Multifunctional Na2TiO3 Coating-Enabled High-Voltage and Capacitive-like Sodium-Ion Storage of Na0.44MnO2

High-Voltage Sodium Layered Cathode Stabilized by Bulk Complex-Composition Doping to Surface Phosphate Coating Design

Layered oxides are considered promising cathode materials for sodium-ion batteries (SIBs) due to their high energy density, flexible compositions, and low cost. However, they encounter significant challenges, such as multiphase transitions and structural instability at high voltages, which limit their large-scale practical application. In this study, we employed a dual modification strategy involving complex composition doping and phosphate coating to fabricate the Na0.67Ni0.255Mn0.645(TiMgCuZn)0.1O2@phosphate cathode (D-NNM). The lattice distortion induced by complex composition doping optimizes the overall properties of the cathode, while the phosphate coating forms a robust electrode interface through stable P-O bonds. This comprehensive modification strategy stabilizes phase transitions and interfacial structure, thereby enhancing Na+ transport and mitigating mechanical degradation and surface reactions at high voltages. Consequently, D-NNM exhibited an initial capacity of 136.9 mA·h·g-1 with an average potential of 3.45 V and maintained 85% capacity after 60 cycles at 4.4 V, twice that of the pristine cathode. D-NNM demonstrated faster Na+ diffusion kinetics at high voltage without any significant particle cracks observed even after 50 cycles. This strategy offers comprehensive protection for layered oxides from bulk to surface and provides insights into the design of high energy density cathodes for SIBs.

Dual-enhancements of stability and wettability in O3-Na0.95Ni1/3Fe1/3Mn1/3O2 cathodes by converting surface residual alkali into ultrathin Na2Ti3O7 coatings

Na-based layered transition metal oxides with an O3-type structure are considered as promising cathode materials for sodium-ion batteries (SIBs) due to their low cost, wide two-dimensional ion channels and high theoretical specific capacity. However, during storage, exposure to moisture and carbon dioxide in the air results in the formation of increased residual sodium compounds. This degradation exacerbates side reactions with the electrolyte and induces structural collapse, ultimately impairing their electrochemical performance. In this study, two titanium sources (e.g., itanium dioxide nanopowders and tetrabutyl titanate ethanol solution) were applied separately to develop two kinds of Na2Ti3O7 coatings via the reactions between the titanium sources and the residual alkaline species on the O3-Na0.95Ni1/3Fe1/3Mn1/3O2 particle surface. Both two Na2Ti3O7 coatings could effectively enhance the electrolyte wettability and Na+ conductivity of the coated cathodes, along with reducing the dissolution of transition metals during cathode cycling. In particular, the tetrabutyl titanate-derived Na2Ti3O7 coatings (5-8 nm) on O3-Na0.95Ni1/3Fe1/3Mn1/3O2 cathodes realized excellent kinetics (101.9 mA h g-1 at 10C) and optimal cycling stability (85.66% retention over 200 cycles at 1C). These findings demonstrate that the ultrathin Na2Ti3O7 coating strategy effectively enhances layered oxide cathode performance through interface engineering, offering a promising approach for developing air-stable cathodes and emerging as a pivotal technology to advance sodium-ion battery applications.

Mn-based tunnel-structured Na0.44MnO2 cathode materials for high-performance sodium-ion batteries: electrochemical mechanism, synthesis and modifications

Sodium-ion batteries (SIBs) have emerged as promising and mature alternatives to lithium-ion batteries (LIBs) in the post-LIB era, necessitating the development of cost-effective and high-performance cathode materials. The unique crystal texture of Mn-based tunnel-structured cathode materials offers outstanding cycling stability, rate capability and air stability, making them a highly attractive option for sodium-ion storage applications. This comprehensive review summarizes recent advancements in the understanding of sodium-ion storage mechanism, synthesis techniques, and modification strategies for Mn-based tunnel-structured cathode materials, thereby significantly contributing to the advancement of high-performance cathodes for SIBs.

Reviving Sodium Tunnel Oxide Cathodes Based on Structural Modulation and Sodium Compensation Strategy Toward Practical Sodium-Ion Cylindrical Battery

As a typical tunnel oxide, Na0.44MnO2 features excellent electrochemical performance and outstanding structural stability, making it a promising cathode for sodium-ion batteries (SIBs). However, it suffers from undesirable challenges such as surface residual alkali, multiple voltage plateaus, and low initial charge specific capacity. Herein, an internal and external synergistic modulation strategy is adopted by replacing part of the Mn with Ti to optimize the bulk phase and construct a Ti-containing epitaxial stabilization layer, resulting in reduced surface residual alkali, excellent Na+ transport kinetics and improved water/air stability. Specifically, the Na0.44Mn0.85Ti0.15O2 using water-soluble carboxymethyl cellulose as a binder can realize a capacity retention rate of 94.30% after 1,000 cycles at 2C, and excellent stability is further verified in kilogram large-up applications. In addition, taking advantage of the rich Na content in Prussian blue analog (PBA), PBA-Na0.44Mn1-xTixO2 composites are designed to compensate for the insufficient Na in the tunnel oxide and are matched with hard carbon to achieve the preparation of coin full cell and 18650 cylindrical battery with satisfactory electrochemical performance. This work enables the application of tunnel oxides cathode for SIBs in 18650 cylindrical batteries for the first time and promotes the commercialization of SIBs.

Fe doping mechanism of Na0.44MnO2 tunnel phase cathode electrode in sodium-ion batteries

Due to its stability and low cost, the tunnel-style sodium-manganese oxide (Na0.44MnO2) material is deemed a popular cathode choice for sodium-ion rechargeable batteries. However, the Jahn-Teller effect caused by Mn3+ in the material results in poor capacity and cycling stability. The purpose of this experimental study is to partially replace Mn3+ with Fe3+, in order to reduce the Jahn-Teller effect of the material during charging and discharging process. The results of Raman spectroscopy and X-ray photoelectron spectroscopy confirmed that the content of Mn3+ decreased after Fe3+ doping. Electrochemical studies show that the Na0.44Mn0.994Fe0.006O2 cathode has better rate performance (exhibits a reversible capacity of 87.9 mAh/g at 2 C) and cycle stability in sodium-ion batteries. The diffusion coefficient of sodium ions increases by Fe3+ doping. The excellent rate performance and capacity improvement are verified by density functional theory (DFT) calculation. After doping, the band gap decreases significantly, and the results show that the state density of O 2p increases near the Fermi level, which promotes the oxidation-reduction of oxygen. This work provides a straightforward approach to enhance the performance of Na0.44MnO2 nanorods, and this performance improvement has guiding significance for the design of other materials in the energy storage domain.

Synthesis of Composite Titanate Photocatalyst via Molten Salt Processing and Its Enhanced Photocatalytic Properties

Photocatalysis plays a pivotal role in environmental remediation and energy production and improving the efficiency of photocatalysts, yet enhancing its efficiency remains a challenge. Titanate has been claimed to be a very promising material amongst various photocatalysts in recent years. In this work, a novel composite photocatalyst of sodium titanate and potassium titanate was synthesized via a simple hydrothermal and molten salt calcination method. Low melting point nitrate was added in the calcination process, which helps reduce the calcination temperature. The as-prepared composite sample showed excellent photocatalytic performance compared with commercial P25 in the visible light range. According to the characterization of XRD, SEM, TEM, BET, UV-Vis, and photocatalytic property testing, the composite's photocatalytic performance results are due to the dual optimization brought about by the layered structure and composite of titanium salts forming a heterojunction. We believe that the composite has significant application potential for the use of titanate in the field of photocatalysis. Notably, this study employed well-documented synthesis methods and adhered to established protocols for experimental procedures.