Sustainable renewable energy generation from sources that would otherwise be environmental pollutants and transportation of such energies for the desired applications would lead to significant global social and economic development. The commercially available energy storage devices such as supercapacitors and Li-ion batteries (LIB) energy and power densities are significantly lower than those necessary for applications in zero-emission transportation such as electric vehicles (EV, >150 Wh kg^–1) & plug-in hybrid electric vehicles (P-HEV, 57 to 97 Wh kg^–1).(1) The Li-ion hybrid electrochemical capacitor (Li-HEC) constructed with Li-ion insertion as anode and double-layer forming component as positive electrode, which provides the desired energy and power densities, respectively. (2, 3)

     Here, the environmentally threatening and invasive weed of Prosopis juliflora is converted as electrode materials. Prior to testing the P. juliflora AC as an electrode for charge storage, we have carried out a systematic study on the preparation of AC from P. juliflora. Firstly, the influence of the pore forming agent, i.e., KOH, and its capacitive behavior has been evaluated in symmetric configuration. Subsequently, the energy density has been increased by introducing a homemade insertion type electrode Li₄Ti₅O₁₂ with P. julifloraderived AC as the supercapacitor component in a Li-HEC assembly. In addition, extensive physico-chemical properties, including XRD, BET surface area, Raman analysis, XPS, and SEM studies, were conducted and are described in detail.

References:

1. E. J. Cairns and P. Albertus, Annual Review of Chemical and Biomolecular Engineering, 1, 299 (2010).

2.  V. Aravindan, J. Gnanaraj, Y.-S. Lee and S. Madhavi, Chemical Reviews, 114, 11619 (2014).

3. K. Naoi, S. Ishimoto, J.-i. Miyamoto and W. Naoi, Energy & Environmental Science, 5, 9363 (2012).

Figure 1. (a) SEM image of as prepared Prosopis juliflora carbon at 900 °C is naturally exist in tubular structure. (b) Plot of cyclic retention vs. cycle number and coulombic efficiency of KC21-900/LTO based Li-HEC at a current density of 1 A g^–1. Here, the current density is based on the total mass loading of the electrode. Inset: typical charge-discharge curves for the first five cycles, (c) Ragone plot of KC21-900 based symmetric and Li-HEC configuration