New electrolytes using Li2O or Li2O2 oxides and tris(pentafluorophenyl) borane as boron based anion receptor for lithium batteries

A new system of electrolytes has been developed and studied for lithium-ion batteries. This new system is based on the interactions between Li₂O or Li₂O₂ and tris(pentafluorophenyl) borane (TPFPB) in carbonate based organic solvents. This opens up a completely new approach in developing non-aqueous electrolytes. In general, the solubility of Li₂O or Li₂O₂ is very low in organic solvents and the ionic conductivities of these solutions are almost undetectable. By adding certain amount of tris(pentafluorophenyl) borane (TPFPB), one type of boron based anion receptors (BBARs), the solubility of Li₂O or Li₂O₂ in carbonate based solvents was significantly enhanced. In addition, the Li⁺ transference numbers of these new electrolytes measured were as high as 0.7, which are more than 100% higher than the values for the conventional electrolytes for lithium-ion batteries. The room-temperature conductivities are around 1 × 10⁻³ S/cm. These new electrolytes are compatible with LiMn₂O₄ cathode for lithium-ion batteries.     

Enhanced electrochemical properties of polyethylene oxide-based composite solid polymer electrolytes with porous inorganic–organic hybrid polyphosphazene nanotubes as fillers

Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO₄, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity values of 1.5 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.8 × 10⁻⁴ S cm⁻¹ at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO₁₀–LiClO₄–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries.     

On the way to high-conductivity single lithium-ion conductors

Solid electrolytes can potentially address three key limitations of the organic electrolytes used in today’s lithium-ion batteries, namely, their flammability, limited electrochemical stability and low cationic transference number. The pioneering works of Wright and Armand, suggesting the use of solid poly(ethylene oxide)-based polymer electrolytes (PE) for lithium batteries, paved the way to the development of solid-state batteries based on PEs. Yet, low cationic mobility–low Li⁺ transference number in polymer materials coupled with sufficiently high room-temperature conductivity remains inaccessible. The current strategies employed for the production of single-ion polymer conductors include designing new lithium salts, bonding of anions with the main polyether chain or incorporating them into the side chains of comb-branched polymers, plasticizing, adding inorganic fillers and anion receptors. Glass and crystalline superionic solids are classical single-ion-conducting electrolytes. However, because of grain boundaries and poor electrode/electrolyte interfacial contacts, achieving electrochemical performance in solid-state batteries comprising polycrystalline inorganic electrolytes, comparable to the existing batteries with liquid electrolytes, is particularly challenging. Quasi-elastic polymer-in-ceramic electrolytes provide good alternatives to the traditional lithium-ion-battery electrolytes and are believed to be the subject of extensive current research. This review provides an account of the advances over the past decade in the development of single-ion-conducting electrolytes and offers some directions and references that may be useful for further investigations.     

Electrical Characterization and Ionic Transport Properties of Carboxyl Methylcellulose-Oleic Acid Solid Polymer Electrolytes

Electrical impedance spectroscopy was used to measure the conductivity of solid polymer electrolytes. From the impedance study, the highest ionic conductivity of solid polymer electrolytes based on carboxyl methylcellulose as polymer host and oleic acid as the doping salt, prepared by the solution casting method at room temperature, σ_r.t, is 2.11 × 10^?5 S cm^?1 for the sample containing 20 wt.% of oleic acid. Transference number measurement was performed to correlate the diffusion phenomena to the conductivity behavior of carboxyl methylcellulose-oleic acid solid polymer electrolytes. From the transference number measurement study, the conduction species carrier of the cation (+) is higher than that of the anion (?). Thus, the results proved that the samples are proton-conducting solid polymer electrolytes.     

Interactions Between Tetra(trifluoromethylsulfonyl)-1,4,8,11-tetraazocyclotetradecane and Perchlorate Anion in Propylene Carbonate, Nitromethane, Acetonitrile, and Tetrahydrofuran

Electrical conductance measurements are reported for lithium perchlorate andthe anion receptor tetra(trifluoromethylsulfonyl)-1,4,8,11-tetraazocyclotetradecane(TTCD) in different aprotic solvents (propylene carbonate, nitromethane,acetonitrile, and tetrahydrofuran). The data have been analyzed by a suitablemethod based on the Lee-Wheaton theory on mixed electrolytes in order to obtainthe true thermodynamic formation constants of macrocyclic-anion complexes andthe ion pairs of both the uncomplexed (ClO₄ ^–)and complexed (TTCD-ClO₄ ^–)anions. The results show that the anion-ligand formation constants increase withdecreasing dielectric constant and that the presence of the ligand increases theionization of lithium perchlorate and enhances the transference number of lithiumion. These findings are of particular interest in view of the technologicalapplication of anion receptors in electrolyte solutions for lithium batteries.     

Improved properties of polymer electrolyte by ionic liquid PP1.3TFSI for secondary lithium ion battery

A new kind of polymer electrolyte is prepared from N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP1.3TFSI), polyethylene oxide (PEO), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). IR and X-ray diffraction results demonstrate that the addition of ionic liquid decreases the crystallization of PEO. Thermal and electrochemical properties have been tested for the solid polymer electrolytes, the addition of the room temperature molten salt PP1.3TFSI to the conventional P(EO)₂₀LiTFSI polymer electrolyte leads to the improvement of the thermal stability and the ionic conductivity (x = 1.27, 2.06 × 10⁻⁴ S cm⁻¹ at room temperature), and the reasonable lithium transference number is also obtained. The Li/LiFePO₄ cell using this polymer electrolyte shows promising reversible capacity, 120 mAh g⁻¹ at room temperature and 164 mAh g⁻¹ at 55 °C.     

Advances in host selection and interface regulation of polymer electrolytes

Polymer electrolyte (PE) has been emerging as a promising alternative to liquid electrolytes due to the unique advantages such as excellent flexibility and processability, high chemical and thermal stability, and low risk of leakage and combustion, especially for lithium-ion batteries (LIBs). Even though abundant attempts focusing on polymer chemistries have been made, the inadequate capacity of lithium-ion transport via segmental motion still cannot provide satisfying room temperature ionic conductivity and lithium-ion transference number. In addition, safety concerns and short lifespan resulted from the brittle and incompatible interface between the electrode and polymer materials also hinder the commercialization of PEs-based LIBs. Hence, for the above performance defects and interface issues, this review provides an overview of polymer electrolytes from the conductivity improvement, polymer selection and mechanical strength enhancement for protrusion suppressing. The improvement of conductivity specifically includes structure modification of poly(ethylene oxide) (PEO) host and novel electrolyte matrix beyond PEO, while the section of interface regulation mainly involves dendrite-inhibited polymers, mechanical strengthening, and in situ polymerization. Finally, perspectives and challenges are pointed out in the development of polymer electrolytes with both excellent electrochemical performance and safety for LIBs.     

The network gel polymer electrolyte based on poly(acrylate-co-imide) and its transport properties in lithium ion batteries

Poly (acrylate-co-imide)-based gel polymer electrolytes are synthesized by in situ free radical polymerization. Infrared spectroscopy confirms the complete polymerization of gel polymer electrolytes. The ionic conductivity of gel polymer electrolytes are measured as a function of different repeating EO units of polyacrylates. An optimal ionic conductivity of the poly (PEGMEMA₁₁₀₀-BMI) gel polymer electrolyte is determined to be 4.8 × 10^–3 S/cm at 25 °C. The lithium transference number is found to be 0.29. The cyclic voltammogram shows that the wide electrochemical stability window of the gel polymer electrolyte varies from −0.5 to 4.20 V (vs. Li/Li⁺). Furthermore, we found the transport properties of novel gel polymer electrolytes are dependent on the EO design and are also related to the rate capability and the cycling ability of lithium polymer batteries. The relationship between polymer electrolyte design, lithium transport properties and battery performance are investigated in this research.     

Solid polymer electrolyte based on tragacanth gum-ammonium thiocyanate

Research towards solid polymer electrolytes based on biopolymers has grown extensively over the past years due to its abundance in nature, non-toxicity, low cost, and biodegradability. When compared to standard biopolymers, electrochemical study on natural gums is very limited. Therefore, in the present work, polymer electrolytes based on gum tragacanth have been prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), thermogravimetry, and transference number studies. The polymer-salt complex formation is confirmed using FTIR studies while XRD spectra reveal the amorphous nature of the polymer membranes. The highest conductivity of 9.161?×?10^?3 S/cm was obtained for the film with 1 g of gum tragacanth and 0.5 g of ammonium thiocyanate. The Thermogravimetry study showed that the electrolyte is thermally stable. The transference number study confirmed that the main charge carriers are ions. The primary battery has been constructed using the prepared electrolyte, and the OCV was found to be 1.31 V.

     

Enhanced Lithium‐Ion Conductivity of Polymer Electrolytes by Selective Introduction of Hydrogen into the Anion

The anion chemistry of lithium salts plays a pivotal role in dictating the physicochemical and electrochemical performance of solid polymer electrolytes (SPEs), thus affecting the cyclability of all‐solid‐state lithium metal batteries (ASSLMBs). The bis(trifluoromethanesulfonyl)imide anion (TFSI^?) has long been studied as the most promising candidate for SPEs; however, the Li‐ion conductivities of the TFSI‐based SPEs still remain low (Li‐ion transference number: ca. 0.2). In this work, we report new hydrogen‐containing anions, conceived based on theoretical considerations, as an electrolyte salt for SPEs. SPEs comprising hydrogen‐containing anions achieve higher Li‐ion conductivities than TFSI‐based ones, and those anions are electrochemically stable for various kinds of ASSLMBs (Li–LiFePO₄, Li–S, and Li–O₂ batteries). This opens up a new avenue for designing safe and high‐performance ASSLMBs in the future.     

PEO-LiClO4-ZSM-5复合聚合物电解质——ZSM-5对锂离子选择通过的影响

通过溶液浇铸法制得了一系列以不同分子筛和蒙脱土为填料的PEO基复合聚合物电解质,利用交流阻抗-稳态电流方法研究了填料对复合聚合物电解质锂离子迁移数(TLi+)的影响.实验结果表明,所有填料都有利于同时提高复合聚合物电解质的TLi+和离子电导率,但以Li-ZSM-5为填料时TLi+最高,这是因为ZSM-5的特殊二维孔道结构有利于阳离子Li+的进入,而排斥阴离子ClO4-的通过.较高的TLi+和室温离子电导率说明PEO-LiClO4-ZSM-5有可能作为全固态锂离子聚合物电池的电解质材料.     

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.     

Anion receptor-coated separator for lithium-ion polymer battery

Anion receptor-coated separators were prepared by coating poly(ethylene glycol) borate ester (PEGB) as an anion receptor and poly(vinyl acetate) (PVAc) as a good adhesive material towards electrodes onto microporous polyethylene (PE) separators. Gel polymer electrolytes were fabricated by soaking them in an liquid electrolyte, 1 M LiPF₆ in EC/DEC/PC (30/65/5, wt.%). As the weight ratio of PEGB to PVAc in a coating layer increased, gel polymer electrolytes showed higher cationic conductivity and electrochemical stability. The cationic conductivity and electrochemical stability of the gel polymer electrolyte based on coated separator with PVAc/PEGB (2/5, weight ratio) could reach 2.8 × 10^–4 S cm^–1 and 4.8 V, respectively. Lithium-ion polymer cells (LiCoO₂/graphite) based on gel polymer electrolytes with and without PEGB were assembled, and their electrochemical performances were evaluated.     

A pentafluorophenylboron oxalate additive in non-aqueous electrolytes for lithium batteries

A novel compound named pentafluorophenylboron oxalate (PFPBO) has been synthesized. PFPBO has a unique molecular structure containing a boron atom center with electron deficiency and an oxalate group. It is found that when PFPBO is used as additive, the solubility of lithium fluoride (LiF) or lithium oxide (Li₂O, Li₂O₂) in propylene carbonate (PC) and dimethyl carbonate (DMC) solvents can be increased dramatically. The new electrolytes show high ionic conductivity, high lithium ion transference number and good compatibility with LiMn₂O₄ cathode and MCMB anode. PFPBO was synthesized with the designed structure to act as a bi-functional additive: boron-based anion receptor (BBAR) additive and stable solid electrolyte interphase (SEI) formation additive in PC-based electrolytes. The results show it does possess these two desired functionalities.     

Proton Conductor of Propylene Carbonate–Plasticized Carboxyl Methylcellulose–Based Solid Polymer Electrolyte

Carboxyl methylcellulose (CMC) solid polymer electrolytes were prepared by utilizing oleic acid (OA) and different wt.% of propylene carbonate (PC) by using the solution casting technique. An ionic conductivity study of the films was done by using impedance spectroscopy. The highest ionic conductivity gained is 2.52 × 10^?7 S cm^?1 at ambient temperature for sample CMC-OA-PC 10 wt.%. From transference number measurement (TNM), the value of cation diffusion coefficient, D₊, and ionic mobility, μ₊, was higher than the value of anion diffusion coefficient, D_?, and ionic mobility, μ_?. Thus, the results prove that the present samples were proton conductors.     

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.     

Electrochemical characterization of plasticized polymer electrolytes based on ABS/PMMA blends

Electrochemical characteristics of plasticized polymer electrolytes based on poly(acrylonitrile-butadene-styrene) and poly(methyl methacrylate) (abbreviated as ABS/PMMA) blends have been studied. The ionic conductivity of the polymer electrolyte with an ABS/PMMA ratio of 6/4 and a plasticizer content of 60% was highest when the LiClO₄ content was 4.8%. The transference numbers (T ₊) of the polymer electrolytes were measured using the steady-state current method, and the T ₊ values were found to be less than 0.5. The electrolyte system was found to have an electrochemical stability window up to 4.5 V. The properties of the electrode interface in contact with the polymer electrolyte were also investigated by impedance spectroscopy, and the evolution of these spectra as a function of storage time was explained and interpreted using a solid-polymer layer (SPL) model. The time evolution of the impedance parameters indicated that a passivation film grew rapidly on the lithium surface immediately after assembly of the cell. Electronic Publication     

Highly concentrated polycarbonate‐based solid polymer electrolytes having extraordinary electrochemical stability

Solid polymer electrolytes (SPEs) are compounds of great interest as safe and flexible alternative ionics materials, particularly suitable for energy storage devices. We study an unusual dependence on the salt concentration of the ionic conductivity in an SPE system based on poly(ethylene carbonate) (PEC). Dielectric relaxation spectroscopy reveals that the ionic conductivity of PEC/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte continues to increase with increasing salt concentration because the segmental motion of the polymer chains is enhanced by the plasticizing effect of the imide anion. Fourier transfer‐infrared (FTIR) spectroscopy suggests that this unusual phenomenon arises because of a relatively loose coordination structure having moderately aggregated ions, in contrast to polyether‐based systems. Comparative FTIR study against PEC/lithium perchlorate (LiClO₄) electrolytes suggests that weak ionic interaction between Li and TFSI ions is also important. Highly concentrated electrolytes with both reasonable conductivity and high lithium transference number (t₊) can be obtained in the PEC/LiTFSI system as a result of the unusual salt concentration dependence of the conductivity and the ionic solvation structure. The resulting concentrated PEC/LiTFSI electrolytes have extraordinary oxidation stability and prevent any Al corrosion reaction in a cyclic voltammetry. These are inherent effects of the highly concentrated salt. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2442–2447     

Enhanced Li+ migration in solid polymer electrolyte driven by anion-containing polymer-chains

Li-ion batteries with solid polymer electrolytes (SPEs) are safer than conventional liquid electrolytes due to the absence of highly flammable liquid electrolytes. However, their performance is limited by the poor Li⁺ transport in SPEs at room temperature. Anion-containing polymer-chains incorporated SPEs (ASPEs) are therefore developed to enhance Li⁺ diffusion kinetics. Herein, we propose a novel and feasible strategy to incorporate the anion-containing polymer-chains, such as lithiated perfluorinated sulfonic acid (PFSA), into polyvinylidene fluoride (PVDF) polymer-based SPEs. The immobile anion groups from the PFSA-chains impede the migration of mobile anion groups dissociated from the Li salt. The transference number is thus raised from ∼0.3 to 0.52 with the introduction of anion-containing polymer-chains into SPEs. The electrostatic repulsion among anion-containing chains also reduces the close chain stacking and brings 159% increase in the ionic conductivity to 0.83 × 10⁻³ S/cm at 30 °C in contrast with the pure PVDF-based SPE. In addition, LiFeO₄/Li batteries with ASPEs exhibit 55% capacity boost at 0.5 C in contrast to the capacity of batteries with pure-PVDF SPEs, and also offer more than 1000 charge/discharge cycles. Our research findings potentially offer a facile strategy to design thermal stable SPEs with superior Li⁺ transport behaviors towards developing high-performance SPEs-based batteries.     

PEO-LiClO4-ZSM5复合聚合物电解质 I. 电化学研究

首次以“择形”分子筛ZSM5为填料, 通过溶液浇铸法制得PEO-LiClO₄-ZSM5全固态复合聚合物电解质(CPE)膜. 交流阻抗实验表明ZSM5的引入可以显著地提高CPE的离子电导率. 利用交流阻抗-稳态电流相结合的方法对CPE的锂离子迁移数进行了测定, 结果表明掺入ZSM5后锂离子迁移数明显升高. ZSM5的含量为10%时, CPE同时具有最高离子电导率1.4×10^－5 S•cm^－1(25 ℃)和最大锂离子迁移数0.353. PEO-LiClO₄-ZSM5/Li电极界面稳定性实验表明PEO-LiClO₄-ZSM5复合聚合物电解质在全固态锂离子电池领域具有良好的应用前景.