| Silica（SiO2）is expected to become the next generation of anode materials for commercial lithium-ion batteries because of its advantages such as high theoretical specific capacity and low discharge potential.However,due to the existence of strong Si-O bonds inside SiO2,it usually exhibits relatively poor ionic conductivity and electronic conductivity.In addition,the alloying reaction that occurs during lithium insertion will also bring about a certain volume expansion effect.Therefore,these characteristics are problems that need to be solved urgently if the SiO2 material wants to go to practical production and application.In view of the poor conductivity of SiO2and the volume expansion effect,this paper mainly conducts modification studies from the perspectives of nanostructured design and composite.Firstly,we used ammonium DL-tartrate as the soft template and tetraethyl orthosilicate（TEOS）as the SiO2 source,and investigated the preparation process of SiO2 nanotubes through the soft template method and the sol-gel method.The influence of different ammonia concentration and the dropping rate of ammonia on the yield of SiO2 nanotubes was studied.Through SEM observation,it was determined that the rapid addition of ammonium hydroxide and the ammonium hydroxide concentration of12 mol/L were the optimal experimental process methods and parameters.After assembling a half-cell with SiO2 nanotubes as the anode material and conducting charge-discharge performance tests,it was found that at a current density of 0.1 A g-1,the first discharge capacity of 570 m Ah g-1 was achieved.Although the initial discharge capacity is not high,the Coulomb efficiency has exceeded 97%since the seventh cycle.Such excellent cycling stability is attributed to the fact that the hollow structure of SiO2nanotube plays a role in alleviating volume expansion during charging and discharging.Furthermore,in order to enhance the conductivity of the SiO2 nanotubes material,we designed and prepared a N-doped carbon-coated SiO2 nanotubes（SNTs@NC）composites.XRD,XPS,SEM and TEM were used to characterize the phase and micro-morphology of SNTs@NC composites.The existence of N-doped carbon on the surface of SiO2 nanotubes was confirmed.The amorphous N-doped carbon layer on the surface It is worth noting that the high specific surface area of nanotubes not only provides more sites for Li+and electron insertion during the lithiation/delithiation process,but also enables them to fully contact the electrolyte.After 200 cycles,the SNTs@NC composites achieved a reversible specific capacity of 781 m Ah g-1 at 100 m A g-1.Even under 1 A g-1 high-rate discharge conditions,the discharge capacity of the composites could still reach 522 m Ah g-1.Finally,in order to further improve the electronic and ionic conductivity of the electrode,carbon nanotubes（CNTs）conductive paper was successfully prepared using CNTs with excellent electrical conductivity and mechanical strength to replace copper foil as the current collector.The three-dimensional network structure of CNTs conductive paper can not only provide favorable transmission path for lithium ions and electrons during the charging and discharging process,but also can accommodate the volume change produced by the electrolytic during intercalation/deintercalation of Li+.Therefore,the electrode material obtains better cycle performance and rate performance.We assembled the half-cell and performed the corresponding electrochemical performance characterization.Among them,the galvanostatic charge-discharge cycle test results at a current density of 100 m A g-1 show that the first discharge capacity and charge capacity of the SNTs@NC electrodes with CNTs conductive paper as the current collector were 1658 and 1028 m Ah g-1,respectively.And the discharge capacity could still be maintained at 1008 m Ah g-1 after 200 cycles.More delightfully,the discharge capacity of 380 m Ah g-1 was still realized even at the discharge rate of 1.8 A g-1. |
