Research on methods to improve the performance of CR1625 battery

　　Li/SOCl2 batteries (lithium sub-batteries) have the advantages of high operating voltage, stable discharge voltage, wide operating temperature range and long storage life. They have been widely used in aerospace, navigation and medical treatment. Li/SOCl2 batteries have problems such as voltage lag and poor safety performance in applications. This article reviews the methods used to improve the performance of Li/SOCl2 batteries in recent years.

　　1Battery safety performance

　　Under short circuit or certain heavy load conditions, organic electrolyte lithium batteries and non-aqueous inorganic electrolyte lithium batteries may explode. The main factors include short circuit, over-discharge, separator decomposition and high temperature burning. The mechanism of Li/SOCl2 battery explosion has not been confirmed so far. Different abuse conditions have different reaction processes.

　　It has been reported that adding 0.19mol/L NbCl5 (niobium pentachloride) to the Li/SOCl2 battery electrolyte, the +5-valent Nb can absorb a large number of electrons generated by the battery under reverse voltage conditions and generate +3-valent Nb, thereby preventing Dendrites form on the surface of the lithium anode and can quickly prevent ignition-type explosions caused by reverse voltage in the presence of sulfur, improving the reliability of Li/SOCl2 batteries. It is also said that after adding pCl5 to the Li/SOCl2 battery, SO2 and pCl5 react to generate liquid products SOCl2 and pOCl3, which prevents the increase in battery internal pressure caused by excessive SO2 and enhances the safety performance of the Li/SOCl2 battery.

　　L1Qiu et al. added Fe2TAp to the Li/SOCl2 battery as an electrolyte catalyst, which increased the operating voltage of the battery, reduced the internal pressure of the battery, and improved the low-temperature performance of the battery. Wang Shengping used foamed nickel materials as the carbon cathode current collector of Li/SOCl2 batteries. The research found that foamed nickel electrodes can reduce electrochemical polarization, improve the electron conduction path of the electrode, and improve the high-current discharge capability of the battery; at the same time, it also The safety performance of the battery can be improved by improving the internal heat transfer mode of the battery.

　　Zhao Xinle and others conducted accelerated experiments on small Li/SOCl2 batteries and used a scanning electron microscope to observe their sealing properties. The results showed that the stainless steel welds were well maintained, but the joints between the ceramic and stainless steel and the performance of the sealing ceramics were uneven. The combined action of temperature, stress and corrosion causes the ceramic sealed insulator to break, resulting in loss of sealing performance and leakage of electrolyte. The key to improvement lies in developing appropriate sealing materials and improving the connection process between sealing materials and stainless steel.

　　2 Methods to improve voltage hysteresis and electrochemical performance

　　After long-term high-temperature storage, voltage hysteresis can be observed when the battery is discharged, especially when discharging at high current and low temperature. This phenomenon is more prominent, among which Li/SOCl2 batteries are the most serious. It is generally believed that in a Li/SOCl2 battery, lithium reacts with SOCl2, and the reaction product LiCl forms an extremely thin, dense crystalline film on the surface of the lithium electrode. This film has electronic insulation and prevents SOCl2 outside the film from further reacting with lithium in the inner layer. As the ambient temperature increases and the battery storage time increases, the crystalline film will gradually expand and thicken, forming a secondary film. The existence of the crystalline film makes the lithium electrode very stable in the electrolyte and improves the storage performance of the battery. Since the crystalline film is a poor conductor of electrons during discharge, it causes severe ohmic polarization of the lithium electrode. Measures to improve voltage lag vary depending on different battery systems. They generally include reducing the concentration of electrolyte salts, using new electrolyte salts, and adding SO2 and BrCl to the battery electrolyte.

　　In order to overcome the voltage hysteresis phenomenon caused by Li/SOCl2 battery discharging at high rates, K1Chung et al. connected an electrochemical capacitor in parallel to the wound Li/SOCl2 battery and used several electrochemical testing techniques to study this hybrid battery. The results show that : In the case of high-rate discharge, the electrochemical capacitor acts as a large current buffer and can eliminate the phenomenon of voltage hysteresis. This Li/SOCl2 battery with an electrochemical capacitor connected in parallel can be used in high-current pulse discharge equipment.

　　Wang Shengping introduced microwave technology into the cathode forming process of Li/SOCl2 batteries. By controlling microwave power, processing time and adjusting the amount of pTFE emulsion, a carbon cathode with appropriate porosity and pore size was made, and the assembled battery was The test results show that the use of microwave technology to process the Li/SOCl2 battery carbon cathode molding process has a certain effect on improving the high-current operation, low-temperature discharge and hysteresis performance of the battery.

　　Many studies have improved the voltage hysteresis of Li/SOCl2 batteries by improving the electrolyte, such as adding SO2, lithium syringyl borate compound, pVC (polyvinyl chloride), VC2VOC (polyethylene vinylene chloride copolymer) to the electrolyte. substance) and BrCl, etc. Xiao Shunhua studied the effects of LiAlCl4 concentration, SO2 concentration and SO2 reflux time on the voltage hysteresis phenomenon of Li/SOCl2 batteries. The results found that: when the LiAlCl4 concentration is high, the discharge capacity of the battery is also high, but the voltage hysteresis is also obvious; the LiAlCl4 concentration is At 112 mol/L, the voltage lag of the battery is smaller and the discharge capacity is also higher. The additive SO2 can greatly improve the voltage hysteresis of the battery. The SO2 mass fraction is about 6%. It is better to control the reflux time of adding SO2 to the electrolyte within 3 to 5 hours.

　　C1Schaikjer et al. added lithium syringyl borate compound as an additive to Li/SOCl2 batteries containing LiAlCl4 electrolyte salt, which helps to weaken the passivation of lithium metal anodes, thus reducing the voltage hysteresis that occurs when starting storage batteries at high temperatures. Haloborates have lower conductivity than LiAlC14. When Li2B10Cl10 is cooled to -35°C, the conductivity decreases. For Li/SOCl2 batteries using this type of salt, no voltage hysteresis or other abnormal phenomena were found when cooled to -60°C, but the high-rate discharge performance of Li/SOCl2 batteries was limited.

　　Ge Honghua and others found through AC impedance spectroscopy that adding BrCl to Li/SOCl2 batteries can reduce the impedance of the positive and negative electrodes, thereby alleviating the voltage hysteresis of the battery to a certain extent. Ma Yongjing summarized several materials that can reduce the voltage hysteresis of Li/SOCl2 batteries, focusing on some details of polymer electrolyte coating on the surface of lithium anodes. He believed that MEEp and its composition can reduce the voltage hysteresis of Li/SOCl2 batteries.

　　C1A1Frysz et al. used ultrafine carbon filaments instead of carbon black as porous reduction electrodes for BCX batteries. Ultra-fine carbon filaments can be made into sheets with a thickness of only 012mm, and the tubular holes they contain improve the porous properties. The application of ultra-fine carbon filaments gives the battery higher capacitance and specific capacitance properties; in addition, the high electrolyte absorption rate and absorption speed of ultra-fine carbon filaments also contribute to the high capacity of the battery.

　　When transition metal organic macrocyclic complexes, such as phthalocyanine complexes and porphyrin complexes are incorporated into the carbon cathode of Li/SOCl2 batteries, they can increase the discharge capacity of the battery and increase the open circuit voltage and operating voltage. Co2TAA can not only increase the discharge capacity and operating voltage of the battery, but also improve the safety of the battery. However, the catalytic components (such as organic ligands, metal complex ions or complex decomposition products, etc.) are still unclear.

　　S1B1Lee et al. used AC impedance spectroscopy and constant current transient measurement technology to study the impact of the tightness of the LiCl film deposited on the carbon cathode on the electrochemical reduction of SOCl2. The experiment used a pure carbon cathode and embedded cobalt phthalocyanine complex. Carbon cathode of material (Co2pC). The NyquiST diagram obtained experimentally can be divided into low-frequency arcs, high-frequency arcs and intermediate frequency straight-line parts. The low-frequency arc is related to the charge transfer process, while the straight-line part is related to the diffusion of SOCl2 in the porous layer. Low-frequency arcs, high-frequency arcs and intermediate frequency straight-line parts appear in the impedance spectrum of pure carbon cathode, while the intermediate straight-line part of the impedance spectrum of carbon cathode containing Co2pC material is absent or very short. In a pure carbon cathode, SOCl2 passes through the porous layer very slowly, and the LiCl film layer is tight enough to prevent SOCl2 from passing through; while in a carbon cathode containing Co2pC material, SOCl2 passes through the porous layer very quickly, and the film layer is tight Lower, SOCl2 can easily diffuse through this film. Co2pC improves the voltage hysteresis of the battery and increases the open circuit voltage and operating voltage of the battery.

　　Directly adding iron phthalocyanine and tetraphenylporphyrin complex to the electrolyte can also catalyze the electrochemical reduction process of SOCl2. The cathodic polarization mechanism of SOCl2 in the porous carbon electrode changes as the discharge process proceeds. This may be due to the change in the composition and morphology of the internal surface film of the carbon electrode. The solid product generated at the same time not only blocks the reduction surface of the electrode, but also blocks the pores in the electrode, causing the electrode to passivate; when Fe2pC is added to the electrolyte After the substance is released, it has little effect on the porous electrode at the open circuit potential, but under cathodic polarization, it improves the surface properties of the membrane, reduces the deposition rate of sediments on the inner surface of the pores, and delays the passivation of the porous carbon electrode. ization, which improves the voltage hysteresis of the battery to a certain extent.

　　Zhang Fuping and others studied Li/SOCl2 batteries containing TAA and Ni2TAA. The results showed that after adding TAA and Ni2TAA to the electrolyte respectively, the cathode polarization of the Li/SOCl2 battery was reduced, and the discharge capacity of the battery was increased by about 10%. and 15%, and does not change the final discharge product of the battery.

　　3 Conclusion

　　In recent years, there have been many studies on improving the performance of Li/SOCl2 batteries in various aspects, especially on battery safety performance and voltage hysteresis, and have achieved good results, but they are basically at the expense of other aspects of the battery. At the expense of performance, it does not fundamentally solve the problem. If the battery is to be widely used in the market, these problems still need to be further solved.

　　With the continuous development of science and technology, the continuous improvement of battery technology, the gradual improvement of electrolyte formula, and the continuous reduction of production costs, it is believed that the safety and voltage lag issues of lithium-ion batteries and other aspects of electrochemical performance will be further improved. Li/SOCl2 batteries will be more widely used.

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