As lithium-ion battery technology has stabilized, the portable electronic devices and electric vehicles industries have flourished, leading to a surge in global demand for lithium-ion batteries. However, prolonged use of lithium-ion batteries causes internal material aging, resulting in reduced capacity and necessitating battery replacement after a period of use. The most common charging method currently available is constant current-constant voltage (CC-CV) charging. However, this method causes the formation of a solid electrolyte interphase (SEI) at the end of the constant current (CC) charging phase, resulting in the loss of cyclic lithium ions and a decrease in battery cycle life.
Chen Baiduan and others from the Condensed Matter Science Research Center at the university applied density functional theory to analyze and calculate the movement of lithium ions inside lithium iron phosphate (LiFePO4) batteries, and established a sinusoidal charging model. This model introduces a negative voltage during the charging process to suppress the formation of the passivation layer.
Researchers compared the battery capacity of the sine wave charging method with that of the traditional CC-CV charging method, using the standard that electric vehicle batteries need to be replaced when their capacity drops below 80%. They simulated the usage scenario of electric vehicles by charging and discharging the batteries with high current. The experimental results showed that the traditional CC-CV charging method reached 80% capacity after 600 cycles, while the battery using the sine wave charging method still had 95% capacity remaining. This indicates that the sine wave charging method has the effect of extending battery life.
Furthermore, charging batteries retired from electric vehicles using sine wave charging can increase capacity by up to 18.7%. During sine wave charging, the battery temperature rises by a maximum of 9°C, and the charging time is only half that of the traditional CC-CV charging method, both of which outperform the traditional CC-CV charging method.
To verify the impact of the sine wave charging method on the internal SEI film impedance of the battery, researchers analyzed the battery using electrochemical impedance spectroscopy (EIS). The results showed that after 600 cycles using this charging method, the battery effectively suppressed SEI film growth compared to the battery using traditional CC-CV, and maintained an internal impedance level similar to that of a brand new battery. This indicates that this charging method causes less damage to the internal material structure of the lithium-ion battery and can provide a longer battery life. Therefore, this charging method will provide a better choice for users of lithium-ion battery products.
