A high-nickel ternary cathode material doped with medium- and high-valent trace elements and modified by La4NiLiO8 epitaxial layer coating, as well as its preparation method and application

Abstract

The present invention provides a high-nickel ternary positive electrode material modified by medium- and high-valent trace element doping in conjunction with La4NiLiO8 epitaxial layer coating, as well as a preparation method and application thereof. A transition metal hydroxide, a La source, and a medium-valent doping element raw material are dispersed in a solvent, stirred evenly, and then heated and evaporated to dryness. A high-valent doping element raw material and a Li source are added to the evaporated sample and mixed and ground; the ground mixture is sintered to obtain the high-nickel ternary positive electrode material modified by medium- and high-valent trace element doping in conjunction with La4NiLiO8 epitaxial layer coating. The present invention effectively overcomes the problems of capacity attenuation of existing high-nickel ternary positive electrode materials caused by bulk lattice collapse, microcracks between grain boundaries, and interface reactions during the cycle process through this strategy of medium- and high-valent trace element doping in conjunction with La4NiLiO8 epitaxial layer coating modification.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of positive electrode materials for lithium-ion batteries, and relates to a high-nickel ternary positive electrode material modified by doping with medium- and high-valent trace elements and synergistically coating a La4NiLiO8 epitaxial layer, as well as a preparation method and application thereof. Background Art

[0002] The depletion of traditional fossil fuels and the increasing environmental pollution are driving the development and utilization of clean energy. To achieve the transition to clean, low-carbon energy, advanced energy storage technologies are becoming a critical link between renewable energy supply and demand. Among various energy storage technologies, lithium-ion batteries have emerged as a key player in the clean technology revolution due to their high energy density, long lifespan, and high efficiency. They are widely used in portable consumer electronics, new energy vehicles, grid energy storage, and many other fields.

[0003] Lithium-ion batteries consist of several key components, including cathode materials, anode materials, separators, and electrolytes. As one of the key materials for increasing energy density, the development of cathode materials has attracted extensive attention from researchers. Among these, high-nickel ternary layered transition metal oxide cathode materials offer high specific capacity, meeting the demand for high energy density. Their low cost and high specific capacity offer significant commercial potential, making them one of the emerging cathode materials.

[0004] The study found that high nickel content will weaken the cycle stability of the positive electrode material. As the nickel content increases, the degree of cation mixing in the high nickel ternary positive electrode material intensifies, and the bulk structure loses stability. In addition, high operating voltage will cause large volume changes and the derivative of microcracks. The electrolyte penetrates into the interior of the secondary spherical particles and interacts with the highly active Ni on the surface of the material. 4+ Side reactions generate an inert rock salt phase, which hinders lithium ion transport, leading to increased impedance and deteriorated battery performance. Therefore, adopting a comprehensive modification strategy to suppress the multiple failure behaviors caused by the increase in Ni content has become the focus of the research and development and application of high-nickel ternary cathode materials.

[0005] The demand for energy density of power batteries continues to increase, which drives the application of high-nickel positive electrode materials to high voltage and high rate conditions, requiring them to have excellent performance under the corresponding conditions. Due to the difference in solubility products of different metal doping elements in the precursor preparation stage of the co-precipitation method, the difficulty of preparing the material is increased, and the calcination process is complicated. The present invention starts from simplifying the modification and sintering process, while taking into account the comprehensive performance of high-nickel ternary positive electrode materials under high voltage, and proposes the optimization of medium and high-priced doping elements. It adopts simple and convenient liquid phase mixing and solid phase powder mixing, and realizes the successful preparation of multiple modified medium and high-priced trace element doping and La4NiLiO8 epitaxial layer coating high nickel ternary positive electrode materials through only one-step sintering heat treatment process. At the same time, the bulk and interface structure of the material are stabilized, and it has excellent cycle and rate performance at high cut-off voltage. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-nickel ternary positive electrode material modified by doping with medium- and high-valent trace elements and synergistically coating with La4NiLiO8 epitaxial layer, as well as a preparation method and application thereof. Before heat treatment and sintering, the present invention adds doping and modifying elements on the surface of the hydroxide precursor, uniformly mixes the doping elements and pre-coates them in situ, in the hope of successfully preparing the high-nickel ternary positive electrode material modified by doping with medium- and high-valent trace elements and synergistically coating with La4NiLiO8 epitaxial layer.

[0007] The present invention provides a high-nickel ternary cathode material modified by doping with medium- and high-valent trace elements and coating with a La4NiLiO8 epitaxial layer, and a preparation method thereof, comprising the following experimental steps:

[0008] A) dispersing a transition metal hydroxide, a La source, and a medium-valent doping element raw material in a solvent, stirring them uniformly, and then heating and evaporating them to dryness. Adding a high-valent doping element raw material and a Li source to the evaporated sample, mixing and grinding;

[0009] B) The ground mixture is sintered to obtain the medium- and high-valent trace element doped synergistically La4NiLiO8 epitaxial layer coated modified high-nickel ternary positive electrode material.

[0010] Preferably, the medium valence doping element in step A) is Al 3+ 、Ga 3+ 、Zr 4+ 、Ti 4+ One of the following: the high-valent doping element is Nb 5+ 、Ta 5+ 、W 6+ 、Mo 6+ One of the transition metal hydroxides; the transition metal hydroxide is Ni m Co n Mn 1-m-n(OH)2, where 0.5≤m≤0.9, 0<n<0.2.

[0011] Preferably, the transition metal hydroxide in step A) is Ni 0.83 Co 0.12 Mn 0.05 (OH)2; the La source is one of soluble salts such as lanthanum nitrate, lanthanum oxalate, and lanthanum chloride; the medium-valence doping element raw material is selected from the group consisting of Al 3+ 、Ga 3+ 、Zr 4+ 、Ti 4+ A soluble metal salt of one of the elements; the high-valent doping element raw material is selected from Nb 5+ 、Ta 5+ 、W 6+ 、Mo 6+ A metal oxide of one of the elements; the Li source is one of lithium hydroxide monohydrate, lithium carbonate, and lithium acetate;

[0012] The molar ratio of La source, medium-valent doping element, high-valent doping element and transition metal hydroxide is (0.0025~0.02):(0.00125~0.01):(0.00125~0.01):(0.96~0.995), and the molar ratio of Li source and transition metal hydroxide is (1.01~1.10):1.

[0013] Preferably, in step A), the molar ratio of the La source, the medium-valent doping element, the high-valent doping element and the transition metal hydroxide is 0.005:0.0025:0.0025:0.99, and the molar ratio of the Li source to the transition metal hydroxide is 1.05:1.

[0014] Preferably, the solvent in step A) is deionized water or ethanol solution;

[0015] Preferably, the temperature of the heating and evaporation is 60-100°C.

[0016] Preferably, the sintering process in step B) is to heat from room temperature to 710-800°C at a rate of 2-10°C / min, keep warm for 10-20 hours, cool to 400±50°C at a rate of 1-8°C / min, and then cool to room temperature.

[0017] Preferably, the sintering process in step B) requires the introduction of oxygen, and the oxygen flow rate is 10 to 80 mL / min.

[0018] A high-nickel ternary positive electrode material prepared by the above method is doped with medium- and high-valent trace elements and synergistically coated with a La4NiLiO8 epitaxial layer.

[0019] The invention relates to an application of a high-nickel ternary positive electrode material prepared by the above method by doping with medium- and high-valent trace elements and synergistically coating with a La4NiLiO8 epitaxial layer in lithium-ion batteries.

[0020] The beneficial effects of the present invention are:

[0021] The present invention utilizes a technical solution that utilizes doping with medium- and high-valent trace elements in conjunction with La4NiLiO8 epitaxial layer coating modification. This simple one-step sintering process achieves multiple modifications during the high-temperature lithiation stage of the hydroxide precursor. The use of medium-valent doping element ions broadens lithium ion diffusion channels, achieving uniform bulk doping and stabilizing the bulk structure. Due to their low solid solubility, the high-valent doping element is partially concentrated at the grain boundaries of the high-nickel ternary cathode material particles, inhibiting primary particle growth, regulating particle size, and mitigating the generation of microcracks caused by stress and strain concentration. Simultaneously, the resulting surface layered La4NiLiO8 perovskite coating exhibits fast ion conductor properties, facilitating interfacial ion and electron transport. It exhibits excellent compatibility with the bulk material and improves surface electronic and ionic conductivity. Its abundant oxygen vacancies and interstitials can capture highly reactive lattice oxygen that escapes from the bulk structure, effectively suppressing surface side reactions. This strategy of doping with medium- and high-valent trace elements in conjunction with La4NiLiO8 epitaxial layer coating provides comprehensive protection for the bulk structure and surface interface of the high-nickel ternary cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 XRD patterns of high-nickel ternary positive electrode materials prepared in Comparative Example 1 and Examples 1 to 4 of the present invention;

[0023] Figure 2 This is an SEM image of the original high-nickel ternary positive electrode material prepared in Comparative Example 1 of the present invention;

[0024] Figure 3 This is an SEM image of the modified high-nickel ternary cathode material prepared in Example 2 of the present invention by doping with medium- and high-valent trace elements and coating with a La4NiLiO8 epitaxial layer;

[0025] Figure 4 This is a cycle performance diagram of the high-nickel ternary positive electrode material prepared in Comparative Example 1 and Examples 1 to 4 of the present invention;

[0026] Figure 5 This is a graph showing the cycle performance of the high-nickel ternary positive electrode materials prepared in Comparative Examples 1 to 4 and Example 2 of the present invention;

[0027] Figure 6 This is a rate performance diagram of the high-nickel ternary positive electrode material prepared in Comparative Example 1 and Examples 1 to 4 of the present invention;

[0028] Figure 7This is a rate performance diagram of the high-nickel ternary positive electrode materials prepared in Comparative Examples 1 to 4 and Example 2 of the present invention;

[0029] Figure 8 This is a thermal stability test diagram of the high-nickel ternary positive electrode material prepared in Comparative Example 1 and Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described in further detail below in conjunction with the embodiments of the present invention and the accompanying drawings.

[0031] Example 1

[0032] A method for preparing a high-nickel ternary cathode material by doping with medium- and high-valent trace elements and synergistically coating a La4NiLiO8 epitaxial layer, comprising the following steps:

[0033] (1) According to the molar ratio of transition metal hydroxide: La source: Zr source = 99.5:0.25:0.125, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 0.0237g La(NO3)3·6H2O and 0.0117g Zr(NO3)4·5H2O were added to 50mL anhydrous ethanol and stirred for 30min to fully dissolve to obtain solution A;

[0034] (2) Solution A was heated and stirred in an oil bath at 80°C, evaporated to dryness, and then ground to obtain precursor B;

[0035] (3) Weigh 0.0063 g of WO3 at a transition metal hydroxide: W source molar ratio of 99.5:0.125, weigh 0.9521 g of LiOH·H2O at a transition metal hydroxide: Li source molar ratio of 1:1.05, and grind them together with precursor B to obtain ground sample C;

[0036] (4) The ground sample C was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 hours. Then, the temperature was lowered to 400°C within 180 minutes, and the sample was naturally cooled to room temperature in the furnace to obtain a ternary high-nickel ternary positive electrode material (marked as 0.25% LaZrW) doped with medium and high-valent trace elements and coated with a La4NiLiO8 epitaxial layer.

[0037] Example 2

[0038] A method for preparing a high-nickel ternary cathode material by doping with medium- and high-valent trace elements and synergistically coating a La4NiLiO8 epitaxial layer, comprising the following steps:

[0039] (1) According to the molar ratio of transition metal hydroxide: La source: Zr source = 99:0.5:0.25, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 0.0474g La(NO3)3·6H2O and 0.0234g Zr(NO3)4·5H2O were added to 50mL anhydrous ethanol and stirred for 30min to fully dissolve to obtain solution A;

[0040] (2) Solution A was heated and stirred in an oil bath at 80°C, evaporated to dryness, and then ground to obtain precursor B;

[0041] (3) Weigh 0.0127 g of WO3 at a transition metal hydroxide: W source molar ratio of 99:0.25, weigh 0.9521 g of LiOH·H2O at a transition metal hydroxide: Li source molar ratio of 1:1.05, and grind them together with precursor B to obtain ground sample C;

[0042] (4) The ground sample C was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 hours. Then, the temperature was lowered to 400°C within 180 minutes, and the sample was naturally cooled to room temperature in the furnace to obtain a ternary high-nickel ternary positive electrode material (marked as 0.5% LaZrW) doped with medium and high-valent trace elements and synergistically coated with a La4NiLiO8 epitaxial layer.

[0043] Example 3

[0044] A method for preparing a high-nickel ternary cathode material by doping with medium- and high-valent trace elements and synergistically coating a La4NiLiO8 epitaxial layer, comprising the following steps:

[0045] (1) According to the molar ratio of transition metal hydroxide: La source: Zr source = 98:1:0.5, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 0.0964g La(NO3)3·6H2O and 0.0473g Zr(NO3)4·5H2O were added to 50mL anhydrous ethanol and stirred for 30min to fully dissolve to obtain solution A;

[0046] (2) Solution A was heated and stirred in an oil bath at 80°C, evaporated to dryness, and then ground to obtain precursor B;

[0047] (3) Weigh 0.0256 g of WO3 at a transition metal hydroxide: W source molar ratio of 98:0.5, weigh 0.9521 g of LiOH·H2O at a transition metal hydroxide: Li source molar ratio of 1:1.05, and grind them together with precursor B to obtain ground sample C;

[0048] (4) The ground sample C was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 hours. Then, the temperature was lowered to 400°C within 180 minutes, and the sample was naturally cooled to room temperature in the furnace to obtain a ternary high-nickel ternary positive electrode material (marked as 1% LaZrW) doped with medium and high-valent trace elements and coated with a La4NiLiO8 epitaxial layer.

[0049] Example 4

[0050] A method for preparing a high-nickel ternary cathode material by doping with medium- and high-valent trace elements and synergistically coating a La4NiLiO8 epitaxial layer, comprising the following steps:

[0051] (1) According to the molar ratio of transition metal hydroxide: La source: Zr source = 96:2:1, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 0.1969 g La(NO3)3·6H2O and 0.0966 g Zr(NO3)4·5H2O were added to 50 mL of anhydrous ethanol and stirred for 30 min to fully dissolve to obtain solution A;

[0052] (2) Solution A was heated and stirred in an oil bath at 80°C, evaporated to dryness, and then ground to obtain precursor B;

[0053] (3) Weigh 0.0522 g of WO3 at a transition metal hydroxide: W source molar ratio of 96:1, weigh 0.9521 g of LiOH·H2O at a transition metal hydroxide: Li source molar ratio of 1:1.05, and grind them together with precursor B to obtain ground sample C;

[0054] (4) The ground sample C was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 hours. Then, the temperature was lowered to 400°C within 180 minutes, and the sample was naturally cooled to room temperature in the furnace to obtain a ternary high-nickel ternary positive electrode material (marked as 2% LaZrW) doped with medium and high-valent trace elements and coated with a La4NiLiO8 epitaxial layer.

[0055] Comparative Example 1

[0056] The preparation method of the original high-nickel ternary positive electrode material comprises the following steps:

[0057] (1) According to the molar ratio of transition metal hydroxide to Li source = 1:1.05, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05(OH)2 and 0.9521g LiOH·H2O, then mixed and ground evenly;

[0058] (2) The ground sample was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 h. Then, the sample was cooled to 400°C within 180 min and naturally cooled to room temperature in the furnace to obtain the original high-nickel ternary positive electrode material (labeled as Pristine).

[0059] Comparative Example 2

[0060] A method for preparing a La-modified high-nickel ternary cathode material comprises the following steps:

[0061] (1) According to the molar ratio of transition metal hydroxide to La source = 99.5:0.5, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05 (OH)2 and 0.0475 g La(NO3)3·6H2O were added to 50 mL of anhydrous ethanol and stirred for 30 min to fully dissolve to obtain solution A;

[0062] (2) Solution A was heated and stirred in an oil bath at 80°C, evaporated to dryness, and then ground to obtain precursor B;

[0063] (3) According to the molar ratio of transition metal hydroxide to Li source = 1:1.05, 0.9521 g of LiOH·H2O was weighed and added to precursor B, mixed and ground uniformly to obtain ground sample C;

[0064] (4) The ground sample C was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 h. Then, the temperature was lowered to 400°C within 180 min and naturally cooled to room temperature in the furnace to obtain a La element-modified high-nickel ternary positive electrode material (marked as 0.5% La).

[0065] Comparative Example 3

[0066] A method for preparing a Zr element-modified high-nickel ternary cathode material comprises the following steps:

[0067] (1) According to the molar ratio of transition metal hydroxide to Zr source = 99.75:0.25, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05 (OH)2 and 0.0233 g Zr(NO3)4·5H2O were added to 50 mL of anhydrous ethanol and stirred for 30 min to fully dissolve to obtain solution A;

[0068] (2) Solution A was heated and stirred in an oil bath at 80°C, evaporated to dryness, and then ground to obtain precursor B;

[0069] (3) According to the molar ratio of transition metal hydroxide to Li source = 1:1.05, 0.9521 g of LiOH·H2O was weighed and added to precursor B, mixed and ground uniformly to obtain ground sample C;

[0070] (4) The ground sample C was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 h. Then, the temperature was lowered to 400°C within 180 min and naturally cooled to room temperature in the furnace to obtain a Zr element-modified high-nickel ternary positive electrode material (marked as 0.25% Zr).

[0071] Comparative Example 4

[0072] A method for preparing a W-modified high-nickel ternary cathode material comprises the following steps:

[0073] (1) According to the molar ratio of transition metal hydroxide to W source = 99.75:0.25, weigh 2g of transition metal hydroxide Ni 0.83 Co 0.12 Mn 0.05 (OH)2 and 0.0127g WO3, according to the transition metal hydroxide: Li source molar ratio = 1:1.05, weigh 0.9521g LiOH·H2O and grind it evenly;

[0074] (2) The ground sample was placed in a tubular furnace, introduced into an oxygen atmosphere, and heated to 760°C at a heating rate of 2°C / min and calcined for 14 h. Then, the sample was cooled to 400°C within 180 min and naturally cooled to room temperature in the furnace to obtain a W-modified high-nickel ternary positive electrode material (marked as 0.25% W).

[0075] Half-cell assembly:

[0076] According to the mass ratio of active material: conductive agent: binder of 8:1:1, 0.64g of the high nickel positive electrode active material prepared in the embodiment or comparative example was weighed and placed in a blender with 0.08g of conductive agent carbon black (Super P), 0.08g of binder polyvinylidene fluoride (PVDF) and 2mL of organic solvent N-methylpyrrolidone (NMP) for homogenization. After the slurry was mixed evenly, it was evenly coated on a flat aluminum foil current collector. The temperature in the vacuum drying oven was set to 80°C. After drying for 12h, the aluminum foil was punched into a battery pole piece with a diameter of 12mm. The prepared pole piece was used as the positive electrode and the lithium sheet was used as the counter electrode. The battery shell model used was CR2025. The battery was assembled in a glove box (Ar atmosphere, H2O, O2 content was less than 0.01ppm). The assembled battery needed to stand at room temperature for more than 12h to allow the diaphragm pores therein to fully contact the electrolyte and the Li in the electrolyte to form a 200μm dia. + It can migrate quickly between the positive and negative electrodes, facilitating a series of subsequent electrochemical performance tests.

[0077] Charge and discharge test:

[0078] The button cell battery charging and discharging was carried out in the LAND battery test system with a voltage range of 2.8 to 4.5 V. Before the cycle test, the battery was activated three times with a smaller current density of 0.1 C. Then, the charge and discharge cycle test was carried out with a current density of 1 C within the same voltage range.

[0079] Button battery removal:

[0080] After passing certain test conditions, the button battery was moved into the glove box for disassembly. The electrode was soaked in organic solvent dimethyl carbonate (DMC) or diethyl carbonate (DEC) for half an hour and then rinsed clean. The electrode was dried naturally in the glove box for subsequent structural and morphological characterization tests.

[0081] Table 1 shows the electrochemical properties (2.8-4.5 V) of the high nickel ternary positive electrode materials of Examples 1-4 and Comparative Examples 1-4.

[0082] Table 1

[0083]

[0084] Figure 1 The XRD patterns of the high nickel ternary positive electrode materials prepared in Comparative Example 1 and Examples 1 to 4 of the present invention are as follows: the main phase of the modified high nickel ternary positive electrode materials prepared in Examples 1 to 4 by doping with medium and high valence trace elements and coating with La4NiLiO8 epitaxial layers is consistent with the structure of the original high nickel ternary positive electrode materials in Comparative Example 1, and belongs to the hexagonal system. The layered structure of the space group α-NaFeO2 is obtained, and the degree of lithium-nickel mixing is relatively small. In addition, a layered perovskite phase La4NiLiO8 also appears. With the regulation of variables, the (003) amplification peak shifts to the left and the peak intensity decreases. The c-axis interlayer spacing in the corresponding lattice becomes larger and the (003) crystal plane orientation becomes weaker. The (108) / (110) peak splitting degree gradually decreases, and its layered structural characteristics are weakened compared with the original material.

[0085] Figure 2 and Figure 3 The SEM images of the high nickel ternary positive electrode materials prepared in comparative example 1 and example 2 respectively show that the original high nickel ternary positive electrode material prepared in comparative example 1 has a smooth surface and a clear boundary, while the surface state of the modified high nickel ternary positive electrode material in example 2 is significantly changed by the doping of medium and high valence trace elements in conjunction with the La4NiLiO8 epitaxial layer coating. A fuzzy coating layer exists on the surface of the primary particles, and the size of the primary particles is also observed to be reduced accordingly. While forming an effective surface protective layer, the high valence doping element W 6+ Inhibit the growth of primary particles and effectively control the microscopic size of particles.

[0086] Figures 4 to 7 They are respectively the cycle performance graphs of the high nickel ternary positive electrode materials prepared in comparative example 1 and examples 1 to 4 of the present invention, the cycle performance graphs of the high nickel ternary positive electrode materials prepared in comparative examples 1 to 4 and example 2, the rate performance graphs of the high nickel ternary positive electrode materials prepared in comparative example 1 and examples 1 to 4 of the present invention, and the rate performance graphs of the high nickel ternary positive electrode materials prepared in comparative examples 1 to 4 and example 2. Figure 4 The original high-nickel ternary positive electrode material of comparative example 1 has a capacity retention rate of 83.23% after 100 cycles at a current density of 1C, while the capacity retention rate of the modified high-nickel ternary positive electrode material prepared in Example 2 by doping with medium and high-valent trace elements and synergistically coating with La4NiLiO8 epitaxial layer under the same conditions is 94.52%. Figure 6 It shows that the modified high-nickel ternary positive electrode material prepared in Example 2 by doping with medium and high-valent trace elements and synergistically coating with La4NiLiO8 epitaxial layer still has the highest discharge specific capacity at a high current of 20C. After the high current charge and discharge test, it has good reversibility and still maintains the highest discharge specific capacity at 0.1C charge and discharge. Figure 4 and Figure 6Performance comparison of Examples 1 to 4 shows that the modified high-nickel ternary positive electrode material prepared in Example 2 with medium and high valent trace element doping and La4NiLiO8 epitaxial layer coating has the best electrochemical performance. The electrochemical performance of the modified high-nickel ternary positive electrode material in Example 1 with reduced content of modifying elements is weakened. As the content of modifying elements increases, the reversible discharge specific capacity of the modified high-nickel ternary positive electrode material in Example 4 with medium and high valent trace element doping and La4NiLiO8 epitaxial layer coating is reduced, and the addition of excessive non-electrochemically active elements sacrifices part of the capacity. Figure 5 、 7 Analysis shows that the cycle performance and rate performance of the modified high-nickel ternary positive electrode material prepared in Example 2 by doping with medium and high-valent trace elements in conjunction with La4NiLiO8 epitaxial layer coating are better than those of comparative examples 1 to 4. In summary, it is proved that the capacity of the high-nickel ternary positive electrode material is not significantly affected while the cycle stability of the material is improved by doping with medium and high-valent trace elements in conjunction with La4NiLiO8 epitaxial layer coating. It shows better cycle performance and rate performance as a whole. The main reason for this is that the modified high-nickel ternary positive electrode material by doping with medium and high-valent trace elements in conjunction with La4NiLiO8 epitaxial layer coating can effectively stabilize the bulk interface structure of the material and alleviate interface reactions.

[0087] Figure 8 This is a thermal stability test diagram of the high-nickel ternary positive electrode material prepared in Comparative Example 1 and Example 2 of the present invention. Differential scanning calorimetry (DSC) is used to test the thermal stability of the material. The exothermic peak temperature of the original high-nickel ternary positive electrode material prepared in Comparative Example 1 is 241°C, and the exothermic peak temperature of the high-nickel ternary positive electrode material modified by doping with medium and high-valent trace elements and synergistically coating with La4NiLiO8 epitaxial layer prepared in Example 2 is 248°C. The modification corresponds to increasing the lattice oxygen release temperature of the material, greatly reducing the heat release, and improving the thermal stability of the high-nickel ternary positive electrode material.

[0088] In summary, in the preparation method described, one-step sintering successfully realizes the doping of medium- and high-valent trace elements in conjunction with the La4NiLiO8 epitaxial layer coating modification of the high-nickel ternary positive electrode material. The intermediate-valence doping elements doped in the bulk lattice can stabilize the bulk structure and slow down the collapse of the lithium interlayer spacing in the highly charged state. The high-valence doping elements regulate the primary particle size, relieve stress and strain, and inhibit the generation of microcracks. The La4NiLiO8 epitaxial layer has abundant oxygen vacancies and oxygen interstices, which can effectively inhibit the precipitation of lattice oxygen and form a stable surface / interface layer during the cycle. The crystal structure and surface chemistry of the high-nickel ternary positive electrode material are modified in multiple ways by doping with medium- and high-valent trace elements in conjunction with the La4NiLiO8 epitaxial layer coating modification, which significantly improves the cycle stability and thermal stability of the high-nickel ternary positive electrode material, and effectively improves the multiple failure behaviors of the existing high-nickel ternary positive electrode material during the electrochemical reaction.

[0089] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will appreciate that various improvements and modifications may be made to the present invention without departing from the principles of the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a high-nickel ternary cathode material by doping with medium- and high-valent trace elements and coating with a La4NiLiO8 epitaxial layer, characterized in that: The following steps are involved: A) dispersing a transition metal hydroxide, a La source, and a medium-valent doping element raw material in a solvent, stirring them uniformly, and then heating and evaporating them to dryness. Adding a high-valent doping element raw material and a Li source to the evaporated sample, mixing and grinding; B) sintering the ground mixture to obtain the medium- and high-valent trace element doped synergistically La4NiLiO8 epitaxial layer-coated modified high-nickel ternary positive electrode material; The medium valence doping element in step A) is Al 3+ 、Ga 3+ 、Zr 4+ 、Ti 4+ One of the following: the high-valent doping element is Nb 5+ 、Ta 5+ 、W 6+ 、Mo 6+ One of the following; The molar ratio of La source, medium-valent doping element, high-valent doping element and transition metal hydroxide is (0.0025-0.02): (0.00125-0.01): (0.00125-0.01): (0.96-0.995), and the molar ratio of Li source and transition metal hydroxide is (1.01-1.10):1; In step B), the sintering process is to increase the temperature from room temperature to 710-800°C at a rate of 2-10°C / min, keep the temperature for 10-20 hours, cool the temperature down to 400±50°C at a rate of 1-8°C / min, and then cool to room temperature. The sintering process in step B) requires the introduction of oxygen, and the oxygen flow rate is 10-80 mL / min.

2. The preparation method according to claim 1, characterized in that The transition metal hydroxide in step A) is Ni m Co n Mn 1-m-n (OH)2, where 0.5≤m≤0.9, 0<n<0.

2.

3. The preparation method according to claim 1, characterized in that The transition metal hydroxide in step A) is Ni 0.83 Co 0.12 Mn 0.05 (OH)2; the La source is one of lanthanum nitrate, lanthanum oxalate, and lanthanum chloride soluble salts; the medium valence doping element raw material is selected from the group consisting of Al 3+ 、Ga 3+ 、Zr 4+ 、Ti 4+ A soluble metal salt of one of the elements; the high-valent doping element raw material is selected from Nb 5+ 、Ta 5+ 、W 6+ 、Mo 6+ A metal oxide of one of the elements; the Li source is one of lithium hydroxide monohydrate, lithium carbonate, and lithium acetate.

4. The preparation method according to claim 1, characterized in that In step A), the molar ratio of the La source, the medium-valent doping element, the high-valent doping element and the transition metal hydroxide is 0.005: 0.0025: 0.0025: 0.99, and the molar ratio of the Li source to the transition metal hydroxide is 1.05:

1.

5. The preparation method according to claim 1, characterized in that The solvent in step A) is deionized water or ethanol solution; The temperature of the heating evaporation is 60-100°C.

6. A high-nickel ternary positive electrode material prepared by the preparation method according to any one of claims 1 to 5, which is doped with medium- and high-valent trace elements and synergistically coated with a La4NiLiO8 epitaxial layer.

7. Use of the modified high-nickel ternary cathode material doped with medium- and high-valent trace elements and coated with La4NiLiO8 epitaxial layer as claimed in claim 6 in lithium-ion batteries.

8. A lithium ion battery, characterized in that: Contains the high-nickel ternary positive electrode material doped with medium- and high-valent trace elements as described in claim 7 and coated with a La4NiLiO8 epitaxial layer.

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