Author: Yinshi Li (Xi’an Jiaotong University) - Flow batteries and lithium-ion batteries are both critical energy storage technologies, yet each exhibits distinct limitations. Flow batteries suffer from aggravated polarization during the final stages of charge/discharge cycles due to reactant depletion, leading to reduced system capacity utilization, often below 80%. Although lithium-ion batteries demonstrate higher efficiency, their coupled power-capacity characteristics make them unsuitable for prolonged charging/discharging cycles. To address these complementary characteristics, this study proposes a hybrid energy storage system configuration dominated by a high-power flow battery (main unit) supplemented by a low-power lithium battery (auxiliary component). The lithium-ion battery operates exclusively during the final stages of flow battery charging/discharging, thereby alleviating the load on the flow battery and improving its overall performance. The experimental results show that when the total power of the system remains unchanged, the combined charging and discharging of the two increases the energy efficiency by 0.71% compared with their independent charging and discharging at the average power respectively, and the capacity utilization rate of the flow battery energy storage system increases by 6.15%. If the designed power of the flow battery system is taken as the total power and only lithium-ion batteries are used as a supplement to the flow battery system, the energy efficiency can be increased by 2.01%. The results demonstrate that adopting a hybrid energy storage strategy primarily based on flow batteries with lithium-ion batteries as supplementary can effectively enhance the capacity utilization of the flow battery energy storage component, thereby improving its economic performance.
