The Study Of Si/C Composites Anode For Lithium-ion Battery

Based on the structure of porous Si/C composites,our work mainly focuses on the four parts:(1)the study of synthesis and properties of porous Si/C composites,(2)the preparation of Si/CNT/C composites by polyvinyl alcohol(PVA)hydrogel method,(3)the preparation of Si/CNT/C composites by phase inversion,(4)the preparation of binder-free Si/G/C electrode assisted by Cu2+.(1)The study of synthesis and properties of porous Si/C compositesIn this work,different structures of the porous Si/C composites based on silicon or carbon framework were synthesized respectively.The development of multi-carbon matrix Si/C composites,which the design idea of this thesis,is confirmed by compare the performance of single-carbon matrix and multi-carbon matrix Si/C composites.(2)The preparation of Si/CNT/C composites by polyvinyl alcohol(PVA)hydrogel methodA novel polyvinyl alcohol(PVA)hydrogel method is developed to synthesize Si/CNT/C composites.In this unique structured Si/CNT/C composites,the CNT form a porous network acting both as conductive agent for electron transfer and buffer space to accommodate huge Si volume change during lithiation/delithiation process,while the Si nanoparticles and CNT are 'position'locked up by PVA hydrogel in a simple aqueous solution process,the coating layer of carbon carbonized from polyvinyl alcohol(PVA)hydrogel is conducive to stabilize the interweaved composite structure.The Si/CNT/C composites exhibit an initial reversible capacity of nearly 800 mAh g-1,an excellent capacity retention of 97.1%after 100 cycles at the rate of 0.1 C,and high capacity retention even at high current rate.(3)The preparation of Si/CNT/C composites by phase inversionThe Si/CNT/C composites were fabricated by phase inversion method.In this unique structured Si/CNT/C composites,the porous skeleton established by CNT not only provides buffer space for silicon,but also makes a great contribution to the electrical conductivity of the composites;while,the carbonization of PAN mainly acts as "binder" to reinforce the stability of the skeleton,and further strengthens the connection between Si and CNT.Therefore,the Si/CNT/C composites with the feed ratio of Si:CNT:PAN is 2:2:4 exhibit an initial reversible capacity of nearly 960 mAh g-1,a relatively good capacity retention of 79.1%after 100 cycles at the rate of 0.1 C.(4)The preparation of binder-free Si/G/C electrode assisted by Cu2+Since the complexation between graphene oxide and copper ions,graphene oxide aggregates with silicon particles inside in the case of copper ion added,then binder-free Si/G/C composite electrode prepared through droping-drying method directly.In this unique structured Si/G/C electrode,the structure of copper foam improves both the loading of active materials and the conductivity of the electrode;graphenes build good conductive network,and provide good support for the elastic silicon volume expansion;copper ion is beneficial to the homogeneous dispersion of graphene and silicon,meanwhile,Cu3Si alloy which generated from Cu and Si in high temperature disperses in silicon particles,improves the conductivity of silicon particles and reduces the volume variation of silicon particles to a certain extent;the conductive carbon is conducive to strengthen the electrical contact between silicon and graphene or graphene layers.The prepared Si/G/C composite electrode exhibit an initial Kulun efficiency of 81%,an excellent retention capacity of?2200 mAh g-1 at 0.1 C after 100 cycles with no attenuation barely,moreover,it exhibit the retention capacity of?1700mAhg-1 at 1 C after 100 cycles.