Morphology Control Of MnO₂ And Its Composite Separator For Lithium Battery

Nowadays,the electrochemical performance of cathode and anode of lithium-ion battery has gradually approached its theoretical capacity,which hinders developments of lithium-ion battery.The lithium metal anode and sulfur cathode are considered to the candidates of anode and cathode for the next generation of lithium-ion batteries due to their high specific energy density.However,due to the dendrite growth in lithium metal anode and the"shuttle effect"in sulfur cathode,these problems affect the application of this materials in lithium-ion batteries.Separator is an important part of lithium-ion battery.By developing new separator and modifying the PP separator,we can inhibit lithium dendrite or"shuttle effect",so as to improve the electrochemical performance of lithium metal battery and lithium sulfur battery.The specific content of this research is mainly reflected in the following three parts:First,realizing homogenous ion flux by separator is critical for uniform lithium deposition to suppress dendrite growth.A flexible bacterial cellulose/Si O₂-based composite separator,containing 80 wt%silica nanoparticles,is developed to achieve dendrite-free lithium anode.Furthermore,a thin MnO₂ layer is integrated with Si O₂ substrate to produce a bilayer composite separator.The resultant lithium metal battery with Li Fe PO₄ cathode shows a high specific capacity of 159.1 m Ah/g after 100 cycles at 0.2 C.The improved battery performance arises from stable lithium anode and active MnO₂ layer facing Li Fe PO₄cathode.Secondly,the nano MnO₂ NTs synthesized by using potassium permanganate as manganese source.And PPy@MnO₂NT that is MnO₂NT in situ growth polypyrrole on its surface.PPy@MnO₂ NT was coated on Celgard 2400 separator to prepare the PPy@MnO₂NT/PP composite separator.PPy@MnO₂ NT with pore specific surface area of 62.44 m~2/g and it can adsorb polysulfides.This separator shown high ionic conductivity（0.78 ms/cm）and good electrochemical performance.The lithium sulfur battery assembled with PPy@MnO₂ NT/PP composite separator shows high specific discharge capacity of 821m Ah/g at 0.5 C rate and retain 472.7 m Ah/g after 300 cycles,which is higher than the battery compared with commercial separator.Because of PPy@MnO₂ NT low specific surface area,in this chapter,The MnO₂hs（hollow sphere）was prepared.And,PPy@MnO₂ hollow sphere was synthesized from it in situ growth polypyrrole on its surface.PPy@MnO₂ hs shows a high specific surface area of 229.29 m~2/g and excellent adsorption for polysulfides.Blend of PPy@MnO₂ hs and Super P Li was coated on Celgard 2400 separator to prepare the PPy@MnO₂ hs/PP composite separator.This separator demonstrated conductivity of 58.41 m S/cm and wonderful rate performance at high rate.The lithium sulfur battery with PPy@MnO₂ hs/PP composite separator present a high specific capacity of 553 m Ah/g at 2C rate.