Synthesis And Electrochemical Performance Of Carbon Based Anode Materials

In the past two decades,lithium-ion batteries?LIBs?are considered to be promising candidates in energy-storage systems because of their high energy density,long cycling life.However,the use of lithium is hampered by the limited resources of lithium.Recently,increasing attentions are turning to Na-ion batteries?NIBs?due to the low-cost and plentiful Na resource.The abundance in the earth and low cost of Na become greatly advantageous when large amount of electrode materials are demanded for energy storage.Since the energy density and cycle lifetime of batteries are mainly determined by their electrode materials,the development of high performance electrode materials have attracted intensive research interests.Carbon materials are considered promising anode materials.In this thesis,carbon materials of covalent organic frameworks and graphene were prepared,and used as anode materials for Li⁺battery and Na⁺battery.The main contents of this thesis are summarized as followed:?1?Two commercially available dianhydrides namely pyromellitic dianhydride?PMDA?and naphthalene-1,4,5,8-tetracarboxylic dianhydride?NTCDA?were used as building blocks to polymerize with melamine for fabricating dianhydride based polyimides?NTCDA-based polyimide?PI-1?,PMDA-based polyimide?PI-2??.In sodium ion batteries?NIBs?,the capacity of PI-1 could be maintained 177 mAh·g^-1 after 100 charge/discharge cycles at a current density of 500 mA·g^-1.Even at much highercurrent density of 5 A·g^-1,a reversible capacity of 89 mAh·g^-1 can be achieved after 1000 cycles.However,a reversible capacity of51 mAh·g^-1 can be obtained for PI-2.The performances of PI-1 and PI-2 in lithium ion batteries?LIBs?are as well as those in NIBs.?2?During the long cycles the battery could produce much heat and furthermore cause series safety problems.In order to solve this problem,polyphosphonitrilic/graphene nanocomposites with high security were prepared.In LIBs,the capacity of PPN/GN could be maintained at 321 mAh·g^-1 after 1200 cycles at a current density of 5 A·g^-1,which is 1.5 times of graphene?GN?.Even at higer current densities of 2 A·g^-1 and 5 A·g^-1,the PPN/GN still shows high capacities of 508 mAh·g^-11 and 456 mAh·g^-1.When the current density was reduced backed to the 100 mAh·g^-1,a specific capacity of 1001 mAh·g^-1 could be restored,demonstrating an excellent reversibility.The performances of PPN/GN in lithium ion batteries?LIBs?are better than its of NIBs.