Positive electrode material, method for preparing the same, secondary battery, and electric device

Abstract

The application provides a positive electrode material, a preparation method thereof, a secondary battery and an electric device. The positive electrode material comprises positive electrode material particles with a core-shell structure, the core layer of the positive electrode material particles comprises lithium nickel cobalt manganese oxide, the surface of the core layer is provided with a first shell layer and a second shell layer, the first shell layer is arranged between the core layer and the second shell layer, the first shell layer comprises lithium nickel cobalt manganese aluminum oxide, and the second shell layer comprises lithium nickel cobalt aluminum oxide. The positive electrode material has the advantages of high nickel cobalt manganese material specific capacity and good nickel cobalt aluminum material stability, can balance high specific capacity, good cycle performance and safety performance, and has a wide application prospect.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high energy density, low self-discharge rate, and long service life. They have been widely used in 3C electronic products, electric vehicles, large-scale energy storage and other fields. Among them, ternary positive electrode materials have occupied half of the market share in the power battery field due to their advantages such as high gram capacity, high compaction density and low cost. Currently, high-nickel materials are divided into two categories: nickel-cobalt-manganese materials (NCM) and nickel-cobalt-aluminum materials (NCA). Both materials have high reversible capacity, and their application is expected to enable the energy density of power lithium-ion batteries to exceed 300wh / kg. High-nickel materials have a high nickel content and undergo multiple phase changes during the charging process, resulting in poor structural stability and seriously affecting the cycle life of the battery.

[0003] Among them, NCM has an ultra-high gram capacity, but it is prone to cation mixing and H2-H3 phase changes, which lead to problems such as transition metal ion dissolution and cracking of positive electrode material particles, seriously affecting its stability and safety in use. Moreover, the Li / Ni mixing of NCM materials is more serious after long-term cycling, especially when cycling at high voltage. The degree of Li desorption of the material is high, which further promotes Li / Ni mixing, resulting in a faster decay rate of NCM in long-term cycling. In summary, the cycle stability, high-temperature gas production performance and safety performance of NCM are reduced, limiting its application in the field of lithium-ion battery technology. In contrast, NCA has a lower degree of cation mixing, higher stability and safety performance, but its gram capacity is low and cannot meet the needs of high-energy-density power cells. Therefore, it is of great significance to develop high-nickel materials that have high gram capacity, high cycle performance and high safety performance. Summary of the Invention

[0004] The main purpose of the present invention is to provide a positive electrode material and a preparation method thereof, a secondary battery and an electrical device, so as to solve the problem that high nickel positive electrode materials in the prior art cannot achieve both high gram capacity and good cycle performance and safety performance.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a positive electrode material is provided, comprising positive electrode material particles with a core-shell structure, wherein the core layer of the positive electrode material particles comprises lithium nickel cobalt manganese oxide, and a first shell layer and a second shell layer are arranged on the surface of the core layer, the first shell layer is arranged between the core layer and the second shell layer, the first shell layer comprises lithium nickel cobalt manganese aluminum oxide, and the second shell layer comprises lithium nickel cobalt aluminum oxide.

[0006] Furthermore, the molar percentage of nickel in the core layer is defined as W Ni0, the molar percentage of cobalt is W Co0 , the molar percentage of manganese is W Mn0 ; The molar percentage of nickel in the first shell is W Ni1 , the molar percentage of cobalt is W Co1 , the molar percentage of manganese is W Mn1 , the molar percentage of aluminum is W Al1 ; The molar percentage of nickel in the second shell is W Ni2 , the molar percentage of cobalt is W Co2 , the molar percentage of aluminum is W Al2 , then the positive electrode material particles meet at least one of the following conditions: (i) W Mn0 %>W Mn1 %; (ii) W Al1 %<W Al2 %; (iii) W Ni0 %≥80%,W Ni1 %≥80% and W Ni2 %≥80%; (iv)W Co0 %≥1%,W Co1 %≥1% and W Co2 %≥1%.

[0007] Furthermore, the average diameter of the core layer is 5 to 9 μm; and / or the thickness of the first shell layer is 2 to 5 μm; and / or the thickness of the second shell layer is 1 to 2 μm.

[0008] Furthermore, a coating layer is provided on the surface of the second shell layer, the coating layer comprises a coating element G, wherein G comprises one or more of Al, Ti, B, Sr, Y and W; and / or the coating layer comprises G m O n , where 1≤m≤3, 1≤n≤4; and / or G m O n Contains one or more of Al2O3, TiO2, B2O3, W2O3 and Y2O3; and / or the thickness of the coating layer is 10 to 50 nm.

[0009] Furthermore, the positive electrode material particles further include a doping element M, wherein M is one or more of Cr, Sr, Y, W, Zr, Ti, La, Nb and Mo.

[0010] Furthermore, the positive electrode material particles include secondary particles composed of primary particles; preferably, the average particle size of the primary particles is 100 to 500 nm, and the average particle size of the positive electrode material particles is 8 to 15 μm.

[0011] Furthermore, the specific surface area of ​​the positive electrode material particles is 0.2 to 0.7 m 2 / g, tap density is 2.2~3.0g / cm3 , the residual lithium content on the surface is 1000-1500ppm.

[0012] According to another aspect of the present invention, a method for preparing the above-mentioned positive electrode material is provided, comprising the following steps: step S1, adding a solution containing nickel, cobalt and manganese, a first complexing agent and a first precipitant to a reactor, performing a first coprecipitation to obtain a nickel-cobalt-manganese layer; step S2, continuing to add a solution containing nickel, cobalt, manganese and aluminum, a second complexing agent and a second precipitant to the reactor, performing a second coprecipitation to obtain a positive electrode material composite; step S3, continuing to add a solution containing nickel, cobalt and aluminum, a third complexing agent and a third precipitant to the reactor, performing a third coprecipitation to obtain a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor; step S4, treating the nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor with the nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor. The cathode material is mixed with a lithium source and a doping substance, and subjected to a first high-temperature sintering to obtain a sintered product; in step S5, the sintered product and the coating substance are mixed, and subjected to a second high-temperature sintering to obtain a cathode material; wherein, the cathode material composite is sequentially nickel-cobalt-manganese layer-nickel-cobalt-manganese-aluminum layer from the inside to the outside; the nickel-cobalt-manganese-aluminum quaternary cathode material precursor is sequentially nickel-cobalt-manganese layer-nickel-cobalt-aluminum layer from the inside to the outside; the cathode material includes cathode material particles; wherein, the doping substance is one or more oxides and / or hydroxides of Cr, Sr, Y, W, Zr, Ti, La, Nb, and Mo; and the coating substance is one or more oxides and / or hydroxides of Al, Ti, B, Sr, Y, and W.

[0013] According to another aspect of the present invention, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises the positive electrode material of the present invention or the positive electrode material prepared by the above preparation method.

[0014] According to another aspect of the present invention, there is provided an electric device comprising the above-mentioned secondary battery.

[0015] The positive electrode material of the present invention has a multi-layer core-shell structure, with a core layer comprising lithium nickel cobalt manganese oxide as the energy core, a first shell layer comprising lithium nickel cobalt manganese aluminum oxide as the transition layer, and a second shell layer comprising lithium nickel cobalt aluminum oxide as the stability shell, which can make up for the respective disadvantages of nickel cobalt manganese material and nickel cobalt aluminum material, so that the positive electrode material has the advantages of high gram capacity of nickel cobalt manganese material and good stability of nickel cobalt aluminum material. Among them, the first shell layer comprising lithium nickel cobalt manganese aluminum oxide can also play a buffering role, which can significantly alleviate the internal stress of the positive electrode material and reduce the problem of particle breakage that is easy to occur in the material during long-term circulation, thereby improving the cycle performance of the positive electrode material. In summary, the positive electrode material of the present invention can take into account high gram capacity and good cycle performance and safety performance, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 A schematic diagram of the particle structure of the positive electrode material according to Example 1 of the present invention is shown;

[0018] Figure 2 shows an SEM image of the positive electrode material according to Example 1 of the present invention;

[0019] Figure 3 shows an XRD pattern of the positive electrode material according to Example 1 of the present invention;

[0020] Figure 4 shows the EDS analysis results of the particle cross section of the positive electrode material according to Example 1 of the present invention; and

[0021] Figure 5 The first charge and discharge curve of the battery of the positive electrode material according to Example 1 of the present invention is shown.

[0022] The above drawings include the following reference numerals:

[0023] A, core layer; B, first shell layer; C, second shell layer; D, coating layer; a, charging curve; b, discharge curve. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] It should be noted that the nitrogen used in the present invention is a high-purity gas with a purity of ≥99.99%, and the oxygen is industrial-grade oxygen.

[0026] It should be noted that the primary particle size mentioned in the present invention refers to the particle size of the crystal grains, and the secondary particle size refers to the particle size of the agglomerated particles.

[0027] It should be noted that the DSC described in the present invention refers to: a positive electrode sheet containing a positive electrode material, and the highest peak temperature in the DSC spectrum tested when the electrolyte is added at full charge of 4.2V can reflect the difference in thermal stability of the positive electrode material itself.

[0028] As described in the background of the present invention, the prior art has the problem that high-nickel positive electrode materials cannot achieve both high gram capacity and good cycle performance and safety performance. To address the above problems, in a typical embodiment of the present invention, a positive electrode material is provided, comprising positive electrode material particles having a core-shell structure, wherein the core layer of the positive electrode material particles comprises lithium nickel cobalt manganese oxide, and a first shell layer and a second shell layer are provided on the surface of the core layer, wherein the first shell layer is disposed between the core layer and the second shell layer, the first shell layer comprises lithium nickel cobalt manganese aluminum oxide, and the second shell layer comprises lithium nickel cobalt aluminum oxide.

[0029] As mentioned above, nickel-cobalt-manganese material (NCM) has an ultra-high gram capacity, but its stability and safety of use are relatively low. Nickel-cobalt-aluminum material (NCA) has higher stability and safety performance, but its gram capacity is relatively low. The positive electrode material of the present invention is provided with a multi-layer core-shell structure, with a core layer comprising lithium nickel-cobalt-manganese oxide as the energy core, a first shell comprising lithium nickel-cobalt-manganese aluminum oxide as the transition layer, and a second shell comprising lithium nickel-cobalt-aluminum oxide as the stability shell, so that the positive electrode material can have the advantages of high gram capacity of NCM material and good stability of NCA material. Moreover, the surface of the second shell is rich in Al and poor in Mn, which can inhibit the irreversible phase change of the interface and alleviate the dissolution of transition metals. The transition layer can play a buffering role, reducing the problem of particle breakage that is easy to occur in the material during long-term circulation, thereby improving the cycle performance of the positive electrode material. The core-shell material without a transition layer is prone to severe cracking after lithium intercalation and deintercalation due to large core stress and small shell stress, and the circulation and gas production performance deteriorate. In summary, the positive electrode material of the present invention can already take into account high gram capacity and good cycle performance and safety performance, and has broad application prospects.

[0030] In a preferred embodiment, the molar percentage of nickel in the core layer is defined as W Ni0 , the molar percentage of cobalt is W Co0 , the molar percentage of manganese is W Mn0 ; The molar percentage of nickel in the first shell is W Ni1 , the molar percentage of cobalt is W Co1 , the molar percentage of manganese is W Mn1 , the molar percentage of aluminum is W Al1 ; The molar percentage of nickel in the second shell is W Ni2 , the molar percentage of cobalt is W Co2 , the molar percentage of aluminum is W Al2 , then the positive electrode material particles meet at least one of the following conditions: (i) W Mn0 %>W Mn1 %; (ii) W Al1 %<W Al2 %; (iii) W Ni0 %≥80%,W Ni1 %≥80% and WNi2 ≥ 80%; (iv) W Co0 ≥ 1%, W Co1 ≥ 1% and W Co2 ≥ 1%.

[0031] In a preferred embodiment, the molar percentage content of nickel in the core is defined as W Ni0 , the molar percentage content of cobalt is defined as W Co0 , the molar percentage content of manganese is defined as W Mn0 , the molar percentage content of aluminum is defined as W Al0 ; the molar percentage content of nickel in the first shell is defined as W Ni1 , the molar percentage content of cobalt is defined as W Co1 , the molar percentage content of manganese is defined as W Mn1 , the molar percentage content of aluminum is defined as W Al1 ; the molar percentage content of nickel in the second shell is defined as W Ni2 , the molar percentage content of cobalt is defined as W Co2 , the molar percentage content of manganese is defined as W Mn2 , the molar percentage content of aluminum is defined as W Al2 , then the positive electrode material particle satisfies at least one of the following conditions: (i) W Mn0 > W Mn1 > W Mn2 ; (ii) W Al0 < W Al1 < W Al2 ; (iii) W Ni0 = W Ni1 = W Ni2 ; (iv) W Co0 = W Co1 = W Co2 .

[0032] Controlling the above elements of each layer of material within the above range can better maintain the purpose of the positive electrode material to gradually reduce the Mn content from the center of the inner core to the surface of the shell structure, gradually increase the Al content from the center of the inner core to the surface of the shell structure, and maintain the content trend of the Ni content and Co content from the center of the inner core to the surface of the shell structure, thereby better balancing the capacity, cycle performance and safety performance.

[0033] In order to further control the thickness of different structural layers, make the difference of Mn content and Al content in the material more reasonable, and further improve the specific capacity, stability and safety of the positive electrode material, in a preferred embodiment, the average diameter of the core layer is 5-9 μm, which is convenient for subsequent precipitation as the first shell layer and the second shell layer; and / or the thickness of the first shell layer is 2-5 μm; and / or the thickness of the second shell layer is 1-2 μm, so that the positive electrode material can better combine the advantages of high specific capacity of NCM material and good stability of NCA material.

[0034] In a preferred embodiment, the surface of the second shell layer is further provided with a cladding layer, and the cladding layer contains cladding elements G, wherein G contains one or more of Al, Ti, B, Sr, Y and W; and / or the cladding layer contains G m O n , wherein 1≤m≤3, 1≤n≤4; and / or G m O n contains one or more of Al2O3, TiO2, B2O3, W2O3 and Y2O3, and preferably the weight of the cladding element is 500-2000 ppm of the weight of the positive electrode material. The above-mentioned cladding layer can better inhibit the dissolution of nickel, cobalt, manganese and aluminum elements in the positive electrode material, further improve the charge transfer rate of the positive electrode material body (i.e. the core layer and the first shell layer and the second shell layer), and the ion transfer rate between the material and the electrolyte, thereby promoting the embedding and extraction of lithium ions, reducing the side reaction of high-valence nickel, residual lithium and electrolyte on the surface of the positive electrode material, and further improving the specific capacity, stability and safety and other electrochemical properties of the positive electrode material. When the thickness of the cladding layer is too small, it cannot play a cladding effect on the core layer structure and the shell structure; when the thickness of the cladding layer is too large, it is not conducive to the capacity performance of the material, therefore the thickness of the cladding layer is further preferably 10-50 nm.

[0035] In order to further improve the long-term cycle performance and safety performance of the positive electrode material, in a preferred embodiment, the positive electrode material particle further comprises a doping element M, wherein M is one or more of Cr, Sr, Y, W, Zr, Ti, La, Nb and Mo. The above-mentioned doping element exists in the core layer, the first shell layer and the second shell layer at the same time, which can not only improve the electrochemical properties and structural stability of the positive electrode material, but also can play the role of a dissolving agent, realize low-temperature high-crystallinity sintering of high-nickel materials, especially when applied to the positive electrode material of the present application, which can reduce the sintering temperature, help particle growth, and at the same time ensure that the material has a high crystallinity, avoid the problem of increasing oxygen defects on the surface of the material caused by high-temperature sintering, so that the material maintains a difference in the distribution of gradually decreasing Mn content and gradually increasing Al content from the inside to the outside, and at the same time avoids the problem of increasing oxygen defects on the surface of the material caused by high-temperature sintering.

[0036] For the purpose of better exerting the high capacity performance of NCM material and the high cycle performance and safety performance of NCA material, and obtaining positive electrode material with better performance, in a preferred embodiment, the elements of the positive electrode material particles satisfy the following general formula: Li θ (Ni a Co b Mn c Al d ) 1-x M x O2, wherein 0.95≤θ≤1.07, 0.8≤a≤0.99, 0≤b≤0.15, 0≤c≤0.10, 0≤d≤0.02, 0≤x≤0.005, and θ, a, b, c, d and x satisfy the valence balance; for further reducing the sintering temperature, and making the material better maintain the element difference distribution from inside to outside, preferably, 0.0005≤x≤0.005.

[0037] In a preferred embodiment, the chemical formula of the core layer comprises Li θ1 (Ni a1 Co b1 Mn c1 ) 1-x1 M x1 O2, wherein 0.95≤θ1≤1.07, 0.8≤a1≤0.99, 0≤b1≤0.15, 0≤c1≤0.08, 0≤x1≤0.005; and / or the chemical formula of the first shell layer comprises Li θ2 (Ni a2 Co b2 Mn c2 Al d2 ) 1-x2 M x2 O2, wherein 0.95≤θ2≤1.07, 0.8≤a2≤0.99, 0≤b2≤0.15, 0≤c2≤0.06, 0≤d2≤0.02, 0≤x2≤0.005; and / or the chemical formula of the second shell layer comprises Li θ3 (Ni a3 Co b3 Al d3 ) 1-x3 M x3 O2, wherein 0.95≤θ3≤1.07, 0.8≤a3≤0.99, 0≤b3≤0.15, 0≤d3≤0.08, 0≤x3≤0.005.

[0038] By controlling the element content of each layer of material within the above range, the ratio of the NCM material with high capacity and the NCA material with good stability can be better balanced, and the composition of the NCMA intermediate layer is controlled, so that the positive electrode material can better maintain the trend that the Mn content gradually decreases from the core center to the surface of the shell structure, the Al content gradually increases from the core center to the surface of the shell structure, and the Ni content and Co content remain almost unchanged from the core center to the surface of the shell structure. For example, in some embodiments, from the core structure to the shell structure, the molar ratio of Mn gradually decreases from 0.03-0.08 to 0.005-0.02, and the molar ratio of Al gradually increases from 0.005-0.02 to 0.03-0.08.

[0039] In a preferred embodiment, the positive electrode material particles comprise secondary particles composed of primary particles, and the secondary particles are formed by agglomeration of primary particles. When the particle size of the primary particles is too small or too large, the concentration difference of Mn and Al is difficult to appear, and therefore the average particle size of the primary particles is preferably 100-500 nm. The primary particles with the above particle size increase the metal ion diffusion distance, which can effectively control the diffusion degree of metal ions during sintering, so that the material after sintering still maintains the gradient structure of the precursor. The average particle size of the positive electrode material particles is preferably 8-15 μm, which is more conducive to the formation and maintenance of the concentration difference of Mn and Al in the material, and also has a more suitable specific surface area, and the diffusion path of lithium ions is shorter, which is beneficial to the intercalation and deintercalation of lithium ions in the material under high current density, thereby further improving the rate performance and cycle performance of the material.

[0040] In a preferred embodiment, the specific surface area of the positive electrode material particles is 0.2-0.7 m 2 / g, the tap density is 2.2-3.0 g / cm 3 , and the surface residual lithium content is 1000-1500 ppm. The positive electrode material within the above range can further reduce the formation of CEI film, the contact area between the material and the electrolyte is moderate, the side reaction during the cycle process is less, the cycle performance is excellent, and it is more conducive to processing and preparation.

[0041] In another typical embodiment of the present invention, a method for preparing the above-mentioned positive electrode material is also provided, comprising the following steps: step S1, adding a solution containing nickel, cobalt and manganese, a first complexing agent and a first precipitant to a reactor, performing a first coprecipitation to obtain a nickel-cobalt-manganese layer; step S2, continuing to add a solution containing nickel, cobalt, manganese and aluminum, a second complexing agent and a second precipitant to the reactor, performing a second coprecipitation to obtain a positive electrode material composite; step S3, continuing to add a solution containing nickel, cobalt and aluminum, a third complexing agent and a third precipitant to the reactor, performing a third coprecipitation to obtain a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor; step S4, treating the nickel-cobalt-manganese-aluminum quaternary positive electrode material. The precursor is mixed with a lithium source and a doping substance, and a first high-temperature sintering is performed to obtain a sintered product; in step S5, the sintered product is mixed with a coating substance, and a second high-temperature sintering is performed to obtain a positive electrode material; wherein, the positive electrode material composite is sequentially nickel-cobalt-manganese layer-nickel-cobalt-manganese-aluminum layer from the inside to the outside; the nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is sequentially nickel-cobalt-manganese layer-nickel-cobalt-aluminum layer from the inside to the outside; the positive electrode material includes positive electrode material particles; wherein, the doping substance is one or more oxides and / or hydroxides of Cr, Sr, Y, W, Zr, Ti, La, Nb, Mo; and the coating substance is one or more oxides and / or hydroxides of Al, Ti, B, Sr, Y, W.

[0042] The preparation process of the positive electrode material in the present invention is a continuous preparation. Through three co-precipitations, nickel-cobalt-manganese, nickel-cobalt-manganese-aluminum and nickel-cobalt-aluminum are precipitated in sequence to form different structural layers, and then lithium is mixed in to obtain the positive electrode material with a multi-layer core-shell structure of the present invention. Specifically, a solution containing nickel, cobalt and manganese, a first chelating agent and a first precipitant are first added to a reactor to carry out a first coprecipitation to obtain a nickel-cobalt-manganese core layer of a precursor; a solution containing nickel, cobalt, manganese and aluminum, a second chelating agent and a second precipitant are continuously added to the reactor to carry out a second coprecipitation to grow a nickel-cobalt-manganese-aluminum transition layer on the surface of the nickel-cobalt-manganese core layer to obtain a nickel-cobalt-manganese-aluminum layer; a solution containing nickel, cobalt and aluminum, a third chelating agent and a third precipitant are continuously added to the reactor to carry out a third coprecipitation to grow a nickel-cobalt-aluminum layer on the surface of the nickel-cobalt-manganese-aluminum transition layer to obtain a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor which is nickel-cobalt-manganese-aluminum layer-nickel-cobalt-aluminum layer from the inside to the outside, wherein the manganese content gradually decreases from the inside to the outside, the aluminum content gradually increases from the inside to the outside, and the nickel content and the cobalt content remain unchanged from the inside to the outside.

[0043] Then the precursor is mixed with a lithium source and a doping material, and first high-temperature sintering is performed to make lithium ions diffuse into the material structure, thereby obtaining a sintered product. The above-mentioned doping material of the present application has a better solubilization effect, which is conducive to reducing the sintering temperature, realizing low-temperature high-crystallinity sintering of high-nickel materials, and better avoiding the uniform diffusion of Al and Mn caused by high-temperature sintering, so that the material after sintering can maintain the differential distribution of Mn and Al. Finally, the sintered product is mixed with a coating material, and second high-temperature sintering is performed to make the coating material form a solid solution and coat the surface, thereby obtaining a positive electrode material. The above-mentioned coating material can better inhibit the dissolution of nickel, cobalt, manganese and aluminum elements in the positive electrode material, further improve the charge transfer rate of the material body and the ion transfer rate between the material and the electrolyte, thereby further improving the specific capacity, stability and safety of the positive electrode material and other electrochemical properties.

[0044] The inventors found in the actual preparation process that, since the precipitation rate of aluminum ions is obviously greater than that of nickel, cobalt and manganese ions, it is very easy to form a colloid in the coprecipitation process of nickel, cobalt and aluminum. The preparation method of the present application uses nickel, cobalt and manganese as crystal nuclei, and makes the nickel, cobalt, manganese and aluminum layers and the nickel, cobalt and aluminum layers grow on the surface of nickel, cobalt and manganese in turn, which can effectively avoid the generation of nano-flocculent precipitates and improve the crystallinity of the material. The sequential coprecipitation of the layers can also make the pores between the primary particles from the inner core to the outer shell uniform and fine, which is conducive to the extraction and embedding of lithium ions, and the positive electrode material after sintering can well inherit the internal structural characteristics of the precursor. The positive electrode material prepared by the above-mentioned method has a core layer containing lithium nickel cobalt manganese oxide as an energy core, a first shell layer containing lithium nickel cobalt manganese aluminum oxide as a transition layer, and a second shell layer containing lithium nickel cobalt aluminum oxide as a stability outer shell, which can have the advantages of high specific capacity of NCM material and good stability of NCA material. The above-mentioned preparation method is simple in process, low in cost, controllable in composition, and can be well applied to existing reaction equipment, has small difficulty in mass production conversion, and is convenient for large-scale industrial production.

[0045] Preferably, the lithium source is lithium hydroxide and / or lithium carbonate; more preferably, the molar ratio of lithium in the lithium source to nickel, cobalt and aluminum in the positive electrode material precursor is (1-1.05):1, so as to ensure the diffusion of lithium ions into the material structure while avoiding the waste of lithium source.

[0046] If the total molar concentration of nickel, cobalt, manganese and aluminum in the co-precipitation process is too low, the co-precipitation time is too long, which is not conducive to production; if it is too high, the settling effect is poor, therefore, in order to better balance the rate and effect of the co-precipitation reaction, and at the same time form a structure layer with the target composition, in a preferred embodiment, the solution containing nickel, cobalt and manganese is a mixed solution of soluble nickel salt, soluble cobalt salt and soluble manganese salt, wherein the total molar concentration of nickel, cobalt and manganese is 2-4 mol / L, and the molar ratio of nickel, cobalt and manganese meets the composition of the nickel-cobalt-manganese core layer; preferably, the solution containing nickel, cobalt, manganese and aluminum is a mixed solution of soluble nickel salt, soluble cobalt salt, soluble manganese salt and soluble aluminum salt, wherein the total molar concentration of nickel, cobalt, manganese and aluminum is 2-3 mol / L, and the molar ratio of nickel, cobalt, manganese and aluminum meets the composition of the nickel-cobalt-manganese-aluminum layer; preferably, the solution containing nickel, cobalt and aluminum is a mixed solution of soluble nickel salt, soluble cobalt salt and soluble aluminum salt, wherein the total molar concentration of nickel, cobalt and aluminum is 1-2 mol / L, and the molar ratio of nickel, cobalt and aluminum meets the composition of the NCA layer. The total molar concentration of the three co-precipitated raw material solutions is distinguished by the above-mentioned, which is more conducive to achieving the differential distribution effect of manganese and aluminum between different structure layers and the uniform distribution effect of nickel and cobalt in the subsequent process, further improving the specific capacity, stability and cycle performance of the positive electrode material.

[0047] The above-mentioned soluble salt can be any salt commonly used in the field of lithium ion battery positive electrode material preparation, in order to further improve the effect of co-precipitation, preferably, the soluble nickel salt is one or more of nickel sulfate, nickel acetate and nickel nitrate; the soluble cobalt salt is one or more of cobalt sulfate, cobalt acetate and cobalt nitrate; the soluble manganese salt is one or more of manganese sulfate, manganese acetate and manganese nitrate; the soluble aluminum salt is one or more of aluminum sulfate, aluminum chloride and aluminum nitrate.

[0048] If the molar concentration of the complexing agent is too low, the metal ions cannot be completely complexed, and if it is too high, it is not conducive to the formation of metal ion precipitate; and if the molar concentration of the precipitant is too low, it is also not conducive to the complexation and precipitation of metal ions, and if it is too high, it is difficult to effectively control the pH value of the reaction solution, therefore, in a preferred embodiment, the first, second and third complexing agents are ammonia water; the first, second and third precipitants are independently selected from aqueous solutions of sodium hydroxide and / or potassium hydroxide; preferably, the molar concentration of the first complexing agent is 0.2-0.4 mol / L, and the molar concentration of the first precipitant is 2-4 mol / L; the molar concentration of the second complexing agent is 0.1-0.3 mol / L, and the molar concentration of the second precipitant is 2-3 mol / L; the molar concentration of the third complexing agent is 0.05-0.2 mol / L, and the molar concentration of the third precipitant is 1-2 mol / L. Under the above-mentioned conditions, the complexation and precipitation effect of each metal ion raw material solution is better.

[0049] When the reaction temperature and the reaction time are too high or too low, the formation of crystal nucleus and the growth of crystal are not controlled, and the particle size, sphericity and uniformity of the prepared precursor are affected. Therefore, in a preferred embodiment, the reaction temperature of the first co-precipitation is 60-80°C, the pH of the reaction system is 10-12, and the reaction time is 72-120 h; preferably, the reaction temperature of the second co-precipitation is 50-70°C, the pH of the reaction system is 8-11, and the reaction time is 24-48 h; preferably, the reaction temperature of the third co-precipitation is 40-50°C, the pH of the reaction system is 8-11, and the reaction time is 24-48 h. The pH of the reaction system is adjusted by the precipitant, and under the above pH, the growth rate of the particles of each structure layer is not too fast or too slow. The above co-precipitation conditions are helpful for the nucleation and growth of each structure layer of the positive electrode material, thereby controlling the crystal form, improving the quality, providing a solid skeleton for the subsequent growth of the secondary particles, preventing the positive electrode material precursor from cracking during the growth process, and controlling the thickness of different structure layers in an appropriate range, further improving the specific capacity, cycle performance and safety performance of the material.

[0050] When the sintering temperature is too high or the sintering time is too long, the primary particles grow too large, the lithium ion deintercalation path is expanded, the specific capacity and rate performance of the material are reduced, and the lithium salt is decomposed and lost seriously during long-time high-temperature sintering, the material is not fully lithiated, and the specific capacity is reduced. When the sintering temperature is too low or the sintering time is too short, the material has insufficient crystallinity, and the electrochemical performance is affected. When the heating rate is too fast, the material reaction is difficult to ensure sufficient, especially affecting the process of lithium ion diffusion into the structure of the material, and when the heating rate is too slow, it is not conducive to industrial production. Preferably, the first high-temperature sintering in step S4 is carried out in an oxygen atmosphere, the heating rate is 0.5-2°C / min, the sintering temperature is 650-800°C, the holding time is 10-24 h, and the cooling rate is 2-3°C / min; preferably, the second high-temperature sintering is carried out in an air atmosphere, the heating rate is 3-5°C / min, the sintering temperature is 200-600°C, the holding time is 6-12 h, and the cooling rate is 2-3°C / min.

[0051] The sintering conditions are more conducive to the formation and maintenance of the structure of the positive electrode material, and the secondary high-temperature sintering conditions are also conducive to the formation of a solid solution of the coating material on the surface of the positive electrode material body layer, thereby improving the coating effect. In addition, as described above, the positive electrode material of the present application adds a doping material during preparation, which can act as a dissolving agent, can reduce the sintering temperature, and realize low-temperature high-crystallinity sintering of high-nickel materials. Therefore, the present application can use a lower sintering temperature, thereby avoiding the uniform diffusion of Al and Mn caused by high-temperature sintering, so that the material maintains a gradient distribution of gradually decreasing Mn content and gradually increasing Al content from the inside to the outside. At the same time, the problem of increasing surface oxygen defects of the material caused by high-temperature sintering is avoided, and the long-term cycle performance and thermal stability of the nickel-cobalt-manganese-aluminum positive electrode material are further improved. The improvement of thermal stability is reflected in the significant improvement of the main exothermic temperature of DSC.

[0052] In another typical embodiment of the present application, a secondary battery is also provided, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet includes the above-mentioned positive electrode material of the present application.

[0053] In another typical embodiment of the present application, a secondary battery is also provided, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet includes the above-mentioned positive electrode material of the present application.

[0054] The present application will be further described in detail below in conjunction with specific examples, which cannot be understood as limiting the scope of the present application.

[0055] Example 1

[0056] A 2 mol / L nickel-cobalt-manganese solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.86:0.11:0.03 was prepared, and 0.2 mol / L ammonia water and 2 mol / L sodium hydroxide aqueous solution were added to a nitrogen atmosphere reactor simultaneously for a first coprecipitation. The reaction temperature was controlled at 80°C, the pH of the reaction system was 11, and the reaction time was 5 days to obtain a nickel-cobalt-manganese core. After the first coprecipitation was completed, a 2 mol / L nickel-cobalt-manganese-aluminum solution containing nickel sulfate, cobalt sulfate, manganese sulfate, and aluminum sulfate in a molar ratio of 0.86:0.11:0.02:0.01 was prepared, and 0.1 mol / L ammonia water and 2 mol / L sodium hydroxide aqueous solution were added to a nitrogen atmosphere reactor simultaneously for a second coprecipitation. The reaction temperature was controlled at 70°C, the pH of the reaction system was 10.5, and the reaction time was 1 day to grow a nickel-cobalt-manganese-aluminum transition layer on the surface of the nickel-cobalt-manganese core. After the second coprecipitation is completed, a 1 mol / L nickel-cobalt-aluminum solution with a molar ratio of nickel sulfate, cobalt sulfate, and aluminum sulfate of 0.86:0.11:0.03 is prepared, and 0.05 mol / L ammonia water and 1 mol / L sodium hydroxide aqueous solution are added to a nitrogen atmosphere reactor at the same time to carry out a third coprecipitation. The reaction temperature is controlled at 50°C, the pH of the reaction system is 9, and the reaction time is 1 day, so that the nickel-cobalt-aluminum layer grows on the surface of the nickel-cobalt-manganese-aluminum transition layer, and a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is obtained, which is nickel-cobalt-manganese core-nickel-cobalt-manganese-aluminum transition layer-nickel-cobalt-aluminum layer from the inside to the outside.

[0057] The prepared nickel-cobalt-manganese-aluminum quaternary cathode material precursor was washed, filtered, and dried, and then a certain amount of lithium hydroxide and strontium oxide were added. After ball milling and mixing, the mixture was placed in an oxygen furnace at 800°C for 24 hours at a heating rate of 0.5°C / min and a cooling rate of 3°C to obtain a sintered product. The amount of lithium hydroxide added was calculated based on a total molar ratio of lithium to nickel-cobalt-manganese-aluminum of 1.05, and the amount of strontium oxide was calculated based on a strontium weight of 3000ppm based on the weight of the cathode material.

[0058] The sintered product was crushed, washed, filtered, and dried, then ball-milled and mixed evenly with alumina, with the amount of alumina calculated to achieve 500 ppm of aluminum relative to the weight of the cathode material. The mixture was then placed in an air furnace at 600°C for a second high-temperature sintering for 12 hours, with a heating rate of 5°C and a cooling rate of 3°C, to obtain the cathode material.

[0059] The positive electrode material prepared in this embodiment has the chemical formula Li(Ni 0.86 Co 0.11 Mn 0.02 Al 0.01 ) 0.997 Sr 0.003O2, the coating layer is Al2O3. The morphology is spherical secondary particles with an average particle size of 10μm, an average core diameter of 5μm, an average thickness of the first shell layer of 3μm, an average thickness of the second shell layer of 2μm, and a coating layer thickness of 20nm. The average particle size of the primary particles on the surface of the material is 200nm, and the BET is 0.5m 2 / g, tap density is 2.5g / cm 3 The residual lithium content on the surface is 1200ppm. The particle structure diagram of the positive electrode material is shown in Figure 1 , SEM images are shown in Figure 2 , XRD pattern see Figure 3 , the EDS analysis results of the particle cross section are shown in Figure 4 . Figure 3 The diffraction peaks are all characteristic peaks of the aNaFeO2 layered structure of the R3m space group, indicating that the core-shell structure material has typical layered structural characteristics. Figure 4 It can be clearly seen that from the core to the shell of the positive electrode material particles, the Ni and Co element contents remain basically unchanged, the Mn element content gradually decreases, and the Al element content gradually increases.

[0060] Example 2

[0061] A 2.5 mol / L nickel-cobalt-manganese solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.86:0.06:0.08 was prepared, and 0.3 mol / L ammonia water and 2.5 mol / L sodium hydroxide aqueous solution were added to a nitrogen atmosphere reactor to perform a first coprecipitation. The reaction temperature was controlled at 60°C, the pH of the reaction system was 10, and the reaction time was 3 days to obtain a nickel-cobalt-manganese core. After the first coprecipitation was completed, a 2 mol / L nickel-cobalt-manganese-aluminum solution containing nickel sulfate, cobalt sulfate, manganese sulfate, and aluminum sulfate in a molar ratio of 0.86:0.06:0.06:0.02 was prepared, and 0.2 mol / L ammonia water and 2 mol / L sodium hydroxide aqueous solution were added to a nitrogen atmosphere reactor to perform a second coprecipitation. The reaction temperature was controlled at 60°C, the pH of the reaction system was 9, and the reaction time was 2 days to grow a nickel-cobalt-manganese-aluminum transition layer on the surface of the nickel-cobalt-manganese core. After the second coprecipitation is completed, a 1 mol / L nickel-cobalt-aluminum solution with a molar ratio of nickel sulfate, cobalt sulfate, and aluminum sulfate of 0.86:0.06:0.08 is prepared, and 0.1 mol / L ammonia water and 1 mol / L sodium hydroxide aqueous solution are added to a nitrogen atmosphere reactor at the same time to carry out a third coprecipitation. The reaction temperature is controlled at 40°C, the pH of the reaction system is 8, and the reaction time is 1 day, so that the nickel-cobalt-aluminum layer grows on the surface of the nickel-cobalt-manganese-aluminum transition layer, and a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is obtained, which is nickel-cobalt-manganese core-nickel-cobalt-manganese-aluminum transition layer-nickel-cobalt-aluminum layer from the inside to the outside.

[0062] The prepared nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is washed, filtered and dried, then a certain amount of lithium carbonate and zirconium hydroxide is added, the mixture is uniformly ball-milled and placed in an oxygen furnace at 750°C for 18h high-temperature sintering, with a heating rate of 1°C / min and a cooling rate of 2°C, to obtain a sintered product. The amount of lithium carbonate added is calculated according to the total molar ratio of lithium element and nickel-cobalt-manganese-aluminum element being 1.03, and the amount of zirconium hydroxide is calculated according to the weight of zirconium element accounting for 2000ppm of the weight of the positive electrode material.

[0063] The sintered product is crushed, washed with water, filtered, dried, and then ball-milled with titanium oxide, the amount of titanium oxide being calculated according to the weight of titanium element accounting for 1000ppm of the weight of the positive electrode material. The mixture is placed in an air furnace at 500°C for 8h secondary high-temperature sintering, with a heating rate of 3°C and a cooling rate of 3°C, to obtain a positive electrode material.

[0064] The positive electrode material prepared in this example has a chemical formula of Li(Ni 0.86 Co 0.06 Mn 0.07 Al 0.01 ) 0.998 Zr 0.002 O2, and a coating layer of TiO2. The morphology is spherical secondary particles with an average particle size of 11μm, the average diameter of the core layer is 8μm, the average thickness of the first shell layer is 2μm, the average thickness of the second shell layer is 1μm, and the thickness of the coating layer is 30nm. The average particle size of the primary particles on the surface of the material is 100nm, the BET is 0.4m 2 / g, the tap density is 2.2g / cm 3 , and the surface residual lithium content is 1000ppm.

[0065] Example 3

[0066] A 2.5 mol / L nickel-cobalt-manganese solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.93:0.04:0.03 was prepared, and added simultaneously with 0.4 mol / L ammonia water and 2.5 mol / L sodium hydroxide aqueous solution to a nitrogen atmosphere reactor for a first coprecipitation. The reaction temperature was controlled at 60°C, the pH of the reaction system was 12, and the reaction time was 5 days to obtain a nickel-cobalt-manganese core. After the first coprecipitation was completed, a 2 mol / L nickel-cobalt-manganese-aluminum solution containing nickel sulfate, cobalt sulfate, manganese sulfate, and aluminum sulfate in a molar ratio of 0.93:0.04:0.02:0.01 was prepared, and added simultaneously with 0.2 mol / L ammonia water and 2 mol / L sodium hydroxide aqueous solution to a nitrogen atmosphere reactor for a second coprecipitation. The reaction temperature was controlled at 50°C, the pH of the reaction system was 9, and the reaction time was 1 day to grow a nickel-cobalt-manganese-aluminum transition layer on the surface of the nickel-cobalt-manganese core. After the second coprecipitation is completed, a 1.5 mol / L nickel-cobalt-aluminum solution with a molar ratio of nickel sulfate, cobalt sulfate, and aluminum sulfate of 0.93:0.04:0.03 is prepared, and 0.1 mol / L ammonia water and 1.5 mol / L sodium hydroxide aqueous solution are added into a nitrogen atmosphere reactor at the same time to carry out a third coprecipitation. The reaction temperature is controlled at 40°C, the pH of the reaction system is 8, and the reaction time is 1 day, so that the nickel-cobalt-aluminum layer grows on the surface of the nickel-cobalt-manganese-aluminum transition layer, and a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is obtained, which is nickel-cobalt-manganese core-nickel-cobalt-manganese-aluminum transition layer-nickel-cobalt-aluminum layer from the inside to the outside.

[0067] The prepared nickel-cobalt-manganese-aluminum quaternary cathode material precursor was washed, filtered, and dried, and then a certain amount of lithium hydroxide and tungsten oxide were added. After ball milling and mixing, the mixture was placed in an oxygen furnace at 800°C for 20 hours at a heating rate of 0.5°C / min and a cooling rate of 2°C to obtain a sintered product. The amount of lithium hydroxide added was calculated based on a total molar ratio of lithium to nickel-cobalt-manganese-aluminum of 1.05, and the amount of tungsten oxide was calculated based on a tungsten weight of 4000ppm based on the weight of the cathode material.

[0068] The sintered product was crushed, washed, filtered, and dried, then ball-milled and mixed with boron oxide (the amount of boron oxide was calculated to be 2000 ppm by weight of the positive electrode material). The mixture was then placed in an air furnace at 200°C for a second high-temperature sintering for 6 hours at a heating rate of 3°C and a cooling rate of 2°C to obtain the positive electrode material.

[0069] The positive electrode material prepared in this embodiment has the chemical formula Li(Ni 0.93 Co 0.04 Mn 0.02 Al 0.01 ) 0.998 W 0.002O2, the coating layer is B2O3. The morphology is spherical secondary particles with an average particle size of 14μm, an average core diameter of 9μm, an average thickness of the first shell layer of 3μm, an average thickness of the second shell layer of 2μm, and a coating layer thickness of 20nm. The average particle size of the primary particles on the surface of the material is 300nm, and the BET is 0.6m 2 / g, and the tap density is 2.9g / cm 3 The residual lithium content on the surface is 1300ppm.

[0070] Example 4

[0071] A 2.5 mol / L nickel-cobalt-manganese solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.93:0.05:0.02 was prepared, and added to a nitrogen atmosphere reactor simultaneously with 0.4 mol / L ammonia water and 2.5 mol / L sodium hydroxide aqueous solution for a first coprecipitation. The reaction temperature was controlled at 70°C, the pH of the reaction system was 11, and the reaction time was 5 days to obtain a nickel-cobalt-manganese core. After the first coprecipitation was completed, a 2 mol / L nickel-cobalt-manganese-aluminum solution containing nickel sulfate, cobalt sulfate, manganese sulfate, and aluminum sulfate in a molar ratio of 0.93:0.05:0.01:0.01 was prepared, and added to a nitrogen atmosphere reactor simultaneously with 0.2 mol / L ammonia water and 2 mol / L sodium hydroxide aqueous solution for a second coprecipitation. The reaction temperature was controlled at 60°C, the pH of the reaction system was 11, and the reaction time was 2 days to grow a nickel-cobalt-manganese-aluminum transition layer on the surface of the nickel-cobalt-manganese core. After the second coprecipitation is completed, a 1 mol / L nickel-cobalt-aluminum solution with a molar ratio of nickel sulfate, cobalt sulfate, and aluminum sulfate of 0.93:0.05:0.02 is prepared, and 0.05 mol / L ammonia water and 1 mol / L sodium hydroxide aqueous solution are added into a nitrogen atmosphere reactor at the same time to carry out a third coprecipitation. The reaction temperature is controlled at 50°C, the pH of the reaction system is 9, and the reaction time is 2 days, so that the nickel-cobalt-aluminum layer grows on the surface of the nickel-cobalt-manganese-aluminum transition layer, and a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is obtained, which is nickel-cobalt-manganese core-nickel-cobalt-manganese-aluminum transition layer-nickel-cobalt-aluminum layer from the inside to the outside.

[0072] The prepared nickel-cobalt-manganese-aluminum quaternary cathode material precursor was washed, filtered, and dried, and then a certain amount of lithium hydroxide and yttrium oxide were added. After ball milling and mixing, the mixture was placed in an oxygen furnace at 650°C for 24 hours at a heating rate of 0.5°C / min and a cooling rate of 2°C to obtain a sintered product. The amount of lithium hydroxide added was calculated based on a total molar ratio of lithium to nickel-cobalt-manganese-aluminum of 1.05, and the amount of yttrium oxide was calculated based on the weight of yttrium accounting for 1500ppm of the weight of the cathode material.

[0073] The sintered product was crushed, washed, filtered, and dried, then ball-milled and mixed evenly with tungsten hydroxide. The amount of tungsten hydroxide was calculated based on 1000 ppm of tungsten element weight relative to the weight of the cathode material. The mixture was then placed in a 500°C air furnace for a second high-temperature sintering for 12 hours, with a heating rate of 3°C and a cooling rate of 2°C, to obtain the cathode material.

[0074] The positive electrode material prepared in this embodiment has the chemical formula Li(Ni 0.93 Co 0.05 Mn 0.01 Al 0.01 ) 0.998 Y 0.002 O2, the coating layer is W2O3. The morphology is spherical secondary particles with an average particle size of 9μm, an average core diameter of 5μm, an average thickness of the first shell layer of 3μm, an average thickness of the second shell layer of 1μm, and a coating layer thickness of 10nm. The average particle size of the primary particles on the surface of the material is 400nm, and the BET is 0.7m 2 / g, tap density is 2.5g / cm 3 , the residual lithium content on the surface is 1500ppm.

[0075] Example 5

[0076] A 3 mol / L nickel-cobalt-manganese solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.98:0.01:0.01 was prepared, and 0.3 mol / L ammonia water and 2 mol / L sodium hydroxide aqueous solution were added to a nitrogen atmosphere reactor simultaneously for a first coprecipitation. The reaction temperature was controlled at 70°C, the pH of the reaction system was 11, and the reaction time was 4 days to obtain a nickel-cobalt-manganese core. After the first coprecipitation was completed, a 2 mol / L nickel-cobalt-manganese-aluminum solution containing nickel sulfate, cobalt sulfate, manganese sulfate, and aluminum sulfate in a molar ratio of 0.98:0.01:0.005:0.005 was prepared, and 0.2 mol / L ammonia water and 2 mol / L sodium hydroxide aqueous solution were added to a nitrogen atmosphere reactor simultaneously for a second coprecipitation. The reaction temperature was controlled at 60°C, the pH of the reaction system was 10.5, and the reaction time was 1 day to grow a nickel-cobalt-manganese-aluminum transition layer on the surface of the nickel-cobalt-manganese core. After the second coprecipitation is completed, a 1 mol / L nickel-cobalt-aluminum solution with a molar ratio of nickel sulfate, cobalt sulfate, and aluminum sulfate of 0.98:0.01:0.01 is prepared, and 0.1 mol / L ammonia water and 1 mol / L sodium hydroxide aqueous solution are added to a nitrogen atmosphere reactor at the same time to carry out a third coprecipitation. The reaction temperature is controlled at 40°C, the pH of the reaction system is 9, and the reaction time is 1 day, so that the nickel-cobalt-aluminum layer grows on the surface of the nickel-cobalt-manganese-aluminum transition layer, and a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is obtained, which is nickel-cobalt-manganese core-nickel-cobalt-manganese-aluminum transition layer-nickel-cobalt-aluminum layer from the inside to the outside.

[0077] The prepared nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor is washed, filtered, and dried, and then a certain amount of lithium hydroxide and titanium oxide is added, the mixture is uniformly ball milled, and then is placed in an oxygen furnace at 750°C for high-temperature sintering for 18h, with a heating rate of 0.5°C / min and a cooling rate of 2°C. The amount of lithium hydroxide is calculated according to the total molar ratio of lithium elements and nickel-cobalt-manganese-aluminum elements, which is 1.03, and the amount of titanium oxide is calculated according to the weight percentage of titanium elements in the positive electrode material, which is 2000ppm.

[0078] The sintered product is crushed, washed with water, filtered, dried, and then is uniformly ball milled with yttrium oxide, and the amount of yttrium oxide is calculated according to the weight percentage of yttrium elements in the positive electrode material, which is 1500ppm. The mixture is placed in an air furnace at 600°C for secondary high-temperature sintering for 12h, with a heating rate of 3°C and a cooling rate of 3°C, to obtain a positive electrode material.

[0079] The positive electrode material prepared in this example has a chemical formula of Li(Ni 0.98 Co 0.01 Mn 0.005 Al 0.005 ) 0.996 Ti 0.004 O2, and a coating layer of Y2O3. The morphology is spherical secondary particles, with an average particle size of 9μm, an average diameter of the core layer of 5μm, an average thickness of the first shell layer of 3μm, an average thickness of the second shell layer of 1μm, and a thickness of the coating layer of 50nm. The average particle size of the primary particles on the surface of the material is 200nm, the BET is 0.6m 2 / g, the tap density is 2.7g / cm 3 , and the surface residual lithium content is 1000ppm.

[0080] Example 6

[0081] Example 6 differs from Example 1 in that the soluble nickel salt used in the coprecipitation reaction is all nickel acetate, the soluble cobalt salt is all cobalt acetate, the soluble manganese salt is all manganese acetate, and the soluble aluminum salt is all aluminum chloride; 4mol / L nickel-cobalt-manganese-containing solution and 0.2mol / L ammonia water, 4mol / L sodium hydroxide aqueous solution are used for the first coprecipitation, 3mol / L nickel-cobalt-manganese-aluminum-containing solution and 0.3mol / L ammonia water, 3mol / L sodium hydroxide aqueous solution are used for the second coprecipitation, and 2mol / L nickel-cobalt-aluminum-containing solution and 0.2mol / L ammonia water, 2mol / L sodium hydroxide aqueous solution are used for the third coprecipitation.

[0082] The positive electrode material prepared in this example has a chemical formula of Li(Ni 0.86 Co 0.11 Mn 0.02 Al 0.01 ) 0.997 Sr 0.003O2, coating layer Al2O3. The morphology is spherical secondary particles with an average particle size of 13 μm, the average diameter of the core layer is 6 μm, the average thickness of the first shell layer is 5 μm, the average thickness of the second core layer is 2 μm, and the thickness of the coating layer is 20 nm. The average particle size of the primary particles on the surface of the material is 400 nm, the BET is 0.4 m 2 / g, and the tap density is 2.7 g / cm 3 , and the surface residual lithium content is 1000 ppm.

[0083] Comparative Example 1

[0084] Comparative Example 1 differs from Example 1 in that the second co-precipitation and the third co-precipitation are not performed, and a lithium nickel cobalt manganese positive electrode material with uniform concentration distribution is obtained, with an average particle size of 10 μm and a chemical formula of Li(Ni 0.83 Co 0.11 Mn 0.06 ) 0.997 Sr 0.003 O2, and the coating layer is Al2O3, with a coating layer thickness of 20 nm.

[0085] Comparative Example 2

[0086] Comparative Example 2 differs from Example 1 in that the first co-precipitation and the second co-precipitation are not performed, and a lithium nickel cobalt aluminum positive electrode material with uniform concentration distribution is obtained, with an average particle size of 10 μm and a chemical formula of Li(Ni 0.86 Co 0.11 Al 0.03 ) 0.997 Sr 0.003 O2, and the coating layer is Al2O3, with a coating layer thickness of 20 nm.

[0087] Comparative Example 3

[0088] Comparative Example 3 differs from Example 1 in that the first co-precipitation and the third co-precipitation are not performed, and a lithium nickel cobalt manganese aluminum positive electrode material with uniform concentration distribution is obtained, with an average particle size of 10 μm and a chemical formula of Li(Ni 0.86 Co 0.11 Mn 0.02 Al 0.01 ) 0.997 Sr 0.003 O2, and the coating layer is Al2O3, with a coating layer thickness of 20 nm.

[0089] Performance test:

[0090] Preparation of the positive electrode sheet:

[0091] The positive electrode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were mixed with the conductive agent acetylene black and the binder PVDF in a mass ratio of 90:5:5, the solvent NMP was added, and the mixture was vacuum stirred until the system became uniform to obtain a positive electrode slurry, which was then evenly coated on the upper and lower surfaces of the positive electrode current collector aluminum foil. After drying at room temperature, the mixture was transferred to an oven for further drying, and then cold pressed and cut to obtain a positive electrode sheet.

[0092] Preparation of negative electrode sheet:

[0093] The negative electrode active material graphite, conductive agent acetylene black, thickener CMC, and binder SBR are mixed in a mass ratio of 96:1:1:2, and deionized water solvent is added and stirred until the system becomes uniform to obtain a negative electrode slurry, which is then evenly coated on the upper and lower surfaces of the negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for further drying, and then cold pressed and cut to obtain a negative electrode sheet.

[0094] Preparation of electrolyte:

[0095] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0096] The obtained positive electrode sheet, polyethylene film, and obtained negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, injected with the above-mentioned electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to prepare a soft-pack lithium-ion battery. The following performance tests are then carried out. The test results are shown in Table 1, and the first charge and discharge curve of the battery of Example 1 is shown in FIG. Figure 5 .

[0097] 1. Gram capacity: The capacity is tested at room temperature with the following process: charge to 4.2V at a constant current of 0.33C, then charge at a constant voltage of 4.2V until the current is less than 0.05C. After standing for 5 minutes, discharge to 2.8V at a current of 0.33C to obtain the first discharge gram capacity.

[0098] 2. Cycle performance test: charge and discharge current is 1C, voltage range is 2.8-4.2V, 500th cycle capacity retention rate = 500th cycle capacity ÷ first cycle capacity × 100%.

[0099] 3. DSC test: After fully charging the positive electrode to 4.2V, the DSC test was performed in a high-pressure crucible. The electrolyte addition amount was 0.42μg / mg, the heating rate was 5℃ / min, and the temperature was raised to 350℃.

[0100] Table 1

[0101]

[0102]

[0103] As can be seen from Table 1, the positive electrode material prepared by the present invention has higher gram capacity, better cycle stability and high thermal stability, and better safety performance. Comparing Example 1 with Comparative Example 1, it can be seen that the gram capacity of the positive electrode material is equivalent to that of the lithium nickel cobalt manganese positive electrode material, but shows better cycle performance and safety performance. Comparing Example 1 with Comparative Example 2, it can be seen that the positive electrode material is equivalent to the cycle performance and safety performance of the lithium nickel cobalt aluminum positive electrode material, and has a higher gram capacity. Comparing Example 1 with Comparative Example 3, it can be seen that since Al on the surface of the material is more stable than Mn, the positive electrode material of the present invention has better cycle performance and safety performance than the conventional lithium nickel cobalt manganese aluminum positive electrode material with a uniform distribution of element content.

[0104] In summary, the positive electrode material of the present invention uses a core layer comprising lithium nickel cobalt manganese oxide as an energy core, a first shell layer comprising lithium nickel cobalt manganese aluminum oxide as a transition layer, and a second shell layer comprising lithium nickel cobalt aluminum oxide as a stability shell, so that the positive electrode material presents a distribution in which the Ni content and Co content remain unchanged from the inside to the outside, the Mn content gradually decreases, and the Al content gradually increases. The uniform distribution of Ni and Co can retain the original high gram capacity and cycle performance of the high nickel material, and the core-shell structure is more stable. At the same time, the respective disadvantages of the nickel cobalt manganese material and the nickel cobalt aluminum material can be compensated for, so that the positive electrode material has the advantages of high gram capacity of the nickel cobalt manganese material and good stability of the nickel cobalt aluminum material. Among them, the first shell layer comprising lithium nickel cobalt manganese aluminum oxide can also play a buffering role, which can significantly relieve the internal stress of the positive electrode material and reduce the problem of particle breakage that is easy to occur in the material during long-term circulation, thereby improving the cycle performance of the positive electrode material. Therefore, the positive electrode material of the present invention can already take into account high gram capacity and good cycle performance and safety performance.

[0105] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that A positive electrode material particle having a core-shell structure, wherein the core layer of the positive electrode material particle comprises lithium nickel cobalt manganese oxide, a first shell layer and a second shell layer are provided on the surface of the core layer, the first shell layer is provided between the core layer and the second shell layer, the first shell layer comprises lithium nickel cobalt manganese aluminum oxide, and the second shell layer comprises lithium nickel cobalt aluminum oxide; a coating layer is further provided on the surface of the second shell layer, and the positive electrode material particle further comprises a doping element; The molar percentage of manganese in the core layer is defined as W Mn0 , the molar percentage of aluminum is W Al0 ; The molar percentage of manganese in the first shell is W Mn1 , the molar percentage of aluminum is W Al1 The molar percentage of manganese in the second shell is W Mn2 , the molar percentage of aluminum is W Al2 , then the positive electrode material particles meet the following conditions: (i)W Mn0 %>W Mn1 %>W Mn2 %; (ii)In Al0 %<W Al1 %<W Al2 %; The average diameter of the core layer is 5-9 μm, the thickness of the first shell layer is 2-5 μm, and the thickness of the second shell layer is 1-2 μm.

2. The positive electrode material according to claim 1, characterized in that The molar percentage of nickel in the core layer is defined as W Ni0 , the molar percentage of cobalt is W Co0 ; The molar percentage of nickel in the first shell is W Ni1 , the molar percentage of cobalt is W Co1 The molar percentage of nickel in the second shell is W Ni2 , the molar percentage of cobalt is W Co2 , the positive electrode material particles meet at least one of the following conditions: (iii)W Ni0 % ≥ 80%, W Ni1 % ≥ 80% and W Ni2 % ≥ 80%; (iv)W Co0 % ≥ 1%, W Co1 % ≥ 1% and W Co2 % ≥ 1%.

3. The positive electrode material according to claim 1 or 2, characterized in that The coating layer comprises a coating element G, wherein G comprises one or more of Al, Ti, B, Sr, Y and W; And / or, the coating layer comprises G m O n , where 1≤m≤3, 1≤n≤4; and / or, the G m O n Containing one or more of Al2O3, TiO2, B2O3, W2O3 and Y2O3; And / or, the coating layer has a thickness of 10 to 50 nm.

4. The positive electrode material according to claim 1 or 2, characterized in that The positive electrode material particles further include a doping element M, wherein M is one or more of Cr, Sr, Y, W, Zr, Ti, La, Nb and Mo.

5. The positive electrode material according to claim 1, characterized in that The positive electrode material particles include secondary particles composed of primary particles; and / or the average particle size of the primary particles is 100-500 nm, and the average particle size of the positive electrode material particles is 8-15 μm.

6. The positive electrode material according to claim 1, characterized in that The specific surface area of ​​the positive electrode material particles is 0.2~0.7m 2 / g, tap density is 2.2~3.0g / cm 3 , the residual lithium content on the surface is 1000~1500ppm.

7. A method for preparing the positive electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step S1, adding a solution containing nickel, cobalt and manganese, a first complexing agent and a first precipitant into a reactor to perform a first coprecipitation to obtain a nickel-cobalt-manganese layer; Step S2, continuing to add a solution containing nickel, cobalt, manganese and aluminum, as well as a second complexing agent and a second precipitant to the reactor to perform a second coprecipitation to obtain a positive electrode material composite; Step S3, continuing to add the solution containing nickel, cobalt and aluminum, as well as the third complexing agent and the third precipitant to the reactor to perform a third coprecipitation to obtain a nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor; Step S4, mixing the nickel-cobalt-manganese-aluminum quaternary positive electrode material precursor with a lithium source and a doping substance, and performing a first high-temperature sintering to obtain a sintered product; Step S5, mixing the sintered product and the coating material, and performing a second high-temperature sintering to obtain the positive electrode material; The cathode material composite comprises a nickel-cobalt-manganese layer and a nickel-cobalt-manganese-aluminum layer from the inside out; the nickel-cobalt-manganese-aluminum quaternary cathode material precursor comprises a nickel-cobalt-manganese layer, a nickel-cobalt-manganese-aluminum layer and a nickel-cobalt-aluminum layer from the inside out; and the cathode material comprises cathode material particles. The doping material is one or more oxides and / or hydroxides of Cr, Sr, Y, W, Zr, Ti, La, Nb, and Mo; and the coating material is one or more oxides and / or hydroxides of Al, Ti, B, Sr, Y, and W.

8. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 6 or the positive electrode material prepared by the preparation method according to claim 7.

9. An electrical device, characterized in that: The secondary battery according to claim 8 is included.

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