Cobalt-free Layered Oxide Cathode: An Attempt to Counter the Perennial Problems of Cobalt In Lithium-Ion Batteries

Abstract

The sale of electric vehicleshas witnessed significant jump in recent timesowing to the emergence of high energy density lithium-ion batteries (LIBs) comprising nickel-rich layered oxide cathodes (NCM) paired with graphite anodes. However, the presence of cobalt in nickel-rich LiNi0.8Co0.1Mn0.1O2(NCM811) cathodes is a serious issueowingto demographic constraints and price fluctuation of cobalt-based compounds in international market affecting global supply chain. Here, we proposea cobalt-free and nickel-rich layered oxide cathode-LixNi0.8Mg0.1Mn0.1O2(NMM811), as an alternative to NCM-based cathodes. Powder X-ray diffraction (PXRD) and Rietveld refinement with electrochemical characterizations, including cyclic voltammetry and galvanostatic charge/discharge in a 2032 coin-typecell of the pristine/cycled electrodes illustrate that divalent metal cations (Mg2+) substitution instead of cobalt is feasible without affecting the structure, electrochemical properties and importantly suppressing the Li+/Ni2+cation mixing. The XPS and XANES analysis using synchrotron radiation shows the surface chemical composition and geometric information of the NMM cathode, respectively, revealing the state of phases and extent of Li+/Ni2+cation mixing in detail. The electronic structure and valence states were probed through density functional theory (DFT), showing an increase in the band gap (~3.17 eV) of NMM811. Electrochemical measurements revealed the initial discharge capacity of NMM811 cathode was ~198 mAh.g-1with a capacity retention of ~74.3% after 100 cycles between 3.0-4.5 V at 0.1C rate. The excellent cyclic performance of NMM811 stems from strong Ni-O bonding energy, low lattice expansion, and low Li+/Ni2+cation mixing. Overall, the present invention opens a new possibility for developing Ni-rich and Co-free NMM811 akin to NCM811 for high energy density LIBs cathodes.