Abstract
Uncontrolled growth of insulating lithium sulfide leads to passivation of sulfur cathodes, which limits high sulfur utilization in lithium-sulfur batteries. Sulfur utilization can be augmented in electrolytes based on solvents with high Gutmann Donor Number; however, violent lithium metal corrosion is a drawback. Here we report that particulate lithium sulfide growth can be achieved using a salt anion with a high donor number, such as bromide or triflate. The use of bromide leads to ~95 % sulfur utilization by suppressing electrode passivation. More importantly, the electrolytes with high-donor-number salt anions are notably compatible with lithium metal electrodes. The approach enables a high sulfur-loaded cell with areal capacity higher than 4 mA h cm−2 and high sulfur utilization ( > 90 %). This work offers a simple but practical strategy to modulate lithium sulfide growth, while conserving stability for high-performance lithium-sulfur batteries.
Highlights
Uncontrolled growth of insulating lithium sulfide leads to passivation of sulfur cathodes, which limits high sulfur utilization in lithium-sulfur batteries
The sudden voltage drop at the beginning of the lower plateau indicates rapid electrode passivation by Li2S deposition, which limits a further reduction of the lithium polysulfide (LiPS) remaining in the electrolyte
Because the lower plateau reaction is mainly limited by electrode passivation from insulation by Li2S, extension of the lower voltage plateau with increasing the Donor Number (DN) of the anion suggests that the high-DN anions can retard the surface passivation
Summary
Uncontrolled growth of insulating lithium sulfide leads to passivation of sulfur cathodes, which limits high sulfur utilization in lithium-sulfur batteries. Practical applications of Li–S batteries are still hampered by intrinsic problems such as the low conductivity of sulfur and lithium sulfide (Li2S)[3,4,5], large volumetric changes of the electrode[6,7,8], and dissolution of intermediate lithium polysulfide (LiPS) species during cycling[9,10,11] These limitations result in low sulfur utilization[12,13], low coulombic efficiency[14,15], and fast capacity fading[16,17] of Li–S batteries. The discharge capacity remains limited due to passivation of the conducting network
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