Quantum sensing of electric field distributions of liquid electrolytes with NV-centers in nanodiamonds

TL;DR

This paper demonstrates that NV-centers in nanodiamonds can be used to accurately measure electric field distributions and ionic concentrations inside liquid electrolytes, enabling in-situ analysis of battery degradation.

Contribution

The study introduces a novel protocol using NV-centers to reconstruct electric fields and infer ionic concentrations in electrolytes with high spatial resolution.

Findings

Electric field can be reconstructed with high accuracy using microwave pulse sequences.

A relationship between electric field standard deviation and ionic concentration is established.

NV-centers can measure both electric fields and local ionic concentrations inside electrolytes.

Abstract

To use batteries as large-scale energy storage systems it is necessary to measure and understand their degradation \textit{in-situ} and \textit{in-operando}. As a battery's degradation is often the result of molecular processes inside the electrolyte, a sensing platform which allows to measure the ions with a high spatial resolution is needed. Primary candidates for such a platform are NV-centers in diamonds. We propose to use a single NV-center to deduce the electric field distribution generated by the ions inside the electrolyte through microwave pulse sequences. We show that the electric field can be reconstructed with great accuracy by using a protocol which includes different variations of the Free Induction Decay to obtain the mean electric field components and a modified Hahn-echo pulse sequence to measure the electric field's standard deviation $\sigma_E$. From a semi-analytical ansatz we find that for a lithium ion battery there is a direct relationship between $\sigma_E$ and the ionic concentration. Our results show that it is therefore possible to use NV-centers as sensors to measure both the electric field distribution and the local ionic concentration inside electrolytes.