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

Ni-based metal organic frameworks (Ni-MOFs) with unique hierarchical hollow ball-in-ball nanostructure were synthesized by solvothermal reactions. After successive carbonization and oxidation treatments, hierarchical NiO/Ni nanocrystals covered with a graphene shell were obtained with the hollow ball-in-ball nanostructure intact. The resulting materials exhibited superior performance as the anode in lithium ion batteries (LIBs): they provide high reversible specific capacity (1144 mAh/g), excellent cyclability (nearly no capacity loss after 1000 cycles) and rate performance (805 mAh/g at 15 A/g). In addition, the hierarchical NiO/Ni/Graphene composites demonstrated promising performance as anode materials for sodium-ion batteries (SIBs). Such a superior lithium and sodium storage performance is derived from the well-designed hierarchical hollow ball-in-ball structure of NiO/Ni/Graphene composites, which not only mitigates the volume expansion of NiO during the cycles but also provides a continuous highly conductive graphene matrix to facilitate the fast charge transfer and form a stable SEI layer.

Metal Organic Frameworks Derived Hierarchical Hollow NiO/Ni/Graphene Composites for Lithium and Sodium Storage

The roles of oxygen vacancies in electrocatalytic oxygen evolution reaction

To advance current Li rechargeable batteries further, tremendous emphasis has been made on the development of anode materials with higher capacities than the widely commercialized graphite. Some of these anode materials exhibit capacities above the theoretical value predicted based on conventional mechanisms of Li storage, namely insertion, alloying, and conversion. In addition, in contrast to conventional observations of loss upon cycling, the capacity has been found to increase during repeated cycling in a significant number of cases. As the internal environment in the battery is very complicated and continuously changing, these abnormal charge storage behaviors are caused by diverse reactions. In this review, we will introduce our current understanding of reported reactions accounting for the extra capacity. It includes formation/decomposition of electrolyte-derived surface layer, the possibility of additional charge storage at sharp interfaces between electronic and ionic sinks, redox reactions of Li-containing species, unconventional activity of structural defects, and metallic-cluster like Li storage. We will also discuss how the changes in the anode can induce capacity increase upon cycling. With this knowledge, new insights into possible strategies to effectively and sustainably utilize these abnormal charge storage mechanisms to produce vertical leaps in performance of anode materials will be laid out.

Exploring Anomalous Charge Storage in Anode Materials for Next-Generation Li Rechargeable Batteries.

Metal–organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure–property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

Advances in metal-organic framework coatings: versatile synthesis and broad applications.

Synthesis of a novel porous silicon microsphere@carbon core-shell composite via in situ MOF coating for lithium ion battery anodes

Hierarchically nanostructured binary/multiple transition-metal oxides with electrically conductive coatings are very attractive for lithium-ion batteries owing to their excellent electrochemical properties induced by their unique compositions and microstructures. Herein, hierarchical MnO-doped Fe3O4@C composite nanospheres are prepared by a simple one-step annealing in Ar atmosphere, using Mn-doped Fe-based metal–organic frameworks (Mn-doped MIL-53(Fe)) as precursor. The MnO-doped Fe3O4@C composite particles have a uniform nanosphere structure with a diameter of ∼100 nm, and each nanosphere is composed of clustered primary nanoparticles with an amorphous carbon shell, forming a unique hierarchical nanoarchitecture. The as-prepared hierarchical MnO-doped Fe3O4@C composite nanospheres exhibit markedly enhanced lithium-storage performance, with a large capacity of 1297.5 mAh g–1 after 200 cycles at 200 mA g–1. The cycling performance is clarified through analyzing the galvanostatic discharge/charge voltage p...

MOF-Derived Hierarchical MnO-Doped Fe3O4@C Composite Nanospheres with Enhanced Lithium Storage.

Hierarchically nanostructured transition metal oxides are very attractive for electrochemical energy storage systems owing to the enhanced electrochemical performance induced by their unique microstructures. Herein, a hierarchical CoO microflower film is prepared by a low-temperature solvothermal method with subsequent annealing treatment. The CoO microflowers with an average size of about 6 μm consist of hexagonal nanosheets with a loose exterior layer, exhibiting a unique hierarchical micro–nanostructure. The hierarchical CoO microflower film electrode delivers a high capacity of 1297.9 mA h g−1 after 500 cycles at 454.5 mA g−1, manifesting superior lithium storage performance. The phenomenon of the lithium storage capacity increase during the initial 150 cycles is analyzed by comparing the galvanostatic discharge/charge voltage profiles at different cycles. For sodium storage, the CoO microflower film electrode shows a larger capacity of 277.8 mA h g−1 after 100 cycles at a current density of 90.9 mA g−1. Based on the physical characterization results of the cycled film electrodes, the sodium storage mechanism of CoO is clarified.

Liang-ai Huang

Papers

Synthesis of a novel porous silicon microsphere@carbon core-shell composite via in situ MOF coating for lithium ion battery anodes

MOF-Derived Hierarchical MnO-Doped Fe3O4@C Composite Nanospheres with Enhanced Lithium Storage.

Hierarchical CoO microflower film with excellent electrochemical lithium/sodium storage performance

Pd nanoparticles supported on N and P dual-doped graphene as an excellent composite catalyst for methanol electro-oxidation

Novel Hierarchically Branched CoC2O4@CoO/Co Composite Arrays with Superior Lithium Storage Performance