Insight into Ca‐Substitution Effects on O3‐Type NaNi_1/3Fe_1/3Mn_1/3O₂ Cathode Materials for Sodium‐Ion Batteries Application

Abstract

O3-type NaNi Fe Mn O (NaNFM) is well investigated as a promising cathode material for sodium-ion batteries (SIBs), but the cycling stability of NaNFM still needs to be improved by using novel electrolytes or optimizing their structure with the substitution of different elements sites. To enlarge the alkali-layer distance inside the layer structure of NaNFM may benefit Na diffusion. Herein, the effect of Ca-substitution is reported in Na sites on the structural and electrochemical properties of Na Ca NFM (x = 0, 0.05, 0.1). X-ray diffraction (XRD) patterns of the prepared Na Ca NFM samples show single α-NaFeO type phase with slightly increased alkali-layer distance as Ca content increases. The cycling stabilities of Ca-substituted samples are remarkably improved. The Na Ca Ni Fe Mn O (Na Ca NFM) cathode delivers a capacity of 116.3 mAh g with capacity retention of 92% after 200 cycles at 1C rate. In operando XRD indicates a reversible structural evolution through an O3-P3-P3-O3 sequence of Na Ca NFM cathode during cycling. Compared to NaNMF, the Na Ca NFM cathode shows a wider voltage range in pure P3 phase state during the charge/discharge process and exhibits better structure recoverability after cycling. The superior cycling stability of Na Ca NFM makes it a promising material for practical applications in sodium-ion batteries.

High‐Abundance and Low‐Cost Metal‐Based Cathode Materials for Sodium‐Ion Batteries: Problems, Progress, and Key Technologies

“…The O3‐type iron‐ and manganese‐containing NaNi 1/3 Fe 1/3 Mn 1/3 O 2 and Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O 2 oxides have demonstrated the most realistic commercial perspectives for SIBs, since they can meet most of the requirements mentioned above and their full‐cell performances have been shown to be outstanding. Furthermore, in‐depth investigations of their hygroscopic properties, voltage decay mechanism, and full‐cell suitability/configuration are still urgently required to bring these low‐cost layered oxides to the commercial market …”

Industrialization of Layered Oxide Cathodes for Lithium‐Ion and Sodium‐Ion Batteries: A Comparative Perspective

“…However, pillaring ions also reduce sodium diffusivity by blocking the sodium diffusion pathway. [136] Dopants that reside in the transition-metal plane can be utilized in slightly higher quantities and tend to have a wide range of influence on the cathode material. For example, dopants have been credited with densifying the material for improved surface reactivity, [138] increasing the interlayer distance for improved rate capability, [138] improving air stability, [131,139] and improving structural stability and cycle life.…”

“…[132] The improved structural stability tends to prevent unfavorable phase transitions and improves overall cycle life. [133][134][135][136][137] Rate capability also increases with titanium substitution, potentially due to an increase in the sodium interlayer distance, but evidence justifying this assertion is minimal. [134,135] Although relatively large quantities of cation substitution can be beneficial, smaller quantities are often used for both lithium and sodium layered oxides, typically termed "dopants".…”

Layer‐Based Heterostructured Cathodes for Lithium‐Ion and Sodium‐Ion Batteries

“…A lower diffusion barrier is also expected in the P2‐phase due to its wider diffusion path for Na + . The Na + migrates from prismatic sites to its adjacent sites via open square bottlenecks that are surrounded by four oxygen ions, which enforce weaker repulsion compared to the interstitial tetrahedral sites in O3‐structure, and thus generally lead to better rate performance …”