Ternary positive electrode material, preparation method thereof and electrochemical device

Abstract

The invention discloses a ternary positive electrode material, a preparation method thereof and an electrochemical device, and the preparation method comprises the following steps: mixing a nickel-cobalt-manganese precursor and a lithium source, and carrying out primary sintering to obtain a base material; mixing the base material, lithium aluminum titanium phosphate and water at the temperature of 10-20 DEG C, and carrying out filter pressing to obtain a solid material; the solid material and lithium phosphate are mixed and subjected to secondary sintering, so that a composite coating layer is formed on the surface of the base material, the composite coating layer comprises titanium aluminum lithium phosphate and lithium phosphate, and the ternary positive electrode material is obtained. By means of low-temperature washing and composite coating, the conductivity and cycling stability of the ternary positive electrode material are improved.

Description

Technical Field

[0001] The present application relates to the technical field of new energy, and particularly relates to a ternary cathode material, a preparation method thereof, and an electrochemical device. Background Art

[0002] In recent years, with the rapid development of the new energy vehicle industry, the demand for lithium-ion batteries has increased rapidly, especially the demand for lithium-ion batteries with high energy density has been continuously climbing. The high-nickel ternary cathode material has received wide attention because of its high capacity, which can meet the requirement of longer cruising range.

[0003] However, the high-nickel ternary cathode material has the problem of high residual lithium content in the preparation process. The existence of these residual lithium salts has the following negative effects on the performance of the material: on the one hand, it reduces the electronic conductivity of the ternary cathode material, resulting in large polarization during the battery cycling process; on the other hand, the residual lithium salts will react with the electrolyte, causing the loss of effective components in the electrolyte, increasing the interfacial impedance, and reducing the cycle life and rate performance of the battery. In addition, at high temperature, lithium carbonate on the surface of the ternary cathode material particles will also cause serious swelling, resulting in an increase in the internal pressure of the battery cell and bringing potential safety hazards. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, the present application provides a preparation method of a ternary cathode material.

[0005] In addition, the embodiments of the present application also provide a ternary cathode material prepared by the preparation method of the foregoing ternary cathode material, and an electrochemical device using the ternary cathode material.

[0006] In a first aspect, the embodiments of the present application provide a preparation method of a ternary cathode material, the preparation method including the following steps: mixing a nickel-cobalt-manganese precursor and a lithium source and performing a first sintering to obtain a matrix material; mixing the matrix material, lithium titanium aluminum phosphate, and water and performing pressure filtration to obtain a solid material, wherein the temperature of the water is 10°C to 20°C; and mixing the solid material and lithium phosphate and performing a second sintering to form a composite coating layer on the surface of the matrix material, the composite coating layer including lithium titanium aluminum phosphate and lithium phosphate, thereby obtaining the ternary cathode material.

[0007] In some possible embodiments, the median particle size D50 of the particles of the lithium titanium aluminum phosphate is greater than the median particle size D50 of the particles of the lithium phosphate; and / or The mass ratio of the lithium titanium aluminum phosphate to the lithium phosphate is 1:(0.5 to 0.9).

[0008] In some possible embodiments, the mass percentage of the lithium titanium aluminum phosphate in the matrix material is 2% to 4%.

[0009] In some possible embodiments, in the step of mixing the matrix material, lithium aluminum titanium phosphate and water, the mass ratio of the matrix material to water is 1:(0.9 - 1.5); and / or In the step of mixing the matrix material, lithium aluminum titanium phosphate and water, the mixing time is 10 min to 30 min.

[0010] In some possible embodiments, the pressure filtration includes vacuum pressure filtration, and the pressure of the vacuum pressure filtration is -0.08 MPa to -0.095 MPa.

[0011] In some possible embodiments, the mass percentage of lithium phosphate in the matrix material is 1.0% to 1.8%; and / or In the step of mixing the solid material and lithium phosphate, the mixing time is 15 min to 30 min.

[0012] In some possible embodiments, the temperature of the first sintering is 700 °C to 900 °C, and the time of the first sintering is 10 h to 20 h; and / or The temperature of the second sintering is 300 °C to 600 °C, and the time of the second sintering is 5 h to 10 h.

[0013] In some possible embodiments, before the step of mixing the solid material and lithium phosphate, the preparation method further includes: Drying the solid material, and the drying temperature is 80 °C to 120 °C.

[0014] In a second aspect, an embodiment of the present application further provides a ternary cathode material. The ternary cathode material is prepared by the preparation method of the ternary cathode material described above. The ternary cathode material includes a matrix material and a composite coating layer located on the surface of the matrix material. The composite coating layer includes lithium aluminum titanium phosphate and lithium phosphate.

[0015] In a third aspect, an embodiment of the present application further provides an electrochemical device. The electrochemical device includes a positive electrode plate, and the positive electrode plate includes a positive electrode material, and the positive electrode material is the ternary cathode material described above.

[0016] Compared with the prior art, the ternary cathode material and its preparation method provided by the embodiments of the present application mix the matrix with lithium aluminum titanium phosphate and water at a relatively low temperature and then press-filter. At this temperature, while efficiently removing the residual lithium on the surface of the matrix material, lithium aluminum titanium phosphate can be uniformly coated on the surface of the matrix material by the wet method, achieving a balance between efficient removal of residual lithium and improvement of the coating effect. In addition, by mixing the solid product with lithium phosphate and performing secondary sintering by the dry coating method, a composite coating layer containing lithium aluminum titanium phosphate and lithium phosphate can be formed on the surface of the matrix material. Among them, lithium aluminum titanium phosphate in the composite coating layer can form a stable crystal structure and continuous lithium ion channels on the surface of the matrix material, reducing the Li + / Ni 2+ mixing phenomenon, improving the ionic conductivity, and offsetting the lithium-nickel mixing and lithium loss problems caused by the water washing process. In addition, lithium phosphate in the composite coating layer can improve the electronic conductivity of the ternary cathode material, and cooperate with lithium aluminum titanium phosphate to form a stable coating layer interface, improving the cycle stability of the ternary cathode material. Brief Description of the Drawings

[0017] Figure 1 It is a process flow chart of the preparation method of the ternary cathode material provided by an embodiment of the present application.

[0018] Figure 2 It is a scanning electron microscope image of the ternary cathode material provided by Example 1 of the present application.

[0019] Figure 3 It is a comparison chart of the free lithium content of the ternary cathode materials provided by Examples 1-2, Comparative Example 2 and Comparative Example 4 of the present application.

[0020] Figure 4 It is a comparison chart of the first discharge capacity of the batteries prepared from the ternary cathode materials provided by Examples 1-2, Comparative Example 2 and Comparative Example 4 of the present application.

[0021] Figure 5 It is a comparison chart of the capacity retention rate after 50 cycles of the batteries prepared from the ternary cathode materials provided by Examples 1-2, Comparative Example 2 and Comparative Example 4 of the present application. Detailed Embodiments

[0022] Embodiments of the present application will be described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. It should be noted that unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. Many specific details are set forth in the following description to facilitate a full understanding of the present application. The described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0023] Please refer to Figure 1 As shown, the embodiment of the present application provides a method for preparing a ternary cathode material, which specifically includes the following steps: Step S1, mixing a nickel-cobalt-manganese precursor and a lithium source and performing a first sintering to obtain a matrix material.

[0024] In some embodiments, the chemical formula of the nickel-cobalt-manganese precursor may be Ni x Co y Mn 1-x-y (OH) 2 , where 0.8 < x < 0.85 and 0.1 < y < 0.15. Nickel element has high electrochemical activity and can improve the discharge capacity and energy density of the material. The nickel-cobalt-manganese precursor with a higher nickel content can provide a higher theoretical capacity for the ternary cathode material and improve the energy density of the ternary cathode material.

[0025] In some embodiments, the lithium source may include at least one of lithium hydroxide, lithium carbonate, and lithium oxalate, etc.

[0026] In some embodiments, the ratio of the number of moles of lithium in the lithium source to the total number of moles of transition metals in the nickel-cobalt-manganese precursor may be (1~1.07):1, which is beneficial to the full incorporation of lithium ions during the formation of the matrix material, promotes the uniform distribution of lithium ions in the matrix material, and improves the electrochemical performance and structural stability of the ternary cathode material.

[0027] In some embodiments, the mixing method of the nickel-cobalt-manganese precursor, the lithium source, and the aluminum source may include mixing with a high-speed mixer, a plow mixer, a ribbon mixer, stirring, or grinding, etc., which can effectively mix the lithium source with the nickel-cobalt-manganese precursor and promote the interaction between the two. It can be understood that the mixing methods include but are not limited to the above methods, and any method that can achieve the mixing of the lithium source and the nickel-cobalt-manganese precursor is acceptable.

[0028] In some embodiments, the temperature of the first sintering can be 700°C to 900°C. A higher temperature of the first sintering can evenly disperse lithium elements in the nickel-cobalt-manganese precursor, promote the grain growth of the matrix material, and reduce the number of grain boundaries and grain boundary defects. Exemplarily, the temperature of the first sintering can be 700°C, 750°C, 800°C, 850°C, 900°C or any value within the range composed of any two of the above values. Further, the temperature of the first sintering can be 800°C to 900°C.

[0029] The time of the first sintering can be 10h to 20h, which is beneficial to fully sinter and form the matrix material. Exemplarily, the time of the first sintering can be 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h or any value within the range composed of any two of the above values. Further, the time of the first sintering can be 12h to 18h.

[0030] In some embodiments, the atmosphere of the first sintering can be air atmosphere, oxygen-rich atmosphere or pure oxygen atmosphere, which is beneficial to keeping metal ions in the matrix material in the oxidized state. Further, the atmosphere of the first sintering can be oxygen-rich atmosphere or pure oxygen atmosphere, which is beneficial to forming a stable crystal structure of the matrix material.

[0031] In some embodiments, the chemical formula of the matrix material can be LiNi x Co y Mn 1-x-y O 2 , where 0.8 < x < 0.85 and 0.1 < y < 0.15.

[0032] Step S2: Mix the matrix material, lithium titanium aluminum phosphate and water, and perform pressure filtration to obtain a solid material, where the temperature of the water is 10°C to 20°C.

[0033] Specifically, mix the matrix material, lithium titanium aluminum phosphate (LATP) and water, control the temperature of the water to be 10°C to 20°C, fully mix evenly, and then perform pressure filtration. By means of dissolution and pressure filtration, the residual lithium and impurities on the surface of the matrix material are removed, and LATP is coated on the surface of the matrix material.

[0034] First, wash the matrix material with water to remove the residual lithium on the surface and other small particle impurities adsorbed on the surface of the matrix material, remove the filtrate, and obtain the washed solid material. The residual lithium on the surface of the matrix material may include unreacted lithium sources, such as alkaline lithium sources like lithium carbonate and lithium hydroxide. These surface residual lithium increase the internal resistance of the ternary cathode material, reduce the cycle life and rate performance of the ternary cathode material. Reducing the surface residual lithium is beneficial to improving the conductivity, cycle life and rate performance of the ternary cathode material, reducing the side reaction between the ternary cathode material and the electrolyte, and reducing the internal resistance and gas generation of the ternary cathode material.

[0035] In addition, water washing can also remove dust and impurities on the surface of the matrix material, improve the surface properties, obtain a purer surface, and is beneficial to the formation of a stable solid electrolyte interface (SEI) film.

[0036] However, there are also some drawbacks during the water washing process: the high-nickel ternary cathode material is sensitive to water, and Li + / Ni 2+ mixing may occur during the water washing process, resulting in structural damage and capacity attenuation; water washing will also dissolve part of the active lithium, resulting in lithium loss and affecting the capacity of the ternary cathode material.

[0037] Therefore, in this application, during the water washing process, LATP is coated on the surface of the matrix material synchronously through a wet coating process. On the one hand, it can form a stable crystal structure on the surface of the matrix material to prevent Ni 2+ from entering the Li layer, thereby reducing the phenomenon of lithium-nickel mixing, inhibiting phase transformation, and improving the structural stability of the ternary cathode material; on the other hand, LATP has a NASICON structure, so there are three-dimensional ion migration channels in the LATP crystal framework, which is beneficial to the formation of continuous lithium ion channels on the surface of the matrix material and improves ion conductivity. LATP can effectively offset part of the lithium-nickel mixing caused by the water washing process and supplement lithium at the same time to solve the problem of lithium loss and improve the structural stability and ion conductivity of the ternary cathode material.

[0038] Moreover, during the water washing process, LATP is in-situ coated on the surface of the matrix material. The surface water washing and in-situ coating of the matrix material are carried out simultaneously, optimizing the preparation process and improving production efficiency. And, due to the removal of the residual lithium and impurities on the surface of the matrix material, LATP can better combine with the matrix material, improving the uniformity and firmness of the coating.

[0039] In addition, in this application, by controlling the water temperature during the water washing process to be 10°C to 20°C, the solubility of residual lithium (such as lithium carbonate and lithium hydroxide) increases with the decrease of temperature, which can minimize the content of residual lithium and improve the improvement degree of the electrochemical performance of the ternary cathode material. At the same time, controlling the temperature at 10°C to 20°C is also beneficial to the full dispersion of LATP in water and maintaining the stable properties of LATP, which is beneficial to the uniform coating of LATP on the surface of the matrix material. The water temperature can be, for example, 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C or any value within the range composed of any two of the above values.

[0040] Furthermore, the water temperature can be 10°C to 15°C, which is beneficial to further synchronously improving the residual lithium removal effect and the LATP coating effect.

[0041] In some embodiments, the mass ratio of the matrix material to water can be 1:(0.9 - 1.5), which is conducive to fully dissolving the residual lithium and impurities on the surface of the matrix material, thereby reducing the residual lithium content on the surface of the matrix material and cleaning the surface of the matrix material. Exemplarily, the mass ratio of the matrix material to water can be 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 or any value within the range formed by any two of the above values. Further, the mass ratio of the matrix material to water can be 1:(1 - 1.5).

[0042] In some embodiments, the mass percentage of lithium aluminum titanium phosphate in the matrix material can be 2% - 4%. By controlling the content of lithium aluminum titanium phosphate, lithium aluminum titanium phosphate can be moderately coated on the matrix surface, effectively improving the ionic conductivity and structural stability of the ternary cathode material. Exemplarily, the mass percentage of lithium aluminum titanium phosphate in the matrix material can be 2%, 2.5%, 3%, 3.5%, 4% or any value within the range formed by any two of the above values. Further, the mass percentage of lithium aluminum titanium phosphate in the matrix material can be 2% - 3%.

[0043] In some embodiments, the mixing time of the matrix material, lithium aluminum titanium phosphate and water can be 10 min - 30 min, which is conducive to the full mixing of the three, so as to fully dissolve the residual lithium on the surface and improve the uniformity of the in-situ coating of lithium aluminum titanium phosphate. Exemplarily, the mixing time of the matrix material, lithium aluminum titanium phosphate and water can be 10 min, 15 min, 20 min, 25 min, 30 min or any value within the range formed by any two of the above values. Further, the mixing time of the matrix material, lithium aluminum titanium phosphate and water can be 20 min - 30 min.

[0044] In some embodiments, the pressure filtration can include vacuum pressure filtration. Using negative pressure to push the liquid through the filter medium (such as filter membrane, filter cloth, etc.), it can wash and coat the matrix material in large quantities and with high efficiency, and is applicable to scenarios where a large amount of slurry needs to be processed. It can be understood that any method capable of realizing solid-liquid separation is acceptable.

[0045] In some embodiments, the pressure of the vacuum pressure filtration can be -0.08 MPa - 0.095 MPa, which means that the pressure of the vacuum pressure filtration is 0.08 MPa - 0.095 MPa lower than the atmospheric pressure, which can accelerate the filtration speed and improve the removal effect of the residual lithium and impurities on the surface. Exemplarily, the pressure of the vacuum pressure filtration can be -0.08 MPa, -0.09 MPa, -0.095 MPa or any value within the range formed by any two of the above values.

[0046] In some embodiments, the moisture content of the solid material obtained by pressure filtration can be 0.1% - 0.3%, indicating that most of the water in the solid material has been effectively removed, facilitating the subsequent secondary sintering reaction, and can further reduce the lithium-nickel mixing in the matrix material, improving the quality of the ternary cathode material.

[0047] In some embodiments, the solid material can also be dried to further reduce the moisture content of the solid material and reduce the caking phenomenon of the solid material. The drying temperature can be 80°C - 120°C, which helps to improve the drying speed and degree.

[0048] Step S3: Mix the solid material and lithium phosphate and perform secondary sintering to form a composite coating layer on the surface of the matrix material. The composite coating layer includes lithium titanium aluminum phosphate and lithium phosphate, thereby obtaining the ternary cathode material.

[0049] Specifically, mixing and dispersing the solid material and lithium phosphate evenly can enable the solid material and lithium phosphate to come into full contact, and lithium phosphate can be evenly coated on the surface of the solid material, that is, lithium phosphate can be coated on the outer surface of lithium titanium aluminum phosphate and the surface of part of the matrix material not coated by lithium titanium aluminum phosphate. Under certain sintering conditions, the mixture of the solid material and lithium phosphate is subjected to secondary sintering to form a composite coating layer on the surface of the matrix material. The composite coating layer includes LATP and lithium phosphate, thereby obtaining the ternary cathode material.

[0050] The applicant's research found that when only LATP is used for coating, although it can offset part of the lithium-nickel mixing and lithium loss problems caused by the water washing process, the overall conductivity of the ternary cathode material coated with LATP alone is reduced. This may be because LATP itself is an insulator, and there may be problems with the interfacial compatibility between LATP and the high-nickel ternary cathode material, resulting in interfacial chemical reactions. Specifically, the high-nickel ternary matrix material has strong oxidizing properties and may oxidize the components in LATP (such as Ti 4+ or PO 4 3- ), resulting in interfacial side reactions, thus reducing the conductivity of the ternary cathode material and affecting the cycle life of the battery. Therefore, in this application, on the basis of coating the matrix material with LATP, lithium phosphate is further coated by a dry method. As a good ionic conductor, lithium phosphate can improve the electronic conductivity of the ternary cathode material, make up for the decrease in conductivity caused by the single coating of LATP, and lithium phosphate has good chemical stability. The synergistic effect of lithium phosphate and LATP can jointly form a more stable coating layer interface, improving the cycle stability of the ternary cathode material.

[0051] In some embodiments, the mass percentage of lithium phosphate in the matrix material can be 1.0% to 1.8%, which is conducive to the moderate coating of lithium phosphate on the surface of the solid material, further improving the electronic conductivity and cycle stability of the ternary positive electrode material. The mass percentage of lithium phosphate in the matrix material can be 1.0%, 1.2%, 1.4%, 1.6%, 1.8% or any value within the range of any two of the above values. The mass percentage of lithium phosphate in the matrix material can further be 1.3% to 1.6%.

[0052] In some embodiments, the median particle size D50 of lithium aluminum titanium phosphate particles is larger than the median particle size D50 of lithium phosphate particles, and lithium phosphate with smaller particle size is coated on the outer surface of the lithium aluminum titanium phosphate and part of the surface of the matrix material not coated by the lithium aluminum titanium phosphate, effectively filling the gap between the lithium aluminum titanium phosphate with larger particle size and the matrix material, effectively improving the interface contact between the lithium aluminum titanium phosphate and the matrix material, and facilitating the further formation of a more stable coating layer interface.

[0053] In some embodiments, the mass ratio of lithium aluminum titanium phosphate to lithium phosphate can be 1:(0.5-0.9), balancing the ratio of lithium aluminum titanium phosphate to lithium phosphate in the composite coating layer, which is beneficial to improving the stability of the composite coating layer and the bonding strength between the composite coating layer and the substrate material. The mass ratio of lithium aluminum titanium phosphate to lithium phosphate can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or any value within the range of any two of the above values.

[0054] In some embodiments, the solid material and lithium phosphate may be mixed for 15 min to 30 min, which is conducive to sufficient mixing of the solid material and lithium phosphate.

[0055] In some embodiments, the rotation speed of the solid material and lithium phosphate can be 400 rpm to 700 rpm, which is conducive to sufficient mixing of the solid material and lithium phosphate.

[0056] In some embodiments, the temperature of the secondary sintering can be 300°C to 600°C. A lower secondary sintering temperature can obtain a more uniform and stable composite coating layer, reducing over-sintering or uneven sintering. In addition, a lower secondary sintering temperature is also beneficial for protecting the matrix material, reducing lattice changes and lithium-nickel mixing. The temperature of the secondary sintering can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C or any value within the range of any two of the above values. The temperature of the secondary sintering can further be 300°C to 400°C.

[0057] The time for secondary sintering can be 5h to 10h, which is beneficial to fully sinter and form a composite coating layer. Exemplarily, the time for secondary sintering can be 5h, 6h, 7h, 8h, 9h, 10h or any value within the range composed of any two of the above values. The time for primary sintering can further be 5h to 8h.

[0058] In some embodiments, the atmosphere for secondary sintering can be an oxygen-rich atmosphere or a pure oxygen atmosphere, which is beneficial to protecting the matrix material.

[0059] Compared with the prior art, the preparation method of the ternary cathode material provided by the embodiments of the present application has the following beneficial effects: 1. By adopting the method of low-temperature water washing at 10°C to 20°C, the residual lithium is efficiently dissolved and removed, reducing the content of residual alkali and other impurities on the surface of the matrix material, improving the conductivity, cycle life and rate performance of the ternary cathode material, and thus effectively enhancing the first discharge capacity and capacity retention rate of the ternary cathode material.

[0060] 2. During the water washing process, since the temperature of the water is controlled at 10°C to 20°C, LATP is highly dispersed in the water and its performance remains stable, and LATP can be uniformly coated on the surface of the matrix material in situ synchronously. On the one hand, it can reduce the phenomenon of lithium-nickel mixing and improve the structural stability of the ternary cathode material; on the other hand, LATP forms continuous lithium ion channels on the surface of the matrix material, improving the ionic conductivity. LATP can effectively offset the problems of lithium-nickel mixing and lithium loss caused by part of the water washing process, and improve the structural stability and ionic conductivity of the ternary cathode material.

[0061] 3. Lithium phosphate is co-coated to form a composite coating layer of LATP and lithium phosphate. Lithium phosphate can improve the electronic conductivity of the ternary cathode material, and together with LATP, form a more stable coating layer interface, improving the cycle stability of the ternary cathode material.

[0062] In addition, the embodiments of the present application also provide a ternary cathode material prepared by the foregoing preparation method of the ternary cathode material. The ternary cathode material includes a matrix material and a composite coating layer located on the surface of the matrix material. Among them, the matrix material is a ternary material, and the composite coating layer includes lithium aluminum titanium phosphate and lithium phosphate.

[0063] Compared with the prior art, since the matrix material of the ternary cathode material provided by the embodiments of the present application has been treated by low-temperature water washing, the ternary cathode material has a low free lithium content, and thus has good conductivity, cycle life and rate performance. And, the ternary cathode material also has a composite coating layer containing LATP and lithium phosphate. Among them, LATP can form a stable crystal structure and continuous lithium ion channels on the surface of the matrix material, reducing Li + / Ni 2+The mixing phenomenon can improve the ionic conductivity and offset the problems of lithium-nickel mixing and lithium loss caused by the water washing process. Lithium phosphate can improve the electronic conductivity of the ternary cathode material, and cooperate with lithium titanium aluminum phosphate to form a stable coating interface, thereby improving the cycle stability of the ternary cathode material.

[0064] An embodiment of the present application provides an electrochemical device (such as a battery), which includes a positive electrode plate, and the positive electrode plate includes a positive electrode material, and the positive electrode material is the aforementioned ternary positive electrode material.

[0065] Compared with the prior art, the electrochemical device provided by the embodiment of the present application is prepared by using the aforementioned ternary positive electrode material, and has good energy density and cycle stability.

[0066] The aforementioned ternary positive electrode material, its preparation method and electrochemical device are further described below through specific embodiments.

[0067] Example 1 Step S1: Mix nickel-cobalt-manganese precursor Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and lithium hydroxide. Among them, the molar ratio of lithium in lithium hydroxide to the total molar number of transition metals in the nickel-cobalt-manganese precursor is 1.05:1; and in an oxygen atmosphere, sinter at 800 °C for 15 h to obtain a matrix material.

[0068] Step S2: Mix the matrix material, lithium titanium aluminum phosphate and water at 10 °C for 30 min, and perform pressure filtration with a pressure of -0.09 MPa through a vacuum filter press to separate solid and liquid, obtaining a solid material, and then use a vacuum drying oven to dry the solid material at 100 °C to further remove the moisture in the solid material. Among them, the mass ratio of the matrix material to water is 1:1, the mass percentage of lithium titanium aluminum phosphate in the matrix material is 2%, and the median particle size D50 of LATP particles is 2.96 μm.

[0069] Step S3: Mix the dried solid material and lithium phosphate in a high-speed mixer at 600 rpm for 20 min. Among them, the mass percentage of lithium phosphate in the matrix material is 1.4%, and the median particle size D50 of lithium phosphate particles is 1.88 μm, and perform secondary sintering at 400 °C for 6 h in an oxygen atmosphere to form a composite coating layer on the surface of the matrix material. The composite coating layer includes lithium titanium aluminum phosphate and lithium phosphate, thereby obtaining the ternary positive electrode material.

[0070] Example 2 The difference from Example 1 is that in Step S2, the temperature of water is 15 °C. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0071] Example 3 The difference from Example 1 is that in step S2, the temperature of water is 20 °C. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0072] Example 4 The difference from Example 1 is that the median particle size D50 of lithium phosphate particles is 1.88 μm, that is, the median particle size D50 of LATP particles is smaller than that of lithium phosphate particles. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0073] Example 5 The difference from Example 1 is that in step S3, the mass percentage of lithium phosphate in the matrix material is 2.2%, that is, the mass ratio of LATP to lithium phosphate is 1:1.1. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0074] Comparative Example 1 The difference from Example 1 is that in step S2, lithium aluminum titanium phosphate is not added. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0075] Comparative Example 2 The difference from Example 1 is that in step S2, the temperature of water is 25 °C. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0076] Comparative Example 3 The difference from Example 1 is that in step S3, lithium phosphate is not added. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0077] Comparative Example 4 The difference from Example 1 is that in step S2, the temperature of water is 4 °C. Other steps are basically the same as those in Example 1, please refer to Example 1.

[0078] The following tests are carried out on the ternary cathode materials obtained in Examples 1 - 5 and Comparative Examples 1 - 4.

[0079] (I) Scanning electron microscope (SEM) test: A JSM-IT210 model scanning electron microscope is used. This model instrument has high-resolution imaging ability and can clearly observe the microscopic morphology and structural characteristics of the cathode material. The acceleration voltage is 10.00 kV and the magnification is 3000 times.

[0080] (II) Surface residual alkali (free lithium) test: A potentiometric titrator is used, and the test is carried out using the method specified in the standard drafted by the National Nonferrous Metals Standardization Technical Committee, "Determination of Magnetic Foreign Matter Content and Residual Alkali Content in Cathode Materials for Lithium-Ion Batteries".

[0081] (3) Electrical property test: The SP:PVDF:ternary cathode material was mixed evenly according to the mass ratio of 5:3:2 to make a positive electrode sheet. Using metallic lithium as the negative electrode material, a CR2025 button cell was made and tested within the voltage range of 2.5~4.5V.

[0082] The test steps for the first charge-discharge efficiency include: Under the normal temperature condition of 25°C, the lithium-ion battery was charged at a constant current of 0.1C (C represents the current rate, 1C = 2A) to 4.5V, and then charged at a constant voltage until the current dropped to 0.05C, and the charging stopped. Record the first charge capacity; then discharge at 0.1C to the cut-off voltage of 2.5V, record the first discharge capacity, calculate the 0.1C gram capacity of the positive electrode material based on the first discharge capacity, and calculate the first charge-discharge efficiency of the battery according to the following formula, that is, the first efficiency: First charge-discharge efficiency = (First discharge capacity / First charge capacity) * 100%.

[0083] The test steps for the cycle performance include: The test working voltage range is 2.8V~4.3V, the temperature is 45°C, the charge-discharge rate is +1C / -1C, and when the CV cut-off current is 0.01C, the capacity retention rate after 50 cycles is tested.

[0084] The relevant preparation processes and test results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 1. Among them, D50, that is, the median particle size, represents the particle size corresponding to a cumulative distribution of 50%.

[0085] The above results show that: Figure 2 This is the scanning electron microscope image of the ternary cathode material provided in Example 1 of this application. The composite coating on the surface of the ternary cathode material particles is evenly coated, and the particle shape is regular, which is beneficial to improving the interfacial stability between the ternary cathode material and the electrolyte and the lithium-ion transmission rate.

[0086] Combined with Figures 3 to 5 Comparing Examples 1-5, Comparative Example 2 and Comparative Example 4 with the data in Table 1, it can be seen that controlling the washing temperature within 10°C~20°C is beneficial to dissolving the residual lithium on the surface of the matrix material. The free lithium content of the ternary cathode material after washing is significantly reduced from 1401ppm in Comparative Example 2 (water temperature is 25°C). The free lithium content of the ternary cathode material in Example 1 is only 1083ppm. The first discharge, first efficiency and capacity retention rate of the ternary cathode material prepared into a battery in Examples 1-5 have all been improved. Although the water temperature in Comparative Example 4 is lower (water temperature is 4°C), the effect of dissolving residual lithium is improved, and the free lithium in Comparative Example 4 is lower, but too low water temperature affects the dissolution of LATP and the coating effect is poor, resulting in the first discharge, first efficiency, and capacity retention rate being lower than those in Example 1.

[0087] Comparing Example 1 with Comparative Example 1, it was found that in Example 1, due to the simultaneous wet coating of LATP during the water washing process, the structural stability and ionic conductivity of the ternary cathode material were improved, thereby enhancing the electrochemical performance of the battery.

[0088] Comparing Example 1 with Comparative Example 3, compared with Comparative Example 3 where only LATP was coated, in Example 1, due to the dry coating of lithium phosphate, the problems of slightly decreased overall conductivity caused by only coating the insulator LATP and poor interfacial compatibility between LATP and the high-nickel ternary cathode material, which reduced the cycle life of the battery, were solved. As a good ionic conductor, lithium phosphate improved the electronic conductivity of the ternary cathode material, and lithium phosphate also had good chemical stability. Lithium phosphate and LATP synergistically formed a more stable composite coating interface, improving the cycle stability of the ternary cathode material, thereby significantly enhancing the capacity retention rate of the battery.

[0089] Comparing Example 1 with Example 4, compared with the particle size combination in Example 4 where the median particle size D50 of LATP particles was smaller than the median particle size D50 of lithium phosphate particles, in Example 1, the median particle size D50 of LATP particles was larger than the median particle size D50 of lithium phosphate particles. The smaller-sized lithium phosphate was coated on the outer surface of lithium titanium aluminum phosphate and the surface of the matrix material that was partially not coated by lithium titanium aluminum phosphate, effectively filling the gap between the larger-sized lithium titanium aluminum phosphate and the matrix material, effectively improving the interfacial contact between lithium titanium aluminum phosphate and the matrix material, which was beneficial to further form a more stable coating interface, thereby further enhancing the electrochemical properties of the prepared battery, especially its cycling performance, and significantly improving the capacity retention rate after 50 cycles.

[0090] Comparing Example 1 with Example 5, in Example 5, the mass ratio of LATP to lithium phosphate exceeded the range of 1:(0.5 - 0.9), while in Example 1, the balanced mass ratio of LATP to lithium phosphate was 1:0.7, which was beneficial to improving the stability of the composite coating layer and the bonding force between the composite coating layer and the matrix material, thereby further enhancing the electrochemical performance of the battery.

[0091] It can be seen that in Examples 1 - 5 of the present application, by performing low-temperature water washing on the matrix material during the preparation process to remove surface residual alkali, wet coating of LATP combined with dry coating of lithium phosphate to form a composite coating layer, the conductivity and cycle stability of the ternary cathode material were effectively improved.

[0092] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present invention, and the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing a ternary positive electrode material, characterized in that: The preparation method comprises: The nickel-cobalt-manganese precursor and the lithium source are mixed and sintered once to obtain a matrix material; Mixing the matrix material, lithium aluminum titanium phosphate and water and filtering them to obtain a solid material, wherein the temperature of the water is 10° C. to 20° C.; and The solid material and lithium phosphate are mixed and subjected to secondary sintering to form a composite coating layer on the surface of the base material, wherein the composite coating layer includes lithium aluminum titanium phosphate and lithium phosphate, thereby obtaining the ternary positive electrode material.

2. The method for preparing the ternary positive electrode material according to claim 1, characterized in that: The median particle size D50 of the lithium aluminum titanium phosphate particles is greater than the median particle size D50 of the lithium phosphate particles; and / or The mass ratio of the lithium aluminum titanium phosphate to the lithium phosphate is 1:(0.5-0.9).

3. The method for preparing the ternary positive electrode material according to claim 1, characterized in that: The mass percentage of the lithium aluminum titanium phosphate in the matrix material is 2% to 4%.

4. The method for preparing a ternary cathode material according to claim 1, characterized in that: In the step of mixing the matrix material, lithium aluminum titanium phosphate and water, the mass ratio of the matrix material to water is 1:(0.9-1.5); and / or In the step of mixing the matrix material, lithium aluminum titanium phosphate and water, the mixing time is 10 min to 30 min.

5. The method for preparing the ternary cathode material according to claim 1, characterized in that: The pressure filtration includes vacuum pressure filtration, and the pressure of the vacuum pressure filtration is -0.08MPa~-0.095MPa.

6. The method for preparing a ternary cathode material according to claim 1, characterized in that: The mass percentage of the lithium phosphate in the matrix material is 1.0% to 1.8%; and / or In the step of mixing the solid material and lithium phosphate, the mixing time is 15 minutes to 30 minutes.

7. The method for preparing a ternary cathode material according to claim 1, characterized in that: The primary sintering temperature is 700° C. to 900° C., and the primary sintering time is 10 h to 20 h; and / or The temperature of the secondary sintering is 300° C. to 600° C., and the time of the secondary sintering is 5 h to 10 h.

8. The method for preparing a ternary cathode material according to claim 1, characterized in that: Before the step of mixing the solid material and lithium phosphate, the preparation method further comprises: The solid material is dried at a temperature of 80°C to 120°C.

9. A ternary positive electrode material, characterized in that: Prepared by the preparation method of the ternary positive electrode material according to any one of claims 1 to 8, the ternary positive electrode material comprises a base material and a composite coating layer located on the surface of the base material, the composite coating layer comprises lithium aluminum titanium phosphate and lithium phosphate.

10. An electrochemical device, characterized in that: The electrochemical device comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode material, and the positive electrode material is the ternary positive electrode material as described in claim 9.

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