Morphology, topography, chemical composition of Li-ion batteries

A great deal of research is being carried out within the battery industry to develop future energy storage systems. This task is one of the most important modern technological challenges. First marketed in 1991, the lithium-ion battery offers relatively low self-discharge compared with other batteries. The principle of this accumulator is the displacement of the lithium ion between two electrodes, one positive (cobalt or manganese dioxide) and the other negative (graphite).

It is essential to carry out a series of analyses and characterize the effect of the reaction of the various elements present on the electrodes, particularly on their surface and in the interface zones.

Different types of Li-ion batteries exist, some designed for small products and others as high-power industrial accumulators for hybrid vehicles or aeronautics. This requires analytical techniques capable of differentiating chemical states with high sensitivity and spatial resolution. 
This has led to in-depth research into Li-ion batteries, as they are envisaged as the basis for high-power-density secondary sources for electric vehicles and storage devices for the smart grid.

The vital performance of Li-ion batteries, such as service life, internal resistance and capacity, is closely linked to the microstructure of the electrodes. The solid electrolyte interphase (SEI) has proven to be crucial for increasing the performance and lifetime of lithium-ion batteries. It is therefore necessary to understand the mechanisms and reactions that lead to the formation of SEI layers on Li-ion battery electrodes.

High-resolution imaging reveals microstructural information about the composite structure made up of spherical microparticles of the active material held together by the polymer matrix.

SEM is a technique capable of producing high-resolution images of the surface of a sample. It is used in many fields, from biology to materials science and microelectronics, and on all types of sample. Even insulating materials can be observed after metallization, in a controlled inert atmosphere or at low voltages (close to kV).

SEM is generally used to study the 3D morphology of a surface or object with nanometric resolution. Elemental chemical composition can also be obtained by X-ray microanalysis.

The principle of this technique is based on the use of an incident electron beam of a few tens of kilovolts scanning the surface of the sample, which then re-emits a whole spectrum of particles and radiation: secondary electrons, backscattered electrons, Auger electrons and X-rays. Detection of the various particles or radiation emitted provides information about the sample: its morphology, topography, crystalline structure, elemental chemical composition (qualitative and semi-quantitative analysis)...

TESCAN ANALYTICS has over 30 years' expertise in the use of SEM/FIB/EDX on all types of materials, whether insulating or conductive... With state-of-the-art instruments, our team of experts works with all industrial sectors.

In these non-exhaustive examples, it has been demonstrated that scanning electron microscopy (SEM), with or without FIB and EDX, is an ultra-powerful microscopy tool for the structural and chemical study of Li-ion batteries.

With an excellent depth of field (~ 100 x that of optical microscopy), SEM provides high-resolution images of all materials.

For more applications of SEM analysis or our other analytical techniques and microscopy, click here.

The combination of SEM/EDX and ToF-SIMS techniques facilitates comprehensive analysis of material composition. X-ray tomography enables non-destructive visualization of internal features such as porosity, cracks and phase distribution. In dynamic mode, it is possible to visualize 3D changes in internal structures when they undergo modifications such as loading or liquid absorption.