Composite positive electrode material and preparation method thereof, battery and electric device

Abstract

The invention discloses a composite positive electrode material and a preparation method thereof, a battery and a power utilization device. The composite positive electrode material comprises an inner core, wherein the inner core comprises a polycrystalline ternary material; the surface of the inner core is coated with the shell layer, the shell layer comprises a mixture of a single crystal ternary material and an active material LiMnxFe1-xPO4, and x is larger than or equal to 0 and smaller than 1. The composite positive electrode material has the advantages of long service life, high safety and high rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a composite positive electrode material and a preparation method thereof, a battery, and an electrical device. Background Art

[0002] Lithium iron manganese phosphate is highly safe and is often used as a positive electrode active material. Currently, lithium iron manganese phosphate is generally used in combination with ternary materials or alone. In the related technology, when lithium iron manganese phosphate is used in combination with ternary materials, neither lithium iron manganese phosphate nor ternary materials can play the advantages of their respective materials and avoid the shortcomings of their respective materials, resulting in the cycle performance, safety performance and rate performance of the composite positive electrode material still need to be further improved. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the present invention provides a composite positive electrode material with long life, high safety and high rate, a preparation method thereof, a battery and an electric device.

[0004] The first aspect of the present invention provides a composite positive electrode material, comprising:

[0005] a core comprising a polycrystalline ternary material; and

[0006] Shell layer, the shell layer is coated on the surface of the core, and the shell layer includes single crystal ternary material and active material LiMn x Fe 1-x Mixture of PO4, 0≤x<1.

[0007] The present invention uses a polycrystalline ternary material with good rate performance but poor life and safety as the core, and uses a single crystal ternary material with better life and LiMn with better safety. x Fe 1-x PO4 composite heterogeneous structure as the shell. This design of the material structure gives full play to the rate performance of polycrystalline ternary materials, avoiding the characteristics of poor life and poor safety of polycrystalline; at the same time, it gives full play to the single crystal ternary material and LiMn x Fe 1-x PO4 has the characteristics of long life and relatively high safety, avoiding the single crystal ternary material and LiMn x Fe 1-x The poor rate performance of PO4 is achieved by taking advantage of its strengths to make up for its weaknesses. Therefore, the present invention provides a composite positive electrode material with long life, high safety and high rate.

[0008] In some embodiments, 0<x<1, the active material is lithium iron manganese phosphate. Lithium iron manganese phosphate is relatively safe and matches the voltage range of the ternary material. The heterostructure of lithium iron manganese phosphate material and single crystal ternary material is used as the shell layer and polycrystalline ternary material is used as the core, so that the polycrystalline ternary material has the characteristics of long life and relatively high safety, avoiding the single crystal ternary material and LiMn x Fe 1-x PO4 has the characteristics of poor rate performance.

[0009] In some embodiments, the D50 particle size of the active material is smaller than the D50 particle size of the single crystal ternary material; preferably, the particle size range of the active material is 100nm-15μm, and the particle size range of the single crystal ternary material is 2-20μm. The particle size is designed in this way based on the intrinsic characteristics of the material to maximize its strengths and avoid its weaknesses. First of all, the material stability of the outer layer coated single crystal ternary material is higher than that of the inner layer polycrystalline ternary material, but the rate performance of the single crystal ternary material itself is lower than that of the polycrystalline ternary material. In order to give full play to the rate performance of the single crystal ternary material, the particle size of the single crystal ternary material is designed as a small particle as a whole to shorten the lithium ion diffusion path and improve the rate performance. Secondly, small particles of single-crystal ternary materials exposed to the electrolyte have a large specific surface area and a fast side reaction rate. Therefore, selecting active materials with smaller particle sizes (such as lithium iron phosphate) to composite with single-crystal ternary materials in the shell layer can achieve the coating of single-crystal ternary particles by active material particles, thereby solving the problem of fast side reaction rate of single-crystal ternary materials. The smaller particle size of lithium iron phosphate also solves the inherent characteristic of poor intrinsic rate performance of lithium iron phosphate.

[0010] In some embodiments, the polycrystalline ternary material has a radial or porous structure inside; preferably, the core is spherical. The polycrystalline ternary material has a radial or porous structure inside, which can shorten the lithium ion diffusion path and improve the rate performance of the positive electrode material.

[0011] In some embodiments, the mass ratio of the core to the shell is (80-95): (20-5). Controlling the mass ratio of the core to the shell within the scope of the present invention is beneficial to further improve the life, safety and rate performance of the battery.

[0012] In some embodiments, the shell layer further comprises a conductive agent. The conductive agent can improve the conductivity of the positive electrode material itself. Preferably, the conductive agent comprises a carbonaceous material.

[0013] In some embodiments, the composite positive electrode material further includes: a coating layer, the coating layer is coated on the outer surface of the shell layer, and the coating layer includes metal oxide or carbon material; preferably, the metal oxide includes one or more of oxides of second main group metals, oxides of third main group metals, and transition metal oxides; preferably, the carbon material includes at least one of glucose and cellulose. The coating layer is coated on the outer surface of the shell layer to protect the inner layer material, make the inner layer material more stable, and further improve the life, safety and rate performance of the battery.

[0014] The second aspect of the present invention provides a method for preparing the composite positive electrode material of the first aspect of the present invention, comprising the following steps:

[0015] Provide polycrystalline ternary materials;

[0016] The polycrystalline ternary material, the active material LiMn x Fe 1-x PO4, single crystal ternary material and solvent are mixed, spray dried and sintered to obtain the composite positive electrode material.

[0017] The method of the present invention can be used to prepare a composite positive electrode material with long life, high safety and high rate. At the same time, the method of the present invention is simple to operate, has low production process difficulty, is easy to repeat and realize industrial production.

[0018] In some embodiments, the mixing includes: mixing the active material, the single crystal ternary material, the solvent and the carbon source together to obtain a suspension; adding the polycrystalline ternary material to the suspension and mixing; wherein the ratio of the mass of the polycrystalline ternary material to the total mass of the single crystal ternary material, the active material and the carbon source is (0.8-0.95):(0.05-0.2). By controlling the mass ratio of the polycrystalline ternary material, the active material, the single crystal ternary material and the carbon source, the mass ratio of the core to the shell in the composite positive electrode material can be controlled, which is conducive to further improving the life, safety and rate performance of the battery.

[0019] In some embodiments, sintering is performed in an inert atmosphere; preferably, the sintering temperature is 300-800° C. and the sintering time is 3-12 hours. By optimizing the sintering conditions, a stable core-shell structure is formed, which further improves the life, safety and rate performance of the battery.

[0020] In some embodiments, providing a polycrystalline ternary material includes:

[0021] Mixing a nickel-cobalt-manganese salt solution, an alkali solution, and a complexing agent to react to obtain a polycrystalline ternary precursor;

[0022] Sintering the polycrystalline ternary precursor and lithium salt at 600-1000° C. to obtain the polycrystalline ternary material;

[0023] Preferably, the concentration of the nickel-cobalt-manganese salt solution is 0.1-3 mol / L;

[0024] Preferably, the alkaline solution includes one or more of sodium hydroxide solution and sodium bicarbonate solution;

[0025] Preferably, the complexing agent includes one or more of ammonia water and hydrazine hydrate compounds.

[0026] The polycrystalline ternary material prepared by the present invention has a radial or porous structure inside, which can shorten the lithium ion diffusion path and improve the rate performance of the positive electrode material.

[0027] In some embodiments, after sintering, the method further comprises: forming a coating layer on the surface of the obtained composite positive electrode material. The coating layer can protect the inner layer material, make the inner layer material more stable, and further improve the life, safety and rate performance of the battery.

[0028] The third aspect of the present invention provides a battery, comprising the composite positive electrode material of the first aspect of the present invention or the composite positive electrode material obtained by the method of the second aspect of the present invention. Due to the use of the composite positive electrode material of the present invention, the battery of the present invention has long life, high safety and high rate performance.

[0029] The fourth aspect of the present invention provides an electrical device, comprising the battery of the third aspect of the present invention. The electrical device has all the features and advantages of the composite positive electrode material or battery described above, which will not be described one by one here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the structure of composite positive electrode materials of some embodiments of the present invention.

[0031] Figure 2 It is a schematic diagram of the structure of composite positive electrode materials of other embodiments of the present invention.

[0032] Figure 3 100% DOD cycle life curves of the batteries corresponding to the composite positive electrode materials prepared in Example 1 of the present invention and Comparative Example 1.

[0033] Figure 4 4.3V DSC curves of the composite positive electrode materials prepared in Example 1 and Comparative Example 1 of the present invention.

[0034] Figure 5 This is an electron microscope photograph of the composite positive electrode material prepared in Example 1 of the present invention after cutting (the inner core is radial).

[0035] Figure 6 This is an electron microscope photograph of the composite positive electrode material prepared in Example 1 of the present invention after cutting (the inner core has a porous structure). DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] Lithium iron manganese phosphate is highly safe and is often used as a positive electrode active material. Currently, lithium iron manganese phosphate is generally used in combination with ternary materials or alone. In related technologies, lithium iron manganese phosphate is used in combination with ternary materials through mechanical mixing. Lithium iron manganese phosphate and ternary materials each exert their own performance, without the effect of complementing each other's strengths, resulting in the need for further improvement in the cycle performance, safety performance and rate performance of composite positive electrode materials.

[0038] In order to further improve the cycle performance, safety performance and rate performance of the composite positive electrode material, the present invention designs a composite positive electrode material, which uses a polycrystalline ternary material with good rate performance but poor life and safety as the core, and a single crystal ternary material with good life and LiMn with good safety. x Fe 1-x PO4 composite heterogeneous structure as the shell. This design of the material structure gives full play to the rate performance of polycrystalline ternary materials, avoiding the characteristics of poor life and poor safety of polycrystalline; at the same time, it gives full play to the single crystal ternary material and LiMn x Fe 1-x PO4 has the characteristics of long life and relatively high safety, avoiding the single crystal ternary material and LiMn x Fe 1-x The poor rate performance of PO4 is achieved by taking advantage of its strengths to make up for its weaknesses.

[0039] Specifically, the present invention proposes a composite positive electrode material, comprising: a core, the core comprising a polycrystalline ternary material; and a shell layer, the shell layer covering the surface of the core, the shell layer comprising a single crystal ternary material and an active material LiMn x Fe 1-x Mixture of PO4, 0≤x<1.

[0040] The composite positive electrode material of the present invention has a core-shell structure, the polycrystalline ternary material in the core has high rate performance; the single crystal ternary material in the shell has a longer life than the polycrystalline ternary material in the core, and the LiMn in the shell has a higher rate performance than the single crystal ternary material in the core. x Fe 1-xPO4 is relatively safer than ternary materials. The single crystal ternary material and active material of the shell layer improve safety and lifespan. Due to the presence of the multiphase layer of the shell layer, the high voltage resistance of the polycrystalline ternary material of the core is also improved. The polycrystalline ternary material of the core shortens the lithium ion transmission path due to its radial or porous structure, so that the composite achieves high rate, long life and high safety. The present invention improves the life, safety and rate performance of the composite positive electrode material by designing a suitable structure so that the three materials can comprehensively exert their respective advantages while avoiding their respective disadvantages.

[0041] In some embodiments, x may be 0, in which case the active material LiMn x Fe 1-x PO4 is lithium iron phosphate.

[0042] In some embodiments, 0<x<1, in this case, the active material LiMn x Fe 1-x PO4 is lithium iron manganese phosphate. Lithium iron manganese phosphate is relatively safe and matches the voltage range of ternary materials. The heterogeneous structure of lithium iron manganese phosphate and single crystal ternary materials is used as the shell layer and polycrystalline ternary materials are used as the core, which is more conducive to giving full play to the long life and relatively high safety characteristics of single crystal ternary materials and lithium iron manganese phosphate, avoiding the single crystal ternary materials and LiMn x Fe 1-x PO4 has the characteristics of poor rate performance.

[0043] In some embodiments, the D50 particle size of the active material is smaller than the D50 particle size of the single crystal ternary material. The D50 particle size refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. In the shell structure, the D50 particle size of the active material particles is smaller than the D50 particle size of the single crystal ternary material particles, which can form a good coating effect on the single crystal ternary material, further improve the stability of the single crystal ternary material in the shell, and improve the life of the positive electrode material.

[0044] In some embodiments, the particle size of the active material may range from 100 nm to 15 μm. The particle size of the single crystal ternary material may range from 2 to 20 μm.

[0045] In some specific embodiments, the particle size of the active material can be 100 nm-500 nm, 500 nm-800 nm, 800 nm-1 μm, 1 μm-5 μm, 5 μm-10 μm, or 10 μm-15 μm.

[0046] In some specific embodiments, the particle size of the single crystal ternary material may be in the range of 2-5 μm, 5-10 μm, 10-15 μm or 15-20 μm.

[0047] Controlling the particle sizes of the active material and the single crystal ternary material within the scope of the present invention is conducive to forming a better coating effect, improving the stability of the single crystal ternary material in the shell layer, and increasing the life of the positive electrode material.

[0048] In some embodiments, the polycrystalline ternary material has a radial or porous structure inside. The polycrystalline ternary material has a radial or porous structure inside, which can shorten the lithium ion diffusion path and improve the rate performance of the positive electrode material.

[0049] Figure 1 A schematic structural diagram of composite positive electrode material particles including radially shaped polycrystalline ternary materials is given. Figure 2 A schematic structural diagram of composite positive electrode material particles including a polycrystalline ternary material with a porous structure is given.

[0050] In some embodiments, the core is spherical. The use of a spherical core is conducive to obtaining a spherical composite positive electrode material, which is conducive to improving the electrochemical performance, cycle stability, voltage stability and low temperature performance of the battery, while reducing costs and improving energy density. In some specific embodiments, the particle size range of the core is 3-20 μm, for example, 3-5 μm, 5-10 μm, 10-15 μm or 15-20 μm.

[0051] In some embodiments, the mass ratio of the core to the shell may be (80-95): (20-5). Controlling the mass ratio of the core to the shell within the scope of the present invention is beneficial to further improve the life, safety and rate performance of the battery.

[0052] In some specific embodiments, the mass ratio of the inner core to the outer shell may be 80:20, 85:15, 90:10 or 95:5.

[0053] In the present invention, the mass ratio of the inner core to the shell layer is the mass ratio of the raw material forming the inner core to the raw material forming the shell layer. For example, the mass ratio of the inner core to the shell layer is the ratio of the mass of the polycrystalline ternary material to the total mass of the active material and the single crystal ternary material; or, the mass ratio of the inner core to the shell layer is the ratio of the mass of the polycrystalline ternary material to the total mass of the active material, the single crystal ternary material and the carbon source.

[0054] In some embodiments, the shell layer further comprises a conductive agent, which can improve the conductivity of the positive electrode material itself.

[0055] In some embodiments, the composite cathode material further includes: a coating layer, which is coated on the outer surface of the shell layer, and the coating layer includes a metal oxide. Coating the outer surface of the shell layer can protect the inner layer material, making the inner layer material more stable, and further improving the battery life, safety and rate performance. By organically combining the core, the shell layer and the coating layer, the high safety, long cycle performance and high rate performance of the cathode material can be ensured.

[0056] In some specific embodiments, the metal oxide includes one or more of oxides of Group II metals, oxides of Group III metals, and transition metal oxides.

[0057] In some specific embodiments, the metal oxide includes one or more of aluminum oxide, magnesium oxide, and zirconium oxide.

[0058] In some specific embodiments, the carbon material includes at least one of glucose and cellulose.

[0059] In some embodiments, the composition chemical formula of the polycrystalline ternary material is LiNi a Co b Mn c O2, where 0.7 < a < 1, 0 < b < 0.3, 0 < c < 0.3, and a + b + c = 1. The composition chemical formula of the single crystal ternary material is LiNi x Co y Mn z O2, where 0.3 < x < 0.7, 0 < y < 0.4, 0 < z < 0.4, and x + y + z = 1.

[0060] The second aspect of the present invention proposes a method for preparing the composite cathode material of the first aspect of the present invention, including the following steps:

[0061] Provide a polycrystalline ternary material;

[0062] Mix the polycrystalline ternary material, the active material LiMn x Fe 1-x PO4, the single crystal ternary material, and a solvent, spray dry, and sinter to obtain the composite cathode material.

[0063] The present invention prepares a composite cathode material with a core-shell structure by mixing raw materials, spray drying and then sintering. This material has the advantages of long life, high safety, high rate, etc. At the same time, the method of the present invention is simple in operation, low in production process difficulty, easy to repeat and realize industrial production.

[0064] In some embodiments, the mixing includes: mixing the active material, the single crystal ternary material, the solvent and the carbon source together to obtain a suspension; adding the polycrystalline ternary material to the suspension and mixing; wherein the ratio of the mass of the polycrystalline ternary material to the total mass of the single crystal ternary material, the active material and the carbon source is (0.8-0.95):(0.05-0.2). By controlling the mass ratio of the polycrystalline ternary material, the active material, the single crystal ternary material and the carbon source, the mass ratio of the core to the shell in the composite positive electrode material can be controlled, which is conducive to further improving the life, safety and rate performance of the battery.

[0065] In some specific embodiments, the ratio of the mass of the polycrystalline ternary material to the total mass of the single crystal ternary material, the active material and the carbon source is 0.95:0.05, 0.9:0.1, 0.85:0.15 or 0.8:0.2.

[0066] The carbon source is carbonized during the sintering process to form a conductive carbonaceous material, which not only enhances the conductivity of the cathode material itself, but also forms oxygen defects on the surface of the single crystal ternary material, thereby improving the rate performance of the single crystal ternary material. Furthermore, since the material stability of the shell is higher than that of the core, the overall stability and safety of the cathode material are improved.

[0067] In some embodiments, the carbon source includes one or more of glucose, hydroxymethyl cellulose, sucrose, and fructose. Preferably, the carbon source includes glucose and hydroxymethyl cellulose. These carbon sources can not only be carbonized to form conductive carbonaceous materials, but also have a certain thickening effect when forming a suspension, which is conducive to forming the core-shell structure of the present invention.

[0068] In some embodiments, the solvent includes one or more of water, alcohol, and propylene glycol.

[0069] In some embodiments, the particle size of the active material may range from 100nm to 15μm. The particle size of the single crystal ternary material may range from 2 to 20μm. In some specific embodiments, the particle size of the active material may range from 100nm to 500nm, 500nm to 800nm, 800nm ​​to 1μm, 1μm to 5μm, 5μm to 10μm, or 10μm to 15μm. In some specific embodiments, the particle size of the single crystal ternary material may range from 2 to 5μm, 5 to 10μm, 10 to 15μm, or 15 to 20μm.

[0070] In some embodiments, the particle size of the polycrystalline ternary material is in the range of 3-20 μm, for example, 3-5 μm, 5-10 μm, 10-15 μm or 15-20 μm.

[0071] In some embodiments, sintering is performed in an inert atmosphere. Preferably, the sintering temperature is 300-1000° C. and the sintering time is 3-48 hours. By optimizing the sintering conditions, a stable core-shell structure is formed, which further improves the life, safety and rate performance of the battery.

[0072] In some specific embodiments, the sintering temperature may be 300° C., 400° C., 500° C., 600° C., 700° C., 800° C., 900° C., or 1000° C. The sintering time may be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 12 h, 24 h, 36 h, or 48 h.

[0073] In some embodiments, providing a polycrystalline ternary material includes:

[0074] Mixing a nickel-cobalt-manganese salt solution, an alkali solution, and a complexing agent to react to obtain a polycrystalline ternary precursor;

[0075] The polycrystalline ternary precursor and the lithium salt are sintered at 600-1000° C. to obtain the polycrystalline ternary material.

[0076] The polycrystalline ternary material prepared by the present invention has a radial or porous structure inside, which can shorten the lithium ion diffusion path and improve the rate performance of the positive electrode material.

[0077] In some specific embodiments, the concentration of the nickel-cobalt-manganese salt solution is 0.1-3 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.2 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0078] In some specific embodiments, the alkaline solution includes one or more of a sodium hydroxide solution and a sodium bicarbonate solution.

[0079] In some specific embodiments, the complexing agent includes one or more of ammonia water and hydrazine hydrate compounds.

[0080] In some embodiments, the molar ratio of lithium salt to polycrystalline ternary precursor is 1.0 to 1.2:1, such as 1:1, 1.1:1 or 1.2:1, in terms of Li / Me; wherein Me represents all metal elements in the polycrystalline ternary precursor.

[0081] In some embodiments, the sintering of the polycrystalline ternary precursor and the lithium salt may be performed at 600°C, 700°C, 800°C, 900°C, or 1000°C.

[0082] In some embodiments, the particle size of the polycrystalline ternary precursor is in the range of 3-20 μm, for example, 3-5 μm, 5-10 μm, 10-15 μm or 15-20 μm.

[0083] In some embodiments, after sintering, the method further comprises: forming a coating layer on the surface of the obtained composite positive electrode material. The coating layer can protect the inner layer material, make the inner layer material more stable, and further improve the life, safety and rate performance of the battery.

[0084] In some specific embodiments, forming the coating layer comprises: ball milling the obtained composite positive electrode material and the coating material, and sintering them in an inert atmosphere to form the coating layer. The coating material comprises a metal oxide or a carbon material. The metal oxide may comprise one or more of an oxide of a second main group metal, an oxide of a third main group metal, and a transition metal oxide; the carbon material may comprise at least one of glucose and cellulose.

[0085] In some embodiments, after spray drying and before sintering, the particles formed after spray drying are mixed with glucose or polyvinyl pyrrolidone (PVP) and dried. Glucose and polyvinyl pyrrolidone are both carbonaceous substances, which can be dehydrogenated to form carbon after sintering.

[0086] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0087] Example 1

[0088] (1) Use deionized water to prepare nickel-cobalt-manganese sulfate solution, remove impurities from the solution and set it aside; ammonia water and liquid caustic soda are set aside. The concentration range of the salt solution is 3 mol / L. The liquid caustic soda is sodium hydroxide solution with a concentration of 4 mol / L.

[0089] (2) Adding nickel-cobalt-manganese sulfate solution (with a molar ratio of nickel:cobalt:manganese = 8:1:1), liquid alkali, and ammonia water into a reactor at a fixed flow rate, and mixing and controlling the pH to 11 to react, thereby obtaining a spherical polycrystalline ternary precursor with a particle size of 3 to 20 μm.

[0090] (3) Sintering the lithium salt and the polycrystalline ternary precursor in a muffle furnace at a Li / Me molar ratio of 1.0 to 1.2, wherein the sintering temperature is between 700° C. to obtain a polycrystalline ternary material.

[0091] (4) Mix lithium manganese iron phosphate (particle size between 100nm and 15μm, D50 particle size of 1.5um, Mn / Fe of 6:4), single crystal 6 series ternary material (purchased from Dangsheng Technology Co., Ltd., particle size between 2 and 20μm, D50 particle size of 5μm) with glucose, hydroxymethyl cellulose, and deionized water to form a suspension. After the above suspensions are mixed, add the polycrystalline ternary material prepared in step 3 and continue stirring. Composite particles are obtained after spray drying at a temperature of 200°C. The composite particles are mixed with a 2mo / L glucose solution and then dried.

[0092] (5) The material obtained in step 4 is placed in a muffle furnace and sintered in an argon atmosphere; wherein the sintering temperature is 450° C. and the sintering time is 6 hours.

[0093] (6) The material obtained in step 5 was ball-milled with alumina at a material:alumina mass ratio of 0.999:0.001 for 6 h, and then sintered in an argon atmosphere, wherein the sintering temperature was 400° C. and the sintering time was 5 h.

[0094] The core of the prepared composite cathode material is radial or porous, and after cutting, it is shown under an electron microscope as follows: Figure 5 , Figure 6 shown.

[0095] Example 2

[0096] A composite positive electrode material was prepared according to the method of Example 1, except that lithium manganese iron phosphate was replaced by lithium iron phosphate.

[0097] Example 3

[0098] A composite positive electrode material is prepared according to the method of Example 1, except that the mass ratios of the polycrystalline ternary material, the active material, the single crystal ternary material, and the carbon source are shown in Table 1 below.

[0099] Example 4

[0100] A composite positive electrode material is prepared according to the method of Example 1, except that the mass ratios of the polycrystalline ternary material, the active material, the single crystal ternary material, and the carbon source are as shown in Table 1 below.

[0101] Example 5

[0102] A composite positive electrode material was prepared according to the method of Example 1, except that step 6 was not performed.

[0103] Comparative Example 1

[0104] According to steps 1 to 3 of Example 1, a polycrystalline ternary material was prepared as a positive electrode material.

[0105] Comparative Example 2

[0106] The composite positive electrode material is prepared according to the method of Example 1, except that in step 4, no single crystal 6-series ternary material is used.

[0107] Comparative Example 3

[0108] The composite positive electrode material was prepared according to the method of Example 1, except that lithium manganese iron phosphate was not used in step 4.

[0109] According to the following general method, lithium ion batteries were prepared respectively using the positive electrode materials prepared in Examples 1 to 7 and Comparative Examples 1 to 3.

[0110] Preparation of lithium-ion batteries

[0111] (1) Preparation of positive electrode sheet

[0112] The positive electrode material, conductive carbon SP, and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:1:1, and N-methyl-2-pyrrolidone (NMP) was added and mixed evenly. 2 The surface density of the electrode was coated on aluminum foil and dried at 120°C for 8 hours. After drying, the electrode was cut into electrode pieces using a cutting tool.

[0113] (2) Preparation of negative electrode sheet

[0114] Graphite, conductive carbon SP, and adhesive PVDF were mixed in a mass ratio of 8:1:1, and NMP was added to mix evenly. The mixture was coated on aluminum foil at a surface density corresponding to the positive electrode and dried at 120°C for 8 hours. After drying, the electrode was cut into electrode pieces using a cutting tool.

[0115] (3) Assembling lithium-ion batteries

[0116] The positive electrode sheet, negative electrode sheet, separator and aluminum-plastic film are assembled into a battery.

[0117] Composite cathode materials and lithium-ion battery performance testing

[0118] (1) 100% DOD cycle performance test of lithium-ion batteries:

[0119] The button cell was assembled according to the methods of GB / T 37201 and GB / T 42161, and the test voltage range was 2.8 V to 4.35 V. The test results are shown in Table 1 below.

[0120] (2) DSC test of composite cathode materials:

[0121] Weigh 5 mg of the material and place it in a crucible; the heating rate is 5°C / min, the temperature range is 25°C to 400°C, and the curve in the temperature range of 175°C to 350°C is intercepted for plotting. The test results are shown in Table 1 below. The higher the absorption peak, the better the safety.

[0122] (3) Rate performance test

[0123] Assemble button cells according to the method of GB / T 37201. After fully charging the assembled battery, discharge it at a discharge rate of 0.33C and record the capacity C1. Then, fully charge it again and discharge it at a discharge rate of 5C, record the capacity C2. The ratio of C2 / C1 is used to examine the rate performance of the battery material. The larger the C2 / C1, the better the rate performance. The test results are shown in Table 1 below.

[0124] Table 1

[0125]

[0126] By comparing the embodiments with the comparative examples, it can be seen that the present invention uses a polycrystalline ternary material with good rate performance but poor life and safety as the core, and uses a single crystal ternary material with good life and LiMn with good safety. x Fe 1-x The PO4 composite heterostructure is used as the shell layer. This design of the material structure gives full play to the rate performance of polycrystalline ternary materials, avoiding the poor life and safety of polycrystalline materials; at the same time, it gives full play to the single crystal ternary materials and LiMn x Fe 1-x PO4 has the characteristics of long life and relatively high safety, avoiding the single crystal ternary material and LiMn x Fe 1-x The poor rate performance of PO4 is achieved by taking advantage of its strengths to make up for its weaknesses. Therefore, the present invention provides a composite positive electrode material with long life, high safety and high rate.

[0127] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0128] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0129] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A composite positive electrode material, characterized in that: include: a core, the core comprising a polycrystalline ternary material; as well as Shell layer, the shell layer is coated on the surface of the core, and the shell layer includes single crystal ternary material and active material LiMn x Fe 1-x Mixture of PO4, 0≤x<1.

2. The composite positive electrode material according to claim 1, characterized in that 0<x<1, the active material is lithium manganese iron phosphate.

3. The composite positive electrode material according to claim 1 or 2, characterized in that: The D50 particle size of the active material is smaller than the D50 particle size of the single crystal ternary material; the particle size range of the active material is 100nm-15μm, and the particle size range of the single crystal ternary material is 2-20μm.

4. The composite positive electrode material according to claim 1 or 2, characterized in that: The polycrystalline ternary material has a radial or porous structure inside; the inner core is spherical.

5. The composite positive electrode material according to claim 1 or 2, characterized in that: The mass ratio of the inner core to the outer shell is (80-95):(20-5).

6. The composite positive electrode material according to claim 1 or 2, characterized in that: The shell layer also includes a conductive agent.

7. The composite positive electrode material according to claim 1 or 2, characterized in that: Also includes: A coating layer, the coating layer is coated on the outer surface of the shell layer, and the coating layer includes a metal oxide or a carbon material; The metal oxide includes one or more of oxides of metals of the second main group, oxides of metals of the third main group, and transition metal oxides; and the carbon material includes at least one of glucose and cellulose.

8. A method for preparing the composite positive electrode material according to any one of claims 1 to 7, characterized in that: The following steps are involved: Provide polycrystalline ternary materials; The polycrystalline ternary material, the active material LiMn x Fe 1-x PO4, single crystal ternary material and solvent are mixed, spray dried and sintered to obtain the composite positive electrode material.

9. The method according to claim 8, characterized in that The mixing includes: mixing the active material, the single crystal ternary material, the solvent and the carbon source together to obtain a suspension; adding the polycrystalline ternary material to the suspension and mixing; wherein the ratio of the mass of the polycrystalline ternary material to the total mass of the single crystal ternary material, the active material and the carbon source is (0.8-0.95):(0.05-0.2).

10. The method according to claim 8 or 9, characterized in that: The sintering is carried out in an inert atmosphere; the sintering temperature is 300-800°C and the sintering time is 3-12h.

11. The method according to claim 8 or 9, characterized in that: The polycrystalline ternary materials provided include: Mixing a nickel-cobalt-manganese salt solution, an alkali solution, and a complexing agent to react to obtain a polycrystalline ternary precursor; Sintering the polycrystalline ternary precursor and lithium salt at 600-1000° C. to obtain the polycrystalline ternary material; The concentration of the nickel-cobalt-manganese salt solution is 0.1-3 mol / L; The alkaline solution includes one or more of a sodium hydroxide solution and a sodium bicarbonate solution; The complexing agent includes one or more of ammonia water and hydrazine hydrate compounds.

12. The method according to claim 8 or 9, characterized in that: After sintering, the method further comprises: forming a coating layer on the surface of the obtained composite positive electrode material.

13. A battery, characterized in that: The invention comprises the composite positive electrode material according to any one of claims 1 to 7 or the composite positive electrode material obtained by the method according to any one of claims 8 to 12.

14. An electrical device, characterized in that: Comprising the battery of claim 13.

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