Sn metal is believed to be one of the most promising alternative anodes to commercial graphite thanks to the high theoretical capacity and abundant storage. However, large volume change results in pulverization of the bulk electrode, which is more serious in microsized particles, leading to rapid capacity degradation. Therefore, microsized Sn was never successfully applied as the anode for Li-ion batteries. Herein, we report that the as-received Sn microparticles (325 mesh, or ∼45 μm) could be directly used as anodes for LIBs in 2.0 M LiPF6 2-MeTHF or 2.0 M LiPF6 THF/2-MeTHF electrolyte, delivering a high capacity of ∼750 mA h g−1, initial coulombic efficiency of >90%, average cycling coulombic efficiency of ∼99.9%, and capacity retention of 84.1% after 400 cycles at a rate of 2C. This work demonstrated that alloying anodes could be realized by exploring compatible electrolytes and forming compact SEI layers, representing a breakthrough for commercialization of LIBs based on alloying anodes.
Hongyu Lv,Qian Yao,Cheng Zheng,Yanan Sun,Zhao Qian,Zhikai Wei,Fang Xie,Rajeev Ahuja,Jian Yang
Sodium-ion batteries (SIBs) are attractive for large-scale energy storage and have to work at a wide temperature range. Compared to the performance at room temperature, the low-temperature performance of SIBs is always poor. Herein, tetrahydrofuran (THF) and 2-methyltetrahydrofuran (MTHF) are mixed as a model of weak solvating effect to improve the low-temperature performance. In the mixed electrolyte, the anion-dipole expulsion and steric hindrance in the solvation sheath increase, which weakens the cation-dipole attraction and reduces the desolvation energy. Meanwhile, the weak dipole-dipole interaction between THF and MTHF lowers the electrolyte viscosity and improves the ionic conductivity. The change in the solvation structure also results in an entropy increase, facilitates the cleavage of P-F in PF 6 ‾ , and the formation of NaF-rich solid electrolyte interphase (SEI). Using commercial Sn microparticles as a model, the mixed electrolyte enables them to deliver a capacity of 328 mAh g −1 after 1000 cycles at −40 °C, much better than the cases only using THF or MTHF alone. The electrolyte can be also successfully adapted to Bi and hard carbon, confirming its good compatibility with different anode materials. These results provide an in-depth understanding of low-temperature electrolytes for advanced sodium-ion batteries.
Youwen Tian,Wei Luo,Yedan Wang,Yun Yu,Wanzhen Huang,Haodong Tang,Yifan Zheng,Zongjian Liu
Although the traditional Stoˇber process-based methods are widely used for encapsulation of metal nanoparticles in SiO 2 , these time-consuming methods are not effective for coating metal microparticles with a uniform SiO 2 layer of desired thickness. Herein, an ultrasound-assisted, interface-confined sol–gel method is proposed for fast encapsulation of metal microparticles in SiO 2 , and the encapsulation of Sn microparticles is chosen as an example to illustrate its feasibility. The proposed method involves covering metal microparticles with liquid films that contain water, alcohol, surfactant (Span-80) and catalyst (NH 4 F) and then ultrasonically dispersing these particles into cyclohexane, where tetraethylorthosilicate (TEOS) is added. To ensure the hydrolysis-condensation reactions of TEOS occurring at the particle-cyclohexane interface so that the formed SiO 2 is coated on the particles, the microparticles should be well dispersed into cyclohexane with the liquid films being not broken away from their surfaces. It is found that the assistance of probe sonication and the addition of surfactant are crucial to achievement of a good dispersion of metal microparticles in cyclohexane. And using high-viscosity alcohol (namely glycerol), controlling the volume ratio of water to alcohol and the amount of water, and choosing a suitable ultrasonic power are essential for preventing the formation of free SiO 2 (namely SiO 2 that is not coated on the particles), which is a result that the liquid films escape from the particle surfaces under ultrasonic cavitation. Our results have also revealed that the thickness of SiO 2 layer can be adjusted by changing the reaction time or the total amount of water. In particular, the thickness of SiO 2 layer can be easily raised by simply repeating the encapsulation procedure. Compared with the traditional Stoˇber process-based methods, the proposed method is time-saving (reaction time: about 30 min vs. more than 12 h) and extremely effective for coating microparticles with a continuous, uniform SiO 2 layer of desired thickness.
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