Nickel-based ternary positive electrode material, preparation method thereof, positive electrode sheet, secondary battery and electric device

Abstract

The application provides a nickel-based ternary positive electrode material and a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. The nickel-based ternary positive electrode material comprises: a nickel-based positive electrode material substrate containing a boron element, wherein the molecular formula of the nickel-based positive electrode material substrate containing the boron element is LiNi x1 Co y1 Mn z1‑a B a O2, x1+y1+z1+a=1, 0<x1<1, 0<y1<1, 0<z1<1, 0<a<0.5; and a coating layer coated on at least part of the surface of the nickel-based positive electrode material substrate containing the boron element, wherein the coating layer contains a lithium phosphate salt with a molecular formula of Li b M c P d O4, 0

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and particularly to a nickel-based ternary cathode material, a preparation method thereof, a cathode pole piece, a secondary battery, and an electrical device using the same. Background Art

[0002] Secondary batteries represented by lithium-ion batteries have advantages such as high energy density, high safety, and high power density, and have been widely used in fields such as electric vehicles and electronic devices. With the continuous development of the new energy industry, people's requirements for the energy density and safety of secondary batteries are also increasing. Currently, in traditional secondary batteries, ternary materials such as nickel, cobalt, and manganese are widely used as cathode materials due to their advantages such as high capacity and energy density. However, secondary batteries containing ternary cathode materials such as nickel, cobalt, and manganese have problems of poor rate performance and cycling performance. Summary of the Invention

[0003] Based on this, the present application provides a nickel-based ternary cathode material, a preparation method thereof, a cathode pole piece, a secondary battery, and an electrical device using the same, which can improve the rate performance and cycling performance of the secondary battery.

[0004] The first aspect of the present application provides a nickel-based ternary cathode material, comprising:

[0005] A nickel-based cathode material matrix containing boron element, wherein the molecular formula of the nickel-based cathode material matrix containing boron element is LiNi x1 Co y1 Mn z1-a B a O2, where x1 + y1 + z1 + a = 1, 0 < x1 < 1, 0 < y1 < 1, 0 < z1 < 1, 0 < a < 0.5; and

[0006] A coating layer covering at least a part of the surface of the nickel-based cathode material matrix containing boron element, wherein the coating layer contains a lithium phosphate salt with the molecular formula Li b M c P d O4, 0 < b < 5, 0 < c < 5, 0 < d < 5.

[0007] In some embodiments of the present application, the nickel-based ternary cathode material satisfies at least one of the following conditions:

[0008] (1) The molecular formula of the nickel-based cathode material matrix containing boron element is LiNi x1 Co y1 Mn z1-a B a O2, wherein x1 + y1 + z1 + a = 1, 0 < x1 < 1, 0 < y1 < 1, 0 < z1 < 1, 0 < a < 0.5;

[0009] (2) The boron element in the nickel-based ternary cathode material accounts for 0.1% to 10% by mass, and optionally, the boron element in the nickel-based ternary cathode material accounts for 1% to 8% by mass;

[0010] (3) The phosphorus element in the coating layer accounts for 0.1% to 10% of the mass of the nickel-based ternary cathode material.

[0011] Optionally, the phosphorus element in the coating layer accounts for 1% to 8% of the mass of the nickel-based ternary cathode material.

[0012] In some embodiments of this application, the nickel-based ternary cathode material satisfies at least one of the following conditions:

[0013] (1) The thickness of the coating layer is 0.5 nm to 50 nm, and optionally, the thickness of the coating layer is 5 nm to 45 nm;

[0014] (2) The average particle size D50 of the nickel-based ternary cathode material is 4 μm to 15 μm;

[0015] (3) The powder compaction density of the nickel-based ternary cathode material at 150 MPa is 3.20 g / cm³. 3 The above can be selected as 3.20g / cm. 3 ~3.50g / cm 3 .

[0016] The second aspect of this application provides a method for preparing a nickel-based ternary cathode material, comprising:

[0017] Pre-calcination treatment was performed on precursor powder containing nickel-cobalt-manganese ternary precursors and boric acid to obtain pre-calcined material;

[0018] The pre-calcined material is mixed with a lithium source and then subjected to a sintering process to obtain a boron-containing nickel-based cathode material matrix, wherein the molecular formula of the boron-containing nickel-based cathode material matrix is ​​LiNi. x1 Co y1 Mn z1-a B a O2, x1+y1+z1+a=1, 0 <x1<1,0<y1<1,0<z1<1,0<a<0.5;

[0019] The boron-containing nickel-based cathode material matrix is ​​mixed with metaphosphate and then subjected to a secondary sintering process to form a coating layer on at least a portion of the surface of the boron-containing nickel-based cathode material matrix, thereby obtaining a nickel-based ternary cathode material. The coating layer contains Li. b M c P dLithium phosphate of O4, 0 <b<5,0<c<5,0<d<5。

[0020] In some embodiments of this application, the preparation method satisfies at least one of the following conditions:

[0021] (1) The temperature of the pre-firing treatment is 200℃~600℃;

[0022] (2) The sintering time for the pre-sintering treatment is 3h to 12h;

[0023] (3) The heating rate of the pre-burning treatment is 1℃ / min to 4℃ / min.

[0024] In some embodiments of this application, the step of mixing the pre-burned material with a lithium source and then performing a sintering process includes:

[0025] The pre-burned material is mixed evenly with the lithium source to obtain a first mixture;

[0026] The first mixture is subjected to a single sintering treatment at 500℃~1000℃ for 3h~12h.

[0027] Optionally, the heating rate of the primary sintering process is 1°C / min to 5°C / min;

[0028] Optionally, the molar ratio of lithium in the lithium source to all transition elements in the pre-burned material is (1.0 to 1.1):1;

[0029] Optionally, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate.

[0030] In some embodiments of this application, the secondary sintering treatment following mixing the boron-containing nickel-based cathode material matrix with metaphosphate includes:

[0031] The boron-containing nickel-based cathode material matrix is ​​mixed evenly with the metaphosphate to obtain a second mixture;

[0032] The second mixture is subjected to a secondary sintering treatment at 600℃~1000℃ for 6h~18h;

[0033] Optionally, the heating rate of the secondary sintering treatment is 1℃ / min to 10℃ / min;

[0034] Optionally, the mass ratio of the boron-containing nickel-based cathode material matrix to the metaphosphate is 1:(0.0005-0.05), or optionally 1:(0.002-0.01).

[0035] Optionally, the molecular formula of the metaphosphate is MPO3, and M includes one or more of Al, Ti, Mg, Zr, Y, and W.

[0036] In some embodiments of the present application, the preparation method further includes the step of preparing the precursor powder:

[0037] Mix the nickel-cobalt-manganese ternary precursor and the boric acid in a solvent containing a dispersant to form a mixed solution;

[0038] After ball-milling the mixed solution, perform a drying treatment to obtain the precursor powder;

[0039] Optionally, the mass ratio of the nickel-cobalt-manganese ternary precursor, the dispersant, the solvent, and the boric acid is 1:(0.01 - 1):(0.5 - 10):(0.001 - 0.5).

[0040] Optionally, the average particle size D50 of the precursor powder is 2 μm to 15 μm.

[0041] In some embodiments of the present application, the preparation method satisfies at least one of the following conditions:

[0042] (1) The molecular formula of the nickel-cobalt-manganese ternary precursor is Ni x2 Co y2 Mn z2 (OH)2, where 0 < x2 < 1, 0 < y2 < 1, 0 < z2 < 1, and x2 + y2 + z2 = 1;

[0043] (2) The dispersant includes cetyltrimethylammonium chloride and / or dodecyltrimethylammonium bromide;

[0044] (3) The solvent includes one or more of pure water, isopropanol, ethanol, and acetone.

[0045] The third aspect of the present application provides a positive electrode sheet, including the nickel-based ternary positive electrode material of the first aspect of the present application or the nickel-based ternary positive electrode material prepared by the preparation method of the second aspect of the present application.

[0046] In some embodiments of the present application, the lithium-ion conductivity of the positive electrode sheet is above (8×10 -11 S / cm), and can be optionally (8×10 -11 S / cm) to (10×10 -11 S / cm).

[0047] The fourth aspect of the present application provides a secondary battery, including the positive electrode sheet of the third aspect of the present application.

[0048] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0049] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0050] The nickel-based ternary cathode material provided in this application includes a boron-containing nickel-based cathode material matrix and a coating layer containing lithium phosphate. Some boron in the nickel-based cathode material matrix exists at grain boundaries and in the shallow surface layer of the material. Because boron is electron-deficient, while phosphorus in the lithium phosphate coating layer is electron-rich, phosphorus and boron can form strong chemical bonds by phosphorus atoms donating excess paired electrons to boron atoms. Through this chemical bond interaction, phosphorus and boron can synergistically provide better structural support, enhancing the structural stability of the shallow surface layer of the material. This synergistic effect can enhance the mechanical strength and density of the coating layer, isolate the reaction between highly oxidized transition metal elements in the nickel-based ternary cathode material and the electrolyte, thereby reducing the formation of hydrofluoric acid and decreasing the dissolution of transition metal elements caused by hydrofluoric acid corrosion of the nickel-based ternary cathode material surface. This reduces the distortion of the surface structure of the nickel-based ternary cathode material caused by the dissolution of transition metal elements, thus improving the interfacial stability of the cathode. Meanwhile, the lithium-ion conductivity at the electrode interface is increased by about 15% compared to the lithium-ion conductivity of the traditional phosphate coating method, thus effectively reducing the increase in interface impedance and improving the rate performance and cycle performance of the secondary battery.

[0051] Furthermore, the preparation method provided in this application is simple to implement, the equipment is highly versatile, and it is easy to scale up production. More importantly, the nickel-based ternary cathode material prepared by this method has good structural stability. It can maintain the integrity of the crystal structure even under high rolling strength, and is not prone to grain boundary breakage. The material has high capacity, high and low temperature cycling performance, and rate performance. Attached Figure Description

[0052] Figure 1 The images show the XRD patterns of the nickel-based ternary cathode materials in Examples 1-2 and Comparative Examples 1-2.

[0053] Figure 2 The CP diagrams are of the nickel-based ternary cathode materials in Example 1 and Comparative Example 1 after 200 cycles.

[0054] Figure 3 The graphs show the rate performance test results of the lithium-ion batteries in Examples 1-2 and Comparative Examples 1-2. Detailed Implementation

[0055] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0056] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be noted that, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items, "above," "below," includes the stated number, and "one or more" with "multiple" means two or more.

[0058] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0059] At present, to improve the energy density of secondary batteries, it is usually achieved by reducing the primary grain size of the cathode material. That is, by reducing the size of the primary grains of the cathode material and using the secondary spherical particles formed by the smaller-sized primary grains as the cathode material of the secondary battery, the energy density of the secondary battery can be effectively improved. However, during the research process, the inventors found that the secondary spherical particles of the cathode material have the following disadvantages during the cycling process: (1) The secondary spherical particles are prone to breakage under high compaction conditions and during high-voltage charge and discharge processes, leading to an aggravation of side reactions; (2) The primary grains contained in the secondary spherical particles are usually arranged and grown disorderly, which easily causes the accumulation of structural stress during the lithium-ion insertion and extraction processes, resulting in the pulverization of the grains; (3) The primary grains contained in the secondary spherical particles have a small size, which will result in a large contact area between the electrode and the electrolyte, more electrode side reactions, and easily cause the dissolution of transition metals on the electrode surface. All of the above aspects are likely to cause the collapse of the microstructure and the cracking of grain boundaries of the cathode material after long-term cycling at high temperature and high voltage, thereby leading to a decline in the rate performance and cycling performance of the secondary battery. To solve the aforementioned technical problems, the inventors proposed the following technical solutions in this application.

[0060] In a first aspect of an embodiment of this application, a nickel-based ternary cathode material is provided, including: a nickel-based cathode material matrix containing a boron element, wherein the molecular formula of the nickel-based cathode material matrix containing a boron element is LiNi x1 Co y1 Mn z1- a B a O2, x1 + y1 + z1 + a = 1, 0 < x1 < 1, 0 < y1 < 1, 0 < z1 < 1, 0 < a < 0.5; and a coating layer covering at least a part of the surface of the nickel-based cathode material matrix containing a boron element, wherein the coating layer contains a lithium b M c P d O4 lithium phosphate salt, 0 < b < 5, 0 < c < 5, 0 < d < 5.

[0061] The nickel-based ternary cathode material provided in this application includes a boron-containing nickel-based cathode material matrix and a coating layer containing lithium phosphate. Some of the boron in the nickel-based cathode material matrix exists at grain boundaries and in the shallow surface layer of the material. Because boron is electron-deficient, while phosphorus in the lithium phosphate coating layer is electron-rich, phosphorus and boron can form strong chemical bonds through electron pairing. Utilizing this chemical bond, phosphorus and boron can synergistically enhance the density and uniformity of the coating layer, thereby increasing its strength. This results in a material with high compaction density. Under high compaction strength, the electrode can maintain the integrity of the coating without grain boundary breakage. The capacity, high and low temperature cycling performance, and rate performance of the material are significantly superior to those of traditional doping methods. In addition, it helps stabilize the electrode / electrolyte interface of the secondary battery cathode, isolates the reaction between high oxidation state transition metal elements in the nickel-based ternary cathode material and the electrolyte, thereby reducing the formation of hydrofluoric acid and reducing the dissolution of transition metal elements caused by hydrofluoric acid corrosion of the nickel-based ternary cathode material surface. This weakens the distortion of the surface structure of the nickel-based ternary cathode material caused by the dissolution of transition metal elements, thereby improving the interface stability of the cathode and thus improving the rate performance and cycle performance of the secondary battery.

[0062] In the nickel-based ternary cathode material provided in this application, the role of boron is mainly to dope into the bulk structure. In the layered transition metal layer, there are still many empty orbitals, which can be considered as boron atoms occupying some of the metal's empty orbitals. Therefore, the boron content can be determined by EDS testing, allowing the molecular formula of the nickel-based cathode material matrix to be expressed as: LiNi x1 Co y1 Mn z1-a B a O2. The coating layer contains phosphate Li. b M c P d The specific content and elemental ratio of O4 can be analyzed by photoelectron spectroscopy (XPS), or the Li / P ratio after coating the material surface can be simply determined by EDS, thereby inferring the composition of the coating layer.

[0063] In some embodiments, the boron element constitutes 0.1% to 10% of the mass of the nickel-based ternary cathode material. For example, the mass percentage of boron in the nickel-based ternary cathode material can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or any range thereof. Optionally, the mass percentage of boron in the nickel-based ternary cathode material is 1% to 8%.

[0064] In some embodiments, the phosphorus element in the coating layer accounts for 0.1% to 10% of the mass of the nickel-based ternary cathode material. For example, the mass percentage of phosphorus element in the nickel-based ternary cathode material can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or any range thereof. Optionally, the mass percentage of phosphorus element in the coating layer in the nickel-based ternary cathode material is 1% to 8%.

[0065] When the mass ratio of boron and phosphorus in nickel-based ternary cathode materials is within a suitable range, it is beneficial to enhance the synergistic effect between the two elements, thereby enhancing the density, uniformity, and strength of the coating layer, and further improving the rate performance and cycle performance of the secondary battery.

[0066] In some embodiments, the thickness of the coating layer is 0.5 nm to 50 nm. Optionally, the thickness of the coating layer is 5 nm to 45 nm. A coating layer thickness within a suitable range effectively isolates the nickel-based ternary cathode material from direct contact with the electrolyte without affecting the insertion / extraction of active ions such as lithium ions.

[0067] In some embodiments, the average particle size D50 of the nickel-based ternary cathode material is 4 μm to 15 μm.

[0068] In some embodiments, the powder compaction density of the nickel-based ternary cathode material at 150 MPa is 3.20 g / cm³. 3 The above can be selected as 3.20g / cm. 3 ~3.50g / cm 3 .

[0069] A second aspect of this application provides a method for preparing a nickel-based ternary cathode material, which may include the following steps:

[0070] S10. Pre-calcining treatment is performed on the precursor powder containing nickel-cobalt-manganese ternary precursor and boric acid to obtain pre-calcined material;

[0071] S20. The pre-burned material is mixed with a lithium source and then subjected to a sintering process to obtain a boron-containing nickel-based cathode material matrix, wherein the molecular formula of the boron-containing nickel-based cathode material matrix is ​​LiNi. x1 Co y1 Mn z1-a B a O2, x1+y1+z1+a=1, 0 <x1<1,0<y1<1,0<z1<1,0<a<0.5;

[0072] S30. The boron-containing nickel-based cathode material matrix is ​​mixed with metaphosphate and then subjected to a secondary sintering treatment to form a coating layer on at least a portion of the surface of the boron-containing nickel-based cathode material matrix, thereby obtaining a nickel-based ternary cathode material, wherein the coating layer contains Li. b M c P d Lithium phosphate of O4, 0 <b<5,0<c<5,0<d<5。

[0073] The preparation method provided in this application incorporates boric acid as a flux during the preparation process. Due to the low melting point of boric acid, it forms a liquid phase during sintering, providing a liquid flow environment for the nickel-cobalt-manganese ternary precursor. This liquid flow environment facilitates the diffusion of the nickel-cobalt-manganese ternary precursor. Simultaneously, the boric acid in the liquid phase can be adsorbed on the surface of the precursor, reducing the interfacial energy of the precursor and thus lowering the grain boundary fusion energy. This accelerates the diffusion rate of boron atoms into the nickel-cobalt-manganese ternary precursor and disperses some boron atoms at grain boundaries and in the shallow surface layer of the material, improving the structural stability of the material.

[0074] Furthermore, by leveraging the effect of boric acid in reducing grain boundary fusion energy, the directional growth of microcrystal nuclei in the ternary precursor can be achieved during the pre-sintering process. The directionally grown microcrystal nuclei can then achieve directional growth of crystal nuclei in the subsequent sintering process, thereby forming orderly arranged grains. This inhibits grain cracking and pulverization during material cycling, and improves the structural stability and cycling performance of the material.

[0075] Furthermore, by coating the material surface with metaphosphate to form a phosphate coating layer, a dense and uniform coating layer can be obtained through the synergistic effect of boron in the nickel-based cathode material matrix and phosphorus in the coating layer. This better isolates the direct contact reaction between the nickel-based ternary cathode material and the electrolyte, thereby reducing the formation of hydrofluoric acid and decreasing the dissolution of transition metal elements caused by hydrofluoric acid corrosion of the nickel-based ternary cathode material surface. This weakens the distortion of the surface structure of the nickel-based ternary cathode material caused by the dissolution of transition metal elements, thereby improving the interfacial stability of the cathode and ultimately improving the rate performance and cycle performance of the secondary battery.

[0076] In some embodiments, the preparation method may further include the following steps for preparing the precursor powder:

[0077] S410. The nickel-cobalt-manganese ternary precursor and the boric acid are mixed in a solvent containing a dispersant to form a mixture.

[0078] S420. The mixture is ball-milled and then dried to obtain the precursor powder.

[0079] In some embodiments, the mass ratio of the nickel-cobalt-manganese ternary precursor, the dispersant, the solvent, and the boric acid is 1:(0.01-1):(0.5-10):(0.001-0.5).

[0080] In some embodiments, the average particle size D50 of the precursor powder is 2 μm to 15 μm.

[0081] In some embodiments, the molecular formula of the nickel-cobalt-manganese ternary precursor is Ni. x2 Co y2 Mn z2 (OH)2, where 0 < x2 < 1, 0 < y2 < 1, 0 < z2 < 1, and x2 + y2 + z2 = 1.

[0082] In some embodiments, the dispersant comprises hexadecyltrimethylammonium chloride and / or dodecyltrimethylammonium bromide.

[0083] In some embodiments, the solvent includes one or more of pure water, isopropanol, ethanol, and acetone.

[0084] As a non-limiting example of preparing the precursor powder, a nickel-cobalt-manganese ternary precursor, a solvent, a dispersant and boric acid can be mixed, pretreated by wet ball milling, and then spray-dried to obtain the precursor powder.

[0085] After granulating the nickel-cobalt-manganese ternary precursor and flux boric acid with the aid of dispersant and solvent, liquid-phase mixing can help the flux boric acid enter the interior of the precursor particles and achieve uniform coverage on the precursor surface, thus improving the uniformity of mixing.

[0086] It should be noted that boric acid was chosen as the flux in this application because it has a low melting point and can melt into a liquid state at a relatively low temperature, forming a flowing liquid environment. This liquid environment facilitates the diffusion of boron atoms into the nickel-cobalt-manganese ternary precursor. Simultaneously, the liquid boric acid can be adsorbed onto the surface of the precursor, reducing its interfacial energy and increasing the reaction rate.

[0087] In some embodiments, the pre-firing temperature is between 200°C and 600°C. For example, the pre-firing temperature can be 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 450°C, or within any range of the above values.

[0088] In some embodiments, the sintering time of the pre-sintering treatment is 3h to 12h.

[0089] In some embodiments, the heating rate of the pre-firing treatment is 1°C / min to 4°C / min.

[0090] In this application, the pre-sintering treatment at the aforementioned lower temperature ensures the formation of a certain amount of initial crystal nuclei in the nickel-cobalt-manganese ternary precursor. Subsequently, lithium is further fused into these nuclei, leading to ordered growth and the formation of grains. If pre-sintering is not performed and high-temperature sintering is carried out directly, the excessively high growth energy may result in disordered grain growth, preventing the achievement of directional grain growth.

[0091] In some embodiments, the step of mixing the pre-burned material with a lithium source and then performing a sintering process may include the following steps:

[0092] S210. The pre-burned material is mixed evenly with the lithium source to obtain a first mixture;

[0093] S220. The first mixture is subjected to a single sintering treatment at 500℃~1000℃ for 3h~12h.

[0094] In some embodiments, the heating rate of the primary sintering process is 1°C / min to 5°C / min. For example, the heating rate of the primary sintering process can be 2°C / min, 3°C / min, 4°C / min, or within any of the above values.

[0095] Controlling the heating rate of the first sintering process within a suitable range helps to control the growth rate of crystal nuclei, making the structure of the crystal nuclei more complete, reducing the formation of defects in the grains, and improving the structural stability of nickel-based ternary cathode materials.

[0096] In some embodiments, the molar ratio of lithium in the lithium source to all transition elements in the pre-burned material is (1.0 to 1.1):1. Optionally, the molar ratio of lithium in the lithium source to all transition elements in the pre-burned material is 1.05.

[0097] In this application, the molar ratio of lithium to transition elements, namely Li / M, is used to design the sintering formula. The molar ratio of lithium to transition elements Li / M is controlled within a suitable range, so that excess lithium can be obtained during the sintering process. The excess lithium can help improve the electrochemical performance of nickel-based ternary cathode materials, such as suppressing the mixing and occupation of lithium-nickel Li / Ni.

[0098] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate.

[0099] In some embodiments, after the first mixture undergoes a sintering process, the sintered material may optionally be pulverized, sieved, and demagnetized to obtain a boron-containing nickel-based cathode material matrix, LiNi. x1 Co y1 Mn z1-a Ba O2, x1+y1+z1+a=1, 0 <x1<1,0<y1<1,0<z1<1,0<a<0.5。

[0100] In some embodiments, the pulverizing method may be one or more of the following: jaw crusher, roller mill, ball mill, mechanical pulverizer, air jet mill, and ball mill.

[0101] In some embodiments, the secondary sintering treatment following mixing the boron-containing nickel-based cathode material matrix with metaphosphate may include the following steps:

[0102] S310. The boron-containing nickel-based cathode material matrix is ​​mixed evenly with the metaphosphate to obtain a second mixture;

[0103] S320. The second mixture is subjected to a secondary sintering treatment at 600℃~1000℃ for 6h~18h.

[0104] In some embodiments, the heating rate of the secondary sintering process is 1°C / min to 10°C / min. For example, the heating rate of the secondary sintering process can be 2°C / min, 4°C / min, 6°C / min, 8°C / min, or within any range of the above values.

[0105] Controlling the heating rate of the secondary sintering process within a suitable range is beneficial for controlling the growth rate of crystal nuclei, making the structure of crystal nuclei more complete, reducing the formation of defects in the grains, and improving the structural stability of nickel-based ternary cathode materials.

[0106] In some embodiments, the mass ratio of the boron-containing nickel-based cathode material matrix to the metaphosphate is 1:(0.0005-0.05), and optionally 1:(0.002-0.01).

[0107] A high amount of metaphosphate can affect the material's capacity and other properties; while a low amount is insufficient to achieve the desired effect. Therefore, the mass ratio of the boron-containing nickel-based cathode material matrix to the metaphosphate must be controlled within the aforementioned suitable range.

[0108] In some embodiments, the molecular formula of the metaphosphate is MPO3, where M includes one or more of Al, Ti, Mg, Zr, Y, and W.

[0109] This application selects the aforementioned metaphosphate as a coating agent, which forms a phosphate after sintering. The reason for this selection is that the phosphate has high strength, and after being coated on the material surface, it can maintain the integrity of the coating layer during subsequent secondary battery fabrication, pressing, and high-temperature, high-pressure cycling processes. Furthermore, the phosphate also has high active ion and electronic conductivity, which is beneficial for improving the rate capability and cycle performance of ternary materials.

[0110] In the aforementioned preparation method provided in this application, boron is added during the low-temperature pre-calcination process. Some of the boron is present at the grain boundaries and shallow surface of the nickel-based ternary cathode material. Because boron is electron-deficient, it can form strong bonds with electron-rich elements, thus stabilizing the structure. The phosphorus in the phosphate coating is an electron-rich element with three pairs of unpaired electrons, and therefore can form strong chemical bonds with the boron at the grain boundaries and shallow surface. Compared to doping boron alone or coating phosphate alone, doping boron and coating phosphate can further enhance the strength of the coating layer, improve the structural stability of the nickel-based ternary cathode material, and increase its conductivity for active ions such as lithium ions by leveraging the synergistic effect between boron and phosphorus, thereby improving the rate performance of the secondary battery.

[0111] A third aspect of the embodiments of this application provides a positive electrode sheet, including the nickel-based ternary positive electrode material of the first aspect of this application or the nickel-based ternary positive electrode material prepared according to the preparation method of the second aspect of this application.

[0112] In some embodiments, the lithium-ion conductivity of the positive electrode is (8 × 10⁻⁶). -11 For values ​​above (S / cm), (8×10) can be selected. -11 S / cm)~(10×10 -11 S / cm).

[0113] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the nickel-based ternary positive electrode material of the first aspect of this application.

[0114] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0115] A fourth aspect of the embodiments of this application provides a secondary battery, including the positive electrode provided in the third aspect of this application.

[0116] In some implementations, the type of secondary battery is not specifically limited and may include any battery in which an electrochemical reaction occurs to convert chemical energy into electrical energy, such as a lithium-ion battery or a sodium-ion battery.

[0117] In some embodiments, the secondary battery also includes a negative electrode, an electrolyte, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0118] A fifth aspect of the embodiments of this application provides an electrical device including the secondary battery provided in the fourth aspect of this application. The secondary battery can be used as a power source in the electrical device.

[0119] In some embodiments, the type of electrical device is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices may include, but are not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0120] Example

[0121] The following are specific embodiments, which describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0122] Example 1

[0123] (1) 2 kg of 10 μm Ni 0.6 Co 0.1 Mn 0.3(OH)2 precursor, 20g hexadecyltrimethylammonium chloride and 2L deionized water were mixed, 2kg zirconium balls were added, and the mixture was ball-milled at 800rpm / min for 6h-12h until the D50 was 9μm-11μm. Then 5.1g boric acid was added, and the mixture was ball-milled at 1000r / min for 30min. After ball milling, the mixture was spray-dried and granulated to obtain the precursor dry material. The precursor powder dry material was heated to 350℃ at a heating rate of 1.5℃ / min and sintered for 10h to obtain the pre-sintered material. The pre-sintered material was then processed by a jaw crusher and a double roller mill.

[0124] (2) The pre-burned material from step (1) and 500g of lithium hydroxide were loaded into a high-speed mixer and mixed at a speed of 1000r / min for 30min. The mixture was heated to 950℃ at a heating rate of 1.5℃ / min and sintered for 10h. The mixture was then processed by a jaw crusher and a roller mill to obtain the pulverized material.

[0125] (3) The primary crushed material obtained in step (2) and 10g of aluminum metaphosphate coating agent are put into a high-speed mixer and mixed at a speed of 1000r / min for 30min to obtain a coating mixture. The coating mixture is heated to 600℃ at a heating rate of 8℃ / min and sintered for 12h to obtain a secondary sintered material. The secondary sintered material is processed by a jaw crusher, a roller mill, and an air jet mill in sequence to obtain a nickel-based ternary cathode material.

[0126] Example 2

[0127] (1) 2 kg of 10 μm Ni 0.6 Co 0.1 Mn 0.3 (OH)2 precursor, 20g hexadecyltrimethylammonium chloride and 2L deionized water were mixed, 2kg zirconium balls were added, and the mixture was ball-milled at 800rpm / min for 6h-12h until D50 was 9μm-11μm. Then 5.1g boric acid was added, and the mixture was ball-milled at 1000r / min for 30min. After ball milling, the mixture was spray-dried and granulated to obtain the precursor dry material. The precursor powder dry material was mixed at 1000r / min for 30min. The mixture was sintered at 350℃ for 10h at a heating rate of 1.5℃ / min to obtain the pre-sintered material. The pre-sintered material was processed by a jaw crusher and a double roller mill in sequence.

[0128] (2) The pre-burned material from step (1) and 500g of lithium hydroxide were loaded into a high-speed mixer and mixed at a speed of 1000r / min for 30min. The mixture was heated to 950℃ at a heating rate of 1.5℃ / min and sintered for 10h. The mixture was then processed by a jaw crusher and a roller mill to obtain the pulverized material.

[0129] (3) The primary crushed material obtained in step (2) and 10g of titanium metaphosphate coating agent are put into a high-speed mixer and mixed at a speed of 1000r / min for 30min to obtain a coating mixture. The coating mixture is heated to 600℃ at a heating rate of 8℃ / min and sintered for 10h to obtain a secondary sintered material. The secondary sintered material is processed by a jaw crusher, a roller mill, and an air jet mill in sequence to obtain a nickel-based ternary cathode material.

[0130] Example 3

[0131] (1) 2 kg of 10 μm Ni 0.6 Co 0.1 Mn 0.3 (OH)2 precursor, 20g hexadecyltrimethylammonium bromide and 2L deionized water were mixed, 2kg zirconium balls were added, and the mixture was ball-milled at 1000rpm / min for 6h-12h until the D50 was 9μm-11μm. Then 5.1g boric acid was added, and the mixture was ball-milled at 1000r / min for 30min. After ball milling, the mixture was spray-dried and granulated to obtain the precursor dry material. The precursor powder dry material was heated to 350℃ at a heating rate of 2.0℃ / min and sintered for 10h to obtain the pre-sintered material. The pre-sintered material was then processed by a jaw crusher and a double roller mill.

[0132] (2) The pre-burned material from step (1) and 500g of lithium hydroxide were loaded into a high-speed mixer and mixed at a speed of 1000r / min for 30min. The mixture was heated to 950℃ at a heating rate of 1.5℃ / min and sintered for 10h. The mixture was then processed by a jaw crusher and a roller mill to obtain the pulverized material.

[0133] (3) The primary crushed material obtained in step (2) and 10g of magnesium metaphosphate coating agent are put into a high-speed mixer and mixed at a speed of 1000r / min for 30min to obtain a coating mixture. The coating mixture is heated to 600℃ at a heating rate of 8℃ / min and sintered for 10h to obtain a secondary sintered material. The secondary sintered material is processed by a jaw crusher, a roller mill, and an air jet mill in sequence to obtain a nickel-based ternary cathode material.

[0134] Example 4

[0135] (1) 2 kg of 15 μm Ni 0.6 Co 0.1 Mn 0.3(OH)2 precursor, 18g hexadecyltrimethylammonium bromide and 2L deionized water were mixed, 2kg zirconium balls were added, and the mixture was ball-milled at 1200rpm / min for 6h-12h until the D50 was 6μm-8μm. Then 5.1g boric acid was added, and the mixture was ball-milled at 1000r / min for 30min. After ball milling, the mixture was spray-dried and granulated to obtain the precursor dry material. The precursor powder dry material was heated to 400℃ at a heating rate of 2.0℃ / min and sintered for 10h to obtain the pre-sintered material. The pre-sintered material was then processed by a jaw crusher and a double roller mill.

[0136] (2) The pre-burned material from step (1) and 500g of lithium hydroxide were loaded into a high-speed mixer and mixed at a speed of 1200r / min for 30min. The mixture was heated to 950℃ at a heating rate of 1.5℃ / min and sintered for 10h. The mixture was then processed by a jaw crusher and a roller mill to obtain the pulverized material.

[0137] (3) The primary crushed material obtained in step (2) and 15g of zirconium metaphosphate coating agent are put into a high-speed mixer and mixed at a speed of 1200r / min for 60min to obtain a coating mixture. The coating mixture is heated to 550℃ at a heating rate of 6℃ / min and sintered for 12h to obtain a secondary sintered material. The secondary sintered material is processed by a jaw crusher, a roller mill, and an air jet mill in sequence to obtain a nickel-based ternary cathode material.

[0138] Example 5

[0139] (1) 2 kg of 12 μm Ni 0.6 Co 0.1 Mn 0.3 (OH)2 precursor, 15g hexadecyltrimethylammonium bromide and 2L deionized water were mixed, 2kg zirconium balls were added, and the mixture was ball-milled at 1500rpm / min for 6h-12h until the D50 was 6μm-8μm. Then 5.5g boric acid was added, and the mixture was ball-milled at 1000r / min for 30min. After ball milling, the mixture was spray-dried and granulated to obtain the precursor dry material. The precursor powder dry material was heated to 450℃ at a heating rate of 2.0℃ / min and sintered for 10h to obtain the pre-sintered material. The pre-sintered material was then processed by a jaw crusher and a double roller mill.

[0140] (2) The pre-burned material from step (1) and 500g of lithium hydroxide were loaded into a high-speed mixer and mixed at a speed of 1100r / min for 45min. The mixture was heated to 950℃ at a heating rate of 2.0℃ / min and sintered for 10h. It was then processed by a jaw crusher and a roller mill to obtain the pulverized material.

[0141] (3) The primary crushed material obtained in step (2) and 15g of yttrium metaphosphate coating agent are put into a high-speed mixer and mixed at a speed of 1200r / min for 60min to obtain a coating mixture. The coating mixture is heated to 550℃ at a heating rate of 6℃ / min and sintered for 12h to obtain a secondary sintered material. The secondary sintered material is processed by a jaw crusher, a roller mill, and an air jet mill in sequence to obtain a nickel-based ternary cathode material.

[0142] Example 6

[0143] (1) 2 kg of 12 μm Ni 0.6 Co 0.1 Mn 0.3 (OH)2 precursor, 15g hexadecyltrimethylammonium bromide and 2L deionized water were mixed, 2kg zirconium balls were added, and the mixture was ball-milled at 1500rpm / min for 6h-12h until the D50 was 6μm-8μm. Then 5.5g boric acid was added, and the mixture was ball-milled at 1000r / min for 30min. After ball milling, the mixture was spray-dried and granulated to obtain the precursor dry material. The precursor powder dry material was heated to 450℃ at a heating rate of 2.0℃ / min and sintered for 10h to obtain the pre-sintered material. The pre-sintered material was then processed by a jaw crusher and a double roller mill.

[0144] (2) The pre-burned material from step (1) and 500g of lithium hydroxide were loaded into a high-speed mixer and mixed at a speed of 1100r / min for 45min. The mixture was heated to 950℃ at a heating rate of 2.0℃ / min and sintered for 10h. It was then processed by a jaw crusher and a roller mill to obtain the pulverized material.

[0145] (3) The primary crushed material obtained in step (2) and 15g of tungsten metaphosphate coating agent are put into a high-speed mixer and mixed at a speed of 1200r / min for 60min to obtain a coating mixture. The coating mixture is heated to 550℃ at a heating rate of 6℃ / min and sintered for 12h to obtain a secondary sintered material. The secondary sintered material is processed by a jaw crusher, a roller mill, and an air jet mill in sequence to obtain a nickel-based ternary cathode material.

[0146] Comparative Example 1

[0147] The preparation method of Comparative Example 1 is similar to that of Example 1, except that boric acid is not added in step (1).

[0148] Comparative Example 2

[0149] The preparation method of Comparative Example 2 is similar to that of Example 1, except that aluminum metaphosphate is not added in step (3).

[0150] Comparative Example 3

[0151] The preparation method of Comparative Example 3 is similar to that of Example 1, except that in step (3), aluminum metaphosphate is replaced with other conventional coating agents (e.g., oxide coating agent aluminum oxide).

[0152] Comparative Example 4

[0153] The preparation method of Comparative Example 4 is similar to that of Example 1, except that the pre-sintering treatment is omitted.

[0154] Comparative Example 5

[0155] Comparative Example 5 shows an alumina-coated nickel-based ternary cathode material prepared by a conventional method. The preparation process is as follows:

[0156] (1) 10μm 1kg Ni 0.6 Co 0.1 Mn 0.3 The (OH)2 precursor and 500g of lithium hydroxide were added to a high-speed mixer and mixed at a speed of 1000r / min for 30min to obtain a mixture. This mixture was then heated to 790℃ at a heating rate of 8℃ / min and sintered for 12h to obtain a primary sintered product.

[0157] (2) Take 1 kg of the first sintered material from step (1) and mix it evenly with 8 g of alumina. Then, perform a second sintering at 600℃. The mixture is then processed by a jaw crusher, a roller mill, and an air jet mill to obtain alumina-coated nickel-based ternary cathode material.

[0158] The nickel-based ternary cathode materials prepared in Examples 1-6 and Comparative Examples 1-5, or the lithium-ion batteries further prepared therefrom, were subjected to relevant performance tests. The test results are shown in Table 1 below.

[0159] The test conditions or standards for each performance test item are as follows:

[0160] (1) XRD testing of nickel-based ternary cathode materials

[0161] Nickel-based ternary cathode material powder was placed in the sample stage of an XRD testing instrument (model Bruker D8), and XRD diffraction patterns were obtained using a scanning rate of 2° / min and a scanning angle range of 10° to 90°.

[0162] (2) CP testing of nickel-based ternary cathode materials

[0163] The nickel-based ternary cathode material after 200 cycles was subjected to CP testing, and the testing method is as follows:

[0164] 1) Take 0.5g of powder sample and mix it evenly with the adhesive;

[0165] 2) Dry the adhesive under vacuum;

[0166] 3) After drying, the sample was cut with subion and the cross-section was observed with an electron microscope.

[0167] (3) Lithium-ion battery rate and cycle performance testing

[0168] The battery was charged at 25°C with a constant current of 1C to 4.4V, then charged with a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as D01. The lithium-ion battery was subjected to the above charge-discharge process for 3000 cycles, and the discharge capacity of the 50th cycle was recorded as D1.

[0169] (4) Powder compaction density test of nickel-based ternary cathode material at 150 MPa

[0170] Weigh 3.0g of material and put it into the mold (mold diameter 15mm). Place the mold into the tablet press and apply pressure of 150MPa. After pressing, test the height of the sample tablet and calculate the compaction density using the formula: compaction density = mass / electrode area.

[0171] (5) Lithium-ion conductivity test of positive electrode sheet

[0172] The Loresta-GXMCP-T700 DC four-probe tester was used, and the test method was as follows:

[0173] After pressing the tablet with a mold diameter of 15mm and a pressure of 150MPa, fix two probes at a distance of 3mm on the tablet, adjust the constant current to 2A, and read the voltage value on the device. Perform three tests and take the average value. According to the formula, conductivity = V / I*(W*H / S), where V is the voltage value read by the device, I is the current value, H is the tablet thickness, W is the tablet diameter, and S is the probe spacing.

[0174] Table 1

[0175]

[0176] Table 1 shows that comparing Examples 1-6 with Comparative Examples 1-3, it can be seen that when boric acid or aluminum metaphosphate is not added during the preparation process, and when conventional coating agents are used instead of aluminum metaphosphate, the lithium-ion conductivity, discharge capacity, and capacity retention of the electrode are significantly reduced. This indicates that the use of boric acid and aluminum metaphosphate can indeed improve the conductivity, rate capability, and cycle performance of ternary materials. Furthermore, comparing Examples 1-6 with Comparative Example 5 shows that, compared with the traditional alumina coating method, the ternary cathode material prepared using the preparation method provided in this application can indeed effectively improve its rate capability and cycle performance.

[0177] From the appendix Figure 1The XRD patterns show that no impurity peaks appeared in the samples prepared according to the methods of Comparative Examples 1-2 and Examples 1-2, indicating that the addition of boric acid and metaphosphate did not change the crystal structure of the material. The intensity ratio of the 003 / 104 peaks of the samples all exceeded 1.2, and the surface material had a low Li / Ni mixing value.

[0178] From the appendix Figure 2 As can be seen from the CP diagram, Example 1 ( Figure 2 The nickel-based ternary cathode material provided in (b) of the example maintained its intact cross-sectional structure without structural cracks and the grain boundaries of the primary grains after long-term cycling; while the nickel-based ternary cathode material provided in Comparative Example 1 (b) showed that the cross-sectional structure remained intact after long-term cycling, and the grain boundaries of the primary grains remained intact. Figure 2 In (a) of this paper, the nickel-based ternary cathode material prepared without the addition of boric acid showed obvious cracks after 200 cycles, indicating that the nickel-based ternary cathode material with directional grain growth prepared in this application can effectively suppress lattice stress and crack generation, and has good cycle performance.

[0179] Through append Figure 3 It can be seen that the rate performance of the nickel-based ternary cathode materials provided in Examples 1-2 of this application is significantly better than that of Comparative Examples 1 and 2, indicating that the nickel-based ternary cathode materials prepared in this application can achieve charge and discharge at high rates under the synergistic effect of boric acid and metaphosphate, and have high rate performance.

[0180] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0181] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A nickel-based ternary cathode material, characterized in that, Comprise: A nickel-based positive electrode material substrate containing boron elements, wherein a molecular formula of the nickel-based positive electrode material substrate containing boron elements is LiNi x1 Co y1 Mn z1-a B a O2, x1+y1+z1+a=1, 0 The boron elements in the nickel-based positive electrode material substrate exist in the grain boundaries and the superficial layer of the material, and the mass ratio of the boron elements in the nickel-based ternary positive electrode material is 0.1% to 10%. A coating layer covering at least part of the surface of the nickel-based positive electrode material substrate containing boron elements, wherein the coating layer contains a lithium phosphate salt of formula Li b M c P d O4, 0<b<5, 0<c<5, 0<d<5, M includes one or more of Al, Ti, Mg, Zr, Y and W; the mass ratio of phosphorus elements in the coating layer in the nickel-based ternary positive electrode material is 0.1%~10%. The preparation method of the nickel-based ternary positive electrode material comprises: The precursor powder containing a nickel-cobalt-manganese ternary precursor and boric acid is pre-sintered to obtain a pre-sintered material; The pre-sintered material is mixed with a lithium source and then subjected to a first sintering treatment to obtain a nickel-based positive electrode material substrate containing boron elements; The nickel-based positive electrode material substrate containing boron elements is mixed with a metaphosphate and then subjected to a second sintering treatment to form the coating layer on at least part of the surface of the nickel-based positive electrode material substrate containing boron elements, thereby obtaining the nickel-based ternary positive electrode material.

2. The nickel-based ternary cathode material of claim 1, wherein, The nickel-based ternary positive electrode material satisfies at least one of the following conditions: (1) The mass percentage of boron elements in the nickel-based ternary positive electrode material is 1% to 8%; (2) The mass percentage of phosphorus elements in the coating layer in the nickel-based ternary positive electrode material is 1% to 8%.

3. The nickel-based ternary cathode material according to claim 1 or 2, characterized in that, The nickel-based ternary positive electrode material satisfies at least one of the following conditions: (1) The thickness of the coating layer is 5nm to 50nm; (2) The average particle size D50 of the nickel-based ternary positive electrode material is 4μm to 15μm; (3) the powder compaction density of the nickel-based ternary positive electrode material under 150 MPa is 3.20 g / cm 3 The above.

4. The nickel-based ternary cathode material of claim 3, wherein, Satisfy one or more of the following conditions: (1) The thickness of the coating layer is 5nm to 45nm; (2) the powder compaction density of the nickel-based ternary positive electrode material under 150 MPa is 3.20 g / cm 3 3.50 g / cm 3 .

5. A method for preparing the ternary cathode material of claim 1, characterized in that, Comprise: The precursor powder containing a nickel-cobalt-manganese ternary precursor and boric acid is pre-sintered to obtain a pre-sintered material; After mixing the pre-sintering material with a lithium source, a sintering treatment is performed to obtain a nickel-based positive electrode material matrix containing boron elements, wherein a molecular formula of the nickel-based positive electrode material matrix containing boron elements is LiNi x1 Co y1 Mn z1-a B a O2, x1+y1+z1+a=1, 0 The nickel-based positive electrode material substrate containing boron elements is mixed with a metaphosphate and then subjected to secondary sintering treatment, so as to form a coating layer on at least part of the surface of the nickel-based positive electrode material substrate containing boron elements, thereby obtaining a nickel-based ternary positive electrode material, wherein the coating layer contains a lithium phosphate salt of formula Li b M c P d O4, 0<b<5, 0<c<5, 0<d<5.

6. The preparation method according to claim 5, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The pre-sintering temperature is 200℃ to 600℃; (2) The sintering time of the pre-sintering is 3h to 12h; (3) The heating rate of the pre-sintering is 1℃ / min to 4℃ / min.

7. The preparation method according to claim 5, characterized in that, The pre-sintered material is mixed with a lithium source and then subjected to a first sintering treatment to obtain a nickel-based positive electrode material substrate containing boron elements; The pre-sintered material is uniformly mixed with the lithium source to obtain a first mixed material; The first mixed material is subjected to a first sintering treatment at 500℃ to 1000℃ for 3h to 12h.

8. The preparation method according to claim 7, characterized in that, Satisfy one or more of the following conditions: (1) The heating rate of the first sintering treatment is 1℃ / min to 5℃ / min; (2) The molar ratio of lithium elements in the lithium source to all transition elements in the pre-sintered material is (1.0-1.1):1; (3) The lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate.

9. The preparation method according to claim 5, characterized in that, The pre-sintered material is mixed with a lithium source and then subjected to a first sintering treatment to obtain a nickel-based positive electrode material substrate containing boron elements; The pre-sintered material is uniformly mixed with the lithium source to obtain a first mixed material; The first mixed material is subjected to a first sintering treatment at 500℃ to 1000℃ for 3h to 12h.

10. The method of claim 9, wherein, Satisfy one or more of the following conditions: (1) The heating rate of the first sintering treatment is 1℃ / min to 5℃ / min; (2) The molar ratio of lithium elements in the lithium source to all transition elements in the pre-sintered material is (1.0-1.1):1; (3) The lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate.

11. The method of claim 10, wherein, The pre-sintered material is mixed with a lithium source and then subjected to a first sintering treatment to obtain a nickel-based positive electrode material substrate containing boron elements; The mass ratio of the nickel-based positive electrode material substrate containing boron elements to the metaphosphate is 1:(0.002-0.01).

12. The method of claim 5, wherein, The preparation method further comprises a step of preparing the precursor powder: mixing the nickel-cobalt-manganese ternary precursor and the boric acid in a solvent containing a dispersant to form a mixed solution; ball-milling the mixed solution and then performing a drying treatment to obtain the precursor powder.

13. The method of claim 12, wherein, One or more of the following conditions are met: (1) the mass ratio of the nickel-cobalt-manganese ternary precursor, the dispersant, the solvent and the boric acid is 1:(0.01-1):(0.5-10):(0.001-0.5); (2) the average particle size D50 of the precursor powder is 2-15 μm.

14. The method of claim 12, wherein, The preparation method meets at least one of the following conditions: (1) the molecular formula of the nickel-cobalt-manganese ternary precursor is Ni x2 Co y2 Mn z2 (OH)2, wherein 0 < x2 < 1, 0 < y2 < 1, 0 < z2 < 1, and x2 + y2 + z2 = 1. (2) the dispersant comprises hexadecyl trimethyl ammonium chloride and / or dodecyl trimethyl ammonium bromide; (3) the solvent comprises one or more of pure water, isopropyl alcohol, ethanol and acetone.

15. A positive electrode sheet characterized by comprising: The nickel-based ternary positive electrode material according to any one of claims 1-4 or prepared by the preparation method according to any one of claims 5-14.

16. The cathode sheet of claim 15, wherein, The lithium ion conductivity of the positive electrode tab is 8 x 10 -11 S / cm or more.

17. The cathode sheet of claim 16, wherein, The lithium ion conductivity of the positive electrode tab is (8 x 10 -11 S / cm)~(10 x 10 -11 S / cm).

18. A secondary battery characterized by comprising: The positive electrode sheet according to any one of claims 15-17.

19. An electrical device, comprising: The secondary battery according to claim 18.

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