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

Li-rich electrode materials of the family xLi 2 MnO 3 •(1-x)LiNi a Co b Mn c O 2 (a + b + c = 1) suffer a voltage fade upon cycling that limits their utilization in commercial batteries despite their extremely high discharge capacity, ca. 250 mAhg -1 . We exposed Li-rich, 0.35Li 2 MnO 3 •0.65LiNi 0.35 Mn 0.45 Co 0.20 O 2 , to NH 3 at 400 °C , producing materials with improved characteristics: enhanced electrode capacity and a limited average voltage fade during 100 cycles in half cells vs. Li. We established three main changes caused by NH 3 treatment. First, a general bulk reduction of Co and Mn was observed via XPS and XANES. Next, a structural rearrangement lowered the coordination number of Co-O and Mn-O bonds, as well as formation of a surface spinel-like structure. Additionally, Li + removal from the bulk causes the formation of surface LiOH, Li 2 CO 3 , and Li 2 O. These structural and surface changes can enhance the voltage and capacity stability of the Li-rich material electrodes after moderate NH 3treatment times of 1 -2 hours.

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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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