Depolarized and fully active cathode based on Li(Ni0.5Co0.2Mn0.3)O2 embedded in carbon nanotube network for advanced batteries.

Improving battery capacity and power is a daunting challenge, and in Li-ion batteries positive electrodes often set the limitation on both properties. Layered transition-metal oxides have served as the mainstream cathode materials for high-energy batteries due to their large theoretical capacity (∼ 280 mAh/g). Here we report a significant enhancement of cathode capacity utilization through a novel concept of material design. By embedding Li(Ni0.5Co0.2Mn0.3)O2 in the single wall carbon nanotube (CNT) network, we created a composite in which all components are electrochemically active. Long-term charge/discharge stability was obtained between 3.0 and 4.8 V, and both Li(Ni0.5Co0.2Mn0.3)O2 and CNT contribute to the overall reversible capacity by 250 and 50 mAh/g, respectively. The observed improvement causes significant depolarization within the electrodes through the CNT network system. Additionally, the depolarization provides the ideal template to understand the solid reaction mechanism of Li(Ni0.5Co0.2Mn0.3)O2 by demonstrating well-defined two-stage delithiation kinetics consistent with first-principle calculations, which would be otherwise impossible. These results deliver new insights on both practical designs and fundamental understandings of battery cathodes.