Memory effect in a lithium-ion battery

Memory effects are well known to users of nickel–cadmium and nickel–metal-hydride batteries. If these batteries are recharged repeatedly after being only partially discharged, they gradually lose usable capacity owing to a reduced working voltage. Lithium-ion batteries, in contrast, are considered to have no memory effect. Here we report a memory effect in LiFePO 4 —one of the materials used for the positive electrode in Li-ion batteries—that appears already after only one cycle of partial charge and discharge. We characterize this memory effect of LiFePO 4 and explain its connection to the particle-by-particle charge/discharge model. This effect is important for most battery uses, as the slight voltage change it causes can lead to substantial miscalculations in estimating the state of charge of batteries. Nickel–cadmium and nickel–metal hydride batteries exhibit memory effects but lithium-ion batteries are widely believed to have none. Now, a memory effect for LiFePO 4 positive electrodes that appears after only one cycle of partial charge and discharge is reported. This observation is important as the slight voltage change that it causes can lead to substantial erroneous estimation of the state of charge of batteries.