Cathode material, preparation method thereof, lithium ion battery and electric device

Abstract

This application belongs to the field of battery technology, and specifically discloses a cathode material, its preparation method, a lithium-ion battery, and an electrical device. The cathode material includes: Li 1+a1 (Ni x1 Co y1 Mn z1 M 1 m1 )M 2 m2 O2, M 1 includes at least one of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, Ba, and B; M 2 includes at least one of W, Mo, Zr, Al, V, Ti, B, Co, and Nb; the pressure P x -microstrain change △N Px The fitting straight line satisfies △N Px = kP x , 0 < k < 0.0012; where k is the slope, and P x is the pressure applied to the cathode material before testing the microstrain, in MPa, and the microstrain change △N Px is the difference between the microstrain of the cathode material after applying the pressure P x and the microstrain of the cathode material without applying the pressure. Thus, this cathode material has better processing performance and higher compressive strength, with fewer cracks generated on the surface of the particles after pole piece rolling, and the cycle performance is significantly improved.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a cathode material and its preparation method, a lithium-ion battery, and an electrical device. Background Technology

[0002] Cathode materials possess advantages such as high energy density, long cycle life, and low gas production, and are widely used in lithium-ion batteries. Failure analysis of cathode materials reveals that, unlike agglomerated materials that pulverize and fragment after long-term charge-discharge cycles, cathode materials maintain an intact structure even after multiple charge-discharge cycles. However, cracks may appear on the surface of some particles. These cracks expose the uncoated inner surface to the electrolyte, exacerbating corrosion and electrolyte consumption, leading to irreversible capacity loss and deterioration of cycle performance.

[0003] The cracking of cathode materials is generally attributed to their physicochemical properties during battery use, including volume contraction and expansion during charging and discharging, severe polarization due to long lithium-ion diffusion paths, and electrolyte decomposition and corrosion caused by excessively high operating voltages. Studies have found that even when cathode materials are fabricated into cathode sheets without undergoing charging and discharging, cracks can still be observed, indicating that the charging and discharging process is not the primary cause of cracking. The cracks mainly originate during the electrode rolling process, resulting from crystal plane slip, stacking faults, and tearing under pressure.

[0004] Traditional approaches to cathode material development focus on bulk doping, surface coating, and morphology control to improve cycle performance by enhancing lithium-ion migration kinetics and reducing side reactions between the cathode material and the electrolyte. However, there are currently no effective methods to address the problem of cracks forming after rolling in cathode materials. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in the related art. To this end, this application proposes a positive electrode material with low stress or high compressive strength, a method for preparing the same, a lithium-ion battery, and an electrical device thereof.

[0006] The first aspect of this application proposes a cathode material, comprising:

[0007] Li 1+a1 (Ni x1 Co y1 Mn z1 M 1 m1 M 2 m2 O2

[0008] Where, -0.1 ≤ a1 ≤ 0.1, 0.5 ≤ x1 < 1, 0 < y1 ≤ 0.4, 0 < z1 ≤ 0.6, 0 ≤ m1 ≤ 0.1, 0 ≤ m2 ≤ 0.02;

[0009] M 1 includes at least one of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, Ba, and B;

[0010] M 2 includes at least one of W, Mo, Zr, Al, V, Ti, B, Co, and Nb;

[0011] The pressure P of the positive electrode material x - Microstrain change △N Px The fitted straight line satisfies △N Px = kP x , 0 < k < 0.0012;

[0012] Where, k is the slope, and P x is the pressure applied to the positive electrode material before testing the microstrain, in MPa, and the microstrain change △N Px [[ID=2,8]]is the difference between the microstrain of the positive electrode material after applying the pressure P x and the microstrain of the positive electrode material without applying pressure.

[0013] In this application, an X-ray diffractometer is used to analyze the structure of the single-crystalline multi-component positive electrode material, and the microstrain of the material is obtained through refined calculation. The microstrain under different pressures is tested to characterize the material, and then the structural stability of the positive electrode material is evaluated. With the above composition, and when the pressure P x - Microstrain change △N <, Px fitted straight line satisfies the above conditions, the positive electrode material has better structural stability and processing performance, produces fewer cracks on the surface of the particles after pole piece rolling, and the cycle performance is significantly improved.

[0014] In some embodiments, 0 < k < 0.001. When the k value is within this range, it indicates that the degree of microstrain change of the positive electrode material is weak, indicating that the material structure is more stable, which can ensure the structural stability of the material during high-voltage charge and discharge tests and greatly improve the cycle performance.

[0015] In some embodiments, the microstrain N of the positive electrode material without applying pressure P0 < 0.1%; in some other embodiments, N P0 <,000008%. Therefore, the microstrain of the positive electrode material is small, the structural stability is better, and it has a high compressive strength.

[0016] In some embodiments, the microstrain N of the cathode material after applying a pressure of 500 MPa is... P500 <0.18%; in other embodiments, N P500 <0.16%. Therefore, the micro-strain of this cathode material is small, its structural stability is better, and it has high compressive strength.

[0017] In some embodiments, the D of the positive electrode material when no pressure is applied 50 Particle size D 50(P0) and the D of the cathode material when a pressure of 500 MPa is applied 50 Particle size D 50(P500) Satisfy: (D) 50(P0) -D 50(P500) ) / D 50(P0) <30%; in other embodiments, (D 50(P0) -D 50(P500) ) / D 50(P0) <20%. This can further improve the compressive strength and cycle performance of the cathode material.

[0018] In some embodiments, the D of the positive electrode material when no pressure is applied 50 Particle size D 50(P0) The value is 2–6 μm; in other embodiments, D 50(P0) The thickness ranges from 2.5 to 4.5 μm. This is beneficial for improving the energy density of lithium-ion batteries.

[0019] In some embodiments, the particle size distribution width (SPAN) of the cathode material when no pressure is applied P0 Satisfies: 0.8 P0 <1.4; in other embodiments, 0.9 P0 <1.3; where SPAN P0 =(D 90(P0) -D 10(P0) ) / D 50(P0) D 10(P0) D of the positive electrode material when no pressure is applied 10 Particle size, D 50(P0) D of the positive electrode material when no pressure is applied 50 Particle size, D 90(P0) D of the positive electrode material when no pressure is applied 90 Particle size. This is beneficial for improving the compaction density and volumetric energy density of the cathode material.

[0020] In some embodiments, the specific surface area of ​​the positive electrode material when no pressure is applied is denoted as S. P0 The specific surface area of ​​the cathode material when a pressure of 500 MPa is applied is denoted as S. P500 Satisfy: (S)​​P500 -S P0 ) / S P0 <75%; in other embodiments, (S P500 -S P0 ) / S P0 <50%. This can further improve the compressive strength and cycle performance of the cathode material.

[0021] In some embodiments, the specific surface area of ​​the positive electrode material when no pressure is applied is denoted as S. P0 The concentration is 0.3–1.2 g / cm³. 2 In other embodiments, S P0 It ranges from 0.4 to 1.0 g / cm³. 2 This is beneficial for improving the cycle performance of lithium-ion batteries.

[0022] The second aspect of this application discloses a method for preparing a cathode material, comprising:

[0023] The precursor, lithium source, and optional M 1 The raw materials are mixed to obtain a mixture of raw materials;

[0024] The raw material mixture is subjected to a first sintering, which includes heating the raw material mixture to a first temperature T1 and holding it at that temperature for a first time, then cooling it from T1 to 600°C at an average cooling rate of ≤2°C / min, and then naturally cooling it to room temperature to obtain a primary sintered material.

[0025] The primary sintering material and the first M 2 The mixture is mixed with the source material and then subjected to a second sintering to obtain a secondary sintered material.

[0026] This application describes a method for preparing a cathode material with low stress and high compressive strength by controlling the temperature gradient during high-temperature solid-state sintering. This cathode material exhibits better processing performance, fewer cracks on the particle surface after electrode rolling, and significantly improved cycle performance. The core of this preparation method lies in controlling the cooling rate, performing medium-to-high temperature annealing at the end of high-temperature sintering to eliminate internal stress in the cathode material and improve its compressive strength.

[0027] In some embodiments, the first sintering includes: heating the raw material mixture to a first temperature T1 and holding it at that temperature for a first time, then cooling it from T1 to T1-80°C at an average cooling rate of ≤1°C / min, then cooling it from T1-80°C to 600°C at an average cooling rate of ≤2°C / min, and then naturally cooling it to room temperature.

[0028] In some embodiments, T1-80℃ > 800℃, the temperature is reduced from T1-80℃ to 800℃ at an average cooling rate of ≤1.5℃ / min, and then further reduced from T1-80℃ to 600℃ at an average cooling rate of ≤2℃ / min, and then naturally cooled to room temperature.

[0029] In some embodiments, 600℃≤T1-80℃≤800℃, the temperature is reduced from T1-80℃ to 600℃ at an average cooling rate of ≤2℃ / min, and then naturally cooled to room temperature.

[0030] When the above sintering process is met, it is beneficial to obtain cathode materials with lower stress and higher compressive strength, thereby improving the cycle performance of lithium-ion batteries.

[0031] In some embodiments, the method for preparing the cathode material further includes: mixing the secondary sintering material with a second M... 2 The source is mixed, and the resulting mixture is then subjected to a third sintering to obtain a tertiary sintered material. This can further improve the energy density and cycle performance of the cathode material.

[0032] In some embodiments, the lithium source includes one of lithium carbonate, lithium hydroxide, anhydrous lithium hydroxide, and lithium oxide. Therefore, the material is widely available and the cost is low.

[0033] In some embodiments, the M 1 Sources include those containing M 1 It contains at least one of the following: oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides of the element. Therefore, the material is widely available and inexpensive.

[0034] In some embodiments, the first M 2 Source and second M 2 Each source contains M independently 2 It contains at least one of the following: oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides of the element. Therefore, the material is widely available and inexpensive.

[0035] In some embodiments, the second sintering temperature is 400–800°C, and the holding time is 4–10 h.

[0036] In some embodiments, the temperature of the third sintering is 300–600°C, and the holding time is 4–10 h.

[0037] A third aspect of this application discloses a lithium-ion battery comprising the positive electrode material described in the first aspect of this application or the positive electrode material prepared by the method described in the second aspect of this application. Therefore, this lithium-ion battery exhibits good cycle performance.

[0038] The fourth aspect of this application discloses an electrical device including the lithium-ion battery described in the third aspect of this application. Therefore, the electrical device has a long service life. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the gradient cooling sintering curve of this application.

[0040] Figure 2 This is a SEM image of the cathode material of this application after undergoing pressure fracturing treatment at 500 MPa. Detailed Implementation

[0041] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0042] The first aspect of this application proposes a cathode material, comprising:

[0043] Li 1+a1 (Ni x1 Co y1 Mn z1 M 1 m1 M 2 m2 O2

[0044] In the formula, -0.1≤a1≤0.1, 0.5≤x1<1, 0<y1≤0.4, 0<z1≤0.6, 0≤m1≤0.1, 0≤m2≤0.02;

[0045] M 1 Including at least one of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, Ba, and B;

[0046] M 2 Including at least one of W, Mo, Zr, Al, V, Ti, B, Co, and Nb;

[0047] The pressure P of the positive electrode material x -Microscopic strain change ΔN Px The fitted straight line satisfies △N Px =kP x 0 <k<0.0012;

[0048] Where k is the slope, P x The pressure applied to the cathode material in MPa before testing microstrain, and the microstrain change ΔN Px It is the applied pressure P xThe difference between the microstrain of the positive electrode material described later and the microstrain of the positive electrode material without applied pressure.

[0049] In this application, an X-ray diffractometer is used to perform structural analysis on the positive electrode material. The microstrain of the material is obtained through refined calculation, and the microstrain under different pressures is tested to characterize the material, and then the structural stability of the positive electrode material is evaluated. The above positive electrode material of this application satisfies 0 < k < 0.0012, with a relatively small degree of change in microstrain, having better structural stability and processing performance, generating fewer cracks on the surface of the particles after pole piece rolling, and significantly improving the cycling performance.

[0050] In some embodiments, 0 < k < 0.001, for example, it can be 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009 or 0.001, etc. Among them, the value of k reflects the degree of change in the microstrain of the material under different pressure conditions. The lower the k value, the weaker the degree of change in the microstrain of the material as the pressure increases, indicating that the material structure is more stable. Materials with lower k values can ensure that the material maintains structural stability during high-voltage charge-discharge tests, significantly improving the cycling performance.

[0051] In this article, the pressure P of the positive electrode material x and the change in microstrain △N Px The method of fitting into a straight line includes:

[0052] Step 1: Measure n portions of the positive electrode material. Define the n portions of the positive electrode material as the 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., the nth portion of the positive electrode material, where n is an integer greater than or equal to 5;

[0053] Step 2: Add the 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., the nth portion of the positive electrode material into the mold respectively, and apply the 1st pressure, the 2nd pressure,..., the nth pressure that increase sequentially from small to large one by one. Then dissociate the obtained tablets to obtain the 1st sample, the 2nd sample,..., the nth sample correspondingly. The positive electrode material without applied pressure constitutes the initial sample;

[0054] Step 3: After calibrating the position of the goniometer and the width of the instrument of the X-ray powder diffractometer, use the X-ray powder diffractometer to perform X-ray diffraction tests on the initial sample, the 1st sample, the 2nd sample,..., the nth sample respectively to obtain X-ray diffraction data;

[0055] Step 4: According to the X-ray diffraction data, calculate the microstrains N P0 、NP1 N P2 ... N Pn Then, the micro-strain change ΔN was calculated separately. P1＝ N P1 -N P0 , △N P2＝ N P2 -N P1 ..., △N Pn＝ N Pn -N Pn-1 ;

[0056] Step 5: Plot the micro-strain change and the pressure using scatter plots and fit a straight line. Determine the structural stability of the cathode material based on the slope of the fitted straight line.

[0057] It should be noted that the pressure applied to the positive electrode material must be within a reasonable range. In some embodiments, the pressure P1 of the positive electrode material is 50-150 MPa (e.g., 50 MPa, 80 MPa, 100 MPa, 120 MPa, or 150 MPa); in other embodiments, the pressure P1 of the positive electrode material is 80-120 MPa.

[0058] In some embodiments, the pressure P of the positive electrode material n The pressure is 150–900 MPa (e.g., 150 MPa, 200 MPa, 300 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, or 900 MPa, etc.); in other embodiments, the pressure P of the positive electrode material is... n The pressure ranges from 160 to 600 MPa.

[0059] In some embodiments, the pressure P of the positive electrode material i With P i-1 The difference is 20 to 200 MPa (e.g., 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, 120 MPa, 140 MPa, 160 MPa, 180 MPa or 200 MPa, etc.); in other embodiments, the difference is 50 to 100 MPa, where i is an integer from 2 to n, and n is an integer greater than or equal to 5 (e.g., 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15, etc.).

[0060] As an example, when n=7, the pressure P of the positive electrode material is... x and micro-strain change ΔN Px The specific methods for fitting a line include:

[0061] Step 1: Treat the surface moisture of the positive electrode material, usually by drying it at 100°C for 2 hours in a forced-air oven or vacuum oven.

[0062] Step 2: Weigh the sample. Weigh the processed sample according to the following standards: For D 50 For samples ≤3μm, the sample size is 0.5–1.5 g; for samples ≤3μm D 50 For samples ≤7μm, the sample size is 1.5–3g; for D 50 For samples ≥7μm, take 3–5g. Transfer the weighed sample to the compaction mold and gently shake the mold to flatten the sample surface.

[0063] Step 3: Place the mold containing the sample into the equipment and slowly apply pressure to the specified pressure (specifically, 50MPa, 100MPa, 200MPa, 300MPa, 400MPa, 500MPa, or 600MPa). The pressure applied by the equipment / mold area equals the pressure. After standing for 30 seconds, remove the mold and demold the sample. Only one pressure point can be measured per sample preparation.

[0064] Step 4: Place the demolded positive electrode tablet into a mortar, gently separate the tablet and sieve it with a standard sieve to ensure that the tablet is completely pulverized without any flaky particles. Pack the processed sample into a bag, label it and store it.

[0065] Step 5: Perform instrument parameter calibration of the X-ray powder diffractometer. Use standard Si powder to calibrate the position of the goniometer and use standard LaB6 to calibrate the instrument width.

[0066] Under the determined test conditions, the position and width of the goniometer were calibrated. The standard materials (Si powder, LaB6) were prepared on the sample stage, the spectrum was acquired, the instrument was calibrated, and the data was saved.

[0067] Step 6: Prepare materials with different pressures onto the sample stage, perform X-ray powder diffraction tests under defined conditions, and save the data for analysis; the samples prepared on the sample stage should be flat, and the sample height should be kept consistent each time.

[0068] Step 7: Import the test data into the refinement software for data processing.

[0069] (1) First, perform peak position processing, select the maximum peak value for processing, and ensure that the software can identify the position of all peaks;

[0070] (2) Perform phase identification using the PDF5+ database (International Diffraction Data Center), requiring the test data to be highly consistent with the card information;

[0071] (3) Add instrument width calibration data (external standard calibration width), select all crystal planes to calculate material micro-stress data using the Halder-Wagner method.

[0072] Step 8: Analyze the micro-strain data of the material calculated using the Halder-Wagner method.

[0073] Step 9: Perform scatter plot analysis on the micro-strain data and pressure, and determine the slope k.

[0074] In some embodiments, the microstrain N of the unstressed cathode material P0 <0.1%, for example, it can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or 0.09%, etc.; in other embodiments, N P0 <0.08%. The microstrain within the above range indicates that the cathode material has good structural stability and high compressive strength.

[0075] In some embodiments, the microstrain N of the cathode material after applying a pressure of 500 MPa is... P500 <0.18%, for example, it can be 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.13%, 0.15%, or 0.17%, etc.; in other embodiments, N P500 <0.16%. The micro-strain of this cathode material is small after pressure is applied, and it has high compressive strength.

[0076] In some embodiments, the D of the positive electrode material when no pressure is applied 50 Particle size D 50(P0) and the D of the cathode material when a pressure of 500 MPa is applied 50 Particle size D 50(P500) Satisfy: (D) 50(P0) -D 50(P500) ) / D 50(P0) <30%, for example, it can be 1%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, or 28%, etc.; in other embodiments, (D 50(P0) -D 50(P500) ) / D 50(P0) <20%. This can further improve the compressive strength and cycle performance of the cathode material.

[0077] In some embodiments, the D of the positive electrode material when no pressure is applied 50 Particle size D 50(P0)The diameter is 2–6 μm, for example, it can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm, etc.; in other embodiments, the D of the positive electrode material when no pressure is applied is... 50 Particle size D 50(P0) The thickness ranges from 2.5 to 4.5 μm. This is beneficial for improving the energy density of lithium-ion batteries.

[0078] In some embodiments, the particle size distribution width (SPAN) of the cathode material when no pressure is applied P0 Satisfies: 0.8 P0 <1.4, for example, it can be 0.9, 1, 1.1, 1.2, or 1.3, etc.; in other embodiments, 0.9 P0 <1.3; where SPAN P0 =(D 90(P0) -D 10(P0) ) / D 50(P0) D 10(P0) D of the positive electrode material when no pressure is applied 10 Particle size, D 50(P0) D of the positive electrode material when no pressure is applied 50 Particle size, D 90(P0) D of the positive electrode material when no pressure is applied 90 Particle size. A particle size distribution within the above range is beneficial for improving the compaction density and volumetric energy density of the cathode material.

[0079] In particle size distribution, D 50 Also known as the median particle size, it means that 50% of the volume of particles are smaller than or equal to this value, D. 90 This means that 90% of the volume of particles is smaller than or equal to this value, D 10 This means that 10% of the volume of particles are smaller than or equal to this value. (D) 10 D 50 D 90 The measurement can be performed using a Malvern particle size analyzer: disperse the cathode material in a dispersant (ethanol, acetone, or other surfactant), sonicate for 30 minutes, add the sample to the Malvern particle size analyzer, and start the test.

[0080] In some embodiments, the specific surface area of ​​the positive electrode material when no pressure is applied is denoted as S. P0 The specific surface area of ​​the cathode material when a pressure of 500 MPa is applied is denoted as S. P500 Satisfy: (S) P500 -S P0 ) / S P0 ​​<75%, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, or 70%, etc.; in other embodiments, (S P500 -S P0 ) / S P0 <50%.

[0081] In some embodiments, the specific surface area of ​​the positive electrode material when no pressure is applied is denoted as S. P0 The diameter is 0.3–1.2 m. 2 / g, for example, can be 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m 2 / g or 1.2m 2 / g, etc.; in other embodiments, S P0 The range is 0.4–1.0 m. 2 / g. This is beneficial for improving the cycle performance of lithium-ion batteries.

[0082] In this article, the specific surface area of ​​the cathode material refers to the surface area per unit mass of cathode material, S. P0 and S P500 It can be measured using a surface area analyzer.

[0083] The second aspect of this application discloses a method for preparing a cathode material, comprising:

[0084] S1: Precursor, lithium source, and optional M 1 The raw materials are mixed to obtain a mixture.

[0085] In this step, the precursor, lithium source, and optional M are... 1 There are no particular restrictions on the specific method of mixing the source; for example, a mixer can be used. It is understood that in this step, M can be flexibly selected as needed. 1 Should the source be added?

[0086] In some embodiments, the lithium source includes one of lithium carbonate, lithium hydroxide, anhydrous lithium hydroxide, and lithium oxide. Therefore, the material is widely available and the cost is low.

[0087] In some embodiments, the M 1 Sources include those containing M 1It contains at least one of the following: oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides of the element. Therefore, the material is widely available and inexpensive.

[0088] S2: The raw material mixture is subjected to a first sintering, which includes heating the raw material mixture to a first temperature T1 and holding it at that temperature for a first time, then cooling it from T1 to 600°C at an average cooling rate of ≤2°C / min, and then naturally cooling it to room temperature to obtain a primary sintered material.

[0089] The average cooling rate should be calculated by dividing the total temperature difference from T1 to 600℃ by the total time from T1 to 600℃. The specific implementation process can adopt a continuous cooling method or a constant temperature holding method by setting an intermediate temperature. During the cooling process, it is permissible for a certain period of the cooling process to have an instantaneous cooling rate higher than 2℃ / min. As long as the average cooling rate from T1 to 600℃ is <2℃ / min, it meets the requirements of this patent. The same applies to the average cooling rate of the process described below.

[0090] In some embodiments, the first sintering includes: heating the raw material mixture to a first temperature T1 and holding it at that temperature for a first time, then cooling it from T1 to T1-80°C at an average cooling rate of ≤1°C / min, then cooling it from T1-80°C to 600°C at an average cooling rate of ≤2°C / min, and then naturally cooling it to room temperature.

[0091] When T1-80℃ > 800℃, cool from T1-80℃ to 800℃ at an average cooling rate of ≤1.5℃ / min, continue cooling from T1-80℃ to 600℃ at an average cooling rate of ≤2℃ / min, and then allow to cool naturally to room temperature;

[0092] When 600℃≤T1-80℃≤800℃, the temperature is reduced from T1-80℃ to 600℃ at an average cooling rate of ≤2℃ / min, and then naturally cooled to room temperature.

[0093] When the cooling rate is within the above range, the distribution of metal elements in the bulk phase of the multi-element cathode material can be more uniform, effectively improving problems such as lattice defects and intracrystalline segregation caused by excessively fast cooling rates, reducing the concentration of internal micro-strain, and making the layered structure more stable.

[0094] It should be noted that the specific cooling procedure in this application is not particularly limited and can be divided into different stages. For example, please refer to... Figure 1 The raw material mixture is heated to a first temperature T1 and held at that temperature for a first time. Then, it is cooled from T1 to T2 at an average cooling rate of v2, then from T2 to T3 at an average cooling rate of v3, and finally from T3 to T4 at an average cooling rate of v4. The mixture is then held at that temperature for a period of time to obtain a primary sintered material.

[0095] S3: Combine the primary sintering material and the first M 2 The mixture is mixed with the source material and then subjected to a second sintering to obtain a secondary sintered material.

[0096] In this step, the primary sintering material and the first M are... 2 There are no particular restrictions on the specific method of mixing the source; for example, a mixer can be used for mixing.

[0097] In some embodiments, the method for preparing the cathode material further includes: mixing the secondary sintering material with a second M... 2 The mixture is mixed with the source material and then subjected to a third sintering process to obtain a tertiary sintered material.

[0098] In some embodiments, the first M 2 Source and second M 2 The sources are independent and include M. 2 It contains at least one of the following: oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides of the element. Therefore, the material is widely available and inexpensive.

[0099] In some embodiments, the temperature of the second sintering is 400-800℃ (e.g., 400℃, 500℃, 600℃, 700℃ or 800℃), and the holding time is 4-10h (e.g., 4h, 5h, 6h, 7h, 8h, 9h or 10h).

[0100] In some embodiments, the temperature of the third sintering is 300-600℃ (e.g., 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃, etc.), and the holding time is 4-10h (e.g., 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc.).

[0101] This application controls the temperature gradient during high-temperature solid-state sintering and increases the holding time in the mid-to-high temperature range above 600℃ (i.e., reduces the cooling rate), resulting in a more uniform distribution of metal elements within the bulk phase of the cathode material. This effectively improves problems such as lattice defects and intracrystalline segregation caused by excessively rapid cooling, reduces the concentration of internal micro-strain, and makes the layered structure more stable. The resulting cathode material exhibits low stress and high compressive strength, with better processing performance, fewer cracks on the particle surface after electrode rolling, and significantly improved cycle performance. This preparation method, through controlled cooling rate and mid-to-high temperature annealing at the end of high-temperature sintering, eliminates internal stress in the cathode material and improves its compressive strength. Furthermore, the process is simple and controllable, has low production costs, and can be mass-produced.

[0102] A third aspect of this application discloses a lithium-ion battery comprising the positive electrode material described in the first aspect of this application or the positive electrode material prepared by the method described in the second aspect of this application. Therefore, this lithium-ion battery exhibits good cycle performance.

[0103] It is understandable that there are no particular restrictions on the specific type of lithium-ion battery; it can be a primary battery or a secondary battery. The shape of the lithium-ion battery can be cylindrical, square, or any other shape. According to the outer packaging, lithium-ion batteries can be hard-shell batteries, soft-pack batteries, etc.

[0104] Typically, a lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode, negative electrode, and separator are fabricated into electrode assemblies using winding or stacking processes. The electrode assemblies and electrolyte are housed in an outer package. During the charging and discharging process of a lithium-ion battery, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through.

[0105] In some embodiments, the positive electrode sheet may include a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, a conductive agent, and a binder. The positive current collector may include a metal foil, for example, aluminum foil. The positive active material may include the positive electrode material of the first aspect of this application or the positive electrode material prepared by the method described in the second aspect of this application. The conductive agent may include acetylene black, single-walled carbon nanotubes, and conventional materials in the art. The binder may be polyvinylidene fluoride (PVDF) and conventional materials in the art.

[0106] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a layer of negative electrode active material disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material, a thickener, a conductive agent, and a binder. The negative electrode current collector may be a metal foil, for example, copper foil. The negative electrode active material may include artificial graphite, natural graphite, silicon-carbon based composite materials, lithium metal composite materials, lithium metal materials, and other negative electrode active materials commonly used in the art. The thickener may be sodium carboxymethyl cellulose (CMC-Na) and other conventional materials in the art. The conductive agent may be acetylene black and other conventional materials in the art. The binder may be styrene-butadiene rubber and other conventional materials in the art.

[0107] In some embodiments, the separator may be a separator known in the art that can be used in lithium-ion batteries and is stable to the electrolyte used, such as a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene composite separator, etc.

[0108] The fourth aspect of this application discloses an electrical device including the lithium-ion battery described in the third aspect of this application. Therefore, the electrical device has a long service life.

[0109] In some embodiments, the lithium-ion battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, 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.

[0110] The embodiments of this application are described in detail below.

[0111] Example 1

[0112] (1) Ni multi-material precursor 0.6 Co 0.1 Mn 0.3 (OH)2 and lithium carbonate are mixed evenly and subjected to high-temperature solid-state sintering at 1000℃ for 10 hours. The temperature is then reduced to 920℃ at a rate of 0.5℃ / min, then to 800℃ at a rate of 1℃ / min, and then to 600℃ at a rate of 2℃ / min. The mixture is then allowed to cool naturally to room temperature. After crushing and sieving, the sintered material is obtained.

[0113] (2) The primary sintering material and the coating agent Al2O3 are mixed evenly, heat-treated at 500℃ and kept at the temperature for 8 hours, and then crushed and sieved to obtain a single-crystal multi-element cathode material.

[0114] Examples 2 to 23

[0115] Same as Example 1, with specific differences shown in Tables 1 and 2.

[0116] Comparative Example 1

[0117] The solid-state sintering at 1000℃ in Example 1 was carried out for 10 hours and then naturally cooled to room temperature, with the rest remaining unchanged.

[0118] Comparative Example 2

[0119] The solid-state sintering at 1000℃ in Example 1 was carried out for 10 hours and then cooled to 600℃ at a rate of 4℃ / min. The solid-state sintering was then carried out naturally to room temperature, while the rest remained unchanged.

[0120] The specific parameters of the above embodiments and comparative examples are shown in Tables 1 and 2.

[0121] Table 1 Chemical composition of cathode materials

[0122]

[0123]

[0124]

[0125] Performance testing:

[0126] 1. Microscopic strain testing:

[0127] Step 1: Perform surface moisture treatment on the single-crystal multi-element cathode material, usually by drying in a forced-air oven or vacuum oven at 100-150℃ for 1-2 hours;

[0128] Step 2: Weigh the sample. Weigh the processed sample according to the following standards: For D 50 For samples ≤3μm, the sample size is 0.5–1.5 g; for samples ≤3μm D 50 For samples ≤7μm, the sample size is 1.5–3g; for D 50 For samples ≥7μm, take 3–5g. Transfer the weighed sample to a compaction mold and gently shake the mold to flatten the sample surface.

[0129] Step 3: Place the mold containing the sample into the equipment and slowly apply pressure to different levels (specifically, apply pressures of 50MPa, 100MPa, 200MPa, 300MPa, 400MPa, and 500MPa). After standing for 30 seconds, remove the mold and demold the sample. Only one pressure point can be measured per sample preparation.

[0130] Step 4: Place the demolded positive electrode tablet into a mortar, gently separate the tablet, and sieve it using a standard sieve to ensure complete pulverization without any flaky particles. Pack the processed sample into bags, label them, and store them. Standard sieve specifications: 200-400 mesh;

[0131] Step 5: Perform instrument parameter calibration for the X-ray powder diffractometer. Use standard Si powder to calibrate the position of the goniometer and use standard LaB6 diameter to calibrate the instrument width. The operation is as follows:

[0132] Test conditions: Voltage 40kV; Current 200mA; Step: 0.02°; Scan angle 5-120°; Acquisition time 45 minutes; Required peak intensity greater than 10000cps;

[0133] Under the determined test conditions, the position and width of the goniometer were calibrated. The standard materials (Si powder, LaB6) were prepared on the sample stage, the spectrum was acquired, the instrument was calibrated and the data was saved.

[0134] Step 6: Prepare materials with different pressures onto the sample stage, perform X-ray powder diffraction tests under defined conditions, and save the data for analysis; ensure that the samples prepared on the sample stage are flat and that the sample height remains consistent each time.

[0135] Step 7: Import the test data into the refinement software for data processing.

[0136] (1) First, perform peak position processing, select the maximum peak value for processing, and ensure that the software can identify the position of all peaks;

[0137] (2) Perform phase identification using PDF5+ database (International Diffraction Data Center), requiring a high degree of consistency between test data and card information;

[0138] (3) Add instrument width calibration data (external standard calibration width), select all crystal planes to calculate material microstrain data using the Halder-Wagner method.

[0139] 2.D 50 Test results were obtained using a Malvern Mastersize 2000 laser particle size analyzer.

[0140] 3. Particle Size Distribution Width (SPAN) P0 Test: The particle size distribution was measured using a Malvern Mastersizer 2000 laser particle size analyzer.

[0141] 4. Specific surface area test: Measured using a Tristar II 3020 specific surface area analyzer from Micromertics, USA;

[0142] 5. Cyclic performance test:

[0143] (1) Battery composition: 9.5g of positive electrode active material sample, 0.25g of acetylene black and 0.25g of polyvinylidene fluoride (PVDF) were mixed to form a positive electrode slurry. The slurry was coated on aluminum foil and dried. It was then pressed into a diameter of 12mm and a thickness of 120μm under a pressure of 100MPa and dried in a vacuum drying oven at 120℃ for 12h to obtain the positive electrode sheet.

[0144] The negative electrode uses a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator uses a polyethylene porous membrane with a thickness of 25 μm; a 1.0 mol / L LiPF6 solution is used as the electrolyte, in which an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) is used as the solvent.

[0145] The positive electrode, separator, negative electrode, and electrolyte are assembled into a 2025 type coin cell.

[0146] (2) 80-cycle retention rate: The charge and discharge voltage range was controlled at 3.0V-4.45V. At a constant temperature of 45℃, the coin cell was charged and discharged once at 0.1C and then charged and discharged 80 times at 1C to evaluate the high-temperature cycle capacity retention rate of the cathode material.

[0147] 6. Morphology test: The results were obtained using a Hitachi S-4800 scanning electron microscope from Japan.

[0148] The performance parameters of the positive electrode active materials prepared in the above embodiments and comparative examples are shown in Table 3.

[0149] Table 3 Test Results

[0150]

[0151] According to the data in Table 3, comparing Examples 1-23 and Comparative Examples 1-2, it can be seen that this application effectively reduces the micro-strain of the cathode material, reduces crack generation, and significantly improves the cycle performance of lithium-ion batteries by controlling the temperature gradient of high-temperature solid-state sintering and increasing the holding time in the medium-high temperature range above 600°C.

[0152] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0153] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0154] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrode material, characterized in that, include: Li 1+a1 (Ni x1 Co y1 Mr z1 M 1 m1 )M 2 m2 O2 In the formula, -0.1≤a1≤0.1, 0.5≤x1<1, 0<y1≤0.4, 0<z1≤0.6, 0≤m1≤0.1, 0≤m2≤0.02; M 1 Including at least one of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, Ba, and B; M 2 Including at least one of W, Mo, Zr, Al, V, Ti, B, Co, and Nb; The pressure P of the positive electrode material x -Microscopic strain change ΔN Px The fitted straight line satisfies △N Px =kP x 0 <k<0.0012; Where k is the slope, P x The pressure applied to the cathode material in MPa before testing microstrain, and the microstrain change ΔN Px It is the applied pressure P x The difference between the microstrain of the cathode material after pressure is applied and the microstrain of the cathode material before pressure is applied.

2. The cathode material according to claim 1, characterized in that, 0<k<0.001。 3. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: The microstrain N of the cathode material without applied pressure P0 <0.1%, preferred N P0 <0.08%; The microstrain N of the cathode material after applying a pressure of 500 MPa P500 <0.18%, preferred N P500 <0.16%.

4. The cathode material according to claim 1, characterized in that, The positive electrode material D when no pressure is applied 50 Particle size D 50(P0) The D of the cathode material when a pressure of 500 MPa is applied 50 Particle size D 50(P500) Satisfy: (D) 50(P0) -D 50(P500) ) / D 50(P0) <30%; preferred (D) 50(P0) -D 50(P500) ) / D 50(P0) <20%.

5. The positive electrode material according to claim 1, characterized in that, The positive electrode material D when no pressure is applied 50 Particle size D 50(P0) The micrometer size is 2–6 μm; preferably 2.5–4.5 μm.

6. The cathode material according to claim 1, characterized in that, The particle size distribution width (SPAN) of the cathode material when no pressure is applied P0 Satisfies: 0.8 P0 <1.4, preferably 0.9 P0 <1.3;​​ Among them, SPAN P0 =(D 90(P0) -D 10(P0) ) / D 50(P0) D 10(P0) D of the positive electrode material when no pressure is applied 10 Particle size, D 50(P0) D of the positive electrode material when no pressure is applied 50 Particle size, D 90(P0) D of the positive electrode material when no pressure is applied 90 Particle size.

7. The cathode material according to claim 1, characterized in that, The specific surface area of ​​the cathode material when no pressure is applied is denoted as S. P0 The specific surface area of ​​the cathode material when a pressure of 500 MPa is applied is denoted as S. P500 satisfy: (S P500 -S P0 ) / S P0 <75%, preferred (S) P500 -S P0 ) / S P0 <50%.

8. The positive electrode material according to claim 1, characterized in that, The specific surface area of ​​the cathode material when no pressure is applied is denoted as S. P0 The diameter is 0.3–1.2 m. 2 / g; preferably 0.4~1.0m 2 / g.

9. A method for preparing the cathode material according to any one of claims 1 to 8, characterized in that, include: The precursor, lithium source, and optional M 1 The raw materials are mixed to obtain a mixture of raw materials; The raw material mixture is subjected to a first sintering, which includes heating the raw material mixture to a first temperature T1 and holding it at that temperature for a first time, then cooling it from T1 to 600°C at an average cooling rate of ≤2°C / min, and then naturally cooling it to room temperature to obtain a primary sintered material. The primary sintering material and the first M 2 The mixture is mixed with the source material and then subjected to a second sintering to obtain a secondary sintered material.

10. The method according to claim 9, characterized in that, The first sintering includes: The raw material mixture is heated to a first temperature T1 and held at that temperature for a first time. Then, it is cooled from T1 to T1-80℃ at an average cooling rate of ≤1℃ / min, and then cooled from T1-80℃ to 600℃ at an average cooling rate of ≤2℃ / min, and then naturally cooled to room temperature.

11. The method according to claim 10, characterized in that, The first sintering includes: The raw material mixture is heated to a first temperature T1 and held at that temperature for a first time, then cooled from T1 to T1-80℃ at an average cooling rate of ≤1℃ / min, and meets any one of the following conditions: If T1-80℃ > 800℃, cool from T1-80℃ to 800℃ at an average cooling rate of ≤1.5℃ / min, continue cooling from T1-80℃ to 600℃ at an average cooling rate of ≤2℃ / min, and then allow to cool naturally to room temperature. 600℃≤T1-80℃≤800℃, cool from T1-80℃ to 600℃ at an average cooling rate of ≤2℃ / min, and then cool naturally to room temperature.

12. The method according to claim 9, characterized in that, Also includes: The secondary sintering material and the second M 2 The mixture is mixed with the source material and then subjected to a third sintering process to obtain a tertiary sintered material.

13. The method according to claim 9, characterized in that, in, The lithium source includes one of lithium carbonate, lithium hydroxide, anhydrous lithium hydroxide, and lithium oxide; The M 1 The source includes M 1 At least one of the following: oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides of an element; The first M 2 Source and second M 2 Each source contains M independently 2 At least one of the following: oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides of an element.

14. The method according to claim 12, characterized in that, The second sintering temperature is 400–800℃, and the holding time is 4–10 hours; The third sintering temperature is 300–600℃, and the holding time is 4–10 hours.

15. A lithium-ion battery, characterized in that, The cathode material includes any one of claims 1 to 8 or the cathode material prepared by any one of claims 9 to 14.

16. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 15.

Images