No abstract

Water‐processable composite electrodes are attractive both ecologically and economically. The binders sodium carboxymethyl cellulose (CMC‐Na) and poly(sodium acrylate) (PAA‐Na) were shown to have improved electrochemical performance over conventional binders. In many studies, a binder content of approximately 10 wt % has been applied, which is not suitable for large‐scale electrode production due to viscosity and energy‐density considerations. Therefore, we examined herein three electrode formulations with binder contents of 4 wt %, namely, CMC‐Na:SBR (SBR=styrene butadiene rubber), PAA‐Na, and CMC‐Na:PAA‐Na, on both laboratory and pilot scales. The formulations were evaluated on the basis of slurry rheology, coating adhesion, and electrochemical behavior in half‐ and full‐cells. CMC‐Na:SBR composites provided the best coating adhesion, independent of the mass loading and scale, and also showed the best capacity retention after 100 cycles. Previously reported merits of better cycling efficiencies and solid–electrolyte interphase formation for graphite–PAA composites appeared to vanish upon reducing the binder content to realistic levels.

Due to their extreme volume expansion, Si/C-composites suffer from fracture or delamination and consequent capacity fading during the Li-ion cell operation. One approach to reduce the electrical contact loss and improve the performance is the application of mechanical pressure on the cell. Therefore, a comprehensive aging study of Si/C|NMC811 pouch cells is conducted with cells in different compression configurations as uncompressed and under flexible and fixed compression at pressure levels in the range of 0.08 MPa, 0.42 MPa, and 0.84 MPa. In-situ swelling measurements by dilation as well as in-operando mapping of the pressure distribution on the cell surfaces reveal the positive influence of the low pressure fixed and the middle pressure flexible compression on the cycle life. For the heavily fixed compressed cells, an inhomogeneous pressure distribution and occurring pressure hot -spots close to the cell current collectors of up to 5.2 MPa are found. An extensive post-mortem analysis including SEM cross-sectioning and EIS measurements of the aged anodes and the separator confirms cell failure by different aging mechanisms depending on the type of compression. Aging experiments of Si/C|NMC811 cylindrical 18650-cells show local differences along the jelly roll which are explained by the help of the pouch cell results.

No abstract

Addition of a certain amount of Si to state of the art graphite anodes has become the most prominent option to increase the energy density of Li-ion cells. However, the distribution of Si in the depth of Si/C anodes is difficult to measure with established methods. In this paper, we present a semiquantitative depth profiling method based on glow discharge optical emission spectroscopy (GD-OES). The calibration of this method covers 0−100 wt % Si content in the anode and is validated by pilot-line-coated Si/C anodes with known Si contents. The quantified depth profiles with different pristine anodes show a homogeneous distribution of Si before contact with electrolyte. In contrast to that, pilot-line-coated electrodes after formation and long-term cycled cells with Si/C composite anodes from a commercially available 18650-type cell, as control measurement, reveal a peak near the anode surface, which corresponds to a new aging mechanism. This aging mechanism is verified by interrupted GD-OES sputtering. Raman spectroscopy and ICP-OES substantiate the dissolution of Si species in the electrolyte.