High-Capacity Lithium-Containing Anodes:Fabrication And Lithium Storage Performance

Nowadays,the actual gravimetric specific capacity of commercial traditional graphite anodes based on lithium intercalation reaction mechanism is reaching the theoretical limitation(372 m Ah g^-1).High-capacity lithium-containing anodes such as lithium metal anodes（LMAs）and lithium alloy anodes could deliver several times higher specific capacity than graphite anodes,and play crucial roles in the next-generation high-energy lithium-based rechargeable batteries to meet the fast-growing demands for electric vehicles,smart grids,consumer electronics,etc.However,the poor cycling life and rate performance impede its practical implantation.In this dissertation,a series of composite electrode structures have been designed to improve electrochemical performance.The main research achievements are as follows:（1）To overcome the structural instability caused by the huge volume change in the LMAs,a“laminate/uniform pillars”composite host structure was designed.Highly conductive and light-weight layered reduced graphene oxide（r GO）was used as the laminate,and lithium-silicon alloy(Li₂₁Si₅)nanoparticles with excellent lithiophilicity were uniformly distributed and anchored between the r GO layers as the pillars to co-construct a high-performance lithium-metal composite anode(Li/r GO-Li₂₁Si₅).During the fabrication,the precursor of silicon（Si）nanoparticles was pre-treated for superficial hydroxylation to eliminate self-agglomeration and produce a uniform and stable Si/r GO composite film.Li/r GO-Li₂₁Si₅ composite anodes were finally obtained via the composite of Si/r GO composite film and molten lithium.Stable cycling life for more than 600 h was realized in symmetric cells at 1 m A cm^-2 and 1 m Ah cm^-2 in a carbonate-based electrolyte.（2）The sluggish transmission of Li ions further hinders the rate performance of LMAs.Herein,an inorganic/organic composite Li-ion conductive matrix was designed.Lithium silver alloy（Li Ag）and polymer（PDOL）were introduced into lithium metal to co-construct a high-performance lithium metal composite anode（Li/PDOL-Li Ag）.The Li Ag alloy with high lithiophilicity and high Li-ion conductivity could reduce the nucleation barrier,accelerate the Li-ion transmission,and homogenize the Li plating/striping behavior.The interconnecting polymer network（PDOL）with high ionic conductivity could cooperatively improve the Li-ion transmission,enhance the stability of the electrode structure,and reduce the volume change in the cycles.Excellent high-rate performance of the Li/PDOL-Li Ag composite anode was achieved in symmetrical cell that could cycle for more than 150 h at10 m A cm^-2 and 1 m Ah cm^-2 at room temperature（25℃）in a carbonate-based electrolyte.Superior performance at low temperature（-20℃and-40℃）were also achieved.（3）Ultra-thin anodes（≤50μm）are highly desirable for the practical LMAs.However,complicated fabrication and poor cycling stability hamper the applications.Herein,a disordered r GO host（Dr GO）structure was designed to construct a high-performance ultra-thin（10-50μm）lithium metal composite anode（Li/Dr GO）using a bottom-up fabrication strategy.The r GO sheets and molten Li were stirred at 200℃ to produce r GO/Li sheets in micrometer and these sheets were further calendared repeatedly to form the ultra-thin Li/Dr GO composite foil,in which r GO sheets were disorderedly distributed to form a three-dimensional network.Benefiting from the Dr GO host,the ultra-thin Li/Dr GO composite anodes achieved superior mechanical and electrochemical performances.Stable cycling for more than 1600 h was realized at 1 m A cm^-2 and 1 m Ah cm^-2 in an ether-based electrolyte in symmetrical cell consisting of 50μm-thick Li/Dr GO composite foils anodes.（4）Lithium alloy anodes also show potential for high-energy-density batteries.However,several severe issues hinder its practical applications including poor conductivity and unstable structure.As a typical example,a Li₃P/C composite material was designed,which was featured by Li₃P ultrafine nanodomains embedded in micrometer-scale porous carbon（C）matrix.The interconnected porous carbon network could accelerate electron transport and improve the conductivity of active materials.The incompletely filled porous carbon could buffer the volume change of Li₃P during cycling and improve the electrochemical stability at both materials and electrode levels.The as-achieved Li₃P/C composite anodes displayed a high capacity of 791 m Ah g^-1（calculated based on the mass of Li₃P/C）at 0.1 C during the initial delithiation process（reaching～80%of the theoretical value）and showed high-capacity retention of 626 m Ah g^-1 after 100 cycles.Besides,the Li₃P/C composite also demonstrated superior rate capability and good ambient air stability.