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Spatio-Chemical Deconvolution of the LiNi0.6Co0.2Mn0.2O2/Li6PS5Cl Interphase Layer in All-Solid-State Batteries Using
Barthélémy Lelotte1, Carlos A F Vaz2, Linfeng Xu1
1PSI Center for Energy and Environmental Sciences, 5232 Villigen PSI, Switzerland.
ACS Applied Materials & Interfaces
|February 24, 2025
Summary
Investigating the interface between Li6PS5Cl and NCM622 solid-state batteries reveals that initial impedance rise is due to inactive surface layer formation and contact loss. Further resistance increases may stem from LPSC polymerization and NCM622 structural changes.
Area of Science:
- Materials Science
- Electrochemistry
- Solid-State Batteries
Background:
- Solid-state electrolytes offer enhanced safety for next-generation batteries.
- Understanding interfacial degradation is crucial for improving solid-state battery performance.
- Li6PS5Cl (LPSC) and LiNi0.6Co0.2Mn0.2O2 (NCM622) are promising materials for solid-state batteries.
Purpose of the Study:
- To systematically investigate the electrochemical degradation at the LPSC-NCM622 interface.
- To correlate interphase evolution with battery performance using advanced characterization techniques.
- To elucidate the mechanisms behind impedance rise during battery cycling.
Main Methods:
- Nondestructive synchrotron X-ray absorption spectroscopy and X-ray photoemission electron microscopy for surface chemical depth profiling and elemental imaging.
- Galvanostatic cycling, impedance spectroscopy, and operando cell pressure measurements.
- Analysis of both LPSC and NCM622 particles to understand interfacial reactions.
Main Results:
- Identified polysulfide byproducts and LPSC particle contact loss as causes of initial cell resistance increase.
- Detected SO3^2-, SO4^2-, and PO4^3- species and reduced transition metals on NCM622 surfaces after initial charge.
- Observed interphase thickness below ~3 nm on both LPSC and NCM622 surfaces.
- Found that initial impedance rise is primarily due to inactive NCM622 surface formation and LPSC byproducts.
Conclusions:
- The formation of an electrochemically inactive NCM622 surface layer is a primary cause of impedance rise during the first charge.
- LPSC byproducts and particle contact loss also contribute to initial resistance increase.
- Continuous resistance increase after the first charge is hypothesized to result from LPSC polymerization and NCM622 structural changes, not further interphase growth.
