Study Of First Cycle Electrochemical Characteristics Of Graphite Anode For Lithium Lon Battery

Lithium ion battery (LIB) has a wide application due to its advantagesincluding high energy density, long cycle life, etc. Graphite is the mostpopular anode material used in the commercialized LIB today. SEI film whichformed during the first charge/discharge cycle may consume a part of lithiumion. However, SEI film has great influence on electrochemical performance,the study in this field became very necessary and important.In this work, studies were carried out for the influence of graphitecharacteristics, formation condition and electrolyte composition on the firstcycle electrochemical performance of the anode, including irreversiblecapacity, coulombic efficiency, electrochemical reactions, etc.For the Meso-carbon micro-beads (MCMB), its particle size are between6μm to23μm, with the increasing of the particle size, the BET surface areaand irreversible capacity decrease, while first cycle columbic efficiencyincreases. Among NG, MCP and AG, graphitization degree decreased in theorder of NG>MCP>AG. Within suitable electrolyte, the irreversible capacityof all three types of graphite was not too much and the first coulombicefficiency will be higher than92%. However, as NG and MCP were sensitiveto PC containing electrolyte, within it, the irreversible capacity could becomevery large and the first cycle columbic efficiency would be very low.30%PCcontent was the critical point for graphite exfoliation. VC and PS, which canform a SEI film prior to the PC intercalation, were added into the electrolyteto restrain the exfoliation reaction.Studies were carried out with different formation condition to investigatethe intercalation process of lithium ion and the formation of SEI film. Theoptimized formation condition showed much higher first cycle coulombicefficiency and better capacity retention.