The Impact of Electrolyte Oxidation Products in LiNi0.5Mn1.5O4/Li4Ti5O12 Cells

It has long been suspected that parasitic reaction products created at one electrode of a Li-ion battery can migrate to the other electrode and influence its operation. In order to demonstrate that these "electrode-electrode interactions" do occur, four types of coin cells were investigated. Two of these were Li4Ti5O12-limited and LiNi0.5Mn1.5O4-limited LiNi0.5Mn1.5O4/Li4Ti5O12 (LNMO/LTO) "full cells". In order to prevent electrode-electrode interactions, LTO/Li and Li/LNMO coin cells were connected by a wire joining the negative (Li) sides of the two coin cells making a simulated LNMO/LTO Li-ion cell with separate electrolyte compartments for the positive and negative electrodes. Virtually no parasitic reactions were observed at the LTO electrode in Li/LTO cells as evidenced by a coulombic efficiency near 1.0000. By contrast, severe electrolyte oxidation, leading to Charge end point capacity slippage and poor coulombic efficiency was observed in Li/LNMO cells. The behavior of the simulated LNMO/LTO Li-ion cells could be well understood and predicted based on the behavior of the half cells. By contrast, true LNMO/LTO Li-ion cells showed severe parasitic reactions-occurring at the LTO electrode due to electrolyte oxidation products from the LNMO electrode migrating to the LTO electrode. Understanding such electrode-electrode interactions is critical in making long-lived Li-ion batteries and also for understanding the mechanisms governing the function of electrolyte additives. Similar effects, albeit at much smaller effective currents, can be occurring in Li-ion cells with standard positive and negative electrodes. (C) 2013 The Electrochemical Society. All rights reserved.