Gas Evolution Kinetics in Overlithiated Positive Electrodes and its Impact on Electrode Design

Abstract Increasing lithium contents within the lattice of positive electrode materials is projected in pursuit of high‐energy‐density batteries. However, it intensifies the release of lattice oxygen and subsequent gas evolution during operations. This poses significant challenges for managing internal pressure of batteries, particularly in terms of the management of gas evolution in composite electrodes—an area that remains largely unexplored. Conventional assumptions postulate that the total gas evolution is estimated by multiplying the total particle count by the quantities of gas products from an individual particle. Contrarily, this investigation on overlithiated materials—a system known to release the lattice oxygen—demonstrates that loading densities and inter‐particle spacing in electrodes significantly govern gas evolution rates, leading to distinct extents of gas formation despite of an equivalent quantity of released lattice oxygen. Remarkably, this study discoveres that O2 and CO2 evolution rates are proportional to 1O2 concentration by the factor of second and first‐order, respectively. This indicates an exceptionally greater change in the evolution rate of O2 compared to CO2 depending on local 1O2 concentration. These insights pave new routes for more sophisticated approaches to manage gas evolution within high‐energy‐density batteries

A Facile, Dry-Processed Lithium Borate-Based Cathode Coating for Improved All-Solid-State Battery Performance

Sulfide-based solid electrolytes are known to have narrow electrochemical windows which limit their practical use in all-solid-state batteries (ASSBs). Specifically, when paired with a high-voltage transition metal oxide (TMO) cathode, the electrolyte will typically undergo unwanted degradation via chemical reactions or electrochemical oxidation, especially upon charging to voltages beyond the electrochemical stability window of the electrolyte. To mitigate these undesired reactions, thin (<10 nm), conformal, ionically-conducting, and electronically-insulating oxide-based protective coating layers have been applied on the cathode, typically via a solution process. In this work, a lithium borate-based (LBO) coating, prepared instead with a dry coating process, was shown to have the same beneficial properties. As evidenced by electrochemical characterization, the developed LBO coating shows good cycling performance and even performs better than the LiNbO3 coating commonly used in the literature. This new solvent-free coating method can thus be used to fabricate longer-lasting ASSBs

A Facile, Dry-Processed Lithium Borate-Based Cathode Coating for Improved All-Solid-State Battery Performance

Sulfide-based solid electrolytes are known to have narrow electrochemical windows which limit their practical use in all-solid-state batteries (ASSBs). Specifically, when paired with a high-voltage transition metal oxide (TMO) cathode, the electrolyte will typically undergo unwanted degradation via chemical reactions or electrochemical oxidation, especially upon charging to voltages beyond the electrochemical stability window of the electrolyte. To mitigate these undesired reactions, thin (<10 nm), conformal, ionically-conducting, and electronically-insulating oxide-based protective coating layers have been applied on the cathode, typically via a solution process. In this work, a lithium borate-based (LBO) coating, prepared instead with a dry coating process, was shown to have the same beneficial properties. As evidenced by electrochemical characterization, the developed LBO coating shows good cycling performance and even performs better than the LiNbO3 coating commonly used in the literature. This new solvent-free coating method can thus be used to fabricate longer-lasting ASSBs

Stack Pressure Considerations for Room-Temperature All-Solid-State Lithium Metal Batteries

All-solid-state batteries are expected to enable batteries with high energy density with the use of lithium metal anodes. Although solid electrolytes are believed to be mechanically strong enough to prevent lithium dendrites from propagating, various reports today still show cell failure due to lithium dendritic growth at room temperature. While cell parameters such as current density, electrolyte porosity and interfacial properties have been investigated, mechanical properties of lithium metal and the role of applied stack pressure on the shorting behavior is still poorly understood. Here, we investigated failure mechanisms of lithium metal in all-solid-state batteries as a function of stack pressure, and conducted in situ characterization of the interfacial and morphological properties of the buried lithium in solid electrolytes. We found that a low stack pressure of 5 MPa allows reliable plating and stripping in a lithium symmetric cell for more than 1000 hours, and a Li | Li6PS5Cl | LiNi0.80Co0.15Al0.05O2 full cell, plating more than 4 um of lithium per charge, is able to cycle over 200 cycles at room temperature. These results suggest the possibility of enabling the lithium metal anode in all-solid-state batteries at reasonable stack pressures.Comment: 13 pages, 5 figure

Understanding the Irreversible Reaction Pathway of the Sacrificial Cathode Additive Li6CoO4

The use of a sacrificial cathode additive that contains a large amount of lithium is one potential solution to compensate for the irreversible capacity loss associated with next-generation anodes such as silicon. Antifluorite-type Li6CoO4 has attracted attention as a potential cathode additive owing to its remarkably high theoretical lithium extraction capacity. However, the complex mechanism of lithium extraction as well as the oxygen loss from Li6CoO4 is not well understood. A generalizable computational thermodynamics and experimental framework is presented to understand the lithium-extraction pathway of Li6CoO4. It is found that one lithium per formula unit can be topotactically extracted from Li6CoO4, followed by an irreversible and nontopotactic phase transformation to Li2CoO3 or LiCoO2 depending on the temperature. The results show that peroxide species may form to charge-compensate for Li extraction which is undesirable as this can lead to gas release during battery operation. It is suggested that charging Li6CoO4 at an elevated temperature that the electrolyte can withstand, redirects the reaction pathway and prevents the formation of intermediate peroxide species making it an effective and stable sacrificial cathode additive

Site selectivity of single dopant in high-nickel cathodes for lithium-ion batteries

Improving the structural stability of high-capacity high-Ni cathodes through doping has been investigated, but the structural stabilization mechanisms of dopants remain unclear. This study focused on unraveling the influence of individual dopants, Aluminium, Titanium, or Zirconium, on the structural stabilization of high-Ni cathodes. X-ray Diffraction and High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) were employed for quantitative analysis of cation mixing, and for the first time, HAADF-STEM and deep learning were combined to improve the accuracy and efficiency of the analysis. The atomic-scale energy dispersive spectroscopy analysis identified transition metal sites as the primary doping sites in doped high-Ni cathodes. Density funtional theory calculations revealed that dopants enhance the interatomic bonds between Ni and O, thereby inhibiting cation mixing. Among the studied dopants, Ti was found to have the most substantial influence in enhancing structural stability. This study contributes to an understanding of single dopant on the structural stability of high-Ni cathodes, aiding the design of next-generation lithium-ion batteries. © 2024 The Authors11Nsciescopu