A zinc-doped lithium nickel cobalt manganese oxide cathode material, a preparation method and application thereof

Abstract

The application provides a preparation method of a zinc-doped lithium nickel cobalt manganese oxide positive electrode material, and the preparation method comprises the following steps: S1, mixing a nickel source, a cobalt source, a manganese source and a zinc source to obtain a mixed salt solution; S2, in an inert atmosphere, mixing the mixed salt solution and a precipitant solution by simultaneously dropping, continuously dropping the precipitant solution to adjust the pH value of the mixed solution to 10-11, performing a co-precipitation reaction, and obtaining a precursor slurry; S3, adjusting the pH value of the precursor slurry in step S2 to 7-8, performing solid-liquid separation, and drying the precipitate to obtain a precursor; and S4, mixing the precursor in step S3 with a lithium source, and sintering to obtain the zinc-doped lithium nickel cobalt manganese oxide positive electrode material. The method provided by the application can reduce the surface residual alkali content of the positive electrode material, and excellent cycle stability is obtained.

Description

Technical Field

[0001] This application relates to the field of battery electrode technology, specifically to a zinc-doped lithium nickel cobalt manganese oxide cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their advantages such as high energy density, long cycle life, and no memory effect. The cathode material, as a core component of lithium-ion batteries, directly determines key performance indicators such as energy density, cycle stability, and rate performance.

[0003] Lithium nickel cobalt manganese oxide (LiNi) x Co y Mn 1-x-y O2 (NCM) cathode materials have become one of the mainstream cathode materials in the current power battery field due to their high specific capacity and good overall performance. Among them, high-nickel NCM materials (Ni content ≥ 80%) have attracted widespread attention because they have a higher specific capacity (up to 200 mAh / g or more), which can significantly improve the energy density of the battery. However, with the increase of nickel content, high-nickel NCM materials have problems such as serious surface side reactions, high residual alkali content, and shortened cycle life.

[0004] To address these issues, researchers have attempted to modify NCM materials by introducing zinc. However, existing zinc doping techniques have significant shortcomings: First, using "post-modification" or "surface coating" methods, zinc is mainly distributed on the particle surface as zinc oxide (ZnO), making it difficult to effectively penetrate the material's crystal lattice and stabilize the crystal structure at the bulk level. Furthermore, the surface ZnO layer is prone to detachment during cycling or undergoing side reactions with the electrolyte. Second, existing "bulk doping" methods typically employ solid-phase mixing, resulting in uneven zinc distribution within the particles, leading to localized enrichment or segregation and poor electrochemical consistency. Neither of these methods effectively reduces the residual alkali content on the surface of high-nickel NCM materials, nor significantly extends the battery's cycle life. Therefore, there is an urgent need to develop a method for preparing NCM cathode materials that can achieve uniform bulk zinc doping, thereby reducing surface residual alkali and improving cycle stability. Summary of the Invention

[0005] This application provides a zinc-doped lithium nickel cobalt manganese oxide cathode material, its preparation method, and its application, in order to solve the problem that uneven zinc doping in existing zinc-doped lithium nickel cobalt manganese oxide preparation methods leads to high residual alkali content on the surface and poor cycle stability.

[0006] In a first aspect, this application provides a method for preparing a zinc-doped lithium nickel cobalt manganese oxide cathode material, comprising the following steps: S1, mixing a nickel source, a cobalt source, a manganese source, and a zinc source to obtain a mixed salt solution; S2, in an inert atmosphere, mixing the mixed salt solution and a precipitant solution by simultaneous dropwise addition, and continuing to add the precipitant solution to adjust the pH value of the mixture to 10-11, and carrying out a co-precipitation reaction to obtain a precursor slurry; S3, adjusting the pH of the precursor slurry in step S2 to 7-8, separating the solid and liquid, and drying the precipitate to obtain a precursor; S4, mixing the precursor in step S3 with a lithium source and sintering to obtain a zinc-doped lithium nickel cobalt manganese oxide cathode material.

[0007] In an optional embodiment, the molar ratio of Ni in the nickel source, Co in the cobalt source, and Mn in the manganese source in step S1 is (0.75-0.85):(0.05-0.15):(0.05-0.15).

[0008] In one optional embodiment, the molar amount of Zn in the zinc source is 0.5%-1%, based on the total molar amount of metal elements in the mixed salt solution.

[0009] In one optional embodiment, the total molar concentration of metal ions in the mixed salt solution in step S1 is 1-2 mol / L.

[0010] In one alternative embodiment, the nickel source includes one or more of nickel nitrate, nickel acetate, and nickel sulfate.

[0011] In one alternative embodiment, the cobalt source includes one or more of cobalt nitrate, cobalt acetate, and cobalt sulfate.

[0012] In one alternative embodiment, the manganese source includes one or more of manganese nitrate, manganese acetate, and manganese sulfate.

[0013] In one alternative embodiment, the zinc source includes one or more of zinc nitrate, zinc acetate, and zinc sulfate.

[0014] In one alternative embodiment, the precipitant solution comprises a precipitant and a solvent, wherein the solvent comprises water; In one optional embodiment, the precipitant includes at least one of NaOH and NH3·H2O.

[0015] In one optional embodiment, the precipitant solution is a mixed aqueous solution of NaOH and NH3·H2O, wherein the mass ratio of NaOH to NH3·H2O is (10-15):1.

[0016] The mixed salt solution and the precipitant solution are mixed by dropping them together at a rate of 5-15 mL / min for both the mixed salt solution and the precipitant solution.

[0017] In one optional embodiment, the mixed salt solution and the precipitant solution are mixed under stirring conditions, with the stirring temperature at 50-70°C and the stirring speed at 300-500 rpm. In one alternative embodiment, the coprecipitation reaction takes 2-4 hours.

[0018] In one optional embodiment, the pH value of the precursor slurry is adjusted by washing in step S3. The washing reagents include one or more of deionized water, dilute ammonia (concentration of 0.1-0.5 mol / L), and anhydrous ethanol.

[0019] In one optional embodiment, the drying temperature of the precipitate in step S3 is 80-100℃, and the drying time is 12-24h.

[0020] In one optional implementation, in step S4, the mass ratio of the precursor to the lithium source is 1:(1.02-1.10).

[0021] In one optional embodiment, the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; In an optional embodiment, step S4 uses a gradient sintering method to sinter the mixture of precursor and lithium source. The gradient sintering step includes first heating the temperature to 450-550℃ at a heating rate of 2-5℃ / min and holding it at that temperature for 3-5 hours, and then heating the temperature to 750-850℃ at a heating rate of 1-3℃ / min and holding it at that temperature for 8-12 hours. In an optional embodiment, step S4 further includes the steps of crushing and sieving the sintered material after sintering; In one optional embodiment, the sieve mesh size is 200-400 mesh.

[0022] Secondly, this application provides a zinc-doped lithium nickel cobalt manganese oxide cathode material, prepared according to the above-described preparation method.

[0023] In one optional embodiment, the zinc-doped lithium nickel cobalt manganese oxide cathode material has the general chemical formula Li[(Ni x Co y Mn z ) a Zn bO2, where 0.75 ≤ x ≤ 0.85, 0.05 ≤ y ≤ 0.15, 0.05 ≤ z ≤ 0.15, and x+y+z=1; a+b=1, 0.99 ≤ a ≤ 0.995, 0.005 ≤ b ≤ 0.01.

[0024] Thirdly, this application provides a lithium-ion battery, including the zinc-doped lithium nickel cobalt manganese oxide cathode material prepared by the above-described preparation method or the zinc-doped lithium nickel cobalt manganese oxide cathode material described above.

[0025] Compared with the prior art, the beneficial effects of this application are as follows: 1. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material provided in this application employs a co-precipitation method, in which a zinc source is directly added to a solution of nickel, cobalt, and manganese salts, causing Zn... 2+ Zn is uniformly mixed with other transition metal ions at the atomic level and subjected to a co-precipitation reaction. 2+ By uniformly embedding zinc into the precursor lattice, compared to solid-phase mixing or surface coating, the preparation method provided in this application fundamentally solves the problems of uneven zinc distribution and local segregation, ensuring uniform zinc doping from the bulk phase to the surface of the material. On one hand, by simultaneously adding the mixed salt solution and the precipitant solution dropwise, the supersaturation in the reaction system is maintained at a stable and low level, which is conducive to the slow and uniform growth of the precursor nuclei, thereby forming a hydroxide precursor with high sphericity, narrow particle size distribution, and tightly packed primary particles. This dense spherical morphology facilitates subsequent uniform mixing and sintering with the lithium source and improves the tap density of the cathode material. On the other hand, in the co-precipitation reaction, pH directly determines the nucleation and growth rate, morphology (sphericity, density), and uniformity of elemental distribution of the precursor. For high-nickel (Ni content ≥ 80%) precursors, too low pH will result in excessively coarse primary particles, a loose precursor, and low tap density of the sintered material; too high pH will result in excessively rapid nucleation, excessively fine primary particles, forming amorphous or flocculent precipitates that are difficult to filter and wash, and ultimately, the cathode material and electrolyte will undergo violent side reactions. In this application, the pH of the mixture formed by the mixed salt solution and the precipitant solution is controlled to be 10-11. At this pH, the precipitation rate of Ni / Co / Mn / Zn is optimally matched, which can form a layered hydroxide precursor with a perfect lattice structure and uniform elemental distribution. This avoids elemental phase separation caused by inconsistent precipitation rates and can obtain a precursor with high sphericity, narrow particle size distribution, and high tap density, which is a key prerequisite for achieving uniform zinc doping and reducing residual alkali. Meanwhile, this application controls the pH value of the slurry to 7-8 through washing, which can effectively remove Na adsorbed on the surface of the precursor. + SO4 2- Impurity ions and free OH- -To prevent these impurities from being introduced into subsequent sintering processes, which could react with the lithium source to form electrochemically inert sodium salts (reducing capacity) or promote the formation of surface residual alkali (LiOH / Li2CO3) (deteriorating cycle life), this application improves the purity of the cathode material and reduces surface residual alkali. This application employs a co-precipitation method to dope zinc, simultaneously adding a mixed salt solution and a precipitant solution, controlling the pH of the co-precipitation reaction to 10-11, and using washing to control the pH of the slurry to 7-8. This ensures uniform distribution of zinc in the precursor and that the precursor has high sphericity and high tap density, providing a high-quality template for subsequent sintering. This eliminates the source of residual alkali impurities at the source, perfectly transforming the structural advantages of the precursor into excellent electrochemical performance of the cathode material. The synergistic effect of the complete process flow from doping, precipitation, purification to crystallization ultimately achieves uniform bulk doping of zinc and reduces the surface residual alkali content of the cathode material, thereby obtaining excellent cycle stability.

[0026] 2. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material provided in this application, based on the total molar amount of metal elements in the mixed salt solution, has a Zn element molar amount of 0.5%-1% in the zinc source. Excessive zinc doping (>1.5%) introduces too much non-electrochemically active ZnO phase or generates too many defects in the crystal lattice, leading to a significant decrease in the initial specific capacity of the material. Insufficient doping (<0.3%) fails to effectively stabilize the crystal structure and suppress phase transitions during cycling. This application controls the zinc content to 0.5%-1%, which effectively improves cycle stability without excessively sacrificing the preferred range of initial capacity.

[0027] 3. The method for preparing zinc-doped nickel-cobalt-manganese lithium cathode material provided in this application employs a gradient sintering process to sinter a mixture of precursor and lithium source. This application uses a two-step gradient sintering process of "low-temperature pre-sintering + high-temperature sintering." The first step involves holding at 450-550℃ to allow the precursor (hydroxide or carbonate) to fully decompose into oxides and release gas, while the lithium source begins to melt and initially embed. The second step involves high-temperature sintering at 750-850℃ to promote the Li-244 lithium-ion lithium oxide deposition. + The lithium diffuses fully into the crystal lattice and completes the crystallization of the layered structure. This gradient heating method can effectively avoid incomplete decomposition of the precursor, loss of lithium source due to volatilization, or lattice defects caused by excessively rapid heating, thereby obtaining a perfect layered structure with high crystallinity and low cation mixing. Detailed Implementation

[0028] The following embodiments are provided to better understand this application. However, the following embodiments do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining the features of this application with other prior art, falls within the scope of protection of this application.

[0029] 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.

[0030] The ammonia water in the embodiments and comparative examples of this application refers to pure ammonia water.

[0031] Example 1 This embodiment provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material, including the following steps: (1) According to the general chemical formula Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 The molar ratio of each metal element in O2 (Ni:Co:Mn:Zn=0.794:0.09925:0.09925:0.0075) was determined. Nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate were weighed and mixed with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.5 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 12.5:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 3 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 10 mL / min, and the drop rate of the precipitant solution was controlled at 10 mL / min. The stirring and heating temperature was 60℃, and the stirring speed was 400 rpm. After the addition was completed, the pH of the reaction system was adjusted to 10.5 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 3 h to obtain the precursor slurry.

[0032] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 7.5. After filtration, dry the precipitate at 90°C for 18 h to obtain the precursor.

[0033] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.06, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 500℃ at a heating rate of 3.5℃ / min and held for 4 h; then, the temperature was raised to 800℃ at a heating rate of 2℃ / min and held for 10 h; after natural cooling to room temperature, the mixture was crushed and passed through a 300-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 O2.

[0034] Example 2 This embodiment provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material, including the following steps: (1) According to the general chemical formula Li[(Ni 0.75 Co 0.15 Mn 0.1 ) 0.995 Zn 0.005 The molar ratio of each metal element in O2 was determined by weighing nickel sulfate, cobalt sulfate, manganese sulfate, and zinc sulfate, and mixing them with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.0 mol / L. (2) Dissolve NaOH and NH3·H2O in deionized water according to the mass ratio of NaOH and NH3·H2O of 10:1 to prepare a precipitant solution with a concentration of 2 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 5 mL / min, and the drop rate of the precipitant solution was controlled at 5 mL / min. The stirring and heating temperature was 50℃, and the stirring speed was 300 rpm. After the addition was completed, the pH of the reaction system was adjusted to 10.0 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 2 h to obtain the precursor slurry.

[0035] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 7.0. After filtration, dry the precipitate at 80°C for 12 h to obtain the precursor.

[0036] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.02, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 450℃ at a heating rate of 2℃ / min and held for 3 h; then, the temperature was raised to 750℃ at a heating rate of 1℃ / min and held for 8 h; after natural cooling to room temperature, the mixture was crushed and passed through a 200-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.75 Co 0.15 Mn 0.1 ) 0.995 Zn 0.005 O2.

[0037] Example 3 This embodiment provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material, including the following steps: (1) According to the general chemical formula Li[(Ni 0.85 Co 0.05 Mn 0.1 ) 0.99 Zn 0.01 The molar ratio of each metal element in O2 was determined by weighing nickel acetate, cobalt acetate, manganese acetate, and zinc acetate, and mixing them with deionized water to prepare a mixed salt solution with a total metal ion concentration of 2.0 mol / L. (2) Dissolve NaOH and NH3·H2O in deionized water according to the mass ratio of NaOH and NH3·H2O of 15:1 to prepare a precipitant solution with a concentration of 4 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 15 mL / min, and the drop rate of the precipitant solution was also controlled at 15 mL / min. The stirring and heating temperature was 70℃, and the stirring speed was 500 rpm. After the addition was completed, the pH of the reaction system was adjusted to 11 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 4 h to obtain the precursor slurry.

[0038] (3) Wash the precursor slurry in step (2) with dilute ammonia water (0.1mol / L) until the pH of the precursor slurry is 8. After filtration, dry the precipitate at 100℃ for 24 h to obtain the precursor.

[0039] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.10 and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 550℃ at a heating rate of 5℃ / min and held for 5 h; then, the temperature was raised to 850℃ at a heating rate of 3℃ / min and held for 12 h; after natural cooling to room temperature, the mixture was crushed and passed through a 400-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.85 Co 0.05 Mn 0.1 ) 0.99 Zn 0.01 O2.

[0040] Example 4 This embodiment provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material, including the following steps: (1) According to the general chemical formula Li[(Ni 0.78 Co 0.12 Mn 0.1 ) 0.994 Zn 0.006 The molar ratio of each metal element in O2 was determined by weighing nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate, and mixing them with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.5 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 11:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 1.2 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 8 mL / min, and the drop rate of the precipitant solution was controlled at 6 mL / min. The stirring and heating temperature was 65℃, and the stirring speed was 350 rpm. After the addition was completed, the pH of the reaction system was adjusted to 10.3 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 2.5 h to obtain the precursor slurry.

[0041] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 7.3. After filtration, dry the precipitate at 85°C for 15 h to obtain the precursor.

[0042] (4) The precursor and lithium carbonate were mixed in step (3) with lithium hydroxide at a mass ratio of 1:1.04. The mixture was placed in a crucible and subjected to gradient sintering in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was increased from room temperature to 480℃ at a heating rate of 2.5℃ / min and held for 3.5 h; then, the temperature was increased to 780℃ at a heating rate of 1.5℃ / min and held for 9 h; after natural cooling to room temperature, the mixture was crushed and passed through a 250-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.78 Co 0.12 Mn 0.1 ) 0.994 Zn 0.006 O2.

[0043] Example 5 This embodiment provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material, including the following steps: (1) According to the general chemical formula Li[(Ni 0.82 Co 0.08 Mn 0.1 ) 0.991 Zn 0.009 The molar ratio of each metal element in O2 was determined by weighing nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate, and mixing them with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.8 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 14:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 3.5 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 12 mL / min, and the drop rate of the precipitant solution was controlled at 1 mL / min. The stirring and heating temperature was 65℃, and the stirring speed was 450 rpm. After the addition was completed, the pH of the reaction system was adjusted to 10.8 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 3.5 h to obtain the precursor slurry.

[0044] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 7.7. After filtration, dry the precipitate at 90°C for 20 h to obtain the precursor.

[0045] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.08, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 520℃ at a heating rate of 4.5℃ / min and held for 4.5 h; then, the temperature was raised to 820℃ at a heating rate of 2.5℃ / min and held for 11 h; after natural cooling to room temperature, the mixture was crushed and passed through a 350-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.82 Co 0.08 Mn 0.1 ) 0.991 Zn 0.009 O2.

[0046] Comparative Example 1 This comparative example provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material, which differs from Example 1 only in that: in step (2), a precipitant solution is added dropwise to the mixed salt solution. The specific steps are as follows: (1) According to the general chemical formula Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 The molar ratio of each metal element in O2 (Ni:Co:Mn:Zn=0.794:0.09925:0.09925:0.0075) was determined. Nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate were weighed and mixed with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.5 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 12.5:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 3 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. The mixed salt solution from step (1) was placed in the mixed salt solution. While stirring and heating, the precipitant solution was added dropwise to the reactor. The dropwise rate of the precipitant solution was controlled at 10 mL / min. The stirring and heating temperature was 60℃, and the stirring speed was 400 rpm. The pH of the reaction system was adjusted to 10.5 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 3 h to obtain the precursor slurry.

[0047] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 7.5. After filtration, dry the precipitate at 90°C for 18 h to obtain the precursor.

[0048] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.06, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 500℃ at a heating rate of 3.5℃ / min and held for 4 h; then, the temperature was raised to 800℃ at a heating rate of 2℃ / min and held for 10 h; after natural cooling to room temperature, the mixture was crushed and passed through a 300-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 O2.

[0049] Comparative Example 2 This comparative example provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material. The only difference between this method and Example 1 is that in step S2, after the addition is complete, the pH of the reaction system is adjusted to 9.0. The remaining steps and parameters are exactly the same as in Example 1. The specific steps are as follows: (1) According to the general chemical formula Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 The molar ratio of each metal element in O2 (Ni:Co:Mn:Zn=0.794:0.09925:0.09925:0.0075) was determined. Nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate were weighed and mixed with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.5 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 12.5:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 3 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 10 mL / min, and the drop rate of the precipitant solution was controlled at 10 mL / min. The stirring and heating temperature was 60℃, and the stirring speed was 400 rpm. After the addition was completed, the pH of the reaction system was adjusted to 9 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 3 h to obtain the precursor slurry.

[0050] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 7.5. After filtration, dry the precipitate at 90°C for 18 h to obtain the precursor.

[0051] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.06, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 500℃ at a heating rate of 3.5℃ / min and held for 4 h; then, the temperature was raised to 800℃ at a heating rate of 2℃ / min and held for 10 h; after natural cooling to room temperature, the mixture was crushed and passed through a 300-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 O2.

[0052] Comparative Example 3 This comparative example provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material. The only difference between this method and Example 1 is that in step S2, after the addition is complete, the pH of the reaction system is adjusted to 12. The remaining steps and parameters are exactly the same as in Example 1. The specific steps are as follows: (1) According to the general chemical formula Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 The molar ratio of each metal element in O2 (Ni:Co:Mn:Zn=0.794:0.09925:0.09925:0.0075) was determined. Nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate were weighed and mixed with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.5 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 12.5:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 3 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 10 mL / min, and the drop rate of the precipitant solution was controlled at 10 mL / min. The stirring and heating temperature was 60℃, and the stirring speed was 400 rpm. After the addition was completed, the pH of the reaction system was adjusted to 12 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 3 h to obtain the precursor slurry.

[0053] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 7.5. After filtration, dry the precipitate at 90°C for 18 h to obtain the precursor.

[0054] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.06, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 500℃ at a heating rate of 3.5℃ / min and held for 4 h; then, the temperature was raised to 800℃ at a heating rate of 2℃ / min and held for 10 h; after natural cooling to room temperature, the mixture was crushed and passed through a 300-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 O2.

[0055] Comparative Example 4 This comparative example provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material. The only difference from Example 1 is that in step S3, the precursor slurry is washed until the pH of the filtrate reaches 9.0. All other steps and parameters are identical to those in Example 1. The specific steps are as follows: (1) According to the general chemical formula Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 The molar ratio of each metal element in O2 (Ni:Co:Mn:Zn=0.794:0.09925:0.09925:0.0075) was determined. Nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate were weighed and mixed with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.5 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 12.5:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 3 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 10 mL / min, and the drop rate of the precipitant solution was controlled at 10 mL / min. The stirring and heating temperature was 60℃, and the stirring speed was 400 rpm. After the addition was completed, the pH of the reaction system was adjusted to 10.5 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 3 h to obtain the precursor slurry.

[0056] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 9. After filtration, dry the precipitate at 90°C for 18 h to obtain the precursor.

[0057] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.06, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 500℃ at a heating rate of 3.5℃ / min and held for 4 h; then, the temperature was raised to 800℃ at a heating rate of 2℃ / min and held for 10 h; after natural cooling to room temperature, the mixture was crushed and passed through a 300-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 O2.

[0058] Comparative Example 5 This comparative example provides a method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material. The only difference from Example 1 is that in step S3, the precursor slurry is washed until the pH of the filtrate is 6. The remaining steps and parameters are exactly the same as in Example 1. The specific steps are as follows: (1) According to the general chemical formula Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 The molar ratio of each metal element in O2 (Ni:Co:Mn:Zn=0.794:0.09925:0.09925:0.0075) was determined. Nickel nitrate, cobalt nitrate, manganese nitrate, and zinc nitrate were weighed and mixed with deionized water to prepare a mixed salt solution with a total metal ion concentration of 1.5 mol / L. (2) According to the mass ratio of NaOH to NH3·H2O of 12.5:1, NaOH and NH3·H2O are dissolved in deionized water to prepare a precipitant solution with a concentration of 3 mol / L of NaOH and NH3·H2O mixture; Nitrogen gas was introduced for protection. While stirring and heating, the mixed salt solution and precipitant solution from step (1) were simultaneously added dropwise to the reactor. The drop rate of the mixed salt solution was controlled at 10 mL / min, and the drop rate of the precipitant solution was controlled at 10 mL / min. The stirring and heating temperature was 60℃, and the stirring speed was 400 rpm. After the addition was completed, the pH of the reaction system was adjusted to 10.5 by continuing to add the precipitant solution. The co-precipitation reaction was carried out for 3 h to obtain the precursor slurry.

[0059] (3) Wash the precursor slurry in step (2) with deionized water until the pH of the precursor slurry is 6. After filtration, dry the precipitate at 90°C for 18 h to obtain the precursor.

[0060] (4) The precursor and lithium hydroxide were mixed in step (3) at a mass ratio of 1:1.06, and placed in a crucible. Gradient sintering was carried out in a muffle furnace under an air atmosphere. The specific steps of sintering were as follows: first, the temperature was raised from room temperature to 500℃ at a heating rate of 3.5℃ / min and held for 4 h; then, the temperature was raised to 800℃ at a heating rate of 2℃ / min and held for 10 h; after natural cooling to room temperature, the mixture was crushed and passed through a 300-mesh sieve to obtain zinc-doped nickel-cobalt-manganese lithium oxide cathode material Li[(Ni 0.8 Co 0.1 Mn 0.1 ) 0.9925 Zn 0.0075 O2.

[0061] Experimental Example 1 - Determination of residual alkali content (LiOH and Li2CO3) on the surface of positive electrode material: Test method: Take 10g of the positive electrode material sample to be tested, add it to 100mL of deionized water, sonicate for 30min, and then stir with a magnetic stirrer for 2h. After standing, filter with a Buchner funnel, take 50mL of filtrate, and perform potentiometric titration with 0.1mol / L hydrochloric acid standard solution. Record the volume of hydrochloric acid consumed at pH=8.5 and pH=4.5, and calculate the contents of LiOH, Li2CO3 and the total residual alkali (in ppm, i.e., parts per ten thousand). The results are shown in Table 1.

[0062] Table 1. Test results of surface residual alkali content

[0063] As shown in Table 1, the total residual alkali content of the cathode materials prepared in each embodiment of this application is less than 2500 ppm, while the total residual alkali content of Comparative Example 1 (co-precipitation pH=9.0) and Comparative Example 2 (washed to pH=9) both exceed 4300 ppm, indicating that the pH range and washing conditions specified in this application play a key role in reducing residual alkali.

[0064] Experimental Example 2 - Button Cell Cycle Performance Test (Capacity Retention after 500 Cycles at 1C): Test method: The prepared positive electrode material, conductive carbon black (Super P), and binder (PVDF) were mixed at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added to form a slurry, which was then coated onto aluminum foil. After drying, rolling, and cutting, the positive electrode sheet was obtained. Using lithium metal sheet as the negative electrode, LiPF6 (1 mol / L), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (EC, DMC, and EMC in a volume ratio of 1:1:1) were used as the electrolyte, and Celgard 2400 was used as the separator. CR2032 coin cells were assembled in an argon glove box. At 25±1℃, the system was first activated for two cycles at 0.1C (voltage range 2.8-4.3V), and then subjected to constant current charge-discharge cycles of 1C for 500 cycles. The ratio of the discharge capacity at the 500th cycle to the discharge capacity at the 3rd cycle (as the initial capacity) was calculated, which is the capacity retention rate (%) after 500 cycles. The results are shown in Table 2.

[0065] Table 2 Electrochemical performance test results

[0066] As shown in Table 2, the cathode materials prepared in each embodiment of this application exhibit high initial discharge specific capacity (all ≥195 mAh / g), and the capacity retention rate after 500 cycles at 1C is all above 89%, especially Example 1, which reaches 91.2%. In contrast, the capacity retention rates of Comparative Examples 1-5 are below 84.1%, and their initial discharge capacities are significantly lower than those of the Examples. This indicates that the preparation method of this application can significantly improve the cycle stability of the cathode material while maintaining good initial capacity.

[0067] 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 application.

Claims

1. A method for preparing a zinc-doped lithium nickel cobalt manganese oxide cathode material, characterized in that, Includes the following steps: S1. Mix the nickel source, cobalt source, manganese source and zinc source to obtain a mixed salt solution; S2. In an inert atmosphere, the mixed salt solution and the precipitant solution are mixed by simultaneous dropwise addition. The pH value of the mixture is adjusted to 10-11 by continuing to add the precipitant solution dropwise, and a co-precipitation reaction is carried out to obtain the precursor slurry. S3. Adjust the pH of the precursor slurry in step S2 to 7-8, and after solid-liquid separation, dry the precipitate to obtain the precursor. S4. The precursor from step S3 is mixed with the lithium source and sintered to obtain zinc-doped lithium nickel cobalt manganese oxide cathode material.

2. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, In step S1, the molar ratio of Ni in the nickel source, Co in the cobalt source, and Mn in the manganese source is (0.75-0.85):(0.05-0.15):(0.05-0.15). And / or, based on the total molar amount of metal elements in the mixed salt solution, the molar amount of Zn in the zinc source is 0.5%-1%; And / or, the total molar concentration of metal ions in the mixed salt solution in step S1 is 1-2 mol / L.

3. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material according to claim 1 or 2, characterized in that, The nickel source includes one or more of nickel nitrate, nickel acetate, and nickel sulfate; And / or, the cobalt source includes one or more of cobalt nitrate, cobalt acetate, and cobalt sulfate; And / or, the manganese source includes one or more of manganese nitrate, manganese acetate, and manganese sulfate; And / or, the zinc source includes one or more of zinc nitrate, zinc acetate, and zinc sulfate.

4. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, The precipitant solution comprises a precipitant and a solvent, wherein the solvent comprises water; And / or, the mixed salt solution and the precipitant solution are mixed by dropping, with the dropping rate of the mixed salt solution being 5-15 mL / min and the dropping rate of the precipitant solution being 5-15 mL / min.

5. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material according to claim 4, characterized in that, Under stirring conditions, the mixed salt solution and the precipitant solution are mixed at a temperature of 50-70℃ and a stirring speed of 300-500 rpm. And / or, the reaction time of the coprecipitation reaction is 2-4 hours; And / or, the precipitant includes at least one of NaOH and NH3·H2O.

6. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material according to claim 5, characterized in that, In step S3, the drying temperature of the precipitate is 80-100℃, and the drying time is 12-24h. And / or, the precipitant solution is a mixed aqueous solution of NaOH and NH3·H2O, wherein the mass ratio of NaOH to NH3·H2O is (10-15).

7. The method for preparing zinc-doped lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, In step S4, the mass ratio of the precursor to the lithium source is 1:(1.02-1.10). And / or, the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; And / or, in step S4, the mixture of precursor and lithium source is sintered using a gradient sintering method. The gradient sintering steps include first heating the temperature to 450-550℃ at a heating rate of 2-5℃ / min and holding it at that temperature for 3-5 hours, and then heating the temperature to 750-850℃ at a heating rate of 1-3℃ / min and holding it at that temperature for 8-12 hours. And / or, step S4 may further include the steps of crushing and sieving the sintered material after sintering.

8. A zinc-doped lithium nickel cobalt manganese oxide cathode material, characterized in that, Prepared by the method according to any one of claims 1-7.

9. The zinc-doped lithium nickel cobalt manganese oxide cathode material according to claim 8, characterized in that, The general chemical formula of the zinc-doped lithium nickel cobalt manganese oxide cathode material is Li[(Ni x Co y Mn z ) a Zn b O2, where 0.75 ≤ x ≤ 0.85, 0.05 ≤ y ≤ 0.15, 0.05 ≤ z ≤ 0.15, and x+y+z=1; a+b=1, 0.99 ≤ a ≤ 0.995, 0.005 ≤ b ≤0.

01.

10. A lithium-ion battery, characterized in that, This includes zinc-doped lithium nickel cobalt manganese oxide cathode materials prepared by the preparation method according to any one of claims 1-7, or zinc-doped lithium nickel cobalt manganese oxide cathode materials according to claim 8 or 9.

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