One size does not fit all in the application or in the evaluation

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A review article by a research team from Tianjin University of Technology used various advanced techniques of electron microscopy and related characterization to clarify two mechanisms based on the structure of lithium-ion batteries. Credit: Nanometer Research EnergyTsinghua University Press

Seeing is believing, or rather seeing can help understanding, especially when it comes to the mechanics behind lithium-ion batteries. Despite near-ubiquitous use in cell phones, computers, and the like, the complex electrochemical environments of lithium-ion batteries remain obscure.

To better understand and improve battery performance, researchers reviewed current scientific literature and used electron microscopy to take a closer look at the lithium-ion charge transfer and migration mechanisms that produce energy. This study was published in Nanometer Research Energy.

“Commercial lithium-ion batteries are widely used as energy storage devices, including electric vehicles, portable electronic devices and grid energy storage,” said Yi Ding, a professor at the University of Technology. from Tianjin. “Energy, power, charge-discharge rate, cost, life, safety and environmental impact must be considered when adopting lithium-ion batteries for a suitable application, but each specific application faces a variety of different challenges.”

The amount of stored energy is important for portable electronics, while cost and safety are more important for electric vehicles, for example. Cost and safety are also important for energy grid needs, but energy density becomes less so than for electric vehicles. The trade-off between these elements changes as needed, but the ability to tune performance is limited by an incomplete understanding of the materials used in the batteries.

“The active electrode materials are the main part responsible for cell chemistry and performance, and ultimately affect the marketability of the battery built,” Ding said.

“The performance, such as lifetime and energy density, of existing commercial electrode material systems still needs to be improved, so it is important to understand the inherent physical and chemical properties, such as structural evolution /kinetics during lithium decay and the effect of the electrode-electrolyte interface on the performance of lithium-ion batteries.”

The researchers reviewed recent advances in electron microscopy to see how traditional characterization techniques stack up when it comes to understanding the structure-activity relationships of commercial lithium-ion batteries.

“By comparing with the characterization content obtained by traditional characterization techniques, such as X-ray diffraction and X-ray photoelectron spectroscopy, we illustrate the advantages and limitations of common electron microscopes and advanced electron microscopic characterization techniques. recently developed technologies, such as in situ electron microscopy technology, in this critical research,” Ding said.

Researchers examined how advanced electron microscopy and associated characterization techniques can provide different insights into how, for example, lithium ions migrate through the battery to produce charge or how charge transfer can trigger the consumption of energy.

They specifically focused on the dissolution of transition metals and the charge transfer mechanism in the charge-discharge process of the positive electrodes of lithium-ion batteries; the structure and evolution of cathode-electrode interfaces and the solid electrolyte interphase during long-term cycling; and the effect of electrode structure and interface on lithium-ion migration.

The bottom line, according to Ding, is that next-generation lithium-ion battery technologies with better cost and performance benefits are needed.

“We propose the possibility of combining electron microscopy with other techniques to obtain more complete information,” Ding said, noting that electron microscopy has three common limitations in battery evaluation.

These include inconsistent electrochemical environments between electron microscopy fields and real batteries; unstable time windows that can distort the data related to the evolution of the sample; and some batteries cannot be quantified at the nanoscale. “Even with limitations, these discussions provide researchers with a better understanding of how commercial lithium-ion batteries operate at the microscopic scale and provide guidance for practical high-performance battery design strategies,” the researchers noted.

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More information:
Kexin Zhang et al, Status and Prospects of Key Materials for PEM Electrolyzer, Nanometer Research Energy (2022). DOI: 10.26599/NRE.2022.9120032

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