The high charge-state dopant Zr4+ improves the structural stability and electrochemical behavior of the lithiated transition metal oxide LiNi0.6Co0.2Mn0.2O2.

One of the major hurdles of Ni‐rich cathode materials Li1+x(NixCozMnz)wO2, y > 0.5 for lithium‐ion batteries is their low cycling stability especially for compositions with Ni ≥ 60%, which suffer from severe capacity fading and impedance increase during cycling at elevated temperatures (e.g., 45 °C). Two promising surface and structural modifications of these materials to alleviate the above drawback are (1) coatings by electrochemically inert inorganic compounds (e.g., ZrO2) or (2) lattice doping by cations like Zr4+, Al3+, Mg2+, etc. This paper demonstrates the enhanced electrochemical behavior of Ni‐rich material LiNi0.8Co0.1Mn0.1O2 (NCM811) coated with a thin ZrO2 layer. The coating is produced by an easy and scalable wet chemical approach followed by annealing the material at ≥700 °C under oxygen that results in Zr doping. It is established that some ZrO2 remains even after annealing at ≥800 °C as a surface layer on NCM811. The main finding of this work is the enhanced cycling stability and lower impedance of the coated/doped NCM811 that can be attributed to a synergetic effect of the ZrO2 coating in combination with a zirconium doping.

Ni-rich Li-based layered Ni, Co, and Mn (NCM) materials have shown tremendous promise in recent years as positive electrode materials for Li-ion batteries. This is evident as companies developing batteries for electrical vehicles are currently commercializing these materials. Despite the considerable research performed on LiNiαCoβMnγO2 systems, we do not yet have a complete atomic level understanding of these materials. In this work we study the cationic ordering, thermodynamics, and diffusion kinetics of LiNi0.5Co0.2Mn0.3O2 (NCM-523). Initially, we show that cationic ordering can be predicted employing cheap atomistic simulations, instead of using expensive first-principles methods. Subsequently, we investigate the electrochemical, thermodynamic and kinetic properties of NCM-523 using density functional theory (DFT). Our results demonstrate the importance of including dispersion corrections to standard first principles functionals in order to correctly predict the lattice parameters of layered cathode materials. We also demonstrate that a careful choice of computational protocol is essential to reproduce the experimental intercalation potential trends observed in the LiNi0.5Co0.2Mn0.3O2 electrodes. Analysis of the electronic structure confirms an active role of Ni in the electrochemical redox process. Moreover, we confirm the experimental finding that on complete delithiation, this material remains in an O3 phase, unlike LiCoO2 and NCM-333. Finally, we study various pathways for the Li-ion diffusion in NCM-523, and pinpoint the preferred diffusion channel based on first principles simulations. Interestingly, we observe that the Li diffusion barrier in NCM-523 is lower than that in LiCoO2.

W-doping produced the two-phase (Fm3̄m and R3̄m) structure which improved the cycling and thermal stability of the Ni-rich layered cathodes.

Ni-rich lithiated layered oxides composed of Ni, Co, and Mn (NCMs) have shown tremendous promise as cathode materials in lithium-ion batteries (LIB) for electromobility applications. The capacity of these materials increases with nickel content, but there is a concomitant decrease in stability and stable operating voltage during cycling. Hence, it is of great importance to probe ways to increase the nickel content without sacrificing other important aspects. In this study, we performed a detailed comparative theoretical study of Ni-rich NCMs to advance our understanding of the cycling and thermal stability. On the basis of extensive analysis of density of states, magnetic structure, bond covalency, molecular orbital diagrams, Bader atomic charges, and oxygen binding energies, we draw several crucial conclusions: as the NCM materials become increasingly rich in Ni, (1) the amount of high-valence Ni-ions increases (i.e., N 3+ , Ni 4+ ), (2) Ni 4+ ions are readily reduced due to a low-lying LUMO, and hence can easily react with electrolyte species, (3) Ni 4+ -O bonds become increasingly covalent, and (4) molecular oxygen release becomes more feasible and, hence, may result in cathode degradation. Importantly, these conclusions are found to be appropriate also for the deintercalation process for all NCM materials and therefore also explain cycling behavior. On the basis of the current results, we suggest that a strategy of doping NCMs with highvalent cations, which suppresses Ni-ions in high oxidation states via charge compensation, should be adopted. These results will be beneficial for understanding and designing high capacity LIB cathodes for electric vehicles.

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.

Terpene cyclases catalyze the highly stereospecific molding of polyisoprenes into terpenes, which are precursors to most known natural compounds. The isoprenoids are formed via intricate chemical cascades employing rich, yet highly erratic, carbocation chemistry. It is currently not well understood how these biocatalysts achieve chemical control. Here, we illustrate the catalytic control exerted by trichodiene synthase, and in particular, we discover two features that could be general catalytic tools adopted by other terpenoid cyclases. First, to avoid formation of byproducts, the enzyme raises the energy of bisabolyl carbocation, which is a general mechanistic branching point in many sesquiterpene cyclases, resulting in an essentially concerted cyclization cascade. Second, we identify a sulfur–carbocation dative bonding interaction that anchors the bisabolyl cation in a reactive conformation, avoiding tumbling and premature deprotonation. Specifically, Met73 acts as a chameleon, shifting from an initial sulfur–π interaction in the Michaelis complex to a sulfur–carbocation complex during catalysis.

This paper is dedicated to studies of the electrochemical behavior, the structural and thermal features of the Ni-rich LiNi 0.5 Co 0.2 Mn 0.3 O 2 undoped and Al-doped (∼0.01 at.%) materials for positive electrodes of lithium batteries. We have found that structural characteristics of these materials are quite similar from the crystallographic point of view. It was demonstrated that Al substitution in the doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 is preferred at Ni sites over Co sites, and the thermodynamic preference for Al 3+ substitutions follows the order: Ni>Co>Mn. The lower capacity fading of the Al-doped electrodes upon cycling and aging of the cells in a charged state (4.3 V) at 60 • C, as well as more stable mean voltage behavior, are likely due to the chemical and structural modifications of the electrode/solution interface. The Al-doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 electrodes demonstrate also lower resistances of the surface film and charge-transfer as well as lower activation energies for the discharge process. From XPS studies we conclude that the modified stable and less resistive interface on the Al-doped particles comprises the Li + -ion conducting nano-sized centers like LiAlO 2 , AlF 3 , etc., which promote, to some extent, the Li + ionic transport to the bulk. A partial layered-to-spinel transformation was established upon cycling of LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathodes.One of the major challenges in lithium batteries technology is, undoubtedly, the further improvement of battery components -electrodes, solutions, and separators. 1-7 Among several modern strategies to improve electrochemical performance and structural characteristics of materials for positive electrodes, doping has attracted the attention of scientists over the years. This is due to the effectiveness of dopants in stabilizing the structure of materials (even in minute amounts) and thus to increase the electrochemical cycling activity and to diminish the heat evolution of the electrodes in a charged state. A variety of dopant ions, like Co 2+ , Al 3+ , Ti 4+ , Zr 4+ , Zn 2+ , Fe 3+ , Cu 2+ , and Cr 3+ , has been used to improve the stability, morphology and microstructure of cathode materials, to enhance the electrode cycleability and rate capability, and to reduce capacity fading upon cycling. 8-13 For instance, doping of LiNi 0.5 Mn 0.5 O 2 with Co, Al, Ti resulted in decrease of the irreversible capacity loss and in almost no capacity fading of the doped electrodes. 14,15 In a systematic study of the Al-doped Ni-rich electrodes (LiNi 0.8 Co 0.15 Al 0.05 O 2 ), which are promising materials for use in batteries for electromotive applications, the authors have shown high cycling stability of these electrodes upon accelerated testing. 16 Several other doping metals, such as silver, magnesium, cobalt, gallium, lanthanum, bismuth, 17-19 as well as non-metallic ions (boron, fluorine), 20,21 were also explored in an attempt to increase the electrochemical cycling behavior of cathodes (both of layered and spinel structures) and to reduce their in...