Effective Stabilization of Organic Cathodes Through Formation of a Protective Solid Electrolyte Interface Layer via Reduction

Organic electrode materials offer a promising alternative for lithium-ion batteries due to their lower costs, reduced environmental impact, renewability, and high theoretical capacity. Among them, 2,5-dihydroxy-1,4-benzoquinone (DHBQ) is a promising cathode material, but its high solubility in electrolytes leads to rapid capacity degradation of the battery. This study investigates the dilithium salt of DHBQ, Li₂DHBQ, as a cathode material for LIBs. Despite its minimal solubility in the electrolyte, Li₂DHBQ cathodes suffer rapid capacity decay due to severe morphological damage within the voltage range of 1.5-3.0 V. To achieve morphological stabilization, we promoted the formation of a protective solid electrolyte interphase (SEI) layer on Li₂DHBQ particles by lowering the discharge cutoff voltage. Cycling the battery with a 0.5 V discharge cutoff voltage achieved the optimal thickness and organic-rich composition of the SEI layer, leading to significantly improved morphological stability of Li₂DHBQ. Consequently, the battery maintained 170 mAh g^-1 with a low decay rate of 0.16 % within a voltage range of 0.5-3.0 V after 200 cycles at 500 mA g^-1. Furthermore, initial cycling with a discharge cutoff voltage of 0.5 V for 20 cycles to form an SEI layer, followed by cycling at a normal discharge cutoff voltage of 1.5 V, retained an even higher capacity of 187 mAh g^-1 after 200 cycles at 500 mA g^-1. These are significant improvements compared to the battery cycled only in the normal range of 1.5-3.0 V, which retained a capacity of 87 mAh g^-1. This study demonstrates the effectiveness of forming a cathode SEI layer at low discharge voltages as a new approach to stabilizing organic cathode materials.