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    微量AlCl3辅助构筑高性能石墨负极材料

    Trace-AlCl3 assisted constructing high-performance graphite anode

    • 摘要: 石墨具有成本低、稳定性高、电压平台低等优势,被视为商用锂电池负极的首选材料。但在长时间的充放电过程中,石墨负极存在膨胀、脱落、粉化等问题,导致其循环和倍率性能变差。为解决上述问题,设计新型石墨结构已成为提高储锂性能的主要方法。鉴于此,采用空气预氧化和引入微量高价态金属氯化物AlCl3插层剂相结合的方法来调控鳞片石墨的微观结构,包括层间距、结晶度、缺陷度和C=O含量等。通过XRD、XPS、Raman、BET、TEM等表征手段分析改性石墨(GOAl)的微观结构变化,分析不同微观结构对石墨负极材料储锂性能的影响,揭示改性石墨的储锂机制,建立了高性能石墨负极材料的可控制备技术。研究发现:该改性策略能够增大鳞片石墨的层间距,引入丰富的C=O官能团和缺陷结构,从而有效地提升石墨负极的比容量、倍率和循环稳定性能。在0.1 C(1 C=372 mA/g)下,GOAl负极的储锂比容量为357.55 mAh/g,在2 C下循环200圈后仍有267 mAh/g的储锂比容量。采用GITT、dQ/dV和EIS等手段对GOAl负极进行动力学分析,测试结果表明:相比纯石墨,该负极具有更快的锂离子扩散速率、更低的极化电压和更小的电荷转移阻抗。这主要归因于GOAl负极具有更大的层间距、丰富的C=O官能团和缺陷结构,从而加速锂离子去溶剂化速率,降低去溶剂化能垒,增大储锂空间,有效提升石墨负极材料的电化学性能。

       

      Abstract: Graphite owning low cost, high stability, and low voltage platform has been regarded as the preferred commercial anode material in lithium batteries (LIBs). However, the graphite anode is prone to expansion, exfoliation, and pulverization during a long-term charge and discharge process in LIBs, thereby leading to poor cycling and rate performance. To solve the above problems, designing new-type structures in graphite has become the main method to improve its lithium-ion storage performance. Herein, this work integrates air pre-oxidation with introducing trace high valence metal chloride of AlCl3 intercalation agent to regulate the microstructure in flake graphite, including interlayer spacing, crystallinity, defect degree and C=O content. To well investigate the microstructure changes of the modified graphite (GOAl), some characterization techniques including XRD, XPS, Raman, BET and TEM have been employed to fabricate the relationships between various microstructures of GOAl and lithium-ion storage performance, and thus revealing the lithium-ion storage mechanism to effectively establish a controllable preparation technology of high-performance graphite anode materials in LIBs. It has been demonstrated that this modification strategy can expand the carbon interlayer spacing, introduce rich C=O groups and defect structures, thereby effectively enhance the specific capacity, rate performance and cycling stability of graphite anode. The modified graphite anode exhibits a specific capacity of 357.55 mAh/g at 0.1 C (1 C=372 mA/g), and still delivers a high specific capacity of 267 mAh/g at 2 C after 200 cycles. The reaction kinetics of GOAl anode have been analyzed by using GITT, dQ/dV and EIS. These results demonstrate that the GOAl anode has a faster lithium-ion diffusion rate, lower polarization voltage and smaller charge transfer impedance compared with pure graphite. These improved electrochemical properties of graphite anode can be ascribed to the enhanced interlayer spacing, abundant C=O groups and defect structures in GOAl, which can effectively reduce the binding energy between solvated Li+ with C to facilitate Li+ de-solvation process, meanwhile increases lithium-ion storage room.

       

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