Unlocking the potential of weberite-type metal fluorides in electrochemical energy storage

Sodium-ion batteries (NIBs) are a front-runner among the alternative battery technologies suggested for substituting the state-of-the-art lithium-ion batteries (LIBs). The specific energy of Na-ion batteries is significantly lower than that of LIBs, which is mainly due to the lower operating potentials and higher molecular weight of sodium insertion cathode materials. To compete with the high energy density of LIBs, high voltage cathode materials are required for NIBs. Here we report a theoretical investigation on weberite-type sodium metal fluorides (SMFs), a new class of high voltage and high energy density materials which are so far unexplored as cathode materials for NIBs. The weberite structure type is highly favorable for sodium-containing transition metal fluorides, with a large variety of transition metal combinations (M, M’) adopting the corresponding Na2MM’F7 structure. A series of known and hypothetical compounds with weberite-type structure were computationally investigated to evaluate their potential as cathode materials for NIBs. Weberite-type SMFs show two-dimensional pathways for Na+ diffusion with surprisingly low activation barriers. The high energy density combined with low diffusion barriers for Na+ makes this type of compounds promising candidates for cathode materials in NIBs

Enhancement of the electrochemical properties of Li1Mn2O4 through chemical substitution

The link between room temperature (RT) cycling failure for Li1Mn2O4-type spinels and elevated temperature (ET) failure of Li1.05Mn1.95O4 materials was investigated by physical and electrochemical characterization. Failure for both ET and RT cycling occurred at the end of discharge. Substantial evidence suggesting a link based on the cooperative Jahn-Teller distortion was found. Based on this knowledge, LiAlxMn2-xO4-δFZ materials were fabricated. These novel compounds were found to offer much improved capacity and ET performance than present generation materials. Three hundred cycles at 55°C resulted in 15% capacity loss. Storage in charged and discharged state for 4 days at 70°C revealed less than 1.6% irreversible capacity loss. © 1999 Elsevier Science S.A. All rights reserved

Metal oxides as negative electrode materials in Li-ion cells

The electrochemical performance of 3d metal oxide (MO) electrode materials for Li-ion batteries was studied in the form of Li/CoO(Co3O4) half-cells. Reversible capacity in the 750-1000 mAh/g range was achieved and sustained over numerous charge-discharge cycles both at room temperature and at 55°C. The studied oxides were then used as negative-electrode active materials to assemble larger plastic MO/LiCoO2 Li-ion cells, which exhibited an average output voltage of 2 V and a stable reversible specific energy of 120 Wh/kg during extended cycling at ambient and elevated temperatures. This value can be compared to 180 Wh/kg obtained for similar C/LiCoO2 Li-ion cells. Based on modeling, several scenarios involving material considerations present the optimum method for boosting the energy density of such MO/LiCoO2 Li-ion systems. © 2002 The Electrochemical Society. All rights reserved

Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors

10.1038/srep03002Scientific Reports3