Mechanistic Analysis of Mechano-Electrochemical Interaction in Silicon Electrodes with Surface Film

Abstract

High-capacity anode materials for lithium-ion batteries, such as silicon, are prone to large volume change during lithiation/delithiation which may cause particle cracking and disintegration, thereby resulting in severe capacity fade and reduction in cycle life. In this work, a stochastic analysis is presented in order to understand the mechano-electrochemical interaction in silicon active particles along with a surface film during cycling. Amorphous silicon particles exhibiting single-phase lithiation incur lower amount of cracking as compared to crystalline silicon particles exhibiting two-phase lithiation for the same degree of volumetric expansion. Rupture of the brittle surface film is observed for both amorphous and crystalline silicon particles and is attributed to the large volumetric expansion of the silicon active particle with lithiation. The mechanical property of the surface film plays an important role in determining the amount of degradation in the particle/film assembly. A strategy to ameliorate particle cracking in silicon active particles is proposed. Lithium ion battery (LIB) technology has become the prevalent energy storage and supply system for portable electronics.1 In recent years, the application of LIBs is extending to large scale applications such as electric vehicles, 2-4 commercial aircrafts 5,6 and grid energy storage. 7,8 The widespread usage of LIBs in high energy and power applications is predicated on robust improvement of energy and power densities afforded by the LIB which is directly correlated with the anode 9,10 and cathode 11,12 active materials utilized. Current commercial batteries use graphite 13 as anode and lithium cobalt oxide/lithium nickel manganese cobalt oxide 14,15 as cathode material. Graphite exhibits a maximum specific capacity of 372 mAh/g graphite while the current cathode materials are limited to a maximum of 200 mAh/g AM . These chemistries have been utilized in electric vehicle batteries, however, the low capacity necessitates use of bulky and expensive battery packs to power the vehicle which form the major impediment to commercialization of electric vehicles.Extensive efforts have been invested in identifying high capacity anode and cathode materials for usage in next generation lithium ion batteries.10 Silicon has been the focus of several researchers as an anode material owing to its high theoretical specific capacity of 4200 mAh/g Si , approximately ten times that of graphite. [16][17][18] This high capacity is a result of large lithium intercalation ability of silicon as compared to graphite; a silicon atom can intercalate a maximum of 4.4 atoms of lithium (Li 4.4 Si) while graphite can accommodate a maximum of 1 lithium atom per graphite molecule (LiC 6 ).17 However, experimental analysis of silicon anode lithium ion battery has revealed much lower capacities (∼75% of the theoretical capacity) during initial cycles 19 as well as rapid capacity degradation with charge-discharge cycling. Capacity fade of the order of 20% is observed within the first...

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“…[31,[62][63][64] Several groups developed mechanistic models to describe the mechanical response of the SEI on battery cycling. [14,[64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79] However, these models focus on SEI mechanics and incorporate at most simple SEI growth models. [14,[65][66][67][68]75,79] In this paper, we develop a detailed electrochemo-mechanical model to describe SEI mechanics and growth on a deforming electrode particle.…”

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