A high-nickel single-crystal positive electrode material, a preparation method therefor, and an application thereof

Abstract

The application provides a high-nickel single-crystal positive electrode material and a preparation method and application thereof, and adopts a multi-stage sintering method assisted by a dopant to synthesize single-crystal LiNi x Co y M 1‑x‑y O2. The multi-stage sintering method can shorten the high-temperature sintering time on the basis of synthesizing single crystals, is conducive to reducing the agglomeration of single-crystal particles, and reduces lithium-nickel mixed arrangement defects in the structure of the high-nickel single-crystal positive electrode. In addition, the oxygen flow is finely controlled in the high-temperature sintering stage, and the volatilization loss of lithium salt is reduced. Meanwhile, in the multi-stage sintering process, a low-melting-point oxide is introduced as a sintering flux, which can stabilize the crystal structure of the high-nickel single-crystal positive electrode material and improve the electrochemical performance of the high-nickel single-crystal positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a high-nickel single-crystal cathode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have high energy density, low memory effect, good cycle performance, low self-discharge and other advantages, and are widely used in electric vehicles and consumer electronic products and large-scale energy storage. With the continuous popularity of electric vehicles and battery energy storage, people have higher requirements for the energy density, service life and cost of batteries. The cathode material is an important component in lithium ion batteries, and its capacity limits the energy density of lithium ion batteries, and its production cost accounts for a large part of the cost of lithium ion batteries. LiNi x Co y Mn 1-x-y O2 ternary cathode material is one of the mainstream lithium battery cathode materials, and has the advantages of high capacity and low cost. With the scarcity of cobalt resources and the rise of cobalt prices, the ternary cathode material is developing towards high-nickel and low-cobalt.

[0003] High-nickel ternary cathode material is a very promising cathode material, and has the advantages of high capacity and low cost, and has received extensive attention. Its capacity increases with the increase of nickel content, and the disadvantages are the decrease of structural stability and rapid capacity decay. High-nickel ternary cathode material is generally a secondary particle sphere, which is aggregated by nanometer-sized primary grains. When high-nickel ternary cathode material releases higher capacity and continuously embeds and extracts more lithium, the volume change causes anisotropic lattice stress and internal grain boundary cracks; electrolyte invades the cracks, aggravates the side reaction, and causes capacity decay. Constructing a single crystal structure in high-nickel ternary material can eliminate the internal pores and grain boundaries of the particles, better solve the problem of grain boundary micro-cracks, help to inhibit the side reaction with electrolyte, improve the cycle stability and safety performance of the battery; and the single-crystal high-nickel ternary material has better mechanical properties and higher compaction density, which can improve the volume specific energy density of the battery.

[0004] There are still problems to be solved in the high-nickel single-crystal ternary material. The high-nickel ternary material has poor structural stability, and there is an irreversible phase transition from a layered phase to a spinel phase to a rock salt phase in the cycle process. This requires ion doping of the crystal structure of the high-nickel single-crystal material to improve it. There are also problems in the synthesis process of the high-nickel single-crystal positive electrode material. The preparation of the high-nickel single-crystal positive electrode material often requires a higher sintering temperature and the addition of more excess lithium salt, which causes serious agglomeration of single-crystal particles. Mechanical crushing is needed to separate the agglomerated single-crystal particles, which can damage the single-crystal particles. Flux can effectively reduce the sintering temperature and also has a good separation effect on the crystal grains. However, the subsequent removal of the flux requires water washing, and the high-nickel single-crystal positive electrode material is sensitive to water, which can cause surface structure phase transition and capacity loss of the material.

[0005] Therefore, it is of great value and significance to develop a high-nickel single-crystal positive electrode material with regular morphology, good dispersity and excellent electrochemical performance for the lithium battery industry. SUMMARY

[0006] In order to improve the particle agglomeration and cycle performance of the high-nickel single-crystal material, the application provides a high-nickel single-crystal positive electrode material and a preparation method. Through a multi-stage sintering method with doping assistance, the precursor is first sintered at a low temperature to pretreat the precursor and improve the reactivity of the raw material. The particles are initially phase transitioned at a medium temperature in the second stage. The third stage is a high-temperature short-time sintering to improve the reaction rate and make the crystal grains grow rapidly into micron single crystals. A relatively short duration can avoid excessive adhesion of the particles, and the oxygen flow is reduced during the high-temperature sintering process to reduce the volatilization loss of lithium salt. The crystal structure is perfected in the fourth stage of medium-temperature sintering. In addition, the introduction of a low-melting-point dopant during the sintering process not only reduces the sintering temperature and improves the particle dispersity, but also reduces the surface energy of the material and controls the directional growth of the high-nickel single-crystal crystal face to prepare a high-nickel single crystal with regular morphology. The addition of the dopant improves the stability of the crystal structure. The first-cycle discharge capacity of the high-nickel single-crystal material is more than 210 mAhg -1 , and the cycle retention rate at the 50th cycle is more than 95%.

[0007] One of the purposes of the application is to provide a high-nickel single-crystal positive electrode material obtained by multi-stage sintering of components including a high-nickel hydroxide precursor, a metal lithium salt and a dopant. The multi-stage sintering includes the steps of first temperature rising sintering and then temperature reduction sintering.

[0008] According to the application, the chemical formula of the high-nickel single-crystal positive electrode material is LiNi x Co y M 1-x-y O2, wherein M is at least one of B, V, Bi, Mn, Mo, Sb, Se and Te, 0.8≤x<1 and 0<y≤0.1.

[0009] The high-nickel single-crystal positive electrode material is in a polyhedral morphology.

[0010] The particle size of the high-nickel single-crystal positive electrode material is 0.1-10 microns, preferably 1-3 microns.

[0011] According to the application, the high-nickel single-crystal positive electrode material contains:

[0012] The high-nickel hydroxide precursor has a chemical formula of Ni x Co y Mn 1-x-y (OH)2, wherein 0.8≤x<1 and 0<y≤0.1.

[0013] The particle size of the high-nickel hydroxide precursor is 1-20 microns, preferably 3-5 microns.

[0014] The metal lithium salt is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate and lithium acetate.

[0015] The dopant is selected from at least one of inorganic oxides with a melting point lower than 1000℃, preferably B2O3, V2O5, Bi2O3, MnO2, MoO3, Sb2O3, SeO2 and TeO2.

[0016] According to the application, the high-nickel single-crystal positive electrode material contains:

[0017] The molar ratio of the metal lithium salt to the high-nickel hydroxide precursor is (0.9-1.25):1, preferably (1-1.15):1.

[0018] The molar ratio of the dopant to the high-nickel hydroxide precursor is (0.1-10):100, preferably (0.5-3):100.

[0019] The second object of the application is to provide a preparation method of the high-nickel single-crystal positive electrode material.

[0020] S1, mixing a high-nickel hydroxide precursor, a metal lithium salt and a dopant to obtain a mixture;

[0021] S2, subjecting the mixture obtained in step S1 to multi-stage sintering of first temperature rising sintering and then temperature dropping sintering in an oxygen atmosphere to obtain the high-nickel single-crystal positive electrode material.

[0022] According to the application, in the preparation method of the high-nickel single-crystal positive electrode material, step S2:

[0023] The end point temperature of the temperature rising sintering is 850-1000℃.

[0024] The temperature rising sintering includes at least 3 stages.

[0025] The temperature reduction sintering includes at least two stages.

[0026] According to the application, in the preparation method of the high-nickel single-crystal positive electrode material, the multi-stage sintering includes the following steps:

[0027] 2-1) increasing the temperature from room temperature to 300-500℃ at a temperature increasing rate of 3-10℃ / min, and keeping the temperature for 1-5 hours;

[0028] 2-2) continuing to increase the temperature to 700-850℃ at a temperature increasing rate of 1-5℃ / min, and keeping the temperature for 1-5 hours;

[0029] 2-3) continuing to increase the temperature to 850-1000℃ at a temperature increasing rate of 1-10℃ / min, and keeping the temperature for 0.5-5 hours;

[0030] 2-4) decreasing the temperature to 700-850℃ at a temperature decreasing rate of 1-5℃ / min, and keeping the temperature for 1-5 hours;

[0031] 2-5) cooling to room temperature at a temperature decreasing rate of 3-10℃ / min.

[0032] According to the application, in the preparation method of the high-nickel single-crystal positive electrode material, in the multi-stage sintering, from the beginning of the last temperature increasing process to the first temperature decreasing process, the oxygen flow rate is reduced, preferably, the oxygen flow rate is reduced to 40-60% of the initial flow rate, and the initial oxygen flow rate is 80-200ml / min.

[0033] Specifically, in the multi-stage sintering operation:

[0034] In steps 2-1 and 2-2, the oxygen flow rate is 80-200ml / min;

[0035] In step 2-3, the oxygen flow rate is 30-100ml / min;

[0036] In step 2-4, the oxygen flow rate in the temperature decreasing process is 30-100ml / min, and the oxygen flow rate in the temperature keeping process is 80-200ml / min;

[0037] In step 2-5, the oxygen flow rate in the temperature decreasing process is 80-200ml / min.

[0038] The third object of the application is to provide the high-nickel single-crystal positive electrode material or the high-nickel single-crystal positive electrode material obtained by the above preparation method, for use in battery materials.

[0039] The application adopts a multi-stage sintering method assisted by a dopant to synthesize single-crystal LiNi x Co y M 1-x-yO2; compared with the common long-time high-temperature sintering, the multi-stage sintering method can shorten the high-temperature sintering time on the basis of synthesizing single crystals, which is conducive to reducing the agglomeration of single crystal particles and reducing the lithium-nickel mixed arrangement defects in the high-nickel single crystal positive electrode structure; and the oxygen flow is finely controlled in the high-temperature sintering stage to reduce the volatilization loss of lithium salt. At the same time, in the multi-stage sintering process, the oxide with a melting point lower than 1000 DEG C is introduced as a sintering flux to reduce the sintering temperature of material synthesis, strengthen the mass transfer in the sintering process, accelerate the grain growth of high-nickel single crystal materials, and improve the dispersity of the crystal particles; the dopant can reduce the surface energy of the high-nickel single crystal, control the directional growth of the material crystal face, and show a regular polyhedral morphology; while adjusting the morphology of the high-nickel single crystal, the dopant can enter the high-nickel single crystal structure without introducing impurities, without the need for additional water washing removal, and stabilize the crystal structure of the high-nickel single crystal material, and improve the electrochemical performance of the high-nickel single crystal positive electrode material.

[0040] Compared with the prior art, the advantages of the present application are that:

[0041] 1. The high-nickel single crystal positive electrode material synthesized by the present application has a regular polyhedral morphology, high particle dispersity, and stronger structural stability, and the first cycle discharge capacity is greater than 210 mAhg -1 , and the capacity retention rate after 50 charge-discharge cycles is greater than 95%.

[0042] 2. The multi-stage sintering technology adopted in the present application has a short high-temperature stage time (850-1000 DEG C), which helps to alleviate the problem of single crystal particle agglomeration, shorten the high-temperature sintering time, reduce the lithium-nickel mixed arrangement of high-nickel single crystals, and improve the electrochemical performance of high-nickel single crystal positive electrodes; at the same time, the oxygen flow is controlled in the sintering process to reduce the volatilization loss of lithium at high temperature; and the addition of the dopant has a fluxing effect, which not only stabilizes the crystal structure of the high-nickel single crystal, but also reduces the surface energy of the material, controls the regular growth of the single crystal, and effectively disperses the single crystal particles.

[0043] 3. The multi-stage sintering technology provided by the present application has a simple preparation method, and the sintering conditions can be adjusted on the existing mature production line process without the need for additional water washing steps to remove the fluxing agent, which is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 It is the temperature curve and oxygen flow diagram in the multi-stage sintering process of Example 1.

[0045] Figure 2 It is the temperature curve and oxygen flow diagram in the long-time high-temperature sintering process of Comparative Example 2.

[0046] Figure 3 It is the SEM diagram of the high-nickel single crystal positive electrode material obtained in Example 1.

[0047] Figure 4 SEM image of high-nickel single-crystal cathode material obtained for Example 2.

[0048] Figure 5 SEM image of high-nickel single-crystal cathode material obtained for Example 3.

[0049] Figure 6 SEM image of high-nickel single-crystal cathode material obtained for Example 4.

[0050] Figure 7 SEM image of high-nickel single-crystal cathode material obtained for Comparative Example 1.

[0051] Figure 8 SEM image of high-nickel single-crystal cathode material obtained for Comparative Example 2.

[0052] Figure 9 SEM image of high-nickel single-crystal cathode material obtained for Comparative Example 3.

[0053] Figure 10 SEM image of high-nickel single-crystal cathode material obtained for Example 5.

[0054] Figure 11 SEM image of high-nickel single-crystal cathode material obtained for Example 6.

[0055] Figure 12 Surface energy change chart of different crystal planes of materials before and after molybdenum doping for Example 1 and Comparative Example 1.

[0056] Figure 13 XRD chart and Rietveld refinement of high-nickel single-crystal cathode material obtained for Example 1.

[0057] Figure 14 XRD chart and Rietveld refinement of high-nickel single-crystal cathode material obtained for Comparative Example 1.

[0058] Figure 15 XRD chart and Rietveld refinement of high-nickel single-crystal cathode material obtained for Comparative Example 2.

[0059] Figure 16 XRD chart and Rietveld refinement of high-nickel single-crystal cathode material obtained for Comparative Example 3.

[0060] Figure 17 First-cycle charge-discharge curve chart of batteries assembled using high-nickel single-crystal cathode materials of Example 1 and Comparative Examples 1-3.

[0061] Figure 18 Cycle performance chart of batteries assembled using high-nickel single-crystal cathode materials of Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described herein are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0063] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0064] Example 1:

[0065] Preparation of high-nickel single-crystal cathode materials:

[0066] S1) Mixing: The high-nickel hydroxide precursor Ni with an average diameter of 4 micrometers is mixed... 0.90 Co 0.05 Mn 0.05 (OH)2, lithium salt compound LiOH·H2O and dopant MoO3 are mixed in a molar ratio of 1:1.06:0.01. The preliminary mixture is first manually ground, and then a planetary mixer is used to further homogenize the preliminary mixture at a speed of 1000 rpm for 10 min to obtain the mixture.

[0067] S2) Sintering: The mixture obtained in step S1 is placed in an oxygen furnace with an oxygen flow rate of 100 ml / min (normal value). The oxygen furnace is first heated to 500°C at a heating rate of 5°C / min and held for 3 hours, then heated to 775°C at a heating rate of 2.75°C / min and held for 3 hours. The oxygen flow rate is then reduced to 50 ml / min, while the temperature is increased to 985°C at a heating rate of 3.5°C and held for 1 hour. The temperature is then decreased to 775°C at a cooling rate of 3.5°C / min, the oxygen flow rate is restored to the normal value of 100 ml / min, and the temperature is held for 3 hours. Finally, the temperature is decreased to room temperature at a cooling rate of 4°C / min to obtain molybdenum-doped high-nickel single-crystal cathode material A, with the chemical formula LiNi. 0.9 Co 0.05 Mn 0.05 Mo 0.01 O2, with an average particle size of 1.2 micrometers.

[0068] Figure 1 The temperature curves and oxygen flow diagrams for preparing high-nickel single crystals using the multi-segment sintering method in Example 1 are shown. During the high-temperature sintering stage, reducing the oxygen flow rate reduces the volatilization loss of lithium salts, which is beneficial for crystal growth.

[0069] Example 2:

[0070] Compared with Example 1, high-nickel single-crystal cathode materials were prepared by adding different amounts of lithium salt compounds using a multi-stage sintering method. The preparation process includes the following steps:

[0071] S1) Mixing: The high-nickel hydroxide precursor Ni with an average diameter of 4 micrometers is mixed... 0.90 Co 0.05 Mn 0.05 (OH)2, lithium salt compound LiOH·H2O and dopant MoO3 are mixed in a molar ratio of 1:1.10:0.01. The preliminary mixture is first manually ground, and then a planetary mixer is used to further homogenize the preliminary mixture at a speed of 1000 rpm for 10 min to obtain the mixture.

[0072] S2) Sintering: The mixture obtained in step S1 is placed in an oxygen furnace with an oxygen flow rate of 100 ml / min (normal value). The oxygen furnace is first heated to 500°C at a heating rate of 5°C / min and held for 3 hours, then heated to 775°C at a heating rate of 2.75°C / min and held for 3 hours. The oxygen flow rate is then reduced to 50 ml / min, while the temperature is increased to 985°C at a heating rate of 3.5°C and held for 1 hour. The temperature is then reduced to 775°C at a cooling rate of 3.5°C / min, the oxygen flow rate is restored to the normal value of 100 ml / min, and the temperature is held for 3 hours. Finally, the temperature is reduced to room temperature at a cooling rate of 4°C / min to obtain molybdenum-doped high-nickel single-crystal cathode material B, with the chemical formula LiNi. 0.9 Co 0.05 Mn 0.05 Mo 0.01 O2, with an average particle size of 1.5 micrometers.

[0073] Example 3:

[0074] Compared with Example 1, high-nickel single-crystal cathode materials were prepared by adding different amounts of dopants and using a multi-stage sintering method. The preparation process includes the following steps:

[0075] S1) Mixing: The high-nickel hydroxide precursor Ni with an average diameter of 4 micrometers is mixed... 0.90 Co 0.05 Mn 0.05 (OH)2, lithium salt compound LiOH·H2O and dopant MoO3 are mixed in a molar ratio of 1:1.06:0.005. The preliminary mixture is first manually ground, and then the preliminary mixture is further uniformly mixed using a planetary mixer with a speed of 1000 rpm and a mixing time of 10 min to obtain the mixture.

[0076] S2) Sintering: The mixture obtained in step S1 is placed in an oxygen furnace with an oxygen flow rate of 100 ml / min (normal value). The oxygen furnace is first heated to 500°C at a heating rate of 5°C / min and held for 3 hours, then heated to 775°C at a heating rate of 2.75°C / min and held for 3 hours. The oxygen flow rate is then reduced to 50 ml / min, and the furnace is simultaneously heated to 985°C at a heating rate of 3.5°C and held for 1 hour. Subsequently, the furnace is cooled to 775°C at a cooling rate of 3.5°C / min, the oxygen flow rate is restored to the normal value of 100 ml / min, and the furnace is held for 3 hours. Finally, the furnace is cooled to room temperature at a cooling rate of 4°C / min to obtain the molybdenum-doped high-nickel single-crystal cathode material with the chemical formula LiNi. 0.9 Co 0.05 Mn 0.05 Mo 0.01 O2, with an average particle size of 1.9 micrometers.

[0077] Example 4:

[0078] Compared with Example 1, the oxygen flow conditions during sintering are different. The multi-stage sintering method for preparing high-nickel single-crystal cathode materials includes the following steps:

[0079] S1) Mixing: The high-nickel hydroxide precursor Ni with an average diameter of 4 micrometers is mixed... 0.90 Co 0.05 Mn 0.05 (OH)2, lithium salt compound LiOH·H2O and dopant MoO3 are mixed in a molar ratio of 1:1.06:0.01. The preliminary mixture is first manually ground, and then a planetary mixer is used to further homogenize the preliminary mixture at a speed of 1000 rpm for 10 min to obtain the mixture.

[0080] S2) Sintering: The mixture obtained in step S1 is placed in an oxygen furnace with an oxygen flow rate of 150 ml / min (normal value). The oxygen furnace is first heated to 500°C at a heating rate of 5°C / min and held for 3 hours, then heated to 775°C at a heating rate of 2.75°C / min and held for 3 hours. After that, the oxygen flow rate is reduced to 50 ml / min, and the temperature is increased to 985°C at a heating rate of 3.5°C and held for 1 hour. Then, the temperature is reduced to 775°C at a cooling rate of 3.5°C / min, the oxygen flow rate is restored to the normal value of 150 ml / min, and the temperature is held for 3 hours. Finally, the temperature is reduced to room temperature at a cooling rate of 4°C / min to obtain molybdenum-doped high-nickel single-crystal cathode material D, with the chemical formula LiNi. 0.9 Co 0.05 Mn 0.05 Mo 0.01 O2, with an average particle size of 1.1 micrometers.

[0081] Example 5:

[0082] A high-nickel single-crystal positive electrode material was prepared by a multi-stage sintering method with the addition of different dopants. The preparation process included the following steps:

[0083] S1) Mixing: high-nickel hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, lithium salt compound LiOH·H2O and dopant B2O3 were mixed in a molar ratio of 1:1.06:0.01. The mixture was first manually ground, and then further mixed uniformly using a planetary mixer at a speed of 1000 rpm for 10 min to obtain a mixed material;

[0084] S2) Sintering: The mixed material obtained in step S1 was placed in an oxygen furnace with a normal oxygen flow rate of 100 ml / min. First, it was heated to 500°C at a rate of 5°C / min and kept for 3 hours. Then, it was heated to 775°C at a rate of 2.75°C / min and kept for 3 hours. After that, the oxygen flow rate was reduced to 50 ml / min, and it was heated to 985°C at a rate of 3.5°C / min and kept for 1 hour. Subsequently, it was cooled to 775°C at a rate of 3.5°C / min, the oxygen flow rate was restored to the normal value of 100 ml / min, and it was kept for 3 hours. Finally, it was cooled to room temperature at a rate of 4°C / min to obtain a high-nickel single-crystal positive electrode material H with a chemical formula of LiNi 0.90 Co 0.05 Mn 0.05 B 0.02 O2, with an average particle size of 1.9 microns.

[0085] Example 6:

[0086] A high-nickel single-crystal positive electrode material was prepared by a multi-stage sintering method with the addition of different dopants. The preparation process included the following steps:

[0087] S1) Mixing: high-nickel hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, lithium salt compound LiOH·H2O and dopant V2O5 were mixed in a molar ratio of 1:1.06:0.01. The mixture was first manually ground, and then further mixed uniformly using a planetary mixer at a speed of 1000 rpm for 10 min to obtain a mixed material;

[0088] S2) sintering: the mixture obtained in step S1 was placed in an oxygen furnace, the normal flow rate of oxygen was 100 ml / min, first heated to 500°C at a heating rate of 5°C / min, and kept for 3 hours, then heated to 775°C at a heating rate of 2.75°C / min, and kept for 3 hours, then the oxygen flow rate was reduced to 50 ml / min, and heated to 985°C at a heating rate of 3.5°C, and kept for 1 hour, then cooled to 775°C at a cooling rate of 3.5°C / min, the oxygen flow rate was restored to the normal value of 100 ml / min, and kept for 3 hours, and finally cooled to room temperature at a cooling rate of 4°C / min, to obtain a high-nickel single-crystal positive electrode material I, the chemical formula of which was LiNi 0.90 Co 0.05 Mn 0.05 V 0.02 O2, with an average particle size of 2.5 microns.

[0089] Comparative Example 1:

[0090] Compared with Example 1, no dopant was added, and a high-nickel single-crystal positive electrode material was prepared by a multi-stage sintering method, and the preparation process included the following steps:

[0091] S1) mixing: high-nickel hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, and lithium salt compound LiOH·H2O were mixed in a molar ratio of 1:1.06, the preliminary mixture was first manually ground, and then further uniformly mixed by using a planetary mixer, the rotation speed was set to 1000 rpm, and the mixing time was 10 min, to obtain a mixture.

[0092] S2) sintering: the mixture obtained in step S1 was placed in an oxygen furnace, the normal flow rate of oxygen was 100 ml / min, first heated to 500°C at a heating rate of 5°C / min, and kept for 3 hours, then heated to 775°C at a heating rate of 2.75°C / min, and kept for 3 hours, then the oxygen flow rate was reduced to 50 ml / min, and heated to 985°C at a heating rate of 3.5°C, and kept for 1 hour, then cooled to 775°C at a cooling rate of 3.5°C / min, the oxygen flow rate was restored to the normal value of 100 ml / min, and kept for 3 hours, and finally cooled to room temperature at a cooling rate of 4°C / min, to obtain a high-nickel single-crystal positive electrode material E, the chemical formula of which was LiNi 0.90 Co 0.05 Mn 0.05 O2, with an average particle size of 2.0 microns.

[0093] Comparative Example 2:

[0094] Compared with Example 1, a high-nickel single-crystal positive electrode material is prepared by long-time high-temperature sintering without adding a dopant, and the preparation process comprises the following steps:

[0095] S1) Mixing: high-nickel hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2with an average diameter of 4 microns, and lithium salt compound LiOH·H2O are mixed in a molar ratio of 1:1.06, the mixture is first preliminarily manually ground, and then the preliminarily mixed material is further mixed and uniformly mixed by using a planetary mixer, the rotating speed is set to 1000 rpm, and the mixing time is 10 min, to obtain a mixed material;

[0096] S2) Sintering: the mixed material obtained in step S1 is placed in an oxygen furnace for sintering, the oxygen flow is kept at 100 ml / min, first, the temperature is raised to 500℃ at a temperature raising rate of 5℃ / min, and then kept for 3 hours, then the temperature is raised to 900℃ at a temperature raising rate of 4℃ / min, and then kept for 10 hours, finally, the temperature is reduced to room temperature at a temperature reducing rate of 4℃ / min, to obtain a high-nickel single-crystal positive electrode material F, the chemical formula of which is LiNi 0.90 Co 0.05 Mn 0.05 O2, and the average particle size is 1.9 microns.

[0097] Figure 2 For the temperature curve and oxygen flow of the high-nickel single crystal in the sintering process of Comparative Example 2, the oxygen flow is not controlled during long-time high-temperature calcination, and the volatilization of lithium salt is accelerated at high temperature, causing excessive loss of lithium in the material synthesis process.

[0098] Comparative Example 3:

[0099] Compared with Example 1, a high-nickel single-crystal positive electrode material is prepared by long-time high-temperature sintering with the addition of a dopant, and the preparation process comprises the following steps:

[0100] S1) Mixing: high-nickel hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, lithium salt compound LiOH·H2O and dopant MoO3 are mixed in a molar ratio of 1:1.08:0.01, the mixture is first preliminarily manually ground, and then the preliminarily mixed material is further mixed and uniformly mixed by using a planetary mixer, the rotating speed is set to 1000 rpm, and the mixing time is 10 min, to obtain a mixed material;

[0101] S2) Sintering: The mixture obtained in step S1 is placed in an oxygen furnace for sintering, with the oxygen flow rate maintained at 100 ml / min. First, the temperature is increased to 500℃ at a heating rate of 5℃ / min and held for 3 hours. Then, the temperature is increased to 960℃ at a heating rate of 4℃ / min and held for 10 hours. Finally, the temperature is reduced to room temperature at a cooling rate of 4℃ / min to obtain the high-nickel single-crystal cathode material G, with the chemical formula LiNi. 0.90 Co 0.05 Mn 0.05 Mo 0.01 O2, with an average particle size of 1.6 micrometers.

[0102] Test Example 1: High-nickel single-crystal cathode materials prepared in Examples 1-6 and Comparative Examples 1-3 were tested using scanning electron microscopy (SEM).

[0103] Figures 3-6 The images show SEM images of the molybdenum-doped high-nickel single-crystal particles obtained in Examples 1-4. It can be seen that the high-nickel single-crystal cathode material particles prepared in the four examples are similar, with a polyhedral morphology and a particle size between 1 and 2 micrometers. There are pores between the single-crystal particles, which facilitates separation. There is no severe particle adhesion, and the dispersion is good.

[0104] Depend on Figure 7 and Figure 8 It can be seen that the particle size of Comparative Example 1 and Comparative Example 2 is 1-3 micrometers, with severe adhesion between particles and large particles; the high-nickel single crystal cathode prepared by the multi-segment sintering method in Comparative Example 1 has an octahedral morphology, while the high-nickel single crystal cathode prepared by the long-term high-temperature sintering method in Comparative Example 2 is irregular; comparing Example 1 and Comparative Example 1 shows that molybdenum doping changes the particle morphology of the high-nickel single crystal cathode material and improves the particle dispersibility. Figure 9 Comparative Example 3 uses molybdenum oxide as a dopant to prepare high-nickel single crystal particles for a long time at high temperature. Although the particles have a certain regular morphology, it can be seen that there is still adhesion between the particles. Comparing Example 1 and Comparative Example 3, it can be seen that the multi-stage sintering method alleviates particle agglomeration and improves the dispersibility of single crystal particles. Figures 10-11 Examples 4 and 5 used a multi-segment sintering method to prepare high-nickel single-crystal cathode materials by adding different dopants, B2O3 and V2O5. The addition of B2O3 and V2O5 made the morphology of the single-crystal particles more regular. Compared with Comparative Examples 1-3, the morphology of Examples 1-4 is more regular and the dispersion is better, indicating that the molybdenum-doped multi-segment sintering method has a positive impact on the morphology of high-nickel single-crystal cathodes, regulating the regular growth of grains and improving particle agglomeration and adhesion. This is beneficial for maintaining the integrity of the particles in the cathode sheet during preparation and testing, suppressing crack formation, and improving cycle stability.

[0105] Test Example 2: X-ray diffractometer was used to test the high-nickel single-crystal positive electrode material prepared in Example 1 and Comparative Examples 1-3

[0106] Figure 13 The XRD pattern of the high-nickel single-crystal positive electrode material A obtained in Example 1 shows that the prepared high-nickel single-crystal positive electrode material has good crystallinity, and the refinement result shows that the lithium-nickel mixing ratio is 2.7%; Figure 14 In Comparative Example 1, the high-nickel single-crystal positive electrode material E prepared has a lithium-nickel mixing ratio of 4.9%, Figure 15 In Comparative Example 2, the high-nickel single-crystal positive electrode material F prepared has a lithium-nickel mixing ratio of 5.1%, and Figure 16 In Comparative Example 3, the high-nickel single-crystal positive electrode material G prepared has a higher lithium-nickel mixing ratio of 5.6%; the high-nickel single-crystal positive electrodes of Comparative Examples 2 and 3 have more lithium-nickel mixing defects due to long-time high-temperature sintering, while the high-nickel single-crystal positive electrodes prepared by the multi-stage sintering method of Example 1 and Comparative Example 1 have lower lithium-nickel mixing defects, indicating that the high-nickel single-crystal positive electrodes prepared by the multi-stage sintering method have more ordered crystal structures and fewer defects, and the crystal structure is more stable, which is beneficial to better electrochemical performance.

[0107] Simulation calculation of surface energy: In the framework of density functional theory (DFT), the Vienna ab initio simulation package (VASP) is used, and the calculation method can refer to the literature (Surface Structure, Morphology, and Stability of Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2 Cathode Material, Juan C. Garcia, et al., J. Phys. Chem. C 2017, 121, 8290-8299). Figure 12 The surface energy of Mo-doped LiNi 0.90 Co 0.05 Mn 0.05 O2 and undoped LiNi 0.90 Co 0.05 Mn 0.05 O2 was calculated, and the results of the simulation calculation showed that Mo doping reduced the surface energy of the (003), (012), and (104) crystal planes of LiNi 0.90 Co 0.05 Mn 0.05 O2, which regulated the regular growth of high-nickel single crystals, which well explained the experimental results of the regular morphology of Example 1, indicating that Mo doping can reduce the surface energy and thus regulate the regular growth of high-nickel single crystals.

[0108] Test Example 3: Electrochemical performance test

[0109] The high-nickel single-crystal cathode material prepared in Example 1 and Comparative Examples 1-3 was tested for electrochemical performance in a button cell CR2032, including first-cycle charge-discharge testing and charge-discharge cycle testing.

[0110] Battery assembly process: The examples and comparative examples were mixed in a mass ratio of 85:10:5 of cathode active material: conductive carbon: binder PVDF, the cathode slurry viscosity was adjusted with solvent N-methyl pyrrolidone (NMP), the slurry was uniformly coated on an aluminum foil, and dried in a vacuum oven for 12 hours, with a temperature setting of 120°C; the dried electrode was rolled and the coated aluminum foil was cut into 12mm diameter discs using a slicer, and transferred into a glove box to assemble the battery, with an atmosphere of O2<0.1ppm, H2O<0.1ppm in the glove box; Celgard2325 was used as a separator, lithium metal as a negative electrode, and 1M LiPF6 solution as an electrolyte, with EC / DMC (volume ratio 1:1) as a solvent. The assembled button cell was allowed to stand for 10h, and then electrochemical testing was performed after the electrolyte was fully soaked.

[0111] Electrochemical testing: first-cycle charge-discharge testing, voltage range 2.7-4.3V, rate 0.1C; charge-discharge cycle testing, voltage range 2.7-4.3V, rate 0.5C.

[0112] From Figure 17 It can be seen that the molybdenum-doped Example 1 has the highest first-cycle discharge capacity, reaching 214.6mAhg -1 -1, with a first-cycle coulombic efficiency of 89.6%; the first-cycle discharge capacity of Comparative Example 1 is 209.5mAhg -1 -1, with a first-cycle coulombic efficiency of 85.5%; the first-cycle discharge capacity of Comparative Example 2 is 201.4mAhg -1 -1, with a first-cycle coulombic efficiency of 82.8%; the first-cycle discharge capacity of Comparative Example 3 is 191.6mAhg -1 -1, with a first-cycle coulombic efficiency of 81.2%; indicating that the high-nickel single-crystal cathode material prepared in Example 1 of the present application has higher first-cycle discharge capacity and initial coulombic efficiency.

[0113] From Figure 18It can be seen that the high-nickel single-crystal positive electrode material A of the embodiment 1 of the present application has superior cycle performance, and the capacity retention rate of the battery of the embodiment 1 is 95.2% after 50 cycles of charging and discharging. The high-nickel single-crystal positive electrode material E of the comparative example 1 does not use a dopant, and the battery containing the high-nickel single-crystal positive electrode material of the comparative example 1 has poor cycle performance, and the capacity retention rate of the battery is 90.8% after 50 cycles. The comparison between the comparative example 1 and the comparative example 2 shows that the addition of the molybdenum oxide dopant stabilizes the crystal structure of the high-nickel single-crystal positive electrode material and improves the cycle performance. The battery containing the high-nickel single-crystal positive electrode material F of the comparative example 2 has poorer cycle performance, and the capacity retention rate of the battery is only 87.7% after 50 cycles of charging and discharging. The battery containing the high-nickel single-crystal positive electrode material H of the comparative example 3 has poor cycle performance, and the capacity retention rate of the battery is 89.3% after 50 cycles of charging and discharging. The comparison between the comparative example 2 and the comparative example 1 shows that the multi-stage sintering technology shortens the time of high-temperature sintering and can also improve the cycle performance of the high-nickel single crystal. The comparison between the embodiment 1 and the comparative example 3 shows that, under the condition of adding the same dopant, the high-nickel single-crystal positive electrode material prepared by the multi-stage sintering has better cycle performance compared with the long-time high-temperature sintering.

[0114] Compared with the comparative examples 1-3, the high-nickel single-crystal positive electrode material A prepared by the multi-stage sintering method of the embodiment 1 has better electrochemical performance, not only has higher first-cycle discharge capacity, but also has more stable cycle performance, which shows that the multi-stage sintering technology assisted by doping used in the present application effectively improves the electrochemical performance of the high-nickel single-crystal positive electrode.

[0115] The present application uses the multi-stage sintering technology assisted by doping to reduce the duration of high-temperature sintering, reduce the lithium-nickel mixing ratio of the synthesized high-nickel single-crystal positive electrode material, and regulate the oxygen flow during the high-temperature sintering stage to reduce the volatilization loss of lithium salt. In addition, a low-melting-point dopant is introduced during the sintering process to reduce the surface energy of the material, regulate the regular growth of the crystal of the high-nickel single-crystal positive electrode material, improve the particle agglomeration of the high-nickel single crystal, stabilize the crystal structure of the high-nickel single crystal, and improve the electrochemical performance of the high-nickel single-crystal positive electrode material.

[0116] The present application has been described in detail in the foregoing general description and specific embodiments, and the above embodiments are only used to illustrate the technical solutions of the present application, and are not limited to the scope of the present application. It should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the protection scope of the present application is subject to the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A high-nickel single-crystal cathode material, obtained by multi-stage sintering of components including a high-nickel hydroxide precursor, a metal lithium salt, and a dopant selected from at least one of B 2 O 3, V 2 O 5, and MoO 3, wherein the molar ratio of the dopant to the high-nickel hydroxide precursor is (0.5-1) : 100; the high-nickel single-crystal cathode material has a polyhedral morphology; and the multi-stage sintering comprises the steps of first-stage sintering at a rising temperature and second-stage sintering at a falling temperature. The multi-stage sintering comprises the following steps: 2-1) rising the temperature from room temperature to 300-500℃ at a rising rate of 3-10℃ / min, and maintaining the temperature for 1-5 hours; 2-2) continuing to rise the temperature to 700-850℃ at a rising rate of 1-5℃ / min, and maintaining the temperature for 1-5 hours; 2-3) continuing to rise the temperature to 850-985℃ at a rising rate of 1-10℃ / min, and maintaining the temperature for 1-5 hours; 2-4) falling the temperature to 700-850℃ at a falling rate of 1-5℃ / min, and maintaining the temperature for 1-5 hours; 2-5) cooling to room temperature at a falling rate of 3-10℃ / min; In the multi-stage sintering, a reduced oxygen flow rate is used from the start of the last-stage rising process to the end of the first-stage falling process before the start of the temperature-maintaining process, and the oxygen flow rate is reduced to 40-60% of the initial flow rate; and the initial oxygen flow rate in the multi-stage sintering operation is 80-200 ml / min. 2.The high-nickel single-crystal cathode material according to claim 1, wherein the particle size of the high-nickel single-crystal cathode material is 0.1-10 microns. The high-nickel single-crystal cathode material has a chemical formula of LiNi x Co y M 1-x-y O2, wherein M is at least one of B, V, Mo, 0.8≤x<1, and 0<y≤0.1; and / or, 3.The high-nickel single-crystal cathode material according to claim 2, wherein the particle size of the high-nickel single-crystal cathode material is 1-3 microns. 4.The high-nickel single-crystal cathode material according to claim 1, wherein the particle size of the high-nickel hydroxide precursor is 1-20 microns; and / or the metal lithium salt is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate; and / or the dopant is selected from at least one of B 2 O 3, V 2 O 5, and MoO 3. 5.The high-nickel single-crystal cathode material according to claim 4, wherein the particle size of the high-nickel hydroxide precursor is 3-5 microns. 6.The high-nickel single-crystal cathode material according to claim 1, wherein the molar ratio of the metal lithium salt to the high-nickel hydroxide precursor is (0.9-1.25) :

1. The high nickel hydroxide precursor has a chemical formula of Ni x Co y Mn 1-x-y (OH)2, wherein 0.8≤x<1, 0<y≤0.1; and / or, 7.The high-nickel single-crystal cathode material according to claim 6, wherein the molar ratio of the metal lithium salt to the high-nickel hydroxide precursor is (1-1.15) :

1. 8.A method for preparing the high-nickel single-crystal cathode material according to any one of claims 1-7, comprising the following steps: S1, mixing a high-nickel hydroxide precursor, a metal lithium salt, and a dopant to obtain a mixture; S2, subjecting the mixture obtained in step S1 to multi-stage sintering at a rising temperature and then at a falling temperature in an oxygen atmosphere to obtain the high-nickel single-crystal cathode material. ​ ​ ​ ​ ​ ​ ​ ​ The dopant is selected from at least one of B2O3, V2O5, MoO3, and the molar ratio of the dopant to the high-nickel hydroxide precursor is (0.5-1):100; The multi-stage sintering comprises the following steps: 2-1) heating from room temperature to 300-500°C at a heating rate of 3-10°C / min, and maintaining for 1-5 hours; 2-2) continuing to heat to 700-850°C at a heating rate of 1-5°C / min, and maintaining for 1-5 hours; 2-3) continuing to heat to 850-985°C at a heating rate of 1-10°C / min, and maintaining for 1-5 hours; 2-4) cooling to 700-850°C at a cooling rate of 1-5°C / min, and maintaining for 1-5 hours; 2-5) cooling to room temperature at a cooling rate of 3-10°C / min; In the multi-stage sintering, a reduced oxygen flow is used from the beginning of the last heating process to the end of the first cooling process before the beginning of the maintaining, and the oxygen flow is reduced to 40-60% of the initial flow; in the multi-stage sintering operation, the initial oxygen flow is 80-200 ml / min.

9. The high-nickel single-crystal cathode material of any one of claims 1-7 or prepared by the preparation method of claim 8, for use in a battery material.

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