First-principles computational insights into lithium battery cathode materials

Exploring the Mechanism of Surface Cationic Vacancy Induces High Activity of Metastable Lattice Oxygen in Li- and Mn-Rich Cathode Materials

Li- and Mn-rich layered oxides exhibit high specific capacity due to the cationic and anionic reaction process during high-voltage cycling (≥4.6 V). However, they face challenges such as low initial coulombic efficiency (~70 %) and poor cycling stability. Here, we propose a combination of H3BO3 treatment and low temperature calcination to construct a shell with cationic vacancy on the surface of Li1.2Ni0.2Mn0.6O2 (LLNMO). The H3BO3 treatment produces cationic vacancy and lattice distortion, forming an oxidized On- (0 Collapse

Key Words

• Li-rich cathodes
• cationic vacancy
• coulombic efficiency
• metastable state
• oxygen activation

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Grants

• 22108218 the National Natural Science Foundation of China
• 22105059 the National Natural Science Foundation of China

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Affiliation(s)

Tian Zhao School of Chemical Engineering and Technology, Xi'an Jiaotong University, No. 28, West Xianning Road, Xi'an, Shaanxi, 710049, China
Jilu Zhang School of Chemical Engineering and Technology, Xi'an Jiaotong University, No. 28, West Xianning Road, Xi'an, Shaanxi, 710049, China Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
Kai Wang School of Materials and Energy, Lanzhou University, No. 222, Tianshui South Road, Lanzhou, 730000, China
Yao Xiao College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, 325035, P. R. China
Qin Wang School of Chemical Engineering and Technology, Xi'an Jiaotong University, No. 28, West Xianning Road, Xi'an, Shaanxi, 710049, China School of Chemical Engineering, Sichuan University, No. 24 South Section 1, Yihuan Road, 610065, Chengdu, China
Longfei Li School of Chemistry, Engineering Research Center of Energy Storage Materials, Devices of Ministry of Education, National Innovation Platform (Center) for Industry-Education Integration of Energy Storage Technology, Xi'an Jiaotong University, Xi'an, 710049, Shanxi, China
Jochi Tseng Diffraction and Scattering Division, Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198, Japan
Meng-Cheng Chen Department of Applied Chemistry and Center for Emergent Functional Matter Science, National Yang Ming Chiao Tung University, Hsinchu, 300, Taiwan
Jian-Jie Ma Department of Applied Chemistry and Center for Emergent Functional Matter Science, National Yang Ming Chiao Tung University, Hsinchu, 300, Taiwan
Ying-Rui Lu National Synchrotron Radiation Research Center, Hsinchu, 300, Taiwan
Ishii Hirofumi National Synchrotron Radiation Research Center, Hsinchu, 300, Taiwan
Yu-Cheng Shao National Synchrotron Radiation Research Center, Hsinchu, 300, Taiwan
Xiaoxian Zhao Department of Chemistry, College of Science, Hebei Agriculture University, Baoding, 071001, P. R. China
Sung-Fu Hung Department of Applied Chemistry and Center for Emergent Functional Matter Science, National Yang Ming Chiao Tung University, Hsinchu, 300, Taiwan
Yaqiong Su School of Chemistry, Engineering Research Center of Energy Storage Materials, Devices of Ministry of Education, National Innovation Platform (Center) for Industry-Education Integration of Energy Storage Technology, Xi'an Jiaotong University, Xi'an, 710049, Shanxi, China
Xiaoke Mu School of Materials and Energy, Lanzhou University, No. 222, Tianshui South Road, Lanzhou, 730000, China
Weibo Hua School of Chemical Engineering and Technology, Xi'an Jiaotong University, No. 28, West Xianning Road, Xi'an, Shaanxi, 710049, China Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany

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Recent Advances in High-Entropy Layered Oxide Cathode Materials for Alkali Metal-Ion Batteries

Since the electrochemical de/intercalation behavior is first detected in 1980, layered oxides have become the most promising cathode material for alkali metal-ion batteries (Li+/Na+/K+; AMIBs) owing to their facile synthesis and excellent theoretical capacities. However, the inherent drawbacks of unstable structural evolution and sluggish diffusion kinetics deteriorate their electrochemical performance, limiting further large-scale applications. To solve these issues, the novel and promising strategy of high entropy has been widely applied to layered oxide cathodes for AMIBs in recent years. Through multielement synergy and entropy stabilization effects, high-entropy layered oxides (HELOs) can achieve adjustable activity and enhanced stability. Herein, the basic concepts, design principles, and synthesis methods of HELO cathodes are introduced systematically. Notably, it explores in detail the improvements of the high-entropy strategy on the limitations of layered oxides, highlighting the latest advances in high-entropy layered cathode materials in the field of AMIBs. In addition, it introduces advanced characterization and theoretical calculations for HELOs and proposes potential future research directions and optimization strategies, providing inspiration for researchers to develop advanced HELO cathode materials in the areas of energy storage and conversion.

Co-free gradient lithium-rich cathode for high-energy batteries with optimized cyclability

Lithium-rich layered oxides (LLOs) hold the promise for high-energy battery cathodes. However, its application has been hindered by voltage decay associated with irreversible reactions at high voltages despite decades of intensive efforts. Here, we first theoretically studied the molecular orbitals of Mn-based Li-rich configurations. We found that the π-bond ring formed within the LiMn6 structure could participate in stable redox reactions as one unit, but Co could disrupt its symmetry. We thus designed and synthesized Co-free concentration-gradient LLOs (CF-CG-LLOs) materials. The combination of concentration gradient and Co removal leads to exceptional capacity retention without any fading over 100 cycles of the pouch cell. More importantly, it exhibits an extraordinarily low voltage decay of 0.15 mV/cycle, accompanied by a high Coulombic efficiency of 99.86%. This concept and demonstration of CF-CG-LLO cathodes reveal a viable avenue toward low-cost, high-energy-density battery cathodes.

Surface Engineering via Rare Earth Oxide Composite Coating to Enhance the High-Voltage Stability of the LiCoO2 Cathode

The commercial application of high-voltage LiCoO2 (LCO) faces significant challenges due to rapid capacity decay, primarily attributed to an unstable interface and structure at deeply delithiated states. Herein, a unique rare earth oxide composite coating comprising La2O3, Y2O3, and LaYO3 has been prepared to stabilize LCO at high voltage. The synergistic effect between these rare earth oxides significantly reinforces the protective capabilities of the coating, effectively enhancing the interfacial/structural stability of LCO. When tested at 4.6 V, the coated LCO exhibits an excellent capacity retention of 94.4% after 300 cycles at 1 C. Even after an ultralong charge/discharge test of 700 cycles at 2 C, the coated LCO retains 85.2% of its initial specific capacity, which significantly outperforms the uncoated LCO (6.3%). Moreover, the coated LCO shows enhanced cycling performance at a high temperature of 45 °C, owing to the outstanding thermal stability of the La-Y-O composite. Additionally, the superior cycling stability of the coated LCO at 4.7 V, compared to the uncoated LCO, demonstrated the promising potential of the La-Y-O composite coating in improving electrochemical performance of LCO at higher cutoff voltages. These findings highlight an efficacious strategy to enhance the interfacial/structural stability of high-voltage LCO using rare earth oxides.

A theoretical study of surface lithium effects on the [111] SiC nanowires as anode materials

CONTEXT

Silicon carbide nanowires (SiCNWs) are considered a promising alternative material for application in lithium-ion batteries, with researchers striving to develop new electrode materials that exhibit high capacity and high charge/discharge rate performance. To gain a deeper understanding of the application of SiCNWs in semiconductor material science and energy supply fields, we investigated the effects of nanoscale and surface lithiation on the electrical and mechanical properties of SiCNWs grown along the [111] direction. First-principles calculation was used to study their geometries, electronic structures, and associated electrochemical properties. Herein, we considered SiCNWs with full hydrogen passivation, full lithium passivation, and mixed passivation at different sizes. The formation energy indicates that the stability of SiCNWs increases with the increasing diameter, and the surface-lithiated SiC nanowires (Li-SiCNWs) are found to be energetically stable. The mixed passivated SiCNWs exhibit the properties of indirect band gap with the increase of lithium atoms on the surface, while the fully lithium passivated nanowires exhibit metallic behavior. Charge analysis shows that a portion of the electrons on the lithium atoms are transferred to the surface atoms of the nanowires and electrons prefer to cluster more near the C atoms. Additionally, Li-SiCNWs still have good mechanical resistance during the lithiation process. The stable open-circuit voltage range and theoretical capacity of these SiCNWs indicate their suitability as anode materials.

METHOD

In this study, Materials Studio 8.0 was used to construct the models of the SiCNWs. And all the density functional theory (DFT) calculations were performed by the Vienna ab initio Simulation Package (VASP). The self-consistent field calculations are performed over a Monkhorst-Pack net of 1 × 1 × 6 k-points. The energy convergence criteria for the self-consistent field calculation were set to 10-5 eV/atom with a cutoff energy of 400 eV.

Analyzing the Li-Al-O Interphase of Atomic Layer-Deposited Al2O3 Films on Layered Oxide Cathodes Using Atomistic Simulations

Alumina surface coatings are commonly applied to layered oxide cathode particles for lithium-ion battery applications. Atomic layer deposition (ALD) is one such surface coating technique, and ultrathin alumina ALD films (<2 nm) are shown to improve the electrochemical performance of LiNixMnyCo1-x-yO2 materials, with groups hypothesizing that a beneficial Li-Al-O product is being formed during the alumina ALD process. However, the atomic structure of these films is still not well understood, and quantifying the interface of ultrathin (∼1 nm) ALD films is an arduous experimental task. Here, we perform molecular dynamics simulations of amorphous alumina films of varying thickness in contact with the (0001) LiCoO2 (LCO) surface to quantify the film nanostructure. We calculate elemental mass density profiles through the films and observe that the Li-Al-O interphase extends ∼2 nm from the LCO surface. Additionally, we observe layering of Al and O atoms at the LCO-film interface that extends for ∼1.5 nm. To access the short-range order of the amorphous film, we calculated the Al coordination numbers through the film. We find that while [4]Al is the prevailing coordination environment, significant amounts of [6]Al exist at the interface between the LiCoO2 surface and the film. Taken together, these principal findings point to a pseudomorphic Li-Al-O overlayer that approximates the underlying layered LiCoO2 lattice but does not exactly replicate it. Additionally, with sufficient thickness, the Li-Al-O film transitions to an amorphous alumina structure. We anticipate that our findings on the ALD-like, Li-Al-O film nanostructure can be applied to other layered LiNixMnyCo1-x-yO2 materials because of their shared crystal structure with LiCoO2. This work provides insight into the nanostructure of amorphous ALD alumina films to help inform their use as protective coatings for Li-ion battery cathode active materials.

Density Functional Theory Approximations and Experimental Investigations on Co1-xMoxTe2 Alloy Electrocatalysts Tuning the Overall Water Splitting Reactions

Understanding the relationship between electronic structure, surface characteristic, and reaction process of a catalyst helps to architect proficient electrodes for sustainable energy development. The highly active and stable catalysts made of earth-abundant materials provide a great endeavor toward green hydrogen production. Herein, we assembled the Co_1-xMo_xTe (x = 0-1) nanoarray structures into a bifunctional electrocatalyst to achieve high-performance hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics under alkaline conditions. The designed Co_0.75Mo_0.25Te and Co_0.50Mo_0.50 electrocatalysts require minimum overpotential and Tafel slope for high-efficacy HER and OER, respectively. Furthermore, we constructed a Co_0.50Mo_0.50Te₂∥Co_0.50Mo_0.50Te₂ device for overall water splitting with an overpotential of 1.39 V to achieve a current density of 10 mA cm^-2, which is superior to noble electrocatalyst performance, with stable reaction throughout the 50 h continuous process. Density functional theory approximations and Gibbs free energy calculations validate the enhanced water splitting reaction catalyzed by the Co_0.50Mo_0.50Te₂ nanoarrays. The partial replacement of Co atoms with Mo atoms in the Co_0.50Mo_0.50Te₂ structure substantially enhances the water electrolysis kinetics through the synergistic effects between the combined metal atoms and the bonded chalcogen.

Modulation of Local Charge Distribution Stabilized the Anionic Redox Process in Mn-Based P2-Type Layered Oxides

An anionic redox reaction is an extraordinary method for obtaining high-energy-density cathode materials for sodium-ion batteries (SIBs). The commonly used inactive-element-doped strategies can effectively trigger the O redox activity in several layered cathode materials. However, the anionic redox reaction process is usually accompanied by unfavorable structural changes, large voltage hysteresis, and irreversible O₂ loss, which hinders its practical application to a large extent. In the present work, we take the doping of Li elements into Mn-based oxide as an example and reveal the local charge trap around the Li dopant will severely impede O charge transfer upon cycling. To overcome this obstacle, additional Zn²⁺ codoping is introduced into the system. Theoretical and experimental studies show that Zn²⁺ doping can effectively release the charge around Li⁺ and homogeneously distribute it on Mn and O atoms, thus reducing the overoxidation of O and improving the stability of the structure. Furthermore, this change in the microstructure makes the phase transition more reversible. This study aimed to provide a theoretical framework for further improve the electrochemical performance of similar anionic redox systems and provide insights into the activation mechanism of the anionic redox reaction.

First-Principles Study of the Effect of Ni-Doped on the Spinel-Type Mn-Based Cathode Discharge

Spinel-type manganese oxide is considered as a typical cobalt-free high-voltage cathode material for lithium-ion battery applications because of its low cost, non-toxicity, and easy preparation. Nevertheless, severe capacity fading during charge and discharge limits its commercialization. Therefore, understanding the electrochemical properties and its modification mechanism of spinel-type manganese oxide for a lithium-ion battery is of great research interest. Herein, we presented a theoretical study regarding the discharge process of LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ using first-principles calculations based on density functional theory. We found that the discharge process is accompanied by an increase in unit cell volume and lattice distortion. Moreover, 25% Ni-substitution increases the average calculated voltage of LiMn₂O₄ from 3.83 to 4.61 V, which is very close to the experimental value. The electronic structure is further discussed to understand the mechanism of voltage increase. In addition, the Ni element also reduces the Li-ion diffusion barrier by 0.06 eV, which helps to improve the intrinsic rate performance of LiMn₂O₄. Our research can provide insight into how Ni-substitution influences the voltage and diffusion barrier of LiMn₂O₄ and pave the way for other spinel-type manganese oxide electrode applications.

Tailoring electronic-ionic local environment for solid-state Li-O2 battery by engineering crystal structure

Solid-state Li-O2 batteries (SSLOBs) have attracted considerable attention because of their high energy density and superior safety. However, their sluggish kinetics have severely impeded their practical application. Despite efforts to design highly efficient catalysts, efficient oxygen reaction evolution at gas-solid interfaces and fast transport pathways in solid-state electrodes remain challenging. Here, we develop a dual electronic-ionic microenvironment to substantially enhance oxygen electrolysis in solid-state batteries. By designing a lithium-decorative catalyst with an engineering crystal structure, the coordinatively unsaturated sites and high concentration of defects alleviate the limitations of electronic-ionic transport in solid interfaces and create a balanced gas-solid microenvironment for solid-state oxygen electrolysis. This strategy facilitates oxygen reduction reaction, mediates the transport of reaction species, and promotes the decomposition of the discharge products, contributing to a high specific capacity with a stable cycling life. Our work provides previously unknown insight into structure-property relationships in solid-state electrolysis for SSLOBs.