Reducing Diffusion Induced Stress of Bilayer Electrode System by Introducing Pre-Strain in Lithium-Ion Battery

Lithium-ion battery (LIB), as energy storage devices, is widely used in portable electronic devices and have the promising applications in electric vehicles. The volume change and large stress can lead to electrode pulverization and resultant loss of electrical contact from current collector, which is considered to be one of the main reasons in capacity degradation of LIB. To reduce diffusion induced stress of electrode system during lithium ion diffusion, a chemo-mechanical coupled theoretical model of bilayer electrode system of electrode layer bonded to the current collector is established. The theoretical results show that diffusion induced stresses at the electrode-collector interface and maximum tensile stress at the top surface of electrode layer are alleviated greatly by introducing pre-strain. The effects of pre-strain and lithium ion concentration on chemo-mechanical coupled behavior of bilayer electrode system are discussed. In particular, the lithium ion concentration difference strongly depends on the diffusion thickness and time. In addition, the effects of plastic deformation of current collector and diffusion time on biaxial stress distribution are also discussed. The biaxial stress decreases with the increasing of pre-strain and with the decreasing of time during galvanostatic charging. The curvature and biaxial stress when considering plastic deformation is smaller than that when not considering the plastic deformation. The results obtained from this investigation will provide the reference to reduce the diffusion induced stress and improve the ion diffusion performance of LIB.

Analytical Solution for Coupled Diffusion Induced Stress Model for Lithium-Ion Battery

Electric cycling is one of the major damage sources in lithium-ion batteries and extensive work has been produced to understand and to slow down this phenomenon. The damage is related to the insertion and extraction of lithium ions in the active material. These processes cause mechanical stresses which in turn generate crack propagation, material loss and pulverization of the active material. In this work, the principles of diffusion induced stress theory are applied to predict concentration and stress field in the active material particles. Coupled and uncoupled models are derived, depending on whether the effect of hydrostatic stress on concentration is considered or neglected. The analytical solution of the coupled model is proposed in this work, in addition to the analytical solution of the uncoupled model already described in the literature. The analytical solution is a faster and simpler way to deal with the problem which otherwise should be solved in a numerical way with finite difference method or a finite element model. The results of the coupled and uncoupled models for three different state of charge levels are compared assuming the physical parameters of anode and cathode active material. Finally, the effects of tensile and compressive stress are analysed.