Mg2+ and Cr3+ Co-Doped LiNi0.5Mn1.5O4 Derived from Ni/Mn Bimetal Oxide as High-Performance Cathode for Lithium-Ion Batteries.

Abstract

In this study, pure and Mg²⁺/Cr³⁺ co-doped Ni/Mn bimetallic oxides were used as precursors to synthesize pristine and doped LNMO samples. The LNMO samples exhibited the same crystal structure as the precursors. XRD analysis confirmed the successful synthesis of LNMO cathode materials using Ni/Mn bimetallic oxides as precursors. FTIR and Raman spectroscopy reveal that Mg²⁺/Cr³⁺ co-doping promotes the formation of the Fd3m disordered phase, effectively reducing electrochemical polarization and charge transfer resistance. Furthermore, co-doping significantly lowers the Mn³⁺ content on the LNMO surface, thereby mitigating Mn³⁺ dissolution. Significantly, Mg²⁺/Cr³⁺ co-doping induces the emergence of high-surface-energy {100} crystal facets in LNMO grains, which promote lithium-ion transport and, finally, enhance rate capability and cycling performance. Electrochemical analysis indicates that the initial discharge capacities of LNMO-0, LNMO-0.005, LNMO-0.010, and LNMO-0.015 were 126.4, 125.3, 145.3, and 138.2 mAh·g^-1, respectively, with capacity retention rates of 82.45%, 82.93%, 83.32%, and 82.08% after 100 cycles. Furthermore, the impedance of LNMO-0.010 prior to cycling was 97.38 Ω, representing a 14.35% reduction compared to the pristine sample. After 100 cycles, its impedance was only 58.61% of that of the pristine sample, highlighting its superior rate capability and cycling stability. As far as we know, studies on the synthesis of LNMO cathode materials via the design of Ni/Mn bimetallic oxides remain limited. Accordingly, this work provides an innovative approach for the preparation and modification of LNMO cathode materials. The investigation of Ni/Mn bimetallic oxides as precursors, combined with co-doping by Mg²⁺ and Cr³⁺, for the synthesis of high-performance LiNi_0.5Mn_1.5O₄ (LNMO) aims to provide insights into improving rate capability, cycling stability, reducing impedance, and enhancing capacity retention.