Abstract
Lean electrolyte (small E/S ratio) is urgently needed to achieve high practical energy densities in Li–S batteries, but there is a distinction between the cathode's absorbed electrolyte (AE) which is cathode‐intrinsic and total added electrolyte (E) which depends on cell geometry. While total pore volume in sulfur cathodes affects AE/S and performance, it is shown here that pore morphology, size, connectivity, and fill factor all matter. Compared to conventional thermally dried sulfur cathodes that usually render “open lakes” and closed pores, a freeze‐dried and compressed (FDS‐C) sulfur cathode is developed with a canal‐capillary pore structure, which exhibits high mean performance and greatly reduces cell‐to‐cell variation, even at high sulfur loading (14.2 mg cm−2) and ultralean electrolyte condition (AE/S = 1.2 µL mg−1). Interestingly, as AE/S is swept from 2 to 1.2 µL mg−1, the electrode pores go from fully flooded to semi‐flooded, and the coin cell still maintains function until (AE/S)min ≈ 1.2 µL mg−1 is reached. When scaled up to Ah‐level pouch cells, the full‐cell energy density can reach 481 Wh kg−1 as its E/S ≈ AE/S ratio can be reduced to 1.2 µL mg−1, proving high‐performance pouch cells can actually be working in the ultralean, semi‐flooded regime.
Highlights
The MIT Faculty has made this article openly available
When scaled up to Ah-level pouch cells, the full-cell energy density can reach 481 Wh kg−1 as its E/S ≈ absorbed electrolyte (AE)/S ratio can be reduced to 1.2 μL mg−1, proving high-performance pouch cells can be working in the ultralean, semi-flooded regime
A uniform slurry composed of raw commercial sulfur powder, Ketjen Black (KB) and LA133 binder was cast on Al current collector and lyophilized at −40 °C
Summary
As a standard technique used in fabricating porous ceramics[15,19] and carbonaceous materials,[16] lyophilization ( called freezedrying) has been widely adopted in the preparation of hierarchically porous materials. Other than the routine electrochemical characterizations, we pay close attention to the variation of Li–S cell performance, which is evaluated by the standard deviation of battery performance of the same batch of cells, made by nominally the same materials and process Compared with several recent works on lean electrolyte condition of Li–S batteries,[14,21,27] it can be concluded from Figure 5f that our FDS-C electrode that used only low-cost raw material and convenient large-batch processing method (host-less) would be highly competitive at lean-electrolyte and high sulfur loading condition. The “drying of the river bed” may be of a chemical nature, instead of a purely physical or geometric nature
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