ABSTRACT
Porous composite battery electrode performance is influenced by a large number of manufacturing decisions. While it is common to evaluate only finished electrodes when making process adjustments, one must then make inferences about the fabrication process dynamics from static results, which makes process optimization very costly and time-consuming. To get information about the dynamics of the manufacturing processes of these composites, we have built a miniature coating and drying apparatus capable of fabricating lab-scale electrode laminates while operating within an X-ray beamline hutch. Using this tool, we have collected the first radiography image sequences of lab-scale battery electrode coatings in profile, taken throughout drying processes conducted under industrially relevant conditions. To assist with interpretation of these image sequences, we developed an automated image analysis program. Here, we discuss our observations of battery electrode slurry samples, including stratification and long-term fluid flow, and their relevance to composite electrode manufacturing.
ABSTRACT
We report the effects of component ratios and mixing time on electrode slurry viscosity. Three component quantities were varied: active material (graphite), conductive material (carbon black), and polymer binder (carboxymethyl cellulose, CMC). The slurries demonstrated shear-thinning behavior, and suspension properties stabilized after a relatively short mixing duration. However, micrographs of the slurries suggested their internal structures did not stabilize after the same mixing time. Increasing the content of polymer binder CMC caused the greatest viscosity increase compared to that of carbon black and graphite.
ABSTRACT
Correction for 'Lithium dendrite growth mechanisms in polymer electrolytes and prevention strategies' by Pallab Barai et al., Phys. Chem. Chem. Phys., 2017, 19, 20493-20505.
ABSTRACT
Future lithium-ion batteries must use lithium metal anodes to fulfill the demands of high energy density applications with the potential to enable affordable electric cars with 350-mile range. However, dendrite growth during charging prevents the commercialization of this technology. It has been demonstrated that the presence of a compressive mechanical stress field around a dendritic protrusion prevents growth. Several techniques based on this concept, such as protective layers, externally applied pressure and solid electrolytes have been investigated by other researchers. Because of the low coulombic efficiencies associated with the stiff protective layers and high-pressure conditions, implementation of these techniques in commercial cells is complicated. Polymer-based solid electrolytes demonstrate better efficiency and capacity retention capabilities. However, dendrite growth is still possible in polymer electrolytes at higher current densities. The simulations described in this article provide guidance on the conditions under which dendrite growth is possible in polymer cells and targets for material properties needed for dendrite prevention. Increasing the elastic modulus of the electrolyte prevents the growth of dendritic protrusions in two ways: (i) higher compressive mechanical stress leads to reduced exchange current density at the protrusion peak compared to the valley, and (ii) plastic deformation of lithium metal results in reduction of the height of the dendritic protrusion. A phase map is constructed, showing the range of operation (applied current) and design (electrolyte elastic modulus) parameters that corresponds to stable lithium deposition. It is found that increasing the yield strength of the polymer electrolyte plays a significant role in preventing dendrite growth in lithium metal anodes, providing a new avenue for further exploration.
ABSTRACT
Control over porous electrode microstructure is critical for the continued improvement of electrochemical performance of lithium ion batteries. This paper describes a convenient and economical method for controlling electrode porosity, thereby enhancing material loading and stabilizing the cycling performance. Sacrificial NaCl is added to a Si-based electrode, which demonstrates an areal capacity of â¼4 mAh/cm(2) at a C/10 rate (0.51 mA/cm(2)) and an areal capacity of 3 mAh/cm(2) at a C/3 rate (1.7 mA/cm(2)), one of the highest material loadings reported for a Si-based anode at such a high cycling rate. X-ray microtomography confirmed the improved porous architecture of the SiO electrode with NaCl. The method developed here is expected to be compatible with the state-of-the-art lithium ion battery industrial fabrication processes and therefore holds great promise as a practical technique for boosting the electrochemical performance of lithium ion batteries without changing material systems.
