Graphite negative electrode material and secondary battery

Abstract

The invention discloses a graphite negative electrode material and a secondary battery. Graphite of the graphite negative electrode material has dye adsorption sites, the dye adsorption amount is smaller than or equal to 1.1 mg / g, and the dye desorption amount / dye adsorption amount is smaller than or equal to 0.25; the dye adsorption amount is the saturated adsorption amount of the graphite to the dye at 25 DEG C, and the dye desorption amount is the desorption amount when the temperature is raised to 35 DEG C from 25 DEG C. The cycle performance of the lithium ion battery adopting the graphite with the dye adsorption capacity of less than or equal to 1.1 mg / g and the dye desorption capacity / dye adsorption capacity of less than or equal to 0.25 as the negative electrode material is more than 5000 circles, and the secondary battery provided by the invention has excellent long cycle performance.

Description

Technical Field

[0001] The invention belongs to the technical field of negative electrode materials for lithium ion batteries, and in particular relates to a graphite negative electrode material and a preparation method thereof, and a secondary battery. Background Art

[0002] As the mainstream negative electrode material for lithium-ion batteries, graphite has received widespread attention, and cycle performance is one of the key properties that affect its application.

[0003] The presence of defects will make non-polar graphite show a certain polarity, resulting in differences in electron cloud density, presenting a "rough surface" structure with undulating electronic structure, affecting the interaction between the graphite negative electrode and SEI. At the same time, the "rough surface" structure caused by defects may promote the occurrence of side reactions, thereby affecting the stability of the SEI film. Therefore, the "rough surface" structure caused by defects in the graphite surface is the core factor affecting the cycle performance of the graphite negative electrode. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the graphite negative electrode material in the prior art cannot meet the cycle performance requirements of lithium-ion batteries, thereby providing a graphite negative electrode material and a preparation method thereof, and a secondary battery.

[0005] To this end, the present invention provides the following technical solutions:

[0006] In one aspect, the present invention provides a graphite negative electrode material, wherein the graphite has an adsorption site for a dye.

[0007] Among them, the dye adsorption amount is ≤1.1mg / g, and the dye desorption amount / dye adsorption amount is ≤0.25;

[0008] The dye adsorption amount is the saturated adsorption amount of the dye by graphite at 25°C, and the dye desorption amount is the desorption amount when the temperature is increased from 25°C to 35°C.

[0009] The adsorption sites of graphite for dyes are mainly: "rough surface" caused by defects and crystal end faces exposed on the surface of graphite particles. The more defects on the graphite surface, the larger the area of ​​"rough surface" caused by defects, and the greater the adsorption of dyes. The adsorption of dyes by "rough surface" mainly depends on weak electrostatic force / dispersion force. The adsorption of dyes by the crystal end faces exposed on the surface of graphite particles depends on π-π stacking, and the interaction strength is higher than the adsorption force caused by the "rough surface". When desorption occurs, the "rough surface" should desorb before the crystal end faces. Therefore, under appropriate and equal conditions, the desorption amount is proportional to the number of "rough surfaces" caused by defects in the graphite sample. Under the condition of a certain adsorption amount, the greater the desorption amount / adsorption amount, the greater the proportion of "rough surface" caused by defects under the same conditions. The "rough surface" structure caused by defects on the graphite surface is the core factor affecting the cycle performance of graphite negative electrode. The greater the desorption amount / adsorption amount, the larger the "rough surface" area contained in each gram of graphite, the greater the defect concentration, and the worse the cycle performance.

[0010] The cycle performance of a lithium ion battery using graphite with a dye adsorption amount of ≤1.1 mg / g and a dye desorption amount / dye adsorption amount of ≤0.25 as a negative electrode material is more than 5000 cycles. The secondary battery provided by the present invention has excellent long cycle performance.

[0011] Furthermore, the dye adsorption amount is ≤0.9 mg / g.

[0012] Furthermore, the dye is methyl orange or methylene blue.

[0013] Furthermore, the specific surface area of ​​the graphite is 0.8 to 2.0 m 2 / g. The larger the specific surface area, the more surface defects and end face sites are exposed, which will cause the SEI stability to deteriorate and the cycle to deteriorate. The specific surface area of ​​graphite within the range defined in the present invention can avoid the deterioration of the cycle performance.

[0014] Furthermore, the D50 of the graphite is 4 to 20 μm;

[0015] Furthermore, the graphitization degree of the graphite is 92-96%;

[0016] Furthermore, the tap density of the graphite is 0.75 to 1.40 g / cm 3 ;

[0017] Furthermore, the compaction density of the graphite at 5T is ≥1.8g / cm 3 .

[0018] Furthermore, the graphite is artificial graphite.

[0019] Furthermore, the preparation method of the graphite negative electrode material comprises the following steps: using raw coke with an average particle size of 1 to 100 μm, ash content ≤0.5%, S content ≤1.5%, and Hastelloy grindability index of 70 to 140 as a raw material, and preparing the graphite negative electrode material through graphitization.

[0020] In the present invention, the coke raw material is pulverized, shaped, and graphitized to obtain graphite. The coke raw material is preferably: raw coke with S (sulfur) content ≤1.5%, ash content ≤0.5%, and Hastelloy grindability index of 70-140. The S in the coke will overflow during the graphitization process, generating pores, resulting in an increase in the specific surface area of ​​the graphite, an increase in the formation of SEI, and a deterioration in the cycle; while the ash content is mainly composed of metal impurities, and some transition metals have a catalytic graphitization effect, resulting in multiple nucleation points of graphite crystals and excessive growth, resulting in an increase in defects; the Hastelloy grindability index can reflect the hardness of the coke, which is related to the sp 3 The content of hybrid carbon, the lower the Hastelloy grindability index, the higher the sp 3 The more the content of hybrid carbon, the more difficult it is to graphitize, and the more defects are produced after graphitization. Therefore, the smaller the S content and ash content in the coke, the larger the Hastelloy Grindability Index, the fewer pores and defects in the graphite obtained after graphitization, and the milder the cyclic attenuation caused by this.

[0021] Furthermore, the graphitization temperature is 2800-3200° C., and / or the graphitization time is 1 to 8 hours.

[0022] Furthermore, the raw coke includes at least one of petroleum coke and pitch coke.

[0023] In a second aspect, the present invention provides a secondary battery comprising the above-mentioned graphite negative electrode material.

[0024] The secondary battery prepared by using the graphite of the present invention as the negative electrode material has a cycle performance of more than 5000 cycles. DETAILED DESCRIPTION

[0025] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0026] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0027] Example 1

[0028] This embodiment provides a graphite negative electrode material, including graphite 1. The adsorption and desorption amounts of the dye by graphite 1 are shown in Table 1.

[0029] The present embodiment provides a method for preparing a graphite negative electrode material, comprising: pulverizing a petroleum coke raw material having a sulfur content of 0.30 wt%, an ash content of 0.10 wt%, and a Hastelloy grindability index of 100, grading, and shaping to obtain coke powder with an average particle size of 11.4 μm, and graphitizing at 3090° C. for 2 h to obtain graphite 1.

[0030] Example 2

[0031] This embodiment provides a graphite negative electrode material, including graphite 2. The adsorption and desorption amounts of the dye by graphite 2 are shown in Table 1.

[0032] The present embodiment provides a method for preparing a graphite negative electrode material, comprising: pulverizing a pitch coke raw material having a sulfur content of 0.52 wt%, an ash content of 0.15 wt%, and a Hastelloy grindability index of 97, grading, shaping, obtaining coke powder with an average particle size of 16.8 μm, and graphitizing at 3090° C. for 2 h to obtain graphite 2.

[0033] Example 3

[0034] This embodiment provides a graphite negative electrode material, including graphite 3. The adsorption and desorption amounts of the dye by graphite 3 are shown in Table 1.

[0035] The present embodiment provides a method for preparing a graphite negative electrode material, comprising: pulverizing a petroleum coke raw material having a sulfur content of 0.25 wt %, an ash content of 0.02 wt %, and a Hastelloy grindability index of 111, grading, shaping, obtaining coke powder with an average particle size of 15 μm, and graphitizing at 3090° C. for 2 h to obtain graphite 3.

[0036] Example 4

[0037] This embodiment provides a graphite negative electrode material, including graphite 4. The adsorption and desorption amounts of the dye by graphite 4 are shown in Table 1.

[0038] The present embodiment provides a method for preparing a graphite negative electrode material, comprising: pulverizing a petroleum coke raw material having a sulfur content of 0.75 wt %, an ash content of 0.35 wt %, and a Hastelloy grindability index of 89, grading, shaping, obtaining coke powder with an average particle size of 13.2 μm, and graphitizing at 3090° C. for 2 h to obtain graphite 4.

[0039] Example 5

[0040] This embodiment provides a graphite negative electrode material, including graphite 5. The adsorption and desorption amounts of the dye by graphite 5 are shown in Table 1.

[0041] The present embodiment provides a method for preparing a graphite negative electrode material, comprising: pulverizing a petroleum coke raw material having a sulfur content of 0.94 wt%, an ash content of 0.39 wt%, and a Hastelloy grindability index of 83, grading, shaping, obtaining coke powder with an average particle size of 10.8 μm, and graphitizing at 3090° C. for 2 h to obtain graphite 5.

[0042] Example 6

[0043] This embodiment provides a graphite negative electrode material, including graphite 6. The adsorption and desorption amounts of the dye by graphite 6 are shown in Table 1.

[0044] The present embodiment provides a method for preparing a graphite negative electrode material, comprising: pulverizing a petroleum coke raw material having a sulfur content of 1.45 wt%, an ash content of 0.50 wt%, and a Hastelloy grindability index of 71, grading, and shaping to obtain coke powder with an average particle size of 11.2 μm, and graphitizing at 3090° C. for 2 h to obtain graphite 6.

[0045] Test example

[0046] The graphite of the embodiment was tested:

[0047] (1) Dye adsorption test method:

[0048] A. Prepare dye standard solutions with concentrations of 0.1, 0.5, 1.0, 2.5, 5.0, 7.5, and 10.0 mg / g, and perform ultraviolet absorption spectrum test on the prepared solutions at the maximum absorption wavelength of the dye (the maximum absorption wavelength of methylene blue is 664 nm, and the maximum absorption wavelength of methyl orange is 464 nm) to obtain the absorbance of solutions with different concentrations at the maximum absorption wavelength, and obtain the standard curve of the dye molecule according to Lambert-Beer law;

[0049] B. Mix 2.00 g of different graphite samples with 500 mL of dye solution (5 mg / L methylene blue solution or 5 mg / L methyl orange solution), stir continuously at 25 °C for 4 h, take samples, and perform ultraviolet absorption spectrum test on the obtained supernatant. According to the obtained standard curve, the dye adsorption amount of different samples is converted.

[0050] (2) Testing method of desorption amount:

[0051] 2.00 g of different graphite samples were mixed with 500 mL of dye solution (5 mg / L methylene blue solution or 5 mg / L methyl orange solution), and the mixture was stirred at 25 °C for 4 h. Then, a sample was taken and the mixture was heated to 35 °C and kept warm until desorption equilibrium was reached. Then, a sample was taken and the absorbance of the two samples was measured. The adsorption amount of the two samples was calculated using the standard curve obtained, and the difference was the desorption amount when the temperature was raised from 25 °C to 35 °C.

[0052] (3) Cycle performance test method: The graphite negative electrode material of the present invention is used as the negative electrode material and lithium cobalt oxide is used as the positive electrode material to assemble 3 pcs of battery cells. In a constant temperature box at 25°C, the battery is charged at 1C to 4.2V and then stopped at 0.05C; left for 5 minutes; discharged at 1C to 3.0V; the cycle is completed after 1000 cycles, and an extension line is made on this basis to predict its cycle performance.

[0053] The test results are shown in Table 1.

[0054] Table 1 Dye adsorption and desorption of graphite and lithium ion battery cycle performance

[0055]

[0056]

[0057] Table 2 Physical properties of graphite in the examples

[0058]

[0059] Table 3 Parameters of graphite precursor (coke) of Example

[0060]

[0061] TD-tapped density, SSA-specific surface area, compaction 1T-compacted density when compaction conditions are 1 ton, compaction 5T-compacted density when compaction conditions are 5 tons.

[0062] It can be seen from Table 1 that the cycle performance of the lithium ion battery using graphite with a dye adsorption amount of ≤1.1 mg / g and a dye desorption amount / dye adsorption amount of ≤0.25 as the negative electrode material is more than 5000 cycles. The secondary battery provided by the present invention has excellent long cycle performance.

[0063] The cycle performance of a lithium-ion battery using graphite as a negative electrode material with a dye adsorption amount of ≤0.9 mg / g and a dye desorption amount / dye adsorption amount of ≤0.25 is more than 6000 cycles.

[0064] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A graphite negative electrode material, characterized in that: Graphite has adsorption sites for dyes, wherein the dye adsorption amount is ≤1.1 mg / g, and the dye desorption amount / dye adsorption amount is ≤0.25; The dye adsorption amount is the saturated adsorption amount of the dye by graphite at 25°C, and the dye desorption amount is the desorption amount when the temperature is increased from 25°C to 35°C.

2. The graphite negative electrode material according to claim 1, characterized in that The dye adsorption amount is ≤0.9 mg / g.

3. The graphite negative electrode material according to claim 1 or 2, characterized in that: The dye is methyl orange or methylene blue.

4. The graphite negative electrode material according to any one of claims 1 to 3, characterized in that: The specific surface area of ​​the graphite is 0.8 to 2.0 m 2 / g.

5. The graphite negative electrode material according to any one of claims 1 to 4, characterized in that: The graphite satisfies at least one of the following conditions: (1) The D50 of the graphite is 4 to 20 μm; (2) The graphitization degree of the graphite is 92-96%; (3) The tap density of the graphite is 0.75 to 1.40 g / cm 3 ; (4) The compaction density of the graphite under the compaction condition of 5T is ≥1.8g / cm 3 .

6. The graphite negative electrode material according to any one of claims 1 to 5, characterized in that: The graphite is artificial graphite.

7. The graphite negative electrode material according to any one of claims 1 to 6, characterized in that: The preparation method of the graphite negative electrode material comprises the following steps: taking green coke with an average particle size of 1 to 100 μm, ash content ≤0.5%, S content ≤1.5%, and Hastelloy grindability index of 70 to 140 as raw material, and preparing the graphite negative electrode material through graphitization.

8. The graphite negative electrode material according to claim 7, characterized in that: The graphitization temperature is 2800-3200° C., and / or the graphitization time is 1-8 hours.

9. The graphite negative electrode material according to claim 7 or 8, characterized in that: The green coke includes at least one of petroleum coke and pitch coke.

10. A secondary battery, characterized in that: The invention comprises the graphite negative electrode material according to any one of claims 1 to 9.

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