GeV4 S8 : a Novel Bimetallic Sulfide for Robust and Fast Potassium Storage.

Potassium-ion batteries (PIBs) have attracted much attention due to their low production cost and abundant resources. Germanium is a promising alloying-type anode with a high theoretical capacity for PIBs, yet suffering significant volume expansion and sluggish potassium-ion transport kinetics. Herein, a rational strategy is formulated to disperse Ge atoms into transition metal V-S sulfide frameworks to form a loosely packed and metallic GeV4 S8 medium. The theoretical prediction shows that GeV4 S8 is conducive to the adsorption and diffusion of K+ . The V-S frameworks provide fast ion/electron diffusion channels and also help to buffer the volume expansion during K+ insertion. In situ and ex situ characterizations manifest that KGe alloy clusters are constrained and dispersed by potassiated VS2 topological structure during discharging, and revert to the original GeV4 S8 after charging. Consequently, as a novel anode for PIBs, GeV4 S8 provides a high specific capacity of ≈400 mAh g-1 at 0.5 C, maintaining 160 mAh g-1 even at 12.5 C and ≈80% capacity after 1000 cycles at 5 C, superior to most of the state-of-the-art anode materials. The proposed strategy of combining alloy and intercalation dual-functional units is expected to open up a new way for high-capacity and high-rate anode for PIBs.

Boosting Cycling Stability of Polymer Sodium Battery by "Rigid-Flexible" Coupled Interfacial Stress Modulation.

The discontinuous interfacial contact of solid-state polymer metal batteries is due to the stress changes in the electrode structure during cycling, resulting in poor ion transport. Herein, a rigid-flexible coupled interface stress modulation strategy is developed to solve the above issues, which is to design a rigid cathode with enhanced solid-solution behavior to guide the uniform distribution of ions and electric field. Meanwhile, the polymer components are optimized to build an organic-inorganic blended flexible interfacial film to relieve the change of interfacial stress and ensure rapid ion transmission. The fabricated battery comprising a Co-modulated P2-type layered cathode (Na0.67Mn2/3Co1/3O2) and a high ion conductive polymer could deliver good cycling stability without distinct capacity fading (72.8 mAh g-1 over 350 cycles at 1 C), outperforming those without Co modulation or interfacial film construction. This work demonstrates a promising rigid-flexible coupled interfacial stress modulation strategy for polymer-metal batteries with excellent cycling stability.

Nanoscale Borate Coating Network Stabilized Iron Oxide Anode for High-Energy-Density Bipolar Lithium-Ion Batteries.

High-capacity metal oxides based on non-toxic earth-abundant elements offer unique opportunities as advanced anodes for lithium-ion batteries (LIBs). But they often suffer from large volumetric expansion, particle pulverization, extensive side reactions, and fast degradations during cycling. Here, an easy synthesis method is reported to construct amorphous borate coating network, which stabilizes conversion-type iron oxide anode for the high-energy-density semi-solid-state bipolar LIBs. The nano-borate coated iron oxide anode has high tap density (1.6 g cm-3 ), high capacity (710 mAh g-1 between 0.5 - 3.0 V, vs Li/Li+ ), good rate performance (200 mAh g-1 at 50 C), and excellent cycling stability (≈100% capacity resention over 1,000 cycles at 5 A g-1 ). When paired with high-voltage cathode LiCoO2 , it enables Cu current collector-free pouch-type classic and bipolar full cells with high voltage (7.6 V with two stack layers), achieving high energy density (≈350 Wh kg-1 ), outstanding power density (≈6,700 W kg-1 ), and extended cycle life (75% capacity retention after 2,000 cycles at 2 C), superior to the state-of-the-art high-power LIBs using Li4 Ti5 O12 anode. The design and methodology of the nanoscale polyanion-like coating can be applied to other metal oxides electrode materials, as well as other electrochemical materials and devices.

Recent Advances on High-Capacity Sodium Manganese-Based Oxide Cathodes for Sodium-ion Batteries.

Sodium manganese-based oxides (NMO) are attracting huge attention as safe and cost-effective cathode materials for sodium-ion batteries (SIBs). To date, one of the most important challenges of NMO-based cathodes is the relatively low capacity. Therefore, it is of great significance to develop high-capacity NMO-based cathodes. Great efforts have been made to enhance the reversible capacity of NMO-based cathodes, achieving considerable progress not only on electrochemical performance, but also the mechanism of massive sodium ion storage. In this paper, the structure and sodium storage mechanism for typical phases of NMO are reviewed, including P2, P3, O3, tunnel-type, and spinel-type NMO-based cathodes. Strategies for high-capacity NMO-based cathodes, such as cationic substitution, anion redox activation, etc are introduced in detail. Last but not least, the future opportunities and challenges for high-capacity NMO-based cathode are prospected.

Solid Base Assisted Dual-Promoted Heterogeneous Conversion of PVC to Metal-Free Porous Carbon Catalyst.

Polyvinyl chloride (PVC) is widely used in daily life, but its waste has become a serious environmental problem. A solid base assisted low-temperature solvothermal dehalogenation was developed in this work to sustainably and efficiently transform PVC into high-value dimethylamine hydrochloride (DMACl) chemical and N,O co-doped carbon monolith with hierarchically porous structure. The synergistic promotion of solid-base catalyst and solvent decomposition with the removal of HCl can shift forward the chemical equilibrium to promote the dechlorination of PVC and increase the carbon yield. Meanwhile, the solid-base catalyst can also act as a pore-forming additive to fabricate the carbon monolith with hierarchical pores. Induced by the high specific surface area, hierarchical pores and N,O co-doped structure, the generated carbon monolith exhibits superior electrocatalytic performance towards H2 evolution. These discoveries shed light on the design of synergistically coupled solvent and solid catalyst to promote the heterogeneous conversion of waste chlorinated plastics into high-value chemicals for a sustainable future.

Flexible yet Robust Framework of Tin(II) Oxide Carbodiimide for Reversible Lithium Storage.

Metal-organic frameworks (MOFs) can become promising electrode materials for advanced lithium-ion batteries (LIBs), because their loosely packed porous structures may mitigate volume expansion and metal atom aggregation, which occur at the respective metal oxides. However, they suffer from poor electrical conductivity and irreversible structural degradation upon charge/discharge processes, which impede their practical utilization. Herein, we investigate MOF-like Sn2 O(CN2 ) as a new electrode material. The conductive yet flexible [N=C=N] linkers are tilted between [Sn4 O] nodes and cross-linked into a porous quasi-layered structure. Such structure offers abundant channels for fast Li-ion transport and tolerance of enormous volume expansion. Notably, anisotropic [N=C=N]2- arrays hardly migrate so that Sn0 nanodots are physically separated via robust [N=C=N]2- framework during discharge, thereby effectively preventing the formation of large Sn islands. Owing to the structural advantage, the Sn2 O(CN2 ) electrode exhibits an initial Coulombic efficiency as high as ∼80 %. With the addition of graphite as conductive supporter, the electrode provides 978 mAh g-1 at 1.0 A g-1 even after 300 cycles. Such MOF-like carbodiimides hold potential for the advanced electrodes in LIBs and other battery systems.

Ruthenium-Doped Cobalt-Chromium Layered Double Hydroxides for Enhancing Oxygen Evolution through Regulating Charge Transfer.

Exploring the origin of transition metal (TM) lattice-doped layered double hydroxides (LDHs) toward the oxygen evolution reaction (OER) plays a crucial role in engineering efficient electrocatalysts. Without understanding the physics behind the TM-induced catalytic enhancements, it would be challenging to design the next generation of electrocatalysts. Herein, single Ru atoms are introduced into a CoCr LDHs lattice to improve activity. In 0.1 m KOH, CoCrRu LDHs require only 290 mV overpotential to drive to 10 mA cm-2 and show a Tafel slope of 56.12 mV dec-1 . Electronic structure analyses based on density functional theory confirm that promoted OER activity originates from synergetic charge transfer among Ru, Cr, and Co elements. Specifically, Ru dopants can downshift d states of Co and enhance electron donation of Cr to oxygenates, which essentially breaks the scaling relation and achieves higher activity. This work provides insights into how single atomic Ru dopant tunes the electronic structures of its neighbor's active site Co and thus increases OER activities.

Well-Dispersed Ruthenium in Mesoporous Crystal TiO2 as an Advanced Electrocatalyst for Hydrogen Evolution Reaction.

TiO2 mesoporous crystal has been prepared by one-step corroding process via an oriented attachment (OA) mechanism with SrTiO3 as precursor. High resolution transmission electron microscopy (HRTEM) and nitrogen adsorption-desorption isotherms confirm its mesoporous crystal structure. Well-dispersed ruthenium (Ru) in the mesoporous nanocrystal TiO2 can be attained by the same process using Ru-doped precursor SrTi1- xRu xO3. Ru is doped into lattice of TiO2, which is identified by HRTEM and super energy dispersive spectrometer (super-EDS) elemental mapping. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) suggest the pentavalent Ru but not tetravalent, while partial Ti in TiO2 accept an electron from Ru and become Ti3+, which is observed for the first time. This Ru-doped TiO2 performs high activity for electrocatalytic hydrogen evolution reaction (HER) in alkaline solution. First-principles calculations simulate the HER process and prove TiO2:Ru with Ru5+ and Ti3+ holds high HER activity with appropriate hydrogen-adsorption Gibbs free energies (Δ GH).

Observation of High-Capacity Monoclinic B-Nb2O5 with Ultrafast Lithium Storage.

Apart from Li4Ti5O12, there are few anode substitutes that can be used in commercial high-power lithium-ion batteries. Orthorhombic T-Nb2O5 has recently been proven to be another substitute anode. However, monoclinic B-Nb2O5 of same chemistry is essentially inert for lithium storage, but the underlying reasons are unclear. In order to activate the "inert" B-Nb2O5, herein, nanoporous pseudocrystals to achieve a larger specific capacity of 243 mAh g-1 than Li4Ti5O12 (theoretical capacity: 175 mAh g-1) are proposed. These pseudocrystals are rationally synthesized via a "shape-keep" topological microcorrosion process from LiNbO3 precursor. Compared to pristine B-Nb2O5, experimental investigations reveal that B-Nb2O5- x delivers ≈3000 times higher electronic conductivity and tenfold enhanced Li+ diffusion coefficient. An ≈30% reduction of energy barrier for Li-ion migration is also confirmed by the theoretical calculations. The nanoporous B-Nb2O5- x delivers unique ion/electron transport channels to proliferate the reversible and deeper lithiation, which activate the "inert" B-Nb2O5. The capacitive-like behavior is observed to endow B-Nb2O5- x ultrafast lithium storage ability, harvesting 136 mAh g-1 at 100 C and 72 mAh g-1 even at 250 C, superior to Li4Ti5O12. Pouch-type full cells exhibit the energy density of ≈251 Wh kg-1 and ultrahigh power density up to ≈35 kW kg-1.

1D Insertion Chains Induced Small-Polaron Collapse in MoS2 2D Layers Toward Fast-Charging Sodium-Ion Batteries.

Molybdenum disulfide (MoS2 ) with high theoretical capacity is viewed as a promising anode for sodium-ion batteries but suffers from inferior rate capability owing to the polaron-induced slow charge transfer. Herein, a polaron collapse strategy induced by electron-rich insertions is proposed to effectively solve the above issue. Specifically, 1D [MoS] chains are inserted into MoS2 to break the symmetry states of 2D layers and induce small-polaron collapse to gain fast charge transfer so that the as-obtained thermodynamically stable Mo2 S3 shows metallic behavior with 107 times larger electrical conductivity than that of MoS2 . Theoretical calculations demonstrate that Mo2 S3 owns highly delocalized anions, which substantially reduce the interactions of Na-S to efficiently accelerate Na+ diffusion, endowing Mo2 S3 lower energy barrier (0.38 vs 0.65 eV of MoS2 ). The novel Mo2 S3 anode exhibits a high capacity of 510 mAh g-1 at 0.5 C and a superior high-rate stability of 217 mAh g-1 at 40 C over 15 000 cycles. Further in situ and ex situ characterizations reveal the in-depth reversible redox chemistry in Mo2 S3 . The proposed polaron collapse strategy for intrinsically facilitating charge transfer can be conducive to electrode design for fast-charging batteries.

High Initial Coulombic Efficiency Hard Carbon Anodes Enabled by Facile Surface Annealing Engineering.

Hard carbon (HC) anode shows great potential due to its high capacity and excellent rate performance. However, state-of-the-art HC anode still suffers insufficient initial Coulomb efficiency (ICE) due to the abundant Li-trapping sites. Herein, we demonstrate a facile annealing engineering for HC anodes to improve the ICE and the mechanism is systematically studied. Accordingly, during the annealing process, metastable O- and N-containing functional groups are pyrolyzed, which cause the microstructure reconstruction of HC. Therefore, irreversible lithium ions adsorption is reduced significantly and the conversion of sp3 to sp2 C contributes to the localized graphitization of HC. Consequently, the optimized HC achieves ultra-high ICE of 90% from initial 61%. It is demonstrated that HC will adsorb H2 O and some organic species from environment gradually, causing conversion of some electrochemical stable functional groups to the irreversible Li-trapping sites. This work provides facile strategy and novel insight for high ICE HC anodes.

In-Situ-Polymerized 1,3-Dioxolane Solid-State Electrolyte with Space-Confined Plasticizers for High-Voltage and Robust Li/LiCoO2 Batteries.

In-situ-polymerized solid-state electrolytes can significantly improve the interfacial compatibility of Li metal batteries. Typically, in-situ-polymerized 1,3-dioxolane electrolyte (PDOL) exhibits good compatibility with Li metal. However, it still suffers from the narrow electrochemical window (4.1 V), limiting the application of high-voltage cathodes. Herein, a novel modified PDOL (PDOL-F/S) electrolyte with an expanded electrochemical window of 4.43 V and a considerable ionic conductivity of 1.95 × 10-4 S cm-1 is developed by introducing high-voltage stable plasticizers (fluoroethylene carbonate and succinonitrile) to its polymer network. The space-confined plasticizers are beneficial to construct a high-quality cathode-electrolyte interphase, hindering the decomposition of lithium salts and polymers in electrolytes at high voltage. The as-assembled Li|PDOL-F/S|LiCoO2 battery delivers superior cycling stability (capacity retention of 80% after 400 cycles) at 4.3 V, superior to that of pristine PDOL (3% after 120 cycles). This work provides new insights into the design and application of high-voltage solid-state lithium metal batteries by in situ polymerization.

Multifunctional Na2TiO3 Coating-Enabled High-Voltage and Capacitive-like Sodium-Ion Storage of Na0.44MnO2.

Sodium-ion batteries, as an attractive option for large-scale energy storage, still face the problems of low energy density and unsatisfactory rate performance. Among various cathodes, the tunnel-type Na0.44MnO2 with large S-shaped Na+ transport tunnels is one of the promising cathode materials for fast and robust sodium-ion storage, yet suffering from Mn dissolution and structural collapse. Herein, a Na-rich layered oxide Na2TiO3 is first constructed as a multifunctional coating layer on the surface of the Na0.44MnO2 nanorod. Na2TiO3 not only acts as an Na+ reservoir, but also serves as a protective layer to prevent Na0.44MnO2 from electrolyte etching. Besides, the derived Ti-doped Na0.44MnO2 transition layer supplies additional Na+ diffusion pathways along the radial direction of the nanorod with a short migration distance. The optimized 3 wt % Na2TiO3-coated Na0.44MnO2 exhibits enhanced an initial capacity of 127 mAh g-1 at 2-4.5 V. In addition, it shows an ultra-high capacitive-like capacity ratio of 96.7%, hence delivering an excellent rate performance of 80.2 mAh g-1 at 20C. Long-term cycling tests indicate splendid stability against high voltage, achieving 97.7% capacity retention at 20C after 900 cycles. This work provides an effective strategy to improve the rate performance and high-voltage stability of Na0.44MnO2 for high energy and power density batteries.

High-Entropy Layered Oxide Cathode Enabling High-Rate for Solid-State Sodium-Ion Batteries.

Na-ion O3-type layered oxides are prospective cathodes for Na-ion batteries due to high energy density and low-cost. Nevertheless, such cathodes usually suffer from phase transitions, sluggish kinetics and air instability, making it difficult to achieve high performance solid-state sodium-ion batteries. Herein, the high-entropy design and Li doping strategy alleviate lattice stress and enhance ionic conductivity, achieving high-rate performance, air stability and electrochemically thermal stability for Na0.95Li0.06Ni0.25Cu0.05Fe0.15Mn0.49O2. This cathode delivers a high reversible capacity (141 mAh g-1 at 0.2C), excellent rate capability (111 mAh g-1 at 8C, 85 mAh g-1 even at 20C), and long-term stability (over 85% capacity retention after 1000 cycles), which is attributed to a rapid and reversible O3-P3 phase transition in regions of low voltage and suppresses phase transition. Moreover, the compound remains unchanged over seven days and keeps thermal stability until 279 ℃. Remarkably, the polymer solid-state sodium battery assembled by this cathode provides a capacity of 92 mAh g-1 at 5C and keeps retention of 96% after 400 cycles. This strategy inspires more rational designs and could be applied to a series of O3 cathodes to improve the performance of solid-state Na-ion batteries.

Ultrathin Mo2S3 Nanowire Network for High-Sensitivity Breathable Piezoresistive Electronic Skins.

Flexible piezosensing electronic skins (e-skins) have attracted considerable interest owing to their applications in real-time human-health monitoring, human-machine interactions, and soft bionic robot perception. However, the fabrication of piezosensing e-skins with high sensitivity, biological affinity, and good permeability at the same time is challenging. Herein, we designed and synthesized Mo2S3 nanowires by inserting ∞1[Mo2+S] chains between MoS2 interlayers. The resulting Mo2S3 nanowires feature high conductivity (4.9 × 104 S m-1) and a high aspect ratio (∼200). An ultrathin (∼500 nm) Mo2S3 nanowire network was fabricated using a simple liquid/liquid interface self-assembly method, showing high piezoresistive sensitivity (5.65 kPa-1), a considerably low pressure detection limit (0.08 Pa), and gratifying air permeability. Moreover, this nanowire network can be directly attached to human skin for real-time human pulse detection, finger movement monitoring, and sign language recognition, exhibiting excellent potential for health monitoring and human-machine interactions.

Assembling Iron Oxide Nanoparticles into Aggregates by Li3PO4: A Universal Strategy Inspired by Frogspawn for Robust Li-Storage.

The poor ionic conductivity of transition metal oxides (TMOs) is a huge obstacle to their practical application as anodes for lithium-ion batteries (LIBs). Although good performance can be harvested by constructing nanostructures, some other foundmental issues including low tap density and serious electrolyte consumption come along. Herein, inspired by frogspawn, we propose a universal strategy of using lithium salts to assemble TMO nanoparticles into large aggregates to improve their Li+ conductivity. In such a frogspawn-like structure, lithium salt networks can not only realize the rapid transmission of Li+ but also alleviate the volume change during the charging/discharging process. When Li3PO4 is applied to assemble iron oxides nanoparticles, aggregates with size over 1 µm and tap density up to 1.33 g cm-3 can be obtained, which even hasve an ionic conductivity up to 9.61 × 10-5 S cm-1. Fe3O4 was also introduced through reduction to boost electron transfer. Consequently, this carbon-free composite delivered a capacity up to 896 mA h g-1 even after 1000 cycles at 5 A g-1, which can also be maintained under high mass loading. When using lithium salts such as Li2SO4, Li2CO3, LiBO2, and LiCl, the corresponding composites also showed similar performance. This strategy is also effective for TMOs such as NiO, Co3O4, and ZnO, demonstrating the universality of this frogspawn-inspired design.

Constructing Robust Cathode/Electrolyte Interphase for Ultrastable 4.6 V LiCoO2 under -25 °C.

Improving the durability of cathode materials at low temperature is of great importance for the development nowadays of lithium ion batteries, since the practical capacity and cycling stability of the electrode are reduced significantly at low temperature. Herein, by amorphous Zr3(PO4)4 surface engineering, we realize a stable high-voltage LiCoO2 operation (4.6 V) at -25 °C. The highly amorphous surface layer can help to form a high-quality cathode-electrolyte interphase with strong stability and low interface resistance, especially at low temperature. Such a surface-engineered LiCoO2 shows a capacity of 179.2 mAh g-1 at 0.2C and an excellent cyclability with 91% capacity retention after 300 cycles (1C). As a comparison, bare LiCoO2 shows only 161.6 mAh g-1 and 1% capacity retention under the same circumstances. This work confirms that surface regulation and control engineering is an effective route to improve the high-voltage and low-temperature performance of LiCoO2.

A uniform and high-voltage stable LiTMPO4 coating layer enabled high performance LiNi0.8Co0.15Mn0.05O2 towards boosting lithium storage.

LiTMPO4 materials, such as LiNiPO4, can maintain structural stability and Li+ transport activity up to 4.8 V, showing great potential to stabilize layered nickel-rich cathodes at high voltage. But achieving a uniform LiTMPO4 coating layer remains a great challenge. Herein, an ultrathin and uniform LiTMPO4 layer (mainly LiNiPO4) is successfully coated on the surface of LiNi0.8Co0.15Mn0.05O2 (NMC@LTMP) via utilizing the surface chelation of phytic acid with NMC precursors and a subsequent high-temperature in situ reaction. The reconstructed surface and interface could act as stable paths for Li+ transport and efficient barriers against electrolyte corrosion. Thus, harmful side reactions like solid electrolyte interphase overgrowth, irreversible phase transformation, and metal dissolution are inhibited simultaneously. Impressively, the optimized NMC@LTMP2 cathode exhibits remarkably improved capacity, as high as 215 mA h g-1 at 2.8-4.5 V, with capacity retention of 87.21% after 200 cycles and outstanding rate capability of 140 mA h g-1 at 10C, significantly better than a pristine cathode. Furthermore, a pouch cell assembled with an NMC@LTMP2 cathode and graphite anode also exhibits robust capacity retention of 82.42% after 100 cycles. These results provide useful insights towards enabling the application of NMC cathodes via developing facile modification methods.

Micrometer-Sized, Dual-Conductive MoO2 /ß-MoO3- x Mosaics for High Volumetric Capacity Li/Na-Ion Batteries.

The transition metal oxides (TMOs) with high volumetric capacities are promising anodes for the future electronics, however, they usually suffer from severe capacity decay and poor rate capability. Carbon hybridization and nanosizing can resolve these challenges, yet these significantly compromise the volumetric capacity. Herein, both high capacity and long cycling stability are simultaneously achieved in the micrometer-sized Mo-based oxide particles by designing the dual conductive MoO2 /ß-MoO3- x mosaics. The rational combination of the highly electronically conductive MoO2 with the highly ionically conductive and open-structured ß-MoO3 achieves a promising volumetric capacity of 1742 mAh cm-3 , which is four times higher than the commercial graphite. Simultaneously, both stable cycling performance (87% retention after 500 cycles) and excellent rate capability (outperformed a majority of the MoO2 -based anodes reported in literature) are obtained in the lithium-ion batteries. For the sodium-ion batteries, the composite exhibits three times higher Na+ storage than pure MoO2 . Moreover, the decisive role of the bond energy on the electrochemical performance of TMOs is also identified. This study may open up new perspectives for choosing and designing the TMO anodes with a high volumetric capacity for the practical applications.

Co5.47N loaded N-doped carbon as an efficient bifunctional oxygen electrocatalyst for a Zn-air battery.

Highly active bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a pivotal role in Zn-air batteries. The high cost, scarcity and instability of precious-metal-based electrocatalysts for the ORR and OER dramatically hamper their practical application in such clean-energy set-ups. Here, we report highly active Co5.47N-loaded N-doped carbon (CoNMC), prepared via the direct NH3 annealing of a millet-CoCl2 mixture, which is a cheap and mass-producible form of biomass. The optimized product shows superior ORR activity (a half-wave potential of 0.81 V vs. RHE) and electrochemical stability (a 16.5 mV negative shift of the half-wave potential after 2000 cycles) in alkaline media. Also, it shows appealing OER activity (an operating potential at 10 mA cm-2 of 1.62 V vs. RHE). This excellent electrochemical performance can be attributed to the formation of active Co5.47N nanoparticles, the large specific surface area, the abundance of nitrogen active sites, and the high graphitization degree. When assembled into a Zn-air battery, the CoNMC-based cell shows comparable performance to a Pt/C-RuO2 one.