Date Published: January 18, 2016
Publisher: John Wiley and Sons Inc.
Author(s): Feng Wu, Nan Chen, Renjie Chen, Qizhen Zhu, Guoqiang Tan, Li Li.
The lack of suitable nonflammable electrolytes has delayed battery application in electric vehicles. A new approach to improve the safety performance for lithium battery is proposed here. This technology is based on a nanogelator‐based solid electrolyte made of porous oxides and an ionic liquid. The electrolyte is fabricated using an in situ method and the porous oxides serve as a nonflammable “nanogelator” that spontaneously immobilizes the ionic liquid. The electrolyte exhibits a high liquid‐like apparent ionic conductivity of 2.93 × 10−3 S cm−1 at room temperature. The results show that the nanogelator, which possess self‐regulating ability, is able to immobilize imidazolium‐, pyrrolidinium‐, or piperidinium‐based ionic liquids, simply by adjusting the ion transport channels. Our prototype batteries made of Ti‐nanogeltor solid electrolyte outperform conventional lithium batteries made using ionic liquid and commercial organic liquid electrolytes.
Electrochemical storage has attracted a great deal of attention as power storage system for contemporary and emerging technologies,1, 2, 3, 4 such as smart phone, intelligent robot, unmanned aerial vehicle, and electric vehicles. Usually these electronic devices need to be used in extreme environment (low or high temperature). As everyone knows, batteries may trigger fires or explosions when exposed to certain undesirable conditions.5, 6 This issue can be circumvented through the use of solid—that is, glass, ceramic or polymer‐based—electrolytes. However, the applications of such electrolytes are limited due to moderate ionic conductivity. Ionic liquid electrolytes (ILEs) are considered a potential means of improving the safety of lithium‐ion batteries.7, 8 Liquid state of ILEs require separators for mechanical stability, thus introduce several constraints on cell safety and design. Most research has focused on immobilizing ILEs by impregnating them with polymeric materials such as poly(ethylene oxide) and poly(acrylonitrile).9, 10, 11 Actually, safety issues are not completely eliminated owing to the intrinsic flammability of polymer‐based materials.
In summary, immobilizing ionic liquids within an inorganic solid matrix hold substantial promise for large‐scale lithium batteries applications by virtue of nonflammability. The idea also provides direction for the future study of safety electrolytes. The self‐regulating characteristics of nanogelator should also be used to prepare tunable pore diameter of catalyst, ceramic materials and drug‐delivery carriers. The sol–gel approach is an efficient and low cost approach to synthesis Ti‐nanogelator. Thanks to the short gel time, the ink‐jet printing technology can be used to mass production in the future. Those features will make nanogelator‐based solid electrolytes strong forerunners in the race to replace organic solvents in lithium‐ion batteries, Na+ ion batteries, supercapacitors, solar cells and fuel cells. In this race however there are still numerous hurdles to be overcome, additional work is certainly needed to further improve the properties of these batteries, especially in terms of cycle life, interfacial compatibility with electrodes, and reaction mechanism between electrolyte and nanogelator‐based electrolyte at high temperature.
Electrolyte Synthesis: Ti‐based nanogelator solid electrolytes were prepared by nonaqueous self‐assembly sol–gel processing. All of the ionic liquids (purity >99%) were obtained from Shanghai Cheng Jie. A typical example, the LiTFSI (1.37 g, 3 m, 99%), was completely dissolved in Py13TFSI (6.90 g) to form an ionic liquid electrolyte (ILE). Tetrabutyl titanate (4.77 mL, Aldrich, 99%) was added to the ILE and stirred for 20 min. After homogenization, formic acid (4 mL, Aldrich, 98%) was added drop by drop while the mixture was stirred for 1 min. The mixture was then poured into stainless steel molds. Gelation was completed at room temperature over 36 h, after which the molds were dried at 60 °C in a vacuum for 3 d to remove unreacted formic acid and volatile side products. The entire procedure was conducted under an argon atmosphere.