Effect of the Position of Oligo(ethylene oxide) Segment on the Performance of Naphthalimide-Based Polymer Cathode Materials for Lithium-Ion Batteries

The effect of the linking position of the oligo(ethylene oxide) segment on the electrochemical properties of naphthalimide-based polymer cathode materials was investigated. For comprehensive analysis, the influence of the alkyl segment in the main chain on the performance of the polymer was also compared. Polymers with alkyl backbone, oligo(ethylene oxide) backbone, and oligo(ethylene oxide) side chains are termed PNDIB, PNDIO, and PNIOS, respectively. The mobility of lithium ion in polymer PNDIB, PNDIO, and PNIOS electrodes was assessed via the galvanostatic intermittent titration technique (GITT). Relative to the alkyl backbone polymer PNDIB, PNIOS, and PNDIO with oligo(ethylene oxide) chains have a higher mobility of lithium ions because the ether groups are favorable for lithium ion transport. Meanwhile, polymer PNIOS has better electronic conductivity due to the advantage of a conjugated backbone for electron transport. Therefore, PNIOS has the best conductivity of the three polymers, resulting in the highest discharge specific capacity and superior cyclic and rate performance. Specifically, PNIOS delivers an initial discharge specific capacity of 162.9 mAh g^–1 at 0.1C, retaining 91.4% of its capacity after 120 cycles. At a high rate of 5C, it maintains a discharge capacity of 130.5 mAh g^–1 after 5000 cycles. These findings position PNIOS as a promising candidate for lithium-ion battery cathodes.