Recent Advances and Future Perspective of Scaffolded Lithium Metal Anode with Carbon-Based Three-Dimensional Skeleton
Due to high theoretical specific capacity density(3860 mAh·g-1),lower reduction potential(-3.04 V,relative to standard hydrogen electrode),and lower density(0.534 g·cm-3),lithium metal has been considered to be one of the most promising anode materials for improving the energy density of lithium batteries.However,serious dendrite growth and poor cycling performance of lithium seriously restrict its large-scale commercial application.The main challenges of lithium metal can be summarized as high reactivity,serious lithium dendrite growth and huge volume expansion.These issues have seriously impeded the practical use of lithium metal.In recent years,researchers had put forward a series of solutions to stabilize the lithium metal anode:(1)constructing an artificial protective layer on lithium metal surface to reduce the side reaction between lithium metal and electrolyte;(2)replacing traditional liquid electrolyte with solid electrolyte to inhibit the growth of lithium dendrites;(3)introducing electrolyte additives to uniform lithium deposition;(4)adopting a three-dimensional(3D)conducting host to uniform lithium ion flux and relieve volume expansion;(5)regulating lithium uniform nucleation and growth by external pressure or magnetic field.Particularly,scaffolded lithium metal anode with three-dimensional skeleton had been considered as one of the most effective,low cost and facile technique to improve lithium metal.According to Sand's time model,reducing current density could delay the initial time of lithium dendrite formation.Due to the high specific surface area of the 3D host,the local current density could be effectively reduced,thus the growth of lithium dendrites could be delayed.In addition,the 3D host delivered abundant holes and large cavity structure,which could alleviate the infinite volume expansion of lithium metal anode in the process of electrochemical cycling.In order to meet the requirements of lithium metal batteries,the ideal 3D host should also exhibits the following advantages:(1)high electron conduction network to realize rapid charge transfer and reducing interface resistance;(2)excellent lithiophilicity to reduce lithium nucleation overpotential and guide lithium uniform nucleation and growth;(3)strong mechanical and electrochemical stability to maintain excellent electrochemical cycling without rupture and collapse;(4)low-cost,simple and easy production method to promote large-scale industrial production.At present,the reported host of lithium metal included carbon material,metal material,MXene material,etc.In particular,carbon material was one of the most promising host materials due to its light weight,which could minimize the loss of the overall mass density of lithium metal anode.According to the structure,the carbon host could be divided into carbon spheres,carbon nanotubes,carbon nanofibers and graphene.The carbon host with large surface area effectively reduced the current density and inhibits the growth of lithium dendrites.The porous and cavity structure effectively alleviated the huge volume change during the electrical cycling.In order to improve the lithiophilicity of the host,the introduction of lithiophilic sites was essential.The lithiophilic sites could be divided into single functional sites and bifunctional sites.Single functional sites included metallic and nonmetallic elements.The bifunctional sites were mainly transition metal compounds.Due to the high reducibility of lithium,transition metal compounds could be in-situ reduced to lithiophilic metallic sites and high ionic conductive lithium-containing compounds.The synergistic effect of metallic sites and lithium-containing compounds could reduce the nucleation potential of lithium and afford a stable solid electrolyte layer on Li metal surface.To promote the practical usage of scaffolded lithium metal anode,the amount of lithium metal and electrolyte should be controlled strictly.In addition,as the pouch cell was closer to the actual cycle conditions,the electrochemical performance of pouch cell must be studied systematically to promote the practical application of the 3D lithium metal anode with carbon host.Especially,the cycle performance under harsh conditions should be studied.At the same time,the thickness and mass of the carbon host needed to be strictly controlled to maximize the mass energy density of the battery.The following problems needed to be solved before realizing the practical application of carbon-based scaffolded 3D lithium metal anode:(1)designing low-density host to minimize the capacity sacrifice from the host;(2)constructing highly durable and high effective lithiophilic sites in scaffolded Li metal anode.Also analyzing the failure mechanism of the lithiophilic sites was extremely essential to prolong the battery cycling life;(3)fabricating robust artificial solid electrolyte layer on 3D Li metal anode was extremely necessary;(4)developing safe,facile and large-scalable method to prepare carbon scaffolded Li metal anode.In summary,3D lithium metal anode based on carbon host was one of the most effective strategies to stabilize lithium metal anode.There was still a long way to realize the practical application of 3D lithium metal anode,which required continuous breakthroughs in manufacturing technology and production cost.And intimate cooperation between universities and enterprises was extremely vital.In the near future,the 3D lithium metal anode based on carbon host would promote the commercialization of lithium metal anode.
three-dimensional lithium metal anodecarbon hostlithiophilic sitedendrite-free
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