Superior dual-ion batteries enabled by mildly expanded graphite cathode and hierarchical MoS2@C anode

Abstract

Dual-ion batteries (DIBs) have received tremendous attention due to the high energy density provided by the high operating voltage and the low cost as a result of the abundance of active materials. However, the overall performance of known DIBs is far below expectations. In particular, graphite cathode with fast charge/discharge abilities and high-capacity anode materials still need to be further explored. Herein, a sophisticated overall DIB design is proposed by employing a mildly expanded graphite (MEG) as the cathode and a hierarchical carbon coated MoS2 sphere (MoS2@C) as the anode. MEG with suitable layer spacing facilitates the intercalation/de-intercalation of the large size anions, greatly enhancing the reaction kinetics. The distinctive structural design of MoS2@C not only shortens the Li+ diffusion channel, but also improves the electrical conductivity and significantly relieves the volume expansion during repeated cycles. The as-built MEG-2//MoS2@C-800 full DIB demonstrates better specific capacity and higher discharge medium voltage (77.29 mAh g−1 at 1 C and discharge medium voltage remains above 3.5 V after 200 cycles). More impressively, this DIB can deliver an outstanding energy density of 286.97 Wh kg−1 at the power density of 775.59 W kg−1, which is superior to other energy storage devices including Ni-Cd batteries, lead-acid batteries, electrochemical capacitors, Li-ion batteries and most previously reported DIBs.