High-energy Lithium Metal Batteries Research Articles

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.

Novel Current Collector for High Energy Density Lithium-Metal Batteries

The energy density of lithium-metal batteries (LMBs) relies to a substantial fraction on the thickness of the lithium-metal anode.1,2 Additionally, the commonly used copper current collector adds a significant mass to the electrode weight (e.g., 77% when considering a 50 μm thick lithium and 10 μm thick copper), but the thinner the lithium foil, the more important becomes the current collector to provide suitable mechanical properties and ensure a good electronic contact across the whole negative electrode.Herein, we report the design of a novel current collector (patent application pending) that enables a substantial reduction in mass, while providing high electronic conductivity and suitable mechanical properties. Moreover, LMBs with a thin lithium foil and a Ni-rich NMC cathode comprising such new current collector reveal a superior performance compared to those containing a standard copper foil. References 1 Liu, J. et al. Pathways for practical high-energy long-cycling lithium metal batteries. Nat. Energy 4, 180-186, (2019).2 Niu, C. et al. Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. Nat. Energy, 6, 723–732, (2021).

External Pressure Affecting Dendrite Growth and Dissolution in Lithium Metal Batteries During Cycles.

Lithium (Li) metal has garnered significant attention as the preferred anode for high-energy lithium metal batteries. However, safety concerns arising from the growth of Li dendrites have hindered the advancement of Li metal batteries. In this study, we first elucidate the impact of external pressure and internal stress on dendrite growth and dissolution behavior of Li metal batteries during continuous charging-discharging cycles, employing a developed electrochemomechanical phase-field model. A typical parameter is defined to calculate the amount of dead Li that affects the electrochemical performance of Li metal batteries during multiple cycles. The underlying mechanisms of dendrites observed from in situ experiments are explained through the developed phase-field model. After charging/discharging, dendrites with a treelike structure yield a greater amount of dead Li compared to those with a needlelike configuration. Increasing the pressure appropriately can effectively reduce the growth points of dendrites and suppress the Li dendrite growth. Excessive pressure not only induces dendritic fractures that lead to the formation of dead Li but also undermines the battery performance. The accumulated internal stress might threaten the structural stability of the Li metal, thereby influencing the evolution of the Li dendrite morphology. A reasonable strategy is proposed to strike a balance between external pressure and the growth and dissolution of Li dendrites. These findings offer valuable insights into the judicious application of pressure to mitigate the advancement of electroplating reactions.

Surface modified by SnI2 boosts Dendrite-Free all-solid-state lithium metal batteries

Lithium metal is the most promising next-generation anode due to its extremely high theoretical specific capacity and lowest operation potential. However, the high reactivity of lithium brings about a series of side reactions and fast capacity decay. Moreover, the inevitably growth of lithium dendrite will cause short circuit or other safety issues. Here, an artificial mixed ionic/electronic SEI (solid electrolyte interphase) is designed by treating the lithium anode with SnI2 solution in a simple drop coating method. The artificial SEI can inhibit the dendrite growth by forming nuclear agent sites and enable uniform current distribution. Solid state electrolyte is further utilized to improve the safety of battery. The symmetrical cells can cycle for > 750 h at 0.2 mA cm−2. Notably, all-solid-state LiFePO4 (LFP)/Li battery can deliver excellent capacity remains 120.6 mAh g−1 after 1000 cycles at 1C with a higher Coulombic efficiency at 99.8%. These results may be also useful for the developing of high energy and high safety lithium metal batteries.

Single-Ion Conducting Polymer Electrolyte for Superior Sodium-Metal Batteries.

Sodium-metal batteries (SMBs) are considered a potential alternative to high-energy lithium-metal batteries (LMBs). However, the high reactivity of metallic sodium towards common liquid organic electrolytes renders such battery technology particularly challenging. Herein, we propose a multi-block single-ion conducting polymer electrolyte (SIPE) doped with ethylene carbonate as suitable electrolyte system for SMBs. This novel SIPE provides a very high ionic conductivity (2.6 mS cm-1) and an electrochemical stability window of about 4.1 V at 40 °C, enabling stable sodium stripping and plating and excellent rate capability of Na||Na3V2(PO4)3 cells up to 2C. Remarkably, such cells provide a capacity retention of about 85% after 1,000 cycles at 0.2C thanks to the very high Coulombic efficiency (99.9%), resulting from an excellent interfacial stability towards sodium metal and the Na3V2(PO4)3 cathode.

Non-flammable solvent-free liquid polymer electrolyte for lithium metal batteries

As a replacement for highly flammable and volatile organic liquid electrolyte, solid polymer electrolyte shows attractive practical prospect in high-energy lithium metal batteries. However, unsatisfied interface performance and ionic conductivities are two critical challenges. A common strategy involves introducing organic solvents or plasticizers, but this violates the original intention of security design. Here, an electrolyte concept called liquid polymer electrolyte without any small molecular solvents is proposed for safe and high-performance batteries, based on the design of a room-temperature liquid-state brush-like polymer as the sole solvent of lithium salts. This liquid polymer electrolyte is non-flammable and exhibits high ionic conductivity (1.09 times 10−4 S cm−1 at 25 °C), significant lithium dendrite suppression, and stable long-term cycling over a wide operating temperature range ( ≥ 1000 cycles at 60 °C and 90 °C). Moreover, the pouch cell can resist thermal abuse, vacuum environment, and mechanical abuse. This electrolyte and design strategy are expected to provide enlightening ideas for the development of safe and high-performance polymer electrolytes.

Engineering the Structural Uniformity of Gel Polymer Electrolytes via Pattern-Guided Alignment for Durable, Safe Solid-State Lithium Metal Batteries.

Ultrathin and super-toughness gel polymer electrolytes (GPEs) are the key enabling technology for durable, safe, and high-energy density solid-state lithium metal batteries (SSLMBs) but extremely challenging. However, GPEs with limited uniformity and continuity exhibit an uneven Li+ flux distribution, leading to nonuniform deposition. Herein, a fiber patterning strategy for developing and engineering ultrathin (16µm) fibrous GPEs with high ionic conductivity (≈0.4 mS cm-1 ) and superior mechanical toughness (≈613%) for durable and safe SSLMBs is proposed. The special patterned structure provides fast Li+ transport channels and tailoring solvation structure of traditional LiPF6 -based carbonate electrolyte, enabling rapid ionic transfer kinetics and uniform Li+ flux, and boosting stability against Li anodes, thus realizing ultralong Li plating/stripping in the symmetrical cell over 3000h at 1.0mA cm-2 , 1.0 mAh cm-2 . Moreover, the SSLMBs with high LiFePO4 loading of 10.58mg cm-2 deliver ultralong stable cycling life over 1570 cycles at 1.0 C with 92.5% capacity retention and excellent rate capacity of 129.8 mAh g-1 at 5.0 C with a cut-off voltage of 4.2V (100% depth-of-discharge). Patterned GPEs systems are powerful strategies for producing durable and safe SSLMBs.

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.

Bifunctional lithiophilic carbon fibers with hierarchical structure for high-energy lithium metal batteries

Lithium (Li) metal is an impeccable candidate anode for satisfying the energy density requirements of next-generation Li batteries. However, Li dendritic growth and fragile solid-elecrolyte interphase (SEI) caused by the high reactivity between Li and electrolyte are the primary challenges for its large-scale applications. Herein, a bifunctional lithiophilic hierarchical substrate composed of high-density nitrogen-doped carbon nanotubes and Co nanoparticles encapsulated in graphene (Co@G) decorated carbon fibers (Co-N-CNT-CF) can modulate the structural dimensions and hierarchy of Li nucleation/growth and alleviate Li volume expansion, achieving the homogeneous Li plating/stripping behavior. Density functional theory (DFT) calculations and experimental results confirm the highly lithiophilicity of the substrate, which exhibits a low Li nucleation overpotential, enhanced Coulombic efficiency (CE), small voltage hysteresis, and ultrastable lifespan without dendritic formation. As coupled with the thick LiFePO4 and LiCoO2 (∼2 mA h cm−2) cathodes, the Co-N-CNT-CF@Li composite anode (N/P = 3) enables a high reversible capacity, high Li utilization, and improved cycle stability. This work engineers a hierarchical structure of the three-dimensional (3D) lithiophilic carbon substrate for realizing highly reversible, dendritic-free Li metal anodes.

Artificial Interphase Design Employing Inorganic–Organic Components for High-Energy Lithium-Metal Batteries

To increase the energy density of today's lithium batteries, it is necessary to develop an anode with higher energy density than graphite or carbon/silicon composites. Hence, research on metallic lithium has gained a steadily increasing momentum. However, the severe safety issues and poor Coulombic efficiency of this highly reactive metal hinder its practical application in lithium-metal batteries (LMBs). Herein, the development of an artificial interphase is reported to enhance the reversibility of the lithium stripping/plating process and suppress the parasitic reactions with the liquid organic carbonate-based electrolyte. This artificial interphase is spontaneously formed by an alloying reaction-based coating, forming a stable inorganic/organic hybrid interphase. The accordingly modified lithium-metal electrodes provide substantially improved cycle life to symmetric Li||Li cells and high-energy Li||LiNi0.8Co0.1Mn0.1O2 cells. For these LMBs, 7 μm thick lithium-metal electrodes have been employed while applying a current density of 1.0 mA cm-2, thus highlighting the great potential of this tailored interphase.

Roles of Trimethyl Borate in Constructing an Interphase on Li Anode: Angel or Demon?

Although coupling a lithium metal anode with a Ni-rich layer cathode is a promising approach for high-energy lithium metal batteries, both electrodes are plagued by their intrinsic unstable interfaces which trigger electrolyte decomposition, lithium dendritic growth, and transition metal dissolution during cycling. Making use of electrolyte additives is one of the most effective solutions to address this issue. In this paper, we explore the roles of trimethyl borate (TMB)─a common film-forming additive to protect high-nickel-ratio ternary cathodes─in suppressing lithium dendrite growth. It is found that, on the one hand, the borate-containing solid electrolyte interphase (SEI) derived from the decomposition of TMB facilitates Li+ transport, homogenizing the deposition of Li ions. On the other hand, TMB as an anion receptor provokes LiPF6 decomposition, prompting the formation of SEI with superfluous LiF. As a result, it is imperative to raise awareness of this double-edge additive when using it to be immune to lithium dendrite and cathodic degradation.

Moderately concentrated electrolyte enabling high-performance lithium metal batteries with a wide working temperature range

The electrolyte integrated with lithium metal anodes is subjected to the issues of interfacial compatibility and stability, which strongly influence the performances of high-energy lithium metal batteries. Here, we report a new electrolyte recipe viz. a moderately concentrated electrolyte comprising of 2.4 M lithium bis(fluorosulfonyl)imide (LiFSI) in a cosolvent mixture of fluorinated ethylene carbonate (FEC) and dimethyl carbonate (DMC) with relatively high ion conductivity. Owing to the preferential decomposition of LiFSI and FEC, an inorganic-rich interphase with abundant Li2O and LiF nanocrystals is formed on lithium metal with improved robustness and ion transfer kinetics, enabling lithium plating/stripping with an extremely low overpotential of ∼ 8 mV and the average CE of 97%. When tested in Li||LiFePO4 cell, this electrolyte provides long-term cycling with a capacity retention of 98.3% after 1000 cycles at 1 C and an excellent rate performance of 20 C, as well as an areal capacity of 1.35 mA h cm−2 at the cathode areal loading of 9 mg cm−2. Moreover, the Li||LiFePO4 cell exhibits excellent wide-temperature performances (-40 ∼ 60 ℃), including long-term cycling stability over 2600 cycles without visible capacity fading at 0 ℃, as well as extremely high average CEs of 99.6% and 99.8% over 400 cycles under −20 ℃ and 45 ℃.

Highly-concentrated bis(fluorosulfonyl)imide-based ternary gel polymer electrolytes for high-voltage lithium metal batteries

Polymer electrolytes (PEs) have arisen as the most promising candidates for being used in rechargeable lithium metal batteries (LMBs). However, classic gel polymer electrolytes (GPEs) with volatile plasticizers show poor inherent safety, despite their higher ionic conductivities vs. dry PE systems, which largely hampers the practical deployment of GPE-based LMBs. Herein, we report the electrochemical performances of a highly-concentrated bis(fluorosulfonyl)imide (FSI)-based ternary gel polymer electrolyte (TGPE) comprising a plasticized polymerized ionic liquid as polymer scaffold. The as-prepared FSI-TGPEs show high lithium-ion conductivities at room temperature, wide electrochemical stability both at oxidative and reductive potentials, and superior compatibility with lithium metal electrode. These unique properties of FSI-TGPE enable stable Li plating and stripping processes, as well as high discharge capacity of a Li||Li(Ni0.6Mn0.2Co0.2)O2 cell at ambient temperatures. The present work offers not only safe and highly conductive PEs but also a better understanding on the determining role of FSI− anions in high-energy LMBs.

A low-cost Al-doped garnet Li7La3Zr2O12 with high ionic conductivity for high-energy solid-state lithium metal batteries

As a promising candidate of current solid-state electrolytes with various advantages, such as broad electrochemical stability window, high thermal stability, and chemical stability, garnet-type solid-state electrolyte Li7La3Zr2O12 (LLZO) attracts extensive research attention. Researchers usually use the element doping method to improve the lithium ion conductivity of LLZO and to stabilize the cubic phase. However, the improvements either increase the cost of raw materials or need complex process. In this work, the preparation process of Al-doped LLZO is optimized by a simple post-doping method (LLZO-Al), and the as-prepared LLZO-Al shows a high lithium ion conductivity of 5.331 × 10−4 S cm−1 and an activation energy of 0.25 eV at room temperature. In addition, the LLZO-Al exhibits excellent stability against Li in LiǁLLZO-AlǁLi symmetric cell, and the LiNi0.8Co0.1Mn0.1O2 (NCM811)ǁLLZO-AlǁLi solid-state cell delivers a stable cycle of 120 cycles at 0.1C. This work offers a low-cost preparation method of LLZO-based solid-state electrolytes with high ionic conductivities for high-energy solid-state lithium metal batteries.

0D Physics-Based Modeling of High Energy Lithium Metal Batteries with Pulsing Requirements

Lithium metal batteries are promising candidates for high energy storage solutions. To further increase capacity, electrolyte components can have a secondary function of storing charge through electrochemical reactions. This work focuses on modeling high-energy lithium metal anode and metal oxide cathode material and potentially other materials with additional capacity from electrolyte components. Physics-based modeling can be utilized to explore design space and predict battery performance under various conditions. This work utilizes a zero-dimensional model with thermodynamics, kinetics, transport, and morphology changes of the solution and solid-phase species. The effect of the additional electrolyte components on the transport, capacity, and voltage behavior will be explored. Pulse power will also be discussed, and this talk may include comparisons to experimental data.