Enhanced Thermal Stability of Si/Graphene Composite Anode in the Presence of Fluoroethylene Carbonate Additive

Silicon-based materials are becoming very promising next generation anode materials for lithium ion battery application after intensive research efforts (1-2), which address the volume expansion by new material development, solid electrolyte interface (SEI) formation by introducing additive(4),  and electrode integrity by choosing appropriate binders (3). However, compared to electrochemical performance of silicon based electrode, thermal characteristics of silicon composite material has not been fully illustrated. In this study, we carried out differential scanning calorimetry (DSC) experiments on lithiated Si/graphene composite electrode in carbonate electrolyte with fluoroethylene carbonate (FEC) as additive.

Series electrolytes with various FEC concentration (0, 5, 10 and 20 wt%) were prepared using 1.2M LiPF₆ in EC/EMC (3/7, by wt) electrolyte. Electrodes were prepared by casting the mixture of Si/graphene composite material (XG sciences), graphene (XG sciences) and poly acrylic acid (PAA) on copper foil. All electrodes had been cycled for three cycles, and then lithiated to various lithiation states. The samples were then sealed in the DSC sample holder with additional electrolyte and tested using Pyris 1 DSC (Perkin Elmer). The test results are shown in Fig. 1. It is very clear from DSC results that FEC additive play an important role to the thermal stability of the silicon based electrode. When there is no FEC additive, the on-set temperature for exothermic reaction is lower than that with FEC.  The exothermic reaction at lower temperature is related to the breakdown of SEI layer with electrolyte (5-7). The less exothermic reaction of silicon composite electrodes with FEC indicates that the better thermal stability of SEI is formed by FEC additive. In this work, the thermal effect of both FEC concentration and the state of lithiation in the silicon composite electrode will also be presented.

Acknowledgement

The silicon material is provided by XG sciences. The validation was conducted under Cell Analysis, Modeling, and Prototyping (CAMP) Facility at ANL. Support from David Howell and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies is gratefully acknowledged.

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