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“Layered”/“cation-ordered”/O3-type Li-TM-oxides (TM: transition metal) suffer from structural instability due to “TM migration” from the TM layer to the Li layer upon Li removal (viz., “cation disordering”). This phenomenon gets exacerbated upon excessive Li removal, with Ni ions being particularly prone to migration. When used as cathode material in Li-ion batteries, the “TM migration” and associated structural changes cause rapid impedance buildup and capacity fade, thus limiting the cell voltages to ≤4.3 V for stable operation and lowering the usable Li-storage capacity (concomitantly, energy density). Looking closely at the “TM migration” pathway, one realizes that the tetrahedral site (t-site) of the Li layer forms an intermediate site. Accordingly, the present work explores a new idea concerning suppression of “Ni migration” by “blocking” the intermediate crystallographic site (viz., the t-site) with a dopant, which is the most stable at that site. In this regard, density functional theory (DFT)-based simulations indicate that the concerned t-site is energetically the most preferred and stable site for d 10 Zn2+. Detailed analysis of crystallographic data (including bond valence sum) obtained with the as-prepared Zn-doped Li-NMC supports the same. Furthermore, the simulations also predict that Zn doping is likely to suppress “Ni migration” upon Li removal. Supporting these predictions, galvanostatic delithiation/lithiation studies with Zn-doped and undoped Li-NMCs demonstrate significantly improved cyclic stability, near-complete suppression of “cation mixing”, and negligible buildup of impedance (as well as potential hysteresis) for the former, even upon being subjected to long-term cycling using a high upper cut-off potential of 4.7 V (vs Li/Li+). Accordingly, such subtle tuning of the composition and structure, in the light of electronic configuration of the dopant and specific crystallographic site occupancy, is likely to pave the way toward the development of Ni-containing stable high voltage O3-type Li-TM-oxide cathodes for the next-generation Li-ion batteries.

Air-stable solid electrolytes, possessing good Li-ion conductivity and facilitating low resistance at electrode/electrolyte interface, are essential towards facile development/handling of safe-cum-stable solid-state Li-ion batteries, possessing desired power densities. In this context, we report here the design and development of Al/Mg co-doped Li-La-zirconate (LLZO) based solid electrolytes that address the concerns associated with inferior air stability of Al-doped LLZO, while retaining Li-ion conductivity (∼4.7 × 10 −4 s cm −1 ) as good as that for similarly developed Al-doped LLZO and higher than that for Mg-doped counterpart. Doping as "little" as 0.1 mole of Mg-ion (per mole of LLZO), as for the optimized Al(0.2)/Mg(0.1) co-doped LLZO, is sufficient to impart long term phase and structural stability in air, unlike that for Al-doped LLZO. Accordingly, Li-ion conductivity of Al(0.2)/ Mg(0.1) co-doped LLZO gets nearly retained even after air-exposure for 50 days, in contrast to lowering of conductivity for Aldoped LLZO by ∼3 orders of magnitude after 24 days. The influence of excellent air stability and Li-ion conductivity could be seen on the Li/LLZO interfacial resistance, with the Al(0.2)/Mg(0.1) co-doped LLZO possessing the lowest area specific resistance of ∼18 Ω cm 2 among those investigated, which is also among the lowest reported to-date, without any additional surface/interfacial engineering being done.

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