Cobalt Hydroxide Carbonate/Reduced Graphene Oxide Anodes Enabled by a Confined Step-by-Step Electrochemical Catalytic Conversion Process for High Lithium Storage Capacity and Excellent Cyclability with a Low Variance Coefficient.

Transition metal carbonates/hydroxides have attracted much attention as appealing anode materials due to their considerable reversible electrochemical catalytic conversion capacity. However, their serious positive or negative trends with cycles caused by the electrochemical catalytic conversion seriously affect their practical applications. Herein, novel one-dimensional cobalt hydroxide carbonate (CHC) nanomaterials are tightly anchored on reduced graphene oxide (RGO) sheets via a facile one-pot hydrothermal synthesis, forming surface-confined domains to further restrict the electrochemical catalytic conversion process. The analysis on the cycled electrodes at varied potentials confirms that the added capacity of CHC arises from the step-by-step reversible reactions of Li2CO3 and LiOH under the electrochemical catalysis of Co metal generated by the conversion reaction of CHC. The reversible reaction of Li2CO3 is followed closely by that of LiOH in the discharge process, while the order is opposite in the charge process. Such a step-by-step electrochemical catalytic conversion process could confine each other to accommodate the volume change and avoid side reactions. The confined effect is further enhanced by limiting the width and length of the CHC, which are determined by regulating the nucleation and growth of CHC on the surface of RGO, leading to an extraordinary cyclability. The optimized CHC/RGO hybrid maintains a high reversible capacity of 1110 mA h g-1 after 100 cycles at 0.1 A g-1, which is much higher than the theoretical value of CHC (506 mA h g-1) on the basis of the recognized conversion reaction. Furthermore, it keeps high reversible capacities of 755 and 506 mA h g-1 after 200 cycles at 1 and 2 A g-1, respectively, exhibiting a high-rate cyclability with the lowest coefficient of variance of 9.4% among the reported ones. The confined step-by-step electrochemical catalytic conversion process facilitates high lithium storage capacity and satisfactory cyclability with a pretty low variance coefficient.

Dual-Carbon-Confined Fe7 S8 Anodes with Enhanced Electrochemical Catalytic Conversion Process for Ultralong Lithium Storage.

Although the electrochemical catalytic conversion process is effective in increasing the reversible capacity of lithium-ion batteries, the low contact efficiency between metal catalyst and substrate and pulverization of the solid electrolyte interface (SEI) film without protection are not beneficial for the electrochemical reactions. Herein, Fe7 S8 nanoparticles are confined by both reduced graphene oxide (RGO) and in-situ-formed amorphous carbon (C) to form dual-carbon-confined Fe7 S8 as a lithium-ion anode. The dual-carbon-confined structure provides a confined space to prevent pulverization of the SEI film and increases the local concentration of intermediate phases, which could be electrocatalytically decomposed by Fe nanoparticles formed in situ to increase the reversibility of the electrochemical reactions and gain high reversible capacity. In addition, the dual-carbon-confined structure ensures fast transfer of electrons and boosts transport of lithium ions due to the highly conductive dual-carbon shell. Thus, the Fe7 S8 /C/RGO anode delivers an excellent rate performance and long cycling stability. At current densities of 2000 and 5000 mA g-1 , the reversible capacities are 520 mA h g-1 over 1500 cycles and 294 mA h g-1 over 2000 cycles, respectively.

High Lithium Storage Capacity and Long Cycling Life Fe3S4 Anodes with Reversible Solid Electrolyte Interface Films and Sandwiched Reduced Graphene Oxide Shells.

Increasing demands for lithium-ion batteries (LIBs) with high energy density and high power density require highly reversible electrochemical reactions to enhance the cyclability and capacities of electrodes. As the reversible formation/decomposition of the solid electrolyte interface (SEI) film during the lithiation/delithiation process of Fe3S4 could bring about a higher capacity than its theoretical value, in the present work, synthesized Fe3S4 nanoparticles are sandwich-wrapped with reduced graphene oxide (RGO) to fabricate highly reversible and long cycling life anode materials for high-performance LIBs. The micron-sized long slit between sandwiched RGO sheets effectively prevents the aggregation of intermediate phases during the discharge/charge process and thus increases cycling capacity because of the reversible formation/decomposition of the SEI film driven by Fe nanoparticles. Furthermore, the RGO sheets interconnect with each other by a face-to-face mode to construct a more efficiently conductive network, and the maximum interfacial oxygen bridge bonds benefit the fast electron hopping from RGO to Fe3S4, improving the depth of the electrochemical reactions and facilitating the highly reversible lithiation/delithiation of Fe3S4. Thus, the resultant Fe3S4/RGO hybrid shows a highly reversible charge capacity of 1324 mA h g-1 over 275 cycles at a current density of 100 mA g-1, even retains 480 mA h g-1 over 500 cycles at 1000 mA g-1, which are much higher than reported values.