Preparation and application of a joule heat synthesized graphene and lithium iron phosphate composite material

Abstract

The application provides a preparation and application of a graphene and lithium iron phosphate composite material synthesized by Joule heat, and relates to the technical field of new energy lithium ion battery material synthesis. The preparation of the graphene and lithium iron phosphate composite material comprises the following steps: S101, a product obtained by acid treatment and heat treatment of natural graphite is a graphite precursor, and then the graphite precursor is used to prepare super-large flake graphene oxide by a modified Hummers method; S102, the super-large flake graphene oxide in the step S101 is converted into large flake low-defect graphene material by high voltage, high heat and high pressure of rapid Joule heat; and S103, the graphene material in the step S102 and lithium iron phosphate powder are transferred into a ball mill for ball milling, and finally a composite material is obtained. In the application, the performance of the lithium iron phosphate battery is improved by means of doping and coating, and a new electrode material is adopted to optimize the battery structure, so that the energy density and low-temperature performance are improved, and a green and low-cost preparation method is developed to reduce the production cost.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new energy lithium ion battery material synthesis, in particular to preparation and application of a graphene and lithium iron phosphate composite material synthesized by joule heat. BACKGROUND

[0002] With the rapid development of the global economy, energy demand continues to grow. The traditional energy structure has been unable to meet the demand for sustainable development, and the development and utilization of new energy has become the focus of global attention. In this context, lithium batteries, as an efficient and environmentally friendly energy storage device, play an important role in the field of new energy.

[0003] Among many lithium battery systems, lithium iron phosphate batteries have received widespread attention due to their high safety, environmental protection, and relatively low cost. The application of lithium iron phosphate batteries in batteries mainly reflects the following aspects: first, in the field of new energy vehicles, lithium iron phosphate batteries serve as power batteries, providing reliable and durable energy support for electric vehicles; second, in the field of energy storage, lithium iron phosphate batteries have broad application prospects in peak shaving and standby power sources; third, in portable electronic devices such as mobile phones and laptops, lithium iron phosphate batteries have been applied to some extent due to their safety performance.

[0004] However, lithium iron phosphate batteries also face some difficulties in their development. First, the energy density is relatively low, and compared to ternary material batteries, lithium iron phosphate batteries have a disadvantage in terms of endurance; second, the low-temperature performance is poor, especially in cold northern regions, the discharge performance and charging speed of lithium iron phosphate batteries will be greatly affected; third, the production cost is high, although the cost of lithium iron phosphate batteries is relatively low, the preparation process is complex, and the energy consumption is large during production, resulting in a space for overall cost reduction. SUMMARY

[0005] (I) Technical problems solved

[0006] In view of the deficiencies of the prior art, the application provides a preparation and application of a graphene and lithium iron phosphate composite material synthesized by joule heat, which solves the problems of relatively low energy density of traditional lithium iron phosphate batteries and relatively low endurance compared to ternary lithium batteries.

[0007] (II) Technical solutions

[0008] To achieve the above purpose, the application is implemented by the following technical solutions:

[0009] A preparation of a graphene and lithium iron phosphate composite material synthesized by joule heat, comprising the following steps,

[0010] S101. The product of acid treatment and heat treatment of natural graphite is a graphite precursor, and then the super-large flake graphene oxide is prepared by improved Hummers method;

[0011] S102. The super-large flake graphene oxide in step S101 is converted into large flake low-defect graphene material by high voltage, high heat and high pressure of rapid Joule heat;

[0012] By the above technical solution, high-quality, low-defect graphene with good electrical conductivity and stability can be obtained by combining improved Hummers method and Joule heat treatment.

[0013] Further, the graphite precursor is prepared according to the following steps:

[0014] The natural graphite and concentrated sulfuric acid are mixed and stirred, and then concentrated nitric acid is added, and stirred at room temperature. Then, ultra-pure water is slowly poured into the mixture, and the resulting product is washed several times with ultra-pure water, followed by centrifugation and drying at 60℃ for 24h. The dried powder is heat treated at 1000℃ to obtain the graphite precursor;

[0015] Further, the concentration of sulfuric acid is 70-98%(wt%), the concentration of nitric acid is 86%-97.5%(wt%), the volume ratio of graphite mass to concentrated sulfuric acid is 1:20-1:50, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 2:1-4:1, and the stirring time at room temperature is 18-36 hours;

[0016] By the above technical solution, the degree of graphene oxide can be controlled to ensure the quality and reaction efficiency of graphene oxide. Strong or weak acidic conditions will affect the degree of oxidation and size, and the optimized conditions can ensure that the graphene oxide has appropriate size, good dispersibility and suitable oxidation functional groups, which is beneficial to the subsequent processing and performance improvement of composite materials.

[0017] Further, the temperature of heat treatment in step S101 is 800-1200℃, and the time is 10-40 seconds;

[0018] Further, the discharge time of rapid Joule heat in step S102 is 100-800ms;

[0019] Further, the rapid Joule heat in step S102 needs to be pretreated, the capacitance voltage of pretreatment is 80-250V, and the number of pretreatment is 1-10 times;

[0020] Further, the capacitance voltage of rapid Joule heat in step S102 is 100-300V, the current is 10-80A, and the discharge number is 1-5 times;

[0021] By adjusting the voltage, current, discharge time and other parameters of the Joule heat treatment, the degree of reduction of graphene oxide and the defect density of the material can be accurately controlled, so that the final graphene material has good electrical conductivity and stable structure, providing ideal electrochemical properties and mechanical properties for the composite material. The optimization of Joule heat can also reduce the heat loss and time consumption that may occur during production, thereby improving production efficiency.

[0022] Further, the ball milling time in the step S103 is 1-6 hours, the ball milling rotation speed is 200-600 rpm / min, and the ball milling ball-to-material ratio is 2:1-1:1.

[0023] Through the above technical scheme, the optimization of the ball milling process can ensure the full contact and uniform dispersion of graphene and lithium iron phosphate, and appropriate ball milling time and rotation speed can avoid excessive wear or agglomeration of the material, ensuring the uniformity and stability of the composite material. The ball milling process not only helps to improve the electrical conductivity of the composite material, but also improves the cycle stability and service life of the material.

[0024] Further, the graphene and lithium iron phosphate composite material prepared by the rapid Joule heat method according to any one of the above is applied as an electrode in an ion battery.

[0025] (III) Beneficial effects

[0026] The present application provides a preparation and application of a graphene and lithium iron phosphate composite material synthesized by Joule heat. It has the following beneficial effects:

[0027] 1. The present application provides a preparation and application of a graphene and lithium iron phosphate composite material synthesized by Joule heat. At the material level, the performance of lithium iron phosphate battery is improved by doping and coating, at the structural design level, new electrode materials are used and the battery structure is optimized to improve the energy density and low temperature performance, and at the preparation process level, green and low-cost preparation methods are developed to reduce production cost.

[0028] 2. The present application provides a preparation and application of a graphene and lithium iron phosphate composite material synthesized by Joule heat. Joule heat synthesis directly converts current into heat energy without external heat source, and is concerned in the preparation of new energy battery materials. It simplifies the high-temperature synthesis process, improves the purity and performance of the material, especially in the preparation of battery anode materials, Joule heat synthesis promotes the improvement of battery energy density and stability, and provides a new way for new energy battery technology innovation.

[0029] 3. The application provides a preparation and application of a graphene and lithium iron phosphate composite material synthesized by Joule heat, wherein the Joule heat treatment can rapidly heat graphene oxide by electric current, efficiently reduce the oxidation groups of the graphene oxide in a short time, reduce the damage of high-temperature treatment to the material structure, rapidly and energy-savingly reduce the graphene, accurately control the reduction degree, avoid over-reduction or structure damage in the traditional reduction method, and realize the uniform distribution of graphene on the surface of lithium iron phosphate particles by compounding the ball-milled graphene and lithium iron phosphate, so as to improve the electronic conductivity and stability of the lithium iron phosphate battery. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A step flow chart of the application;

[0031] Figure 2 An SEM electron microscope graph of graphene of the application;

[0032] Figure 3 An XRD graph of graphene of the application;

[0033] Figure 4 An XRD graph of the graphene and lithium iron phosphate composite material of the application;

[0034] Figure 5 A performance comparison graph of the graphene and lithium iron phosphate composite material of the application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0036] Embodiment 1:

[0037] 3g of natural graphite and 100mL of concentrated sulfuric acid with a concentration of 95% were mixed and stirred, 30mL of concentrated nitric acid with a concentration of 95% was added to the mixture, and the mixture was stirred at room temperature for 24 hours. Ultra-pure water was slowly added to the mixture, and then the mixture was washed with ultra-pure water for 5 times, centrifuged, and dried at 60℃ overnight. The obtained powder was heated at 1000℃ for 20 seconds to prepare a graphite precursor.

[0038] Then, the obtained graphite precursor was used to prepare large flake graphene by modified Hummers method: 2 g of graphite precursor and 60 mL of concentrated sulfuric acid were stirred and mixed for 5 min, and 10 g of KMnO4 was added to the mixture and stirred and mixed for another 15 min. Then it was placed in a constant temperature water bath at 45 °C for 1 h to obtain a dark brown solution. The solution was transferred to an ice bath, and 200 mL of deionized water and 50 mL of 30% H2O2 (wt%) were slowly added to the mixture, and the solution color changed to light brown.

[0039] The GO particles were washed with an HC1 solution and deionized water until the pH value of the solution became 6-7. The obtained product was centrifuged and dried at 90 °C overnight to obtain a large flake graphene oxide powder.

[0040] A quartz tube with an inner diameter of 8 mm and a length of 70 mm was taken, one end was fitted with a conductive plug, the other end was fitted with large flake graphene oxide powder, and another conductive plug was fitted to form a relatively closed reaction tube. The capacitor group was composed of 5 capacitors; before the reaction, it was subjected to vacuum treatment to make the air pressure as low as 0.02 MPA, then a direct current power supply was used to charge the capacitor group, the parameters were set as follows: pretreatment capacitor voltage 50 V, pretreatment times 1, applied capacitor voltage 190 V, discharge times 1. After the reaction, the device was quickly cooled to room temperature, and the capacitor group was completely discharged. Then, the product was collected.

[0041] The lithium iron phosphate powder and the collected product were placed in a ball mill tank according to a mass ratio of 97:3, the ball-to-material ratio was 1:1, the ball mill speed was 300 rpm / min, and the ball milling time was 1 h. After ball milling, the product was collected. Figure 5 is a performance comparison chart of large flake low-defect graphene and lithium iron phosphate composite material. It can be clearly seen that compared with ordinary lithium iron phosphate, the performance of large flake low-defect graphene and lithium iron phosphate composite material has been greatly improved. The specific capacity is increased from the initial 147.68 mAh / g to 157.67 mAh / g. Even after 350 cycles, compared with the ordinary lithium iron phosphate 141.48 mAh / g, it still shows a specific capacity of 151.17 mAh / g, showing excellent cycle stability. Figure 4 is the XRD pattern of large flake low-defect graphene and lithium iron phosphate composite material, the characteristic peaks are consistent with those of lithium iron phosphate, and the characteristic peak of graphene (002) appears near 27°.

[0042] Example 2:

[0043] The process method of Example 1 was used, and in the preparation process of the graphite precursor, the amount of concentrated sulfuric acid with a concentration of 95% was changed to 60 mL, the amount of concentrated nitric acid with a concentration of 95% was changed to 15 mL, and the stirring time at room temperature was changed to 36 h. Thus, graphite precursors prepared under different conditions were obtained.

[0044] The precursor was collected and the material was prepared into graphene according to the process of Example 1, and then was compounded with ordinary lithium iron phosphate, to obtain graphene-lithium iron phosphate composites under different conditions.

[0045] Example 3:

[0046] The process of Example 1 was used, and during the preparation of the graphite precursor, 3 g of natural graphite and 100 mL of concentrated sulfuric acid with a concentration of 70% were mixed and stirred, 30 mL of concentrated nitric acid with a concentration of 86% was added to the mixture, and the mixture was stirred at room temperature for 24 hours. Ultra-pure water was slowly added to the mixture, and then the mixture was washed 5 times with ultra-pure water, centrifuged, and dried at 60°C overnight. The obtained powder was heated at 800°C for 25 seconds to obtain a graphite precursor. Graphene materials under different conditions were obtained.

[0047] The precursor was collected and the material was prepared into graphene according to the process of Example 1, and then was compounded with ordinary lithium iron phosphate, to obtain graphene-lithium iron phosphate composites under different conditions.

[0048] Example 4:

[0049] The process of Example 1 was used, and during the rapid Joule heat treatment, the number of capacitors in the capacitor bank was switched to one, and the parameters were adjusted: pre-treatment capacitor voltage 50V, pre-treatment number 1, applied capacitor voltage 150V, discharge number 6. Subsequently, the product was collected.

[0050] Graphene materials under different rapid Joule heat voltages were obtained. The material was compounded with ordinary lithium iron phosphate according to the process of Example 1, to obtain graphene-lithium iron phosphate composites under different conditions.

[0051] Example 5:

[0052] The process of Example 1 was used, and during the rapid Joule heat treatment, the parameters were adjusted: pre-treatment capacitor voltage 80V, pre-treatment number 5, applied capacitor voltage 120V, discharge number 2. Subsequently, the product was collected.

[0053] Graphene materials under different rapid Joule heat voltages were obtained. The material was compounded with ordinary lithium iron phosphate according to the process of Example 1, and the ball milling parameters were changed: ball-to-material ratio 1.5:1, ball mill speed 200 rpm / min, ball milling time 1 h, to obtain graphene-lithium iron phosphate composites under different conditions.

[0054] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A method for preparing a composite material of graphene and lithium iron phosphate synthesized by Joule heating, characterized in that, Includes the following steps, S101. The product of acid treatment and heat treatment of natural graphite is used as a graphite precursor, and then ultra-large sheet diameter graphene oxide is prepared by the improved Hummers method. S102. The ultra-large diameter graphene oxide from step S101 is transformed into large diameter low-defect graphene material using high voltage, high heat and high pressure of rapid Joule heating. S103. Transfer the graphene material and lithium iron phosphate powder from step S102 into a ball mill for ball milling to finally obtain the composite material; The graphite precursor is prepared according to the following steps: Natural graphite and concentrated sulfuric acid were mixed and stirred, then concentrated nitric acid was added and stirred at room temperature. Ultrapure water was then slowly poured into the mixture, and the resulting product was washed several times with ultrapure water. The product was then centrifuged and dried at 60°C for 24 hours. The dried powder was then heat-treated at 1000°C to obtain the graphite precursor.

2. The method for preparing a composite material of graphene and lithium iron phosphate synthesized by Joule heating according to claim 1, characterized in that: The sulfuric acid concentration is 70-98 wt%, the nitric acid concentration is 86-97.5 wt%, the graphite mass to concentrated sulfuric acid volume ratio is 1:20-1:50, the concentrated sulfuric acid to concentrated nitric acid volume ratio is 2:1-4:1, and the stirring time at room temperature is 18-36 hours.

3. The method for preparing a composite material of graphene and lithium iron phosphate synthesized by Joule heating according to claim 1, characterized in that: The heat treatment time in step S101 is 10-40 seconds.

4. The method for preparing a composite material of graphene and lithium iron phosphate synthesized by Joule heating according to claim 1, characterized in that: The discharge time of rapid Joule heating in step S102 is 100-800ms.

5. The method for preparing a composite material of graphene and lithium iron phosphate synthesized by Joule heating according to claim 1, characterized in that: In step S102, rapid Joule heating requires pretreatment. The capacitor voltage for pretreatment is 80-250V, and the number of pretreatment cycles is 1-10.

6. The method for preparing a composite material of graphene and lithium iron phosphate synthesized by Joule heating according to claim 1, characterized in that: In step S102, the capacitor voltage for rapid Joule heating is 100-300V, the current is 10-80A, and the number of discharges is 1-5 times.

7. The method for preparing a composite material of graphene and lithium iron phosphate synthesized by Joule heating according to claim 1, characterized in that: In step S103, the ball milling time is 1-6 hours, the ball milling speed is 200-600 rpm / min, and the ball-to-material ratio is 2:1-1:

1.

8. The application of a graphene-lithium iron phosphate composite material prepared by the method according to any one of claims 1-7 as an electrode in an ion battery.

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