Preparation Of Carbon-Based Anode Material With High Capacitance Ratio And Its Fast Charging Application In Lithium And Sodium-Ion Batteries

Lithium-ion and sodium-ion batteries,as clean energy storage devices,are favored by many researchers because of their considerable energy density and cycle life,and are widely used in the electric vehicle industry.However,the problem of long charging time and mileage anxiety limits the widespread popularity of electric vehicles.Shortening the charging time of batteries is the main measure to solve the above problems.According to the typical charging processes of lithium-ion batteries,the slow diffusion kinetics of Li⁺in anode should be a major obstacle restricting the ability of fast-charging.As a result,developing anode materials with rapid reaction kinetics has received widespread attention.Among all anode materials,carbon-based materials have attracted high-profile due to their low cost,high safety,high conductivity,excellent magnification performance and considerable cycle stability.However,the low capacity and anode failure problem under fast-charging greatly restrict their applications.Pseudo-capacitance materials have fast and reversible surface reaction kinetics,which can maintain high capacity at high current density.Therefore,increasing the pseudo-capacitance contribution of materials to toward the fast-charging ability of Lithium-ion and sodium-ion batteries has attracted extensive interest of researchers.In this paper,the design of fast-charging anode materials is intended to be realized by improving the capacitance contribution of carbon-based materials.MoS₂/rGO composites with high capacitance contribution are prepared by introducing pseudo-capacitance materials（MoS₂）.Single hard carbon（RF_C-Fe）anode materials with high pseudo-capacitance behavior are prepared by doping metal ions.The above two materials were used in the study of fast-charging of Lithium-ion and sodium-ion batteries.The main contents and results includes the followings:（i）Graphene with high electronic conductivity is selected as the matrix,and a few layers of aminated MoS₂ nanosheets are fixed in-situ by rich oxygen-containing functional groups on its surface.After annealing,MoS₂/rGO composites with pinned structure are obtained,in which graphene is used as the matrix and conductive network,and nano-sized MoS₂ provides more ion storage sites.It is applied to fast-charging anode materials of Lithium-ion and sodium-ion batteries respectively,and its fast-charging performance and energy storage mechanism are studied.Above mentioned material is used in sodium-ion batteries and displays reversible capacity of602 m Ah g^-1,achieving excellent fast-charging performance of 69%in 25 minutes and 44%in 3.2 minutes.The charging capacity can reach 214.2 m Ah g^-1 at current density of 10.0 A g^-1,meeting the evaluation criteria for fast-charging of anode materials.At the same time,it can stably cycle for 1,000 cycles at a current density of3.0 A g^-1,which is superior to many carbon-based composite materials reported currently.In lithium-ion batteries,the highly reversible charge capacity is 910.5 m Ah g^-1,while there is almost no capacity loss after 1,000 cycles at high current density of 2.0 A g^-1.In addition,the electrochemical storage mechanism of the MoS₂/rGO in the two batteries is qualitatively and quantitatively analyzed,and it is determined that the improvement of the fast-charging ability of the two batteries is mainly attributed to the high capacitance ratio of the composite materials,thus realizing the fast reversible storage dynamics.This work verifies the significance of the pseudo-capacitance contribution to the design of fast-charging anode materials.（ii）The hard carbon is selected as the research object,and the electron cloud structure of the material is changed by doping metallic iron,so as to improve the conductivity and micro-control the carbon structure at the same time.In addition,the electrochemical performance and storage mechanism of RF_C-Fe in Lithium-ion and sodium-ion batteries are studied,and the differences and reasons of fast-charging performance between the two ion batteries are further explored.In sodium-ion batteries,55.3%of the full capacity can be reached after charging for 3 minutes,demonstrating significantly improved fast-charging performance.In addition,capacity retention rate of 98.6%can be held after cycling for 1,500 cycles at high current density.In lithium-ion batteries,it displays a high reversible specific capacity of 570.8 m Ah g^-1.After 1,200 cycles at high current density,the capacity can keep at99.3%,indicating that the prepared materials have significantly improved fast-charging capacity in both batteries.Through calculation and analysis,the improvement of fast-charging ability comes from the improvement of capacitance contribution and the increase of conductivity of carbon materials by iron doping.RF_C-Fe has more outstanding fast-charging ability in sodium-ion batteries,which mainly because it has higher initial capacitance ratio and meets the small capacity loss under large current density.