基于半导体光电极构筑新型太阳能辅助充电锂硫电池及其电化学性能调控

A new prototype of solar-driven chargeable energy storage device for direct conversion and storage of solar energy can not only provide a promising solution to the challenges of energy shortage and environment pollution, but also avoid the dependence of powering portable electronics on the power grid. However, the solar-driven chargeable energy storage devices reported to date exhibited a very low overall photo-electric storage-conversion efficiency and discharge capacity. The search for an effective solar energy storage system is highly required, yet remains a challenge. Lithium-sulfur (Li-S) battery exhibits 3-7 times higher energy density than that of conventional lithium-ion batteries, and thus makes a promising choice for solar energy storage. In this project, we proposed a new strategy to build a solar-assisted chargeable Li-S battery by integrating a photoelectrode in the cathode. With the aid of photoelectrode, the solar energy will be utilized to simultaneously oxidize discharge products S2- ions to polysulfide ions in cathode and reduce Li+ ions to metal Li, realizing the charge process. On charging under illumination, the photovoltage generated on the photoelectrode will compensate the Li-S battery’s charging voltage. By utilizing photoelectrode, this designed device will realize the storage of solar energy in Li-S batteries. Various photoelectrodes will be utilized to study the effect of photoelectrode on the solar-assisted chargeable Li-S battery. This study will clarify the mechanism and general rules of effects of the conduction band, band gap and surface structure of photoelectrode on electrochemical performance of solar-assisted chargeable Li-S battery. The results obtained could guide the development of high-efficiency and stable solar-driven chargeable energy storage devices.

新型太阳能可充电储能器件可以实现太阳能至电能的直接转化与存储，能够有效缓解能源危机和环境污染问题，同时可避免电子产品充电时对电网的依赖。而至今报道的太阳能可充电储能器件普遍面临放电容量和光-电转化存储效率低的瓶颈。基于锂硫电池具有高的比容量和能量密度（为目前商品化锂离子电池的3-7倍）的优点，本项目提出通过半导体光电极的植入，利用其在光照下产生的光生空穴和电子分别将正极硫离子氧化和负极锂离子还原，构建太阳能辅助充电锂硫电池的新思路。光照充电时，光电极产生的光电压部分补偿充电电压，间接实现太阳能至电能的转化存储。深入研究半导体光电极的本征结构特性对电池的作用机制，旨在建立半导体导带位置、带隙宽度、表面结构对太阳能辅助充电锂硫电池性能的调控规律，并阐明其调控机理，进而构建高效稳定的太阳能辅助充电锂硫电池，为其他光-电转化存储器件的设计提供科学依据和指导。

锂硫电池因其能量密度高、成本低等优势，是极具潜力的下一代电化学储能器件。本项目提出通过半导体光电极的植入，利用其在光照下产生的光生空穴和电子分别将溶于电解液的Li2S4氧化和负极锂离子还原，构建光辅助充电锂硫电池。依据材料电子结构与锂硫电池工作电压的匹配性，制备了具有合适带边位置的TiO2、ZnO以及ZnS光电极材料，研究三种光电极材料带边位置及带隙对光充电电压的影响，验证了提出的反应机理；发现导带位置低的材料利于节省锂硫电池充电电能，当以ZnS作为光电极组装电池时可节省电能24.6%。本项目在构筑高效稳定的光辅助充电锂硫电池用光电极方面取得了创新性研究成果，制备了三种不同形貌的TiO2光电极，研究形貌对光电极催化活性的影响，发现纳米棒阵列由于具有更负的平带电位，受激发电子还原能力强，可获得更低的光充电电压及优异的稳定性，证实了光电极表面结构的调控可有效提高光辅助充电锂硫电池性能。构建了ZnO/CdS/PDA异质结光电极，发现异质结可拓宽ZnO的光吸收范围并促进光生载流子的分离，减小了光生载流子的复合机率，提高了太阳光的利用效率，获得了高性能光辅助充电锂硫电池。基于本项目研究成果，作为第一作者或通讯作者已在国际核心刊物发表SCI论文4篇，申请发明专利2项，项目执行期间，培养毕业研究生3名。达到了项目预期研究目标。