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Nickel particles with different contents of Ni 3 S 2 surface layer were prepared for their application as cathode materials in Na/NiCl 2 batteries. The surface modification of nickel particles is found to prevent their growth and battery degradation during cycling. The optimum level of surface modification was determined by electrochemical tests and morphology characterization. Excessive Ni 3 S 2 layer seems to cause particle aggregation resulting in low reversible capacity. The capacity of the cell with optimum level of Ni 3 S 2 surface modification layer after 50 cycles is about 4 times greater than that without Ni 3 S 2 surface modification layer. [ABSTRACT FROM AUTHOR]

The charged-state NiCl 2 -rGO aerogel cathode shows superior cycle performance in Na-NiCl 2 batteries. [Display omitted] • Charged-state NiCl 2 -rGO aerogels are prepared by freeze-drying methods. • Conductive rGO aerogels effectively improve the performance of NiCl 2. • The molar ratio of Ni/NaCl can be reduced to the stoichiometric ratio (0.5). • The NiCl 2 -rGO aerogel cathode shows excellent electrochemical performance. The hierarchical nickel chloride/reduced graphene oxide (NiCl 2 -rGO) aerogels are synthesized via a facile hydrothermal and freeze-drying methods using low-cost nickel chloride hexahydrate (NiCl 2 ·6H 2 O) as raw material. The NiCl 2 -rGO hybrid aerogel structure enables the uniform distribution of lamellar NiCl 2 on the three-dimensional (3D) cross-linked conductive graphene sheets. When employed as cathode for sodium-nickel chloride (Na-NiCl 2) batteries, the as-obtained NiCl 2 -rGO aerogels exhibit excellent electrochemical performance with high reversible capacities (116 mAh g−1 after 50 cycles, 128 mAh g−1 in a fixed capacity window (20%–80% state of charge (SOC)) after 50 cycles), and a ultra-low polarization (0.05 V in the fixed capacity window). The outstanding performance of NiCl 2 -rGO aerogels can be attributed to the excellent conductivity of graphene. Moreover, the strong contact between NiCl 2 and graphene sheets can effectively promote the transfer of electrons. Compared with traditional tubular Na-NiCl 2 batteries, the molar ratio of Ni/NaCl of NiCl 2 -rGO aerogels can be decreased from 1.8 to the stoichiometric ratio (0.5). To the best of our knowledge, this work paves a perspective way for the first time to develop charged-state NiCl 2 -based cathodes with splendid performance for Na-NiCl 2 batteries. [ABSTRACT FROM AUTHOR]

The charged-state NiCl 2 -rGO aerogel cathode shows superior cycle performance in Na-NiCl 2 batteries. [Display omitted] • Charged-state NiCl 2 -rGO aerogels are prepared by freeze-drying methods. • Conductive rGO aerogels effectively improve the performance of NiCl 2. • The molar ratio of Ni/NaCl can be reduced to the stoichiometric ratio (0.5). • The NiCl 2 -rGO aerogel cathode shows excellent electrochemical performance. The hierarchical nickel chloride/reduced graphene oxide (NiCl 2 -rGO) aerogels are synthesized via a facile hydrothermal and freeze-drying methods using low-cost nickel chloride hexahydrate (NiCl 2 ·6H 2 O) as raw material. The NiCl 2 -rGO hybrid aerogel structure enables the uniform distribution of lamellar NiCl 2 on the three-dimensional (3D) cross-linked conductive graphene sheets. When employed as cathode for sodium-nickel chloride (Na-NiCl 2) batteries, the as-obtained NiCl 2 -rGO aerogels exhibit excellent electrochemical performance with high reversible capacities (116 mAh g−1 after 50 cycles, 128 mAh g−1 in a fixed capacity window (20%–80% state of charge (SOC)) after 50 cycles), and a ultra-low polarization (0.05 V in the fixed capacity window). The outstanding performance of NiCl 2 -rGO aerogels can be attributed to the excellent conductivity of graphene. Moreover, the strong contact between NiCl 2 and graphene sheets can effectively promote the transfer of electrons. Compared with traditional tubular Na-NiCl 2 batteries, the molar ratio of Ni/NaCl of NiCl 2 -rGO aerogels can be decreased from 1.8 to the stoichiometric ratio (0.5). To the best of our knowledge, this work paves a perspective way for the first time to develop charged-state NiCl 2 -based cathodes with splendid performance for Na-NiCl 2 batteries. [ABSTRACT FROM AUTHOR]