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

We report herein on the synthesis of “layered-layered” integrated xLi2MnO3⋅(1−x)LiMn1/3Ni1/3Co1/3normalO2 materials ( x=0.3 , 0.5, and 0.7) using the self-combustion reaction in solutions containing metal nitrates and sucrose. The nanoparticles of these materials were obtained by further annealing of the as-prepared product in air at 700°C for 1 h and submicrometric particles were obtained by further annealing at 900°C for 22 h. The effect of composition on the electrochemical performance was explored in this work. By a rigorous study with high resolution transmission electron microscopy (HRTEM), it became clear that the syntheses with the above stoichiometries produce two-phase materials comprising nanodomains of both rhombohedral LiNiO2 -like and monoclinic Li2MnO3 structures, which are closely integrated and interconnected with one another at the atomic level. Stable reversible capacities ∼220mAh/g were obtained with composite electrodes containing submicrometer particles of 0.5Li2MnO3⋅0.5LiMn1/3Ni1/3Co1/3normalO2 . Structural aspects, activation of the monoclinic component, and stabilization mechanisms are thoroughly discussed using Raman spectroscopy, solid-state NMR, HRTEM, and X-ray diffraction (including Rietveld analysis) in conjunction with electrochemical measurements. This work provides a further indication that this family of integrated compounds contains the most promising cathode materials for high energy density Li-ion batteries.

We investigated the structural characteristics of Li-rich xLi2MnO3·(1-x)Li[MnyNizCow]O2 cathode material (x around 0.5, y:z:w around 2:2:1) and its electrochemical performance in lithium cells at 30 and 60°C. It was established that nanoparticles of the xLi2MnO3·(1-x)Li[MnyNizCow]O2 compound are intergrown on the nano-scale and are built of thin plates of 40–50 Å. We demonstrated that xLi2MnO3·(1-x)Li[MnyNizCow]O2 electrodes exhibited at 60°C high capacities of ∼270 and ∼220 mAh/g at 1C and 2C rates, respectively. They can be cycled effectively at 30 and 60°C providing capacity ∼250 mAh/g in the initial cycles, but it fades upon prolonged cycling due, to some extent, to increasing the electrode impedance (charge-transfer resistance) especially at the elevated temperature. The effective chemical diffusion coefficient of Li+ in these electrodes measured during charge to 4.7 V by potentiostatic intermittent titration technique (PITT) was found to be ∼10−10 cm2/s. From convergent beam electron diffraction and Raman spectroscopy studies we established, for the first time, that partial structural transition from layered-type to spinel-type ordering in xLi2MnO3·(1-x)Li[MnyNizCow]O2 electrodes occurred in the initial charge to 4.7 V and even at the early stages of charging at 4.1 V–4.4 V. The thermal behavior of the xLi2MnO3·(1-x)Li[MnyNizCow]O2 material and electrodes are also discussed.

We report herein on the study of Li and Mn rich Lix[MnNiCo]O2 cathode materials with an emphasis on the effect of AlF3 coating on their electrochemical performance. The initial stoichiometry of these materials was xLi2MnO3.(1-x)LiMnyNizCowO2 where x is in the range 0.4-0.5 and the y:z:w ratio was as we previously reported. Their structure was considered on the basis of two-components model, namely monoclinic Li2MnO3 (C2/m) and rhombohedral LiMO2 (R-3m) (M = Mn, Ni, Co) that are structurally compatible and closely integrated phases. Based on TEM studies we concluded that the coating had a crystalline tetragonal structure t-AlF3 (P4nmm symmetry) and AlF3 nano-crystals were regularly distributed over the particles surface. Amorphous clusters of AlF3 and/or other Al-containing species, like AlFxOy, Al[FOH], etc. may also present, as it follows from solid-state NMR measurements. It was shown that electrodes comprising the AlF3-coated material exhibited higher reversible capacities of ∼250 mAh/g at a C/5 rate, more stable cycling behavior, higher lithium storage capability at 60°C, and lower impedance measured during Li-deinteraclation comparing to electrodes prepared from the uncoated material. An important finding is that Lix[MnNiCo]O2 /AlF3 materials revealed much higher thermal stability both in the pristine (lithiated) and cycled (delithiated) states than their uncoated counterparts.

We report on the behavior of nanometric LiMn1/3Ni1/3Co1/3normalO2 (LiMNC) as a cathode material for Li-ion batteries in comparison with the same material with submicrometric particles. The LiMNC material was produced by a self-combustion reaction, and the particle size was controlled by the temperature and duration of the follow-up calcination step. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, Raman spectroscopy, electron paramagnetic resonance, inductively coupled plasma, and atomic force microscopy were used in conjunction with standard electrochemical techniques (cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) for characterizing the electrode materials. The effect of cycling and aging at 60°C was also explored. Nanomaterials are much more reactive in standard electrolyte solutions than LiMNC with a submicrometric particle. They develop surface films that impede their electrochemical response, while their bulk structure remains stable during aging and cycling at elevated temperatures. The use of nanomaterials in Li-ion batteries is discussed.

We studied the electrochemical behavior of aluminum electrodes in solutions comprising ethylene carbonate (EC)–dimethyl carbonate (DMC) and lithium salts: lithium hexafluorophospate (LiPF6) , lithium perchlorate (LiClO4) , or lithium bis(oxalato)borate (LiBOB). Under anodic polarization within the potential range of 3.00–4.00 V in these solutions, aluminum electrodes demonstrate a stable behavior due to their passivation by surface films. Aluminum electrodes passivate in EC–DMC/ LiPF6 and EC–DMC/LiBOB solutions both at 30 and 60°C , whereas these electrodes remain active and corrode in EC–DMC/ LiClO4 solutions. LiBOB may decompose at anodic potentials, thus forming passive films comprising normalB2normalO3 and metal-oxalate species on the aluminum electrodes polarized to 4.50–5.30 V. Li2CO3 , LiF and AlPO4 , and LiCl species were also detected on the electrodes anodically polarized in LiBOB-, LiPF6 -, and LiClO4 -containing solutions, respectively. At some conditions, current oscillations can be developed on aluminum electrodes upon their polarization at constant potentials. These oscillations may relate to the successive formation and dissolution of the passivating surface films formed on electrodes. The development of normalF2P(=O)normalO− species due to the polarization of aluminum electrodes in EC–DMC/ LiPF6 solutions was confirmed by solution NMR studies.

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