Long-term Cycling Performance Research Articles

3D printing of porous hollow nanosphere MoS2@NiS/rGO scaffolds empowering long-cycle sodium-ion batteries

Sodium-ion batteries (SIB), as one of the most appealing electrochemical energy storage devices in the field of energy storage, consistently require optimization for both capacity and long-term cycling performance. The amalgamation of diverse material modification techniques with up-and-coming 3D printing technology presents a promising yet relatively underexplored avenue. Herein, we report a composite material, MoS2@NiS/rGO, as the anode material for SIB, achieving high reversible capacity and outstanding long-term cycling performance, surpassing current reported levels. Through carefully designed anode electrode structure and component interface engineering, the material rate capability (with a capacity of 289.5 mAh g-1 at 0.1Ag-1 and 66.8 mAh g-1 at 5Ag-1) and cycling stability (maintaining a capacity of 131.3 mAh g-1 after 800 cycles at 1Ag-1) are significantly enhanced. The reasons for the improvement in electrochemical performance are elucidated through detailed electrochemical analysis. Encouragingly, we showcase the fabrication of a sodium-ion full battery entirely through 3D printing (3DP), achieving an area loading capacity as high as 8.23mgcm-2 and retaining a capacity of 82.1 mAh g-1 after 240 cycles at 0.1Ag-1. This work underscores the pivotal significance of 3D-printed sodium-ion batteries in advancing the frontier of energy storage technology.

Rational Design of LixSiOy-Based Pre-SEI through Thermal-Evaporated Li-Metal Prelithiated SiOx Anode Enabling Extremely Stable and High-Rate Lithium Microbatteries

Recently, silicon oxides families (SiOx) have been commercialized as high capacity anode materials growing rapidly owing to their natural resource abundance and low-cost.(1) However, both the poor electron/ionic conductivity, and quite low initial coulombic efficiency (ICE) (normally < 60%) limits the further development into next generation SiOx anodes. (2) To address these two critical issues, various pre-lithiation strategies have emerged and systematically investigated with significant progress.(3, 4) Here, we provide a facile approach to prelithiate SiOx films by optimizing RF power and precisely controlling Li-metal deposition to overcome the current challenges of SiOx anodes. We found a strong correlation between the surface chemical state of SiOx and the pre-formation of LixSiOy SEI layers. The optimal prelithiation strategy achieves remarkable rate performance of 72.8% at 20C, and extremely excellent long-term cycling performance of 54.2% over 5000 cycles at 10C. This study significantly promotes SiOx-based anodes development, offering a promising strategy for extreme fast-charging and long-term stability not only overcoming the limitations in microbattery but scalable to practical electrodes.Reference: Q. Mai, Chem. Soc. Rev., 48, 285 (2019). M. L. Jiao, Y. F. Wang, C. L. Ye, C. Y. Wang, W. K. Zhang and C. Liang, J. Alloy. Compd., 842, 21 (2020). R. M. Zhan, X. C. Wang, Z. H. Chen, Z. W. Seh, L. Wang and Y. M. Sun, Adv. Energy Mater., 11, 20 (2021). X. Q. Min, G. J. Xu, B. Xie, P. Guan, M. L. Sun and G. L. Cui, Energy Storage Mater., 47, 297 (2022).

Chemical Substitution Strategies for Tailoring P2- and O3-Type Layered Oxide Cathodes in Sodium-Ion Batteries

Among cathodes for sodium-ion batteries (SIBs), layered transition metal oxides Na x MO2 (M = transition metal) are very promising due to their easy synthesis and high theoretical capacity.1,2 In this class, Ni/Mn/Fe-based layered oxides are attractive due to the high redox potential of Ni2+/ Ni4+ and Jahn Teller inactive centers (Ni2+, Fe3+,and Mn4+).3 However, complex phase transitions, Na+/vacancy ordering and transition-metal (TM) migration degrade their electrochemical performances.4 To address the issues, a widely studied cathode- P2-type Na0.67[Ni0.33Mn0.67]O2 is chosen and Li+ is substituted in the TM-layer to tailor a series of high Na-content cathodes. Among them, Na0.85[Li0.14Ni0.29Mn0.57]O2 cathode with optimal Li-substitution exhibits a reversible capacity of 168 mAh g-1 at 0.1 C rate and good cycling stability (82% retention after 100 cycles).5 In-situ XRD measurement reveals a complete solid-solution formation and X-ray absorption spectroscopy studies confirm the participation of Ni4+/Ni2+ and Mn4+/Mn3+ redox couples during Na+-extraction/insertion. Lastly, a full Na-ion cell with hard carbon is demonstrated with an energy density of 420 Wh kg-1. In subsequent work, a Li and Ti co-substitution strategy is applied to design a high-entropy O3-type NaLixNiyFezMn0.5Ti0.5-aO2 cathode.6 It retains 77% of its initial capacity after 400 cycles at a 2 C rate with a facile O3-P3-OP2-P3-O3 phase transition. The co-substitution strategy uplifts the average voltage of the system, improves the reversibility of the high-voltage OP2 phase, and enhances the Na-ion diffusion rate. A mere 1.32% unit cell volume change and diminishing electrochemical cell resistance over cycling ensure its superior long-term cycling performance. A full cell is fabricated, which holds 62% of its initial capacity even after 1000 cycles at a 0.5 C rate. Therefore, mono- and di-ion substitution strategies hold enormous potential for designing high-performing P2- and O3-type cathode materials for practical SIBs. References T. Hosaka, K. Kubota, A. S. Hameed, and S. Komaba, Chem. Rev., 120, 6358–6466 (2020).J. Y. Hwang, S. T. Myung, and Y. K. Sun, Chem. Soc. Rev., 46, 3529–3614 (2017).F. Zhang, J. Liao, L. Xu, W. Wu, and X. Wu, ACS Appl. Mater. Interfaces, 13, 40695–40704 (2021).Z. Lu and J. R. Dahn, J. Electrochem. Soc., 148, A1225 (2001).A. Ghosh, B. Senthilkumar, S. Ghosh, P. Amonpattaratkit, and P. Senguttuvan, J. Electrochem. Soc., 170, 030538 (2023).A. Ghosh, R. Hegde, and P. Senguttuvan, J. Mater. Chem. A., submitted(2023).

Construction of 2D/1D rGO/H2Ti3O7 composite as anode for high performance lithium-ion batteries

Ultrafine one-dimensional (1D) H2Ti3O7 nanowires were prepared by a hydrothermal reaction with high concentration of KOH as base source. Then 2D/1D rGO/H2Ti3O7 architecture was constructed and investigated as the anode material for lithium-ion batteries. Benefiting from the addition of rGO nanosheets and the retention of ultrafine 1D H2Ti3O7 nanowires, the rGO/H2Ti3O7 electrode presented superior electrochemical performance with excellent rate capability, long cycling stability and high capacity in half cells. It delivered high reversible capacities of 274 mAh g−1 at 0.1 A g−1 and 163 mAh g−1 at 1 A g−1, as well as a long-term cycling performance (259.3 mAh g−1 at 0.2 A g−1 after 1000 cycles). The excellent electrochemical performance of the composite can be attributed to the unique architecture with smaller diameter of 1D H2Ti3O7 nanowires and conductive rGO nanosheets to shorten the transmission distance of electrons and Li+ and improve the electrical conductivity in rGO/H2Ti3O7 composite.

Hybrid of sub-1 nm single-dispersed polyoxometalate and reduced graphene oxide as advanced anodes for durable sodium-ion batteries

Polyoxometalates (POMs) are widely thought as promising choices for sodium-ion batteries (SIBs) because of their refined molecular structures and excellent reversible multielectron charge-discharge behaviors. Nevertheless, the POMs anion clusters could dissolve in the electrolyte when attacked by solvent molecules, thus reducing active sites and affecting the actual performance of these POMs-based electrodes. Herein, we report the development of a new type of electrode system that produces single-dispersed POMs molecular cluster/polydopamine/reduced graphene oxide composites ({PMo12}/PDA@rGO) through a self-assembly method. PDA acts as the role of “killing two birds with one stone”. It not only works as the linker to promote the formation of stable and uniform monodisperse {PMo12} clusters on the rGO surface, but also prevents the POMs from desorbing and dissolving upon deep cycling test. As a consequence, when used as the anode material for SIBs, the obtained {PMo12}/PDA@rGO exhibits an admirable long-term cycling performance, for instance, it holds a high Na-storage capacity of 277.5 mAh g−1 with an average Coulomb efficiency up to 99.89 % over 2000 cycles at 1 A g−1. This work offers versatile possibilities for designing POMs-based composites and provides new insight into developing single dispersed POMs for advanced SIBs.

An all-fluorinated electrolyte with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether as co-solvent for lithium-ion cells with advanced electrochemical and safety properties at high voltage

To enable high-performance lithium-ion cells at high voltage, this work proposes a series of all-fluorinated electrolytes with fluoroethylene carbonate (FEC), bis (2,2,2-trifluoroethyl) carbonate (TFEC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) as co-solvents. It is found that a moderate increase in lithium salt concentration within the FEC-TFEC-TTE solvent enhances the long-term cycling performance of cells at high voltage, while excessive lithium salt cannot further improve the cells' performance but leads to high cost and viscosity and harms the cells’ high-temperature property. Thus, the blend named FTT1.5, i.e., 1.5 M lithium hexafluorophosphate (LiPF6) in FEC, TFEC and TTE with a ratio of 2:6:2, is selected, which outperforms not only the commercial electrolyte (EE) but another all-fluorinated electrolyte, i.e., 1.5 M LiPF6 in FEC, methyl (2,2,2-trifluoroethyl) carbonate (FEMC), and TTE with a ratio of 2:6:2, implying that TFEC cooperates better with FEC and TTE than FEMC. This mainly results from the low binding energy between TFEC and Li+ and the enhanced solvation structure that enables fast Li+ desolvation, reduces lithium plating, and suppresses parasitic reactions at high voltage. The strengthened combination between FEC and TTE with Li+ attributes to the improvement of the anode stability and the generation of reliable and thin passivation layers rich in lithium fluoride. As a result, side reactions at high voltage are successfully restrained, to further obtain high-voltage cells with promising electrochemical performance. Besides this, both the all-fluorinated electrolyte and the system utilizing this electrolyte demonstrate more advanced safety properties when subjected to typical abusing scenarios, with no thermal runaway.

Self-assembled 3D CoSe-based sulfur host enables high-efficient and durable electrocatalytic conversion of polysulfides for flexible lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as promising candidates for next-generation energy storage systems. However, the commercial applications are severely limited by the sluggish kinetics and shuttling effect. Herein, we have designed an integrated free-standing functional CoSe-CNF-GO-MXene (CCGM) sulfur host with a “point-line-plane” 3D porous structure for Li-S batteries. The two-dimensional (2D) graphene, MXene and one-dimensional (1D) nanocellulose fibers combined with zero-dimensional (0D) transition metal selenide (CoSe) shows good electrical conductivity and enhanced catalytic performance, respectively. Additionally, the rationally designed porous structure (from 0D to 3D) demonstrates well-connected ion/electron transport channels, conferring the good kinetic performance. Electrochemical tests show that CoSe catalytic materials with moderate adsorption energies can catalyse both precipitation and dissolution processes of Li2S, enabling fast conversion kinetics. The density functional theory (DFT) calculations show that the synergistic effect of CoSe, Ti3C2Tx, and graphene can improve the chemisorption and catalytic performance. As a result, the 3D porous S@CCGM cathode exhibits a high initial discharge capacity of 1205.1 mAh g−1 at 0.2C and good long-term cycling performance with a low decay rate of 0.055 % per cycle at 1C. Furthermore, the gel electrolyte Li-S pouch cell successfully passes the 0–180° bending test, nailing test, and cutting test. Such design offers a new perspective for the commercialization of safe and flexible electrochemical energy-storage devices especially in Li-S batteries.

Electronic Properties and Mechanical Stability of Multi-Ion-Co-Intercalated Bilayered V2O5.

Incorporating metal cations into V2O5 has been proven to be an effective method for solving the poor long-term cycling performance of vanadium-based oxides as electrodes for mono- or multivalent aqueous rechargeable batteries. This is due to the existence of a bilayer structure with a large interlayer space in the V2O5 electrode and to the fact that the intercalated ions act as pillars to support the layered structure and facilitate the diffusion of charged carriers. However, a fundamental understanding of the mechanical stability of multi-ion-co-intercalated bilayered V2O5 is still lacking. In this paper, a variety of pillared vanadium pentoxides with two types of co-intercalated ions were studied. The root-mean-square deviation of the V-O bonds and the elastic constants calculated by density functional theory were used as references to evaluate the stability of the intercalated compounds. The d-band center and electronic band structures are also discussed. Our theoretical results show that the structural characteristics and stability of the system are quite strongly influenced by the intercalating strategy.

V2O3/VO2@NC@GO ultrathin nanosheets as a high-performance cathode for aqueous zinc-ion batteries

Recently, vanadium oxides have attracted much attention as advanced cathodes for aqueous zinc-ion batteries on account of their high theoretical specific capacity, multi-electron transfer and easy synthesis; however, structural instability and poor conductivity of the materials limit their practical application. Herein, N-doped carbon-coated V2O3/VO2 hybrid nanosheets were encapsulated into graphene oxide (V2O3/VO2@NC@GO) as an advanced cathode for aqueous zinc-ion batteries by the combined process of hydrothermal treatment, high-temperature annealing and freeze drying. The multi-valence of vanadium element activates diverse redox reactions and thus results in high specific capacity, while graphene oxide and N-doped carbon layer derived from polyvinyl pyrrolidone establish an efficient conductive network for electronic transfer and provide a rigid skeleton for enhancing the structural stability of the hybrid nanosheets. Benefiting from the above unique advantages of composition and micromorphology, the V2O3/VO2@NC@GO cathode exhibits excellent reaction dynamics and rapid electron transfer, generating high specific capacities of 493.0 mAh g−1 at 0.5 A g−1 and 411.9 mAh g−1 at 5 A g−1 and outstanding long-term cycling performance with a retention of 92.4 % after 1000 cycles at 5 A g−1. This work offers a viable approach for developing high-performance vanadium oxide-based cathodes for aqueous zinc-ion batteries by enriching the valence states of vanadium and encapsulating active materials into highly conductive carbon materials.

Construction of Co9S8/SnS heterostructures encapsulated in multi-channel carbon nanofibers as long-term stable anodes for sodium-ion batteries

This study presents the design and fabrication of multi-channel self-supported anode materials Co9S8/SnS@MCNFs, through the electrospinning technique. The high compatibility of Co9S8 and SnS at the interface enables the synthesis of a more complete heterostructure within the material, enhancing the electrochemical reaction process through rational heterostructure design. Additionally, the incorporation of high theoretical capacity SnS improves sodium storage performance. The design of multi-channel carbon nanofibers (MCNFs) effectively addresses challenges such as material volume expansion and metal particle aggregation during cycling by providing large specific surface areas and enabling carbon encapsulation. The resulting pore structure and heterostructure formation, coupled with introduction of more defects, enhance the availability of Na+ active sites for electrochemically reversible processes. As expected, Co9S8/SnS@MCNFs exhibit remarkable initial coulombic efficiency (ICE = 92.6 %) and demonstrate stable long-term cycling performance (222.5 mA h g−1 at 2 A g−1 after 400 cycles) for sodium storage, with only a 0.18 % decay rate per cycle. These findings suggest promising application for the electrode material in sustained high-current discharges and long-endurance performance.

Ultra-Fast-Charging, Long-Duration, and Wide-Temperature-Range Sodium Storage Enabled by Multiwalled Carbon Nanotube-Hybridized Biphasic Polyanion-Type Phosphate Cathode Materials.

Sodium-ion batteries (SIBs) represent a promising energy storage technology with great safety. Because of their high operating potential, superior structural stability, and prominent thermal stability, polyanion-type phosphates have garnered significant interest in superior prospective cathode materials for SIBs. Nevertheless, the disadvantages of poor intrinsic electronic conductivity, sluggish kinetics, and volume variation during sodiation/desodiation remain great challenges for satisfactory rate performance and cycle stability, which severely hinder their further practical applications. In this work, by adjusting the amounts of pretreated multiwalled carbon nanotubes (CNT) added intentionally at the beginning of the preparation, biphasic polyanion-type phosphate materials (marked as NFC) are synthesized through a one-pot solid state reaction methodology, which are composed of CNT-interwoven Na3V2(PO4)2F3 (NVPF) and a small amount of Na3V2(PO4)3 (NVP). Benefiting from the improved electronic conductivity and unique composition and structure, the optimized sample (labeled as NFC-2) illustrates exceptional cycle stability and remarkable rate performance. The discharge capacities of the NFC-2 electrode are 114.8 and 78.6 mAh g-1 tested at 20 and 5000 mA g-1, respectively. Notably, such an electrode still gives out 75.7% capacity retention upon 10 000 cycles at 5000 mA g-1. In situ X-ray diffraction analysis demonstrates that the NFC-2 cathode has outstanding structural reversibility during charge/discharge cycles. More importantly, such a biphasic material has achieved impressive electrochemical performance within a wide operating temperature range of -20-50 °C. When temperature is decreased to -20 °C, the NFC-2 electrode still delivers an initial discharge capacity of 102.4 mAh g-1 and exhibits a remarkable capacity retention of 97.8% even after 500 cycles at 50 mA g-1. In addition, the sodium-ion full cell assembled by integrating NFC-2 cathode and hard carbon anode shows a satisfying energy density of 431.3 Wh kg-1 at 20 mA g-1 with a better long-term cycle performance. The synergistic effect among high energy NVPF, conductive CNT, and stable NVP may lead to the great improvement in the electrochemical sodium storage performance of the NFC-2 sample. Such biphasic polyanion-type phosphate materials will inject new ideas into the material design for SIBs with excellent electrochemical performance and further promote practical applications of this advanced energy storage technology.

One-step and universal fabrication of MXene/metal sodiophilic frameworks via Lewis acidic etching toward dendrite-free sodium metal anodes

Although MXene-based 3D scaffolds have boosted the cyclability of Na metal, the complex and harsh synthetic process deteriorates their practical application. Herein, a series of MXene/metal sodiophilic frameworks are constructed through one-step Lewis acidic etching, and metal nanoparticles are uniformly distributed on the surface or intercalated into the large interlayer gaps of MXenes. Notably, MXenes with superior Na+/electron transport kinetics and mechanical flexibility remarkably reduce the local current density, homogenize Na+ flux and cushion huge volume change of Na metal. Moreover, sodiophilic species including MXenes and metals effectively induce Na uniform nucleation and smooth deposition among the 3D matrixes, leading to dendrite-free morphology. Consequently, MXene/metal hosts exhibit stable Na plating/stripping process for 900 cycles with high average Coulombic efficiencies of 99.9% (2 mA cm−2, 1 mAh cm−2). The MXene/metal-Na symmetric cells achieve low overpotentials of less than 15 mV and stable cycling for 2200 h (2 mA cm−2, 4 mAh cm−2). When paired with Na3V2(PO4)3 cathode, the full cells with a low N/P ratio (around 2) demonstrate high discharge capacity and excellent long-term cyclic performance over 600 cycles. The presented universal, safe and one-step approach in fabricating MXene/metal scaffolds shows bright prospects and may promote the development of alkali metal-based batteries.

Healable and Conductive Two-Dimensional Sulfur Iodide for High-Rate Sodium Batteries.

Self-healing functional materials can repair cracks and damage inside the battery, ensuring the stability of the battery material structure. This feature minimizes performance degradation during the charging and discharging processes, improving the efficiency and stability of the battery. Here, we have developed a novel healing conductive two-dimensional sulfur iodide (SI4) composite cathode. This process integrates both sulfur and iodine compounds into carbon nanocages, forming a SI4@C core-shell structure. This cathode design improves electrical conductivity and repairability, facilitates rapid activation, and ensures structural integrity, resulting in a typical Na-SI4 battery with high capacity and an exceptionally long cycle life. At 10.0 A g-1, the capacity of the Na-SI4 battery can still reach 217.4 mAh g-1 after more than 500 cycles, and the capacity decay rate per cycle is only 0.06%. In addition, the cathode exhibits a cascade redox reaction involving S and I, contributing to its high capacity. The in situ growth of a carbon shell further enhances the conductivity and structural robustness of the entire cathode. The flexibility and bendability of SI4@C-carbon cloth make it applicable for flexible electronic devices, providing more possibilities for battery design. The strategy of engineering a two-dimensional self-healing structure to construct a superior cathode is expected to be widely applied to other electrode materials. This study provides a new pathway for designing novel binary-conversion-type sodium-ion batteries with excellent long-term cycling performance.

Heat-Resistant Carbon-Coated Potassium Magnesium Hexacyanoferrate Nanoplates for High-Performance Potassium-Ion Batteries.

Metal hexacyanoferrates (HCFs) are regarded as promising cathode materials for potassium-ion batteries (PIBs) on account of their low cost and high energy density. However, the difficult-to-remove [Fe(CN)6] vacancies and crystal water lead to structural instability and capacity deterioration as well as the stereotype of poor thermostability of conventional HCFs. Herein, we report (100) face-oriented potassium magnesium hexacyanoferrate (KMgHCF) nanoplates with low [Fe(CN)6] vacancies and high crystallinity, enabling thermostability up to 550 °C, high-temperature carbon coating and crystal water elimination. The as-obtained KMgHCF/C nanoplates exhibit superior potassium storage properties, including a large reversible capacity of 84.6 mAh g-1, a high voltage plateau of 3.87 V, excellent long-term cycling performance over 15000 cycles and high rate capability at 5 A g-1. The unprecedented cycling stability of KMgHCF/C is attributed to the synergistic effect of a highly reversible two-phase reaction, low [Fe(CN)6] vacancies and no crystal water, a specially exposed steady (100) surface, and a protective carbon coating. This work provides a new material selection and modification strategy for the practical application of HCFs in PIBs.

Stepwise Construction of MoS2@CoAl-LDH/NF 3D Core-Shell Nanoarrays with High Hole Mobility for High-Performance Asymmetric Supercapacitors.

Supercapacitors (SCs) have received widespread attention as excellent energy storage devices, and the design of multicomponent electrode materials and the construction of ingenious structures are the keys to enhancing the performance of SCs. In this paper, MoS2 nanorods were used as the carrier structure to induce the anchoring of CoAl-LDH nanosheets and grow on the surface of nickel foam (NF) in situ, thus obtaining a uniformly distributed MoS2 nanorod@CoAl-LDH nanosheet core-shell nanoarray material (MoS2@CoAl-LDH/NF). On the one hand, the nanorod-structured MoS2 as the core provides high conductivity and support, accelerates electron transfer, and avoids agglomeration of CoAl-LDH nanosheets. On the other hand, CoAl-LDH nanosheet arrays have abundant interfacially active sites, which accelerate the electrolyte penetration and enhance the electrochemical activity. The synergistic effect of the two components and the unique core-shell nanostructure give MoS2@CoAl-LDH/NF a high capacity (14,888.8 mF cm-2 at 2 mA cm-2) and long-term cycling performance (104.4% retention after 5000 charge/discharge cycles). The integrated MoS2@CoAl-LDH/NF//AC device boasts a voltage range spanning from 0 to 1.5 V, achieving a peak energy density of 0.19 mW h cm-2 at 1.5 mW cm-2. Impressively, it maintains a capacitance retention rate of 84.6% after enduring 10,000 cycles, demonstrating exceptional durability and stability.

Polypyride intercalation boosting the kinetics and stability of V3O7·H2O cathodes for aqueous zinc-ion batteries

V3O7·H2O (VO) is a high capacity cathode material in the field of aqueous zinc ion batteries (AZIBs), but it is limited by slow ion migration and low electrical conductivity. In this paper, polypyridine (PPyd) intercalated VO with nanoribbon structure was prepared by a simple in-situ pre-intercalation, which is noted VO-PPyd. The total density of states (TDOS) shows that after the pre-intercalation of PPyd, an intermediate energy level appears between the valence band and conduction band, which provides a step that can effectively reduce the band gap and enhance the electron conductivity. Furthermore, the density functional theory (DFT) results found that Zn2+ is more easily de-intercalated from the V-O skeleton, which proves that the embeddedness of PPyd improves the diffusion kinetics of Zn2+. Electrochemical studies have shown that VO-PPyd cathode materials exhibit excellent rate performance (high specific capacity of 465 and 192 mA h g−1 at 0.2 and 10 A g−1, respectively) and long-term cycling performance (92.7% capacity retention rate after 5300 cycles), due to their advantages in structure and composition. More importantly, the energy density of VO-PPyd//Zn at 581 and 5806 W kg−1 is 375 and 247 W h kg−1, respectively. VO-PPyd exhibits excellent electrochemical properties compared to previously reported vanadium based cathodes, which makes it highly competitive in the field of high-performance cathode materials of AZIBs.

Heterogeneous MoS2 Nanosheets on Porous TiO2 Nanofibers toward Fast and Reversible Sodium-Ion Storage.

2D layered molybdenum disulfide (MoS2) has garnered considerable attention as an attractive electrode material in sodium-ion batteries (SIBs), but sluggish mass transfer kinetic and capacity fading make it suffer from inferior cycle capability. Herein, hierarchical MoS2 nanosheets decorated porous TiO2 nanofibers (MoS2 NSs@TiO2 NFs) with rich oxygen vacancies are engineered by microemulsion electrospinning method and subsequent hydrothermal/heat treatment. The MoS2 NSs@TiO2 NFs improves ion/electron transport kinetic and long-term cycling performance through distinctive porous structure and heterogeneous component. Consequently, the electrode exhibits excellent long-term Na storage capacity (298.4mAhg-1 at 5Ag-1 over 1100 cycles and 235.6mAhg-1 at 10Ag-1 over 7200 cycles). Employing Na3V2(PO4)3 as cathode, the full cell maintains a desirable capacity of 269.6mAhg-1 over 700 cycles at 1.0Ag-1. The stepwise intercalation-conversion and insertion/extraction endows outstanding Na+ storage performance, which yields valuable insight into the advancement of fast-charging and long-cycle life SIBs anode materials.

Rational design of nitrogen-doping Ti3C2Tx microspheres with enhanced polysulfide catalytic activity for lithium-sulfur batteries

The primary challenges that impede the practical applications of lithium-sulfur batteries are the significant shuttle effect of polysulfides, huge volume expansion, and slow redox kinetics. In this work, three-dimensional nitrogen doping Ti3C2Tx MXenes (3D N-Ti3C2Tx ) were successfully synthesized by spray drying and subsequent annealing, and hydrochloric acid-treated melamine effectively reduces the oxidation of MXenes in these processes. The formation of a unique nanoflower-shaped microsphere endows 3D N-Ti3C2Tx with a significant specific surface area and pore volume. The combination of nitrogen doping and the large specific surface area increased adsorption capacity and catalytic conversion ability for polysulfide intermediates. Consequently, the obtained 3D N-Ti3C2Tx /S cathode exhibited high-capacity retention (578.5 mAh g-1 after 500 cycles at 0.5 C and 462.5 mAh g-1 after 1,000 cycles at 1 C), superior rate performance (651.2 mAh g-1 at 3 C), and excellent long-term cycling performance (capacity fading rate of 0.076% per cycle at 0.5 C and 0.046% per cycle at 1 C). This work expands the potential applications of MXenes for lithium-sulfur batteries.

Functionally Modified Polymer Electrolyte Based on Noncovalent Interaction for Stable Lithium Metal Batteries.

The charge transfer efficiency of the solid electrolyte depends on the number of lithium ions that can be effectively transported and participate in the electrode reaction. However, limited by the strong coupling relationship between Li+ and Lewis basic sites on the polymer chain, the Li+ transference number (tLi+) of the solid polymer electrolyte (SPE) based dual-ion conductor is typically low, resulting in excessive anion aggregation at the electrode side and inducing concentration polarization. In this study, we present a functionalized modified polymer electrolyte (FMPE) with selective cation transport, which was synthesized by embedding 4-(trifluoromethyl)styrene (TFS) functionalized groups onto the poly(diethylene glycol diacrylate) polymer chain. The TFS group formed noncovalent couplings with TFSI- anions through hydrogen bondings and dipole-dipole interactions, which effectively limited the migration of the anions and contributed to the elevated tLi+ of the FMPEs to 0.595 and 0.699 at 25 and 60 °C, respectively. Density functional theory (DFT) calculations were performed to verify the increased anion migration barriers for different noncovalent interactions and revealed that the conjugated system formed by the delocalized π electrons of the benzene ring and the C═O groups helped to disperse the electron distribution of the polymer chains. Consequently, the decrease in the degree of Li+ immobilization promotes the decoupling and migration of Li+ between the polymer chains. Benefiting from optimized Li+ transport behavior, the lithium metal batteries (LMBs) assembled by FMPEs and LiFePO4 exhibit excellent rate performance (discharge specific capacity of 88.8 mAh g-1 at 5 C) and stable long-term cycle performance (capacity decay rate of only 0.064% per cycle for 500 cycles at 25 °C and 0.5 C).

Gradient fluorination engineering through interdiffusion reaction for high-voltage LiCoO2

The advancement of high charging cut-off voltage stands as a crucial avenue to enhance the energy density of LiCoO2 (LCO). However, LCO faces severe interface and bulk phase issues at high voltage (≥ 4.6 V), resulting in poor cycling stability. In this study, we reconstruct the surface structure of LCO based on the interdiffusion reaction between LCO and MgF2 in a high-temperature sintering process. Specifically, this interdiffusion reaction yields an ultra-thin LiF coating layer, artificially reinforcing the chemical structure of the cathode-electrolyte interphase (CEI) during cycling. This LiF-rich CEI not only effectively protects the surface structure of LCO, but also facilitates the lithium-ion diffusion. Furthermore, the diffusion of F and Mg into the LCO lattice significantly strengthens the structure, which inhibits unfavorable phase transitions from the O3 phase to the H1–3 phase at high voltage. Consequently, such modified LCO with concurrently enhanced interface and bulk structure exhibits outstanding long-term cycling performance within 3.0–4.6 V at 1 C, achieving a capacity retention of 84.9 % after 1000 cycles. Meanwhile, it also demonstrates excellent high-temperature performance, with a capacity retention of 85.0 % after 200 cycles under 45 °C.