Sodium-ion batteries are a promising alternative to lithium-ion batteries. In particular, organic sodium-ion batteries employing environmentally friendly organic materials as electrodes are gaining increasing research interest for developing secondary batteries as a result of the ease of processing, low cost, and flexibility of the organic electrode materials. Triquinoxalinylene (TQA) is a very promising organic electrode material for sodium-ion batteries. However, the poor cycling stability of TQA is impeding its adoption as an electrode material. In this work, we investigated the sodium-ion storage mechanism in TQA and the decay in capacity using both experimental and computational means. A strategy for improving the cycling stability is proposed, and it is demonstrated that the retention of capacity can be significantly improved from 31 to 85%.