Ternary positive electrode material, preparation method, screening method and secondary battery

Abstract

The present disclosure relates to the technical field of positive electrode materials. Disclosed are a ternary positive electrode material, a preparation method, a screening method and a secondary battery. Particles of the ternary positive electrode material comprise an active material matrix and a coating layer coating the active material matrix. The coating effective factor A of the ternary positive electrode material is 0.001 GPa / nm2 to 0.2 GPa / nm2. Formula (I) represents the average value of the ratio of the thickness of the coating layer of the particles of the ternary positive electrode material to the diameter of the active material matrix, with formula (II) having no units; formula (III) represents the average Young modulus of the particles of the ternary positive electrode material, with the units of formula (IV) being GPa; and SN 2 is the variance of the thickness of the coating layer of the particles of the ternary positive electrode material, with the unit of SN 2 being nm2. The coating effective factor A of the ternary positive electrode material in the present disclosure is within the range above, and the ternary positive electrode material has the characteristics of high structural stability, high cycle performance, low capacity fade rate and low residual alkali amount.

Description

Ternary cathode materials, preparation methods, screening methods, and secondary batteries

[0001] Cross-reference to related applications

[0002] This disclosure claims priority to Chinese Patent Application No. 2024117196893, filed on November 28, 2024, entitled "Ternary Cathode Material, Preparation Method, Screening Method and Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of secondary battery cathode material technology, specifically to ternary cathode materials, preparation methods, screening methods, and secondary batteries. Background Technology

[0004] Lithium nickel manganese oxide (NiCoMnO), a ternary cathode material for lithium-ion batteries, is considered the most likely candidate for widespread application in power batteries due to its advantages such as high discharge capacity, low production cost, stable layered structure, and good thermal stability. However, ternary cathode materials exhibit severe capacity loss, voltage decay, and unsatisfactory rate performance during cycling, significantly hindering their commercial application.

[0005] Existing research indicates that the main causes of capacity loss, voltage decay, and poor rate performance include: Firstly, during charging and discharging, direct contact between the cathode material and the electrolyte leads to side reactions, such as the dissolution of active materials and the decomposition of the electrolyte on the surface of highly oxidized active materials. Secondly, the repeated expansion and contraction of crystals during charging and discharging causes cracks between primary particles, disrupting their continuity and hindering electron transport. When the electrolyte penetrates into the secondary particles through these microcracks, more severe side reactions occur. These microcracks become more severe with increasing cutoff voltage, resulting in an excessively thick CEI film, which reduces the material's interfacial activity and electrochemical performance. Currently, the industry widely employs surface modification coatings for ternary cathode materials to alleviate problems such as cathode / electrolyte interface reactions and intergranular cracking. Conventional chemical coating methods include co-precipitation, sol-gel, hydrothermal, and solid-state methods; traditional deposition methods include spray drying, pulsed laser deposition, physical vapor deposition, and chemical vapor deposition; advanced deposition methods include atomic layer deposition and molecular layer deposition.

[0006] Existing coated and modified ternary cathode materials have poor stability and are still prone to structural changes during use, leading to capacity loss, voltage decay, and poor rate performance in lithium-ion batteries.

[0007] In view of this, this disclosure is hereby made. Summary of the Invention

[0008] This disclosure provides ternary cathode materials, preparation methods, screening methods, and secondary batteries, wherein the ternary cathode materials have superior structural stability and cycle performance, and low capacity decay rate.

[0009] This disclosure is implemented as follows:

[0010] In a first aspect, this disclosure provides a ternary cathode material, wherein the particles of the ternary cathode material comprise an active material matrix and a coating layer coated on the active material matrix, and the effective coating factor A of the ternary cathode material is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 ,in, This represents the average ratio of the coating thickness of the ternary cathode material particles to the diameter of the active material matrix. Unitless; This represents the average Young's modulus of the ternary cathode material particles. The unit is GPa; S N 2 S represents the variance of the coating thickness of the ternary cathode material particles. N 2 The unit is nm 2 .

[0011] In an optional implementation, the The value is 0.001-0.1. Among them, di 层厚 The thickness of the coating layer on the ternary cathode material particles is expressed in nm; di 内径 The diameter of the active material matrix in the ternary cathode material particles is in nm; N is the sample size of the ternary cathode material particles.

[0012] And / or, the The range is 160 GPa to 350 GPa, among which Where N is the sample size of the ternary cathode material particles, and E i The value represents the Young's modulus of the ternary cathode material particles measured by nanoindentation, in GPa.

[0013] And / or, the S N 2 10nm 2 -3500nm 2 ,in The average thickness of the coating layer on the ternary cathode material particles is given in nm; N is the sample size of the ternary cathode material particles.

[0014] In an optional implementation, the di 层厚 The wavelength range is 10nm-1000nm, and the di层厚 It is the average of the sum of the coating thicknesses on the maximum Ferete diameter and the sum of the coating thicknesses on the minimum Ferete diameter of the ternary cathode material particles;

[0015] And / or, the di 内径 The diameter is 1μm-20μm, and the di 内径 It is the average of the active material matrix length on the maximum Ferete diameter and the active material matrix length on the minimum Ferete diameter of the ternary cathode material particles.

[0016] In an optional implementation, the sample size N of the ternary cathode material particles is ≥10.

[0017] In an optional embodiment, the general formula of the active material matrix is ​​Li. x Ni a Co b M c M' 1-a-b-c A y O 2-y Wherein, M is selected from at least one of Al and Mn; M' is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, C, Si, Ca, Cu, La, Ce, Bi, In, Nb and Y; A is selected from at least one of P and F; wherein 0.95≤x<1.1, a>0, b>0, c>0, 0.95≤(a+b+c)≤1, 0≤y≤0.01;

[0018] And / or, the coating layer is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3 and MgF2.

[0019] Secondly, this disclosure provides a method for preparing the ternary cathode material according to any one of the foregoing embodiments, comprising:

[0020] Pre-coating: The active material matrix is ​​dry-coated with a first coating agent and then calcined for the first time to obtain a pre-coated ternary cathode material.

[0021] The pre-coated ternary cathode material is wet-coated using a mixed coating agent and then calcined a second time to obtain the ternary cathode material.

[0022] In an optional implementation, the preparation method satisfies at least one of the following characteristics AF:

[0023] A. The first coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3, and MgF2;

[0024] B. The mass ratio of the first coating agent to the active material matrix is ​​0.05%-2%;

[0025] C. The first roasting temperature is 400℃-700℃, the atmosphere is oxygen, and the roasting time is 3h-10h;

[0026] D. The preparation of the active material matrix includes: calcining a mixture comprising a ternary cathode material precursor, a dopant, and a lithium source, or a mixture comprising a ternary cathode material precursor and a lithium source, to obtain the active material matrix.

[0027] E. The coating process includes: drying and granulating a slurry comprising a pre-coated ternary cathode material, a mixed coating agent and a solvent to obtain a powder, and washing, drying, second calcining and crushing the powder to obtain the ternary cathode material;

[0028] F. The second roasting temperature is 400℃-700℃, the atmosphere is oxygen, and the roasting time is 3h-10h;

[0029] In an optional implementation, the coating satisfies at least one of the following characteristics:

[0030] a. The mass ratio of the mixed coating agent to the pre-coated ternary cathode material in the slurry is 5%-25%;

[0031] b. The mixed coating agent comprises a second coating agent and a surfactant, wherein the mass ratio of the surfactant to the second coating agent in the mixed coating agent is (15-25):1;

[0032] c. The mixed coating agent comprises a second coating agent and a surfactant, wherein the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, Tween-80, polymethacrylic acid, polyethylene glycol, and ammonium polymethacrylate;

[0033] d. The mixed coating agent comprises a second coating agent and a surfactant, wherein the second coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, Mn3(PO4)2, AlPO4, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3, and MgF2;

[0034] e. The solid content of the slurry is 100g / L-200g / L;

[0035] f. The solvent is selected from at least one of methanol, ethanol, isopropanol, and butanol;

[0036] g. The drying temperature is 60℃-200℃, and the drying time is 10h-25h;

[0037] h. The mixed coating agent is used to prepare the slurry after being subjected to airflow crushing, wherein the airflow crushing pressure is 5MPa-12MPa and the time is 2.5h-8h.

[0038] Thirdly, this disclosure provides a method for screening ternary cathode materials as described in the foregoing embodiments, wherein the ternary cathode material satisfies the following conditions:

[0039] ①The ternary cathode material includes an active material matrix and a coating layer covering the active material matrix;

[0040] ② The ternary cathode material satisfies the following condition: the effective coating factor A is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 ,in, This represents the average ratio of the coating thickness of the ternary cathode material particles to the diameter of the active material matrix. Unitless; This represents the average Young's modulus of the ternary cathode material particles. The unit is GPa; S N 2 S represents the variance of the coating thickness of the ternary cathode material particles. N 2 The unit is nm 2 .

[0041] Fourthly, this disclosure provides a secondary battery, comprising the ternary cathode material described in any one of the foregoing embodiments or the ternary cathode material prepared by the preparation method described in any one of the foregoing embodiments.

[0042] This disclosure has the following beneficial effects:

[0043] In this disclosure, the effective coating factor A of the ternary cathode material is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 The ternary cathode material coating and active material matrix within this range satisfy S N 2 , and Due to their coordinated relationship, this ternary cathode material has the characteristics of high structural stability, high cycle performance, low capacity decay rate, and low residual alkali content. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 is a TEM image of the ternary cathode material prepared in Example 1;

[0046] Figure 2 is a TEM image of the ternary cathode material prepared in Comparative Example 5. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0048] Among existing coating modification methods, the solid-state method is the easiest to achieve. It only requires mixing the coating material with the cathode material precursor and lithium source or cathode powder, followed by calcination to complete the coating. However, the thickness and uniformity of the coating layer are difficult to control. The applicant has found that the thickness and uniformity of the coating layer affect its ability to resist stress changes during the contraction and expansion processes of the active material during charging and discharging. Furthermore, if the coating amount is small, the coating layer uniformity is poor, and the coating layer does not completely cover the active material, it will lead to the exposure of the active material. This can result in the active material reacting with water and carbon dioxide in the air during storage to form residual alkali, and being corroded by the electrolyte during charging and discharging. Ultimately, this leads to changes in the material structure, causing capacity loss, voltage decay, and poor rate performance in lithium-ion batteries.

[0049] This disclosure provides a ternary cathode material, wherein the particles of the ternary cathode material include an active material matrix and a coating layer coated on the active material matrix, and the effective coating factor A of the ternary cathode material is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 Specifically, it can be 0.001 GPa / nm 2 0.002 GPa / nm 2 0.003 GPa / nm 2 0.005 GPa / nm 2 0.010 GPa / nm 2 0.020 GPa / nm 2 0.030 GPa / nm 2 0.050 GPa / nm 2 0.070 GPa / nm 2 0.090 GPa / nm 2 0.110 GPa / nm 2 0.130 GPa / nm 2 0.150 GPa / nm 2 0.2 GPa / nm 2 or 0.001 GPa / nm 2 -0.2 GPa / nm 2 any value between, where, This represents the average ratio of the coating thickness of the ternary cathode material particles to the diameter of the active material matrix. Unitless; This represents the average Young's modulus of the ternary cathode material particles. The unit is GPa; S N 2 S represents the variance of the coating thickness of the ternary cathode material particles. N 2 The unit is nm 2 .

[0050] The coating layer of the ternary cathode material can serve as a protective layer, protecting the ternary cathode material from electrolyte corrosion during charge-discharge cycles, enhancing the ternary cathode material's resistance to surrounding air H2O and CO2, and suppressing cracks caused by repeated expansion and contraction of crystals during the charge-discharge process.

[0051] When the amount of coating material in a ternary cathode material is relatively large compared to the cathode material, but the coating layer has poor uniformity and mechanical properties, the active material matrix may be exposed, resulting in poor structural stability of the ternary cathode material. Conversely, when the amount of coating material is relatively small compared to the cathode material, but the coating layer has good uniformity and mechanical properties, high coating effectiveness and structural stability may occur. Even when the amount of coating material is relatively large compared to the cathode material, the active material is completely coated, and the mechanical properties are excellent, the coating layer may still be too thick relative to the active material matrix, resulting in poor coating uniformity, which in turn leads to low coating effectiveness and poor structural stability. Therefore, the structural stability of a ternary cathode material must be determined by combining the ratio of coating layer thickness to the diameter of the active material matrix, the average Young's modulus, and the variance of the coating layer thickness. No single factor or even two of these factors can definitively indicate the structural stability of the ternary cathode material.

[0052] In this disclosure, the effective coating factor A of the ternary cathode material is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 Within this range, it indicates that both the ternary cathode material coating layer and the active material simultaneously satisfy S N 2 , and The cathode material with a well-coordinated structure and sufficient coating factor has the characteristics of high structural stability, high cycle performance, low capacity decay rate and low residual alkali content.

[0053] In some embodiments, the The value can be between 0.001 and 0.1, specifically, it can be any value between 0.001, 0.003, 0.005, 0.007, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, or 0.001-0.1. Among them, di 层厚 The thickness of the coating layer on the ternary cathode material particles is expressed in nm; di 内径 , where is the diameter of the active material matrix in the ternary cathode material particles, in nm; N is the sample size of the ternary cathode material particles.

[0054] Because of d 层厚 The D value cannot reflect the relative relationship between the coating thickness and the particle size of the active material matrix in the ternary cathode material. Therefore, in this embodiment, D is used to evaluate the relative relationship between the coating and the active material matrix in the ternary cathode material. The D value reflects the relative content of the coating and the active material matrix in the ternary cathode material. If the value is too high, it will reduce the proportion of active material in the ternary cathode material. If the D value is too low, the coating is not enough to play its protective role for the active material.

[0055] In some embodiments, the The range is 160 GPa to 350 GPa, specifically, it can be any value between 160 GPa, 170 GPa, 190 GPa, 210 GPa, 230 GPa, 250 GPa, 270 GPa, 290 GPa, 310 GPa, 330 GPa, 350 GPa, or 160 GPa to 350 GPa. N is the sample size of the ternary cathode material particles, E i The value represents the Young's modulus of the ternary cathode material particles measured by nanoindentation, expressed in GPa.

[0056] The Young's modulus (E) is used to evaluate the mechanical properties of ternary cathode materials composed of the coating layer and the active material matrix. Under the premise of the same active material matrix, the magnitude of E is related to the type of coating agent, the thickness of the coating layer, and the uniformity of the coating layer thickness. The higher the Young's modulus of the selected coating agent, the thicker the coating layer, and the higher the uniformity of the coating layer thickness, the larger the E of the corresponding cathode material; conversely, the smaller the E of the corresponding cathode material. Ternary cathode materials with high E have coating layers that can suppress the generation of microcracks and voids caused by stress changes in the active material matrix during charging and discharging. Specifically, the relationship between force and indenter displacement during the slow indentation of the indenter into the material surface can be recorded using atomic force microscopy, and the Young's modulus of the sample particles can be calculated by the system.

[0057] In some implementations, the S N 2 10nm 2 -3500nm 2 Specifically, it can be 10nm. 2 30nm 2 50nm 2 100nm 2 300nm 2 500nm 2 1000nm 2 1500nm 2 2000nm 2 2500nm 2 3000nm 2 3500nm 2 or 10nm 2 -3500nm 2 any value between, where The average thickness of the coating layer on the ternary cathode material particles is given in nm; N is the sample size of the ternary cathode material particles.

[0058] With S N 2To evaluate the uniformity of the coating thickness of the cathode material, since there are differences in coating uniformity even with the same amount of coating and active material, S is used as the metric. N 2 This indicates the uniformity of the coating layer on the surface of the active material. If poor coating uniformity leads to partial exposure of the active material, the exposed portion will form lithium oxides during storage and cycling, reacting with H2O and CO2 in the air to form residual alkali. This residual alkali reacts with the electrolyte to form HF, which in turn reacts with Li2CO3 to generate CO2, causing the battery to bulge and gas, affecting its cycle performance and safety (potential fire and explosion hazards). HF can also dissolve transition metal ions from the ternary cathode material NCM / NCA, disrupting its layered crystal structure and worsening the capacity retention of the electrode material. Furthermore, nickel-rich materials can undergo side reactions with the electrolyte, generating byproducts that hinder lithium-ion transport and a rock-salt-like Ni-O resistive layer, increasing diffusion resistance.

[0059] In some implementations, the di 层厚 The wavelength range is 10nm-1000nm, specifically, it can be any value between 10nm, 30nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, or 10nm-1000nm. 层厚 It is the average of the sum of the coating thicknesses on the maximum Ferete diameter and the sum of the coating thicknesses on the minimum Ferete diameter of the ternary cathode material particles;

[0060] And / or, the di 内径 The value can be 1μm-20μm, specifically, it can be any value between 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm or 1μm-20μm. 内径 It is the average of the active material matrix length on the maximum Ferete diameter and the active material matrix length on the minimum Ferete diameter of the ternary cathode material particles.

[0061] In some embodiments, the maximum and minimum Ferrette diameters are obtained by analyzing sample images using Matlab, and the length of the active material matrix and the thickness of the coating layer are obtained by analyzing sample images using ImageJ.

[0062] Specifically, after determining the maximum and minimum Ferrette diameters using Matlab analysis, the sample images were analyzed using ImageJ. The thickness of the coating layer on the longest and shortest Ferrette diameters of the ternary cathode material was measured. It should be noted that coating layers exist at both ends of both the longest and shortest Ferrette diameters, and the thickness of the coating layers at both ends was measured. Then, the sum of the coating layer thicknesses at both ends of the longest and shortest Ferrette diameters was calculated, and finally, the average of the sum of the coating layer thicknesses at both ends of the longest and shortest Ferrette diameters was calculated to obtain d. 层厚 And calculate its corresponding variance to obtain S. N 2 Using ImageJ to analyze sample images, the average lengths of the active material matrix on the longest and shortest Feret diameters of the ternary cathode material were measured to obtain d. 内径 , Then, the mean value of D for the N cathode material particles is calculated, denoted as...

[0063] It should be noted that the sample images can be TEM, SEM, or other images that can show the thickness of the ternary cathode material coating and the size of the active material matrix.

[0064] In some implementations, the number of ternary cathode material particles, N ≥ 10. A larger sample size is more likely to capture the diversity of the population, which helps to reduce sampling error. The samples selected for testing and calculating each parameter can be different, and the number of samples selected can be the same or different.

[0065] In some embodiments, the general formula of the active material matrix is ​​Li. x Ni a Co b M c M' 1-a-b-c A y O 2-y Wherein, M is selected from at least one of Al and Mn; M' is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, C, Si, Ca, Cu, La, Ce, Bi, In, Nb and Y; A is selected from at least one of P and F; wherein 0.95≤x<1.1, a>0, b>0, c>0, 0.95≤(a+b+c)≤1, 0≤y≤0.01;

[0066] And / or, the coating layer is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3 and MgF2.

[0067] Doping elements can be introduced into the active material matrix as needed to improve certain properties of the prepared cathode material. Coating the active material matrix with oxides, fluorides, or fast ion conductors can improve the conductivity and cycle stability of the prepared ternary cathode material while isolating the active material matrix from the electrolyte.

[0068] This disclosure provides a method for preparing the ternary cathode material according to any one of the foregoing embodiments, comprising:

[0069] Pre-coating: The active material matrix is ​​dry-coated with a first coating agent and then calcined for the first time to obtain a pre-coated ternary cathode material.

[0070] The pre-coated ternary cathode material is wet-coated using a mixed coating agent and then calcined a second time to obtain the ternary cathode material.

[0071] A uniform coating layer is formed on the surface of a ternary cathode material through a two-stage coating process involving dry and wet methods. The first coating, performed using a dry method, specifically includes: mixing a first coating agent, the active material matrix, and a dispersant (such as water and ethanol) via ball milling, and then pre-coating the active material matrix surface. This pre-coating may not form a uniform coating layer, but it can reduce the contact area between the active material matrix and the liquid to a certain extent during subsequent secondary coating with solvents and water, thus inhibiting the deterioration of the material structure by water.

[0072] Subsequently, a second coating process is performed on the pre-coated ternary cathode material using a wet coating method. Specifically, this may include: mixing a mixed coating agent, the pre-coated ternary cathode material, and a solvent to obtain a slurry, allowing coating agent particles to deposit on the surface of the pre-coated ternary cathode material. This process not only compensates for the defects of the first coating and achieves uniform coating, but also increases the structural stability and uniformity of the coating layer, thereby improving the S... N 2 Within a preset range, the uniform coating layer formed by the two coating processes effectively isolates the active material matrix from the air, making it difficult for H2O and CO2 in the air to react with residual lithium on the surface to form Li2CO3 or LiOH, thus suppressing side reactions at the cathode electrode / electrolyte interface and inhibiting Li +Significant loss reduces the dissolution of transition metal ions, prevents the structural collapse of the ternary cathode material during cycling, and improves the structural stability and cycling performance of the electrode material.

[0073] In some embodiments, the preparation method satisfies at least one of the following characteristics AF:

[0074] A. The first coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3, and MgF2;

[0075] B. The mass ratio of the first coating agent to the active material matrix is ​​0.05%-2%, specifically, it can be any value between 0.05%, 0.06%, 0.08%, 0.10%, 0.12%, 0.14%, 0.16%, 0.18%, 2%, or 0.05%-2%;

[0076] C. The first roasting temperature is 400℃-700℃, specifically, it can be any value between 400℃, 500℃, 600℃, 700℃ or 400℃-700℃, the atmosphere is oxygen, and the roasting time is 3h-10h, specifically, it can be any value between 3h, 4h, 6h, 8h, 10h or 3h-10h;

[0077] D. The preparation of the active material matrix includes: calcining a mixture comprising a ternary cathode material precursor, a dopant, and a lithium source, or a mixture comprising a ternary cathode material precursor and a lithium source, to obtain the active material matrix.

[0078] E. The coating process includes: drying and granulating a slurry comprising a pre-coated ternary cathode material, a mixed coating agent, and a solvent to obtain a powder; and washing, drying, second calcining, and crushing the powder to obtain the ternary cathode material.

[0079] F. The second firing temperature is 400℃-700℃, specifically, it can be any value between 400℃, 500℃, 600℃, 700℃ or 400℃-700℃, the atmosphere is oxygen, and the firing time is 3h-10h, specifically, it can be any value between 3h, 4h, 6h, 8h, 10h or 3h-10h.

[0080] Among them, since the uniformity of the coating layer obtained by dry coating is relatively poor, in order to avoid the defect of the uniformity of the coating layer obtained by the first coating cannot be compensated in wet coating, the dosage of the first coating agent should not be too much.

[0081] In some embodiments, the active material matrix can be a commercially available active material, or can be prepared by the following method: mixing a ternary cathode material precursor, a dopant (if any), and a lithium source in a chemical formula ratio, ball milling at a rotation speed of 150-500 rpm for 1-10 h, and after uniform mixing, calcining at 700-1000 °C in an air or oxygen atmosphere for 15-30 h to obtain a nickel cobalt manganese ternary cathode material;

[0082] Among them, the elements of the dopant include at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, C, Si, Ca, Cu, La, Ce, Bi, In, Nb, Y, Al, Mn, P, and F. The doping can be an oxide, fluoride, carbonate, hydroxide, nitride, boride, nitrate of the corresponding doping element, or any combination. The molar ratio of the doping substance to the precursor can be (0.01-0.05):1; the ternary cathode material precursor can be Ni x Co y Mn 1-x-y (OH)2, (0.25 < x < 0.9, 0 < y < 1, and x + y < 1); the lithium source can be at least one of lithium hydroxide, lithium nitrate, lithium carbonate, lithium oxalate, lithium acetate, and their hydrates.

[0083] In some embodiments, the coating satisfies at least one of the following characteristics a-h:

[0084] a. The mass ratio of the mixed coating agent to the pre-coated ternary cathode material in the slurry is 5%-25%. Specifically, it can be 5%, 10%, 15%, 20%, 25%, or any value between 5%-25%;

[0085] b. The mixed coating agent includes a second coating agent and a surfactant. The mass ratio of the surfactant to the second coating agent in the mixed coating agent is (15-25):1. Specifically, it can be 15:1, 17:1, 19:1, 21:1, 23:1, 25:1, or any value between (15-25):1;

[0086] c. The mixed coating agent includes a second coating agent and a surfactant. The surfactant is selected from at least one of sodium dodecylbenzenesulfonate, Tween-80, polymethacrylic acid, polyethylene glycol, and ammonium polymethacrylate;

[0087] d. The mixed coating agent comprises a second coating agent and a surfactant, wherein the second coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, Mn3(PO4)2, AlPO4, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3, and MgF2;

[0088] e. The solid content of the slurry is 100g / L-200g / L, specifically, it can be any value between 100g / L, 120g / L, 140g / L, 160g / L, 180g / L, 200g / L or 100g / L-200g / L;

[0089] f. The solvent is selected from at least one of methanol, ethanol, isopropanol, and butanol;

[0090] g. The drying temperature is 60℃-200℃, specifically, it can be any value between 60℃, 100℃, 150℃, 200℃ or 60℃-200℃, and the drying time is 10h-25h, specifically, it can be any value between 10h, 15h, 20h, 25h or 10h-25h.

[0091] h. The mixed coating agent is used to prepare the slurry after being subjected to airflow crushing, wherein the airflow crushing pressure is 5MPa-12MPa and the time is 2.5h-8h.

[0092] During the second coating, the introduction of sufficient surfactants into the mixed coating agent can prevent the polymerization of the second coating agent. At the same time, the mixed coating agent is broken down by airflow before the slurry is prepared, which can refine the mixed coating agent and make the two fully mixed. This is more conducive to preventing the agglomeration of the second coating agent and promoting the uniform mixing of the second coating agent and the pre-coated ternary cathode material, so as to make up for the relatively poor uniformity of the coating layer during the first coating.

[0093] Spray drying can be used to dry and granulate the slurry in order to improve the sphericity of the powder. At the same time, spray drying can produce relatively dense particles, which helps to reduce the damage to the particles in the subsequent washing step. The conditions for spray drying can be an inlet temperature of 200℃-260℃ and an outlet air temperature of 100℃-210℃.

[0094] Since ternary cathode materials are prone to chemical delithiation when exposed to water, leading to deterioration of material structure and electrochemical performance, this invention discloses washing the powder after granulation to remove excess lithium oxide formed by calcination of lithium source. At the same time, the coating layer obtained by the previous pre-coating plays a protective role for the cathode material, reducing the material structure deterioration caused by chemical delithiation during the washing process, and effectively reducing the amount of residual lithium in the active material.

[0095] This disclosure provides a method for screening ternary cathode materials as described in the foregoing embodiments, wherein the ternary cathode material satisfies the following conditions:

[0096] ①The ternary cathode material includes an active material matrix and a coating layer covering the active material matrix;

[0097] ② The ternary cathode material satisfies the following condition: the effective coating factor A is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 ,in, This represents the average ratio of the coating thickness of the ternary cathode material particles to the diameter of the active material matrix. Unitless; This represents the average Young's modulus of the ternary cathode material particles. The unit is GPa; S N 2 S represents the variance of the coating thickness of the ternary cathode material particles. N 2 The unit is nm 2 .

[0098] The effective coating factor A of the ternary cathode material is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 Within the range, it indicates that both the coating layer and the active material of the ternary cathode material simultaneously satisfy S N 2 , and The cathode material with a well-coordinated structure and sufficient coating factor has the characteristics of high structural stability, high cycle performance, low capacity decay rate and low residual alkali content.

[0099] This disclosure also provides a positive electrode sheet, comprising the ternary positive electrode material described in the foregoing embodiments or the ternary positive electrode material prepared by any of the methods described in the foregoing embodiments.

[0100] This disclosure provides a secondary battery comprising the ternary cathode material described in any of the foregoing embodiments.

[0101] In the positive electrode sheet disclosed herein, the positive electrode material layer typically comprises the aforementioned positive electrode material, as well as a binder and a conductive agent, and is usually formed by coating a positive electrode slurry and then drying and cold pressing it. The positive electrode slurry is typically formed by dispersing the aforementioned positive electrode material, conductive agent, and binder in a solvent and stirring them evenly. The solvent may be N-methylpyrrolidone (NMP).

[0102] In some optional embodiments, the cathode material layer may contain 70wt%-97wt% ternary cathode material, based on the total weight of the cathode material layer. Optionally, the weight percentage of the ternary cathode material in the cathode material layer is 85%-97%, 90%-97%, or 95%-97%. By adjusting the proportion of ternary cathode material in the cathode material layer, the energy density and cycle life of the lithium-ion battery can be further improved.

[0103] In some embodiments, the binder for the positive electrode material layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and modified polymers thereof.

[0104] Conductive agents can improve the electronic conductivity of the positive electrode material layer. In some optional embodiments, the positive electrode material layer may contain 2 wt% to 20 wt% of conductive agent based on the total weight of the positive electrode material layer. Optionally, the conductive agent may account for 2% to 10% or 2% to 5% of the weight of the positive electrode material layer.

[0105] In some embodiments, the conductive agent of the positive electrode material layer may include one or more of superconducting carbon, carbon black (such as Super P, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] This disclosure provides a lithium-ion battery, including the positive electrode sheet described in the foregoing embodiments, and also including a negative electrode sheet, an electrolyte, and a separator.

[0107] [Negative electrode plate]

[0108] The negative electrode sheet disclosed herein includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0109] As an example, the negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is laminated on either or both of the two opposite surfaces of the negative electrode current collector.

[0110] The negative electrode current collector can be made of a material with good conductivity and mechanical strength, serving both as a conductor and a current collector. In some embodiments, the negative electrode current collector can be made of copper foil.

[0111] In the negative electrode sheet disclosed herein, the negative electrode film layer typically comprises a negative electrode active material, as well as a binder, a conductive agent, and other optional additives. It is usually formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode and positive electrode materials, along with optional conductive agents, optional binders, and optional additives, in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0112] In some embodiments, the negative electrode active material may include one or more of artificial graphite, natural graphite, silicon-based materials, and tin-based materials. Optionally, the negative electrode active material includes one or more of artificial graphite and natural graphite. Optionally, the negative electrode active material includes artificial graphite.

[0113] In some embodiments, the conductive agent may include one or more of superconducting carbon, carbon black (e.g., Super P, acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the adhesive may include one or more of styrene-butadiene rubber (SBR), waterborne acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0115] In some embodiments, other optional additives include thickeners (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0116] [Electrolytes]

[0117] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from electrolyte solutions. The electrolyte solution includes an electrolyte salt and a solvent.

[0118] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0119] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0120] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0121] [Isolation membrane]

[0122] A separator is disposed between the positive and negative electrode plates, serving as a barrier. The lithium-ion battery disclosed herein does not impose any particular limitation on the type of separator; any known porous separator used in lithium-ion batteries can be selected. For example, the separator can be selected from one or more of the following: glass fiber film, non-woven fabric film, polyethylene film, polypropylene film, polyvinylidene fluoride film, and multilayer composite films comprising one or more of these materials.

[0123] Positive electrode, negative electrode, and separator can be stacked or wound to form an electrode assembly, with the separator positioned between the positive and negative electrode to provide isolation. The electrode assembly is then placed in an outer package, filled with electrolyte, and sealed to obtain a lithium-ion battery.

[0124] The outer packaging of a lithium-ion battery is used to encapsulate the electrode assembly and electrolyte. In some embodiments, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging of a lithium-ion battery can also be a pouch, such as a pouch. The material of the pouch can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0125] This disclosure does not impose any particular limitation on the shape of the lithium-ion battery, which can be cylindrical, square, or any other arbitrary shape.

[0126] In some embodiments, lithium-ion batteries can be assembled into battery modules, and the number of lithium-ion batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0127] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0128] This disclosure also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. The device can select a secondary battery, battery module, or battery pack according to its usage requirements.

[0129] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0130] Example 1:

[0131] This embodiment provides a method for preparing a ternary cathode material, specifically including the following steps:

[0132] Ni cobalt manganese hydroxide precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and lithium carbonate were mixed in a high-speed mixer, with the molar ratio of nickel cobalt manganese hydroxide precursor to lithium carbonate being 1:1.04. The mixture was stirred at 500 rpm for 5 min, and then dispersed at 1000 rpm for 15 min. The material was then placed in a bowl and heated to 850℃ in an oxygen atmosphere. After holding at this temperature for 25 h, the mixture was cooled to room temperature and further pulverized by a mechanical mill. The particle size D50 of the mechanical mill was controlled to be 9.3 μm, thus obtaining the nickel cobalt manganese ternary cathode material.

[0133] A mixture containing nano-alumina, the obtained nickel-cobalt-manganese ternary cathode material, and ethanol was mixed at 500 rpm for 3 minutes, and then mixed at 1000 rpm for 30 minutes to obtain a first mixture. The mass of the nano-alumina was 0.2 wt% of the obtained nickel-cobalt-manganese ternary cathode material, and the mass of ethanol was 15 wt% of the total mass of the nano-alumina and the obtained nickel-cobalt-manganese ternary cathode material. The first mixture was subjected to a second calcination treatment at a temperature of 500°C in an oxygen atmosphere for 6 hours, followed by natural cooling to obtain a pre-coated ternary cathode material.

[0134] Sodium dodecylbenzenesulfonate and nano-alumina were mixed in a mass ratio of 20:1 and subjected to airflow agitation to obtain a mixed coating agent. The airflow agitation pressure was 8 MPa and the time was 4 h.

[0135] A slurry was formed by mixing a mixed coating agent, pre-coated ternary cathode material, and ethanol. The mixture was stirred at 1000 rpm for 30 min. The mixed coating agent accounted for 10% of the mass of the pre-coated ternary cathode material. The slurry concentration was 150 g / L. After spray drying, powder was obtained. The spray drying parameters were: inlet temperature 260℃ and outlet air temperature 120℃. The powder was washed twice with deionized water and dried at 100℃ for 20 h. Then, a third calcination was performed. The calcination was carried out at 500℃ for 8 h in an oxygen atmosphere. After crushing, alumina-coated ternary cathode material was obtained. The TEM image is shown in Figure 1, showing a relatively uniform coating layer.

[0136] Example 2:

[0137] This embodiment provides a method for preparing a ternary cathode material, specifically including the following steps:

[0138] Ni cobalt aluminum hydroxide precursor Ni 0.83 Co 0.15 Al 0.02 (OH)2 and lithium carbonate were mixed in a high-speed mixer, with the molar ratio of nickel cobalt aluminum hydroxide precursor to lithium carbonate being 1:1.04. The mixture was stirred at 500 rpm for 5 min, and then dispersed at 1000 rpm for 15 min. The material was then placed in a bowl and heated to 850℃ in an oxygen atmosphere. After holding at this temperature for 25 h, the mixture was cooled to room temperature and further pulverized by a mechanical mill. The particle size D50 of the mechanical mill was controlled to be 15.0 μm to obtain the nickel cobalt aluminum ternary cathode material.

[0139] A mixture containing nano-alumina, the obtained nickel-cobalt-aluminum ternary cathode material, and ethanol was mixed at 500 rpm for 3 minutes, and then at 1000 rpm for 20 minutes to obtain a first mixture. The mass of the nano-alumina was 0.05 wt% of the obtained nickel-cobalt-aluminum ternary cathode material, and the mass of the ethanol was 15 wt% of the total mass of the mixture of nano-alumina and the obtained nickel-cobalt-aluminum ternary cathode material. The first mixture was subjected to a second calcination treatment at a temperature of 500°C in an oxygen atmosphere for 6 hours, followed by natural cooling to obtain a pre-coated ternary cathode material.

[0140] Sodium dodecylbenzenesulfonate and nano-alumina were mixed in a mass ratio of 25:1 and subjected to airflow crushing treatment to obtain a mixed coating agent. The airflow crushing pressure was 6 MPa and the time was 4 h.

[0141] A slurry was formed by mixing a mixed coating agent, pre-coated ternary cathode material, and ethanol. The slurry was stirred at 1000 rpm for 30 minutes. The mixed coating agent accounted for 8% of the mass of the pre-coated ternary cathode material. The slurry concentration was 150 g / L. After spray drying, powder was obtained. The spray drying parameters were: inlet temperature 220℃ and outlet air temperature 210℃. The powder was washed twice with deionized water and dried at 100℃ for 20 hours. Then, a third calcination was carried out. The calcination was held at 500℃ for 8 hours in an oxygen atmosphere. After crushing, alumina-coated ternary cathode material was obtained.

[0142] Example 3:

[0143] This embodiment provides a method for preparing a ternary cathode material, specifically including the following steps:

[0144] Ni cobalt manganese hydroxide precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2, lithium fluoride, and lithium chloride were mixed in a high-speed mixer with a molar ratio of nickel cobalt manganese hydroxide precursor, lithium fluoride, and lithium chloride of 1:1.02:0.04. The mixture was stirred at 500 rpm for 5 min and then dispersed at 1000 rpm for 15 min. The material was then placed in a bowl and heated to 850℃ in an oxygen atmosphere. After holding at this temperature for 25 h, the mixture was cooled to room temperature and further pulverized by a mechanical mill. The particle size D50 of the mechanical mill was controlled to be 10.1 μm to obtain the nickel cobalt manganese ternary cathode material.

[0145] A mixture containing nano-titanium dioxide, the obtained nickel-cobalt-manganese ternary cathode material, and ethanol was mixed at 500 rpm for 3 minutes, and then mixed at 1000 rpm for 30 minutes to obtain a first mixture. The mass of the nano-titanium dioxide was 0.05 wt% of the obtained nickel-cobalt-manganese ternary cathode material, and the mass of ethanol was 15 wt% of the total mass of the nano-titanium dioxide and the obtained nickel-cobalt-manganese ternary cathode material. The first mixture was subjected to a second calcination treatment at a temperature of 500°C for 6 hours in an oxygen atmosphere, followed by natural cooling to obtain a pre-coated ternary cathode material.

[0146] Sodium dodecylbenzenesulfonate and nano-titanium dioxide were mixed in a mass ratio of 20:1 and subjected to airflow agitation to obtain a mixed coating agent. The airflow agitation pressure was 9 MPa and the time was 3 h.

[0147] A slurry was formed by mixing a mixed coating agent, pre-coated ternary cathode material, and ethanol. The slurry was stirred at 1000 rpm for 30 minutes. The mixed coating agent accounted for 10% of the mass of the pre-coated ternary cathode material. The slurry concentration was 150 g / L. After spray drying, powder was obtained. The spray drying parameters were: inlet temperature 200℃ and outlet air temperature 100℃. The powder was washed twice with deionized water and dried at 100℃ for 20 hours. Then, a third calcination was carried out. The calcination was held at 500℃ for 8 hours in an oxygen atmosphere. After crushing, nano-titanium dioxide-coated ternary cathode material was obtained.

[0148] The main differences between Examples 4-12 and Comparative Examples 1-2 and Example 1 are shown in Table 1. In addition to the differences in Table 1, Example 7 also has the following differences: both the first coating agent and the second coating agent are zinc oxide.

[0149] Table 1

[0150] Comparative Example 3:

[0151] This embodiment provides a method for preparing a ternary cathode material, which differs from Embodiment 1 only in that water washing is performed during the preparation of the pre-coated ternary cathode material. Specifically, it includes the following steps:

[0152] Ni cobalt manganese hydroxide precursor Ni 0.8 Co 0.1 Mn 0.1(OH)2 and lithium carbonate were mixed in a high-speed mixer, with the molar ratio of nickel cobalt manganese hydroxide precursor to lithium carbonate being 1:1.04. The mixture was stirred at 500 rpm for 5 min, and then dispersed at 1000 rpm for 15 min. The material was then placed in a bowl and heated to 850℃ in an oxygen atmosphere. After holding at this temperature for 25 h, the mixture was cooled to room temperature and further pulverized by a mechanical mill. The particle size D50 of the mechanical mill was controlled to be 9.3 μm, thus obtaining the nickel cobalt manganese ternary cathode material.

[0153] A mixture containing nano-alumina, the obtained nickel-cobalt-manganese ternary cathode material, and ethanol was mixed at 500 rpm for 3 minutes, and then at 1000 rpm for 30 minutes to obtain a first mixture. The mass of the nano-alumina was 0.2 wt% of the obtained nickel-cobalt-manganese ternary cathode material, and the mass of ethanol was 15 wt% of the total mass of the nano-alumina and the obtained nickel-cobalt-manganese ternary cathode material. The first mixture was subjected to a second calcination treatment at a temperature of 500°C in an oxygen atmosphere for 6 hours. After natural cooling, it was washed twice with deionized water and then dried at 100°C for 20 hours to obtain a pre-coated ternary cathode material.

[0154] Sodium dodecylbenzenesulfonate and nano-alumina were mixed in a mass ratio of 20:1 and subjected to airflow agitation to obtain a mixed coating agent. The airflow agitation pressure was 8 MPa and the time was 4 h.

[0155] A slurry was formed by mixing a mixed coating agent, pre-coated ternary cathode material, and ethanol. The slurry was stirred at 1000 rpm for 30 minutes. The mixed coating agent was 10% of the mass of the pre-coated ternary cathode material. The concentration of the slurry was 150 g / L. After spray drying, powder was obtained. The spray drying parameters were: inlet temperature 260℃ and outlet air temperature 120℃. The powder was then calcined for the third time at 500℃ for 8 hours in an oxygen atmosphere. After crushing, alumina-coated ternary cathode material was obtained.

[0156] Comparative Example 4:

[0157] This embodiment provides a method for preparing a ternary cathode material. The only difference from Embodiment 1 is that no mixed coating agent is prepared. Instead, sodium dodecylbenzenesulfonate and nano-alumina are directly mixed with the pre-coated ternary cathode material and a solvent to prepare a slurry. The specific steps include:

[0158] Ni cobalt manganese hydroxide precursor Ni 0.8 Co 0.1 Mn 0.1(OH)2 and lithium carbonate were mixed in a high-speed mixer, with the molar ratio of nickel cobalt manganese hydroxide precursor to lithium carbonate being 1:1.04. The mixture was stirred at 500 rpm for 5 min, and then dispersed at 1000 rpm for 15 min. The material was then placed in a bowl and heated to 850℃ in an oxygen atmosphere. After holding at this temperature for 25 h, the mixture was cooled to room temperature and further pulverized by a mechanical mill. The particle size D50 of the mechanical mill was controlled to be 9.3 μm, thus obtaining the nickel cobalt manganese ternary cathode material.

[0159] A mixture containing nano-alumina, the obtained nickel-cobalt-manganese ternary cathode material, and ethanol was mixed at 500 rpm for 3 minutes, and then mixed at 1000 rpm for 30 minutes to obtain a first mixture. The mass of the nano-alumina was 0.2 wt% of the obtained nickel-cobalt-manganese ternary cathode material, and the mass of ethanol was 15 wt% of the total mass of the nano-alumina and the obtained nickel-cobalt-manganese ternary cathode material. The first mixture was subjected to a second calcination treatment at a temperature of 500°C in an oxygen atmosphere for 6 hours, followed by natural cooling to obtain a pre-coated ternary cathode material.

[0160] Nano-alumina, sodium dodecylbenzenesulfonate, pre-coated ternary cathode material, and ethanol were mixed to form a slurry, which was stirred at 1000 rpm for 30 min. The total mass of nano-alumina and sodium dodecylbenzenesulfonate was 10% of the mass of the pre-coated ternary cathode material, and the mass ratio of sodium dodecylbenzenesulfonate to nano-alumina was 20:1. The slurry concentration was 150 g / L. After spray drying, the parameters were: inlet temperature 260℃ and outlet air temperature 120℃. The powder was washed twice with deionized water and dried at 100℃ for 20 h. Then, it was calcined for a third time at 500℃ for 8 h in an oxygen atmosphere. After crushing, alumina-coated ternary cathode material was obtained.

[0161] Comparative Example 5:

[0162] This embodiment provides a method for preparing a ternary cathode material. The only difference from Embodiment 1 is that the total amount of nano-alumina used is the same as in Embodiment 1, and only one dry coating is performed. The TEM image is shown in Figure 2.

[0163] Comparative Example 6:

[0164] This embodiment provides a method for preparing a ternary cathode material. The only difference from Embodiment 1 is that the total amount of nano-alumina used is the same as in Embodiment 1, and only one wet coating is performed.

[0165] The ternary cathode materials prepared in the above embodiments and comparative examples were tested, and the specific items and methods are as follows:

[0166] 1. Residual alkali test procedure:

[0167] (1) Sample preparation: Weigh 10g of sample into a 250mL dry beaker, add 100mL of pure water, add a magnetic stir bar to the beaker and cover with plastic wrap, stir with a magnetic stirrer for 30min, let stand for 2min after stirring, take a clean funnel and place it on a clean conical flask, fold the circular filter paper in half and put it into the funnel for filtration, after filtration, put the conical flask with a rubber cap; use hydrochloric acid as titrant, after the acid-base titration reaches the endpoint, determine the lithium hydroxide and lithium carbonate content by the amount of hydrochloric acid used and the titration inflection point.

[0168] 2. Assembly of the coin cell battery:

[0169] To test the electrochemical performance of the materials, this disclosure discloses the fabrication of a 2032-type button cell for various electrochemical performance tests. The specific fabrication steps of the button cell are as follows: For the positive electrode preparation, the positive electrode materials prepared in each example and comparative example were first placed in an 85°C vacuum oven for 6 hours of vacuum baking. Then, active material, polyvinylidene fluoride, and acetylene black were weighed in a mass ratio of 90:6:4 and added to a homogenizer. A certain amount of N-methylpyrrolidone and zirconium beads were also added. The homogenizer was run at 500 rpm for 5 minutes, then at 2000 rpm for 15 minutes to ensure uniform mixing of the binder, conductive agent, and active material. The mixed slurry was then uniformly coated onto a flat aluminum foil. The coated electrode was placed in a vacuum constant temperature drying oven and baked for 10 hours at a temperature of 120°C. After drying, the electrode was rolled and stamped to obtain a positive electrode with a diameter of 12 mm. The CR2032 battery was assembled in an argon-filled glove box. The positive electrode, negative electrode (lithium plate), separator, and gasket were placed into the battery case, electrolyte was added, and the case was sealed to obtain the button cell to be tested.

[0170] The long-cycle test conditions are as follows: window voltages of 3.0V and 4.3V, charge / discharge rate of 1C (1C = 200mA / g), and test temperature of 25℃.

[0171] 3. Young's modulus: Observed using a Bruker atomic force microscope, nanoindentation was tested in an argon-filled glove box using an Agilent NanoIndenter G200 from Keysight. E was measured using a Berkovich indenter and the Oliver Pharr method.

[0172] (1) For each batch of samples without cyclic testing, 10 particles are randomly selected and tested. The average value is then taken as the Young's modulus E of the material.

[0173] (2) Test the Young's modulus of the sample after cycling: Take out the NMC electrode after cycling from the coin cell, wash it several times with dimethyl carbonate (DMC), and dry it overnight in a vacuum oven at room temperature to obtain the test sample after cycling. For each batch of samples, 10 particles are randomly selected for testing and the average value is taken.

[0174] (3) and S N 2 TEM images of the cathode materials obtained in each embodiment and comparative example were analyzed using Matlab and ImageJ. Ten particles were randomly selected from each batch of samples, and calculations were performed. and S N 2 .

[0175] The test results are shown in Tables 2 and 3.

[0176] Table 2

[0177] Table 3

[0178] According to the data in Tables 2 and 3, cathode materials with the same chemical composition correspond to different... E and S N 2 The size of the effective coating factor varies, affecting the physical and chemical properties of the cathode material. Specifically, within the specified parameter range, a higher effective coating factor indicates better electrochemical and / or cycle performance of the cathode material, and / or lower residual alkali content on the cathode material surface. This is because the coating layer effectively isolates the cathode material from the corrosion of water, carbon dioxide, and electrolyte in the air during storage, while also resisting the formation of cracks during charging and discharging. However, excessively thick layers not only reduce the proportion of active material but also increase the path distance for lithium-ion insertion / extraction; similarly, excessively thin or uneven layer thicknesses fail to provide adequate insulation and stress resistance.

[0179] As can be seen from Comparative Example 1 and Example 1, for the same active material with similar particle diameters, different amounts of coating agent result in significant differences in the effective coating factor, leading to substantial differences in the electrochemical performance of the resulting battery materials. As can be seen from Examples 1 to 7, different... Different Young's moduli, simultaneously S N 2 The differences resulted in significant variations in the effective coating factor, leading to marked differences in electrochemical performance. Examples 10-12, compared to Example 1, showed differences in the effective coating factor, although the effective coating factor was around 0.001 GPa / nm. 2-0.2 GPa / nm 2 Within the range, but and S N 2 If any one of them is outside the preferred range, such as Exceeding 0.001-0.1 Exceeding 160GPa-350GPa, S N 2 Beyond 10nm 2 -3500nm 2 All of these will lead to a decrease in the electrochemical performance of the battery; as can be seen from the comparison between Comparative Example 2 and Example 1, Within the range of 0.001-0.1 Within the range of 160GPa-350GPa, S N 2 At 10nm 2 -3500nm 2 Within the optimal range, but when the effective coating factor is outside the preferred range, the physical and chemical properties of the corresponding cathode material are significantly reduced. Therefore, by adjusting the ratio of the coating layer thickness to the diameter of the active material substrate... resistance to stress and uniformity of coating S N 2 This ensures that the effective coating factor is at 0.001 GPa / nm. 2 -0.2 GPa / nm 2 Within this range, the obtained cathode material exhibits superior physical and electrochemical properties.

[0180] As shown in Comparative Example 3, the capacity retention rate was significantly reduced after a single coating and subsequent water washing. This is because the single coating did not achieve complete and uniform coating of the material, leaving exposed active material sites. Since active materials are very sensitive to water, the more easily the material undergoes chemical deLi removal reactions in water, leading to deterioration of the material structure and electrochemical performance, thus reducing the capacity retention rate and the energy (E) of the material before and after cycling.

[0181] In the preparation process, the secondary coating agent and surfactant were not mixed. As shown in Comparative Example 4, the energy efficiency (E) decreased both before and after cycling compared to Example 1. This is because not mixing the secondary coating agent and surfactant results in poor uniformity of the coating layer on the material surface, leading to a decrease in E. Consequently, the capacity retention rate of the material in Comparative Example 4 was lower than that in Example 1.

[0182] The coating layer obtained by dry coating has poor uniformity, as shown in Figures 1 and 2. The coating layer uniformity of Comparative Example 5 is worse than that of Example 1, which leads to a decrease in the E of the material. This causes the active material to react with water and carbon dioxide in the air during storage, and the exposed active material will also react with the electrolyte during cycling, causing damage to the cathode material. Ultimately, this manifests as the accumulation of stress damage caused by contraction / expansion during electrochemical cycling, resulting in a significant decrease in E after cycling.

[0183] However, if only wet coating is used in the preparation process, it will also cause the coating agent nanoparticles to agglomerate and form large particle coatings. Therefore, whether only dry coating or wet coating is performed, the uniformity of coating will be reduced. In Comparative Examples 5 and 6, the material capacity retention rate and the E of the material before and after cycling are both lower than those in Example 1.

[0184] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure. Industrial applicability

[0185] In this disclosure, the effective coating factor A of the ternary cathode material is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 The ternary cathode material coating and active material matrix within this range satisfy S N 2 , and Due to their coordinated relationship, this ternary cathode material has the characteristics of high structural stability, high cycle performance, low capacity decay rate, and low residual alkali content.

Claims

1. A ternary cathode material, characterized in that, The ternary cathode material particles comprise an active material matrix and a coating layer covering the active material matrix, wherein the effective coating factor A of the ternary cathode material is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 ,in, This represents the average ratio of the coating thickness of the ternary cathode material particles to the diameter of the active material matrix. Unitless; This represents the average Young's modulus of the ternary cathode material particles. The unit is GPa; S N 2 S represents the variance of the coating thickness of the ternary cathode material particles. N 2 The unit is nm 2 .

2. The ternary cathode material according to claim 1, characterized in that, The The value is 0.001-0.

1. Among them, di 层厚 The thickness of the coating layer on the ternary cathode material particles is expressed in nm; di 内径 The diameter of the active material matrix in the ternary cathode material particles is in nm; N is the sample size of the ternary cathode material particles. And / or, the The range is 160 GPa to 350 GPa, among which Where N is the sample size of the ternary cathode material particles, and E i The value represents the Young's modulus of the ternary cathode material particles measured by nanoindentation, in GPa. And / or, the S N 2 10nm 2 -3500nm 2 ,in The average thickness of the coating layer on the ternary cathode material particles is given in nm; N is the sample size of the ternary cathode material particles.

3. The ternary cathode material according to claim 2, characterized in that, The di 层厚 The wavelength range is 10nm-1000nm, and the di 层厚 It is the average of the sum of the coating thicknesses on the maximum Ferete diameter and the sum of the coating thicknesses on the minimum Ferete diameter of the ternary cathode material particles; And / or, the di 内径 The diameter is 1μm-20μm, and the di 内径 It is the average of the active material matrix length on the maximum Ferete diameter and the active material matrix length on the minimum Ferete diameter of the ternary cathode material particles.

4. The ternary cathode material according to any one of claims 2-3, characterized in that, The sample size N of the ternary cathode material particles is ≥10.

5. The ternary cathode material according to any one of claims 1-4, characterized in that, The general formula of the active material matrix is ​​Li. x Ni a Co b M c M' 1-a-b-c A y O 2-y Wherein, M is selected from at least one of Al and Mn; M' is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, C, Si, Ca, Cu, La, Ce, Bi, In, Nb and Y; A is selected from at least one of P and F; wherein 0.95≤x<1.1, a>0, b>0, c>0, 0.95≤(a+b+c)≤1, 0≤y≤0.01; And / or, the coating layer is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3 and MgF2.

6. A method for preparing a ternary cathode material according to any one of claims 1-5, characterized in that, include: Pre-coating: The active material matrix is ​​dry-coated with a first coating agent and then calcined for the first time to obtain a pre-coated ternary cathode material. The pre-coated ternary cathode material is wet-coated using a mixed coating agent and then calcined a second time to obtain the ternary cathode material.

7. The method for preparing the ternary cathode material according to claim 6, characterized in that, The preparation method satisfies at least one of the following characteristics: A. The first coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3, and MgF2; B. The mass ratio of the first coating agent to the active material matrix is ​​0.05%-2%; C. The first roasting temperature is 400℃-700℃, the atmosphere is oxygen, and the roasting time is 3h-10h; D. The preparation of the active material matrix includes: calcining a mixture comprising a ternary cathode material precursor, a dopant, and a lithium source, or a mixture comprising a ternary cathode material precursor and a lithium source, to obtain the active material matrix; E. The coating process includes: drying and granulating a slurry comprising a pre-coated ternary cathode material, a mixed coating agent and a solvent to obtain a powder, and washing, drying, second calcining and crushing the powder to obtain the ternary cathode material; F. The second roasting temperature is 400℃-700℃, the atmosphere is oxygen, and the roasting time is 3h-10h.

8. The method for preparing the ternary cathode material according to claim 7, characterized in that, The coating satisfies at least one of the following characteristics: a. The mass ratio of the mixed coating agent to the pre-coated ternary cathode material in the slurry is 5%-25%; b. The mixed coating agent comprises a second coating agent and a surfactant, wherein the mass ratio of the surfactant to the second coating agent in the mixed coating agent is (15-25):1; c. The mixed coating agent comprises a second coating agent and a surfactant, wherein the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, Tween-80, polymethacrylic acid, polyethylene glycol, and ammonium polymethacrylate; d. The mixed coating agent comprises a second coating agent and a surfactant, wherein the second coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, Mn3(PO4)2, AlPO4, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3, and MgF2; e. The solid content of the slurry is 100g / L-200g / L; f. The solvent is selected from at least one of methanol, ethanol, isopropanol, and butanol; g. The drying temperature is 60℃-200℃, and the drying time is 10h-25h; h. The mixed coating agent is used to prepare the slurry after being subjected to airflow crushing, wherein the airflow crushing pressure is 5MPa-12MPa and the time is 2.5h-8h.

9. A method for screening ternary cathode materials according to claim 1, characterized in that, The ternary cathode material satisfies the following conditions: ①The ternary cathode material includes an active material matrix and a coating layer covering the active material matrix; ② The ternary cathode material satisfies the following condition: the effective coating factor A is 0.001 GPa / nm. 2 -0.2 GPa / nm 2 ,in, This represents the average ratio of the coating thickness of the ternary cathode material particles to the diameter of the active material matrix. Unitless; This represents the average Young's modulus of the ternary cathode material particles. The unit is GPa; S N 2 S represents the variance of the coating thickness of the ternary cathode material particles. N 2 The unit is nm 2 .

10. A secondary battery, characterized in that, The ternary cathode material includes any one of claims 1-5 or any one of claims 6-8.

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