Preparation Of Biomimetically-structured Energy Storage Composites And Their Applications In Lithium Batteries

Rechargeable batteries have attracted extensive attention.Among them,Li-ion batteries possess advantages of high energy density,no memory effect,etc.High-energy-density secondary Li-S battery has potential applications in long term vehicle industries,owing to the higher energy density,thus it is promising to be the next generation energy storage system.However,there are still some defects restrict the development of the electrodes of Li battery,such as there is still a huge research space of high capacity anode for Li-ion battery and shuttle effect of polysulfides,large volume-change and poor conductivity of sulfur in Li-S battery.This paper aims at studying a novel high capacity material for Li batteries,the structure-electrochemical performance connections and the energy storage mechanism is further studied to provide some new ideas for developing high-performance batteries.The research contents and innovations are as follows:（1）Inspired from the structure of natural mimosa,a novel mimosa leaf-like SiO₂was prepared by template method as the anode of Li-ion battery.The robust mechanical properties of the SnO₂ anode are demonstrated through density functional theory（DFT）.The strength change of lithiation structures are calculated.Real-time lithiation is observed using an in-situ transmission electron microscopy（TEM）technology.The presented anode shows a stable capacity of 760 mAh g^-1 after 200 cycles at 0.2 C,and a high capacity retention of 99%is achieved after three rounds of measurements.（2）Based on the results above mentioned,a novel nanocomposite consisting of mimosa leaf-like carbon and sulfur was prepared for Li-S battery.The biomimetic structure is able to accommodate the volume-change of sulfur during charge/discharge process;and the carbon matrix provides a good conductivity for rapid electron transfer.The carbon/sulfur composite-based Li-S batteries exhibit a good electrochemical performance including a stable capacity after 1000 cycles,along with a Coulombic efficiency as high as 99.6%.In addition,the density functional theory method is employed,which analyzes the adsorption between carbon and polysulfides including Li₂S₄,Li₂S₆,and Li₂S₈,enabling a long-term cycling stability.（3）We present a novel semispherical composite consisting of sulfur and polyaniline（PANI）hydrogel coating on a bowl-shaped hollow TiO₂ for Li-S batteries.The TiO₂@PANI/S composites show an excellent performance with a high capacity of 1058mAh g^-1 after 200 cycles at 0.2 C,with a stable Columbic efficiency of 99.8%.The composite also possesses a recoverable rate-performance under repeated tests.The Li⁺ion diffusion coefficient is studied,which indicates that the semispherical composite enables a rapid Li⁺ion transportation.In addition,the density functional theory（DFT）calculations further confirm a strong adsorption of TiO₂ for polysulfides including Li₂S₄,Li₂S₆,and Li₂S₈,which efficiently suppress the shuttle effect.In conclusion,the research provides a new idea for addressing the structure-changes issues of electrode materials during battery charge and discharge,which is expected to solve a series of problems and exhibits a good potential for applications.