Study On The Performance Improvement Of Lithium Metal Anodes By Surface Hydrophilic Modification Of Three-dimensional Current Collectors

Lithium-ion battery has become one of the popular energy storage devices due to its advantages of high safety,less self-discharge and long cycle life.Its successful commercialization has also accelerated the rapid industrialization of portable electronic products,electric vehicles and smart grids.However,due to the limited theoretical capacity of graphite anodes,lithium-ion batteries can no longer meet the high-energy-density requirements of various electronic devices.Lithium metal has become an ideal anode material for the next generation of lithium batteries due to its ultra-high theoretical capacity and extremely low electrochemical potential.However,lithium metal still faces many challenges when used as an anode,including uncontrollable growth of lithium dendrites,unstable solid electrolyte interfaces,and infinite volume changes of lithium metal during battery cycling.Developing three-dimensional current collectors is an important method to solve the above challenges.Industrialized carbon cloth is a three-dimensional material with large specific surface area,porosity,and high mechanical strength.The high specific surface area of carbon cloth can reduce local current density to achieve uniform lithium metal deposition,and the larger internal space is also conducive to alleviating the volume change of lithium metal during battery charging and discharging.However,the lithiophobic carbon cloth is not conducive to the uniform deposition of lithium metal,which requires lithiophilic materials for modification of carbon cloth.Manganese dioxide,as a lithiophilic metal oxide,has the characteristics of low cost,abundant resources,and environmental friendliness.Using it as a surface modification material for carbon cloth is beneficial for improving the electrochemical performance of lithium metal anodes.This thesis uses lithiophilic metal oxide manganese dioxide to modify carbon cloth with overall and unilateral lithiophilic modifications.Through structural regulation of lithiophilic sites,the uniformity of lithium metal deposition is improved,emphasizing of solving the main problems of uncontrollable lithium dendrite growth,solid-state electrolyte interface instability,and volume change of lithium metal in lithium metal anodes.The corresponding contents are as follows:(1)The study on the overall lithiophilic modification of carbon cloth current collector by manganese dioxide,corresponding to Chapter 2 of this thesis.In order to solve the lithiophobility of three-dimensional porous carbon cloth,lithiophilic metal oxide manganese dioxide was used to modify the carbon cloth as a whole.Compared with bare carbon cloth,the modified carbon cloth improved the overall lithiophobility with reduced nucleation and deposition barrierries of lithium.As a result,the lithium anodes achieved a uniform lithium metal deposition process with an effectively suppression of the growth of lithium dendrites,and thus significantly improved the cycling stability of batteries.(2)The study on the unilateral lithiophilic modification of carbon cloth current collector by manganese dioxide,corresponding to Chapter 3 of this thesis.Using lithiophilic manganese dioxide to modify one side of the carbon cloth,while retaining the high conductivity of the carbon cloth on the other side.Then,the modified side was placed away from the separator.During the battery cycling,the upper carbon cloth was used to alleviate the volume expansion of lithium metal.Due to the limited presence of lithium,it also inhibited the growth of lithium dendrites;The lithium metal at the bottom was served as a lithium source to timely supplement the consumption of lithium metal,significantly improved the Coulombic efficiency of the battery.