Reaction Mechanisms of Sodium‐Ion Batteries under Various Charge and Discharge Conditions in a Three‐Electrode Setup. Issue 17 (27th June 2018)

• Record Type: Journal Article
• Authors: Song, Xiaona; Zhou, Xunfu; Zhou, Yanxue; Deng, Yaoming; Meng, Tao; Gao, Aimei; Nan, Junmin; Shu, Dong; Yi, Fenyun
• Is Part Of: ChemElectroChem. Volume 5:Issue 17(2018)
• Page Start: 2475
• Page End: 2481
• Publication Date: 2018-06-27
• Subjects: sodium-ion battery -- three-electrode setup -- charge−discharge condition -- solid-electrolyte interphase film -- hard carbon; Electrochemistry -- Periodicals; 541.37
• DOI: 10.1002/celc.201800387
• Languages: English
• ISSNs: 2196-0216

Abstract

Abstract: Charge‐discharge reaction mechanisms of sodium‐ion batteries under various condition are studied by using a three‐electrode setup of a pouch‐type sodium‐ion battery. The sodium‐ion battery is constructed by using cost‐effective ternary layered Na0.76 Ni0.3 Fe0.4 Mn0.3 O2 and commercial hard carbon as the cathode and anode materials, respectively, and 1.0 M NaPF6 in mixed carbonate solvent as the electrolyte. The electrochemical impedance spectroscopy (EIS) results and transmission electron microscopy (TEM) images show that an apparent solid‐electrolyte interphase (SEI) film is formed on anode material surface during the formation (pre‐charging) process, and the potentials for the SEI film formation of the solvents (ethylene carbonate and ethylene carbonate) and the additive (fluorinated ethylene carbonate) in the electrolyte are 2.04 and 2.79 V, respectively. The X‐ray diffraction (XRD) results demonstrate that, during charge, the crystal structure of cathode material changes significantly with the deintercalation of Na + . When the battery is charged to 5.0 V, the diffraction peak corresponding to the (002) plane disappears, as Na + is further deintercalated, and the structure changes from the hexagonal phase to the monoclinic phase, causing the rapid degradation of the cycle performance. When the battery is overdischarged to 0 V, the EIS results and TEM images show that the SEI film is destroyed completely, and the cycle life performance is significantly deteriorated. Abstract : Using the differential d Q /d V value and the battery voltage as the horizontal and vertical coordinates, respectively, the differential capacity curve was obtained. Four distinct peaks appear during the formation process. The first peak at 2.04 V corresponds to the reduction potential of fluorinated ethylene carbonate to form the solid‐electrolyte interphase (SEI) film; the second peak at 2.79 V corresponds to the reduction potential of ethylene carbonate and propylene carbonate to form the SEI film; the next two peaks correspond to intercalation of sodium ions.