High Mass Loading Copper Sulfide Based Composite Cathodes for All-Solid-State Lithium Sulfur Batteries Enables High Volumetric Capacity

The current state of the art insertion cathode materials provides energy density around 700 Wh kg -1 . In order to improve the energy density of batteries, conversion type materials are considered. Among these, Sulfur is regarded as promising cathode material as it theoretically provides a high specific capacity of 1672 mAh g-1 and energy density of 2500 Wh kg -1 , a value three times higher than the conventional state of the art cathode materials.[1] Unfortunately, the Sulfur conversion reaction is accompanied by 80% volume change and polysulfide shuttling[2]. The use of composite cathodes, incorporating carbonaceous materials and metal sulfides, can help improve cell performance by buffering volume changes while creating effective electron conduction pathways and enhancing sulfur utilization by catalytic effects[3]. Recently we studied the effect of different metal sulfides on the sulfur cathode and realized their beneficial effect towards improved electrochemical performance. This work shows how the synergy between CuS (a transition metal sulfide) and S can lead to extraordinary high areal capacities, improved cycling life, higher energy efficiency, and volumetric energy density compared to a pure S cathode. The all-solid-state cell using an inorganic solid-state Li 2 S-P 2 S 5 -LiI electrolyte, metal sulfides-containing composite cathodes, and Li metal showed stable cycling (1200 cycles over one year) with high specific capacity up to (970 mAh g -1 ). High mass loading (5 mg cm -2 of active material equivalent to 22 mg cm -2 of total cathode mass) cells using composite (CuS-Sulfur) electrodes deliver capacities as high as 1600 mAh g -1 (CuS+S) and 7 mAh cm -2 at 20 °C. The higher density of CuS also leads to larger volumetric capacities, up to 3900 mAh cm -3 (CuS+S), thus enabling an energy density gain up to 15% with respect to a conventional Carbon-Sulfur cathode. Different technics such as ex-situ XRD, SEM, EIS and Galvanostatic cycling elucidate the metal sulfide conversion mechanism. Figure 1