A lithium-sodium composite lithium-rich manganese-based cathode material, its preparation method and application

Abstract

This invention relates to the field of battery technology, and discloses a lithium-sodium composite lithium-rich manganese-based cathode material, its preparation method, and its applications. The preparation method includes: grinding and mixing a lithium source, a sodium source, a dopant, a nickel-manganese hydroxide precursor, and water to obtain a slurry; drying the slurry; and performing a first sintering to obtain a first-sintered product; reacting the first-sintered product in a weakly acidic salt solution with a pH of 2-4 to construct surface defects, followed by washing, filtration, and drying to obtain a dried product; and uniformly mixing the dried product with an oxide containing oxygen vacancies and performing a second sintering to form a double-layer coating of spinel phase and oxide, thereby obtaining the lithium-sodium composite lithium-rich manganese-based cathode material. The oxide containing oxygen vacancies includes one or more of CeO2, TiO2, La2O3, Y2O3, Co3O4, and perovskite. This invention features simple steps, low cost, and the prepared cathode material exhibits good electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a lithium-sodium composite lithium-rich manganese-based cathode material, its preparation method, and its application. Background Technology

[0002] Against the backdrop of rising fossil fuel prices and environmental pollution, clean energy has been vigorously developed; however, due to the generally high price of new energy vehicles, their adoption rate is not as high as that of traditional vehicles; reducing the watt-hour cost of batteries while increasing energy density is the key to development.

[0003] Layered lithium-rich manganese-based cathode materials are considered promising cathode materials for lithium-ion batteries due to their high capacity (>200mAh / g) and high energy density. Compared with other ternary materials, they use manganese, which is relatively inexpensive, as the main element, and require less of the more expensive metal elements such as nickel and cobalt, making their cost comparable to lithium iron phosphate. However, their over-lithiation characteristics require the addition of more lithium during the synthesis process, which increases the cost.

[0004] To further reduce costs, sodium, which is cheaper, more abundant, and more evenly distributed, is gaining increasing attention. Lithium and sodium share similar properties, with a standard electrode potential difference of only 0.3V and similar electrochemical mechanisms. Many electrode materials with similar structures can be used in both sodium-ion and lithium-ion batteries, thus sodium can partially replace lithium in lithium-ion batteries. However, because the ionic radius of sodium ions (0.113 nm) is larger than that of lithium ions (0.076 nm), sodium ions have difficulty diffusing into the material during solid-state sintering and instead accumulate on the material surface, resulting in excessively high residual alkali and reduced reversible specific capacity.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-sodium composite lithium-rich manganese-based cathode material, its preparation method, and its application.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing a lithium-sodium composite lithium-rich manganese-based cathode material, comprising:

[0009] The lithium source, sodium source, dopant, nickel manganese hydroxide precursor and water are ground and mixed to obtain a slurry. The slurry is dried and then sintered for the first time to obtain a first-sintered product.

[0010] The calcined product was placed in a weakly acidic salt solution with a pH of 2-4 to react and construct surface defects. Then, it was washed, filtered, and dried to obtain the dried product.

[0011] The dried product is mixed evenly with an oxide containing oxygen vacancies and then sintered a second time to form a double-layer coating of spinel phase and oxide, thereby obtaining a lithium-sodium composite lithium-rich manganese-based cathode material. The oxide containing oxygen vacancies includes one or more of CeO2, TiO2, La2O3, Y2O3, Co3O4 and perovskite.

[0012] In an optional embodiment, the ratio of the total molar amount of lithium sodium to the molar amount of the nickel manganese hydroxide precursor is 1.1 to 1.5:1;

[0013] And / or, the molar ratio of sodium to sodium lithium is 0.09 to 0.25:1;

[0014] And / or, the mass of the dopant is 0.1% to 0.5% of the mass of the nickel manganese hydroxide precursor;

[0015] And / or, the water-to-material ratio during grinding and mixing is 2 to 3:1, the grinding speed during grinding and mixing is 1500 to 3500 r / min, and the grinding and mixing time is 60 to 150 min.

[0016] In an optional embodiment, the concentration of the weakly acidic salt solution is 0.1–1 mol / L;

[0017] And / or, the weakly acidic salt solution is one or more of hydrogen phosphate, Al2(SO4)3, AlCl3 and NH4F;

[0018] And / or, the reaction time of the calcined product with the weakly acidic salt solution is 10 to 30 minutes.

[0019] In an optional embodiment, the mass of the oxide containing oxygen vacancies is 0.1% to 1% of the mass of the dried product;

[0020] And / or, the second sintering is carried out in an air atmosphere, at a sintering temperature of 400–700°C, and for a sintering time of 4–10 h.

[0021] In an optional embodiment, the lithium source is one or more of Li2CO3, LiOH, and LiCl;

[0022] And / or, the sodium source is one or more of Na2CO3, NaHCO3, NaCOOH, CH3COONa, CH3CH2COONa, and Na2C2O4;

[0023] And / or, the dopant is one or more of Nb, W, Mo, F, P, and Al.

[0024] In an optional embodiment, the first sintering is a two-stage sintering. The first stage sintering temperature is 500-700℃, the heating rate is 2-5℃ / min, and the holding time is 1-5h. The second stage sintering temperature is 850-1000℃, and the holding time is 10-20h. Both stages are carried out in an air atmosphere.

[0025] In an optional embodiment, the nickel-manganese hydroxide precursor is Ni x Mn 1-x (OH)₂, where 0.25 ≤ x ≤ 0.4;

[0026] Preferably, the nickel-manganese hydroxide precursor is prepared by a co-precipitation method.

[0027] Secondly, the present invention provides a lithium-sodium composite lithium-rich manganese-based cathode material, which is prepared by the preparation method of lithium-sodium composite lithium-rich manganese-based cathode material as described in any of the foregoing embodiments.

[0028] Thirdly, the present invention provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on the positive current collector, wherein the positive electrode film layer includes a lithium-sodium composite lithium-rich manganese-based positive electrode material as described in the foregoing embodiments.

[0029] Fourthly, the present invention provides the application of the lithium-sodium composite lithium-rich manganese-based cathode material as described in the foregoing embodiments or the cathode sheet as described in the foregoing embodiments in the preparation of batteries.

[0030] The present invention has the following beneficial effects:

[0031] The present invention provides a method for preparing lithium-sodium composite lithium-rich manganese-based cathode materials. By introducing sodium to replace lithium, the material cost is reduced. This process forms a P2 phase, increasing the intergranular spacing and stabilizing the material structure and improving its bulk dynamics. Simultaneously, the introduction of sodium stabilizes the structure and increases the lithium-ion transport rate. By milling, the larger, higher-melting-point sodium and lithium sources are uniformly mixed, reducing both particle size and melting point. This ensures the diffusion of lithium and sodium ions into the material during sintering, while mitigating the problem of large Na ions being difficult to penetrate the bulk phase, thus reducing residual lithium on the surface. This also prevents Na accumulation on the surface of the first-burned product, reducing residual alkali on the surface. Furthermore, the present invention uses a strong acid-weak base salt to promote the ionization of sodium salts that have not entered the bulk phase, reducing residual lithium. Simultaneously, the weakly acidic H... +The substitution of surface Li to form vacancies promotes lithium-ion transport and activates Li₂MnO₃ to increase its capacity. Subsequently, the dried product is blended with an oxygen-vacancy-containing coating and then sintered a second time. During the sintering process, surface defects are transformed into a spinel phase, forming a spinel phase coating layer. At the same time, oxides form an oxygen-vacancy-containing coating layer on the surface of the spinel phase coating layer, thus forming a double coating of spinel phase and oxide. The structure of spinel is beneficial to improving lithium-ion conduction, and the coating of oxygen-vacancy-containing materials is beneficial to capturing oxygen spilled during the electrochemical process, improving oxygen reversibility, and stabilizing the structure, thereby achieving the purpose of improving material performance. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a SEM image of the lithium-sodium composite lithium-rich manganese-based cathode material provided in Example 1 of this application;

[0034] Figure 2 This is an SEM image of the calcined product obtained in step S2 of Embodiment 1 of this application;

[0035] Figure 3 SEM image of the calcined product obtained in step S2 of Comparative Example 1 of this application;

[0036] Figure 4 This is a SEM image of the lithium-sodium composite lithium-rich manganese-based cathode material obtained in Comparative Example 3 of this application;

[0037] Figure 5 This is a TEM image of the lithium-sodium composite lithium-rich manganese-based cathode material obtained in Comparative Example 3 of this application;

[0038] Figure 6 This is a SEM image of the lithium-sodium composite lithium-rich manganese-based cathode material obtained in Comparative Example 4 of this application;

[0039] Figure 7 This is a TEM image of the lithium-sodium composite lithium-rich manganese-based cathode material obtained in Comparative Example 4 of this application;

[0040] Figure 8 The XPS O1s spectra of the lithium-sodium composite lithium-rich manganese-based cathode materials obtained in Example 1 and Comparative Example 5 of this application are shown. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0042] This invention provides a method for preparing a lithium-sodium composite lithium-rich manganese-based cathode material, comprising:

[0043] The lithium source, sodium source, dopant, nickel manganese hydroxide precursor and water are ground and mixed to obtain a slurry. The slurry is dried and then sintered for the first time to obtain the first-sintered product.

[0044] The product was placed in a weakly acidic salt solution to react and construct surface defects. Then it was washed, filtered and dried to obtain the dried product.

[0045] After the dried product is mixed evenly with oxides containing oxygen vacancies, a second sintering is performed to form a double-layer coating of spinel phase and oxide, thus obtaining lithium sodium composite lithium-rich manganese-based cathode material.

[0046] The present invention provides a method for preparing a lithium-sodium composite lithium-rich manganese-based cathode material. After preparing a nickel-manganese hydroxide precursor, the precursor is milled with a sodium source, a lithium source, and a dopant, followed by sintering. The method utilizes low-cost sodium salt to replace part of the lithium source, forming a P2 phase to increase intergranular spacing, thereby stabilizing the material structure and improving its bulk dynamics. Milling ensures uniform mixing of the larger-particle, higher-melting-point sodium and lithium sources, simultaneously reducing particle size and melting point. This guarantees the diffusion of lithium and sodium ions into the material during sintering, preventing accumulation on the surface of the first-burned product and reducing residual alkali. Then, the first-burned product is acid-washed in a weakly acidic salt solution. The weak acidity promotes the dissolution of unreacted residual sodium, while H... + With the surface Li + The process involves substitution to form transition metals and lithium defects, which increase the diffusion rate of lithium ions and activate Li2MnO3. Subsequently, the dried product is blended with an oxygen-vacancy coating and then sintered a second time. During the sintering process, surface defects are transformed into a spinel phase, forming a spinel phase coating layer. At the same time, oxides form an oxygen-vacancy coating layer on the surface of the spinel phase coating layer, thus forming a double coating of spinel phase and oxides, thereby achieving the purpose of improving material performance.

[0047] Specifically, the preparation method of the present invention includes the following steps:

[0048] S1. Preparation of nickel manganese hydroxide precursor.

[0049] Nickel-manganese hydroxide precursors were prepared by a co-precipitation method. The nickel-manganese hydroxide precursor was Ni.x Mn 1-x (OH)2, where 0.25≤x≤0.4.

[0050] The specific operation method of co-precipitation in this invention is a conventional method. No specific limitations are imposed in this invention. The specific preparation parameters and conditions can be referred to conventional techniques, and will not be elaborated in this invention.

[0051] S2. Preparation of the calcined product.

[0052] The lithium source, sodium source, dopant, nickel-manganese hydroxide precursor, and water were ground and mixed. The molar ratio of total lithium and sodium to nickel-manganese hydroxide precursor was 1.1–1.5:1; the molar ratio of sodium to lithium and sodium was 0.09–0.25:1; and the mass of the dopant was 0.1%–0.5% of the mass of the nickel-manganese hydroxide precursor. The water-to-material ratio during grinding and mixing was 2–3:1, the grinding speed was 1500–3500 r / min, and the grinding and mixing time was 60–150 min.

[0053] In some embodiments, the molar ratio of total lithium-sodium content to the nickel-manganese hydroxide precursor is a range of 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1, or 1.5:1. The molar ratio of sodium to lithium-sodium can, for example, be a range of 0.09:1, 0.10:1, 0.13:1, 0.15:1, 0.18:1, 0.20:1, 0.22:1, or 0.25:1. The mass of the dopant is a range of 0.1%, 0.2%, 0.3%, 0.4%, or 0.5% of the nickel-manganese hydroxide precursor mass.

[0054] In some embodiments, the water-to-material ratio during grinding and mixing is any one of 2:1, 2.5:1, 3:1, or any combination thereof. The grinding speed during grinding and mixing is, for example, any one of 1500 r / min, 1800 r / min, 2000 r / min, 2200 r / min, 2500 r / min, 2800 r / min, 3500 r / min, or any combination thereof. The grinding and mixing time is any one of 60 min, 90 min, 120 min, 150 min, or any combination thereof.

[0055] The lithium source includes, but is not limited to, one or more of Li₂CO₃, LiOH, and LiCl; the sodium source includes, but is not limited to, one or more of Na₂CO₃, NaHCO₃, NaCOOH, CH₃COONa, CH₃CH₂COONa, and Na₂C₂O₄; and the dopant includes, but is not limited to, one or more of Nb, W, Mo, F, P, and Al. The addition of dopant can improve the crystal structure, surface electronic structure, and ionic conductivity of the material, thereby improving the battery's energy storage capacity, cycle life, and safety performance.

[0056] The slurry was spray-dried and granulated at 180–280℃, and then sintered for the first time to obtain the first-stage product. The first sintering was a two-stage sintering process. The first stage sintering temperature was 500–700℃, the heating rate was 2–5℃ / min, and the holding time was 1–5h. The second stage sintering temperature was 850–1000℃, and the holding time was 10–20h. Both stages were carried out in an air atmosphere.

[0057] In this invention, a two-stage calcination process is used to preheat the material at a low temperature to melt the nano-source and lithium source, making it easier for the nano-source and lithium source to penetrate into the material. Then, a second stage of high-temperature sintering is carried out to form a first-stage calcination product.

[0058] The sintering temperature for the first stage can be, for example, any one or a range between 500℃, 550℃, 600℃, 650℃, and 700℃. The heating rate can be, for example, any one or a range between 2℃ / min, 3℃ / min, 4℃ / min, and 5℃ / min. The holding time can be, for example, any one or a range between 1h, 2h, 3h, 4h, and 5h. The sintering temperature for the second stage can be, for example, any one or a range between 850℃, 900℃, 950℃, and 1000℃. The holding time can be, for example, any one or a range between 10h, 12h, 15h, 16h, 18h, and 20h.

[0059] S3. Prepare the dried product.

[0060] The calcined product was placed in a weakly acidic salt solution and reacted for 10–30 min to construct surface defects. Then, it was washed with deionized water until the pH of the filtrate was neutral. The product was then filtered and dried at 60–80 °C for 12–24 h to obtain the dried product.

[0061] The concentration of the weak acid salt solution is 0.1–1 mol / L. In this invention, the weak acid salt solution is selected from strong acid-weak base salts. Strong acid-weak base salts are salts formed by the reaction of an acid and a weak base, and they are weakly acidic. In this invention, strong acid-weak base salts are selected as weak acid salt solutions because they can utilize the metal ions, such as P and Al, in the weak acid salt solution. These metal ions can replace the Na ions on the surface of the calcined product, thereby loading a small amount of metal ions to improve the performance of the material.

[0062] Specifically, the pH of the weakly acidic salt solution is 2 to 4; the weakly acidic salt solution includes, but is not limited to, one or more of hydrogen phosphate, Al2(SO4)3, AlCl3 and NH4F.

[0063] In some embodiments, the concentration of the weakly acidic salt solution can be, for example, any one of 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, or 1 mol / L, or a range between any two. This invention has found that when the concentration of the weakly acidic salt solution is too low, it cannot effectively remove impurities through acid washing, and a certain amount of sodium carbonate will remain on the surface of the calcined product. Conversely, when the concentration of the weakly acidic salt solution is too high, the pH of the solution is below 2, resulting in excessive acidity and a significant decrease in capacity after acid washing. S4. Preparation of lithium-sodium composite lithium-rich manganese-based cathode material.

[0064] After the dried product is mixed evenly with oxides containing oxygen vacancies, a second sintering is performed to form a double-layer coating of spinel phase and oxide, thus obtaining lithium sodium composite lithium-rich manganese-based cathode material.

[0065] The oxides containing oxygen vacancies include one or more of CeO2, TiO2, La2O3, Y2O3, Co3O4, and perovskites; the mass of the oxides containing oxygen vacancies is 0.1% to 1% of the mass of the dried product. In this invention, the oxides containing oxygen vacancies can capture oxygen spilled during the electrochemical process, which is beneficial to improving oxygen reversibility and stabilizing the structure. The choice of the main element (e.g., Ce, Ti, La, Y, Co) of the oxides containing oxygen vacancies has a significant impact on the material's capacity. Ce, Ti, La, Y, and Co can be inserted into the material without damaging its cycling performance, while other oxides containing oxygen vacancies may either be unable to insert or may damage the material's cycling performance. Therefore, not all oxides containing oxygen vacancies can achieve high capacity and stable structure.

[0066] The second sintering is carried out in an air atmosphere at a temperature of 400–700°C for 4–10 hours. In some embodiments, the sintering temperature can be any one or a range between 400°C, 500°C, 600°C, and 700°C, and the sintering time can be any one or a range between 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, and 10 hours.

[0067] The lithium-sodium composite lithium-rich manganese-based cathode material prepared by the above-described method in this invention exhibits high capacity and structural stability. It can be widely used in battery manufacturing.

[0068] Correspondingly, the present invention provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on the positive current collector, wherein the positive electrode film layer comprises the aforementioned lithium-sodium composite lithium-rich manganese-based positive electrode material. This positive electrode sheet can also be widely used in the preparation of batteries.

[0069] In addition, the present invention also provides a battery comprising the above-mentioned positive electrode plate. The battery in the present invention can be a sodium-ion battery and / or a lithium-ion battery, and has a wide range of applications.

[0070] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0071] Example 1

[0072] This embodiment provides a method for preparing a lithium-sodium composite lithium-rich manganese-based cathode material, which includes the following steps:

[0073] S1. A ternary solution is obtained by mixing a nickel source, a cobalt source, and a manganese source. The ternary solution, liquid alkali, and ammonia are added to the bottom solution in parallel to carry out a co-precipitation reaction to obtain precursor particles.

[0074] S2. Disperse sodium carbonate, lithium carbonate, niobium oxide, and the precursor in water. The total molar ratio of lithium and sodium to the precursor is 1.35:1, and the molar ratio of sodium to lithium and sodium is 0.15:1. Mix them uniformly at a water-to-material ratio of 2:1. Mill the mixture at 2000 r / min for 60 min. Dry the mixture at 260℃. Place the mixture in an air atmosphere and sinter at 500℃ for 5 h, then sinter at 950℃ for 10 h. Finally, pass the sintered material through a 300-mesh sieve to obtain the first-stage product.

[0075] S3. The product was acid-washed with aluminum chloride at a water-to-material ratio of 2:1, a salt solution concentration of 0.5 mol / L, a solution pH of 2.5, a reaction time of 30 min, and a stirring speed of 300 r / min. After filtration, the product was washed with deionized water until the pH of the filtrate was neutral, and then dried at 80℃ for 12 h to obtain the dried product.

[0076] S4. The dried product is mixed uniformly with an oxide containing oxygen vacancies (CeO2), with the oxide coating amount being 0.3% of the dried product. A second sintering is then performed at 500°C in air for 6 hours to obtain a lithium-sodium composite lithium-rich manganese-based cathode material. (Please refer to...) Figure 1 ,from Figure 1 It can be seen that after sanding and pickling, there is no obvious residual sodium carbonate on the surface of the material.

[0077] Example 2

[0078] This embodiment provides a method for preparing a lithium-sodium composite lithium-rich manganese-based cathode material, which includes the following steps:

[0079] S1. A ternary solution is obtained by mixing a nickel source, a cobalt source, and a manganese source. The ternary solution, liquid alkali, and ammonia are added to the bottom solution in parallel to carry out a co-precipitation reaction to obtain precursor particles.

[0080] S2. Disperse sodium carbonate, lithium carbonate, niobium oxide, and the precursor in water. The molar ratio of total lithium and sodium to the precursor is 1.1:1, and the molar ratio of sodium to lithium and sodium is 0.09:1. Mix them uniformly at a water-to-material ratio of 3:1. Mill the mixture at 1500 r / min for 150 min. Dry the mixture at 180℃. Place the mixture in an air atmosphere and sinter at 600℃ for 3 h, followed by sintering at 850℃ for 20 h. Then, pass the sintered material through a 300-mesh sieve to obtain the first-stage product.

[0081] S3. The product was acid-washed with ammonium hydrogen phosphate at a water-to-material ratio of 2:1, a salt solution concentration of 0.1 mol / L, a solution pH of 4, a reaction time of 30 min, and a stirring speed of 300 r / min. After filtration, the product was washed with deionized water until the pH of the filtrate was neutral, and then dried at 60℃ for 24 h to obtain the dried product.

[0082] S4. The dried product is mixed evenly with oxides containing oxygen vacancies (TiO2), with the coating amount of the oxides containing oxygen vacancies being 0.1% of the dried product. The mixture is then sintered for a second time at 400°C in air for 10 hours to obtain a lithium-sodium composite lithium-rich manganese-based cathode material.

[0083] Example 3

[0084] This embodiment provides a method for preparing a lithium-sodium composite lithium-rich manganese-based cathode material, which includes the following steps:

[0085] S1. A ternary solution is obtained by mixing a nickel source, a cobalt source, and a manganese source. The ternary solution, liquid alkali, and ammonia are added to the bottom solution in parallel to carry out a co-precipitation reaction to obtain precursor particles.

[0086] S2. Disperse sodium carbonate, lithium carbonate, niobium oxide, and the precursor in water. The total molar ratio of lithium and sodium to the precursor is 1.5:1, and the molar ratio of sodium to lithium and sodium is 0.25:1. Mix them uniformly at a water-to-material ratio of 2.5:1. Mill the mixture at 3000 r / min for 60 min. Dry the mixture at 280℃. Place the mixture in an air atmosphere and sinter at 700℃ for 1 h, then sinter at 1000℃ for 15 h. Finally, pass the sintered material through a 300-mesh sieve to obtain the first-stage product.

[0087] S3. The product was acid-washed with Al2(SO4)3 at a water-to-material ratio of 2:1, with a salt solution concentration of 1 mol / L, a solution pH of 3, a reaction time of 10 min, and a stirring speed of 300 r / min. After filtration, the product was washed with deionized water until the pH of the filtrate was neutral, and then dried at 70℃ for 18 h to obtain the dried product.

[0088] S4. The dried product is mixed evenly with oxides containing oxygen vacancies (a 1:1 mixture of La2O3 and Y2O3), with the coating amount of the oxides containing oxygen vacancies being 1% of the dried product. The mixture is then sintered for a second time at 700°C in air for 4 hours to obtain a lithium-sodium composite lithium-rich manganese-based cathode material.

[0089] Comparative Example 1

[0090] This comparative example is basically the same as Example 1, except that in this comparative example, the lithium source, sodium source, dopant and precursor are not subjected to sand milling treatment, and the precursor is directly mixed with lithium salt.

[0091] Specifically, step S2 includes: mixing sodium carbonate, lithium carbonate, niobium oxide, and the precursor evenly, with the total molar ratio of lithium and sodium to the precursor being 1.35:1 and the molar ratio of sodium to lithium and sodium being 0.15:1; placing the mixture in an air atmosphere and sintering it at 500°C for 5 hours, followed by sintering at 950°C for 10 hours; and then passing the sintered material through a 300-mesh sieve to obtain a sintered product.

[0092] Comparative Example 2

[0093] This comparative example is basically the same as Example 1, except that in this comparative example, step S3 is not acid washing, but only conventional water washing, and the other steps are the same as in Example 1.

[0094] Specifically, step S3 includes: washing the calcined product with water at a water-to-material ratio of 2:1, a reaction time of 30 min, a stirring speed of 300 r / min, filtering, washing with deionized water until the pH of the filtrate is neutral, and drying at 80°C for 12 h to obtain the dried product.

[0095] Comparative Example 3

[0096] This comparative example is basically the same as Example 1, except that in this comparative example, step S4 does not cover the oxide containing oxygen vacancies, and the dried product is directly sintered for the second time. The remaining steps are the same as in Example 1.

[0097] Specifically, step S4 includes: sintering the dried product for a second time at 500°C in air for 6 hours to obtain a lithium-sodium composite lithium-rich manganese-based cathode material.

[0098] Comparative Example 4

[0099] This comparative example is basically the same as Example 1, except that in this comparative example, step S3 is not acid washing, but only conventional water washing, and step S4 does not cover the oxide containing oxygen vacancies, but directly performs a second sintering on the dried product. The remaining steps are the same as in Example 1.

[0100] Specifically, step S3 includes: washing the calcined product with water at a water-to-material ratio of 2:1, a reaction time of 30 min, a stirring speed of 300 r / min, filtering, washing with deionized water until the pH of the filtrate is neutral, and drying at 80°C for 12 h to obtain the dried product.

[0101] Step S4 includes: subjecting the dried product to a second sintering at 500°C in air for 6 hours to obtain a lithium-sodium composite lithium-rich manganese-based cathode material.

[0102] Comparative Example 5

[0103] This comparative example is basically the same as Example 1, except that in this comparative example, step S4 does not cover the oxide containing oxygen vacancies, but covers the conventional fluoride. The remaining steps are the same as in Example 1.

[0104] Specifically, step S4 includes: mixing the dried product with fluoride (CeF4) evenly, with the fluoride coating amount being 0.3% of the dried product, and performing a second sintering at 500°C in air for 6 hours to obtain a lithium-sodium composite lithium-rich manganese-based cathode material.

[0105] Comparative Example 6

[0106] This comparative example is basically the same as Example 1, except that in this comparative example, step S4 does not cover the oxide containing oxygen vacancies, but covers CuO containing oxygen vacancies. The remaining steps are the same as in Example 1.

[0107] Specifically, step S4 includes: mixing the dried product with an oxide (CuO) containing oxygen vacancies evenly, with the fluoride coating amount being 0.3% of the dried product, and performing a second sintering at 500°C in air for 6 hours to obtain a lithium-sodium composite lithium-rich manganese-based cathode material.

[0108] Comparative Example 7

[0109] This comparative example is basically the same as Example 1, except that the salt solution concentration in step S3 of this comparative example is 1.2 mol / L, and the other steps are the same as in Example 1.

[0110] Specifically, step S3 includes: acid washing the calcined product with aluminum chloride at a water-to-material ratio of 2:1, a salt solution concentration of 1.2 mol / L, a solution pH of 1.2, a reaction time of 30 min, a stirring speed of 300 r / min, filtration, washing with deionized water until the pH of the filtrate is neutral, and drying at 80℃ for 12 h to obtain the dried product.

[0111] Comparative Example 8

[0112] This comparative example is basically the same as Example 1, except that the salt solution in step S3 of this comparative example is ammonium nitrate, and the other steps are the same as in Example 1.

[0113] Specifically, step S3 includes: acid washing the calcined product with ammonium nitrate, with a water-to-material ratio of 2:1, a salt solution concentration of 0.5 mol / L, a solution pH of 5.5, a reaction time of 30 min, a stirring speed of 300 r / min, filtration, washing with deionized water until the pH of the filtrate is neutral, and drying at 80℃ for 12 h to obtain the dried product.

[0114] Comparative Example 9

[0115] This comparative example is basically the same as Example 1, except that the acid used in step S3 of this comparative example is hydrochloric acid with a concentration of 0.01 mol / L and a solution pH of 2.5.

[0116] Comparative Example 10

[0117] This comparative example is basically the same as Example 1, except that in this comparative example, the coating amount of the oxide containing oxygen vacancies in step S4 is 2% of the dried product.

[0118] Experimental Example 1: Material Characterization

[0119] SEM images of the calcined product of Example 1 and the calcined product of Comparative Example 1 are shown below. Figure 2 and Figure 3 As shown, the calcined product of Comparative Example 1 has more impurities on its surface compared to the calcined product of Example 1, indicating that more sodium carbonate remains on the surface and has not entered the bulk phase. The comparison reveals that sand milling can significantly promote the uniform incorporation of sodium doping into the bulk phase and reduce residual lithium on the surface.

[0120] Please refer to the SEM images of Comparative Examples 3 and 4 for Example 1. Figure 4 and Figure 6 Please refer to the TEM image. Figure 5 and Figure 7As can be seen from the comparison, the water washing method in Comparative Example 4 can remove most of the surface impurities, but some are still coated on the surface and are not easy to remove. In Comparative Example 3, after adding a weak acid, due to the ionization equilibrium, the undissolved sodium carbonate on the surface can dissolve in water and clean the surface.

[0121] Experimental Example 2: Electrical Performance

[0122] The lithium-sodium composite lithium-rich manganese-based cathode materials prepared in Examples 1-3 and Comparative Examples 1-8 were subjected to electrical performance tests. The test results are shown in Table 1.

[0123] Table 1. Statistical table of electrical performance tests for different examples

[0124]

[0125] As can be seen from the table above, Comparative Example 2 did not use acid washing, but only water washing. In this case, water washing can remove most of the surface impurities, but some are still coated on the surface and are not easy to remove. As a result, the first-time efficiency, rate capability, and cycle retention of the material are significantly lower than those of Example 1. After weak acid washing, metal atoms or oxygen atoms are missing. The surface of the manganese-rich material has more spinel layers and rock salt phases, which improves the surface stability and can greatly improve the reversible capacity of the material. The cycle data also proves this conclusion. After the surface is constructed with spinel, the cycle capability is significantly improved, which in turn improves the rate capability and cycle retention, which are significantly lower than those of Example 1. In contrast, Comparative Example 3 did not have oxide coating with oxygen vacancies. It can be seen that its first-time efficiency is slightly higher than that of Example 1, but its rate capability and cycle retention are significantly lower than those of Example 1. This is because the oxide coating on the surface of Example 1 forms an oxygen-vacancy coating layer, which is conducive to improving the ion diffusion rate between lithium-rich manganese-based cathode materials, effectively improving the capacity of the lithium-rich manganese cathode material, and at the same time improving the rate capability. In Comparative Example 4, neither acid washing nor coating of oxides containing oxygen vacancies was performed. The effect was significantly lower than in Example 1, and also lower than in Comparative Examples 2 and 3, fully demonstrating the synergistic effect of acid washing and coating of oxides containing oxygen vacancies. In Comparative Example 5, conventional fluorides were coated. The O1s plots of Comparative Example 5 and Example 1 (…) Figure 8It can be seen that coating with oxygen-containing vacancies significantly increases the number of oxygen vacancies on the surface. Combined with the cycling data, the introduction of oxygen vacancies improves structural stability and stabilizes the structural phase transition during cycling. Other fluorides cannot achieve similar results. In Comparative Example 6, other oxygen-containing oxides, such as CuO, are coated. It can be seen that the main element Cu in these oxides affects the capacity of the system, resulting in an effect even lower than that of Comparative Example 5. In Comparative Example 7, the concentration of the weakly acidic salt solution used for pickling is too high, resulting in a pH of 1.2, which is highly acidic and significantly reduces the capacity. In Comparative Example 8, other salts are used as the pickling solution. In this case, the pH is high (5.5), which does not achieve the desired pickling effect. Therefore, a strong acid-weak base salt with a specific high acidity is required. Comparative Example 9 used a strong acid with a pH of 2.5. Its performance was still lower than that of Example 1. The reason for this is that although the pH of Comparative Example 9 was the same as that of Example 1, the aluminum chloride in Example 1 contained metal ions. During the pickling process, these metal ions replaced the Na ions on the surface of the calcined product, thus loading a small amount of metal ions to improve the material's performance. In Comparative Example 10, the coating of oxides containing oxygen vacancies was relatively large, which led to a decrease in the material's conductivity, hindered lithium-ion transport, and deteriorated electrical performance.

[0126] In summary, the method for preparing lithium-sodium composite lithium-rich manganese-based cathode material provided by this invention reduces material costs by introducing Na to replace lithium, forming a P2 phase to increase intergranular spacing, thereby stabilizing the material structure and improving bulk dynamics. Simultaneously, the introduction of sodium stabilizes the structure and increases the lithium-ion transport rate. By using a sand milling process to uniformly mix the larger, higher-melting-point sodium source with the lithium source, both particle size and melting point are reduced, ensuring the diffusion of lithium and sodium ions into the material interior during sintering. This also reduces the difficulty of large Na ions entering the bulk phase, thus reducing residual lithium on the surface. It also prevents Na accumulation on the surface of the first-burned product, reducing residual alkali on the surface. Furthermore, this invention uses a strong acid-weak base salt to promote the ionization of sodium salts that have not entered the bulk phase, reducing residual lithium. Simultaneously, the weakly acidic H... + The substitution of surface Li to form vacancies promotes lithium-ion transport and activates Li₂MnO₃ to increase its capacity. Subsequently, the dried product is blended with an oxygen-vacancy-containing coating and then sintered a second time. During the sintering process, surface defects are transformed into a spinel phase, forming a spinel phase coating layer. At the same time, oxides form an oxygen-vacancy-containing coating layer on the surface of the spinel phase coating layer, thus forming a double coating of spinel phase and oxide. The structure of spinel is beneficial to improving lithium-ion conduction, and the coating of oxygen-vacancy-containing materials is beneficial to capturing oxygen spilled during the electrochemical process, improving oxygen reversibility, and stabilizing the structure, thereby achieving the purpose of improving material performance.

[0127] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-sodium composite lithium-rich manganese-based cathode material, characterized in that, It includes: The lithium source, sodium source, dopant, nickel manganese hydroxide precursor and water are ground and mixed to obtain a slurry. The slurry is dried and then sintered for the first time to obtain a first-sintered product. The calcined product was placed in a weakly acidic salt solution with a pH of 2-4 to react and construct surface defects. Then, it was washed, filtered, and dried to obtain the dried product. The dried product is mixed evenly with an oxide containing oxygen vacancies and then sintered a second time to form a double-layer coating of spinel phase and oxide, thereby obtaining a lithium-sodium composite lithium-rich manganese-based cathode material. The oxide containing oxygen vacancies includes one or more of CeO2, TiO2, La2O3, Y2O3, Co3O4 and perovskite.

2. The preparation method of the lithium-sodium composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The ratio of the total molar amount of lithium and sodium to the molar amount of the nickel-manganese hydroxide precursor is 1.1 to 1.5:1; And / or, the molar ratio of sodium to sodium lithium is 0.09 to 0.25:1; And / or, the mass of the dopant is 0.1% to 0.5% of the mass of the nickel manganese hydroxide precursor; And / or, the water-to-material ratio during grinding and mixing is 2 to 3:1, the grinding speed during grinding and mixing is 1500 to 3500 r / min, and the grinding and mixing time is 60 to 150 min.

3. The method for preparing the lithium-sodium composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The concentration of the weakly acidic salt solution is 0.1–1 mol / L; And / or, the weakly acidic salt solution is one or more of hydrogen phosphate, Al2(SO4)3, AlCl3 and NH4F; And / or, the reaction time of the calcined product with the weakly acidic salt solution is 10 to 30 minutes.

4. The preparation method of the lithium-sodium composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The mass of the oxide containing oxygen vacancies is 0.1% to 1% of the mass of the dried product; And / or, the second sintering is carried out in an air atmosphere, at a sintering temperature of 400–700°C, and for a sintering time of 4–10 h.

5. The method for preparing the lithium-sodium composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The lithium source is one or more of Li2CO3, LiOH, and LiCl; And / or, the sodium source is one or more of Na2CO3, NaHCO3, NaCOOH, CH3COONa, CH3CH2COONa, and Na2C2O4; And / or, the dopant is one or more of Nb, W, Mo, F, P, and Al.

6. The method for preparing the lithium-sodium composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The first sintering is a two-stage sintering process. The first stage sintering temperature is 500-700℃, the heating rate is 2-5℃ / min, and the holding time is 1-5h. The second stage sintering temperature is 850-1000℃, and the holding time is 10-20h. Both stages are carried out in an air atmosphere.

7. The method for preparing the lithium-sodium composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The nickel-manganese hydroxide precursor is Ni x Mn 1-x (OH)2, where 0.25≤x≤0.

4.

8. The method for preparing the lithium-sodium composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The nickel-manganese hydroxide precursor was prepared by a co-precipitation method.

9. A lithium-sodium composite lithium-rich manganese-based cathode material, characterized in that, It is prepared using the method for preparing lithium-sodium composite lithium-rich manganese-based cathode materials as described in any one of claims 1 to 8.

10. A positive electrode plate, characterized in that, It includes a positive current collector and a positive electrode film layer disposed on the positive current collector, wherein the positive electrode film layer includes the lithium-sodium composite lithium-rich manganese-based positive electrode material as described in claim 9.

11. The application of the lithium-sodium composite lithium-rich manganese-based cathode material as described in claim 9 or the cathode sheet as described in claim 10 in the preparation of batteries.

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