Cobalt Borate Complex With Tetrahedrally Coordinated Co 2+ ‐ Promotes Lithium Superoxide Formation in Li‐O 2 Batteries

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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.
Funding Information
  • Deutsche Forschungsgemeinschaft (INST 40/575‐1 FUGG)
  • Department of Science and Technology, Ministry of Science and Technology, India (DST/CEST/AMEST/2022/65(G)))

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