(LiNi 0.5 Co 0.2 Mn 0.3 O 2  + AC)/graphite hybrid energy storage device with high specific energy and high rate capability

In this work, we have fabricated a novel hybrid electrochemical energy storage device with composite cathode containing LiNi0.5Co0.2Mn0.3O2 and activated carbon (AC), and graphite anode. The specific energy increases with the content of LiNi0.5Co0.2Mn0.3O2 in composite cathode. The hybrid device possesses a specific energy 5.7 times higher than that of the electrical double layer capacitor. Meanwhile, the hybrid device can deliver 62.6% and 42.1% of its capacity at the rate of 30C and 50C, respectively. A 107.8-mAh hybrid device has been assembled, and the specific energy of 36.2 Wh kg−1 can be achieved at an average specific power of 39.1 W kg−1, even 8.9 Wh kg−1 at 2380 W kg−1. Combining the high specific energy with the high power capability, the (LiNi0.5Co0.2Mn0.3O2 + AC)/graphite hybrid system has demonstrated high performances for electrochemical energy storage applications.