Bio-templated Fabrication And Electrochemical Properties Of SiOC-based Anode Materials

In order to meet people's increasing demand for power batteries,it has become the focus of current research to develop electrode materials with high power density for Li-ion batteriys?LIBs?.Silicon oxycarbide?SiOC?material has been considered as a promising anode because it can not only maintains the high reversible capacity of Si-based anodes,but also keeps the structure intact taking advantages of the malleability of C-based materials.However,the large irreversible capacity,poor cyclic stability and inferior rate capability greatly restrict its practical applications.In this paper,a new bio-template method combined with supercritical fluid technology is reported to fabricate amorphous SiOC microspheres.Meanwhile,MnO and Sn nanoparticles are introduced to improve the electrochemical properties of SiOC-based anode materials.The main contents are as follows:?1?Two kinds of SiOC microspheres with specific morphology and uniform size have been prepared using supercritical fluid technology in which Chlorella serves as both bio-template and carbon source.Amorphous SiOC is mainly composed of disordered carbon networks and SiOC glass phase units.There are more electrochemical active sites?SiOC glass phase units?in the SiOC sample synthesized through the hydrolysis process,leading to better electrochemical properties.After 300cycles at 100 mA g^-1,SiOC2 sample can still deliever the discharge capacity of 377mAh g^-1.All the samples exhibit great electrochemical atability.The intact structure and constant morphology can be hold during cycling.?2?C/MnO/SiOC composite has been fabricated through the hydrolysis of tetraethyl orthosilicate under supercritical condition,in which Chlorella serves as both bio-template and carbon source,and MnO nanoparticles are introduced by bio-sorption and one-step calcination.Materials characterizations demonstrate that strip-shaped MnO nanoparticles with the size of about 10 nm are wrapped on the surface of SiOC microspheres.All the elements reach uniform distribution in samples.As anode materiales for LIBs,the introduction of MnO nanoparticles enhances the reversible capacity of the whole electrode.After 200 cycles at 100 mA g^-1,C/MnO/SiOC exhibits the reversible capacity of 770 mAh g^-1.Structural integrity can be kept in C/MnO/SiOC because carbon-rich SiOC matrix can act as buffer agent.At the same time,carbon coating layer can encapsulate MnO particles.Thus,great electrochemical stability can be achieved.?3?Sn⁴⁺ions can be imported using the heavy metal ion bio-sorption feature of Chlorella.On this basis,Sn@SiOC composite can be synthesized by bio-template method,supercritical fluid technology and subsequent one-step calcination.Sn nanoparticles with the size of several nanometers are totally embedded inside the amorphous SiOC matrix,and all the elements distribute uniformly in samples.Electrochemical measurements indicate that the introduction of Sn nanoparticles efficiently improve the rate capability of samples.The reversible capacity of Sn@SiOC at 100 and 5000 mA g^-1 are 1.1 and 1.6 times higher than those of SiOC,respectively.Amorphous SiOC surrounding matrix for Sn can not only buffer the volume change,but also prevent the aggregation of Sn nanoparticles during cycling.As a result,the intact structure and constant morphology of Sn@SiOC composite can be hold during repeated intercalation/deintercalation processes.