Study on Sodium Ion Supplementation Performance of CNT-Coated Sodium Oxalate in Sodium Ion Batteries

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 with 10% CNT-10@Na 2 C 2 O 4 and hard carbon (HC) anode, demonstrating a discharge retention capacity of 38.35 mAh g -1 after 100 cycles, higher than retained capacity only 15.16 mAh g -1 of 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 improving the specific capacity and cycling performance of sodium-ion batteries.