Battery tech: CityU scientists achieve minimal voltage decay

Such an invention has profound implications in the energy sector, which could potentially lead to higher energy storage capacity, a statement by the university said. 

Addressing voltage decay in LiBs

The team of researchers addressed the persistent challenge of voltage decay in lithium-ion batteries (LiBs). The use of these batteries is significant in electronic devices.

The statement emphasized that lithium-(Li) and manganese-rich (LMR) layered oxides are a promising class of cathodes for LiBs due to their high capacity and low cost. However, the long-standing problem of voltage decay hinders their application.

Due to this, scientists sought to devise a solution that stabilized the honeycomb-like structure within the cathode material. As a result, the process led to the innovation of longer-lasting and more efficient batteries with negligible voltage decay.

The researchers – Professor Ren Yang, head and chair professor of the Department of Physics (PHY), Professor Liu Qi, PHY, and the team have created a type of battery that could change how devices are powered today.

Tackling the honeycomb structure

In order to achieve the goal of developing battery technology with minimal voltage decay, the team assessed the honeycomb structure at the atomic level. They integrated the additional transition metal ions into the cathode material and reinforced the honeycomb structure.

“This resulted in a negligible voltage decay of just 0.02 mV per cycle,” noted the scientists, “the first time that LMR cathode material with such a low level of voltage decay has been reported.”

By utilizing sophisticated atomic-scale measurements and calculations, the team discovered that interlayer transition metal ions serve as protective caps above or below the honeycomb structure. These caps prevent cation migration and uphold stability, preserving the structural integrity of the batteries, even under high cut-off voltages and throughout cycles.

Professor Liu stated: “Our work has solved the voltage decay problem in the LMR cathode, with a capacity almost two times higher than the widely used cathode materials, ultimately paving the way for more powerful and sustainable energy storage solutions.”

The study was published on July 6 in the journal Nature Energy.

Study abstract:

With high capacity at low cost, Li- and Mn-rich (LMR) layered oxides are a promising class of cathodes for next-generation Li-ion batteries. However, substantial voltage decay during cycling, due to the unstable Li2MnO3 honeycomb structure, is still an obstacle to their practical deployment. Here we report a Co-free LMR Li-ion battery cathode with negligible voltage decay. The material has a composite structure consisting of layered LiTMO2 and various stacked Li2MnO3components, where transition metal (TM) ions that reside in the Li layers of Li2MnO3 form caps to strengthen the stability of the honeycomb structure. This capped-honeycomb structure is persistent after high-voltage cycling and prevents TM migration and oxygen loss as shown by experimental and computational results. This work demonstrates that the long-standing voltage decay problem in LMRs can be effectively mitigated by internally pinning the honeycomb structure, which opens an avenue to developing next-generation high-energy cathode materials.