Effects of Electrolyte Additives on the Suppression of Mn Deposition on the Edge Plane of HOPG for Lithium-ion Battery

Introduction Spinel LiMn2O4 is a promising positive-electrode material in lithium-ion battery for high-power application such as electrical vehicles owing to its safety characteristic and low cost. However, it is widely known that the charge and discharge capacities for the LiMn2O4/C cell fade rapidly during charge/discharge cycles and storage, in particular at elevated temperatures. One of the possible mechanisms for the capacity fading is the dissolution of Mn species from LiMn2O4 into an electrolyte. The dissolved Mn species are known to deposit on the graphite negative-electrode, and lead to significant capacity loss. We have so far investigated this degradation mechanism by using edge plane of highly oriented pyrolytic graphite (HOPG) as a model electrode. In Mn-ion-containing electrolyte, charge transfer resistance due to lithium-ion transfer at the interface between the HOPG electrode and electrolyte remarkably increased, and small particles were formed on the edge plane HOPG. These particles were precipitated as a form of Mn metal or Mn-containing compounds. In this work, to suppress the Mn deposition on graphite, the effects of several additives in the electrolyte, such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), were investigated.