Mingbo Zheng

High performance electrochemical capacitor materials focusing on nickel based materials

Of the two major capacitances contributing to electrochemical storage devices, pseudo-capacitance, which results from the reversible faradaic reactions, can be much higher than the electric double layer capacitance. Transition metal compounds are emerging electrode materials for pseudo-capacitors due to their multiple oxidation states and different ions. As one of the most well-known electroactive inorganic materials, nickel based materials are being developed for this purpose. Nickel based materials have been intensively investigated and evaluated as potential electrode materials for pseudo-capacitors due to their thermal stability and chemical stability, high theoretical specific capacity, low price and environment friendliness. A variety of synthetic methods such as hydrothermal/solvothermal methods, sol–gel, electrodeposition, and the spray deposition method have been successfully applied to prepare nickel based compounds and composite materials. In this review, comprehensive summaries and evaluations have been given to show the recent progress. And we introduce the nickel based compounds and composites electrode materials for supercapacitors via synthesis methods, the electrochemical performances of the electrode materials and the devices.

Activated carbon with ultrahigh specific surface area synthesized from natural plant material for lithium–sulfur batteries

Porous activated carbon with a ultrahigh specific surface area (3164 m2 g−1) and large pore volume (1.88 cm3 g−1) was prepared from waste litchi shells with channel-like macropores via a KOH activation method. The macroporous structure of litchi shells is believed to be conducive to distribute the activation agent, which enables sufficient activation. The as-prepared activated carbon was developed as a conducting framework for lithium–sulfur battery cathode materials. The resulting activated carbon/sulfur composite cathode possesses a high specific capacity, good rate capability, and long-term cycling performance. At 200 mA g−1 current density, the initial discharge capacity of the activated carbon/sulfur composite cathode with 60 wt% sulfur content is 1105 mA h g−1. At a current density of 800 mA g−1, the activated carbon/sulfur composite cathode shows 51% capacity retention over 800 cycles with a fade rate of 0.06% per cycle. The coulombic efficiency of the cell remains at approximately 95%. By adding LiNO3 in the electrolyte, the activated carbon/sulfur composite electrode tested at 800 mA g−1 shows a high coulombic efficiency (>99%). The activated carbon/sulfur composites exhibited similar capacity value and cycling trends with an increase in sulfur content from 60% to 68%. The good electrochemical performance can be attributed to the excellent structural parameters of the activated carbon. The ultrahigh specific surface area and large pore volume not only enhances the sulfur content but also ensures dispersion of elemental sulfur in the conducting framework, thereby improving sulfur utilization. The small nanopores of the activated carbon can effectively inhibit the diffusion of polysulfides during the charge/discharge process.

Flexible cathodes and multifunctional interlayers based on carbonized bacterial cellulose for high-performance lithium-sulfur batteries

A three-dimensional (3D) carbonaceous aerogel derived from sustainable bacterial cellulose (BC) is introduced as a flexible framework for sulfur in lithium–sulfur batteries. The 3D carbonized BC (CBC) with highly interconnected nanofibrous structure exhibits good electrical conductivity and mechanical stability. The intrinsic macroporous structure of CBC contributes to a high sulfur loading of 81 wt%. Microstructure and morphology characterization results demonstrate that the sulfur species wrapped around CBC nanofibers are well dispersed. Even at such a high loading, the S/CBC composite still contains sufficient free space to accommodate the volume expansion of sulfur during lithiation. Furthermore, with an ultralight CBC interlayer inserted between the sulfur cathode and separator, significant improvement is achieved in active material utilization, cycling stability, and coulombic efficiency. The CBC interlayer can provide an extra conductive framework and adsorb migrating polysulfides to a certain degree. The CBC interlayer can also act as an additional collector for sulfur and thus could prevent the over-aggregation of insulated sulfur on the cathode surface. The good electrochemical performance reported in this work can be ascribed to the flexible 3D-interconnected nanostructure of the carbon framework and the rational design of battery configuration.

Facile synthesis of an accordion-like Ni-MOF superstructure for high-performance flexible supercapacitors

Metal–organic frameworks have received increasing attention as promising electrode materials in supercapacitors. In this study, we have successfully synthesized a novel accordion-like Ni-MOF superstructure ([Ni3(OH)2(C8H4O4)2(H2O)4]·2H2O), for the first time, and used it as an electrode material for supercapacitors. The supercapacitors with the novel electrode exhibited excellent electrochemical performance. For example, the accordion-like Ni-MOF electrode showed specific capacitances of 988 and 823 F g−1 at current densities of 1.4 and 7.0 A g−1, respectively, while maintaining outstanding cycling stability (capacitance retention of 96.5% after 5000 cycles at a current density of 1.4 A g−1). More importantly, the accordion-like Ni-MOF and activated carbons were assembled into a high-performance flexible solid-state asymmetric supercapacitor with a specific capacitance of 230 mF cm−2 at a current density of 1.0 mA cm−2. The cycle test showed that the device can offer 92.8% capacity of the initial capacitance at 5.0 mA cm−2 after 5000 cycles with little decay. The maximum energy density of the device can achieve 4.18 mW h cm−3 and the maximum power density can also achieve 231.2 mW cm−3.

Mesoporous NiO with a single-crystalline structure utilized as a noble metal-free catalyst for non-aqueous Li–O2 batteries

Mesoporous NiO nanosheets with a single-crystalline structure were investigated as an oxygen electrode catalyst in a non-aqueous Li–O2 battery. The recharge voltage plateau achieved for the NiO-based Li–O2 battery was ca. 3.95 V, ca. 200 mV negatively shifted compared with that for β-Ni(OH)2 and acetylene black. The reaction mechanism during the charge process for the NiO-based Li–O2 battery was intensively researched. The results of X-ray photoelectron spectroscopy characterization indicated that Li2O2 and Li2CO3 were formed during the discharge process, which can be decomposed after recharge. These demonstrated that the NiO nanosheet exhibited a good activity for the decomposition of Li2O2 and Li2CO3. Furthermore, the results of the gas chromatography-mass spectrometry test reflected two steps of the recharge process, i.e., the oxidation of Li2O2 when the potential was below 4.0 V and the decomposition of Li2O2 and Li2CO3 when the potential was above 4.0 V. Moreover, no obvious performance decay was observed in the NiO-based battery even after 40 cycles when the capacity was limited to 500 mA h g−1, indicating an impressive cycling performance.

Mesoporous iron oxide directly anchored on a graphene matrix for lithium-ion battery anodes with enhanced strain accommodation

A continuous mesoporous iron oxide nanofilm was directly formed on graphene nanosheets through the in situ thermal decomposition of Fe(NO3)3·9H2O and was anchored tightly on the graphene surface. The lithiation-induced strain was naturally accommodated, owing to the constraint effect of graphene and the mesoporous structure. Hence, the pulverization of the iron oxide nanofilm was effectively prevented.

Rechargeable zinc–air batteries: a promising way to green energy

As a promising technology, electrically rechargeable zinc–air batteries have gained significant attention in the past few years. Herein, in this review, we focused on the main challenges of the electrically rechargeable zinc–air batteries in alkaline electrolytes and the up-to-date progress from materials to technologies towards overcoming these technical barriers. We first overviewed the design and working mechanism of the battery and classified the hindrances into dendritic growth at the anode, lack of higher performance bifunctional catalysts at the air electrode, and electrolyte-related problems. Then, detailed discussions have been provided on the latest progress to address these technical issues based on the nano/micro-materials. Flexible zinc–air batteries as a new development have also been discussed in a separate section. Finally, conclusions have been provided followed by future perspective.

Facile synthesis of amorphous aluminum vanadate hierarchical microspheres for supercapacitors

Micro-nanostructured mixed metal vanadates have recently garnered enormous attention owing to their remarkable performances in catalysis, energy storage and conversion. In this work, we report the synthesis of amorphous aluminum vanadate hierarchical microspheres via a simple hydrothermal approach with polyvinylpyrrolidone as a surface directing agent. Amorphous aluminum vanadate hierarchical microspheres are firstly described as a kind of electrode material for supercapacitors. The measured specific capacitance of the amorphous aluminum vanadate electrode is 497 F g−1 at 1 A g−1 with good stability and a retention capacity of 89% after 10 000 cycles. In addition, the fabricated asymmetric supercapacitor device delivered better performance with an extended operating voltage window of 1.5 V, excellent cycle stability (10 000 cycles, 85% capacitance retention), high energy density (37.2 W h kg−1 at 1124.4 W kg−1) and high power density (11 250 W kg−1 at 25 W h kg−1). This study essentially offers a new kind of vanadate as an electrochemical active material for the development of supercapacitors.

Hierarchically Nanostructured Transition Metal Oxides for Lithium‐Ion Batteries

Abstract Lithium‐ion batteries (LIBs) have been widely used in the field of portable electric devices because of their high energy density and long cycling life. To further improve the performance of LIBs, it is of great importance to develop new electrode materials. Various transition metal oxides (TMOs) have been extensively investigated as electrode materials for LIBs. According to the reaction mechanism, there are mainly two kinds of TMOs, one is based on conversion reaction and the other is based on intercalation/deintercalation reaction. Recently, hierarchically nanostructured TMOs have become a hot research area in the field of LIBs. Hierarchical architecture can provide numerous accessible electroactive sites for redox reactions, shorten the diffusion distance of Li‐ion during the reaction, and accommodate volume expansion during cycling. With rapid research progress in this field, a timely account of this advanced technology is highly necessary. Here, the research progress on the synthesis methods, morphological characteristics, and electrochemical performances of hierarchically nanostructured TMOs for LIBs is summarized and discussed. Some relevant prospects are also proposed.

Activated graphene with tailored pore structure parameters for long cycle-life lithium–sulfur batteries

Activated graphene (AG) with various specific surface areas, pore volumes, and average pore sizes is fabricated and applied as a matrix for sulfur. The impacts of the AG pore structure parameters and sulfur loadings on the electrochemical performance of lithium-sulfur batteries are systematically investigated. The results show that specific capacity, cycling performance, and Coulombic efficiency of the batteries are closely linked to the pore structure and sulfur loading. An AG3/S composite electrode with a high sulfur loading of 72 wt.% exhibited an excellent long-term cycling stability (50% capacity retention over 1,000 cycles) and extra-low capacity fade rate (0.05% per cycle). In addition, when LiNO3 was used as an electrolyte additive, the AG3/S electrode exhibited a similar capacity retention and high Coulombic efficiency (∼98%) over 1,000 cycles. The excellent electrochemical performance of the series of AG3/S electrodes is attributed to the mixed micro/mesoporous structure, high surface area, and good electrical conductivity of the AG matrices and the well-distributed sulfur within the micro/mesopores, which is beneficial for electrical and ionic transfer during cycling.