High-performance Lithium Metal Batteries Research Articles

Ultra-Tough Dynamic Supramolecular Ion-Conducting Elastomer Induced Uniform Li+ Transport and Stabilizes Interphase Ensures Dendrite-Free Lithium Metal Anodes.

Artificial polymer solid electrolyte interphases (SEIs) with microphase-separated structures provide promising solutions to the inhomogeneity and cracking issues of natural SEIs in lithium metal batteries (LMBs). However, achieving homogeneous ionic conductivity, excellent mechanical properties, and superior interfacial stability remains challenging due to interference from hard-phase domains in ion transport and solid-solid interface issues with lithium metal. Herein, we present a dynamic supramolecular ion-conducting poly (urethane-urea) interphase (DSIPI) that achieves these three properties through modulating the hard-phase domains and constructing a composite SEI in situ. The soft-phase polytetrahydrofuran backbone, featuring loose Li+-O coordinating interactions, ensures uniform Li+ transport. Concurrently, sextuple hydrogen bonds in the hard phase dissipate strain energy through sequential bond cleavage, thereby imparting exceptional mechanical properties. Moreover, enriched bis (trifluoromethanesulfonyl) imide anion (TFSI-) in DSIPI promotes the in situ formation of a stable polymer-inorganic composite SEI during cycling. Consequently, the DSIPI-protected lithium anode (DSIPI@Li) enables symmetric cells with exceptional cyclability exceeding 4,000 hours at an ultra-high current density of 20 mA cm-2, thereby demonstrating excellent cycling stability. Furthermore, DSIPI@Li facilitates stable operation of the pouch cells under the constraints of a high-loading LiNi0.8Co0.1Mn0.1O2 cathode and low negative/positive capacity (N/P) ratio. This work presents a powerful strategy for designing artificial SEIs and high-performance LMBs.

Perfluoropolyether-terminated Single-ion Polymer for Enhancing Performance of PEO-based Solid Polymer Electrolyte.

Solid-state electrolytes are receiving increasing attention in lithium metal batteries due to the advantage of high energy density. Poly(ethylene oxide) (PEO) electrolyte possesses good compatibility with lithium salts. However, PEO suffers from a low lithium-ion transference number and poor high-voltage resistance, which significantly hinder its application in lithium metal batteries. Herein, a perfluoropolyether-terminated single-ion polymer (PFPE-polymer) is designed and synthesized in this contribution. By incorporating the PFPE-polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into PEO via casting, the polymer electrolyte (PFPE-SE) is successfully prepared. Compared to PEO-based electrolytes, PFPE-SE forms a solid electrolyte interface (SEI) layer and inhibits the growth of lithium dendrites on the anode. At 70°C, the lithium-ion transference number and the electrochemical window reach 0.72 and 4.7V, respectively. When tested at a discharge rate of 0.5 C, the Li|PFPE-SE|LFP cell exhibits a specific capacity of 156.0 mAh g-1, with a capacity retention of 74.3% after 230 cycles, superiority the performance of the electrolyte prepared by mixing PEO with LiTFSI. This work presents a promising polymer electrolyte strategy for achieving high-performance lithium metal batteries, leveraging the in situ construction of the SEI layer and the utilization of a single-ion polymer.

High-Performance Solid-State Lithium Metal Batteries of Garnet/Polymer Composite Thin-Film Electrolyte with Domain-Limited Ion Transport Pathways.

The integrated approach of interfacial engineering and composite electrolytes is crucial for the market application of Li metal batteries (LMBs). A 22 μm thin-film type polymer/Li6.4La3Zr1.4Ta0.6O12 (LLZTO) composite solid-state electrolyte (LPCE) was designed that combines fast ion conduction and stable interfacial evolution, enhancing lithium metal interface stability and cycling performance. The ether-based molecular coordination groups/clusters formed by triethylene glycol dimethyl ether (TGDE) and anions facilitated the movement of Li+ between the polymer chain segments. These specific coordination clusters significantly "constrained" the interaction between anions and Li+, inducing the anions to follow the clusters to the Li metal and preferentially participate in solid electrolyte interface (SEI) derivatization. The inorganic salt-rich gradient SEI modulates Li+ deposition and inhibits uncontrolled dendrite growth, achieving stable cycling of Li symmetric cell at 0.2 mA cm-2 for over 2000 h. Furthermore, the Li||NCM811 cell at a rate of 0.1 C exhibits an initial discharge capacity of 194.5 mAh g-1, maintaining a capacity retention rate of over 90% after 500 cycles. This work demonstrates the importance of domain-limited ion clusters in ion transport and interfacial evolution, providing a perspective for solid-state LMBs.

Three-dimensional Covalent Organic Framework with Dense Lithiophilic Sites as Protective Layer to Enable High-Performance Lithium Metal Battery.

Lithium (Li) metal batteries with remarkable energy densities are restrained by short lifetime and low Coulombic efficiency (CE), resulting from the accumulative Li dendrites and dead Li during cycling. Here, we prepared a new three-dimensional (3D) covalent organic framework (COF) with dense lithiophilic sites (heteoatom weight contents of 32.32wt%) as an anodic protective layer of Li metal batteries. The 3D COF was synthesized using a [6+4] synthesis strategy by inducing flexible 6-connected cyclotriphosphazene derivative aldehyde and 4-connected porphyrin-based tetraphenylamines. Both phosphazene and porphyrin rings in the COF served as electron-rich and lithiophilic sites, enhancing a homogeneous Li+ flux via 3D direction towards highly smooth and compact Li deposition. The Li/Por-PN-COF-Cu cells achieved a record average CE of 99.1% for 320 cycles with smooth Li deposition. Meanwhile, the abundant lithiophilic sites can promote fast Li+ transport with Li+ transference number of 0.87, enabling LiFePO4 full cell with stable stripping/plating processes even at a harsh rate of 5 C. Theoretical calculations revealed that the strong interaction force between Li+ and the COF facilitated the dissolution of Li+ from the electrolyte, and the low migration barrier of 1.08 eV indicated a favorable interaction between the Li+ ions and the π-electron system.

In Situ Optical Observation of Lithium Dendrite Pattern in Solid Polymer Electrolytes.

Solid polymer electrolytes (SPEs) have been treated as a viable solution to build high-performance solid-state lithium metal batteries (SSLMBs) at the industrial level, bypassing the safety and energy density dilemmas experienced by today's lithium-ion battery technology. To promote a wider application of SPEs-based SSLMBs, the chemical and electrochemical characteristics of lithium metal (Li°) electrode in SPEs have to be clearly elucidated. In this work, the morphological evolution of Li° electrode in the SPEs-based SSLMBs is comprehensively investigated, via a customized electrochemical cell allowing optical microscopic analyses. The results demonstrate that differing from inorganic solid electrolytes, the elastic feature of SPEs eliminates the "memory effect" of the dendrite formation, in which the previously formed dendrites can be dissolved and the resulting space can be simultaneously occupied by electrolyte components, instead of leaving for a second-round growth of Li° dendrites. Furthermore, the largely increased electronic conductivities of the as-formed interphases between Li° electrode and SPEs are found to be responsible for the notoriously soft short-circuit behavior observed during cycling. These findings bring a fresh understanding of the formation and evolution of lithium dendrites in SPE-based cells, which are vital for improving the long-term stability of SSLMBs and other related high-energy battery systems.

Thermal stability of PVDF-HFP based gel electrolyte for high performance and safe lithium metal batteries

Thermal stability of PVDF-HFP based gel electrolyte for high performance and safe lithium metal batteries

Surface-functionalized metal–organic framework with high specific surface area optimizing composite solid electrolyte for high-performance solid-state lithium metal batteries

Surface-functionalized metal–organic framework with high specific surface area optimizing composite solid electrolyte for high-performance solid-state lithium metal batteries

Dual driven asymmetric electrolyte with gradient distributed UPy-CNTs for high-performance lithium metal batteries

Dual driven asymmetric electrolyte with gradient distributed UPy-CNTs for high-performance lithium metal batteries

Tailoring Ce-Centered Metal-Organic Frameworks for Fast Li+ Transport in Composite Polymer Electrolyte.

Regulating metal nodes to innovate the metal-organic framework (MOF) structure is of great interest to boost the performance of MOFs-incorporated composite solid electrolytes. Herein, Ce4+ with a low-lying 4f orbital is selected as metal center to coordinate with organic ligand to prepare MOF of Ce-UiO-66. The unsaturated open metal sites and defected oxygen vacancies furnish Ce-UiO-66 with strengthened Lewis acidity, which promotes Ce-UiO-66 interacting effectively with both poly(ethylene oxide) (PEO) and Li salt anions. Accordingly, Ce-UiO-66 as additive fillers can be uniformly dispersed in PEO matrix to form an advanced composite solid-state electrolyte (Ce-UiO@PEO) with accelerated Li+ transport. The optimized Ce-UiO@PEO displays a boosted ionic conductivity of 4.20 × 10-4 S cm-1 and an improved Li+ transference number of 0.39 at 60 °C, which are highly comparable to those of other MOFs@PEO electrolytes. Combined with the mechanical and thermal stabilities, such a Ce-UiO@PEO electrolyte enables Li/Li symmetric and Li/LiFePO4 full cells with superior cycling stability and rate performance. The Ce-UiO@PEO electrolytes are of great potential to be applied in high-performance lithium metal batteries.

Halogen-Bonding Nanoarchitectonics in Supramolecular Plasticizers for Breaking the Trade-Off between Ion Transport and Mechanical Strength of Polymer Electrolytes for High-Voltage Li-Metal Batteries.

The low ionic conductivity of poly(ethylene oxide) (PEO)-based polymer electrolytes at room temperature impedes their practical applications. The addition of a plasticizer into polymer electrolytes could significantly promote ion transport while inevitably decreasing their mechanical strength. Herein, we report a supramolecular plasticizer (SMP) to break the trade-off effect between ionic conductivity and mechanical properties in PEO-based polymer electrolytes. Accordingly, the SMP is constructed by tetraethylene glycol dimethyl ether (G4) and SbF3 through halogen bonds. The SMP-plasticized PEO electrolyte (PEO/SMP) presents a simultaneously enhanced ionic conductivity of 2.4 × 10-4 S cm-1 (25 °C) and a high mechanical strength of 8.1 MPa, compared to those of pristine PEO-based electrolytes. Benefiting from the halogen bonds between G4 and SbF3, the Li-O coordination in PEO/SMP is evidently weakened, and thus rapid Li+ transport is achieved. Furthermore, the PEO/SMP electrolyte possesses a wide electrochemical stability window of 4.5 V and, importantly, derives an inorganic-rich SEI with a low interfacial resistance on a lithium metal surface. By using PEO/SMP, the lithium-metal battery with the LiNi0.5Co0.2Mn0.3O2 cathode exhibits a good rate and long-term cycling performance with a capacity retention of 75.3% (500 cycles). This work offers a rational guideline for the design of polymer electrolytes suitable for high-performance lithium-metal batteries.

Non-consumable gamma-cyclodextrin additive constructing anti-solvation interphase realizing dendrites free and high-performance lithium metal batteries

Relying on surpassing high theoretical capacity (3,865 mAh/g) and the lowest relative electrode potential (0 V vs. metallic Li), lithium metal batteries (LMBs) have been regarded as the “holy grail” of next-generation energy storage technology. Whereases, the instability of pristine solid electrolyte interphase (SEI) layers and the disorderly growth of lithium dendrites are still significant challenges to the commercialisation of LMBs. In this study, a novel approach is introduced to homogenise Li deposition by incorporating an environmentally friendly electrolyte additive, gamma-cyclodextrin (γ-CD), in ether-based electrolytes. Through host-guest interactions, γ-CD additives not only form inclusion complexes to improve Li+ transference number to 0.86 but also encapsulate TFSI- anions and other solvent molecules within the “cavity effect” to relieve unfavourable solvent effect. Electrochemical characterisations demonstrate that introducing 1 wt% γ-CD elevates the oxidation decomposition voltage of ether electrolytes to 4.15 V, thereby inhibiting the decomposition of ether electrolytes and reducing the fracture of SEI layers. According to reduce the nucleate potential, the Li//Cu half battery exhibits improved stability for 100 cycles, with an improved average Coulombic efficiency (CE) maintained above 98.4 %. Even if applied at high current densities of 5.0 mA cm−2 for a capacity of 1.0 mAh cm−2, the Li//Li symmetric battery can cycle for over 800 h, and the Li//Li4Ti5O12 (LTO) full battery retains 98.8 % of the initial capacity after 1,400 cycles.

Li-Ga Alloy-Contained Hybrid Solid Electrolyte Interphase Induced by In Situ Polymerization for High-Performance Lithium Metal Batteries.

Construction of quasi-solid-state lithium metal batteries (LMBs) by in situ polymerization is considered a key strategy for the next generation of energy storage systems with high specific energy and safety. Poly(1,3-dioxolane) (PDOL)-based electrolytes have attracted wide attention among researchers, benefiting from the low cost and high ionic conductivity. However, interfacial deterioration and uncontrollable growth of lithium dendrites easily appeared in LMBs due to the high reactivity of lithium metal, resulting in the failure of LMBs. In this work, a strategy is developed of using Ga(OTF)3 as the initiator to obtain a PDOL-based gel electrolyte (GaPD). In addition, a hybrid stable solid electrolyte interphase (SEI) of lithium fluoride/Li2O/Li-Ga alloys is observed on the surface of lithium metal. Combined with density functional theory calculations, the hybrid SEI shows high affinity toward Li+, indicating that a uniform deposition of Li+ could be achieved. Therefore, the Li/GaPD/Li cell operates stably for 1600 h at room temperature. In addition, the LiFePO4/GaPD/Li cell retains a capacity retention rate of 90.2% over 200 cycles at 1 C. This work provides a reference for the practical application of in situ polymerization technology in high-performance and safe LMBs.

Biomimetic Channels Design in Metal-Organic Framework Enabling Highly Lithium-Ion Conduction for Lithium-Metal Batteries.

Solid-state electrolytes (SSEs) based on metal-organic frameworks (MOFs) are an ideal material for constructing high-performance lithium metal batteries (LMBs). However, the low ion conductivity and poor interface contact (especially at low temperatures) still seriously hinder its further application. Herein, inspired by the Na+/K+ conduction in biology systems, a series (NH2, OH, NH-(CH2)3-SO3H)-modified MIL-53-X as SSEs is reported. These functional groups are similar to anions suspended in biological ion channels, partially repelling anions while allowing cations to be effectively transported through pore channels. Subsequently, MIL-53-X with hierarchical pore structure (H-MIL-53-X) is obtained by introducing lauric acid as a regulator, and then the effects of structural design and morphology control on its performance are explored. The conductivity of H-MIL-53-NH-SO3Li with multi-level pore structure and modified by sulfonic acid groups reached 2.2×10-3Scm-1 at 25°C, lithium-ion transference number of 0.78. Besides, the H-MIL-53-NH-SO3Li still has an excellent conductivity of 10-4Scm-1 at -40°C. Additionally, LiFePO4/Li batteries equipped with H-MIL-53-NH-SO3Li SSEs could operate stably for over 200 cycles at 0.1C. The strategy of combining structural and morphological design of MOFs with biomimetic ion channels opens new avenues for the design of high-performance SSEs.

A biomass-based protective layer with rigid structure and ion conductivity for high-performance lithium metal batteries

Lithium (Li) metal has been considered as an effective anode material because of its high theoretical capacity, but the uncontrolled dendrite growth and the unstable electrode/electrolyte interface limit its practical application. In this work, proanthocyanidin (PA), a natural extracted biomass, was designed and developed as a coating material to guide homogeneous deposition and restrain side reaction for lithium metal batteries. The rigid benzene ring structure of PA can increase the mechanical strength to restrain dendrite growth on Li surface. Moreover, the spontaneous formation of organolithium (PA-Li) structure from the reaction of phenolic hydroxyl group with Li metal increase the ion transportation ability of PA layer and induce the uniform deposition of Li+ ions to hinder the growth of Li dendrites, as well as prevent the direct contact of organic electrolyte with Li metal to suppress the interface side reaction. As a result, Li metal anode with PA-Li exhibits stable cycling properties for 2800 h at 2 mA cm-2 and 2 mAh cm-2, better that of bare Li (200 h). Li-sulfur full battery with PA-Li can still achieve a capacity of 570 mAh g-1 after 300 cycles. This work provides an effective strategy for the construction a natural functional layer on Li surface to enhance the electrochemical performance, as well as the implementation of high-value utilization for natural biomass.

Facile self-assembled monolayer deposition on copper foil for high-performance lithium-metal batteries

Li metal is widely acknowledged as the optimal negative electrode material for high-energy-density Li rechargeable batteries. However, challenges arise owing to the formation of Li dendrites and poor surface stability, leading to reduced cycle life and energy efficiency, thereby limiting widespread application. In this study, we introduced a novel approach of a molecular single-layer surface modification onto a Cu foil using a self-assembled monolayer with hexamethyldisilane (HMDS) to enhance the performance of Li-metal electrodes. The deposition of a single molecular layer at the Å-level was achieved by a simple combination of precursor casting and heat treatment without greatly affecting the energy and power density. Furthermore, this process was both scalable and cost-effective, making it highly suitable for large-scale battery manufacturing. The molecular deposition of HMDS effectively mitigated electrolyte decomposition and promoted uniform Li deposition by enhancing the surface stability under repeated Li plating–stripping processes. Optical microscopy revealed the homogeneous Li plating even after extended cycling; the first cycle on the modified surface depicted uniform plating without blank spots owing to the reduced gas-phase by-products from electrolyte decomposition. Thus, HMDS modification greatly improved the cycle stability of Li-metal batteries by successfully mitigating polarization due to electrolyte decomposition. Such improvement improved the Coulombic efficiencies and enhanced the energy efficiency, especially over a wide current density range of 1–5 mA cm−2. Furthermore, full cells with LiFePO4 cathodes and HMDS-modified Cu foils exhibited extended cyclability with increased energy efficiencies.

Modulating the Inner Helmholtz Plane towards Stable Solid Electrolyte Interphase by Anion-π Interactions for High-Performance Anode-Free Lithium Metal Batteries.

Anode-freelithium (Li) metal batteries (AFLBs) featured high energy density are viewed as the viable future energy storage technology. However, the irregular Li deposition and unstable solid electrolyte interphase (SEI) on anode current collectors reduce their cycling performance. Here, we propose a concept of anion-recognition electrodes enabled by anion-π interactions to regulate the inner Helmholtz plane (IHP) and electrolyte solvation chemistry for high-performance AFLBs. By engineering the electrodes with electron-deficient aromatic-π systems that possess high permanent quadrupole moment (Qzz),the anion-π interactions can be generated to concentrate the anions on the electrode surface and tune the IHP structure to construct a stable anion-derived SEI layer, thus achieving highly reversible Li plating/stripping process. Through designing various current collectors with different Qzz values, the intimate correlations among the surface charge of the electrode, competitive adsorption of the IHP, and SEI structures are demonstrated. Particularly, the modified carbon cloth current collector with a high Qzz value (+35.1) delivers a high average Li stripping/plating Coulombic efficiency of 99.1% over 230 cycles in the carbonated electrolyte, enabling a long lifespan and high capacity retention of LiNi0.8Co0.1Mn0.1O2-based AFLBs with a commercial-level areal capacity (4.1 mA h cm-2).

Permselective Metal–Organic Framework-Based Separators via In Situ Self-Assembly for High-Performance Lithium Metal Batteries

Permselective Metal–Organic Framework-Based Separators via In Situ Self-Assembly for High-Performance Lithium Metal Batteries

Boron-containing cross-linker assisted single-ion conducting polymer electrolytes for high-performance and dendrite-free Li-metal batteries

Nowadays, single-ion conducting polymer electrolytes for high efficiency, stable, safe and dendrite-free Li-metal batteries are in great need to protect lithium metal anode. In this work, a boron-containing single-ion polymer electrolyte (BSPE), prepared by the copolymerization of allyl diglycol carbonate (ADC), lithium bis((trifluoromethyl)sulfonyl)amide (LiTFSI), and diisopropyl allylboronate (DPAB). The weak coordination interaction between Li+ and polar carbonate enhances Li+ transport ability. Further, the boron-containing cross-linker fixes the counter anions on the polymer backbones, limiting the movement of the anions and promoting the rapid and uniform Li+ transference. The BSPE with 3 wt% DPAB exhibits higher Li+ transference number (t+ = 0.77) and better ionic conductivity (1.36 × 10−4 S cm−1 at 25 °C) compared with that without DPAB. The wider electrochemical window (5.6 V vs. Li+/Li), stable polarization and suppressed lithium dendrites during the plating/stripping cycle at a current density of 0.2 mAcm−2 for 600 h provide the metal-lithium batteries with better safety and higher efficiency. In addition, the initial discharge capacity of LiFePO4/BSPE/Li is 140.7 mAh g−1 with 95.2 % coulombic efficiency, and the capacity retention still remains 98.7 % after 200 cycles at 0.1C. The excellent performance endows the BSPE with the potential application in high-performance lithium metal batteries.

Multifunctional quasi-solid state electrolytes based on “reverse” plant cell structure for high-performance lithium metal batteries

Quasi-solid state electrolytes (QSSEs) combine the benefits of both solid and liquid electrolytes, making them promising for high-performance lithium metal batteries (LMBs). However, developing QSSEs that achieve high ionic conductivity, a continuous electrode/electrolyte interface, and significant mechanical robustness remains challenging. Plant cell walls provide mechanical strength, while the cell membrane offers excellent material transport capabilities, making them effective models for quasi-solid electrolytes. However, using plant cells as a model can result in poor interface contacts due to the rigid components on the exterior. To address this, a “reverse” plant cell QSSE with a multifunctional bilayer architecture has been proposed. The outer layer acts as a functional reaction interface to enhance Li⁺ transmission, improve interfacial contact, and significantly reduce interfacial impedance. Meanwhile, the inner layer is designed to provide mechanical robustness and shorten ion transport distances. The QSSE inspired by “reverse” plant cells has an ionic conductivity of 4.26 × 10−3 S cm−1, a Li+ transference number (tLi+) of 0.91, and an electrochemical stability window (ESW) of 4.83 V. Li−LiFePO4 (LFP) full cells based on the “reverse” plant cell QSSE can maintain a cycling capacity of 137 mAh g−1 after 500 cycles at 1 C, with 95 % retention.

Non-Fluorinated Cyclic Ether-Based Electrolyte with Quasi-Conjugate Effect for High-Performance Lithium Metal Batteries.

Fluorinated ether-based electrolytes are commonly employed in lithium metal batteries (LMBs) to attenuate the coordination ability of ether solvents with Li+ and induce inorganic-rich interphase, whereas fluorination inevitably introduces exorbitant production expenses and environmental anxieties. Herein, a non-fluorinated molecular design strategy has been conceptualized by incorporating methoxy as an electron-donating group to generate a quasi-conjugate effect for tuning the affinity of Li+-solvent, thereby enabling the cyclic ether solvent 2-methoxy-1,3-dioxolane with weak solvation ability and exceptional Li metal-compatibility. Accordingly, the optimized electrolyte exhibits anion-dominant solvation structure for inorganic-rich interphase and fulfills an impressive Li plating/stripping Coulombic efficiency of 99.6%. As-fabricated Li||LiFePO4 full cells with limited Li (N/P = 2.5) showcase a high capacity retention of 83% after 150 cycles, indicating excellent cycling stability. Moreover, the full LMBs demonstrate exceptional tolerance towards a wide temperature range from -20 oC to 60 oC, displaying a remarkable capacity retention of 90% after 110 cycles at -20 oC. Such a molecular design strategy offers a promising avenue for electrolyte engineering beyond fluorination in order to cultivate high-performance LMBs.