Empowering Battery Research and Manufacturing

Lithium batteries with solid electrolytes are currently the focus of electrochemical research due to their potential for achieving higher energy densities and enhanced safety compared to liquid electrolytes. Polymer-based electrolytes are particularly promising, as they are flexible, cost-effective to manufacture, and enable good wetting of the electrodes, which compensates for volume differences during the charging and discharging of the cell.

However, the polymer systems presently available generally exhibit insufficient ionic conductivity at room temperature, which is essential for high-performance batteries. Composite materials composed of a polymer matrix and ionically conductive particles could address this deficit by combining the advantageous properties of both materials.

The interface between the particles and the matrix is believed to play a crucial role in the conduction mechanism of lithium ions through the composite. A better understanding of these underlying processes can pave the way for the development of new and improved composite materials.

Kerstin Neuhaus and other researchers at the Helmholtz Institute Münster , an outpost of the Jülich Research Center, have successfully characterized the electrochemical properties of the interfaces between the polymer and particles at the nanometer scale. (Figure 1) and illuminating these with the local lithium activity. A Kelvin probe is used to investigate the difference in the Volta potential between the particles and the polymer and to analyze local differences in the conductivity of lithium transfer. This new characterization technique can facilitate the optimization of polymer-based lithium batteries.

For more information on characterization options for energy materials on the nanometer scale with our Atomic Force Microscopes, talk to our expert.

Figure 1: The distribution of the Volta potential of an ion-conductive LLZ particle in a MEEP polymer matrix shows a reduced potential at the interface and an increased potential within the particle. This indicates different lithium ion activities and varying concentrations of anions. See “Buchheit et al., J. Electrochem. Soc. 168, 010531 (2021)"

Current liquid electrolyte solutions in new types of batteries and accumulators have a significant impact on their energy density, service life, safety and costs. The components in these solutions are individually selected and optimized to achieve the desired properties in the end product. Therefore, a precise analysis of all components of electrolytes in lithium-ion accumulators is essential. Typically, these solutions consist of a mixture of organic solvents, an inorganic lithium-containing salt and other additives; some of them in a concentration of less than 2%.

Benchtop nuclear magnetic resonance (NMR) spectroscopy is an ideal method for investigating the structure and concentration of unknown materials in electrolytes and comparing them with other components or comparison samples. In addition, important physical parameters such as the diffusion coefficient and ionic conductivity can be determined. NMR is increasingly becoming an important method for material analysis throughout the entire life cycle of batteries - from accelerating the development of new electrolyte compositions to quality control in production and identifying the causes of errors at the end of the life of batteries.

A unique feature of the X-Pulse broadband benchtop spectrometer is the ability to analyze any type of electrolyte. It is the only commercial benchtop instrument that can measure all relevant nuclei (H, C, F, B, P, Li, Na, Si) for a comprehensive understanding of electrolyte systems. Each analysis can be performed directly and quickly in any working environment, be it in the laboratory or at production sites, even by untrained personnel.

Figure 2: ¹⁹ F 1D NMR spectrum of a defective lithium-ion battery electrolyte. The degradation products could be identified and quantified.
Figure 2 shows an example in which NMR was used to determine the cause of the decomposition of the conductive salt Li[PF ₆ ] and the associated loss of performance in an electrolyte made of methyl carbonate and ethylene carbonate. First, by comparing with a reference electrolyte, it was determined that the solvent was not involved in this degradation. However, the ¹⁹ F spectrum in Figure 2 indicates a hydrolysis of [PF ₆ ] − to difluorophosphoric acid, which is already present in a ratio of 0.006 : 1 compared to [PF ₆ ] − . Furthermore, LiF was identified as an undesirable byproduct of this hydrolysis.

As we move towards a zero-emission and environmentally friendly future, battery innovations for electric vehicles are crucial. These batteries must be durable, safe, fast-charging, and have high charge capacities. Beyond their role in mobility, batteries are essential for storing energy from renewable sources such as solar, wind, water, biomass, tides, and geothermal energy. To improve performance, new and complex materials are needed, while maintaining high standards for safety and recyclability. Used batteries can be repurposed for large-scale energy storage before their final recycling.

Effective material characterization is vital throughout the entire lifecycle of batteries. Energy-dispersive spectroscopy (EDS) is a key technique here, offering fast, non-destructive analysis with high sample throughput. Cathodes often consist of nickel, cobalt, manganese, and sometimes aluminum, with a trend toward replacing cobalt due to cost and ethical concerns.

The Oxford Instruments Ultim Extreme EDS detector, with its ability to operate at low voltages and detect lithium, plays a significant role in this analysis. The AztecBattery software complements this by providing automated, precise quantification of transition metals, which is essential for quality control and optimizing cathode materials during production.

Figure 3: Automated particle analysis of lithium nickel cobalt manganate (NCM) using AZtecBattery. The software can automatically calculate the ratio of transition metals in each ternary cathode particle.

Significant development is taking place to Li-ion batteries to get the best performance for each of the many applications that they are used for. Optimising the cathode material is an area of key interest for the current generation of Li-ion battery

technologies as even small changes to the cathode can have large overall effects on the battery.

Electron Backscatter Diffraction (EBSD) is a SEM based technique which can measure local crystal orientations. The data can be used to extract information about grain boundaries, grain size and texture which might relate to the electrical performance and stability of the material. It therefore provides a method to quantify the variations which can be seen in the electron image. The data was collected using AZtec software and a Symmetry CMOS EBSD detector at high speeds – which allowed the electron dose to the sample to be limited thereby reducing damage; at 20kV using a probe current of approximately 10nA.

This case study on WMG, University of Warwick demonstrates how cathode materials can be analysed in the SEM using EBSD or TKD depending on the spatial resolution required.

For more information on characterization options for battery material analysis with SEM based technologies, talk to our expert.

Figure 4: Band contrast map to the left and IPFz map to the right.

Understanding the relationships between structure and properties is fundamental for developing more powerful, durable, and cost-effective Li-ion batteries. RISE microscopy (Raman Imaging and Scanning Electron Microscope) is an extremely useful tool to visualise structural and chemical information, including: molecular composition, grain fractures, solid electrolyte interphase (SEI) formation and electrode degradation. 

High-resolution scanning electron microscopy (SEM) characterises electrode ultrastructure and energy-dispersive X-ray spectroscopy (EDS) detects incorporated elements. Li-containing molecules are identified by Raman spectra, which reveals localisation, concentration and polymorph changes.

Using a WITec alpha300 confocal Raman microscope integrated with SEM, we examined cross sections of 18650 Li-ion battery cells before and after cycling. SEM-EDS of the new battery reveals the cathode consists of Co/Ni (pink) and Mn-rich parts (cyan) (Fig. 1a). Raman imaging additionally identifies the graphite (cyan) and amorphous carbon (blue) in the anode, and amorphous carbon and lithium with manganese oxides (MO, red) in the cathode (Fig. 1b). The separator layer of polyethylene (PE, green) between two layers of polypropylene (PP, yellow). During cycling (Fig. 1c), the uniaxial polymer chains deteriorate, appearing as bi-axial PP in the used battery and are likely to significantly reduce battery performance.

We then analysed Lithium-Nickel-Manganese-Cobalt-Oxide (NMC) batteries that underwent fast recharging with 40% loss of capacity. Reduced performance often occurs from inhomogeneous electrode microstructure degradation. Thanks to the RISE, it was caputured that the new charged cathode particles consist of uniform MO. Rapid cycling induced significant changes in particle lithiation with the Raman spectral peaks broadening and shifting. The RISE image of one cycled MO particle reveals a high level of inhomogeneity and degradation in the form of cracks.

This case demonstrates the power of RISE microscopy for pinpointing causes of degradation occurring during cycling at both cathode and separator that reduce both battery lifespan and charge/discharge performance.

Figure 5: Raman microscopy and SEM-EDS mapping investigation of 18650 cell LMO batteries.