Abstract
Stress-affected two-phase lithiation reactions in spherical elasto-viscoplastic Si particles for Li-ion batteries are studied here to determine the effects of a hyperelastic polymer coating on particle stresses, reaction front velocity, and degree of lithiation. The problem is modelled using finite-strain chemo-mechanical equations that couple stress, with Li-ion diffusion and reaction front velocity, and are solved using the finite-element (FE) approach, taking advantage of spherical symmetry of the problem. FE simulations and the sensitivity analysis reveal: (1) coating thickness is the most influential design parameter that affects the velocity of the reaction front, and (2) increasing values of the coating shear and bulk moduli, and the coating thickness reduce tensile circumferential stresses at the edge of the particle. The latter minimises the risk of particle cracking in the opening mode, but it can also accelerate the arrest of the reaction front, and thus reduce the particle lithiation degree in Li-ion battery anodes.
Highlights
Lithium-ion batteries (LIBs) are some of the most widely employed energy storage devices, used in a range of applications such as electric vehicles, large-scale energy storage grids, and portable electronic devices [1,2,3]
While most commercial LIBs use graphite as an active anode material, silicon (Si) particles have been the subject of intense research in recent years as a possible replacement, as depending on form, Si has approximately 10 times the capacity of graphite [4,5,6]
The expansion of Si during lithiation leads to severe mechanical stresses in the anode material over multiple cycles, which can lead to cracking of the surface of the particle [10,11]
Summary
Lithium-ion batteries (LIBs) are some of the most widely employed energy storage devices, used in a range of applications such as electric vehicles, large-scale energy storage grids, and portable electronic devices [1,2,3]. The proposed study provided some useful qualitative direction for maximising the capacity of carbon-coated Si particles, the analysis did not capture the lithiation-reaction in Si particles observed experimentally It is well-known that the two-phase lithiation process occurs in Si particles, with the lithiated material separated from the unlithiated one by a reaction front which is driven by an electrochemical force [27,28]. A nonlinear chemo-mechanical model [30] that captures stress-affected two-phase lithiation as a non-stationary reaction process in Si particles is extended to account for the presence of a polymer coating around Si particles. The extended model is implemented into a nonlinear large-strain finite-element framework to enable simulations of the stress-affected lithiation reaction in polymer-coated Si particles, and provide new insights into the effects of material properties and thickness of a polymer coating on stresses, reaction front velocity, and degree of lithiation
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