Synthesis Of Lignin-Based Carbon/Zinc Oxide Composite And Its Application As Anode Material For Lithium Ion Batteries

Zinc oxide(ZnO)has the advantages of high theoretical lithium storage capacity,environmentally friendliness,being easy to prepare and low cost.It is considered as a new type of lithium battery(LIBs)anode material with great development potential.However,the ZnO negative electrode has the problems of serious capacity decay caused by volume expansion during charging and discharging,and poor high-rate performance caused by poor conductivity.The way to solve these problems is to nanoize ZnO and composite it with carbon-based materials.As the second largest biomass resource in nature,lignin has a carbon content of up to 40-60%,abundant oxygen-containing functional groups on the surface,and a unique three-dimensional network structure.Using the structural characteristics of lignin to prepare a composite of lignin carbon and ZnO can not only limit the growth of ZnO particle size and generate nanometer ZnO,but also effectively inhibit the volume expansion of ZnO during charge and discharge.Porous carbon has the advantages of stable structure,high theoretical lithium storage capacity,and good electrical conductivity.It is also considered to be a promising LIBs anode material.On the basis of the lignin carbon/zinc oxide composite,nano-ZnO is used as a template to prepare lignin porous carbon with developed mesoporous structure,which can be used as a negative electrode material with high lithium storage capacity,good rate performance,and stable cycle performance in lithium ion batteries.Therefore,the preparation of lignin carbon/ZnO composite material and lignin porous carbon and the research on the related composite mechanism and formation mechanism have important application value and theoretical significance.In this paper,a series of LC/ZnO-(1:X),NLC/ZnO-(Y)and NLC were prepared by using alkaline hydrothermal method,combined with carbonization and acid etching to remove templates.The main conclusions are as follows:(1)By controlling the carbon/zinc source input ratio,LC/ZnO-(1:X)with different morphologies and structures can be prepared.Among them,LC/ZnO-(1:5)has a reasonable structural composition,and the mass content of ZnO reaches 72%.The particle size of ZnO is about 10 nm and the average particle size of the composite is about 50 nm.As a negative electrode material for lithium-ion batteries,LC/ZnO-(1:5)shows the best cycle performance and rate performance.When cycling at a current density of 200 m A·g^-1,its first charge-discharge specific capacity is 760 m Ah·g^-1 and 1254 m Ah·g^-1 respectively,and the first coulombic efficiency reached 60.6%.After 200 cycles,its reversible specific capacity reached604 m Ah·g^-1.(2)Nano ZnO in LC/ZnO-(1:5)was used as template to form pores by etching.NLC/ZnO-(Y)with different ZnO remaining amount and NLC were prepared by etching LC/ZnO-(1:5)by controlling the acid concentration.Among them,NLC presents a nanocarbon accumulation structure with a particle size of about 50 nm.The mesopores with pore size of about 10 nm were well developed.and the specific surface area and pore volume of NLC reached 833.25 m²·g^-1and 1.08 cm³·g^-1 respectively.The mesopores with pore size of about 10 nm were well developed in NLC.As a negative electrode material for lithium-ion batteries,NLC has a further breakthrough in cyclic reversible capacity.After 200 cycles at a current density of 200 m A·g^-1,its reversible specific capacity is as high as 706 m Ah·g^-1.(3)Alkaline hydrothermal method can degrade lignin macromolecules,release more oxygen-containing active functional groups,and complex the intermediate Zn(OH)₄^2-through electrostatic interaction to realize the anchored growth of ZnO crystal nuclei.Utilizing the characteristics of the three-dimensional network structure of lignin to highly disperse ZnO crystal nuclei and inhibit the agglomeration growth of ZnO.And the LWL/ZnO with nano-zinc oxide highly dispersed in low-molecular-weight lignin(LWL)was prepared.Utilizing the pyrolytic self-shrinkage of lignin,the LWL is decomposed and finely divided around nano-zinc oxide through carbonization.And the NLC/ZnO-(100%),combined from lignin nano-carbon and nano-zinc oxide,was formed in this way.Finally,nano-zinc oxide was removed as a template to obtain NLC with nanometer size and rich mesoporous structure.In conclusion,lignin is an excellent precursor material of biomass hard carbon,and the composite prepared by combining with nano-ZnO shows good electrochemical performance as anode material of LIBs.Therefore,lignin hard carbon has great potential application value in electrochemical field.