Kinetics-Controlled Degradation Reactions at Crystalline LiPON/Li_xCoO₂ and Crystalline LiPON/Li-Metal Interfaces

Graphical Abstract

Stable faces from two sides: In solid-state batteries, lithium/lithium phosphorous oxynitride (LiPON) and Li_xCoO₂/LiPON interfaces are predicted to be thermodynamically unstable. Experiments suggest that more substantial disorder exists at the cathode interface. Using DFT methods and LiPON models with atomic layer deposition-like stoichiometry, we predict much faster degradation rates at Li_xCoO₂/LiPON interfaces. LiPON structural motifs which readily react are identified.

Abstract

Detailed understanding of solid–solid interface structure–function relationships is critical for the improvement and wide deployment of all-solid-state batteries. The interfaces between lithium phosphorous oxynitride (LiPON) solid electrolyte material and lithium metal anode, and between LiPON and Li_xCoO₂ cathode, have been reported to generate solid–electrolyte interphase (SEI)-like products and/or disordered regions. Using electronic structure calculations and crystalline LiPON models, we predict that LiPON models with purely P−N−P backbones are kinetically inert towards lithium at room temperature. In contrast, transfer of oxygen atoms from low-energy Li_xCoO₂(104) surfaces to LiPON is much faster under ambient conditions. The mechanisms of the primary reaction steps, LiPON structural motifs that readily reacts with lithium metal, experimental results on amorphous LiPON to partially corroborate these predictions, and possible mitigation strategies to reduce degradations are discussed. LiPON interfaces are found to be useful case studies for highlighting the importance of kinetics-controlled processes during battery assembly at moderate processing temperatures.