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 applica-tion 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 insol-ubility and less steric hindrance, and gives a high actual capacity of 109 mA h g-1 (active groups utiliza-tion 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 cath-ode and 3,4,9,10-Perylenetetracarboxylic diimide (PTCDI) as anode and displays long-term cycling per-formance of 87.5 mA h g-1 after 800 cycles. This study will stimulate further developments in designing all organic battery systems.(c) 2023 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences Published by Elsevier B.V. All rights reserved.