Towards high-volumetric performance of Na/Li-ion batteries: a better anode material with molybdenum pentachloride-graphite intercalation compounds (MoCl5-GICs)

Molybdenum pentachloride (MoCl5)-graphite intercalation compounds (GICs) have remarkably high chemical stability, electronic conductivity and bulk density among various transition metal chloride-GICs, but its electrochemical performance has not yet been exploited. Here for the first time we report MoCl5-intercalated GICs as excellent anode materials for sodium and lithium storage. The MoCl5 species are effectively intercalated and tightly immobilized between the adjacent graphite layers to form acceptor-type GICs with adjustable stage 1 and stage 2 structures. This study reveals that the intercalated MoCl5 monolayers can induce a strong charge transfer chemical doping effect with a high electronic conductivity of 2.8 x 10(5) S cm(-1) and increase the moderate interlayer distance of graphite layers with a high tap density of 1.55 g cm(-3), thus making the GICs promising electrodes for electrochemical batteries. As a result, the MoCl5-GIC anode delivers high gravimetric/volumetric capacities of 275 mA h g(-1) and 426 mA h cm(-3) for sodium-ion batteries, respectively. In lithium-ion batteries, a reversible lithium capacity of 1099 mA h g(-1) (1703 mA h cm(-3)) is stably maintained after 100 cycles. More importantly, the strong interaction force between MoCl5 and graphite layers helps to firmly immobilize soluble chlorides during repeated charge/discharge processes, leading to excellent sodium storage cyclability with nearly no capacity loss during 1000 cycles. The excellent structural stability and high electrical conductivity allow it to be designed into thick electrode films with a tunable thickness up to 120 mu m, resulting in a state-of-the-art areal capacity reaching 0.88 mA h cm(-2). Our findings open a new avenue to modulate the intercalant species in graphite as high-performance electrode materials for electrochemical ion storage.