Systems and methods that utilize a separator coated by particles for Li dendrite detection in an ordinary two-electrode battery system. The particles can be red phosphorus (RP) particles and/or other particles that are poor electronic conductors, are able to react with Li, and will form an insoluble product with Li, such as silicon, germanium, arsenic, metal oxides, metal halides, metal chalcogenides, chalcogenides, and LiM x E y O z (M=metal, E=nonmetal, 0=oxygen, x≥0, y≥0, z≥0). These other particles can be used by themselves or in combination with one another. No additional electrode is needed, and the presence of Li dendrites can be detected simply based on the voltage profile during the charging step.