Low Pressure Crystallization Method Of Black Phosphorus Preparation And Its Application In Lithium/Sodium-Ion Battery

A new two-dimensional materials named black phosphorus as anode materials for lithium/sodium-ion battery has high theoretical capacity.However,it has a large capacity volume change working as anode material during charge and discharge process.Regarding to its preparation method,the traditional one requires complex procedure with high risk.To overcome these shortcomings,black phosphorus was prepared by a new strategy named low-pressure crystallization.The as-prepared black phosphorus was then exfoliated into phosphorene with the thickness of only a few nanometers by the means of ultra-sonication.After coating with graphene,phosphorene is functioned as anode material for lithium/sodium batteries.Graphene can effectively improve the structural stability of black phosphorus and improve the cycle capacity.In this paper,black phosphorus’ s preparation method,microstructure,chemical bonding and electrochemical properties were studied.The conclusions are obtained as follows:(1)Compared to other preparation method of black phosphorus,the "Low pressure crystallization" method obtains mild preparation condition and the process is more safe and the as-prepared black phosphorus has high purity and high crystallinity.With red phosphorus,tin and tin iodide as raw materials,orthorhombic black phosphorus can be obtained in the low pressure environment after heat treatment.This method is very suitable in the laboratory preparation for high pure black phosphorus.(2)By analyzing the lithium intercalation/extration mechanism in black phosphorus,this part reveals the main reason for the low Coulombic efficiency of black phosphorus directly used as anode material.By the means of hydrothermal reaction,black phosphorus was hybridized with graphene resulting in BPGO composite with a specific capacity of 780 mAh/g during 200 cycles in the current density of 0.1 A/g.In addition,a new strategy on preparing button battery is applied for the very first time.This method is not the same as traditional way of coating anode material on copper foil but directly depositing anode material on lithium battery separator by vacuum filtration.The as-prepared thin film electrode is flexible with a layer of graphene,BPGO hybrid and another layer of graphene resulting in a sandwiched structure so as to further improve the cycle performance.The G-BPGO thin film electrode maintains a specific capacity of 1400 mAh/g at a current density of 0.1 A/g during 200 cycles.(3)By a new type of chemical modification,the surface of phosphorene was modified with a layer of polymer which was connected with phosphorene by phosphorus-carbon bond.Such a chemical bond is necessary to prevent phosphorene from oxided in an ambient condition.In order to improve the conductivity and structure stability of the modified phosphorene,graphene was applied to wrap in it by hydrothermal reaction.The phosphorus-carbon bond and phosphorus-oxygen-carbon bond are the bridge between two of them while the polymer in between forms hollow structure for sodium atoms.Therefore,sodium ions have enough space to react with black phosphorus improving the reversible capacity.This modified 4-RBP composite used as anode materials for sodium ion battery maintains a specific capacity of 1472 mAh/g at a current density of 0.1 A/g during 50 cycles.In a high current density of 1 A/g it also obtains a remarkable capacity of 650 mAh/g during 200 cycles.