Conductivity Of Solid Polymer Electrolytes Research Articles

In Situ Generation of a Gel Polymer Electrolyte via the Controlled Formation of Ethylene Carbonate in a Poly(ethylene carbonate)‐Hydrogenated Nitrile Butadiene Rubber Solid Polymer Electrolyte

AbstractElectrolytes play an essential role in electrochemical energy storage devices. Liquid electrolytes have good ionic conductivity but tend to be flammable, prompting some of the safety concerns that are associated with these devices. Solid polymer electrolytes (SPEs) are presented as a potential solution to this problem. These materials have higher mechanical stability and can be formulated to be non‐flammable. However, ionic conductivity in solid polymer electrolytes tends to be several orders of magnitude lower than that of liquid electrolytes, significantly limiting device performance making electrolyte safety and performance difficult to optimize simultaneously. However, gel electrolytes which combine lower flammability, higher mechanical strength, and adequate ionic conductivity may present a solution to this challenge. To this end, the melt processing of hydrogenated nitrile rubber (HNBR) with poly(ethylene carbonate) (PEC) followed by the in situ formation of ethylene carbonate (EC) is reported. Conversion of PEC to EC is confirmed via NMR spectroscopy. Electrochemical testing reveals improved ionic conductivity following the conversion of the solid polymer electrolyte to the gel polymer electrolyte. Improvements in ionic conductivity, relative to the initial SPE, are attributed to decreased salt‐polymer interactions in favor of salt‐EC interactions as observed via differential scanning calorimetry, Fourier transform infrared, and nuclear magnetic resonance spectroscopy.

A novel hyperbranched polyurethane solid electrolyte for room temperature ultra-long cycling lithium-ion batteries

Low room temperature ionic conductivity of solid polymer electrolytes (SPE) greatly constraints its application in the solid lithium-ion batteries. Hyperbranched polymer with unique topological structure as matrix of SPE is expected to solve this issue due to its low crystallinity and rich functional groups which helps dissociation of lithium salt. Herein, a hyperbranched polyurethane (HPU) solid electrolyte is prepared by the reaction of hyperbranched polyethylene glycol and isophoradione diisocyanate in the presence of lithium salt and ionic liquid for the first time. The obtained HPU1.5-IL1.5 electrolyte possesses a high room temperature ionic conductivity of 0.4 mS cm−1 and a wide electrochemical window of 4.95 V (vs Li/Li+). It is worth noting that the prepared HPU1.5-IL1.5 electrolyte can be adapted to multiple electrodes. Specifically, the assembled LFP half-cell can achieve long cycling up to 1000 cycles at 0.5 C with 83 % capacity retention at room temperature. Notably, the NCM811|HPU1.5-IL1.5|Li cells and LTO|HPU1.5-IL1.5|Li cells can deliver the initial discharge capacity of 148 mAh g−1 at 0.1 C for 160 cycles and the initial discharge capacity of 150 mAh g−1 at 0.2 C for 440 cycles at room temperature, respectively. Meanwhile, the safety of the pouch cell has been confirmed under some extreme conditions.

A Step Towards the Impossible – the Combination of High Ionic Conductivity and Mechanical Stability in Highly Crystalline Solid Polyketone Electrolytes

Implementation of solid polymer electrolytes (SPEs) is believed to be one pathway forward in the development of lithium-metal batteries (LMBs) that are both safe and possesses high capacities. This combination is possible since the free-standing SPE maintains its mechanical integrity during electrochemical and thermal exposure while utilizing lithium metal as the negative electrode, thus accessing the extremely high theoretical capacity of lithium metal. The main drawback for SPEs are however the poor ionic conductivity compared to the liquid electrolytes used in lithium-ion batteries today.[1] The low ionic conductivity for SPEs stems from the conduction mechanism of the ions, which is a slower process in SPEs compared to in liquid electrolytes. In general, the conductivity in SPEs are confined to the amorphous regions, where segmental motion of the polymer chains facilitates the ion transport; while the crystalline regions restrict the movements of the polymer chains and impairs the ion transport.[2] The highly crystalline polyketone poly(1-oxoheptamethylene) (POHM) is a material that has shown interesting characteristics for implementation as a SPE in batteries. In earlier studies, the polyketone revealed an extensive improvement of the ionic conductivity upon increasing the salt concentration, although the crystallinity remained with a high melting point.[3] Herein this study, the effect of the crystallinity on the characteristics and the performance was investigated further. To understand its effect, a second less hydrogenated version of POHM was synthesized, POHM-75, which is fully amorphous at high salt concentrations. The characteristics of the polyketones were in addition also compared with the more well-studied SPEs, that is polyethylene oxide (PEO) and poly(trimethylene carbonate) (PTMC). Focus of the presentation is on the interplay between the ionic conductivity and mechanical stability for the polyketones, for which something different to the normally observed tradeoff between the two properties is observed. The electrochemical performance of the polyketones are furthermore evaluated when implemented as SPEs in LMBs at extreme temperature environments, a possible application area for mechanically stable SPEs.[1] D. Zhou, D. Shanmukaraj, A. Tkacheva, M. Armand, G. Wang, Chem 2019, 5, 2326-2352.[2] M. A. Ratner, P. Johansson, D. F. Shriver, MRS Bulletin 2011, 25, 31-37.[3] T. Eriksson, H. Gudla, Y. Manabe, T. Yoneda, D. Friesen, C. Zhang, Y. Inokuma, D. Brandell, J. Mindemark, Macromolecules 2022, 55, 10940-10949. Figure 1

Photo‐Thermal Mediated Li‐ion Transport for Solid‐State Lithium Metal Batteries

AbstractThe development of lithium‐based solid‐state batteries (SSBs) has to date been hindered by the limited ionic conductivity of solid polymer electrolytes (SPEs), where nonsolvated Li‐ions are difficult to migrate in a polymer framework at room temperature. Despite the improved cationic migration by traditional heating systems, they are far from practical applications of SSBs. Here, an innovative strategy of light‐mediated energy conversion is reported to build photothermal‐based SPEs (PT‐SPEs). The results suggest that the nanostructured photothermal materials acting as a powerful light‐to‐heat converter enable heating within a submicron space, leading to a decreased Li+ migration barrier and a stronger solid electrolyte interface. Via in situ X‐ray diffraction analysis and molecular dynamics simulation, it is shown that the generated heating effectively triggers the structural transition of SPEs from a highly crystalline to an amorphous state, that helps mediate lithium‐ion transport. Using the assembled SSBs for exemplification, PT‐SPEs function as efficient ion‐transport media, providing outstanding capacity retention (96% after 150 cycles) and a stable charge/discharge capacity (140 mA g−1 at 1.0 C). Overall, the work provides a comprehensive picture of the Li‐ion transport in solid polymer electrolytes and suggests that free volume may be critical to achieving high‐performance solid‐state batteries.

ИССЛЕДОВАНИЕ ТВЕРДЫХ ЭЛЕКТРОЛИТОВ НА ОСНОВЕ СМЕСИ ПОЛИМЕРОВ ПОЛИВИНИЛИДЕНФТОРИДА И ГИДРИРОВАННОГО БУТАДИЕН-НИТРИЛЬНОГО КАУЧУКА

The paper discusses the preparation of solid polymer electrolytes based on a blend of polyvinylidene fluoride and hydrogenated butadiene nitrile rubber with lithium bis(trifluorosulfonyl)imide prepared by solution casting technique. The films were characterized by X-ray diffraction analysis, FTIR spectroscopy, scanning electron microscopy, and differential scanning calorimetry. The influence of the polymer blend composition on the ionic conductivity of electrolytes was studied. According to the impedance spectroscopy data, it was found that the ionic conductivity of solid polymer electrolytes increases from 10-5 to 10-4 S/cm at room temperature with increasing the content of hydrogenated butadiene nitrile rubber up to 50 wt. % in the polymer blend matrix.

Ionic conductivity of solid polymer electrolytes depending on elongation

Research on solid polymer electrolytes (SPEs) based on poly(ethylene oxide) (PEO) is essential to propose an alternative to the conventional liquid electrolyte in order to increase both the mechanical properties and the ionic conductivity. Strategies to increase the ionic conductivity of SPEs are typically based on the development of new polymer architectures, lithium salt natures, plasticizers, or additives. In addition, applying an external field such as magnetic, electric, pressure, or a mechanical deformation onto the SPEs can alter the resulting ionic transport properties. For the later one, the main difficulty lies in obtaining the instantaneous evolution of the ionic conductivity coupled with the mechanical deformation and its geometrical change, especially when a striction domain appears. For this, a dedicated sample environment was designed to perform tensile tests in an inert atmosphere on SPE membranes at different temperatures (below and above the PEO melting temperature). Moreover, a methodology to calculate the instantaneous in-plane ionic conductivity is proposed based on COMSOL simulations to back out the sample geometrical changes during elongation. A strong impact on the in-plane ionic conductivity is observed when comparing PEO electrolyte architectures; from homopolymer to crosslinked single-ion conducting via binary conducting block copolymer electrolytes. Below the PEO melting temperature, a striction domain appears upon elongation whose conductivity is higher than the one of the bulk by a factor 1.7 and 18 for PEO homopolymer and binary conducting PEO-based block copolymer electrolytes, respectively.

The Deep Eutectic Solvent in Used Batteries as an Electrolyte Additive for Potential Chitosan Solid Electrolyte Membrane

The electrolyte or ion conductor acts as a bridge to transfer the ions the electrodes generate. In general, electrolytes are in the form of liquids. However, liquid electrolytes have drawbacks, including needing to be more practical and leaking quickly. Therefore, people switch to solid matrix electrolytes as battery electrolytes. An ideal solid electrolyte membrane must have chemical stability, thermal stability, high ionic conductivity, high flexibility, low cost, and abundant material availability. Lithium extraction from used batteries using Deep Eutectic Solvent (DES) was found to be an intelligent solvent. Mixing the method with lithium salt on a chitosan membrane can increase conductivity. This study aims to determine the lowest resistance value and highest conductivity of solid polymer electrolytes using Li2CO3 from used batteries. After separating the Lithium-Cobalt component from the used battery, it was extracted with deep DES solvent and precipitated using Na2CO3 to produce the Li2CO3 compound. Polymer electrolyte was synthesized by mixing polyvinyl alcohol and adding 0.2 grams, 0.4 grams, 0.6 grams, 0.8 grams, and 1 gram of chitosan. Li2CO3 variables are 0.2 grams, 0.4 grams, 0.6 grams, 0.8 grams, and 1 gram. The results showed that the higher content of chitosan and Li2CO3 led to an increase in ionic conductivity. These results concluded that the best solid electrolyte membrane was obtained with a variation ratio of 0.2 grams of chitosan with the addition of 1 gram of Li2CO3.

Inorganic Composites Improving Conductivities of Solid Polymer Electrolytes for Lithium Batteries: A Review

AbstractFor high‐energy‐density lithium batteries, the research and development of solid‐state electrolytes is crucial. Inorganic‐organic composite electrolytes with high mechanical strength and ionic conductivity of inorganic ceramic electrolytes, as well as high interfacial compatibility of polymer electrolytes, have become a current research hotspot. Based on a brief discussion of lithium dendrite growth and Li+ ion transport mechanisms, this article provides a comprehensive review of the nanostructure design and performance of inorganic‐organic composite electrolytes in recent years, and focuses on the mechanism of homogeneous monolayer composite electrolytes and heterogeneous multilayer composite electrolytes to enhance the performance of electrolytes. In addition, the future prospect of inorganic‐organic composite electrolytes is discussed, providing practical guidance for researchers in this field.

Measuring the ionic conductivity of solid polymer electrolyte powders

Ex-situ characterization of solid polymer electrolytes plays an important role in their development as materials for energy applications, with ionic conductivity being a crucial parameter to quantify. Conventional measurements of ionic conductivity often require the formation of a free-standing polymer film which in many instances is difficult to fabricate, thus there may be a need to quantify their ionic conductivity in powder form. In this work, we present a practical and reproducible method for measuring the ionic conductivity of solid polymer electrolytes (SPEs) in their powder form. By using a modified configuration of a through-plane cell, demonstrated with both a proton conducting- and an anion conducting-solid polymer electrolyte powder (SPEP), we are able to obtain ionic conductivity values under variable conditions in order to explore the influence of external parameters on the ionic conductivity of powders. Two types of SPEs in insoluble powder form were employed in this work: (1) a proton-exchange material (SPEP-H+) based on a hyperbranched, sulfo-phenylated poly(phenylene) SPEP (HB-sPPT-H+), with measured ionic conductivity of ⁓ 210 mS cm−1 at 80 °C and 95 % of relative humidity (RH); (2) an anion-exchange conducting polymer in its chloride form (SPEP-Cl-), consisting of a radiation-grafted ultra-high density polyethylene insoluble SPEP containing covalently-bonded benzyltrimethylammonium (BTMA) head-groups, with measured ionic conductivity of ⁓ 53 mS cm−1 at 80 °C and 95 % RH.

Nanoscale Confinement Effects on Ionic Conductivity of Solid Polymer Electrolytes: The Interplay between Diffusion and Dissociation.

Solid polymer electrolytes (SPEs) are attractive for next-generation lithium metal batteries but still suffer from low ionic conductivity. Nanostructured materials offer design concepts for SPEs with better performance. Using molecular dynamics simulation, we examine SPEs under nanoscale confinement, which has been demonstrated to accelerate the transport of neutral molecules such as water. Our results show that while ion diffusion indeed accelerates by more than 2 orders of magnitude as the channel diameter decreases from 15 to 2 nm, the ionic conductivity does not increase significantly in parallel. Instead, the ionic conductivity shows a nonmonotonic variation, with an optimal value above, but on the same order as, its bulk counterparts. This trend is due to enhanced ion association with decreasing channel size, which reduces the number of effective charge carriers. This effect competes with accelerated ion diffusion, leading to the nonmonotonicity in ion conductivity.

Versatile Zn-salt additive enabling superior solid polymer electrolyte for dendrite-free all-solid-state Li metal batteries

The development of all-solid-state rechargeable batteries is plagued by low ionic conductivity of solid polymer electrolytes and large interfacial resistance between electrolyte and Li metal anode. The introduction of versatile zinc bis(trifluoromethanesulfonyl)imide (Zn(TFSI)2) into polyethylene oxide (PEO) solid polymer electrolyte reduces the parasitic reaction with Li anode, increases the cycle life and allows a high rate performance of dendrite-free batteries. The competitive ion-dipolar interaction of Zn2+ promotes free Li+ transportation in PEO and enhances ion transfer number. Furthermore, the Zn2+ makes Li-Zn alloy in the solid electrolyte film by in-situ chemical reaction, this improves the mechanical modulus from 1.94 GPa to 38.47 GPa, homogenizes Li+ deposition and makes close electrolyte/Li metal contact. Benefiting from the structure and functional advantages, the Li/Li symmetric cell with a Zn(TFSI)2-contained electrolyte can achieve stable cycling over 600 h at a current density of 0.2 mA cm−1. The LiFePO4/Li cell can stably cycle over 900 cycles at 1 C rate at 60 °C. The idea of introducing Zn-salt for modifying PEO electrolytes may be extended to other all-solid-state batteries.

Poly (vinylidene fluoride) solid polymer electrolyte structure revealed by secondary ion mass spectrometry

Due to the processability safety, polymer-matrix composites can be considered as a solid polymer electrolytes and have attracted widespread attention. However, their electrical properties, as low ionic conductivity cannot meet the requirements of practical applications. Using the high energy mixing technique, the ionic conductivity was increased from 1.6 × 10 −6 to 9.4 × 10 −5 S cm −1 . The application of the Secondary Ion Mass Spectrometry technique revealed the distribution of lithium ions in the structure of the polymer matrix, which allows to directly connect the conductive properties and the homogeneity of the polymer composite. • High energy mixing technique increased conductivity of solid polymer electrolytes. • Increased conductivity results from changes in the structure of the composites. • Changes were detected and confirmed using the SIMS technique. • Secondary Ion Mass Spectrometry technique is an effective tool to assess charge carriers localization in composite materials.

Bifunctional LiI additive for poly(ethylene oxide) electrolyte with high ionic conductivity and stable interfacial chemistry

The development of polymer-based solid-state batteries is severely limited by the low ionic conductivity of solid polymer electrolyte and the instable interface between polymer electrolyte and Li-metal anode. In this work, lithium iodide (LiI) as a bifunctional additive was introduced into the poly(ethylene oxide) (PEO)-based electrolyte to improve the ionic conductivity and to construct a stable interphase at the Li/PEO interface. I− anions offer a strong electrostatic interaction with hydrogen atoms on PEO chains (HPEO) and forming massive I–H bonds that cross-link PEO chains, decrease crystallinity of PEO, and thus improve Li+ interchain transport. In addition, LiI participates in the formation of an inorganic-rich interphase layer, which decreases the energy barrier of Li+ transport across the interface and thus inhibits the growth of lithium dendrites. As a result, the composite PEO electrolyte with 2 wt% LiI (PEO-2LiI) presents a very high ionic conductivity of 2.1 × 10−4 S cm−1 and a critical current density of 2.0 mA cm−2 at 45 °C. Li symmetric cell with this PEO-2LiI electrolyte exhibits a long-term cyclability over 600 h at 0.2 mA cm−2. Furthermore, solid-state LiFePO4 and LiNi0.8Mn0.1Co0.1O2 batteries with the PEO-2LiI electrolyte show an impressive electrochemical performance with outstanding cycling stability and rate capability at 45 °C.

Ionic Association in CH3-(CH2-CF2) n -CH3(PVDF)-Li+-(CF3SO2)2N- for n = 1, 4: A Computational Approach.

The ionic conductivity of solid polymer electrolytes is governed by the ionic association caused by the polymer···Li+ and the anion···Li+ interactions. We performed the density functional calculation to analyze the molecular interactions in the CH3–(CH2–CF2)n–CH3–Li+–(CF3SO2)2N– for n = 1,4 systems. The gauche conformation is predicted in the lowest energy conformer of pure polymer except for n = 1. The lithium coordination number with the polymer is changed from 3 to 2 in the presence of anion for n = 2, 4 systems. The consequences of the Li+ ion and Li+–(CF3SO2)2N– to the vibrational spectrum are studied to understand the ionic association at the molecular level.

Micro-Structural Design of Soft Solid Composite Electrolytes With Enhanced Ionic Conductivity

Abstract Electrolyte in a rechargeable Li-ion battery plays a critical role in determining its capacity and efficiency. While the typically used electrolytes in Li-ion batteries are liquid, soft solid electrolytes are being increasingly explored as an alternative due to their advantages in terms of increased stability, safety and potential applications in the context of flexible and stretchable electronics. However, ionic conductivity of solid polymer electrolytes is significantly lower compared to liquid electrolytes. In a recent work, we developed a theoretical framework to model the coupled deformation, electrostatics and diffusion in heterogeneous electrolytes and also established a simple homogenization approach for the design of microstructures to enhance ionic conductivity of composite solid electrolytes. Guided by the insights from the theoretical framework, in this paper, we examine specific microstructures that can potentially yield significant improvement in the effective ionic conductivity. We numerically implement our theory in the open source general purpose finite element package FEniCS to solve the governing equations and present numerical solutions and insights on the effect of microstructure on the enhancement of ionic conductivity. Specifically, we investigate the effect of shape by considering ellipsoidal inclusions. We also propose an easily manufacturable microstructure that increases the ionic conductivity of the composite electrolyte by 40 times, simply by the addition of dielectric columns parallel to the solid electrolyte phase.

A simple low-cost method to prepare gel electrolytes incorporating graphene oxide with increased ionic conductivity and electrochemical stability

It has been reported that the existence of graphene oxide (GO) provides a fast-conducting pathway, promoting ionic conductivity in solid polymer electrolytes. However, the preparation of gel polymer electrolytes with GO has been less discussed. In addition, gel polymer electrolytes are usually prepared by adding polymers to organic solvent-based electrolyte solutions. In this study, we propose a facile method for preparing composite gel polymer electrolytes using gelators in low molecular weight (exhibited the liquid state) poly(ethylene glycol) (PEG)-based electrolytes. Mixing GO in PEG-based electrolytes results in precipitation due to significant aggregation of GO. However, PEG/GO composite gel electrolytes are obtained with an inexpensive organogelator, 1,3:2,4-dibenzylidene-d-sorbitol (DBS). The DBS gels entrap the GO and prevent its aggregation. The prepared composite gel electrolytes with GO show higher ionic conductivity and a wider electrochemical stability window, indicating that these electrolytes would be suitable for electrochemical devices.

A strong Lewis acid imparts high ionic conductivity and interfacial stability to polymer composite electrolytes towards all-solid-state Li-metal batteries

The development of high-performance solid polymer electrolytes is crucial for producing all-solid-state lithium metal batteries with high safety and high energy density. However, the low ionic conductivity of solid polymer electrolytes and their unstable electrolyte/electrode interfaces have hindered their widespread utilization. To address these critical challenges, a strong Lewis acid (aluminum fluoride (AlF3)) with dual functionality is introduced into polyethylene oxide) (PEO)-based polymer electrolyte. The AlF3 facilitates the dissociation of lithium salt, increasing the iontransfer efficiency due to the Lewis acid-base interaction; further the in-situ formation of lithium fluoride-rich interfacial layer is promoted, which suppresses the uneven lithium deposition and continuous undesired reactions between the Li metal and PEO matrix. Benefiting from our rational design, the symmetric Li/Li battery with the modified electrolyte exhibits much longer cycling stability (over 3600 h) than that of the pure PEO/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte (550 h). Furthermore, the all-solid-state LiFePO4 full cell with the composite electrolyte displays a much higher Coulombic efficiency (98.4% after 150 cycles) than that of the electrolyte without the AlF3 additive (63.3% after 150 cycles) at a large voltage window of 2.4–4.2 V, demonstrating the improved interface and cycling stability of solid polymer lithium metal batteries.

Fingerprint of semi-crystalline structure memory in the thermal and ionic conduction properties of amorphous ureasil-polyether hybrid solid electrolytes.

Correlations among the structure, thermal properties, and ionic conductivity of solid polymer electrolytes (SPEs) were studied using a ureasil–polyethylene oxide (U-PEO) organic–inorganic hybrid prepared according to a simple sol–gel route, employing a low molecular weight PEO macromer (Mw = 1900 g mol−1). The behavior of an amorphous sample loaded with lithium triflate (LiTFSI) at an optimum ratio between ether oxygen and lithium (EO/Li+ = 15) was compared with that of a semicrystalline sample prepared without salt loading. The temperature range investigated by differential scanning calorimetry (DSC), Raman spectroscopy, small angle X-ray scattering (SAXS), and complex impedance spectroscopy covered both the glass transition and the melting temperature of the U-PEO. The gauche to trans conformational transformation of the (O–C–C–O)Li+ sequence showed similarity between the temperature evolution of the semi-crystalline U-PEO and amorphous U-PEO:Li+ samples, providing an indication of the local structural memory of crystalline state in the amorphous SPE. The linear thermal expansion of the average correlation distance between the siloxane crosslink nodes and the long-distance period of the lamellar semi-crystalline edifice were determined by SAXS. Comparison of the expansion curves suggested that although the siloxane nodes were excluded from the PEO crystalline edifice, the sharp expansion of the amorphous region between the lamellae during melting permitted modulation of the free volume of the hybrid network. In addition, the temperature-induced Li+-EO decomplexation observed by Raman spectroscopy explained the change of the average activation energy of the conduction process revealed by the different Arrhenius regimes. These results evidence the key role of the ionic conductivity decoupling from the segmental motion of chain pair channels on the improvement of ion mobility through the free volume between chains. This concept may inspire materials chemistry researchers to design optimized structures of polymer electrolytes with minimized structural memory of crystaline building blocks and improved ionic conductivity.

Research progress on solid polymer electrolytes

<p indent="0mm">Since the commercialization of lithium-ion batteries in the 1990s, lithium-ion batteries have been successfully applied in portable electronics, electric vehicles, and grid energy storage. Although current organic liquid electrolytes have high ionic conductivities, they are inherently flammable, volatile, and prone to leakage. Moreover, severe side reactions and dendrite growth on the surface of the lithium anode during the charge-discharge process can cause safety hazards, which greatly impede their applications in lithium metal batteries. Solid electrolytes, including inorganic solid electrolytes and polymer electrolytes, are regarded as effective alternatives to organic liquid electrolytes for the construction of lithium metal batteries with high energy density and safety. Among them, solid polymer electrolytes offer excellent flexibility, processability, and interfacial compatibility over inorganic solid electrolytes, and they are extraordinarily promising for lithium metal batteries with high energy density and safety. Ideal solid polymer electrolytes should have following features: (1) High ionic conductivity (&gt; <sc>10 ^–4 S cm ^–1) </sc> at room temperature; (2) high lithium ion transference number (~1) to reduce the concentration polarization and improve the rate performance of batteries; (3) intimate contact at the electrode/electrolyte interfaces; (4) wide electrochemical window <sc>(&gt;4.5 V</sc> vs. Li/Li ⁺) to match high-voltage cathodes and improve the energy density of batteries; (5) good mechanical stability to resist processing, buffer electrode volume change and inhibit dendrite growth; (6) good thermal stability to withstand environmental changes. Generally, the ionic conductivity of pure solid polymer electrolytes at room temperature is low <sc>(~10 ^–6 S cm ^–1). </sc> Researchers have tried to improve the ionic conductivities by adjusting the lithium salt concentration, such as developing “polymer-in-salt” solid electrolytes. However, increasing the concentration of lithium salt leads to the deterioration of the mechanical strength. Strategies such as developing novel lithium salts, modifying polymer matrix, and incorporating inorganic fillers into solid polymer electrolytes are proposed to promote ionic conductivities of solid polymer electrolytes. In particular, composite polymer electrolytes, fabricated by dispersing a certain amount of inorganic fillers into solid polymer electrolytes, have improved ionic conductivities without sacrificing their mechanical performances. Poor interfacial property between electrodes and electrolytes is also a critical issue for solid polymer electrolytes. On one hand, poor and uneven solid/solid contacts at the electrode/electrolyte interfaces lead to high resistance and sluggish ionic transport kinetics. Furthermore, the volume change of the positive and negative electrodes in the charge/discharge process deteriorates the interfacial contacts, blocks the ion and electron transport through the interfaces, and greatly reduces the electrochemical reaction kinetics. On the other hand, the electrochemical windows of solid polymer electrolytes are usually narrow <sc>(＜4.5 V).</sc> During cycling, redox reactions are prone to occur at the electrode/electrolyte interfaces, causing battery failure. Solid polymer electrolytes have also poor thermal and mechanical stabilities. Therefore, design and synthesis of polymer-based solid electrolytes with excellent comprehensive performances and construction of fast and stable ion transport channels at the electrolyte/electrode interfaces are of great significance for the successful development of solid-state lithium metal batteries. This paper presents a brief review of the research progress in solid polymer electrolytes from two aspects: Improving the ionic conductivities of solid polymer electrolytes and enhancing the interfacial performance at electrolyte/electrode interfaces. First, targeted optimization strategies on ionic conductivities of solid polymer electrolytes, including constructing continuously aligned ionic transport paths and shortening the ionic transport distance, are summarized. Second, interface optimization strategies, including constructing wetting interfaces and synthesizing asymmetric electrolytes, are presented to reduce the interface resistance and improve the interfacial contact. Finally, perspectives on the development of solid polymer electrolytes and high-performance solid-state lithium metal batteries are discussed, and key research directions and advanced test methods are proposed. This review may provide a comprehensive understanding and further guidance for not only the material design of solid polymer electrolytes, but also the structural design of lithium metal batteries with favorable electrochemical and interfacial performances.

Ce(NO3)3 as an electrolyte additive to regulate uniform lithium deposition for stable all-solid-state batteries

All-solid-state lithium metal batteries (LMBs) have attracted extensive attention because of their high energy density and good safety performance. But the ionic conductivity at low temperature and dendritic growth hinder their further development. In this work, a flexible all solid-state electrolyte consisted with Ce(NO3)3, lithium bis(fluorosulfonyl) imide (LiFSI), and poly(ethylene oxide) (PEO) is synthesized. Ce(NO3)3 as an effective additive can enhance the ionic conductivity of solid polymer electrolytes (SPEs) by regulating Li+ transporting and stabilizing the interface between lithium metal anode and electrolyte by forming a stable and uniform solid electrolyte interphase (SEI) on lithium metal anode surface. The as-prepared electrolyte exhibits a good ionic conductivity of 1.6 × 10−4 S cm−1 at 60 °C and a wide electrochemical window of 4.4 V. The Li//Li symmetric cell with PEO + LiFSI+1%Ce(NO3)3 electrolyte displays a long cycling lifespan of over 1100 h at 0.1 mA cm−2 at 60 °C. Moreover, the corresponded LiFePO4 (LFP)//Li cell exhibits a long cycling lifespan of 300 cycles and excellent rate capability. This work proposes an effective additive to improve ionic conductivity and stabilize the Li metal/electrolyte interface.