The Characteristic Research Of Al₂SiO₅ Ceramic Separator And Binder-Free Sulfur Cathode In Li Storage

Up to date,lithium-ion batteries（LIBs）have been widely used in digital products,mobile power-supply devices and electric vehicles.In parallel,lithium-sulfur cells are highly expected to become one of promising next-generation energy-storage systems due to their high specific energy and abundant sulfur resources.However,under hot working conditions,the polymer separator for LIBs would shrink,resulting in a short circuit in batteries and triggering safety accidents like battery thermal runaway,catching fire,and explosion,etc.Lithium-sulfur cells would encounter many problems involving low actives loading ratio,sulfur dissolution,and polysulfide shuttling effect.Aiming at LIB systems,we propose to develop a type of ceramic separator with stable thermal properties,capable of elevating the LIBs safety without sacrificing their energy-storage behaviors.As for lithium-sulfur cells,we propose a three-dimensional（3D）current collector electrode,enabling the construction of binder-free sulfur cathode and trying to solve key issues of lithium-sulfur cells by virtues of its unique structure advantages/functionality.Herein,Al₂SiO₅ceramic films with high thermal stability are used to replace commercial polypropylene separators for making high-safety LIBs.Furthermore,a 3D current collector electrode is designed and used to realize the construction of high actives loading and binder-free sulfur cathode.The delicate structure characterization and electrochemical analysis toward distinct separators and sulfur cathodes are carried out to explore their working mechanism in Li storage.The major research contents involve:1.The application research of Al₂SiO₅ ceramic separators in LIBs:The commercial polypropylene and Al₂SiO₅ ceramic separators are both used in three different Li-storage cathode systems（LiFePO₄,LiNiO₂,S）,respectively.The testing shows such Al₂SiO₅ ceramic separators not only own excellent thermal properties and good electrolyte affinity,but also exhibit good compatibility/electrochemical stability with either the cathode or anode.Especially in LiNiO₂ cathode systems,batteries made of Al₂SiO₅ ceramic separators show outstanding cyclic stability（the discharge specific capacity retention retains 83%after 500 cycles at 1 C current rate）.In lithium deposition testing,Li//Li symmetric cells assembled by ceramic separators are very stable within1000 h,showing a tiny potential difference lower than 14 mV;their polarization voltage almost keeps a linear growth relationship with the current rate.By contrast,batteries made by polypropylene separators shows a higher potential change（≥20 mV）,and they tend to suffer the voltage runaway at large current densities.Besides,this ceramic separator can inhibit the growth of lithium dendrite,greatly improving the full-battery safety performances.This work may provide the new concept and methods for the development of LIBs in specific circumstances.2.Preparation of High S Filling and Binder-Free Cathodes for Lithium-Sulfur Cells:Besides tough kinetic issues in S cathodes,a poor S filling ratio,and a low compact density in films led by the overuse of porous hosts,conducting agents or other additives impede the further progress of Li-S cells.To overcome these constraints,we herein propose the rational design of robust NiO nanoframeworks to make high S filling and binder-free cathodes.Notably,such arrayed thick frameworks have an impressive spatial filling ability,showing a remarkable S filling ratio of 77.6%.To further optimize the cell behaviors,all of the arrayed NiO matrix surface is evenly paved by graphitic carbon shells,and the open-up architecture for S-filled frameworks is intactly encapsulated by functionalized nickel nitrate hydroxide layers.Thanks to subtle interfacial engineering and smart hybrid configurations,a high initial discharge capacity of over 1481 mAh g^-1and a longer-term cyclic lifespan are achieved at 0.1 C.Also,this optimized binder-free cathode leads to great improvements in Coulombic efficiency,the S utilization ratio,and rate capabilities.Our work presents not only an appealing route to making high S filling and binder-free cathodes for Li-S cells but also insight for the smart design of integrated film electrodes for other electrochemical applications.