New Insights in All-Solid-State Ceramic Batteries: Dendrite Growth through Pressure and Density Effects
Authors: Fleutot Benoit , Gagnon Catherine , Girard Marc-André , Dubé Joël , Fitoussi Fouad , Koh Ki Seok , Kim Chisu , Zaghib Karim 
Published: May 2020

Despite some progress performed, state-of-the-art lithium ion batteries still require improvements in energy and power to extend the range of electric vehicles and reduce charging time. In this domain, all-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium ion transport number, and no-liquid nature. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, allowing all-solid-state batteries to be easily prepared via simple mixing and cold-pressing processes, facilitating the scale-up.

Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Indeed, lithium metal is believed to be the most promising negative electrode due to its specific large capacity (3862 mAh.g-1), low volumetric density (0.534 g.cm-3 at 20°C) and the lowest electrochemical potential (-3.03V vs ENH). Nevertheless, like most metal, lithium metal is morphologically dynamic. Its surface morphology is modified, since during the electrochemical cycling, a part of lithium migrates to the other electrode to react and is then plating on its surface heterogeneously, leading to a volume change and sometimes dendrite growth with potential internal short circuit and life-threatening accidents. Ceramic solid electrolytes have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. In the same time, the chemical nature and composition of ceramic solid electrolyte can affect the dendrite growth by the interfacial chemical and electrochemical stability with lithium metal forming solid electrolyte interphase as a passivating layer. Since the lithium dendrites have to grow through this layer, its composition should play an important role in the dendrite formation. Moreover, it is known that the stack can be easily deformed because lithium dendrite growth with a high shear modulus, indicating that the solid electrolyte and its interface with lithium metal should be sufficiently strong to endure the pressure originating from lithium dendrite growth. The oxide–based ceramic solid electrolytes can be shaped by sintering at high temperature, leading to a grain and grain-boundary microstructure with some porosity, facilitating the lithium dendrite growth through grain boundaries. Due to the low density and plasticity of sulfide based inorganic solid electrolyte, the dendrite growth through the particle-particle contact can be reduced but still present.

Different parameters can influence the lithium dendrite growth and the critical current density in ceramic all-solid-state configuration, such as the solid electrolyte chemical composition, particle size, and the compactness of ceramic solid electrolyte. The pressure effect on the electrochemical performances of sulfide electrolytes was investigated. The pressure affects resistive grain boundaries, contact between lithium metal and solid electrolyte and lithium plating. As, the kinetics of reaction is derived from thermodynamic parameters, the temperature can affect the plating/stripping phenomena. These different parameters and the relationship between them will be presented and explained through complete studies based on sulfide solid electrolytes with the combination of various chemical and electrochemical techniques.