Mn-based disordered rock-salt (DRX) cathode materials offer high theoretical capacities and operating voltages, rendering them promising candidates for high-energy-density lithium-ion batteries. However, severe interfacial reactions between Mn-based DRX cathodes and the electrolyte can induce surface degradation and a pronounced increase in interfacial impedance. In this study, a LAGP glass ceramic coating layer was introduced onto the surface of Li_1.2Cr_0.3Ti_0.3Mn_0.3O_1.9F_0.1 (LCTMOF) particles to minimize direct contact between the active material and the electrolyte, thereby enhancing the capacity retention over 50 cycles. It delivered an initial discharge capacity of 278.7 mAh g⁻¹ and retained 227.3 mAh g⁻¹ after 50 cycles. Relative to the pristine uncoated cathode, the LAGP glass ceramic coating material achieved a capacity retention of 81.5% together with improved rate performance, retaining a high specific capacity of 184.5 mAh g⁻¹ at a current density of 500 mA g⁻¹. Surface XPS analysis, together with the electrochemical results, suggests that the LAGP glass ceramic coating mitigates cathode interfacial degradation under the investigated cycling conditions.