Editorial Article: The future of energy storage: Improving lithium-ion batteries and exploring alternatives

Prof. Roberto Torresi shares his current research aimed at enhancing the capacity, safety, and sustainability of energy storage systems

22 May 2023

Prof. Roberto Torresi, professor at the Institute of Chemistry of the University of São Paulo, Brazil

The advent of modern energy storage systems has revolutionized the way we use electricity, from powering everyday devices to making renewable energy sources more viable. Among the many energy storage technologies, lithium-ion batteries have emerged as the most widely used due to their comparatively low weight, low self-discharge, and high capacity. However, as the demand for energy continues to grow, there is an urgent need to improve consolidated technology and develop new battery chemistries with even higher energy density and power.

In this SelectScience® interview, we speak with Professor Roberto Torresi to learn more about his research on developing new materials for lithium-ion batteries and exploring promising alternatives.

Prof. Torresi is a full professor at the Institute of Chemistry of the University of São Paulo and has published more than 250 peer-reviewed papers encompassing a broad range of electrochemical application fields. In this article, he shares the battery materials he and his team are currently focusing their efforts on, highlights the potential of novel material synthesis techniques, and reveals what he sees for the future of energy storage.

The hunt for new and improved battery materials

Lithium-ion batteries (LIB) consist of three basic components: a cathode, which is typically based on metal oxides, an anode, which is generally made of graphite, and an electrolyte, which can be either in a solid, liquid, or gel form. When a lithium-ion battery discharges, a chemical reaction occurs, causing lithium ions to move from the anode through the electrolyte to the cathode, while electrons flow from the anode to the cathode through an external circuit, generating an electrical current. As LIBs are rechargeable, this chemical reaction can be reversed when an external current is applied, enabling energy to be stored and supplied over numerous charging and discharging cycles.

LIBs are one of the most popular types of rechargeable batteries, powering everything from phones and laptops to hybrid electric and electric vehicles. However, their large-scale application is hindered by significant safety risks when their cells are subjected to harsh mechanical, thermal, or electrical conditions. This, coupled with the increasing demand for energy storage, has prompted the need to improve the stability and capacity of LIBs – and Prof. Torresi is at the forefront of these efforts.

According to Prof. Torresi, he and his team are mainly interested in three different types of materials. “The first are materials that have a high positive potential, such as nickel,” he says. Here, his team is investigating nickel-containing lithium metal oxides, such as nickel-rich manganese cobalt oxide (NMC), that could offer higher capacity and stability than the conventional cathode materials used in LIBs. “In the case of this type of material, the stability of the electrolyte is also extremely important,” he adds. “So, we’re also investigating the use of ionic liquids as electrolytes for this kind of high-potential material.” Ionic liquids have garnered significant interest in recent years due to their range of unique properties, such as high ionic conductivity, thermal and chemical stability, and non-flammability, which make them a promising replacement for the flammable organic electrolyte materials typically used in lithium-ion batteries.

Despite the potential of metal rich cathode materials for LIBs, the rising cost of metals such as nickel and cobalt, along with environmental and social concerns surrounding their extraction, pose challenges to their long-term use. With this in mind, the second material Prof. Torresi and his team are concentrating on is sulfur, which has the advantage of being comparatively cheap and abundant. “Many research groups are working on sulfur because it is readily available as a byproduct of several industries, including fossil fuel refining, where it is extracted from oil and natural gas,” he says. At the same time, lithium-sulfur cells offer a theoretical energy density that is at least three times that of the traditional lithium-ion battery, making it a promising candidate for next-generation energy storage.

Prof. Torresi's third focus is on developing materials for use in aqueous batteries (ABs). These types of batteries use water-based electrolytes and offer a reliable and cost-effective alternative for safe and scalable energy storage. However, Prof. Torresi notes a persistent challenge of ABs is their low voltage output, which is typically less than 1.5 volts. In addition, current anode materials often suffer from high solubility towards aqueous electrolytes, resulting in a loss of capacity and poor cycle life. To overcome these challenges and enhance the performance of ABs, it is crucial to identify materials that are electrochemically reversible, have a large electrochemical potential window, and are chemically robust in aqueous solutions.

Going for green

Improvements in electrochemical energy storage devices will open a variety of possibilities, from well-known mobile applications such as electrical vehicles to assisting national energy distribution and driving the decarbonization of energy production. “Alongside benefits to the transport industry, one of the most significant impacts of the next generation of batteries will be in stationary applications, such as in electricity distribution, enabling excess energy to be stored and returned to the grid on demand,” explains Prof. Torresi. “New batteries will also revolutionize the way renewable energy is utilized. By pairing efficient batteries with renewable energy sources, green energy can be stored and used as required, even if its generation is variable.”

Choosing the right equipment

Electrochemical experiments require precise and accurate instrumentation to produce reliable and high-quality results. When choosing new equipment for the lab, Prof. Torresi notes several decision-making criteria. Firstly, it is important to consider technical support and after-sale service, particularly for researchers located far from the countries where instrument providers are based. It is also essential to evaluate the equipment's ability to meet evolving experimental needs, including specifications for use with specific types of batteries or currents. He notes the use of  multi-channel potentiostats and those with features such as built-in memory, which can be useful for long-term experiments with low sweep rates. Finally, he emphasizes the importance of finding the best equipment at the most affordable price, while also considering software quality.

While recognizing these benefits, Prof. Torresi notes that the increased demand for batteries such as LIBs will also affect the exploitation of finite resources that are required for battery production. In addition to developing materials that present high energy density, high-rate capability, and cycling performance, he stresses that environmental friendliness should be fundamental to the future advancement of lithium-ion batteries. “As well as testing new materials, we are also investigating new methods to synthesize battery materials that are more sustainable, such as using mechanochemistry techniques,” he says. Mechanochemistry involves using mechanical energy to induce organic reactions rather than relying on conventional solvent and thermal-based routes. “Using methods such as ball milling, it is possible to do chemical synthesis in a much greener way,” Prof. Torresi enthuses, although he acknowledges that this technique is not amenable to all materials.

The future of energy storage

Battery research is an area of innovation and development that is rapidly expanding. Looking ahead, Prof. Torresi expects to see a variety of technologies being utilized, each with their own specific challenges and applications. “It is difficult to think that the future will feature only one technology,” he says. “Perhaps there are some technologies like lithium-ion batteries that will be readily applied for transportation and other technologies such as sodium-ion batteries that could be better suited for stationary applications.”

“The hope is that within the next five years, there will be answers to the current problems of finding cheaper materials, using previously unusable materials, and developing higher potential positive materials for cathodes and more stable electrolytes,” he continues. “We also cannot forget that the materials must be more sustainable. If not, it is less advantageous to utilize batteries. This should be a guiding principle in all future battery research, as we move closer to realizing the next generation of energy storage technology.”

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