B, N-co-doped graphene supported sulfur for superior stable Li-S half cell and Ge-S full battery.

B, N-co-doped graphene supported sulfur (S@BNG) composite is synthesized by using melamine diborate as precursor. XPS spectra illustrates that BNG with a high percentage and dispersive B, N (B: 13.47 %, N: 9.17 %) and abundant pyridinic-N and N-B/N=B bond, which show strong interaction with Li2Sx proved by simulation experiments. As cathode for Li-S half cell, S@BNG with a sulfur content of 75 % displays a high capacity of 765 mA h g-1 at 1 C even after 500 cycles with a low fading rate of 0.027 % per cycle. Even at a high sulfur loading of 4.73 mg cm-2, S@BNG still shows a high reversible areal capacity of 3.5 mA h cm-2 after 50 cycles. When S@BNG composite as cathode combines with high performance lithiated Ge anode (discharge capacity of 1138 mA h g-1 at 1 C over 1000 cycles in half cell), the assembled Ge-S full battery exhibits a superior capacity of 530 mA h g-1 at 1 C over 500 cycles.