Low-cost surface titanium doping method for lithium-rich cathode material

Abstract

The application relates to a low-cost surface titanium doping method of a lithium-rich positive electrode material and belongs to the field of lithium ion battery positive electrode materials. Specifically, the method comprises the following steps: placing the positive electrode material into a solution with a specific pH, then continuously stirring and adding a titanium sulfate solution into the solution; filtering the solid powder obtained after reaction for a certain time, drying, and sintering at high temperature to obtain the titanium surface-doped positive electrode material. The lithium-rich positive electrode material prepared by the method has improved first circle coulomb efficiency, discharge specific capacity and cycle performance, the process is simple, the cost is lower than that of an organic titanium source, the method is suitable for large-batch treatment of the lithium-rich positive electrode material, the use demand of the power battery can be met, and the method has a good application prospect.

Description

Technical Field

[0001] The present invention relates to a low-cost surface titanium doping method for a lithium-rich cathode material, belonging to the fields of lithium-ion battery cathode materials and electrochemistry technology. Background Art

[0002] With the continuous development and progress of society, fossil fuels such as coal, oil, and natural gas have been overexploited and used, which not only causes severe environmental pollution but also gradually aggravates the energy crisis. As a clean and efficient energy storage and conversion device, lithium-ion batteries are widely used in fields such as electric vehicles, energy storage power stations, and portable electronic devices, and are currently a research hotspot. Among the many components of lithium-ion batteries, the cathode material has the highest cost and lower capacity than the anode, which restricts the further development of the battery. Currently, the mainstream cathode materials include layered LiCoO2, LiNi 1-x-y Mn x Co y O2, etc., spinel-structured LiMn2O4, etc., and polyanionic LiFePO4, etc. However, their capacities are generally below 200 mAh / g, and it is increasingly difficult to meet the current demand for high-energy-density batteries.

[0003] Lithium-rich layered oxide cathode materials xLi2MnO3·(1-x)LiTMO2 (0 < x < 1, TM is a transition metal) have become strong competitors for the next-generation lithium-ion battery cathodes due to their high discharge specific capacity (>250 mAh / g). However, lithium-rich materials still have many drawbacks, such as low initial Coulomb efficiency, poor cycle stability, and poor rate performance, which limit their practical applications. There are various modification methods for lithium-rich materials, including element doping, gradient design, surface regulation, etc. Among them, element doping is a relatively effective method with many optional elements and obvious performance improvement. Titanium element doping can improve the conductivity of the material and generate stronger Ti-O bonds to reduce the release of irreversible oxygen, thereby improving the electrochemical performance of lithium-rich materials. However, as an inactive element, the introduction of a large amount of titanium into the bulk of the material will lead to a decrease in capacity. Therefore, only a small amount of doping on the surface can avoid a significant decrease in capacity and generate a surface inert layer to inhibit the occurrence of side reactions.

[0004] In order to achieve uniform surface doping of titanium, it is necessary to deposit titanium uniformly on the surface of the lithium-rich material. Patent CN104617267 uses an organic titanium source dissolved in an organic solvent and uses the principle of ester hydrolysis for coating. However, the organic titanium source has a high price and it is difficult to control the hydrolysis rate for treating different amounts of materials. Patent CN 114762148 uses atomic layer deposition (ALD) technology for coating at the atomic level, which can precisely control the deposition amount and has a good effect. However, the ALD treatment cost is high and it is difficult to treat a large amount of materials.

[0005] In industrial production, titanium oxysulfate is a primary raw material for producing titanium dioxide due to its low cost. Therefore, this patent selects inorganic titanium oxysulfate as the titanium source and uses an aqueous solution of titanium oxysulfate to treat lithium-rich cathode materials, forming a uniform Ti(OH)4 precipitate on their surface. It is worth noting that since titanium oxysulfate only dissolves in strongly acidic solutions, the lithium-rich material also undergoes an acid washing process during the titanium oxysulfate solution treatment. This acid washing process removes residual alkali from the surface of the lithium-rich particles and facilitates proton exchange with the material surface. In the subsequent heat treatment process, the lithium-rich material forms a spinel structure on its surface, which synergistically optimizes the cathode interface with the surface titanium doping. This method is simple, easy to implement, and low-cost, making it suitable for large-scale processing of lithium-rich cathode materials to promote their industrialization. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost surface titanium doping method for lithium-rich cathode materials, which aims to solve the problems of low first-cycle coulombic efficiency, poor rate performance, and poor cycle performance in lithium-rich cathode materials. After surface modification, the lithium-rich material exhibits significantly improved first-cycle coulombic efficiency and rate performance, and enhanced cycle stability.

[0007] The technical solution of this invention is as follows:

[0008] A low-cost surface titanium doping method for lithium-rich cathode materials is proposed. The lithium-rich cathode material is treated with an aqueous solution of titanium oxysulfate and then subjected to heat treatment. This method achieves both surface titanium doping and the construction of a surface spinel structure, thereby improving the first-cycle coulombic efficiency, cycle stability, and rate performance of the lithium-rich material.

[0009] The low-cost surface titanium doping method for the above-mentioned lithium-rich cathode material includes the following steps:

[0010] (1) Prepare a sulfuric acid solution, then add titanium oxysulfate solid powder into the sulfuric acid solution and stir continuously until a clear solution is obtained, thus obtaining a titanium oxysulfate solution;

[0011] (2) Prepare an acidic solution with pH = 2-5 and place it in a water bath at 25-80℃;

[0012] (3) Place the lithium-rich cathode material powder into the acidic solution obtained in step (2), stir for a short time, and then slowly add the titanium oxysulfate solution from step (1) into it while stirring continuously.

[0013] (4) After adding the titanium oxysulfate solution for 5-30 minutes, the titanium is fully precipitated on the surface of the lithium-rich material in the form of Ti(OH)4. Then, the powder in the liquid is filtered out, and the powder is rinsed several times with deionized water and alcohol and then dried in a vacuum drying oven.

[0014] (5) Heat-treat the material obtained after drying in step (4) in a muffle furnace, heating it to 500 - 900 °C at a heating rate of 1 - 10 °C / min, holding for 1 - 8 h, and then cooling it to room temperature with the furnace, thus obtaining a lithium-rich cathode material with surface titanium doping.

[0015] In step (1), the concentration of the titanium oxysulfate solution is 0.001 - 5 M, pH ≤ 2.2, and the molar ratio of titanium oxysulfate to the lithium-rich cathode material in step (3) is 0.001 - 0.2.

[0016] In step (2), the acid solution includes but is not limited to sulfuric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, phosphoric acid, oxalic acid, etc., or is an acidic buffer solution including but not limited to acetic acid / ammonium acetate, formic acid / ammonium formate, disodium hydrogen phosphate / citric acid, etc.

[0017] In step (3), the lithium-rich cathode material is a homogeneous component with the chemical formula: xLi2MnO3·(1 - x)LiTMO2 (TM = one or more of Mn, Ni, Co, Fe, etc.); or a gradient lithium-rich cathode material: the core is aLi2MnO3·(1 - a)LiTMO2, and the shell is bLi2MnO3·(1 - b)LiTMO2 (TM = one or more of Mn, Ni, Co, Fe, etc., and 0 ≤ b < a ≤ 1). The particle morphology is spherical aggregates or single crystals, and the particle size is 0.1 - 20 μm. The present invention has the following advantages:

[0018] (1) The first Coulombic efficiency is improved

[0019] The formation of stronger Ti - O bonds on the surface inhibits the release of irreversible oxygen and improves the Coulombic efficiency.

[0020] (2) The battery capacity is improved

[0021] Titanium in the lattice improves the electrical conductivity of the material, and at the same time, the surface spinel structure is conducive to Li + transport, and the capacity during cycling at a current density of 1C is improved.

[0022] (3) The cycle stability is improved

[0023] Stronger Ti - O bonds improve the stability of oxygen, thus inhibiting oxygen vacancies and structural degradation, and therefore maintaining better stability during electrochemical cycling.

[0024] (4) Low cost and conducive to batch processing of materials

[0025] Compared with the treatment methods using organic titanium sources such as tetrabutyl titanate and titanium isopropoxide, this invention uses inorganic titanium sources and aqueous solutions, with a significant reduction in cost, and the synthesis conditions are simple and easy to adjust, and a large amount of lithium-rich materials can be processed. Brief Description of the Drawings

[0026] Figure 1 The X-ray diffraction patterns of Example 1 and the comparative example are shown below;

[0027] Figure 2 Raman spectra of Example 1 and the comparative example;

[0028] Figure 3 The transmission electron microscopy (TEM) spectrum of Example 1;

[0029] Figure 4 The first charge-discharge curves of Example 1 and the comparative example are shown in the working voltage range of 2-4.8V.

[0030] Figure 5 The diagram shows the cycling performance of Example 1 and the comparative example at operating voltages of 2-4.6V. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be noted that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that those skilled in the art can make modifications, alterations, and substitutions to the present invention within the scope of its conceptual design. These simple variations and combinations should also be considered as part of the content disclosed in this invention and are all within the protection scope of this invention.

[0032] Comparative Example

[0033] Gradient lithium-rich cathode material, with the chemical formula: core component 0.5Li₂MnO₃·0.5LiNi 0.42 Mn 0.42 Co 0.16 O2; Shell composition: 0.3Li2MnO3·0.7LiNi 0.42 Mn 0.42 Co 0.16 O2. This material is untreated.

[0034] Example 1

[0035] (1) Take 80 ml of deionized water and add 500 μL of concentrated sulfuric acid. Weigh titanium oxysulfate according to the designed ratio of titanium oxysulfate to lithium-rich cathode of 10:99, dissolve it in the above solution and stir until clear, then make up to 100 mL.

[0036] (2) Prepare a sulfuric acid solution with pH=3.2 at room temperature and stir continuously. Weigh the graded lithium-rich cathode material from Comparative Example 1 according to the designed ratio, pour the material into the sulfuric acid solution and keep stirring.

[0037] (3) Add the titanium oxysulfate solution prepared in step (1) dropwise to the solution in step (2) at a rate of 1 mL / min for 10 min. After the addition is complete, stir for 1 min, filter immediately, and rinse the positive electrode powder several times with deionized water and alcohol respectively. Place the positive electrode in a vacuum drying oven and dry at 50°C for 8 h.

[0038] (4) Take out the dried cathode powder, heat it to 700°C in a muffle furnace at a heating rate of 5°C / min, keep it at that temperature for 5 hours, and take it out after cooling in the furnace. This is the lithium-rich cathode material with titanium doping on the surface.

[0039] Example 2

[0040] This embodiment is used to illustrate another type of surface titanium doping method of the present invention that has the same processing method as Embodiment 1, but has a different lithium-rich cathode chemical formula.

[0041] The method is the same as in Example 1, except that the gradient lithium-rich cathode in step (2) has the chemical formula of core 0.5Li2MnO3·0.5LiNi. 0.5 Mn 0.5 O2; shell is 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2.

[0042] Example 3

[0043] This embodiment illustrates another type of surface titanium doping method of the present invention that has the same processing method as Embodiment 1, but uses a different amount of titanium oxysulfate.

[0044] The method of Example 1 is different in that the molar ratio of titanium oxysulfate to lithium-rich cathode is 30:97.

[0045] Example 4

[0046] This embodiment illustrates another type of surface titanium doping method of the present invention that has the same processing method as Embodiment 1, but with a different acid solution composition.

[0047] The method of Example 1 differs in that a pH 3.2 acetic acid / ammonium acetate acidic buffer solution is prepared in step (2).

[0048] Example 5

[0049] This embodiment illustrates another type of surface titanium doping method of the present invention that has the same processing method as Embodiment 1, but with a different coating temperature.

[0050] The method of Example 1 differs in that the water bath temperature in step (2) is 60°C.

[0051] Example 6

[0052] This embodiment is used to illustrate another type of surface titanium doping method of the present invention that has the same processing method as Embodiment 1, but with a different coating time.

[0053] The method of Example 1 differs in that the total processing time in step (3) is 30 minutes.

[0054] Example 7

[0055] This embodiment illustrates another type of surface titanium doping method of the present invention that has the same processing method as Embodiment 1, but with a different heat treatment temperature.

[0056] The method of Example 1 differs in that the temperature is raised to 600°C in step (4).

Claims

1. A low-cost surface titanium doping method for lithium-rich cathode materials, characterized in that, The lithium-rich cathode material was treated with an aqueous solution of titanium oxysulfate, followed by heat treatment, which achieved both surface titanium doping and the construction of a surface spinel structure; the steps included: (1) Prepare a sulfuric acid solution, then add titanium oxysulfate solid powder into the sulfuric acid solution and stir continuously until a clear solution is obtained, thus obtaining a titanium oxysulfate solution; (2) Prepare an acidic solution with pH=2-5 and place it in a water bath at 25-80℃; (3) Place the lithium-rich cathode material powder into the acidic solution obtained in step (2), stir for a short time, and then slowly drop the titanium oxysulfate solution from step (1) into it while continuously stirring. (4) After adding the titanium sulfate solution for 5-30 minutes, allow the titanium to fully precipitate on the surface of the lithium-rich material in the form of Ti(OH)4. Then filter out the powder in the liquid, rinse several times with deionized water and alcohol, and dry in a vacuum drying oven. (5) The material obtained after drying in step (4) is placed in a muffle furnace for heat treatment. The temperature is raised to 500-900℃ at a heating rate of 1-10℃ / min, held for 1-8h, and then cooled to room temperature with the furnace to obtain a lithium-rich cathode material with titanium doping on the surface. In step (1), the concentration of the titanium oxysulfate solution is 0.001~5M, the pH is ≤2.2, and the molar ratio of titanium oxysulfate to the lithium-rich cathode material in step (3) is 0.001~0.

2. In step (3), the lithium-rich cathode material is a homogeneous component with the chemical formula: xLi2MnO3·(1-x)LiTMO2, where TM = one or more of Mn, Ni, Co, and Fe.

2. A low-cost surface titanium doping method for a lithium-rich cathode material according to claim 1, characterized in that, In step (2), the acid solution is sulfuric acid, nitric acid, hydrochloric acid, acetic acid, formic acid, phosphoric acid or oxalic acid, or an acidic buffer solution selected from acetic acid / ammonium acetate, formic acid / ammonium formate or disodium hydrogen phosphate / citric acid.

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