Using tea waste to produce a high-performance lithium-ion capacitor—Bio-graphite/ Li4Ti5O12 (LTO)

Abstract

Lithium-Ion Capacitors (LICs) show promise as electrochemical energy storage devices (EESDs) that combine a supercapacitor-type cathode and a Lithium Ion-type anode with an organic electrolyte containing lithium salts. In this study, porous carbon (LICs cathode) was synthesized from tea waste biomass using a potassium carbonate (K2CO3) activator. During synthesis, the weight ratios for carbon and activator were 1:2 (GAC-2); 1:3 (GAC-3); and, 1:4 (GAC-4), respectively. Meanwhile, the synthesis of Li4Ti5O12 material (LICs anode) was carried out using a salt-assisted solid-state method. Based on X-ray diffraction patterns (XRD), the synthesized carbon material initially showed an amorphous structure (without activator), which was followed by the formation of graphite peaks (activator addition). The XRD pattern of prepared LTO material matched the cubic spinel structure of Li4Ti5O12 (Fd-3m, PDF no. 49–0207). Scanning electron microscope (SEM) analysis revealed macropores in the synthesized carbon material in all samples whereas the LTO material displayed a cubic morphology with a smooth surface. The specific discharge capacity of the prepared LTO was 160 mAh/g (half-cell vs. Li). The Specific Discharge Capacities of Lithium ion capacitor (LIC) of LTO/HC, LTO/GAC-2, LTO/GAC-3, and LTO/GAC-4 samples were 22, 36, 42 and 51 mAh/g, respectively. The Cyclic voltammetry verified that the prepared cells have stable pseudocapacity properties. The prepared LIB from tea waste bio-graphite/LTO shows its high-performance characteristic indicates from its energy density, power density and lifetime.

Keywords

• Lithium ion capacitors
• Lithium titanate
• Tea waste
• Bio-graphite
• Specific discharge