Preparation Of Metal Sulfide /Selenide/Oxide Nano-composites And Their Applications As Anode Materials For Flexible Lithium/Sodium Ion Batteries

Lithium/sodium ion batteries?LIBs/SIBs?have been widely used in portable electronic devices and electric vehicles owing to their high energy density,environmental friendliness and long cycling performance.Considering the practical application,the current energy density of LIBs still needs to be further improved.However,the electrode still face some fatal problems,such as low ion/electron conductivity,poor stability and poor rate performance.It is strongly urgent to explore the new electrode materials with both high power densities and long-life cycling ability.The electrochemical performances of electrodes are highly dependent on their structure,conductivity and reactivity with Li/Na.Therefore,great efforts have been made on improvement of ion/electron conductivity and design of novel architectures to achieve high-performance electrode materials for LIBs/SIBs.Several candidate materials,such as Fe₂O₃,Nb₂O₅,MoS₂,MoSe₂,and Mo₂C with various hybrid architectures have exhibited excellent performances,it is of great importance to explore novel electrode materials with high reversible capacity and long cyclability to meet with the increasing flexible electronic devices markets.The carbon cloth?CC?woven by carbon fibers possesses a series of advantages,such as good flexibility and high electrical conductivity,and can be used as flexible/wearable electrode substrate.So,it is imperative to design and fabricate the active electrode materials on CC to promote their applications in flexible devices.The main research contents are as follows:?1?We report a hierarchical architecture consisting of the interconnected carbon fiber cloth network decorated with MoS₂ microflowers through in situ hydrothermal method and the subsequent calcination treatment.The MoS₂/CC can be directly used as flexible binder-free anode without NMP,it shows amazing cyclicality and high reversible capacity for both lithium and sodium storages As for lithium ion batteries,the MoS₂/carbon cloth composite delivers a high specific capacity of 1263 mAh g^-1after cycled for 100 times at 0.1 A g^-1.A rate capacity of 838 mAh g^-1 can be obtained at 2.0 A g^-1 after 100 cycles.A reversible capacity of 515 mAh g^-1 can be retained after 100 cycles at a current density of 0.1 A g^-1 in sodium ion batteries.The enhanced electrochemical properties can be attributed to the following effects:?1?the carbon cloth offers an amazing conductivity environment without the addition of insulative binder or additive;?2?the sheet-like structure of MoS₂ provides the short Li ions diffusion path and can accommodate stress during cyclings;?3?the novel 3D architecture ensures the well preserved structural integrity.These results show the MoS₂/carbon cloth composites hold great promise as flexible anodes for practical applications in next-generation lithium/sodium ion batteries.?2?We designed MoSe₂@carbon cloth?MoSe₂@CC?composites through an in situ hydrothermal approach followed by annealing.The as-synthesized MoSe₂@CC composites are constructed by MoSe₂ nanoflowers assembled by sheet-like MoSe₂layers anchored on CC network,which can be used as anodes directly for LIBs and SIBs without organic solvent or binder.As expected,the as-prepared MoSe₂@CC composites perform excellent lithium storage,such as,superior rate capacity(1337,1092,952,831 and 749 mAh g^-1 at current densities of 0.1,0.2,0.5,1.0,and 2.0 A g^-1.)and super long-life cycling stability(638 mAh g^-1 remains even after 1200 cycles at5.0 A g^-1).As for SIBs,the MoSe₂@CC electrode delivered a high initial discharge capacity of 839 mAh g^-1 and long-life cycling stability,retaining 202 mAh g^-1 after1000 cycles with an average capacity fading of 0.012%per cycle after the second cycle.Kinetics results indicate that the Li⁺and Na⁺storages are both pseudocapacitive dominating process,thus greatly improve the rate performance for LIBs/SIBs.The CC provides a conductive network and more electrochemical accessible active sites to improve the electrochemical performance.?3?We prepare Nb₂O₅@GO composites by a facile ultrasonic-assisted hydrothermal method.The SEM and TEM results confirm that the Nb2O5nanoparticles with sizes of¹00 nm distributed uniformly on the surface of graphene nanosheets.The graphene nanosheets can form a three-dimensional network for the transportation of Li⁺/Na⁺ions and electrons.As for LIBs,the Nb₂O₅@GO composite delivers a high capacity of 382 mAh g^-1 after 100 cycles at 0.1 A g^-1.A rate capacity of183 mAh g^-1 can be obtained at 2 A g^-1 after 100 cycles.A reversible capacity of 210mAh g^-1 can be retained after 100 cycles at a current density of 0.1 A g^-1 in SIBs.At a current density of 5.0 A g^-1,the Nb₂O₅@GO achieved a higher reversible density of210 mA h g^-1 after 1000 cycles in LIBs.As for sodium storage,the Nb₂O₅@GO still maintains a reversible capacity of 52 mAh g^-1 after 1000 cycles.This unique architecture can maintain the structural integrity of the electrode during the charge/discharge processes.