Characterizing and analyzing the failure of materials is a vital procedure towards optimizing the manufacturing processes of lithium-ion batteries (LIBs). By mixing active materials together with a series of binders, additives and solvents, a slurry can be formed and coated onto a current collector foil and dried, to produce LIB porous electrodes.
Throughout the whole process, that is from the raw material stage up until the actual electrode manufacturing process and assembly, materials characterization provides much needed critical control parameters to ensure that the final battery performance meets expectations.
Failure analysis also provides an insight as to why the performance of a battery degrades over time, whilst ensuring that the manufacturing process to fabricate the battery is optimized to minimize performance degradation.
Herein, we discuss the analysis of key materials characterization parameters throughout the LIB manufacturing and failure analysis processes, whilst outlining the analysis solutions offered by Micrometrics.
Particle size and shape
The size and shape of the particles in the raw materials of the manufacturing of LIBs have a significant influence on the packing density of the produced electrode, which in turn affects the thickness and energy density of the electrode. Particles which are too large can induce large volume changes whilst cycling, thus, increasing the potential for a fracture to occur, producing a limiting effect on the battery lifetime.
The particle size distribution within graphite anodes is also known to affect the electrochemical performance of the cell, therefore, it is essential to ensure that the raw materials used in the manufacturing of an electrode possess the correct particle size.
Micrometrics offers a number of solutions for measuring a material’s particle size. The Sub-Sieve AutoSizer, for example, allows for the determination of particles within the range of 0.2-75 μm using air-permeability. On the other hand, the Saturn DigiSizer II is the first commercially available particle sizing instrument that uses light scattering techniques to produce a particle size analysis with a high resolution, accuracy, repeatability and reproducibility.
Another instrument, the Particle Insight, provides a combination of particle size measurements and shape analyzes, using dynamic image analysis, for particles 3-300 μm in size.
See more about particle size measurement solutions
Solid Fraction Determination
The process of passing electrode sheets through rollers to compact them is commonly known as calendaring and increases the energy density by reducing the thickness and porosity of the electrode.
By exposing the electrode to calendaring process, the pore structure of the electrode changes and in turn impacts the wetting behavior of the electrode film through the electrolyte. Calendaring is seen as a critical step in the production of a high performance electrode and by increasing the calendaring you decrease the porosity of the electrode. This means that too much calendaring can have a negative effect on the electrode and induce capacity loss, high cycling rates and a poor longevity in the cycle performance of the final battery.
The determination of the solid fraction, or relative density, of the electrodes can be used as a useful control parameter to identify the ideal setting for optimal calendaring, and thus, allowing for a consistent calendaring and electrochemical performance from batch to batch.
Calculating the solid fraction parameter is obtained through the simple division of the envelope density of the electrode by the absolute density– meaning both the envelope and absolute density values are required to perform the solid fraction calculation.
Micrometrics offers the ideal solution for solid fraction determination, in the form of the AccuPyc 1340 and GeoPyc 1365 Instrument Porosity Bundle. The combination of both instruments provides all of the necessary information to calculate the solid fraction, with the AccuPyc 1340 determining the absolute density using gas pycnometry and the GeoPyc1365 determining the envelope density using quasi-fluid displacement.
Learn more about Micromeritics solutions for solid fraction determination
It is a fact that the electrochemical performance of LIBs degrades over time. The drop in performance is often recognized through capacity fade during charge and discharge cycles, or by a reduction in the shelf life. The reasons for capacity fade and impedance are complex, but material characterization techniques can help to understand and limit the performance degradation.
The analysis of the surface area, porosity, pore size distribution and morphology of both fresh and aged battery components can provide insights as to why the battery performance degrades with time, and enables the manufacturing process to be optimized to limit performance degradation within the battery.
The expansion and contraction of the electrode during battery cycling can cause stresses that affect the performance of the battery, particle density and porosity, with the possibility of delamination and a reduction in the contact between the electrode and current collector occurring. Changes in these properties, caused by volume changes during the cycling process, can be monitored by comparing the properties of both aged and newly produced materials.
Micrometrics offers several key instruments for the physical evaluation of new and degraded battery materials. The AccuPyc 1340 and GeoPyc 1365, TriStar II Plus and AutoPore V provide pore size and porosity measurements, whilst Phenom Pro SEM can be used to determine the whole surface morphology and pore size of electrode materials.
Learn more about pore characterization solutions
Utilizing material characterization techniques before, during and after battery manufacturing is a crucial process which ensures that the manufacturing process is optimized and the performance of the final battery meets expectations. Micrometrics offers a number of instruments which meet the analysis needs of LIB manufacturers.
"Lithium Ion Batteries and their Manufacturing Challenges" - C. Daniel, The Bridge Magazine, National Academy of Engineering, 2015
“Particle size polydispersity in Li-ion batteries” - D. W. Chung et al, J. Electrochem. Soc. 2014. DOI: 10.1149/2.097403jes
“Simulating the impact of particle size distribution on the performance of graphite electrodes in lithium-ion batteries” - F. Röder et al, Energy Technology 2016. DOI: 10.1002/ente.201600232
“High-performance lithium-ion anodes using a hierarchical bottom-up approach” - A. Magasinki et al, Nature Materials 2010. DOI: 10.1038/nmat2725
Solid Fraction Data and Its Importance in Pharmaceutical Roller Compaction Operations - AZoM
"Process development and optimization for Li-ion battery production" - M. Wolter et al, EVS27 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium, Barcelona, Spain, 2013
"In Situ Stress Measurement Techniques on Li-ion Battery Electrodes: A Review" - X. Cheng & M. Pecht, Energies 2017. DOI: 10.3390/en10050591
"Lithium Ion Battery Anode Aging Mechanisms" - V. Agubra & J. Fergus, Materials 2013. DOI: 10.3390/ma6041310
"Understanding Volume Change in Lithium-Ion Cells during Charging and Discharging Using In Situ Measurements" - X. Wang et al, J. Electrochem. Soc. 2007, DOI: 10.1149/1.2386933
This information has been sourced, reviewed and adapted from materials provided by Micromeritics Instrument Corporation.
For more information on this source, please visit Micromeritics Instrument Corporation.