Introduction In the late 1990s, due to the large-scale safety problems of lithium-ion lithium-ion batteries, research and development of polymer lithium-ion batteries were conducted. In addition to the performance advantages of liquid lithium-ion batteries, polymer lithium-ion batteries also have higher energy density, better safety, and a more flexible shape design. Research on polymer lithium-ion batteries has recently focused on two aspects. One is a lithium-ion polymer battery prepared by an in-situ polymerization method. Usually, a mixed solution containing a liquid electrolyte solution, a polymer, a cross-linking agent, and an initiator is first prepared, and then the mixed solution is injected into the inside of the battery and passed through the heating and microwaves. Or, the radiation method initiates a polymerization reaction, and a gel-state polymer electrolyte is formed inside the battery to prepare a polymer lithium ion battery. On the other hand, a porous polymer film is first prepared, and then a polymer lithium ion battery is prepared for the separator assembly battery.
The use of porous polymer membranes to prepare polymer lithium-ion batteries can not only improve the performance of various aspects of the battery, but also reduce the cost of the battery, and is very suitable for industrial production of polymer lithium-ion batteries. To prepare a porous polymer membrane, a polymer solution is usually prepared first, then coated, subjected to steps such as natural drying and vacuum drying, and finally cut to obtain a finished product.
However, this method of film production requires the use of a coater, which is expensive, and has the disadvantages of strict parameter requirements and complicated steps. In the author's previous work, the negative electrode sheet was treated by coating a polymer film, and the battery was assembled using the coating layer as a separator to improve the performance of the polymer lithium ion battery. However, this method of coating a polymer film is not suitable for large-scale industrial production of polymer lithium-ion batteries. Therefore, on the basis of drawing on the coating spraying process, we selected the appropriate conditions, and processed the negative electrode sheet by spraying to make a polymer lithium-ion battery and tested its performance. The polymer lithium ion produced by this method was found. The battery has superior electrochemical performance.
1 Experiment 1.1 Materials and Equipment Positive Electrode Active Material Lithium Manganate, Negative Electrode Active Material Graphite, Conductive Agent Graphite (KS215) and Acetylene Black (SuperP) from Timcal, and Adhesive Polyvinylidene Fluoride (PVDF, Kynar761) Use N2 methylpyrrolidone as a dispersion solvent.
Polyvinylidene fluoride 2 hexafluoropropylene (PVDF2HFP, Kynar 2801) was vacuum dried at 85°C for 24 hours. Silica powder (SiO2, ~12 nm, Cabosil TS2530) was vacuum dried at 120°C for 24 hours.
Butanone and butanol were purchased from Beijing Reagent Company and analyzed pure. Diethyl carbonate (DEC) was purchased from Zhangjiagang Electrolyte Factory and the battery was pure. All liquid reagents are used directly after purchase.
Membrane equipment includes an air compressor and a liquid spray gun (W271, Yigong). The test equipment is a blue lithium battery performance tester (Wuhan Lixing).
1.2 Preparation of solutions and preparation of polymer films Based on previous work experience, the composition of the polymer solution was initially determined. It was found in the experiment that if the concentration of the solution is reduced, the spraying operation is more convenient and does not affect the performance of the polymer film, so the mass ratio of the components of the solution is determined as: m (butanone):m(PVDF2HFP):m(SiO2) : m (DEC) : m (butanol) = 10 : 1 : 011 : 319 : 4 . The PVDF2HFP was placed in 50°C butanone and stirred to completely dissolve. The appropriate amount of SiO2 was dispersed in a mixture of DEC and butanol using a sonicator; then, the SiO2 dispersion was slowly added dropwise to the PVDF2HFP solution under stirring. In the end, a uniformly mixed slurry is finally obtained. Transfer the slurry to the reservoir of the spray gun and maintain the temperature of the slurry with a 50°C water bath. The slurry was sprayed on the negative electrode with a spray gun under suitable parameters, and after drying naturally, it was dried in a vacuum drying oven at 100° C. for 24 hours.
1.3 Assembly and Performance Test of Polymer Lithium Ion Secondary Battery The polymer electrolyte lithium ion secondary battery was prepared by winding the negative electrode sheet that was sprayed, and the liquid was converted into a charge, and then charge and discharge cycles, rate discharge, and high Low temperature discharge and other performance tests.
2 Results and Discussion 2.1 Effect of Spray Gun Parameters on the Treatment of Negative Electrode When spray guns are used for spraying, the discharge amount of slurry can generally be adjusted with the limit screw. Changing the position of the nozzle can adjust the spray flow of different shapes. In the experiment, controlling the air compressor pressure and the parameters of the spray gun is very important for obtaining a uniform thickness and rich pore polymer film on the surface of the negative electrode sheet. When the air pressure is too low, the polymer film thickness obtained when the nozzle spray area is small is large, and the porosity is not abundant, as shown in Fig. 1(a); when the air pressure and the spray area are appropriate, the obtained polymer film is uniform in thickness, Pore ​​rich, as shown in Figure 1 (b). Due to the small concentration of the polymer solution, a certain thickness of the polymer film to be formed on the surface of the negative electrode sheet requires multiple spraying on the negative electrode sheet. Therefore, it can be seen from the figure that the sprayed layer seems to be composed of a plurality of layers each having a large number of holes. structure. A large amount of electrolyte solution is adsorbed in the pores, and the ionic conductivity of the polymer film is high, which can improve the performance of the battery. When the air compressor air pressure is 415×10 5 Pa, and the nozzle is 15 cm away from the negative plate, the thickness of the polymer film is about 25 μm.
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Fig.1 Surface morphology of the negative electrode after treatment After the sprayed negative electrode sheet was dried and then immersed in the electrolyte solution for 2 hours, the difference in the mass of the lead sheet before and after the immersion was compared, and the percentage increase in the mass of the electrode was calculated as the amount of electrolyte solution adsorbed. .
The electrolyte solution adsorption amount of the negative electrode sheet shown in FIG. 1(b) was 28%, which was larger than the electrolyte solution adsorption amount (about 15%) of the untreated negative electrode sheet. The adsorption of more electrolyte solution by the pole pieces means that the lithium ion migration resistance is reduced, the internal resistance of the battery can be reduced, and the performance of the battery can be improved. In this article, a polymer lithium-ion battery with a designed capacity of 66 has an internal resistance of 35Ω, which is similar to the internal resistance of the same type of liquid lithium-ion battery. It can be predicted that the polymer lithium-ion battery has better performance.
2.2 Cyclic Performance of Polymer Lithium Ion Batteries The activated polymer lithium ion battery is continuously charged and discharged to test the cycle performance. The battery is charged and discharged with a voltage range of 310 to 4.25V and a current of 330mA (0.5C). The Coulomb efficiency of a polymer lithium-ion battery during charging and discharging is approximately 100%, indicating that the polymer film is stable and does not cause side reactions. The charge-discharge cycle of the polymer lithium-ion battery is shown in FIG. 2 , and the discharge capacity of the battery decreases slowly and the amplitude is stable, indicating that the battery has good cycle performance.
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Figure 2. Cyclic Performance of Polymer Lithium-Ion Batteries 2.3 Rate Performance of Polymer Lithium-Ion Batteries Lithium-ion polymer batteries are fully charged (0.2C current) and discharged at currents of 0.2, 0.5, 1 and 2C, respectively. The ratio of discharge capacity to 0.2C discharge capacity is the rate characteristic. The discharge curves of polymer lithium-ion batteries under different currents are shown in Fig. 3. The discharge capacities at 0.5, 1 and 2 C currents are 9914%, 9418% and 8214% of the 0.2C discharge capacities, respectively, indicating that the polymer lithium-ion batteries are Different discharge currents have good discharge performance. At the same time, the discharge curve of the current under the platform is higher, said polymer lithium-ion battery has a better load capacity.
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Figure 3. Rate performance of polymer lithium-ion batteries 2.4 High- and low-temperature performance of polymer lithium-ion batteries The fully-charged polymer lithium-ion batteries were left at -18, 0, 25, and 55°C for 4 hours, and then discharged to 3.0V. The ratio of the discharge capacity at different temperatures to the discharge capacity at 25°C is expressed as the high- and low-temperature discharge performance of polymer lithium-ion batteries. The discharge curves of polymer lithium-ion batteries at different temperatures are shown in Fig. 4. The discharge capacities at -18, 0, and 55°C are 9512%, 9619%, and 9511% of the 25°C discharge capacities, respectively. It can be seen that the polymer lithium-ion battery discharge performance at a relatively low temperature is very good, to meet the general requirements of low temperature use. At high temperature, due to some side reactions and self-discharge inside the battery during the shelving process, the discharge capacity is slightly reduced, but it can still meet the requirements for use. Therefore, polymer lithium-ion batteries can be used very well at different temperatures and exhibit superior high and low temperature performance.
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Figure 4 High and Low Temperature Performance of Polymer Lithium Ion Batteries 3 Conclusion This paper used the method of spraying to treat the negative electrode sheet and assemble the lithium ion polymer battery to test its performance. The results show that under certain operating conditions, the spraying method can form a uniform thickness and rich pore polymer film on the surface of the negative electrode sheet; the polymer lithium ion battery assembled by the negative electrode sheet has superior performance. The test results show that this method can be used for industrial production of lithium-ion polymer batteries.
The use of porous polymer membranes to prepare polymer lithium-ion batteries can not only improve the performance of various aspects of the battery, but also reduce the cost of the battery, and is very suitable for industrial production of polymer lithium-ion batteries. To prepare a porous polymer membrane, a polymer solution is usually prepared first, then coated, subjected to steps such as natural drying and vacuum drying, and finally cut to obtain a finished product.
However, this method of film production requires the use of a coater, which is expensive, and has the disadvantages of strict parameter requirements and complicated steps. In the author's previous work, the negative electrode sheet was treated by coating a polymer film, and the battery was assembled using the coating layer as a separator to improve the performance of the polymer lithium ion battery. However, this method of coating a polymer film is not suitable for large-scale industrial production of polymer lithium-ion batteries. Therefore, on the basis of drawing on the coating spraying process, we selected the appropriate conditions, and processed the negative electrode sheet by spraying to make a polymer lithium-ion battery and tested its performance. The polymer lithium ion produced by this method was found. The battery has superior electrochemical performance.
1 Experiment 1.1 Materials and Equipment Positive Electrode Active Material Lithium Manganate, Negative Electrode Active Material Graphite, Conductive Agent Graphite (KS215) and Acetylene Black (SuperP) from Timcal, and Adhesive Polyvinylidene Fluoride (PVDF, Kynar761) Use N2 methylpyrrolidone as a dispersion solvent.
Polyvinylidene fluoride 2 hexafluoropropylene (PVDF2HFP, Kynar 2801) was vacuum dried at 85°C for 24 hours. Silica powder (SiO2, ~12 nm, Cabosil TS2530) was vacuum dried at 120°C for 24 hours.
Butanone and butanol were purchased from Beijing Reagent Company and analyzed pure. Diethyl carbonate (DEC) was purchased from Zhangjiagang Electrolyte Factory and the battery was pure. All liquid reagents are used directly after purchase.
Membrane equipment includes an air compressor and a liquid spray gun (W271, Yigong). The test equipment is a blue lithium battery performance tester (Wuhan Lixing).
1.2 Preparation of solutions and preparation of polymer films Based on previous work experience, the composition of the polymer solution was initially determined. It was found in the experiment that if the concentration of the solution is reduced, the spraying operation is more convenient and does not affect the performance of the polymer film, so the mass ratio of the components of the solution is determined as: m (butanone):m(PVDF2HFP):m(SiO2) : m (DEC) : m (butanol) = 10 : 1 : 011 : 319 : 4 . The PVDF2HFP was placed in 50°C butanone and stirred to completely dissolve. The appropriate amount of SiO2 was dispersed in a mixture of DEC and butanol using a sonicator; then, the SiO2 dispersion was slowly added dropwise to the PVDF2HFP solution under stirring. In the end, a uniformly mixed slurry is finally obtained. Transfer the slurry to the reservoir of the spray gun and maintain the temperature of the slurry with a 50°C water bath. The slurry was sprayed on the negative electrode with a spray gun under suitable parameters, and after drying naturally, it was dried in a vacuum drying oven at 100° C. for 24 hours.
1.3 Assembly and Performance Test of Polymer Lithium Ion Secondary Battery The polymer electrolyte lithium ion secondary battery was prepared by winding the negative electrode sheet that was sprayed, and the liquid was converted into a charge, and then charge and discharge cycles, rate discharge, and high Low temperature discharge and other performance tests.
2 Results and Discussion 2.1 Effect of Spray Gun Parameters on the Treatment of Negative Electrode When spray guns are used for spraying, the discharge amount of slurry can generally be adjusted with the limit screw. Changing the position of the nozzle can adjust the spray flow of different shapes. In the experiment, controlling the air compressor pressure and the parameters of the spray gun is very important for obtaining a uniform thickness and rich pore polymer film on the surface of the negative electrode sheet. When the air pressure is too low, the polymer film thickness obtained when the nozzle spray area is small is large, and the porosity is not abundant, as shown in Fig. 1(a); when the air pressure and the spray area are appropriate, the obtained polymer film is uniform in thickness, Pore ​​rich, as shown in Figure 1 (b). Due to the small concentration of the polymer solution, a certain thickness of the polymer film to be formed on the surface of the negative electrode sheet requires multiple spraying on the negative electrode sheet. Therefore, it can be seen from the figure that the sprayed layer seems to be composed of a plurality of layers each having a large number of holes. structure. A large amount of electrolyte solution is adsorbed in the pores, and the ionic conductivity of the polymer film is high, which can improve the performance of the battery. When the air compressor air pressure is 415×10 5 Pa, and the nozzle is 15 cm away from the negative plate, the thickness of the polymer film is about 25 μm.
Fig.1 Surface morphology of the negative electrode after treatment After the sprayed negative electrode sheet was dried and then immersed in the electrolyte solution for 2 hours, the difference in the mass of the lead sheet before and after the immersion was compared, and the percentage increase in the mass of the electrode was calculated as the amount of electrolyte solution adsorbed. .
The electrolyte solution adsorption amount of the negative electrode sheet shown in FIG. 1(b) was 28%, which was larger than the electrolyte solution adsorption amount (about 15%) of the untreated negative electrode sheet. The adsorption of more electrolyte solution by the pole pieces means that the lithium ion migration resistance is reduced, the internal resistance of the battery can be reduced, and the performance of the battery can be improved. In this article, a polymer lithium-ion battery with a designed capacity of 66 has an internal resistance of 35Ω, which is similar to the internal resistance of the same type of liquid lithium-ion battery. It can be predicted that the polymer lithium-ion battery has better performance.
2.2 Cyclic Performance of Polymer Lithium Ion Batteries The activated polymer lithium ion battery is continuously charged and discharged to test the cycle performance. The battery is charged and discharged with a voltage range of 310 to 4.25V and a current of 330mA (0.5C). The Coulomb efficiency of a polymer lithium-ion battery during charging and discharging is approximately 100%, indicating that the polymer film is stable and does not cause side reactions. The charge-discharge cycle of the polymer lithium-ion battery is shown in FIG. 2 , and the discharge capacity of the battery decreases slowly and the amplitude is stable, indicating that the battery has good cycle performance.
Figure 2. Cyclic Performance of Polymer Lithium-Ion Batteries 2.3 Rate Performance of Polymer Lithium-Ion Batteries Lithium-ion polymer batteries are fully charged (0.2C current) and discharged at currents of 0.2, 0.5, 1 and 2C, respectively. The ratio of discharge capacity to 0.2C discharge capacity is the rate characteristic. The discharge curves of polymer lithium-ion batteries under different currents are shown in Fig. 3. The discharge capacities at 0.5, 1 and 2 C currents are 9914%, 9418% and 8214% of the 0.2C discharge capacities, respectively, indicating that the polymer lithium-ion batteries are Different discharge currents have good discharge performance. At the same time, the discharge curve of the current under the platform is higher, said polymer lithium-ion battery has a better load capacity.
Figure 3. Rate performance of polymer lithium-ion batteries 2.4 High- and low-temperature performance of polymer lithium-ion batteries The fully-charged polymer lithium-ion batteries were left at -18, 0, 25, and 55°C for 4 hours, and then discharged to 3.0V. The ratio of the discharge capacity at different temperatures to the discharge capacity at 25°C is expressed as the high- and low-temperature discharge performance of polymer lithium-ion batteries. The discharge curves of polymer lithium-ion batteries at different temperatures are shown in Fig. 4. The discharge capacities at -18, 0, and 55°C are 9512%, 9619%, and 9511% of the 25°C discharge capacities, respectively. It can be seen that the polymer lithium-ion battery discharge performance at a relatively low temperature is very good, to meet the general requirements of low temperature use. At high temperature, due to some side reactions and self-discharge inside the battery during the shelving process, the discharge capacity is slightly reduced, but it can still meet the requirements for use. Therefore, polymer lithium-ion batteries can be used very well at different temperatures and exhibit superior high and low temperature performance.
Figure 4 High and Low Temperature Performance of Polymer Lithium Ion Batteries 3 Conclusion This paper used the method of spraying to treat the negative electrode sheet and assemble the lithium ion polymer battery to test its performance. The results show that under certain operating conditions, the spraying method can form a uniform thickness and rich pore polymer film on the surface of the negative electrode sheet; the polymer lithium ion battery assembled by the negative electrode sheet has superior performance. The test results show that this method can be used for industrial production of lithium-ion polymer batteries.
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