Abstract
Low initial coulombic efficiency of hard carbon anodes and irreversible sodium loss during cycling in sodium-ion batteries (SIBs) lead to reduced specific capacity and shortened cycle life. Introducing sodium supplementation can effectively enhance the specific capacity and cycle life of SIBs. Na(2)C(2)O(4) was selected as the sodium compensation agent owing to its high theoretical capacity, excellent chemical stability, and environmental friendliness. To improve conductivity and reduce decomposition voltage of Na(2)C(2)O(4), carbon nanotubes (CNTs) were employed for coating. The optimized 10% CNT-coated sodium oxalate (CNT-10@Na(2)C(2)O(4)) exhibited a reduced initial decomposition voltage of 3.82 V (vs. Na(+)/Na) and delivered an irreversible (sodium compensation) capacity of 392.65 mAh g(-1). NNFMO-CN||HC full cells were assembled using NaNi(1/3)Fe(1/3)Mn(1/3)O(2) cathode containing 10% CNT-10@Na(2)C(2)O(4) and hard carbon anode, demonstrating a discharge retention capacity of 38.35 mAh g(-1) after 100 cycles, higher than the retained capacity of only 15.16 mAh g(-1) of the NNFMO||Na cell without CNT-10@Na(2)C(2)O(4). These results indicate that CNT-10@Na(2)C(2)O(4) significantly improves the specific capacity and cycling performance of SIBs.