Effect of Polymer Interlayer Thickness on Solid-State Battery Performance with Electrochemo-Mechanical Coupling

Solid-state batteries provide higher capacity and wider electrochemical and thermal stability when used with lithium metal anode than conventional batteries. In solid-state batteries (SSBs), solid inorganic electrolytes such as Li₇La₃Zr₂O₁₂ (LLZO) offer superior ionic conductivity and safety. As the inorganic solid electrolytes (ISEs) are brittle, creating thin layers and interfaces poses mechanical problems. Also, there is a chance of lithium dendrite formation in solid inorganic electrolytes even at low currents due to the rough and rigid contact surface of inorganic electrolytes. Such problems can be alleviated by introducing a polymer interlayer between the lithium metal anode and the ISE. However, there is a difference in the Li-ion conductivity in polymer and inorganic electrolytes. Besides, the volume expansion due to ion transport is comparatively greater in polymers than in ISE. Hence, in this study, the electrochemical performance of the battery is coupled with the mechanical properties of electrode and electrolyte materials to study the effects of introducing polymer interlayer. It is observed that charge transfer overpotential increases more rapidly with time for thinner interlayer thickness cells when operated under galvanostatic conditions. When the polymer interlayer is reduced, the rate of through-plane stress generation becomes more rapid. Besides, the effect of plating, elastic, and plastic deformation on the dimension change of lithium metal anode is also studied. It is found that the dimensional change of the metal anode is more for higher current density and higher interlayer thickness. Moreover, it is obtained that 5 $\mu m$$\mu m$ to 7.5 $\mu m$$\mu m$ is the most suitable polymer interlayer thickness considering minimal overpotential loss. Thus, the present model provides insight into making a suitable electrolyte for next-gen SSBs while combining the good contact properties of the polymer and the higher shear modulus of solid inorganics.