Solid Electrolytes With High Li Ion Conductivity and Low Young Modulus

These batteries can operate stably up to 9800 cycles with around 77% capacity retention at a high rate of 3.4C in a freezing environment of −10°C.

Researchers at University of Science and Technology of China (USTC) have introduced a new class of amorphous Li–Ta–Cl-based chloride solid electrolytes (SEs). These SEs demonstrate high lithium-ion conductivity (up to 7.16 mS  cm^-1 ) and a low Young’s modulus (approximately 3GPa). The high conductivity facilitates efficient lithium-ion transport, while the low Young’s modulus ensures good physical contact among the rigid components within ASSLBs, both critical factors for battery performance.

The research represents a significant advancement in the development of all-solid-state lithium batteries (ASSLBs), particularly in the context of SEs. SEs are crucial for the performance of ASSLBs due to their role in facilitating lithium-ion conduction. Amorphous solid electrolytes (ASEs) are especially promising for ASSLBs because they lack grain boundaries, which typically impede ion conduction. This grain-boundary-free structure promotes intact solid–solid contact and uniform lithium-ion conduction, essential for high-performance cathodes.

The existing amorphous oxide SEs suffer from limited ionic conductivities. Glassy Sulphide SEs are constrained by narrow electrochemical windows. As a result they have been unable to support high-nickel cathodes effectively. High-nickel cathodes are desirable in lithium batteries for their high energy density, but they also pose challenges in terms of stability and compatibility with SEs.

The research team used machine-learning simulation, solid-state 7Li nuclear magnetic resonance, and X-ray absorption analysis to characterise the structure of the amorphous Li–Ta–Cl matrix. They discovered that it comprises LiCl₄^3–, LiCl₅^4–, LiCl₆^5– polyhedra, and TaCl₆^– octahedra. This unique composition contributes to the SEs’ high performance.

These amorphous chloride SEs exhibit excellent compatibility with high-nickel cathodes. The study demonstrates that ASSLBs equipped with these SEs and high-nickel single-crystal cathodes (specifically LiNi_0.88Co_0.07Mn_0.05O₂) show remarkable performance. They maintain approximately 99% capacity retention after 800 cycles at around 3C under 1 mA h cm^–2 and about 80% capacity retention after 75 cycles at 0.2C, even with a high areal capacity of 5mA h cm^–2. Most notably, these batteries can operate stably up to 9800 cycles with around 77% capacity retention at a high rate of 3.4C in a freezing environment of −10°C.

The introduction of amorphous chloride SEs is a major step towards high-performance, high-nickel cathodes for high-energy-density ASSLBs. This development has the potential to significantly enhance the efficiency, capacity, and durability of lithium batteries, paving the way for more advanced energy storage solutions.