Power Storage - a Disruptive Development Space

April 18, 2019 Alix Paultre

We are in the midst of an energy revolution, one that started over a decade ago and shows no sign of slowing down. One aspect, energy storage, is one that has been under intense developmental pressure. Even further back, in the relatively technically-sparse 1970s, portable radios eating “D”-cell batteries like peanuts made some people highly conscious of the issue.

Energy storage has migrated into multiple spaces, and is now far more than just a way to power a portable device. From electric vehicles to grid-level load-shifting, batteries and other energy-storage technologies are a significant infrastructure for multiple elements of society. Every advance in energy storage will add significant value to a myriad of application spaces.

Better Electrodes

Making better batteries is a hot area of development, as faster charging and better-performing batteries would be very empowering (pun intended). Making a high-capacity lithium-ion battery that can charge quickly is a grail many are pursuing. This goal has come closer to reality due to a breakthrough in electrode materials from Rensselaer Polytechnic Institute. 

Based on an electrochemical reaction between an anode and cathode, a lithium-ion batteries’ operation is dependent on the performance of the electrodes. In a traditional lithium-ion battery, the anode is graphite, and the cathode is made of lithium cobalt oxide. If you improve the materials used for the electrodes, you improve the battery performance.

Nikhil Koratkar, professor of mechanical, aerospace, and nuclear engineering at Rensselaer, has been conducting extensive research into nanotechnology and energy storage. Recently, Koratkar and his team improved electrode performance by substituting cobalt oxide with vanadium disulfide (VS2) a highly-conductive lighter material that enables a higher energy density (Figure 1).

Figure 1: Rensselaer researchers improved electrode performance by substituting cobalt oxide with vanadium disulfide (VS2).

The biggest hurdle to VS2 adoption was its instability, and the Rensselaer researchers determined the source of the instability and means to mediate it and make it more suitable for use as an electrode material. The team, which also included Vincent Meunier, head of the Department of Physics, Applied Physics, and Astronomy, and others, found that asymmetry in the spacing between vanadium atoms, called Peierls distortion, caused VS2 breakup.

By covering VS2 flakes with a nanolayered coating of titanium disulfide (TiS2) prevents Peierls distortion, stabilizing them and improving their performance. The TiS2 coating creates a buffer layer that supports and holds the VS2 material together. VS2-TiS2 electrodes can enable a Li-ion battery to deliver a high capacity and energy density in a smaller package.

Solid-State Batteries

Another promising energy storage technology is the solid-state battery. Made using solid electrolytes, instead of liquid or polymer materials, they promise to deliver higher capacities and energy densities. In addition, they would also address many of the shortcomings involved with liquid-based storage systems.

A group of scientists from Tohoku University and the High Energy Accelerator Research Organization created a complex hydride lithium superionic conductor, which could help create cost-effective and high-performance solid-state batteries (Figure 2). The new solid electrolyte material is made from structures of hydrogen clusters (complex anions), with high stability in conjunction with lithium-metal anodes, addressing the high lithium-ion transfer resistance in current solutions.

Figure 2: A complex hydride lithium superionic conductor could create cost-effective and high-performance solid-state batteries.

The Tohoku University research team was led by Sangryun Kim from the Institute of Material Research (IMR) and Shin-ichi Orimo from the Advanced Institute for Materials Research (AIMR). Members included Dorai Arunkumar, Naoaki Kuwata and Junichi Kawamura from the university's Institute of Multidisciplinary Research for Advanced Materials (IMRAM), as well as Toshiya Otomo from the High Energy Accelerator Research Organization.

Better Battery Oversight

Another way to make energy storage better is to improve how we use the batteries we have, and better battery monitoring is critical to optimal management and performance. Another important aspect of battery monitoring is in manufacturing, where it can be used for binning devices by operational expectancy.

Beyond advanced sensors and probes, next-generation software solutions like AI can significantly add to our ability to make and use batteries. One effort to use AI to accurately predict battery lifetimes is being led by Stanford and MIT researchers, as the technique could be used to sort manufactured cells, as well as help new battery design development (Figure 3).

Figure 3: Stanford graduate students Nicholas Perkins, left, Peter Attia, and Norman Jin are among the researchers who found the key for accurately predicting the useful life of lithium-ion batteries. (Image credit: Dean Deng).

Scientists at Stanford University, the Massachusetts Institute of Technology, and the Toyota Research Institute created a machine learning model, using a few hundred million points of battery charge/discharge data, to predict how many cycles each battery would last. Observing voltage declines, and a few other factors, in the first five charge/discharge cycles of a battery’s operation, have resulted in lifetime predictions with 95 percent accuracy.

The work was carried out at the Center for Data-Driven Design of Batteries, and the Stanford researchers, led by William Chueh, assistant professor in materials science and engineering, conducted the battery experiments. MIT’s team, led by Richard Braatz, professor in chemical engineering, performed the machine learning work. Kristen Severson was the co-lead author of the research.

Looking Forward

While there are some who believe that battery densities are high enough, advances in high-efficiency next-generation power electronics will provide the lion’s share of technical progress in EVs and grid-balancing systems. However, the bottom line is that smaller and lighter batteries, with higher capacities and energy densities, will improve every application stored energy is used in considerably, and magnify any improvements in any related power systems.

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