Scalable Synthesis of Bilayer Graphene at Ambient Temperature.

In this work, we develop for the first time a facile chemical lithiation-assisted exfoliation approach to the controllable and scalable preparation of bilayer graphene. Biphenyl lithium (Bp-Li), a strong reducing reagent, is selected to realize the spontaneous Li-intercalation into graphite at ambient temperature, forming lithium graphite intercalation compounds (Li-GICs). The potential of Bp-Li (0.11 V vs Li/Li+), which is just lower than the potential of stage-2 lithium intercalation (0.125 V), enables the precise lithiation of graphite to stage-2 Li-GICs (LiC12). Intriguingly, the exfoliation of LiC12 leads to the bilayer-favored production of graphene, giving a high selectivity of 78%. Furthermore, the mild intercalation-exfoliation procedure yields high-quality graphene with negligible structural deterioration. The obtained graphene exhibits ultralow defect density (ID/IG ∼ 0.14) and a considerably high C/O ratio (∼29.7), superior to most current state-of-the-art techniques. This simple and scalable strategy promotes the understanding of chemical Li-intercalation methods for preparing high-quality graphene and shows great potential for layer-controlled engineering.

Reconstructing Helmholtz Plane Enables Robust F-Rich Interface for Long-Life and High-Safe Sodium-Ion Batteries.

Hard carbon (HC) is the most commonly used anode material in sodium-ion batteries. However, the solid-electrolyte-interface (SEI) layer formed in carbonate ester-based electrolytes has an imperceptible dissolution tendency and a sluggish Na+ diffusion kinetics, resulting in an unsatisfactory performance of HC anode. Given that electrode/electrolyte interface property is highly dependent on the configuration of Helmholtz plane, we filtrated proper solvents by PFBE (PF6 - anion binding energy) and CAE (carbon absorption energy) and disclosed the function of chosen TFEP to reconstruct the Helmholtz plane and regulate the SEI film on HC anode. Benefiting from the preferential adsorption tendency on HC surface and strong anion-dragging interaction of TFEP, a robust and thin anion-derived F-rich SEI film is established, which greatly enhances the mechanical stability and the Na+ ion diffusion kinetics of the electrode/electrolyte interface. The rationally designed TFEP-based electrolyte endows Na||HC half-cell and 2.8 Ah HC||Na4Fe3(PO4)2P2O7 pouch cell with excellent rate capability, long cycle life, high safety and low-temperature adaptability. It is believed that this insightful recognition of tuning interface properties will pave a new avenue in the design of compatible electrolyte for low-cost, long-life, and high-safe sodium-ion batteries.

LiNO3 -Based Electrolytes via Electron-Donation Modulation for Sustainable Nonaqueous Lithium Rechargeable Batteries.

LiPF6 as a dominant lithium salt of electrolyte is widely used in commercial rechargeable lithium-ion batteries due to its well-balanced properties, including high solubility in organic solvents, good electrochemical stability, and high ionic conductivity. However, it suffers from several undesirable properties, such as high moisture sensitivity, thermal instability, and high cost. To address these issues, herein, we propose an electron-donation modulation (EDM) rule for the development of low-cost, sustainable, and electrochemically compatible LiNO3 -based electrolytes. We employ high donor-number solvents (HDNSs) with strong electron-donation ability to dissolve LiNO3 , while low donor-number solvents (LDNSs) with weak electron-donation ability are used to regulate the solvation structure to stabilize the electrolytes. As an example, we design the LiNO3 -DMSO@PC electrolyte, where DMSO acts as an HDNS and PC serves as an LDNS. This electrolyte exhibits excellent electrochemical compatibility with graphite anodes, as well as the LiFePO4 and LiCoO2 cathodes, leading to stable cycling over 200 cycles. Through spectroscopy analyses and theoretical calculation, we uncover the underlying mechanism responsible for the stabilization of these electrolytes. Our findings provide valuable insights into the preparation of LiNO3 -based electrolytes using the EDM rule, opening new avenues for the development of advanced electrolytes with versatile functions for sustainable rechargeable batteries.

Exfoliation of MoS2 Nanosheets Enabled by a Redox-Potential-Matched Chemical Lithiation Reaction.

Ion intercalation assisted exfoliation is the oldest and most popular method for the scalable synthesis of molybdenum disulfide (MoS2) nanosheets. The commonly used organolithium reagents for Li+ intercalation are n-butyllithium (n-BuLi) and naphthalenide lithium (Nap-Li); however, the highly pyrophoric nature of n-BuLi and the overly reducing power of Nap-Li hinder their extensive application. Here, a novel organolithium reagent, pyrene lithium (Py-Li), which has intrinsic safe properties and a well-matched redox potential, is reported for the intercalation and exfoliation of MoS2. The redox potential of Py-Li (0.86 V vs Li+/Li) is located just between the intercalation (1.13 V) and decomposition (0.55 V) potentials of bulk MoS2, thus allowing precise Li+ intercalation to form a lamellar LiMoS2 compound without undesirable structural damage. The lithiation reaction can be accomplished within 1 h at room temperature and the exfoliated nanosheets are almost single layer. This method also offers the advantages of low cost, high repeatability, and ease in realizing large-scale production.

A Solid-Phase Conversion Sulfur Cathode with Full Capacity Utilization and Superior Cycle Stability for Lithium-Sulfur Batteries.

Solid phase conversion sulfur cathode is an effective strategy for eliminating soluble polysulfide intermediates (LiPSs) and improving cyclability of Li-S batteries. However, realizing such a sulfur cathode with high sulfur loading and high capacity utilization is very challenging due to the insulating nature of sulfur. In this work, a strategy is proposed for fabricating solid phase conversion sulfur cathode by encapsulating sulfur in the mesoporous channels of CMK-3 carbon to form a coaxially assembled sulfur/carbon (CA-S/C) composite. Vinyl carbonate (VC) is simultaneously utilized as the electrolyte cosolvent to in-situ form a dense solid electrolyte interface (SEI) on the CA-S/C composite surface through its nucleophilic reaction with the freshly generated polysulfides at the beginning of initial discharge, thus separating the direct contact of interior sulfur with the outer electrolyte. As expected, such a CA-S/C cathode can operate in a solid phase conversion manner in the VC-ether cosolvent electrolyte to exhibit a full capacity utilization (1667 mA h g-1 , ≈100%), a high rate capability of 2.0 A g-1 and excellent long-term cyclability over 500 cycles even at a high sulfur loading (75%, based on the weight of CA-S/C composite), demonstrating great promise for constructing high-energy-density and cycle-stable Li-S batteries.

Microstructure-Dependent Charge/Discharge Behaviors of Hollow Carbon Spheres and its Implication for Sodium Storage Mechanism on Hard Carbon Anodes.

Hard carbons are actively developed as a promising anode material for sodium ion batteries (SIBs). However, their sodium storage mechanism is poorly understood, leading to difficulties in design and development of high-performance hard carbon anode materials. In this work, hollow carbon spheres (HCSs) with different shell thickness as a model material to investigate the correlation between the microstructural change and resulting Na+ storage behavior during charge/discharge cycles are designed and synthesized. Ex situ X-ray diffraction and Raman evidences reveal that an interlayer spacing change of the graphitic nanodomains occurs in HCS electrode, leading to a shift of the reversible capacity from the high-potential sloping (HPS) region to the low-potential plateau (LPP) region. This unusual capacity shift suggests a microstructure-dependent Na+ storage reaction on the HCS electrode and can be well explained by "adsorption-intercalation" mechanism for these HCS materials. This work strengthens the understanding of the sodium storage behavior and provides a new perspective for the morphological and structural design of hard carbon anode materials for high-performance SIBs.

Chemically Prelithiated Hard-Carbon Anode for High Power and High Capacity Li-Ion Batteries.

Hard carbons (HC) have potential high capacities and power capability, prospectively serving as an alternative anode material for Li-ion batteries (LIB). However, their low initial coulombic efficiency (ICE) and the resulting poor cyclability hinder their practical applications. Herein, a facile and effective approach is developed to prelithiate hard carbons by a spontaneous chemical reaction with lithium naphthalenide (Li-Naph). Due to the mild reactivity and strong lithiation ability of Li-Naph, HC anode can be prelithiated rapidly in a few minutes and controllably to a desirable level by tuning the reaction time. The as-formed prelithiated hard carbon (pHC) has a thinner, denser, and more robust solid electrolyte interface layer consisting of uniformly distributed LiF, thus demonstrating a very high ICE, high power, and stable cyclability. When paired with the current commercial LiCoO2 and LiFePO4 cathodes, the assembled pHC/LiCoO2 and pHC/LiFePO4 full cells exhibit a high ICE of >95.0% and a nearly 100% utilization of electrode-active materials, confirming a practical application of pHC for a new generation of high capacity and high power LIBs.

Surface Modification of Fe7 S8 /C Anode via Ultrathin Amorphous TiO2 Layer for Enhanced Sodium Storage Performance.

Iron sulfides with high theoretical capacity and low cost have attracted extensive attention as anode materials for sodium ion batteries. However, the inferior electrical conductivity and devastating volume change and interface instability have largely hindered their practical electrochemical properties. Here, ultrathin amorphous TiO2 layer is constructed on the surface of a metal-organic framework derived porous Fe7 S8 /C electrode via a facile atomic layer deposition strategy. By virtue of the porous structure and enhanced conductivity of the Fe7 S8 /C, the electroactive TiO2 layer is expected to effectively improve the electrode interface stability and structure integrity of the electrode. As a result, the TiO2 -modified Fe7 S8 /C anode exhibits significant performance improvement for sodium-ion batteries. The optimal TiO2 -modified Fe7 S8 /C electrode delivers reversible capacity of 423.3 mA h g-1 after 200 cycles with high capacity retention of 75.3% at 0.2 C. Meanwhile, the TiO2 coating is conducive to construct favorable solid electrolyte interphase, leading to much enhanced initial Coulombic efficiency from 66.9% to 72.3%. The remarkable improvement suggests that the interphase modification holds great promise for high-performance metal sulfide-based anode materials for sodium-ion batteries.

Highly Electrochemically-Reversible Mesoporous Na2 FePO4 F/C as Cathode Material for High-Performance Sodium-Ion Batteries.

As promising cathode materials, iron-based phosphate compounds have attracted wide attention for sodium-ion batteries due to their low cost and safety. Among them, sodium iron fluorophosphate (Na2 FePO4 F) is widely noted due to its layered structure and high operating voltage compared with NaFePO4 . Here, a mesoporous Na2 FePO4 F@C (M-NFPF@C) composite derived from mesoporous FePO4 is synthesized through a facile ball-milling combined calcination method. Benefiting from the mesoporous structure and highly conductive carbon, the M-NFPF@C material exhibits a high reversible capacity of 114 mAh g-1 at 0.1 C, excellent rate capability (42 mAh g-1 at 10 C), and good cycling performance (55% retention after 600 cycles at 5 C). The high plateau capacity obtained (>90% of total capacity) not only shows high electrochemical reversibility of the as-prepared M-NFPF@C but also provides high energy density, which mainly originates from its mesoporous structure derived from the mesoporous FePO4 precursor. The M-NFPF@C serves as a promising cathode material with high performance and low cost for sodium-ion batteries.

Recent Progress in Rechargeable Sodium-Ion Batteries: toward High-Power Applications.

The increasing demands for renewable energy to substitute traditional fossil fuels and related large-scale energy storage systems (EES) drive developments in battery technology and applications today. The lithium-ion battery (LIB), the trendsetter of rechargeable batteries, has dominated the market for portable electronics and electric vehicles and is seeking a participant opportunity in the grid-scale battery market. However, there has been a growing concern regarding the cost and resource availability of lithium. The sodium-ion battery (SIB) is regarded as an ideal battery choice for grid-scale EES owing to its similar electrochemistry to the LIB and the crust abundance of Na resources. Because of the participation in frequency regulation, high pulse-power capability is essential for the implanted SIBs in EES. Herein, a comprehensive overview of the recent advances in the exploration of high-power cathode and anode materials for SIB is presented, and deep understanding of the inherent host structure, sodium storage mechanism, Na+ diffusion kinetics, together with promising strategies to promote the rate performance is provided. This work may shed light on the classification and screening of alternative high rate electrode materials and provide guidance for the design and application of high power SIBs in the future.

Sulfur-Based Electrodes that Function via Multielectron Reactions for Room-Temperature Sodium-Ion Storage.

Emerging rechargeable sodium-ion storage systems-sodium-ion and room-temperature sodium-sulfur (RT-NaS) batteries-are gaining extensive research interest as low-cost options for large-scale energy-storage applications. Owing to their abundance, easy accessibility, and unique physical and chemical properties, sulfur-based materials, in particular metal sulfides (MSx ) and elemental sulfur (S), are currently regarded as promising electrode candidates for Na-storage technologies with high capacity and excellent redox reversibility based on multielectron conversion reactions. Here, we present current understanding of Na-storage mechanisms of the S-based electrode materials. Recent progress and strategies for improving electronic conductivity and tolerating volume variations of the MSx anodes in Na-ion batteries are reviewed. In addition, current advances on S cathodes in RT-NaS batteries are presented. We outline a novel emerging concept of integrating MSx electrocatalysts into conventional carbonaceous matrices as effective polarized S hosts in RT-NaS batteries as well. This comprehensive progress report could provide guidance for research toward the development of S-based materials for the future Na-storage techniques.

Recent Progress in Iron-Based Electrode Materials for Grid-Scale Sodium-Ion Batteries.

Grid-scale energy storage batteries with electrode materials made from low-cost, earth-abundant elements are needed to meet the requirements of sustainable energy systems. Sodium-ion batteries (SIBs) with iron-based electrodes offer an attractive combination of low cost, plentiful structural diversity and high stability, making them ideal candidates for grid-scale energy storage systems. Although various iron-based cathode and anode materials have been synthesized and evaluated for sodium storage, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this Review, progress in iron-based electrode materials for SIBs, including oxides, polyanions, ferrocyanides, and sulfides, is briefly summarized. In addition, the reaction mechanisms, electrochemical performance enhancements, structure-composition-performance relationships, merits and drawbacks of iron-based electrode materials for SIBs are discussed. Such iron-based electrode materials will be competitive and attractive electrodes for next-generation energy storage devices.

High Rate, Long Lifespan LiV3 O8 Nanorods as a Cathode Material for Lithium-Ion Batteries.

LiV3 O8 nanorods with controlled size are successfully synthesized using a nonionic triblock surfactant Pluronic-F127 as the structure directing agent. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques are used to characterize the samples. It is observed that the nanorods with a length of 4-8 µm and diameter of 0.5-1.0 µm distribute uniformly. The resultant LiV3 O8 nanorods show much better performance as cathode materials in lithium-ion batteries than normal LiV3 O8 nanoparticles, which is associated with the their unique micro-nano-like structure that can not only facilitate fast lithium ion transport, but also withstand erosion from electrolytes. The high discharge capacity (292.0 mAh g-1 at 100 mA g-1 ), high rate capability (138.4 mAh g-1 at 6.4 A g-1 ), and long lifespan (capacity retention of 80.5% after 500 cycles) suggest the potential use of LiV3 O8 nanorods as alternative cathode materials for high-power and long-life lithium ion batteries. In particular, the synthetic strategy may open new routes toward the facile fabrication of nanostructured vanadium-based compounds for energy storage applications.

Graphene-Wrapped Na2C12H6O4 Nanoflowers as High Performance Anodes for Sodium-Ion Batteries.

Graphene-wrapped organic nanoflowers are synthesized from ultrasonic treatment of a simple microsized disodium salt (Na212H6O4) and graphene, which demonstrates a greatly enhanced electrochemical capacity, rate capability and cycling stability as organic Na(+) storage anode. This work suggests an effective architecture to make organic materials electrochemically energetic and stable for energy storage applications.

Synergistic Na-storage reactions in Sn4P3 as a high-capacity, cycle-stable anode of Na-ion batteries.

Room-temperature Na-ion batteries have attracted great interest as a low cost and environmentally benign technology for large scale electric energy storage, however their development is hindered by the lack of suitable anodic host materials. In this paper, we described a green approach for the synthesis of Sn4P3/C nanocomposite and demonstrated its excellent Na-storage performance as a novel anode of Na-ion batteries. This Sn4P3/C anode can deliver a very high reversible capacity of 850 mA h g(-1) with a remarkable rate capability with 50% capacity output at 500 mA g(-1) and can also be cycled with 86% capacity retention over 150 cycles due to a synergistic Na-storage mechanism in the Sn4P3 anode, where the Sn nanoparticles act as electronic channels to enable electrochemical activation of the P component, while the elemental P and its sodiated product Na3P serve as a host matrix to alleviate the aggregation of the Sn particles during Na insertion reaction. This mechanism may offer a new approach to create high capacity and cycle-stable alloy anodes for Na-ion batteries and other electrochemical energy storage applications.

Mesoporous amorphous FePO4 nanospheres as high-performance cathode material for sodium-ion batteries.

FePO4 nanospheres are synthesized successfully through a simple chemically induced precipitation method. The nanospheres present a mesoporous amorphous structure. Electrochemical experiments show that the FePO4/C electrode demonstrates a high initial discharging capacity of 151 mAh g(-1) at 20 mA g(-1), stable cyclablilty (94% capacity retention ratio over 160 cycles), as well as high rate capability (44 mAh g(-1) at 1000 mA g(-1)) for Na-ion storage. The superior electrochemical performance of the FePO4/C nanocomposite is due to its particular mesoporous amorphous structure and close contact with the carbon framework, which significantly improve the ionic and electronic transport and intercalation kinetics of Na ions.

Revisit of Polyaniline as a High-Capacity Organic Cathode Material for Li-Ion Batteries.

Polyaniline (PANI) has long been explored as a promising organic cathode for Li-ion batteries. However, its poor electrochemical utilization and cycling instability cast doubt on its potential for practical applications. In this work, we revisit the electrochemical performance of PANI in nonaqueous electrolytes, and reveal an unprecedented reversible capacity of 197.2 mAh g-1 (244.8 F g-1) when cycled in a wide potential range of 1.5 to 4.4 V vs. Li+/Li. This ultra-high capacity derives from 70% -NH- transformed to =NH+- during deep charging/discharging process. This material also demonstrates a high average coulombic efficiency of 98%, an excellent rate performance with 73.5 mAh g-1 at 1800 mA g-1, and retains 76% of initial value after 100 cycles, which are among the best reported values for PANI electrodes in battery applications.

High capacity and rate capability of amorphous phosphorus for sodium ion batteries.

Turning on your P/C: An amorphous phosphorus/carbon (a-P/C) composite was synthesized using simple mechanical ball milling of red phosphorus and conductive carbon powders. This material gave an extraordinarily high sodium ion storage capacity of 1764 mA h g(-1) (see graph) with a very high rate capability, showing great promise as a high capacity and high rate anode material for sodium ion batteries.

Routes to Electrochemically Stable Sulfur Cathodes for Practical Li-S Batteries.

Lithium-sulfur (Li-S) batteries have been investigated intensively as a post-Li-ion technology in the past decade; however, their realizable energy density and cycling performance are still far from satisfaction for commercial development. Although many extremely high-capacity and cycle-stable S cathodes and Li anodes are reported in literature, their use for practical Li-S batteries remains challenging due to the huge gap between the laboratory research and industrial applications. The laboratory research is usually conducted by use of a thin-film electrode with a low sulfur loading and high electrolyte/sulfur (E/S) ratios, while the practical batteries require a thick/high sulfur loading cathode and a low E/S ratio to achieve a desired energy density. To make this clear, the inherent problems of dissolution/deposition mechanism of conventional sulfur cathodes are analyzed from the viewpoint of polarization theory of porous electrode after a brief overview of the recent research progress on sulfur cathodes of Li-S batteries, and the possible strategies for building an electrochemically stable sulfur cathode are discussed for practically viable Li-S batteries from the authors' own understandings.

Controllable synthesis of a Na-enriched Na4V2(PO4)3 cathode for high-energy sodium-ion batteries: a redox-potential-matched chemical sodiation approach.

Exploring a sodium-enriched cathode (i.e. Na4V2(PO4)3, which differs from its traditional stoichiometric counterpart Na3V2(PO4)3 that can provide extra endogenous sodium reserves to mitigate the irreversible capacity loss of the anode material (i.e. hard carbon), is an intriguing presodiation method for the development of high energy sodium-ion batteries. To meet this challenge, herein, we first propose a redox-potential-matched chemical sodiation approach, utilizing phenazine-sodium (PNZ-Na) as the optimal reagent to sodiate the Na3V2(PO4)3 precursor into Na-enriched Na4V2(PO4)3. The spontaneous sodiation reaction enables a fast reduction of one-half V ions from V3+ to V2+, followed by the insertion of one Na+ ion into the NASICON framework, which only takes 90 s to obtain the phase-pure Na4V2(PO4)3 product. When paired with a hard carbon anode, the resulting Na4VP‖HC full cell exhibits a high energy density of 251 W h kg-1, which is 58% higher than that of 159 W h kg-1 for the Na3VP‖HC control cell. Our chemical sodiation methodology provides an innovative approach for designing sodium-rich cathode materials and could serve as an impetus to the development of advanced sodium-ion batteries.