Naphthalimide-based conjugated polymer cathode materials with nitroxide radical substituents for organic lithium-ion battery

In order to obtain naphthalimide-based polymer cathode materials with high discharge voltage, two conjugated polymers PNIT-Th and PNIT-DTh were designed and synthesized using naphthalimide-thiophene (NI-Th) or naphthalimide-dithiophene (NI-DTh) as the electrochemically active backbone and 2,2,6,6-tetramethylpiperidine-1-oxo radical (TEMPO) units with high redox potential as N-position substituents. As expected, the average discharge voltages of PNIT-Th and PNIT-DTh are both relatively high, at 3.12 V (vs Li/Li + ) and 3.20 V (vs Li/Li + ), respectively, which are higher than the N-alkyl-substituted polymer PNI-DTh (2.35 V (vs Li/Li + )). Benefiting from the electroactive main chain and side groups, PNIT-Th and PNIT-DTh both exhibited high initial discharge specific capacities at 0.1C, with 222.2 mAh g −1 and 240.5 mAh g −1 , respectively. The high discharge voltage and discharge specific capacities of the two polymers result in high energy density. At 0.1C, the specific energy densities of PNIT-Th and PNIT-DTh are 711.2 Wh kg −1 and 794.6 Wh kg −1 , respectively. It is satisfactory that these two polymers also exhibit excellent long-cycle and rate performance. At 5C, the capacity retention rate remained above 90% after 4000 cycles. The experimental results indicate that polymers containing TEMPO groups are a class of potential cathode materials for lithium-ion batteries. • Two naphthalimide-based conjugated polymers with TEMPO substituents were synthesized. • TEMPO units can increase the discharge voltage of naphthalimide-based polymers. • Polymer cathode materials show high average discharge voltage and specific capacity. • Polymers have excellent long-term cycle stability and rate performance.