Nanoscale Interface Modification of LiCoO₂by Al₂O₃Atomic Layer Deposition for Solid-State Li Batteries

Cycle stability of solid-state lithium batteries (SSLBs) using a LiCoO 2 cathode is improved by atomic layer deposition (ALD) on active material powder with Al 2 O 3 . SSLBs with LiCoO 2 /Li 3.15 Ge 0.15 P 0.85 S 4 /77.5Li 2 S-22.5P 2 S 5 /Li structure were constructed and tested by charge-discharge cycling at a current density of 45 μA cm −2 with a voltage window of 3.3 ∼ 4.3 V (vs. Li/Li + ). Capacity degradation during cycling is suppressed dramatically by employing Al 2 O 3 ALD-coated LiCoO 2 in the composite cathode. Whereas only 70% of capacity retention is achieved for uncoated LiCoO 2 after 25 cycles, 90% of capacity retention is observed for LiCoO 2 with ALD Al 2 O 3 layers. Electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM) studies show that the presence of ALD Al 2 O 3 layers on the surface of LiCoO 2 reduces interfacial resistance development between LiCoO 2 and solid state electrolyte (SSE) during cycling.