Molten Salt-Assisted Construction of Hollow Carbon Spheres with Outer-Order and Inner-Disorder Heterostructure for Ultra-Stable Potassium Ion Storage.

The central goal of high-performance potassium ion storage is to control the function of the anode material via rational structural design. Herein, N- and S-doped hollow carbon spheres with outer-short-range-order and inner-disorder structures are constructed to achieve highly efficient and ultra-stable potassium ion storage using a low-temperature molten salt system. The ultrathin carbon walls and uniform mesoporous as well as unique heterostructure synergistically realize significant potassium storage performance via facilitating rapid diffusion of potassium ions and alleviating substantial volume expansion. Furthermore, as the anode of a potassium ion battery, the as-prepared MSTC electrode demonstrates a state-of-the-art cycling capability of 221.3 mAh g-1 at 1 A g-1 after 20,000 cycles. The assembled potassium ion hybrid capacitor device demonstrates a high energy of 157 Wh kg-1 at 956 W kg-1 and excellent reversibility at a current density of 5.0 A g-1 after 20,000 cycles with 82.7% capacity retention. Accordingly, our work provides new ideas for designing advanced carbon anode materials and understanding the charge storage mechanism in potassium ion battery, as well as constructing high energy-power density potassium-ion hybrid capacitors (PIHCs).

N-doped engineering of a high-voltage LiNi0.5Mn1.5O4 cathode with superior cycling capability for wide temperature lithium-ion batteries.

Spinel LiNi0.5Mn1.5O4 (LNMO) is one potential cathode candidate for next-generation high energy-density lithium-ion batteries (LIBs). However, serious capacity decay from its poor structural stability, especially at high operating temperatures, shadows its application prospects. In this work, N-doped LNMO (LNMON) was synthesized by a facile co-precipitation method and multistep calcination, exhibiting a unique yolk-shell architecture. Concurrently, N dopants are introduced into a LNMO lattice, endowing LNMON with a more stable structure via stronger Ni-N/Mn-N bindings. Benefiting from the synergistic effect of the yolk-shell structure and N-doped engineering, the obtained LNMON cathode exhibits an impressive rate and the state-of-the-art cycling capability, delivering a high capacity of 103 mA h g-1 at 25 °C after 8000 cycles. Even at a high operating temperature of 60 °C, the capacity retention remains at 92% after 1000 cycles. The discovery of N dopants in improving the cycling capability of LNMO in our case offers a prospective approach to enable 5 V LNMO cathode materials with excellent cycling capability.

Biomineralized Mesocrystal KCl Microreactor for Solid-State Synthesis of Non-Oxide Nanomaterials.

Inspired by natural biomineralization, a biomineralized microreactor with a mesocrystal KCl shell (BM-KCl-MMs) is made by a facile freezing dry process, exhibiting a good availability for high-temperature solid-state synthesis of nanomaterials. Benefiting from the good thermal stability, stiffness, and mechanical strength of KCl mesocrystal shells, the employment of BM-KCl-MMs in the transition metal (TM)-S-Se system not only realizes for the first time, the production of TMSx Se2- x /C nanocomposites in air atmosphere, but also reaches a high reagent-utilization and high yield, as well as minimum wastes. More importantly, based on the soaking effect of the KCl shells, the resultant stable reaction microenvironment inside endows the microreactors with a well-controlled synthesis of nanomaterials with very even size, uniform dispersion, and novel functionalities. As one example, the as-prepared MoSx Se2- x /C composites as the electrodes of K-ion batteries and K-ion hybrid supercapacitors deliver the state of the art cycling capability of 248 mAh g-1 at 2 A g-1 after 5000 cycles and an 87.1% capacity retention at 5.0 A g-1 after 20 000 cycles, respectively, demonstrating a significant potential of BM-KCl-MMs on design and synthesis of novel functional nanomaterials.

Fe nanopowder-assisted fabrication of FeOx/porous carbon for boosting potassium-ion storage performance.

The electrode materials of potassium ion storage system have attracted considerable attention given the promising prospect of a potassium ion system in large-scale electrochemical energy storage applications. Despite the excellent anode performance of metal oxides in Li+ and Na+ batteries, the study on their K+ storage performance is still rarely reported. In this study, we report a safe and low-cost strategy to prepare FeOx/N-doped carbons by using NaHCO3 and Fe nanopowder. Benefiting from the oxidation of Fe to Fe3O4, an interesting "one stone, two birds" role of the Fe powder can be identified in the heating process. As a reduction agent, the Fe powder can consume the excess oxygen in the bio-massed carbon framework, facilitating the formation of short-range-ordered domains in the biomass-derived carbon materials (FeOx@GBHCs). Moreover, the close combination of oxidization products (Fe3O4 particles) and carbon matrix leads to numerous FeOx clusters grafted on the surface of the carbon framework via the strong C-O-Fe binding. Therefore, the resultant FeOx/porous carbon exhibits a high reversible capacity of 410 mA h g-1 and an excellent cycling capability. The assembled FeOx@GBHCs//AC potassium-ion hybrid supercapacitor delivers a high energy density of 133 W h kg-1 at a power density of 700 W kg-1, demonstrating a potential prospect of metal oxides in boosting the potassium ion storage performance.

Fatigue-Resistant, Notch-Insensitive Zwitterionic Polymer Hydrogels with High Self-Healing Ability.

Introducing self-healing properties into hydrogels can prolong their application lifetime. However, achieving mechanical strength without sacrificing self-healing properties is still a major challenge. We prepared a series of zwitterionic polymer hydrogels by random copolymerization of zwitterionic ionic monomer (SBMA), cationic monomer (DAC) and hydrophilic monomer (HEMA). The ionic bonds and hydrogen bonds formed in the hydrogels can efficiently dissipate energy and rebuild the network. The resulting hydrogels show high mechanical strength (289-396 KPa of fracture stress, 433-864 % of fracture stress) and have great fatigue resistance. The hydrogel with a 1 : 1 molar ratio of SBMA:DAC possesses the best self-healing properties (self-healing efficiency up to 96.5 % at room temperature for 10 h). The self-healing process is completely spontaneous and does not require external factors to assist. In addition, the hydrogel also possesses notch insensitivity with a fracture energy of 12000 J m-2 . After combining the conductivity of RGO aerogel, the hydrogel/RGO composites show good strain sensitivity with high reliability and self-healing ability, which has certain significance in broadening the application of these zwitterionic hydrogels.

Template-assisted loading of Fe3O4 nanoparticles inside hollow carbon "rooms" to achieve high volumetric lithium storage.

The design of electrodes with simultaneously high compaction density, developed porosity, and structural stability has always been a challenge so as to meet the demand of high volumetric performance lithium ion storage devices. In this paper, we demonstrate a new compositing method for hollow carbon "room" loading of Fe3O4 nanoparticles (HCR@Fe3O4) with the assistance of Na2CO3 salt crystal templates. The as-obtained HCR@Fe3O4 composites have a massive compaction density (1.79 g cm-3), abundant multimodal pores (1.26 cm3 g-1), and a large content of Fe3O4 (64.2 wt%), which leads to excellent volumetric capacitive performance. More importantly, the unique compositing model not only provides a fast transmission channel for Li+ but also alleviates the mechanical strain efficiently through the cavity between the Fe3O4 nanoparticles and the carbon wall. When evaluated as an anode of lithium ion batteries, the resultant HCR@Fe3O4 electrode exhibits a remarkable volumetric capacity of 2044 mA h cm-3 at 0.2 A g-1 and a stable cycle life of 828 mA h cm-3 after 1000 cycles at 5 A g-1. The assembled HCR@Fe3O4//AC lithium ion hybrid capacitor device exhibits a high energy density of 173 W h L-1 at a power density of 190 W L-1, demonstrating its high-level integrated volumetric density/power density.

Rigid-Flexible Coupling Carbon Skeleton and Potassium-Carbonate-Dominated Solid Electrolyte Interface Achieving Superior Potassium-Ion Storage.

Potassium-ion energy-storage devices are highly attractive in the large-scale energy storage field, but the intercalation of large K ions greatly worsens the stability of electrode structures and solid electrolyte interphase (SEI) films, causing slow reaction dynamics and poor durability. In this Article, inspired by bubble wraps in our life, a bubble-wrap-like carbon sheet (BPCS) with a rigid-flexible coupling porous architecture is fabricated on the microscale, exhibiting strong structural stability and good accommodation for volume expansion. In the meantime, a K2CO3·1.5H2O-dominated SEI is created by an interfacial transfer behavior of carbonate groups. These K2CO3·1.5H2O nanograins not only enhance the stability of the SEI by constructing a stable scaffold but also create more diffusion routes for K ions. On the basis of the above, using the BPCS as the anode of potassium-ion batteries delivers reversible capacities of 463 mAh g-1 at 50 mA g-1 and 195 mAh g-1 at 10 A g-1 with a long cycling life. The assembled BPCS//NPC potassium-ion hybrid capacitor exhibits a high energy density of 167 Wh kg-1 and a superior cycling capability with 80.8% capacity retention over 10 000 cycles with nearly 100% Coulombic efficiency. Even at the higher current density of 10 A g-1, the device could deliver an energy density of 92.9 Wh kg-1 over 5000 cycles at a power density of 9200 W kg-1 with only 0.002% fading per cycle, which can rival lithium-ion hybrid supercapacitors.

Bio-derived yellow porous TiO2: the lithiation induced activation of an oxygen-vacancy dominated TiO2 lattice evoking a large boost in lithium storage performance.

Oxygen deficient TiO2 has attracted extensive attention owning to its narrow bandgap and high electrical conductivity. In this work, novel yellow TiO2 with hierarchically porous architecture is fabricated by a facile pyrolysis method in air via a biomass template. The obtained yellow TiO2 exhibits interesting lithiation induced activation during cycling, which gives rise to a phase change from poorly crystallized TiO2 to an amorphous phase, accompanied by a colour change from yellow to black. In contrast to the intercalation mechanism reported in most of the literature on the TiO2 anode of LIBs, notably, the reversible redox reaction between Ti3+ and metal Ti can be verified in this case, demonstrating the novel conversion reaction mechanism of the TiO2 electrode. Based on this, the yellow porous TiO2 delivers enhanced electrochemical performance as an anode for LIBs with a superior capacity of 480 mA h g-1 at 5 A g-1 and a high capacity of 206 mA h g-1 at 10 A g-1 after 8000 cycles.

Cable-like heterogeneous porous carbon fibers with ultrahigh-rate capability and long cycle life for fast charging lithium-ion storage devices.

In this paper, we propose a space-confined foaming approach to fabricate cable-like heterogeneous porous carbon fibers (Si-CPCFs) containing an inner graphitized carbon "conductor" and an outer Si-doping amorphous carbon "shield". Benefiting from the fast Li+ intercalation and high conductivity of the "inner conductor", and the rich pseudocapacitance of the "outer shield", the Si-CPCFs exhibit an ultrahigh-rate capability and cycling performance, leading to a high capacity of 132 mA h g-1 even at an ultra-high current density of 100 A g-1 after 10 000 cycles. The assembled lithium ion hybrid supercapacitors (LIHCs) also deliver a superior energy density of 50 W h kg-1 at an ultra-high power density of 113 kW kg-1, really achieving both a high energy density and power density of LIHCs. The success of the cable-like heterogeneous porous carbon architecture proposes a new direction to circumvent the discrepancy in kinetics and capacity mismatch, and also attracts more attention to heterogeneous nanostructures with multiple functions.

Bioinspired Mineralization under Freezing Conditions: An Approach to Fabricate Porous Carbons with Complicated Architecture and Superior K+ Storage Performance.

Bioinspired mineralization is a powerful method for designing and preparing nanomaterials. In this work, we developed a bioinspired mineralization approach under freezing conditions and fabricated methyl cellulose (MC)/NaHCO3 flake precursors with a sophisticated hierarchical structure. Based on this, amazing wing-like porous carbon sheets (WPCSs) assembled by numerous interconnected hollow carbon bubbles were obtained after carbonization and removal of inorganic crystals, which are seldom obtained by other artificial methods. Benefiting from their open framework, large surface area, and enlarged interlayer spacing of graphitized nanocrystallites, the obtained WPCSs exhibited an obvious boost in potassium storage performance. As an anode of potassium-ion batteries, they showed high reversible capacities of 347 mAh g-1 at 50 mA g-1 and 122 mAh g-1 at 20 A g-1 and relatively stable cyclability for 3000 cycles. The assembled WPCS//WPCS potassium-ion hybrid supercapacitor delivered a high energy density of 108 Wh kg-1 at a power density of 280 W kg-1. Given the cost effectiveness and green process, the modified bioinspired mineralization under freezing conditions would provide a facile and green way for exploring porous carbons with controlled structures and rich multifunction.

Recent Achievements of Self-Healing Graphene/Polymer Composites.

Self-healing materials have attracted much attention because that they possess the ability to increase the lifetime of materials and reduce the total cost of systems during the process of long-term use; incorporation of functional material enlarges their applications. Graphene, as a promising additive, has received great attention due to its large specific surface area, ultrahigh conductivity, strong antioxidant characteristics, thermal stability, high thermal conductivity, and good mechanical properties. In this brief review, graphene-containing polymer composites with self-healing properties are summarized including their preparations, self-healing conditions, properties, and applications. In addition, future perspectives of graphene/polymer composites are briefly discussed.