Development of Electrolyte Additives to Enable High-Voltage LiNi0.5Mn1.5O4 Lithium Ion Batteries

Abstract

Electrochemical energy storage (EES) is still key to realize wide spread use of renewable energies. For large-scale EES production, the development of high energy density, non-toxic, cost-effective materials is necessary. In this study, a cobalt free active material, Lithium Nickel Manganese Oxide, LiNi0.5Mn1.5O4 (LNMO), was employed in the production of cathodes for high voltage lithium ion battery (LIB) applications. LNMO is an attractive cathode active material due to its high operating potential (~4.7 vs. Li/Li+ [1]), non-toxicity and low cost. The practical application of LNMO cathodes in LIBs has been relatively limited, especially for large scale application, due challenges associated with the material (i.e. electrolyte decomposition at high voltage, self-discharge and dissolution of the transition metals [2]).Electrolyte additives are an effective way to address these challenges, without major cost increase or changes to the production approach. In this study the role of different electrolyte additives in high-voltage full-cell LIBs with both graphite and silicon-graphite anodes is investigated. Additives known for their solid electrolyte interphase (SEI) forming ability (i.e. vinylene carbonate (VC) and fluoroethylene carbonate (FEC)), as well as additives that play additional roles such as cathode electrolyte interface formation or HF scavenging (i.e. tris(trimethylsilyl) phosphite (TMSP) and succinate anhydride (SA)), are used [3]. Galvanostatic cycling measurements were performed in 3-electrode cells in order to investigate the rate capability and long term cycling stability of LMNO/Gr and LMNO/Gr-Si full-cells with different electrolyte additives. The electrochemical characterization was verified with post mortem analysis to confirm the SEI composition, chemical and mechanical stability of the electrodes and lack of lithium plating. Post mortem investigations were done with Raman spectroscopy, scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) and optical microscopy. Improved rate performance and better long term cycling stability of both full-cell chemistries was achieved for electrolytes containing the TMSP additive.