Ternary high-nickel lithium ion battery cathode material and preparation method thereof

Abstract

The present application relates to ternary high-nickel lithium-ion battery cathode materials and a preparation method thereof. The general expression of the cathode material is Li(Ni 1‑a‑b‑c Co a Mn b D c )O2, 0.01

Description

Technical Field

[0001] This invention generally belongs to the field of lithium-ion battery cathode material preparation technology, and specifically relates to ternary high-nickel lithium-ion battery cathode materials with dual gradient distribution of grain size and element concentration, and their preparation methods. Background Technology

[0002] Lithium-ion batteries, as a new type of rechargeable battery, have significant advantages over lead-acid batteries in terms of operating voltage, energy density, and cycle life, and are currently widely used in new energy transportation vehicles such as electric vehicles (EVs) and hybrid electric vehicles (EVs). In lithium-ion batteries, the cathode material is a key component determining its performance. In the current commercially available cathode material market, high-nickel ternary materials are considered the most promising due to their high specific capacity. However, as the nickel content increases, ternary materials undergo pulverization during charging and discharging. Side reactions occur in the areas in contact with the electrolyte, leading to gas production. Furthermore, cracks appear on the surface of the cathode material, exposing more contact areas and forming a CEI passivation film, causing the active material to fail and resulting in a significant drop in capacity. The pulverization of high-nickel ternary lithium batteries is caused by their own crystal structure. During charging, as lithium ions are released, an irreversible phase transition from H2 to H3 occurs inside the material, turning it into a rock salt phase. At the same time, the material shrinks excessively, and cracks appear on the surface. This leads to further contact with the electrolyte, resulting in new side reactions. This cycle repeats, reducing the material's structural and thermal stability, which in turn leads to a rapid decline in material performance during long cycles. More seriously, it can also cause a series of safety problems.

[0003] To address the aforementioned shortcomings, improving the performance of high-nickel ternary materials through a series of modification methods has become a major research hotspot in the lithium battery field. To further enhance the performance of high-nickel ternary cathode materials, researchers have employed methods such as element doping, surface coating, morphology and size control, and element concentration distribution. Among these methods, the modification technique of preparing a concentration gradient cathode material does not introduce other elements. By reducing the nickel content on the material surface without altering the overall metallic composition, it effectively balances the advantages of high capacity and high surface stability. Some researchers, when preparing concentration gradient materials, typically prepare two separate salt solutions, one high-nickel and one low-nickel, and control the feed rates of these two solutions to achieve the element concentration gradient distribution. However, since the co-precipitation conditions required for precursors with different elemental compositions differ, controlling the stability of the conditions during the preparation process using this method is extremely difficult, resulting in poor repeatability and the prepared precursors lacking optimal crystallinity, which may prevent the material from fully realizing its performance. Summary of the Invention

[0004] In view of the above problems, one or more embodiments of the present application provide a ternary high-nickel lithium-ion battery cathode material with a double-gradient distribution of grain size and element concentration, and a preparation method thereof.

[0005] One or more embodiments of the present application provide a ternary high-nickel lithium-ion battery cathode material, wherein the general expression of the cathode material is Li(Ni Co a Mn b D c )O2, where 0.01 < a < 0.12, 0.01 < b < 0.1, 0.001 < c < 0.05, the D element is Sr or Mg or a mixture of Sr and Mg, the grain size of the cathode material changes in a gradient from large to small from the surface to the inside, and the concentration of the D element and Mn ions gradually decreases from the surface to the inside.

[0006] In one or more embodiments, a is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11 or 0.12.

[0007] In one or more embodiments, b is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0008] In one or more embodiments, c is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04 or 0.05.

[0009] In one or more embodiments, the D element makes the grain size of the cathode material change in a gradient from large to small from the surface to the inside.

[0010] In one or more embodiments, the expression of the precursor of the cathode material is Ni x Co y (OH)2, where 0.85 < x < 1, x + y = 1.

[0011] In one or more embodiments, x is 0.85, 0,.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or 1.

[0012] In one or more embodiments, the precursor has crystallinity.

[0013] In one or more embodiments, the surface sulfur content of the precursor is less than 2000 ppm.

[0014] In one or more embodiments, the precursor surface S content is less than 1500 ppm.

[0015] In one or more embodiments, the surface sulfur content of the precursor is less than 1000 ppm.

[0016] In one or more embodiments, the precursor surface S content is less than 500 ppm.

[0017] In one or more embodiments, the surface sulfur content of the precursor is less than 200 ppm.

[0018] In one or more embodiments, the surface sulfur content of the precursor is less than 100 ppm.

[0019] In one or more embodiments, the total content of magnetic foreign matter is less than 50 ppb.

[0020] In one or more embodiments, the total content of magnetic foreign matter is less than 40 ppb.

[0021] In one or more embodiments, the total content of magnetic foreign matter is less than 30 ppb.

[0022] In one or more embodiments, the total content of magnetic foreign matter is less than 20 ppb.

[0023] In one or more embodiments, the total content of magnetic foreign matter is less than 10 ppb.

[0024] In one or more embodiments, the cathode material has a core-shell structure with a concentration gradient, characterized by a manganese-rich surface and a nickel-rich interior, and the grain size of the cathode material is distributed in a gradient from large to small from the surface to the interior.

[0025] One or more embodiments of this application provide a method for preparing a ternary high-nickel lithium-ion battery cathode material, including the following steps:

[0026] (1) Solution preparation: Prepare a nickel-cobalt mixed metal salt solution using nickel salt and cobalt salt, prepare an alkaline solution as a precipitant solution, and prepare a complexing agent solution;

[0027] (2) Coprecipitation reaction: Add the metal salt solution, precipitant solution, and complexing agent solution from step (1) to the reaction vessel, stir to carry out the coprecipitation reaction, and wait for D... 50 When the particle size reaches 10-14 μm, the precursor slurry is subjected to centrifugation, washing, drying, iron removal and sieving in sequence to obtain nickel-cobalt binary precursor;

[0028] (3) Sintering: The precursor obtained in step (2) is mixed evenly with Mn salt, Sr or Mg or a mixture of Sr and Mg in a molar ratio of (1-10):(0.1-5), and then mixed evenly with lithium hydroxide in a ball mill in a molar ratio of 1:(1-1.5). The mixture is then calcined at 800-1000℃ for 4-20 hours in an oxygen atmosphere. After the reaction is completed, the mixture is naturally cooled to room temperature. The resulting material is the lithium nickel cobalt manganese oxide ternary cathode material.

[0029] In one or more embodiments, an automatic control system is used to maintain a constant pH in the precipitant solution system.

[0030] In one or more embodiments, the reactor is a 20L reactor.

[0031] In one or more embodiments, the precursor is expressed as Ni. x Co y (OH)2, of which 0.85 <x<1,x+y=1。

[0032] In one or more embodiments, the precursor is crystalline.

[0033] In one or more embodiments, the Mn salt is MnCO3.

[0034] In one or more embodiments, the Sr salt is one or more of strontium carbonate, strontium hydroxide, and strontium oxide.

[0035] In one or more embodiments, the Mg salt is one or more of magnesium carbonate, magnesium hydroxide, and magnesium oxide.

[0036] In one or more embodiments, the mixture is homogenized with lithium hydroxide in a ball mill at a molar ratio of 1:(1-1.1).

[0037] In one or more embodiments, the mixture is homogenized with lithium hydroxide at a molar ratio of 1:1.05 in a ball mill.

[0038] In one or more embodiments, in step (1), the nickel salt is at least one of NiSO4·6H2O, Ni(NO3)2·6H2O, Ni(CH3COO)2·4H2O and NiCl2·6H2O.

[0039] In one or more embodiments, in step (1), the nickel salt is NiSO4·6H2O.

[0040] In one or more embodiments, the cobalt salt is at least one of CoSO4·7H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, and CoCl2·6H2O.

[0041] In one or more embodiments, the cobalt salt is CoSO4·7H2O.

[0042] In one or more embodiments, the concentration of the nickel-cobalt mixed metal salt solution is 1-4 mol / L.

[0043] In one or more embodiments, the concentration of the nickel-cobalt mixed metal salt solution is 1, 2, 3 or 4 mol / L.

[0044] In one or more embodiments, the precipitant solution is at least one of NaOH, KOH, and LiOH.

[0045] In one or more embodiments, the precipitant solution is a NaOH solution.

[0046] In one or more embodiments, the complexing agent solution is at least one of ammonia, ammonium sulfate, and amino acid-based organic complexing agents.

[0047] In one or more embodiments, the complexing agent solution is ammonia.

[0048] In one or more embodiments, in step (2), the feed rate of the metal salt is 0.80-1.50 L / h (e.g., 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, or 1.5 L / h), the reaction temperature is 50-80°C (e.g., 50, 60, 70, or 80°C), the stirring speed is 300-800 rpm (e.g., 300, 400, 500, 600, 700, or 800 rpm), the pH of the reaction system is maintained at 10.00-12.00 (e.g., 10, 11, or 12), the ammonia concentration is 0.08-1.00 mol / L (e.g., 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1 mol / L), D 50 It is 4-15μm (e.g., 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15μm).

[0049] In one or more embodiments, in step (2), the washing time is at least 2-5 hours (e.g., 2, 3, 4 or 5 hours), and the drying temperature is 90-110°C (e.g., 90, 100 or 110°C).

[0050] One or more embodiments of this application provide a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is prepared from the positive electrode material of this application.

[0051] In one or more embodiments, the cathode material has a dual gradient distribution of grain size and elemental concentration.

[0052] In one or more embodiments, the positive electrode material is formed by uniformly coating the positive electrode material, conductive additives, and binders.

[0053] In one or more embodiments, the conductive additive is superconducting carbon and carbon nanotubes.

[0054] In one or more embodiments, the adhesive is polyvinylidene fluoride.

[0055] In one or more embodiments, the negative electrode is formed by coating graphite material, conductive additives and binders, or is a high-purity lithium sheet.

[0056] In one or more embodiments, the membrane is a polyolefin membrane.

[0057] In one or more embodiments, the electrolyte is a mixed solvent of LiPF6 dissolved in carbonates.

[0058] In one or more embodiments, the concentration of the electrolyte is 0.5-2 mol / L.

[0059] In one or more embodiments, the concentration of the electrolyte is 0.5, 0.6, 0.7, 0.8, 0.9, 1 or 2 mol / L.

[0060] One or more embodiments of this application provide the use of the cathode material of this application in the preparation of lithium-ion batteries.

[0061] In one or more embodiments, this application provides a ternary high-nickel lithium-ion battery cathode material with a dual gradient distribution of grain size and elemental concentration, wherein the surface is a large-grained material rich in manganese and low in nickel, and the interior is a high-nickel small-size polycrystalline material.

[0062] In one or more embodiments, the precursor is co-precipitated from two elements, nickel and cobalt, which have similar solubility products, and the cathode material formed by sintering the precursor with them has better crystallinity.

[0063] In one or more embodiments, a large-sized manganese-rich, low-nickel shell on the outer surface protects the internal high-nickel material, preventing it from directly contacting the electrolyte. This can suppress the continuous side reactions between the high-nickel material and the electrolyte after the irreversible H2 to H3 phase transition and crack formation following excessive delithiation, thereby avoiding rapid cyclic degradation.

[0064] In one or more embodiments, nickel salt and cobalt salt are used as raw materials for co-precipitation reaction, and nickel-cobalt hydroxide is prepared as the core. During the precursor sintering process, it is fully mixed with manganese salt, Sr salt and / or Mg salt, and calcined to produce a ternary high-nickel cathode material with a dual gradient distribution of manganese concentration gradually decreasing from the surface to the core and grain size gradually decreasing.

[0065] In one or more embodiments, the preparation method of this application is as follows:

[0066] (1) Solution preparation: Prepare a nickel-cobalt mixed metal salt solution of a certain concentration, an alkaline solution of a certain concentration as a precipitant, and a complexing agent solution of a certain concentration;

[0067] (2) Coprecipitation reaction: The mixed metal salt solution, precipitant solution and complexing agent solution obtained in step (1) are added to a 20L reactor at a specific rate. The pH of the system is kept constant by an automatic control system. The coprecipitation reaction is carried out by stirring at a certain temperature. When D50 grows to the target particle size, the precursor slurry is centrifuged, washed, dried, iron removed and sieved in sequence to obtain nickel-cobalt binary precursor.

[0068] (3) Sintering: The precursor obtained in step (2) is mixed evenly with a certain proportion of Mn salt and D salt, and then mixed evenly with lithium hydroxide in a ball mill at a molar ratio of 1:(1.00-1.50). The mixture is calcined at 800-1000℃ for 4-20 hours in an oxygen atmosphere. After the reaction is completed, it is naturally cooled to room temperature. The resulting material is lithium nickel cobalt manganese oxide ternary cathode material, which has a core-shell structure with a concentration gradient of manganese on the surface and nickel in the interior, and the grain size is distributed in a gradient from large to small from the outside to the inside.

[0069] In one or more embodiments, in the preparation method of the above-mentioned ternary high-nickel lithium-ion battery cathode material with dual gradient distribution of grain size and element concentration, in step (1), the nickel salt is one of NiSO4·6H2O, Ni(NO3)2·6H2O, Ni(CH3COO)2·4H2O and NiCl2·6H2O, preferably NiSO4·6H2O; the cobalt salt is any one of CoSO4·7H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O and CoCl2·6H2O, preferably CoSO4·7H2O; the concentration of the salt solution is 1-4 mol / L, preferably 2 mol / L.

[0070] In one or more embodiments, the precipitant solution is one of NaOH, KOH, and LiOH, preferably a NaOH solution.

[0071] In one or more embodiments, the complexing agent solution is one of ammonia, ammonium sulfate, or amino acid-based organic complexing agents, preferably an ammonia solution.

[0072] In one or more embodiments, in the preparation method of the above-mentioned ternary high-nickel lithium-ion battery cathode material with dual gradient distribution of grain size and elemental concentration, in step (2), the feed rate of the metal salt is 0.80-1.50 L / h, the reaction temperature is 50-80℃, the stirring speed is 300-800 rpm, the pH of the reaction system is maintained at 10.00-12.00, the ammonia concentration is 0.08-1.00 mol / L, and D 50 It is 4-15μm.

[0073] In one or more embodiments, in the above-mentioned method for preparing ternary high-nickel lithium-ion battery cathode material with dual gradient distribution of grain size and element concentration, in step (2), the washing time is greater than 2 hours, the drying temperature is 90-110℃, the surface S content of the obtained precursor is less than 2000ppm, and the total content of magnetic foreign matter is less than 50ppb.

[0074] In one or more embodiments, in the above-mentioned method for preparing a ternary high-nickel lithium-ion battery cathode material with a dual gradient distribution of grain size and element concentration, in step (3), the Mn salt is preferably MnCO3.

[0075] In one or more embodiments, in the above-mentioned method for preparing a ternary high-nickel lithium-ion battery cathode material with a dual gradient distribution of grain size and element concentration, in step (3), D salt is one or more of strontium carbonate, strontium hydroxide, strontium oxide, magnesium carbonate, magnesium hydroxide, and magnesium oxide.

[0076] In one or more embodiments, the above-mentioned ternary high-nickel lithium-ion battery cathode material with dual gradient distribution of grain size and element concentration has a manganese ion concentration that gradually increases from the inside to the outside and a grain size that gradually decreases from the outside to the inside.

[0077] One or more embodiments of the present invention have at least one of the following beneficial effects:

[0078] (1) Compared with the traditional nickel-cobalt-manganese co-precipitation method for preparing precursors, the process of this application is simpler, and the prepared precursor has better crystallinity. This is because nickel and cobalt have similar properties, but their concentration products with manganese ions differ significantly, and Mn... 2+ Nickel-cobalt-manganese coprecipitation is easily oxidized during the reaction, therefore it usually requires an inert gas atmosphere, which increases the difficulty of the coprecipitation reaction. This invention can synthesize a precursor with better crystallinity without the need for a gas atmosphere.

[0079] (2) Through special elements and structural design, large grains with low nickel and high manganese on the surface are formed, which encapsulate the high nickel polycrystalline material inside, which is beneficial to improving the cycle stability of the material.

[0080] (3) Compared with the method of preparing concentration gradient precursors and cathode materials by controlling the feeding ratio of different elements, this method has a simple process. Removing manganese during the co-precipitation process can reduce the difficulty of the co-precipitation reaction and avoid the problem of oxidation during the reaction. The resulting precursor has better crystallinity. The dual gradient design of large grains with low nickel and high manganese content on the surface and high nickel polycrystalline content on the inside is beneficial to enhancing the stability of high nickel cathode materials and improving the cycle performance of the materials.

[0081] (4) Ternary high-nickel cathode materials with dual gradient distribution of grain size and element concentration can maintain high capacity and have excellent cycle stability. Detailed Implementation

[0082] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0083] Example 1

[0084] The ternary high-nickel lithium-ion battery cathode material with a dual gradient distribution of grain size and elemental concentration prepared in this example includes the following steps:

[0085] (1) Solution preparation: Prepare 4 mol / L sodium hydroxide solution as precipitant, 1 mol / L ammonia solution as complexing agent, and the same volume of 2 mol / L nickel-rich metal salt solution (Ni:Co = 87:13).

[0086] (2) Preparation of precursor by co-precipitation reaction: An alkaline base solution with pH 11.00 and ammonia concentration of 0.1 mol / L was prepared in a 20L reactor. The reaction system temperature was maintained at 60℃ by water bath heating, and the stirring speed was 500 rpm. The metal salt solution was uniformly pumped into the reactor at a rate of 800 ml / h using a peristaltic pump. The feed rate of sodium hydroxide precipitant was adjusted by negative feedback from the pH electrode, and the ammonia complexing agent was pumped into the reactor at a rate of 27 ml / h. The pH and ammonia concentration were kept stable during the reaction. When D 50 Feeding was stopped when the precursor slurry grew to 10 μm. The slurry was then subjected to centrifugation, washing, drying, iron removal, and sieving to obtain the nickel-cobalt binary precursor Ni. 0.87 Co 0.13 (OH)2.

[0087] (3) Sintering: Weigh 88g Ni 0.87 Co0.13 (OH)2 was uniformly mixed with 6g MnCO3 and 1g SrCO3, and then mixed with LiOH·H2O at a molar ratio of 1:1.04. The mixture was then pre-calcined at 500℃ for 2h in a tube furnace under a pure oxygen atmosphere, and then held at 900℃ for 8h. After the reaction was completed, the sintered product was sieved to obtain a lithium-ion battery cathode material with a dual gradient distribution of grain size and element concentration.

[0088] Charge and discharge tests were conducted using CR2032 coin cells. Under constant temperature conditions of 25℃, the voltage range was 3.0-4.3V. The discharge specific capacity and first-cycle coulombic efficiency were tested at 0.33C, and the cycle retention rate was tested at 1C for 50 cycles.

[0089] Example 2

[0090] The ternary high-nickel lithium-ion battery cathode material with a dual gradient distribution of grain size and elemental concentration prepared in this example includes the following steps:

[0091] (1) Solution preparation: Prepare 4 mol / L sodium hydroxide solution as precipitant, 1 mol / L ammonia solution as complexing agent, and the same volume of 2 mol / L nickel-rich metal salt solution (Ni:Co = 89:11).

[0092] (2) Preparation of precursor by co-precipitation reaction: An alkaline base solution with pH 11.00 and ammonia concentration of 0.1 mol / L was prepared in a 20L reactor. The reaction system temperature was maintained at 60℃ by water bath heating, and the stirring speed was 500 rpm. The metal salt solution was uniformly pumped into the reactor at a rate of 800 ml / h using a peristaltic pump. The feed rate of sodium hydroxide precipitant was adjusted by negative feedback from the pH electrode, and the ammonia complexing agent was pumped into the reactor at a rate of 27 ml / h. The pH and ammonia concentration were kept stable during the reaction. When D 50 Feeding was stopped when the precursor slurry grew to 10 μm. The slurry was then subjected to centrifugation, washing, drying, iron removal, and sieving to obtain the nickel-cobalt binary precursor Ni. 0.89 Co 0.11 (OH)2.

[0093] (3) Sintering: Weigh 88g Ni 0.89 Co 0.11 (OH)2 was uniformly mixed with 6g MnCO3 and 0.8g MgCO3, and then mixed with LiOH·H2O at a molar ratio of 1:1.04. The mixture was then pre-calcined at 500℃ for 2h in a tube furnace under a pure oxygen atmosphere, and then held at 900℃ for 8h. After the reaction was completed, the sintered product was sieved to obtain a lithium-ion battery cathode material with a core-shell structure of surface concentration gradient layer.

[0094] Charge and discharge tests were conducted using CR2032 coin cells. Under constant temperature conditions of 25℃, the voltage range was 3.0-4.3V. The discharge specific capacity and first-cycle coulombic efficiency were tested at 0.33C, and the cycle retention rate was tested at 1C for 50 cycles.

[0095] Comparative Example 1

[0096] In this comparative example, a conventional high-nickel ternary cathode material was prepared, and the preparation method included the following steps:

[0097] (1) Solution preparation: Prepare 4 mol / L sodium hydroxide solution as precipitant, 1 mol / L ammonia solution as complexing agent, and the same volume of 2 mol / L nickel-rich metal salt solution (Ni:Co:Mn=83:12:05).

[0098] (2) Preparation of precursor by co-precipitation reaction: An alkaline base solution with pH 11.00 and ammonia concentration of 0.1 mol / L was prepared in a 20L reactor. The reaction system temperature was maintained at 60℃ by water bath heating, and the stirring speed was 500 rpm. The metal salt solution was uniformly pumped into the reactor at a rate of 800 ml / h using a peristaltic pump. The feed rate of sodium hydroxide precipitant was adjusted by negative feedback from the pH electrode, and the ammonia complexing agent was pumped into the reactor at a rate of 27 ml / h. The pH and ammonia concentration were kept stable during the reaction. When D 50 Feeding was stopped when the precursor slurry grew to 10 μm. The slurry was then subjected to centrifugation, washing, drying, iron removal, and sieving to obtain the nickel-cobalt ternary precursor Ni. 0.83 Co 0.12 Mn 0.05 (OH)2.

[0099] (3) Sintering: Ni 0.83 Co 0.12 Mn 0.05 (OH)2 and LiOH·H2O were mixed evenly at a molar ratio of 1:1.04 and pre-calcined at 500℃ for 2 hours in a tube furnace under a pure oxygen atmosphere, and then held at 900℃ for 8 hours. After the reaction was completed, the sintered product was sieved to obtain a lithium-ion battery cathode material with a surface concentration gradient layer core-shell structure.

[0100] Charge and discharge tests were conducted using CR2032 coin cells. Under constant temperature conditions of 25℃, the voltage range was 3.0-4.3V. The discharge specific capacity and first-cycle coulombic efficiency were tested at 0.33C, and the cycle retention rate was tested at 1C for 50 cycles.

[0101] Table 1 Electrochemical performance data

[0102]

[0103] As can be seen from the data in the table above, the ternary high-nickel lithium-ion battery cathode materials obtained in Examples 1 and 2 achieved a higher capacity retention rate than the battery cathode material in Comparative Example 1.

Claims

1. A ternary high-nickel lithium-ion battery cathode material, wherein the general expression of the cathode material is Li(Ni 1-a-b- c Co a Mn b D c )O2, 0.01 < a < 0.12, 0.01 < b < 0.1, 0.001 < c < 0.05, the D element is Sr or Mg or a mixture of Sr and Mg, the grain size of the cathode material changes in a gradient from large to small from the surface to the inside, and the concentrations of the D element and Mn ions gradually decrease from the surface to the inside; in, The precursor of the cathode material is expressed as Ni. x Co y (OH)2, 0.85 <x<1,x+y=1。 2. The ternary high-nickel lithium-ion battery cathode material as described in claim 1, wherein the D element causes the grain size of the cathode material to change in a gradient from large to small from the surface to the interior.

3. The ternary high-nickel lithium-ion battery cathode material as described in claim 1, wherein the precursor is crystalline; the S content on the surface of the precursor is less than 2000 ppm, and the total content of magnetic foreign matter is less than 50 ppb.

4. The ternary high-nickel lithium-ion battery cathode material as described in claim 1, wherein the cathode material has a core-shell structure with a concentration gradient of manganese-rich surface and nickel-rich interior, and the grain size of the cathode material is distributed in a gradient from large to small from the surface to the interior.

5. A method for preparing ternary high-nickel lithium-ion battery cathode material, comprising the following steps: (1) Solution preparation: Prepare a nickel-cobalt mixed metal salt solution using nickel salt and cobalt salt, prepare an alkaline solution as a precipitant solution, and prepare a complexing agent solution; (2) Coprecipitation reaction: Add the metal salt solution, precipitant solution and complexing agent solution from step (1) to the reaction vessel, stir to carry out the coprecipitation reaction, and wait for D 50 When the particle size reaches 10–14 μm, the precursor slurry is sequentially subjected to centrifugation, washing, drying, iron removal, and sieving to obtain a nickel-cobalt binary precursor; the precursor is expressed as Ni… x Co y (OH)2, of which 0.85 <x<1,x+y=1; (3) Sintering: The precursor obtained in step (2) is mixed with Mn salt, Sr or Mg or a mixture of Sr and Mg in a molar ratio of (1-10):(0.1-5). Then it is mixed with lithium hydroxide in a ball mill in a molar ratio of 1:(1-1.5). The mixture is calcined in an oxygen atmosphere at 800-1000℃ for 4-20 hours. After the reaction is completed, it is naturally cooled to room temperature. The resulting material is lithium nickel cobalt manganese oxide ternary cathode material.

6. The preparation method of claim 5, wherein the pH of the precipitant solution system is maintained constant by an automatic control system; and / or, The reactor is a 20L reactor; and / or, The precursor is crystalline; and / or, The Mn salt is MnCO3; and / or, The Sr salt is one or more of strontium carbonate, strontium hydroxide, and strontium oxide; and / or, The Mg salt is one or more of magnesium carbonate, magnesium hydroxide, and magnesium oxide; and / or, The precursor obtained in step (2) is mixed with Mn salt, Sr or Mg or a mixture of Sr and Mg in a molar ratio of (1-10):(0.1-5), and then mixed with lithium hydroxide in a ball mill in a molar ratio of 1:(1-1.1).

7. The preparation method according to claim 5, wherein in step (1), the nickel salt is at least one selected from NiSO4·6H2O, Ni(NO3)2·6H2O, Ni(CH3COO)2·4H2O, and NiCl2·6H2O; the cobalt salt is at least one selected from CoSO4·7H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, and CoCl2·6H2O; and / or, the concentration of the nickel-cobalt mixed metal salt solution is 1–4 mol / L; The precipitant solution is at least one of NaOH, KOH, and LiOH; The complexing agent solution is at least one of ammonia, ammonium sulfate, and amino acid-based organic complexing agents.

8. The preparation method according to claim 5, wherein the nickel salt is NiSO4·6H2O; and / or, The cobalt salt is CoSO4·7H2O; and / or, The concentration of the nickel-cobalt mixed metal salt solution is 2 mol / L; and / or, The precipitant solution is a NaOH solution; and / or, The complexing agent solution is ammonia.

9. The preparation method according to claim 5, wherein in step (2), the feed rate of the metal salt is 0.80–1.50 L / h, the reaction temperature is 50–80 °C, the stirring speed is 300–800 rpm, the pH of the reaction system is maintained at 10.00–12.00, the ammonia concentration is 0.08–1.00 mol / L, and D 50 The size is 4–15 μm.

10. The preparation method according to claim 5, wherein in step (2), the washing time is at least 2 to 5 hours and the drying temperature is 90 to 110°C.

11. A lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is prepared from the positive electrode material according to any one of claims 1 to 4.

12. The lithium-ion battery of claim 11, wherein the positive electrode material has a dual gradient distribution of grain size and element concentration.

13. The lithium-ion battery of claim 11, wherein the positive electrode material is uniformly coated with the positive electrode material, conductive additive and binder.

14. The lithium-ion battery of claim 13, wherein the conductive additive is superconducting carbon and carbon nanotubes; And / or, the adhesive is polyvinylidene fluoride; And / or, the negative electrode is formed by coating graphite material, conductive additives and binders or is a high-purity lithium sheet; And / or, the membrane is a polyolefin membrane; And / or, the electrolyte is a mixed solvent of LiPF6 dissolved in carbonates.

15. The lithium-ion battery of claim 13, wherein the concentration of the electrolyte is 0.5 to 2 mol / L.

16. The lithium-ion battery of claim 13, wherein the concentration of the electrolyte is 1 mol / L.

17. Use of the cathode material according to any one of claims 1 to 4 in the preparation of lithium-ion batteries.

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