High-nickel positive electrode material residual alkali cleaning solvent and process based on pH intelligent response

Abstract

The invention relates to a high-nickel positive electrode material residual alkali cleaning solvent and process based on pH intelligent response, and belongs to the technical field of secondary battery positive electrodes. According to the cleaning solvent, a pH response type polymer serves as a core and is matched with an organic cosolvent, deionized water and an additive, the pH response type polymer has the characteristics of dissolution under the alkaline condition and precipitation under the neutral condition, and self-sensing, self-judgment and self-termination can be achieved in the washing process. According to the corresponding cleaning process, automatic precipitation and solid-liquid separation of the polymer are completed by dynamically adjusting and monitoring the pH change, and material drying and solvent regeneration can be achieved. According to the method, the residual alkali on the surface of the high-nickel positive electrode can be accurately removed (the content of the residual alkali is stably controlled to be 0.2% or below), meanwhile, the layered structure of the material is protected, dissolution of transition metal is inhibited, the method is suitable for high-nickel materials such as NCM811 and NCM90, the solvent recycling rate is high, and a key technical support is provided for large-scale industrialization of the high-nickel positive electrode material.

Description

TECHNICAL FIELD

[0001] The application relates to a pH-intelligent-response-based residual alkali cleaning solvent and process for a high-nickel positive electrode material, and belongs to the technical field of secondary battery positive electrodes. BACKGROUND

[0002] The high-nickel layered oxide positive electrode material (LiNi 1-x-y Co x Mn y O2, NCM) has become a key positive electrode material for the next generation of high-energy-density lithium-ion batteries due to its high specific capacity (>200 mAh g -1 ) and high energy density. However, as the nickel content increases (usually Ni >= 80%), the surface activity of the material significantly increases, and during the lithiumation high-temperature sintering stage in the later synthesis, an excess of lithium source (such as LiOH H2O) is often added to compensate for lithium evaporation and ensure stoichiometry, resulting in a large amount of residual alkali lithium compounds on the surface of the material, mainly including LiOH and Li2CO3. In addition, high-nickel materials are extremely sensitive to H2O and CO2 in the air, and even during storage, reactions will occur, further exacerbating the accumulation of residual alkali on the surface. Studies have shown that the residual alkali content on the surface of untreated NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) can reach several to tens of thousands of ppm, and the situation is even more serious for NCM90 series ultra-high nickel materials.

[0003] The presence of these residual alkalis has triggered a series of serious material processing and electrochemical performance problems. During the electrode preparation stage, residual alkalis can significantly increase the pH value of the slurry, cause side reactions with the commonly used N-methyl pyrrolidone (NMP) solvent, and cause dehydrofluorination of the binder polyvinylidene fluoride (PVDF), leading to slurry gelation, causing coating difficulties, poor uniformity, and seriously affecting electrode quality. During battery cycling, the harm of residual alkalis is more serious: Li2CO3 will decompose when the charging voltage is higher than 4.3V, producing CO2 gas, leading to battery swelling and interface instability; LiOH will react with LiPF6 in the electrolyte to generate HF, which will corrode the positive electrode material and catalyze the dissolution of transition metals (Ni, Co, Mn). The dissolved transition metal ions will migrate to the negative electrode, destroy the solid electrolyte interface film (SEI), catalyze lithium dendrite growth, cause active lithium loss and impedance surge. More seriously, the presence of surface residual alkalis exacerbates the release of lattice oxygen at high voltage, induces phase transformation, forms an electrochemically inert rock salt phase (NiO-like phase), and further causes intergranular cracks to form and expand, ultimately leading to rapid capacity decay and a significant increase in thermal safety risk.

[0004] To address the above challenges, the industry and academia generally adopt washing process as a key post-processing step to remove surface residual alkali. The current mainstream methods include water washing and organic solvent washing. Water washing is widely adopted due to its low cost and high solubility of LiOH and Li2CO3. However, the water washing process is accompanied by a strong Li + / H + Ion exchange reaction: H + will replace Li in the surface layer lattice of the material + , resulting in lattice lithium loss and forming a few nanometer thick lithium-deficient layer on the surface. The lithium-deficient layer structure changes from layered (R3-m) to rock salt phase (Fm3-m), which has extremely low ionic conductivity, seriously hindering lithium ion transport, resulting in increased battery polarization, decreased rate performance and initial capacity loss. Although the use of non-aqueous solvents such as ethanol and isopropanol can to some extent reduce Li + / H + exchange, avoid the generation of a large amount of rock salt phase, but also brings new problems: the solubility of non-aqueous solvents for residual alkali is relatively weak, and the end point of washing is difficult to control accurately. Insufficient washing will result in residual alkali, which cannot achieve the purpose of improving processability and electrochemical performance; while excessive washing may not only dissolve the surface residual alkali, but also cause non-selective dissolution of transition metal ions, destroying the stoichiometric ratio of the material surface, also having a negative impact on performance. In addition, organic solvents are high in cost, volatile, have safety hazards, and lack real-time monitoring means for changes in ion concentration in the washing liquid, making it difficult to achieve precise control of the washing process and recycling of solvents.

[0005] In the prior art, although some studies have tried to introduce additives (such as ammonium carbonate, boric acid, ammonium dihydrogen phosphate, etc.) to convert residual alkali or form a protective layer, or use a composite solvent strategy in the solvent system, these methods still have core problems such as end point judgment relying on experience, process parameters being fixed, being unable to respond to material differences in real time, and solvent recovery being difficult. Traditional washing processes are mostly simple batch static immersion, lacking dynamic monitoring and feedback mechanisms for the chemical environment of the washing liquid (such as pH, conductivity, and specific ion concentration), and being unable to achieve intelligent process control and optimization based on the washing state.

[0006] Therefore, developing an intelligent washing system that can sense the washing process in real time, automatically and accurately determine the end point of washing, and integrate the functions of efficient separation of impurities and recycling of solvents is a key to breaking through the performance, consistency and safety bottlenecks of high-nickel NCM cathode materials and meeting the large-scale industrialization needs of NCM cathode materials. Based on the reversible phase change behavior of pH-responsive intelligent polymers, an intelligent solvent system is constructed, which has efficient removal of residual alkali, real-time monitoring of the process, and self-determination of the end point of washing, providing an innovative solution for the accurate, green and efficient removal of residual alkali on the surface of NCM cathode materials. SUMMARY

[0007] In order to overcome the defects existing in the prior art, one of the purposes of the present application is to provide a pH intelligent response-based high-nickel positive electrode material residual alkali cleaning solvent, which realizes "self-sensing-self-judging-self-terminating" of the washing process by constructing a composite solvent system containing a pH-responsive polymer, an organic cosolvent and a functional additive, and can effectively reduce the content of positive electrode residual alkali on the surface of the high-nickel positive electrode.

[0008] The second purpose of the present application is to provide a pH intelligent response-based high-nickel positive electrode material residual alkali cleaning process, which realizes dynamic regulation of the chemical environment of the washing liquid and recycling and regeneration of the solvent by integrating an online monitoring and feedback control system, and improves the green economy of the process.

[0009] The purpose of the present application is achieved by the following technical solutions.

[0010] A pH intelligent response-based high-nickel positive electrode material residual alkali cleaning solvent, the solvent is composed of the following components:

[0011] The solvent contains a pH-responsive polymer, an organic cosolvent, deionized water and an additive;

[0012] The mass fraction of the pH-responsive polymer in the solvent is 2%-5%;

[0013] The mass fraction of the organic cosolvent in the solvent is 8%-35%;

[0014] The mass fraction of the deionized water in the solvent is 60%-90%;

[0015] The mass fraction of the additive in the solvent is 0%-5%;

[0016] The pH-responsive polymer is a linear or branched polymer with carboxyl or amine groups that can ionize, which dissolves in the solvent under alkaline conditions and precipitates from the solvent under neutral conditions; the pH-responsive polymer includes at least one of poly(acrylic acid-co-methyl propenoate alkyl ester), polyurethane, cellulose derivative, poly(N-isopropyl acrylamide-co-acrylic acid);

[0017] In the poly(acrylic acid-co-methyl propenoate alkyl ester), the alkyl chain length of the alkyl ester is C1-C8, and the phase transition precipitation pH value is 6.8-7.5;

[0018] The number average molecular weight of the pH-responsive polyurethane is 10,000-100,000 g / mol -1 , and the phase transition precipitation pH value is 7.0-7.6;

[0019] The pH-responsive cellulose derivative is sodium carboxymethyl cellulose or hydroxypropyl methyl cellulose, with a substitution degree of 0.5-1.5 and a phase transition pH value of 6.5-7.3;

[0020] The mole fraction of the acrylic acid unit in the poly(N-isopropyl acrylamide-co-acrylic acid) is 10%-40%, which has both temperature and pH dual response characteristics, and a phase transition pH value of 6.8-7.4;

[0021] The organic co-solvent is at least one of ethanol, isopropanol, n-propanol, and ethylene glycol monomethyl ether;

[0022] The additive is at least one of disodium ethylenediaminetetraacetate, sodium citrate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate buffer, aluminum nitrate, tetraethyl orthosilicate, carbon nanotubes, and graphene;

[0023] Preferably, the pH-responsive polymer is poly(acrylic acid-co-butyl methacrylate), and the mass fraction of the pH-responsive polymer in the solvent is 3%-4%.

[0024] Preferably, the mass fraction of the organic co-solvent in the solvent is 10%-20%.

[0025] Preferably, the organic co-solvent is a mixture of ethanol and isopropanol, and the mass ratio of ethanol to isopropanol is 1:1-1:2.

[0026] Preferably, the mass fraction of deionized water in the solvent is 75%-85%.

[0027] Preferably, the additive contains ammonium dihydrogen phosphate with a mass fraction of 0.5%-1.5% and aluminum nitrate with a mass fraction of 1%-2%.

[0028] A high-nickel positive electrode material residual alkali cleaning process based on pH intelligent response, using the cleaning solvent described above, the process comprises the following steps:

[0029] (1) Initial mixing and penetration: the high-nickel positive electrode material is mixed with the cleaning solvent according to a solid-liquid ratio of 1:3, and initial mixing is performed at 30°C with a stirring speed of 300 rpm, the mixing time is 10 min, and a slurry is formed; the initial pH value of the slurry is controlled at 9 by adding an alkaline adjusting agent; the alkaline adjusting agent is at least one of ammonia and lithium hydroxide aqueous solution;

[0030] (2) Dynamic washing and pH monitoring: continuously stirring the slurry, and using an online pH sensor to monitor the pH value of the slurry in real time; as the residual alkali dissolves and neutralizes, the pH value of the slurry gradually decreases;

[0031] (3) Intelligent termination and phase separation: stop stirring when the online pH sensor detects that the slurry pH value drops to the preset termination point, which is 0.3 units higher than the phase separation pH value of the pH-responsive polymer;

[0032] After stopping stirring, the slurry is allowed to stand for 20 min to cause the pH-responsive polymer to undergo phase separation and form flocs, and to capture residual ions in the solution; then solid-liquid separation is performed by decantation, filtration or centrifugation to obtain the washed positive electrode material, polymer flocs and clear liquid;

[0033] (4) Post-treatment and solvent regeneration: vacuum drying the washed positive electrode material at 110°C for 12 h to obtain a low-residual-alkali positive electrode material; mixing the polymer flocs with an alkali solution with a mass concentration of 0.3 mol / L at 30°C for 1.5 h to cause the polymer to redissolve and regenerate into a polymer solution for use in step (1); and evaporating and concentrating the clear liquid to recover lithium salt therefrom. -1

[0034] Preferably, the high-nickel positive electrode material in step (1) is LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.9 Co 0.05 Mn 0.05 O2(NCM90).

[0035] Preferably, the centrifugation conditions in step (3) are a centrifugation rate of 2000 rpm and a centrifugation time of 8 min.

[0036] Preferably, the alkali solution used to regenerate the polymer flocs in step (4) is a sodium hydroxide solution or a lithium hydroxide solution.

[0037] Preferably, the lithium salt recovered in step (4) is lithium carbonate or lithium hydroxide.

[0038] Advantages

[0039] ​(1) This invention provides a pH-responsive intelligent solvent for cleaning residual alkali on high-nickel cathode materials. By introducing a pH-responsive polymer, an intelligent solvent system with "self-sensing-self-judgment-self-termination" characteristics is constructed, achieving efficient and precise removal of residual alkali from the surface of high-nickel cathode materials. The pH-responsive polymer remains in a dissolved state in the initial stage of alkaline washing. When the residual alkali is gradually neutralized and the pH value of the solution drops to its preset phase transition point (e.g., pH 7.0-7.5), the polymer rapidly undergoes a phase transition and precipitates, forming micron-sized flocs. This process not only automatically judges and terminates washing, avoiding the problems of "insufficient washing" or "over-washing" caused by insufficient human experience in traditional methods, but also effectively captures residual Li in the solution through the flocs. + CO3 2- It also contains trace amounts of transition metal ions, preventing their re-adsorption onto the material surface. This intelligent termination mechanism stably controls the residual alkali content to below 0.2%, significantly improving the electrochemical stability and batch consistency of the high-nickel cathode material.

[0040] (2) This invention provides a pH-responsive residual alkali cleaning process for high-nickel cathode materials. This process utilizes the reversible phase transition behavior of pH-responsive polymers and three-phase separation technology to achieve efficient impurity capture and solvent recycling, exhibiting outstanding green and economical advantages. At the washing termination stage, the precipitated polymer flocs form a three-phase system with significant density differences with the cathode material and the clarified liquid. Efficient separation can be achieved through simple settling or low-speed centrifugation. The process has low energy consumption, is easy to operate, and is suitable for continuous production. The separated polymer flocs are then treated with a dilute alkali solution (e.g., 0.3 mol / L). -1 The solution can be regenerated and reused after treatment with NaOH, and its dissolution-precipitation cycle can be repeated more than 5 times without significantly reducing the collection efficiency. Lithium salts (such as Li2CO3 and LiOH) in the clarified solution can be recovered through evaporation and crystallization, with a recovery rate of over 80%. This closed-loop process significantly reduces the consumption of fresh solvents and wastewater treatment costs, meeting the industrial requirements of green manufacturing and resource recycling.

[0041] (3) This invention provides a pH-responsive solvent and process for cleaning residual alkali in high-nickel cathode materials. The solvent system, through the synergistic effect of an organic co-solvent and functional additives, effectively removes alkali while suppressing surface structural damage, thus ensuring the bulk electrochemical performance of the high-nickel cathode. The introduction of the organic co-solvent (such as ethanol or isopropanol) significantly reduces water activity, inhibiting the displacement reaction of water molecules on lithium ions on the material surface, and preventing Li... + / H +The exchange leads to the generation of a rock salt phase and capacity loss. At the same time, additives such as ammonium dihydrogen phosphate and the like can form a lithium salt passivation layer (such as Li3PO4) on the surface of the material during the washing process, further blocking the regeneration of residual alkali and the dissolution of transition metals. The synergistic protection mechanism enables the layered structure of the material after washing to be maintained, and the charge and discharge efficiency to be improved.

[0042] (4) The application provides a pH intelligent response-based high-nickel positive electrode material residual alkali cleaning solvent and process. The system has good engineering adaptability and multifunctional expansion capability, can flexibly adjust the formula according to different nickel content positive electrode materials (such as NCM811 and NCM90), and realizes integrated treatment of "washing-modification". By adjusting the type and phase transition point of the pH response polymer, the proportion of the organic cosolvent and the composition of the additive, the washing needs of conventional high-nickel materials to super-high-nickel materials can be adapted. For example, in a low water activity system (water content 30%), super-high-nickel NCM90 materials sensitive to water can be effectively treated; by introducing aluminum nitrate and the like to coat the precursor, a uniform Al2O3 coating layer can be formed after heat treatment after washing, and the interface stability of the material is improved; the addition of carbon nanotubes and the like can simultaneously build a conductive network, and reduce the electrode impedance. The multifunctional integrated design significantly simplifies the post-treatment process, improves the overall process efficiency, and provides key technical support for the large-scale industrialization of high-nickel positive electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 Cycle Number and Specific Capacity of the Li||NCM811 battery assembled by the positive electrode treated by the pH intelligent response-based high-nickel positive electrode material residual alkali cleaning solvent of the application in Example 1. DETAILED DESCRIPTION

[0044] The technical solutions of the application will be described clearly and completely in combination with specific embodiments. The methods are all conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0045] The assembly steps of the coin cell battery: all the batteries are assembled into CR2016 type coin batteries, and all the assembly processes are carried out in an argon-filled glove box. The assembly process is carried out in the order of positive electrode, separator, electrolyte and negative electrode, and the amount of electrolyte added to all the batteries is 60 μL.

[0046] Example 1

[0047] A pH intelligent response-based high-nickel positive electrode material residual alkali cleaning solvent, the solvent is composed of the following components:

[0048] pH-responsive polymer: poly(acrylic acid-co-butyl methacrylate), mass fraction in solvent 2%;

[0049] Organic co-solvent: ethanol, mass fraction in solvent 8%;

[0050] Deionized water: mass fraction in solvent 90%;

[0051] Additive: none.

[0052] In the poly(acrylic acid-co-alkyl methacrylate), the alkyl chain length of the alkyl ester is C1, and the phase separation pH value is 6.8;

[0053] A high-nickel positive electrode material residual alkali cleaning process based on pH intelligent response, using the cleaning solvent described above, the process comprises the following steps:

[0054] (1) Initial mixing and penetration: mix the NCM positive electrode material with the cleaning solvent (solid-liquid ratio 1:3), and perform initial mixing at 30°C with a stirring speed of 300 rpm, the mixing time is 10 min, to form a slurry; the initial pH value of the slurry is adjusted to 9 by adding ammonia water;

[0055] (2) Dynamic washing and pH monitoring: continuously stir the slurry, and monitor the pH value of the slurry in real time using an online pH sensor;

[0056] (3) Intelligent termination and phase separation: when the online pH sensor monitors that the pH value of the slurry drops to 0.3 units higher than the phase separation pH value of the pH-responsive polymer, stop stirring; let the slurry stand for 20 min, so that the pH-responsive polymer undergoes phase separation to form flocculation; then perform solid-liquid separation by centrifugation at 2000 rpm for 8 min, to obtain the washed positive electrode material, polymer flocculation and supernatant;

[0057] (4) Post-treatment and solvent regeneration: vacuum dry the washed positive electrode material at 110°C for 12h to obtain a low-residual-alkali positive electrode material; mix the polymer flocculation with a 0.3 mol L-1 NaOH solution, and stir at 30°C for 1.5h to make the polymer redissolve and regenerate; perform evaporation and concentration treatment at 80°C on the supernatant to recover lithium carbonate.

[0058] The NCM positive electrode material treated in Example 1 was subjected to residual alkali content testing (titration method) and electrochemical performance testing. The test results showed that the material surface residual alkali content decreased from 0.82% before cleaning to 0.09%. The Li||NCM811 battery assembled had a capacity retention rate of 71.8% after 175 cycles at 1C rate (see Figure 1 ).

[0059] Example 2

[0060] Example 2 is only based on Example 1, and the “poly(acrylic acid-co-butyl methacrylate), mass fraction in solvent is 2%”, “ethanol, mass fraction in solvent is 8%”, “deionized water: mass fraction in solvent is 60%”, “alkyl chain length of alkyl ester is C1, phase separation pH value is 6.8” in Example 1 are respectively replaced by “poly(acrylic acid-co-butyl methacrylate), mass fraction in solvent is 5%”, “ethanol, mass fraction in solvent is 35%”, “deionized water: mass fraction in solvent is 60%”, “alkyl chain length of alkyl ester is C8, phase separation pH value is 7.5”, and other conditions remain unchanged.

[0061] The NCM positive electrode material treated in Example 2 is subjected to residual alkali content test (titration method) and electrochemical performance test. The test results show that the residual alkali content on the surface of the material is reduced from 0.82% before cleaning to 0.10%. The Li||NCM90 battery assembled has a capacity retention rate of 65.1% after 175 cycles at 1C rate.

[0062] Example 3

[0063] Example 3 is only based on Example 1, and the “poly(acrylic acid-co-butyl methacrylate), mass fraction in solvent is 2%”, “ethanol, mass fraction in solvent is 8%”, “deionized water: mass fraction in solvent is 60%”, “additive: none” in Example 1 are respectively replaced by “poly(acrylic acid-co-butyl methacrylate), mass fraction in solvent is 5%”, “ethanol, mass fraction in solvent is 30%”, “deionized water: mass fraction in solvent is 60%”, “additive: mass fraction in solvent is 5%”, and other conditions remain unchanged.

[0064] The NCM positive electrode material treated in Example 3 is subjected to residual alkali content test (titration method) and electrochemical performance test. The test results show that the residual alkali content on the surface of the material is reduced from 0.82% before cleaning to 0.15%. The Li||NCM811 battery assembled has a capacity retention rate of 79.1% after 175 cycles at 1C rate.

[0065] Example 4

[0066] Example 4 is only based on Example 1, and the "pH-responsive polymer: poly(butyl methacrylate-co-acrylic acid)" and "the alkyl chain length of the alkyl ester in the poly(acrylic acid-co-alkyl methacrylate) is C1, and the phase transition precipitation pH value is 6.8" in Example 1 are replaced by "pH-responsive polymer: polyurethane" and "the number average molecular weight of the polyurethane is 10,000 g mol-1, and the phase transition precipitation pH value is 7.0", respectively, and other conditions remain unchanged.

[0067] The residual alkali content test (titration method) and the electrochemical performance test of the NCM positive electrode material treated in Example 4 were carried out. The test results showed that the residual alkali content on the surface of the material was reduced from 0.82% before cleaning to 0.16%. The capacity retention rate of the assembled Li||NCM811 battery was 74.2% after 175 cycles at 1C rate.

[0068] Example 5

[0069] Example 5 is only based on Example 1, and the "pH-responsive polymer: poly(butyl methacrylate-co-acrylic acid)" and "the alkyl chain length of the alkyl ester in the poly(acrylic acid-co-alkyl methacrylate) is C1, and the phase transition precipitation pH value is 6.8" in Example 1 are replaced by "pH-responsive polymer: polyurethane" and "the number average molecular weight of the polyurethane is 100,000 g mol-1, and the phase transition precipitation pH value is 7.6", respectively, and other conditions remain unchanged.

[0070] The residual alkali content test (titration method) and the electrochemical performance test of the NCM positive electrode material treated in Example 5 were carried out. The test results showed that the residual alkali content on the surface of the material was reduced from 0.82% before cleaning to 0.13%. The capacity retention rate of the assembled Li||NCM811 battery was 74.6% after 175 cycles at 1C rate.

[0071] Example 6

[0072] Example 6 is only based on Example 1, and the "pH-responsive polymer: poly(butyl methacrylate-co-acrylic acid)" and "the alkyl chain length of the alkyl ester in the poly(acrylic acid-co-alkyl methacrylate) is C1, and the phase transition precipitation pH value is 6.8" in Example 1 are replaced by "pH-responsive polymer: cellulose derivative" and "the pH-responsive cellulose derivative is sodium carboxymethyl cellulose, the degree of substitution is 0.5, and the phase transition precipitation pH value is 6.5", respectively, and other conditions remain unchanged.

[0073] The NCM positive electrode material treated in Example 6 was subjected to residual alkali content testing (titration method) and electrochemical performance testing. The test results showed that the residual alkali content on the surface of the material decreased from 0.82% before cleaning to 0.15%. The Li||NCM811 battery assembled had a capacity retention rate of 72.1% after 175 cycles at a 1C rate.

[0074] Example 7

[0075] Example 7 is only based on Example 1, and the “pH-responsive polymer: poly(butyl methacrylate-co-acrylic acid)” and “the alkyl chain length of the alkyl ester in the poly(acrylic acid-co-alkyl methacrylate) is C1, and the phase transition precipitation pH value is 6.8” in Example 1 are replaced by “pH-responsive polymer: cellulose derivative” and “the pH-responsive cellulose derivative is sodium carboxymethyl cellulose, the degree of substitution is 1.5, and the phase transition precipitation pH value is 7.3”, respectively, and other conditions remain unchanged.

[0076] The NCM positive electrode material treated in Example 7 was subjected to residual alkali content testing (titration method) and electrochemical performance testing. The test results showed that the residual alkali content on the surface of the material decreased from 0.82% before cleaning to 0.16%. The Li||NCM811 battery assembled had a capacity retention rate of 71.9% after 175 cycles at a 1C rate.

[0077] Example 8

[0078] Example 8 is only based on Example 1, and the “pH-responsive polymer: poly(butyl methacrylate-co-acrylic acid)” and “the alkyl chain length of the alkyl ester in the poly(acrylic acid-co-alkyl methacrylate) is C1, and the phase transition precipitation pH value is 6.8” in Example 1 are replaced by “pH-responsive polymer: poly(N-isopropyl acrylamide-co-acrylic acid)” and “the mole fraction of the acrylic acid unit in the poly(N-isopropyl acrylamide-co-acrylic acid) is 10%, and the phase transition precipitation pH value is 6.8”, respectively, and other conditions remain unchanged.

[0079] The NCM positive electrode material treated in Example 8 was subjected to residual alkali content testing (titration method) and electrochemical performance testing. The test results showed that the residual alkali content on the surface of the material decreased from 0.82% before cleaning to 0.14%. The Li||NCM811 battery assembled had a capacity retention rate of 76.2% after 175 cycles at a 1C rate.

[0080] Example 9

[0081] Example 9 is only based on Example 1, and the "pH-responsive polymer: poly(acrylic acid-co-butyl methacrylate)" and "the alkyl chain length of the alkyl ester in the poly(acrylic acid-co-alkyl methacrylate) is C1, and the phase separation pH value is 6.8" in Example 1 are replaced by "pH-responsive polymer: poly(N-isopropylacrylamide-co-acrylic acid)" and "the molar fraction of the acrylic acid unit in the poly(N-isopropylacrylamide-co-acrylic acid) is 40%, and the phase separation pH value is 7.4", respectively, and other conditions remain unchanged.

[0082] The NCM positive electrode material treated in Example 9 was subjected to residual alkali content test (titration method) and electrochemical performance test. The test results showed that the residual alkali content on the surface of the material was reduced from 0.82% before cleaning to 0.15%. The Li||NCM811 battery assembled had a capacity retention rate of 75.3% after 175 cycles at a 1C rate.

[0083] The above is only a preferred embodiment of the present application, and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A residual alkali cleaning solvent for high-nickel cathode materials based on pH intelligent response, characterized in that: The solvent is composed of a pH-responsive polymer, an organic co-solvent, deionized water and an additive; The mass fraction of the pH-responsive polymer in the solvent is 2%-5%; The mass fraction of the organic co-solvent in the solvent is 8%-35%; The mass fraction of the deionized water in the solvent is 60%-90%; The mass fraction of the additive in the solvent is 0%-5%; The pH-responsive polymer is a linear or branched polymer with ionizable groups of carboxyl or amine, which is dissolved in the solvent under alkaline conditions and precipitates from the solvent under neutral conditions; the pH-responsive polymer is at least one selected from poly(acrylic acid-co-methyl acrylate), polyurethane, cellulose derivative and poly(N-isopropyl acrylamide-co-acrylic acid); The organic co-solvent is at least one selected from ethanol, isopropanol, n-propanol and ethylene glycol monomethyl ether; The additive is at least one selected from disodium ethylenediaminetetraacetate, sodium citrate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, aluminum nitrate, tetraethyl orthosilicate, carbon nanotube and graphene.

2. The cleaning solvent according to claim 1, characterized in that: In the poly(acrylic acid-co-methyl acrylate), the alkyl chain length of the alkyl ester is C1-C8, and the phase transition precipitation pH value is 6.8-7.

5.

3. The cleaning solvent according to claim 1, characterized in that: The number average molecular weight of the pH-responsive polyurethane is 10,000-100,000 g / mol -1 and the phase transition precipitation pH value is 7.0-7.

6.

4. The cleaning solvent of claim 1, wherein: The pH-responsive cellulose derivative is sodium carboxymethyl cellulose or hydroxypropyl methyl cellulose, with a substitution degree of 0.5-1.5 and a phase transition precipitation pH value of 6.5-7.

3.

5. The cleaning solvent of claim 1, wherein: In the poly(N-isopropyl acrylamide-co-acrylic acid), the molar fraction of the acrylic acid unit is 10%-40%, and the phase transition precipitation pH value is 6.8-7.

4.

6. The cleaning solvent of claim 1, wherein: The pH-responsive polymer is poly(acrylic acid-co-butyl methacrylate), with a mass fraction of 3%-4% in the solvent.

7. The cleaning solvent of claim 1, wherein: The mass fraction of the organic co-solvent in the solvent is 10%-20%.

8. The cleaning solvent of claim 1, wherein: The mass fraction of the deionized water in the solvent is 75%-85%.

9. The cleaning solvent of claim 1, wherein: The additive contains ammonium dihydrogen phosphate with a mass fraction of 0.5%-1.5% and aluminum nitrate with a mass fraction of 1%-2%.

10. A pH-intelligently responsive residual alkali cleaning process for high-nickel positive electrode material, using the cleaning solvent according to any one of claims 1-9, characterized in that The method comprises the following steps: (1) initial mixing and penetration: high-nickel positive electrode material is mixed with a cleaning solvent at a solid-liquid ratio of 1:3, and initial mixing is performed at 30°C with a stirring speed of 300 rpm for 10 min to form a slurry; the initial pH value of the slurry is controlled at 9 by adding an alkaline adjusting agent; (2) dynamic washing and pH monitoring: the slurry is continuously stirred, and the pH value of the slurry is monitored in real time by using an online pH sensor; (3) intelligent termination and phase transition separation: when the online pH sensor detects that the pH value of the slurry decreases to a preset termination point, the stirring is stopped; the preset termination point is 0.3 units higher than the phase transition precipitation pH value of the pH-responsive polymer; After the stirring is stopped, the slurry is left to stand for 20 min to cause the pH-responsive polymer to undergo phase transition precipitation and form flocculation; then, solid-liquid separation is performed by decantation, filtration or centrifugation to obtain the washed positive electrode material, polymer flocculation and supernatant; (4) Post-treatment and solvent regeneration: the washed positive electrode material is vacuum dried at 110℃ for 12h to obtain a positive electrode material with low residual alkali; the polymer flocculation is mixed with an alkali solution with a mass concentration of 0.3mol L-1, and stirred at 30℃ for 1.5h to make the polymer redissolved and regenerated; the supernatant is treated by evaporation and concentration to recover the lithium salt therein.

11. The cleaning process of claim 10, wherein: The high-nickel positive electrode material in the step (1) is LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) and LiNi 0.9 Co 0.05 Mn 0.05 O2(NCM90).

12. The cleaning process of claim 10, wherein: The basic regulator in the step (1) is ammonia water or lithium hydroxide aqueous solution.

13. The cleaning process of claim 10, wherein: The centrifugal separation condition in the step (3) is a centrifugal rate of 2000rpm and a centrifugal time of 8min.

14. The cleaning process of claim 10, wherein: The alkali solution used for regenerating the polymer flocculation in the step (4) is sodium hydroxide solution or lithium hydroxide solution.

15. The cleaning process of claim 10, wherein: The lithium salt recovered in the step (4) is lithium carbonate or lithium hydroxide.

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