Our connected world is dependent on batteries, but there are challenges for safety, power, and lifespan. A recent Collection showcases research across several core topics helping to shape the design of safer and more sustainable battery options.
Battery technology is a field that has become increasingly vital in our rapidly evolving digital world. A recent Collection from ACS Energy Letters showcases cutting-edge battery advancements and challenges—from the intricate thermal management in electric vehicles to the promising yet complex realm of lithium-metal batteries—uncovering insights into the intricate balance between efficiency, safety, and environmental impact.
Safety
Batteries have become especially important with the advent of electric vehicles, where thermal management is a key aspect of safety.1 There are fundamental principles governing the safety of batteries at high temperatures. Battery life can be maximized when operated at an optimal temperature by balancing competing degradation mechanisms. But cooling the large number of cells needed in a vehicle is a challenge, because competition exists between the battery thermal management system weight/volume and cooling capacity. These issues can affect the vehicle’s range, reduce battery life, and increase safety concerns.
Current thermal management designs use classic air cooling, direct or indirect liquid cooling, or make use of an extended heat transfer area with fins to increase thermal conductance. Passive approaches such as heat pipes could be an option, but it is clear that heat-resistant materials represent an important direction for future research and development.
Electrolytes
Energy storage devices are changing the picture for lithium-ion batteries. Although graphite anodes may be approaching the theoretical limit of energy densities, they fall well short of the increasing demand of devices with higher energy density. A different approach pairing metallic lithium with high-voltage nickel-rich cathodes may achieve a high cell energy density of over almost twice that of lithium-ion batteries, but these lithium-metal batteries are affected by the electrochemical instability of their electrolyte solvents, which limits practical application.
One recent study details a new bipolar molecule-regulated electrolyte, with a capsule-like solvation structure and nonflammability that could be the key to stabilizing high-voltage lithium metal batteries.2 Several advanced electrolytes (mainly ether-based) have also demonstrated electrochemical performance in high-energy-density lithium-metal batteries, which could prove a promising option for safety electrolytes of the future.3
Other groups are looking at harnessing organic electrolytes for rechargeable lithium batteries.4 The team behind this research argue that an intrinsically safe organic electrolyte should “show simultaneous low total heat release, low maximum heat release rate, long time to ignition, and short self-extinguishing time”, with experiments showing that a cocktail of polyfluorinated solvents and high-boiling point solvents is the optimal choice for nonflammable electrolytes.
To complement this, a review article from a team at the University of Houston, United States, considers the feasibility of combining organic battery electrode materials (OBEM) with solid-state electrolytes—a peculiar combination but one that could generate interesting new cell configurations.5 OBEM are derived from naturally abundant elements such as carbon, hydrogen, nitrogen, oxygen, and sulfur—and as such could be generated from renewable biomass. Since organic materials are composed of non-toxic elements, all-organic batteries are expected to have high safety and low environmental impact at end-of-life.
Electrode & Interface
The interface between the electrolyte and its electrode profoundly affects battery performance, but this relationship in solid-state batteries has traditionally been elusive due to the subsurface nature of interfaces and the lack of proper characterization methods. A team working in China and the United States has employed ultrasonic imaging to better understand the interfacial stability in solid-state cells.6 This novel use approach allows gradual oxidation at the cathode interface to be tracked, as well as distinguishing increased interfacial resistance from either contact loss or passivation layer growth. The findings highlight a role for ultrasonic imaging as a powerful tool to evaluate the interfacial stability, which may help to guide new interface designs and ultimately improve performance.
Other teams looking at a garnet-based electrolyte have come up with a way to systematically regulate the interface chemistry for solid-state batteries.7 Crucially, this uses a polyphosphoric acid coating—providing a lithiophilic and elastic interlayer for uniform lithium cycling—as well as an electron-insulating interphase at the grain boundary to prevent filament growth inside the garnet.
Recycling
The manufacture and disposal of batteries has become a critical issue. Reserves of lithium, cobalt, and other metals is limited, and right from the point of extraction these resources are associated with significant pollution. Battery waste is a huge problem—and anticipated to be in the region of 8 million tons by 2040—but recycling is not straightforward. A recent review article summarizes and compares different recycling techniques for lithium-ion batteries, including pyrometallurgical and hydrometallurgical methods for recovering active materials. One of the major drawbacks is the need for manual disassembly. To address this, secondary utilization of retired lithium-ion batteries could be beneficial—especially when you consider that lithium-ion batteries in electric vehicles must be retired when capacity decays to less than 80% of the original, but there is still potential life is these resources can be reused safety in other lower-energy applications, or as storage devices.
At present, this too requires manual intervention, but researchers are working on machine leaning methods to sort and estimate the remaining capacity of retired batteries.9 Ultimately it is hoped that new discoveries will drive the recycling industry, and help to conserve resources and provide global sustainability.
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References
- Longchamps, R. S. et al. Fundamental Insights into Battery Thermal Management and Safety. ACS Energy Lett. 2022, 7, 3, 1103–1111.
- Zhang, G. et al. A Nonflammable Electrolyte for High-Voltage Lithium Metal Batteries. ACS Energy Lett. 2023, 8, 7, 2868–2877.
- Buyuker, I. S. et al. Voltage and Temperature Limits of Advanced Electrolytes for Lithium-Metal Batteries. ACS Energy Lett. 2023, 8, 4, 1735–1743.
- Yang, A. et al. Benchmarking the Safety Performance of Organic Electrolytes for Rechargeable Lithium Batteries: A Thermochemical Perspective. ACS Energy Lett. 2023, 8, 1, 836–843.
- Zhao, L. et al. Roadmap of Solid-State Lithium-Organic Batteries toward 500 Wh kg–1. ACS Energy Lett. 2021, 6, 9, 3287–3306.
- Huo, H. et al. Evaluating Interfacial Stability in Solid-State Pouch Cells via Ultrasonic Imaging. ACS Energy Lett. 2022, 7, 2, 650–658.
- Xiong, B.- O. et al. Transforming Interface Chemistry throughout Garnet Electrolyte for Dendrite-Free Solid-State Batteries. ACS Energy Lett. 2023, 8, 1, 537–544.
- Baum, Z. J. et al. Lithium-Ion Battery Recycling─Overview of Techniques and Trends. ACS Energy Lett. 2022, 7, 2, 712–719.
- Ran, A. et al. Fast Clustering of Retired Lithium-Ion Batteries for Secondary Life with a Two-Step Learning Method. ACS Energy Lett. 2022, 7, 11, 3817–3825.