Positive electrode material, positive plate and lithium ion battery

Abstract

The invention provides a positive electrode material, a positive plate and a lithium ion battery, the positive electrode material is a ternary layered oxide and comprises single crystal particles and polycrystal particles, the mass ratio of the polycrystal particles to the single crystal particles satisfies 9: 1-6: 4, the positive electrode material has a chemical general formula LiNixCoyMzO2, M is Mn or Al, x is more than or equal to 0.80 and less than or equal to 0.95, y is more than 0 and less than 0.25, and z is more than 0 and less than 0.2; the polycrystalline particles are secondary particles formed by sintering and agglomerating primary crystal grains at a high temperature, and the particle size of the primary crystal grains meets the following conditions: the shortest Freight diameter A is more than or equal to 0.1 mu m and less than or equal to 0.6 mu m; the longest Feret diameter B is greater than or equal to 0.2 mu m and less than or equal to 1.0 mu m; an aspect ratio B / A: 1.0 < = B / A < = 3.5; the morphology of the polycrystalline particles meets the relational expression that (B / A) * e ((k * c / a)) is larger than or equal to 30 and smaller than or equal to 100, and c / a is the lattice constant ratio of the polycrystalline particles; and k is the ratio of I003 to I104. According to the control standard for monitoring the two-dimensional microtopography of the primary crystal grains and the secondary particles of the polycrystalline particles by using a relational expression that (B / A). E ((k. C / a)) is greater than or equal to 30 and less than or equal to 100, the electrochemical performance of the positive electrode material can be evaluated more accurately, and the performance standardization control effect of a terminal battery product is improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a cathode material, a cathode sheet, and a lithium-ion battery. Background Technology

[0002] With market demand for high cycle life and high rate capability in batteries, cathode materials for lithium-ion batteries face new challenges. Common ternary cathode materials can be broadly classified into monocrystalline and polycrystalline particles. Monocrystalline particles are highly ordered and have no grain boundaries, which can suppress crack propagation during cycling, reduce electrolyte side reactions, and significantly improve cycle life; however, monocrystalline particles also have long lithium-ion diffusion paths, resulting in relatively poor rate performance. Polycrystalline particles are generally formed by the agglomeration of many primary grains, with high disorder and short lithium-ion diffusion paths, which can improve fast charge and discharge capabilities and achieve considerable rate performance; however, the presence of grain boundaries within the particles can easily lead to cation mixing, hindering lithium-ion transport. Furthermore, anisotropic stress at grain boundaries can easily cause cracks, exacerbating side reactions, leading to capacity decay and poor cycle performance.

[0003] Based on the advantages and disadvantages of the two types of particles, most cathode materials currently used in the market mainly use a mixture of single-crystal and polycrystalline particles. Polycrystalline particles are used to optimize the ion diffusion kinetics of the cathode material system, while single-crystal particles are used to provide structural stability for the cathode material system and reduce side reactions. The synergy of the two can improve the cycle life and rate performance of the battery.

[0004] Current methods of mixing materials mainly refer to the mass ratio of monocrystalline to polycrystalline particles, for example, 50 wt% monocrystalline particles and 50 wt% polycrystalline particles. However, the inventors found in the process of implementation that using only the mass ratio as a qualitative standard for cathode materials cannot reflect the differences in microstructure. In the mass production process, there are large differences in the performance of cathode materials between batches, which is not conducive to the standardized management of the performance of end battery products. Summary of the Invention

[0005] To address the aforementioned issues and establish quantitative standards for the microstructure of cathode materials, thereby improving the consistency of cathode material performance, the first aspect of this application provides a cathode material that is a ternary layered oxide comprising single-crystal particles and polycrystalline particles. The mass ratio of the polycrystalline particles to the single-crystal particles satisfies 9:1 to 6:4, and the material has the general chemical formula LiNi. x Co y M z O2, M is Mn or Al, 0.80≤x≤0.95, 0<y<0.25, 0<z<0.2;

[0006] The polycrystalline particles are secondary particles formed by the high-temperature sintering and agglomeration of primary grains. The particle size of the primary grains satisfies the following conditions: shortest Fret diameter A: 0.1μm≤A≤0.6μm, longest Fret diameter B: 0.2μm≤B≤1.0μm, and aspect ratio B / A: 1.0≤B / A≤3.5.

[0007] The morphology of the polycrystalline particles satisfies the following relationship: 30≤(B / A)·e^((k·c / a))≤100, where c / a is the lattice constant ratio of the polycrystalline particles; k is the lattice constant of the crystal. 003 / I 104 The ratio of I 003 I represents the diffraction peak intensity of the (003) crystal plane. 104 The intensity of the diffraction peak of the (104) crystal plane.

[0008] In some optional embodiments, the particle morphology of the polycrystalline particles satisfies the relationship: 40≤(B / A)·e^((k·c / a))≤70.

[0009] In some optional embodiments, the lattice constant ratio c / a of the polycrystalline particles satisfies: 4.80 ≤ c / a ≤ 5.00, wherein I 003 / I 104 The ratio k satisfies: 1.0 ≤ k ≤ 1.8.

[0010] In some optional embodiments, the secondary particle size distribution D50 of the polycrystalline particles is 8-15 μm, and satisfies 1.1≤(D90-D10) / D50≤1.5.

[0011] In some optional embodiments, the grain boundary spacing λ between the primary grains of the polycrystalline particles satisfies: 50 ≤ λ ≤ 100 nm, and the grain boundary density ρ GB Satisfy: 3.5 × 10 6 m -1 ≤ρ GB ≤1×10 7 m -1 .

[0012] In some alternative embodiments, the ternary layered oxide is further doped with a dopant element, which includes one or more of Al, Mg, Ti, Zr, Cr, Ce, Te, W, Nb, Sr, Y, La, F, B, and P.

[0013] In some optional embodiments, the surface of the single-crystal particles and / or the polycrystalline particles has a coating layer, said coating layer being composed of Al2O3, TiO2, ZrO2, B2O3, AlPO4, Li3PO4, LiAlO2, Li2ZrO3, and Li4Ti5O. 12One or more of the following components are present, wherein the total porosity of the coating layer is <5%.

[0014] In some optional embodiments, the average minor diameter C and average major diameter D of the single crystal particles satisfy: D / C≤1.5, particle surface roughness 20nm≤Ra1≤50nm, and particle size distribution 1.15≤(D90-D10) / D50≤1.75.

[0015] In some optional embodiments, the mixed particle tap density TD of the polycrystalline particles and the monocrystalline particles satisfies: TD ≥ 2.8 g / cm³ 3 The specific surface area BET satisfies: 0.3 ≤ BET ≤ 1.0 m² 2 / g.

[0016] A second aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode material coated on at least one surface of the positive current collector, wherein the positive electrode material is the positive electrode material according to any one of the preceding claims, and the current collector is a carbon-coated aluminum foil, wherein the areal density L of the carbon coating layer satisfies: 0.5 ≤ L ≤ 2 g / m³ 2 The aluminum foil thickness H satisfies: 10 ≤ H ≤ 16 μm, and the roughness Ra2 satisfies: Ra2 ≤ 50 nm.

[0017] In some optional embodiments, the positive electrode sheet has a gap fill rate M ≥ 85%, a peel strength E ≥ 15 N / m, and a compaction density of 3.4 g / cm³. 3 ≤PD≤3.70g / cm 3 .

[0018] In some optional embodiments, the two sides of the carbon-coated aluminum foil are respectively coated with a first material layer and a second material layer composed of the positive electrode material. The surfaces of the first material layer and the second material layer are respectively provided with a first recess and a second recess. The first recess and the second recess are staggered in the orthographic projection view of the positive electrode sheet. In the orthographic projection view, the distance between the central axes of two adjacent first recesses is b, and the distance between the central axes of adjacent first recesses and second recesses is a, satisfying: 0 < a / b ≤ 0.5.

[0019] In some optional embodiments, the thicknesses of the first material layer and the first recess are h1 and h3, respectively, and the thicknesses of the second material layer and the second recess are h2 and h4, respectively, satisfying 0.75≤h3 / h1≤0.82 and 0.75≤h4 / h2≤0.82.

[0020] A third aspect of this application provides a lithium-ion battery comprising a core formed by winding a positive electrode, a separator, and a negative electrode, wherein the positive electrode is a positive electrode according to any one of the preceding claims.

[0021] This application has at least the following technical effects:

[0022] 1) A first aspect of this application provides a cathode material comprising single-crystal particles and polycrystalline particles, wherein the mass ratio of the polycrystalline particles to the single-crystal particles satisfies 9:1-6:4. The morphology of the polycrystalline particles is comprehensively evaluated using the relationship 30≤(B / A)·e^((k·c / a))≤100, where c / a is the lattice constant ratio of the polycrystalline particles; k is the lattice constant ratio of the single-crystal particles. 003 / I 104 The ratio of I 003 By measuring the intensity of the (003) crystal plane diffraction peak and combining it with the dual-dimensional micromorphological monitoring of the primary and secondary grains of polycrystalline particles, the electrochemical performance of cathode materials can be more accurately evaluated, thereby improving the standardized management and control of terminal battery products.

[0023] 2) The second aspect of this application provides a positive electrode sheet in which the morphology of polycrystalline particles satisfies the relationship 30≤(B / A)·e^((k·c / a))≤100. Based on this, polycrystalline particles are combined with single-crystal particles, which can better balance the structural stability and ion diffusion performance of the positive electrode sheet, and the electrochemical performance of the positive electrode sheet is consistent.

[0024] 3) The third aspect of this application provides a lithium-ion battery in which the positive electrode sheet has the above-mentioned technical effects, and the lithium-ion battery of this application also has the characteristic of good consistency in electrochemical performance, which is conducive to the standardized management of battery production. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application 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 these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of an optional embodiment of the positive electrode sheet of this application, wherein the solid frame represents the first recess on the surface of the first material layer, and the dashed frame represents the projection of the second recess of the second material layer away from the first material layer onto the surface of the first material layer.

[0027] Figure 2 This is a cross-sectional schematic diagram along the length of an optional embodiment of the positive electrode sheet of this application. Detailed Implementation

[0028] The embodiments of this implementation are described in detail below. In the description of this implementation, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. If "first" and "second" are mentioned, they are only used to distinguish technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0029] In the description of this embodiment, unless otherwise explicitly limited, terms such as setting, installing, and connecting should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this embodiment in conjunction with the specific content of the technical solution.

[0030] In this embodiment, the lithium-ion battery includes a core, an electrolyte, and a casing. The core is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet stacked together. The positive electrode sheet includes a positive current collector and a positive active material layer formed on at least one surface of the positive current collector. The positive active material layer is formed by curing a positive electrode slurry coated on the surface of the positive current collector. The positive electrode slurry includes a positive electrode material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode sheet includes a negative current collector and a negative active material layer formed on at least one surface of the negative current collector. The negative active material layer is formed by curing a negative electrode slurry coated on the surface of the negative current collector. The negative electrode slurry includes a negative active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbide, silicon oxide, and pre-lithium silicon oxide. The negative electrode conductive agent is selected from carbon nanotubes or a combination of carbon nanotubes and carbon black. The negative electrode binder is selected from at least one of polyacrylic acid, polyacrylonitrile, and polystyrene-acrylic acid. The electrolyte includes: lithium salt, solvent, and additives; the lithium salt is selected from any one or more combinations of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; the solvent is selected from any one or more combinations of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate; the additives are selected from any one or more combinations of propylene carbonate, butenyl carbonate, ethyl acetate, methyl ethyl carbonate, and fluoroethylene carbonate. The casing is cylindrical, with the internal cavity for accommodating the core. The top is the positive terminal, and the bottom is the negative terminal. The casing can be steel or aluminum, and the ratio of the battery's diameter to its height is >1.6.

[0031] In the current lithium-ion battery industry, cathode materials often employ a mixture of monocrystalline and polycrystalline particles. However, simply controlling the mass ratio of monocrystalline to polycrystalline particles to predict the performance of finished batteries lacks a means to accurately reflect the microstructure of the mixed cathode materials. Furthermore, during mass production, significant performance differences can occur between different batches of finished batteries using cathode materials with the same proportion of monocrystalline and polycrystalline particles. Among these, the morphological differences between polycrystalline particles are a major factor affecting the electrochemical performance of cathode materials. This is because the factors influencing the morphology of polycrystalline particles are relatively complex; the shape and size of primary grains, the density of primary grain aggregation, and the anisotropy of crystal growth within secondary particles all affect the final morphology of the polycrystalline particles. Therefore, this application proposes a control standard that combines monitoring of the microstructure of both primary and secondary polycrystalline particles, enabling a more accurate assessment of the electrochemical performance of cathode materials and improving the standardized management of end-product performance.

[0032] Based on this, the first aspect of this application provides a cathode material, which is a ternary layered oxide comprising single-crystal particles and polycrystalline particles, wherein the mass ratio of the polycrystalline particles to the single-crystal particles satisfies 9:1-6:4, and has the chemical formula LiNi. x Co y M z O2, M is Mn or Al, 0.80≤x≤0.95, 0<y<0.25, 0<z<0.2;

[0033] The polycrystalline particles are secondary particles formed by the high-temperature sintering and agglomeration of primary grains. The particle size of the primary grains satisfies the following conditions: shortest Fret diameter A: 0.1μm≤A≤0.6μm; longest Fret diameter B: 0.2μm≤B≤1.0μm; aspect ratio B / A: 1.0≤B / A≤3.5.

[0034] The morphology of the polycrystalline particles satisfies the following relationship: 30≤(B / A)·e^((k·c / a))≤100, where c / a is the lattice constant ratio of the polycrystalline particles; k is the lattice constant of the crystal. 003 / I 104 The ratio of I 003 I represents the diffraction peak intensity of the (003) crystal plane. 104 The intensity of the diffraction peak of the (104) crystal plane.

[0035] For example, the value of (B / A)·e^((k·c / a)) can be 38.7, 88.6, or 96.7, to include the relationship between the particle size aspect ratio B / A, the lattice constant ratio c / a, and the intensity ratio k of the diffraction peaks of the characteristic crystal planes, which are used to represent the primary grain morphology of polycrystalline particles. This relationship links the primary grain morphology of polycrystalline particles with the morphology of secondary particles after aggregation, comprehensively evaluates the diffusion ability of polycrystalline particles to lithium ions from both nanoscale and microscale dimensions, and constrains the value range of the relationship, establishing a quantitative standard for the microstructure of cathode materials, unifying the electrochemical performance of cathode materials, and improving the quality control effect of end battery products.

[0036] Among them, B / A reflects the anisotropy of the primary grain shape to a certain extent, c / a can be used to characterize the degree of lattice distortion of the layered structure of ternary layered oxides, and k characterizes the correlation strength between lattice and morphology. The relationship is: (B / A)*e^((k·c / a) is used to describe the nonlinear exponential relationship between crystal structure and morphology. When the value exceeds the range of 30-100, the performance stability of the cathode material deteriorates sharply.

[0037] In the specific implementation process, the testing methods for the primary grain size of the polycrystalline particles and the particle size of the secondary particles are as follows:

[0038] The polycrystalline particles were tested using scanning electron microscopy (SEM): the polycrystalline particle samples were dispersed in conductive adhesive, sputtered with gold, and then observed using SEM; the particle morphology was directly observed using high-resolution imaging, and the geometric dimensions of the primary grains were measured, including the shortest Fret diameter A and the longest Fret diameter B. The boundaries of the secondary particles were marked using software such as ImageJ, and the average particle size and distribution D50, D10, and D90 of more than 100 secondary particles were calculated.

[0039] The method for testing the lattice constant ratio c / a of the polycrystalline particles and the diffraction peak intensities of the (003) and (104) crystal planes is as follows:

[0040] Sample preparation: First, the sample powder of the polycrystalline particles is pressed into a tablet and the material is ground into a uniform powder to avoid particle agglomeration affecting the diffraction signal. At the same time, it is ensured that the sample surface is flat to reduce test errors.

[0041] XRD test parameters: Select the scanning range 2θ = 10°-80°, use high resolution mode (step size ≤ 0.02°) to ensure accurate peak position identification;

[0042] Lattice constant calculation: Characteristic peak selection: Based on the hexagonal crystal system (space group), the characteristic peaks of the (003) and (104) crystal planes are selected, and the intensity of the characteristic peaks of the (003) and (104) crystal planes can be read; Bragg equation: The interplanar spacing d is calculated by 2dsinθ=nλ, combined with the formula: The values ​​of a and c were obtained by fitting.

[0043] Refinement Analysis: Use software (such as Fullprof, Jade) to refine the diffraction pattern using Rietveld, optimize the unit cell parameters, and directly output the c / a value after refinement.

[0044] k = I 003 / I 104 The value of k is related to the nickel content, and the nickel content is usually negatively correlated with the k value, reflecting the degree of cation mixing (e.g., Ni). 2 +Occupying Li+ sites), reflecting the lattice order of the layered structure; on the other hand, it can be used to evaluate the anisotropy of crystal plane growth, reflecting the difference in the relative growth rate between the (003) crystal plane and the (104) crystal plane. When the k value is high, for example, k = 1.5, it may indicate that the (003) crystal plane grows too fast, indirectly revealing the orientation preference of the crystal morphology, such as tending towards lamellar growth or equiaxed growth. The correlation between the k value and the electrochemical performance of polycrystalline particles is as follows: when k > 1.2, it reflects that the polycrystalline particles have low mixing and high order, and the lithium ion diffusion path is unobstructed, with excellent rate performance and cycle performance; when 1.0 ≤ k ≤ 1.2, the polycrystalline particles are moderately mixed, and the Li+ transport at the grain boundary is restricted, resulting in a decrease in rate performance; when k < 1.0, the polycrystalline particles are severely mixed, the lattice distortion is aggravated, microcracks and phase transitions are triggered, and the cycle stability is poor.

[0045] Furthermore, the morphology of the polycrystalline particles satisfies the relationship: 40 ≤ (B / A)·e^((k·c / a)) ≤ 70, for example, 42.3, 67.2, 52.4, 59.8. When the value of the relationship is between 40 and 70, the cycle performance of the resulting lithium-ion battery can be further improved.

[0046] In some optional embodiments, the lattice constant ratio c / a of the polycrystalline particles satisfies: 4.80 ≤ c / a ≤ 5.00, wherein I 003 / I 104 The ratio k satisfies: 1.0 ≤ k ≤ 1.8. Polycrystalline particles that meet the above conditions have low interlattice stress, good structural stability, moderate lithium layer spacing, low Li+ diffusion barrier, and improved rate performance.

[0047] In some optional embodiments, the secondary particle size distribution D50 of the polycrystalline particles is 8-15 μm, and satisfies 1.1≤(D90-D10) / D50≤1.5. Optimizing the particle size distribution creates a hierarchical packing effect: large particles (D90) form the skeleton, dispersing roller pressure; medium-sized particles (D50) are uniform in size, forming rigid contact points during rolling; small particles (D10) fill the voids, reducing porosity; stress is uniformly transmitted, reducing stress concentration during electrode rolling.

[0048] In some optional embodiments, the grain boundary spacing λ within the primary grains of the polycrystalline particles satisfies: 50 ≤ λ ≤ 100 nm. This ensures that the size of the primary grains is within a suitable range. On the one hand, it avoids excessive grain boundaries due to excessively small size, which would lead to weak interfacial bonding. On the other hand, it avoids stress concentration due to particle volume changes caused by excessively large size, which could lead to crack formation. This suppresses particle surface pulverization and cracking, and optimizes lithium-ion transport kinetics. Furthermore, the grain boundary density ρ... GB Satisfy: 3.5 × 10 6 m -1 ≤ρ GB ≤1×10 7 m -1 It can effectively alleviate interface side reactions.

[0049] In some optional embodiments, the ternary layered oxide is further doped with doping elements, including one or more of Al, Mg, Ti, Zr, Cr, Ce, Te, W, Nb, Sr, Y, La, F, B, and P. It is understood that doping elements can be incorporated into the grains through lattice substitution, interstitial doping, surface modification, etc. Taking cation doping of elements such as Al, Mg, Ti, and Zr as an example, the doping elements improve lattice stability by substituting transition metal sites (Ni / Co / Mn) to generate more stable chemical bonds (e.g., Al-O bonds), or by occupying Li sites to reduce cation mixing and improve cycle performance. Correspondingly, the chemical formula of the cathode material becomes: LiNi. x Co y M z D q O2 and D represent doping elements, which can be one or more.

[0050] It is understandable that elements M and D are different elements. For example, when M is Al, then D is not Al. When there are two or more doping elements, the chemical formula of the cathode material becomes LiNi. x Co y M z D q E t O2, and so on, can also be doped with a third or fourth doping element.

[0051] In some optional embodiments, the surface of the single-crystal particles and / or the polycrystalline particles has a coating layer, said coating layer being composed of Al2O3, TiO2, ZrO2, B2O3, AlPO4, Li3PO4, LiAlO2, Li2ZrO3, and Li4Ti5O. 12One or more of the following components are used in the coating layer, wherein the total porosity of the coating layer is <5%. The coating layer is formed by adhering nanoscale compounds to the surface of single-crystal particles and / or polycrystalline particles. In specific implementation, the coating layer is mainly formed by mechanically mixing the nanoscale compounds with single-crystal particles and / or polycrystalline particles, followed by sintering and solidification. The total porosity of the coating layer <5% can improve mechanical support and buffer volumetric strain on the one hand, and block electrolytes and reduce side reactions such as transition metal dissolution on the other hand. The total porosity of the coating layer is evaluated by comparing the changes in specific surface area and pore volume of the particle samples before and after coating. The selection of coating material type, particle size, mixing ratio of mechanical mixing, and temperature control of the sintering and solidification process can all affect the total porosity of the coating layer to a certain extent.

[0052] In some optional embodiments, the average minor diameter C and average major diameter D of the single crystal particles satisfy: D / C≤1.5, and the particle surface roughness 20nm≤Ra1≤50nm, which can enhance ion transport at the electrode-electrolyte interface, accelerate lithium-ion insertion / extraction, and improve rate performance; the single crystal particle D50 satisfies 1.15≤(D90-D10) / D50≤1.75, controlling the particle size range of the single crystal particles, avoiding rigid stacking caused by excessively uniform particle size, resulting in excessive porosity, and at the same time avoiding small particles (D10) from blocking the gaps between large particles (D90) and forming local dense areas, resulting in uneven electrolyte wetting. Within the range of 1.15-1.75, large particles (D90) form a skeleton to maintain pore connectivity, while small particles (D10) appropriately fill the pores of large particles, increasing the compaction density.

[0053] In some optional embodiments, the tap density TD of the mixture of the polycrystalline particles and the monocrystalline particles satisfies: TD ≥ 2.8 g / cm³ 3 The specific surface area BET satisfies: 0.3 ≤ BET ≤ 1.0 m² 2 / g. Mixed particles within this range exhibit good electrochemical performance of the cathode material.

[0054] A second aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode material coated on at least one surface of the positive current collector, wherein the positive electrode material is the positive electrode material according to any one of the preceding claims, and the current collector is a carbon-coated aluminum foil, wherein the areal density L of the carbon coating layer satisfies: 0.5 ≤ L ≤ 2 g / m³ 2 The aluminum foil thickness H satisfies: 10 ≤ H ≤ 16 μm, and the roughness Ra2 satisfies Ra2 ≤ 50 nm. The carbon coating layer is used to form a uniform conductive layer and suppress interfacial polarization of the positive electrode material. The aluminum foil thickness is used to balance mechanical strength and volumetric energy density. The surface roughness of the aluminum foil affects the adhesion of the carbon coating layer, but excessive roughness may pose a risk of puncturing the separator.

[0055] In some optional embodiments, the positive electrode sheet has a gap fill rate M ≥ 85%, a peel strength E ≥ 15 N / m, and a compaction density of 3.4 g / cm³. 3 ≤PD≤3.70g / cm 3 .

[0056] Preferably, the compaction density is 3.60 g / cm³. 3 ≤PD≤3.67g / cm 3 .

[0057] The gap filling rate of the positive electrode sheet can be used to quantify the degree to which the gaps between particles in the positive electrode material are filled by conductive agent / binder. M≥85% ensures the structural strength of the positive electrode material coating. The greater the peel strength, the greater the bonding force between the positive electrode material coating and the aluminum foil, which is used to ensure the stability of the positive electrode sheet structure. Appropriate compaction density can ensure the volumetric energy density of the positive electrode material.

[0058] In some optional embodiments, the two sides of the carbon-coated aluminum foil are respectively coated with a first material layer and a second material layer made of the positive electrode material. The surfaces of the first material layer and the second material layer are respectively provided with a first recess 10 and a second recess 12. The first recess 10 and the second recess 12 are staggered in the orthographic projection view of the positive electrode sheet. In the orthographic projection view, the distance between the central axes of two adjacent first recesses is b, and the distance between the central axes of adjacent first recesses 10 and second recesses 12 is a, satisfying: 0 < a / b ≤ 0.5.

[0059] The first recess 10 and the second recess 12 are designed to enhance the wetting effect of the electrolyte on the first material layer and the second material layer. The staggered arrangement of the first recess 10 and the second recess 12 reduces the impact of the recess arrangement on the structural strength of the positive electrode sheet. The distance between the central axes of adjacent first recesses 10 and second recesses 12 is a, and the distance between the central axes of two adjacent first recesses 10 is b, satisfying: 0 < a / b ≤ 0.5, ensuring that there is sufficient first material layer and second material layer structure between adjacent first recesses 10 and second recesses 12 to maintain the mechanical strength of the positive electrode sheet.

[0060] In some optional embodiments, the thicknesses of the first material layer and the first recess 10 are h1 and h3, respectively, and the thicknesses of the second material layer and the second recess 12 are h2 and h4, respectively, satisfying 0.75≤h3 / h1≤0.82 and 0.75≤h4 / h2≤0.82.

[0061] Limiting the thickness of the recessed portion corresponding to the positive electrode material layer ensures that the lithium-ion channels of the first recessed portion 10 and the second recessed portion 12 have sufficient space for lithium-ion insertion, which is beneficial to the rate performance of the lithium-ion battery.

[0062] A third aspect of this application provides a lithium-ion battery, comprising a core formed by winding a positive electrode, a separator, and a negative electrode, wherein the positive electrode is the positive electrode according to any of the preceding claims. When the positive electrode used has the aforementioned technical effects, the lithium-ion battery of this application also possesses the characteristic of good electrochemical performance consistency, which is beneficial for the standardized control of battery production.

[0063] In some alternative embodiments, the diameter of the battery ranges from 20 mm to 50 mm, and the height ranges from 60 mm to 180 mm, wherein the ratio of the battery's diameter to its height is greater than 1.6.

[0064] The technical solution of this application will be described below with reference to Examples 1-7 and Comparative Examples 1-4.

[0065] Example 1

[0066] Example 1 provides a lithium-ion battery prepared by the following method:

[0067] Preparation of positive electrode: Weigh out the molecular formula LiN i0.80 Co 0.05 Mn 0.14 Al 0.01 O2 polycrystalline particles and single-crystal particles, wherein the mass ratio of polycrystalline particles to single-crystal particles is 9:1, are mixed to obtain a positive electrode material; polyvinylidene fluoride (PVDF) and Super-P (conductive carbon black) conductive agent are added to the positive electrode material, wherein the mass percentage of the positive electrode material is 96 wt%, the mass percentage of PVDF is 2 wt%, and the mass percentage of Super-P is 2 wt%; the above solid materials are added to the solvent NMP and stirred to obtain a positive electrode slurry with a solid content of 68%, which is coated on both sides of carbon-coated aluminum foil, dried and rolled to form the first material layer and the second material layer, thus obtaining a positive electrode sheet.

[0068] Preparation of negative electrode sheet: The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode active material layer coated on both sides of the copper foil. The negative electrode active material includes 96 wt% artificial graphite and silicon carbide, 1.0 wt% conductive agent, 1.0 wt% thickener and 2 wt% binder by mass percentage. The above negative electrode active material is added to the solvent deionized water and stirred to obtain a negative electrode slurry with a solid content of 40%. The slurry is then coated on both sides of the copper foil to obtain the negative electrode sheet.

[0069] Preparation of electrolyte: Lithium salt LiPF6 is dissolved in an organic solvent, which is prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate in a volume ratio of 1:1:1, wherein the additive content is 0.2-5wt%, and finally an electrolyte with a lithium ion concentration of 1mol / L is prepared.

[0070] Preparation of the diaphragm: A high porosity diaphragm is used, with a base membrane PE thickness of 9μm, ceramic coatings on both sides of 1μm thickness, and a PVDF coating on the outer side of the ceramic coating of 1μm thickness. The air permeability of the diaphragm is ≤100s / 100mL.

[0071] Battery assembly: The positive electrode sheet is formed into the first recess 10 and the second recess 12 on the first material layer and the second material layer using a laser device. The distance between the central axes of two adjacent first recesses 10 is b, and the distance between the central axes of adjacent first recesses 10 and second recesses 12 is a, satisfying a / b = 0.4. The thicknesses of the first material layer and the first recess 10 are h1 and h3, respectively, and the thicknesses of the second material layer and the second recess 12 are h2 and h4, respectively, satisfying h3 / h1 = 0.8 and h4 / h2 = 0.8. Subsequently, the positive electrode sheet and the negative electrode sheet are cut and die-cut, and then wound together with the separator to obtain the battery core. The core is then inserted into the battery casing, and the liquid injection, sealing, and formation processes are completed to obtain the lithium-ion battery of this embodiment 1.

[0072] The parameter changes of Examples 2-7 and Comparative Examples 1-4 compared to Example 1 are shown in the table below:

[0073]

[0074]

[0075] The following table shows the changes in the ratio of polycrystalline to monocrystalline particles, the cathode compaction density (PD), and the surface depression treatment parameters in Examples 1-7 and Comparative Examples 1-4:

[0076] Polycrystalline particles: Monocrystalline particles <![CDATA[PD(g / cm 3 )]]> a / b h3 / h1 h4 / h2 Example 1 9:1 3.45 0.40 0.80 0.80 Example 2 8:2 3.53 0.40 0.78 0.80 Example 3 7:3 3.58 0.50 0.82 0.80 Example 4 6:4 3.58 0.35 0.80 0.79 Example 5 7:3 3.65 0.50 0.80 0.81 Example 6 8:2 3.55 0.45 0.85 0.78 Example 7 7:3 3.58 0.50 0.78 0.80 Comparative Example 1 8:2 3.55 0.50 0.50 0.80 Comparative Example 2 5:5 3.58 0.70 0.78 0.80 Comparative Example 3 10:0 3.43 0.5 0.82 0.80 Comparative Example 4 0:10 3.70 0.45 0.78 0.80

[0077] The capacity performance of the lithium-ion batteries from Examples 1-7 and Comparative Examples 1-4 was evaluated using the following methods:

[0078] Test 1: Capacity retention test (capacity retention after 500 cycles at 25℃ and 1C / 1C rate):

[0079] The novel lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-4 were placed in a constant temperature chamber at 25°C for more than 4 hours and tested according to the following steps:

[0080] (1) Discharge the battery at a constant current of 0.1C until it is cut off at 2.5V, and let it stand for 5 minutes;

[0081] (2) Charge the battery at a constant current of 0.2C until it reaches 4.2V and then charge it at a constant voltage until it reaches 0.05C and then let it stand for 5 minutes.

[0082] (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.

[0083] (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.

[0084] (5) Discharge the battery at a constant current of 1.0C until it is cut off at 2.5V, and let it stand for 5 minutes;

[0085] (6) Repeat steps (4) and (5) 500 times;

[0086] (7) The ratio of the discharge capacity C500 in the 500th cycle to the discharge capacity C0 in the 1st cycle is C500 / C0*100%, which is the capacity retention rate.

[0087] The rate performance of the lithium-ion batteries from Examples 1-7 and Comparative Examples 1-4 was evaluated using the following methods:

[0088] The batteries prepared in the above embodiments and comparative examples were placed in a constant temperature chamber at 25°C for more than 4 hours, with a voltage window of 2.5V-4V, and tested according to the following steps:

[0089] (1) Discharge the battery at a constant current of 0.1C until it is cut off at 2.5V, and let it stand for 10 minutes;

[0090] (2) Charge the battery at a constant current of 0.1C until it reaches 4.2V and then charge it at a constant voltage until it reaches 0.01C and then let it stand for 10 minutes.

[0091] (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 point. 0.1 ;

[0092] (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.

[0093] (5) Discharge the battery at a constant current of 0.5C until it is cut off at 2.5V, and let it stand for 10 minutes;

[0094] (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.

[0095] (7) Discharge the battery at a constant current of 1C until it is cut off at 2.5V, and let it stand for 10 minutes;

[0096] (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.

[0097] (9) Discharge the battery under constant current at 2C until it is cut off at 2.5V, and let it stand for 10 minutes;

[0098] (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.

[0099] (11) Discharge the battery under 3C conditions at a constant current until it is cut off at 2.5V, and let it stand for 10 minutes;

[0100] (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.

[0101] (13) Discharge the battery under constant current at 4C until it is cut off at 2.5V, and let it stand for 10 minutes;

[0102] (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.

[0103] (15) Discharge the battery at a constant current of 5C until it is cut off at 2.5V, and let it stand for 10 minutes;

[0104] (16) The discharge capacity at a 5C discharge rate is C5. Take C5 and the discharge capacity at a 0.1C discharge rate as C. 0.1 The ratio C5 / C 0.1 *100%, the resulting capacity retention rate can be used to evaluate the rate performance of the battery.

[0105] Test 3: Hot Box Test

[0106] The novel lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-4 were placed in a constant temperature chamber at 25°C for more than 4 hours and tested according to the following steps:

[0107] (1) Discharge the battery at a constant current of 0.1C until it is cut off at 2.5V, and let it stand for 5 minutes;

[0108] (2) Charge the battery at a constant current of 0.2C until it reaches 4.2V and then charge it at a constant voltage until it reaches 0.05C. Let it stand for 5 minutes.

[0109] (3) Place the battery in a constant temperature chamber, set the heating rate to 5K / min, heat to 130℃, and maintain for 2 hours. Then stop heating and allow it to cool down to below 30℃.

[0110] (4) If the battery does not catch fire or smoke, it is considered to pass; otherwise, it is considered to fail. Test 5 batteries in parallel and record the pass rate.

[0111] The performance test results of the lithium-ion batteries of Examples 1-7 and Comparative Examples 1-4 are shown in the table below.

[0112]

[0113]

[0114] Comparing Examples 1, 3, 4, 6 and Examples 2, 5, 7, it can be seen that (B / A)·e^((k·c / a)) in the 40-70 range shows improved cycle performance compared to the 30-40 and 70-100 ranges. Comparing Examples 1-4, with an increased proportion of single-crystal particles, the lithium-ion battery maintains high cycle performance and rate performance through precise evaluation of the morphology and surface modification of polycrystalline particles. This indirectly proves that the grain morphology quantification standard established in this application can more accurately evaluate the electrochemical performance of cathode materials and improve the standardized management effect of end-product batteries.

[0115] Comparing Examples 1-7 with Comparative Examples 1-4, it can be seen that using only polycrystalline particles (Comparative Example 3) significantly reduces the cycle performance and safety performance of the battery, especially in the hot box test, where all five batteries failed. Using only monocrystalline particles (Comparative Example 4) results in a significant decrease in rate performance, with the 5C discharge capacity retention rate dropping to 41.3%. Comparative Example 1 and Examples 2 and 6 use the same ratio of polycrystalline particles to monocrystalline particles, but the morphology of the polycrystalline particles in Comparative Example 1 does not satisfy the aforementioned relationship, and the corresponding cycle performance, rate performance, and safety performance all collapse. This shows that simply controlling the mass ratio of polycrystalline particles to monocrystalline particles is insufficient to guarantee the electrochemical performance of the finished battery.

[0116] In summary, the quantitative standard provided in this application, which combines monitoring of the primary and secondary microstructures of polycrystalline particles, enables a more accurate evaluation of the electrochemical performance of cathode materials, improves the standardized control of end-product performance, and establishes a new dimension of quality control standards for cathode materials. By monitoring the dual-dimensional microstructure of polycrystalline particles, lithium-ion batteries with high cycle performance, high rate performance, and high consistency are achieved, with a capacity retention rate of 95.6% after 500 cycles and a 5C rate discharge capacity retention rate of 88.4%.

[0117] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.

Claims

1. A positive electrode material, characterized in that, The cathode material is a ternary layered oxide, comprising single-crystal particles and polycrystalline particles, wherein the mass ratio of the polycrystalline particles to the single-crystal particles satisfies 9:1-6:4, and it has the general chemical formula LiNi. x Co y M z O2, M is Mn or Al, 0.80≤x≤0.95, 0<y<0.25, 0<z<0.2; the polycrystalline particles are secondary particles formed by high-temperature sintering and agglomeration of primary grains, and the particle size of the primary grains satisfies: shortest Fret diameter A: 0.1μm≤A≤0.6μm, longest Fret diameter B: 0.2μm≤B≤1.0μm, aspect ratio B / A: 1.0≤B / A≤3.5; The morphology of the polycrystalline particles satisfies the following relationship: 30≤(B / A)·e^((k·c / a))≤100, where c / a is the lattice constant ratio of the polycrystalline particles; k is the lattice constant of the crystal. 003 / I 104 The ratio of I 003 I represents the diffraction peak intensity of the (003) crystal plane. 104 The intensity of the diffraction peak of the (104) crystal plane.

2. The cathode material according to claim 1, characterized in that, The morphology of the polycrystalline particles satisfies the following relationship: 40≤(B / A)·e^((k·c / a))≤70.

3. The cathode material according to claim 1, characterized in that, The lattice constant ratio c / a of the polycrystalline particles satisfies: 4.80 ≤ c / a ≤ 5.00, and the I 003 / I 104 The ratio k satisfies: 1.0 ≤ k ≤ 1.

8.

4. The cathode material according to claim 1, characterized in that, The secondary particles of the polycrystalline particles have a particle size distribution D50 of 8-15 μm, and satisfy 1.1≤(D90-D10) / D50≤1.

5.

5. The positive electrode material according to claim 4, characterized in that, The grain boundary spacing λ between the primary grains of the polycrystalline particles satisfies: 50 ≤ λ ≤ 100 nm, and the grain boundary density ρ GB Satisfy: 3.5 × 10 6 m -1 ≤ρ GB ≤1×10 7 m -1 .

6. The cathode material according to claim 1, characterized in that, The ternary layered oxide is further doped with doping elements, including one or more of Al, Mg, Ti, Zr, Cr, Ce, Te, W, Nb, Sr, Y, La, F, B and P.

7. The cathode material according to claim 1, characterized in that, The surface of the single-crystal particles and / or the polycrystalline particles has a coating layer, the coating layer being composed of Al2O3, TiO2, ZrO2, B2O3, AlPO4, Li3PO4, LiAlO2, Li2ZrO3, and Li4Ti5O. 12 One or more of the following components are present, wherein the total porosity of the coating layer is <5%.

8. The positive electrode material according to claim 1, characterized in that, The average minor diameter C and average major diameter D of the single crystal particles satisfy the following conditions: D / C≤1.5, particle surface roughness 20nm≤Ra1≤50nm, and particle size distribution 1.15≤(D90-D10) / D50≤1.

75.

9. The positive electrode material according to claim 1, characterized in that, The particle tap density (TD) of the mixture of polycrystalline and monocrystalline particles satisfies: TD ≥ 2.8 g / cm³ 3 The specific surface area BET satisfies: 0.3 ≤ BET ≤ 1.0 m² 2 / g.

10. A positive electrode sheet, comprising a positive current collector and a positive electrode material coated on at least one surface of the positive current collector, characterized in that, The positive electrode material is the positive electrode material according to any one of claims 1-9, and the current collector is a carbon-coated aluminum foil, wherein the areal density L of the carbon coating layer satisfies: 0.5 ≤ L ≤ 2 g / m³ 2 The aluminum foil thickness H satisfies: 10≤H≤16μm, and the roughness Ra2 satisfies Ra2≤50nm.

11. The positive electrode sheet according to claim 10, characterized in that, The positive electrode sheet has a gap filling rate M ≥ 85%, a peel strength E ≥ 15 N / m, and a compaction density of 3.4 g / cm³. 3 ≤PD≤3.70g / cm 3 .

12. The positive electrode sheet according to claim 10, characterized in that, The carbon-coated aluminum foil has a first material layer and a second material layer made of the positive electrode material coated on both sides. The surfaces of the first material layer and the second material layer are respectively provided with a first recess and a second recess. The first recess and the second recess are staggered in the orthographic projection view of the positive electrode sheet. In the orthographic projection view, the distance between the central axes of two adjacent first recesses is b, and the distance between the central axes of adjacent first recesses and second recesses is a, satisfying: 0 < a / b ≤ 0.

5.

13. The positive electrode sheet according to claim 12, characterized in that, The thicknesses of the first material layer and the first recess are h1 and h3, respectively, and the thicknesses of the second material layer and the second recess are h2 and h4, respectively, satisfying 0.75≤h3 / h1≤0.82 and 0.75≤h4 / h2≤0.

82.

14. A lithium-ion battery, comprising a core formed by winding a positive electrode, a separator, and a negative electrode, characterized in that, The positive electrode is the positive electrode according to any one of claims 10-13.

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