Recent Advances and Future Perspectives of Composite Electrolytes for Solid Lithium-Metal Batteries
Solid-state lithium-metal battery,based on solid electrolyte(SSE),are considered a research hotspot in the field of ener-gy storage due to their advantages of high energy density and high safety.The use of solid electrolytes,rather than conventional toxic and flammable liquid electrolytes,can fundamentally address safety concerns.The development of solid electrolytes has also made the practical application of lithium metal possible.Li metal anodes have gained significant attention due to their ultrahigh specific capacity(3860 mAh·g-1),low density and the lowest electrochemical potential(-3.04 V).The successful substitution of Li metal anode for the graphite anode can lead to a significant increase in the cell energy density.Various types of solid electrolytes have been reported for the construction of solid-state Li metal batteries.Inorganic solid electrolytes typically exhibit high ionic conductivity and mechanical strength.However,their commercial manufacturing is significantly limited by poor electrode/electrolyte interfacial compatibility and a tedious preparation procedure.In contrast,polymeric solid electrolytes offer good flexibility,low cost and excellent processability.Nevertheless,their low ionic conductivity at room temperature and poor mechanical strength seriously hindered their practical usage.The development of organic-inorganic composite solid electrolyte(O-ICSE)has effectively integrated the advantages of polymeric and inorganic solid electrolytes,making it the most promising solid electrolytes for large-scale practical application.Incorporating inorgan-ic fillers into the polymer host can reduce the crystallinity of the polymer matrix and improve the fast ion transport.In addition,the fill-ers can immobilize anions,allowing for the rapid transport of Li+and subsequent reduction of battery polarization.Inorganic fillers can be mainly categorized as either inert or active ones,with active fillers able to conduct ions themselves in addition to enhancing the transport of lithium ions by reducing the polymer matrix's crystallinity and providing an inorganic/polymeric interface.Garnet-type LL-ZO and its derivatives are commonly used as active fillers for the preparation of O-ICSE due to their high ionic conductivity,wide elec-trochemical window and good thermal stability.Various inorganic fillers with different structures,including low-dimensional materials(nanoparticles,nanofibers and nanoplates)as well as three-dimensional materials,have been incorporated into solid electrolytes.Par-ticularly,three-dimensional inorganic fillers can be particularly advantageous as they can form continuous organic/inorganic interfac-es,enabling the construction of three-dimensional and continuous ionic transport channels.Furthermore,the three-dimensional struc-ture can also significantly enhance the mechanical strength of the composite electrolyte membranes.These three-dimensional inorganic fillers are typically prepared through electrospinning,freeze-drying,sacrificing templates methods,and other techniques.Multilayer composite solid electrolytes are designed to enhance the interfacial compatibility between electrolyte and electrode.For instance,in-serting a flexible polymer solid electrolyte layer between the rigid oxide inorganic solid electrolyte and the electrode can significantly re-duce the interface impedance prominently.However,there are still several pressing issues that need to be addressed before composite solid electrolytes can be widely adopted.These issues can be summarized into two points:(1)Despite the fact that the ionic conductiv-ity of most composite solid electrolytes can reach 1×10-4 S·cm-1,there is still a significant disparity compared with liquid electrolyte(1×10-3～1×10-2 S·cm-1).These results directly lead to the large internal resistance for the solid-state battery,which restricts the cell from cycling at high rates.Additionally,the solid-solid interface impedance between the solid electrolyte and the electrode is large,leading to low cathode loading and overall battery energy density.As a result,it is challenging to attain practical usage of state-of-the-art solid-state batteries.(2)The production process is complex and expensive,and the existing production technology is not yet ma-ture enough.These issues hinder the application of solid-state batteries.In order to realize the wide application of solid-state lithium-metal battery in the future,it is it is essential to enhance the overall electrochemical performance of solid electrolytes,including the ionic conductivity,electrochemical window,high-voltage stability and long-term cycle performance.Additionally,there is an urgent need to simplify the preparation process and reduce the cost.The ultra-thin design of solid electrolyte is vital to maximize the energy density of the battery.The introduction of a mechanical framework to host the composite solid electrolyte is one of the most effective strategies to achieve the ultrathin composite solid electrolytes.In addition to the ultrathin design of solid electrolyte,it is also important to carefully control the negative to positive electrode ratio.However,most of the reported works are based on far more excess Li metal.And the current reported electrochemical performance with excess Li metal cannot reflect the actual electrochemical performance.In particular,the electrochemical cycling performance of pouch cell should also be provided since the pouch cells are much closer to the actual operation of batteries.This review summarized the research progress of organic-inorganic composite solid electrolytes in recent years,including the structural design,ultra-thin solid electrolyte design and the corresponding electrochemical performance of electro-lytes.Furthermore,the practical application and the future development had also been prospected.
solid electrolyte(SSE)solid lithium metal batterystructure designelectrochemical performance
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