Method for preparing ternary positive electrode composite material and ternary positive electrode composite material

Abstract

The invention discloses a method for preparing a ternary positive electrode composite material. The method comprises the following steps: sintering a ternary positive electrode material precursor and a lithium source in an oxygen atmosphere to obtain a ternary positive electrode material; and introducing mixed gas of acid gas and oxygen into the ternary positive electrode material under the condition that the temperature does not exceed 900 DEG C to obtain the ternary positive electrode composite material. By adopting the technical scheme, on one hand, overgrowth or abnormal growth of crystal grains caused by overhigh temperature can be prevented; on the other hand, the residual alkali on the surface is effectively removed and is converted into inorganic salt with more stable thermodynamics, and the surface of the ternary positive electrode material is coated with the inorganic salt layer, so that the interface stability and the cycling stability of the material can be remarkably improved, and the resource utilization of wastes is also realized. The invention also discloses the ternary positive electrode composite material. The ternary positive electrode composite material is prepared by adopting the preparation method. The invention also discloses a lithium battery and a ternary positive electrode composite material.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a method for preparing a ternary cathode composite material, a ternary cathode composite material, a lithium battery, and a ternary cathode composite material. Background Art

[0002] Lithium-ion batteries occupy a large market share in the current 3C (computers, communications, and consumer electronics), power battery, and energy storage fields, and are very common energy storage and conversion devices. With the increasing market demand for battery capacity, the ternary cathode material Li(Ni x Co y Mn 1-x-y )O2, especially the ternary cathode material with a high nickel content (x≥0.8), has received extensive attention in the industry due to its higher battery energy density.

[0003] In the preparation process of ternary cathode materials (such as NCM811), ternary cathode material precursors, such as Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and a lithium source (usually LiOH or LiOH·H2O) are usually mixed and sintered. To ensure the full progress of the lithiation reaction, the lithium source needs to be added in excess, which makes the final product (i.e., the ternary cathode material) alkaline (pH>11), and LiOH that has not participated in the lithiation reaction remains on the surface of the final product (i.e., residual alkali). This residual alkali LiOH will have various negative impacts on the battery. On the one hand, LiOH will subsequently undergo a defluorination reaction with the PVDF (polyvinylidene fluoride) binder to generate insoluble cross-linked substances, resulting in the gelation of the slurry (the viscosity increases by more than 10 times), thus causing defects such as uneven coating and cracking of the electrode sheet. On the other hand, LiOH will react with LiPF6 in the electrolyte to generate corrosive substances such as HF, which will corrode the cathode material, increase the interfacial impedance, and reduce the rate performance of the battery. On the other hand, during the storage, transportation, and battery manufacturing process of the material, the residual alkali is very likely to absorb moisture and CO2 due to exposure to the environment, and thus is converted into Li2CO3. The generated lithium carbonate will also undergo side reactions with the electrolyte.

[0004] In order to control the residual alkali content, most of the existing technologies use methods such as optimizing the feed ratio of lithium source and ternary positive electrode material precursor, water washing method and adding acidic additives during the slurrying process. For example, CN118811877A discloses a method for preparing a three-sintered ternary positive electrode material, in which the secondary sintered product is mixed with water for washing, and the washed product obtained after drying is mixed with boric acid to form a third mixture, and the three-sintered ternary positive electrode material is obtained through the third sintering; CN117658241A discloses a method for preparing a ternary single crystal positive electrode material, in which the residual alkali on the surface of the sintered product is removed by water washing, thereby avoiding the active material coated on the surface of the positive electrode material from reacting with the electrolyte to produce gas; CN113937249A discloses a method for preparing a high-nickel ternary positive electrode slurry, in which an acidic additive is added during the preparation of the slurry, such as an organic acid containing an unsaturated carbon-carbon double bond, which can be quickly adsorbed onto the surface of the high-nickel ternary material and react with OH - 、CO3 2- The reaction can reduce the residual alkali content, thereby inhibiting the defluorination reaction between the residual alkali and PVDF, which can not only prevent the gelation of the slurry, but also effectively improve the fluidity of the slurry and the electrochemical performance of the high-nickel ternary positive electrode material.

[0005] However, the above three methods of controlling the residual alkali content all have limitations. Specifically, for the method of optimizing the feeding ratio of lithium source and ternary positive electrode material precursor, since lithium salt and ternary positive electrode material precursor are mostly mixed by solid phase dry method, reducing the feeding ratio of lithium source is very likely to lead to insufficient lithium source, affecting the progress of lithiation reaction, resulting in insufficient crystal growth, so that the crystal fails to grow successfully to the expected effect. For the water washing method, although water washing can effectively remove most of the residual LiOH on the surface of the material, its treatment process will cause irreversible damage to the surface structure of the material crystal, resulting in capacity loss. In order to repair the structural defects caused by water washing and increase the capacity, secondary sintering is often required for surface modification and capacity enhancement (increasing battery capacity) treatment, which not only prolongs the process cycle, but also increases production costs. For the method of adding acidic additives in the process of synthesizing slurry, first of all, the choice of acidic additives is strictly limited. The acidic additives must have good compatibility with NMP (N-methylpyrrolidone) solvent, otherwise it will lead to uneven dispersion, which seriously affects the reaction efficiency with the residual alkali on the surface of the material. Secondly, the dosage of acidic additives needs to be dynamically adjusted based on parameters such as the residual alkali content and specific surface area of the material. However, this dynamic adjustment is extremely difficult to achieve in actual production. Furthermore, acidic additives themselves are not active components. If added in excess, they will not only disrupt the chemical balance of the slurry system but may also change the rheological properties of the slurry, ultimately negatively affecting the electrochemical performance of the battery. Summary of the Invention

[0006] The present invention provides the following technical solutions to solve the above technical problems.

[0007] The present invention provides a method for preparing a ternary cathode composite material, which includes a ternary cathode material and an inorganic salt layer coated on the surface of the ternary cathode material. The chemical formula of the ternary cathode material is Li(Ni x Co y Mn z )O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1. The chemical formula of the inorganic salt is Li m AO n , where A is selected from one of S and N, m is 1, 2, or 3, and n is 3 or 4. The method includes:

[0008] Sintering a ternary cathode material precursor and a lithium source in an oxygen atmosphere to obtain a ternary cathode material;

[0009] Introducing a mixed gas of an acidic gas and oxygen into the ternary cathode material under the condition that the temperature does not exceed 900 °C to obtain a ternary cathode composite material. The acidic gas is SO x , NO x One of them, where x is a positive integer other than 1.

[0010] With the above technical solution, on the one hand, introducing a mixed gas of an acidic gas and oxygen at a temperature of 900 °C can prevent excessive or abnormal grain growth caused by too high a temperature, and at the same time, the grain size can be controlled within the range of 3 - 5 μm. Among them, the oxygen in the mixed gas can protect the crystal structure from being damaged during this process. On the other hand, the introduced acidic gas will react with the residual surface alkali, not only effectively removing the residual surface alkali, but also converting it into thermodynamically more stable inorganic lithium salts such as Li2SO4 or LiNO3, etc. These inorganic salt layers coated on the surface of the ternary cathode material can significantly improve the interface stability and cycle stability of the material, and thus realize the resource utilization of waste, that is, turning waste into treasure.

[0011] Optionally, the volume ratio of the acidic gas to oxygen in the mixed gas is 0.01:1 to 0.1:1.

[0012] Optionally, the introduction duration of the mixed gas is 1 - 5 h.

[0013] Optionally, the mixed gas is introduced into the ternary cathode material under the condition that the temperature is 500 - 700 °C.

[0014] Optionally, the molar ratio of the lithium source to the ternary cathode material precursor is 1.03:1 to 1.08:1.

[0015] Optionally, the sintering temperature is 900 - 1050 °C, and the sintering duration is 3 - 10 h.

[0016] Optionally, the method further includes:

[0017] Preparing a ternary cathode material precursor: dissolving nickel salt, cobalt salt and manganese salt in the same solvent to obtain a mixed solution, and then adding a complexing agent and a precipitating agent to the mixed solution and stirring under the conditions of pH 11 - 12, temperature 50 - 60 °C, and rotation speed 200 - 1000 rpm to prepare the ternary cathode material precursor.

[0018] The present invention also provides a ternary cathode composite material, which is prepared by the method in any of the above embodiments.

[0019] Adopting the above technical solution, the ternary cathode composite material has better interfacial stability and cycling stability.

[0020] Optionally, the particle size D50 of the grains of the ternary cathode composite material is 3 - 5 μm;

[0021] Alternatively, the pH of the ternary cathode composite material is 10.5 - 12.5;

[0022] Alternatively, the content of residual alkali LiOH in the ternary cathode composite material is less than 3000 ppm;

[0023] Alternatively, the content of residual alkali Li2CO3 in the ternary cathode composite material is less than 5000 ppm, where the content of residual alkali LiOH = mass of residual alkali LiOH / mass of the ternary cathode composite material, and the content of residual alkali Li2CO3 = content of residual alkali Li2CO3 / mass of the ternary cathode composite material.

[0024] The present invention also provides a lithium battery, which includes the ternary cathode composite material in each of the above embodiments.

[0025] Adopting the above technical solution, the lithium battery has a longer cycle life, higher safety and better rate performance.

[0026] The present invention also provides a ternary cathode composite material, which includes a ternary cathode material and an inorganic salt layer coated on the surface of the ternary cathode material. The chemical formula of the ternary cathode material is Li(Ni x Co y Mn z )O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1. The chemical formula of the inorganic salt is Li m AO n , where A is selected from one of S and N, m is 1, 2 or 3, and n is 3 or 4.

[0027] With the above technical solution, the ternary cathode composite material has better interfacial stability and cycling stability. Brief Description of the Drawings

[0028] Figure 1 Shows the SEM image of the ternary cathode composite material in Example 1 of the present invention;

[0029] Figure 2 Shows the SEM image of the ternary cathode material in Example 1 of the present invention.

[0030] Figure 3 Shows the schematic diagram of the specific capacity change of the batteries in Application Example 1 and Application Comparative Example 1 of the present invention;

[0031] Figure 4 Shows the schematic diagram of the change in the number of cycling times of the batteries in Application Example 1 and Application Comparative Example 1. Detailed Description of the Invention

[0032] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention will be introduced in conjunction with the preferred embodiments, this does not mean that the features of this invention are limited to this implementation manner. On the contrary, the purpose of introducing the invention in conjunction with the implementation manner is to cover other alternatives or modifications that may be extended based on the claims of the present invention. In order to provide a deep understanding of the present invention, many specific details will be included in the following description. The present invention can also be implemented without these details. In addition, in order to avoid confusing or obscuring the key points of the present invention, some specific details will be omitted in the description. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0033] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0034] To make the purpose, technical solution and advantages of the present invention clearer, the implementation manners of the present invention will be further described in detail below with reference to the drawings.

[0035] The present invention provides a method for preparing a ternary cathode composite material, which ternary cathode composite material includes a ternary cathode material and an inorganic salt layer coated on the surface of the ternary cathode material. The chemical formula of the ternary cathode material is Li(Ni x Co y Mn z )O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1. The chemical formula of the inorganic salt is Lim AO n , wherein A is selected from one of S and N, m is 1, 2 or 3, and n is 3 or 4. The method includes:

[0036] Mixing a ternary cathode material precursor (such as Ni x Co y Mn z (OH)2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1), and a lithium source (such as LiOH·H2O) are sintered in an oxygen atmosphere to obtain a ternary cathode material. The crystal surface morphology of the obtained ternary cathode material presents obvious rough characteristics. Through high-magnification SEM observation, it can be found that a large number of white granular protrusions are distributed on the material surface, and these white particles are mainly residual lithium hydroxide (LiOH) or lithium carbonate (Li2CO3) (refer to Figure 2 , in the figure, the relatively large number of white particles piled up on the crystal surface are residual lithium hydroxide or lithium carbonate, that is, residual alkali).

[0037] During the above sintering process, the ternary cathode material has completed the crystal nucleation and growth stages. To maintain the stability of the formed crystal structure and effectively remove the surface residual alkali, next, a mixed gas of an acidic gas and oxygen needs to be introduced into the above ternary cathode material under the condition that the temperature does not exceed 900 °C to obtain a ternary cathode composite material. The acidic gas is SO x , NO x One of them, where x is a positive integer other than 1. For example, X can be 2, 3, etc. When X is 2, the acidic gas is SO2, NO2, and the inorganic salts generated are Li2SO4, LiNO3. When X is 3, the acidic gas is SO3, NO3, and the inorganic salts generated are Li2SO4, LiNO3. Specifically, X is 2 or 3. On the one hand, introducing a mixed gas of an acidic gas and oxygen at a temperature of 900 °C can prevent excessive grain growth or abnormal growth caused by too high a temperature, and at the same time, the particle size D50 of the ternary cathode composite material grains can be controlled within the range of 3 - 5 μm. Among them, the oxygen in the mixed gas can protect the crystal structure from being damaged during this process. On the other hand, the introduced acidic gas will react with the surface residual alkali, not only effectively removing the surface residual alkali, but also converting it into thermodynamically more stable inorganic lithium salts such as Li2SO4 or LiNO3, etc. These inorganic salt layers are coated on the surface of the ternary cathode material, which can significantly improve the material interface stability and cycle stability. Thus, the resource utilization of waste is also realized, that is, turning waste into treasure. As Figure 1 shown, the surface of the finally prepared ternary cathode material is smoother, and the white granular protrusions are significantly reduced.

[0038] Compared with the prior art which controls residual alkali by optimizing the feeding ratio of lithium source and ternary cathode material precursor, in the present invention, after the ternary cathode material is prepared, residual alkali is removed by introducing a mixed gas of acidic gas and oxygen. Therefore, the amount of lithium source used in the early stage is not overly restricted, that is, it is allowed to be slightly excessive in the early stage. This can ensure that the lithiation reaction proceeds fully, enabling sufficient crystal growth to form an ideal layered structure. This can avoid the situation where crystal growth fails to reach the expected effect due to insufficient lithium source. Compared with the water washing method, in the above technical solution provided by the present invention, since a mixed gas of acidic gas and oxygen is introduced into the ternary cathode material under the condition that the temperature does not exceed 900 °C, it will not only not damage the crystal surface structure and avoid capacity reduction, but also convert the residual alkali into more thermodynamically stable inorganic lithium salts such as Li2SO4 or LiNO3. While greatly shortening the process cycle and reducing production costs, it can also improve the material interface stability and cycle stability. Compared with the method of adding acidic additives during the synthesis of the slurry, in the above technical solution of the present invention, since a mixed gas of acidic gas and oxygen is introduced to remove residual alkali during the preparation stage of the ternary cathode composite material (rather than the slurry preparation stage), the compatibility problem between the additive and the NMP solvent is fundamentally avoided. In addition, the gas reactants are selective and only react with the surface residual alkali to form stable inorganic salts, and the unreacted gas is completely discharged from the system without remaining on the material surface. Therefore, it will neither disrupt the chemical balance of the slurry system nor have a negative impact on the electrochemical performance of the battery. Based on the better stability of the formed inorganic salts, it can instead enhance the material interface stability and cycle stability.

[0039] Further, in the above embodiment, the volume ratio of the acidic gas to oxygen in the mixed gas is 0.01:1 to 0.1:1. Controlling the volume ratio of the acidic gas to oxygen in the mixed gas within the above range, on the one hand, can ensure that the acidic gas completely reacts with the residual alkali on the material surface, thereby effectively removing the residual alkali and forming a dense inorganic salt coating layer. On the other hand, the high proportion of oxygen component can effectively maintain an oxidizing atmosphere, thereby effectively preventing Ni 3 + from being reduced, thus better protecting the crystal structure from being damaged, that is, maintaining the integrity of the crystal structure, and effectively avoiding abnormal growth and morphological changes of the grains.

[0040] Further, in the above embodiment, the introduction duration of the mixed gas is 1 - 5 h. Controlling the introduction duration of the mixed gas to be 1 h or more can ensure that the acidic gas fully reacts with the residual alkali (complete reaction); controlling the introduction duration to be 5 h or less can avoid the crystal surface from being reconstructed due to too long treatment time, and avoid affecting the crystal structure such as morphology, size or shape for too long time. At the same time, the energy consumption cost can be controlled within a reasonable range.

[0041] Further, in the above-described embodiments, a mixed gas is introduced into the ternary cathode material under the condition that the temperature is 500 - 700 °C. On the one hand, when the temperature exceeds 500 °C, lithium hydroxide turns into a molten state, and its fluidity is significantly improved (the viscosity is reduced by about 2 orders of magnitude), which increases the contact area between the acidic gas and the residual alkali by more than 10 times (the reaction rate constant k value is increased by 3 - 5 orders of magnitude). Therefore, when the temperature is controlled at 500 °C and above, the reaction rate of the acidic gas and the residual alkali can be increased. On the other hand, controlling the temperature at 700 °C and below can further prevent abnormal grain growth.

[0042] Further, in the above-described embodiments, the molar ratio of the lithium source to the ternary cathode material precursor is 1.03:1 - 1.08:1. When the molar ratio of the lithium source to the ternary cathode material precursor is within the range of 1.03:1 - 1.08:1, moderate lithium excess can not only promote the full progress of the lithiation reaction, avoid crystal growth defects caused by insufficient lithium, thereby promoting the crystal to achieve the expected crystal growth effect, but also control the residual alkali within a certain range. For example, the surface residual alkali content is controlled below 2000 ppm (the residual alkali content in each gram of the ternary cathode material is less than 2000 μg), so that the time for subsequent introduction of the mixed gas can be shortened.

[0043] Further, in the above-described embodiments, the sintering temperature is 900 - 1050 °C, and the sintering duration is 3 - 10 h. Controlling the sintering temperature and time within the above range can ensure that the ternary cathode material precursor is completely decomposed and fully reacts with the lithium source to form a ternary cathode material with uniform grains and stable structure, providing a reliable guarantee for the subsequent preparation of a ternary cathode composite material with stable structure and stable cycling performance. Among them, the heating rate during the sintering process can be 1 - 5 °C / min.

[0044] Further, in the above-described embodiments, the method for preparing the ternary cathode composite material further includes:

[0045] Preparing a ternary cathode material precursor: Dissolving nickel salt, cobalt salt, and manganese salt in the same solvent (such as deionized water) to obtain a mixed solution, and then adding a complexing agent (such as an ammonia water solution) and a precipitating agent (such as a sodium hydroxide solution) to the mixed solution and stirring under the conditions of pH 11 - 12, temperature 50 - 60 °C, and rotation speed 200 - 1000 rpm to prepare the ternary cathode material precursor. In the present invention, by co-dissolving nickel salt, cobalt salt, and manganese salt in a solvent to form a mixed solution, and then adding a complexing agent and a precipitating agent, and carrying out a coprecipitation reaction under the conditions of strictly controlling pH 11 - 12, temperature 50 - 60 °C, and stirring rotation speed 200 - 1000 rpm, it helps the crystal to grow successfully to the expected effect. Thereby, the ternary cathode material obtained after sintering can have better interfacial stability.

[0046] The present invention also provides a ternary cathode composite material, which is prepared by the method in any of the above embodiments.

[0047] Adopting the above technical solution, the ternary cathode composite material has better interfacial stability and cycling stability.

[0048] The chemical formula of the ternary cathode material is Li(Ni x Co y Mn z )O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1. As the content of nickel increases, the pH and residual alkali content of the ternary cathode material obtained after sintering will also increase. For the ternary cathode composite material prepared by the method in any of the above embodiments provided by the present invention, the particle size D50 of the grains of the obtained ternary cathode composite material is 3 - 5 μm, or the pH of the obtained ternary cathode composite material is 10.5 - 12.5, or the content of residual alkali LiOH in the ternary cathode composite material is less than 3000 ppm, or the content of residual alkali Li2CO3 in the ternary cathode composite material is less than 5000 ppm. Among them, the content of residual alkali LiOH = mass of residual alkali LiOH / mass of ternary cathode composite material, and the content of residual alkali Li2CO3 = content of residual alkali Li2CO3 / mass of ternary cathode composite material. Specifically, the particle size D50 of the grains of the obtained ternary cathode composite material is 3 - 5 μm, the pH of the obtained ternary cathode composite material is 10.5 - 12.5, the content of residual alkali LiOH in the ternary cathode composite material is less than 3000 ppm, and the content of residual alkali Li2CO3 in the ternary cathode composite material is less than 5000 ppm. More specifically, when x is 0.8, the pH of the obtained ternary cathode composite material is 10.5 - 11.5, the content of residual alkali LiOH in the ternary cathode composite material is less than 1300 ppm, and the content of residual alkali Li2CO3 in the ternary cathode composite material is less than 2100 ppm. When x is 0.85, the pH of the obtained ternary cathode composite material is 11.0 - 12.0, the content of residual alkali LiOH in the ternary cathode composite material is less than 1600 ppm, and the content of residual alkali Li2CO3 in the ternary cathode composite material is less than 2500 ppm. When x is 0.96, the pH of the obtained ternary cathode composite material is less than 11.5 - 12.5, the content of residual alkali LiOH in the ternary cathode composite material is less than 3000 ppm, and the content of residual alkali Li2CO3 in the ternary cathode composite material is less than 5000 ppm. The present invention also provides a lithium battery, which includes the ternary cathode composite material in the above embodiment.

[0049] Adopting the above technical solution, the lithium battery has a longer cycle life, higher safety, and better rate performance.

[0050] The present invention also provides a ternary cathode composite material, which includes a ternary cathode material and an inorganic salt layer coated on the surface of the ternary cathode material. The chemical formula of the ternary cathode material is Li(Ni x Co y Mn z )O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1. The chemical formula of the inorganic salt is Li m AO n , where A is selected from one of S and N, m is 1, 2 or 3, and n is 3 or 4.

[0051] Adopting the above technical solution, the ternary cathode composite material has better interfacial stability and cycling stability.

[0052] The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0053] Example 1

[0054] The general formula of the high-nickel ternary precursor is Ni x Co y Mn z (OH)2, where: x + y + z = 1, x = 0.85, y = 0.10, z = 0.05. According to the stoichiometric ratio of the ternary cathode material precursor Ni 0.85 Co 0.10 Mn 0.05 (OH)2, nickel sulfate, cobalt sulfate salt, and manganese sulfate are dissolved in a certain amount of deionized water to obtain a mixed solution. The total concentration of the above metal ions is 2 mol / L. Then, the mixed solution, ammonia water solution, and NaOH solution are added to the reaction kettle, and the pH in the reaction kettle is controlled to be 11.4 - 11.6, the temperature is 55 - 58 °C, and stirring is carried out at a rotation speed of 600 rpm to carry out a coprecipitation reaction. After the reaction is completed, centrifugation, drying, and sieving are carried out to obtain the ternary precursor Ni 0.85 Co 0.10 Mn 0.05 (OH)2;

[0055] The ternary cathode material precursor Ni 0.85 Co 0.10 Mn 0.05(OH)2 and lithium salt LiOH·H2O are sintered once in an oxygen atmosphere to obtain a ternary cathode material. Among them, the molar ratio of the lithium salt to the ternary cathode material precursor is 1.05:1, the temperature during the sintering process is 950 °C, the heating rate during the sintering process is 2 °C / min, and the sintering duration is 8 h. After the sintering is completed, the above ternary cathode material is cooled until the temperature reaches 750 °C. Next, a mixed gas of acidic gas and oxygen is introduced into the ternary cathode material for 3 h to obtain a ternary cathode composite material. Among them, the acidic gas is SO3, and the volume ratio of the acidic gas to oxygen is 0.05:1. During this process, the ternary cathode material is in a natural cooling state. Since the natural cooling rate is relatively fast, it is necessary to start the heating and heat preservation program to ensure that the temperature remains at 550 °C, where the heating rate is 2 °C / min. After that, the obtained ternary cathode composite material is naturally cooled to room temperature.

[0056] Example 2

[0057] Same as Example 1, except that the acidic atmosphere in this example is NO2.

[0058] Example 3

[0059] Same as Example 1, except that after the sintering is completed, the above ternary cathode material is cooled until the temperature reaches 750 °C. Next, a mixed gas of acidic gas and oxygen is introduced into the ternary cathode material for 3 h to obtain a ternary cathode composite material. During this process, the ternary cathode material is in a natural cooling state (even if the temperature is lower than 550 °C, the heating process is not adopted).

[0060] Example 4

[0061] Same as Example 1, except that the volume ratio of the acidic gas to oxygen in this example is 0.2:1.

[0062] Comparative Example 1

[0063] The general formula of the high-nickel ternary precursor is Ni x Co y Mn z (OH)2, where: x + y + z = 1, x = 0.85, y = 0.10, z = 0.05. According to the ternary cathode material precursor Ni 0.85 Co 0.10 Mn 0.05The stoichiometric ratio of (OH)₂ is used to dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in a certain amount of deionized water to obtain a mixed solution. The total concentration of the above metal ions is 2 mol / L. Then, the mixed solution, ammonia water solution, and NaOH solution are added to a reaction kettle, and the pH in the reaction kettle is controlled to be 11.4 - 11.6, the temperature is 55 - 58 °C, and stirring is carried out at a rotation speed of 600 rpm to carry out a coprecipitation reaction. After the reaction is completed, centrifugation, drying, and sieving are carried out to obtain the ternary precursor Ni 0.85 Co 0.10 Mn 0.05 (OH)₂;

[0064] The ternary cathode material precursor Ni 0.85 Co 0.10 Mn 0.05 (OH)₂ and the lithium salt LiOH·H₂O are sintered once in an oxygen atmosphere to obtain the ternary cathode material. Among them, the molar ratio of the lithium salt to the ternary cathode material precursor is 1.05:1, the temperature during the sintering process is 900 °C, the heating rate during the sintering process is 2 °C / min, and the sintering duration is 8 h. After the sintering is completed, the obtained ternary cathode material is cooled to room temperature. Then, the ternary cathode material and deionized water are mixed at a mass ratio of 0.05:1, and then stirred and washed for 4 h at a condition of 500 rpm. After the washing is completed, suction filtration is carried out and vacuum drying is carried out at a temperature of 120 °C for 10 h to obtain the water-washed ternary cathode material.

[0065] Next, the moisture content, pH, residual alkali, and coin cell electrical performance of the ternary cathode composite materials in Examples 1 - 4 and the water-washed ternary cathode material in Comparative Example 1 are tested respectively. Among them, the moisture test method and steps are as follows: Weigh 0.2000 g of the ternary cathode composite materials in Examples 1 - 4 into different flasks respectively. Put the flasks into a Karl Fischer (KF) heating furnace preheated to 170 °C, set the injection time to 200 s, so that the moisture in the ternary cathode composite materials volatilizes at high temperature and is carried into the KF titration cell by the carrier gas (dry air). Then, the moisture content (unit: ppm) is measured by the coulometric method, and it is repeated three times in parallel and recorded in Table 1. Similarly, weigh 0.2000 g of the water-washed ternary cathode material in Comparative Example 1 into another flask, and then repeat the above operation, and record the results in Table 1 as well.

[0066] The pH test method is as follows: Weigh 5.000 g of the ternary cathode composite materials in Examples 1 - 4 and the washed ternary cathode material in Comparative Example 1 respectively, and place them in different 50 mL conical flasks. Add magnetic stirrers into the flasks, and place the conical flasks on a magnetic stirrer. Quickly seal the bottle mouths with sealing films to avoid interference of carbon dioxide in the air on the experimental results. Set the stirring speed to 800 rpm (800 revolutions per minute) and the stirring time to 1 minute. Subsequently, leave the conical flasks in a constant temperature environment at 25 °C for 1 hour. After the time is up, use a pH meter to measure the pH value of the solution in the conical flasks, and repeat this operation three times. Record all the data in Table 2.

[0067] The residual alkali test method is as follows: Accurately weigh 5 g of the ternary cathode composite materials in Examples 1 - 4 and 5 g of the washed ternary cathode material in Comparative Example 1 respectively, and dissolve them in 100 mL of deionized water. Then use a stirrer to stir at a rate of 800 revolutions per minute for 5 minutes to ensure that the materials are fully dispersed in water. After stirring, use a vacuum filtration device to separate the above materials from water, and record the mass of the filtrate as m. Subsequently, transfer the filtrate to a potentiometric titrator and titrate it with a 0.1 mol / L hydrochloric acid standard titration solution. During the titration process, record the volumes of hydrochloric acid consumed at two equivalence points, namely Ep1 (pH ≈ 8.5) and Ep2 (pH ≈ 4.5), denoted as V1 and V2 respectively (Ep1 (pH ≈ 8.5): the complete neutralization point of LiOH, Ep2 (pH ≈ 4.5): the complete neutralization point of Li2CO3).

[0068] According to the titration data, calculate the mass fraction ω of residual lithium carbonate in Examples 1 - 4 Li2CO3 , and the formula is: ω Li2CO3 = [0.1 * (V2 - V1) * 100 * 73.89] / (1000 * 5 * m) * 100%. At the same time, calculate the mass fraction ω of residual lithium hydroxide LiOH , and the formula is: ω LiOH = [0.1 * V2 - 2 * (V2 - V1) * 100 * 23.95] / (1000 * 5 * m) * 100%. The above experimental steps are repeated in parallel three times, and the results are recorded in Table 3 (where Example 1 - LiOH refers to the content of residual alkali LiOH in Example 1, and Example 1 - Li2CO3 refers to the content of residual alkali LiOH in Example 1).

[0069] The method and steps for button cell assembly and testing are as follows: First, put 3.6 grams of the ternary cathode composite material in each of the above embodiments, 0.2 grams of conductive agent SP, 4 grams of NMP solution containing 5% PVDF, and 1.8 grams of NMP solvent into the slurry mixing tank. Then, use a slurry mixer for stirring. The stirring procedure is: first rotate at a speed of 800 rpm for 1.5 minutes, then increase to 1950 rpm and continue stirring for 10 minutes, and finally rotate at a speed of 800 rpm for 1.5 minutes to eliminate bubbles. Pour the uniformly stirred slurry into a coater and coat it evenly on the carbon-coated aluminum foil with a coating thickness of 400 microns. After coating, place the aluminum foil in an oven at 90 °C for drying, and then transfer it to a vacuum oven at 120 °C for overnight drying. The dried electrode material is punched into sheets using a 12-mm punching machine, and then assembled with a lithium metal sheet into button-type half-cells Application Examples 1-4 and Application Comparative Example 1 (in Application Example 1, the ternary cathode composite material of the battery is the ternary cathode composite material in Example 1, and so on). During the assembly process, a conventional ceramic separator is used (wherein, the base film is made of polypropylene (PP) with a thickness of 9 microns, and the ceramic thickness on both sides of the base film is 1.5 microns), and 1M LiPF6 (containing 1 mole of lithium salt lithium hexafluorophosphate (LiPF6) per liter of solution) electrolyte (the solvent and ratio are ethylene carbonate (EC): dimethyl carbonate (DMC) = 1:1). After the battery assembly is completed, set the working voltage range to 2.8 - 4.35 volts. Conduct electrical performance tests and record the first charge-discharge specific capacity, first efficiency, charge-discharge curves at a 0.2C rate, and the capacity retention rate after 100 cycles at a 1C / 1C rate. Among them, the test results of the first efficiency (initial efficiency) are shown in Table 4, the charge-discharge curves are as Figure 3 shown, and the capacity retention rate after 100 cycles at a 1C / 1C rate is as Figure 4 shown (wherein, the blue curve A in Figure 3 and Figure 4 is the test result of the battery in Application Example 1, and the red curve B is the test result of the battery 1 in Application Comparative Example 1).

[0070] Table 1 Moisture content of materials in each example and comparative example (unit: ppm)

[0071] Test Result 1 Test Result 2 Test Result 3 Mean Value Example 1 98 112 103 104 Example 2 137 160 148 148 Example 3 203 232 215 217 Example 4 78 96 91 88 Comparative Example 1 239 254 277 257

[0072] Table 2 pH values of materials in each example and comparative example

[0073] Test Result 1 Test Result 2 Test Result 3 Mean Value Example 1 11.68 11.65 11.69 11.67 Example 2 11.70 11.72 11.72 11.71 Example 3 11.76 11.78 11.78 11.77 Example 4 11.66 11.63 11.64 11.64 Comparative Example 1 11.80 11.82 11.83 11.82

[0074] Table 3 Residual alkali content values of materials in each example and comparative example (unit: ppm)

[0075] Test Result 1 Test Result 2 Test Result 3 Mean Value Example 1 - LiOH 1086 1204 1173 1154 <![CDATA[Example 1 - Li2CO3]]> 1927 1885 1933 1915 Example 2 - LiOH 1135 1214 1246 1198 <![CDATA[Example 2 - Li2CO3]]> 2073 1986 2119 2059 Example 3 - LiOH 1548 1617 1590 1585 <![CDATA[Example 3 - Li2CO3]]> 2432 2379 2475 2429 Example 4 - LiOH 1015 1007 983 1002 <![CDATA[Example 4 - Li2CO3]]> 1795 1840 1872 1836 Comparative Example 1 - LiOH 1892 1905 1933 1910 <![CDATA[Comparative Example 1 - Li2CO3]]> 2836 2919 2901 2885

[0076] Table 4

[0077]

[0078] As can be seen from Tables 1 - 3, although the moisture detection results of the materials in Examples 1 - 4 and Comparative Example 1 all meet the general industry standards (less than 300 - 400 ppm), from the average data (mean value), although Examples 1 - 4 were not treated with water washing, after surface residual alkali treatment, the obtained ternary cathode composite material significantly decreased in moisture absorption capacity. The reason is that the obtained ternary cathode composite material has a lower residual alkali content on its surface (the higher the residual alkali content, the higher the pH of the material; the higher the residual alkali content, the stronger the water absorption of the material).

[0079] Furthermore, in Examples 1 - 2 and Example 4, since a mixed gas was introduced into the ternary cathode material under the condition of a temperature of 500 - 700 °C, the residual alkali at this temperature was in a molten state, and the reaction between the acidic gas and the residual alkali was more sufficient, resulting in less residual of the residual alkali LiOH. Therefore, the water absorption, residual alkali content, and pH of the materials in Examples 1 - 2 and Example 4 are all lower than those in Example 3.

[0080] According to Table 4 and Figure 3 it can be seen that the initial efficiency and specific capacity of Application Examples 1 - 4 are both higher than those of Application Comparative Example 1. (Among them, Figure 3 only the specific capacity change curves of the battery in Application Example 1 and the battery in Application Comparative Example 1 are shown), because the ternary cathode material in Application Comparative Example 1 was subjected to a water washing step, which damaged the interface of the material and thus lost some active lithium. In the present invention, the ternary cathode composite materials in Application Examples 1 - 4 do not adopt the water washing method, but introduce a mixed gas of acidic gas and oxygen into the ternary cathode material under the condition of a temperature not exceeding 900 °C, which not only does not damage the crystal surface structure but also avoids the reduction of capacity.

[0081] According to Figure 4 it can be seen that after 100 charge - discharge cycles, the capacity retention rate of the battery in Application Example 1 is significantly better than that of Application Comparative Example 1 (Application Example 1 remains at 86%, while Application Comparative Example is only 75%). The reason is that in the present invention, the ternary cathode composite materials in Examples 1 - 4 do not adopt the water washing method, but introduce a mixed gas of acidic gas and oxygen into the ternary cathode material under the condition of a temperature not exceeding 900 °C. While avoiding the reduction of capacity, it can also convert the residual alkali into an inorganic lithium salt with better thermodynamic stability. The obtained ternary cathode composite material has better interface stability and cycle stability. Finally, it is reflected that the cycle stability of Application Example 1 is better than that of Application Comparative Example 1.

[0082] Although the present invention has been illustrated and described with reference to certain preferred embodiments thereof, those of ordinary skill in the art should understand that the above is a further detailed description of the present invention in connection with specific embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. Those skilled in the art can make various changes in form and detail, including making several simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing a ternary cathode composite material, characterized in that, The ternary cathode composite material includes a ternary cathode material and an inorganic salt layer coated on the surface of the ternary cathode material. The chemical formula of the ternary cathode material is Li(Ni x Co y Mn z )O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1. The chemical formula of the inorganic salt is Li m AO n , where A is selected from one of S and N, m is 1, 2 or 3, and n is 3 or 4. The method includes: Sinter the ternary cathode material precursor and a lithium source in an oxygen atmosphere to obtain the ternary cathode material; A mixed gas of an acidic gas and oxygen is introduced into the ternary cathode material under the condition that the temperature does not exceed 900 °C to obtain the ternary cathode composite material, and the acidic gas is SO x , NO x One of them, where x is a positive integer other than 1.

2. The method for preparing the ternary cathode composite material according to claim 1, wherein The volume ratio of the acidic gas to oxygen in the mixed gas is 0.01:1 to 0.1:

1.

3. The method for preparing the ternary cathode composite material according to claim 1, characterized in that, The introduction duration of the mixed gas is 1 - 5 h.

4. The method for preparing the ternary cathode composite material according to claim 1, wherein Introduce the mixed gas into the ternary cathode material under the condition that the temperature is 500 - 700 °C.

5. The method for preparing the ternary cathode composite material according to claim 1, wherein The molar ratio of the lithium source to the ternary cathode material precursor is 1.03:1 to 1.08:

1.

6. The method for preparing the ternary cathode composite material according to claim 1, wherein The sintering temperature is 900 - 1050 °C, and the sintering duration is 3 - 10 h.

7. The method for preparing the ternary cathode composite material according to claim 1, wherein The method further includes: Prepare a ternary cathode material precursor: Dissolve nickel salt, cobalt salt, and manganese salt in the same solvent to obtain a mixed solution, and then add a complexing agent and a precipitating agent to the mixed solution and stir under the conditions that the pH is 11 - 12, the temperature is 50 - 60 °C, and the rotation speed is 200 - 1000 rpm to prepare the ternary cathode material precursor.

8. A ternary cathode composite material, characterized in that, The ternary cathode composite material is prepared by using the method for preparing a ternary cathode composite material according to any one of claims 1 - 7 above.

9. The ternary cathode composite material according to claim 8, wherein, The particle size D50 of the grains of the ternary cathode composite material is 3 - 5 μm; Or, the pH of the ternary cathode composite material is 10.5 - 12.5; Or, the content of residual alkali LiOH in the ternary cathode composite material is less than 3000 ppm; Or, the content of residual alkali Li2CO3 in the ternary cathode composite material is less than 5000 ppm, where the content of residual alkali LiOH = the mass of residual alkali LiOH / the mass of the ternary cathode composite material, and the content of residual alkali Li2CO3 = the content of residual alkali Li2CO3 / the mass of the ternary cathode composite material.

10. A lithium battery, characterized in that, The lithium battery includes the ternary cathode composite material according to any one of claims 8 - 9.

11. A ternary cathode composite material, characterized in that, The ternary cathode composite material includes a ternary cathode material and an inorganic salt layer coated on the surface of the ternary cathode material. The chemical formula of the ternary cathode material is Li(Ni x Co y Mn z )O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1. The chemical formula of the inorganic salt is Li m AO n , where A is selected from one of S and N, m is 1, 2, or 3, and n is 3 or 4.

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