Electrochemical lithium sensing for environmental and process liquids: ion-selective electrodes, complementary electrochemical platforms, and monitoring readiness in waters, brines, and leachates

This critical narrative review evaluates electrochemical strategies for Li⁺ measurement in environmental and process liquids, including groundwater, drinking water, desalination concentrates, geothermal and salar brines for direct lithium extraction (DLE), oil-and-gas produced water, and battery-recycling leachates. A structured, matrix-aware evidence synthesis compares liquid-contact and all-solid-state ion-selective electrodes (ISEs) with voltammetric, insertion-material, microfluidic, solid-electrolyte, and light-addressable potentiometric platforms. Potentiometric ISEs remain the most mature direct, low-power option for field or in-line use, whereas complementary methods generally require discrete conditioning, waveform, or regeneration steps. Across platforms, deployment depends on matrix-specific selectivity, reference-electrode and liquid-junction stability, drift, response-time definition, activity-to-concentration conversion, fouling and aging, recalibration or regeneration, authentic-matrix testing over application-relevant durations, uncertainty estimation, and independent validation against ICP-OES, ICP-MS, or ion chromatography. The literature reports promising slopes, detection limits, linear ranges, and useful short-term selectivity, including several real-sample demonstrations; however, no study in the compiled evidence set provides the complete monitoring-ready (R3) validation package. Near-R3 evidence includes 14–15 d operation in Li-adjusted wastewater and lithium-rich brine and dynamic monitoring of a battery-material recovery process, but these controlled demonstrations do not establish broadly replicated performance across unspiked matrices, sites, or full operating cycles. The principal bottleneck is therefore not Li⁺ responsiveness or the absence of continuous demonstrations, but the scarcity of independently validated measurement systems with transparent calibration transfer, uncertainty, maintenance, and failure criteria. The review consequently proposes matrix-specific, evidence-based readiness tags, standardized selectivity and response-time reporting, and a metrological checklist linking analytical performance to traceability, deployment requirements, and monitoring decisions.