The specific capacity and energy of batteries with LiCoO2 electrodes can be improved by the addition of Li2RuO3 to the cathodes, particularly at high rates. LiCoO2 is a standard active material used in Li-ion batteries, and Li2RuO3 is a highly stable Li-insertion compound with high electronic and Li-ion conductivity. Batteries with LiCoO2 and Li2RuO3 cathodes are compared to those with blends of the two active materials when discharged from 4.2 to 2.0 V at C/5 and 2C rates. The Li-ion batteries with a 58: 42 w/w LiCoO2/Li2RuO3 blend have a disproportionate increase of 25 and 36%, respectively, in their expected specific capacity and energy relative to LiCoO2 when the batteries are charged and discharged at a 2C rate. X-ray diffraction of the electrodes at a high state of charge confirms that the LiCoO2 and Li2RuO3 phases remain distinct in the electrodes. Analysis of the discharge curves in combination with electrochemical impedance spectroscopy shows that Li2RuO3 lowers the electrical resistance of the electrodes when combined in parallel with the LiCoO2. This simple approach may be used to improve the capacity of Li-ion batteries for high rate applications. (c) 2005 The Electrochemical Society.