The global lithium-ion battery market was already worth nearly 42 billion dollars in 2021 and still has incredible growth predicted – up to 18.1% yearly.1 The reason behind this vast market and growing demand is the prevalence of lithium-ion batteries as rechargeable power sources and key technology in enabling energy storage.
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Rechargeable batteries work by utilizing chemical reactions that can restore their cell potential. Achieving recharging means applying an external current to the cathode and anode that drives the movement of lithium ions between them in the electrolyte of the battery to create a potential difference between the two electrodes.
The movement of the lithium ions between the electrodes of the battery provides a current or helps to recharge it. Ideally, lithium-ion batteries offer shorter charging times than traditional lead-acid batteries and can be practical for many portable devices as lithium-ion batteries are typically much lower weights.
One of the problems with lithium-ion batteries is that their ability to charge and discharge and follow such cycles does not last forever. Poorer charge retention and eventual battery failure can sometimes come from degradation processes.2 Batteries are often relatively hot while in use, so one of the contributing factors to this degradation can be thermally induced breakdown of the electrodes.
Ultimately, chemical or physical degradation of the battery cell limits the overall battery life and can also mean reduced energy storage capacity over time. Being able to understand the mechanisms of battery degradation is key to being able to improve lithium-ion battery design in the future.
Batteries are chemically complex, with many different materials and compounds in their composition. Understanding which components are failing means those can be improved.
Raman Spectroscopy to Help Understand Lithium-Ion Battery Degradation
One of the tools being used to understand lithium-ion battery degradation is Raman spectroscopy.3
With the use of fiber-optic cables to deliver and collect light from the battery in the experiment, it is possible to perform operando measurements of batteries where the degradation products can be monitored under actual operating conditions.
Other types of fiber design, such as hollow-core fibers, are also being used to enhance the performance of Raman spectroscopy for battery analysis.3
Raman spectroscopy is a powerful tool for qualitative and quantitative chemical analysis as it can recover a ‘spectral fingerprint’ of the vibrational modes of a molecule or material. If there are changes in the chemical bonding environment around any chemical sites with Raman active modes, the intensity or frequency of the observed transitions in the Raman spectrum can change.
While the Raman effect is weak and can be challenging to achieve good signal levels, the sensitivity of Raman signals to even small changes in the chemical environment makes it an excellent technique for understanding the complex electrochemical environments in batteries.
Raman spectroscopy has been used to understand how lithium ions introduce and interact with the graphite electrodes and other materials and has helped identify materials for battery designs with larger charging capacities.4
Historically, improving battery capacities and performance has been a relatively slow task, with lithium-ion batteries only showing an 8% performance improvement year on year.4
Electrolytes in Lithium-Ion Batteries
The electrolyte is one of the most essential components in a lithium-ion battery. The electrolyte is typically a liquid in these batteries and allows the lithium ions to move between the cathode and anode.
It also provides the chemical environment to which the electrodes will be exposed in operation. This exposure means that the chemical composition of the electrolyte has a vital role in the cell’s ion mobility, the electrode’s chemical stability, and the overall lifetime of the battery.
LiPF6 is a commonly used electrolyte for lithium-ion batteries. However, degradation products involve the formation of gaseous species.5
Excess production of gases in batteries is a huge safety risk as it can build pressure in the device and further enhance electrode degradation.6
By using Raman spectroscopy in operando, it is possible to monitor many of the chemical species formed and their changing concentrations during battery operation, such as vinylenes, along with the solvation dynamics of the lithium ions.3
Using non-silica hollow-core fibers can help remove contamination of signals from silica in the Raman spectrum, improving the signal-to-noise of measurements.
New methods are continually being developed to facilitate the measurement of whole fuel cells.
While it is highly desirable to perform true in operando measurements of a complete fuel cell rather than using model half cells or simplified devices, coupling fuel cells with spectroscopic methods can be logistically challenging to transmit light in and out.
Improvements in fiber technologies and sensitivities of methods such as Raman for better detection limits mean detecting even trace amounts of breakdown products will be possible. This information can then be used to improve battery safety and design.
References and Further Reading
- Grand View Research (2022) Lithium-ion battery market, https://www.grandviewresearch.com/industry-analysis/lithium-ion-battery-market, accessed July 2022
- Wang, Changhong, Tao Deng, Xiulin Fan, Matthew Zheng, Ruizhi Yu, Qingwen Lu, Hui Duan, Huan Huang, Chunsheng Wang, and Xueliang Sun. 2022. “Identifying Soft Breakdown in All-Solid-State Lithium Battery.” Joule 1–12. doi: 10.1016/j.joule.2022.05.020.
- Miele, Ermanno, Wesley M. Dose, Ilya Manyakin, Michael H. Frosz, Zachary Ruff, Michael F. L. De Volder, Clare P. Grey, Jeremy J. Baumberg, and Tijmen G. Euser. 2022. “Hollow-Core Optical Fibre Sensors for Operando Raman Spectroscopy Investigation of Li-Ion Battery Liquid Electrolytes.” Nature Communications 13(1):1–10. doi: 10.1038/s41467-022-29330-4.
- Stancovski, Victor, and Simona Badilescu. 2014. “In Situ Raman Spectroscopic-Electrochemical Studies of Lithium-Ion Battery Materials: A Historical Overview.” Journal of Applied Electrochemistry 44(1):23–43. doi: 10.1007/s10800-013-0628-0.
- Guéguen, Aurélie, Daniel Streich, Minglong He, Manuel Mendez, Frederick F. Chesneau, Petr Novák, and Erik J. Berg. 2016. “ Decomposition of LiPF 6 in High Energy Lithium-Ion Batteries Studied with Online Electrochemical Mass Spectrometry.” Journal of The Electrochemical Society 163(6):A1095–1100. doi: 10.1149/2.0981606jes.
- Rowden, Ben, and Nuria Garcia-Araez. 2020. “A Review of Gas Evolution in Lithium Ion Batteries.” Energy Reports 6:10–18. doi: 10.1016/j.egyr.2020.02.022.