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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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the oceans. Thus, sodium storage systems would likely be far more economically competitive for large-format applications where low price, little pollution, and long cycle life may outweigh energy density considerations. [3] In recent years, rechargeable aqueous sodium-ion battery systems received attention as large-scale energy storage systems owing to their various potential merits. Aqueous batteries are non-flammable, environmentally friendly, and have great potential to be low cost. [4] In the last decade, several cathode compounds were reported to couple with Na-compatible anodes to form full cells including Prussian blue analogs, [5] polyanionic compounds, [6] vanadium oxides, [7] and manganese oxides. [8] Manganese-based cathodes have received particular attention due to their low cost and earth abundance in comparison to other transition metal-based cathodes. Tunnel-structured Na 0.4 MnO 2 (NMO) is of particular interest as cathode material owing to its unique large tunnels that are suitable for sodium intercalation in both aqueous and non-aqueous electrolyte solutions. [9,10] The crystal structure of Na 0.4 MnO 2 is shown in Figure 1a. This system usually exists in the orthorhombic structure. There are five crystallographic manganese sites; the first two are occupied by Mn 3+ , and the latter are occupied by Mn 4+. These crystallographic attributes exhibit a unique charge ordering as reported by previous computational studies. [11] The structure framework is based on double and triple linear chains using edge-shared Mn(2-5)O 6 octahedra and single chains of corner-shared Mn(1)O 5. The three different sodium sites are shown within the tunnel frame, assembled by MnO 6 and MnO 5 polyhedrons. Two sites (Na(2) and Na(3)) are situated in large "S" shaped cavities (Figure 1b), the third site, Na(1), is located in smaller tunnels (Figure 1c). Typically, manganese-based cathode structures are unstable during redox reactions due to Jahn-Teller distortions. However, this tunnel-type structure is very stable, even during long-term electrochemical sodium intercalation and deintercalation reactions in an aqueous solution. Nevertheless, Na 0.4 MnO 2 still faces significant barriers to commercialization as a large-scale energy storage system. These barriers stem, in large, from the limited electrochemical performance, in particular the stability, rate capability, and discharge capacity.

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Li+ conducting halide solid-state electrolytes (SEs) are developing as an alternative to contemporary oxide and sulfide SEs for all-solid-state batteries (ASSBs) due to their high ionic conductivity, excellent chemical and electrochemical oxidation stability, and good deformability. However, the instability of halide SEs against the Li anode is still one of the key challenges that need to be addressed. Among halides, fluorides have shown a wider electrochemical stability window due to fluoride’s high electronegativity and smaller ionic radius. However, the ionic conductivity of fluoride-based SEs is lower compared to other halide-based SEs. To achieve better interface stability with the Li anode, the presence of fluoride is not only advantageous for a wider potential window but also forms a stable passivation layer at the Li/SEs interface. Therefore, developing mixed halogen-based solid electrolytes, particularly fluorine and chlorine-based SEs are promising in ASSBs. Herein, we report dual halogen-based SEs, Li2ZrF6–x Cl x (0 ≤ x ≤ 2), synthesized via ball-milling. The X-ray diffraction results revealed that Li2ZrF6–x Cl x compounds crystallize in the trigonal phase (P3̅1m). Using impedance spectroscopy, an increase in Li+ conductivity with the increase in Cl content was observed for Li2ZrF6–x Cl x . Compared with x = 0, Li+ conductivity for the sample with x = 1 improved by ∼5 orders of magnitude. The Li+ conductivities for Li2ZrF5Cl1 at 25 and 100 °C are 5.5 × 10–7 and 2.1 × 10–5 S/cm, respectively. Moreover, Li2ZrF5Cl1 exhibits the widest electrochemical stability window and excellent Li interface stability. Our work indicates Li2ZrF6–x Cl x as an attractive material for optimization in the class of halide-based solid-state Li-ion conductors.