  Understanding microscopic properties of LiNiO$_2$, a Li-ion battery cathode
material with extraordinarily high reversible capacity, has remained a
challenge for decades. Based on extensive electronic structure calculations,
which reveal a large number of nearly degenerate phases involving local
Jahn-Teller effect as well as bond and oxygen-based charge disproportionation,
we propose that LiNiO$_2$ exists in a high-entropy charge-glass like state at
and below ambient temperatures. Recognizing the glassy nature of LiNiO$_2$ does
not only explain its key experimental features, but also opens a new path in
designing entropy-stabilized battery cathodes with superb capacities.
