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

Abstract

The application discloses a high-nickel single-crystal positive electrode material and a preparation method and application thereof, and belongs to the technical field of lithium ion battery positive electrode materials. A high-nickel hydroxide precursor, lithium hydroxide and a nanoscale metal oxide dopant are mixed and then placed in an oxygen atmosphere, and a high-nickel single-crystal positive electrode material is obtained through staged sintering. Through the staged sintering, the sintering time of the high-temperature stage is shortened, the agglomeration of single-crystal particles is reduced, and the lithium-nickel mixing in the structure of the high-nickel single-crystal positive electrode is relieved. On the basis of the staged sintering, the sintering time of the high-temperature stage is further shortened through the addition of the metal oxide dopant, and the prepared high-nickel single-crystal positive electrode material has excellent electrochemical performance. When the high-nickel single-crystal positive electrode material is used as a lithium ion battery positive electrode material, the first circle discharge capacity of the battery is 193.3-196.4 mAh / g, and the capacity retention rate after 100 circle charge-discharge cycles is 85.8-91.3% (2C).

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] Clean primary energy such as wind energy, water energy and solar energy is difficult to be directly utilized, and generally needs to be converted into secondary energy such as electric energy for practical application, and therefore, it is an important task to construct an efficient energy storage battery system, in which, the related research on lithium ion batteries is most concerned, and a cathode material is an important component in a lithium ion battery, and the capacity and stability of the cathode material have a direct influence on the performance of the lithium ion battery. As one of mainstream lithium battery cathode materials, a layered cathode material has the advantages of high capacity and low cost, and is developing towards high-nickel and low-cobalt.

[0003] The layered cathode material is divided into a polycrystal material and a single-crystal material. The single-crystal layered cathode material has significant advantages compared with the polycrystal layered cathode material. The single-crystal material can effectively alleviate a series of stability problems such as gas production and cracking caused by the increase of Ni content. Compared with the preparation of the polycrystal material, a high sintering temperature is required to ensure the growth of the crystal nucleus for the preparation of the single-crystal material, but the sintering at a too high temperature is easy to cause lithium-nickel mixing, aggravate material agglomeration, and result in the deterioration of the initial capacity and the cycle stability of the material; and insufficient holding time may result in incomplete development of the crystal structure. At present, the synthesis of the reported single-crystal high-nickel cathode material mostly adopts a two-step high-temperature sintering method. For example, a modified single-crystal high-nickel cathode material and a preparation method thereof are disclosed in a Chinese patent document with the publication number CN 116864636 A, but due to the high nucleation temperature and the long sintering time, the synthesized material is obviously agglomerated, and the long sintering time also provides more favorable conditions for the formation and development of defects in the material. The crystal structure defects will affect the electrochemical performance of the material. The lattice distortion may hinder the diffusion of lithium ions, and reduce the charge-discharge efficiency of the material. The grain boundary defects may become a weak link of the material in the cycle process, and easily cause the generation and expansion of micro-cracks, and reduce the cycle stability of the material. Therefore, it is still a big problem to accurately control the sintering temperature, adjust the sintering atmosphere, and optimize the sintering time in the sintering process of the high-nickel single-crystal cathode material, so as to optimize the crystal structure and improve the charge-discharge performance of the material. SUMMARY

[0004] One of the purposes of the application is to provide a high-nickel single-crystal cathode material with high discharge capacity and high cycle stability.

[0005] In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] A preparation method of a high-nickel single-crystal positive electrode material, comprising the following steps: mixing a high-nickel hydroxide precursor, lithium hydroxide and a nanoscale metal oxide dopant, and then placing the mixture in an oxygen atmosphere to obtain the high-nickel single-crystal positive electrode material through staged sintering.

[0007] The staged sintering comprises the following steps:

[0008] heating to 500-550°C at a heating rate of 3-5°C / min, and maintaining the temperature for 5-6h;

[0009] continuing to heat to 800-850°C at a heating rate of 3-5°C / min, and maintaining the temperature for 5-6h;

[0010] continuing to heat to 900-1000°C at a heating rate of 10-15°C / min, and maintaining the temperature for 0.5-3h;

[0011] cooling to 750-800°C at a cooling rate of 3-5°C / min, and maintaining the temperature for 3-5h.

[0012] Further, the molar ratio of metal elements in the high-nickel hydroxide precursor, lithium hydroxide and nanoscale metal oxide dopant is 1:1.03-1.10:0.003-0.008.

[0013] Further, the chemical formula of the high-nickel hydroxide precursor is Ni x Co y Mn z (OH)2, 0.7≤ x <0.8, 0< y ≤0.1, 0< z ≤0.2, x + y + z =1.

[0014] The nanoscale metal oxide dopant is selected from one of MgO, Al2O3, ZrO2, Nb2O3, MoO3 and WO3.

[0015] The second object of the present application is to provide a high-nickel single-crystal positive electrode material prepared by the above preparation method, which has a chemical general formula of LiNi x Co y Mn z M 1-x-y-z O2, wherein M is one of Mg, Al, Zr, Nb, Mo and W, 0.7≤ x <0.8, 0< y ≤0.1, 0<z≤0.2.

[0016] The third object of the present application is to provide an application of the high-nickel single-crystal positive electrode material in a lithium ion battery positive electrode material.

[0017] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0018] (1) The present application discloses a preparation method of a high-nickel single-crystal positive electrode material. The high-nickel hydroxide precursor, lithium hydroxide and nanoscale metal oxide dopant are mixed and then placed in an oxygen atmosphere for step-by-step sintering to obtain the high-nickel single-crystal positive electrode material. The step-by-step sintering includes the following steps: low-temperature section: first, heat to 500-550°C at a heating rate of 3-5°C / min, and keep the temperature for 5-6h; medium-temperature section: continue to heat to 800-850°C at a heating rate of 3-5°C / min, and keep the temperature for 5-6h; high-temperature section: continue to heat to 900-1000°C at a heating rate of 10-15°C / min, and keep the temperature for 0.5-3h; medium-temperature section: cool to 750-800°C at a cooling rate of 3-5°C / min, keep the temperature for 3-5h, and naturally cool to room temperature, and the sintering is completed. The low-temperature section is the stage for the formation of crystal nuclei of the material, and by controlling the sintering temperature and sintering time, the preliminary crystal structure is ensured to be formed quickly; in the medium-temperature section, the crystal nuclei are preliminarily grown by increasing the sintering temperature; in the high-temperature section, the crystal nuclei are rapidly grown into micron single crystals by rapidly heating to 900-1000°C and keeping the temperature for a short time. In the high-temperature section, the crystal particles are prone to adhesion, and the lithium-nickel mixing in the crystal is intensified, so shortening the sintering time in the high-temperature section is the key to reducing the adhesion of the particles, relieving the lithium-nickel mixing, and reducing the internal defects of the material; after the short high-temperature sintering, the temperature is reduced to the medium-temperature section, so that the ions in the bulk phase are rearranged, the lithium-nickel mixing rate is reduced, the crystal structure defects are repaired, the crystallinity and structural integrity of the material are improved, and the overall performance of the material is improved. Compared with the prior art, the high-nickel single-crystal positive electrode material prepared by the above method has good dispersibility, few internal defects, stable crystal structure, and improved electrochemical performance of the crystal.

[0019] 2) The nanoscale metal oxide dopant used in the preparation method of the high-nickel single-crystal positive electrode material disclosed in the present application has the effects of stabilizing the crystal structure of the high-nickel single-crystal positive electrode material and reducing the agglomeration of the material particles. On the basis of step-by-step sintering, using different metal oxide dopants can also produce other different effects. The nanoscale metal oxide doping can improve the thermal decomposition temperature of the high-nickel positive electrode material. After MgO doping, Mg 2+Into the lattice, enhance the chemical bond energy of the material, make the material more difficult to decompose at high temperature, so as to improve the thermal stability of the material, reduce the risk of thermal runaway of the battery in high temperature environment; After the nanoscale metal oxide is doped, the high nickel single crystal positive electrode material will cause slight distortion of the crystal lattice, and the distortion can inhibit the lattice change of the high nickel positive electrode material in the charging and discharging process, and maintain the stability of the layered structure (such as Al2O3); After zirconium oxide (ZrO2) is doped, a dense zirconium oxide film will be formed on the surface of the material, which can prevent the positive electrode material from directly contacting with the electrolyte and inhibit the interface side reaction, such as decomposition of electrolyte, dissolution of transition metal ions and the like, thereby improving the cycle stability and service life of the material; Some nanoscale metal oxides have good electrical conductivity, and after being doped, they can form a conductive network in the high nickel positive electrode material, improve the electronic conductivity of the material, make the electrode reaction more efficient, and help to improve the charge and discharge efficiency and rate performance of the material (such as Nb2O3); The high nickel positive electrode material is easy to lose lattice oxygen under high pressure, which leads to structure collapse, and after using WO3 doping, W 6+ Can form a strong chemical bond with oxygen ions, stabilize the lattice oxygen, reduce the release of oxygen, and thus maintain the integrity of the material structure.

[0020] 3) The preparation method of the high nickel single crystal positive electrode material provided by the application shortens the sintering time at high temperature, reduces energy consumption and damage to equipment and requirements; The high nickel single crystal positive electrode material synthesized by the application has high particle dispersity, few internal defects and stronger structural stability, and when used as a positive electrode material of a lithium ion battery, the first circle discharge capacity of the battery is 193.3-196.4 mAh / g, and the capacity retention rate after 100 cycles of charge and discharge cycles at 2.0 C is 85.8-91.3%. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 respectively, are SEM images of the high nickel single crystal positive electrode material obtained in example 1;

[0022] Figure 2 respectively, are SEM images of the high nickel single crystal positive electrode material obtained in example 2;

[0023] Figure 3 respectively, are SEM images of the high nickel single crystal positive electrode material obtained in example 3;

[0024] Figure 4 respectively, are SEM images of the high nickel single crystal positive electrode material obtained in example 4;

[0025] Figure 5 respectively, are SEM images of the high nickel single crystal positive electrode material obtained in example 5;

[0026] Figure 6 respectively, are SEM images of the high nickel single crystal positive electrode material obtained in example 6;

[0027] Figure 7 SEM image of high-nickel single-crystal cathode material obtained from Example 7;

[0028] Figure 8 SEM image of high-nickel single-crystal cathode material obtained from Comparative Example 1;

[0029] Figure 9 SEM image of high-nickel single-crystal cathode material obtained from Comparative Example 2;

[0030] Figure 10 SEM image of high-nickel single-crystal cathode material obtained from Comparative Example 3;

[0031] Figure 11 SEM image of high-nickel single-crystal cathode material obtained from Comparative Example 4;

[0032] Figure 12 XRD image of high-nickel single-crystal cathode material obtained from Example 1 and Comparative Example 1;

[0033] Figure 13 Cycle performance image of high-nickel single-crystal cathode material obtained from Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0034] The present application will be further described in conjunction with the accompanying drawings and specific examples so that those skilled in the art can better understand and implement the present application, but the protection scope of the present application is not limited thereto. The reagents and raw materials used in the examples of the present application are commercially available unless otherwise specified, and the high-nickel hydroxide precursor used in the present application is purchased from Shenzhen Youyan Technology Co., Ltd.; other drugs and reagents are purchased from Aladdin and National Pharmaceutical Reagent Network. Example 1

[0035] Preparation of high-nickel single-crystal cathode material:

[0036] S1) Mixing: high-nickel hydroxide precursor Ni 0.70 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH and nanoscale metal oxide dopant MgO (30-50 nm) were mixed in a molar ratio of 1:1.07:0.005, and the materials were initially mixed with a three-dimensional mixer, and then further uniformly mixed with a planetary ball mill at a rotation speed of 500 rpm for 6 h to obtain the mixed materials.

[0037] S2) sintering: the mixture obtained in step S1 is placed in an oxygen furnace, the oxygen flow is the normal value 100 mL / min, the oxygen furnace is first heated to 550°C at a heating rate of 3°C / min, and then heated to 850°C at a heating rate of 3°C / min, and then heated to 970°C at a heating rate of 10°C / min, and then heated to 800°C at a heating rate of 3°C / min, and then naturally cooled to room temperature, to obtain a magnesium-doped high-nickel single-crystal positive electrode material A.

[0038] By Figure 1 It can be seen that the particle size of the obtained high-nickel single-crystal positive electrode material is 2-5 μm, and the dispersion is good and the agglomeration is less. It shows that the magnesium-doped multi-stage sintering method has a positive effect on the morphology of the high-nickel single-crystal positive electrode, improves the particle agglomeration and adhesion, is conducive to maintaining the particle integrity of the positive electrode sheet during preparation and testing, inhibits the generation of cracks, and improves the cycle stability. At the same time, the XRD pattern of Figure 12 It can be seen that the obtained high-nickel single-crystal positive electrode material has low lithium-nickel mixing degree (I(003) / I(104)=1.5>1.2). Example 2

[0039] Compared with Example 1, different amounts of lithium salt compounds are added, and a high-nickel single-crystal positive electrode material is prepared by a multi-stage sintering method, and the preparation process includes the following steps:

[0040] S1) mixing: high-nickel hydroxide precursor Ni 0.75 Co 0.1 Mn 0.15 (OH)2, lithium hydroxide LiOH and nano-sized metal oxide dopant MgO (30-50 nm) are mixed in a molar ratio of 1:1.10:0.005, and the mixture is first mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a speed of 500 rpm for 6 h to obtain a mixture.

[0041] S2) sintering: the mixture obtained in step S1 is placed in an oxygen furnace, the oxygen flow is the normal value 100 mL / min, the oxygen furnace is first heated to 550°C at a heating rate of 3°C / min, and then heated to 800°C at a heating rate of 3°C / min, and then heated to 970°C at a heating rate of 10°C / min, and then heated to 800°C at a heating rate of 3°C / min, and then naturally cooled to room temperature, to obtain a magnesium-doped high-nickel single-crystal positive electrode material B.

[0042] By Figure 2 It can be seen that the particle size of the obtained high-nickel single-crystal positive electrode material is 2-8 μm, and the dispersion is good and the agglomeration is less. Example 3

[0043] Compared with Example 1, a high-nickel single-crystal cathode material was prepared using a lower end temperature and a segmented sintering method, and the preparation process included the following steps.

[0044] S1) Mixing: high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH, and nanoscale metal oxide dopant MgO (30-50 nm) were mixed in a molar ratio of 1:1.07:0.005, and the materials were first mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a speed of 500 rpm for 6 h to obtain the mixed materials.

[0045] S2) Sintering: The mixed materials obtained in step S1 were placed in an oxygen furnace with an oxygen flow of 100 mL / min, and the oxygen furnace was first heated to 500°C at a rate of 5°C / min, and then heated to 850°C at a rate of 5°C / min, and then heated to 900°C at a rate of 10°C / min, and then cooled to 750°C at a rate of 5°C / min, and then naturally cooled to obtain the magnesium-doped high-nickel single-crystal cathode material C.

[0046] By Figure 3 It can be seen that the particle size of the obtained high-nickel single-crystal cathode material is 1-5 μm. Example 4

[0047] Compared with Example 1, a high-nickel single-crystal cathode material was prepared using a higher end temperature and a segmented sintering method, and the preparation process included the following steps.

[0048] S1) Mixing: high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH, and nanoscale metal oxide dopant MgO (30-50 nm) were mixed in a molar ratio of 1:1.07:0.005, and the materials were first mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a speed of 500 rpm for 6 h to obtain the mixed materials.

[0049] S2) Sintering: the mixture obtained in step S1 is placed in an oxygen furnace, the oxygen flow is the normal value 100 mL / min, the oxygen furnace is first heated to 550°C at a heating rate of 4°C / min, and then heated to 850°C at a heating rate of 4°C / min, and then heated to 1000°C at a heating rate of 15°C / min, and then heated to 775°C at a heating rate of 4°C / min, and then naturally cooled to obtain a magnesium-doped high-nickel single-crystal positive electrode material D.

[0050] By Figure 4 It can be seen that the obtained high-nickel single-crystal positive electrode material has a particle size of 2-5 μm and is well dispersed with little agglomeration. Example 5

[0051] Compared with Example 1, different proportions of MgO are used to prepare a high-nickel single-crystal positive electrode material using a step-sintering method, and the preparation process includes the following steps.

[0052] S1) Mixing: high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH and nanoscale metal oxide dopant MgO (30-50 nm) are mixed in a molar ratio of 1:1.07:0.005, and the mixture is first mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a speed of 500 rpm for 6 h to obtain a mixture.

[0053] S2) Sintering: the mixture obtained in step S1 is placed in an oxygen furnace, the oxygen flow is the normal value 100 mL / min, the oxygen furnace is first heated to 550°C at a heating rate of 4°C / min, and then heated to 850°C at a heating rate of 4°C / min, and then heated to 1000°C at a heating rate of 15°C / min, and then heated to 775°C at a heating rate of 4°C / min, and then naturally cooled to obtain a magnesium-doped high-nickel single-crystal positive electrode material D.

[0054] By Figure 5 It can be seen that the obtained high-nickel single-crystal positive electrode material has a particle size of 2-5 μm and is well dispersed with little agglomeration. Example 6

[0055] Compared with Example 1, different proportions of MgO are used to prepare a high-nickel single-crystal positive electrode material using a step-sintering method, and the preparation process includes the following steps.

[0056] S1) Mixing: high-nickel hydroxide precursor Ni 0.7 Co0.1 Mn 0.2 LiOH and nano-sized metal oxide dopant WO3(30-50 nm) were mixed in a molar ratio of 1:1.07:0.005, the materials were initially mixed by a three-dimensional mixer, and then the initially mixed materials were further uniformly mixed by a planetary ball mill at a rotation speed of 500 rpm for 6 h to obtain the mixed materials.

[0057] S2) Sintering: the mixed materials obtained in step S1 were placed in an oxygen furnace, the oxygen flow was the normal value of 100 mL / min, the oxygen furnace was first heated to 550°C at a heating rate of 3°C / min, and then kept for 5 h, then heated to 850°C at a heating rate of 3°C / min, and kept for 5 h, then increased to 970°C at a heating rate of 10°C / min, and kept for 3 h, then decreased to 800°C at a heating rate of 3°C / min, and kept for 5 h, and then naturally cooled to obtain the tungsten-doped high-nickel single-crystal positive electrode material F.

[0058] From Figure 6 It can be seen that the obtained high-nickel single-crystal positive electrode material has a particle size of 1-5 μm and is well dispersed with little agglomeration. Example 7

[0059] Compared with Example 1, a different metal oxide dopant was used, and a high-nickel single-crystal positive electrode material was prepared by using a segmented sintering method, and the preparation process included the following steps.

[0060] S1) Mixing: high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 LiOH and nano-sized metal oxide dopant ZrO2(10-20 nm) were mixed in a molar ratio of 1:1.07:0.005, the materials were initially mixed by a three-dimensional mixer, and then the initially mixed materials were further uniformly mixed by a planetary ball mill at a rotation speed of 500 rpm for 6 h to obtain the mixed materials.

[0061] S2) Sintering: the mixed materials obtained in step S1 were placed in an oxygen furnace, the oxygen flow was the normal value of 100 mL / min, the oxygen furnace was first heated to 550°C at a heating rate of 3°C / min, and then kept for 5 h, then heated to 850°C at a heating rate of 3°C / min, and kept for 5 h, then increased to 970°C at a heating rate of 10°C / min, and kept for 2 h, then decreased to 800°C at a heating rate of 3°C / min, and kept for 3 h, and then naturally cooled to obtain the zirconium-doped high-nickel single-crystal positive electrode material G.

[0062] From Figure 7It can be seen that the obtained high-nickel single-crystal positive electrode material has a particle size of 1-5 pm and is well dispersed with little agglomeration. Example 8

[0063] Compared with Example 1, a high-nickel single-crystal positive electrode material is prepared by using a different metal oxide dopant and a segmented sintering method. The preparation process includes the following steps.

[0064] S1) Mixing: high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH, and nanoscale metal oxide dopant Al2O3 (10-20 nm) are mixed in a molar ratio of 1:1.07:0.005. The materials are initially mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a rotation speed of 500 rpm for 6 h to obtain a mixed material.

[0065] S2) Sintering: the mixed material obtained in step S1 is placed in an oxygen furnace with an oxygen flow of 100 mL / min. The oxygen furnace is first heated to 550°C at a heating rate of 3°C / min, and then heated to 800°C at a heating rate of 3°C / min, and then heated to 970°C at a heating rate of 10°C / min, and then heated to 800°C at a heating rate of 3°C / min, and then naturally cooled to obtain an aluminum-doped high-nickel single-crystal positive electrode material H. Comparative Example 1

[0066] Compared with Example 1, a high-nickel single-crystal positive electrode material is prepared by using a micron-scale metal oxide dopant and a segmented sintering method. The preparation process includes the following steps:

[0067] S1) Mixing: high-nickel hydroxide precursor Ni 0.70 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH, and micron-scale metal oxide dopant MgO (1-10 pm) are mixed in a molar ratio of 1:1.07:0.005. The materials are initially mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a rotation speed of 500 rpm for 6 h to obtain a mixed material.

[0068] S2) sintering: the mixture obtained in step S1 was placed in an oxygen furnace, the oxygen flow was the normal value of 100 mL / min, the oxygen furnace was first heated to 550 °C at a heating rate of 3 °C / min, and then heated to 850 °C at a heating rate of 3 °C / min, and then heated to 970 °C at a heating rate of 10 °C / min, and then heated to 800 °C at a heating rate of 3 °C / min, and then naturally cooled to obtain a magnesium-doped high-nickel single-crystal positive electrode material I.

[0069] By Figure 8 It can be seen that due to the use of micron-sized metal oxide dopant, the obtained high-nickel single-crystal positive electrode material particles appear to be agglomerated, which is due to the use of micron-sized metal oxide with larger size, under the same mixing conditions, the mixture is not uniform, resulting in that under the same sintering conditions, lithium-nickel mixing cannot be effectively reduced, thereby reducing the formation of surface residual alkali, and thus the material is more prone to agglomeration. By Figure 12 The XRD pattern of the obtained high-nickel single-crystal positive electrode material can be seen that the degree of lithium-nickel mixing is high (I (003) / I (104) =1.19<1.2). Comparative Example 2

[0070] Compared with Example 1, the low-temperature sintering temperature was increased to prepare a high-nickel single-crystal positive electrode material, and the preparation process comprises the following steps:

[0071] S1) mixing: high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH and nanoscale metal oxide dopant MgO (30-50 nm) were mixed in a molar ratio of 1:1.07:0.005, the mixture was first mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a rotation speed of 500 rpm for 6 h to obtain a mixture.

[0072] S2) sintering: the mixture obtained in step S1 was placed in an oxygen furnace, the oxygen flow was the normal value of 100 mL / min, the oxygen furnace was first heated to 550 °C at a heating rate of 3 °C / min, and then heated to 850 °C at a heating rate of 3 °C / min, and then heated to 970 °C at a heating rate of 10 °C / min, and then heated to 800 °C at a heating rate of 3 °C / min, and then naturally cooled to obtain a magnesium-doped high-nickel single-crystal positive electrode material I.

[0073] By Figure 9It can be seen that, compared with Example 1, the low-temperature sintering temperature is increased to 700°C, which forms more initial crystal nuclei, and under the same sintering conditions, the obtained high-nickel single-crystal positive electrode material particles are smaller in diameter and are obviously agglomerated, and cannot obtain single-crystal morphology. Comparative Example 3

[0074] Compared with Example 1, the high-nickel single-crystal positive electrode material is prepared without using staged sintering, and the preparation process comprises the following steps.

[0075] S1) Mixing: high-nickel hydroxide precursor Ni 0.70 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH and nanoscale metal oxide dopant MgO (30-50 nm) are mixed in a molar ratio of 1:1.07:0.005, the materials are first preliminarily mixed by using a three-dimensional mixer, and then the preliminarily mixed materials are further uniformly mixed by using a planetary ball mill, the rotating speed is set to 500 rpm, and the mixing time is 6 h, to obtain mixed materials.

[0076] S2) Sintering: the mixed materials obtained in step S1 are placed in an oxygen furnace, the oxygen flow is the normal value 100 mL / min, the oxygen furnace is first heated to 850°C at a heating rate of 3°C / min, and then held for 15 h, and naturally cooled to obtain magnesium-doped high-nickel single-crystal positive electrode material K.

[0077] From Figure 10 It can be seen that, compared with Example 1, the high-temperature sintering time is longer without using staged sintering, and the too long sintering time leads to obvious agglomeration of the obtained material particles. Comparative Example 4

[0078] Compared with Example 1, the high-nickel single-crystal positive electrode material is prepared by using a staged sintering method by increasing the high-temperature sintering temperature, and the preparation process comprises the following steps.

[0079] S1) Mixing: high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH and nanoscale metal oxide dopant MgO (30-50 nm) are mixed in a molar ratio of 1:1.07:0.005, the materials are first preliminarily mixed by using a three-dimensional mixer, and then the preliminarily mixed materials are further uniformly mixed by using a planetary ball mill, the rotating speed is set to 500 rpm, and the mixing time is 6 h, to obtain mixed materials.

[0080] S2) Sintering: The mixture obtained in step S1 was placed in an oxygen furnace with a normal oxygen flow of 100 mL / min. The oxygen furnace was first heated to 550°C at a heating rate of 4°C / min, and then held for 5 h. The temperature was then increased to 850°C at a heating rate of 4°C / min, and then held for 5 h. The temperature was then increased to 1100°C at a heating rate of 15°C / min, and then held for 0.5 h. The temperature was then decreased to 750°C at a heating rate of 4°C / min, and then held for 4 h. The temperature was then naturally decreased to obtain a magnesium-doped high-nickel single-crystal positive electrode material L.

[0081] By Figure 11 It can be seen that, due to the high sintering temperature in the high-temperature stage, although the sintering time in the high-temperature stage is shortened, the sintering temperature is too high, and the material agglomeration is intensified during the sintering process. Finally, the obtained high-nickel single-crystal positive electrode material is agglomerated into spherical particles, instead of a single-crystal morphology. Comparative Example 5

[0082] Compared with Example 1, the sintering temperature in the high-temperature stage is increased, the sintering time in the high-temperature stage is shortened, and a high-nickel single-crystal positive electrode material is prepared by using a stepwise sintering method. The preparation process includes the following steps.

[0083] S1) Mixing: A high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2, lithium hydroxide LiOH and nanoscale metal oxide dopant MgO (30-50 nm) were mixed in a molar ratio of 1:1.07:0.005. The mixture was first mixed by a three-dimensional mixer, and then further uniformly mixed by a planetary ball mill at a rotation speed of 500 rpm for 6 h to obtain a mixed material.

[0084] S2) Sintering: The mixture obtained in step S1 was placed in an oxygen furnace with a normal oxygen flow of 100 mL / min. The oxygen furnace was first heated to 550°C at a heating rate of 4°C / min, and then held for 5 h. The temperature was then increased to 850°C at a heating rate of 4°C / min, and then held for 5 h. The temperature was then increased to 1100°C at a heating rate of 15°C / min, and then held for 0.5 h. The temperature was then decreased to 750°C at a heating rate of 4°C / min, and then held for 4 h. The temperature was then naturally decreased to obtain a magnesium-doped high-nickel single-crystal positive electrode material L. Comparative Example 6

[0085] Compared with Example 1, the sintering time in the low-temperature stage is extended, and a high-nickel single-crystal positive electrode material is prepared by using a stepwise sintering method. The preparation process includes the following steps.

[0086] S1) Mixing: A high-nickel hydroxide precursor Ni 0.7 Co 0.1 Mn0.2 The high-nickel single-crystal cathode material N was prepared by using the doping agent MgO (30-50 nm) and the lithium salt compound LiOH in a molar ratio of 1:1.07:0.005. The mixture was first mixed by a three-dimensional mixer and then further mixed by a planetary ball mill at a speed of 500 rpm for 6 h.

[0087] S2) Sintering: The mixture obtained in step S1 was placed in an oxygen furnace with a normal oxygen flow of 100 mL / min. The oxygen furnace was first heated to 550 °C at a rate of 3 °C / min, and then kept at 550 °C for 8 h. Then, the temperature was increased to 850 °C at a rate of 3 °C / min, and kept at 850 °C for 5 h. Subsequently, the temperature was increased to 970 °C at a rate of 10 °C / min, and kept at 970 °C for 0.5 h. Then, the temperature was decreased to 800 °C at a rate of 3 °C / min, and kept at 800 °C for 3 h. Finally, the temperature was naturally cooled to room temperature to obtain the magnesium-doped high-nickel single-crystal cathode material N. Comparative Example 7

[0088] In comparison with Example 1, the high-nickel single-crystal cathode material was prepared by using a step-sintering method without using a doping agent. The preparation process included the following steps.

[0089] S1) Mixing: The high-nickel hydroxide precursor Ni 0.70 Co 0.1 Mn 0.2 The high-nickel single-crystal cathode material O was prepared by mixing the high-nickel hydroxide precursor Ni

[0090] S2) Sintering: The mixture obtained in step S1 was placed in an oxygen furnace with a normal oxygen flow of 100 mL / min. The oxygen furnace was first heated to 550 °C at a rate of 3 °C / min, and then kept at 550 °C for 5 h. Then, the temperature was increased to 850 °C at a rate of 3 °C / min, and kept at 850 °C for 5 h. Subsequently, the temperature was increased to 970 °C at a rate of 10 °C / min, and kept at 970 °C for 1 h. Then, the temperature was decreased to 800 °C at a rate of 3 °C / min, and kept at 800 °C for 3 h. Finally, the temperature was naturally cooled to room temperature to obtain the high-nickel single-crystal cathode material O.

[0091] Electrochemical performance test

[0092] The high-nickel single-crystal cathode materials prepared in Examples 1-8 and Comparative Examples 1-7 were tested for electrochemical performance in a button cell CR2032, including first-cycle charge-discharge test and charge-discharge cycle test.

[0093] Battery assembly process: the examples and comparative examples were mixed according to the mass ratio of positive active material: conductive carbon: binder PVDF 90:5:5, the positive electrode slurry viscosity was adjusted with solvent N-methyl pyrrolidone (NMP), the slurry was uniformly coated on aluminum foil, and dried in a vacuum oven for 12 h, the temperature was set to 120°C; the dried electrode was rolled, and the coated aluminum foil was cut into 12 mm diameter discs with a slicer, and transferred into a glove box to assemble the battery, the atmosphere in the glove box was maintained at O2<0.1 ppm, H2O<0.1 ppm; lithium metal as the negative electrode, electrolyte was 1M LiPF6 solution, solvent was EC / DMC / EMC (volume ratio 1:1:1). The assembled button cell needed to be left for 4h, and then electrochemical test was carried out after the electrolyte was fully soaked.

[0094] Electrochemical test: first cycle charge-discharge test, voltage range 2.8~4.5V, rate 0.1C; charge-discharge cycle test, voltage range 2.8~4.5V; rate 2.0C. The results are as follows in Table 1:

[0095]

[0096] From Table 1 and Figure 13 It can be seen that the magnesium-doped example 1 has a high first cycle discharge capacity of 194.3 mAhg -1 , and the first cycle coulombic efficiency is 87.9%; the first cycle discharge capacity of comparative example 1 is 185.8 mAhg -1 ; the first cycle coulombic efficiency is 86.4%; it shows that the high-nickel single-crystal positive electrode material prepared in example 1 of the present application has higher first cycle discharge capacity and initial coulombic efficiency.

[0097] 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 91.3% after 100 cycles of charging and discharging, which is because the material obtained by using the segmented sintering method combined with metal element doping has less agglomeration, low lithium-nickel mixing degree, complete and stable structure. Similarly, it can be seen from the above table that the high-nickel single-crystal positive electrode materials obtained by the embodiments 2-8 have better cycle stability and discharge capacity than the comparative examples 1-6. The micron-sized metal oxide dopant is used in the high-nickel single-crystal positive electrode material of the comparative example 1, and the capacity retention rate of the battery is 69.3% after 100 cycles, which is mainly because the micron-sized metal oxide dopant particles are too large, resulting in poor mixing effect, and the uniform and effective doping in the sintering process cannot be achieved to stabilize the crystal structure of the high-nickel single-crystal positive electrode material, and the effect of improving and enhancing the electrochemical performance of the material is poor; the nucleation temperature in the low-temperature stage of the comparative example 2 is too high and the nucleation time in the low-temperature stage of the comparative example 6 is too long, which increases the number of crystal nuclei and leads to small particle diameter and obvious agglomeration; the segmented sintering is not used in the comparative example 3 and the sintering temperature in the high-temperature stage is too high in the comparative example 4, both of which lead to obvious agglomeration of the material, so that the initial discharge capacity and cycle stability are lower than those of the embodiments; the higher temperature is used in the high-temperature stage of the comparative example 5, although the sintering time is shortened, but the agglomeration leads to obvious agglomeration of the material, which affects its performance. The comparative example 7 does not use a dopant, so the doping of the material cannot be achieved in the sintering process, thus the structure cannot be effectively stabilized, and the agglomeration of the material cannot be reduced, thus the performance of the material is poor.

[0098] The segmented sintering technology assisted by doping reduces the lithium-nickel mixing ratio of the synthesized high-nickel single-crystal positive electrode material, regulates the regular growth of the crystal of the high-nickel single-crystal positive electrode material, improves the particle agglomeration of the high-nickel single crystal, stabilizes the crystal structure of the high-nickel single crystal, and improves the electrochemical performance of the high-nickel single-crystal positive electrode material.

[0099] The present application has been described in detail in the foregoing with 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 ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection 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 method for preparing a high-nickel single-crystal cathode material, characterized in that, It comprises the following steps: A high-nickel hydroxide precursor, lithium hydroxide and a nanoscale metal oxide dopant are mixed and then placed in an oxygen atmosphere to obtain a high-nickel single-crystal positive electrode material by stage sintering; the chemical formula of the high-nickel hydroxide precursor is Ni x Co y Mn z (OH)2, 0.7≤ x <0.8, 0< y ≤0.1, 0< z ≤0.2, x + y + z =1; the stage sintering step is: Rising to 500-550°C at a temperature rising speed of 3-5°C / min, and keeping for 5-6h; Continuing to rise to 800-850°C at a temperature rising speed of 3-5°C / min, and keeping for 5-6h; Continuing to rise to 900-1000°C at a temperature rising speed of 10-15°C / min, and keeping for 0.5-3h; Lowering to 750-800°C at a temperature lowering speed of 3-5°C / min, and keeping for 3-5h; The nanoscale metal oxide dopant is selected from one of MgO, Al2O3, ZrO2 and WO3; The molar ratio of the metal elements in the high-nickel hydroxide precursor, lithium hydroxide and nanoscale metal oxide dopant is 1:1.03-1.10:0.003-0.

008.

2. The high nickel single-crystal cathode material prepared by the preparation method according to claim 1, characterized in that, The high-nickel single-crystal cathode material has a chemical formula of LiNi x Co y Mn z M 1-x-y-z O2, wherein M is one of Mg, Al, Zr, and W, 0.7≤ x <0.8, 0< y ≤0.1, 0< z ≤0.

2.

3. The high nickel single-crystal cathode material of claim 2, wherein, The high-nickel single-crystal positive electrode material is applied to a lithium ion battery positive electrode material.

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