Ultra-high volume specific capacity flexible lithium-sulfur battery comes out, pointing to the wearable field

by:CTECHi     2021-07-22

Lithium-sulfur batteries have received widespread attention due to their high energy density and are considered to be one of the alternatives to traditional lithium-ion batteries. However, due to the poor conductivity of lithium-sulfur battery charge and discharge products (S and Li2S or Li2S2), the shuttle effect of lithium polysulfide during charge and discharge, and the lower density of sulfur, the preparation has high volumetric energy density and long cycle life. Of lithium-sulfur batteries are facing huge challenges. At the same time, with the rapid development of wearable devices, it is imperative to prepare flexible batteries with high specific capacity.

▲ Figure 1. Material preparation process

Fudan University Xu Yuxi's research group prepared a 'sandwich' structure for the above problems Graphene/nanosulfur/conductive polymer (PEDOT:PSS) flexible and dense electrode material (Figure 1). First, nano-sulfur was grown in situ on the surface of graphene oxide (GO) (Figure 1-Ⅰ), and then PEDOT:PSS was introduced as a functional dispersant to reduce GO to obtain a 'sandwich' structure of graphene/nanosulfur/high conductivity The uniform molecular composite nanosheet dispersion (Figure 1-Ⅱ), and finally the flexible and dense but still porous film is prepared by the self-assembly method of suction filtration (Figure 1-Ⅲ). The composite electrode material has the following advantages: (1) The graphene/conductive polymer network with excellent conductivity can provide sufficient ion/electron transmission channels, and combined with nano-sulfur, it can significantly increase the utilization rate of active materials and make the battery It has high specific capacity and good rate performance, and can effectively alleviate the volume change during charging and discharging; (2) The functional groups of graphene and conductive polymer can effectively adsorb lithium polysulfide and inhibit its damage during charging and discharging. The shuttle effect greatly improves the cycle life of the battery; (3) The dense structure produced by the suction filter self-assembly greatly increases the volume density of the electrode active material, so that the battery has a higher volumetric specific capacity.

▲ Figure 2 Electrochemical performance of lithium-sulfur button battery

Based on the above advantages, the composite material is used as the positive electrode The volumetric specific capacity of the lithium-sulfur battery is as high as 1432Ah L-1 at a rate of 0.1C, and it is cycled for 500 cycles at a charge-discharge rate of 1C, and the capacity retention rate reaches 80%, and the specific capacity decay rate per cycle is only 0.04%. At a charge-discharge rate of 4C (6700 mA g-1), the discharge specific capacity is still as high as 701 mAh g-1.

▲ Figure 3. Lithium-sulfur soft pack battery performance

Based on the above results, we further increase the sulfur loading and Prepared lithium-sulfur soft pack battery. Under different folding angles, the capacity displayed by the soft-pack battery and the brightness of the diode lit by it does not change significantly. After a long cycle, the capacity hardly decays, indicating that the electrode material has great practical application value in flexible batteries. . This work provides a useful perspective for the in-depth understanding of the electrode structure-performance relationship and the preparation of new high-performance flexible lithium-sulfur electrode materials and devices. The paper was published in the journal 'Advanced Materials'.

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