Retention Of Initial Capacitance Research Articles

Heterostructure Engineering of Biphase‐Coupled Ternary Transition Metal Phosphoselenide by Topological Transformation Enabling High Performance for Supercapacitors

AbstractThe exploration of promising electrode materials with structural stability and rapid interfacial reaction kinetics is highly desirable for supercapacitors toward large‐scale applications. Herein, the synthesis of biphase‐coupled CoPSe/NiP0.24Se1.76 with multiple in‐plane heterointerfaces using the in situ topological transformation approach is presented. As a novel ternary metal phosphoselenide (TMPSe) for supercapacitor cathode that is fabricated by synchronous phosphoselenization strategy, it realizes a superior lifespan with cycling compared to conventional transition metal selenides. The depleted anti‐bonding eg* orbitals of transition metal ions (Co/Ni) in the CoPSe/NiP0.24Se1.76, as proved by preliminary theoretical calculations, strengthens the chemical bonding between Co/Ni and coordinating atoms, thereby enhancing the chemical stability. Simultaneously, the CoPSe/NiP0.24Se1.76 in‐plane multi‐heterostructures can not only alleviate the volume change during the charge–discharge process but also expose more active sites, promoting the adsorption of OH− ions, which is conducive to the rapid redox reaction kinetics of the CoPSe/NiP0.24Se1.76, and consequently, it delivers a remarkable reversible capacity and excellent long‐term cycle stability with 97.7% initial capacitance retention over 16 000 cycles. Moreover, the asymmetric supercapacitors with this cathode demonstrate outstanding rate capability and high energy density. This strategy of constructing biphase‐coupled CoPSe/NiP0.24Se1.76 by topological transformation is of great potential application for the high‐performance electrode material.

Metal‐Organic Framework Hosted Silicon for Long‐Cycling, Low‐Cost, and Flexible Batteries

AbstractDeveloping biodegradable electrodes is a significant step toward environmental sustainability and cost reduction in battery technology. This paper presents a new approach that utilizes metal‐organic framework (MOF)‐encapsulated silicon nanoparticles (SiNPs) as the active anode material within a cellulose‐based electrode. The electrode is free‐standing, flexible, biodegradable, and significantly reduces the strain experienced by SiNPs during volume expansion, resulting in improved capacity and cycle life stability of SiNPs. The high porosity of the electrode creates efficient lithium (Li+) ion transport channels and enhances electrolyte absorption, thus promoting effective contact between the electrolyte and active material. The outcome is rapid electrode kinetics and a highly reversible discharge capacity of 1744.6 mAh g−1 at 0.5 A g−1 versus Li/Li+ over 1000 cycles. Further, full cell tests are conducted that demonstrate a stable cycle performance exceeding 3400 cycles, with an initial discharge capacity retention of 80.5% at 0.5 A g−1. By employing cellulose and avoiding toxic organic solvents and binders, the proposed approach is promising for a substantial reduction of the production costs of Li‐ion batteries. The scalability of the proposed method further enhances its practical viability, offering intriguing economic implications for the future of battery technology.

A stable ZnMn2O4 cathode for aqueous Zn-ion batteries via Ni doping to suppress Mn dissolution

ZnMn2O4 (ZMO) emerges as a promising cathode for aqueous Zn-ion batteries due to its high theoretical capacity of 224 mAh g−1 and operating voltage of ∼1.9 V (vs. Zn2+/Zn). However, it suffers from capacity degradation over cycling, attributed to the dissolution of redox-active Mn through Mn3+ disproportionation. In this study, we propose a strategy to stabilize ZMO cathodes by transforming Mn3+ into Mn4+ via Ni doping, aiming for charge balance. The ZnMn2−xNixO4 (x = 0, 0.5, 1.0, and 1.5) with different Ni amounts was prepared by straightforward precipitation and calcination. The mitigation of redox-active Mn dissolution enhanced the specific capacity of all Ni-doped ZMO compared to 201 mAh g−1 of ZMO. ZnMn1.5Ni0.5O4 and ZnMnNiO4 exhibit 277 and 278 mAh g−1, respectively, surpassing ZMO’s theoretical capacity (224 mAh g−1) of ZMO. This additional capacity was attributed to MnOx deposition on the cathode and the charge storage reaction with Zn-ion within the MnOx deposit. Furthermore, Ni doping induces a structural transition of the tetragonal into a cubic spinel, expanding the unit cell volume. This structural modification combined with suppressed Mn dissolution contributes to improved cycling stability. ZnMnNiO4 exhibits 80 % retention of initial capacity after 1000 cycles, outperforming ZMO (57 % retention). The expanded unit cell reduces repulsion between inserted Zn ions, enabling a higher rate performance than pure ZMO. The change in Mn valence states induced by Ni doping enhanced the lifespan and rate capability of ZMO cathodes, underscoring their potential as cathodes for Zn-ion batteries.

MOF-on-MOF-derived double-shelled iron-doped cobalt sulfide nanosheet arrays modified by CeO2 for asymmetric supercapacitors

Through deliberate design of nanostructures and modifications to the surface, significant advancements in energy storage performance can be achieved. This work focuses on the creation of iron-doped cobalt sulfide hollow nanosheets, featuring a distinctive double-shelled structure. This unique architecture is achieved by replacing the ligand within zeolitic imidazole framework (ZIF)-L with K4Fe (CN)6, followed by a sulfurization process. Subsequently, a layer of CeO2 cladding is integrated using solvothermal synthesis. The resulting hollow double-shelled structure fosters intimate contact between the electrode material and electrolyte, effectively mitigating the challenges associated with substantial volume fluctuations during electrochemical processes. Additionally, the porous characteristics inherited from ZIF, augmented redox reactions resulting from elemental doping, and coordination with the external CeO2 modification further enhance the electrochemical performance of the electrode. Consequently, the Fe-CoS/CeO2 electrode exhibits an impressive specific capacitance of 3727.5 F g−1 at 1 A g−1. When employed in an asymmetric supercapacitor configuration with activated carbon (AC) serving as the negative electrode, the Fe-CoS/CeO2//AC demonstrates exceptional energy storage capabilities, achieving 36.4 W h kg−1 at 800.0 W kg−1 and exhibiting superior long-term stability with 89.8 % retention of initial capacitance after 10,000 cycles at 10 A g−1.

Stress-Relieving Carboxylated Polythiophene/Single-Walled Carbon Nanotube Conductive Layer for Stable Silicon Microparticle Anodes in Lithium-Ion Batteries.

Stress-relieving and electrically conductive single-walled carbon nanotubes (SWNTs) and conjugated polymer, poly[3-(potassium-4-butanoate)thiophene] (PPBT), wrapped silicon microparticles (Si MPs) have been developed as a composite active material to overcome technical challenges such as intrinsically low electrical conductivity, low initial Coulombic efficiency, and stress-induced fracture due to severe volume changes of Si-based anodes for lithium-ion batteries (LIBs). The PPBT/SWNT protective layer surrounding the surface of the microparticles physically limits volume changes and inhibits continuous solid electrolyte interphase (SEI) layer formation that leads to severe pulverization and capacity loss during cycling, thereby maintaining electrode integrity. PPBT/SWNT-coated Si MP anodes exhibited high initial Coulombic efficiency (85%) and stable capacity retention (0.027% decay per cycle) with a reversible capacity of 1894 mA h g-1 after 300 cycles at a current density of 2 A g-1, 3.3 times higher than pristine Si MP anodes. The stress relaxation and underlying mechanism associated with the incorporation of the PPBT/SWNT layer were interpreted by quasi-deterministic and quantitative stress analyses of SWNTs through in situ Raman spectroscopy. PPBT/SWNT@Si MP anodes can maintain reversible stress recovery and 45% less variation in tensile stress compared with SWNT@Si MP anodes during cycling. The results verify the benefits of stress relaxation via a protective capping layer and present an efficient strategy to achieve long cycle life for Si-based anodes for next-generation LIBs.

Achieving Superior Cyclability Pouch Cells with Oxygen Vacancy-Moderated P'2/P3 Hybrid Layered Sodium Cathode Materials.

Layered P2-type sodium manganese oxide has emerged as a promising cathode candidate for sodium-ion batteries due to its appealing cost-effectiveness and high discharge voltage. However, its practical capacity within the voltage range of 2.0-4.0 V (vs Na+/Na) is relatively low, and its rate capability is hampered by the adverse charge/vacancy ordering during charge/discharge. In this study, a layered P'2/P3 mixed-phase Na0.8-aMn0.675Ni0.225Li0.1O2-x cathode with high (003) crystal plane intensity was designed by introducing oxygen vacancies to P2-structured materials. Aided by these advantages, the hybrid cathode material demonstrates impressive structural and thermal stability and faster Na-ion diffusion kinetics compared to a regular P2 material. Half-cell shows an initial discharge capacity retention of 101 mA h/g at 12 mA/g and 92.25% retention after 500 cycles at 120 mA/g. In combination with a hard carbon anode, the 0.5 A h pouch cell achieved a prevailing capacity retention of 95.2% after 2600 cycles at 36 mA/g. This work opens new dimensions for layered cathode materials with the aim of achieving superior cyclabilities.

Nitrogen and phosphorus enriched nanoporous carbonaceous material for gas sorption and supercapacitor applications

Nitrogen and phosphorous-enriched heteroatoms-based nanoporous carbonaceous material (designated as HPHMC900) possesses a high surface area of 1668 m2 g−1 was synthesized. HPHMC900 captures 5.6 and 3 mmol g−1 of CO2 and CH4 at 273 K and 1 bar, respectively. Further, the material has 11.95 mmol g−1 of H2 adsorption capability at 77 K and 1 bar. HPHMC900 has been investigated for supercapacitor application. Further, a symmetric supercapacitor device (SSD) fabricated using the HPHMC900, has a specific capacitance (Csp) of 233 F g−1, energy (E) of 46.6 Wh kg−1, and power (P) of 289 W kg−1, respectively. The high Csp and high energy were achieved at low-concentrated aqueous electrolyte (0.5 M KOH), without using any redox-active agents. Further, it shows 100 % coulombic efficiency and initial capacitance retention (94.9 %) after 10,000 cycles. This research elucidates the correlation between high surface area and heteroatom enrichment with enhanced charge storage and gas adsorption efficiency.

Optimizing Graphene Anode Performance in Lithium‐Ion Batteries: Investigating the Effects of Diverse Thermal Conditions

Herein, the graphene nanoplatelets (GNPs) anode is prepared using a facile, chemical‐free, and scalable approach that combines probe sonication and microwave treatment in an argon condition. The resulting GNPs exhibit a significant number of structural defects (ID/IG: 0.262), which provide abundant active sites to store lithium ions and offer sufficient pathways for the quick transfer of lithium ions and electrons. In lithium‐ion batteries (LIBs), the GNPs anode exhibits an outstanding electrochemical performance, achieving a high reversible 414 mAh g−1 capacity at the high current density of 1 A g−1 after 350 cycles. The anode maintains desirable capacities of 167 and 150 mAh g−1 even at elevated current densities of 4 and 5 A g−1, respectively. Importantly, it exhibits remarkable cycling performance with more than 100% of the initial reversible capacity retention after 350 cycles. The outcomes show noticeably enhanced performance characteristics, suggesting the potential for developing microwave‐treated graphene anode for long‐lasting and high‐performance LIBs.

Modifying lignite-derived hard carbon with micron carbon tubes to improve sodium-ion storage

Lignite is a feasible raw material for the development of hard carbon anodes for sodium-ion batteries because of its high abundance and cheap cost. However, the existence of more defects in lignite-derived carbon, leads to unsatisfactory electrochemical performance as the anode of sodium-ion batteries, such as the initial Coulombic efficiency (ICE) and capacity retention rate. In this work, we introduce a preparation process of lignite-derived hard carbon using carbonized lignite and oleic acid (C9H16O2) as precursors. The micron carbon tubes (MCTs) generation on the hard carbon surface can provide additional Na+ active sites and reduce the defects, which effectively enhances the specific capacity and ICE of the anode. Benefiting the MCT modification, the hard carbon anode has a high reversible capacity of 244.8 mAh g−1 and ICE of 76.72%, which is respectively 30% and 10% higher than that of the bare hard carbon anode, this is of significance for the practical application of coal-based hard carbon in sodium-ion batteries.

High-Performance All-Solid-State on-Chip Planar Micro-Supercapacitors Based on Aminated Graphene Quantum Dots by Photolithography

Rapid development of portable miniaturized electronic devices has put forward higher requirements for microenergy. Functionalized graphene quantum dots combine the properties of both functionalized graphene and quantum dots, and are expected to promote further development of high-performance energy storage devices. Here, all-solid-state on-chip planar micro-supercapacitors (PMSCs) were fabricated based on aminated graphene quantum dots by modified liquid-gas interface self-assembly and photolithography, with the electrode width/gap of 24 μm/8 μm. The electrochemical performance was analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectrometry and cycle stability in PVA/H2SO4 gel electrolyte. The results indicated that the fabricated PMSCs showed good capacitive response at the scan rates of 0.01 V s−1 to 10000 V s−1. The CV curves of the PMSCs displayed a typical pseudocapacitive feature at the scan rates of 0.01 V s−1 to 1 V s−1. The PMSCs had ultrahigh rate capability of up to 10000 V s−1, and the GCD curves were near triangle-shaped curves, demonstrating excellent electrochemical reversibility. The PMSCs showed ideal capacitive behavior at the low frequency region of the Nyquist plot. The Nyquist plot of the PMSCs showed a semicircle at the high frequency region. The relaxation time constant of the PMSCs were 3.59 μs, indicating that the PMSCs had fast frequency response. After 10000 charge-discharge cycles at the scan rate of 500 V s−1, the initial capacitance retention rate of the PMSCs were 99.17%, indicating that the PMSCs possessed good long-term electrochemical stability. This study provides an important reference for the application of functional graphene quantum dots in the field of the PMSCs.

Spheroidization: The Impact of Precursor Morphology on Solid-State Lithiation Process for High-Quality Ultrahigh-Nickel Oxide Cathodes.

Layered oxides with ultrahigh nickel content are considered promising high energy cathode materials. However, their cycle stability is constrained by a series of heterogeneous structural transformations during the complex solid-state lithiation process. By in-depth investigation into the solid-state lithiation process of LiNi0.92Co0.04Mn0.04O2, it is found that the protruded parts on the surface of precursor particles tend to be surrounded by locally excessive LiOH, which promotes the formation of a rigid and dense shell during the early stage of lithiation process. The shell will hinder the diffusion of lithium and topotactic lithiation within the particles, culminating in spatially heterogeneous intermediates that can impair the electrochemical properties of the cathode material. The spheroidization of the precursor can enhance uniformity in structural evolution during solid-phase lithiation. Ultrahigh nickel cathodes derived from spherical precursors demonstrate high initial discharge specific capacity (234.2 mAh g-1, in the range of 2.7-4.3 V) and capacity retention (89.3 % after 200 cycles), significantly superior to the non-spherical samples. This study not only sheds light on the intricate relationship between precursor shape and structural transformation but also introduces a novel strategy for enhancing cathode performance through precursor spheroidization.

One-Pot Direct Mechanochemical Silicon Replacement of Sodium Fluorosilicate into Sodium Fluorozirconate and Functionalization of Graphite for Enhanced Sodium-Ion Storage.

Efficient sodium ion storage in graphite is as yet unattainable, because of the thermodynamic instability of sodium ion intercalates-graphite compounds. In this work, sodium fluorozirconate (Na3ZrF7, SFZ) functionalized graphite (SFZ-G) is designed and prepared by the in situ mechanochemical silicon (Si) replacement of sodium fluorosilicate (Na2SiF6, SFS) and functionalization of graphite at the same time. During the mechanochemical process, the atomic Si in SFS is directly replaced by atomic zirconium (Zr) from the zirconium oxide (ZrO2) balls and container in the presence of graphite, forming SFZ-G. The resulting SFZ-G, working as an anode material for sodium ion storage, shows a significantly enhanced capacity of 418.7 mAh g-1 at 0.1 C-rate, compared to pristine graphite (35 mAh g-1) and simply ball-milled graphite (BM-G, 200 mAh g-1). In addition, the SFZ-G exhibits stable sodium-ion storage performance with 86% of its initial capacity retention after 1000 cycles at 2.0 C-rate.

Nitrogen-enriched nanoporous polytriazine as efficient electrode material for high-performance supercapacitor application in non-aqueous medium with high cyclic stability

Nitrogen-enriched nanoporous polytriazine (NENP) synthesized by conventional heating method possesses a high specific surface area (SABET) of 966 m2 g−1, controlled pore size distribution (1.6, 5, and 8.3 nm) and total pore volume of 2.73 cm3 g−1. The synthesized specimen was utilized as an electrode material for supercapacitor (SC) application in non-aqueous media. The electrodes of NENP were fabricated by two approaches viz., conventional binder-based method and a binder-free electrophoretic deposition (EPD) approach. In case of electrode fabrication by controlled EPD process, the mass of 0.58 mg was obtained as the optimized mass achieved at pH = 2, deposition voltage = 20 V and deposition time = 6 min. The optimized electrodes and tetraethylammonium tetrafluoroborate in adiponitrile (TEA-BF4/ADP) non-aqueous electrolyte were used to fabricate symmetric supercapacitor devices (SC). The SC device, with EPD- based binder-free electrodes, exhibited higher specific capacitance (Csp = 84 F g−1), energy density (Esp = 118.8 Wh kg−1) and power density (Psp = 17 kW kg−1) compared to SC device (49 F g−1, 68.8 Wh kg−1, and 11 kW kg−1 at 0.8 A g−1) fabricated using electrode made from the binder based method. To enhance the SC performance, KI was added as a redox additive to the non-aqueous electrolyte (TEA-BF4/ADP). The SC device, with NENP binder-free electrodes and redox-active nonaqueous electrolyte (TEA-BF4/ADP/KI), achieved the highest Csp, Esp, and Psp (112 F g−1, 150.5 Wh kg−1, and 27 kW kg−1) and demonstrated high cyclic stability (~80.2 % initial capacitance retention after 30,000 cycles, at 5 A g−1).

A Protective Layer of UIO-66/Reduced Graphene Oxide to Stabilize Zinc-Metal Anodes toward High-Performance Aqueous Zinc-Ion Batteries.

Rechargeable aqueous Zn-ion batteries with a Zn anode hold great promise as promising candidates for advanced energy storage systems. The construction of protective layer coatings on Zn anode is an effective way to suppress the growth of Zn dendrites and water-induced side reactions. Herein, we reported a series of UIO-66 materials with different concentrations of reduced graphene oxide (rG) coated onto the surface of Zn foil (Zn@UIO-66/rGx; x = 0.05, 0.1, and 0.2). Benefiting from the synergistic effect of UIO-66 and rG, symmetric cells with Zn@UIO-66/rGx (x = 0.1) electrodes exhibit excellent reversibility (e.g., long cycling life over 1100 h at 1 mA cm-2/1 mAh cm-2) and superior rate capability (e.g., over 1100 and 400 h at 5 mA cm-2/2.5 mAh cm-2 and 10 mA cm-2/5 mAh cm-2, respectively). When the Zn@UIO-66/rG0.1 anode was paired with the NaV3O8·1.5H2O (NVO) cathode, the Zn@UIO-66/rG0.1||NVO cell also delivered a high reversible capacity of 189.9 mAh g-1 with an initial capacity retention of 61.3% after 500 cycles at 1 A g-1, compared to the bare Zn||NVO cell with only 92 cycles.

Elucidating the Impact of Li3InCl6-Coated LiNi0.8Co0.15Al0.05O2 on the Electro-Chemo-Mechanics of Li6PS5Cl-Based Solid-State Batteries.

Li6PS5Cl has attracted significant attention due to its high Li-ion conductivity and processability, facilitating large-scale solid-state battery applications. However, when paired with high-voltage cathodes, it experiences adverse side reactions. Li3InCl6 (LIC), known for its higher stability at high voltages and moderate Li-ion conductivity, is considered a catholyte to address the limitations of Li6PS5Cl. To extend the stability of Li6PS5Cl toward LiNi0.8Co0.15Al0.05O2 (NCA), we applied nanocrystalline LIC as a 180 nm-thick protective coating in a core-shell-like fashion (LIC@NCA) via mechanofusion. Solid-state batteries with LIC@NCA allow an initial discharge specific capacity of 148 mA h/g at 0.1C and 80% capacity retention for 200 cycles at 0.2C with a cutoff voltage of 4.2 V (vs Li/Li+), while cells without LIC coating suffers from low initial discharge capacity and poor retention. Using a wide spectrum of advanced characterization techniques, such as operando XRD, XPS, FIB-SEM, and TOF-SIMS, we reveal that the superior performance of solid-state batteries employing LIC@NCA is related to the suppression of detrimental interfacial reactions of NCA with Li6PS5Cl, delamination, and particle cracking compared to uncoated NCA.

Exploring polyaniline nanofiber synthesis at vegetable oil-water interfaces for high-performance hybrid electrochemical capacitors

Polyaniline (PANI) nanofibers are synthesized at five different vegetable oil-water interfaces by a modified interfacial polymerization method. A series of syntheses is performed to study the effect of vegetable oil- water interfaces on the sizes, morphologies and corresponding electrochemical performances of resultant PANI nanofiber samples. Five PANI nanofiber samples are synthesized and the corresponding electrochemical performances as electrochemical capacitor (EC) electrodes are evaluated. It is observed that the PANI nanofiber sample prepared at water-sunflower oil interface, PANI5 possesses the lowest diameter and highest specific capacitance among all the prepared samples. Herein, we have fabricated an all-solid-state asymmetric electrochemical capacitor (AEC) of PANI5 and bio-derived chemically activated carbon (AC). The electrochemical measurements show that PANI5 and AC exhibits specific capacitance of 395 F g−1 and 240 F g−1 respectively at current density 1 A g−1. The fabricated PANI5//AC AEC exhibits areal capacitance of 70 mF cm−2 at current density of 1 mA cm−2. The energy density (Ed) and power density (Pd) of constructed AEC are found to be 19 µW h cm−2 and 696 µW cm−2, respectively. It gives the cyclic stability of 62 % retention of initial areal capacitance after completing 5000 galvanostatic charge-discharge cycles.

Core-shell NiCo2S4@C with three dimensional carbon frameworks for enhanced asymmetrical supercapacitor and lithium storage performance

Transition-metal sulfides have been considered as promising candidates for electrochemical supercapacitor and lithium ion batteries. Unfortunately, the shortcomings including large volume change, low conductivity as well as severe structural exfoliation from conductive substrate or current collector inhibit their practical application. Herein, the hydrothermal and solvothermal approach are developed for the controllable synthesis of core-shell NiCo2S4@C with three dimensional carbon frameworks. As an asymmetric supercapacitor, the NiCo2S4@C/YP-50 F displays a high energy density of 46.7 Wh kg−1 at a power density of 0.8 kW kg−1 and the good cycling stability (∼110 % of the initial capacitance retention at 16 kW kg−1 over 2000 cycles). Furthermore, the NiCo2S4@C exhibits the specific capacity of 414 mAh g−1 after 500 cycles at 2000 mA g−1 when evaluated as anode for lithium ion batteries. The excellent performance can be ascribed to the core-shell structure and the three dimensional carbon frameworks. The synthetic approach can be extended to fabricate other high performance metal sulfides for energy storage.

Heterostructure Ni3P/CoP2/NiCo2O4/CC nanowire material as a trifunctional electrode for high-performance supercapacitors and electrocatalysis

The design and preparation of efficient and cost-effective multifunctional active materials for energy storage and conversion are essential component in achieving the current clean energy development. Herein, we have successfully synthesized heterostructure Ni3P/CoP2/NiCo2O4/CC nanowires with vertical array structure on carbon cloth by a simple strategy of solvothermal-annealing and phosphate treatment. The abundant heterogeneous interfaces and synergistic effect between the transition metal oxides/phosphides endow the material with excellent multifunctional properties. As a supercapacitor electrode, the Ni3P/CoP2/NiCo2O4/CC electrode possesses an exceptional specific capacitance of 2349 F g−1 at 1 A g−1. At a power density of 900 W kg−1, the built asymmetric supercapacitor achieves a high energy density of 37.5 Wh kg−1. Furthermore, an initial capacitance retention rate of 85 % was still maintained after 25,000 cycles. When used as electrocatalyst, the required oxygen evolution reaction and hydrogen evolution reaction overpotentials for a current density of 10 mA cm−2 are only 267 mV and 98 mV, respectively. Meanwhile, it presents superior overall water splitting activity (1.64 V@10 mA cm−2) and catalytic stability. This study affords additional perspectives for the reasonable design of non-noble metal based multifunctional materials to meet the diversified energy development.

Building Flame-Retardant Polymer Electrolytes via Microcapsule Technology for Stable Lithium Batteries.

Flame retardants could improve the safety properties of lithium batteries (LBs) with the sacrifice of electrochemical performance due to parasitic reactions. To concur with this, we designed thermal-response clothes for hexachlorophosphazene (HCP) additives by the microcapsule technique with urea-formaldehyde (UF) resin as the shell. HCP@UF combines with polyacrylonitrile (PAN) by hydrogen bonds successfully to form PAN-HCP@UF as the flame-retardant solid polymer electrolyte. The hydrogen bonds ensure excellent mechanical properties of the polymer electrolyte. The multiscale free radical-annihilating agent HCP effectively eliminates hydrogen free radicals of electrolytes under high temperature, showing excellent flame retardation. During the operation of the battery, functional groups on the UF resin act as active sites to promote the migration of lithium ions, while the internal HCP is protected from electrochemical reaction. With 25% HCP@UF addition, the limiting oxygen index of the PAN-HCP@UF increases to 28% and the Li+ transfer number up to 0.80. By UF protection, the initial capacity retention rate of the Li||LFP battery that assembles with PAN-HCP@UF is 88.8% after 500 cycles at 0.5 C. Thus, the microcapsule-encapsulated approach is deemed to provide an innovative strategy to prepare high-safety solid-state LB with a stable long cycle life.

Modulating solvated structure of Zn2+ and inducing surface crystallography by a simple organic molecule with abundant polar functional groups to synergistically stabilize zinc metal anodes for long-life aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have attracted significant attention owing to their inherent security, low cost, abundant zinc (Zn) resources and high energy density. Nevertheless, the growth of zinc dendrites and side reactions on the surface of Zn anodes during repeatedly plating/stripping shorten the cycle life of AZIBs. Herein, a simple organic molecule with abundant polar functional groups, 2,2,2-trifluoroether formate (TF), has been proposed as a high-efficient additive in the ZnSO4 electrolyte to suppress the growth of Zn dendrites and side reaction during cycling. It is found that TF molecules can infiltrate the solvated sheath layer of the hydrated Zn2+ to reduce the number of highly chemically active H2O molecules owing to their strong binding energy with Zn2+. Simultaneously, TF molecules can preferentially adsorb onto the Zn surface, guiding the uniform deposition of Zn2+ along the crystalline surface of Zn(002). This dual action significantly inhibits the formation of Zn dendrites and side reactions, thus greatly extending the cycling life of the batteries. Accordingly, the Zn//Cu asymmetric cell with 2 % TF exhibits stable cycling for more than 3,800 cycles, achieving an excellent average Columbic efficiency (CE) of 99.81 % at 2 mA cm−2/1 mAh cm−2. Meanwhile, the Zn||Zn symmetric cell with 2 % TF demonstrates a superlong cycle life exceeding 3,800 h and 2,400 h at 2 mA cm−2/1 mAh cm−2 and 5 mA cm−2/2.5 mAh cm−2, respectively. Simultaneously, the Zn//VO2 full cell with 2 % TF possesses high initial capacity (276.8 mAh/g) and capacity retention (72.5 %) at 5 A/g after 500 cycles. This investigation provides new insights into stabilizing Zn metal anodes for AZIBs through the co-regulation of Zn2+ solvated structure and surface crystallography.