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Oxygen loss is an elusive phenomenon that accompanies oxygen redox in lithium-rich layered oxides in batteries. Now, multi-length-scale characterization reveals that oxygen originating from the oxide bulk is eventually released after prolonged cycling.

Na-ion cathode materials operating at high voltage with a stable cycling behavior are needed to develop future high-energy Na-ion cells. However, the irreversible oxygen redox reaction at the high-voltage region in sodium layered cathode materials generates structural instability and poor capacity retention upon cycling. Here, we report a doping strategy by incorporating light-weight boron into the cathode active material lattice to decrease the irreversible oxygen oxidation at high voltages (i.e., >4.0 V vs. Na + /Na). The presence of covalent B–O bonds and the negative charges of the oxygen atoms ensures a robust ligand framework for the NaLi 1/9 Ni 2/9 Fe 2/9 Mn 4/9 O 2 cathode material while mitigating the excessive oxidation of oxygen for charge compensation and avoiding irreversible structural changes during cell operation. The B-doped cathode material promotes reversible transition metal redox reaction enabling a room-temperature capacity of 160.5 mAh g −1 at 25 mA g −1 and capacity retention of 82.8% after 200 cycles at 250 mA g −1 . A 71.28 mAh single-coated lab-scale Na-ion pouch cell comprising a pre-sodiated hard carbon-based anode and B-doped cathode material is also reported as proof of concept. The irreversible oxygen redox reaction during charging to the high-voltage region causes cathode structural degradation and Na-ion cell capacity fading. Here, the authors report a B-doped cathode active material to mitigate the irreversible oxygen oxidation and increase the cell capacity.

The microstructure of a composite electrode determines how individual battery particles are charged and discharged in a lithium-ion battery. It is a frontier challenge to experimentally visualize and, subsequently, to understand the electrochemical consequences of battery particles’ evolving (de)attachment with the conductive matrix. Herein, we tackle this issue with a unique combination of multiscale experimental approaches, machine-learning-assisted statistical analysis, and experiment-informed mathematical modeling. Our results suggest that the degree of particle detachment is positively correlated with the charging rate and that smaller particles exhibit a higher degree of uncertainty in their detachment from the carbon/binder matrix. We further explore the feasibility and limitation of utilizing the reconstructed electron density as a proxy for the state-of-charge. Our findings highlight the importance of precisely quantifying the evolving nature of the battery electrode’s microstructure with statistical confidence, which is a key to maximize the utility of active particles towards higher battery capacity. Developing understanding of degradation phenomena in nickel rich cathodes is under intense investigation. Here the authors use learning-assisted statistical analysis and experiment-informed mathematical modelling to resolve the microstructure of a Ni-rich NMC composite cathode.

Lithium-ion battery (LIB) technology is the most attractive technology for energy storage systems in today’s market. However, further improvements and optimizations are still required to solve challenges such as energy density, cycle life, and safety. Addressing these challenges in LIBs requires a fundamental understanding of the reaction mechanisms in various physical/chemical processes during LIB operation. Advanced in situ/operando synchrotron-based X-ray characterization techniques are powerful tools for providing valuable information about the complicated reaction mechanisms in LIBs. In this review, several state-of-the-art in situ/operando synchrotron-based X-ray techniques and their combination with other characterization tools for battery research are introduced. Various in situ cell configurations and practical operating tips for cell design and experimental set-ups are also discussed.

Rational design and controlled synthesis of hybrid structures comprising multiple components with distinctive functionalities are an intriguing and challenging approach to materials development for important energy applications like electrocatalytic hydrogen production, where there is a great need for cost effective, active and durable catalyst materials to replace the precious platinum. Here we report a structure design and sequential synthesis of a highly active and stable hydrogen evolution electrocatalyst material based on pyrite-structured cobalt phosphosulfide nanoparticles grown on carbon nanotubes. The three synthetic steps in turn render electrical conductivity, catalytic activity and stability to the material. The hybrid material exhibits superior activity for hydrogen evolution, achieving current densities of 10 mA cm −2 and 100 mA cm −2 at overpotentials of 48 mV and 109 mV, respectively. Phosphorus substitution is crucial for the chemical stability and catalytic durability of the material, the molecular origins of which are uncovered by X-ray absorption spectroscopy and computational simulation. Rational design and synthesis are important for the development of materials for energy applications. Here, the authors sequentially synthesize pyrite structured cobalt phosphosulfide nanoparticles on carbon nanotubes, probing the role of phosphorous substitution on catalyst stability and durability.

Despite the importance of studying the instability of delithiated cathode materials, it remains difficult to underpin the degradation mechanism of lithium-rich cathode materials due to the complication of combined chemical and structural evolutions. Herein, we use state-of-the-art electron microscopy tools, in conjunction with synchrotron X-ray techniques and first-principle calculations to study a 4 d -element-containing compound, Li 2 Ru 0.5 Mn 0.5 O 3 . We find surprisingly, after cycling, ruthenium segregates out as metallic nanoclusters on the reconstructed surface. Our calculations show that the unexpected ruthenium metal segregation is due to its thermodynamic insolubility in the oxygen deprived surface. This insolubility can disrupt the reconstructed surface, which explains the formation of a porous structure in this material. This work reveals the importance of studying the thermodynamic stability of the reconstructed film on the cathode materials and offers a theoretical guidance for choosing manganese substituting elements in lithium-rich as well as stoichiometric layer-layer compounds for stabilizing the cathode surface. The authors show that after cycling the model cathode material Li 2 Ru 0.5 Mn 0.5 O 3 undergoes ruthenium segregation and even exsolution at the reconstructed oxide surface, which triggers a progressive degradation process. The insights enable new dimensions in choosing dopants for stabilized cathode surface.

Aqueous K-ion batteries (AKIBs) are promising candidates for grid-scale energy storage due to their inherent safety and low cost. However, full AKIBs have not yet been reported due to the limited availability of suitable electrodes and electrolytes. Here we propose an AKIB system consisting of an Fe-substituted Mn-rich Prussian blue K x Fe y Mn 1 −  y [Fe(CN) 6 ] w · z H 2 O cathode, an organic 3,4,9,10-perylenetetracarboxylic diimide anode and a 22 M KCF 3 SO 3 water-in-salt electrolyte. The cathode achieves 70% capacity retention at 100  C and a lifespan of over 10,000 cycles due to the mitigation of phase transitions by Fe substitution. Meanwhile, the electrolyte can help decrease the dissolution of both electrodes owing to the lack of free water. The AKIB exhibits a high energy density of 80 Wh kg −1 and can operate well at rates of 0.1–20  C and over a wide temperature range (−20 to 60 °C). We believe that our demonstration could pave the way for practical applications of AKIBs for grid-scale energy storage. Intensive efforts are underway towards developing battery-based grid-scale storage technologies. Here, the authors report an aqueous K-ion battery that offers many attractive advantages over various battery alternatives.

Owing to the worldwide abundance and low-cost of Na, room-temperature Na-ion batteries are emerging as attractive energy storage systems for large- scale grids. Increasing the Na content in cathode materials is one of the effective ways to achieve high energy density. Prussian blue and its analogues （PBAs） are promising Na-rich cathode materials since they can theoretically store two Na＋ ions per formula unit. However, increasing the Na content in PBAs cathode materials remains a major challenge. Here we show that sodium iron hexacyanoferrate with high Na content can be obtained by simply controlling the reducing agent and reaction atmosphere during synthesis. The Na content can reach as high as 1.63 per formula, which is the highest value for sodium iron hexacyanoferrate. This Na-rich sodium iron hexacyanoferrate demonstrates a high specific capacity of 150 mAh·g^-1 and remarkable cycling performance with 90% capacity retention after 200 cycles. Furthermore, the Na intercalation/ de-intercalation mechanism has been systematically studied by in situ Raman spectroscopy, X-ray diffraction and X-ray absorption spectroscopy analysis for the first time. The Na-rich sodium iron hexacyanoferrate can function as a plenteous Na reservoir and has great potential as a cathode material for practical Na-ion batteries.

Lithium-rich nickel-manganese-cobalt (LirNMC) layered material is a promising cathode for lithium-ion batteries thanks to its large energy density enabled by coexisting cation and anion redox activities. It however suffers from a voltage decay upon cycling, urging for an in-depth understanding of the particle-level structure and chemical complexity. In this work, we investigate the Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 particles morphologically, compositionally, and chemically in three-dimensions. While the composition is generally uniform throughout the particle, the charging induces a strong depth dependency in transition metal valence. Such a valence stratification phenomenon is attributed to the nature of oxygen redox which is very likely mostly associated with Mn. The depth-dependent chemistry could be modulated by the particles’ core-multi-shell morphology, suggesting a structural-chemical interplay. These findings highlight the possibility of introducing a chemical gradient to address the oxygen-loss-induced voltage fade in LirNMC layered materials. Lithium-rich layered material deserves in-depth understanding because it has large capacity enabled by both cation and anion activities. Here, authors apply 3D spectro-tomography with nano resolution to reveal the multi-layer morphology and depth-dependent transition metal valence distribution associated with oxygen redox.

Room-temperature sodium-ion batteries have shown great promise in large-scale energy storage applications for renewable energy and smart grid because of the abundant sodium resources and low cost. Although many interesting positive electrode materials with acceptable performance have been proposed, suitable negative electrode materials have not been identified and their development is quite challenging. Here we introduce a layered material, P2-Na 0.66 [Li 0.22 Ti 0.78 ]O 2 , as the negative electrode, which exhibits only ~0.77% volume change during sodium insertion/extraction. The zero-strain characteristics ensure a potentially long cycle life. The electrode material also exhibits an average storage voltage of 0.75 V, a practical usable capacity of ca. 100 mAh g −1 , and an apparent Na + diffusion coefficient of 1 × 10 −10  cm −2  s −1 as well as the best cyclability for a negative electrode material in a half-cell reported to date. This contribution demonstrates that P2-Na 0.66 [Li 0.22 Ti 0.78 ]O 2 is a promising negative electrode material for the development of rechargeable long-life sodium-ion batteries. Anode materials in sodium-ion batteries can undergo significant volume change upon sodium insertion and extraction, leading to deteriorated cycling performance. Wang et al . report a layered metal oxide anode with zero-strain characteristics, which may lead to extended battery cycle life.