Department of Energy Engineering (Battery Science and Technology)With increasing demand for the application of conventional lithium-ion batteries (LIBs) to large-scale energy storage devices, associated safety concerns arising from the flammable organic liquid electrolytes (LEs) become more critical. Recently, all-solid-state lithium-ion batteries (ASLBs) using inorganic solid electrolytes (SEs) are considered a promising alternative to conventional LIBs in perspective of battery safety and energy density. Especially, sulfide SE materials are attracting great attention owing to high Li+ conductivities of 10-2-10-3 S cm-1 and deformability. From practical point of view, development of sheet-type electrodes and thin SE membranes are imperative for realizing practical high-energy all-solid-state cells. The solution-based process including polymeric components is common protocol for fabricating sheet-type electrodes in conventional LIBs. However, severe reactivity of sulfide SEs to common polar solvents and the particulate properties of these SEs lead to serious complications in the wet-slurry process for used to fabricate ASLB electrodes or SE membranes, such as the availability of solvents and polymeric binders and the formation of ionic contacts and percolation.
In this work, a new scalable fabrication protocol for sheet-type ASLB is developed by solution-processable sulfide SEs (Li6PS5[Cl,Br]), combined with the conventional composite LIB electrodes or porous polymer membranes. Firstly, fabrication of the sheet-type ASLB electrode is demonstrated. The liquefied SE is infiltrated into the pores of LIB electrodes and then solidified, achieving high surface coverage of SE and favorable Li+ pathways. The SE-infiltrated LiCoO2 (LCO) and graphite (Gr) electrodes show high reversible capacities, which is comparable to LE-based cells and outperforms to conventional dry-mixed electrodes. The all-solid-state LCO/Gr full cells using SE-infiltrated electrodes demonstrate the promising electrochemical performance at both 30 ??C and 100 ??C, highlighting the excellent thermal stability of ASLBs.
Moreover, sheet-type Si electrodes is fabricated and their electrochemical performance with variation of particle size of Si, polymeric binders, and external pressure is systematically investigated. Owing to intimate ionic contact by homogenous SE solution, the SE-infiltrated Si electrodes show high reversible capacities of over 3000 mA h g-1 and initial Coulombic efficiencies (CEs) over 80% at 30 ??C. The large difference in initial CEs between Si electrode with external pressure of 20 MPa and 5 MPa indicates the importance of engineering of external pressure. The high energy density of 338 W h kgLCO+Si-1 is achieved for the LCO/Si full cell, which is improved by 21% compared to that of LCO/Gr full cell.
Finally, the flexible and thin (40-70 um) SE membranes are developed by combining solution-processable SEs (Li6PS5Cl0.5Br0.5 (LPSClBr)) with mechanically compliant and thermally stable polymer membranes (polyimide (PI)). The PI-LPSClBr membrane exhibits the Li+ conductivity of 0.2 mS cm-1 at 30 ??C with significantly reducing the mass loading of SE layer (5.0-9.5 mg cm-2 for PI-LPSClBr and 113 mg cm-2 for thick SE layer). The LiNi0.6Co0.2Mn0.2O2/graphite full cell using PI-LPSClBr shows promising electrochemical performance (at 30 ??C without liquid electrolytes) and excellent thermal stability, outperforming the ASLBs using composite solid electrolyte (PEO-LiTFSI including inorganic filler). Finally, the SE injection process, similar to liquid electrolyte injection in conventional LIBs, is successfully demonstrated.clos
