Modified high-nickel ternary monocrystalline positive electrode material and preparation method therefor, lithium-ion battery, and electric device

Abstract

The present application discloses a modified high-nickel ternary monocrystalline positive electrode material and a preparation method therefor, a lithium-ion battery, and an electric device. The modified high-nickel ternary monocrystalline positive electrode material comprises a high-nickel ternary monocrystalline positive electrode material matrix, the bulk phase of the matrix is doped with Co and Al, and the surface of the matrix is coated with a coating layer containing Co, Al, and Ni. From the coating layer to the bulk phase, the content of Co and the content of Al gradually decrease, and the content of Ni gradually increases.

Description

Modified high-nickel ternary single-crystal cathode material, preparation method thereof, lithium ion battery and electric device

[0001] Related Applications

[0002] The present application claims priority to the Chinese patent application No. 202411289070.3, filed on September 14, 2024, entitled "Modified high-nickel ternary single-crystal cathode material, preparation method thereof, lithium ion battery and electric device", the contents of which are hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application belongs to the field of lithium ion batteries, and particularly relates to a modified high-nickel ternary single-crystal cathode material, a preparation method thereof, a lithium ion battery and an electric device. BACKGROUND

[0004] High-nickel ternary materials have become the main development direction of ternary cathode materials due to their advantages of high energy density and high discharge capacity. However, compared with low-nickel cathode materials, the high-nickel cathode materials have poor thermal stability and cycle performance due to the strong oxidation of high-valence Ni 4+ . In addition, the impurities of lithium carbonate and lithium hydroxide are difficult to control during the synthesis and storage of high-nickel cathode materials, resulting in high residual alkali on the surface of the material, which is not conducive to the production of batteries.

[0005] In order to overcome the above problems, researchers currently conduct research in the directions of material bulk optimization, material structure regulation, and material surface / interface optimization. For example, the patent application with publication No. CN 110224124 A reports a Co-Al active material coated nickel-cobalt-manganese ternary layered cathode material and a preparation method thereof. The patent first disperses the nickel-cobalt-manganese ternary cathode material precursor in an ethanol aqueous solvent to obtain dispersion liquid I, then adds a cobalt salt and an aluminum salt to obtain dispersion liquid II; subsequently, an alkali is added to dispersion liquid II, heated and stirred to react to generate a Co-Al layered double hydroxide precursor material; finally, the material is mixed with a lithium source and calcined to prepare a Co-Al active material coated nickel-cobalt-manganese ternary layered cathode material. The above wet coating method has problems of solvent selection and concentration regulation, and the synthesis process is complex and the production cost is high; and the Co-Al layered double hydroxide precursor material and the lithium source are mixed and sintered, which cannot control the lithium carbonate and lithium hydroxide impurities during the reaction process, cannot reduce the residual alkali on the surface of the material, and the electrochemical performance needs to be improved. SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the deficiencies and defects mentioned in the above background, and to provide a modified high-nickel ternary single-crystal cathode material, a preparation method thereof, a lithium ion battery and an electric device.

[0007] To solve the above technical problems, the technical solution proposed by the present application is:

[0008] The embodiment of the present application provides a modified high-nickel ternary single-crystal positive electrode material, which comprises a high-nickel ternary single-crystal positive electrode material base, Co elements and Al elements are doped in the bulk phase of the base, a coating layer containing Co, Al and Ni elements is coated on the surface of the base, and the content of the Ni elements gradually increases and the content of the Co elements and the Al elements gradually decreases from the surface coating layer to the bulk phase.

[0009] In some examples, the modified high-nickel ternary single-crystal positive electrode material is a spherical particle, the modified high-nickel ternary single-crystal positive electrode material is divided into three regions by EPMA analysis from the surface of the spherical particle to the center of the spherical particle, wherein the region with a distance of 0≤L≤180 nm from the surface of the spherical particle is the first region, the region with a distance of 180 nm

[0010] The element concentration referred to in the present application is measured by EPMA (Electron Probe X-ray Microanalyzer) with a field of view of 43000 times and a 2.998*10 -8 The current of A is measured under the measurement conditions of a voltage of 20 KV and a beam diameter of 400 μm.

[0011] In some examples, the modified high-nickel ternary single-crystal positive electrode material is a spherical particle, the modified high-nickel ternary single-crystal positive electrode material is divided into three regions by EPMA analysis from the surface of the spherical particle to the center of the spherical particle, wherein the region with a distance of 0≤L≤180 nm from the surface of the spherical particle is the first region, the region with a distance of 180 nm

[0012] In some examples, the modified high-nickel ternary single-crystal positive electrode material is a spherical particle, the modified high-nickel ternary single-crystal positive electrode material is divided into three regions by EPMA analysis from the surface of the spherical particle to the center of the spherical particle, wherein the region with a distance of 0≤L≤180 nm from the surface of the spherical particle is the first region, the region with a distance of 180 nm

[0013] The first region is the surface of the single crystal particle, the second region is the near interior of the single crystal particle, and the third region is the interior of the particle. From the first region to the third region, the coated Co and Al materials and the Ni element in the high-nickel single crystal positive electrode material matrix mutually diffuse, and the Co element reacts with the residual lithium on the surface during the sintering process, while reducing the surface Ni content, thereby forming a concentration gradient phenomenon. From the particle surface coating layer to the interior, the Co content decreases, the Ni content increases, and the Al content decreases. Not only does this effectively reduce the residual lithium on the surface of the high-nickel material, but the formation of the layered Co-rich coating layer on the surface is also conducive to improving the ion diffusion coefficient of the material surface and reducing the DCR. In addition, the reduction of the surface Ni content and the increase of the Al element are conducive to improving the stability of the material surface. The distribution of each doping element in the third region is uniform, which is conducive to stabilizing the lattice structure of the high-nickel single crystal positive electrode material. The high Ni content in the interior is conducive to improving the capacity and energy density of the material. The introduction of the Co element can reduce the irreversible capacity and energy loss, improve the Li + diffusion coefficient, thereby improving the cycle stability of the high-nickel positive electrode material. In addition, the doping of the Al element is also conducive to improving the stability of the high-nickel positive electrode material. Through the synergistic doping effect of the three elements, the overall performance of the material can be maximized.

[0014] In some examples, the modified high-nickel ternary single crystal positive electrode material has a chemical formula of LiNi x Co y Mn 1-x-y M z O2, wherein 0.8≤x<1, 0≤y<1, and 0≤z<1, and M is one or more of Ti, Mg, Zr, W, and Sr.

[0015] Based on the overall inventive concept, the application also provides a preparation method of the modified high-nickel ternary single crystal positive electrode material, which comprises the following steps:

[0016] (1) mixing and sintering a nickel-cobalt-manganese hydroxide precursor, a lithium salt, and a M-containing compound to obtain a matrix material, wherein M is one or more of Ti, Mg, Zr, W, and Sr;

[0017] (2) mixing the matrix material with a coating agent and then sintering to obtain a modified high-nickel ternary single crystal positive electrode material, wherein the coating agent comprises a Co-containing compound and an Al-containing compound.

[0018] The application can realize that Co and Al partially enter the body phase and partially form a uniform coating layer on the surface of the material by one-time coating. At the same time, the coating material and Ni in the high-nickel layered oxide inter-diffuse, and reacts with the residual lithium on the surface during the sintering process, which can not only significantly reduce the residual lithium on the surface of the material, but also reduce the content of Ni on the surface of the material, thereby forming a concentration gradient distribution of Co, Al and Ni, which plays a synergistic effect of doping to improve the crystal structure and coating to improve the stability of the material. The prepared modified high-nickel ternary single-crystal positive electrode material can significantly improve the first charge-discharge capacity, capacity and coulombic efficiency of the material, and can improve the high-temperature cycle and high-temperature DCR growth of the material to some extent.

[0019] In some examples, the preparation method of the modified high-nickel ternary single-crystal positive electrode material, in step (1), the sintering is performed in an oxygen atmosphere, first heated to 300-500℃ at a heating rate of 1-3℃ / min for 1-5h, then continuously heated to 750-970℃ for 6-15h, and naturally cooled to room temperature to obtain the base material.

[0020] In some examples, the preparation method of the modified high-nickel ternary single-crystal positive electrode material, in step (2), the Co-containing compound is selected from one or more of Co(OH)2, CoOOH, CoO, Co3O4 and (CH3CO2)2Co, and the Al-containing compound is selected from one or more of Al2O3, Al(OH)3 and AlOOH.

[0021] In some examples, the preparation method of the modified high-nickel ternary single-crystal positive electrode material, in step (2), the molar ratio of the base material to the coating agent is 1:0.001-0.06.

[0022] In some examples, the preparation method of the modified high-nickel ternary single-crystal positive electrode material, in step (2), the sintering is gradient sintering, first heated from room temperature to 200-400℃ at a heating rate of 1-3℃ / min and kept for 1-6h, then heated to 600-775℃ at a rate of 0.5-3℃ / min and kept for 6-10h.

[0023] Based on one general inventive concept, the application further provides a lithium ion battery comprising the modified high-nickel ternary single-crystal positive electrode material or comprising the modified high-nickel ternary single-crystal positive electrode material prepared by the preparation method.

[0024] Based on one general inventive concept, the application further provides an electric device comprising the lithium ion battery.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] (1) The modified high-nickel ternary single-crystal positive electrode material of the present application comprises a high-nickel ternary single-crystal positive electrode material substrate, the substrate is doped with Co and Al elements in the bulk phase, and the surface of the substrate is coated with a coating layer containing Co, Al and Ni elements. From the surface coating layer to the bulk phase, the content of Co and Al elements gradually decreases, and the content of Ni element gradually increases, which can significantly improve the first charge / discharge capacity and coulombic efficiency, and can improve the high-temperature cycle and high-temperature DCR growth of the material to a certain extent.

[0027] (2) In the modified high-nickel ternary single-crystal positive electrode material substrate of the present application, part of the surface layer Ni diffuses to the bulk phase, and at the same time, part of the Co and Al in the coating layer diffuses to the bulk phase, which reduces the Ni content of the surface layer of the high-nickel material and forms a concentration gradient material, thereby improving the stability of the material surface.

[0028] (3) In the modified high-nickel ternary single-crystal positive electrode material substrate of the present application, part of the surface layer Ni diffuses to the bulk phase, and at the same time, part of the Co and Al in the coating layer diffuses to the bulk phase, which plays a synergistic role of improving the crystal structure by doping and improving the stability of the material by coating.

[0029] (4) The present application utilizes the reaction of Co with residual lithium on the surface to form a Co-rich coating layer, which can significantly reduce the residual lithium on the surface of the high-nickel material. The residual lithium value can be reduced by about 39.8-72.3%, and the Li / Ni mixing degree can be reduced by about 2%-35%, indicating that the material has good stability.

[0030] (5) The rate of the button cell prepared by using the modified high-nickel ternary single-crystal positive electrode material of the present application is 92.5-93% at 2C, the capacity retention rate is 96.1%-96.8% after 50 cycles at room temperature at 1C, the capacity retention rate is 96%-96.7% after 50 cycles at high temperature at 0.5C, and the DCR growth rate is 29.5%-34.3% after 50 cycles at high temperature.

[0031] (6) Based on the doped ternary positive electrode material, the modified high-nickel ternary single-crystal positive electrode material can be prepared by physically mixing the coating agent with the positive electrode material and then sintering once. The preparation method is simple, easy to operate, low in cost, and can be implemented on a large scale, which is conducive to industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the disclosed drawings.

[0033] Figure 1 is an EPMA area mapping of the ternary positive electrode material of Example 1 of the present application;

[0034] Figure 2 is an EPMA line mapping of the ternary positive electrode material of Example 1 of the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without any creative work, fall within the scope of protection of the present application.

[0036] Unless otherwise defined, all the professional terms used in the present application have the same meanings as commonly understood by those skilled in the art. The professional terms used in the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the scope of protection of the present application.

[0037] Unless otherwise specified, the various raw materials, reagents, instruments and equipment, etc. used in the present application can be purchased from the market or can be prepared by the existing methods.

[0038] The element concentrations in the following examples and comparative examples are measured by EPMA (Electron Probe X-ray Microanalyzer) with a field of view of 43000 times and a measurement condition of 2.998*10 -8 The current of A is measured under the measurement condition of a voltage of 20KV and a beam diameter of 400μm.

[0039] Example 1:

[0040] The modified high-nickel ternary single-crystal positive electrode material of the present application comprises a high-nickel ternary single-crystal positive electrode material matrix LiNi 0.8861 Co 0.037 Mn 0.073 Zr 0.0039 O2, the matrix is doped with Co and Al elements in the bulk phase, and the surface of the matrix is coated with a coating layer containing Co, Al and Ni elements.

[0041] The preparation method of the modified high-nickel ternary single-crystal positive electrode material of the present embodiment comprises the following steps:

[0042] (1) commercially available nickel-cobalt-manganese hydroxide precursor Ni 0.89 Co 0.037 Mn 0.073The (OH)2and LiOH-H2O are mixed uniformly in a ratio of Li:Me = 1:1.045, then 2500 ppm of ZrO2is added and mixed uniformly, heated to 500℃ at a rate of 3℃ / min in an oxygen atmosphere, and then heated to 837℃ at a rate of 1℃ / min for 12 h, and then naturally cooled to room temperature to obtain a sintered substrate LiNi 0.8861 Co 0.037 Mn 0.073 Zr 0.0039 O2;

[0043] (2) The sintered substrate obtained in step (1) is mixed uniformly with the coating agent CoOOH and Al2O3 under high-speed stirring, wherein the molar ratio of the sintered substrate to CoOOH is 1:1%, and the molar ratio of the sintered substrate to Al2O3 is 1:1.2%, and then calcined in a kiln, with the calcination conditions being: an oxygen atmosphere, first heated to 300℃ at a rate of 3℃ / min for 3 h, and then heated to 700℃ at a rate of 1℃ / min for 7 h, and then naturally cooled to room temperature to obtain a modified high-nickel ternary single-crystal positive electrode material.

[0044] The modified high-nickel ternary single-crystal positive electrode material of the present embodiment is a spherical particle. The EPMA line scan graph of the modified high-nickel ternary single-crystal positive electrode material prepared in the present embodiment is shown in FIG. 1. From the surface of the spherical particle to the center of the spherical particle, the modified high-nickel ternary single-crystal positive electrode material is divided into three regions, wherein the region with a distance of 0≤L≤180 nm from the surface of the spherical particle is the first region, the region with a distance of 180 nm

[0045] The modified high-nickel ternary single-crystal positive electrode material of the embodiment can reduce the Li / Ni mixing degree by 34.2%, the prepared button cell has a rate of 93% at 2C, a capacity retention rate of 96.8% after 50 cycles at room temperature at 1C, a capacity retention rate of 96.7% after 50 cycles at high temperature at 0.5C, and a DCR growth rate of 29.5% after 50 cycles at high temperature, which is due to the formation of the Co, Al and Ni three-element concentration gradient, thereby realizing the synergistic effect of improving the crystal structure by doping and improving the material stability by coating.

[0046] Example 2:

[0047] The difference between the preparation method of the modified high-nickel ternary single-crystal positive electrode material of the embodiment and that of Example 1 is that the coating agent is changed to Co(OH)2 and AlOOH in step (2), the molar ratio of the one-shot base material to Co(OH)2 is 1:1%, the molar ratio of the one-shot base material to AlOOH is 1:1.2%, and the rest is the same as that of Example 1.

[0048] The particles of the modified high-nickel ternary positive electrode material of the embodiment are analyzed by EPMA: in the first region, divided into three intervals every 60 nm, in the three intervals, the Co element concentration decreases by 28.9%, 18.3% and 15.1% from outside to inside in gradient distribution, the Al element concentration decreases by 31.2%, 27.9% and 24.5% from outside to inside in gradient distribution, and the Ni element concentration increases by 18.9%, 18.4% and 7.6% from outside to inside in gradient distribution; in the second region, divided into two intervals every 275 nm, in the two intervals, the difference between the maximum value and the minimum value of the Co element concentration is 105 cps, the Al element concentration decreases by 23.8% and 17.2% from outside to inside in gradient distribution, and the Ni element concentration increases by 16.9% and 8.5% from outside to inside in gradient distribution; in the third region, the difference between the maximum value and the minimum value of the Co element concentration is 110 cps, the difference between the maximum value and the minimum value of the Ni element concentration is 411 cps, and the difference between the maximum value and the minimum value of the Al element concentration is 61 cps.

[0049] The modified high-nickel ternary single-crystal positive electrode material of the embodiment can reduce the Li / Ni mixing degree by 28.4%, the prepared button cell has a rate of 92.7% at 2C, a capacity retention rate of 96.5% after 50 cycles at room temperature at 1C, a capacity retention rate of 96.2% after 50 cycles at high temperature at 0.5C, and a DCR growth rate of 32.6% after 50 cycles at high temperature.

[0050] Example 3:

[0051] The preparation method of the modified high-nickel ternary single-crystal positive electrode material of the embodiment is different from that of Example 1 only in that, in step (2), the coating agent is changed to Co3O4 and Al(OH)3, the molar ratio of the sintered substrate to Co3O4 is 1:1%, and the molar ratio of the sintered substrate to Al(OH)3 is 1:1.2%, and the rest is the same as that of Example 1.

[0052] The particles of the modified high-nickel ternary positive electrode material of the embodiment are analyzed by EPMA: in the first region, divided into three intervals every 60 nm, in the three intervals, the Co element concentration decreases by 27.5%, 16.8% and 14.4% from outside to inside in a gradient distribution, the Al element concentration decreases by 29.9%, 26.7% and 25.1% from outside to inside in a gradient distribution, and the Ni element concentration increases by 17.7%, 16.5% and 8.3% from outside to inside in a gradient distribution; in the second region, divided into two intervals every 275 nm, in the two intervals, the difference between the maximum value and the minimum value of the Co element concentration is 97 cps, the Al element concentration decreases by 24.2% and 15.6% from outside to inside in a gradient distribution, and the Ni element concentration increases by 17.1% and 8.8% from outside to inside in a gradient distribution; in the third region, the difference between the maximum value and the minimum value of the Co element concentration is 95 cps, the difference between the maximum value and the minimum value of the Ni element concentration is 395 cps, and the difference between the maximum value and the minimum value of the Al element concentration is 58 cps.

[0053] The Li / Ni mixing degree of the modified high-nickel ternary single-crystal positive electrode material of the embodiment can be reduced by 26.7%, the rate of the prepared button cell at 2C is 92.5%, the capacity retention rate after 50 cycles at room temperature at 1C is 96.4%, the capacity retention rate after 50 cycles at high temperature at 0.5C is 96%, and the DCR growth rate after 50 cycles at high temperature is 34.3%.

[0054] Example 4:

[0055] The preparation method of the modified high-nickel ternary single-crystal positive electrode material of the embodiment is different from that of Example 2 only in that, in step (2), the sintering temperature is 650°C, and the rest is the same as that of Example 2.

[0056] The particles of the ternary positive electrode material of the embodiment are analyzed by EPMA: in the first region, divided into three intervals of every 60 nm, in the three intervals, the Co element concentration decreases by 21.5%, 13.8% and 11.7% from outside to inside in a gradient distribution, the Al element concentration decreases by 24.9%, 20.6% and 18.3% from outside to inside in a gradient distribution, and the Ni element concentration increases by 15.8%, 14.1% and 7.2% from outside to inside in a gradient distribution; in the second region, divided into two intervals of every 275 nm, in the two intervals, the difference between the maximum value and the minimum value of the Co element concentration is 80 cps, the Al element concentration decreases by 17.4% and 13.2% from outside to inside in a gradient distribution, and the Ni element concentration increases by 15.1% and 5.3% from outside to inside in a gradient distribution; in the third region, the difference between the maximum value and the minimum value of the Co element concentration is 70 cps, the difference between the maximum value and the minimum value of the Ni element concentration is 350 cps, and the difference between the maximum value and the minimum value of the Al element concentration is 45 cps.

[0057] The Li / Ni mixing degree of the modified high-nickel ternary single-crystal positive electrode material of the embodiment can be reduced by 29.8%, the rate of the prepared button cell at 2C is 92.7%, the capacity retention rate after 50 cycles at room temperature at 1C is 96.2%, the capacity retention rate after 50 cycles at high temperature at 0.5C is 96.1%, and the DCR growth rate after 50 cycles at high temperature is 32%.

[0058] Example 5:

[0059] The preparation method of the modified high-nickel ternary single-crystal positive electrode material of the embodiment is different from that of Example 4 only in that the molar amount of CoOOH in step (2) is different, and in the embodiment, the molar ratio of the one-burned substrate to CoOOH is 1:3%, and the rest is the same as Example 4.

[0060] The particles of the modified high-nickel ternary positive electrode material of the present example were analyzed by EPMA: in the first region, divided into three intervals of every 60 nm, in the three intervals, the Co element concentration decreased by 26.1%, 15.7% and 13.3% from outside to inside in a gradient distribution, the Al element concentration decreased by 24.2%, 19.8% and 17.9% from outside to inside in a gradient distribution, and the Ni element concentration increased by 16.4%, 13.7% and 6.3% from outside to inside in a gradient distribution; in the second region, divided into two intervals of every 275 nm, in the two intervals, the difference between the highest value and the lowest value of the Co element concentration was 110 cps, the Al element concentration decreased by 17.7% and 14.1% from outside to inside in a gradient distribution, and the Ni element concentration increased by 14.8% and 5.4% from outside to inside in a gradient distribution; in the third region, the difference between the highest value and the lowest value of the Co element concentration was 89 cps, the difference between the highest value and the lowest value of the Ni element concentration was 330 cps, and the difference between the highest value and the lowest value of the Al element concentration was 51 cps.

[0061] The Li / Ni mixing degree of the modified high-nickel ternary single-crystal positive electrode material of the present example can be reduced by 32.9%, the rate of the prepared button cell at 2C is 92.6%, the capacity retention rate after 50 cycles at room temperature at 1C is 96.1%, the capacity retention rate after 50 cycles at high temperature at 0.5C is 96.4%, and the DCR growth rate after 50 cycles at high temperature is 30.8%.

[0062] Example 6:

[0063] The preparation method of the modified high-nickel ternary single-crystal positive electrode material of the present example is different from that of example 1 only in that the amount of the coating agent CoOOH and Al2O3 in step (2) is different, wherein the molar ratio of the calcined substrate to CoOOH is 1:0.3%, the molar ratio of the calcined substrate to Al2O3 is 1:8%, and the rest is the same as example 1.

[0064] The particles of the ternary positive electrode material of the embodiment are analyzed by EPMA: in the first region, divided into three intervals of every 60 nm, in the three intervals, the Co element concentration decreases by 10.1%, 8.1% and 5.3% from outside to inside in a gradient distribution, the Al element concentration decreases by 42.1%, 39.7% and 35.8% from outside to inside in a gradient distribution, and the Ni element concentration increases by 23.7%, 21.8% and 19.1% from outside to inside in a gradient distribution; in the second region, divided into two intervals of every 275 nm, in the two intervals, the difference between the maximum value and the minimum value of the Co element concentration is 35 cps, the Al element concentration decreases by 32.2% and 28.7% from outside to inside in a gradient distribution, and the Ni element concentration increases by 18.9% and 17.3% from outside to inside in a gradient distribution; in the third region, the difference between the maximum value and the minimum value of the Co element concentration is 30 cps, the difference between the maximum value and the minimum value of the Ni element concentration is 300 cps, and the difference between the maximum value and the minimum value of the Al element concentration is 110 cps.

[0065] Comparative Example 1

[0066] The preparation method of the modified high-nickel ternary single-crystal positive electrode material of the comparative example is different from that of Example 1 only in that the sintering temperature in step (2) is 800°C, and the rest is the same as that of Example 1.

[0067] The particles of the modified high-nickel ternary single-crystal positive electrode material of the comparative example are analyzed by EPMA: in the three regions, the difference between the maximum value and the minimum value of the Co element concentration is 65 cps, the difference between the maximum value and the minimum value of the Ni element concentration is 300 cps, and the difference between the maximum value and the minimum value of the Al element concentration is 40 cps.

[0068] Comparative Example 2

[0069] The preparation method of the modified high-nickel ternary single-crystal positive electrode material of the comparative example comprises the following steps:

[0070] A commercially available nickel-cobalt-manganese hydroxide precursor Ni 0.89 Co 0.037 Mn 0.073 After the commercially available nickel-cobalt-manganese hydroxide precursor Ni (OH) 2 and LiOH·H2O are uniformly mixed in a proportion of Li:Me=1:1.045, ZrO2, CoOOH and Al2O3 are then added and uniformly mixed under high-speed stirring, wherein ZrO2 accounts for 2500 ppm of the mixed material, the molar ratio of the mixed material to CoOOH is 1:1%, and the molar ratio of the mixed material to Al2O3 is 1:1.2 mol%, the temperature is raised to 500°C at a rate of 3°C / min under an oxygen atmosphere, and then the temperature is continuously raised to 837°C and kept for 12 h, and then naturally cooled to room temperature, to obtain a ternary positive electrode material.

[0071] The particles of the ternary positive electrode material of the present comparative example were analyzed by EPMA: the difference between the maximum value and the minimum value of the Co element concentration was 60 cps, the difference between the maximum value and the minimum value of the Ni element concentration was 278 cps, and the difference between the maximum value and the minimum value of the Al element concentration was 35 cps.

[0072] The ternary positive electrode material samples prepared in Examples 1-6 and Comparative Examples 1-2 were assembled into CR2025 button half-cells as ternary positive electrode active materials: first, 8:1:1 single-crystal positive electrode active material, acetylene black conductive agent and polyvinylidene fluoride (PVDF) binder were mixed, then an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added, and the collected slurry was uniformly coated on an aluminum foil. After drying at 120°C for 12 h, a cathode active material with a loading mass of 2.5 mg / cm2was prepared. The batteries were assembled in an Ar-filled glove box, lithium metal was used as the anode, polypropylene (Celgard 2400) was used as the separator, and 1 mol / L LiPF6dissolved in a mixture of ethyl carbonate and dimethyl carbonate (EC:DMC = 1:1 by volume) was used as the electrolyte. The button half-cells were assembled and subjected to electrochemical performance testing. 2 The button half-cells assembled from the single-crystal positive electrode materials prepared in Examples 1-6 and Comparative Examples 1-2 were tested at a voltage window of 3.0-4.3 V, and the resulting capacity, rate capability, room temperature cycling, high temperature cycling performance and high temperature DCR growth rate performance were as shown in Table 1.

[0073] The button half-cells assembled from the single-crystal positive electrode materials prepared in Examples 1-6 and Comparative Examples 1-2 were tested at a voltage window of 3.0-4.3 V, and the resulting capacity, rate capability, room temperature cycling, high temperature cycling performance and high temperature DCR growth rate performance were as shown in Table 1.

[0074] Table 1 Electrochemical performance of the ternary positive electrode materials of each example and comparative example

[0075] The surface residual lithium results of the modified high-nickel ternary positive electrode materials in Examples 1-6 and Comparative Examples 1-2 are shown in Table 2. In Examples 1-5, sufficient Co coating amount reacted with the surface residual lithium at a suitable sintering temperature, forming a Co-rich coating layer on the surface, thereby significantly reducing the residual lithium of the prepared modified high-nickel ternary single-crystal positive electrode material. In Example 6, the Co coating amount was too small to completely react with the surface residual lithium, resulting in excessively high residual lithium. In Comparative Example 1, the Co uniformly diffused into the bulk phase due to the excessively high sintering temperature, and the amount of Co on the surface was insufficient to completely react with the residual lithium. In Comparative Example 2, the Co source was added during the first sintering, and the Co source acted as a doping element and could not react with the residual lithium formed by the first sintering product, so the residual lithium value was relatively high.

[0076] Table 2 Residual lithium values of the ternary positive electrode materials of each example and comparative example

[0077] Any combination of the technical features in the above-described embodiments can be made, and for the sake of brevity, not all possible combinations are described, however, it is to be understood that the application embraces all such possible combinations.

[0078] The above-described embodiments only express several implementation manners of the application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the application. It should be pointed out that, for ordinary skilled persons in the art, some modifications and improvements can be made without departing from the concept of the application, and these all belong to the protection scope of the application. Therefore, the patent protection scope of the application should be subject to the appended claims.

Claims

1. A modified high-nickel ternary single-crystal cathode material, comprising a high-nickel ternary single-crystal cathode material matrix, the matrix being doped with Co and Al elements in the bulk phase, and the surface of the matrix being coated with a coating layer containing Co, Al and Ni elements, the content of Co and Al elements gradually decreasing and the content of Ni element gradually increasing from the coating layer on the surface of the matrix to the bulk phase of the matrix.

2. The modified high-nickel ternary single-crystal cathode material of claim 1, wherein, The modified high-nickel ternary single-crystal cathode material is a spherical particle, and the modified high-nickel ternary single-crystal cathode material is divided into three regions from the surface of the spherical particle to the center of the spherical particle, wherein the region with a distance of 0≤L≤180 nm from the surface of the spherical particle is the first region, the region with a distance of 180 nm<L≤730 nm from the surface of the spherical particle is the second region, and the region with a distance of 730 nm<L≤R from the surface of the spherical particle is the third region, wherein R is the radius of the spherical particle. In the first region, the concentration of Co element is gradiently distributed from the outer surface of the spherical particle to the inside at a rate of 11.7% to 28.9% per 60 nm, the concentration of Al element is gradiently distributed from the outer surface of the spherical particle to the inside at a rate of 17.9% to 31.2% per 60 nm, and the concentration of Ni element is gradiently distributed from the outer surface of the spherical particle to the inside at a rate of 6.3% to 18.9% per 60 nm.

3. The modified high-nickel ternary single-crystal cathode material of claim 2, wherein, In the second region, the difference between the maximum value and the minimum value of the concentration of Co element is 80 cps to 110 cps.

4. The modified high-nickel ternary single-crystal cathode material of any one of claims 2-3, wherein, In the second region, the concentration of Al element is gradiently distributed from the outside to the inside at a rate of 13.2% to 24.2% per 275 nm.

5. The modified high-nickel ternary single-crystal cathode material of any one of claims 2-4, wherein, In the second region, the concentration of Ni element is gradiently distributed from the outside to the inside at a rate of 5.3% to 17.1% per 275 nm.

6. The modified high-nickel ternary single-crystal cathode material of any one of claims 2-5, wherein, In the third region, the difference between the maximum value and the minimum value of the concentration of Co element is 70 cps to 110 cps.

7. The modified high-nickel ternary single-crystal cathode material of any one of claims 2-6, wherein, In the third region, the difference between the maximum value and the minimum value of the concentration of Ni element is 330 cps to 411 cps.

8. The modified high-nickel ternary single-crystal cathode material according to any one of claims 2-7, wherein, In the third region, the difference between the maximum value and the minimum value of the concentration of Al element is 45 cps to 61 cps.

9. The modified high-nickel ternary single-crystal cathode material according to any one of claims 1-8, wherein, The high-nickel ternary single-crystal positive electrode material matrix has a chemical formula of LiNi x Co y Mn 1-x-y M z O2, wherein 0.8≤x<1, 0≤y<1, 0≤z<1, and M is one or more of Ti, Mg, Zr, W, and Sr elements. 10.A method for preparing the modified high-nickel ternary single-crystal cathode material according to any one of claims 1 to 9, comprising the following steps: (1) mixing nickel-cobalt-manganese hydroxide precursor, lithium salt and M-containing compound, and then sintering to obtain a base material; wherein, M is one or more of Ti, Mg, Zr, W and Sr elements; (2) mixing the matrix material with a coating agent and then sintering to obtain the modified high-nickel ternary single-crystal cathode material, wherein the coating agent comprises a Co-containing compound and an Al-containing compound.

11. The production method according to claim 10, wherein In step (1), the sintering is performed in an oxygen atmosphere, first heated to 300-500℃ at a heating rate of 1-3℃ / min and kept for 1-5 h, then continuously heated to 750-970℃ and kept for 6-15 h, and then naturally cooled to room temperature to obtain the matrix material.

12. The production method according to any one of claims 10 to 11, wherein In step (2), the Co-containing compound is selected from one or more of Co(OH)2, CoOOH, CoO, Co3O4 and (CH3CO2)2Co.

13. The production method according to any one of claims 10 to 12, wherein In step (2), the Al-containing compound is selected from one or more of Al2O3, Al(OH)3, and AlOOH.

14. The production method according to any one of claims 10 to 13, wherein In step (2), the molar ratio of the base material to the coating agent is 1:0.001-0.

06.

15. The production method according to any one of claims 10 to 14, wherein In step (2), the sintering is gradient sintering, first increasing the temperature from room temperature to 200-400°C at a rate of 1-3°C / min and maintaining the temperature for 1-6h, and then increasing the temperature to 600-775°C at a rate of 0.5-3°C / min and maintaining the temperature for 6-10h. 16.A lithium ion battery comprising the modified high-nickel ternary single-crystal cathode material according to any one of claims 1-9 or comprising the modified high-nickel ternary single-crystal cathode material prepared by the preparation method according to any one of claims 10-15. 17.An electric device comprising the lithium ion battery according to claim 16.

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