Recently, the iChEM researcher, Prof. Yonggang Wang of Fudan University and his colleagues, designed a flexible aqueous Li-ion battery with high safety and large volumetric energy density. The flexible and wearable aqueous Li-ion battery is based on spinel Li_1.1Mn₂O₄ cathode and a carbon-coated NASICON-type LiTi₂(PO₄)₃ anode. This work was published on Angew. Chem. Int. Ed., entitled “Flexible Aqueous Li-ion Battery with High Safety and Large Volumetric Energy Density” (Angew. Chem. Int. Ed. 2016, 55, 1 – 5, DOI: 10.1002/anie.201602766).

Flexible, portable and wearable electronic devices have found a wide variety of promising applications such as smart clothes, rollup displays, wireless sensors, wearable devices and implantable medical devices and gained increasing interests in recent years. A lot of efforts have been made to develop flexible and lightweight LIBs while maintaining their high capacity. However, all reported flexible Li-ion batteries are based on highly toxic and flammable organic electrolyte, which can cause safety hazards. An attractive approach to circumvent this problem is to use an aqueous electrolyte for LIBs, which adopt a “rocking-chair” concept similar to the organic LIBs. On the other hand, most reports about electrode preparation were through directly printing, coating, spraying or weaving active materials on/in the carbon substrates, where the carbon materials play the role of current collector. This approach can efficiently utilize the characteristic of carbon substrates, including high flexibility, porous structure and high electronic conductivity, and thus ensure the electrochemical and mechanical properties of electrode at deformed states. However, the key disadvantage is that the mass loading of electrode materials is quite low, which much limited the practical energy density, especially in volumetric energy density. To solve these problems, the authors developed a flexible and wearable aqueous Li-ion battery through a direct rolling method.

Compared with the flexible batteries reported up to present, the flexible aqueous Li-ion battery obtained a mass loading of as high as 20 mg cm^-2, which ensured the large volumetric energy density (124 mWh cm^-3) and volumetric power density (11.1W cm^-3). The obtained energy density and power density are seven times larger than the largest reported till now. The full cell can keep its capacity without significant loss under different bending states, which shows excellent flexibility. Furthermore, two such flexible cells in series with an operation voltage of 4 V can be compatible with current non-aqueous Li-ion batteries. Therefore, such a flexible cell can potentially be put into practical applications for wearable electronics. In addition, a self-chargeable unit is realized by integrating a single flexible aqueous Li-ion battery with a commercial flexible solar cell, which may facilitate the long-time outdoor operation of flexible and wearable electronic devices.

The work is supported by the Natural Science Foundation of China (21333002, 21373060), Shanghai Science & Technology Committee (13JC1407900) and Collaborative Innovation Center of Chemistry for Energy Materials (2011•iChEM).

Link: http://onlinelibrary.wiley.com/doi/10.1002/anie.201602766/full