Polymeric Lithium Salt Research Articles

Constructing the lithium polymeric salt interfacial phase in composite solid-state electrolytes for enhancing cycle performance of lithium metal batteries

The solid-state lithium metal batteries are considered a promising direction for developing lithium-based energy storage devices because of their superiority over lithium-ion batteries containing liquid electrolytes in energy density and safety performance. However, the design, preparation, and optimization of solid-state electrolytes (SSEs), especially composite solid-state electrolytes (CSEs), still face critical construction design and composite process challenges. This work proposes and designs a method to construct a highly compatible and lithium-ion conductive interfacial phase by coating the inorganic phase with polymeric lithium salt in the composite solid electrolytes. The introduction of the lithium salt interfacial phase efficiently improves the cycle performance and stability of CSEs in lithium metal batteries by synergistic optimization of the composite interfacial phase. We investigate two different modification methods (solvent-free and in-situ methods) in two different inorganic systems (Li6.4La3Zr1.4Ta0.6O12 (LLZTO) and LiTa2PO8 (LTPO)) to demonstrate the practical value of this design. The highest ionic conductivity of the modified PEO/LTPO CSEs (50 wt%) can be improved to 9.3 × 10-4 S·cm−1 at 80℃ and 4.0 × 10-5 at RT (∼25℃, hereinafter inclusive), while those of the modified PEO/LLZTO CSEs can reach 1.4 × 10-3 S·cm−1 at 80℃ and 5.5 × 10-5 at RT. The results demonstrate that the interfacial phase also enhances the electrochemical and cycle stability of CSEs.

High-Performance Polymeric Lithium Salt Electrode Material from Phenol–Formaldehyde Condensation

In spite of the recent progress made in organic electrode materials, high-performance candidates are still lacking, especially when taking affordability into account. Herein, we report a novel polymeric lithium salt, namely dilithium salt of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (Li2PDBM), which can be easily synthesized by phenol-formaldehyde condensation, followed by lithiation in LiOH solution to eliminate the negative effect of phenol groups in PDBM. Benefiting from a high theoretical capacity (327 mA h g-1), structure stability, insolubility, and redox reversibility, Li2PDBM exhibits superior electrochemical performance as a cathode for rechargeable lithium batteries, including a high reversible capacity (256 mA h g-1), a high rate capability (79% @ 2000 mA g-1), and a high cycling stability (77% @ 2000th cycle). Besides the cost-effective electrode material synthesis approach, this work also provides an important mechanistic understanding of the structure-performance relationship of carbonyl-based electrode materials, especially those with -OH or -OM (M = Li, Na, and K) substituents.

Electrolyte-Solvent-Modified Alternating Copolymer as a Single-Ion Solid Polymer Electrolyte for High-Performance Lithium Metal Batteries.

Significant progress has been made to replace graphite anode materials with Li metal in next-generation Li ion batteries, called Li metal batteries (LMBs). However, the development of practical LMBs requires the suppression of Li dendrites. Owing to their ability to relax polarization, single-ion solid polymer electrolytes (SSPEs) are widely considered as an effective strategy for preventing dendrite generation. The novel SSPE membrane prepared in this work, which consists of a polymeric lithium salt modified with an electrolyte solvent, shows single-ion conducting behavior that results in the effective restriction of Li dendritic growth. The SSPE membrane delivers an ionic conductivity as high as 1.42 × 10-4 S cm-1 at room temperature. A LiFePO4 (LFP) coin cell assembled with the SSPE membrane shows excellent rate performance and outstanding cycling stability. In addition, the LFP flexible battery using the SSPE membrane exhibits good practicability and environmental adaptability.

Polymer-inorganic solid-electrolyte interphase for stable lithium metal batteries under lean electrolyte conditions.

The solid-electrolyte interphase (SEI) is pivotal in stabilizing lithium metal anodes for rechargeable batteries. However, the SEI is constantly reforming and consuming electrolyte with cycling. The rational design of a stable SEI is plagued by the failure to control its structure and stability. Here we report a molecular-level SEI design using a reactive polymer composite, which effectively suppresses electrolyte consumption in the formation and maintenance of the SEI. The SEI layer consists of a polymeric lithium salt, lithium fluoride nanoparticles and graphene oxide sheets, as evidenced by cryo-transmission electron microscopy, atomic force microscopy and surface-sensitive spectroscopies. This structure is different from that of a conventional electrolyte-derived SEI and has excellent passivation properties, homogeneity and mechanical strength. The use of the polymer-inorganic SEI enables high-efficiency Li deposition and stable cycling of 4 V Li|LiNi0.5Co0.2Mn0.3O2 cells under lean electrolyte, limited Li excess and high capacity conditions. The same approach was also applied to design stable SEI layers for sodium and zinc anodes.

Hybrid Ion Conductor: Polysulfide Exclusion for Advanced Lithium Sulfur Batteries

Today’s lithium ion batteries, which have more than twice energy of those first released 25 years ago, power most of mobile electronic devices. However, their energy density is not high enough to provide electric vehicles and drones with mobility freedom. To make electric vehicles and drones more affordable, one needs batteries that can offer a longer cruise range with a lower cost. In this regard, lithium–sulfur (Li–S) battery is now considered a promising candidate to succeed lithium-ion batteries owing to its high theoretical energy density of 2500 Wh∙kg-1, non-toxic nature, low cost, and natural abundance. Despite such promises, the commercialization of Li–S batteries has yet to succeed even after sustained effort spanning several decades. Significant problems encountered have included low sulfur utilization, short cycle life, low cycling efficiency, and high self-discharge rate. These are mainly attributed to a process known as the polysulfide (PS) shuttle; PS chains dissolved in the electrolyte diffuse to the Li anode where they directly react with the Li metal to produce lower order PS species, which diffuse back to the sulfur cathode to regenerate higher PS forms. The PS shuttle leads to incomplete charging of the sulfur electrode, corrosion of the Li electrode, and formation of electrochemically inactive lithium sulfates (LixSOy) on the sulfur electrode, thus resulting in poor battery performance. Prevention of the PS shuttle is therefore extremely important for the practical use of Li–S batteries. In this talk, we present a single ion conductor which effectively rejects PS when used as an electrolyte medium for lithium sulfur battery and demonstrate a quasi-solid state lithium sulfur battery employing it. The ion conductor features a perfluorinated lithium sulfonate polymer swollen with organic polar solvents. For the ion conduction, Li+ is the sole charge carrier, because the SO3 - groups attached to the polymer chain are immobilized and the ion conductor does not include any bi-ionic lithium salt. The solvents selected from an intensive screening process dissociate polymeric lithium salts and form a 5~6 nm-sized Li+ conducting channels. As a result, the ion conductivity of the ion conductor is as high as 10-4 S cm-1 in its quasi-solid state. To our interest, the PS solubility of the hybrid ion conductor is quite low although the solvents have high PS solubility. This behavior originates from Donnan exclusion principle; the fixed negative charges decrease the Donnan potential of the conductor, with lowering its equilibrium PS concentration. Such Donnan exclusion effect is more intensified in the absence of bi-ionic lithium salt, therefore, to strengthen PS rejection function, the hybrid ion conductor is designed without any lithium salts. The sulfur battery based on the hybrid ion conductor has highly interesting features. The composite sulfur cathode comprising of sulfur/carbon composite and the hybrid ion conductor effectively confines PS in the vicinity of the carbon matrix owing to the nearby PS-rejecting hybrid ion conductors. Moreover, the polymer electrolyte membrane between the sulfur cathode and lithium further blocks PS passage. Owing to its quasi-solid state nature, the hybrid ion conductor allows the design of bipolar stack-type lithium sulfur battery. Because the electrolyte phases of each cell are spatially separated in bipolar configuration, shunt current, which is unavoidable for liquid electrolyte based batteries, can be eliminated. The electrochemical characteristics and performances of the quasi-solid state lithium sulfur battery are presented and the underlying physics is discussed.

Functionalized meso/macro-porous single ion polymeric electrolyte for applications in lithium ion batteries

We report a method to significantly enhance the conductivity of lithium ions in a polymeric lithium salt membrane by introducing functionalized meso/macro-pores to accommodate a mixture of organic solvents in the polymer matrix.

Electrospun poly(lithium 2-acrylamido-2-methylpropanesulfonic acid) fiber-based polymer electrolytes for lithium-ion batteries

Novel single-ion conducting polymer electrolytes based on electrospun poly(lithium 2-acrylamido-2-methylpropanesulfonic acid) (PAMPSLi) membranes were prepared for lithium-ion batteries. The preparation started with the synthesis of polymeric lithium salt PAMPSLi by free-radical polymerization of 2-acrylamido-2-methylpropanesulfonic acid, followed by ion-exchange of H+ with Li+. Then, the electrospun PAMPSLi membranes were prepared by electrospinning technology, and the resultant PAMPSLi fiber-based polymer electrolytes were fabricated by immersing the electrospun membranes into a plasticizer composed of ethylene carbonate and dimethyl carbonate. PAMPSLi exhibited high thermal stability and its decomposition did not occur until 304°C. The specific surface area of the electrospun PAMPSLi membranes was raised from 9.9 m2/g to 19.5 m2/g by varying the solvent composition of polymer solutions. The ionic conductivity of the resultant PAMPSLi fiber-based polymer electrolytes at 20°C increased from 0.815 × 10−5 S/cm to 2.12 × 10−5 S/cm with the increase of the specific surface area. The polymer electrolytes exhibited good dimensional stability and electrochemical stability up to 4.4 V vs. Li+/Li. These results show that the PAMPSLi fiber-based polymer electrolytes are promising materials for lithium-ion batteries. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Lithium sulfonate promoted compatibilization in single ion conducting solid polymer electrolytes based on lithium salt of sulfonated polysulfone and polyether epoxy

Polymeric lithium salts of sulfonated polysulfone (SPSU(X)Li) were synthesized via post sulfonation route followed by ion exchange. A novel single ion conducting solid polymer electrolyte (SPE) was prepared by curing poly(ethylene glycol)diglycidyl ether (PEGDGE) with 4,4′ diaminodiphenyl sulfone (DDS) in SPSU(X)Li matrix. The ionic conductivity, thermal stability and tensile properties were investigated as a function of degree of sulfonation and PEGDGE concentration. The introduction of lithium sulfonate groups in polysulfone promoted compatibility of SPSU(X)Li and PEGDGE in SPE. AFM analysis demonstrated heterogeneous phase morphology and reduction in size of dispersed PEGDGE phase with increasing degree of sulfonation. The interactions between lithium sulfonate and polyether epoxy improved thermal stability of the epoxy network. The enhanced compatibility also caused improvement in elongation at break compared to neat SPSU(X)Li. The higher Li+ ion concentration and the segmental mobility of the polymer chains above Tg contributed to the high ionic conductivity at high temperature in the single ion conducting SPE.

A simple method for synthesizing polymeric lithium salts exhibiting relatively high cationic transference number in solid polymer electrolytes

Two polymeric lithium salts, lithium polyperfluorobutylene-1,4-bis-sulfonylimide (LiPBSI) and lithium polyperfluorohexylene-1,6-bis-sulfonylimide (LiPHSI), with different CF 2 backbone lengths were synthesized by a new and easy method. These two polymeric lithium salts were successfully converted, via ion exchange and Li 2CO 3 treatment, from polymeric potassium salts which were prepared by condensation polymerizations of perfluoroalkylene-bis-sulfonyl fluorides (FSO 2C 4F 8SO 2F and FSO 2C 6F 12SO 2F) with 15% potassium hexamethyldisilizane in toluene. Both LiPBSI and LiPHSI were characterized by multi-nuclear ( 1H, 19F, or 13C) NMR, FT-IR, TGA, DSC, GPC, and so on. The ionic conductivity results of solid polymer electrolytes prepared by resulting lithium salts and poly(ethylene oxide) (PEO) showed that LiPBSI/PEO electrolyte had higher ionic conductivity. Furthermore, the lithium ion transference number of both LiPBSI/PEO and LiPHSI/PEO films were close to 0.4, which was twice that of film prepared from commercial lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

Synthesis, Characterization, and Ion-Conductive Behavior in an Organic Solvent and in a Polyether of a Novel Lithium Salt of a Perfluorinated Polyimide Anion

To achieve highly conductive polymer electrolytes with a controllable ionic transference number, a novel polymeric lithium salt was synthesized and characterized. The novel lithium salt of a perfluorinated polyimide anion, poly(5-oxo-3-oxy-4-trifluoromethyl-1,2,4-pentafluoropentylene sulfonylimide lithium) (LiPPI), has a polyanionic backbone with a repeating unit resembling highly dissociable, thermally and electrochemically stable imide salts, such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The ion-conductive behavior of LiPPI in an organic solvent and in a polyether was extensively studied by using pulse-gradient spin-echo NMR, in addition to differential scanning calorimetry, complex impedance measurement, and dynamic mechanical analysis. Solutions of LiPPI in ethylene carbonate (EC) exhibited a high degree of dissociation and high ionic conductivity, and the self-diffusion coefficient of the anion was lower than that of the cation. Solvent-free polymer electrolytes were prepared by dissolving LiPPI in a matrix polyether to afford a compatible polymer alloy, and the ionic conductivity of the new polymer alloy electrolytes reached ca. 10-5 S cm-1 at 30 °C. Although the lithium ionic transference number in the organic electrolyte solution was approximately the same as that of LiTFSI in EC, the polymer alloy electrolyte gave an apparent transference number higher than 0.7, which was considerably higher than that of LiTFSI in the same polyether.

Anionic effect on ion transport properties in network polyether electrolytes

The anionic effect on ion transport properties in network polyether electrolytes has been studied. A novel lithium salt of polymeric imide anion, poly(5-oxo-3-oxy-4-trifluoromethyl-1,2,4-pentafluoropentylene sulfonylimide lithium) (LiPPI), has a structure resembling highly dissociable imide salts such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and is considered as their polymer analogue. LiPPI has a long spacer between anionic sites in the polymer backbone, compared with a polymeric lithium salt, poly(2-oxo-1-difluoroethylene sulfonylimide lithium) (LiPEI), as reported before. Network polymer electrolytes were prepared by dissolving LiPPI in polyether networks to afford a compatible polymer alloy. The ionic conductivity of the new polymer alloy electrolytes reached ca. 10 −5 S/cm at 30°C, which was higher than those containing LiPEI by two orders of magnitude. Such difference of ionic conductivity between LiPPI and LiPEI was caused by the variation of dissociation ability of these polymeric lithium salts. The apparent Li + transference number of the network polymer alloy electrolyte containing LiPPI was higher than 0.7, considerably higher than that of the network polymer electrolytes containing a monomeric lithium salt, LiTFSI. In this study, the possibility to control the Li + transference number by using polymeric lithium salts in polymer electrolytes is demonstrated.

Gel polyelectrolytes based on lithium carboxylates

The passivation phenomena at the lithium-gel polyelectrolyte interface were examined by means of the impedance spectroscopy and the dc polarization of cells. Polymeric lithium salts with immobilized carboxylic anions, plasticized with dimethoxyethylenesulfoxide, were used as the electrolyte. It was found that passivation layers could be formed in these systems both on the surface of the electrode and the polymeric membrane. The generation of mobile anions and decrease of the lithium transference number accompany the passivation. The passivation undergoes strong inhibition in the presence of BF3.

Photorefractivity Based on Photoinduced Ionic-conductivity Changes with Crowned Spirobenzopyran

Abstract Significant light diffraction by photorefractive effect has been realized with composite films consisting of a nonlinear optical compound, crowned spirobenzopyran, a polymeric lithium salt, and poly(methyl methacrylate), based on a mechanism of photochemical ionic-conduction control by the photochromic crown ether.

Dynamics of lithium ions in monoconducting polymer electrolytes: A 7Li spin‐lattice‐relaxation study

AbstractIn monoconducting gel electrolytes prepared from polymeric lithium salt, poly(ethylene glycol), dimethylsulfoxide or propylene carbonate 7Li(I= 3/2) NMR spin‐lattice relaxation times (T1) at two resonance frequencies (24.5 and 77.5 MHz) have been measured for various compositions of the above system over the temperature region 0.75 to 2 Tg, with the glass transition temperature T″g≈200 K. The T1 data as a function of inverse temperature exhibit a cationic diffusion‐induced minimum. Both the temperature and the frequency of T1, indicate a change in the dynamical process at about 1.3 Tg.

Effects of the Conductivity of Sulfonated Poly(phenylene oxide) lithium by the Complexation of Poly(ethylene oxide)

In the present paper, the structure and conductivity for the complex of sulfonated poly(phenylene oxide) lithium (SPPOLi) and poly(ethylene oxide) (PEG) were studied. Glass transition temperature change determined by differential scanning calorimeter analysis desmonstrated that the two components had some compatibility. X-ray diffraction showed that PEG could decrease the regularity of SPPOLi to some extent. The compatibility and PEG's effect on the regularity may be due to the interaction between the lithium ions of SPPOLi and the oxygen atoms of PEG. Under polarization by electric field, the bands between lithium ions and sulfonation groups relaxed. Meanwhile, the complexation of oxygen atoms could enhance the dissociation of the polymeric lithium salts. Then lithium ions were transported in the process of alternate complexing and decomplexing. The action between lithium ions and oxygen atoms could explain the improvement on the conductivity of SPPOLi.