Deciphering the Origin of Interface‐Induced High Li and Na Ion Conductivity in Nanocomposite Solid Electrolytes Using X‐Ray Raman Spectroscopy

Abstract

Solid‐state electrolytes (SSEs) with high ionic conductivities are crucial for safer and high‐capacity batteries. Interface effects in nanocomposites of SSEs and insulators can lead to profound increases in conductivity. Understanding the composition of the interface is crucial for tuning the conductivity of composite solid electrolytes. Herein, X‐ray Raman Scattering (XRS) spectroscopy is used for the first time to unravel the nature of the interface effects responsible for conductivity enhancements in nanocomposites of complex hydride‐based electrolytes (LiBH4, NaBH4, and NaNH2) and oxides. XRS probe of the Li, Na, and B local environments reveals that the interface consists of highly distorted/defected and structurally distinct phase(s) compared to the original compounds. Interestingly, nanocomposites with higher concentrations of the interface compounds exhibit higher conductivities. Clear differences are observed in the interface composition of SiO2‐ and Al2O3‐based nanocomposites, attributed to differences in the reactivity of their surface groups. These results demonstrate that interfacial reactions play a dominant role in conductivity enhancement in composite solid electrolytes. This work showcases the potential of XRS in investigating interface interactions, providing valuable insights into the often complex ion conductor/insulator interfaces, especially for systems containing light elements such as Li, B, and Na present in most SSEs and batteries.

Effect of Preparation Methods on the Interface of LiBH4/SiO2 Nanocomposite Solid Electrolytes

“…12,14−17 In melt-infiltrated LiBH 4 /(porous) SiO 2 nanocomposites, the formation of Si•••H•••BH 3 complexes and Li + exchange with protons of silanol (SiOH) sites plays a pivotal role in the ionic conductivity increase. 18,19 Nanocomposites of complex metal hydrides and oxides are most commonly prepared via two strategies: ball milling or melt infiltration. Ball milling, or mechanosynthesis, is based on high-energy impacts on the mixture to induce interface contacts.…”

“…A different strategy to increase the room temperature ion conductivity of complex metal hydrides involves the formation of nanocomposites, specifically bringing the hydride in contact with an oxide, such as silica. − This approach has been shown to increase the conductivity of LiBH 4 /SiO 2 by at least 3 orders of magnitude at ambient temperatures. , It was revealed that the ion mobility at the interface between the oxide and the metal hydride was greatly enhanced. ,− In melt-infiltrated LiBH 4 /(porous) SiO 2 nanocomposites, the formation of Si···H···BH 3 complexes and Li + exchange with protons of silanol (SiOH) sites plays a pivotal role in the ionic conductivity increase. , …”

“… 12 , 14 − 17 In melt-infiltrated LiBH 4 /(porous) SiO 2 nanocomposites, the formation of Si···H···BH 3 complexes and Li + exchange with protons of silanol (SiOH) sites plays a pivotal role in the ionic conductivity increase. 18 , 19 …”