Magnesium‐ion batteries (MIB) have gradually attracted attention owing to their high theoretical capacity, high safety, and low cost. A bimetallic metal–organic framework self‐sacrificing template ...and a co‐assembly strategy are used to prepare a high‐performance, stable cycling NiSe2‐CoSe2@TiVCTx (NCSe@TiVC) heterostructure MIB cathode that can be used as a flexible integrated unit to power future self‐powered systems. Benefiting from the synergistic effect of TiVCTx MXene and NCSe, the NCSe@TiVC heterostructure electrode has a discharge‐specific capacity of 136 mAh g−1 at 0.05 A g−1 and high cycling stability of over 500 cycles; the assembled pouch‐cell device as flexible integrated unit exhibits good practicability. The magnesium ion storage mechanism is also validated using quantitative kinetic analysis, ex situ XRD, and XPS techniques. Density functional theory analysis indicates the most stable Mg‐atom adsorption sites in the heterostructure. This study broadens the possibilities for applying the TiVCTx MXene heterostructure to energy storage materials and future self‐powered flexible systems.
The 3D porous spherical structured NCSe/TiVC is built via a self‐sacrificing template co‐assembly strategy, in which the TiVCTx MXene exhibits the synergistic effect of enhancing the reaction kinetics. NCSe@TiVC‐MIB cathode can be used as a flexible integrated unit to power future self‐powered systems. This study broadens the possibilities for applying the TiVCTx MXene to energy storage materials and future self‐powered flexible systems.
Impossible voltage plateau regulation for the cathode materials with fixed active elemental center is a pressing issue hindering the development of Na‐superionic‐conductor (NASICON)‐type ...Na3V2(PO4)2F3 (NVPF) cathodes in sodium‐ion batteries (SIBs). Herein, a high‐entropy substitution strategy, to alter the detailed crystal structure of NVPF without changing the central active V atom, is pioneeringly utilized, achieving simultaneous electronic conductivity enhancement and diffusion barrier reduction for Na+, according to theoretical calculations. The as‐prepared carbon‐free high‐entropy Na3V1.9(Ca,Mg,Al,Cr,Mn)0.1(PO4)2F3 (HE‐NVPF) cathode can deliver higher mean voltage of 3.81 V and more advantageous energy density up to 445.5 Wh kg−1, which is attributed by the diverse transition‐metal elemental substitution in high‐entropy crystalline. More importantly, high‐entropy introduction can help realize disordered rearrangement of Na+ at Na(2) active sites, thereby to refrain from unfavorable discharging behaviors at low‐voltage region, further lifting up the mean working voltage to realize a full Na‐ion storage at the high voltage plateau. Coupling with a hard carbon (HC) anode, HE‐NVPF//HC SIB full cells can deliver high specific energy density of 326.8 Wh kg−1 at 5 C with the power density of 2178.9 W kg−1. This route means the unlikely potential regulation in NASICON‐type crystal with unchangeable active center becomes possible, inspiring new ideas on elevating the mean working voltage for SIB cathodes.
A high‐entropy effect is delicately introduced into fluorophosphate cathode for sodium‐ion batteries by in situ partial substitution of active V central atom, preparing a high‐entropy carbon‐free Na3V1.9(Ca,Mg,Al,Cr,Mn)0.1(PO4)2F3 cathode, suppressing the occurrence of detrimental phase transition process in the low‐voltage region, and further lifting up the mean working voltage of pristine Na3V2(PO4)2F3, enhancing sodium storage behavior, rate capability, and cycle performance.
The rapid developments of the Internet of Things (IoT) and portable electronic devices have created a growing demand for flexible electrochemical energy storage (EES) devices. Nevertheless, these ...flexible devices suffer from poor flexibility, low energy density, and poor dynamic stability of power output during deformation, limiting their practical applications. Carbon nanofibers (CNFs) with high conductivity, good flexibility, and large‐scale preparation are regarded as promising electrodes for flexible EES devices. Based on the issues of current flexible EES devices, this review presents various strategies from the design of CNFs‐based electrodes to the fabrication of devices and overviews their applications in various flexible metal ion/air batteries (Li/Na/K‐ion batteries, Li‐S batteries, metal–air batteries, and other novel secondary batteries) and supercapacitors. Finally, the remaining challenges and perspectives on the CNFs‐based flexible EES devices are proposed to provide guidance for the researchers concentrating on high‐performance flexible EES devices.
Flexible electrochemical energy storage (EES) devices is currently a research hotspot in the field of energy storage. This review indicates the existing issues of flexible EES devices and proposes various effective solution strategies from CNFs‐based electrodes to devices and the corresponding development in flexible EES devices, aiming to provide important guidance for designing high‐performance flexible EES devices.
Sodium‐ion batteries (SIBs) have great potential for large‐scale energy storage. Cellulose is an attractive material for sustainable separators, but some key issues still exist affecting its ...application. Herein, a cellulose‐based composite separator (CP@PPC) was prepared by immersion curing of cellulose‐based separators (CP) with poly(propylene carbonate) (PPC). With the assistance of PPC, the CP@PPC separator is able to operate the cell stably at high voltages (up to 4.95 V). The “pore‐hopping” ion transport mechanism in CP@PPC opens up extra Na+ migration paths, resulting in a high Na+ transference number (0.613). The separator can also tolerate folding, bending and extreme temperature under certain circumstances. Full cells with CP@PPC reveal one‐up capacity retention (96.97 %) at 2C after 500 cycles compared to cells with CP. The mechanism highlights the merits of electrolyte analogs in separator modification, making a rational design for durable devices in advanced energy storage systems.
Immersion curing of a cellulose‐based separator (CP) with poly(propylene carbonate) (PPC) results in a cellulose‐based composite separator (CP@PPC) for sodium‐ion batteries. The “pore‐hopping” ion transport mechanism in CP@PPC allows a high Na+ transference number. PPC enhances the mechanical properties of the separator and the battery thermal safety, further promotes ion transport and improves the overall performance of the battery.
After application in electric vehicles, spent LiFePO4 (LFP) batteries are typically decommissioned. Traditional recycling methods face economic and environmental constraints. Therefore, direct ...regeneration has emerged as a promising alternative. However, irreversible phase changes can significantly hinder the efficiency of the regeneration process owing to structural degradation. Moreover, improper storage and treatment practices can lead to metamorphism, further complicating the regeneration process. In this study, a sustainable recovery method is proposed for the electrochemical repair of LFP batteries. A ligand‐chain Zn‐complex (ZnDEA) is utilized as a structural regulator, with its ─NH─ group alternatingly facilitating the binding of preferential transition metal ions (Fe3+ during charging and Zn2+ during discharging). This dynamic coordination ability helps to modulate volume changes within the recovered LFP framework. Consequently, the recovered LFP framework can store more Li‐ions, enhance phase transition reversibility between LFP and FePO4 (FP), modify the initial Coulombic efficiency, and reduce polarization voltage differences. The recovered LFP cells exhibit excellent capacity retention of 96.30% after 1500 cycles at 2 C. The ligand chain repair mechanism promotes structural evolution to facilitate ion migration, providing valuable insights into the targeted ion compensation for environmentally friendly recycling in practical applications.
The introduction of the ligand chain within the Zn complex dynamically modulates the variational structure, enlarging the main framework of LFP and expediting the de‐intercalation of Li+. This process revitalizes the composition, structure, and electrochemical performance of LFP, restoring them to levels comparable to that of newly produced LFP even under severe degradation conditions during the operation of regenerated batteries.
During multivalent ions insertion processes, intense electrostatic interaction between charge carriers and host makes the high‐performance reversible Al3+ storage remains an elusive target. On ...account of the strong electrostatic repulsion and poor robustness, Prussian Blue analogues (PBAs) suffer severely from the inevitable and large strain and phase change during reversible Al3+ insertion. Herein, we demonstrate an entropy‐driven strategy to realize ultralong life aqueous Al‐ion batteries (AIBs) based on medium entropy PBAs (ME‐PBAs) host. By multiple redox active centers introduction, the intrinsic poor conductivity can be enhanced simultaneously, resulting in outstanding capabilities of electrochemical Al3+ storage. Meanwhile, the co‐occupation at metal sites in PBA frameworks can also increase the M−N bond intensity, which is beneficial for constraining the phase change during consecutive Al3+ reversible insertion, to realize an extended lifespan over 10,000 cycles. Based on the calculation at different operation states, the fluctuation of ME‐PBA lattice parameters is only 1.2 %. Assembled with MoO3 anodes, the full cells can also deliver outstanding electrochemical properties. The findings highlight that, the entropy regulation strategy could uncover the isochronous constraint on both strain and phase transition for long‐term reversible Al3+ storage, providing a promising design for advanced electrode materials for aqueous multivalent ions batteries.
The successful implementation of an entropy‐regulation approach is proposed by using PBAs as cathode for aqueous AIBs, resulting in excellent electrochemical performance. As‐designed medium‐entropy cathode could deliver a high capacity for reversible Al3+ storage, which is attributed to the activation of numerous redox centres and low strain, further enabling ultra‐high rates of ion storage and an exceptionally long lifespan.
The stable phase transformation during electrochemical progress drives extensive research on vanadium‐based polyanions in sodium‐ion batteries (SIBs), especially Na3V2(PO4)3 (NVP). And the electron ...transfer between V3+/4+ redox couple in NVP could be generally achieved, owing to the confined crystal variation during battery service. However, the more favorable V4+/5+ redox couple is still in hard‐to‐access situation due to the high barrier and further brings about the corresponding inefficiency in energy densities. In this work, the multilevel redox in NVP frame (MLNP) alters reaction pathway to undergo homeostatic solid solution process and breaks the high barrier of V4+/5+ at high voltage, taking by progressive transition metal (V, Fe, Ti, and Cr) redox couple. The diversified reaction paths across diffusion barriers could be realized by distinctive release/uptake of inactive Na1 site, confirmed by the calculations of density functional theory. Thereby its volume change is merely 1.73% during the multielectron‐transfer process (≈2.77 electrons). MLNP cathode could achieve an impressive energy density of 440 Wh kg−1, driving the leading development of MLNP among other NASICON structure SIBs. The integration of multiple redox couples with low strain modulates the reaction pathway effectively and will open a new avenue for fabricating high‐performance cathodes in SIBs.
The homeostatic solid solution characteristics drive the phosphate with multilevel redox (MLNP) in sodium‐ion batteries (SIBs), breaking through the high barrier of intrinsic mono‐redox center with sluggish reactivity by differentiating each redox couple. This establishes fast and stable reaction kinetics, balancing multi‐electron transfer and low strain to develope high energy‐density and durable NASICON cathodes for SIBs.
Sodium‐ion batteries (SIBs) have gradually become one of the most promising energy storage techniques in the current era of post‐lithium‐ion batteries. For anodes, transitional metal selenides (TMSe) ...based materials are welcomed choices , owing to relatively higher specific capacities and enriched redox active sites. Nevertheless, current bottlenecks are blamed for their poor intrinsic electronic conductivities, and uncontrollable volume expansion during redox reactions. Given that, an interfacial‐confined isochronous conversion strategy is proposed, to prepare orthorhombic/cubic biphasic TMSe heterostructure, namely CuSe/Cu3VSe4, through using MXene as the precursor, followed by Cu/Se dual anchorage. As‐designed biphasic TMSe heterostructure endows unique hierarchical structure, which contains adequate insertion sites and diffusion spacing for Na ions, besides, the surficial pseudocapacitive storage behaviors can be also proceeded like 2D MXene. By further investigation on electronic structure, the theoretical calculations indicate that biphasic CuSe/Cu3VSe4 anode exhibits well‐enhanced properties, with smaller bandgap and thus greatly improves intrinsic poor conductivities. In addition, the dual redox centers can enhance the electrochemical Na ions storage abilities. As a result, the as‐designed biphasic TMSe anode can deliver a reversible specific capacity of 576.8 mAh g−1 at 0.1 A g−1, favorable Na affinity, and reduced diffusion barriers. This work discloses a synchronous solution toward demerits in conductivities and lifespan, which is inspiring for TMSe‐based anode development in SIBs systems.
An interfacial‐confined isochronous conversion strategy is conducted to prepare a hierarchical biphasic selenide, by choosing metallic conductive V2CTx MXene as the precursor. As‐designed biphasic selenide exhibits excellent electronic conductivity and abundant active sites for Na ions. Besides, the carbonaceous matrix can serve as a stable buffer layer to alleviate the volume expansion of selenides during battery operation.
Abstract
The NASICON cathode, Na
3
V
2
(PO
4
)
3
, has garnered significant attention due to its robust framework with fast Na
+
migration. To expand its application scenarios by diversified ...electronic reaction, the substitution of vanadium with cost‐effective and abundant redox elements is a special research topic. Nevertheless, in terms of reducing toxicity, increasing Na content and widening voltage range, the V
4+/5+
redox couple in Na
4
FeV(PO
4
)
3
often accompanies asymmetric and irreversible electrochemical reactions that pose a dilemma for capacity and structural stability, especially at high currents. Herein, in this work, Na
4
FeV
1/3
Ti
2/3
(PO
4
)
3
(NFVT) has achieved highly reactive of multiple electron transfer (Ti
2+/3+
, Fe
2+
/
3+
, and V
3+/4+
/
5+
) by utilizing the redox reaction with quasi‐monophase behavior, and it can reserve great capacity retention after 3,000 cycles. More competitively, its boosting kinetics makes the fast‐charging characteristic, just requiring only 3.63 min to reach 80% state of charge at 2 C. The rapid ion/electron transport dynamics can achieve the decay of only 0.043% per cycle by unlocking the quasi‐monophase behavior in the framework of NFVT full cells. The present study provides a fresh perspective on designing cathode materials with fast‐charging capabilities for sodium‐ion batteries.
