Jie Song

Sodium is globally available, which makes a sodium-ion rechargeable battery preferable to a lithium-ion battery for large-scale storage of electrical energy, provided a host cathode for Na can be found that provides the necessary capacity, voltage, and cycle life at the prescribed charge/discharge rate. Low-cost hexacyanometallates are promising cathodes because of their ease of synthesis and rigid open framework that enables fast Na(+) insertion and extraction. Here we report an intriguing effect of interstitial H2O on the structure and electrochemical properties of sodium manganese(II) hexacyanoferrates(II) with the nominal composition Na2MnFe(CN)6·zH2O (Na2-δMnHFC). The newly discovered dehydrated Na2-δMnHFC phase exhibits superior electrochemical performance compared to other reported Na-ion cathode materials; it delivers at 3.5 V a reversible capacity of 150 mAh g(-1) in a sodium half cell and 140 mAh g(-1) in a full cell with a hard-carbon anode. At a charge/discharge rate of 20 C, the half-cell capacity is 120 mAh g(-1), and at 0.7 C, the cell exhibits 75% capacity retention after 500 cycles.

A novel air-stable sodium iron hexacyanoferrate (R-Na1.92Fe[Fe(CN)6]) with rhombohedral structure is demonstrated to be a scalable, low-cost cathode material for sodium-ion batteries exhibiting high capacity, long cycle life, and good rate capability. The cycling mechanism of the iron redox is clarified and understood through synchrotron-based soft X-ray absorption spectroscopy, which also reveals the correlation between the physical properties and the cell performance of this novel material. More importantly, successful preparation of a dehydrated iron hexacyanoferrate with high sodium-ion concentration enables the fabrication of a discharged sodium-ion battery with a non-sodium metal anode, and the manufacturing feasibility of low cost sodium-ion batteries with existing lithium-ion battery infrastructures has been tested.

By a novel in situ chemical vapor deposition, activated N-doped hollow carbon-nanotube/carbon-nanofiber composites are prepared having a superhigh specific Brunauer–Emmett–Teller (BET) surface area of 1840 m(2) g(–1) and a total pore volume of 1.21 m(3) g(–1). As an anode, this material has a reversible capacity of ~1150 mAh g(–1) at 0.1 A g(–1) (0.27 C) after 70 cycles. At 8 A g(–1) (21.5 C), a capacity of ~320 mAh g(–1) fades less than 20% after 3500 cycles, which makes it a superior anode material for a Li-ion battery.

Abstract This report provides an overview of development activities that enable the scale‐up and thereby a pathway toward the commercialization of sodium‐ion battery technologies for the energy storage market. The electrochemical performance of active materials and full cell performance of batteries developed by two startup companies, Novasis Energies, Inc. and Faradion Limited, are discussed in detail. Both companies offer low‐cost sodium‐ion battery chemistries with uniquely developed active materials that afford high rate capability and cycling stability. Their technologies are highly scalable due to the implementation of abundant and predominantly nontoxic elements and the ability to utilize common battery fabrication and manufacturing equipment. Both companies utilize active materials that are cost competitive compared to low‐cost lithium‐ion battery materials while exhibiting very similar specific capacity. In addition, improved safety characteristics with respect to operation and transportation distinguish the described sodium‐ion batteries from their incumbent lithium‐ion counterparts. The featured technology is particularly attractive for large‐scale energy storage applications.

Investigation of the high-voltage Li[Ni0.5–xMn1.5+x]O4 (x = 0, 0.05, 0.08) spinels prepared at temperatures of T ≤ 900 °C and given different thermal treatments has shown that the solubility limit for oxygen vacancies in the disordered spinel phase is small at 600 °C. With x = 0, long-range ordering of Ni2+ and Mn4+ and elimination of all oxygen vacancies occurs after an anneal at 700 °C. Above 700 °C, a reversible transition from spinel to rock-salt is initiated, to accommodate oxygen loss. A sample quenched from 900 °C into liquid nitrogen traps some rock-salt second phase; the volume fraction of rock-salt phase decreases with oxygen uptake to 600 °C. However, upon slow cooling (1 °C min–1) from 900 °C, the particles have time to eliminate most of the rock-salt phase by 700 °C; upon further cooling below 700 °C, the spinel phase and the oxygen gain are retained. However, the spinel phase retains oxygen vacancies and attendant Mn3+ with only short-range order of Ni and Mn. The rock-salt phase lowers sharply the electrochemical capacity of the quenched sample; but retention of Mn3+ in the slow-cooled sample improves the electrochemical performance relative to that of an oxygen-stoichiometric spinel formed by annealing at 700 °C. The Mn-rich Li[Ni0.45Mn1.55]O4 sample annealed at 700 °C exhibits a segregation of a long-range-ordered spinel phase and a Ni-deficient spinel phase having a larger fraction near the particle surface. Removal of the Ni4+/Ni2+ redox reactions from the surface stabilizes the electrochemical performance at 55 °C, but the problem of Mn2+ dissolution resulting from surface disproportionation of Mn3+ to Mn2+ and Mn4+ remains.