Long-term Cycle Life Research Articles

Morphology-controllable synthesis of bimetallic oxide Bi2Fe4O9 as novel electrode materials for high-performance supercapacitors

Supercapacitors have grabbed a lot of limelight and have been under extensive scrutiny by researchers for their advantages over competitors, such as high power density, long-term cycle life, accelerated charging and discharging, security, and environmental sustainability. Herein, the hydrothermal combination with co-precipitation approach is effectively used to create Bi2Fe4O9 particles with various morphologies through controlling the concentrations of NaOH, and they show significant discrepancies in their electrochemical characteristics. The chamfered square plate-like Bi2Fe4O9 particles (Bi2Fe4O9–3) obtained at a NaOH concentration of 12 M demonstrate pseudocapacitive or battery-like behavior in a three-electrode system and exhibited optimum electrochemical properties, displaying a mass-specific capacitance of 443.8 F g−1 at 1.0 A g−1. In terms of electrochemical characteristics and long-term cycling stability, the Bi2Fe4O9–3 sample also displays an extraordinary Coulombic efficiency of 98.87 % and capacitance retention rate of 142 % after completing 5000 cycles of galvanostatic charge-discharge. Moreover, the self-assembled asymmetric supercapacitor device has an energy density of 21.11 Wh kg−1 at a power density of 424.26 W kg−1. Bi2Fe4O9–3 has been meticulously fabricated as an innovative and inimitable electrode material that manifests brilliant electrochemical properties, rendering it prospective for progressive application in the supercapacitors realm by researchers in the future.

Constructing a stable interface on Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode via lactic acid-assisted engineering strategy

Ni-rich layered oxides are potential cathode materials for next-generation high energy density Li-ion batteries due to their high capacity and low cost. However, the inherently unstable surface properties, including high levels of residual Li compounds, dissolution of transition metal cations, and parasitic side reactions, have not been effectively addressed, leading to significant degradation in their electrochemical performance. In this study, we propose a simple and effective lactic acid-assisted interface engineering strategy to regulate the surface chemistry and properties of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode. This novel surface treatment method successfully eliminates surface residual Li compounds, inhibits structural collapse, and mitigates cathode-electrolyte interface film growth. As a result, the lactic acid-treated LiNi0.8Co0.1Mn0.1O2 achieved a remarkable capacity retention of 91.7% after 100 cycles at 0.5 C (25 °C) and outstanding rate capability of 149.5 mA h g−1 at 10 C, significantly outperforming the pristine material. Furthermore, a pouch-type full cell incorporating the modified LiNi0.8Co0.1Mn0.1O2 cathode demonstrates impressive long-term cycle life, retaining 81.5% of its capacity after 500 cycles at 1 C. More importantly, the thermal stability of the modified cathode is also dramatically improved. This study offers a valuable surface modification strategy for enhancing the overall performance of Ni-rich cathode materials.

3D hierarchically fractal structure stabilized anode for achieving long-term cycle life of aqueous Zn-ion batteries

The cycling stability of aqueous Zn-ion battery (AZIB) is a serious issue for their successful application, mainly due to the considerable growth of Zn dendrites and the existence of side effects during operation. Herein, the hierarchically three-dimensional (3D) fractal structure of the ZnO/Zn/CuxO@Cu (ZZCC) anode is prepared by a two-step process, where CuxO nanowires are prepared on Cu foam by thermal oxidation method and Zn layer and ZnO surface are formed by plating. This fractal structure increases the electrodynamic surfaces and reduces the local current density, which can regulate Zn plating and inhibit dendritic growth and side effects. Apparently, the symmetric ZZCC-based cell shows a long-term operation time of 3000 h at 1 mA cm−2 with 1 mAh cm−2, and an operation time of more than 1000 h with a discharge depth of 15.94%. Compared with the bare Zn foil anode, the AZIB assembled with the composite of Mn-doped vanadium oxide and reduced graphene oxide cathode and ZZCC anode (MnVO@rGO//ZZCC) exhibits significantly improved cyclability (i.e. with 88.5% capacity retention) and achieves a Coulomb efficiency of 99.4% at 2 A g-1. This hierarchically 3D structure strategy to design anodes with superior cyclic stability contributes to the next generation of secure energy.

A Polytetrafluoroethylene-Based Solvent-Free Procedure for the Manufacturing of Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) have recently become popular for energy storage due to their high energy density, storage capacity, and long-term cycle life. Although binders make up only a small proportion of LIBs, they have become the key to promoting the transformation of the battery preparation process. Along with the development of binders, the battery manufacturing process has evolved from the conventional slurry-casting (SC) process to a more attractive solvent-free (SF) method. Compared with traditional LIBs manufacturing method, the SF method could dramatically reduce and increase the energy density due to the reduced preparation steps and enhanced electrode loading. Polytetrafluoroethylene (PTFE), as a typical binder, has played an important role in fabricating high-performance LIBs, particularly in regards to the SF technique. In this paper, the development history and application status of PTFE binder was introduced, and then its contributions and the inherent problems involved in the SF process were described and analyzed. Finally, the viewpoints concerning the future trends for PTFE-based SF manufacturing methods were also discussed. We hope this work can inspire future research concerning high-quality SF binders and assist in promoting the evolution of the SF manufacturing technology in regards to LIBs.

Unlocking the Effect of Chain Length and Terminal Group on Ethylene Glycol Ether Family Toward Advanced Aqueous Electrolytes.

Constructing high-performance hybrid electrolyte is important to advanced aqueous electrochemical energy storage devices. However, due to the lack of in-depth understanding of how the molecule structures of cosolvent additives influence the properties of electrolytes significantly impeded the development of hybrid electrolytes. Herein, a series of hybrid electrolytes are prepared by using ethylene glycol ether with different chain lengths and terminal groups as additives. The optimized 2m LiTFSI-90%DDm hybrid electrolyte prepared from diethylene glycol dimethyl ether (DDm) molecule showcases excellent comprehensive performance and significantly enhances the operating voltage of supercapacitors (SCs) to 2.5V by suppressing the activity of water. Moreover, the SC with 2m LiTFSI-90%DDm hybrid electrolyte supplies a long-term cycling life of 50000 cycles at 1Ag-1 with 92.3% capacitance retention as well as excellent low temperature (-40ºC) cycling performance (10000 times at 0.2Ag-1). Universally, Zn//polyaniline full cell with 2m Zn(OTf)2-90%DDm electrolyte manifests outstanding cycling performance in terms of 77.9% capacity retention after 2,000 cycles and a dendrite-free Zn anode. This work inspires new thinking of developing advanced hybrid electrolytes by cosolvent molecule design toward high-performance energy storage devices.

Fe-substituted SrCoO3 perovskites as electrode materials for wide temperature-tolerant supercapacitors

Sr-based perovskites represent enormous potential as supercapacitor electrode materials. However, the wide-temperature supercapacitor application for perovskite-based electrodes has not been studied yet. Thus, there is a pressing need for comprehensive research and investigation in the wide-temperature range to unlock the full capabilities of Sr-based perovskite and pave the way for its successful integration into versatile supercapacitor systems. In this study, SrCo1-xFexO3-δ (x = 0.05, 0.10, 0.15 and 0.20) were synthesized by solid-state sintering method, as oxygen-intercalated electrode materials for wide temperature-tolerant supercapacitors. SrCo1-xFexO3-δ contains orthogonal and monoclinic phases for x = 0.05 and x = 0.10, and a stable monoclinic phase can be obtained when the substitution amount is at least 15 %. The best electrochemical performance was obtained in x = 0.10, with a specific capacitance of 526.6 F g−1 at 1 A g−1. This can be attributed to the lowest resistance and richest oxygen vacancies of SrCo0.9Fe0.1O3-δ, which are conducive to oxygen-intercalated energy storage. The SrCo0.9Fe0.1O3-δ@CC//AC@CC supercapacitor device displays a working voltage of 1.6 V and a stable long-term cycle life with 85.71 % capacity retention after 5000 cycles. Furthermore, the temperature-dependent electrochemical characterization indicates an improvement of electrochemical performance for both electrode and device as temperature increases, which may be ascribed to the enhanced ion migration in the electrolyte. From 0 to 85 °C, the specific capacitance of SrCo0.9Fe0.1O3-δ@CC electrode increases from 91.8 to 1035.9 F g−1 at 1A g−1, and the energy density of the device also increases from 7.6 to 26.2 Wh kg−1 when the power density is 800 W kg−1.

Breaking Barriers to High-Practical Li-S Batteries with Isotropic Binary Sulfiphilic Electrocatalyst: Creating a Virtuous Cycle for Favorable Polysulfides Redox Environments.

Investigations into lithium-sulfur batteries (LSBs) has focused primarily on the initial conversion of lithium polysulfides (LiPSs) to Li2 S2 . However, the subsequent solid-solid reaction from Li2 S2 to Li2 S and the Li2 S decomposition process should be equally prioritized. Creating a virtuous cycle by balancing all three chemical reaction processes is crucial for realizing practical LSBs. Herein, amorphous Ni3 B in synergy with carbon nanotubes (aNi3 B@CNTs) is proposed to implement the consecutive catalysis of S8(solid) → LiPSs(liquid) → Li2 S(solid) →LiPSs(liquid) . Systematic theoretical simulations and experimental analyses reveal that aNi3 B@CNTs with an isotropic structure and abundant active sites can ensure rapid LiPSs adsorption-catalysis as well as uniform Li2 S precipitation. The uniform Li2 S deposition in synergy with catalysis of aNi3 B enables instant/complete oxidation of Li2 S to LiPSs. The produced LiPSs are again rapidly and uniformly adsorbed for the next sulfur evolution process, thus creating a virtuous cycle for sulfur species conversion. Accordingly, the aNi3 B@CNTs-based cell presents remarkable rate capability, long-term cycle life, and superior cyclic stability, even under high sulfur loading and extreme temperature environments. This study proposes the significance of creating a virtuous cycle for sulfur species conversion to realize practical LSBs.

Pseudocapacitive lithium-rich disordered rock salt vanadium oxide with 3D lithium-ion transport pathways for high-performance lithium-ion capacitor

Pseudocapacitive materials with high-rate behavior of lithium-ion charge storage offer a pathway to narrow the kinetics gap with capacitive porous carbon cathode toward lithium-ion capacitors both with high energy and high power densities. However, most of pseudocapacitive materials are subject to their relatively high redox potential, thus resulting in an undesirable decrease in energy density. Here, we demonstrate that lithium-rich disordered rock salt vanadium oxide (DRX-Li3V2O5), electrochemically transformed from V2O5 bulk, exhibits typical pseudocapacitive behaviors within a low working potential range between 0.1 and 2.0 V (vs. Li/Li+). The pseudocapacitive behaviors of DRX-Li3V2O5 mainly arise upon a percolating network that offers three-dimensional Li + transport pathways confirmed by Monte Carlo simulations. When the V2O5 bulk precursor is replaced by V2O5 nanosheets, as-obtained DRX-Li3V2O5 electrode displays a nearly symmetrical cyclic voltammetry curve, suggesting an ideal pseudocapacitive behavior. A lithium-ion capacitor further assembled by this pseudocapacitive DRX-Li3V2O5 anode, yields a cell voltage of 4.0 V, a maximum energy density of 186 Wh kg−1 and a maximum power density of 51,680 W kg−1 as well as long-term cycling life over 30,000 cycles, which are higher than or comparable to that of the state-of-art lithium-ion capacitors based on graphite and other pseudocapacitive materials.

Covalently bridged bond assembly of MoS2 lamellae onto a graphene sheet: an outstanding electrode for high rate and long-life lithium/sodium-ion batteries

The practical application of Molybdenum sulphide (MoS2) electrodes has been hindered by its structural instability, and poor electrical conductivity. To enhance the cycle stability and rate performance of MoS2 in lithium/sodium-ion batteries (LIBs/SIBs), we synthesized a graphene-supported MoS2 composite (MoS2@rGO) with affluent covalent bridged bonds through a facile and scalable hydrothermal and annealing process. The covalent bridged bonds of Mo–S–C, Mo–O–C and C–O–S provide an effective charge transfer path between MoS2 and graphene, facilitating fast charge hopping and improving rate performance. As anode materials for LIBs, the MoS2@rGO exhibited exceptional long-term cycle life (906 mAh g−1 at 1.0 A g−1 after 400 cycles) and outstanding rate capability (1267.7/314.7 mAh g−1 at 0.1/6.5 A g−1). Additionally, the MoS2@rGO electrode demonstrated a stable reversible capacity of 521.7 mAh g−1 at 1.0 A g−1 after 700 cycles and excellent rate capabilities of 665.1 and 326.3 mAh g−1 at 0.1 and 10.0 A g−1 in SIBs. The edge Mo of MoS2 is directly coupled with the oxygen of the functional group on rGO, achieved by adjusting the pH value of the solution to tune the surface charge feature, can effectively enhance the structural stability of electrode even under higher current density.

Thermal polymerization of ion-modified carbon dots into multi-functional LiF-carbon interface for stabilizing SiO anode

SiO has been demonstrated as one type of promising high-capacity anode for Li-ion batteries. However, the parasitic reactions between the electrolyte and SiO interface, severer than that of the well-developed graphite, are generally overlook. Herein, a multi-functional LiF-carbon co-coating layer on SiO (SiO@LCD) is designed to resist the interfacial reactions, which originates from thermal-assembly of zero-dimensional Li-absorbed and F-doped carbon dots produced by hydro/alcohol-thermal reaction of discarded wood sawdust with a high yield of 96.9 %. Combined with advanced spectroscopy characterizations and theoretical calculations, the LiF-carbon co-coating layer has been determined to induce preferential decomposition of LiPF6 to form a thin and dense solid electrolyte interface (SEI) with LiF-rich inner layer, and promote the rapid transmission of ion/electron. As a result, the initial Coulombic efficiency (CE) of the SiO@LCD increases from 66.1 % to 78.6 %, and the average CE is increased by 0.3 % at 0.2 A g−1 with enhanced rate capability and cycling stability during the (de)lithiation process. More importantly, the assembled 3.7 Ah pouch cell exhibits a long-term cycling life over 400 cycles at 0.2 C with the capacity retention of 85.1 %.

Interface engineering of Ruddlesden–Popper perovskite/CeO2/carbon heterojunction for rechargeable zinc-air batteries

The development of noble metal-based bifunctional electrocatalysts is the key to driving the sluggish oxygen reduction/evolution reaction (ORR/OER) for rechargeable zinc-air battery applications. There is an urgent need to design and construct robust and cost-efficient bifunctional electrocatalysts. Herein, an interface engineering strategy of Ruddlesden–Popper (RP) perovskite/CeO2/carbon heterojunction with core–shell nanostructures is described. Ce-based metal–organic framework derived CeO2-C nanosheets are decorated on the surface of RP type perovskite Pr3Sr(Ni0.5Co0.5)3O10−δ (PSNC) nanofibers. Benefiting from the favorable conductivity, abundant oxygen vacancies and strong interfacial coupling, the hierarchical CeO2-C/PSNC electrode delivers a half-wave potential of 0.78 V (ORR), and an OER overpotential of 370 mV at 10 mA cm−2, respectively. A liquid rechargeable zinc-air battery (ZAB) assembled with CeO2-C/PSNC electrocatalysts as the air cathode exhibits a peak power density of 161 mW cm−2 and a long-term cycling life over 219 h. In addition, the CeO2-C/PSNC-based all-solid-state cable-type ZAB provides a high open-circuit voltage (∼1.44 V), good flexibility and durability. Our study opens a new insight into the design of efficient electrocatalysts for rechargeable ZABs by constructing hierarchical heterojunctions.

Activating Gel Polymer Electrolyte Based Zinc-Ion Conduction with Filler-Integration for Advanced Zinc Batteries.

Quasi solid zinc batteries (QSZBs) based on gel electrolyte have performed as a significant application prospect as advanced high energy density electrochemical storage devices with safety, low cost, eco-friendliness, and flexibility. While, the practical application of QSZBs was enormously restricted by low ionic conductivity and poor strength of pure gel electrolyte. Here, in order to activate the zinc ion conduction in gel electrolyte, the kinds of inorganic fillers constituting the composite electrolyte was investigated. The theoretical study was also revealed by density functional theory to have deep insight into the mechanism. In particular, appropriate filler amount (ZnO#20) can make a noteworthy ion conductivity elevation (1.3 × 10-3 S cm-1) which is much better than the control sample (2.0 × 10-4 S cm-1) at -20 °C. As a result, the symmetric cell with ZnO#20 can achieve a long-term cycling life of over 1500 h. Moreover, the pouch cell coupled with vanadium pentoxide is assembled, and corresponding versatility is also identified with twisting, refrigeration (-20 °C) and cutting.

One dimensional pea-shaped NiSe2 nanoparticles encapsulated in N-doped graphitic carbon fibers to boost redox reversibility in sodium-ion batteries

In recent years, sodium-ion batteries (SIBs) have emerged as a promising technology for energy storage systems (ESSs) because of the abundance and affordability of sodium. Recently, metal selenides have been studied as promising high-performance conversion-type anode materials in SIBs. Among them, nickel selenide (NiSe2) has received considerable attention due to its high theoretical capacity of 495 mAh g–1 and conductivity. However, it still suffers from poor cycling stability because of the low electrochemical reactivity, large volume expansion, and structural instability during cycles. To address these challenges, NiSe2 nanoparticles encapsulated in N-doped graphitic carbon fibers (NiSe2@NGCF) were synthesized by using ZIF-8 as a template. NiSe2@NGCF showed a high discharge capacity of 558.3 mAh g–1 with a fading rate of 0.14% per cycle after 200 cycles at 0.5 A g–1 in 0.01–3.0 V. At a very high current density of 5 A g–1, the capacity still displayed excellent long-term cycle life with a discharge capacity of 406.1 mAh g–1 with a fading rate of 0.016% per cycle after 3000 cycles. The mechanism of the excellent electrochemical performance of NiSe2@NGCF was thoroughly investigated by ex-situ XRD, TEM, and SEM analyses. Furthermore, NiSe2@NGCF//Na3V2(PO4)3 full-cell also delivered an excellent reversible capacity of 378.7 mAh g−1 at 0.1 A g−1 after 50 cycles, demonstrating its potential for practical application in SIBs.

Amorphous Vanadium Oxide Nanosheets with Alterable Polyhedron Configuration for Fast-Charging Lithium-Ion Batteries.

Transition metal oxides with high theoretical capacities are promising anode materials for lithium-ion batteries (LIBs). However, the sluggish reaction kinetics remain a bottleneck for fast-charging applications due to its slow Li+ migration rate. Herein, a strategy is reported of significantly reducing the Li+ diffusion barrier of amorphous vanadium oxide by constructing a specific ratio of the VO local polyhedron configuration in amorphous nanosheets. The optimized amorphous vanadium oxide nanosheets with a ratio ≈1:4 for octahedron sites (Oh ) to pyramidal sites (C4v ) revealed by Raman spectroscopy and X-ray absorption spectroscopy (XAS) demonstrate the highest rate capability (356.7mAhg-1 at 10.0Ag-1 ) and long-term cycling life (455.6mAhg-1 at 2.0Ag-1 over 1200 cycles). Density functional theory (DFT)calculations further verify that the local structure (Oh :C4v = 1:4) intrinsically changes the degree of orbital hybridization between V and O atoms and contributes to a higher intensity of electron occupied states near the Fermi level, thus resulting in a low Li+ diffusion barrier for favorable Li+ transport kinetics. Moreover, the amorphous vanadium oxide nanosheets possess a reversible VO vibration mode and volume expansion rate close to 0.3%, as determined through in situ Raman and in situ transmission electron microscopy.

A novel boron-doping approach for long-term cycling life of Li-rich layered cathode

The commercial application of Li-rich Mn-based layered oxides (LLOs) is hindered due to their instability of lattice oxygen and dissolution of manganese. Herein, an effective and large-scale production co-precipitation boron-doping strategy was proposed to improve the performance of Li1.15Mn0.53Ni0.22Co0.1O2. We found that the boron introduced in the co-precipitation process will be uniformly distributed in the bulk and the resulting boron-doped Li1.15Mn0.53Ni0.22Co0.1O2 shows excellent electrochemical properties with low doping amount. Multi-dimensional analysis shows that boron doping significantly improves the structural stability of materials. After 1200 cycles at 1C, boron-doped sample can deliver 147 mAhg−1 with an excellent retention of 80.1%, which is much higher than that of the pristine sample of 44% after 700 cycles. Moreover, the discharge voltage decay of the boron-doped samples is only 0.54 mV per cycle (1.39 mV for pristine). It is worth mentioning that the pouch-cell full battery cycle performance of doped samples is also excellent. The doped cathode//graphite shows a superior capacity retention of 83.6% after 500 cycles without gas generation, while the pristine//graphite only hold the 46.6% of initial capacity. The dQ/dV curves and the SEM/EDS of electrode analysis verified higher reversibility of lattice oxygen, less manganese dissolution and more stable microstructure, which greatly improved the cycling life after boron doping.

In Situ Polymerized Flame Retardant Gel Electrolyte for High-Performance and Safety-Enhanced Lithium Metal Batteries.

A flame retardant gel electrolyte (FRGE) is deemed as one of the most promising electrolytes to relieve the problems of safety hazards and interfacial incompatibility of Li metal batteries. Herein, a novel solvent triethyl 2-fluoro-2-phosphonoacetate (TFPA) with outstanding flame retardancy is introduced in the polymer skeleton synthesized by in situ polymerization of the monomer polyethylene glycol dimethacrylate (PEGDMA) and the cross-linker pentaerythritol tetraacrylate (PETEA). The FRGE exhibits superb interfacial compatibility with Li metal anodes and inhibits uncontrolled Li dendrite growth. This can be ascribed to the restriction of free phosphate molecules by the polymer skeleton, thus realizing a stable cycling performance over 500 h at 1 mA cm-2 and 1 mAh cm-2 in the Li||Li symmetric cell. In addition, the high ionic conductivity (3.15 mS cm-1) and Li+ transference number (0.47) of the FRGE further enhance the electrochemical performance of the correspondent battery. As a result, the LiFePO4|FRGE|Li cell exhibits excellent long-term cycling life with a capacity retention of 94.6% after 700 cycles. This work points to a new pathway for the practical development of high-safety and high-energy-density Li metal-based batteries.

Novel porous CoS1.097@carbon nanofibers as flexible and binder-free anode material for sodium-ion batteries

Transition metal sulfides (TMSs) have received numerous attention as anode materials for sodium-ion batteries because of the high theoretical capacity. So far, the Na-storage performance of TMSs is still unsatisfactory due to the structural degeneration that induced by the volume change upon redox process. Herein, a novel flexible and binder-free anode material of porous CoS1.097@carbon nanofibers was facilely constructed by means of the electrospinning, carbonization and sulfidation processes. The porous CoS1.097@carbon nanofibers display unique structure with CoS1.097 nanoparticles confined into porous N-doped carbon nanofibers, and can provide sufficient active sites, high electrical conductivity, reduced ion diffusion distance, abundant ion migration pathways, desirable voids for alleviating the volume variation, and rigid structural stability for efficient Na-storage. In consequence, the flexible and binder-free electrode material delivers high initial discharge capacity, enhanced rate capability and long-term cycling life. Besides, intrinsic diffusion and electrochemical storage behavior of Na+ ions were emphatically disclosed. This work paves a facile route for the synthesis of flexible and binder-free TMSs-based anode materials, promoting the practical application of wearable sodium-ion batteries.

Construction of a robust solid electrolyte interphase on Ge anode to achieve a superior long-term cycle life of lithium-ion battery

Alloy-based materials are suffering a huge volume expansion/shrink during the repeated lithium-ion intercalation/deintercalation process, so they always display an unsatisfied electrochemical performance, especially for the cycle life. In this work, we design a localized highly concentrated electrolyte (LHCE) for Ge anode, by dissolving LiFSI in DME/TTE (3:7 by volume). Raman spectra illustrate that most FSI- anions in LHCE coordinate with Li+ ions, producing the solvated structure in form of AGGs or CIPs. XPS spectra prove that the solid electrolyte interphase (SEI) is rich in inorganic phase, such as Li2CO3, Li3N, LiF and Li2O. So the SEI is more stable and thinner, and it can keep the integrity of Ge particles and avoid their crushing during a long-term cycle. Although a serious capacity decrease at around the 30th cycle is found in esters electrolytes, the similar phenomenon is never seen in LHCE. The PM-550 @Ge in LHCE remains a reversible capacity of 1040 mAh g−1 after 300 cycles at 0.5 A g−1, and the capacity retention ratio is as high as 84%. Even after a long cycling of 500 cycles, the PM-550 @Ge delivers a high reversible capacity of 951 mAh g−1 at 1.0 A g−1.

Construction of Alkaline Gel Polymer Electrolytes with a Double Cross-Linked Network for Flexible Zinc–Air Batteries

Flexible zinc–air batteries have broad potential as the next generation of energy storage component in wearable electronic devices. However, the mechanical performance and ionic conductivity of electrolytes are urgent issues that hinder the commercial application of flexible batteries. Herein, the alkaline gel polymer electrolyte (AGPE) with a double-network structure is developed, which consists of a covalently cross-linked polyacrylamide (PAM) by in situ polymerization and a physically cross-linked poly(vinyl alcohol) (PVA) by the freeze–thaw method. The freestanding PVA/N-PAM/KOH gel electrolyte demonstrates high ionic conductivity (309.9 mS cm–1) and excellent mechanical toughness (0.69 MJ m–3), benefiting from the synergistic effect of the double cross-linked system and hydrogen bonds. Meanwhile, the assembled ″sandwich″-type zinc–air battery presents excellent power density (40.43 mW cm–2), long-term cycle life (113 cycles), super-high-energy efficiency (70.2%), and stable discharge plateau. Impressively, the PVA/N-PAM/KOH-based batteries attached to the human body surface are reliably capable of powering light-emitting diodes.

Nitrogen-Doped Carbon Coated Na3V2(PO4)2F3 Derived from Polyvinylpyrrolidone as a High-Performance Cathode for Sodium-Ion Batteries

Na super ionic conductor (NASICON)-type Na3V2(PO4)2F3 (NVPF) has been regarded as a prospective candidate of cathode materials for sodium-ion batteries due to its excellent structural stability, relatively high capacity and working voltage. However, the poor cyclability and rate capability, resulting from its low intrinsic electronic conductivity, have become a serious obstacle to their practical large-scale application. In this work, N-doped carbon coated NVPF composites (NVPF@NC) were successfully synthesized via a simple sol–gel method, in which low-cost polyvinylpyrrolidone was introduced as a nitrogen source. After high-temperature pyrolysis, a highly conductive N-doped carbon layer was in-situ constructed on the particle surface to enhance the sodium storage performance of NVPF. The optimized NVPF@NC cathode delivered high reversible capacity, excellent rate capability and long-term cycle life compared to pristine NVPF@C. The remarkable electrochemical performance of NVPF@NC cathode benefits from the modification strategy of introducing a heteroatom-doped carbon layer, triggering the formation of extrinsic defects and active sites in the N-doped amorphous carbon layer, which greatly enhances the electrical conductivity and the diffusion rate of sodium ions. This work provides a facile and effective approach for the preparation of N-doped carbon coated NVPF with remarkable sodium storage properties, which could be extended to other electrode materials electrochemical for energy storage.