Preparation method of lithium ion battery cathode material copper-based lithium titanate with high rate capability

Abstract

The invention discloses a preparation method of a lithium ion battery cathode material copper-based lithium titanate with high rate performance. The preparation process comprises the following steps: weighing a certain amount of lithium titanate (LTO) and cupric oxalate (CuC2O4), and controlling the molar ratio of Ti to Cu to be (4-6): (1-2); then fully grinding the mixture in an agate mortar for 10-20 minutes to obtain a uniformly dispersed mixture; and then, putting the mixture into a muffle furnace, calcining in an air atmosphere at 400-600 DEG C for 1-3 hours, and naturally cooling to room temperature to obtain the novel copper-based lithium titanate material. The specific discharge capacity of the material is 12-15 times of that of commercial LTO after the material is used as a lithium ion battery negative electrode material and is circulated for 500 circles at 40 DEG C, and the material shows excellent high-rate performance and excellent cycling stability. The preparation method is simple, does not need special equipment, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to a method for preparing an anode material of a lithium-ion battery, in particular to a method for preparing copper-based lithium titanate with high rate performance and used as an anode material of a lithium-ion battery, belonging to the technical field of energy materials. Background Art

[0002] Lithium-ion batteries have been widely used in the fields of electronic products, electric vehicles, energy storage systems, aerospace, etc. due to their advantages such as stable performance, convenient use, environmental protection and safety. With the rapid development of drones, robots and artificial intelligence, higher requirements are put forward for the performance of lithium-ion batteries. Generally, a lithium-ion battery is mainly composed of five parts: positive and negative electrode materials, separator, current collector, electrolyte and shell. Among them, the negative electrode material is one of the decisive factors affecting the energy density, cycle life and safety of lithium-ion batteries. Currently, the commercially available negative electrode materials for lithium-ion batteries are mainly graphite and lithium titanate. Research shows that when a lithium-ion battery is overcharged, lithium dendrites will precipitate on the surface of the graphite negative electrode material. The precipitated lithium dendrites may pierce the separator under certain conditions, causing a short circuit and posing a safety hazard. Lithium titanate (molecular formula Li4Ti5O12, abbreviated as LTO), which is safe and environmentally friendly and has a relatively high lithium intercalation potential, thus avoiding the precipitation of lithium dendrites on its surface during charge and discharge, and eliminating the occurrence of safety accidents such as short circuits to a certain extent. At the same time, LTO has the characteristic of zero strain force, showing good long-cycle stability. Research shows that LTO also has the ability of fast charge and discharge. Therefore, LTO has become one of the current important research hotspots in the negative electrode materials of lithium-ion batteries. However, the low conductivity of LTO seriously limits its application in high-power batteries. Currently, scientific researchers mainly start from three aspects: conductivity, ion diffusion rate and structural stability to improve the electrochemical performance of LTO. Literature research shows that the three main methods for modifying LTO are: (1) Surface modification and carbon coating. That is, a conductive carbon layer is formed on the surface of LTO, which can not only inhibit particle agglomeration but also greatly improve the conductivity of LTO. For example, Huo Yanfang et al. (CN119419237A) disclosed a preparation method of a carbon-coated nano-tubular lithium titanate / carbon composite negative electrode material, which can significantly improve the electron / ion transport kinetics during charge and discharge, making the product have excellent rate performance and cycle performance. Wang Bo et al. (CN110854375A) disclosed a preparation method of a composite material containing Ti-MOF metal-organic framework material, carbon material and lithium titanate. The applicant believes that the presence of the metal-organic framework material can significantly improve the conductivity of the material, and the introduction of the carbon material can not only increase the conductivity but also increase the specific surface area of lithium titanate, making LTO and the electrolyte contact more fully. (2) Nanometerization of size and morphology control. That is, by reducing the particle size of LTO particles to increase the specific surface area and shorten the diffusion path of lithium ions to improve the electrochemical performance of LTO. For example, Wu Mingwu et al. (CN111960462A) disclosed a preparation method of lithium titanate with a nano-sheet morphology. The applicant believes that the two-dimensional nano-sheet structure can effectively shorten the diffusion distance of lithium ions and improve the fast charge and discharge ability of LTO.Chen Zehua et al. (CN115321588A) disclosed a preparation method of lithium titanate bowl-shaped microspheres. The prepared lithium titanate microspheres have the advantages of large specific surface area and allowing rapid extraction and insertion of lithium ions, and show excellent electrochemical lithium storage performance as the anode material of lithium-ion batteries. (3) Element doping. That is, by doping different elements to improve the structural stability of the material, and then improving the electrochemical performance of LTO. For example, Li Wenyao et al. (CN119481027A) disclosed a preparation method of a three-site co-doped carbon-coated lithium titanate material. The applicant doped potassium, aluminum, and fluorine to replace the lithium, titanium, and oxygen sites in the lithium titanate material respectively to obtain co-doped LTO. Practice has proved that this method can improve the electrochemical performance of LTO by increasing the electronic conductivity on the surface of LTO. Meng Weiwei et al. (CN107808957A) disclosed a preparation method of lithium titanate containing trivalent titanium. This method can improve the conductivity of LTO to achieve the purpose of improving the electrochemical performance of LTO without destroying the initial morphology of lithium titanate. Due to the deficiencies such as high preparation cost and complex preparation process in the above several preparation methods, few of them are truly commercialized. Therefore, the research and development of modified LTO remains a research hotspot and difficulty in the field of lithium-ion batteries at present. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of copper-based lithium titanate, a new type of anode material for lithium-ion batteries with high rate performance. The present invention prepared a copper-based lithium titanate by calcining a mixture of LTO and copper oxalate (CuC2O4) in an air atmosphere, and used it as the anode material of lithium-ion batteries. Compared with commercial lithium titanate, the capacity of this material after 500 cycles at 40C is 12-15 times that of commercial LTO, and it shows extraordinary excellent performance in terms of discharge specific capacity and cycle life. The preparation process of the present invention is simple, the raw materials are easy to obtain, and the price is low, which is suitable for industrial scale production.

[0004] Specifically, the present invention provides a preparation method of copper-based lithium titanate with high rate performance as the anode material of lithium-ion batteries, including the following steps: (1) Preparation of materials Lithium titanate (LTO); copper oxalate (CuC2O4); acetylene black; polyvinylidene fluoride (PVDF); N-methylpyrrolidone (NMP); Celgard 2400 microporous polypropylene membrane; CR2430 type button battery case; (2) Preparation of organic electrolyte A The organic electrolyte A is: 1 mol L-1 LiPF6. The preparation method is: dissolve LiPF6 in a mixed solvent, and the mixed solvent used is dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and vinylene carbonate (VC), which are mixed in a volume ratio of 1:1:1:1; (3)Sample preparation According to the molar ratio of Ti to Cu being (4~6):(1~2), weigh LTO and CuC2O4, mix them and place them in a muffle furnace, and calcine them in an air atmosphere at 400°C~600°C for 1 h~3 h to obtain the product sample lithium copper titanate; As a preferred condition, in step (3), the molar ratio of Ti to Cu is 5:1; As a preferred condition, in step (3), the calcination temperature of the LTO and CuC2O4 mixture in the muffle furnace is 500°C; As a preferred condition, in step (3), the calcination time of the LTO and CuC2O4 mixture in the muffle furnace is 1 h; (4)Preparation of electrodes and assembly of batteries The application of the prepared material lithium copper titanate as the negative electrode material of a lithium-ion battery is specifically as follows: For comparison, the prepared sample is denoted as sample a, and the commercial lithium titanate is named sample o; Weigh sample a, PVDF and acetylene black separately and place them in an agate mortar. When weighing, control the mass ratio of sample a, PVDF and acetylene black to be (8~9):(1~1.5):(1~1.5). The mixture of the three is thoroughly ground in the agate mortar for 15~30 min. Then, gradually add N-methylpyrrolidone (NMP) and stir while adding to make the mixture of the three into a paste. Subsequently, use a glass slide to evenly apply the obtained paste on a commercial copper (Cu) foil current collector. Immediately after that, place the current collector coated with the paste in a vacuum drying oven and dry it at 100~120°C for 4 h~8 h. After naturally cooling to room temperature, take it out and use a cutter to cut it into several electrode sheets with a diameter of 1 cm~2 cm (the loading amount of sample a on each electrode sheet is approximately between 0.82 mg cm-2 and 1.32 mg cm-2), and electrode a is obtained. Replace sample a with commercial lithium titanate, and prepare the LTO electrode under the same other conditions, denoted as electrode o.

[0005] Using the prepared electrode a as the positive electrode, a lithium sheet as the negative electrode, a Celgard 2400 microporous polypropylene membrane as the separator, organic electrolyte A as the electrolyte, and a CR2430 type button battery case as the battery case, assemble it into a half-cell in a glove box filled with nitrogen and label it as battery a. Replace electrode a with electrode o and, according to the above steps, assemble a half-cell under the condition that other conditions remain unchanged and label it as battery o. The charge and discharge experiments of the half-cell are carried out on a high-precision battery charge and discharge tester (model CT-3008W-5V20mA-S4, Shenzhen Neware Electronic Co., Ltd.).

[0006] As a preferred condition, in step (4), the mass ratio of sample a, PVDF, and acetylene black is 8:1:1; As a preferred condition, in step (4), the grinding time of the mixture of sample a, PVDF, and acetylene black is 20 min; As a preferred condition, in the electrode preparation process of step (4), the temperature in the vacuum drying oven is 120 °C; As a preferred condition, in the electrode preparation process of step (4), the vacuum drying time is 6 h.

[0007] The preparation process of the present invention is safe, pollution-free, has a simple process, and low cost, and is suitable for industrial-scale production. The sample prepared by the present invention has a first discharge specific capacity that can be increased by 70% - 80% compared with commercial LTO at 0.2 C. Especially at a high rate of 40 C, the discharge specific capacity after 500 cycles is 12 - 15 times that of commercial LTO batteries, and it has good cycle stability. This shows that the copper-based lithium titanate material prepared by the present invention is an ideal anode material for lithium-ion batteries and has broad application prospects.

[0008] The beneficial effects achieved by the present invention are: The present invention has a simple process. By simply air-calcining a mixture of LTO and CuC2O4, a new type of copper-based lithium titanate anode material with high-rate performance can be prepared. This anode material has a very high discharge specific capacity and excellent performance especially during high-rate charge and discharge. Description of the Drawings

[0009] Figure 1 XRD patterns of commercial LTO (o) and the prepared copper-based lithium titanate (a) materials.

[0010] Figure 2 Charge and discharge cycle diagrams of the half-cell assembled with commercial LTO (o) and the half-cell assembled with the prepared copper-based lithium titanate (a) at different rates, where 1 C = 175 mA g-1.

[0011] Figure 3Cycling diagrams of half-cells assembled with commercial LTO (o) and half-cells assembled with the prepared copper-based lithium titanate (a) after 50 charge-discharge cycles at 20 °C, 50 charge-discharge cycles at 30 °C, and then immediately 500 charge-discharge cycles at 40 °C. Detailed implementation

[0012] The following examples are used to illustrate the present invention. Example 1

[0013] Weigh 0.5 g of LTO and 0.1649 g of CuC2O4, so that the molar ratio of Ti to Cu is 5:1. Grind the above mixture composed of lithium titanate and copper oxalate in an agate mortar for 15 min to obtain a relatively uniformly dispersed mixture. Subsequently, place this mixture in a muffle furnace and calcine it at 500 °C for 1 h in an air atmosphere to obtain a product sample, which is denoted as sample a. For comparison, the commercial lithium titanate material is named sample o.

[0014] Weigh sample a, PVDF, and acetylene black separately into an agate mortar, and control the mass ratio of sample a, PVDF, and acetylene black to be 8:1:1 during weighing. Grind them thoroughly for 20 min, and then gradually add N-methylpyrrolidone (NMP) dropwise while stirring to adjust the mixture of the three into a paste. Subsequently, evenly apply the paste on a commercial Cu foil current collector with a glass sheet, place the coated current collector in a vacuum drying oven, dry it at 120 °C for 6 h, take it out after naturally cooling to room temperature, and use a cutter to cut it into several electrode sheets with a diameter of 1 cm (the loading amount of sample a on each electrode sheet is 1.00 mg cm-2), that is, electrode a is obtained. Replace sample a with commercial lithium titanate, and prepare an LTO electrode under the same other conditions, denoted as electrode o. Finally, use the prepared electrode a as the positive electrode, a lithium sheet as the negative electrode, a Celgard 2400 microporous polypropylene membrane as the separator, organic electrolyte A as the electrolyte, and a CR2430 type button battery case as the battery case, and assemble it into a half-cell in a glove box filled with nitrogen, denoted as battery a. Replace electrode a with electrode o, and assemble a half-cell according to the above steps under the same other conditions, denoted as battery o.

[0015] See Figure 1 , Figure 1XRD patterns of copper-based lithium titanate (a) and commercial LTO (o), as well as XRD standard patterns of LTO and CuO, where spectra a and o correspond to the XRD patterns of copper-based lithium titanate (a) and commercial LTO (o), respectively. Obviously, characteristic diffraction peaks of LTO appear in spectra a and o, respectively, that is, the diffraction peaks at 18.4°, 35.9°, 43.3°, 57.2°, 62.9° and 66.1° correspond to the (111), (311), (400), (333), (440) and (531) crystal planes of Li4Ti5O12 (JCPDS, No: 49-207), which strongly proves the existence of lithium titanate in copper-based lithium titanate and the high crystallinity of lithium titanate. Different from spectrum o, characteristic diffraction peaks belonging to CuO appear in spectrum a, that is, the diffraction peaks at 38.8° and 48.8° correspond to the (200), (-202) crystal planes of CuO (JCPDS, No: 2-1040). This indicates that after calcination, there is not only lithium titanate but also copper oxide transformed from copper oxalate in sample a. Literature research shows that the study on transforming copper oxalate into copper oxide by calcination in the presence of lithium titanate to obtain a new composite material composed of copper oxide and lithium titanate has not been reported yet.

[0016] See Figure 2 , Figure 2 Charge-discharge cycling diagrams of the half-cell assembled with commercial LTO (o) and the half-cell assembled with the prepared copper-based lithium titanate (a) at different rates. The rates are 0.2 C, 0.5 C, 1 C, 3 C, 5 C to 10 C in sequence, and all cells are cycled 5 times at the given rate, where 1 C is calculated as 1 C = 175 mA g-1. It can be seen that the initial discharge specific capacities of cells o and a at 0.2 C are 172 mAh g-1 and 299 mAh g-1, respectively, and cell a is 1.7 times that of cell o. At all given rates, the discharge specific capacity of cell a is much higher than that of cell o. Especially at the high rate of 10 C, the average discharge specific capacity of cell a is 116 mAh g-1, which is much higher than 56 mAh g-1 of cell o. When a series of rate tests are carried out and the rate returns to 0.2 C again, the discharge specific capacity of cell a is still much higher than that of cell o, and the capacity retention rate of cell a is higher than 80%, showing excellent reversibility of rate change. Therefore, using the copper-based lithium titanate prepared by the present invention as the anode material of a lithium-ion battery can significantly improve the rate performance of a traditional LTO electrode.

[0017] See Figure 3 , Figure 3The figure shows the charge-discharge cycles of two batteries. First, they are charged and discharged 50 times at 20 °C and then 50 times at 30 °C, and then 500 times at 40 °C. After 50 cycles at 20 °C, the discharge specific capacities of batteries o and a are 53.2 mAh g-1 and 87.8 mAh g-1 respectively, and battery a is 1.7 times that of battery o. After 50 cycles at 30 °C, the discharge specific capacities of batteries o and a are 32.7 mAh g-1 and 69.3 mAh g-1 respectively, and battery a is 2.1 times that of battery o. Unexpectedly, after 500 cycles at 40 °C, the discharge specific capacities of batteries a and o are 40.0 mAh g-1 and 2.7 mAh g-1 respectively, and battery a is still higher than battery o, being 14.8 times that of battery o. This shows that compared with traditional commercial LTO, battery a can better adapt to charge-discharge cycles at high currents. Figure 3 The upper side shows the relationship between the Coulombic efficiency and the number of cycles of the two batteries. It can be seen that the Coulombic efficiency of battery o fluctuates greatly and is unstable, while the Coulombic efficiency of battery a is more stable and is above 97% in both cases, indicating that battery a has less energy loss during charge and discharge. Example 2

[0018] Weigh 0.5 g of LTO and 0.2046 g of CuC2O4 so that the molar ratio of Ti to Cu is 4:1. Then, thoroughly grind the mixture of lithium titanate and copper oxalate in an agate mortar for 15 minutes to obtain a relatively homogeneous mixture. Subsequently, place this mixture in a muffle furnace and calcine it at 500 °C for 1 hour in an air atmosphere to obtain the product sample, which is denoted as sample a. For comparison, the commercial lithium titanate material is named sample o. Assemble it into a half-cell according to the method of Example 1 and finally conduct electrochemical performance tests. The results show that at 0.2 C, the first discharge specific capacity of battery a is 240 mAh g-1, which is 1.4 times that of battery o. After 500 cycles at 40 °C, the discharge specific capacity of battery a is 38 mAh g-1, which is 14.1 times that of battery o. Example 3

[0019] Weigh 0.5 g of LTO and 0.1364 g of CuC₂O₄ to make the molar ratio of Ti to Cu 6:1. Subsequently, thoroughly grind the above mixture composed of lithium titanate and copper oxalate in an agate mortar for 13 min to obtain a relatively evenly dispersed mixture. Then, place this mixture in a muffle furnace and calcine it at 550 °C for 1.5 h in an air atmosphere to obtain the product sample, which is denoted as sample a. For comparison, the commercial lithium titanate material is named sample o. Assemble it into a half-cell according to the method of Example 1, and finally conduct electrochemical performance tests. The results show that the initial discharge specific capacity of cell a is 196 mAh g⁻¹ at 0.2 C, which is 1.1 times that of cell o. After cycling 500 times at 40 C, the discharge specific capacity of cell a is 28 mAh g⁻¹, which is 10.4 times that of cell o. Example 4

[0020] Weigh 0.5 g of LTO and 0.1649 g of CuC₂O₄ to make the molar ratio of Ti to Cu 5:1. Subsequently, thoroughly grind the above mixture composed of lithium titanate and copper oxalate in an agate mortar for 15 min to obtain a relatively evenly dispersed mixture. Then, place this mixture in a muffle furnace and calcine it at 550 °C for 1 h in an air atmosphere to obtain the product sample, which is denoted as sample a. For comparison, the commercial lithium titanate material is named sample o. Assemble it into a half-cell according to the method of Example 1, and finally conduct electrochemical performance tests. The results show that the initial discharge specific capacity of cell a is 194 mAh g⁻¹ at 0.2 C, which is 1.1 times that of cell o. After cycling 500 times at 40 C, the discharge specific capacity of cell a is 37 mAh g⁻¹, which is 13.7 times that of cell o. Example 5

[0021] Weigh 0.5 g of LTO and 0.1649 g of CuC₂O₄ to make the molar ratio of Ti to Cu 5:1. Subsequently, thoroughly grind the above mixture composed of lithium titanate and copper oxalate in an agate mortar for 18 min to obtain a relatively evenly dispersed mixture. Then, place this mixture in a muffle furnace and calcine it at 540 °C for 1.5 h in an air atmosphere to obtain the product sample, which is denoted as sample a. For comparison, the commercial lithium titanate material is named sample o. Assemble it into a half-cell according to the method of Example 1, and finally conduct electrochemical performance tests. The results show that the initial discharge specific capacity of cell a is 202 mAh g⁻¹ at 0.2 C, which is 1.2 times that of cell o. After cycling 500 times at 40 C, the discharge specific capacity of cell a is 30 mAh g⁻¹, which is 11.1 times that of cell o. Example 6

[0022] Prepare a mixture containing LTO and CuC2O4, that is, weigh 0.5 g of LTO and 0.3274 g of CuC2O4 and grind them thoroughly to form a mixture with a molar ratio of Ti to Cu of 5:2. Place the mixture in a muffle furnace and calcine it at 450 °C for 2 h in an air atmosphere. Denote the obtained sample as sample a. Use the prepared sample as the anode material. Weigh 0.5 g of LTO and 0.3274 g of CuC2O4 to make the molar ratio of Ti to Cu 5:2. Subsequently, thoroughly grind the above mixture composed of lithium titanate and copper oxalate in an agate mortar for 15 min to obtain a relatively homogeneous mixture. Then, place the mixture in a muffle furnace and calcine it at 450 °C for 2 h in an air atmosphere to obtain the product sample, which is denoted as sample a. For comparison, name the commercial lithium titanate material sample o. Assemble it into a half-cell according to Example 1 and finally conduct electrochemical performance tests. The results show that the initial discharge specific capacity of cell a is 251 mAh g-1 at 0.2 C, which is 1.5 times that of cell o. After cycling 500 times at 40 C, the discharge specific capacity of cell a is 36 mAh g-1, which is 13.3 times that of cell o.

Claims

1. A preparation method of a copper-based lithium titanate anode material for a lithium-ion battery with high rate performance, characterized in that It includes the following steps: (1)Preparation of materials Lithium titanate (LTO); Copper oxalate (CuC2O4); Acetylene black; Polyvinylidene fluoride (PVDF); N-methylpyrrolidone (NMP); Celgard 2400 microporous polypropylene membrane; CR2430 button battery case (2)Preparation of organic electrolyte A Organic electrolyte A is: 1 mol / L -1 of LiPF6, and the preparation method is: dissolve LiPF6 in a mixed solvent, where the mixed solvent is composed of dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and vinylene carbonate (VC), mixed in a volume ratio of 1:1:1:1; (3)Sample preparation Weigh LTO and CuC2O4 according to the molar ratio of Ti to Cu being (4~6):(1~2). After mixing them, place them in a muffle furnace and calcine at 400°C~600°C for 0.5 h~3 h in an air atmosphere to obtain the product sample copper-based lithium titanate, which is denoted as sample a (4)Preparation of electrodes and assembly of batteries For comparison, commercial lithium titanate is named sample o. Weigh sample a, PVDF, and acetylene black and place them in an agate mortar. When weighing, control the mass ratio of sample a, PVDF, and acetylene black to be (8~9):(1~1.5):(1~1.5). Grind the mixture of the three in the agate mortar for 15~30 min. Then, gradually add N-methylpyrrolidone (NMP) and stir while adding to make the mixture into a paste. Subsequently, use a glass slide to evenly coat the obtained paste on a commercial copper (Cu) foil current collector. Immediately after that, place the coated current collector in a vacuum drying oven and dry it at 100~120°C for 4 h~8 h. After naturally cooling to room temperature, take it out and use a cutter to cut it into several electrode sheets with a diameter of 1 cm~2 cm to obtain electrode a. Replace sample a with commercial lithium titanate and prepare the LTO electrode under the same other conditions, which is denoted as electrode o. Using the prepared electrode a as the positive electrode, a lithium sheet as the negative electrode, Celgard 2400 microporous polypropylene membrane as the separator, organic electrolyte A as the electrolyte, and CR2430 button battery case as the battery case, assemble it into a half-cell in a glove box filled with nitrogen, which is denoted as battery a. Replace electrode a with electrode o and assemble a half-cell according to the above steps under the same other conditions, which is denoted as battery o 2. The preparation method according to claim 1, characterized in that, In step (3), the molar ratio of Ti to Cu is 5:1 3. The preparation method according to claim 1, wherein, In step (3), the calcination temperature of the LTO and CuC2O4 mixture in the muffle furnace is 500°C 4. The preparation method according to claim 1, characterized in that, In step (3), the calcination time of the LTO and CuC2O4 mixture in the muffle furnace is 1 h 5. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of sample a, PVDF, and acetylene black is 8:1:1 6. The preparation method according to claim 1, characterized in that, In step (4), the grinding time of the mixture of sample a, PVDF, and acetylene black is 20 min 7. The preparation method according to claim 1, characterized in that, In step (4) during the electrode preparation process, the temperature in the vacuum drying oven is 120°C 8. The preparation method according to claim 1, wherein, In step (4) during the electrode preparation process, the drying time in the vacuum drying oven is 6 h

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