Conductive Carbons by Design: Electrochemically Tailored Carbon Nanotube Conductive Additives for High-Rate Battery Electrodes | Final Report
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Herein we report on using a well known pigment that was used by ancient Egyptians and called Egyptian blue as an anode material for Li-ion batteries (background photo by Kokhanchikov via Adobe Stock).
2D nanosheets have been widely explored as electrode materials owing to their extraordinarily high electrochemical activity and fast solid-state diffusion. However, the scalable electrode fabrication based on this type of material usually suffers from severe performance losses due to restricted ion-transport kinetics in a large thickness. Here, a novel strategy based on evaporation-induced assembly to enable directional ion transport via forming vertically aligned nanosheets is reported. The orientational ordering is achieved by a rapid evaporation of mixed solvents during the electrode fabrication process. Compared with conventional drop-cast electrodes, which exhibit a random arrangement of the nanosheets and obvious decrease of rate performance with increasing thickness, the electrode based on the vertically aligned nanosheets is able to retain the original high rate capability even at high mass loadings and electrode thickness. Furthermore, combined electrochemical and structural characterization reveals the electrode composed of orientation-controlled nanosheets to possess lower charge-transfer resistances, leading to more complete phase transformation in the active material.
A quantitative link between crack evolution in lithium-ion positive electrodes and the degrading performance on cells is not yet well established nor is any single technique capable of doing so widely available. Here, we demonstrate a widely accessible high-throughput approach to quantifying crack evolution within electrodes. The approach applies super-resolution scanning electron microscopy (SEM) imaging of cross-sectioned NMC532 electrodes, followed by segmentation and quantification of crack features. Crack properties such as crack intensity, crack width and length are quantified as a function of charge rate (1C, 6C, and 9C) and cycle number (25, 225, and 600 cycles). Hundreds of particles are characterized for statistical confidence in the quantitative crack measurements. The data on crack evolution is compared to electrochemical data from full cells and half cells with the NMC532 positive electrodes. We show that while crack evolution strongly correlates with capacity fade in the first 25 cycles, it does not correlate well for the following hundreds of cycles indicating that cracking may not be the dominant cause of capacity fade throughout the cycle-life of cells.
Here, 3D structured Se-loaded bicontinuous porous carbon (BPC) electrodes were fabricated through colloidal templating of BPC followed by pulsed-voltage Se electrodeposition. The resultant electrodes were found to deliver a specific capacity of 665 mA h g -1 at a rate of 0.1 C, near the theoretical value for Se. When a vinylene carbonate containing electrolyte was utilized, the capacity fade over 500 cycles at 1 C rate was as small as a few percent. Impedance measurements and physical characterization of cycled electrodes indicated the exceptionally stable cycling performance was possibly due to vinylene carbonate resulting in formation of a stable SEI during cycling. Along with cycling stability, the rate performance of the 3D Se/BPC electrodes was also good. Due to the bicontinuous structure of carbonaceous current collector at rates as high as 5 C, the deliverable capacity was about 300 mA h g -1 .
By first exploring the limitations of thick planer electrodes, advanced predictive models were prepared to identify optimal electrode patterns for improved cycling performance. Herein, the impact of electrode laser patterning will be discussed in detail. First, materials characterization techniques (SEM-EDS, XRD) were used to explore the effect ultrafast laser ablation had on the electrode materials' morphology and structure. Next, the improvements in the patterned electrodes' electrochemical cycling performances and degrees of wetting will be compared to a pristine baseline case. Finally, the correlation between experimentally obtained data and model predictions will be presented and discussed.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.