Free-Standing Sulfide Electrolyte Thin Film for Solid-State Lithium Battery Applications

The great attention to low carbon economy through the electric vehicles grows the market of lithium ion battery (LIB) rapidly because of its high power and energy density. However, a liquid carbonate electrolyte employed in the LIB is flammable, thus being able to cause severe safety issues. To reduce the safety issues, a solid electrolyte (SE) instead of the currently commercialized liquid electrolyte has been introduced to fabricate solid-state lithium batteries [1,2]. Even though the prevailing SEs (that is, sulfide, polymer, garnet and sodium superionic conductor) do not simultaneously satisfy all the stability requirements such as mechanical, chemical, electrochemical and thermal stabilities, sulfides have the highest ionic conductivities and the favorable mechanical properties among them, thereby being considered to work reasonably well in the conventional sandwich battery structure [2].<br/>To prepare the sulfide SE, a slurry coating technology has been generally used. However, the traditional wet method charges additional cost coming from using an environmentally harmful organic liquid solvent and the resulting production of a solvent recovery system. In addition, strong reactivity between a polar liquid solvent and the sulfide leads to the decrease in the ionic conductivity of the sulfide SE [2]. Thus, the introduction of a liquid-free dry process is necessary to obtain the sulfide electrolyte. Furthermore, thin and free-standing SEs are preferred for high efficiency batteries with a high degree of freedom of electrode material selection.<br/>In this work, separate sulfide electrolyte films with a thickness of several dozens of micrometers are demonstrated by a dry procedure which is composed of the following three steps [3]: first, an agyrodite-type sulfide and a binder powders are mixed. Next, the two nonsticky powders are ground homogeneously to fabricate a sticky sulfide-binder dough. Then, the dough is fed into rollers to obtain the independent SE layer with a thickness of below one hundred micrometers.<br/>Microstructural and elemental analyses are carried out utilizing a field emission scanning electron microscope and energy dispersive X-ray microanalysis, respectively. Alternating voltages are applied by a frequency response analyzer (10^-1-10⁵ Hz, Solartron HF 1225, AMETEK Scientific Instruments) to get Nyquist plots and calculate ion conductivities of dry- and wet-processed sulfide SE samples. Charging-discharging cycling experiments are performed under galvanostatic cycling condition from 3.0 to 4.3 V (Toscat-3000, Toyo System). The test results are presented and discussed in the talk.<br/><br/>[1] D. O. Shin et al, <i>ACS Appl. Mater. Interfaces</i> 2023, 15, 13131-13143<br/>[2] R. Chen et al, <i>Chem. Rev.</i> 2020, 120, 6820-6877<br/>[3] S. Yoon et al, Korea patent, application number 10-2023-0030160 (Application date March 7th, 2023)<br/><br/>Acknowledgement<br/>This work was supported by internal fund/grant of Electronics and Telecommunications Research Institute (ETRI). [23YB2600, Development of Fundamental Technology for Non-Lithium Resources Based Next Generation Aqueous-Type Multivalence-Metal-Ion Battery]