Co-Crosslinked Water-Soluble Biopolymers as a Binder for High-Voltage LiNi0.5 Mn1.5 O4 |Graphite Lithium-Ion Full Cells.

The use of water-soluble, abundant biopolymers as binders for lithium-ion positive electrodes is explored because it represents a great step forward towards environmentally benign battery processing. However, to date, most studies that employ, for instance, carboxymethyl cellulose (CMC) as a binder have focused on rather low electrode areal loadings with limited relevance for industrial needs. This study concerns the use of natural guar gum (GG) as a binding agent for cobalt-free, high-voltage LiNi0.5 Mn1.5 O4 (LNMO), which realizes electrodes with substantially increased areal loadings, low binder content, and greatly enhanced cycling stability. Co-crosslinking GG through citric acid with CMC allows for an enhanced rate capability and essentially maintains the beneficial impact of using GG as a binder rather than CMC only. Lithium-ion full cells based on water-processed LNMO and graphite electrodes provide a remarkably high cycling stability with 80 % capacity retention after 1000 cycles at 1 C.

Understanding the Electrode/Electrolyte Interface Layer on the Li-Rich Nickel Manganese Cobalt Layered Oxide Cathode by XPS.

Layered lithium-rich nickel manganese cobalt oxide (LR-NMC) represents one of the most promising cathode materials for application in high energy density lithium-ion batteries. The extraordinary capacity delivered derives from a combination of both cationic and anionic redox processes. However, the latter ones lead to oxygen evolution which triggers structural degradation and electrode/electrolyte interface (EEI) instability that hinders the use of LR-NMC in practical application. In this work, we investigate the surface chemistry of LR-NMC and its evolution upon different conditions to give further insights into the processes occurring at the EEI. X-ray photoelectron spectroscopy studies reveal that once the organic component of the layer is formed, it remains stable independently on the higher cutoff voltage applied, while continuous growth of inorganics along with oxygen evolution occurs. The results performed on lithiated and delithiated LR-NMC surfaces indicate an instability of the EEI layer formed at high voltages, which undergoes a partial decomposition. Furthermore, the tris(pentafluorophenyl)borane electrolyte additive simultaneously prevents excess LiF formation and changes the chemical composition of the EEI layer. The latter is characterized by a higher amount of poly(ethylene oxide) oligomer species and LixPOyFz formation. In addition, the presence of boron-containing compounds in the EEI layer cannot be excluded, which may be also responsible of the increased thickness of the EEI layer. Finally, fast kinetics at elevated temperatures exacerbate the salt decomposition which results in the formation of an EEI which is thicker and richer in LiF.

Comparative Analysis of Aqueous Binders for High-Energy Li-Rich NMC as a Lithium-Ion Cathode and the Impact of Adding Phosphoric Acid.

Even though electrochemically inactive, the binding agent in lithium-ion electrodes substantially contributes to the performance metrics such as the achievable capacity, rate capability, and cycling stability. Herein, we present an in-depth comparative analysis of three different aqueous binding agents, allowing for the replacement of the toxic N-methyl-2-pyrrolidone as the processing solvent, for high-energy Li1.2Ni0.16Mn0.56Co0.08O2 (Li-rich NMC or LR-NMC) as a potential next-generation cathode material. The impact of the binding agents, sodium carboxymethyl cellulose, sodium alginate, and commercial TRD202A (TRD), and the related chemical reactions occurring during the electrode coating process on the electrode morphology and cycling performance is investigated. In particular, the role of phosphoric acid in avoiding the aluminum current collector corrosion and stabilizing the LR-NMC/electrolyte interface as well as its chemical interaction with the binder is investigated, providing an explanation for the observed differences in the electrochemical performance.