Sn4 P3 is introduced for the first time as an anode material for Na-ion batteries. Sn4 P3 delivers a high reversible capacity of 718 mA h g(-1), and shows very stable cycle performance with negligible capa-city fading over 100 cycles, which is attributed to the confinement effect of Sn nanocrystallites in the amorphous phosphorus matrix during cycling.

A new polyanion‐based compound, Na3.12M2.44(P2O7)2 (M = Fe, Fe0.5Mn0.5, Mn) is synthesized and examined as a cathode for Na ion batteries. Off‐stoichiometric synthesis induces the formation of a Na‐rich phase, Na3.32Fe2.34(P2O7)2 ‐ a member of the solid solution series Na4‐αFe2+α/2(P2O7)2 (2/3 ≤ α ≤ 7/8) ‐ which delivers a reversible capacity of about 85 mA h g−1 at ca. 3 V vs. Na/Na+ and exhibits very stable cycle performance. Above all, it shows fast kinetics for Na ions, delivering an almost constant 72% reversible capacity at rates between C/10 and 10C without the necessity for nanosizing or carbon coating. We attribute this to the spacious channel size along the a‐axis, along with a single phase transformation upon de/sodiation.

Sodium‐ion batteries are an attractive alternative to replace Lithium‐ion batteries and Ni–metal hydride batteries for electric vehicle and smart grid applications. Kyu Tae Lee, Linda F. Nazar, and co‐workers demonstrate , for the first time, the synthesis of new polyanion‐based compounds, Na3.12M2.44(P2O7)2 (M=Fe, Fe0.5Mn0.5, Mn), and their electrochemical performance as a cathode material for Na ion batteries. The deliberate synthesis of the off‐stoichiometric phase, Na3.42Fe2.44(P2O7)2.05 shows excellent cycle and rate performance, and this is attributed to the spacious channel size along the a‐axis, along with a single phase transformation upon de/sodiation.

Nanosized Si-based materials have been extensively investigated because of their high gravimetric capacity and stable cycle performance. However, the tap density of nanosized materials is poor, leading to poor volumetric capacity. In this regard, micrometer-sized Si nanoparticles and carbon composites have been introduced to improve the volumetric energy density of Li-ion cells. However, most synthesis methods for these Si/C composites are complex, and thus, only a few methods among them are scalable for mass production. Herein, a scalable solid-state synthesis through self-assembly due to the relative miscibility of hydrophobic and hydrophilic precursors is introduced to obtain micrometer-sized porous carbon spheres containing nanosized Si particles. The self-assembly synthesis uses hydrophilic Si/SiO 2 core-shell nanoparticles, hydrophilic phenolic resins, and hydrophobic fumed silica. Because phenolic resin melts and Si/SiO 2 core-shells are miscible, the Si/SiO 2 core-shells are embedded in the phenolic resins. Immiscible phenolic resin melts and fumed silica lead to the formation of spherical resins. Eventually, the self-assembled micrometer-sized Si/C composite spheres are obtained after heating and HF etching. The tap density of the self-assembled Si/C spheres is much higher than that of the bare Si nanoparticles. In addition, the self-assembled Si/C composite shows excellent cycle performance because of voids in the composite.

Sn4P3 is prepared by ball milling of Sn and red phosphorus powders (Ar atmosphere, 1 h) and characterized by powder XRD, FESEM, TEM, and electrochemical measurements.