High-Entropy Na-Deficient Layered Oxides for Sodium-Ion Batteries

Abstract

Sodium layered oxides always suffer from sluggish kinetics and deleterious phase transformations at deep-desodiation state (i.e., >4.0 V) in O3 structure, incurring inferior rate capability and grievous capacity degradation. To tackle these handicaps, here, a configurational entropy tuning protocol through manipulating the stoichiometric ratios of inactive cations is proposed to elaborately design Na-deficient, O3-type Na x TmO2 cathodes. It is found that the electrons surrounding the oxygen of the TmO6 octahedron are re­arranged by the introduction of MnO6 and TiO6 octahedra in Na-deficient O3-type Na0.83­Li0.1­Ni0.25­Co0.2­Mn0.15­Ti0.15­Sn0.15­O2−δ (MTS15) with expanded O–Na–O slab spacing, giving enhanced Na+ diffusion kinetics and structural stability, as disclosed by theoretical calculations and electrochemical measurements. Concomitantly, the entropy effect contributes to the improved reversibility of Co redox and phase-transition behaviors between O3 and P3, as clearly revealed by ex situ synchrotron X-ray absorption spectra and in situ X-ray diffraction. Notably, the prepared entropy-tuned MTS15 cathode exhibits impressive rate capability (76.7% capacity retention at 10 C), cycling stability (87.2% capacity retention after 200 cycles) with a reversible capacity of 109.4 mAh g–1, good full-cell performance (84.3% capacity retention after 100 cycles), and exceptional air stability. This work provides an idea for how to design high-entropy sodium layered oxides for high-power density storage systems.

Inducing Na+ Site Rearrangement Through a Cosubstitution Strategy for Rapid Na Diffusion Kinetics of P2-Type Layered Metal Oxides

“…The results showed that the Li element was successfully doped into the host phase. In addition, compared to the expected stoichiometry, the content of Na and Li is relatively low, while the proportion of other elements is close, which is attributed to the volatilization of Na and Li caused by high temperature …”

“…In addition, compared to the expected stoichiometry, the content of Na and Li is relatively low, while the proportion of other elements is close, which is attributed to the volatilization of Na and Li caused by high temperature. 29 Usually, microstresses within the lattice can lead to structural instability, which is detrimental to long-term cyclic stability. 30,31 The (002) peak is taken as the research object for calculating the microstress of the material based on eq 1.…”

Ti/Co co-doped O3-Na(Ni0.3Fe0.2Mn0.5)0.85Ti0.1Co0.05O2 with high rate and durable cathode material for sodium-ion batteries

“…The high-resolution Fe 2p spectra of NFM can be divided to four peaks located at 710.4, 715.8, 723.3 and 730.7eV, which are attributed to the state of Fe 2+ and Fe 3+ [43]. The high-resolution Ti 2p spectra consists of Ti 2p3/2 peak at 457.9 eV and Ti 2p1/2 peak at 463.4 eV as well as the Na auger peak at 453.7eV, which are characteristic of Ti 4+ [44]. The Co 2p3/2, 2p1/2 peaks located at 780.3 and 795.4eV manifest that the oxidation state of Co is +3 in NFMTC [15].…”

Stabilized O3‐Type Layered Sodium Oxides with Enhanced Rate Performance and Cycling Stability by Dual‐Site Ti4+/K+ Substitution

“…The anode is pre-cycled three times before assembling the full cell due to the low coulombic efficiency of hard carbon (HC) in the first cycle. [22] Figures S17 and S18 (Supporting Information) show the rate performance and GCDs profiles of the HC anode, respectively. NaK 0.01 NMTi 0.1 O delivers a high reversible capacity of 95.5 mAh g −1 and a high average working voltage of ≈3.24 V, and can successfully illuminate commercial light-emitting diodes (Figure 2f).…”