Investigation on the Copolymer Electrolyte of Poly(1,3‐dioxolane‐ co ‐formaldehyde)

Strategies for Enhancing the Stability of Lithium Metal Anodes in Solid-State Electrolytes

The current commercially used anode material, graphite, has a theoretical capacity of only 372 mAh/g, leading to a relatively low energy density. Lithium (Li) metal is a promising candidate as an anode for enhancing energy density; however, challenges related to safety and performance arise due to Li's dendritic growth, which needs to be addressed. Owing to these critical issues in Li metal batteries, all-solid-state lithium-ion batteries (ASSLIBs) have attracted considerable interest due to their superior energy density and enhanced safety features. Among the key components of ASSLIBs, solid-state electrolytes (SSEs) play a vital role in determining their overall performance. Various types of SSEs, including sulfides, oxides, and polymers, have been extensively investigated for Li metal anodes. Sulfide SSEs have demonstrated high ion conductivity; however, dendrite formation and a limited electrochemical window hinder the commercialization of ASSLIBs due to safety concerns. Conversely, oxide SSEs exhibit a wide electrochemical window, but compatibility issues with Li metal lead to interfacial resistance problems. Polymer SSEs have the advantage of flexibility; however their limited ion conductivity poses challenges for commercialization. This review aims to provide an overview of the distinctive characteristics and inherent challenges associated with each SSE type for Li metal anodes while also proposing potential pathways for future enhancements based on prior research findings.

PDOL-Based Solid Electrolyte Toward Practical Application: Opportunities and Challenges

Polymer solid-state lithium batteries (SSLB) are regarded as a promising energy storage technology to meet growing demand due to their high energy density and safety. Ion conductivity, interface stability and battery assembly process are still the main challenges to hurdle the commercialization of SSLB. As the main component of SSLB, poly(1,3-dioxolane) (PDOL)-based solid polymer electrolytes polymerized in-situ are becoming a promising candidate solid electrolyte, for their high ion conductivity at room temperature, good battery electrochemical performances, and simple assembly process. This review analyzes opportunities and challenges of PDOL electrolytes toward practical application for polymer SSLB. The focuses include exploring the polymerization mechanism of DOL, the performance of PDOL composite electrolytes, and the application of PDOL. Furthermore, we provide a perspective on future research directions that need to be emphasized for commercialization of PDOL-based electrolytes in SSLB. The exploration of these schemes facilitates a comprehensive and profound understanding of PDOL-based polymer electrolyte and provides new research ideas to boost them toward practical application in solid-state batteries.

In Situ Forming Gel Polymer Electrolyte for High Energy-Density Lithium Metal Batteries

In situ forming gel polymer electrolyte (GPE) is one of the most feasible ways to improve the safety and cycle performances of lithium metal batteries with high energy density. However, most of the in situ formed GPEs are not compatible with high-voltage cathode materials. Here, this work provides a novel strategy to in situ form GPE based on the mechanism of Ritter reaction. The Ritter reaction in liquid electrolyte has the advantage of appropriate reaction temperature and no additional additives. The polymer chains are cross-linked by amide groups with the formation of GPE with superior electrochemical properties. The GPE has high ionic conductivity (1.84 mS cm-1 ), wide electrochemical stability window (>5.25 V) and high lithium ion transference number (≈0.78), compatible with high-voltage cathode materials. The Li|LiNi0.6 Co0.2 Mn0.2 O2 batteries with in situ formed GPE show excellent long-term cycle stability (93.4%, 300 cycles). The density functional theory calculation and X-ray photoelectron spectroscopy results verify that the amide and nitrile groups are beneficial for stabilizing cathode structure and promoting uniform Li deposition on Li anode. Furthermore, the in situ formed GPE exhibits excellent electrochemical performance in Graphite|LiMn2 O4 and Graphite|LiNi0.5 Co0.2 Mn0.3 O2 pouch batteries. This approach is adaptable to current battery technologies, which will be sure to promote the development of high energy-density lithium-ion batteries.

Hybrid Polymer-Alloy-Fluoride Interphase Enabling Fast Ion Transport Kinetics for Low-Temperature Lithium Metal Batteries

Low-temperature lithium metal batteries are of vital importance for cold-climate condition applications. Their realization, however, is plagued by the extremely sluggish Li+ transport kinetics in the vicinity of Li metal anode at low temperatures. Different from the widely adopted electrolyte engineering, a functional interphase design concept is proposed in this work to efficiently improve the low-temperature electrochemical reaction kinetics of Li metal anodes. As a proof of concept, we design a hybrid polymer-alloy-fluoride (PAF) interphase featuring numerous gradient fluorinated solid-solution alloy composite nanoparticles embedded in a polymerized dioxolane matrix. Systematic experimental and theoretical investigations demonstrate that the hybrid PAF interphase not only exhibits superior lithiophilicity but also provides abundant ionic conductive pathways for homogeneous and fast Li+ transport at the Li-electrolyte interface. With enhanced interfacial dynamics of Li-ion migration, the as-designed PAF-Li anode works stably for 720 h with low voltage hysteresis and dendrite-free electrode morphology in symmetric cell configurations at -40 °C. The full cells with PAF-Li anode display a commercial-grade capacity of 4.26 mAh cm-2 and high capacity retention of 74.7% after 150 cycles at -20 °C. The rational functional interphase design for accelerating ion-transfer kinetics sheds innovative insights for developing high-areal-capacity and long-lifespan lithium metal batteries at low temperatures.

High Lithium Salt Content PVDF-Based Solid-State Composite Polymer Electrolyte Enhanced by h-BN Nanosheets

Due to the unique safety qualities, solid composite polymer electrolyte (SCPE) has achieved considerable attentions to fabricate high-energy-density lithium metal batteries, but its overall performance still has to be improved. Herein, a high lithium salt content poly(vinylidene fluoride) (PVDF)-based SCPE was developed, enhanced by hexagonal boron nitride (h-BN) nanosheets, presenting perfect electrochemical performance, fast ion transport, and efficient inhibition of lithium dendrite growth. The optimized SCPE (PVDF-L70-B5) could deliver high ionic conductivity (2.98×10^-4  S cm^-1 ), ultra-high Li⁺ ion transfer number (0.62), wide electrochemical stability window (5.24 V), and strong mechanical strength (3.45 MPa) at room temperature. Density functional theory calculation further confirmed that the presence of h-BN could promote the dissociation of bis(trifluoromethanesulfonyl)imide lithium (LiTFSI) and the rapid transfer of Li⁺ ions. As a result, the assembled symmetric Li/Li battery and asymmetric Li/LiFePO₄ battery using PVDF-L70-B5 SCPEs both exhibited high reversible capacity, long-term cycle stability, and high-rate performance when cycled at 60 or 30 °C. The designed SCPEs will open up a new route to synthesize solid-state lithium batteries with high energy density and high safety.

Self-Enhancing Gel Polymer Electrolyte by In Situ Construction for Enabling Safe Lithium Metal Battery

Lithium metal battery (LMB) possessing a high theoretical capacity is a promising candidate of advanced energy storage devices. However, its safety and stability are challenged by lithium dendrites and the leakage of liquid electrolyte. Here, a self-enhancing gel polymer electrolyte (GPE) is created by in situ polymerizing 1,3-dioxolane (DOL) in the nanofibrous skeleton for enabling safe LMB. The nanofiber membrane possesses a better affinity with poly-DOL (PDOL) than commercial separator for constructing homogeneous GPE with enhanced ion conductivity. Furthermore, polydopamine is introduced on nanofiber membrane to form hydrogen bonding with PDOL and bis((trifluoromethyl)sulfonyl)imide anion, dramatically improving the mechanical strength, ionic conductivity, and transference number of GPE. Besides, molecular dynamic simulation is used to reveal the intrinsic factors of high ionic conductivity and reinforcing effect in the meantime. Consequently, the LiFePO4 //Li batteries using self-enhancing GPE show extraordinary cyclic stability over 800 cycles under high current density of 2 C, with a capacity decay of 0.021% per cycle, effectively suppressing the growth of lithium dendrites. This ingenious strategy is expected to manufacture advanced performance and high safety LMBs and compatible with the current battery production.

SnF2 -Catalyzed Formation of Polymerized Dioxolane as Solid Electrolyte and its Thermal Decomposition Behavior

Polymerized-dioxolane(P-DOL) is of potential as a solid-polymer-electrolyte(SPE) due to its high Li⁺ -conductivity, good compatibility with Li-metal and desired preparation method of in situ polymerization in cells. In this study, SnF₂ was demonstrated not only to be an efficient catalyst for the polymerization of DOL at room temperature, but also an effective additive for improving interfacial wettability and suppressing dendrite through the reaction with Li-metal and the formation of LiF/Li_x Sn based composite solid electrolyte interlayer(SEI). Using the SnF₂ polymerized P-DOL containing 1 M LiTFSI as SPE(P-DOL-SPE), obviously denser Li-deposition was obtained, and the all-solid-state(ASS) Li/LiFePO₄ cell delivered stable cycling over 350 cycles at 45 °C. At the same time, the irreversible decomposition of P-DOL-SPE into formaldehyde and small molecule epoxides are observed at 110 °C, which is even initiated at lower temperature of 40 °C under vacuum. This thermal decomposition of P-DOL-SPE in pouch cell causes huge volume swell, and therefore putting a strict limitation on the operating temperature window for the P-DOL based electrolytes.

Designing Polymer-in-Salt Electrolyte and Fully Infiltrated 3D Electrode for Integrated Solid-State Lithium Batteries

Solid-state lithium batteries (SSLBs) are promising owing to enhanced safety and high energy density but plagued by the relatively low ionic conductivity of solid-state electrolytes and large electrolyte-electrode interfacial resistance. Herein, we design a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer-in-salt solid electrolyte (PISSE) with high room-temperature ionic conductivity (1.24×10^-4  S cm^-1 ) and construct a model integrated TiO₂ /Li SSLB with 3D fully infiltration of solid electrolyte. With forming aggregated ion clusters, unique ionic channels are generated in the PISSE, providing much faster Li⁺ transport than common polymer electrolytes. The integrated device achieves maximized interfacial contact and electrochemical and mechanical stability, with performance close to liquid electrolyte. A pouch cell made of 2 SSLB units in series shows high voltage plateau (3.7 V) and volumetric energy density comparable to many commercial thin-film batteries.

Synthesis and properties of poly(1,3-dioxolane) in situ quasi-solid-state electrolytes via a rare-earth triflate catalyst

We report a rare-earth triflate catalyst Sc(OTf)3 for the ring-opening polymerization of 1,3-dioxolane and the in situ production of a quasi-solid-state poly(1,3-dioxolane) electrolyte, which not only demonstrates a superior ionic conductivity of 1.07 mS cm-1 at room temperature, but achieves dendrite-free lithium deposition and a high Coulombic efficiency of 92.3% over 200 Li plating/striping cycles.