Lithium-ion (Li-ion) batteries that rely on cationic redox reactions are the primary energy source for portable electronics. One pathway toward greater energy density is through the use of Li-rich layered oxides. The capacity of this class of materials (>270 milliampere hours per gram) has been shown to be nested in anionic redox reactions, which are thought to form peroxo-like species. However, the oxygen-oxygen (O-O) bonding pattern has not been observed in previous studies, nor has there been a satisfactory explanation for the irreversible changes that occur during first delithiation. By using Li2IrO3 as a model compound, we visualize the O-O dimers via transmission electron microscopy and neutron diffraction. Our findings establish the fundamental relation between the anionic redox process and the evolution of the O-O bonding in layered oxides.

The demand for rechargeable batteries with high gravimetric and volumetric energy density will continue to grow due to the rapidly increasing integration of renewable energy into the global energy scheme. In terms of energy density, modern high-end rechargeablebattery technology is reaching its fundamental limits and no big advancement leaps in this field are expected. The energy-cost model, developed for comparative evaluation of battery cell chemistries in a commercial type pouch cell configuration, helps us to find the relationship between cost and energy density, enabling the prediction of the most promising material combinations for near-future non-aqueous rechargeable batteries for portable electronics and automotive applications. Among the wide variety of positive electrode materials only few show enough potential for commercialization, and, clearly, the immediate future will still be dominated by Li-ion technology, with Li-rich and Ni-rich materials as definite winners, and with Li-S and Na-ion emerging as contestants due to low cost and abundance of their key components. As further significant improvements in gravimetric/volumetric energy density and cost cannot be achieved through new battery chemistries, then the engineering, targeting cost reduction and safety assurance, will most likely be the main driving force behind future rechargeable battery development.One of the most important roles of research and development today is to steer technology toward long-term sustainability for generation, storage, and consumption of energy. Handling global warming, pollution, and energy shortage is a serious challenge, and failure to address it timely will have severe environmental and political consequences. Only a widespread integration of renewable energy generation, supported by efficient energy storage, can provide a long-term solution. Fortunately, renewables have already begun to affect several major societal energy sectors, such as transportation and electrical grids, albeit so far to a very moderate extent due to inefficient and costly energy storage. 1,2 Electrochemical energy storage provides the most efficient, clean, and feasible solution for high-end applications, as illustrated by the successful battery integration into long drive-range electric vehicles (EV). Because of the immense interest in electrochemical energy storage from both government funding agencies and industry in recent years, activities in this field have surged. This makes the continuous critical reassessment of new battery chemistries and concepts based on the latest state of research valuable.Here we assess active materials designated for high-performance non-aqueous rechargeable batteries for portable electronics and automotive applications according to their commercialization potential within the coming decade. Non-aqueous electrolytes generally offer higher energy densities due to their wider electrochemical stability window, enabling a higher cell voltage (>2 V). In this respect, Liion is the superior battery technology, outp...

The lithium (de)-insertion mechanism from Li-Ni 0.80 Co 0.15 Al 0.05 O 2 (NCA) has been investigated by means of combined electrochemical analysis, operando differential electrochemical mass spectrometry (DEMS) experiments, and in situ X-ray diffraction (XRD) experiments during the first three cycles. Qualitative analysis of cyclic voltammetry data illustrated a possible irreversible activation of the material. Operando DEMS and internal cell pressure measurements combined with ex situ XRD and electrochemical impedance spectroscopy demonstrated that Li 2 CO 3 surface film on the NCA electrode degrades on oxidation and reforms on reduction, which has an effect on the lithium (de)-insertion reaction kinetics. In situ XRD studies clearly show mechanistic differences in the reaction pathways between the first and second cycle/following cycles. While the first charge reveals a combination of an irreversible two-phase transition plus a reversible solid solution reaction mechanism, the second charge is mainly dominated by a solid solution process. Such differences have been ascribed to changes in two factors, the electronic conductivity and the Li ion mobility of the NCA electrode.

The intercalation of solvated sodium ions into graphite from ether electrolytes was recently discovered to be a surprisingly reversible process. The mechanisms of this “cointercalation reaction” are poorly understood and commonly accepted design criteria for graphite intercalation electrodes do not seem to apply. The excellent reversibility despite the large volume expansion, the small polarization and the puzzling role of the solid electrolyte interphase (SEI) are particularly striking. Here, in situ electrochemical dilatometry, online electrochemical mass spectrometry (OEMS), a variety of other methods among scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) as well as theory to advance the understanding of this peculiar electrode reaction are used. The electrode periodically “breathes” by about 70–100% during cycling yet excellent reversibility is maintained. This is because the graphite particles exfoliate to crystalline platelets but do not delaminate. The speed at which the electrode breathes strongly depends on the state of discharge/charge. Below 0.5 V versus Na+/Na, the reaction behaves more pseudocapacitive than Faradaic. Despite the large volume changes, OEMS gas analysis shows that electrolyte decomposition is largely restricted to the first cycle only. Combined with TEM analysis and the electrochemical results, this suggests that the reaction is likely the first example of a SEI‐free graphite anode.

A new nanostructured metallic metal oxide shows excellent ORR/OER properties in a Li–air cell, and highlights the importance of controlling the cathode interface to achieve better Li–O2cell round-trip efficiency.

The chemical and electrochemical instabilities of LiPF 6 in carbonate electrolytes for Li-ion batteries were studied with online electrochemical mass spectrometry (OEMS). Decomposition of carbonate electrolytes based on LiPF 6 eventually results in the formation of POF 3 , which is readily detected and followed in situ during operation of Li-rich HE-NCM-based Li-ion cells. Electrode potentials above ∼4.2 V leads to carbonate solvent oxidation and presumably the formation of ROH species, which subsequently hydrolyze the LiPF 6 salt and initiate a thermally activated autocatalytic electrolyte decomposition cycle involving POF 3 as a reactive intermediate. Activation of the Li 2 MnO 3 domains of the Li-rich cathode contributes along with electrolyte and separator impurities to further POF 3 generation. Electrode potentials below ∼2.5 V vs. Li + /Li impede POF 3 formation and presumably also further electrolyte decomposition by scavenging reactive intermediate species. As a result, much less POF 3 gas was detected upon the 2 nd charge when using Li metal counter electrode, contrary to delithiated LiFePO 4 . In situ OEMS confirm that the parasitic reactions involving LiPF 6 constitute an intricate reaction scheme, but more importantly, provide further evidence about what the components of this scheme are and how these may interact with each other. Rechargeable Li-ion batteries are nowadays extensively used to power electronics and are entering the transportation sector by powering electric vehicles (EV). A wide range of both negative (e.g. graphite) and positive electrode materials (e.g. layered cobalt oxides, spinel-type manganese oxides, and olivine-type iron phosphates) have been thoroughly investigated and are now in widespread use in commercial batteries. The specific energy of Li-ion batteries is limited mainly by the positive electrode materials, having typical practical specific charges of ∼150 mAh/g and average operating potentials of ∼3.8 V vs. Li + /Li, which significantly inhibits the introduction of Li-ion batteries as power source in new applications. In recent years, the layered Li-rich cobalt-nickel-manganese oxides xLi 2 MnO 3 (1−x)(LiMO 2 ) (x ∼ 0.5, M = Co, Ni, Mn), hereafter called HE-NCM, have been shown to exhibit a high and reversible specific charge (∼250 mAh/g) and a competitive average operating potential (∼3.75 V vs. Li + /Li). [1][2][3][4] The origin of such a high specific charge is not yet completely understood, as the exact structure of the HE-NCM materials is highly dependent on the synthesis conditions and models coming from structural characterization are still under debate. Several reports have shown the presence of so-called Li 2 MnO 3 domains in the compound 5,6 whereas other groups demonstrated the monophasic character of their materials.7 However, during the first charge, a long potential plateau at ∼4.5 V vs. Li + /Li, not observed for conventional layered oxides, results from the delithiation process of the Li 2 MnO 3 domains accompanied by oxygen extraction. The extracted oxy...

Nickel-rich layered lithiated Ni−Co−Mn oxides (NCMs) are emerging as the most promising candidates for next-generation Li-ion battery cathodes. Progress, however, is hindered by an incomplete understanding of processes that lead to performance-limiting impedance growth and reduced cycling stability. These processes typically involve surface reconstruction and O 2 release at the cathode surface, both of which are difficult to monitor in the working cell. We demonstrate that online electrochemical mass spectrometry can be used to measure the gas release from NCMs of varying Ni content at practically relevant potentials and under operando electrochemical conditions. We find that for cathode potentials up to 4.3 V (vs Li + /Li) there is virtually no trade-off between Ni-mediated specific-charge enhancement and parasitic surface reactions. However, at potentials greater than 4.3 V, surface-reconstruction processes giving rise to substantial CO 2 and O 2 release occur, implying that surfacereconstructed layers a few nanometers thick may form already after the first charge. Ni content and the Ni/Co ratio are found to govern the onset, rate, and extent of these surface-reconstruction processes. These results provide novel insights into the role of Ni in governing the surface stability and performance of Li-ion layered oxides.

a High-voltage aqueous electrolyte based supercapacitors (U 4 1.23 V) attract significant attention for next-generation high power, low cost and environmentally friendly energy storage applications. Cell ageing is however markedly pronounced at elevated voltages and results in accelerated overall performance fade and increased safety concerns. Online electrochemical mass spectrometry, combined with cell pressure analysis, is for the first time shown to provide a powerful means for in situ investigation of degradation mechanisms in aqueous electrolyte/carbon based supercapacitors. The activated carbon electrodes possess high specific surface area and oxygen-based surface functionalities (mainly phenol, lactone and anhydride groups), which are oxidized already at a cell voltage of 0.6 V to provoke the evolution of minor amounts of CO and CO 2 . Noticeable water decomposition starts at a high voltage of 1.6 V with the evolution of H 2 on the negative electrode and carbon corrosion on the positive electrode with the generation of predominantly CO. In this paper we also report that short-term cycling leads to partly reversible gas evolution/consumption side-reactions giving negligible capacitance.On the other hand, long-term cycling causes irreversible side-reactions, deteriorates the electrochemical performance, and increases the internal pressure of the cell. Repeated cycling (U o 2 V) is confirmed as a more harmful technique for the electrode integrity compared to the voltage holding in a floating test.In situ gas analysis is shown to provide valuable insights into the electrochemical cell ageing aspects, such as the nature and potential onsets of side-reactions, hence paving the way for fundamental understanding and mitigating the performance and safety loss of high-energy aqueous supercapacitors. Broader contextGlobal energy consumption and environmental concerns steadily increase with the growth of the world's population and the technical development of our society. Future sustainability is largely dependent upon the widespread implementation of renewable energy generation and storage. Supercapacitors constitute a crucial part in the effective energy storage and delivery, e.g. in electric vehicles (start-stop systems) and wind mills (balancing the energy provided to the grid), because of their exceptional power capability and long cycle life. Supercapacitors with high surface area carbon electrodes operating in aqueous electrolytes offer high power rates, low cost, safe and environmental benign devices, but at moderate energy densities. Significant energy enhancement can be achieved by applying higher operating cell voltages (U 4 1.23 V) when using sulphate-based electrolytes. However, for practical implementations a fundamental understanding of their premature ageing as well as related safety issues are required. In the present work, state-of-the-art in situ gas analysis is shown to deliver valuable insights into the governing mechanisms behind the ageing of these devices. Assignment of safe operating voltage ...