Revving up energy storage systems

The future of EV battery ecosystem looks bright and green with many scientists focusing on improving energy storage, writes Sudhira H S

The shift to alternative and renewable energy sources has renewed the focus on enhancing energy storage technologies. Unlike conventional sources like fossil fuels, renewable energy sources like solar and wind are available intermittently.

Using efficient energy storage systems, such as batteries, has been important. Researchers are now focusing on the type of batteries and materials used, measuring their performance, and improving the power distribution systems.

At present, lithium-ion batteries are popular and widely used in electric vehicles (EV). They are currently manufactured mostly in China and Indian EV manufacturers import them. Researchers at the Indian Institute of Technology Madras (IITM) are developing mechanically-rechargeable zinc-air batteries as an alternative to this.

Search for better materials

Zinc is a widely available resource and thus could make them cost-effective. At present, they have developed zinc-air cells and are working towards developing zinc-air packs for EVs. The researchers claim that these have a longer shelf life.

Relying on the ‘battery swapping’ system, they are looking forward to developing zinc cassettes that can swap used zinc cassettes of the battery with fully-charged ones. The researchers have also filed patents for their innovation, and are teaming up with the industry to bring this to market.

The Department of Science and Technology (DST), Government of India, has established ‘DST-IISc Energy Storage Platform on Supercapacitors and Power Dense Devices’ at the Indian Institute of Science (IISc) to address some of the critical challenges and carry out research in this direction. One of them has been to explore alternatives to the popular lithium and cobalt used in batteries.

The scarcity of lithium and cobalt could limit the larger adoption of such lithium-ion batteries. Therefore, they are exploring utilising elements that are abundant in India, like sodium-ion (Na-ion) batteries, and using metallic electrodes like magnesium (Mg) in sodium/magnesium batteries.

Prof Abha Misra, Department of Instrumentation and Applied Physics, IISc, says, “Recently, sodium and potassium ions-based hybrid supercapacitors have gained a lot of momentum and success due to larger energy density as well as leading to a safer operation, potentially avoiding environmental pollutions and complex manufacturing processes.”

Co-operative charging

Harnessing solar energy has been seen as another way to enhance the sustainability of the EV segment. However, given the variations in the incident sunlight and the resultant fluctuations in voltage, using them for charging electrical storage devices has been a challenge. This will require an efficient power distribution system that can take care of these fluctuations and also minimise distribution losses.

Researchers at the Indian Institute of Technology Guwahati (IITG) have tried to address this by developing optimised control schemes for active power distribution networks. This could enable the coordinated operation of photovoltaic power generation and EV charging stations.

The research team has developed a three-stage model-predictive control approach to schedule charging of EVs and other devices. Researchers say that this model helps maintain bus voltage magnitudes and state-of-charge of the EV battery within safe limits with minimal usage of control resources and electricity.

Their research proposes a three-stage voltage control method for transitioning from passive power distribution to active. In this, both solar power generation and EV can enable the transition of power distribution from a passive state (unidirectional flow of power from the grid to the consumer), to an active system. This implies that bidirectional power flow from the grid to the point of use and the reverse would also be possible.

While in the grid-to-vehicle model, a vehicle is charged by the power from a grid, the reverse, vehicle–to–grid model enables energy to be pushed back to the power grid from the battery of an electric car. Thus, the model ensures that the voltage of every end device in the system is within allowable upper and lower limits.

The research promises to increase the use of solar energy for charging EVs by using a coordinated control of the power distribution system that reduces voltage fluctuation. With coordinated charging, energy loss decreases by 20.16% compared to the uncoordinated charging method. With an optimal scheduling model for charging and discharging, this system promises to be efficient with reduced losses during distribution. In such a distributed system, all devices participate actively, in a true cooperative sense.

Super-capacitors

Researchers at IISc are also working on supercapacitors. Supercapacitors store energy in the form of electrochemical energy, similar to a battery but with high power density, rapid charge/discharge rates, and long cycling life, and are favoured for their environmental compatibility.

A supercapacitor has two electrodes composed of electrochemically active porous materials with a larger surface area. It stores the charge as positive and negative ionic charges build up on the two electrodes. The barrier layer separates electrodes.

Working on supercapacitors towards translating them into viable products in the market remains a challenge. In the coming days, we may very well see supercapacitors replacing our conventional batteries used in mobile devices and perhaps, EVs.

Determining the threshold

Recently, researchers at the Indian Institute of Science (IISc) have developed a new technique to assess battery performance. One of the crucial aspects that affect battery performance is the migration barrier. This is the energy threshold that the ions need to overcome to traverse through the electrode. It is determined by the rate at which ions move through an electrode inside the battery and, eventually, the rate at which it charges or discharges. Measuring this is crucial to assessing the performance of a battery, and that remained a challenge.

Now, IISc researchers have used different computer simulations to rapidly predict the migration barrier values that have also been experimentally verified. They have proposed a set of guidelines to help choose the appropriate computational framework for testing materials used to develop efficient batteries. This study would help researchers to test newer materials before they are used for battery-related applications.

Prof Abha Misra says that the development of industrial-scale energy storage systems in India has already started. The government has initiated research funding in collaboration with the industries to achieve goals in demand quickly. The active parallel research on materials, electrode design and other aspects boost the possibility of larger platform energy storage systems. With all these innovations and the thrust toward EVs, the transition to sustainable mobility solutions seems imminent.