Impacts of electrode shape on lithiation performance: the edge effect on lithium intercalation

Abstract

With respect to the increasing applications of irregular shape electrodes in stretchable and flexible batteries, the impacts of electrode shape on lithiation performance are investigated in this manuscript. Firstly, square and circular side-to-side electrodes are prepared and employed for charge and discharge cycles. The lithiation profiles of the graphite electrode are in-situ observed and the electrochemical cyclic performances are recorded. It is found uneven lithiation is more significant in the square electrode than the circular electrode, leading to more side reaction products and poorer cyclic performance. Numerical simulations are conducted to investigate the intrinsic mechanism of the uneven lithiation. It is found the electric field is extraordinarily strong near the electrode edges, resulting in highly inhomogeneous lithium flux in electrolyte. The electrode edges are exposed to excessive lithium supply in electrolyte, leading to fast lithiation saturation and even lithium dendrite growth. Meanwhile, the core area of the electrode cannot obtain sufficient lithium from electrolyte and, therefore, remain in low lithiation level even after charge operation. The sharper the electrode tip is, the stronger the edge effect is. Finally, different irregular shape face-to-face electrodes are prepared and examined. The edge effects are also found in the face-to-face electrodes and lead to a fake lithiation saturation phenomenon. Therefore, strategies to minimize the edge effects, such as decreasing the curvatures of the electrode sharp tips, are suggested to promote the electrochemical performance.