Self-Healable, Self-Adhesive and Degradable MXene-Based Multifunctional Hydrogel for Flexible Epidermal Sensors.

Conductive hydrogels have garnered significant interest in the realm of wearable flexible sensors due to their close resemblance to human tissue, wearability, and precise signal acquisition capabilities. However, the concurrent attainment of an epidermal hydrogel sensor incorporating reliable self-healing capabilities, biodegradability, robust adhesiveness, and the ability to precisely capture subtle electrophysiological signals poses a daunting and intricate challenge. Herein, an innovative MXene-based composite hydrogel (PBM hydrogel) with exceptional self-healing, self-adhesive, and versatile functionality is engineered through the integration of conductive MXene nanosheets into a well-structured poly(vinyl alcohol) (PVA) and bacterial cellulose (BC) hydrogel three-dimensional (3D) network, utilizing multiple dynamic cross-linking synergistic repeated freeze-thaw strategy. The hydrogel harnesses the presence of dynamically reversible borax ester bonds and multiple hydrogen bonds between its constituents, endowing it with rapid self-healing efficiency (97.8%) and formidable self-adhesive capability. The assembled PBM hydrogel epidermal sensor possesses a rapid response time (10 ms) and exhibits versatility in detecting diverse external stimuli and human movements such as vocalization, handwriting, joint motion, Morse code signals, and even monitoring infusion status. Additionally, the PBM hydrogel sensor offers the added advantage of swift degradation in phosphate-buffered saline solution (within a span of 56 days) and H2O2 solution (in just 53 min), maintaining an eco-friendly profile devoid of any environmental pollution. This work lays the groundwork for possible uses in electronic skins, interactions between humans and machines, and the monitoring of individualized healthcare.

Phase-Stabilized Crystal Etching to Unlock An Oxygen-Vacancy-Rich Potassium Vanadate For Ultra-Fast Zn Storage.

Despite holding the advantages of high theoretical capacity and low cost, the practical application of layered-structured potassium vanadates in zinc ion batteries (ZIBs) has been staggered by the sluggish ion diffusion, low intrinsic electronic conductivity, and unstable crystal structure. Herein, for the first time, a phase stabilized crystal etching strategy is proposed to innovate an oxygen-vacancy-rich K0.486 V2 O5 nanorod composite (Ov-KVO@rGO) as a high-performance ZIB cathode. The in situ ascorbic acid assisted crystal etching process introduces abundant oxygen-vacancies into the K0.486 V2 O5 lattices, not only elaborately expanding the lattice spacing for faster ion diffusion and more active sites due to the weakened interlayer electrostatic interaction, but also enhancing the electronic conductivity by accumulating electrons around the vacancies, which is also evidenced by density functional theory calculations. Meanwhile, the encapsulating rGO layer ably stabilizes the K0.486 V2 O5 crystal phase otherwise is hard to endure subject to such a harsh chemical etching. As a result, the optimized Ov-KVO@rGO electrode delivers record-high rate capabilities with 462 and 272.39 mAh g-1 at 0.2 and 10 A g-1 , respectively, outperforming all previously reported potassium vanadate cathodes and most other vanadium-based materials. This work highlights a significant advancement of layer-structured vanadium based-materials towards practical application in ZIBs.

Ultrathick GeP Anode To Balance the Extreme Load and Compliance for High Areal Capacity Flexible Sodium-Ion Batteries.

The ever-growing application of miniaturized electric devices calls for the manufacturing of energy storage systems with a high areal energy density. Thick electrode design is a promising strategy to acquire high areal energy density by enhancing active mass loading and minimizing inactive components. However, the sluggish reaction kinetics and poor electrode mechanical stability that are accompanied by the increased electrode thickness remain unsolved problems. Herein, for the first time, we propose a novel chemical cross-linking strategy to fabricate GeP thick electrodes with adjustable electrode thicknesses and active mass loadings for high areal capacity sodium-ion batteries (SIBs). The chemical cross-linking between carboxylic multiwalled carbon nanotubes (CNTs) and pyrolysis cellulose nanofibers (CNFs) forms a 3D network that encloses GeP nanoparticles, which guarantees fast charge transfer, efficient stress relief, and alleviated volume expansion/shrinkage of the electrode. The hierarchical porous structure generates numerous interconnected channels for unfettered Na+ diffusion, ensuring uncompromised reaction kinetics as the electrode thickness increases. As a result, the ultrathick 1031 µm GeP@C-CNTs-CNFs electrode featuring a mass loading of 18.3 mg cm-2 delivers an ultrahigh areal capacity of 10.58 mAh cm-2 accompanied by superior cycling stability, which outperforms all reported Ge-based electrodes (generally below 1.5 mAh cm-2). This work sheds insightful light on designing high areal capacity flexible thick electrodes for the applications of miniaturized electric devices.

Direct Ink Writing 3D Printing for High-Performance Electrochemical Energy Storage Devices: A Minireview.

Despite tremendous efforts that have been dedicated to high-performance electrochemical energy storage devices (EESDs), traditional electrode fabrication processes still face the daunting challenge of limited energy/power density or compromised mechanical compliance. 3D thick electrodes can maximize the utilization of z-axis space to enhance the energy density of EESDs but still suffer from limitations in terms of poor mechanical stability and sluggish electron/ion transport. Direct ink writing (DIW), an eminent branch of 3D printing technology, has gained popularity in the manufacture of 3D electrodes with intricately designed architectures and rationally regulated porosity, promoting a triple boost in areal mass loading, ion diffusion kinetics, and mechanical flexibility. This focus review highlights the fundamentals of printable inks and typical configurations of 3D-printed devices. In particular, preparation strategies for high-performance and multifunctional 3D-printed EESDs are systemically discussed and classified according to performance evaluation metrics such as high areal energy density, high power density, high volumetric energy density, and mechanical flexibility. Challenges and prospects for the fabrication of high-performance 3D-printed EESDs are outlined, aiming to provide valuable insights into this thriving field.

3D Printing of Electron/Ion-Flux Dual-Gradient Anodes for Dendrite-Free Zinc Batteries.

3D porous Zn-metal anodes have aroused widespread interest for Zn-ion batteries (ZIBs). Nevertheless, the notorious "top-growth" dendrites caused by the intrinsic top-concentrated ions and randomly distributed electrons may ultimately trigger a cell failure. Herein, an electron/ion-flux dual-gradient 3D porous Zn anode is reported for dendrite-free ZIBs by adopting 3D printing technology. The 3D-printed Zn anode with layer-by-layer bottom-up attenuating Ag nanoparticles (3DP-BU@Zn) establishes dual-gradient electron/ion fluxes, i.e., an internal bottom-up gradient electron flux created by bottom-rich conductive Ag nanoparticles, and a gradient ion flux resulting from zincophilic Ag nanoparticles which pump ions toward the bottom. Meanwhile, the 3D-printing-enabled hierarchical porous structure and continuously conducting network endow unimpeded electron transfer and ion diffusion among the electrode, dominating a bottom-preferential Zn deposition behavior. As a result, the 3DP-BU@Zn symmetrical cell affords highly reversible Zn plating/stripping with an extremely small voltage hysteresis of 17.7 mV and a superior lifespan over 630 h at 1 mA cm-2 and 1 mAh cm-2 . Meanwhile, the 3DP-BU@Zn//VO2 full cell exhibits remarkable cyclic stability over 500 cycles. This unique dual-gradient strategy sheds light on the roadmap for the next-generation safe and durable Zn-metal batteries.

Densifiable Ink Extrusion for Roll-To-Roll Fiber Lithium-Ion Batteries with Ultra-High Linear and Volumetric Energy Densities.

Conventional bulky and rigid planar architecting power systems are difficult to satisfy the growing demand for wearable applications. 1D fiber batteries bearing appealing features of miniaturization, adaptability, and weavability represent a promising solution, yet challenges remain pertaining to energy density and scalability. Herein, an ingenious densifiable functional ink is invented to fabricate scalable, flexible, and high-mass-loading fiber lithium-ion batteries (LIBs) by adopting a fast ink-extrusion technology. In the formulated ink, pyrrole-modified reduced graphene oxide is elaborately introduced and exerts multiple influences; it not only assembles carbon nanotubes and poly(vinylidene fluoride-co-hexafluoropropylene) to compose a sturdy, conductive, and agglomeration-free 3D network that realizes an ultra-high content (75 wt%) of the active materials and endows the electrode excellent flexibility but also serves as a capillary densification inducer, encouraging an extremely large linear mass loading (1.01 mg cm-1 per fiber) and packing density (782.1 mg cm-3 ). As a result, the assembled fiber LIBs deliver impressive linear and volumetric energy densities with superb mechanical compliance, demonstrating the best performance among all the reported extruded fiber batteries. This work highlights a highly effective and facile approach to fabricate high-performance fiber energy storage devices for future practical wearable applications.

3D printing of fast kinetics reconciled ultra-thick cathodes for high areal energy density aqueous Li-Zn hybrid battery.

The limitation of areal energy density of rechargeable aqueous hybrid batteries (RAHBs) has been a significant longstanding problem that impedes the application of RAHBs in miniaturized energy storage. Constructing thick electrodes with optimized geometrical properties is a promising strategy for achieving high areal energy density, but the sluggish ion/electron transfer and poor mechanical stability, as well as the increased electrode thickness, itself present well-known problems. In this work, a 3D printing technique is introduced to construct an ultra-thick lithium iron phosphate (LFP)/carboxylated carbon nanotube (CNT)/carboxyl terminated cellulose nanofiber (CNF) composite electrode with uncompromised reaction kinetics for high areal energy density Li-Zn RAHBs. The uniformly dispersed CNTs and CNFs form continuous interconnected 3D networks that encapsulate LFP nanoparticles, guaranteeing fast electron transfer and efficient stress relief as the electrode thickness increases. Additionally, multistage ion diffusion channels generated from the hierarchical porous structure assure accelerated ion diffusion. As a result, LFP/Zn hybrid pouch cells assembled with 3D printed electrodes deliver a well-retained reversible gravimetric capacity of about 143.5 mAh g-1 at 0.5 C as the electrode thickness increases from 0.52 to 1.56 mm, and establish a record-high areal energy density of 5.25 mWh cm-2 with an impressive utilization of active material up to 30 mg cm-2 for an ultra-thick (2.08 mm) electrode, which outperforms almost all reported zinc-based hybrid-ion and single-ion batteries. This work opens up exciting prospects for developing high areal energy density energy storage devices using 3D printing.

Harnessing Plasma-Assisted Doping Engineering to Stabilize Metallic Phase MoSe2 for Fast and Durable Sodium-Ion Storage.

Metallic-phase selenide molybdenum (1T-MoSe2 ) has become a rising star for sodium storage in comparison with its semiconductor phase (2H-MoSe2 ) owing to the intrinsic metallic electronic conductivity and unimpeded Na+ diffusion structure. However, the thermodynamically unstable nature of 1T phase renders it an unprecedented challenge to realize its phase control and stabilization. Herein, a plasma-assisted P-doping-triggered phase-transition engineering is proposed to synthesize stabilized P-doped 1T phase MoSe2 nanoflower composites (P-1T-MoSe2 NFs). Mechanism analysis reveals significantly decreased phase-transition energy barriers of the plasma-induced Se-vacancy-rich MoSe2 from 2H to 1T owing to its low crystallinity and reduced structure stability. The vacancy-rich structure promotes highly concentrated P doping, which manipulates the electronic structure of the MoSe2 and urges its phase transition, acquiring a high transition efficiency of 91% accompanied with ultrahigh phase stability. As a result, the P-1T-MoSe2 NFs deliver an exceptional high reversible capacity of 510.8 mAh g-1 at 50 mA g-1 with no capacity fading over 1000 cycles at 5000 mA g-1 for sodium storage. The underlying mechanism of this phase-transition engineering verified by profound analysis provides informative guide for designing advanced materials for next-generation energy-storage systems.

Cobalt-Catalyzed Carbonization Incorporating Disordered Defects in Ordered Graphitic Domains for Fast and Ultrastable Potassium-Ion Battery.

Carbonaceous materials featuring both ordered graphitic structure and disordered defects hold great promise for high-performance K-ion batteries (KIBs) due to the concurrent advantages of high electronic conductivity, fast and reversible K+ intercalation/deintercalation, and abundant active K+ storage sites. However, it has been a lingering problem and remains a big challenge because graphitization and defects are intrinsic trade-off properties of carbonaceous materials. Herein, for the first time, we propose a cobalt-catalyzed carbonization strategy to fabricate porous carbon nanofibers that incorporate disordered defects in graphitic domain layers (PCNFs-DG) for fast and durable K+ storage. The Co catalyst not only ensures the formation of highly graphitized carbon shells around the Co particles but also introduces nanopores and doping defects in the following catalyst removal process. This idea of architecting defected-ordered graphitic carbon engineering guarantees fast reaction kinetics as well as structural stability with negligible interlayer expansion/contraction owing to the uncompromised electronic conductivity, expanded interlayer spacing, and regulated K+ storage mechanism. These appealing features translate to a high reversible capacity of 318.5 mAh g-1 at 100 mA g-1 and ultrahigh stability with almost 100% capacity retention over 2000 cycles in KIBs. This work puts in perspective that defected and ordered carbonaceous materials could be simultaneously achieved, advancing their performance for next-generation energy storage systems.

A Review on Mechanochemistry: Approaching Advanced Energy Materials with Greener Force.

Mechanochemistry with solvent-free and environmentally friendly characteristics is one of the most promising alternatives to traditional liquid-phase-based reactions, demonstrating epoch-making significance in the realization of different types of chemistry. Mechanochemistry utilizes mechanical energy to promote physical and chemical transformations to design complex molecules and nanostructured materials, encourage dispersion and recombination of multiphase components, and accelerate reaction rates and efficiencies via highly reactive surfaces. In particular, mechanochemistry deserves special attention because it is capable of endowing energy materials with unique characteristics and properties. Herein, the latest advances and progress in mechanochemistry for the preparation and modification of energy materials are reviewed. An outline of the basic knowledge, methods, and characteristics of different mechanochemical strategies is presented, distinguishing this review from most mechanochemistry reviews that only focus on ball-milling. Next, this outline is followed by a detailed and insightful discussion of mechanochemistry-involved energy conversion and storage applications. The discussion comprehensively covers aspects of energy transformations from mechanical/optical/chemical energy to electrical energy. Finally, next-generation advanced energy materials are proposed. This review is intended to bring mechanochemistry to the frontline and guide this burgeoning field of interdisciplinary research for developing advanced energy materials with greener mechanical force.

In-Situ Templating Growth of Homeostatic GeP Nano-Bar Corals with Fast Electron-Ion Transportation Pathways for High Performance Li-ion Batteries.

We propose an in situ template method to directionally induce the construction of germanium phosphide nanobar (GeP-nb) corals with an adjustable aspect ratio. The GeP nanobars grown onto conductive matrix with high aspect ratio expose more quickest electron-ion transportation facets for fast reaction dynamics. The customized GeP-nb electrode delivers a self-healable homeostatic behavior by reversibly stabilizing GeP crystalline structure through multi-phase reactions to maintain structural integrity and cycling stability (850 mAh g-1 at 1 A g-1 after 500 cycles). As a result, the GeP-nb presents the highest Li+ diffusion coefficient (6.21×10-11  cm2 s-1 ) among all the Ge-based anode materials studied so far, rendering an excellent rate performance (620 mAh g-1 at 5 A g-1 ) as a lithium-ion battery (LIB) anode.

Selective Interface Synthesis of Cobalt Metaphosphate Nanosheet Arrays Motivated by Functionalized Carbon Cloths for Fast and Durable Na/K-Ion Storage.

Exploiting novel nanomaterials with fast and durable sodium/potassium ion storage capability is key to alleviate the application limitations of lithium-ion batteries. Herein, a novel energy storage material based on cobalt metaphosphate nanosheet arrays self-supported on carbon cloths [Co(PO3)2 NSs/CC] is fabricated by a two-step strategy. This rationally designed strategy avoids the preparation of the complex {Co[O2P(OtBu)2]2}n precursor, which significantly simplifies the synthesis process. The active CC acts not only as an electrically conductive substrate as usual but also as a functional basis to suppress PH3-involved reaction and to promote HPO3-involved reaction during the phosphating process, contributing to the formation of Co(PO3)2. The mutual cross-linked porous Co(PO3)2 nanosheets vertically grow on the surface of activated CC, ensuring sufficient electrolyte infiltration and fast electron transport among the electrodes. Sodium ion storage analysis for the Co(PO3)2 NSs/CC electrode reveals a multi-step reaction mechanism with high reversibility, as reflected by the high reversible capacity (667 mA h g-1 at 50 mA g-1) and excellent cyclability (with almost no capacity decay over 500 cycles). This novel electrode is also well capable of storing potassium ions, exhibiting high reversible capacity, which outperforms most reported anodes for potassium-ion batteries. The development of this novel high-performance nanomaterial would advance the performance of sodium/potassium-ion batteries toward practical applications.

Electron-Injection-Engineering Induced Phase Transition toward Stabilized 1T-MoS2 with Extraordinary Sodium Storage Performance.

Phase transition engineering, with the ability to alter the electronic structure and physicochemical properties of materials, has been widely used to achieve the thermodynamically unstable metallic phase MoS2 (1T-MoS2), although the complex operating conditions and low yield of previous strategies make the large-scale fabrication of 1T-MoS2 a big challenge. Herein, we report a facile electron injection strategy for phase transition engineering and fabricate a composite of conductive TiO chemically bonded to 1T-MoS2 nanoflowers (TiO-1T-MoS2 NFs) on a large scale. The underlying mechanism analysis reveals that electron-injection-engineering triggers a reorganization of the Mo 4d orbitals and results in a 100% phase transition of MoS2 from 2H to 1T. In the TiO-1T-MoS2 NFs composite, the 1T-MoS2 demonstrates a higher electronic conductivity, a lower Na+ diffusion barrier, and a more restricted S release than 2H-MoS2. In addition, conductive TiO bonding successfully resolves the stability challenge of the 1T phase. These merits endow TiO-1T-MoS2 NFs electrodes with an excellent rate capability (650/288 mAh g-1 at 50/20 000 mA g-1, respectively) and an outstanding cyclability (501 mAh g-1 at 1000 mA g-1 after 700 cycles) in sodium ion batteries. Such an improvement signifies that this facile and scalable phase-transition engineering combined with a deep mechanism analysis offers an important reference for designing advanced materials for various applications.

Tunable Hollow Nanoreactors for In Situ Synthesis of GeP Electrodes towards High-Performance Sodium Ion Batteries.

The practical application of germanium phosphide (GeP) in battery systems is seriously impeded referring to the sluggish reaction kinetics and severe volume change. Nanostructure design that elaborately resolves the above issues is highly desired but still remains a big challenge. Herein, unique hollow nanoreactors assembled with nitrogen-doped carbon networks for in situ synthesis of the GeP electrodes are proposed for the first time. Such nanoreactors form a self-supported conductive network, ensuring sufficient electrolyte infiltration and fast electron transport. They restrain crystal growth and accommodate the volume expansion of GeP simultaneously. Reaction kinetics and confinement effect are optimized through nanoreactor size regulation. The optimized GeP electrode has high reversible capacities and outstanding cyclability and rate performance for sodium storage, outperforming most previously reported phosphides.

Oxygen Vacancy Engineering in Titanium Dioxide for Sodium Storage.

Titanium dioxide (TiO2 ) is a promising anode material for sodium-ion batteries (SIBs) due to its low cost, natural abundance, nontoxicity, and excellent electrochemical stability. Oxygen vacancies, the most common point defects in TiO2 , can dramatically influence the physical and chemical properties of TiO2 , including band structure, crystal structure and adsorption properties. Recent studies have demonstrated that oxygen-deficient TiO2 can significantly enhance sodium storage performance. Considering the importance of oxygen vacancies in modifying the properties of TiO2 , the structural properties, common synthesis strategies, characterization techniques, as well as the contribution of oxygen-deficient TiO2 on initial Coulombic efficiency, cyclic stability, rate performance for sodium storage are comprehensively described in this review. Finally, some perspectives on the challenge and future opportunities for the development of oxygen-deficient TiO2 are proposed.

Nano-size porous carbon spheres as a high-capacity anode with high initial coulombic efficiency for potassium-ion batteries.

Hard carbon materials have been recognized as a promising family of anode materials for potassium ion batteries (PIBs), but their practical application is severely hindered due to the inferior initial coulombic efficiency (ICE) and low capacity. Herein, we report our findings in simultaneously improved potassium storage capacity and ICE through the design of nano-size and porous structure and the appropriate selection of electrolytes. Benefiting from the high specific surface area, stable electrode|electrolyte interface, and fast potassium ion and electron transfer, the optimized electrode exhibits a high ICE of up to 68.2% and an outstanding reversible capacity of 232.6 mA h g-1 at 200 mA g-1. In particular, superior cycling stability of 165.2 mA h g-1 at 1000 mA g-1 and 129.7 mA h g-1 at 2000 mA g-1 can be retained after 1500 cycles, respectively. Quantitative analysis reveals that this optimized structure leads to an enhanced surface-controlled contribution, resulting in fast potassiation kinetics and electronic|ionic conductivities, which are regarded as essential features for potassium storage. Our findings in this work provide an efficient strategy to significantly improve potassium storage capacity while maintaining a high ICE for hard carbon electrodes.

Designing a hybrid electrode toward high energy density with a staged Li+ and PF6 - deintercalation/intercalation mechanism.

Existing lithium-ion battery technology is struggling to meet our increasing requirements for high energy density, long lifetime, and low-cost energy storage. Here, a hybrid electrode design is developed by a straightforward reengineering of commercial electrode materials, which has revolutionized the "rocking chair" mechanism by unlocking the role of anions in the electrolyte. Our proof-of-concept hybrid LiFePO4 (LFP)/graphite electrode works with a staged deintercalation/intercalation mechanism of Li+ cations and PF6 - anions in a broadened voltage range, which was thoroughly studied by ex situ X-ray diffraction, ex situ Raman spectroscopy, and operando neutron powder diffraction. Introducing graphite into the hybrid electrode accelerates its conductivity, facilitating the rapid extraction/insertion of Li+ from/into the LFP phase in 2.5 to 4.0 V. This charge/discharge process, in turn, triggers the in situ formation of the cathode/electrolyte interphase (CEI) layer, reinforcing the structural integrity of the whole electrode at high voltage. Consequently, this hybrid LFP/graphite-20% electrode displays a high capacity and long-term cycling stability over 3,500 cycles at 10 C, superior to LFP and graphite cathodes. Importantly, the broadened voltage range and high capacity of the hybrid electrode enhance its energy density, which is leveraged further in a full-cell configuration.

Anion Vacancies Regulating Endows MoSSe with Fast and Stable Potassium Ion Storage.

Vacancy engineering is a promising approach for optimizing the energy storage performance of transition metal dichalcogenides (TMDs) due to the unique properties of vacancies in manipulating the electronic structure and active sites. Nevertheless, achieving effective introduction of anion vacancies with adjustable vacancy concentration on a large scale is still a big challenge. Herein, MoS2(1-x)Se2x alloys with anion vacancies introduced in situ have been achieved by a simple alloying reaction, and the vacancy concentration has been optimized through adjusting the chemical composition. Experimental and density functional theory calculation results suggest that the anion vacancies in MoS2(1-x)Se2x alloys could enhance the electronic conductivity, induce more active sites, and alleviate structural variation in the alloys during the potassium storage process. When applied as potassium ion battery anodes, the most optimized vacancy-rich MoSSe alloy delivered high reversible capacities of 517.4 and 362.4 mAh g-1 at 100 and 1000 mA g-1, respectively. Moreover, a reversible capacity of 220.5 mAh g-1 could be maintained at 2000 mA g-1 after 1000 cycles. This work demonstrates a practical approach to modifying the electronic and defect properties of TMDs, providing an effective strategy for constructing advanced electrode materials for battery systems.

Defect-Assisted Selective Surface Phosphorus Doping to Enhance Rate Capability of Titanium Dioxide for Sodium Ion Batteries.

Phosphorus doping is an effective strategy to simultaneously improve the electronic conductivity and regulate the ionic diffusion kinetics of TiO2 being considered as anode materials for sodium ion batteries. However, efficient phosphorus doping at high concentration in well-crystallized TiO2 nanoparticles is still a big challenge. Herein, we propose a defect-assisted phosphorus doping strategy to selectively engineer the surface structure of TiO2 nanoparticles. The reduced TiO2-x shell layer that is rich in oxygen defects and Ti3+ species precisely triggered a high concentration of phosphorus doping (∼7.8 at. %), and consequently a TiO2@TiO2-x-P core@shell architecture was produced. Comprehensive characterizations and first-principle calculations proved that the surface-functionalized TiO2-x-P thin layer endowed the TiO2@TiO2-x-P with substantially enhanced electronic conductivity and accelerated Na ion transportation, resulting in great rate capability (167 mA h g-1 at 10 000 mA g-1) and stable cycling (99% after 5000 cycles at 10 A g-1). Combining in/ex situ X-ray diffraction with ex situ electron spin resonance clearly demonstrated the high reversibility and robust mechanical behavior of TiO2@TiO2-x-P upon long-term cycling. This work provides an interesting and effective strategy for precise heteroatoms doping to improve the electrochemical performance of nanoparticles.

Morphology-dependent electrochemical performance of Ni-1,3,5-benzenetricarboxylate metal-organic frameworks as an anode material for Li-ion batteries.

The performance of energy storage materials is substantially dependent on their nanostructures. Herein, Ni-1,3,5-benzenetricarboxylate metal-organic frameworks (Ni-BTC MOFs) with different morphologies are controllably synthesized using a facile solvothermal method by simply adjusting the solvent and their electrochemical performance as an anode material for lithium-ion batteries is thoroughly investigated. Among the synthesized Ni-BTC MOFs with different morphologies, a hierarchical mesoporous flower-like Ni-BTC MOF (Ni-BTCEtOH) assembled from two-dimensional nanosheets shows the best electrochemical properties including a high capacity of 1085 mA h g-1 at 100 mA g-1 (358 mA h g-1 at 5000 mA g-1), excellent cycling stability at 1000 mA g-1 for 1000 cycles, and great rate performance, which is superior to most of the reported MOF-based anode materials for lithium-ion batteries. The outstanding electrochemical performance of Ni-BTCEtOH is originated from its unique and stable hierarchical mesoporous morphology with a high specific surface area and improved electrical/ionic conductivity. Moreover, our study demonstrates that the charge-discharge mechanism of the Ni-BTCEtOH electrode involves the insertion/extraction of Li ions to/from the organic moieties in Ni-BTCEtOH during the charge-discharge process without the direct engagement of Ni2+. This work highlights that the nanostructure design is an effective strategy to obtain promising energy storage materials.