Microstructure Study of Electrochemically Driven LixSi

We report the direct observation of microstructural changes of LixSi electrode with lithium insertion. HRTEM experiments confirm that lithiated amorphous silicon forms a shell around a core made up of the unlithiated silicon and that fully lithiated silicon contains a large number of pores of which concentration increases toward the center of the particle. Chemomechanical modeling is employed in order to explain this mechanical degradation resulting from stresses in the LixSi particles with lithium insertion. Because lithiation‐induced volume expansion and pulverization are the key mechanical effects that plague the performance and lifetime of high‐capacity Si anodes in lithium‐ion batteries, our observations and chemomechanical simulation provide important mechanistic insight for the design of advanced battery materials. Microstructural changes in electrochemically driven LixSi are studied. HRTEM observation of Li2Si samples confirms that a two‐phase region is formed with amorphous LixSi at the surface and a crystalline Si phase in the core of particle. A large variety and number of pores are observed in fully lithiated Si anode samples.