Study on electrochemical lithiation stress model of graphite-carbon fiber bilayer electrode

Abstract

Graphite–carbon fiber bilayer electrodes (GCBEs), as part of composite structural batteries, are capable of both energy storage and load bearing without the requirement of an extra structure. However, carbon fiber (CF) as a current collector exists lithiation stress, the stress of this bilayer electrode structure is still unclear. In this study, the relationship between the potential and deflection deformation of GCBEs at various thickness ratios is experimentally recorded using an in situ electrochemical cell device. The GCBE bends and recovers with a decrease and increase in potential, respectively. In addition, a cantilever stress model is established to depict the effect of the Li+ concentration difference and thickness ratio on the GCBE lithiation deflection and stress distribution. The results show that the concentration difference and thickness ratio are positively correlated with the deflection and stress, and the stress is discontinuous at the interlayer interface of the electrode. Finite element simulation shows that the Li+ concentration in the graphite layer is approximately three times more than CFs. Compared to the commercial graphite-copper bilayer electrode, the GCBE is experimentally proven to better suppress lithiation deformation. Meanwhile, the influence of solid electrolyte interphase (SEI) is considered by a simplified strain transfer model.