Solution-Phase Synthesis and Electrochemical Properties of Lepidocrocite Titanate-Reduced Graphene Oxide Composites

Abstract

Stepped layered titanates can be used as anodes for lithium, sodium or potassium batteries in conventional or flow cell configurations. They are attractive due to their low cost, low toxicity, and high abundancy. However, their low conductivity and poor cycling performance are major hurdles for these materials.The addition of carbon can be used to overcome electronic transport limitations to some extent, but for nonconventional configurations, it is preferable to build in the conductivity by manipulating the structure. For example, in the case of layered materials, this can be done by incorporating a conductive component such as reduced graphene oxide (rGO) in the van der Waals gaps to make 2D heterostructures, the approach we are using here.In this presentation, solution-phase synthesis of K0.8[Ti1.73Li0.27]O4 (lepidocrocite titanate, LT)- rGO composite is demonstrated. After synthesis by conventional solid-state routes, K0.8[Ti1.73Li0.27]O4 is proton exchanged and ion-exchanged with bulky cations, causing expansion of the structure, and exfoliated by mechanical shaking. Exfoliated layered titania sheets are combined with reduced graphene oxide (rGO) to assemble into heterostructures through flocculation. Counter cations (e.g. Mg2+, Na+) are used for the self-assembly of negatively charged LT and rGO nanosheets via flocculation. Mg2+-coagulated composites with 15 wt% rGO have higher capacities than Na+-coagulated composites with the same rGO content in the lithium half-cell configurations, whereas Na+-coagulated composites deliver higher capacity than that of Mg2+-coagulated composites in the sodium half-cell configurations. Both Mg2+-coagulated and Na+-coagulated LT-rGO samples exhibit capacities which are more than two times higher than the capacities of pristine lepidocrocite titanate (K0.8[Ti1.73Li0.27]O4), and display good capacity retention after 50 cycles in both lithium and sodium half-cells configurations.