Carbon coated nano-LiTi ₂(PO ₄) ₃ electrodes for non-aqueous hybrid supercapacitors

The Pechini type polymerizable complex decomposition method is employed to prepare LiTi ₂(PO ₄) ₃ at 1000 °C in air. High energy ball milling followed by carbon coating by the glucose-method yielded C-coated nano-LiTi ₂(PO ₄) ₃ (LTP) with a crystallite size of 80(±5) nm. The phase is characterized by X-ray diffraction, Rietveld refinement, thermogravimetry, SEM, HR-TEM and Raman spectra. Lithium cycling properties of LTP show that 1.75 moles of Li (∼121 mA h g ^-1 at 15 mA g ^-1 current) per formula unit can be reversibly cycled between 2 and 3.4 V vs. Li with 83% capacity retention after 70 cycles. Cyclic voltammograms (CV) reveal the two-phase reaction mechanism during Li insertion/extraction. A hybrid electrochemical supercapacitor (HEC) with LTP as negative electrode and activated carbon (AC) as positive electrode in non-aqueous electrolyte is studied by CV at various scan rates and by galvanostatic cycling at various current rates up to 1000 cycles in the range 0-3 V. Results show that the HEC delivers a maximum energy density of 14 W h kg ^-1 and a power density of 180 W kg ^-1.