Study Shows How Ions and Electrons Migrate in Composite Solid Electrolytes

Researchers from the Advanced lithium-ion Battery Engineering Laboratory at the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS) have identified the mechanism of ion and electron migration in composite solid electrolytes (CSEs).

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This was done with the help of conductive atomic force microscopy (c-AFM), which makes it easier to design high-performance solid electrolytes. The study was published in the Energy Storage Materials journal.

In contrast to the conventional lithium-ion (Li-ion) battery, the solid-state battery with solid materials as electrolyte possesses higher safety and energy density. As a combination of solid polymer electrolytes (SPEs) and inorganic solid electrolytes (ISEs), CSEs displayed high ionic conductivity and great contact with electrodes. But the role of migration of Li-ions and inorganic particles is still debatable.

To handle this problem, Dr Cai Shen together with his collaborators at NIMTE has made Li7La3Zr2O12-polyethylene oxide (LLZO-PEO) CSEs with various ratios of LLZO, that is, 0, 50, 75 wt %.

The c-AFM was powered by a quantitative nano-mechanical measurement module (QNM), which gathered the topography and sample current while the mechanical information was also obtained. Thanks to the c-AFM, the impacts of temperature and LLZO content on the migration of electrons and ions in CSEs were examined.

At low temperatures, Li-ions can move only along the amorphous PEO irrespective of LLZO content. The increase of LLZO results in the development of the PEO amorphous region at the interface between LLZO and PEO, thereby decreasing the PEO’s glass transition temperature and crystallinity.

At high temperatures, Li-ions mostly tended to migrate along the amorphous PEO with the addition of a small amount (that is, 0 and 50 wt %) of LLZO particles. When the LLZO content (75 wt. %) increased, a constant ionic conductive network in the PEO matrix was developed by the LLZO particles, and then lithium ions migrated via LLZO particles.

The as-prepared electrolyte exhibited dominant Li-ion migration, which was found to be three orders of magnitude greater compared to the electronic current. Besides, the electronic current from PEO is far greater than that of LLZO, which denotes that the increase in LLZO can enhance the electronic insulation of CSEs.

Moreover, as a result of the high modulus and outstanding insulation properties of the LLZO, the addition of LLZO into the electrolytes is anticipated to hinder the growth of Li dendrites in the lithium anodes.

This study demonstrated the impact of inorganic particle content and working temperature on the performance of CSEs, which offers better insights into the design and growth of CSEs for solid-state batteries.

Journal Reference:

Shen, C., et al. (2021) Unraveling the mechanism of ion and electron migration in composite solid-state electrolyte using conductive atomic force microscopy. Energy Storage Materials.


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