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The use of key parameters of the SiOx/graphite electrode formulation, and their critical values, makes it possible, without any trial-and-error type experimentation, to identify optimal electrode formulations for different SiOx/graphite mass ratios ranging up to 40:60. From the first attempt, electrodes presenting good cyclability at high surface capacity of 5.2 mA h cm−2 were formulated, reaching for example more than 93% capacity retention after 60 cycles in a full cell, with an electrolyte rich in FEC and EC-free, however with a prelithiation strategy. With a positive electrode based on NMC811, the gains in volumetric energy and power density are + 18 and + 28% compared to graphite, considering only the electrode volumes. The principle of using the key electrode formulation parameters introduced here is expected to accelerate and facilitate the optimization of electrode formulations. [ABSTRACT FROM AUTHOR]

The optimization of composite electrodes based on a silicon/graphite mixture is essential for battery performance, but is complex due to the multiplicity of parameters that come into play. In this direction, we propose to adjust the amount of surface area developed by all the graphitic carbons, including the conductive additive to that of the silicon phase. This concept, introduced here as graphite and carbon‐to‐silicon contact ratio, is based on the importance of contacts on the mechanical, electrical and electrochemical properties of composite electrodes. The validity of this new formulation parameter is studied here for SiOx/Graphite composite electrodes, which differ in the proportions of two types of graphite (spherical or platelet form) and for different types of conductive additives (carbon black and carbon nanotubes). An optimal contact ratio is determined, allowing at the same time the best gravimetric and volumetric capacities, the best cyclability, and the best power performance. [ABSTRACT FROM AUTHOR]

The physical crosslinking of polymeric binders through coordination chemistry significantly improves the electrochemical performance of silicon‐based negative electrodes. Scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy is used to probe the nanoscale morphology of such electrodes. This technique reveals the homogeneous coordination of carboxylated binder with Zn cations and its layering on the silicon surface. The solid electrolyte interphase (SEI) formed after the first cycle is denser with Zn‐coordinated binder and preferentially observed on binder‐depleted zones. The superiority of coordinated binders can be attributed to their capacity to better stabilize the electrode and the SEI layer due to improved mechanical properties. This results in a lower SEI impedance, a higher first cycle coulombic efficiency, and a 40% improvement of capacity retention after 50 cycles for highly loaded electrodes of over 6 mAh cm–2. [ABSTRACT FROM AUTHOR]

In this work, exhaustive characterizations of 3D geometries of LiNi1/3Mn1/3Co1/3O2 (NMC), LiFePO4 (LFP), and NMC/LFP blended electrodes are undertaken for rational interpretation of their measured electrical properties and electrochemical performance. X-ray tomography and focused ion beam in combination with scanning electron microscopy tomography are used for a multiscale analysis of electrodes 3D geometries. Their multiscale electrical properties are measured by using broadband dielectric spectroscopy. Finally, discharge rate performance are measured and analyzed by simple, yet efficient methods. It allows us to discriminate between electronic and ionic wirings as the performance limiting factors, depending on the discharge rate. This approach is a unique exhaustive analysis of the experimental relationships between the electrochemical behavior, the transport properties within the electrode, and its 3D geometry. [ABSTRACT FROM AUTHOR]

The structure of solid and liquid electrodes strongly affects the performance of Lithium batteries and of Semi-solid Redox-Flow cells. Thus understanding the formation of the structure of electrodes is an important issue. This paper proposes to study the aggregation processes that occur in electrode slurries by means of numerical simulations. For that Brownian dynamics simulations are developed and applied to a suspension composed of silicon nanoparticles and carbon black. Special attention is paid to the effects of the size of nanoparticles and of the interactions between the different components. The percolation of the carbon network and the number of contacts between the active mass and the conductive additive particles are quantified. Simulations results are found in good agreement with our previous experimental studies, showing that they can be used to improve the formulation of the slurry of electrodes. [ABSTRACT FROM AUTHOR]

This work reveals the great potential of in situ dielectric spectroscopy for deciphering the motion of ions and electrons on different scales in lithium-ion battery electrodes. One of the main bottlenecks limiting composite electrode kinetics and energy density, is a critical lack of fundamental understanding with respect to the electronic and the ionic transport within the electrode architecture. The latter is a granular material made up of clusters of particles, in which the particles are separated by boundaries that limit the electronic transport. The ionic transport is also severely restricted due to its tortuous porosity. Here, in situ dielectric spectroscopy is used to study the lithium-ion battery LiNi1/3Co1/3Mn1/3O2 composite electrodes. Short- and long-range motions of ions are evident in the low-frequency region. At higher frequencies, the influence of the adsorbed electrolyte ions on the electronic transfer at the micrometer scale is shown. [ABSTRACT FROM AUTHOR]

Cu foam is evaluated as a replacement for metal foil current collectors to create 3D composite electrodes with the objective to produce Si-based anodes with high loadings. The electrodes are prepared by casting the slurry into the porosity of the foam. With such a design, the loading and the surface capacity can reach values as high as 10 mg cm−2 and 10 mAh cm−2. Compared to the common 2D design, the 3D copper framework shows a great advantage in the cycle life (more than 400 cycles at a Si loading of 10 mg cm−2 with commercial micrometric particles) and power performance. The thinness of the composite coating on the foam walls favors a better preservation of the electronic wiring upon cycling and fast lithium ion diffusion. A higher coulombic efficiency in half cells with lithium metal as the counter electrode is achieved by using carbon nanofibers (CNF) rather than carbon black (CB). The possibility to reach, in practice, higher surface capacity could allow a significant increase in both the volumetric and gravimetric energy densities by 23% and 19%, respectively, for the Cu foam-silicon//LiFePO4 stack compared to the graphite/LiFePO4 stack of traditional design. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) is used as a conductive additive for nanosilicon-based lithium battery anodes with the high active-mass loading typically required for industrial applications. In contrast to conventional Si electrodes that use acetylene black (AcB) as an additive, the rGO system shows pronounced improvement of electrochemical performance, irrespective of the cycling conditions. With capacity limitation, the rGO system results in improved coulombic efficiency (99.9%) and longer cycle life than conventional electrodes. Upon cycling without capacity limitation, much higher discharge capacity is maintained (2000 mAh g−1 after 100 cycles for 2.5 mg of Si cm−2). Used in conjunction with the bridging carboxymethyl cellulose binder, the crumpled and resilient rGO allows highly reversible functioning of the electrode in which the Si particles repeatedly inflate and deflate upon alloying and dealloying with lithium. [ABSTRACT FROM AUTHOR]

Abstract: The different functions of polymer binders on the processing of the electrode, the electrical (electronic and ionic) and mechanical properties of the electrode, and as a consequence on the electrochemical performance are discussed. The role of the polymer binder on the solid–electrolyte interface (SEI) layer and the cyclability of the graphite- and silicon-based negative electrodes is also addressed. All these properties critically depend on the very thin layer formed by the polymer at the surface of the active and conductive particles. That is where research efforts have to focus on, now, for further optimization of electrodes through tailoring of the binder combination. [Copyright &y& Elsevier]

Abstract: We studied the effect of the dispersion and/or morphology within the positive composite electrode on the lithium battery performance. Model electrodes have been prepared in which the surrounding of the same AM (Li1.1V3O8) is changed by playing with plasticization of the polymeric binder (B) (PMMA) by ethylene carbonate (EC) and propylene carbonate (PC). We have also varied the concentration, and the nature of the solvent used for the electrode elaboration (THF and CHCl3). The cycled capacity varies between 100 and 250mAh/g (C/5 rate, 3.3–2V) depending on these parameters. The performance was shown to depend on the quality of AM, B, and carbon black (CB) dispersion within the electrode. The quality of the AM dispersion depends on the solvent concentration that affects the mixture viscosity. Formation of AM agglomerates results from high viscosity, while gradient concentrations appear due to sedimentation in low viscosity suspensions. Optimal distribution and subsequent electrode performance result from optimal solvent concentration. Better CB dispersion was obtained in the case of favourable interactions between the solvent and the polymer. This resulted in a higher electronic conductivity, a higher porosity, and improved electrochemical performance. Finally, the addition of EC–PC also favours the CB dispersion and further increases the cycling capacity. [Copyright &y& Elsevier]

An effective route to enhance the volume ratio of active materials in a lithium‐ion battery (LIB) or sodium‐ion battery (NaB) consists in increasing the electrode thickness, that is, active mass loading, as it reduces the volume and weight fractions of the separator and current collectors in the cell. This approach also serves to reduce the battery cost, chiefly associated with the expensive polymeric separator. However, following the standard industrial coating process, the mechanically stable electrode can hardly exceed an active mass loading of about 30 mg cm−2, corresponding to a nominal areal capacity around 6 mAh cm−2 due to the binder migration during the drying step. Herein, a straightforward manufacturing process based on a filtration technique is developed. It enables the design of LIB electrodes with a nominal areal capacity up to 20 mAh cm−2. A pierced and serrated current collector allows at the same time both filtration and mechanical interlocking of the electrode layer. Cells assembled with such ultra‐thick filtered electrodes exhibit very promising performances, thereby promoting the design of high‐energy and low‐cost LIBs and NaBs by a fast fabrication process. [ABSTRACT FROM AUTHOR]

A better understanding of the charge transport (ions and electrons) kinetics limitations through the electrode is required to improve the Li‐ion battery's energy and power density in view of electrical cars deployment. In article number 1602239, Bernard Lestriez and co‐workers connect for the first time the parameters describing the microstructure of electrodes with both measurements of their transport properties and their electrochemical performance. [ABSTRACT FROM AUTHOR]

Abstract: The local composition of negative silicon electrodes is studied by ex situ electron energy-loss spectroscopy along the first delithiation in a lithium battery. By measuring dozens of sample areas for over a dozen compositions, the local and overall inhomogeneities in these practical electrodes are evaluated. The statistical treatment of the data highlights the existence of larger inhomogeneities at the beginning of the delithiation as well as at a 100nm scale. It is also shown that, even if incremental capacity curves are different, the compositional changes during delithiation are identical for nano- and micro-Si. Namely, an initial Li15Si4 phase is replaced by a Li2±0.3Si amorphous phase in a biphasic process, the latter compound being further delithiated to amorphous silicon in single phase process. Results also show that the electrochemical irreversibility associated with the liquid electrolyte reduction/degradation is generated during the lithiation process, not the delithiation process. [Copyright &y& Elsevier]

[Display omitted] • Tannic acid can be used as a binder in Li-ion silicon electrodes. • Tannic acid can be used as an electronic conductor precursor in electrodes. • Tannic acid transforms in situ into a conducting and likely polymeric species. State of-the-art Si electrodes for Li-ion batteries typically require the addition of an advanced polymeric binder and a conductive carbon additive to the active material in order to circumvolve the issues associated with silicon, namely its poor conductivity in the oxidized state, and its high volume variation upon lithiation which give rise to several failure mechanisms. Here, we demonstrate that both additives can be replaced by a cheap, naturally available, polyphenol, tannic acid (TA). We show that Si/TA electrodes (80/20 wt%), even with a high loading (∼2 mg _Si cm−2), can retain a specific capacity above 2000 mAh g−1 after 50 cycles. This unexpected result appears to result from the irreversible reduction of TA during the first cycle, into a conducting, likely polymeric, species. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemically roughened copper foil was evaluated as a current collector for micrometric Si powder (ball-milled) based electrodes prepared by the conventional slurry-coating method. The formation of a bunch of copper nanowires on the current collector provides a rough surface, which enhances the adhesion of the Si composite electrode as confirmed from scratch tests. This produces a major decrease of the irreversible capacity associated with the electrical disconnection of the Si particles with cycling, which results in a great improvement of the electrode cycle life. With such a roughened Cu current collector, the micrometric Si-based electrode is able to maintain a discharge capacity of 1200mAhg−1 for at least 1000 cycles. [Copyright &y& Elsevier]

Abstract: To improve the performance of the positive electrode in batteries, it is important to thoroughly characterize these materials during battery cycling, beyond just electrochemical characterization. Among the very few techniques available for operando studies, X-ray Absorption Spectroscopy (XAS) appears very powerful, with high spatial and time resolutions provided by synchrotron radiation. Moreover XAS is well known for its capabilities in charge transfer and structure determinations, both being the major changes induced by electrochemical cycling of electrode materials. By an appropriate combination of three XAS beamlines using a specially designed electrochemical cell, we have studied composite positive electrodes made with LiFePO4 as the active material. We directly observed the heterogeneity of the electrode during operation, some parts being delayed and others advanced, compared to the mean charge state of the electrode. A mapping of this heterogeneity was made at different length scales. [Copyright &y& Elsevier]

Abstract: A simple analysis of the polarization resistance of the electrodes as function of the loading mass for various cycling rates allows identifying the fading mechanism on cycling of NiSb2, a typical conversion material: pulverization of active mass and further degradation of the electronic wiring at high rate and agglomeration of the active mass at low rate. Such rate-control of the degradation mechanism might reflect a thermodynamic instability of interfaces in the lithiated compound, which would however be in kinetic competition with the Lithium de-insertion. The analysis of the electrode polarization resistance fingerprint to rapidly identify the failure mechanism in a composite electrode can be generalized to other active materials. [Copyright &y& Elsevier]

Abstract: Aqueous processing would reduce the costs and toxicity associated with the making of the composite electrode. In the present study, carboxymethyl cellulose is used as a binder for 5V cathode material LiNi0.4Mn1.6O4. Compared with electrodes using polyvinylidene difluoride binder, CMC-based LiNi0.4Mn1.6O4 electrodes display a better discharge capacity at all rates. At 0.2C, the discharge capacity is close to the theoretical capacity (146mAhg−1) and the self-discharge is 10% lower. Polyvinylidene difluoride can be efficiently replaced by carboxymethyl cellulose for LiNi0.4Mn1.6O4 in terms of electrochemical performance and brings the advantage of an environment friendly and low cost electrode processing. [Copyright &y& Elsevier]

In the present work, an alternative to the standard ex-situ and destructive focused ion beam scanning electron microscopy (FIB/SEM) analysis procedure is demonstrated for monitoring the morphological degradation of a single Si/graphite (1/1 mass ratio) blended electrode for Li-ion batteries. For this purpose, a FIB milled microcavity is created in the pristine electrode, which is observed in FIB- polished cross section by SEM at different cycling periods (pristine, 1st, 9th and 50th cycles). This allows studying the same cycled electrode as for an in-situ method. Its cycling-induced morphological change is characterized at the electrode and particle scales by monitoring the evolution of the electrode thickness, mass and porosity, the Si particle morphology, Si interparticle distance, surface fraction and twisting of the graphite flakes. This is correlated to the evolution of the electrode discharge capacity and impedance. As a result, a more comprehensive view of the degradation phenomena of the Si/graphite blended electrode is established. [Display omitted] • An investigation technique based on sequential FIB/SEM analysis is demonstrated. • Cycling-induced morphological change of a single Si/Gr electrode is studied. • Morphological changes are correlated with EIS measurements. • The methodology can be extended to other battery systems. [ABSTRACT FROM AUTHOR]