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For Li-ion batteries, AlF3 coating has been known to modify the over-lithiated layered oxide (OLO) cathodes to produce stable cathodes, but during synthesis procedure, the environment of excess amount of Li metal and free-exposed oxygen may cause the formation of Al2O3 and LiF materials, separately. We investigated the possibility of separated coating formation of Al as Al2O3 and F as LiF from AlF3 using density functional theory calculation, which suggests a favorable binding affinity of both Al2O3 and LiF phases to the OLO surface to support the preferable formation of coating layer of Al2O3 and LiF. Meanwhile, we found the well-distributed surface modification with the coating layers and a small amount of AlF3 (

To meet the requirement of large-scale simulation technics for Li-ion battery electrode materials, we introduce the charge-transfer modified embedded-atom method (CT-MEAM) in which the complex nature of the chemical bonding in transition metal (TM) oxides is described as a balance between metallic/covalent and ionic contributions by MEAM and a variable-charge model, respectively. The method is applied to Li 2 MnO 3 , and the parameterization is performed through fitting the energy–strain curves of Li 2 MnO 3 under uniaxial, biaxial and hydrostatic strains to a training set from ab initio density-functional theory calculations. The CT-MEAM prediction of the critical physical properties such as charge states and redox potentials match quite well with the ab initio results in various Li–Mn–O compounds beyond Li 2 MnO 3 . The constructed Li–Mn–O phase diagram is also qualitatively consistent with the ab initio reference work. The excellent transferability ensures use of the present method for a wide range of oxidation states in complex ternary TM oxides. Therefore, it will facilitate large-scale atomistic calculations required for the optimal design of many TM oxide applications including lithium-ion battery cathode materials.

Doping is the most common strategy to suppress the intrinsic structural instability of several families of cathode materials, thus improving their electrochemical performance. During the electrode synthesis, the dopants have a low probability to occupy cationic Li sites, but it is well-known that, during the normal operation of the battery, such probability increases via inter- or intralayer diffusion. In this work, we investigate the effect of 10 Li-site cationic dopants (Mg, Ti, V, Nb, Fe, Ru, Co, Ni, Cu, Al) on the electrochemical properties of Li2MnO3 and LiMnO2 cathode materials using density functional theory. Our results show that, although Mn sites are thermodynamically favorable over Li-site doping, the small thermodynamic barriers between both configurations can be easily overcome during the material synthesis and/or the extraction/insertion of Li during the cycling process of the battery. Also, due to charge balance and diffusion channel opening, some of the Li-site dopants were found to act as...

Thermal stability is one of the critical requirements for commercial operation of high energy lithium-ion batteries. In this study, we use in situ X-ray diffraction technique to elucidate the thermal degradation mechanism of 0.5Li 2 MnO 3 -0.5LiNi 0.33 Co 0.33 Mn 0.33 O 2 lithium rich cathode material in the absence and presence of electrolyte to simulate the real life battery conditions and compare its thermal behavior with the commercial LiNi 0.33 Co 0.33 Mn 0.33 O 2 cathode material. We show that the thermal induced phase transformations in delithiated lithium rich cathode material are much more intense compared to similar single phase layered cathode material in the presence of electrolyte. The structural changes in both cathode materials with the temperature rise follow different trends in the absence and presence of electrolyte between 25 and 600 °C. Phase transitions are comparatively simple in the absence of electrolyte, the fully charged lithium rich cathode material demonstrates better thermal stability by maintaining its phase till 379 °C, and afterwards spinel structure is formed. In the presence of electrolyte, however, the spinel structure appears at 207 °C, subsequently it transforms to rock salt type cubic phase at 425 °C with additional metallic, metal fluoride, and metal carbonate phases.

Due to a high voltage of 4.6 V and large practical capacity of ~260 mAh/g, the over-lithiated-oxides (OLOs) which are often represented as Li2MnO3·LiMO2 (M = Mn, Co, Ni), have been intensely investigated as a promising candidate of the next generation cathode materials for Li-ion battery. The Li2MnO3 composite structure plays an important role in providing high capacity and phase stability to the system. However, during cathode charge-discharge operation, Li2MnO3 is unstable and partly transforms into LiMnO2, indicating that the phase used in practice has mixed both Li2MnO3 and LiMnO2. In this work, the effects of Li-site doping from 10 cationic dopants (Mg, Ti, V, Nb, Fe, Ru, Co, Ni, Cu, Al) on the electrochemical properties of both oxides are studied using density functional theory. The calculations show that, comparing with the Mn-site doped phases, Li-site doping is thermodynamically unstable for the ground states, but the small transition barriers can be easily overcome under high thermal fluctuations during the realistic cathode synthesis process. The redox potentials of both oxides can be lowered by most of the Li-site dopants. For example, Nb strongly lowers the redox potential of the LiMnO2 phase, and Ru shows an unexpected effect on the Li2MnO3 phase: it activates the Li atoms in the Li-layer and, at the same time, it immobilizes the Li atoms in the Li-Mn mixed-layer by increasing the redox potential. These results support the experimental observations about Li-site doping and provide an explanation about the effects of Li-site doping on the electrochemical properties.

Electrochemically active Li 2 MnO 3 nanoparticle dispersed on carbon nanotube (CNT) network has been successfully synthesized by microwave-assisted hydrothermal (MAH) process. To the best of our knowledge, this is the first report showing the formation of Li 2 MnO 3 nanoparticle on CNT network using MnO 2 -coated CNT composite. Appearance of superlattice peak in X-ray diffraction (XRD) pattern and Raman-active modes near the lower wavelength region of Raman spectra reveals the structure transition from spinel LiMn 2 O 4 to layered-type Li 2 MnO 3 phase. The X-ray absorption near edge spectra (XANES) shows increase in average oxidation state of Mn ion from 3.5+ to 4+, and Mn–O and Mn–Mn peak intensity variations observed from extended X-ray absorption fine structure (EXAFS) are well evidenced for the formation of ordered Li 2 MnO 3 structure. Electrochemical performance of Li 2 MnO 3 nanocomposite electrode material prepared from higher LiOH concentration shows much higher capacity than spinel component alone. This synthetic strategy opens a new way for effective synthesis of electrochemically active Li 2 MnO 3 on CNT network, making it suitable for advanced lithium ion battery.

Direct internal pressure measurements of the cylindrical Li-ion cells with a mixture of LiCoO 2 and Li 1.167 Ni 0.233 Co 0.1 Mn 0.467 Mo 0.033 O 2 (a solid solution between 0.4 Li 2 Mn 0.8 Ni 0.1 Mo 0.1 O 3 and 0.6 LiNi 0.4 Co 0.2 Mn 0.4 O 2 ) as cathode and graphite as anode have been performed during cell charging. Cell internal pressure at the end of charging is greatly reduced from 2.85 to 0.84–1.84 bar by adding a small amount of phosphorus derivatives such as triphenyl phosphine (TPP), ethyl diphenylphosphinite (EDP), and triethyl phosphite (TEP) into a carbonate-based electrolyte. The phosphorus derivatives are supposed to react with O 2 generated from the decomposition of the Li 2 MnO 3 component. The chemical states of additive molecules before and after the charging process have been characterized with a nuclear magnetic resonance (NMR) spectroscopy and gas chromatography–mass spectrometry (GC–MS). It has also been shown that those additives improve the cycle life when applied in coin full cells.

The real time detection of quantitative oxygen release from the cathode is performed by in-situ Gas Chromatography as a tool to not only determine the amount of oxygen release from a lithium-ion cell but also to address the safety concerns. This in-situ gas chromatography technique monitoring the gas evolution during electrochemical reaction presents opportunities to clearly understand the effect of surface modification and predict on the cathode stability. The oxide cathode, 0.5Li2MnO3∙0.5LiNi0.4Co0.2Mn0.4O2, surface modified by amorphous cobalt-phosphate nanoparticles (a-CoPO4) is prepared by a simple co-precipitation reaction followed by a mild heat treatment. The presence of a 40 nm thick a-CoPO4 coating layer wrapping the oxide powders is confirmed by electron microscopy. The electrochemical measurements reveal that the a-CoPO4 coated overlithiated layered oxide cathode shows better performances than the pristine counterpart. The enhanced performance of the surface modified oxide is attributed to the uniformly coated Co-P-O layer facilitating the suppression of O2 evolution and offering potential lithium host sites. Further, the formation of a stable SEI layer protecting electrolyte decomposition also contributes to enhanced stabilities with lesser voltage decay. The in-situ gas chromatography technique to study electrode safety offers opportunities to investigate the safety issues of a variety of nanostructured electrodes.