Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.

Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of π–π interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graph...

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Noncovalent Functionalization of Graphene and Graphene Oxide for Energy Materials, Biosensing, Catalytic, and Biomedical Applications

Thermal runaway mechanism of lithium ion battery for electric vehicles: A review

Notably, many significant breakthroughs for a new generation of supercapacitors have been reported in recent years, related to theoretical understanding, material synthesis and device designs. Herein, we summarize the state-of-the-art progress toward mechanisms, new materials, and novel device designs for supercapacitors. Firstly, fundamental understanding of the mechanism is mainly focused on the relationship between the structural properties of electrode materials and their electrochemical performances based on some in situ characterization techniques and simulations. Secondly, some emerging electrode materials are discussed, including metal–organic frameworks (MOFs), covalent organic frameworks (COFs), MXenes, metal nitrides, black phosphorus, LaMnO3, and RbAg4I5/graphite. Thirdly, the device innovations for the next generation of supercapacitors are provided successively, mainly emphasizing flow supercapacitors, alternating current (AC) line-filtering supercapacitors, redox electrolyte enhanced supercapacitors, metal ion hybrid supercapacitors, micro-supercapacitors (fiber, plane and three-dimensional) and multifunctional supercapacitors including electrochromic supercapacitors, self-healing supercapacitors, piezoelectric supercapacitors, shape-memory supercapacitors, thermal self-protective supercapacitors, thermal self-charging supercapacitors, and photo self-charging supercapacitors. Finally, the future developments and key technical challenges are highlighted regarding further research in this thriving field.

Latest advances in supercapacitors: from new electrode materials to novel device designs.

To explore good anode materials of high safety, high reversible capacity, good cycling, and excellent rate capability, a Li3VO4 microbox with wall thickness of 40 nm was prepared by a one-pot and template-free in situ hydrothermal method. In addition, its composite with graphene nanosheets of about six layers of graphene was achieved. Both of them, especially the Li3VO4/graphene nanosheets composite, show superior electrochemical performance to the formerly reported vanadium-based anode materials. The composite shows a reversible capacity of 223 mAh g–1 even at 20C (1C = 400 mAh g–1). After 500 cycles at 10C there is no evident capacity fading.

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Hollow structured Li3VO4 wrapped with graphene nanosheets in situ prepared by a one-pot template-free method as an anode for lithium-ion batteries.

A composite membrane based on electrospun poly(vinylidene fluoride) (PVDF) and lithium polyvinyl alcohol oxalate borate (LiPVAOB) exhibiting high safety (self-extinguishing) and good mechanical property is prepared. The ionic conductivity of the as-prepared gel polymer electrolyte from this composite membrane saturated with 1 mol L−1 LiPF6 electrolyte at ambient temperature can be up to 0.26 mS cm−1, higher than that of the corresponding well-used commercial separator (Celgard 2730), 0.21 mS cm−1. Moreover, the lithium ion transference in the gel polymer electrolyte at room temperature is 0.58, twice as that in the commercial separator (0.27). Furthermore, the absorbed electrolyte solvent is difficult to evaporate at elevated temperature. Its electrochemical performance is evaluated by using LiFePO4 cathode. The obtained results suggest that this gel-type composite membrane shows great possibilities for use in large-capacity lithium ion batteries that require high safety.

A Composite Gel Polymer Electrolyte with High Performance Based on Poly(Vinylidene Fluoride) and Polyborate for Lithium Ion Batteries

To reduce the reaction time, electrical energy consumption, and cost, LiFePO4/C/graphene has been synthesized by a rapid, one-pot, microwave-assisted hydrothermal method within 15 min at a temperature of 200 °C, followed by sintering at 600 °C for 2 h under a H2/Ar (5 : 95, v/v) atmosphere. The microstructure and morphology of the LiFePO4/C/graphene products were characterized by means of X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The carbon coated LiFePO4/C nanoparticles, around 200 nm in size, are thoroughly wrapped by crumpled micrometer-size graphene sheets. In this kind of structure, the bridging graphene nanosheets can form an effective conducting network and provide interconnected open pores that favor electrolyte absorption and reduce the diffusion path of the lithium ions. The cyclic voltammograms, charge/discharge profiles, and AC impedance measurements indicated that the kinetics of the LiFePO4/C/graphene was better than that of LiFePO4/C. The LiFePO4/C/graphene composite exhibited a discharge capacity of 165 mA h g−1 at 0.1 C and 88 mA h g−1 at 10 C, respectively. Therefore, the LiFePO4/C/graphene composite is a promising candidate for the development of high-performance, cost-effective lithium batteries for the hybrid vehicle and electric vehicle markets.

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Graphene wrapped LiFePO4/C composites as cathode materials for Li-ion batteries with enhanced rate capability

A composite membrane based on poly(vinylidene fluoride) (PVDF) and lithium polyacrylic acid oxalate borate (LiPAAOB) exhibiting high safety (self-extinguishing) and good mechanical property was prepared. The ionic conductivity of the gel polymer electrolyte (GPE) by saturating with 1 mol L−1 LiPF6 electrolyte at ambient temperature can be up to 0.35 mS cm−1, higher than that of the well-used commercial separator (Celgard 2730), 0.21 mS cm−1. The lithium ion transference in the GPE at room temperature is 0.58, twice that in the commercial separator (0.27). Moreover, the GPE presents a true shut-down behavior, which is quite different from the not-real shut-down behaviour of the commercial separators. Furthermore, the absorbed electrolyte solvent is difficult to evaporate at elevated temperature. Its electrochemical performance is evaluated by using LiFePO4 cathode. The obtained results suggest that this composite GPE is very attractive to large-capacity battery systems requiring high safety and low cost.

A trilayer poly(vinylidene fluoride)/polyborate/poly(vinylidene fluoride) gel polymer electrolyte with good performance for lithium ion batteries

A hybrid of V2O5 nanowires and MWCNTs coated with polypyrrole (PPy) was prepared as an anode material for ARLBs. The hybrid shows a good electrochemical reversibility since the PPy coating can effectively prevent the dissolution of the reduced vanadium ions.

A hybrid of V2O5 nanowires and MWCNTs coated with polypyrrole as an anode material for aqueous rechargeable lithium batteries with excellent cycling performance

Yi Shi

Papers

Hollow structured Li3VO4 wrapped with graphene nanosheets in situ prepared by a one-pot template-free method as an anode for lithium-ion batteries.

A Composite Gel Polymer Electrolyte with High Performance Based on Poly(Vinylidene Fluoride) and Polyborate for Lithium Ion Batteries

Graphene wrapped LiFePO4/C composites as cathode materials for Li-ion batteries with enhanced rate capability

A trilayer poly(vinylidene fluoride)/polyborate/poly(vinylidene fluoride) gel polymer electrolyte with good performance for lithium ion batteries

A hybrid of V2O5 nanowires and MWCNTs coated with polypyrrole as an anode material for aqueous rechargeable lithium batteries with excellent cycling performance