Part 6: Physical & Thermal Properties - BET & DSC/TGA
Surface Area & Porosity
Technique
Brunauer-Emmett-Teller (BET) nitrogen adsorption measures surface area and pore volume, describing how porous and reactive a material is.
Observation:
Specific surface area - is it within the ideal range?
Pore structure - are pores open or blocked?
Adsorption-desorption curve - does it indicate macro or microporosity?
“Surface area affects electrolyte contact and ion diffusion. Too high or too low porosity alters reaction kinetics and stability.”
NCM v LFP
NCM: 1–5 m² g⁻¹ surface area minimizes side reactions at high voltage.
LFP: 5–15 m² g⁻¹ surface area enhances electrolyte wetting and Li⁺ transport, but excessive area risks instability.
Impact on Cell KPIs
Optimal surface area balances rate performance, safety, and longevity.
Thermal Stability
Technique
Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) evaluate how materials respond to heat, detecting decomposition, oxygen release, or mass loss.
Observation
Onset temperature - when does decomposition start?
Weight loss profile - is oxygen evolution observed?
Heat flow - are exothermic peaks sharp or broad?
“Thermal stability defines safety under high temperatures or overcharge. Materials releasing oxygen at low temperatures risk thermal runaway.”
NCM v LFP
NCM: Begins oxygen release near 280 °C, triggering thermal runaway unless surface-modified.
LFP: Stable up to ~400 °C due to strong P-O bonds, offering superior safety.
Impact on Cell KPIs
Thermal response dictates cell safety and reliability in real-world operation.
