Chemo‐Mechanical Model of SEI Growth on Silicon Electrode Particles**

Abstract

Silicon anodes promise high energy densities of next-generation lithium-ion batteries, but suffer from shorter cycle life. The accelerated capacity fade stems from the repeated fracture and healing of the solid-electrolyte interphase (SEI) on the silicon surface. This interplay of chemical and mechanical effects in SEI on silicon electrodes causes a complex aging behavior. However, so far, no model mechanistically captures the interrelation between mechanical SEI deterioration and accelerated SEI growth. In this article, we present a thermodynamically consistent continuum model of an electrode particle surrounded by an SEI layer. The silicon particle model consistently couples chemical reactions, physical transport, and elastic deformation. The SEI model comprises elastic and plastic deformation, fracture, and growth. Capacity fade measurements on graphite anodes and in-situ mechanical SEI measurements on lithium thin films provide parametrization for our model. For the first time, we model the influence of cycling rate on the long-term mechanical SEI deterioration and regrowth. Our model predicts the experimentally observed transition in time dependence from square-root-of-time growth during battery storage to linear-in-time growth during continued cycling. Thereby our model unravels the mechanistic dependence of battery aging on operating conditions and supports the efforts to prolong the battery life of next-generation lithium-ion batteries.

Rechargeable Batteries of the Future—The State of the Art from a BATTERY 2030+ Perspective

“…[92] Its continued reformation leads to linear-in-time capacity fade increasing with applied current. [83,94] Understanding and mitigating this effect is crucial for the development of high-energy silicon electrodes.…”

Transition between growth of dense and porous films: theory of dual-layer SEI

“…The concentration c 0 = c ref exp(ÀeU 0 /k B T) at the anode-SEI interface depends on the open circuit voltage (OCV) U 0 , which results from the state of charge SoC via the OCV-curve. 31,40,62 At this point, we summarize and non-dimensionalize the model equations. We use the characteristic time 1/(r 0 a 2 ) and the characteristic energy scale k B T. Table 1 lists the dimensionless parameters of our model.…”

“…The concentration c 0 = c ref exp(− eU 0 / k B T ) at the anode-SEI interface depends on the open circuit voltage (OCV) U 0 , which results from the state of charge SoC via the OCV-curve. 31,40,62…”

Direct-Contact Prelithiation of Si–C Anode Study as a Function of Time, Pressure, Temperature, and the Cell Ideal Time

“…It was demonstrated that the composite Si can give higher cyclic stability as compared to bare Si as an anode material . The SEI formation on the anode surface protects the electrolyte from further decomposition and enhances the safety, cycle life, and performance. − However, the initial capacity loss (ICL) of the Si anode is high due to the formation of surface film compounds on the anode surface during the first discharge process, and it is irreversible in nature. − In addition, it also hinders the Li-ion transport, limiting the LIB’s capacity and dynamic reactivity, and the resistance across the layer restricts the current flow, resulting in a high ICL . The high ICL (∼60 to 65%) mainly restricts these high-capacity anodes in the full-cell fabrication and prevents their further commercial use. , …”