Enhancing the Kinetics Using Lithium-Powder Electrode As an Anode in Lithium-Oxygen Batteries

Lithium-oxygen battery(Li-O2 battery) is a promising candidate for use in large-scale storage systems such as electric vehicles and energy storage system. Li-O2 battery has a significantly higher theoretical energy density than conventional Li-ion batteries by using lithium metal anode which has the lowest electrochemical potential(-3.04V versus the standard hydrogen electrode) and unlimited cathode active material. However, Li-O2 battery still suffers from drawbacks such sluggish ORR/OER kinetics at the cathode, dendrite growth on the lithium metal anode and the decomposition of the electrolyte. In ORR/OER process, lithium oxide intermediate, LiO2 is generated at the cathode/electrolyte interface. It induces a high discharge/charge overpotential, which reduces round trip efficiency. And also due to its high reactivity, it makes side product reacting with electrolyte. Due to sluggish ORR/OER kinetics, LiO2 residues in the electrolyte for a long period thereby increases overpotential and reacts with electrolyte severely. It was previously reported that lithium powder electrode inhibits dendrite growth by reducing the effective current density. Also it has a capability to use more Li than conventional lithium foil electrode. In this study, lithium powder electrode(LPE) was applied as an anode in Li-O2 battery. It is proposed that lithium powder electrode not only inhibits dendrite growth on anode but also increases lithium ion diffusion thus promoting the ORR/OER kinetics at the cathode. By Cyclic voltammetry(CV) and Linear sweep voltammetry(LSV), it was confirmed that lithium powder increased kinetics of the cathodic reaction and also lithium ion diffusion coefficient was calculated using Randles-sevcik equation. The result showed that lithium powder enhances lithium ion diffusion at the cathode by increasing the electrochemically active surface area when comparing with lithium foil electrode. The morphology and chemical reaction after cycling was investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). Fourier-transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS) also demonstrated that side product on cathode of LPE used Li-O2 battery was reduced. Consequently, LPE used Li-O2 battery(2800mAh/g) exhibited higher discharge capacity than lithium foil electrode(LFE) used Li-O2 battery(2200mAh/g) and much better cycle performance. In conclusion, the larger electrochemically active surface area of LPE enhances the lithium ion diffusion thereby promotes ORR/OER kinetics and reduces LiO2 residual time. As a result, improved kinetics and reduced residual time of LiO2 contribute to the higher discharge capacity, better cycle performance and decreased side reaction product.