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Preparation And Performance Of Carbon-based Composites For Lithium-sulfur Batteries

Posted on:2018-04-02Degree:MasterType:Thesis
Country:ChinaCandidate:H H DengFull Text:PDF
GTID:2321330518475036Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Now,energy crisis and environment issues have become the biggest challenge that hinders the sustainable development of economy.Meanwhile,with the rapid development of renewable energy sources such as wind and solar power,it is stringent requirement researching new energy storage equipment.Lithium-Sulfur(Li-S)batteries have already become appealing technology in the numerous technologies,owing to their conspicuous advantages such as incomparable theoretical energy density(2500 Wh/kg),high theoretical capacity(1675 mAh/g),high security,rich raw material resources and environmental friendliness.However,it suffers from serious issues like poorer conductivity of sulfur,remarkable volume expansion during the lithiation process,and the irreversible dissolution of polysulfides(Li2Sn,4?n?8)in the electrolyte resulting in the shuttle effect.These shortcomings limit the practical application of Li-S batteries.In this paper,different approaches including addition of conductive functional interlayer,the composites structure design of sulfur cathode and the porous carbon structure design of sulfur cathode have been employed to address the above issues.1.The addition of nitrogen-doped 3D graphene functional interlayer to enhance the performance of Li-S batteries.A freestanding nitrogen-doped graphene functional interlayer placed between the sulfur cathode and the separator has been investigated to enhance the electrochemical performance for Li-S batteries.The interlayer with three-dimensional porous structure and abundant of N-doping active sites,not only can increase electron transport pathway and the storage capacity of liquid electrolyte,but also can physically and chemically adsorb the highly soluble lithium polysulfides to reduce the loss of active material.With a pure sulfur electrode(high sulfur content of 70 wt%),the as-assembled Li-S battery delivers a high initial discharge capacity up to 1481 mAh/g at a rate of 0.1C,and maintains a reversible capacity of 956 mAh/g after 50 cycles of charge/discharge.Comparing with conventional cells,we have highly improved the electrochemical performance for Li-S batteries.2.The preparation of S@MWCNT-PANI-G composite for enhance the performance of Li-S batteries.We have prepared a MWCNT-PANI-G composite as sulfur host by a simple self-assembly approach for Li-S batteries.The resultant S@MWCNT-PANI-G composite with a sulfur content of 68 wt%shows a high initial discharge capacity up to 1290 mAh/g,good capacity retention of 784 mAh/g after 100 cycles of charge/discharge at the current density of 330 mA/g,and good rate capability of 663 mAh/g and 548 mAh/g at 1.65 and 3.3 A/g,respectively.The remarkable electrochemical performances are mainly attributed to the unique architecture of MWCNT-PANI-G with an enhanced electronic and ionic conductivity.Furthermore,this special architecture can provide strong physical and chemical confinement to the active materials and the soluble lithium polysulphides.3.The preparation of S@porous carbon composite for enhancing the performance Li-S batteries.We prepared novel free-standing nitrogen-doping porous carbon foam(PCF),which was obtained by pyrolysis and activation of the natural melaleuca bark,and then it was employed as a binder-free current collector to host sulfur.The study shows that the obtained PCF possesses sheet-like porous carbon structures,high specific surface area,large pore volume and in situ N-doping.By taking advantage of these properties,the resulting PCF/S electrodes exhibit an initial discharge capacity of 1330 mAh/g,good reversible capacity of 880 mAh/g after 100 cycles at 0.2C rate,and deliver an excellent cycling stability(over 250 cycles at 0.5C with 0.14%capacity fading per cycle).In addition,the PCF/S electrodes with areal mass loading of 6 ng/cm2 show a high areal capacity of 4.14 Ah/cm2.
Keywords/Search Tags:Lithium sulfur batteries, Energy storage, Graphene, Electrolyte, Porous carbon, Composites
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