# All-Solid-State Ion-Selective Electrode Inspired from All-Solid-State Li-Ion Batteries

## TL;DR

This paper presents a new all-solid-state ion-selective electrode inspired by battery technology, offering high stability and accurate detection of lithium ions.

## Contribution

The novel design integrates solid-state battery components to create a durable and selective lithium ion sensor.

## Key findings

- The electrode shows a Nernstian slope of 60.8 ± 0.5 mV dec–1 for Li+ detection.
- It achieves a limit of detection of 10–4.9±0.4 and minimal potential variation over 17 days.
- Using a two-phase LiFePO4/FePO4 layer improves the stability of the reference potential.

## Abstract

Solid electrolytes employed in all-solid-state Li-ion
batteries
(ASSBs) electronically isolate the positive and negative electrodes,
while allowing the carrier ions, Li+, to pass through.
Inorganic solid-state electrolytes, which typically exhibit a Li+-transference number of 1, are theoretically applicable as
ion-sensitive membranes of potentiometric ion-selective electrodes
(ISEs). Inspired by the ASSB architecture, an all-solid-state Li ISE
was developed in a two-layer stacking configuration using a redox-active
material (LiFePO4) and a solid electrolyte (Li1+x+yAlx(Ti, Ge)2–xSiyP3–yO12) as inner
and outer layers, respectively, on the substrate (i.e., current collector).
The solid electrolyte acts as an ion-selective membrane because the
Donnan membrane potential obeys a Nernstian response to Li+ activity in the analyte solution. The fabricated ASSB-inspired ISE
selectively responds to Li ions, exhibiting a Nernstian slope of 60.8
± 0.5 mV dec–1, limit of detection of 10–4.9±0.4, and minimal potential variation (−3
to +6 mV over 17 d). Using a two-phase LiFePO4/FePO4 layer with a highly stable potential as the inner reference
electrode significantly minimizes the deviations in the response potential.
Moreover, applying Li1+x+yAlx(Ti, Ge)2–xSiyP3–yO12 as a durable and highly ion-conductive inorganic
solid electrolyte enables remarkable long-term stability.