CO 2 emissions. Hence, transportation dependent on electrical propulsion (electric vehicles) instead of internal combustion engines can greatly reduce the pollution caused by our transportation infrastructure. While rechargeable Li-ion batteries are the major power source for portable electronic devices such as smartphones and laptop computers, further improvements in their energy density is required in order to promote electrochemical propulsion devices that can compete with internal combustion engines. [1] The energy density of Li-ion batteries depends on the specific capacities and redox potentials of their electrode materials. Layered lithiated transition metal oxides such as LiCoO 2 , LiNi 1/2 Mn 1/2 O 2 , and LiNi 1/3 Mn 1/3 Co 1/3 O 2 ("NMC 111") were extensively studied as cathodes, which can exhibit specific capacities ≤160 mA h g −1 with an upper potential limit of 4.3 V versus Li. [2] The high cost, low thermal stability, and fast capacity fading at high current rates or during deep cycling of currently used LiCoO 2 necessitated the development of other layered cathodes, such as LiNi 1/2 Mn 1/2 O 2 , NMC 111, etc. The electrochemical performance of these layered metal oxides was recently reviewed by Yushin and coworkers. [3] Higher capacities can be extracted from layered metal oxide cathodes by cycling to upper potentials of about 4.5 V, however, driving these layered cathode materials to such high potentials enhances the structural instability and impedance growth. [4,5] Another important direction is the development of Ni-rich NCM cathode materials. As the content of Ni is higher, the specific capacity that can be extracted is higher as

We report excellent cycling performance for P2− Na 0.6 Li 0.2 Mn 0.8 O 2 , an auspicious cathode material for sodium-ion batteries. This material, which contains mainly Mn 4+ , exhibits a long voltage plateau on the first charge, similar to that of high-capacity lithium and manganese-rich metal oxides. Electrochemical measurements, X-ray diffraction, and elemental analysis of the cycled electrodes suggest an activation process that includes the extraction of lithium from the material. The "activated" material delivers a stable, high specific capacity up to ∼190 mAh/g after 100 cycles in the voltage window between 4.6−2.0 V versus Na/Na + . DFT calculations locate the energy states of oxygen atoms near the Fermi level, suggesting the possible contribution of oxide ions to the redox process. The addition of Li to the lattice improves structural stability compared to many previously reported sodiated transition-metal oxide electrode materials, by inhibiting the detrimental structural transformation ubiquitously observed with sodium manganese oxides during cycling. This research demonstrates the prospect of intercalation materials for Na-ion battery technology that are active based on both cationic and anionic redox moieties.

Electrodes prepared from lithium-rich (Li-rich) xLi 2 MnO 3 ·(1-x)LiNi a Co b Mn c O 2 materials (a + b + c = 1) show extremely high discharge capacities, arising from excess Li + present in their Li 2 MnO 3 component, and the ability to reversibly store charge with O 2− anions. These electrodes suffer serious voltage and capacity fading however, due to the migration of transition metals to the Li-layer at advanced states of charging, partial structural layered-to-spinel transformation and other reasons. In this focus paper, the current understanding of the above materials is summarized, briefly concluding with attempts by our groups to mitigate the voltage and capacity fade of these electrodes.

Li-ion batteries (LIBs) today face the challenge of application in electrified vehicles (xEVs) which require increased energy density, improved abuse tolerance, prolonged life, and low cost. LIB technology can significantly advance through more realistic approaches such as: i) stable high-specific-energy cathodes based on Li Ni Co Mn O (NCM) compounds with either Ni-rich (x = 0, y → 1), or Li- and Mn-rich (0.1 < x < 0.2, w > 0.5) compositions, and ii) chemically active separators and binders that mitigate battery performance degradation. While the stability of such cathode materials during cell operation tends to decrease with increasing specific capacity, active material doping and coatings, together with carefully designed cell-formation protocols, can enable both high specific capacities and good long-term stability. It has also been shown that major LIB capacity fading mechanisms can be reduced by multifunctional separators and binders that trap transition metal ions and/or scavenge acid species. Here, recent progress on improving Ni-rich and Mn-rich NCM cathode materials is reviewed, as well as in the search for inexpensive, multifunctional, chemically active separators. A realistic overview regarding some of the most promising approaches to improving the performance of rechargeable batteries for xEV applications is also presented.

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Amongst a number of different cathode materials, the layered nickel-rich LiNi y Co x Mn 1−y−x O 2 and the integrated lithium-rich xLi 2 MnO 3 ·(1 − x)Li[Ni a Co b Mn c ]O 2 (a + b + c = 1) have received considerable attention over the last decade due to their high capacities of~195 and~250 mAh·g −1 , respectively. Both materials are believed to play a vital role in the development of future electric vehicles, which makes them highly attractive for researchers from academia and industry alike. The review at hand deals with both cathode materials and highlights recent achievements to enhance capacity stability, voltage stability, and rate capability, etc. The focus of this paper is on novel strategies and established methods such as coatings and dopings.

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Porous α-Fe 2 O 3 nanostructures have been synthesized by sol-gel route. The effect of preparation temperature on the morphology, structure, and electrochemical stability upon cycling has been studied for supercapacitor application. The discharge capacitance of α-Fe 2 O 3 prepared at 300 °C is 193 F g −1 , when the electrodes are cycled in 0.5 M Na 2 SO 3 at a specific current of 1 A g −1 . The capacitance retention after 1,000 cycles is about 92 % of the initial capacitance at a current density of 2 A g −1 . The high discharge capacitance as well as stability of α-Fe 2 O 3 electrodes is attributed to large surface area and porosity of the material. There is a decrease in specific capacitance (SC) on increasing the preparation temperature. As iron oxides are inexpensive, the synthetic route adopted for α-Fe 2 O 3 in the present study is convenient and the SC is high with good cycling stability, the porous α-Fe 2 O 3 is a potential material for supercapacitors.