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

Solvation Regulation Reinforces Anion-Derived Inorganic-Rich Interphase for High-Performance Quasi-Solid-State Li Metal Batteries

Solid-state polymer lithium metal batteries are an important strategy for achieving high safety and high energy density. However, the issue of Li dendrites and inherent inferior interface greatly restricts practical application. Herein, this study introduces tris(2,2,2-trifluoroethyl)phosphate solvent with moderate solvation ability, which can not only complex with Li+ to promote the in-situ ring-opening polymerization of 1,3-dioxolane (DOL), but also build solvated structure models to explore the effect of different solvation structures in the polymer electrolyte. Thereinto, it is dominated by the contact ion pair solvated structure with pDOL chain segments forming less lithium bonds, exhibiting faster kinetic process and constructing a robust anion-derived inorganic-rich interphase, which significantly improves the utilization rate of active Li and the high-voltage resistance of pDOL. As a result, it exhibits stable cycling at ultra-high areal capacity of 20 mAh cm-2 in half cells, and an ultra-long lifetime of over 2000 h in symmetric cells can be realized. Furthermore, matched with LiNi0.9Co0.05Mn0.05O2 cathode, the capacity retention after 60 cycles is as high as 96.8% at N/P value of 3.33. Remarkably, 0.7 Ah Li||LiNi0.9Co0.05Mn0.05O2 pouch cell with an energy density of 461 Wh kg-1 can be stably cycled for five cycles at 100% depth of discharge.

An initiator loaded separator triggering in situ polymerization of a poly(1,3-dioxolane) quasi-solid electrolyte for lithium metal batteries

An in situ polymerization strategy is regarded as a promising approach to fabricate gel polymer electrolytes (GPEs) and improve interface contact between the electrolyte and electrodes, in which the initiator is initially dissolved in the precursor solution. Herein, aluminum trifluoromethanesulfonate (Al(OTf)3) is preloaded onto a separator sheet as the initiator to trigger the ring-opening reaction of 1,3-dioxolane (DOL). The polymer matrix near the separator has a higher crystallization degree than that far away from the separator. Fluoroethyl carbonate (FEC) is further introduced as a liquid plasticizer to produce an amorphous GPE for enhanced ionic conductivity and interfacial stability. As a result, the as-synthesized FEC based GPE exhibits a substantial ionic conductivity of 1.5 × 10-4 S cm-1 at room temperature, an expanded electrochemical window of 4.8 V, and a high Li+ transference number of 0.63. The symmetric Li|Li cell exhibits a stable lifespan for 650 h at 1 mA cm-2 and 1 mA h cm-2. Moreover, the LiFePO4 full cell exhibits stable cycling for 300 cycles at 1C with a capacity retention of 94.5%. This work provides a novel idea for the in situ synthesis of advanced GPEs toward practical application of solid-state lithium metal batteries.

Anode-Free Lithium-Sulfur Batteries with a Rare-Earth Triflate as a Dual-Function Electrolyte Additive

Anode-free lithium-sulfur batteries feature a cell design with a fully lithiated cathode and a bare current collector as an anode to control the total amount of lithium in the cell. The lithium stripping and deposition are key factors in designing an anode-free full cell to realize a practical cell configuration. To realize effective anode protection and achieve a good performance of the anode-free full cell, manipulation of the electrolyte chemistry toward the modification of the solid-electrolyte interphase on the anode is considered a feasible approach. In this study, the use of neodymium triflate, Nd(OTf)3, as a dual-function electrolyte additive is demonstrated to promote homogeneous catalysis on the cathode conversion reactions and the anode stabilization. Nd(OTf)3 not only facilitates the conversion reaction by promoting the polysulfide adsorption but also effectively protects the lithium-metal anode and stabilizes the lithium stripping and deposition during cycling. With this electrolyte modification, both Li∥Li2S half cells and Ni∥Li2S anode-free full cells support a high areal capacity of 5.5-7.0 mA h cm-2 and maintain a high Coulombic efficiency of 94-95% during cycling.

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.

Contributing to the Revolution of Electrolyte Systems via In Situ Polymerization at Different Scales: A Review

Solid-state batteries have become the most anticipated option for compatibility with high-energy density and safety. In situ polymerization, a novel strategy for the construction of solid-state systems, has extended its application from solid polymer electrolyte systems to other solid-state systems. This review summarizes the application of in situ polymerization strategies in solid-state batteries, which covers the construction of polymer, the formation of the electrolyte system, and the design of the full cell. For the polymer skeleton, multiple components and structures are being chosen. In the construction of solid polymer electrolyte systems, the choice of initiator for in situ polymerization is the focus of this review. New initiators, represented by lithium salts and additives, are the preferred choice because of their ability to play more diverse roles, while the coordination with other components can also improve the electrical properties of the system and introduce functionalities. In the construction of entire solid-state battery systems, the application of in situ polymerization to structure construction, interface construction, and the use of separators with multiplex functions has brought more possibilities for the development of various solid-state systems and even the perpetuation of liquid electrolytes.

A Biodegradable High-Performance Microsupercapacitor for Environmentally Friendly and Biocompatible Energy Storage

Biodegradable and biocompatible microscale energy storage devices are very crucial for environmentally friendly microelectronics and implantable medical applications. Herein, a biodegradable and biocompatible microsupercapacitor (BB-MSC) with satisfying overall performance is realized via the combination of three-dimensional (3D) printing technique and biodegradable materials. Due to the 3D-interconnected structure of electrodes and elaborated design of electrolyte, the as-prepared BB-MSC exhibits superior overall performance than most of biodegradable devices, including a wide operation voltage of 1.8 V, high areal specific capacitance of 251 mF/cm2, good cycle stability, and favorable low-temperature resistance (-20 °C), demonstrative of reliability and practicality of our devices even in frosty environments. Importantly, the smooth degradation has been realized for the BB-MSC after being buried in natural soil for ∼90 days, and its implantation does not affect the healthy status of SD rats. Therefore, this work explores avenues for the design and construction of environmentally friendly and biocompatible microscale energy storage devices.

Initiator-free in-situ synthesized polymer electrolytes with high ionic conductivity for dendrite-free lithium metal batteries

In-situ preparation of polymer electrolytes (PEs) can enhance electrolyte/electrode interface contact and accommodate the current large-scale production line of lithium-ion batteries (LIBs). However, reactive initiators of in-situ PEs may lead to low capacity, increased impedance and poor cycling performance. Flammable and volatile monomers and plasticizers of in-situ PEs are potential safety risks for the batteries. Herein, we adopt lithium difluoro(oxalate)borate (LiDFOB)-initiated in-situ polymerization of solid-state non-volatile monomer 1,3,5-trioxane (TXE) to fabricate PEs (In-situ PTXE). Fluoroethylene carbonate (FEC) and methyl 2,2,2-trifluoroethyl carbonate (FEMC) with good fire retardance, high flash point, wide electrochemical window and high dielectric constant were introduced as plasticizers to improve ionic conductivity and flame retardant property of In-situ PTXE. Compared with previously reported in-situ PEs, In-situ PTXE exhibits distinct merits, including free of initiators, non-volatile precursors, high ionic conductivity of 3.76 × 10^-3 S cm^-1, high lithium-ion transference number of 0.76, wide electrochemical stability window (ESW) of 6.06 V, excellent electrolyte/electrode interface stability and effectively inhibition of Li dendrite growth on the lithium metal anode. The fabricated LiFePO₄ (LFP)/Li batteries with In-situ PTXE achieve significantly boosted cycle stability (capacity retention rate of 90.4% after 560 cycles) and outstanding rate capability (discharge capacity of 111.7 mAh g^-1 at 3C rate).

Study of Codoping Effects of Ta5+ and Ga3+ on Garnet Li7La3Zr2O12

Garnet Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid electrolyte for all-solid-state Li-ion batteries because of its outstanding performance. However, LLZO exists in two polymorphic phases, tetragonal (∼10^-3 mS cm^-1) and cubic (1-10^-1 mS cm^-1), where the cubic phase exhibits higher Li-ion conductivity but is thermodynamically unstable at ambient room temperature. To stabilize the cubic phase with high ionic conductivity, we fabricated mono- and codoped garnet with Ta⁵⁺ and Ga³⁺ (Li_7-3x-z=6.4Ga _x La₃Zr_2-z Ta _z O₁₂) and investigated the doping effects. The doping effects on the crystal structure and ionic conductivity were systematically investigated using X-ray diffraction, Raman scattering, scanning electron microscopy, alternative current (AC) impedance, and direct current (DC) polarization methods. The characterization results revealed that Ta-doping favors higher occupation of Li-ions on the mobile octahedral (LiO₆) site and improves ionic conductivity of the grain boundary. However, it showed poor total ionic conductivity (2.044 × 10^-4 S cm^-1 at 1100 °C for 12 h) due to the low sinterability [relative density (RD): ∼80.3%]. On the other hand, Ga-doping provides better sinterability (RD: ∼93.1%) and bulk conductivity. Considering the beneficial effects of Ga- and Ta-doping, codoped Li_6.4Ga_0.133La₃Zr_1.8Ta_0.2O₁₂ garnet with enhanced ionic conductivity (6.141 × 10^-4 S cm^-1) and improved high-density microstructure (RD: ∼95.7%) was obtained.

In Situ Constructing Ultrathin, Robust-Flexible Polymeric Electrolytes with Rapid Interfacial Ion Transport in Lithium Metal Batteries

Safety of lithium metal batteries (LMBs) has been improved by using the solid-state polymer electrolytes, but the performance of LMBs is still troubled by the poor interface of solid electrolytes/electrodes, leading to insufficient interfacial Li⁺ transport. Here, a novel ultrathin, robust-flexible polymeric electrolyte is achieved by in situ polymerization of 1,3-dioxolane in soft nanofibrous skeleton at room temperature without any extra initiator or plasticizer, leading to the electrolyte with rapid interfacial ion transport. This facilitated Li⁺ transportation is demonstrated by molecular dynamics simulation. Consequently, the as-prepared electrolyte exhibits excellent cycling performance. The results indicate that the electrolyte works well in the LiFePO₄ //Li cell at elevated temperature up to 90 °C, and further matches with the high-voltage LiNi_0.8 Mn_0.1 Co_0.1 O₂ cathode. This study provides an effective approach to constructing a practical polymeric electrolyte for fabrication of safe, high performance LMBs.

Enabling high-performance all-solid-state hybrid-ion batteries with a PEO-based electrolyte

All-solid-state hybrid-ion batteries exhibiting a synergistic Na⁺/Li⁺ de/intercalation mechanism were designed and assembled, by using modified PEO-based solid polymer electrolyte, Na₂V₂(PO₄)₂O₂F cathode, and Li metal anode. The batteries exhibited a high average working voltage of 3.88 V, and an energy density of 432.37 W h kg^-1, providing a new avenue for the development of high-safety and low-cost secondary batteries.

Solid electrolytes for solid-state Li/Na–metal batteries: inorganic, composite and polymeric materials

This feature article presents the electrolyte synthetic approaches, design strategies, and merging materials that may address the critical issues of solid electrolytes for solid-state Li/Na–metal batteries.

High-Performance Room Temperature Lithium-Ion Battery Solid Polymer Electrolytes Based on Poly(vinylidene fluoride-co-hexafluoropropylene) Combining Ionic Liquid and Zeolite

The demand for more efficient energy storage devices has led to the exponential growth of lithium-ion batteries. To overcome the limitations of these systems in terms of safety and to reduce environmental impact, solid-state technology emerges as a suitable approach. This work reports on a three-component solid polymer electrolyte system based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]), and clinoptilolite zeolite (CPT). The influences of the preparation method and of the dopants on the electrolyte stability, ionic conductivity, and battery performance were studied. The developed electrolytes show an improved room temperature ionic conductivity (1.9 × 10^-4 S cm^-1), thermal stability (up to 300 °C), and mechanical stability. The corresponding batteries exhibit an outstanding room temperature performance of 160.3 mAh g^-1 at a C/15-rate, with a capacity retention of 76% after 50 cycles. These results represent a step forward in a promising technology aiming the widespread implementation of solid-state batteries.

High sodium ionic conductivity in PEO/PVP solid polymer electrolytes with InAs nanowire fillers

Solid-state sodium ion batteries are frequently referred to as the most promising technology for next-generation energy storage applications. However, developing a suitable solid electrolyte with high ionic conductivity, excellent electrolyte-electrode interfaces, and a wide electrochemical stability window, remains a major challenge. Although solid-polymer electrolytes have attracted great interest due to their low cost, low density and very good processability, they generally have significantly lower ionic conductivity and poor mechanical strength. Here, we report on the development of a low-cost composite solid polymer electrolyte comprised of poly(ethylene oxide), poly(vinylpyrrolidone) and sodium hexafluorophosphate, mixed with indium arsenide nanowires. We show that the addition of 1.0% by weight of indium arsenide nanowires increases the sodium ion conductivity in the polymer to 1.50 × 10^-4 Scm^-1 at 40 °C. In order to explain this remarkable characteristic, we propose a new transport model in which sodium ions hop between close-spaced defect sites present on the surface of the nanowires, forming an effective complex conductive percolation network. Our work represents a significant advance in the development of novel solid polymer electrolytes with embedded engineered ultrafast 1D percolation networks for near-future generations of low-cost, high-performance batteries with excellent energy storage capabilities.