Small-particle-size single-crystal positive electrode material, preparation method thereof, and lithium-ion battery

Abstract

The present application discloses a method for preparing a small-particle-size single-crystal positive electrode material, comprising the following steps: taking a lithium source compound, a nickel source compound, a cobalt source compound and a manganese source compound according to a stoichiometric ratio, mixing them with an aqueous solution of a complexing agent A, and reacting to obtain a mixed solution; adding an aqueous solution of a complexing agent B to the mixed solution, and reacting to obtain a sol; heating the sol, evaporating and concentrating it to form a gel; and calcining the gel in steps to obtain a small-particle-size single-crystal positive electrode material. Wherein, the complexing agent A is at least one of 2-hydroxypropionic acid, aspartic acid, quinic acid, succinic acid or formic acid; and the complexing agent B is at least one of ascorbic acid, glucosamine, tyrosine or aminobutyric acid. The present application also discloses a small-particle-size single-crystal positive electrode material and a lithium-ion battery comprising the positive electrode material.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a small-particle single-crystal positive electrode material and a preparation method thereof and a lithium-ion battery. Background Art

[0002] Small-particle single-crystal cathode materials (usually refers to the median particle size D50 less than 5μm) have the advantages of stable electrochemical performance, excellent cycle performance, and high specific capacity. In addition, due to their small particle size, the path for lithium ions to escape / embed from the particles is short and the time is short. This can not only improve the specific capacity of the material under high voltage, but also effectively improve the material's high-temperature cycle, flatulence, specific capacity recovery and other issues. Therefore, the preparation research of small-particle single-crystal cathode materials has received widespread attention.

[0003] The existing method for preparing single crystal positive electrode materials generally adopts the controlled crystallization method to first precipitate the mixed metal salt solution under the action of the complexing agent and the precipitant to prepare a small-particle polycrystalline precursor, and then mix the positive electrode material precursor with the lithium source, calcine, and crush to obtain the single crystal positive electrode material. At present, most of the particles synthesized by this process are 5-12um in size, and the calcination is difficult and the process requirements are high. Summary of the invention

[0004] In order to solve the above problems, the present application provides a method for preparing a small-particle single-crystal positive electrode material with simple operation, low cost and controllable particle size.

[0005] Another object of the present application is to provide a small-particle single-crystal positive electrode material prepared by the above-mentioned preparation method.

[0006] Another object of the present application is to provide a lithium-ion battery comprising the above-mentioned small-particle-size single-crystal positive electrode material.

[0007] The present application provides a method for preparing a small-particle-size single-crystal positive electrode material, comprising the following steps:

[0008] S1: taking a lithium source compound, a nickel source compound, a cobalt source compound and a manganese source compound according to a stoichiometric ratio, mixing them with an aqueous solution of a complexing agent A, and reacting to obtain a mixed solution;

[0009] S2: adding an aqueous solution of complexing agent B to the mixed solution to react to obtain a sol;

[0010] S3: heating the sol to evaporate and concentrate it to form a gel;

[0011] S4: calcining the gel step by step to obtain a small-particle-size single-crystalline positive electrode material;

[0012] The chemical formula of the small-particle single-crystal cathode material is Li k Nix Co y Mn z O2, x:y:z=(0.10~0.85):(0.05~0.40):(0.10~0.35), 0.95≤k≤1.15; the complexing agent A is at least one of 2-hydroxypropionic acid, aspartic acid, quinic acid, succinic acid or formic acid; the complexing agent B is at least one of ascorbic acid, glucosamine, tyrosine or aminobutyric acid.

[0013] The present application also provides a small-particle single-crystal positive electrode material prepared by the above-mentioned preparation method, wherein the particle size D50 of the small-particle single-crystal positive electrode material is 1.5 μm to 5 μm.

[0014] In addition, the present application also provides a lithium-ion battery comprising the above-mentioned small-particle-size single-crystal positive electrode material.

[0015] Compared with the prior art, the advantages of the preparation method of small-particle-size single-crystal positive electrode material provided in this application are:

[0016] (1) In the present application, two complexing agents are used in combination and react in steps. The two complexing agents act synergistically and promote the cross-linking efficiency, so that the prepared small-grained single-crystal positive electrode material has high crystallinity, high mechanical strength and good single-crystal morphology.

[0017] (2) The small-particle single-crystal positive electrode material prepared in the present application has the characteristics of highly flat and smooth single-crystal particles, with a particle size D50 of 1.5 μm to 5 μm. After being assembled into a lithium-ion battery, the contact area between the particle surface and the electrolyte is reduced, and the corresponding side reactions between the positive electrode material and the electrolyte are significantly reduced, effectively reducing the heat release and gas release caused by the side reactions, so that the battery has better high-temperature safety performance, high-temperature rate performance and charge and discharge voltage platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of a method for preparing a small-particle single-crystal positive electrode material provided in one embodiment of the present application.

[0019] Figure 2 This is the SEM image of the small-particle single-crystal positive electrode material prepared in Example 1.

[0020] Figure 3 This is the XRD diagram of the small-particle single-crystal positive electrode material prepared in Example 1.

[0021] Figure 4 The first charge and discharge curves of the lithium-ion batteries prepared in Example 1 and Comparative Examples 1-3 at 1C rate and 60°C are shown.

[0022] Figure 5The cycle curves of the lithium-ion batteries prepared in Example 1 and Comparative Examples 1-3 at 8C rate and 60°C are shown. DETAILED DESCRIPTION

[0023] The present application is further described below in conjunction with examples. These examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods in the following examples that do not specify specific conditions are usually carried out in accordance with conventional conditions in the art or in accordance with the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present application are within the scope of protection claimed in the present application.

[0024] See also Figure 1 The present application provides a method for preparing a small-particle-size single-crystal positive electrode material, comprising the following steps:

[0025] S1: taking a lithium source compound, a nickel source compound, a cobalt source compound and a manganese source compound according to a stoichiometric ratio, mixing them with an aqueous solution of a complexing agent A, and reacting to obtain a mixed solution;

[0026] S2: adding an aqueous solution of complexing agent B to the mixed solution to react to obtain a sol;

[0027] S3: heating the sol to evaporate and concentrate it to form a gel;

[0028] S4: calcining the gel step by step to obtain a small-particle-size single-crystalline positive electrode material;

[0029] The chemical formula of the small-particle single-crystal cathode material is Li k Ni x Co y Mn z O2, x:y:z=(0.10~0.85):(0.05~0.40):(0.10~0.35), 0.95≤k≤1.15; the complexing agent A is at least one of 2-hydroxypropionic acid, aspartic acid, quinic acid, succinic acid or formic acid; the complexing agent B is at least one of ascorbic acid, glucosamine, tyrosine or aminobutyric acid.

[0030] In the present application, a small-particle-size single-crystal positive electrode material is prepared by using a sol-gel method by combining a complexing agent A and a complexing agent B. In the conventional sol-gel method, usually only one complexing agent is used, and it is usually sucrose, ethylene glycol, citric acid or polyacrylic acid, etc. In the gel-calcination process, since there is only one carbon frame structure (a complexing agent) in the system, the growth mode of the organic carbon frame of the complexed metal ions in the gel process tends to be regularly arranged and directional growth, and it is very easy to grow into large-particle-size single crystals or polycrystals. In the present application, a specific type of complexing agent A with acidity is used, combined with a specific type of complexing agent B with reducing properties, and added in steps, which can greatly eliminate this effect. In particular, the complexing agent B, which has a stronger complexing ability than A, can effectively inhibit the excessive growth of the crystal nucleus and increase the entropy value of the reaction system. The small-grained single crystal will not grow excessively during the growth process. The crystal nucleus generation-growth is in a balanced state during the gelation process. The lithium source compound, nickel source compound, cobalt source compound and manganese source compound fully react to form a gel, and finally a small-grained single crystal can be prepared.

[0031] In addition, through many studies, it was found that when only the aqueous solution of complexing agent A or the aqueous solution of complexing agent B was added, the reaction would be incomplete. If the aqueous solution of complexing agent A or the aqueous solution of complexing agent B were added at the same time, the structure of complexing agent B would be destroyed due to the different reaction conditions applicable to the two, and thus the reaction would not be sufficient, and the size and performance of the subsequently obtained positive electrode material would be affected.

[0032] It can be understood that the stoichiometric ratio described in the present application is the molar ratio of lithium, nickel, cobalt and manganese elements in the small-particle single crystal positive electrode material.

[0033] In some embodiments, the lithium source compound, nickel source compound, cobalt source compound and manganese source compound are each independently at least one of an oxide, acetate or oxalate of lithium, nickel, cobalt or manganese.

[0034] Since some metal oxides are not soluble metal salts, such as cobalt tetroxide and manganese dioxide, they are insoluble in water and difficult to dissolve in weak acids. In particular, cobalt tetroxide requires a reducing agent to convert the insoluble +3 cobalt ions (Co 3+ ) is reduced to a soluble +2 state (Co 2+ ). Conventional organic acids or complexing agents (ethylene glycol, citric acid or polyacrylic acid, etc.) cannot dissolve lithium, nickel, cobalt, and manganese oxides to form gels. In the present application, by using an acidic complexing agent A combined with a reducing complexing agent B, a variety of metal compounds can be fully dissolved and reacted.

[0035] In some embodiments, the mass ratio of the complexing agent A to the total mass of the lithium source compound, the nickel source compound, the cobalt source compound and the manganese source compound is (5-50): (50-95). The mass ratio of the complexing agent B to the mass of the small-particle single crystal positive electrode material is 5-500:1000.

[0036] In a specific embodiment, the complexing agent A and the complexing agent B are first added to deionized water to form an aqueous solution of the complexing agent A and an aqueous solution of the complexing agent B. The concentration of the aqueous solution of the complexing agent B is 0.01-3 mol / L.

[0037] In some embodiments, a flow pump is used to slowly pump the aqueous solution of the complexing agent B into the mixed solution, and the feed flow rate of the aqueous solution of the complexing agent B is 0.1 to 20 L / h.

[0038] The reaction temperature in step S1 is 30-70°C, the reaction time is 0.1-1h, and the stirring speed is 200-600r / min.

[0039] The reaction temperature in step S2 is 30-70° C., the reaction time is 0.1-1 h, and the stirring speed is 300-800 r / min.

[0040] Before step S3, the method further includes: adjusting the pH of the sol to 6.5-7.5; and heating the sol to 40-90°C.

[0041] Wherein, the reagent for adjusting pH is at least one of ammonia water, ammonium acetate or ammonium citrate.

[0042] In some embodiments, the viscosity of the gel is 40,000-100,000 mPa.s.

[0043] The viscosity of the gel reflects the amount of water in the gel. The more water it contains, the lower the viscosity. Conversely, the less water it contains, the higher the viscosity. The viscosity of the gel has a great influence on the preparation of the positive electrode material. On the one hand, if the gel viscosity is low, the water content is high, and the subsequent calcination energy consumption is high; on the other hand, if the gel viscosity is low, the complex composed of organic matter and metal ions will be deposited at the bottom of the sintering vessel during the calcination process, which will cause uneven distribution of metal ions after calcination.

[0044] The calcination in step S4 includes: calcining the gel in at least two steps under an oxygen or air atmosphere.

[0045] In some embodiments, the first step calcination temperature is 300-450°C, the residence time is 2-12h, and the heating rate is 1-10°C / min; the second step calcination temperature is 550-900°C, the residence time is 1-15h, and the heating rate is 5-20°C / min.

[0046] In some embodiments, the temperature of the first calcination step is 100-400°C, the residence time is 2-15h, and the heating rate is 1-10°C / min; the temperature of the second calcination step is 450-900°C, the residence time is 1-12h, and the heating rate is 1-20°C / min; the temperature of the third calcination step is 350-850°C, the residence time is 1-9h, and the cooling rate is 5-20°C / min.

[0047] In some embodiments, the temperature of the first calcination step is 100-250°C, the residence time is 2-12 hours, and the heating rate is 1-10°C / min, the temperature of the second calcination step is 300-450°C, the residence time is 1-15 hours, and the heating rate is 5-20°C / min, and the temperature of the third calcination step is 500-880°C, the residence time is 1-15 hours, and the heating rate is 5-20°C / min.

[0048] Wherein, the calcining equipment includes one of a rotary kiln, a tubular furnace, a box furnace, a bell furnace or a roller kiln.

[0049] In this application, a sol-gel method combined with step-by-step calcination is used to prepare a small-particle single-crystal positive electrode material. The first step of calcination is to fully remove the organic matter or organic carbon chain of the sol-gel process at a relatively low temperature to prepare for the next step of material crystallization. The second step of calcination is the process of achieving material crystallization at a higher temperature, that is, the process of building the material structure. The material prepared in this process basically reaches the applicable level. The third step of calcination is an optimization process of the material, which will repair and optimize the lattice defects, crystallinity defects and other problems that occurred in the previous synthesis process of the material. If step-by-step calcination is not used, insufficient removal of organic matter or organic carbon chains may result, rapid crystallization of the material, and residual organic impurities, which will seriously affect the performance.

[0050] The present application also provides a small-particle single-crystal positive electrode material prepared by the above-mentioned preparation method, wherein the particle size D50 of the small-particle single-crystal positive electrode material is 1.5 μm to 5 μm.

[0051] The small-particle single crystal positive electrode material prepared in the present application has a small particle size, highly flat and smooth single crystal particle characteristics, high crystallinity and high mechanical strength. After the small-particle single crystal positive electrode material is assembled into a lithium-ion battery, the contact area between the particle surface and the electrolyte is reduced, and the corresponding side reactions between the positive electrode material and the electrolyte are significantly reduced, effectively reducing the heat release and gas release caused by the side reactions, so that the battery has better high-temperature safety performance, high-temperature rate performance and charge and discharge voltage platform.

[0052] The following specific examples and comparative examples are used to illustrate the preparation method and performance of the small-particle single-crystal positive electrode material of the present application.

[0053] Example 1

[0054] This embodiment provides a method for preparing a small-particle single-crystal positive electrode material. The chemical formula of the small-particle single-crystal positive electrode material to be prepared is LiNi 0.53 Co 0.23 Mn 0.24 O2. The preparation method specifically comprises the following steps:

[0055] S1: 55 g of 2-hydroxypropionic acid was added to 3 L of deionized water to obtain an aqueous solution of complexing agent A. According to the molar ratio of nickel, cobalt, manganese and lithium ions being 0.53:0.23:0.24:1.08, 802 g of nickel acetate, cobalt acetate, manganese oxalate and lithium oxide were added to the aqueous solution of complexing agent A. The mixture was reacted at 40° C. and 300 r / min of stirring for 0.2 h to obtain a mixed solution.

[0056] S2: 20 g of ascorbic acid and 1 g of tyrosine were added to 4.8 L of deionized water to obtain a 0.025 mol / L aqueous solution of complexing agent B. The aqueous solution of complexing agent B was pumped into the mixed solution at a feed rate of 4.8 L / h, the reaction conditions were a temperature of 45° C., a stirring speed of 350 r / min, and the pumping was completed after 1 h to obtain a sol.

[0057] S3: Add ammonium acetate solution to the above sol to adjust the pH to 7.1, evaporate and concentrate under heating conditions of 50° C. to remove most of the water and form a gel with a viscosity of 60,000 mPa.s.

[0058] S4: The gel is transferred to a roller kiln and calcined in oxygen atmosphere in steps. The first step of calcination is at a temperature of 250°C, a residence time of 3 hours, and a heating rate of 5°C / min; the second step of calcination is at a temperature of 800°C, a residence time of 10 hours, and a heating rate of 10°C / min; the third step of calcination is at a temperature of 400°C, a residence time of 3 hours, and a cooling rate of 10°C / min. The calcined material is sieved to obtain a small-particle single crystal positive electrode material.

[0059] Figure 2 This is a SEM image of the small-particle single-crystal positive electrode material prepared in Example 1. Figure 2 It can be seen that the surface of the small-particle single-crystal positive electrode material is highly flat and smooth, and the whole is in an irregular granular shape. Figure 3 The XRD diagram of the small-particle single-crystal positive electrode material shows that the positive electrode material prepared in this embodiment is LiNi with a single-crystal structure. 0.53 Co 0.23 Mn 0.24 O2, each diffraction peak is sharp and has a high degree of crystallinity.

[0060] Example 2

[0061] This embodiment provides a method for preparing a small-particle single-crystal positive electrode material. The chemical formula of the small-particle single-crystal positive electrode material to be prepared is LiNi 0.6 Co 0.2 Mn 0.2 The preparation method specifically comprises the following steps:

[0062] S1: 510 g of 2-hydroxypropionic acid and 10 g of quinic acid were added to 30 L of deionized water to obtain an aqueous solution of complexing agent A, and then 9045 g of nickel oxalate, cobalt acetate, manganese oxalate and lithium acetate were added to the above solution at a molar ratio of nickel, cobalt, manganese and lithium ions of 0.6:0.2:0.2:1.06, and the mixture was reacted at 50° C. and 400 r / min of stirring for 0.2 h to obtain a mixed solution.

[0063] S2: 130 g of ascorbic acid and 10 g of tyrosine were added to 20 L of deionized water to obtain a 0.04 mol / L aqueous solution of complexing agent B. The aqueous solution of complexing agent B was pumped into the mixed solution at a flow rate of 20 L / h. The reaction conditions were a temperature of 45° C. and a stirring speed of 450 r / min. The pumping was completed after 1 h to obtain a gel.

[0064] S3: Add ammonia water and ammonium citrate solution to the above sol to adjust the pH to 7.0, evaporate and concentrate under heating conditions of 55° C. to remove most of the water and form a gel with a viscosity of 80,000 mPa.s.

[0065] S4: The gel is transferred to a roller kiln for step-by-step calcination in an oxygen atmosphere. The first step of calcination is at a temperature of 300°C, a residence time of 3 hours, and a heating rate of 5°C / min; the second step of calcination is at a temperature of 850°C, a residence time of 11 hours, and a heating rate of 10°C / min. The calcined material is sieved to obtain a small-particle single crystal positive electrode material.

[0066] Example 3

[0067] This embodiment provides a method for preparing a small-particle single-crystal positive electrode material. The chemical formula of the small-particle single-crystal positive electrode material to be prepared is LiNi 0.5 Co 0.2 Mn 0.3 The preparation method specifically comprises the following steps:

[0068] S1: 1000 g of 2-hydroxypropionic acid and 50 g of succinic acid were added to 90 L of deionized water to obtain an aqueous solution of complexing agent A. According to the molar ratio of nickel, cobalt, manganese and lithium ions of 0.5:0.2:0.3:1.06, 14.1 kg of nickel oxide, cobalt acetate, manganese oxalate and lithium acetate were added to the aqueous solution of complexing agent A above, and the mixture was reacted for 0.4 h under heating conditions of 45° C. and stirring conditions of 350 r / min to obtain a mixed solution.

[0069] S2: 200 g of ascorbic acid and 50 g of glucosamine were added to 18 L of deionized water to obtain a 0.08 mol / L aqueous solution of complexing agent B. The aqueous solution of complexing agent B was pumped into the mixed solution at a flow rate of 18 L / h, the reaction conditions were a temperature of 55° C., a stirring speed of 500 r / min, and the pumping was completed after 1 h to obtain a sol.

[0070] S3: Add ammonium acetate and ammonium citrate solution to the above sol to adjust the pH to 7.0, evaporate and concentrate under heating conditions of 50° C. to remove most of the water and form a gel with a viscosity of 50,000 mPa.s.

[0071] S4: The gel is transferred to a rotary kiln and calcined in air atmosphere in steps. The first step is calcined at a temperature of 200°C, a residence time of 4 hours, and a heating rate of 50°C / min; the second step is calcined at a temperature of 450°C, a residence time of 4 hours, and a heating rate of 10°C / min; the third step is calcined at a temperature of 800°C, a residence time of 8 hours, and a heating rate of 15°C / min. The calcined material is sieved to obtain a small-particle single crystal positive electrode material.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that only the aqueous solution of complexing agent A is added to the reaction system without adding the aqueous solution of complexing agent B, that is, the reaction in step S2 is not performed. The aqueous solution of complexing agent A is prepared by adding 75 g of 2-hydroxypropionic acid into 8 L of deionized water.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 1 is that an aqueous solution of complexing agent A and an aqueous solution of complexing agent B are added simultaneously to carry out the reaction.

[0076] Step S1 is: 55g of 2-hydroxypropionic acid, 20g of ascorbic acid and 1g of tyrosine are added to 8L of deionized water, and then 802g of nickel acetate, cobalt tetroxide, manganese oxalate and lithium oxide are added to the mixed solution of the above complexing agents A and B according to the molar ratio of nickel, cobalt, manganese and lithium ions of 0.53:0.23:0.24:1.08, and the reaction is carried out under heating conditions of 45°C and stirring conditions of 350r / min for 1.2h. The reaction is completed to obtain a sol.

[0077] The remaining steps are the same as those in Example 1 and will not be described again.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 1 is that only an aqueous solution of complexing agent A is added, and no step-by-step calcination is performed. Specifically, the following steps are included:

[0080] S1: 75 g of 2-hydroxypropionic acid was added to 8 L of deionized water to obtain an aqueous solution of complexing agent A. Then, 802 g of nickel acetate, cobalt tetroxide, manganese oxalate and lithium oxide were added to the aqueous solution of complexing agent A according to the molar ratio of nickel, cobalt, manganese and lithium ions of 0.53:0.23:0.24:1.08. The mixture was heated at 45° C. and stirred at 350 r / min for 1.2 h. The reaction was completed to obtain a sol.

[0081] S2: Add ammonium acetate solution to the above sol to adjust the pH to 7.1, evaporate and concentrate under heating conditions of 50°C to remove most of the water and form a gel with a viscosity of 60,000 mPa.s.

[0082] S3: The gel is transferred to a roller kiln for calcination in an oxygen atmosphere at a calcination temperature of 800°C, a residence time of 16 hours, and a heating rate of 10°C / min. The calcined material is sieved to obtain a small-particle single crystal positive electrode material.

[0083] The small-particle single crystal positive electrode materials prepared in the above Examples 1-3 and Comparative Examples 1-3 were subjected to a 50 MPa compaction test to test the change in the median particle size D50 of the materials before and after compaction, so as to evaluate the mechanical strength of the materials. The test results are shown in Table 1.

[0084] Table 1 Material mechanical strength test results

[0085] Particle size D50 before compaction (μm) After compaction D50 (μm) D50 loss rate (%) Example 1 3.18 3.10 2.5 Example 2 2.52 2.45 2.8 Example 3 3.82 3.78 1.0 Comparative Example 1 3.40 3.08 9.4 Comparative Example 2 3.29 2.99 9.1 Comparative Example 3 3.48 3.01 13.5

[0086] As can be seen from Table 1, the particle size D50 of the small-particle single-crystal positive electrode material prepared in the present application is 1.5 μm to 5 μm, the D50 loss rate before and after compaction is low, and the mechanical strength of the material is high.

[0087] The small-particle single crystal positive electrode materials prepared in Example 1 and Comparative Examples 1-3 were added with acetylene black and polytetrafluoroethylene (PVDF) respectively, mixed evenly, ground into a uniform slurry and coated on aluminum foil to make a positive electrode, and a button cell was made with a metal lithium sheet as a negative electrode and LiPF6 as an electrolyte. The electrochemical test voltage was 4.3V, and a high-temperature charge and discharge test was carried out at a rate of 1C at a temperature of 60°C.

[0088] Figure 4 The first charge and discharge curves of the lithium-ion batteries prepared in Example 1 and Comparative Examples 1-3 at 1C rate and 60°C are as follows. It can be seen from the figure that the first charge specific capacity of the positive electrode material prepared in Example 1 can be as high as 179.9 mAh / g, and the first discharge specific capacity can be as high as 171.1 mAh / g, which are significantly higher than Comparative Examples 1-3.

[0089] Figure 5 The graph is a cycle curve of the lithium ion battery prepared in Example 1 and Comparative Examples 1-3 at 8C rate and 60°C. It can be seen from the graph that the lithium ion battery prepared in Example 1 has an initial discharge capacity of 159.3 mAh / g. After 50 cycles, the discharge capacity remains at 156.4 mAh / g, which is significantly better than Comparative Examples 1-3.

[0090] In summary, the present application adopts the combination of complexing agent A and complexing agent B, step-by-step reaction, and adopts the sol-gel method combined with step-by-step calcination to prepare a small-particle single-crystal positive electrode material with small particle size, high crystallinity, and high mechanical strength. After the small-particle single-crystal positive electrode material is assembled into a lithium-ion battery, the contact surface between the particle surface and the electrolyte is reduced, and the corresponding side reaction between the positive electrode material and the electrolyte is significantly reduced, effectively reducing the heat release and gas release caused by the side reaction, so that the lithium-ion battery has better high-temperature safety performance, high-temperature rate performance, and charge and discharge voltage platform.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A method for preparing a small-particle single-crystal positive electrode material, characterized in that: The following steps are involved: S1: taking a lithium source compound, a nickel source compound, a cobalt source compound and a manganese source compound according to a stoichiometric ratio, wherein the lithium source compound, the nickel source compound, the cobalt source compound and the manganese source compound are independently oxides of lithium, nickel, cobalt and manganese elements, and mixing them with an aqueous solution of a complexing agent A to react to obtain a mixed solution; S2: adding an aqueous solution of complexing agent B to the mixed solution to react to obtain a sol; S3: heating the sol to evaporate and concentrate it to form a gel; S4: calcining the gel step by step to obtain a small-particle-size single-crystalline positive electrode material; The chemical formula of the small-particle single-crystal cathode material is Li k Ni x Co y Mn z O2, x:y:z=(0.10~0.85):(0.05~0.40):(0.10~0.35), 0.95≤k≤1.15; the complexing agent A is at least one of 2-hydroxypropionic acid, aspartic acid, quinic acid, succinic acid or formic acid; the complexing agent B is at least one of ascorbic acid, glucosamine, tyrosine or aminobutyric acid.

2. The preparation method according to claim 1, characterized in that The ratio of the mass of the complexing agent A to the total mass of the lithium source compound, the nickel source compound, the cobalt source compound and the manganese source compound is (5-50): (50-95).

3. The preparation method according to claim 1, characterized in that: The mass ratio of the complexing agent B to the mass ratio of the small-particle-size single-crystal positive electrode material is 5-500:1000; The concentration of the aqueous solution of the complexing agent B is 0.01-3 mol / L; the feed flow rate of adding the aqueous solution of the complexing agent B to the mixed solution is 0.1-20 L / h.

4. The preparation method according to claim 1, characterized in that: The reaction temperature in step S1 is 30-70°C, the reaction time is 0.1-1h, and the stirring speed is 200-600r / min; The reaction temperature in step S2 is 30-70° C., the reaction time is 0.1-1 h, and the stirring speed is 300-800 r / min.

5. The preparation method according to claim 1, characterized in that: Before step S3, the method further includes: adjusting the pH of the sol to 6.5-7.5; and the heating temperature in step S3 is 40-90°C.

6. The preparation method according to claim 1, characterized in that: The viscosity of the gel is 40000-100000 mPa.s.

7. The preparation method according to claim 1, characterized in that The stepwise calcination in step S4 comprises: calcining the gel in at least two steps under an oxygen or air atmosphere; The first step of calcination is performed at a temperature of 300-450°C, a residence time of 2-12 hours, and a heating rate of 1-10°C / min; the second step of calcination is performed at a temperature of 550-900°C, a residence time of 1-15 hours, and a heating rate of 5-20°C / min; or The first step of calcination is at a temperature of 100-400°C, a residence time of 2-15h, and a heating rate of 1-10°C / min; the second step of calcination is at a temperature of 450-900°C, a residence time of 1-12h, and a heating rate of 1-20°C / min; the third step of calcination is at a temperature of 350-850°C, a residence time of 1-9h, and a cooling rate of 5-20°C / min; or The temperature of the first calcination step is 100~250℃, the residence time is 2~12h, and the heating rate is 1~10℃ / min. The temperature of the second calcination step is 300~450℃, the residence time is 1~15h, and the heating rate is 5~20℃ / min. The temperature of the third calcination step is 500~880℃, the residence time is 1~15h, and the heating rate is 5~20℃ / min.

8. A small-particle single-crystal positive electrode material, characterized in that: The small-particle single crystal positive electrode material is prepared by the preparation method described in any one of claims 1 to 7; the particle size D50 of the small-particle single crystal positive electrode material is 1.5 μm~5 μm.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises the small-particle-size single-crystal positive electrode material as claimed in claim 8.

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