Preparation And Properties Of High-performance Anode Materials For Energy Storage Batteries

With the increasing demand in the renewable energy,development and exploitation of clean energy are more urgent than before.As the highly-efficient energy storage and conversion devices,lithium-ion and sodium-ion batteries have attracted more attention in the past decades.However,one of the most important issues that limits the energy and power densities of rechargeable batteries is the low theoretical capacity of commercial graphite.Among the next-generation anode materials for lithium-ion batteries,Mo-based transition metal oxides are widely considered as the potential anode owing to the multiple electron reaction with the result of high theoretical capacity.Furthermore,low-cost sodium-ion batteries attracted more attention than before because of ever-growing price of lithium carbonaceous as well as lithium-ion batteries.Metal Sb with the advantages of natural abundance,low cost,and high theoretical capacity is a promising anode material for lithium-ion batteries.In this thesis,we start from the functional design of anode materials,and then select proper synthesis methods to acquire high-performance electrode materials for lithium-ion and sodium-ion batteries applications.Furthermore,the energy storage mechanism and reaction processes are also investigated,which is beneficial to the design of novel anode materials with high specific capacity.The main conclusions are summarized as following:Firstly,we prepared Ag₂Mo₂O₇ micro-rods materials via hydrothermal method.The electrochemical performance and ionic storage mechanism in lithium ion batteries are comprehensively studied.The Ag₂Mo₂O₇ materials could deliver a high specific capacity of 868 m A h g-1,and maintain 825 m A h g-1 after 100 cycles with the capacity retention of 95%.We also studied the lithium-ion storage mechanism of Ag₂Mo₂O₇ as an anode material by using ex-situ XRD and HRTEM.Ag₂Mo₂O₇ electrode decomposes into amorphous Mo and Ag nanoparticles during the first discharge process,and the conversion reaction of the molybdenum element is response for the high capacity during the subsequent electrochemical cycles.The generated Ag nanoparticles do not participate in the electrochemical reaction,and form a uniform conductive network to enhance the electronic conductivity of the working electrode,resulting in the improvement of the rate performance.Secondly,we devoted to the design and synthesis of new anode materials for sodium-ion batteries.The Ti₃C₂T_x@Sb nanocomposite materials were synthesized by liquid phase reduction method for the first time,in which Sb nanoparticles are in-situ decorated on the surface of MXene?Ti₃C₂T_x?.The best synergistic effect can be achieved by adjusting the different composite ratio of high conductivity material Ti3C2 Tx and high capacity material Sb.The Ti₃C₂T_x@Sb-0.5 shows the best cycling performance and rate performance,in which the capacity retention is almost 92.3% even after 8000 cycles at the current density of 1 A g-1.The outstanding sodium storage performance of Ti₃C₂T_x@Sb-0.5 composites can be understood as followings: On the one hand,the layer structure of Ti3C2 Tx can effectively suppress the huge volume expansion of Sb alloying reaction;On the other,the volume expansion of Sb can enlarge the spacing of Ti3C2 Tx layer beneficial to the sodium insertion reaction.The synergistic effect of the abovementioned two effects is beneficial to acquire a long-term stability and high-rate capability.In this dissertation,we focus on the relative scientific questions related to the electrochemical conversion and alloying reactions.We designed and synthesized the anode materials with superior electrochemical performance by optimizing the preparation conditions.The research strategy and content in this thesis would contribute to the theoretical and experimental design of high-capacity type anode materials in future.