Currently, lithium batteries using lithium-rich/manganese-rich layered oxide (LMR-NMC) have an energy density about 20% higher than traditional nickel-cobalt-manganese lithium batteries, making them a more economical and sustainable alternative. It is considered as the next-generation lithium-ion battery (LIB) cathode material. However, over time, this material tends to release oxygen, reducing the battery’s capacity and voltage, leading to irreversible consequences.
A team from the Battery Engineering Department at Pohang University of Science and Technology (POSTECH) in South Korea has discovered a strong correlation between the phase transition pathways on the surface of LMR-NMC particles and oxygen stability. By modifying the durability of lithium-rich layered oxide (LLO) in lithium batteries, they were able to effectively extend the lifespan of the batteries.
To assess the impact of electrolyte-cathode interactions on the electrochemistry of lithium batteries, they first created traditional LP30 electrolytes and a new type of 2LPDMC electrolyte, and conducted long-term charge-discharge tests on LMR-NMC half-cells with carbonate ethyl acetate/carbonate dimethyl carbonate (EC/DMC).
The results showed that the LP30 and 2LPDMC electrolytes had significantly different effects on the LMR-NMC half-cells. The LP30 electrolyte caused the LMR-NMC half-cell to retain only 70% of its original capacity after 100 to 300 charge-discharge cycles, while the 2LPDMC electrolyte maintained 96.5% capacity even after about 700 cycles.
Furthermore, after 100 cycles, LP30 and LMR-NMC showed minimal activation of manganese ions but decreased lithium vacancy concentration, while 2LPDMC exhibited atomic restructuring on the cathode surface, leading to noticeable oxidation-reduction phenomena of manganese ions.
The research team attributed these phenomena to LP30 electrolytes in LMR-NMC charge-discharge processes severely inhibiting the normal oxidation-reduction of anions in the battery, releasing oxygen and disrupting the overall stability of LLO. In contrast, 2LPDMC showed normal oxidation-reduction with less oxygen released.
The 2LPDMC electrolyte maintained an average energy retention rate of 84.3% after 500 to 700 charge-discharge cycles in LMR-NMC half-cells, while the LP30 electrolyte only retained 37.1% energy after 300 cycles.
These findings suggest that structural changes on the surface of electrochemical LLO materials have a significant impact on the overall stability of LMR-NMC battery materials. By addressing these changes, battery cathode lifespan and performance can be significantly improved, while minimizing unnecessary reactions such as electrolyte decomposition within the battery.
Researchers aim to further develop stable battery cathodes and establish stable solid electrolyte interfaces through additional research to ultimately reduce rechargeable battery costs and improve efficiency.
Professor Jihyun Hong from the Battery Engineering Department at the Institute of Black Metal and Ecological Materials Technology at the university stated, “By analyzing the differences in structure between the surface and interior of cathode particles using a synchrotron radiation accelerator, we have found that the stability of the cathode surface is crucial for the overall structural integrity of the material, providing a new direction for developing next-generation cathode materials.”
This research was published in the Energy & Environmental Science journal at the end of November 2024, with support from the South Korean National Research Foundation, Ministry of Trade, Industry and Energy, Korea Technology Development Institute, and Ministry of Science and ICT in South Korea.