Special research on lithium thionyl chloride batteries provided by electronic enthusiasts. Special research on lithium thionyl chloride batteries. Advantages of Li/SOCl2 batteries: 1. Large specific energy. Since it is both a solvent and a positive active material, its specific energy can generally reach 420Wh. /Kg, up to 650Wh/K at low rate discharge Special research on lithium thionyl chloride battery

★Advantages of Li/SOCl2 battery 1. Large specific energy. Because it is both a solvent and a positive active material, its specific energy can generally reach 420Wh/Kg, and can reach up to 650Wh/Kg when discharging at a low rate.

2. The voltage is very high. The open circuit voltage of the battery is 3.65V, at 1mA/cm2. When discharging, the voltage can be maintained at 3.3V, and the voltage remains unchanged within 90% of the capacity range.

3. Batteries with large specific power can be discharged at a current density of 10mA/cm2 or higher.

4. High voltage accuracy and extremely flat discharge curve during normal temperature and medium current density discharge.

5. It has good high and low temperature performance and can generally work normally within -40-50℃, even between -50-150℃; the capacity at -40℃ is about 50% of the normal temperature capacity.

6. Good storage performance, generally can be left wet for 5 years or more.

7. Fully sealed design

8. The battery has no internal pressure. There is no internal pressure at the beginning, and a certain pressure does not appear until the end of discharge.

★Disadvantages of Li/SOCl2 batteries 1. Voltage hysteresis. After long-term storage at room temperature or room temperature, when discharged with a larger current, the operating voltage drops sharply, and then slowly returns to normal.

2. Safety issues Although certain measures have been taken, it is still possible to store the product in a discharged state, causing uncontrollable heat eruption and explosion during high-temperature discharge.

3. The price is more expensive

4. Environmental pollution SOCl2 decomposes into hydrochloric acid and sulfur dioxide after absorbing water. It is extremely corrosive, so the production site must be well ventilated.

★Properties of SOCl2 (ThionylChloride) SOCl2 is a liquid covalent inorganic compound. It serves as both a positive electrode reactant and a solvent in the electrolyte solution in the battery. SOCl2 is a light yellow to red liquid with a density of 1.638, a boiling point of 78.8°C, and a melting point of -105°C. It can be miscible with benzene, chloroform, carbon tetrachloride, etc., and decomposes in water to form sulfurous acid and hydrochloric acid. It decomposes when heated to form sulfur dioxide, chlorine and sulfur monoxide. It can be formed by the interaction of sulfur dichloride and sulfur trioxide. , liquid at room temperature.

★Li/SOCl2 battery working principle Li/SOCl2 battery uses lithium as the negative electrode, carbon as the positive electrode, the SOCl2 solution of anhydrous lithium tetrachloroaluminate (LiAlCl4) as the electrolyte, and SOCl2 as the positive electrode active material. Polypropylene felt or glass fiber paper is used as the separator, and its open circuit voltage is 3.65V. The battery system can be expressed by the following formula: Li/LiACl4-SOCl2/C negative electrode: 4Li=4Li++4e positive electrode: 2SOCL2+4e=2SO2+4Cl- 2SO→←(SO)2(SO)2→←S+SO2 total battery reaction: 4Li+2SOCl2→4LiCl+S+SO2SO2 is all dissolved in SOCl2, S precipitates in large amounts and is deposited in the positive electrode carbon black. LiCl is insoluble. . In this kind of battery, when Li comes into contact with SOCl2, the following reaction will occur: 8Li+4SOCl2→6LiCl+Li2S2O4+S2Cl2 or 8Li+3SOCl2→6LiCl+Li2SO3+2S. Because of this reaction, although the positive active material of the Li/SOCl2 battery SOCl2 tightly surrounds the negative electrode, but no short circuit actually occurs. This is because an extremely thin and dense LiCl protective film (primary film) is formed on the surface of the negative electrode. This film has electronic insulation and can penetrate ions. transparent, thereby preventing further reaction between external SOCl2 and lithium, making lithium very stable in the SOCl2 electrolyte. As the ambient temperature increases and the battery storage time prolongs, the primary film will gradually expand and thicken to form the so-called secondary film. Once the film is removed, the battery will have a good storage life. Therefore, Li/SOCl2 batteries have a serious voltage hysteresis phenomenon. This hysteresis phenomenon makes the voltage generally return to 95% of the peak voltage within a few minutes. After two years of storage at 25°C, the Li/SOCl2 battery has a lower initial voltage due to the LiCl passivation layer formed on the lithium surface. If the battery is short-circuited or discharged with large currents multiple times, the LiCl film can be broken and the working voltage can be reduced. recover. The products LiCl (white) and S (yellow) are precipitated in the positive electrode carbon black, partially blocking the micropores in the positive electrode. On the one hand, it causes some expansion of the positive electrode, on the other hand, it hinders the diffusion of electrolyte, increases concentration polarization, and gradually causes the battery to fail.

★Materials that reduce voltage hysteresis of Li/SOCl2 batteries. The main disadvantage of Li/SOCl2 batteries is its voltage hysteresis. This phenomenon is especially serious after high-temperature storage and then use at room temperature. The cause of voltage lag in Li/SOCl2 batteries: Mainly due to the use of lithium aluminum tetrachloride (liAlCl4) electrolyte salt in the battery system. The electrolyte solution containing this salt and the lithium anode can produce a spontaneous chemical reaction, and the product is LiCl, and LiCl covers the surface of the lithium anode in the form of a thin film, preventing the contact between lithium and the electrolyte solution, ultimately leading to voltage hysteresis. Ways to solve the voltage lag of Li/SOCl2 batteries: add additives: such as pVC, VC-VDC, SO2, Li2B10Cl10, Li2B10B10; add electrolyte salts that replace liAlCl4: haloborate, LiGaCl4; utilize the lithium anode interface effect: such as in lithium anodes Apply polymer electrolyte coating; reduce electrolyte salt concentration.

★The structure of Li/SOCl2 battery Because the interaction between LiAlCl4: SOCl2 solution and water is very intense, even a very small amount of water can easily interact with it to produce HCl gas, causing severe corrosion and eventual battery failure. Therefore, this kind of battery rarely adopts a button structure or a semi-sealed crimp structure. This kind of battery shell material generally uses stainless steel (1Cr18Ni9TI). This is because stainless steel is stable in the fully sealed anhydrous LiAlCl4:SOCl2 electrolyte, and polyethylene, polypropylene, nylon, etc. cannot resist the corrosion of the electrolyte. The most commonly used ones are metal/glass or metal/ceramic insulated TIG or laser welded fully sealed structures. There are two key aspects to a fully sealed structure: 1. Metal/glass insulating beads. Valveable materials are generally used for the upper cover and liquid injection tube because their thermal expansion coefficients are closest to those of glass. The sintering between the glass in the upper cover and the valve material is a key process. After sintering, the temperature should drop as slowly as possible, otherwise it will cause excessive internal stress and cause the battery to suddenly rupture after use or storage for a certain period of time.

2. Laser welding place.

★Li/SOCl2 battery types and their performance. From the appearance point of view, there are mainly cylindrical types (including AA, C, D types), rectangular and oblate shapes; from the discharge rate point of view, there are mainly two types: low-rate batteries and high-rate batteries; From the perspective of electrode structure, there are three types: 1. Carbon-packed structure, the positive electrode is made into a cylindrical shape, and the negative electrode lithium is wrapped outside

2. The positive and negative electrodes of the rolled electrode structure are made into strips, so the contact area is much larger than that of the carbon package type, and the total current output is larger.

3. Rectangular electrode

★Li/SOCl2 battery production process 1, carbon electrode production: Mix 80% acetylene black and 20% polytetrafluoroethylene emulsion, add ethanol, stir thoroughly to form a paste, take it out, and continuously crush it at a certain temperature to make Cut it into thin slices, then cut it into the required size, put a piece of nickel mesh with tabs on it, pressurize it, and finally put it in an electric vacuum box for heating and dehydration. The nickel mesh serves as a conductive skeleton, and the shape between the nickel mesh and the nickel strip tabs has a great relationship with increasing the battery current density. In cell-type structures, this is often not a problem, because the current output of cell-type batteries is generally not large. Only in spiral-type high-power Li/SOCl2 batteries, this is an issue that must be considered.

2. The negative electrode is made of lithium foil pressed on a nickel mesh. Generally, the polarization of the negative electrode is very small, and the utilization rate is close to 100%.

3. Battery separator material Li/SOCl2 battery separator is mostly made of a non-woven glass fiber membrane made of glass fiber filaments, with a thickness of 0.1-0.2mm. Organic separators are not used due to instability in LiAlCl4:SOCl2 electrolyte.

4. Preparation of electrolyte. Before preparing the electrolyte, the raw materials should be passivated. SOCl2 can be refined by distillation in a well-ventilated environment. Anhydrous LiCl is dehydrated by vacuum heating, and anhydrous AlCl3 can be recrystallized by sublimation to remove impurities.

① Preparation of LiAlCl4 Grind anhydrous LiCl and anhydrous AlCl3 in dry air and mix thoroughly, then heat to 180°C in an argon atmosphere. At this time, the powder dissolves into LiAlCl4. After cooling, crush it in a drying box and bottle it for later use.

② LiAlCl4: SOCl2 electrolyte is prepared in a dry atmosphere. Slowly add a certain amount of LiAlCl4 to the SOCl2 solvent and stir continuously to avoid exotherming too quickly. Pour the solution into a volumetric flask, wash the electrolyte container with solvent, and then add it into the flask until the liquid level is consistent with the scale. When the electrolyte concentration is 1.73 mol, the conductivity can reach 2.04×10-2 ohm-1·cm-1. In order to remove impurities that interact with lithium, the electrolyte should be purified. The treatment method is as follows: put a bright lithium belt and the above-mentioned electrolyte into a glass vessel, seal it, and then heat it at a temperature above 70°C for a long time to allow the impurities and lithium belt to fully After action, set aside for later use.

★Li/SOCl2 battery inspection standards and methods 1, environmental test The following method is the U.S. ECOMSCS-459 test standard ① The mechanical vibration frequency increases from 10HZ to 55HZ, and then drops to 10HZ, the change speed is 1HZ/min, and the amplitude is 0.76 mm, conduct one test each in the transverse and longitudinal directions of the battery, lasting 95 minutes ② Impact with an acceleration of 150g for 6 milliseconds, in the transverse and longitudinal directions of the battery ③ Thermal shock The battery drops from room temperature to -40°C within half an hour, constant temperature 1.5 Hours later, it was suddenly raised to 70°C, kept at constant temperature for another 2 hours, and then suddenly dropped to -40°C. This was repeated four times before returning to room temperature. ④Put the battery in a container with a pressure of 4 atmospheres for 12 hours and measure the change in open circuit voltage. Then discharge it at 60mA (D type) and record the changes in weight and volume before and after the test. ⑤Altitude test will The battery is placed in a vacuum container, simulating the air pressure at a height of 1,500 meters, and measuring the open circuit voltage. After the test, discharge at 60 mA (D type), record the weight and volume changes before and after the test. ⑥ Collision: Give the battery an impact of 14000g in both the longitudinal and transverse directions (AA type). After the battery has passed the above assessment, there should be no change in open circuit voltage, no voltage hysteresis beyond the specified limit, no obvious loss of capacity, no leakage and no change in weight, etc.

2. The following safety test method is the U.S. ECOMSCS-459 test standard. ① Penetration test: For D-type batteries with full capacity and discharge state, under the conditions of 25℃ and 70% relative humidity, a nail with a diameter of 3.2mm is penetrated through the battery from the transverse direction. , observe the changes within 24 hours, there should be no expansion and serious leakage ② Pressure test applies pressure in the transverse direction of the battery, a short circuit occurs when compressing 30% of the diameter, but there is no explosion or leakage ③ Short circuit test at 25℃ Welding at both poles of the battery The upper nickel tab has an effective resistance of 0.005 ohms, short circuit for 24 hours, the maximum short circuit current is 6.5A (D type), there is a slight expansion on the bottom and cover, but the weight and diameter of the battery should not change, and there is no leakage ④ Reduce load resistance test: D-type battery is discharged at 50mA at the beginning, and then gradually reduces the external resistance to a short circuit. There should be no expansion and leakage of electrolyte. ⑤ Forced discharge test: D-type battery is discharged at 60mA to the end voltage of 2.0V, and then uses 500mA current. Forced to pass for 12 hours, at the beginning, the battery voltage immediately reversed, and then stabilized at -0.6V. The temperature of the battery was about 70°C, but it should not leak, and there was no change in volume or weight. ⑥ Electric furnace heating test Place the battery vertically or horizontally On the electric furnace, the electric furnace rises from room temperature to 250℃, record the open circuit voltage, the temperature of the electric furnace and the upper part of the battery. If the bottom and upper cover of the battery expand, there should be no leakage. ⑦ Charge the D-type battery of the discharged battery to the termination voltage at 60mA, and then After charging at 500mA for 12 hours, the open circuit voltage rose to 5.0V, then stabilized at 3.7V, and the battery temperature rose to 53°C. But there should be no change in weight and volume, and no leakage. ⑧ The rechargeable D-type battery of the new battery is charged at 500mA for 12 hours. The initial voltage rises to 4.0V and remains unchanged thereafter. The maximum temperature of the battery rises to 622.0V, but there should be no change in weight and volume to dig out leaks

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