Flexible electronic devices are becoming increasingly needed nowadays. Especially to support for products such as sports equipment, pressure sensors, military uniforms and medical devices that can be attached to the body. The challenge that must be faced is how to fabricate electronic devices that are very flexible, durable, and can save energy despite the change of shape.
Previous research conducted by a team from Columbia University to create prototype lithium ion battery that resembles flexible human spine. This prototype managed to turn on an LED light and smart watch . When the battery is bent or twisted, the resulting voltage value is not affected by the shape change. Read also: Human Spine Inspires the Birth of a Flexible Lithium Ion Battery
The development of a flexible energy storage unit is continuously made to obtain a high energy density despite a battery shift. In March 2018, researchers from City University of Hong Kong, Shenzhen University, Harbin Institute of Technology and Tsinghua University have made a breakthrough in making flexible batteries.
The research team used zinc and MnO 2 and Polyacrylamide (PAM) electrolytes . Zinc (Zn) and MnO 2 materials are the most widely used primary battery materials in the world  . ABC / Alkaline battery or so-called zinc carbon battery is a primary (non-rechargeable) battery that uses zinc as anode, carbon as cathode and MnO 2as electrolyte. The Zn-MnO 2 battery is selected because it is cheap, environmentally friendly, high specific capacitance and easy to fabricate. The researchers used Carbon Nanotubes (CNTs) or simple languages of carbon nanotubes as substrates for the attachment of zinc (Zn) and MnO2  .
Figure 1. (a) Zn-MnO 2 / Zinc Ion Battery (ZIB) fabrication scheme (b) Manufacture of Zn / CNT (anode) and MnO 2 / CNT (cathode) electrodes 
Making Zinc Ion Battery (ZIB) begins with superimposing Zinc and MnO 2 to CNT. Zinc coating to CNT uses electodeposition method while coating MnO 2 to CNT using Dip-Coating method . The purpose of CNT use is to increase strength and robustness when there is a change in shape. PAM electrolytes are made from acrylamide monomers with hydrogen bonds  . The last stage of PAM electrolyte manufacture is to soak PAM in a mixture of ZnSO 4 and MnSO 4 solutions . After that, the already-coated CNTs Zinc and MnO 2then wrapped with a PAM electrolyte on an elastic fiber that acts as a current collector . The principle of a zinc ion battery is the same as a lithium ion battery but on an ion zinc battery, a zinc ion that will move from the anode to the cathode through an electrolyte.
Figure 2. (a) Stretching zinc ion batteries up to 3000% (b) ionized zinc batteries at bended condition (c) ion zinc batteries cut into 4 parts 
The results of the zinc ion battery test showed amazing results. When stretched to 3000%, the PAM electrolyte ionic conductivity value decreased slightly from 17.3 x 10 -3 S / cm to 16.5 x 10 -3 S / cm  . Under bended conditions, the zinc ion battery can still turn on the digital watch . Even when cut into 4 parts, the zinc ion battery can still turn on the digital watch. The ion zinc battery also produces high induced capacitance of 302.1 mAh / g and an energy density of 53.8 Wh / L  . This battery also has other advantages besides the flexibility problem that is waterproof ( waterproof). In addition, the zinc ion battery is tested to power 100 cm 2electroluminescent panels of pandas. The zinc ion battery is arranged in series and also tested on the condition of the panel is bent. The researchers hope that zinc ion batteries can be applied to various fields, especially in the textile field. Textile products can be coated with zinc ion batteries because the coating technique can follow woven or woven patterns. The other most important thing is the rechargeable ion battery zinc.
Figure 3. Trial zinc ion battery test at 100 cm 2 electroluminescent panel 
 American Chemical Society. 2018. Knitting Electronics with Yarn Batteries . Retrieved from: https://techxplore.com/news/2018-03-electronics-yarn-batteries.html on April 1, 2018
 Motivans, E. 2018. Yarn-Like Battery Can Be Knit Into Clothing . Retrieved from: https://www.zmescience.com/research/inventions/yarn-like-battery-can-knit-clothing/ on April 1, 2018
 Li, H., Liu, Z., Liang, G., Huang, Y., Huang, Y., Zhu, M., Pei, Z., Xue Q., Tang, Z., Wang, Y ., Li, B., and Zhi, C. 2018. Waterproof and Tailorable Elastic Rechargeable Yarn Zinc Ion Batteries by Cross-Linked Polyacrylamide Electrolyte . ACS Nano, DOI: 10.1021 / acsnano.7b09003
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