Monocrystal ternary positive electrode material and preparation method thereof, lithium ion battery and electric equipment

Abstract

The invention discloses a single-crystal ternary positive electrode material. The average primary particle diameter of the single-crystal ternary positive electrode material is 0.7-1.3 [mu] m. The preparation method comprises the following steps: mixing a positive electrode material precursor, a lithium source and a dopant, and performing first sintering to obtain a primary sintered material; uniformly mixing the primary sintering material with a first coating agent, and performing secondary sintering to obtain a secondary sintering material; and uniformly mixing the secondary sintering material with a second coating agent, and carrying out third sintering to obtain the single-crystal ternary positive electrode material. The invention also discloses a lithium ion battery and electric equipment comprising the single crystal ternary positive electrode material. The average primary particle diameter of the single crystal ternary positive electrode material is relatively small, the dynamic performance can be greatly enhanced, the material polarization can be greatly reduced and the lithium ion transmission path can be shortened in the charging and discharging process, so that the material has enough Li vacancies for smooth reembedding of lithium ions at the discharging tail end, and the discharging specific capacity of the material is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and particularly relates to a single-crystal ternary lithium-ion battery cathode material and its preparation method, as well as lithium-ion batteries and electrical devices. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, no memory effect, and low self-discharge rate, are widely used in all aspects of human society, including clothing, food, housing, and transportation. Currently, lithium-ion batteries almost completely dominate the 3C consumer electronics market, and their market share in the power sector is also continuously increasing. As the core of lithium-ion batteries, cathode materials undoubtedly have enormous development opportunities.

[0003] Most commercially available high-nickel ternary cathode materials are polycrystalline, which leads to severe microcracks near the grain boundaries during charge-discharge cycles, causing accelerated performance degradation in lithium-ion batteries. Single-crystal high-nickel ternary cathode materials can effectively reduce microcrack formation and have become a hot research topic in lithium-ion battery cathode materials in recent years.

[0004] Single-crystal ternary cathode materials possess more stable interfaces, which is beneficial for suppressing transition metal dissolution, resulting in shorter lithium-ion diffusion distances and superior rate and cycle performance. However, as the market demands higher energy density from materials, the requirements for Ni content in ternary cathode materials are becoming increasingly stringent, as are the requirements for the fabrication process. Traditional single-crystal ternary cathode materials typically have an average primary particle diameter between 1.5 and 5 μm. Simply increasing the Ni content of the cathode material can lead to a series of problems, such as slow kinetics and severe cycle degradation, and may even prevent further improvement in energy density. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a single-crystal ternary cathode material and its preparation method, a lithium-ion battery and an electrical device thereof.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A single-crystal ternary cathode material, wherein the average primary particle diameter of the single-crystal ternary cathode material is 0.7μm-1.3μm.

[0008] In this invention, the "average primary particle diameter" of the cathode material is obtained by measuring the maximum diameter of all fully visible primary particles in a 10,000x SEM image using Nano Measure software, and then calculating the average of the measured values. "Fully visible" refers to the ability to accurately measure the maximum diameter of the primary particle from the electron microscope image.

[0009] Preferably, in the above-mentioned single-crystal ternary cathode material, the specific capacity and voltage graph of the single-crystal ternary cathode material shows two staggered discharge plateaus between 3.4V and 3.68V. The discharge plateau between 3.4V and 3.56V is the characteristic discharge plateau of the material. Differentiating the voltage with the specific capacity yields the DQ / DV graph. In the DQ / DV differential discharge data of this single-crystal ternary cathode material, there are two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak is between 3.4V and 3.56V, and the maximum peak value of the second discharge peak is between 3.56V and 3.68V. The maximum peak intensity of the discharge characteristic peak between 3.4V and 3.56V is -400 to -1000.

[0010] Conventional high-nickel ternary single-crystal cathode materials have no discharge peak or a very small peak intensity between 3.4V and 3.56V. In this invention, a discharge peak with a peak intensity of -400 to -1000 appears between 3.4V and 3.56V. The appearance of this discharge peak greatly increases the discharge specific capacity of the material, improving the capacity by more than 5 mAh / g.

[0011] Through exploratory research, the applicant believes that the discharge peak in the single-crystal ternary cathode material of this invention between 3.4V and 3.56V may be due to the following reasons:

[0012] (1) The discharge plateau and discharge characteristic peak between 3.4-3.56V are at the end of the discharge. Under this voltage, the lithium in the lattice of traditional single-crystal ternary materials is basically saturated. The lithium ion transport is affected by the reduction of lithium vacancies and the long transport path. Lithium ions are blocked by lithium in the lattice and are difficult to insert, thus accumulating on the material surface, causing the voltage to drop rapidly to the termination voltage, resulting in the capacity not being fully released under this voltage. However, the single-crystal material of the present invention has a short lithium transport path, and more importantly, the material has enough lithium vacancies for lithium ion transport. Even at the end of the discharge, lithium ions can still be successfully reinserted.

[0013] (2) In the preparation process of this invention, a three-stage sintering process is adopted. In the first and second stages of sintering, lithium ions completely diffuse into the material, and crystals are formed. In the third stage of cooling sintering, the crystals shrink, increasing the stress between the crystals, so that the single crystal particles are completely separated and do not stick together. Moreover, the sintering temperature of the third stage is lower than that of the second stage, so that the lithium salts remaining on the surface of the material during the sintering process can fully re-enter the crystal lattice, improving the Li... + The utilization rate is improved, the surface residual lithium generation after the first burning is reduced, the surface area of ​​the highly dispersed low residual lithium single crystal material is higher, there are more lithium ion re-intercalation paths, and the subsequent coating is more uniform.

[0014] (3) During charging and discharging, cathode materials are easily corroded by the electrolyte, causing a significant decrease in capacity and cycle performance. Secondly, oxygen evolution and lithium-nickel mixing on the material surface easily lead to capacity reduction. Furthermore, high-nickel cathode materials are prone to alkalinity reactions, resulting in increased residual lithium on the material surface, affecting capacity and DCR performance. In the preparation process of this invention, a double coating is used to reduce residual lithium on the material surface, repair and stabilize the surface structure, isolate electrolyte corrosion, reduce material impedance, and allow Li... + Successful re-insertion improved the material's capacity and initial coulombic efficiency performance.

[0015] Therefore, the single-crystal ternary material of the present invention has a significant discharge characteristic peak at 3.4V-3.56V, thereby achieving the effect of greatly improving capacity and first coulombic efficiency.

[0016] Preferably, the single-crystal ternary cathode material described above has the chemical formula Li. x Ni a Co b Mn c M p A z O f Wherein, 1.0≤x≤1.08, 0.92≤a<1.0, 0<b≤0.08, 0<c<0.08, 0≤p≤0.05, 1.8≤f≤2.2, 0<z≤0.1; M is a doping element, including one or more of Zr, Ti, Mg, Al, Sb, Ca, Nb, Co, B, Sr, Y and Ba; A is a coating element, A is selected from one or more of Co, Zr, Sr, Ti, Al, B, W, F and Ca.

[0017] Preferably, the single-crystal ternary cathode material described above has a specific surface area of ​​0.7 m². 2 / g-1.4m 2 / g.

[0018] Preferably, the single-crystal ternary cathode material described above has a primary particle size of 190nm-260nm as determined by XRD testing.

[0019] As a general inventive concept, the present invention also provides a method for preparing the above-mentioned single-crystal ternary cathode material, comprising the following steps:

[0020] (1) The cathode material precursor, lithium source and dopant are mixed and then sintered for the first time to obtain the first sintered material;

[0021] (2) After the first sintering material is mixed evenly with the first coating agent, a second sintering is carried out to obtain the second sintering material;

[0022] (3) After the secondary sintering material is mixed evenly with the second coating agent, a third sintering is carried out to obtain a single crystal ternary cathode material.

[0023] In the above preparation method, preferably, in step (1), the D50 of the cathode material precursor is 1.0 μm-2.5 μm. The particle size of the cathode material precursor in this invention was measured using a Malvern 3000 instrument.

[0024] In the above preparation method, preferably, in step (1), the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, and lithium acetate, and the dopant is selected from one or more of compounds including Zr, Ti, Mg, Al, Sb, Ca, Nb, Co, B, Sr, Y, and Ba.

[0025] In the above preparation method, preferably, in step (1), the first sintering is segmented sintering. First, the temperature is raised to 400℃~600℃ for the first segment sintering, and the holding time for the first segment sintering is 2h~8h. Then, the temperature is raised to 600℃~800℃ for the second segment sintering, and the holding time for the second segment sintering is 8h~25h. Finally, the temperature is lowered to 500℃~750℃ for the third segment sintering, and the holding time for the third segment sintering is 2h~15h.

[0026] In the above preparation method, preferably, in step (1), the temperature of the first sintering stage in the first sintering is lower than the temperature of the second sintering stage.

[0027] In the above preparation method, preferably, in step (1), the sintering temperature of the first stage in the first sintering is 150℃~250℃ lower than the sintering temperature of the second stage, and the sintering temperature of the second stage is 10℃~80℃ higher than the sintering temperature of the third stage.

[0028] In the above preparation method, preferably, in step (2), the second sintering temperature is 400℃~700℃ and the sintering time is 6h~12h.

[0029] In the above preparation method, preferably, in step (3), the temperature of the third sintering is 200℃~500℃ and the sintering time is 6h~12h.

[0030] In the above preparation method, preferably, the first coating agent and the second coating agent are selected from compounds containing one or more of Co, Zr, Sr, Ti, Al, B, W, F, and Ca. The amount of the first coating agent does not exceed 5 mol% of the primary sintering material, and the amount of the second coating agent does not exceed 2 mol% of the secondary sintering material.

[0031] As a general inventive concept, the present invention also provides a lithium-ion battery, wherein the cathode material is the above-mentioned single-crystal ternary cathode material or the single-crystal ternary cathode material prepared by the above-mentioned preparation method.

[0032] As a general inventive concept, the present invention also provides an electrical device including the aforementioned lithium-ion battery.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The single-crystal ternary cathode material of the present invention has a small average primary particle diameter, which can greatly enhance the dynamic performance. During the charging and discharging process, it can greatly reduce the polarization of the material, shorten the lithium ion transport path, and make the material have enough Li vacancies for lithium ions to be smoothly re-inserted at the end of the discharge, thereby improving the discharge specific capacity of the material.

[0035] (2) In the DQ / DV differential discharge data of the single-crystal ternary cathode material of the present invention, there are two completely separated discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak is between 3.4V and 3.56V, and the maximum peak value of the second discharge peak is between 3.56V and 3.68V. The peak value intensity of the discharge peak between 3.4V and 3.56V is -400 to -1000. This discharge peak indicates that at the end of the discharge, lithium ions can still be successfully re-inserted into the lattice. It has one more discharge platform than other high-nickel single-crystal ternary materials, providing a discharge specific capacity far exceeding that of general high-nickel single-crystal ternary materials.

[0036] (3) Compared with traditional ultra-high nickel single crystal cathode materials, the single crystal ternary cathode material of the present invention has higher first efficiency and capacity performance, with a first coulombic efficiency of ≥94% and a first discharge capacity of ≥235mAh / g at 0.1C.

[0037] (4) In the preparation process of the single-crystal ternary cathode material of the present invention, a three-stage sintering process is adopted. In the first and second stages of sintering, lithium ions completely diffuse into the material, and crystals are formed. In the third stage of cooling sintering, the crystals shrink, increasing the stress between the crystals, so that the single-crystal particles are completely separated and do not stick together. Moreover, the sintering temperature of the third stage is lower than that of the second stage, which allows the lithium salts remaining on the surface of the material during the sintering process to fully re-enter the crystal lattice, improving the Li-ion concentration. + Utilization rate is improved, and the surface residual lithium generation after the first burn is reduced. Highly dispersed, low-residual-lithium single-crystal cathode materials have a higher surface area. + More back-embedding paths and more uniform subsequent wrapping result in higher capacity and longer cycling performance.

[0038] (5) The single-crystal unit cathode material prepared by the present invention has good dispersibility and does not require the use of traditional air jet milling for dispersion, thereby reducing the production process and achieving the effect of cost reduction and efficiency improvement. Attached Figure Description

[0039] Figure 1 This is a SEM image of the single-crystal ternary cathode material prepared in Example 1 of the present invention;

[0040] Figure 2 This is a SEM image of the large single-crystal ternary cathode material prepared in Comparative Example 1 of this invention;

[0041] Figure 3 This is a SEM image of the quasi-single-crystal ternary cathode material prepared in Comparative Example 2 of this invention;

[0042] Figure 4 The charge-discharge curves and DQ / DV diagrams of the single-crystal ternary cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown.

[0043] Figure 5 This is a particle size distribution diagram of the single-crystal ternary cathode material prepared in Example 1 of the present invention;

[0044] Figure 6 This is a particle size distribution diagram of the single-crystal ternary cathode material prepared in Comparative Example 1 of this invention;

[0045] Figure 7 This is a particle size distribution diagram of the single-crystal ternary cathode material prepared in Comparative Example 2 of this invention;

[0046] Figure 8 This is a comparison diagram of the 1C cycle of the coin cell assembled in Embodiment 2 and Comparative Example 2 of the present invention. Detailed Implementation

[0047] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0048] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0049] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0050] In the following examples and comparative cases, the "average primary particle diameter" was obtained by measuring the maximum diameter of all fully visible primary particles in a 10,000x SEM image using Nano Measure software, and then averaging the measured values. "Fully visible" refers to the maximum diameter of the primary particle that can be accurately measured from the electron microscope image.

[0051] The DQ / DV plots in the following examples and comparative examples use the first charge / discharge data of the coin cell at 25°C and 0.1C. The specific capacity and voltage data are extracted, imported into Origin, and the analysis-mathematics-interpolation / extrapolation is selected. The number of points is set to 200. The voltage is differentiated using the data of the selected points, and then the differentiated data is plotted. Finally, the charging and discharging data plots are combined to obtain the complete DQ / DV curve.

[0052] In the following examples and comparative examples, the composition of the ternary cathode materials prepared in each example and comparative example was tested using ICP-AES; the grain size of the materials was tested using the Lorentzian method with XRD. The specific surface area of ​​the ternary cathode materials prepared in each example and comparative example was determined using a BET analyzer with nitrogen low-temperature adsorption; the ternary cathode materials prepared in each example and comparative example were measured using SEM, and then the particle size of the primary particles in the SEM images was statistically analyzed to calculate the average particle size. The average particle size of the precursor was tested using a Malvern 3000.

[0053] Example 1:

[0054] A single-crystal ternary cathode material of the present invention has the general chemical formula Li. 1.06 Ni 0.95 Co 0.02 Mn 0.01 Sr 0.0006 Co 0.02 B 0.009 Al 0.0005 O2 has an average primary particle diameter of 0.90 μm and a specific surface area of ​​1.101 m². 2 / g, XRD analysis showed that the primary particle size was 234.4nm. In its DQ / DV differential discharge data, there were two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak was between 3.4V and 3.56V, and the maximum peak value of the second discharge peak was between 3.56V and 3.68V. The peak intensity of the discharge peak between 3.4V and 3.56V was -700.

[0055] The preparation method of the single-crystal ternary cathode material in this embodiment includes the following steps:

[0056] (1) A solution A with a metal ion concentration of 2 mol / L was prepared by using cobalt sulfate solution, manganese sulfate solution, and nickel sulfate solution in a ratio of nickel:cobalt:manganese = 97:2:1. Solution A, along with 5 mol / L sodium hydroxide precipitant and 10 mol / L ammonia solution, was simultaneously injected into a reactor. The reaction was carried out under a nitrogen atmosphere. The stirring speed was controlled at 700 r / min, the temperature at 55℃, the pH at 11.1, and the reaction time at 5 h. An ultra-high nickel ternary precursor with an average particle size of 1.5 μm was obtained, and its general formula is Ni. 0.97 Co 0.02 Mn 0.01 (OH)2;

[0057] (2) The ultra-high nickel ternary precursor prepared in step (1) is mixed with lithium hydroxide at a molar ratio of Li:(Ni+Co+Mn)=1.06, and SrCO3 accounting for 0.0006mol% of the precursor is added and mixed evenly until there are no white spots.

[0058] (3) The mixture obtained in step (2) is placed in a sintering furnace for the first sintering. The temperature is first raised to 500℃ for the first stage of sintering. The first stage of sintering is held for 4 hours. Then the temperature is raised to 700℃ for the second stage of sintering. The second stage of sintering is held for 12 hours. Finally, the temperature is lowered to 680℃ for the third stage of sintering. The third stage of sintering is held for 6 hours. After sintering, the mixture is cooled and sieved to obtain the first sintered material.

[0059] (4) After the primary sintering material is mixed evenly with CoOOH accounting for 2 mol% of the primary sintering material, a second sintering is carried out at a sintering temperature of 600℃ and held for 8 hours to obtain the secondary sintering material.

[0060] (5) The secondary sintering material was mixed with 0.9 mol% H3BO3 and 0.05 mol% Al2O3, and then subjected to a third sintering at a temperature of 300℃ for 8 hours to obtain a single-crystal ternary cathode material. Its electron micrograph is shown below. Figure 1 As shown, the particle size distribution diagram is as follows: Figure 5 As shown.

[0061] Example 2:

[0062] The single-crystal ternary cathode material in this embodiment has the general chemical formula Li. 1.06 Ni 0.95 Co 0.02 Mn 0.01 Zr 0.0008 Co 0.02 B 0.009 Al 0.0005 O2 has an average primary particle diameter of 0.80 μm and a specific surface area of ​​1.089 m².2 / g, XRD analysis showed that the primary particle size was 221nm. In its DQ / DV differential discharge data, there were two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak was between 3.4V and 3.56V, and the maximum peak value of the second discharge peak was between 3.56V and 3.68V. The peak intensity of the discharge peak between 3.4V and 3.56V was -510.

[0063] The preparation method of the single-crystal ternary cathode material in this embodiment includes the following steps:

[0064] (1) Prepare an ultra-high nickel ternary precursor according to the same preparation method as in Example 1. Then, mix the precursor with lithium hydroxide according to the molar ratio of Li:(Ni+Co+Mn)=1.06, and add ZrO2 accounting for 0.0008mol% of the precursor molar content and mix until there are no white spots.

[0065] (2) The mixture obtained in step (1) is placed in a sintering furnace for the first sintering. The temperature is first raised to 500℃ for the first stage of sintering. The first stage of sintering is held for 4 hours. Then the temperature is raised to 690℃ for the second stage of sintering. The second stage of sintering is held for 12 hours. Finally, the temperature is lowered to 670℃ for the third stage of sintering. The third stage of sintering is held for 6 hours. After sintering, the mixture is cooled and sieved to obtain the first sintered material.

[0066] (3) After the primary sintering material is mixed evenly with CoOOH accounting for 2 mol% of the primary sintering material, a second sintering is carried out at a sintering temperature of 650℃ and held for 8 hours to obtain the secondary sintering material.

[0067] (4) The secondary sintering material is mixed with H3BO3 (0.9 mol% of the secondary sintering material) and Al2O3 (0.05 mol% of the secondary sintering material) and then subjected to a third sintering at a temperature of 350℃ and a holding time of 8h to obtain a single crystal ternary cathode material.

[0068] Example 3

[0069] The single-crystal ternary cathode material in this embodiment has the general chemical formula Li. 1.06 Ni 0.95 Co 0.02 Mn 0.01 Zr 0.0008 Sr 0.0006 Ti 0.001 Co 0.02 B 0.009 Al 0.0005 O2 has an average primary particle diameter of 1.02 μm and a specific surface area of ​​0.90 m². 2 / g, XRD analysis showed that the primary particle size was 257nm. In its DQ / DV differential discharge data, there were two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak was between 3.4V and 3.56V, and the maximum peak value of the second discharge peak was between 3.56V and 3.68V. The peak intensity of the discharge peak between 3.4V and 3.56V was -450.

[0070] The preparation method of the single-crystal ternary cathode material in this embodiment includes the following steps:

[0071] (1) A high-nickel ternary precursor was prepared according to the same preparation method as in Example 1. Then, the precursor was mixed with lithium hydroxide at a molar ratio of Li:(Ni+Co+Mn)=1.06. At the same time, 0.0008mol% ZrO2, 0.0006mol% SrCO3 and 0.001mol% TiO2 of the precursor were added and mixed until there were no white spots.

[0072] (2) The mixture obtained in step (1) is placed in a sintering furnace for the first sintering. The temperature is first raised to 500℃ for the first stage of sintering. The first stage of sintering is held for 4 hours. Then the temperature is raised to 720℃ for the second stage of sintering. The second stage of sintering is held for 12 hours. Finally, the temperature is lowered to 700℃ for the third stage of sintering. The third stage of sintering is held for 6 hours. After sintering, the mixture is cooled and sieved to obtain the first sintered material.

[0073] (3) After the primary sintering material is mixed evenly with CoOOH accounting for 2 mol% of the primary sintering material, a second sintering is carried out at a sintering temperature of 620℃ and held for 8 hours to obtain the secondary sintering material.

[0074] (4) The secondary sintering material is mixed with H3BO3 (0.9 mol% of the secondary sintering material) and Al2O3 (0.05 mol% of the secondary sintering material) and then subjected to a third sintering at a temperature of 275℃ and a holding time of 8h to obtain a single crystal ternary cathode material.

[0075] Example 4:

[0076] The preparation method of the single-crystal ternary cathode material in this embodiment differs from that in Example 1 only in that the third sintering in step (5) is not performed, and the process of the second sintering in step (4) is also different. The specific operation of step (4) is as follows: the first sintering material is mixed evenly with 2 mol% of CoOOH, 0.9 mol% of H3BO3 and 0.05 mol% of Al2O3, which account for 2 mol% of the first sintering material, and then the second sintering is performed. The temperature is raised to 600℃ and held for 8 hours to obtain the single-crystal ternary cathode material.

[0077] The single-crystal ternary cathode material obtained in this embodiment has an average primary particle diameter of 0.91 μm and a specific surface area of ​​1.06 m². 2 / g, XRD analysis showed that the primary particle size was 231.6nm. In its DQ / DV differential discharge data, there were two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak was between 3.4V and 3.56V, and the maximum peak value of the second discharge peak was between 3.56V and 3.68V. The peak intensity of the discharge peak between 3.4V and 3.56V was -350.

[0078] Comparative Example 1:

[0079] The preparation method of the single-crystal ternary cathode material in this comparative example differs from that in Example 1 only in the sintering procedure of step (3). The operation steps of step (3) in this comparative example are as follows: the mixture obtained in step (2) is placed in a sintering furnace for the first sintering. The temperature is first raised to 500°C for the first stage of sintering, and the holding time for the first stage of sintering is 4 hours. Then the temperature is raised to 800°C for the second stage of sintering, and the holding time for the second stage of sintering is 12 hours. Finally, the temperature is lowered to 780°C for the third stage of sintering, and the holding time for the third stage of sintering is 6 hours. After sintering, the material is cooled and sieved to obtain the first sintered material. The other steps and parameters are exactly the same as those in Example 1.

[0080] The electron microscope image of the single-crystal ternary cathode material in this comparative example is shown below. Figure 2 As shown, its particle size distribution diagram is as follows: Figure 6 As shown, the average primary particle diameter is 1.84 μm, and XRD analysis reveals a primary particle grain size of 314 nm and a specific surface area of ​​0.55 m². 2 In the / g, DQ / DV differential discharge data, there is no discharge peak between 3.4V and 3.56V.

[0081] Comparative Example 2:

[0082] The ternary cathode material in this comparative example differs from that in Example 1 only in the timing of the co-precipitation reaction. Step (1) of this comparative example involves preparing a solution A with a metal ion concentration of 2 mol / L using cobalt sulfate solution, manganese sulfate solution, and nickel sulfate solution in a ratio of nickel:cobalt:manganese = 97:2:1. Solution A, along with 5 mol / L sodium hydroxide precipitant and 10 mol / L ammonia, is simultaneously injected into the reactor. The reaction is carried out under a nitrogen atmosphere, with a stirring speed of 700 r / min, a temperature of 55℃, a pH of 11.1, and a reaction time of 10 h. This yields an ultra-high nickel ternary precursor with an average particle size of 3.0 μm, whose general formula is Ni. 0.97 Co 0.02 Mn 0.01(OH)2; other steps and parameters are exactly the same as in Example 1.

[0083] The electron microscope image of the ternary cathode material in this comparative example is shown below. Figure 3 As shown, its particle size distribution diagram is as follows: Figure 7 As shown, this ternary cathode material exhibits severe agglomeration that cannot be separated. The average primary particle diameter is 1.37 μm, and XRD analysis reveals a primary particle grain size of 230 nm and a specific surface area of ​​0.81 m². 2 / g, its charge-discharge curve and DQ / DV differential diagram are as follows Figure 4 As shown, in the DQ / DV differential discharge data, there are two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak is between 3.4V and 3.56V, and the maximum peak value of the second discharge peak is between 3.56V and 3.68V. There is a weak discharge peak between 3.4V and 3.56V, and the peak value intensity of the discharge peaks is -150.

[0084] Comparative Example 3:

[0085] The preparation method of the ternary cathode material in this comparative example differs from that in Example 1 only in the sintering procedure of step (3). The operation steps of step (3) in this comparative example are as follows: the mixture obtained in step (2) is placed in a sintering furnace for the first sintering, the temperature is raised to 700°C, the holding time is 12h, and after sintering, it is cooled and sieved to obtain the first sintered material; the other steps and parameters are exactly the same as those in Example 1, and a quasi-single crystal ternary cathode material is obtained.

[0086] The ternary cathode material obtained in this comparative example exhibited severe agglomeration and could not be separated. The average primary particle diameter was 1.35 μm, and XRD analysis revealed a primary particle grain size of 239 nm and a specific surface area of ​​0.78 m². 2 In the / g, DQ / DV differential discharge data, there are two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak is between 3.4V and 3.56V, and the maximum peak value of the second discharge peak is between 3.56V and 3.68V. There is a weak discharge peak between 3.4V and 3.56V, and the peak value intensity of the discharge peaks is -380.

[0087] Performance testing:

[0088] The positive electrode material, conductive agent SP, and binder (PVDF) were mixed evenly in a ratio of 92.5:5:2.5. An appropriate amount of NMP (N-methylpyrrolidone) solution was added to the mixed powder material using a pipette as a solvent. The mixture was stirred, coated, and dried in a forced-air drying oven at 80°C to assemble CR2032 coin cells. The coin cell solvent formulation was: EC / DMC = 1 / 2 (vol%), 1M LiPF6, VC 1.5wt%, PS 0.5%, where EC is ethylene carbonate, DMC is dimethyl carbonate, VC is vinylene carbonate, and PS is sulfite. After encapsulation, the cells were allowed to stand for 12 hours. The completed coin cells were then placed on a Blue Battery testing system for electrochemical performance testing. The test conditions for the first charge and discharge were: 25℃, 2.8-4.3V, rest for 10h, charge at 0.1C rate to 4.3V, then perform constant voltage charging, rest for 5min, and discharge at 0.1C rate to 2.8V. The test data are shown in Table 1.

[0089] Table 1. Performance of the ternary cathode materials in each embodiment and comparative example.

[0090]

[0091] The SEM images of Example 1, Comparative Example 1, and Comparative Example 2, along with Table 1, clearly show that the material in Example 1 has a small particle size, good particle dispersion, and perfectly exhibits a single-crystal morphology. Comparative Example 2 has reached the near-single-crystal limit, but the crystal particles still cannot be dispersed and adhere together. The average primary particle diameter of Examples 1-3 is small, with a high initial discharge capacity exceeding 234.9 mAh / g and a high initial coulombic efficiency all greater than 94%.

[0092] The charge-discharge curves and DQ / DV diagrams of the single-crystal ternary cathode materials prepared in Examples 1, 1, and 2 are shown below. Figure 4 As shown, Example 1 exhibits a distinct discharge characteristic peak in the 3.4V-3.56V discharge range, with a clear discharge plateau appearing in the corresponding charge-discharge curve between 3.4V and 3.56V. Comparative Example 1, due to its higher sintering temperature, has an average primary particle diameter of 1.84µm, thus exhibiting no discharge characteristic peak between 3.4V and 3.56V. Comparative Example 2 differs from Example 1 only in the precursor particle size; however, because the precursor of this size cannot be dispersed into single crystals after sintering, it can only be prepared as a near-single crystal. This results in only a weak discharge peak between 3.4V and 3.56V. This is because the near-single crystals adhere together, reducing the lithium-ion diffusion rate. Lithium ions cannot be quickly reinserted, causing a rapid voltage drop and preventing the complete release of the final capacity.

[0093] The comparison diagram of the 1C cycle of the coin cell assembled in Example 2 and Comparative Example 2 is shown below. Figure 8 As shown, from Figure 8It can be seen that during the cycle, the material in Example 2 has a small particle size, high capacity, and excellent cycle performance.

[0094] Compared with Comparative Example 3, Comparative Example 3 only had one sintering stage in one firing, which resulted in the inability to separate the finished particles, poor particle dispersion, and a morphology similar to single crystals. The discharge capacity was only 231.7 mAh / g, which was far lower than the capacity of the normal example. The characteristic peaks in DQ / DV were also very small.

[0095] Compared with Example 4, Example 4 only involves two sinterings and one coating, resulting in a lower capacity than Example 1, and the characteristic peak intensity in DQ / DV is lower than that in Example 1.

[0096] This invention has illustrated its principles and implementation methods using specific examples. The descriptions of these embodiments are merely illustrative of the method and core ideas of this invention, including the best mode, and are intended to enable any person skilled in the art to practice this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A single-crystal ternary cathode material, characterized in that, The average primary particle diameter of the single-crystal ternary cathode material is 0.7 μm to 1.3 μm.

2. The single-crystal ternary cathode material as described in claim 1, characterized in that, In the DQ / DV differential discharge data of the single-crystal ternary cathode material, there are two completely separate discharge peaks between 3.4V and 3.68V. The maximum peak value of the first discharge characteristic peak is between 3.4V and 3.56V, and the maximum peak value of the second discharge characteristic peak is between 3.56V and 3.68V. The maximum peak value intensity of the discharge characteristic peak between 3.4V and 3.56V is -400 to -1000.

3. The single-crystal ternary cathode material as described in claim 1, characterized in that, The chemical formula of the single-crystal ternary cathode material is Li. x Ni a Co b Mn c M p A z O f Wherein, 1.0≤x≤1.08, 0.92≤a<1.0, 0<b≤0.08, 0<c<0.08, 0≤p≤0.05, 0<z≤0.1, 1.8≤f≤2.2; M is a doping element, including one or more of Zr, Ti, Mg, Al, Sb, Ca, Nb, Co, B, Sr, Y and Ba; A is a coating element, A including one or more of Co, Zr, Sr, Ti, Al, B, W, F and Ca.

4. The single-crystal ternary cathode material as described in claim 1, characterized in that, The specific surface area of ​​the single-crystal ternary cathode material is 0.7 m². 2 / g~1.4m 2 / g.

5. The single-crystal ternary cathode material according to any one of claims 1 to 4, characterized in that, The single-crystal ternary cathode material was tested by XRD, and the grain size of its primary particles was 190nm to 260nm.

6. A method for preparing a single-crystal ternary cathode material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) The cathode material precursor, lithium source and dopant are mixed and then sintered for the first time to obtain the first sintered material; (2) After the primary sintering material is mixed evenly with the first coating agent, a second sintering is performed to obtain the secondary sintering material; (3) After the secondary sintering material is mixed evenly with the second coating agent, a third sintering is carried out to obtain a single crystal ternary cathode material.

7. The preparation method according to claim 6, characterized in that, In step (1), the D50 of the cathode material precursor is 1.0 μm-2.5 μm.

8. The preparation method according to claim 6, characterized in that, In step (1), the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, and lithium acetate, and the dopant is selected from one or more of compounds including Zr, Ti, Mg, Al, Sb, Ca, Nb, Co, B, Sr, Y, and Ba.

9. The preparation method according to claim 6, characterized in that, In step (1), the first sintering is a segmented sintering. First, the temperature is raised to 400℃~600℃ for the first segment sintering, and the holding time for the first segment sintering is 2h~8h. Then, the temperature is raised to 600℃~800℃ for the second segment sintering, and the holding time for the second segment sintering is 8h~25h. Finally, the temperature is lowered to 500℃~750℃ for the third segment sintering, and the holding time for the third segment sintering is 2h~15h.

10. The preparation method according to claim 9, characterized in that, In step (1), the temperature of the first sintering stage in the first sintering is lower than the temperature of the second sintering stage.

11. The preparation method according to claim 10, characterized in that, In step (1), the sintering temperature of the first stage in the first sintering is 150℃~250℃ lower than that of the second stage, and the sintering temperature of the second stage is 10℃~80℃ higher than that of the third stage.

12. The preparation method according to claim 6, characterized in that, In step (2), the second sintering temperature is 400℃~700℃ and the sintering time is 6h~12h.

13. The preparation method according to claim 6, characterized in that, In step (3), the temperature of the third sintering is 200℃~500℃, and the sintering time is 6h~12h.

14. The preparation method according to claim 6, characterized in that, The first coating agent and the second coating agent are selected from compounds containing one or more of Co, Zr, Sr, Ti, Al, B, W, F, and Ca. The amount of the first coating agent does not exceed 5 mol% of the primary sintering material, and the amount of the second coating agent does not exceed 2 mol% of the secondary sintering material.

15. A lithium-ion battery, characterized in that, The single-crystal ternary cathode material includes any one of claims 1 to 5, or the single-crystal ternary cathode material prepared by any one of claims 6 to 14.

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

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