No abstract

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 LiNiMnCoO (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.

Lithium-rich transition-metal-oxide cathodes are among the most promising materials for the next lithium-ion-batteries generation because they operate at high voltages and deliver high capacities. However, their cycle-life remains limited and individual roles of the transition-metals are still not fully understood. By bulk-sensitive X-ray absorption and emission spectroscopy on Li[Li 0.2 Ni 0.16 Mn 0.56 Co 0.08 ]O 2 we inspect the behavior of Mn, generally considered inert upon the electrochemical process. During the first charge Mn appears to be redox-active showing a partial transformation from high-spin Mn 4+ to Mn 3+ in both high and low spin configurations, where the latter is expected to favor reversible cycling. The Mn redox-state along cycling continues changing in opposition to the expected charge compensation and is correlated with Ni oxidation/reduction, also spatially. The findings suggest the strain induced on the Mn-O sublattice by the Ni oxidation to trigger the Mn reduction. These results unravel the Mn role in controlling the electrochemistry of Li-rich cathodes. The wide use of rechargeable lithium-ion batteries and the continuously growing demands of increased energy and power densities stimulate the investigation of novel high-voltage cathode materials. 1, 2 Lithiated transition-metal-oxides are under intensive investigation as cathode materials for Li-ion batteries. The best performing cathodes show an ordered layered structure, which locates the Li ions in between the metal-oxygen layers. 3, 4 Generally these materials offer the best cycle life when the layered structure is maintained during the delithiation/lithiation process. Among Mn, Co, and Ni, only Co 3+ and Ni 3+ enable 2D layered Li-based oxides. LiNiO 2 , however, has various drawbacks related to its crystal structure: difficulty to be synthesized, poor cycling performance, and poor thermal stability. 5 As a matter of fact, LiCoO 2 is the 2D layered oxide showing the best electrochemical performance and the most commonly used material in Li-ion batteries 6. The