Preparation and performance research of CR2430 battery

　　introduction

　　In the late 1990s, because liquid lithium cobalt oxide lithium-ion batteries had major safety issues, people researched and developed polymer lithium-ion batteries. In addition to the performance advantages of liquid lithium-ion batteries, polymer lithium-ion batteries also have higher energy density, better safety and more flexible shape design. Research on polymer lithium-ion batteries has recently focused on two aspects. One is to prepare lithium-ion polymer batteries by in-situ polymerization. Usually, a mixed solution containing liquid electrolyte solution, polymer, cross-linking agent and initiator is first prepared, and then the mixed solution is injected into the battery and heated and microwaved. , or use radiation to initiate a polymerization reaction to form a gel polymer electrolyte inside the battery to prepare a polymer lithium-ion battery. On the other hand, a porous polymer membrane is first prepared, and then used as a separator to assemble a battery to prepare a polymer lithium-ion battery.

　　The use of porous polymer separators to prepare polymer lithium-ion batteries can not only improve the performance of the battery in all aspects, 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 separator, a polymer solution is usually prepared first, then coated, followed by natural drying, vacuum drying and other steps, and finally cut to obtain the finished product.

　　However, this film-making method requires the use of a coating machine, which is relatively expensive. It also has the disadvantages of strict parameter requirements and complicated steps. In the author's preliminary work, the negative electrode sheet was treated by coating a polymer film, and the coating layer was used as a separator to assemble the battery, which improved the performance of the polymer lithium-ion battery. However, this method of coating polymer films is not suitable for large-scale industrial production of polymer lithium-ion batteries. Therefore, based on the paint spraying process, we selected appropriate conditions, treated the negative electrode sheet by spraying, made a polymer lithium-ion battery and tested its performance, and found that the polymer lithium-ion prepared by this method The battery has superior electrochemical properties.

　　1 experiment

　　1.1 Materials and equipment

　　The positive active material lithium manganate, the negative active material graphite, the conductive agent graphite (KS215) and acetylene black (Superp) are from Timcal, the binder is polyvinylidene fluoride (pVDF, Kynar761), and N2 methyl- Pyrrolidone was used as dispersion solvent.

　　Polyvinylidene fluoride 2 hexafluoropropylene (pVDF2HFp, Kynar2801) was vacuum dried at 85°C for 24 hours before use. Silica powder (SiO2, ~12nm, Cabosil TS2530) was vacuum dried at 120°C for 24 hours before use.

　　Methyl ketone and butanol were purchased from Beijing Reagent Company and were of analytical grade. Diethyl carbonate (DEC) was purchased from Zhangjiagang Electrolyte Factory and is battery pure. All liquid reagents are used directly after purchase.

　　The film-making equipment includes an air compressor and a liquid spray gun (W271, Yigong). The testing equipment is a blue lithium battery performance tester (Wuhan Lixing).

　　1.2 Preparing solution and preparing polymer membrane

　　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 each component of the solution is determined as: m (butanone): m (pVDF2HFp): m (SiO2) ∶m(DEC)∶m(butanol)=10∶1∶011∶319∶4. Place pVDF2HFp in 50°C butanone and stir to completely dissolve it. Use an ultrasonicator to disperse an appropriate amount of SiO2 in the mixture of DEC and butanol; then slowly add the SiO2 dispersion dropwise to the pVDF2HFp solution while stirring. , and finally obtain a uniformly mixed slurry. Transfer the slurry to the liquid storage tank of the spray gun and maintain the temperature of the slurry with a 50°C water bath. Use a spray gun to spray the slurry on the negative electrode sheet under appropriate parameters. After natural drying, dry it in a vacuum drying oven at 100°C for 24 hours before use.

　　1.3 Assembly and performance testing of polymer lithium-ion secondary batteries

　　The spray-coated negative electrode sheet is prepared into a polymer lithium-ion secondary battery by winding, and is liquefied into the battery. Then, performance tests such as charge and discharge cycles, rate discharge, and high and low temperature discharge are performed.

　　2 Results and discussion

　　2.1 Effect of spray gun parameters on processing negative electrode sheets

　　When using a spray gun for spraying, the spray volume of the slurry can generally be adjusted with a limit screw, and different shapes of spray flows can be adjusted by changing the position of the nozzle. Controlling the air pressure of the air compressor and the parameters of the spray gun during the experiment are very important to obtain a polymer film with uniform thickness and rich pores on the surface of the negative electrode sheet. When the air pressure is too low and the spray area of the nozzle is small, the thickness of the polymer film obtained is larger and the pores are not abundant, as shown in Figure 1(a); when the air pressure and spray area are appropriate, the thickness of the polymer film obtained is uniform. There are abundant pores, as shown in Figure 1(b). Since the concentration of the polymer solution is small, forming a polymer film of a certain thickness on the surface of the negative electrode requires spraying the negative electrode multiple times. Therefore, it can be seen from the picture that the sprayed layer seems to be composed of multiple layers, and each layer is composed of a large number of holes. structure. A large amount of electrolyte solution is adsorbed in the pores, and the ionic conductivity of the polymer membrane is high, which can improve battery performance. When the air pressure of the air compressor is 415×105pa and the nozzle is 15cm away from the negative electrode sheet, the thickness of the polymer film is approximately 25μm.

　　Dry the spray-treated negative electrode sheet and then immerse it in the electrolyte solution for 2 hours. Compare the difference in mass of the electrode sheet before and after immersion, and calculate the percentage increase in the mass of the electrode sheet, which is the adsorption amount of the electrolyte solution.

　　The electrolyte solution adsorption capacity of the negative electrode sheet shown in (b) is 28%, which is greater than the electrolyte solution adsorption capacity of the untreated negative electrode sheet (about 15%). The adsorption of more electrolyte solution by the pole piece means that the resistance to lithium ion migration is reduced, which can reduce the internal resistance of the battery and improve the performance of the battery. The internal resistance of the polymer lithium-ion battery with a designed capacity of 66 in this article is 35Ω, which is similar to the internal resistance of the liquid lithium-ion battery of the same model. It can be predicted that the polymer lithium-ion battery has better performance.

　　2.2 Cycle performance of polymer lithium-ion batteries

　　The activated polymer lithium-ion battery was continuously charged and discharged to test the cycle performance. The battery charging and discharging voltage range is 310~4.25V, and the current is 330mA (0.5C). The Coulombic efficiency of polymer lithium-ion batteries is about 100% during the charge and discharge process, indicating that the polymer film has stable properties and no side reactions occur. The charge and discharge cycle of the polymer lithium-ion battery is shown in Figure 2. The battery discharge capacity decreases slowly and steadily, indicating that the battery has good cycle performance.

　　2.3 Rate performance of polymer lithium-ion batteries

　　Fully charge the polymer lithium-ion battery (0.2C current) and discharge it at currents of 0.2, 0.5, 1 and 2C respectively. The ratio of the discharge capacity under different currents to the 0.2C discharge capacity is the rate characteristic. The discharge curves of polymer lithium-ion batteries at different currents are shown in Figure 3. The discharge capacities at 0.5, 1 and 2C currents are 9914%, 9418% and 8214% of the 0.2C discharge capacity respectively, indicating that the polymer lithium-ion battery is It has good discharge performance under different discharge currents. At the same time, the platform of the discharge curve at each current is higher, which means that the polymer lithium-ion battery has better load capacity.

　　2.4 High and low temperature performance of polymer lithium-ion batteries

　　The fully charged polymer lithium-ion battery was 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 represents 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 Figure 4. The discharge capacities at -18, 0 and 55°C are 9512%, 9619% and 9511% of the 25°C discharge capacity respectively. It can be seen that polymer lithium-ion batteries have excellent discharge performance at lower temperatures and can meet general low-temperature use requirements. At high temperatures, due to some side reactions and self-discharge phenomena occurring inside the battery during storage, the discharge capacity decreases slightly, but it can still meet the usage requirements. Therefore, polymer lithium-ion batteries can be used well at different temperatures, showing superior high and low temperature performance.

　　3Conclusion

　　This article uses spraying to treat the negative electrode sheet and assemble a lithium-ion polymer battery to test its performance. The research results show that under certain operating conditions, the spraying method can form a polymer film with uniform thickness and rich pores on the surface of the negative electrode sheet; the polymer lithium-ion battery assembled with this negative electrode sheet has superior performance. The test results show that this method can be used for industrial production of polymer lithium-ion batteries.

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