FeP@C Nanotube Arrays Grown on Carbon Fabric as a Low Potential and Freestanding Anode for High-Performance Li-Ion Batteries

Electrochemically Dealloying Engineering toward Integrated Monolithic Electrodes with Superior Electrochemical Li-Storage Properties

Integrated monolithic electrodes (IMEs) free of inactive components demonstrate great potential in boosting energy-power densities and cycling life of lithium-ion batteries. However, their practical applications are significantly limited by low active substance loading (< 4.0 mg cm-2 and 1.0 g cm-3), complicated manufacturing process, and high fabrication cost. Herein, employing industrial Cu-Mn alloy foil as a precursor, a simple neutral salt solution-mediated electrochemical dealloying strategy is proposed to address such problems. The resultant Cu-Mn IMEs achieve not only a significantly larger active material loading due to the in situ generated Cu2O and MnOx (ca. 16.0 mg cm-2 and 1.78 g cm-3), simultaneously fast transport of ions and electrons due to the well-formed nanoporous structure and built-in Cu current collector, but also high structural stability due to the interconnected ligaments and suitable free space to relieve the volume expansion upon lithiation. As a result, they demonstrate remarkable performances including large specific capacities (> 5.7 mAh cm-2), remarkable pseudocapacitive effect despite the battery-type constitutes, long cycling life, and good working condition in a lithium-ion full cell. This study sheds new light on the further development of IMEs, enriches the existing dealloying techniques, and builds a bridge between the two.

A Metal-Organic Framework-Derived Strategy for Constructing Synergistic N-Doped Carbon-Encapsulated NiCoP@N-C-Based Anodes toward High-Efficient Lithium Storage

Transition metal phosphides (TMPs) have been regarded as the prospective anodes for lithium-ion batteries (LIBs). However, their poor intrinsic conductivity and inevitable large volume variation result in sluggish redox kinetics and the collapse of electrode structure during cycling, which substantially hinders their practical use. Herein, an effective composite electrodes design strategy of "assembly and phosphorization" is proposed to construct synergistic N-doped carbon-encapsulated NiCoP@N-C-based composites, employing a metal-organic frameworks (MOFs) as sacrificial hosts. Serving as the anodes for LIBs, one representative P-NCP-NC-600 electrode exhibits high reversible capacity (858.5 mAh g-1 , 120 cycles at 0.1 A g-1 ) and superior long-cycle stability (608.7 mAh g-1 , 500 cycles at 1 A g-1 ). The impressive performances are credited to the synergistic effect between its unique composite structure, electronic properties and ideal composition, which achieve plentiful lithium storage sites and reinforce the structural architecture. By accompanying experimental investigations with theoretical calculations, a deep understanding in the lithium storage mechanism is achieved. Furthermore, it is revealed that a more ideal synergistic effect between NiCoP components and N-doped carbon frameworks is fundamentally responsible for the realization of superb lithium storage properties. This strategy proposes certain instructive significance toward designable high-performance TMP-based anodes for high-energy density LIBs.

A densely packed air-stable free-standing film with FeP nanoparticles@C@P-doped reduced graphene oxide for sodium-ion batteries

Developing a facile strategy which enhances the structural stability and air/moisture stability of transition metal phosphides for practical applications is important but challenging. Herein, we designed a densely packed free-standing film consisting of carbon-coated FeP nanoparticles anchored on P-doped graphene (FeP@C@PG film) through solventless thermal decomposition and the roll-press method. Phytic acid serves a multifunctional role as both a phosphorus source to prepare ultrafine FeP nanoparticles and a protective layer to improve air stability along with hydrophobic graphene and maximize the utilization of phosphide. This structure can enhance electron/ion transport kinetics, allowing for full utilization of active materials, and buffer large volume expansions while preventing pulverization/aggregation during cycling. Noticeably, the densely packed structure can greatly enhance oxidation resistance by effectively blocking the penetration of air/moisture. Therefore, the FeP@C@PG film delivers a stable reversible capacity of 536.6 mA h g-1 after 1000 cycles at 1 A g-1 with good capacity retention, an excellent rate capability of 440.7 mA h g-1 at 5 A g-1, and excellent oxidation stability at 80 °C in air. Furthermore, a pouch-type full-cell exhibits excellent rate/cycling performance and bendability. This study provides a new direction for the rational design and practical applications of advanced P-based materials used in alkali metal-ion batteries.

Homogeneous regulation of arranged polymorphic manganese dioxide nanocrystals as cathode materials for high-performance zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have emerged as attractive energy storage devices by virtue of their low cost, high safety and eco-friendliness. However, zinc-ion cathodes are bottlenecked by their vulnerable crystal structures in the process of zinc embedding and significant capacity fading during long-term cycling. Herein, we report the rational and homogeneous regulation of polycrystalline manganese dioxide (MnO₂) nanocrystals as zinc cathodes via a surfactant template-assisted strategy. Benefiting from the homogeneous regulation, MnO₂ nanocrystals with an ordered crystal arrangement, including nanorod-like polyvinylpyrrolidone-manganese dioxide (PVP-MnO₂), nanowire-like sodium dodecyl benzene sulfonate-manganese dioxide and nanodot-like cetyltrimethylammonium bromide-manganese dioxide, are obtained. Among these, the nanorod-like PVP-MnO₂ nanocrystals exhibit stable long-life cycling of 210 mAh g^-1 over 180 cycles at a high rate of 0.3 A g^-1 and with a high capacity retention of 84% over 850 cycles at a high rate of 1 A g^-1. The good performance of this cathode significantly results from the facile charge and mass transfer at the interface between the electrode and electrolyte, featuring the crystal stability and uniform morphology of the arranged MnO₂ nanocrystals. This work provides crucial insights into the development of advanced MnO₂ cathodes for low-cost and high-performance rechargeable aqueous zinc-ion batteries.

Single-Phase Ternary Compounds with a Disordered Lattice and Liquid Metal Phase for High-Performance Li-Ion Battery Anodes

Si is considered as the promising anode materials for lithium-ion batteries (LIBs) owing to their high capacities of 4200 mAh g-1 and natural abundancy. However, severe electrode pulverization and poor electronic and Li-ionic conductivities hinder their practical applications. To resolve the afore-mentioned problems, we first demonstrate a cation-mixed disordered lattice and unique Li storage mechanism of single-phase ternary GaSiP2 compound, where the liquid metallic Ga and highly reactive P are incorporated into Si through a ball milling method. As confirmed by experimental and theoretical analyses, the introduced Ga and P enables to achieve the stronger resistance against volume variation and metallic conductivity, respectively, while the cation-mixed lattice provides the faster Li-ionic diffusion capability than those of the parent GaP and Si phases. The resulting GaSiP2 electrodes delivered the high specific capacity of 1615 mAh g-1 and high initial Coulombic efficiency of 91%, while the graphite-modified GaSiP2 (GaSiP2@C) achieved 83% of capacity retention after 900 cycles and high-rate capacity of 800 at 10,000 mA g-1. Furthermore, the LiNi0.8Co0.1Mn0.1O2//GaSiP2@C full cells achieved the high specific capacity of 1049 mAh g-1 after 100 cycles, paving a way for the rational design of high-performance LIB anode materials.

Hierarchical manganese valence gradient MnO2via phosphorus doping for cathode materials with improved stability

The search for a method for enhancing the electrochemical performance of manganese dioxide is still a challenge. Herein, we report a rod-like P-MnO_x cathode material with a hierarchical manganese gradient valence through the phosphatization process. For the incorporation of P, Mn₃O₄ was formed on the surface of MnO₂ and exhibited a gradient valence structure, while the oxygen defect concentration in P-MnO_x increased. The unique structure was verified via XRD, TEM and XPS. As the cathode material for a supercapacitor, the specific capacitance of P-MnO_x was 126.3 F g^-1, which was four times that of MnO₂. The assembling of the coin cells of aqueous ZIBs with P-MnO_x also showed good rate performance. The electrochemical performance of the synthesised P-MnO_x cathode was enhanced for the synergistic effect of improved conductivity and structural stability.

In Situ Growth of CoP Nanosheet Arrays on Carbon Cloth as Binder-Free Electrode for High-Performance Flexible Lithium-Ion Batteries

Cobalt phosphide (CoP) is considered as one of the most promising candidates for anode in lithium-ion batteries (LIBs) owing to its low-cost, abundant availability, and high theoretical capacity. However, problems of low conductivity, heavy aggregation, and volume change of CoP, hinder its practical applicability. In this study, a binder-free electrode is successfully prepared by growing CoP nanosheets arrays directly on a carbon cloth (CC) via a facile one-step electrodeposition followed by an in situ phosphorization strategy. The CoP@CC anode exhibits good interfacial bonding between the CoP and CC, which can improve the conductivity of the integrated electrode. More importantly, the 3D network structure composed of CoP nanosheets and CC provides sufficient space to alleviate the volume expansion of CoP and shorten the electron/ion transport paths. Moreover, the support of CC effectively prevents the agglomeration of CoP. Based on these advantages, when CoP@CC is paired with the NCM523 cathode, the full cell delivers a high discharge capacity 919.6 mAh g^-1 (2.1 mAh cm^-2 ) after 200 cycles at 0.5 A g^-1 . The feasibility and safety of producing pouch cells are also explored, which show good flexibility and safety despite rigorous strikes (mechanical damage and severe deformations), implying a great potential for practical applications.

Realizing the high energy density and flexibility of a fabric electrode through hierarchical structure design

The exploration of high-energy density flexible electrodes through reasonable structural design is the key to realizing the overall portability and wearability of devices. Herein, a free-standing hybrid nanofabric with superior mechanical and electrochemical stabilities is reported for flexible lithium-ion batteries (LIBs). The hybrid nanofabric is prepared by electrospinning and carbonization, during which the self-cyclization of polyacrylonitrile (PAN) is hindered by its reaction with melamine, resulting in a highly disordered and expanded turbostratic carbon structure with nickel metal thiophosphate (NiPS₃) nanosheets embedded in it. The coordinated movement of the electrospun-derived 1D nanofiber, the super toughness of the hard carbon structure and the interlayer slipping of NiPS₃ endow the hybrid nanofabric with excellent tolerance to large-scale deformation. It can be folded three times in half and quickly return to its original state. When used as the anode for LIBs, no additional binder, conducting agent and current collector are needed. The free-standing anode not only shows excellent cycling (797.5 mA h g^-1 after 1000 cycles at 1 A g^-1) and rate (more than 56% capacity retained from 0.1 to 2 A g^-1) performances, but also maintains its original electrochemical properties after being folded 300 times at 120°, 180° and 360°. This work provides a synergistic strategy to simultaneously enhance the energy density and flexibility of a fabric electrode, paving the way for the application of advanced flexible energy storage systems.

Self-Sacrifice Template Construction of Uniform Yolk-Shell ZnS@C for Superior Alkali-Ion Storage

Secondary batteries have been widespread in the daily life causing an ever-growing demand for long-cycle lifespan and high-energy alkali-ion batteries. As an essential constituent part, electrode materials with superior electrochemical properties play a vital role in the battery systems. Here, an outstanding electrode of yolk-shell ZnS@C nanorods is developed, introducing considerable void space via a self-sacrificial template method. Such carbon encapsulated nanorods moderate integral electronic conductivity, thus ensuring rapid alkali-ions/electrons transporting. Furthermore, the porous structure of these nanorods endows enough void space to mitigate volume stress caused by the insertion/extraction of alkali-ions. Due to the unique structure, these yolk-shell ZnS@C nanorods achieve superior rate performance and cycling performance (740 mAh g^-1 at 1.0 A g^-1 after 540 cycles) for lithium-ion batteries. As a potassium-ion batteries anode, they achieve an ultra-long lifespan delivering 211.1 mAh g^-1 at 1.0 A g^-1 after 5700 cycles. The kinetic analysis reveals that these ZnS@C nanorods with considerable pseudocapacitive contribution benefit the fast lithiation/delithiation. Detailed transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses indicate that such yolk-shell ZnS@C anode is a typical reversible conversion reaction mechanism accomplished by alloying processes. This rational design strategy opens a window for the development of superior energy storage materials.

An expanded sandwich-like heterostructure with thin FeP nanosheets@graphene via charge-driven self-assembly as high-performance anodes for sodium ion battery

In this work, we simply fabricate a novel expanded sandwich-like heterostructure of iron-phosphide nanosheets in between reduced graphene oxide (expanded FeP NSs@rGO) with a high ratio of FeP/Fe-PO_x and an expanded structure via a charge-driven self-assembly method by exploiting polystyrene beads (PSBs) as a sacrificial template. In such a design, even after the decomposition of PSBs during the annealing process, the PSBs successfully provide ample space between the nanosheets, enabling a structure with long-term stability and high ionic conductivity. Importantly, the PSBs are decomposed and simultaneously reacted with oxidized iron-phosphide (Fe-PO_x) on the surface of the nanosheets to reduce into FeP. As a result, the expanded FeP NSs@rGO results in a high content of FeP (52.3%) and remarkable electrochemical performances when it is used for sodium-ion battery anodes. The expanded FeP NSs@rGO exhibits a high capacity of 916.1 mA h g^-1 at 0.1 A g^-1, a superior rate capability of 440.9 mA h g^-1 at 5 A g^-1, and a long-term cycling stability of 85.4% capacity retention after 1000 cycles at 1 A g^-1. In addition, the full cell also exhibits excellent capacity, rate capability, and cycling stability. This study clearly demonstrates that an increase in FeP proportion is directly related to an increase in capacity. This facile method of synthesizing rationally designed heterostructures is expected to provide a novel strategy to create nanostructures for advanced energy storage applications.

Direct Double Coating of Carbon and Nitrogen on Fluoride-Doped Li4Ti5O12 as an Anode for Lithium-Ion Batteries

Graphite as a commercial anode for lithium-ion batteries has significant safety concerns owing to lithium dendrite growth at low operating voltages. Li4Ti5O12 is a potential candidate to replace graphite as the next-generation anode of lithium-ion batteries. In this work, fluoride-doped Li4Ti5O12 was successfully synthesized with a direct double coating of carbon and nitrogen using a solid-state method followed by the pyrolysis process of polyaniline. X-ray diffraction (XRD) results show that the addition of fluoride is successfully doped to the spinel-type structure of Li4Ti5O12 without any impurities being detected. The carbon and nitrogen coating are distributed on the surface of Li4Ti5O12 particles, as shown in the Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy (SEM-EDS) image. The Transmission Electron Microscopy (TEM) image shows a thin layer of carbon coating on the Li4Ti5O12 surface. The fluoride-doped Li4Ti5O12 has the highest specific discharge capacity of 165.38 mAh g−1 at 0.5 C and capacity fading of 93.51% after 150 cycles compared to other samples, indicating improved electrochemical performance. This is attributed to the synergy between the appropriate amount of carbon and nitrogen coating, which induced a high mobility of electrons and larger crystallite size due to the insertion of fluoride to the spinel-type structure of Li4Ti5O12, enhancing lithium-ion transfer during the insertion/extraction process.

A Coral-Like FeP@NC Anode with Increasing Cycle Capacity for Sodium-Ion and Lithium-Ion Batteries Induced by Particle Refinement

We present a coral-like FeP composite with FeP nanoparticles anchored and dispersed on a nitrogen-doped 3D carbon framework (FeP@NC). Due to the highly continuous N-doped carbon framework and a spring-buffering graphitized carbon layer around the FeP nanoparticle, a sodium-ion battery with the FeP@NC composite exhibits an ultra-stable cycling performance at 10 A g^-1 with a capacity retention of 82.0 % in 10 000 cycles. Also, particle refinement leads to a capacity increase during cycling. The FeP nanoparticles go through a refining-recombination process during the first cycle and present a global refining trend after dozens of cycles, which results in a gradually increase in graphitization degree and interface magnetization, and further provides more active sites for Na⁺ storage and contributes to a rising capacity with cycling. The capacity ascending phenomenon can also extend to lithium-ion batteries.

High-Rate Aqueous Aluminum-Ion Batteries Enabled by Confined Iodine Conversion Chemistry

Most reported cathode materials for rechargeable aqueous Al metal batteries are based on an intercalative-type chemistry mechanism. Herein, iodine embedded in MOF-derived N-doped microporous carbon polyhedrons (I₂ @ZIF-8-C) is proposed to be a conversion-type cathode material for aqueous aluminum-ion batteries based on "water-in-salt" electrolytes. Compared with the conventional Al-I₂ battery using ionic liquid electrolyte, the proposed aqueous Al-I₂ battery delivers much enhanced electrochemical performance in terms of specific capacity and voltage plateaus. Benefitting from the confined liquid-solid conversion of iodine in hierarchical N-doped microporous carbon polyhedrons and enhanced reaction kinetics of aqueous electrolytes, the I₂ @ZIF-8-C electrode delivers high reversibility, superior specific capacity (≈219.8 mAh g^-1 at 2 A g^-1 ), and high rate performance (≈102.6 mAh g^-1 at 8 A g^-1 ). The reversible reaction between I₂ and I^- , with I₃ ^- and I₅ ^- as intermediates, is confirmed via ex situ Raman spectra and X-ray photoelectron spectroscopy. Furthermore, solid-state hydrogel electrolyte is employed to fabricate a flexible Al-I₂ battery, which shows performance comparable to batteries using liquid electrolyte and can be integrated to power wearable devices as a reliable energy supply.

Iron Phosphide Confined in Carbon Nanofibers as a Free-Standing Flexible Anode for High-Performance Lithium-Ion Batteries

Iron phosphide with high specific capacity has emerged as an appealing candidate for next-generation lithium-ion battery anodes. However, iron phosphide could undergo conversion reactions and generally suffer from a rapid capacity degradation upon cycling due to its structure pulverization. Chemomechanical breakdown of iron phosphide due to its rigidity has been a challenge to fully realizing its electrochemical performance. To address this challenge, we report here on an enticing opportunity: a flexible, free-standing iron phosphide anode with Fe₂P nanoparticles confined in carbon nanofibers may overcome existing challenges. For the synthesis, we introduce a facile electrospinning strategy that enables in situ formation of Fe₂P within a carbon matrix. Such a carbon matrix can effectively minimize the structure change of Fe₂P particles and protect them from pulverization, allowing the electrodes to retain a free-standing structure after long-term cycling. The produced electrodes showed excellent electrochemical performance in lithium-ion half and full cells, as well as in flexible pouch cells. These results demonstrate the successful development of iron phosphide materials toward high capacity, light weight, and flexible energy storage.

Multifunctional Metal Phosphides as Superior Host Materials for Advanced Lithium-Sulfur Batteries

For the past few years, a new generation of energy storage systems with large theoretical specific capacity has been urgently needed because of the rapid development of society. Lithium-sulfur (Li-S) batteries are regarded as one of the most promising candidates for novel battery systems, since their resurgence at the end of the 20th century Li-S batteries have attracted ever more attention, attributed to their notably high theoretical energy density of 2600 W h kg^-1 , which is almost five times larger than that of commercial lithium-ion batteries (LIBs). One of the determining factors in Li-S batteries is how to design/prepare the sulfur cathode. For the sulfur host, the major technical challenge is avoiding the shuttling effect that is caused by soluble polysulfides during the reaction. In past decades, though the sulfur cathode has developed greatly, there are still some enormous challenges to be conquered, such as low utilization of S, rapid decay of capacity, and poor cycle life. This article spotlights the recent progress and foremost findings in improving the performance of Li-S batteries by employing multifunctional metal phosphides as host materials. The current state of development of the sulfur electrode of Li-S batteries is summarized by emphasizing the relationship between the essential properties of metal phosphide-based hybrid nanomaterials, the chemical reaction with lithium polysulfides and the latter's influence on electrochemical performance. Finally, trends in the development and practical application of Li-S batteries are also pointed out.

Nanostructured metal phosphides: from controllable synthesis to sustainable catalysis

Metal phosphides (MPs) with unique and desirable physicochemical properties provide promising potential in practical applications, such as the catalysis, gas/humidity sensor, environmental remediation, and energy storage fields, especially for transition metal phosphides (TMPs) and MPs consisting of group IIIA and IVA metal elements. Most studies, however, on the synthesis of MP nanomaterials still face intractable challenges, encompassing the need for a more thorough understanding of the growth mechanism, strategies for large-scale synthesis of targeted high-quality MPs, and practical achievement of functional applications. This review aims at providing a comprehensive update on the controllable synthetic strategies for MPs from various metal sources. Additionally, different passivation strategies for engineering the structural and electronic properties of MP nanostructures are scrutinized. Then, we showcase the implementable applications of MP-based materials in emerging sustainable catalytic fields including electrocatalysis, photocatalysis, mild thermocatalysis, and related hybrid systems. Finally, we offer a rational perspective on future opportunities and remaining challenges for the development of MPs in the materials science and sustainable catalysis fields.

Improved performances of lithium-ion batteries by conductive polymer modified copper current collector

Copper current collector coated with conductive polymer by electrochemical polymerization improves the capacity and long-life of LIBs.

A Robust Strategy for Engineering Fe7S8/C Hybrid Nanocages Reinforced by Defect-Rich MoS2 Nanosheets for Superior Potassium-Ion Storage

Metal sulfides have attracted tremendous research interest for developing high-performance electrodes for potassium-ion batteries (PIBs) for their high theoretical capacities. Nevertheless, the practical application of metal sulfides in PIBs is still unaddressed due to their intrinsic shortcomings of low conductivity and severe volume changes during the potassiation/depotassiation process. Herein, robust Fe₇S₈/C hybrid nanocages reinforced by defect-rich MoS₂ nanosheets (Fe₇S₈/C@d-MoS₂) were designed, which possess abundant multichannel and active sites for potassium-ion transportation and storage. Kinetic analysis and theoretical calculation verify that the introduction of defect-rich MoS₂ nanosheets dramatically promotes the potassium-ion diffusion coefficient. The ex-situ measurements revealed the potassium-ion storage mechanism in the Fe₇S₈/C@d-MoS₂ composite. Benefitting from the tailored structural design, the Fe₇S₈/C@d-MoS₂ hybrid nanocages show high reversible capacity, exceptional rate property, and superior cyclability.

Scalable One-Pot Synthesis of Hierarchical Bi@C Bulk with Superior Lithium-Ion Storage Performances

Lithium-ion batteries (LIBs), the most successful commercial energy storage devices, are now widespread in our daily life. However, the lack of appropriate electrode materials with long lifespan and superior rate capability is the urgent bottleneck for the development of high-performance LIBs. Herein, a hierarchical Bi@C bulk is developed via a scalable pyrolysis method. Due to the ultrafine size of Bi nanoparticles and in situ generated porous carbon framework, this Bi@C anode evidently facilitates the diffusion of Li⁺/electron, availably inhibits the agglomeration of active nano-Bi, and effectively mitigates the volume fluctuation. This hierarchical Bi@C bulk exhibits stable cycling performance for both LIBs (256 mAh g^-1 at 1.0 A g^-1 over 1400 cycles) and potassium-ion batteries (271 mAh g^-1 at 0.1 A g^-1 for 200 cycles). More importantly, when coupled with a commercial LiCoO₂ cathode, the assembled LiCoO₂//Bi@C cells provide an output voltage of 2.9 V and retain a capacity of 202 mAh g^-1 at 0.15 A g^-1. Moreover, kinetic analysis and in situ X-ray diffraction characterization reveal that the Bi@C anode displays a dominated pseudocapacitance behavior and a typical alloying storage mechanism during the cycling process.

Efficient Laser-Induced Construction of Oxygen-Vacancy Abundant Nano-ZnCo2 O4 /Porous Reduced Graphene Oxide Hybrids toward Exceptional Capacitive Lithium Storage

Recently, binary ZnCo₂ O₄ has drawn enormous attention for lithium-ion batteries (LIBs) as attractive anode owing to its large theoretical capacity and good environmental benignity. However, the modest electrical conductivity and serious volumetric effect/particle agglomeration over cycling hinder its extensive applications. To address the concerns, herein, a rapid laser-irradiation methodology is firstly devised toward efficient synthesis of oxygen-vacancy abundant nano-ZnCo₂ O₄ /porous reduced graphene oxide (rGO) hybrids as anodes for LIBs. The synergistic contributions from nano-dimensional ZnCo₂ O₄ with rich oxygen vacancies and flexible rGO guarantee abundant active sites, fast electron/ion transport, and robust structural stability, and inhibit the agglomeration of nanoscale ZnCo₂ O₄ , favoring for superb electrochemical lithium-storage performance. More encouragingly, the optimal L-ZCO@rGO-30 anode exhibits a large reversible capacity of ≈1053 mAh g^-1 at 0.05 A g^-1 , excellent cycling stability (≈746 mAh g^-1 at 1.0 A g^-1 after 250 cycles), and preeminent rate capability (≈686 mAh g^-1 at 3.2 A g^-1 ). Further kinetic analysis corroborates that the capacitive-controlled process dominates the involved electrochemical reactions of hybrid anodes. More significantly, this rational design holds the promise of being extended for smart fabrication of other oxygen-vacancy abundant metal oxide/porous rGO hybrids toward advanced LIBs and beyond.

Boosting Lithium Storage in Free-Standing Black Phosphorus Anode via Multifunction of Nanocellulose

Layer-structured black phosphorus (BP) demonstrating high specific capacity has been viewed as a very promising anode material for future high-energy-density Li-ion batteries (LIBs). However, its practical application is hindered by large volume change of BP and poor mechanical stability of BP anodes by traditional slurry casting technology. Here, a free-standing flexible anode composed of BP nanosheets and nanocellulose (NC) nanowires is fabricated via a facile vacuum-assisted filtration approach. The constructed free-standing BP@NC composite anode offers three-dimensional (3D) mixed-conducting network for Li⁺/e^- transports. The substrate of NC film has a certain flexibility up to 10.2% elongation that can restrain the volume change of BP and electrode during operation. In addition, molecular dynamic (MD) simulation and density function theory (DFT) show the greatly enhanced Li⁺ diffusion in BP@NC composite where the Li ions receive less repulsive force at the interface of BP interlayer and nanocellulose. Benefiting from above multifunction of nanocellulose, the BP@NC composite exhibits high capacities of 1020.1 mAh g^-1 at 0.1 A g^-1 after 230 cycles and 994.4 mAh g^-1 at 0.2 A g^-1 after 400 cycles, corresponding to high capacity retentions of 87.1% and 84.9%, respectively. Our results provide a low-cost and effective strategy to develop advanced electrodes for next-generation rechargeable batteries.

An intrinsically stretchable and compressible Zn–air battery

An intrinsically 300% stretchable and 85% compressible Zn–air rechargeable battery with good electrochemical performances was fabricated for the first time.

Rational design of Ni/Ni2P heterostructures encapsulated in 3D porous carbon networks for improved lithium storage

Nickel phosphides are considered to be a promising lithium storage host due to their high theoretical capacities. However, the volume change during the charge-discharge process and inherent poor reaction kinetics limit their electrochemical performance. To solve these problems, Ni/Ni₂P heterostructures encapsulated in 3D porous carbon networks are fabricated. The macro/micro-pores-rich carbon networks are in situ constructed via a freeze-drying method and subsequent pyrolysis route using NaCl as a template. In the following phosphorization process, Ni/Ni₂P nanoparticles are homogenously embedded in the carbon matrix. When used as anodes for lithium ion batteries, the Ni/Ni₂P/porous carbon networks deliver high discharge capacity, good cycling stability as well as good rate performance. It is believed that metallic Ni and porous carbon networks significantly improve the conductivity of electrodes. Moreover, the 3D conductive matrix can not only alleviate the volume change, but also prevent the aggregation and pulverization of Ni₂P nanoparticles during the charge-discharge process.

Defect Promoted Capacity and Durability of N-MnO2- x Branch Arrays via Low-Temperature NH3 Treatment for Advanced Aqueous Zinc Ion Batteries

Defect engineering (doping and vacancy) has emerged as a positive strategy to boost the intrinsic electrochemical reactivity and structural stability of MnO₂ -based cathodes of rechargeable aqueous zinc ion batteries (RAZIBs). Currently, there is no report on the nonmetal element doped MnO₂ cathode with concomitant oxygen vacancies, because of its low thermal stability with easy phase transformation from MnO₂ to Mn₃ O₄ (≥300 °C). Herein, for the first time, novel N-doped MnO_{2- x} (N-MnO_{2- x} ) branch arrays with abundant oxygen vacancies fabricated by a facile low-temperature (200 °C) NH₃ treatment technology are reported. Meanwhile, to further enhance the high-rate capability, highly conductive TiC/C nanorods are used as the core support for a N-MnO_{2- x} branch, forming high-quality N-MnO_{2- x} @TiC/C core/branch arrays. The introduced N dopants and oxygen vacancies in MnO₂ are demonstrated by synchrotron radiation technology. By virtue of an integrated conductive framework, enhanced electron density, and increased surface capacitive contribution, the designed N-MnO_{2- x} @TiC/C arrays are endowed with faster reaction kinetics, higher capacity (285 mAh g^-1 at 0.2 A g^-1 ) and better long-term cycles (85.7% retention after 1000 cycles at 1 A g^-1 ) than other MnO₂ -based counterparts (55.6%). The low-temperature defect engineering sheds light on construction of advanced cathodes for aqueous RAZIBs.

Three-Dimensional Hierarchical Flowerlike FeP Wrapped with N-Doped Carbon Possessing Improved Li+ Diffusion Kinetics and Cyclability for Lithium-Ion Batteries

Transition-metal phosphides have a potential application in lithium-ion batteries (LIBs) because of their high theoretical capacities and low cost; nevertheless, they possess dramatic volumetric variation during cycling associated with poor conductivity, limiting their practical applications. Here, a three-dimensional (3D) hierarchical flowerlike FeP coated with nitrogen-doped carbon layer (FeP@N,C hybrid) was constructed through a solvothermal method, followed by a phosphating approach under low temperature. N-doped carbon not only suppresses the volume fluctuation of FeP, but also promotes electron transfer, accompanied by catalyzing the decomposition of Li₃P to improve the reversibility of the FeP@N,C hybrid during cycling processes. In addition, a 3D flowerlike architecture assembled from porous nanosheets is also beneficial for shortening the migration path of ions as well as improving the contact area of electrode with electrolyte, which enhances the reaction kinetics and is proved by both experimental measurement of Li⁺ diffusion coefficient and resistivity, along with the calculation of density functional theory. Consequently, the 3D hierarchical flowerlike FeP@N,C hybrid performs excellent cyclic stability (569 mA h g^-1 at a current density of 500 mA g^-1 for the 300th cycle) and rate performance (331.94 mA h g^-1 at a high current density of 5 A g^-1) for LIBs. Based on above results, the fabrication strategy in this work could offer a thought to design other high-performance metal phosphide hybrids.

Facile Synthesis of Peapod-Like Cu3 Ge/Ge@C as a High-Capacity and Long-Life Anode for Li-Ion Batteries

As anode materials for high-performance Li-ion batteries, peapod-like Ge-based composites, including Ge, a Li-inactive conducting Cu₃ Ge, and a porous carbon matrix are synthesized simply by annealing CuGeO₃ @dopamine in a H₂ /Ar atmosphere. The introduction of the carbon layer and inactive alloying phase Cu₃ Ge not only enhances the electrical conductivity of the Ge anode, but also reduces the volume change of Ge during the cell cycle as a buffer. In particular, the anode of this peapod-like Cu₃ Ge/Ge@C shows an excellent long cycle life as well as outstanding capacity performance, with a discharge specific capacity up to 934 mA h g^-1 after 500 cycles.

Mechanistic Understanding of Metal Phosphide Host for Sulfur Cathode in High-Energy-Density Lithium-Sulfur Batteries

For solving the drawbacks of low conductivity and the shuttle effect in a sulfur cathode, various nonpolar carbon and polar metal compounds with strong chemical absorption ability are applied as sulfur host materials for lithium-sulfur (Li-S) batteries. Nevertheless, previous research simply attributed the performance improvement of sulfur cathodes to the chemical adsorption ability of polar metal compounds toward lithium polysulfides (LPS), while a deep understanding of the enhanced electrochemical performance in these various sulfur hosts, especially at the molecular levels, is still unclear. Herein, for a mechanistic understanding of superior metal phosphide host in Li-S battery chemistry, an integrated phosphide-based host of CF/FeP@C (carbon cloth with grown FeP@C nanotube arrays) is chosen as the model, and this binder-free cathode can exclude interference from the binder and conductive additives. With a systematic electrochemical investigation of the loading sulfur in such oxide- and phosphide-based hosts (CF/Fe₃O₄@C and CF/FeP@C), it is found that CF/FeP@C@S shows much superior Li-S performances. The greatly enhanced performance of CF/FeP@C@S suggests that FeP can well suppress the shuttle effect of LPS and accelerate their transformation during the charge-discharge process. The first-principles calculations reveal the performance variations of Fe₃O₄ and FeP in Li-S batteries mainly because the shifts of the p band of the FeP could accelerate the interfacial electronics transfer dynamics by increasing the electronic concentration in the Fermi level of adsorbed Li₂S₄. The current work sheds light on the promising design of superior Li-S batteries from both theoretical and experimental aspects.

MoP hollow nanospheres encapsulated in 3D reduced graphene oxide networks as high rate and ultralong cycle performance anodes for sodium-ion batteries

Molybdenum phosphide (MoP), regarded as a promising anode material for sodium-ion batteries due to its superior conductivity and high theoretical specific capacity, still suffers from rapid capacity decay because of a large volume change and weak diffusion kinetics. Hollow nano-structures will be an effective solution to alleviate structural strain and improve cycling stability. Yet the preparation of MoP needs a high temperature phosphorization procedure which would cause agglomeration and structure collapse, making it difficult to achieve hollow nano-structures. Herein, caged by 3D graphene networks, MoP hollow nanospheres encapsulated in 3D reduced graphene oxide networks (H-MoP@rGO) were prepared successfully, and benefiting from the merits of the hollow nano-structure and flexibility of rGO, H-MoP@rGO demonstrates a superior cycle performance of 353.8 mA h g-1 at 1 A g-1 after 600 cycles and an extraordinary rate performance of 183.4 mA h g-1 at an ultrahigh current density of 10 A g-1 even after 3000 cycles.

An FeP@C nanoarray vertically grown on graphene nanosheets: an ultrastable Li-ion battery anode with pseudocapacitance-boosted electrochemical kinetics

In order to develop promising anode materials for lithium-ion batteries (LIBs), a unique nanocomposite abbreviated as G⊥FP@C-NA, in which a carbon-coated FeP nanorod array (FP@C-NA) is vertically grown on a conductive reduced graphene oxide (G) network, has been successfully prepared via a scalable strategy. Benefiting from the distinctive structure, G⊥FP@C-NA exhibits much improved conductivity, structural stability and pseudocapacitance-boosted ultrafast electrochemical kinetics for Li storage. As a result, the G⊥FP@C-NA delivers a high Li-storage capacity (1106 mA h g-1 at 50 mA g-1), outstanding rate capability (565 mA h g-1 at 5000 mA g-1) and long-term cycling stability (1009 mA h g-1 at 500 mA g-1 after 500 cycles and 310 mA h g-1 at 2000 mA g-1 after 2000 cycles) when used as an anode material for LIBs. As expected, this kind of nanoarray structure is attractive and can also be extended to other electrode materials for various energy storage systems.

Phytic Acid-Assisted Formation of Hierarchical Porous CoP/C Nanoboxes for Enhanced Lithium Storage and Hydrogen Generation

Application of transition metal phosphides (TMPs) for electrochemical energy conversion and storage has great potential to alleviate the energy crisis. Although there are many methods to get TMPs, it is still immensely challenging to fabricate hierarchical porous TMPs with superior electrochemical performances by a simple, green, and secure approach. Herein, we report a facile method to synthesize the CoP/C nanoboxes by pyrolysis of phytic acid (PA) cross-linked Co complexes that are acquired from reaction of PA and ZIF-67. The PA can not only slowly etch ZIF-67 and gain a hollow structure but also act as a source of phosphorus to prepare CoP/C nanoboxes. The CoP/C nanoboxes deliver an ultrahigh specific capacity (868 mA h g^-1 at 100 mA g^-1) and excellent cycle stability (523 mA h g^-1 after 1000 cycles at 500 mA h g^-1) when used as anode materials for lithium-ion batteries. Moreover, when used as an electrocatalyst for hydrogen evolution reaction, the CoP/C nanoboxes exhibit ultralow overpotential, small Tafel slope, and excellent durability in acidic media. The method to produce CoP/C nanoboxes is easy and environmentally friendly and can be readily extended to design other TMPs/C nanocomposites.