Interplay of Inhomogeneous Electrochemical Reactions with Mechanical Responses in Silicon-Graphite Anode and its Impacts on Degradation

Abstract

Enhanced EV market penetration requires durability of the battery with high energy throughput. For long-term cycle stability of silicon-graphite anode capable of high energy density, the reversible redox reactions are crucial. Here, we unveil intriguing electrochemical phenomena such as crosstalk of lithium ion ($Li^{+}$) between silicon and graphite, $Li^{+}$ accumulation in silicon, and capacity depression of graphite under high pressure, which engender the irreversible redox reactions. Active material properties, i.e. the size of silicon and the hardness of graphite, silicon-graphite anode, are modified based on the unveiled results to enhance the reaction homogeneity and reduce subsequent degradation. Owing to the property change of the anode active materials, silicon-graphite anode paired with high nickel cathode allows the prismatic cell with 8.7 Ah to reach cycling performance over 750 cycles with volumetric energy density of 665 $Whl^{-1}$, which is corresponding to 800 $Whl^{-1}$ in the prismatic cell with 87 Ah. Finally, the cycling performance can be tailored by the design of electrode regulating $Li^{+}$ crosstalk. Our findings provide electrochemical insights into degradation mechanisms and a promising direction on the progressive improvement of materials and the design of electrodes in silicon-graphite anode.