In this study we demonstrate a cheap and sustainable ammonothermal approach towards nitrogen-doped porous carbons. Sodium borate (borax) is employed as a catalyst during the synthesis resulting in the formation of small interconnected primary particles of <100 nm in size. Microporosity is created in these nitrogen-doped, ammonothermal carbon samples by a synchronous activation and post carbonization procedure at 850 °C, while the interconnected primary particles offer larger interstitial void spaces including mesopores. Variation of the starting ammonia concentration allows for the facile adjustment of the final nitrogen content, reaching up to 7 wt.% after post carbonization. Electrochemical characterization is carried out in two and three electrode modes by means of cyclic voltammetry and galvanostatic cycling at different scan rates and current densities, respectively. The sample prepared at a high glucose-to-ammonia ratio shows high specific capacitance of 185 and 144 F g−1 at 0.2 and 20 A g−1, respectively (271 F g−1 in a three electrode mode at 1 A g−1). All samples demonstrate a very stable capacitance over the tested 5000 cycles at 10 A g−1 with no degradation and an excellent coulombic efficiency of >99%. Comparison of different pore systems indicates that a continuous pore size distribution may explain improved rate performances.

Ni-rich materials of layered structure LiNixCoyMnzO2 , x > 0.5, are promising candidates as cathodes in high-energy-density Li-ion batteries for electric vehicles. The structural and cycling stability of Ni-rich cathodes can be remarkably improved by doping with a small amount of extrinsic multivalent cations. In this study, we examine development of a fast screening methodology for doping LiNi0.8Co0.1Mn0.1O2 with cations Mg2+, A(13+), Si4+, Ti4+, zr(4+), and Ta5+ by a "top-down" approach. The cathode material is coated by a precursor layer that contains the dopant, which then is introduced into the particles by diffusion during heat treatment at elevated temperatures. The methodology described herein can be applied to Ni-rich cathode materials and allows relatively easy and prompt identification of the most promising dopants. Then further optimization work can lead to development of high-capacity stable cathode materials. The present study marks Ta5+ cations as very promising dopants for Ni-rich NCM cathodes.

Beside the development of novel cathode materials with higher capacity and cyclability, the optimization of commercial used materials are necessary as well. Therefore the materials, as spinels, olivines or layered oxides can be modified to improve their electrochemical performance. Two promising technologies for material modification are doping or coating. Both approaches are introduced and explain by examples.

Mild fluorination of high-energy nickel-cobalt-manganese (HE-NCM) materials with low pressures of elementary fluorine gas (F-2) at room temperature was systematically studied. The fluorinated HE-NCM samples were analysed by ion chromatography, inductively coupled plasma mass spectrometry, FT-IR spectroscopy, powder X-ray diffraction, magic angle spinning NMR spectroscopy, scanning electron microscopy, thermo-gravimetric analysis, differential thermal analysis, electrochemical testing, and X-ray photoelectron spectroscopy. The treatment of the cathode materials with low pressures (a few hundred mbar) of elementary fluorine gas at room temperature led to the elimination of the basic surface film (LiOH, Li2CO3, Li2O, etc.), and the resulting thin amorphous LiF film led to increased capacity and long-term stability of the battery. Impedance built-up was greatly reduced for these systems throughout cycling. Fluorination with F-2 only causes the formation of O-Me-F bonds (Me=Transition Metal), when treated with F-2 at higher pressures. If O-Me-F bonds are formed, it may be detrimental to the electrode surface film resistance and cycle stability of the electrodes. However, it may be that the LiF surface content, which can expand as long as the LiMeO2 structure can be oxidized and Li+ can be extracted, has become too large and thus detrimental. Considering the evolution of differential capacity plots and taking into account the thermodynamic driving force of the F-2 treatment, it is likely that the same activation processes that occur electrochemically in Li-rich materials also occur chemically, when the material is exposed to F-2. Differential capacity plots show enhanced Mn4+ reduction peaks upon lithiation, when the material was exposed to F-2, only possible after activation of the Li2MnO3 phase. For this reason, we believe fluorination promotes to some extent an activation of this phase.

Li and Mn-rich layered oxides, xLi(2)MnO(3)(1-x)LiMO2 (M=Ni, Mn, Co), are promising cathode materials for Li-ion batteries because of their high specific capacity that can exceed 250 mA h g(-1). However, these materials suffer from high 1(st) cycle irreversible capacity, gradual capacity fading, low rate capability, a substantial charge-discharge voltage hysteresis, and a large average discharge voltage decay during cycling. The latter detrimental phenomenon is ascribed to irreversible structural transformations upon cycling of these cathodes related to potentials 4.5 V required for their charging. Transition metal inactivation along with impedance increase and partial layered-to-spinel transformation during cycling are possible reasons for the detrimental voltage fade. Doping of Li, Mn-rich materials by Na, Mg, Al, Fe, Co, Ru, etc. is useful for stabilizing capacity and mitigating the discharge-voltage decay of xLi(2)MnO(3)(1-x)LiMO2 electrodes. Surface modifications by thin coatings of Al2O3, V2O5, AlF3, AlPO4, etc. or by gas treatment (for instance, by NH3) can also enhance voltage and capacity stability during cycling. This paper describes the recent literature results and ongoing efforts from our groups to improve the performance of Li, Mn-rich materials. Focus is also on preparation of cobalt-free cathodes, which are integrated layered-spinel materials with high reversible capacity and stable performance.

Li-rich cathode materials of the formula xLi(2)MnO(3)center dot yLiNi(a)Co(b)Mn(c)O(2) (x + y = 1, a + b + c = 1) boast very high discharge capacity, ca. 250 mAh/g. Yet, they suffer capacity decrease and average voltage fade during cycling in Li-ion batteries that prohibit their commercialization. Treatment of the materials with NH3(g) at high temperatures produces improved electrodes with higher stability of capacity and average voltage. The present study follows the changes occurring in the materials upon treatment with ammonia gas, through Li-6 and Li-7 solid-state NMR investigations of the untreated and ammonia treated 0.35Li(2)MnO(3)center dot 0.65LiNi(0.35)Mn(0.45)Co(0.20)O(2) as well as its constituent phases, Li2MnO3 and LiNi0.4Co0.2Mn0.4O2. The NMR analysis demonstrates the biphasic nature of these materials. Furthermore, it shows that the Li2MnO3 component phase in the integrated material is the phase mostly being affected by the gas treatment. A thickening of a protective surface film in the integrated material, with the right exposure time to the reactive gas, is observed, which further precludes Ni leach out from the bulk and leads to improved electrode performance. Formation of minor electrochemically inactive oxide phases in the integrated material and similarly in the Li2MnO3 alone upon longer exposure to the gas suggests that the performance deterioration observed can be linked to the rearrangement of ions in the Li2MnO3 constituent phase in the integrated material.

This presentation summarizes the recent studies in Bar-Ilan University of materials for positive electrodes of Li-ion batteries. The materials included lithiated oxides of Ni-based family Li[Ni-Co-Mn]O2 (layered, R-3m space group) and of Li,Mn-rich layered-layered xLi2MnO3 .(1-x)LiMO2 (M=Ni, Co, Mn), 03+, Zr4+ of the above materials in relation to the electrode behavior, structural stability, and thermal reactions [1, 2]. For Li[Ni0.5Co0.2Mn0.3]O2 materials, using density functional theory calculations, we have shown that Al3+ doping is preferred at Ni sites and the thermodynamic preference follows the order: Ni>Co>Mn. It was concluded from XPS studies that the modified stable and less resistive interface on the Al-doped particles comprised the Li+-ion conducting centers like LiAlO2, AlF3, etc., which promote, to some extent, the Li+ transport to the bulk and therefore facilitate the electrochemical reactions [2]. We discuss also the following issues: ab-initio calculations of the preferential substitution of Zr4+ at Mn, Co or Ni sites; influence of Zr4+ and Mo6+ ions on the Li+/Ni2+ mixing, charge distribution, the lattice constants, as well as partial layered-to-spinel structural transformation and thermal characteristics of cathode materials in reactions with solutions. In case of Li,Mn-rich cathode materials, we used thin surface coatings, as well as gas treatment with ammonia at 400 °C to stabilize these materials. The AlF3-coated electrodes exhibit stable charge-discharge behavior providing higher capacities and lower fade upon prolonged cycling at 60 °C. It has been found 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 oC, 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 [1]. Ammonia treatment of Li,Mn-rich materials for 2 h improves discharge capacity, lowers capacity and mean voltage fading during cycling. The mechanism of the ammonia treatment will be discussed. Further work will explore full cell studies with graphite anodes to confirm if NH3 treatment can indeed improve the likelihood of commercialization of the above materials [3]. Fig : 1 Discharge capacity of the electrodes comprising NH3-treated and untreated Li,Mn-rich 0.35Li2MnO3·0.65LiNi0.35Mn0.45Co0.20O2 materials. The treatment was performed for 1, 2 and 4 hours, as indicated. References : [1] S. F. Amalraj, M. Talianker, B. Markovsky et al. J. Electrochem. Soc. 160 (2013) A2220. [2] D. Aurbach, O. Srur-Lavi, C. Ghanty et al. J. Electrochem. Soc. 162 (2015) A1014. [3] Evan M. Erickson, Hadar Sclar, Florian Schipper, B. Markovsky et al., Adv. Energy Mater., 7, (2017) 1700708 Figure 1

One of the major hurdles of Ni-rich cathode materials Li1+x(NixCozMnz)(w)O-2, 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 degrees 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 degrees C under oxygen that results in Zr doping. It is established that some ZrO2 remains even after annealing at 800 degrees 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.

Electrodes prepared from lithium-rich (Li-rich) xLi(2)MnO(3) center dot (1-x) LiNiaCobMncO2 materials (a + b + c = 1) show extremely high discharge capacities, arising from excess Li+ present in their Li2MnO3 component, and the ability to reversibly store charge with O2- anions. These electrodes suffer serious voltage and capacity fading however, due to the migration of transition metals to the Li-layer at advanced states of charging, partial structural layered-to-spinel transformation and other reasons. In this focus paper, the current understanding of the above materials is summarized, briefly concluding with attempts by our groups to mitigate the voltage and capacity fade of these electrodes. (C) The Author(s) 2017. Published by ECS. All rights reserved.

Activation of Li-rich cathode materials at low-temperatures (0 or 15 °C) results in ∼10% higher discharge capacities than activation at 30 °C.

Li‐rich electrode materials of the family xLi2MnO3·(1−x)LiNiaCobMncO2 (a + b + c = 1) suffer a voltage fade upon cycling that limits their utilization in commercial batteries despite their extremely high discharge capacity, ≈250 mA h g−1. Li‐rich, 0.35Li2MnO3·0.65LiNi0.35Mn0.45Co0.20O2, is exposed to NH3 at 400 °C, producing materials with improved characteristics: enhanced electrode capacity and a limited average voltage fade during 100 cycles in half cells versus Li. Three main changes caused by NH3 treatment are established. First, a general bulk reduction of Co and Mn is observed via X‐ray photoelectron spectroscopy and X‐ray absorption near edge structure. Next, a structural rearrangement lowers the coordination number of CoO and MnO bonds, as well as formation of a surface spinel‐like structure. Additionally, Li+ removal from the bulk causes the formation of surface LiOH, Li2CO3, and Li2O. These structural and surface changes can enhance the voltage and capacity stability of the Li‐rich material electrodes after moderate NH3 treatment times of 1–2 h.

This research sheds light on the intriguing phenomena of structural transformations that take place in spinel LiMn2O4 (space group Fd3m) when charged to high anodic potentials (4.3 to 5.1 V) in lithium cells. It was established from the XRD and electron diffraction analyses that the orthorhombic o-LiMnO2 (space group Pnma) is formed due to the partial transformation of spinel starting at 4.7 V. The Raman spectroscopy measurements of the LiMn2O4 samples charged to 5.1 V also provided evidence of o-LiMnO2, although its band overlaps with the delithiated spinel species. An additional important finding is that some layered-type LiMnO2 is formed upon cycling of the spinel material to 4.5 V, even upon the first charge. LiMnO2 exists as a stable component of the solid electrolyte interphase developed on these electrodes. We also concluded the formation of the layered LiMnO2 structure via solid-state Li-7 NMR. The analysis of those results further indicated that the onset of the creation of the intermediate spinel-layered ("splayered") phase clearly takes place between 4.5 and 4.7 V.

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., N3+, Ni4+), (2) Ni4+ ions are readily reduced due to a low-lying LUMO, and hence can easily react with electrolyte species, (3) Ni4+-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 high-valent 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.

Amongst a number of different cathode materials, the layered nickel-rich LiNiyCoxMn1−y−xO2 and the integrated lithium-rich xLi2MnO3·(1 − x)Li[NiaCobMnc]O2 (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.

Lithium ion batteries have become an integral part of our daily lives. Among a number of different cathode materials nickel-rich LiNixCoyMnzO2 is particularly interesting. The material can deliver high capacities of similar to 195 mAh g(-1) putting it on the map for electric vehicles. With an increasing nickel content, a number of issues arise in the material limiting its performance. The Li/Ni mixing, highly reactive surface and formation of micro cracks are the most pressing ones. An overview of recent literature exploring these phenomena is herein summarized and were applicable solutions will be highlighted. (C) The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. All rights reserved.

Layered structure transition metal oxides of the form LiNixCoyMnzO2 (x + y + z = 1), are commercially available lithium ion battery materials that provide capacities of 140 – 200 mAhrg-1 over long lifetimes, ca. 3000 cycles with 80 % capacity retention. The composition of these materials can be used to tailor specific properties such as capacity, cycle life, low impedance, toxicity or cost. In order to enhance capacity and average operating voltage fade, Ni rich materials (x ≥ 0.65), can be used, but surface Ni-oxide and hydroxide moieties are highly alkaline, tending to react strongly with the standard electrolyte solutions, what limits the electrodes’ cycle life. One method to increase cycle life of electrodes, comprising Ni-rich material, is to synthesize materials with a low Ni surface content and high Ni concentration at the core. It is possible to synthesize Li[NiCoMn]O2 materials with Ni and Mn concentration gradients. Many different gradient variables may be explored, for example thickness of core and shell, differences between surface and bulk concentrations and the structure of the gradient, e.g. linear, exponential, single or multiphase. For our work, we have synthesized cathode materials utilizing the coprecipitation method, exploring first different annealing protocols to produce Ni-rich LiNi0.65Co0.08Mn0.27O2. After optimization of the annealing conditions, we have monitored the effect of metal chelation agent concentration on the electrochemical performance of the battery material. Then, we explore an even more nickel-rich gradient material, the LiNi0.7Co0.1Mn0.2O2, also introducing a two-phase gradient with two distinct Ni/Mn concentration slopes. The materials are cycled in both half cells (vs. Li) and full cells vs. graphite, to explore short term and long term effects, respectively. Electrochemical impedance spectroscopy is utilized to monitor the evolution of surface film impedance during cycling. High temperature (up to 60 oC) cycling and mean discharge voltage stability are studied, exhibiting the enhanced stabilizing effects of the Ni/Mn gradients. In addition, bulk and surface changes such as the alteration of the gradient structure after prolonged cycling is explored via TEM and electron diffraction measurements. The extent of transition metal ions dissolution is measured by chemical analysis of anodes, removed after cycling, on which the metals are partially reduced. Figure 1 depicts typical galvanostatic cycling results of LiNi0.65Co0.08Mn0.27O2 vs. graphite full cells at hard conditions: high rate and elevate temperature, demonstrating an advantage to the cathode material with gradient concentration. The entire study have proven that for Ni rich Li[NiCoMn]O2 cathode materials, the concentration gradient enables a better performance compared to similar cathode materials with uniform concentration. Figure 1: Galvanostatic cycling of gradient (FCGT, red) and standard, non-gradient (CC, black) cathode materials at high rates (2C for 29 cycles, then 1 cycle at C/10, repeated), at 45 oC vs. graphite full cells. Figure 1

In this work, nickel-rich, layered-structure LiNi0.65Co0.08Mn0.27O2 cathode materials were synthesized and compared with materials of the same overall composition, but with a concentration gradient throughout the particles: the Ni concentration is higher at the center of the particles and lower at surface, while the opposite is true for the Mn concentration. The co-precipitation synthesis parameters were optimized, with two different annealing protocols for the final products and the effect of chelating agent concentration during synthesis examined. The gradientmaterials provided superior capacity and rate capability than their respective non-gradient-materials, at normal operating potentials and temperatures, e.g. 30 degrees C up to 4.3 V vs. Li. The reasons for the improved discharge capacity of the gradient materials were explored through impedance spectroscopy and post-mortem characterization. The gradient structure evolution was examined via TEM and electron diffraction measurements of particle cross-sections. Prolonged cycling, even at elevated temperatures, did not change the initial concentration profiles determined by the synthesis. Additionally, long-term cycling experiments of the second-generation material electrodes vs. graphite electrodes in full cells were performed in order to explore the practical advantage of these novel materials. (C) 2016 The Electrochemical Society. All rights reserved.

The review summarizes the development of lithium ion batteries beginning with the research of the 1970–1980s which lead to modern intercalation type batteries. Following the history of lithium ion batteries, material developments are outlined with a look at cathode materials, electrolyte solutions and anode materials. Finally, with lithium sulfur and lithium oxygen batteries two post intercalation type lithium batteries are discussed. The focus of the material discussions lies on basic understanding, problems and opportunities related to the materials.

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