آماده سازي و مشخصه يابي الكترود كامپوزيت نانو الياف كربن و سيليسيم براي آند باتريهاي يون ليتيم

چكيده انگليسي :

Preparation and Characterization of Composite Carbon Nanofibers and Silicon Electrode to be used as Anodes for Lithium Ion Batteries Elmira Ghanbari e ghanbari@ma iut ac ir Date of Submission Feb 20 2012 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisors Prof Ahmad Saatchi Supervisor Email asaatchi@cc iut ac irAssoc Prof Keyvan Raeissi Supervisor Email k raeissi@cc iut ac irAbstractA great attention is drawn to lithium ion batteries LIBs by the burgeoning dominance of the technology Developments in cathode materials that have effectively doubled the capacity within the past few yearsdemand an anode to match Carbonaceous materials as the most commonly used anode material have beenstudied and developed immensely in recent years but they have a serious drawback of low theoreticalcapacity This calls for new anode materials to substitute carbon Si based anode materials are among themost promising choices for further studies The reason is that Si is the lightest member of Group IVelements after carbon and shows the highest gravimetric capacities up to 4000 mAhgr 1 for the endmember Li21Si5 although achieving this at ambient temperature is difficult Thus even small amounts ofSi 20 wt in a composite material would lead to impressive results The formation of lithiumintercalation compounds within Silicon is associated with a large volume expansion that results inpulverization of the electrode material and loss of electrical contact between the material grains onprolonged cycling The resulting rapid capacity fade reduces its practical use as electrode Many researchershave addressed this problem by using nanometer sized particle to reduce the absolute volume changes ofsilicon anodes during cycling Others efforts have been directed toward preparation of compositescontaining small silicon particles uniformly distributed within an electrochemically active or inactive solidphase and acting as a mechanical and electrochemical buffer The latter is necessary for preventingelectrochemical sintering of the silicon particles which takes place during alloying with Li Carbonaceousphases are the logical choice of buffering media for silicon containing composites because they are notonly electrochemically active but also have good electrical conductivity and permeability for Li In thepresent study such a composite has been made by electrodepositing amorphous silicon on carbon nanofiber CNF membrane as an anode material for LIBs Electrically conductive CNFs are produced byelectrospinning and later heat treating polyacrylonitrile PAN precursor Another nanofibrous substrate hasbeen made by electroless plating of Ni on stabilized PAN nanofibers which is also utilized for siliconelectrodepositon to prepare another composite anode material The electrochemical performances of both ofthe composite materials have been evaluated in LIB charge discharge testing The Si CNF compositepresented a considerable capacity for lithium ions which makes it an ideal candidate for the anode materialof high power LIBs The other composite having a pre coat of Ni which is electrochemically inactive withlithium ions allowed a more precise evaluation of the Si coat It is shown that Electrospinning is astraightforward and effective method for producing nanofiber structures that by controlling heat treatmentparameters can lead to the production of conductive CNFs which make a promising substrate and a templatefor the electrodeposition of Si By controlling the electrodeposition time in 2 8 V vs Pt QRE a nanometriclayer of Si was formed over the CNFs resulting in randomly distributed Si nanowires It is envisaged thatthe resulting composite as the anode material is effective in providing room for expansion and preventingparticle re aggregation in the cycling of LIB Keywords Lithium Ion Battery Anode Material Silicon Carbon Nanofiber Electrodeposition Electrospinning Electroless

قنبري، الميرا

آماده سازي و مشخصه يابي الكترود كامپوزيت نانو الياف كربن و سيليسيم براي آند باتريهاي يون ليتيم

الكتروريسي , رسوب دهي الكتريكي سيليسيم