High-energy Lithium Metal Batteries Research Articles

Accurately constituting robust interfaces for high-performance high-energy lithium metal batteries.

High-energy lithium metal batteries (LMBs) have received ever-increasing interest. Among them, coupling lithium metal (Li) with nickel-rich material, LiNixMnyCozO2 (NMCs, x ≥ 0.6, x + y + z = 1), is promising because Li anodes enable an extremely high capacity (∼3860 mA h g-1) and the lowest redox potential (-3.04 V vs. standard hydrogen electrode), while NMCs can achieve a much higher capacity of ∼200 mA h g-1 and lower cost than those of LiCoO2. However, the resultant Li‖NMC cells have been hindered from commercialization due to a series of challenges related to the interface stability of both Li anodes and NMC cathodes. Specifically, Li anodes suffer from Li dendritic growth and the formation of solid electrolyte interphase (SEI), while NMC cathodes suffer from the formation of cathode electrolyte interphase (CEI) and other interface-related issues, including transition metal dissolution, oxygen release, cracking, and so on. To tackle these issues, recently, two sister techniques, atomic and molecular layer deposition (ALD and MLD), have emerged and exhibit tremendous capabilities to accurately constitute robust interfaces to achieve high-performance Li‖NMC LMBs. They can uniquely develop uniform and conformal films as surface coatings of LMBs in a precisely controllable mode at the atomic/molecular level, while proceeding with film deposition at low temperatures (e.g., ≤250 °C). In this Feature Article, we review the latest research progress in developing novel surface coatings via ALD and MLD for Li‖NMC LMBs and discuss outcomes for pursuing high performance.

Enhancing the Stability of Lithium Metal Batteries with the Polydopamine-Coated Insulating Scaffold

Lithium metal is the most promising candidate for a high-capacity anode material in Li-ion batteries owing to its high theoretical theoretical capacity (3,860 mAh g-1) and the lowest redox potential (-3.04 V vs S.H.E.).[1] Despite these advantages, the practical application of Li metal anodes (LMAs) is hindered by a number of significant challenges. For instance, LMAs tend to form non-uniform dendrite, continuous dead Li growth, and infinite volume expansion.[2] These issues result in short circuits and continuous consumption of the active material, consequently lowering the Coulombic efficiency (CE) and cycling stability of LMAs.Using a 3D scaffold in the anode is an effective method for to address the issue of infinite volume expansion. The porous structure of the 3D scaffold provides ample space to accommodate Li metal.[3] Among them, electrically insulating scaffolds that do not support electron transport not only promote bottom-up Li deposition behavior but also minimize side reactions between the electrolyte and the scaffold. However, a high current density can lead to the formation of dendritic Li, which can make it challenging to achieve uniform and dense lithium growth on the surface during repeated plating/stripping processes. Therefore, the use of an insulating scaffold requires the introduction of functionalized materials to suppress dendritic formation of Li metal.Furthermore, to achieve further improvements, some studies have investigated the incorporation of polar functional groups into the insulating 3D structure.[4] Notably, these polar functional groups possess the capability to establish strong interactions with Li ions, which can facilitate the uniform distribution of these ions and prevent dendrite formation.[5] In this study, we utilized polydopamine (PDA) which contains polar functional groups such as O-H and N-H2, on a 3D insulating scaffold. These polar functional groups promote increased ionic conductivity and uniform deposition of Li ions by interacting with Li ions through Columbic forces.[6] Consequently, we expected that the advantageous properties of PDA would enhance the charge transfer reaction rate and cycling stability of LMBs.In this study, we aimed to introduce the utilization of a 3D polytetrafluoroethylene (PTFE) scaffold coated with PDA to achieve highly stable and high-energy LMBs. The insulating nature of the PTFE scaffold is expected to facilitate the "bottom-up" formation of Li deposition, while the PDA coating attracts Li ions, enabling homogenization of the Li-ion distribution and uniform growth of Li (Figure 1a). This design aims to simultaneously achieve both high energy density and improved cyclic stability in LMB full cells using our 3D scaffold.To elucidate the enhanced performance of the Lithium Metal Batteries (LMBs) equipped with PDA-coated 3D PTFE scaffold (PD-3P), we conducted a comparative study, including bare Cu foil and the 3D PTFE scaffold (3P) as control groups. Specifically, when tested at a high current density of 1 C with a 3.2 mAh cm-2 NCM, the PD-3P scaffold-based full cell exhibited a stable discharge capacity (Figure 1b).

A Physical Approach to Practical Applications of Lithium Metal Anode Using High-Flatness Cu Mesh Inducing Epitaxial Li Plating for All Solid-State Battery

Lithium metal batteries (LMBs) have been highlighted as next-generation energy storage systems due to their high energy density. However, dead Li and dendritic Li, induced by the large volume change of Li and inhomogeneous Li+ flux during Li plating/stripping, hinder the practical application of the LMBs. Especially, the copper foil, which serves as a two-dimensional substrate, increases the local current density and forms sharp Li nuclei due to its poor lithiophilicity. Furthermore, spatially varying surface kinetics induce repetitive volume expansion, resulting in the rupture of the solid electrolyte interface and reduced battery cycle stability. Therefore, numerous papers introduced 3D hosts (mesh, foam, gauze, and coil) to induce the dense Li deposition via reducing the local current density. In addition, the mechanically stable and spacious structure of 3D hosts easily accommodates the internal stress fluctuation and homogenizes spatially varying surface kinetics. Although these strategies effectively increase the safety and lifespan of LMBs, they are still impractical due to the large thickness and the long manufacturing time of the 3D-hosted lithium metal anode (LMA).Herein, we report a facile physical approach to the fast fabrication of thin and lightweight 3D LMAs with ultralong cycle stability. The pressed Cu mesh (PCM) using a simple roll-pressing process could be fabricated speed of 0.2 m2 min− 1 and easy to scale up. In particular, the shape of the Cu wire had been modified from round to flat to enhance the lithiophicity. Therefore, the PCM uniformly coated with molten lithium (PCM-Li) achieved a thickness of 38 μm and a light weight of 11.9 mg cm−2. In symmetrical cell evaluation under 1mAh cm− 2@1mA cm− 2, the PCM-Li showed an ultrastable overpotential of 9.6 mV over 1,000 cycles. Furthermore, the PCM-Li maintained stable voltage behavior for more than 600 h even under 5mAh cm−2@5mA cm−2. Interestingly, in the SEM image of the PCM-Li after 1,000 cycles, no mossy or dendritic Li was observed, as Li was epitaxially plated along the flat Cu wires. Finally, we assembled a 1-Ah-scale high-energy LMB (351 Wh kg− 1) with the PCM-Li anodes and dry-coated NCM811 cathodes to demonstrate practical application. The LMB using the PCM-Li represented excellent practicality showing capacity retention of 80% during 200 cycles. This facile physical approach is helpful to the commercialization of next-generation lithium-based batteries and broadens the scope for subsequent research, such as lithiophilic materials coating for anode-free batteries. Figure 1

Advancements in Thin Solid-State Electrolytes for High-Energy Lithium Metal Batteries

ABSTRACT In the next generation of lithium-ion batteries (LIBs) utilizing lithium metal as the anode material, a theoretical capacity of 3860 mAh·g-1 can be expected [1]. However, several challenges such as safety issues due to lithium dendrite diffusion during charge-discharge cycling still remain unresolved [2]. The penetration of lithium dendrites remains a concern in traditional solution-based LIBs [3]. As an alternative approach to address the challenges of LIBs, solid-state electrolytes (SSEs) with high ionic conductivity and lithium metal stability have garnered attention [4]. The SSE category includes polymer electrolytes, inorganic sulfide electrolytes, and inorganic oxide electrolytes [5]. Among SSEs, garnet-type Li7La3Zr2O7 (LLZO), is a promising candidate due to its high ionic conductivity within the range of 10- 4 to 10- 3 S∙cm- 1 as well as its thermodynamics reduction stability against Li metal [6, 7].The introduction of SSB oxide electrolytes would improve packing density and could potentially lead to batteries with negligible self-discharge and longer lifespan of over 104 cycles [8]. During cell operation, solid electrolytes should be mechanically robust and as thin as possible to maximize the valuable volume remaining for the electrodes in SSB cell designs [9]. To compete with the approximately 20μm-thick polymer separators in traditional LIBs, ceramic manufacturing strategies for SSB electrolytes are necessary [10]. Recent estimations suggest that assuming a 25μm-thick solid electrolyte, a lithium metal SSB pouch cell could offer an energy density of 350Wh/kg [11]. In our study, we achieved ultra-thin electrolytes via tape-casting technique into Li-metal battery system. Li symmetric cells based on the ultra-thin electrolyte show exceptional low bulk resistance, attributed to extremely thin electrolyte. Moreover, symmetrical Li cell maintains steady Li plating/stripping cycles for long duration. Keywords: Lithium-ion batteries, LLZTO, thick solid electrolyte References [1] J. M. Tarascon, M. Armand, Nat., 414, (2001) 359-367.[2] J. Qian, W. A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin, J. G. Zhang, Nat Commun., 6, (2015) 6362.[3] Y. Guo, H. Li, T. Zhai, Adv. Mater., 29, (2017) 29.[4] J. Janek, W. G. Zeier, Nat. Energy., 1, (2016) 16141.[5] L. J. Miara, S. P. Ong, Y. Mo, W. D. Richards, Y. Park, J. M. Lee, H. S. Lee, G. Ceder, Chem. Mater., 25, (2013) 3048-3055.[6] L. J. Miara, S. P. Ong, Y. Mo, W. D. Richards, Y. Park, J. M. Lee, H. S. Lee, G. Ceder, Chem. Mater., 25, (2013) 3048-3055.[7] Y. Zhu, X. He, Y. Mo, ACS Appl. Mater. Interfaces, 7, (2015) 23685-23693.[8] T. Mageto, S. D. Bhoyate, F. M. de Souza, K. Mensah-Darkwa, A. Kumar, R. K. Gupta, J. Energy Storage, 55, (2022) 105688.[9] M. Balaish, J. C. Gonzalez-Rosillo, K. J. Kim, Y. Zhu, Z. D. Hood, J. L. M. Rupp, Nat. Energy, 6, (2021), 227–239.[10] L. Li, Y. Dian, Polymers, 15, (2023) 3690.[11] X. Wu, K. Pan, M. Jia, Y. Ren, H. He, L. Zhang, S. J. Zhang, GEE, 4, (2019) 360-374.

Unveiling the Role of Filler Characteristics in Enhancing the High-Voltage Performance of Succinonitrile-Based Solid-State Lithium-Metal Batteries.

For exploiting high-energy lithium-metal batteries, it is of utmost importance to develop electrolytes that possess exceptional ionic conductivity and an extensive electrochemical stability range. In this study, 3D PAN nanofibers and polymer electrolytes incorporating various inorganic fillers with different Lewis acid-base properties were fabricated. PAN@Al-SSE exhibits exceptional ionic conductivity (0.48 mS·cm-2 at room temperature), a high Li+ transference number (0.41), and a wide electrochemical window (5.26 V). The device is able to operate stably in Li symmetric cells for more than 1000 h under a potential of 0.03 V under a current density of 0.2 mA·cm-2. Besides, the groundbreaking technology equips high-voltage Li-LiCoO2 solid-state batteries with exceptional cycling performance (91.3% and 82.1% retention after 100 cycles at 0.2 and 1 C, respectively) at room temperature. Mechanistic studies indicate that the Lewis acid-base properties of surface fillers are instrumental and crucial to form a stable solid-electrolyte interphase layer. γ-Al2O3, in particular, with more Lewis acid sites, ensures the dissociation of LiTFSI and induces the excessive decomposition and polymerization of succinonitrile. There exists an equilibrium effect between dissociation and polymerization in a succinonitrile-based solid electrolyte, which plays a critical role in improving the manifestation of succinonitrile-based solid-state lithium cells, especially under high-voltage conditions.

Phosphorized 3D Current Collector for High-Energy Anode-Free Lithium Metal Batteries.

The anode-free lithium metal battery (AF-LMB) demonstrates the emerging battery chemistry, exhibiting higher energy density than the existing lithium-ion battery and conventional LMB empirically. A systematic step-by-step while bottom-up calculation system is first developed to quantitatively depict the energy gap from theory to practice. The attainable high energy of AF-LMB necessitates a homogeneous Li+ flux on the anode side to achieve an improved Li reversibility against inventory loss. On such basis, a lithiophilic Cu3P-decorated 3D copper foil to promote dendrite-free lithium deposition is further reported. The phosphorized surface of high affinity toward Li+ incorporating the nanostructure of abundant nucleation sites synergistically regulates the Li nucleation/growth behavior, extending the cycling lifespan of high-loading AF-LMBs. The processed foil featuring lightweight and ultrathin merits further increases the energy density, both gravimetrically and volumetrically. This study provides a novel scheme for simultaneously realizing the uniform deposition of lithium and increasing the energy density of future AF-LMBs.

In-Situ Polymerized High-Voltage Solid-State Lithium Metal Batteries with Dual-Reinforced Stable Interfaces.

Solid polymer electrolytes (SPEs) represent a pivotal advance toward high-energy solid-state lithium metal batteries. However, inadequate interfacial contact remains a significant bottleneck, impeding scalability and application. Inadequate interfacial contact remains a significant bottleneck, impeding scalability and application. Recent efforts have focused on transforming liquid/solid interfaces into solid/solid ones through in situ polymerization, which shows potential especially in reducing interface impedance. Here, we designed high-voltage SSLMBs with dual-reinforced stable interfaces by combining interface modification with an in situ polymerization technology inspired by targeted effects in medicine. Theoretical calculations and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis demonstrate that tetramethylene sulfone (TMS) and bis(2,2,2-trifluoromethyl) carbonate (TFEC) exhibit selective adsorption at the interface of the LiNi0.8Co0.1Mn0.1O2 (NCM) cathode and Li anode, respectively. These compounds further decompose to form a stable cathode-electrolyte interface (CEI) film and a solid electrolyte interface (SEI) film, thereby simultaneously achieving a superior interface between the SPE and both the Li anode and NCM cathode. The developed Li||SPE||Li cell sustained cycling for more than 1000 h at 0.3 mA cm-2, and the NCM||SPE||Li cell also demonstrated an excellent capacity retention of 86.8% after 1000 cycles at 1 °C. This work will provide valuable insights for the rational design of high-voltage SSLMBs with stable interfaces, leveraging in situ polymerization as a cornerstone technology.

Seeding and Growing Plain Li-Metal Surfaces - New Approaches to Increase the Coulombic Efficiency of Anodeless Lithium-Metal Batteries

In the pursuit of higher energy densities, lithium-ion batteries with lithium metal anode appear as one particular promising technology. Especially the option to plate non-dendritic, superficially even Li-layers [1] directly onto the current collector of the negative electrode without the use of an anode active material (“anode-less battery design”) should enable gravimetric energy densities of up to 400 Wh/kg [2] and 1200 Wh/l [3] in future cell systems [4].In the presented work, Swagelok-cells in “anode-less” configuration, comprising a NMC 811-cathode and an ether-based electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1,2-dimethoxyethane (DME) in 1.2:3 molar ratio, 1.5 M LiFSI [2] were cycled under the application of pressure (up to 400 kPa) onto the cell stack.As the proper formation of Li-nuclei (number, morphology, etc.) and the even growth of lithium-layers onto the Cu-based anode (Figure 1) seems from great importance to plate and stripe Li-metal at high coulombic efficiencies, several charging programs with presumably Li-nucleation promoting effects were tested in a cycling experiment along 50 full cycles (Figure 2). As a promising result and as clear improvement compared to standard charging processes (e.g. 0.1 C), average coulombic efficiencies as high as 99.2 % together with low capacity fading were observed.Due to the design-related limitation of Swagelok-based cells and a noticeable diffusion of air fractions (N2, O2, H2O) across the PFA-seals into the cell, in a second experimental part the influence of ambient air on the cycling performance was tested under three conditions (Figure 2, left, middle and right diagram): a) Cells cycling in common (humid), laboratory air, b) under dry air (P2O5) in sealed steel-containers and c) inside an argon filled glovebox (< 0.1 ppm H2O, < 0.1 ppm O2). As a result, a strong sensitivity of operating Li-metal cells not solely versus traces of ambient, humid air, but also versus P2O5-dried nitrogen and oxygen was obvious. Reference s [1] Fang, C.; Lu, B.; Pawar, G.; Zhang, M.; Cheng, D.; Chen, S.; Ceja, M.; Doux, J.-M.; Musrock, H.; Cai, M.; Liaw, B.; Meng, Y. S., Pressure-tailored lithium deposition and dissolution in lithium metal batteries. Nature Energy 2021, 6, (10), 987-994.[2] Niu, C.; Liu, D.; Lochala, J. A.; Anderson, C. S.; Cao, X.; Gross, M. E.; Xu, W.; Zhang, J.-G.; Whittingham, M. S.; Xiao, J.; Liu, J., Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. Nature Energy 2021, 6, (7), 723-732.[3] Louli, A. J.; Eldesoky, A.; Weber, R.; Genovese, M.; Coon, M.; deGooyer, J.; Deng, Z.; White, R. T.; Lee, J.; Rodgers, T.; Petibon, R.; Hy, S.; Cheng, S. J. H.; Dahn, J. R., Diagnosing and correcting anode-free cell failure via electrolyte and morphological analysis. Nature Energy 2020, 5, (9), 693-702.[4] Li, Q.; Yang, Y.; Yu, X.; Li, H., A 700 W⋅h⋅kg−1 Rechargeable Pouch Type Lithium Battery. Chinese Physics Letters 2023, 40, (4), 048201. Figure 1

Lightweight Electrolyte Design for Li/Sulfurized Polyacrylonitrile (SPAN) Batteries.

Sulfurized polyacrylonitrile (SPAN) recently emergesas a promising cathode for high-energy lithium (Li) metal batteries owing to its high capacity, extended cycle life, and liberty from costly transition metals. As the high capacities of both Li metal and SPAN lead to relatively small electrode weights, the weight and specific energy density of Li/SPAN batteries are particularly sensitive to electrolyte weight, highlighting the importance of minimizing electrolyte density. Besides, the large volume changes of Li metal anode and SPAN cathode require inorganic-rich interphases that can guarantee intactness and protectivity throughout long cycles. This work addresses these crucial aspects with an electrolyte design where lightweight dibutyl ether (DBE) is used as adiluent for concentrated lithium bis(fluorosulfonyl)imide(LiFSI)-triethyl phosphate (TEP) solution. The designed electrolyte (d = 1.04g mL-1) is 40%-50% lighter than conventional localized high-concentration electrolytes (LHCEs), leading to 12%-20% extra energy density at the cell level. Besides, the use of DBE introduces substantial solvent-diluent affinity, resulting in a unique solvation structure with strengthened capability to form favorable anion-derived inorganic-rich interphases, minimize electrolyte consumption, and improve cell cyclability. The electrolyte also exhibits low volatility and offers good protection to both Li metal anode and SPAN cathode under thermal abuse.

Unveiling the role of fluorinated interface on anionic redox chemistry in Li-rich layered oxide cathode materials towards high-energy Li metal batteries

The utilization of Lithium-rich materials (LR) with oxygen anionic redox (OAR) activity as cathode materials in Li metal batteries has gradually emerged as a prevailing trend in designing high-specific energy batteries. However, the interface design of LR and its influence mechanism on anionic redox chemistry are still ambiguous. Herein, in-situ interface engineering with an LiF-rich cathode-electrolyte interface (CEI) using all-fluorinated electrolyte was proposed and the role of the CEI on OAR was clarified. The shielding effect on high-valence oxygen ions is revealed that the dense, uniform, thin, and robust LiF-rich CEI protects high-valence oxygen ions from the electrolyte, inhibits electrolyte decomposition and interface thickening, and ameliorates structural degradation and oxygen loss of LR. And a more critical effect of CEI on the OAR process is demonstrated that the LiF-rich CEI layer prevents molecular oxygen in the bulk from escaping into the electrolyte as O2 gas and makes the oxidized oxygen exists more in the form of peroxo-like oxygen dimer O2n−. Besides the stabilization of OAR in the cathode side, the all-fluorinated electrolyte along with its enhancement in the Li anode enable high safety, excellent cycling stability, and fast charging performance for high energy lithium metal batteries.

A new ionic liquid-based electrolyte with both high conductivity and electrochemical stability

Ionic liquids with non-flammability and wide electrochemical window are the promising candidates for the next-generation high-energy lithium metal batteries (LMBs). However, their high viscosity and low ionic conductivity lead to a limited cycling performance, hindering their commercial application. Herein, a new ionic liquid-based electrolyte (ILE) composed of lithium bis(fluorosulfonyl)imide (LiFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI), ethyl methyl carbonate (EMC) and fluorinated ethylene carbonate (FEC) is designed to address this barrier. The new ILE exhibits high conductivity, which is twice that of pure ILE. In addition, FEC that is weakly coordinated to Li+ increases the combination between Li+ and FSI− indirectly, inducing a deeper co-decomposition of FSI− and FEC, thereby leading to a construction of LiF-rich solid electrolyte interphase (SEI). Consequently, Li/Cu battery maintains a higher lithium stripping/plating Coulombic efficiency (CE) of 96.3 % at 250 cycles and Li/LiFePO4 battery reaches a 93.2 % capacity retention at 150 cycles with an average CE of 99.8 %. The designed ILE with both high conductivity and electrochemical stability opens up a new insight for the rational design of electrolytes applied in next-generation LMBs.

Intrinsically Safe Lithium Metal Batteries Enabled by Thermo-Electrochemical Compatible In Situ Polymerized Solid-State Electrolytes.

In situ polymerized solid-state electrolytes have attracted much attention due to high Li-ion conductivity, conformal interface contact, and low interface resistance, but are plagued by lithium dendrite, interface degradation, and inferior thermal stability, which thereby leads to limited lifespan and severe safety hazards for high-energy lithium metal batteries (LMBs). Herein, an in situ polymerized electrolyte is proposed by copolymerization of 1,3-dioxolane with 1,3,5-tri glycidyl isocyanurate (TGIC) as a cross-linking agent, which realizes a synergy of battery thermal safety and interface compatibility with Li anode. Functional TGIC enhances the electrolyte polymeric level. The unique carbon-formation mechanism facilitates flame retardancy and eliminates the battery fire risk. In the meantime, TGIC-derived inorganic-rich interphase inhibits interface side reactions and promotes uniform Li plating. Intrinsically safe LMBs with nonflammability and outstanding electrochemical performances under extreme temperatures (130°C) are achieved. This functional polymer design shows a promising prospect for the development of safe LMBs.

Mechanothermal-milling-assisted removal of native passivation layer for refreshing lithium metal anodes

Securing the stable and reliable operation of high-energy lithium (Li) metal batteries (LMBs) is crucial for fundamental studies and practical applications. However, commercial Li metal anodes (LMAs) suffer from unreliable pre-passivation during vendor-specific manufacturing, which deteriorates their surface quality and compromises the reproducibility of novel post-treatments and new electrolytes. To avoid chemical and structural degradation originating from the initial LMA, this study presents a mechanothermal milling (MTM) method using heating blades to smoothly peel off the native passivation layer (NPL) on the LMA surface, thereby exposing near-fresh Li. Compared to as-received LMA, the LMA revitalized by the MTM process (MTM-Li) exhibited faster kinetics and less interfacial resistance, promoting spatially uniform, dendrite-less Li plating and pit-less Li stripping. The MTM-guided surface equalization of the LMA enables an accurate comparison of the electrolyte-derived SEI properties, which is essential for identifying an electrolyte that is genuinely compatible with freshly exposed Li. By combining it with highly stable electrolytes, MTM-Li can regulate the structural evolution of LMAs, effectively securing cycling stability for LMBs, even under stringent conditions.

A novel polymeric lithicone coating for superior lithium metal anodes

Lithium metal (Li) is commonly regarded as the “holy grail” of rechargeable batteries and can serve as anodes for constituting various high-energy lithium metal batteries (LMBs). However, it suffers from two notorious issues: (1) continuous formation of inhomogeneous solid electrolyte interphase and (2) Li dendritic growth. In this study, we developed a novel polymeric lithicone via a new molecular layer deposition (MLD) process, using lithium tert-butoxide (LTB) and hydroquinone (HQ) as precursors. We revealed that such an MLD process enabled the resultant LiHQ to grow linearly in a highly controllable and cyclic mode at a growth rate of 4 Å cycle−1. Furthermore, its low process deposition temperature of 150 °C made it possible to practice high-quality coatings over Li anodes directly. We demonstrated that, very compellingly, this LiHQ coating could protect Li anodes from corrosion and dendritic growth. As a consequence, this LiHQ coating has enabled Li||Li symmetric cells an extremely long cyclability up to 8000 Li-plating/stripping cycles without failure. More excitingly, we demonstrated that, coupled with LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes, the LiHQ-modified Li anodes could help the resultant Li||NMC811 realize a much better capacity retention and much longer cyclability. Thus, this study represents a strategic route for developing commercializeable LMBs.

Hybridizing carbonate and ether at molecular scales for high-energy and high-safety lithium metal batteries

Commonly-used ether and carbonate electrolytes show distinct advantages in active lithium-metal anode and high-voltage cathode, respectively. While these complementary characteristics hold promise for energy-dense lithium metal batteries, such synergy cannot be realized solely through physical blending. Herein, a linear functionalized solvent, bis(2-methoxyethyl) carbonate (BMC), is conceived by intramolecularly hybridizing ethers and carbonates. The integration of the electron-donating ether group with the electron-withdrawing carbonate group can rationalizes the charge distribution, imparting BMC with notable oxidative/reductive stability and relatively weak solvation ability. Furthermore, BMC also offers advantages including the ability to slightly dissolve LiNO3, excellent thermostability and nonflammability. Consequently, the optimized BMC-based electrolyte, even with typical concentrations in the single solvent, demonstrates high-voltage tolerance (4.4 V) and impressive Li plating/stripping Coulombic efficiency (99.4%). Moreover, it fulfills practical lithium metal batteries with satisfactory cycling performance and exceptional tolerance towards thermal/mechanical abuse, showcasing its suitability for safe high-energy lithium metal batteries.

Lithium Superionic Conductive Nanofiber-Reinforcing High-Performance Polymer Electrolytes for Solid-State Batteries.

Although composite solid-state electrolytes (CSEs) are considered promising ionic conductors for high-energy lithium metal batteries, their unsatisfactory ionic conductivity, low mechanical strength, poor thermal stability, and narrow voltage window limit their practical applications. We have prepared a new lithium superionic conductor (Li-HA-F) with an ultralong nanofiber structure and ultrahigh room-temperature ionic conductivity (12.6 mS cm-1). When it is directly coupled with a typical poly(ethylene oxide)-based solid electrolyte, the Li-HA-F nanofibers endow the resulting CSE with high ionic conductivity (4.0 × 10-4 S cm-1 at 30 °C), large Li+ transference number (0.66), and wide voltage window (5.2 V). Detailed experiments and theoretical calculations reveal that Li-HA-F supplies continuous dual-conductive pathways and results in stable LiF-rich interfaces, leading to its excellent performance. Moreover, the Li-HA-F nanofiber-reinforced CSE exhibits good heat/flame resistance and flexibility, with a high breaking strength (9.66 MPa). As a result, the Li/Li half cells fabricated with the Li-HA-F CSE exhibit good stability over 2000 h with a high critical current density of 1.4 mA cm-2. Furthermore, the LiFePO4/Li-HA-F CSE/Li and LiNi0.8Co0.1Mn0.1O2/Li-HA-F CSE/Li solid-state batteries deliver high reversible capacities over a wide temperature range with a good cycling performance.

A Triply-Periodic-Minimal-Surface Structured Interphase based on Fluorinated Polymers Strengthening High-energy Lithium Metal Batteries.

The challenge of constructing a mechanically robust yet lightweight artificial solid-electrolyte interphase layer on lithium (Li) anodes highlights a trade-off between high battery safety and high energy density. Inspired by the intricate microstructure of the white sea urchin, we first develop a polyvinyl fluoride-hexafluoropropylene (PVDF-HFP) interfacial layer with a triple periodic minimal surface structure (TPMS) that could offer maximal modulus with minimal weight. This design endows high mechanical strength to an ordered porous structure, effectively reduces local current density, polarization, and internal resistance, and stabilizes the anode interface. At a low N/P ratio of ~3, using LiFePO4 as the cathode, Li anodes protected by TPMS-structured PVDF-HFP achieve an extremely low capacity-fading-rate of approximately 0.002 % per cycle over 200 cycles at 1 C, with an average discharge capacity of 142 mAh g-1. Meanwhile, the TPMS porous structure saves 50 wt % of the interfacial layer mass, thereby enhancing the energy density of the battery. The TPMS structure is conducive to large-scale additive manufacturing, which will provide a reference for the future development of lightweight, high-energy-density secondary batteries.

Wide-Temperature and High-Rate Operation of Lithium Metal Batteries Enabled by an Ionic Liquid Functionalized Quasi-Solid-State Electrolyte.

The development of high-energy-density solid-state lithium metal battery has been hindered by the unstable cycling of Ni-rich cathodes at high rate and limited wide-temperatures adoptability. In this study, an ionic liquid functionalized quasi-solid-state electrolyte (FQSE) is prepared to address these challenges. The FQSE features a semi-immobilized ionic liquid capable of anchoring solvent molecules through electrostatic interactions, which facilitates Li+ desolvation and reduces deleterious solvent-cathode reactions. The FQSE exhibits impressive electrochemical characteristics, including high ionic conductivity (1.9mScm-1 at 30°C and 0.2mScm-1 at -30°C) and a Li+ transfer number of 0.7. Consequently, Li/NCM811 cells incorporating FQSE demonstrate exceptional stability during high-rate cycling, enduring 700 cycles at 1 C. Notably, the Li/LFP cells with FQSE maintain high capacity across a wide temperature range, from -30 to 60°C. This research provides a new way to promote the practical application of high-energy lithium metal batteries.

Pendulum-swing coordination boosting “liquid-like” Li-ion conduction within asymmetric lamellar fillers for solid polymer electrolytes

Solid polymer electrolytes have shown great prospect in high-energy lithium-metal batteries, yet the most critical challenge is their unsatisfactory ionic conductivity. A common strategy involves the incorporation of symmetric lamellar fillers with ions/molecules fixed in interlayers. However, because of strong fixation, it sacrifices “liquid-like” flow properties as small-molecular solvents in polymer matrices. Herein, a novel concept of pendulum-swing coordination within interlayers is proposed to integrate advantages from both scenarios, based on the design of one-side fixation of solvents in asymmetric lamellar fillers. This delicate modulation of the coordination environment ensures the weakened Li+-solvent interaction and the strengthened anion-cation dissociation of lithium salts. More importantly, it enhances dynamic motion of the “hanged” solvents in highly-confined space, activating “liquid-like” Li-ion conduction. Meanwhile, the confined solvent does not plasticize polymer matrices, thus excellent mechanical property maintains. As a result, the developed electrolyte exhibits an impressive ionic conductivity of 1.35 × 10−4 S/cm at room temperature and exceptional anodic stability with stable Li stripping/platting cycles for over 2000 h. Solid-state Li-LiFePO4 batteries exhibit good rate behavior and remarkable capacity retention of 85.4% after 400 cycles at 0.5C. This work provides enlightening ideas for continuous development of high-performance polymer electrolytes towards real applications of lithium-metal batteries.

Electrolyte design combining fluoro- with cyano-substitution solvents for anode-free Li metal batteries

Fluoro-substitution solvents have achieved great success in electrolyte engineering for high-energy lithium metal batteries, which, however, is beset by low solvating power, thermal and chemical instability, and possible battery swelling. Instead, we herein introduce cyanogen as the electron-withdrawing group to enhance the oxidative stability of ether solvents, in which cyanogen and ether oxygen form the chelating structure with Li+ not notably undermining the solvating power. Cyano-group strongly bonds with transition metals (TMs) of NCM811 cathode to attenuate the catalytic reactivity of TMs toward bulk electrolytes. Besides, a stable and uniform cathode-electrolyte interphase (CEI) inhibits the violent oxidation decomposition of electrolytes and guarantees the structural integrity of the NCM811 cathode. Also, a N-containing and LiF-rich solid-electrolyte interphase (SEI) in our electrolyte facilitates fast Li+ migration and dense Li deposition. Accordingly, our electrolyte enables a stable cycle of Li metal anode with Coulombic efficiency of 98.4% within 100 cycles. 81.8% capacity of 4.3 V NCM811 cathode remains after 200 cycles. Anode-free pouch cells with a capacity of 125 mAh maintain 76% capacity after 100 cycles, corresponding to an energy density of 397.5 Wh kg-1.