Spiro-based triphenylamine molecule with steric structure as a cathode material for high-stable all organic lithium dual-ion batteries

Redox p-type organic compounds are promising cathode materials for dual-ion batteries. However, the triphenylamine-based polymers usually with agglomerate and intertwined molecular chain nature limit the maximum reaction of their active sites with large-sized anions. Herein, we demonstrate the application of a small molecule with rigid spirofluorene structure, namely 2,2′,7,7′-tetrakis(diphenylamine)-9,9′-spirobifluorene (Spiro-TAD), as a cathode material for lithium dual-ion batteries. The inherent sterical structure endows the Spiro-TAD with good chemical stability and large internal space for fast diffusion kinetics of anions in the organic electrolyte. As a result, the Spiro-TAD electrode shows significant insolubility and less steric hindrance, and gives a high actual capacity of 109 mA h g−1 (active groups utilization ratio approximately 100%) at 50 mA g−1 with a high discharge voltage of 3.6 V (vs. Li+/Li), excellent rate capability (60 mA h g−1 at 2000 mA g−1) and extremely stable cycling life (98.4% capacity retention after 1400 cycles at 500 mA g−1) in half cells. Such good electrochemical performance is attributed to the robust and rapid adsorption/desorption of ClO4− anions, which can be proved by the in-situ FTIR and XPS. Moreover, an all-organic lithium dual-ion battery (a-OLDIBs) is constructed using the Spiro-TAD as cathode and 3,4,9,10-Perylenetetracarboxylic diimide (PTCDI) as anode and displays long-term cycling performance of 87.5 mA h g−1 after 800 cycles. This study will stimulate further developments in designing all organic battery systems.