posted on 2024-03-14, 15:06authored byJianli Cheng, Xinxing Peng, Ya-Qian Zhang, Yaosen Tian, Tofunmi Ogunfunmi, Andrew Z. Haddad, Andrew Dopilka, Gerbrand Ceder, Kristin A. Persson, Mary C. Scott
All solid-state batteries (SSBs) are considered the most
promising
path to enabling higher energy-density portable energy, while concurrently
improving safety as compared to current liquid electrolyte solutions.
However, the desire for high energy necessitates the choice of high-voltage
cathodes, such as nickel-rich layered oxides, where degradation phenomena
related to oxygen loss and structural densification at the cathode
surface are known to significantly compromise the cycle and thermal
stability. In this work, we show, for the first time, that even in
an SSB, and when protected by an intact amorphous coating, the LiNi0.5Mn0.3Co0.2O2 (NMC532) surface transforms from a layered structure into a rocksalt-like
structure after electrochemical cycling. The transformation of the
surface structure of the Li3B11O18 (LBO)-coated NMC532 cathode in a thiophosphate-based
solid-state cell is characterized by high-resolution complementary
electron microscopy techniques and electron energy loss spectroscopy.
Ab initio molecular dynamics corroborate facile transport of O2– in the LBO coating and in other typical coating materials.
This work identifies that oxygen loss remains a formidable challenge
and barrier to long-cycle life high-energy storage, even in SSBs with
durable, amorphous cathode coatings, and directs attention to considering
oxygen permeability as an important new design criteria for coating
materials.