Emergent and Evolving Battery Technologies

Listicle 1 Emergent and Evolving Battery Technologies Alexander Beadle Now, more than ever, the world runs on batteries. Take the automobile market as an example; the share of electric cars in total vehicle sales has more than tripled in recent years, from 4% in 2020 to around 14% in 2022.1 High-performance batteries will also play a key role in the green energy transition, as their advanced energy storage capabilities give the energy grid some flexibility in storing and distributing low-carbon electricity during periods of low or high demand. Lithium-ion (Li-ion) batteries are currently the dominant commercial battery type, with their high energy efficiency and power density making them ideal for most low- and medium-size applications.2 However, doubts have been raised over the capability of the Li-ion battery to keep up with the demands of the evolving electric vehicle (EV) market and larger-scale strategic applications such as energy grid storage and aerospace technologies.3 For these applications, researchers have become increasingly interested in alternative battery technologies that can improve the capabilities of the Li-ion battery, or completely new battery chemistries that may one day outperform the Li-ion class. Innovation in lithium batteries Smaller and lighter than the previous generation of nickel-based batteries that came before it, the Li-ion battery quickly displaced its predecessor as the go-to battery chemistry for powering portable devices. Since they were first developed in the 1970s, the batteries have been continuously improved to match the safety requirements and performance demands being made on them. Today, substantial progress is still being made in improving Li-ion batteries, with alternative cathode materials and novel electrolyte types giving rise to the next generation. Cobalt-free cathode materials The cathode – the positive end of the battery that absorbs lithium ions as the battery discharges – has been the site of substantial innovation in recent years. While this was first driven by the desire for improved battery performance, there is now also a significant push to develop cathodes that avoid certain materials. EMERGENT AND EVOLVING BATTERY TECHNOLOGIES 2 Listicle Lithium cobalt oxides are one of the best cathodes developed to date in terms of performance.4 However, the geographic limitations of cobalt mining, combined with reports of serious human rights abuses and environmental damage in cobalt mines in the Democratic Republic of the Congo, have sparked demand and investment in the development of a new generation of cobalt-free cathode materials.5 Currently, cobalt-free cathodes made of lithium-rich oxides, nickel-rich layered oxides and spinel lithium nickel manganese oxide (LNMO) have all demonstrated promise as alternative cathode materials; LNMO material in particular has demonstrated relatively few issues and a low cost. Still, before this material can become a commercial alternative to the traditional Li-ion battery, researchers have some significant hurdles to overcome concerning known interface problems that have been observed between the cathode and electrolyte.6 Lithium-air battery The lithium-air battery is another instance of using a novel battery architecture to improve upon lithium-ion batteries. This battery type uses a semi-open cathode structure to draw in ambient air and make use of its oxygen content. In operation, the lithium ions will move from a lithium metal anode through an electrolyte, before combining with these oxygen molecules during discharge to form lithium peroxide or superoxide at the cathode.7 These compounds are then broken back down during charging, allowing for a rechargeable battery. Theoretical calculations estimate that a lithium-air battery would have a mass-specific energy density greater than a gasoline engine and up to 10 times greater than conventional Li-ion batteries.8 Such a battery would be a significant step forward for the EV market. However, no group has yet been able to produce a reversible Li-air cell that can be cycled deep into its theoretical capacity. There are several reasons for this, including the need to better manage the precipitation and dissolution of the lithium peroxide and superoxide products, obtaining high capacity in the cathode and ensuring the supply of contaminant-free oxygen to the system.9 Lithium solid-state battery In addition to experimenting with the types of cathode materials being used in batteries, researchers are also investigating the potential of various novel electrolyte types to improve the performance of lithium-based batteries. With the discovery of new highly conductive solid-state electrolytes, the development of new lithium solid-state batteries has been identified as a potential solution to the energy density limitations and other safety issues that are associated with traditional lithium-ion batteries.10 In a solid-state lithium battery, the solid electrolyte fulfils a dual purpose; it is both an ionic conductor and electronic insulator to ferry lithium ions between the electrodes, and a physical separator between those electrodes to prevent the risk of short circuits. Solid electrolytes made from inorganic, organic and composite materials have all been reported in the scientific literature, demonstrating good thermal stability and in some cases an ionic conductivity that surpassed that of common liquid electrolytes.11 The potential for improved performance over other Li-ion batteries has made the solid-state lithium battery a key interest for EV manufacturers, with some brands – most prominently the French manufacturer Bolloré and their Bolloré Bluecar – having already launched lines of electric cars that make use of lithium polymer batteries. EMERGENT AND EVOLVING BATTERY TECHNOLOGIES 3 Listicle Still, several key areas will need further research efforts before the wider commercialization of solid-state batteries for larger-scale applications can be realized. This includes the development of solid electrolytes with better chemical and mechanical stability, improved processing techniques and a better understanding of the solid-solid interface interactions taking place in the cell.10 Beyond lithium-ion Lithium batteries may be smaller and lighter than the generation of batteries they replaced, but what if there was a new wave of batteries that could overtake lithium? This is the question being asked by research groups around the world, as they aim to create new and improved batteries based on other elements while also side-stepping forecasted problems with lithium scarcity.12 Sodium-ion batteries Li-ion batteries work thanks to the movement of positively charged lithium ions (Li+ ) through the battery. Swapping out lithium for a similar ion – such as sodium (Na+), which exists in the same periodic table group as lithium – is proving to be a very promising avenue for battery science research. The operating principles and cell processing systems are extremely similar when comparing Li-ion and sodium-ion batteries. From a manufacturing point of view, this makes the sodium battery an attractive prospect as the current synthesis and processing methods are largely transferrable with only minor tweaks.13 Both being Group 1 elements, the two elements have broadly similar physiochemical properties. However, unlike lithium, sodium is extremely abundant in the Earth’s crust and so is much easier and cheaper to obtain. Additionally, sodium-containing metal oxides and cathode materials can be fabricated using abundant metals – such as iron, manganese or vanadium – which conveniently avoids the cobalt supply issues that affect lithium batteries.14 High-temperature sodium-sulfur batteries have already achieved commercial success. The challenge now is for researchers to develop sodium batteries that are effective at lower temperatures so that this technology can be applied to a wider array of applications.15 The development of more stable electrode materials and improved electrolytes will be key to this endeavor. All-graphene battery In the past decade, researchers have proposed the possibility of exploring another novel energy storage system: the all-graphene battery. Graphene has already emerged as one of the most interesting materials for use in supercapacitors.16 Supercapacitors and batteries are similar in that they are both used for the same function (charging and discharging energy), however they differ in a few key ways. In terms of performance, supercapacitors tend to have better power density (i.e. faster charge and discharge rates) than batteries, while batteries have the superior energy density, which is why batteries are more commonly used in applications that require more energy storage.17 Now, researchers are interested in assessing whether graphene materials might also be suitable for battery design. In a 2014 paper published in Scientific Reports, researchers presented an all-graphene “battery” which they say could bridge the gap between batteries and supercapacitors.17 Their fabricat- EMERGENT AND EVOLVING BATTERY TECHNOLOGIES 4 Listicle ed cell was made from functionalized graphene cathodes and reduced graphene oxide anodes, using mass-scalable methods for the graphene production. Testing revealed that the all-graphene battery delivered a very high-power density, as expected from a setup similar to a graphene supercapacitor. However, it also demonstrated an energy density similar to that of commercial Li-ion batteries, which the researchers say is due to a wider difference in potential between the new graphene-based anode and cathode. Such a technology may not be ready to supersede the lithium battery yet. However, the development of alternative energy storage devices that can bridge the performance gap between Li-ion batteries and supercapacitors, all while not relying on rare earth metals, is still a valuable advancement in energy storage technology. Redox flow batteries Another alternative to the conventional rechargeable battery, redox flow batteries are rechargeable cells intended for storing large-scale volumes of energy. They have a unique design, operating through the flow of two electrolyte solutions containing elements in different redox states. The so-called “catholyte” and “anolyte” are separated by a thin membrane that allows ions to pass through it. This ion exchange then triggers reversible electrochemical reactions that store or release energy.19 Comparisons between the vanadium redox flow battery – the most developed battery of this type – and traditional lithium batteries have found that the flow battery has a significantly lower environmental impact than Li-ion batteries.20 Redox flow batteries are still a relatively new concept, but they have a bright future ahead of them. Their novel design and smart use of electrolytes could be of significant interest in sectors demanding low-cost, high-energy density and high-power density options for energy storage. With a myriad of promising new battery architectures and chemistries actively being investigated, research and development scientists are leaving no stone unturned in their efforts to improve upon the traditional Li-ion battery. Whether this involves the development of new electrolytes, cathode materials or even a complete departure from the classical idea of a battery, these emerging technologies will help to support the industry as it seeks to meet the demand for new and improved batteries. References 1. Electric vehicles. International Energy Agency. Accessed January 8, 2024. https://www.iea.org/energy-system/transport/ electric-vehicles 2. Kebede AA, Kalogiannis T, Van Mierlo J, Berecibar M. A comprehensive review of stationary energy storage devices for large scale renewable energy sources grid integration. Renew Sust Energ Rev. 2022;159:112213. doi: 10.1016/j. rser.2022.112213 3. Verma J, Kumar D. Metal-ion batteries for electric vehicles: current state of the technology, issues and future perspectives. Nanoscale Adv. 3(12):3384-3394. doi: 10.1039/d1na00214g 4. Manthiram A. A reflection on lithium-ion battery cathode chemistry. Nat Commun. 2020;11(1):1550. doi: 10.1038/s41467- 020-15355-0 5. Haider SA. 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ACS Energy Lett. 2020;5(11):3544- 3547. doi: 10.1021/acsenergylett.0c02181 15. Karabelli D, Singh S, Kiemel S, et al. Sodium-based batteries: In search of the best compromise between sustainability and maximization of electric performance. Front Energy Res. 2020;8. doi: 10.3389/fenrg.2020.605129 16. Goyal D, Dang RK, Goyal T, Saxena KK, Mohammed KA, Dixit S. Graphene: a path-breaking discovery for energy storage and sustainability. Materials. 2022;15(18):6241. doi: 10.3390/ma15186241 17. Winter M, Brodd RJ. What are batteries, fuel cells, and supercapacitors? Chem Rev. 2004;104(10):4245-4270. doi: 10.1021/ cr020730k 18. Kim H, Park KY, Hong J, Kang K. All-graphene-battery: bridging the gap between supercapacitors and lithium ion batteries. Sci Rep. 2014;4(1):5278. doi: 10.1038/srep05278 19. Chen R, Kim S, Chang Z. Redox flow batteries: fundamentals and applications. In: Redox - Principles and Advanced Applications. IntechOpen; 2017. doi: 10.5772/intechopen.68752 20. da Silva Lima L, Quartier M, Buchmayr A, et al. Life cycle assessment of lithium-ion batteries and vanadium redox flow batteries-based renewable energy storage systems. Sustain Energy Technol Assess. 2021;46:101286. doi: 10.1016/j. seta.2021.101286 About the author: Alexander Beadle is a science writer and editor for Technology Networks. Prior to this, he worked as a freelance science writer. Alexander holds an MChem in materials chemistry from the University of St Andrews, where he won a Chemistry Purdie Scholarship and conducted research into zeolite crystal growth mechanisms and the action of single-molecule transistors.