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Analysing lithium ion batteries using electron paramagnetic resonance spectroscopy

What types of materials can EPR spectroscopy be used to study?

Electron paramagnetic resonance (EPR) spectroscopy can be used to study any material with unpaired electrons, known as paramagnetic materials. These electrons exhibit noticeable changes in behaviour when subjected to an external magnetic field.

In electrochemical manufacturing and studies, such as lithium ion batteries (LIBs), EPR proves valuable for studying transitional metal ions and rare earth ions. Unpaired electrons in their outer shells or unique structures make them paramagnetic. When exposed to specific electromagnetic frequencies, these electrons can change energy levels, revealing the electron structure and magnetic properties of these particles.

Furthermore, EPR can study ion clusters, revealing distinct magnetic behaviours of unpaired electrons. This insight can inform the arrangement of ions and atomic interactions, and is applicable to doped and defective materials. The introduction of foreign elements , or irregular arrangements, can introduce unpaired electrons. In study, this allows observation of the impact on material properties in electrochemical manufacturing.

Finally, EPR holds potential in analysing reactive paramagnetic free radicals and metalloproteins. This enables structural study of free radicals, as well as exploration of paramagnetic properties of metalloproteins, and how they interact with their environment and function, particularly in the medical industry.

What are the main parts of a lithium ion battery?

LIB’s find widespread use in diverse electronics like electronic vehicles, power grids and computers. Remarkably simple in structure, they consist of just four key parts; the positive cathode, negative anode, electrolyte and diaphragm.

In the process of charging and discharging the battery, chemical reactions produce paramagnetic particles that impact the performance of the battery due to microstructural changes, leading to decay. By using EPR to study the relationship between performance and electrochemical reactions in LIBs, electrochemical researchers can develop new and novel techniques needed to improve the performance of these batteries.

What parts of a lithium ion battery can be monitored using EPR?

EPR enables study of paramagnetic particles produced in the various parts of the LIB. In electrodes, the presence of transition metal ions like cobalt, nickel, iron, and manganese can be studied. These ions have unpaired electrons, and can provide insight into electronic behaviour and interactions during charge-discharge cycles.

The concept extends to the electrolyte, an ionic solution containing diverse ions, some being paramagnetic. Detecting these ions during redox reactions in the electrolyte aids investigation of their role in battery charge cycles.

EPR can also be used to examine the formation of free radicals, providing insight into their behaviour, and quantifying its concentration at different battery cycle stages.

Can Oxygen and peroxide species during the redox reaction in a lithium ion battery be studied using EPR?

EPR is used to study oxygen and peroxide species in battery redox reactions. Oxygen ions participate in many electrochemical reactions, especially in electrode materials. These changes result in paramagnetic oxygen species with unpaired electrons. EPR detects and quantifies these oxygen radicals, allowing engineers to study to understand their impact on battery behaviour and capacity

Similarly, electrolyte redox reactions  generate peroxide species, many of which are paramagnetic. EPR’s role is to identify and categorise these newly formed species, detailing its formation, concentration and predictive role in battery behaviour.

Can EPR be used to study the formation and reduction of radicals during charge and discharge in organic electrode material systems?

During LIB’s charge-discharge cycles, chemical reactions in organic electrode material generates free radicals. EPR uses distinct electromagnetic frequencies to detect and quantify these paramagnetic radicals by gauging energy transitions within the electron structure. EPR can thereby determine the presence, concentration and properties of radicals formed during Lib charging and discharging reactions.

During the discharge phase of the LIB energy cycle, electrical energy release prompts reduction reactions in the radicals, causing them to gain electrons and become less reactive, as their unpaired electrons become paired.  EPR tracks the paramagnetic properties changes  of the reacting radicals in real time.

Real-time monitoring of EPR allows researchers to observe radical formation and reduction as it occurs. This facilitates analysis of how these processes influence electrode performance and behaviour.

How to select EPR instrumentation

SciMed offers four primary EPR spectroscopes.

  • The Ciqtek EPR-W900, capable of continuous wave and pulse EPR, explores electronic properties and defects in electrode materials, aiding in defect formation understanding and its impact on battery performance. T
  • The highly sensitive Ciqtek EPR200-Plus delves into paramagnetic species in battery electrolytes, offering insights into reactive radicals during battery operation.
  • The Ciqtek EPR200M focuses on battery quality control, ensuring production materials lack unwanted paramagnetic particles that could hamper performance.
  • The Ciqtek EPR100 specialises in pulse EPR for studying battery degradation mechanisms, including radical formation and role in battery aging.
    The choice of spectrometer hinges on specific lithium battery analysis goals.

For personalised recommendations, consult the SciMed team.

How to interpret EPR results

EPR spectroscopy measures radiation absorption and generates a results graph depicting magnetic field strength versus signal intensity. Peaks on the spectrum represent energy transitions of paramagnetic electrons, with each peak indication a paramagnetic species. Peak intensity and shape offer insights into species concentration and properties during battery cycling. High peaks signify elevated paramagnetism. The Ciqtek EPR spectroscope facilitates real-time measurement of these changes, reflecting battery dynamics.

Comparing results to reference spectra enables precise determination of electron species concentrations and characteristics. Engineers and researchers can draw conclusions about the types of paramagnetic species and battery defects, assessing their potential impact on performance and safety, such as degradation processes.

What to do next?

To find out more about the Ciqtek EPR spectroscopy offering, visit SciMed’s web pages for the EPR-W900, EPR200-Plus, EPR200M and the EPR100.

Alternatively, to speak to one of SciMed’s team about how you can use the Ciqtek EPR product range to monitor electrode materials and redox mechanisms in real time, contact us below.

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