Many lithium intercalation compounds, which have successful applications as lithium-ion battery electrode materials, are used not in individual state, but as a part of specially organized composites containing also auxiliary components distributed over the surface of intercalation-material particles, as well as in the interparticle space. The applied modifier-substances affect such characteristics of intercalation materials as capacity, its reversibility, and persistence during long-term cycling in the charge–discharge mode, as well as with varying the electrode current and potential ranges. In this work, the behavior of a modifying agent, belonging to the class of compounds known in the literature as MAX phases, is studied in detail in the composition of an electroactive composite. The MAX-phase agents have general formula Mn + 1AXn, where M is the transition metal, A is the element of the Periodic Table III–VI groups, and X is C or N. The temperature required for the Ti3SiC2 compound synthesis is close to 1500°C. We succeeded in reducing the temperature by means of preliminary mechanochemical treatment of the reagents’ mixture. The action mechanism of the Ti3SiC2-modifier is considered in comparison with similar models proposed in the literature. Comparison of the characteristics of composite materials with different Ti3SiC2-content and different types of modified intercalation compounds (substrates) showed a positive effect of the modifier both on the kinetics of electrode processes and the rate of degradation of the materials’ capacitive characteristics.