Hetero-atom Doped Carbon Nanotube Structured Electrode To Stabilize Lithium Metal Anode

The widespread use of lithium-ion batteries(LIBs)has had a huge impact on our daily lives.Due to the limitation of electrode materials,the energy density of existing lithium ion batteries cannot meet the growing demand for portable electronic products,electric vehicles and grid-scale energy storage.Therefore,research on high energy density batteries other than LIBs has become a hot spot for current researchers.Lithium metal battery(LMBs)is considered as the most promising next generation high energy storage device because of its high theoretical capacity and low electrochemical potential.However,in the process of repeated removal/deposition of metallic lithium as the negative electrode,dendrites of dendritic lithium will be formed,resulting in huge volume change,dead lithium generation,and penetration of battery diaphragm,etc.,reducing the stability of battery cycle and causing safety problems.Therefore,the development of effective strategies to improve the stability of lithium metal anode is the key to the commercial application of LMBs in the future.Among many strategies,the design of carbon nanomaterials with porous micro-nano structure and unique lipophilic surface has been proved to be one of the most effective strategies to induce uniform nucleation deposition of lithium and inhibit the growth of lithium dendrites.In this paper,two different heteroatom-doped carbon nanotube network electrodes were successfully fabricated by "top-down" metal-organic framework precursor calcination and "bottom-up" alcohol lamp method.The prepared hetero atom-doped carbon nanotube electrode has good lipophilic performance,can effectively regulate the reversible nucleation and growth of metallic lithium,and inhibit the formation of lithium dendrites.At the same time,the heteroatom doping on carbon nanotubes is proved to be the affinity active site of lithium by theoretical calculation and experimental means.The work of this paper provides an effective strategy for the controllable preparation of hetero-atom-doped carbon nanotube electrode and the enhancement of the stability of lithium metal anode.The specific research contents are as follows:(1)"Top-down" strategy to construct Co,N-doped carbon nanotubes for stabilizing metallic lithium anodesIn this work,MOFs precursors were prepared on the surface of copper mesh by electrochemical synthesis,and then N-doped carbon nanotube networks(N-CNTs)were obtained by high-temperature carbonization.XPS characterization proves that N exists in a Co,N structure and is named Co,N-CNT.The prepared carbon nanotubes were dense and uniformly anchored on the surface of copper mesh with the diameter of about 9 nm.In addition,pure N-doped carbon nanotube network(NCNT)can be prepared by acid etching.The electrochemical results show that the Co,N-CNT network has good lipophilic performance with nucleation overpotential of only-33.2 mV at the current density of 0.5 mA cm-2,which was smaller than the nucleation potential of the control sample NCNT(-44.1 mV)In addition,the half-cell consisting of Co,N-CNT network has a coulombic efficiency of up to 99%at the Li-plating capacity of 2 mAh cm-2 and the current density of 1 mA cm-2 and 2 mA cm-2.At the same time,the symmetric battery shows a Li deposition/stripping potential of only 10 mV at the constant area capacity of 1 mAh cm-2 and current density of 1 mA cm-2.Moreover,the Co,N-CNT@Li?LFP full battery has a capacity retention rate of up to 85%after 200 cycles at the current density of 2 C(2 C=350 mA.g-1;1.4 mA cm-2),while the capacity retention rate of NCNT@Li?LFP is only 60%.Both the experimental and DFT calculations show that the N is the real lipophilic active site to regulate the uniform nucleation and growth of metallic lithium and inhibit the generation of lithium dendrites.(2)"Bottom-up" strategy to construct oxygen-rich carbon nanotubes for stabilizing lithium metal anodes.This work innovatively uses a simple "barbecue" method to rapidly and extensively prepare oxygen-rich carbon nanotube networks(O-CNTs)on the surface of nickel foam substrate.The diameter of the carbon nanotubes is 9-10 nm and the length is about several hundred nanometers.The O-CNTs electrode was directly used as a three-dimensional skeleton for lithium metal deposition which possesses a low lithium nucleation potential of only-31.3 mV at the current density of 0.5 1A cm12,which was smaller than the nucleation potential of the control sample R-CNT(-41.3 mV).In terms of electrochemical properties,the CE of half-cell composed of O-CNT network is as high as 99%when the surface capacity of Li is 2 mAh cm-2 and the current density is 1 mA cm-2.The Li deposition/stripping potential in symmetrical battery composed of O-CNT@Li was 35 mV and 68 mV at the constant area capacity of 1 mAh cm-2 and current density of 2 mA cm-2 and 4 mA cm-2.Moreover,the O-CNT@Li ?LFP full battery had low voltage polarizability and the capacitance retention rate was still as high as 88%after 150 cycles at 0.5 C(1 C=175 mA.g-1;0.7 mA cm-2),while the capacity retention rate of R-CNT@Li?LFP is only 65%.Both the DFT calculation and experimental results have proved that the oxygen-containing group(C=O)on the surface of carbon nanotubes is an effective lipophilic active site to guide the nucleation and growth of lithium metal.In addition,the porous network composed of O-CNTs and porous metal substrates ensures excellent electrical conductivity and effectively promotes the transport of electrons and lithium ions.