Selenium-Doped Sulfurized Polyacrylonitrile Hybrid Cathodes with Ultrahigh Sulfur Content for High-Performance Solid-State Lithium Sulfur Batteries.

The solid-state lithium sulfur battery (SSLSB) is an attractive next-generation energy storage system by reason of its remarkably high energy density and safety. However, the SSLSB still faces critical challenges, such as sluggish reaction kinetics, mismatched interface, and undesirable reversible capacity. Herein, a high-performance SSLSB is reported using sulfurized polyacrylonitrile with rich selenium-doped sulfur (Se/S-S@pPAN) as a cathode and poly(ethylene oxide)/Li7La3Zr1.4Ta0.6O12 (PEO-LLZTO) as an electrolyte. The sulfur content of the cathode up to 60.9 wt % can be achieved by dispersing selenium sulfide (SeSx) species in the sulfurized polyacrylonitrile (S@pPAN) skeleton at a molecular level. Selenium as a eutectic accelerator can be uniformly distributed in the composite through the Se-S bond and can accelerate the reaction kinetics. The PEO-LLZTO hybrid solid-state electrolyte (SSE) displays an attractive electrochemical performance and provides an intimate contact with electrodes. At 60 °C, Se/S-S@pPAN delivers an impressive discharge capacity of 1042 mAh g-1 at 0.1C and 445 mAh g-1 at 1C. Additionally, the LiFePO4 cathodes combined with PEO-LLZTO deliver a high reversible capacity (158.9 mAh g-1, 1C) and an ultralong lifespan (a capacity retention of 80%, 1000 cycles) at 1C. The synergetic design of the high-performance sulfur cathode and the organic/inorganic hybrid electrolyte is crucial for enabling the high-performance SSLSB.

Tailoring Electric Double Layer by Cation Specific Adsorption for High-Voltage Quasi-Solid-State Lithium Metal Batteries.

The interfacial instability of high-nickel layered oxides severely plagues practical application of high-energy quasi-solid-state lithium metal batteries (LMBs). Herein, a uniform and highly oxidation-resistant polymer layer within inner Helmholtz plane is engineered by in situ polymerizing 1-vinyl-3-ethylimidazolium (VEIM) cations preferentially adsorbed on LiNi0.83Co0.11Mn0.06O2 (NCM83) surface, inducing the formation of anion-derived cathode electrolyte interphase with fast interfacial kinetics. Meanwhile, the copolymerization of [VEIM][BF4] and vinyl ethylene carbonate (VEC) endows P(VEC-IL) copolymer with the positively-charged imidazolium moieties, providing positive electric fields to facilitate Li+ transport and desolvation process. Consequently, the Li||NCM83 cells with a cut-off voltage up to 4.5 V exhibit excellent reversible capacity of 130 mAh g-1 after 1000 cycles at 25 °C and considerable discharge capacity of 134 mAh g-1 without capacity decay after 100 cycles at -20 °C. This work provides deep understanding on tailoring electric double layer by cation specific adsorption for high-voltage quasi-solid-state LMBs.

d-p Hybridization-Induced "Trapping-Coupling-Conversion" Enables High-Efficiency Nb Single-Atom Catalysis for Li-S Batteries.

Single-atom catalysts have been paid more attention to improving sluggish reaction kinetics and anchoring polysulfide for lithium-sulfur (Li-S) batteries. It has been demonstrated that d-block single-atom elements in the fourth period can chemically interact with the local environment, leading to effective adsorption and catalytic activity toward lithium polysulfides. Enlightened by theoretical screening, for the first time, we design novel single-atom Nb catalysts toward improved sulfur immobilization and catalyzation. Calculations reveal that Nb-N4 active moiety possesses abundant unfilled antibonding orbitals, which promotes d-p hybridization and enhances anchoring capability toward lithium polysulfides via a "trapping-coupling-conversion" mechanism. The Nb-SAs@NC cell exhibits a high capacity retention of over 85% after 1000 cycles, a superior rate performance of 740 mA h g-1 at 7 C, and a competitive areal capacity of 5.2 mAh cm-2 (5.6 mg cm-2). Our work provides a new perspective to extend cathodes enabling high-energy-density Li-S batteries.

Architecting FeNx on High Graphitization Carbon for High-Performance Oxygen Reduction by Regulating d-Band Center.

Fe single atoms and N co-doped carbon nanomaterials (Fe-N-C) are the most promising oxygen reduction reaction (ORR) catalysts to replace platinum group metals. However, high-activity Fe single-atom catalysts suffer from poor stability owing to the low graphitization degree. Here, an effective phase-transition strategy is reported to enhance the stability of Fe-N-C catalysts by inducing increased degree of graphitization and incorporation of Fe nanoparticles encapsulated by graphitic carbon layer without sacrificing activity. Remarkably, the resulted Fe@Fe-N-C catalysts achieved excellent ORR activity (E1/2  = 0.829 V) and stability (19 mV loss after 30K cycles) in acid media. Density functional theory (DFT) calculations agree with experimental phenomena that additional Fe nanoparticles not only favor to the activation of O2 by tailoring d-band center position but also inhibit the demetallization of Fe active center from FeN4 sites. This work provides a new insight into the rational design of highly efficient and durable Fe-N-C catalysts for ORR.

Tailoring the p-Band Center of NS Pair for Accelerating High-Performance Lithium-Oxygen Battery.

The local coordination environment of catalytical moieties directly determines the performance of electrochemical energy storage and conversion devices, such as Li-O2 batteries (LOBs) cathode. However, understanding how the coordinative structure affects the performance, especially for non-metal system, is still insufficient. Herein, a strategy that introduces S-anion to tailor the electronic structure of nitrogen-carbon catalyst (SNC) is proposed to improve the LOBs performance. This study unveils that the introduced S-anion effectively manipulates the p-band center of pyridinic-N moiety, substantially reducing the battery overpotential by accelerating the generation and decomposition of intermediate products Li1-3 O4 . The lower adsorption energy of discharging product Li2 O2 on NS pair accounts for the long-term cyclic stability by exposing the high active area under operation condition. This work demonstrates an encouraging strategy to enhance LOBs performance by modulating the p-band center on non-metal active sites.

DNA Helix Structure Inspired Flexible Lithium-Ion Batteries with High Spiral Deformability and Long-Lived Cyclic Stability.

With the development of flexible devices, it is necessary to design high-performance power supplies with superior flexibility, durability, safety, etc., to ensure that they can be deformed with the device while retaining their electrochemical functions. Herein, we have designed a flexible lithium-ion battery inspired by the DNA helix structure. The battery structure is mainly composed of multiple thick energy stacks for energy storage and some grooves for stress buffers, which realized the spiral deformation of batteries. According to the results, the batteries exhibit less than 3% capacity degradation even after more than 31000 times of in situ dynamic mechanical loadings. Moreover, the mechanism of the battery with spiral deformability is further revealed. It is anticipated that this bioinspired design strategy could create unique opportunities for the commercialization of flexible batteries and fill the current gap in realizing battery-specific deformations to meet various requirements for future complex device designs.

Kirigami-Inspired Flexible Lithium-Ion Batteries via Transformation of Concentrated Stress into Segmented Strain.

Emerging directions in the growing wearable electronics market have spurred the development of flexible energy storage systems that require deformability while maintaining electrochemical performance. However, the traditional fabrication approaches of lithium-ion batteries (LIBs) are challenging to withstand long-cycle bending alternating loads due to the stress concentration caused by the nonuniformity of the actual deformation. Herein, inspired by kirigami, a segmented deformation design of full-cell scale thin-type flexible lithium-ion batteries (FLIBs) with large-scale manufacturing characteristics via the current collector's mechanical blanking process is reported. This strategy allows the battery's elliptical deformation of the actual state to be transformed into the circular strain of the ideal configuration, thereby dispersing the stress concentration on the top of the battery. According to the results, the designed battery maintains >95% capacity after >20 000 harsh in situ dynamic tests. In addition, finite element analysis further reveals the mechanism that the segmented deformation strategy bears the mechanical stress. This work can enlighten the rational design and customization of electrode patterns for high compatibility with various devices, thereby providing potential opportunities for the application of FLIBs.

Single-Atom Tailored Hierarchical Transition Metal Oxide Nanocages for Efficient Lithium Storage.

Mitigating the mechanical degradation and enhancing the ionic/electronic conductivity are critical but challengeable issues toward improving electrochemical performance of conversion-type anodes in rechargeable batteries. Herein, these challenges are addressed by constructing interconnected 3D hierarchically porous structure synergistic with Nb single atom modulation within a Co3 O4 nanocage (3DH-Co3 O4 @Nb). Such a hierarchical-structure nanocage affords several fantastic merits such as rapid ion migration and enough inner space for alleviating volume variation induced by intragrain stress and optimized stability of the solid-electrolyte interface. Particularly, experimental studies in combination with theoretical analysis verify that the introduction of Nb into the Co3 O4 lattice not only improves the electron conductivity, but also accelerates the surface/near-surface reactions defined as pesudocapacitance behavior. Dynamic behavior reveals that the ensemble design shows huge potential for fast and large lithium storage. These features endow 3DH-Co3 O4 @Nb with remarkable battery performance, delivering ≈740 mA h g-1 after ultra-long cycling of 1000 times under a high current density of 5 A g-1 . Importantly, the assembled 3DH-Co3 O4 @Nb//LiCoO2 pouch cell also presents a long-lived cycle performance with only ≈0.059% capacity decay per cycle, inspiring the design of electrode materials from both the nanostructure and atomic level toward practical applications.

Structural Distortion Induced by Manganese Activation in a Lithium-Rich Layered Cathode.

The search for batteries with high energy density has highlighted lithium-rich manganese-based layered oxides due to their exceptionally high capacity. Although it is clear that both cationic and anionic redox are present in the charge compensation mechanism, the microstructural evolution of the Li2MnO3-like phase during anionic redox and its role in battery performance and structural stability are still not fully understood. Here, we systematically probe microstructural evolution using spatially resolved synchrotron X-ray measurements and reveal an underlying interaction between the Li2MnO3-like domains and bulk rhombohedral structure. Mn ion activation and a previously unobserved structural distortion are discovered at high voltages, and can be related to structural strain present in the Li2MnO3-like phase upon substantial lithium ion extraction. Moreover, we elucidate a correlation between this structural distortion and irreversible phase transitions by thermally perturbing delithiated samples. These insights highlight a pathway toward achieving high capacity cathode materials required for future commercial applications.

ZIF-8 with Ferrocene Encapsulated: A Promising Precursor to Single-Atom Fe Embedded Nitrogen-Doped Carbon as Highly Efficient Catalyst for Oxygen Electroreduction.

The oxygen reduction reaction (ORR) plays an important role in the fields of energy storage and conversion technologies, including metal-air batteries and fuel cells. The development of nonprecious metal electrocatalysts with both high ORR activity and durability to replace the currently used costly Pt-based catalyst is critical and still a major challenge. Herein, a facile and scalable method is reported to prepare ZIF-8 with single ferrocene molecules trapped within its cavities (Fc@ZIF-8), which is utilized as precursor to porous single-atom Fe embedded nitrogen-doped carbon (Fe-N-C) during high temperature pyrolysis. The catalyst shows a half-wave potential (E1/2 ) of 0.904 V, 67 mV higher than commercial Pt/C catalyst (0.837 V), which is among the best compared with reported results for ORR. Significant electrochemical properties are attributed to the special configuration of Fc@ZIF-8 transforming into a highly dispersed iron-nitrogen coordination moieties embedded carbon matrix.

Highly reversible Mg insertion in nanostructured Bi for Mg ion batteries.

Rechargeable magnesium batteries have attracted wide attention for energy storage. Currently, most studies focus on Mg metal as the anode, but this approach is still limited by the properties of the electrolyte and poor control of the Mg plating/stripping processes. This paper reports the synthesis and application of Bi nanotubes as a high-performance anode material for rechargeable Mg ion batteries. The nanostructured Bi anode delivers a high reversible specific capacity (350 mAh/gBi or 3430 mAh/cm(3)Bi), excellent stability, and high Coulombic efficiency (95% initial and very close to 100% afterward). The good performance is attributed to the unique properties of in situ formed, interconnected nanoporous bismuth. Such nanostructures can effectively accommodate the large volume change without losing electric contact and significantly reduce diffusion length for Mg(2+). Significantly, the nanostructured Bi anode can be used with conventional electrolytes which will open new opportunities to study Mg ion battery chemistry and further improve its properties.

Corrosion/fragmentation of layered composite cathode and related capacity/voltage fading during cycling process.

The Li-rich, Mn-rich (LMR) layered structure materials exhibit very high discharge capacities exceeding 250 mAh g(-1) and are very promising cathodes to be used in lithium ion batteries. However, significant barriers, such as voltage fade and low rate capability, still need to be overcome before the practical applications of these materials. A detailed study of the voltage/capacity fading mechanism will be beneficial for further tailoring the electrode structure and thus improving the electrochemical performances of these layered cathodes. Here, we report detailed studies of structural changes of LMR layered cathode Li[Li0.2Ni0.2Mn0.6]O2 after long-term cycling by aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The fundamental findings provide new insights into capacity/voltage fading mechanism of Li[Li0.2Ni0.2Mn0.6]O2. Sponge-like structure and fragmented pieces were found on the surface of cathode after extended cycling. Formation of Mn(2+) species and reduced Li content in the fragments leads to the significant capacity loss during cycling. These results also imply the functional mechanism of surface coatings, for example, AlF3, which can protect the electrode from etching by acidic species in the electrolyte, suppress cathode corrosion/fragmentation, and thus improve long-term cycling stability.

Delocalized electronic engineering of TiNb2O7 enables low temperature capability for high-areal-capacity lithium-ion batteries.

High areal capacity and low-temperature ability are critical for lithium-ion batteries (LIBs). However, the practical operation is seriously impeded by the sluggish rates of mass and charge transfer. Herein, the active electronic states of TiNb2O7 material is modulated by dopant and O-vacancies for enhanced low-temperature dynamics. Femtosecond laser-based transient absorption spectroscopy is employed to depict carrier dynamics of TiNb2O7, which verifies the localized structure polarization accounting for reduced transport overpotential, facilitated electron/ion transport, and improved Li+ adsorption. At high-mass loading of 10 mg cm-2 and -30 °C, TNO-x@N microflowers exhibit stable cycling performance with 92.9% capacity retention over 250 cycles at 1 C (1.0-3.0 V, 1 C = 250 mA g-1). Even at -40 °C, a competitive areal capacity of 1.32 mAh cm-2 can be achieved. Such a fundamental understanding of the intrinsic structure-function put forward a rational viewpoint for designing high-areal-capacity batteries in cold regions.

Electrolyte-assisted low-voltage decomposition of Li2C2O4 for efficient cathode pre-lithiation in lithium-ion batteries.

Lithium oxalate (Li2C2O4) is an attractive cathode pre-lithiation additive for lithium-ion batteries (LIBs), but its application is hindered by its high decomposition potential (>4.7 V). Due to the liquid-solid synergistic effect of the NaNO2 additive and the LiNi0.83Co0.07Mn0.1O2 (NCM) cathode material, the decomposition efficiency of micro-Li2C2O4 reaches 100% at a low charge cutoff voltage of 4.3 V. Our work boosts the widespread practical application of Li2C2O4 by a simple and promising electrolyte-assisted cathode pre-lithiation strategy.

Long-sequence voltage series forecasting for internal short circuit early detection of lithium-ion batteries.

Accurate early detection of internal short circuits (ISCs) is indispensable for safe and reliable application of lithium-ion batteries (LiBs). However, the major challenge is finding a reliable standard to judge whether the battery suffers from ISCs. In this work, a deep learning approach with multi-head attention and a multi-scale hierarchical learning mechanism based on encoder-decoder architecture is developed to accurately forecast voltage and power series. By using the predicted voltage without ISCs as the standard and detecting the consistency of the collected and predicted voltage series, we develop a method to detect ISCs quickly and accurately. In this way, we achieve an average percentage accuracy of 86% on the dataset, including different batteries and the equivalent ISC resistance from 1,000 Ω to 10 Ω, indicating successful application of the ISC detection method.

Hierarchical NiMn/NiMn-LDH/ppy-C induced by a novel phase-transformation activation process for long-life supercapacitor.

For micron-sized nickel-based hydroxides sheets, the reaction and migration of anions/water molecules in the inner region tends to lag behind those along the edge, which can cause structure mismatch and capacity degradation during cycles. Nanosizing and structure design is a feasible solution to shorten the ion/electron path and improve the reaction homogeneity. Herein, this study reports a novel three-stage strategy (self-assembly of NiMn-LDH/ppy-C - reduction to NiMn/ppy-C - in situ phase transformation into NiMn/NiMn-LDH/ppy-C) to reduce the sheet size of NiMn-LDH to nanometer. Triggered by electrochemical activation, NiMn-LDH nanosheets can hereby easily and orderly grow on the exposed active (111) crystal plane of Ni to establish NiMn-LDH/NiMn heterostructure around ppy-C. Importantly, nanosizing and hierarchical structure play a synergistic role to maintain structural integrity and to promote the electron/mass transfer kinetics. The NiMn/NiMn-LDH/ppy-C composite delivers superior cycling stability with almost no decay of capacity retention after 40,000 cycles at 5 A g-1. Our hierarchical morphology modulation provides an ingenious, efficient way to boost the performance of Ni-based layered hydroxide materials.

Chelated electrolytes for divalent metal ions.

Chelating electrolytes reorganize ion solvation and enable reversible magnesium batteries.

Recent Progress of Electrochemical Production of Hydrogen Peroxide by Two-Electron Oxygen Reduction Reaction.

Shifting electrochemical oxygen reduction reaction (ORR) via two-electron pathway becomes increasingly crucial as an alternative/green method for hydrogen peroxide (H2 O2 ) generation. Here, the development of 2e- ORR catalysts in recent years is reviewed, in aspects of reaction mechanism exploration, types of high-performance catalysts, factors to influence catalytic performance, and potential applications of 2e- ORR. Based on the previous theoretical and experimental studies, the underlying 2e- ORR catalytic mechanism is firstly unveiled, in aspect of reaction pathway, thermodynamic free energy diagram, limiting potential, and volcano plots. Then, various types of efficient catalysts for producing H2 O2 via 2e- ORR pathway are summarized. Additionally, the catalytic active sites and factors to influence catalysts' performance, such as electronic structure, carbon defect, functional groups (O, N, B, S, F etc.), synergistic effect, and others (pH, pore structure, steric hindrance effect, etc.) are discussed. The H2 O2 electrogeneration via 2e- ORR also has various potential applications in wastewater treatment, disinfection, organics degradation, and energy storage. Finally, potential future directions and prospects in 2e- ORR catalysts for electrochemically producing H2 O2 are examined. These insights may help develop highly active/selective 2e- ORR catalysts and shape the potential application of this electrochemical H2 O2 producing method.

A Scalable Cathode Chemical Prelithiation Strategy for Advanced Silicon-Based Lithium Ion Full Batteries.

A silicon anode with ultra-high specific capacity has motivated tremendous exploration for high-energy-density lithium ion batteries while it still faces serious issues of irreversible lithium loss, unstable electrode electrolyte interface (SEI), and huge volume expansion. Prelithiation is a crucial technology to alleviate the harm of active lithium loss of silicon-based full-cell systems. Herein, we reported a cathode prelithiation method using Li2S-PAN as a lithium "donor", which was synthesized via chemical reaction between sulfurized polyacrylonitrile and Li-biphenyl complex. The Li2S-PAN with an initial charging capacity of 668 mAh g-1 (2.5-4.0 V) is loaded on the LiFePO4 electrode, and the LiFePO4/Li2S-PAN composite electrode displays a high initial charge capacity of 206 mAh g-1, which is 22.3% higher than the pristine LiFePO4. With a silicon/graphite/carbon (Si/G/C) composite anode, the Si/G/C||LiFePO4/Li2S-PAN full cell exhibits a reversible capacity of 123 and 107 mAh g-1 in the 1st and 10th cycle, which is 15.5 and 24.5% higher than the Si/G/C||LiFePO4 battery, respectively. The SEI layer of the silicon anode in the Si/G/C||LiFePO4/Li2S-PAN cell contains abundant conductive LiF species, which can enhance the interfacial stability and reaction kinetics of the cells. The proposed cathode prelithiation process is compatible with the industrial roll-to-roll electrode preparation process, exhibiting a promising application prospect.

Stabilizing Lithium Metal Anode Enabled by a Natural Polymer Layer for Lithium-Sulfur Batteries.

The lithium-sulfur (Li-S) battery with a high theoretical energy density (2560 Wh kg-1) is one of the most promising candidates in next-generation energy storage systems. However, its practical application is impeded by the shuttle effect of lithium polysulfides, huge volume expansion, and overgrowth dendrite of lithium. Herein, we propose an artificial conformal agar polymer coating on a lithium anode (marked as A-Li). The functional layer facilitating the formation of a compact interphase on the lithium anode can effectively accommodate expansive volume and restrain the growth of dendritic lithium. The Li/Li symmetric cell with A-Li delivers stable plating/stripping cycling over 300 h at a high current density of 3.0 mA cm-2 and a high fixed areal capacity of 3.0 mAh cm-2. The cycle life of Li-Cu cells with A-Li is twice longer than that of pristine cells, and the Li-S batteries equipped with A-Li anodes also deliver an enhanced specific capacity and high Coulombic efficiencies. This work provides a pathway to protect metal Li anodes and contributes to the development of high-performance Li-S batteries.