Engineering topics

Lacivita, Valentina

Publications and source records attributed to Lacivita, Valentina.

3 records

DOE OSTI2023

Design principles for NASICON super-ionic conductors

Na Super Ionic Conductor (NASICON) materials are an important class of solid-state electrolytes owing to their high ionic conductivity and superior chemical and electrochemical stability. In this paper, we combine first-principles calculations, experimental synthesis and testing, and natural language-driven text-mined historical data on NASICON ionic conductivity to achieve clear insights into how chemical composition influences the Na-ion conductivity. These insights, together with a high-throughput first-principles analysis of the compositional space over which NASICONs are expected to be stable, lead to the successful synthesis and electrochemical investigation of several new NASICONs solid-state conductors. Among these, a high ionic conductivity of 1.2 mS cm ₋1 could be achieved at 25 °C. We find that the ionic conductivity increases with average metal size up to a certain value and that the substitution of PO 4 polyanions by SiO 4 also enhances the ionic conductivity. While optimal ionic conductivity is found near a Na content of 3 per formula unit, the exact optimum depends on other compositional variables. Surprisingly, the Na content enhances the ionic conductivity mostly through its effect on the activation barrier, rather than through the carrier concentration. These deconvoluted design criteria may provide guidelines for the design of optimized NASICON conductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Enhanced ionic conductivity and lack of paddle-wheel effect in pseudohalogen-substituted Li argyrodites

Superionic conductors are key to the development of safe and high-energy-density, all-solid-state batteries. Using a combined theoretical and experimental approach, we explore the feasibility of increasing the ionic conductivity through pseudohalogen substitution in the Li argyrodite structure. Under the guidance of calculated thermodynamic stability, BH 4 -substituted Li argyrodite, Li 5.91 PS 4.91 (BH 4 ) 1.09 , was successfully synthesized via a mechanochemical method. As-synthesized BH 4- substituted Li argyrodite displays an ionic conductivity of 4.8 mS/cm at 25°C. Ab initio molecular dynamics simulation trajectory analysis was used to investigate how BH 4 facilitates Li-ion diffusion and indicates only a weak correlation with the B–H bond motion. Here, we find that the enhanced conductivity mainly originates from the weak interaction between Li and BH 4 and find no evidence of a paddle-wheel effect from the polyanion. This work provides insight into how cluster ions enhance Li diffusion and systematically describes how to explore superionic conductors with pseudohalogen substitution.

25 ENERGY STORAGE↗

DOE OSTI2021

Synthetic accessibility and stability rules of NASICONs

In this paper we develop the stability rules for NASICON-structured materials, as an example of compounds with complex bond topology and composition. By first-principles high-throughput computation of 3881 potential NASICON phases, we have developed guiding stability rules of NASICON and validated the ab initio predictive capability through the synthesis of six attempted materials, five of which were successful. A simple two-dimensional descriptor for predicting NASICON stability was extracted with sure independence screening and machine learned ranking, which classifies NASICON phases in terms of their synthetic accessibility. This machine-learned tolerance factor is based on the Na content, elemental radii and electronegativities, and the Madelung energy and can offer reasonable accuracy for separating stable and unstable NASICONs. This work will not only provide tools to understand the synthetic accessibility of NASICON-type materials, but also demonstrates an efficient paradigm for discovering new materials with complicated composition and atomic structure.

25 ENERGY STORAGE↗