Enhancing the Structural and Surface Properties of Ni-Rich LiNi0.91Co0.06Mn0.03O2 Ncm Cathode Material By Mg Doping and Li3PO4 Coating

Abstract

The increasing demand of energy has surge the prices of fossil fuels. In addition, the CO2 emissions has increased exponentially which prompts the global warming [1]. Therefore, to cope-up these concerns clean alternative energy sources has been investigated, in which lithium-ion batteries (LIBs) has been focused due to their excellent rate capability, high discharge capacity and low cost [2]. The main components of LIBs are anode, cathode, electrolyte and separator. Cathode electrode plays an important role in determining the cost and energy density of the LIBs [3]. The Ni-rich NCM cathode materials are promising candidates for the electric vehicles (EVs), plug-in hybrid electric vehicles (PHEVs) and energy storage systems (ESS). Unfortunately, Ni-rich NCM suffers from continuous structural degradation which leads to the rapid capacity fading and rise in impedance during charge-discharge process [4]. In addition, the consumption of Li-ions for the solid electrolyte interphase severely damages the electrochemical performance of the LIBs [5]. Recently, an innovative approach has been introduced to resolve these issues. The one-step process stabilizes the crystal lattice and protects the active material from hostile attack of electrolyte. In this study, MgHPO4 has been utilized to modify the structural and surface properties of LiNi0.91Co0.06Mn0.03O2 NCM cathode material. The samples were characterized by SEM, XRD, XPS and Nano-SIMS. The electrochemical properties were measured by assembling the coin cells.The shifting of (003) diffraction peak to the low angle confirms the Mg doping. The peaks of Li3PO4 has been indexed which confirms that the NCM cathode material is coated with lithium phosphate. The presence of Mg and P is validated from the XPS results. SEM images confirms that the particles have sustain their original spherical morphology which confirms that the Mg doping has not increased the internal stresses. The 1 mol. % NCM samples shows the superior electrochemical properties due to optimized amount of dopant and coating.The Mg2+ provides the pillar effect in the Li-slabs which prevents the structural collapse during Li-ion de/intercalation. Li3PO4 coating inhibits the side reactions of active material with the electrolyte while keeping enabling the smooth Li-ion diffusion.