Phosphorus-based Materials For High-performance Potassium Ion Batteries

In recent years,with the continuous improvement of energy storage technology,new potassium ion battery has been developed rapidly.Red phosphorus is considered to be the primary choice for the investigation of potassium ion battery anode materials because of its low cost and high theoretical capacity.However,this kind of materials suffer from poor electrical conductivity and large volume expansion during cycling,hindering its application in practical production.Thus,this work aims to modify the red phosphorus and Ni PS₃ materials reasonably to develop phosphorus-based materials with remarkable potassium storage performance.In this thesis,strategies such as constructing different substrates and modulating the material morphology are used to improve electrochemical properties of red phosphorus and Ni PS₃ materials.The main research contents are as follows:Firstly,we started from the perspective of modifying the substrate.Ni O-reduced graphene oxide（r GO）layer modified nickel foam（M-NF）was constructed as a current collector.Red phosphorus nanoparticles were embedded into r GO nanosheets to form a complex（P-r GO）and loaded on M-NF to obtain a binder-free and self-supporting potassium ion battery anode material（P-r GO@M-NF）.The material showed excellent rate performance and outputed a specific capacity of 361.2 m A h g^-1 in tests after 125cycles at a current density of 0.1 A g^-1.The theoretical calculation revealed that the conductivity of red phosphorus was improved and potassium atoms were more readily adsorbed after loading on the Ni O substrate.In addition,the Ni O layer anchored red phosphorus nanoparticles by forming Ni-O-P bonds,which ensured the cyclic stability of the P-r GO@M-NF material.Secondly,the bulk Ni PS₃ material was electrochemically exfoliation into layered structure and the r GO was covered on the sheet Ni PS₃（e NPS）by ultrasound to obtain the composite（e NPS/r GO-n）.The composite not only combined the advantages of the high specific capacity of e NPS and the high conductivity of r GO but also effectively further improved the stability of the materials.Among them,the e NPS/r GO-2 electrode with a high ratio of r GO exhibited excellent electrochemical performance,it could deliver a specific capacity of 193.2 m A h g^-1 after 60 cycles at a current density of 0.1 A g^-1.Finally,Ni PS₃ sheets were embedded in a cross-linked network of nitrogen-doped carbon nanotubes containing Ni particles（Ni-NCNT）.Ni-NCNT were used as precursors and performed one-step phosphorylation-sulfuration reactions at different temperatures to obtain Ni PS₃ materials（NPS/Ni-NCNT-n）.Studies showed that some Ni particles in NCNT were retained in addition to generating Ni PS₃ after the reaction at 550℃.The Ni-NCNT cross-linked network structure limited the size growing as well as the stacking of Ni PS₃.The presence of Ni monomer in NCNT could further improve the electrical conductivity of the material.Combining these advantages,the NPS/Ni-NCNT-2 electrode had a specific capacity of 252.3 m A h g^-1 at the tested current density of 0.1 A g^-1 after100 cycles.When the current density was increased to 1.0 A g^-1,the electrode maintained a reversible specific capacity of 127.7 m A h g^-1 after 1000 cycles.