Effects Of Carbon Carrier On Loading Red Phosphorus And Performance Of The Phosphorus Based Anode For Lithium-Ion Batteries

The conventional graphite anode is difficult to meet the requirements of power battery for fast charging and high-energy density.Red phosphorus（RP）,one of the promising anode materials for high power/energy density lithium-ion batteries,offers the high theoretical specific capacity of 2596 m Ah/g and suitable lithiation potential（～0.7 V vs Li⁺/Li）.To solve the inherent poor electrical conductivity(～10^-12 S/m)and large volume expansion（～300%）of RP anode,one of the effective strategies is typically to build up various conductive carbon matrices for preparing red phosphorus-carbon（RP-C）composites by the vaporization-condensation strategy.However,the low conversion efficiency of white phosphorus（P₄）to RP in the vaporization-condensation process leads to two problems:（1）The low P mass loading in the carbon-based frameworks（～30 wt%）limits the energy density.（2）The residual white phosphorous（WP）leads to the problems of flammability and high toxicity.In this thesis,the interactions between P₄ and various carbon structures(C_surf,C_edge,C-N-5,C-N-6,C-N_g,C-S-5,C-S-6,C=O,C-O-C,C-OH,COOH)were systematically revealed at the atomic level by the density functional theory calculation（DFT）,which offers a new theoretical basis for the choice of carbon carrier in the vaporization-condensation process.According to the above results,the porous carbon（PC）with plenty of edge carbons(C_edge)was prepared by KOH activation method.The RP-PC composite was prepared using RP and PC as raw materials with a P/C weight ratio of 1:1 by vaporization-condensation method.The relationship between the structure and electrochemical performance of phosphorus/carbon anode was clarified.The conclusions are shown as follows.（1）DFT results showed that the edge carbon atom offers the high adsorption energy for P₄ molecule via the strong P-C bond,which accelerated the adsorption and polymerization of P₄.The PC provided a large amount of C_edge sites for the adsorption and polymerization of P₄ molecular,which can realize the RP nanolization（～15.68 nm）,the high RP mass loading of 49.4 wt%（closed to the highest theoretical mass loading of 50 wt%calculated based on the feeding ratio of RP/PC）,and the high P₄ conversion efficiency（no presence of WP）.In addition,the conversion degree of P₄ to RP was improved by prolonging the transformation time.（2）The excellent electrochemical performance of RP-PC anode can be ascribed to the RP nanolization,the confinement effect of PC,and the strong and stable P-C bond between RP and PC.The RP-PC anode provided a high specific capacity of 965.2m Ah/g even after 1100 cycles at 1000 m A/g（equivalent to 1 C）and a high-rate capacity of 496.8 m Ah/g at 8320 m A/g（equivalent to 16.7 C）after 1000 cycles（the current density and specific capacity were calculated based on the total weight of RP and PC）.The design strategy of RP-PC presented great promise for the large-scale safety production of the RP-based anodes with excellent performance.