J-YH and S-TM contributed equally to this work This work was supported by the Human Resources Development program (Grant No 20154010200840) from a Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant, funded by the Ministry of Trade, Industry and Energy of the Korean government, and supported by the Global Frontier RaD program (Grant No 2013M3A6B1078875) of the Center for Hybrid Interface Materials (HIM) of the Ministry of Science and ICT

Recent Progress in Rechargeable Potassium 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

Batteries have shaped much of our modern world. This success is the result of intense collaboration between academia and industry over the past several decades, culminating with the advent of and improvements in rechargeable lithium-ion batteries. As applications become more demanding, there is the risk that stunted growth in the performance of commercial batteries will slow the adoption of important technologies such as electric vehicles. Yet the scientific literature includes many reports describing material designs with allegedly superior performance. A considerable gap needs to be filled if we wish these laboratory-based achievements to reach commercialization. In this Perspective, we discuss some of the most relevant testing parameters that are often overlooked in academic literature but are critical for practical applicability outside the laboratory. We explain metrics such as anode energy density, voltage hysteresis, mass of non-active cell components and anode/cathode mass ratio, and we make recommendations for future reporting. We hope that this Perspective, together with other similar guiding principles that have recently started to emerge, will aid the transition from lab-scale research to next-generation practical batteries. This Perspective discussed the best practices for reporting lab-scale performance metrics in battery papers.

Bridging the academic and industrial metrics for next-generation practical batteries.

Despite the ever-growing demand in safe and high power/energy density of Li+ ion and Li metal rechargeable batteries (LIBs), materials-related challenges are responsible for the majority of performance degradation in such batteries. These challenges include electrochemically induced phase transformations, repeated volume expansion and stress concentrations at interfaces, poor electrical and mechanical properties, low ionic conductivity, dendritic growth of Li, oxygen release and transition metal dissolution of cathodes, polysulfide shuttling in Li-sulfur batteries, and poor reversibility of lithium peroxide/superoxide products in Li-O2 batteries. Owing to compelling physicochemical and structural properties, in recent years two-dimensional (2D) materials have emerged as promising candidates to address the challenges in LIBs. This Review highlights the cutting-edge advances of LIBs by using 2D materials as cathodes, anodes, separators, catalysts, current collectors, and electrolytes. It is shown that 2D materials can protect the electrode materials from pulverization, improve the synergy of Li+ ion deposition, facilitate Li+ ion flux through electrolyte and electrode/electrolyte interfaces, enhance thermal stability, block the lithium polysulfide species, and facilitate the formation/decomposition of Li-O2 discharge products. This work facilitates the design of safe Li batteries with high energy and power density by using 2D materials.

Two-Dimensional Materials to Address the Lithium Battery Challenges

A high entropy oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O) with superior lithium storage performance

Transition metal oxides (TMOs) based on conversion reactions are attractive candidate anode materials for lithium-ion batteries (LIBs) because of their high theoretical capacity and safety characteristics. In this review, we have summarized recent progress in the rational design and efficient synthesis of TMOs with controllable morphologies, compositions, and micro-/nanostructures, along with their Li storage behaviors. Single metal oxides of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), ruthenium (Ru), chromium (Cr), molybdenum (Mo), and tungsten (W) and their common binary metal oxides have been discussed in this review. Finally, the less well-known merits of conversion reactions are put forward, and the design of metal oxide electrodes making full use of these merits has been proposed.

Kangzhe Cao

Papers

Recent progress in conversion reaction metal oxide anodes for Li-ion batteries