image: Elevating the sintering temperature from 850 to 900°C transform the lithium-manganese-rich cathode from solid-solution structure to chemical separated two-phase structure, which is triggered by the migration of Li, Ni and Mn ions.
Credit: ©Science China Press
The research team, led by Professors Dong Su, Miao Liu, and Dr. Xincheng Lei from the Chinese Academy of Sciences’ Institute of Physics, along with Professor Xin Wang and Dr. Jiayi Wang from Zhejiang Wanli University, used advanced transmission electron microscopy to analyze structural changes during the synthesis of the cathode material Li1.2Ni0.2Mn0.6O2 at the atomic scale. Their findings showed that ion migration during the synthesis process facilitates the formation of a unique two-phase structure, which could transform the way lithium-ion batteries are engineered.
Lithium-ion battery cathode materials have come a long way since Nobel laureate John Goodenough developed the LiCoO2 cathode in 1980, marking the beginning of their practical commercialization. Over the years, researchers have sought to replace cobalt with nickel to achieve higher capacity and lower costs. However, even cobalt-free LiNiO2 cathodes fall short of meeting the ever-growing demand for higher energy density.
One promising solution is the development of lithium-rich cathodes, which can deliver energy densities as high as 1000 Wh/kg—enough to power long-range electric vehicles or even electric airplanes. Despite this potential, scientists have struggled to fully understand the atomic structure of these materials, a knowledge gap that hinders their improvement.
For over two decades, researchers have debated whether lithium-rich cathodes exhibit a solid-solution structure or a two-phase structure. To resolve this question, the team conducted a detailed analysis of the Li1.2Ni0.2Mn0.6O2 cathode during synthesis. They discovered that when the heating temperature exceeds 900°C, the material undergoes a structural transition from a solid-solution phase to a separated two-phase structure. Unlike previous assumptions that the two phases are mixed at the nanoscale, the researchers found that they are distinctly separated at microscale. This transition is primarily driven by the migration of cations within the cathode particles under higher temperatures.
“Imagine a gemstone that is half diamond and half ruby—something entirely unique,” one of the researchers explained. “This new structure exhibits dramatically different electrochemical properties, broadening our understanding of lithium-rich cathodes. It opens the door to a new era of cathode phase engineering at microscale, which could lead to breakthroughs in creating high-energy-density lithium-ion batteries.”
This discovery not only enhances the understanding of lithium-rich cathode materials but also provides a foundation for designing next-generation batteries capable of meeting the demands of future technologies.