Fused ring and linking groups effect on overcharge protection for lithium-ion batteries

The derivatives of 1,3-benzodioxan (DBBD1) and 1,4-benzodioxan (DBBD2) bearing two tert-butyl groups have been synthesized as new redox shuttle additives for overcharge protection of lithium-ion batteries. Both compounds exhibit a reversible redox wave over 4 V vs Li/Li+ with better solubility in a commercial electrolyte (1.2 M LiPF6 dissolved in ethylene carbonate/ethyl methyl carbonate (EC/EMC 3/7) than the di-tert-butyl-substituted 1,4-dimethoxybenzene (DDB). The electrochemical stability of DBBD1 and DBBD2 was tested under charge/discharge cycles with 100% overcharge at each cycle in MCMB/LiFePO4 and Li4Ti5O12/LiFePO4 cells. DBBD2 shows significantly better performance than DBBD1 for both cell chemistries. The structural difference and reaction energies for decomposition have been studied by density functional calculations.