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【国新动力•技术前沿】锂金属电池固态电解质—从疏锂到亲锂的蜕变

高工锂电2020-06-29 14:05:33
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  【文/一缕阳光,来源:低维材料】


  为满足能源需求,高容量电池体系如锂硫电池、锂-空气电池、锂金属电池等成为研究热点。在这些体系中,锂金属负极存在许多问题:

 

  (1)锂枝晶的生长容易引发短路,造成安全隐患;

 

  (2)固体电解质界面膜(Solid electrolyteinter phase, SEI)的不稳定性,导致电解液的消耗并降低电池库伦效率和循环寿命,这些问题严重阻碍了这些高容量电池体系的发展和实际应用。

 

  固态电解质具有较高的离子电导率和一定的机械强度,在很大程度上可提高锂电池安全性,即使在全固态锂电池(All-solid-state Li batteries,ASSLBs)中发生短路,不可燃的固态电解质也可避免着火和爆炸的发生。

 

  另外,固态电解质可保证电池的高能量/功率密度和长循环寿命,在提高电池稳定性方面有很大发展潜力。但电解质-电极间往往有较大界面电阻,阻碍了离子传输。

 

  最近,Luo等通过在石榴石型固态电解质表面沉积硅层,实现电解质表面从疏锂到亲锂的转变,减小固-固界面电阻,对提高锂金属电池的安全稳定性有重要意义。

 

 

  Figure 1. Transitionfrom Super-lithiophobicity to Super-lithiophilicity of Garnet leads to a muchsmaller interfacial resistance.

 

  实验以NbCa共掺杂Li7La3Zr2O12为研究体系,制备Li6.85La2.9Ca0.1Zr1.75Nb0.25O12(LLZ)固态电解质。其中Nb可稳定立方相,增强锂离子传导;Ca可降低烧结温度。通过PECVD在表面沉积很薄的硅层,可使界面电阻减小7倍,并保持稳定的循环性能。该团队还通过理论计算对该现象进行论证。

 

  综上,该工作提出通过沉积亲锂金属可有效降低固态电解质-电极界面电阻,对提高锂金属电池的安全性具有指导意义。

 

 

  Figure 2.Evaluation of LLZ wettability with Li metal. (a) Schematic showing the designed LLZ pellet with only one half (orange) selectively coated with amorphous Si.(b) SEM image showing the contrast between the bare LLZ area and the Si-coatedarea. (c) A homemade setup for the wettability evaluation, where molten Li was loaded in a stainless steel boat on a hot plate (200 °C). Digitalimages of the half-coated LLZ pellet before and after dipping in molten Li for.(d) 0, (e) 1, and (f) 4 s. This shows the dramatic wettability transition of LLZ from superlithiophobicity to superlithiophilicity using an amorphous Si coating.

 

 

  Figure 3. Electrochemical performance of symmetriccells using Si-coated and bare LLZ. Schematic illustration showing the structure of symmetric cells with (a) LLZ or (b) Si-coated LLZ SSEs.(c)Electrochemical impedance spectroscopy (EIS) measurements of symmetric cells where the interfacial resistance of the Si-coated garnet cell was significantlydecreased. (inset) Digital image of a Li/Si-coated LLZ/Li symmetric cell. (d)Long-term cycling performance of the Li/Si-coated LLZ/Li symmetric cell at current densities of 0.05 and 0.1mA/cm2. (e) Voltage profiles of theLi/Si-coated LLZ/Li symmetriccell at current densities of 0.1 and 0.2 mA/cm2.

 

  相关研究成果发表在著名刊物Journal of the American Chemical Society(DOI10.1021/jacs.6b06777. WeiLuo,Yunhui Gong,Yizhou Zhu,Kun Kelvin Fu et al. Transition from Superlithiophobicity to Superlithiophilicity of Garnet Solid-State Electrolyte.J. Am. Chem. Soc. 2016.)


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