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Hybrid Energy Storage Devices: The Future of Sustainable Transport



The world energy demand increases exponentially. The generation of energy is mainly from fossil fuels. It causes 254.6 million metric tonnes of carbon dioxide emission which places Malaysia as the 25th in the world. The transport industry contributes the major portion of carbon dioxide emission.


Various initiatives carried out by the countries have shown considerable progress in reducing greenhouse gas emission. Implementation of electric/hybrid vehicles is one of the major steps to improve environmental cleanliness. Malaysia’s Ministry of Transport is focusing on the National Transport Policy towards electrification of vehicles towards synergistic benefit on energy security, environment and climate change. To achieve this goal, sustainable energy resources and efficient energy storage systems are very much essential.



Our research team has been working on the development of the components of energy storage systems. We have developed different types of electrolytes such as solid polymer electrolyte, gel electrolyte, composite electrolyte and hydrogel electrolyte using synthetic and natural based materials. We have also synthesized various electrode materials using advanced synthesis methods. The developed materials have shown excellent results when compared to the commercially available materials.


Our new invention is a hybrid device which can overcome the disadvantages of the existing devices such as supercapacitor, battery and fuel cell. This device possesses much higher energy density than supercapacitors and superior power density than batteries and fuel cell. These devices have been fabricated with the utilization of Malaysian natural resources - natural rubber (as a main component in electrolyte) and tin (as a main component in electrode).


The device can be fabricated by sandwiching flexible two dimensional (2D) layered Tin based composite electrode and flexible three dimensional (3D) natural rubber hydrogel electrolyte.


The developed components can be very flexible with excellent performance. In addition, the loathsomely structural changes during repeated charge/discharge processes that result in the mechanical fracture problems of polymers inside energy storage devices, which in turn significantly reduce the cycling lifetimes can be overcome using intrinsic self-healing natural rubber polymers as substitutes.


This is because self-healing polymers spontaneously eliminate the mechanical cracks or damages and result in greatly enhanced electrochemical performances. The novel research approaches result in obtaining excellent energy storage devices with fast charging, economic, safe, long life-span features.


Fabricating multiples modules of the devices can be built power sources for electric/hybrid vehicles. Implementation of our technology development in the energy storage systems will be an advantage in transportation and electronics which is in-line with our government’s initiatives for National Automotive Policy and Sustainable Development Goals etc.


Utilization of our natural resources is an excellent attempt for creating new opportunities and enhancing employability and economics.



Nowadays, with the rise of the human population, energy consumption has also increased daily. To fulfill the global energy demand, fossil fuel consumption which has been the primary source of energy production for over 150 years, will also increase.


Fossil fuels are non-renewable energy sources, and their consumption leads to pollutions and global warming due to carbon dioxide emissions. Renewable energy and energy storage systems have become an attractive alternative to overcome this issue and achieve sustainable energy storage systems (ESS).


ESS play their role to accommodate unstable renewable energy sources, due to certain conditions. They helped to manage the integration of renewable energies and nowadays, the expanding development in microgrids, electric vehicles, wearable and portable devices have increased the production of flexible electrochemical energy storage systems such as batteries and supercapacitors.


However, both devices have certain limitations in their structure and performance. Batteries require a long time to charge, and their life span is limited due to the redox reaction. The reaction also causes the battery to degrade faster. In supercapacitors, they charge and discharge quickly.


Thus, to improve the performance by having short charging, long discharge time, and having excellent energy density, UM researchers have come up with the invention of the supercapattery, a hybrid device. Supercapattery is an innovated hybrid electrochemical energy storage device that combines the merits of rechargeable battery and supercapacitor characteristics into one device.


The most critical components which affect a device’s performance are the electrodes and electrolytes. The electrode used in the usual energy storage device is a binder electrode. These electrodes have their limitation. The binder-type electrode may reduce a device’s conductivity by causing the electrode to be brittle, hard, and break easily.


A binder-free electrode that we use is more beneficial as it increases flexibility, enhances conductivity, and heightens the rate capability of the electrode and device. Liquid electrolytes and solid electrolytes have been widely used through the years. However, liquid electrolytes can potentially leak, burn, and distort the internal structure of a device.


While in solid electrolytes, the mobility of ions is low, which leads to low ionic conductivity, specific capacitance, and energy and power densities. To improve the ability and performance of our supercapattery, a hydrogel electrolyte, which has a 3D cross-linked polymeric network, is introduced. In our research, the polymers involved are from natural resources such as starch and natural rubber.


These hydrogels are biodegradable, flexible, stretchable, safe, leakage-free, and have good contact with the electrode materials. By using binder-free electrodes and hydrogel electrolytes, our supercapattery has achieved capacitance up to 385 F/g, energy density of 54 Wh/kg, and power density of 60 000 W/kg.


 



Prof. Dr. Ramesh T Subramaniam, Department of Physics, Faculty of Science

ramesh@um.edu.my

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