3, China Automotive Battery Research Institute, Beijing, , China
2, University of Science and Technology Beijing, Beijing, , China
All-solid-state lithium (ion) batteries show great advantages over traditional lithium ion batteries by replacing flammable organic electrolytes with solid electrolytes, provide enhanced safety, higher working voltage, easy packing et al., and have attracted great interests from fundamental study to commercial application. However, two core elements are required before their real application. Firstly, solid electrolyte has to satisfy (1) high ionic conductivity, (2) negligible electronic conductivity, (3) good chemical/electrochemical stability, (4) easy preparation, (5) low cost and so on. Secondly, the interfacial engineering between solid and solid is challenging because of their stiffness in nature.
Oxide-based solid electrolytes meet most of above requirements, and up to now, the highest ionic conductivity can reach 10-3 S cm-1 with the aid of high temperature and high pressure during preparation.[i] However, the sluggish interfacial engineering retards the development of oxide-based all-solid-state batteries. The simple press of solid electrolytes with electrode materials could not facilitate the solid-solid interface. While post high temperature treatment could improve the adhesion between solid electrolyte and electrode materials, chemical reactions always accompany at this high temperature, which are detrimental to the interfacial properties.[ii] Although sputtering technique can enable the interface in film batteries, the energy density is far away from enough. Therefore, it is urgent to develop a new technique for constructing both solid electrolyte and interfacial engineering at low temperatures, at least under the reaction temperature of solid electrolyte and electrode materials.
Cold sintering technique, enhancing the interfacial properties (grain boundaries and interfaces between solid electrolytes and electrode materials) by dissolution-precipitation of target materials with the aid of liquid solution at low temperatures, is ideal for the assembly of solid-state batteries.[iii] Herein, with the help of cold sintering technique, we successfully prepared the solid electrolytes Li1.3Al0.3Ti1.7 (PO4)3 (LATP), Li1.3Al0.3Ge1.7(PO4)3 (LAGP), and composite cathode LiNi0.6Mn0.2Co0.2O2/TiN/LAGP. The ionic conductivities of LATP and LAGP are close to 10-4 S cm-1 after heat treatment at 650 °C, which is about 200-300 °C lower than that of conventional sintering. The composite cathode LiNi0.6Mn0.2Co0.2O2/TiN/LAGP exhibits a specific capacity of 132 mAh g-1 when test in liquid electrolyte, while further increase of ionic conductivity could enable it in all-solid-state batteries.
[i] J. C. Bachman et al., Chem. Rev. 2016, 116, 140-162.
[ii] M. Fingerle et al., Chem. Mater.2017, 29, 7675-7685.
[iii] J. Guo et al., Angew. Chem. Int. Ed. Engl. 2016, 55, 11457.