Density Lithium Metal Batteries Research Articles

PVDF/lithiated sulfonated poly (ether ether ketone) blend coated PE separators for high-performance lithium metal batteries

Ionic conductivity and lithium ion transference number (tLi+) of electrolytes are essential parameters governing the performances of high energy density lithium metal batteries. Although the importance of tLi+versus ionic conductivity has been theorized by simulation, the systematically experimental study of their respective effects on lithium dendrite suppression and battery performances is rarely carried out. Here, a series of polyvinylidene fluoride and lithated sulfonated poly (ether ether ketone) blend (PVDF/SPEEK-Li) coated polyethylene (PE) separators with exactly the same composition but different pore morphologies are fabricated by vapor and non-solvent induced phase separation. The effects of sulfonate group–ion interaction and pore morphologies on ionic conductivity and tLi+ of the electrolytes are studied. The performances of lithium metal batteries can be obviously improved by subtle increase of the tLi+, especially at high charge rates and even with a decrease in conductivity. Even at a high current density of 3 C, the PVDF/SPEEK-Li coated PE separator assembled lithium metal battery using a LiFePO4 cathode with a mass loading of 10.5 mg cm−2 can run stably for 200 cycles with a capacity retention of 79 %, which is superior to the PE separator assembled battery with a life of only 55 cycles.

Oriented Structures for High Safety, Rate Capability, and Energy Density Lithium Metal Batteries.

Lithium metal batteries (LMBs) have emerged in recent years as highly promising candidates for high-density energy storage systems. Despite their immense potential, mutual constraints arise when optimizing energy density, rate capability, and operational safety, which greatly hinder the commercialization of LMBs. The utilization of oriented structures in LMBs appears as a promising strategy to address three key performance barriers: 1) low efficiency of active material utilization at high surface loading, 2) easy formation of Li dendrites and damage to interfaces under high-rate cycling, and 3) low ionic conductivity of solid-state electrolytes in high safety LMBs. This review aims to holistically introduce the concept of oriented structures, provide criteria for quantifying the degree of orientation, and elucidate their systematic effects on the properties of materials and devices. Furthermore, a detailed categorization of oriented structures is proposed to offer more precise guidance for the design of LMBs. This review also provides a comprehensive summary of preparation techniques for oriented structures and delves into the mechanisms by which these can enhance the energy density, rate capability, and safety of LMBs. Finally, potential applications of oriented structures in LMBs and the crucial challenges that need to be addressed in this field are explored.

UV cross-linked highly stable polymer garnet composite electrolyte with improved interphase for lithium metal batteries

The next-generation electric vehicles heavily rely on high-energy–density lithium metal batteries with enhanced safety. Replacing liquid electrolytes with solid-state polymer electrolytes offers superior protection, high flexibility, and stability. However, inadequate ionic conductivity and poor compatibility at the interfaces with the electrodes hinder the practical application of solid-state electrolytes. In this work, we developed a polyethylene glycol-based, highly cross-linked polymer electrolyte with a garnet-type, fast Li+ conductive Li6.2Al0.24La3Zr2O12 (Al-LLZO) filler. The Al-LLZO filler was incorporated into a cross-linking functional polymeric matrix of polyethylene glycol diacrylate, pentaerythritol tetrakis (3-mercaptopropionate), and lithium perchlorate salt. The cross-linked polymer garnet composite electrolyte (CPGCE) was prepared via UV-induced photo-polymerization. The resulting CPGCE exhibits superior free-standing flexibility, a desired ionic conductivity of 4.4 × 10−4 S cm−1, and a wide potential window up to 4.2 V. The Li|CPGCE|Li symmetric cell underwent stripping and plating at varying current densities of 0.05 to 0.3 mA cm−2, displaying a low overpotential range from ±0.02 V to ±0.08 V over 500 cycles. Similarly, the as-cycled Li|CPGCE|Li showed excellent stripping and plating performance at 0.1 mA cm−2 for 500 cycles at 60 °C. The incorporation of the Al-LLZO nanofiller provided active sites with continuous Li+ conducting pathways, suppressing the growth of dead lithium dendrites. The Li|CPGCE|LiFePO₄ full cell exhibited a discharge capacity of 155 mAh g−1 at a rate of 0.1C, with a coulombic efficiency of 96 % over 50 cycles at 25 °C. This work offers a straightforward and convenient approach to creating highly durable polymer composite electrolytes with enhanced interfacial stability, advancing the implementation of all-solid-state lithium metal batteries.

Interfacial fusion-enhanced 11 µm-thick gel polymer electrolyte for high-performance lithium metal batteries

In the pursuit of ultrathin polymer electrolyte (<20 μm) for lithium metal batteries, achieving a balance between mechanical strength and interfacial stability is crucial for the longevity of the electrolytes. Herein, 11 μm-thick gel polymer electrolyte is designed via an integrated electrode/electrolyte structure supported by lithium metal anode. Benefiting from an exemplary superiority of excellent mechanical property, high ionic conductivity, and robust interfacial adhesion, the in-situ formed polymer electrolyte reinforced by titanosiloxane networks (ISPTS) embodies multifunctional roles of physical barrier, ionic carrier, and artificial protective layer at the interface. The potent interfacial interactions foster a seamless fusion of the electrode/electrolyte interfaces and enable continuous ion transport. Moreover, the built-in ISPTS electrolyte participates in the formation of gradient solid-electrolyte interphase (SEI) layer, which enhances the SEI’s structural integrity against the strain induced by volume fluctuations of lithium anode. Consequently, the resultant 11 μm-thick ISPTS electrolyte enables lithium symmetric cells with cycling stability over 600 h and LiFePO4 cells with remarkable capacity retention of 96.6% after 800 cycles. This study provides a new avenue for designing ultrathin polymer electrolytes towards stable, safe, and high-energy–density lithium metal batteries.

In-situ coating strategy to synthesize ultra-soft sulfide solid-state electrolytes for dendrite-free lithium metal batteries

High energy density lithium metal batteries play a crucial role in future energy storage. High ionic conductivity argyrodite-type Li5.5PS4.5Cl1.5 is a promising candidate for future lithium metal all-solid-state batteries. However, under cold pressing conditions, the combination of high electronic conductivity and high porosity significantly accelerates the growth of lithium dendrites, resulting in low capacity and a short lifespan. In this study, we combined a simple wet ball milling and in-situ polymerization process to fabricate a polyvinylene carbonate-coated sulfide composite solid electrolyte. The ultra-soft particle, when cold-pressed without binders, completed a tightly packed and void-free internal structure. This electrolyte, combined with a stable LiF-rich interface layer on lithium metal, held a higher critical current density of 2.0 mA cm−2 than 0.65 mA cm−2 of uncoated argyrodite and a 2000-hour stable cycle at 0.5 mA cm−2 in lithium symmetric cells. The unique coating structure also mitigated the chemomechanical failure between electrolyte and electrode, preventing the rapid increase of interface impedance and achieving a high initial capacity of 173.5 mAh g−1 without a short circuit for 300 cycles in LiNi0.6Co0.2Mn0.2O2//Li cells.

LPEO enhanced LAGP composite solid electrolytes for lithium metal batteries

The application of solid electrolyte is expected to realize the commercialization of high energy density lithium metal batteries (LMBs). While the interfacial contact between solid inorganic electrolyte and electrodes has become a stumbling block for achieving stable cycling in LMBs. In this work, a Li-containing polyethylene oxide (LPEO) was introduced between LAGP and electrodes as a buffer layer to regulate the interfacial compatibility and reduce interfacial impedance, inhibiting the side reactions. Moreover, ether-oxygen bond on LPEO chain can coordinate with Li+ and guide the transportation of Li+, achieving fast Li+ diffusion between Li1+xAlxGe2-x(PO4)3 (LAGP) and electrodes. Specifically, the growth of lithium dendrites is effectively suppressed in LAGP with LPEO modification, which would lead to remarkable cycling stability and rate capability. Therefore, the Li|LPEO-LAGP|Li battery can cycle stably for more than 600h at 0.1mAcm−2. In addition, long-term performance of Li|LPEO-LAGP| LiFePO4(LFP) battery was achieved at a rate of 0.4C, and capacity retention is more than 74 % after 200 cycles. The Li|LPEO-LAGP|LiNi0.8Co0.1Mn0.1O2 also realized the steady operation in the voltage range of 2.8–4.3V.

Anion‐Derived Solid Electrolyte Interphase Enabled by Diluent Modulated Dimethyl Carbonate‐Based Localized High Concentration Electrolytes for Lithium Metal Batteries

AbstractCarbonate‐based electrolytes generally suffer from low Coulombic efficiency and poor cycling stability in lithium metal batteries. In this work, localized high concentration electrolytes (LHCEs) based on dimethyl carbonate (DMC) with varying diluent additions are designed. LHCEs demonstrate higher Li+ transference numbers and a greater proportion of contact ion pairs (CIPs) and ion pair aggregates (AGGs) in the solvation structures, facilitating the formation of anion‐derived solid electrolyte interphase (SEI). Furthermore, LHCEs enhance the Coulombic efficiency of Li||Cu cells and improve the anodic stability against lithium. One of these LHCEs, prepared with appropriate diluent addition, exhibits excellent capacity retention in Li||NCM622 cells at 0.5 C after 150 cycles, thus presenting promising possibilities for the development of high energy density lithium metal batteries.

Phase Morphology Dependence of Ionic Conductivity and Oxidative Stability in Fluorinated Ether Solid-State Electrolytes.

Solid-state polymer electrolytes can enable the safe operation of high energy density lithium metal batteries; unfortunately, they have low ionic conductivity and poor redox stability at electrode interfaces. Fluorinated ether polymer electrolytes are a promising approach because the ether units can solvate and conduct ions, while the fluorinated moieties can increase oxidative stability. However, current perfluoropolyether (PFPE) electrolytes exhibit deficient lithium-ion coordination and ion transport. Here, we incorporate cross-linked poly(ethylene glycol) (PEG) units within the PFPE matrix and increase the polymer blend electrolyte conductivity by 6 orders of magnitude as compared to pure PFPE at 60 °C from 1.55 × 10-11 to 2.26 × 10-5 S/cm. Blending varying ratios of PEG and PFPE induces microscale phase separation, and we show the impact of morphology on ion solvation and dynamics in the electrolyte. Spectroscopy and simulations show weak ion-PFPE interactions, which promote salt phase segregation into-and ion transport within-the PEG domain. These polymer electrolytes show promise for use in high-voltage lithium metal batteries with improved Li|Li cycling due to enhanced mechanical properties and high-voltage stability beyond 6 V versus Li/Li+. Our work provides insights into transport and stability in fluorinated polymer electrolytes for next-generation batteries.

Interphase Engineering via Solvent Molecule Chemistry for Stable Lithium Metal Batteries

AbstractLithium metal battery has been regarded as promising next‐generation battery system aiming for higher energy density. However, the lithium metal anode suffers severe side‐reaction and dendrite issues. Its electrochemical performance is significantly dependant on the electrolyte components and solvation structure. Herein, a series of fluorinated ethers are synthesized with weak‐solvation ability owing to the duple steric effect derived from the designed longer carbon chain and methine group. The electrolyte solvation structure rich in AGGs (97.96 %) enables remarkable CE of 99.71 % (25 °C) as well as high CE of 98.56 % even at −20 °C. Moreover, the lithium‐sulfur battery exhibits excellent performance in a wide temperature range (−20 to 50 °C) ascribed to the modified interphase rich in LiF/LiO2. Furthermore, the pouch cell delivers superior energy density of 344.4 Wh kg−1 and maintains 80 % capacity retention after 50 cycles. The novel solvent design via molecule chemistry provides alternative strategy to adjust solvation structure and thus favors high‐energy density lithium metal batteries.

Interphase Engineering via Solvent Molecule Chemistry for Stable Lithium Metal Batteries.

Lithium metal battery has been regarded as promising next-generation battery system aiming for higher energy density. However, the lithium metal anode suffers severe side-reaction and dendrite issues. Its electrochemical performance is significantly dependant on the electrolyte components and solvation structure. Herein, a series of fluorinated ethers are synthesized with weak-solvation ability owing to the duple steric effect derived from the designed longer carbon chain and methine group. The electrolyte solvation structure rich in AGGs (97.96 %) enables remarkable CE of 99.71 % (25 °C) as well as high CE of 98.56 % even at -20 °C. Moreover, the lithium-sulfur battery exhibits excellent performance in a wide temperature range (-20 to 50 °C) ascribed to the modified interphase rich in LiF/LiO2. Furthermore, the pouch cell delivers superior energy density of 344.4 Wh kg-1 and maintains 80 % capacity retention after 50 cycles. The novel solvent design via molecule chemistry provides alternative strategy to adjust solvation structure and thus favors high-energy density lithium metal batteries.

In-situ Construction of Poly(tetraisopentyl acrylate) based Gel Polymer Electrolytes with Lix La2-x TiO3 for High Energy Density Lithium-Metal Batteries.

As promising alternatives to liquid electrolytes, polymer electrolytes attract much research interest recently, but their widespread use is limited by the low ionic conductivity. In this study, we use electrostatic spinning to introduce particles of an ionic conductor into polyacrylonitrile (PAN) fibers to prepare a porous membrane as the host of gel polymer electrolytes (GPEs). The relevant in-situ produced GPE performs a high ionic conductivity of 6.0×10-3 S cm-1 , and a high lithium transfer number (tLi + ) of 0.85 at 30 °C, respectively. A symmetrical Li cell with this GPE can cycle stably for 550 h at a current density of 0.5 mA cm-2 . While the capacity retention of the NCM|GPE|Li cell is 79.84 % after 500 cycles at 2 C. Even with an increased cut-off voltage of 4.5 V, the 1st coulomb efficiency reaches 91.58 % with a specific discharge capacity of 213.4 mAh g-1 . This study provides a viable route for the practical application of high energy density lithium metal batteries.

Upgrading the Separators Integrated with Desolvation and Selective Deposition toward the Stable Lithium Metal Batteries.

A practical and effective approach to improve the cycle stability of high-energy density lithium metal batteries (LMBs) is to selectively regulate the growth of the lithium anode. The design of desolvation and lithiophilic structure have proved to be significant means to regulate the lithium deposition process. Here, a fluorinated polymer lithiophilic separator (LS) loaded with a metal-organic framework (MOF801) is designed, which facilitates the rapid transfer of Li+ within the separator owing to the MOF801-anchored PF6 - from the electrolyte, Li deposition is confined in the plane resulting from the polymer fiber layer rich in lithiophilic groups (C─F). The numerical simulation results confirm that LS induces a uniform electric field and Li+ concentration distribution. Visualization technology records the behavior of regular Li deposition in Li||Li and Li||Cu cells equipping LS. Therefore, LS exhibits an ultrahigh Li+ transference number (tLi + = 0.80) and a large exchange current density (j0 = 1.963mA cm-2). LS guarantees the stable operation of Li||Li cells for over 1000h. In addition, the LiNi0.8Co0.1Mn0.1O2||Li cell equipped with LS exhibits superior rate and cycle performances owing to the formation of LiF-rich robust SEI layers. This study provides a way forward for dendrite-free Li anodes from the perspective of separator engineering.

An Ultrathin Composite Polymer Electrolyte Dual-Reinforced by a Polymer of Intrinsic Microporosity (PIM-1) and Poly(tetrafluoroethylene) (PTFE) Porous Membrane.

The performances of solid-state polymer electrolytes are urgently required to be further improved for high energy density lithium metal batteries. Herein, a highly reinforced ultrathin composite polymer electrolyte (PLPP) is successfully fabricated in a large scale by densely filling the well-dispersed mixture of polyethylene oxide (PEO), Li-salt (LiTFSI) and a polymer of intrinsic microporosity (PIM-1) into porous poly(tetrafluoroethylene) (PTFE) matrix. Based on the macro-plus-micro synergistic enhancement of the PTFE with excellent mechanical properties and the soluble PIM-1 with suitable functional groups, the PLPP electrolyte exhibits excellent properties including mechanical stress, thermal stability, lithium-ion transference number, voltage window and ionic conductivity, which are all superior to the typical PEO/LiTFSI electrolytes. As a result, the Li/PLPP/Li symmetric cell can stably cycle for > 2000h, and the LiFePO4/PLPP/Li full cell exhibits excellent rate performance (>10 C) and high cycling stability with an initial capacity of 158.8 mAh g-1 and a capacity retention of 78.8% after 300 cycles. In addition, the excellent mechanical properties as well as the wide voltage window reasonably result in the stable operation of full cells with either high-loading cathode up to 28.1mg cm-2 or high voltage cathode with high energy density.

Understanding steric hindrance effect of solvent molecule in localized high-concentration electrolyte for lithium metal batteries

High energy density lithium metal batteries (LMBs) have garnered significant research interests in the past decades. However, the growth of lithium dendrites and the low Coulombic efficiency (CE) of Li metal anode pose significant challenges for the development of LMBs. Herein, we report a triethyl orthoformate (TEOF)-based localized high-concentration electrolyte (LHCE) that facilitates a highly reversible Li metal anode with dendrite-free deposition morphologies and an average Coulombic efficiency of 99.1% for 450 cycles. Mechanistic study reveal that the steric hindrance caused by the terminal ethyl groups in the TEOF solvent molecule results in a weak solvating ability, leading to the formation of anion-dominant solvation structures. The anion-dominant solvation sheaths play an essential role in the formation of a LiF-rich solid-electrolyte interphase (SEI), which effectively suppresses the growth of Li dendrites. Furthermore, the TEOF-based electrolyte demonstrates the stable cycling of high-voltage Li||NMC811 cells. These results provide insights into understanding of steric hindrance effect on electrolyte solvation structure and offer valuable guidance for the design of electrolyte solvents in the development of lithium metal batteries.

Accelerated ion transportation in liquid crystalline polymer networks for superior solid-state lithium metal batteries

The application of solid polymer electrolyte in high energy density lithium metal batteries is limited by low Li+ mobility, low ionic conductivity and poor cycle stability at room temperature. In the study, the free-standing flexible polymeric electrolytes (PCREs) with semi-interpenetrating-network in the topological nanostructures were fabricated through the in-situ UV-photopolymerization of the liquid crystalline monomers and poly(ethylene glycol) diglycidyl ether. Remarkably, by optimizing the relative proportion of the two liquid crystalline monomers with different methylene chains as connected bridge band between rigid center and terminal acrylate functional groups, the electrochemical properties of the prepared PCREs were successfully improved, which might contributed to the suitable ion transport channels in the porous polymer network structures. The prepared PCRE exhibited increased ion migration number, excellent ionic conductivity and a wide electrochemical window. Through the calculation of density functional theory and molecular dynamics simulation, the difference in the molecular orbital of liquid crystalline polymers and the mechanism of PCREs enhancement tLi+ were well understood. The study may provide new perspectives for the design and fabrication of high-performance polymer electrolyte materials, which will promote the development and practical application of the all-solid lithium metal batteries.

Preparation and electrochemical performance of ultra-thin reduced graphene oxide/lithium metal composite foils

Ultra-thin (≤50 μm) lithium metal anodes (LMAs) are highly desirable for high energy density lithium metal batteries (LMBs). However, their fabrication is complicated and costly due to the sticky and brittle nature of metallic Li, and they have a worse cycling stability than their thick counterparts. We report the fabrication of ultra-thin reduced graphene oxide/Li metal (rGO/Li) composite foils with thicknesses ranging from 10 to 50 μm. During the fabrication, disordered rGO sheets and molten metallic Li were stirred and combined at 200 ºC to produce micrometer-thick rGO/Li sheets, which were processed to form an ultra-thin uniform composite foil. The rGO sheets were randomly distributed in the rGO/Li composite to form a three-dimensional network, which is different from the laminated rGO structure previously reported, and supported stable Li plating/stripping behavior. As expected, a superior electrochemical performance was achieved using this composite sheet for the anode. A 50 μm-thick rGO/Li composite foil electrode displayed stable cycling for > 1 600 h at 1 mA cm−2 and 1 mAh cm−2 in symmetrical cells in an ether-based electrolyte. A full cell consisting of a 50 μm-thick rGO/Li composite foil anode and a sulfurized polyacrylonitrile cathode had a high capacity retention of 675 mAh g−1 after 220 cycles at 0.2 C.

Enhancing the performance of Ni-rich lithium metal batteries through the utilization of amine-functionalized 1D/3D nano shields and additives in high-voltage operation

The development of high-energy–density lithium metal batteries (LMB) is of paramount importance for various emerging energy storage applications, and high-voltage operating system based on high-capacity nickel-rich layer LiNixCoyMn1−x−yO2 (Ni-rich NCM, x ≥ 0.6) cathode combined with a Li metal anode is a representative promising solution. However, it is challenging to stabilize the lithium metal anodes with severe operating conditions, mainly because dissolved transition metal (TM) ions from the cathode trigger harmful side reactions, such as electrolytic decomposition and the growth of dendritic Li structures, resulting in serious safety hazards. In this study, we fabricated an ion-entrapping functional separator using amine-functionalized 1D or 3D inorganic particles confirmed by DFT calculation. Then, we applied in the Ni-rich LMB, demonstrating suppression of TM ion cross-over of 47% compared to conventional PE separators leading to improved cycle numbers and capacity retention at high-voltage operation. Further, combining functional additive introduction with the transition metal cross-over shielding separator resulted in synergistic ion capturing up to 84%. The results of this study provide new insights into the design of advanced LMB for high-energy–density.

The Interaction in Electrolyte Additives Accelerates Ion Transport to Achieve High-Energy Non-Aqueous Lithium Metal Batteries.

Electrolyte engineering is a feasible strategy to realize high energy density lithium metal batteries. However, stabilizing both lithium metal anodes and nickel-rich layered cathodes is extremely challenging. To break through this bottleneck, a dual-additives electrolyte containing fluoroethylene carbonate (10vol.%) and 1-methoxy-2-propylamine (1vol.%) in conventional LiPF6 -containing carbonate-based electrolyte is reported. The two additives can polymerize and thus generate dense and uniform LiF and Li3 N-containing interphases on both electrodes' surfaces. Such robust ionic conductive interphases not only prevent lithium dendrite formation in lithium metal anode but also suppress stress-corrosion cracking and phase transformation in nickel-rich layered cathode. The advanced electrolyte enables Li||LiNi0.8 Co0.1 Mn0.1 O2 stably cycle for 80 cycles at 60mAg-1 with a specific discharge capacity retention of 91.2% under harsh conditions.

Stannic oxide quantum dots constructed evenly alloyable layer stabilizing lithium metal batteries

Dendrite growth is still a problem that high energy density lithium metal batteries must face to commercialize. At present, the introduction of lithiophilic materials on the current collector has proved to be an effective strategy. However, most works are not conducive to the practical application of lithium metal batteries due to the neglect of the preparation cost and the excessive and uncontrollable modifier. Herein, stannic oxide (SnO2) quantum dots (QDs) were prepared by a simple dehydration reaction to construct a lithiophilic modification layer on the surface of copper foil. In addition, SnO2 QDs could induce uniform nucleation and growth of lithium ions at the quantum scale. More importantly, when the copper collector was modified by SnO2 QDs, the symmetric cell could cycle stably for 3200 h at a current density of 1 mA cm−2, which is better than other reports. LiFePO4 was employed as cathodic materials to fabricate a full battery, which delivered a capacity of 130.4 mAh g−1 with a capacity retention rate of 87.75% at 0.5 C for 200 cycles. Therefore, this work can be extended to practical applications, and help lithium metal batteries to be industrialized.

A new fluorine-containing sulfone-based electrolyte for advanced performance lithium metal batteries

Lithium dendrite growth greatly limits the application of lithium metal batteries. Herein, a new fluorine-containing sulfone-based electrolyte is proposed for lithium metal batteries. Benefiting from the synergistic effect of lithium bis(fluorosulfonyl)imide (LiFSI) and fluoroethylene carbonate (FEC), a LiF-rich stable SEI with compact and uniform morphology is formed on lithium metal anode, suppressing the Li dendrite formation and enhance the cycling life. In Li||Cu half-battery, a remarkable Coulombic efficiency of 95.9 % within 130 cycles and 93.5 % within 100 cycles are realized at 0.5 mA·cm−2 and 1 mA·cm−2, respectively. In Li||Li symmetric battery, the cycling life is about 480 h at 1.0 mA·cm−2 which is double as the commercial electrolyte. Moreover, in Li||LiFePO4 battery, a significantly improved capacity retention of 94.3 % with a high average Coulombic efficiency of 99.8 % after 100 cycles is achieved at 0.5C. The designed new fluorine-containing sulfone-based electrolyte provides new strategy toward high energy density lithium metal batteries.