In this research, high rate performance of LiNi_0.5Mn_1.5O₄ cathode has been explained in details by a model, numerical simulation technique and experimental verification. The proposed model which was verified by experimental data and simulation could estimate the capacity dependency of LiNi_0.5Mn_1.5O₄ to diffusion coefficient of lithium ions in active materials and c-rate of discharging. Results showed that LiNi_0.5Mn_1.5O₄ has capacity higher than 80 mAhg^-1 even for c-rate up to 10C discharging and facilitating the movement of lithium ions in active material and reducing thickness of electrolyte has reasonable impact on achievable final capacity of LiNi_0.5Mn_1.5O₄. In addition, higher rate performance of mentioned active material would be enhanced by an increase in Li ion diffusion coefficient from 10^-11 cm².s^-1 to 5×10^-10 cm².s^-1 which was explained and verified by experiment. Achieved capacity at 200C would be less than 40 mAh.g^-1 in cathode materials with Li ion diffusion coefficient 10^-11 cm².s^-1. Whereas, cathode materials with Li ion diffusion coefficient 5×10^-10 cm².s^-1 showed achieved capacity higher than 100 mAh.g^-1 at 200C.