Photo-Enhanced Li-Ion Batteries Based on Conversion Type Hematite Phase Iron Oxide Nanostructures

Abstract

To address the intermittency and energy deficit associated with solar energy, photo-rechargeable batteries (PRBs) can offer energy solutions for remote and off-grid locations. A PRB can simultaneously perform energy harvesting and energy storage in the form of electrochemical energy in a single device. Such devices minimize ohmic losses, the number of electrodes, materials, packaging requirements, and as a result, total device cost. In recent years 2D metal halide perovskites, MoS₂ and V₂O₅ have been used as active material for Li-PRBs, but these devices suffer either from low stability, complex synthesis of active material, and complex fabrication routes. Iron oxide (α-Fe₂O₃) anodes offer high theoretical capacity (1006 mAh g⁻¹) for conventional Li-ion battery (LIB) applications, as well as are highly stable in liquid electrolyte environments. Moreover, its suitable bandgap (~2.1 eV) in the visible region makes it a potential active material for high-performance PRB applications. Here, we provide initial results on the fabrication of nanoporous crystalline α phase Fe₂O₃ (hematite) electrodes based photocathodes for photo-enhanced LIBs using a conversion mechanism. The demonstrated Li-PRB showed a specific capacity of 689.3 mAh g⁻¹ under dark conditions at a current density of 1000 mA g⁻¹ after 100 cycles in a voltage range of 3.0–0.01 V. The Li-PRB showed an enhancement of up to 92.96% in the specific capacities when exposed to white light LED (broad spectra in the visible region, 12 mW cm⁻²) at a current density of 2000 mA g⁻¹. The photocharging effect is also confirmed by performing various in-situ measurements such as cyclic voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic charging discharging (GCD) under dark and illuminated conditions.