Suppressed phase separation in spinel LiNi_0.5Mn_1.5O₄ cathode via interstitial sites modulation

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is widely utilized because of its high-energy-density and high-voltage. Unfortunately, there is still much research to be done for LNMO due to its poor structural stability. Here, a strategy is confirmed to stabilize LNMO via modulating interstitial sites. The interstitial 16c sites of the octahedron are partially occupied by Ni²⁺ to suppress the migration and dissolution of manganese ions upon electrochemical cycling and stabilize lithium-ion vacancies in the state of charge. Unexpectedly, this protocol not only suppresses the phase separation restraining the phase boundary dislocations and stress but also decreases the magnitude of cell volume change during cycling, which originates from the change in Ni redox couple energy states. This two-pronged modification strategy endows the cathode material with a lower charge transfer barrier and faster Li⁺ transfer kinetics, revealing superior electrochemical performance. The regulated cathode material remains robust after 900 cycles at 1C and its capacity retention rate is 29% higher than that of the original sample. Our research is useful for providing a concrete example of how the electrochemical performance of spinel LNMO and other high voltage cathode materials can be enhanced.