Biomass Derived Hard Carbon As Anode Material For Sodium-ion Batteries

Fossil fuels have been considered as the main energy sources in the development of modern societies.However,with the transitional use of fossil fuels,a series of serious environmental problems have been observed,including global warming,acidification of soil and rivers,destruction of the stratospheric ozone layer etc.Based on the discontinuity and problem of clean energy such as wind energy and solar energy;the development of advanced electrochemical energy storage technology is the key to the efficient utilization of such clean energy.Due to the abundant sodium resources and low cost,sodium-ion batteries are a promising alternative for energy storage technology.Therefore,the design of high specific energy electrode materials is particularly important for the development of sodium-ion batteries.Biomass carbon materials have the advantages of low cost and easy regulation.However,the current carbon materials have the problems of low initial coulombic efficiency(ICE)and low specific capacity.In response to this,a series of biomass hard carbon electrode materials were developed,and the influencing factors of atomic doping,surface and interface functional groups,interlayer spacing,temperature,etc.on its electrochemical performance were explored,which effectively improved the ICE.In view of the problems of low coulombic efficiency and poor rate performance of hard carbon(HC)anodes,a series of camphor tree-derived HC anode materials were constructed and their electrochemical sodium ions storage properties were studied.The effect of pyrolysis temperature on the ICE and extreme rate performance was observed.The first discharge capacity of Cmph-HC prepared at 1500°C(Cmph-1500)was 333.9 m Ah/g and the ICE was 50.11%.Rate performance with specific capacities of157.4,114.2,65.4,47.1,29.5 and 15.40 m Ah/g were observed,at current densities of 40,80,200,400,800 and 2000 m A/g respectively.The ICE and rate performance of the of the Cmph-1500 are higher than those of the HCs obtained at other temperatures due to the increased degree of graphitization of Cmph-1500 and the reduction of the defects and surface functional groups due to high pyrolysis temperature.To overcome the problems of low ICE and low capacity of hard carbon anodes,a series of heteroatom(S,N and P)doped hard carbon anode materials were developed,and the optimal pyrolysis temperature of heteroatom doping was explored.To further enhance the performance of Cmph-HC,diatomic(P-N,P-S,and N-S)and triple(P-N-S)doping were also performed at a pyrolysis temperature of 700°C.When cycled at current densities of 40,80,200,400,800 and 2000m A/g,the S-Cmph-700 provided an initial discharge capacity of 616.7m Ah/g and exhibited an ICE of 66.61%,the rate performance with specific capacities of 372.3,323,282.6,252.6,221,181.2 m Ah/g.A specific capacity of 356.8 m Ah/g was recovered,when the current density returned to at 40 m A/g;while the ICE of N-Cmph-800 and P-Cmph-800 were 45.42%and 51.26%,respectively;and the rate performances with the specific capacities of 155.2,125.9,108.2,87.7,69.2,40.6m Ah/g and 163.1,135.3110.9;86.6,67.2 and 38.9 m Ah/g respectively;at the given current densities.P-S,N-S and P-N-S-Cmph provided the highest ICE of 75.88,81.93 and 70.74%,and excellent rate performances with specific capacities of 636.7,541.6,494.2,454.9,405.4 and 379.5 m Ah/g;513.2,411.2,373.1,341.9,307.3,and 257.3 m Ah/g and 521.6,452.4,403.8,366.2,330.7,and282.3 m Ah/g at 80,200,400,800,and 2000 m A/g,respectively.They provided initial discharge capacities of 879.6,766.6 and 791.3 m Ah/g.When the current density was restored to 40 m A/g,the recovered specific capacities of the electrode materials were 548.5,434.8 and 455.8 m Ah/g for P-S-Cmph,N-S-Cmph and P-N-S-Cmph,respectively.Furthermore,P-S-Cmph,N-S-Cmph,and P-N-S-Cmph exhibited excellent cycling performance,maintaining specific capacities of about 370,290,and 280m Ah/g after 500 cycles at a current density of 2000 m Ah/g,respectively.The improvement in material properties of doped Cmph-HCs is attributed to the increased interlayer spacing of HCs caused by heteroatom doping,especially sulfur-doped Cmph-HCs,which promotes the reversible intercalation/deintercalation of Na~+ions in the interlayer spacing of anode materials and the presence of more active sites in HCs for Na~+storage.Note that N-and P-doped Cmph-HC-derived anodes have been shown to display more oxygen containing functional groups.Therefore,the low performance compared with S doping can be attributed to the irreversible trapping of Na~+ions by functional groups.This study provides a simple,fast,and efficient method for constructing high-ICE and high-performance anode materials for SIB commercialization.