What XRD configuration is best for analysing battery cathode active materials? 

par Umesh Tiwari, Friday, 15th November 2024

X-ray diffraction (XRD) is vital in manufacturing lithium-ion battery cathode materials because it ensures the correct crystal structure, phase, and purity, essential for battery performance. XRD detects phase composition, cation mixing, crystallite size, and strain—all crucial factors affecting capacity, stability, and cycle life. This non-destructive technique is used in quality control to verify material specifications and in R&D to optimize and innovate cathode materials. By providing detailed structural information, XRD helps manufacturers produce reliable, high-performing cathodes, directly enhancing battery efficiency, longevity, and safety. However, correct analysis with XRD requires a bit of knowledge about its optical configurations and their suitability for specific material types. 

What happens if a wrong XRD configuration is used? 

Commercial cathode materials such as lithium iron phosphate (LFP) and nickel manganese cobalt oxide (NMC) often contain transition metals (e.g., Ni, Mn, Co) that fluoresce strongly under XRD, especially with a copper (Cu) anode, leading to a high background and reduced sensitivity. With the choice of proper optics and detectors, this background can be reduced or eliminated leading to far better sensitivity to the minor phases. However, the various optics and detector options on an XRD makes it difficult for a materials scientist to buy an XRD with right configuration for his materials needs.  

Possible XRD Configurations 

  • Motorized Slits with Beam Knife: This setup is cost-effective and performs well at low angles but requires a beta filter to remove kβ peaks, which can reduce beam intensity. 
  • BBHD (iCore) Multilayer Mirror Optics: This monochromator setup eliminates beta and white radiation, providing excellent low-angle performance with low noise, resulting in a clearer diffractogram. 
  • 1D Detectors:  Some detectors have high energy resolution (<350 eV). These are preferred for materials that fluoresce, as they reduce background noise. conventional 1D detectors with normal resolution (>1500 eV) struggle with high fluorescence samples. 

Case Study of Li-NCM111 Material 

In this case study, different XRD configurations were used, combining either motorized slits or BBHD optics with 1D detectors of various resolutions. Results showed that a high-energy resolution (340 eV) detector significantly improved the signal-to-background (S/B) ratio. The highest quality data was obtained by pairing BBHD optics with a high-energy resolution detector, achieving an S/B ratio of 46.7. 

Conclusion 

High-energy resolution detectors (<350 eV) with BBHD optics for analyzing cathode materials provide the best results, minimizing fluorescence interference. This setup enables detailed data analysis, such as measuring cation mixing and crystallite size, crucial for battery performance optimization. 

Curious? Read the full report for details of the full case study. 

Further reading:

Read the application note