All-Solid-State Battery Using Interface Engineering of Garnet-Type Solid Electrolytes

Abstract

Currently, the demand for lithium-ion batteries is high due to its application in portable electronics, electric vehicles, and grid energy storage.1-2 The safety threat imposed by the liquid organic electrolyte can be eliminated by employing solid-state electrolytes (SSEs) that would also potentially enable the use of lithium metal anode (highest theoretical capacity, 3861 mAh g-1).3 Among several SSEs, garnet-type SSEs are comparatively stable with metallic lithium and they possess a wide electrochemical stability window.4 However, there are several unaddressed issues like the high interfacial resistance, instability of garnets in moisture containing atmosphere, propagation of lithium dendrites, etc. that hinders their practical application.3 Our investigation focuses on the removal of the detrimental lithium carbonate and lithium hydroxide layers from the surface of the garnets using two methods, namely argon-ion sputtering and ultra-high vacuum annealing. Precise control of the surface contaminant removal was achieved using in-situ X-ray photoelectron spectroscopy (XPS).5 The pristine garnet surface was found to be extremely atmosphere sensitive through XPS measurements. To overcome the sensitivity issue, atomic layer deposition (ALD) of 3 nm of h-BN was carried out using tris(dimethylamino)borane and ammonia precursors at 450 oC. The initial layers close to the garnet were present in an oxidized form (BNxOy) due to the oxygen-rich composition of garnet and the h-BN was capped over these layers, which were confirmed using angle-resolved XPS. The interfacial resistance drastically reduced from 1145 to 18 Ω cm2 through these processes. The inherent insulating nature of h-BN blocked the leakage of electrons across the solid-electrolyte and prevented the propagation of lithium dendrites. This enabled the plating and stripping of lithium in a symmetrical cell at a current density of 0.5 mA cm-2 with uniform polarization for over 200 hours. All-solid-state battery assembled using LiFePO4 cathode and Li anode exhibited stable cycling with a capacity of 130 mAh g-1 with minimum capacity fade.