Crystalline Poly Ethylene Oxide Research Articles

Self‐Supporting Solid Electrolyte Based on Supramolecular Interaction for Stable Li Metal Batteries

AbstractLi metal batteries based on solid polymer electrolytes offer the benefits of high energy density and safety, as well as extended cycling life, making them an excellent candidate for the next‐generation battery system. However, current solid polymer electrolytes still suffer from low ion conductivity and Li+ transfer number, which seriously restricts its practical application. Herein, a self‐supporting composite solid polymer electrolyte was prepared, where phenolic resin rich in hydroxyl groups (BR) and polyethylene oxide (PEO) are mixed evenly and poured onto a cellulose membrane in one step. In such an electrolyte, PEO and BR combine to form intermolecular hydrogen bonds, lowering the crystallinity of PEO and increasing the Li+ transfer number. Lastly, the obtained solid electrolytes exhibited a high ion conductivity (1.1×10−4 S cm−1) and Li+ transfer number (0.53), as well as improved electrochemical window. Consequently, Li || Li symmetrical cells can run stably for more than 700 h at 0.1 mA cm−2/0.25 mAh cm−2. And full cells with LiFePO4 cathode can also demonstrate high discharge capacity of 152.12 mAh g−1 and rate performance. We believe that such a design based on supramolecular interaction offer a new avenue to advanced solid polymer electrolytes.

Breaking the Trade‐Off between Ionic Conductivity and Mechanical Strength in Solid Polymer Electrolytes for High‐Performance Solid Lithium Batteries

AbstractSolid polymer electrolytes (SPEs) are among the most promising candidates for solid‐state batteries due to their easy processibility, interface compatibility, and cost efficiency. However, the trade‐off between the ionic conductivity and mechanical strength of SPEs, which has persisted for decades, hinders their application in solid‐state lithium (Li) metal batteries. In this study, the aim is to break this trade‐off by utilizing poly(p‐phenylene benzobisoxazole) (PBO) nanofibers as a mechanically strong backbone and polyethylene oxide (PEO) as an ionically conductive network. The PBO/PEO composite electrolyte reduces the crystallinity of PEO while increasing the mechanical strength (74.4 MPa, ≈14 times that of PEO). Thus, PBO/PEO simultaneously improves ionic conductivity and mechanical strength both at room temperature and elevated temperatures, enabling uniform and smooth Li deposition. Thus, a long cycle life of solid‐state Li symmetric cells for 1000 h at 60 °C is achieved, and stable cycling of solid‐state Li metal full batteries at 60 °C and even 100 °C. Furthermore, the solid‐state pouch cell using this SPE exhibits excellent performance reliably after bending. The study clearly indicates that simultaneously improving mechanical properties and conductivity is the indispensable path to the practical application of solid‐state electrolytes.

Liquid Metal Loaded Molecular Sieve: Specialized Lithium Dendrite Blocking Filler for Polymeric Solid-State Electrolyte.

All-solid-state lithium metal batteries (LMBs) are currently one of the best candidates for realizing the yearning high-energy-density batteries with high safety. However, even polyethylene oxide (PEO), the most popular polymeric solid-state electrolyte (SSE) with the largest ionic conductivity in the category so far, has significant challenges due to the safety issues of lithium dendrites, and the insufficient ionic conductivity. Herein, molecular sieve (MS) is integrated into the PEO as an inert filler with the liquid metal (LM) as a functional module, forming an "LM-MS-PEO" composite as both SSE with enhanced ionic conductivity, and protection layer against lithium dendrites. As demonstrated by theoretical and experimental investigations, LM released from MS can be uniformly and efficiently distributed in PEO, which could avoid agglomeration, enable the effective blocking of lithium dendrites, and regulate the mass transport of Li ions, thus achieving even deposition of lithium during charge/discharge. Moreover, MS could reduce the crystallinity of PEO, improve lithium-ion conductivity, and reduce operating temperature. Benefiting from the introduction of the functional MS/LM, the LM-MS-PEO electrolyte exhibits fourfold higher lithium ionic conductivity than the pristine PEO at 40°C, while the as-assembled all-solid-state LMBs have four to five times longer stable cycle life.

Solid polymer nanocomposite electrolytes based on poly(ε‐caprolactone)‐based waterborne polyurethane–polyethylene oxide and fluorine‐doped carbon quantum dot‐MXene

AbstractThe need for higher energy storage capability has encouraged researchers to move toward lithium‐metal batteries (LMBs). Due to the safety issue associated with liquid electrolytes, solid polymer electrolytes (SPEs) the main focus on polyethylene oxide (PEO) were at the center of the research. However, high crystallization, fast decomposition, and low thermomechanical stability has limited its application. Low lithium‐ion transference number () is another issue leading to polarization of the SPEs and consequently, triggering dendrite nucleation and growth. Here, we developed a series of SPEs based on PEO‐waterborne polyurethane (WPU) and nanoparticles of fluorine‐doped carbon quantum dot (fCQD) and MXene. The host polymer matrix was a blend of poly(ε‐caprolactone) (PCL)‐based WPU and PEO. The use of WPU and the nanoparticles increased the thermomechanical stability and suppressed PEO crystallinity through disrupting the spherulites growth and reducing the thermal stability of the crystallites. Using the WPU led to significant increase in () compared with previous reports. The prepared SPEs showed high‐electrochemical stability and ionic conductivity at and based on the results of cycling performance, a discharge capacity of 120.58 mAh/g and coulombic efficiency of 99.1% was achieved after 200 cycles.

Effect of directional arrangement one-dimensional Fe3O4-coated sepiolite structure on the Li+ conduction of PEO-based polymer electrolyte

The low Li+ conductivity and high cost of polyethylene oxide (PEO)-based polymer electrolytes still restrict their application. Herein, a natural one-dimensional sepiolite (SEP) material is coated with Fe3O4 (FSEP) to construct a FSEP-PEO composite polymer electrolyte (CPE) with a directional arrangement structure, which significantly improved the Li+ conductivity. Results show that the Li+ conductivity of CPE (9.1 ×10−5 S cm−1) based on vertical arrangement FSEP is 43 times higher than that of PEO (2.1 ×10−6 S cm−1), and 9.1 times and 3.1 times higher than that of parallel (1.0 ×10−5 S cm−1) and disordered arrangement (2.9 ×10−5 S cm−1), respectively. The arrangement direction of FSEP has no obvious effect on the crystallinity of PEO and the dissociation degree of LiTFSI, while it has a great influence on the Li+ migration number (tLi+). The tLi+ of CPE with vertical arrangement (0.333) increased by 99.4% compared with that of the parallel arrangement (0.167), suggesting a short and fast migration path. Through multi-physical field simulation, the high current density in CPE is mainly distributed at the FSEP/PEO interface, indicating that the FSEP/PEO interface plays a dominant role in Li+ conduction. In addition, lithium symmetric batteries and LiFePO4 batteries based on vertically arranged CPE have excellent cycle and rate performance.

One-dimensional sepiolite confined ionic liquids structure to improve the electrochemical performance of polyethylene-oxide based composite polymer electrolyte

Polyethylene-oxide (PEO) based composite polymer electrolytes (CPEs) with one-dimensional sepiolite confined ionic liquids (ILs) structure is constructed to further improve Li+ conductivity and reduce cost. Silicon nanorods (SNRs) is obtained by microwave-assisted acid activation of sepiolite and then ILs is confined into SNRs by supercritical CO2 fluid. The specific surface area of SNRs reduces from 170.88 m2 g-1 to 2.19 m2 g-1 after ILs confining, and the morphology and component of ILs in SNRs channel are clearly detected, indicating that the SNRs confined ILs structure (ILs@SNRs) is successfully obtained. The Li+ conductivity of CPEs increases from 1.40 × 10-6 S cm-1 to 0.922 × 10-4 S cm-1, which indicates that ILs confined in SNRs provide a fast channel for Li+ transmission. Besides, the reduction of PEO crystallinity is also favorable to Li+ transmission. The corresponding lithium symmetrical battery and LiFePO4 battery has excellent electrochemical performances. The good rate performance is attributed to the high Li+ migration number of 0.261 compare to 0.122 of PEO. Compared with the simple mixing of polymer and ILs, the confined ILs in SNRs channel will not be lost, which maintains the stability of Li+ transmission and reduces the consumption amount of ILs thus greatly reducing the cost of CPEs.

Formation of Size-Controllable Tetragonal Nanoprisms by Crystallization-Directed Ionic Self-Assembly of Anionic Porphyrin and PEO-Containing Triblock Cationic Copolymer.

The creation of anisotropic nanostructures with precise size control is desirable for new properties and functions, but it is challenging for ionic self-assembly (ISA) because of the non-directional electrostatic interactions. Herein, the formation of size-controllable tetragonal nanoprisms is reported via crystallization-directed ionic self-assembly (CDISA) through evaporating a micellar solution on solid substrates. First, ISA is designed with a crystalline polyethylene oxide (PEO) containing cationic polymer poly(2-(2-guanidinoethoxy)ethyl methacrylate)-b-poly(ethyleneoxide)-b-poly(2-(2-guanidinoethoxy)-ethylmethacrylate) (PGn -PEO230 -PGn ) and an anionic 5,10,15,20-Tetrakis(4-sulfonatophenyl) porphyrin (TPPS) to form micelles in aqueous solution. The PG segments binds excessive TPPS with amplenet chargeto form hydrophilic corona, while the PEO segments are unprecedentedly dehydrated and tightly packed into cores. Upon naturally drying the micellar solution on a silicon wafer, PEO crystallizationdirects the micelles to aggregate into square nanoplates, which are further connected to nanoprisms. Length and width of the nanoprisms can be facilely tuned by varying the initial concentration. In this hierarchical process, the aqueous self-assembly is prerequisite and the water evaporation rate is crucial for the formation of nanostructures, which provides multiple factors for morphology regulating. Such precise size-control strategy is highly expected to provide a new vision for the design of advanced materials with size controllable anisotropic nanostructures.

Incorporating 2D γ-Al2O3 nanosheets into the flexible PEO-based solid electrolyte for lithium metal batteries

Solid polymer electrolytes using polyethylene oxide (PEO) are promising for boosting the safety of lithium metal batteries (LMBs), but suffer from low ionic conductivity due to high crystallinity and poor segment motion of PEO. Adding plasticizers like succinonitrile (SN) is one of the solutions to improve the ionic conductivity of PEO, but it sacrifices the cycle performances of LMBs. In addition, the ability to conduct lithium ions of PEO-SN matrixes is yet to be improved. Herein, two-dimensional γ-Al2O3 nanosheets are first introduced into the PEO-SN matrix to facilitate the long-range migration of lithium ions and improve the electrochemical properties of PEO-SN matrix, realizing the new design of traditional materials. The mechanism between γ-Al2O3 nanosheets and the polymer matrix is discussed. The addition of γ-Al2O3 nanosheets improves the ionic conductivities and cycle performances of PEO-LiTFSI-SN (PLS) electrolytes. In specific, the ionic conductivity at 25 °C of the PEO-LiTFSI-SN-Al2O3 nanosheet (PLS-A) electrolyte is up to 2.02 × 10−4 S cm−1. Meanwhile, the electrochemical properties of Li/PLS-A/LiFePO4 are tested, with a low overpotential change of 0.06 V, coulombic efficiency above 99.6%, and capacity retention of 95% at 0.5C and 60 °C after 50 cycles. The solid electrolyte system provides a feasible strategy for the application of 2D nanofillers in PEO polymer electrolytes.

Retarding Li dendrites growth via introducing porous g-C3N4 into polymer electrolytes for solid-state lithium metal batteries

Solid polymer electrolytes (SPEs) based solid-state lithium metal batteries (SSLMBs) are widespreadly practiced as one of the main technical routes aiming for chemically essential safety with acceptable energy density. However, uncontrollable Li dendrites growth and sluggish Li+ transport remain obstacles to the further development of SPEs-based SSLMBs. Herein, a porous g-C3N4 (PCN) is designed and introduced into polyethylene oxide (PEO). Within the following synthesized PEO-based composite solid electrolyte (PEO/PCN/LiTFSI CSE), PCN is found to be an attractive multifunctional filler. For its porous morphology and high specific surface area, abundant Lewis basic active sites are exposed, which facilitates Li+ to be uniformly distributed in PEO/PCN/LiTFSI CSE and thus more effectively mitigates the Li dendrites growth comparing to those with bulk g-C3N4 filler, making PCN-involved Li symmetrical cell (Li|PEO/PCN/LiTFSI|Li) run steadily for 1400 h under the current density of 0.1 mA cm−2 at 60 °C. PCN also accelerates Li+ transport in the manner of reducing PEO crystallinity and promoting LiTFSI dissociation. The Li+ conductivity of PEO/PCN/LiTFSI CSE reaches 3.47 × 10−4 S cm−1 at 60 °C. Therefore, long life span and high rate performances are together achieved in SSLMB assembled with PEO/PCN/LiTFSI CSE. This work reveals a feasible strategy to fabricate dendrite-free SSLMBs cycling within a fairly long time.

Thermal initiation/ultraviolet cross-linking process in polyethylene oxide@Li6·75La3Zr1·75Ta0·25O12-based composite electrolyte with high room-temperature ionic conductivity and long life cycle

Organic-inorganic composite electrolytes (PL-SCEs) based on polyethylene oxide (PEO) and Li6·75La3Zr1·75Ta0·25O12 (LLZTO) are considered to be one of the most promising solid electrolytes. However, the low room-temperature ionic conductivity caused by the inherent high crystallinity of PEO severely hinders its practical application. Herein, a novel PL-SCE is synthesized through a facile thermal induction and ultraviolet crosslinking process, using fluoroethylene carbonate (FEC) and 4-methylbenzophenone as thermal/ultraviolet triggers, and tetraethylene glycol dimethyl ether (TEGDME) as an ion conductive plasticizer. The F atom in the FEC can attack the C–O bond in the PEO chain and abstract the hydrogen attached to the C atom to form an active site, prompt TEGDME and PEO to achieve a higher degree of cross-linking, thus endowing PL-SCE with high Li-ion conductivity of 5.35 × 10−4 S cm−1 at 25 °C. Besides, the obtained PL-SCE exhibits excellent wettability and compatibility with Li metal anodes, the interfacial impedance is only 44 Ω cm2. The LiFePO4||Li full cell based on the proposed PL-SCE exhibits an excellent room-temperature cycling performance with a capacity retention rate up to 88% and the average Coulombic efficiency above 98% upon 450 cycles at 1 C. Prospectively, this work provides a promising alternative method for the practical application of PL-SCEs.

Synergistically reinforced poly(ethylene oxide)-based composite electrolyte for high-temperature lithium metal batteries

Traditional liquid lithium-ion batteries are not applicable for extreme temperatures, due to the shrinkage of separators and volatility of electrolytes. It is necessary to develop advanced electrolytes with desirable characteristics in terms of thermal stability, electrochemical stability and mechanical properties. Solid-state electrolytes, such as polyethylene oxide (PEO), outperform other types and bring the opportunity to realize the high-temperature lithium-ion batteries. However, the softness of PEO at elevated temperatures leads to battery failure. In this work, a three-dimensional fiber-network-reinforced PEO-based composite polymer electrolyte is prepared. The introduced polyimide (PI) framework and trimethyl phosphate (TMP) plasticizer decrease the crystallinity of PEO and increase the ionic conductivity at 30 °C from 8.79 × 10−6 S cm−1 to 4.70 × 10−5 S cm−1. In addition, the PEO bonds tightly with PI fiber network, improving both the mechanical strength and thermal stability of the prepared electrolyte. With the above strategies, the working temperature range of the PEO-based electrolytes is greatly expanded. The LiFePO4/Li cell assembled with the PI-PEO-TMP electrolyte stably performs over 300 cycles at 120 °C. Even at 140 °C, the cell still survives 80 cycles. These excellent performances demonstrate the potential application of the PI-PEO-TMP electrolyte in developing safe and high-temperature lithium batteries.

Composite solid electrolytes containing single-ion lithium polymer grafted garnet for dendrite-free, long-life all-solid-state lithium metal batteries

Compared with traditional liquid electrolytes, the composite solid electrolytes (CSE) composed of polymer and inorganic particle fillers show better electrochemical stability and safety in lithium-ion batteries. However, the low lithium ion transference number (tLi+) and filler agglomeration still threat CSE performance. In response to these threats, we proposed a flexible anion-immobilized modified ceramic-polymer composite solid electrolyte, which significantly increased the lithium ion transference number and showed promising performance after assembled in an all-solid-state battery. Primarily, the surface of Ta-doped garnet Li6.4La3Zr1.4Ta0.6O12 (@LLZTO) was modified by a silane coupling agent bearing C = C bonds, then the lithium single-ion polymer (lithium (4-styrenesulfonyl) (trifluoromethanesulfonyl) imide (LiSTFSI)) was chemically grafted onto the above particles resulting in the ceramic-polymer composite particles (Li@LLZTO). These particles can be uniformly distributed in the polyethylene oxide (PEO) matrix to form composite solid electrolyte (PL@LCSE). It is found that the PL@LCSE promotes the dissociation of lithium salt and reduces the crystallinity of PEO, and shows a relatively high restriction on the migration of anions. Therefore, PL@LCSE shows a high ionic conductivity (1.5 mS·cm−1), a wide electrochemical window (∼5.3 V vs. Li/ Li+) and a high tLi+ (0.77). The Li/PL@LCSE/Li battery exhibits long cycle stability (cycling more than 1000 h). Excellent cycling stability and high rate capability are demonstrated in the all-solid-state batteries with LiFePO4 and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode. Consequently, the synthesized garnet-lithium single-ion polymer composite micron particles have great potential in the next generation of all-solid-state lithium metal batteries.

3D flame-retardant skeleton reinforced polymer electrolyte for solid-state dendrite-free lithium metal batteries

For solid polymer electrolytes (SPEs), improving their mechanical and electrochemical properties is the key to obtaining batteries with higher safety and higher energy density. Herein, a novel synergistic strategy proposed is preparing a 3D flame-retardant skeleton (3DPA) and adding nano-multifunctional fillers (Li-ILs@ZIF-8). In addition to providing mechanical support for the polyethylene oxide (PEO) matrix, 3DPA also has further contributed to the system's flame retardancy and further improved the safety. Simultaneously, the electrochemical performance is fully guaranteed by rigid Li-ILs@ZIF-8, which provides fast migration channels for Li+, reduces the crystallinity of PEO and effectively inhibits lithium dendrites. The limiting oxygen index of the optimal sample (PL3Z/PA) is as high as 20.5%, and the ionic conductivity reaches 2.89 × 10−4 and 0.91 × 10−3 S cm−1 at 25 and 55 °C, respectively. The assembled Li|PL3Z/PA|Li battery can be cycled stably for more than 1000 h at a current density of 0.1 mA cm−2 without short circuit being pierced by lithium dendrites. The specific capacity of the LFP|PL3Z/PA|Li battery was 160.5 mAh g−1 under a current density of 0.5 C, and the capacity retention rate was 90.0% after 300 cycles.

Poly(ionic liquid)-functionalized graphene oxide towards ambient temperature operation of all-solid-state PEO-based polymer electrolyte lithium metal batteries

Endowing polyethylene oxide (PEO)-based electrolyte with low crystallinity and high efficient Li+ transport channels is urgently required for next generation all-solid-state lithium metal batteries (LMBs). Herein, a new type of oxyethyl containing poly(ionic liquid) modified graphene oxide nanoparticles (ox-PIL@GO) is coincidentally proposed for preparing PEO based organic–inorganic composite electrolyte membranes (CPEs). Both experimental and DFT simulation results indicate that the dissociation of the LiTFSI is significantly enhanced by the anticipated electrostatic interaction between imidazolium cation and TFSI- anions in CPEs. In addition, the formed electrostatic interaction can also inhibit the movement of TFSI-, giving rise to the increased lithium transference number of 0.61 from 0.21 for the neat PEO/LiTFSI electrolyte. Furthermore, the ion–dipole interaction between imidazolium cation and PEO chain largely reduces the crystallinity of PEO and the ionic conductivity of 1.01 × 10-4 S cm−1 at 40 °C is successfully obtained. As a result, the ox-PIL@GO incorporated PEO electrolyte enables the Li||Li symmetric cell with long-term, square-wave galvanostatic cycling test of 800 h at current density of 0.1 mA cm−2 at 50 °C and the solid-state LiFePO4|CPE|Li battery with high discharge specific capacity of 116 mAh g−1 at 40 °C at 1C for 300 cycles.

Hybrid covalent organic-framework-based electrolytes for optimizing interface resistance in solid-state lithium-ion batteries

High ion conductivity and low electrode-electrolyte interface resistance are intensively pursued topics for the development of solid-state Li-ion batteries with high safety and energy density. Here, we propose a design using keto-enamine covalent organic frameworks (TPBD) and polyethylene oxide (PEO) to prepare a solid-state electrolyte (TPBD-LiPF 6 @PEO), achieving a high ion conductivity of 0.543 mS cm −1 at 25°C and optimizing the electrode-electrolyte interface resistance in Li-ion batteries. Solid-state nuclear magnetic resonance experiments and density functional theory calculations show that the strong interaction between the –C=O site in TPBD and Li + ions promotes the dissociation of LiPF 6 . The assembled LiFePO 4 |TPBD-LiPF 6 @PEO|Li batteries without using liquid electrolytes offer a specific capacity of nearly 140 mAh g −1 at 0.2 C with a columbic efficiency of 99.6% after 200 cycles at 25°C. This strategy for preparing solid-state electrolytes provides practical ideas and suggestions in the development of solid-state energy devices. • The –C=O groups in TPBD frameworks promote the dissociation of LiPF 6 • TPBD reduces the crystallinity of PEO and enhances mechanical strength of the electrolyte • Fast ion conduction is achieved due to the optimized interface resistance • Solid-state Li-ion batteries can operate at 25°C without adding any liquid electrolyte The low conductivity of solid electrolytes and the interface resistance of solid-state batteries have long been scientific problems that plague the development of solid-state Li-ion batteries. Cheng et al. report a fibrous covalent organic framework TPBD that can promote the dissociation of LiPF 6 , combining with flexible PEO to prepare an inorganic/polymer solid electrolyte. The results show that the electrode-electrolyte interface impedance is greatly reduced, realizing the operation of solid-state battery at room temperature without the addition of liquid electrolyte.

Impacts of Lithium Salts on the Thermal and Mechanical Characteristics in the Lithiated PEO/LAGP Composite Electrolytes

Lithium batteries utilizing solid-state electrolytes have the potential to alleviate their safety hazard, reduce packaging volume, and enable flexible design. Polymer/ceramic composite electrolytes (CPE) are more attractive because the combination is capable of remedying and/or transcending individual constituent’ properties. Recently, we fabricated a series of free-standing composite electrolyte membranes consisting of Li1.4Al0.4Ge1.6(PO4)3 (LAGP), polyethylene oxide (PEO), and lithium salts. In this study, we characterized thermal and mechanical properties of the CPEs with two representative lithium salts, i.e., lithium boron fluoride (LiBF4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We found that the type of lithium salt can prevail the LAGP ceramic loadings on altering the key properties. It is observed that LiTFSI, compared with LiBF4, causes more significant reduction in terms of the crystallinity of PEO, melting transition, and mechanical strengths. The differences in these aspects can be ascribed to the interactions between the polymer matrix and anions in lithium salt.

Fiber‐Reinforced Composite Polymer Electrolytes for Solid‐State Lithium Batteries

AbstractSolid‐state composite polymer electrolytes (CPEs) have attracted much attention due to their flexibility and low interfacial impedance. Researchers have been improving their ionic conductivity at room temperature, ionic transference number, and (electro)chemical stability. Here, a fiber‐reinforced CPE is prepared by infusing polyethylene oxide (PEO) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) electrolytes onto polyacrylonitrile (PAN) nanofiber networks. The introduction of both inorganic ceramic filler LLZTO and plasticizer succinonitrile (SN) reduces the crystallinity of PEO, increases the solubility of lithium salts, and further improves ionic transport kinetics. The ionic conductivity of CPE is 2.57 × 10−4 S cm−1 at 30 °C and the lithium‐ion transference number is 0.6. Meanwhile, the high content of LLZTO (60 wt.%) brings a better capability to suppress lithium dendrites, and thus lithium symmetrical cells based on this CPE can be stably cycled for up to 500 h. In addition, the PAN fiber network endows CPE with high mechanical strength and high oxidation resistivity, and accordingly an electrochemical stability window as high as 4.7 V. Both LiFePO4/CPE/Li and LiNi1/3Co1/3Mn1/3O2/CPE/Li cells can be operated at 30 °C for 100 cycles. This work provides a promising strategy for the preparation of thin CPEs for solid‐state lithium metal batteries.

Synthesis of Electrospun NASICON Li1.5Al0.5Ge1.5(PO4)3 Solid Electrolyte Nanofibers by Control of Germanium Hydrolysis

We report the synthesis of ceramic Li1.5Al0.5Ge1.5(PO4)3 (LAGP) nanofibers by combining sol–gel and electrospinning techniques. A homogeneous and stable precursor solution based on chlorides was achieved by controlling Ge hydrolysis. Subsequent electrospinning and heat treatment resulted in highly porous nanostructured NASICON pellets. After a full chemical-physical characterization, various amounts of LAGP nanofibers were used as a filler to develop polyethylene oxide (PEO)-based composite electrolytes. The addition of 10% LAGP nanofibers has allowed doubling the ionic conductivity of the plain polymer electrolyte, by providing longer ion-conductive paths and reducing PEO crystallinity. These findings are promising towards developing solution-based synthesis approaches featuring Ge precursors. In addition, the achieved LAGP nanofibers proved to be a promising nanofiller candidate to develop composite electrolytes for next-generation solid-state batteries.

Ultraviolet-cured polyethylene oxide-based composite electrolyte enabling stable cycling of lithium battery at low temperature

The room and low-temperature performances of solid-state lithium batteries are crucial to expand their practical application. Polyethylene oxide (PEO) has received great attention as the most representative polymer electrolyte matrix. However, most PEO-based solid-state batteries need to operate at high temperature due to low room temperature ionic conductivity. Improving the ionic conductivity by adding plasticizers or reducing the crystallinity of PEO often compromises its mechanical strength. Here, an amorphous PEO-based composite solid-state electrolyte is obtained by ultraviolet (UV) polymerizing PEO and methacryloyloxypropyltrimethoxy silane (KH570)-modified SiO2 which demonstrates both satisfactory mechanical performance and high ionic conductivity at room (3.37 × 10−4 S cm−1) and low temperatures (1.73 × 10−4 S cm−1 at 0 °C). In this electrolyte, the crystallinity of PEO is reduced through cross-linking, and therefore provides a fast Li+ ions transfer area. Moreover, the KH570-modified SiO2 inorganic particles promote the dissociation of lithium salts by Lewis acid centers to increase the ionic conductivity. Importantly, this kind of cross-linking networks endows the final electrolyte much higher mechanical strength than the pure PEO polymer electrolyte or PEO-inorganic filler blended systems. The solid-state LiFePO4/Li cell assembled with this electrolyte exhibits excellent cycling performance and high capacity at room and low temperatures.

Regulating Li-Ion Migration in Solid-State Electrolytes for Li Metal Anodes

Lithium (Li) metal batteries are strongly considered one of the most promising candidates for next-generation rechargeable batteries due to their high theoretical specific capacity and low reduction potential. However, Li metal anodes are suffering from limited cycle life, low cycling efficiency, and severe safety concerns resulting from sharp Li dendrites and electrolyte degradation.The uncontrollable Li dendrite growth caused by the uneven distribution of Li ions is an extremely complicated issue coupled with the transport of anions, cations and electrons, as well as the chemical and electrochemical reactions at the anode-electrolyte interphase. In terms of the ion migration, space-charge theory indicates that the electrolyte is divided into a quasi-neutral region and a space-charge region. The quasi-neutral region approaches the cathode side, at which the ion transfer is governed by diffusion. In contrast, when ions travel close to the anode side, the ion transport is mainly driven by the electric field, leaving a space-charge region that accounts for ramified Li metal growth. Consequently, it is rewarding to design electrolytes that can regulate the ion distribution (including both Li cations and the counter anions) to inhibit Li dendrite growths.Immobilizing anion has been theoretically proved to influence cation distribution, where a portion of immobilized anions (even as small as 10%) contribute to stable Li electrodeposition. Here, we develop an anion-immobilized solid-state composite electrolyte for Li metal anodes. Garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZTO) ceramic particles are well dispersed in a polymer matrix to synthesize a polyethylene oxide (PEO)–lithium bis(trifluoromethylsulphonyl)imide (LiTFSI)–LLZTO (PLL) solid electrolyte. In contrast to routine electrolytes with mobile anions, the PLL solid electrolyte contributes to effective immobilization of anions for uniform ion distribution and dendrite-free Li deposition. Chemical and mechanical interactions between ceramic particles and the polymer matrix result in reduced PEO crystallinity and pinned TFSI−anions, enabling relatively fast Li+conduction. We further demonstrate the application of this flexible membrane in all–solid-state LiFePO4 (LFP) || Li and LiNi0.5Co0.2Mn0.3O2(NCM) || Li batteries.Moreover, ion migration in batteries can be analogized to the fluid transportation in packed towers in the field of chemical industry. Redistributors are used to intensify the heat and mass transfer processes in a packed tower. Solid-state electrolyte LLZTO, with abundant 3D ion conduction channels, can act as a redistributor to regulate Li-ion distribution. We propose a concept of ion redistributors to eliminate dendrites by redistributing Li ions with LLZTO coated polypropylene (PP) separators in Li metal batteries. The standard deviation of ion concentration beneath the LLZTO composite separator is 13 times less than that beneath the routine PP separator. This approach enables a high specific capacityfor LiFePO4|| Li pouch cells and prolonged cycle life span of 800 hours for Li || Li pouch cells. This strategy is facile and efficient in regulating Li-ion deposition by separator modifications and is a universal method to protect alkali metal anodes in rechargeable batteries.