Solid–solid reactions are very effective for solving the main challenges of lithium–sulfur (Li–S) batteries, such as the shuttle effect of polysulfides and the high dependence of electrolyte consumption. However, the low sulfur content and sluggish redox kinetics of such cathodes dramatically limit the practical energy density of Li–S batteries. Here a rationally designed hierarchical cathode to simultaneously solve above‐mentioned challenges is reported. With nanoscale sulfur as the core, selenium‐doped sulfurized polyacrylonitrile (PAN/S7Se) as the shell and micron‐scale secondary particle morphology, the proposed cathode realizes excellent solid–solid reaction kinetics in a commercial carbonate electrolyte under high active species loading and a relatively low electrolyte/sulfur ratio. Such an approach provides a promising solution toward practical lithium sulfur batteries.

Lithium-sulfur (Li-S) batteries are competitive for the next-generation energy storage applications. However, soluble polysulfides cause severe shuttle effect and electrolyte abuse. Solid-solid and quasi-solid conversions are effective to address the...

More importantly, Se is more compatible with cost-effective, safe carbonatebased electrolytes, while S is largely limited to expensive, unsafe ether-based electrolytes. [11,12] It is found that the Se confined in mesoporous carbon matrix can directly converted to Li 2 Se in the carbonate-based electrolytes without any formation of soluble polyselenides. [13][14][15] Unfortunately, due to the nucleophilic reaction of carbonate solvents between polysulfides, the S/mesoporous carbon composite is incompatible with the carbonate-based electrolytes and therefore commonly operates in ether-based electrolytes. [16][17][18] In this case, the Li-S batteries may face "shuttle effect" issue due to the high solubility of intermediate polysulfides in ether-based electrolytes. [19] Additionally, ether-based electrolytes exhibit low flash points, posing a potential risk for batteries operating at elevated temperatures. [20,21] Despite the perceived advantages, as compared with Li-S batteries, the applications of Li-Se batteries are limited by the less abundance of Se in earth and higher material cost. [22][23][24][25] Based on the above-mentioned opposite but complementary features between Se and S, heteroatomization of Se and S has been proposed as an attractive strategy to enable highperformance cathode material for lithium storage. [26,27] Actually, previous reports of Li-Se x S y batteries have demonstrated enhanced higher energy density than Li-Se batteries and improved rate performance and cycling stability compared to Li-S batteries. [28][29][30] However, the research on Li-Se x S y batteries is focused on obtaining optimal performances in etherbased electrolytes (Figure 1a). The Li-Se x S y battery in carbonate-based electrolytes is still in its infancy, since the Se x S y based cathodes usually exhibit poor electrochemical performances due to the nucleophilic reactions between carbonate-based electrolytes and sulfur species. To the best of our knowledge, there are no reports on the electrochemical performances of Se x S y /mesoporous carbon cathodes with high content of active material Se x S y (≥60 wt%) in the commercial carbonate-based electrolytes (Figure 1a). Additionally, it is still unclear why Se/mesoporous carbon can work well in the carbonate-based electrolytes but S/mesoporous carbon can't work. What would happen when the isolated heteroatom S is doped into Se 8 instead of doping Se into the isolating S 8 which Lithium-sulfur/selenium batteries have attracted broad interest and achieved good performance using ether-based electrolytes. However, when the ether-based electrolytes are employed, Li-S/Se battery systems still have several inevitable drawbacks inhibiting their practical applications, such as intermediate product dissolution issues, and a dependency on a high content of electrolyte. Thus, it is urgent to pay attention to the electrochemical properties of Se x S y cathodes in carbonate-based electrolytes, which may avoid the above mentioned problems. In this work, a series of mesoporous carbon/Se x S ...

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