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 (LiFePO(4)) and a solid electrolyte (Li(1+x+y)Al(x)(Ti, Ge)(2-x)Si(y)P(3-y)O(12)) 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 LiFePO(4)/FePO(4) layer with a highly stable potential as the inner reference electrode significantly minimizes the deviations in the response potential. Moreover, applying Li(1+x+y)Al(x)(Ti, Ge)(2-x)Si(y)P(3-y)O(12) as a durable and highly ion-conductive inorganic solid electrolyte enables remarkable long-term stability.