Li-Ion batteries are rechargeable devices with higher performances and efficiency than the traditional non-rechargeable alkaline and zinc-carbon batteries, thanks to the high energy density, the resistance to self-discharge and the reduced memory effect. Li-Ion batteries are widely used for consumer electronic (mobile phones, tablet, laptop…), automotive (EV Electric Vehicles), and large scale energy storage. The characterization of the physical properties of the several components – electrodes, separator, electrolyte – is crucial in research & development to improve the performances (capacity, durability..) of the Li-Ion batteries, as well as in quality and production control.
Alfatestlab has the technologies and the competences to support your Li-Ion batteries characterization needs.
Electrodes properties characterization
Porosity, Particle Size and Shape, Packing Density, viscosity: all these characteristics influence the performances (life, charge cycling) and the capacity of the electrodes of a Li-Ion battery. Porosity for instance, influences the interactions between the active material and the conductive diluent and is essential for the transport of Li-Ion between the electrodes. Particle Size and shape have to be controlled in order to ensure a high packing density (polydisperse size and circular shape) and high power. Electrodes showing high surface area have a better efficiency in the electrochemical reactions and a better ion exchange between electrolyte and electrode, at the same time electrodes showing low surface area and high density materials normally offer a longer lifetime.
Regarding the initial slurry, its quality will strongly depend on the properties of the powder, mixed with solvents and binder, to get the correct fineness of the grain, solid content and viscosity for the process. The rheological properties of the powder will rule the mixing dispersion to create the slurry. Viscosity of the slurry itself will have a meaningful influence to obtain a proper coating and a correct calendering and therefore to ensure the quality of the final electrodes.
Calendering process is the most important part in the process of electrodes production, i.e. the common compaction process for lithium-ion battery electrodes. Calendering has a
substantial impact on the pore structure and therefore the electrochemical performance of Lithium-ion battery cells. Increasing the calendaring will decrease the thickness and by consequence the percentage of porosity of the electrode. Above the correct level of calendering, the pore size and the porosity can be reduced to the point to cause a loss of capacity and a bad longevity in cycle performance.
In Alfatestlab technological platform includes:
- Porosity and BET surface area measurements by Gas adsorption
- Density by Helium pycnometer
- Porosity, Surface Roughness, Failure Analysis by Scanning Electron Mi-croscopy (SEM) and elemental analysis (EDX)
- Particle Size and Particle Shape Analysis by Laser diffraction, DLS Dy-namic Light Scattering, Automated Image Analysis (Static and Dynamic)
- Powder rheology using FT4 Powder rheometer
- Viscosity using Rotational Rheometer
Separator and Electrolyte characterization
The separator has the function to isolate the cathode from the anode, at the same time the separator has to promote as a catalyst the flow of the ions from cathode to anode during the charge and oppositely during discharge. The separator membrane is normally made of a highly porous material, like polyolefins and is wetted with the electrolyte.
The porosity is by default a fundamental parameter to be measured and controlled, since a high porosity tend to keep the electrolyte entrapped within the pores that helps the ionic movement from cathode to the anode and gives a higher energy density. On the other hand a too high porosity can limit the capacity of the separator to shut down and generate overheating of the battery closing the pores.
Alfatestlab can support you to achieve uniform porosity, constant flow of ions and an homogeneous current distribution by controlling the porosity. The pore size distribution of the membrane has to be smaller than the particle size of the electrodes material to prevent from entering the separator pores.
The affinity between the material used in the separator membrane and the electrolyte, that will affect the mechanism of transport, can be evaluated measuring the Zeta Potential.
In Alfatestlab we provide:
- Porosity and BET surface area measurements by Gas adsorption and SEM with Porometric software
- Density by Helium Pycnometer
- Zeta Potential by Electrophoretic Light Scattering
Thanks to a large number of analytical services, Alfatestlab allows you to test the materials present in almost all the different battery systems
- Powdered materials
- Electrode materials
- Liquid and solid electrolytes
- Charge separators
- Current collectors
More information on our Battery characterization services are presented here below:
Particle size analysis
Alfatestlab provides particle size distribution by laser diffraction in the range 0.01 μm – 3500 μm and by dynamic light scattering in the range 0.3nm-10um. AlfatestLab is equipped with other granulometry techniques such as Nanoparticle Tracking Analysis NTA (10-2000nm), automatic image analysis (0.1-10000 um) or scanning electron microscopy SEM with Particlemetric software to provide particle size distribution. These techniques allow a precise and fast measurement of battery materials, for instance solid electrolytes or graphite electrodes powders.
BET Surface area and porosity analysis
Alfatestlab provides BET specific surface area, pore size distribution and volume measurement of solids and powders using gas physisorption techniques. In Alfatestlab, we perform specific surface area and porosity measurements on various types of materials used for electrodes and solid electrolytes (such as: NCA, LTO, graphite…) using different gases: N2, Kr and Ar (depending on the surface of the material).
Powder and material density
Real density analysis of solids and powders are performed in Alfatestlab by helium picnometry. This technique allows us to provide accurate values of the density of powdered battery materials or its components.
Powder and liquid rheology
As described previously, the properties of the initial slurry to produce the Li-ion battery electrodes will strongly impact the electrodes performances. Powders mixed with solvents and binder should show the correct viscosity for the process, to obtain a proper coating and a correct calendering. The rheological properties of the powder will rule the mixing process to create the slurry. Alfatestlab provides rotational rheology and powder rheology analysis to allow you a complete characterization of the raw materials and final slurries to quote your electrodes.
Alfatestlab offers combined STA (TG-DTA) measurements as well as DSC analysis on polymer and polymer-ceramic composite used as electrode binders, charge separators, and solid electrolytes in batteries. Thermal analysis provides an in-depth insight into the properties of your sample: thermogravimetry measures any mass change in the sample subjected to a temperature ramp, such as thermal or oxidative decomposition, oxidation, dehydration, and vaporization. Differential Scanning Calorimetry (DSC), on the other hand, characterizes a wide range of physical phenomena, such as phase transitions (polymer melting points, crystallization, glass transition…), chemical reactions (oxidation and curing or polymerization) and many others.
Microscopy and elemental mapping
In Alfatestlab we use scanning electron microscopy (SEM) images, combined with EDX (energy dispersive x-ray analysis) elemental analysis to provide high resolution structural analysis of battery materials, and elemental mapping of the distributions and migration of chemical elements before and after cycling. We also use the image analysis software such as Particlemetric to obtain particle size distribution from SEM images.