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The reversibility of the redox processes plays a crucial role in the electrochemical performance of lithium-excess cation-disordered rocksalt (DRX) cathodes. Here, we report a comprehensive analysis of the redox reactions in a representative Ni-based DRX cathode. The aim of this work is to elucidate the roles of multiple cations and anions in the charge compensation mechanism that is ultimately linked to the unique electrochemical performance of Ni-based DRX cathodes. Generally, the low-voltage discharge plateau that results in the low energy efficiency and strong voltage hysteresis is associated with the low-voltage oxygen redox. However, incorporating Mo cation promotes the oxygen activity and the Mo migration between octahedral and tetrahedral sites enhances the O reduction potential as well as energy efficiency. This work highlights the important role that electrochemically inactive transition metal plays in the redox chemistry and provides useful insights into the potential pathway to further address the challenges in Ni-based DRX systems.
In this report, we describe the electrochemistry of hybrid dual silver vanadium phosphorus oxide/carbon fluoride (Ag 2 VO 2 PO 4 /CF x ) cathodes with various weight ratios. Through modification of the Ag 2 VO 2 PO 4 /CF x ratio, we can control the gravimetric and volumetric capacity, as well as mitigate the voltage drop during high current pulses. The increase in impedance caused by irreversible LiF formation in CFx was reduced by the silver reduction-displacement during electrochemical discharge of the Ag 2 VO 2 PO 4 . Moreover, the addition of graphite was shown to reduce initial voltage delay. When Ag 2 VO 2 PO 4 dominates the electrode mass (i.e. 75/25 Ag 2 VO 2 PO 4 /CF x ) in the hybrid cathode, pulse testing shows less voltage drop and delay, but at the expense of capacity and energy density. As the amount of CFx in the composite increases (i.e. Ag 2 VO 2 PO 4 /CF x ratio of to 50/50 or 25/75), charge capacity and energy density increases, but at the expense of larger voltage drops and delays early in the discharge process. Thus, controlling the Ag 2 VO 2 PO 4 /CF x ratio can be used to tune the electrochemical properties of the dual cathode, allowing for optimization of capacity and power depending on the application.
This project has characterized the bulk emission properties of carbon nanotube (CNT) forest cathodes fabricated with varied geometries. The overall goal of the project has been to evaluate CNT forest cathodes as a potential replacement for thermionic cathodes currently used in accelerator systems.
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In this work, we present synchrotron x-ray investigations of thin film La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) model cathodes for solid oxide fuel cells, grown on electrolyte substrates by pulse laser deposition, in situ during half-cell operations. We observed dynamic segregations of cations, such as Sr and Co, on the surfaces of the film cathodes. The effects of temperature, applied potentials, and capping layers on the segregations were investigated using a surfacesensitive technique of total external reflection x-ray fluorescence. We also studied patterned thin film LSCF cathodes using high-resolution micro-beam diffraction measurements. We find chemical expansion decreases for narrow stripes. This suggests the expansion is dominated by the bulk pathway reactions. Lastly, the chemical expansion vs. the distance from the electrode contact was measured at three temperatures and an oxygen vacancy activation energy was estimated to be ~1.4 eV.
Abstract not provided
The first-cycle behavior of layered Li-rich oxides, including Li 2 MnO 3 activation and cathode electrolyte interphase (CEI) formation, significantly influences their electrochemical performance. However, the Li 2 MnO 3 activation pathway and the CEI formation process are still controversial. Here, the first-cycle properties of xLi 2 MnO 3 ·(1- x) LiNi 0.3 Co 0.3 Mn 0.4 O 2 ( x = 0, 0.5, 1) cathode materials were studied with an in situ electrochemical quartz crystal microbalance (EQCM). The results demonstrate that a synergistic effect between the layered Li 2 MnO 3 and LiNi 0.3 Co 0.3 Mn 0.4 O 2 structures can significantly affect the activation pathway of Li 1.2 Ni 0.12 Co 0.12 Mn 0.56 O 2 , leading to an extra-high capacity. It is demonstrated that Li 2 MnO 3 activation in Li-rich materials is dominated by electrochemical decomposition (oxygen redox), which is different from the activation process of pure Li 2 MnO 3 governed by chemical decomposition (Li 2 O evolution). CEI evolution is closely related to Li + extraction/insertion. Finally, the valence state variation of the metal ions (Ni, Co, Mn) in Li-rich materials can promote CEI formation. This study is of significance for understanding and designing Li-rich cathode-based batteries.
Li metal batteries pairing Li metal anode with high-nickel layer structured oxide cathode are a promising energy storage technology to achieve high energy density. To obtain long cycling life for Li metal batteries, the electrolyte plays a pivotal role in stabilizing both the Li metal anode and the high-nickel cathode upon electrochemical cycling. Herein, we report a carbonate electrolyte that enables a Li||LiNi 0.8 Mn 0.1 Co 0.1 O 2 pouch cell to achieve a high gravimetric energy density of 366 Wh/kg and unprecedented cycling stability with 80% capacity retention after 335 cycles. Here, the 19 F quantitative nuclear magnetic resonance spectroscopy and interface characterization demonstrate that FEC and LiDFOB can reduce the consumption rate of each other and the electrolyte, form a robust LiF-rich SEI on Li metal anode, and improve the microstructure integrity of the high-nickel cathode.
Cobalt-free lithium nickel oxide (LNO) has garnered significant interest as the end member of high-nickel layered oxide cathodes for next-generation batteries. However, its practical performance notably underperforms expectations because of the structural degradation and unstable interfacial chemistry with electrolytes during cycling. Here, in this study, we report that a durable cathode-electrolyte interface (CEI), enriched by in situ formed sulfides and borides, can inhibit LNO structural degradation and suppress Ni ion dissolution. With the CEI protection, the stability of LNO can be remarkably extended, and batteries demonstrate a capacity retention rate of 84% (30 °C) and 79% (50 °C) after 200 cycles at 1C, respectively. These results demonstrate that enriching CEI with sulfur-containing species can effectively stabilize the interfacial chemistry of LNO, particularly at an elevated temperature of 50 °C. This finding provides valuable perspectives on designing electrolytes for cobalt-free LNO and other high-Ni cathodes toward the development of next-generation high-energy-density lithium-ion batteries.
Here, to reduce the cost of fuel cell stacks and systems, it is important to create commercial catalysts that are free of platinum group metals (PGMs). To do this, such catalysts must have very high activity, but also have the correct microstructure to facilitate the transport of reactants and products. Here, we show a high-performing commercial oxygen reduction catalyst that was specifically developed for operation in alkaline media and is demonstrated in the cathode of operating anion-exchange membrane fuel cells (AEMFCs). With H 2 /O 2 reacting gases, AEMFCs made with Fe–N–C cathodes achieved a peak power density exceeding 2 W cm –2 (>1 W cm –2 with H 2 /air) and operated with very good voltage durability for more than 150 h. These AEMFCs also realized an iR-corrected current density at 0.9 V of 100 mA cm –2 . Finally, in a second configuration, Fe–N–C cathodes paired with low-loading PtRu/C anodes (0.125 mg PtRu per cm 2 , 0.08 mg Pt per cm 2 ) demonstrated a specific power of 10.4 W per mg PGM (16.25 W per mg Pt).