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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...

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.

We combine electromechanical measurements with ab initio density-functional calculations to settle the controversy about the origin of torsion-induced conductance oscillations in multiwall carbon nanotubes. Contrary to intuition, the observed oscillation period in multiwall tubes exhibits the same inverse-squared diameter dependence as in single-wall tubes with the same diameter. This finding suggests an intrawall origin of the oscillations and an effective electronic decoupling of the walls, which we confirm in calculations of multiwall nanotubes subject to differential torsion. We exclude the alternative origin of the conductance oscillations due to changes in the interwall registry, which would result in a different diameter dependence of the oscillation period.

Aluminum doped mixed metal oxides are popular positive electrode materials for Li-ion batteries. They are used extensively in many applications, yet their operation and limitations are not entirely understood. This work shows the advantage of using solid-state 7Li and 27Al NMR for monitoring the electrochemical properties of the doped nickel–cobalt oxide cathode material, LiNi0.8Co0.15Al0.05O2 (NCA), particularly during the first few charge/discharge cycles. The changes in the state of the material as lithium ions are intercalated and deintercalated during discharge and charge, respectively, are highlighted via the Li nuclei as a dynamic reporter and the Al nuclei as a static, material-embedded reporter. In particular, the NMR view of the cyclic change of Ni ions between paramagnetic and diamagnetic oxidation states is enhanced by monitoring both nuclei. Two protocols of cycling the NCA electrode are compared: one employing a smaller voltage window, cycled against graphite as anode, and one using a wider voltage window, cycled against a lithium metal anode. The NMR analysis unveils notable differences in the reversibility of the changes in the Ni oxidation states as charge carriers are shuttled in and out of the cathode material. The 27Al NMR data of the pristine material shows the existence of at least two distinct configurations of Ni ions around the Al dopant ions, suggesting coexistence of two disparate phases, which remain intact upon cycling. The protocol employing slower cycling versus Li anode delivers better cathode performance in the sense that more extensive relithiation occurs, and here, it is shown that the return of the local environments to their pristine electronic configurations is more complete. The 27Al and 7Li NMR results are integrated into a simple scheme exemplifying how better understanding of the local electronic changes in paramagnetic electrode materials can be captured in simple progressive plots.

In this paper, we studied the influence of LiAlO 2 coatings of 0.5, 1 and 2 nm thickness prepared by Atomic Layer Deposition onto LiNi 0.8 Co 0.15 Al 0.05 O 2 electrodes, on their electrochemical behavior at 30 and 60 • C. It was demonstrated that upon cycling, 2 nm LiAlO 2 coated electrodes displayed ∼3 times lower capacity fading and lower voltage hysteresis comparing to bare electrodes. We established a correlation among the thickness of the LiAlO 2 coating and parameters of the self-discharge processes at 30 and 60 • C. Significant results on the elevated temperature cycling and aging of bare and LiAlO 2 coated electrodes at 4.3 V were obtained and analyzed for the first time. By analyzing of X-ray diffraction patterns of bare and 2 nm coated LiNi 0.8 Co 0.15 Al 0.05 O 2 electrodes after cycling, we concluded that cycled materials preserved their original structure described by R-3m space group and no additional phases were detected. The lithium-ion batteries (LIB) market nowadays has expanded widely from cellular phones, computers and other electronic devices to the automotive industry. Positive electrodes for LIBs to be explored in electric vehicles are mainly based on lithiated transition-metal oxides comprising Ni, Co and Mn (LiNi y Co x Mn 1-y-x O 2 ) and designated as NCM.1,2 They have attracted much attention as promising materials and therefore many research projects have been dedicated to them in the past 20 years. [3][4][5][6][7][8][9][10][11][12][13] In studies of LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333) cathodes, it was demonstrated 4-6 that they provided a capacity of 200 mAh/g in the voltage range of 2.5-4.6 V, or ∼155 mAh/g if the cutoff voltage is limited by 4.3 V.7 A substantially improved high-voltage performance of NCM333 electrodes (up to 4.6 V) was achieved by introducing tris(2,2,2-trifluoroethyl) borate additive in the electrolyte solution.8 These authors suggest that the additive takes part in the formation of the solid-electrolyte interface by lowering and stabilization of the interfacial resistance. NCM333 and NCM424 materials were studied in our group from the viewpoint of their electrochemical behavior, aging mechanisms, thermal properties, and surface chemistry developed upon cycling in ethylene carbonate-dimethyl carbonate/LiPF 6 based solutions.9 LiNi y Co x Mn 1-y-x O 2 materials with higher Ni content (y > 5) are important due to high capacity that can be extracted by charging up to 4.3 V only. However, Ni-rich NCMs suffer from their low cycling stability especially for compositions with Ni ≥ 60%, severe capacity fading and impedance increase during cycling at elevated temperatures (e.g. 45• C). One of the effective ways to stabilize the structure of NCM materials, to increase cycling activity and to diminish the heat evolution of the electrodes in a charged 14 There is a consensus in the literature that the above drawbacks originate from the unstable Ni 4+ ions developed in the charge state (high anodic potential, most Li + extracted from NCA). These Ni-ions can be readily reduce...

In this presentation, we report on studies of novel positive electrode materials for lithium-ion batteries with the main emphasis on their structural and surface modifications by cation doping and coating. We have chosen three families of materials: Li- and Mn-rich high-energy density and high capacity (HE-NCM)(1), Ni-rich layered materials Li[NixCoMn]O2 (x>0.5),(2) and gradient materials of the general formulae of LiNi0.65Co0.08Mn0.27O2 . Al3+ and other cations as dopants(3) and salts such as AlF3 as  coating materials were studied(4). We have demonstrated the impact of a minor level of Al-doping on the electrochemical characteristics of LiNi0.5Co0.2Mn0.3O2 electrodes and on the interfacial reactions.(4) We propose that the lower capacity fading of the Al-doped electrodes upon aging of the cells in a charged state (4.3 V) at 60 0C in comparison with their undoped counterparts, as well as more stable mean voltage behavior, are likely due to the chemical and structural modifications of the electrode/solution interface. The lower electrochemical impedance of Al-doped LiNi0.5Co0.2Mn0.3O2 electrodes can be explained by more stable surface chemistry developed on the doped particles due to the interfacial reactions of the dopant in Al3+ enriched surface layer (“segregated” aluminum) with an EC-EMC/LiPF6 solution. The modified interface on the Al-doped particles is less resistive and comprises the Li+-ion conducting nano-sized centers like AlF3, which promote Li+ ionic transport to the bulk.             Furthermore, we present our recent results on the study of Ni-rich, layered-structure LiNi0.65Co0.08Mn0.27O2 cathode materials and compare their electrochemical performance with materials of the same overall composition, but with a concentration gradient throughout the particles. The gradient was organized as follows: the Ni concentration is higher at the center of the particles but lower at surface, while the Mn concentration is higher at the surface and lower at the center. The synthesis parameters of the co-precipitation method were optimized comparing annealing periods, followed by electrochemical testing. Three different sets of gradient and standard non-gradient materials were explored, and all gradient materials provided superior capacity and rate capability than their respective non-gradient materials. The reasons for the improved discharge capacity of the gradient materials at moderate temperatures and cut-off potentials were explored through impedance spectroscopy and post-mortem characterization. The Mn-rich surface of the gradient material limits the growth of too resistive surface films during cycling, even at extreme temperatures and potentials, improving stability of these cathode materials. The evolution of the gradient structure was examined via TEM and EDX of FIB-produced particle cross-sections. We have established that prolonged cycling, even at elevated temperatures, did not change the initial concentration profiles determined by the synthesis. Transition metal ion dissolution from the cathode was confirmed via ICP of dissolved Li metal anodes, showing a greater degree of Mn dissolution from the non-gradient materials, possibly due to nickel-manganese segregation tendencies. This greater degree of Mn dissolution from non-gradient materials was confirmed in EDX of cycled particles. Electron diffraction measurements of these cycled particles show that spinel formation during cycling of the gradient materials is limited or even eliminated likely due to the higher concentration of Ni in the bulk of the gradient materials opposed to the non-gradient materials. Finally, we demonstrate long-term, (>1000 cycles) experiments of the gradient material electrodes vs. graphite electrodes in full cells that were performed in order to explore the practical advantage of these materials. 1.         P. K. Nayak, J. Grinblat, M. Levi, B. Markovsky and D. Aurbach, Journal of the Electrochemical Society, 161, A1534 (2014). 2.         C. Ghanty, B. Markovsky, E. M. Erickson, M. Talianker, O. Haik, Y. Tal-Yossef, A. Mor, D. Aurbach, J. Lampert, A. Volkov, J.-Y. Shin, A. Garsuch, F. F. Chesneau and C. Erk, Chemelectrochem, 2, 1479 (2015). 3.         D. Aurbach, O. Srur-Lavi, C. Ghanty, M. Dixit, O. Haik, M. Talianker, Y. Grinblat, N. Leifer, R. Lavi, D. T. Major, G. Goobes, E. Zinigrad, E. M. Erickson, M. Kosa, B. Markovsky, J. Lampert, A. Volkov, J.-Y. Shin and A. Garsuch, Journal of the Electrochemical Society, 162, A1014 (2015). 4.         F. Amalraj, M. Talianker, B. Markovsky, L. Burlaka, N. Leifer, G. Goobes, E. M. Erickson, O. Haik, J. Grinblat, E. Zinigrad, D. Aurbach, J. K. Lampert, J.-Y. Shin, M. Schulz-Dobrick and A. Garsuch, Journal of the Electrochemical Society, 160, A2220 (2013).