Search

Mastering electrodes' formulations is a complex and tedious task, because for each composition of electroactive material(s) it is necessary to adjust the inactive additives nature and content to optimize battery performance. In this direction, the amount of binder is proposed to be adjusted to the surface developed by all of the powders involved in the composition of the electrode, i.e., the electroactive materials and electronic conductive additives. This concept, introduces here as binder‐to‐powders coverage ratio, relies upon the micromechanical models developed in the field of polymer‐based composite materials. The validity of this new electrode formulation parameter is shown here for two different SiOx/Graphite blends, which differ in the type of graphite, and for blends of two different binders, polyacrylic acid and styrene−butadiene rubber. At the optimal coverage ratio, a satisfactory capacity retention is obtained in full cell with an ethylene carbonate free and fluoroethylene carbonate rich electrolyte. [ABSTRACT FROM AUTHOR]

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 influence of the Cu current collector grade (cold‐rolled, annealed, or textured) and the ink solid fraction (SF) on the performance of Si‐based electrodes for Li‐ion batteries is investigated. Two binders are considered for this study: one of carboxymethyl cellulose and citric acid and the other which consists of the same organic components with added Zn(II) cations. These ones cross‐link the carboxylate moieties through coordination bonds. The fracture behavior and cyclability of the Zn‐free electrodes show a strong dependence on the Cu current collector grade. For this formulation, which has lower cohesion, the increase in electrode adhesion from the roughening of the surface of the current collector and/or the decrease of the current collector yield strength contribute to mitigate the electrode mechanical damage, therefore improving its cyclability. Such a dependence is not observed for the Zn cross‐linked electrodes which have a higher cohesion. Regarding the impact of the ink solid fraction, when a higher SF is used, the capacity retention and coulombic efficiency are enhanced for both formulations, though much more significantly for the Zn‐free formulation. The underlying mechanism causing this improvement may be partially related to the enhanced adsorption of binder on silicon particles with increasing SF. [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]

The polymer binder is a key constituent of silicon‐based electrode formulation for lithium‐ion batteries. However, its extremely difficult visualization in fresh electrodes becomes completely impossible in cycled electrodes. Here, the combination of scanning transmission electron microscopy—valence electron energy‐loss spectroscopy with the use of a specific electrolyte solvent composition (a mixture of dimethyl carbonate and fluoroethylene carbonate, without ethylene carbonate) allows the visualization, for the first time, of the binder in silicon‐based electrodes, even cycled up to 100 cycles. Such an observation is possible as the only solid degradation product of this electrolyte is LiF, as confirmed by quantitative 7Li and 19F magic angle spinning nuclear magnetic resonance. The electrodes, based on a blend of silicon and graphite, have a very high surface capacity, 6.5 mAh cm−2, which makes them meaningful for electric vehicle applications. The performance is appreciable, in particular the first cycle efficiency approaching that of commercial graphite electrodes, as well as the capacity retention in full cell, versus LiNi0.5Mn0.3Co0.2O2, 60% after 100 cycles. This work also illustrates the ultimate state of destructuration of silicon after long cycling, which invites new ways of thinking about the design of this material. [ABSTRACT FROM AUTHOR]

Considerable effort has been devoted to improving the cyclability of silicon (Si) negative electrodes for lithium-ion batteries because it is a promising high specific capacity alternative to graphite. In this work, the electrochemical behaviour of Si in two ionic liquid (IL) electrolytes, triethyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1222FSI) and N-propyl-N-methylpyrrolidinium- FSI (C3mpyrFSI) with high and low lithium (Li) salt content is investigated at 50 °C. Results highlight that higher capacity and better cycling stability are achieved over 50 cycles with high salt concentration, the first time for a pyrrolidinium-based electrolyte in the area of Si negative electrodes. However, the Si cycling performance was far superior in the P1222FSI-based high salt content electrolyte compared to that of the C3mpyrFSI. To understand this unexpected result, diffusivity measurements of the IL-based electrolytes were performed using PFG-NMR, while their stability was probed using MAS-NMR and XPS after long-term cycling. A higher apparent transport number for Li ions in highly concentrated ILs, combined with a significantly lower extent of electrolyte degradation explains the superior cycle life of the highly concentrated phosphonium-based system. Si/concentrated P1222FSI-LiFSI/lithium nickel cobalt aluminum oxide (NCA) full cells with more than 3 mAh cm−2 nominal capacity deliver a promising cycle life and good rate capability. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that the mechanical properties of lithium‐ion battery electrodes impact their electrochemical performance. This is especially critical for Si‐based negative electrodes, which suffer from large volume changes of the active mass upon cycling. Here, this study presents a postprocessing treatment (called maturation) that improves the mechanical and electrochemical stabilities of silicon‐based anodes made with an acidic aqueous binder. It consists of storing the electrode in a humid atmosphere for a few days before drying and cell assembly. This results in a beneficial in situ reactive modification of the interfaces within the electrode. First, the binder tends to concentrate at the silicon interparticle contacts. As a result, the cohesion of the composite film is strengthened. Second, the corrosion of the copper current collector, inducing the formation of copper carboxylate bonds, improves the adhesion of the composite film. The great improvement of the mechanical stability of the matured electrode is confirmed by in‐operando optical microscopy showing the absence of film delamination. The result is a significant electrochemical performance gain, up to a factor 10, compared to a not‐matured electrode. This maturation procedure can be applied to other types of electrodes for improving their electrochemical performance and also their handling during cell manufacturing. [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 discovery of conducting lithium-doped polyaniline with reversible redox chemistry allows simultaneous unprecedented capacity and stability in a non-aqueous Li battery. This compound (lithium emeraldinate) was synthesized by lithium-proton exchange on the emeraldine base in an anhydrous lithium-based electrolyte. A combination of UV/Vis-NIR spectroelectrochemistry, XPS, FTIR, and EQCM characterization allowed a unified description of the chemical and electrochemical behavior, showing facile charge delocalization of the doped states and the reversibility of the redox processes in this form of polyaniline. From a practical point of view, lithium emeraldinate behaves as a high-capacity organic active material (230 mAh g−1) that enables preparation of relatively thick composite electrodes with a low amount of carbon additives and high energy density (460 Wh kg−1). Concomitantly, at 1 C rate, 400 cycles were achieved without significant capacity loss, while the coulombic efficiency is greater than 99 %. [ABSTRACT FROM AUTHOR]

Understanding the aging mechanism of silicon-based negative electrodes for lithium-ion batteries upon cycling is essential to solve the problem of low coulombic efficiency and capacity fading and further to implement this new high-capacity material in commercial cells. Nevertheless, such studies have so far focused on half cells in which silicon is cycled versus an infinite reservoir of lithium. In the present work, the aging mechanism of silicon-based electrodes is studied upon cycling in a full Li-ion cell configuration with LiCoO2 as the positive electrode. Postmortem analyses of both electrodes clearly indicate that neither one of them contains lithium and that no discernible degradation results from the cycling. The aging mechanism can be explained by the reduction of solvent molecules. Electrons extracted from the positive electrode are responsible for an internal imbalance in the cell, which results in progressive slippage of the electrodes and reduces the compositional range of cyclable lithium ions for both electrodes. [ABSTRACT FROM AUTHOR]

The nonaqueous suspensions of carbon nanofibers (CNFs) in 1 M lithium bis(trifluoromethanesulfonaimide) in propylene carbonate electrolyte reveal unique structural evolution and shear-induced transition due to the high aspect ratio. The rheo-electrical behavior elucidates a microstructural transition from entangled-to-aggregated networks above a distinct percolation threshold. Under shear flow, both networks show a three-regime flow curve and an inverted-bell-like conductivity curve as a consequence of shear-induced alignment (entangled network) and shear-induced breaking up (aggregated network). The different particle morphology of carbon nanofibers (anisometric) and carbon black (CB; isometric) causes different aggregation mechanisms (aggregate vs. particulate) and then varied microstructure for their suspensions in the same electrolyte. This fact explains the higher rigidity and lower electric conductivity of CNFs than CB suspensions. Interestingly, the suspension of hybrid carbons at the optimum mixing ratio merges the advantages of both carbons to operate efficiently as precursors in the formulation of electrodes for energy storage systems. [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]

A suspension of Li4Ti5O12 and of Ketjen black in a solution of 1 M lithium bis(trifluoromethanesulfonyl)imide in propylene carbonate is studied as the anolyte for semisolid redox flow batteries. The rheological behavior and electronic conductivity are studied both at rest and under shear flow. The electrochemical behavior is evaluated at rest as a function of the charge/discharge rates and of the thickness of the suspension in the electrochemical cell. The highly beneficial influence of the addition of a non-ionic surfactant in the composition of the suspension is demonstrated. All practical properties are improved with respect to semisolid redox flow applications. The viscosity decreases, the electronic conductivity increases and is less affected by the shear flow, and the electrochemical performance is improved. Moreover, the suspension shows much better stability, so its performance is preserved over time. [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]

Solid and flexible ionogel‐based membranes are obtained by a simple one‐step process. Tuning the composition of the silica–polymer hybrid membranes allows the attainment of highly specific properties. The high ionic conductivities of the solid membranes are in the range of those of the ionic liquid electrolytes on which they are based. Good mechanical properties and high transparency from 250 to 1000 nm are also observed. The membranes are successfully applied within entirely solid lithium batteries. [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]

We report on the rheological and electrical properties of non-aqueous carbon black (CB) suspensions at equilibrium and under steady shear flow. The smaller the primary particle size of carbon black is, the higher the magnitude of rheological parameters and the conductivity are. The electrical percolation threshold ranges seem to coincide with the strong gel rather than the weak gel rheological threshold ones. The simultaneous measurements of electrical properties under shear flow reveal the well-known breaking-and-reforming mechanism that characterises such complex fluids. The small shear rate breaks up the network into smaller agglomerates, which in turn transform into anisometric eroded ones at very high shear rates, recovering the network conductivity. The type of carbon black, its concentration range and the flow rate range are now precisely identified for optimizing the performance of a redox flow battery. A preliminary electrochemical study for a composite anolyte (CB/Li4Ti5O12) at different charge–discharge rates and thicknesses is shown. [ABSTRACT FROM AUTHOR]

The simple addition of a Zn(II) precursor to a preoptimized poly(carboxylic acid) binder solution enhances the electrochemical performance and cycle life of silicon‐based electrodes. The binder/cation couple forms a cross‐linked coordinated binder that plays a key role in enhancing the mechanical and chemical stability of the electrode microstructure. The impact of the addition of the Zn precursor on the microstructural evolution of the electrode during cycling is investigated at different scales (from cell/electrode to silicon particle scale) using complementary operando, in situ, and ex situ X‐ray tomography techniques. Comparative analyses conducted on the reference and with Zn electrode formulations using operando and in situ X‐ray micro‐tomography allow for monitoring of the electrode morphological deformations along with the crack pattern formation and evolution during cycling. The benefits of the precursor addition include enhancing the mechanical stability of the electrode through a strengthened microstructure more apt to maintaining its integrity, as well as a better anchoring to the current collector leading to decreased electrical disconnections and capacity fade. Moreover, complementary ex situ X‐ray nano‐tomography measurements highlight the benefits of the precursor addition in terms of chemical stability with mitigated solid electrolyte interface (SEI) formation over the electrode cycling. [ABSTRACT FROM AUTHOR]

The alloying reaction of silicon with lithium in negative electrodes for lithium‐ion batteries causes brutal morphological changes that severely degrade their cyclability. In this study, the dynamics of their expansion and contraction, of their cracking in the bulk and of their debonding at the interface with the current collector are visualized by in situ synchrotron X‐ray computed tomography and quantified from appropriate 3D imaging analyses. Two electrodes made with same silicon material having reasonable particle size distribution from an applied point of view are compared: one fabricated according to a standard process and the other one prepared with a maturation step, which consists in storing the electrode in a humid atmosphere for a few days before drying and cell assembly. All morphological degradations are significantly restrained for the matured electrode, confirming the great efficiency of this maturation step to produce a more ductile and resilient electrode architecture, which is at the origin of the major improvement in their cyclability. [ABSTRACT FROM AUTHOR]

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]