Biomass-Derived Carbon Materials for Electrochemical Energy Storage.

The environmental impact from the waste disposal has been widely concerned around the world. The conversion of wastes to useful resources is important for the sustainable society. As a typical family of wastes, biomass materials basically composed of collagen, protein and lignin are considered as useful resources for recycle and reuse. In recent years, the development of carbon material derived from biomasses, such as plants, crops, animals and their application in electrochemical energy storage have attracted extensive attention. Through the selection of the appropriate biomass, the optimization of the activation method and the control of the pyrolysis temperatures, carbon materials with desired features, such as high-specific surface area, variable porous framework, and controllable heteroatom-doping have been fabricated. Herein, this review summarized the preparation methods, morphologies, heteroatoms doping in the plant/animal-derived carbonaceous materials, and their application as electrode materials for secondary batteries and supercapacitors, and as electrode support for lithium-sulfur batteries. The challenges and prospects for the controllable synthesis and large-scale application of biomass-derived carbonaceous materials have also been outlooked.

Tailoring the growth route of lithium peroxide through the rational design of a sodium-doped nickel phosphate catalyst for lithium-oxygen batteries.

Tailoring the morphology and structure of Li2O2, the discharge product of lithium-oxygen batteries (LOBs), through the rational design of cathode catalysts is an efficient strategy to promote the electrochemical performance of LOBs. In this work, sodium-doped nickel phosphate nanorods (Na-NiPO NRs) grown on Ni foam (NF) were prepared by the hydrothermal method and subsequent calcination. For the Na-NiPO NRs, the electronic structure could be optimized and abundant void space among the nanorods would provide abundant transport channels. Adopted as the cathodes, the Na-NiPO NRs could facilitate the uniform growth of sea cucumber-like Li2O2 with sufficient Li2O2-electrolyte and Li2O2-catalyst interfaces, significantly promoting the charge process. Therefore, LOBs could deliver a high discharge capacity of 10365.0 mA h g-1 at 100 mA g-1. And a low potential gap of 1.16 V can be achieved at 200 mA g-1 with a capacity of 500 mA h g-1. The proposed strategy demonstrates the role of the morphology and electronic structure of the cathode catalysts in tuning the Li2O2 morphology and provides a novel approach for achieving high-performance LOBs.

Poly(p-phenylenediamine)-Coated Metal-Organic Frameworks for High-Performance Sodium-Ion Batteries: The Balance of Capacity and Stability.

Metal-organic frameworks (MOFs) with well-defined porous structures and highly active frameworks are considered as promising electrode materials for sodium-ion batteries (SIBs). However, the structure pulverization upon sodiation/desodiation impacts on their practical application in SIBs. To address this issue, poly(p-phenylenediamine) (PPA) was uniformly coated onto the surface of MIL-88A, a typical Fe-based MOF through in situ polymerization initiated by the metal ions (Fe3+) of MIL-88A. Used as an anode material for SIBs, the PPA-coated MIL-88A, denoted as PPA@MIL-88A, showed significantly improved electrochemical performance. A reversible capacity as high as 230 mAh g-1 was achieved at 0.2 A g-1 even after 500 cycles. MIL-88A constructed with electrochemically active Fe3+ and fumaric acid ligands guarantees the high specific capacity, while the PPA polymer coating effectively inhibits the pulverization of MIL-88A. This work provides an efficient strategy for improving the structure and cycling stability of MOFs-based electrode materials.

Tailoring the Growth and Morphology of Lithium Peroxide: Nickel Sulfide/Nickel Phosphate Nanotubes with Optimized Electronic Structure for Lithium-Oxygen Batteries.

Heterogeneous crystalline-amorphous structures, with tunable electronic structures and morphology, hold immense promise as catalysts for lithium-oxygen batteries (LOBs). Herein, a nanotube network constructed by crystalline nickel sulfide/amorphous nickel phosphate (NiS/NiPO) heterostructure is prepared on Ni foam through the sulfurization of the precursor generated hydrothermally. Used as cathodes, the NiS/NiPO nanotubes with optimized electronic structure can induce the deposition of the highly porous and interconnected structure of Li2 O2 with rich Li2 O2 -electrolyte interfaces. Abundant active sites can be created on NiS/NiPO through the charge redistribution for the uniform nucleation and growth of Li2 O2 . Moreover, nanotube networks endow cathodes with efficient transport channels and sufficient space for the accommodation of Li2 O2 . A high discharge capacity of 27 003.6 mAh g-1 and a low charge overpotential of 0.58 V at 1000 mAh g-1 can be achieved at 200 mA g-1 . This work provides valuable insight into the unique role of the electronic structure and morphology of catalysts in the formation mechanisms of Li2 O2 and the performances of LOBs.

High-Performance PEO-Based All-Solid-State Battery Achieved by Li-Conducting High Entropy Oxides.

A rock-salt-structured Li-conducting high entropy oxide was prepared and utilized as an active filler in a polyethylene oxide (PEO)-based solid-state composite electrolyte. X-ray diffraction and high-resolution transmission electron microscopy were adopted to analyze the crystal structure of the high entropy oxide containing 20% of Li ions (HL20). The HL20 was crystallized in the Fm3̅m space group with Li+ ions located at the center of the MO6 octahedra. The ionic conductivity of the composite membrane at 30 °C reaches 3.44 × 10-5 S cm-1. The inflection point of activation energy of the membrane with HL20 decreases by 5 °C compared with that of the pure PEO membrane. In the galvanostatic plating/stripping test, the Li||Li symmetric batteries could be cycled at a current density of 200 µA cm-2 for over 1200 h with an overpotential of 140 mV. The Li||LiFePO4 full battery could be charged/discharged at 0.5 C for 100 circles with a high capacity retention rate of 91%. Excellent rate performance is also achieved at lower temperatures and higher rates, showing the superiority of HL20 as an active filler. This work sheds light on the development of high entropy oxide as a new type of fast ionic conductor, promoting the practical application of all-solid-state batteries at a lower temperature.

Highly Crystalline Polyimide Covalent Organic Framework as Dual-Active-Center Cathode for High-Performance Lithium-Ion Batteries.

Polyimide covalent organic framework (PI-COF) materials that can realize intrinsic redox reactions by changing the charge state of their electroactive sites are considered as emerging electrode materials for rechargeable devices. However, the highly crystalline PI-COFs with hierarchical porosity are less reported due to the rapid reaction between monomers and the poor reversibility of the polyimidization reaction. Here, we developed a water-assistant synthetic strategy to adjust the reaction rate of polyimidization, and PI-COF (COFTPDA-PMDA) with kgm topology consisting of dual active centers of N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine (TPDA) and pyromellitic dianhydride (PMDA) ligands was successfully synthesized with high crystallinity and porosity. The COFTPDA-PMDA possesses hierarchical micro-/mesoporous channels with the largest surface area (2669 m2/g) in PI-COFs, which can promote the Li+ ions and bulky bis(trifluoromethanesulfonyl)imide (TFSI-) ions in organic electrolyte to sufficiently interact with the dual active sites on COF skeleton to increase the specific capacity of cathode materials. As a cathode material for lithium-ion batteries, COFTPDA-PMDA@50%CNT which integrated high surface area and dual active center of COFTPDA-PMDA with carbon nanotubes via π-π interactions gave a high initial charge capacity of 233 mAh/g (0.5 A/g) and maintains at 80 mAh/g even at a high current density of 5.0 A/g after 1800 cycles.

Nanofibrous Cathode Catalysts with MoC Nanoparticles Embedded in N-Rich Carbon Shells for Low-Overpotential Li-CO2 Batteries.

Li-CO2 batteries with high theoretical energy densities are recognized as next-generation energy storage devices for addressing the range anxiety and environmental issues encountered in the field of electric transportation. However, cathode catalysts with unsatisfactory activity toward CO2 absorption and reduction/evolution reactions hinder the development of Li-CO2 batteries with desired specific capacities and sufficient cycle numbers. In this work, a multifunctional nanofibrous cathode catalyst that integrates N-rich carbon shells embedded with molybdenum carbide nanoparticles and multiwalled carbon nanotube cores was designed and prepared. The N-rich carbon shell could strengthen the absorption capacity of CO2 and Li2CO3. The molybdenum carbide nanoparticles would improve the catalytic activity of both CO2 reduction and evolution reactions. The carbon nanotube cores would provide an efficient network for electron transportation. The synergistic effect of the cathode catalysts enhances the electrochemical performance of Li-CO2 batteries. A high cycling stability of more than 150 cycles at a current density of 250 mA g-1 with a cutoff capacity of 1000 mAh g-1 and a charge/discharge overpotential of less than 1.5 V is achieved. This work provides a feasible strategy for the design of a high-performance cathode catalyst for lithium-air batteries.

Highly Reversible Zinc Anode Enabled by a Cation-Exchange Coating with Zn-Ion Selective Channels.

Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted extensive attention due to their low cost and high safety. However, the critical issues of dendrite growth and side reactions on the Zn metal anode hinder the commercialization of ZIBs. Herein, we demonstrated that the formation of Zn4SO4(OH)6·5H2O byproducts is closely relevant to the direct contact between the Zn electrode and SO42-/H2O. On the basis of this finding, we developed a cation-exchange membrane of perfluorosulfonic acid (PFSA) coated on the Zn surface to regulate the Zn plating/stripping behavior. Importantly, the PFSA film with abundant sulfonic acid groups could simultaneously block the access of SO42- and H2O, accelerate the Zn2+ ion transport kinetics, and uniformize the electrical and Zn2+ ion concentration field on the Zn surface, thus achieving a highly reversible Zn plating/stripping process with corrosion-free and dendrite-free behavior. Consequently, the PFSA-modified Zn anode exhibits high reversibility with 99.5% Coulombic efficiency and excellent plating/stripping stability (over 1500 h), subsequently enabling a highly rechargeable Zn-MnO2 full cell. The strategy of the cation-exchange membrane proposed in this work provides a simple but efficient method for suppression of side reactions.

Toward Hydrogen-Free and Dendrite-Free Aqueous Zinc Batteries: Formation of Zincophilic Protective Layer on Zn Anodes.

Rechargeable aqueous Zn-ion batteries (ZIBs) are regarded as one of the most promising devices for the next-generation energy storage system. However, the uncontrolled dendrite growth on Zn metal anodes and the side hydrogen evolution reaction, which has not yet been well considered, hinder the practical application of these batteries. Herein, a uniform and robust metallic Sb protective layer is designed based on the theoretic calculation and decorated on Zn plate via in situ replacement reaction. Compared with the bare Zn plate, the as-prepared Zn@Sb electrode provides abundant zincophilic sites for Zn nucleation, and homogenizes the electric field around the Zn anode surface, both of which promote the uniform Zn deposition to achieve a dendrite-free morphology. Moreover, the Gibbs free energy (∆GH ) calculation and in situ characterization demonstrate that hydrogen evolution reaction can be effectively suppressed by the Sb layer. Consequently, Sb-modified Zn anodes exhibit an ultralow voltage hysteresis of 34 mV and achieve excellent cycling stability over 1000 h with hydrogen- and dendrite-free behaviors. This work provides a facile and effective strategy to suppress both hydrogen evolution reaction and dendrite growth.

Construction of Large Non-Localized π-Electron System for Enhanced Sodium-Ion Storage.

Organic electrode materials with the advantages of renewability, environment-friendliness, low cost, and high capacity have received widespread attention in recent years for sodium-ion batteries. However, small molecular organic materials suffer from issues such as low conductivity and the high dissolution rate in electrolytes. Herein, a phthalocyanine derivative (TPcDS) with a large non-localized π-electron system, obtained through thermodynamic polymerization of 4-aminophthalonitrile (AP) monomers, is designed to address these issues. According to the density function theory calculation, six sodium ions can be attracted by one polymer molecule, indicating a high theoretical capacity of 375 mA h g-1 . The TPcDS molecule realizes sodium storage through a non-localized π-electron system of phthalocyanine macrocycles. When employed as an anode material for sodium-ion batteries, the functional groups of phthalocyanine macrocycles, such as CN groups in TPcDS, experience obviously reversible structural variation upon discharge/charge. A high reversible capacity of 364 mAh g-1 is achieved at a current density of 0.05 A g-1 , and a charge capacity of as high as 246 mAh g-1 is still maintained after 500 cycles at 0.1 A g-1 . This work provides an effective strategy for the design and synthesis of new oligomeric organic electrode materials.

Enhanced Electrochemical Performance of Aprotic Li-CO2 Batteries with a Ruthenium-Complex-Based Mobile Catalyst.

Li-CO2 batteries are regarded as next-generation high-energy-density electrochemical devices. However, the greatest challenge arises from the formation of the discharge product, Li2 CO3 , which would accumulate and deactivate heterogenous catalysts to cause huge polarization. Herein, Ru(bpy)3 Cl2 was employed as a solution-phase catalyst for Li-CO2 batteries and proved to be the most effective one screened so far. Spectroscopy and electrochemical analyses elucidate that the RuII center could interact with both CO2 and amorphous Li2 C2 O4 intermediate, thus promoting electroreduction process and delaying carbonate transformation. As a result, the charge potential is reduced to 3.86 V and over 60 discharge/charge cycles are achieved with a fixed capacity of 1000 mAh g-1 at a current density of 300 mA g-1 . Our work provides a new avenue to improve the electrochemical performance of Li-CO2 batteries with efficient mobile catalysts.

Isolated copper-tin atomic interfaces tuning electrocatalytic CO2 conversion.

Direct experimental observations of the interface structure can provide vital insights into heterogeneous catalysis. Examples of interface design based on single atom and surface science are, however, extremely rare. Here, we report Cu-Sn single-atom surface alloys, where isolated Sn sites with high surface densities (up to 8%) are anchored on the Cu host, for efficient electrocatalytic CO2 reduction. The unique geometric and electronic structure of the Cu-Sn surface alloys (Cu97Sn3 and Cu99Sn1) enables distinct catalytic selectivity from pure Cu100 and Cu70Sn30 bulk alloy. The Cu97Sn3 catalyst achieves a CO Faradaic efficiency of 98% at a tiny overpotential of 30 mV in an alkaline flow cell, where a high CO current density of 100 mA cm-2 is obtained at an overpotential of 340 mV. Density functional theory simulation reveals that it is not only the elemental composition that dictates the electrocatalytic reactivity of Cu-Sn alloys; the local coordination environment of atomically dispersed, isolated Cu-Sn bonding plays the most critical role.

Phosphazene-derived stable and robust artificial SEI for protecting lithium anodes of Li-O2 batteries.

A stable artificial solid electrolyte interphase (ASEI) containing phosphazene and perfluoroalkoxy groups was designed to protect Li anodes. The ASEI with high ionic conductivity and mechanical robustness successfully suppressed the growth of Li dendrites, significantly enhancing the electrochemical performance of the Li-O2 batteries.

Multistaged discharge constructing heterostructure with enhanced solid-solution behavior for long-life lithium-oxygen batteries.

Inferior charge transport in insulating and bulk discharge products is one of the main factors resulting in poor cycling stability of lithium-oxygen batteries with high overpotential and large capacity decay. Here we report a two-step oxygen reduction approach by pre-depositing a potassium carbonate layer on the cathode surface in a potassium-oxygen battery to direct the growth of defective film-like discharge products in the successive cycling of lithium-oxygen batteries. The formation of defective film with improved charge transport and large contact area with a catalyst plays a critical role in the facile decomposition of discharge products and the sustained stability of the battery. Multistaged discharge constructing lithium peroxide-based heterostructure with band discontinuities and a relatively low lithium diffusion barrier may be responsible for the growth of defective film-like discharge products. This strategy offers a promising route for future development of cathode catalysts that can be used to extend the cycling life of lithium-oxygen batteries.

Core-shell anatase anode materials for sodium-ion batteries: the impact of oxygen vacancies and nitrogen-doped carbon coating.

In this work, the impact of oxygen vacancies and nitrogen-doped carbon coating on the sodium-ion storage properties of anatase TiO2 has been demonstrated. Oxygen vacancies and nitrogen-doped carbon coating were introduced simultaneously by the calcination of core-shell structured TiO2 spheres in a reducing atmosphere. Compared to the anatase TiO2 with and without oxygen vacancies, TiO2-x@NC exhibits much better electrochemical performance in the storage of sodium ions. A high reversible capacity of 245.6 mA h g-1 is maintained at 0.1 A g-1 after 200 cycles, and a high specific capacity of 155.6 mA h g-1 is achieved at a high rate of 5.0 A g-1. The significantly improved electrochemical performance of the core-shell structured anatase TiO2 spheres is attributed to the synergistic effect of the oxygen vacancies in the anatase lattice and surface nitrogen-doped carbon coating. This work provides an efficient strategy for improving the electrochemical performance of metal-oxide-based electrode materials for sodium-ion batteries.

Isolated Diatomic Ni-Fe Metal-Nitrogen Sites for Synergistic Electroreduction of CO2.

Polynary single-atom structures can combine the advantages of homogeneous and heterogeneous catalysts while providing synergistic functions based on different molecules and their interfaces. However, the fabrication and identification of such an active-site prototype remain elusive. Here we report isolated diatomic Ni-Fe sites anchored on nitrogenated carbon as an efficient electrocatalyst for CO2 reduction. The catalyst exhibits high selectivity with CO Faradaic efficiency above 90 % over a wide potential range from -0.5 to -0.9 V (98 % at -0.7 V), and robust durability, retaining 99 % of its initial selectivity after 30 hours of electrolysis. Density functional theory studies reveal that the neighboring Ni-Fe centers not only function in synergy to decrease the reaction barrier for the formation of COOH* and desorption of CO, but also undergo distinct structural evolution into a CO-adsorbed moiety upon CO2 uptake.

Neuron-Inspired Design of High-Performance Electrode Materials for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are generally considered as promising cheap alternatives of lithium-ion batteries for stationary renewable energy storage and have received increasing attention in recent years. The exploration of anode materials with efficient electron transportation is essential for improving the performance of SIBs. Inspired by the signal transfer mode of a neuron, we designed a composite by stringing MoS2 nanoflower (soma) with multiwall carbon nanotubes (MWCNTs) (axons). High-resolution TEM observation reveals a lattice matching growth mechanism of MoS2 nanosheets on the interface of MWCNTs and the lattice expansion of the (002) plane of MoS2. The lattice matching among the MoS2 nanosheet and MWCNT could facilitate electron transfer and structure maintenance upon cycling. The expanded distance of the (002) plane of MoS2 would also promote the sodium-ion intercalation/deintercalation kinetics of the composite. Benefiting from the structural features, when used as an anode material for SIBs, the composite exhibits excellent electrochemical performance, including high specific capacity, excellent cycle stability, and superior rate capabilities. A stable capacity of 527.7 mAh g-1 can be achieved after 110 cycles at a current density of 100 mA g-1. The neuron-inspired design proposed is a promising and efficient strategy for the development of electrode materials for SIBs with high mass transport kinetics and structural stability.

Top-down fabrication of hierarchical nanocubes on nanosheets composite for high-rate lithium storage.

A top-down method was developed to synthesize hierarchical composites consisting of NiCo2O4 nanocubes and graphene nanosheets through the electrostatic interaction of negatively charged graphene oxide nanosheets and positively charged NiCo2O4 spheres. Employed as anode materials for lithium-ion batteries, the hierarchical composites exhibit remarkably high electrochemical performance, including large reversible capacity, superior rate capability, and excellent cycling performance. Large reversible capacities of 1024 and 648 mA h g-1 are maintained at a current density of 500 and 3000 mA g-1, respectively, for over 200 cycles. The excellent electrochemical performance of the composite is attributed to the synergistic effect of the hierarchical structure, the well dispersed NiCo2O4 nanocubes and the uniform graphene coating. This work provides an effective and promising strategy for the rational structural design of the metal oxide electrode material.

Non-Conjugated Dicarboxylate Anode Materials for Electrochemical Cells.

Classical organic anode materials for Na-ion batteries are mostly based on conjugated carboxylate compounds, which can stabilize added electrons by the double-bond reformation mechanism. Now, 1,4-cyclohexanedicarboxylic acid (C8 H12 O4 , CHDA) with a non-conjugated ring (-C6 H10 -) connected with carboxylates is shown to undergo electrochemical reactions with two Na ions, delivering a high charge specific capacity of 284 mA h g-1 (249 mA h g-1 after 100 cycles), and good rate performance. First-principles calculations indicate that hydrogen-transfer-mediated orbital conversion from antibonding π* to bonding σ stabilize two added electrons, and reactive intermediate with unpaired electron is suppressed by localization of σ-bonds and steric hindrance. An advantage of CHDA as an anode material is good reversibility and relatively constant voltage. A large variety of organic non-conjugated compounds are predicted to be promising anode materials for sodium-ion batteries.

Strategies toward High-Performance Cathode Materials for Lithium-Oxygen Batteries.

Rechargeable aprotic lithium (Li)-O2 batteries with high theoretical energy densities are regarded as promising next-generation energy storage devices and have attracted considerable interest recently. However, these batteries still suffer from many critical issues, such as low capacity, poor cycle life, and low round-trip efficiency, rendering the practical application of these batteries rather sluggish. Cathode catalysts with high oxygen reduction reaction (ORR) and evolution reaction activities are of particular importance for addressing these issues and consequently promoting the application of Li-O2 batteries. Thus, the rational design and preparation of the catalysts with high ORR activity, good electronic conductivity, and decent chemical/electrochemical stability are still challenging. In this Review, the strategies are outlined including the rational selection of catalytic species, the introduction of a 3D porous structure, the formation of functional composites, and the heteroatom doping which succeeded in the design of high-performance cathode catalysts for stable Li-O2 batteries. Perspectives on enhancing the overall electrochemical performance of Li-O2 batteries based on the optimization of the properties and reliability of each part of the battery are also made. This Review sheds some new light on the design of highly active cathode catalysts and the development of high-performance lithium-O2 batteries.