Peter Axmann

LiMn2O4 Spinel/LiNi0.8Co0.15Al0.05O2 Blends as Cathode Materials for Lithium-Ion Batteries

The influence of blending LiMn 2 O 4 spinel with LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) onto the electrochemical and thermal behaviors of the resulting blend electrodes was investigated. The results indicate that NCA addition has a beneficial effect on the discharge capacity of the blends, and thus on the energy density, but in the same time increases the irreversible capacity loss in the first cycle. Also, it deteriorates the rate capability. DSC/TG measurements showed that heat generation for blends containing 50 wt% NCA or less is significantly lower than in the case of pure NCA. Mn dissolution from spinel was considerably reduced by the addition of NCA. Among all investigated blends, the one with 33.3 wt% NCA showed the best behavior in all tested matters.

Combining Optimized Particle Morphology with a Niobium-Based Coating for Long Cycling-Life, High-Voltage Lithium-Ion Batteries.

Morphologically optimized LiNi0.5 Mn1.5 O4 (LMNO-0) particles were treated with LiNbO3 to prepare a homogeneously coated material (LMNO-Nb) as cathode in batteries. Graphite/LMNO-Nb full cells present a twofold higher cycling life than cells assembled using uncoated LMNO-0 (graphite/LMNO-0 cell): Graphite/LMNO-0 cells achieve 80 % of the initial capacity after more than 300 cycles whereas for graphite/LMNO-Nb cells this is the case for more than 600 cycles. Impedance spectroscopy measurements reveal significantly lower film and charge-transfer resistances for graphite/LMNO-Nb cells than for graphite/LMNO-0 cells during cycling. Reduced resistances suggest slower aging related to film thickening and increase of charge-transfer resistances when using LMNO-Nb cathodes. Tests at 45 °C confirm the good electrochemical performance of the investigated graphite/LMNO cells while the cycling stability of full cells is considerably lowered under these conditions.

Preparation of LiBOB via rheological phase method and its application to mitigate voltage fade of Li1.16[Mn0.75Ni0.25]0.84O2 cathode

Lithium bis(oxalato)borate (LiBOB) was synthesized via a novel rheological phase reaction method without any recrystallization procedure. The purity of the as-obtained LiBOB has been identified in comparison with the commercial sample and our sample prepared from solid-state reaction method. The results of XRD, ICP, and 11B NMR demonstrate that high pure LiBOB has been synthesized via rheological phase reaction method with significantly simplified synthetic process. Moreover, LiBOB sample has been investigated as electrolyte additive to improve the electrochemical performances of high-energy lithium-rich layered oxide. The cycling performances imply that 0.03 M and 0.05 M LiBOB additive can mitigate discharge voltage fade and enhance the cycle stability of Li1.16[Mn0.75Ni0.25]0.84O2 material. The CV, EIS and XPS data indicate that LiBOB oxidizes at ∼4.3 V (vs. Li/Li+) on the cathode surface during the first charge to form a specific SEI layer with larger amount of organic species and fairly less content of LiF, which decreases the interfacial polarization and protects the active material from surface degradation, thereby mitigates the voltage-fade of Li-rich cathode.

A High‐Voltage and High‐Capacity Li1+xNi0.5Mn1.5O4 Cathode Material: From Synthesis to Full Lithium‐Ion Cells

Abstract We report Co‐free, Li‐rich Li1+xNi0.5Mn1.5O4 (0<x<1) compounds as high‐voltage and high‐capacity cathode materials for Li‐ion cells. Their tailored morphology allows high density and facile processability for electrode development. In the potential range 2.4–4.9 V, the cathode material of composition Li1.5Ni0.5Mn1.5O4 shows excellent performance in terms of capacity and cycling stability in half‐cells. In addition, for the first time, we demonstrate the application of the high‐voltage and high‐capacity cathode in full Li‐ion cells with graphite anodes with very high cycling stability. The electrochemical performance and low cost of the cathode material, together with the feasibility of a chemical method to obtain Li‐rich Li1+xNi0.5Mn1.5O4 (0<x<1), make practical applications of high‐energy density Li‐ion batteries possible.

Insights into the Impact of Impurities and Non‐Stoichiometric Effects on the Electrochemical Performance of Li2MnSiO4

A series of Li2 MnSiO4 samples with various Li, Mn, and/or Si concentrations are reported to study for the first time the effect of impurities and deviation from ideal stoichiometry on electrochemical behavior. Carbon-coated and nanosized powders are obtained at 600 °C and compared with those synthetized at 900 °C. Samples are investigated using XRD, SEM, high-resolution TEM, attenuated total reflection infrared spectroscopy and Brunauer-Emmett-Teller surface area to characterize crystal structure, particle size, impurity amount, morphology, and surface area. Electrochemical performance depends on impurities such as MnO as well as crystallite size, surface area, and non-stoichiometric phases, which lead to the formation of additional polymorphs such as Pmnb and P21 /n of Li2 MnSiO4 at low calcination temperatures. A systematic analysis of the main parameters affecting the electrochemical behavior is performed and trends in synthesis are identified. The findings can be applied to optimize different synthesis routes for attaining stoichiometric and phase-pure Pmn21 Li2 MnSiO4 as cathode material for Li-ion batteries.

Structural study of β-Ni(OH)2 and α-Ni(OH)2 variants for electrode applications

Abstract Powder samples of β-Ni(OH)2 and doped variants of the α-Ni(OH)2 structure type were prepared by a coprecipitation method. Chemical composition was analysed by ICP. Samples were measured by X-ray powder diffraction (XRD). Single peak profiles were analysed by fitting a splitted Pearson VII funktion to the measured patterns. Peak profile data were collected and a strong anisotropic peak broadening was observed. Structure models of possible stacking orders in β-Ni(OH)2 and doped α-Ni(OH)2 were developed. DIFFaX simulations of structure models with statistical stacking orders were carried out. The simulated peak profiles were compared to the measured ones and a fairly good agreement was found. A semiquantitative analysis of the stacking faults in these materials is shown.

Influence of the molecular weight of poly-acrylic acid binder on performance of Si-alloy/graphite composite anodes for lithium-ion batteries

Abstract 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.

Understanding the Effect of the Preparation Process on the Electrochemical Properties of 0.25Li2MnO3∙0.75LiNi1/2Mn1/2O2 by Rietveld Refinement Method

0.25Li2MnO3•0.75LiNi1/2Mn1/2O2 solid solution was prepared via a two-step calcination technique. No appreciable difference between the end products can be detected from the X-ray diffraction patterns including the superstructure reflections. However, the material prepared from preheating the precursor at 450°C for 4h in N2 delivers a high first charge capacity of 287mAhg-1 between 2.5and 4.8V at 0.5C, while the samples obtained from preheating the precursor for 10h in air exhibit a low capacity of 199 mAhg-1 and an undetectable plateau around 4.5V in the initial charge curve. With an aim to identify the influence of preparation process on the structural and electrochemical properties, Rietveld refinement method was performed on the detailed structure testing with the model integrating R m layered rock salts and Fd m cubic ones. The end products prepared from precalcining the precursor in N2 shows low proportion of Fd m domain about 8.0% and larger Li-O slab space in dominating R m rock salts. By contrast, the samples obtained from prolonging the process-prheating time to 10h in air consists of 12.7% Fd m cubic rock salts and 87.3% R m layered ones. The observations indicate that the samples obtained from different precursor-preheating process appear a variation in the local environment of Li+ insertion/extraction, which give an evidence on their electrochemical lithiation/delithiation process shown in the CV curves.