Search

Layered oxide cathodes usually exhibit high compositional diversity, thus providing controllable electrochemical performance for Na‐ion batteries. These abundant components lead to complicated structural chemistry, closely affecting the stacking preference, phase transition and Na+ kinetics. With this perspective, we explore the thermodynamically stable phase diagram of various P2/O3 composites based on a rational biphasic tailoring strategy. Then a specific P2/O3 composite is investigated and compared with its monophasic counterparts. A highly reversible structural evolution of P2/O3–P2/O3/P3–P2/P3–P2/Z/O3′–Z/O3′ based on the Ni2+/Ni3.5+, Fe3+/Fe4+ and Mn3.8+/Mn4+ redox couples upon sequential Na extraction/insertion is revealed. The reduced structural strain at the phase boundary alleviates the phase transition and decreases the lattice mismatch during cycling, endowing the biphasic electrode a large reversible capacity of 144 mAh g−1 with the energy density approaching 514 Wh kg−1. [ABSTRACT FROM AUTHOR]

Layered transition metal oxide P2‐Na2/3Ni1/3Mn2/3O2 usually suffers from large‐volume phase transitions and different Na‐vacancy ordering during sodium (de)intercalation, incurring rapid capacity decline and poor rate capability. Herein, an effective strategy based on synergetic effect of selected multiple metal ions is designed for P2‐type cathodes with improved performance. The role of tetravalent titanium provides high redox potential, inactive divalent magnesium stabilizes the structure, and the monovalent lithium smooths the electrochemical curves. The combined analysis of in operando X‐ray diffraction, in operando X‐ray absorption spectroscopy and density functional theory calculations demonstrates the contribution of multi‐metal ions converts the unfavorable and large‐volume P2 to O2 transition into a moderate "Z"‐intergrowth structure by increasing the energy barrier of transition metal slab gliding. As a consequence, the resultant P2‐Na0.7Li0.03Mg0.03Ni0.27Mn0.6Ti0.07O2 electrode delivers a reversible capacity of 134 mAh g−1, a working voltage of 3.57 V, excellent cycling stability (82% of capacity retention after 200 cycles), and superior rate performance (110 mAh g−1 at 4 C). Full cells fabricated with a hard carbon anode achieve an energy density of 296 Wh kg−1. This study presents a route to rationally design cathode materials with this functionalization to improve the cell performance for sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Organic room-temperature sodium-ion battery electrodes with carboxylate and carbonyl groups have been widely studied. Herein, for the first time, we report a family of sodium-ion battery electrodes obtained by replacing stepwise the oxygen atoms with sulfur atoms in the carboxylate groups of sodium terephthalate which improves electron delocalization, electrical conductivity and sodium uptake capacity. The versatile strategy based on molecular engineering greatly enhances the specific capacity of organic electrodes with the same carbon scaffold. By introducing two sulfur atoms to a single carboxylate scaffold, the molecular solid reaches a reversible capacity of 466 mAh g−1 at a current density of 50 mA g−1. When four sulfur atoms are introduced, the capacity increases to 567 mAh g−1 at a current density of 50 mA g−1, which is the highest capacity value reported for organic sodium-ion battery anodes until now. [ABSTRACT FROM AUTHOR]

Atomic-layer-deposition (ALD) coatingshave been increasingly usedto improve battery performance. However, the electrochemical and mechanisticroles remain largely unclear, especially for ALD coatings on electrodesthat undergo significant volume changes (up to 100%) during charging/discharging.Here we investigate an anode consisting of tin nanoparticles (SnNPs)with an ALD-Al2O3coating. For the first time,in situ transmission electron microscopy unveiled the dynamic mechanicalprotection of the ALD-Al2O3coating by coherentlydeforming with the SnNPs under the huge volume changes during charging/discharging.Battery tests in coin-cells further showed the ALD-Al2O3coating remarkably boosts the cycling performance of theSn anodes, comparing with those made of bare SnNPs. Chemomechanicalsimulations clearly revealed that a bare SnNP debonds and falls offthe underlying substrate upon charging, and by contrast the ALD-Al2O3coating, like ion-conductive nanoglue, robustlyanchors the SnNP anode to the substrate during charging/discharging,a key to improving battery cycle performance. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) are promising candidatesfor the applicationsof large-scale energy storage due to their cost-effective and environmental-friendlycharacteristics. Nevertheless, it remains a practical challenge tofind a cathode material of SIBs showing ideal performance (capacity,reversibility, etc.). We report here a nanocomposite material of amorphous,porous FePO4nanoparticles electrically wired by single-wallcarbon nanotubes as a potential cathode material for SIBs. The hydrothermallysynthesized nanocomposite shows excellent cell performance with unprecedentedcycling stability and reversibility. The discharge capacity of ashigh as 120 mAh/g is delivered at a 0.1 C rate (10 mA/g). The capacityretentions are about 70 mAh/g, 60 mAh/g, and 55 mAh/g at higher currentsof 20 mA/g, 40 mA/g, and 60 mA/g, respectively. Even at a 1 C rate(100 mA/g), a capacity of about 50 mAh/g is still retained after 300cycles. With a simple synthetic procedure, cost-effective chemicals,and desirable cell performance, this method offers a highly promisingcandidate for commercialized cathode materials of SIBs. [ABSTRACT FROM AUTHOR]

Sodium (Na)-ion batteries offer anattractive option for low cost grid scale storage due to the abundanceof Na. Tin (Sn) is touted as a high capacity anode for Na-ion batterieswith a high theoretical capacity of 847 mAh/g, but it has severallimitations such as large volume expansion with cycling, slow kinetics,and unstable solid electrolyte interphase (SEI) formation. In thisarticle, we demonstrate that an anode consisting of a Sn thin filmdeposited on a hierarchical wood fiber substrate simultaneously addressesall the challenges associated with Sn anodes. The soft nature of woodfibers effectively releases the mechanical stresses associated withthe sodiation process, and the mesoporous structure functions as anelectrolyte reservoir that allows for ion transport through the outerand inner surface of the fiber. These properties are confirmed experimentallyand computationally. A stable cycling performance of 400 cycles withan initial capacity of 339 mAh/g is demonstrated; a significant improvementover other reported Sn nanostructures. The soft and mesoporous woodfiber substrate can be utilized as a new platform for low cost Na-ionbatteries. [ABSTRACT FROM AUTHOR]