Multiple Influences of Nickel Concentration Gradient Structure and Yttrium Element Substitution on the Structural and Electrochemical Performances of the NaNi_0.25Mn_0.25Fe_0.5O₂ Cathode Material

Abstract

The research and development of sodium-ion battery (SIB) cathode materials are crucial for the commercialization of SIBs as important energy storage and conversion devices. This work aims to provide new insights into the electrochemical behavior of the NaNi0.25Mn0.25Fe0.5O2 (NMF) cathode material, especially improving its cycle life and rate capability. Herein, a novel nickel concentration gradient NMF material (NCG-NMF) was designed to utilize the characteristic reaction of dimethylglyoxime with nickel. This approach not only demonstrates the role of high nickel content in the core for the high discharge capacity of materials but also observes excellent cycling stability with the manganese-rich outer layer. To further optimize the cycle stability and rate performance, we select the Y element with a strong Y–O binding energy to replace the transition metal in the NCG-NMF material. The Y dopants can promote the Na-ion transport and inhibit the phase transformation of materials from layered structure to spinel or to the rock-salt phase. The Y-doped NCG-NMF material exhibits excellent capacity retention of 71% after 100 cycles at the current density of 125 mA g–1 under a cutoff voltage of 4.2 V, which is much higher than that of the NMF cathode material (42%). These findings provide a new concept for designing and developing high-performance SIB cathode materials.

Designing a durable high-rate K0.45Ni0.1Fe0.1Mn0.8O2 cathode for K-ion batteries: A joint study of theory and experiment

“…We 1c). Increasing lattice parameter c originates from the increasing repulsion force between the face-to-face oxygen layers, a phenomenon that is common in layered oxide cathodes [41,42]. A similar variation trend can be seen in K x Ni 0.1 Co 0.1 Mn 0.8 O 2 (0.33 ≤ x ≤ 0.89, Fig.…”

Surface chemistry engineering of layered oxide cathodes for sodium‐ion batteries

“…However, in Figure 6b 4 , NaPO 3 -coated electrode could suppress structural change and then delay oxygen release from the bulk structure, thereby improving the thermal stability. Wu et al [87] selected the Y element with a strong | 103 Y-O binding energy via coating and doping dual strategy design to modify NaNi 0.25 Mn 0.25 Fe 0.5 O 2 (NMF) cathode material (Figure 7a). Through the introduction of Y, NMF can retain structure promoted during charging/ discharging progress, inhibiting the degradation of structure from layered structure to spinel or to the rock-salt phase to a great extent.…”

“…Simultaneously, the calcination process, as part and parcel of F I G U R E 7 (a) Schematic illustration of the synthesis of the NMF-Y cathode material. [87] Copyright 2021, America Chemical Society. (b 1 ) Schematic of Na 2 SiO 3 coating process on NFMO; (b 2 ) DSC profiles of the bare and 3% Na 2 SiO 3 -coated NFMO charged to 4.2 V. [88] Copyright 2021, Elsevier.…”

Gradient Designs for Efficient Sodium Batteries

“…With such a strategy, improvements in electrode performance and stability have also been observed in other materials. 57,58 More importantly, this gradient structuring can integrate the characteristics of each component to realize multiple functionalities, thereby providing fresh opportunities in sodium materials. Boosting Structure Stability.…”

“…Also, high voltages accelerate side reactions between the electrode and electrolyte, causing the degradation of the electrode surface and cathode–electrolyte interphase (CEI). To suppress the irreversible phase transition while minimizing the capacity decline rooting from the doping of inactive species, gradient doping might be an effective solution, capable of suppressing phase transitions without sacrificing capacity. , In this structure, inactive components are enriched on the surface and deficient in the interior. The design boosts structural stability by suppressing CEI evolution and phase transition while minimizing capacity loss.…”