You are not mistaken, is that love Holy Land Columbia University, Liu Qiang East and his wife Zhang Zetian, Wang Lee Hom and wife Li Liang Lei, Li Yundi and his girlfriend Tian Fei are here to meet.Columbia University in China can be said to have long been prestigious, former Hu Shi, Feng Youlan, Xu Zhimo, Wen Yiduo and other such people, followed by Kai-fu Lee, Yang Lan and other such celebrities, so Columbia University can be said to be a household name in China in recent years, Columbia University is more successful with the entertainment industry, the early entry into Hollywood, Zhang Ziyi had Columbia University to learn English, Zhang Yimou's eldest daughter Zhang Chang Columbia University at the end of a law degree.College of course, not only a romantic love story, Columbia's research strength is also the world's top, in 2018 US News and World Report (US News & World Report), Columbia ranked No. 5, and by 2017 a total of 96 Nobel laureates had studied or worked in Columbia, and Columbia even trained four U.S. presidents, including We are most familiar with Obama and Roosevelt.
Today, we want to introduce the scientific research results from Columbia University, in recent years with the rapid development of wearable devices, the demand for flexible flexible batteries also increased rapidly, a variety of flexible battery design is endless, but most of the flexibility In order to solve this problem, Guoyu Qian et al. Of Columbia University, inspired by the biological spine structure, have developed a flexible lithium ion Batteries, while maintaining good flexibility, also maintain the advantage of high volume energy density.
The structure of the flexible battery As shown above, the basic structure of a flexible battery can be divided into a trunk, and branches connected with the trunk, these branches around the trunk winding, and ultimately the formation of animal-like vertebra structure from the trunk And external circuit connection.This structure not only ensures that the battery has good flexibility, but also greatly improve the flexible battery energy density, the use of LiCoO 2/ Graphite as an active material, the structure of the battery volume ratio of energy up to 242Wh / L.
In the electrochemical test, the cycle performance of the battery with this structure was not affected regardless of bending (bending radius of 20 mm, 10000 times) or twisting (turning of 90 degrees and 1000 times), and the battery was cycled 100 times at 0.2C rate , The capacity retention rate of up to 94.3%, Coulomb efficiency of 99.9% from the battery voltage curve shown in Figure c can also see that, whether bent or twisted have no significant impact on the battery's electrical performance.
The flexible battery may experience thousands of bends and twists throughout its lifetime, so Guoyu Qian uses a mechanical structure to evaluate the stability of the structure's flexible battery under mechanical loads. As can be seen from the graph c, Even with a battery bending radius of 20 mm, the battery was able to perform stable charge and discharge with only a slight decrease in capacity, indicating that most of the active material remained in contact with the current collector during bending without Significant active substance shedding occurred.
In order to study the strain distribution in the battery during bending, Guoyu Qian picked one of the most common situations - worn as a wristband on his wrist and analyzed the strain distribution inside it using finite element analysis tools. The results are shown in the following figure Guoyu Qian found that the maximum strain of flexible cells with bionic structure was only 0.08% in bending and 1.8% in square cells, while the yield strains of Al foil and Cu foil were 0.47% and 0.73% respectively, , Which shows that the strain of the flexible battery with biomimetic structure is within the tolerance range of Al foil and Cu foil and the square battery has exceeded the yield limit of Al foil and Cu foil.This shows Guoyu Qian's bionic structure design can be extremely large The reduction of the electrode in the battery bending strain, reduce the deformation of the current collector and the destruction of active substances to improve the battery cycle performance.
Guoyu Qian's design fully draws on the characteristics of animal spine, combined with the structural characteristics of lithium-ion batteries, through the bionic structure greatly reduces the bending and torsion deformation of the current collector and the active material damage caused by the battery While being flexible, the energy density of the flexible battery is greatly improved and the practicability is enhanced. The battery has broad application prospects in future wearable devices, especially smart watches.
