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Message: Silicon and Lithium (from journal "Chemical Science")
Silicon and Lithium Issue 30, 2019
Silicon and lithium metal are considered as promising alternatives to state-of-the-art graphite anodes for higher energy density lithium batteries because of their high theoretical capacity. However, significant challenges such as short cycle life and low coulombic efficiency have seriously hindered their practical applications. In the past decades, various strategies have been proposed to address the major problems of Si and Li anodes. In this review, we summarize the understanding on Si and Li anodes, highlight the recent progress in the development and introduce advanced characterization techniques. We also indicate the remaining challenges of Si and Li anodes requiring more efforts for future widespread applications. We expect that this review provides an overall picture of the recent progress and inspires more efforts in the fundamental understanding and practical applications of Si and Li anodes.
Conclusions and outlook
Si and Li anodes have shown great promise as next generation lithium battery anodes due to their high capacity, while major problems such as large volume changes during cycling limit their applications. In this review, we have summarized the recent progress in Si and Li anodes as well as the discussion of the principles for design to improve the performance. We also took some typical examples to illustrate these principles.
Although progress has been made, the as-developed strategies remain far from the requirements of commercialization. For Si anodes, the initial CE at least reaching 90% and the average CE of >99.8% in the subsequent cycles are favorable to minimize the consumption of Li in the practical cell. However, the present Si anodes still cannot meet this demand yet. Besides, to alleviate the large volume change of Si anodes during cycling, the excess space designed for volume expansion always reduces the specific volume capacity. This calls for new advanced full cell designs. For Li anodes, while host design, surface engineering and electrolyte modification can relieve the problem of Li dendrite growth, stable long cycle performance is limited in practical full cells. Solid electrolyte is a promising choice to resolve most problems, but its low ion conductivity and poor interfacial contact need much improvement.
We think future practical Si and Li anodes need to combine several possible solutions mentioned above or need design of brand-new structures, which involves complicated system engineering. In the meantime, with the help of advanced characterization tools and simulation methods, the underlying fundamental mechanism in Si and Li anodes can be uncovered, which will provide the guidance for the design. The wide-application of higher energy lithium-based rechargeable batteries with Si and Li as anodes is the critical enabler for the transformation towards an electrified future, and it is now on its way.
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