Unlocking the Na-Storage Behavior in Hard Carbon Anode by Mass Spectrometry
Jiyuan Xue, Haitang Zhang, Jianken Chen, Kai Fang, Yilong Chen, Yeguo Zou, Yuhao Hong, Yu Qiao, Shi‐Gang Sun
Abstract
Hard carbon (HC) is a promising anode candidate for Na-ion batteries (NIBs) because of its excellent Na-storage performance, abundance, and low cost. However, a precise understanding of its Na-storage behavior remains elusive. Herein, based on the D 2 O/H 2 SO 4 -based TMS results collected on charged/discharged state HC electrodes, detailed Na-storage mechanisms (the Na-storage states and active sites in different voltage regions), specific SEI dynamic evolution process (formation, rupture, regeneration and loss), and irreversible capacity contribution (dead Na 0, NaH, etc.) were elucidated. Moreover, by employing the online electrochemical mass spectrometry (OEMS) to monitor the gassing behavior of HC-Na half-cell during the overdischarging process, a surprising rehydrogen evolution reaction (re-HER) process at around 0.02 V vs Na + /Na was identified, indicating the occurrence of Na-plating above 0 V vs Na + /Na. Additionally, the typical fluorine ethylene carbonate (FEC) additive was demonstrated to reduce the accumulation of dead Na 0 and inhibit the re-HER process triggered by plated Na.