A low-residual-alkali high-nickel cathode material, its preparation method and application

Abstract

The present invention discloses a low-residual-alkali high-nickel cathode material, a preparation method thereof, and an application thereof. The low-residual-alkali high-nickel cathode material provided by the present invention includes a matrix and a coating layer on the surface of the matrix. The matrix is a high-nickel cathode material, and the coating layer includes an AlCl3 layer and porous γ-Al2O3 particles embedded in the AlCl3 layer. At least part of the porous γ-Al2O3 particles are in contact with the high-nickel cathode material. In the present invention, through the organic-inorganic interface formed in the dispersion system, the step of washing the high-nickel cathode material with water to reduce the residual alkali and the step of coating the surface of the high-nickel cathode material are respectively carried out in the upper aqueous phase and the lower organic phase, so as to realize the synchronous progress of water washing and surface coating. Then, low-temperature sintering is carried out to fix the porous γ-Al2O3 particles on the surface of the high-nickel cathode material by using the AlCl3 film, making it not easy to fall off. The low-residual-alkali high-nickel cathode material prepared by the present invention has the advantages of low residual alkali value, high specific capacity, and good cycling performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more particularly, to a low-residual-alkali high-nickel cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of new energy, there is an increasing need for higher energy density, and high-nickel cathode materials are currently the best choice. However, as the nickel content increases, the residual alkali of high-nickel cathode materials becomes higher and higher. High residual alkali not only affects the homogenization and coating in the preparation process, but also causes gas generation during the cycling process, leading to bloating and safety accidents, and the cycling performance also deteriorates.

[0003] Currently, the main methods for reducing residual alkali include adjusting the raw material ratio and the first firing process, water washing and coating, and dry coating. Among them, coating after water washing is the most effective way to reduce residual alkali. However, there are many factors affecting water washing, including the water-to-material ratio, water washing time, and stirring intensity, etc. The process of each material is different, the experimental intensity is large, and the experimental period is long. At the same time, the coating mostly uses inorganic materials for surface dot or bread coating. After coating, it is easy to fall off from the high-nickel cathode material as the volume of the high-nickel cathode material shrinks and expands during the charging process.

[0004] How to quickly, efficiently and controllably reduce residual alkali and more effectively coat has become an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-residual-alkali high-nickel cathode material, a preparation method thereof, and an application thereof to overcome the above-mentioned defects existing in the prior art.

[0006] The present invention solves its technical problems by adopting the following technical solutions.

[0007] The present invention provides a low-residual-alkali high-nickel cathode material, including a matrix and a coating layer on the surface of the matrix. The matrix is a high-nickel cathode material, and the coating layer includes an AlCl3 layer and porous γ-Al2O3 particles embedded in the AlCl3 layer. At least part of the porous γ-Al2O3 particles are in contact with the high-nickel cathode material.

[0008] The present invention also provides a preparation method of the above-mentioned low-residual-alkali high-nickel cathode material, including: adding water to an organic solvent containing a high-nickel cathode material to obtain a dispersion system of an upper water phase and a lower organic phase; stirring to make the high-nickel cathode material move upward into the upper water phase, and washing with water to remove the residual alkali on the surface of the high-nickel cathode material; depositing and adsorbing Al(OH)3 on the surface of the high-nickel cathode material, and then coating the high-nickel cathode material with AlCl3; finally, performing low-temperature sintering to obtain the low-residual-alkali high-nickel cathode material.

[0009] The present invention also provides a lithium battery, and the positive electrode of the lithium battery includes the above-mentioned low-residual-alkali high-nickel cathode material.

[0010] The present invention has the following beneficial effects:

[0011] The present invention provides a low-residual-alkali high-nickel cathode material, a preparation method thereof, and an application thereof. The low-residual-alkali high-nickel cathode material provided by the present invention includes a matrix and a coating layer on the surface of the matrix. The matrix is a high-nickel cathode material, and the coating layer includes an AlCl3 layer and porous γ-Al2O3 particles embedded in the AlCl3 layer. At least part of the porous γ-Al2O3 particles are in contact with the high-nickel cathode material. In the present invention, through the organic-inorganic interface formed in the dispersion system, the steps of washing the high-nickel cathode material to reduce the residual alkali and the step of coating the surface of the high-nickel cathode material are respectively carried out in the upper aqueous phase and the lower organic phase, so as to realize the synchronous progress of washing and surface coating. Then, low-temperature sintering is carried out to fix the porous γ-Al2O3 particles on the surface of the high-nickel cathode material by using the AlCl3 film, and the fixed coating is not easy to fall off on the surface of the high-nickel cathode material. The low-residual-alkali high-nickel cathode material prepared by the present invention has the advantages of low residual alkali value, high specific capacity, and good cycle performance. Description of the Drawings

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0013] Figure 1 It is a schematic structural diagram of the low-residual-alkali high-nickel cathode material prepared in the embodiment of the present invention;

[0014] Figure 2 It is a schematic diagram of the experimental process for preparing the low-residual-alkali high-nickel cathode material in the embodiment of the present invention. Detailed Embodiments

[0015] In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0016] High-nickel cathode materials have rapidly become one of the preferred high-nickel cathode materials for high specific energy batteries due to their high voltage platform, high energy density, high tap density, etc. However, with the increase in nickel content, the structural stability of high-nickel cathode materials deteriorates, resulting in poor cycle stability. Improving the structural stability of high-nickel cathode materials by surface coating is an effective solution. For example, materials such as AIF3, A1203, and Li3PO4 are common surface coatings. However, when using the above materials for coating, it is mostly surface dot or bread coating. The coating is simply dispersed on the surface of the high-nickel cathode material by physical adsorption. The binding force between the two is not strong, and there is a gap between the two. The expansion and contraction of the high-nickel cathode material are likely to cause the coating to fall off.

[0017] To achieve more effective and stable coating, an embodiment of the present invention provides a preparation method of a low-residual-alkali high-nickel cathode material, which includes: first, setting a dispersion system of an upper aqueous phase and a lower organic phase containing the high-nickel cathode material. Then, through the constructed organic-inorganic interface, washing to remove residual alkali and surface coating are carried out above and below the interface respectively. Specifically: using stirring to make the high-nickel cathode material turn upward, water removes the residual alkali on the surface of the high-nickel cathode material, and the organic solvent reduces the contact between water and the high-nickel cathode material, protecting the high-nickel cathode material from further damage by water, realizing the removal of residual alkali from the high-nickel cathode material above the organic-inorganic interface, and monitoring the effect of removing residual alkali from the high-nickel cathode material by online detecting the pH value of the aqueous solution, and preparing a high-nickel cathode material with low residual alkali and the structure of the high-nickel cathode material not being damaged in one step. Under the action of gravity, the high-nickel cathode material moves downward to realize the separation of the high-nickel cathode material from water; then, using the hydrolysis property of the aluminate to hydrolyze in the upper aqueous solution to generate Al(OH)3 precipitate, the Al(OH)3 precipitate settles to the lower organic solvent and adsorbs and coats on the surface of the high-nickel cathode material, and then adding an AlCl3 solution to the organic solvent to also coat it on the surface of the high-nickel cathode material to obtain a coating precursor; finally, performing low-temperature calcination, Al(OH)3 is transformed into porous γ-Al2O3 particles at low temperature, and at the same time, using low-melting-point AlCl3 to "shape" and coat the porous γ-Al2O3 particles, fixing the coating on the surface of the high-nickel cathode material and not easily falling off, increasing the coating contact effect and increasing the coating strength.

[0018] The following specifically describes a low-residual-alkali high-nickel cathode material provided by the present invention, its preparation method and application:

[0019] In the first aspect, an embodiment of the present invention provides a low-residual-alkali high-nickel cathode material, which includes a matrix and a coating layer on the surface of the matrix. The matrix is a high-nickel cathode material, and the coating layer includes an AlCl3 layer and porous γ-Al2O3 particles embedded in the AlCl3 layer, and at least part of the porous γ-Al2O3 particles are in contact with the high-nickel cathode material.

[0020] SeeFigure 1 , for the low-residual-alkali high-nickel cathode material provided by the embodiments of the present invention, the distribution of the porous γ-Al2O3 particles embedded in the AlCl3 layer may be diverse. For example, some porous γ-Al2O3 particles penetrate the AlCl3 layer and connect with the high-nickel cathode material, some porous γ-Al2O3 particles connect with the high-nickel cathode material but do not penetrate the AlCl3 layer, some porous γ-Al2O3 particles are completely embedded in the AlCl3 layer, and some porous γ-Al2O3 particles are only partially embedded in the AlCl3 layer and do not contact the high-nickel cathode material.

[0021] It can be seen that for the low-residual-alkali high-nickel cathode material provided by the embodiments of the present invention, the solidification of the porous γ-Al2O3 coating is realized by the "shaping" coating effect of AlCl3. It can be understood that the so-called "shaping" coating here means that AlCl3 is coated on the surface of the high-nickel cathode material in the form of a film, which can be formed according to the shape of the high-nickel cathode material and is not easy to fall off. At the same time, AlCl3 fixes the porous γ-Al2O3 particles on the surface of the high-nickel cathode material in the form of a film, making the porous γ-Al2O3 particles not easy to fall off, increasing the coating contact effect and the coating strength. At the same time, the porous γ-Al2O3 particles and the AlCl3 film coated on the surface of the high-nickel cathode material play a role in isolating the electrolyte and the high-nickel cathode material, and the porous and thin-film design can also provide channels for lithium ions without reducing the capacity and rate.

[0022] In an alternative embodiment, the chemical formula of the high-nickel cathode material is LiNi x M 1-x O2, where 0.6 ≤ x ≤ 1.0, and M is selected from at least one of Co, Mn, and Al.

[0023] In an alternative embodiment, the composition of the low-residual-alkali high-nickel cathode material includes: LiNi x Mn y O2, LiNi x Co y O2, LiNi x Co y Mn z O2, LiNi x Co y Al z O2, LiNi x Co y Mn z Al w O2, etc.

[0024] In an alternative embodiment, the thickness of the coating layer on the surface of the low-residual-alkali high-nickel cathode material is 0.5 nm - 50 nm.

[0025] Second aspect, the embodiments of the present invention further provide a preparation method of the above-mentioned low-residual-alkali high-nickel cathode material, including: adding water into an organic solvent containing a high-nickel cathode material to obtain a dispersion system of an upper water phase and a lower organic phase; stirring to make the high-nickel cathode material move upward into the upper water phase, and washing with water to remove the residual alkali on the surface of the high-nickel cathode material; depositing and adsorbing Al(OH)3 on the surface of the high-nickel cathode material, and then coating the high-nickel cathode material with AlCl3; finally, performing low-temperature sintering to obtain the low-residual-alkali high-nickel cathode material.

[0026] See Figure 2 , in the preparation method of the above-mentioned low-residual-alkali high-nickel cathode material provided by the embodiments of the present invention, through the organic-inorganic interface formed in the dispersion system, the steps of washing the high-nickel cathode material with water to reduce the residual alkali and the surface coating step of the high-nickel cathode material can be carried out in the upper water phase and the lower organic phase respectively, realizing the synchronization of water washing and surface coating. After that, low-temperature sintering is carried out, which can solidify the coating and increase the coating contact effect. Specifically:

[0027] Adding water into an organic solvent containing a high-nickel cathode material to obtain a dispersion system of an upper water phase and a lower organic phase, stirring to make the high-nickel cathode material move upward into the upper water phase, washing the residual alkali with water, and at the same time using the organic solvent to isolate water from further reacting with the high-nickel cathode material to protect the structure of the high-nickel cathode material from being damaged, which can efficiently reduce the residual alkali while protecting the structure of the high-nickel cathode material from being damaged. It reduces the complexity of the traditional water washing process by repeatedly adjusting experimental parameters such as the water-to-material ratio, water washing time, stirring intensity, and water temperature through orthogonal experiments. At the same time, it also eliminates the uncontrollability of the high-nickel cathode material contacting water during the processes of feeding, discharging, filtering, and drying, greatly reducing uncontrollable factors and lowering the experimental intensity.

[0028] After washing the high-nickel cathode material with water in the upper water phase to remove the residual alkali to obtain a high-nickel cathode material with qualified residual alkali, adding a meta-aluminate to the mixed solution, and using the water and pH value of the supernatant after water washing to hydrolyze the meta-aluminate to generate Al(OH)3 precipitate. At the same time, the generated Al(OH)3 precipitate settles to the lower organic phase and adsorbs on the surface of the high-nickel cathode material. Then, adding an AlCl3 solution to the lower organic solvent to coat the high-nickel cathode material with AlCl3. After that, low-temperature sintering is carried out. Low-temperature sintering can convert Al(OH)3 into solid porous γ-Al2O3 particles, and AlCl3 into liquid AlCl3. In this process, the porous γ-Al2O3 particles are embedded in AlCl3. After the temperature cools down, AlCl3 solidifies to form an AlCl3 layer, which then contacts the high-nickel cathode material. See again Figure 1 , porous γ-Al2O3 particles with different morphologies and particle sizes are all embedded in the AlCl3 layer, increasing the coating contact effect and the coating strength.

[0029] The above method for preparing a low-residual-alkali high-nickel cathode material uses low-melting-point AlCl3 to coat porous γ-Al2O3 particles, so as to contact and coat the high-nickel cathode material in a better form, and at the same time prevent the porous γ-Al2O3 from falling off during the charge and discharge process of the high-nickel cathode material due to volume expansion and losing the coating effect. At the same time, the porous γ-Al2O3 particles and the AlCl3 film coated on the surface of the high-nickel cathode material play a role in isolating the electrolyte and the high-nickel cathode material. At the same time, the porous and film structures can also provide channels for lithium ions without reducing the capacity and rate. It can be seen that the solution provided by the embodiment of the present invention efficiently and rapidly reduces the residual alkali content of the high-nickel cathode material and realizes the surface coating of the high-nickel cathode material through the constructed organic-inorganic interface. The preparation method provided by the embodiment of the present invention has a simple process, reduces a large number of cathode experiments, improves the experimental efficiency, and the prepared low-residual-alkali high-nickel cathode material has the advantages of low residual alkali value, high specific capacity, and good cycle performance.

[0030] In an alternative embodiment, the method includes the following steps:

[0031] Mix the high-nickel cathode material with an organic solvent, start low-speed stirring, and then add water to obtain a dispersion system with an upper aqueous phase and a lower organic phase;

[0032] Increase the stirring speed to make the high-nickel cathode material in the dispersion system contact with the upper aqueous phase to wash away the residual alkali on the surface of the high-nickel cathode material, and then reduce the stirring speed to make the high-nickel cathode material sink to the lower organic phase to obtain a mixed solution with qualified residual alkali on the surface of the high-nickel cathode material;

[0033] Deposit and adsorb Al(OH)3 on the surface of the high-nickel cathode material, then add an AlCl3 solution to the lower organic phase, perform solid-liquid separation to collect the solid, and obtain a coating precursor;

[0034] Sinter the coating precursor at a low temperature to obtain a low-residual-alkali high-nickel cathode material.

[0035] In an alternative embodiment, the preparation of the dispersion system includes: mixing the high-nickel cathode material with an organic solvent, starting low-speed stirring, controlling that there is no precipitation of the high-nickel cathode material, and then adding water to obtain a dispersion system with an upper aqueous phase and a lower organic phase;

[0036] Preferably, the organic solvent includes one or more of chloroform, carbon tetrachloride, dichloroethane, dibromomethane, bromoform, chlorobenzene, and carbon disulfide;

[0037] Preferably, the solid content in the dispersion system is 10%-70%;

[0038] Preferably, the stirring speed of the low-speed stirring is 0-150 rpm.

[0039] In an alternative embodiment, the preparation of the mixed solution includes: increasing the stirring speed of the dispersion system. Under high-speed stirring conditions, the high-nickel cathode material moves upward to contact with water to wash away the residual alkali. The on-line pH monitoring system monitors the pH change in the water in real time. When the pH reaches the target value, the stirring speed is reduced, and the high-nickel cathode material sinks to be separated from the water;

[0040] Preferably, the stirring speed of high-speed stirring is 200 - 500 rpm, and the stirring speed of low-speed stirring is 0 - 150 rpm;

[0041] Preferably, the ratio of water to the high-nickel cathode material is controlled to be 0.5 - 30;

[0042] Preferably, the formula: "J 水洗后高镍正极材料残碱 = J 高镍正极材料初始残碱 - J 水溶剂碱 " is used to calculate and determine the residual alkali content of the high-nickel cathode material in the solution, where: J 水溶剂碱 is detected by the on-line pH monitoring system;

[0043] Preferably, the residual alkali content on the surface of the high-nickel cathode material is sampled and detected. If the residual alkali value of the high-nickel cathode material is unqualified, continue stirring and monitoring until the residual alkali of the high-nickel cathode material is qualified.

[0044] The preparation method of the low-residual-alkali high-nickel cathode material provided by the embodiment of the present invention uses on-line detection of pH to monitor the pH value of the aqueous solution in real time, can monitor the water washing effect in real time, and can terminate the residual alkali washing reaction at any time using the organic-inorganic interface.

[0045] In an alternative embodiment, the preparation of the coating precursor includes: adding meta-aluminate to the mixed solution, and using the Al(OH)3 generated by the hydrolysis of the meta-aluminate to settle and adsorb on the surface of the high-nickel cathode material. After the precipitation of Al(OH)3 is completed, the supernatant is drawn off, an AlCl3 solution is added, and solid-liquid separation is carried out to collect the solid to obtain the coating precursor;

[0046] Preferably, the meta-aluminate includes one or more of NaAlO2 and KAlO2;

[0047] Preferably, the molar ratio of Al in the meta-aluminate to the high-nickel cathode material is controlled to be 0.005% - 2%;

[0048] Preferably, the molar ratio of AlCl3 in the AlCl3 solution to the high-nickel cathode material is controlled to be 0.005% - 2%;

[0049] Preferably, after the precipitation of Al(OH)3 is completed, the supernatant is drawn off, an AlCl3 solution is added, and after mixing for 1 h, solid-liquid separation is carried out to collect the solid to obtain the coating precursor.

[0050] In the preparation method of the above-mentioned low-residual-alkali high-nickel cathode material provided by the embodiment of the present invention, through the constructed organic-inorganic interface, after washing with water in the aqueous phase, aluminates are added. By using the water and pH value of the supernatant after washing with water, Al(OH)3 generated by the hydrolysis of aluminates is controlled. By controlling the addition rate of aluminates, Al(OH)3 precipitate can slowly and evenly settle and adsorb onto the surface of the high-nickel cathode material in the lower-layer organic solvent. Then, AlCl3 is added to the organic solvent and coated on the high-nickel cathode material to obtain a coated precursor.

[0051] In an alternative embodiment, the preparation of the low-residual-alkali high-nickel cathode material includes: sintering the coated precursor at 150°C - 300°C for 2h - 10h to obtain a crude product;

[0052] Preferably, the sintering is carried out in an oxygen atmosphere, and the oxygen concentration ≥ 99%;

[0053] Preferably, it further includes: cooling the crude product to below 80°C, taking it out, grinding and sieving to obtain the finished product of the low-residual-alkali high-nickel cathode material;

[0054] Preferably, the heating rate and the cooling rate are both controlled at 3°C / min.

[0055] In the preparation method of the above-mentioned low-residual-alkali high-nickel cathode material provided by the embodiment of the present invention, after obtaining the coated precursor, the coated precursor is subjected to low-temperature sintering. Low-temperature sintering can transform Al(OH)3 adsorbed on the surface of the high-nickel cathode material into porous γ-Al2O3 particles, and at the same time, the low-melting-point AlCl3 on the surface of the high-nickel cathode material plastically coats the porous γ-Al2O3 particles. Specifically:

[0056] The coated precursor is subjected to low-temperature sintering. During the low-temperature sintering process, Al(OH)3 will be transformed into active porous γ-Al2O3 under the action of low-temperature sintering. At the same time, the AlCl3 existing on the surface of the high-nickel cathode material is in a liquid state at a temperature of 150°C - 300°C, the porous γ-Al2O3 is in a solid state, and AlCl3 is in a liquid state. One is solid and the other is liquid, and it can plastically coat the high-nickel cathode material better. That is, at a temperature higher than the melting point of AlCl3 (the melting point of AlCl3 is 194°C), AlCl3 is coated on the surface of the high-nickel cathode material in the form of a "film", and the porous γ-Al2O3 particles are embedded in AlCl3. After the temperature cools, AlCl3 solidifies to form an AlCl3 layer, which better solidifies the porous γ-Al2O3 particles and the high-nickel cathode material. During the battery cycle, the high-nickel cathode material will expand and contract. The method provided by the present invention enables AlCl3 to have a good wrapping and solidifying effect on the high-nickel cathode material, and at the same time effectively prevents γ-Al2O3 from falling off the high-nickel cathode material due to the expansion and contraction of the high-nickel cathode material.

[0057] As can be seen above, the above preparation method provided by the embodiments of the present invention can rapidly, efficiently and controllably prepare a high-nickel cathode material with low residual alkali and an undamaged structure of the high-nickel cathode material in one step by utilizing the organic-inorganic interface. It reduces the complexity of traditional water washing processes that repeatedly adjust experimental parameters such as the water-to-material ratio, water washing time, stirring intensity, and water temperature through orthogonal experiments. At the same time, it also reduces the uncontrollability of contact with water during the processes of adding, discharging, filtering, and drying the high-nickel cathode material, significantly reducing uncontrollable factors, lowering the experimental intensity, shortening the experimental cycle, improving production efficiency, and fixing AlCl3 in the form of a film on the surface of the porous γ-Al2O3 particles on the high-nickel cathode material, making the porous γ-Al2O3 particles on the surface of the high-nickel cathode material not easily fall off. This method is simple to operate and has the potential for large-scale promotion.

[0058] In a third aspect, an embodiment of the present invention provides a lithium battery, and the positive electrode of the lithium battery includes the above-mentioned low-residual-alkali high-nickel cathode material.

[0059] The following further describes the present invention in conjunction with embodiments.

[0060] A preparation method of a low-residual-alkali high-nickel cathode material includes the following steps:

[0061] Step 1: Mix a high-nickel precursor, lithium hydroxide, lithium carbonate, etc. evenly and then sinter to prepare a high-nickel cathode material S1.

[0062] Step 2: Add the high-nickel cathode material S1 obtained in Step 1 to an organic solvent to obtain a mixed solution, and control the solid content to be 10%-70%. When the rotation speed is low, it is ensured that there is no precipitation of the high-nickel cathode material, and the thickness of the supernatant of the mixed solution is greater than 0.

[0063] Step 3: Start stirring, add water to the mixed solution obtained in Step 2, and control the ratio of water to the high-nickel cathode material to be 0.5-30. Increase the stirring intensity, use the stirring paddle to drive the high-nickel cathode material to move upward to contact with water to wash away the residual alkali, while the high-nickel cathode material moves downward under its own gravity to separate from the water contact. At the same time, use the organic solvent to isolate the high-nickel cathode material and water, protect the high-nickel cathode material from being overwashed by water and causing structural changes due to excessive delithiation, and prevent the internal lithium from migrating to the outside. Start real-time online pH monitoring of the pH change in the water, and use the formula:

[0064] “J 水洗后高镍正极材料残碱 =J 高镍正极材料初始残碱 -J 水溶剂碱 ”

[0065] to calculate and determine the residual alkali content of the high-nickel cathode material in the solution, where J 水溶剂碱 is detected by an online pH monitoring system. When the pH reaches the target value, reduce the stirring intensity to let the high-nickel cathode material sink and separate from the water.

[0066] Sample and detect the residual alkali of the high-nickel cathode material. If the residual alkali value of the high-nickel cathode material is unqualified, continue with Step 3 until the residual alkali of the high-nickel cathode material is qualified.

[0067] Step 4: After the residual alkali value of the high-nickel cathode material obtained in Step 3 is qualified, add a NaAlO₂ solution to the solution in Step 3, and slowly produce Al(OH)₃ with the water solution for washing the residual alkali and precipitate it on the surface of the high-nickel cathode material. Control the addition rate of NaAlO₂ to control the slow and uniform sedimentation and adsorption of the Al(OH)₃ precipitate on the surface of the high-nickel cathode material. Control the molar ratio of Al in NaAlO₂ to the high-nickel cathode material to be 0.005% - 2%. After the precipitation of Al(OH)₃ is completed, add an AlCl₃ solution to the lower-layer organic solvent, control the molar ratio of AlCl₃ to the high-nickel cathode material to be 0.005% - 2%, mix for 1 h, then perform solid-liquid separation and filtration to obtain the coated precursor S2.

[0068] Step 5: Sinter the coated precursor S2 obtained in Step 4 in an oxygen atmosphere at 150°C - 300°C for 2 - 10 h to obtain the crude product S3. Control the heating and cooling rate to 3°C / min, take it out and grind and screen it after the temperature drops to ≤80°C to obtain the finished product of the low-residual-alkali high-nickel cathode material.

[0069] Example 1

[0070] A preparation method of a low-residual-alkali high-nickel cathode material, comprising the following steps:

[0071] Mix the precursor Ni 0.92 Co 0.08 Mn 0.02 and lithium hydroxide evenly, and then sinter in 99% oxygen, sinter at 550°C for 2 h and at 710°C for 12 h. Among them, control the heating rate and cooling rate at 3°C / min. After the temperature drops below 100°C, grind and screen to obtain the intermediate product S1 (which can also be called the first sintered material).

[0072] Add 20 kg of the intermediate product S1 to 40 L of carbon tetrachloride solution, with a stirring speed of 100 rpm, and then add 40 L of water; increase the stirring intensity to 200 rpm, and monitor the pH change in the water in real time online. When the pH value reaches 12.96, reduce the stirring to 100 rpm, sample and detect the residual alkali of the high-nickel cathode material. After testing that the residual alkali of the product is lower than 4000 ppm, add 2 L of 1 mol / L NaAlO₂ to the solution and add it evenly within 0.5 h. Continue stirring for 0.5 h, then pump out the supernatant, add 2 L of 1 mol / L AlCl₃ / carbon tetrachloride solution to the mixed solvent, and filter the mixed solution of the high-nickel cathode material and the organic solvent, and dry at 120°C for 2 h to obtain the coated precursor S2.

[0073] The coated precursor S2 is sintered at 200 °C for 5 h to obtain the crude product S3. The heating and cooling rates are controlled at 3 °C / min. After the temperature is cooled to ≤80 °C, it is taken out, ground and sieved to obtain the finished product of the low residual alkali high-nickel cathode material.

[0074] Example 2

[0075] A preparation method of a low residual alkali high-nickel cathode material, comprising the following steps:

[0076] Mix Ni 0.95 Co 0.03 Mn 0.02 and lithium hydroxide evenly and sinter in 99% oxygen, sinter at 550 °C for 2 h, and sinter at 700 °C for 12 h. Among them, the heating rate and the cooling rate are controlled at 3 °C / min. When the temperature drops below 100 °C, grind and sieve to obtain the intermediate product S1 (which can also be called the first sintered material).

[0077] Add 15 kg of the intermediate product S1 to 30 L of carbon tetrachloride solution, with a stirring speed of 100 rpm, and then add 30 L of water; increase the stirring intensity to 200 rpm, and the on-line pH monitoring system monitors the pH change in the water in real time. When the pH value reaches 13.03, the stirring is reduced to 100 rpm, and the residual alkali of the high-nickel cathode material is sampled and detected. After testing that the residual alkali of the product is lower than 5000 ppm, add 2 L of 1 mol / L NaAlO2 to the solution and add it evenly within 0.5 h. After continuing to stir for 0.5 h, draw off the supernatant, add 2 L of 1 mol / L AlCl3 / carbon tetrachloride solution to the mixed solvent, filter the mixed solution of the high-nickel cathode material and the organic solvent, and dry at 120 °C for 2 h to obtain the coated precursor S2.

[0078] The coated precursor S2 is sintered at 250 °C for 5 h to obtain the crude product S3. The heating and cooling rates are controlled at 3 °C / min. After the temperature is cooled to ≤80 °C, it is taken out, ground and sieved to obtain the finished product of the low residual alkali high-nickel cathode material.

[0079] Comparative Examples 1 - 4:

[0080] Mix the precursor Ni 0.92 Co 0.08 Mn 0.02 and lithium hydroxide evenly and sinter in 99% oxygen, sinter at 550 °C for 2 h, and sinter at 710 °C for 12 h. Among them, the heating rate and the cooling rate are controlled at 3 °C / min. When the temperature drops below 100 °C, grind and sieve to obtain the intermediate product S1.

[0081] Add 20 kg of the intermediate product S1 to 40 L of water, with a stirring intensity of 200 rpm, and the stirring times are 5 min, 10 min, 15 min, and 20 min respectively. After stirring, add 2 L of 1 mol / L NaAlO 2。Subsequently, filter and dry at 120 °C for 2 h to obtain coated precursors S2-1, S2-2, S2-3, S2-4. Sinter the coated precursors S2-1, S2-2, S2-3, S2-4 at 400 °C for 5 h to obtain finished high-nickel cathode material coated precursors S3-1, S3-2, S3-3, S3-4. Control the heating and cooling rate at 3 °C / min. After cooling to ≤80 °C, take out, grind and screen to obtain the finished product.

[0082] Comparative Example 5

[0083] Mix the precursor Ni 0.92 Co 0.08 Mn 0.02 and lithium hydroxide evenly, then sinter in 99% oxygen, sinter at 550 °C for 2 h, and sinter at 710 °C for 12 h. Among them, control the heating rate and cooling rate at 3 °C / min. Wait until the temperature drops below 100 °C, grind and screen to obtain the intermediate product S1 (which can also be called the first sintered material).

[0084] Add 20 kg of the intermediate product S1 into 40 L of carbon tetrachloride solution, with a stirring speed of 100 rpm, and then add 40 L of water; increase the stirring intensity to 200 rpm, and monitor the pH change in water in real time online. When the pH value reaches 12.96, reduce the stirring to 100 rpm, sample and detect the residual alkali of the high-nickel cathode material. After testing that the residual alkali of the product is lower than 4000 ppm, add 2 L of 1 mol / L NaAlO2 to the solution and add it evenly within 0.5 h. Continue to stir for 0.5 h, then draw off the supernatant, filter the mixed solution of the high-nickel cathode material and the organic solvent, and dry at 120 °C for 2 h to obtain the coated precursor S2.

[0085] Sinter the coated precursor S2 at 200 °C for 5 h to obtain the crude product S3. Control the heating and cooling rate at 3 °C / min. After cooling to ≤80 °C, take out, grind and screen to obtain the finished product of the high-nickel cathode material with low residual alkali.

[0086] Comparative Example 6

[0087] A preparation method of a high-nickel cathode material with low residual alkali, comprising the following steps:

[0088] Mix the precursor Ni 0.92 Co 0.08 Mn 0.02 and lithium hydroxide evenly, then sinter in 99% oxygen, sinter at 550 °C for 2 h, and sinter at 710 °C for 12 h. Among them, control the heating rate and cooling rate at 3 °C / min. Wait until the temperature drops below 100 °C, grind and screen to obtain the intermediate product S1 (which can also be called the first sintered material).

[0089] Add 20 kg of intermediate product S1 to 40 L of carbon tetrachloride solution, with a stirring speed of 100 rpm, and then add 40 L of water; increase the stirring intensity to 200 rpm, and monitor the pH change in water in real-time online. When the pH value reaches 12.96, reduce the stirring speed to 100 rpm, take a sample to detect the residual alkali of the high-nickel cathode material. After testing that the residual alkali of the product is lower than 4000 ppm, stir at a uniform speed for 0.5 h. After continuing to stir for 0.5 h, draw off the supernatant, add 2 L of 1 mol / L AlCl3 / carbon tetrachloride solution to the mixed solvent, filter the mixed solution of the high-nickel cathode material and the organic solvent, and dry at 120 °C for 2 h to obtain the coated precursor S2.

[0090] Sinter the coated precursor S2 at 200 °C for 5 h to obtain the crude product S3, control the heating and cooling rate at 3 °C / min, take it out and grind and screen it after the temperature drops to ≤80 °C to obtain the finished product of the high-nickel cathode material with low residual alkali.

[0091] For the products prepared in Examples 1 to 2 and the products prepared in Comparative Examples 1 to 6, respectively, weigh the corresponding masses of the materials according to the mass ratio of 80:10:10 with the conductive agent (SuperC) and the binder (PVDF), mix them evenly, and prepare a slurry in a homogenizer. Control the solid content at 20 - 50%, and evenly coat it on a 20-μm aluminum foil with a coating thickness of 0.25 mm. After the electrode sheet is dried and roll-pressed, a positive electrode sheet with a diameter of 12 mm is prepared. Use metallic lithium for the negative electrode, and assemble a CR2032 coin cell using a LiPF6 / EC / EMC electrolyte and a PE separator.

[0092] Cyclic test: After placing the above coin cell for 10 h, place it on the Blue Electric Tester (CT2001C) for charge-discharge cyclic performance test. The test conditions are set as: 25 °C, 2.8 - 4.3 V, 1C = 200 mAhg -1 , perform 3 cycles of 0.1C / 0.1C coin half-cell test, and cycle 100 weeks at 1C / 1C to investigate the specific capacity and cyclic performance of the products prepared in Examples 1 to 2 and the products prepared in Comparative Examples 1 to 6. The specific electrochemical performance is shown in Table 1 below:

[0093] Table 1

[0094]

[0095]

[0096] It can be seen from Table 1 above that: After removing the residual alkali and double coating by this technology, both the capacity and the rate are significantly improved, and the capacity retention rate is significantly improved.

[0097] The following Table 2 shows the surface residual alkali detection results of the products prepared in Examples 1 - 2 and Comparative Examples 5 - 6 at different stirring times.

[0098] Table 2

[0099]

[0100] As can be seen from Table 2 above: with the prolongation of the stirring time, the residual alkali content on the surface of the high-nickel cathode material gradually decreases.

[0101] The following Table 3 shows the surface residual alkali detection results of the products prepared in Examples 1-2 and Comparative Examples 1-6.

[0102] Table 3

[0103] Sample LiOH % <![CDATA[Li2CO3%]]> Residual alkali ppm Example 1 2322 1190 3512 Example 2 2760 1805 4345 Comparative Example 1 4815 3590 8405 Comparative Example 2 2576 2012 4588 Comparative Example 3 2595 1300 3895 Comparative Example 4 2045 980 3025 Comparative Example 5 2355 1250 3605 Comparative Example 6 2305 1170 3475

[0104] As can be seen from Table 3 above: in Comparative Examples 1-4, the traditional water washing method can reduce the residual alkali value by increasing the water washing time. However, while the time is prolonged, the high-nickel cathode material is in contact with water all the time. Combining with Table 1, it can be seen that after the time is prolonged, the capacity, especially the rate and cycle performance, decrease significantly. This is because when the high-nickel cathode material is in contact with water for a long time, the lattice lithium in the high-nickel cathode material inevitably precipitates, resulting in an inevitable decrease in the rate and cycle. As can be seen from Comparative Examples 5 and 6, the back-end coating has little effect on the residual alkali. However, combining with Table 1, when single-coated with Al2O3 or AlCl3, the cycle performance and rate are improved to varying degrees, but lower than the effect of double coating with porous Al2O3 particles combined with an AlCl3 film.

[0105] In summary, for the solution provided in the embodiments of the present invention, an organic solvent is used to isolate the effective contact time between water and the high-nickel cathode material, preventing the washing out of lattice lithium. Porous Al2O3 isolates the electrolyte and at the same time provides a lithium ion transmission channel, while the AlCL3 film can further isolate the contact between the electrolyte and the high-nickel cathode material during cycling to reduce the occurrence of side reactions, and at the same time control the coating amount of AlCL3 to control the film thickness and thus reduce the influence on lithium ion transmission. After the above treatment, a low-residual-alkali high-nickel cathode material with a low residual alkali value, improved capacity, rate and cycle can be obtained.

[0106] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a low residual alkali high nickel positive electrode material, characterized in that: include: Adding water to an organic solvent containing the high-nickel positive electrode material to obtain a dispersion system of an upper aqueous phase and a lower organic phase; stirring the high-nickel positive electrode material to move upward into the upper aqueous phase, washing with water to remove residual alkali on the surface of the high-nickel positive electrode material; depositing and adsorbing Al(OH)3 on the surface of the high-nickel positive electrode material, and then coating the high-nickel positive electrode material with AlCl3; and finally performing low-temperature sintering to obtain the low-residual-alkali high-nickel positive electrode material; The low residual alkali high nickel positive electrode material includes a substrate and a coating layer on the surface of the substrate, the substrate is a high nickel positive electrode material, the coating layer includes an AlCl3 layer and porous γ-Al2O3 particles embedded in the AlCl3 layer, and at least part of the porous γ-Al2O3 particles are in contact with the high nickel positive electrode material.

2. The preparation method according to claim 1, characterized in that: The following steps are involved: The high-nickel positive electrode material is mixed with the organic solvent, stirred at a low speed, and then the water is added to obtain a dispersion system of an upper aqueous phase and a lower organic phase; Increasing the stirring speed to make the high-nickel positive electrode material in the dispersed system contact with the upper aqueous phase to wash away the residual alkali on the surface of the high-nickel positive electrode material, and then reducing the stirring speed to make the high-nickel positive electrode material sink into the lower organic phase to obtain a mixed solution with qualified residual alkali on the surface of the high-nickel positive electrode material; Depositing and adsorbing Al(OH)3 on the surface of the high-nickel positive electrode material, adding AlCl3 solution to the lower organic phase, and collecting the solid by solid-liquid separation to obtain a coating precursor; The coated precursor is sintered at low temperature to obtain the low residual alkali and high nickel positive electrode material.

3. The preparation method according to claim 2, characterized in that: The preparation of the dispersion system comprises: mixing the high-nickel positive electrode material with the organic solvent, starting low-speed stirring, and then adding water to obtain a dispersion system of an upper aqueous phase and a lower organic phase.

4. The preparation method according to claim 3, characterized in that: The organic solvent includes one or more of chloroform, carbon tetrachloride, ethylene dichloride, dibromomethane, bromoform, chlorobenzene and carbon disulfide.

5. The preparation method according to claim 3, characterized in that: The solid content in the dispersed system is 10%-70%.

6. The preparation method according to claim 3, characterized in that: The stirring speed of the low-speed stirring is 0-150 rpm.

7. The preparation method according to claim 2, characterized in that: The preparation of the mixed solution includes: increasing the stirring speed of the dispersed system, and under high-speed stirring conditions, allowing the high-nickel positive electrode material to move upward and contact the water to wash away residual alkali, an online pH value monitoring system to monitor the pH change in the water in real time, and when the pH reaches the target value, reducing the stirring speed to allow the high-nickel positive electrode material to sink and separate from the water.

8. The preparation method according to claim 7, characterized in that: The ratio of the water to the high-nickel positive electrode material is controlled to be 0.5-30.

9. The preparation method according to claim 7, characterized in that: The stirring speed of the high-speed stirring is 200-500 rpm, and the stirring speed of the low-speed stirring is 0-150 rpm.

10. The preparation method according to claim 7, characterized in that: Using the formula: "J 水洗后高镍正极材料的表面残碱 =J 高镍正极材料初始残碱 -J 水溶剂碱 ” Calculate and determine the surface residual alkali content of the high nickel positive electrode material in the solution, where: J 水溶剂碱 Detected using an online pH monitoring system.

11. The preparation method according to claim 7, characterized in that: Sampling is performed to detect the residual alkali content on the surface of the high-nickel positive electrode material. If the residual alkali content on the surface of the high-nickel positive electrode material is unqualified, stirring and monitoring are continued until the residual alkali content on the surface of the high-nickel positive electrode material is qualified.

12. The preparation method according to claim 2, characterized in that: The preparation of the coating precursor includes: adding aluminate to the mixed solution, allowing the Al(OH)3 produced by the hydrolysis of the aluminate to precipitate and adsorb to the surface of the high-nickel positive electrode material, after the Al(OH)3 precipitation is completed, extracting the supernatant, adding AlCl3 solution, separating the solid from the liquid, and collecting the solid to obtain the coating precursor.

13. The preparation method according to claim 12, characterized in that: The aluminate includes one or more of NaAlO2 and KAlO2.

14. The preparation method according to claim 12, characterized in that: The molar ratio of Al in the aluminate to the high-nickel positive electrode material is controlled to be 0.005%-2%.

15. The preparation method according to claim 12, characterized in that: The molar ratio of AlCl3 in the AlCl3 solution to the high-nickel positive electrode material is controlled to be 0.005%-2%.

16. The preparation method according to claim 12, characterized in that: After the Al(OH)3 precipitation is completed, the supernatant is extracted, the AlCl3 solution is added, and after mixing for 1 hour, the solid is collected by solid-liquid separation to obtain a coating precursor.

17. The preparation method according to claim 2, characterized in that: The preparation of the low residual alkali high nickel positive electrode material comprises: sintering the coated precursor at 150° C.-300° C. for 2 h-10 h to obtain a crude product.

18. The preparation method according to claim 17, characterized in that: The sintering is carried out in an oxygen atmosphere, and the oxygen concentration is ≥ 99%.

19. The preparation method according to claim 17, characterized in that: Also includes: The crude product is cooled to below 80° C., taken out, ground and sieved to obtain a finished product of a low-residual-alkali and high-nickel positive electrode material.

20. The preparation method according to claim 17, characterized in that: The heating rate and cooling rate were both controlled at 3°C / min.

21. The preparation method according to claim 1, characterized in that: The chemical formula of the high nickel positive electrode material is LiNi x M 1-x O2, wherein 0.6≤x≤1.0, and M is selected from at least one of Co, Mn, and Al.

22. The preparation method according to claim 1, characterized in that: The thickness of the coating layer on the surface of the low residual alkali and high nickel positive electrode material is 0.5 nm-50 nm.

23. A lithium battery, characterized in that The lithium battery positive electrode comprises a low residual alkali and high nickel positive electrode material prepared by the preparation method described in any one of claims 1 to 22.

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