Lithium ion batteries (LIBs) are the most popular battery technology in the world today due to their use in consumer electronic devices, electronic vehicles (EVs), and energy-storage systems. Although new types of batteries under development, such as flow cell and solid state technologies, promise greater benefits, Li-ion batteries are expected to remain the dominant battery technology in the near future due to EV demand, falling prices, as well as investments in R&D and manufacturing capacity by major suppliers. Goldman Sachs estimates a 21.5% growth rate for the rechargeable lithium battery market this year.
The EV market, in particular, is driving demand. Bloomberg New Energy Research (BNER) forecasts EVs to account for 40% of LIB GwH demand by 2020, rising to 58% by 2024. EV demand for LIBs has increased from 19 GwH in 2010 to 123 GwH in 2015 and will hit 408 GwH by 2025. Also growing is demand for LIB use for stationary storage, including electrical power grids. This market is estimated at 1 GwH installed currently and forecast to reach 81 GwH in 2024, according to BNER.
Continual improvements are required for LIB technology to more effectively meet market demand as well as specific application requirements. Primary issues with the current LIBs include cost, energy density, recharging times, life cycle and safety.
At the heart of LIB R&D is materials characterization, primarily the characterization of electrode materials. New electrode materials are critical to increasing energy density and life cycle, while ensuring safety and lower costs. For cathode materials, advancements have been made via new composite materials based on new formulation and combination of metals such as cobalt, nickel, manganese and iron. The crystal structure of such materials determine the amount of lithium a battery can store and thus its energy capacity. Next generation cathode materials under development include nanomaterials and 3D metal oxides, promising the storage of more energy in less space. Advances in anode materials include the addition of graphite. Silicon composites are expected to play a major role in anode materials going forward.
A wide range of analytical techniques are employed to characterize the material structural and chemical composition and changes during battery charging and discharging. Examples include the investigation of particle morphology, composite formation and material defects.
Spectrometry, spectroscopy and microscopy techniques are each used for LIB material characterization. Atomic spectroscopy techniques provide structural analysis as well as determination of elemental composition. Molecular spectroscopy can be used to image structural changes as well as chemical changes. Advanced microscopy techniques provide detailed structural images.
Since LIB R&D remains active and increasingly challenging, demand for analytical instrumentation from the LIB market has been growing. Analytical techniques offered by JEOL for battery research include electron microscopy, Auger electron spectrometry, electron probe microanalysis, x-ray photoelectron spectrometry, XRF spectrometry, NMR and GC/MS.
“The market is driven by the need to develop and improve Li battery electrodes and other materials for faster charging, longer battery life and higher energy-storage density, as well as to understand why batteries fail and what is the chemistry involved.”
As Michael Frey, PhD, Analytical Instruments Product Manager at JEOL, and Natasha Erdman, PhD, Product Manager, told IBO, “We have seen an upward trend in this market space, likely due to increased needs for high-resolution imaging and characterization as drivers for improvements in electrode material developments and manufacturing.” Such research addresses the fundamental shortcomings of today’s battery materials. “The market is driven by the need to develop and improve Li battery electrodes and other materials for faster charging, longer battery life and higher energy-storage density, as well as to understand why batteries fail and what is the chemistry involved.”
Dr. Erdman discussed the use of SEM in LIB research. JEOL’s SEM offerings include the JSM-7800F FE-SEM with resolution of 0.8 nm at 15 kV and 1.2 nm at 1kV. “From the SEM and sample preparation perspective, we provide the tools that assist in morphological (surface) and compositional characterization of the battery materials without any air exposure.” An example is sample transfer devices. “JEOL offers special holders and specimen loading devices that allow seamless transition between a sample preparation device, such as cross-section polisher and an imaging platform (SEM),” he explained. Exposure to the air can create deposits on the sample surface.
Specific features for JEOL’s SEMs address the requirements working with LIB materials. As Dr. Erdman said, “We offer a specialized specimen preparation device (cross-section polisher) that can prepare air isolated specimens, which is critical for Li battery industry (air exposure alters battery surface via oxidation); JEOL also offers a way to transfer this sample directly into the SEM for observation without any additional air exposure.”
Ultra-low voltage SEM enables higher-resolution surface imaging and increased contrast, enabling greater examination of pore structure and size. One example of next generation cathode materials are sulfur/carbon composites, whose beneficial features center on porosity, pore volume and surface area. “Ultra-low voltage electron microscopy, combined with signal filtering, allows direct imaging and analysis of cathode materials at ultra-high resolution,” noted Dr. Erdman. “Ultra-low voltage imaging combined with signal filtering in the SEM allows direct imaging and analysis of battery constituents (anode and cathode) with nanometer resolution.” Both cathodes and anodes suffer cracking, affecting safety as well as life cycle.
SEM is often used on combination with other techniques to provide elemental composition as well as structure. One example is Energy Dispersive Spectroscopy (EDS). “As a result of JEOL’s unique combination of sub-nm resolution SEM for imaging and high probe current for analytical work, we are a leader in low-voltage imaging and simultaneous EDS analysis,” explained Dr. Erdman. “This allows us to unambiguously pinpoint the location of various constituents within the battery materials, including fluorine.” Fluorine containing compounds are among the next generation polyanionic materials being studied for cathodes.
Likewise JEOL’s NNR systems are used in LIB research. NMR provides chemical characterization with high resolution. “NMR is used to understand the changes at a molecular chemistry level that occur during battery charging and discharging cycling and to understand the bulk chemistry of the battery materials,” said Dr. Frey. “NMR has been increasingly used because it is able to reveal the chemistry at the electrode interfaces and in the bulk materials with a level of detail that has been unavailable in the past.”
Like JEOL, HORIBA offers multiple techniques for both LIB R&D and manufacturing. “HORIBA has a number of groups and products that are used for lithium ion battery technology. Particle analysis is used to determine size distribution due to the effect of size on charge transfer, and reaction rates. Also, the behavior of the slurries used for the binders is in part determined by the size of the particles in the slurries,” explained Dr. Jeff Bodycomb, product manager.
“Since there is a rapid growth in the use of new materials, as well as increased sales of existing materials; it is certainly an area for growth in sales. This is especially true for our particle characterization technologies.”
Examining structural properties and changes also includes in-depth analysis of particles, including particle size distribution. “Since there is a rapid growth in the use of new materials, as well as increased sales of existing materials; it is certainly an area for growth in sales. This is especially true for our particle characterization technologies.”
For electrode material chemical and structural characterization, HORIBA offers a wide range of techniques. Among the applications are the examination of material degradation and changes. “Our spectroscopy tools are also used to probe the battery materials. Raman spectroscopy can be used to monitor changes in crystal structure in both cathode and anode materials.” In addition, the company provides atomic spectroscopy techniques. “XRF and ED-XRF are excellent tools for foreign material and impurity analysis. Optical emission spectroscopy can be used to determine composition such as the oxygen deficiency in the cathode.”
Use of the techniques extend beyond LIB R&D. “As with most markets, our technologies are used throughout the entire supply chain,” noted Dr. Bodycomb. “For the battery electrode materials, as an example, all the way from removing the minerals from the ground to the actual preparation of the electrodes, QA must be performed on the materials.”
Many of the same techniques are used throughout the process. “There is still a large amount of research going into battery materials. As each new material is developed, it must be characterized completely prior to being considered as a replacement for existing components,” noted Dr. Bodycomb. “For example, with electrode materials, the particle size distribution, surface area, porosimetry and other techniques will come into play. Even as these materials move into actual production, these techniques must be used to perform QA on the production samples.”
Like HORIBA, Thermo Fisher Scientific’s analytical instrument offerings are also positioned to offer a range of characterization techniques for LIB materials characterization in both R&D and manufacturing. Investigation of materials requires a thorough understanding of physical, chemical and structural behavior and interactions.
Fitz DeSmet, vice president of Marketing, Materials and Structural Analysis, at Thermo Fisher Scientific told IBO, “As lithium ion batteries power more and more items of our everyday life, it is increasingly important to improve their performance by accurately identifying microscopic defects in the final product and thereby improving the manufacturing process.” Discussing an example of the use of atomic and imaging techniques, he commented that EDS “complements SEM and TEM analysis by adding elemental and phase mapping to microscopic samples. As lighter elements and energy sensitive samples in materials become critical components, the ability to understand materials with fewer and fewer x-ray events becomes critical.”
Analytical imaging techniques meet specific challenges of material investigation, particularly as it relates to charge transport. “We currently see two main use cases for imaging and analysis with our EM solutions. The first is generating improved 3D reconstructions of the battery to better understand the flow of lithium and charge carriers,” noted Mr. DeSmet. “This is a combination of micro-CT-based visualization, revealing the internal porosity and other defects of the entire structure of interest, and Plasma FiB-SEM imaging, allowing researchers to generate a field of view in 3D and at nanometer resolution that is representative of the entire sample’s transport properties.” As with other techniques, these techniques also can detect cracks in the cathode structure. “The second use case is imaging the crystal structure of the cathode active material with the TEM.”
Molecular spectroscopy techniques also provide structural information about particle and crystal analysis at a molecular level in addition to the atomic level view of imaging and EM surface analysis. “IR (e.g., Raman and FTIR) spectroscopy is used to characterize the effect on the structure of cathode materials in the process of lithium-ion insertion/extraction, enabling the improvement of the performance of lithium-ion batteries,” said Mr. DeSmet.
He added, “Additionally, it is also used for evaluation of crystallinity and morphology of materials, which affects performance. Understanding the SEI [Solid Electrolyte Interphase] layer is an area of significant interest, so that it can be controlled and therefore improve cell performance.” Analysis of deeper layers of the material is also provided by XPS. “XPS depth profiling offers a way of chemically characterizing the complex mix that makes up the interphase layer, allowing an identification of the chemistries that comprise the SEI.”
“The energy storage market is experiencing high growth, with lithium ion batteries outpacing other technologies. The typical customer used to be academic institutes working in close collaboration with industrial customers but more recently we see an increasing number of industrial customers adapting EM technology in their own R&D labs.”
According to Mr. DeSmet, demand is robust. “The energy storage market is experiencing high growth, with lithium ion batteries outpacing other technologies. The typical customer used to be academic institutes working in close collaboration with industrial customers but more recently we see an increasing number of industrial customers adapting EM technology in their own R&D labs.”
Although challenged by new battery technologies, R&D remains a central focus for LIB R&D as a number of hurdles remain. Mr. DeSmet listed these hurdles. “Some of the key challenges developers and manufacturers in the industry face are: (1) minimizing degradation processes to extend battery life; (2) designing methods to achieve longer discharge, extending range of electric vehicles on a single charge; (3) rapid charging of the battery in minutes, and (4) reaction dynamics during normal operation.”
And while many types of analytical techniques are required, automated integration of results is increasingly being realized. As Mr. DeSmet put it, “Our focus going forward is to make it easier for customers to link the data sets from the different tools and length scales together in their labs so that they can ultimately get a better understanding of their sample and make timely decisions about improvements in their manufacturing process.”