Single-crystal ternary positive electrode material, preparation method and application thereof

Abstract

The application provides a single-crystal ternary positive electrode material and a preparation method and application thereof. m [Ni x Co y Mn z ]O2, wherein 0.98 0.6

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion batteries, and relates to a single-crystal ternary positive electrode material, in particular to a single-crystal ternary positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] High-nickel ternary positive electrode materials have become one of the most important positive electrode materials for electric vehicle power batteries due to their advantages in energy density and cycle life. In practical applications, higher requirements are put forward for ternary positive electrode materials in order to obtain longer cruising range.

[0003] At present, the cruising range is usually prolonged by increasing the nickel content in the ternary positive electrode material or increasing the charge cut-off voltage of the positive electrode material. However, both methods will greatly damage the structural stability and thermal stability of the ternary positive electrode material, thereby greatly reducing the cycle life and safety performance of the battery. The single-crystal ternary positive electrode material has higher structural stability and thermal stability than the polycrystal ternary positive electrode material, and although it can improve the cycle performance and safety performance of the battery to some extent, it still cannot meet the requirements.

[0004] Therefore, it is urgent to study a single-crystal ternary positive electrode material with higher cycle performance and safety performance. SUMMARY

[0005] In view of the above defects, the application provides a single-crystal ternary positive electrode material, which has higher structural stability and thermal stability, and can effectively improve the cycle performance and safety performance of a lithium ion battery.

[0006] The application provides a preparation method of a single-crystal ternary positive electrode material. The single-crystal ternary positive electrode material prepared by the preparation method has higher structural stability and thermal stability, and when applied to a lithium ion battery, can effectively improve the cycle performance and safety performance of the battery.

[0007] The application provides a positive electrode sheet. Since the positive electrode sheet comprises the single-crystal ternary positive electrode material or the single-crystal ternary positive electrode material prepared by the preparation method, when the positive electrode sheet is applied to a lithium ion battery, the cycle performance and safety performance of the battery can be effectively improved.

[0008] The application provides a lithium ion battery comprising the single-crystal ternary positive electrode material or the single-crystal ternary positive electrode material prepared by the preparation method, or the positive electrode sheet. Therefore, the lithium ion battery has a longer cycle life and higher safety performance.

[0009] The application provides a single-crystal ternary positive electrode material, which comprises a chemical composition of Li m [Nix Co y Mn z ]O2, wherein 0.98 < m < 1.03, 0.6 ≤ x < 1, 0 < y < 0.1, and 0 < z < 0.1;

[0010] The base material is doped with Ce elements, M1 elements and M2 elements, the M1 elements include at least one of Mo, W and Te, and the M2 elements include at least one of Al, Zr, Y, La, Ta and Ga;

[0011] The X-ray diffraction pattern of the single-crystal ternary positive electrode material has a diffraction peak of a (111) crystal plane of CeO2 at 2θ of 28°-29°, and the half-peak width of the diffraction peak is 0.09-0.2;

[0012] The mass percentage of the Ce elements in the single-crystal ternary positive electrode material is 2500-5000 ppm.

[0013] Further, the mass percentage of the M1 elements in the single-crystal ternary positive electrode material is 500-2000 ppm, and / or the mass percentage of the M2 elements in the single-crystal ternary positive electrode material is 500-4000 ppm.

[0014] Further, the single-crystal ternary positive electrode material includes the base material and a coating layer coated on at least part of the surface of the base material, the bulk phase of the base material is doped with M2, the surface of the base material is doped with Ce and M1, and the coating layer is CeO2.

[0015] Further, the X-ray diffraction pattern of the single-crystal ternary positive electrode material has a diffraction peak of a (003) crystal plane at 2θ of 18.2°-19.0°, a diffraction peak of a (012) crystal plane at 2θ of 38.2°-38.3°, and a diffraction peak of a (104) crystal plane at 2θ of 44.35°-44.45°;

[0016] The surface energy E (104) of the (003) crystal plane, (003) and the surface energy E (012) of the (012) crystal plane satisfy formula 1 and formula 2,

[0017] 50% E (003) < E (104) < 70% E (003) Formula 1

[0018] 20% E (012) < E (104) < 30% E (012) Formula 2.

[0019] Further, the single-crystal ternary cathode material comprises single-crystal primary particles;

[0020] The average particle size of the single-crystal primary particles is 1.5-4 μm.

[0021] Further, the median particle size of the single-crystal ternary cathode material is 3-8 μm, and / or the specific surface area of the single-crystal ternary cathode material is 0.2-1 m 2 / g, and / or the tap density of the single-crystal ternary cathode material is > 2.2 g / cm 3 .

[0022] Further, in a DSC test of the single-crystal ternary cathode material, the thermal decomposition temperature of the single-crystal ternary cathode material is not less than 225℃;

[0023] and / or the lithium-nickel mixing rate of the single-crystal ternary cathode material is < 2%.

[0024] The present application provides a preparation method of a single-crystal ternary cathode material, comprising the following steps:

[0025] (1) mixing a ternary cathode material precursor Li m Ni x Co y Mn z (OH)2, a Li source, a Ce source, a M1 source and a M2 source, and performing first sintering, second sintering, third sintering and fourth sintering under an oxygen atmosphere;

[0026] The temperature T1 of the first sintering is 400-600℃, and the holding time t1 is 4-6 h;

[0027] The temperature T2 of the second sintering is 900-1000℃, and the holding time t2 is t1-1≤t2

[0028] The temperature T3 of the third sintering is T2-100

[0029] The temperature T4 of the fourth sintering is T3-70

[0030] (2) after the fourth sintering is completed, natural cooling is performed to obtain the single-crystal ternary cathode material.

[0031] The present application provides a positive electrode sheet, which comprises the single-crystal ternary cathode material of any one of the above or the single-crystal ternary cathode material prepared by the above preparation method.

[0032] The application provides a lithium ion battery, which comprises the single-crystal ternary positive electrode material of any one of the above, or the single-crystal ternary positive electrode material prepared by the preparation method, or the positive electrode sheet.

[0033] The single-crystal ternary positive electrode material of the application comprises a base material with a chemical composition of Li m [Ni x Co y Mn z ]O2, wherein the mass percentage of Ce in the single-crystal ternary positive electrode material is 2500-5000 ppm, and the X-ray diffraction pattern of the single-crystal ternary positive electrode material has a diffraction peak of the (111) crystal plane of CeO2 at 2θ of 28-29°, and the half-peak width of the diffraction peak is 0.09-0.1. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The XRD pattern of the positive electrode material prepared in Example 1 and Comparative Example 1 of the application;

[0035] Figure 2 The SEM image of the positive electrode material prepared in Example 1 of the application;

[0036] Figure 3 The SEM image of the positive electrode material prepared in Comparative Example 1 of the application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below in combination with the embodiments of the application. Obviously, the described embodiments are some embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0038] The first aspect of the application provides a single-crystal ternary positive electrode material, which comprises a base material with a chemical composition of Li m [Ni x Co y Mn z ]O2, wherein 0.98

[0039] The base material is doped with Ce element, M1 element and M2 element, the M1 element includes at least one of Mo, W and Te, and the M2 element includes at least one of Al, Zr, Y, La, Ta and Ga;

[0040] In the X-ray diffraction pattern of the single-crystal ternary positive electrode material, there is a diffraction peak of the (111) crystal face of CeO2 at 28°-29°, and the half-peak width of the diffraction peak is 0.09-0.2.

[0041] The mass percentage content of the Ce element in the single-crystal ternary positive electrode material is 2500-5000 ppm.

[0042] The Ce element, the M1 element and the M2 element in the application can exist in the form of oxides or be doped in the base material in the form of elements.

[0043] The single-crystal ternary positive electrode material in the application is prepared by doping specific elements in the base material with a chemical composition of Li m [Ni x Co y Mn z ]O2, controlling the mass percentage content of the Ce element, and making the X-ray diffraction pattern of the single-crystal ternary positive electrode material have a diffraction peak with a specific half-peak width at a specific position. The application is based on the phenomenon that the single-crystal ternary positive electrode material has high thermal stability and structural stability, thereby effectively improving the cycle performance and safety performance of the lithium ion battery.

[0044] In addition, the single-crystal ternary positive electrode material can also reduce the side reaction between the electrolyte and the positive electrode material, further improving the cycle performance and safety performance of the battery.

[0045] In an embodiment, the mass percentage of the M1 element in the single-crystal ternary cathode material is 500-2000 ppm. Within this range, the Ce element, the M1 element and the M2 element can better synergize, not only further improving the morphology uniformity of the primary particles, but also avoiding the problems of too small particle size and poor morphology uniformity of the single-crystal primary particles caused by too much M1 element, thereby improving the capacity of the battery.

[0046] In an embodiment, the mass percentage of the M2 element in the single-crystal ternary cathode material is 500-4000 ppm. Within this range, the Ce element, the M1 element and the M2 element can better synergize and have stronger binding energy with oxygen, thereby improving the bulk structure stability of the cathode material and its cycle performance and avoiding the impact on capacity performance caused by too much content.

[0047] In an embodiment, the single-crystal ternary cathode material comprises a base material and a coating layer coated on at least part of the surface of the base material, the base material is doped with M2 in the bulk phase, the surface of the base material is doped with Ce and M1, and the coating layer is CeO2. At this time, the primary particles in the single-crystal ternary cathode material have high morphology uniformity and dispersity, which helps to further improve the cycle performance and safety of the battery; at the same time, a higher tap density can also be achieved, thereby improving the compaction density of the cathode sheet and the energy density of the battery.

[0048] In an embodiment, the X-ray diffraction pattern of the single-crystal ternary cathode material has a diffraction peak of the (003) crystal face at 2θ of 18.2°-19.0°, a diffraction peak of the (012) crystal face at 2θ of 38.2°-38.3°, and a diffraction peak of the (104) crystal face at 2θ of 44.35°-44.45°.

[0049] the surface energy E of the (104) crystal face (104) the surface energy E of the (003) crystal face (003) the surface energy E of the (012) crystal face (012) satisfy formula 1 and formula 2,

[0050] 50% E (003) <E (104) <70% E (003) Formula 1

[0051] 20% E (012) <E (104) <30% E (012)Formula 2. Specifically, by controlling the kind or doping amount of the Ce element and the M1 element in the preparation process, the surface energy can be further controlled, so that the surface energy of the (104) crystal plane satisfies both Formula 1 and Formula 2. Since the (104) crystal plane has a fast lithium ion diffusion channel, when E (104) When Formula 1 and Formula 2 are satisfied at the same time, the single-crystal ternary positive electrode material has high rate performance.

[0052] The surface energy of the (104) crystal plane, the surface energy of the (003) crystal plane, and the surface energy of the (012) crystal plane in the present application are calculated by DFT (density functional theory).

[0053] In one specific embodiment, the single-crystal ternary positive electrode material comprises single-crystal primary particles; the average particle size of the single-crystal primary particles is 1.5-4 μm. When the average particle size of the single-crystal primary particles is in this range, the primary particle size is large, the specific surface area is small, the contact area with the electrolyte can be reduced, thereby reducing the side reaction with the electrolyte, and the cycle performance and safety of the battery can be further improved; at the same time, the large size can improve the dispersibility of the positive electrode material, thereby effectively improving the tap density, making the uniformity of the positive electrode slurry better, the compaction density of the positive electrode sheet larger, and the energy density of the battery higher.

[0054] The average particle size in the present application refers to that, by performing SEM testing on the single-crystal ternary positive electrode material, the diameters of not less than 100 primary particles in an arbitrary 3000-fold region are measured, and the average value is taken as the average particle size of the single-crystal primary particles.

[0055] In one specific embodiment, the median particle size of the single-crystal ternary positive electrode material is 3-8 μm, and / or the specific surface area of the single-crystal ternary positive electrode material is 0.2-1 m 2 / g, and / or the tap density of the single-crystal ternary positive electrode material is > 2.2 g / cm 3 When the median particle size of the single-crystal ternary positive electrode material is in the aforementioned range, it is helpful to achieve a smaller specific surface area and a larger tap density, so that the specific surface area is between 0.2-1 m 2 / g, and the tap density is > 2.2 g / cm 3 , thereby further improving the uniformity of the positive electrode slurry, thereby improving the compaction density of the positive electrode sheet, and making the battery have higher cycle performance and volumetric energy density.

[0056] The median particle size in the present application is measured by a laser particle size analyzer.

[0057] The specific surface area and the tap density in the present application are measured by a conventional method in the art.

[0058] In a specific embodiment, the thermal decomposition temperature of the single-crystal ternary cathode material is not less than 225 DEG C in a DSC test. Specifically, the thermal stability of the single-crystal ternary cathode material can be improved by controlling the process parameters in the preparation process, such as the doping amount of the Ce element, the M1 element and the M2 element, the sintering temperature, the holding time, so that the thermal decomposition temperature of the single-crystal ternary cathode material at the charge cut-off voltage is not less than 225 DEG C. At this time, the lithium ion battery comprising the cathode material has high safety performance.

[0059] The DSC test in the present application includes: at 25 DEG C and normal pressure (0.1 MPa), the single-crystal ternary cathode material, conductive carbon black and binder polyvinylidene fluoride (PVDF) in the present application are mixed uniformly in N-methyl pyrrolidone solvent at a mass percentage ratio of 95:3:2 to obtain a cathode slurry, the cathode slurry is coated on the surface of an aluminum foil, and a cathode sheet comprising a 100-micron cathode active layer is obtained after drying and cold pressing, the compaction density of the cathode sheet is 4.5 g / cm 3 ; the cathode sheet, lithium sheet, separator and electrolyte are assembled into a CR2032 button cell in a button cell box, wherein the electrolyte comprises ethylene carbonate (EC), methyl ethyl carbonate (EMC) and LiPF6, the volume ratio of ethylene carbonate (EC) to methyl ethyl carbonate (EMC) is 3:7, and the mass percentage of LiPF6 in the electrolyte is 12.5wt%.

[0060] After the prepared CR2032 button cell is charged at a constant current of 0.2C rate to a cut-off voltage of 4.3V, the cathode sheet is disassembled, and the cathode sheet is subjected to a DSC test. The DSC test conditions are as follows: the disassembled cathode sheet is cleaned with DMC and dried, a certain amount of electrolyte (1 / 3 of the mass of the sample) is added, a TA-DSC thermal analyzer is used to test the thermal decomposition curve, and the thermal decomposition temperature of the single-crystal ternary cathode material is obtained. In the test, the equilibrium temperature is set to 50 DEG C, the heating rate is set to 10 DEG C / min, the temperature range is 50-350 DEG C, the sample mass is 2-3 mg, the purge gas is N2, and the flow value is 10 mL / min.

[0061] In a specific embodiment, the lithium-nickel mixing rate of the single-crystal ternary cathode material is <2%. Specifically, the structural stability of the single-crystal ternary cathode material can be improved by controlling the process parameters in the preparation process, such as the doping amount of the Ce element, the M1 element and the M2 element, the sintering temperature, the holding time, so that the lithium-nickel mixing rate of the single-crystal ternary cathode material is <2%. At this time, the rapid embedding and migration of lithium ions can be realized, so that the lithium ions of the cathode active material can migrate smoothly in the charge and discharge process, and the first coulomb efficiency, capacity and cycle performance of the lithium ion battery comprising the cathode material are effectively improved.

[0062] The second aspect of the present application provides a preparation method of the single-crystal ternary cathode material of the first aspect, comprising the following steps:

[0063] (1) mixing a ternary cathode material precursor Li m Ni x Co y Mn z (OH)2, a Li source, a Ce source, an M1 source and an M2 source, and performing first sintering, second sintering, third sintering and fourth sintering in an oxygen atmosphere;

[0064] The temperature T1 of the first sintering is 400-600℃, and the holding time t1 is 4-6h;

[0065] The temperature T2 of the second sintering is 900-1000℃, and the holding time t2 is t1-1≤t2<t1;

[0066] The temperature T3 of the third sintering is T2-100<T3≤T2-30, and the holding time t3 is t2<t3<t1+1;

[0067] The temperature T4 of the fourth sintering is T3-70<T4≤T3-30, and the holding time t4 is t2<t4<t1+1;

[0068] (2) after the fourth sintering is completed, natural cooling is performed to obtain the single-crystal ternary cathode material.

[0069] Specifically, in step (1), the ternary cathode material precursor with a chemical composition of Li m Ni x Co y Mn z (OH)2is uniformly mixed with a Li source, a Ce source, an M1 source and an M2 source, and then first sintering is performed in an oxygen atmosphere, the temperature T1 of the first sintering is 400-600℃, and the holding time t1 is 4-6h; after the first sintering is completed, the temperature is raised to the second sintering temperature, the temperature T2 of the second sintering is 900-1000℃, and the holding time t2 is t1-1≤t2<t1; after the second sintering is completed, the temperature is lowered to the third sintering temperature, the temperature T3 of the third sintering is T2-100<T3≤T2-30, and the holding time t3 is t2<t3<t1+1; after the third sintering is completed, the temperature is continuously lowered to the fourth sintering temperature, the temperature T4 of the fourth sintering is T3-70<T4≤T3-30, and the holding time t4 is t2<t4<t1+1.

[0070] The Li source in the present application refers to a raw material providing lithium element, the Ce source refers to a raw material providing Ce element, the M1 source refers to a raw material providing M1 element, and the M2 source refers to a raw material providing M2 element, as long as containing the target element (Li, Ce, M1, M2), it belongs to the limitation of the present application. For example, the Li source includes at least one of lithium hydroxide, lithium carbonate and lithium nitrate; the Ce source includes at least one of cerium oxide and cerium nitrate; the M1 source includes at least one of molybdenum oxide, tellurium dioxide, tungsten dioxide, molybdenum disulfide, yellow tungsten and purple tungsten; and the M2 source includes at least one of aluminum oxide, zirconium dioxide, yttrium sesquioxide, lanthanum sesquioxide, tantalum pentoxide and gallium oxide.

[0071] The present application does not make specific limitation to the source of the ternary positive electrode material precursor, the Li source, the Ce source, the M1 source and the M2 source, which can be obtained by market or conventional preparation means.

[0072] The present application does not make specific limitation to the addition amount of the Ce source, only needs to make the mass percentage content of Ce element in the finally prepared single-crystal ternary positive electrode material be 2500-5000 ppm, and in the X-ray diffraction pattern of the single-crystal ternary positive electrode material, there is a diffraction peak of (111) crystal face of CeO2 at 28°-29° of 2θ, and the half-peak width of the diffraction peak is 0.09-0.2.

[0073] The present application does not make specific limitation to the addition amount of the lithium source, only needs to make the chemical composition of the matrix material included in the finally prepared single-crystal ternary positive electrode material be Li m [Ni x Co y Mn z ]O2.

[0074] The present application does not make specific limitation to the addition amount of the M1 source and the M2 source, further, by controlling the addition amount of the M1 source and / or the M2 source, the mass percentage content of M1 element in the single-crystal ternary positive electrode material can be further controlled to be 500-2000 ppm, and / or the mass percentage content of M2 element in the single-crystal ternary positive electrode material can be further controlled to be 500-4000 ppm.

[0075] The present application does not make specific limitation to the heating rate and the cooling rate in the sintering process.

[0076] The present application does not make specific limitation to the mixing method, only needs to uniformly mix the ternary positive electrode material precursor, the Li source, the Ce source, the M1 source and the M2 source, for example, can be mixed by a high-speed mixer.

[0077] In step (2), after the fourth sintering is finished, natural cooling to room temperature is carried out, and the obtained product is crushed and sieved to obtain a single-crystal ternary positive electrode material.

[0078] The application prepares a single-crystal ternary cathode material by mixing a lithium source, a cerium source, a M1 source and a M2 source with a ternary cathode material precursor Li m Ni x Co y Mn z (OH)2, a lithium source, a cerium source, a M1 source and a M2 source are mixed and sintered at specific different temperature platforms for a certain time, specifically, two-stage temperature rising sintering and two-stage temperature falling sintering are respectively performed, in the process of temperature rising sintering, the Ce element and the M1 element are gradually doped into the surface of the matrix material, the M2 element is gradually doped into the bulk phase of the matrix material, and as the temperature decreases, the Ce element gradually accumulates on the surface of the matrix material, and finally a CeO2 coating layer in rock salt phase is formed on the surface. Thus, the Ce source, the M1 source and the M2 source in the finally prepared single-crystal ternary cathode material are mutually synergistic, promoting the growth of primary particles, and the CeO2 coating layer can promote the atomic diffusion of crystal faces in the sintering process of the single-crystal material, separate the primary particles, and improve the dispersity of the primary particles. At the same time, the segmented sintering at specific different temperature platforms also helps to relieve the residual stress in the crystal during the sintering process, which further improves the morphology uniformity and dispersity of the single-crystal primary particles. In addition, the distribution order of the M2 element in the crystal can also be improved, so that the M2 element is uniformly distributed in the bulk phase of the crystal, improving the stability of the crystal lattice and interface, thereby further improving the structural stability of the cathode material. Thus, the structural stability and thermal stability of the cathode active material are comprehensively improved, and the cycle performance and safety performance of the battery are improved.

[0079] The third aspect of the application provides a cathode sheet comprising the single-crystal ternary cathode material of the first aspect, or the single-crystal ternary cathode material prepared by the preparation method of the second aspect. Since the single-crystal ternary cathode material has high thermal stability and structural stability, the cycle performance and safety performance of the lithium ion battery comprising the cathode sheet can be effectively improved.

[0080] In a specific embodiment, the compaction density of the cathode sheet is not less than 3.5 g / cm 3 Within this range, the compaction density of the cathode sheet is high, which can effectively improve the energy density of the lithium ion battery.

[0081] The fourth aspect of the application provides a lithium ion battery comprising the single-crystal ternary cathode material of the first aspect, or the single-crystal ternary cathode material prepared by the preparation method of the second aspect, or the cathode sheet of the third aspect, which has a long cycle life and high safety performance.

[0082] Hereinafter, the single-crystal ternary cathode material of the application will be described in detail through specific embodiments.

[0083] Example 1

[0084] Lithium hydroxide, a ternary cathode material precursor Li0.83 Co 0.06 Mn 0.11 (OH)2, CeO2, MoO3 and Al2O3 were mixed uniformly in a high-speed mixer, the mixture was loaded into a crucible, and sintering was performed in a high-temperature atmosphere box furnace with an oxygen atmosphere; the temperature was raised to 500 DEG C at a rate of 3 DEG C / min to perform first sintering, after 4 h of heat preservation, the temperature was raised to 930 DEG C at a rate of 3 DEG C / min to perform second sintering, after 3 h of heat preservation, the temperature was lowered to 860 DEG C to perform third sintering, after 6 h of heat preservation, the temperature was lowered to 800 DEG C to perform fourth sintering, after 6 h of heat preservation, the temperature was lowered to room temperature naturally, and a sintered product was obtained; after the sintered product was subjected to roll-pressing, crushing and sieving, a single-crystal ternary positive electrode material of the example was obtained, and the chemical composition of the matrix material in the single-crystal ternary positive electrode material was Li 1.05 [Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Ce element was 3000 ppm, the doping amount of Mo element was 1000 ppm, and the doping amount of Al element was 1000 ppm.

[0085] Example 2

[0086] The preparation method of the single-crystal ternary positive electrode material in the example was basically the same as that in Example 1, except that the chemical composition of the ternary positive electrode material precursor was Ni 0.6 Co 0.1 Mn 0.3 (OH)2; the temperature of second sintering was 970 DEG C; and the chemical composition of the matrix material in the single-crystal ternary positive electrode material prepared in the example was Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element was 3000 ppm, the doping amount of Mo element was 1000 ppm, and the doping amount of Al element was 1000 ppm.

[0087] Example 3

[0088] The preparation method of the single-crystal ternary positive electrode material in the example was basically the same as that in Example 1, except that the chemical composition of the ternary positive electrode material precursor was Ni 0.9 Co 0.05 Mn 0.05 (OH)2; the temperature of second sintering was 910 DEG C; and the chemical composition of the matrix material in the single-crystal ternary positive electrode material prepared in the example was Li 1.05 [Ni 0.9 Co 0.05 Mn 0.05Li2 / 3Ni2 / 3Mn1 / 3O2, the doping amount of Ce element is 3000ppm, the doping amount of Mo element is 1000ppm, and the doping amount of Al element is 1000ppm.

[0089] Example 4

[0090] The preparation method of the single-crystal ternary cathode material in the example is basically the same as that in Example 1, except that the adding amounts of CeO2, MoO3 and Al2O3 in the mixture are changed; the chemical composition of the base material in the single-crystal ternary cathode material prepared in the example is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 4000ppm, the doping amount of Mo element is 800ppm, and the doping amount of Al element is 800ppm.

[0091] Example 5

[0092] The preparation method of the single-crystal ternary cathode material in the example is basically the same as that in Example 1, except that the adding amounts of CeO2 and MoO3 in the mixture are changed; the chemical composition of the base material in the single-crystal ternary cathode material prepared in the example is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 5000ppm, the doping amount of Mo element is 1200ppm, and the doping amount of Al element is 1000ppm.

[0093] Example 6

[0094] The preparation method of the single-crystal ternary cathode material in the example is basically the same as that in Example 1, except that WO2 is used to replace MoO3, ZrO2 is used to replace Al2O3, and the adding amount of ZrO2 is changed; the chemical composition of the base material in the single-crystal ternary cathode material prepared in the example is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 3000ppm, the doping amount of W element is 1000ppm, and the doping amount of Zr element is 2000ppm.

[0095] Example 7

[0096] The preparation method of the single-crystal ternary cathode material in the embodiment is basically the same as that in Embodiment 1, except that TeO2 is used to replace MoO3, Y2O3 is used to replace Al2O3, and the addition amount of Y2O3 is changed. The chemical composition of the single-crystal ternary cathode material prepared in the embodiment is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of Te element is 1000 ppm, and the doping amount of Y element is 1200 ppm.

[0097] Embodiment 8

[0098] The preparation method of the single-crystal ternary cathode material in the embodiment is basically the same as that in Embodiment 1, except that La2O3 is used to replace Al2O3, and the addition amount of La2O3 is changed. The chemical composition of the single-crystal ternary cathode material prepared in the embodiment is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of Mo element is 1000 ppm, and the doping amount of La element is 800 ppm.

[0099] Embodiment 9

[0100] The preparation method of the single-crystal ternary cathode material in the embodiment is basically the same as that in Embodiment 1, except that WO2 is used to replace MoO3, and Ta2O5 is used to replace Al2O3. The chemical composition of the single-crystal ternary cathode material prepared in the embodiment is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of W element is 1000 ppm, and the doping amount of Ta element is 1000 ppm.

[0101] Embodiment 10

[0102] The preparation method of the single-crystal ternary cathode material in the embodiment is basically the same as that in Embodiment 1, except that TeO2 is used to replace MoO3, and Ga2O3 is used to replace Al2O3. The chemical composition of the single-crystal ternary cathode material prepared in the embodiment is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3Li2 / 3Mo5 / 12Al1 / 6O2, the doping amount of Ce element is 3000 ppm, the doping amount of Te element is 1000 ppm, and the doping amount of Ga element is 800 ppm.

[0103] Example 11

[0104] The preparation method of the single-crystal ternary cathode material in the example is basically the same as that in Example 1, except that the addition amount of MoO2 is changed. The chemical composition of the base material in the single-crystal ternary cathode material prepared in the example is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of Mo element is 2500 ppm, and the doping amount of Al element is 1000 ppm.

[0105] Example 12

[0106] The preparation method of the single-crystal ternary cathode material in the example is basically the same as that in Example 1, except that the addition amount of Al2O3 is changed. The chemical composition of the base material in the single-crystal ternary cathode material prepared in the example is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of Mo element is 1000 ppm, and the doping amount of Al element is 4500 ppm.

[0107] Comparative Example 1

[0108] The preparation method of the single-crystal ternary cathode material in the example is basically the same as that in Example 1, except that the addition amount of CeO2 in the mixture is changed. The chemical composition of the base material in the single-crystal ternary cathode material prepared in the example is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3 ]O2, the doping amount of Ce element is 2000 ppm, the doping amount of Mo element is 1000 ppm, and the doping amount of Al element is 1000 ppm.

[0109] Comparative Example 2

[0110] The preparation method of the single-crystal ternary cathode material in the example is basically the same as that in Example 1, except that the addition amount of CeO2 in the mixture is changed. The chemical composition of the base material in the single-crystal ternary cathode material prepared in the example is Li 1.05 [Ni 0.6 Co 0.1 Mn 0.3Li2 / 3Ni1 / 3Mn1 / 3O2, the doping amount of Ce element is 5500 ppm, the doping amount of Mo element is 1000 ppm, and the doping amount of Al element is 1000 ppm.

[0111] Comparative Example 3

[0112] The preparation method of the single-crystal ternary cathode material in the present comparative example is basically the same as that in Embodiment 1, except that the mixture is sintered in a high-temperature atmosphere box furnace, and the sintering atmosphere is oxygen; the temperature is raised to 500 ℃ at a temperature raising rate of 3 ℃ / min, the temperature is raised to 930 ℃ after 4 h of heat preservation, and then the temperature is naturally lowered to room temperature after 15 h of heat preservation, thereby obtaining the single-crystal ternary cathode material of the present comparative example.

[0113] The chemical composition of the matrix material in the single-crystal ternary cathode material prepared in the present comparative example is Li 1.05 [Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of Mo element is 1000 ppm, and the doping amount of Al element is 1000 ppm.

[0114] Comparative Example 4

[0115] The preparation method of the single-crystal ternary cathode material in the present comparative example is basically the same as that in Embodiment 1, except that the mixture does not include CeO2.

[0116] The chemical composition of the matrix material in the single-crystal ternary cathode material prepared in the present comparative example is Li 1.05 [Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Mo element is 1000 ppm, and the doping amount of Al element is 1000 ppm.

[0117] Comparative Example 5

[0118] The preparation method of the single-crystal ternary cathode material in the present comparative example is basically the same as that in Embodiment 1, except that the mixture does not include MoO3.

[0119] The chemical composition of the matrix material in the single-crystal ternary cathode material prepared in the present comparative example is Li 1.05 [Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Ce element is 3000 ppm, and the doping amount of Al element is 1000 ppm.

[0120] Comparative Example 6

[0121] The preparation method of the single-crystal ternary positive electrode material in the present comparative example is basically the same as that in Embodiment 1, except that the mixture does not include Al2O3.

[0122] The chemical composition of the base material in the single-crystal ternary positive electrode material prepared in the present comparative example is Li 1.05 [Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Ce element is 3000 ppm, and the doping amount of Mo element is 1000 ppm.

[0123] Comparative Example 7

[0124] The preparation method of the single-crystal ternary positive electrode material in the present comparative example is basically the same as that in Embodiment 1, except that the temperature of the first sintering is adjusted to 450°C, and the holding time is adjusted to 3 h; the temperature of the second sintering is adjusted to 890°C, and the holding time is adjusted to 2 h, and the others remain unchanged.

[0125] The chemical composition of the base material in the single-crystal ternary positive electrode material prepared in the present comparative example is Li 1.05 [Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of Mo element is 1000 ppm, and the doping amount of Al element is 1000 ppm.

[0126] Comparative Example 8

[0127] The preparation method of the single-crystal ternary positive electrode material in the present comparative example is basically the same as that in Embodiment 1, except that the temperature of the third sintering is adjusted to 750°C, and the holding time is adjusted to 2.5 h.

[0128] The chemical composition of the base material in the single-crystal ternary positive electrode material prepared in the present comparative example is Li 1.05 [Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Ce element is 3000 ppm, the doping amount of Mo element is 1000 ppm, and the doping amount of Al element is 1000 ppm.

[0129] Comparative Example 9

[0130] The preparation method of the single-crystal ternary positive electrode material in the present comparative example is basically the same as that in Embodiment 1, except that the temperature of the fourth sintering is adjusted to 700°C, and the holding time is adjusted to 2.5 h.

[0131] The chemical composition of the base material in the single-crystal ternary positive electrode material prepared in the present comparative example is Li 1.05[Ni 0.83 Co 0.06 Mn 0.11 ]O2, the doping amount of Ce element is 3000ppm, the doping amount of Mo element is 1000ppm, and the doping amount of Al element is 1000ppm.

[0132] Test Example

[0133] 1. Physicochemical performance characterization was performed on the ternary positive electrode material prepared in the above examples and comparative examples:

[0134] (1) X-ray diffraction

[0135] XRD (X-ray diffraction) test was performed on the ternary positive electrode material powder prepared in the above examples and comparative examples, and the corresponding XRD diffraction spectrum was obtained, from which the CeO2(111) crystal face diffraction peak at 28°-29° of 2θ and the half-peak width of the diffraction peak, and the lithium-nickel mixing rate of the ternary positive electrode material were obtained.

[0136] The test results are shown in Tables 1, 3 and Figure 1 .

[0137] Figure 1 The XRD spectrum of the ternary positive electrode material in Example 1 and Comparative Example 1 is shown in Figure 1 It can be seen that the ternary positive electrode material in Example 1 has a diffraction peak of the (111) crystal face of CeO2 at 28.53° of 2θ, and the half-peak width of the diffraction peak is 0.15; while the ternary positive electrode material in Comparative Example 1 obviously does not have the diffraction peak.

[0138] (2) ICP-AES test

[0139] The mass percentage content of each element in the ternary positive electrode material prepared in the above examples and comparative examples was determined, and the results are shown in Table 1.

[0140] (3) Surface energy

[0141] The ternary positive electrode material prepared in the above examples and comparative examples was modeled and calculated by DFT (density functional theory), and the surface energy of the (003) crystal face, (012) crystal face and (104) crystal face of the ternary positive electrode material in each example and comparative example was obtained.

[0142] The test results are shown in Table 2.

[0143] (4) SEM test

[0144] The ternary positive electrode materials prepared in the above examples and comparative examples were subjected to SEM test, and SEM test images under 3000 times were obtained. The diameters of not less than 100 primary particles in the SEM images were measured, and the average particle diameter of the primary particles was obtained by taking the average value. The measurement results are shown in Table 3 and Table 4. Figure 2 , Figure 3 .

[0145] Figure 2 and Figure 3 are SEM images of the ternary positive electrode materials prepared in Example 1 and Comparative Example 1, respectively. As can be seen from the images, the ternary positive electrode material prepared in Example 1 is a single crystal particle, and has uniform morphology and high dispersibility; while the primary particles in the ternary positive electrode material prepared in Comparative Example 1 have obvious agglomeration phenomenon, and have poor dispersibility and morphology uniformity.

[0146] (4) Median particle diameter

[0147] The ternary positive electrode materials prepared in the above examples and comparative examples were subjected to ultrasonic dispersion in a solvent, and then subjected to particle size test using a Malvern 3000 laser particle size instrument. The test results are shown in Table 3.

[0148] (5) Specific surface area

[0149] 5 g of the ternary positive electrode material sample prepared in each of the examples and comparative examples was respectively loaded into a long tube with a ball bubble, and was subjected to vacuum treatment at 2 h / 200°C, followed by gas adsorption using N2. The adsorption amount of the measured sample to the adsorbate molecules (N2) was determined according to the pressure or weight change before and after adsorption, and thus the specific surface area was obtained. The test results are shown in Table 3.

[0150] (6) Tap density

[0151] The ternary positive electrode materials prepared in each of the examples and comparative examples were respectively loaded into a graduated cylinder, and the graduated cylinder was fixed on a mechanical vibration device. The mechanical vibration device was vertically vibrated by a vibration motor, and the graduated cylinder loaded with the ternary positive electrode material was vibrated in a rhythmic manner with the mechanical vibration device. With the increase of the vibration frequency, the powder or particles in the graduated cylinder were gradually vibrated and compacted. After the vibration frequency reached the set frequency, the mechanical vibration device stopped vibrating, and the volume of the graduated cylinder was read. According to the definition of density, the mass divided by the volume, the density after vibration was obtained, i.e. the tap density. The test results are shown in Table 3.

[0152] (7) Thermal decomposition temperature

[0153] The single-crystal ternary positive electrode material, conductive carbon black and binder polyvinylidene fluoride (PVDF) in the application are mixed uniformly in N-methyl pyrrolidone solvent at a mass percentage ratio of 95:3:2 at 25°C under normal pressure (0.1 MPa) to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of an aluminum foil, and a positive electrode sheet containing a 100-μm positive electrode active layer is obtained after drying, cold pressing, etc. The compaction density of the positive electrode sheet is 4.5 g / cm 3 The positive electrode sheet, lithium sheet, separator and electrolyte are assembled into a CR2032 button cell in a button cell box, wherein the electrolyte comprises ethylene carbonate (EC), methyl ethyl carbonate (EMC) and LiPF6, the volume ratio of ethylene carbonate (EC) to methyl ethyl carbonate (EMC) is 3:7, and the mass percentage of LiPF6 in the electrolyte is 12.5%.

[0154] After the prepared CR2032 button cell is charged at a rate of 0.2C to a cutoff voltage of 4.3V, the positive electrode sheet is disassembled, and the positive electrode sheet is subjected to DSC testing. The DSC testing conditions are as follows: the disassembled positive electrode sheet is cleaned with DMC and dried, a certain amount of electrolyte (1 / 3 of the mass of the sample) is added, a TA-DSC thermal analyzer is used to test the thermal decomposition curve, and the thermal decomposition temperature of the single-crystal ternary positive electrode material is obtained. In the test, the equilibrium temperature is set to 50°C, the heating rate is set to 10°C / min, the cutoff temperature is 50-350°C, the sample mass is 2-3 mg, the purge gas is N2, and the flow value is 10 mL / min.

[0155] The test results are shown in Table 3.

[0156] Table 1

[0157]

[0158]

[0159] Table 2

[0160]

[0161]

[0162] Table 3

[0163]

[0164] From Tables 1-3, it can be seen that:

[0165] The ternary positive electrode material prepared in Examples 1-12 has a (111) crystal face diffraction peak with a half-peak width of 0.09-0.2 at 28°-29°, and the mass percentage of Ce in the ternary positive electrode material is 2500-5000 ppm; meanwhile, the surface energy of the (104) crystal face of the ternary positive electrode material is smaller than the surface energy of the (003) crystal face and the surface energy of the (012) crystal face, so that the battery has higher rate performance; in addition, the lithium-nickel mixing rate and the thermal decomposition temperature of the ternary positive electrode material prepared in the examples are both high. Therefore, the ternary positive electrode material in the application can effectively improve the safety performance and electrochemical performance of the battery.

[0166] 2. The ternary positive electrode material prepared in the above examples and comparative examples is made into a button cell, including the following steps:

[0167] The capacity, rate performance, cycle performance and safety of the button cell prepared above are tested:

[0168] (1) Capacity

[0169] Charge at a 0.2C rate to a cut-off voltage of 4.3V, then charge at a constant voltage under the cut-off voltage to a current less than 0.05C, record the charge capacity at this time as the first cycle charge specific capacity, then stand for 5 min, then discharge at a 0.2C rate to a voltage of 2.5V, record the discharge capacity at this time as the first cycle discharge specific capacity, which is the initial capacity.

[0170] (2) Rate performance

[0171] Charge at a 0.1C rate to a cut-off voltage of 4.3V, then charge at a constant voltage under the cut-off voltage to a current less than 0.05C, then stand for 5 min, then discharge at a 0.2C rate to a voltage of 2.5V, the capacity at this time is recorded as the discharge capacity at a 0.2C rate C0; stand for 10 min, charge at a 1C rate to a cut-off voltage of 4.5V, then charge at a constant voltage under the cut-off voltage to a current less than 0.05C, then stand for 5 min, then discharge at a 2C rate to a voltage of 2.5V, the capacity at this time is recorded as the discharge capacity at a 2C rate C1, and the 2C rate performance is the ratio of C1 to C2.

[0172] (3) Cycle performance

[0173] The ternary positive electrode material prepared in the above examples and comparative examples was prepared into a positive electrode sheet according to the preparation method in the above button cell, the negative electrode was graphite, the separator was polyethylene, the electrolyte included ethylene carbonate (EC), methyl ethyl carbonate (EMC) and LiPF6, the volume ratio of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) was 3:7, the mass percentage of LiPF6 in the electrolyte was 12.5%, and a laminated battery was assembled.

[0174] The laminated battery prepared above was subjected to charge and discharge at 45°C in a voltage range of 2.5-4.3V at a rate of 1C to obtain the initial discharge capacity; after 300 cycles of cyclic charge and discharge at the above charge and discharge mechanism, the discharge capacity after cycling was obtained, and the cycle capacity retention rate was the ratio of the discharge capacity after cycling to the initial discharge capacity.

[0175] (4) Safety

[0176] The safety of the battery was characterized by the battery expansion rate. Specifically, the full battery assembled above was fully charged to the set voltage of 4.3V, the thickness L0 of the battery was tested by a PPG battery thickness gauge, then the battery was taken out after being placed in a 70°C constant temperature box for 28 days, the thickness L1 of the battery at this time was tested by a PPG battery thickness gauge, and the battery expansion rate was calculated by formula 1,

[0177] Battery expansion rate (%) = (L1-L0) / L0x100% formula 1

[0178] The calculation results are shown in Table 4.

[0179] Table 4

[0180]

[0181] From Table 4, it can be seen that:

[0182] The comprehensive electrochemical performance and safety of the lithium ion battery prepared in Examples 1-12 were better than those of Comparative Examples 1-9, wherein the 1C 300 cycle retention rate of Example 2 was the highest at 95.1%, the cell expansion rate was the lowest at 12.3%, correspondingly, the 0.2C button capacity was as high as 201.3 mAh / g, and the 2C / 0.2C rate performance was 89.5%. It can be seen that the single-crystal ternary positive electrode material in the application has high structural stability and thermal stability, which can effectively improve the cycle performance and safety performance of the lithium ion battery, and also has capacity and rate performance.

[0183] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A single-crystal ternary cathode material, characterized in that, The single-crystal ternary cathode material includes materials with a chemical composition of Li. m [Ni x Co y Mn z The matrix material of O2, wherein 0.98 < m < 1.03, 0.6 ≤ x < 1, 0 < y < 0.1, 0 < z < 0.1; The matrix material is doped with Ce, M1 and M2 elements, wherein M1 element includes at least one of Mo, W and Te, and M2 element includes at least one of Al, Zr, Y, La, Ta and Ga. In the X-ray diffraction pattern of the single-crystal ternary cathode material, there is a diffraction peak of the (111) crystal plane of CeO2 at 2θ of 28° to 29°, and the full width at half maximum (FWHM) of the diffraction peak is 0.09 to 0.

2. The mass percentage of Ce element in the single-crystal ternary cathode material is 2500–5000 ppm; The single-crystal ternary cathode material includes the matrix material and a coating layer covering at least a portion of the surface of the matrix material. The matrix material is bulk doped with M2, and the surface of the matrix material is doped with Ce and M1. The coating layer is CeO2. The mass percentage of M1 element in the single-crystal ternary cathode material is 500–2000 ppm, and the mass percentage of M2 element in the single-crystal ternary cathode material is 500–4000 ppm.

2. The single-crystal ternary cathode material according to claim 1, characterized in that, In the X-ray diffraction pattern of the single-crystal ternary cathode material, there are diffraction peaks of the (003) crystal plane at 2θ of 18.2° to 19.0°, diffraction peaks of the (012) crystal plane at 2θ of 38.2° to 38.3°, and diffraction peaks of the (104) crystal plane at 2θ of 44.35° to 44.45°. The surface energy E of the (104) crystal plane (104) The surface energy E of the (003) crystal plane (003) and the surface energy E of the (012) crystal plane (012) Satisfying Equations 1 and 2, 50%E (003) <E (104) <70%E (003) formula 1 20%E (012) <E (104) <30%E (012) Formula 2.

3. The single-crystal ternary cathode material according to claim 1, characterized in that, The single-crystal ternary cathode material includes single-crystal primary particles; The average particle size of the single-crystal primary particles is 1.5–4 μm.

4. The single-crystal ternary cathode material according to claim 3, characterized in that, The median particle size of the single-crystal ternary cathode material is 3–8 μm, and / or the specific surface area of ​​the single-crystal ternary cathode material is 0.2–1 m². 2 / g, and / or, the tap density of the single-crystal ternary cathode material is >2.2g / cm³. 3 .

5. The single-crystal ternary cathode material according to any one of claims 1-4, characterized in that, In the DSC test of the single-crystal ternary cathode material, the thermal decomposition temperature of the single-crystal ternary cathode material is not lower than 225℃; And / or, the lithium-nickel mixing ratio of the single-crystal ternary cathode material is <2%.

6. A method for preparing a single-crystal ternary cathode material according to any one of claims 1-5, characterized in that, Includes the following steps: (1) The ternary cathode material precursor Li m Ni x Co y Mn z (OH)2, Li source, Ce source, M1 source and M2 source are mixed and subjected to first sintering, second sintering, third sintering and fourth sintering under an oxygen atmosphere; The first sintering temperature T1 is 400-600℃, and the holding time t1 is 4-6h; The second sintering temperature T2 is 900~1000℃, and the holding time t2 is t1-1≤t2<t1; The third sintering temperature T3 is T2-100<T3≤T2-30, and the holding time t3 is t2<t3<t1+1; The fourth sintering temperature T4 is T3-70<T4≤T3-30, and the holding time t4 is t2<t4<t1+1; (2) After the fourth sintering is completed, the material is naturally cooled to obtain the single crystal ternary cathode material.

7. A positive electrode plate, characterized in that, The cathode material comprises the single-crystal ternary cathode material according to any one of claims 1-5, or the single-crystal ternary cathode material prepared by the preparation method according to claim 6.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes the single-crystal ternary cathode material according to any one of claims 1-5, or the single-crystal ternary cathode material prepared by the preparation method according to claim 6, or the cathode sheet according to claim 7.

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