Investigation of Effect of Natural Salts on Discharge Time of Remaining Voltage of Lithium-Ion Batteries during Crushing Stage

Abstract

The use of lithium-ion batteries has increased significantly in recent years due to their high energy density and the presence of valuable materials such as cobalt and nickel, making them an important source for secondary material recovery. However, recycling these batteries presents substantial safety risks, primarily from fire and explosion hazards caused by unwanted short circuits and high voltage components. These risks are especially pronounced during mechanical preparation, crushing, storage, and transportation, where damaged or improperly handled batteries can ignite or explode. To mitigate these hazards, rapid and controlled discharge of batteries before recycling is critical. Discharging using salt solutions is recognized as a simple, fast, and cost-effective method to reduce residual charge and minimize the risk of fire during subsequent handling. In this research, four different types of natural salts at various concentrations were tested, prioritizing the use of accessible, low-cost, and impure salts over pure laboratory-grade salts to enhance scalability and economic feasibility. Initial experiments involved direct immersion of batteries in salt solutions at concentrations of 10%, 15%, and 20% by weight. Among the complementary processes evaluated, the use of a high-speed magnetic stirrer, iron powder, and ultrasonic operations (ultrasonic bath and probe) were found to further reduce discharge time and help achieve target voltages more quickly. Notably, ultrasonic agitation at 28 kHz was particularly effective, significantly accelerating the discharge process and enabling the batteries to reach lower voltage thresholds such as 0.5 volts in a shorter time.