Advances in Nanomaterials for Lithium-Ion/Post-Lithium-Ion Batteries and Supercapacitors.

Energy storage and conversion are key factors for enabling the transition from fossil fuels to intermittent renewables [...].

Stripping and Plating a Magnesium Metal Anode in Bromide-Based Non-Nucleophilic Electrolytes.

A non-nucleophilic Hauser base hexamethyldisilazide (HMDS) magnesium electrolyte possesses inherent properties required for a magnesium-sulfur battery. However, the development of full cell batteries using HMDSCl-based electrolytes is still hampered by a low coulombic efficiency. A new electrolyte formulation of non-nucleophilic HMDS magnesium containing bromide as a halide instead of chloride was obtained through a simple and straightforward synthesis route. The electrochemistry of magnesium was investigated through plating and stripping in three different HMDSBr-based electrolytes: Mg(HMDS)Br, Mg(HMDS)Br-BEt3 , and Mg(HMDS)Br-AlEt3 dissolved in tetrahydrofuran. The different magnesium species present in the electrolytes were determined using NMR. Weak electron-withdrawing Lewis acids, BEt3 and AlEt3 were used intentionally and their impact was investigated. Contrary to expectation, the substitution of chloride by bromide does not drastically narrow the electrochemical stability window. HMDSBr-based electrolytes demonstrated long-term (1000 cycles) stable reversibility and highly efficient (≈99 %) magnesium plating/tripping without a high ratio of bromide compared with the MgHMDSCl-based electrolytes. The aprotic electrolyte shows comparatively high anodic stability (≈2.4 V vs. Mg/Mg2+ ) and high ionic conductivity of 1.16 mS cm-1 at room temperature. Plating of magnesium with low overpotential (<188 mV) revealed a morphology dependence on the electrolyte type with a shiny metallic homogenous layer, suggesting a rational balance between the nucleation and growth process in HMDSBr-based electrolytes.

Influence of the Molecular Weight of Poly-Acrylic Acid Binder on Performance of Si-Alloy/Graphite Composite Anodes for Lithium-Ion Batteries.

In this study Si-alloy/graphite composite electrodes are manufactured using water-soluble poly-acrylic acid (PAA) binder of different molecular weights (250, 450 and 1250 kg mol-1). The study aims to assess the behavior of the different binders across all the steps needed for electrodes preparation and on their influence on the electrodes electrochemical behavior. At first, rheological properties of the water-based slurries containing Si-alloy, graphite, conductive carbon and PAA are studied. After coating, the adhesion strength and electronic conductivity of the manufactured electrodes are evaluated and compared. Finally, the electrochemical behavior of the composite anodes is evaluated. The electrodes show high gravimetric as well as high areal capacity (∼750 mAh/g; ∼3 mAh/cm2). The influence of the binder on the first cycle irreversible loss is considered as well as its effectiveness in minimizing the electrode volume variation upon lithiation/de-lithiation. It is finally demonstrated that the use of 8 wt.% of PAA-250k in the electrode formulation leads to the best performance in terms of high rate performance and long term stability.

Magnesocene-Based Electrolytes: A New Class of Electrolytes for Magnesium Batteries.

Unlike ferrocene, bis(η5 -cyclopentadienyl)magnesium (magnesocene, MgCp2 ) is slightly dissociated in solvents, such as ethers, resulting in electrolyte solutions with low conductivity. MgCp2 /tetrahydrofuran solutions make possible reversible magnesium plating and stripping with low over-potentials for many cycles. The Mg deposits appear with a cauliflower-like morphology. IR and NMR spectroscopy confirm that the electrolyte is stable and not decomposed during prolonged cycling. The anodic stability limit is in the range of 1.5 V (at platinum) and 1.8 V versus Mg/Mg2+ (at stainless steel), which may be sufficient for low-voltage cathode materials. MgCp2 is a first example of a completely new class of halide-free electrolytes, which may open up a new research direction for future magnesium metal and magnesium-ion batteries.

Study of Water-Based Lithium Titanate Electrode Processing: The Role of pH and Binder Molecular Structure.

This work elucidates the manufacturing of lithium titanate (Li4Ti5O12, LTO) electrodes via the aqueous process using sodium carboxymethylcellulose (CMC), guar gum (GG) or pectin as binders. To avoid aluminum current collector dissolution due to the rising slurries' pH, phosphoric acid (PA) is used as a pH-modifier. The electrodes are characterized in terms of morphology, adhesion strength and electrochemical performance. In the absence of phosphoric acid, hydrogen evolution occurs upon coating the slurry onto the aluminum substrate, resulting in the formation of cavities in the coated electrode, as well as poor cohesion on the current collector itself. Consequently, the electrochemical performance of the coated electrodes is also improved by the addition of PA in the slurries. At a 5C rate, CMC/PA-based electrodes delivered 144 mAh·g-1, while PA-free electrodes reached only 124 mAh·g-1. When GG and pectin are used as binders, the adhesion of the coated layers to the current collector is reduced; however, the electrodes show comparable, if not slightly better, electrochemical performance than those based on CMC. Full lithium-ion cells, utilizing CMC/PA-made Li[Ni0.33Mn0.33Co0.33]O2 (NMC) cathodes and LTO anodes offer a stable discharge capacity of ~120 mAh·g-1(NMC) with high coulombic efficiencies.

An in situ SEM-FIB-based method for contrast enhancement and tomographic reconstruction for structural quantification of porous carbon electrodes.

A new in situ Scanning Electron Microscope-Focused Ion Beam-based method to study porous carbon electrodes involving Pt filling of pores from gaseous precursors has been demonstrated to show drastically improved image contrast between the carbon and porous phases when compared with the Si-resin vacuum-impregnation method. Whereas, the latter method offered up to 20% contrast, the new method offers remarkably higher contrast (42%), which enabled fast semi-automated demarcation of carbon boundaries and subsequent binarization of the images with very high fidelity. Tomographic reconstruction of the porous carbon electrode was then obtained from which several morphological parameters were quantified. The porosity was found to be 72±2%. The axial and radial tortuosites were 1.45±0.04 and 1.43±0.04, respectively. Pore size, which is defined to be the distance from the medial axis of the pore to the nearest solid boundary, was quantified. Average pore size determined from the pore size distribution was 90 nm and the corresponding 1 sigma ranges from 45 to 134 nm. Surface-to-volume ratio of the carbon phase was 46.5 µm(-1). The ratio of total surface area to the total volume of electrode including pores (i.e., specific surface area) was 13 µm(-1).

Electrochemical and electron microscopic characterization of Super-P based cathodes for Li-O2 batteries.

Aprotic rechargeable Li-O2 batteries are currently receiving considerable interest because they can possibly offer significantly higher energy densities than conventional Li-ion batteries. The electrochemical behavior of Li-O2 batteries containing bis(trifluoromethane)sulfonimide lithium salt (LiTFSI)/tetraglyme electrolyte were investigated by galvanostatic cycling and electrochemical impedance spectroscopy measurements. Ex-situ X-ray diffraction and scanning electron microscopy were used to evaluate the formation/dissolution of Li2O2 particles at the cathode side during the operation of Li-O2 cells.