Study Of Electrode Design And Regulation Strategies For Sulfide All-Solid-State Batteries

Lithium-ion battery is one of the most widely used electrochemical energy storage technologies,but the safety concerns derived from organic electrolytes are hindering their development.Solid-state electrolytes have the properties of high decomposition temperature,non-volatility,and noninflammability,which can significantly reduce the security risks of batteries.In addition,solid-state electrolytes work very well with high specific energy lithium metal anodes.The all-solid-state batteries with lithium metal anodes are expected to realize high energy density and high safety electrochemical energy storage.There are numerous solid-state electrolytes have been developed in recent years.Among them,sulfide solid-state electrolytes deliver the ionic conductivities comparable to that of organic electrolytes and exhibit good processability,and are regarded as one of the most promising solid-state electrolytes.However,in sulfide all-solid-state batteries,the volume change of electrode materials,insufficient ductility of electrolytes,and poor(electro)chemical compatibility between electrolytes and electrode materials induce many problems,which includes electrochemo-mechanical failures on the cathode side,side reactions on the cathode/electrolyte interfaces,sluggish charge transfer kinetics in composite cathodes,and poor contact of lithium anode/electrolyte interfaces,etc.This dissertation mainly solves these problems from material modification,interface engineering and electrode design.The main contents are as follows:(1)The microstructure engineering strategies for cathode materials are developed to enhance the electrochemo-mechanical stability of the cathode.First,the sintering process is optimized to prepare polycrystalline Ni-rich particles composed of densely stacked large-size primary particles.The structural characterization and finite element simulation results indicate that this unique microstructure can suppress the stress accumulation and crack formation inside particles during the electrode densification process and charge/discharge process,thus maintaining the integrity of the microstructure of cathode particles and composite cathodes.Thus,the composite cathodes based on mechanically reinforced polycrystalline Ni-rich particles deliver the fast and stable charge transfer networks.The electrochemical test results demonstrate that the mechanically reinforced polycrystalline Ni-rich cathodes achieve superior rate capability and cyclic stabilityIn view of the insufficiency of polycrystalline structures in electrochemomechanical stability and charge transportation,the well-dispersed single-crystalline Nirich materials are developed as cathodes.The structural characterizations verify that the integrated single-particle structure can withstand the anisotropic lattice strain during high-voltage cycling to impede the formation of intergranular cracks.Moreover,the well-dispersed single-crystalline particles build the fast ionic percolation networks in composite cathodes.Compared to polycrystalline counterparts,single-crystalline Nirich cathodes deliver better rate performances,longer cycle life,and also show advantages in both operating at high temperature and high mass loading conditions.(2)A fluoride-rich cathode protective layer is designed to improve the(electro)chemical compatibility of Ni-rich cathode/electrolyte interfaces.The surface chemical analysis results illustrate that the interfacial protective layers with good electrochemical stability and electronic insulation can function as a shield to the high electrode potential in Ni-rich cathodes,and consequently reduce the side reactions on the cathode/electrolyte interfaces.Moreover,the LiF components in interfacial protective layers can accelerate the ionic conduction on cathode particle surfaces,thus constructing the fast ionic transfer channels in composite cathodes.The application of surface modified single-crystalline Ni-rich cathodes greatly improve the rate capability and cyclic stability of all-solid-state batteries.(3)In order to reveal the design principle of Ni-rich electrodes in all-solid-state batteries,a comprehensive investigation on the particle sizes and mass fractions of active materials is carried out during electrode design.The electrochemical test results demonstrate that there is a positive correlation between particle sizes and mass fractions of Ni-rich cathodes during electrode design,that is,as particle size increases,the higher mass fractions are required to build the fast charge transfer networks inside composite cathodes.The combined structural characterizations and electrochemical kinetic tests indicate that the competition between ionic conduction and electronic conduction inside composite cathodes is critical to the battery performances.Engineering the microstructure by optimizing electrode compositions can balance the ionic conduction and electronic conduction in composite cathodes,and further realize the best rate performances.(4)An adhesive protective layer is designed to enhance the stability of lithium anode/electrolyte interfaces.The hot-melt adhesive fibers are decorated on the surface of sulfide electrolyte films to construct the adhesive interface layers between lithium anodes and electrolyte films.The peel strength tests verify that the introduction of adhesive interface layers is the key to realize the intimate and stable lithium anode/electrolyte contact interfaces.The test results based on lithium symmetric batteries and full cells confirm the importance of the adhesive interface layers in suppressing inhomogeneous lithium plating/stripping and prolonging cyclic life.