As society seeks to advance electrification in pursuit of global sustainability goals, demand for ever-better performance from devices such as lithium-ion batteries is growing steadily. To meet this demand, lithium-ion battery researchers are seeking to gain more control of the materials used and their physical properties. Particle characterization plays a crucial role in realizing this. This article outlines the fundamentals of particle characterization as it pertains to lithium-ion battery R&D and highlights instruments used to conduct this technique.

What is particle characterization?

Particle characterization is the process of analyzing and describing the physical and chemical properties of particles. Particles can vary significantly in size, shape, composition, and other attributes, and understanding these characteristics is essential in lithium-ion battery R&D to improve their efficiency, lifespan, and safety.

Check out the applications note on particle analysis of lithium-ion batteries:

Applications note on particle analysis of lithium-ion batteries

How is particle characterization used in lithium-ion battery R&D?

The performance of lithium-ion batteries directly correlates to the properties of the materials of which they are made. Below are several ways in which particle characterization is used in lithium-ion battery R&D.

Cathode and anode materials 

Anode and cathode materials are key components of lithium-ion batteries. A partial list of cathode and anode materials includes:

Understanding the particle size and size distribution of cathode and anode materials provides insights into electrode performance, the metrics of which include:

• Capacity: The amount of electric charge that an electrode can store.
• Charge/discharge rates: How quickly or slowly an electrode can accept or deliver an electrical charge.
• Cycle life: The number of charge and discharge cycles a battery or electrochemical device can undergo before its capacity significantly degrades or it becomes less effective. It is a critical factor in determining the lifespan and durability of a battery.

The shape of particles of cathode and anode materials can affect:

• Packing density: This refers to how closely the particles are packed together. The shape of the particles can influence how efficiently they fit together, affecting the overall density of the material. Higher packing density generally means more lithium ions can be stored in a given volume.
• Porosity: Porosity is a measure of the empty spaces or pores within a material. The shape of the particles can influence the porosity of the cathode and anode materials. Porosity is important because it affects the accessibility of lithium ions to the interior of the material, impacting the efficiency of ion movement within the electrode.

Diffusion of lithium ions: The shape of the particles affects how easily lithium ions can move within the material. Different shapes may generate pathways that promote or impede the movement of ions. Efficient ion diffusion is crucial for the performance of a lithium-ion battery because it affects how quickly ions can move between the cathode and anode during charging and discharging.

Electrolyte and separator materials

As with electrode materials, knowing the particle size and distribution of components in the electrolyte (including salts and solvents) and separator materials helps optimize electrolyte conductivity and separator properties.

Binder and conductive additives

Binder and conductive additives impact electrode integrity and electrical conductivity. Characterizing their particle size and distribution helps optimize electrode structure and improve electron and ion transport.

Degradation analysis

As lithium-ion batteries go through charge and discharge cycles, the properties of the electrode materials can change. Monitoring changes in particle size, shape, and surface area over time helps researchers understand degradation mechanisms and improve battery lifespan.

Safety considerations

Particle characterization techniques can be used to study the thermal properties of battery components. Understanding how materials respond to changes in temperature is crucial for assessing and improving the safety of lithium-ion batteries.

Characterization of Solid Electrolyte Interphase (SEI):

The SEI layer forms on the surface of the electrodes during the initial cycles and significantly impacts battery performance. Characterizing the composition, thickness, and properties of the SEI layer is critical for understanding and optimizing battery behaviour.

Horiba Scientific instruments for particle characterization

HORIBA Scientific has 200 years of experience in developing high-performance scientific instruments and analytical solutions. It offers an impressive range of instruments for particle characterization, including the Horiba LA-960V2 laser scattering particle size analyzer depicted below.

This latest evolution in the LA series continues a long-standing tradition of leading the industry with innovative hardware and software design. The new optical design allows the user to visualize particle dispersion in real-time.

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SRC continues to offer our customers a range of innovative, high-quality scientific products and laboratory services throughout Canada for industrial and scientific markets. For more information about Horiba Scientific instruments for particle characterization for lithium-ion batteries and other applications, please contact a member of our staff.

What is Raman spectroscopy?

Raman spectroscopy is a non-destructive materials analysis technique in which a monochromatic light source, usually a laser, is directed onto a sample of the materials being analyzed. The interplay of the light and the vibrations of the molecules in the materials generate spectra that can be used to identify materials, characterize molecular structure, assess morphology, and observe dynamic processes. Raman spectroscopy requires little sample preparation and can be used in situ or ex situ.

Obtaining Raman spectroscopy measurements was a time consuming, complex process. As a result of advances in Raman spectroscopy, the technique now delivers much higher sensitivity, better resolution, and a broader range of battery R&D applications. What’s more, current Raman spectroscopy instruments are relatively quick and easy to use, allowing even those with limited science expertise to operate them effectively.

How is Raman spectroscopy used in battery R&D?

Raman spectroscopy plays an important role in advancing battery technology by providing critical information that can be used to analyze battery components, such as cathode, anode and electrolyte materials. Cathode and anode materials degrade over time, but Raman spectroscopy provides insights into their molecular structures, helping researchers measure degradation rates. Reducing the degradation rates of these materials is a key step in developing better batteries.

Raman spectroscopy helps advance understanding of the properties of both liquid and solid electrolytes, including ion transport mechanisms, phase changes, and chemical interactions. This information is indispensable for creating more efficient and stable electrolytes.

A versatile tool, Raman spectroscopy can help evaluate the degree of interaction among electrolyte ions within solutions and polymeric substances. These interactions directly impact battery performance. Additionally, the technique offers valuable insights into the composition of polymer matrices and the ways in which additives can influence their crystalline structure, another factor impacting battery performance.

An extension of Raman spectroscopy, Raman mapping and imaging helps analyze the distribution of materials on electrode surfaces, or across cross-sections. The data obtained can be quantified, giving metrics such as fraction estimates and particle statistics.

Detecting low concentrations of binder. Raman map of an anode (superimposed on an optical microscope image). The colours represent: SBR styrene-butadiene rubber binder (red); graphite (green); acetyl black (blue). The relative concentrations, as determined by the map, are, respectively: 1%, 97%, and 2%.

Operando studies of an anode. As the potential is changed, the anode’s appearance changes. The graphite G-band Raman peak also changes, indicating intercalation of lithium (shifting the peak to higher wavenumbers) and then a peak-splitting reflecting the intercalation penetrating to interior layers, rather than just the boundary layers. Data courtesy of Prof. Y. A. Kim, Shinshu University, Japan.

In situ analysis of batteries is conducted with batteries that are fully assembled and in operation. With Raman spectroscopy instruments, in situ analysis can provide information on chemical reactions that occur as batteries are charged and discharged, helping in the development of new battery materials.

After new materials are produced and prototype batteries are produced with them, it is essential to determine how these materials impact performance, and what it is that makes them either better or worse than their predecessors. This is when ex situ analysis is done, a process requiring disassembly of the batteries and analysis of their components in an inert environment using Raman spectroscopy instruments.

Understanding the Solid-Electrolyte Interphase (SEI) layer is essential for battery safety and performance. Raman spectroscopy is used to analyze the SEI layer’s composition and thickness, helping to minimize issues like capacity fading and dendrite formation. Raman spectroscopy can also be used to study the thermal behaviour of battery materials and investigate safety concerns, such as the risk of thermal runaway.

Raman spectroscopy can also be employed for quality control in battery manufacturing to ensure that materials and components meet the desired specifications, preventing defects and inconsistencies.

Supporting electric vehicle battery range performance research

Automotive R&D is increasingly focused on new propulsion technologies for the next generation of hybrid and electric vehicles (EV). At the heart of EV product development is the pursuit of extended range through motor efficiency and battery effectiveness.

Renishaw Raman technologies offer a non-destructive method of monitoring and imaging battery chemistry so that the most suitable materials can be developed and their performance limits understood. Renishaw’s inVia™ confocal Raman microscope, for example, enables automotive battery manufacturers to examine battery chemistry under a range of operating conditions (such as fast-charging and extremes of temperature) to see how the battery reacts and work out how to improve its efficiency.

Apart from R&D of lithium-ion batteries widely used to power electric vehicles, Raman spectroscopy contributes to the development of emerging, next-generation battery technologies, such as lithium-sulfur and solid-state batteries, by helping researchers investigate the unique challenges and materials associated with these systems.

In summary, Raman spectroscopy is an invaluable analytical tool for battery R&D, providing critical information about the characterization, optimization, and safety assessment of various battery components, all of which are essential for advancing battery applications.

Renishaw Raman spectroscopy instruments

Renishaw produces a wide range of Raman spectroscopy instruments, including research-grade microscopes, routine bench-top analysers, transportable fibre-optic analysers and combined (hybrid) systems. These state-of-the-art instruments help researchers gain insights across a range of battery applications. Click here to learn more.

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Click here to contact SRC and speak directly with our experts on Renishaw Raman Spectroscopy Instruments.

What is XPS?

X-ray photoelectron spectroscopy (XPS) is a powerful surface analysis technique used to identify the elements in and the chemical states of the top layers of materials. It works by bombarding the surface of a material with X-rays (photons) and then measuring the kinetic energy of the photoelectrons ejected from the surface of a material. This energy is directly related to the photoelectrons’ binding energy within the parent atom and is characteristic of the element and its chemical state. Only electrons generated near the surface can escape without losing too much energy for detection. As a result, XPS data is obtained only from the top few nanometers of the surface. XPS surface selectivity, combined with quantitative chemical state identification, makes XPS highly useful in many applications, including battery research.

Vital role of battery research

Batteries have a vital role to play in the world’s transition from fossil fuels to renewable energy. In 2022, EVs accounted for 10% of global vehicle sales and by 2030 they are expected to reach 30% of global vehicle sales.  Governments around the world are contributing to this growth through policies that are directing billions of dollars into battery research and manufacturing and by providing subsidies for consumers to purchase EVs.  Ambitious cost and performance targets for the electrification of transportation will require the development of next-generation batteries produced on a commercial that are cost-effective, safe, renewably sourced, and high-performing with long lifetimes.

How XPS is used in battery research

There are multiple components and interfaces that are crucial to understand to develop high-performing and stable batteries. These include the cathode, anode, separator, electrolyte, and all interfaces formed between these layers, particularly the electrode-electrolyte interfaces. XPS can be used to study all of these materials and interfaces, such as next-generation cathode/anode active materials and how their composition changes with cycling; how the solid electrolyte interphase (SEI) layer varies in composition as a function of depth; and how surface pre-treatments affect the chemistry of the active electrode material. The quantitative chemical-state information provided by XPS makes it a versatile tool to understand many properties and guide the design of optimized batteries that meet ambitious targets.

Battery research challenges and XPS solutions:

• Analyzing SEI layer growth: Ongoing charging and discharging of a battery causes the SEI layer to form on the anode, reducing battery capacity. Analysis of the SEI layer helps researchers better understand and control this phenomenon and thereby improve battery performance and longevity. XPS depth profiling can chemically characterize the complex mixture that makes up the SEI layer, from the anode side all the way to the electrolyte side, for chemical understanding of the entire layer.
• Investigating the role of impurities and contaminants: Impurities and contaminants in battery materials can adversely affect performance and safety. XPS is highly sensitive to trace elements and can identify the presence and identity ofimpurities or contaminants on the surfaces of battery materials, helping researchers understand the sources of impurities and their impact on battery performance.
• Understanding the stoichiometry of solid electrolyte films: Chemical state analysis provided by XPS can be used to identify the stoichiometry of materials, including depth profiling to quantify elements at each depth and track any differences in stoichiometry throughout a film.
• Studying interface chemistry: Interfaces between different components of a battery play a crucial role in battery performance and long-term stability. XPS provides insights into the chemistry of interfaces, helping researchers optimize interface design for enhanced performance.
• Examining degradation in separator chemistry: XPS can provide valuable insights into degradation in separator chemistry during a cell’s lifetime by analyzing the surface chemistry and composition of the separator material.
• Environmental impact and recycling: XPS can be used to analyze the chemical composition of battery materials before and after recycling processes. It can help assess the effectiveness of recycling methods and the feasibility of reusing materials.
• Analyzing in situ electrode cycling: In situ XPS experiments can provide real-time insights into the electrochemical behavior and surface chemistry of electrode materials during cycling.

The best XPS for battery research from SRC

PHI’s XPS instruments use a unique scanned, finely-focused X-ray beam to create X-ray induced secondary electron images (SXIs), similar to an SEM, for easy sample navigation with 100% certainty in analysis position.  This imaging capability can be used to easily drive around the sample in live mode or to save positions for compositional analysis including point or large-area spectroscopy, line scans, depth profiling, or chemical mapping. The size of the X-ray beam can be selected to support the efficient analysis of larger samples with homogeneous composition or small heterogeneities. This feature is indispensable for analyzing battery materials and interfaces, ensuring identification of impurities or other heterogeneities in composition, and absolute certainty that data is acquired from the exact feature of interest. In contrast to SEM/EDS, which has a typical analysis depth of 1-3 µm, XPS is a surface-sensitive technique with a typical analysis depth of less than 5 nm, making it better suited for the compositional analysis of ultra-thin layers and thin microscale sample features.

The PHI Genesis is the latest generation of PHI’s highly successful multi-technique XPS product line with PHI’s patented, monochromatic, micro-focused, scanning X-ray source. It is an easy-to-use, fully automated system with auto-tuning and calibration and multiple parking positions for high throughput. The fully integrated multi-technique platform of the PHI Genesis offers an array of optional excitation sources, sputter ion sources, and sample treatment and transfer capabilities that are all aligned to the same sample location. These features are essential in studying all relevant properties of advanced battery materials and interfaces, including small impurities or compositional heterogeneities, access to buried interfaces, electronic energy gap measurements, and operando experiments for a direct link between chemistry and performance. PHI Genesis offers high sensitivity and high throughput for large areas and small areas down to 5 µm and unique high-throughput non-destructive depth profiling using the optional hard X-ray Cr source. The instrument is fully customizable to address all analytical needs.

For more information on how PHI Genesis can be used to address your battery characterization challenges, please visit the PHI YouTube channel to watch a recent PHI.

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