Analysis Examples of Cathode Materials for Lithium-ion Batteries and Next-generation Battery Systems Using XRD

We bring you feedback from customers at Hanyang University in South Korea.

Hanyang University owns Malvern Panalytical’s X-ray diffraction device Empyrean. The university is researching the analysis of cathode materials for advanced lithium-ion batteries and next-generation battery systems.

User

Mr. Nam-Yung Park (박남영)
Hanyang University (한양대) Energy engineering department (에너지공학과),
Prof Yang-Kook , Sun (Highly Cited Researcher in the field of Materials Science – 2022)
Energy Storage & Conversion Materials Lab

Could you tell us about your research theme?

Our laboratory focuses on the research and development of higher capacity, longer cycle, and safer battery materials, centering on cathode materials for advanced lithium-ion batteries and next-generation systems. Based on a basic understanding of the physical and electrochemical properties of materials, we develop and evaluate innovative cathode materials to improve the energy density, cycle life, and safety of lithium-ion batteries.

We conduct research and development of core technologies with chemical manufacturers, secondary battery manufacturers, and automotive manufacturers both domestically and abroad, and conduct experiments on currently commercially available technologies. Additionally, we are exploring and aiming to realize next-generation battery systems. We aim to build an environmentally friendly world for the future by utilizing these innovative battery materials.

What are the significant challenges or issues you are facing that need to be resolved?

When the Ni content in the Li[Ni_xCo_yMn_1-x-y]O2 (NCM) cathode exceeds 60%, the range of microcracks increases rapidly due to the accumulation of anisotropic strain caused by sudden lattice volume change during H2 phase-H3 phase transition. As a result, microcracks occur within the Ni-rich cathode particles, allowing the electrolyte to penetrate the interior of the particles, increasing the surface area exposed to the electrolyte. This increase in surface area further accelerates the capacity decline of Ni-rich cathodes. To suppress the deterioration of Ni-rich cathode materials, we are focusing on modifying microstructures that can disperse internal strain caused by lattice volume change.

The microstructure of cathode materials is greatly influenced by the hydroxide precursor and sintering processes. Sintering a mixture of hydroxide precursor and lithium hydroxide at high temperatures (700–800°C) forms a layered crystal structure capable of (de)intercalating Li+ ions. However, if the primary particles coarsen during sintering, the microstructure gets destroyed, compromising the mechanical stability of the cathode against microcrack formation. On the other hand, restricting sintering temperature and dwell time to adjust the morphology of the primary particles hinders complete crystallization of the cathode, which subsequently leads to cycle performance degradation due to cation mixing. Therefore, achieving complete crystallization without coarsening cathode materials is considered one of the most critical issues to be resolved.

What approaches or solutions have you considered or evaluated? Please explain the evaluation process and selection criteria.

In general, there is an optimal temperature during sintering where hydroxide precursors completely crystallize. High temperatures can anneal structural defects like antisite defects. On the other hand, excessively high temperatures can induce Li deficiency and cation mixing. The temperature of cation mixing, where Li and Ni interchange due to similar radii (Li+ (0.076nm) and Ni2+ (0.069nm)), can be used to judge the crystallinity of the layered structure. This structural information combined with scanning electron microscopy (SEM) microstructure of cathode particles and their respective electrochemical performance determine the optimal sintering temperature for cathode materials.

How did you evaluate before using Malvern Panalytical’s XRD?

Before utilizing X-ray diffraction devices, we conducted XRD analysis using particle accelerators located in Pohang. Additionally, we performed transmission electron microscopy (TEM) analysis to determine the crystal structure at the atomic level.

Why did you choose Malvern Panalytical’s XRD, and how does it fit into the manufacturing/research/development processes?

XRD can obtain a lot of crystal structure information, so we sought a compact yet powerful XRD device that could be installed in the lab. Malvern Panalytical’s X-ray diffraction device allows analysis of not only powder samples but also pouch-type cells without disassembling them. In-situ XRD analysis of the cell allows detailed understanding of structural changes accompanying battery charge-discharge cycles. Since the capacity degradation mechanism of Ni-rich cathode materials is significantly influenced by the H2-H3 phase transition where sudden structural changes occur, analyzing structural changes of the cathode without disassembling the cell is considered crucial for developing high-energy Ni-rich cathode materials.

How does our equipment help solve various challenges?

What equipment are you using?

What data can you obtain by using the equipment, and does it meet your expectations?

Our laboratory owns an XRD analysis device Empyrean capable of analyzing in reflection and transmission modes. Reflection mode is used to analyze powder samples of the cathode to determine lattice constants and layering. Transmission mode is used to analyze pouch-type cells composed of many parts (electrodes, separators, AI pouch, etc.). We analyzed the shift of peaks corresponding to structural changes in cathode materials due to charging and discharging. For example, changes in lattice constants due to the chemical composition of cathode materials can be analyzed using the Rietvelt method. Furthermore, deconvolution (003) by reflecting H2 and H3 peaks during H2-H3 phase transition allows comparison of structural reversibility of cathode materials. Structural information of cathode materials obtained from XRD analysis sufficiently met our laboratory’s expectations.

How was your experience using the equipment? Did it meet your expectations?

An intuitive interface allows for accurate analysis. Various accessories can also be utilized according to the purpose.

How can Empyrean contribute to your research in the future? Are you considering further application development or system additions and expansions?

Our laboratory plans to conduct TR (time-resolved)-XRD analysis using a high-temperature reaction vessel. By performing TR-XRD analysis, it becomes possible to analyze phase transitions and phase evolution during heat treatment close to the actual sintering process in real-time.

What do you expect from working with Malvern Panalytical in the future?

In addition to the analysis of cathode materials where crystal structure significantly relates to electrochemical performance, it is believed to be immensely useful in analyzing crystal structures in next-generation battery materials (all-solid-state batteries, Li-sulfur batteries, etc.).