Poly Ethylene Oxide Electrolytes Research Articles

PEO-Based Solid-State Polymer Electrolytes for Wide-Temperature Solid-State Lithium Metal Batteries.

Developing solid-state lithium metal batteries with wide operating temperature range is important in future. Polyethylene oxide (PEO)-based solid-state electrolytes are extensively studied for merits including superior flexibility and low glass transition temperature. However, ideal usage temperatures for conventional PEO-based solid-state electrolytes are between 60 and 65°C, and unequable temperature degrades their electrochemical performances at low and high temperatures (≤25°C and ≥80°C). Herein, modification methods of PEO electrolytes for low, high especially wide-temperature applications are reviewed based on detailed analyses of mechanisms involved in its modification at different temperatures. First, shortcomings of PEO solid electrolytes due to influence of temperature are pointed out. Second, existing modification strategies are summarized in detail from three aspects of high, low especially wide temperatures, including application of PEO derivatives or chain segment modification treatment of PEO, addition of fillers, and other modification methods such as reasonable regulation of lithium salts, introduction of functional layers and addition of metal-organic frameworks (MOFs) or covalent organic frameworks (COFs). Finally, a summary and description of PEO-based solid electrolyte research and development trends for wide-temperature applications are provided. The review aims to offer some guidance for the creation of PEO solid batteries with wider working temperature ranges.

Unveiling the Interfacial Composition of Li-Metal | Polymer Electrolytes during Lithium Plating-Stripping Employing Operando ATR-FTIR Spectroscopy

The Li-metal interphases formed in contact with solid-state (polymer) electrolytes (SSE) during electrochemical plating and stripping influences remarkably the lifespan and safety of solid-state batteries (SSBs). Effective interphases play a crucial role in impeding the continuous decomposition of electrolytes, the growth of dendrites, and consequently, enhancing the overall battery performance. However, the investigation of interphases of solid electrolytes remains a challenge, necessitating development of advanced techniques and methodologies. Moreover, highly sensitive instruments are demanded to detect the extremely thin interphases. Furthermore, real-time monitoring experimentations are needed to capture the interfacial dynamics. Addressing the interphase in solid-state battery under real working conditions is another major complication regarding the signal acquisition of the buried interfacial products between non-transparent electrodes. As a result, there are very limited studies of such a kind, which make our state-of-the-art understanding of interfacial process in SSBs very poor.Towards addressing this, we have developed and operando spectroscopy technique based-on Attenuated Total Reflection Fourier-Transform Infrared (ATR-FTIR) for real time monitoring of interphase composition between Li-metal and solid polymer electrolytes. ATR-FTIR spectroscopy is a powerful analytical technique that offers several significant advantages, including rapid data acquisition, applicability for various sample forms, and high sensitivity to trace even small amounts of substances non-destructively. The preservation of the original interphase composition is crucial for the characterization under real working conditions. Moreover, it is rather straightforward to combine the ATR-FTIR measurements with the electrochemical system by utilizing specifically designed spectro-electrochemical cells.Our team has been developing the advanced ATR-FTIR set-up for operando interphase analysis, which has already worked successfully for characterizing the interphases of liquid electrolyte system on Si and Li-metal electrode1. Based on the successful implementation of this technique, we further developed the setup for the analysis the interphases on solid-state electrolytes with lithium metal in anode-free configuration. In our investigation, a well-known system comprising polyethylene oxide (PEO) polymer, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and benzophenone as photoinitiated crosslinker, was chosen for use as a proof of concept. PEO is one of the most extensively used polymer for SSE, its conductivity at room temperature is however relatively low, as its optimated usage temperature is above 60oC. To ensure that our experimental setup remains comparable to contemporary research on PEO electrolytes, a temperature control system was implemented in the design of our spectro-electrochemical cell, besides, pressure controlling is also incorporated to enhance internal material adhesion. Furthermore, the ATR-FTIR instrument is equipped with adjustable incident angles for the IR beam, enabling the characterization of the interphases at different penetration depths. In terms of cell internal configuration, an anode-free setup was opted, which not only facilitates penetration of infrared beam, but is also regarded as a promising configuration for next-generation SSBs.Following the acquisition of IR spectrum during the Li plating-stripping process, it was observed that certain bands exhibited intensity variations, as a result of dynamicity in interfacial composition. Notably, some prominent variations were observed in the IR spectrum around 1500-1750 cm-1, primarily originated from bands associated with benzophenone. The reactions of the crosslinker may undergo within the electrolyte system during electrochemical process are often overlooked, which is due to the lack of techniques with the ability to monitor these reactions. The presented study outlines the need for advanced operando methods to increase the understanding of interphases formed by solid-electrolytes.In future perspectives, efforts will be directed towards further optimizing the cell setups and with the aim of applying this technique to investigate interphases and aging mechanisms in various solid electrolyte systems.Reference: Weiling, Matthias, et al. "Mechanistic Understanding of Additive Reductive Degradation and SEI Formation in High‐Voltage NMC811|| SiOx‐Containing Cells via Operando ATR‐FTIR Spectroscopy." Advanced Energy Materials5 (2024): 2303568.

Flexible Electrolyte Sheets Using Sulfonated Cellulose Nanofiberfor Sheet-Type All-Solid-State Batteries

With the rapid spread of electric vehicles that do not use fossil fuels for suppression of global warming, all-solid-state batteries (ASSBs) have been studied as a next-generation battery to improve the cruising range and safety. In general, ASSBs use solid-state electrolyte such as polymer or inorganic electrolytes instead of organic electrolyte solutions, which prevent from electrolyte leakage and its degradation especially at high temperatures. Therefore, it is possible to simplify for the cell design and to increase the energy density. However, for the practical use relatively high interface resistance between electrode and solid-state electrolyte is one of the critical problems. Recently, addition of cellulose nanofiber (CNF) into polyethylene oxide (PEO) electrolyte was reported to improve flexibility and mechanical strength. Also, this method can reduce the interface resistance and improve the cycle performance [1]. In this study, we prepared new composite electrolyte membranes by using sulfonated CNF (S-CNF, Yokokawa Bio Frontia Inc.), together with a low molecular weight PEO, i.e. tetraglyme (G4), and some amounts of ceramic powders to support the ionic conductivity and mechanical strength. The electrochemical properties were investigated by using SUS | SUS and Li | Li symmetric cells to elucidate the mechanism of ionic transport. Mixtures of S-CNF, Lithium-Ion Conducting Glass-Ceramics (LiCGCTM, OHARA) or SiO2 powders, Lithium Bis(trifluoromethanesulfonyl) imide (LiTFSI) salt and G4 solvent were prepared in a predetermined ratio. The resulting solutions were coated onto PET film and dried in vacuum to form membranes, and then peeled off to obtain the S-CNF composite electrolyte membranes. The ion conductivity was measured by AC impedance method at a frequency range from 1 MHz to 100 mHz and applied voltage of ±50 mV by using a SUS | SUS symmetric cell. The interface resistances were evaluated by using a Li | Li symmetric cell to subject to a Li dissolution/ deposition test at 25°C. The tests was conducted in a constant current mode with a voltage range of -2.0 to 2.0 V, a current density of 0.50 mA cm- 2 and a capacity limit of 0.50 mAh cm-2. Fig. 1 shows Nyquist plots of a LICGC pellet and the S-CNF composite membranes containing LiCGC or SiO2 powder. The composite membranes has no semicircular component different from the LICGC pellt. This indicates that the interface resistance between the electrolyte menbranes and Li metal is drastically reduced owing to the flexibility. Also, both case of S-CNF composite menbrane exhibited almost same plots. This indicates that the contribution for ionic conductivity by the LICGC solid-state electrolyte is smaller than that by the polymer electrolyte conponent of LiTFSI/G4. In fact, the ion conductivity calclated from the Nyquist plots were 55.0 and 51.7 μS cm-1 for the S-CNF composite menbranes containing LICGC and SiO2 powder, respectively. These values were five times higher than that of pure LICGC pellet (9.53 μS cm-1). On the other hand, Li |Li symmetric cell test exhibited a quite stable polarization curves for the both S-CNF menbranes remaining the overpotential below 5 mV for up to 200 cycles. This also indicates the good chemical stability against Li metal. The mechanism of ionic conductivity, the role of S-CNF in the composite menbranes and the mechanical strength will be totally discussed in the meeting.

Molecular Control Based on Electrostatically Driven Modification for Solid-State Lithium Metal Batteries.

With the rapid development of energy vehicles, the demand for high-safety and high-energy-density battery systems, such as solid-state lithium metal batteries, is becoming increasingly urgent. Polyethylene oxide (PEO), as a commonly used electrolyte in solid-state batteries, has the advantages of easy processing and good interface compatibility but also faces the issue of poor ionic conductivity. In this study, we have enhanced the mechanical properties and ion conductivity of PEO electrolytes significantly, stabilizing electrochemical cycling, utilizing positively charged MXene as a modifying material for PEO solid electrolytes and leveraging stronger electrostatic forces. With these enhanced properties, the modified solid electrolyte in Li/Li cells demonstrates excellent cycling stability of over 430 h at 0.1 mA cm-2. Furthermore, the Li/LiFePO4 cells show excellent cycling performance, and the capacity retention rate is 92.1%.

Heterometallic metal-organic cage doped PEO composite electrolyte for solid lithium ion battery

PEO (polyethylene oxide)-based electrolytes, which is characteristic of the advantages such as good film-forming properties, ease of mechanical processing, and non-reactivity with lithium metal, have been extensively studied. However, there still exist some certain issues related to energy and lifespan of all-solid-state lithium-ion batteries (ASSLIBs). The Cd-In cage [Cd2In3L2Cl5(H2O)9]Cl2 (L = 2,2′,2″-(nitrilotris(methylene))tris(1H-benzo[d]imidazole-5-carboxylic acid) in this research can greatly disperse into PEO without significant agglomeration. The intrinsic cavities from the Cd-In cages form channels for lithium ion transport but inhibiting the transport of the corresponding counter anions, thereby protecting the electrode interface by reducing the interfacial reaction. For LFP||PEO-LiTFSI/Cage||Li cell at a fixed current density of 1.0 C, the specific capacity maintained a consistent level of 136 mA h/g over a span of 100 cycles. This value was higher than those of cells prepared with pristine PEO electrolyte.

Regulating Li+ transport behavior by cross-scale synergistic rectification strategy for dendrite-free and high area capacity polymeric all-solid-state lithium batteries

The inability to effectively inhibit the lithium (Li) dendrite growth is identified as the real culprit hindering the practical application of polyethylene oxide (PEO)-based electrolytes. Herein, a novel PEO composite electrolyte with ion rectifier is developed based on the cross-scale synergistic rectification strategy. At the micro-scale, the array structure of the ion rectifier suppresses the growth of PEO crystals and their distribution in the non-ionic conduction direction through space confinement, alleviating ion-migration crosstalk and enabling polymer chain rectification. Furthermore, the matrix contains abundant copper ions and oxygen-containing groups that inhibit anion conduction and accelerate Li+ migration at the nanoscale, respectively, to achieve ion flow rectification. Implementing this strategy results in a uniform, fast, and stable Li+ migration/diffusion behavior from the electrolyte to anode interface. The critical current density of the PEO electrolyte is increased to 2.5 mA cm−2, indicating a significant improvement in dendrite growth inhibition. Impressively, the composite electrolytes exhibit long-term stability (>4000 h at 0.2 mA cm−2) and ultra-high current-density tolerance (>200 h at 1 mA cm−2). Moreover, the composite electrolytes enable stable cycling of high-area-capacity (3.11 mAh cm−2, 20 mg cm−2) LiFePO4/Li pouch cells, highlighting the importance of this strategy for the practical application of PEO electrolytes.

Poly(ethylene) Oxide Electrolytes for All-Solid-State Lithium Batteries Using Microsized Silicon/Carbon Anodes with Enhanced Rate Capability and Cyclability.

Silicon (Si) has been widely studied as one of the promising anodes for lithium-ion batteries (LIBs) because of its ultrahigh theoretical specific capacity and low working voltage. However, the poor interfacial stability of silicon against conventional liquid electrolytes has largely impeded its practical use. Therefore, the combination of silicon-based anodes and solid electrolytes has attracted a great deal of attention in recent years. Here, we demonstrate three types of microsized porous silicon/carbon (Si/C) electrodes (i.e., pristine, prelithiated by liquid electrolyte, and preinfiltrated by polymer electrolyte) that are paired with poly(ethylene) oxide (PEO)-based electrolytes for all-solid-state lithium batteries (ASSLBs). We found that when compared with ionic conductivity, the mechanical stability of the PEO electrolyte dominates the electrochemical performance of ASSLBs using Si/C electrodes at elevated temperature. Additionally, both prelithiated and preinfiltrated Si/C electrodes show higher specific capacity in comparison to the pristine electrode, which is attributed to continuous lithium-ion conducting pathways within the electrode and thus improved utilization of active material. Moreover, owing to good interfacial lithium-ion transport in the electrode, a solid-state half-cell with preinfiltrated Si/C electrode and PEO-lithium bis (trifluoromethanesulfonyl)imide electrolyte delivers a specific capacity of ∼1,000 mAh g-1 after 100 cycles under 800 mA g-1 at 60 °C with average Coulombic efficiency >98.9%. This work provides a strategy for rationally designing the microstructure of silicon-based electrodes with solid electrolytes for high-performance all-solid-state lithium batteries.

Application of Li6.4La3Zr1.45Ta0.5Mo0.05O12/PEO Composite Solid Electrolyte in High-Performance Lithium Batteries.

Replacing the flammable liquid electrolytes with solid ones has been considered to be the most effective way to improve the safety of the lithium batteries. However, the solid electrolytes often suffer from low ionic conductivity and poor rate capability due to their relatively stable molecular/atomic architectures. In this study, we report a composite solid electrolyte, in which polyethylene oxide (PEO) is the matrix and Li6.4La3Zr1.45Ta0.5Mo0.05O12 (LLZTMO) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) are the fillers. Ta/Mo co-doping can further promote the ion transport capacity in the electrolyte. The synthesized composite electrolytes exhibit high thermal stability (up to 413 °C) and good ionic conductivity (LLZTMO-PEO 2.00 × 10-4 S·cm-1, LLZTO-PEO 1.53 × 10-4 S·cm-1) at 35 °C. Compared with a pure PEO electrolyte, whose ionic conductivity is in the range of 10-7~10-6 S·cm-1, the ionic conductivity of composite solid electrolytes is greatly improved. The full cell assembled with LiFePO4 as the positive electrode exhibits excellent rate performance and good cycling stability, indicating that prepared solid electrolytes have great potential applications in lithium batteries.

Revealing the effect of double bond-modified Li6.75La3Zr1.75Ta0.25O12 on the Li-ion conduction of composite solid electrolytes

Lithium metal batteries with polyethylene oxide (PEO) electrolytes have shown great potential to be one of the next-generation energy candidates. As the branch family of PEO electrolytes, poly(ethylene glycol) acrylates (PEGAs) attract more attention owing to their better electrochemical properties than that of PEO electrolytes. Introducing double bond-modified Li6.75La3Zr1.75Ta0.25O12 fillers (KH@LLZTO) has been a popular method to improve the electrochemical properties of PEGAs electrolytes due to the homogeneous dispersion of LLZTO. However, in this work, an inverse phenomenon is discovered. The electrochemical properties of PEGAs electrolytes get worse when introducing KH@LLZTO. By exploring the Li+ transport mechanism, the reason for the inverse phenomenon is revealed. More importantly, the design principle of PEGAs electrolytes with fast ionic conductor fillers is presented. Double bond-modified LLZTO can decrease the electrochemical properties of PEGAs electrolytes instead when there are low-molecular weight monomers that can participate in the PEGAs polymer network and interact with Li+, while the double bond-modified LLZTO can improve the electrochemical properties of PEGAs electrolytes when there are not aforementioned low-molecular weight monomers. This work provides a new understanding for componential design and optimization of PEGAs electrolytes with fast ionic conductors, hoping to promote the practical application of PEGAs electrolytes.

In-situ electrochemical passivation for constructing high-voltage PEO-based solid-state lithium battery

Polyethylene oxide (PEO) is one of the promising substrates for polymer solid electrolyte. However, when coupled with high energy density nickel-rich layered cathode materials, PEO faces the risk of catalytic decomposition by delithium nickel-rich materials. In this work, the in-situ electrochemical passivation strategy is employed to obtain high voltage PEO-based solid-state lithium battery. Trace commercial liquid electrolyte was added on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM811) electrode, and liquid electrolyte is prior to PEO electrolyte to react with the cathode during charge/discharge process, leading to the formation of cathode-electrolyte interface (CEI) layer. The CEI layer avoids the direct contact between PEO and NCM811, thus effectively prevents PEO from being decomposed by NCM811 under high voltage. As a result, the optimized NCM811||PEO||Li battery displays enhanced electrochemical performance, especially cycling performance. This simple but effective strategy not only simplifies the manufacturing process, but also has instructional guidance for high-voltage PEO-based battery.

Polyethylene oxide-Based solid electrolytes with fast Li-ion transport channels constructed from 2D montmorillonite for solid-state lithium-metal batteries

Polyethylene oxide (PEO)-based solid-state electrolytes (SSEs) typically struggle with poor ionic conductivity, low lithium (Li)-ion transference number, and narrow electrochemical window. For overcoming these drawbacks, we designed a promising composite SSE (CSSE), i.e., a Li-containing ionic liquid (LiIL) was inserted into the Li-montmorillonite (LiMNT) layered structure to form an active filler (LiIL@LiMNT), involving two-dimensional (2D) fast transport channels of Li-ion inside PEO electrolyte. Benefitting from an enhancement of the 2D Li-ion transport channels, the obtained CSSE exhibited an excellent ion conductivity of 1.38 × 10−4 S cm−1 at 30 °C as well as a satisfactory Li-ion transference number (0.38). A Li symmetric battery with the CSSE exhibited a steady cycle for 3000 h with 0.2 mA cm−2 at 60 °C. Under the rate of 0.5C at 60 °C, the solid-state Li-metal batteries (SSLMBs) assembled with LiFePO4 and LiNi0.33Co0.33Mn0.33O2 cathodes maintained a considerable reversible capacity after 400 and 100 cycles, respectively. The assembled SSLMB also achieved a satisfactory performance at 40 °C. The 2D active filler prepared in this work forms efficient 2D Li-ion transport channels inside the CSSE while maintaining a tight interfacial contact with electrodes, which is crucial to achieve a superior performance for CSSEs. This strategy of constructing 2D ion transport channels in polymer electrolytes also provides another way for the design of other CSSEs.

Cationic cellulose nanofiber solid electrolytes: A pathway to high lithium-ion migration and polysulfide adsorption for lithium-sulfur batteries

Polyethylene oxide (PEO) solid electrolytes, acknowledged for their safety advantages over liquid counterparts, confront inherent challenges, including low ionic conductivity, restricted lithium ion migration, and mechanical fragility, notably pronounced in lithium‑sulfur batteries due to the polysulfide shuttling phenomenon. To address these limitations, we integrate a quaternary ammonium cation-modified cellulose (QACC) nanofiber, electrospun with cellulose acetate (CA) from recycled cigarette filters, into the PEO electrolyte matrix. The nitrogen atom within the quaternary ammonium group exhibits a pronounced affinity for polysulfide compounds, effectively curtailing polysulfide migration. Concurrently, Lewis acid-base interactions between quaternary ammonium groups and lithium salt anions facilitate the release of additional Li+, achieving a lithium-ion transference number 1.5 times higher than its pure PEO counterpart. Furthermore, the introduction of a larger trifluoromethanesulfonimide (TFSI) group on the QACC macromolecule (TFSI-QACC) disrupts the ordered arrangement of PEO macromolecules, resulting in a noteworthy enhancement in ionic conductivity, reaching 2.07 × 10−4 S cm−1 at 60 °C, thus addressing the challenge of low PEO electrolyte conductivity. Moreover, the nanofiber enhances the mechanical strength of the PEO electrolyte from 0.49 to 7.50 MPa, mitigating safety concerns related to lithium dendrites puncturing the electrolyte. Consequently, the composite PEO demonstrates exemplary performance in lithium symmetrical batteries, enduring 500 h of continuous operation and completing 100 cycles at both room and elevated temperatures. This integrated approach, transitioning from waste to wealth, adeptly addresses a spectrum of challenges in the efficiency of solid-state electrolytes, holding considerable promise for advancing lithium‑sulfur battery technology.

Review on Comparative Study of Solid Polymer Electrolyte Polyethylene Oxide (PEO) Doped with Ionic Liquid

AbstractFuture demands for energy shortages have prompted a lot of effort to be put into finding alternatives. The use of renewable energies as a revolutionary energy source has gained acceptance. Due to their high flexibility and the interaction between the electrode and the electrolyte, solid polymer electrolytes are employed as a favorable electrolyte for application of electrochemical devices to storage renewable energy. As these are easy in synthesis, have much lower mass density, shows high mechanical stability, also have low binding energy with salts, and high mobility of charge carriers, polyethylene Oxide (PEO) based electrolyte has attracted a lot of interest. Configuration rectification combining PEO with ionic liquids has been introduced to enhance the low ionic conductivity and poor thermodynamic stability of the PEO materials in high‐voltage devices at ambient temperature. This configuration modification can successfully validate the applications of PEO polymer electrolyte with large electro‐stable voltage ranges. Solution casting method has been used for the synthesis of polymer electrolyte. The essential physical characteristics of PEO in polymer matrices work as a polymer host in SPEs has been described in this review paper, along with several modifications to overcome these limitations. It has been seen that the addition of ionic liquid increases the all over conductivity of the solid polymer electrolyte in most cases also improves the electrical stability of the electrolyte.

A strategy involving the use of 3D self-supporting B·N co-doped carbon nanofiber composite solid polymer electrolytes to stabilize the interface between polymer electrolytes and lithium metal.

All-solid-state batteries (ASSBs) have gained significant attention in the field of energy storage owing to their enhanced safety features based on the nonflammable solid-state electrolyte (SSE). To achieve high energy density, lithium metal is commonly considered the best choice as an anode material. However, the compatibility issues at the interface between polymer electrolytes and lithium metal pose significant challenges to their practical implementation. In this work, we present a new strategy to protect the typical polymer electrolyte polyethylene oxide (PEO) from significant decomposition and puncture caused by lithium dendrites, which is achieved through the combination of PEO and B·N co-doped carbon nanofibers (B·N-CNF) to modify the surface of the lithium anode. The stable cycling performance of the symmetric battery can last over 900 h at a high current density of 1 mA cm-2. The ASSBs (LiFePO4 is used as the cathode and Li metal is employed as the anode) exhibit a high capacity close to 120 mA h g-1 at 2C and cycle for over 300 cycles at 0.2C stably. This work provides inspiration for the rational design of a modification layer on the Li anode, enabling the development of high-performance ASSBs based on polymer electrolytes.

Metal-Organic Framework Glass as a Functional Filler Enables Enhanced Performance of Solid-State Polymer Electrolytes for Lithium Metal Batteries.

Polymers are promising candidates as solid-state electrolytes due to their performance and processability, but fillers play a critical role in adjusting the polymer network structure and electrochemical, thermal, and mechanical properties. Most fillers studied so far are anisotropic, limiting the possibility of homogeneous ion transport. Here, applying metal-organic framework (MOF) glass as an isotropic functional filler, solid-state polyethylene oxide (PEO) electrolytes are prepared. Calorimetric and diffusion kinetics tests show that the MOF glass addition reduces the glass transition temperature of the polymer phase, improving the mobility of the polymer chains, and thereby facilitating lithium (Li) ion transport. By also incorporating the lithium salt and ionic liquid (IL), Li-Li symmetric cell tests of the PEO-lithium salt-MOF glass-IL electrolyte reveal low overpotential, indicating low interfacial impedance. Simulations show that the isotropic structure of the MOF glass facilitates the wettability of the IL by enhancing interfacial interactions, leading to a less confined IL structure that promotes Li-ion mobility. Finally, the obtainedelectrolyte is used to construct Li-lithium iron phosphate full batteries that feature high cycle stability and rate capability. This work therefore demonstrates how an isotropic functional filler can be used to enhance the electrochemical performance of solid-state polymer electrolytes.

Unravelling stability of current collectors in lithium bis(trifluoromethanesulfonyl)imide salt and polyethylene oxide electrolyte for solid-state lithium batteries

Recent interest in solid-state lithium batteries prevails in the battery community because of their superiority in terms of safety concerns. Many works have been reported for electrodes and electrolytes and their suitability for solid-state polymer electrolytes to adopt in lithium batteries. Herein, for the first time, we report on the electrochemical stabilities of Cu and Al current collectors in a polyethylene oxide (PEO)-based solid-state electrolyte containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. Our work on the electrochemical dynamic- and transient-mode polarization of these electrodes indicates that Cu metal undergoes Cu–O passivation below 3 V. The adhered Cu-F layer on the CuO passive layer may be beneficial to delay undesired reaction such as corrosion. And it is further confirmed that Al metal passivates stably even up to 5 V; namely, the Al surface forms double layers of the outer Al–F and inner Al–O layers. These F- and O-based layers are attributed to the combination of the Al and O from the reductively decomposed PEO and further progress of Al2O3 and HF (H+ + F− →HF), decomposed from the PEO (H+) and TFSI− (F−). Therefore, we verify that successful passivation on Cu and Al metal surfaces facilitates their suitability as current collectors for solid-state polymer lithium batteries.

Li1.3Al0.3Ti1.7(PO4)3 /PEO Polymer Double-Layer Electrolyte to Improve Electrochemical Properties of Li-CO2 Battery

Li−CO2 batteries are explored as promising power systems to alleviate environmental issues and to implement space applications. However, sluggish cathode kinetics of CO2 reduction/evolution result in low round-trip efficiency and poor cycling stability of the fabricated energy-storage devices.Herein, we design a double-layer solid electrolyte to decrease interfacial resistance. Li-CO2 battery with high stability and energy density was developed using Li1.3Al0.3Ti1.7(PO4)3 (LATP) as the solid-state electrolyte and a polyethylene oxide (PEO) polymer electrolyte film together. The oxide solid electrolyte LATP has temperature stability and physical solidity, but it has a metal substitution reaction with lithium metal and a low interfacial stability with the electrode. However, this drawback can be solved by using the polymer electrolyte PEO to avoid direct contact between the lithium metal electrode and LATP. The mechanism of the Li-CO2 battery, a carbon capture technology, is used, and the characteristics of the oxide solid electrolyte and polymer electrolyte are combined to suggest a new solution for improving the stability and performance of the battery.

Synergy of PVDF-HFP and ZIF-8 promotes PEO electrolyte towards all-solid-state lithium battery

Polyethylene oxide (PEO)-based electrolytes are considered to be promising for all-solid-state battery, benefiting from the superior flexibility, excellent processability and well compatibility. However, the low ionic conductivity at room temperature and poor stability under high voltage limit their further application. Herein, ZIF-8@PVDF-HFP/PEO (PPZ) solid electrolyte was successfully prepared by facial electrospinning process. On one side, the cooperation of PVDF-HFP and ZIF-8 was benefit to decrease the crystallization degree of PEO and thus promoted the Li+ transfer. Moreover, the in-situ formed LiF layer derived from the decomposition of PVDF-HFP protected the electrolyte from contacting directly with the electrode, contributing to a stable electrode/electrolyte interface. The results demonstrated that the electrochemical stability and mechanical property of PPZ electrolyte were significantly improved when compared to the bare PEO electrolyte. The tensile strength increased from 0.5 to 6.7 MPa and the Li+ transference number enlarged from 0.17 to 0.48. More importantly, the assembled LCO(LiCoO2)||PPZ||Li all-solid-state battery delivered a discharge specific capacity of 144.7 mAh g-1 at 0.2 C, nearly 1.6 times than that of the LCO||PEO||Li (90.7 mAh g-1). Besides that, the retention maintained at 86.3 % even after 200 cycles, manifesting a long-term cycling stability. This work provides a new idea for the practical application of PEO under high voltage.

Co-Sintering of Li1.3Al0.3Ti1.7(PO4)3 and LiFePO4 in Tape-Casted Composite Cathodes for Oxide Solid-State Batteries

Solid-state batteries (SSBs) with Li-ion conductive electrolytes made from polymers, thiophosphates (sulfides) or oxides instead of liquid electrolytes have different challenges in material development and manufacturing. For oxide-based SSBs, the co-sintering of a composite cathode is one of the main challenges. High process temperatures cause undesired decomposition reactions of the active material and the solid electrolyte. The formed phases inhibit the high energy and power density of ceramic SSBs. Therefore, the selection of suitable material combinations as well as the reduction of the sintering temperatures are crucial milestones in the development of ceramic SSBs. In this work, the co-sintering behavior of Li1.3Al0.3Ti1.7(PO4)3 (LATP) as a solid electrolyte with Li-ion conductivity of ≥0.38 mS/cm and LiFePO4 with a C-coating (LFP) as a Li-ion storage material (active material) is investigated. The shrinkage behavior, crystallographic analysis and microstructural changes during co-sintering at temperatures between 650 and 850 °C are characterized in a simplified model system by mixing, pressing and sintering the LATP and LFP and compared with tape-casted composite cathodes (d = 55 µm). The tape-casted and sintered composite cathodes were infiltrated by liquid electrolyte as well as polyethylene oxide (PEO) electrolyte and electrochemically characterized as half cells against a Li metal anode. The results indicate the formation of reaction layers between LATP and LFP during co-sintering. At Ts > 750 °C, the rhombohedral LATP phase is transformed into an orthorhombic Li1.3+xAl0.3−yFex+yTi1.7−x(PO4)3 (LAFTP) phase. During co-sintering, Fe3+ diffuses into the LATP phase and partially occupies the Al3+ and Ti4+ sites of the NASICON structure. The formation of this LAFTP leads to significant changes in the electrochemical properties of the infiltrated composite tapes. Nevertheless, a high specific capacity of 134 mAh g−1 is measured by infiltrating the sintered composite tapes with liquid electrolytes. Additionally, infiltration with a PEO electrolyte leads to a capacity of 125 mAh g−1. Therefore, the material combination of LATP and LFP is a promising approach to realize sintered ceramic SSBs.

Enabling metal substrates for garnet-based composite cathodes by laser sintering

In this study, a laser irradiation method developed by Fraunhofer ILT was used to sinter screen-printed cathode layers of LiCoO2 (LCO) and Li7La3Zr2O12 (LLZO) directly on a stainless steel current collector. The laser sintering method was proved to be a promising method to sinter the composite cathode onto steel with greatly reduced side reactions and material degradation. In comparison, conventional sintering and another light-absorption-based sintering method, namely rapid thermal processing (RTP) in a lamp furnace, led to almost complete decomposition of the LLZO phase accompanying with the detrimental formation of LaCoO3 and CoO. Phase and morphology analysis of the laser-sintered cathodes using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy confirmed sintering of LCO and LLZO through the layer with small amounts of secondary phases (LaCoO3, Li0.5La2Co0.5O4 and CoO). The resulting porous matrix of the laser-sintered cathode was infiltrated with a polyethylene oxide (PEO) electrolyte to connect the cathode to an LLZO separator and a Li metal anode without an additional sintering step. This model cell was used to evaluate the electrochemical activity of the laser-sintered composite cathodes, which exhibited a specific discharge capacity of 102 mAh g−1 at 4.0 V in the first electrochemical cycle.