Performance Of Li Metal Batteries Research Articles

Enhanced Free Li-Ion Mobility in Solid-State Electrolytes via Long-Range Assembly of Porous Materials.

Metal-organic frameworks (MOFs), with their tunable pore sizes and high surface areas, are gaining prominence in Li metal battery applications, including their use as nanofillers in solid composite electrolytes (SCEs) for enhanced ionic conductivity. Yet, when used in SCEs, individual dispersed MOF particles in isolation as nanofillers can impede efficient ion transport in all-solid-state batteries due to the insufficient supply of ionic transport pathways within SCEs. Here, we introduced a continuous SCE nanofiller with long-range assembly interconnected porous MOFs (IMOF_SCE) for effective ion transport pathway supply along the interface between the nanofiller and the polymer matrix. IMOF_SCE achieved Li-ion conductivity (6.72 × 10-5 S cm-1 at 20 °C) and Li-ion transference number (tLi+ = 0.855), resulting in the improved electrochemical performance of Li metal batteries. Additionally, the Li/LiFePO4 full cell integrated with IMOF_SCE achieved an outstanding stable capacity retention of 98.8% in 300 cycles. This work offers insights into the design strategy of effective nanofillers for SCEs and can be adapted for other porous materials.

Boosted Li+ transport ensured by high-entropy Prussian blue analogues with tuned PF6− adsorption for stable Li metal anode

The inhomogeneous lithium metal (Li) deposition and low lithium ion (Li+) mobility lead to the formation and growth of Li dendrites, which impede the desirable performance of Li metal batteries (LMBs) with high energy density in widely practical applications. Herein, a high-entropy MnCoNiCuZn-Prussian blue analogue (HE-PBA) is utilized to modify the commercial polypropylene separator (PP@HE-PBA), which will form an artificial protective layer on the surface of Li. The polar –CN groups of HE-PBA can enhance the wettability of PP to the electrolyte, while the movement of PF6− anions are flexibly tuned by the appropriate absorption ability and synergistic effect of multiple metal ions in HE-PBA. A high Li+ transference number of 0.69 is achieved, which can relieve the Li+ concentration polarization, regulate the Li+ flow, and realize the uniform Li deposition. With PP@HE-PBA, the Li||Li symmetric cells display durability up to 600 h in the ester-based electrolyte at 1 mA cm−2 for 1 mAh cm−2. Also, the PP@HE-PBA exhibits great potential in LMBs, where the Li4Ti5O12 (LTO) ||Li and sulfated polyacrylonitrile (S-PAN) ||Li batteries deliver superior cycling performance to those without PP@HE-PBA.

Laser‐Constructing 3D Copper Current Collector with Crystalline Orientation Selectivity for Stable Lithium Metal Batteries

The practical application of lithium (Li) metal anodes in high‐capacity batteries is impeded by the formation of hazardous Li dendrites. To address this challenge, this research presents a novel methodology that combines laser ablation and heat treatment to precisely induce controlled grain growth within laser‐structured grooves on copper (Cu) current collectors. Specifically, this approach enhances the prevalence of Cu (100) facets within the grooves, effectively lowering the overpotential for Li nucleation and promoting preferential Li deposition. Unlike approaches that modify the entire surface of collectors, our work focuses on selectively enhancing lithiophilicity within the grooves to mitigate the formation of Li dendrites and exhibit exceptional performance metrics. The half‐cell with these collectors maintains a remarkable Coulombic efficiency of 97.42% over 350 cycles at 1 mA cm−2. The symmetric cell can cycle stably for 1600 h at 0.5 mA cm−2. Furthermore, when integrated with LiFePO4 cathodes, the full‐cell configuration demonstrates outstanding capacity retention of 92.39% after 400 cycles at a 1C discharge rate. This study introduces a novel technique for fabricating selective lithiophilic three‐dimensional (3D) Cu current collectors, thereby enhancing the performance of Li metal batteries. The insights gained from this approach hold promise for enhancing the performance of all laser‐processed 3D Cu current collectors by enabling precise lithiophilic modifications within complex structures.

Important Role of Ion Flux Regulated by Separators in Lithium Metal Batteries.

Polyolefin separators are the most common separators used in rechargeable lithium (Li)-ion batteries. However, the influence of different polyolefin separators on the performance of Li metal batteries (LMBs) has not been well studied. By performing particle injection simulations on the reconstructed three-dimensionalpores of different polyethylene separators, it is revealed that the pore structure of the separator has a significant impact on the ion flux distribution, the Li deposition behavior, and consequently, the cycle life of LMBs. It is also discovered that the homogeneity factor of Li-ion toward Li metal electrode is positively correlated to the longevity and reproducibility of LMBs. This work not only emphasizes the importance of the pore structure of polyolefin separators but also provides an economic and effective method to screen favorable separators for LMBs.

Recovery of isolated lithium through discharged state calendar ageing.

Rechargeable Li-metal batteries have the potential to more than double the specific energy of the state-of-the-art rechargeable Li-ion batteries, making Li-metal batteries a prime candidate for next-generation high-energy battery technology1-3. However, current Li-metal batteries suffer from fast cycle degradation compared with their Li-ion battery counterparts2,3, preventing their practical adoption. A main contributor to capacity degradation is the disconnection of Li from the electrochemical circuit, forming isolated Li4-8. Calendar ageing studies have shown that resting in the charged state promotes further reaction of active Li with the surrounding electrolyte9-12. Here we discover that calendar ageing in the discharged state improves capacity retention through isolated Li recovery, which is in contrast with the well-known phenomenon of capacity degradation observed during the charged state calendar ageing. Inactive capacity recovery is verified through observation of Coulombic efficiency greater than 100% on both Li||Cu half-cells and anode-free cells using a hybrid continuous-resting cycling protocol and with titration gas chromatography. An operando optical setup further confirms excess isolated Li reactivation as the predominant contributor to the increased capacity recovery. These insights into a previously unknown pathway for capacity recovery through discharged state resting emphasize the marked impact of cycling strategies on Li-metal battery performance.

Impact of the fluorination degree of ether-based electrolyte solvents on Li-metal battery performance

Electrolytes using fluorinated solvents have proven effective in improving the cycling life of Li-metal batteries, by forming a robust solid–electrolyte interphase through decomposition of anion and fluorinated solvent molecules.

Improvement of Charge/Discharge Performance of Li Metal Battery Using Ionic Liquid Electrolyte with 3DOM PI Separator

Ionic liquid electrolytes (ILEs) have attracted attention as promising electrolyte candidates. ILEs can realize non-flammable rechargeable batteries. In addition, other advantages of ILEs are negligible volatility and high thermal stability. These properties can improve the safety of Li metal batteries. However, conventional polyolefin separators cannot be used due to low affinity with highly viscos electrolytes such as highly concentrated electrolytes and ILEs. So far, glass filters with thicknesses of several hundred micrometers have been used as alternatives. However, it is too thick to realize a real cell. Furthermore, the glass filter shows low reversibility of Li deposition/dissolution due to its non-uniform pore structure. It is known that Li deposition/dissolution sometime results in an internal short circuit which is caused by inhomogeneous Li deposition. The separator has a large effect on the uniformity of Li deposition/dissolution behavior. Therefore, new separators with good properties, such as high affinity with electrolyte, hightypemechanical strength, suitable thickness and excellent reversibility of Li deposition/dissolution are strongly required. So far, we have developed a three-dimensionally ordered macroporous polyimide (3DOM PI) memblane with a thickness of 30 micrometers as a separator having a good affinity with ILEs. In this study, we improved the performance of Li metal batteries by using both ILEs and 3DOM PI separator. Three types of separators were used in this study; glass filter (Whatman, GF/A, 260 μm), surfactant coated polypropylene (PP) (25 μm) and 3DOM PI separator (30 μm). 3DOM PI separator was prepared by using a colloidal template method. Lithium bis(fluorosulfonyl)imide and N-metyl-N-Propylpyrrolidinium bis(fluorosulfonyl)imide mixture with a molar ratio 1:1 was used as the ILE. Li deposition/dissolution was carried out by using Li symmetric cell with three types of separators and the ILE, in order to investigate the Li deposition/dissolution behavior. The Li deposition/dissolution capacities for all tests were 1 mA h cm-2. Fig. 1 shows the voltage profiles during the Li deposition/dissolution using different current densities. In the case of the 3DOM PI separator, the stable Li deposition/dissolution behavior was observed up to the current density of 3.0 mA cm-2. In the case of the surfactant coated PP separator, the applicable maximum current density was 1.5 mA cm-2. In the case of the glass filter, an internal short circuit was observed even at lower current density. The Li deposition/dissolution behavior strongly depends on the types of separators, and the 3DOM PI separator provides most stable Li deposition/dissolution, especially at high current density. Fig. 2 shows the voltage profiles during the Li deposition/dissolution cycles at the current density of 1 mA cm-2. In the case of the 3DOM PI separator, the highly stable Li deposition/dissolution was observed over 150 cycles. In contrast, in the case of the surfactant coated PP separator, unstable Li deposition/dissolution was observed after the 50th cycle, probably due to micro-short circuit. In the case of the glass filter, the internal short circuit was more clearly observed at the initial cycles. From the above results, it is confirmed that the 3DOM PI separator can provide stable Li deposition/dissolution behavior. This is due to the uniform structure of the 3DOM PI separator and high stability of ILE. Figure 1

Artificial SEI Layer Combined with Single-Ion Polymer Electrolytes to Prevent Dendrite Growth in Lithium Metal Batteries

Li-metal batteries have the potential to become the next generation of batteries since they can provide an increased energy density vs. Li-ion batteries. However, the safety issue caused by the inhomogeneous Li deposition and Li dendrite growth greatly limits their commercial application. Several methods have been proposed to address this issue. On the one hand, when Li ions are released from one electrode and consumed at the other electrode, it causes a salt concentration gradient. Besides, the electrical migration of anions in the opposite direction aggravates the concentration of gradient since anions do not react at the electrodes. Fast dendritic growth then occurs when the current is high enough to fully deplete the Li+ ion at the anode during charge. Thus, suppressing concentration gradient by immobilizing the anions would in principle solve the fast dendritic growth issue. On the other hand, the Solid Electrolyte Interphase (SEI) plays a crucial role in the operation of Li metal batteries since it prevents further reduction and continuous electrolyte reaction. SEI derives from the passivation layer formed onto the surface of Li metal under dry air during lithium foil extrusion and then evolves further in contact with the electrolytes and during subsequent electrochemical Li stripping/plating. The SEI is inhomogeneous and since it contains lower resistance pathways for Li+ transport, it favors inhomogeneous deposition at any current. Thus, SEI engineering, in order to favor the homogeneity of current density and enhanced mechanical properties to confine lithium could, in principle, improve the performance of Li metal batteries.Thus, we studied the use of single-ion conducting polymers with high cationic transference numbers (tLi+ close to 1) as artificial SEIs (art-SEIs) since they include immobile anions and thus prevent Li+ depletion during charge and, at the same time, improve lithium metal confinement and the homogeneity of current density. Our results show much improved homogeneity of Li deposition and cycling stability after single-ion art-SEI coating using an ether-based liquid electrolyte combined with a separator. Nevertheless, it could not enable long-term cycling as the separator does not enable homogeneous pressure and current density onto the lithium anode. Thus, the use of a single-ion conducting solid polymer electrolyte was combined with a single-ion conducting art-SEI (as illustrated in Figure 1). This strategy allows the suppression of salt concentration gradients, inhomogeneous pressure and current density, thus enables homogeneous Li deposition and long-term cycling of Li metal anode. Figure 1

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.

The shield-like nano-sized Si3N4 derivatives to defend against the attack of lithium dendrites

The unrestrained Li dendrite growth impedes the performance of Li metal batteries (LMBs) and brings safety concerns. To mitigate the unfavorable effect of Li dendrites, in this work, a shield-like artificial interlayer composed of Si3N4 is employed to achieve the desirable electrochemical performance of LMBs. The Si3N4-based interlayer can in-situ electrochemically react with Li to generate inorganic Li3N and LixSi alloys: the former with high ionic conductivity can effectively enhance the Li+ transference, while the latter with reversibility for Li+ insertion/deinsertion can act as Li+ reservoir to modulate Li+ platting/stripping. Thus, the Si3N4-derived compound shield effectively defends against the attack of Li dendrites and suppresses their growth, with which the Li||Li cells can cycle at 1 mA cm−2 (1 mAh cm−2) up to 500 h and the LiFePO4 (LFP) ||Li batteries can operate 400 cycles at 1C with 91.5 % capacity retention.

Radiation effects on lithium metal batteries

The radiation tolerance of energy storage batteries is a crucial index for universe exploration or nuclear rescue work, but there is no thorough investigation of Li metal batteries. Here, we systematically explore the energy storage behavior of Li metal batteries under gamma rays. Degradation of the performance of Li metal batteries under gamma radiation is linked to the active materials of the cathode, electrolyte, binder, and electrode interface. Specifically, gamma radiation triggers cation mixing in the cathode active material, which results in poor polarization and capacity. Ionization of solvent molecules in the electrolyte promotes decomposition of LiPF6 along with its decomposition, and molecule chain breaking and cross-linking weaken the bonding ability of the binder, causing electrode cracking and reduced active material utilization. Additionally, deterioration of the electrode interface accelerates degradation of the Li metal anode and increases cell polarization, hastening the demise of Li metal batteries even more. This work provides significant theoretical and technical evidence for development of Li batteries in radiation environments.

The Inducement and "Rejuvenation" of Li Dendrites by Space Confinement and Positive Fe/Co-Sites.

The high reactivity of Li metal and the inhomogeneous Li deposition leads to the formation of Li dendrites and "dead" Li, which impedes the performance of Li metal batteries (LMBs) with high energy density. The regulating and guiding the Li dendrite nucleation is a desirable tactic to realize concentrated distribution of Li dendrites instead of completely inhibiting dendrite formation. Here, a Fe-Co-based Prussian blue analog with hollow and open framework (H-PBA) is employed to modify the commercial polypropylene separator (PP@H-PBA). This functional PP@H-PBA can guide the lithium dendrite growth to form uniform lithium deposition and activate the inactive Li. In details, the H-PBA with macroporous structure and open framework can induce the growth of lithium dendrites via space confinement, while the positive Fe/Co-sites lowered by polar cyanide (-CN) of PBA can reactivate the inactive Li. Thus, the Li|PP@H-PBA|Li symmetric cells exhibit long-term stability at 1mA cm-2 for 1 mAh cm-2 over 500h. And the Li-S batteries with PP@H-PBA deliver favorable cycling performance at 500mA g-1 for 200 cycles.

Revealing the Multifunctions of Li3N in the Suspension Electrolyte for Lithium Metal Batteries

Inorganic-rich solid-electrolyte interphases (SEIs) on Li metal anodes improve the electrochemical performance of Li metal batteries (LMBs). Therefore, a fundamental understanding of the roles played by essential inorganic compounds in SEIs is critical to realizing and developing high-performance LMBs. Among the prevalent SEI inorganic compounds observed for Li metal anodes, Li3N is often found in the SEIs of high-performance LMBs. Herein, we elucidate new features of Li3N by utilizing a suspension electrolyte design that contributes to the improved electrochemical performance of the Li metal anode. Through empirical and computational studies, we show that Li3N guides Li electrodeposition along its surface, creates a weakly solvating environment by decreasing Li+-solvent coordination, induces organic-poor SEI on the Li metal anode, and facilitates Li+ transport in the electrolyte. Importantly, recognizing specific roles of SEI inorganics for Li metal anodes can serve as one of the rational guidelines to design and optimize SEIs through electrolyte engineering for LMBs.

Ion modulation engineering toward stable lithium metal anodes.

Homogeneous ion transport during Li+ plating/stripping plays a significant role in the stability of Li metal anodes (LMAs) and the electrochemical performance of Li metal batteries (LMBs). Controlled ion transport with uniform Li+ distribution is expected to suppress notorious Li dendrite growth while stabilizing the susceptible solid electrolyte interfacial (SEI) film and optimizing the electrochemical stability. Here, we are committed to rendering a comprehensive study of Li+ transport during the Li plating/stripping process related to the interactions between the Li dendrites and SEI film. Moreover, rational ion modulation strategies based on functional separators, artificial SEI films, solid-state electrolytes and structured anodes are introduced to homogenize Li+ flux and stabilize the lithium metal surface. Finally, the current issues and potential opportunities for ion transport regulation to boost the high energy density of LMBs are described.

Regulating Li-ion flux via engineering oxidized ZIF-8/polyacrylonitrile fiber interlayer for Li metal batteries with high performance

A novel oxidized ZIF-8/polyacrylonitrile fiber interlayer with excellent lithophilicity and uniform microporous structure could regulate Li-ion flux to obtain high performance of Li metal batteries.

Lithiophilic single-atom Co on carbon nanosheets synergistically modulates Li deposition enable dendrite-free lithium metal batteries

Lithium metal batteries with proud energy density gained wide research interest in the past decades. Unfortunately, the uneven lithium deposition and the uncontrollable lithium dendrites growth leading to low coulombic efficiency and poor cycling stability remain unresolved. Herein, advanced approach via constructing 3D hierarchical single-atom Co anchored nitrogen carbon nanosheets-carbon fiber cloth (CC@CN-SACo) is reported that enables uniform Li deposition and offers high performance of Li metal batteries. The design of active single-atom in CC@CN-SACo achieves enhanced lithophilicity that effectively reduces the nucleation overpotential. Owing to the enlarge specific area and numerous lithophilic single atom Co sites, the current density is significantly reduced and the Li+ ion flux is uniformly distributed. Density functional theory calculations also reveal that the electron-delocalized sp2 hybridized 2D carbon plane between Co sites on the CN-SACo nanosheet and the active s(Li)-dz2/dxz(Co) interactions takes a pivotal role in improving Li deposition thermodynamics as well as the diffusion kinetics of Li+ and effectively modulates the deposition/stripping behavior of Li at lithium metal anode, thereby preventing the formation of Li dendrites. As a consequence, CC@CN-SACo@Li electrode assembled with Li foil delivers a superior cycling stability with 2000 h, 1400 h, and 500 h at 1 mA cm−2/1mAh cm−2, 2 mA cm−2/1mAh cm−2, and 5 mA cm−2/5mAh cm−2, respectively. The full cells assembled with LiFePO4 achieve a capacity retention of 96.6% with 2 mg cm−2 LiFePO4 and 81% with N/P ratio of 5 at 1C is attained. Surprisingly, CC@CN-SACo@Li also presents superior performances with 718.4 mAh g−1 reversible capacity after 300 cycles when applied in lithium-sulfur batteries, suggesting its universality for different high-energy batteries.

A new approach to stabilize the electrochemical performance of Li metal batteries through the structure alteration of CNT scaffolds

Recently, interest in Li-metal batteries (LMBs) has been revived because the high specific capacity and lowest operating potential of Li-metal anodes help in resolving the existing issues of conventional Li-ion batteries. Unfortunately, the main problems associated with poor coulombic efficiency and dendritic Li formation impede the use of Li-metal anodes for commercial batteries. Among various strategies to address these intrinsic challenges of Li-metal anodes, the approach to utilize 3D current collectors has shown attractive results in terms of electrochemical stability. Herein, we assessed two different carbon nanotubes (e.g., double-walled nanotubes (DWNTs) and multi-walled nanotubes (MWNTs) scaffolds to study how the structure of carbon-based current collectors affects the coulombic efficiency and electrochemical stability of LMBs. As MWNTs have a more favorable structure for the reversible storage/release of Li-ion than DWNTs, they facilitate uniform and stable Li deposition over the entire surface of the MWNT matrix, thereby diminishing the growth of sharp dendritic Li. This resulting effect directly contributes to the stable operation of Li-metal cells at high current densities. Moreover, it has shown a remarkable improvement in electrochemical stability when the MWNT current collector was applied to the anode-free cell using a LiCoO2 cathode. The MWNT/LiCoO2 cell exhibited excellent cycle retention (97% at 50 cycles) with a high coulombic efficiency (99%). This work suggests that the material of the current collectors plays an apparently important role in the electrochemical stability of LMBs.

Fluorinated ether decomposition in localized high concentration electrolytes

Localized high concentration electrolytes (LHCEs) are a promising class of battery materials to enable stable cycling of the lithium metal anode. Here, we report the use of operando nuclear magnetic resonance (NMR) spectroscopy to observe electrolyte decomposition during Li stripping/plating and identify the influence of individual components in LHCEs on Li metal battery performance. Data from operando19F solution NMR indicates that both bis(fluorosulfonyl)imide (FSI−) salt and bis(2,2,2-trifluoroethyl) ether (BTFE) diluent molecules play a key role in solid electrolyte interphase (SEI) formation. Three-electrode electrochemical impedance spectroscopy (EIS) of commercial pouch cells also shows differences in interfacial resistances between LHCE and standard high concentration electrolytes (HCEs) that may be explained by incorporation of BTFE and BTFE reaction products into the SEI. Based on solid-state NMR and X-ray photoelectron spectroscopic characterization, we find that BTFE diluents decompose to form CF2- and CF3-containing fragments within a LiF-rich SEI deposited on the anode surface. The CEI on the cathode (here, LiNi0.8Mn0.1Co0.1O2) side of the battery also contains higher quantities of LiF and trapped LiFSI after cycling in the LHCE compared to a HCE that are attributed to diluent decomposition and correlated with lower impedance at the cathode. Overall, this work provides a new framework to consider highly fluorinated ether molecules—instead of functioning purely as diluting agents in LHCEs, these fluorinated ethers exhibit tunable interfacial reactivity that can be leveraged to control Li deposition behavior.

Nonflammable Localized High-Concentration Electrolytes with Long-Term Cycling Stability for High-Performance Li Metal Batteries.

High-concentration electrolytes (HCEs) can effectively enhance interface stability and cycle performance of Li metal batteries (LMBs). However, HCEs suffer from low ionic conductivity, high viscosity, high cost, and high density. Herein, fluorobenzene (FB) diluted localized high-concentration electrolytes (LHCEs) consisting of lithium bis(fluorosulfonyl)imide (LiFSI)/triethyl phosphate (TEP)/FB are developed. 2.3 M LHCE can reserve concentrated Li+-FSI--TEP solvation structures. Diluent FB possesses low density, low viscosity, low cost, low dielectric constant, low LUMO, and a good fluorine-donating property, which can significantly reduce viscosity, improve ionic conductivity, promote the formation of LiF-rich SEI, and enhance interaction of Li+-TEP and Li+-FSI- ion-pairs of the electrolytes. 2.3 M LHCE is a highly safe nonflammable electrolyte. 2.3 M LHCE can effectively inhibit dendrite growth on Li metal anode. 2.3 M LHCE endows LiFePO4 cells with good rate capability (discharge capacity of 112.7 mAh g-1 at 5 C rate) and excellent cycling performance (capacity retention of 95.4% after 1000 cycles). 2.3 M LHCE also shows good compatibility with LiNi0.8Co0.1Mn0.1O2 and exhibits outstanding cycle stability (capacity retention of 86.4% after 500 cycles). Therefore, 2.3 M LHCE is a promising electrolyte for practical applications in LMBs.

Electrochemical behavior and morphological evolution of Li metal anode under high cycling capacity

Despite the high theoretical capacity and low reduction potential of Li metal, low Coulombic efficiency and safety issues of Li metal batteries have hindered their commercialization. In this work, we explore the processes significantly impacting on Coulombic efficiency and overpotential in Li||Cu asymmetric cells depending on “cycling capacity”. To understand this behavior, we focused on three overshooting peaks in voltage profiles, and as each peak involves both Li plating and stripping at two electrodes, we could extract the six individual processes. Among them, the decreasing values of overpotential with increasing cycling capacity (or equivalently, “cycling time” at a fixed current density) are clearly observed, confirming their influence on cell performance. This comprehensive understanding of Coulombic efficiency, overpotential and morphological evolutions from the perspective of time provides new insight to the performance of Li metal batteries.