Quasi Solid State Li-S Battery Enabled By a Triple Layer Garnet Framework
Authors: Xu Shaomao , McOwen Dennis W. , Wachsman Eric D. , Hu Liangbing 
Published: February 2020

Lithium sulfur (Li-S) battery has been considered as one of the most promising next generation energy storage devices, especially for the emerging electric vehicles.1 Unlike the state-of-art lithium ion (Li-ion) batteries, the Li-S battery is based on the conversion reaction between lithium and sulfur instead of lithium intercalation/deintercalation mechanism, which leads to an exceptionally high theoretical energy density of over 500 Wh/kg.1 Despite the high energy density, there are still many problems to tackle for the application of Li-S battery. One of the biggest problems is the polysulfide shuttling effect. Massive improvements have been achieved recently to resolve the shuttling effect. However, since most methods are employed in conventional Li-S batteries, where liquid electrolyte is used, there is always dissolution of Li2Sxin the battery, leading to the decay of performance upon long term operation.

Solid state electrolyte has attracted massive research attention recently due to their ability to block lithium dendrite growth and sustain safe operation. Garnet type LLCZN electrolyte has shown excellent performance due to its high ionic conductivity and stability.2-3 The nature of ceramic electrolyte can prevent the lithium polysulfide from reaching anode side, thus eliminating the polysulfude shuttling. Therefore, a solid state Li-S battery based on garnet electrolyte which can completely resolve the polysulfide shuttling problem can be a crucial step towards the actual application of Li-S battery.

In this study, we introduce a solid-state Li-S battery based on a triple layer garnet type ceramic electrolyte, where a thin dense layer of garnet was sandwiched by two porous layer. Lithium and sulfur are molten infiltrated into the different porous sides of the garnet electrolyte and are separated by the dense layer of garnet. Therefore, it is impossible for Li2Sxto migrate to from the cathode to the sulfide, thus completely eliminating the shuttling effect. The proposed quasi solid state Li-S battery promotes a new design for high energy Li-S batteries.

The tri-layer garnet structure was prepared via a tape casting technique. The dense layer is 30 µm thick while both the porous layers are 70 µm thick with a porosity of ~67%. The sintered trilayer was characterized via SEM, XRD and XPS. The product shows characteristic cubic garnet phase which ensures high ionic conductivity. The lithium can be stripped from one side of the other, thus enabling the operation of solid-state Li-S battery. The solid-state Li-S battery based on tri-layer garnet show high capacity of 1200 mAh/gsulfur and stable coulombic efficiency of nearly 100% after 50 cycles. Moreover, even with the extra weight introduce by the ceramic garnet electrolyte, the Li-S cell still delivered an impressive energy density of 250 Wh/kgcell. Such a high energy density makes the tri-layer Li-S battery superior compared to state-of-art Li-ion batteries. Moreover, the utilization of the solid-state electrolyte also prevents the growth of lithium dendrite, enabling a much safer battery operation. As far as we know, this is the first time a high energy density Li-S battery with all solid-state anode framework is developed. The high energy density, all-in-one configuration, solid-state Li-S battery introduces a new route for future energy storage system.

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