Enhanced Lithium Storage Capacity of a Tetralithium 1,2,4,5-Benzenetetracarboxylate (Li₄C₁₀H₂O₈) Salt Through Crystal Structure Transformation

다국어 초록 (Multilingual Abstract)

<P>Because of their low price, design flexibility, and sustainability, organic-based electrode materials are considered one of the most promising next-generation alternatives to inorganic materials in Li-ion batteries. However, a clear understanding of the changes in the molecular crystal structure during Li-ion insertion/extraction and its relationship to excess capacity (over theoretical capacity) is still lacking. Herein, the tetralithium 1,2,4,5-benzenetetracarboxylate (Li<SUB>4</SUB>C<SUB>10</SUB>H<SUB>2</SUB>O<SUB>8</SUB>, Li<SUB>4</SUB>BTC) salt was prepared using a simple ion-exchange reaction at room temperature and under solvothermal conditions (100 °C). The solvothermally synthesized salt (Li<SUB>4</SUB>BTC-S) exhibited a well-ordered nanosheet morphology, whereas the room-temperature salt (Li<SUB>4</SUB>BTC-R) was comprised of irregularly shaped particles. During the cycling of Li<SUB>4</SUB>BTC-S, molecular rearrangement occurred to reduce the stress caused by repeated Li-ion insertion/extraction, resulting in a change in the crystal structure from triclinic to monoclinic and an increased free volume. This contributed to an increase in the reversible capacity to 1016 mAh g<SUP>-1</SUP> during the initial 25 cycles at 0.1 A g<SUP>-1</SUP>, and finally the capacity stabilized at ca. 600 mAh g<SUP>-1</SUP> after 100 cycles, which is much higher than its theoretical capacity (234 mAh g<SUP>-1</SUP>). Compared with Li<SUB>4</SUB>BTC-R, Li<SUB>4</SUB>BTC-S delivered a higher reversible capacity of 190 mAh g<SUP>-1</SUP> at a high current density of 2 A g<SUP>-1</SUP>, with an excellent long-term cyclability of up to 1000 cycles, which was attributed to the straight free volume columns and the low-charge-transfer limitation.</P>
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