Enhancing Li+ transport efficiency in solid-state Li-ion batteries with a ceramic-array-based composite electrolyte

Abstract

The electrochemical properties and potential applications of a composite solid electrolyte (CSE) named array-CSE, consisting of a Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) array structure embedded in a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix, have been investigated. The LLZTO array is fabricated using the innovative three-dimensional printing technique, enabling precise control over its architecture. In comparison to the conventional composite electrolyte containing distributed LLZTO particles in PVDF-HFP, referred to as dispersion-CSE, the array-CSE demonstrates efficient Li⁺ migration along a continuous ceramic pathway, while the dispersion-CSE shows inefficient Li⁺ transport due to indirect trajectories. Experimental results confirm higher Li⁺ conductivity, lower activation energy, and a higher Li⁺ transference number in the array-CSE than in the dispersion-CSE. Through numerical simulations, the Li⁺ transport behaviors and fluxes across the individual LLZTO and PVDF-HFP regions within the CSE are clarified, and the difference in the Li⁺ fluxes between the array-CSE and dispersion-CSE is revealed, which is consistent with the experimental findings. When assembled into LiFePO₄ batteries, the array-CSE demonstrates superior capacity and rate performance, as well as a longer cycle life. These advantages can be attributed to its enhanced conductivity and reduced void formation at the anode interface during Li stripping. These findings offer valuable insights for the design of CSEs in solid-state Li-ion batteries, with the potential for increased energy density and stability.