Designing Solid Electrolytes for Rechargeable Solid-State Batteries

Lithium-ion battery (LIB) is an indispensable energy storage device in portable electronics, and its applications in electric vehicles and grid-level energy storage are increasing dramatically in recent years due to high demands. To meet energy demands and address fire hazards, next generation batteries with better safety, higher energy density, and longer cycle life have been actively investigated. In this thesis, works on polymer and ceramic solid electrolytes to improve safety and energy density of rechargeable solid-state batteries are discussed. In the first section, a flexible composite solid electrolyte is presented. Since ceramic electrolytes have high conductivities but are fragile, and polymer electrolytes are easy to process but have low conductivities, we propose a composite structure that combines these advantages. A vertically aligned and connected ceramic electrolyte is realized through the ice-templating method to improve the ionic conduction. Then a polyether-based polymer electrolyte is added to make the composite electrolyte flexible. Specifically, vertically aligned and connected LATP and LAGP nanoparticles (NPs) in the polyethylene oxide (PEO) matrix are made. The conductivity reaches 0.52 × 10-4 S/cm for LATP/PEO, and 1.67 × 10-4 S/cm for aligned LAGP/PEO composite electrolytes, which are several times higher than that with randomly dispersed LATP/LAGP NPs in PEO. Compared to the pure PEO electrolyte, the mechanical and thermal stabilities of the composite solid electrolyte are higher. The LFP-LAGP/PEO-Li cell with 148.7 mAh/g during the first discharge at 0.3C has over 95% capacity retention after 200 cycles. This method opens a new approach to optimize ion conduction in composite solid electrolytes for solid-state batteries. In the next section, polyether-based polymer electrolytes such as PEO and PEG are studied. Polyether-based electrolytes are electrochemically unstable above 4 V, restricting their use with high voltage cathodes such as NMC for high energy density. A technique involving atomic layer deposition (ALD) of Al2O3 to stabilize the polyether-based electrolyte with 4 V class cathodes is described. With a 2 nm Al2O3 coating, the capacity retention stays at 84.7% after 80 cycles and 70.3% after 180 cycles for the polyether-based electrolyte. Without the coating, the capacity drops more than 50% after only 20 cycles. This study opens new opportunity to develop safe electrolytes for lithium batteries with high energy density. In the final section, we propose a new polymer electrolyte, a poly(vinylidene fluoride) (PVDF) polymer electrolyte with organic plasticizer dimethylformamide (DMF), which possesses compatibility with 4V cathode for high energy density and high ionic conductivity (1.2×10-4 S/cm) at room temperature. This polymer electrolyte can be used as a supplement for the polyether-based electrolytes we discussed in the first two sections. In this polymer electrolyte, palygorskite ((Mg,Al)2Si4O10(OH)) nanowires are introduced to form composite solid electrolytes (CPE) to enhance both stiffness and toughness of PVDF/DMF-based polymer electrolyte. With 5 wt % of palygorskite nanowires, the elastic modulus of the PVDF-DMF CPE increases from 9.0 MPa to 96 MPa, and its yield stress increases by 200%. We further demonstrate that full cells composed of Li(Ni1/3Mn1/3Co1/3)O2 (NMC 111) cathode, PVDF-DMF/palygorskite CPE, and lithium metal anode, can be cycled over 200 times at 0.3 C, with 97% capacity retention. Moreover, the PVDF-DMF electrolyte is nonflammable, making it a safer alternative to the conventional liquid electrolyte. Our work illustrates that the PVDF-DMF/palygorskite CPE is a promising electrolyte for solid state batteries with better safety and cycling performance. Collectively, we study the polyether-based polymer electrolyte and ceramic electrolyte to combine their advantages through the ice-templating method in a battery, use ALD technique to stabilize polyether-based electrolyte for high energy density, and propose an alternative PVDF/DMF-based polymer electrolyte with nanowire additives for high energy density and stable cycling, contributing to the rechargeable solid-state batteries, with better safety, higher energy density and better cycling stability

Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite

Lead halide perovskites such as methylammonium lead triiodide (MAPI) have outstanding optical and electronic properties for photovoltaic applications, yet a full understanding of how this solution processable material works so well is currently missing. Previous research has revealed that MAPI possesses multiple forms of static disorder regardless of preparation method, which is surprising in light of its excellent performance. Using high energy resolution inelastic X-ray (HERIX) scattering, we measure phonon dispersions in MAPI and find direct evidence for another form of disorder in single crystals: large amplitude anharmonic zone-edge rotational instabilities of the PbI_6 octahedra that persist to room temperature and above, left over from structural phase transitions that take place tens to hundreds of degrees below. Phonon calculations show that the orientations of the methylammonium couple strongly and cooperatively to these modes. The result is a non-centrosymmetric, instantaneous local structure, which we observe in atomic pair distribution function (PDF) measurements. This local symmetry breaking is unobservable by Bragg diffraction, but can explain key material properties such as the structural phase sequence, ultra low thermal transport, and large minority charge carrier lifetimes despite moderate carrier mobility.Comment: 30 pages, 11 figure

The Beneficial Effects of Bisphosphonate-enoxacin on Cortical Bone Mass and Strength in Ovariectomized Rats

Osteoporosis is a major age-related bone disease characterized by low bone mineral density and a high risk of fractures. Bisphosphonates are considered as effective agents treating osteoporosis. However, long-term use of bisphosphonates is associated with some serious side effects, which limits the widespread clinical use of bisphosphonates. Here, we demonstrate a novel type of bone-targeting anti-resorptive agent, bisphosphonate-enoxacin (BE). In this study, ovariectomized rat model was established and treated with PBS, zoledronate (50 μg/kg) and different dose of BE (5 mg/kg and 10 mg/kg), respectively. The rats subjected to sham-operation and PBS treatment were considered as control group. Then, micro-computed tomography scanning, biomechanical tests, nano-indentation test and Raman analysis were used to compare the effects of zoledronate and BE on cortical bone mass, strength, and composition in ovariectomized rats. We found that both zoledronate and BE were beneficial to cortical bone strength. Three-point bending and nano-indentation tests showed that zoledronate- and BE-treated groups had superior general and local biomechanical properties compared to the ovariectomized groups. Interestingly, it seemed that BE-treated group got a better biomechanical property than the zoledronate-treated group. Also, BE-treated group showed significantly increased proteoglycan content compared with the zoledronate-treated group. We hypothesized that the increased bone strength and biomechanical properties was due to altered bone composition after treatment with BE. BE, a new bone-targeting agent, may be considered a more suitable anti-resorptive agent to treat osteoporosis and other bone diseases associated with decreased bone mass

Establishment of Constitutive Model and Analysis of Dynamic Recrystallization Kinetics of Mg-Bi-Ca Alloy during Hot Deformation

The flow behavior of the solution-treated Mg-3.2Bi-0.8Ca (BX31, wt.%) alloy was systematically investigated during hot compression at different deformation conditions. In the present study, the strain-related Arrhenius constitutive model and dynamic recrystallization (DRX) kinetic model were established, and the results showed that both two models had high predictability for the flow curves and the DRX behavior during hot compression. In addition, the hot processing maps were also made to confirm a suitable hot working range. Under the assistance of a hot processing map, the extrusion parameters were selected as 573 K and 0.5 mm/s. After extrusion, the as-extruded alloy exhibited a smooth surface, a fine DRX structure with weak off-basal texture and good strength–ductility synergy. The newly developed strong and ductile BX31 alloy will be helpful for enriching low-cost, high-performance wrought Mg alloy series for extensive applications in industries

Research on the application of residual networks considering attention mechanism in concrete curing robot

Manual curing after concrete pouring is mainly divided into two methods: plastic film curing and water spray curing, both of which have shortcomings, such as high working intensity and intense subjectivity. Current intelligent curing methods mainly focus on establishing intelligent water spray curing systems according to site needs and have poor versatility. There are currently no relevant intelligent curing measures for plastic film curing after concrete pouring. To solve the above problems, we designed and developed a concrete curing robot system based on the com-puter vision technique, including the concrete curing robot body and a corresponding control terminal, which realizes the intelligent operation of concrete plastic film curing and water spray curing. Through the classification model based on the improved ResNet-18 concrete curing surface image, the robot can make scientific judgments and decisions on the water spray curing independently. After the research and development of the robot were completed, we tested and verified the feasibility of the concrete curing robot system design at the project of Tianjin Lingang Hospital. This paper provides new ideas and technical schemes for intelligent and automatic control of concrete curing, especially for plastic film curing and water spray curing. It has essential scientific and practical significance for concrete curing, especially large-volume concrete curing

Effect of Bi Addition on the Heat Resistance of As-Extruded AZ31 Magnesium Alloy

In this work, we investigate the impact of Bi addition on the heat resistance of as-extruded AZ31 alloy during high-temperature annealing and hot compression. Electron backscattered diffraction (EBSD) technique and quasi in situ scanning electron microscopy (SEM) are used to analyze the evolution of microstructures during high-temperature annealing and hot compression, respectively. The test results show that with a prolonged annealing time, the as-extruded AZB313 alloy exhibited a lower grain growth rate, due to the pinning effect of Mg3Bi2 phases distributed at grain boundaries. On the other hand, as the compressive temperature increased, the downtrend of strength is delayed in the as-extruded AZB313 alloy. Thermally stable Mg3Bi2 phases dispersed within the grains act as barriers, hindering the motion of dislocations, which not only provides a more effective precipitation strengthening effect, but also increases the resistance to deformation of grains. Moreover, grain boundary sliding can also be restricted by Mg3Bi2 phases located at grain boundaries. This work provides a new idea for the development of heat-resistant wrought Mg alloys

Achieving extremely high speed extrusion and medium strength in a Mg–Bi–Si ternary alloy

In this work, we report a new Mg–5Bi–1Si (wt.%) alloy showing a synergy of extrusion speed (ES) and tensile yield strength (TYS). At high ESs, it still has a good alloy surface, owing to the formation of thermally stable Mg3Bi2 and Mg2Si phases and the disappearance of small-sized low-melting divorced eutectic Mg3Bi2 phases for the as-cast alloy. During 70 m/min extrusion, the fragmentation of pre-existing eutectic (Mg3Bi2 and Mg2Si) phases and the dynamic precipitation of new (Mg3Bi2) phases impede the excessive grain coarsening and provide the effective strengthening contributions on the TYS of ∼253 MPa. After T5 peak aging, two types of basal Mg3Bi2 precipitates are found and further enhance the TYS to ∼280 MPa

Grading and Detection Method of Asparagus Stem Blight Based on Hyperspectral Imaging of Asparagus Crowns

This study adopted hyperspectral imaging technology combined with machine learning to detect the disease severity of stem blight through the canopy of asparagus mother stem. Several regions of interest were selected from each hyperspectral image, and the reflection spectra of the regions of interest were extracted. There were 503 sets of hyperspectral data in the training set and 167 sets of hyperspectral data in the test set. The data were preprocessed using various methods and the dimension was reduced using PCA. K−nearest neighbours (KNN), decision tree (DT), BP neural network (BPNN), and extreme learning machine (ELM) were used to establish a classification model of asparagus stem blight. The optimal model depended on the preprocessing methods used. When modeling was based on the ELM method, the disease grade discrimination effect of the FD−MSC−ELM model was the best with an accuracy (ACC) of 1.000, a precision (PREC) of 1.000, a recall (REC) of 1.000, an F1-score (F1S) of 1.000, and a norm of the absolute error (NAE) of 0.000, respectively; when the modeling was based on the BPNN method, the discrimination effect of the FD−SNV−BPNN model was the best with an ACC of 0.976, a PREC of 0.975, a REC of 0.978, a F1S of 0.976, and a mean square error (MSE) of 0.072, respectively. The results showed that hyperspectral imaging of the asparagus mother stem canopy combined with machine learning methods could be used to grade and detect stem blight in asparagus mother stems

A Flexible Solid Composite Electrolyte with Vertically Aligned and Connected Ion-Conducting Nanoparticles for Lithium Batteries

Replacing flammable organic liquid electrolytes with solid Li-ion conductors is a promising approach to realize safe rechargeable batteries with high energy density. Composite solid electrolytes, which are comprised of a polymer matrix with ceramic Li-ion conductors dispersed inside, are attractive, since they combine the flexibility of polymer electrolytes and high ionic conductivities of ceramic electrolytes. However, the high conductivity of ceramic fillers is largely compromised by the low conductivity of the matrix, especially when nanoparticles (NPs) are used. Therefore, optimizations of the geometry of ceramic fillers are critical to further enhance the conductivity of composite electrolytes. Here we report the vertically aligned and connected Li_1+<i>x</i>Al_<i>x</i>Ti_2–<i>x</i>(PO₄)₃ (LATP) NPs in the poly­(ethylene oxide) (PEO) matrix to maximize the ionic conduction, while maintaining the flexibility of the composite. This vertically aligned structure can be fabricated by an ice-templating-based method, and its conductivity reaches 0.52 × 10^–4 S/cm, which is 3.6 times that of the composite electrolyte with randomly dispersed LATP NPs. The composite electrolyte also shows enhanced thermal and electrochemical stability compared to the pure PEO electrolyte. This method opens a new approach to optimize ion conduction in composite solid electrolytes for next-generation rechargeable batteries