Application and Methodological Study of the Double Bridge Low-Resistance Measurement Technique in the Precise Measurement of Solid Electrolyte Ionic Conductivity—A “Dynamic Self-Calibration” Measurement Method Based on the Fusion of the Kelvin Double Bridge and the Four-Point Probe

Solid-state electrolytes are the key materials for the fabrication of all-solid-state lithium-ion batteries. Their intrinsic ionic conductivity corresponds to the bulk resistance in the low-impedance measurement field. The current mainstream characterization method is electrochemical impedance spectroscopy. However, this method has limitations in measuring this resistance. It is based on an equivalent circuit model, making it difficult to separate the bulk resistance from the grain boundary resistance. The measurement uncertainty is limited by the fitting covariance, and the relative expanded uncertainty is relatively high. This study introduces the classic Kelvin double bridge method into the characterization of the bulk resistance of solid-state electrolytes. For the relevant measurements of pure ionic conductors, a dynamic self-calibration double bridge measurement method is proposed. This method has innovations in three aspects. First, methodological innovation: for the first time, the four-terminal precise direct measurement principle of the Kelvin double bridge method is systematically applied to this measurement, and the design eliminates the problem of direct current polarization drift; second, instrument and equipment innovation: a complete measurement system was built, and the extraction time of the bulk resistance was shortened from minutes to microseconds through algorithms; third, application innovation: the expanded uncertainty of the room temperature conductivity was significantly reduced, verifying the repeatability of the method, and the measured target parameter results showed a statistically reasonable range of differences relative to the literature data. This method has measurement accuracy that conforms to relevant national standards and industrial requirements, providing a new method for the evaluation of key materials for solid-state batteries.