Meso-structural Carbon Nanocages:Controllable Preparation And Energy Storage Applications

The exploration of novel structural carbon nanomaterials for energy storage materials is the main objective today.Based on the progresses and remaining existing problems of the Li-ion batteries negative materials and Li-S batteries positive materials,this dissertation is focusing on the controllable preparation and energy storage applications of the hierarchical carbon nanocages(hCNC).The main contents are summarized as followed.1.The controllable preparation of hCNC.As electrode materials,3D hierarchical carbon nanomaterials with abundant porous tunnel and interconnected framework structure greatly favor the electrolyte penetration,ion diffusion,electron conduction and structural stability.Hence,the novel structural carbon nanomaterials have drawn lots of attention.Recently,we developed an in situ MgO template method to produce the carbon nanocages.In this work,by selecting the basic magnesium carbonate with 3D hierarchical structure as precursor,the 3D hierarchical carbon nanocages has been prepared featured by the well-defined multiscale characters in atomic scale,nanoscale and mesoscale,with coexisting micro-/meso-/macro-pores.The new carbon nanomaterials possess the large specific surface area(1276 m2/g),high pore volume(4.178 cm3/g),and good conductivity(183 S/m),which greatly favors the electrolyte penetration,ion diffusion,electron conduction and structural stability.Thus the unique hCNC demonstrates the great potential in energy storage from the Li-ion batteries to Na-ion,Li-S,Li-air batteries.2.hCNC as high-rate Li-ion batteries negative electrode.Recent progress in the high-rate positive materials of Li-ion batteries has reached the half-cell capacity up to 60 mAh/g at an ultrahigh rate of 400C.The exploration of matchable ultrahigh-rate negative counterparts has become an imperative challenge to realize the dramatic performance improvement of the full cells with charging/discharging on the order of seconds.In this study,the obtained hCNC was performed as Li-ion batteries negative.The unique structure of hCNC greatly favors the electrolyte penetration,Li-ion diffusion,electron conduction and structural stability,resulting in an ultrahigh rate capability and excellent cyclability.The corresponding electrode stabilizes at 229 mAh/g even over 10000 cycles at an ultrahigh rate of 25 A/g(33 s for full-charging)while delivering a large specific power of 37 kW/kgelectrode and specific energy of 339 Wh/kgelectrode.The correlation of the advanced performance with multiscale characters also provides a demonstration for the emerging exciting frontier of mesoscale science of multidisciplinary interests.In addition,the hCNC also demonstrates excellent sodium storage performance.3.hCNC confining high-loading sulfur for high-rate Li-S batteries positive electrode.Li-S batteries are now hindered by the low utilization of sulfur,short cycle life and poor rate capability,due to the natural insulation of sulfur and the dissolution of intermediate polysulfides.The obtained hCNC in this study owns the high pore volume,network geometry and good conductivity.By making full use of the unique structure of the hCNC,we have realized the high-loading confinement of sulphur inside the nanocages(up to-80 wt%),meanwhile,much alleviated the polysulfides dissolution.The 3D hierarchical architecture also increases the conductivity and favors the Li-ion diffusion.The so-constructed carbon-sulphur composites with S loading of 79.8 wt%presents the superb performance as the Li-S cathode with large capacity,high-rate capability and long cycle life,which could shorten the charging time for the mobile devices from hours to minutes.The excellent performance suggests the great potential for practical applications.4.hCNC as high-performance Li-air batteries positive electrode.The obtained hCNC in this study owns the large specific surface area,high pore volume,network geometry and good conductivity,which favors the O2 gas transportation,electrolyte penetration,Li-ion diffusion,and the disperse deposition of insulating discharge product(Li2O2)as Li-air batteries positive.hCNC presents preliminarily excellent performance,reaching a high specific discharge capacity over 10000 mAh/g at 0.1 A/g and cycling 30 cycles with limited capacity of 800 mAh/g at a high rate of 1 A/g.