Saturday, June 22, 2024

Simple, environmentally friendly coating can boost battery performance

Lithium-ion batteries became the gold standard because of their ability to store a large quantity of energy and recharge many times with minimal degradation. However, as the demand for safe and effective batteries increases, researchers are racing to find what’s next.

All-solid-state lithium batteries could be an alternative to current lithium-ion battery technology, but improvements in their capacity are needed.

Now, researchers from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) have published a study that shows how ferroelectric cathode coatings significantly boost the electrochemical performances of all-solid-state lithium batteries.

Ferroelectric materials possess an inherently polarized electric field that is widely used to accelerate the separation and transfer of charges in many electrochemical types of research.

“In the field of all-solid-state lithium batteries, it is widely accepted that the ferroelectric polarization induces the built-in electric field at the electrode/solid-state electrolytes interface, which could suppress the space charge layer and boost lithium transportation,” said Dr. LI Wenru, first author of the study. “However, the construction mechanism of the ferroelectric built-in electric field in these batteries is poorly understood. Revealing this construction mechanism becomes a critical challenge.”

To better understand how the ferroelectric material improves battery function, the researchers covered the lithium cobalt oxide cathode in guanidinium perchlorate, a coating layer made from an organic-inorganic hybrid ferroelectric material. These coatings were found to possess a single-domain state, which means the inner ferroelectric dipoles point in the same direction. This behavior eventually creates the downward built-in electric field at the cathode/electrolyte interface.

Guanidium perchlorate can be made by evaporating solvents like ethyl alcohol, making it an inexpensive and environmentally friendly option for battery manufacturing.

Molecular ferroelectric coating inhibits the space charge layer and enhances the Li+ transport at the cathode/electrolyte interface.
Molecular ferroelectric coating inhibits the space charge layer and enhances the Li+ transport at the cathode/electrolyte interface. Credit: Li Wenru and Ma Jun

In their study, researchers found that the capacities of the all-solid-state lithium batteries with the ferroelectric coating on the cathode are nearly the same as the current liquid lithium-ion battery, which is much higher than the capacities of the all-solid-state lithium batteries using the uncoated cathode.

The team also examined how the active particles interacted with the electrolyte in the cathode with and without the coating. When the lithium cobalt oxide meets the solid-state electrolyte, a space charge layer forms, which interferes with the movement of electrons through the battery.

The space charge layer limits the transport of lithium and reduces the capacity of the battery. Despite the space charge layer, the battery capacity was improved when the coatings were applied to the cathode because the effective ferroelectric built-in electric field made the lithium move more fluently through the cathode/electrolyte interface.

“We found that the flexoelectric effect caused by the lattice mismatch is the primary factor for the self-polarization effect of the coatings. Our study not only designs the all-solid-state lithium batteries with excellent electrochemical performance but also discovers the scientific theoretical guidance for constructing the ferroelectric coating layers in promoting performances of electrochemical energy storage,” said Dr. LI.

In future work, researchers will look at different combinations of materials to expand the possibilities for all-solid-state lithium batteries.

“We hope to expand this research idea to different combinations of cathode and ferroelectric materials in future work and obtain experimental rules for optimal battery performance,” said Prof. CUI Guanglei, corresponding author of the study. “The ultimate goal is to have a universal strategy improving lithium battery performance in practical applications.”

Journal reference:

  1. Wenru Li, Shu Zhang, Weijie Zheng, Jun Ma, Lin Li, Yue Zheng, Deye Sun, Zheng Wen, Zhen Liu, Yaojin Wang, Guangzu Zhang, Guanglei Cui. Self-Polarized Organic–Inorganic Hybrid Ferroelectric Cathode Coatings Assisted High Performance All-Solid-State Lithium Battery. Advanced Functional Materials, 2023; DOI: 10.1002/adfm.202300791