1. Potassium Hexafluorophosphate Additive Enables Stable Lithium-Sulfur Batteries
Jingru Li, Sufu Liu, Yongliang Cui, Shengzhao Zhang, Xianzhang Wu, Jiayuan Xiang, Min Li, Xiuli Wang, Xinhui Xia, Changdong Gu, Jiangping Tu ACS Appl Mater Interfaces. 2020 Dec 16;12(50):56017-56026. doi: 10.1021/acsami.0c17406. Epub 2020 Dec 3.
Uncontrollable dendrite growth and low Coulombic efficiency are the two main obstacles that hinder the application of rechargeable Li metal batteries. Here, an optimized amount of potassium hexafluorophosphate (KPF6, 0.01 M) has been added into the 2 M LiTFSI/ether-based electrolyte to improve the cycling stability of lithium-sulfur (Li-S) batteries. Due to the synergistic effect of self-healing electrostatic shield effect from K+ cations and the LiF-rich solid electrolyte interphases derived from PF6- anions, the KPF6 additive enables a high Li Coulombic efficiency of 98.8% (1 mA cm-2 of 1 mAh cm-2). The symmetrical Li cell can achieve a stable cycling performance for over 200 cycles under a high Li utilization up to 33.3%. Meanwhile, the polysulfide shuttle has been restrained due to the higher concentration of the LiTFSI in the electrolyte. As a result, the assembled Li-S full cell displays excellent capacity retention with only 0.25% decay per cycle in the final electrolyte. Our work offers a smart approach to improve both the anode and cathode performance by the electrolyte modification of rechargeable Li-S batteries.
2. Interplay among Hexafluorophosphate, Difluoro(oxalato)borate Anions and Ethylene Carbonate during Their Insertion into a Graphite Electrode
Jia Zhang, Congcong Chen, Dandan Zhu, Yunju Wang, Boyu Wang, Ying Wang, Shunchao Ma, Hongyu Wang Langmuir. 2022 Mar 29;38(12):3824-3831. doi: 10.1021/acs.langmuir.1c03485. Epub 2022 Mar 16.
Ethylene carbonate solutions dissolving mixed lithium salts composed of both difluoro(oxalato)borate (DFOB-) and hexafluorophosphate (PF6-) anions are introduced into Li/graphite cells. The anions' intercalation procedures into the graphite positive electrode from these solutions are explored by charge/discharge, cyclic voltammetry, and impedance spectroscopic tests in combination with electrochemical in situ characterization including X-ray diffraction (XRD) and Raman spectroscopy. Furthermore, these solutions are characterized by ionic conductivity together with nuclear magnetic resonance measurements. The properties of the solutions are linked to the capacity values delivered by Li/graphite cells.
3. Synthesis and Electrochemical Properties of Aluminum Hexafluorophosphate
Xiaoyu Wen, Jian Zhang, Hewei Luo, Jiayan Shi, Charlene Tsay, Huanhuan Jiang, Ying-Hsuan Lin, Marshall A Schroeder, Kang Xu, Juchen Guo J Phys Chem Lett. 2021 Jul 1;12(25):5903-5908. doi: 10.1021/acs.jpclett.1c01236. Epub 2021 Jun 21.
We report the first synthesis of aluminum hexafluorophosphate (Al(PF6)3) and its electrochemical properties in dimethyl sulfoxide (DMSO). The single crystal structure of the synthesized Al(PF6)3 is revealed as [Al(DMSO)6](PF6)3, and 0.25 M Al(PF6)3 in DMSO with high ionic conductivity is obtained. The purity of this electrolyte was further confirmed with nuclear magnetic resonance spectroscopy and electrospray ionization mass spectrometry. We then demonstrated the reversibility of Al deposition-stripping in this electrolyte using scanning electron microscopy and an X-ray photoelectron spectroscopy depth profiling study. The parasitic reaction involving DMSO decomposition during Al deposition is also identified via gas chromatography/electron ionization mass spectrometry.