Understanding Advanced Batteries for Electrochemical Processes

To better understand the electrochemical processes that occur during battery cycling, modern advanced batteries need a variety of specialized analytical tools. EAG offers a wide scope of material characterization services specifically for the battery industry to aid battery manufacture, failure analysis and materials R&D.

Raw Materials

Throughout battery manufacture a crucial element, influencing performance, and potentially safety, is the consistency in impurity and composition levels in the raw electrode materials. There are a variety of different analytical techniques available to tackle this:

  • ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) is used for accurately determining lower level elemental impurities.
  • ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) is commonly used for analyzing the composition of electrodes.
  • IGA (Instrumental Gas Analysis) is the technique of choice when analyzing for low levels of gas forming elements such as H, C, N, O and S.
  • GDMS (Glow Discharge Mass Spectrometry) allows full periodic table trace element analysis in a single measurement and is an ideal technique for monitoring the presence of unwanted impurities.

The table below shows ICP-OES data from LiNiCoAlO2 cathode samples from 3 different raw material suppliers showing variations in composition.

Elements Supplier #1, wt % Supplier #2, wt % Supplier #3, wt %
Li 7.6 6.1 6.3
Al 1.2 1.3 1.5
Co 8.9 9.3 9.1
Ni 46.6 51.0 50.0

 

Atmospheric species measured using IGA from a LiNiCoAlO2 cathode.

Elements Composition wt %
O 30.9
C 0.3
N 0.2
S <0.001

 

GDMS data acquired from eight LiFePO4 cathode samples from a range of suppliers is shown in this plot. For clarity, only selected elements are shown. The existence of a number of different unwanted impurities was repeatable over a number of samples from a particular batch and provided valuable information to the battery manufacturer.

Unusually high amounts of impurities, in particular Mn and Mg, were found in one supplier’s batch. Which resulted in an unacceptable cycle life for the batteries manufactured.

Surface Chemistry and Composition

With demand increasing for improved safety and higher battery performance, a clearer knowledge of the factors affecting cycle life, performance and possible failure mechanisms is vital. Gauging the chemical state of the battery components such as the contact layers, electrolyte, cathode, anode, separator and additives, at various stages of cycling, supplies crucial details regarding the electrochemical processes occurring during battery use.

EAG offers molecular and elemental analyses using a variety of different analytical tools for this purpose. Moisture sensitive materials are extracted from cells in a moisture controlled environment and can be moved to instruments for analysis with no exposure to moisture or air.

XPS (X-Ray Photoelectron Spectroscopy) is a commonly used method for investigating the surface chemistry of electrodes. Using this, the phosphorus chemistry on a graphitic anode before and after battery cycling is compared. There is a clear increase in phosphate bonding relative to LiPF6 after cycling.

TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) has the distinct ability of analyzing both organic and inorganic components, allowing for an in-depth analysis of the presence of impurities; decomposition products; or any other surface changes during cycling. This spectrum was taken from a cycled battery with a LiCoO2 cathode using LiPF6 electrolyte. Many molecular species of interest are recognized on the surface of the cathode that did not originate there.

This is a secondary ion image documented from the surface of a lithium titanate (Li4Ti5O12) anode. TOF-SIMS allows a greater comprehension of the lateral chemical distribution of species of interest at varying stages of cycling by imaging different species on the sample.

Species of interest can be depth profiled by sputtering with an ion beam, which is especially useful when studying the chemical composition of SEI layers as a function of depth.

Auger Electron Spectroscopy allows elemental analysis by utilizing an electron beam focused down to ~10-20 nm. This allows specific parts of interest on electrode particles to be examined. Here, the surface of a cycled graphitic anode is analyzed showing the presence of species characteristic of both the anode and the electrolyte.

A cycled LiNiMnCoO2 cathode is analyzed showing a high carbon signal at the extreme surface, from electrolyte residue surrounding the cathode particles, using the elemental mapping capability of Auger Electron Spectroscopy (AES).

Electron microscopy methods such as TEM (Transmission Electron Microscopy), Dual Beam Focused Ion Beam (DB-FIB) and SEM (Scanning Electron Microscopy) imaging are essential techniques to inspect particle coatings, morphology, mixing efficiency, particle size and defects.

These techniques generally use elemental mapping capabilities such as EDS (Energy Dispersive X-Ray Spectroscopy) and EELS (Electron Energy Loss Spectroscopy). These can provide further valuable information about location/distribution and elemental composition.

This is an example of an SEM image of a cycled lithium polymer battery prepared by ion milling. Each layer can be further inspected at greater magnification. Imperfections at the interfaces and film thickness variation can be inspected easily.

This TEM image of a freshly prepared cathode displays an amorphous carbon coating on a LiFePO4 particle. The elemental composition of the coating can be confirmed by EELS and the thickness can be measured precisely, allowing thickness variation to be monitored.

This is an SEM image of a freshly prepared carbon based anode film. Variation in particle size and mixing efficiency can be investigated easily. There is software available to aid in further image processing.

This is a TEM image of a cycled LiFePO4 particle showing the formation of an SEI (solid-electrolyte interface) layer on the surface. Key insights into potential SEI growth mechanisms can be provided by determining the composition of SEI layers via EELS or EDS.

Technique Typical Battery Applications
ICP-OES Electrode composition
SEM Morphology, mixing and film uniformity, particle size
GDMS Raw material quality control
Raman / FTIR Impurity detection, carbon phase
TEM / STEM Particle size, particle coating analysis, crystallinity phase
EELS / EDS Elemental analysis/mapping, SEI characterization
XPS Chemical state, composition
TOF-SIMS Organic composition, SEI characterization
Auger Elemental mapping, particle depth profiling
TGA / DTA / DSC Thermal properties
SIMS Elemental depth profiling of metals
GC-MS, LC-MS Characterization of volatile organic species, electrolyte characterization
XRD Crystallographic phase, crystallite size
IGA Levels of atmospheric species
ICP-MS Electrode impurities
RTX Alignment of internal components
XRF Elemental composition

 

This information has been sourced, reviewed and adapted from materials provided by EAG Laboratories.

For more information on this source, please visit EAG Laboratories.

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