Part 2: Morphology & Composition - FE-SEM & EDS
Morphology
Technique
Field-Emission Scanning Electron Microscopy (FE-SEM) is used to visualize the surface of battery materials at the nanoscale. By bombarding a sample with a focused electron beam it produces ultra-high-resolution images that reveal fine surface details.
Observation:
Particle size and distribution - are the particles uniform or varied in size?
Cracks, agglomeration, and coating quality - are particles clumping together, or are coatings evenly applied?
Surface texture - is the surface smooth or rough?
“The particle size, shape, and how tightly they pack together decides ion facilitation through the material and how mechanically stable it is during battery cycling (charge/discharge). ”
NCM v LFP
NCM cathodes are made up of secondary particles roughly 5-15 µm wide, each built from much smaller primary particles (100-200 nm). Their nearly spherical form allows them to pack tightly together, giving the material excellent energy density and mechanical strength. Think of it like stacking smooth marbles, they fit neatly, making the most of the available space.
LFP has a completely different architecture. Its olivine crystal structure comes with two key drawbacks: one-dimensional Li⁺ diffusion pathways and an electronically insulating framework. These characteristics limit both ionic and electronic transport within the material, making pristine LFP inherently less conductive than layered oxides like NCM. Its electronic conductivity is extremely low (around 10-9 S/cm, at room temperature), which significantly restricts charge transport across the electrode. To overcome this limitation, LFP must be manufactured with much smaller, nanosized particles to shorten Li⁺ diffusion distances and provide more conductive contact points between grains. The primary particles, typically rod- or platelet-shaped (0.1-1 µm), facilitate faster lithium insertion and extraction, enabling higher charge-discharge rates and reducing mechanical stress during cycling. Additionally, conductive carbon coatings or dopants are applied to enhance electron mobility and create efficient percolation networks throughout the electrode, collectively improving the overall electrochemical performance.
Structural Composition
Technique
Energy-Dispersive X-ray Spectroscopy (EDS), typically coupled with SEM, detects the unique X-ray emissions produced when a material is bombarded with electrons. This allows us to identify and quantify the elemental makeup of the sample, ensuring stoichiometric accuracy and uniform distribution.
Observation
Elemental uniformity and stoichiometry - Are all key elements evenly distributed
Elemental ratio accuracy - Does the atomic ratio match theoretical values?
Contaminants or dopants - Are unwanted impurities present?
“Accurate structural composition ensures predictable electrochemical behaviour. A slight deviation in elemental ratio can alter conductivity, stability, or safety.”
NCM v LFP
NCM: The Ni: Co: Mn ratio controls electrochemical balance.
Higher Ni content → increases capacity but reduces structural stability
Higher Co content → enhances conductivity but adds cost
Higher Mn content → improves safety but lowers conductivity
LFP: A Fe: P ratio close to 1 confirms proper stoichiometry. Carbon is often detected as a coating residue that enhances electrical contact.
Impact on Cell KPIs
The cathode composition directly influences energy density, lifespan, safety, and cost.
