Study On Fabrication And Performance Of Phosphorus Based Anode Materials Of Lithium-Ion Batteries

Lithium-ion batteries,as a new type of high-energy battery,are favored because of their advantages such as high specific energy,and no pollution.In order to obtain high energy density lithium-ion batteries,the fabrication of anode materials has become a research focus.Phosphorus-based materials is highly attractive as a potential anode material candidate for lithium-ion batteries owing to its excellent electrochemical performance.However,its poor electrical conductivity and large volumetric changes during the charge-discharge process hinders its practical application.In this work,two optional approaches are applied to promote the electrochemical performance of phosphorus,based on the preparation of P/C composite materials.One effective strategy is adding accessory ingredient to P/C composites.Another effective way is to replace active carbon with a more excellent matrix material.The main research contents and results are as follows:1.P/C composite is prepared via simple and efficient ball milling using red phosphorus and cost-effective active carbon as raw materials.It is concluded that 10 hours is the optimal ball milling time;and red phosphorus:activated carbon=9:1(mass ratio)is the optimal ratio.The P/C composite material exhibits a specific discharge capacity is 612 mAh g-1 after 50 cycles at 200 mA g-1 current density.The results indicate that active carbon not only enhances the conductivity of the P/C composite material,but also reduces direct contact between red phosphorus and the electrolyte,thereby greatly improves the cycle performance.2.Based on P/C composite materials,the electrochemical performance of red phosphorus is further improved via introducing sulfur as an activation agent.The lithium ion diffusion coefficient and electronic conductivity of PS/C electrode are calculated about 4.2×10-12 cm2 s-1.At a current density of 200 mA g-1,the PS/C electrode delivers a reversible capacity of 935.3 mAh g-1 after 200 cycles.In addition,it is amazing to find that the capacity retention of 473.8 mAh g-1 could be kept even after 450 cycles at a current density of 2000 mA g-1,presenting amazing cycling performance for phosphorus-containing electrodes.The results show that partial sulfur is strategically incorporated with phosphorus to construct PS/C composite by P-S bonding force.The results demonstrate that P-S bonding greatly improves the conductivity and activity of phosphorus.Part of the sulfur forms Li-S intermediates during the electrochemical lithiation process.The solvable Li-S intermediates formed could be anchored on the surface of phosphorous to reduce direct contact between phosphorus and the electrolyte and improve the cycle stability of the phosphorus.3.The active carbon is replaced to rGO-C3N4 matrix with relatively stable mechanical structure.A novel P/rGO-C3N4 composite is designed and synthetized successfully via a facile high-energy ball-milling method.The strategic incorporation of rGO-C3N4 plays an important role in the formation of admirable interface connection between red phosphorus and rGO-C3N4 framwork via P-N and P-C bonding,leading to fluent ion/electron-diffusion tunnel and admirable mechanical structure.After 600 cycles,the P/rGO-C3N4 electrode maintains a reversible capacity of 1032.6 mAh g-1 with a high coulombic efficiency of 99.0%at the current density of 200 mA g-1,exhibiting amazing cyclability and high reversibility.Furthermore,a specific discharge capacity of 800 mAh g-1 or so is kept even at the high current density of 2000 mA g-1,demonstrating the outstanding rate performance of P/rGO-C3N4 composite.Therefore,P/rGO-C3N4 composite significantly enhances conductivity of red phusphorus via chemical bonding.In addition,the rGO-C3N4 matrix could effectively alleviate the structure collapse,stabilize the electrode structure,and thereby improve the electrochemical,performance.