Stress-Modulated Driving Force For Lithiation Reaction In Hollow Nano-Spherical Anodes
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STRESS-MODULATED DRIVING FORCE FOR LITHIATION REACTION IN HOLLOW NANO-SPHERICAL ANODES Zheng Jia1, Teng Li1 1
Department of Mechanical Engineering, University of Maryland, College Park, MD 20742,
U.S.A.
ABSTRACT Recent experimental evidence on nano-particle and nano-wire silicon anodes showed an initial rapid velocity of reaction front at the initial stage of lithiation, followed by an apparent slowing or even halting of the reaction front propagation. This intriguing phenomenon is attributed to the lithiation-induced mechanical stresses across the reaction front which is believed to play an important role in the kinetics of reaction at the front. Here, through theoretical formulation, we presented a comprehensive study on lithiation-induced stress field and its contribution to the driving force of lithiation in hollow spherical anodes with different boundary conditions at the inner surface of the particle. Our results reveal that hollow spherical silicon anodes can be lithiated more easily than solid spherical silicon particles and thus may serve as an optimal design of high performance anodes of lithium-ion battery. INTRODUCTION There has been a surge of interest in developing next-generation lithium-ion batteries with high capacity. Silicon is emerging as the most promising anode material due to its highest specific capacity, which is about ten times of current graphite anode. The high theoretical capacity of silicon stems from the fact that one silicon atom can host up to 3.75 lithium atoms [1]. However, on the other hand, insertion of large amount of lithium atoms causes excessive volume change (~300%) and large mechanical stresses, which may eventually fracture the silicon anodes and lead to irreversible capacity loss [2]. Therefore, mechanical failure initiated by the large volumetric expansion is the key issue that hinders the mass application of silicon as anodes. To mitigate mechanical failure induced by the large volume expansion, intensive research efforts are focused on developing nanostructured anodes including nanowires [2], thin film [3], nanoporous structures [4], nano-sized beaded-string structure [5], nanowall [6] and hollow nanoparticles [7]. To optimize the design of these nano-sized anodes for high-performance lithium-ion batteries, a comprehensive understanding of the lithiation kinematics and associated mechanical stress evolution is fundamental and vital. Recent evidence has accumulated that the lithiation of silicon advances by the movement of a automatically-sharp reaction front [8-11], which separates an unlithiated pristine silicon phase and a fully lithiated silicon phase (as shown by the schematics of figure 1(b)). This indicates that the lithiation process is controlled by the reaction of lithium and silicon at the reaction front, rather than the diffusion of lithium through the lithiated silicon. Recent experimental
measurements of reaction velocity in solid particles reveal that the reaction front usually slows down as it progresses into the solid particles. A theoretical model
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