A Soft-Solid Co-Crystalline Electrolyte Combining Advantages of Organics and Ceramics: Thermally, Electrochemically Stable, Highly Conductive (Adiponitrile)2LiPF6

12 August 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The solid electrolyte (ADN)2LiPF6 is described. The structure exhibits adiponitrile (ADN)-based channels based on XRD analysis, through which the -C≡N-solvated Li+ ions migrate. High conductivity (σ ~ 10-4 S/cm) and high lithium ion transference number (tLi+ = 0.54) results from weak interactions between “hard” (charge-dense) Li+ ions and “soft” (electronically polarizable) -C≡N, compared with the stronger interactions of previously reported “hard” ether oxygen contacts of polyethylene oxide (PEO) or glymes. The surface of the crystal is a liquid nanolayer that binds the grains so that ionically conductive pellets are easily formed without high pressure/temperature treatments. (ADN)2LiPF6(s) has a wide electrochemical stability window of 0 to 5 V. Li0/(ADN)2LiPF6/LiFePO4 half cells exhibit cycling for > 50 cycles at C/20, C/10, C/5 rates with capacities of 140 mAh-g-1 to 100 mAh-g-1 and efficiencies > 95%. MD simulations and PWDFT calculations offer insights into the molecular basis of the physical and conductivity properties.

Keywords

battery electrolytes
lithium batteries
soft-solids
cocrystals
computer simulations
grain-boundary

Supplementary materials

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Supporting Information
Description
Powder X-ray diffraction, data, TGA, SEM, DC polarization and cycling data, additional details of simulation and DFT, and crystallographic tables. Crystallographic data is also available from the CCDC under deposition number 1986269.
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