Revealing the Impact of Space-Charge Layers on the Li-Ion Transport in All-Solid-State Batteries

The influence of space-charge layers on the ionic charge transport over cathode-solid electrolyte interfaces in all-solid-state batteries remains unclear because of the difficulty to unravel it from other contributions to the ion transport over the interfaces. Here, we reveal the effect of the space-charge layers by systematically tuning the space-charge layer on and off between LixV2O5 and Li1.5Al0.5Ge1.5(PO3)4 (LAGP), by changing the LixV2O5 potential and selectively measuring the ion transport over the interface by two-dimensional (2D) NMR exchange. The activation energy is demonstrated to be 0.315 eV for lithium-ion exchange over the space-charge-free interface, which increases dramatically to 0.515 eV for the interface with a space-charge layer. Comparison with a space-charge model indicates that the charge distribution due to the space-charge layer is responsible for the increased interface resistance. Thereby, the present work provides selective and quantitative insight into the effect of space-charge layers over electrode-electrolyte interfaces on ionic transport. [Display omitted] •The space-charge layer is controlled through the chemical potential of the electrode•NMR exchange selectively measures Li-ion transport over the space-charge layer•The barrier for Li-ion diffusion increases significantly due to the space-charge layer All-solid-state batteries attract great attention because of their intrinsic safety and high energy density. However, the solid electrolyte-electrode interfaces pose several challenges toward the required Li-ion transport. One of the most difficult processes to expose is the influence of space charges at the electrode-solid electrolyte interface, and thus its effect on battery performance remains unclear. Here, we quantitatively reveal the Li-ion transport over the space-charge layer by 2D NMR exchange experiments, demonstrating that the activation energy for Li-ion exchange increases significantly because of the presence of the space-charge layer, lowering the exchange current density and raising the internal resistance. This work points out the importance to mitigate space-charge layers at the cathode-solid electrolyte interfaces to improve the charge transport in all-solid-state batteries. Direct and quantitative measurement of the effect of space charges in solid-state batteries remains very challenging. Here, we reveal the effect on the Li-ion transport quantitatively by NMR 2D exchange experiments and space-charge lay