A positive electrode composite material, a preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a positive electrode composite material and a preparation method and application thereof. The positive electrode composite material comprises a core-shell structure ternary material and a metal oxide coating layer coated on the outer surface of the core-shell structure ternary material, the core-shell structure ternary material comprises a nickel-cobalt-manganese ternary material outer shell and a nickel-cobalt-manganese ternary material inner core formed in the nickel-cobalt-manganese ternary material outer shell; the chemical formula of the nickel-cobalt-manganese ternary material inner core and the nickel-cobalt-manganese ternary material outer shell is LiNi x Co y Mn 1‑x‑y O2, wherein x < 1, y > 0, and x + y < 1; the molar concentrations of nickel, cobalt and manganese in the core-shell structure ternary material are distributed in an equal concentration gradient along the radial direction; and the metal in the metal oxide coating layer comprises at least one of Zr, Mg, Al and Ti. The positive electrode composite material has high capacity and good cycle performance and safety performance at the same time.

Description

Technical Field

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

[0002] With continuous breakthroughs in lithium-ion battery technology, the application of lithium-ion batteries is becoming increasingly widespread, and sales of new energy vehicles equipped with lithium-ion batteries are repeatedly hitting new highs. However, the capacity of lithium-ion batteries still needs improvement. To increase battery capacity, ternary lithium-ion batteries have been making great strides towards high-nickel materials in recent years. Although high-nickel ternary materials have higher capacity than other ternary materials, their capacity degrades rapidly during cycling, affecting battery lifespan. Furthermore, the relatively poor safety performance of high-nickel ternary battery materials also limits their application.

[0003] To achieve high capacity while maintaining good cycle performance and safety, core-shell materials have become a promising solution. However, the production process of core-shell materials currently cannot be precisely controlled, leading to excessively large internal and external gradients, i.e., large differences in nickel, cobalt, and manganese concentrations between different cores and shells. This is detrimental to product capacity and results in poor cycle stability. Furthermore, the production process is complex and difficult to operate, making it challenging to flexibly adjust the proportions during production. The reason is that traditional methods use mixed nickel-cobalt-manganese salt solutions with different nickel, cobalt, and manganese ratios to prepare core-shell materials. This requires pre-preparing the mixed salt solutions, and achieving multiple gradients necessitates changing multiple mixed salt solutions, with only one change possible at a time. Excessively high nickel, cobalt, and manganese concentration differences can increase the lithium-ion migration barrier, hindering lithium-ion insertion and extraction and affecting the material's cycle performance.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a positive electrode composite material that, while possessing high capacity, also exhibits excellent cycle performance and safety performance.

[0006] The second objective of this invention is to provide a method for preparing a cathode composite material. This method is simple and easy to implement, allows for control of the molar ratio of nickel, cobalt, and manganese in the cathode composite material, and can improve the capacity, cycle performance, and safety performance of the cathode composite material.

[0007] The third objective of this invention is to provide a positive electrode sheet.

[0008] The fourth objective of this invention is to provide a lithium-ion battery.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] In a first aspect, the present invention provides a cathode composite material, comprising a core-shell ternary material and a metal oxide coating layer covering the outer surface of the core-shell ternary material. The core-shell ternary material comprises a nickel-cobalt-manganese (NiCoMn) ternary material shell and a NiCoMn ternary material core formed inside the NiCoMn ternary material shell. That is, the cathode composite material comprises, from the inside out, a NiCoMn ternary material core, a NiCoMn ternary material shell, and a metal oxide coating layer. The cathode composite material is a coated, isoconcentration gradient core-shell ternary cathode material.

[0011] The chemical formula of the nickel-cobalt-manganese ternary material core and the nickel-cobalt-manganese ternary material shell is LiNi. x Co y Mn 1-x-y O2, where x < 1, y > 0, x + y < 1; where x includes, but is not limited to, any point value from the ranges 0.99, 0.98, 0.97, 0.96, 0.95, 0.94, 0.93, 0.92, 0.91, 0.90, 0.85, 0.8, 0.75, 0.7, 0.65, 0.6, 0.55, 0.5, 0.4, 0.3, 0.2, 0.1. Or a range of values ​​between any two; y includes, but is not limited to, point values ​​of any one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9 or a range of values ​​between any two.

[0012] The molar concentrations of nickel, cobalt, and manganese in the core-shell ternary material exhibit an equal concentration gradient along the radial direction.

[0013] The metal in the metal oxide coating layer includes at least one of Zr, Mg, Al, and Ti. That is, the metal oxide coating layer includes at least one of zirconium oxide, magnesium oxide, aluminum oxide, and titanium oxide.

[0014] This invention achieves a radially uniform concentration gradient distribution of nickel, cobalt, and manganese in a core-shell ternary material. This not only facilitates high capacity utilization but also reduces barriers to lithium-ion migration, improving lithium-ion insertion and extraction efficiency, thereby enhancing the cycle performance of the cathode composite material. Furthermore, the uniform concentration gradient distribution promotes stress release within the cathode composite material, improving its structural stability, lifespan, and safety performance.

[0015] Furthermore, by providing a metal oxide coating layer on the outer surface of the core-shell ternary material, the present invention can reduce the direct contact between the cathode composite material and the electrolyte, reduce the occurrence of side reactions, and thus further improve the cycle performance and service life of the cathode composite material.

[0016] Preferably, in the direction from the core of the nickel-cobalt-manganese ternary material to the outer shell of the nickel-cobalt-manganese ternary material, the molar concentration of nickel decreases at an equal gradient, the molar concentration of cobalt increases at an equal gradient, and the molar concentration of manganese increases at an equal gradient, and the increasing gradients of cobalt and manganese are the same.

[0017] Preferably, the positive electrode composite material has an initial discharge capacity greater than 180 mAh / g at 1C rate, including but not limited to any one of 181 mAh / g, 182 mAh / g, 183 mAh / g, 184 mAh / g, 185 mAh / g, 186 mAh / g, 187 mAh / g, 188 mAh / g, 189 mAh / g, and 190 mAh / g, or a range between any two; a capacity retention rate greater than 92% after 100 cycles, including but not limited to any one of 92.5%, 93%, 93.5%, 94%, and 95%, or a range between any two; and a capacity retention rate greater than 87% after 200 cycles, including but not limited to any one of 87.5%, 88%, 88.5%, 89%, and 90%, or a range between any two.

[0018] The positive electrode composite material provided by this invention has advantages such as high capacity, good cycle performance and safety performance.

[0019] Secondly, the present invention provides a method for preparing the positive electrode composite material as described above, comprising the following steps:

[0020] (a) A nickel source solution, a cobalt source solution, a manganese source solution, a complexing agent solution, and a precipitant solution are added (continuously) (preferably dropwise) to the base solution to carry out a coprecipitation reaction; wherein the molar concentrations of the nickel source solution, the cobalt source solution, and the manganese source solution are the same.

[0021] The nickel source solution, cobalt source solution, manganese source solution, complexing agent solution, and precipitant solution are each fed through separate pipelines, without affecting each other. Preferably, a precision metering pump is used to feed the nickel source solution, cobalt source solution, manganese source solution, complexing agent solution, and precipitant solution separately for individual feeding.

[0022] During the coprecipitation reaction, the total feed flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution (the total feed flow rate, i.e., the sum of the feed flow rates of the nickel source solution, the cobalt source solution, and the manganese source solution) is kept constant. Furthermore, for every b μm increase in the D50 particle size of the solid particles generated by the coprecipitation reaction, the percentage of the feed flow rate of the nickel source solution to the total feed flow rate is decreased by 2a%, and the percentages of the feed flow rates of the cobalt source solution and the manganese source solution to the total feed flow rate are increased by a%, respectively.

[0023] After the particle size of the solid particles generated by the coprecipitation reaction reaches the target particle size, solid-liquid separation is performed, followed by drying, sieving and demagnetization to obtain a nickel-cobalt-manganese ternary precursor with a core-shell structure and a radially equal concentration gradient distribution of nickel, cobalt and manganese elements.

[0024] (b) The mixture containing the nickel-cobalt-manganese ternary precursor and the coating agent is pre-calcined to obtain a pre-calcined material; wherein the coating agent includes at least one of Zr source, Mg source, Al source and Ti source;

[0025] (c) The pre-burned material is mixed evenly with lithium salt and then sintered at high temperature to obtain the positive electrode composite material.

[0026] The method for preparing the cathode composite material provided by this invention has the advantages of being simple and easy to implement, and being able to control the molar ratio of nickel, cobalt and manganese in the cathode composite material, thereby improving the capacity, cycle performance and safety performance of the cathode composite material.

[0027] Specifically, this invention separately prepares nickel sulfate, cobalt, and manganese solutions and feeds them separately through different pipelines. By adjusting the feed flow rates of the nickel sulfate, cobalt, and manganese solutions, the ratio of nickel, cobalt, and manganese is adjusted to obtain a ternary precursor with an equal concentration gradient. This achieves an equal concentration gradient distribution, enabling high capacity while maintaining good cycle performance. Furthermore, after uniform mixing with a coating agent, pre-calcination and high-temperature sintering are performed to obtain a coated, equal concentration gradient core-shell ternary cathode material, further improving the material's cycle performance.

[0028] Compared with traditional methods, this invention achieves the latest precipitated nickel, cobalt, and manganese ratio equal to the feed flow rate ratio of nickel, cobalt, and manganese salts by preparing equimolar concentration nickel, cobalt, and manganese sulfate solutions and feeding them separately. The nickel, cobalt, and manganese ratio can be changed at any time by adjusting the feed flow rate. The method is simple and easy to implement.

[0029] By adjusting the flow rate during the preparation process to achieve a uniform concentration gradient distribution of nickel, cobalt, and manganese in the core and shell, the barrier to lithium-ion migration is reduced, improving lithium-ion insertion and extraction efficiency and enhancing the material's cycle performance. Furthermore, the uniform concentration gradient distribution facilitates the release of internal stress, improving structural stability and lifespan.

[0030] Furthermore, by using material coating, the direct contact between the positive electrode material and the electrolyte is reduced, thereby reducing the occurrence of side reactions, further improving the material's cycle performance, and enhancing its service life.

[0031] Preferably, in step (a), as the D50 particle size of the solid particles generated by the co-precipitation reaction increases by 1-5 μm (i.e., b = 1-5), the percentage of the feed flow rate of the nickel source solution to the total feed flow rate decreases by 4%-8% (i.e., 2a = 4%-8%), and the percentage of the feed flow rates of the cobalt source solution and the manganese source solution to the total feed flow rate increases by 2%-4% (i.e., a = 2%-4%), respectively; this enables gradient control of the molar ratio of nickel, cobalt, and manganese in the cathode composite material.

[0032] For example, for every 3 μm increase in the D50 particle size of the solid particles generated by the co-precipitation reaction, the percentage of the feed flow rate of the nickel source solution to the total feed flow rate decreases by 4%, while the percentage of the feed flow rate of the cobalt source solution and the manganese source solution to the total feed flow rate increases by 2%, respectively.

[0033] Alternatively, for every 2 μm increase in the D50 particle size of the solid particles generated by the co-precipitation reaction, the percentage of the feed flow rate of the nickel source solution to the total feed flow rate is reduced by 6%, while the percentage of the feed flow rates of the cobalt source solution and the manganese source solution to the total feed flow rate is increased by 3%, respectively.

[0034] Alternatively, for every 1 μm increase in the D50 particle size of the solid particles generated by the co-precipitation reaction, the percentage of the feed flow rate of the nickel source solution to the total feed flow rate is reduced by 8%, while the percentage of the feed flow rates of the cobalt source solution and the manganese source solution to the total feed flow rate is increased by 4%, respectively.

[0035] Preferably, in step (a), the total feed flow rate is 100 to 400 L / h; including but not limited to any one of 150 L / h, 200 L / h, 250 L / h, 300 L / h, 350 L / h, and 400 L / h, or a range between any two.

[0036] Preferably, in step (a), the initial feed flow rates (i.e., the feed flow rates at the initial addition of the nickel, cobalt, and manganese source solutions) of the nickel source solution, the cobalt source solution, and the manganese source solution are 90–98:1–5:1–5. Within this ratio range, the initial feed flow rate of the nickel source solution includes, but is not limited to, any one of 91, 92, 93, 94, 95, 96, 97, and 98, or a range between any two; the initial feed flow rate of the cobalt source solution includes, but is not limited to, any one of 1, 2, 3, 4, and 5, or a range between any two; and the initial feed flow rate of the manganese source solution includes, but is not limited to, any one of 1, 2, 3, 4, and 5, or a range between any two.

[0037] Preferably, in step (a), the D50 particle size of the nickel-cobalt-manganese ternary precursor is 8 to 18 μm, including but not limited to the point value of any one of 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, and 17 μm, or the range between any two.

[0038] In some specific embodiments of the present invention, in step (a), the particle size distribution range of the nickel-cobalt-manganese ternary precursor is 6 to 24 μm, including but not limited to point values ​​or ranges between any one of 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, and 23 μm.

[0039] That is, in step (a), the particle size distribution range of the target particle size is 6 to 24 μm, and the D50 particle size of the target particle size is 8 to 18 μm.

[0040] In some specific embodiments of the present invention, in step (a), the specific surface area of ​​the nickel-cobalt-manganese ternary precursor is 3-10 m². 2 / g, including but not limited to 4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 The point value of any one of / g or the range value between any two.

[0041] In some specific embodiments of the present invention, in step (a), nickel source solution, cobalt source solution and manganese source solution are prepared separately, and then nickel source solution, cobalt source solution, manganese source solution, complexing agent solution and precipitant solution are simultaneously introduced into the reaction vessel (reaction kettle) through different pipelines (using precision metering pumps). During the co-precipitation process, the concentration of ammonium ions and pH value in the system are kept stable. The ratio of nickel, cobalt and manganese in the product is adjusted by adjusting the feed ratio of nickel source solution, cobalt source solution and manganese source solution.

[0042] In some specific embodiments of the present invention, in step (a), the molar concentrations of the nickel source solution, the cobalt source solution, and the manganese source solution are 0.1 to 4 mol / L, including but not limited to any one of 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, and 3.5 mol / L, or any range between two of them.

[0043] In some specific embodiments of the present invention, in step (a), the complexing agent solution comprises an ammonia solution. Preferably, the molar concentration of the ammonia solution is 0.5–15 mol / L, including but not limited to a point value or a range between any one of 1 mol / L, 3 mol / L, 5 mol / L, 7 mol / L, 9 mol / L, 10 mol / L, 12 mol / L, and 14 mol / L.

[0044] In some specific embodiments of the present invention, in step (a), the precipitant solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and potassium carbonate solution. Preferably, the molar concentration of the precipitant solution is 0.5 to 15 mol / L, including but not limited to the point value of any one of 1 mol / L, 3 mol / L, 5 mol / L, 7 mol / L, 9 mol / L, 11 mol / L, and 13 mol / L, or a range between any two.

[0045] In some specific embodiments of the present invention, in step (a), the feed flow rate of the complexing agent solution is 10 to 70 L / h, including but not limited to any one of 20 L / h, 30 L / h, 40 L / h, 50 L / h, and 60 L / h, or any range between any two; the feed flow rate of the precipitant solution is 30 to 120 L / h, including but not limited to any one of 40 L / h, 50 L / h, 60 L / h, 70 L / h, 80 L / h, 90 L / h, 100 L / h, and 110 L / h, or any range between any two.

[0046] In some specific embodiments of the present invention, in step (a), the base solution is prepared from pure water, ammonia solution, and alkaline solution. Preferably, the pH value of the base solution is 9-12, including but not limited to any one of 9.5, 10, 10.5, 11, and 11.5 or any range between two values; the mass concentration of ammonium ions in the base solution is 2-12 g / L, including but not limited to any one of 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, and 11 g / L or any range between two values. The alkaline solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and potassium carbonate solution.

[0047] In some specific embodiments of the present invention, in step (a), the coprecipitation reaction is carried out in a reaction vessel. Specifically, a nickel source solution, a cobalt source solution, a manganese source solution, a complexing agent solution, and a precipitant solution are added to a reaction vessel containing a base liquid to carry out the coprecipitation reaction. The amount of the base liquid added is 1 / 4 to 2 / 4 of the reaction vessel volume.

[0048] In some specific embodiments of the present invention, in step (a), during the coprecipitation reaction, the temperature, pH, and concentration of ammonium ions in the material within the reaction vessel (reactor) are kept stable (unchanged). Preferably, during the coprecipitation reaction, the reaction temperature is 30–75°C, including but not limited to any one of 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, and 70°C, or a range between any two. That is, during the coprecipitation reaction, the temperature of the material within the reaction vessel (reactor) is maintained at 30–75°C.

[0049] Meanwhile, the mass concentration of ammonium ions in the material within the reaction vessel (reactor) is maintained at 2–12 g / L, including but not limited to any one of 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, or 11 g / L, or a range between any two; and the pH value of the material is maintained at 9–12, including but not limited to any one of 9.5, 10, 10.5, 11, or 11.5, or a range between any two.

[0050] In some specific embodiments of the present invention, in step (a), during the coprecipitation reaction, stirring is performed at a speed of 100 to 400 r / min, including but not limited to any one of 150 r / min, 200 r / min, 250 r / min, 300 r / min, and 350 r / min, or any range between two of them.

[0051] In some specific embodiments of the present invention, in step (a), the coprecipitation reaction is carried out under an inert atmosphere. The inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere. Preferably, the nitrogen gas introduction rate in the nitrogen atmosphere is 0.5–5 m³ / s. 2 / h, including but not limited to 1m 2 / h、2m 2 / h、3m 2 / h、4m 2 The point value of any one of / h or the range value between any two.

[0052] In some specific embodiments of the present invention, in step (a), during the co-precipitation reaction, when the liquid level in the reaction vessel (reactor) exceeds the baffle, stirring is stopped and the inert gas is turned off. The mixture is allowed to stand for 1–6 hours (including but not limited to any one of 2 hours, 3 hours, 4 hours, or 5 hours, or a range between any two), and then the supernatant is removed using a pneumatic pump (the remaining reaction liquid volume is 1 / 3 to 2 / 3 of the reaction vessel's volume). Then, the mixture is pumped at 0.5–5 m... 2 Inert gas is continuously introduced at a rate of / h (1–3 h, e.g., 2 h), followed by stirring (30–60 min, e.g., 45 min). Then, nickel source solution, cobalt source solution, manganese source solution, complexing agent solution, and precipitant solution are introduced into the reaction vessel. The above steps can be repeated multiple times.

[0053] In some specific embodiments of the present invention, step (a) further includes a step of transferring the reacted material to an aging tank and aging it for 5 to 7 hours (e.g., 6 hours) after the particle size of the solid particles generated by the co-precipitation reaction reaches the target particle size and before the solid-liquid separation.

[0054] In some specific embodiments of the present invention, step (a) further includes washing the solid material after solid-liquid separation with an alkaline solution of 0.1 to 1.5 mol / L, and then continuously washing it with deionized water until the pH value of the washing water is 7 to 7.5.

[0055] In some specific embodiments of the present invention, in step (a), the drying temperature is 100 to 140°C, including but not limited to a point value of any one of 110°C, 120°C, and 130°C, or a range between any two.

[0056] Preferably, in step (b), the Zr source includes at least one of Zr(NO3)4, ZrCl4, Zr(SO4)2, and Zr(CO3)2;

[0057] Preferably, the Mg source includes at least one of Mg(NO3)2, MgCl2, MgSO4 and MgCO3;

[0058] Preferably, the Al source includes at least one of Al(NO3)3, Al(OH)3, Al2(CO3)3, and Al2(SO4)3;

[0059] Preferably, the Ti source includes at least one of tetrabutyl titanate, TiO2, Ti(OH)4, Ti(NO3)4 and TiCl4.

[0060] Preferably, in step (b), the molar ratio of the nickel-cobalt-manganese ternary precursor and the coating agent in the mixture is 1:0.01 to 0.05; for example, 1:0.02, 1:0.03 or 1:0.04.

[0061] Preferably, in step (b), the pre-firing temperature is 300–600°C, including but not limited to any one of 320°C, 350°C, 380°C, 400°C, 430°C, 450°C, 480°C, 500°C, 520°C, 550°C, and 580°C, or a range between any two; the pre-firing time is 4–8 hours, including but not limited to any one of 5 hours, 6 hours, and 7 hours, or a range between any two.

[0062] Preferably, in step (b), the preparation method of the mixture containing the nickel-cobalt-manganese ternary precursor and the coating agent includes the following steps: adding the nickel-cobalt-manganese ternary precursor and the coating agent to a solvent, heating and stirring, and then drying to obtain the mixture containing the nickel-cobalt-manganese ternary precursor and the coating agent.

[0063] Preferably, the solvent includes at least one selected from ethanol, propanol, isopropanol, and isobutanol.

[0064] Preferably, the heating temperature is 50 to 90°C; including but not limited to a point value of any one of 60°C, 70°C, and 80°C, or a range between any two.

[0065] Preferably, the drying temperature is 70 to 130°C, including but not limited to any one of 80°C, 90°C, 100°C, 110°C, and 120°C, or a range between any two.

[0066] Preferably, in step (c), the molar ratio of the lithium salt to the nickel-cobalt-manganese ternary precursor in the pre-burned material is 1.04 to 1.12:1; including but not limited to any one of 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.10:1, 1.11:1 or any range between the two.

[0067] Preferably, the lithium salt comprises lithium carbonate and / or lithium hydroxide.

[0068] Preferably, in step (c), the high-temperature sintering temperature is 500–950°C, including but not limited to any one of 550°C, 600°C, 650°C, 700°C, 800°C, and 900°C, or a range between any two; the high-temperature sintering time is 8–25 h, including but not limited to any one of 10 h, 12 h, 15 h, 18 h, 20 h, and 23 h, or a range between any two.

[0069] Thirdly, the present invention provides a positive electrode sheet, which is mainly prepared from the positive electrode composite material as described above, or from the positive electrode composite material prepared by the method described above.

[0070] Fourthly, the present invention provides a lithium-ion battery, including the positive electrode sheet as described above.

[0071] This lithium-ion battery has advantages such as high capacity, good cycle performance, and good safety performance.

[0072] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0073] (1) The cathode composite material provided by this invention, by distributing the molar concentrations of nickel, cobalt, and manganese in the core-shell ternary material in a radially uniform concentration gradient, can reduce the barrier to lithium-ion migration, improve lithium-ion insertion and extraction efficiency, which is not only beneficial for high capacity utilization, but also improves the cycle performance of the cathode composite material. Furthermore, the uniform concentration gradient distribution is conducive to the release of internal stress in the cathode composite material, which can improve its structural stability and service life, and enhance safety performance.

[0074] (2) The positive electrode composite material provided by the present invention can reduce the direct contact between the positive electrode composite material and the electrolyte by setting a metal oxide coating layer on the outer surface of the core-shell structure ternary material, thereby reducing the occurrence of side reactions and further improving the cycle performance and service life of the positive electrode composite material.

[0075] (3) The method for preparing the positive electrode composite material provided by the present invention has the advantages of being simple and easy to implement, being able to control the molar ratio of nickel, cobalt and manganese in the positive electrode composite material, and being able to improve the capacity, cycle performance and safety performance of the positive electrode composite material. Attached Figure Description

[0076] 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.

[0077] Figure 1 This is a cross-sectional schematic diagram of the positive electrode composite material provided in Embodiment 1 of the present invention;

[0078] Figure 2 A physical image of the nickel-cobalt-manganese ternary precursor obtained in step (1) of Embodiment 1 of the present invention. Detailed Implementation

[0079] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0080] Example 1

[0081] The method for preparing the positive electrode composite material provided in this embodiment includes the following steps:

[0082] (1) Prepare nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution with equimolar concentrations (all 1.5 mol / L), and prepare sodium hydroxide solution with a molar concentration of 10 mol / L and ammonia solution with a molar concentration of 7 mol / L. Add appropriate amounts of pure water, sodium hydroxide solution, and ammonia solution to a continuously stirred reactor as a base solution (the pH of the base solution is 11.5, the mass concentration of ammonium ions in the base solution is 4 g / L, and the amount of base solution added is 1 / 4 of the reactor volume). Use nitrogen as a protective atmosphere (introduction rate is 3 m³ / s). 2 The material in the reactor is heated to 60°C ( / h), and the stirring speed is adjusted to 400 r / min.

[0083] Sodium hydroxide was used as a precipitant, and ammonia as a complexing agent. The prepared nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, sodium hydroxide solution (feed flow rate 150 L / h), and ammonia solution (feed flow rate 50 L / h) were simultaneously added dropwise to a continuously stirred reactor containing the aforementioned base solutions to induce a co-precipitation reaction. During this process, the pH of the mixture in the reactor was controlled at 11.5, the temperature at 60°C, and the ammonium ion concentration at 8 g / L.

[0084] During the coprecipitation reaction, the total feed flow rate of nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution was maintained at 400 L / h, with an initial feed flow rate of nickel sulfate solution:cobalt sulfate solution:manganese sulfate solution = 96:2:2. For every 3 μm increase in the D50 particle size of the solid particles generated by the coprecipitation reaction, the percentage of the nickel source solution feed flow rate in the total feed flow rate decreased by 4%, while the percentages of the cobalt and manganese source solutions feed flow rates in the total feed flow rate increased by 2%. That is, the initial feed flow rate of nickel sulfate solution was 384 L / h, and for every 3 μm increase in D50, the feed flow rate of nickel sulfate solution decreased by 16 L / h, while the feed flow rates of cobalt sulfate solution and manganese sulfate solution increased by 8 L / h respectively.

[0085] During the coprecipitation reaction, when the liquid level in the reactor exceeds the baffle, stop stirring and shut off the inert gas. After standing for 3 hours, use a pneumatic pump to remove the supernatant (the volume of the remaining material should be 1 / 3 of the reactor volume). Then, pump at 3m... 2 Inert gas was continuously introduced at a rate of / h for 1h, followed by stirring for 30min, and then nickel source solution, cobalt source solution, manganese source solution, complexing agent solution and precipitant solution were introduced into the reactor.

[0086] The reaction was stopped when the D50 particle size of the solid particles generated by the co-precipitation reaction reached 15 μm, and the mixture was transferred to an aging tank for 6 hours. Then, a centrifuge was used for solid-liquid separation, and the solid material after solid-liquid separation was washed sequentially with 1 mol / L sodium hydroxide solution, followed by continuous washing with deionized water until the pH of the washing water was 7. After centrifugation and dehydration, it was placed in an oven (130℃) for drying. Finally, after sieving and demagnetization, a nickel-cobalt-manganese ternary precursor with a core-shell structure and a radially equal concentration gradient distribution of nickel, cobalt, and manganese was obtained.

[0087] (2) The nickel-cobalt-manganese ternary precursor and coating agent Zr(NO3)4·5H2O obtained in step (1) were added to ethanol at a molar ratio of 1:0.03, heated and stirred at 60°C for 120 min, and then dried (at 120°C) to obtain a mixture containing the nickel-cobalt-manganese ternary precursor and coating agent. The mixture was then pre-calcined at 500°C for 4 h to obtain a pre-calcined material.

[0088] (3) After mixing the lithium salt (lithium carbonate) with the pre-burned material obtained in step (2) at a molar ratio of 1.08:1 for the lithium salt and the nickel-cobalt-manganese ternary precursor in the pre-burned material, the mixture is sintered at 780°C for 10 hours to obtain the cathode composite material.

[0089] The cathode composite material prepared in this embodiment includes a core-shell ternary material and a metal oxide coating layer (ZrO coating layer) covering the outer surface of the core-shell ternary material. The core-shell ternary material includes a nickel-cobalt-manganese ternary material shell and a nickel-cobalt-manganese ternary material core formed inside the nickel-cobalt-manganese ternary material shell (that is, the cathode composite material includes a nickel-cobalt-manganese ternary material core, a nickel-cobalt-manganese ternary material shell and a metal oxide coating layer from the inside to the outside).

[0090] The core-shell ternary material has the following chemical composition from the inside out: LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.92 Co 0.04 Mn 0.04 O2, LiNi 0.88 Co 0.06 Mn 0.06 O2, LiNi 0.84 Co 0.08 Mn 0.08 O2, LiNi 0.80 Co 0.10 Mn 0.10 O2.

[0091] That is, the molar concentrations of nickel, cobalt, and manganese in the core-shell ternary material exhibit an equal concentration gradient distribution along the radial direction. Specifically, along the direction from the core to the shell of the nickel-cobalt-manganese ternary material, the molar concentration of nickel decreases at an equal gradient, while the molar concentrations of cobalt and manganese increase at an equal gradient.

[0092] Example 2

[0093] The method for preparing the positive electrode composite material provided in this embodiment includes the following steps:

[0094] (1) Prepare nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution with equimolar concentrations (all 1.5 mol / L), and prepare sodium hydroxide solution with a molar concentration of 10 mol / L and ammonia solution with a molar concentration of 7 mol / L. Add appropriate amounts of pure water, sodium hydroxide solution, and ammonia solution to a continuously stirred reactor as a base solution (the pH of the base solution is 11.5, the mass concentration of ammonium ions in the base solution is 4 g / L, and the amount of base solution added is 1 / 4 of the reactor volume). Use nitrogen as a protective atmosphere (introduction rate is 3 m³ / s). 2 The material in the reactor is heated to 60°C ( / h), and the stirring speed is adjusted to 400 r / min.

[0095] Sodium hydroxide was used as a precipitant and ammonia as a complexing agent. The prepared nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, sodium hydroxide solution, and ammonia solution were simultaneously added dropwise to a continuously stirred reactor containing the aforementioned base liquid using a precision metering pump to induce a co-precipitation reaction. During this process, the pH of the mixture in the reactor was controlled at 11.5, the temperature at 60°C, and the ammonium ion concentration at 8 g / L.

[0096] During the coprecipitation reaction, the total feed flow rate of nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution was maintained at 400 L / h, with an initial feed flow rate of nickel sulfate solution:cobalt sulfate solution:manganese sulfate solution = 96:2:2. For every 3 μm increase in the D50 particle size of the solid particles generated by the coprecipitation reaction, the percentage of the nickel source solution feed flow rate in the total feed flow rate decreased by 6%, while the percentages of the cobalt and manganese source solutions feed flow rates in the total feed flow rate increased by 3%. That is, the initial feed flow rate of nickel sulfate solution was 384 L / h, and for every 3 μm increase in D50, the feed flow rate of nickel sulfate solution decreased by 24 L / h, while the feed flow rates of cobalt sulfate solution and manganese sulfate solution increased by 12 L / h respectively.

[0097] During the coprecipitation reaction, when the liquid level in the reactor exceeds the baffle, stop stirring and shut off the inert gas. After standing for 3 hours, use a pneumatic pump to remove the supernatant (the volume of the remaining material should be 1 / 3 of the reactor volume). Then, pump at 3m... 2 Inert gas was continuously introduced at a rate of / h for 1h, followed by stirring for 30min, and then nickel source solution, cobalt source solution, manganese source solution, complexing agent solution and precipitant solution were introduced into the reactor.

[0098] The reaction was stopped when the D50 particle size of the solid particles generated by the co-precipitation reaction reached 15 μm, and the mixture was transferred to an aging tank for 6 hours. Then, a centrifuge was used for solid-liquid separation, and the solid material after solid-liquid separation was washed sequentially with 1 mol / L sodium hydroxide solution, followed by continuous washing with deionized water until the pH of the washing water was 7. After centrifugation and dehydration, it was placed in an oven (130℃) for drying. Finally, after sieving and demagnetization, a nickel-cobalt-manganese ternary precursor with a core-shell structure and a radially equal concentration gradient distribution of nickel, cobalt, and manganese was obtained.

[0099] (2) The nickel-cobalt-manganese ternary precursor and coating agent Zr(NO3)4·5H2O obtained in step (1) were added to ethanol at a molar ratio of 1:0.03, heated and stirred at 60°C for 120 min, and then dried (at 120°C) to obtain a mixture containing the nickel-cobalt-manganese ternary precursor and coating agent. The mixture was then pre-calcined at 500°C for 4 h to obtain a pre-calcined material.

[0100] (3) After mixing the lithium salt (lithium carbonate) with the pre-burned material obtained in step (2) at a molar ratio of 1.08:1 for the lithium salt and the nickel-cobalt-manganese ternary precursor in the pre-burned material, the mixture is sintered at 780°C for 10 hours to obtain the cathode composite material.

[0101] The cathode composite material prepared in this embodiment includes a core-shell ternary material and a metal oxide coating layer (ZrO coating layer) covering the outer surface of the core-shell ternary material. The core-shell ternary material includes a nickel-cobalt-manganese ternary material shell and a nickel-cobalt-manganese ternary material core formed inside the nickel-cobalt-manganese ternary material shell (that is, the cathode composite material includes a nickel-cobalt-manganese ternary material core, a nickel-cobalt-manganese ternary material shell and a metal oxide coating layer from the inside to the outside).

[0102] The core-shell ternary material has the following chemical composition from the inside out: LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.90 Co 0.05 Mn 0.05 O2, LiNi 0.84 Co 0.08 Mn 0.08 O2, LiNi 0.78 Co 0.11 Mn 0.11 O2, LiNi 0.72 Co 0.14 Mn 0.14 O2.

[0103] That is, the molar concentrations of nickel, cobalt, and manganese in the core-shell ternary material exhibit an equal concentration gradient distribution along the radial direction. Specifically, along the direction from the core to the shell of the nickel-cobalt-manganese ternary material, the molar concentration of nickel decreases at an equal gradient, while the molar concentrations of cobalt and manganese increase at an equal gradient.

[0104] Example 3

[0105] The method for preparing the positive electrode composite material provided in this embodiment includes the following steps:

[0106] (1) Prepare nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution with equimolar concentrations (all 1.5 mol / L), and prepare sodium hydroxide solution with a molar concentration of 10 mol / L and ammonia solution with a molar concentration of 7 mol / L. Add appropriate amounts of pure water, sodium hydroxide solution, and ammonia solution to a continuously stirred reactor as a base solution (the pH of the base solution is 11.5, the mass concentration of ammonium ions in the base solution is 4 g / L, and the amount of base solution added is 1 / 4 of the reactor volume). Use nitrogen as a protective atmosphere (introduction rate is 3 m³ / s). 2 The material in the reactor is heated to 60°C ( / h), and the stirring speed is adjusted to 400 r / min.

[0107] Sodium hydroxide was used as a precipitant and ammonia as a complexing agent. The prepared nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, sodium hydroxide solution, and ammonia solution were simultaneously added dropwise to a continuously stirred reactor containing the aforementioned base liquid using a precision metering pump to induce a co-precipitation reaction. During this process, the pH of the mixture in the reactor was controlled at 11.5, the temperature at 60°C, and the ammonium ion concentration at 8 g / L.

[0108] During the coprecipitation reaction, the total feed flow rate of nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution was maintained at 400 L / h, with an initial feed flow rate of nickel sulfate solution:cobalt sulfate solution:manganese sulfate solution = 96:2:2. For every 3 μm increase in the D50 particle size of the solid particles generated by the coprecipitation reaction, the percentage of the nickel source solution feed flow rate in the total feed flow rate decreased by 8%, while the percentages of the cobalt and manganese source solutions feed flow rates in the total feed flow rate increased by 4%. That is, the initial feed flow rate of nickel sulfate solution was 384 L / h, and for every 3 μm increase in D50, the feed flow rate of nickel sulfate solution decreased by 32 L / h, while the feed flow rates of cobalt sulfate solution and manganese sulfate solution increased by 16 L / h respectively.

[0109] During the coprecipitation reaction, when the liquid level in the reactor exceeds the baffle, stop stirring and shut off the inert gas. After standing for 3 hours, use a pneumatic pump to remove the supernatant (the volume of the remaining material should be 1 / 3 of the reactor volume). Then, pump at 3m...2 Inert gas was continuously introduced at a rate of / h for 1h, followed by stirring for 30min, and then nickel source solution, cobalt source solution, manganese source solution, complexing agent solution and precipitant solution were introduced into the reactor.

[0110] The reaction was stopped when the D50 particle size of the solid particles generated by the co-precipitation reaction reached 15 μm, and the mixture was transferred to an aging tank for 6 hours. Then, a centrifuge was used for solid-liquid separation, and the solid material after solid-liquid separation was washed sequentially with 1 mol / L sodium hydroxide solution, followed by continuous washing with deionized water until the pH of the washing water was 7. After centrifugation and dehydration, it was placed in an oven (130℃) for drying. Finally, after sieving and demagnetization, a nickel-cobalt-manganese ternary precursor with a core-shell structure and a radially equal concentration gradient distribution of nickel, cobalt, and manganese was obtained.

[0111] (2) The nickel-cobalt-manganese ternary precursor and coating agent Zr(NO3)4·5H2O obtained in step (1) were added to ethanol at a molar ratio of 1:0.03, heated and stirred at 60°C for 120 min, and then dried (at 120°C) to obtain a mixture containing the nickel-cobalt-manganese ternary precursor and coating agent. The mixture was then pre-calcined at 500°C for 4 h to obtain a pre-calcined material.

[0112] (3) After mixing the lithium salt (lithium carbonate) with the pre-burned material obtained in step (2) at a molar ratio of 1.08:1 for the lithium salt and the nickel-cobalt-manganese ternary precursor in the pre-burned material, the mixture is sintered at 780°C for 10 hours to obtain the cathode composite material.

[0113] The cathode composite material prepared in this embodiment includes a core-shell ternary material and a metal oxide coating layer (ZrO coating layer) covering the outer surface of the core-shell ternary material. The core-shell ternary material includes a nickel-cobalt-manganese ternary material shell and a nickel-cobalt-manganese ternary material core formed inside the nickel-cobalt-manganese ternary material shell (that is, the cathode composite material includes a nickel-cobalt-manganese ternary material core, a nickel-cobalt-manganese ternary material shell and a metal oxide coating layer from the inside to the outside).

[0114] The core-shell ternary material has the following chemical composition from the inside out: LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.88 Co 0.06 Mn 0.06 O2, LiNi 0.80 Co 0.10 Mn 0.10 O2, LiNi 0.72 Co 0.14 Mn 0.14O2, LiNi 0.64 Co 0.18 Mn 0.18 O2.

[0115] That is, the molar concentrations of nickel, cobalt, and manganese in the core-shell ternary material exhibit an equal concentration gradient distribution along the radial direction. Specifically, along the direction from the core to the shell of the nickel-cobalt-manganese ternary material, the molar concentration of nickel decreases at an equal gradient, while the molar concentrations of cobalt and manganese increase at an equal gradient.

[0116] Example 4

[0117] The preparation method of the positive electrode composite material provided in this embodiment is basically the same as that in Example 2, except that in step (2), Zr(NO3)4·5H2O is replaced with an equimolar amount of Mg(NO3)2·6H2O.

[0118] Example 5

[0119] The preparation method of the positive electrode composite material provided in this embodiment is basically the same as that in Example 2, except that in step (2), Zr(NO3)4·5H2O is replaced with an equimolar amount of Al(NO3)3·9H2O.

[0120] Example 6

[0121] The preparation method of the positive electrode composite material provided in this embodiment is basically the same as that in Example 2, except that in step (2), Zr(NO3)4·5H2O is replaced with an equimolar amount of tetrabutyl titanate.

[0122] Comparative Example 1

[0123] The method for preparing the cathode material provided in this comparative example includes the following steps: A nickel-cobalt-manganese ternary mixed salt solution with a total molar concentration of 2 mol / L and molar ratios of nickel, cobalt, and manganese of 90:5:5 and 6:2:2, respectively, is prepared. Appropriate amounts of pure water, NaOH solution, and ammonia solution are added as a base liquid to a continuously stirred reactor. Nitrogen gas is used as a protective atmosphere, and the temperature is raised to 50°C. The stirring speed is adjusted to 400 r / min. Using sodium hydroxide solution as a precipitant and ammonia solution as a complexing agent, a nickel-cobalt-manganese ternary mixed salt solution (2.0 mol / L), a sodium hydroxide solution (10 mol / L), and an ammonia solution (7 mol / L) with a nickel-cobalt-manganese molar ratio of 90:5:5 are simultaneously added dropwise to the continuously stirred reactor to carry out a co-precipitation reaction, controlling the pH of the solution to 11.5. After the precipitation reaction reached a particle size D50 of 13 μm, the solution was replaced with a ternary mixed salt solution of nickel, cobalt, and manganese (NiCoMn) with a molar ratio of 6:2:2 (2.0 mol / L) until the particle D50 grew to 15 μm. The particles were transferred to an aging tank, then washed sequentially with NaOH solution and pure water using a centrifuge. After centrifugation and dehydration, the particles were dried in an oven (130℃) and finally demagnetized by sieving to obtain the ternary precursor. The obtained precursor was heated and mixed evenly with Zr(NO3)4·5H2O in ethanol, filtered and dried, and then pre-calcined at 500℃ for 4 hours to obtain the pre-calcined material. The lithium salt and the pre-calcined material were then mixed evenly at a molar ratio of lithium salt to NiCoMn ternary precursor in the pre-calcined material of 1.08:1, and sintered at 780℃ to obtain the cathode material.

[0124] All parameters not mentioned in the above preparation method are the same as those in Example 2.

[0125] Comparative Example 2

[0126] The preparation method of the cathode material provided in this comparative example is basically the same as that in Example 2. The only difference is that step (2) is not set. Instead, the nickel-cobalt-manganese ternary precursor obtained in step (1) is directly mixed with lithium salt (lithium carbonate) at a molar ratio of 1:1.08 and then sintered at high temperature (the temperature and time of high-temperature sintering are the same as those in Example 2).

[0127] Comparative Example 3

[0128] The preparation method of the cathode material provided in this comparative example is basically the same as that in comparative example 1. The only difference is that step (2) is not set. Instead, the nickel-cobalt-manganese ternary precursor obtained in step (1) is directly mixed with lithium salt (lithium carbonate) at a molar ratio of 1:1.08 and then sintered at high temperature (the temperature and time of high-temperature sintering are the same as those in comparative example 1).

[0129] Experimental Example

[0130] The positive electrode composite materials prepared in each of the above embodiments and the positive electrode materials prepared in each comparative example were assembled into batteries. Then, the charge and discharge performance of each battery group at a 1C rate was tested using an electrochemical workstation. The results are shown in Table 1.

[0131] The charge / discharge performance was tested within a voltage range of 2.75–4.2V, with the battery undergoing charge / discharge cycles at a rate of 1C. Battery capacity retention was measured as the ratio of the discharge capacity after 100 and 200 cycles to the initial discharge capacity.

[0132] The method for assembling the battery includes: preparing a positive electrode sheet by combining positive electrode material, binder PVDF, and conductive agent Super-P in a ratio of 90:6:4. Then, assembling the positive electrode sheet, lithium negative electrode, PP separator, and electrolyte into a button cell assembly box under argon protection.

[0133] Table 1. Test results of charge and discharge performance of each battery group at 1C rate.

[0134] Group Initial discharge capacity Capacity retention rate after 100 cycles Capacity retention after 200 cycles Example 1 186.4mAh / g 92.4％ 87.5％ Example 2 184.8mAh / g 93.1％ 87.2％ Example 3 181.9mAh / g 92.8％ 88.1％ Example 4 184.3mAh / g 92.9％ 87.4％ Example 5 184.7mAh / g 92.4％ 87.0％ Example 6 185.1mAh / g 92.6％ 87.7％ Comparative Example 1 183.9mAh / g 91.3％ 86.4％ Comparative Example 2 182.2mAh / g 91.1％ 85.4％ Comparative Example 3 181.1mAh / g 89.5％ 83.3％

[0135] As can be seen from Table 1, the cathode composite materials prepared in each embodiment have higher capacity and better cycle performance.

[0136] like Figure 1 The figure shown is a cross-sectional schematic diagram of the positive electrode composite material provided in Embodiment 1 of the present invention.

[0137] like Figure 2 The image shown is a physical picture of the nickel-cobalt-manganese ternary precursor obtained in step (1) of Embodiment 1 of the present invention.

[0138] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A positive electrode composite material, characterized in that, The positive electrode composite material comprises a core-shell structure ternary material and a metal oxide coating layer coated on the outer surface of the core-shell structure ternary material, wherein the core-shell structure ternary material comprises a nickel-cobalt-manganese ternary material outer shell and a nickel-cobalt-manganese ternary material inner core formed inside the nickel-cobalt-manganese ternary material outer shell; The chemical formula of the nickel-cobalt-manganese ternary material inner core and the nickel-cobalt-manganese ternary material shell is LiNi x Co y Mn 1-x- y O2, wherein x < 1, y > 0, and x + y < 1. The molar concentrations of nickel, cobalt and manganese elements in the core-shell structure ternary material are radially distributed in an equal concentration gradient; The metal in the metal oxide coating layer comprises at least one of Zr, Mg, Al and Ti; In the direction from the nickel-cobalt-manganese ternary material inner core to the nickel-cobalt-manganese ternary material outer shell, the molar concentration of the nickel element decreases in an equal gradient, and the molar concentrations of the cobalt element and the manganese element increase in an equal gradient, and the increasing gradients of the cobalt element and the manganese element are the same.

2. The positive electrode composite according to claim 1, characterized by The positive electrode composite material has a first discharge capacity greater than 180 mAh / g at a 1C rate, a capacity retention rate greater than 92% after 100 cycles, and a capacity retention rate greater than 87% after 200 cycles.

3. The method for producing a positive electrode composite material according to claim 1 or 2, characterized by, The method comprises the following steps: (a) adding nickel source solution, cobalt source solution, manganese source solution, complexing agent solution and precipitant solution into a bottom liquid respectively to perform a co-precipitation reaction; wherein the molar concentrations of the nickel source solution, the cobalt source solution and the manganese source solution are the same; During the co-precipitation reaction, the total feed flow rate of the nickel source solution, the cobalt source solution and the manganese source solution is kept unchanged, and for each increase of b μm in the D50 particle size of the solid particles generated by the co-precipitation reaction, the percentage of the feed flow rate of the nickel source solution in the total feed flow rate is reduced by 2a%, and the percentages of the feed flow rates of the cobalt source solution and the manganese source solution in the total feed flow rate are increased by a% respectively; After the particle size of the solid particles generated by the co-precipitation reaction reaches a target particle size, solid-liquid separation is performed, followed by drying, sieving and magnetic removal in sequence to obtain a nickel-cobalt-manganese ternary precursor with a core-shell structure; (b) pre-burning a mixture containing the nickel-cobalt-manganese ternary precursor and a coating agent to obtain a pre-burning material; wherein the coating agent comprises at least one of a Zr source, a Mg source, an Al source and a Ti source; (c) uniformly mixing the pre-burning material with a lithium salt and then performing high-temperature sintering to obtain the positive electrode composite material.

4. The method of claim 3, wherein the lithium metal oxide is LiFe0.9Mn0.1PO4. In step (a), for each increase of 1-5 μm in the D50 particle size of the solid particles generated by the co-precipitation reaction, the percentage of the feed flow rate of the nickel source solution in the total feed flow rate is reduced by 4%-8%, and the percentages of the feed flow rates of the cobalt source solution and the manganese source solution in the total feed flow rate are increased by 2%-4% respectively.

5. The method of claim 3, wherein the lithium metal oxide is LiFe0.9Mn0.1PO4. In step (a), the total feed flow rate is 100-400 L / h.

6. The method of claim 3, wherein the lithium metal oxide is LiFe0.9Mn0.1PO4. In step (a), the ratio of the initial feed flow rates of the nickel source solution, the cobalt source solution and the manganese source solution is 90-98: 1-5: 1-5.

7. The method of claim 3, wherein the lithium metal oxide is LiFe0.9Mn0.1PO4. In step (a), the D50 particle size of the nickel-cobalt-manganese ternary precursor is 8-18 μm.

8. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. In step (b), the Zr source comprises at least one of Zr(NO3)4, ZrCl4, Zr(SO4)2 and Zr(CO3)2.

9. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. The Mg source includes at least one of Mg(NO3)2, MgCl2, MgSO4 and MgCO3.

10. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. The Al source includes at least one of Al(NO3)3, Al(OH)3, Al2(CO3)3 and Al2(SO4)3.

11. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. The Ti source includes at least one of tetrabutyl titanate, TiO2, Ti(OH)4, Ti(NO3)4 and TiCl4.

12. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. In step (b), the molar ratio of the nickel-cobalt-manganese ternary precursor and the coating agent in the mixed material is 1:0.01-0.

05.

13. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. In step (b), the pre-burning temperature is 300-600℃, and the pre-burning time is 4-8h.

14. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. In step (b), the preparation method of the mixed material containing the nickel-cobalt-manganese ternary precursor and the coating agent includes the following steps: adding the nickel-cobalt-manganese ternary precursor and the coating agent into a solvent, heating and stirring, and then drying to obtain the mixed material containing the nickel-cobalt-manganese ternary precursor and the coating agent.

15. The method of claim 14, wherein the positive electrode composite is prepared by a process comprising: (a) mixing the lithium metal oxide, the binder, and the conductive agent; and (b) coating the mixture onto the current collector. The solvent includes at least one of ethanol, propanol, isopropanol and isobutanol.

16. The method for preparing the positive electrode composite material according to claim 14, characterized in that, The heating temperature is 50-90℃.

17. The method for preparing the positive electrode composite material according to claim 14, characterized in that, The drying temperature is 70-130℃.

18. The method for preparing the positive electrode composite material according to claim 3, characterized in that, In step (c), the molar ratio of the lithium salt and the nickel-cobalt-manganese ternary precursor in the pre-burning material is 1.04-1.12:

1.

19. The method of claim 3, wherein the positive electrode composite is prepared by mixing the lithium metal oxide, the carbon material, and the binder in a solvent. In step (c), the lithium salt includes lithium carbonate and / or lithium hydroxide.

20. The method for preparing the positive electrode composite material according to claim 3, characterized in that, In step (c), the high-temperature sintering temperature is 500-950℃, and the high-temperature sintering time is 8-25h.

21. A positive electrode sheet characterized by comprising: Prepared mainly from the positive electrode composite material according to any one of claims 1-2.

22. A lithium-ion battery, characterized by, The positive electrode plate includes the positive electrode composite material according to claim 21.

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