Triple modified high-nickel positive electrode material and one-step modification method thereof

Abstract

The invention relates to a triple modified high-nickel positive electrode material and a one-step modification method thereof, the triple modified high-nickel positive electrode material is a polycrystalline secondary spheroid particle formed by doping Mg < 2 + > in a high-nickel positive electrode material bulk phase, the surface of the high-nickel positive electrode material contains oxygen vacancies, and a fast ion conductor Li3PO4 coating layer generated in situ coats the outer surface of the high-nickel positive electrode material particle. The one-step modification method comprises the following steps: uniformly mixing the high-nickel positive electrode material with magnesium ammonium phosphate, carrying out one-step sintering in an inert protective atmosphere, and cooling to room temperature to obtain the triple modified high-nickel positive electrode material. The triple modified high-nickel positive electrode material is regular in morphology, uniform in distribution, high in structural stability and thermal stability and excellent in electrochemical performance. The method is simple in process, low in raw material cost and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to a modified high-nickel cathode material and a modification method thereof, and particularly to a triple-modified high-nickel cathode material and a one-step modification method thereof. Background Art

[0002] High-nickel cathode materials are one of the most promising cathode materials for lithium-ion batteries. However, increasing the nickel content in the material to improve the energy density will exacerbate some problems of high-nickel cathode materials, such as poor structural stability and poor thermal stability. These disadvantages seriously hinder their commercial application in lithium-ion batteries. The main reasons include that during the charge-discharge cycle of high-nickel materials, the layered structure transforms into a disordered spinel structure and then into an inactive rock-salt structure, resulting in poor structural stability, and there are a large number of residual lithium compounds on the surface. These changes lead to serious structural collapse and capacity decay during the cycle.

[0003] To address the above problems, most studies modify the material by bulk doping to improve structural stability or surface coating on a single aspect. However, single-sided doping or coating often shows disadvantages during long cycles.

[0004] CN117996012A discloses a crack-free magnesium-doped high-nickel ternary layered cathode material and a preparation method thereof. The matrix includes a magnesium-doped high-nickel ternary cathode material, and the composite coating layer includes lithium phosphate and calcium carbonate. This method first makes Mg doped in the high-nickel ternary cathode grains by a composite doping method, and then fully mixes the Mg-doped ternary cathode material with a mixture of lithium phosphate and calcium carbonate and performs a second sintering in an oxygen atmosphere to obtain a Mg-doped ternary cathode material with a composite layer coating. This method further optimizes the preparation method on the basis of Mg doping and proposes an external composite coating of Li3PO4 and CaCO3 layers. However, this doping and coating are completed in two completely different stages; and in an oxygen atmosphere, the matrix ternary material and the coating material are prone to react during the high-temperature process, resulting in a transformation of the crystal structure on the surface layer of the high-nickel ternary material, thereby sacrificing the capacity performance of the active material.

[0005] CN112811403A discloses a Mg / Ti co-doped Li3PO4-coated high-nickel ternary cathode material and a preparation method thereof. This method first mixes a high-nickel precursor with a lithium source, a magnesium source, and a titanium source and performs two-stage sintering to obtain a doped matrix material, and then mixes the doped matrix material with a lithium phosphate compound and performs a second sintering in an oxygen atmosphere to obtain a lithium phosphate-coated cathode material. This method also completes doping and coating in two steps. The magnesium source and the titanium source are added during the lithium-mixing sintering process to achieve doping, and then the lithium phosphate is sintered in an oxygen atmosphere to achieve coating. The sintering process in an oxygen atmosphere to achieve coating will affect the structure of the matrix material.

[0006] In summary, there is an urgent need to find a triple-modified high-nickel cathode material with regular morphology, uniform distribution, high structural stability and thermal stability, and excellent electrochemical performance, as well as a one-step modification method for the triple-modified high-nickel cathode material with simple process, low raw material cost and suitable for industrial production. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a triple-modified high-nickel cathode material with regular morphology, uniform distribution, good structural stability and excellent electrochemical performance.

[0008] The further technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a one-step modification method for the triple-modified high-nickel cathode material with simple process, low raw material cost and suitable for industrial production.

[0009] The technical solution adopted by the present invention to solve its technical problems is as follows: A triple-modified high-nickel cathode material is composed of Mg 2+ doped in the bulk phase of the high-nickel cathode material, the surface of the high-nickel cathode material contains oxygen vacancies, and a polycrystalline secondary spherical-like particle is formed by in-situ generating a fast ion conductor Li3PO4 coating layer covering the outer surface of the high-nickel cathode material particles. In the triple-modified high-nickel cathode material of the present invention, Mg 2+ doping can stabilize the internal structure of the material. The pre-formed oxygen vacancies on the material surface help to improve the lithium ion diffusion rate, while the Li3PO4 coating can improve the Li transport efficiency and inhibit the side reaction between the material and the electrolyte. The synchronous construction of doping, coating and oxygen vacancy co-modification in the material of the present invention can improve the ion transport during charge and discharge while stabilizing the material structure, advantageously combining the advantages of triple modification and improving the electrochemical performance of the material during charge and discharge cycling.

[0010] Preferably, the chemical formula of the high-nickel cathode material is LiNi x Co y Mn (1-x-y) O2, where 0.8 ≤ x < 1 and 0 < y ≤ 0.2.

[0011] Preferably, the doping amount of the Mg 2+ is equivalent to 0.3-5.0 mol% (more preferably 0.5-2.5 mol%) of the total molar number of transition metals. If the doping amount of Mg 2+ is too small, the doping effect is not obvious and the structural stability is insufficient; if the doping amount of Mg 2+ is too large, the proportion of the active material occupied increases, thereby reducing the reversible capacity.

[0012] Preferably, the average thickness of the Li3PO4 coating layer is 5 to 50 nm. If the coating layer is too thin, the effective amount of Li3PO4 for coating is too small to effectively suppress the interfacial side reaction. If the coating layer is too thick and dense, it will hinder the deintercalation / insertion of Li, resulting in a decline in rate performance.

[0013] Preferably, the average particle size of the triple-modified high-nickel cathode material is 3 to 6 μm.

[0014] Preferably, the preparation method of the high-nickel cathode material is as follows: uniformly mix the high-nickel precursor material and the lithium source, and perform two-stage sintering in an oxidizing atmosphere, and cool to room temperature to obtain the high-nickel cathode material.

[0015] Preferably, the molar ratio of the total of nickel, cobalt, and manganese elements in the high-nickel precursor to the lithium element in the lithium source is 1:1.02 to 1.10.

[0016] Preferably, the high-nickel precursor material includes nickel cobalt manganese hydroxide or nickel cobalt manganese carbonate, etc. The high-nickel precursor material is prepared by a co-precipitation reaction in the early stage.

[0017] Preferably, the lithium source includes one or more of lithium hydroxide and / or lithium carbonate, and their hydrates, etc.

[0018] Preferably, the mixing method is as follows: place it in a sealed ball milling tank, without adding ball milling beads, and perform high-speed mixing rotation. Since the high-nickel cathode material is a secondary spherical particle, not adding ball milling beads can prevent particle breakage, and in order to prevent the influence of the environment such as moisture, mixing is carried out in a sealed environment.

[0019] Preferably, the rotation speed of the high-speed mixing rotation is 400 to 600 rpm, and the time is 5 to 8 h.

[0020] Preferably, the two-stage temperature-raising sintering means: first raise the temperature to 350 to 550 °C at a rate of 1 to 10 °C / min (more preferably 3 to 8 °C / min), sinter for 2 to 8 h (more preferably 3 to 6 h), and then raise the temperature to 550 to 1000 °C (more preferably 600 to 900 °C) at a rate of 1 to 10 °C / min (more preferably 3 to 8 °C / min), and sinter for 8 to 20 h. During the first-stage sintering process, the decomposition reactions of the precursor and the lithium source mainly occur. During the second-stage sintering process, the chemical reaction of the decomposed oxides of the precursor and the lithium source in an oxygen atmosphere mainly occurs. If the heating rate is too fast, it is difficult to ensure that the material reacts sufficiently. If the heating rate is too slow, it is not conducive to industrial production. If the sintering temperature is too high or the time is too long, the material is prone to caking, and it is difficult to release the capacity during the charge and discharge process. If the sintering temperature is too low or the time is too short, it is difficult to form the required morphology, affecting the electrochemical performance.

[0021] Preferably, the oxidizing atmosphere includes air atmosphere and / or oxygen atmosphere, etc.

[0022] The technical solution adopted by the present invention to further solve its technical problems is as follows: a one-step modification method of a triple-modified high-nickel positive electrode material, wherein the high-nickel positive electrode material is evenly mixed with magnesium ammonium phosphate, sintered in one step under an inert protective atmosphere, and cooled to room temperature to obtain a triple-modified high-nickel positive electrode material.

[0023] The inventive idea of ​​the one-step modification method of the present invention is: using magnesium ammonium phosphate to perform a high-temperature treatment on the high-nickel positive electrode material, and at the same time constructing the triple modification effects of doping, oxygen vacancy and coating. MgNH4PO4 decomposes at high temperature, wherein Mg 2 + Realize bulk doping of high-nickel cathode materials; the NH3 gas produced by decomposition captures lattice oxygen and forms pre-oxygen vacancies on the surface of high-nickel cathode materials; PO4 3- React with residual lithium on the surface to form a Li3PO4 coating layer. The combination of doping and coating can maximize the structural stability and electronic conductivity, while the acquisition of oxygen vacancies helps to further improve the lithium ion diffusion rate. The present invention achieves triple modification through a one-step method, namely, controlling bulk doping, oxygen vacancy regulation and surface coating in one step. The synergistic effect achieved by the multi-path modification method is advanced and has significant advantages.

[0024] Preferably, the molar ratio of the sum of the moles of nickel, cobalt and manganese in the high-nickel positive electrode material to the magnesium in magnesium ammonium phosphate is 1:0.003-0.050 (more preferably 1:0.005-0.025). If the amount of magnesium ammonium phosphate is too much, it may cause side reactions and affect the capacity of the positive electrode active material; if the amount of magnesium ammonium phosphate is too little, the triple modification effect will not be obvious.

[0025] Preferably, the mixing method is: placing in a closed ball mill jar, without adding ball mill beads, and mixing at high speed.

[0026] Preferably, the high-speed mixing has a rotation speed of 400 to 600 rpm and a time of 5 to 8 hours.

[0027] Preferably, the one-step sintering means: heating to 600 - 700 °C (more preferably 600 - 680 °C) at a rate of 1 - 10 °C / min (more preferably 3 - 8 °C / min) and sintering for 4 - 6 h. If the heating rate is too fast, the decomposition reaction of magnesium ammonium phosphate is too fast, and the modification of the high-nickel cathode material is incomplete; if the heating rate is too slow, the decomposition products of magnesium ammonium phosphate are prone to other reactions and cause waste. If the sintering temperature is too high, the performance of the matrix high-nickel cathode material will be affected; if the sintering temperature is too low, the decomposition reaction of magnesium ammonium phosphate is incomplete, resulting in residual intermediate products and a low NH3 release rate. If the sintering time is too long, crystal growth will occur in the high-nickel cathode material, thus affecting the electrochemical performance and causing waste; if the sintering time is too short, the decomposition of magnesium ammonium phosphate is incomplete, and it is difficult to achieve the modification effect.

[0028] Preferably, the inert protective atmosphere includes argon and / or nitrogen atmosphere, etc. The inert protective atmosphere used in the present invention is a high-purity atmosphere with a purity ≥ 99.999%.

[0029] The beneficial effects of the present invention are as follows: (1) For the one-step triple-modified high-nickel cathode material of the present invention, magnesium ammonium phosphate simultaneously realizes triple modification effects of doping, coating, and oxygen vacancy construction on the high-nickel cathode material, with regular morphology, uniform distribution, high structural stability and thermal stability, and excellent electrochemical performance; (2) For the battery assembled with the one-step triple-modified high-nickel cathode material of the present invention, at a charge-discharge voltage of 2.7 - 4.3 V and a current density of 1 C, the initial charge specific capacity can be as high as 200 mAh / g, the initial discharge specific capacity can be as high as 195.4 mAh / g. After 100 cycles, the charge specific capacity is 181.7 mAh / g, and the discharge specific capacity can still be as high as 181.6 mAh / g. The capacity retention rate of the discharge specific capacity can be as high as 92.94%. Under the condition of a large current density of 5 C, the charge specific capacity is as high as 180.2 mAh / g, and the discharge specific capacity is as high as 178.3 mAh / g. This shows that the one-step triple-modified high-nickel cathode material of the present invention is beneficial to the transport of lithium ions during the charge-discharge process, with stable discharge specific capacity, charge-discharge performance and Coulomb efficiency, and good cycle performance; (3) The method of the present invention has a simple process, low raw material cost, and is suitable for industrial production. Description of the Drawings

[0030] Figure 1 XRD pattern of Example 1 of the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material; Figure 2is the SEM image of Example 1 of the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material; Figure 3 is the charge-discharge cycle curve of the battery assembled with the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material at a 1C current density; Figure 4 is the charge-discharge rate curve of the battery assembled with the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material; Figure 5 is the charge-discharge cycle curve of the battery assembled with the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Comparative Example 1 of the present invention at a 1C rate; Figure 6 is the charge-discharge rate curve of the battery assembled with the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Comparative Example 1 of the present invention. Detailed implementation manners

[0031] The present invention will be further described below in conjunction with examples and drawings.

[0032] The inert protective atmosphere used in the examples or comparative examples of the present invention is a high-purity atmosphere with a purity ≥ 99.999%; the raw materials or chemical reagents used in the examples of the present invention are all obtained through conventional commercial channels unless otherwise specified.

[0033] Reference Example 1 For every 1.0 g of the precursor material Ni 0.90 Co 0.05 Mn 0.05(OH)2 (containing 9.144 mmol of Ni, 0.482 mmol of Co, and 0.497 mmol of Mn) and 0.4459 g (10.629 mmol) of lithium hydroxide monohydrate were placed in a sealed ball milling jar without ball milling beads. Under 500 rpm, they were mixed at high speed for 6 h until evenly mixed. Then, under an oxygen atmosphere, two-stage temperature-rising sintering was carried out: first, it was heated to 450 °C at a rate of 5 °C / min and sintered for 4 h. After that, it was heated to 750 °C at a rate of 5 °C / min and sintered for 12 h, and then cooled to room temperature to obtain the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material.

[0034] A 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material, Example 1 The 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material is composed of Mg 2+ doped in the bulk phase of the high-nickel cathode material. The surface of the high-nickel cathode material contains oxygen vacancies, and a fast ion conductor Li3PO4 coating layer is in-situ generated and coated on the outer surface of the high-nickel cathode material particles to form polycrystalline secondary spherical-like particles; the doping amount of the Mg 2+ is equivalent to 1.5 mol% of the total molar number of Ni, Co, and Mn; the average thickness of the Li3PO4 coating layer is 20 nm; the average particle size of the triple-modified high-nickel cathode material is 3 μm.

[0035] As Figure 1 shown, the characteristic peaks of the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material in Example 1 of the present invention conform to the characteristic peaks of the PDF card LiNiO2 (PDF#74-0919), belonging to the R-3m space group, and no impurity phase is generated.

[0036] As Figure 2 shown, the morphology of the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material in Example 1 of the present invention preferably inherits the morphology of the high-nickel ternary cathode material. There is a coating layer on the surface, the secondary particles are polycrystalline spherical-like, and the average particle size is 3 μm.

[0037] Detected by EDS, the results show that Mg2+ Uniform distribution; detected by EPR, the result shows an increase in oxygen vacancies.

[0038] A one-step modification method for a 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material, Example 1 Put 1 g (10.26 mmol) of the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Reference Example 1 and 21.135 mg (0.1539 mmol) of MgNH4PO4 into a sealed ball milling tank, without adding ball milling beads, rotate at 500 rpm at high speed for 6 h until evenly mixed, and then under the protection of high-purity nitrogen atmosphere, perform one-step sintering: heat up to 650 °C at a rate of 5 °C / min, sinter for 5 h, cool to room temperature, to obtain 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material.

[0039] Battery assembly: Weigh 0.08 g of the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in the embodiment of the present invention, add 0.01 g of acetylene black as a conductive agent and 0.01 g of PVDF (polyvinylidene fluoride) as a binder, and use N-methylpyrrolidone as a solvent, mix and grind to form a cathode material; coat the obtained cathode material on the surface of an aluminum foil to make a pole piece; in a sealed glove box filled with argon, use this pole piece as the positive electrode, a lithium metal sheet as the negative electrode, a microporous polypropylene membrane as the separator, and 1 mol / L LiPF6 / EC:DMC:DEC (volume ratio 1:1:1) as the electrolyte, assemble into a CR2025 coin cell, and perform charge and discharge performance tests.

[0040] As Figure 3 、 4 shown, the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05The battery assembled with the O2 cathode material can achieve a first charge specific capacity of up to 200.0 mAh / g and a first discharge specific capacity of up to 195.4 mAh / g at a charge-discharge voltage of 2.7 - 4.3 V and a 1C current density. After 100 cycles, the charge specific capacity is 181.7 mAh / g, and the discharge specific capacity can still reach up to 181.6 mAh / g, with the capacity retention rate of the discharge specific capacity being as high as 92.94%. Under the condition of a large current density of 5 C, the charge specific capacity can still reach up to 180.2 mAh / g, and the discharge specific capacity can still reach up to 178.3 mAh / g. It shows that after triple modification of the high-nickel cathode material by the one-step modification method of the present invention, it is beneficial to the transportation of lithium ions during the charge-discharge process, and the discharge specific capacity, charge-discharge performance, and Coulomb efficiency are stable, with good cycle and high-rate performance.

[0041] A 1mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material Example 2 The 1mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material is formed by doping Mg 2+ in the bulk phase of the high-nickel cathode material. The surface of the high-nickel cathode material contains oxygen vacancies, and a fast ion conductor Li3PO4 coating layer is in-situ generated and coated on the outer surface of the high-nickel cathode material particles to form polycrystalline secondary spherical-like particles; the doping amount of the Mg 2+ is equivalent to 1.0mol% of the total molar amount of Ni, Co, and Mn; the average thickness of the Li3PO4 coating layer is 10 nm; the average particle size of the triple-modified high-nickel cathode material is 3μm.

[0042] After detection, the characteristic peaks of the 1mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material of Example 1 of the present invention conform to the characteristic peaks of the PDF card LiNiO2 (PDF#74-0919), belonging to the R-3m space group, and no impurity phase is generated.

[0043] After detection, the morphology of the 1mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material of Example 1 of the present invention preferably inherits the morphology of the high-nickel ternary cathode material, with a coating layer on the surface, the secondary particles being polycrystalline spherical-like, and the average particle size being 3 μm.

[0044] After EDS detection, the results show that Mg2+ Uniform distribution; detected by EPR, the result shows an increase in oxygen vacancies.

[0045] One-step modification method of a 1mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material, Example 2 Take 1 g (10.26 mmol) of the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Reference Example 1, and 14.09 mg (0.1026 mmol) of MgNH4PO4 are placed in a sealed ball milling jar without ball milling beads. At 500 rpm, high-speed mixing and rotation are carried out for 6 h until evenly mixed. Then, under the protection of high-purity nitrogen atmosphere, one-step sintering is carried out: heating to 600 °C at a rate of 5 °C / min, sintering for 6 h, and cooling to room temperature to obtain 1mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material.

[0046] Battery assembly: The same as in Method Example 1.

[0047] After testing, for the battery assembled with the 1mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in the embodiment of the present invention, at a charge-discharge voltage of 2.7 - 4.3 V and a current density of 1C, the initial charge specific capacity can be as high as 198.5 mAh / g, the initial discharge specific capacity can be as high as 195.48 mAh / g. After 100 cycles, the charge specific capacity is 181.03 mAh / g, and the discharge specific capacity can still be as high as 176.82 mAh / g. The capacity retention rate of the discharge specific capacity can be as high as 90.45%; under the condition of a large current density of 5 C, the charge specific capacity can still be as high as 178.2 mAh / g, and the discharge specific capacity can still be as high as 176.4 mAh / g; it shows that after triple modification of the high-nickel cathode material by the one-step modification method of the present invention, it is beneficial to the transportation of lithium ions during the charge-discharge process, and the discharge specific capacity, charge-discharge performance, and Coulomb efficiency are stable, and the cycle and high-rate performance are good.

[0048] A 2mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material, Example 3 The 2mol% MgNH4PO4 triple-modified LiNi 0.90 Co0.05 Mn 0.05 The MnO₂ cathode material is composed of Mg 2+ doped in the bulk phase of the high-nickel cathode material. The surface of the high-nickel cathode material contains oxygen vacancies, and a fast ion conductor Li₃PO₄ coating layer is coated on the outer surface of the high-nickel cathode material particles to form polycrystalline secondary spherical particles; the doping amount of the Mg 2+ is equivalent to 2.0 mol% of the total molar amount of Ni, Co, and Mn; the average thickness of the Li₃PO₄ coating layer is 40 nm; the average particle size of the triple-modified high-nickel cathode material is 3 μm.

[0049] After testing, the characteristic peaks of the 2 mol% MgNH₄PO₄ triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O₂ cathode material in Example 1 of the present invention conform to the characteristic peaks of the PDF card LiNiO₂ (PDF#74-0919), belonging to the R-3m space group, and no impurity phase is generated.

[0050] After testing, the morphology of the 2 mol% MgNH₄PO₄ triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O₂ cathode material in Example 1 of the present invention preferably inherits the morphology of the high-nickel ternary cathode material. There is a coating layer on the surface, the secondary particles are polycrystalline spherical, and the average particle size is 3 μm.

[0051] After EDS testing, the results show that Mg 2+ is evenly distributed; after EPR testing, the results show that the oxygen vacancies increase.

[0052] An example 3 of the one-step modification method of a 2 mol% MgNH₄PO₄ triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O₂ cathode material Put 1 g (10.26 mmol) of the LiNi 0.90 Co 0.05 Mn 0.05 O₂ cathode material obtained in Reference Example 1 and 28.18 mg (0.2052 mmol) of MgNH₄PO₄ into a sealed ball milling tank. Without adding ball milling beads, rotate at a high speed of 500 rpm for 6 h until evenly mixed, and then perform one-step sintering under a high-purity nitrogen protection atmosphere: heat up to 650 °C at a rate of 5 °C / min, sinter for 4 h, and cool to room temperature to obtain a 2 mol% MgNH₄PO₄ triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O₂ cathode material.

[0053] Battery assembly: same as in Method Example 1.

[0054] After testing, for the battery assembled with the 2mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in the embodiment of the present invention, at a charge-discharge voltage of 2.7 - 4.3 V and a 1C current density, the initial charge specific capacity can be as high as 198.6 mAh / g, the initial discharge specific capacity can be as high as 195.5 mAh / g. After 100 cycles, the charge specific capacity is 181.6 mAh / g, and the discharge specific capacity can still be as high as 177.4 mAh / g. The capacity retention rate of the discharge specific capacity can be as high as 90.74%. Under the condition of a 5C high current density, the charge specific capacity can still be as high as 176.8 mAh / g, and the discharge specific capacity can still be as high as 175.0 mAh / g. This shows that after the high-nickel cathode material is triple-modified by the one-step modification method of the present invention, it is beneficial to the transportation of lithium ions during the charge-discharge process, and the discharge specific capacity, charge-discharge performance, and Coulomb efficiency are stable, and the cycle and high-rate performance are good.

[0055] Comparative Example 1 That is, the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Reference Example 1.

[0056] After testing, the characteristic peaks of the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in this comparative example conform to the characteristic peaks of the PDF card LiNiO2 (PDF#74-0919), belonging to the R-3m space group, and no impurity phase is generated.

[0057] After testing, the surface of the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in this comparative example has no coating layer, the secondary particles are polycrystalline spherical, and the average particle size is 3 μm.

[0058] Battery assembly: same as in Example 1.

[0059] As Figure 5 、 6 shown, the LiNi 0.90 Co 0.05 Mn 0.05The battery assembled with the O2 cathode material has an initial charge specific capacity of 193.7 mAh / g and an initial discharge specific capacity of 190.3 mAh / g at a charge-discharge voltage of 2.7 - 4.3 V and a current density of 1 C. After 100 cycles, the charge specific capacity is 155.6 mAh / g, and the discharge specific capacity is only 156.3 mAh / g, with the capacity retention rate of the discharge specific capacity being only 82.13%. Under the condition of a large current density of 5 C, the charge specific capacity is only 166.3 mAh / g, and the discharge specific capacity is only 163.9 mAh / g. This shows that when the high-nickel cathode material is not modified at all, the capacity retention rate is low and the high-rate performance is poor.

[0060] Comparative Example 2 Put 1 g (10.26 mmol) of the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Reference Example 1 and 6.046 mg (0.150 mmol) of MgO into a sealed ball milling tank. Without adding ball milling beads, rotate at a high speed of 500 rpm for 6 h until evenly mixed. Then, under the protection of high-purity nitrogen atmosphere, perform one-step sintering: heat up to 650 °C at a rate of 5 °C / min, sinter for 5 h, and cool to room temperature to obtain 1.5 mol% Mg 2+ doped LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material.

[0061] After testing, the characteristic peaks of the 1.5 mol% Mg 2+ doped LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in this comparative example conform to the characteristic peaks of the PDF card LiNiO2 (PDF#74 - 0919), belonging to the R-3m space group, and no impurity phase is generated.

[0062] After testing, the surface of the 1.5 mol% Mg 2+ doped LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in this comparative example has no coating layer, and the secondary particles are polycrystalline spherical with an average particle size of 3 μm.

[0063] Battery assembly: The same as in Example 1.

[0064] After testing, the 1.5 mol% Mg 2+ doped LiNi 0.90 Co 0.05 Mn 0.05The battery assembled with the O2 cathode material has an initial charge specific capacity of 194.11 mAh / g and an initial discharge specific capacity of up to 193.87 mAh / g at a charge-discharge voltage of 2.7 - 4.3 V and a current density of 1 C. After 100 cycles, the charge specific capacity is only 161.72 mAh / g and the discharge specific capacity is only 163.85 mAh / g, and the capacity retention rate of the discharge specific capacity is only 84.52%. Although the electrochemical performance is improved compared with the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Comparative Example 1, it is worse than the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Example 1 under the same modification conditions.

[0065] Comparative Example 3 1 g (10.26 mmol) of the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Reference Example 1 and 17.82 mg (0.1539 mmol) of Li3PO4 were placed in a sealed ball milling jar without milling beads. Under 500 rpm, they were mixed at high speed for 6 h until evenly mixed. Then, under a high-purity nitrogen protection atmosphere, one-step sintering was carried out: heating to 650 °C at a rate of 5 °C / min, sintering for 5 h, and cooling to room temperature to obtain 1.5 mol% Li3PO4-coated LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material.

[0066] It was detected that the characteristic peaks of the 1.5 mol% Li3PO4-coated LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in this comparative example match the characteristic peaks of the PDF card LiNiO2 (PDF#74-0919), belonging to the R-3m space group, and no impurity phase is generated.

[0067] It was detected that the surface of the 1.5 mol% Li3PO4-coated LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in this comparative example has a coating layer, and the secondary particles are polycrystalline spherical with an average particle size of 3 μm.

[0068] Battery assembly: The same as in Example 1.

[0069] It was detected that the 1.5 mol% Li3PO4-coated LiNi0.90 Co 0.05 Mn 0.05 For the battery assembled with the O2 cathode material, at a charge-discharge voltage of 2.7 - 4.3 V and a current density of 1 C, the initial charge specific capacity is 196.57 mAh / g, and the initial discharge specific capacity can be as high as 194.29 mAh / g. After 100 cycles, the charge specific capacity is only 162.66 mAh / g, and the discharge specific capacity is only 163.69 mAh / g. The capacity retention rate of the discharge specific capacity is only 84.25%. The electrochemical performance is improved compared with that of the LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material, but it is worse than that of the 1.5 mol% MgNH4PO4 triple-modified LiNi 0.90 Co 0.05 Mn 0.05 O2 cathode material obtained in Example 1 under the same modification conditions.

Claims

1. A triple-modified high-nickel cathode material, characterized in that: is composed of Mg 2+ doped in the bulk phase of the high-nickel cathode material, the surface of the high-nickel cathode material contains oxygen vacancies, and a polycrystalline secondary spherical-like particle formed by in-situ generating a fast ion conductor Li3PO4 coating layer coated on the outer surface of the high-nickel cathode material particles.

2. The triple-modified high-nickel cathode material according to claim 1, wherein: The chemical formula of the high-nickel cathode material is LiNi x Co y Mn (1-x-y) O2, where 0.8 ≤ x < 1 and 0 < y ≤ 0.2; the doping amount of the Mg 2+ is equivalent to 0.3 to 5.0 mol% of the total molar amount of the transition metals; the average thickness of the Li3PO4 coating layer is 5 to 50 nm; the average particle size of the triple-modified high-nickel cathode material is 3 to 6 μm.

3. The triple-modified high-nickel cathode material according to claim 1 or 2, characterized in that: The preparation method of the high-nickel cathode material is as follows: uniformly mix the high-nickel precursor material with a lithium source, and conduct two-stage sintering in an oxidizing atmosphere, then cool to room temperature to obtain the high-nickel cathode material; the molar ratio of the total of nickel, cobalt, and manganese elements in the high-nickel precursor to the lithium element in the lithium source is 1:1.02 - 1.10; the high-nickel precursor material includes nickel cobalt manganese hydroxide or nickel cobalt manganese carbonate; the lithium source includes lithium hydroxide and / or lithium carbonate, and one or more of their hydrates; the mixing method is: place it in a sealed ball milling tank, without adding ball milling beads, and conduct high-speed mixing rotation; the rotation speed of the high-speed mixing rotation is 400 - 600 rpm, and the time is 5 - 8 h; the two-stage temperature rise sintering means: first heat up to 350 - 550 °C at a rate of 1 - 10 °C / min, sinter for 2 - 8 h, and then heat up to 550 - 1000 °C at a rate of 1 - 10 °C / min, and sinter for 8 - 20 h; the oxidizing atmosphere includes air atmosphere and / or oxygen atmosphere.

4. One-step modification method for the triple-modified high-nickel cathode material according to any one of claims 1 to 3, characterized in that: Uniformly mix the high-nickel cathode material with magnesium ammonium phosphate, and conduct one-step sintering in an inert protective atmosphere, then cool to room temperature to obtain the triple-modified high-nickel cathode material.

5. The one-step modification method of the triple-modified high-nickel cathode material according to claim 4, characterized in that: The molar ratio of the total of nickel, cobalt, and manganese elements in the high-nickel cathode material to the magnesium element in magnesium ammonium phosphate is 1:0.003 - 0.050; the mixing method is: place it in a sealed ball milling tank, without adding ball milling beads, and conduct high-speed mixing rotation; the rotation speed of the high-speed mixing rotation is 400 - 600 rpm, and the time is 5 - 8 h; the one-step sintering means: heat up to 600 - 700 °C at a rate of 1 - 10 °C / min, and sinter for 4 - 6 h; the inert protective atmosphere includes argon and / or nitrogen atmosphere.

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