Electroactive redox materials, encompassing redox polymers, metal-organic frameworks, and intercalation materials, play an important role in a wide range of emerging applications. However, many theoretical issues concerning quantitative thermodynamic description of such materials remain unclear so far. Existing variants of electrochemical intercalation isotherms (namely, the Langmuir-Frumkin isotherm, which often applies to redox polymers and electroactive solid materials, and the reformulated isotherm, accounting for the phase character of the potential distribution within the material) do not explain the dependence of redox materials' voltammetric responses on the electrolyte concentration. In addition to that, studies show that the reformulated isotherm has a higher value of the so-called short-range interaction parameter at which phase separation starts and asymmetric single-phase regions in comparison to the Langmuir-Frumkin isotherm. A simple modification, accounting for the possibility of both positive and negative ions of the electrolyte solution to intercalate the electroactive redox material, leads to a new variant of electrochemical intercalation isotherm, which includes Langmuir-Frumkin and reformulated isotherms as limiting cases. The new model explains the dependence of redox materials' voltammetric responses on the electrolyte concentration. Theory predicts the dependence of short-range interaction parameters at which phase separation starts on the electrolyte composition. Thus, the new electrochemical intercalation isotherm shows the dependence of its unstable, metastable, and stable regions on the electrolyte concentration and ion distribution coefficients. It opens up a possibility to tune material characteristics such as sizes of single-phase/two-phase regions. In some particular cases, it is possible to induce or eliminate the phase transition by changing the concentration of the electrolyte. We believe that studying such properties may help in future realization of new smart materials with superior characteristics for electrochemical energy storage, use in chemical sensors, medical applications, and so forth.