Preparation And Electrochemical Properties Of MoS₂/Carbon Composites

Lithium-ion batteries have become one of the most promising ways to store energy in the future due to their high specific capacity,long cycle life,and environmental friendliness.Among a series of anode materials,molybdenum disulfide（MoS₂）makes lithium ion intercalation and deintercalation conveniently due to the layered structure,and has high specific capacity,which makes it promising candidate to be one of the commercialized anode materials.However,the restack caused by volume expansion and the intrinsic poor conductivity make it’s cycling and rate performance unsatisfactory.Petal-like graphene oxide-MoS₂（GO-MoS₂）composites are prepared by the hydrothermal method.The structural characterizations confirm the metallic phase（1T）of MoS₂ sheets with a few layers,and the uniform distribution of graphene oxide（GO）and MoS₂.However,the functional groups on the surface of GO and the intrinsic low conductivity of MoS₂ lead to the poor electrochemical performance of GO-MoS₂ in lithium ion batteries.N-doped GO-MoS₂（N-GO-MoS₂）composites are prepared by N plasma treatment on GO-MoS₂ composites at room temperature.N is clearly confirmed to be doped into both GO and MoS₂ uniformly,and MoS₂ changes to semiconducting phase（2H）.In lithium-ion batteries,it is found that the initial capacity increases from 561.4 mAh·g^-1 for GO-MoS₂ to 726.9 mAh·g^-1 for N-GO-MoS₂ at 1 C.After 100 cycles,N-GO-MoS₂ still exhibits capacity of 592.7mAh·g^-1(1.34 mAh·g^-1 loss per cycles and 81.5%capacity retention rate),which is much better than that of GO-MoS₂(only 31.6 mAh·g^-1 after 100 cycles).The significantly improved high-rate cycling electrochemical performance for N-GO-MoS₂ can be attributed to the improved stability of MoS₂ by the phase transition from 1T to 2H,the enhanced electron transportation by the reduction of GO to graphene and the simultaneous N doping in MoS₂ and GO.In order to further improve the electrochemical performance of MoS₂,we optimized the previous experiment in two aspects.One is to increase the content of GO in the sample,and the other is to synthesize MoS₂ with the L-cysteine assisted synthesis.The presence of L-cysteine can not only make the growth of MoS₂ directly on GO,but also reduce GO to graphene.Plasma treatment technology with the help of L-cysteine assisted synthesis can almost completely reduce GO to graphene with the simultaneous N doping in MoS₂ and graphene.N-rGO-MoS₂ has stable electrochemical performance and excellent high rate performance,the specific discharge capacity of N-rGO-MoS₂ have 1286.11 and 635.77 mAh·g^-1 at 500 mA·g^-1before and after 400 cycles while GO-MoS₂ is only 831.03 and 477.49 mAh·g^-1.The N-rGO-MoS₂ with the assisted synthesis of L-cysteine and plasma treatment significantly improves the cycle stability and rate performance of MoS₂ as an anode electrode material.