Long-Term Cycling of a Mn-Rich High-Voltage Spinel Cathode by Stabilizing the Surface with a Small Dose of Iron

Abstract

The high-voltage, cobalt-free spinel cathode LiNi0.5Mn1.5O4 (LNMO) is receiving extensive attention for lithium-ion batteries due to its low cost, high operating voltage and energy density, superior power density, and good thermal stability. However, its high operating voltage hampers its stability with commercial electrolytes and makes its practical viability challenging. We present here a Mn-rich LNMO cathode to encourage the disordering of Mn and Ni in the lattice and the incorporation of a small dose of Fe into Mn-rich LNMO (Fe-LNMO) to improve the cycling stability. The introduction of Fe further increases the cation disorder between Mn and Ni, thus enabling a better rate capability. Electron energy loss spectroscopy analysis indicates that Fe is concentrated on the surface, and X-ray photoelectron spectroscopy analysis shows that Fe-LNMO alleviates the aggressive reaction between the cathode surface and the electrolyte, thus stabilizing the interface and cycle life. Furthermore, a full cell assembled with a graphite anode with an areal capacity of 3 mA h cm–2 displays a capacity retention of 90% over 300 cycles. The present work demonstrates an effective way to promote cation disordering and lower the surface reactivity of LNMO with the electrolyte, thereby enhancing the conductivity, stabilizing the cathode–electrolyte interphase, and making LNMO promising for practical applications.

Laser-Assisted Surface Lithium Fluoride Decoration of a Cobalt-Free High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode for Long-Life Lithium-Ion Batteries

“…To date, lattice doping and surface decoration are regarded as the most effective ways to ameliorate cathode–electrolyte reactivity and reduce the generation of crossover species and their accumulation on the graphite anode. Elements, such as Al, Fe, Cr, Mg, etc., have been proved to improve the stability of the LNMO cathode and examined extensively to uncover the underlying composition–structure–interphase–performance relationships. − However, most elemental doping in LNMO cathodes shares the common drawbacks, including lowered capacity, possible inhomogeneous dopant distribution, and insufficient surface passivation. In comparison, surface engineering is proposed to be more beneficial due to its ability to reduce cathode–electrolyte reactivity and transition-metal dissolution and crossover. − For instance, surface Al 2 O 3 coating on the LNMO cathode through atomic layer deposition can extend the cycle life of high-mass-loading (over 3 mA h cm –2 ) Gr||LNMO full cells to almost 300 cycles .…”

Paving Pathways Toward Long‐Life Graphite/LiNi0.5Mn1.5O4 Full Cells: Electrochemical and Interphasial Points of View

“…Note that by virtue of a protective Fe‐rich surface layer, the 5 mol% Fe‐doped Fe‐LNMO cathode used in this study is more stable than the undoped LiNi 0.5 Mn 1.5 O 4 cathode. [ 32 ] Therefore, it is proposed that the interphasial degradations in Gr||LNMO cells would happen more intensively, which is plotted in the form of a schematic figure ( Figure a). As shown, the acid species, such as HF and HPO 2 F 2 generated through the hydrolysis and ethylene carbonate‐involved oxidative reactions of LiPF 6 , will migrate together with Mn 2+ ions from the cathode side to the Gr anode.…”

“…The as‐cleaned Ni 0.244 Mn 0.756 (OH) 2 was then mixed with Fe 2 O 3 and LiOH·H 2 O to complete the calcination step as it was reported before, yielding a LiNi 0.476 Mn 1.475 Fe 0.049 O 4 (Fe‐LNMO) cathode material. [ 32 ]…”

“…The as-cleaned Ni 0.244 Mn 0.756 (OH) 2 was then mixed with Fe 2 O 3 and LiOH•H 2 O to complete the calcination step as it was reported before, yielding a LiNi 0.476 Mn 1.475 Fe 0.049 O 4 (Fe-LNMO) cathode material. [32] Electrochemical Test: To prepare the cathode slurry, the calcined Fe-LNMO cathode material, TimCal C65 carbon black, carbon fiber, and poly(vinylidene) fluoride (PVDF) were mixed at a weight ratio of 94 : 1.74: 0.76 : 3.5 with a proper amount of N-methyl-2-pyrolidone (NMP) solvent with a Thinky mixer (2000 rpm) for 20 min. The slurries were then cast onto an aluminum sheet with an active material loading controlled at 1.8 mA h cm −2 or 3.2 mA h cm −2 .…”

“…On the other hand, the inadequate energy density and rate performance (especially at low cycle life of LNMO cathode. [31][32][33][34] However, severe Gr anode degradations can hardly be fully alleviated by the cathode doping strategy. On the other hand, surface coating strategy can be applied on both the Gr anode and LNMO cathode to construct desirable artificial electrode-electrolyte interphases (EEIs).…”