Researchers at Zhengzhou University, Tsinghua University and Stanford University have developed a solid-electrolyte-based liquid Li-S and Li-Se (SELL-S and SELL-Se, respectively) battery system with the potential to deliver energy densities exceeding 500 Wh kg-1 and and 1,000 Wh L-1, together with the ability of low-cost and stable electrochemical performance for future concentrated and large-scale storage applications.
The batteries use a Li6.4La3Zr1.4Ta0.6Othe (LLZTO) ceramic tube as electrolyte and work at temperatures higher than the melting point of lithium. Polysulfide or polyselenide shuttle effects and lithium dendrite growth are effectively prevented, and high energy density, together with high stability, fast charge/discharge capability, high Coulombic efficiency, and high energy efficiency, can be achieved. A paper on their work is published in the journal Joule.
The current state-of-the-art lithium-ion batteries (LIBs) have an energy density of less than 300 Wh kg-1 and 750 Wh L-1 . Sulfur (S) and selenium (Se), which are in the same group (VIA), are promising candidates to replace commercial metallic oxide cathodes for LIBs because of their high capacity (1,670 mAh g-1 when lithiated to Li2S and 675 mAh g-1 when lithiated to Li2Se), high theoretical energy density (~2,600 Wh kg-1 and 2,800 Wh L-1 for Li-S battery; ~1,160 Wh kg-1 and 2,530 Wh L-1 for Li-Se battery), and correspondingly low cost ($41 kWh-1 for Li-Se and $15 kWh-1 for Li-S based on electrode materials).
Since the initial use of S and Se as electrodes in batteries, investigations of Li-S and Li-Se batteries have attracted substantial attention. Previous research has mostly focused on batteries with a solid-state Li-metal anode, a solid-state S or Se cathode (powder or different S/C or Se/C composites), and a liquid organic electrolyte. However, due to the use of solid lithium metal and a liquid organic electrolyte, the above battery structure has certain intrinsic issues: (1) poor cycling stability and low Coulombic efficiency because of the shuttling effect caused by dissolution of short-chain Li2Sx or Li2Sex in the liquid organic electrolyte, safety issues associated with the high flammability of the liquid organic electrolyte, and (3) dendritic growth of the lithium anode and its side reactions in the electrolyte.
Additionally, a large volume change of solid S and Se during charge and discharge causes the abscission of active S or Se from the current collector, causing cycling instability and decreasing the usage of Se and S. These issues have seriously impeded the development of Li-S and Li-Se batteries.—Jin et al.
Structure and schematic diagram of SELL-S and SELL-Se battery system. (A) Structure of the SELL-S and SELL-Se batteries. Cross section of the battery. (B) Optical image of a SELL-S and SELL-Se cell case. (C) Process of S/C secondary particle preparation using isotactic cool pressing. (D) Charge and discharge schematic of SELL-S and SELL-Se batteries. Jin et al.
The SELL-S and SELL-Se batteries consist of a liquid lithium-metal anode; a molten S or Se cathode with carbon black, and an LLZTO ceramic tube electrolyte. The Lithium-metal anode is inside the LLZTO tube, and a stainless steel rod is inserted, serving as the current collector for the anode.
A S(Se) cathode with a carbon black conductive additive (with a mass ratio of m(S or Se):m(C) = 9:1) is inserted into the stainless steel cylindrical container outside the LLZTO tube, being physically and electronically separated from the lithium anode by the LLZTO tube.
The stainless steel cylinder works as current collector for the cathode at the same time. The conductive carbon needed for molten S and Se only occupies 10% of the total electrode weight, so the dead weight is minimized.
Jin et al. (2019) “High-Energy-Density Solid-Electrolyte-Based Liquid Li-S and Li-Se Batteries,” Joule doi: 10.1016/j.joule.2019.09.003