Are Polymer-Based Electrolytes Ready for High-Voltage Lithium Battery Applications? An Overview of Degradation Mechanisms and Battery Performance

High-voltage lithium polymer cells are considered an attractive technology
that could out-perform commercial lithium-ion batteries in terms of safety,
processability, and energy density. Although significant progress has been
achieved in the development of polymer electrolytes for high-voltage applications
(> 4 V), the cell performance containing these materials still encounters
certain challenges. One of the major limitations is posed by poor cyclability,
which is affected by the low oxidative stability of standard polyether-based
polymer electrolytes. In addition, the high reactivity and structural instability
of certain common high-voltage cathode chemistries further aggravate
the challenges. In this review, the oxidative stability of polymer electrolytes
is comprehensively discussed, along with the key sources of cell degradation,
and provides an overview of the fundamental strategies adopted for
enhancing their cyclability. In this regard, a statistical analysis of the cell
performance is provided by analyzing 186 publications reported in the last
17 years, to demonstrate the gap between the state-of-the-art and the requirements
for high-energy density cells. Furthermore, the essential characterization
techniques employed in prior research investigating the degradation
of these systems are discussed to highlight their prospects and limitations.
Based on the derived conclusions, new targets and guidelines are proposed
for further research.