Solid-State Ionic Conductivity in Energy Storage Materials

Solid-state ionic conductivity underpins the performance of next-generation energy storage devices by enabling safe, high-density charge transport without flammable liquid electrolytes. Inorganic and hybrid solid electrolytes—including ceramics, glasses and composites—are engineered to achieve conductivities approaching those of liquid counterparts, while offering enhanced mechanical robustness and broad electrochemical stability windows suitable for metallic anodes. Ion transport is governed by crystal structure topology, defect chemistry, grain-boundary resistance and electrode–electrolyte interfacial compatibility. Recent progress has shifted from empirical tuning of established materials to atomistic design of open-framework hosts, targeted doping strategies and interface engineering. Advanced characterisation techniques such as operando impedance spectroscopy and nuclear magnetic resonance have elucidated migration pathways and rate-limiting steps in both bulk and interfacial regions. These insights are guiding the integration of solid electrolytes into all-solid-state batteries and supercapacitors, targeting improvements in safety, cycle life and energy density for electric vehicles and grid-scale storage. Emphasis on scalable fabrication methods, low-temperature processing and discovery of novel superionic phases aims to overcome historic barriers in interfacial resistance and long-term stability.

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Research from all publishers

One study demonstrates the fabrication of bilayer cathode–electrolyte assemblies via a cold sintering process, achieving intimate contact between LiFePO₄ cathodes and NASICON-type composite solid electrolytes at temperatures below 150 °C. The resulting bilayers exhibit ionic conductivities around 0.5 mS cm⁻¹ and stable specific capacities, while operando electrochemical impedance spectroscopy reveals interfacial kinetic limitations and volume-induced capacity decay under high pressure. A second work introduces a boron-based open-framework electrolyte, Li₆B₁₈(Li₃N), featuring large hexagonal pores that support one-dimensional Li⁺ strands. Variable-temperature NMR spectroscopy shows an activation energy below 19 kJ mol⁻¹ and exceptionally high ion mobility, with defect engineering enabling precise tuning of lithium vacancies across the solid solution. A third report describes Li₉AlP₄, a lithium phosphidoaluminate superionic conductor synthesised by ball-milling and moderate annealing. It delivers an ionic conductivity of 3 mS cm⁻¹ and an activation barrier of 29 kJ mol⁻¹, with temperature-dependent NMR confirming rapid Li hopping via interstitial sites. Together, these studies illustrate advances in interface engineering, process innovation and crystal chemistry design for enhanced ion transport.

Solid-State Ionic Conductivity in Energy Storage Materials publication trend

The graph below shows the total number of articles in solid-state ionic conductivity in energy storage materials across all publications each year (not limited to Nature Index journals).

Technical terms

Solid electrolyte: A non-liquid ionic conductor that separates electrodes while allowing ion transport.

Ionic conductivity: A measure of an electrolyte’s ability to transport charged ions under an electric field, expressed in S cm⁻¹.

Activation energy: The energy barrier that ions must overcome to migrate between lattice sites, typically in kJ mol⁻¹.

NASICON: A family of sodium super-ion conductor structures with a three-dimensional phosphate framework supporting high sodium or lithium mobility.

Grain boundary: The interface between crystallites in a polycrystalline material, often impeding ion conduction relative to the bulk.

Cold sintering: A low-temperature densification process combining pressure and a transient liquid phase to consolidate ceramics at ≤ 200 °C.

References

1. Electrochemical Response of Cold‐Sintered Cathode‐Hybrid Electrolyte Bilayers: Deep Insights into the Determining Kinetic Mechanisms via Operando Electrochemical Impedance Characterization. Energy & Environmental Materials (2025).
2. Lithium‐ion Mobility in Li6B18(Li3N) and Li Vacancy Tuning in the Solid Solution Li6B18(Li3N)1−x(Li2O)x. Angewandte Chemie International Edition (2023).
3. Fast Lithium Ion Conduction in Lithium Phosphidoaluminates. Angewandte Chemie International Edition (2020).