The Future Direction of Lithium-Ion Batteries
The development of the first lithium-ion battery (LIBs) in the 1970s and the commercialization of lithium-ion batteries in 1991 marked a profound change in the electronics market.
The watershed moment in energy density variation of these batteries foreshadowed the arrival of a new era for smartphones and fashionable portable computers. In 2007, Apple introduced the first iPhone powered by lithium-ion batteries.
One of the greatest achievements in battery technology is perhaps the application of lithium-ion technology in hybrid and pure electric vehicles (BEVs).
Currently, most new energy vehicles use lithium-ion batteries, which is crucial for the future of the global ecosystem.
From powering our mobile phones and laptops through large-scale stationary battery storage to the emergence of the next generation of electric vehicles, lithium-ion batteries have found extensive applications across various industries.
Moreover, with the growing demand to reduce greenhouse gas emissions in power supply and minimize the impact of climate change, the importance of research in this field is self-evident.
Battery lifespan, operational safety, energy and power density, and charging speed are critical performance characteristics for the widespread adoption and commercial success of batteries.
Additionally, raw material supply and production efficiency are key decision factors for choosing specific electrochemical battery products.
The focus of LIB research has shifted to meet consumer demands, encompassing not only the aspects mentioned but also considering sustainable materials, improving the working and environmental conditions in material mining countries.
To achieve these goals and develop the next generation of technologies capable of overcoming the current energy limitations of lithium-ion batteries, it is essential to gain a deeper understanding of the materials’ potential electrochemical performance.
Nuclear Magnetic Resonance (NMR) is a well-established technology with a long history in the fields of medicine, clinical research, and materials science. NMR analysis is now being used for groundbreaking fundamental research and product innovation, to develop and design new devices for energy production, storage, and conversion.
01 How do Rechargeable Lithium Batteries Work?
In simple terms, rechargeable batteries rely on electrochemical reactions, where the movement of ions and electrons in the electrolyte between two electrodes converts chemical energy into electrical energy and vice versa. In rechargeable batteries, these electrochemical reactions are reversible.
During discharge, lithium ions are transported from the anode to the cathode through the electrolyte and separator, carrying the internal current within the battery. During charging, an external power source applies a higher voltage than the battery generates, forcing the charging current from the cathode to the anode. Lithium ions are embedded in porous anode materials, where they store charge for future release.
02 Traditional Analytical Techniques
Techniques like electronic and optical microscopes provide high-resolution imaging of materials but are often limited to surface imaging, making quantitative explanations challenging.
Nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy are non-invasive analytical methods with quantitative and structural characterization capabilities, and ongoing research is continually improving their sensitivity and resolution.
NMR methods have been used for research and development to monitor structural changes that occur during battery operation, studying the effects of rapid charging and cycling on batteries.
A recent paper examined how chemical and electrochemical reactions at the lithium-ion battery cathode-electrolyte interface affect the battery’s cycle life and safety. Analyzing the electrolyte using solution nuclear magnetic resonance spectroscopy can identify any soluble degradation products that have formed.
03 Higher Ion Mobility Can Improve Battery Performance
Nuclear magnetic resonance spectroscopy can be used to reveal structural details, such as electronic structure.
Researching the dynamics of battery materials, including potential alternative electrode materials and electrolyte components like lithium salts, solvents, and additives, as well as other solid forms. Improving the target ion mobility can reduce LIB’s internal resistance and enhance its performance.
Pulsed Gradient Spin Echo (PGSE) nuclear magnetic resonance can study ion mobility by separately, independently, and in situ measuring the diffusion rates of different ions, as well as measuring the diffusion rates of different atomic nuclei (including 1H, 19F, and 7Li) over a wide temperature range.
04 Prolonging Battery Life
Nuclear magnetic resonance analysis has deepened our understanding of the formation of the Solid-Electrolyte Interface (SEI) and dendrite formation processes that affect lithium-ion batteries during their initial charge.
The stable formation of SEI determines many parameters that influence battery performance and lifespan. During the charging process, as lithium ions move towards the anode, they may undergo electroplating, leading to dendrite formation, which can result in short circuits and fires. There is currently insufficient research in this area of preventing dendrite formation.
Nuclear magnetic resonance can separate and quantitatively identify various aspects of the battery layers. For example, 7Li and 19F Magic Angle Spinning (MAS) nuclear magnetic resonance can identify and quantify lithium fluoride (LiF) in the SEI on the anode and electrode.
Changes in the Li peak intensity during the cycling process can be correlated with the growth of dendritic microstructures and the deposition of smooth metal.
One study found that in-situ nuclear magnetic resonance can determine that up to 90% of the lithium deposited during slow charging of Li/LiCoO2 batteries is dendritic in nature.
This technology can also be used to test methods to prevent dendrite formation, including electrolyte additives, advanced separators, battery pressure, temperature, and electrochemical cycling conditions.
The advantages of nuclear magnetic resonance in researching new battery materials and performance are increasingly recognized. Future applications also include studying LIB capacity decay, inspecting batteries after numerous cycles of use, and high-stress and accelerated aging testing.
05 Heading Towards the Future of Batteries
Solid-state battery technology is set to redefine the industry. Solid-state batteries are a new type of battery technology that replaces liquid electrolytes with solid electrolyte compounds, while still allowing the movement of lithium ions.
Although not a new concept, the new solid electrolytes have high ionic conductivity, similar to liquid electrolytes. Due to their reduced flammability when heated, solid-state designs significantly enhance safety and allow the use of high-voltage, high-capacity materials, overcoming performance issues caused by the high internal resistance of lithium ions. This significantly improves the energy density and cycling performance of batteries.
Nuclear Magnetic Resonance (NMR) plays a crucial role in defining the electrochemical reactions of the new generation of chemical energy storage. In 2022, the introduction of pure electric vehicles powered by sodium-ion batteries marked a redefinition of the compromise between material availability and battery performance.
Another example is the silicon anode materials used to extend storage capacity, which can replace graphite, reducing the demand for graphite in the market.
NMR technology helps define and understand the future of battery electrochemistry. Its integration into the battery manufacturing industry contributes to improving production efficiency.
If we are to transition to a carbon-neutral society, breaking through the performance limits of batteries will be the foundation for providing sustainable portable power in the future.
Researchers worldwide continue to seek ways to make batteries safer, more powerful, and longer-lasting. Using nuclear magnetic resonance spectroscopy analysis will support the development and production of new products, ensuring that our future energy storage needs are met.
About the Authors:
Joerg Koehler, Director of the BioSpin Industrial Division at Bruker Corporation.
Alain Belguise, Academic Director of the BioSpin Business Unit at Bruker Corporation.
Oliver Pecher, CEO of ePROBE GmbH, Blumenstr. 70 Haus 3, 99092 Erfurt, Germany.
References:
（i）B.M. Meyer, N. Leifer, S. Sakamoto, S.G. Greenbaum and C.P. Grey, “High field multinuclear NMR investigation of the SEI layer in lithium rechargeable batteries”, Electrochem. Solid-State Lett. 8(3), A145–A148 (2005). https://doi.org/10.1149/1.1854117
（ii）R. Bhattacharyya, B. Key, H. Chen, A.S. Best, A.F. Hollenkamp and C.P. Grey, “In situ NMR observation of the formation of metallic lithium microstructures in lithium batteries”, Nat. Methods 9, 504–510 (2010). https://doi.org/10.1038/nmat2764
（iii）O. Pecher, J. Carretero-Gonzáelz, K.J. Griffith and C.P. Grey, “Materials’ methods: NMR in battery research”, Chem. Mater. 29, 213–242 (2016). https://doi.org/10.1021/acs.chemmater.6b03183