Li Metal Deposition Research Articles

Graphene membrane hosted compact lithium metal anode enabled by capillary force-tuned lithium infiltration

Lithium metal anodes, the promising anodes for next-generation batteries, are troubled by the instability and safety issues induced by the dendrite growth. Three-dimensional hosts are widely used to accommodate lithium metal to solve the above problems. However, they are constantly challenged by large thickness and excess space in the host, lowering the volumetric energy density of batteries. Here, we used the reduced graphene oxide membrane (rGOM) assembled with small graphene oxide sheets as the host and obtained a compact, ultrathin (<20 μm) and free-standing lithium metal-rGO composite anode with good flexibility and high volumetric capacity. The overlap sites derived from the stacking of small size of GO act as abundant diffusion channels for the gas release during the spark reduction process, producing narrow interlamellar space in the rGOM and thus enhancing the capillary molten Li infusion to form a compact composite anode. These sites also guide the uniform deposition of Li metal on the surface and interior of the membrane, effectively suppressing the dendrite growth. This compact composite anode delivers a high volumetric capacity (1223 mAh cm−3) and stable cycling performance in the symmetrical cells and the full cells coupled with high mass loading LiFePO4 cathode under a low N/P ratio.

Dual‐Functional Stacked Polymer Fibers for Stable Lithium Metal Batteries in Carbonate‐Based Electrolytes

Lithium (Li) metal has long been thought to be an ideal anode material for high‐energy‐density Li metal batteries (LMBs). Nonetheless, a variety of safety risks and short cycle life due to uncontrollable Li dendrite growth limit its practical application. Here, a novel polymer‐based 3D host composed of stacked polymer fibers (SPF) is purposefully designed using a simple electrospinning method to achieve dual‐functional properties that endow bottom‐up Li filling and morphologically regulate Li metal deposition over the host structure. As a result, the SPF allows for uniform Li‐ion flux in the electrode, leading to densely packed Li deposition and further stable cycling in conventional carbonate‐based electrolytes. Besides, a full cell paired with LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode results in a high‐energy‐density battery with a low negative/positive capacity ratio and a wide operating temperature range. This study presents a rational design for improving the stability and safety of Li metal anodes in conventional carbonate‐based electrolytes for advanced LMBs.

Electrodeposition and Electrodissolution of Li Metal in Nanohole Arrays of Anodic Porous Alumina

Electrodeposition and electrodissolution of Li metal in an anodic porous alumina that has an ideal hole array structure were demonstrated. Electrodeposition and electrodissolution of Li metal in the hole array structures could be repeatedly carried out without any formation of dendritic Li. Although the hole diameter of the anodic porous alumina was reduced from the micrometer to nanometer scale, deposition and dissolution of Li metal could be stably conducted. The present process is expected to be applicable to the fabrication of a safe rechargeable Li-metal battery.

Serrated lithium fluoride nanofibers-woven interlayer enables uniform lithium deposition for lithium-metal batteries

The uncontrollable formation of Li dendrites has become the biggest obstacle to the practical application of Li-metal anodes in high-energy rechargeable Li batteries. Herein, a unique LiF interlayer woven by millimeter-level, single-crystal and serrated LiF nanofibers (NFs) was designed to enable dendrite-free and highly efficient Li-metal deposition. This high-conductivity LiF interlayer can increase the Li+ transference number and induce the formation of 'LiF-NFs-rich' solid-electrolyte interface (SEI). In the 'LiF-NFs-rich' SEI, the ultra-long LiF nanofibers provide a continuously interfacial Li+ transport path. Moreover, the formed Li-LiF interface between Li-metal and SEI film renders low Li nucleation and high Li+ migration energy barriers, leading to uniform Li plating and stripping processes. As a result, steady charge-discharge in a Li//Li symmetrical cell for 1600h under 4mAhcm-2 and 400 stable cycles under a high area capacity of 5.65mAhcm-2 in a high-loading Li//rGO-S cell at 17.9mAcm-2 could be achieved. The free-standing LiF-NFs interlayer exhibits superior advantages for commercial Li batteries and displays significant potential for expanding the applications in solid Li batteries.

Self-healing artificial solid electrolyte interphase enhanced by quadruple hydrogen bonding for stable lithium metal anode

Lithium metal is considered as the ultimate anode material for lithium batteries due to its high theoretical specific capacity and lowest redox potential. However, the growth of lithium dendrites and strong side reactions seriously hinder the commercialization of Li metal anode. Here, we modify the Li metal anode with a self-healing artificial solid electrolyte interphase (SEI), where PVA-Upy with quadruple hydrogen bonds is formed on Li metal by a simple drop-coating method. This polymer artificial SEI possesses self-healing hydrogen bonds and abundant lithiophilic bonds, which can simultaneously suppress the generation of microcracks in the SEI and enable uniform deposition of Li metal. Hence, the PVA-Upy@Li symmetric cell can stably cycle for more than 2000 h (1 mA cm−2, 1 mAh cm−2) with only about 10 mV of voltage polarization. This artificial SEI provides new insight into the subsequent modification strategies of Li metal anode and can be extended to the protection of other alkali metal anodes.

Hybrid solid state electrolytes blending NASICON-type Li1+xAlxTi2–x(PO4)3 with poly(vinylidene fluoride-co-hexafluoropropene) for lithium metal batteries

Lithium-ion batteries (LIBs) with Li metal as the anode electrode are very promising energy storage systems for high energy/power density applications. However, Li dendrite formation and growth on the Li anode due to non-uniform Li metal deposition is one of the major issues yet to be addressed. In this work, novel hybrid solid state electrolytes (SSEs) were developed through blending poly(vinylidene fluoride-hexafluoro propylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and sodium superionic conductor (NASICON)-type Li1+xAlxTi2‒x(PO4)3 (LATP) powders. The LATP powders were synthesized by the sol-gel technique followed by calcination at 850 °C. The as-prepared LATP particles formed a well-defined crystalline structure with a rhombohedral lattice. The LATP content within the hybrid SSEs plays a crucial role in improving the mechanical durability, ionic conductivity, rate capability, discharge capacity, and cyclic stability. Analyzing various SSE configurations, an optimal ratio of LATP was determined (i.e., 10–15 wt.%) enabling an ultra-high ionic conductivity of ∼1.11 × 10–4 S cm–1. Employing the LATP-based SSE developed in this work, the dissolution of iron from the LiFePO4 cathode was mitigated and a stable solid electrolyte interphase layer was formed resulting in uniform Li metal deposition along with exceptional cyclic durability during long-duration charge/discharge cycling.

(Invited) Lithium Metal Nucleation and Growth on Conductive Substrates— a Multi-Scale Understanding from Micro, Meso, to Macro-Scales

Repetitive lithium (Li) metal deposition and stripping on conductive substrates such as copper is a critical process involved in the rechargeable Li batteries for high energy applications. Most of the time, the reversibility of this deposition and stripping process by electrochemical methods is of paramount importance for long life performance of these batteries. Solid electrolyte interphase (SEI) formation and the dendritic formation of Li whiskers are often cited as the challenges in achieving a uniform, reversible Li deposition and stripping in the process, rendering a short life duration of these batteries for practical applications. The fundamental question of how Li metal nucleates and grows on the conductive substrate has not been well understood until some recent experiments and in situ, operando observations [1,2] began to shed light on this process to offer some clues how to control the morphology of the Li deposition and stripping process.Here, a collection of experimental evidence and molecular dynamics simulations are presented to provide some insight of this seemingly straightforward process of elemental metal deposition. An explanation to peel off the mystery of the Li nucleation and growth from the atomic level to the micro (<20 nm), meso (20-100 nm), and the macro-scale (>100 nm) is offered to provide some guidance of the control needed to regulate the morphology. Success to demonstrate some highly dense and reversible Li deposition and stripping is shown.

Probing the Li Metal Solid Electrolyte Interphase Using a Stable Nitroxide Radical

The solid electrolyte interphase (SEI) on a Li metal anode is important in protecting the Li from further oxidation. Previous work has demonstrated that the SEI formed in a lithium-air battery (LAB) can be tailored depending on the gas species present. Oxygen helps create an oxide-rich SEI and promotes uniform Li metal deposition as opposed to dendritic Li which are formed when only argon is present. In order to compare the protective quality of the SEI formed under O2 or under Ar, we used TEMPO, (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl, as a probe. First, we studied the possible reduction products of TEMPO. We found that TEMPO initially reduces to TEMPO-, then undergoes further reductive degradation such as ring opening or formation of amines. Next, we exposed a Li metal electrode with SEI formed either under O2 or Ar to an electrolyte solution containing TEMPO. We characterized the ability of the SEI to prevent TEMPO reduction using operando Electron Paramagnetic Resonance (EPR) spectroscopy as well as ex situ solid-state and solution Nuclear Magnetic Resonance (NMR) spectroscopy. We show that the concentration of TEMPO in the electrolyte decreases more slowly and fewer TEMPO reduction products are formed when the Li metal has an oxide-rich SEI. This suggests that the oxide-rich SEI is better at protecting the Li metal from oxidation and that TEMPO is a suitable probe for SEI quality.

Superdry poly(vinylidene fluoride-co-hexafluoropropylene) coating on a lithium anode as a protective layer and separator for a high-performance lithium-oxygen battery

In this study, a dense polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) coating is fabricated on a lithium (Li) anode sheet, which acts as a synergistic protective layer and electrolyte separator for Li-oxygen (Li-O2) batteries. This thin coating is dried through slow solvent evaporation and vacuum drying methods. The solvent-free, dense PVDF-HFP coating has a thickness of 45 µm and can absorb 62% of electrolyte. The battery containing the PVDF-HFP coating demonstrates a maximum peak power density of 3 mW cm−2, significantly higher than that of the battery with the PVDF coating (0.8 mW cm−2) but lower than that without coating (equipped with a commercial glass fiber separator, 7.3 mW cm−2). However, the PVDF-HFP coating enables the Li-O2 battery to reach a capacity of 4400 mA h g−1, much higher than that without the coating (glass fiber separator, 850 mA h g−1). The symmetric Li-Li cells further confirm steady and low overpotentials using the anode coating at a high current density of 1.0 mA cm−2, indicating stable Li plating/stripping process. The PVDF-HFP-coated battery has a longer cycling lifetime (1700 h) than those with the PVDF coating (120 h) and a glass fiber separator (670 h). The Raman spectra show that there are lithium compounds (mainly lithium hydroxide) and residual PVDF-HFP on the aged anode surface. The dense PVDF-HFP coating on the Li anode plays dual roles: it creates a strong protective layer for stabilizing the solid-electrolyte interface (in the solid phase), and acts as a separator for modulating the Li metal deposition and stripping behaviors in liquid electrolyte.

Laser irradiation illuminates uncertain degradation, leading to thermal runaway of 18650 cells charged/discharged at low temperatures

The safety of Li-ion secondary cells decreases during charging and discharging at low temperatures due to the deposition of Li metal that reduces the cell thermal stability. Generally, the thermal stability of Li-ion cells is evaluated by an accelerating rate calorimeter (ARC). Therefore, in this study, degraded cells with low capacities have been prepared by charge/discharge cycling at a low temperature. After confirming the decrease in thermal stability by ARC heating, the degraded cells are charged at room temperature, and a thermal runaway is initiated by both ARC heating and laser irradiation. During ARC heating, the exothermic behavior of the degraded cell is identical to that of a new cell; however, the degraded cell undergoes a thermal runaway after laser irradiation at an input energy 100 times lower than that required to induce the runaway of a new cell. Therefore, the degradation of cells due to charge/discharge cycling at low temperatures can be detected by the laser irradiation method despite the decreased thermal stability undetectable by the ARC.

Hybrid Lithium‐Ion/Metal Electrodes Enable Long Cycle Stability and High Energy Density of Flexible Batteries

AbstractHigh‐energy, stable, and flexible lithium batteries are highly demanded for next‐generation flexible and wearable electronics. Although the cycling stability of flexible lithium‐ion batteries (LIBs) is high, their energy density reaches the bottleneck because of the use of graphite anode. On the other hand, flexible lithium‐metal batteries provide higher energy density because of the use of lithium (Li) metal anode, but the cycling stability is poor. Herein, a new type of flexible hybrid lithium‐ion/metal battery (f‐LIMB) is reported, which simultaneously possesses enhanced energy density, stable cycling behavior, and outstanding flexibility. f‐LIMB is enabled by using the prelithiated carbon cloth as the anode, which improves the initial Coulombic efficiency by a prior formation of solid electrolyte interface, benefits the subsequent deposition of Li metal due to the preformed lithiophilic LixC6 compounds, and enhances the cycle life and energy density of batteries through a Li compensation mechanism. The f‐LIMB full cell possesses an improved gravimetric and volumetric energy density by as much as 64% and 67%, in comparison to the flexible LIB counterpart, and pertains high capacity retention of 84% after 1000 charge/discharge cycles. In addition, the f‐LIMB can be readily bent down to a small radius of 2.5 mm.

Optical Study of the Surface Film Formed during Li-Metal Deposition and Dissolution Investigated by Surface Plasmon Resonance Spectroscopy.

The features of the electrode surface film during Li-metal deposition and dissolution cycles are essential for understanding the mechanism of the negative electrode reaction in Li-metal battery cells. The physical and chemical property changes of the interface during the initial stages of the reaction should be investigated under operando conditions. In this study, we focused on the changes in the optical properties of the electrode surface film of the negative electrode of a Li-metal battery. Cu-based electrochemical surface plasmon resonance spectroscopy (EC-SPR) was applied because of its high sensitivity to optical phenomena on the electrode surface and its stability against Li-metal deposition. The feature of SPR reflectance dip depends on the optical properties of the electrode surface; namely, the wavelength and depth of the reflectance dip directly connected the refractive index and extinction coefficient (color of electrode surface film), which was confirmed by reflectance simulation. In the operando EC-SPR experiment, various changes in optical properties were clearly observed during the cycles. In particular, the change in the extinction coefficient was more remarkable at the second process than the first process of Li-metal deposition. By electrochemical quartz-crystal microbalance (EQCM) measurements, surface film formation was confirmed during the first Li-metal deposition process. The remarkable change in the extinction coefficient is based on the color change of the surface film, which is caused by the chemical condition change during Li-metal deposition cycles.

Regulating Li‐ion Flux through a Dense yet Highly Ionic Conductive Interlayer for Stable Li Deposition

AbstractThe practical use of Li metal anode is severely hindered by the uncontrollable dendrite growth, and the main cause is the uneven deposition of Li metal. In the liquid electrolyte, the Li‐ion distribution on the electrode surface is difficult to be regulated, which largely affects the Li deposition behavior. The authors design a dense Li‐ion flux regulating layer on the separator to well guide the Li‐ion transport that is composed of metal/lithium oxide (Li2O). Such a layer is generated from the in situ lithiation of transition metal oxide nanoparticle (TMO NP) coating, in which the lithiation‐induced volume expansion of TMO NPs makes the coating very dense yet highly ionic conductive due to the rich boundaries between the formed metal/Li2O. Such a layer enables the redistribution of Li ions on the surface of the electrode to effectively suppress the dendrite growth. The symmetric cells with such layers maintain stable cycling over 400 h under 3 mA cm–2, and the full cell coupled with LiFePO4 presents a highly stable cycling performance with high‐capacity retention of 85.2% after 350 cycles at 0.5 C with a low N/P ratio, promising a potential application in next‐generation Li metal batteries.

Vertically Aligned MXene Nanosheet Arrays for High‐Rate Lithium Metal Anodes

AbstractLithium (Li) metal is considered as one of the best anode materials due to its high theoretical capacity and low reduction potential. However, its practical application is restricted by uneven Li metal dendrite growth. Herein, vertically aligned Ti3C2Tx MXene nanosheet arrays synthesized by a facile ice template assisted blade coating method are adopted to regulate Li metal nucleation and guide Li metal deposition. This kind of vertical structure exhibits low tortuosity that can achieve homogeneous and fast Li transport. In addition, the rich F and O groups on the Ti3C2Tx surface are conducive to the formation of a uniform solid–electrolyte interphase layer, which plays an important role in regulating the nucleation and growth of Li metal. Consequently, the vertically aligned Ti3C2Tx electrodes achieve high Coulombic efficiencies (98.8%) for more than 450 cycles at a fixed areal capacity of 1.0 mAh cm−2 with a current density of 1.0 mA cm−2. Moreover, it can maintain stable lithium plating/striping behaviors even at an ultrahigh current density of 5.0 mA cm−2 and high areal capacity of 5.0 mAh cm−2. Furthermore, full batteries (LiFePO4 as cathode) paired with these vertically aligned Ti3C2Tx electrodes show superior stability and rate performance than the horizontally aligned Ti3C2Tx electrodes.

The effect of alloy type of lithophilic Cu-Sn interface layer on the deposition/stripping behavior of lithium metal anode

Lithium (Li) metal is one of the best anode candidates for high energy density battery because of the lowest electrode potential and high theoretical capacity. However, the unstable electrode/electrolyte interface will cause uneven Li deposition and induce the formation of Li dendrites. The Cu-Sn alloy interface layer has been proven to be an effective strategy to inhibit the growth of Li dendrites, but how the alloy type of Cu-Sn alloy affects the deposition/exfoliation behavior of Li metal is still unclear. Here, we used a simple and fast chemical plating method to prepared lithophilic Cu3Sn and Cu6Sn5 pure phase interface layers on the surface of the Cu foil by controlling the temperature. Then, the effects of two different alloy types on the deposition/stripping behavior of Li metal anodes were studied. Compared with Cu3Sn@Cu, Cu6Sn5@Cu has a more uniform surface structure and higher surface free energy. Uniform electron distribution and fast reaction kinetics are conducive to the uniform deposition of Li metal. Meanwhile, Cu6Sn5@Cu also has higher electrolyte wettability. This helps to reduce the interphase impedance and polarization, thereby avoiding the growth of Li dendrites. These advantages make deposition mechanism of Li metal on the Cu6Sn5@Cu surface a unidirectional "Parallel-Deposition", while on the Cu3Sn@Cu surface it is a multi-directional "Preferred-Deposition". After being modified by Cu6Sn5, a more reasonable deposition mechanism reduces the overpotential of Li deposition on Cu foil by half. Even under the high deposition capacity of 10 mAh cm−2, Cu6Sn5@Cu can still cycle stably for more than 900 h. In addition, Li-Cu6Sn5@Cu has also been proved to have more stable rate performance and higher capacity retention rate than Li-Cu3Sn@Cu when it is used in full cell with LiFePO4.

Operando Synchrotron Studies of Inhomogeneity during Anode-Free Plating of Li Metal in Pouch Cell Batteries

Operando synchrotron X-ray diffraction (XRD) studies have not previously been used to directly characterize Li metal in standard batteries due to the extremely weak scattering from Li atoms. In this work, it is demonstrated the stripping and plating of Li metal can be effectively quantified during battery cycling in appropriately designed synchrotron XRD experiments that utilize an anode-free battery configuration in which a Li-containing cathode material of LiNi0.6Mn0.2Co0.2O2 (NMC622) is paired with a bare anode current collector consisting of either Cu metal (Cu/NMC) or Mo metal (Mo/NMC). In this configuration, it is possible to probe local variations in the deposition and stripping of Li metal with sufficient spatial sensitivity to map the inhomogeneity in pouch cells and to follow these processes with sufficient time resolution to track state-of-charge-dependent variations in the rate of Li usage at a single point. For the Cu/NMC and Mo/NMC batteries, it was observed that the initial plating of Li occurred in a very homogeneous manner but that severe macroscopic inhomogeneity arose on a mm-scale during the subsequent stripping of Li, contrasting with the conventional wisdom that the greatest challenges in Li metal batteries are associated with Li deposition.

Effect of the supergravity on the formation and cycle life of non-aqueous lithium metal batteries

Extra-terrestrial explorations require electrochemical energy storage devices able to operate in gravity conditions different from those of planet earth. In this context, lithium (Li)-based batteries have not been fully investigated, especially cell formation and cycling performances under supergravity (i.e., gravity > 9.8 m s−2) conditions. To shed some light on these aspects, here, we investigate the behavior of non-aqueous Li metal cells under supergravity conditions. The physicochemical and electrochemical characterizations reveal that, distinctly from earth gravity conditions, smooth and dense Li metal depositions are obtained under supergravity during Li metal deposition on a Cu substrate. Moreover, supergravity allows the formation of an inorganic-rich solid electrolyte interphase (SEI) due to the strong interactions between Li+ and salt anions, which promote significant decomposition of the anions on the negative electrode surface. Tests in full Li metal pouch cell configuration (using LiNi0.8Co0.1Mn0.1O2-based positive electrode and LiFSI-based electrolyte solution) also demonstrate the favorable effect of the supergravity in terms of deposition morphology and SEI composition and ability to carry out 200 cycles at 2 C (400 mA g−1) rate with a capacity retention of 96%.

Circumferential Li metal deposition at high rates enabled by the synergistic effect of a lithiophilic and ionic conductive network

LLTO/C composites form fast Li+ diffusion paths. The lithiophilic Au layer coated on LLTO/C improves the surface lithiophilicity and further accelerates Li+ diffusion, realizing uniform Li metal deposition at high rates.

Advances in the Emerging Gradient Designs of Li Metal Hosts.

Developing host has been recognized a potential countermeasure to circumvent the intrinsic drawbacks of Li metal anode (LMA), such as uncontrolled dendrite growth, unstable solid electrolyte interface, and infinite volume fluctuations. To realize proper Li accommodation, particularly bottom-up deposition of Li metal, gradient designs of host materials including lithiophilicity and/or conductivity have attracted a great deal of attention in recent years. However, a critical and specialized review on this quickly evolving topic is still absent. In this review, we attempt to comprehensively summarize and update the related advances in guiding Li nucleation and deposition. First, the fundamentals regarding Li deposition are discussed, with particular attention to the gradient design principles of host materials. Correspondingly, the progress of creating different gradients in terms of lithiophilicity, conductivity, and their hybrid is systematically reviewed. Finally, future challenges and perspective on the gradient design of advanced hosts towards practical LMAs are provided, which would provide a useful guidance for future studies.

A polymeric separator membrane with chemoresistance and high Li-ion flux for high-energy-density lithium metal batteries

Lithium (Li) metal batteries are limited by the unstable deposition structure of Li metal, triggering aggressive electrolyte consumption and presenting safety concerns. A fundamental solution regulating the Li metal deposition structure is contingent on the homogeneity of Li-ion flux at the Li-electrolyte interface and electrolyte-infiltrated separator matrix. Here, we report a rational design for a separator coupling with two functional polymers, i.e., ferroelectric terpolymer-polydopamine in a core-shell structure. A conformal polydopamine layer prevents electrolyte dissolution of the terpolymer, improves electrolyte affinity, and suppresses detrimental chemical crossover. Incorporating the high ferroelectricity of the terpolymer increases the Li-ion transference number and ionic conductivity, ensuring the homogeneity of Li-ion transport through the separator's pore network. With this bicomponent separator, stable cycling of a pouch-type full cell is achieved, comprising a thin Li metal (20 µm) anode and a layered oxide cathode under the limited electrolyte condition.