Composite coated medium nickel positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a medium-nickel ultrahigh-voltage positive electrode material and a preparation method and application thereof.The composite coated medium-nickel positive electrode material comprises a base material and a coating layer coating the outer surface of the base material, and the coating layer comprises a first coating layer and a second coating layer; the first coating layer at least coats part of the surface of the base material, and the second coating layer at least coats part of the surface of the first coating layer; the first coating layer contains a cobalt element; the second coating layer contains a first metal element, and the first metal element comprises at least one of aluminum, tungsten and titanium. A core-shell structure is formed through in-situ high-entropy doping and cobalt element and metal element coating to relieve structural deterioration caused by cation mixing and rock salting phase change, stabilize a lattice oxygen structure and inhibit interface side reaction, so that the cycle life is prolonged, the rate capability is improved, and the safety is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite coated nickel cathode material, its preparation method, and its application. Background Technology

[0002] Medium-nickel cathode materials (such as NCM523 / 622) are considered ideal candidates for power batteries due to their advantages such as low nickel content, low cost, good thermal stability, and long cycle life. However, their energy density is significantly lower than that of high-nickel cathode materials (such as NCM811 / NCA), which limits their application in high-end electric vehicles.

[0003] To overcome this bottleneck, increasing the charging cutoff voltage has become a key strategy. Existing technologies often use ultra-high voltage (4.45V) to force the medium-nickel cathode material to release more lithium ions at a higher potential, directly increasing the discharge specific capacity. While this can effectively compensate for the inherent deficiency of the low specific capacity of medium-nickel materials, the ultra-high voltage presents the following challenges: Ultra-high voltage exacerbates side reactions at the cathode / electrolyte interface, leading to continuous oxidation and decomposition of the electrolyte, gas production, and the formation of a thick and highly impedance harmful interface film (CEI), which consumes active lithium and electrolyte, resulting in a rapid decline in battery cycle life; at the same time, deep delithiation under high voltage can easily trigger harmful phase transitions (layered → spinel / rock salt phase), leading to structural collapse, a surge in impedance, and a drop in capacity; it also exacerbates the dissolution of transition metal ions (Mn / Ni), damaging the electrode structure and poisoning the negative electrode, resulting in poor battery structural stability; the high impedance layer at the interface and structural degradation hinder lithium ion diffusion, resulting in poor rate performance. In addition, the increased activity of lattice oxygen at high potentials may lead to irreversible oxygen release, resulting not only in capacity loss but also serious safety hazards (gas production and thermal runaway risks).

[0004] Therefore, how to optimize and adjust the medium-nickel cathode material and its preparation method to prepare a structurally stable medium-nickel cathode material, so as to improve the cycle life, rate performance and safety of lithium-ion batteries, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a composite coated nickel cathode material to solve the problems of short cycle life, poor rate performance, and poor safety in existing lithium-ion batteries.

[0006] In a first aspect, the present invention provides a composite coated nickel cathode material, comprising a matrix material and a coating layer covering the outer surface of the matrix material, the coating layer comprising a first coating layer and a second coating layer, wherein the first coating layer covers at least a portion of the surface of the matrix material, and the second coating layer covers at least a portion of the surface of the first coating layer; In the matrix material, the concentration of cobalt increases in a gradient from the center of the matrix material toward its outer surface; The matrix material includes at least one of tungsten, zirconium, aluminum, titanium, magnesium, and niobium; The first coating layer contains cobalt; the second coating layer contains a first metal element, which includes at least one of aluminum, tungsten, and titanium.

[0007] In some alternative embodiments, the cobalt content in the first coating layer is 0.5wt%-1.0wt% based on the mass of the matrix material.

[0008] In some alternative embodiments, the content of the first metal element in the second coating layer is 0.1wt%-0.5wt% based on the mass of the matrix material.

[0009] In some alternative embodiments, the matrix material has the chemical formula Li. e (Ni a Co b Mn c M d O2, wherein 0.6≤a≤0.7, 0.05≤b≤0.3, 0.2≤c≤0.3, 0.01≤d≤0.18, 1.0≤e≤1.1, and M is selected from at least one of tungsten, zirconium, aluminum, titanium, magnesium, and niobium.

[0010] In a second aspect, the present invention provides a method for preparing the composite-coated nickel cathode material described in the first aspect, comprising the following steps: (1) The nickel source is configured as the first solution, the first cobalt source is configured as the second solution, the manganese source is configured as the third solution, and the dopant containing the second metal is configured as the fourth solution; (2) The first solution, the second solution, the third solution and the fourth solution are mixed by drop addition. By dynamically adjusting the dropping rate of the second solution, the molar concentration of the first cobalt element in the mixture is made to increase. The reaction is carried out to obtain the nickel-cobalt-manganese precursor. (3) The nickel-cobalt-manganese precursor and the lithium source are mixed and then subjected to a first sintering to obtain the matrix material; (4) The matrix material and the second cobalt source are mixed and then subjected to a second sintering to obtain a cobalt-coated matrix material; (5) The cobalt-coated matrix material and the coating agent containing the first metal are mixed and then subjected to a third sintering to prepare a composite coated nickel cathode material.

[0011] In some alternative embodiments, during the initial stage of addition, the dropping rate of the first, third, and fourth solutions is 70 mL / min to 90 mL / min; and the dropping rate of the second solution is 10 mL / min to 30 mL / min.

[0012] In some optional embodiments, at the end of the dropping stage, the molar ratio of nickel, cobalt, and manganese in the mixture is 0.6-0.7:0.05-0.3:0.2-0.3.

[0013] In some optional embodiments, the molar ratio of nickel, cobalt, and manganese in the nickel-cobalt-manganese precursor to lithium in the lithium source is 1:1-1.1.

[0014] In some alternative embodiments, the mass of the second cobalt element in the second cobalt source accounts for 0.5%-1.0% of the mass of the matrix material.

[0015] In some alternative embodiments, the mass of the first metallic element accounts for 0.1wt%-0.5wt% of the mass of the matrix material.

[0016] In some alternative embodiments, the nickel source includes at least one of nickel sulfate, nickel nitrate, and nickel chloride.

[0017] In some alternative embodiments, the first cobalt source includes at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride.

[0018] In some alternative embodiments, the manganese source includes at least one of manganese sulfate, manganese nitrate, and manganese chloride.

[0019] In some alternative embodiments, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium chloride, and lithium nitrate.

[0020] In some alternative embodiments, the dopant containing the first metal includes at least one of a first tungsten source, a first aluminum source, and a first titanium source.

[0021] In some optional embodiments, the coating agent containing the second metal includes a second tungsten source, a zirconium source, a second aluminum source, a second titanium source, a magnesium source, and a niobium source.

[0022] In some alternative implementations, the first tungsten source and the second tungsten source are each independently selected from tungsten chloride.

[0023] In some alternative embodiments, the zirconium source includes at least one of zirconium oxychloride, zirconium nitrate, and zirconium sulfate.

[0024] In some alternative embodiments, the first aluminum source and the second aluminum source are each independently selected from at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride.

[0025] In some alternative embodiments, the first titanium source and the second titanium source are each independently selected from at least one of titanium chloride and titanium oxalate.

[0026] In some alternative embodiments, the magnesium source includes at least one of magnesium nitrate, magnesium sulfate, and magnesium chloride.

[0027] In some alternative embodiments, the niobium source includes at least one of niobium oxalate, niobium ethoxide, and niobium chloride.

[0028] In some alternative embodiments, the second cobalt source includes at least one of cobalt hydroxyoxide and cobalt hydroxide.

[0029] In some optional embodiments, the dropwise addition step (2) further includes the addition of a precipitant and a complexing agent; the precipitant includes an aqueous solution of sodium hydroxide; and the complexing agent includes ammonia.

[0030] In some alternative implementations, the reaction temperature in step (2) is 49°C-65°C.

[0031] In some optional embodiments, in step (3), the first sintering step includes: sintering at 500℃-800℃ for 3h-7h, and then sintering at 910℃-980℃ for 8h-12h.

[0032] In some optional embodiments, in step (4), the second sintering temperature is 600℃-900℃, the time is 5h-8h, and the sintering atmosphere is oxygen.

[0033] In some alternative implementations, in step (5), the temperature of the third sintering is 300℃-500℃ and the time is 4h-6h.

[0034] Thirdly, the present invention provides an application of the composite coated nickel cathode material described in the first aspect or the composite coated nickel cathode material prepared by the preparation method described in the second aspect in lithium-ion batteries.

[0035] The technical solution of this invention has the following advantages: 1. The composite coated nickel cathode material provided by the present invention includes a matrix material and a coating layer covering the outer surface of the matrix material. The coating layer includes a first coating layer and a second coating layer. The first coating layer covers at least a portion of the surface of the matrix material, and the second coating layer covers at least a portion of the surface of the first coating layer. In the matrix material, the concentration of cobalt increases gradient from the center of the matrix material to its outer surface. The matrix material includes at least one of tungsten, zirconium, aluminum, titanium, magnesium, and niobium. The first coating layer contains cobalt. The second coating layer contains a first metal element, which includes at least one of aluminum, tungsten, and titanium. The present invention alleviates the structural degradation caused by cation mixing and rock salting phase transition, stabilizes the lattice oxygen structure, and suppresses interfacial side reactions by forming a core-shell structure through in-situ high-entropy doping and coating with cobalt and metal elements, thereby improving the cycle life, rate performance, and safety of lithium-ion batteries. Specifically, by enriching cobalt (Co) on the outer surface of the matrix material, a more stable and conductive Co can be formed. 3+ Oxidized state (compared to Ni in the high-nickel state) 3+ / Ni 4+ In synergy with the second coating layer, the nickel cathode material effectively suppresses side reactions such as oxidative decomposition of the electrolyte under high pressure, forming a low-impedance interface and reducing the excessive growth and gas generation of harmful ion exchange films (CEIs). Simultaneously, it suppresses surface phase transitions, maintains the integrity of the surface crystal structure and the unobstructed flow of lithium-ion channels, improving the rate performance of lithium-ion batteries. Furthermore, as an ion conductor, the coating layer forms a high-speed ion diffusion bridge between the electrolyte and the substrate material, reducing the resistance to interfacial ion migration and improving battery performance. Doping the substrate material with high-entropy ions broadens and stabilizes lithium-ion channels, preventing excessive lattice contraction during delithiation and excessive expansion during lithium insertion, maintaining the stability of the lithium-ion interlayer spacing. It also suppresses harmful phase transitions, maintaining structural coherence. Additionally, it modulates the electronic structure, lowers the migration barrier, weakens the binding force between lithium ions and surrounding lattice points, and reduces the activation energy required for lithium ions to jump between lattice sites, allowing for faster diffusion. This, in turn, ensures the structural stability of the nickel cathode material in the composite coating, improving the rate performance and cycle life of lithium-ion batteries. In the matrix material, the concentration of cobalt increases in a gradient from the center of the matrix material to its outer surface. This can suppress interfacial side reactions, reduce structural degradation, ensure the structural stability of the nickel cathode material in the composite coating, and improve the rate performance and cycle life of lithium-ion batteries. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 This is a scanning electron microscope image of the composite-coated nickel cathode material prepared according to Example 1 of the present invention. Detailed Implementation

[0038] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0039] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0040] Example 1 This embodiment provides a method for preparing a composite-coated nickel-containing cathode material, including the following steps: (1) Prepare nickel sulfate solution with a concentration of 0.67 mol / L, cobalt sulfate solution with a concentration of 0.05 mol / L, and manganese sulfate solution with a concentration of 0.28 mol / L respectively; prepare a mixed salt solution according to the molar ratio of tungsten chloride, zirconium nitrate, aluminum nitrate, and titanium oxalate in tungsten chloride, zirconium nitrate, aluminum nitrate, and titanium oxalate as 0.01:0.02:0.01:0.01; in the mixed metal salt solution, the concentrations of tungsten chloride, zirconium nitrate, aluminum nitrate, and titanium oxalate are 0.01 mol / L, 0.02 mol / L, 0.01 mol / L, and 0.01 mol / L, respectively; (2) Pump nickel sulfate solution, manganese sulfate solution, mixed salt solution, 3 mol / L NaOH solution and 7 mol / L NH3·H2O solution at a rate of 80 mL / min, and simultaneously pump cobalt sulfate solution at a rate of 10 mL / min, gradually increasing the dropping rate of cobalt sulfate solution. Nitrogen protective gas is introduced during the reaction process, the rotation speed is controlled at 500 rpm, the reaction temperature is 59℃, and the reaction is continued until the particle size D50 is 3-4 μm. After the dropping is completed, the molar ratio of nickel:cobalt:aluminum in the mixed solution is 0.67:0.05:0.28. After stopping the feeding, the mixture is aged for 6 hours, filtered, washed and dried to obtain precursor powder. (3) The above precursor powder was mixed with lithium carbonate. The molar ratio of nickel, cobalt and manganese in the precursor powder to lithium in the lithium source was 1:1.04. The mixture was calcined at 800°C for 5 hours in air and then calcined at 950°C for 10 hours. After pulverization, the matrix material Li was obtained. 1.04 (Ni 0.67 Co 0.05 Mn 0.28 W 0.01 Zr 0.02 Al 0.01 Ti 0.01 O2; (4) The matrix material obtained in step (3) is mixed with cobalt hydroxyoxide, wherein the amount of cobalt added in cobalt hydroxyoxide is 0.8 wt% of the mass of the matrix material, and then calcined at 700°C for 7 h in an oxygen atmosphere to form a cobalt-coated matrix material; after pulverization, it is mixed with aluminum chloride, wherein the amount of aluminum added in aluminum chloride is 0.1 wt% of the mass of the matrix material, and then sintered at 400°C for 5 h to form a metal coating layer, thus preparing a composite coated nickel cathode material; based on the mass of the matrix material, the cobalt content in the first coating layer is 0.8 wt%, and the aluminum content in the second coating layer is 0.1 wt%.

[0041] Example 2 This embodiment provides a method for preparing a medium-nickel cathode material, including the following steps: (1) Prepare nickel nitrate solution with a concentration of 0.65 mol / L, cobalt chloride solution with a concentration of 0.15 mol / L, and manganese nitrate solution with a concentration of 0.2 mol / L respectively; prepare a mixed salt solution according to the molar ratio of titanium, magnesium, niobium, and aluminum in titanium chloride, magnesium sulfate, niobium chloride, and aluminum chloride of 0.01:0.03:0.02:0.01; in the mixed metal salt solution, the concentrations of titanium chloride, magnesium sulfate, niobium chloride, and aluminum chloride are 0.01 mol / L, 0.03 mol / L, 0.02 mol / L, and 0.01 mol / L, respectively; (2) Pump nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, mixed salt solution, 3 mol / L NaOH solution and 7 mol / L NH3·H2O solution at a rate of 80 mL / min, and simultaneously pump cobalt sulfate solution at a rate of 20 mL / min, gradually increasing the dropping rate of cobalt sulfate solution. Nitrogen protective gas is introduced during the reaction process, the rotation speed is controlled at 600 rpm, the reaction temperature is 49℃, and the reaction is continued until the particle size D50 is 3-4 μm. After the dropping is completed, the molar ratio of nickel:cobalt:aluminum in the mixed solution is 0.65:0.15:0.2. After stopping the feeding, the mixture is aged for 6 hours, filtered, washed and dried to obtain precursor powder. (3) The above precursor powder was mixed with lithium hydroxide. The molar ratio of nickel, cobalt and manganese in the precursor powder to lithium in the lithium source was 1:1.08. The mixture was calcined at 500°C for 7 hours in air, and then calcined at 980°C for 8 hours. After pulverization, the matrix material Li was obtained. 1.08 (Ni 0.65 Co 0.15 Mn 0.20 Ti 0.01 Mg 0.03 Nb 0.02 Al 0.01 O2; (4) The matrix material obtained in step (3) is mixed with cobalt hydroxide, wherein the amount of cobalt added in cobalt hydroxide is 0.5 wt% of the mass of the matrix material, and then calcined at 900°C for 5 h in an oxygen atmosphere to form the first coating layer; after pulverization, it is mixed with tungsten chloride, wherein the amount of tungsten added in tungsten chloride is 0.5 wt% of the mass of the matrix material, and then sintered at 300°C for 4 h to form the metal coating layer, thus preparing the composite coated nickel cathode material; based on the mass of the matrix material, the cobalt content in the first coating layer is 0.5 wt%, and the tungsten content in the metal coating layer is 0.5 wt%.

[0042] Example 3 This embodiment provides a method for preparing a medium-nickel cathode material, including the following steps: (1) Prepare nickel sulfate solution with a concentration of 0.63 mol / L, cobalt nitrate solution with a concentration of 0.17 mol / L, and manganese chloride solution with a concentration of 0.2 mol / L respectively; prepare a mixed salt solution according to the molar ratio of tungsten chloride, aluminum sulfate, titanium oxalate, niobium ethanol, and magnesium chloride of 0.03:0.02:0.03:0.02:0.01; in the mixed metal salt solution, the concentrations of tungsten chloride, aluminum sulfate, titanium oxalate, niobium ethanol, and magnesium chloride are 0.03 mol / L, 0.01 mol / L, 0.03 mol / L, 0.02 mol / L, and 0.01 mol / L, respectively; (2) Pump nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, mixed salt solution, 3 mol / L NaOH solution and 7 mol / L NH3·H2O solution at a rate of 80 mL / min, and simultaneously pump cobalt sulfate solution at a rate of 30 mL / min, gradually increasing the dropping rate of cobalt sulfate solution. Nitrogen protective gas is introduced during the reaction process, the rotation speed is controlled at 800 rpm, the reaction temperature is 55℃, and the reaction is continued until the particle size D50 is 3-4 μm. After the dropping is completed, the molar ratio of nickel:cobalt:aluminum in the mixed solution is 0.63:0.17:0.2. After stopping the feeding, the mixture is aged for 6 hours, filtered, washed and dried to obtain precursor powder. (3) The above precursor powder was mixed with lithium chloride, and the molar ratio of nickel, cobalt and manganese in the precursor powder to lithium in the lithium source was 1:1. The mixture was calcined at 600°C for 6 hours in air atmosphere, and then calcined at 960°C for 12 hours. After pulverization, the matrix material Li was obtained. 1.0 (Ni 0.63 Co 0.17 Mn 0.2 W 0.03 Al 0.02 Ti 0.03 Nb 0.02 Mg 0.01 O2; (4) The matrix material obtained in step (3) is mixed with cobalt hydroxyl oxide, wherein the amount of cobalt added in cobalt hydroxyl oxide is 0.6 wt% of the mass of the matrix material, and then calcined at 800°C for 6 h in an oxygen atmosphere to form the first coating layer; after pulverization, it is mixed with titanium chloride, wherein the amount of titanium added in titanium chloride is 0.3 wt% of the mass of the matrix material, and then sintered at 500°C for 6 h to form the metal coating layer, thus preparing the composite coated nickel cathode material; based on the mass of the matrix material, the cobalt content in the first coating layer is 0.6 wt%, and the titanium content in the metal coating layer is 0.3 wt%.

[0043] Example 4 This embodiment provides a method for preparing a medium-nickel cathode material, including the following steps: (1) Prepare nickel chloride solution with a concentration of 0.6 mol / L, cobalt chloride solution with a concentration of 0.15 mol / L, and manganese sulfate solution with a concentration of 0.25 mol / L respectively; prepare a mixed salt solution according to the molar ratio of tungsten chloride, zirconium sulfate, aluminum nitrate, titanium chloride, magnesium nitrate, and niobium oxalate in 0.02:0.01:0.03:0.01:0.03:0.02; in the mixed metal salt solution, the concentrations of tungsten chloride, zirconium sulfate, aluminum nitrate, titanium chloride, magnesium nitrate, and niobium oxalate are 0.02 mol / L, 0.01 mol / L, 0.03 mol / L, 0.01 mol / L, 0.03 mol / L, and 0.02 mol / L respectively; (2) Pump nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, mixed salt solution, 3 mol / L NaOH solution and 7 mol / L NH3·H2O solution at a rate of 80 mL / min, and simultaneously pump cobalt sulfate solution at a rate of 25 mL / min, gradually increasing the dropping rate of cobalt sulfate solution. Nitrogen protective gas is introduced during the reaction process, the rotation speed is controlled at 1000 rpm, the reaction temperature is 65℃, and the reaction is continued until the particle size D50 is 3-4 μm. After the dropping is completed, the molar ratio of nickel:cobalt:aluminum in the mixed solution is 0.6:0.15:0.25. After stopping the feeding, age for 6 hours, filter, wash and dry to obtain precursor powder; (3) The above precursor powder was mixed with lithium nitrate. The molar ratio of nickel, cobalt and manganese in the precursor powder to lithium in the lithium source was 1:1.1. The mixture was calcined at 700°C for 3 hours in air, and then calcined at 970°C for 11 hours. After pulverization, the matrix material Li was obtained. 1.1 (Ni 0.60 Co 0.15 Mn 0.25 W 0.02 Zr 0.01 Al 0.03 Ti 0.01 Mg 0.03 Nb 0.02 O2; (4) The matrix material obtained in step (3) is mixed with cobalt hydroxyoxide, wherein the amount of cobalt added in cobalt hydroxyoxide is 1 wt% of the mass of the matrix material, and then calcined at 600°C for 8 h in an oxygen atmosphere to form the first coating layer; after pulverization, it is mixed with tungsten chloride, wherein the amount of tungsten added in tungsten chloride is 0.2 wt% of the mass of the matrix material, and then sintered at 350°C for 5 h to form the metal coating layer, thus preparing the composite coated nickel cathode material; based on the mass of the matrix material, the cobalt content in the first coating layer is 1 wt%, and the total tungsten content in the metal coating layer is 0.2 wt%.

[0044] Comparative Example 1 This comparative example provides a method for preparing a composite-coated nickel cathode material, comprising the following steps: (1) Prepare nickel sulfate solution with a concentration of 0.67 mol / L, cobalt sulfate solution with a concentration of 0.05 mol / L, and manganese sulfate solution with a concentration of 0.28 mol / L respectively; pump nickel sulfate solution, manganese sulfate solution, 3 mol / L NaOH solution and 7 mol / L NH3·H2O solution at a rate of 80 mL / min, and simultaneously pump cobalt sulfate solution at a rate of 10 mL / min, gradually increasing the dropping rate of cobalt sulfate solution. During the reaction, nitrogen protective gas is introduced, the rotation speed is controlled at 500 rpm, the reaction temperature is 59℃, and the reaction is continued until the particle size D50 is 3-4 μm, and after the dropping is completed, the molar ratio of nickel element: cobalt element: aluminum element in the mixture is 0.67:0.05:0.28. After stopping the feeding, age for 6 hours, filter, wash and dry to obtain precursor powder; (2) Prepare a mixed salt solution with the molar ratio of tungsten, zirconium, aluminum and titanium in ammonium tungstate, zirconium nitrate, aluminum nitrate and titanium oxalate being 0.02:0.01:0.01:0.68; in the mixed metal salt solution, the concentrations of tungsten chloride, zirconium nitrate, aluminum nitrate and titanium oxalate are 0.01mol / L, 0.02mol / L, 0.01mol / L and 0.01mol / L, respectively; mix the precursor powder prepared in step (1) with the mixed salt solution, control the molar ratio of nickel content in the nickel-cobalt-manganese precursor to tungsten in tungsten chloride to be 0.67:0.02, stir, and heat to 40°C until the water evaporates to dryness to obtain the metal-doped precursor powder; (3) Steps (3) and (4) are the same as in Example 1.

[0045] Comparative Example 2 This comparative example provides a method for preparing a composite coated nickel cathode material, which is basically the same as the steps in Example 1, except that in step (2), the pumping rate of the cobalt sulfate solution remains unchanged, that is, 80 mL / min.

[0046] Comparative Example 3 This comparative example provides a method for preparing a composite coated nickel cathode material, which is basically the same as the steps in Example 1, except that the formation of the first coating layer is omitted in step (4).

[0047] Comparative Example 4 This comparative example provides a method for preparing a composite coated nickel cathode material, which is basically the same as the steps in Example 1, except that the formation of the metal coating layer is omitted in step (4).

[0048] Experimental Example 1 The composite-coated nickel cathode material prepared in Example 1 was subjected to scanning electron microscopy (SEM) analysis. The results are shown in the figure below. Figure 1 As shown. From Figure 1As can be seen, the nickel cathode material in the composite coating prepared by this invention has a relatively uniform size and is a single crystal structure.

[0049] Example 2 The cathode materials prepared in Examples 1-4 and Comparative Examples 1-4 were used as the main materials to assemble lithium-ion batteries, and their electrochemical performance was tested. The results are shown in Table 1. The specific steps were as follows: using N-methylpyrrolidone as a dispersant, cathode material:super-P:PVDF (polyvinylidene fluoride) was mixed at a mass ratio of 90:5:5 to prepare cathode slurries. The cathode slurries were then uniformly coated onto carbon-coated aluminum foil with a coating density of 12 cm⁻¹. 2 The positive electrode was obtained by drying the positive electrode at 80°C for 2 hours in an oven. The negative electrode was then assembled using a Celgard 2500 separator and lithium metal sheets in an argon atmosphere in a glove box. The negative electrode, electrolyte, separator, and positive electrode were then assembled into a CR2032 button cell. The charging cutoff voltage was 4.45V, and the discharging cutoff voltage was 3.0V. The cycle consisted of 0.1C charging and 0.1C discharging in the first cycle, 0.5C charging and 1C discharging in the second cycle, and 0.5C charging and 1.0C discharging in the third cycle, for a total of 50 cycles.

[0050] Table 1. Performance test results of button batteries prepared from the cathode materials of each embodiment and comparative example.

[0051] As can be seen from Table 1, the initial discharge specific capacity of the button batteries prepared with the cathode materials prepared in Examples 1-4 is 197.1 mAh g. -1 -198.9mAh g -1 Within the range, all were higher than the comparative example's 195.3 mAh g. -1 -196.4mAh g -1 The first efficacy was in the range of 88.3%-89.3%, which was higher than the comparative sample's 87.1%-88.1%; the capacity retention rate was in the range of 95.1%-97.2%, which was higher than the comparative sample's 93.4%-94.3%.

[0052] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite-coated nickel-metal hydride cathode material, comprising a matrix material and a coating layer covering the outer surface of the matrix material, characterized in that, The coating layer includes a first coating layer and a second coating layer, wherein the first coating layer covers at least a portion of the surface of the base material, and the second coating layer covers at least a portion of the surface of the first coating layer; In the matrix material, the concentration of cobalt increases in a gradient from the center of the matrix material toward its outer surface; The matrix material includes at least one of tungsten, zirconium, aluminum, titanium, magnesium, and niobium; The first coating layer contains cobalt; the second coating layer contains a first metal element, which includes at least one of aluminum, tungsten, and titanium.

2. The composite-coated nickel cathode material according to claim 1, characterized in that, Based on the mass of the matrix material, the cobalt content in the first coating layer is 0.5wt%-1.0wt%.

3. The composite-coated nickel cathode material according to claim 2, characterized in that, Based on the mass of the matrix material, the content of the first metal element in the second coating layer is 0.1wt%-0.5wt%.

4. The composite-coated nickel cathode material according to claim 1, characterized in that, The chemical formula of the matrix material is Li e (Ni a Co b Mn c M d O2, wherein 0.6≤a≤0.7, 0.05≤b≤0.3, 0.2≤c≤0.3, 0.01≤d≤0.18, 1.0≤e≤1.1, and M is selected from at least one of tungsten, zirconium, aluminum, titanium, magnesium, and niobium.

5. A method for preparing a composite-coated nickel cathode material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) The nickel source is configured as the first solution, the first cobalt source is configured as the second solution, the manganese source is configured as the third solution, and the dopant containing the second metal is configured as the fourth solution; (2) The first solution, the second solution, the third solution and the fourth solution are mixed by drop addition. By dynamically adjusting the dropping rate of the second solution, the molar concentration of the first cobalt element in the mixture is made to increase. The reaction is carried out to obtain the nickel-cobalt-manganese precursor. (3) The nickel-cobalt-manganese precursor and the lithium source are mixed and then subjected to a first sintering to obtain the matrix material; (4) The matrix material and the second cobalt source are mixed and then subjected to a second sintering to obtain a cobalt-coated matrix material; (5) The cobalt-coated matrix material and the coating agent containing the first metal are mixed and then subjected to a third sintering to prepare a composite coated nickel cathode material.

6. The method for preparing the composite-coated nickel cathode material according to claim 5, characterized in that, In the initial stage of addition, the dropping rate of the first, third, and fourth solutions was 70 mL / min-90 mL / min; the dropping rate of the second solution was 10 mL / min-30 mL / min. And / or, at the end of the dropping stage, the molar ratio of nickel, cobalt, and manganese in the mixture is 0.6-0.7:0.05-0.3:0.2-0.

3.

7. The method for preparing the composite-coated nickel cathode material according to claim 5, characterized in that, The molar ratio of nickel, cobalt, and manganese in the nickel-cobalt-manganese precursor to lithium in the lithium source is 1:1-1.

1. And / or, the mass of the second cobalt element in the second cobalt source accounts for 0.5%-1.0% of the mass of the matrix material; And / or, the mass of the first metallic element accounts for 0.1wt%-0.5wt% of the mass of the matrix material.

8. The method for preparing the composite-coated nickel cathode material according to claim 5, characterized in that, The nickel source includes at least one of nickel sulfate, nickel nitrate, and nickel chloride; And / or, the first cobalt source includes at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride; And / or, the manganese source includes at least one of manganese sulfate, manganese nitrate, and manganese chloride; And / or, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium chloride, and lithium nitrate; And / or, the dopant containing the first metal includes at least one of a first tungsten source, a first aluminum source, and a first titanium source; And / or, the coating agent containing the second metal includes at least one of the following: a second tungsten source, a zirconium source, a second aluminum source, a second titanium source, a magnesium source, and a niobium source; Optionally, the first tungsten source and the second tungsten source are each independently selected from tungsten chloride; Optionally, the zirconium source includes at least one of zirconium oxychloride, zirconium nitrate, and zirconium sulfate; Optionally, the first aluminum source and the second aluminum source are each independently selected from at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride; Optionally, the first titanium source and the second titanium source are each independently selected from at least one of titanium chloride and titanium oxalate; Optionally, the magnesium source includes at least one of magnesium nitrate, magnesium sulfate, and magnesium chloride; Optionally, the niobium source includes at least one of niobium oxalate, niobium ethoxide, and niobium chloride; Optionally, the second cobalt source includes at least one of cobalt hydroxyoxide and cobalt hydroxide; And / or, the dropwise addition step (2) further includes the addition of a precipitant and a complexing agent; the precipitant includes an aqueous solution of sodium hydroxide; the complexing agent includes ammonia.

9. The method for preparing the composite-coated nickel cathode material according to claim 4, characterized in that, In step (2), the reaction temperature is 49℃-65℃; And / or, in step (3), the first sintering step includes: sintering at 500℃-800℃ for 3h-7h, and then sintering at 910℃-980℃ for 8h-12h; And / or, in step (4), the temperature of the second sintering is 600℃-900℃, the time is 5h-8h, and the sintering atmosphere is oxygen; And / or, in step (5), the temperature of the third sintering is 300℃-500℃ and the time is 4h-6h.

10. The application of the composite coated nickel cathode material according to any one of claims 1-4 or the composite coated nickel cathode material prepared by the preparation method according to any one of claims 5-9 in lithium-ion batteries.

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