Enhanced initial coulombic efficiency (above 90%) of Li1.14Ni0.16Co0.08Mn0.57O2 (LMO) cathode materials are achieved by utilizing a NaCl molten-salt method. Anaerobic environment can be controlled via adjusting the weight ratio of LMO and NaCl molten-salt. The morphology and structure of all samples are detected by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The modified samples have smaller particle sizes and abundant mesopores, compared with the pristine LMO sample. The change of crystal parameters, XPS analysis and HRTEM images demonstrate the effect of anaerobic environment offered by NaCl molten-salt on the structure of LMO material. More oxygen vacancies could exist in the modified LMO materials due to the anterobic environment offered by a lot of NaCl molten-salt. It should be responsible for the enhanced initial coulombic efficiency. The higher reversible capacities mainly come from smaller particle size and abundant mesopores of the modified LMO samples, in which the utilization ratio of active mass is improved due to the shortened diffusion length for Li ions. A tiny spinel phase generates in the modified samples controlled by the amount of NaCl additive. The excellent cycling stability and improved rate capacity of the modified materials are also achieved due to its good thermal stability and the 3D structure of the spinel phase. These results give a new insight into preparing lithium-rich cathode materials with high initial coulombic efficiency as well as superior performance for advanced lithium-ion batteries.High initial coulombic efficiency (above 90%) and enhanced cyclic stability of the modified LMO samples are achieved by controlling the reaction medium via a simple and facile molten-salt route.

Li-rich layered oxides Li(Li0.17Ni0.2Co0.05Mn0.58)O2 (LNCMO) and LiAlO2-coated samples were prepared by sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The LiAlO2-coated sample shows good electrochemical performance compared with that of the pristine sample such as initial coulombic efficiency, cyclic performance, and rate capability. The LiAlO2-coated sample can deliver high initial discharge capacities of 268.2 and 191.9 mAh g−1 at 0.1 and 1 C rates with a capacity retention rate of 91.7 and 91.3 % after about 70 and 140 cycles, respectively. Meanwhile, it shows outstanding high-rate capability cyclability with less than 5 % capacity fade after 70 cycles at 5 C rate. The electrochemical impedance spectra (EIS) data indicate that the LiAlO2 coating can remarkably suppress the increase of the charge transfer resistance and restrain the structure change of LNCMO during the cycles which should make a great contribution to the high-rate capability of LiAlO2-coated LNCMO material.

An in situ sulfur deposition route has been developed for synthesizing sulfur–carbon composites as cathode materials for lithium–sulfur batteries. This facile synthesis method involves the precipitation of elemental sulfur into the nanopores of conductive carbon black (CCB). The microstructure and morphology of the composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that most of the sulfur in the amorphous phase is chemically well-dispersed in the nanopores of the CCB. The sulfur content in the composites is confirmed using thermogravimetry analysis (TGA). The S–CCB composites with different sulfur content (52 wt%, 56 wt% and 62 wt%) deliver remarkably high initial capacities of up to 1534.6, 1357.4 and 1185.9 mA h g−1 at the current density of 160 mA g−1, respectively. Correspondingly, they maintain stable capacities of 1012.2, 957.9 and 798.6 mA h g−1 with the capacity retention of over 75.1% after 100 cycles, exhibiting excellent cycle stability. The electrochemical reaction mechanism for the lithium–sulfur batteries during the discharge process is investigated by electrochemical impedance spectroscopy (EIS). The significantly improved electrochemical performance of the S–CCB composite is attributed to the carbon-wrapped sulfur structure, which suppresses the loss of active material during charging–discharging and the restrained migration of the polysulfide ions to the anode. This facile in situ sulfur deposition method represents a low-cost approach to obtain high performance sulfur–carbon composite cathodes for rechargeable lithium–sulfur batteries.

In this work, Lithium rich layered oxide Li1.17Ni0.2Co0.05Mn0.58O2 (LNCMO) is prepared and coated with Li3V2(PO4)3 (LVP) by a chemical deposition method. The surface modification with LVP is introduced into Li-rich layered oxides LNCMO for the first time. After 100 cycles of charging and discharging at various rates, the Li3V2(PO4)3-coated Li1.17Ni0.2Co0.05Mn0.58O2 (LVP-coated LNCMO) (5 wt%) still provides a large capacity of 261.4 mAh g-1, much higher than the pristine LNCMO (211.5 mAh g-1). At 5 C rate, the LVP-coated LNCMO exhibits a stable cyclic capacity of 153.4 mAh g-1, higher than 114.1 mAh g-1 of the pristine LNCMO. The electrochemical impedance spectroscopy (EIS) analysis demonstrates the LVP coating layer can suppress interaction between the cathode surface and the electrolyte and enhance the kinetics of lithium-ion diffusion, contributing to the stable cyclic performance with more cyclic capacity as well as at the high current density.

•The effect of the specific adsorption of BMIM+ on EDL of GC electrode is experimentally studied.•The specific adsorption of BMIM+ on GC electrode changes the EDL structure.•The specific adsorption causes a positive shift of the PZC of BMIM+/PF6−/GC.The differential capacitance/potential curves of two ionic liquid (IL) electrolytes, 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIM+/PF6−) and N-butyl-N-methyl-pyrrolidinium hexafluorophosphate (Pyr14+/PF6−) on a glassy carbon (GC) electrode were measured experimentally. The differential capacitance of BMIM+/PF6−/GC is higher in the negative polarization, while the differential capacitance of Pyr14+/PF6−/GC is higher in the positive polarization, although both ILs are composed of common anions, with cations of similar ionic structures and diameters. Such an opposite trend may be understood in terms of the specific adsorption between BMIM+ and the GC electrode, caused by the π-stacking interaction between the aromatic imidazolium ring and the sp2 graphite surface. The specific adsorption effectively shortens the electric double layer (EDL) thickness on the negatively charged electrode but elongates the EDL thickness on the positively charged electrode. Such an effect is manifested in the differential capacitance, with a higher value on the negative polarization branch than on the positive polarization branch. The impact of the specific adsorption is also seen from the positive shift of the potential of zero charge of BMIM+/PF6−/GC in comparison with that of Pyr14+/PF6−/GC.The effect of the specific adsorption on electric double layer (EDL) structure is studied by comparing the experimental differential capacitance curves of two ionic liquid electrolytes of common anion, BMIM+/PF6− and Pyr14+/PF6−, with glassy carbon (GC) electrode. The specific adsorption between BMIM+ and GC electrode changes the differential capacitance and EDL structure. In addition, the specific adsorption also causes the potential of zero charge of BMIM+/PF6−/GC positively shifted in comparison with that of Pyr14+/PF6−/GC.

The K2FeO4/TiB2 battery has a significant advantage of battery capacity due to their multi-electron discharge reaction both of the cathode K2FeO4 (3e−) and the anode TiB2 (6e−). However, the more positive reduction potential of TiB2 anode results in a lower discharge voltage plateau of K2FeO4/TiB2 battery, compared with the K2FeO4/Zn battery. The simple modification of Fe(VI) cathode with CuO additive was used to improve the cathode reduction kinetics and decrease the polarization potential in the discharge process. Another electrocatalysis media RuO2 with excellent electric conductivity is used as additive in K2FeO4 cathode to demonstrate which effect is more important for the discharge voltage plateau, electrocatalysis or electron conductivity of additives. The results show that the 5% CuO additive modified K2FeO4/TiB2 battery exhibits an enhanced discharge voltage plateau (1.5 V) and a higher cathode specific capacity (327 mAh/g). The advanced discharge voltage plateau can be due to the electrocatalysis of additives on the electrochemical reduction kinetics of Fe(VI) cathode in the whole discharge process, rather than the good electronic conductivity of additives.Highlights► Focus on the average discharge voltage of alkaline super-iron/TiB2 batteries. ► Commercial CuO and exorbitant RuO2 powder as modifier for Fe (VI) cathode. ► The electrocatalysis of the modifiers enables a higher average discharge voltage. ► More than 5% of CuO additive leads to an evident capacity loss of Fe (VI) cathode.

Micrometer-scale pristine and phosphate-doped spinel LiMn2O4 materials with homogeneous size distribution were synthesized by a one-step hydrothermal method. The composition, structure and morphology of the as-prepared samples were characterized using inductively coupled plasma atomic emission spectroscopy (ICP-AES), chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of phosphate doping on the structural and electrochemical properties of spinel LiMn2O4 was investigated by Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The phosphate-doped LiMn2O4 cathode (with a molar ratio of PO43−:LiMn2O4 = 1.5%) exhibits good high-rate discharge capability with 94 mAh/g at a current density of 2960 mA/g. The analyses demonstrate that compared with the pristine LiMn2O4 sample, the phosphate-doped samples have a relatively large Li-ion diffusion coefficient and smaller charge-transfer resistance due to the increase of the unit cell volume of spinel LiMn2O4 caused by the doping of phosphate.

An in situ sulfur deposition route has been developed for synthesizing sulfur–carbon composites as cathode materials for lithium–sulfur batteries. This facile synthesis method involves the precipitation of elemental sulfur into the nanopores of conductive carbon black (CCB). The microstructure and morphology of the composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that most of the sulfur in the amorphous phase is chemically well-dispersed in the nanopores of the CCB. The sulfur content in the composites is confirmed using thermogravimetry analysis (TGA). The S–CCB composites with different sulfur content (52 wt%, 56 wt% and 62 wt%) deliver remarkably high initial capacities of up to 1534.6, 1357.4 and 1185.9 mA h g−1 at the current density of 160 mA g−1, respectively. Correspondingly, they maintain stable capacities of 1012.2, 957.9 and 798.6 mA h g−1 with the capacity retention of over 75.1% after 100 cycles, exhibiting excellent cycle stability. The electrochemical reaction mechanism for the lithium–sulfur batteries during the discharge process is investigated by electrochemical impedance spectroscopy (EIS). The significantly improved electrochemical performance of the S–CCB composite is attributed to the carbon-wrapped sulfur structure, which suppresses the loss of active material during charging–discharging and the restrained migration of the polysulfide ions to the anode. This facile in situ sulfur deposition method represents a low-cost approach to obtain high performance sulfur–carbon composite cathodes for rechargeable lithium–sulfur batteries.