Electrochemical energy storage devices consist of electrode materials, electrolyte, and current collector, which is critical to the overall electrochemical performance. There is an urgent need to solve the safety problems of lithium ion battery (LIB) for application in electric vehicles and power storage. The commercial separators (polypropylene and polyethylene membranes) suffer from poor dimensional thermo-stability, flammability and poor wettability, although these separators deliver moderate electrochemical properties for LIB.

Professor CUI Guanglei and his colleagues from Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, reported a promising composite membrane of glass microfiber and polyimide with favorable interfacial stability and compatibility. This separator significantly improves thermo-stability of LIB due to its excellent dimensional thermo-stability and flame retarding. The cell with the composite membrane as separator shows superior cycling performance at elevated temperature of 120℃. The composite separator will be a promising separator for high power battery, with an enhanced safety property of LIB in future (Nano Energy, 2014, 10, 277).

The flexible pyrolytic polyimide graphite film (PGF) is explored as a cathode current collector in LIB using lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) based electrolyte. PGF possesses a highly in-plane oriented structure, which endows it with excellent interface corrosion resistance and exhibits much better interface stability than aluminum current collectors in LiTFSI based electrolyte. With regard to the LiMn₂O₄/PGF electrode, the capacity retention ratio remains 89% after 1000 cycles. And at an elevated temperature of 55℃, the capacity retention ratio keeps at 81% after 300 cycles. On the other hand, for the LiMn₂O₄/aluminum electrode, there is hardly any capacity retained after 10 cycles at room temperature (Electrochem. Commun., 2014, 44, 70).

Lithium-oxygen (Li-O₂) batteries have received considerable attention recently because of their exceptionally high theoretical gravimetric energy densities. The discharge product of Li-O₂ cell, Li₂O₂ is insoluble in the non-aqueous electrolyte. Therefore, the reversible formation and decomposition of the electrode/electrolyte interface is of the most importance to Li-O₂ batteries study. Professor CUI works in corporation with professor GU Lin in Institute of Physics, Chinese Academy of Sciences, to directly observe the atomic-scale structure of Li₂O₂ by combining annular bright field scanning transmission electron microscopy. A unique stage ordering in Li₂O₂ is characterized on NiCo₂O₄ based cathodes. The presence of these ordered defects may facilitate the electronic transport of Li₂O₂. These findings may open up new opportunities to investigate the structure evolution of Li₂O₂ during discharge or charge, hence enable improved understanding of the mechanism of oxygen reaction in Li₂O₂ batteries (Adv. Energy Mater., 10.1002/aenm.201400664).

Sodium batteries attract much attention owing to its natural abundance, low cost, and high theoretical capacity. Professor CUI’s group described a facile strategy to construct monolithic Ni₃S₂-Poly(3,4- ethylenedioxythiophene) (PEDOT) electrodes with stable interface for sodium batteries. Ni₃S₂ is directly grown on Ni foam substrate with superior electron transport efficiency. The PEDOT layer would efficiently protect the Ni₃S₂ from being wrecked by the severe volume expansion during charge-discharge process. The as-prepared Ni₃S₂-PEDOT electrodes display a reversible specific capacity of with promising cycle performance (Electrochem. Commun., 2015, 50, 24-27).

These researches have been published in Nano Energy, Electrochemistry Communications, and Advanced Energy Materials, which are supported by the fundings from Chinese Academy of Sciences and the National Natural Science Foundation of China.

Reference:
1.      Nano Energy, 2014, 10, 277
2.      Electrochem. Commun., 2014, 44, 70
3.      Adv. Energy Mater., 10.1002/aenm.201400664
4.      Electrochem. Commun., 2015, 50, 24-27