The Composites Of Chlorophyll And Two-dimensional Materials As Anode For Lithium-ion Battery

As a key energy storage device,lithium-ion batteries(LIB)are widely used in portable consumer electronic products such as mobile phones and notebooks,and are gradually moving towards medical,submarine,aerospace,and other fields.As far as the electrochemical performance of lithium-ion batteries is concerned,the core part of the electrode-the negative electrode material plays a vital role.Therefore,the determination of anode materials for lithium-ion batteries plays a key role.So,it is of vital importance to find anode materials with excellent electrochemical performance.Anode materials with two-dimensional morphology and ultra-high surface area have become the most promising candidates for promoting Li⁺insertion in lithium-ion batteries due to their high energy density and excellent stability.Among the negative electrode materials with two-dimensional morphology,a new two-dimensional transition metal carbide or nitride-based material named"MXene"has become a hot spot in the current energy field due to ultra-high specific surface area,a stable layered structure,excellent electrical conductivity,and intercalation capacity of cation.At the same time,another type of Mo S₂ has also attracted attention due to its large lithium-ion storage capacity and abundant natural storage.In this paper,MXene materials represented by Ti₃C₂ and Nb₂C,and Mo S₂ are the research objects.The main research contents are as follows:First,we use commercial titanium powder,aluminum powder,and carbon black as raw materials,adjust the atomic ratio,and prepare MAX phase Ti₃Al C₂ by solid-state sintering.On this basis,Ti₃Al C₂ is etched into Ti₃C₂ with hydrochloric acid solution and lithium fluoride,organic dyes(Zinc methyl3-devinyl-3-hydroxymethyl-pyropheophorbide a(Chl))and Ti₃C₂ were simply compounded to prepare Chl@Ti₃C₂ composite samples for lithium-ion battery anode materials.The crystallinity,morphology and chemical elements of the samples were studied by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and energy spectrometer,etc.,and then combined with related testing methods(such as constant current charge and discharge,etc.)to analyze the performance in the LIB.The results show that the prepared Chl@Ti₃C₂ composite sample has a wider interlayer spacing,and when applied to the negative electrode of LIB,the reversible capacity and cycle performance have been significantly improved,and as the number of cycles increases,the discharge specific capacity also continues to increase,which is attributed to the gradual activation of the composite sample accompanied by electrochemical reactions.At 500 m A g^-1,the initial discharge specific capacity of Ti₃C₂ is relatively low,only 117.9 m A h g^-1,but the initial discharge specific capacity of 1wt%Chl@Ti₃C₂ is as high as 239.7 m A h g^-1,the initial discharge specific capacity of 2wt%Chl@Ti₃C₂ is also as high as 226.8 m A h g^-1.And after a long cycle(800 times),the discharge specific capacity is maintained from 91.9 m A h g^-1(Ti₃C₂)to 173.4 m A h g^-1(1wt%Chl@Ti₃C₂)and 138.3 m A h g^-1(2wt%Chl@Ti₃C₂)Secondly,we use commercial niobium powder,aluminum powder,carbon black as raw materials,adjust the atomic ratio,the MAX phase Nb₂Al C was prepared by solid-state sintering method,etch Nb₂Al C with hydrochloric acid solution and lithium fluoride into Nb₂C.The Chl@Nb₂C samples were compositely prepared as anode materials for lithium-ion batteries by using organic dyes Chl and Nb₂C for physical methods.From the X-ray diffraction,we found that the(002)main peak diffraction degree of Chl@Nb₂C sample is lower indicating that the addition of Chl causes the interlayer spacing of Nb₂C to increase.From scanning electron microscopy and transmission electron microscopy,it was found that Chl molecules were inserted into the Nb₂C layer and distributed on the surface.The Chl@Nb₂C samples were analyzed by using cyclic voltammetry and AC impedance and other test methods,the results show that Chl@Nb₂C samples have better cycle performance and rate performance.At 100 m A g^-1,the initial discharge specific capacity of Nb₂C is relatively low,only295 m A h g^-1,while the initial discharge specific capacity of Chl@Nb₂C is as high as384 m A h g^-1(1wt%Chl@Nb₂C)and 363 m A h g^-1(2wt%Chl@Nb₂C).After a short cycle(50 times),the discharge specific capacity increased from 126 m A h g^-1(Nb₂C)to 169 m A h g^-1(1wt%Chl@Nb₂C)and 170 m A h g^-1(2wt%Chl@Nb₂C).Finally,we use organic dyes Chl to control the interlayer of Mo S₂ as an anode material of lithium-ion batteries.After the regulation of Chl,the Chl@Mo S₂ sample showed a lower degree of diffraction by X-ray diffraction.This structure can accommodate more Li⁺insertion and extraction.At 100 m A g^-1,the initial discharge specific capacity of Mo S₂ is relatively low,only 772 m A h g^-1,while the initial specific discharge capacity of the composite sample Chl@Mo S₂ reaches 867 m A h g^-1(1wt%Chl@Mo S₂)and 828 m A h g^-1(2wt%Chl@Mo S₂),much higher than that of Mo S₂.And after 100 cycles,the discharge specific capacity was promoted from 95m A h g^-1(Mo S₂)to 228 m A h g^-1(1wt%Chl@Mo S₂)and 161 m A h g^-1(2wt%Chl@Mo S₂).