Enhancing the Rate Capability and Cycling Stability of Na_0.67Mn_0.7Fe_0.2Co_0.1O₂ through a Synergy of Zr⁴⁺ Doping and ZrO₂ Coating

Abstract

Sodium-ion batteries (SIBs) have aroused great interest as large-scale energy storage devices because of the abundant Na resource. However, the lack of high-performance cathode materials is still a big challenge for the practical application of SIBs. Herein, the synergic modification of Zr 4+ d o p i n g a n d Z r O 2 c o a t i n g o n P 2 -s t r u c t u r e Na 0.67 Mn 0.7 Fe 0.2 Co 0.1 O 2 (MFC) has been achieved by a facile Zr(OC 4 H 9 ) 4 -mediated sol−gel method. The rate capability and cycling stability are simultaneously enhanced, and their synergetic mechanism is revealed. The enhancement of the rate capability is largely attributed to the expansion of the interlayer spacing and the enlargement of Na−O bond length, which decreases the Na + migration barrier and the electrostatic attraction between Na and O. This facilitates Na ions intercalation/extraction and enhances the rate capability. The improvement of the cycling stability is first attributed to the protection of ZrO 2 coating, which reduces the side reactions between the electrode and electrolyte and benefits to the stability of the layered structure. In addition, doping of Zr 4+ also reduces the bond length of TM−O/O−O and increases its bonding energy, which further enhances the layered structure stability. Last but not least, the relative content of Mn 3+ is also mitigated which alleviates Jahn−Teller distortion and further enhances the structure stability. In situ X-ray diffraction is also performed to probe the structure evolution of ZrO 2 @MFC during the sodiation/desodiation. The proposed synergetic strategy is also suitable to modify other cathode materials.

Tuning fermi level and band gap in Li4Ti5O12 by doping and vacancy for ultrafast Li+ insertion/extraction

“…Neutron powder diffraction, which is a powerful tool for determining the elements with the near-atomic number and light elements 31,32 (such as Li, O), was further carried out to analyze the structural information as shown in Figure S3. Site positions and occupancy of atoms obtained by Rietveld refinement were summarized in Table S1.…”

Multiphase layered transition metal oxide positive electrodes for sodium ion batteries

“…The simplicity of the liquid‐based coating techniques is a strength, but still more complex than the formation of coatings spontaneously from thermodynamically favorable processes during the typical calcination process. Certain electrode compositions have been observed to spontaneously segregate certain elements to their surface, forming surface oxides with remarkably different properties than the composition in the bulk 22,91,92 . This is in contrast to the kinetic control of element distribution employed in coprecipitation or surface coating methods.…”

“…Surface coating methods such as sol‐gel and wet chemical process, 73,86,89,112 melt‐impregnation, 90 and magnetron sputtering 113 can all provide significant performance benefits, but may not achieve the high degree of conformality and thickness uniformity provided by more complex techniques such as atomic layer deposition (ALD) 70–72,94 . Surface phases may also spontaneously (partially) segregate from the bulk 22,91,92 …”

Novel P2-type layered medium-entropy ceramics oxide as cathode material for sodium-ion batteries

“…In addition, cation doping is a favorable way to improve the electrochemical performance, such as electrolyte oxidative-decomposition prevention [30], TMS-dissolution inhibition [31], P2-O2 phase-transition inhibition [32], Jahn-Teller TM cation-distortion inhibition [33], metaloxygen bond enhancement [34], and surface basicity change [35]. Therefore, many researchers have studied the doping of different metals in P2-type SIB cathode materials, such as Mg [36], Zr [37], Cu [38], CO [39], Ti [40], and Al [41]. Doping is conducted through traditional synthesis methods, such as solid-state [42], sol-gel [43], and co-precipitation [44].…”