Bioinspired Surface Layer for the Cathode Material of High‐Energy‐Density Sodium‐Ion Batteries

Abstract

Cathode materials are usually active in the range of 2–4.3 V, but the decomposition of the electrolytic salt above 4 V versus Na+/Na is common. Arguably, the greatest concern is the formation of HF after the reaction of the salts with water molecules, which are present as an impurity in the electrolyte. This HF ceaselessly attacks the active materials and gradually causes the failure of the electrode via electric isolation of the active materials. In this study, a bioinspired β‐NaCaPO4 nanolayer is reported on a P2‐type layered Na2/3[Ni1/3Mn2/3]O2 cathode material. The coating layers successfully scavenge HF and H2O, and excellent capacity retention is achieved with the β‐NaCaPO4‐coated Na2/3[Ni1/3Mn2/3]O2 electrode. This retention is possible because a less acidic environment is produced in the Na cells during prolonged cycling. The intrinsic stability of the coating layer also assists in delaying the exothermic decomposition reaction of the desodiated electrodes. Formation and reaction mechanisms are suggested for the coating layers responsible for the excellent electrode performance. The suggested technology is promising for use with cathode materials in rechargeable sodium batteries to mitigate the effects of acidic conditions in Na cells.

P2‐K0.75[Ni1/3Mn2/3]O2 Cathode Material for High Power and Long Life Potassium‐Ion Batteries

“…This finding suggests that Mn 4+ in the structure plays a significant role in supporting the crystal structure. The P2‐O2 phase transition is known as the result in a volume change of ≈23% in P2‐Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 , which accelerates drastic capacity fading. The present P2‐K 0.75 [Ni 1/3 Mn 2/3 ]O 2 experiences a single‐phase reaction maintaining the P2 phase, such that the corresponding volume change was only ≈3.1%.…”

“…The observed pattern matched well with the calculated one without impurities. The calculated lattice parameters were a = 2.884(2) Å and c = 11.133(2) Å, which are consistent with the values in literature . The obtained particle was flat with an estimated size of about 2 µm, and Na, Mn, and Ni were homogeneous distributed in the particles (Figure b) The XANES spectra of the Mn and Ni K‐edges for the as‐synthesized P2‐Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 indicate that the oxidation state of Mn was close to 4+ (Figure c), whereas the Ni had a photon energy similar to that of Ni 2+ O (Figure d).…”

“…The presence of long plateaus above 4.1 V versus Na + /Na, attributed to the P2–O2 phase transition, is typical in P2‐Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 (Figure S1, Supporting Information), whereas the phase transition is not evident at the first charge. In addition, the obtained charge capacity in the K cell was lower than that for testing in Na cells (generally, ≈170 mAh g −1 ) . The operation voltage observed in the K cells was lower and steeper than that observed in Na cells, which may be attributed to the intercalation of different ionic species, as the shapes of the first and second charge curves differed.…”

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

“…It was discovered that the change provides smoother electrochemistry, increases rate performance and capacity retention, which can be explain by the reduced amount of Mn 3+ , delayed phase transformation, and lattice oxygen stabilization by Mg 2+ at high voltage . Finally, to address the atmospheric and electrochemical corrosion on layered cathodes, surface coating layers including spinel‐like titanium (III) oxides, β‐NaCaPO 4 , Al 2 O 3 , etc., were designed to scavenge HF and H 2 O, which would stabilize electrode/electrolyte interface and promote ion diffusion …”

C60/Na4FeO3/Li3V2(PO4)3/soft carbon quaternary hybrid superstructure for high-performance battery-supercapacitor hybrid devices

“…Therefore, chemistries beyond the Li ion and Na ion, such as the merging of battery and supercapacitor chemistries, are currently being investigated. In recent years, hybrid energy-storage devices, such as batterysupercapacitor hybrid devices (BSHs) based on a battery electrode and a supercapacitor electrode, have received significant attention [4][5][6] . The nanostructured hybrid electrodes enable the integration of the high energy from batteries with a high power and the long lifetime from supercapacitors.…”