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Recently, Zhu Jia's research group of Modern Engineering College of Nanjing University, inspired by the ancient battlefield "spear and shield", combined with nano scale mechanical analysis and micro nano structure design, designed a "nano shield" on the lithium metal battery diaphragm to resist the growth of dendrites. This achievement was recently published on angelw. Chem. Int. ed. (DOI: 10.1002 / anie. 201915440) under the title of "a nano ‐ shield design for separators to resist dendrite formation in lithium ‐ metal batteries".
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Lithium metal anode has become a hot spot in energy storage research because of its high theoretical specific capacity (3860 MAH / g) and the lowest electrochemical potential (- 3.04 V). However, the growth of lithium cathode dendrite is not controllable, and it is easy to break the diaphragm, resulting in short circuit and other problems, which seriously hinders its practical application and development. How to resist the lithium dendrite and prolong the cycle life of lithium metal battery is very important.
Fig. 1 Schematic diagram of nano shield modified diaphragm: a-b) schematic diagram of shield effect with different curvature; c) simulation calculation and analysis results of maximum stress and stress reduction of shield with different curvature; D-E) comparison diagram of common diaphragm and nano shield modified diaphragm on lithium dendrite growth.
(source: angelw. Chem. Int. ed.)
In view of this, the researchers, inspired by the ancient battlefield "spear and shield", combined with nano scale mechanical analysis and micro nano structure design, designed a "nano shield" on the lithium metal battery diaphragm to resist the growth of dendrites. Based on the inspiration of the attack of shield against spear and the evolution process of shield, the influence of the bending degree of "nano shield" shield on the resistance to dendrite is studied. Through the calculation and analysis of mechanical stress, it is found that the bending shield surface reduces the stress on the puncture of dendrite, and when the curvature of nano shield is the same as that of the tip of dendrite, the stress decreases most significantly (Figure 1 ) Therefore, the researchers used the nano shield of PS sphere and silica on the diaphragm, which is the same curvature as the tip of the dendrite, to reduce the stress, so as to prevent the lithium dendrite from puncturing the diaphragm and further avoid the safety problems caused by the short circuit inside the lithium metal battery. At the same time, it is found that the membrane modified by silica nano shield is more compatible with the electrolyte, which can make the lithium metal deposit more smoothly and stably, and maintain a good morphology before and after the cycle (Fig. 2). The Li / / Li symmetrical battery with the nano shield modified membrane can keep the stable lithium deposition for more than 110 hours, and its life is five times longer than that of the ordinary membrane symmetrical battery. The researchers further used in-situ observation experiments to directly observe the effect of nano shield on the resistance of dendrite to break the diaphragm. In the constant current charge and discharge test of symmetrical battery, the battery with nano shield diaphragm also has more stable cycle performance. This work provides a new way for the mechanical understanding and shape design of the diaphragm to extend the life of lithium metal battery and alleviate the dendrite short circuit.
F I g. 2 a-b) SEM before the circulation of the air separator and the nano shield diaphragm; c) electrolyte contact angle test of the air separator and the nano shield diaphragm; d-f) SEM of the surface, section and diaphragm of the metal lithium electrode after 200 cycles of the air separator battery; G-I) SEM of the surface, section and diaphragm of the metal lithium electrode after 200 cycles of the nano shield diaphragm battery.
(source: angelw. Chem. Int. ed.)
The corresponding authors of this paper are Professor Zhu Jia and Dr. Zhu bin of modern engineering college. The first author is Liang Jie, a postgraduate of Modern Engineering College of Nanjing University. Chen Qiyuan, an undergraduate of Nanjing University, and Yao Pengcheng, a doctoral student, are working together. Professor Chen Xi of Columbia University and Dr. Liao Xiangbiao have given strong support in theoretical calculation. The research was supported by the National Laboratory of solid microstructure (Preparatory) micro processing center, supported by the national key R & D plan, the National Natural Science Fund, Jiangsu Natural Science Fund and the special fund for basic scientific research fees of Central University.
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