In Situ Plastic-Crystal-Coated Cathode toward High-Performance Na-Ion Batteries

Abstract

Cathode materials are critical for Na-ion batteries while facing challenges due to the instability of the structure and interfaces. In this work, we propose a strategy to achieve an in situ plastic-crystal Na3–3x Al x PO4 coating and bulk Al doping for an O3-NaNi0.4Fe0.2Mn0.4O2 cathode through a simple one-step method. Na3–3x Al x PO4 exhibits high ion transport performance due to its unique “paddle-wheel” mechanism. The in situ formed Na3–3x Al x PO4 could consume the residual alkali compounds and induce the formation of a Na-deficient phase, thus leading to enhanced Na+ transport kinetics. Furthermore, strong Al–O bonds formed in the bulk further enhance the crystal structure stability. In a full cell, the capacity retention rate reached 70% after 500 cycles, making its commercial operation possible. Altogether, these results suggest that the in situ plastic-crystal-coating strategy can significantly improve the surface and bulk structure stability of NaNi0.4Fe0.2Mn0.4O2, thus leading to improved electrochemical performance.

Practical Cathodes for Sodium‐Ion Batteries: Who Will Take The Crown?

“…To suppress interfacial parasitic reactions and alleviate the dissolution of active materials, researchers proposed a surface coating strategy to improve the interface stability, including coatings of C, [136,235] oxides, [236,237] fluorides, [238] and phosphates. [239,240] The introduced surface-modification layers have the following functions: 1) Improve ionic/electronic conductivity. A surface modification layer with high ionic/electronic conductivity can effectively improve the surface properties of cathode materials and reduce the internal reaction resistance.…”

“…Considering that one of the main factors leading to rapid capacity degradation is the residual Na-based impurities, such as NaOH and Na 2 CO 3 with poor conductivity, reducing or removing such surface compounds to improve structural stability is an effective modification strategy for layered oxide cathodes. [232,240] Therefore, simultaneously consuming surface residues and applying a protective coating in situ is an effective method for overcoming the shortcomings related to Na residues and interfacial instability. [254] The in-situ formation of a plastic-crystal Na 3−3x Al x PO 4 coating on the outer surface of an O3-NaNi 0.4 Fe 0.2 Mn 0.4 O 2 cathode was demonstrated using a wetchemical method, while a thin Na-deficient phase was formed on the inner surface due to the extraction of Na from the crystal lattice.…”

Recent Progress in the Emerging Modification Strategies for Layered Oxide Cathodes toward Practicable Sodium Ion Batteries

“…The K + pillar and the coherent spinel-like surface structure enlarge interlayer spacing and enhance Na + kinetics, thus improving the rate performance. Most recently, Wang et al [159] proposed an in situ plastic-crystal Na 3−3x Al x PO 4 coated and bulk Al 3+ doped O3-NaNi 0.4 Fe 0.2 Mn 0.4 O 2 (NFM424) cathode through a simple one step method. The in situ Na 3−3x Al x PO 4 plastic-crystal coating can induce the formation of a Na-deficient phase by consuming the residual alkali compounds, thus facilitating Na + transport kinetics.…”

Structural and electrochemical progress of O3-type layered oxide cathodes for Na-ion batteries

“…70,71 Elemental doping is an effective strategy for stabilising the structural properties of materials and improving the electrochemical performance of layered oxides, such as Li, Mg, Al, Ti, Fe, Cu, and Sn. [72][73][74][75][76] Fig. 6a summarises the performance comparison of the different elemental dopings, and Table 1 summarises the electrochemical properties of some of the O3-type element doped cathodes reported in the literature.…”