Practical Application Of Li Metal Batteries Research Articles

Directing the uniform and dense Li deposition via graphene-enhanced separators for high-stability Li metal batteries

Lithium (Li) has been widely studied as a next-generation anode material owing to its high theoretical capacity (3860 mAh g−1) and lowest negative potential (−3.04 V vs. SHE). However, the practical applications of Li-metal batteries (LMBs) are hindered by uncontrolled Li deposition during the charging/discharging process and low Coulombic efficiency. Among the numerous strategies, surface optimization of polymer separators with functional nanomaterials, especially graphene, has achieved significant progress in both academic and industrial fields. In this study, we elucidate how the graphene-enhanced separator (GES) improves the electrochemical reversibility of Li deposition/dissolution and consequently extends the cyclability of LMBs. When the GES is employed in Li|Cu cells, a dense Li layer forms between the graphene layer and Cu current collector after multiple Li deposition/dissolution cycles. Furthermore, when the graphene-modified current collector (GMCC) is employed, Li dendrites predominantly grow on the graphene surface and migrate toward the separator, alleviating the risk of separator puncture. The Li|Cu cell with GES demonstrates a higher cycle stability and Coulombic efficiency under high current conditions (∼99 % at 4 mA cm−2) than the Li|Cu and Li|GMCC cells. Moreover, anode-free cells paired with the GES exhibited high capacities and consistent cycle performances under both low- and high-current conditions.

Iodine-containing additive engineering for rejuvenating inactive lithium and constructing highly stable lithium metal anodes

Inactive (‘dead’) lithium and conventional fragile solid-electrolyte interphase (SEI) usually cause performance degradation and safety hazards in Li-metal batteries. Recovering inactive lithium and constructing stable SEI are urgently required to enhance the capacity and lifespan of lithium metal batteries. Herein, we have designed a novel dual-additives electrolyte containing an I3−/I− redox couple for reviving the inactive lithium, and caffeic acid (CA) that can be anion-polymerised to modulate the composition and improve stability of the SEI. It’s found that the generated I3−/I− redox couple can turn the inactive Li2O into soluble Li+, and prompt the formation of SEI composed of inorganic LiI, Li3N and organic RCOOLi with high stability. Density functional theory (DFT) calculations indicate that the diffusion potential barrier of Li+ is significantly lower on the LiI-rich SEI interface, which can not only accelerate the transport of Li+ at the interface, but also effectively prevent I3− from attacking Li metal. Benefiting from this elaborate dual-additives electrolyte design, the symmetrical-cells present a superior electrochemical performance, i.e., high critical current density up to 10 mA cm−2, ultra-long lifespan over 7000 h at 1 mA cm−2, and over 2500 cycles under harsh conditions of high temperature (50 °C) and high current density (5 mA cm−2). In addition, as a proof of concept for practical applications of Li-metal batteries, Li|LiFePO4 full cell delivers excellent cycle stability and rate performance with low hysteresis voltage at a high cathode loading of 17.4 mg cm−2.

The Entanglement of Li Capping and Deposition: An Operando Optical Microscopy Study.

Dendrite growth and low Coulombic efficiency impede the practical application of Li-metal batteries. As such, monitoring Li deposition and stripping in real-time is crucial to understanding the fundamental lithium growth kinetics. This work presents an operando optical microscopic technique that enables precise current density control and quantification of Li layer properties (i.e., thickness and porosity) to study Li growth in various electrolytes. We discover the robustness and porosity of the remaining capping layer after the Li stripping process as the critical features governing the subsequent dendrite propagation behavior, resulting in distinct capping and stacking phenomena that affect Li growth upon cycling. While dendrite propagation quickly occurs through the fracture of the fragile Li capping layer, uniform Li plating/stripping can be facilitated by the compact and robust capping layer even at high current densities. This technique can be extended to evaluate dendrite suppression treatments in various metal batteries, providing in-depth information on metal growth mechanisms.

Negatively Charged Holey Titania Nanosheets Added Electrolyte to Realize Dendrite-Free Lithium Metal Battery.

Electrolyte modulation and electrode structure design are two common strategies to suppress dendrites growth on Li metal anode. In this work, a self-adaptive electrode construction method to suppress Li dendrites growth is reported, which merges the merits of electrolyte modulation and electrode structure design strategies. In detail, negatively charged titania nanosheets with densely packed nanopores on them are prepared. These holey nanosheets in the electrolyte move spontaneously onto the anode under electrical field, building a mesoporous structure on the electrode surface. The as-formed porous electrode has large surface area with good lithiophilicity, which can efficiently transfer lithium ion (Li+ ) inside the electrode, and induce the genuine lithium plating/stripping. Moreover, the negative charges and nanopores on the sheets can also regulate the lithium-ion flux to promote uniform deposition of Li metal. As a result, the symmetric and full cells using the holey titania nanosheets containing electrolyte, show much better performance than the ones using electrolyte without holey nanosheets inside. This work points out a new route for the practical applications of Li-metal batteries.

Synergistic effects between dual salts and Li nitrate additive in ether electrolytes for Li-metal anode protection in Li secondary batteries

The practical applications of Li-metal batteries (LMBs) are limited by dendrite formation. Thus, a synergistic approach for enhancing the cycling performance of LMBs by combining dual salts with lithium nitrate as an additive in an ether-based electrolyte system is presented. The dual salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(oxalate)borate (LiBOB), and lithium nitrate (LiNO3), are dissolved in a dual ether-based solvent composed of 1,2-dimethoxyethane and 1,3-dioxane. The electrolyte shows high electrochemical stability of up to ∼ 4.6 V, circumventing the drawback of ether-based solvents, which are known to exhibit an oxidation potential of <4 V. Moreover, dendrite inhibition is enhanced by the formation of a robust and passivating solid-electrolyte interface (SEI). Additionally, the rate capability and cycling performance are enhanced up to 1000 cycles, with a 90.0% discharge capacity retention at 1C for the lithium iron phosphate (LFP)/Li battery. Furthermore, Li/Li symmetric cells exhibit a high stability with >2300 h of repeated stripping and plating at 0.5 mA cm−2, which is an enhancement of approximately 300% compared with the reference electrolyte. This study provides a promising strategy for the practical application of ether-based electrolytes for Li-metal anodes in rechargeable batteries at low salt concentrations.

Electrode-customized separator membranes based on self-assembled chiral nematic liquid crystalline cellulose nanocrystals as a natural material strategy for sustainable Li-metal batteries

Despite their enormous potential as a high-energy-density power source, practical applications of Li-metal batteries have been plagued mainly by poor electrochemical longevity. Here, we present an electrode-customized separator (EC separator) based on self-assembled chiral nematic liquid crystalline cellulose nanocrystal (LC–CNC) as a natural material strategy to simultaneously address the electrochemical reversibility issues of both Li-metal anodes and high-capacity cathodes in Li-metal full cells. The EC separator (thickness ∼ 10 μm) comprises a 3-glycidyloxypropyl trimethoxysilane (GPTMS)-modified LC–CNC layer on a polyethylene (PE) separator support layer. The LC–CNC layer enables facile/uniform Li+ flux toward Li-metal anodes owing to its ordered nanoporous channels and nanofluidic ion migration effect, thus improving Li plating/stripping cyclability. The GPTMS of the LC–CNC layer chelates heavy metal ions dissolved from high-capacity LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes, thereby enhancing structural stability of the cathodes. The resulting EC separator enables a Li-metal full cell to improve the volumetric energy density (1016 Wh Lcell−1), cycling retention (84% after 100 cycles vs. 0% for the pristine PE separator), and dimensional stability of the Li-metal anode under constrained cell conditions (thin Li-metal anode (20 μm)/high-capacity NCM811 cathode), which outperform those of previously reported synthetic material-based separators for Li-metal full cells.

Suppressing Li Dendrite Puncture with a Hierarchical h-BN Protective Layer.

Lithium metal has been perceived as an extremely attractive anode due to its superior energy density and low redox potential. However, great challenges affiliated with the operating security of Li metal batteries (LMBs) posed by growing Li dendrites hamper the widespread application of rechargeable LMBs. In this study, hierarchical hairball-like boron nitride (h-BN) was fabricated on a Li metal anode using the pulsed laser deposition (PLD) method. The chemically inert and mechanically robust dielectric h-BN coating on the Li anode can act as an interfacial layer conducive to enhancing the stability and extending the battery lifetime of LMBs by suppressing the formation and propagation of dendrites during the recurrent plating and stripping process. Moreover, the h-BN layer favors the drift of Li ions and mitigates electrolyte depletion, therefore demonstrating a reduced polarization in the voltage profiles, which further facilitates the uniform deposition of Li ions during battery operation. As proof, the Li/BN || BN/Li symmetrical cells can circulate steadily for 1800 h with no observable polarization at constant current density. Thus, the three-dimensional h-BN interface layer is efficacious for Li dendrite suppression during the practical application of LMBs, and it may also be promising for tackling dendrite issues in other metal ion battery systems.

Building more secure LMBs with gel polymer electrolytes based on dual matrices of PAN and HPMC by improving compatibility with anode and tuning lithium ion transference

Li metal is considered as a “Holy Grail” anode material for Li metal batteries (LMBs). Unfortunately, the interface problems including the interface reaction of lithium metal anode and the generation of lithium dendrite between lithium metal anode and electrolyte are still the major obstacles in the practical application of LMBs. Here, a novel gel polymer electrolyte (GPE) is attempted to solve these issues. The membrane of polymer composite matrix is successfully prepared by blending hydroxypropyl methyl cellulose (HPMC) with polyacrylonitrile (PAN) through a simple phase inversion method, and finally the corresponding GPE is obtained by an activation process in electrolyte. The polymer composite membrane overcomes some shortcomings of traditional PAN matrix, and meanwhile the corresponding GPE exhibits superior electrochemical performances. As a result, an ultralong-term reversible lithium plating/stripping cycle at a moderate current density (1 mA cm−2) with dendrite-free is achieved for lithium metal anodes. The full cell test results show a higher reversible capacity (106 mAh g−1) at 2C, capacity retention (94.2%) after 100 cycles and a stable coulomb efficiency (98.9%). This study emphasizes the capacity of the designed GPE in stabilizing lithium metal anode and opens a new perspective on the synergy of between different materials.

Double-Layered Multifunctional Composite Electrolytes for High-Voltage Solid-State Lithium-Metal Batteries.

The need for safe storage systems with a high energy density has increased the interest in high-voltage solid-state Li-metal batteries (LMBs). Solid-state electrolytes, as a key material for LMBs, must be stable against both high-voltage cathodes and Li anodes. However, the weak interfacial contact between the electrolytes and electrodes poses challenges in the practical applications of LMBs. In this study, a double-layered solid composite electrolyte (DLSCE) was synthesized by introducing an antioxidative poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-10 wt % Li1.3Al0.3Ti1.7(PO4)3 (LATP) to the cathode interface, whereas a lithium-friendly poly(oxyethylene) (PEO)-5 wt % LATP was made to come into contact with Li metal. Owing to the heterogeneous double-layered structure of the DLSCE, a high ionic transfer number (0.43), high ionic conductivity (1.49 × 10-4 S/cm), and a wide redox window (4.82 V) were obtained at ambient temperature. Moreover, the DLSCE showed excellent Li-metal stability, thereby enabling the Li-Li symmetric cells to stably run for over 600 h at 0.2 mA/cm2 with effective lithium dendrite inhibition. When paired with a high-voltage LiNi1/3Co1/3Mn1/3O2 cathode, the Li/DLSCE/NCM111 cell exhibited excellent electrochemical performance: long-term cyclability with 85% capacity retention could be conducted at 0.2C after 100 cycles corresponding to 100% Coulombic efficiencies.

High-loading lateral Li deposition realized by a Scalable Fluorocarbon Bonded Laminates

High-energy-density lithium (Li) metal batteries (LMBs) have been intensely revisited in recent years due to the urgent need of advanced energy storage technologies. However, a step towards the practical application of LMBs is still plagued by the lack of scalable method for Li metal protection. Rationally designed carbon nanostructures have been employed to stabilize Li metal anode, but only demonstrated as model structures without scalable productions. Herein, a type of fluorocarbon (–CFx) bonded carbon nanoparticles is developed, which not only exhibit much better manoeuvrability to form uniform and crack-free laminates as large-area Li protective structure, but the presence of –CFx also leads to the formation of a high-content lithium fluoride (LiF) interphase via a lithiation route, endowing high-loading lateral Li deposition by the increase of interfacial energy between the substrate and the highly fluorinated interphase. Based on the efficacious Li protection by the –CFx bonded carbon laminates, a stable cycling of 300 cycles is achieved for Li||LiNi0.88Co0.09Al0.03O2 (NCA) full cell with a high NCA loading of 5 mAh cm−2. These results demonstrate that protecting high-loading Li metal anodes in the practical LMBs is feasible by the functional carbon synthesized from our easy-scalable method.

Evaluating Solid-Electrolyte Interphases for Lithium and Lithium-free Anodes from Nanoindentation Features

Summary The morphology and mechanical property of SEIs for lithium anodes crucially affect the electrochemical cycling performance of Li-metal batteries such as Li-S and Li-O2 batteries. Herein, we establish the standards for rapidly assessing SEIs for Li and Li-free type of anodes by AFM nanoindentation features toward prediction of corresponding electrochemical performances. A series of single-layered and multi-layered SEIs with known composition and structures are purposely constructed. A set of unique nanoindentation features representative of mechanical properties of the basic SEIs are formed, serving as the standards for rapidly assessing the mechanical properties and electrochemical performances of unknown SEIs together with their Young’s modulus, smoothness, and thickness. To validate the applicability of the method, SEIs formed by electrochemical aging and formed on Cu substrates are further evaluated. Our work not only contributes to understanding the influence of SEIs on cycling performances but also provides a rapid way for screening SEIs.

In-Plane Lithium Growth Enabled by Artificial Nitrate-Rich Layer: Fast Deposition Kinetics and Desolvation/Adsorption Mechanism.

An artificial lithium-nitrate (LiNO3 )-rich layer (LN-RL) is developed to address dendritic lithium (Li) growth by a fusing-infusing strategy, in which LiNO3 is loaded into stainless steel mesh and a Li-metal anode (LN-RL@Li) is obtained by casting this LN-RL onto Li foil. The LN-RL enables fast Li deposition kinetics in carbonates and endows LN-RL@Li with excellent cycleability. The underneath mechanism on the contribution of LN-RL is uncovered by detailed characterizations combining with theoretical simulations. The LN-RL promotes the desolvation and capacitive adsorption of Li ions and induces in-plane Li growth along the edges of preplated Li with planar morphology. The improved cycleability of LN-RL(@Li) is demonstrated by LiǁCu cell that presents a coulombic efficiency of 97.2% after 280 cycles and LiǁLi cell that proceeds over 1000 h at 0.5 mA cm-2 in carbonates. Additionally, the LiǁLiFePO4 cell shows a capacity retention of 58% after 400 cycles at 1 C (1 C = 170 mA g-1 ), compared to the 35% after 180 cycles for the control. This work presents not only a promising strategy for practical applications of Li-metal batteries, but also a new understanding on the role of nitrate in Li plating/stripping kinetics.

Protected Lithium-Metal Anodes in Batteries: From Liquid to Solid.

High-energy lithium-metal batteries are among the most promising candidates for next-generation energy storage systems. With a high specific capacity and a low reduction potential, the Li-metal anode has attracted extensive interest for decades. Dendritic Li formation, uncontrolled interfacial reactions, and huge volume effect are major hurdles to the commercial application of Li-metal anodes. Recent studies have shown that the performance and safety of Li-metal anodes can be significantly improved via organic electrolyte modification, Li-metal interface protection, Li-electrode framework design, separator coating, and so on. Superior to the liquid electrolytes, solid-state electrolytes are considered able to inhibit problematic Li dendrites and build safe solid Li-metal batteries. Inspired by the bright prospects of solid Li-metal batteries, increasing efforts have been devoted to overcoming the obstacles of solid Li-metal batteries, such as low ionic conductivity of the electrolyte and Li-electrolyte interfacial problems. Here, the approaches to protect Li-metal anodes from liquid batteries to solid-state batteries are outlined and analyzed in detail. Perspectives regarding the strategies for developing Li-metal anodes are discussed to facilitate the practical application of Li-metal batteries.