基于钴酸锂载体构筑高体积比容量硫基复合材料

锂-硫电池具有高的理论质量/体积能量密度,因而成为最具发展潜力的高比能二次电池体系. 然而,由于硫载体通常采用轻质的碳纳米材料,导致硫基复合材料的振实密度和体积比容量均偏低,制约了电池体积能量密度的提升. 本文尝试采用具有高密度特征的钴酸锂(LiCoO₂)作为硫的载体材料,以构筑高振实密度的硫基复合材料,进而提高硫正极的体积比容量. 研究显示,LiCoO₂对可溶性多硫化物具有较强的吸附作用,能够促进硫的电化学转化,因而提高了硫的活性物质利用率和循环稳定性. 同时,由于具有高的振实密度(1.90 g·cm^-3),S/LiCoO₂复合材料的首周体积比容量高达1750.5 mAh·cm^-3,是常规硫/碳复合材料的2.2倍. 因此,本文利用具有高密度特征的LiCoO₂作为硫载体来提升硫复合材料的体积比容量,有助于实现锂-硫电池的高体积能量密度.

LiCoO2 as Sulfur Host to Enhance Cathode Volumetric Capacity for Lithium-Sulfur Battery

Lithium-sulfur battery is one of the most promising secondary battery systems due to its super high theoretical gravimetric and volumetric energy densities (2600 Wh·kg^-1 and 2800 Wh·L^-1, respectively). However, the practical volumetric capacity of sulfur cathode is still unsatisfied due to the overuse of low-density host materials, such as carbon nanomaterials. Herein, commercial LiCoO₂ with the high tap density of 2.94 g·cm^-3 was used as the host material to build high density sulfur-based composite and compact electrode for increasing the volumetric capacity. Obviously, the tap density of the as-prepared S/LiCoO₂ composite was 1.90 g·cm^-3, larger than that of the conventional S/carbon composite (0.89 g·cm^-3). Correspondingly, the pressed electrode density could be increased to 2.60 g·cm^-3 by using the S/LiCoO₂ composite. In particular, LiCoO₂ showed an effective adsorption and electrocatalytic conversion toward soluble intermediate polysulfides, and facilitied to achieve the high utilization of sulfur and cycle stability. As expected, the S/LiCoO₂ composite exhibited larger capacity and slower capacity decay rate at 0.1 C rate as compared with the S/carbon composite. Meanwhile, the polarization in discharge-charge processes was smaller for the S/LiCoO₂ composite, showing the enhanced reaction kinetics by adopting LiCoO₂ host. Therefore, the S/LiCoO₂ composite showed superior rate capability and cycle performance at large current density. By virtue of the high tap density, the S/LiCoO₂ composite delivered a larger volumetric capacity (1750.5 mAh·cm^-3_-composite), almost 2.2 times of the S/carbon composite (811.4 mAh·cm^-3_-composite). Furthermore, the volumetric capacity of the pressed S/LiCoO₂ electrode could reach 1676.8 mAh·cm^-3_-electrode based on the electrode level, almost 2.5 times of the S/carbon electrode (676.5 mAh·cm^-3_-electrode). This work provides a feasible strategy to achieve the high volumetric capacity and energy density of cathode based on LiCoO₂ as sulfur host, which provides reference for further developing high volumetric energy density cathode materials for lithium-sulfur battery.