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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]

The conductive polymers PEDOT:PSS coated Li 1.20 [Mn 0.53 Ni 0.13 Co 0.13 Nb 0.01 O 2 cathode materials were synthesized via using the sol-gel method, followed by the wet solution process. And the X-ray diffraction (XRD), Rietveld refinement, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) were adopted to investigate the morphology and constituents of as-prepared cathode materials. The results demonstrated that a PEDOT:PSS layer was uniformly distributed on the surface of bulk Li 1.20 Mn 0.54 Ni 0.13 Co 0.13 O 2 with Nb5+ doping successfully. And the PEDOT:PSS surface coating and Nb5+ doping modifications showed a significant improvement on the electrochemical properties of cathode. In particular, the 2 wt% PEDOT:PSS coated Li 1.20 [Mn 0.53 Ni 0.13 Co 0.13 Nb 0.01 O 2 delivered a supernal discharge capacity of 145.6 mAhg−1 at 5C high rate and retained a high capacity retention of 90.8% after 200 cycles at 45 °C, which were more superior than those of the pristine cathode (90.2 mAhg−1 and 80.7%). The enhanced electrochemical properties could be attributed to the facilitation of Lithium ions diffusion, the lower cation mixing and restriction of the side reactions between cathode surfaces with electrolyte by the Nb5+ doping and PEDOT:PSS coating. The 2 wt % PEDOT:PSS coated Li 1.20 [Mn 0.53 Ni 0.13 Co 0.13 Nb 0.01 O 2 is covered by the PEDOT:PSS coating layer with a thickness of 20–30 nm. And after 200 cycles at 45 °C, the Li 1.20 [Mn 0.53 Ni 0.13 Co 0.13 Nb 0.01 O 2 and PEDOT:PSS coated Li 1.20 [Mn 0.53 Ni 0.13 Co 0.13 Nb 0.01 O 2 with the coating content of 1 wt%, 2 wt% and 3 wt% deliver the discharge capacity of 178.2, 192.7, 207.2 and 198.6 mA h g−1, corresponding to the capacity retention of 83.4%, 87.7%, 90.8% and 89.2, respectively. By contrast, the capacity of the pristine Li 1.20 Mn 0.54 Ni 0.13 Co 0.13 O 2 attenuates drastically from 202.3 mA h g−1 to 163.2 mA h g−1 at 0.5C rate, with only capacity retention of 80.7% left. Image 1 • The electrochemical properties of Li 1.20 Mn 0.54 Ni 0.13 Co 0.13 O 2 are enhanced by the PEDOT:PSS coating and Nb5+ doping. • The PEDOT:PSS coating layer could cover the cathode surface uniformly and efficiently resist against HF corrosion. • The Nb5+ doping can reduce the cation mixing and improve the high rate performance. • 2wt% PEDOT:PSS coated Li 1.20 [Mn 0.53 Ni 0.13 Co 0.13 Nb 0.01 O 2 expresses the outstanding electrochemical properties. [ABSTRACT FROM AUTHOR]

The 3D conducting network structure endows the superior cycle performance of MWCNTs/CF/Ni/NaCl composite for Na-NiCl 2 batteries cathode. • MWCNTs/CF/Ni/NaCl cathodes are prepared by the vacuum filtration technique. • MWCNTs/CF/Ni/NaCl cathodes possess high electronic conductivity. • The molar ratio of Ni/NaCl in the Na-NiCl 2 batteries cathode can be reduced to 1.0. • MWCNTs/CF/Ni/NaCl-1 electrode shows excellent long-term cycling performance. The sodium-nickel chloride (Na-NiCl 2) batteries technology has been considered as one of the most promising candidates for large-scale electrical energy storage application owing to its abundant electrode material resource, high energy density and safety. However, ultra-excessive Ni in the cathode leads to high material cost and the growth of cathode particles during cycles makes degradation of batteries performances, which hinder the further application of Na-NiCl 2 batteries. To address these challenges, we designed a free-standing Ni-less cathode with Ni/NaCl particles uniformly distributed in the three-dimensional (3D) conductive matrix constructed by carbonfiber (CF) and multiwalled carbon nanotubes (MWCNTs). The 3D hierarchical structure synthesized by low-cost vacuum filtration method can offer sufficient void space to accommodate the growth of NaCl particles and effectively enhance the electronic conductivity of the cathode. When the molar ratio of Ni/NaCl in the cathode is reduced to 1.0, a specific capacity of 90 mAh g−1 for planar Na-NiCl 2 batteries can be achieved after 170 cycles at 190 °C with a capacity retention of 67%, which is higher than that of traditional tubular Na-NiCl 2 batteries. [ABSTRACT FROM AUTHOR]