Akshay Jain

Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors

In this manuscript, a dramatic increase in the energy density of ~ 69 Wh kg−1 and an extraordinary cycleability ~ 2000 cycles of the Li-ion hybrid electrochemical capacitors (Li-HEC) is achieved by employing tailored activated carbon (AC) of ~ 60% mesoporosity derived from coconut shells (CS). The AC is obtained by both physical and chemical hydrothermal carbonization activation process, and compared to the commercial AC powders (CAC) in terms of the supercapacitance performance in single electrode configuration vs. Li. The Li-HEC is fabricated with commercially available Li4Ti5O12 anode and the coconut shell derived AC as cathode in non-aqueous medium. The present research provides a new routine for the development of high energy density Li-HEC that employs a mesoporous carbonaceous electrode derived from bio-mass precursors.

Unveiling TiNb2O7 as an Insertion Anode for Lithium Ion Capacitors with High Energy and Power Density

This is the first report of the utilization of TiNb2 O7 as an insertion-type anode in a lithium-ion hybrid electrochemical capacitor (Li-HEC) along with an activated carbon (AC) counter electrode derived from a coconut shell. A simple and scalable electrospinning technique is adopted to prepare one-dimensional TiNb2 O7 nanofibers that can be characterized by XRD with Rietveld refinement, SEM, and TEM. The lithium insertion properties of such electrospun TiNb2 O7 are evaluated in the half-cell configuration (Li/TiNb2 O7 ) and it is found that the reversible intercalation of lithium (≈3.45 mol) is feasible with good capacity retention characteristics. The Li-HEC is constructed with an optimized mass loading based on the electrochemical performance of both the TiNb2 O7 anode and AC counter electrode in nonaqueous media. The Li-HEC delivers very high energy and power densities of approximately 43 Wh kg(-1) and 3 kW kg(-1) , respectively. Furthermore, the AC/TiNb2 O7 Li-HEC delivers a good cyclability of 3000 cycles with about 84% of the initial value.

Hydrothermal pre-treatment for mesoporous carbon synthesis: enhancement of chemical activation

This work presents a resource-friendly process to produce high surface area mesoporous activated carbons from biomass. ZnCl2 as an activating agent was incorporated into the biomass (coconut shells) during a hydrothermal pre-treatment step. The pre-treatment was followed by pyrolysis accompanied by physical activation. The resultant mesoporous activated carbons possessed a higher total surface area and a greater degree of mesoporosity compared to the biomass that was pyrolysed without hydrothermal treatment. The cause of higher mesoporosity is inferred to be the more conducive environment for accessibility of ZnCl2 due to reduced diffusion resistance to the biomass provided by the hydrothermal treatment. In addition, the hydrothermal environment facilitated the generation of oxygen-containing functional groups that contributed to the enhanced activity of ZnCl2. Up to 67% increase in the mesoporous surface area was achieved with the inclusion of the pre-treatment step. Analogously, 50% more ZnCl2 was required to deliver the same performance in the absence of the pre-treatment step. The mesoporous activated carbons were tested for adsorption of textile dyes and possessed high adsorption capacities of up to 526 mg and 630 mg per g of carbon for methylene blue and erythrosine red, respectively. The incorporation of the hydrothermal pre-treatment is an important step in developing processes for converting biomass that make efficient and effective use of activating agents.