Preparation method of anode heterojunction structure lithium vanadate compound for lithium ion battery

Abstract

The invention provides a preparation method of a positive electrode heterojunction structure lithium vanadate compound for a lithium ion battery, and relates to the technical field of lithium ion batteries, and the preparation method comprises the following steps: mixing a V2O5 precursor and LiH according to a set molar ratio, and sintering at a first set temperature for a first set time to obtain a positive electrode precursor for the lithium ion battery; the molar ratio is set to be (0.01-0.2): 1; the first set temperature is 300 to 600 DEG C; stirring and cleaning the positive electrode precursor for the lithium ion battery in deionized water for a second set time, and analyzing to obtain a solid phase; performing vacuum drying on the solid phase at a second set temperature for a third set time to obtain the lithium vanadate compound with the heterojunction structure; the lithium vanadate compound with the heterojunction structure is a LiV3O8 / LiV6O15 composite material. The LiV3O8 / LiV6O15 composite material prepared by the invention has the advantages of long circulation, high capacity, low resistance and the like.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing a positive electrode heterojunction structure lithium vanadate compound for lithium ion batteries. Background Art

[0002] With the rapid development of modern industry and technology, traditional fossil energy represented by coal and oil is being consumed at an accelerated rate, further exacerbating global environmental pollution and climate problems. Therefore, the development and application of clean energy has become the key to the development of human society in the 21st century. Power batteries are the heart of electric vehicles and the key to the development of the new energy vehicle industry.

[0003] Traditional ternary nickel cobalt manganese oxide and lithium iron phosphate cathode materials face several challenges: the toxicity of metals such as Co and Mn, the high cost of Ni, and the low operating voltage and low capacity of lithium iron phosphate. The V element, like most transition metals, has multiple valence states, and its toxicity and cost are relatively low. Compared with vanadium-based oxides, pre-lithiated vanadium oxide "monoclinic LiV3O8" has higher structural stability and higher specific discharge capacity than vanadium phosphate salts.

[0004] However, extensive research on LiV3O8 often involves complex synthesis processes to achieve the desired morphology and particle size. Although the storage capacity and rate performance of lithium are improved with the change of morphology and the reduction of particle size, it still cannot meet the requirements of long cycle life and high energy density in practical applications due to low operating voltage and poor structural stability. Moreover, the synthesis of most LVO cathode materials relies on liquid phase chemical reactions or long-term solid phase ball milling or ultrasonic processes, which are inefficient and not suitable for practical production applications. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a positive electrode heterojunction structure lithium vanadate compound for lithium ion batteries, and the prepared LiV3O8 / LiV6O 15 The composite material has the advantages of long cycle, high capacity and low resistance characteristics.

[0006] A method for preparing a positive electrode heterojunction structure lithium vanadate compound for a lithium ion battery, comprising:

[0007] The V2O5 precursor and LiH are mixed in a set molar ratio and sintered at a first set temperature for a first set time to obtain a positive electrode precursor for a lithium ion battery; the set molar ratio is 0.01-0.2:1; the first set temperature is 300-600°C;

[0008] The positive electrode precursor for the lithium ion battery is stirred and washed in deionized water for a second set time to analyze the solid phase;

[0009] The solid phase is vacuum dried at the second set temperature for a third set time to obtain a lithium vanadate compound with a heterojunction structure; the lithium vanadate compound with a heterojunction structure is LiV3O8 / LiV6O 15 Composite materials.

[0010] Optionally, the sintering atmosphere is any one of an argon atmosphere and a nitrogen atmosphere.

[0011] Optionally, the first set time is 2-10 hours.

[0012] Optionally, the second set time is 20-30 hours.

[0013] Optionally, the mass ratio of the positive electrode precursor for lithium-ion batteries to the deionized water is 0.01-0.1:1.

[0014] Optionally, the second set temperature is 60-100°C.

[0015] Optionally, the third set time is 12-36 hours.

[0016] Optionally, LiV3O8 and LiV6O in the heterojunction lithium vanadate compound 15 The molar ratio is 0.5-0.8:1.

[0017] The effects of the present invention are as follows:

[0018] The preparation method of the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery of the present invention can obtain LiV3O8 / LiV6O by controlling the molar ratio of V2O5 precursor and LiH and the sintering mixing degree. 15 Composite materials with high Li + Diffusion channels and excellent ionic conductivity and long-term cycle performance are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of the preparation method of the positive electrode heterojunction structure lithium vanadate compound for lithium ion batteries of the present invention;

[0020] Figure 2 It is LiV3O8 / LiV6O prepared in Example 2 of the present invention. 15 X-ray powder diffraction pattern of the composite material;

[0021] Figure 3 LiV3O8 / LiV6O prepared in Example 2 of the present invention 15 X-ray photoelectron spectroscopy of element V of the composite material;

[0022] Figure 4LiV3O8 / LiV6O prepared in Example 2 of the present invention 15 Scanning electron microscopy images of the composite material;

[0023] Figure 5 LiV3O8 / LiV6O prepared in Example 2 of the present invention 15 Schematic diagram of the electrochemical performance cycle specific capacity and coulombic efficiency test results of the composite material;

[0024] Figure 6 Schematic diagram of rate performance test results of heterojunction structure lithium vanadate compounds prepared in Example 2, Example 3 and Example of the present invention;

[0025] Figure 7 LiV3O8 / LiV6O prepared in Example 2 of the present invention 15 Electrochemical impedance spectroscopy of the composite materials. DETAILED DESCRIPTION

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0027] Example 1

[0028] Figure 1 The present invention is a flow chart of the preparation method of the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery. Figure 1 As shown, the present invention provides a method for preparing a positive electrode heterojunction structure lithium vanadate compound for a lithium ion battery, which comprises:

[0029] S1, mixing a V2O5 precursor and LiH in a set molar ratio, and sintering at a first set temperature for a first set time to obtain a positive electrode precursor for a lithium ion battery. Preferably, the molar ratio is set to 0.01-0.2:1; the first set temperature is 300-600°C; the first set time is 2-10h. The sintering atmosphere is either an argon atmosphere or a nitrogen atmosphere.

[0030] S2, stirring and washing the positive electrode precursor for lithium ion batteries in deionized water for a second set time to separate out the solid phase. The second set time is 20-30 hours, preferably 24 hours. The mass ratio of the positive electrode precursor for lithium ion batteries to deionized water is 0.01-0.1:1.

[0031] S3, vacuum drying the solid phase at the second set temperature for a third set time to obtain a lithium vanadate compound with a heterojunction structure. The lithium vanadate compound with a heterojunction structure is LiV3O8 / LiV6O 15 Composite material. The second set temperature is 60-100°C, preferably 80°C. The third set time is 12-36h, preferably 24h. LiV3O8 and LiV6O in the heterojunction structure lithium vanadate compound15 The molar ratio is 0.5-0.8:1.

[0032] Example 2

[0033] The V2O5 precursor and LiH were added into a high-speed mixer at a molar ratio of 0.2:1, and mixed for 30 minutes under an argon atmosphere to achieve uniform mixing. The mixed material was placed in a sintering furnace, and the argon atmosphere was maintained in the furnace. The temperature in the furnace was increased from room temperature to 500°C at a rate of 5°C / min, and maintained at this sintering temperature for 4 hours to fully sinter and obtain a positive electrode precursor for a lithium-ion battery.

[0034] The positive electrode precursor for lithium ion batteries was stirred and washed in deionized water for 24 hours, and then the solid phase was analyzed by suction filtration. The mass ratio of the positive electrode precursor for lithium ion batteries to deionized water was 0.01:1.

[0035] The solid phase was dried under vacuum at 80 °C for 24 h to obtain a lithium vanadate compound with a heterojunction structure, namely LiV3O8 / LiV6O 15 Composite materials. Scanning electron microscope images of heterojunction structured lithium vanadate compounds are shown in Figure 2. Figure 4 The electrochemical performance cycle specific capacity and coulombic efficiency test results of the heterojunction structure lithium vanadate compound are shown in Figure 5 The electrochemical impedance spectrum of the heterojunction structure lithium vanadate compound is shown in Figure 7 shown.

[0036] The heterojunction structure lithium vanadate compound obtained in this example was subjected to XRD (X-ray powder diffraction) test, and the results are as follows: Figure 2 As shown by Figure 2 It can be observed that the comparison with the standard card shows that the monoclinic LiV6O 15 The diffraction peak of the composite material corresponds to the C2 / m space group, and the diffraction peak of the monoclinic LiV3O8 corresponds to the P21 / m space group. The prominent and narrow diffraction peaks indicate that LiV3O8 / LiV6O 15 The composite materials have higher crystallinity and smaller grain size.

[0037] The heterojunction structure lithium vanadate compound obtained in this embodiment was subjected to XPS (X-ray photoelectron spectroscopy) test, and the results are as follows: Figure 3 As shown by Figure 3 It can be observed that V 2p3 / 2 and V 2p1 / 2 The V peak on the track is clearly split into V4 + and V5 + , V4 + The existence of LiV6O 15 According to the fitting results, Table 1 lists the distribution ratios of V in different valence states.

[0038] Table 1 Distribution ratios of different valence bond states and different valence states of V elements

[0039] Valence bond status percentage Valence percentage <![CDATA[V 2p3 / 2 ]]> 76.4％ <![CDATA[V 5+ ]]> 68.0％ <![CDATA[V 2p1 / 2 ]]> 23.6％ <![CDATA[V 4+ ]]> 32.0％

[0040] Example 3

[0041] The molar ratio of the V2O5 precursor to LiH was set to 0.4:1, and the other parameters were the same as those in Example 2 to prepare a lithium vanadate compound with a heterojunction structure.

[0042] Example 4

[0043] The molar ratio of the V2O5 precursor to LiH was set to 0.6:1, and the other parameters were the same as those in Example 2 to prepare a lithium vanadate compound with a heterojunction structure.

[0044] The lithium heterojunction structure lithium vanadate compounds prepared in Example 2, Example 3 and Example 4 were used to prepare button batteries for electrical performance evaluation and comparison. The button battery model is CR2032, and the negative electrode uses a lithium sheet. The test conditions of the button battery are: temperature is 25°C, the charge and discharge voltage range is 2.8-4.3V; the charge and discharge rate of the specific capacity test is 0.1C, the charge and discharge rate of the cycle test is 1C, and the number of cycles is 100. Some results are shown as follows: Figure 6 shown.

[0045] The heterojunction structure lithium vanadate compound prepared by the present invention was compared with the existing positive electrode material in a cycle test, and the results are shown in Table 2.

[0046] Table 2 Comparison results of cycle experiments

[0047] Cathode Materials Number of cycles (n) Capacity retention rate (%) <![CDATA[LiPO4]]> 800 34.8 NCM523 800 50.6 NCM811 800 73.7 <![CDATA[LiV3O8]]> 800 22.8 Embodiment 2 of the present invention 800 81.3

[0048] It can be seen from Table 2 that the heterojunction lithium vanadate compound prepared in Example 2 of the present invention has significantly improved cycle performance compared with existing positive electrode materials.

[0049] The above embodiments are only descriptions of the preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a positive electrode heterojunction structure lithium vanadate compound for lithium ion batteries, It is characterized in that It includes: V 2 O 5 The precursor and LiH are mixed in a set molar ratio and sintered at a first set temperature for a first set time to obtain a positive electrode precursor for a lithium ion battery; the set molar ratio is 0.01-0.2:1; the first set temperature is 300-600°C; The positive electrode precursor for the lithium ion battery is stirred and washed in deionized water for a second set time to analyze the solid phase; The solid phase is vacuum dried at the second set temperature for a third set time to obtain a lithium vanadate compound with a heterojunction structure; the lithium vanadate compound with a heterojunction structure is LiV 3 O 8 / LiV 6 O 15 Composite materials.

2. The method for preparing the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery according to claim 1, It is characterized in that The sintering atmosphere is either an argon atmosphere or a nitrogen atmosphere.

3. The method for preparing the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery according to claim 1, It is characterized in that The first setting time is 2-10 hours.

4. The method for preparing the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery according to claim 1, It is characterized in that The second setting time is 20-30h.

5. The method for preparing the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery according to claim 1, It is characterized in that The mass ratio of the positive electrode precursor for lithium ion batteries to the deionized water is 0.01-0.1:

1.

6. The method for preparing the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery according to claim 1, It is characterized in that The second set temperature is 60-100°C.

7. The method for preparing the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery according to claim 1, It is characterized in that The third setting time is 12-36h.

8. The method for preparing the positive electrode heterojunction structure lithium vanadate compound for lithium ion battery according to claim 1, It is characterized in that The LiV 3 O 8 and LiV 6 O 15 The molar ratio is 0.5-0.8:1.

Images