Abstract
Due to the ever-growing demand for high-density energy storage devices, lithium-ion batteries with a high-capacity cathode and anode are thought to be the next-generation batteries for their high energy density. Lithium sulfide (Li2S) is considered the promising cathode material for its high theoretical capacity, high melting point, affordable volume expansion, and lithium composition. This review summarizes the activation and lithium storage mechanism of Li2S cathodes. The design strategies in improving the electrochemical performance are highlighted. The application of the Li2S cathode in full cells of lithium-ion batteries is discussed. The challenges and new directions in commercial applications of Li2S cathodes are also pointed out.
Highlights
Lithium-ion batteries (LIBs) are widely used in portable electronic equipment, electric vehicles, and large-scale energy storage devices due to their relatively high energy density and long cycle life
A sulfur-based composite cathode should be coupled with the lithium metal or lithium-containing anode. e low electronic and ionic conductivity is the intrinsic characteristics of elemental sulfur, leading to low specific capacity and poor rate performance. e various soluble lithium polysulfides (3 ≤ n ≤ 8) are produced during charging and discharging. e shuttle effect of dissolved lithium polysulfides results in active material loss and rapid capacity fading. e volume change is as high as 80% in the conversion of S (2.07 g·cm− 3) into Li2S (1.66 g·cm− 3). e repeated volumetric expansion and contraction will accelerate the cathode pulverization and the loss of electronic contact [3,4,5,6]
To meet the ever-growing demand for high-density energy storage devices, lithium-ion battery cathodes with high specific capacity are the bottlenecks of present LIBs
Summary
Lithium-ion batteries (LIBs) are widely used in portable electronic equipment, electric vehicles, and large-scale energy storage devices due to their relatively high energy density and long cycle life. Lithium-sulfur (Li-S) batteries as the representative of nonintercalation-type lithium storage materials have very high energy density (2600 W·h·kg− 1), more than 8 times that of currently commercialized LIBs [1, 2], and are regarded as one of the most promising secondary batteries with high energy density Both sulfur and its fully lithiated state of Li2S can be used as active cathode materials for Li-S batteries. Compared with the Li-S batteries, the LIBs using the Li2S materials as cathodes can reach an energy density as high as that of Li-S batteries, which is several times that of the current commercial LIBs which use intercalation-type cathode materials such as LiFePO4, LiMnO4, and LiCoO2, and advance in safety by avoiding the use of lithium metal anodes. We hope that this review will provide a fundamental understanding on the lithium storage mechanism of the advanced cathode materials
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