利用原位氟化保护层改善三维锡锂合金/碳纸负极贫电解液下性能

金属锂具有最高的理论比容量(3860 mAh·g^?1)和最低的还原电势(?3.04 V),是新型高能量密度电池负极材料的最佳选择之一。然而由于金属锂负极表面自发生成的固态电解质界面(SEI)十分不稳定,导致锂枝晶的产生和电池容量快速衰减,严重限制了锂金属电池的商业化应用。因此,本工作利用碳酸双(2,2,2-三氟乙基)酯(DTFEC)添加剂在三维锡锂合金/碳纸负极(SnLi/Cp)表面原位构筑了高机械强度和离子穿透性的含氟化物(LiF和SnF2)保护层,有效地改善了锂负极的倍率性能和循环稳定性。结果显示,SnLi/Cp对称电池在8 mA·cm^?2的电流密度下经过100次循环后过电位仅为90 mV。当将电解液降低到12μL(1.5μL·(mAh)?1)时,在5 mA·cm^?2的电流密度下对称电池仍具有优异的稳定性;SnLi/Cp||NMC811电池在1C(1.5 mA·cm^?2)条件下能稳定循环300圈以上,库伦效率高达98.1%。这种方法能够显著改善锂金属负极的循环稳定性,有助于实现高能量密度锂金属电池的实际应用。

Improvement in Performance of Three-Dimensional SnLi/Carbon Paper Anode in Lean Electrolyte with In Situ Fluorinated Protection Layer

The emerging market for consumer electronics and electric vehicles has stimulated intensive research on lithium metal batteries (LMBs) with high energy densities and large cycle lifetimes. A metallic Li anode has a high theoretical specific capacity of 3860 mAh·g^-1 and lowest redox potential of -3.04 V (vs. the standard hydrogen electrode) and is generally considered an ideal electrode for next-generation high-energy-density LMBs. However, their deployment in practical batteries is severely hindered by the formation of unsafe dendrites and fast capacity decay due to the uncontrollable formation of fragile solid electrolyte interfaces (SEIs). Herein, we describe the stable cycling of carbon paper (Cp)-supported Li-Sn alloy anodes in carbonate electrolytes modified with 1 mol·L^-1 bis(2, 2, 2-trifluorotoluene) carbonate (DTFEC). The molten Li-Sn alloy with 8% (mass fraction) Sn was synthesized through thermal treatment at 400 ℃ in an atmosphere of Ar. The Li-Sn-alloy-coated carbon paper (SnLi/Cp) was obtained after the molten alloy was conformally loaded onto the surface of a carbon paper under the action of capillarity. The as-synthesized interconnected SnLi/Cp composite was characterized by X-ray diffraction, energy-dispersive spectrometry, and scanning electron microscopy. The porous SnLi/Cp composite consisted of only Li and Sn₅Li₂₂ phases supported by the mechanically strong carbon paper with a good conductivity; no impurity was observed in the XRD results. The synergy of the DTFEC additive and alloying with Sn provided composite anodes with significantly improved rate capability and remarkable stability owing to the formation of a dense fluorinated SEI layer with high mechanical strength and ion penetration. Moreover, with the porous SnLi alloy covered by a fluorinated protection layer, lithium avoids the intrinsic issues of uncontrollable volume expansion and dendrite growth, which restrict the practical application of Li metal, exhibiting a stabilized over-potential of only 90 mV after 100 cycles at 8 mA·cm^-2. Notably, stable cycling with a 12 μL lean electrolyte was also observed at 5 mA·cm^-2. Overall, the prototype full cell assembled with the SnLi/Cp anode and NMC811 cathode exhibited a high Coulombic efficiency (98.1%) and remarkable cycling stability for 300 cycles at 1C (1.5 mA·cm^-2). The rate capability was evaluated at various rates of 0.5C to 5C. Compared to pure Li, the SnLi/Cp anode in the full cell exhibited a higher capacity, particularly at a high rate (~126 mAh·g^-1 at 5C). Our approach provides integrated Li metal electrodes with effectively improved cycle stabilities and is very attractive for practical high-energy-density lithium batteries.