Improved High Rate Performance and Cycle Performance of Al-Doped O3-Type NaNi_0.5Mn_0.5O₂ Cathode Materials for Sodium-Ion Batteries

Abstract

O3-type layered transition metal oxides have shown great promise as high-capacity cathode materials for sodium-ion batteries in large-scale energy storage, due to their low cost and the abundance of sodium resources. However, the limited interlayer spacing and the unstable structure of the O3 phase result in inferior cycling stability and poor rate capability, which could even hinder their practical application process. Hereby, we present that doping with nonelectrochemically active Al in NaAl x (Ni 0.5 Mn 0.5 ) 1−x O 2 (x = 0, 0.02, 0.06, 0.1) can effectively alleviate these issues. Among these materials, materials with x = 0.02 exhibited the best electrochemical behavior with improved capacity and better cycling property than other materials. Specifically, the discharge capacity of a 2 mol % Al-doped material possesses 63.2% capacity retention after 200 cycles at a current density of 240 mA g −1 , which is 21.4% higher than that in NaNi 0.5 Mn 0.5 O 2 . In addition, a 2 mol % Al-doped electrode also shows outstanding rate capability and delivers 90 mAh g −1 at a high rate of 480 mA g −1 , compared to only 67 mAh g −1 for that of the pristine one. X-ray diffraction (XRD), cyclic voltammetry (CV), and galvanostatic intermittent titration technique (GITT) analysis elucidated that the introduced Al dopant can effectively improve the structural stability and promote kinetics of Na + diffusion mobility. Therefore, the strategy of doping inactive aluminum elements for optimizing the electrochemical performance of NaNi 0.5 Mn 0.5 O 2 was verified, which could also open an avenue for the design of other O3-type sodium cathode materials.

Synergistically Controlled Mechanism of Sodium Birnessite with a Larger Interlayer Distance for Fast Ion Intercalation toward Sodium-Ion Batteries

“…After linear fitting between Z ′ (real part of impedance, Ω) and ω –1/2 (frequency, Hz), σ (Warburg factor, Ω s –1/2 ) is obtained as the value of the slope, as shown in Figure b. The Na + diffusion coefficients ( D ) of the three samples are calculated based on EIS spectra and eq S1 in the Supporting Information. − The D Na + value of the Bir-TMA electrode is calculated as 4.79 × 10 –12 cm 2 s –1 , which is much higher than those of Bir-Na (3.8 × 10 –13 cm 2 s –1 ) and Bir-H (2.15 × 10 –13 cm 2 s –1 ) (Table S1). We found that D Na + of Bir-H is slightly less than that of Bir-Na.…”

N-Doped Carbon-Wrapped Cobalt–Manganese Oxide Nanosheets Loaded into a Three-Dimensional Graphene Nanonetwork as a Free-Standing Anode for Lithium-Ion Storage

“…The 3D NG-loaded vertical nanosheet structure of the CoMnO/NC electrode provides a shorter pathway for both charge transfer and ion diffusion, along with larger active surface areas. In view of high specific capacity and superior rate capacity of the NG/CoMnO/NC composite electrode, it is essential to investigate the capacitive effect, which is quite relative and sensitive to surface regions . The CV measurement is further performed at various sweep rates from 0.1 to 1 mV s –1 .…”

“…In view of high specific capacity and superior rate capacity of the NG/CoMnO/NC composite electrode, it is essential to investigate the capacitive effect, which is quite relative and sensitive to surface regions. 45 The CV measurement is further performed at various sweep rates from 0.1 to 1 mV s −1 . Two pairs of redox peaks involving active metallic oxides are observed in the CV curves shown in Figure 7c.…”

Structural degradation mechanisms and modulation technologies of layered oxide cathodes for sodium‐ion batteries

“…[79] Al 3+ doped in the TM layer could induce a decrease in the thickness of the TMO 6 octahedron and increase the d-spacing of the Na diffusion layer due to the higher bond energy of Al−O (501.9 ± 10.6 kJ mol −1 ) and reduced Al−O bond length. [86,88] Furthermore, the lower electronegativity of Al also increases the ionic bonding strength during cycling. [87] Additionally, Al 3+ (radius: 0.535 Å) can also be introduced into the TM layer to decrease the number of Mn 3+ (radius: 0.645 Å), thereby mitigating undesired J-T distortion, resulting in much more moderate structural transition.…”