钒基硫化物-MXene异质催化剂的制备及锂硫电池催化机理对比研究

    Preparation of Vanadium-based Sulfide-MXene Hetero-Catalysts and Comparative Study of Catalytic Mechanism of Lithium-sulfur Batteries

    • 摘要: 锂硫电池因其高的理论比容量与能量密度而被视为最具前景的储能电池之一,但锂硫电池中活性物质硫及其放电产物Li2S的低导电性、充放电过程产生的中间产物的穿梭效应、缓慢的硫氧化还原动力学等问题造成了严重的容量衰减,限制了其实际应用。本文通过一步水热法合成3种不同的钒基硫化物@MXene异质结构催化剂,并将其应用于锂硫电池正极宿主。结果表明相比于VS4@MXene 和V5S8@MXene,VS2@MXene具有更大的比表面积与电化学活性面积,为锂硫电池提供了更多的活性位点,从而提高电化学反应动力学。本文实验与密度泛函理论 (Density Functional Theory, DFT)计算结果表明, VS2@MXene具有更强的多硫化物吸附能力与电子导电性,有效地缓解了多硫化物的穿梭效应并提高了硫的利用率。以S/VS2@MXene为正极的锂硫电池,在1 C的电流密度下实现了815.4 mAh·g−1的首圈放电比容量, 并在400圈循环后, 仍然能保持在645.4 mAh·g−1的可逆比容量。本文为锂硫电池中钒基硫化物正极催化材料的选择提供了一定的思路。

       

      Abstract: Because of high theoretical specific capacity and energy density, lithium-sulfur batteries (LSBs) are regarded as one of the most promising energy storage batteries. However, the low conductivity of the active sulfur and the Li2S discharge product, the shuttle effect of intermediate products produced by the charging and discharging process, and serious capacity degradation caused by the slow sulfur redox kinetics, limits the practical application of LSB. Herein, three different vanadium sulfide@MXene hetero-structure catalysts were synthesized by one-step hydrothermal method and applied to the cathode host in LSBs. Compared with VS4@MXene and V5S8@MXene, VS2@MXene has the largest specific surface area and electrochemical active surface area, which provides more active sites in LSBs, thereby improving the electrochemical reaction kinetics. Meanwhile, the experimental and Density Functional Theory(DFT) theoretical calculation results show that the VS2@MXene has the strongest polysulfide adsorption ability and electronic conductivity, which effectively alleviates the shuttle effect of polysulfides and improves the utilization of sulfur. LSBs with S/VS2@MXene as the cathode achieve an initial discharge specific capacity of 815.4 mAh·g−1 and still maintain a reversible specific capacity of 645.4 mAh·g−1 after 400 cycles at 1 C. This research provides some insights for the selection of vanadium-based sulfide as the catalytic materials and hosts in lithium-sulfur batteries.

       

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