| The development of energy storage technology has become extremely important owing to the growing global demand for energy and the strong development of electric vehicles and portable electronic devices.Due to their low weight and higher energy storage abilities compared to other kinds of batteries,lithium-ion(Li-ion)batteries are commonly used as electrical energy storage technologies in different wearable electronic devices.Moreover,for a wide range of applications,like electric vehicles with a similar driving range to combustion engines,lithium-ion battery innovation would not fulfill the high energy and power requirements.Traditional Li-ion batteries are currently experiencing their energy density limit based on intercalation substances,and many scientific studies have focused on the development of new energy storage technologies with high energy densities.The advantages of sulfur cathode material,including its high capacity(1672 mAh g-1),inexpensive,extensive sources,as well as especially non-toxicity.Hence,next generation lithium sulfur batteries with high theoretical specific energy(2600Whkg-1)have been extensively prosecuted lately.Nevertheless,the intrinsic insulating nature of sulfur,as well as the special "solid-liquid-solid" phase transitions of sulfur cathode during cycling,would give rise to the dissolution and shuttle effect of long-chain lithium polysulfides(Li2Sx,4 ?x?8)and considerable volume change(?79.2%).This might in turn result in the severe loss of active materials,lithium metal consumption,limited Coulombic efficiency and heavy polarization,rendering the high-loading sulfur cathodes to suffer from low capacity and poor cyclability.To tackle these challenges,tremendous efforts have been devoted to the rational design of the composition and architecture of Li-S batteries in the past decade.Very recently,growing research efforts have manifested that a great deal of key battery characteristics,encompassing reversible capacity,rate capability,and stability,are critically dependent upon the electrically inactive components,such as functional binders.Generally,the functional binders have been proved to significantly promote the electrochemical performance of Li-S batteries through the following two aspects:(1)Restricting the dissolution and free diffusion of long-chain polysulfides into the electrolyte through functional polar groups,thus greatly inhibiting the shuttle effect of soluble polysulfides;(2)aiding to construct three-dimensional high-strength and high-conductivity skeleton to maintain the structural/electrical integrity of the sulfur cathodes during long-term cycling.Given the above,high-strength polar binders are ideal for constructing high-sulfur-loading Li-S batteries.Nevertheless,most of the current high-load Li-S batteries can be only cycled for a limited number of times under very low current densities.This may due to a fact that the binders show very weak interfacial interaction with the non-polar sulfur surface,therefore sulfur materials are difficult to effectively integrate into the conductive network formed by the binder and conductive additives despite the high mechanical strength of cross-linked binders.In this regard,enhancing the interaction between sulfur and high-strength polar binders is the key to guaranteeing the achievement of a highly integrated electrode structure.This thesis work explains the important research improvement of functional binders for high-loading sulfur cathodes.We devise an interface assembly strategy to construct a highly integrated sulfur@polydopamine/cross-linked polyacrylamide(c-PAM)binder composite cathodes,targeting durable high sulfur-loading Li-S batteries.The catechol and amine functional groups on polydopamine(PD)can be covalently and non-covalently correlated with any organic/inorganic surfaces,endowing the PD layer with powerful adhesion and film-forming capability.Hence,the high-adhesion PD can be firmly anchored onto the graphene/sulfur(G-S)surface and form a uniform and ultra-thin coating layer.Meanwhile,the PD coating also presents a strong affinity to the c-PAM binder,thus tightly integrating sulfur with the binder and greatly boosting the overall mechanical strength of the laminate.Moreover,the PD coating and c-PAM network rich in polar amine and amide groups can act as two effective blockades against the effusion of soluble polysulfides through powerful capture.The PD-c-PAM double-layer structure can also effectively release stress from volume changes by adjusting its own elastic deformation during cycling.Consequently,the G-S@PD-c-PAM cathodes present an excellent anti-deformation upon folding and pressing.The 2.2 mg cm-2 sulfur-loaded G-S@PD-c-PAM cathode exhibits a capacity of 500 mAh g-1 after 800 cycles at 4 C while retaining the capacity of 480 mAh g-1 after 300 cycles at 1C upon the sulfur loading rises to 4.5 mg cm-2(1 C=1600 mA g-1).Even at a high sulfur loading of 9.1 mg cm-2(66.4 wt%sulfur content),the integrated cathode can still achieve a capacity of 396 mAh g-1 after 50 cycles at 0.2 C.Impressively,the high-sulfur loading Li-S coin cells can power 120 light-emitting diodes and an electric fan,verifying their high energy density for potential practical applications.This work provides a system-wide concept for constructing high-loading sulfur cathodes through integrated structural design... |
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