Rectangular Tunnel‐Structured Na_0.4MnO₂ as a Promising Cathode Material Withstanding a High Cutoff Voltage for Na‐Ion Batteries

Abstract

The structural characteristics and electrochemical properties of Na 0.4 MnO 2 (Na 2 Mn 5 O 10 ) as a cathode material in sodium-ion batteries are systematically investigated. Na 0.4 MnO 2 possesses a unique (2 × 3) rectangular tunnel structure and the barrier for Na diffusion along the rectangular channel is only 18 meV, based on density functional theory calculations. Na 0.4 MnO 2 nanorods show good rate capability and cycle performance with coulombic efficiencies near 100 % in the voltage range of 2.0-4.0 V as well as 2.0-4.5 V. It delivers an initial discharge capacity of 83.7 mAh g À 1 at 0.1 C and maintains 84.7 % after 50 cycles and 74.5 % after 100 cycles with a voltage range of 2.0-4.0 V. It is interesting that the Na 0.4 MnO 2 nanorod cathode shows a much better electrochemical performance when adjusting the high cutoff voltage to 4.5 V. The discharge capacity of 98.3 mAh g À 1 can be obtained after 50 cycles with a capacity retention as high as 89.1 % at 0.1 C and a capacity retention of 86.6 % can be maintained after 100 cycles in a voltage range of 2.0-4.5 V. Even at 4 C, a high discharge capacity of 79.3 mAh g À 1 can be obtained. These data strongly suggest that Na 0.4 MnO 2 with a (2 × 3) rectangular tunnel structure is a promising cathode material for sodium-ion batteries.

Fabrication of Na0.4MnO2 Microrods for Room-Temperature Oxidation of Sulfurous Gases

“…The HRXPS Na 1s spectra of NMO samples have a peak at 1071.2–1071.4 eV for Na + ions (Figure a) . The HRXPS Mn spectrum of NMO-300 has two peaks at 642.4 and 654.3 eV for 2p 3/2 and 2p 1/2 doublets, respectively.…”

Synthesis, Structure, Electrochemical Mechanisms, and Atmospheric Stability of Mn-Based Layered Oxide Cathodes for Sodium Ion Batteries

“…Two phases with tunnel structures exist in the sodium content range of 0.4–0.45, i.e., Na 0.40 MnO 2 and Na 0.44 MnO 2 , which are both electrochemically active. As compared to Na 0.40 MnO 2 , , Na 0.44 MnO 2 , attracts much more attention because of its relatively higher reversible specific capacity, better cycling stability, and fewer structural evolutions (Table ). In addition, among all Na x MnO 2 phase, tunnel Na 0.44 MnO 2 shows high atmospheric and electrochemical stability but exhibits a low specific capacity of ∼100 mAh g −1 .…”

Faradaic Electrodes Open a New Era for Capacitive Deionization

“…Coupled with an AgCl as Cl − capture electrode, the as prepared Na 0.4 MnO 2 //AgCl cell showed an energy consumption of 0.29 Wh L −1 for 25% salt removal of seawater. Nevertheless, some additional phases like Na 2 Mn 3 O 7 , Mn 2 O 3 , and other electrochemically inert unknown impurities could be generated during the synthesis of Na 0.4 MnO 2 , [39,171] thus the annealing temperature of the precursor should be optimized to achieve the min-imum impurity in the target product. Moreover, the structural characteristics and Na + capture performance of this material need to be thoroughly investigated for further understanding.…”

“…Although the mechanism of Na + insertion into Na 0.4 MnO 2 is not fully understood and the exact site of Na + within the tunnels remains unclear, at least 0.3 mol of Na + could be reversibly extracted into/from the large open tunnel structure. [ 169 ] Density functional theory (DFT) calculations imply that the energy barrier for Na diffusion along this rectangular channel is only 18 meV, [ 171 ] which is much lower than that of S‐type tunnel structural Na 0.44 MnO 2 (126–289 meV), indicating the ease of ion migration and storage.…”