Interface Affinity Regulation Of Multi-Dimensional Phosphorus/Carbon Conductive Network For Potassium Storage

Potassium ion batteries(KIBs)have emerged as one of the most promising alternatives to lithium-ion battery due to its abundant potassium storage,low cost and suitable redox potential.However,for most current KIBs anode materials,their inherent large volume variations and slow charge/mass transfer dynamics severely limit longlife cycle,rate performance and further applications.Red phosphorus(RP)is a promising anode for KIBs due to its low cost,non-toxicity,stable chemical properties,high theoretical capacity and ideal redox potential.However,the inherent poor electronic conductivity and large stress caused by huge volume expansion of RP anode remain great hinders for its application.Structurally construction of phosphate-based materials while achieving high electrochemical performance is a challenge for the development of phosphorus-based anodes for high-performance potassium ion batteries.In order to solve the above problems,this dissertation proposed and constructed a“strain-relaxation" freestanding three-dimensional RP anode composite(RP@S-NCNFs)via designing an interface affinity engineering.And established a dynamic model of material evolution under electrochemical action.Red phosphorus was encapsulated in sulfur and nitrogen co-doped carbon nanofibers(RP@S-N-CNFs)via freeze-drying,high temperature and evaporative condensation.The close relationship between structure and properties was clarified by exploring the interface regulation mechanism of materials and doping elements.At the same time,the mechanism of potassium storage in the electrochemical process was explored and analyzed.In addition,the intrinsic reason for its excellent performance was revealed by in situ characterization technique and theoretical calculation.The main results are as follows:1.Using bacterial cellulose membrane as a three-dimensional self-supporting carbon network,and the amorphous red phosphorus was uniformly confined in the pores of sulfur and nitrogen co-doped carbon nanofibers by changing the types of doping elements.The theory calculation show that the adsorption energy of red phosphorus atom on the doped carbon matrix is increased by the design of sulfur and nitrogen co-doping and the construction of surface interface affinity engineering.Electrochemical test results show that the discharge capacity can reach 282 mAh g-1 at a current density of 2.0 A g-1 for 2000 cycles.2.The K+storage mechanism of RP materials was revealed by in-situ Raman,exsitu XRD tests,and combining with electrochemical performance tests:the highly reversible one-electron transfer mechanism and the final KP discharge product(865 mAh g-1).In addition,electrochemical testing and analysis combined with theoretical calculations show that sulfur and nitrogen co-doping improves the K+adsorption kinetics and diffusion kinetics,enabling fast charge transfer at the red phosphorus anode.3.Further in situ TEM experiments reveal the stable structure integrity of the electrode and a complete shrink observed for the first time come from the spontaneous polymerization of potassiation nanocrystals,which can adaptively release strain and stabilize the electrode structure.The finite element simulation provided in-depth understanding of the strain-relaxation behavior during cycling,and established a dynamic model of the material evolution under electrochemical action.Due to the unique strain relaxation mechanism,the resultant RP@S-N-CNFs anode manifests superior electrochemical potassium storage properties including high specific capacity,excellent rate capability and ultra-long cycling stability.