A button cell test used to obtain the open-circuit potential (OCP) curves of lithium-ion battery electrodes requires destructive disassembly of the battery, and the battery is highly susceptible to contamination during the process. To address this issue, a method utilizing a pseudo-reference electrode to acquire the relative OCP curves of the electrodes of lithium-ion batteries was proposed. In this method, the lithium battery casing was used as a reference electrode, and the relative OCP between the electrode and the casing was directly measured through low-rate charge-discharge tests. The method was experimentally validated using commercial lithium titanate batteries, and the results showed that the root mean square error (RMSE) between the calculated and the actual measured battery voltages was only 4.2 mV. Moreover, the thermodynamic parameters identified from the same batch of batteries decreased as the battery capacity decayed. The experimental results confirm that the pseudo-reference electrode method can obtain reliable relative OCP curves without damaging the battery.