Poly Ethylene Oxide Electrolytes Research Articles

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.

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.

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.

In situ formation of stable solid electrolyte interphase with high ionic conductivity for long lifespan all-solid-state lithium metal batteries

Parasitic reactions inevitably occur at the interface of lithium (Li) metal and polymer electrolytes due to ultrahigh Li reducibility coupled with poor interfacial stability or ionic conductivity. This leads to significant capacity loss and inferior lifespan of Li metal batteries (LMBs). Herein, we engineered a stable solid electrolyte interphase (SEI) layer at the interface of Li metal and polyethylene oxide (PEO) electrolyte via incorporation of phosphazene molecules. The phosphazene-solid polymer electrolyte (P-SPE) shows a significantly higher long-term stability against Li metal anode when compared with non-modified SPE. Using cryogenic transmission electron microscopy (cryo-TEM) and X-ray photon spectroscopy (XPS), Li3N, LiF, Li3P and Li3PO4 nanocrystals were identified in the SEI layer. The Li|Li cell with P-SPE cycle for 1800 cycles at 0.2 mA cm‒2. The Li||LFP cells with P-SPE deliver a specific capacity of ∼150 mAh g−1 and ∼120 mAh g−1 at 1C and 2C charge/discharge rates, respectively, with up to 80% capacity retention after 500 and 1000 cycles, respectively. Critical role of phosphazene-modified SEI in improving electrochemical performance is further investigated by density function theory (DFT) and ab-initio molecular dynamic (AIMD) calculations. This study offers a promising approach for engineering a stable and ion-conductive Li|polymer electrolyte interface for long lifespan LMBs.

Vanadium doped ceramic matrix Li6.7La3Zr1.7V0.3O12 enabled PEO-based solid composite electrolyte with high lithium ion transference number and cycling stability

Solid polymer electrolytes (SPEs) have attracted much attention because of their potential in improving energy density and safety. Vanadium doped ceramic matrix Li6.7La3Zr1.7V0.3O12 (LLZVO) was synthesized by high-temperature annealing, and formed a composite electrolyte with polyethylene oxide (PEO). Compared with pure PEO electrolyte membrane, the composite electrolyte membrane exhibited better ionic conductivity (30 °C: 3.2 × 10−5 S cm−1; 80 °C: 3.6 × 10−3 S cm−1). The combination of LLZVO was beneficial to improve the lithium ion transference number (tLi+) of SPE, which was as high as 0.81. The Li/SPE/LiFePO4 battery shows good cycling ability, with a specific capacity of 142 mAh g−1 after a stable cycle of 150 cycles. Meanwhile, the symmetrical lithium battery with composite electrolyte can work continuously for 1200 h without short circuit at the current density of 0.1 mA cm−2 at 50 °C, and the capacity is 0.176 mAh. Vanadium doped ceramic matrix LLZVO as an active ionic conductor, improved the overall performance of solid electrolyte.

Bifunctional MOF Doped PEO Composite Electrolyte for Long-Life Cycle Solid Lithium Ion Battery.

A highly stable composite electrolyte was developed in this research to address the performance decline over time in a solid lithium ion battery (SLIB). It involved the synthesis of bifunctional MOF material (MOF-2) from two different functionalized UiO-66 materials containing carboxyl groups and amine groups, respectively, and the subsequent blending of PEO (polyethylene oxide) with the MOF-2 to form the novel composite solid electrolyte (PEO-MOF-2). The composite electrolytes showed higher ionic conductivity (5.20 × 10-4 S/cm) than that of pristine PEO. The LiFePO4||Li cells constructed with PEO-MOF-2 exhibited 98.45% capacity retention with 149.92 mA h/g after 100 cycles operation at 1.0 C, which was higher than those cells prepared with pristine PEO electrolyte or with PEO-based electrolytes that were only doped by aminated MOF or carboxylated MOF. Furthermore, our experiments showed that there was about a 40% increase in the potential window (from 3.5 to 5.0 V) and 80% increase in the lithium ion transfer number (from 0.20 to 0.36 at 60 °C) as a result of replacing pristine PEO electrolyte with PEO-MOF-2.

Stabilizing lithium plating in polymer electrolytes by concentration-polarization-induced phase transformation

<h2>Summary</h2> It is widely accepted that concentration polarization in liquid electrolytes promotes whisker growth during metal deposition, and therefore, high salt concentration is favored. Here, we report unexpected opposite behaviors in solid polymer electrolytes: concentration polarization can induce phase transformation in a polyethylene oxide (PEO) electrolyte, forming a new PEO-rich but salt-/plasticizer-poor phase at the lithium/electrolyte interface, as unveiled by stimulated Raman scattering microscopy. The new phase has a significantly higher Young's modulus (∼1–3 GPa) than a bulk polymer electrolyte (<1 MPa). We hereby propose a design rule for PEO electrolytes: their compositions should be near the boundary between single-phase and two-phase regions in the phase diagram so that the applied current can induce the formation of a mechanically rigid PEO-rich phase to suppress lithium whiskers. LiFePO₄/PEO/Li cells with concentration-polarization-induced phase transformation can be reversibly cycled 100 times, while cells without such transformation fail within 10 cycles, demonstrating the effectiveness of this strategy.

In-situ forming lithiophilic-lithiophobic gradient interphases for dendrite-free all-solid-state Li metal batteries

Solid polymer electrolytes offer a promise for all-solid-state Li batteries due to their low cost and good processability. However, dendrites and the associated contact loss occurring at the undesirable Li/electrolyte interface during repeated plating and stripping remain a challenge. To address the issue, here, we propose to coat a thin layer containing Al/Li dual-salt onto the polyethylene oxide (PEO) electrolyte. When cycled with the Li metal anode, the salts are sequentially reduced, in-situ forming a lithiophilic Li-Al alloy-rich layer near the anode and a lithiophobic LiF-rich layer close to the electrolyte. The former improves the interfacial adhesion and regulates the Li nucleation, while the latter contributes to dendrite suppression due to its high interface energy against Li. As a result, the gradient interphase enables a Li/Li symmetrical cell to be stably cycled for over 1000 h without short circuits. Moreover, the full cell paired with the LiFePO4 cathode shows enhanced cyclability, retaining 89.1% capacity after 350 cycles at 0.5 C. A pouch cell using the dual-salt coated electrolyte demonstrates good performance and safety. This work provides a facile yet effective approach to construct functional interphase for achieving stable batteries using solid polymer electrolytes.

Enabling Scalable Polymer Electrolyte with Synergetic Ion Conductive Channels via a Two Stage Rheology Tuning UV Polymerization Strategy.

Lithium metal batteries with polyethylene oxide (PEO) electrolytes are considered as one of the ideal candidates for next generation power sources. However, the low ambient operation capability and conventional solvent-based fabrication process of PEO limit their large-scale application. In this work, a comb-like quasi-solid polymer electrolyte (QPE) reinforced with polyethylene glycol terephthalate nonwoven is fabricated. Combining the density functional theory calculation analysis and polymer structure design, optimized and synergized ion conductive channels are established by copolymerization of tetrahydrofurfuryl acrylate and introduction of plasticizer tetramethyl urea. Additionally, a unique two-stage solventless UV polymerization strategy is utilized for rheology tuning and electrolyte fabrication. Compared with the conventional one-step UV process, this strategy is ideally suited for the roll-to-roll continuous coating fabrication process with environmental friendliness. The fabricated QPE exhibits high ionic conductivity of 0.40 mS cm-1 and Li+ transference number (t= 0.77) at room temperature. LiFePO4 //Li batteries are assembled to evaluate battery performance, which deliver excellent discharge capacity (144.9 mAh g-1 at 0.5 C) and cycling stability (with the retention rate 94.5% at 0.5 C after 200 cycles) at room temperature. The results demonstrate that it has high potential for solid-state lithium metal batteries.