Design And Optimization Of Electrolytes And Electrode Materials For Dual-Ion Batteries

Dual-ion batteries（DIBs）have aroused much attention due to their high energy density,low cost,and environmental friendliness.In contrast to conventional alkali metal-ion batteries,DIBs possess a novel working mechanism via the simultaneous intercalation/deintercalation of anions into/from cathode and alkali metal cations into/from anode during the charge/discharge process.Moreover,the DIB configuration utilizing carbonaceous electrodes as both cathode and anode can avoid the usage of costly and toxic metallic compound electrode materials.However,such a battery configuration is still hampered by several negative issues,including an undesirable electrolyte decomposition due to the high voltage characteristics of the cathode,the structural collapse of the graphite cathode caused by repeated anions intercalation/de-intercalation,and limited specific capacity ascribed to the intercalation-type graphite electrodes.In order to overcome the above problems,we herein focus on both the electrolytes and electrode materials.On the one hand,we construct a stable electrolyte system by adjusting the electrolyte concentration and types to meet the requirements of anions and cations intercalation process.On the other hand,we prepare cathode and anode materials with tunable defects for PF₆^-and Li⁺intercalation in one synthesis system by adjusting the content of boron doping in the complex of amino acid with iron（III）.The main contents are listed below:（1）By selecting natural graphite and soft carbon as electrode materials,the effects of electrolyte concentration and types on the PF₆^-intercalation behaviors and the compatibility between solvent composition and anodes are investigated.The intercalation behaviors of anions and cations are strongly dependent on the concentration and composition of electrolytes.A highly concentrated electrolyte can reduce PF₆^-intercalation onset voltage,while a diluted electrolyte can facilitate PF₆^-transport dynamics.The linear EMC solvent is more favorable to the PF₆^-insertion into the graphene layers than cyclic EC solvents.Moreover,EC solvent is the key component for the stability of anodes,and graphite and soft carbon anodes exhibit excellent long cycle stability in EC-containing electrolytes.Among them,soft carbon anode exhibits good rate performance due to its large interlayer spacing and partially amorphous structure.Ascribed to the high capacity and high rate performance of graphite cathode and soft carbon anode,the graphite//soft carbon DIB in the mixed electrolyte of 1 M Li PF₆-EC/EMC（3:7,v/v）electrolyte can provide an energy density of 98 Wh kg^-1 at a power density of 580 W kg^-1 and a capacity retention rate of 86.9%after 1000 cycles at 1 A g^-1.（2）Graphitic mesoporous carbon cathode for PF₆^-insertion and boron-doped porous carbon anode for Li⁺insertion are prepared based on coordination chemistry by using nitrogen-rich amino acid,iron chloride,and boric acid as precursors and regulating boron content in the metallic complex.Porous structure supplies PF₆^-anion expansion/contraction space and highly graphitic structure facilitates the dynamics of PF₆^-intercalation.The graphitic mesoporous carbon cathode with minimal defects shows a superb rate capability(rate retention of 78%at a high current density of 5 A g^-1)cycling stability for PF₆^-insertion(an inspiring capacity retention rate of 95.7%after 1000 cycles at 5 A g^-1).B-doping design introduces abundant defects,increases active sites,and prompts Li⁺diffusion kinetics.The boron-doped porous carbon anode with maximal defects delivers an excellent capacity of up to 606 m Ah g^-1 for Li⁺storage at 0.2 A g^-1.The DIB assembled by the above cathode and anode can exhibit a maximum energy density of 130 Wh kg^-1 at a power density of 580 W kg^-1,and even at an ultrahigh power density of 29000 W kg^-1,the energy density can maintain up to 74 Wh kg^-1.