Cyclolated polyacrylonitrile coated iron oxide negative electrode material as well as preparation method and application thereof

Abstract

The invention provides a cyclized polyacrylonitrile-coated iron oxide negative electrode material as well as a preparation method and application thereof, and belongs to the technical field of preparation of lithium ion battery negative electrode materials, polyacrylonitrile coating mainly comprises the following steps: growing polyacrylonitrile on the surface of iron oxide in situ, and coating the iron oxide after thermal cyclization. According to the invention, cyclized polyacrylonitrile is innovatively synthesized on the surface of iron oxide in situ, and an iron oxide material is coated in a hollow structure through a structure provided by the cyclized polyacrylonitrile, so that volume expansion and shrinkage of the iron oxide in charge and discharge processes are effectively buffered. And by regulating and controlling the cyclization time of the cyclized polyacrylonitrile, the high-rate discharge performance and the specific discharge capacity of the iron oxide negative electrode are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode material preparation, and particularly relates to a cyclized polyacrylonitrile coated iron oxide negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in portable electronic products, electric vehicles and a series of energy storage systems due to their high voltage, high specific energy and super long cycle life. As a key component of lithium ion batteries, the negative electrode material directly affects the insertion and extraction of lithium ions, the capacity of the battery, the formation of the SEI film, the service life and safety. Although the commercial graphite anode material has reached a theoretical capacity of 372 mAh / g, it still cannot meet the requirements of large-scale energy storage infrastructure. Therefore, there is an urgent need for new lithium ion battery negative electrode materials to provide better energy density and cycle stability.

[0003] In the past few decades, transition metal oxides have attracted great attention from scientists due to their unique properties and potential applications. Among them, iron oxide (Fe2O3) is one of the most promising choices for lithium ion battery negative electrode materials due to its significant theoretical capacity (1007 mAh / g), sustainability and economy. However, during the charging and discharging process, Fe2O3 has low electrical conductivity and significant volume expansion, leading to severe capacity decay and irreversible electrode polarization during the cycle process. In order to solve these problems, a lot of work has been done to improve the structural integrity and cycle stability of Fe2O3 anode materials. The main methods include creating nanostructures or applying conductive carbon material coatings such as amorphous carbon, graphene and carbon nanotubes. Building nanostructures can reduce the volume effect during the charging and discharging process, while increasing the electroactive sites and reducing the diffusion distance of lithium ions and electrons. The combination with carbon-based materials significantly improves the electronic conductivity and structural integrity of the electroactive material, improving the cycle stability and performance of the electrode at high rates.

[0004] However, although these methods have alleviated the volume expansion problem of Fe2O3 negative electrode materials to some extent, they have not fundamentally solved the problem of electrode structure destruction and capacity decay caused by volume change during the charging and discharging process. Therefore, it is particularly important to develop a negative electrode material that can further optimize the structure of Fe2O3 negative electrode material to significantly reduce its volume expansion effect and improve its cycle stability and electrochemical performance. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, a polyacrylonitrile coated iron oxide negative electrode material and a preparation method and application thereof are provided. By coating polyacrylonitrile on the surface of iron oxide and heat cyclization treatment, the volume expansion of iron oxide during the charging and discharging process can be effectively inhibited, the loss of irreversible capacity can be reduced, and the electrochemical performance of the iron oxide negative electrode can be improved.

[0006] The specific technical solutions of the present application are as follows: A cyclized polyacrylonitrile-coated iron oxide negative material, which is composed of iron oxide nanoparticles and cyclized polyacrylonitrile, wherein the mass ratio of iron oxide to cyclized polyacrylonitrile is 1:0.1, and the cyclized polyacrylonitrile uniformly coats the surface of the iron oxide to form a hollow structure.

[0007] A preparation method of the cyclized polyacrylonitrile-coated iron oxide negative material, comprising the following steps: (1) Iron concentrate is subjected to leaching reaction with sulfuric acid, the leaching time is 4 h, the leaching temperature is 90 ℃, the liquid-solid ratio is 15:1, the sulfuric acid concentration is 40%, and the leaching liquid is obtained by filtration; (2) A precipitating agent is added to the leaching liquid, the precipitating agent is ammonia water with a concentration of 1.0 mol / L, the pH is adjusted to 3.2, and the iron hydroxide precursor is obtained after 4 h of precipitation; (3) The iron hydroxide precursor is sintered under an argon atmosphere, the sintering temperature is 500 ℃, and the holding time is 2 h to obtain the iron oxide; (4) The iron oxide, polyacrylonitrile, and DMF solution are mixed and stirred, the mass ratio of the iron oxide to the polyacrylonitrile is 1:0.1, the stirring speed is 400 rpm, and the stirring time is 24 h to obtain the polyacrylonitrile-coated iron oxide composite material; (5) The composite material is subjected to thermal cyclization treatment under an argon atmosphere, the cyclization temperature is 300 ℃, and the cyclization time is 6-12 h to obtain the cyclized polyacrylonitrile-coated iron oxide negative material.

[0008] In step (1), the acid is at least one of sulfuric acid, hydrochloric acid, and nitric acid, and the concentration of the acid is 1-3 mol / L. In step (2), the precipitating agent is at least one of sodium carbonate, sodium hydroxide, and ammonia water, and the concentration of the precipitating agent is 1-2 mol / L.

[0009] The material is used for lithium ion battery negative material, and the discharge specific capacity is not less than 941.38 mAh / g after 200 cycles at a current density of 500 mA / g.

[0010] A lithium ion battery, wherein the negative electrode sheet of the battery comprises a cyclized polyacrylonitrile-coated iron oxide composite material, a conductive agent, and a binder, and the mass ratio of the three is 7:2:1; the electrolyte is a mixed solution of 1M LiPF6, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC), and the volume ratio of EC, DMC, and EMC is 1:1:1. The discharge specific capacity of the battery is not less than 941.38 mAh / g after 200 cycles at a current density of 500 mA / g in the voltage range of 0.01-3.0 V.

[0011] Advantages of the present application: 1) The present application first uses iron concentrate leaching solution as iron source to prepare polyacrylonitrile coated iron oxide, which has a short process flow, is simple and reliable, has good repeatability, strong operability, low cost, is suitable for industrial production, and the electrochemical performance of the coated iron oxide is obviously improved, which has a broad development prospect.

[0012] 2) The present application can improve the electron and lithium ion transfer rate of the composite material, improve the rate performance of the material, and significantly improve the electrochemical performance by constructing polyacrylonitrile coated iron oxide.

[0013] 3) In the polyacrylonitrile coated iron oxide material of the present application, the iron oxide particles are uniformly coated inside the polyacrylonitrile layer, which can effectively buffer the volume expansion of iron oxide during charging and discharging, improve the interface stability of the material and electrolyte, and greatly improve the structural stability of iron oxide.

[0014] 4) The polyacrylonitrile coated iron oxide material of the present application has high rate performance and long service life when applied in the field of lithium ion secondary batteries. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 SEM images of (a) iron oxide and (b) polyacrylonitrile coated iron oxide prepared by the present application; Figure 2 Long cycle performance graph of polyacrylonitrile coated iron oxide prepared by the present application as a lithium ion battery negative material; Figure 3 Rate performance graph of polyacrylonitrile coated iron oxide prepared by the present application as a lithium ion battery negative material. DETAILED DESCRIPTION

[0016] The present application will be further described below in conjunction with the drawings and examples, but in no way limits the present application, any transformation or replacement based on the teaching of the present application belongs to the protection scope of the present application.

[0017] Example 1: Effect of different cyclization times on material performance Step 1: Iron concentrate is subjected to leaching reaction with sulfuric acid, the leaching time is 4 h, the leaching temperature is 90 ℃, the liquid-solid ratio is 15:1, the sulfuric acid concentration is 40%, and the filtrate is obtained by filtration; Step 2: Add 1.0 mol / L ammonia solution to the leaching solution, adjust the pH to 3.2, and precipitate for 4 h to obtain iron hydroxide precursor; Step 3: Sinter the iron hydroxide precursor under argon atmosphere, the sintering temperature is 500 ℃, and the holding time is 2h, to obtain iron oxide; Step 4: The iron oxide, polyacrylonitrile and DMF solution were mixed and stirred at a mass ratio of iron oxide to polyacrylonitrile of 1:0.1, a stirring speed of 400 rpm and a stirring time of 24 h to obtain a cyclized polyacrylonitrile-coated iron oxide composite material.

[0018] Step 5: The above composite material was subjected to thermal cyclization treatment under an argon atmosphere at a cyclization temperature of 300 ℃ for 6 h, 9 h and 12 h, respectively, to obtain polyacrylonitrile-coated iron oxide composite materials with different cyclization times, which were labeled as Fe2O3@PAN-6, Fe2O3@PAN-9 and Fe2O3@PAN-12, respectively.

[0019] Step 6: The above composite material was mixed with conductive agent Super P and binder PVDF at a mass ratio of 7:2:1, and an appropriate amount of N-methyl pyrrolidone (NMP) was added to prepare a slurry, which was uniformly coated on a copper foil current collector. After vacuum drying at 120 ℃ for 12 h, the electrode sheet was punched into a diameter of 14 mm. The mass loading of active material in the electrode sheet was about 1.2 mg / cm².

[0020] Step 7: A CR2032 type button cell was assembled in an argon glove box using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator and 1 M LiPF6 / EC:DMC (1:1, v / v) as the electrolyte.

[0021] Step 8: Constant current charge and discharge tests were performed using a blue light test system in the voltage range of 0.01-3.0 V at a current density of 500 mA / g.

[0022] Conclusion: After 200 cycles at a current density of 500 mA / g, the discharge specific capacity of Fe2O3@PAN-6 was 852.4 mAh / g, and the capacity retention rate was 78.2%; After 200 cycles under the same conditions, the discharge specific capacity of Fe2O3@PAN-9 was 941.38 mAh / g, and the capacity retention rate was 86.5%; After 200 cycles under the same conditions, the discharge specific capacity of Fe2O3@PAN-12 was 896.7 mAh / g, and the capacity retention rate was 82.1%.

[0023] Conclusion: When the cyclization time is 9 h, the material has the highest discharge specific capacity and the best cycle stability, indicating that the cyclization degree of PAN is optimal at this cyclization time, forming a coating layer with the best conductivity and mechanical strength.

[0024] Example 2: Rate performance test at different current densities Step 1: Iron concentrate was reacted with sulfuric acid for leaching, the leaching time was 4 h, the leaching temperature was 90 ℃, the liquid-solid ratio was 15:1, and the sulfuric acid concentration was 40%, and the leaching solution was obtained by filtration.

[0025] Step 2: Ammonia solution of 1.0 mol / L was added to the leaching solution, the pH was adjusted to 3.2, and the iron hydroxide precursor was obtained by precipitation for 4 h.

[0026] Step 3: The iron hydroxide precursor was sintered under argon atmosphere, the sintering temperature was 500 ℃, and the holding time was 2 h, and the iron oxide was obtained.

[0027] Step 4: The iron oxide, polyacrylonitrile and DMF solution were mixed and stirred, the mass ratio of iron oxide to polyacrylonitrile was 1:0.1, the stirring speed was 400 rpm, and the stirring time was 24 h, and the polyacrylonitrile coated iron oxide composite material was obtained.

[0028] Step 5: The above composite material was subjected to thermal cyclization treatment under argon atmosphere, the cyclization temperature was 300 ℃, and the cyclization time was 9 h, and the polyacrylonitrile coated iron oxide composite material was obtained.

[0029] Step 6: The above composite material was mixed with conductive agent Super P and binder PVDF according to a mass ratio of 7:2:1, and an appropriate amount of N-methyl pyrrolidone (NMP) was added to prepare a slurry, which was uniformly coated on a copper foil current collector. After vacuum drying at 120 ℃ for 12 h, the electrode sheet was punched into a diameter of 14 mm. The mass loading of active material in the electrode sheet was 1.2 mg / cm².

[0030] Step 7: A CR2032 type button cell was assembled in an argon glove box with lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1 M LiPF6 / EC:DMC (1:1, v / v) as the electrolyte.

[0031] Step 8: The rate performance was tested using a blue light test system: first, cycle 5 times at a current density of 0.1 A / g for activation, then cycle 10 times at current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g and 5 A / g respectively, and finally return the current density to 0.1 A / g and cycle for another 10 times.

[0032] Conclusion: At a current density of 0.1 A / g, the average discharge specific capacity was 1052.6 mAh / g; At a current density of 0.2 A / g, the average discharge specific capacity was 978.3 mAh / g; At a current density of 0.5 A / g, the average discharge specific capacity was 941.38 mAh / g; The average discharge specific capacity was 872.5 mAh / g at a current density of 1 A / g; The average discharge specific capacity was 735.4 mAh / g at a current density of 2 A / g; The average discharge specific capacity was 372.1 mAh / g at a current density of 5 A / g.

[0033] When the current density returned to 0.1 A / g, the capacity returned to 1028.7 mAh / g, and the capacity recovery rate reached 97.7%. The results showed that the material had good rate performance and structural stability, and even at a high current density of 5 A / g, it still maintained a reversible capacity of 372.1 mAh / g, which was much higher than the theoretical capacity of graphite negative electrode.

[0034] Example 3: Long cycle performance test Step 1: Iron concentrate was reacted with sulfuric acid for leaching, the leaching time was 4 h, the leaching temperature was 90 ℃, the liquid-solid ratio was 15:1, the sulfuric acid concentration was 40%, and the filtrate was obtained by filtration.

[0035] Step 2: Add 1.0 mol / L ammonia solution to the leaching solution, adjust the pH to 3.2, and precipitate for 4 h to obtain the iron hydroxide precursor.

[0036] Step 3: The iron hydroxide precursor was sintered under argon atmosphere, the sintering temperature was 500 ℃, and the holding time was 2 h to obtain the iron oxide.

[0037] Step 4: Mix the iron oxide, polyacrylonitrile and DMF solution, the mass ratio of iron oxide to polyacrylonitrile is 1:0.1, the stirring speed is 400 rpm, and the stirring time is 24 h to obtain the polyacrylonitrile coated iron oxide composite material.

[0038] Step 5: The above composite material was subjected to thermal cyclization treatment under argon atmosphere, the cyclization temperature was 300 ℃, and the cyclization time was 9 h to obtain the polyacrylonitrile coated iron oxide composite material.

[0039] Step 6: Mix the above composite material with conductive agent Super P, binder PVDF according to the mass ratio of 7:2:1, add appropriate amount of N-methyl pyrrolidone (NMP) to make slurry, uniformly coat on copper foil current collector, and cut into 14 mm diameter pole piece after vacuum drying at 120 ℃ for 12 h. The mass loading of active material in the pole piece is 1.2 mg / cm².

[0040] Step 7: CR2032 button cell was assembled in an argon-filled glove box with lithium foil as the counter electrode, Celgard 2400 as the separator, and 1 M LiPF6 / EC:DMC (1:1, v / v) as the electrolyte.

[0041] Step 8: Long cycle performance test was conducted at a large current density of 1 A / g using a blue electric test system, with a voltage range of 0.01-3.0 V.

[0042] Conclusion: The first discharge specific capacity was 1253.8 mAh / g, and the first coulombic efficiency was 78.4%; After 100 cycles, the discharge specific capacity remained 895.6 mAh / g; After 200 cycles, the discharge specific capacity remained 782.3 mAh / g; After 300 cycles, the discharge specific capacity remained 703.8 mAh / g; After 400 cycles, the discharge specific capacity remained 652.1 mAh / g; After 500 cycles, the discharge specific capacity remained 619.12 mAh / g.

[0043] The capacity retention rate reached 85.3% (relative to the 10th cycle capacity), and the average capacity decay rate per cycle was only 0.029%. The results showed that the material had excellent long cycle stability, which was mainly due to the PAN coating layer effectively buffering the volume change of Fe2O3 during charging and discharging, maintaining the structural integrity of the electrode.

Claims

1. A cyclized polyacrylonitrile-coated iron oxide negative electrode material, characterized by, The material is composed of iron oxide nanoparticles and polyacrylonitrile, wherein the mass ratio of iron oxide to polyacrylonitrile is 1:0.1-0.5, and the cyclized polyacrylonitrile uniformly coats the surface of the iron oxide to form a hollow structure.

2. A process for the production of the polyacrylonitrile cyclized-coated iron oxide negative electrode material according to claim 1, characterized by, The method comprises the following steps: The iron concentrate is subjected to leaching reaction with an acid, the leaching time is 60-300 min, the leaching temperature is 60-90 DEG C, and the leaching liquid is obtained by filtration; (2) A precipitating agent is added to the leaching liquid, the precipitating agent is at least one of sodium carbonate, sodium hydroxide and ammonia water, the reaction temperature is 60-90 DEG C, the reaction time is 2 h, the precipitation temperature is 60 DEG C, the precipitation time is 4 h, and the iron hydroxide precursor is obtained; (3) The iron hydroxide precursor is sintered under argon or nitrogen atmosphere, the sintering temperature is 350-500 DEG C, the holding time is 2-4 h, and the iron oxide is obtained; (4) The iron oxide, polyacrylonitrile and dimethylformamide solution are mixed and stirred, the stirring speed is 200-400 rpm, the stirring time is 12-24 h, and after filtration and drying, the cyclized polyacrylonitrile coated iron oxide negative material is obtained by calcination under argon atmosphere at 260-300 DEG C.

3. The production method according to claim 2, characterized by, In step (1), the acid is at least one of sulfuric acid, hydrochloric acid and nitric acid, and the concentration of the acid is 1-3 mol / L.

4. The preparation method according to claim 2, characterized in that, In step (2), the precipitating agent is at least one of sodium carbonate, sodium hydroxide and ammonia water, and the concentration of the precipitating agent is 1-2 mol / L.

5. The cyclized polyacrylonitrile-coated iron oxide negative electrode material according to any one of claims 1 to 4, characterized in that The material is used for lithium ion battery negative material, and the discharge specific capacity is not less than 941.38 mAh / g after 200 cycles at a current density of 500 mA / g.

6. The lithium-ion battery of claim 1, wherein the lithium-ion battery is a lithium-ion battery. The negative electrode sheet of the battery comprises the cyclized polyacrylonitrile coated iron oxide composite material, a conductive agent and a binder, and the mass ratio of the three is 7:2:1; the electrolyte is a mixed solution of 1M LiPF6, ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC), and the volume ratio of EC, DMC and EMC is 1:1:

1.

7. The lithium-ion battery of claim 6, wherein the lithium-ion battery is characterized by: The battery has a discharge specific capacity of not less than 941.38 mAh / g after 200 cycles at a current density of 500 mA / g in a voltage range of 0-3 V.

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