The Synthesis And Application Of Prussian Blue Analogue Derived Composite Materials In Sodium-ion Battery Anodes

It is of great importance to develop green and recyclable energy storage techniques under the circumstance of globally increasing energy demand,depletion of unrenewable fossil fuel and global warming.Since Lithium-ion batteries?LIBs?based on LiCoO2 cathode and graphite anode were first successfully commercialized in 1990s,the seek for low-cost and high-performance energy storage technology is always the hot topic in both industry and academic study.Sodium-ion batteries?SIBs?are drawing considerable attention because of their low cost and outstanding electrochemical performance.Searching for electrode materials which can exploit the advantages of SIBs is one of tho important topics.Prussian blue analogues?PBA?is a family of transition metal coordination compounds with three-dimensional micro/nano structures and adjustable chemical compositions,from which composite electrode materials that can improve the performance of SIBs are expected to be derived due to PBAs' unique structural and chemical properties.In this dissertation,different PBAs are used as precursors,through composition control and micro-structure design,several types of transition metal selenides,phosphides,sulfides and carbonaceous materials were developed by wet chemistry,heat treatment and gas-phase reactions.The electrochemical performance of these PBA derivatives are systematically tested and studieid as anodes of SIBs.The study proved that these PBA derivatives could effectively solve the problems such as huge volume change and low conductivity in SIBs application,thus improving the cycling stability and rate performance.The detailed works are listed below:1.Dual-carbon confined CoSe₂ microbox?DCC-CoSe₂?is prepared using Co₃[Co?CN?₆]₂ Prussian blue analogue?Co-Co PBA?as precursor,via polydopamine?PDA?coating,gas-phase reaction methods.The DCC-CoSe₂ preserved the cubic structure of Co-Co PBA precursor,the double carbon layer coating the CoSe₂ nanoparticles prevents the structure destruction during cycling and improves the conductivity.Thus,effectively enhances the cycling stability and rate capability,as well as keeping a high capacity.A high specific capacity of45o mAh g^-1 is achieved at a current density of 100 mA g^-1 after 100 cycles and the capacity can still be up to 480 mAh g^-1 at 100 mA g^-1,in rate performance test,the capacity can remain 281 mAh g^-1 at a current density of 5000 mA g^-1 and restore 95%of the capacity when switched back to a small current density of 100 mA g^-1.Additionally,the Na3V2?PO4?3/DCC-CoSe₂ full cell can stably charge and discharge for over 200 cycles under a current density of 500 mA g^-1.N-doped dual carbon?NDC?is prepared by etching the precursor with acid.The NDC electrode presents an exeellent rate capability,and achieves a capacity of 140 and 98 mAh g^-1 under a current density of 0.1 and 5 A g^-1,respectively.2.Carbon confined NiSe₂,NiS₂ and Ni₂P[CC-NiSe₂,CC-NiS₂ and CC-Ni₂P)are prepared with Ni₃[Co?CN?₆]₂ Prussian blue analogue?Ni-Co PBA?as precursor via PDA coating,ion exchange and gas-phase reaction.Proving Ni-Co PBA can be used as a universal precursor for multiple pure-phased SIB electrode materials.CC-NiSe₂,CC-NiS₂ and CC-Ni₂P achieved a capacity of 386 mAh g^-1,354 mAh g^-1 and 442 mAh g^-1,respectively,under a current density of 100mA g^-1.And achieved a capacity of 244 mAh g^-1,197 mAh g^-1 and 340 mAh g^-1,respectively,under a current density of 2000 mA g^-1.In rate stability test,after cycling under a high rate of 5000 mA g^-1,the capacity retention of CC-NiSe₂,CC-NiS₂ and CC-Ni₂P are 94%,87%and 91%,respectively.3.N-doped carbon confined CoSe₂?NCC-CoSe₂?is prepared with Zn₃[Co?CN?₆]₂ Prussian blue analogue?Zn-Co PBA?as precursor via gas-phase reaction,selectively acid etching and thermal treatment.NCC-CoSe₂ material derived from Zn-Co PBA achieved a capacity of 332 mAh g^-1 at a current density of 100 mA g^-1,and a capacity of 232 mAh g^-1 at a current density of 5000 mA g^-1.When compared with NCC-ZnSe₂/CoSe₂ electrode,NCC-CoSe₂ electrcyde exhibits a greatly improved rate capability.The carbon structure derived from Zn-Co PBA helps to improve the structural stability and conductivity of NCC-CoSe₂,and single-phased CoSe₂ prevents the structural damage caused by the tension between different metal selenides in charge/discharge cycles,thus ensuring improved cycling stability and rate performance when comparing with control group composed by mixed transition metal selenides.