Multi-ion defect model for space-charge layer formation at LiPON/LixV2O5 electrochemical interfaces

Space-charge layers (SCLs) at heterogeneous interfaces generate electrostatic potential drops that can enhance or impede ionic and electronic transport near the interface. In solid-state Li-ion batteries, previous models typically only consider Li-ions as the mobile defect, even though cations, anions, and electrons can all participate in SCL formation. Here, we introduce a general first-principles defect-based framework to quantify these multi-species contributions and apply it to LiPON/Li x V 2 O 5 interfaces ( x = 0, 1, 2 for the alpha, delta, and gamma phases). A systematic screening of charged point defect formation energies identified Li-ion vacancies, Li-ion interstitials, and O-ion vacancies as dominant species. The model reveals spontaneous Li-ion transfer from LiPON into Li x V 2 O 5 and O-species transfer in the opposite direction, behaviors missed by Li-only treatments. Band alignments across the interfaces show electrons initially transferring from LiPON into V 2 O 5 , however, when the lithium content increases in Li x V 2 O 5 , the direction of electron transfer reverses. Consequently, the predicted band-bending switches from downward bending in V 2 O 5 to upward bending in the LiV 2 O 5 and Li 2 V 2 O 5 phases. The implications of these SCL-induced potentials for Li-ion and electron transport are discussed for solid-state batteries and electrochemical neuromorphic devices, highlighting the importance of explicitly accounting for multi-ion defect transfer.