Heterostructured Lepidocrocite Titanate-Carbon Nanosheets for Electrochemical Applications

Abstract

Lepidocrocite-type titanates that reversibly intercalate sodium ions at low potentials (~0.6 V vs. Na/Na + ) are promising anode candidates for sodium ion batteries. However, large amounts of carbon additives are often used to improve their electrical conductivity and overcome poor cycling performance in the electrode composites. To ameliorate electronic transport issues of lepidocrocite titanate (K0.8Ti1.73Li0.27O4, KTL) in sodium ion batteries, we have designed and synthesized heterostructures of exfoliated lepidocrocite-type titanium oxide nanosheets (LTO) with alternating carbon layers via a solutionbased self-assembly approach. Positively charged dopamine (Dopa) was used as the carbon precursor and intercalated between negatively charged exfoliated titania nanosheets through electrostatic interaction. Dopamine-intercalated LTO was then annealed under argon to form conductive carbon layers between titania sheets. The carbon content in the heterostructures was controlled by modifying self-assembly conditions (i.e. pH, stirring duration, and Dopa to LTO ratio). Electrodes were prepared using carbonized heterostructures (LTO-C) without adding more carbon to the composites and tested in sodium half-cell configurations. Higher capacities and improved capacity retention over 250 cycles, and lower impedance were observed as the carbon content of LTO-C heterostructures was increased from 0% (LTO nanosheets) to 30%. These results indicate that the self-assembly approach for 2D heterostructured electrode materials is a promising strategy to overcome electronic transport limitations of layered transition metal oxides and improve their electrochemical performance for next generation energy storage applications.

Lepidocrocite Titanate–Graphene Composites for Sodium-Ion Batteries

“…The loss in the first cycle is due to formation of a solid-electrolyte interphase, decomposition of binder, decomposition of adventitious water, and side reactions involving electrolyte and/or binder at low potentials. An average operating potential of 0.6 V vs Na + /Na was measured, comparable to the previous reports on the lepidocrocite type sodium titanates, and lower than that of anatase TiO 2 (0.8 V vs Na + /Na). − ,, Rate capability results using current densities ranging from 15 to 500 mA g –1 are presented in Figure c. While capacities decreased as the current was raised, the starting capacity was partially recovered after reversing the current density to 15 mA g –1 .…”

“…We reported a similar hybrid capacitive/intercalation behavior for dopamine-derived LTO–30%C heterostructures. However, the contribution of the diffusion-controlled mechanism (75%) was much higher at a 0.05 mV s –1 scan rate for this material . We speculate that Mg in the LTO–rGO composites may block or inhibit diffusion of sodium, resulting in a lower overall capacity for these materials compared to those made with dopamine.…”

“…The second semicircle at middle frequencies is associated with processes at the composite electrode (R3), and the straight line at low frequencies is due to the ionic diffusion (Warburg diffusion) in the electrode. These assignments are based on analogies to similar cells. , The interfacial impedance of sodium anodes can vary considerably depending on electrolyte and usage . In general, these values tend to be low when glymes are used as solvents in electrolytic solutions, although they vary somewhat with the type of salt used .…”

“…Dopamine-intercalated titania sheets were then annealed under argon to form conductive carbon layers between titania sheets. The carbon content in the heterostructures was tuned from 17.5 to 30% by changing experimental parameters . Electrodes that were prepared using as-prepared heterostructures without extra carbon additives exhibited higher capacities, better capacity retention over 100 cycles, and lower impedance when compared to titania sheets in sodium half-cell configurations.…”

The Dopamine Assisted Synthesis of MoO3/Carbon Electrodes With Enhanced Capacitance in Aqueous Electrolyte

“…Additionally, α-MoO 3 has a low intrinsic electronic conductivity ( de Castro et al, 2017 ), which leads to structural degradation during cycling because of the hyperpolarization effect ( Xiao et al, 2014 ; He et al, 2019 ; Shan et al, 2019 ; Elkholy et al, 2021 ). The electronic conductivity can be improved by integrating MoO 3 with carbon and introducing a stable oxide/carbon heterointerface, similar to the vanadium and titanium oxide systems ( Clites et al, 2020 ; Barim et al, 2021 ). Interestingly, the same strategy was shown to also result in slowing the capacity decay over cycling ( Clites et al, 2020 ), which is highly desirable for α-MoO 3 electrodes.…”