RESUMO
Sodium manganese-based oxides (NMO) are attracting huge attention as safe and cost-effective cathode materials for sodium-ion batteries (SIBs). To date, one of the most important challenges of NMO-based cathodes is the relatively low capacity. Therefore, it is of great significance to develop high-capacity NMO-based cathodes. Great efforts have been made to enhance the reversible capacity of NMO-based cathodes, achieving considerable progress not only on electrochemical performance, but also the mechanism of massive sodium ion storage. In this paper, the structure and sodium storage mechanism for typical phases of NMO are reviewed, including P2, P3, O3, tunnel-type, and spinel-type NMO-based cathodes. Strategies for high-capacity NMO-based cathodes, such as cationic substitution, anion redox activation, etc are introduced in detail. Last but not least, the future opportunities and challenges for high-capacity NMO-based cathode are prospected.
RESUMO
Advanced lithium-ion batteries utilize high upper cut-off voltages up to 4.8 V versus lithium metal to reach extraordinary energy densities. Such a harsh environment challenges the cathode stability and requires the construction of robust cathode electrolyte interphases at their electrochemical interface. Inspired by carbonated beverages with supersaturated CO2, here, a surface modification strategy that produces effective passivation layer of low modulus from the weakest link, is proposed CO2 bubbles preferentially nucleate and grow at rough surfaces, which in oxide cathodes, are also the local regions offering fast degradation pathway. Metal ion exchange on carbonated layer assists the construction of highly elastic interface under the guidance of packing factor. This method enables surface reconstruction at both primary and secondary particle levels for various cathodes exemplified by high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811) and LiCoO2 (LCO). Remarkably, with ultra-high upper cut-off voltage of 4.8 V versus Li+/Li, over 235 mAh g-1 discharge capacity, and over 900 W h kg-1 discharge energy at cathode level, ≈90% capacity retention can be obtained for LiNi0.8Co0.1Mn0.1O2 over 100 cycles at 0.5 C with commercial carbonate electrolytes. This carbonated beverage chemistry is promising for constructing high-quality surface passivation in many extreme-condition applications beyond battery cathodes.
RESUMO
Sodium-ion batteries, as an attractive option for large-scale energy storage, still face the problems of low energy density and unsatisfactory rate performance. Among various cathodes, the tunnel-type Na0.44MnO2 with large S-shaped Na+ transport tunnels is one of the promising cathode materials for fast and robust sodium-ion storage, yet suffering from Mn dissolution and structural collapse. Herein, a Na-rich layered oxide Na2TiO3 is first constructed as a multifunctional coating layer on the surface of the Na0.44MnO2 nanorod. Na2TiO3 not only acts as an Na+ reservoir, but also serves as a protective layer to prevent Na0.44MnO2 from electrolyte etching. Besides, the derived Ti-doped Na0.44MnO2 transition layer supplies additional Na+ diffusion pathways along the radial direction of the nanorod with a short migration distance. The optimized 3 wt % Na2TiO3-coated Na0.44MnO2 exhibits enhanced an initial capacity of 127 mAh g-1 at 2-4.5 V. In addition, it shows an ultra-high capacitive-like capacity ratio of 96.7%, hence delivering an excellent rate performance of 80.2 mAh g-1 at 20C. Long-term cycling tests indicate splendid stability against high voltage, achieving 97.7% capacity retention at 20C after 900 cycles. This work provides an effective strategy to improve the rate performance and high-voltage stability of Na0.44MnO2 for high energy and power density batteries.