A modified high-nickel cathode material, its preparation method and application

Abstract

This invention relates to the field of battery technology, and provides a modified high-nickel cathode material, its preparation method, and its applications. The modified high-nickel cathode material comprises large particles with a Dv50 of d1 and small particles with a Dv50 of d2, where d1 > d2; both the large and small particles have a secondary spherical structure and each includes a matrix material and a coating material attached to the surface of the matrix material; the chemical formula of each particle is independently Li. a Ni x Co y Al w M z O2, where 0.80≤x≤0.95, M is selected from at least one of Zr, Sr, Ca, Mg, Ba, Y, Nb, Ti, Mo, Sn, Ta, Sb, Bi and W; the matrix material of large particles includes a core, an intermediate layer and an outer layer from the inside out, and the porosity φ2 of the intermediate layer is greater than the porosity φ3 of the outer layer and the porosity φ1 of the core.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a modified high-nickel positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in mobile phones, notebook computers and other portable mobile devices, and electric vehicles due to their high energy density, long cycle life and low environmental pollution. As the most critical component, the positive electrode determines the electrochemical performance of the lithium ion battery.

[0003] Currently, the positive electrode materials that are being studied include ternary LiNi x Co y Al 1-x-y O2(NCA), which has better structural stability due to higher bond energy of Al-O bond under the same nickel / cobalt content. However, it is found that the NCA positive electrode material is prone to irreversible phase transition after high-voltage cycling, resulting in rapid capacity decay and poor rate performance. In addition, in order to further improve the specific capacity of lithium ion batteries and reduce the use of scarce resources Co, researchers propose to further increase the Ni content. However, when the Ni 2+ content in high-nickel materials is too high, the Li + / Ni 2+ mixing degree is large, which leads to poor electrochemical performance of the material, and the material is prone to decomposition at high temperature and phase transition during charging and discharging, which hinders the development of high-nickel ternary materials to some extent. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a modified high-nickel positive electrode material and a preparation method and application thereof. The modified high-nickel positive electrode material has high cycle retention rate and high rate performance. In addition, the preparation method is simple and easy to industrialize, and has good application prospect.

[0005] According to one aspect of the present application, a modified high-nickel positive electrode material is provided, wherein the modified high-nickel positive electrode material comprises large particles with a Dv50 of d1 and small particles with a Dv50 of d2, and d1>d2;

[0006] The large particles and the small particles both have a secondary spherical structure and both comprise a base material and a coating material attached to the surface of the base material;

[0007] The chemical formula of the large particles and the small particles is independently Li a Ni x Co y Al w Mz O2, wherein 0.80≤x≤0.95, M is selected from at least one of Zr, Sr, Ca, Mg, Ba, Y, Nb, Ti, Mo, Sn, Ta, Sb, Bi and W;

[0008] The matrix material of the large particle comprises, from inside to outside, a core, an intermediate layer and an outer layer, and the porosity φ2 of the intermediate layer is greater than the porosity φ3 of the outer layer and the porosity φ1 of the core.

[0009] The element M is doped in the positive electrode material, which is beneficial to improve the lithium ion migration rate in the positive electrode material, reduce the internal impedance of the material, and thus improve the rate performance of the positive electrode material. Through particle size grading, the positive electrode material can obtain higher compaction density. In addition, the matrix material of the large particle modified high-nickel positive electrode material in the application adopts a three-layer structure, and the porosity of the intermediate layer is greater than the porosity of the outer layer and the core. The advantages are as follows: the existence of the maximum porosity of the intermediate layer in the application is beneficial to regulate the diffusion rate of the doped element in the internal during the sintering process, so as to form a structure in which the doped element in the outer layer is gradiently distributed and the doped element in the inner layer is uniformly distributed; it is also beneficial to regulate the stress distribution of the inner and outer layers, weaken the internal stress of the material as a whole, and improve the stability of the overall internal structure, so as to inhibit the stress accumulation in the material during the cycle process and enhance the stability during the cycle process; the existence of the internal pores is also beneficial to shorten the migration path of lithium ions and enhance the lithium ion transmission capacity, so as to improve the rate performance.

[0010] In some embodiments of the application, the coating material of the large particle and / or the coating material of the small particle comprises at least one of elements Al, Co, Ti, W, B, Nb, and has the following advantages: (1) it is beneficial to form a fast ion conductor coating layer and improve the lithium ion transmission capacity of the material, so as to improve its rate performance; (2) surface coating helps to reduce the contact between the material surface and the electrolyte and weaken the occurrence of side reactions, so as to improve its cycle performance. Preferably, the coating material of the large particle and / or the coating material of the small particle comprises at least one of elements Al, Co and Ti.

[0011] In some embodiments of the application, the thickness of the coating material in the large particle and the small particle is independently 0.01-0.5 μm.

[0012] In some embodiments of the application, 0.9≤a≤1.1, 0.05≤y≤0.20, 0.005≤w≤0.04, 0≤z≤0.01, and x+y+w+z=1.

[0013] Preferably, the mole amount of the doping element M is in the range of 0.001≤z≤0.01 (for example, 0.001≤z≤0.005). If z is too large, too much inert component will be generated, which will inhibit the capacity of the obtained ternary positive electrode material; on the contrary, if z is too small, the doping amount is too small, which will result in that the doping element cannot fully play a role.

[0014] In some embodiments of the present application, M is selected from at least one of Zr, Mg, Ti, and W.

[0015] In some embodiments of the present application, d1 is 12-20 μm, for example, 12-18 μm, 14-16 μm, 14.5-15.5 μm, 15-15.5 μm.

[0016] In some embodiments of the present application, d2 is 1.5-5.5 μm, for example, 2-5.5 μm, 4-5.5 μm.

[0017] In some embodiments of the present application, the matrix material of the large particles and / or the matrix material of the small particles has an Al element concentration gradient decreasing from outside to inside. This is because: the matrix material is doped with Al itself, and by coating the Al element, the Al element partially penetrates into the matrix material with voids, in addition, due to the existence of pores in each layer of the matrix material, the porosity of the middle layer and the outer layer is greater than that of the inner core, which is conducive to the difference in diffusion and penetration of aluminum elements in the inside, thereby forming an aluminum concentration gradient. Finally, the outer layer of the matrix material has a large aluminum concentration relative to the middle layer and the inner layer. The effect advantages brought by the matrix material with an Al element concentration gradient decreasing from outside to inside include: the higher Al concentration of the outer layer is conducive to maintaining the stability of the material surface structure, thereby improving the cycle performance, and the lower Al concentration of the inner layer can reduce the adverse effects of inert Al components on capacity performance, which is conducive to the full play of the internal performance of the material.

[0018] In some embodiments of the present application, the radius of the inner core is 0.5-3 μm, for example, 1-3 μm, 2-3 μm, 2-2.1 μm; the thickness of the middle layer is 1.5-4 μm, for example, 1.5-3 μm, 2-3 μm, 2-2.5 μm, 2.1-2.5 μm, 2.2-2.5 μm, 2.3-2.5 μm, 2.4-2.5 μm; the thickness of the outer layer is 1.5-5 μm, for example, 1.5-4 μm, 2-3 μm, 2-2.5 μm, 2.1-2.5 μm, 2.2-2.5 μm, 2.3-2.5 μm, 2.4-2.5 μm.

[0019] In some embodiments of the present invention, φ1 is 0~0.5%, for example, 0~0.4%, 0~0.3%, 0~0.2%, 0~0.1%; φ2 is 2%~11%, for example, 2%~10%, 3%~8%, 4%~6%, 5%~6%; φ3 is 0.3%~2.0%, for example, 0.4%~1.5%, 0.5%~1.2%, 0.6%~0.8%, 0.7%~0.8%.

[0020] In some embodiments of the present invention, the matrix material of the small particles has a hollow structure or a solid structure, preferably a hollow structure, because: a hollow structure is beneficial to reduce internal stress, inhibit material cracking, and improve cycle capacity.

[0021] In some embodiments of the present invention, the matrix material of the small particles has a hollow structure, and the diameter of the hollow cavity of the matrix material is 0.5~3 μm, for example, 0.5~2 μm, 1~2 μm, or 1.5~2 μm.

[0022] In some embodiments of the present invention, the matrix material of the small particles has a solid structure, i.e., a solid structure, and the diameter of the matrix material is 0.5~3 μm, for example, 0.5~2 μm, 1~2 μm, or 1.5~2 μm.

[0023] In some embodiments of the present invention, the mass ratio of the large particles to the small particles is 1 to 9:1, for example, 2 to 9:1, 3 to 8:1, or 4 to 8:1. Sintering the large and small particles separately and then blending them results in a more reasonable particle size distribution, which is beneficial for increasing the compaction density of the matrix and thus helps to improve the energy density of lithium-ion batteries.

[0024] According to another aspect of the present invention, a method for preparing the above-mentioned modified high-nickel cathode material is provided, comprising the following steps:

[0025] In an oxygen-rich environment, a first nickel-cobalt oxide precursor, a first lithium source, a first additive containing M, and a first additive containing Al are mixed and subjected to a first sintering process to obtain the large particles.

[0026] In an oxygen-rich environment, a second nickel-cobalt oxide precursor, a second lithium source, a second additive containing M, and a second additive containing Al are mixed and subjected to a second sintering process to obtain the small particles.

[0027] The large particles and the small particles are mixed in a certain proportion to obtain the final product.

[0028] The first nickel-cobalt oxide precursor includes a central region, an intermediate region, and an outer region from the inside out, and the porosity of the intermediate region is greater than that of the outer region and the central region.

[0029] The first sintering and the second sintering each include three heat preservation platforms, wherein the temperature of the third heat preservation platform is independently any value in the range of 700~760℃, and the temperature of the third heat preservation platform in the first sintering is higher than the temperature of the third heat preservation platform in the second sintering.

[0030] This invention utilizes a precursor with a higher porosity in the middle layer than in the outer and core layers, inheriting the porosity differences of the precursor. Therefore, the middle layer of the precursor is relatively porous (the middle layer of the precursor itself already possesses a certain degree of porosity). During the sintering diffusion process, the porosity difference in the middle layer further increases, resulting in a three-layer structure with varying porosities. Furthermore, this invention employs a three-stage heat preservation platform for the lithiation reaction. The Al source added during sintering is excessive relative to the precursor. Additionally, due to the three-stage sintering process, the additives fully contact the material and diffuse from the surface to the interior, forming a gradient doping from the outside in, and creating a fast-ion conductor coating on the surface. Excessive heat preservation temperature can lead to over-sintering and adhesion of the material, affecting its performance; conversely, insufficient heat preservation temperature can result in incomplete sintering and failure to achieve adequate lithiation.

[0031] In some embodiments of the present invention, the first nickel-cobalt oxide precursor and the second nickel-cobalt oxide precursor are each independently Ni x’ Co y’ (OH)2, where 0.80≤x'≤0.95, 0.05≤y'≤0.20, x'+y'=1.

[0032] In some embodiments of the present invention, the particle size of the first nickel-cobalt oxide precursor is 12-20 μm, for example, 12-18 μm, 14-16 μm, 14.5-15.5 μm, or 15-15.5 μm.

[0033] In some embodiments of the present invention, the first nickel-cobalt oxide precursor Ni x’ Co y’ (OH)2 is prepared by the following steps:

[0034] S1. Adjust the alkalinity of the complexing agent solution with water, then mix it with the precipitant solution to adjust the pH of the reaction system to 11-12. Introduce a protective gas, then introduce a nickel-cobalt mixed salt solution and the precipitant solution to carry out the nucleation stage reaction. After every 1-2 hours, decrease the pH by 0.2-0.4 until the pH value reaches 9.5-10.9. Then maintain the pH to allow particle growth. Stop the reaction when the particle size reaches 4.5-5.5 μm, separate the solid and liquid, and obtain the precursor seed crystals.

[0035] S2. Add a complexing agent solution to the aqueous solution of the precursor seed crystals to adjust the alkalinity, then add a nickel-cobalt mixed salt solution and a precipitant solution, and control the fluid-to-solid ratio at 0.35-0.80 for the first 2-10 hours. Stop the reaction when the particle size reaches 12-20 μm. After solid-liquid separation, aging, and drying, the precursor is obtained.

[0036] Preferably, the precipitant solution is selected from sodium hydroxide solution, and the concentration of the precipitant solution is 4~10 mol / L.

[0037] Preferably, the complexing agent solution is selected from ammonia solution, and the concentration of the complexing agent solution is 2~10 mol / L, for example 4~8 mol / L.

[0038] Preferably, the protective gas includes at least one of nitrogen and argon.

[0039] Preferably, in step S1, the alkalinity is adjusted to 2~4 g / L.

[0040] Preferably, in step S1, a nickel-cobalt mixed salt solution and a precipitant solution with a volume ratio of 1:0.3~0.4 are introduced to carry out the nucleation stage reaction.

[0041] Preferably, in step S2, the alkalinity is adjusted to 7~9 g / L.

[0042] Preferably, in step S2, a nickel-cobalt mixed salt solution and a precipitant solution with a volume ratio of 1:0.3~0.4 are introduced in parallel.

[0043] Preferably, in step S2, the fluid-to-solid ratio is controlled to be 0.4 to 0.7 for the first 2 to 6 hours.

[0044] Preferably, in step S2, the reaction is stopped when the particle size reaches 14.5~18 μm (e.g., 14.5~15.5 μm).

[0045] In some embodiments of the present invention, the particle size of the second nickel-cobalt oxide precursor is 1.5 to 5.5 μm, for example 2.5 to 3.5 μm.

[0046] In some embodiments of the present invention, the second nickel-cobalt oxide precursor Ni x’ Co y’ (OH)2 is prepared by the following steps:

[0047] Adjust the alkalinity of the complexing agent solution with water, then mix it with the precipitant solution to adjust the pH of the reaction system to 11-13 and the alkalinity to 5-25 g / L (e.g., 15-20 g / L). Introduce a protective gas, then introduce a nickel-cobalt mixed salt solution and the precipitant solution, maintaining the alkalinity at 5-25 g / L (e.g., 15-20 g / L). Decrease the pH value to 11-12 at a rate of 0.1-0.5 per hour, then maintain a constant pH. Stop the reaction when the particle size reaches 2.5-4.5 μm (e.g., 2.5-3.5 μm). Separate the solid and liquid components, age, and dry to obtain the final product.

[0048] Preferably, the precipitant solution is selected from sodium hydroxide solution, and the concentration of the precipitant solution is 4~10 mol / L.

[0049] Preferably, the complexing agent solution is selected from ammonia solution, and the concentration of the complexing agent solution is 2~10 mol / L, for example 4~6 mol / L.

[0050] Preferably, the alkalinity is adjusted to 12-16 g / L, for example, 12-15 g / L.

[0051] Preferably, the protective gas includes nitrogen or argon.

[0052] Preferably, the volume ratio of the nickel-cobalt mixed salt solution to the precipitant solution is 1:0.3~0.4.

[0053] In some embodiments of the present invention, the first lithium source and the second lithium source each independently include hydrated lithium and / or anhydrous lithium hydroxide, such as lithium hydroxide monohydrate.

[0054] In some embodiments of the present invention, the first additive containing M and the second additive containing M each independently include at least one of the following: oxide, hydroxide, sulfate, hydrochloride, nitrate, and carbonate of M.

[0055] In some embodiments of the present invention, the first additive containing Al and the second additive containing Al each independently include at least one of Al2O3, Al2(SO4)3, AlCl3, Al(NO3)3, Al2(CO3)3, Al(OH)3, NaAlO2, and KAlO2.

[0056] In some embodiments of the present invention, the temperature of the first stage of the heat preservation platform in the first sintering and the second sintering is independently any value within the range of 250~400 ℃, for example, 300~400 ℃ or 300~350 ℃; the heat preservation time of the first stage of the heat preservation platform is independently 1~3 h, for example, 1~2.5 h, 1~2 h, or 1~1.5 h; and the heating rate of the first stage of the heat preservation platform is independently 2~10 ℃ / min, for example, 3~8 ℃ / min, 4~6 ℃ / min, or 5 ℃ / min. The first stage of heat preservation in the present invention can remove moisture from the raw materials and enhance the contact between solid powders (precursor, lithium hydroxide, and additives). If the heat preservation temperature is too low, it cannot effectively remove moisture from the raw materials; if it is too high, moisture evaporation and diffusion will occur simultaneously, affecting the effectiveness of the diffusion process.

[0057] In some embodiments of the present invention, the temperatures of the second-stage holding platforms in the first and second sintering processes are each independently set to any value within the range of 450–600 °C, for example, 500–600 °C or 500–550 °C; the holding times of the second-stage holding platforms are each independently set to 2–5 h, for example, 2–4 h or 2–3 h; and the heating rates of the second-stage holding platforms are each independently set to 1–10 °C / min, for example, 2–5 °C / min. The second-stage holding in the present invention ensures sufficient contact and diffusion between the precursor and lithium hydroxide and additives. If the holding temperature is too low, sufficient diffusion is impossible; if it is too high, the formal lithiation process will occur directly.

[0058] In some embodiments of the present invention, the temperature of the third heat preservation platform in the first sintering and the second sintering is independently 700~760 ℃, for example, 700~750 ℃, 710~740 ℃, 720~730 ℃, or 725~730 ℃; the heat preservation time of the third heat preservation platform is independently 9~16 h, for example, 10~15 h or 10~12 h; and the heating rate of the third heat preservation platform is independently 1~10 ℃ / min, for example, 2~5 ℃ / min.

[0059] In some embodiments of the present invention, the aerobic environment has an oxygen concentration of ≥85%, preferably ≥95%, and more preferably ≥99%.

[0060] According to another aspect of the present invention, a positive electrode is provided, the positive electrode comprising a current collector and a positive electrode film, wherein the raw materials for preparing the positive electrode film include the modified high-nickel positive electrode material as described above.

[0061] According to another aspect of the present invention, a lithium secondary battery is provided, the lithium secondary battery comprising a separator, an electrolyte, a negative electrode, and a positive electrode as described above.

[0062] According to some embodiments of the present invention, at least the following beneficial effects are achieved:

[0063] The modified high-nickel cathode material prepared by this invention has high cycle retention rate, low impedance, and high rate cycling performance. In addition, the preparation method of this invention is simple and easy to industrialize.

[0064] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0065] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0066] Figure 1 This is a cross-sectional SEM image of the matrix material according to an embodiment of the present invention;

[0067] Figure 2 This is a cross-sectional SEM image of a precursor material according to an embodiment of the present invention;

[0068] Figure 3 This is an electron probe microanalysis pattern of a matrix material according to an embodiment of the present invention, wherein A is a cross-sectional morphology of the matrix material and B is a distribution map of aluminum in the matrix material. Detailed Implementation

[0069] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0070] Unless otherwise specified, the word "and / or" in this invention is used to indicate that one or both of the described situations may occur. For example, A and / or B includes (A and B) and (A or B).

[0071] Unless otherwise specified, in this invention, "about" means that the allowable error is within ±20%, further, within ±10%, and even further, within ±5%.

[0072] Unless otherwise specified, "room temperature" in this invention means (25±5)℃.

[0073] Unless otherwise specified, the porosity of different regions in this invention is calculated using ImageJ according to the formula "porosity = pore area of ​​each region / cross-sectional area of ​​each region × 100%".

[0074] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0075] Example 1

[0076] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is composed of large particles and small particles. The particle size Dv50 of the large particles is about 15.5 μm, and the particle size Dv50 of the small particles is about 4.4 μm.

[0077] Both large and small particles have a secondary spherical structure and are composed of a matrix material and a coating material attached to the surface of the matrix material.

[0078] Both the large and small particles have the chemical formula Li. 1.01 Ni 0.881 Co 0.099 Al 0.017 Zr 0.003 O2;

[0079] like Figure 1 As shown, the matrix material of large particles consists of a core, an intermediate layer, and an outer layer from the inside out. The core has a radius of about 2.04 μm and a porosity of about 0.1%; the intermediate layer has a thickness of about 2.34 μm and a porosity of about 5%; and the outer layer has a thickness of about 2.43 μm and a porosity of about 0.7%.

[0080] This embodiment also provides a method for preparing the above-mentioned modified high-nickel nickel-cobalt-aluminum ternary cathode material:

[0081] (1) The first nickel-cobalt oxide (Ni) with a three-layer structure 0.9 Co 0.1 Preparation of (OH)2 precursor:

[0082] S1: Based on the molecular formula Ni 0.9 Co 0.1 Prepare a mixed salt solution of nickel sulfate and cobalt sulfate with a total nickel and cobalt concentration of 2 mol / L using (OH)2;

[0083] S2: Add pure water to the reactor, filling 2 / 3 of its volume. Add 6 mol / L ammonia solution (complexing agent solution) to adjust the alkalinity to 3 g / L. Then add 10 mol / L sodium hydroxide solution (precipitant solution) to adjust the pH to 11.5. Purge with nitrogen for protection. Flow the prepared salt solution and precipitant solution into the reactor in a volume ratio of 1:0.35 to carry out the nucleation stage reaction. Decrease the pH by 0.30 every 60 min. After the reaction pH reaches 10.60, maintain the pH to allow particle growth until the particle Dv50 reaches 5.0 µm. Stop the reaction and perform solid-liquid separation to obtain precursor seed crystals.

[0084] S3: Add pure water to the reactor, filling 2 / 3 of its volume. Start stirring and heat to 60°C. Then add the precursor seed crystals obtained in step S2. Add 6 mol / L ammonia solution to adjust the alkalinity to 8 g / L. Introduce a mixed metal salt solution and precipitant solution in a 1:0.38 volume ratio concurrently into the reactor. Control the flow-to-solid ratio (i.e., the flow rate of the salt solution per hour (L / h) ÷ the solid content in the reactor (g / L)) to approximately 0.60 for the first 3 hours to obtain a product with a special cyclic structure. Further react until the particle size reaches the target Dv50 (15.3 μm), then stop the reaction. Aging, washing, filtering, and drying of the reaction slurry yields the following product: Figure 2 The first nickel-cobalt oxide (Ni) shown has a three-layer structure. 0.9 Co 0.1 (OH)2) precursor;

[0085] (2) Second nickel-cobalt oxide (Ni 0.9 Co 0.1 Preparation of (OH)2 precursor:

[0086] Pure water, filling 2 / 3 of the reactor volume, was added to the reactor. A 6 mol / L ammonia solution was added to adjust the alkalinity to 15 g / L. Then, a 10 mol / L sodium hydroxide solution (precipitant solution) was added to adjust the pH of the reaction system to 12.3. After introducing the alkaline solution, the alkalinity of the system was measured to be 18 g / L. Nitrogen gas was introduced for protection. A prepared nickel-cobalt mixed salt solution and precipitant solution were introduced into the reactor at a volume ratio of 1:0.38. The ammonia flow rate was adjusted to maintain the alkalinity at 18 g / L. The pH was decreased by 0.30 per hour until it reached 11.70, after which the pH was maintained constant. The reaction was stopped when the particle size reached approximately 3 μm. After solid-liquid separation, aging, and drying, a second nickel-cobalt oxide (Ni) with a particle size Dv50 of approximately 2.9 μm was obtained. 0.9 Co 0.1 (OH)2) precursor;

[0087] (3) Weigh and prepare various raw materials according to the element ratio in the above chemical formula of positive electrode material;

[0088] (4) In an aerobic environment (oxygen concentration of 99%), the first nickel-cobalt oxide (Ni) with a three-layer structure and a particle size Dv50 of 15.3 μm prepared in (1) is subjected to a process that involves the reaction of the first nickel-cobalt oxide (Ni) with a three-layer structure and a particle size Dv50 of 15.3 μm. 0.9 Co 0.1 The precursor (OH)2, lithium hydroxide monohydrate (lithium source), zirconium oxide, and alumina are mixed and sintered once. During the sintering process, the diffusion rate of lithium hydroxide monohydrate and zirconium oxide after pyrolysis is faster than that of alumina after pyrolysis, so they can preferentially diffuse into the porous structure of the precursor. Therefore, after the precursor and its internal lithium hydroxide monohydrate, zirconium oxide, and alumina are sintered together, an internally doped matrix material is obtained. However, since the diffusion rate of alumina after pyrolysis is relatively slow, only a portion of Al can form internal doping, while a considerable portion of Al accumulates on the surface of the precursor and gradually forms a coating layer after sintering. After sintering, large particles with a particle size of about 15.5 μm are obtained.

[0089] The sintering process includes three holding platforms: the first holding platform is at 350 ℃, with a heating rate of 5 ℃ / min and a holding time of 1.5 h; the second holding platform is at 550 ℃, with a heating rate of 2 ℃ / min and a holding time of 3.0 h; and the third holding platform is at 727 ℃, with a heating rate of 2 ℃ / min and a holding time of 12.0 h.

[0090] (5) In an aerobic environment (oxygen concentration of 99%), the second nickel-cobalt oxide (Ni) with a particle size Dv50 of 2.9 μm obtained in (2) is subjected to... 0.9 Co 0.1 (OH)2) precursor, lithium hydroxide monohydrate (lithium source), zirconium oxide, and alumina are mixed and sintered once; during the sintering process, since the temperature of the third stage heat preservation platform is lower than that in step (4), the diffusion rate of lithium hydroxide monohydrate and zirconium oxide after pyrolysis is faster than that of alumina after pyrolysis. Therefore, the precursor and the fast-diffusion lithium hydroxide monohydrate, zirconium oxide, and alumina are sintered together to obtain the matrix material; while since the diffusion rate of alumina after pyrolysis is slower, only a portion of Al enters the matrix material, and a considerable portion of Al accumulates on the outermost surface, gradually forming a coating layer after sintering; after sintering, small particles with a particle size of about 4.4 μm are obtained;

[0091] The sintering process consists of three holding platforms: the first holding platform is at 350 ℃, with a heating rate of 5 ℃ / min and a holding time of 1.5 h; the second holding platform is at 550 ℃, with a heating rate of 2 ℃ / min and a holding time of 3.0 h; and the third holding platform is at 719 ℃ (the third holding temperature for small particles is about 10 ℃ lower than that for large particles to prevent over-sintering and adhesion), with a heating rate of 2 ℃ / min and a holding time of 12 h.

[0092] (6) After sintering the large particles and small particles separately, they are mixed in a ratio of 8:2.

[0093] It should be noted that there is no sequential relationship between steps (1) and (2), and steps (4) and (5). The numbering is only for the convenience of explanation.

[0094] Depend on Figure 3 It can be seen that the alumina in both large and small particles diffuses from the surface to the inside, forming a gradient doping from the outside to the inside, and forming a fast ion conductor coating on the surface.

[0095] Example 2

[0096] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is basically the same as that in Example 1, except that the chemical formula of the matrix material in both large and small particles is Li. 1.01 Ni 0.881 Co 0.099 Al 0.017 Sr 0.003 O2.

[0097] The preparation method of this embodiment is basically the same as that of Example 1, except that zirconium oxide in (4) and (5) is replaced with strontium oxide.

[0098] Example 3

[0099] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is basically the same as that in Example 1, except that the chemical formula of the matrix material in both the large and small particles is Li. 1.01 Ni 0.86 Co 0.099 Al 0.038 Zr 0.003 O2.

[0100] The preparation method in this embodiment is basically the same as that in Example 1, the only difference being: (3) refers to Li 1.01 Ni 0.86 Co 0.099 Al 0.038 Zr 0.003 The elemental ratios in O2 are used to weigh and prepare various raw materials.

[0101] Example 4

[0102] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is basically the same as that in Example 1, except that the particle size Dv50 of the large particles is about 15.5 μm and the particle size Dv50 of the small particles is about 5.5 μm.

[0103] The preparation method of this embodiment is basically the same as that of Example 1, except that: (2) the reaction is stopped after the particles grow to a particle size of about 4.5 μm.

[0104] Example 5

[0105] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is the same as in Embodiment 1.

[0106] The preparation method of this embodiment is basically the same as that of Example 1, except that in (6), large particles and small particles are sintered separately and then mixed, with a mixing ratio of 9:1.

[0107] Example 6

[0108] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, the preparation method of which is basically the same as that in Example 1, the only difference being:

[0109] In step (4), the first sintering includes three heat preservation platforms: the first heat preservation platform is 250 ℃, the heating rate is 3.5 ℃ / min, and the heat preservation time is 1.5 h; the second heat preservation platform is 450 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 3 h; the third heat preservation platform is 757 ℃, the heating rate is 3.5 ℃ / min, and the heat preservation time is 12 h.

[0110] In step (5), the first sintering includes three heat preservation platforms: the first heat preservation platform is 250 ℃, the heating rate is 3.5 ℃ / min, and the heat preservation time is 1.5 h; the second heat preservation platform is 450 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 3 h; the third heat preservation platform is 739 ℃, the heating rate is 3.5 ℃ / min, and the heat preservation time is 12 h.

[0111] Example 7

[0112] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, the preparation method of which is basically the same as that in Example 1, the only difference being:

[0113] In step (4), the first sintering includes three heat preservation platforms: the first heat preservation platform is 350 ℃, the heating rate is 5 ℃ / min, and the heat preservation time is 4.5 h; the second heat preservation platform is 550 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 5.0 h; the third heat preservation platform is 727 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 9 h.

[0114] In step (5), the sintering process includes three heat preservation platforms: the first heat preservation platform is 350 ℃, the heating rate is 5 ℃ / min, and the heat preservation time is 4.5 h; the second heat preservation platform is 550 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 5.0 h; and the third heat preservation platform is 719 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 9 h.

[0115] Example 8

[0116] This embodiment provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, the preparation method of which is the same as in Example 1, the only difference being:

[0117] In step (4), the sintering process includes three heat preservation platforms: the first heat preservation platform is 350 ℃, the heating rate is 5 ℃ / min, and the heat preservation time is 1.5 h; the second heat preservation platform is 550 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 3 h; the third heat preservation platform is 850 ℃, the heating rate is 3.5 ℃ / min, and the heat preservation time is 12 h.

[0118] In step (5), the sintering process includes three heat preservation platforms: the first heat preservation platform is 350 ℃, the heating rate is 5 ℃ / min, and the heat preservation time is 1.5 h; the second heat preservation platform is 550 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 3 h; the third heat preservation platform is 840 ℃, the heating rate is 3.5 ℃ / min, and the heat preservation time is 12 h.

[0119] Comparative Example 1

[0120] This comparative example provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is basically the same as that in Example 1, except that the particle size Dv50 is about 15.5 μm.

[0121] The preparation method of this comparative example is basically the same as that of Example 1, except that (2) and (5) are omitted.

[0122] Comparative Example 2

[0123] This comparative example provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is basically the same as Example 1, except that the particle size Dv50 is about 4.4 μm.

[0124] The preparation method of this comparative example is basically the same as that of Example 1, except that (1) and (4) are omitted.

[0125] Comparative Example 3

[0126] This comparative example provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, which is basically the same as that in Example 1, except that the chemical formula of the matrix material in both large and small particles is Li. 1.01 Ni 0.884 Co 0.099 Al 0.017 O2.

[0127] The preparation method of this comparative example is basically the same as that of Example 1, except that zirconium oxide is omitted in (4) and (5).

[0128] Comparative Example 4

[0129] This comparative example provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, the preparation method of which is the same as in Example 1, the only difference being: (1) is:

[0130] S1: Based on the molecular formula Ni 0.9 Co 0.1 Prepare a mixed salt solution of nickel sulfate and cobalt sulfate with a total nickel and cobalt concentration of 2 mol / L using (OH)2.

[0131] S2: Add pure water to the reactor, along with 10 mol / L sodium hydroxide solution (precipitant solution) and 6 mol / L ammonia solution (complexing agent solution) to adjust the ammonia concentration to 5.5 g / L and the pH to 12. Purge with nitrogen to raise the reaction temperature to 60 ℃, and then introduce the mixed salt solution, precipitant solution, and complexing agent solution for reaction. Initially, control the flow rate of the mixed salt solution at 100 L / h, gradually increasing the flow rate of the metal salt solution to 400 L / h at the reaction endpoint. Simultaneously adjust the flow rates of the precipitant solution and complexing agent solution until the pH reaches 11.2 at the reaction endpoint, yielding seed crystals with a D50 of approximately 3.5 μm.

[0132] S3: Add pure water to the reactor, add 120 kg of the dehydrated dry base material of the above-mentioned seed crystals, add precipitant solution and complexing agent solution, adjust the ammonia concentration to 8 g / L and the pH value to 10.85; purge with nitrogen gas to raise the reaction temperature in the reactor to 60 ℃, and introduce the mixed salt solution, precipitant solution and complexing agent solution to carry out the reaction. During the reaction, maintain the pH value of the system at 10.85, and feed the metal salt solution at a flow rate of 100 L / h. After the pH value of the reaction system stabilizes, immediately increase the flow rate of the mixed salt solution to 200 L / h, and simultaneously raise the temperature of the reaction system to about 75 ℃ at a heating rate of 1 ℃ / 10 min. Then gradually increase the flow rate of the metal salt solution to the final flow rate of 700 L / h, until the product particle size D50 is 12.5 μm; age, wash, filter and dry the reaction slurry to obtain the precursor.

[0133] (2)-(6) Same as Example 1.

[0134] Although the precursor prepared in Comparative Example 4 has a core, intermediate layer and outer layer structure, the porosity of the outer layer is greater than that of the intermediate layer and the core.

[0135] Comparative Example 5

[0136] This comparative example provides a modified high-nickel nickel-cobalt-aluminum ternary cathode material, the preparation method of which is the same as in Example 1, the only difference being:

[0137] In steps (4) and (5), the first sintering includes three heat preservation platforms: the first heat preservation platform is 350 ℃, the heating rate is 5 ℃ / min, and the heat preservation time is 1.5 h; the second heat preservation platform is 550 ℃, the heating rate is 2 ℃ / min, and the heat preservation time is 3.0 h; the third heat preservation platform is 650 ℃, the heating rate is 1 ℃ / min, and the heat preservation time is 12.0 h.

[0138] Test case

[0139] The electrochemical performance, including cycle performance and rate performance, of the modified high-nickel nickel-cobalt-aluminum ternary cathode materials prepared in Examples 1-8 and Comparative Examples 1-5 was tested. The specific test steps and results are as follows:

[0140] The cycle performance test method is as follows: At 25 ℃, the charge / discharge cycle characteristics of the coin cell were tested using a Blue Electric test cabinet, with 1 C = 195 mA / g set. Charging was performed at a 1 C rate, followed by discharging at a 2 C rate within a voltage range of 3.0 V to 4.3 V. Specifically, the cells were charged at a constant current of 1 C to 4.3 V, then charged at a constant voltage of 4.3 V until the cutoff current reached 0.02 C. After a 5-minute rest, the cells were discharged at 2 C to 3.0 V, and then rested for another 5 minutes. The charge / discharge capacity after the first cycle was recorded. This process was repeated 100 times, and the charge / discharge capacity after the 100th cycle was recorded. Cycle capacity retention (%) = (Discharge capacity after 100 cycles / Discharge capacity after 1st cycles) × 100%.

[0141] The rate performance test method is as follows: Button cells were tested in a Blue Electric test cabinet at 25 ℃. 1 C = 195 mA / g was set, and charging / discharging was performed at 0.1 C within a voltage range of 3.0 V to 4.3 V. Specifically, the cells were charged at a constant current of 0.1 C to 4.3 V, then charged at a constant voltage of 4.3 V to a cutoff current of 0.02 C, rested for 5 min, and then discharged at 0.1 C to 3.0 V, rested for 5 min, and the charge / discharge capacity was recorded. This test was then performed continuously at 0.2 C, 0.5 C, 1 C, and 2 C, and the charge / discharge capacity was recorded. The reversible capacity ratio at 2 C / 0.1 C rate was calculated.

[0142] The test results are shown in Table 1 below.

[0143] Table 1

[0144]

[0145] The above description provides a detailed account of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

Claims

1. A modified high-nickel positive electrode material, characterized by, The modified high-nickel positive electrode material comprises large particles with a Dv50 of d1 and small particles with a Dv50 of d2, and d1 is 12-20 μm and d2 is 1.5-5.5 μm; Both the large particles and the small particles have a secondary spherical structure and comprise a base material and a coating material attached to the surface of the base material; the large particles and the small particles each independently have a chemical formula of Li a Ni x Co y Al w M z O2, where 0.9≤a≤1.1, 0.80≤x≤0.95, 0.05≤y≤0.20, 0.005≤w≤0.04, 0<z≤0.01, x+y+w+z=1, and M is selected from at least one of Zr, Sr, Ca, Mg, Ba, Y, Nb, Ti, Mo, Sn, Ta, Sb, Bi, and W. The base material of the large particles comprises an inner core, an intermediate layer and an outer layer from inside to outside, and the porosity φ2 of the intermediate layer is greater than the porosity φ3 of the outer layer and the porosity φ1 of the inner core; and φ1 is 0-0.5%, φ2 is 2%-11%, and φ3 is 0.3%-2.0%; The base material of the large particles and / or the base material of the small particles has a decreasing Al element concentration gradient from outside to inside; The modified high-nickel positive electrode material is prepared by the following preparation method: In an oxygen environment, a first nickel-cobalt oxide precursor, a first lithium source, a first M-containing additive and a first Al-containing additive are mixed and subjected to first sintering to obtain the large particles; In an oxygen environment, a second nickel-cobalt oxide precursor, a second lithium source, a second M-containing additive and a second Al-containing additive are mixed and subjected to second sintering to obtain the small particles; The large particles and the small particles are mixed in a certain proportion to obtain the modified high-nickel positive electrode material; The first nickel-cobalt oxide precursor comprises a central region, an intermediate region and an outer region from inside to outside, and the porosity of the intermediate region is greater than the porosities of the outer region and the central region; The first sintering and the second sintering each independently comprise three-stage holding platforms, wherein the temperature of the third-stage holding platform is any value in the range of 700-760 ℃, and the temperature of the third-stage holding platform in the first sintering is higher than that in the second sintering. 2.The modified high-nickel positive electrode material according to claim 1, characterized in that, The coating material of the large particles and / or the coating material of the small particles comprises at least one of elements Al, Co, Ti, W, B and Nb. 3.The modified high-nickel positive electrode material of claim 1, characterized in that, The mass ratio of the large particles to the small particles is 1-9:

1. 4.The modified high-nickel positive electrode material of claim 1, characterized in that, In the base material of the large particles, the radius of the inner core is 0.5-3 μm, the thickness of the intermediate layer is 1.5-4 μm, and the thickness of the outer layer is 1.5-5 μm. 5.The modified high-nickel positive electrode material of claim 1, wherein, The base material of the small particles is in a hollow structure or a solid structure. 6.The modified high-nickel positive electrode material of claim 1, wherein, The first M-containing additive and the second M-containing additive each independently comprise at least one of oxides, hydroxides, sulfates, hydrochlorides, nitrates and carbonates of M; and / or, The first Al-containing additive and the second Al-containing additive each independently comprise at least one of Al2O3, Al2(SO4)3, AlCl3, Al(NO3)3, Al2(CO3)3, Al(OH)3, NaAlO2 and KAlO2.

7. Use of the modified high-nickel positive electrode material according to any one of claims 1 to 6 in the production of a lithium secondary battery, characterized in that, The lithium secondary battery comprises a separator, an electrolyte, a negative electrode sheet and a positive electrode sheet; and the raw material for preparing the positive electrode sheet comprises the modified high-nickel positive electrode material.

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