Researchers explore increasing the working capacity of LiVO3 cathodes in lithium-ion batteries

As fossil fuel supplies decrease and climate change worsens, both the grid energy storage sector and the automotive industry are stepping up efforts to develop powerful and efficient energy storage technologies. According to foreign media reports, researchers from the School of Energy and Environment at City University of Hong Kong and other institutions have conducted a new study to explore ways to optimize the working capacity of LiVO3 positive electrodes in lithium-ion batteries.

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Developing lithium-ion batteries with higher energy density is a key factor in increasing the range and competitive advantage of electric vehicles . One of the most promising approaches is to broaden the charge cut-off voltage of lithium-ion batteries, allowing manufacturers to extract more lithium from the material, thereby increasing the capacity of lithium-ion batteries. The most obvious obstacle to this process is that removing more lithium from the layered structure will cause the lattice to be unstable. As the battery cycles, it will cause the capacity to decay rapidly.

The use of lithium-rich transition metal oxides is expected to solve this problem. These materials can provide excellent specific capacities when charged to higher voltages, with specific capacities exceeding 250 mAh g−1 or more reported when charged to 4.8 Vh. The advantages of these lithium-rich materials are mainly due to the activation of anionic redox reactions of oxygen anions when they are charged. These oxygen anions can transfer electrons as transition metals and are replaced by lithium.

The study proposes methods to optimize this process. By better stabilizing the crystal structure of oxygen atoms and transition metals used in LIB cathode configurations, it helps alleviate several capacity fade and voltage fade issues. It is worth mentioning that the structural arrangement within these lattices has a significant impact on atomic stability. The bonds between transition metal oxide materials are shorter, and stronger bonds can be produced when these transition metals are tetrahedrally coordinated rather than octahedrally coordinated. This is a key consideration for optimizing cathode materials. These materials may be more stable when undergoing anionic redox reactions. However, their application in battery materials has been little studied to date.

Vanadium-based materials are a popular choice for battery applications due to their ability to transfer charge. With these factors in mind, the researchers explored the capacity of monoclinic LiVO3, which consists of a VO4 tetrahedral structure, to accommodate a high cut-off voltage. The materials were initially charged to 4.8 V. During the charge process, a total of 0.56 mol of lithium could be removed from the material. This provided a reversible capacity of 136 mAh g−1 at an average potential of 3.03 V (minimum 2.4 V, maximum 4.8 V).

The researchers used advanced ex situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) techniques to measure and observe this process. It was found that the anionic redox reaction process is likely to be activated during the initial charge to 4.8V, thereby supporting good charge capacity. In this study, the material even maintained 93% of its capacity after 100 cycles. Even considering the unstable tendency of anionic redox reactions to destroy these materials, it still has excellent stability. The tetrahedral coordination of the material is the main factor in its stability. Through ex situ synchrotron X-ray diffraction (XRD), the researchers observed that the volume change was negligible, only 0.21%, when lithium was transferred out.

Experiments in different voltage ranges had little effect on capacity retention, and it was determined that testing LiVO3 between 1.5V and 4.8V extended the available capacity to 358mAh g−1, with an average potential of 2.55V and an energy density of up to 912.9 Wh kg−1.

The most prominent finding of this study is that the capacity and operating voltage of the material can be improved by taking advantage of anionic redox reactions and advanced tetrahedral coordination.

The development of future breakthrough battery technologies, as well as increased battery capacity, are the cornerstones for mainstreaming electric vehicles and more sustainable transportation. This study provides a solid foundation for future research to further other novel cathode materials for battery applications. Ongoing research to optimize electrodes and electrolytes also has great potential to minimize the capacity loss caused by repeated charging cycles.