Low temperature properties of the Li[Li0.2Co0.4Mn0.4]O2 cathode material for Li-ion batteries

The electrochemical properties of Li[Li0.2Co0.4Mn0.4]O2 were studied at room temperature and − 20 °C. EIS study showed that the electrochemical kinetics of the first charge was more sluggish than subsequent cycles, which became even worse at − 20 °C. This made it difficult for the material to achieve a sufficient oxygen loss reaction at low temperature. XPS analysis showed that almost all of the Mn4+ ions in the material were activated at room temperature, whereas only a few of them were activated at − 20 °C. As a result, the material showed a high discharge capacity of 246 mAh g−1 at room temperature, comparing to the 155 mAh g− 1 at − 20 °C. However, the inactive Mn4+ ions in the electrode suppressed the dissolution of manganese and the Jahn–Teller distortion of the material lattice, both of which resulted in excellent cycle life at low temperature.

► Low temperature electrochemical properties of Li-riched layered cathode materials.
► The loss of oxygen and activation of Mn4+ are strongly temperature dependent.
► Li[Li0.2Co0.4Mn0.4]O2 shows a high discharge capacity of 155 mAh g− 1 at − 20 °C
► The excellent cycle life at low temperature is due to the high concentration of Mn4+ in the electrode.