High Capacity Adsorption—Dominated Potassium and Sodium Ion Storage in Activated Crumpled Graphene

Structurally and chemically defective activated‐crumbled graphene (A‐CG) is employed to achieve unique synergy of large reversible potassium (K) and sodium (Na) ion storage capacity with fast charging and extended cyclability. A‐CG synthesis consists of low temperature spraying of graphene oxide slurry, followed by partial reduction annealing and air activation. For K storage, the reversible capacities are 340 mAh g^?1 at 0.04 A g^?1, 261 mAh g^?1 at 0.5 A g^?1, and 210 mAh g^?1 at 2 A g^?1. For Na storage, the reversible capacities are 280 mAh g^?1 at 0.04 A g^?1, 191 mAh g^?1 at 0.5 A g^?1, and 151 mAh g^?1 at 2 A g^?1. A‐CG shows a stable intermediate rate (0.5 Ag^?1) cycling with both K and Na, with minimal fade after 2800 and 8000 cycles. These are among the most favorable capacity—rate capability—cyclability combinations recorded for potassium‐ion battery and sodium‐ion battery carbons. Electroanalytical studies (cyclic voltammetry, galvanostatic intermittent titration technique, b‐value) and density functional theory (DFT) reveal that enhanced electrochemical performance originates from ion adsorption at various defects, such as Stone–Wales defects. Moreover, DFT highlights enhanced thermodynamic stability of A‐CG with adsorbed K versus with adsorbed Na, explaining the unexpected higher reversible capacity with the former.     

Transition Metal Sulfides Based on Graphene for Electrochemical Energy Storage

Transition metal sulfides, as an important class of inorganics, can be used as excellent electrode materials for various types of electrochemical energy storage, such as lithium‐ion batteries, sodium‐ion batteries, supercapacitors, and others. Recent works have identified that mixing graphene or graphene derivatives with transition metal sulfides can result in novel composites with better electrochemical performance. This review summarizes the latest advances in transition metal sulfide composites with graphene or graphene derivatives. The synthetic strategies and morphologies of these composites are introduced. The authors then discuss their applications in lithium‐ion batteries, sodium‐ion batteries, and supercapacitors. Finally, the authors give their personal viewpoints about the challenges and opportunities for the future development about this direction.     

Vertically Aligned MoS2 Nanosheets Patterned on Electrochemically Exfoliated Graphene for High‐Performance Lithium and Sodium Storage

Molybdenum disulfide (MoS₂) has been recognized as a promising anode material for high‐energy Li‐ion (LIBs) and Na‐ion batteries (SIBs) due to its apparently high capacity and intriguing 2D‐layered structure. The low conductivity, unsatisfied mechanical stability, and limited active material utilization are three key challenges associated with MoS₂ electrodes especially at high current rates and mass active material loading. Here, vertical MoS₂ nanosheets are controllably patterned onto electrochemically exfoliated graphene (EG). Within the achieved hierarchical architecture, the intimate contact between EG and MoS₂ nanosheets, interconnected network, and effective exposure of active materials by vertical channels simultaneously overcomes the above three problems, enabling high mechanical integrity and fast charge transport kinetics. Serving as anode material for LIBs, EG‐MoS₂ with 95 wt% MoS₂ content delivered an ultrahigh‐specific capacity of 1250 mA h g^?1 after 150 stable cycles at 1 A g^?1, which is among the highest values in all reported MoS₂ electrodes, and excellent rate performance (970 mA h g^?1 at 5 A g^?1). Moreover, impressive cycling stability (509 mA h g^?1 at 1 A g^?1 after 250 cycles) and rate capability (423 mA h g^?1 at 2 A g^?1) were also achieved for SIBs. The area capacities reached 1.27 and 0.49 mA h cm^?2 at ≈1 mA cm^?2 for LIBs and SIBs, respectively. This work may inspire the development of new 2D hierarchical structures for high efficiency energy storage and conversion.     

Nanosilicon‐Based Thick Negative Composite Electrodes for Lithium Batteries with Graphene as Conductive Additive

Reduced graphene oxide (rGO) is used as a conductive additive for nanosilicon‐based lithium battery anodes with the high active‐mass loading typically required for industrial applications. In contrast to conventional Si electrodes that use acetylene black (AcB) as an additive, the rGO system shows pronounced improvement of electrochemical performance, irrespective of the cycling conditions. With capacity limitation, the rGO system results in improved coulombic efficiency (99.9%) and longer cycle life than conventional electrodes. Upon cycling without capacity limitation, much higher discharge capacity is maintained (2000 mAh g^?1 after 100 cycles for 2.5 mg of Si cm^?2). Used in conjunction with the bridging carboxymethyl cellulose binder, the crumpled and resilient rGO allows highly reversible functioning of the electrode in which the Si particles repeatedly inflate and deflate upon alloying and dealloying with lithium.     

An Air‐Stable Densely Packed Phosphorene–Graphene Composite Toward Advanced Lithium Storage Properties

Phosphorene, monolayer or few‐layer black phosphorus (BP), has recently triggered strong scientific interest for lithium/sodium ion batteries (LIBs/SIBs) applications. However, there are still challenges regarding large‐scale fabrication, poor air stability. Herein, we report the high‐yield synthesis of phosphorene with good crystallinity and tunable size distributions via liquid‐phase exfoliation of bulk BP in formamide. Afterwards, a densely packed phosphorene–graphene composite (PG‐SPS, a packing density of 0.6 g cm^?3) is prepared by a simple and easily up‐scalable spark plasma sintering (SPS) process. When working as anode materials of LIBs, PG‐SPS exhibit much improved first‐cycle Coloumbic efficiency (60.2%) compared to phosphorene (11.5%) and loosely stacked phosphorene–graphene composite (34.3%), high specific capacity (1306.7 mAh g^?1) and volumetric capacity (256.4 mAh cm^?3), good rate capabilities (e.g., 415.0 mAh g^?1 at 10 A g^?1) as well as outstanding long‐term cycling life (91.9% retention after 800 cycles at 10 A g^?1). Importantly, excellent air stability of PG‐SPS over the 60 days observation in maintaining its high Li storage properties can be achieved. On the contrary, 95.2% of BP in PG sample was oxidized after only 10 days exposure to ambience, leading to severe degradation of electrochemical properties.     

Large‐Sized Few‐Layer Graphene Enables an Ultrafast and Long‐Life Aluminum‐Ion Battery

To develop high‐power and high‐energy batteries with a long life remains a great challenge, even combining the benefits of metal (fast kinetics and high capacity) and carbon materials (robust structure). Among them, Al‐ion batteries based on aluminum anode and graphite carbon cathode have gained lots of interests as one of the most promising technologies. Here, it is demonstrated that the size of graphitic material in ab plane and c direction plays an important role in anion intercalation chemistry. Sharply decreasing the size of vertical dimension (c direction) strongly facilitates the kinetics and charge transfer of anions (de)intercalation. On the other hand, increasing the size of horizontal dimension (ab plane) contributes to improving the flexibility of graphitic materials, which results in raising the cycling stability. Meanwhile, chloroaluminate anions are reversibly intercalated into the interlayer of graphite materials, leading to the staging behaviors. In the end, an ultrafast Al‐ion battery with exceptional long life is achieved based on large‐sized few‐layer graphene as a cathode and aluminum metal as an anode.     

A Ternary Fe1−xS@Porous Carbon Nanowires/Reduced Graphene Oxide Hybrid Film Electrode with Superior Volumetric and Gravimetric Capacities for Flexible Sodium Ion Batteries

Smart construction of ultraflexible electrodes with superior gravimetric and volumetric capacities is still challenging yet significant for sodium ion batteries (SIBs) toward wearable electronic devices. Herein, a hybrid film made of hierarchical Fe_1?xS‐filled porous carbon nanowires/reduced graphene oxide (Fe_1?xS@PCNWs/rGO) is synthesized through a facile assembly and sulfuration strategy. The resultant hybrid paper exhibits high flexibility and structural stability. The multidimensional paper architecture possesses several advantages, including rendering an efficient electron/ion transport network, buffering the volume expansion of Fe_1?xS nanoparticles, mitigating the dissolution of polysulfides, and enabling superior kinetics toward efficient sodium storage. When evaluated as a self‐supporting anode for SIBs, the Fe_1?xS@PCNWs/rGO paper electrode exhibits remarkable reversible capacities of 573–89 mAh g^?1 over 100 consecutive cycles at 0.1 A g^?1 with areal mass loadings of 0.9–11.2 mg cm^?2 and high volumetric capacities of 424–180 mAh cm^?3 in the current density range of 0.2–5 A g^?1. More competitively, a SIB based on this flexible Fe_1?xS@PCNWs/rGO anode demonstrates outstanding electrochemical properties, thus highlighting its enormous potential in versatile flexible and wearable applications.     

Partially Reduced Holey Graphene Oxide as High Performance Anode for Sodium‐Ion Batteries

The current Na⁺ storage performance of carbon‐based materials is still hindered by the sluggish Na⁺ ion transfer kinetics and low capacity. Graphene and its derivatives have been widely investigated as electrode materials in energy storage and conversion systems. However, as anode materials for sodium‐ion batteries (SIBs), the severe π–π restacking of graphene sheets usually results in compact structure with a small interlayer distance and a long ion transfer distance, thus leading to low capacity and poor rate capability. Herein, partially reduced holey graphene oxide is prepared by simple H₂O₂ treatment and subsequent low temperature reduction of graphene oxide, leading to large interlayer distance (0.434 nm), fast ion transport, and larger Na⁺ storage space. The partially remaining oxygenous groups can also contribute to the capacity by redox reaction. As anode material for SIBs, the optimized electrode delivers high reversible capacity, high rate capability (365 and 131 mAh g^?1 at 0.1 and 10 A g^?1, respectively), and good cycling performance (163 mAh g^?1 after 3000 cycles at a current density of 2 A g^?1), which is among the best reported performances for carbon‐based SIB anodes.     

Citrate‐Assisted Growth of NiCo2O4 Nanosheets on Reduced Graphene Oxide for Highly Reversible Lithium Storage

Hybrid nanostructures based on graphene and transition metal oxides hold great promise as high‐performance electrode materials for next‐generation lithium‐ion batteries. In this work, the rational design and fabrication of NiCo₂O₄ nanosheets supported on reduced graphene oxide (denoted as rGO/NiCo₂O₄) is presented as a novel anode material for highly efficient and reversible lithium storage. A solution method is applied to grow Ni‐Co precursor nanosheets on rGO, in which the addition of trisodium citrate is found crucial to guide the formation of uniform Ni‐Co precursor nanosheets. Subsequent thermal treatment results in formation of crystalline NiCo₂O₄ nanosheets on rGO without damaging the morphology. The interconnected NiCo₂O₄ nanosheets form hierarchically porous films on both sides of rGO. Such a hybrid nanostructure would effectively promote the charge transport and withstand volume variation upon prolonged charge/discharge cycling. As a result, the rGO/NiCo₂O₄ nanocomposite demonstrates high reversible capacities of 954.3 and 656.5 mAh g^–1 over 50 cycles at current densities of 200 and 500 mA g^–1 respectively, and remarkable capacity retention at increased current densities.     

Supramolecular Polymerization Promoted In Situ Fabrication of Nitrogen‐Doped Porous Graphene Sheets as Anode Materials for Li‐Ion Batteries

A novel strategy of utilizing supramolecular polymerization for fabricating nitrogen doped porous graphene (NPG) with high doping level of 12 atom% as the anode material for lithium ion batteries is reported for the first time. The introduction of supramolecular polymer (melamine cyanurate) functions not only as a spacer to prevent the restacking of graphene sheets but also as a sacrificial template to generate porous structures, as well as a nitrogen source to induce in situ N doping. Therefore, pores and loose‐packed graphene thin layers with high N doping level are very effectively formed in NPG after the annealing process. Such highly desired structures immediately offer remarkably improved Li storage performance including high reversible capacity (900 mAh g^?1 after 150 cycles) with good cycling and rate performances. The effects of annealing temperature and heating rates on the final electrochemical performance of NPG are also investigated. Furthermore, the low cost, facile, and scalable features of this novel strategy may be helpful for the rational design of functionalized graphene‐based materials for diverse applications.