Rechargeable lithium-sulfur batteries.

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Owing to high specific energy, low cost, and environmental friendliness, lithium–sulfur (Li–S) batteries hold great promise to meet the increasing demand for advanced energy storage beyond portable electronics, and to mitigate environmental problems. However, the application of Li–S batteries is challenged by several obstacles, including their short life and low sulfur utilization, which become more serious when sulfur loading is increased to the practically accepted level above 3–5 mg cm−2. More and more efforts have been made recently to overcome the barriers toward commercially viable Li–S batteries with a high sulfur loading. This review highlights the recent progress in high-sulfur-loading Li–S batteries enabled by hierarchical design principles at multiscale. Particularly, basic insights into the interfacial reactions, strategies for mesoscale assembly, unique architectures, and configurational innovation in the cathode, anode, and separator are under specific concerns. Hierarchy in the multiscale design is proposed to guide the future development of high-sulfur-loading Li–S batteries.

Review on High-Loading and High-Energy Lithium–Sulfur Batteries

As a promising candidate for large-scale energy storage, aqueous zinc-ion batteries (ZIBs) still lack cathode materials with large capacity and high rate capability. Herein, a spherical carbon-confined nanovanadium oxynitride with a polycrystalline feature (VNxOy/C) was synthesized by the solvothermal reaction and following nitridation treatment. As a cathode material for ZIBs, it is interesting that the electrochemical performance of the VNxOy/C cathode is greatly improved after the first charging process viain situ electrochemically oxidative activation. The oxidized VNxOy/C delivers a greatly enhanced reversible capacity of 556 mAh g-1 at 0.2 A g-1 compared to the first discharge capacity of 130 mAh g-1 and a high capacity of 168 mAh g-1 even at 80 A g-1. The ex situ characterizations verify that the insertion/extraction of Zn2+ does not affect the crystal structure of oxidized VNxOy/C to promise a stable cycle life (retain 420 mAh g-1 after 1000 cycles at 10 A g-1). The experimental analysis further elucidates that charging voltage and H2O in the electrolyte are curial factors to activate VNxOy/C in that the oxygen replaces the partial nitrogen and creates abundant vacancies, inducing a conversion from VNxOy/C to VNx-mOy+2m/C and then resulting in considerably strengthened rate performance and improved Zn2+ storage capability. The study broadens the horizons of fast ion transport and is exceptionally desirable to expedite the application of high-rate ZIBs.

In Situ Electrochemically Oxidative Activation Inducing Ultrahigh Rate Capability of Vanadium Oxynitride/Carbon Cathode for Zinc-Ion Batteries.

Fundamental issues relevant to the oxygen reduction reaction (ORR) mechanism and reaction interface are ambiguous in Li–O2 batteries. Herein, we utilized highly sensitive surface-enhanced Raman spectroscopy (SERS) to reveal the spontaneous desorption behavior of insoluble products of lithium peroxide (Li2O2) from the electrode surface. Furthermore, the electrochemical ORR mechanism is elucidated at the electrode/Li2O2 interface based on a dynamic equilibrium between the generation and desorption of Li2O2. The desorption of adsorbed Li2O2 species (Li2O2*) is crucial to releasing surface sites and maintaining the electrochemical ORR process at the electrode substrate surface instead of the Li2O2/electrolyte interface. The proceeding of Li2O2* desorption can guarantee the stability of Li2O2* concentration and the discharge plateau in the galvanostatic ORR process. The suppression of Li2O2* desorption is proved to induce the termination of Li2O2* generation, which is accompanied by the growth of adsorbed lithium superoxide (LiO2*), leading to rapid potential attenuation. 

The Decisive Role of Li2O2 Desorption for Oxygen Reduction Reaction in Li–O2 Batteries

Rational design of covalent organic frameworks with high capacity and stability as a lithium-ion battery cathode.

Failure Mechanisms Investigation of Ultra-Thin Composite Polymer Electrolyte-Based Solid-State Lithium Batteries

As a new class of crystalline materials, covalent organic frameworks (COFs) have long-range ordered channels and feasibility to functionalize. The well-arranged pores make it possible to contain and transport ions. Here, we designed a novel functionalized anionic COF-SS-Li by a post-synthetic method utilizing the Povarov reaction of BDTA-COF, anchoring -SO3- groups to the COF backbone and converting the imine linkage to a more stable quinoline unit. The grafted -SO3- groups and directional channels can promote the lithium-ion transport through a hopping mechanism. As a solid-state lithium-ion electrolyte, COF-SS-Li exhibits the conductivities of 9.63 × 10-5 S cm-1 at 20 °C and 1.28 × 10-4 S cm-1 at 40 °C and a wide electrochemical window of 4.85 V. The assembled Li|COF-SS-Li|Li symmetric cell can cycle stably for 600 h at 0.1 mA cm-2. Also, the Li|COF-SS-Li|LiFePO4 cell delivers an initial capacity of 117 mAh g-1 at 0.1 A g-1 and retains a capacity rate of 56.7% after 500 cycles. The research enriches the solid-state electrolytes for lithium-ion batteries.

Bing Ding

Papers

In Situ Electrochemically Oxidative Activation Inducing Ultrahigh Rate Capability of Vanadium Oxynitride/Carbon Cathode for Zinc-Ion Batteries.

The Decisive Role of Li2O2 Desorption for Oxygen Reduction Reaction in Li–O2 Batteries

Rational design of covalent organic frameworks with high capacity and stability as a lithium-ion battery cathode.

Failure Mechanisms Investigation of Ultra-Thin Composite Polymer Electrolyte-Based Solid-State Lithium Batteries

Post-synthetic Covalent Organic Framework to Improve the Performance of Solid-State Li+ Electrolytes.