Electrochemical properties of mixed titanium‐niobium oxide TiNb2O7 (TNO) synthesized via vacuum annealing as high potential anode material for lithium‐ion batteries were investigated. Crystal structure, size, and morphology are nearly independent of the annealing atmosphere for starting materials but the color of vacuum‐annealed TNO (TNO‐V) is dark blue while white for the air‐annealed one (TNO‐A). X‐ray photoelectron spectroscopy analysis also indicated that Ti4+ and Nb5+ in TNO are partially reduced into Ti3+ and Nb4+ due to the introduction of oxygen vacancy. Electronic conductivity for TNO‐V was around 10−3 S cm−1 at room temperature and much higher than that for TNO‐A (=10−11 S cm−1). In electrochemical testing, both TNO‐A and TNO‐V electrodes showed reversible capacity of 260‐270 mAh g−1 at low current density of 0.5 mA cm−2, while at higher current density of 5.0 mA cm−2, TNO‐V electrode retained higher reversible capacity of 140 mAh g−1 than that for TNO‐A electrode (=80 mAh g−1). The enhancement of intrinsic electronic conductivity greatly contributes to improve the rate performance of TNO.
In this study, we evaluate the electrochemical properties of TiNb 2 O 7 (TNO) single particle using a particle-current collector integrated microelectrode, in which TNO single particle with the size of approximately 10 μm was bonded on the tip of a tungsten microelectrode by platinum deposition using a focused ion beam process unit (FIB). Cyclic voltammogram of TNO single particle showed the reversible redox peaks at around 1.6−1.7 V vs. Li/Li + . Anodic peak current is higher than cathodic one at a fixed scan rate, indicating faster reaction during Li + extraction (i.e. discharge) than Li + insertion (i.e. charge) of TNO particle. This tendency was also confirmed in C-rate dependence of charge and discharge capacities. From the results for galvanostatic intermittent titration testing (GITT), we confirmed that at the equilibrium potential vs. Li/Li + below 1.5 V, apparent chemical diffusion coefficient of Li + in TNO at Li + extraction process is much larger than at Li + insertion process. Furthermore, the capacity retention of TNO single particle tested at current of 10C after 2000 cycles was above 99%, indicating excellent intrinsic stability of TNO single particle for Li + insertion and extraction reaction.
Lithium vanadate Li3VO4 (LVO) is known to be as one of the attractive candidates for negative electrode of lithium-ion battery (LIB) with high safety. Although theoretical capacity of LVO attains to 400 mAh g -1 , the actual charge and discharge capacities are far below due to its low electrical and ionic conductivity. In this study, we synthesized carbon-coated LVO (C-LVO) via one-step solid state reaction method and examined its properties as a negative electrode for LIB. From XRD measurements and SEM observation, crystal structure of C-LVO was nearly identical with non-coated one but grain size of former was much smaller than latter with same annealing temperature, suggesting that introduction of carbon source in starting materials effectively helps to suppress LVO grain growth during annealing. TEM observation of C-LVO also shows that amorphous carbon layer with its thickness of several ten nm was formed on the surface of LVO grain. In electrochemical testing, C-LVO shows much higher charge and discharge capacities than non-coated LVO.
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