A lithium-rich manganese-based positive electrode material containing a spinel structure in a bulk phase and a preparation method thereof, and a lithium ion battery

Abstract

This invention provides a lithium-rich manganese-based cathode material with a spinel structure in bulk, its preparation method, and a lithium-ion battery, relating to the field of battery cathode material preparation technology. The preparation method includes weighing lithium salt in a lower-stoichiometric ratio according to the chemical formula, uniformly mixing it with a precursor, and pre-calcining it in an oxygen-containing atmosphere to obtain an intermediate product; then uniformly mixing the intermediate product with the remaining lithium salt and sintering it at high temperature in an oxygen-containing atmosphere to obtain the lithium-rich manganese-based cathode material with a spinel structure in bulk. By introducing the lithium-containing spinel structure into the primary particles, the lithium-ion transport capacity and bulk structural stability of the lithium-rich manganese-based material can be effectively improved, resulting in a significantly increased cycle life.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material preparation technology, and in particular to a lithium-rich manganese-based cathode material containing a spinel structure in bulk phase, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the development of new energy vehicles and the electrochemical energy storage industry, higher requirements have been placed on the energy density and safety of lithium-ion batteries. Cathode materials are key factors affecting the specific energy, safety, and cost of lithium batteries. Lithium-rich manganese-based cathode materials have a specific capacity exceeding 250 mAh / g, far higher than existing cathode materials on the market. Moreover, due to their high manganese content, they also have advantages such as good thermal stability and low cost, and have gradually attracted the attention of the scientific research and industrial communities.

[0003] Conventional lithium-rich manganese-based materials are composites of two types of structures: hexagonal layered LiMO2 (M represents a transition metal) and monoclinic layered Li2MnO3. The unique crystal and electronic structures give these lithium-rich materials a unique anion charge compensation effect, resulting in ultra-high specific capacity. However, this also leads to a series of problems. Specifically, the poor structural stability and low lithium-ion transport efficiency of the lithium-rich Li2MnO3 phase result in short cycle life and poor rate performance. Introducing a spinel structure can effectively improve these problems because the spinel structure has three-dimensional lithium-ion channels and good lattice matching with the bulk material. For example, Chinese patent CN116143186B discloses a surface-spinned lithium-rich manganese-based material, its preparation method, and its application. The resulting material exhibits high specific capacity, long lifespan, and excellent rate performance. Chinese patent CN107219500B discloses a method for constructing a spinel structure on the surface of a lithium-rich manganese-based cathode material, which also improves the material's rate performance. However, the above solutions only introduce spinel structures onto the material surface and cannot solve the problems of poor lithium-ion transport and structural instability in the Li2MnO3 phase of the bulk material. Chinese patent CN114497533A discloses an in-situ spinel-modified low-cobalt spherical lithium-rich manganese-based cathode material and its preparation method. By reducing the lithium content to create lithium vacancies, lithium-deficient twisted spinel is constructed in the bulk phase. The prepared cathode material exhibits excellent cycle stability, but the twisted lithium-deficient spinel has limited effect on improving rate capability, and the synthesis process is difficult to control. Chinese patent CN116143200B discloses a method for preparing a high-pressure, micron-sized single-crystal lithium-rich manganese-based cathode material. This method prepares the single-crystal lithium-rich material by stepwise addition of a lithium source and molten salt, followed by two calcinations. The main approach involves adding molten salt during the first calcination to optimize the morphology of the single-crystal particles, addressing the synthesis problem of single-crystal lithium-rich manganese-based materials. However, an additional step of washing and drying the intermediate sintering sample is required to remove molten salt impurities. Summary of the Invention

[0004] To address the above problems, this invention aims to provide a lithium-rich manganese-based cathode material with a spinel structure in its bulk phase and its preparation method. The spinel structure is introduced by low-temperature pre-sintering, which significantly improves the cycle life and rate performance of the prepared material. Furthermore, the material has a more uniform and dense primary particle distribution, a lower specific surface area, and a significantly improved compaction density.

[0005] One of the objectives of this invention is to provide a lithium-rich manganese-based cathode material containing a spinel structure in the bulk phase.

[0006] The second objective of this invention is to provide a method for preparing a lithium-rich manganese-based cathode material containing a spinel structure in the bulk phase.

[0007] A third objective of this invention is to provide a lithium-ion battery, including a lithium-rich manganese-based cathode material containing a spinel structure in its bulk phase.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] In a first aspect, the present invention provides a lithium-rich manganese-based cathode material containing a spinel structure in the bulk phase, wherein the chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, wherein M is at least two elements selected from Ni, Co, Mn, Ti, Mo, Ru and Sn, and 0.1≤x≤0.9;

[0010] The lithium-rich manganese-based cathode material consists of secondary spherical or near-spherical particles composed of primary particles with polyhedral shapes, wherein spinel structures are distributed inside the primary particles.

[0011] Those skilled in the art will know that lithium-rich materials are all layered structures.

[0012] In some embodiments, the spinel structure is a lithium-containing spinel with the molecular formula LiMn2O4 or Li4Mn5O4. 12 At least one of them.

[0013] In some embodiments, the spinel structure accounts for ≤5% of the mass of the lithium-rich manganese-based cathode material.

[0014] In some embodiments, the diameter of the primary particles is 300-600 nm, and the specific surface area of ​​the lithium-rich manganese-based cathode material is ≤1.5 m². 2 / g.

[0015] Secondly, the present invention provides a method for preparing a lithium-rich manganese-based cathode material containing a spinel structure in bulk, comprising the following steps:

[0016] (1) Dissolve the soluble metal salt in water according to the chemical formula to form metal salt solution A; dissolve the precipitant in water to form solution B;

[0017] (2) Under a protective atmosphere, solutions A and B are slowly added to the reactor to carry out a co-precipitation reaction. The precipitate is filtered, washed, and dried to obtain the precursor.

[0018] (3) Weigh the precursor and total lithium salt (100-105% of the theoretical amount based on Li) according to the chemical formula of the finished product. First, mix the precursor with lithium salt (30-60% of the total lithium salt) at a lower stoichiometric ratio and then pre-calcine it in an oxygen-containing atmosphere.

[0019] (4) Mix the remaining lithium salt evenly and sinter at high temperature in an oxygen-containing atmosphere to obtain a lithium-rich manganese-based cathode material with a spinel structure in bulk.

[0020] In some embodiments, the soluble metal salt in step (1) is one of sulfate, nitrate, oxalate or acetate, and the concentration of metal salt solution A is 1-4 mol / L; the precipitant is one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.

[0021] For example, soluble metal salts are prepared in appropriate proportions according to chemical formulas, including soluble nickel salts, soluble manganese salts, and soluble cobalt salts. The soluble nickel salts include any one or a combination of at least two of nickel sulfate, nickel acetate, nickel oxalate, or nickel nitrate; the soluble manganese salts include any one or a combination of at least two of manganese sulfate, manganese acetate, manganese oxalate, or manganese nitrate; and the soluble cobalt salts include any one or a combination of at least two of cobalt sulfate, cobalt acetate, cobalt oxalate, or cobalt nitrate.

[0022] In some embodiments, the protective atmosphere described in step (2) is nitrogen or argon;

[0023] In some implementations, the temperature of the co-precipitation reaction in step (2) is 40-70°C.

[0024] In some embodiments, the lithium salt in step (3) includes any one or a combination of at least two of lithium acetate, lithium nitrate, lithium carbonate, and lithium hydroxide;

[0025] In some embodiments, the oxygen-containing atmosphere in step (3) includes air or oxygen, or a mixture of the two in any proportion; the pre-firing temperature is 300-600°C, and the pre-firing time is 1-5 hours.

[0026] In some embodiments, the high-temperature sintering temperature in step (4) is 800-1100℃ and the sintering time is 10-20h.

[0027] Thirdly, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises the aforementioned lithium-rich manganese-based positive electrode material containing a spinel structure in its bulk phase.

[0028] Beneficial effects:

[0029] 1. The lithium-rich manganese-based cathode material containing a spinel structure in the bulk phase of the present invention can effectively improve the lithium-ion transport capability and bulk phase structure stability of the lithium-rich manganese-based material by introducing the lithium-containing spinel structure into the primary particles. The cycle life of the synthesized material is greatly improved, with a capacity retention rate of 99.55% after 140 cycles, while the capacity retention rate of the same number of cycles without spinel structure is less than 90%.

[0030] 2. This invention employs a simple secondary lithium-coating process to introduce spinel structures into the primary particles of lithium-rich manganese-based materials. The process is simple, the conditions are mild, and the cost is low, making it suitable for industrial-scale mass production.

[0031] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the present invention;

[0033] Figure 2 Here is a SEM image of the finished product from Example 1;

[0034] Figure 3 SEM image of the finished product in Comparative Example 1;

[0035] Figure 4 The first charge-discharge curves for Example 1 and Comparative Example 1 are shown below.

[0036] Figure 5 The cycling performance of Example 1 and Comparative Example 1;

[0037] Figure 6 The rate performance of Example 1 and Comparative Example 1 is shown. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0039] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0040] Figure 1 This is a schematic diagram of the lithium-rich manganese-based cathode material containing a spinel structure in the bulk phase of the present invention. The main bulk phase has a layered structure, and spinel structures are distributed inside the particles.

[0041] Example 1

[0042] Manganese sulfate monohydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate were weighed according to a molar ratio of 0.7:0.25:0.05 and dissolved in deionized water to prepare a 2 mol / L metal salt solution A. Sodium hydroxide was dissolved in water to prepare a 2 mol / L precipitant solution B. Under stirring at 500 rpm / min, solutions A and B were slowly added dropwise to deionized water. The pH of the reaction system was controlled at 11.5, and the system temperature was controlled at 55℃. After reacting for 20 h, the resulting precipitate was washed, filtered, and dried to obtain the lithium-rich manganese-based precursor Mn. 0.7 Ni 0.25 Co 0.05 (OH)2.

[0043] According to the molecular formula Li 1.2 Mn 0.56 Ni 0.2 Co 0.04 Weigh out the appropriate amounts of lithium-rich manganese-based precursor and lithium carbonate (calculated as 103% of the theoretically calculated amount based on Li). First, take out 50% of the lithium carbonate and mix it evenly with the precursor in a high-speed mixer. Place it in a muffle furnace for sintering in an air atmosphere. First, heat it to 500°C at a heating rate of 3°C / min, hold it for 5 hours, and cool it to room temperature. Then, mix it evenly with the remaining 50% of lithium carbonate in a high-speed mixer. Place it in a muffle furnace for sintering in an air atmosphere. Heat it to 850°C at a heating rate of 3°C / min, hold it for 15 hours, and cool it to room temperature to obtain the finished lithium-rich manganese-based cathode material containing a spinel structure.

[0044] Figure 2 The image shown is an SEM image of Example 1, which shows that the primary particles are polyhedral in shape and have a diameter of 300-600 nm.

[0045] A slurry is formed by mixing positive electrode active material, acetylene black, polyvinylidene fluoride and N-methylpyrrolidone, and uniformly coating it onto the surface of an aluminum foil sheet to obtain a positive electrode sheet. Then, a lithium sheet is used as the negative electrode sheet, and a 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC volume ratio of 1:1) is used as the electrolyte. The assembly is carried out in a glove box to obtain a lithium-ion battery.

[0046] The cycle performance of the lithium-ion battery was tested using an electrochemical testing instrument at a temperature of 25°C and a current density of 0.1C (1C = 200 mAg). -1 The initial charge / discharge performance of the battery was tested within a charge / discharge voltage range of 4.6–2.0V. Cycle performance was then tested at 2.0–4.6V, 1C / 1C.

[0047] Example 2

[0048] Manganese sulfate monohydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate were weighed according to a molar ratio of 0.7:0.25:0.05 and dissolved in deionized water to prepare a 2 mol / L metal salt solution A. Sodium hydroxide was dissolved in water to prepare a 2 mol / L precipitant solution B. Under stirring at 500 rpm / min, solutions A and B were slowly added dropwise to deionized water. The pH of the reaction system was controlled at 11.5, and the system temperature was controlled at 55℃. After reacting for 20 h, the resulting precipitate was washed, filtered, and dried to obtain the lithium-rich manganese-based precursor Mn. 0.7 Ni 0.25 Co 0.05 (OH)2.

[0049] According to the molecular formula Li 1.2 Mn 0.56 Ni 0.2 Co 0.04 Weigh out the appropriate amounts of lithium-rich manganese-based precursor and lithium carbonate (calculated as 100% of the theoretically calculated amount based on Li). First, take out 50% of the lithium carbonate and mix it evenly with the precursor in a high-speed mixer. Place it in a muffle furnace for sintering in an air atmosphere. First, heat it to 500℃ at a heating rate of 3℃ / min, hold it for 5 hours, and cool it to room temperature. Then, mix it evenly with the remaining 50% of lithium carbonate in a high-speed mixer. Place it in a muffle furnace for sintering in an air atmosphere. Heat it to 850℃ at a heating rate of 3℃ / min, hold it for 15 hours, and cool it to room temperature to obtain the lithium-rich manganese-based cathode material containing a spinel structure.

[0050] The testing method is the same as in Example 1.

[0051] Comparative Example 1

[0052] Manganese sulfate monohydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate were weighed according to a molar ratio of 0.7:0.25:0.05 and dissolved in deionized water to prepare a 2 mol / L metal salt solution A. Sodium hydroxide was dissolved in water to prepare a 2 mol / L precipitant solution B. Under stirring at 500 rpm / min, solutions A and B were slowly added dropwise to deionized water. The pH of the reaction system was controlled at 11.5, and the system temperature was controlled at 55℃. After reacting for 20 h, the resulting precipitate was washed, filtered, and dried to obtain the lithium-rich manganese-based precursor Mn. 0.7 Ni 0.25 Co 0.05 (OH)2.

[0053] According to the molecular formula Li 1.2 Mn 0.56 Ni 0.2 Co 0.04O2 was weighed and the appropriate amounts of lithium-rich manganese-based precursor and lithium carbonate (calculated as 100% of the theoretical amount based on Li) were placed in a high-speed mixer and mixed evenly. The mixture was then placed in a muffle furnace for sintering in an air atmosphere. The temperature was first increased to 500℃ at a rate of 3℃ / min and held for 5 hours. Then, the temperature was increased to 850℃ at the same rate and held for 15 hours. After cooling to room temperature, the lithium-rich manganese-based cathode material was obtained. SEM images are shown below. Figure 3 As shown, its primary particles have a spherical structure with a diameter of approximately 100-300 nm.

[0054] The testing method is the same as in Example 1.

[0055] Comparative Example 2

[0056] Manganese sulfate monohydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate were weighed according to a molar ratio of 0.7:0.25:0.05 and dissolved in deionized water to prepare a 2 mol / L metal salt solution A. Sodium hydroxide was dissolved in water to prepare a 2 mol / L precipitant solution B. Under stirring at 500 rpm / min, solutions A and B were slowly added dropwise to deionized water. The pH of the reaction system was controlled at 11.5, and the system temperature was controlled at 55℃. After reacting for 20 h, the resulting precipitate was washed, filtered, and dried to obtain the lithium-rich manganese-based precursor Mn. 0.67 Ni 0.28 Co 0.05 (OH)2.

[0057] According to the molecular formula Li 1.2 Mn 0.56 Ni 0.2 Co 0.04 O2 is weighed and the corresponding amount of lithium-rich manganese-based precursor and lithium carbonate (calculated as 90% of the theoretical amount based on Li) are placed in a high-speed mixer and mixed evenly. The mixture is then placed in a muffle furnace for sintering in an air atmosphere. The temperature is first raised to 500°C at a heating rate of 3°C / min and held for 5 hours. Then, the temperature is raised to 850°C at the same rate and held for 15 hours. After cooling to room temperature, the lithium-rich manganese-based cathode material is obtained.

[0058] The testing method is the same as in Example 1.

[0059] Comparative Example 3

[0060] Manganese sulfate monohydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate were weighed according to a molar ratio of 0.7:0.25:0.05 and dissolved in deionized water to prepare a 2 mol / L metal salt solution A. Sodium hydroxide was dissolved in water to prepare a 2 mol / L precipitant solution B. Under stirring at 500 rpm / min, solutions A and B were slowly added dropwise to deionized water. The pH of the reaction system was controlled at 11.5, and the system temperature was controlled at 55℃. After reacting for 20 h, the resulting precipitate was washed, filtered, and dried to obtain the lithium-rich manganese-based precursor Mn.0.7 Ni 0.25 Co 0.05 (OH)2.

[0061] According to the molecular formula Li 1.2 Mn 0.56 Ni 0.2 Co 0.04 Take the appropriate amount of lithium-rich manganese-based precursor and lithium carbonate (calculated as 100% of the theoretical amount based on Li). First, take 20% of the lithium carbonate and mix it evenly with the precursor in a high-speed mixer. Place it in a muffle furnace for sintering in an air atmosphere. First, heat it to 500°C at a heating rate of 3°C / min, hold it for 5 hours, and cool it to room temperature. Then, mix it evenly with the remaining 80% of the lithium carbonate in a high-speed mixer. Place it in a muffle furnace for sintering in an air atmosphere. Heat it to 850°C at a heating rate of 3°C / min, hold it for 15 hours, and cool it to room temperature to obtain the lithium-rich manganese-based cathode material.

[0062] The testing method is the same as in Example 1.

[0063] Figure 4 The first charge-discharge curves for Example 1 and Comparative Example 1 are shown below. Figure 5 The cycling performance of Example 1 and Comparative Example 1; Figure 6 The rate performance of Example 1 and Comparative Example 1 is shown. It can be seen that the charge-discharge curves of the examples exhibit a distinct spinel peak, indicating improvements in both rate performance and cycle performance.

[0064] The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A lithium-rich manganese-based cathode material with a spinel structure in bulk phase, characterized in that, The chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where M is at least two elements selected from Ni, Co, Mn, Ti, Mo, Ru and Sn, and 0.1≤x≤0.9; The lithium-rich manganese-based cathode material consists of secondary spherical or near-spherical particles composed of primary particles with polyhedral shapes, wherein spinel structures are distributed inside the primary particles. The diameter of the primary particles is 300-600 nm, and the specific surface area of ​​the lithium-rich manganese-based cathode material is ≤1.5 m². 2 / g; The preparation method of the lithium-rich manganese-based cathode material containing a spinel structure in the bulk phase includes the following steps: (1) Dissolve the soluble metal salt in water according to the chemical formula to form metal salt solution A; dissolve the precipitant in water to form solution B; (2) Under a protective atmosphere, solutions A and B are slowly added to the reactor to carry out a co-precipitation reaction. The precipitate is filtered, washed, and dried to obtain the precursor. (3) Weigh the precursor and total lithium salt according to the chemical formula of the finished product. The amount of total lithium salt is 100-105% of the theoretically calculated amount based on Li. First, mix the precursor with lithium salt at a lower stoichiometric ratio and then pre-calcine it in an oxygen-containing atmosphere. The lithium salt at a lower stoichiometric ratio is 30-60% of the total lithium salt. (4) Mix the remaining lithium salt evenly and sinter at high temperature in an oxygen-containing atmosphere to obtain a lithium-rich manganese-based cathode material with a spinel structure in bulk.

2. The lithium-rich manganese-based cathode material with a spinel structure in bulk phase according to claim 1, characterized in that, The spinel structure is lithium-containing spinel with the molecular formula LiMn2O4 or Li4Mn5O4. 12 At least one of them.

3. The lithium-rich manganese-based cathode material with a spinel structure in bulk phase according to claim 1, characterized in that, The spinel structure accounts for ≤5% of the mass of the lithium-rich manganese-based cathode material.

4. A method for preparing a lithium-rich manganese-based cathode material with a spinel structure in bulk phase as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Dissolve the soluble metal salt in water according to the chemical formula to form metal salt solution A; dissolve the precipitant in water to form solution B; (2) Under a protective atmosphere, solutions A and B are slowly added to the reactor to carry out a co-precipitation reaction. The precipitate is filtered, washed, and dried to obtain the precursor. (3) Weigh the precursor and total lithium salt according to the chemical formula of the finished product. The amount of total lithium salt is 100-105% of the theoretically calculated amount based on Li. First, mix the precursor with lithium salt at a lower stoichiometric ratio and then pre-calcine it in an oxygen-containing atmosphere. The lithium salt at a lower stoichiometric ratio is 30-60% of the total lithium salt. (4) Mix the remaining lithium salt evenly and sinter at high temperature in an oxygen-containing atmosphere to obtain a lithium-rich manganese-based cathode material with a spinel structure in bulk.

5. The preparation method according to claim 4, characterized in that, The soluble metal salt mentioned in step (1) is one of sulfate, nitrate, oxalate or acetate, and the concentration of metal salt solution A is 1-4 mol / L; the precipitant is one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.

6. The preparation method according to claim 4, characterized in that, The protective atmosphere described in step (2) is nitrogen or argon; the temperature of the coprecipitation reaction is 40-70℃.

7. The preparation method according to claim 4, characterized in that, The pre-firing temperature in step (3) is 300-600℃ and the pre-firing time is 1-5h.

8. The preparation method according to claim 4, characterized in that, In step (4), the high-temperature sintering temperature is 800-1100℃ and the sintering time is 10-20h.

9. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises the lithium-rich manganese-based positive electrode material containing a spinel structure in bulk as described in any one of claims 1-3, or the lithium-rich manganese-based positive electrode material containing a spinel structure in bulk prepared by the preparation method described in any one of claims 4-8.

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