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With its high theoretical specific charge, silicon is a promising candidate as electrode additive to enhance specific charge of graphite electrodes for high-energy-density Li-ion batteries. We prepared Si/C composites by a two-step procedure: the ballmilling of silicon nanoparticles with a carbon precursor for homogenization, followed by a carbonization step. The effects of the carbon source and the carbonization parameters on the physical and electrochemical composite properties were identified. Longer cycle life was reached for graphite electrodes containing Si/C composites than with silicon nanoparticles simply mixed with carbon black, and the extent of the improvement was dependent on the physical properties of Si/C composite. A carbon host with a larger pore volume -- obtained using sucrose precursor, especially at lower heat-treatment temperatures, -- enabled a more efficient buffering of the silicon volume changes. However, this did not define good cycling stability. The electrochemical performance was found, instead, being significantly affected by the contact between the silicon nanoparticles and the carbon matrix, and by the structure of the latter. The stacking and in-plane ordering of the graphitic domains in the amorphous carbon -- tuned by the precursor nature and the heat-treatment temperature -- were crucial for effectiveness of lithiation/delithiation processes.

Nano-crystalline LiNi0.80Co0.15Al0.05O2 with and without an electrochemically inactive "Al2O3" surface coating has been successfully prepared by a colloidal synthesis method followed by a chemical lithiation reaction. In situ high temperature X-ray diffraction studies evidenced the slowness of the lithiation reaction due to diffusion and suggested longer calcination holding times at temperatures below 500degC. At 550degC, lithiated compounds were obtained although calcinations to 750degC are necessary to obtain ordered layered structures. Ex situ XRD studies and cyclic voltammograms revealed a single-phase solid solution mechanism taking place during the first charge unlike the two-phase reaction "activation mechanism" seen for micron-sized material. While nano-crystalline LiNi0.80Co0.15Al0.05O2 exhibits cycle stability at 2.4 mA g[?]1 and a good rate capability even at 240 mA g[?]1 in the galvanostatic tests, the specific charge of the surface coated material fades more quickly. These results are caused by the material characteristics such as small particle size and significant amount of microstrains, high degree of cation mixing, and increased compositional inhomogeneity among the nano-particles, compared to the uncoated material.

Rate-capability tests are widely used to highlight advances in Li-S-system development. Here we show, by studying the individual effects of a number of cycling- and electrolyte-related parameters on a simple Li-S cell, that the rate-capability results are sensitive not only to the applied current but also to the cycling prehistory of the cell. On the one hand, the performance is affected by the order in which cycling rate is changed. Slow initial rates aggravate material loss and reduce the achievable capacity. On the other hand, the results of rate-capability tests are significantly different when the rates are varied only on the charge or only on the discharge. The charge rate does not directly affect the measured capacity, whereas the discharge rate does, especially when discharge cutoff voltages are high, due to slow discharge reactions. High charge rates, however, do affect the long-term stability, which is difficult to predict from usual rate-capability tests. Our findings also provide insights into the relative reaction rates and the influence of the general cycling procedures, underlining the importance of understanding the kinetics of Li-S systems, while designing them for high performance batteries.

The chemical and electrochemical instabilities of LiPF6 in carbonate electrolytes for Li-ion batteries were studied with online electrochemical mass spectrometry (OEMS). Decomposition of carbonate electrolytes based on LiPF6 eventually results in the formation of POF3, 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 LiPF6 salt and initiate a thermally activated autocatalytic electrolyte decomposition cycle involving POF3 as a reactive intermediate. Activation of the Li2MnO3 domains of the Li-rich cathode contributes along with electrolyte and separator impurities to further POF3 generation. Electrode potentials below [?]2.5 V vs. Li+/Li impede POF3 formation and presumably also further electrolyte decomposition by scavenging reactive intermediate species. As a result, much less POF3 gas was detected upon the 2nd charge when using Li metal counter electrode, contrary to delithiated LiFePO4. In situ OEMS confirm that the parasitic reactions involving LiPF6 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.

The surface chemistry of the commonly employed positive electrode substrate Super C65 carbon was investigated during the 1st cycle of a Li-O2 battery with a typical ether electrolyte (0.2 M LiTFSI in Diglyme) by performing in situ online electrochemical mass spectrometry (OEMS), ex situ scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). During discharge, a nanometer-thin (< 5 nm) layer of Li2O2 forms homogeneously throughout the electrode before it is passivated at a final specific charge of [?]365 mAh/g. Higher discharge charge rates lead to thinner and more densely packed layers of Li2O2. Electrolyte decomposition also occurs in parallel, as evidenced by the continuous increase of LiF and sulfur containing species of the degraded LiTFSI salt. On charge, O2 evolves initially according to a 2e[?]/O2 rate, but as the cell over-potentials increase, O2 evolution rate approaches 4e[?]/O2, thus demonstrating a significant extent of parasitic side-reactions. Unlike the discharge, the charge leads to inhomogeneous electrode reactions causing a continuous removal of Li2O2 with no indication of LiO2 or Li2O intermediates. The decomposition side-products formed during discharge are also removed and the spectra of the pristine electrode are nearly retained at a full charge. Our results show that the analysis of Li-O2 battery chemistry requires broad approach based on the combination of various electrode surface sensitive techniques, such as XPS and OEMS, in order to provide further fundamental understanding of the mechanisms behind the complex electrochemistry involving the Li and O2 as well as several other predominant degradation products of the electrode and electrolyte.

Spinel LiNi0.5Mn1.5O4 (LNMO) is an attractive next-generation cathode material for Li-ion batteries because of its reversible specific charge at high operating potentials. However, the cycling efficiency of Li-ion cells with LNMO-based cathodes is limited by the poor anodic stability of the most commonly employed alkyl carbonate electrolytes. The electrolyte/electrode stability is investigated by in situ gas analysis techniques, including cell pressure measurements and online electrochemical mass spectrometry (OEMS), to monitor the decomposition of ethylene carbonate (EC) and dimethyl carbonate (DMC) electrolytes on LNMO electrodes. Increasing the DMC content, exchanging the LiPF6 salt for LiClO4, and elevating the cell temperature, all result in higher gas evolution rates. The major volatile side reaction products are H2, CO, CO2, and POF3 (only with LiPF6 salt), which display unique gas evolution profiles depending on electrode potential and electrolyte composition. The significantly higher gas evolution rates for the DMC-rich electrolyte are attributed to an electrolyte solution-mediated decomposition cycle, which is facilitated by the enhanced mass transport induced by the lower viscosity of DMC. Differences in reactivity of the Ni cationic redox state on the LNMO surface toward electrolyte decomposition are indicated.

We report the behavior of full Li-ion cells with a xLi2MnO3*(1 [?] x)LiMO2 (M = Ni, Mn, Co) (hereafter called HE-NCM) cathode and a graphite anode. The cells' cycling behavior, especially with regard to the degradation processes (mainly of the electrolyte) occurring in the 5 V region, does not strongly depend on the cycling rate but rather on the calendar time of cycling. At the fast 1 C rate, we demonstrate 250 cycles with more than 80% capacity retention in a standard carbonate electrolyte. A surface analysis combining post-mortem scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS) revealed differences in the electrodes' surface composition and morphology, and the suggested explanation for these differences was found in the thickness of the polymer layer developed at the surface of the particles.

In Li-ion batteries, Li4Ti5O12 (LTO) has merits of an excellent cycling stability combined with a safe working potential of 1.55 V vs. Li+/Li at which no adverse side-reactions with the electrolyte are expected. Concerns regarding gassing of LTO, especially at elevated temperatures, have however recently been reported. In this work, LTO gassing behavior at 50degC is investigated by in situ pressure and online electrochemical mass spectrometry (OEMS), allowing for both qualitative and quantitative analysis of evolving gases. H2, C2H4, and CO2 are the dominantly evolving gases for ethylene carbonate (EC) based electrolytes. H2 is mainly produced during the first charge step, while C2H4 is observed at lower potentials resulting from the reduction of EC. CO2 evolution mechanism is complex and is promoted at more anodic potentials. Passivating the LTO surface, e.g. by a proper coating, and/or exchanging the LiPF6 salt, may effectively reduce gas evolution, thus clearing the way for future use of LTO in energy storage applications at elevated temperatures.

We have developed a new type of anode material, MSnS2 (M = Fe, Cu), that is able to cycle in both lithium-ion and lithium-sulfur batteries. By tuning the potential window, we attained specific charges greater than 750 mAh/g and 500 mAh/g for the Li-S and Li-ion system,respectively, after 400 cycles. Moreover, we were able to cycle at 1-C rate (loading: 4 mg/cm2) with a Coulombic efficiency greater than 97%.

To obtain the true electrochemical impedance spectrum of a Li-ion battery electrode at different stages of cycling is delicate. Measurement in a 3-electrode setup, to deconvolute the impedance of the working electrode (WE) from the counter electrode (CE), is sensitive to the cell geometry and electrode arrangement, and can lead to artefacts like distortions, induction loops and scaling effects of the spectra. Furthermore, using a CE with higher impedance than the WE also hugely alters the impedance response of the WE. There is little awareness in the field of Li-ion batteries of the occurrence of such impedance spectra falsifications, which are therefore often disregarded. Here, some of the artefacts are experimentally dismantled. Two cell designs for cycling battery electrodes with intermittent impedance measurement are presented and compared. The reusable cells are built for ring electrodes aligned concentrically with a reference electrode (RE) in the center. The reliability of the impedance response measured in these cells is confirmed in a symmetric electrode setup. It is further shown that the cells support lithiation and delithiation behavior conform with established 2-electrode cells.

Crystal structure changes in LiNi0.80Co0.15Al0.05O2 (NCA) during electrochemical (de)intercalation of Li+ ions, charged to different upper cut off potentials, were investigated by means of ex situ X-ray powder diffraction. We have found that the presence of vacancies in the MO2 slabs and subsequent Li/Ni interlayer mixing at high state of charge lead to an increased microstrain in the system. Careful examination of the crystal structures reveal the anisotropic nature of the microstrain which does not completely recover to the pristine material value after full discharge (lithiation). The microstrain created during charge and subsequent cycles has a strong impact on the cycling performance of the NCA material, and thus on the cell cycle-life.

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 rechargeable-battery 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.

We report for the first time the use of a thin-layer electrode of HE-NCM, to study this material without the influence of kinetic limitations coming from the electrode engineering and to avoid the important problem of increasing pressure due to the gas release coming from the activation of Li2MnO3 domains. Surprisingly, the overall kinetics of the electrode could not be improved by using thin layer electrodes. By using different techniques such as post mortem SEM/EDX, and electrochemical impedance spectroscopy we were able to find the cause of this kinetic limitation mainly due to the creation, during cycling, of a thick solid permeable interface layer coming from the electrolyte decomposition. Nevertheless, despite the kinetics of the electrode was not improved due to surface reaction, the cycling stability of the HE-NCM electrodes was improved.

A combined in situ Raman- and external reflectance Fourier transform infrared (FTIR)-microscopic approach aimed at exploiting the complementary nature of these two powerful spectroscopic methods is presented and applied to the same spot on a graphite electrode. Polished single graphite particles were selected because they offer a suitable compromise between acceptable lithium intercalation properties and sufficiently high IR reflectivity. This study constitutes the first application of combined in situ Raman and IR spectroscopy to a material of practical relevance to lithium-ion batteries. In preliminary experiments, scanning electron microscopy (SEM) and attenuated total reflectance (ATR) were employed to characterize the electrodes. In situ Raman microscopy was shown to be particularly sensitive to structural changes in the electrode material whereas in situ IR microscopy provided an efficient way of investigating the interface with the organic electrolyte. The Raman spectra showed clear evidence of lithium intercalation while the IR spectra were dominated by solvation effects determined by the interactions between ethylene carbonate and dimethyl carbonate and Li+.

Fe0.5TiOPO4 and Cu0.5TiOPO4 were identified as electrochemically active materials for lithium-ion batteries. Fe0.5TiOPO4 was prepared by a new, direct way of synthesis, which leads to a carbon coating of the particles during synthesis. The material exhibits a specific charge of 680 Ah/kg in the first lithiation and 490 Ah/kg in the first delithiation. Cu0.5TiOPO4 exhibits a specific charge of 640 Ah/kg in the first lithiation and 250 Ah/kg in the first delithiation. Both titanium oxyphosphates react with over four lithium ions per formula unit upon lithiation. This is more than the 2 lithium ions expected based on the oxidation state of the two metals in the original structure and also more than the 1.5 lithium ions expected based on the vacant octahedral sites in the unit cell. The lithiation results in three plateaus on the galvanostatic curve but at different potentials for both materials. The reactions of lithium with the material take place at [?]1.8 V and [?]0.2 V vs. Li+/Li for both materials, and additionally at [?]0.75 V for Fe0.5TiOPO4 and at [?]1.6 V for Cu0.5TiOPO4.

Structural investigation was performed on a range of NMC materials, Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 (0[?] x [?] 0.13), using in situ X-ray synchrotron diffraction while electrochemically cycling them between 2.5 and 5.0 V vs. Li/Li +. From the analysis of the obtained data, an irreversible phase transformation of part of the starting O3 phase (R m) to the O1 phase (P m1) was observed for all the NMC samples, where the O1 phase was detected at more negative potentials with increasing overlithiation content. Moreover a second irreversible reaction was detected at positive potentials using ex situ X-ray synchrotron diffraction for overlithiated NMC (x = 0.1) that involved loss of Li2MnO3 ordering in the structure.

In this study, detailed insights in the solid electrolyte interphase (SEI) properties and its formation kinetics on different graphite types and in electrolyte mixtures based on ethylene carbonate as well as on propylene carbonate are presented. The competing most important reactions of (i) SEI formation and (ii) solvent cointercalation leading to exfoliation could be controlled by adjusting the specific current in the first cycle; in some cases it was possible to suppress the exfoliation completely and the electrode could be stably cycled. Post mortem scanning electron microscopy clearly revealed differences in the SEI film morphology on graphite particles after electrochemical cycling, depending on the formation conditions. By means of differential electrochemical mass spectrometry (DEMS) the solvent cointercalation prevailing over SEI film formation could be detected in propylene carbonate based electrolytes.

The effect of Mg-substitution in Li(Ni,Co,Al)O2 during overcharge was studied by scanning electron microscopy (SEM) observations and in situ synchrotron X-ray Diffraction (XRD) measurements. The higher Mg-substituted samples showed higher electrochemical stability during the overcharge cycling. After overcharge, the non Mg-substituted sample featured many cracks, not only at the grain boundaries in secondary particles but also inside the primary particles. This morphological change is assigned to the drastic shrinking of the c-axis during overcharge. The Mg-substitution suppressed the c-axis shrinking and consequently avoided the cracking of the particles. This effect of Mg-substitution in Li(Ni,Co,Al)O2 correlates with the electrochemical stability during the overcharge cycling.

(NMC) oxides are believed to be among the most promising positive electrode materials for future lithium-ion batteries. Differential electrochemical mass spectrometry (DEMS) experiments on the NMC oxides revealed oxygen evolution for overlithiated NMC compounds at potentials positive to 4.5 V vs . No oxygen evolution was detected for the stoichiometric NMC compound . An analytical procedure for the quantitative analysis of the DEMS data was developed and applied to the oxygen evolution from overlithiated NMC compounds in acetonitrile (AcN) and ethylene carbonate/dimethylcarbonate-based electrolytes. The analysis of DEMS data acquired in the AcN-based solution was used to quantify the oxygen loss from the structure of the overlithiated compounds. A hypothesis on the origin of the considerably irreversible specific charge observed in the first cycle of the galvanostatic cycling experiments on the overlithiated compounds was formulated.

The volatile alane (H2AlO t Bu)2 decomposes into amorphous HAlO or Al0@Al2O3 nanoparticles upon heating, depending on the time and temperature. By coating the Ni-rich cathode material NCM851005 with this compound, the NCM's cycling stability and electric conductivity were increased. Thus, the coating not only yielded Al0@Al2O3 nanoparticles but also, by reaction with surface Li2O/LiOH/Li2CO3, a Li+ conductive LiAlO2 layer. The coatings with 0.3 and 0.1 wt% (H2AlO t Bu)2, respectively, significantly reduced the resistance build-up to 70/115% after 280 cycles at 1 C (351% without coating). Upon treatment of the 0.3 wt% Al-coating with two equivalents of anhydrous HF, the Al2O3 and LiAlO2 parts were transformed into a Li[AlO(OH)F] layer, which yielded better capacity retention, retaining the low impedance build-up of only +120% (280 cycles at 1 C). This treatment, however, proved to have the same effect as simply reducing the amount of (H2AlO t Bu)2 for the coating to 0.1%.