Positive electrode material, and preparation method therefor and use thereof

Abstract

A positive electrode material, and a preparation method therefor and the use thereof. The positive electrode material comprises a positive electrode active material and nanoparticles covering at least part of the surface of the positive electrode active material, wherein the nanoparticles have a particle size of less than 50 nm and comprise a lithium phosphate material. By limiting the material and the particle size of the nanoparticles, the lithium ion transmission capability of the positive electrode material can be improved, furthermore, the positive electrode active material can be well coated, the positive electrode active material is isolated from contact with an electrolyte, an interface side reaction is reduced, and the amount of manganese dissolution is reduced; and the positive electrode material is applied to a battery, facilitating an improvement in the cycling performance and cycling stability of the battery.

Description

A positive electrode material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 25, 2023, with application number 202311246997.4 and application name “A positive electrode material, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of lithium-ion batteries, and specifically relates to a positive electrode material and a preparation method and application thereof. Background Art

[0003] Lithium-ion batteries are widely used in portable electronics, electric vehicles, and other fields due to their high capacity, compact size, light weight, and environmental friendliness. Energy density and cycle stability are the most direct indicators of lithium-ion battery performance, with cycle performance, in particular, directly impacting battery life and cost. The cathode material is a crucial component of lithium-ion batteries, and its electrochemical properties directly determine the battery's performance.

[0004] Coating modification is a common method to improve the cycle stability of positive electrode materials. Lithium phosphate (Li3PO4) is widely used as a coating material due to its excellent lithium ion conductivity and stable chemical properties. Lithium phosphate can capture Mn ions and inhibit Mn dissolution, and has a special modification effect on high-Mn positive electrode material systems. Traditional lithium phosphate coating methods include solid-phase and liquid-phase methods. For example, patent document CN114524469A directly solid-phase high-temperature sintering of lithium phosphate and ternary positive electrode materials to obtain lithium phosphate-coated ternary positive electrode materials. Patent documents CN114204002A, CN115991505A, etc. use phosphate as the coating raw material to react with the residual alkali on the surface of the positive electrode material in the liquid phase, and then form a lithium phosphate coating layer after high-temperature sintering or spray pyrolysis. However, the coating effect of the above-mentioned solid-phase method is greatly affected by the particle size of the coating material. The particle size of lithium phosphate is generally large and the chemical reaction activity is low; the coating amount of the liquid-phase method is limited by the amount of residual alkali on the surface, and because the long-term high-temperature sintering will cause the particles to grow, the lithium phosphate formed has a large particle size and cannot form nano-scale lithium phosphate; therefore, the lithium phosphate particles located on the surface of the material have a large particle size and are unevenly distributed, making it difficult to form a good coating effect. In addition, lithium phosphate is prone to react during high-temperature sintering to generate by-products, and the coating may become doping under high-temperature conditions, destroying the structure and composition of the coating layer, resulting in problems such as performance degradation of the positive electrode material during the cycle.

[0005] Summary of the Invention

[0006] The present application provides a positive electrode material, which, by limiting the material and particle size of nanoparticles, can not only improve the lithium ion transmission capacity of the positive electrode material, but also form a good coating on the positive electrode active material, isolate the contact between the positive electrode active material and the electrolyte, reduce interfacial side reactions, and reduce the amount of manganese dissolution. The application of this positive electrode material in a battery is beneficial to improving the cycle performance and cycle stability of the battery.

[0007] The present application also provides a method for preparing a positive electrode material, which can produce the above-mentioned positive electrode material with excellent performance by inducing a rapid exothermic reaction of a phosphorus source and a lithium source to generate nanoparticles and coating them on the surface of the positive electrode active material. The preparation process is simple and easy to operate, which is conducive to mass production.

[0008] The present application also provides a positive electrode sheet. Since it includes the above-mentioned positive electrode material, applying the positive electrode sheet to a battery is beneficial to improving the cycle performance and cycle stability of the battery.

[0009] The present application also provides a battery, which includes the above-mentioned positive electrode sheet and has both excellent cycle performance and cycle stability.

[0010] In a first aspect of the present application, a positive electrode material is provided, comprising a positive electrode active material and nanoparticles covering at least a portion of the surface of the positive electrode active material;

[0011] The particle size of the nanoparticles is less than 50 nm, and the material of the nanoparticles includes lithium phosphate.

[0012] The positive electrode material as described above, wherein the average particle size of the nanoparticles is 5 to 20 nm.

[0013] The positive electrode material as described above, wherein the nanoparticles are distributed in a dotted manner on the surface of the positive electrode active material;

[0014] The mass content of the nanoparticles in the positive electrode material is 0.1 to 10 wt %.

[0015] The positive electrode material as described above, wherein the positive electrode material further comprises agglomerates formed by agglomeration of some of the nanoparticles, and the agglomerates are located on the surface of the positive electrode active material;

[0016] The particle size of the agglomerates is 50 to 200 nm.

[0017] The positive electrode material as described above, wherein the specific surface area of ​​the positive electrode material increases by at least 100% relative to the specific surface area of ​​the positive electrode active material.

[0018] The positive electrode material as described above, wherein the specific surface area of ​​the positive electrode material increases by 100% to 300% relative to the specific surface area of ​​the positive electrode active material.

[0019] The positive electrode material as described above, wherein the chemical formula of the positive electrode active material is Li 1+x Ni 0.5+y Mn 1.5+z M u O w , where -0.1≤x≤0.3, -0.2≤y≤0.2, -0.2≤z≤0.2, 0≤u≤0.2, 3.8≤w≤4.3;

[0020] M includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, P, S, and F.

[0021] The positive electrode material as described above, wherein the specific surface area of ​​the positive electrode active material is 0.4 to 0.6 cm 2 / g.

[0022] In a second aspect of the present application, there is provided a method for preparing the positive electrode material according to the first aspect, comprising the following steps: subjecting a mixture of a positive electrode active material, a phosphorus source, and a lithium source to a high-speed mechanical dispersion treatment or thermal initiation to obtain the positive electrode material;

[0023] The time for the high-speed mechanical dispersion treatment and the thermal initiation is no more than 10 minutes.

[0024] In the preparation method as described above, the rotation speed of the high-speed mechanical dispersion treatment is 800 to 3000 rpm, and the time is 0.5 to 10 minutes.

[0025] In the preparation method as described above, the temperature of the thermal initiation is 100-400° C., and the time is 0.5-10 min.

[0026] The preparation method as described above, wherein, before thermal initiation, the method further comprises premixing the positive electrode active material, phosphorus source, and lithium source;

[0027] The temperature of the premix does not exceed 15°C.

[0028] The preparation method as described above, wherein the phosphorus source comprises at least one of ammonium dihydrogen phosphate, ammonium hypophosphite, diammonium hydrogen phosphate, ammonium phosphate, and phosphorus pentoxide; and / or,

[0029] The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium acetate, and lithium citrate.

[0030] In a third aspect of the present application, a positive electrode sheet is provided, which comprises the positive electrode material described in the first aspect or the positive electrode material prepared by the preparation method described in the second aspect.

[0031] A fourth aspect of the present application provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0032] The implementation of this application has at least the following beneficial effects:

[0033] The positive electrode material provided in the present application includes a positive electrode active material and nanoparticles covering the surface of the positive electrode active material, wherein the material of the nanoparticles includes lithium phosphate. Lithium phosphate itself is a fast ion conductor, which is beneficial to improving the transmission of lithium ions. Lithium phosphate does not react with the electrolyte within a wide electrochemical window, has good stability, and is beneficial to improving the cycle performance of the battery. By limiting the particle size of the nanoparticles to less than 50nm, due to the small particle size, on the one hand, the activity of the lithium phosphate is greatly increased, and on the other hand, the contact area between the nanoparticles and the positive electrode active material is increased, forming a good coating effect, and enabling the nanoparticles to be firmly and tightly coated on the surface of the positive electrode active material to avoid falling off. The application of this positive electrode material in the battery is beneficial to improving the cycle performance and cycle stability of the battery.

[0034] The preparation method of the positive electrode material provided in the present application limits the solid-phase mixing of the positive electrode active material, the phosphorus source, and the lithium source, so that the phosphorus source and the lithium source react to form lithium phosphate and generate heat. At the same time, under the heat conditions, the lithium phosphate can be coated on the surface of the positive electrode active material. In addition, by limiting the reaction time, the lithium phosphate is nucleated in large quantities without growing, and nanoparticles with a particle size of less than 50 nm can be produced, thereby obtaining the above-mentioned positive electrode material with excellent performance. The preparation process is simple and easy to operate, which is conducive to mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a SEM image of the positive electrode material in Example 1 of the present application at a first magnification;

[0036] FIG2 is a SEM image of the cathode material in Example 1 of the present application at a second magnification;

[0037] FIG3 is a SEM image of the positive electrode material in Example 3 of the present application at a third magnification;

[0038] FIG4 is a SEM image of the positive electrode material in Example 3 of the present application at a fourth magnification;

[0039] FIG5 is a SEM image of the positive electrode material in Comparative Example 1 of the present application at the first magnification;

[0040] FIG6 is a SEM image of the positive electrode material in Comparative Example 3 of the present application;

[0041] FIG7 is a SEM image of the positive electrode material in Comparative Example 4 of the present application;

[0042] FIG8 is an XRD pattern of lithium phosphate in Comparative Example 5 of the present application;

[0043] FIG9 is a SEM image of lithium phosphate in Comparative Example 5 of the present application at a fourth magnification. DETAILED DESCRIPTION

[0044] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] In a first aspect of the present application, a positive electrode material is provided, comprising a positive electrode active material and nanoparticles covering at least a portion of the surface of the positive electrode active material; the particle size of the nanoparticles is less than 50 nm, and the material of the nanoparticles comprises lithium phosphate.

[0046] The positive electrode active material serves as the core of the positive electrode material, while the nanoparticles covering the surface of the positive electrode active material serve as the coating layer of the positive electrode material. By coating the surface of the positive electrode active material, the positive electrode active material can be separated from the electrolyte, reducing side reactions, inhibiting the dissolution of metal ions in the positive electrode active material, and reducing the collapse of the material structure during charge and discharge, thereby optimizing the material's cycle performance and cycle stability. Furthermore, when the nanoparticles are made of lithium phosphate, the lithium phosphate can capture dissolved manganese ions, further inhibiting their dissolution.

[0047] Prior art nanoparticles commonly suffer from problems such as agglomeration and large size, making it difficult to effectively control the thickness of the nanoparticles. Furthermore, the nanoparticles are unevenly coated on the surface of the material, leading to performance degradation and particle breakage of the positive electrode material during cycling, which in turn affects the battery's cycling performance and stability. This application effectively overcomes these drawbacks by limiting the material and particle size of the nanoparticles. The particle size of the nanoparticles can be determined through SEM testing.

[0048] According to the research of this application, the application of the above-mentioned positive electrode material in the battery is conducive to improving the cycle performance and cycle stability of the battery. This is because, on the one hand, the material of the nanoparticles includes lithium phosphate, which is a fast ion conductor itself, which is conducive to improving the transmission of lithium ions, and lithium phosphate does not react with the electrolyte within a wide electrochemical window, has good stability, and is conducive to improving the cycle performance of the battery; on the other hand, by limiting the particle size of the nanoparticles to less than 50nm, due to the small particle size, on the one hand, the activity of lithium phosphate will increase, and on the other hand, the contact area between the nanoparticles and the positive active material will increase, which is conducive to forming a good coating effect, can play a good isolation role, and can make the nanoparticles firmly and tightly coated on the surface of the positive active material, avoid falling off during the charge and discharge cycle, which is conducive to improving the cycle stability of the battery.

[0049] The smaller the particle size of the nanoparticles, the larger the specific surface area, the larger the contact area between the nanoparticles and the positive electrode active material, and the better coating of the positive electrode active material. In some embodiments, the particle size of the nanoparticles is 5 to 20 nm. If the particle size of the nanoparticles is too large, it is difficult to achieve good coating of the positive electrode active material, which is not conducive to improving the cycle stability of the battery. By further limiting the particle size of the nanoparticles to 5 to 20 nm, it is beneficial to achieve a uniform and dense distribution of the nanoparticles on the surface of the positive electrode active material, thereby achieving maximum coating of the outer surface of the positive electrode active material.

[0050] In some embodiments, the nanoparticles are distributed in a dotted manner on the surface of the positive electrode active material, and the dotted distribution area is dense and uniform, avoiding large-area agglomeration between the nanoparticles, which is conducive to achieving effective coating of the outer surface of the positive electrode active material.

[0051] The present application does not limit the mass content of the nanoparticles, as long as the nanoparticles cover the surface of the positive electrode active material. In some embodiments, the mass content of the nanoparticles in the positive electrode material is 0.1-10 wt%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof, preferably 1%-5%.

[0052] In this application, the cathode material also includes aggregates formed by the aggregation of some nanoparticles, which are located on the surface of the cathode active material. This is because nanoparticles have a small particle size and high reactivity, and a small number of nanoparticles may aggregate to form aggregates. In some embodiments, the particle size of the aggregates is 50 to 200 nm.

[0053] Since the particle size of the nanoparticles is less than 50 nm, the specific surface area of ​​the positive electrode material increases relative to the specific surface area of ​​the positive electrode active material. If the specific surface area of ​​the positive electrode material increases too much, the contact area between the positive electrode material and the electrolyte increases, and side reactions may increase, which is not conducive to the safety performance of the battery. In some embodiments, the specific surface area of ​​the positive electrode material increases by at least 100% relative to the specific surface area of ​​the positive electrode active material before coating, and preferably by 100% to 300%. Growth rate = (specific surface area of ​​the positive electrode material after coating - specific surface area of ​​the positive electrode active material before coating) / BET of the positive electrode active material before coating. By limiting the range of increase in the specific surface area of ​​the positive electrode material, safety performance and cycle performance are beneficial.

[0054] The present application does not limit the specific material of the positive electrode active material, and it can be a conventional positive electrode active material in the art, such as lithium cobalt oxide, ternary positive electrode material, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based material, lithium-rich disordered spinel material, etc. For example, the chemical formula of the positive electrode active material is Li 1+x Ni 0.5+y Mn 1.5+z M u O w , wherein, -0.1≤x≤0.3, -0.2≤y≤0.2, -0.2≤z≤0.2, 0≤u≤0.2, 3.8≤w≤4.3; M includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, P, S, and F.

[0055] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.4 to 0.6 cm 2 / g.

[0056] The positive electrode active material may be a polycrystalline material and / or a single crystal material.

[0057] In this application, the first charge capacity of the positive electrode material in the electrochemical window of 3.5-4.95V and the current density of 0.1C is not less than 138mAh / g, the first discharge capacity is not less than 125mAh / g, and the first efficiency is not less than 85%; and / or, the capacity retention rate of the positive electrode material after 100 charge and discharge cycles in the electrochemical window of 3.5-4.95V and the current density of 2C is not less than 85%.

[0058] In a second aspect of the present application, a method for preparing the positive electrode material provided in the first aspect is provided, comprising the following steps: subjecting a positive electrode active material, a phosphorus source, and a lithium source to high-speed mechanical dispersion or thermal initiation to obtain a positive electrode material;

[0059] The time for high-speed mechanical dispersion treatment and thermal initiation does not exceed 10 minutes. The high-speed mechanical dispersion treatment can be directly carried out in a high-speed mixer, that is, the positive electrode active material, phosphorus source, and lithium source are directly placed in the high-speed mixer for high-speed mechanical dispersion treatment.

[0060] Before thermal initiation, the positive electrode active material, phosphorus source and lithium source are also premixed. The premixing can be carried out in a high-speed mixer. In order to avoid overheating of the high-speed mixer during the mixing stage, which may cause the raw materials to react prematurely, the premixing temperature is usually kept below 15°C. Specifically, circulating cooling water can be used as an aid. For example, circulating cooling water can be used for cooling during premixing, and the temperature of the circulating cooling water does not exceed 15°C.

[0061] High-speed mechanical dispersion and thermal initiation essentially utilize heat to induce a rapid reaction between the phosphorus and lithium sources to form lithium phosphate particles, which are then coated on the surface of the positive electrode active material. By limiting the high-speed mechanical dispersion and thermal initiation times to no more than 10 minutes, the extremely rapid reaction allows lithium phosphate to nucleate in large quantities without growing, resulting in nanoparticles with a particle size of less than 50nm. Simultaneously, the reaction between the phosphorus and lithium sources releases a large amount of heat, which thermodynamically allows the adjacent reactants to reach the reaction conditions. This allows the lithium phosphate nanoparticles to heterogeneously nucleate on the surface of the positive electrode active material and adhere firmly and densely to the surface, forming a good coating, thereby improving cycle stability.

[0062] In some embodiments, the high-speed mechanical dispersion treatment speed is 800-3000 rpm, for example, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm or a range consisting of any two thereof, and the time is 0.5-10 min, preferably 1-3 min; the thermal initiation temperature is 100-400°C, for example, 100°C, 200°C, 300°C, 400°C or a range consisting of any two thereof, and the time is 0.5-10 min.

[0063] The present application does not limit the specific types of phosphorus and lithium sources, as long as the phosphorus and lithium sources can react to form lithium phosphate. For example, in some embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate, ammonium hypophosphite, diammonium hydrogen phosphate, ammonium phosphate, and phosphorus pentoxide; and / or the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium acetate, and lithium citrate.

[0064] It should be noted that after the mixture is subjected to high-speed mechanical dispersion treatment or thermal initiation, post-treatment is also included. For example, the mixture is subjected to high-speed mechanical dispersion treatment or thermal initiation, and after water washing, filtration, and drying, the positive electrode material is obtained.

[0065] In a third aspect of the present application, a positive electrode sheet is provided, which includes the positive electrode material of the first aspect or the positive electrode material prepared by the preparation method of the second aspect.

[0066] The positive electrode sheet of the present application can also be prepared by conventional technical means in the field. Specifically, the above-mentioned positive electrode material, conductive agent, and binder can be uniformly dispersed in a solvent to obtain a positive electrode active layer slurry, and then the positive electrode active layer slurry is coated on at least one functional surface of the positive electrode current collector. After drying, the positive electrode sheet of the present application can be obtained.

[0067] In a fourth aspect of the present application, a lithium-ion battery is provided, wherein the lithium-ion battery includes the positive electrode sheet provided in the third aspect.

[0068] The lithium-ion battery of the present application includes, in addition to the positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The composition of the negative electrode sheet can refer to conventional negative electrode sheets in the art, and the separator can also adopt separators conventionally used in the art, such as PP film, PE film, etc. The lithium-ion battery of the present application can be prepared using conventional methods in the art. Specifically, the positive electrode sheet, separator, and negative electrode sheet can be stacked in sequence, and then a battery cell can be obtained through a lamination or winding process. The above-mentioned lithium-ion battery can then be obtained through processes such as baking, liquid injection, formation, and packaging.

[0069] The capacity retention rate of the above-mentioned lithium-ion battery after at least 257 cycles at 25°C and 1C current density is 80%, that is, the lithium-ion battery is charged and discharged at 25°C and 1C current density, and when the capacity retention rate reaches 80%, it has been cycled for at least 257 cycles; and / or, the capacity retention rate of the lithium-ion battery after at least 84 cycles at 45°C and 1C current density is 80%, that is, the lithium-ion battery is charged and discharged at 45°C and 1C current density, and when the capacity retention rate reaches 80%, it has been cycled for at least 84 cycles.

[0070] The present application will be further described below through specific examples and comparative examples.

[0071] Example 1

[0072] (1) 10 kg of precursor Ni 0.5 Mn 1.5 (OH)4, 2.09 kg of lithium carbonate, and 80 g of Ta2O5 were added to a high-pressure mixer and stirred until uniform to obtain a mixture; the mixture was sintered at 960°C for 10 h, cooled to room temperature at a rate of 1°C / min, crushed, and sieved to obtain modified lithium nickel manganese oxide, which was designated as A1;

[0073] (2) 1 kg Al, 9.93 g ammonium dihydrogen phosphate, and 6.51 g lithium hydroxide were added to a high-speed mixer at a speed of 2000 rpm and stirred for 2 min. The reacted material was added to 3 L deionized water, stirred for 2 min, and then filtered and dried to obtain a positive electrode material, which was recorded as D1.

[0074] Example 2

[0075] The preparation process is basically the same as that of Example 1, except that in step (2), 1 kg of Al, 19.87 g of ammonium dihydrogen phosphate and 13.01 g of lithium hydroxide are added to the high-speed mixer, and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D2.

[0076] Example 3

[0077] The preparation process is basically the same as that of Example 1, except that in step (2), 1 kg of Al, 29.8 g of ammonium dihydrogen phosphate and 19.54 g of lithium hydroxide are added to the high-speed mixer, and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D3.

[0078] Example 4

[0079] The preparation process is basically the same as that of Example 1, except that in step (2), 1 kg of Al, 39.73 g of ammonium dihydrogen phosphate and 26.06 g of lithium hydroxide are added to the high-speed mixer, and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D4.

[0080] Example 5

[0081] The preparation process is basically the same as that of Example 1, except that in step (2), 1 kg of Al, 49.67 g of ammonium dihydrogen phosphate and 32.57 g of lithium hydroxide are added to the high-speed mixer, and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D5.

[0082] Example 6

[0083] The preparation process is basically the same as that of Example 1, except that in step (2), 1 kg of Al, 4.97 g of ammonium dihydrogen phosphate and 3.26 g of lithium hydroxide are added to the high-speed mixer, and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D6.

[0084] Example 7

[0085] The preparation process is basically the same as that of Example 1, except that, in step (2), 1 kg of Al, 9.93 g of ammonium dihydrogen phosphate and 6.51 g of lithium hydroxide are added to a high-speed mixer at a speed of 700 rpm, and intermittently stirred for 20 s and cooled for 1 min under cooling of circulating cooling water, and repeated 6 times to obtain a mixed material; the mixed material is placed in a corundum sagger and placed in a muffle furnace preheated to 200° C. and heated for 3 min; the reacted material is added to 3 L of deionized water, stirred for 2 min, and filtered and dried to obtain a positive electrode material, which is recorded as D7.

[0086] Example 8

[0087] The preparation process is basically the same as that of Example 7, except that in step (2), 1 kg of Al, 29.8 g of ammonium dihydrogen phosphate and 19.54 g of lithium hydroxide are added to the high-speed mixer, and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D8.

[0088] Example 9

[0089] The preparation process is basically the same as that of Example 8, except that in step (2), the mixed material is placed in a corundum sagger and placed in a muffle furnace preheated to 150° C. and heated for 5 minutes; other conditions remain unchanged to obtain a positive electrode material, which is recorded as D9.

[0090] Example 10

[0091] The preparation process is basically the same as that of Example 8, except that in step (2), the mixed material is placed in a corundum sagger and placed in a muffle furnace preheated to 250° C. and heated for 2 minutes; other conditions remain unchanged to obtain a positive electrode material, which is recorded as D10.

[0092] Example 11

[0093] The preparation process is basically the same as that of Example 8, except that in step (2), the mixed material is placed in a corundum sagger and placed in a muffle furnace preheated to 300° C. and heated for 2 min; other conditions remain unchanged to obtain a positive electrode material, which is recorded as D11.

[0094] Example 12

[0095] The preparation process was basically the same as that in Example 1, except that in step (2), 1 kg of Al, 7.17 g of ammonium hypophosphite and 6.7 g of lithium carbonate were added to the high-speed mixer, and other conditions remained unchanged to obtain a positive electrode material, which was recorded as D12.

[0096] Example 13

[0097] The preparation process was basically the same as that in Example 1, except that in step (2), 1 kg of Al, 21.51 g of ammonium hypophosphite and 20.10 g of lithium carbonate were added to the high-speed mixer, and other conditions remained unchanged to obtain a positive electrode material, which was recorded as D13.

[0098] Example 14

[0099] (1) 10 kg of precursor Ni 0.5 Mn 1.5 (OH)4, 2.21 kg of lithium carbonate, and 200 g of NH4H2PO4 were added to a high-pressure mixer and stirred until uniform to obtain a mixture; the mixture was sintered at 960°C for 10 h, cooled to room temperature at a rate of 1°C / min, crushed, and sieved to obtain modified lithium nickel manganese oxide, which was designated as A2;

[0100] (2) 1 kg of A2, 9.93 g of ammonium dihydrogen phosphate, and 6.51 g of lithium hydroxide were added to a high-speed mixer at a speed of 2000 rpm and stirred for 2 minutes. The reacted material was added to 3 L of deionized water, stirred for 2 minutes, and then filtered and dried to obtain a positive electrode material, which was recorded as D14.

[0101] Example 15

[0102] The preparation process is basically the same as that of Example 11, except that in step (2), 1 kg of A2, 29.8 g of ammonium dihydrogen phosphate and 19.54 g of lithium hydroxide are added to the high-speed mixer, and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D15.

[0103] Comparative Example 1

[0104] 10kg of precursor Ni 0.5 Mn 1.5 (OH)4, 2.09 kg of lithium carbonate and 80 g of Ta2O5 were added to a high-pressure mixer and mixed and stirred until uniform to obtain a mixture; the mixture was sintered at 960°C for 10 h, cooled to room temperature at a rate of 1°C / min, and then crushed and sieved to obtain modified lithium nickel manganese oxide (i.e., the positive electrode material of this comparative example), which was recorded as A1.

[0105] Comparative Example 2

[0106] 10kg of precursor Ni 0.5 Mn 1.5 (OH)4, 2.21 kg of lithium carbonate and 200 g of NH4H2PO4 were added to a high-pressure mixer and mixed and stirred until uniform to obtain a mixture; the mixture was sintered at 960°C for 10 h, cooled to room temperature at a rate of 1°C / min, and then crushed and sieved to obtain modified lithium nickel manganese oxide (i.e., the positive electrode material of this comparative example), which was recorded as A2.

[0107] Comparative Example 3

[0108] Add 1 kg of Al to 2 L of water and stir to form a uniform Al mixture. Dissolve 29.80 g of ammonium dihydrogen phosphate and 19.54 g of lithium hydroxide in 500 mL of deionized water to form a solution. While stirring, use a peristaltic pump to simultaneously add the ammonium dihydrogen phosphate aqueous solution and lithium hydroxide aqueous solution dropwise to the Al mixture at a rate of ≤ 100 ml / h. After the addition is complete, continue stirring for 1 hour. Filter and dry the mixture to obtain the positive electrode material D16.

[0109] Comparative Example 4

[0110] The preparation process is basically the same as that of Comparative Example 3, except that a sintering step is added, and the positive electrode material D16 in Comparative Example 3 is sintered at 500° C. for 5 h to obtain the positive electrode material D17.

[0111] Comparative Example 5

[0112] 49.67 g of ammonium dihydrogen phosphate and 32.57 g of lithium hydroxide were added to a high-speed mixer at a speed of 2000 rpm and stirred for 2 minutes. The reacted material was added to 1 L of deionized water and stirred for 2 minutes. After filtration and drying, lithium phosphate was obtained.

[0113] Test example

[0114] Electrochemical performance test:

[0115] 1. Charge and discharge performance test, cycle performance test

[0116] The positive electrode materials of the embodiment and the comparative example were assembled into button-type half-cells (the negative electrode was a metal lithium sheet), and the 0.1C charge-discharge capacity and 2C cycle capacity retention rate were tested, with a voltage window of 3.5 to 4.95V.

[0117] 2. Cyclic stability test

[0118] The positive electrode materials of the embodiment and the comparative example were assembled into a soft-pack full battery (the negative electrode was graphite), and the number of cycles was tested, and the voltage window was 3.5-4.90V.

[0119] The test results are shown in Table 1.

[0120] Table 1

[0121] BET growth rate / %=(specific surface area of ​​the positive electrode material-specific surface area of ​​the modified lithium nickel manganese oxide) / specific surface area of ​​the modified lithium nickel manganese oxide.

[0122] The SEM images of the positive electrode material in Example 1 are shown in Figures 1 and 2, the SEM images of the positive electrode material in Example 3 are shown in Figures 3 and 4, and the SEM image of the positive electrode material in Comparative Example 1 is shown in Figure 5. It can be seen that the modified lithium nickel manganese oxide has a typical octahedral structure and a flat and smooth surface. After being coated with lithium phosphate nanoparticles, a large number of nanoparticles are attached to the surface, and the particle size of the nanoparticles is about 10 nm.

[0123] The SEM image of the positive electrode material in Comparative Example 3 is shown in Figure 6. The lithium phosphate particles on its surface are in a long strip state with a width of about 200 to 500 nm and a length of about 500 to 1500 nm, which is much larger than the particle size of the lithium phosphate on the surface of the positive electrode material in Example 1 and Example 3; the SEM image of the positive electrode material in Comparative Example 4 is shown in Figure 7. After heat treatment at 500°C for 5 hours, the lithium phosphate on the surface of the positive electrode material has further grown; the XRD and SEM images of the lithium phosphate in Comparative Example 5 are shown in Figures 8 and 9. It can be seen from XRD that the phase prepared by this method is lithium phosphate with a particle size of 50 to 100 nm.

[0124] As can be seen from Table 1, the positive electrode material provided in the present application can further improve the cycle performance and cycle stability of the battery while maintaining excellent charge and discharge performance.

[0125] The above describes in detail the preferred embodiments and experimental verifications of the present application. It should be understood that ordinary skill in the art can make numerous modifications and variations based on the concepts of the present application without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art based on the concepts of the present application through logical analysis, reasoning, or limited experimentation on the basis of the existing technology should be within the scope of protection defined by the claims.

Claims

1. A positive electrode material, wherein: It includes a positive electrode active material and nanoparticles covering at least a portion of the surface of the positive electrode active material; The particle size of the nanoparticles is less than 50 nm, and the material of the nanoparticles includes lithium phosphate.

2. The positive electrode material according to claim 1, wherein The particle size of the nanoparticles is 5 to 20 nm.

3. The positive electrode material according to claim 1 or 2, wherein The nanoparticles are distributed in a dotted manner on the surface of the positive electrode active material; The mass content of the nanoparticles in the positive electrode material is 0.1-10 wt %.

4. The positive electrode material according to any one of claims 1 to 3, wherein The positive electrode material also includes agglomerates formed by agglomeration of some of the nanoparticles, and the agglomerates are located on the surface of the positive electrode active material; The particle size of the agglomerates is 50 to 200 nm.

5. The positive electrode material according to claim 4, wherein The specific surface area of ​​the positive electrode material increases by at least 100% relative to the specific surface area of ​​the positive electrode active material.

6. The positive electrode material according to claim 5, wherein The specific surface area of ​​the positive electrode material increases by 100% to 300% relative to the specific surface area of ​​the positive electrode active material.

7. The positive electrode material according to any one of claims 1 to 6, wherein The chemical formula of the positive electrode active material is Li 1+x Ni 0.5+y Mn 1.5+z M u O w , where -0.1≤x≤0.3, -0.2≤y≤0.2, -0.2≤z≤0.2, 0≤u≤0.2, 3.8≤w≤4.3; Among them, M includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, P, S, and F.

8. The positive electrode material according to claim 7, wherein The specific surface area of ​​the positive electrode active material is 0.4 to 0.6 cm 2 / g.

9. A method for preparing the positive electrode material according to any one of claims 1 to 8, wherein: The following steps are involved: The positive electrode material is obtained by subjecting the positive electrode active material, the phosphorus source and the lithium source to high-speed mechanical dispersion or thermal initiation; Wherein, the time of the high-speed mechanical dispersion treatment and the thermal initiation is no more than 10 minutes.

10. The preparation method according to claim 9, wherein: The rotation speed of the high-speed mechanical dispersion treatment is 800 to 3000 rpm, and the time is 0.5 to 10 minutes.

11. The preparation method according to claim 9, wherein: The thermal initiation temperature is 100-400° C. and the time is 0.5-10 min.

12. The preparation method according to claim 9 or 11, wherein: Before thermal initiation, the positive electrode active material, phosphorus source and lithium source are premixed; The temperature of the premix does not exceed 15°C.

13. The preparation method according to any one of claims 9 to 12, wherein: The phosphorus source includes at least one of diammonium phosphate, ammonium hypophosphite, diammonium phosphate, ammonium phosphate, and phosphorus pentoxide; and / or, The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium acetate and lithium citrate.

14. A positive electrode sheet, wherein: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 8 or the positive electrode material prepared by the preparation method according to any one of claims 9 to 13.

15. A lithium ion battery, wherein: The lithium-ion battery comprises the positive electrode sheet according to claim 14.

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