A South Korean research team has answered a long‑standing question for developers of solid‑state batteries: how thin a protective coating on the cathode can be before it stops working. The answer is 2.5 nanometers, a number that gives battery engineers a clear lower bound for the first time. [1]
The team, led by Professor Tae Joo Park of Hanyang University’s Department of Materials Science and Chemical Engineering, used a rotary‑type powder atomic layer deposition (ALD) system to apply lithium niobium oxide (LNO) coatings at thicknesses of 1.0 nm, 2.5 nm, and 5.0 nm onto NCM811 cathode powders. The coated powders were assembled into sulfide‑based all‑solid‑state cells for electrochemical testing.
The results showed a clear trade‑off. The thinnest 1.0 nm coating delivered the highest initial discharge capacity (229 mAh g⁻¹), but its cycle life was 28% shorter than that of the 2.5 nm and 5.0 nm cells, and its interfacial resistance was 59% higher. Spectroscopic analysis confirmed that side reactions between the cathode and the solid electrolyte were effectively suppressed only when the coating reached at least 2.5 nm.