Elevating the charging voltage of lithium-ion batteries with a
LiCoO2
cathode is investigated to develop them toward high capacity and energy density. Three countermeasures are found to be essential to overcome side reactions with subsequent cycle degradations caused by higher cathode potential:
(i)
limiting the charging cut-off potential below
4.5V
vs
Li∕Li+
for the
LiCoO2
cathode,
(ii)
modification of
LiCoO2
particles with
Zr
element, and
(iii)
controlling the ratio of ethylene carbonate in electrolyte, which is found to be a major cause of cycle degradation in an elevated charging potential condition. It is suggested that ethylene carbonate is oxidized and dissolves cobalt on the surface of the
LiCoO2
cathode, degrading cycle performance especially at high potentials. Raising the charging voltage up to 4.4 from
4.2V
for a
650mAh
class test cell demonstrates 10% higher cell capacity with 20% higher
LiCoO2
capacity of
190mAhnormalg−1
and practical cycle performance up to 500 cycles.
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