Ningbo Materials has made a series of progress in the research of high specific energy lithium metal anode protection

Lithium metal secondary batteries are the first choice for next-generation high-energy density energy storage devices. As the "holy grail" anode material for lithium metal batteries, lithium metal has a high specific capacity of 3860 mAh / g and the lowest redox potential. It is a necessary material for realizing future high-energy density systems such as lithium air and lithium sulfur. The medium-term target of the first choice of negative electrode materials for 500 watt-hour / kg-level energy storage batteries. However, subject to the irregular dendrite growth during the lithium metal deposition process and the irreversible reaction between lithium metal and the electrolyte, the lithium metal anode will form an extremely unstable electrode / electrolyte interface during the cycle, which quickly loses battery capacity and increases The internal resistance of the battery has led to many challenges in the practical application of lithium metal anodes in batteries.

In response to the persistent problem of the unstable lithium metal interface, the new energy storage materials and devices team of the Institute of Materials Technology and Engineering of the Chinese Academy of Sciences has conducted a large number of interface protection structure designs for a long time, and has made significant progress in the early stage (the relevant results were published in J. Mater Chem. A, 2016, 4, 2427-2432, ACS Appl. Mater. Interfaces 2016, 8, 26801-26808, J. Mater. Chem. A, 2017, 5, 9339-9349, Nano Energy 2017, 39, 662 –672). On this basis, the team conducted more in-depth basic and applied research based on the interfacial cycling mechanism of lithium metal anodes, and made a series of progress in the near future.

In order to better understand the surface SEI film chemistry and electrochemical reaction mechanism of lithium metal, the team combined in-situ electrochemical-atomic force microscopy with lithium bis (fluorosulfonyl) imide (LiFSI) as the research object to systematically study the lithium salt The effect of concentration on the morphology and mechanical properties of SEI film, and found that by adjusting the salt concentration, SEI films with different modulus and thickness can be obtained (Figure 1a). Such phenomena are reflected in different solvents and are universal (J. Phys. Chem. C 2018, 122, 9825-9834).

Through material optimization and structural design, combined with medium-pressure plasma technology, the team collaborated with the researcher Ye Jichun of the New Energy Institute to develop a carbon paper / sponge carbon double-layer structure, using the low deposition potential of lithium metal on carbon paper and sponge The high mechanical properties and electrochemical inertness of carbon resulted in a directional double-layer carbon structure, which achieved a stable cycle of 4 milliampere hours per square centimeter of lithium metal anodes (Energy Storage Mater. 2018, 11, 47-56, Figure 1b). In addition, the team prepared a special stacked graphene with a high deposition overpotential that conventional graphene cannot. By adsorbing such stacked graphene in a foamed copper structure, the application of filter-type lithium metal deposition in a three-dimensional structure is achieved, and a stable cycle (Energy Storage Mater) at high current density (5 mAh / cm2) is obtained. . 2019, 16, 364-373, Figure 1c). Further, by suction filtering such a dispersion of stacked graphene and lithium fluoride, the team obtained a layered carbon film structure modified with lithium fluoride, and found that during the initial lithium plating process, defects in stacked graphene The conversion of lithium fluoride to fluorocarbon bond occurs to obtain a fluorocarbon bond modified layered protective structure, which greatly improves its protection performance for lithium metal (Adv. Energy Mater. 2019, 1802912, cover article, Figure 1d ).

The team also designed a series of lithium metal host structure materials. For example, a simple Li9Al4-Li3N-AlN lithium metal host structure was efficiently prepared by a simple lithiation reaction of an aluminum nitride precursor, and an effective specific capacity was obtained. The 1540 mAh / g composite lithium metal anode achieves a stable cycle that matches the NCA cathode material with a load of up to 4.5 mAh / cm 2 (Nano Energy 2019, 59, 110–119, Figure 1e). In addition, the team also used nickel foam as the base material and successfully grown a vertical graphene array on the surface using medium-pressure plasma technology, and investigated the gain effect of the host material modified by the pseudo-capacitor interface structure on the cycling stability of lithium metal (Adv . Funct. Mater. 2018, 1805638, Figure 1f).

The above work won the Ningbo Natural Science Foundation (2018A610014), the Zhejiang Natural Science Foundation Youth Project (Q17E020023), the National Natural Science Foundation Foreign Young Researchers Project (51650110490), the Ningbo City 2025 Project (2018B10060), and the National Key R & D Program (2018YFB0905400 )support.

Figure 1 (a) Characterization of the interface of the lithium metal anode interface at different salt concentrations; (b) A guided double-layer carbon structure for lithium metal interface protection; (c) A filtered lithium realized by stacking graphene Metal deposition protection mode; (d) a functional lithium metal protective layer that realizes SEI conversion at the interface conversion of carbon defect sites; (e) a simple Li9Al4-Li3N-AlN structure as an efficient lithium metal host structure; (F) A special interface for lithium ion transport and uniform deposition of lithium metal by a vertical graphene structure.

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