A composite expandable graphite lithium battery negative electrode material and preparation method thereof

Abstract

The present invention provides a composite expandable graphite lithium battery negative electrode material and a preparation method thereof, and relates to the technical field of battery materials. The present invention adopts an electrochemical deposition method, uses carbon cloth or nickel foam as an electrodeposition substrate, a carbon rod as a counter electrode, and Ag / AgCl as a reference electrode, and performs electrodeposition in a solution containing a ZIF reactant and expandable graphite powder, and obtains an expandable graphite negative electrode material with MOFglass as an ion conductor filler after high-temperature quenching treatment. The structure can effectively inhibit the agglomeration of EG sheets, has high ionic conductivity, and has rich pore structure, which is conducive to the transmission of lithium ions and improves the electrochemical performance of lithium ion batteries. The preparation process provided by the present invention is simple in steps, easy to operate, can significantly reduce the preparation cost of composite materials, and can realize large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a composite expandable graphite lithium battery negative electrode material and a preparation method thereof. Background Art

[0002] Expandable graphite is a new type of negative electrode material that can significantly improve the capacity and cycle life of lithium-ion batteries. However, due to its structural defects and expansibility, expandable graphite is prone to interlayer delamination and rupture during the cycle, resulting in a decrease in battery performance.

[0003] In the prior art, some researchers have tried to improve the electrochemical performance of expandable graphite by using materials such as graphene oxide and graphene nitride. However, these methods all have some problems. For example, the cost of graphene oxide and graphene nitride is high, and the preparation process is complicated. In addition, the structure and properties of these materials are different from those of graphite, which can easily affect the stability and cycle life of the battery.

[0004] Therefore, how to improve the electrochemical properties of expandable graphite, promote the reaction between expandable graphite and electrolyte, and improve the performance of the battery is one of the technical problems that need to be solved urgently. Summary of the invention

[0005] To solve the above problems, the present invention uses carbon cloth or nickel foam as an electrodeposition substrate, a carbon rod as a counter electrode, and Ag / AgCl as a reference electrode, and performs electrodeposition in a solution containing a ZIF reactant and expandable graphite powder, and obtains an expandable graphite negative electrode material with MOF glass as an ion conductor filler after high-temperature quenching treatment. This structure can effectively inhibit the agglomeration of EG sheets, has high ionic conductivity, and rich pore structure, which is conducive to the transmission of lithium ions and improves the electrochemical performance of lithium ion batteries. The preparation method of the composite expandable graphite lithium battery negative electrode material of the present invention comprises the following steps:

[0006] (1) The expandable graphite and trimethylammonium sulfate were mixed evenly and added to the mixed solution of DMF and water. After magnetic stirring, Zn(NO 3 ) 2 6H 2 O and stir evenly to prepare an electrolyte solution;

[0007] (2) heating and degassing the electrolyte solution, immersing two copper foil electrodes in the electrolyte solution, and performing electrochemical deposition after heating the electrolyte solution to generate a ZIFs composite expandable graphite material on the anode surface;

[0008] (3) After the electrochemical deposition is completed, the composite material is taken out, washed with deionized water and then dried;

[0009] (4) The dried ZIFs composite expandable graphite material is subjected to high temperature treatment, cooled to room temperature after the treatment, and then melt-quenched to form a crystal structure of the MOF glass ion conductor, washed with deionized water and dried to obtain an expandable graphite lithium battery negative electrode material.

[0010] Furthermore, in the step (1), the concentration of trimethylammonium sulfate is 0.06 to 0.12 mol / L.

[0011] Furthermore, in the step (1), the weight ratio of expandable graphite to trimethylammonium sulfate is 5:1 to 3:1.

[0012] Furthermore, in the step (1), DMF contains 0.12 to 0.3 mol / L of 2-methylimidazole.

[0013] Further, in the step (1), DMF and H 2 The volume ratio of O is 85~25:15~75.

[0014] Furthermore, in the step (1), the material-liquid ratio of expandable graphite to the mixed solution is 1 g:100 mL.

[0015] Furthermore, in step (1), the magnetic stirring time is 30 minutes.

[0016] Furthermore, in the step (1), Zn(NO 3 ) 2 6H 2 The amount of O added was 0.05 mol / L.

[0017] Furthermore, in the step (2), the electrolyte solution is heated to a temperature of 75°C to 85°C.

[0018] Furthermore, in step (2), the electrodeposition current density is 3 to 10 mA / cm 2 The electrodeposition time is 1 to 1.5 h, and the fixed potential difference between the two metal electrodes is 1.5 to 2.5 V.

[0019] Furthermore, in the step (2), ZIFs is ZIF-4 or ZIF-62.

[0020] Furthermore, in the step (2), the coated anode is washed and dried with methanol and distilled water after synthesis to remove unreacted organic ligands and impurities.

[0021] Furthermore, in the step (3), the drying temperature is 60 to 80° C., and the drying time is 12 to 24 hours.

[0022] Furthermore, in the step (4), the heating rate of the high temperature treatment is 5 to 10°C / min, the high temperature treatment temperature is 430 to 530°C, and the high temperature treatment time is 1 to 3 hours.

[0023] Furthermore, in the step (4), the melt quenching temperature is 430°C to 530°C, the melt quenching heating rate is 10°C / min, and the melt quenching holding time is 1h.

[0024] The present invention also provides an expandable graphite lithium battery negative electrode material prepared according to the above method.

[0025] Furthermore, the content of MOF glass in the expandable graphite lithium battery negative electrode material is 5% to 20% of the weight of the expandable graphite.

[0026] The present invention also provides an application of the expandable graphite lithium battery negative electrode material, and the specific method is: using the composite material as the negative electrode material of the lithium ion battery and assembling it with lithium iron phosphate to form a lithium battery.

[0027] The crystal structure of the MOF glass ion conductor in the expandable graphite lithium battery negative electrode material of the present invention has high chemical stability and thermal stability, and has good ionic conductivity and mechanical strength. It is embedded in the expandable graphite, which can effectively inhibit the capacity decay phenomenon of the graphite material and improve the cycle stability. The crystal structure of the MOF glass ion conductor can accommodate more lithium ions and provide more lithium storage sites, thereby improving the lithium ion storage capacity, the energy density and the power density of the battery, overcoming the problem of excessive lithium ion embedding in traditional graphite materials leading to limit expansion, and improving the safety performance of the lithium battery.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are:

[0029] The expandable graphite lithium battery negative electrode material of the present invention has good cycle stability, stable charge and discharge performance, and long cycle life. The lithium battery composed of the expandable graphite lithium battery as the negative electrode has a high charge and discharge capacity of 1 mA / cm 2 After 150 cycles at a current density of , the coulombic efficiency is 99.8% and the capacity retention rate is 96%;

[0030] The preparation process provided by the present invention has simple steps and is easy to operate, can significantly reduce the preparation cost of the composite material, and can realize large-scale industrial production. DETAILED DESCRIPTION

[0031] The technical solution provided by the present invention is further described below in conjunction with embodiments.

[0032] The expandable graphite used in the embodiments and comparative examples of the present invention was purchased from Dongguan Kelude Innovation Technology Co., Ltd.

[0033] The specifications of the lithium batteries assembled in the embodiments of the present invention and the comparative examples are the same.

[0034] Example 1

[0035] A method for preparing a composite expandable graphite lithium battery negative electrode material, the steps are as follows:

[0036] (1) Add 0.5 g of expandable graphite and 0.1 g of trimethylammonium sulfate to 50 mL of DMF and H containing 0.15 mol / L 2-methylimidazole. 2 O in a mixed solution with a volume ratio of 85:25, magnetic stirring was performed for 30 min, and Zn(NO 3 ) 2 6H 2 O to a concentration of 0.05 mol / L, and continue stirring until the solution is uniform to obtain an electrolyte solution;

[0037] (2) Two copper foil electrodes (1 cm × 1 cm) were immersed in a heated, degassed electrolyte solution. The electrolyte solution in the electrochemical cell was heated to 85 °C and the current density was controlled at 3 mA / cm using an electrochemical workstation. 2 , a fixed potential difference of 2.5 V was applied between the two metal electrodes, and the electrodeposition was started for 1 h, and a layer of ZIF-4 composite expandable graphite material was generated on the surface of the anode. The coated anode was washed and dried with methanol and distilled water after synthesis to remove unreacted organic ligands and impurities;

[0038] (3) taking out the composite material after the reaction, washing it with deionized water until it is clean, and then drying it in an oven at 60° C. for 12 h;

[0039] (4) The synthesized composite expandable graphite is then subjected to high temperature treatment, and the temperature is increased to 450°C at a heating rate of 10°C / min in a tubular furnace under nitrogen for 1 hour to improve its expansion performance, and ZIF-4 is transformed into glassy MOFglass at high temperature and embedded between expandable graphite layers. After cooling to room temperature, the temperature is increased to 450°C at a rate of 10°C / min and maintained for 1 hour for melt quenching treatment to form a crystal structure of MOF glass ion conductor. After the treatment is completed, it is cooled to room temperature, then cleaned with deionized water and dried in an oven at 60°C for 12 hours;

[0040] (5) Assemble the obtained composite material and lithium iron phosphate positive electrode material into a lithium battery and test the electrochemical performance.

[0041] It has been determined that the lithium battery has a 2 After 150 cycles at a current density of , the coulombic efficiency was 99.8% and the capacity retention rate was 96%.

[0042] Comparative Example 1

[0043] The solution impregnation method is used to prepare the composite expandable graphite negative electrode material, and the steps are as follows:

[0044] (1) 0.5 g Zn(NO 3 ) 2 6H 2 O was dissolved in 30 mL of DMF and ultrasonically dispersed for 30 min to prepare a uniform salt solution;

[0045] (2) Dissolve 1.05 g of benzimidazole in 30 mL of DMF and disperse by ultrasonic for 30 min to prepare a uniform benzimidazole solution;

[0046] (3) mixing the salt solution and the benzimidazole solution, transferring the mixture into a 100 mL beaker, adding 0.5 g of expandable graphite, and keeping the mixture in air at room temperature and pressure for 6 h;

[0047] (4) The prepared powder was washed and vacuum dried at 60°C for 12 h. The obtained powder was subjected to high temperature treatment by heating to 450°C at a heating rate of 10°C / min in a tube furnace under nitrogen and then kept at this temperature for 1 h. The powder was cooled to room temperature and then washed with deionized water and dried in an oven at 60°C for 12 h.

[0048] (5) Assemble the obtained composite material and lithium iron phosphate positive electrode material into a lithium battery and test the electrochemical performance.

[0049] It has been determined that the lithium battery has a 2 After 100 cycles at a current density of , the coulombic efficiency was 98.2% and the capacity retention rate was 81%.

[0050] Comparative Example 2

[0051] The high-energy ball milling method is used to prepare the composite expandable graphite negative electrode material, and the steps are as follows:

[0052] (1) 1.2 g of Zn(NO 3 ) 2 6H 2 O and 0.9 g of benzimidazole were dissolved in 90 mL of DMF, and ultrasonically dispersed for 30 min to prepare a uniform benzimidazole solution; the mixture was reacted at 100 °C for 72 h, and the ZIF-4 crystals were washed and dried;

[0053] (2) 0.15 g of ZIF-4 crystals were mixed with 1.5 g of expandable graphite, and an appropriate amount of ball milling balls were added to a ball milling jar. High-energy vacuum ball milling was performed at a ball-to-material ratio of 1:10. The ball milling time was 1-10 h, and the ball milling speed was 350 r / min. The prepared mixture was subjected to high-temperature treatment. The temperature was increased to 450 °C at a heating rate of 10 °C / min in a tubular furnace under nitrogen for 1 h, cooled to room temperature, and then washed with deionized water and dried in an oven at 60 °C for 12 h;

[0054] (3) The obtained composite material is assembled with lithium iron phosphate positive electrode material into a lithium battery, and the electrochemical performance is tested.

[0055] It has been determined that the lithium battery has a 2 After 100 cycles at a current density of , the coulombic efficiency was 98.6% and the capacity retention rate was 86%.

[0056] Comparative Example 3

[0057] The expandable graphite was used as the negative electrode material and assembled into a lithium battery with lithium iron phosphate as the positive electrode material, and the electrochemical performance was tested.

[0058] It has been determined that the lithium battery has a 2 After 100 cycles at a current density of , the coulombic efficiency was 86.6% and the capacity retention rate was 74%.

[0059] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing a composite expandable graphite lithium battery negative electrode material, It is characterized in that The following steps are involved: (1) The expandable graphite and trimethylammonium sulfate were mixed evenly and added to the mixed solution of DMF and water. After magnetic stirring, Zn(NO 3 ) 2 6H 2 O and stir evenly to prepare an electrolyte solution; (2) heating and degassing the electrolyte solution, immersing two copper foil electrodes in the electrolyte solution, and performing electrochemical deposition after heating the electrolyte solution to generate a ZIFs composite expandable graphite material on the anode surface; (3) After the electrochemical deposition is completed, the composite material is taken out, washed with deionized water and then dried; (4) The dried ZIFs composite expandable graphite material is subjected to high temperature treatment, cooled to room temperature after the treatment, and then melt-quenched to form a crystal structure of the MOFglass ion conductor. After the treatment, it is cooled to room temperature to obtain an expandable graphite lithium battery negative electrode material.

2. A method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (1), the concentration of trimethylammonium sulfate is 0.06 to 0.12 mol / L.

3. A method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (1), the weight ratio of expandable graphite to trimethylammonium sulfate is 5:1 to 3:

1.

4. A method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (1), DMF contains 0.12-0.3 mol / L of 2-methylimidazole.

5. A method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (1), DMF and H 2 The volume ratio of O is 85~25:15~75.

6. A method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (1), the material-liquid ratio of expandable graphite to the mixed solution is 1 g:100 mL.

7. The method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (1), Zn(NO 3 ) 2 6H 2 The amount of O added was 0.05 mol / L.

8. The method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (2), the electrodeposition current density is 3 to 10 mA / cm 2 The electrodeposition time is 1 to 1.5 h, and the fixed potential difference between the two metal electrodes is 1.5 to 2.5 V.

9. The method for preparing a composite expandable graphite lithium battery negative electrode material according to claim 1, It is characterized in that In the step (4), the heating rate of the high temperature treatment is 5 to 10° C. / min, the high temperature treatment temperature is 430 to 530° C., and the high temperature treatment time is 1 to 3 hours.

10. An expandable graphite lithium battery negative electrode material prepared according to the method according to any one of claims 1 to 9, It is characterized in that The content of MOFglass in the expandable graphite lithium battery negative electrode material is 5% to 20% of the weight of the expandable graphite.