Solid-state Zn-ion batteries using composite cellulose polyethylene oxide materials-Illustration of reaction and capacity fading mechanisms

In this work, the composite materials of cellulose and poly(ethylene oxide) (PEO) materials as the solidelectrolyte separator was electrochemically and mechanically characterized before being incorporated into solid-state Zn-ion batteries (SSZIBs) with LiFePO4 cathode and Zn anode. As understanding fading mechanisms and operational settings is essential to developing long lasting batteries, we further investigated the mechanisms of LiFePO4 lithiation and de-lithiation in SSZIBs. The capacity fading mechanism was elucidated using ex-situ high energy synchrotron XANES measurements on our developed Zn-ion devices at varying charge rates. Long-term cycling was the focus of these investigations, which tracked and assessed chemical and structural changes. The results show that an increase in inactive FePO4 proportional to the loss of active lithium is the primary driver of capacity fading once the lithium source is depleted. XRD confirm that LiFePO4 exists in an olivine phase and reveal that the insertion and deinsertion behaviour of lithium ions in LiFePO4 changes with cycling. The two phases (LiFePO4, FePO4) and the loss of the lithium source may contribute to the reduced rate capability and capacity fading of LiFePO4 cells during prolonged cycling.