Modified ternary cathode material and its preparation method and application

Abstract

The present invention provides a modified ternary cathode material, a preparation method, and an application thereof. The preparation method first mixes the ternary cathode material with a premixed solution obtained by mixing an acid ester solvent, a first additive, and polyvinylidene fluoride, and then constructs a two-layer coating mechanism by sintering and ball milling, respectively, to obtain the modified ternary cathode material. By constructing a two-layer coating mechanism, the preparation method can, on the one hand, fully react the residual alkali on the surface of the ternary cathode material during the coating process and form an in-situ coating layer on the surface of the ternary cathode material, thereby reducing the residual alkali on the surface of the material; on the other hand, the two coating processes respectively use a high-temperature heat treatment method and a ball milling method, which can not only further stabilize the surface structure of the material, inhibit oxygen release from the ternary material under high voltage and high temperature conditions, and improve the electrochemical performance, processability, and cycle stability of the ternary cathode material, but also improve the overall particle size distribution and compaction density of the modified ternary cathode material.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular to a modified ternary cathode material and a preparation method and application thereof. Background Art

[0002] As the field of lithium-ion batteries continues to develop and progress, the market has further put forward higher demands on the performance of lithium-ion batteries. Specifically, higher requirements have been put forward on the performance of lithium-ion batteries in various aspects such as rate, cycle capacity retention rate, and energy density.

[0003] Lithium-ion batteries mainly include a positive electrode, a negative electrode, and an electrolyte. The positive electrode is usually prepared by placing an electrode active material, a binder, and a conductive agent (such as conductive carbon) for improving electronic conductivity in a dispersion medium to form a slurry coating liquid. The coating liquid is then evenly applied to the electrode collector by a coating device. After the dispersion medium evaporates, the positive electrode is obtained. The binder is usually polyvinylidene fluoride (PVDF), and the dispersion medium is usually a non-aqueous dispersion medium such as N-methyl-2-pyrrolidone (NMP). In the process of preparing the positive electrode, it is necessary to ensure the dispersibility and stability of the slurry coating liquid.

[0004] Nickel-cobalt-manganese ternary material is a commonly used electrode active material. Due to its high energy density and relatively low manufacturing cost, it is considered one of the most promising battery cathode materials. However, the application of nickel-cobalt-manganese ternary materials has also encountered some problems, which have seriously restricted its development. These problems mainly include the following aspects: First, as the nickel content in nickel-cobalt-manganese ternary materials increases, the battery will experience severe capacity fade during cycling. This is because unstable lithium residues (mainly Li2CO3 and LiOH) will appear on the surface of the nickel-cobalt-manganese ternary material, which will cause capacity decay. Secondly, the ionic radius of lithium ions and divalent nickel ions is similar, which will cause the formation of lithium-nickel mixed arrays in the battery. As the cycle progresses, the cathode material will transform into a rock salt phase, which is manifested by a significant increase in the direct current resistance (DCR) of the material. The combined effect of these two factors will ultimately lead to severe capacity fade in the battery. Second, the nickel-cobalt-manganese ternary cathode material will produce intergranular cracks during cycling. The electrolyte will erode the material along these cracks, thus shortening the cycle life of the material. Third, because current lithium-ion battery cathodes mostly use polyvinylidene fluoride (PVDF) slurries, they contain excessively high residual alkali content (especially LiOH and LiCO3). Alkaline groups attack the C-F and C-H bonds in polyvinylidene fluoride (PVDF), causing some of the PVDF in the slurry to form carbon-carbon double bonds, which increases the slurry viscosity and even forms a gel. Partial or overall gelation in the slurry can lead to uneven composition of the positive electrode coating, affecting performance during subsequent battery cathode preparation. In addition, materials with excessively high residual alkali content will chemically react with aluminum foil to form insoluble Al(OH)3. This flocculent precipitate can also hinder the circulation of lithium ions in the battery. Furthermore, lithium hydroxide reacts with lithium salts in the electrolyte to produce HF gas, which can cause corrosion of metal parts within the battery, damage the SEI film, consume active lithium in the system, and accelerate battery performance degradation. Lithium carbonate reacts with HF to release CO2 gas, affecting battery safety. Therefore, reducing the LiOH content on the surface of the ternary material is beneficial to improving the electrochemical performance and cycle performance of the battery and thus improving the overall performance of the battery.

[0005] During the preparation of battery positive electrodes, the dispersion and stability of the coating liquid play a crucial role in the performance of ternary electrode sheets and are also crucial for the effective overall performance of battery cells. Dispersion during the slurrying process of nickel-cobalt-manganese ternary materials is a key issue in lithium battery research. Uneven dispersion of the coating liquid can affect the contact between the positive electrode active material and the binder and conductive agent, thereby hindering the transport of conductive electrons and lithium ions, reducing the conductivity and cycling performance of the ternary material, and lowering the compaction density of the electrode sheet. The mixing process of powdered materials is a process of agglomeration, which can be divided into soft agglomeration and hard agglomeration based on the cause of powder agglomeration. Soft agglomerations are formed by the combined action of electrostatic and van der Waals forces between powder particles and are relatively easy to disperse; hard agglomerations, on the other hand, are primarily formed by chemical bonds and are therefore more difficult to disperse. The slurrying process of ternary materials is mostly a soft agglomeration process. Therefore, the dispersibility of the ternary material can be improved by surface modification of the powder of the ternary material. Organic molecules with good compatibility with the liquid solvent are grafted onto the particle surface through chemical reaction to change the surface properties of the particles and achieve a stable dispersion effect.

[0006] In addition, the preparation process of the positive electrode slurry involves the dispersion of the positive electrode material powder. During this process, the positive electrode material is always in the process of high-speed stirring, ball milling or mutual collision. However, this process may damage the surface of the positive electrode material, causing the new surface of the material to be exposed in the slurry. On the one hand, it is easy to generate a large number of dangling bonds on the new interface to capture protons in the slurry; on the other hand, this process will make it easy for lithium ions to detach from the lithium layer, affecting the acidity and alkalinity of the slurry, and then causing the alkalinity of the slurry to increase, resulting in gelation. Therefore, how to improve the dispersibility and stability of the positive electrode material so that its structure is not easily destroyed during the preparation of the positive electrode slurry and improve the electrochemical performance of the material is a technical problem that needs to be solved urgently.

[0007] To sum up, reducing the alkali content in the ternary positive electrode material and improving the internal dispersion of each element in the ternary positive electrode material are the keys to improving the cyclability and stability of the ternary positive electrode material and improving the comprehensive performance of the ternary positive electrode material. Therefore, this application is specially proposed. Summary of the Invention

[0008] The main purpose of the present invention is to provide a method for preparing a modified ternary positive electrode material to solve the problems of uneven internal dispersion of the elements in the material caused by the excessively high alkali content in the ternary positive electrode material in the prior art, which in turn leads to poor conductivity and poor battery cycle stability when the ternary positive electrode material is used in batteries.

[0009] In order to solve the above problems, the present invention provides a preparation method of a modified ternary positive electrode material, which comprises the following steps: step (1), mixing an acid ester solvent, a first additive and polyvinylidene fluoride to obtain a premixed solution; the first additive is a salt of at least one of the metal elements Sn, Zn, Ti, Bi, Ta, Li and Zr; step (2), mixing the premixed solution and the ternary positive electrode material to obtain a mixed slurry; step (3), drying and sintering the mixed slurry to perform a first coating to obtain a mixed material; step (4), mixing the mixed material, a second additive and a lubricant, and then ball milling to perform a second coating to obtain a modified ternary positive electrode material; the second additive is a conductive polymer additive.

[0010] Furthermore, in terms of weight percentage, the first additive in the premixed solution is 5-20%, polyvinylidene fluoride is 5-20%, and the balance is an acid ester solvent; preferably, the weight ratio of the ternary positive electrode material to the premixed solution is (1-5):1.

[0011] Furthermore, the weight ratio of the mixed material to the second additive is 1:(0.01% to 1%); and the amount of the lubricant added is 0.01% to 0.1% of the sum of the weight of the mixed material and the second additive.

[0012] Furthermore, the acid ester solvent is one or more of tributyl citrate, triethyl citrate, tri-n-hexyl citrate, tri(2-ethyl)hexyl citrate, acetyl tributyl citrate, acetyl triethyl citrate, acetyl n-butyl citrate, acetyl tri(2-ethyl)hexyl citrate, triacetin and diethylene glycol ethyl ether acetate; preferably, the first additive is one or more of zinc stannate, bismuth titanate, lithium tantalate, barium titanate, zirconyl titanate; preferably, the second additive is polythiophene and / or sulfonated lignin; preferably, the lubricant is lithium stearate and / or zinc stearate.

[0013] Furthermore, the mixing process in step (2) includes: subjecting the premixed solution and the ternary cathode material to ultrasonic treatment, then aging, and introducing plasma-activated gas during the ultrasonic and aging process; preferably, the plasma-activated gas is an inert gas containing 5 to 20% carbon dioxide, preferably the inert gas is at least one of argon and helium; preferably, the amount of plasma-activated gas introduced is 20 to 100 mL / min; preferably, the power density of the plasma-activated gas is 0.01 to 5 W / cm 2 ; Preferably, the ultrasonic time is 0.5 to 5 hours; Preferably, the aging time is 1 to 12 hours.

[0014] Furthermore, the molecular formula of the ternary cathode material is LiNi x Co y M 1-x-yO2, wherein 0.5≤x<1, 0<y≤0.1, and (x+y)<1, and M is Mn and / or Al.

[0015] Furthermore, in step (3), sintering is carried out in a compressed air atmosphere with a humidity of 40 to 70%; preferably, the sintering temperature is 700 to 900°C; preferably, the sintering time is 2 to 8 hours; preferably, drying is carried out under nitrogen circulation conditions, the drying temperature is 100 to 200°C, and the drying time is 5 to 25 hours.

[0016] Furthermore, grinding balls are added to the mixture of the mixed material, the second additive and the lubricant during ball milling; preferably, the weight ratio of the grinding balls to the mixture consisting of the mixed material, the second additive and the lubricant is 1:(1 to 5); preferably, the ball milling time is 4 to 12 hours; preferably, the particle size of the ternary positive electrode material after ball milling is 2.5≤D50≤4μm.

[0017] According to another aspect of the present invention, a modified ternary cathode material is provided, which is prepared according to the above preparation method.

[0018] According to the third aspect of the present invention, there is also provided a lithium-ion battery, comprising a battery positive electrode prepared from the above-mentioned modified ternary positive electrode material.

[0019] The present invention provides a modified ternary positive electrode material, a preparation method, and an application thereof. The preparation method first mixes the ternary positive electrode material with a premixed solution obtained by mixing an acid ester solvent, a first additive, and polyvinylidene fluoride, and then constructs a two-layer coating mechanism by sintering and ball milling, respectively, to obtain the modified ternary positive electrode material. The two-layer coating mechanism constructed in this preparation method, on the one hand, allows the residual alkali on the surface of the ternary positive electrode material to fully react during the coating process and form an in-situ coating layer on the surface of the ternary positive electrode material, further reducing the residual alkali on the material surface; on the other hand, the two coating processes of the modified ternary positive electrode material respectively use a high-temperature heat treatment method and a ball milling method, which not only further stabilizes the surface structure of the material, inhibits oxygen release from the ternary material under high voltage and high temperature conditions, improves the electrochemical performance, processability, and cycle stability of the ternary positive electrode material, but also improves the overall particle size distribution and compaction density of the modified ternary positive electrode material. The modified ternary positive electrode material prepared by the preparation method of the present invention has better conductivity and cycle stability during application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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:

[0021] Figure 1The modified ternary cathode material in Example 1 of the present invention is shown in SEM images before and after modification, wherein A is the SEM image of the ternary cathode material before modification, and B is the SEM image of the modified ternary cathode material;

[0022] Figure 2 The XRD patterns of the modified ternary cathode material before and after modification in Example 1 of the present invention are shown below:

[0023] Figure 3 This is a diagram showing the change in slurry viscosity when preparing the positive electrode sheet for the modified ternary positive electrode material in Example 1 of the present invention before and after modification. 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] As described in the background technology section, the excessively high alkali content in the ternary positive electrode material is one of the important reasons that affect the comprehensive performance of the ternary positive electrode material. The excessively high alkali content in the ternary positive electrode material will not only cause the alkaline groups therein to attack the CF bonds and CH bonds in polyvinylidene fluoride (PVDF), resulting in an uneven distribution of the material system, but will also react chemically with the aluminum foil to generate Al(OH)3 insoluble substances, further affecting the dispersion of the system. In addition, the alkaline groups will react with the components in the electrolyte to produce HF gas and CO2 gas, which will also affect the safety performance and comprehensive performance of the battery system. Therefore, reducing the alkali content of the ternary positive electrode material and improving the internal dispersion of each element are the keys to improving the comprehensive performance of the ternary positive electrode material.

[0026] In order to solve the above problems, the present invention provides a preparation method of a modified ternary positive electrode material, which comprises the following steps: step (1), mixing an acid ester solvent, a first additive and polyvinylidene fluoride (PVDF) to obtain a premixed solution; wherein the first additive is a salt of at least one of the metal elements Sn, Zn, Ti, Bi, Ta, Li and Zr; step (2), mixing the premixed solution and the ternary positive electrode material to obtain a mixed slurry; step (3), drying and sintering the mixed slurry to perform a first coating to obtain a mixed material; step (4), mixing the mixed material, a second additive and a lubricant, and then ball milling to perform a second coating to obtain a modified ternary positive electrode material; wherein the second additive is a conductive polymer additive.

[0027] In the preparation method of the modified ternary material described in the present invention, the salt additive containing the above-mentioned metal element and polyvinylidene fluoride are first evenly mixed with an acid ester solvent to obtain a premixed solution for modifying the ternary positive electrode material; then the ternary positive electrode material to be modified and the prepared premixed solution are fully infiltrated and mixed to obtain a mixed slurry; the above-mentioned mixed slurry is then subjected to a first coating through operations such as drying and sintering to obtain a mixed material; finally, the mixed material is mixed with a second additive and a lubricant, and the second additive and the mixed material are doped and coated by ball milling to obtain a modified ternary positive electrode material.

[0028] In particular, when preparing the modified ternary positive electrode material, the present invention constructs a two-layer coating mechanism. During the coating process, the residual alkali on the surface of the ternary positive electrode material can be fully reacted and a coating layer can be formed in situ on the surface of the ternary positive electrode material, further reducing the residual alkali on the surface of the material. Specifically, during the preparation process, the present invention first uses a premixed solution prepared with an acid ester solvent, a first additive and polyvinylidene fluoride to perform infiltration and mixing, and then performs the first coating by drying and sintering. When preparing a premixed solution for infiltrating the ternary positive electrode material, an acid ester solvent is used as one of the components of the premixed solution. The acid ester solvent can undergo a hydrolysis reaction during the drying, sintering and other processes to produce an acidic substance, thereby enabling the alkaline substance in the ternary positive electrode material to undergo a neutralization reaction with the generated acidic substance, which helps to reduce the content of alkaline substances in the ternary positive electrode material. PVDF, as an excellent electrode modifier, can improve the electrical conductivity and structural stability of the ternary positive electrode material, which is beneficial to improving the cycle stability of the modified ternary positive electrode material during use. By adding salt additives containing the above-mentioned metal elements to the premixed solution, the good electrical conductivity of the metal ions therein can be utilized to further improve the electrical conductivity of the modified ternary positive electrode material. After the premixed solution composed of the above-mentioned three components and the ternary positive electrode material are fully infiltrated and mixed, they are dried and sintered to achieve full doping and coating of the above-mentioned components with the ternary positive electrode material. In this process, the alkali content in the ternary positive electrode material can be fully reduced and the electrical conductivity and stability of the ternary positive electrode material can be improved. Furthermore, the present invention mixes the mixed material obtained after the first coating with the second additive and the lubricant, and performs a second coating through a ball milling process. During the second coating process, the second additive is added, and the second additive is a conductive polymer additive. The addition of the above-mentioned type of additive is beneficial to improving the electrical conductivity of the ternary material, especially after the addition of the above-mentioned additive, when the prepared ternary positive electrode material is used to prepare a battery positive electrode plate, it can effectively help to improve the electrical conductivity of the plate.

[0029] In addition, the present invention has different ways of constructing the two coating mechanisms when preparing the modified ternary positive electrode material. The first coating mechanism construction process is carried out in the form of high-temperature heat treatment. This process can not only help reduce the alkali content in the ternary material, but also further stabilize the surface structure of the material, inhibit the oxygen release of the ternary material under high voltage and high temperature conditions, and improve the electrochemical performance, process processing performance and cycle stability of the ternary positive electrode material. The second coating mechanism construction process is carried out in the form of ball milling. On the one hand, the morphology of the single crystal particles is trimmed by mechanical ball milling, the roundness of the particles is improved, and the uniformity and dispersibility of the single crystal particles are improved; on the other hand, the organic conductive material can be in-situ coated on the surface of the single crystal material during mechanical ball milling. The addition of organic medium during the grinding process can also reduce the generation of fine powder during the grinding process, improve the overall particle size distribution of the material, improve the dispersion stability of the slurry, and improve the compaction density of the electrode, which is beneficial to improving the electrochemical performance of the battery. The surface coating to form an elastic interface layer is also beneficial to improving the stress caused by the expansion and contraction of the lattice during the charge and discharge process of the material.

[0030] In summary, the preparation method of the present invention, through the construction of two coating processes, on the one hand reduces the alkali content in the ternary positive electrode material, improves the internal dispersion of each element in the ternary positive electrode material, and is beneficial to improving the comprehensive performance of the ternary positive electrode material; on the other hand, the two coating processes improve the conductivity and cycle stability of the ternary positive electrode material during use, so that the modified ternary positive electrode material has excellent comprehensive performance.

[0031] In a preferred embodiment, the first additive in the premix solution is 5-20% by weight, the polyvinylidene fluoride is 5-20% by weight, and the balance is an acid ester solvent; preferably, the weight ratio of the ternary positive electrode material to the premix solution is (1-5):1. The content of the metal salt additive, the polyvinylidene fluoride content, and the acid ester solvent content in the premix solution will affect the improvement of the alkali content, conductivity, and cycle stability of the modified ternary positive electrode material. By controlling the content of each component in the premix solution within the above range and controlling the addition ratio of the ternary positive electrode material to the premix solution within the above range, the prepared modified ternary positive electrode material can have more excellent comprehensive performance.

[0032] In a preferred embodiment, the weight ratio of the mixed material to the second additive is controlled to be 1:(0.01% to 1%); the amount of lubricant added is 0.01% to 0.1% of the combined weight of the mixed material and the second additive. The second additive is a conductive polymer additive, which is the main component of the second coating layer. Controlling the second additive, lubricant, and the mixed material after the first coating within the above range can achieve a better secondary coating effect, which is beneficial to improving the overall performance of the modified ternary cathode material.

[0033] By way of example but not limitation, the acid ester solvent is one or more of tributyl citrate, triethyl citrate, tri-n-hexyl citrate, tri(2-ethyl)hexyl citrate, acetyl tributyl citrate, acetyl triethyl citrate, acetyl n-butyl citrate, acetyl tri(2-ethyl)hexyl citrate, triacetin and diethylene glycol ethyl ether acetate. Acid ester solvents serve to reduce the alkali content in the material during the modification of the ternary positive electrode material, and the selection of the above-mentioned specific acid ester solvents has a better effect. Preferably, the first additive is one or more of zinc stannate, bismuth titanate, lithium tantalate, barium titanate and zirconium titanate; preferably, the second additive is polythiophene and / or sulfonated lignin. The first additive is one of the components in the first coating layer, which can improve the conductivity and cycle stability of the modified ternary positive electrode material. The second additive is a conductive polymer additive, which is the main component in the second coating layer. The selection of the above-mentioned specific types of additives has a better effect on improving the conductivity of the ternary material and the conductivity after the pole piece is compacted, which is beneficial to improving the comprehensive performance of the modified ternary positive electrode material. Preferably, the lubricant is lithium stearate and / or zinc stearate.

[0034] In a preferred embodiment, the mixing process in step (2) includes: subjecting the premix solution and the ternary cathode material to ultrasonic treatment first, then aging, and introducing plasma-activated gas during the ultrasonic and aging process. Ultrasonic treatment and aging during the mixing of the ternary material and the prepared premix solution can facilitate a more uniform mixing and contact between the premix solution and the ternary cathode material. In the ultrasonic and aging process, the introduction of plasma-activated gas can, on the one hand, improve the contact between the ternary cathode material and the premix solution, enhance their bonding force, adhesion and dispersibility, make them more closely and more uniformly contacted, and also help to reduce the alkali content of the material surface; on the other hand, the energy in the plasma-activated gas can make the modified ternary cathode material have better conductivity and cycle stability. Preferably, the plasma-activated gas is an inert gas containing 5-20% carbon dioxide, preferably the inert gas is at least one of argon and helium; preferably, the amount of plasma-activated gas introduced is 20-100 mL / min; preferably, the power density of the plasma-activated gas is 0.01-5 W / cm 2 Selecting a plasma-activated gas with the aforementioned properties can enhance the performance of the modified ternary cathode material. Preferably, the ultrasonication time is 0.5 to 5 hours; preferably, the aging time is 1 to 12 hours. Controlling the ultrasonication time and aging time within the aforementioned ranges can achieve better results in the modified ternary cathode material.

[0035] In a preferred embodiment, the molecular formula of the ternary cathode material is LiNi x Co y M 1-x-yO2, wherein 0.5≤x<1, 0<y≤0.1, and (x+y)<1, and M is Mn and / or Al. The modified preparation method of the ternary cathode material described in the present invention can reduce the alkali content in the ternary cathode material, improve the dispersibility between the various elemental components in the material, and enhance the overall performance of the ternary cathode material. In particular, the modified ternary cathode material having the above-mentioned components and parameters can be modified to obtain a modified ternary cathode material with better overall performance.

[0036] In a preferred embodiment, the sintering in step (3) is carried out in a compressed air atmosphere with a humidity of 40 to 70%. Controlling the humidity of the sintering environment within the above range during sintering can make the alkaline substances in the ternary positive electrode material easily concentrated on the surface of the particles, which is more conducive to the neutralization reaction and thus helps to reduce the content of alkaline substances in the material. Preferably, the sintering temperature is 700 to 900°C; preferably, the sintering time is 2 to 8 hours; preferably, the drying is carried out under nitrogen circulation conditions, the drying temperature is 100 to 200°C, and the drying time is 5 to 25 hours. Controlling the drying and sintering conditions during the first carbon coating process within the above range can achieve better results when the modified ternary positive electrode material is coated for the first time.

[0037] In a preferred embodiment, grinding balls are added to the mixture of the mixed material, the second additive and the lubricant during ball milling; preferably, the weight ratio of the grinding balls to the mixture consisting of the mixed material, the second additive and the lubricant is 1:(1-5). Adding grinding balls to the ball milling system during the ball milling process and controlling the amount of grinding balls added to be within the above range can make the particle size of the modified ternary positive electrode material more uniform. Preferably, the ball milling time is 4 to 12 hours. Further preferably, the particle size of the modified ternary positive electrode material after ball milling is 2.5≤D50≤4μm. Controlling the particle size of the modified ternary positive electrode material within the above range can make the modified ternary positive electrode material have better comprehensive performance.

[0038] According to the second aspect of the present invention, a modified ternary positive electrode material is provided, wherein the modified ternary positive electrode material is prepared by the above-mentioned preparation method, and the content of LiOH and LiCO3 in the modified ternary positive electrode material obtained by the above-mentioned preparation method is significantly lower than that in the ternary positive electrode material before modification.

[0039] According to a third aspect of the present invention, a lithium-ion battery is further provided, comprising a battery positive electrode prepared from the above-mentioned modified ternary positive electrode material.

[0040] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0041] Example 1

[0042] The premixed solution is obtained by mixing triethyl citrate, PVDF and bismuth titanate in a weight ratio of 75%:5%:20%, and then the premixed solution is mixed with the ternary cathode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0043] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0044] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.588 μm is obtained.

[0045] The modified ternary cathode material prepared in this application was characterized, and the results are shown in the accompanying drawings. Figure 1 Figures 2 and 3 are SEM images before and after modification, where A is the SEM image of the ternary cathode material before modification, and B is the SEM image of the ternary cathode material after modification; Figure 2 The XRD patterns of the ternary cathode materials before and after modification; Figure 3 This is a graph showing the viscosity change of the slurry used in preparing positive electrode sheets from ternary positive electrode materials before and after modification.

[0046] Depend on Figure 1 From the SEM image, it can be seen that the modified ternary cathode material prepared by the preparation method of the present invention has a further improved particle roundness compared to the ternary cathode material before modification, which can make the modified ternary cathode material have better specific surface area characteristics, better dispersibility and better compaction density. Figure 2From the XRD diagrams of the modified ternary cathode material and the ternary cathode material before and after modification, it can be seen that the modified ternary cathode material presents a single α-NaFeO2 type layered structure, belonging to the R3m space group. In addition, the (006) / (102) and (108) / (110) peaks are obviously split, further indicating that the material has a good layered structure; and from the XRD diagram, it can be seen that the peak shape of the modified ternary cathode material is sharp and there are no mixed peaks, indicating that it has a good crystal form. The ternary cathode materials before and after modification were used to prepare positive electrode sheets, and the viscosity of the slurry used in the preparation of the positive electrode sheets was tested. The results are as follows: Figure 3 As shown. Figure 3 From the graph of the change in slurry viscosity when preparing positive electrode sheets before and after modification, it can be seen that the viscosity of the slurry when using the modified ternary positive electrode material to prepare positive electrode sheets will not change significantly over a long period of time, especially compared with the viscosity of the positive electrode slurry prepared from the ternary positive electrode material before modification, which shows that the stability and dispersibility of the slurry prepared from the modified ternary positive electrode material are better. This shows that the method for modifying the ternary positive electrode material described in the present invention can greatly improve the stability and dispersibility of the material.

[0047] Example 2

[0048] Triethyl citrate, PVDF and barium titanate are mixed in a weight ratio of 60%:20%:20% to obtain a premixed solution, and then the premixed solution is mixed with the ternary positive electrode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1.5 hours, then letting it stand for 12 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.7 Co 0.1 Mn 0.2 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 5:1. The main component of the plasma activation gas was argon, which contained 20% volume of carbon dioxide. The flow rate of the plasma activation gas was 20 mL / min, and the power density was 0.01 W / cm 2 .

[0049] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 100°C and the drying time was 10 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 70%, the sintering temperature was 900°C and the sintering time was 2 hours to obtain the first coated mixed material.

[0050] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.916 μm is obtained.

[0051] Example 3

[0052] The premixed solution is obtained by mixing triethyl citrate, PVDF and barium titanate in a weight ratio of 90%:5%:5%, and then the premixed solution is mixed with the ternary cathode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1.5 hours, then letting it stand for 2 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.8 Co 0.1 Mn 0.1 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 5:1. The main component of the plasma activation gas was argon, which contained 20% volume of carbon dioxide. The flow rate of the plasma activation gas was 100 mL / min and the power density was 0.01 W / cm 2 .

[0053] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 100°C and the drying time was 20 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 70%, the sintering temperature was 700°C, and the sintering time was 5 hours to obtain the first coated mixed material.

[0054] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.947 μm is obtained.

[0055] Example 4

[0056] The tributyl citrate, PVDF and zinc stannate are mixed in a weight ratio of 75%:5%:20% to obtain a premixed solution, and then the premixed solution is mixed with the ternary positive electrode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 0.5 hours, then letting it stand for 12 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.5 Co 0.1 Mn 0.4 The weight ratio of the added amount of O2 ternary cathode material to the premixed solution is 1:1. The main component of the plasma activation gas is argon, which contains 5% volume of carbon dioxide. The flow rate of the plasma activation gas is 100 mL / min and the power density is 0.01 W / cm 2 .

[0057] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 100°C and the drying time was 25 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 40%, the sintering temperature was 700°C and the sintering time was 8 hours to obtain the first coated mixed material.

[0058] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 1:0.01%, the amount of lubricant lithium stearate added is 0.01% of the sum of the weight of the mixed material and the second additive, and the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:5. After ball milling for 12 hours, a modified ternary positive electrode material with a particle size D50 of 2.502 μm is obtained.

[0059] Example 5

[0060] The tri-n-hexyl citrate, PVDF and lithium tantalate are mixed in a weight ratio of 75%:20%:5% to obtain a premixed solution, and then the premixed solution is mixed with the ternary cathode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 5 hours, then letting it stand for 1 hour, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.9 Co 0.01 Al 0.09 The weight ratio of the added amount of the ternary cathode material to the premixed solution is 5:1. The main component of the plasma activation gas is helium, which contains 20% volume of carbon dioxide. The flow rate of the plasma activation gas is 20 mL / min and the power density is 5 W / cm 2 .

[0061] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 200°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 70%, the sintering temperature was 900°C and the sintering time was 2 hours to obtain the first coated mixed material.

[0062] The above-mentioned first-coated mixture, the second additive sulfonated lignin and the lubricant zinc stearate are mixed, and then ball-milled for the second coating, wherein the weight ratio of the mixture and the second additive is 1:1%, the amount of lubricant lithium stearate added is 0.1% of the sum of the weight of the mixture and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above-mentioned mixture is 1:1, and after ball milling for 4 hours, a modified ternary positive electrode material with a particle size D50 of 4.006 μm is obtained.

[0063] Example 6

[0064] The premixed solution is obtained by mixing tri(2-ethyl)hexyl citrate, PVDF and zirconyl titanate in a weight ratio of 75%:5%:20%, and then the premixed solution is mixed with the ternary cathode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activated gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0065] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0066] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.567 μm is obtained.

[0067] Example 7

[0068] Acetyl tributyl citrate, PVDF and bismuth titanate are mixed in a weight ratio of 75%:5%:20% to obtain a premixed solution, and then the premixed solution is mixed with the ternary positive electrode material. The mixing process includes first stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0069] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0070] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.588 μm is obtained.

[0071] Example 8

[0072] Acetyl triethyl citrate, PVDF and bismuth titanate are mixed in a weight ratio of 75%:5%:20% to obtain a premixed solution, and then the premixed solution is mixed with the ternary positive electrode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2.

[0073] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0074] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.553 μm is obtained.

[0075] Example 9

[0076] Acetyl citrate n-butyl ester, PVDF and bismuth titanate are mixed in a weight ratio of 75%:5%:20% to obtain a premixed solution, and then the premixed solution is mixed with the ternary positive electrode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0077] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0078] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.378 μm is obtained.

[0079] Example 10

[0080] Acetyl citrate tri (2-ethyl) hexyl ester, PVDF and bismuth titanate are mixed in a weight ratio of 75%: 5%: 20% to obtain a premixed solution, and then the obtained premixed solution is mixed with the ternary positive electrode material. The mixing process includes first stirring the above-mentioned mixed slurry under ultrasonic conditions for 1 hour, then letting it stand and age for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0081] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0082] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.445 μm is obtained.

[0083] Example 11

[0084] The premixed solution is obtained by mixing triacetin, PVDF and bismuth titanate in a weight ratio of 75%:5%:20%, and then the premixed solution is mixed with the ternary cathode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0085] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0086] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.532 μm is obtained.

[0087] Example 12

[0088] Diethylene glycol ethyl ether acetate, PVDF and bismuth titanate are mixed in a weight ratio of 75%:5%:20% to obtain a premixed solution, and then the premixed solution is mixed with the ternary positive electrode material. The mixing process includes first stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0089] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0090] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.387 μm is obtained.

[0091] Example 13

[0092] The difference from Example 1 is that during the first coating, the ratio of the acid ester solvent, the first additive, and polyvinylidene fluoride is 68%:30%:2%, and the weight ratio of the ternary positive electrode material to the premixed solution is 0.8:1. During the second coating, the weight ratio of the mixed material and the second additive is 1:10%, and the amount of lubricant added is 1% of the combined weight of the mixed material and the second additive.

[0093] The triethyl citrate, PVDF and bismuth titanate are mixed in a weight ratio of 68%:30%:2% to obtain a premixed solution, and then the premixed solution is mixed with the ternary positive electrode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 0.8:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0094] The mixed slurry obtained above was dried under nitrogen circulation conditions, wherein the drying temperature was 120°C and the drying time was 5 hours; the dried mixture was then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature was 780°C and the sintering time was 5 hours to obtain the first coated mixed material.

[0095] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 1:10%, the amount of lubricant lithium stearate added is 1% of the sum of the weight of the mixed material and the second additive, and the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1. After ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.837 μm is obtained.

[0096] Comparative Example 1

[0097] The ternary material and bismuth titanate were mixed in a weight ratio of 80%:20% and dried under nitrogen circulation conditions. The molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 O2, the drying temperature is 120 ℃, and the drying time is 5h; the dried mixture is then sintered in a compressed air atmosphere with a humidity of 45%, the sintering temperature is 780 ℃, and the sintering time is 5h to obtain the first coated mixed material.

[0098] The mixed material after the first coating obtained above, the second additive polythiophene and the lubricant lithium stearate are mixed, and then ball milled for the second coating, wherein the weight ratio of the mixed material and the second additive is 0.5%:1, the amount of lubricant lithium stearate added is 0.05% of the sum of the weight of the mixed material and the second additive, the ratio of the weight of the grinding balls added during ball milling to the weight of the above mixture is 1:1, and after ball milling for 8 hours, a modified ternary positive electrode material with a particle size D50 of 3.317 μm is obtained.

[0099] Comparative Example 2

[0100] The premixed solution is obtained by mixing triethyl citrate, PVDF and bismuth titanate in a weight ratio of 75% 5%: 20%, and then the premixed solution is mixed with the ternary cathode material. The mixing process includes stirring the mixed slurry under ultrasonic conditions for 1 hour, then letting it stand for 8 hours, and continuously introducing plasma activation gas during the ultrasonic stirring and aging process. After the above operations are completed, a mixed slurry is obtained. Among them, the molecular formula of the ternary material is LiNi 0.65 Co 0.07 Mn 0.28 The weight ratio of the added amount of the ternary cathode material to the premixed solution was 1:1. The main component of the plasma activation gas was argon, which contained 10% volume of carbon dioxide. The flow rate of the plasma activation gas was 50 mL / min, and the power density was 0.05 W / cm 2 .

[0101] The resulting mixed slurry was dried under nitrogen circulation conditions at 120°C for 5 hours. The dried mixture was then sintered at 780°C for 5 hours in a compressed air atmosphere with a humidity of 45% to obtain a mixed material. The coated mixture was ball-milled at a 1:1 ratio of the weight of the grinding balls to the weight of the mixture. After 8 hours of ball milling, a modified ternary cathode material with a particle size (D50) of 3.273 μm was obtained.

[0102] The contents of alkaline substances LiOH and Li2CO3 in the modified ternary positive electrode materials in Examples 1 to 13 and Comparative Examples 1 to 2 before and after modification were tested, and related properties such as the specific surface area (BET) and powder compaction density of the materials were tested. The test results are shown in Table 2 below.

[0103] Among them, regarding the test method of the alkali content in the modified ternary positive electrode material before and after modification: weigh the test material according to the parameters shown in Table 1, accurate to 0.0001g, place the weighed sample in a 100mL beaker, add 50mL of deionized water, and place the magnetic beads in the beaker and seal it with plastic wrap, then place the beaker on a magnetic stirrer and stir for about 15 minutes; let it stand for 5 minutes, filter it with a glass funnel, and the filtered clear liquid is the test solution.

[0104] Table 1

[0105]

[0106] Accurately transfer the solution to be tested into a 100mL beaker and place a stirring rotor. Control the sample volume to approximately 50mL (make up with water if less than 50mL). Place the beaker on the magnetic stirrer of an automatic potentiometric titrator. Add 2 drops of phenolphthalein and titrate with a standard HCl solution selected from Table 1 until the solution changes from red to colorless. The instrument will record the volume Ep1 (V1) of the HCl standard solution consumed at the stoichiometric point and the pH. Then, add 2 drops of methyl orange and continue titrating until the solution changes from yellow to orange. The instrument will record the volume Ep2 (V2) of the HCl standard solution consumed at the stoichiometric point and the pH. The analytical results of the alkali content in the sample are calculated in the following ways:

[0107] (1) When 2V1>V2, it contains LiOH and Li2CO3, and the calculation formula is as follows:

[0108]

[0109] (2) When 2V1<V2, it contains Li2CO3 and LiHCO3, and the calculation formula is as follows:

[0110]

[0111] (3) When 2V1=V2, only Li2CO3 is contained, and the calculation formula is as follows:

[0112]

[0113] Wherein, in the above calculation formula: c is the concentration of HCl standard solution (mol / L); V1(Ep1) is the volume of HCl standard solution consumed at the first equivalence point (mL); V2(Ep2) is the volume of HCl standard solution consumed at the second equivalence point (including the first equivalence point) (mL); V' is the volume of the test solution (mL); V is the volume of the sample (mL); 23.95 is the molar mass of LiOH (g / mol); 73.89 is the molar mass of Li2CO3 (g / mol); 67.96 is the molar mass of LiHCO3 (g / mol); and m is the mass of the sample (g).

[0114] Table 2

[0115]

[0116] The ternary positive electrode materials before and after modification in the above-mentioned Examples 1 to 13 and Comparative Examples 1 to 2 were respectively prepared into positive electrode sheets and button batteries according to the methods described below. The mixed slurry in the process of preparing the positive electrode sheets and the relevant performance of the positive electrode sheets and button batteries were tested. The test methods and the results obtained are shown in the following table.

[0117] Preparation of button cells:

[0118] A positive electrode slurry is prepared by mixing the electrode active material (unmodified ternary cathode material or modified ternary cathode material), the conductive agent acetylene black, and the binder PVDF in a weight ratio of 90:5:5. The preparation method includes: weighing the positive electrode material and acetylene black to the nearest 0.0001g and grinding them in a mortar for 30 minutes. PVDF is dissolved in N-methylpyrrolidone to obtain a 2.5% PVDF solution. The corresponding amount of solution is slowly added dropwise to the mortar and ground until a uniform positive electrode slurry is formed. A suitable area of ​​aluminum foil is cut and laid flat on a smooth glass plate. The resulting slurry is evenly coated on the aluminum foil with a spatula. The organic solvent (NMP) is completely evaporated at 100°C, and the electrode is rolled using a roller press to achieve a compaction density of 3.0g / cc. A manual tablet press is used to cut the aluminum foil, and the area on the aluminum foil with the active material evenly coated is cut into positive electrode sheets with a diameter of 12 mm. The sheets are placed in a vacuum drying oven and dried at 100°C for 5 hours to remove the moisture in the positive electrode sheets. The sheets are then placed in a vacuum drying oven and dried at 100°C for another 5 hours to obtain positive electrode sheets that can be directly assembled into batteries.

[0119] The positive electrode sheet prepared above was assembled into a button-type battery of model CR2016 to assemble a battery with lithium as the counter electrode that can be used for various electrochemical performance tests. The specific steps are: quickly transfer the positive electrode sheet to a glove box, take the positive electrode shell, place the positive electrode sheet with the active material side facing up in the middle of the positive electrode shell, add electrolyte, place the diaphragm, add electrolyte, place the lithium sheet and nickel foam, and finally cover with the negative electrode shell. The battery is placed on a button battery sealing machine and manually pressurized to a certain pressure, and then compressed and packaged to obtain a button battery.

[0120] Button battery performance test: The test uses a LAND battery testing system with model CT2001A. The program setting is to let the battery stand for 6 hours first, wait for the electrolyte to be fully infiltrated, and then start the electrochemical performance test. Since increasing the cut-off voltage can increase the discharge capacity of the material, the cycle stability of the material is tested at a high voltage of 4.5V in this application. In the rate performance test at room temperature of 25℃, the rates are set to 0.2C, 0.33C, 1C, and 3C, and the charge and discharge voltage range is 2.8V to 4.5V. The charge and discharge rate is set to 1C, the charge and discharge voltage range is 2.8V to 4.5V, and the cycle is 50 weeks to test the capacity retention rate of the battery.

[0121] Button battery DCR growth rate test:

[0122] DCR testing: The DC discharge resistance (DCR) is measured in a 25°C constant temperature chamber at a 1C discharge rate for 30 seconds. The DC discharge resistance (DCR) is calculated as follows: DCR = (U0 - U1) / I, where U0 represents the voltage before the 30-second discharge, U1 represents the voltage after the 30-second discharge, and I represents the current at the 1C rate. The button cell under test is cycled at 0.2C over a voltage range of 2.8V-4.5V for two cycles. The average of the two 0.2C discharge capacities is defined as 100% state of charge (SOC). The capacity is then discharged to half at a 0.2C rate, defining the SOC as 50%. The DCR at 50% SOC before the high-temperature test is recorded as DCR0. The cell is then charged in a 25°C constant temperature chamber at a constant current and voltage rate of 0.2C to 4.5V, representing 100% SOC. Then place the button battery in a constant temperature and humidity chamber at 90℃ for 24 hours. Then place the button battery in a constant temperature chamber at 25℃ for 1 hour, repeat the process of setting the capacity at 100% SOC and adjusting it to 50% SOC at 0.2C after the storage, and finally perform the DCR test at 50% SOC after the storage, and record it as DCR. 50 Growth rate before and after high temperature storage R% = (DCR 后 -DCR 前 ) / DCR 前 ×100, where DCR 前The DC internal resistance at 50% SOC at 1C rate tested at 25℃ before high temperature storage is DCR. The DC internal resistance at 50% SOC at 1C rate tested at 25℃ after 90℃ high temperature storage is DCR. 后 .

[0123] Slurry stability test during electrode sheet preparation:

[0124] (1) The ternary positive electrode materials before and after modification in Example 1 were used to prepare positive electrode slurries. 50 mL of the slurry was allowed to stand for a period of time. The viscosity of the slurry at 0 h (i.e., before standing and after mixing), 2 h, 4 h, 8 h, 16 h, 32 h, and 64 h was tested. The obtained data were recorded and plotted. The results are as follows: Figure 3 As shown in the figure, the stability of the slurry can be reflected according to the fluctuation of the slurry viscosity within 64 hours.

[0125] (2) Regarding viscosity difference: The ternary positive electrode materials before and after modification of Examples 1 to 13 and Comparative Examples 1 and 2 were used to prepare positive electrode slurries. 50 mL of the positive electrode slurry was allowed to stand for 64 h. The viscosity of the slurry after uniform mixing was first tested, and then the viscosity of the slurry after standing for 64 h was tested. The viscosity difference before and after standing was taken to reflect the stability of the corresponding slurry. The slurry viscosity difference was recorded as shown in Table 3.

[0126] (3) About fineness test: The fineness of the slurry can reflect the distribution of particles in the slurry. It can be combined with viscosity and other characteristics to comprehensively judge the stability of the slurry. Slurry with good dispersion has a more uniform particle distribution and is not easy to agglomerate and precipitate when placed. The smaller the fineness, the better the stability of the slurry. The fineness test is carried out using a scraper fineness meter.

[0127] (4) Regarding the difference in solid content: 50 mL of the positive electrode slurry prepared from the ternary positive electrode materials of Examples 1 to 13 and Comparative Examples 1 and 2 before and after modification were taken and allowed to stand for 64 h. The upper and lower layers of the slurry were taken, and then the solid contents of the upper and lower layers of the slurry were tested respectively. The difference in solid content between the upper and lower layers can further reflect the sedimentation performance of the slurry, that is, the stability performance.

[0128] Electrode rebound rate test: Electrode rebound rate can be used to evaluate the processing performance of materials. The smaller the electrode rebound rate, the better the processing performance of the corresponding material. The formula for calculating the electrode rebound rate is: (electrode thickness after rebound - electrode thickness before rebound) / electrode thickness before rebound × 100%, where the electrode thickness before rebound is the thickness measured after the electrode is manufactured, and the electrode thickness after rebound is the thickness measured after the electrode is placed at room temperature under high-purity argon protection for 48 hours.

[0129] The modified ternary positive electrode materials in the above-mentioned Examples 1 to 13 and Comparative Examples 1 to 2 were prepared into positive electrode sheets and button batteries according to the above-mentioned methods before and after modification. The results of testing the positive electrode slurry in the process of preparing the positive electrode sheet and the related properties of the positive electrode sheet are shown in Table 3.

[0130] Table 3

[0131]

[0132]

[0133] The modified ternary positive electrode materials in Examples 1 to 13 and Comparative Examples 1 to 2 were prepared into button batteries before and after modification according to the above method. The battery charge and discharge performance and DC resistance growth rate and other related properties were tested. The results are shown in Table 4.

[0134] Table 4

[0135]

[0136]

[0137] As can be seen from Table 2, in Examples 1 to 12 of the present invention, the use of the preparation method of the present invention and the control of the preparation conditions within the preferred range in the preparation of the modified ternary positive electrode material can significantly reduce the content of LiOH and Li2CO3 in the modified ternary positive electrode material compared to the unmodified ternary positive electrode material, effectively achieving the purpose of reducing the content of alkaline substances in the ternary material; in addition, the specific surface area characteristics and powder compaction density characteristics of the modified ternary positive electrode material are also significantly improved compared to the unmodified ternary positive electrode material. Example 13 uses the preparation method of the present invention when preparing the modified ternary positive electrode material, but does not control the preparation conditions within the preferred range. The resulting modified ternary positive electrode material also has a certain degree of improvement in alkali content, specific surface area characteristics, and powder compaction density characteristics compared to the unmodified ternary positive electrode material. Comparative Examples 1 and 2 do not use the modification method of the present invention, and the degree of improvement in alkali content, specific surface area characteristics, and powder compaction density characteristics of the modified ternary positive electrode material obtained compared to the unmodified ternary positive electrode material is not ideal.

[0138] Table 3 presents the performance test results of the unmodified ternary positive electrode materials and the modified ternary positive electrode materials in Examples 1 to 13 and Comparative Examples 1 to 2 when prepared into positive electrode sheets. Analysis of the above data indicates that utilizing the preparation method of the present invention and controlling the preparation conditions within the preferred range when preparing the modified ternary positive electrode materials can further improve the fineness, viscosity, resistivity, and thickness rebound rate of the modified ternary positive electrode materials compared to the unmodified materials. The changes in fineness and viscosity indicate that the overall stability of the slurry is significantly improved when using the modified ternary positive electrode materials to prepare positive electrode sheets; the resistivity of the modified ternary positive electrode materials is also significantly reduced, and the conductive properties are improved. In Example 13, utilizing the preparation method of the present invention but not controlling the preparation conditions within the preferred range when preparing the modified ternary positive electrode materials, the modified ternary positive electrode materials produced exhibit slightly inferior modification effects compared to Examples 1 to 12, but the relevant properties are also improved to a certain extent. However, Comparative Examples 1 and 2 did not adopt the modification method described in the present invention, and the effect of the modified ternary positive electrode material obtained was far different from the modification effect of the modified ternary positive electrode material prepared by the preparation method described in the present invention.

[0139] The data in Table 4 are the results of relevant performance tests of the ternary positive electrode materials before modification and the modified ternary positive electrode materials in Examples 1 to 13 and Comparative Examples 1 to 2 when they are prepared into batteries. It can be seen from Table 4 that when the modified ternary positive electrode materials prepared in Examples 1 to 12 are applied to batteries, the performance in various aspects such as battery capacity, capacity retention rate and DCR growth rate are better than the performance shown by preparing the ternary positive electrode materials before modification into batteries. The modified ternary positive electrode material prepared in Example 13 shows slightly worse results when applied to batteries than those in Examples 1 to 12, but it can still serve the purpose of further improvement. The performance shown by the modified ternary positive electrode materials prepared into batteries in Comparative Examples 1 to 2 does not change significantly compared to the effect before modification, and is very different from the effects shown in Examples 1 to 13.

[0140] In summary, the modified ternary positive electrode material prepared by the preparation method of the modified ternary positive electrode material of the present invention can significantly reduce the content of alkaline substances in the material and improve the material's compaction density and specific surface area and other properties; when it is used to prepare the battery positive electrode plate, the stability of the slurry is significantly improved, and the resistivity and plate thickness rebound rate can also be further improved; and when the modified ternary positive electrode material of the present invention is applied to the battery, the battery capacity, capacity retention rate and DCR growth rate and other aspects of the performance are further improved. It can be seen that the method of the present invention has obvious progressive significance.

[0141] 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 method for preparing a modified ternary cathode material, characterized in that: The preparation method comprises the following steps: Step (1), mixing an acid ester solvent, a first additive and polyvinylidene fluoride to obtain a premixed solution; the first additive is a salt of at least one of the metal elements Sn, Zn, Ti, Bi, Ta, Li and Zr; Step (2), mixing the premixed solution and the ternary cathode material to obtain a mixed slurry; Step (3), drying and sintering the mixed slurry to perform a first coating to obtain a mixed material; Step (4) is to mix the mixed material, the second additive and the lubricant, and then ball mill to perform a second coating to obtain the modified ternary positive electrode material; the second additive is a conductive polymer additive.

2. The method for preparing the modified ternary cathode material according to claim 1, wherein: In terms of weight percentage, the first additive in the premix solution is 5-20%, the polyvinylidene fluoride is 5-20%, and the balance is the acid ester solvent; And / or, the weight ratio of the ternary positive electrode material to the premixed solution is (1-5):

1.

3. The method for preparing the modified ternary cathode material according to claim 1, wherein: The weight ratio of the mixed material to the second additive is 1:(0.01%~1%); the added amount of the lubricant is 0.01%~0.1% of the sum of the weight of the mixed material and the second additive.

4. The method for preparing the modified ternary cathode material according to any one of claims 1 to 3, characterized in that: The acid ester solvent is one or more of tributyl citrate, triethyl citrate, tri-n-hexyl citrate, tri(2-ethyl)hexyl citrate, acetyl tributyl citrate, acetyl triethyl citrate, acetyl n-butyl citrate, acetyl tri(2-ethyl)hexyl citrate, triacetin and diethylene glycol ethyl ether acetate; and / or, the first additive is one or more of zinc stannate, bismuth titanate, lithium tantalate and barium titanate; and / or, the second additive is polythiophene and / or sulfonated lignin; And / or, the lubricant is lithium stearate and / or zinc stearate.

5. The method for preparing the modified ternary cathode material according to any one of claims 1 to 3, characterized in that: The mixing process in step (2) includes: subjecting the premixed solution and the ternary cathode material to ultrasonic treatment first, then aging, and introducing plasma activated gas during the ultrasonic and aging processes.

6. The method for preparing the modified ternary cathode material according to claim 5, characterized in that: The plasma activation gas is an inert gas containing 5-20% carbon dioxide, and the inert gas is at least one of argon and helium; and / or, the plasma activation gas is introduced at a rate of 20 to 100 mL / min; And / or, the power density of the plasma activated gas is 0.01~5W / cm 2 ; And / or, the ultrasonic time is 0.5-5 h; and / or, the aging time is 1-12 h.

7. The method for preparing the modified ternary cathode material according to any one of claims 1 to 3, characterized in that: The molecular formula of the ternary positive electrode material is LiNi x Co y M 1-x-y O2, wherein 0.5≤x<1, 0<y≤0.1, and (x+y)<1, and M is Mn and / or Al.

8. The method for preparing the modified ternary cathode material according to any one of claims 1 to 3, characterized in that: The sintering in step (3) is carried out in a compressed air atmosphere with a humidity of 40-70%; And / or, the sintering temperature is 700-900°C; And / or, the sintering time is 2 to 8 hours; And / or, the drying is carried out under nitrogen circulation conditions, the drying temperature is 100-200° C., and the drying time is 5-25 hours.

9. The method for preparing the modified ternary cathode material according to any one of claims 1 to 3, characterized in that: During the ball milling, grinding balls are added to the mixture of the mixed material, the second additive and the lubricant; the weight ratio of the grinding balls to the mixture of the mixed material, the second additive and the lubricant is 1:(1-5); And / or, the ball milling time is 4 to 12 hours; And / or, the particle size of the ternary positive electrode material after ball milling is 2.5≤D50≤4µm.

10. A modified ternary cathode material, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 9.

11. A lithium-ion battery, characterized in that: It includes a battery positive electrode prepared from the modified ternary positive electrode material according to claim 10.

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