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Micro-sized silicon anodes can significantly increase the energy density of lithium-ion batteries with low cost. However, the large silicon volume changes during cycling cause cracks for both organic-inorganic interphases and silicon particles. The liquid electrolytes further penetrate the cracked silicon particles and reform the interphases, resulting in huge electrode swelling and quick capacity decay. Here we resolve these challenges by designing a high-voltage electrolyte that forms silicon-phobic interphases with weak bonding to lithium-silicon alloys. The designed electrolyte enables micro-sized silicon anodes (5 µm, 4.1 mAh cm−2) to achieve a Coulombic efficiency of 99.8% and capacity of 2175 mAh g−1 for >250 cycles and enable 100 mAh LiNi0.8Co0.15Al0.05O2 pouch full cells to deliver a high capacity of 172 mAh g−1 for 120 cycles with Coulombic efficiency of >99.9%. The high-voltage electrolytes that are capable of forming silicon-phobic interphases pave new ways for the commercialization of lithium-ion batteries using micro-sized silicon anodes. Micro-sized silicon are promising anode materials due to low-cost and high-energy, yet their application is hindered by inaccessible electrolytes. Here, the authors report sulfolane-based electrolytes that form silicon-phobic interphases and enable high-voltage pouch cells to achieve superior cycle life. [ABSTRACT FROM AUTHOR]

Anionic redox is an effective way to boost the energy density of layer‐structured metal‐oxide cathodes for rechargeable batteries. However, inherent rigid nature of the TMO6 (TM: transition metals) subunits in the layered materials makes it hardly tolerate the inner strains induced by lattice glide, especially at high voltage. Herein, P2‐Na0.8Mg0.13[Mn0.6Co0.2Mg0.07□0.13]O2 (□: TM vacancy) is designed that contains vacancies in TM sites, and Mg ions in both TM and sodium sites. Vacancies make the rigid TMO6 octahedron become more asymmetric and flexible. Low valence Co2+/Co3+ redox couple stabilizes the electronic structure, especially at the charged state. Mg2+ in sodium sites can tune the interlayer spacing against O‐O electrostatic repulsion. Time‐resolved in situ X‐ray diffraction confirms that irreversible structure evolution is effectively suppressed during deep desodiation benefiting from the specific configuration. X‐ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations demonstrate that, deriving from the intrinsic vacancies, multiple local configurations of "□‐O‐□", "Na‐O‐□", "Mg‐O‐□" are superior in facilitating the oxygen redox for charge compensation than previously reported "Na‐O‐Mg". The resulted material delivers promising cycle stability and rate capability, with a long voltage plateau at 4.2 V contributed by oxygen, and can be well maintained even at high rates. The strategy will inspire new ideas in designing highly stable cathode materials with reversible anionic redox for sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Aqueous Zn batteries promise high energy density but suffer from Zn dendritic growth and poor low‐temperature performance. Here, we overcome both challenges by using an eutectic 7.6 m ZnCl2 aqueous electrolyte with 0.05 m SnCl2 additive, which in situ forms a zincophilic/zincophobic Sn/Zn5(OH)8Cl2⋅H2O bilayer interphase and enables low temperature operation. Zincophilic Sn decreases Zn plating/stripping overpotential and promotes uniform Zn plating, while zincophobic Zn5(OH)8Cl2⋅H2O top‐layer suppresses Zn dendrite growth. The eutectic electrolyte has a high ionic conductivity of ≈0.8 mS cm−1 even at −70 °C due to the distortion of hydrogen bond network by solvated Zn2+ and Cl−. The eutectic electrolyte enables Zn∥Ti half‐cell a high Coulombic efficiency (CE) of >99.7 % for 200 cycles and Zn∥Zn cell steady charge/discharge for 500 h with a low overpotential of 8 mV at 3 mA cm−2. Practically, Zn∥VOPO4 batteries maintain >95 % capacity with a CE of >99.9 % for 200 cycles at −50 °C, and retain ≈30 % capacity at −70 °C of that at 20 °C. [ABSTRACT FROM AUTHOR]

High-nickel content cathode materials offer high energy density. However, the structural and surface instability may cause poor capacity retention and thermal stability of them. To circumvent this problem, nickel concentration-gradient materials have been developed to enhance high-nickel content cathode materials' thermal and cycling stability. Even though promising, the fundamental mechanism of the nickel concentration gradient's stabilization effect remains elusive because it is inseparable from nickel's valence gradient effect. To isolate nickel's valence gradient effect and understand its fundamental stabilization mechanism, we design and synthesize a LiNi0.8Mn0.1Co0.1O2 material that is compositionally uniform and has a hierarchical valence gradient. The nickel valence gradient material shows superior cycling and thermal stability than the conventional one. The result suggests creating an oxidation state gradient that hides the more capacitive but less stable Ni3+ away from the secondary particle surfaces is a viable principle towards the optimization of high-nickel content cathode materials. High-nickel content cathode materials suffer issues of structural and surface instability. Herewith authors show that introduction of a nickel valence gradient enhances the thermal and cycle stability of high-nickel content cathode materials. [ABSTRACT FROM AUTHOR]

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 Li1.2Ni0.13Mn0.54Co0.13O2 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. [ABSTRACT FROM AUTHOR]

Metal–organic framework cathodes usually exhibit low capacity and poor electrochemical performance for Li‐ion storage owing to intrinsic low conductivity and inferior redox activity. Now a redox‐active 2D copper–benzoquinoid (Cu‐THQ) MOF has been synthesized by a simple solvothermal method. The abundant porosity and intrinsic redox character endow the 2D Cu‐THQ MOF with promising electrochemical activity. Superior performance is achieved as a Li‐ion battery cathode with a high reversible capacity (387 mA h g−1), large specific energy density (775 Wh kg−1), and good cycling stability. The reaction mechanism is unveiled by comprehensive spectroscopic techniques: a three‐electron redox reaction per coordination unit and one‐electron redox reaction per copper ion mechanism is demonstrated. This elucidatory understanding sheds new light on future rational design of high‐performance MOF‐based cathode materials for efficient energy storage and conversion. [ABSTRACT FROM AUTHOR]

Suppressing oxygen release from lithium ion battery cathodes during heating is a critical issue for the improvement of the battery safety characteristics because oxygen can exothermically react with the flammable electrolyte and cause thermal runaway. Previous studies have shown that oxygen release can be reduced by the migration of transition metal cations from octahedral sites to tetrahedral sites during heating. Such site-preferred migration is determined by the electronic structure of cations. Taking advantage of the unique electronic structure of the environmental friendly Fe, this is selected as substitution element in a high energy density material LiNi0.5Mn1.5O4 to improve the thermal stability. The optimized LiNi0.33Mn1.33Fe0.33O4 material shows significantly improved thermal stability compared with the unsubstituted one, demonstrated by no observed oxygen release at temperatures as high as 500°C. Due to the electrochemical contribution of Fe, the high energy density feature of LiNi0.5Mn1.5O4 is well preserved. [ABSTRACT FROM AUTHOR]

The high-energy-density, Li-rich layered materials, i.e., xLiMO2(1- x)Li2MnO3, are promising candidate cathode materials for electric energy storage in plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The relatively low rate capability is one of the major problems that need to be resolved for these materials. To gain insight into the key factors that limit the rate capability, in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) studies of the cathode material, Li1.2Ni0.15Co0.1Mn0.55O2 [0.5Li(Ni0.375Co0.25 Mn0.375)O2·0.5Li2MnO3], are carried out. The partial capacity contributed by different structural components and transition metal elements is elucidated and correlated with local structure changes. The characteristic reaction kinetics for each element are identified using a novel time-resolved XAS technique. Direct experimental evidence is obtained showing that Mn sites have much poorer reaction kinetics both before and after the initial activation of Li2MnO3, compared to Ni and Co. These results indicate that Li2MnO3 may be the key component that limits the rate capability of Li-rich layered materials and provide guidance for designing Li-rich layered materials with the desired balance of energy density and rate capability for different applications. [ABSTRACT FROM AUTHOR]

Metal fluorides/oxides (MFx/MxOy) are promising electrodes for lithium-ion batteries that operate through conversion reactions. These reactions are associated with much higher energy densities than intercalation reactions. The fluorides/oxides also exhibit additional reversible capacity beyond their theoretical capacity through mechanisms that are still poorly understood, in part owing to the difficulty in characterizing structure at the nanoscale, particularly at buried interfaces. This study employs high-resolution multinuclear/multidimensional solid-state NMR techniques, with in situ synchrotron-based techniques, to study the prototype conversion material RuO2. The experiments, together with theoretical calculations, show that a major contribution to the extra capacity in this system is due to the generation of LiOH and its subsequent reversible reaction with Li to form Li2O and LiH. The research demonstrates a protocol for studying the structure and spatial proximities of nanostructures formed in this system, including the amorphous solid electrolyte interphase that grows on battery electrodes. [ABSTRACT FROM AUTHOR]

Poly (ethylene oxide) (PEO) polymer electrolytes are promising candidates for next-generation rechargeable lithium batteries. However, the poor interfacial stability between 4 V cathodes and PEO electrolytes impedes their applications in 4 V lithium batteries with high energy density. Here, we demonstrate a facile and effective strategy to enhance the interfacial stability by the synergy of Li 1.5 Al 0.5 Ge 1.5 (PO 4) 3 (LAGP) coating on the cathode surface, and salt combination in the electrolyte, even with a cut-off voltage of 4.25–4.4 V vs. Li+/Li. Nano-LAGP coated Li|PEO|LiCoO 2 cell delivers stable cycling with a capacity retention of 81.9%/400 cycles and 84.7%/200 cycles at 60 °C when charged to 4.25 and 4.3 V in pure polyether electrolyte, respectively. Steady cycling is also demonstrated at room temperature and with LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) cathode. This work offers a viable and scalable approach to improve the stability between PEO electrolytes and 4 V cathodes and open up new possibilities for practical application of 4 V lithium metal batteries. Image 1 • LCO surface is modified by ceramic solid electrolyte and self-limiting salt decomposition. • The synergy of these two modifications significantly improves the stability of LCO/PEO interface. • High capacity retention of 81.9% over 400 cycles is achieved in 4 V Li|PEO|LCO cell. [ABSTRACT FROM AUTHOR]

We report a new layered Na(Mn 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O 2 compound with O3 oxygen stacking. It delivers 180 mAh/g initial discharge capacity and 578 Wh/kg specific energy density with good cycling capability at high cutoff voltage. In situ X-ray diffraction (XRD) shows a reversible structure evolution of O3-P3-O3′-O3″ upon Na de-intercalation. The excellent capacity and cycling performance at high cutoff voltage make it an important model system for studying the general issue of capacity fading in layered Na cathode compounds. [ABSTRACT FROM AUTHOR]

Abstract: Electric-powered transportation requires an efficient, low-cost, and safe energy storage system with high energy density and power capability. Despite its high specific capacity, the current commercially available cathode material for today's state-of-art Li-ion batteries, lithium nickel–manganese–cobalt oxide Li[Ni1/3 Mn1/3Co1/3]O2 (NMC), suffers from poor cycle life for high temperature operation and marginal rate capability resulting from irreversible degradation of the cathode material upon cycling. Using an atomic-scale surface engineering, the performance of Li[Ni1/3Mn1/3Co1/3]O2 in terms of rate capability and high temperature cycle-life is significantly improved. The Al2O3 coating deposited by atomic layer deposition (ALD) dramatically reduces the degradation in cell conductivity and reaction kinetics. This durable ultra-thin Al2O3-ALD coating layer also improves stability for the NMC at an elevated temperature (55 °C). The experimental results suggest that a highly durable and safe cathode material enabled by atomic-scale surface modification could meet the demanding performance and safety requirements of next-generation electric vehicles. [Copyright &y& Elsevier]

• A novel composition of Co 2.4 Sn 0.6 O 4 is prepared using the precipitation method. • The material is synthesized with self-standing nano-rods type morphology. • Co 2.4 Sn 0.6 O 4 anode delivers outstanding electrochemical properties. • The reaction mechanism of Co 2.4 Sn 0.6 O 4 anode is investigated systematically. • Co 2.4 Sn 0.6 O 4 anode has shown high electrochemical performance in sodium-ion full cell. The self-standing nanorod Co 2.4 Sn 0.6 O 4 is synthesized as a high-performance anode material in search of high capacity and stable anode materials for sodium-ion batteries. The Co 2.4 Sn 0.6 O 4 nanorod exhibits a high reversible capacity of 576 mAh g−1 at a current density of 80 mA g−1 and shows excellent high-rate capability. The X-ray absorption spectroscopy study reveals the mechanisms of charge storage reaction and improved cycling performance of Co 2.4 Sn 0.6 O 4. A partially limited conversion reaction of Co– and Sn-oxide during the cycling effectively regulate the irreversible capacity loss over the cycling that is commonly observed from the conversion and alloying reaction-based anode materials. Furthermore, Co 2.4 Sn 0.6 O 4 also exhibits superior sodium-ion full cell performance when coupled with a NaNi 2/3 Bi 1/3 O 2 cathode, demonstrating an energy density of 262 Wh kg−1. [ABSTRACT FROM AUTHOR]