CN114335470A

CN114335470A - Modified positive electrode material and preparation method and application thereof

Info

Publication number: CN114335470A
Application number: CN202111638599.8A
Authority: CN
Inventors: 董彬彬; 杨琪
Original assignee: Beijing WeLion New Energy Technology Co ltd
Current assignee: Beijing Weilan New Energy Technology Co ltd
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-04-12
Anticipated expiration: 2041-12-29
Also published as: CN114335470B

Abstract

The invention relates to a modified anode material and a preparation method and application thereof, wherein the modified anode material comprises an inner layer, a modified layer and a composite coating layer; the inner layer is of a laminated structure; the inner layer comprises lithium element and nickel element; the modified layer is of a spinel structure; the modified layer coats the inner layer; the composite coating layer is positioned on one side of the modification layer far away from the inner layer and coats the modification layer. According to the cathode material, the modification layer is adopted to cover the inner layer, so that a spinel layer is generated on the surface of the cathode material in situ, the particle strength of the cathode material is increased, and the lattice stability of the material is improved; the alkalinity of the anode material is reduced, the surface property of the anode material is improved, the cycle performance is further improved, high-rate and high-stability cycle is realized, the problem of thermal stability of the high-nickel anode material is solved, and the safety of the material is improved.

Description

Modified positive electrode material and preparation method and application thereof

Technical Field

The invention relates to the technical field of batteries, in particular to a modified positive electrode material and a preparation method and application thereof.

Background

The lithium ion battery is a novel high-efficiency clean green energy due to the characteristics of high energy density and long service life. Among them, the nickel-containing cathode material is widely used because of its advantages of low cost of raw materials, high specific capacity, etc. Along with the increase of the nickel content in the anode material, the scientific specific capacity and the mass energy density can be correspondingly improved, and the overall electrical performance of the battery is improved; however, the safety and the cycling stability of the anode material are reduced along with the increase of the nickel content, and the collapse of the material structure is caused by the deintercalation of Li ions and the change of the valence state of Ni and the like in the charging and discharging processes; in addition, at high temperature, the transition metal ions are dissolved, so that the impedance is increased, and the cycle life of the battery is further shortened.

Therefore, there is a need for developing a positive electrode material having excellent cycle characteristics, thermal stability and safety.

Disclosure of Invention

The modified cathode material is provided aiming at the defects of the prior art, and adopts a structure that the inner layer is coated by the modified layer, so that the spinel layer is generated on the surface of the cathode material in situ, the particle strength of the cathode material is increased, and the lattice stability of the material is improved; the alkalinity of the anode material is reduced, the surface property of the anode material is improved, the cycle performance is further improved, high-rate and high-stability cycle is realized, the problem of thermal stability of the high-nickel anode material is solved, and the safety of the material is improved.

According to one aspect of the present application, there is provided a modified positive electrode material comprising an inner layer, a modified layer, and a composite clad layer; the inner layer is of a laminated structure; the inner layer comprises lithium element and nickel element; the modified layer is of a spinel structure; the modified layer coats the inner layer; the composite coating layer is positioned on one side of the modification layer far away from the inner layer and coats the modification layer.

Optionally, the composite coating layer is obtained by sintering a coating layer material and the modification layer.

Because the surface of the modified anode material has the spinel structure and the composite coating layer, the corrosion of water and electrolyte to internal materials can be prevented, and the dissolution of transition elements is further inhibited; in addition, due to the excellent stability of the spinel structure, the spinel structure can play a supporting role on the whole anode material, so that the collapse of the whole structure is prevented when lithium is removed, and the spinel structure can provide a three-dimensional lithium ion diffusion channel, thereby being more beneficial to lithium ion transmission and improving the cycle performance of the material; and because the surface of the anode material is directly spinelized, the alkalinity of the anode material can be further reduced, and the spinel has higher temperature resistance and can further improve the stability of the anode material at high temperature.

The inner layer structure is a layered structure, and lithium ions are normally extracted and output; the modified layer is of a spinel structure, and for a layered material, the long-term charge-discharge cycle can cause the damage of the surface layered structure, and if the layered material is changed into the spinel structure, the stability of the surface layer structure can be obviously improved, and the long-term cycle can be endured; the composite coating layer is arranged on the outermost layer of the positive electrode particles and is in direct contact with the electrolyte, and the composite coating layer can inhibit the side reaction on the surfaces of the particles more. Optionally, the thickness of the modified layer is 2-300 nm.

Optionally, the thickness of the modification layer is 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 200nm, 300nm, or any of any two values.

Preferably, the thickness of the modified layer is 100-200 nm.

Optionally, the thickness of the modification layer is 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or any of two values.

In the anode material, the stability of the layered structure of the inner layer is relatively poor, particularly the structure of the surface layer is easy to damage in the long-term charge-discharge cycle process, and if a spinel structure with enough thickness can be formed on the surface of the surface layer, the stability of the surface layer structure can be improved; however, if there is not much spinel structure or the modified layer is too thin, i.e. the content of spinel structure is less, a stable frame structure cannot be formed on the inner layer surface, and the structural stability of the whole anode material is not obviously improved; if the modified layer is too thick, the corresponding anode material is particularly stable, but as more spinel is positioned outside the inner layer, the desorption of lithium ions in the inner layer can be influenced, the desorption rate and the desorption amount are reduced, meanwhile, the proportion of the inner layer material is also reduced, and the electrical performance of the whole anode material is further reduced.

Optionally, the thickness of the inner layer is 1.5-10.0 μm.

Optionally, the inner layer has a thickness of 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or any of two values.

In the positive electrode material, the thickness of the inner layer depends on the particle size of the positive electrode material, the thickness is 1.5-10.0 mu m and corresponds to the particle size of the positive electrode particles in the range of 3.0-20.0 mu m, the thicker the thickness, the larger the particle size of the positive electrode particles correspondingly, and the particle size in the range has excellent cycle performance and rate performance. The larger the thickness is, namely the larger the granularity is, the more difficult the preparation process is, and the phenomena of ball cracking and the like are easy to occur, so that the particle strength of the whole material is greatly reduced; in the rolling process, the risk of easy crushing and the like also occurs, and the interface reaction of the anode material and the electrolyte can be increased in the subsequent battery, and the phenomenon of gas generation and the like can occur, so that the cycle performance of the battery is reduced, and the safety of the battery is also adversely affected. If the particle size is too small, the compacted density is too low, which is disadvantageous in capacity exertion, and the processability of the material is also deteriorated.

Optionally, the median particle size of the positive electrode particles is 3.0-20.0 μm.

Alternatively, the median particle size of the positive electrode particles is 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any of any two values.

Optionally, the thickness of the composite coating layer is 2-200 nm.

Optionally, the thickness of the composite coating layer is 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 200nm, or any of two values.

Optionally, the thickness of the composite coating layer is 50-150 nm.

Optionally, the thickness of the composite coating layer is 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, or any of two values.

In the anode material, the outermost composite coating layer has a large influence on the interface performance of the material, and is too thick to facilitate the transmission of lithium ions, so that the multiplying power performance of the material is influenced; too thin may not effectively isolate the electrolyte and inhibit the occurrence of surface side reactions.

Optionally, the layered structure comprises at least one of the chemical formulas shown in formula I,

Li_1+a(Ni_xCo_yMn_zM_m)_1-aO_2±bA_cformula I

Wherein a is more than or equal to 0.1 and less than or equal to 0.1, x is more than 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 0.4, z is more than 0 and less than or equal to 0.6, m is more than or equal to 0 and less than or equal to 0.1, b is more than or equal to 0 and less than 0.02, c is more than or equal to 0 and less than or equal to 0.02, and x + y + z is equal to 1; m is selected from at least one of B, Mg, Al, Ti, Zr, Nb, Y, W, Sn, Mo, La, Er, Sr and Ba; a is selected from at least one of P, F and Cl.

Alternatively, 0< m ≦ 0.1.

Alternatively, a is-0.1, -0.09, -0.08, -0.07, -0.06, -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any of any two values.

Alternatively, x is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or any of any two values.

Alternatively, y is 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or any of any two values.

Alternatively, z is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or any of any two values.

Alternatively, m is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any of any two values.

Alternatively, b is 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, or any of two values.

Alternatively, c is 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, or any of two numerical values.

Optionally, the spinel structure comprises at least one of the chemical formulas shown in formula II,

Li_αMn_βM′_γO₄formula II

Wherein alpha is more than 0.9 and less than or equal to 1.33, beta + gamma is more than 1.66 and less than or equal to 2.00, and gamma is more than or equal to 0 and less than or equal to 0.2; m' is at least two of Ni, Co, B, Mg, Al, Ti, Zr, Nb, Y, W, Sn, Mo, La, Er, Sr and Ba.

Alternatively, α is 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.1, 1.2, 1.3, 1.33, or any of any two values.

Alternatively, β + γ is 1.66, 1.67, 1.68, 1.69, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.90, 2.00, or any of any two values.

Alternatively, γ is 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, or any of any two values.

Alternatively, 0< γ < 0.2.

That is, the spinel layer contains other elements, the additive contains elements, the ionic radius of the cation of the element is equal to that of Ni²⁺The phase difference is not large, the nickel can occupy the 3b position of nickel, nickel ions are prevented from occupying the position of lithium ions, and therefore the mixed arrangement of lithium and nickel can be reduced, namely the mixed arrangement of Li/Ni can be effectively inhibited, the body structure is protected, the ionic conductivity is improved, and the like.

Optionally, the composite cladding comprises an oxide or acid of B, Ti, Si, W, Al and a fast ion conductor.

Optionally, the oxide or acid of B, Ti, Si, W, Al comprises B₂O₃、H₃BO₃、TiO₂、H₂TiO₃、SiO₂、H₂SiO₃、WO₃、H₂WO₄、Al₂O₃、HAlO₂At least one of (1).

Optionally, the fast ion conductor comprises at least one of LATP, LZTO, LLZO, LiPON.

On the basis of spinel on the surface of the anode material, oxide and a fast ion conductor are added for coating, so that on one hand, the defects on the surface of the material can be repaired, the occurrence of side reactions is reduced, the ionic conductivity and the electronic conductivity of the anode material are improved, and the capacity and the rate capability of the material are improved; on the other hand, the corrosion resistance of the cathode material to the electrolyte can be further improved, and the safety of the cathode material is enhanced. Meanwhile, for the inner layer layered material, the long-term charge-discharge cycle can cause the damage of the surface layered structure, and if the surface is changed into a spinel structure, the stability of the surface layer structure can be obviously improved, and the long-term cycle can be endured; the composite coating layer is arranged on the outermost layer of the positive electrode particles and is in direct contact with the electrolyte, and the composite coating layer can inhibit the side reaction on the surfaces of the particles.

According to another aspect of the invention, a preparation method of a modified cathode material is provided, wherein the modified cathode material is at least one of the modified cathode materials.

Optionally, the preparation method comprises:

(1) carrying out primary sintering on a mixed material comprising a nickel-containing anode material precursor, a lithium source and an additive in an oxygen-containing gas atmosphere to obtain a primary sintered product; (2) sintering the primary sintering product in acid gas again to obtain an intermediate substance; (3) and carrying out composite coating on the intermediate substance through a coating material to obtain the modified anode material.

Optionally, the oxygen-containing gas comprises oxygen and/or a mixture comprising oxygen.

Optionally, the nickel-containing cathode material precursor is at least one of a nickel-cobalt-aluminum composite precursor, a nickel-manganese composite precursor, and a nickel-cobalt-manganese composite precursor.

Optionally, the precursor of the nickel-containing cathode material is one or a combination of several of composite oxides and composite hydroxides of nickel, cobalt and manganese.

Alternatively, the molar ratio of nickel, cobalt and manganese is Ni: co: mn is (0.3 to 0.99), (0 to 0.35) and (0.01 to 0.35).

Alternatively, the molar ratio of nickel, cobalt and manganese is Ni: co: mn ═ 0.90:0.05: 0.05.

Optionally, the nickel-containing cathode material precursor is prepared by the following preparation method:

and mixing the mixed solution containing a nickel source, a cobalt source and a manganese source with a precipitator and a complexing agent in an inert gas atmosphere, and performing coprecipitation to obtain the nickel-containing anode material precursor.

Optionally, the nickel source comprises at least one of nickel sulfate, nickel carbonate, nickel chloride, nickel nitrate, and nickel acetate of nickel.

Optionally, the cobalt source comprises at least one of cobalt sulfate, cobalt carbonate, cobalt chloride, cobalt nitrate, and cobalt acetate of cobalt.

Optionally, the source of manganese comprises at least one of manganese sulfate, manganese carbonate, manganese chloride, manganese nitrate and manganese acetate.

Optionally, the precipitant is at least one of sodium hydroxide and potassium hydroxide.

Optionally, the complexing agent is at least one of ammonia, disodium ethylenediaminetetraacetate, ammonium nitrate, ammonium chloride, and ammonium sulfate.

Optionally, the temperature of the coprecipitation is 50-80 ℃; the pH value is more than or equal to 8; the time is 12-36 h.

Optionally, the preparation method comprises: nickel sulfate, cobalt sulfate and manganese sulfate are mixed according to the molar ratio of nickel, cobalt and manganese elements of 90: 5:5 to obtain a mixed salt solution with the concentration of 2.5 mol/L; dissolving sodium hydroxide into a precipitator solution with the concentration of 10 mol/L; dissolving ammonia water into a complexing agent solution with the concentration of 2 mol/L. Introducing 50L of mixed salt solution, precipitator solution and complexing agent solution into a reaction kettle in a parallel flow mode, carrying out coprecipitation for 24 hours under the conditions of 65 ℃ of temperature, 12.3 of pH value, 500rpm of stirring speed and nitrogen atmosphere protection, then carrying out suction filtration and washing on precursor slurry, drying a filter cake at 110 ℃ and then screening to obtain the nickel-containing anode material precursor.

Optionally, the ratio of the number of moles of the nickel-containing cathode material precursor to the number of moles of the lithium source is: 1, (0.9-1.2).

Optionally, the ratio of the number of moles of the nickel-containing positive electrode material precursor to the number of moles of the lithium source is 1:0.9, 1:0.91, 1:0.92, 1:0.93, 1:0.94, 1:0.95, 1:0.96, 1:0.97, 1:0.98, 1:0.99, 1:1.0, 1:1.1, 1:1.2, or any one of any two values.

The mole number of the nickel-containing cathode material precursor is the sum of the moles of metal elements in the nickel-containing cathode material precursor; the number of moles of the lithium source is the sum of the moles of the metallic lithium in the lithium source.

Optionally, the additive is at least one of an oxide, a halide, a phosphate of a non-metal or a basic metal.

Optionally, the oxide, halide, phosphate of the non-metal or alkali metal comprises B₂O₃、MgO、Al₂O₃、TiO₂、ZrO₂、Nb₂O₅、Y₂O₃、WO₃、SnO、MoO₃、La₂O₃、Er₂O₃、MgCO₃、SrCO₃、BaCO₃、MgF₂、MgCl₂、AlF₃、AlPO₄、SrF₂、BaF₂And BaCl₂At least one of (1).

Optionally, the ratio of the number of moles of the additive to the number of moles of the nickel-containing cathode material precursor is: (0.001-0.01): 1.

The excessive amount of the additive can reduce the proportion of the nickel-containing cathode material precursor, so that the capacity, the cycle performance and the like of the cathode material are improved.

Optionally, the ratio of the number of moles of the additive to the number of moles of the nickel-containing positive electrode material precursor is 0.001:1, 0.002:1, 0.003:1, 0.004:1, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, or any one of any two values.

Optionally, the ratio of the number of moles of the additive to the number of moles of the nickel-containing cathode material precursor is: (0.001-0.006): 1.

The mole number of the nickel-containing cathode material precursor is the sum of the moles of metal elements in the nickel-containing cathode material precursor; the mole number of the additive is the sum of the moles of the non-metal or alkali metal in the additive.

Optionally, the lithium source comprises a soluble lithium metal salt and/or lithium hydroxide.

Optionally, the lithium hydroxide is lithium hydroxide monohydrate.

Optionally, the soluble lithium metal salt comprises at least one of lithium carbonate, lithium nitrate, lithium sulfate, lithium chloride, and lithium acetate.

Optionally, in the step (1), the temperature of the primary sintering is 700-1000 ℃; the primary sintering time is 6-20 h.

Optionally, the temperature of the primary sintering is 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃ or any one of any two values.

Optionally, the time for the primary sintering is 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 6h, 7h, 8h, 9h, 20h or any one of any two values.

Optionally, the temperature is increased to the temperature of the primary sintering according to a certain temperature increasing rate.

Optionally, the heating rate is 0.5-10 ℃/min.

Optionally, the heating rate is 0.5 ℃/min, 0.6 ℃/min, 0.7 ℃/min, 0.8 ℃/min, 0.9 ℃/min, 1.0 ℃/min, 2.0 ℃/min, 3.0 ℃/min, 4.0 ℃/min, 5.0 ℃/min, 6.0 ℃/min, 7.0 ℃/min, 8.0 ℃/min, 9.0 ℃/min, 10 ℃/min or any one of any two values.

Optionally, in the step (2), the temperature of the secondary sintering is 700-1000 ℃; and the secondary sintering time is 2-6 h.

Optionally, the temperature of the re-sintering is 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃ or any one of any two values.

Optionally, the time for the second sintering is 2h, 3h, 4h, 5h, 6h or any one of two values.

Optionally, in step (2), the acid gas comprises SO₂、H₂S、CO₂、HCl、NO₂、HF、Cl₂At least one of (1).

In the sintering process, the acid gas can play a role of a lithium removing agent, a spinel structure is formed on the surface of the anode material particles, and lithium vacancies and oxygen vacancies are formed on the surface of the material particles, so that lithium ion diffusion is facilitated, and the multiplying power and the cycle performance are improved. If oxygen is introduced in the whole sintering process, the material structure is a layered structure, and compared with the anode material with the spinel structure on the particle surface, the structure stability is poor, and the long-term circulation performance is poor.

Optionally, after sintering in acid gas again, washing and drying are further included.

Optionally, the water washing is to wash the modified cathode material according to a solid-to-liquid ratio of 1:1.

Optionally, the washing time is 2-10 min.

Preferably, the water washing time is 5 min.

Optionally, the drying temperature is 100-150 ℃; the time is 2-5 h.

Optionally, the cladding material comprises an oxide or acid of B, Ti, Si, W, Al and a fast ion conductor.

B. Oxides of Ti, Si, W and Al and acid can react with residual lithium on the particle surface to reduce the amount of the residual lithium, and the residual lithium is in a molten state through high-temperature sintering, so that the fast ion conductor is fixed on the particle surface to play a role in bonding.

Optionally, the composite coating is: and mixing and sintering the intermediate substance and the coating material in an atmosphere containing oxygen.

The coating material and the modified layer are sintered, so that the surface residual alkali content of the particles is further reduced, and the modified anode material has better stability and protective effect; and through the sintering mode, the anode material is prevented from contacting with water, and the corrosion of the water to the material is avoided.

Optionally, the conditions of the sintering are: the temperature is 200-800 ℃; the time is 8-16 h.

Optionally, the temperature of the re-sintering is 200 ℃, 300 ℃, 400 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃ or any one of any two values.

Optionally, the time for the second sintering is 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h or any one of any two values.

Optionally, the ratio of the mass of the coating material to the sum of the mass of the inner layer and the mass of the modified layer is 0.1-1.0%.

Optionally, the ratio of the mass of the coating material to the sum of the mass of the inner layer and the modified layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any one of any two values.

The content of the coating material is too much, so that the coating layer is too thick, and the capacity of the anode material is not favorably exerted; if the coating amount is too small, the coating is not uniform, and the corresponding protection effect cannot be achieved.

Optionally, the mass ratio of the oxide to the fast ion conductor is 1-5: 1-5.

Optionally, the mass ratio of the oxide to the fast ion conductor is 1:1, 1:2, 1:3, 1:4, 1:5, 2:1, 2:2, 2:3, 2:4, 2:5, 3:1, 3:2, 3:3, 3:4, 3:5, 4:1, 4:2, 4:3, 4:4, 4:5, 5:1, 5:2, 5:3, 5:4, 5:5 or any one of any two values.

According to a further aspect of the present application, there is provided a lithium ion positive electrode comprising at least one of the modified positive electrode material described above, and the modified positive electrode material prepared according to any one of the methods described above.

According to yet another aspect of the present application, a lithium ion battery is provided.

Optionally, the lithium ion battery comprises at least one of the above described lithium ion positive electrodes.

The invention has the following main beneficial effects:

(1) the modified cathode material is provided aiming at the defects of the prior art, and adopts a structure that the inner layer is coated by the modified layer, so that the spinel layer is generated on the surface of the cathode material in situ, the particle strength of the cathode material is increased, and the lattice stability of the material is improved; the problem of the granule intensity that high nickel cathode material exists is low is solved, through granule surface modification, the compressive property of granule is better, and the broken reduction of granule when the pole piece rolls in has effectively improved the granule intensity problem of high nickel cathode material through the spinel on surface.

(2) The method effectively improves the problems of poor multiplying power, poor cycle performance and poor thermal stability of the high-nickel anode material, reduces the alkalinity of the anode material, improves the surface property of the anode material, further improves the cycle performance, realizes high multiplying power and high stable cycle, solves the problem of thermal stability of the high-nickel anode material, and improves the safety of the material; and on the basis of spinel on the surface of the anode material, a fast ion conductor is further added for coating, and the safety, high multiplying power and high cycle stability of the material are further improved through composite modification.

(3) This application is through in the sintering process, with the oxygen atmosphere switch over to acid gas midway, high temperature once sintering method normal position preparation surface spinel petrochemical's modified cathode material promptly, and the normal position forms on the inlayer base member, and does not have the transition layer in the material inside, and technology is simpler, and the cost is cheaper, and the structure is more stable to material processing nature is good.

Drawings

Fig. 1 is a schematic cross-sectional view of a modified cathode material prepared in example 1 of the present application.

Fig. 2 is an SEM image of the modified cathode material prepared in example 1 of the present application.

Fig. 3 is a schematic cross-sectional view of a modified positive electrode material prepared in comparative example 1 of the present application.

Fig. 4 is an SEM image of the modified cathode material prepared in comparative example 3 of the present application.

Fig. 5 is a cycle-specific capacity curve diagram of a battery assembled by modified cathode materials prepared in some examples and comparative examples of the present application; the horizontal axis is the cycle number and unit times; the ordinate is specific capacity, unit mAh/g.

The reference numbers in the drawings are as follows:

1 inner layer

2 modified layer

3 composite coating layer

4 hollow layer

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The reagents, materials and procedures used herein are those widely used in the corresponding fields and are generally available on the market.

Example 1

(1) Nickel sulfate, cobalt sulfate and manganese sulfate are mixed according to the molar ratio of nickel, cobalt and manganese elements of 90: 5:5 to obtain a mixed salt solution with the concentration of 2.5 mol/L; dissolving sodium hydroxide into a precipitator solution with the concentration of 10 mol/L; dissolving ammonia water into a complexing agent solution with the concentration of 2 mol/L. Introducing 50L of mixed salt solution, precipitator solution and complexing agent solution into a reaction kettle in a parallel flow mode, carrying out coprecipitation for 24 hours under the conditions of 65 ℃ of temperature, 12.3 of pH value, 500rpm of stirring speed and nitrogen atmosphere protection, then carrying out suction filtration and washing on precursor slurry, drying a filter cake at 110 ℃ and then screening to obtain the nickel-containing anode material precursor.

(2) Mixing the precursor of the nickel-containing anode material with LiOH and ZrO₂According to the formula of Li/(Ni + Co + Mn)/Zr 1.03: 1: mixing at a molar ratio of 0.004, heating to 820 deg.C in oxygen atmosphere at a heating rate of 3 deg.C/min, maintaining for 8 hr, maintaining the temperature of 820 deg.C, and switching to SO₂Continuously introducing gas, keeping the temperature for 4h, changing oxygen into sulfur dioxide gas, continuously introducing, cooling to room temperature after heat preservation, crushing and screening.

(3) And (3) mixing the substances obtained in the step (2) according to a solid-liquid ratio of 1:1 for 5min, performing suction filtration by using a Buchner funnel after water washing, putting a filter cake after suction filtration into a vacuum oven for drying at the drying temperature of 110 ℃ for 4h, and then sieving the material by using a 400-mesh sieve to obtain an intermediate product.

(4) The intermediate product is reacted with B₂O₃LATP is as follows 1: 0.003: 0.002, heating to 300 ℃ from room temperature in an oxygen atmosphere, preserving the temperature for 10 hours, and naturally cooling to obtain the modified anode material 1.

Wherein the layered structure of the inner layer is LiNi_0.9Co_0.05Mn_0.05Zr_0.004O₂The thickness of the modified layer is 100nm, the thickness of the composite coating layer is 150nm, and the thickness of the inner layer is 8.0 mu m; as shown in fig. 1, the modified cathode material prepared in this example has a three-layer structure, where the composite coating layer is the outermost layer, and coats the inner layer and the modified layer, where the modified layer coats the inner layer, and the inner layer is the innermost layer. As can be seen from FIG. 2, the modified cathode material prepared by the method has a compact surface appearance, and the particle surface and the grain boundary gaps are coated wellAnd (5) modifying.

Example 2

This example differs from example 1 only in that the oxygen is switched to SO₂The sintering temperature in the gas atmosphere was changed to 600 ℃ and other parameters and conditions were exactly the same as those in example 1.

Wherein the layered structure of the inner layer is LiNi_0.9Co_0.05Mn_0.05Zr_0.004O₂The thickness of the modified layer is 80nm, the thickness of the composite coating layer is 150nm, and the thickness of the inner layer is 8.0 μm.

Example 3

The other steps are the same as example 1, the primary sintering additive ZrO₂Is changed into AlF₃。

Wherein the layered structure of the inner layer is LiNi_0.9Co_0.05Mn_0.05Al_0.003O_1.991F_0.009The thickness of the modified layer is 150nm, the thickness of the composite coating layer is 50nm, and the thickness of the inner layer is 8.0 μm.

Example 4

This example differs from example 1 only in that the acid gas used was HCl gas and the other parameters and conditions were exactly the same as in example 1. Wherein, the thickness of the modified layer is 110nm, the thickness of the composite coating layer is 150nm, and the thickness of the inner layer is 8.0 μm.

Example 5

This example differs from example 1 only in that the coating material used is SiO₂And LLZO, the other parameters and conditions were exactly the same as in example 1. Wherein the thickness of the modified layer is 100nm, the thickness of the composite coating layer is 140nm, and the thickness of the inner layer is 8.0 μm.

Example 6

(1) Nickel sulfate and manganese sulfate are mixed according to the molar ratio of nickel to manganese elements of 90: dissolving according to the proportion of 10 to obtain a mixed salt solution with the concentration of 2.5 mol/L; dissolving sodium hydroxide into a precipitator solution with the concentration of 10 mol/L; dissolving ammonia water into a complexing agent solution with the concentration of 2 mol/L. Introducing 50L of mixed salt solution, precipitator solution and complexing agent solution into a reaction kettle in a parallel flow mode, carrying out coprecipitation for 24 hours under the conditions of temperature of 60 ℃, pH value of 12.5, stirring speed of 500rpm and nitrogen atmosphere protection, then carrying out suction filtration and washing on precursor slurry, drying a filter cake at 110 ℃, and then screening to obtain the nickel-containing anode material precursor.

(2) Mixing a nickel-containing anode material precursor with LiOH and SrCO₃According to the formula of Li/(Ni + Mn)/Zr 1.03: 1: mixing at a molar ratio of 0.003, heating to 830 deg.C in oxygen atmosphere at a heating rate of 3 deg.C/min, maintaining for 8 hr, heating to 880 deg.C, and switching to SO₂Continuously introducing gas, keeping the temperature for 4h, changing oxygen into sulfur dioxide gas, continuously introducing, cooling to room temperature after heat preservation, crushing and screening.

(4) The intermediate product is reacted with H₃BO₃LLZO was as follows 1: 0.003: 0.002, heating to 300 ℃ from room temperature in an oxygen atmosphere, preserving the temperature for 10 hours, and naturally cooling to obtain the modified anode material 3.

Wherein the layered structure of the inner layer is LiNi_0.9Mn_0.1Sr_0.003O₂The thickness of the modified layer is 150nm, the thickness of the composite coating layer is 150nm, and the thickness of the inner layer is 8.0 μm.

Comparative example 1

(1) Nickel sulfate, cobalt sulfate and manganese sulfate are mixed according to the molar ratio of nickel, cobalt and manganese elements of 90: 5:5 to obtain a mixed salt solution with the concentration of 2.5 mol/L; dissolving sodium hydroxide into a precipitator solution with the concentration of 10 mol/L; dissolving ammonia water into a complexing agent solution with the concentration of 2 mol/L. Introducing 50L of mixed salt solution, precipitant solution and complexing agent solution into a reaction kettle in a parallel flow manner, coprecipitating at 65 deg.C, pH 12.3 and stirring speed of 500rpm under the protection of nitrogen atmosphere, and continuously precipitating a layer of nickel-manganese hydroxide (Ni) on the surface of the precursor when the particle size of the precursor grows to a certain size_0.5Mn_1.5(OH)₂) And then, carrying out suction filtration and washing on the precursor slurry, drying a filter cake at 110 ℃, and then screening to obtain the nickel-containing anode material precursor.

(2) Mixing the nickel-containing anode material precursor prepared in the step (1) with LiOH and ZrO₂According to the formula of Li/(Ni + Co + Mn)/Zr 1.03: 1: mixing at a molar ratio of 0.004, heating to 820 ℃ from room temperature in an oxygen atmosphere at a heating rate of 3 ℃/min, keeping the temperature for 10h, cooling to room temperature, crushing and screening.

(4) The intermediate product is reacted with B₂O₃LATP is as follows 1: 0.003: 0.002, heating to 300 ℃ from room temperature in an oxygen atmosphere, preserving heat for 10 hours, and naturally cooling to obtain the cathode material, wherein the schematic diagram is shown in figure 3.

However, in the sintering process, because the sintering temperatures of the inner and outer layer precursors are different, a transition layer can be formed inside the particles, so that the particle strength and the performance of the material are reduced, and the thickness of coprecipitation of the precursors is not easy to control, so that the thickness of spinel on the surfaces of the particles after sintering is not easy to control, and the control cannot be accurately performed. From a comparison between fig. 1 and fig. 3, it can be seen that a hollow layer 4 appears between 1 and 2 in fig. 3, and the existence of the hollow layer may cause the particle strength of the positive electrode material to be deteriorated.

Comparative example 2

Otherwise, the same procedure as in example 1 was repeated except that the oxygen gas was not changed to an acidic gas, that is, the sintering was carried out in an oxygen atmosphere throughout the course of the sintering.

The preparation method can not form spinel on the surface because the spinel is not sintered in acid gas, but forms a composite coating layer because of composite coating, namely the whole material only has a two-layer structure of an inner layer and the composite coating layer.

Comparative example 3

Otherwise, the same as in example 1, no final composite coating, i.e. no composite coating layer, was carried out. And as can be seen from fig. 4, the surface of the positive electrode material is very smooth, no coating is on the surface, the edges and corners of the particles are clear, the gaps are obvious, and more pores are formed among the particles. As can be seen from comparison with fig. 2, the surface of the positive electrode material in example 1 contains a coating substance, and the coating substance fills the gaps between the spinel layers, thereby having a good protective effect on the spinel layer and the inner layer.

Comparative example 4

The procedure is otherwise the same as in example 1, except that no additive is added during the single sintering.

Wherein the spinel structure is like Li_αMn_βM_γO4, wherein M comprises Ni, Co and Zr, and the layered structure of the inner layer is LiNi_0.9Co_0.05Mn_0.05Al_0.003O_1.991F_0.009The thickness of the modified layer is 100nm, the thickness of the composite coating layer is 150nm, and the thickness of the inner layer is 8.0 μm.

Performance testing

1. Strength of the particles

The modified positive electrode materials prepared in examples and comparative examples were subjected to a grain strength test. The specific test method is as follows: the particle strength is tested by a micro compression testing machine, test parameters are set, powder particles are observed by a microscope, particles with the diameter of about 10 mu m are selected for testing, the particles are loaded with pressure after being selected until the particles are crushed, and the particle strength can be obtained after further treatment.

Table 1 particle strength of modified positive electrode materials in each example and comparative example

	Particle Strength (MPa)
		Example 1	182
Example 2	176
		Example 3	180
Example 4	181
		Example 5	178
Example 6	177
		Comparative example 1	149
Comparative example 2	155
		Comparative example 3	170
Comparative example 4	178

The comparison of the data shows that the particle strength of the modified cathode material with the in-situ spinel phase in the examples 1-6 and the comparative examples 3 and 4 is superior to that of the cathode material in the comparative examples 1-2, and the original layered structure on the surface layer is spinel-transformed in acid gas to form a spinel structure, so that the structural arrangement of the spinel structure is firmer than that of the layered structure; in the comparative example 1, the structure of the anode material contains a hollow layer due to the preparation method, so that the particle strength of the whole material is greatly reduced; comparative example 2, since sintering was performed only in oxygen, a spinel structure could not be formed and the particle strength was low. .

2. Electrochemical performance tests were performed on the modified positive electrode materials prepared in examples and comparative examples.

Firstly, the modified anode material is assembled into a button cell, the charging and discharging control voltage interval is controlled to be 2.8-4.25V, the button cell is subjected to charging and discharging tests at room temperature under 0.1C, and the first charging and discharging specific capacity and the first charging and discharging efficiency of the anode material are evaluated.

And (3) testing the cycle performance: and controlling the charging and discharging voltage interval to be 2.8-4.25V, and carrying out charging and discharging circulation on the button cell for 2 times at a constant temperature of 45 ℃ at 0.1 ℃, and then carrying out charging and discharging circulation for 100 times at 1 ℃ to evaluate the high-temperature capacity retention rate of the anode material.

(1) First cycle efficiency is first cycle discharge specific capacity (mAh/g)/first cycle charge specific capacity (mAh/g), and first cycle is subjected to charge-discharge test at a multiplying power of 0.1C;

(2) capacity retention rate of 1C cycle 100 times;

table 2 first cycle efficiency and capacity retention ratio of battery prepared from modified cathode material

As can be seen from table 2 and fig. 5, the modified cathode material with the in-situ spinel phase and the coating layer in examples 1 to 4 has a capacity and a cycle retention rate superior to those of the cathode material in the comparative example, and structurally, the spinel phase formed in situ on the particle surface can provide a three-dimensional lithium ion diffusion channel, which is more beneficial to lithium ion transmission and can improve the capacity, rate capability and cycle performance of the cathode material; in terms of the coating, the coated oxide and the acid thereof can react with residual lithium on the surface, the coated fast ion conductor can well transmit lithium ions, and the combination of the coated fast ion conductor and the coated fast ion conductor can improve the capacity and the cycle performance; the comparative example 3 has no coating layer, and residual lithium on the surface of the coating layer has higher activity and is easy to contact with electrolyte to generate side reaction, so that the electrical property of the battery is reduced; in comparative example 2, which has no spinel structure, the particle surface structure is broken and pulverized during long-term circulation, and the properties are reduced particularly at high temperature. Comparative example 4 has no additive, and the lithium-nickel mixed discharge is intensified in the primary sintering process, which finally causes the reduction of the cycle performance of the material; in the comparative example 1, the operation such as rolling is needed during the preparation of the pole piece, so that the structure of the pole piece is broken, and the electrical property of the pole piece is greatly reduced.

3. The modified positive electrode materials prepared in the examples and comparative examples were subjected to safety performance tests.

Firstly, assembling the modified anode material into a button cell, and carrying out safety performance test;

(1) DSC test: charging the assembled button cell to 4.25V at a constant current and a constant voltage of 0.1C, stopping the current to 0.05C, then discharging to 2.8V at a constant current, and then charging to 4.25V in the same way for later use; disassembling the button cell in a glove box filled with argon, taking out the positive pole piece, cleaning the residual electrolyte on the surface by using DMC, taking out the electrolyte after the electrolyte on the surface of the pole piece is volatilized, lightly scraping the active substance by using a knife, taking 5-10 mg of powder, collecting the powder in a sample tube, and sealing the sample tube; and transferring the sample out of the glove box for DSC test, wherein the temperature range is room temperature to 350 ℃, and the heating rate is 5 ℃/min.

(2) And (3) floating charge test: the nominal specific capacity is 200mAh/g, the high-temperature float-charging test is carried out at the temperature of 60 ℃, the voltage range is 2.8-4.55V, the mixture is kept stand for 1h, and 0.2C-CC & CV is carried out for 720 h.

Table 3 safety performance results of batteries prepared from modified cathode materials of examples and comparative examples

	DSC test (A)Peak degree C)	Float charge test h
			Example 1	230.5	348
Example 2	228.4	345
			Example 3	229.2	346
Example 4	227.8	340
			Example 5	226.6	338
Example 6	225.5	335
			Comparative example 1	221.2	249
Comparative example 2	222.5	260
			Comparative example 3	210.7	146
Comparative example 4	208.3	135

Under certain test conditions, when a DSC test is carried out, the higher the peak temperature is, the better the thermal stability of the representative material is, and the better the safety performance is; during the float-fill test, the longer the float-fill time, the better the structural stability of the material, and the better the corresponding material safety. As can be seen from Table 3, the DSC test peak value of the modified cathode material of examples 1-4 is higher than that of the cathode material in the comparative example, and the retention time is longer in the float charge test, which shows that the modified cathode material has better safety performance; although the spinel and the coating layer are also contained in the comparative example 1, a hollow layer is generated, so that the safety performance of the material is greatly reduced; comparative example 2 is only a clad layer and an inner layer, and has no hard spinel structure to maintain the whole structure thereof, thus having poor safety performance; comparative example 3 is without a coating layer, the inner layer material cannot be wrapped, and side reactions are liable to occur; comparative example 4 has no additive, i.e., no fast ion conductor or the like, and severely restricts the safety of the battery.

Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. The modified cathode material is characterized by comprising an inner layer, a modified layer and a composite coating layer;

the inner layer is of a laminated structure; the inner layer comprises lithium element and nickel element;

the modified layer is of a spinel structure;

the modified layer coats the inner layer;

the composite coating layer is positioned on one side of the modification layer far away from the inner layer and coats the modification layer.

2. The modified positive electrode material according to claim 1, wherein the modified layer has a thickness of 2 to 300 nm;

the thickness of the composite coating layer is 1-200 nm;

the thickness of the inner layer is 1.5-10.0 μm.

3. The modified cathode material according to claim 1, wherein the composite clad layer comprises an oxide or acid of B, Ti, Si, W, Al and a fast ion conductor;

the oxide or acid of B, Ti, Si, W, Al comprises B₂O₃、H₃BO₃、TiO₂、H₂TiO₃、SiO₂、H₂SiO₃、WO₃、H₂WO₄、Al₂O₃、HAlO₂At least one of;

the fast ion conductor comprises at least one of LLZO, LZTO, LATP and LiPON.

4. The modified cathode material according to claim 1, wherein the layered structure comprises at least one of the compounds of formula I,

Li_1+a(Ni_xCo_yMn_zM_m)_1-aO_2±bA_cformula I

Wherein a is more than or equal to 0.1 and less than or equal to 0.1, x is more than 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 0.4, z is more than 0 and less than or equal to 0.6, m is more than 0 and less than or equal to 0.1, b is more than or equal to 0 and less than 0.02, c is more than or equal to 0 and less than or equal to 0.02, and x + y + z is equal to 1;

m is selected from at least one of B, Mg, Al, Ti, Zr, Nb, Y, W, Sn, Mo, La, Er, Sr and Ba;

a is selected from at least one of P, F and Cl.

5. A method for preparing a modified positive electrode material according to any one of claims 1 to 4, comprising:

(1) carrying out primary sintering on a mixed material comprising a nickel-containing anode material precursor, a lithium source and an additive in an oxygen-containing gas atmosphere to obtain a primary sintered product;

(2) sintering the primary sintering product in acid gas again to obtain an intermediate substance;

(3) and carrying out composite coating on the intermediate substance through a coating material to obtain the modified anode material.

6. The preparation method according to claim 5, wherein in the step (1), the temperature of the primary sintering is 700 to 1000 ℃; the primary sintering time is 6-20 h;

in the step (2), the temperature of the secondary sintering is 700-1000 ℃; and the secondary sintering time is 2-6 h.

7. The method according to claim 5, wherein in the step (2), the acid gas includes SO₂、H₂S、CO₂、HCl、NO₂、HF、Cl₂At least one of (1).

8. The method according to claim 5, wherein the additive is at least one of an oxide, a halide, and a phosphate of a non-metal or a basic metal;

the oxides, halides and phosphates of said non-metals or alkaline metals include B₂O₃、MgO、Al₂O₃、TiO₂、ZrO₂、Nb₂O₅、Y₂O₃、WO₃、SnO、MoO₃、La₂O₃、Er₂O₃、MgCO₃、SrCO₃、BaCO₃、MgF₂、MgCl₂、AlF₃、AlPO₄、SrF₂、BaF₂And BaCl₂At least one of (1).

9. The method of claim 5, wherein the cladding material comprises an oxide or acid of B, Ti, Si, W, Al and a fast ion conductor;

the composite coating is as follows: mixing and sintering the intermediate substance and the coating material in an atmosphere containing oxygen;

the sintering conditions are as follows: the temperature is 200-800 ℃; the time is 8-16 h.

10. A lithium ion positive electrode comprising at least one of the modified positive electrode material according to any one of claims 1 to 4 and the modified positive electrode material obtained by the production method according to any one of claims 5 to 9.

11. A lithium ion battery comprising at least one of the lithium ion positive electrodes according to claim 10.