Single-crystal positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of positive electrode materials, and particularly relates to a single-crystal positive electrode material and a preparation method and application thereof. The median particle size of the single crystal positive electrode material is 2.8-3.5 microns, and the compaction density is 3.00-3.80 g / cm < 3 >; the specific particle size of the single-crystal positive electrode material is beneficial to lithium ion deintercalation; more reaction interfaces can be provided, and ion movement is facilitated; the specific compaction density ensures that more single crystals can be filled in the same electrode volume, and ensures that the single crystals are in closer and more sufficient contact with other substances in the positive electrode active layer; according to the present invention, the electron conduction impedance is reduced, the single crystal positive electrode material and the conductive agent are completely combined so as to improve the electron conductivity of the single crystal positive electrode material, and the high conductivity ensures that the material can rapidly conduct electrons and ions under the high rate, such that the rate performance of the battery prepared from the single crystal positive electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials, and in particular relates to a single crystal cathode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries with ternary positive electrode materials have relatively high specific capacity and energy density, are environmentally friendly, and have low production costs. In order to increase energy density, positive electrode materials are gradually developing in the direction of high nickel and high voltage. Among the positive electrode materials for solid-state batteries, single crystal positive electrode materials have obvious advantages due to their relatively high mechanical strength and charging and discharging at high voltage. However, single crystal materials are complete, continuous crystals (micrometer level) without grain boundaries. The movement of lithium ions needs to follow specific lattice channels inside the crystal, which takes a long time; and lithium ions need to overcome the energy barriers of adjacent atoms (usually transition metals and oxygen), and the activation energy is high. Therefore, the current single crystal positive electrode materials have the defects of low conductivity and poor rate performance after being prepared into batteries.

[0003] Existing technology selects small precursors (D50≤8μm) to prepare single crystal positive electrode materials. However, small precursors have a large specific surface area and high surface energy, and are prone to excessive growth or adhesion during sintering, resulting in limited improvement in the electrical performance of the resulting single crystal materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low electrical conductivity of existing single crystal positive electrode materials and poor rate performance after being prepared into batteries, thereby providing a single crystal positive electrode material and its preparation method and application.

[0005] To this end, the present invention provides the following technical solutions:

[0006] The first aspect of the present invention protects a single crystal positive electrode material, wherein the median particle size of the single crystal positive electrode material is 2.8-3.5 μm and the compaction density is 3.00-3.80 g / cm 3 .

[0007] In the present invention, Nano Measurer testing software combined with a scanning electron microscope is used to test the median particle size (D50) of the single crystal; a powder compactor from Shenzhen Sansi Company is used to test the compaction density of the single crystal positive electrode material.

[0008] According to the present invention, the median particle size of the single crystal positive electrode material is 3.0-3.2 μm, and the compaction density is 3.50-3.65 g / cm 3 .

[0009] A second aspect of the present invention provides a method for preparing the aforementioned single crystal positive electrode material, wherein the method comprises the following steps:

[0010] S1, mixing a positive electrode material precursor and a lithium source and performing a first sintering;

[0011] S2, after cooling to room temperature, performing a second sintering to obtain a single crystal positive electrode material;

[0012] Wherein, the median particle size of the positive electrode material precursor is 8-15 μm;

[0013] The first sintering includes a primary sintering and a secondary sintering; the primary sintering is heated to 700-900°C at a rate of 3-10°C / min and kept at that temperature for 5-10 hours; the secondary sintering is heated to 900-1085°C at a rate of 3-10°C / min and kept at that temperature for 7-15 hours;

[0014] The second sintering conditions include: heating to 500-800° C. at a rate of 3-10° C. / min and keeping the temperature for 3-5 hours.

[0015] In the present invention, Nano Measurer testing software is used in combination with a scanning electron microscope to test the median particle size (D50) of the positive electrode material precursor.

[0016] In the present invention, the lithium source is a conventional lithium source in the art. Typically, but not limitedly, the lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0017] In the present invention, the molar ratio of the total metal elements in the positive electrode material precursor to the lithium element in the lithium source is 1:(1-1.05).

[0018] In the present invention, a grinding step is further included after the first sintering. Grinding is a conventional operation in the art and the size is not limited as long as the first sintered product can be initially dispersed evenly.

[0019] In the present invention, the second sintering is followed by cooling at a rate of 5-10° C. / min.

[0020] According to the present invention, the method for preparing the positive electrode material precursor comprises the following steps: mixing a metal salt, a precipitant, a complexing agent and water to perform a coprecipitation reaction to obtain the positive electrode material precursor;

[0021] Among them, the coprecipitation reaction is divided into reaction A, reaction B, and reaction C stages;

[0022] The conditions of the reaction stage A include a pH value of 12.3-13. At the end of the reaction stage A, the particle size of the product A is A μm, 1.5<A≤2;

[0023] The conditions of the reaction stage B include a pH value of 11.3-12.3, and at the end of the reaction stage B, the particle size of the product B is B μm, 2<B≤8;

[0024] The conditions of the reaction stage C include a pH value of 10.5-11.3. At the end of the reaction stage C, the particle size of the product C is C μm, 8<C≤15.

[0025] In the present invention, the particle size (D50) of product A, product B, and product C was measured using Nano Measurer testing software combined with a scanning electron microscope.

[0026] In the present invention, the coprecipitation is carried out in a reactor, and a base liquid is added to the reactor. The base liquid is a conventional base liquid in the art. Typically, but not limited to, the base liquid includes sodium hydroxide, ammonia water and water to control the pH of the initial reaction conditions to 12-12.5; the base liquid serves as a dispersion medium to uniformly disperse the reactants in the system, which helps prevent the local concentration of the reactants from being too high.

[0027] In the present invention, the metal salt is added in the form of a metal salt solution, the precipitant is added in the form of a precipitant solution, and the complex is added in the form of a complex solution, which can ensure more uniform mixing and a larger contact area between the components in the solution and other substances, thereby improving the reaction activity and accelerating the reaction process.

[0028] In the present invention, after the coprecipitation reaction, the steps of aging, water washing and drying are further included. The specific conditions of aging, water washing and drying are all conventional conditions in the art. Typically, but not limitedly, the aging time is 20-30 hours.

[0029] According to the present invention, the conditions of reaction A include a pH value of 12.3-12.5.

[0030] According to the present invention, the conditions of reaction B include a pH value of 11.5-12.1.

[0031] According to the present invention, the conditions of reaction C include a pH value of 10.8-11.

[0032] According to the present invention, the temperature of the coprecipitation reaction is 50-80° C., and the rotation speed is 300-600 rpm.

[0033] According to the present invention, the co-precipitation temperature is 60-75° C. and the rotation speed is 400-500 rpm.

[0034] According to the present invention, the metal salt is added with water to prepare a metal salt solution, wherein the content of the metal element in the metal salt solution is 1-6 mol / L.

[0035] In the present invention, the metal salt includes two or three of nickel salt, cobalt salt and manganese salt to prepare a binary positive electrode material, and the metal salt includes nickel salt and manganese salt; the metal elements in the ternary positive electrode material precursor include nickel, cobalt and manganese. The types of nickel salt, cobalt salt and manganese salt are all in the art. Typically, but not limited to, nickel salt includes nickel sulfate, manganese salt includes manganese sulfate, and cobalt salt includes cobalt sulfate. The molar ratio of the nickel salt, cobalt salt and manganese salt is adjusted according to the requirements of the final product. For example, if an NCM811 type positive electrode material is required, the molar ratio of nickel in the nickel salt, cobalt in the cobalt salt and manganese in the manganese salt is controlled to be 8:1:1.

[0036] According to the present invention, the precipitant is added with water to prepare a precipitant solution, wherein the concentration of the precipitant in the precipitant solution is 3-5 mol / L.

[0037] According to the present invention, the complexing agent is added with water to prepare a complexing agent solution, wherein the content of the complexing agent in the complexing agent solution is 5-20 g / L.

[0038] In the present invention, the types of the precipitating agent are conventional in the art, typically but not limited to, including at least one of sodium hydroxide and potassium hydroxide, and industrial alkali solution can generally be selected for cost considerations; the types of the complexing agent are conventional in the art, typically but not limited to, including at least one of ammonia water, citric acid, EDTA, oxalic acid, and urea; the amounts of the precipitating agent and the complex are controlled according to actual conditions to ensure that the pH value meets a specific range.

[0039] According to the present invention, the conditions for the primary sintering include: heating to 750-850° C. at a rate of 5-9° C. / min and maintaining the temperature for 6-9 hours.

[0040] According to the present invention, the conditions for the secondary sintering include: heating to 980-1080° C. at a rate of 5-9° C. / min and keeping the temperature for 10-15 hours.

[0041] According to the present invention, the second sintering conditions include: heating to 600-750° C. at a rate of 5-8° C. / min and keeping the temperature for 4-5 hours.

[0042] According to the present invention, in S1, the mixing step further includes adding a metal oxide dopant.

[0043] In the present invention, the metal oxide dopant is a conventional dopant in the art, typically, but not limited to, at least one of titanium oxide, zirconium oxide, aluminum oxide, yttrium oxide, niobium oxide, strontium oxide, and tungsten oxide. It can further enhance the structural stability of the positive electrode material and improve battery performance. Some of these dopants include multiple valence states, such as niobium oxide, which can be used in the form of niobium pentoxide and niobium trioxide.

[0044] In the present invention, the mass ratio of the positive electrode material precursor to the dopant is 1:(0.003-0.006).

[0045] According to the present invention, in S2, after the temperature is lowered to room temperature, an oxide coating agent is further added.

[0046] In the present invention, the oxide coating agent is a conventional coating agent in the art, typically, but not limited to, a metal oxide and / or a non-metal oxide, and can optionally include at least one of zirconium oxide, aluminum oxide, titanium oxide, cobalt oxide, lanthanum oxide, tungsten oxide, boron oxide, and silicon oxide. This can further improve the density of the interface, reduce the contact area between the material surface and the electrolyte, and reduce side reactions.

[0047] In the present invention, the mass ratio of the positive electrode material precursor to the oxide coating agent is 1:(0.003-0.005).

[0048] A third aspect of the present invention provides a secondary battery, wherein the secondary battery comprises the aforementioned single crystal positive electrode material or the single crystal positive electrode material prepared by the aforementioned preparation method.

[0049] In the present invention, the secondary battery preparation method is a conventional preparation method in the art.

[0050] The technical solution of the present invention has the following advantages:

[0051] 1. The present invention provides a single crystal positive electrode material, wherein the median particle size of the single crystal positive electrode material is 2.8-3.5 μm and the compaction density is 3.00-3.80 g / cm 3 The specific particle size of the single crystal positive electrode material is conducive to the deintercalation and extraction of lithium ions; it can also provide more reaction interfaces, which is conducive to the movement of ions; the specific compaction density ensures that more single crystal positive electrode materials can be filled in the same electrode volume, and ensures that the single crystal positive electrode material and other substances in the positive electrode active layer (such as conductive agents, binders) are in closer and more complete contact; the single crystal positive electrode material and the conductive agent are fully combined, which improves the electronic conductivity of the positive electrode material, and the high conductivity ensures that the material can quickly conduct electrons at high rates, thereby improving the rate performance of batteries made of single crystal positive electrode materials.

[0052] 2. The present invention provides a method for preparing a single crystal positive electrode material, wherein the preparation method comprises the following steps: S1, mixing a positive electrode material precursor and a lithium source and then performing a first sintering; S2, cooling to room temperature and then performing a second sintering to obtain a single crystal positive electrode material; wherein the median particle size of the positive electrode material precursor is 10-15 μm; the first sintering comprises a primary sintering and a secondary sintering; the primary sintering is heated to 700-900°C at a rate of 3-10°C / min and kept at this temperature for 5-10 hours; the secondary sintering is heated to 700-900°C at a rate of 3-10°C / min and kept at this temperature for 5-10 hours; the secondary sintering is heated to 700-900°C at a rate of 3-10°C / min and kept at this temperature for 5-10 hours; The temperature is raised to 900-1085°C and kept warm for 7-15 hours; the second sintering conditions include: heating to 500-800°C at a rate of 3-10°C / min and keeping warm for 3-5 hours; the cathode material precursor with a specific median particle size is subjected to a specific first sintering condition to form relatively large primary grains; the temperature is lowered to weaken the grain boundary bonding force, and then subjected to a specific second sintering condition, the grain boundaries undergo significant migration and fusion, so that multiple small primary grains are merged into single crystals with few internal defects and clear boundaries, so that the obtained single crystal cathode material has excellent rate performance.

[0053] 3. In the present invention, during the preparation of the positive electrode material precursor, co-precipitation is divided into three stages: reaction A, reaction B, and reaction C. In the reaction A stage, the high pH value promotes rapid nucleation and controls the initial crystal nucleus size at the micron level; in the reaction B stage, the medium pH value allows the crystal to grow in a two-dimensional direction; and in the reaction C stage, the low pH value achieves dense filling, so that the positive electrode material precursor reaches a specific size, thereby making the single crystal positive electrode material obtained from the positive electrode material precursor have excellent rate performance.

[0054] 4. The specific co-precipitation conditions of the present invention can further increase the uniform distribution of metal elements, which is beneficial to structural stability.

[0055] 5. In the present invention, in S1, a metal dopant is further added in the mixing step. The metal dopant can enhance the stability of oxygen atoms in the positive electrode material precursor and inhibit oxygen loss. In S2, after cooling to room temperature, an oxide coating agent is further added. The coating agent can inhibit the side reaction of the electrolyte and further improve the excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0057] Figure 1 This is an SEM image of the single crystal positive electrode material of Example 1. DETAILED DESCRIPTION

[0058] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0059] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0060] During the coprecipitation reaction step, Nano Measurer testing software combined with a scanning electron microscope was used to test the particle size of Product A, Product B, and Product C. Samples were taken from the reactor for testing every 2 hours. When the sample size approached the target range, samples were taken from the reactor for testing every 30 minutes. When the sample size fell within the target range, the corresponding reaction stage was considered to have ended, and the sample size point values ​​of the corresponding stage were recorded.

[0061] Use a pH meter to check the pH value.

[0062] Example 1

[0063] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0064] Metal salt solution: nickel sulfate, cobalt sulfate, and manganese sulfate are mixed with water, wherein the total content of the metal elements is 2 mol / L, and the molar ratio of nickel in nickel sulfate, cobalt in cobalt sulfate, and manganese in manganese sulfate is 8:1:1;

[0065] Precipitant solution: 5 mol / L sodium hydroxide solution;

[0066] Complexing agent solution: ammonia solution with an ammonia content of 10 g / L;

[0067] The reactor was filled with nitrogen atmosphere. The bottom liquid in the reactor included sodium hydroxide, ammonia water, and water. The concentration of ammonia water in the bottom liquid was 12 g / L, the pH of the bottom liquid was 12.2, and the rotation speed in the reactor was 450 rpm.

[0068] S1, adding a metal salt solution to a reactor containing a base solution, adding a precipitant solution and a complexing agent to control the pH of the system, and conducting coprecipitation reactions (reaction A, reaction B, reaction C) at a temperature of 60° C. and a rotation speed of 459 rpm; wherein, the pH of reaction A is 12.3, and the particle size of product A is 1.6 μm; the pH of reaction B is 11.6, and at the end of reaction B, the particle size of product B is 6 μm; the pH of reaction C is 10.8, and at the end of reaction C, the particle size of product C is 13 μm. The resulting slurry is aged for 20 hours, washed, dried, sieved, deironed, and packaged to obtain a cathode material precursor. The median particle size of the cathode material precursor is 11 μm as measured by Nano Measurer testing software combined with a scanning electron microscope;

[0069] S2, mix the positive electrode material precursor, lithium carbonate, yttrium trioxide, zirconium oxide, and niobium pentoxide, wherein the molar ratio of the total metal elements in the positive electrode material precursor to the lithium element in the lithium carbonate is 1:1.02; the mass ratio of the positive electrode material precursor to yttrium trioxide, zirconium oxide, and niobium pentoxide is 1:0.002:0.002:0.002; heat to 850°C at a rate of 5°C / min and keep warm for 7 hours for the first sintering, then heat to 1080°C at a rate of 5°C / min and keep warm for 15 hours for the second sintering; grind, add boron oxide, wherein the mass ratio of the positive electrode material precursor to boron oxide is 1:0.003; heat to 600°C at a rate of 5°C / min and keep warm for 5 hours for the second sintering, and cool to 25°C at a rate of 5°C / min to obtain a single crystal positive electrode material, as shown in the electron microscope picture. Figure 1 As shown in the figure, it can be seen that the single crystal structure is complete and the particle size is uniform.

[0070] Example 2

[0071] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0072] Metal salt solution: nickel sulfate, cobalt sulfate, and manganese sulfate are mixed with water, wherein the total content of the metal elements is 1 mol / L, and the molar ratio of nickel in nickel sulfate, cobalt in cobalt sulfate, and manganese in manganese sulfate is 8:1:1;

[0073] Precipitant solution: sodium hydroxide solution with a hydroxide content of 5 mol / L;

[0074] Complexing agent solution: ammonia solution with an ammonia content of 10 g / L;

[0075] The reactor was filled with nitrogen atmosphere. The bottom liquid in the reactor included sodium hydroxide, ammonia water, and water. The concentration of ammonia water in the bottom liquid was 12 g / L, the pH of the bottom liquid was 12.1, and the rotation speed in the reactor was 400 rpm.

[0076] S1, adding a metal salt solution to a reactor containing a base solution, adding a precipitant solution and a complexing agent to control the pH of the system, and conducting coprecipitation reactions (reaction A, reaction B, reaction C), the temperature throughout the process being 50° C. and the rotation speed being 400 rpm; wherein, the pH of reaction A is 12.5, and the particle size of product A is 1.8 μm; the pH of reaction B is 11.3, and at the end of reaction B, the particle size of product B is 5 μm; the pH of reaction C is 10.5, and at the end of reaction C, the particle size of product C is 11 μm. The obtained slurry is aged for 25 hours, washed, dried, sieved, deironed, and packaged to obtain a positive electrode material precursor. The median particle size of the positive electrode material precursor is tested using Nano Measurer testing software combined with a scanning electron microscope and is 9 μm.

[0077] S2, mixing the positive electrode material precursor, lithium carbonate, strontium oxide, zirconium oxide, and tungsten trioxide, wherein the molar ratio of the total metal elements in the positive electrode material precursor to the lithium element in the lithium carbonate is 1:1.03; the mass ratio of the positive electrode material precursor to strontium oxide, zirconium oxide, and tungsten trioxide is 1:0.001:0.003:0.002; heating to 780°C at a rate of 7°C / min and keeping warm for 6 hours for the first sintering, and then heating to 1020°C at a rate of 7°C / min and keeping warm for 13 hours for the second sintering; grinding, adding cobalt tetroxide, wherein the mass ratio of the positive electrode material precursor to cobalt tetroxide is 1:0.005; heating to 600°C at a rate of 5°C / min and keeping warm for 5 hours for the second sintering, and cooling to 25°C at a rate of 10°C / min to obtain a single crystal positive electrode material.

[0078] Example 3

[0079] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0080] Metal salt solution: nickel sulfate, cobalt sulfate, and manganese sulfate are mixed with water, wherein the total content of the metal elements is 6 mol / L, and the molar ratio of nickel in nickel sulfate, cobalt in cobalt sulfate, and manganese in manganese sulfate is 8:1:1;

[0081] Precipitant solution: sodium hydroxide solution with a hydroxide content of 5 mol / L;

[0082] Complexing agent solution: ammonia solution with an ammonia content of 10 g / L;

[0083] The reactor was filled with nitrogen atmosphere. The bottom liquid in the reactor included sodium hydroxide, ammonia water, and water. The concentration of ammonia water in the bottom liquid was 12 g / L, the pH of the bottom liquid was 12.2, and the rotation speed in the reactor was 600 rpm.

[0084] S1, adding a metal salt solution to a reactor containing a base solution, adding a precipitant solution and a complexing agent to control the pH of the system, and conducting coprecipitation reactions (reaction A, reaction B, reaction C) at a temperature of 70° C. and a rotation speed of 600 rpm; wherein, the pH of reaction A is 12.4, and the particle size of product A is 1.7 μm; the pH of reaction B is 12.0, and at the end of reaction B, the particle size of product B is 6 μm; the pH of reaction C is 11, and at the end of reaction C, the particle size of product C is 14 μm. The obtained slurry is aged for 20 hours, washed, dried, sieved, iron removed, and packaged to obtain a positive electrode material precursor. The median particle size of the positive electrode material precursor is tested using Nano Measurer testing software combined with a scanning electron microscope and is 13 μm.

[0085] S2, mixing the positive electrode material precursor, lithium carbonate, titanium dioxide, zirconium oxide, and aluminum oxide, wherein the molar ratio of the total metal elements in the positive electrode material precursor to the lithium element in the lithium carbonate is 1:1.04; the mass ratio of the positive electrode material precursor to strontium oxide, zirconium oxide, and tungsten trioxide is 1:0.001:0.0015:0.001; heating to 700°C at a rate of 8°C / min and keeping warm for 5 hours for the first sintering, and then heating to 900°C at a rate of 8°C / min and keeping warm for 12 hours for the second sintering; grinding, adding silicon dioxide, wherein the mass ratio of the positive electrode material precursor to silicon dioxide is 1:0.003; heating to 600°C at a rate of 5°C / min and keeping warm for 5 hours for the second sintering, and cooling to 25°C at a rate of 10°C / min to obtain a single crystal positive electrode material.

[0086] Example 4

[0087] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0088] The method of Example 1 is followed, except that in step S1, the pH of reaction A is 12.7, and the particle size of product A is 1.9 μm; the pH value of reaction B is 12.1, and at the end of reaction B, the particle size of product B is 7 μm; the pH value of reaction C is 10.5, and at the end of reaction C, the particle size of product C is 12 μm. The obtained slurry is aged for 25 hours, washed, dried, sieved, deironed, and packaged to obtain a positive electrode material precursor. The median particle size of the positive electrode material precursor is tested using Nano Measurer testing software combined with a scanning electron microscope and is 9 μm.

[0089] Example 5

[0090] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0091] The method of Example 1 was followed, except that the coprecipitation reaction was carried out at a temperature of 50° C. and a rotation speed of 600 rpm.

[0092] Example 6

[0093] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0094] The method of Example 1 is the same, except that in step S2, the temperature is raised to 700° C. at a rate of 3° C. / min and kept at that temperature for 10 h for a sintering operation.

[0095] Example 7

[0096] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0097] The method of Example 1 is the same, except that in step S2, the temperature is raised to 900° C. at a rate of 10° C. / min and kept at that temperature for 15 hours for secondary sintering.

[0098] Example 8

[0099] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0100] The method of Example 1 is the same, except that in step S2, the temperature is raised to 550° C. at a rate of 3° C. / min and kept at that temperature for 5 h for the second sintering.

[0101] Example 9

[0102] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0103] The method of Example 1 is different in that no metal dopant is added, that is, the positive electrode material precursor and lithium carbonate are mixed, wherein the molar ratio of the total metal elements in the positive electrode material precursor to the lithium element in the lithium carbonate is 1:1.02.

[0104] Example 10

[0105] This embodiment provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0106] The method of Example 1 is the same except that no oxide coating agent is added, that is, the second sintering is performed after grinding, and then the temperature is increased to 600° C. at a rate of 5° C. / min and kept at that temperature for 5 hours for the second sintering.

[0107] Comparative Example 1

[0108] This comparative example provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0109] S1, the composition of the cathode material precursor is LiNi0.80 Co 0.10 Mn 0.10 O2, the median particle size of the cathode material precursor is 19μm, and the purchasing company is GEM Jingmen New Materials Co., Ltd.

[0110] S2, follow the method of S2 in Example 1.

[0111] Comparative Example 2

[0112] This comparative example provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0113] The method of Example 1 is the same, except that the temperature is kept constant during the first sintering, that is, the temperature is raised to 1000° C. at a rate of 5° C. / min and kept at that temperature for 22 hours for the first sintering.

[0114] Comparative Example 3

[0115] This comparative example provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0116] The method of Example 1 is the same, except that the temperature is raised to 950°C at a rate of 2°C / min and kept at this temperature for 7 hours for the first sintering, and then the temperature is raised to 1090°C at a rate of 2°C / min and kept at this temperature for 15 hours for the second sintering.

[0117] Comparative Example 4

[0118] This comparative example provides a single crystal positive electrode material, and the preparation method includes the following steps:

[0119] The method of Example 2 is followed, except that the second sintering is performed by raising the temperature to 1000° C. at a rate of 15° C. / min and holding the temperature for 6 h.

[0120] Test Case

[0121] (1) Nano Measurer testing software combined with scanning electron microscopy was used to measure the median particle size of single crystal cathode materials;

[0122] The compaction density of the single crystal cathode material was tested using a powder compactor from Shenzhen Sansi Company.

[0123] The conductivity was tested using the four-probe method;

[0124] The specific test results are shown in Table 1;

[0125] Table 1

[0126]

[0127] (2) The single crystal positive electrode material, polyvinylidene fluoride (PVDF), and conductive carbon black (SP) prepared in the embodiment or comparative example were homogenized and coated in a mass ratio of 95:2.5:2.5 to form a pole piece. A metal lithium sheet was used as the counter electrode, a glass fiber was used as the separator, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 was used as the electrolyte to assemble a CR2032 button cell. Finally, the battery was placed in a blue electric test system for electrical performance testing;

[0128] Rate performance test: At 25°C, the battery is charged to 4.4V at a constant current of 0.2C, then charged to 0.05C at a constant voltage, and then discharged to 3.0V at a discharge rate of 0.2C, obtaining a 0.2C discharge capacity C2; at room temperature, the battery is charged to 4.4V at a constant current of 0.2C, then charged to 4.4V at a constant current of 0.2C, then charged to 0.05C at a constant voltage, and then discharged to 3.0V at a discharge rate of 6C, obtaining a 6C discharge capacity C1;

[0129] Rate performance = (discharge capacity C1 / discharge capacity C2) × 100%;

[0130] The specific test results are shown in Table 2;

[0131] Table 2

[0132] Rate performance (%) Example 1 82.3 Example 2 81.9 Example 3 82.2 Example 4 82.1 Example 5 81.8 Example 6 81.7 Example 7 81.6 Example 8 81.9 Example 9 82.0 Example 10 81.5 Comparative Example 1 79.8 Comparative Example 2 80.5 Comparative Example 3 78.3 Comparative Example 4 78.6

[0133] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications derived therefrom remain within the scope of protection of the present invention.

Claims

1. A single crystal positive electrode material, characterized in that The median particle size of the single crystal positive electrode material is 2.8-3.5 μm, and the compaction density is 3.00-3.80 g / cm 3 .

2. The single crystal cathode material according to claim 1, characterized in that The median particle size of the single crystal positive electrode material is 3.0-3.2 μm, and the compaction density is 3.50-3.65 g / cm 3 .

3. A method for preparing a single crystal positive electrode material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: S1, mixing a positive electrode material precursor and a lithium source and performing a first sintering; S2, after cooling to room temperature, performing a second sintering to obtain a single crystal positive electrode material; Wherein, the median particle size of the positive electrode material precursor is 8-15 μm; The first sintering includes a primary sintering and a secondary sintering; the primary sintering is heated to 700-900°C at a rate of 3-10°C / min and kept at that temperature for 5-10 hours; the secondary sintering is heated to 900-1085°C at a rate of 3-10°C / min and kept at that temperature for 7-15 hours; The second sintering conditions include: heating to 500-800° C. at a rate of 3-10° C. / min and keeping the temperature for 3-5 hours.

4. The preparation method according to claim 3, characterized in that The preparation method of the positive electrode material precursor comprises the following steps: mixing a metal salt, a precipitant, a complexing agent and water, and performing a coprecipitation reaction to obtain the positive electrode material precursor; Among them, the coprecipitation reaction is divided into reaction A, reaction B, and reaction C stages; The conditions of the reaction stage A include a pH value of 12.3-13. At the end of the reaction stage A, the particle size of the product A is A μm, 1.5<A≤2; The conditions of the reaction stage B include a pH value of 11.3-12.3, and at the end of the reaction stage B, the particle size of the product B is B μm, 2<B≤8; The conditions of the reaction stage C include a pH value of 10.5-11.

3. At the end of the reaction stage C, the particle size of the product C is C μm, 8<C≤15.

5. The preparation method according to claim 4, characterized in that The conditions of reaction A include a pH value of 12.3-12.5; and / or, the conditions of reaction B include a pH value of 11.5-12.1; And / or, the conditions of reaction C include a pH value of 10.8-11.

6. The preparation method according to any one of claims 4 to 5, characterized in that The coprecipitation reaction temperature is 50-80°C and the rotation speed is 300-600 rpm; Optionally, the co-precipitation temperature is 60-75° C. and the rotation speed is 400-500 rpm.

7. The preparation method according to any one of claims 4 to 6, characterized in that Adding water to a metal salt to prepare a metal salt solution, wherein the content of the metal element in the metal salt solution is 1-6 mol / L; Optionally, the precipitant is added with water to prepare a precipitant solution, wherein the concentration of the precipitant in the precipitant solution is 3-5 mol / L; Optionally, the complexing agent is added with water to prepare a complexing agent solution, wherein the content of the complexing agent in the complexing agent solution is 5-20 g / L.

8. The preparation method according to any one of claims 3 to 7, characterized in that The primary sintering conditions include: heating to 750-850°C at a rate of 5-9°C / min and holding for 6-9 hours; And / or, the secondary sintering conditions include: heating to 980-1080°C at a rate of 5-9°C / min and holding for 10-15h; And / or, the second sintering conditions include: heating to 600-750° C. at a rate of 5-8° C. / min and keeping the temperature for 4-5 hours.

9. The preparation method according to any one of claims 3 to 8, characterized in that In S1, the mixing step also adds a metal oxide dopant; And / or, in S2, after cooling to room temperature, an oxide coating agent is further added.

10. A secondary battery, characterized in that: The secondary battery comprises the single crystal positive electrode material according to claim 1 or 2 or the single crystal positive electrode material prepared by the preparation method according to any one of claims 3 to 9.

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