Preparation method of high-rate copper-based lithium titanate lithium ion battery negative electrode material

Abstract

The invention relates to the technical field of energy materials, in particular to a preparation method of a high-rate copper-based lithium titanate lithium ion battery negative electrode material. The method comprises the following steps: weighing LTO and CuC2O4 according to the molar ratio of titanium in LTO to copper in CuC2O4 of (4-6): (1-2), mixing, fully grinding for 20 minutes, putting the obtained mixture into a muffle furnace, and calcining in an air atmosphere at 400-600 DEG C for 1-3 hours to obtain the copper-based lithium titanate. The copper-based lithium titanate electrode is prepared according to a conventional method and forms a half-cell with a simple substance lithium sheet for electrochemical performance test. During 0.2 C charging and discharging, the first discharge capacity of the copper-based lithium titanate is 1.7 to 2.0 times that of commercial LTO; and the discharge capacity of the copper-based lithium titanate after 100 cycles at 10C is 1.5-1.8 times that of common commercial LTO. The method is simple in process, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of energy materials, and in particular, to a preparation method of a high-rate copper-based lithium titanate anode material for lithium-ion batteries. Background Art

[0002] As a rechargeable battery, lithium-ion batteries have the advantages of high energy density, no memory effect, low self-discharge, environmental friendliness, etc., and are widely used in new energy power, energy storage, military aviation and other fields. Currently, most commercial lithium-ion batteries use graphite and lithium titanate (Li4Ti5O 12 abbreviated as LTO) as the anode material. With the in-depth research, it is found that during long-term cycling, especially in the case of overcharging, lithium dendrites will appear on the surface of graphite. In some specific cases, lithium dendrites will pierce the separator, causing short circuit between the positive and negative electrodes and triggering safety accidents. Compared with graphite, the charge-discharge platform voltage of LTO is about 1.5V (relative to metallic lithium), which can completely avoid the appearance of lithium dendrites during the charge-discharge process. Therefore, LTO has the advantage of high safety. At the same time, LTO has the advantages of low volume change rate and strong cycle stability during charge and discharge. Therefore, LTO has been widely used as the anode material in lithium-ion batteries. However, further research shows that LTO has the disadvantages of low theoretical specific capacity (175mAh g -1 ), poor conductivity, etc., which limit the application of LTO in high-energy density and high-power density lithium-ion batteries. Therefore, how to improve the electrochemical performance of LTO remains one of the hot issues in the research field of lithium-ion batteries.

[0003] Currently, the main methods to improve the electrochemical performance of LTO are as follows: (1) Improving the electrochemical performance of LTO by using the coating or doping of carbon materials. For example, Wang Shurong et al. disclosed a patent for carbon-coated lithium titanate particles and their preparation method (CN118800886A). Using this patent, lithium titanate particles with a high specific capacity and carbon coating can be obtained; (2) Reducing the size of LTO and preparing nano-scale LTO. For example, Zhao Mingcai et al. disclosed a patent for preparing a nano-silicon / lithium titanate composite material (CN118198314A). Using this patent, the size of the material can be reduced to the nano-scale, and the performance of this composite material is significantly better than that of LTO alone; (3) Preparing LTO with a special morphology can also significantly improve the electrochemical performance of LTO. For example, Lu Jiaxue et al. disclosed a method for preparing a belt-shaped lithium titanate negative electrode material (N116864676A). The novel LTO prepared by this method has good rate performance. Although there are many patents and reports on improving LTO, most of them are difficult to truly achieve large-scale commercial production due to deficiencies such as complex processes and high costs. Therefore, developing methods to improve the electrochemical performance of LTO remains one of the hot issues in the field of lithium-ion battery research. Literature research shows that there is no research report on preparing a novel copper-based lithium titanate lithium-ion battery negative electrode material to improve the high-rate performance of LTO by calcining a mixture of LTO and copper oxalate (CuC2O4). Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method for a high-rate copper-based lithium titanate lithium-ion battery negative electrode material, that is, a method to significantly improve the discharge specific capacity and high rate of LTO by calcining a mixture of CuC2O4 and LTO.

[0005] The concept of the present invention is as follows: Copper oxalate is doped into LTO in different molar ratios, and after sufficient grinding, a mixture is obtained. Subsequently, the obtained mixture is calcined in an air atmosphere at a certain temperature for a certain time to obtain copper-containing lithium titanate (named copper-based lithium titanate). Then, using the above calcined product as the active material, a half-cell is assembled for electrochemical performance testing. That is, according to a certain mass ratio, the above active material, acetylene black, and polyvinylidene fluoride (PVDF) are put together to form a mixture. Subsequently, a small amount of N-methylpyrrolidone (NMP) is added dropwise while stirring, and after sufficient stirring, a paste is obtained. Immediately afterwards, the obtained paste is coated on a current collector copper foil, and after vacuum drying, a copper-based lithium titanate electrode is obtained. Then, the above-obtained copper-based lithium titanate electrode is assembled with a lithium metal sheet into a half-cell for electrochemical performance testing. The results show that after 100 cycles at 10C, the discharge capacity of copper-based lithium titanate is 1.5 - 1.8 times that of ordinary commercial LTO, and the high-rate performance of commercial LTO is significantly improved.

[0006] The preparation method of the present invention comprises the following steps:

[0007] (1) Preparation of materials

[0008] Commercial lithium titanate (LTO); copper oxalate (CuC2O4); 1M LiPF6 dissolved in a mixed solvent (dimethyl carbonate (DMC) + ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + vinylene carbonate (VC)); acetylene black; polyvinylidene fluoride (PVDF); N-methylpyrrolidone (NMP).

[0009] (2) Preparation of copper-based lithium titanate and testing of its electrochemical performance

[0010] ① Preparation of copper-based lithium titanate

[0011] Weigh LTO and CuC2O4 respectively according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being (4 - 6):(1 - 2). After mixing the two, grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 400°C - 600°C for 1h - 3h in an air atmosphere. After that, copper-based lithium titanate can be obtained.

[0012] ② Preparation of copper-based lithium titanate electrode

[0013] Weigh copper-based lithium titanate, PVDF, and acetylene black with a mass ratio of (8 - 9):(1 - 1.5):(1 - 1.5) and place them in an agate mortar. Grind them thoroughly for 15 - 30 min to obtain a mixture. Then, gradually add NMP dropwise and stir while adding to adjust the mixture of the above three into a paste. Immediately, evenly apply the paste on a commercial Cu foil current collector. Subsequently, place the coated current collector in a vacuum drying oven and dry it at 100 - 120°C for 4 - 8h. After naturally cooling to room temperature, take it out and label it as electrode a.

[0014] For comparison, replace copper-based lithium titanate with commercial LTO and prepare a commercial LTO electrode according to the above steps, which is labeled as electrode o.

[0015] ③ Assembly of half-cell

[0016] Using the copper-based lithium titanate electrode as the positive electrode, a lithium sheet as the negative electrode, a Celgard 2400 microporous polypropylene membrane as the separator, and 1M LiPF6 dissolved in a mixed solvent (dimethyl carbonate (DMC) + ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + vinylene carbonate (VC)) as the electrolyte, assemble it into a half-cell a in a glove box filled with nitrogen. Replace copper-based lithium titanate with commercial LTO and assemble it into a half-cell according to the above steps, which is labeled as cell o. Conduct electrochemical performance testing.

[0017] ④Electrochemical performance test

[0018] The assembled half-cells were subjected to constant current charge-discharge tests using a high-precision battery performance test system (Shenzhen Neware Electronic Co., Ltd., CT-3008W-5V20mA-S4). The applied charge-discharge current was calculated according to 1C = 175 mAh g -1 The test voltage range was 1.00 V - 2.50 V. The results showed that at 0.2C charge-discharge, the initial discharge capacity of copper-based lithium titanate was 1.7 to 2.0 times that of commercial LTO; after 100 cycles at 10C, the discharge capacity of copper-based lithium titanate was 1.5 - 1.8 times that of ordinary commercial LTO.

[0019] The beneficial effects of the present invention are as follows: The process is simple. The present invention can obtain a novel copper-based lithium titanate anode material for lithium-ion batteries with significantly better battery performance than commercial LTO through a simple calcination method. Especially in terms of high-rate performance, as Figures 1-4 shown, the copper-based lithium titanate anode material of the present invention exhibits excellent performance, that is, after 100 cycles at 10C, the discharge capacity of the novel copper-based lithium titanate of the present invention is 1.5 - 1.8 times that of commercial LTO. Secondly, the preparation process of the present invention is very simple, clean and pollution-free, the raw materials are easily available, and the cost is low, which is very suitable for large-scale commercial production and has great development prospects. Description of the drawings

[0020] Figure 1 is the XRD analysis diagram of copper-based lithium titanate and commercial lithium titanate;

[0021] Figure 2 is the first charge-discharge diagram of the half-cells composed of copper-based lithium titanate and commercial lithium titanate and single lithium metal at 0.2C rate;

[0022] Figure 3 is the relationship diagram between the number of cycles and the discharge capacity at different rates between 0.2C and 10C of the half-cells composed of copper-based lithium titanate and commercial lithium titanate and single lithium metal;

[0023] Figure 4 is the relationship diagram between the number of cycles and the discharge capacity of the half-cells composed of copper-based lithium titanate and commercial lithium titanate and single lithium metal after 100 cycles at 10C. Detailed implementation manners

[0024] The following examples are used to illustrate the present invention.

[0025] Example 1

[0026] Weigh 0.5 g of LTO. Then, weigh CuC2O4 according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being 5:1. After that, mix the weighed LTO and CuC2O4 and grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 500 °C for 1 h in an air atmosphere. After that, copper-based lithium titanate can be obtained. Then, weigh copper-based lithium titanate, PVDF, and acetylene black according to a mass ratio of 8:1:1, place the three in an agate mortar and grind them thoroughly for 20 min. Subsequently, gradually add NMP drop by drop and stir while adding to adjust the mixture of the above three into a paste. Immediately, evenly apply the paste on a commercial Cu foil current collector. Then, place the coated current collector in a vacuum drying oven and dry it at 120 °C for 6 h. Take it out after naturally cooling to room temperature and label it as electrode a. For comparison, replace copper-based lithium titanate with commercial LTO and prepare a commercial LTO electrode according to the above steps, denoted as electrode o.

[0027] After that, use the copper-based lithium titanate electrode as the positive electrode, the lithium sheet as the negative electrode, Celgard 2400 microporous polypropylene membrane as the separator, and 1 M LiPF6 dissolved in a mixed solvent (dimethyl carbonate (DMC) + ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + vinylene carbonate (VC)) as the electrolyte. Assemble it into a half-cell in a glove box filled with nitrogen and label it as cell a for electrochemical performance testing. For comparison, replace copper-based lithium titanate with commercial LTO and prepare a half-cell according to the above steps, denoted as cell o.

[0028] Finally, use a high-precision battery performance testing system (Shenzhen Neware Electronic Co., Ltd., CT-3008W-5V20mA-S4) to conduct a constant current charge-discharge test on the assembled half-cell. Calculate the applied charge-discharge current according to 1C = 175 mAh g -1 The test voltage range is 1.00 V - 2.50 V.

[0029] Figure 1XRD patterns of copper-based lithium titanate (spectrum a) and commercial lithium titanate (spectrum o), as well as standard XRD patterns of LTO and CuO. For commercial lithium titanate (spectrum o), the diffraction peaks at 18.4°, 35.7°, 43.3°, 47.3°, 57.2°, 62.9° and 66.3° correspond to the (111), (311), (400), (311), (333), (440) and (531) crystal planes of LTO (JCPDS, No: 49-207), respectively, and are in good agreement with the XRD pattern of standard LTO. For copper-based lithium titanate (spectrum a), in addition to the diffraction peaks attributed to LTO mentioned above, characteristic diffraction peaks attributed to CuO also appear, that is, the diffraction peaks at 35.5°, 38.75°, 48.8°, 61.6° and 66.3° in spectrum a correspond to the (002), (200), (-202), (-113) and (-311) crystal planes of CuO (JCPDS, No: 45-937), respectively. This indicates that after calcining the mixture of LTO and copper oxalate (CuC2O4), the calcined product is a composite material of LTO and CuO crystals. That is, the copper-based lithium titanate prepared in this patent mainly contains LTO and CuO. Literature research shows that there is no research report on using the composite material of LTO and CuO as the anode material of lithium-ion batteries.

[0030] Figure 2 The first charge-discharge curves of the half-cells composed of copper-based lithium titanate and commercial lithium titanate with a lithium metal sheet at a rate of 0.2C, and the voltage test range is 1.00V - 2.50V. It can be seen that both groups of batteries have a long and flat discharge plateau at about 1.55V. The first discharge specific capacity of battery a is 299mAh g -1 is 1.74 times that of the traditional LTO battery (172mAh g -1 ).

[0031] Figure 3 The relationship between the number of cycles and the discharge capacity of the half-cells composed of copper-based lithium titanate and commercial lithium titanate with a lithium metal sheet at different rates from 0.2C to 10C. Obviously, at all given rates, the discharge specific capacity of battery a is much higher than that of battery o. For example, at 10C, the average discharge specific capacity of battery a is 116mAh g -1 , much higher than 56mAhg -1 of battery o. When a series of rate tests are completed and the rate returns to 0.2C again, the discharge specific capacity of battery a is still much higher than that of battery o, and the capacity retention rate of battery a is higher than 80%. Calcining the mixture of LTO and CuC2O4 can significantly improve the rate performance of traditional lithium titanate.

[0032] Figure 4Relationship diagram between the number of cycles and discharge capacity of half-cells composed of copper-based lithium titanate and commercial lithium titanate with a single lithium sheet at 10C for 100 cycles. It can be seen that after 100 cycles at 10C, the discharge specific capacity of cell a (120 mAh g -1 ) is 1.6 times that of commercial lithium titanate (75 mAh g -1 ), and during the entire cycle process, the capacity of copper-based lithium titanate shows almost no obvious attenuation, indicating that cell a has good cycle stability. Therefore, the copper-based lithium titanate prepared in the present invention has excellent high-rate performance compared to traditional LTO and has great commercial development value.

[0033] Example 2

[0034] Weigh 0.5 g of LTO. Then, weigh CuC2O4 according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being 4:1. After that, mix the weighed LTO and CuC2O4 and grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 500°C for 1.5 h in an air atmosphere. After that, copper-based lithium titanate can be obtained. Immediately, follow Example 1 to prepare the electrode and assemble the half-cell, and then conduct electrochemical performance tests. The results show that at 0.2C, the first discharge specific capacity of cell a is 1.9 times that of the traditional LTO cell; after 100 cycles of charge and discharge at 10C, the discharge specific capacity of cell a is 1.7 times that of cell o.

[0035] Example 3

[0036] Weigh 0.5 g of LTO. Then, weigh CuC2O4 according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being 6:1. After that, mix the weighed LTO and CuC2O4 and grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 500°C for 1 h in an air atmosphere. After that, copper-based lithium titanate can be obtained. Immediately, follow Example 1 to prepare the electrode and assemble the half-cell, and then conduct electrochemical performance tests. The results show that at 0.2C, the first discharge specific capacity of cell a is 1.8 times that of the traditional LTO cell; after 100 cycles of charge and discharge at 10C, the discharge specific capacity of cell a is 1.75 times that of cell o.

[0037] Example 4

[0038] Weigh 0.5 g of LTO. Then, weigh CuC2O4 according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being 6:1. After that, mix the weighed LTO and CuC2O4 and grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 450 °C for 1 h in an air atmosphere. After that, copper-based lithium titanate can be obtained. Immediately afterwards, prepare the electrode and assemble the half-cell according to Example 1 and then conduct the electrochemical performance test. The results show that the initial discharge specific capacity of cell a at 0.2C is 1.9 times that of the traditional LTO cell; after 100 cycles of charge and discharge at 10C, the discharge specific capacity of cell a is 1.73 times that of cell o.

[0039] Example 5

[0040] Weigh 0.5 g of LTO. Then, weigh CuC2O4 according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being 5:1. After that, mix the weighed LTO and CuC2O4 and grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 550 °C for 1 h in an air atmosphere. After that, copper-based lithium titanate can be obtained. Immediately afterwards, prepare the electrode and assemble the half-cell according to Example 1 and then conduct the electrochemical performance test. The results show that the initial discharge specific capacity of cell a at 0.2C is 1.9 times that of the traditional LTO cell; after 100 cycles of charge and discharge at 10C, the discharge specific capacity of cell a is 1.68 times that of cell o.

[0041] Example 6

[0042] Weigh 0.5 g of LTO. Then, weigh CuC2O4 according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being 5:1. After that, mix the weighed LTO and CuC2O4 and grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 500 °C for 2 h in an air atmosphere. After that, copper-based lithium titanate can be obtained. Immediately afterwards, prepare the electrode and assemble the half-cell according to Example 1 and then conduct the electrochemical performance test. The results show that the initial discharge specific capacity of cell a at 0.2C is 1.75 times that of the traditional LTO cell; after 100 cycles of charge and discharge at 10C, the discharge specific capacity of cell a is 1.60 times that of cell o.

Claims

1. A preparation method of a high-rate copper-based lithium titanate anode material for lithium-ion batteries, characterized in that, It includes the following steps: (1) Prepare the following materials: Commercial lithium titanate (LTO); copper oxalate (CuC2O4); 1M LiPF6 dissolved in a mixed solvent, which is a mixture of dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); acetylene black; polyvinylidene fluoride (PVDF); N-methylpyrrolidone (NMP); (2) Preparation of copper-based lithium titanate and testing of its electrochemical performance: ① Preparation of copper-based lithium titanate: Weigh LTO and CuC2O4 respectively according to the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 being 4-6:1-2. After mixing the two, grind them thoroughly for 20 minutes to obtain a mixture. Subsequently, place the obtained mixture in a muffle furnace and calcine it at 400°C - 600°C for 1h - 3h in an air atmosphere. After that, copper-based lithium titanate can be obtained; ② Preparation of copper-based lithium titanate electrode: Weigh copper-based lithium titanate, PVDF, and acetylene black with a mass ratio of 8-9:1-1.5:1-1.5 and place them in an agate mortar, grind them thoroughly for 15-30 min to obtain a mixture. Then, gradually add NMP and stir while adding to adjust the mixture of the above three into a paste; immediately, evenly apply the paste on a commercial Cu foil current collector. Subsequently, place the coated current collector in a vacuum drying oven and dry it at 100 - 120°C for 4 - 8h. Take it out after naturally cooling to room temperature and record it as electrode a; For comparison, replace copper-based lithium titanate with commercial LTO and prepare a commercial LTO electrode according to the above steps, and record it as electrode o; ③ Assembly of half-cell: Respectively use the prepared electrodes as the positive electrode, lithium sheet as the negative electrode, Celgard 2400 microporous polypropylene membrane as the separator, and 1M LiPF6 organic solution containing dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC) as the electrolyte, and assemble them into half-cells o and a in a glove box filled with nitrogen for electrochemical performance testing; ④ Electrochemical performance testing: The assembled half-cell was subjected to constant current charge and discharge tests using a high-precision battery performance test system. The charge and discharge current applied was calculated according to 1C = 175175 mAh g -1 and the test voltage range was 1.00 V - 2.50 V.

2. The preparation method according to claim 1, characterized in that, In the mixture of LTO and CuC2O4, the molar ratio of titanium (Ti) in LTO to copper (Cu) in CuC2O4 is 5:

1.

3. The preparation method according to claim 1, characterized in that, The calcination temperature of the mixture of LTO and CuC2O4 in the muffle furnace is 500°C.

4. The preparation method according to claim 1, wherein The calcination time of the mixture of LTO and CuC2O4 in the muffle furnace is 1 hour.

5. The preparation method according to claim 1, wherein When preparing the copper-based lithium titanate electrode, the mass ratio of copper-based lithium titanate, PVDF, and acetylene black is 8:1:

1.

6. The preparation method according to claim 1, characterized in that, During the electrode preparation process, the temperature in the vacuum drying oven is 120°C.

7. The preparation method according to claim 1, characterized in that, During the electrode preparation process, the vacuum drying time is 6 hours.

Images