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The artificial SEI membrane is "anchored" on the current collector to achieve a long-life lithium metal anode

2019-04-10 来源:转载自第三方
 
Since its commercialization in 1991, lithium-ion batteries have been widely used in people's daily lives. However, as the demand for mobile portable devices (such as mobile phones, tablets, etc.) continues to increase, the demand for higher energy density lithium-ion batteries is even more urgent. However, conventional lithium-ion batteries mostly use graphite as a negative electrode material, and their theoretical capacity is limited. Today's commercial lithium-ion batteries are getting closer to their theoretical specific capacity. Therefore, it is necessary to develop a next-generation lithium battery with high energy density. The theoretical energy density of the metal lithium anode material can be about ten times that of the graphite anode, and thus is an ideal anode material for the next generation lithium battery.
Disadvantages in charging lithium metal
However, as a negative electrode of lithium metal, there are three problems in the process of charge and discharge, including the short circuit caused by the growth of lithium metal; the low coulombic efficiency caused by the high chemical reactivity of metallic lithium and organic solvents; The volume change caused by the deposition process. These problems have always hampered the application of lithium metal batteries. In response to these problems, there are mainly two solutions: (1) constructing a three-dimensional structure current collector, the higher specific surface area can effectively reduce the actual current density, thereby achieving uniform deposition, and the three-dimensional structure can also buffer the deposition of metallic lithium. Volume change. (2) Constructing an artificial SEI film on the surface of metallic lithium. The artificial SEI film can block the direct contact between the electrolyte and the metal lithium, inhibit the growth of the metal lithium dendrites, thereby solving the problems of dendrite growth and high reactivity of the metal lithium. However, the volume change caused by the deposition dissolution causes the peeling of the artificial SEI film and the current collector, causing the failure of the SEI film.
Achieve long life of metallic lithium
The team of Xia Yongyao and Wang Yonggang of Fudan University pointed out the importance of the close combination of SEI membrane and current collector in the research and application of metal lithium anode. The researchers used a garnet-type solid electrolyte LLZTO with excellent lithium ion conductivity as an artificial SEI film by regulating the high-temperature heat treatment method. On the one hand, the cubic phase LLZTO with high ionic conductance is maintained, and the LLZO at the interface is chemically diffused with the current collector, so that the artificial SEI film is tightly "anchored" on the current collector, thus ensuring strong chemical bonding force. It can withstand the volume change caused by the dissolution of metallic lithium deposits. In the specific experiment, the researchers dispersed the LLZTO powder in isopropyl alcohol, dropped on the copper foil, and dried under vacuum at 80 °C to obtain a Cu foil-LLZTO electrode. Then, the Cu foil-LLZTO electrode sheet was sintered at 900 °C for 4 hours under an argon atmosphere protection to obtain Cu foil-LLZTO-900. Under the action of high temperature, between the copper foil and the LLZTO layer, the atomic motion becomes active, and interdiffusion between the two interface layers occurs.
The researchers used Cu foil-LLZTO, Cu foil-LLZTO-900 and copper foil obtained by sintering above as a positive electrode, and metal lithium as a negative electrode to assemble a battery. The results of the half-cell and symmetrical battery show that the Cu foil-LLZTO-900 electrode has excellent electrochemical performance. Its Coulomb is the most efficient, with the largest number of cycles and the least polarization. At the same time, the life of the symmetrical battery has reached more than 4,000 hours. However, in increasing the specific surface area of the copper foil, the Cu-foil-LLZTO-900 electrode can only deposit up to 4 mAh cm-2, and under this deposition condition, the half-cell cycle can only reach More than 60 laps. Therefore, in order to increase the deposition amount of metallic lithium, a commercial foamed copper having a larger specific surface area is selected. The same treatment method gave Cu foam-LLZTO-900.
The limited specific surface area of the copper foil limits the increase in the deposition of metallic lithium. Therefore, the LLZTO solid electrolyte layer was selected to be fixed on the surface of the three-dimensional foam copper to obtain a Cu foam-LLZTO-900 electrode. The half-cell results show that the Cu foam-LLZTO-900 half-cell cycle can reach more than 1200 cycles, and the average coulombic efficiency is above 98%. Moreover, the deposition amount of metallic lithium can be 8 mAh cm-2.
Edited by Suzhou Yacoo Science Co., Ltd.

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