Alkaline cleaning solution, positive electrode material, preparation method thereof and battery

Abstract

This application provides an alkaline washing solution, a positive electrode material, a method for preparing the same, and a battery. The alkaline washing solution includes a quaternary ammonium alkali and sodium hydroxide. By adding the quaternary ammonium alkali, the structural stability of the lithium nickel manganese oxide precursor can be improved, and SO4 can be removed from the crystals of the lithium nickel manganese oxide precursor. 2‑ This effectively cleans the lithium nickel manganese oxide precursor, improving the electrochemical performance of the final lithium nickel manganese oxide cathode material, such as capacity and electronic conductivity. Adding sodium hydroxide further removes SO42- present within the crystals of the lithium nickel manganese oxide precursor. 2‑ Meanwhile, some lithium nickel manganese oxide precursors will undergo phase transition in the high-temperature and strong alkaline environment of alkaline washing, resulting in the formation of a lithium manganese oxide layer on the surface of lithium nickel manganese oxide cathode material particles. This can greatly reduce the surface activity of lithium nickel manganese oxide cathode material, reduce the side reactions between it and the electrolyte, and thus avoid its rapid capacity decay and improve its cycle capacity retention rate.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to an alkaline washing solution, a positive electrode material, a method for preparing the same, and a battery. Background Technology

[0002] Lithium nickel manganese spinel oxide (LiNi) 0.5 Mn 1.5 O4 has a high reaction potential (>4.6V), a high theoretical specific capacity (>140mAh / g), and low cost, so it can theoretically be applied to high energy density power battery systems. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide an alkaline washing solution, a positive electrode material, a method for preparing the same, and a battery.

[0004] To achieve the above objectives, the first aspect of this application provides an alkaline washing solution, which includes a quaternary ammonium base and sodium hydroxide.

[0005] Optionally, the molar ratio of the sodium hydroxide to the quaternary ammonium base is (0.5-4):1.

[0006] Optionally, the quaternary ammonium base is at least one selected from tetramethylammonium hydroxide, trimethyl-ethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0007] Optionally, the concentration of the alkaline washing solution is 1 to 5 mol / L.

[0008] A second aspect of this application provides a method for preparing a lithium nickel manganese oxide cathode material, including,

[0009] The lithium nickel manganese oxide precursor was cleaned using an alkaline cleaning solution as described in any of the first aspects above.

[0010] The cleaned lithium nickel manganese oxide precursor was mixed with a lithium source and calcined to prepare lithium nickel manganese oxide cathode material.

[0011] Optionally, the ratio of the amount of the quaternary ammonium base to the mass of the lithium nickel manganese oxide precursor is (6-20) mol: 1 kg.

[0012] Optionally, the molar ratio of the lithium nickel manganese oxide precursor to the lithium source is 1:(0.49 to 0.55).

[0013] A third aspect of this application provides a lithium nickel manganese oxide cathode material, the lithium nickel manganese oxide cathode material comprising lithium nickel manganese oxide particles and a lithium manganese oxide layer coating the outside of the lithium nickel manganese oxide particles.

[0014] Optionally, the thickness of the lithium manganese oxide layer is 1–10 nm.

[0015] The fourth aspect of this application provides a battery comprising a lithium nickel manganese oxide cathode material prepared by any of the preparation methods described in the second aspect above, or a lithium nickel manganese oxide cathode material described in the third aspect above.

[0016] As can be seen from the above, the alkaline washing solution, positive electrode material, preparation method thereof, and battery provided in this application include a quaternary ammonium alkali and sodium hydroxide in the alkaline washing solution. Adding the quaternary ammonium alkali can improve the structural stability of the lithium nickel manganese oxide precursor and remove SO4 from the crystals of the lithium nickel manganese oxide precursor. 2- This effectively cleans the lithium nickel manganese oxide precursor, mitigating the formation of impurity phases during alkaline washing and improving the electrochemical performance of the final lithium nickel manganese oxide cathode material, such as capacity and electronic conductivity. Furthermore, the addition of sodium hydroxide further removes SO42- present within the crystals of the lithium nickel manganese oxide precursor. 2- Meanwhile, during sodium hydroxide alkaline washing, some lithium nickel manganese oxide precursors undergo phase transformation under the high-temperature, strongly alkaline environment of alkaline washing, which in turn forms impurity phases Mn2O3 / Mn3O4 during subsequent post-processing such as drying. These impurity phases remain in the lithium nickel manganese oxide precursor. During the subsequent calcination process of mixing the lithium nickel manganese oxide precursor with the lithium source, these impurity phases react with the lithium source, ultimately generating a lithium manganese oxide layer coating the surface of the lithium nickel manganese oxide cathode material particles. This can greatly reduce the surface activity of the lithium nickel manganese oxide cathode material, reduce the side reactions between it and the electrolyte, thereby avoiding rapid capacity decay and improving its cycle capacity retention rate. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figures 1A-1D These are scanning electron microscope (SEM) images of the cathode materials used in the embodiments and comparative examples of this application.

[0019] Figure 2 The graph shows the test results of the cycle test of the cathode materials in the embodiments and comparative examples of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0021] It should be noted that, unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and unless otherwise specified, the experimental methods used are conventional methods.

[0022] Since rechargeable lithium-ion batteries entered the consumer market, their use in portable electronic products has revolutionized traditional communication methods. As market demands for the energy density and safety of rechargeable lithium-ion batteries continue to rise, the industry is constantly searching for new battery materials to meet these requirements.

[0023] Lithium nickel manganese spinel oxide (LiNi) 0.5 Mn 1.5 O4 has a high reaction potential (>4.6V), a high theoretical specific capacity (>140mAh / g), and low cost, so it can theoretically be applied to high energy density power battery systems.

[0024] However, in using lithium nickel manganese oxide as the positive electrode material in batteries, the inventors found that the electrochemical performance of lithium nickel manganese oxide, such as capacity and electronic conductivity, was not particularly good, and the cycle capacity retention rate was not high, which could not meet practical requirements. The inventors further discovered that this was because the surface activity of lithium nickel manganese oxide material was very high, so that the surface would undergo violent side reactions with the solvent during charge-discharge cycles, resulting in low electrochemical performance such as capacity, electronic conductivity, and cycle capacity retention rate.

[0025] In the early stages of synthesizing lithium nickel manganese oxide precursors, the raw materials used contained SO4. 2- Therefore, the final synthesized lithium nickel manganese oxide precursor crystal contains a large amount of SO4. 2- This can affect material properties. Typically, in the post-processing of lithium nickel manganese oxide precursors, alkali (NaOH) washing is used to remove SO4 inclusions within the precursor crystals. 2- This allows for the modification of materials, reducing surface side reactions and thereby improving their electrochemical performance.

[0026] However, since the Mn(OH)2-like substances contained in the lithium nickel manganese oxide precursor are relatively unstable in a strongly alkaline environment, the crystal structure of the Mn(OH)2-like substances is prone to phase transformation under the high temperature and strongly alkaline environment of alkaline washing. In subsequent post-processing such as drying, Mn2O3 / Mn3O4 impurity phases are generated. These impurity phases remain in the lithium nickel manganese oxide precursor. In the subsequent process of calcining the lithium nickel manganese oxide precursor and lithium source, these impurity phases react with the lithium source, eventually generating lithium manganese oxide that remains in the lithium nickel manganese oxide cathode material. The presence of a large number of impurity phases reduces the electrochemical performance (such as capacity and electronic conductivity) of the prepared lithium nickel manganese oxide cathode material.

[0027] Furthermore, during the charging and discharging process of the battery, the lithium nickel manganese oxide cathode material has high surface chemical activity, and the violent side reactions lead to a rapid decay of battery capacity, ultimately resulting in a low cycle capacity retention rate.

[0028] Based on this, the inventors conceived that if a small amount of lithium nickel manganese oxide precursor undergoes a phase transition to generate an impurity phase during the alkaline washing process, this small amount of impurity phase can react with the lithium source during the subsequent calcination of the lithium nickel manganese oxide precursor and lithium source, ultimately generating a small amount of lithium manganese oxide coating the outside of the lithium nickel manganese oxide cathode material. This would reduce side reactions between the lithium nickel manganese oxide cathode material and the electrolyte, thereby improving its capacity cycle retention. Simultaneously, the presence of a small amount of lithium manganese oxide would not significantly adversely affect the electrochemical performance of the lithium nickel manganese oxide cathode material.

[0029] Therefore, optimizing the alkaline washing method for lithium nickel manganese oxide precursors to control the phase transition of a small amount of lithium nickel manganese oxide precursors while preventing the phase transition of the majority of lithium nickel manganese oxide precursors is an urgent problem to be solved.

[0030] Based on this, this application provides an alkaline washing solution, a cathode material, a preparation method thereof, and a battery, which can optimize the alkaline washing method of lithium nickel manganese oxide precursor, improve the electrochemical properties of lithium nickel manganese oxide cathode material, and at the same time reduce the surface activity of cathode material, thereby improving its cycle capacity retention rate.

[0031] Specifically, this application provides an alkaline washing solution, which includes a quaternary ammonium base and sodium hydroxide.

[0032] The general structural formula of lithium nickel manganese oxide precursor is Ni x Mn y (OH)₂, where 0.2≤x≤0.3, 0.7≤y≤0.8, x+y=1, such as Ni 0.25 Mn 0.75 (OH)2. The lithium nickel manganese oxide precursor contains a large number of metal ions (such as nickel and manganese ions). Furthermore, as mentioned earlier, due to the influence of the preparation process, the crystal interior of the lithium nickel manganese oxide precursor contains a large amount of SO42-.2- .

[0033] When cleaning lithium nickel manganese oxide precursors with the alkaline washing solution of the present invention, on the one hand, due to the special structure of quaternary ammonium bases, which include nitrogen ions with strong electron-withdrawing ability, nitrogen ions can strongly adsorb with metal ions in lithium nickel manganese oxide precursors, thereby forming complexes with lithium nickel manganese oxide precursors. This can improve the structural stability of lithium nickel manganese oxide precursors, reduce phase transitions in lithium nickel manganese oxide precursors during alkaline washing, and avoid generating too many impurity phases.

[0034] On the other hand, quaternary ammonium bases are strong bases and contain a large amount of OH-. - A large amount of OH - The presence of it serves the same purpose as alkaline washing with sodium hydroxide, resulting in a large amount of OH... - SO4 contained within the crystal of lithium nickel manganese oxide precursor can be removed 2- Replace it so that OH - It remains inside the crystal of the lithium nickel manganese oxide precursor, while SO4 2- It dissolves in solution, thereby removing SO4 from the crystals of lithium nickel manganese oxide precursor. 2- In this process, because the lithium nickel manganese oxide precursor forms a complex with nitrogen ions, the crystal structure of the lithium nickel manganese oxide precursor is less likely to undergo a phase transition under the high temperature and strong alkaline environment of alkaline washing. As a result, less impurity phases are formed in subsequent processes such as drying, which can improve the electrochemical performance of the final lithium nickel manganese oxide cathode material, such as capacity and electronic conductivity.

[0035] Adding sodium hydroxide can further remove SO42- contained within the crystals of the lithium nickel manganese oxide precursor. 2- Meanwhile, during sodium hydroxide alkaline washing, some crystal structures of substances such as Mn(OH)2 in the lithium nickel manganese oxide precursor undergo phase transformation under the high-temperature and strong alkaline environment of alkaline washing, which in turn forms impurity phases Mn2O3 / Mn3O4 in subsequent processes such as drying. These impurity phases remain in the lithium nickel manganese oxide precursor. In the subsequent process of calcining the lithium nickel manganese oxide precursor and lithium source together, these impurity phases react with the lithium source, eventually generating a lithium manganese oxide layer coating the surface of the lithium nickel manganese oxide cathode material particles. This can greatly reduce the surface activity of the lithium nickel manganese oxide cathode material, reduce the side reactions between it and the electrolyte, and thus avoid its rapid capacity decay and improve its cycle capacity retention rate.

[0036] Furthermore, after the lithium nickel manganese oxide precursor, cleaned with the alkaline washing solution of the present invention, reacts with the lithium source to form lithium nickel manganese oxide particles, inductively coupled plasma atomic emission spectrometry (ICP) analysis shows that lithium manganese oxide is formed on the surface of the prepared lithium manganese oxide particles, and the lithium manganese oxide coats the surface of the lithium nickel manganese oxide particles to form a coating layer.

[0037] In the alkaline washing solution of this application, controlling the molar ratio of sodium hydroxide and quaternary ammonium base is crucial. If the molar ratio of the two is not appropriate, it will either result in too much lithium manganese oxide in the generated lithium nickel manganese oxide cathode material, reducing the capacity and electronic conductivity of the lithium nickel manganese oxide cathode material, or it will result in too little lithium manganese oxide in the generated lithium nickel manganese oxide cathode material, which will not be able to improve its surface properties, and thus will not be able to improve the cycle capacity retention rate.

[0038] Based on this, in some embodiments, the molar ratio of sodium hydroxide to quaternary ammonium base is (0.5-4):1.

[0039] Specifically, when the molar ratio of sodium hydroxide to quaternary ammonium base is (0.5–4):1, the ratio of sodium hydroxide to quaternary ammonium base is appropriate, which can effectively remove SO4 from lithium nickel manganese oxide precursor crystals. 2- By controlling the sulfur content in the lithium nickel manganese oxide precursor to a suitable ratio, a phase transition can be achieved in an appropriate amount of lithium nickel manganese oxide precursor during sodium hydroxide alkaline washing. This results in the final lithium nickel manganese oxide cathode material containing an appropriate amount of lithium manganese oxide, ensuring that the presence of this lithium manganese oxide does not affect the electrochemical performance (such as capacity and electronic conductivity) of the lithium nickel manganese oxide cathode material, and can even improve its cycle performance.

[0040] When the molar ratio of sodium hydroxide to quaternary ammonium alkali is less than 0.5:1, the proportion of sodium hydroxide is too small, resulting in very little lithium nickel manganese oxide precursor undergoing phase change during sodium hydroxide alkaline washing. Consequently, the final lithium nickel manganese oxide cathode material contains almost no lithium manganese oxide. Although this can significantly improve the capacity and electronic conductivity of the lithium nickel manganese oxide cathode material, the insufficient lithium manganese oxide coating on the particle surface of the lithium nickel manganese oxide cathode material cannot effectively reduce the surface activity of the material. This leads to violent side reactions with the electrolyte, causing rapid capacity decay and reducing cycle capacity retention.

[0041] When the molar ratio of sodium hydroxide to quaternary ammonium alkali is greater than 4:1, the proportion of sodium hydroxide is too high and the proportion of quaternary ammonium alkali is too low, resulting in poor structural stability of the lithium nickel manganese oxide precursor. Consequently, a large amount of lithium nickel manganese oxide precursor undergoes phase transition during the sodium hydroxide alkaline washing process, leading to a higher content of lithium manganese oxide in the final lithium nickel manganese oxide cathode material. Although this portion of lithium manganese oxide can reduce the surface activity of the lithium nickel manganese oxide cathode material, reduce its side reactions with the electrolyte, and improve the cycle capacity retention rate, the presence of too much lithium manganese oxide will reduce the electronic conductivity and capacity of the lithium nickel manganese oxide cathode material, which is detrimental to its electrical performance.

[0042] For example, the molar ratio of sodium hydroxide to quaternary ammonium base can be 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.

[0043] Preferably, the molar ratio of sodium hydroxide to quaternary ammonium base is (2-3):1.

[0044] Specifically, when the molar ratio of sodium hydroxide to quaternary ammonium base is (2-3):1, the ratio of sodium hydroxide to quaternary ammonium base is optimal, which can effectively remove SO4 from lithium nickel manganese oxide precursor crystals. 2- By controlling the sulfur content in the lithium nickel manganese oxide precursor to an extremely low level, a more suitable amount of lithium nickel manganese oxide precursor can undergo a phase transition during the sodium hydroxide alkaline washing process. This results in the final lithium nickel manganese oxide cathode material containing a more suitable amount of lithium manganese oxide. The presence of this lithium manganese oxide allows the lithium nickel manganese oxide cathode material to have both high capacity and high cycle capacity retention.

[0045] In some embodiments, the quaternary ammonium base is at least one selected from tetramethylammonium hydroxide, trimethyl-ethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0046] Specifically, the quaternary ammonium base can be only tetramethylammonium hydroxide, trimethyl-ethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide, or it can be a mixture of tetramethylammonium hydroxide and trimethyl-ethylammonium hydroxide, or a mixture of tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

[0047] In some embodiments, the concentration of the alkaline washing solution is 1–5 mol / L.

[0048] Specifically, when the concentration of the alkaline washing solution is 1–5 mol / L, the concentration is appropriate and can effectively remove SO4 from the lithium nickel manganese oxide precursor crystals. 2-By controlling the sulfur content in the lithium nickel manganese oxide precursor to a required ratio, a phase transition can be achieved in an appropriate amount of the lithium nickel manganese oxide precursor during sodium hydroxide alkaline washing. This results in the final lithium nickel manganese oxide cathode material containing an appropriate amount of lithium manganese oxide, ensuring that the presence of this lithium manganese oxide does not affect the capacity and electronic conductivity of the lithium nickel manganese oxide cathode material, and can also improve its cycle performance.

[0049] When the concentration of the alkaline washing solution is greater than 5 mol / L, the concentration is too high, which makes the lithium nickel manganese oxide precursor more prone to side reactions during the alkaline washing process, which is not conducive to the structural stability of the lithium nickel manganese oxide precursor. When the concentration of the alkaline washing solution is less than 1 mol / L, the concentration is too low, which results in poor cleaning effect of the lithium nickel manganese oxide precursor.

[0050] For example, the concentration of the alkaline washing solution can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, etc.

[0051] This application also provides a method for preparing a lithium nickel manganese oxide cathode material, including,

[0052] The lithium nickel manganese oxide precursor was cleaned using the alkaline washing solution described in any of the above embodiments as a cleaning agent.

[0053] The cleaned lithium nickel manganese oxide precursor was mixed with a lithium source and calcined to prepare lithium nickel manganese oxide cathode material.

[0054] Specifically, before cleaning, the alkaline cleaning solution can be preheated, and the lithium nickel manganese oxide precursor can be added to the preheated alkaline cleaning solution. The preheating temperature can accelerate the OH-... - SO4 contained within the crystal of lithium nickel manganese oxide precursor 2- This substitution effect enhances the alkaline washing effect.

[0055] The preheating temperature of the alkaline washing solution can be 50℃ to 100℃. Preferably, the preheating temperature of the alkaline washing solution can be 80℃.

[0056] Then, the cleaned lithium nickel manganese oxide precursor is mixed with a lithium source and calcined to prepare a lithium nickel manganese oxide cathode material. The calcination conditions are: sintering at 800-1000℃ for 8-12 hours to ensure that the obtained lithium nickel manganese oxide cathode material meets the requirements and can be used as a positive electrode active material for lithium batteries.

[0057] The molar ratio of lithium nickel manganese oxide precursor to lithium source is 1:(0.49~0.55) to ensure the stoichiometry of the final lithium nickel manganese oxide cathode material.

[0058] Among them, the lithium nickel manganese oxide precursor can be Ni 0.25 Mn 0.75The lithium nickel manganese oxide cathode material prepared by (OH)2 can be lithium nickel manganese oxide (LiNi) 0.5 Mn 1.5 O4.

[0059] In some embodiments, the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is (6-20) mol: 1 kg.

[0060] Specifically, when the molar ratio of quaternary ammonium base to lithium nickel manganese oxide precursor is (6-20) mol: 1 kg, the ratio of quaternary ammonium base to lithium nickel manganese oxide precursor is appropriate. This allows the quaternary ammonium base to effectively improve the structural stability of the lithium nickel manganese oxide precursor, preventing most of the precursor from undergoing side reactions during alkaline washing and thus improving the capacity and electronic conductivity of the final lithium nickel manganese oxide cathode material. Simultaneously, a small amount of lithium nickel manganese oxide precursor undergoes side reactions during alkaline washing, resulting in a lithium manganese oxide layer coating the surface of the final lithium nickel manganese oxide cathode material particles. This lithium manganese oxide layer reduces side reactions between the lithium nickel manganese oxide cathode material and the electrolyte, improving cycle capacity retention.

[0061] When the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is less than 6 mol: 1 kg, the amount of quaternary ammonium base added is too small, which fails to effectively improve the structural stability of the lithium nickel manganese oxide precursor. Consequently, too much lithium nickel manganese oxide precursor undergoes side reactions during the alkaline washing process, resulting in a decrease in the electrochemical performance of the final lithium nickel manganese oxide cathode material, such as capacity and electronic conductivity.

[0062] When the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is greater than 20 mol: 1 kg, the amount of quaternary ammonium base added is too much. This means that almost all lithium nickel manganese oxide precursors will not undergo side reactions during the alkaline washing process, resulting in high capacity and electronic conductivity of the final lithium nickel manganese oxide cathode material. However, since the surface of the lithium nickel manganese oxide cathode material particles is not coated with a lithium manganese oxide layer, its excessively high surface activity leads to severe side reactions with the electrolyte. These severe side reactions cause rapid capacity decay of the battery, which in turn leads to a decrease in its cycle capacity retention rate.

[0063] For example, the molar ratio of the quaternary ammonium base to the mass of the lithium nickel manganese oxide precursor is 6 mol: 1 kg, 7 mol: 1 kg, 8 mol: 1 kg, 9 mol: 1 kg, 10 mol: 1 kg, 11 mol: 1 kg, 12 mol: 1 kg, 13 mol: 1 kg, 14 mol: 1 kg, 15 mol: 1 kg, 16 mol: 1 kg, 17 mol: 1 kg, 18 mol: 1 kg, 19 mol: 1 kg, and 20 mol: 1 kg.

[0064] Preferably, the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is (10-15) mol: 1 kg. At this ratio, the quaternary ammonium base and the lithium nickel manganese oxide precursor are well matched, so that the final lithium nickel manganese oxide cathode material has both good electrochemical performance and high cycle capacity retention.

[0065] This application also provides a lithium nickel manganese oxide cathode material, which includes lithium nickel manganese oxide particles and a lithium manganese oxide layer coating the outside of the lithium nickel manganese oxide particles.

[0066] Specifically, since the surface activity of lithium manganese oxide is much lower than that of lithium nickel manganese oxide, coating the surface of lithium nickel manganese oxide cathode material particles with a lithium manganese oxide layer can greatly reduce the surface activity of lithium nickel manganese oxide cathode material, reduce the side reactions between it and the electrolyte, thereby avoiding rapid capacity decay and improving its cycle capacity retention rate.

[0067] In some embodiments, the thickness of the lithium manganese oxide layer is 1–10 nm. When the thickness of the lithium manganese oxide layer is 1–10 nm, the thickness of the lithium manganese oxide layer is moderate, which can effectively reduce the surface activity of the lithium nickel manganese oxide cathode material, thereby improving its cycle capacity retention, without significantly reducing the electronic conductivity and capacity of the lithium nickel manganese oxide cathode material.

[0068] When the thickness of the lithium manganese oxide layer is less than 1 nm, the thickness of the lithium manganese oxide layer is too thin to effectively reduce the surface activity of the lithium nickel manganese oxide cathode material.

[0069] When the thickness of the lithium manganese oxide layer exceeds 10 nm, the layer becomes too thick. This excessive thickness limits the battery's capacity, leading to rapid capacity decay after a certain number of cycles and failing to effectively improve cycle capacity retention. Furthermore, an excessively thick lithium manganese oxide layer significantly reduces the electronic conductivity and capacity of the lithium nickel manganese oxide cathode material.

[0070] For example, the thickness of the lithium manganese oxide layer can be 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc.

[0071] The lithium nickel manganese oxide cathode material prepared in this application has a lithium manganese oxide layer of appropriate thickness coated on the outer wall of the lithium nickel manganese oxide particles, thereby giving it both good electrochemical performance and high cycle capacity retention.

[0072] This application also provides a battery comprising the lithium nickel manganese oxide cathode material of any of the above embodiments.

[0073] Specifically, the battery includes a positive electrode, a separator, and a negative electrode. The positive electrode includes a lithium nickel manganese oxide positive electrode active material, a conductive agent, and a binder. The negative electrode includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material can be a silicon-based negative electrode active material or a carbon-based negative electrode active material. The separator can be a polyethylene separator or a polypropylene separator, etc.

[0074] The battery of this application has the technical effects of any of the above embodiments, which will not be elaborated here.

[0075] The present application will be further discussed below with reference to specific embodiments.

[0076] Example 1

[0077] An alkaline cleaning solution for cleaning lithium nickel manganese oxide precursors, comprising a quaternary ammonium base and sodium hydroxide, wherein the molar ratio of sodium hydroxide to the quaternary ammonium base is 2.5:1. The quaternary ammonium base is tetramethylammonium hydroxide, and the concentration of the alkaline cleaning solution is 3 mol / L.

[0078] A post-treatment method for a lithium nickel manganese oxide precursor includes: adding the prepared lithium nickel manganese oxide precursor to the preheated alkaline washing solution, stirring at 500 rpm for 60 min, filtering, washing three times with deionized water following the same procedure, and drying in an oven at 120℃ for 8 h to obtain the washed and treated precursor. The molar ratio of the quaternary ammonium base to the mass of the lithium nickel manganese oxide precursor is 10 mol: 1 kg.

[0079] A method for preparing a lithium nickel manganese oxide cathode material includes: mixing the pre-treated precursor with lithium hydroxide for 5 hours and calcining at 900°C for 10 hours to obtain the lithium nickel manganese oxide cathode material. The lithium nickel manganese oxide cathode material comprises lithium nickel manganese oxide particles and a lithium manganese oxide layer coating the outside of the lithium nickel manganese oxide particles. The molar ratio of the pre-treated precursor to lithium hydroxide is 1:0.52.

[0080] A battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte.

[0081] In this process, the prepared lithium nickel manganese oxide cathode material, conductive agent, and binder polyvinylidene fluoride are mixed in a mass ratio of 90:5:5, added to an appropriate amount of N-methylpyrrolidone (NMP) solvent, mixed evenly, and then coated into a cathode sheet. The cathode sheet is then cut into electrode sheets with a diameter of 16 mm, and the mass loading of the active material is 10 ± 1 mg cm-2.

[0082] The negative electrode is made of lithium foil, and the electrolyte is formed by dissolving 1M LiPF6 in a mixed solvent (ethylene carbonate EC / octadecyl dimethyl benzyl ammonium chloride DC / ethyl methyl carbonate EMC = 1 / 1 / 1, volume ratio). The separator is a polyethylene separator.

[0083] Example 2

[0084] The difference from Example 1 is that the quaternary ammonium base is tetraethylammonium hydroxide.

[0085] Example 3

[0086] The difference from Example 1 is that the quaternary ammonium base is tetrapropylammonium hydroxide.

[0087] Example 4

[0088] The difference from Example 1 is that the molar ratio of sodium hydroxide to quaternary ammonium base is 0.5:1.

[0089] Example 5

[0090] The difference from Example 1 is that the molar ratio of sodium hydroxide to quaternary ammonium base is 1:1.

[0091] Example 6

[0092] The difference from Example 1 is that the molar ratio of sodium hydroxide to quaternary ammonium base is 4:1.

[0093] Example 7

[0094] The difference from Example 1 is that the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is 6 mol: 1 kg.

[0095] Example 8

[0096] The difference from Example 1 is that the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is 20 mol: 1 kg.

[0097] Example 9

[0098] The difference from Example 1 is that the concentration of the alkaline washing solution is 1 mol / L.

[0099] Example 10

[0100] The difference from Example 1 is that the concentration of the alkaline washing solution is 5 mol / L.

[0101] Example 11

[0102] The difference from Example 1 is that the molar ratio of sodium hydroxide to quaternary ammonium base is 0.4:1.

[0103] Example 12

[0104] The difference from Example 1 is that the molar ratio of sodium hydroxide to quaternary ammonium base is 4.2:1.

[0105] Example 13

[0106] The difference from Example 1 is that the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is 5 mol: 1 kg.

[0107] Example 14

[0108] The difference from Example 1 is that the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor is 22 mol: 1 kg.

[0109] Example 15

[0110] The difference from Example 1 is that the concentration of the alkaline washing solution is 0.5 mol / L.

[0111] Example 16

[0112] The difference from Example 1 is that the concentration of the alkaline washing solution is 6 mol / L.

[0113] Comparative Example 1

[0114] The difference from Example 1 is that the alkaline washing solution only contains quaternary ammonium base tetramethylammonium hydroxide.

[0115] Comparative Example 2

[0116] The difference from Example 1 is that the alkaline washing solution contains only sodium hydroxide.

[0117] Comparative Example 3

[0118] The difference from Example 1 is that the quaternary ammonium base is replaced with trimethylammonium.

[0119] Comparative Example 4

[0120] The difference from Example 1 is that the quaternary ammonium base is replaced with dimethylammonium.

[0121] Comparative Example 5

[0122] The difference from Example 1 is that the quaternary ammonium base is replaced with methylammonium.

[0123] The experimental parameters for each of the above embodiments and comparative examples are detailed in Table 1 below. In Table 1, n(NaOH) / n(quaternary ammonium base) represents the molar ratio of sodium hydroxide to quaternary ammonium base. n(quaternary ammonium base) / m(precursor) represents the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor.

[0124] The following tests were conducted on the treated precursors, lithium nickel manganese oxide cathode materials, and batteries prepared in each embodiment and comparative example.

[0125] The lithium nickel manganese oxide cathode materials obtained in each embodiment and comparative example were subjected to scanning electron microscopy (SEM) tests. Figure 1A This is a scanning electron microscope image of the lithium nickel manganese oxide cathode material obtained in Example 1; Figure 1B Here is a scanning electron microscope image of the lithium nickel manganese oxide cathode material obtained in Example 5; Figure 1C This is a scanning electron microscope image of the lithium nickel manganese oxide cathode material obtained in Example 11; Figure 1D The image shows a scanning electron microscope (SEM) image of the lithium nickel manganese oxide cathode material obtained in Comparative Example 2.

[0126] The ratio of manganese ions to nickel ions in the pre-treated precursor and the post-treated precursor before washing, the sodium ion content and sulfur ion content in the post-treated precursor, and the thickness of the lithium manganese oxide layer on the surface of the lithium nickel manganese oxide cathode material particles were determined by ICP testing.

[0127] Electrochemical tests were performed on the prepared batteries. The charge / discharge voltage range was 3.5–4.95 V. When testing cycle performance, the batteries were first activated at 0.1 C for two cycles, followed by 100 cycles at 1 C. All electrochemical tests were conducted at 25 °C.

[0128] The test results are shown in Table 2 below.

[0129] In Table 2, Mn / Ni before washing represents the ratio of Mn to Ni content in the pre-treated precursor before washing, and Mn / Ni after washing represents the ratio of Mn to Ni content in the pre-treated precursor after washing. Na (ppm) and S (ppm) represent the sodium ion content and sulfur ion content in the pre-treated precursor after washing, respectively.

[0130] Table 1. List of Experimental Data

[0131]

[0132]

[0133]

[0134] Table 2 Test Data List

[0135]

[0136]

[0137] As shown in Tables 1 and 2 above, in all embodiments, the sodium ion content and sulfur ion content in the preform after washing are both low, which meets the actual process requirements; and the cycle capacity retention rate and battery capacity of the prepared batteries are both high. This is because, in all embodiments, the proportion and content of the added quaternary ammonium base and sodium hydroxide are moderate, and the two work together to simultaneously improve the cycle performance and capacity of the battery.

[0138] Comparing the various embodiments, it can be seen that the lithium nickel manganese oxide cathode material in Embodiment 1 has the best capacity and 100-cycle capacity retention rate. This is because the thickness of the lithium manganese oxide layer in Embodiment 1 is the most suitable, which can effectively improve the surface activity of the cathode material particles and improve its cycle capacity retention rate without affecting the capacity of the cathode material.

[0139] In other embodiments, compared to Embodiment 1, the thickness of the lithium manganese oxide layer is either thinner or thicker. If the lithium manganese oxide layer is too thin, its effect on improving the surface activity of the cathode material particles is slightly worse, resulting in a slightly worse effect on improving the cycle capacity retention rate. If the lithium manganese oxide layer is too thick, the thicker lithium manganese oxide layer will, to some extent, limit the battery's capacity utilization, leading to rapid capacity decay after a certain number of cycles, thus resulting in a slightly worse effect on improving the cycle capacity retention rate. Furthermore, a thicker lithium manganese oxide layer will also reduce the capacity of the cathode material. Therefore, when the thickness of the lithium manganese oxide layer is controlled between 1 and 10 mm, it can simultaneously improve the battery's cycle performance and capacity. When the thickness of the lithium manganese oxide layer is controlled at 4 mm, it can significantly improve the battery's cycle performance and capacity.

[0140] In Example 11, since the molar ratio of sodium hydroxide to quaternary ammonium base is 0.4:1, the proportion of sodium hydroxide is too small, resulting in very little lithium nickel manganese oxide precursor undergoing phase change during sodium hydroxide alkaline washing. Consequently, the final lithium nickel manganese oxide cathode material contains almost no lithium manganese oxide. Although this can significantly improve the capacity and electronic conductivity of the lithium nickel manganese oxide cathode material, the excellent surface activity of the lithium nickel manganese oxide cathode material particles, which are almost completely coated with a lithium manganese oxide layer, leads to violent side reactions with the electrolyte, resulting in rapid capacity decay and ultimately a decrease in cycle capacity retention.

[0141] In Example 12, the molar ratio of sodium hydroxide to quaternary ammonium base was 4.2:1. This ratio of sodium hydroxide to quaternary ammonium base resulted in a high proportion of sodium hydroxide and a low proportion of quaternary ammonium base, leading to poor structural stability of the lithium nickel manganese oxide precursor. Consequently, a large amount of lithium nickel manganese oxide precursor underwent a phase transition during the sodium hydroxide alkaline washing process. This resulted in a high content of lithium manganese oxide in the final lithium nickel manganese oxide cathode material, making the lithium manganese oxide layer too thick. This excessively thick layer limited the battery's capacity, causing rapid capacity decay after a certain number of cycles. Consequently, it failed to effectively improve the cycle capacity retention rate, resulting in a low cycle capacity retention rate. Furthermore, the low capacity of lithium manganese oxide reduced the overall capacity of the lithium nickel manganese oxide cathode material.

[0142] In Example 13, the molar ratio of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor was 5 mol: 1 kg. Compared to Example 1, the amount of quaternary ammonium base added in Example 12 was less, which resulted in insufficient improvement of the structural stability of the lithium nickel manganese oxide precursor. Consequently, more lithium nickel manganese oxide precursor underwent side reactions during the alkaline washing process. Furthermore, since the ratio of quaternary ammonium base to sodium hydroxide was constant, the amount of added quaternary ammonium base was less, and the proportion of added sodium hydroxide was also reduced. Therefore, the thickness of the lithium manganese oxide layer in the final lithium nickel manganese oxide cathode material was not significantly different from that in Example 1. However, due to the relatively low overall content of the alkaline washing solution, the washing was not thorough, resulting in a certain amount of impurities in the generated lithium nickel manganese oxide cathode material, leading to a decrease in its capacity.

[0143] In Example 14, the ratio of the amount of quaternary ammonium base to the mass of lithium nickel manganese oxide precursor was 22 mol: 1 kg. The amount of quaternary ammonium base added was relatively large, which meant that almost all lithium nickel manganese oxide precursors would not undergo side reactions during the alkaline washing process. This resulted in high capacity and electronic conductivity of the final lithium nickel manganese oxide cathode material. However, since the surface of the lithium nickel manganese oxide cathode material particles was almost completely covered with a lithium manganese oxide layer, its excessively high surface activity led to severe side reactions with the electrolyte. These severe side reactions caused rapid capacity decay of the battery, which in turn led to a decrease in its cycle capacity retention rate.

[0144] In Example 15, the concentration of the alkaline washing solution was 0.5 mol / L. At this concentration, the alkaline washing solution was too low, resulting in poor cleaning effect on the lithium nickel manganese oxide precursor.

[0145] In Example 16, the concentration of the alkaline washing solution was 6 mol / L. This concentration was too high, making the lithium nickel manganese oxide precursor more susceptible to side reactions during the alkaline washing process. This resulted in an excessively thick lithium manganese oxide layer, which limited the battery's capacity and caused rapid capacity decay after a certain number of cycles. Consequently, it failed to effectively improve the cycle capacity retention rate, leading to a low cycle capacity retention rate. Furthermore, the low capacity of lithium manganese oxide reduced the capacity of the lithium nickel manganese oxide cathode material.

[0146] In Comparative Example 1, no sodium hydroxide was added to the alkaline washing solution; only tetramethylammonium hydroxide, a quaternary ammonium base, was included. As a result, the crystal structure of the lithium nickel manganese oxide precursor remained very stable during the alkaline washing process, and no phase transition occurred. Consequently, the resulting lithium nickel manganese oxide cathode material did not contain lithium manganese oxide. Although this could significantly improve the electronic conductivity and capacity of the lithium nickel manganese oxide cathode material, its excellent surface activity led to violent side reactions with the electrolyte, resulting in rapid capacity decay and ultimately a decrease in its cycle capacity retention.

[0147] In Comparative Example 2, the alkaline washing solution did not contain quaternary ammonium alkali, only sodium hydroxide. This resulted in instability in the crystal structure of the lithium nickel manganese oxide precursor during the alkaline washing process. Too much lithium nickel manganese oxide precursor underwent a phase transition, leading to an excessive amount of lithium manganese oxide in the final lithium nickel manganese oxide cathode material. This excessive lithium manganese oxide layer limited the battery's capacity, causing rapid capacity decay after a certain number of cycles, thus failing to effectively improve cycle capacity retention. See also... Figure 2 As shown, actual testing revealed that after 60 cycles, the battery experienced rapid capacity decay and the cycle capacity retention rate could not be effectively improved. Furthermore, an excessively thick lithium manganese oxide layer significantly reduces the electronic conductivity and capacity of the lithium nickel manganese oxide cathode material.

[0148] In Comparative Example 3, the quaternary ammonium base was replaced with trimethylammonium. Because the nitrogen atoms in trimethylammonium have a relatively weaker complexing ability compared to the quaternary ammonium base, the crystal structure of the precursor is less stable, resulting in a higher amount of lithium manganese oxide produced and reducing its capacity. Furthermore, because trimethylammonium is less basic than the quaternary ammonium base, the cleaning effect is poor.

[0149] In Comparative Example 4, the quaternary ammonium base was replaced with dimethylammonium. Because the nitrogen atoms in dimethylammonium have a weaker complexing ability than those in the quaternary ammonium base, the crystal structure of the precursor is unstable, resulting in a higher amount of lithium manganese oxide formed and a reduced capacity. Furthermore, the lower alkalinity of dimethylammonium compared to the quaternary ammonium base leads to poor cleaning performance.

[0150] In Comparative Example 5, the quaternary ammonium base was replaced with ammonium methylbenzene. Because the nitrogen atoms in ammonium methylbenzene have a weaker complexing ability than those in the quaternary ammonium base, the crystal structure of the precursor is very unstable, resulting in a large amount of lithium manganate being generated, thus reducing its capacity. Furthermore, because ammonium methylbenzene is less basic than the quaternary ammonium base, the cleaning effect is poor.

[0151] In summary, the alkaline washing solution, cathode material, preparation method, and battery provided in this application include a quaternary ammonium alkali and sodium hydroxide in the alkaline washing solution. Adding the quaternary ammonium alkali can improve the structural stability of the lithium nickel manganese oxide precursor and remove SO4 from the crystals of the lithium nickel manganese oxide precursor. 2- This effectively cleans the lithium nickel manganese oxide precursor, preventing it from reacting during alkaline washing and forming impurity phases, thus improving the capacity and electronic conductivity of the final lithium nickel manganese oxide cathode material. Adding sodium hydroxide further removes SO42- present within the crystals of the lithium nickel manganese oxide precursor. 2-Meanwhile, during sodium hydroxide alkaline washing, some lithium nickel manganese oxide precursors undergo phase transformation under the high-temperature, strongly alkaline environment of alkaline washing, which in turn forms impurity phases Mn2O3 / Mn3O4 in subsequent processes such as drying. These impurity phases remain in the lithium nickel manganese oxide precursor. In the subsequent calcination process using the lithium nickel manganese oxide precursor and lithium source, these impurity phases react with the lithium source, ultimately generating a lithium manganese oxide layer coating the surface of the lithium nickel manganese oxide cathode material particles. This can greatly reduce the surface activity of the lithium nickel manganese oxide cathode material, reduce the side reactions between it and the electrolyte, thereby avoiding rapid capacity decay and improving its cycle capacity retention rate.

[0152] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0153] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. An alkaline washing solution, characterized in that, The alkaline washing solution includes quaternary ammonium alkali and sodium hydroxide.

2. The alkaline washing solution according to claim 1, characterized in that, The molar ratio of sodium hydroxide to the quaternary ammonium base is (0.5-4):

1.

3. The alkaline washing solution according to claim 1, characterized in that, The quaternary ammonium base is at least one of tetramethylammonium hydroxide, trimethyl-ethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

4. The alkaline washing solution according to claim 1, characterized in that, The concentration of the alkaline washing solution is 1–5 mol / L.

5. A method for preparing a lithium nickel manganese oxide cathode material, characterized in that, include, The lithium nickel manganese oxide precursor was cleaned using the alkaline cleaning solution as described in any one of claims 1 to 4 as the cleaning agent. The cleaned lithium nickel manganese oxide precursor was mixed with a lithium source and calcined to prepare lithium nickel manganese oxide cathode material.

6. The preparation method according to claim 5, characterized in that, In the alkaline washing solution, the ratio of the amount of quaternary ammonium base to the mass of the lithium nickel manganese oxide precursor is (6-20) mol: 1 kg.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the lithium nickel manganese oxide precursor to the lithium source is 1:(0.49 to 0.55).

8. A lithium nickel manganese oxide cathode material, characterized in that, The lithium nickel manganese oxide cathode material includes lithium nickel manganese oxide particles and a lithium manganese oxide layer coating the outside of the lithium nickel manganese oxide particles.

9. The lithium nickel manganese oxide cathode material according to claim 8, characterized in that, The thickness of the lithium manganese oxide layer is 1–10 nm.

10. A battery, characterized in that, This includes lithium nickel manganese oxide cathode materials prepared by any one of the preparation methods of claims 5 to 7, or lithium nickel manganese oxide cathode materials as described in any one of claims 8 to 9.

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