Stacking Faults Inducing Oxygen Anion Activities in Li2 MnO3

Constructing LiF-rich cathode electrolyte interphase to enhance the cyclic stability of lithium-rich manganese-based oxide cathode

Lithium-rich manganese-based oxide (LRMO) materials hold great potential for high-energy-density lithium-ion batteries (LIBs) but suffer from severe voltage decay and capacity fading. Herein, we report the in situ construction of LiF-rich solid electrolyte interphase on LRMO through a straightforward ball-milling and electrochemical approach, which exhibits remarkable structural stability and enhanced electrochemical performance.

Towards High-Performance Li-Rich Cathode Materials: from Morphology Design to Electronic Structure Modulation

Lithium-rich cathode materials (LRMs) have garnered significant interest owing to their high reversible discharge capacity (exceeding 250 mAh g⁻¹), which is attributed to the redox reactions of transition metal (TM) ions as well as the distinctive redox processes of oxygen anions. However, there are still many problems, such as their relatively poor rate performance and voltage fading and hysteresis, hindering their practical applications. Herein, the recent insights into the mechanisms and the latest advancements in the research of LRMs are discussed. Strategies to promote the performance of LRMs are discussed following a top-down approach from the morphology design to electronic structure modulation. Finally, the ongoing efforts in this area are also discussed to inspire more new ideas for the future development of LRMs.

Expandable Fast Li-Ion Diffusion Network of Li-Rich Mn-Based Oxides via Single-Layer LiCo(Ni)O2 Segregation

Li-rich Mn-based cathode materials exhibit a remarkable reversible specific capacity exceeding 250 mAh g-1, positioning them as the preferred choice for the next generation of high-energy density lithium-ion battery cathode materials. However, their inferior rate and cycling performance pose significant challenges. In this context, a Li-rich material incorporating an expanded fast Li-ion diffusion network has been successfully synthesized. This advancement involves the introduction of a single-layer of LiCo(Ni)O2 with high Li-ion diffusion coefficients into the crystal structure of Li-rich cathode, thereby enhancing the rate performance, achieving an impressive capacity of 212 mAh g-1 at 5 C. Furthermore, the single-layer LiCo(Ni)O2 can effectively isolates Li2MnO3 phase domains, thereby enhancing the structural stability during the anion redox process, consequently extending the electrochemical stability limits. Operating within a voltage range of 2.1-4.6 V, the capacity retention reaches 80% after 400 cycles, with a voltage decay of merely 0.74 mV per cycle. This innovative utilization of an expanded fast Li-ion diffusion network provides invaluable insights that will guide the development of strategies aimed at unlocking rate capability in layered oxide cathode materials.

Zero Voltage-Degradation of Li2MnO3 with Ultrathin Amorphous Li─Mn─O Coating

Manganese-based lithium-rich layered oxides (Mn-LLOs) are promising candidate cathode materials for lithium-ion batteries, however, the severe voltage decay during cycling is the most concern for their practical applications. Herein, an Mn-based composite nanostructure constructed Li2MnO3 (LMO@Li2MnO3) is developed via an ultrathin amorphous functional oxide LixMnOy coating at the grain surface. Due to the thin and universal LMO amorphous surface layer etched from the lithiation process by the high-concentration alkaline solution, the structural and interfacial stability of Li2MnO3 are enhanced apparently, showing the significantly improved voltage maintenance, cycle stability, and energy density. In particular, the LMO@Li2MnO3 cathode exhibits zero voltage decay over 200 cycles. Combining with ex situ spectroscopic and microscopic techniques, the Mn2+/4+ coexisted behavior of the amorphous LMO is revealed, which enables the stable electrochemistry of Li2MnO3. This work provides new possible routes for suppressing the voltage decay of Mn-LLOs by modifying with the composite functional unit construction.

Advancing Catalysts by Stacking Fault Defects for Enhanced Hydrogen Production: A Review

Green hydrogen, derived from water splitting powered by renewable energy such as solar and wind energy, provides a zero-emission solution crucial for revolutionizing hydrogen production and decarbonizing industries. Catalysts, particularly those utilizing defect engineering involving the strategical introduction of atomic-level imperfections, play a vital role in reducing energy requirements and enabling a more sustainable transition toward a hydrogen-based economy. Stacking fault (SF) defects play an important role in enhancing the electrocatalytic processes by reshaping surface reactivity, increasing active sites, improving reactants/product diffusion, and regulating electronic structure due to their dense generation ability and profound impact on catalyst properties. This review explores SF in metal-based materials, covering synthetic methods for the intentional introduction of SF and their applications in hydrogen production, including oxygen evolution reaction, photo- and electrocatalytic hydrogen evolution reaction, overall water splitting, and various other electrocatalytic processes such as oxygen reduction reaction, nitrate reduction reaction, and carbon dioxide reduction reaction. Finally, this review addresses the challenges associated with SF-based catalysts, emphasizing the importance of a detailed understanding of the properties of SF-based catalysts to optimize their electrocatalytic performance. It provides a comprehensive overview of their various applications in electrocatalytic processes, providing valuable insights for advancing sustainable energy technologies.

Oxygen vacancy chemistry in oxide cathodes

Secondary batteries are a core technology for clean energy storage and conversion systems, to reduce environmental pollution and alleviate the energy crisis. Oxide cathodes play a vital role in revolutionizing battery technology due to their high capacity and voltage for oxide-based batteries. However, oxygen vacancies (OVs) are an essential type of defect that exist predominantly in both the bulk and surface regions of transition metal (TM) oxide batteries, and have a crucial impact on battery performance. This paper reviews previous studies from the past few decades that have investigated the intrinsic and anionic redox-mediated OVs in the field of secondary batteries. We focus on discussing the formation and evolution of these OVs from both thermodynamic and kinetic perspectives, as well as their impact on the thermodynamic and kinetic properties of oxide cathodes. Finally, we offer insights into the utilization of OVs to enhance the energy density and lifespan of batteries. We expect that this review will advance our understanding of the role of OVs and subsequently boost the development of high-performance electrode materials for next-generation energy storage devices.

Gradient Interphase Engineering Enabled by Anionic Redox for High-Voltage and Long-Life Li-Ion Batteries

Intelligent utilization of the anionic redox reaction (ARR) in Li-rich cathodes is an advanced strategy for the practical implementation of next-generation high-energy-density rechargeable batteries. However, due to the intrinsic complexity of ARR (e.g., nucleophilic attacks), the instability of the cathode-electrolyte interphase (CEI) on a Li-rich cathode presents more challenges than typical high-voltage cathodes. Here, we manipulate CEI interfacial engineering by introducing an all-fluorinated electrolyte and exploiting its interaction with the nucleophilic attack to construct a gradient CEI containing a pair of fluorinated layers on a Li-rich cathode, delivering enhanced interfacial stability. Negative/detrimental nucleophilic electrolyte decomposition has been efficiently evolved to further reinforce CEI fabrication, resulting in the construction of LiF-based indurated outer shield and fluorinated polymer-based flexible inner sheaths. Gradient interphase engineering dramatically improved the capacity retention of the Li-rich cathode from 43 to 71% after 800 cycles and achieved superior cycling stability in anode-free and pouch-type full cells (98.8% capacity retention, 220 cycles), respectively.

Manipulated Fluoro-Ether Derived Nucleophilic Decomposition Products for Mitigating Polarization-Induced Capacity Loss in Li-Rich Layered Cathode

Electrolyte engineering is a fascinating choice to improve the performance of Li-rich layered oxide cathodes (LRLO) for high-energy lithium-ion batteries. However, many existing electrolyte designs and adjustment principles tend to overlook the unique challenges posed by LRLO, particularly the nucleophilic attack. Here, we introduce an electrolyte modification by locally replacing carbonate solvents in traditional electrolytes with a fluoro-ether. By benefit of the decomposition of fluoro-ether under nucleophilic O-related attacks, which delivers an excellent passivation layer with LiF and polymers, possessing rigidity and flexibility on the LRLO surface. More importantly, the fluoro-ether acts as "sutures", ensuring the integrity and stability of both interfacial and bulk structures, which contributed to suppressing severe polarization and enhancing the cycling capacity retention from 39 % to 78 % after 300 cycles for the 4.8 V-class LRLO. This key electrolyte strategy with comprehensive analysis, provides new insights into addressing nucleophilic challenge for high-energy anionic redox related cathode systems.