Method for improving low-temperature performance of graphite negative electrode

Abstract

The invention provides a method for improving the low-temperature performance of a graphite negative electrode, which comprises the following steps: S1, mixing asphalt, graphite and niobium oxide to obtain mixed powder; mixing the mixed powder with tetrahydrofuran, and removing the solvent to obtain a negative electrode material precursor; and S2, calcining the negative electrode material precursor in a protective atmosphere to obtain coated modified graphite. According to the invention, a liquid phase coating method is adopted, the surface of graphite is coated with niobium oxide by taking asphalt as a carbon precursor, and the graphite is subjected to coating modification, so that the low-temperature performance of the graphite is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium ion battery negative electrode materials, and in particular relates to a method for improving the low-temperature performance of a graphite negative electrode. Background Art

[0002] Lithium-ion batteries consist of four main components: the positive electrode, negative electrode, electrolyte, and separator. Graphite negative electrode materials are one of the most commonly used negative electrode materials for lithium-ion batteries, due to their high theoretical specific capacity, low operating potential, low cost, and high stability. However, graphite cannot meet the requirements of low-temperature operation.

[0003] At low temperatures, the electrolyte viscosity increases and crystallizes easily, reducing ionic conductivity and increasing resistance to lithium ion transfer at the interface between the graphite electrode and the electrolyte, leading to reduced battery charge and discharge efficiency. The weakened vibration of the graphite lattice restricts the movement of lithium ions within the graphite lattice, making it difficult for the negative electrode to deintercalate lithium. This can easily lead to lithium precipitation during low-temperature charging, resulting in poor battery cycle performance and even safety risks. Summary of the Invention

[0004] Based on the above technical problems, the present invention provides a method for improving the low-temperature performance of graphite negative electrode. The method adopts the liquid phase coating method and uses asphalt as a carbon precursor to coat niobium oxide on the graphite surface, thereby coating and modifying the graphite and effectively improving the low-temperature performance of the graphite.

[0005] The specific scheme of the present invention is as follows:

[0006] The present invention provides a method for improving the low-temperature performance of a graphite negative electrode, comprising the following steps: S1, mixing asphalt, graphite, and niobium oxide to obtain a mixed powder; mixing the mixed powder with tetrahydrofuran, removing the solvent, and obtaining a negative electrode material precursor; S2, calcining the negative electrode material precursor under a protective atmosphere to obtain coated modified graphite.

[0007] Preferably, in S1, the mass ratio of graphite, pitch and niobium oxide is 75-90:1-10:5-15.

[0008] Preferably, in S1, the mass ratio of graphite, asphalt and niobium oxide is 75:10:15.

[0009] Preferably, in S1, the niobium oxide is selected from at least one of niobium pentoxide, niobium oxide, and niobium trioxide.

[0010] Preferably, in S1, the graphite is artificial graphite; and the particle size D50 of the asphalt is 2 to 3 μm.

[0011] Preferably, in S1, the mass volume ratio of the mixed powder to tetrahydrofuran is 100:300-500 in g / ml.

[0012] Preferably, in S1, the mixed powder is mixed with tetrahydrofuran and stirred at 40-60° C. until the solvent is completely volatilized, thereby removing the solvent.

[0013] Preferably, in S2, the protective atmosphere is argon.

[0014] Preferably, in S2, the calcination temperature is 700-1000°C, and the holding time is 3-6 hours. More preferably, during the calcination process, the heating rate is 3-8°C / min. More preferably, in S2, the negative electrode material precursor is placed in a tube furnace for calcination.

[0015] Preferably, in S2, the calcination temperature is 900°C, the holding time is 4 hours, and the heating rate is 5°C / min.

[0016] The beneficial effects of the present invention are:

[0017] The technical concept of the present invention is to reduce the resistance to lithium ion transfer on the one hand, and to improve the low-temperature conductivity of graphite-based composite materials on the other hand. The two work together to improve the low-temperature performance of graphite-based negative electrode materials. Specifically, the present invention uses asphalt as a carbon precursor to coat niobium oxide to modify graphite. After carbonization of the asphalt, an amorphous carbon layer is formed on the outermost layer. It has rich nanopores and defect structures, which can provide more lithium ion transmission channels and reduce the diffusion barrier of lithium ions at the edge of graphite at low temperatures. Niobium oxide realizes electron conduction through an electron hopping mechanism and can maintain a high conductivity at low temperatures (-20°C).

[0018] In a preferred embodiment, the mass ratio of graphite, pitch and niobium oxide is controlled within a specific range to ensure a balance between the conductivity and ion transport of the outer amorphous carbon layer. DETAILED DESCRIPTION

[0019] Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0020] Example 1

[0021] A method for improving the low-temperature performance of a graphite negative electrode comprises the following steps:

[0022] S1. Weigh 10 g of asphalt (D50: 2 μm), 85 g of artificial graphite, and 5 g of niobium pentoxide powder and mix them in a mixer to obtain a mixed powder; add the mixed powder to 300 ml of tetrahydrofuran solution and stir at 50° C. until the solvent is completely evaporated to obtain a negative electrode material precursor.

[0023] S2. Place the negative electrode material precursor obtained in S1 into a tubular furnace protected by an argon atmosphere, heat it to 900°C at a rate of 5°C / min and keep it warm for 4 hours to obtain coated modified graphite.

[0024] Example 2

[0025] A method for improving the low-temperature performance of a graphite negative electrode comprises the following steps:

[0026] S1. Weigh 10 g of asphalt (D50: 2 μm), 80 g of artificial graphite, and 10 g of niobium pentoxide powder and mix them in a mixer to obtain a mixed powder; add the mixed powder to 300 ml of tetrahydrofuran solution and stir at 50° C. until the solvent is completely evaporated to obtain a negative electrode material precursor.

[0027] S2. Place the negative electrode material precursor obtained in S1 into a tubular furnace protected by an argon atmosphere, heat it to 900°C at a rate of 5°C / min and keep it warm for 4 hours to obtain coated modified graphite.

[0028] Example 3

[0029] A method for improving the low-temperature performance of a graphite negative electrode comprises the following steps:

[0030] S1. Weigh 10 g of asphalt (D50: 2 μm), 75 g of artificial graphite, and 15 g of niobium pentoxide powder and mix them in a mixer to obtain a mixed powder; add the mixed powder to 300 ml of tetrahydrofuran solution and stir at 50° C. until the solvent is completely evaporated to obtain a negative electrode material precursor.

[0031] S2. Place the negative electrode material precursor obtained in S1 into a tubular furnace protected by an argon atmosphere, heat it to 900°C at a rate of 5°C / min and keep it warm for 4 hours to obtain coated modified graphite.

[0032] Comparative Example 1

[0033] A method for preparing a negative electrode material comprises the following steps:

[0034] S1. Weigh 100 g of artificial graphite and add it to 300 ml of tetrahydrofuran solution. Stir at 50° C. until the solvent is completely evaporated to obtain a negative electrode material precursor.

[0035] S2. Place the negative electrode material precursor obtained in S1 into a tubular furnace protected by an argon atmosphere, heat it to 900°C at a rate of 5°C / min and keep it warm for 4 hours to obtain the negative electrode material.

[0036] Comparative Example 2

[0037] A method for preparing a negative electrode material comprises the following steps:

[0038] S1. Weigh 10 g of asphalt (D50: 2 μm) and 90 g of artificial graphite and mix them in a mixer to obtain a mixed powder. Add the mixed powder to 300 ml of tetrahydrofuran solution and stir at 50° C. until the solvent is completely evaporated to obtain a negative electrode material precursor.

[0039] S2. Place the negative electrode material precursor obtained in S1 into a tubular furnace protected by an argon atmosphere, heat it to 900°C at a rate of 5°C / min and keep it warm for 4 hours to obtain the negative electrode material.

[0040] Comparative Example 3

[0041] A method for preparing a negative electrode material comprises the following steps:

[0042] S1. Weigh 75 g of artificial graphite and 25 g of niobium pentoxide powder and mix them in a laboratory mixer to obtain a mixed powder; add the mixed powder to 300 ml of tetrahydrofuran solution and stir at 50° C. until the solvent is completely evaporated to obtain a negative electrode material precursor.

[0043] S2. Place the negative electrode material precursor obtained in S1 into a tubular furnace protected by an argon atmosphere, heat it to 900°C at a rate of 5°C / min and keep it warm for 4 hours to obtain coated modified graphite.

[0044] Comparative Example 4

[0045] A method for preparing a negative electrode material comprises the following steps:

[0046] S1. Weigh 15 g of asphalt (D50: 2 μm), 75 g of artificial graphite, and 15 g of niobium pentoxide powder and mix them in a mixer to obtain a mixed powder; add the mixed powder to 300 ml of tetrahydrofuran solution and stir at 50° C. until the solvent is completely evaporated to obtain a negative electrode material precursor.

[0047] S2. Place the negative electrode material precursor obtained in S1 into a tubular furnace protected by an argon atmosphere, heat it to 900°C at a rate of 5°C / min and keep it warm for 4 hours to obtain coated modified graphite.

[0048] The negative electrode materials obtained in the above embodiments and comparative examples were used to assemble button batteries, as follows:

[0049] The coated modified graphite obtained in the above examples and the negative electrode material obtained in the comparative example were stirred and mixed with conductive carbon black and PVDF in a mass ratio of 91.5:2:6.5 to form a slurry. The mixed slurry was evenly coated on a previously prepared copper foil and dried in a vacuum drying oven at 110°C for 12 hours. The slurry was weighed and used as the negative electrode of a simulated battery. The metal lithium sheet was used as the positive electrode, the separator was Celgard 2400, and the electrolyte was 1 mol / LLiPF6 (EC:DMC volume ratio was 1:1). The battery was assembled into a button cell CR 2016 in an argon-filled, deoxygenated and dehydrated glove box.

[0050] The performance data of the button-type batteries corresponding to the above embodiments and comparative examples at -20°C discharge specific capacity and capacity retention rate tests are as follows:

[0051] Table 1. -20℃ discharge specific capacity and capacity retention rate data

[0052]

[0053]

[0054] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for improving the low-temperature performance of a graphite negative electrode, characterized in that: The method comprises the following steps: S1, mixing asphalt, graphite and niobium oxide to obtain mixed powder; mixing the mixed powder with tetrahydrofuran, removing the solvent and obtaining a negative electrode material precursor; S2, calcining the negative electrode material precursor under a protective atmosphere to obtain coated modified graphite.

2. The method for improving the low temperature performance of a graphite negative electrode according to claim 1, characterized in that: In S1, the mass ratio of graphite, pitch and niobium oxide is 75-90:1-10:5-15.

3. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S1, the mass ratio of graphite, pitch and niobium oxide is 75:10:

15.

4. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S1, the niobium oxide is selected from at least one of niobium pentoxide, niobium oxide, and niobium trioxide.

5. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S1, the graphite is artificial graphite; and the particle size D50 of the asphalt is 2 to 3 μm.

6. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S1, the mass volume ratio of the mixed powder to tetrahydrofuran is 100:300-500 in g / ml.

7. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S1, the mixed powder is mixed with tetrahydrofuran and stirred at 40 to 60° C. until the solvent is completely volatilized, thereby removing the solvent.

8. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S2, the protective atmosphere is argon.

9. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S2, the calcination temperature is 700-1000°C and the holding time is 3-6 hours.

10. The method for improving the low temperature performance of a graphite negative electrode according to claim 1 or 2, characterized in that: In S2, the calcination temperature is 900°C, the holding time is 4 h, and the heating rate is 5°C / min.

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