Studies On Carbon Based Nanocomposites For Electrochemical Energy Storage

Considerable efforts have been made on electrochemical energy storage systems, such as lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries and supercapacitors to meet the energy demands. Carbon nanomaterials possess unique morphological, electrical, optical, and mechanical properties which is useful for enhancing the electrochemical energy storage performances. So, carbon and carbon nanocomposites plays a very important role in developing high performance electrodes for electrochemical energy storage.In this paper, we will focus on the research of 3-D porous carbon and carbon nanocomposites for electrochemical energy storage based on graphene oxide and nature cellulose. The synthesis of graphene materials from graphene oxide has many advantages in terms of high yield and low cost. Nature wood cellulose is an abundant, sustainable polymer material, and it is a promising precursor for carbon materials production.1) Natural cellulose paper was successfully converted to porous carbon paper by a one-step thermal carbonization, which has a large specific area of 510 m2 g-1 and can be directly used as flexible, binder-free electrodes in supercapacitors. Such an interesting carbonized cellulose paper (CCP) electrode exhibits a high capacity of 84.5 F g-2. To stretch its potential window and increase the energy density, MnO2 nanoflowers are loaded onto CCP by a simple electrochemical deposition method. This MnO2/CCP electrode delivers a high capacity of 292 mF cm-2. Furthermore, an asymmetric supercapacitor using MnO2/CCP positive electrode and CCP negative electrode delivers an operating voltage of 1.6 V and high energy density of 10.59 Wh kg-1.2) Preparation and electrochemical performance of mesoporous iron oxide/graphene nanosheets (MIO/GNS). Using graphene oxide, graphene nanosheets was prepared by thermally exfoliating method. Thermal exfoliated graphene is made up of few-layered graphene nanosheets. It has a large specific area and a 3-D structure in micro scale. Direct anchored continuous mesoporous iron oxide nanofilms on graphene nanosheets was developed via a new and versatile in-situ thermal decomposition method. The strong covalent chemical bonding between GNS and iron oxide allows the GNS matrix to constrain the volume change of MIO nanofilms. Besides, the mesoporous structure of MIO partially accommodates the volume-induced strain because of its high porosity providing free space. When using as lithium-ion battery anode, the MIO/GNS nanocomposite shows very good electrochemical performance. It has excellent capacity retention (no capacity fading after 400 cycles at 1000 mA g-1), high specific capacity (about 1000 mAh g-1 at 100 mA g-1), and good rate capability. When using as sodium-ion battery anode, it reach about 400 mAh g’1 and be stabilized for over 200 cycles at a current of 100 mA/g. The excellent cycling performance is attributed to the superior strain accommodating capability of the MIO/GNS nanocomposite.3) Preparation and electrochemical performance of graphene aerogel/sulfur composite (GA/S).3-D graphene aerogel (GA) was synthesized via hydrothermal method and supercritical drying. Solution evaporation method at room temperature and sulfur vaper anchoring method were used for the synthesis of GA/S nanocomposite. The high specific area and oxygen-containing groups of graphene aerogel is suitable for sulfur coating. It can relax the volume-induce strain of sulfur and adsorb polysulfide. The porous structure of 3-D graphene aerogel can also inhibit the dissolve of polysufide. When using as lithium-sulfur battery cathode, the GA-S nanocomposite has shown great electrochemical performance. The specific capacity of GA/S nanocomposite using solution evaporation method can reach 1260 mAh g-1 at 200 mA g-1 and retain 840 mAh g-1 after 100 cycles. The specific capacity of GA/S using sulfur vaper anchoring method can reach 1476 mAh g-1 on 1st cycle at 200 mA g-1 and retain 872 mAh g-1 after 50 cycles. The GA/S nanocomposite is also used as free-standing electrode which has also shown excellent performance. The specific capacity of AG/S free-standing cathode is 1257 mAh g-1 at the current density 200 mA g-1 and it can reach 848 mAh g-1 after 100 cycles.