Needle coke graphite negative electrode material and preparation method and application thereof

Abstract

The invention provides a needle coke graphite negative electrode material and a preparation method and application thereof, the preparation method uses oxidation and intercalation reactions to enlarge the graphite interlayer spacing without changing the graphite interlayer structure, so that the diffusion and deintercalation kinetics of lithium ions in the negative electrode material are significantly enhanced, and the performance of the negative electrode material is improved. And meanwhile, the lithium precipitation phenomenon of the needle coke graphite under high-rate charging and discharging is effectively inhibited, so that the rate capability and the cycle life of the needle coke graphite are improved. And the method is controllable in cost and simple in process, and has very high commercial application value.

Description

Technical Field

[0001] This disclosure relates to the field of lithium battery technology, and in particular to a needle-shaped coke graphite anode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, low cost, and environmental friendliness, have become the main power source for new energy electric vehicles. To achieve widespread application in the electric vehicle industry, lithium-ion batteries must possess the characteristics of fast charging and high energy density; therefore, developing fast charging technology for high-capacity graphite anodes has become an urgent problem to be solved.

[0003] Graphite is widely used as a commercial anode material due to its high stability, low discharge platform, and low cost. Needle coke, as a petroleum processing product, is a high-quality raw material for artificial graphite due to its unique needle-like structure, ease of graphitization, high conductivity, and good graphite microcrystalline structure. Under the same graphitization conditions, needle coke is easier to graphitize than other coke sources, and its volume and compaction density are significantly greater than graphite produced from other coke sources.

[0004] However, commercially available needle-shaped coke graphite is characterized by small interlayer spacing and good orientation, resulting in relatively slow lithium-ion insertion / extraction kinetics. Furthermore, graphite exhibits significant volume expansion during cycling, leading to poor rate performance and cycling stability. To improve the electrochemical performance of needle-shaped coke graphite, researchers often employ structural modifications such as particle size reduction, surface carbon coating, and granulation, but these methods still cannot meet the requirements for high-rate graphite applications.

[0005] Therefore, improving the rate performance and cycle stability of needle-shaped graphite has become a current research focus. Summary of the Invention

[0006] To address the aforementioned technical issues, this disclosure provides a needle-shaped coke graphite anode material, its preparation method, and its application. This disclosure improves the interlayer spacing of the needle-shaped coke graphite through an oxidation intercalation method, thereby enhancing its rate performance and cycle performance, and has promising application prospects.

[0007] In a first aspect, this disclosure provides a method for preparing a needle-shaped coke-graphite anode material, the method comprising the following steps: (1) The needle-shaped coke graphite raw material is mixed with an oxidant, a first intercalating agent and a second intercalating agent and reacted. After the reaction, the intermediate product is obtained by solid-liquid separation. The first intercalating agent includes hydrogen peroxide; The second intercalating agent includes one or more of concentrated sulfuric acid, nitric acid, or peracetic acid; The mass ratio of the needle-shaped coke graphite raw material, the oxidant, the first intercalating agent, and the second intercalating agent is 10: (0.5-2): (0.5-2): (10-50); (2) The intermediate product obtained in step (1) is calcined and acid washed in sequence to obtain needle-shaped coke graphite anode material.

[0008] The mass ratio of the needle-shaped coke graphite raw material, the oxidant, the first intercalating agent, and the second intercalating agent can be 10:0.5:0.5:10, 10:1:1:20, 10:1.5:2:30, 10:2:1.5:40, or 10:2:1:50, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0009] This disclosure expands the interlayer spacing of graphite without altering its interlayer structure through a relatively mild oxidation and intercalation reaction, significantly enhancing the diffusion and deintercalation kinetics of lithium ions in the anode material while effectively suppressing lithium plating in needle-like coke graphite under high-rate charge-discharge conditions. First, the oxidant etches the surface and edges of the needle-like coke graphite, making the overall graphite structure more porous, which facilitates the entry of the first and second intercalating agents into the graphite interlayers. Second, the first intercalating agent promotes the pre-expansion of the graphite interlayer spacing by slowly releasing oxygen, which helps to ensure a more complete and uniform expansion process. Then, high-temperature calcination causes the second intercalating agent to generate gas, further increasing the graphite interlayer spacing. After these treatments, the first-cycle coulombic efficiency and energy density of the needle-like coke graphite are not reduced, but the rate performance and cycle life are effectively improved. Furthermore, this method is cost-effective, simple in process, and has high commercial application value.

[0010] Furthermore, this disclosure precisely controls the graphite interlayer spacing by controlling the addition ratio of needle coke graphite raw material, oxidant, and two intercalating agents, thus avoiding a reduction in the cycle life of the anode material due to excessive interlayer spacing expansion.

[0011] The following are preferred technical solutions of this disclosure, but are not intended to limit the technical solutions provided by this disclosure. The technical objectives and beneficial effects of this disclosure can be better achieved through the following technical solutions.

[0012] As a preferred technical solution of this disclosure, the oxidant in step (1) includes one or more of potassium permanganate, potassium dichromate, potassium chlorate, sodium perchlorate, or phosphorus pentoxide.

[0013] As a preferred technical solution of this disclosure, the reaction temperature in step (1) is 40-50℃, such as 40℃, 42℃, 44℃, 46℃, 48℃ or 50℃, etc.; the time is 2-3h, such as 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0014] As a preferred technical solution of this disclosure, the preparation method further includes: before the calcination, the intermediate product in step (1) is subjected to a first water washing and a first drying.

[0015] As a preferred technical solution of this disclosure, the pH of the intermediate product after the first water washing is 6-8, such as 6, 7 or 8, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the temperature of the first drying is 90-120℃, such as 90℃, 100℃, 110℃ or 120℃; the time is 1-3h, such as 1h, 2h or 3h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0017] As a preferred technical solution of this disclosure, the calcination temperature in step (2) is 700-900℃, such as 700℃, 750℃, 800℃, 850℃ or 900℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the calcination time in step (2) is 4-5 hours, such as 4 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours or 5 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] As a preferred technical solution of this disclosure, the pickling agent used in step (2) includes hydrochloric acid.

[0020] As a preferred technical solution of this disclosure, the preparation method further includes: after the acid washing in step (2), a second water washing and a second drying are performed in sequence. The temperature of the second drying is 90-110℃, such as 90℃, 100℃ or 110℃, etc.; the time is 9-12h, such as 9h, 10h, 11h or 12h, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0021] In a second aspect, this disclosure provides a needle-shaped coke-graphite anode material, which is prepared by the preparation method described in the first aspect.

[0022] Thirdly, this disclosure provides a negative electrode sheet comprising the needle-shaped coke-graphite negative electrode material as described in the second aspect.

[0023] Fourthly, this disclosure provides a secondary battery, the secondary battery comprising the negative electrode sheet as described in the third aspect.

[0024] The technical solution provided in this disclosure has the following advantages compared with the prior art: The preparation method disclosed herein expands the interlayer spacing of graphite through relatively mild oxidation and intercalation reactions without altering the graphite interlayer structure. This significantly enhances the diffusion and deintercalation kinetics of lithium ions in the anode material, while effectively suppressing lithium plating in needle-shaped coke graphite under high-rate charge-discharge conditions. Thus, without reducing its first-cycle coulombic efficiency and energy density, this method effectively improves its rate performance and cycle life. Furthermore, the method is cost-effective, simple, and possesses high commercial application value. Detailed Implementation

[0025] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0026] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0027] Example 1 This embodiment provides a method for preparing needle-shaped coke-graphite anode material, the method comprising the following steps: (1) Mix 10g potassium permanganate, 10g hydrogen peroxide and 300g concentrated sulfuric acid evenly, then add 100g needle coke graphite raw material, react at 45℃ for 2h, filter after reaction, wash with pure water until neutral, and dry at 100℃ for 2h to obtain intermediate product. (2) The intermediate product obtained in step (1) is placed in a tube furnace and calcined at 800°C for 4 hours. Then it is washed with hydrochloric acid and water in sequence, and then dried at 100°C for 10 hours to obtain needle-shaped coke graphite anode material.

[0028] Example 2 This embodiment provides a method for preparing needle-shaped coke-graphite anode material, the method comprising the following steps: (1) Mix 5g potassium permanganate, 5g hydrogen peroxide and 300g concentrated sulfuric acid evenly, then add 100g needle coke graphite raw material, react at 45℃ for 2h, filter after reaction, wash with pure water until neutral, and dry at 100℃ for 2h to obtain intermediate product. (2) The intermediate product obtained in step (1) is placed in a tube furnace and calcined at 800°C for 4 hours. Then it is washed with hydrochloric acid and water in sequence, and then dried at 100°C for 10 hours to obtain needle-shaped coke graphite anode material.

[0029] Example 3 This embodiment provides a method for preparing needle-shaped coke-graphite anode material, the method comprising the following steps: (1) Mix 20g potassium permanganate, 10g hydrogen peroxide and 300g concentrated sulfuric acid evenly, then add 100g needle coke graphite raw material, react at 45℃ for 2h, filter after reaction, wash with pure water until neutral, and dry at 100℃ for 2h to obtain intermediate product. (2) The intermediate product obtained in step (1) is placed in a tube furnace and calcined at 800°C for 4 hours. Then it is washed with hydrochloric acid and water in sequence, and then dried at 100°C for 10 hours to obtain needle-shaped coke graphite anode material.

[0030] Example 4 This embodiment provides a method for preparing needle-shaped coke-graphite anode material, the method comprising the following steps: (1) Mix 10g potassium permanganate, 20g hydrogen peroxide and 500g concentrated sulfuric acid evenly, then add 100g needle coke graphite raw material, react at 45℃ for 2h, filter after reaction, wash with pure water until neutral, and dry at 100℃ for 2h to obtain intermediate product. (2) The intermediate product obtained in step (1) is placed in a tube furnace and calcined at 800°C for 4 hours. Then it is washed with hydrochloric acid and water in sequence, and then dried at 100°C for 10 hours to obtain needle-shaped coke graphite anode material.

[0031] Example 5 This embodiment provides a method for preparing needle-shaped coke-graphite anode material, the method comprising the following steps: (1) Mix 10g potassium permanganate, 10g hydrogen peroxide and 100g concentrated sulfuric acid evenly, then add 100g needle coke graphite raw material, react at 45℃ for 2h, filter after reaction, wash with pure water until neutral, and dry at 100℃ for 2h to obtain intermediate product. (2) The intermediate product obtained in step (1) is placed in a tube furnace and calcined at 800°C for 4 hours. Then it is washed with hydrochloric acid and water in sequence, and then dried at 100°C for 10 hours to obtain needle-shaped coke graphite anode material.

[0032] Comparative Example 1 This comparative example provides a method for preparing needle-shaped coke graphite anode material. The preparation method is the same as that in Example 1, except that the mass of potassium permanganate added is 50g.

[0033] Comparative Example 2 This comparative example provides a method for preparing needle-shaped coke graphite anode material. The preparation method is the same as that in Example 1, except that the mass of concentrated sulfuric acid added is 600g.

[0034] Comparative Example 3 This comparative example provides a method for preparing needle-shaped coke graphite anode material. The preparation method is the same as that in Example 1, except that the mass of hydrogen peroxide added is 50g.

[0035] Comparative Example 4 This comparative example provides a method for preparing needle-shaped coke graphite anode material. The preparation method is the same as that in Example 1, except that the mass of potassium permanganate added is 1g.

[0036] Comparative Example 5 This comparative example provides a method for preparing needle-shaped coke graphite anode material. The preparation method is the same as that in Example 1, except that the mass of concentrated sulfuric acid added is 20g.

[0037] Comparative Example 6 This comparative example provides a method for preparing needle-shaped coke graphite anode material, which is the same as the preparation method in Example 1, except that hydrogen peroxide is not added.

[0038] Comparative Example 7 This comparative example provides a method for preparing needle-shaped coke graphite anode material. The preparation method is the same as that in Example 1, except that the calcination temperature in step (2) is 100°C.

[0039] Comparative Example 8 This comparative example provides a needle-shaped coke graphite anode material, which is untreated and is the same raw material used in Example 1.

[0040] Lithium batteries for testing Preparation of a test lithium battery: Preparation of the negative electrode sheet: The needle-shaped coke graphite negative electrode material prepared in the examples and comparative examples was mixed with acetylene black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 95:1.5:1.5:2. Using deionized water as a solvent, the mixture was dispersed at high speed to obtain a negative electrode slurry with a viscosity of 1000~2000 mPa·s. The obtained negative electrode slurry was uniformly coated onto a 6 μm thick copper foil and dried to obtain the negative electrode sheet, wherein the areal density of the negative electrode active layer was 150 g / m². 2 The compacted density is 1.5 g / cm³. 3 .

[0041] Preparation of the positive electrode sheet: Lithium iron phosphate, acetylene black, and polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of 96:2:2. Using N-methylpyrrolidone (NMP) as a solvent, the mixture was dispersed at high speed to obtain a positive electrode slurry with a viscosity of 4000~6000 mPa·s. The obtained positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 13 μm, and after drying, a positive electrode sheet was obtained, wherein the areal density of the positive electrode active layer was 310 g / m². 2 The compacted density is 2.5 g / cm³. 3 .

[0042] Diaphragm: Celgard 2325; Electrolyte: 1 mol / L LiPF6 solution, wherein the solvent volume ratio is EC:DEC = 1:1; The positive electrode, separator, and negative electrode to be assembled are stacked sequentially, with the separator acting as a separator between the positive and negative electrodes. The battery is then encapsulated with an aluminum-plastic film, and after electrolyte injection and formation, a soft-pack battery is obtained. After a capacity grading process, the initial capacity of the battery is approximately 3.5 Ah.

[0043] It should be noted that the lithium battery used for testing described above is only one example listed for testing the performance of needle-shaped coke graphite anode material. This invention is not limited to this type of battery. The raw materials (other than needle-shaped coke graphite anode material), proportions, parameters, and processes can all be replaced with other conventional raw materials, proportions, parameters, and processes in the field to form a battery different from the lithium battery used for testing.

[0044] Test method: 1. The needle-shaped coke graphite anode materials obtained in each embodiment and comparative example were subjected to XRD tests, and the d002 interlayer spacing of the obtained needle-shaped coke graphite anode materials was calculated by Bragg's formula. The results are shown in Table 1.

[0045] 2. The soft-pack batteries obtained in each embodiment and comparative example were subjected to the first charge-discharge test. The cycle life was tested under the charge-discharge conditions of 3.5A constant current (1C rate) and 14A constant current (4C rate). The voltage test range was 2.5-3.65V. The test results are shown in Table 1.

[0046] Table 1

[0047] As shown in Table 1, compared with Comparative Example 8, the interlayer spacing of the needle-shaped coke graphite anode materials prepared by the method of this disclosure in Examples 1-5 is increased to a certain extent, which improves the first-cycle coulombic efficiency, rate performance and cycle life of the battery.

[0048] Compared with Example 1 and Comparative Example 8, Comparative Examples 1-3 either added too much potassium permanganate, too much concentrated sulfuric acid, or too much hydrogen peroxide, which actually reduced the cycle life of the negative electrode material.

[0049] Compared with Example 1 and Comparative Example 8, Comparative Examples 4-5 either had too little potassium permanganate or too little concentrated sulfuric acid added, thus there was no significant improvement effect.

[0050] Compared with Example 1, no hydrogen peroxide was added in Comparative Example 6, which means that no pre-expansion effect was achieved, resulting in a less significant increase in the interlayer spacing of graphite and a low improvement in the rate performance and cycle life of the battery.

[0051] Compared with Example 1, the calcination temperature in Comparative Example 7 was too low, resulting in residual intercalating agent in the graphite material, which seriously affected the charging and discharging process of the graphite.

[0052] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0053] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a needle-shaped coke-graphite anode material, characterized in that, The preparation method includes the following steps: (1) The needle-shaped coke graphite raw material is mixed with an oxidant, a first intercalating agent and a second intercalating agent and reacted. After the reaction, the intermediate product is obtained by solid-liquid separation. The first intercalating agent includes hydrogen peroxide; The second intercalating agent includes one or more of concentrated sulfuric acid, nitric acid, or peracetic acid; The mass ratio of the needle-shaped coke graphite raw material, the oxidant, the first intercalating agent, and the second intercalating agent is 10:(0.5-2):(0.5-2):(10-50); (2) The intermediate product obtained in step (1) is calcined and acid washed in sequence to obtain needle-shaped coke graphite anode material.

2. The preparation method according to claim 1, characterized in that, The oxidant in step (1) includes one or more of potassium permanganate, potassium dichromate, potassium chlorate, sodium perchlorate, or phosphorus pentoxide.

3. The preparation method according to claim 1 or 2, characterized in that, The reaction in step (1) is carried out at a temperature of 40-50℃ for 2-3 hours.

4. The preparation method according to any one of claims 1-3, characterized in that, The preparation method further includes: before the calcination, the intermediate product in step (1) is subjected to a first water wash and a first drying. Preferably, the pH of the intermediate product after the first water washing is 6-8; Preferably, the temperature of the first drying is 90-120℃, and the time is 1-3 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The calcination temperature in step (2) is 700-900℃; Preferably, the calcination time in step (2) is 4-5 hours.

6. The preparation method according to any one of claims 1-5, characterized in that, The pickling agent used in step (2) includes hydrochloric acid.

7. The preparation method according to any one of claims 1-6, characterized in that, The preparation method further includes: after the acid washing in step (2), a second water washing and a second drying are performed in sequence; Preferably, the second drying temperature is 90-110℃ and the time is 9-12h.

8. A needle-shaped coke-graphite anode material, characterized in that, The needle-shaped coke graphite anode material is prepared using the preparation method described in any one of claims 1-7.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the needle-shaped coke graphite negative electrode material as described in claim 8.

10. A secondary battery, characterized in that, The secondary battery includes the negative electrode sheet as described in claim 9.

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