A highly soluble dimethoxybenzene derivative as a redox shuttle for overcharge protection of secondary lithium batteries

A compound 4-tertbutyl-1,2-dimethoxybenzene (TDB) was synthesized and tested as a redox shuttle for overcharge protection of Li–LiFePO₄ batteries. This isomer of tertbutyl-substituted dimethoxybenzene is miscible with the organic polar electrolytes and provides a solution for the poor solubility of ditertbutyl-substituted 1,4-dimethoxybenzenes as a redox shuttle additive. The experimental results demonstrated that the shuttle molecules added in the electrolyte cannot only provide feasible overcharge protection, but also have indiscernible detrimental influences on the charge–discharge behaviors of Li–LiFePO₄ cells, showing a great prospect for practical applications in commercial rechargeable lithium batteries.     

Physical and electrochemical characterizations of LiFePO4-incorporated Ag nanoparticles

Olivine-type LiFePO₄ composite materials for cathode material of the lithium-ion batteries were synthesized by using a sol-gel method and were coated by a chemical deposition of silver particles. As-obtained LiFePO₄/C-Ag (2.1 wt.%) composites were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), conductivity measurements, cyclic voltammetry, as well as galvanostatic measurements. The results revealed that the discharge capacity of the LiFePO₄/C-Ag electrode is 136.6 mAh/g, which is 7.6% higher than that of uncoated LiFePO₄/C electrode (126.9 mAh/g). The LiFePO₄/C coated by silver nanoparticles enhances the electrode conductivity and specific capacity at high discharge rates. The improved capacity at high discharge rates may be attributed to increased electrode conductivity and the synergistic effect on electron and Li⁺ transport after silver incorporation.     

Effect of PPy/PEG conducting polymer film on electrochemical performance of LiFePO4 cathode material for Li-ion batteries

Rechargeable lithium-ion batteries (LIBs) have been the most commonly used batteries in the portable electronics market for many years. Polypyrrole (PPy) was now investigated as a conducting addition agent to enhance the cathode and anode materials performance in LIBs. Actual development in the synthesis and modification of the most promising cathode materials, LiFePO₄, is described in this mini-review. The main aim of this mini-review is to highlight the effect of PPy based conducting polymer films on the electrochemical efficiency of LiFePO₄ based cathode materials for LIBs summarizing our own research. Influence of the polyethylene glycol (PEG) additive in the PPy coating layer was evaluated. The improved electrochemical performance can be attributed to the enhanced electronic conductivity, higher solubility of ions originating from the electrolyte, higher movability of dissolved Li⁺ ions, and improved structural flexibility resulting from the incorporation of the PPy or PPy/PEG conducting polymer layer. The stabilizing effect of PEG in PPy was reflected in lowered cross-linking and reduced structural defects and, in consequence, in higher specific capacity of PPy/PEG-LiFePO₄ cathodes compared to that of PPy-LiFePO₄ cathodes and bare LiFePO₄ cathodes.     

纳米级锂离子电池正极材料LiFePO4

LiFePO₄以其价格便宜,稳定性好,无毒等优点而倍受关注。但是非纳米LiFePO₄的电子导电率低及扩散系数小限制了其在锂离子电池领域的大规模应用。而纳米电极材料以其特有的优点很好的解决了这些问题。本文主要综述了国内外合成纳米级LiFePO₄ 的不同方法及所得材料的对电化学性能和相关机理,以及纳米LiFePO₄作为锂离子正极材料存在的问题。     

Mixed Anionic and Cationic Redox Chemistry in a Tetrathiomolybdate Amorphous Coordination Framework

We report the electrochemistry of a hitherto unexplored Na₂MoS₄ phase as a conversion electrode material for Na‐ and Li‐ion batteries. The material adopts an amorphous coordination polymer structure with mixed Mo and S valences. XPS and XRD analysis reveal a complex interplay between Mo and S redox chemistry, while excluding the formation of free sulfur, lithium sulfide, or other crystalline phases. Na₂MoS₄ behaves as a mixed ionic–electronic conductor, with electronic conductivity of 6.1×10^?4 S cm^?1, that permits carbon‐free application in an electrochemical cell. A reversible capacity of up to 500 mAh g^?1 was attained, corresponding to a five‐electron redox exchange, with species ranging from <Na_<1MoS₄> (highest oxidized state) to <Na_>5MoS₄> (lowest oxidized state). This study emphasizes the excellent charge‐storage performances of Na₂MoS₄ for Li‐ or Na‐ion batteries, and enriches the emerging library and knowledge of sulfide phases with mixed anionic and cationic redox properties.     

Fabrication and characterization of P(VDF-HFP)/SBA-15 composite membranes for Li-ion batteries

This study reports on the preparation of a composite polymer electrolyte for secondary lithium-ion battery. Poly(vinylidiene fluoride-hexafluoropropylene) (P(VDF-HFP)) was used as the polymer host, and mesoporous SBA-15 (silica) ceramic fillers used as the solid plasticizer were added into the polymer matrix. The SBA-15 fillers with mesoporous structure and high specific surface can trap more liquid electrolytes to enhance the ionic conductivity. The ionic conductivity of P(VDF-HFP)/SBA-15 composite polymer electrolytes was in the order of 10⁻³ S cm⁻¹ at room temperature. The characteristic properties of the composite polymer membranes were examined by using FTIR spectroscopies, scanning electron microscopy (SEM), and an AC impedance method. For comparison, the LiFePO₄/Li composite batteries with a conventional microporous polyethylene (PE) separator and pure P(VDF-HFP) polymer membrane were also prepared and studied. As a result, the LiFePO₄/Li composite battery comprised the P(VDF-HFP)/10 wt.% m-SBA-15 composite polymer electrolyte, which achieves an optimal discharge capacity of 88 mAh g⁻¹ at 20 C rate with a high coulomb efficiency of 95%. It is demonstrated that the P(VDF-HFP)/m-SBA-15 composite membrane exhibits as a good candidate for application to LiFePO₄ polymer batteries.     

A new strategy of molecular overcharge protection shuttles for lithium ion batteries

The conventional strategy of overcharge protection for lithium ion batteries uses redox molecules having oxidation potential higher than the cathodic materials in the electrolyte. Here we propose a novel approach by using redox molecules having reduction potentials lower than the anodic materials. This new approach is successfully demonstrated in TiO₂/LiCoO₂ and TiO₂/LiFePO₄ cells by using benzophenone molecule.     

Bifunctional electrolyte additive for lithium-ion batteries

2-(Pentafluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole was reported as a bifunctional electrolyte additive for lithium-ion batteries. It was found that the reported additive had a redox potential of 4.43 V vs. Li⁺/Li with a reversible oxidation/reduction reaction. Therefore, it is a promising redox shuttle for overcharge protection of most positive electrode materials for current lithium-ion-battery technology. At the same time, the boron center of this additive is a strong Lewis acid and can act as an anion receptor to dissolve LiF generated during the operation of lithium-ion batteries. The possibility of using the novel additive as both the redox shuttle and the anion receptor was discussed.     

Large-volume-change electrodes for Li-ion batteries of amorphous alloy particles held by elastomeric tethers

Recently, new electrode materials based on amorphous alloys have been proposed to replace the graphite-based anode materials for lithium-ion batteries. These alloys undergo colossal reversible volume expansions as lithium is added and removed from them electrochemically. We show that if the alloy particles in the electrode are strongly tethered to one another and to the current collector by an elastomeric binder that good capacity retention versus cycle number, in spite of 125% volume expansion and contraction, is possible. To obtain the required mechanical properties, the elastomeric polymer binder is crosslinked and also bonded to the electrode particles using a surface coupling agent. A stable specific capacity of about 800 mAh/g in a-Si_0.64Sn_0.36, corresponding to 125% volume change, was obtained with a poly(vinylidene fluoride–tetrafluoroethylene–propylene)-based elastomeric binder system. Further optimization of the binder system is expected to be possible.     

Enhanced electrochemical properties of a novel polyvinyl formal membrane supporting gel polymer electrolyte by Al2O3 modification

Polyvinyl formal (PVFM)‐based dense polymer membranes with nano‐Al₂O₃ doping are prepared via phase inversion method. The membranes and also their performances as gel polymer electrolytes (GPEs) for lithium ion battery are studied by field emission scanning electron microscope, X‐ray diffraction, differential scanning calorimetry, mechanical strength test, electrolyte uptake test, electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge test. The polymer membrane with 3 wt % nano‐Al₂O₃ doping shows the improved mechanical strength of 12.16 MPa and electrolyte uptake of 431.25% compared with 10.47 MPa and 310.59% of the undoped sample, respectively. The membrane absorbs and swells liquid electrolyte to form stable GPE with ionic conductivity of 4.92 × 10^?4 S cm^?1 at room temperature, which is higher than 1.77 × 10^?4 S cm^?1 of GPE from the undoped membrane. Moreover, the Al₂O₃‐modified membrane supporting GPE exhibits wide electrochemical stability window of 1.2–4.8 V (vs. Li/Li⁺) and good compatibility with LiFePO₄ electrode, which implies Al₂O₃‐modified PVFM‐based GPE to be a promising candidate for lithium ion batteries. © 2014 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 572–577     

Eutectic-Based Polymer Electrolyte with the Enhanced Lithium Salt Dissociation for High-Performance Lithium Metal Batteries

The deployment of lithium metal anode in solid-state batteries with polymer electrolytes has been recognized as a promising approach to achieving high-energy-density technologies. However, the practical application of the polymer electrolytes is currently constrained by various challenges, including low ionic conductivity, inadequate electrochemical window, and poor interface stability. To address these issues, a novel eutectic-based polymer electrolyte consisting of succinonitrile (SN) and poly (ethylene glycol) methyl ether acrylate (PEGMEA) is developed. The research results demonstrate that the interactions between SN and PEGMEA promote the dissociation of the lithium difluoro(oxalato) borate (LiDFOB) salt and increase the concentration of free Li⁺. The well-designed eutectic-based PAN_1.2-SPE (PEGMEA: SN=1: 1.2 mass ratio) exhibits high ionic conductivity of 1.30 mS cm⁻¹ at 30 °C and superior interface stability with Li anode. The Li/Li symmetric cell based on PAN_1.2-SPE enables long-term plating/stripping at 0.3 and 0.5 mA cm⁻², and the Li/LiFePO₄ cell achieves superior long-term cycling stability (capacity retention of 80.3 % after 1500 cycles). Moreover, Li/LiFePO₄ and Li/LiNi_0.6Co_0.2Mn_0.2O₂ pouch cells employing PAN_1.2-SPE demonstrate excellent cycling and safety characteristics. This study presents a new pathway for designing high-performance polymer electrolytes and promotes the practical application of high-stable lithium metal batteries.     

Anion-tethered Single Lithium-ion Conducting Polyelectrolytes through UV-induced Free Radical Polymerization for Improved Morphological Stability of Lithium Metal Anodes

Single Li⁺ ion conducting polyelectrolytes (SICs), which feature covalently tethered counter-anions along their backbone, have the potential to mitigate dendrite formation by reducing concentration polarization and preventing salt depletion. However, due to their low ionic conductivity and complicated synthetic procedure, the successful validation of these claimed advantages in lithium metal (Li⁰) anode batteries remains limited. In this study, we fabricated a SIC electrolyte using a single-step UV polymerization approach. The resulting electrolyte exhibited a high Li⁺ transference number (t₊) of 0.85 and demonstrated good Li⁺ conductivity (6.3×10⁻⁵ S/cm at room temperature), which is comparable to that of a benchmark dual ion conductor (DIC, 9.1×10⁻⁵ S/cm). Benefitting from the high transference number of SIC, it displayed a three-fold higher critical current density (2.4 mA/cm²) compared to DIC (0.8 mA/cm²) by successfully suppressing concentration polarization-induced short-circuiting. Additionally, the t₊ significantly influenced the deposition behavior of Li⁰, with SIC yielding a uniform, compact, and mosaic-like morphology, while the low t₊ DIC resulted in a porous morphology with Li⁰ whiskers. Using the SIC electrolyte, Li⁰||LiFePO₄ cells exhibited stable operation for 4500 cycles with 70.5 % capacity retention at 22 °C.     

Flexible cellulose/LiFePO4 paper-cathodes: toward eco-friendly all-paper Li-ion batteries

Today most of commercial Li-ion batteries (LIBs) are manufactured using toxic solvents and synthetic polymer binders. In order to lower the cost and the environmental impact of LIBs an effort must be made to identify low-cost and environmentally friendly materials and processes. In this work, flexible, self-standing and easily recyclable LiFePO₄ cathodes are obtained using cellulose fibers as biosourced binder and a quick, aqueous filtration process, easily upscalable capitalizing the well-established papermaking know-how. The obtained paper-cathodes show very good mechanical properties, with Young’s modulus as high as 100 MPa, discharge capacity values up to 110 mAh g^?1 and very good cycling performances, comparable with conventional polymer-bonded LiFePO₄ cathodes. Moreover, a complete paper-cell, constituted by a paper-cathode, a paper-separator and a paper-anode is presented, showing good cycling performances in terms of specific capacity, efficiency and stability.     

Ordered and Fast Ion Transport of Quasi-solid-state Electrolyte with Regulated Coordination Strength for Lithium Metal Batteries

Polymer based quasi-solid-state electrolyte (QSE) has attracted great attention due to its assurance for high safety of rechargeable batteries including lithium metal batteries (LMB). However, it faces the issue of low ionic conductivity of electrolyte and solid-electrolyte-interface (SEI) layer between QSE and lithium anode. Herein, we firstly demonstrate that the ordered and fast transport of lithium ion (Li⁺) can be realized in QSE. Due to the higher coordination strength of Li⁺ on tertiary amine (−NR₃) group of polymer network than that on carbonyl (−C=O) group of ester solvent, Li⁺ can diffuse orderly and quickly on −NR₃ of polymer, significantly increasing the ionic conductivity of QSE to 3.69 mS cm⁻¹. Moreover, −NR₃ of polymer can induce in situ and uniform generation of Li₃N and LiN_xO_y in SEI. As a result, the Li||NCM811 batteries (50 μm Li foil) with this QSE show an excellent stability of 220 cycles at ≈1.5 mA cm⁻², 5 times to those with conventional QSE. LMBs with LiFePO₄ can stably run for ≈8300 h. This work demonstrates an attractive concept for improving ionic conductivity of QSE, and also provides an important step for developing advanced LMB with high cycle stability and safety.     

Instability of PVDF Binder in the LiFePO4 versus Li4Ti5O12 Li-Ion Battery Cell

The conventional formulation of electrodes used in Li-ion batteries consists of a mixture of three components: an active material, a conductive additive (carbon), and an organic binder. While the first encompasses a broad spectrum of chemistries, the carbon and the binder are often standard elements of the composite, with the latter being, in most of the cathode cases, the polyvinylidene fluoride (PVDF). The high (electro-)chemical inertia spanning over a broad range of oxidative and reductive potentials gives grounds for this choice. Herein, we demonstrate, contrary to electrochemical expectations, that the PVDF is electrochemically unstable at relatively low potentials. We consider in this study the LiFePO₄ (LFP) cathode cycled versus Li₄Ti₅O₁₂ (LTO) anode as a representative low-voltage battery cell system. The binder degradation process starts upon charge on the LFP electrode at 3.45 V vs. Li⁺/Li when the PVDF binder reacts with lithium and forms LiF. The latter does not precipitate on the LFP but migrates/diffuses towards the LTO counter-electrode, following the Li-ions’ trajectory. X-Ray photoelectron spectroscopy complemented with the high lateral resolution of X-ray photoemission electron microscopy disclosed the formation of a thin layer of LiF homogenously distributed across the LTO electrode, which partially dissolves (or decomposes) upon discharge. The degradation of the PVDF and the deposition and dissolution (and/or decomposition) of the LiF layer continue over subsequent charge and discharge cycles. The process is augmented when the cycling temperature is increased to 80 °C. The results shown in this work are crucial to interpret electrochemical data, such as specific charge decay or impedance rise, and have relevance for all PVDF-based electrodes, especially when employed in high-voltage battery cells where the more extreme cycling conditions exacerbate electrode components’ stability.     

Iron–Oxalato Framework with One‐Dimensional Open Channels for Electrochemical Sodium‐Ion Intercalation

Discovery of a new class of ion intercalation compounds is highly desirable due to its relevance to various electrochemical devices, such as batteries. Herein, we present a new iron–oxalato open framework, which showed reversible Na⁺ intercalation/extraction. The hydrothermally synthesized K₄Na₂[Fe(C₂O₄)₂]₃ ? 2 H₂O possesses one‐dimensional open channels in the oxalato‐bridged network, providing ion accessibility up to two Na⁺ per the formula unit. The detailed studies on the structural and electronic states revealed that the framework exhibited a solid solution state almost entirely during Na⁺ intercalation/extraction associated with the reversible redox of Fe. The present work demonstrates possibilities of the oxalato frameworks as tunable and robust ion intercalation electrode materials for various device applications.     

PEO-LITFSI-SiO2-SN System Promotes the Application of Polymer Electrolytes in All-Solid-State Lithium-ion Batteries

All-solid-state polymer lithium-ion batteries are ideal choice for the next generation of rechargeable lithium-ion batteries due to their high energy, safety and flexibility. Among all polymer electrolytes, PEO-based polymer electrolytes have attracted extensive attention because they can dissolve various lithium salts. However, the ionic conductivity of pure PEO-based polymer electrolytes is limited due to high crystallinity and poor segment motion. An inorganic filler SiO₂ nanospheres and a plasticizer Succinonitrile (SN) are introduced into the PEO matrix to improve the crystallization of PEO, promote the formation of amorphous region, and thus improve the movement of PEO chain segment. Herein, a PEO₁₈−LiTFSI−5 %SiO₂−5 %SN composite solid polymer electrolyte (CSPE) was prepared by solution-casting. The high ionic conductivity of the electrolyte was demonstrated at 60 °C up to 3.3×10⁻⁴ S cm⁻¹. Meanwhile, the electrochemical performance of LiFePO₄/CSPE/Li all-solid-state battery was tested, with discharge capacity of 157.5 mAh g⁻¹ at 0.5 C, and capacity retention rate of 99 % after 100 cycles at 60 °C. This system provides a feasible strategy for the development of efficient all-solid-state lithium-ion batteries.     

Effect of different carbon conductive additives on electrochemical properties of LiFePO4-C/Li batteries

LiFePO₄-C nanoparticles were synthesized by a hydrothermal method and subsequent high-energy ball-milling. Different carbon conductive additives including nanosized acetylene black (AB) and multi-walled carbon nanotube (MWCNT) were used to enhance the electronic conductivity of LiFePO₄. The structural and morphological performance of LiFePO₄-C nanoparticles was investigated by X-ray diffraction (XRD) and scanning electron microscopy. The electrochemical properties of LiFePO₄-C/Li batteries were analyzed by cyclic voltammetry and charge/discharge tests. XRD results demonstrate that LiFePO₄-C nanoparticles have an orthorhombic olivine-type structure with a space group of Pnma. LiFePO₄-C/Li battery with 5 wt% MWCNT displays the best electrochemical properties with a discharge capacity of 142 mAh g⁻¹ at 0.25 C at room temperature.     

Polyoxometalate-Cyclodextrin-Based Cluster-Organic Supramolecular Framework for Polysulfide Conversion and Guest–Host Recognition in Lithium-sulfur Batteries

Developing polyoxometalate-cyclodextrin cluster-organic supramolecular framework (POM-CD-COSF) still remains challenging due to an extremely difficult task in rationally interconnecting two dissimilar building blocks. Here we report an unprecedented POM-CD-COSF crystalline structure produced through the self-assembly process of a Krebs-type POM, [Zn₂(WO₂)₂(SbW₉O₃₃)₂]¹⁰⁻, and two β-CD units. The as-prepared POM-CD-COSF-based battery separator can be applied as a lightweight barrier (approximately 0.3 mg cm⁻²) to mitigate the polysulfide shuttle effect in lithium-sulfur batteries. The designed Li−S batteries equipped with the POM-CD-COSF modified separator exhibit remarkable electrochemical performance, attributed to fast Li⁺ diffusion through the supramolecular channel of β-CD, efficient polysulfide-capture ability by the dynamic host–guest interaction of β-CD, and improved sulfur redox kinetics by the bidirectional catalysis of POM cluster. This research provides a broad perspective for the development of multifunctional supramolecular POM frameworks and their applications in Li−S batteries.     

Charge Storage Mechanism and Structural Evolution of Viologen Crystals as the Cathode of Lithium Batteries

Although organic ionic crystals represent an attractive class of active materials for rechargeable batteries owing to their high capacity and low solubility in electrolytes, they generally suffer from limited electronic conductivity and moderate voltage. Furthermore, the charge storage mechanism and structural evolution during the redox processes are still not clearly understood. Here we describe ethyl viologen iodide (EVI₂) and ethyl viologen diperchlorate (EV(ClO₄)₂) as cathode materials of lithium batteries which crystallize in a monoclinic system with alternating organic EV²⁺ layers and inorganic I^?/ClO₄^? layers. The EVI₂ electrode exhibits a high initial discharge plateau of 3.7 V (vs. Li⁺/Li) because of its anion storage ability. When I^? is replaced by ClO₄^?, the obtained EV(ClO₄)₂ electrode displays excellent rate performance with a theoretical capacity of 78 % even at 5 C owing to the good electron conductivity of ClO₄^? layers. EVI₂ and EV(ClO₄)₂ also show excellent cycling stability (capacity retention >96 % after 200 cycles).