Holy grail or grenade with pin out? -- The road to practical lithium metal anode

Society needs for energy-dense battery system, as a battery with high energy density, lithium metal batteries have drawn great attention. Lithium metal electrode owns a low electrode potential and can express capacity as high as 3860 mAh g^-1; With high energy density, lithium metal anodes shows great potential for application. However, there are challenges for cultivating practical lithium metal batteries, since the lithium metal anode in lithium metal battery is highly reactive which can cause safety implications. Xiaoli Dong and Yongyao Xia et al. from Fudan University published a review article entitled “The pathway toward practical application of lithium-metal anodes for non-aqueous secondary batteries” on the National Science Review, which reviewed failure mechanism and current research of practical lithium metal anodes, providing designs for future investigation.

The usage efficiency of lithium metal is usually low in lithium metal batteries, which tremendously shorten their lifespan. Lithium metal has high reactivity, and sensitive to air and moisture, which makes them easy to fail, and causes safety issues. Researchers analyzed two major failure modes (short-circuiting and capacity loss) of lithium metal anodes. Lithium dendrite is the major cause of short-circuiting: conditions such as non-uniform lithium ion concentration distribution would facilitate the growth of lithium dendrite which could penetrate through the separator and result in short-circuiting. The capacity decay mainly comes from irreversible reactions of lithium metal with electrolyte and lithium metal dusting. Because of high reactivity of lithium metal, a certain amount of active lithium metal would react with electrolyte and cause some capacity degradation; Meanwhile, dusting of lithium metal during charge and discharge process would rise the impedance and consume capacity of batteries. After figuring out two major failure mechanisms of lithium metal anodes, the researchers can conduct their investigation more targetly, and build more practical lithium metal anode.

Subsequently, researchers reviewed and analyzed these targeted works. According to the preparation methods and corresponding applications, five categories of lithium anodes are proposed (Figure 1): stabilized lithium-metal powder anode (SLMP), stabilized lithium-metal anode (SLMA), deposited lithium-metal anode (DLMA), composite lithium-metal anode (CLMA), and anode-free lithium-metal anode (AFLMA). Possibilities for practical application of these anodes are assessed after comparing their pros and cons. SLMP can ably compensate for the irreversible capacity of commercial anodes such as graphite; and SLMA can effectively avoid the dusting of lithium metal and suppress the dendrites. DLMA competently controls the current on the anode interface but it takes a complicated process to prepare; CLMA can form reliable electrode structure easily, preventing complicated preparation process; AFLMA uses copper as anode directly, simplify the manufacture process of batteries. Conclusively, SLMA can be the most promising and practical lithium metal anodes among the five anodes reviewed; and SLMP can be top candidate for energy-dense lithium metal batteries.

Although lithium metal anodes have been investigated comprehensively and thoroughly by current researches, there is still a huge gap between current technology and practical lithium metal anodes. As the development of cutting-edge characterization and manufacture techniques advances, the mechanisms of lithium metal batteries will be investigated more detailedly, and preparation methods will be improved; On this basis, it is not far from the emergence of safe and energy-dense lithium metal batteries which can lead the energy revolution. 

Detailed research content please refer to The pathway toward practical application of lithium-metal anodes for nonaqueous secondary batteries, https://doi.org/10.1093/nsr/nwac031

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