Efficient Li‐Ion‐Conductive Layer for the Realization of Highly Stable High‐Voltage and High‐Capacity Lithium Metal Batteries

Recently, a consensus has been reached that using lithium metal as an anode in rechargeable Li‐ion batteries is the best way to obtain the high energy density necessary to power electronic devices. Challenges remain, however, with respect to controlling dendritic Li growth on these electrodes, enhancing compatibility with carbonate‐based electrolytes, and forming a stable solid–electrolyte interface layer. Herein, a groundbreaking solution to these challenges consisting in the preparation of a Li₂TiO₃ (LT) layer that can be used to cover Li electrodes via a simple and scalable fabrication method, is suggested. Not only does this LT layer impede direct contact between electrode and electrolyte, thus avoiding side reactions, but it assists and expedites Li‐ion flux in batteries, thus suppressing Li dendrite growth. Other effects of the LT layer on electrochemical performance are investigated by scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic intermittent titration technique analyses. Notably, LT layer‐incorporating Li cells comprising high‐capacity/voltage cathodes with reasonably high mass loading (LiNi_0.8Co_0.1Mn_0.1O₂, LiNi_0.5Mn_1.5O₄, and LiMn₂O₄) show highly stable cycling performance in a carbonate‐based electrolyte. Therefore, it is believed that the approach based on the LT layer can boost the realization of high energy density lithium metal batteries and next‐generation batteries.     

3D Printable Ceramic–Polymer Electrolytes for Flexible High‐Performance Li‐Ion Batteries with Enhanced Thermal Stability

This study establishes an approach to 3D print Li‐ion battery electrolytes with controlled porosity using a dry phase inversion method. This ink formulation utilizes poly(vinyldene fluoride) in a mixture of N‐methyl‐2‐pyrrolidone (good solvent) and glycerol (weak nonsolvent) to generate porosity during a simple drying step. When a nanosized Al₂O₃ filler is included in the ink, uniform sub‐micrometer pore formation is attained. In other words, no additional processing steps such as coagulation baths, stretching, or etching are required for full functionality of the electrolyte, which makes it a viable candidate to enable completely additively manufactured Li‐ion batteries. Compared to commercial polyolefin separators, these electrolytes demonstrate comparable high rate electrochemical performance (e.g., 5 C), but possess better wetting characteristics and enhanced thermal stability. Additionally, this dry phase inversion method can be extended to printable composite electrodes, yielding enhanced flexibility and electrochemical performance over electrodes prepared with only good solvent. Finally, sequentially printing this electrolyte ink over a composite electrode via a direct write extrusion technique has been demonstrated while maintaining expected functionality in both layers. These ink formulations are an enabling step toward completely printed batteries and can allow direct integration of a flexible power source in restricted device areas or on nonplanar surfaces.     

Synthesis,Characterization, and Structural Modeling of High‐Capacity,Dual Functioning MnO2 Electrode/Electrocatalysts for Li‐O2 Cells

It has become clear that cycling lithium‐oxygen cells in carbonate electrolytes is impractical, as electrolyte decomposition, triggered by oxygen reduction products, dominates the cell chemistry. This research shows that employing an α‐MnO₂/ramsdellite‐MnO₂ electrode/electrocatalyst results in the formation of lithium‐oxide‐like discharge products in propylene carbonate, which has been reported to be extremely susceptible to decomposition. X‐ray photoelectron data have shown that what are likely lithium oxides (Li₂O₂ and Li₂O) appear to form and decompose on the air electrode surface, particularly at the MnO₂ surface, while Li₂CO₃ is also formed. By contrast, cells without α‐MnO₂/ramsdellite‐MnO₂ fail rapidly in electrochemical cycling, likely due to the differences in the discharge product. Relatively high electrode capacities, up to 5000 mAh/g (carbon + electrode/electrocatalyst), have been achieved with non‐optimized air electrodes. Insights into reversible insertion reactions of lithium, lithium peroxide (Li₂O₂) and lithium oxide (Li₂O) in the tunnels of α‐MnO₂, and the reaction of lithium with ramsdellite‐MnO₂, as determined by first principles density functional theory calculations, are used to provide a possible explanation for some of the observed results. It is speculated that a Li₂O‐stabilized and partially‐lithiated electrode component, 0.15Li₂O·α‐Li_xMnO₂, that has Mn^4+/3+ character may facilitate the Li₂O₂/Li₂O discharge/charge chemistries providing dual electrode/electrocatalyst functionality.     

Extremely High Yield Conversion from Low‐Cost Sand to High‐Capacity Si Electrodes for Li‐Ion Batteries

Although magnesiothermic reduction has attracted immense attention as a facile route for the fabrication of mass‐scale Si nanostructures for high‐capacity lithium‐ion battery applications, its low conversion yield (<50%) and the discovery of a sustainable and low‐cost precursor remain challenging. Here, an unprecedentedly high final conversion yield (>98%) of magnesiothermic reduction based on control of reaction pressure is reported. The successful use of sand as a nearly infinite and extremely low‐cost source for the high‐yield fabrication of nanostructured Si electrodes for Li‐ion batteries is demonstrated. On the basis of a step‐by‐step analysis of the material's structural, morphological, and compositional changes, a two‐step conversion reaction mechanism is proposed that can clearly explain the phase behavior and the high conversion yield. The excellent charge–discharge performance (specific capacities over 1500 mAh g^‐1 for 100 cycles) of the hierarchical Si nanostructure suggests that this facile, fast, and high‐efficiency synthesis strategy from ultralow‐cost sand particles provides outstanding cost‐effectiveness and possible scalability for the commercialization of Si electrodes for energy‐storage applications.     

A New Spinel‐Layered Li‐Rich Microsphere as a High‐Rate Cathode Material for Li‐Ion Batteries

Li‐rich layered materials are considered to be the promising low‐cost cathodes for lithium‐ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres are reported as a new high‐rate cathode material for Li‐ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel‐like component with a layered component by a heat treatment. When calcined at 700 °C, the amount of transition metal Mn and Co in the Li‐Mn‐Co‐O microspheres maintained is similar to at 800 °C, while the structures of constituent particles partially transform from 2D to 3D channels. As a consequence, when tested as a cathode for lithium‐ion batteries, the spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres obtained at 700 °C show a maximum discharge capacity of 185.1 mA h g^?1 at a very high current density of 1200 mA g^?1 between 2.0 and 4.6 V. Such a capacity is among the highest reported to date at high charge‐discharge rates. Therefore, the present spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres represent an attractive alternative to high‐rate electrode materials for lithium‐ion batteries.     

MnMoO4 Electrocatalysts for Superior Long‐Life and High‐Rate Lithium‐Oxygen Batteries

Lithium‐oxygen batteries represent a significant scientific challenge for high‐rate and long‐term cycling using oxygen electrodes that contain efficient electrocatalysts. The mixed transition metal oxide catalysts provide the most efficient catalytic activity for partial heterogeneous surface cations with oxygen vacancies as the active phase. They include multiple oxidation states and oxygen vacancies. Here, using a combination of transmission electron microscopy, differential electrochemical mass spectrometry, X‐ray photoelectron spectroscopy, and electrochemical properties to probe the surface of the MnMoO₄ nanowires, it is shown that the intrinsic MnMoO₄ oxygen vacancies on the oxygen electrode are an effective strategy to achieve a high reversibility and high efficiency for lithium‐oxygen (Li‐O₂) batteries. The modified MnMoO₄ nanowires exhibit a highly stable capacity at a fixed capacity of 5000 mA h g_sp^?1 (calculated weight of Super P carbon black) during 50 cycles, a high‐rate capability at a current rate of 3000 mA g_sp^?1 during 70 cycles, and a long‐term reversible capacity during 188 cycles at a fixed capacity of 1000 mA h g_sp^?1. It is demonstrated that this strategy for creating mixed transition metal oxides (e.g., MnMoO₄) may pave the way for the new structural design of electrocatalysts for Li‐O₂ batteries.     

A Flexible Porous Carbon Nanofibers‐Selenium Cathode with Superior Electrochemical Performance for Both Li‐Se and Na‐Se Batteries

A flexible and free‐standing porous carbon nanofibers/selenium composite electrode (Se@PCNFs) is prepared by infiltrating Se into mesoporous carbon nanofibers (PCNFs). The porous carbon with optimized mesopores for accommodating Se can synergistically suppress the active material dissolution and provide mechanical stability needed for the film. The Se@PCNFs electrode exhibits exceptional electrochemical performance for both Li‐ion and Na‐ion storage. In the case of Li‐ion storage, it delivers a reversible capacity of 516 mAh g^?1 after 900 cycles without any capacity loss at 0.5 A g^?1. Se@PCNFs still delivers a reversible capacity of 306 mAh g^?1 at 4 A g^?1. While being used in Na‐Se batteries, the composite electrode maintains a reversible capacity of 520 mAh g^?1 after 80 cycles at 0.05 A g^?1 and a rate capability of 230 mAh g^?1 at 1 A g^?1. The high capacity, good cyclability, and rate capability are attributed to synergistic effects of the uniform distribution of Se in PCNFs and the 3D interconnected PCNFs framework, which could alleviate the shuttle reaction of polyselenides intermediates during cycling and maintain the perfect electrical conductivity throughout the electrode. By rational and delicate design, this type of self‐supported electrodes may hold great promise for the development of Li‐Se and Na‐Se batteries with high power and energy densities.     

Tunable Free‐Standing Ultrathin Porous Nickel Film for High Performance Flexible Nickel–Metal Hydride Batteries

The nickel matrix has a significant impact on the structure and performance of a nickel–metal hydride (NiMH) battery. However, few studies have focused on the nickel matrix thus far due to the difficulty of fabricating controllable porous nickel materials. In addition, conventional nickel matrices show poor flexibility, making it difficult to fabricate flexible NiMH batteries. To achieve a high performance flexible NiMH battery, the fabrication of a thin, free‐standing, and flexible nickel matrix with an optimized pore structure is a key prerequisite. Here, a novel flexible porous nickel matrix with a controllable pore size, density, and distribution of pore position is developed by nickel electrodeposition on templates that are produced by silkscreen printing different insulating ink microarrays on stainless steel sheets. Benefitting from the excellent structure of the porous nickel matrix, flexible NiMH batteries are fabricated, which show excellent flexibility and very high energy densities of 151.8 W h kg^?1 and 508.5 W h L^?1 as well as high energy efficiencies of 87.9–98.5%. These batteries outperform conventional NiMH batteries and many other commercial batteries, holding great promise for their future practical application. The present strategy provides a new route to promote the development of nickel‐based alkaline rechargeable batteries.     

Al Doping for Mitigating the Capacity Fading and Voltage Decay of Layered Li and Mn‐Rich Cathodes for Li‐Ion Batteries

Li and Mn‐rich layered cathodes, despite their high specific capacity, suffer from capacity fading and discharge voltage decay upon cycling. Both specific capacity and discharge voltage of Li and Mn‐rich cathodes are stabilized upon cycling by optimized Al doping. Doping Li and Mn‐rich cathode materials Li_1.2Ni_0.16Mn_0.56Co_0.08O₂ by Al on the account of manganese (as reflected by their stoichiometry) results in a decrease in their specific capacity but increases pronouncedly their stability upon cycling. Li_1.2Ni_0.16Mn_0.51Al_0.05Co_0.08O₂ exhibits 96% capacity retention as compared to 68% capacity retention for Li_1.2Ni_0.16Mn_0.56Co_0.08O₂ after 100 cycles. This doping also reduces the decrease in the average discharge voltage upon cycling, which is the longstanding fatal drawback of these Li and Mn‐rich cathode materials. The electrochemical impedance study indicates that doping by Al has a surface stabilization effect on these cathode materials. The structural analysis of cycled electrodes by Raman spectroscopy suggests that Al doping also has a bulk stabilizing effect on the layered LiMO₂ phase resulting in the better electrochemical performance of Al doped cathode materials as compared to the undoped counterpart. Results from a prolonged systematic work on these cathode materials are presented and the best results that have ever been obtained are reported.     

Multidimensional Ordered Bifunctional Air Electrode Enables Flash Reactants Shuttling for High‐Energy Flexible Zn‐Air Batteries

Direct growth of electrocatalysts on conductive substrates is an emerging strategy to prepare air electrodes for flexible Zn‐air batteries (FZABs). However, electrocatalysts grown on conductive substrates usually suffer from disorder and are densely packed with “prohibited zones”, in which internal blockages shut off the active sites from catalyzing the oxygen reaction. Herein, to minimize the “prohibited zones”, an ordered multidimensional array assembled by 1D carbon nanotubes and 2D carbon nanoridges decorated with 0D cobalt nanoparticles (referred as MPZ‐CC@CNT) is constructed on nickel foam. When the MPZ‐CC@CNT is directly applied as a self‐supported electrode for FZAB, it delivers a marginal voltage fading rate of 0.006 mV cycle^?1 over 1800 cycles (600 h) at a current density of 50 mA cm^?2 and an impressive energy density of 946 Wh kg^?1. Electrochemical impedance spectroscopy reveals that minimal internal resistance and electrochemical polarization, which is beneficial for the flash reactant shuttling among the triphase (i.e., oxygen, electrolyte, and catalyst) are offered by the open and ordered architecture. This advanced electrode design provides great potential to boost the electrochemical performance of other rechargeable battery systems.     

Ultrathin Li4Ti5O12 Nanosheet Based Hierarchical Microspheres for High‐Rate and Long‐Cycle Life Li‐Ion Batteries

Ultrathin Li₄Ti₅O₁₂ nanosheet based hierarchical microspheres are synthesized through a three‐step hydrothermal procedure. The average thickness of the Li₄Ti₅O₁₂ sheets is only ≈(6.6 ± 0.25) nm and the specific surface area of the sample is 178 m² g^?1. When applied into lithium ion batteries as anode materials, the hierarchical Li₄Ti₅O₁₂ microspheres exhibit high specific capacities at high rates (156 mA h g^?1 at 20 C, 150 mA h g^?1 at 50 C) and maintain a capacity of 126 mA h g^?1 after 3000 cycles at 20 C. The results clearly suggest that the utility of hierarchical structures based on ultrathin nanosheets can promote the lithium insertion/extraction reactions in Li₄Ti₅O₁₂. The obtained hierarchical Li₄Ti₅O₁₂ with ultrathin nanosheets and large specific surface area can be perfect anode materials for the lithium ion batteries applied in high power facilities, such as electric vehicles and hybrid electric vehicles.     

Li2O:Li–Mn–O Disordered Rock‐Salt Nanocomposites as Cathode Prelithiation Additives for High‐Energy Density Li‐Ion Batteries

The irreversible loss of lithium from the cathode material during the first cycles of rechargeable Li‐ion batteries notably reduces the overall cell capacity. Here, a new family of sacrificial cathode additives based on Li₂O:Li_2/3Mn_1/3O_5/6 composites synthesized by mechanochemical alloying is reported. These nanocomposites display record (but irreversible) capacities within the Li–Mn–O systems studied, of up to 1157 mAh g^?1, which represents an increase of over 300% of the originally reported capacity in Li_2/3Mn_1/3O_5/6 disordered rock salts. Such a high irreversible capacity is achieved by the reaction between Li₂O and Li_2/3Mn_1/3O_5/6 during the first charge, where electrochemically active Li₂O acts as a Li⁺ donor. A 13% increase of the LiFePO₄ and LiCoO₂ first charge gravimetric capacities is demonstrated by the addition of only 2 wt% of the nanosized composite in the cathode mixture. This result shows the great potential of these newly discovered sacrificial additives to counteract initial losses of Li⁺ ions and improve battery performance.     

Highly Stable Carbon‐Free Ag/Co3O4‐Cathodes for Lithium‐Air Batteries: Electrochemical and Structural Investigations

Lithium‐air batteries with an aqueous alkaline electrolyte promise a much higher practical energy density and capacity than conventional lithium‐ion batteries. However, high cathode overpotentials are some of the main problems during cycling. In our previous work, a catalyst combination of Ag and Co₃O₄ is found that reduces overpotential significantly, and is highly active and also long‐term stable. In the present investigations, X‐ray diffraction and X‐ray photoelectron spectroscopy are applied to study the structure and composition of the cathode material during oxygen reduction reaction and oxygen evolution reaction. Changes of the oxidation states during cycling are responsible for an enhanced oxygen evolution reaction current density but also for losses due to a lower electronic conductivity of the electrodes. The presence and formation of a mixed oxidation state for silver oxide (Ag^IAg^IIIO₂) at high potentials is identified. In contradiction to literature, time dependent X‐ray diffraction measurements evidence that this phase is not stable under dry conditions and progressively decays to Ag₂O. Electrode mappings show a highly homogeneous oxidation of the electrodes during cycling and quantitative analysis of the observed phases is carried out by Rietveld analysis. Long‐term material behavior completes the investigations.     

Two‐Step Activated Carbon Cloth with Oxygen‐Rich Functional Groups as a High‐Performance Additive‐Free Air Electrode for Flexible Zinc–Air Batteries

A flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn–air batteries. A facile two‐step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen‐rich functional groups and an enhanced surface area, is presented here. Impressively, this two‐step activated CC (CC‐AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen‐doped carbon materials reported to date. Especially, CC‐AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm^?2 in 1 m KOH, which is among the best performances of metal‐free OER electrocatalysts. The practical application of CC‐AC is presented via its use as an FAE in a flexible rechargeable Zn–air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm^?3 at 77.5 mA cm^?3, good cycling performance with a small charge–discharge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high‐performance self‐supported metal‐free electrodes.     

3D Cube‐Maze‐Like Li‐Rich Layered Cathodes Assembled from 2D Porous Nanosheets for Enhanced Cycle Stability and Rate Capability of Lithium‐Ion Batteries

Li‐rich oxide is a promising candidate for the cathodes of next‐generation lithium‐ion batteries. However, its utilization is restricted by cycling instability and inferior rate capability. To tackle these issues, three‐dimensional (3D), hierarchical, cube‐maze‐like Li‐rich cathodes assembled from two‐dimensional (2D), thin nanosheets with exposed {010} active planes, are developed by a facile hydrothermal approach. Benefiting from their unique architecture, 3D cube‐maze‐like cathodes demonstrate a superior reversible capacity (285.3 mAh g^?1 at 0.1 C, 133.4 mAh g^?1 at 20.0 C) and a great cycle stability (capacity retention of 87.4% after 400 cycles at 2.0 C, 85.2% after 600 cycles and 75.0% after 1200 cycles at 20.0 C). When this material is matched with a graphite anode, the full cell achieves a remarkable discharge capacity (275.2 mAh g^?1 at 0.1 C) and stable cycling behavior (capacity retention of 88.7% after 100 cycles at 5.0 C, capacity retention of 84.8% after 100 cycles at 20.0 C). The present work proposes an accessible way to construct 3D hierarchical architecture assembled from 2D nanosheets with exposed high‐energy active {010} planes and verifies its validity for advanced Li‐rich cathodes.     

Ice Templated Free‐Standing Hierarchically WS2/CNT‐rGO Aerogel for High‐Performance Rechargeable Lithium and Sodium Ion Batteries

A hybrid nanoarchitecture aerogel composed of WS₂ nanosheets and carbon nanotube‐reduced graphene oxide (CNT‐rGO) with ordered microchannel three‐dimensional (3D) scaffold structure was synthesized by a simple solvothermal method followed by freeze‐drying and post annealing process. The 3D ordered microchannel structures not only provide good electronic transportation routes, but also provide excellent ionic conductive channels, leading to an enhanced electrochemical performance as anode materials both for lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). Significantly, WS₂/CNT‐rGO aerogel nanostructure can deliver a specific capacity of 749 mA h g^?1 at 100 mA g^?1 and a high first‐cycle coulombic efficiency of 53.4% as the anode material of LIBs. In addition, it also can deliver a capacity of 311.4 mA h g^?1 at 100 mA g^?1, and retain a capacity of 252.9 mA h g^?1 at 200 mA g^?1 after 100 cycles as the anode electrode of SIBs. The excellent electrochemical performance is attributed to the synergistic effect between the WS₂ nanosheets and CNT‐rGO scaffold network and rational design of 3D ordered structure. These results demonstrate the potential applications of ordered CNT‐rGO aerogel platform to support transition‐metal‐dichalcogenides (i.e., WS₂) for energy storage devices and open up a route for material design for future generation energy storage devices.