Native lattice strain induced structural earthquake in sodium layered oxide cathodes

Strain Engineering for Electrocatalytic Overall Water Splitting

Strain engineering is a novel method that can achieve superior performance for different applications. The lattice strain can affect the performance of electrochemical catalysts by changing the binding energy between the surface-active sites and intermediates and can be affected by the thickness, surface defects and composition of the materials. In this review, we summarized the basic principle, characterization method, introduction strategy and application direction of lattice strain. The reactions on hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are focused. Finally, the present challenges are summarized, and suggestions for the future development of lattice strain in electrocatalytic overall water splitting are put forward.

Solvation Effect: The Cornerstone of High-Performance Battery Design for Commercialization-Driven Sodium Batteries

Sodium batteries (SBs) emerge as a potential candidate for large-scale energy storage and have become a hot topic in the past few decades. In the previous researches on electrolyte, designing electrolytes with the solvation theory has been the most promising direction is to improve the electrochemical performance of batteries through solvation theory. In general, the four essential factors for the commercial application of SBs, which are cost, low temperature performance, fast charge performance and safety. The solvent structure has significant impact on commercial applications. But so far, the solvation design of electrolyte and the practical application of sodium batteries have not been comprehensively summarized. This review first clarifies the process of Na+ solvation and the strategies for adjusting Na+ solvation. It is worth noting that the relationship between solvation theory and interface theory is pointed out. The cost, low temperature, fast charging, and safety issues of solvation are systematically summarized. The importance of the de-solvation step in low temperature and fast charging application is emphasized to help select better electrolytes for specific applications. Finally, new insights and potential solutions for electrolytes solvation related to SBs are proposed to stimulate revolutionary electrolyte chemistry for next generation SBs.

Interfacial Spinel Local Interlocking Strategy Toward Structural Integrity in P3 Oxide Cathodes

P3-layered transition oxide cathodes have garnered considerable attention owing to their high initial capacity, rapid Na+ kinetics, and less energy consumption during the synthesis process. Despite these merits, their practical application is hindered by the substantial capacity degradation resulting from unfavorable structural transformations, Mn dissolution and migration. In this study, we systematically investigated the failure mechanisms of P3 cathodes, encompassing Mn dissolution, migration, and the irreversible P3-O3' phase transition, culminating in severe structural collapse. To address these challenges, we proposed an interfacial spinel local interlocking strategy utilizing P3/spinel intergrowth oxide as a proof-of-concept material. As a result, P3/spinel intergrowth oxide cathodes demonstrated enhanced cycling performance. The effectiveness of suppressing Mn migration and maintaining local structure of interfacial spinel local interlocking strategy was validated through depth-etching X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and in situ synchrotron-based X-ray diffraction. This interfacial spinel local interlocking engineering strategy presents a promising avenue for the development of advanced cathode materials for sodium-ion batteries.

A Feasible Dual Modification Strategy of Internal Anion Redox Chemistry and Surface Engineering on P2 Layer-Structured Cathodes in Sodium-Ion Batteries

Boosting the anion redox reaction opens up a possibility of further capacity enhancement on transition-metal-ion redox-only layer-structured cathodes for sodium-ion batteries. To mitigate the deteriorating impact on the internal and surface structure of the cathode caused by the inevitable increase in the operation voltage, probing a solution to promote the bulk-phase crystal structure stability and surface chemistry environment to further facilitate the electrochemical performance enhancement is a key issue. A dual modification strategy of establishing an anion redox hybrid activation trigger agent inside the crystal structure in combination with surface oxide coating is successfully developed. P2-type layer structure cathode materials with Zn/Li (Na-O-Zn@Na-O-Li) anion redox hybrid triggers and a ZnO coating layer possess superior capacity and cycle performance, along with outstanding structural stability, decreased Mn-ion dissolution effect, and less crystal particle cracking during the cycling process. This study represents a facile modification solution to perform structure optimization and property enhancement toward high-performance layered structure cathode materials with anion redox features in sodium-ion batteries.

Electrochemomechanical failure in layered oxide cathodes caused by rotational stacking faults

Electrochemomechanical degradation is one of the most common causes of capacity deterioration in high-energy-density cathodes, particularly intercalation-based layered oxides. Here we reveal the presence of rotational stacking faults (RSFs) in layered lithium transition-metal oxides, arising from specific stacking sequences at different angles, and demonstrate their critical role in determining structural/electrochemical stability. Our combined experiments and calculations show that RSFs facilitate oxygen dimerization and transition-metal migration in layered oxides, fostering microcrack nucleation/propagation concurrently with cumulative electrochemomechanical degradation on cycling. We further show that thermal defect annihilation as a potential solution can suppress RSFs, reducing microcracks and enhancing cyclability in lithium-rich layered cathodes. The common but previously overlooked occurrence of RSFs suggests a new synthesis guideline of high-energy-density layered oxide cathodes.

Negative Lattice Expansion in an O3-Type Transition-Metal Oxide Cathode for Highly Stable Sodium-Ion Batteries

The sodium extraction/insertion in layered transition-metal oxide (TMO) cathode materials are typically accompanied by slab sliding and lattice changes, leading to microstructure destruction and capacity decay. Herein, negative lattice expansion is observed in an O3 type Ni-based layered cathode of Na0.9 Ni0.32 Zn0.08 Fe0.1 Mn0.3 Ti0.2 O2 upon Na+ extraction. It is attributed to the weak Zn2+ -O2- orbital hybridization and increased electron density of the surrounding oxygen for reinforced interlayer O-O repulsive force. This enables gliding of TMO slabs for the intergrowth phase transition of P3→OP2 to alleviate lattice strain with moderate lattice shrinkage, which exhibits general interslab spacings and volume changes as low as 2.4 % and 1.9 %, respectively. The strong Ti-O bonds accommodate the internal distortion of TMO6 octahedra due to the flexibility of TiO6 octahedra during cycling. These endow a high specific capacity of 144.9 mAh g-1 and excellent cycling performance of pouch-type sodium-ion batteries with 93 % capacity retention after 3600 cycles.

Enabling Electrochemical-Mechanical Robustness of Ultra-High Ni Cathode via Self-Supported Primary-Grain-Alignment Strategy

The electrochemical-mechanical degradation of ultrahigh Ni cathode for lithium-ion batteries is a crucial aspect that limits the cycle life and safety of devices. Herein, the study reports a facile strategy involving rational design of primary grain crystallographic orientation within polycrystalline cathode, which well enhanced its electro-mechanical strength and Li+ transfer kinetics. Ex situ and in situ experiments/simulations including cross-sectional particle electron backscatter diffraction (EBSD), single-particle micro-compression, thermogravimetric analysis combined with mass spectrometry (TGA-MS), and finite element modeling reveal that, the primary-grain-alignment strategy effectively mitigates the particle pulverization, lattice oxygen release thereby enhances battery cycle life and safety. Besides the preexisting doping and coating methodologies to improve the stability of Ni-rich cathode, the primary-grain-alignment strategy, with no foreign elements or heterophase layers, is unprecedently proposed here. The results shed new light on the study of electrochemical-mechanical strain alleviation for electrode materials.

Decoding the puzzle: recent breakthroughs in understanding degradation mechanisms of Li-ion batteries

Lithium-ion batteries (LIBs) remain at the forefront of energy research due to their capability to deliver high energy density. Understanding their degradation mechanism has been essential due to their rapid engagement in modern electric vehicles (EVs), where battery failure may incur huge losses to human life and property. The literature on this intimidating issue is rapidly growing and often very complex. This review strives to succinctly present current knowledge contributing to a more comprehensible understanding of the degradation mechanism. First, this review explains the fundamentals of LIBs and various degradation mechanisms. Then, the degradation mechanism of novel Li-rich cathodes, advanced characterization techniques for identifying it, and various theoretical models are presented and discussed. We emphasize that the degradation process is not only tied to the charge-discharge cycles; synthesis-induced stress also plays a vital role in catalyzing the degradation. Finally, we propose further studies on advanced battery materials that can potentially replace the layered cathodes.

A Universal Strategy Based on Bridging Microstructure Engineering and Local Electronic Structure Manipulation for High-Performance Sodium Layered Oxide Cathodes

Due to their high capacity and sufficient Na+ storage, O3-NaNi0.5Mn0.5O2 has attracted much attention as a viable cathode material for sodium-ion batteries (SIBs). However, the challenges of complicated irreversible multiphase transitions, poor structural stability, low operating voltage, and an unstable oxygen redox reaction still limit its practical application. Herein, using O3-NaNi0.5Mn0.5-xSnxO2 cathode materials as the research model, a universal strategy based on bridging microstructure engineering and local electronic structure manipulation is proposed. The strategy can modulate the physical and chemical properties of electrode materials, so as to restrain the unfavorable and irreversible multiphase transformation, improve structural stability, manipulate redox potential, and stabilize the anion redox reaction. The effect of Sn substitution on the intrinsic local electronic structure of the material is articulated by density functional theory calculations. Meanwhile, the universal strategy is also validated by Ti substitution, which could be further extrapolated to other systems and guide the design of cathode materials in the field of SIBs.

Injecting Excess Na into a P2-Type Layered Oxide Cathode to Achieve Presodiation in a Na-Ion Full Cell

The initial Na loss limits the theoretical specific capacity of cathodes in Na-ion full cell applications, especially for Na-deficient P2-type cathodes. In this study, we propose a presodiation strategy for cathodes to compensate for the initial Na loss in Na-ion full cells, resulting in a higher specific capacity and a higher energy density. By employing an electrochemical presodiation approach, we inject 0.32 excess active Na into P2-type Na_0.67Li_0.1Fe_0.37Mn_0.53O₂ (NLFMO), aiming to compensate for the initial Na loss in hard carbon (HC) and the inherent Na deficiency of NLFMO. The structure of the NLFMO cathode converts from P2 to P'2 upon active Na injection, without affecting subsequent cycles. As a result, the HC||NLFMO_preNa full cell exhibits a specific capacity of 125 mAh/g, surpassing the value of 61 mAh/g of the HC||NLFMO full cell without presodiation due to the injected active Na. Moreover, the presodiation effect can be achieved through other engineering approaches (e.g., Na-metal contact), suggesting the scalability of this methodology.

Manipulating of P2/O3 Composite Sodium Layered Oxide Cathode through Ti Substitution and Synthesis Temperature

P2/O3 composite sodium layered oxide has emerged as a promising cathode for high-performance Na-ion batteries. However, it has been challenging to regulate accurately the phase ratio of P2/O3 composite due to their high compositional diversity, which brings about some difficulty in manipulating the electrochemical performance of P2/O3 composite. Here, we explore the effect of Ti substitution and the synthesis temperature on the crystal structure and Na storage performance of Na_0.8Ni_0.4Mn_0.6O₂. The investigation indicates Ti-substitution and altering synthesis temperature can rationally manipulate the phase ratio of P2/O3 composite, thereby purposefully regulating the cycling and rate performance of P2/O3 composite. Typically, O3-rich Na_0.8Ni_0.4Mn_0.4Ti_0.2O₂-950 shows excellent cycling stability with a capacity retention of 84% (3C, 700 cycles). By elevating the proportion of P2 phase, Na_0.8Ni_0.4Mn_0.4Ti_0.2O₂-850 displays concurrently improved rate capability (65% capacity retention at 5 C) and comparable cycling stability. These findings will help guide the rational design of high-performance P2/O3 composite cathodes for sodium-ion batteries.