Lithium-ion batteries are the main representatives of electrochemical energy storage
systems. However, their further use is limited due to safety risks associated with
flammable liquid organic electrolytes. In solid-state batteries, liquid electrolytes are
replaced with solid ones, which increases the safety of the system while also enabling the
use of metal lithium anodes with significantly higher specific capacity. Polyethylene
oxide is a common choice for the preparation of solid polymer electrolytes, as it can
coordinate with Li$^+$ ions, is easy to form and is chemically inert. However, the main
limitations of PEO-based solid electrolytes are their limited ionic conductivity at room
temperature and electrochemical instability when in contact with high-voltage cathodes.
We chose nickel-rich NMC as a promising cathode active material, but in combination
with solid electrolytes, it can cause problems due to chemical instability and poor kinetics.
One possible solution to these problems is the use of polymer surface coatings, which act
as a protective layer between the cathode and the electrolyte. As part of the master's thesis,
we studied the effect of polymer coatings on NMC particles on electrochemical
properties. We assembled cells with NMC cathodes, solid PEO-based electrolytes and a
metallic lithium anode. We characterised the polymer solid electrolytes by determining
their ionic conductivity, critical current density and electrochemical stability window.
Galvanostatic measurements enabled us to compare the performance of cells with coated
and uncoated NMC at different cathode thicknesses and voltage ranges. We found that
coatings improve performance at lower voltages and current densities, while at higher
current densities, a coating degradation and the cell efficiency reduction occur.
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