopts the following technical solution: According to one aspect of the present invention, a positive electrode sheet is provided, comprising a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector, wherein the positive active layer comprises a positive active material, and the positive active material comprises a first type of particle and a second type of particle; The first type of particles is a polycrystalline high-nickel ternary material. The general chemical formula of the first type of particles is LiNia1Cob1Mnc1O2, where a1+b1+c1=1, 0.85≤a1≤0.94; the average particle size of the first type of particles is D1. The second type of particles is a single-crystal high-nickel ternary material; the general chemical formula of the second type of particles is LiNia2Cob2Mnc2O2, where a2+b2+c2=1, 0.88≤a2≤0.96; the average particle size of the second type of particles is D2; Wherein, the volume ratio of the second type of particles to the positive electrode active material is x, 0 <x<1; The coordination factor S of the positive electrode active material is calculated using the following formula, where S≥2: .

[0040] Specifically, in the formula for calculating the coordination factor S, all parameters are dimensionless or are converted to dimensionless values ​​through ratios: a1 and a2 are the stoichiometric coefficients of nickel in the first and second types of particles, respectively, and are pure numerical values, dimensionless. b1, c1, b2, and c2 are the stoichiometric coefficients of cobalt and manganese, respectively, and are pure numerical values, dimensionless; therefore, the ratios b1 / c1 and b2 / c2 are also dimensionless. D1 and D2 are the average particle sizes of the first and second types of particles, respectively; in the ratio D1 / D2, the units cancel each other out, so this ratio is dimensionless. x is the volume ratio of the second type of particles to the positive electrode active material, and is a pure numerical value, dimensionless; therefore, x(1-x) is also dimensionless. In summary, each term in the formula is dimensionless, therefore the final calculated coordination factor S is a dimensionless pure numerical value.

[0041] In a specific embodiment of the present invention, the first type of particles is a polycrystalline high-nickel ternary material, and the chemical formula of the first type of particles is LiNia1Cob1Mnc1O2, wherein a1+b1+c1=1, 0.85≤a1≤0.94, preferably 0.88≤a1≤0.92, and a1 can specifically be 0.88, 0.89, 0.90, 0.91, 0.92, and any value between the above two.

[0042] In a specific embodiment of the present invention, the first type of particles and the second type of particles satisfy: a2 ≥ a1 + 0.02. The present invention ensures that the nickel content of the single-crystal high-nickel ternary material is higher than that of the polycrystalline high-nickel ternary material. On the one hand, the higher thermodynamic instability of the high-nickel component is confined within the structurally intact, grain boundary-free single-crystal particles. The inherent high mechanical strength and structural stability of the single-crystal particles are used to suppress the structural degradation of the high-nickel phase during cycling (such as phase transformation and oxygen release), thereby improving the overall cycling stability of the material. On the other hand, the relatively lower nickel content of the polycrystalline particles helps to reduce the grain boundary stress caused by anisotropic volume changes during cycling, reducing the generation and propagation of microcracks. The combination of these two factors constitutes a stability enhancement mechanism where "high-nickel single crystals provide a stable framework, and medium-to-high-nickel polycrystalline materials provide buffering and kinetic channels."

[0043] In a specific embodiment of the present invention, the first type of particles and the second type of particles satisfy: b2 / c2 ≥ 1.5 × (b1 / c1). By limiting the cobalt-manganese ratio of the single-crystal high-nickel ternary material to be higher than that of the polycrystalline high-nickel ternary material, the present invention can effectively reduce the diffusion barrier of lithium ions in the bulk phase of single-crystal particles, compensating for its kinetic shortcomings. This allows lithium ions to enter and exit the single-crystal particles more rapidly in the cathode active material, thereby significantly improving the capacity retention rate of the cathode active material under high-rate charge-discharge conditions, i.e., rate performance.

[0044] In a specific embodiment of the present invention, D1 is 8µm to 20µm, preferably 10µm to 15µm, and specifically can be 10µm, 11µm, 12µm, 13µm, 14µm, 15µm, or any value between the two mentioned above. The present invention selects the average particle size of the aforementioned first type of particles to ensure that the polycrystalline particles have a sufficiently large size to serve as a framework in the positive electrode sheet, forming a stable main structure. At the same time, this size range also avoids the problems that may arise from excessively large particles, such as poor internal dispersion, decreased coating uniformity, and excessively long diffusion paths of lithium ions within the particles.

[0045] In a specific embodiment of the present invention, D2 is 1µm to 5µm, preferably 2µm to 4µm, and can specifically be 2µm, 2.5µm, 3µm, 3.5µm, 4µm, or any value between the two mentioned above. The present invention selects the average particle size of the aforementioned second type of particles for two reasons: firstly, to ensure that the single crystal particles, as filler particles, are small enough to effectively embed into the pores between larger particles, optimizing the particle packing density of the positive electrode active layer, thereby significantly improving the filling density, i.e., the compaction density, of the positive electrode active layer; secondly, to help form a better ion and electron conductivity network in the electrode, increasing the energy density.

[0046] In a specific embodiment of the present invention, D1 / D2 is preferably 1.6 to 8, specifically 1.6, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, and any value between the two mentioned above. By controlling the particle size ratio within the above range, the present invention enables the particles of different sizes to achieve close packing, thereby obtaining high electrode compaction density and volumetric energy density.

[0047] In a specific embodiment of the present invention, the volume ratio of the second type of particles to the positive electrode active material is x, where 0.2 ≤ x ≤ 0.8, preferably 0.3 ≤ x ≤ 0.5, and x can specifically be 0.3, 0.4, 0.5, or any value between the two. If the proportion of the second type of particles is too low, the "skeleton" role of the single crystal material in stabilizing the structure and improving cycle life cannot be fully utilized; if the proportion of the second type of particles is too high, the overall packing efficiency will be affected due to the excessive number of small particles, resulting in a decrease in compaction density. At the same time, excessive single crystal particles with poor kinetics will reduce the overall rate performance of the positive electrode active material. The present invention selects the above-mentioned volume ratio of the second type of particles to the positive electrode active material so that single crystal particles and polycrystalline particles can form a continuous and mutually penetrating composite structure, achieving a balance and synergy in performance.

[0048] In a specific embodiment of the present invention, the compaction density of the positive electrode sheet is preferably 3.2 g / cm³. 3 ~3.8g / cm 3 Specifically, it could be 3.2 g / cm³. 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 The above-mentioned high compaction density is the result of the combined effect of optimized particle size distribution and particle mixing ratio, which maximizes the active material loading per unit volume of the electrode, thereby significantly improving the volumetric energy density of the battery.

[0049] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode comprises the positive electrode described in the above-described technical solution; thus, the lithium-ion battery has all the features and advantages of the positive electrode described in the above-described technical solution, which will not be repeated here.

[0050] In a specific embodiment of the present invention, the positive electrode includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector, wherein the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0051] In a specific embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material includes first-type particles and second-type particles; the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the positive electrode conductive agent includes one or more of conductive carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The present invention does not impose any special restrictions on the source of the above-mentioned positive electrode active material, positive electrode binder, and positive electrode conductive agent; commercially available products well known to those skilled in the art can be used.

[0052] In a specific embodiment of the present invention, the method for preparing the positive electrode includes: thoroughly mixing a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and a solvent to prepare a slurry; coating the slurry onto a positive electrode current collector; and drying, cold pressing, and slitting to obtain the positive electrode sheet. The positive electrode current collector can be a metal foil such as aluminum foil.

[0053] In a specific embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector; wherein, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0054] In a specific embodiment of the present invention, the negative electrode active layer comprises a negative electrode active material, a binder, a thickener, and a conductive agent; wherein, the negative electrode active material comprises one or more of graphite and silicon; the negative electrode binder comprises one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the thickener comprises one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA); and the negative electrode conductive agent comprises one or more of conductive carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The present invention does not impose any special restrictions on the source of the above-mentioned negative electrode active material, negative electrode binder, thickener, and negative electrode conductive agent; commercially available products well known to those skilled in the art can be used.

[0055] In a specific embodiment of the present invention, the method for preparing the negative electrode includes: thoroughly mixing a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, a thickener, and a solvent to prepare a slurry; coating the slurry onto a negative electrode current collector; and drying, cold pressing, and slitting to obtain the negative electrode sheet. The negative electrode current collector can be a metal foil, such as copper foil.

[0056] In a specific embodiment of the present invention, the electrolyte comprises an organic solvent, an electrolyte lithium salt, and additives. Preferably, the electrolyte lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorosulfonylimide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonylimide). The organic solvent preferably comprises one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate. The additives preferably comprise one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate, and vinyl carbonate. The present invention does not impose any special restrictions on the source of the above-mentioned organic solvent, electrolyte lithium salt, and additives; commercially available products well known to those skilled in the art can be used.

[0057] In a specific embodiment of the present invention, the separator includes a base membrane and a coating disposed on at least one surface of the base membrane. The base membrane preferably includes a polyolefin microporous separator, specifically a polypropylene (PP) membrane, a polyethylene (PE) membrane, a PP / PE / PP composite membrane, etc.; the coating is preferably a ceramic coating and / or a PVDF coating. The present invention does not impose any special restrictions on the source of the separator; commercially available products well known to those skilled in the art can be used.

[0058] In a specific embodiment of the present invention, the lithium-ion battery is preferably formed by stacking a positive electrode, a separator, and a negative electrode, and then winding them together. In a preferred embodiment of the present invention, the battery preparation process includes: sequentially stacking the positive electrode, the separator, and the negative electrode, then winding them together to form an electrode assembly, packaging them with a polymer, filling them with electrolyte, and then performing formation and other processes to form the battery. The specific conditions and parameters for each step in the above preparation process can be achieved using battery preparation techniques well known to those skilled in the art, and the present invention does not impose any special limitations on them.

[0059] In a specific embodiment of the present invention, such as Figure 1 As shown, the lithium-ion battery is a cylindrical battery with all tabs. The current collector edge of the electrode of the lithium-ion battery extends to form an all-tab structure, and the width L2 of the all-tab structure and the width L1 of the positive electrode satisfy: L2 ≥ L1 × 95%. This invention uses a lithium-ion battery with an all-tab structure, which greatly increases the cross-sectional area for current conduction, significantly reduces the battery's internal resistance and ohmic heat during charging and discharging, and, in conjunction with a high-rate-performance positive electrode, enables the battery to achieve high energy density while supporting higher power charging and discharging, with controllable temperature rise, further improving the battery's overall performance and safety.

[0060] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0061] Example 1 (1) Preparation of the positive electrode sheet: LiNi 0.9 Co 0.05 Mn 0.05 O2 and LiNi 0.92 Co 0.06 Mn 0.02 O2 was mixed at a volume ratio of 7:3 to obtain the positive electrode active material. The positive electrode active material, conductive carbon black, and polyvinylidene fluoride (PVDF) were then thoroughly mixed in N-methylpyrrolidone (NMP) at a mass ratio of 94:3.5:2.5 to prepare a positive electrode slurry. The solid content of the positive electrode slurry was 65 wt%. The positive electrode slurry was coated on both sides of an aluminum foil, dried, cold-pressed, and slit to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 3.65 g / cm³. 3 The thickness on one side is 40µm.

[0062] The average particle size of the first type of particles is D1=13µm, the average particle size of the second type of particles is D2=3µm, and D1 / D2=4.33.

[0063] (2) Preparation of negative electrode sheet: Based on weight percentages, 93% artificial graphite, 3% silicon, 1% acetylene black, 1% sodium carboxymethyl cellulose, and 2% polyacrylic acid were added to deionized water and thoroughly mixed to prepare a negative electrode slurry. The negative electrode slurry was then coated onto both sides of a copper foil, dried, cold-pressed, and slit to obtain the negative electrode. The compacted density of the negative electrode was 1.5 g / cm³. 3 .

[0064] (3) Preparation of electrolyte: Ethylene carbonate (EC), ethyl potassium carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Lithium hexafluorophosphate (LiPF6) was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0065] (4) Preparation of lithium-ion batteries: A 9µm thick PE membrane was selected as the base membrane. A 1.0µm thick ceramic coating was coated on both sides of the base membrane. A 1.0µm thick PVDF coating was then coated on the dried ceramic coating. After drying, a diaphragm was obtained. The air permeability of the diaphragm was 120s / 100mL.

[0066] After the positive and negative electrode sheets are rolled, slit, and die-cut, they are wound together with the separator. The positive, negative, and separator are wound together by a winding machine to form a core. The core is then cut and stacked with positive and negative electrode tabs. The positive and negative busbars are then welded to the core, and the negative busbar is welded to the steel shell. An insulating sheet is placed on top of the positive busbar, and the positive busbar is welded to the cap to obtain the lithium-ion battery core. This core is then installed in the battery casing. After liquid injection, sealing, and formation processes, the lithium-ion battery is obtained.

[0067] Example 2 The difference between Example 2 and Example 1 is that in step (1), the volume ratio of the first type of particles and the second type of particles is 1:1.

[0068] Example 3 The difference between Example 3 and Example 1 is that in step (1), the volume ratio of the first type of particles to the second type of particles is 4:1.

[0069] Example 4 The difference between Example 4 and Example 1 is that in step (1), the average particle size of the first type of particles is D1=13µm, the average particle size of the second type of particles is D2=2µm, and D1 / D2=6.5.

[0070] Example 5 The difference between Example 5 and Example 1 is that in step (1), the average particle size of the first type of particles is D1=13µm, the average particle size of the second type of particles is D2=4µm, and D1 / D2=3.25.

[0071] Example 6 The difference between Example 6 and Example 1 is that in step (1), the first type of particles is LiNi. 0.9 Co 0.06 Mn 0.04 O2; the average particle size of the first type of particles is D1=13µm, the average particle size of the second type of particles is D2=4µm, and D1 / D2=3.25.

[0072] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step (1), the second type of particles is LiNi. 0.9 Co 0.066 Mn 0.034 O2.

[0073] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step (1), the second type of particles is LiNi. 0.92 Co 0.04 Mn 0.04 O2.

[0074] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step (1), the average particle size of the first type of particles is D1=13µm, the average particle size of the second type of particles is D2=10µm, and D1 / D2=1.3.

[0075] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in step (1), the volume ratio of the first type of particles and the second type of particles is 1:9.

[0076] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in step (1), the first type of particles is LiNi. 0.9 Co 0.08 Mn 0.02 O2; the volume ratio of the first type of particles to the second type of particles is 4:1; the average particle size of the first type of particles is D1=13µm, the average particle size of the second type of particles is D2=4µm, and D1 / D2=3.25.

[0077] Performance testing: Average particle size test: The positive electrode sheet was cut into small circular pieces with a diameter of 0.7 cm. Under CP-SEM 1000x magnification, the diameter of 100 large particles was measured by software, and the average value was taken as the average particle size D1 of the first type of particles; the diameter of 100 small particles was measured by software, and the average value was taken as the average particle size D2 of the second type of particles.

[0078] Volume ratio measurement of particles: The positive electrode sheet was cut into small circular pieces with a diameter of 0.7 cm. Under CP-SEM magnification of 1000, the number of first-type particles Y1 and the number of second-type particles Y2 were counted in an area of ​​50 µm in length and 30 µm in width. The volume V1 of the first-type particles was approximately calculated as V1 = π × D1 3 / 6, The volume V2 of the second type of particles is approximately calculated as V2=π×D2 3 / 6, then the volume ratio of the second type of particles to the positive electrode active material is x=(Y1×V1) / (Y1×V1+Y2×V2).

[0079] Electrode single-sided thickness test: Cut the positive electrode sheet into small circular pieces with a diameter of 0.7cm. Under CP-SEM 1000x magnification, measure the thickness of the material area using software. This is the single-sided thickness.

[0080] The performance of the positive electrode and lithium-ion battery prepared by the above embodiments and comparative examples was tested, as follows: Electrode compaction density test: (1) Clean the positive electrode sheet with dimethyl carbonate 2-5 times, and dry it in an oven to remove the dimethyl carbonate completely. (2) Cut a circular piece with an area of ​​S from the double-sided coated area of ​​the positive electrode sheet, weigh it to obtain the sum of the mass of aluminum foil and positive active layer M1, and at the same time use a micrometer to measure the sum of the thicknesses of aluminum foil and positive active layer d1. (3) Scrape off the positive active layer from the surface of the circular piece, wipe the surface of the circular piece with NMP to remove the powder completely, dry it completely, weigh it to obtain the mass of aluminum foil M2, and at the same time use a micrometer to measure the thickness of aluminum foil d2. (4) Calculate the compaction density of the positive electrode sheet: ρ=(M2-M1) / (S×(d2-d1)), unit g / cm 3 .

[0081] Volumetric energy density test: The lithium-ion battery was placed in a dry environment at 25±2℃ for at least 3 hours. The battery was charged at a constant current of 0.2C to 4.2V and then charged at a constant voltage of 0.02C using a battery tester. After standing for 30 minutes, it was discharged at a constant current of 0.2C to 2.5V. The battery energy E was recorded. Combined with the battery volume V, the volumetric energy density n of the battery was calculated to obtain the volumetric energy density n=E / V, in Wh / L.

[0082] Cycle performance test: Take a lithium-ion battery with a ternary cathode active material and a voltage window of 2.5V~4.2V. The voltage window needs to be adjusted accordingly for different cathode active materials. Place the battery in a 25℃ constant temperature chamber for at least 4 hours and test according to the following steps: (1) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 5 minutes; (2) Charge the battery at a constant current of 0.2C until it reaches 4.2V, then charge it at a constant voltage until it reaches 0.05C, and let it stand for 5 minutes. (3) Discharge the battery at a constant current of 0.2C until it is cut off at 2.5V, and let it stand for 5 minutes. Then read the capacity value C0 at this time. (4) Charge the battery at a constant current of 1.0C to 4.2V, and then charge it at a constant voltage of 0.05C until it stops, and let it stand for 5 minutes; (5) Discharge the battery at a constant current of 2.0C until it is cut off at 2.5V, and let it stand for 5 minutes; (6) Repeat steps (4) and (5) 600 times and read the capacity value C at this time. 600 ; (7) Cyclic capacity retention rate = C 600 / C0×100%.

[0083] Rate performance test: Take a lithium-ion battery with a ternary cathode active material and a voltage window of 2.5V~4.2V. The voltage window needs to be adjusted accordingly for different cathode active materials. Place the battery in a 25℃ constant temperature chamber for at least 4 hours and test according to the following steps: (1) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 10 minutes; (2) Charge the battery at a constant current of 0.1C until it reaches 4.2V, then charge it at a constant voltage until it reaches 0.01C, and let it stand for 10 minutes. (3) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 10 minutes. Then read the capacity value C at this time. 0.1 ; (4) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (5) Discharge the battery at a constant current of 0.5C until it reaches 2.5V cutoff, let it stand for 10 minutes, and read the capacity value C at this time. 0.5 ; (6) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (7) Discharge the battery at a constant current of 1C until it is cut off at 2.5V, let it stand for 10 minutes, and read the capacity value C1 at this time; (8) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (9) Discharge the battery under constant current at 2C until it is cut off at 2.5V, let it stand for 10 minutes, and read the capacity value C2 at this time; (10) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (11) Discharge the battery under constant current at 3C until it is cut off at 2.5V, let it stand for 10 minutes, and read the capacity value C3 at this time; (12) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (13) Discharge the battery under constant current at 4C until it is cut off at 2.5V, let it stand for 10 minutes, and read the capacity value C4 at this time; (14) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (15) Discharge the battery at a constant current of 5C until it is cut off at 2.5V, let it stand for 10 minutes, and read the capacity value C5 at this time; (16) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C to cut off, and let it stand for 10 minutes; (17) Discharge the battery under constant current at 6C until it is cut off at 2.5V, let it stand for 10 minutes, and read the capacity value C6 at this time; (18) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (19) Discharge the battery under constant current at 8C until it is cut off at 2.5V, let it stand for 10 minutes, and read the capacity value C8 at this time; (20) The rate performance of a single battery, i.e., the high rate performance capacity retention rate, is obtained by the ratio of the capacity of each rate discharge to the capacity of the first discharge.

[0084] The test results are shown in Tables 1 and 2 below.

[0085] Table 1 Parameters of each group of positive electrode active materials Table 2 Performance test data of each group of positive electrode plates and batteries As can be seen from Tables 1 and 2, firstly, the effectiveness of the threshold value of the coordination factor S (S≥2) is verified. All examples with S≥2 exhibit high levels of corresponding volumetric energy density (679Wh / L~702Wh / L), 8C capacity retention (87%~89%), and 600-cycle capacity retention (87%~91%), demonstrating excellent overall performance without any weaknesses. Conversely, all comparative examples have S values ​​less than 2.0, indicating significant degradation in at least one key performance indicator. For example, Comparative Example 1 had a slightly lower volumetric energy density due to the lack of a nickel content gradient (a2=a1); Comparative Example 2 had a significantly lower 8C capacity retention rate to 75% due to the lack of a cobalt-manganese ratio gradient (b2 / c2=b1 / c1); Comparative Example 3 had a sharp drop in compaction density and volumetric energy density due to particle size imbalance (D1 / D2 being too small), and its rate performance and cycle performance were also severely affected; Comparative Example 4 had a lower compaction density and volumetric energy density due to the extreme mixing ratio of the first and second types of particles (1:9), and its rate performance also deteriorated; Comparative Example 5 had a severely degraded cycle life to 75% due to the reverse cobalt-manganese ratio gradient (b1 / c1>b2 / c2) and an excessively large particle size ratio, although its volumetric energy density and rate performance were still acceptable.

[0086] Secondly, there is a strict correlation between performance and design variables. Compacted density is mainly affected by the particle size ratio (D1 / D2) and the proportion of second-type particles (x). When other variables remain constant, a particle size ratio that is too small (Comparative Example 3) or a single-crystal proportion that is too high (Comparative Example 4) will lead to a significant decrease in compacted density. Volumetric energy density is jointly determined by compacted density and the nickel content gradient (a2>a1). For example, Comparative Example 1, lacking a nickel gradient, has a lower volumetric energy density (694Wh / L) than Example 1 (700Wh / L) because the single-crystal particles do not carry a higher nickel content; while Comparative Example 3 has a significantly reduced compacted density, resulting in a decrease in active material per unit volume, leading to a significant reduction in volumetric energy density to 652Wh / L. Comparative Example 4 has a lower volumetric energy density (660Wh / L) due to a high single-crystal proportion leading to a decrease in packing efficiency and thus a lower compacted density. 8C rate capacity retention is mainly affected by the cobalt-manganese ratio gradient; Comparative Example 2 performs the worst due to the lack of a cobalt-manganese ratio gradient (b2 / c2=b1 / c1). The capacity retention rate after 600 cycles is mainly affected by the nickel content gradient (a2>a1) and structural stability. Comparative Example 1 is slightly lower because there is no nickel content gradient (a2=a1), while Comparative Example 5 is significantly lower because the inverse cobalt-manganese ratio gradient (b1 / c1>b2 / c2) leads to interface instability.

[0087] Experimental data fully demonstrate that this invention systematically integrates and quantifies four key design factors—nickel content gradient (a2>a1), cobalt-manganese ratio gradient (b2 / c2>b1 / c1), particle size ratio (D1 / D2), and the proportion of second-type particles (x)—through a coordination factor S. When S≥2, it can ensure that the positive electrode active material system produces a strong synergistic effect, enabling the prepared lithium-ion battery to simultaneously achieve high volumetric energy density, excellent rate performance, and ultra-long cycle life, effectively solving the technical problem of the difficulty in synergistically optimizing the performance of high-nickel positive electrode materials.

[0088] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0089] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0090] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector, wherein the positive active layer includes a positive active material, and the positive active material includes a first type of particles and a second type of particles; The first type of particles is a polycrystalline high-nickel ternary material. The general chemical formula of the first type of particles is LiNia1Cob1Mnc1O2, where a1+b1+c1=1, 0.85≤a1≤0.94; the average particle size of the first type of particles is D1. The second type of particles is a single-crystal high-nickel ternary material; the general chemical formula of the second type of particles is LiNia2Cob2Mnc2O2, where a2+b2+c2=1, 0.88≤a2≤0.96; the average particle size of the second type of particles is D2; Wherein, the volume ratio of the second type of particles to the positive electrode active material is x, 0 <x<1; The coordination factor S of the positive electrode active material is calculated using the following formula, where S≥2: 。 2. The positive electrode sheet according to claim 1, characterized in that, 0.88≤a1≤0.92, and a2≥a1+0.

02.

3. The positive electrode sheet according to claim 1, characterized in that, b2 / c2≥1.5×(b1 / c1).

4. The positive electrode sheet according to claim 1, characterized in that, D1 is 8µm~20µm; And / or, D2 is 1µm~5µm.

5. The positive electrode sheet according to claim 4, characterized in that, D1 is 10µm~15µm; And / or, D2 is 2µm~4µm.

6. The positive electrode sheet according to claim 1, characterized in that, 0.2≤x≤0.8。 7. The positive electrode sheet according to claim 6, characterized in that, 0.3≤x≤0.5。 8. The positive electrode sheet according to claim 1, characterized in that, The compaction density of the positive electrode sheet is 3.2 g / cm³. 3 ~3.8g / cm 3 .

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes the positive electrode as described in any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that, The lithium-ion battery is a full-tab cylindrical battery. The current collector edge of the electrode of the lithium-ion battery extends to form a full-tab structure, and the width L2 of the full-tab structure and the width L1 of the positive electrode satisfy: L2≥L1×95%.

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