Li2RuO3 Research Articles

Improvement in Electrochemical Performance of Lithium Rich Li2RuO3 Cathode With Co-doping Strategy

Lithium-rich layered oxides based on Ru are interesting as cathode materials because they have high energy density and reversible capacity. However, due to the problems of weak structural stability and voltage decay, their commercial utility is limited. To address this, we use a DFT+U quantum mechanics to investigate the co-doping strategy on Li2RuO3 (LRO) for improved battery performance. In particular, the effect of two co-dopants Ti and Co has been studied. The co-doping strategy has been found to significantly improve the structural and thermal stability of LRO. By slowing the oxygen removal reaction, Ti and Co improve structural stability. Co-doping with Ti and Co increases the maximum open circuit voltage at least by 5.5% and decreases the voltage reduction by a minimum of 44%. Bandgap is also increased by a minimum of 6% with co-doping. In particular, Li2Ru0.5Ti0.375Co0.125O3 provides the highest maximum voltage of 4.4V with 61% decrease in the voltage reduction and 40% lower bandgap (0.45eV).

Unveiling the mechanism of charge compensation in Li2RuxMn1−xO3 by tracking atomic structural evolution

The relationship between the structural evolution and redox of Li-rich transition-metal layered oxides (LLOs) cathodes remains ambiguous, obstructing the development of high-performance lithium-ion (Li+) battery. Herein, the coherent effects of local atomic and electronic structure in Li2RuxMn1−xO3 (LRMO) with a wide voltage window (1.3–4.8 V) is identified by in situ X-ray absorption fine spectroscopy (XAFS) and chemometrics. We not only skillfully separated the redox active structures to track the electrochemical path, but also visualized the coupling mechanism between the evolution of Ru-Ru dimer and the (de) excitation of cations and anions. Furthermore, introducing manganese triggers the “heterogeneity” of coordination environment and electronic structure between Ru and Mn after discharge to 3 V. The change of thermodynamic and kinetic paths affects the relithiation, and further leads to the hysteresis of the anion activation structure relaxation of Li2Ru0.4Mn0.6O3 relative to Li2RuO3 (LRO). Additionally, it is demonstrated that the high charge cut-off voltage restrains the relaxation of anionic active structure in LRO from a new perspective through comparative experiments. Our work associates the evolution of atomic structure with charge compensation and negative electrochemical reactions such as voltage hysteresis (VH) and capacity attenuation, deepening the understanding electrochemical reaction mechanism of LLOs during the first cycle and providing a theoretical support for the further design and synthesis of high-efficiency cathodes.

Oxygen Redox Versus Oxygen Evolution in Aqueous Electrolytes: Critical Influence of Transition Metals.

Aqueous lithium‐ion batteries are promising electrochemical energy storage devices owing to their sustainable nature, low cost, high level of safety, and environmental benignity. The recent development of a high‐salt‐concentration strategy for aqueous electrolytes, which significantly expands their electrochemical potential window, has created attractive opportunities to explore high‐performance electrode materials for aqueous lithium‐ion batteries. This study evaluates the compatibility of large‐capacity oxygen‐redox cathodes with hydrate‐melt electrolytes. Using conventional oxygen‐redox cathode materials (Li2RuO3, Li1.2Ni0.13Co0.13Mn0.54O2, and Li1.2Ni0.2Mn0.6O2), it is determined that avoiding the use of transition metals with high catalytic activity for the oxygen evolution reaction is the key to ensuring the stable progress of the oxygen redox reaction in concentrated aqueous electrolytes.

Multiscale Investigation into the Co‐Doping Strategy on the Electrochemical Properties of Li2RuO3 Cathodes for Li‐Ion Batteries

AbstractHerein, a co‐doping strategy is proposed for a Li‐rich layered Ru‐based cathode, Li2RuO3 (LRO), as promising next‐generation cathode materials. Using quantum mechanics, molecular dynamics, and macroscale mathematical modeling, the electrochemical properties such as voltage, electronic structure, thermodynamic structural stability, O2 stability, electrical conductivity coefficient, the energy barrier, theoretical capacity, Li‐ion diffusion coefficient, proportion of the electrode materials in the internal resistance of LIBs, and the percentage of waste energy in charge‐discharge cycles of all samples are calculated and compared. The results show that the cathode with Ti and Zr has the highest maximum voltage and the lowest voltage reduction during the discharge process. Also, it has 25 % lower waste energy in comparison to the undoped cathodes which indicates significant improvements in its efficiency. On the other hand, Li2Ru0.75Ti0.125Cr0.125O3 (LRTCO) has the highest electrical conductivity coefficient, thermodynamic, structural and oxygen stability as well as theoretical capacity, which indicates the highest durability and safety improvement for LRO cathode materials. Moreover, it is shown in this study that the ohmic potential drop for the studied cathodes is negligible and is not worth the investment for reducing the internal resistance. This study can provide a brighter insight into the co‐doping strategy for materials in future investigations.

Enhancement of Electrochemical Properties of Lithium Rich Li2RuO3 Cathode Material

Lithium-rich layered Ru-based oxides are interesting cathode materials due to their high energy density and reversible capacity. However, their poor structural stability and voltage decay hinder their broad commercial applicability. To address this, we investigate the co-doping strategy on Li2RuO3 (LRO) for improved battery performance using a combination of quantum mechanics, molecular dynamics, and pseudo-1-dimensional (P1D) formulations. Specifically, in addition to the effect of Ti as a dopant in Li2Ru0.5Ti0.5O3 (LTO), the effect of three co-dopants, Tc, Rh, or Pd in Li2Ru0.5Ti0.25M0.25O3 has also been studied. It has been found that the co-doping strategy significantly improves the thermal stability of LRO. Tc and Ti improve structural stability by reducing the oxygen removal reaction. Pd and Tc reduce the bandgap considerably, leading to higher electrical conductivity. The results show that co-doping minimizes the energy required for Li-ions diffusion. In particular, Tc significantly enhances the Li-ions diffusion in LRO and LTO. Further co-dopants Rh, Pd, and Tc improve the maximum voltage of LRO, as well as the voltage stability by reducing the voltage reduction. Finally, P1D simulations show that while LTO provides the highest voltage and power operation, doping it with Tc and Pd increases its efficiency by reducing the ohmic potential drop and diffusion polarization.

Novel Ordered Rocksalt-Type Lithium-Rich Li2Ru1–xNixO3−δ (0.3 ≤ x ≤ 0.5) Cathode Material with Tunable Anionic Redox Potential

In this work, a series of ordered rocksalt (OR) type Li-rich Li2Ru1–xNixO3−δ (LRNxO, 0.3 ≤ x ≤ 0.5) are successfully synthesized and investigated for the first time. X-ray diffraction and neutron powder diffraction patterns exhibit an obvious phase transition from layered to an OR structure as the Ni content gradually increases from x = 0 to x = 0.5, which leads to different electrochemical behaviors. In the case of OR-LRN0.4O, an ∼350 mV decrease of the oxygen oxidation potential compared with Li2RuO3 (LRO) is observed from around 4.2 to 3.85 V, which is confirmed by both X-ray photelectron O 1s spectra and dQ/dV results. The role of Ni substitution on the oxygen redox reaction is studied by first-principles calculations, and it is concluded that the formation of the OR structure caused by Ni substitution is the main reason for lowering the oxygen oxidation potential. In addition, the average discharge voltage of OR-LRN0.4O is also enhanced compared with LRO. This work provides a novel innovative strategy to modulate and control the oxygen anion redox reaction for high-energy-density Li-rich materials, which shed light on the fundamental understanding and optimizing of the anion redox process in Li-rich materials.