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 4.5 V 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 4.2 V for a 650 mAh class test cell demonstrates 10% higher cell capacity with 20% higher LiCoO2 capacity of 190 mAh g(-1) and practical cycle performance up to 500 cycles. (c) 2008 The Electrochemical Society.