Abstract
Cryogenic transmission electron microscopy (cryo-TEM) is a valuable tool recently proposed to investigate battery electrodes. Despite being employed for Li-based battery materials, cryo-TEM ...measurements for Na-based electrochemical energy storage systems are not commonly reported. In particular, elucidating the chemical and morphological behavior of the Na-metal electrode in contact with a non-aqueous liquid electrolyte solution could provide useful insights that may lead to a better understanding of metal cells during operation. Here, using cryo-TEM, we investigate the effect of fluoroethylene carbonate (FEC) additive on the solid electrolyte interphase (SEI) structure of a Na-metal electrode. Without FEC, the NaPF
6
-containing carbonate-based electrolyte reacts with the metal electrode to produce an unstable SEI, rich in Na
2
CO
3
and Na
3
PO
4
, which constantly consumes the sodium reservoir of the cell during cycling. When FEC is used, the Na-metal electrode forms a multilayer SEI structure comprising an outer NaF-rich amorphous phase and an inner Na
3
PO
4
phase. This layered structure stabilizes the SEI and prevents further reactions between the electrolyte and the Na metal.
Understanding of H- and J-aggregation behaviors in fluorene-based polymers is significant both for determining the origin of various red-shifted emissions occurring in blue-emitting polyfluorenes and ...for developing polyfluorene-based device performance. In this contribution, we demonstrate a new theory of the H- and J-aggregation of polyfluorenes and oligofluorenes, and understand the influence of chromosphere aggregation on their photoluminescent properties. H- and J-aggregates are induced by a continuous increasing concentration of the oligofluorene or polyfluorene solution. A relaxed molecular configuration is simulated to illustrate the spatial arrangement of the bonding of fluorenes. It is indicated that the relaxed state adopts a 21 helical backbone conformation with a torsion angle of 18° between two connected repeat units. This configuration makes the formation of H- and J-aggregates through the strong π–π interaction between the backbone rings. A critical aggregation concentration is observed to form H- and J-aggregates for both polyfluorenes and oligofluorenes. These aggregates show large spectral shifts and distinct shape changes in photoluminescent excitation (PLE) and emission (PL) spectroscopy. Compared with “isolated” chromophores, H-aggregates induce absorption spectral blue-shift and fluorescence spectral red-shift but largely reduce fluorescence efficiency. “Isolated” chromophores not only refer to “isolated molecules” but also include those associated molecules if their conjugated backbones are not compact enough to exhibit perturbed absorption and emission. J-aggregates induce absorption spectral red-shift and fluorescence spectral red-shift but largely enhance fluorescence efficiency. The PLE and PL spectra also show that J-aggregates dominate in concentrated solutions. Different from the excimers, the H- and J-aggregate formation changes the ground-state absorption of fluorene-based chromophores. H- and J-aggregates show changeable absorption and emission derived from various interchain interactions, unlike the β phase, which has relatively fixed absorption and emission derived from an intrachain interaction.
Electrochromism has received increasing attention due to its unique electrochromic feature and the induced applications. This review provides an overview on the recent developments in the synthesis ...and application of the electrochromic metal oxides in smart windows, display devices, e‐skins, and multifunctional energy storage devices. The main cathodic and anodic electrochromic metal oxides are surveyed here, with the discussion of representative examples in details. The current state‐of‐the‐art research activities of the derived multifunctional electrochromic devices are highlighted, i.e., material systems, components, structures, morphology, the resulting performance, etc. Major challenges and potential solutions are also discussed. Additionally, the future perspective on the development trends in electrochromic metal oxides and the commercialization of relevant devices is also proposed.
The current state‐of‐the‐art research activities on electrochromic metal oxides and the built devices and applications are reviewed. It includes comprehensive literature reviews and critical comments with representative and detailed examples. Application‐specific research challenges, future design considerations, and development directions are also discussed.
The incorporation of inorganic fillers into poly(ethyleneoxide)(PEO)-based solid polymer electrolytes (SPEs) is well known as a low-cost and effective method to improve their mechanical and ...electrochemical properties. Porous zeolitic imidazolate framework-8 (ZIF-8) is firstly used as the filler for PEO-based SPEs in this work. Due to the introduction of ZIF-8, an ionic conductivity of 2.2 × 10
−5
S/cm (30 °C) is achieved for the composite SPE, which is one order of magnitude higher than that of the pure PEO. ZIF-8 also accounts for the broader electrochemical stability window and lithium ion transference number (0.36 at 60 °C) of the composite SPE. Moreover, the improved mechanism of ZIF-8 to the composite SPE is investigated by zeta potential and Fourier transform infrared spectrograph characterizations. The stability at the composite SPE/lithium interface is greatly enhanced. The LiFePO
4
||Li cells using the composite SPE exhibit high capacity and excellent cycling performance at 60 °C, i.e., 85% capacity retention with 111 mA·h/g capacity retained after 350 cycles at 0.5 C. In comparison, the cells using the pure PEO show fast capacity decay to 74 mA·h/g maintaining only 68 capacity. These results indicate that the PEO-based SPEs with ZIF-8 are of great promise for the application in solid-state lithium metal batteries.
The electrochemical stability window of the electrolyte solution limits the energy content of non-aqueous lithium metal batteries. In particular, although electrolytes comprising fluorinated solvents ...show good oxidation stability against high-voltage positive electrode active materials such as LiNi
Co
Mn
O
(NCM811), the ionic conductivity is adversely affected and, thus, the battery cycling performance at high current rates and low temperatures. To address these issues, here we report the design and synthesis of a monofluoride ether as an electrolyte solvent with Li-F and Li-O tridentate coordination chemistries. The monofluoro substituent (-CH
F) in the solvent molecule, differently from the difluoro (-CHF
) and trifluoro (-CF
) counterparts, improves the electrolyte ionic conductivity without narrowing the oxidation stability. Indeed, the electrolyte solution with the monofluoride ether solvent demonstrates good compatibility with positive and negative electrodes in a wide range of temperatures (i.e., from -60 °C to +60 °C) and at high charge/discharge rates (e.g., at 17.5 mA cm
). Using this electrolyte solution, we assemble and test a 320 mAh Li||NCM811 multi-layer pouch cell, which delivers a specific energy of 426 Wh kg
(based on the weight of the entire cell) and capacity retention of 80% after 200 cycles at 0.8/8 mA cm
charge/discharge rate and 30 °C.
Lithium‐ion batteries (LIBs) with higher energy density are very necessary to meet the increasing demand for devices with better performance. With the commercial success of lithiated graphite, other ...graphite intercalation compounds (GICs) have also been intensively reported, not only for LIBs, but also for other metal (Na, K, Al) ion batteries. In this Progress Report, we briefly review the application of GICs as anodes and cathodes in metal (Li, Na, K, Al) ion batteries. After a brief introduction on the development history of GICs, the electrochemistry of cationic GICs and anionic GICs is summarized. We further briefly summarize the use of cationic GICs and anionic GICs in alkali ion batteries and the use of anionic GICs in aluminium‐ion batteries. Finally, we reach some conclusions on the drawbacks, major progress, emerging challenges, and some perspectives on the development of GICs for metal (Li, Na, K, Al) ion batteries. Further development of GICs for metal (Li, Na, K, Al) ion batteries is not only a strong supplement to the commercialized success of lithiated‐graphite for LIBs, but also an effective strategy to develop diverse high‐energy batteries for stationary energy storage in the future.
Applications of graphite intercalation compounds as anodes in alkali ion batteries and as cathodes in aluminium‐ion batteries are briefly reviewed in this Progress Report. We also reach conclusions on the drawbacks, major progress, emerging challenges, and some perspectives on the development of graphite intercalation compounds for metal (Li, Na, K, Al) ion batteries.
To improve the machining accuracy and stability of CNC machine tools, the lead screw is divided into several segments, and the action law of single section thermal deformation is analyzed, then the ...thermal deformation model of lead screw base on subsection processing is established. Then the relative relation of thermal deformation of each segment, the cumulative thermal drift of thermal deformation of each segment itself, the total thermal deformation of the free end of lead screw, and the relationship between them are obtained. Then, a segmented thermal compensator based on PLC for CNC system is developed. The thermal error of each segment of the lead screw is detected and compensated separately, and then the thermal error of the segment where the machine tool worktable moves to the different segment of the lead screw is compensated. Tests show that the segmented thermal compensator has achieved good actual compensation effect, so that the positioning error caused by thermal deformation of each shaft can be reduced by more than 50%.
Acetylated lignin (ACL), obtained from the acetylation of alkali lignin (AL), has been found to self-assemble into ordered colloidal spheres in a THF/H2O media. This colloid formation causes the ...color of ACL to change from dark brown to light yellow. ACL molecules form colloidal spheres at critical water content (CWC) of 48 vol % for an initial concentration of ACL in THF of 0.4 mg/mL. The colloidization process is completed at a water content of 77.75 vol %. The colloidal spheres formed from the gradual hydrophobic aggregation of ACL were approximately 80 nm in size. The concentration of Fe3+ before and after colloid formation did not change significantly, which indicates that the whitening of ACL colloids is not influenced by metal ions, but is affected by the rearrangement of chromophores during self-assembly and the light reflectance of uniform particles. Self-assembly of ACL into colloidal spheres not only whitens the dark color of lignin but also provides a novel method to prepare ordered lignin-based nanomaterials.
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•Non-flammable electrolyte with TMP and F-EPE improves the safety of SIB.•TMP/F-EPE electrolyte stabilizes the interface of NFM cathode during all processes.•The cycling life of ...NFM/HC pouch cell increases by using TMP/F-EPE electrolyte.
Despite their beneficial effect on battery safety, non-flammable electrolytes often have an adverse side effect on the electrochemical performance of lithium and sodium ion batteries due to their poor compatibility with the electrodes. In this paper, we report a new non-flammable electrolyte consisting of trimethyl phosphate (TMP) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (F-EPE) as non-flammable solvents and fluoroethylene carbonate (FEC) as additive with different concentration of Na salts, and a EC-DEC-FEC electrolyte was also prepared as baseline electrolyte. The flammability and non-flammability of the prepared electrolytes was tested. It is shown that the prepared electrolyte not only increases the capacity (129.9 vs. 122.5 mAh g−1 of baseline electrolyte) of NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode but also stabilizes the cyclability (70.8% retention after 500 cycles) of NFM/HC (HC: hard carbon) pouch cells. The dissolution of pristine NaNi1/3Fe1/3Mn1/3O2 cathode material in different solvents and electrolytes, and the XPS patterns of the cycled NFM cathode in the prepared electrolytes were also studied to understand the capacity fading mechanism. These results indicate that this new non-flammable electrolyte holds great potential for application in rechargeable sodium-ion batteries.
Molecular iodine has been introduced into the alkali lignin (AL) solutions to adjust the π−π aggregation, and the effect of lignin−iodine complexes on the aggregation and assembly characteristics of ...AL have been investigated by using fluorescence, UV−vis spectroscopy, light scattering, and viscometric techniques. Results show that AL form π−π aggregates (i.e., J-aggregates) in THF driven by the π−π interaction of the aromatic groups in AL, and the π−π aggregates undergo disaggregation in THF-I2 media because of the formation of lignin−iodine charge-transfer complexes. By using iodine as a probe to investigate the aggregation behaviors and assembly characteristics, it is estimated that about 18 mol % aromatic groups of AL form π−π aggregates in AL molecular aggregates. When molecular iodine is introduced into the AL solutions, lignin−iodine complexes occur with charge-transfer transition from HOMO of the aromatic groups of AL to the LUMO of iodine. The formation of lignin−iodine complexes reduces the affinity of the aromatic groups approaching each other due to the electrostatic repulsion and then eliminates the π−π interaction of the aromatic groups. The disaggregation of the π−π aggregates brings a dissociation behavior of AL chains and a pronounced molecular expansion. This dissociation behavior and molecular expansion of AL in the dipping solutions induce a decrease in the adsorbed amount and an increase in the adsorption rate, when AL is transferred from the dipping solution to the self-assembled adsorbed films. Consequently, the adsorption behavior of AL can be controlled by adjusting the π−π aggregation. Above observations give insight into the occurrence of J-aggregation of the aromatic groups in the AL molecular aggregates and the disaggregation mechanism of AL aggregates induced by the lignin−iodine complexes for the first time. The understanding can provide an academic instruction in the efficient utilization of the alkali lignin from the waste liquor and also leads to further development in expanding functionalities of the aromatic compounds through manipulation of the π−π aggregation.
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