Recent Breakthroughs in All-Solid-State Sulfide Ceramic Batteries: Performances, Safety and Future Developments

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, high ionic conductivity allowing improved all-solid-state batteries performances at room temperature but suffer of moisture exposure that could induce H₂S generation.<br/><br/>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) and the lowest electrochemical potential (-3.03V vs ENH). Ceramic solid electrolytes and especially sulfide composite solid electrolyte have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. At 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. In parallel, the sulfide solid electrolyte reacts with all components constituting the positive electrode as active material, electronic conductor, binder, current collector… Hence, all interfaces can generate side reaction, increase of polarisation, and so rapid battery fading. As demonstrated in literature, an important average pressure increase during cycling and aging can’t allow a future commercialisation of this technology. The safety is a crucial point and the generation of H₂S in the case of all-solid-state battery based on sulfide electrolyte during scale-up phase and operation must be take into account and evaluated specifically.<br/><br/>In this field and since a few years, Hydro-Quebec has decided to conduct specific research on all-solid ceramic batteries and especially in the field of sulfide-based ceramic electrolytes. Based on Hydro-Québec's knowledge with polymers, a solution of all-solid composite battery with ceramic tendency has been developed by generating several industrial properties at the different levels of the battery. The interaction previously observed in positive electrode mixture without binder have been resolved and integrated in slurry. In parallel, the impact between solid electrolyte ceramic film composition, density, reactivity with lithium metal and flexibility were studied to offer high conductivity and easily manipulation. Unlike the general perception that the sulfide electrolyte is not compatible with lithium metal, we successfully stabilized the lithium metal interface reaching the cycle life more than 500 cycles under industry-relevant pressure conditions at moderate temperature under pouch-cell configuration. The constraints of the use of li-ion equipment’s, cost reduction and safety have been considered at each level with quantitative measurements. The different improvements in positive composite electrode, in solid electrolyte ceramic film and in lithium metal interfaces will be explained. The presentation will show how technical and economical issues of sulfide electrolyte can be addressed to bring the technology closer to the market.