The status of ambient temperature sodium ion batteries is reviewed in light of recent developments in anode, electrolyte and cathode materials. These devices, although early in their stage of development, are promising for large‐scale grid storage applications due to the abundance and very low cost of sodium‐containing precursors used to make the components. The engineering knowledge developed recently for highly successful Li ion batteries can be leveraged to ensure rapid progress in this area, although different electrode materials and electrolytes will be required for dual intercalation systems based on sodium. In particular, new anode materials need to be identified, since the graphite anode, commonly used in lithium systems, does not intercalate sodium to any appreciable extent. A wider array of choices is available for cathodes, including high performance layered transition metal oxides and polyanionic compounds. Recent developments in electrodes are encouraging, but a great deal of research is necessary, particularly in new electrolytes, and the understanding of the SEI films. The engineering modeling calculations of Na‐ion battery energy density indicate that 210 Wh kg−1 in gravimetric energy is possible for Na‐ion batteries compared to existing Li‐ion technology if a cathode capacity of 200 mAh g−1 and a 500 mAh g−1 anode can be discovered with an average cell potential of 3.3 V.

Ambient temperature sodium batteries have the potential to meet growing worldwide demand for electrical energy storage, due in part to sodium's widespread availability and low cost. In moving towards this scenario however, new advanced energy materials are required to enable the technology. In this study, a class of layered oxide materials has been discovered, synthesized, and evaluated as cathodes in rechargeable sodium batteries. Specifi cally, a series of layered Na x Li y Ni 0.25 Mn 0.75 O δ oxides within the range 0.7 ≤ x ≤ 1.2; 0 < y ≤ 0.5 were found to reversibly intercalate sodium at high rates, with negligible structural change. For example, Na 1.0 Li 0.2 Ni 0.25 Mn 0.75 O δ possesses well-ordered layers with hexagonal close-packed oxygen stacking. The transition metal layer contains Li, Ni(II) and Mn(IV) in octahedral coordination. The adjacent layer contains only Na in trigonal prismatic coordination, thus negating the cation disorder commonly observed in lithium-only containing materials. The well ordered metal sites remain intact during cycling and less than 1% crystallographic volume change in the structure is observed during cycling. The average voltage of the sodium cell is 3.4 V exhibiting a stable capacity over 50 cycles with about 95 -100 mAhg − 1 . The electroactivity and structural stability of Na 1.0 Li 0.2 Ni 0.25 Mn 0.75 O δ as a new sodium cathode material should hasten the development of ambient temperature sodium batteries for energy storage applications.Non-aqueous electrolyte ambient temperature sodium batteries have many of the basic qualities associated with lithium batteries. Intercalation reactions, material structural and chemical stability, electronic/ionic conductivity, and the electrode/electrolyte interfacial chemistry all play a pivotal role in battery operation. While the voltage of Na/Na + is only ∼ 300 mV less positive than Li/Li + , sodium's molecular weight of ∼ 23 gmol − 1 is much higher than that of Li ( ∼ 7 gmol − 1 ) which lowers the energy density of the material. To overcome this defi ciency, high-performance cathode and anode materials which are easy to synthesize, safe, non-toxic and low-cost are necessary. Such materials must also have appreciable electrochemical performance characteristics to forward their implementation. Examples in the literature of sodium-ion cathode materials include sodium vanadium phosphate fl uoride type materials (NaVPO 4 F) in sodium-ion cells, [ 1 ] lithium sodium vanadium phosphate fl uoride [ 2 ] (which used a mixed lithium and sodium containing electrolyte), and Na 2 MPO 4 F (M = Fe, Mn).[ 3 ] A Na battery study using NaCrO 2 was recently reported.[ 4 ] However, from a practical and environmental standpoint, NaCrO 2 is diffi cult to handle, and chromium is considered toxic. A recent study by Lu and Dahn demonstrated that the P2-layered oxide Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 could reversibly exchange Na in sodium cells, [ 5 ] but these materials were hard to synthesize as annealing temperatures as high as 900 ° C were combined with liqui...

This paper reports the results of an initial investigation into the phenomenon of hysteresis in the charge−discharge profile of high-capacity, lithiumand manganese-rich "layered−layered" xLi 2 MnO 3 •(1−x)LiMO 2 composite cathode structures (M = Mn, Ni, Co) and "layered−layered-spinel" derivatives that are of interest for Li-ion battery applications. In this study, electrochemical measurements, combined with in situ and ex situ X-ray characterization, are used to examine and compare electrochemical and structural processes that occur during charge (lithium extraction) and discharge (lithium insertion) of preconditioned cathodes. Electrochemical measurements of the open-circuit voltage versus lithium content demonstrate a ∼1 V hysteresis in site energy for approximately 12% of the total lithium content during the early cycles, which is markedly different from the hysteresis commonly observed in other intercalation materials. X-ray absorption data indicate structural differences in the cathode at the same state of charge (i.e., the same lithium content) during lithium insertion and extraction reactions. The data support an intercalation mechanism whereby the total number of lithium ions extracted at the top of charge is not reaccommodated in the structure until low states of charge are reached. The hysteresis in this class of materials is attributed predominantly to an inherent structural reorganization after an electrochemical activation of the Li 2 MnO 3 component that alters the crystallographic site energies.

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A new approach to synthesizing high capacity lithium-metal-oxide cathodes for lithium-ion batteries from a Li 2 MnO 3 precursor is described. The technique, which is simple and versatile, can be used to prepare a variety of integrated 'composite' electrode structures, such as 'layered-layered' xLi 2 MnO 3 •(1-x)LiMO 2 , 'layered-spinel' xLi 2 MnO 3 •(1-x)LiM 2 O 4 , 'layered-rocksalt' xLi 2 MnO 3 • (1-x)MO and more complex arrangements, in which M is typically Mn, Ni, and/or Co. Early indications are that electrodes prepared by this method are effective in 1) countering the voltage decay that occurs on cycling 'layered-layered' xLi 2 MnO 3 •(1-x)LiMO 2 electrodes without compromising capacity, and 2) reducing the extent of electrochemical activation required above 4.5 V on the initial charge. In particular, a 0.5Li 2 MnO 3 •0.5LiMn 0.5 Ni 0.5 O 2 electrode, after activation at 4.6 V, delivers a steady capacity of 245 mAh/g between 4.4 and 2.5 V at 15 mA/g (∼C/15 rate) with little change to the voltage profile; a first cycle capacity loss of 12%, which is significantly less than usually observed for 'layered-layered' electrodes, has been achieved with a manganese-rich 0.1Li 2 MnO 3 •0.9LiMn 0.50 Ni 0.37 Co 0.13 O 2 electrode. These results have implications for enhancing the performance of the next generation of high-energy lithium-ion batteries. The flexibility of the method and the variation in electrochemical properties of various composite electrode structures and compositions are demonstrated.