Re-evaluating common electrolyte additives for high-voltage lithium ion batteries

Abstract

Further increase in the specific energy/energy density of lithium ion batteries can be achieved via further increase of charge cell voltage. However, an enhanced electrode cross-talk, i.e., transition metal (TM) dissolution from cathode and deposition on the anode, drastically limits the cycle life, even leading to rollover failure. In this work, the commonly used film-forming electrolyte additives vinylene carbonate (VC), fluoroethylene carbonate (FEC), and lithium difluorophosphate (LiDFP) are thoroughly evaluated regarding their ability to suppress the issues originating from electrode cross-talk. Neither the VC- nor the FEC-containing electrolytes can suppress it, as evidenced by the presence of Ni, Co, and Mn on the graphite anode; although different for the FEC, the deposited TMs and intertwined Li deposits are homogeneously distributed in the presence of VC. Despite suppression of rollover failure in this manner, VC still cannot compete with LiDFP because LiDFP is able to complex TMs and provide TM-scavenging agents, i.e., PO 3 F − and PO 4 2− , thus, effectively suppressing electrode cross-talk in the first place and effectively preventing the concomitant failure cascade. TM-based electrode cross-talk causes Li dendrites and rollover failure Neither VC nor FEC can suppress electrode cross-talk At a minimum, VC promotes homogeneous TM deposition and suppresses rollover failure LiDFP is most effective because it suppresses electrode cross-talk via scavenging Further increases in energy density of Li-ion batteries can be realized by increasing the charge voltage. However, the enhanced transition-metal dissolution from the cathode and deposition on the anode causes severe safety and performance issues. Klein et al. show that scavenging of transition metals can ameliorate those issues.