Cobalt Borate Complex With Tetrahedrally Coordinated Co <sup>2+</sup> ‐ Promotes Lithium Superoxide Formation in Li‐O <sub>2</sub> Batteries
Shivaraju Guddehalli Chandrappa, Katrin Forster‐Tonigold, Vasantha A. Gangadharappa, Pavithra Kannan, Kunkanadu R. Prakasha, Axel Groß, Maximilian Fichtner, Rachel A. Caruso, Guruprakash Karkera, A. S. Prakash
Abstract
Abstract The development of non‐aqueous lithium‐oxygen (Li‐O 2 ) batteries is hindered by inefficient discharge product decomposition, side reactions with the electrolyte, and high charge overpotentials (>1 V). This study explores the use of sodium cobalt borate (Na 3 CoB 5 O 10 , NCBO) with cobalt in tetrahedral geometry as an oxygen electrocatalyst for non‐aqueous Li‐O 2 batteries. The prepared cobalt borate exhibits an oxygen evolution reaction (OER) overpotential of 326 mV RHE at a current density of 10 mA cm −2 and a Tafel slope of 42 mV dec −1 in 1 m KOH. Density Functional Theory (DFT) calculations identify the OH‐covered (101) surface of NCBO as the preferred OER site, with an overpotential between 451 and 544 mV. In Li‐O 2 batteries, the NCBO cathode demonstrates 200 cycles with an overpotential of 1.95 V and 56.00% round‐trip efficiency at a capacity limit of 500 mA h g −1 , along with a smaller charge overpotential of 0.64 V at a capacity limit of 2000 mA h g −1 . Post‐cycling analysis of NCBO electrodes reveals electronically conductive Lithium Superoxide (LiO 2 ) as the dominant discharge product. As revealed by DFT studies, the promising performance of NCBO in Li‐O 2 batteries is attributed to its tetrahedral Co coordination, highlighting its potential for electrocatalytic applications.