Li Dendrite Formation Research Articles

Bis(fluorosulfonyl)imide- and allyl-functionalized electrolyte additive as an interface stabilizer for Li-metal batteries

Lithium (Li) metal anodes have emerged as an appealing advanced electrode material, however, there are numerous limitations because of its unstable chemical and electrochemical reactivities and dendritic Li formation. Here, dually functionalized electrolyte additives using bis(fluorosulfonyl)imide- and allyl-functional groups are designed, and their electrochemical properties are investigated. The electrochemical reduction of allyldimethylpropylammonium bis(fluorosulfonyl)imide (ANP-F) and diallyldimethylammonium bis(fluorosulfonyl)imide (ANA-F) additives results in the formation of an inorganic–organic combined solid electrolyte interphase (SEI) layer on the Li metal surface, which is responsible for the prolonged cycling of the cells. Even after 1100 h, the Li/Li symmetric cells with ANP- and ANA-F additives exhibit stable cycling, and further in- and ex-situ analyses show that electrolyte decomposition and dendritic Li formation on the Li metal surface are suppressed. The cells cycled with 2.0 ANP- and 2.0 ANA-F show an average coulombic efficiency (CE) of 97.7 % and 94.1 %, respectively, as compared to that of the standard electrolyte of 91.3 %. As a result, the 2.0 ANP- and 2.0 ANA-F provide stable cycling retention of Li metal/LFP cells because the bi-functionalized SEI layer produced by the electrochemical reduction of the ANP- and ANA-F additives prevents parasitic reactions at the Li metal interfaces.

Grafting of Lithiophilic and Electron‐Blocking Interlayer for Garnet‐Based Solid‐State Li Metal Batteries via One‐Step Anhydrous Poly‐Phosphoric Acid Post‐Treatment

AbstractGarnet‐based solid‐state Li‐metal batteries (GSSBs) have the merits of high energy density and high safety. However, the realization of a stable and well‐matched Li|garnet interface for GSSBs remains challenging due to electron leakage and lithiophobic Li2CO3 impurity. To address these issues, herein, new surface chemistry is reported that converts the undesired Li2CO3 contaminant into an ultra‐thin lithium polyphosphate (Li‐PPA) layer through anhydrous polyphosphoric acid ‐induced in situ substitution reaction without damaging the water‐sensitive garnet electrolyte. In particular, the Li‐PPA interlayer not only facilitates the homogenous spreading of molten Li but also creates a robust electron‐blocking shield to suppress Li dendrite formation. As a result, the assembled Li symmetric cell exhibits a low interfacial impedance (4 Ω cm2) and high critical current density (1.8 mA cm−2) at 25 °C, which enables the cell to continuously cycle over 2500 h at 0.2 mA cm−2. Furthermore, the GSSBs paired with LiFePO4 deliver a high capacity of 149.3 mAh g−1 at 1 C and maintain 92.3% of the initial capacity after 500 cycles and can be used for solar energy storage, suggesting the feasibility of this interfacial engineering strategy for GSSBs.

Restraining lithium dendrite formation in all-solid-state Li-metal batteries via the surface modification of the ceramic filler

Polymer-based all-solid-state Li-metal batteries (ASSLMBs) have acquired considerable attention owing to their applicability to various systems and their enhanced safety characteristics. Hence, ASSLMBs can potentially replace flammable organic-liquid-electrolyte-based Li-ion batteries. However, owing to the interfacial instability and Li dendrite formation, ASSLMBs exhibit low capacity deprivation. To overcome this limitation, in this study, the hydrophilic nature of SSZ-13 zeolite was altered to hydrophobic using OH-functional silicone-modified polyacrylate (BYK-SILCLEAN 3700). A hydrophobic surface-modified zeolite filler (SSZ-13, MZLT) was incorporated into a polyethylene oxide (PEO) matrix, which permitted considerable Li salt adsorption and ensured the uniform distribution of MZLT in the PEO matrix. This resulted in a substantially improved ionic conductivity (σ) of the electrolyte, thereby enhancing the performance and durability of ASSLMBs. Furthermore, excellent σ (3.46 × 10−2 S cm−1 at 60 °C) was achieved through the surface modification of the filler, resulting in a Li transference number of 0.83. The Li plating–stripping results (for 1800 h of cycling at a discharge current of 100 μA cm−2) suggested satisfactory compatibility of the electrolyte with the Li metal. Scanning electron microscopy and X-ray photoelectron spectroscopy results confirmed that the growth of Li dendrites was significantly suppressed, leading to a retention rate of 98.5% after 200 cycles. Additionally, the fire retardancy was considerably improved. The findings of this study highlight the potential of composite-electrolyte-based ASSLMBs as candidates for energy storage devices.

Electrode structure enabling dendrite inhibition for high cycle stability quasi-solid-state lithium metal batteries

Lithium (Li) metal batteries (LMBs) are widely regarded as the ultimate choice for the next generation of high-energy–density batteries. However, the uncontrollable growth of Li dendrites formed by inhomogeneous deposition seriously hinders its commercialization. Although many studies have achieved significant results in inhibiting the formation of Li dendrites, it is still impossible to eradicate them completely. Therefore, regulating the deposition behavior, such as the growth direction of unevenly deposited Li, is preferable to unilaterally suppressing them in some cases. Here we report a structured anode that can confine the deposited Li within holes and tune it to become vertical-up/horizontal-centripetal mixed growth mode by optimizing the electric field/Li+ concentration gradient. The Li+ adsorbed by the poly(amic acid) (PAA) insulating layer coated on the anode surface can form the Li+ concentration gradient pointing to the center of the hole. Combined with the special electric field formed by the hole structure, it is favorable for the Li+ to move into the vertically arrayed holes and simultaneously deposit on the bottom and walls. Furthermore, both in-situ and ex-situ observations confirm that the growth mode is changed and the Li deposition morphology is denser, which can greatly delay capacity fading and prolong cycle life in both liquid and quasi-solid-state LMBs. All the results show that the novel anode provides a new perspective for deep research into solid-state LMBs.

Flexible Freestanding Thin Polyethylene Oxide‐Based Film as Artificial Solid–Electrolyte Interface to Protect Lithium Metal in Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) that utilize sulfur and lithium (Li) metal as electrode materials are highly attractive for transportation applications due to their high theoretical gravimetric energy density. However, two major challenges currently impede the commercialization of LSB, which are the formation of Li dendrites and polysulfide shuttling. To mitigate these two effects, a protective film or artificial solid–electrolyte interface (SEI) can be applied directly to the Li‐metal surface. Herein, the preparation of freestanding polyethylene oxide (PEO)‐based films using tape casting as a scalable coating technique is presented. Moreover, the films are applied directly to the Li surface via a solvent‐free method. To demonstrate the suitability of the developed PEO‐based films, the long‐term cycling performance of the lithium–sulfur cells is discussed. It is shown that the cells with the Li‐metal surface protected by PEO‐based films achieve better stability and reproducibility, reaching ≈400 mA h g S−1 after 250 cycles compared to ≈200 mA h g S−1 after 250 cycles for the bare Li‐metal electrode. An extensive postmortem analysis of the Li‐metal electrode surface with scanning electron microscopy is additionally shown, revealing that the PEO‐based artificial SEIs form uniformly with a low level of defect layers at the interface with the Li‐metal electrode, which indicates the creation of a stable SEI.

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.

Fe2O3 Nanoparticle Interfacial Reaction Redistributing Li-Ion Flux in Flexible Hierarchically Porous Membrane Electrodes for Dendrite-Free Lithium Metal Batteries

The uncontrollable formation of Li dendrites and the problems arising from it are the major obstacles in the practical application of Li metal batteries. Thereby, it is crucial to induce the uniform dispersion and deposition of Li+. To realize it, we constructed a flexible membrane electrode that facilitated Li+ dispersion by the interwoven conductive porous skeleton and simultaneously promoted Li+ deposition with doped active sites. The skeleton was composed of CNTs cross-linked with polyvinylidene fluoride (PVDF), which ensured the good conductivity and flexibility of membrane, and the −CF2 groups on PVDF chains also accelerated the migration of Li+. The doped Fe2O3 with strong lithiophilicity played a vital role in Li+ deposition. Quasi in situ X-ray photoelectron spectroscopy and in situ X-ray diffraction measurements were employed to reveal the reaction mechanism that Fe2O3 could be partially reduced by Li+ forming LixFe alloy, and reoxidized to amorphous Fe2O3. According to the galvanostatic current test of symmetric battery, the voltage had no significant changed after 1500 h, which proved that multifunctional membrane electrode effectively reduced the effect of Li dendrites. The assembled coin battery delivered an initial capacity of 125.9 mA h g–1 and still maintained at 114.9 mA h g–1 after 200 cycles at 0.5 C, with a capacity decay rate of only 0.048% per cycle. The pouch cell also exhibited excellent cycling stability with a Coulombic efficiency of >99.2% after 70 cycles at 0.5 C. This work provides a novel flexible membrane electrode design in solving the Li dendrites and developing novel electrodes for Li metal batteries.

Fast Ion Transport in Li‐Rich Alloy Anode for High‐Energy‐Density All Solid‐State Lithium Metal Batteries

AbstractAll‐solid‐state Li batteries (ASSLBs) with solid‐polymer electrolytes are considered promising battery systems to achieve improved safety and high energy density. However, Li dendrite formation at the Li anode under high charging current density/capacity has limited their development. To tackle the issue, Li‐metal alloying has been proposed as an alternative strategy to suppress Li dendrite growth in ASSLBs. One drawback of alloying is the relatively lower operating cell voltages, which will inevitably lower energy density compared to cells with pure Li anode. Herein, a Li‐rich Li13In3 alloy electrode (LiRLIA) is proposed, where the Li13In3 alloy scaffold guides Li nucleation and hinders Li dendrite formation. Meanwhile, the free Li can recover Li's potential and facilitate fast charge transfer kinetics to realize high‐energy‐density ASSLBs. Benefitting from the stronger adsorption energy and lower diffusion energy barrier of Li on a Li13In3 substrate, Li prefers to deposit in the 3D Li13In3 scaffold selectively. Therefore, the Li–Li symmetric cell constructed with LiRLIA can operate at a high current density/capacity of 5 mA cm−2/5 mAh cm−2 for almost 1000 h.

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.

Phase Separation–Controlled Assembly of Hierarchically Porous Aramid Nanofiber Films for High‐speed Lithium‐Metal Batteries (Small 52/2022)

Porous Aramid Nanofiber Films In article number 2205355, Jeong Gon Son, Bongjun Yeom, and co-workers report highly porous aramid nanofiber separators with dual porosity (>97%), prepared by a two-step solvent exchange process, for Lithium-metal batteries. The hierarchical porous structure with maximized porosity and selective affinity of the aramid nanofibers to anions shows effectively reduced Li dendrite formation and stable cycling performance under high-speed charge/discharge conditions.

Intrinsic Zinc in Brass Enables Lithium Anode Dendrite‐Free

AbstractBrass foil, composed of copper (Cu) and zinc (Zn), is a commercialized low‐cost Cu‐based matrix with lithiophilic properties. However, brass has never been employed as a current collector of lithium (Li) metal anode to suppress formation of Li dendrite. Here, we show that brass foil is directly utilized as a current collector for Li metal anodes. It exhibits a stable repeated Li plating and stripping for more than 400 h (200 cycles) with a low overpotential (∼0.018 V) and a capacity of 1 mAh cm−2 at a current density of 1 mA cm−2 in a symmetric cell, as well as a higher average Coulombic efficiency of 97.2 % for more than 120 cycles with a capacity of 1 mAh cm−2 at a current density of 0.5 mA cm−2. Thanks to the lithiophilicity of homogeneous Zn in brass, the nucleation overpotential of Li is effectively reduced and Li is uniformly deposited on the current collector without dendrite formation. Our investigation might inspire the ancient brass to apply to lithium‐ion battery.

Structurally Tailored Hierarchical Cu Current Collector with Selective Inward Growth of Lithium for High‐Performance Lithium Metal Batteries

AbstractLi‐metal is gaining attention as a next generation anode active material, of which the primary attribute is its energy density. However, Li dendrite formation is the primary challenge. Herein, a design strategy with increased structural dimensions and hierarchy for Li‐metal anode is investigated to stabilize the dendrite formation for extending the cycle life with high reversibility. For this, diverse structural current collectors (CCs) are fabricated by manipulating structural design in different length scales and characterized as a Li‐metal anode. The hierarchy (i.e., nanostructures inside the microcavities) can not only reduce the current density on entire anode surface but also concentrate the local electrical field onto inner surfaces of the microstructures, inducing preferential Li nucleation inside microcavities and promoting confined growth of Li. It is confirmed that introduction of structural hierarchy can enhance the cycle life by 364% and the preservation of coulombic efficiency > 90% by 266%. The design strategy is extended by exploring a practical one‐step fabrication of the hierarchical CC with even greater performance via the inward growth mechanism. This work elucidates the mechanism of inward Li growth using tailored surface geometries for Li dendrite suppression, which can be a guideline for designing structured anode CCs for Li‐metal batteries.

Highly conductive Poly(ε-caprolactone) and chitosan based polymer electrolyte for lithium metal battery

Poly (ε-caprolactone) (PCL) is an attractive polymer electrolyte material due to its ultralow glass transition temperature, high dielectric constant as well as excellent electrochemical stability, but its practical application has been greatly hindered due to the low ionic conductivity induced by the semi-crystalline structure. Herein, we elaborately modify PCL with chitosan (CS) to obtain an amorphous PCL-CS composite membrane, and develop a fast Li+ conducting quasi-solid polymer electrolyte (QPE) with lithium bis(trifluoro methane sulphonyl)imide (LiTFSI) and merely 10 wt% plasticizer. The optimized QPE with 50 wt% LiTFSI exhibits an ionic conductivity of 7.7 × 10−4 S cm−1, which is the highest among PCL-based polymer electrolyte. Fourier Transform Infrared spectroscopy and Raman spectra reveal that Li+ conducting via the solvation of partial plasticizer as well as contacted ionic clusters. In addition, its excellent stability and compatibility are validated by the integrated symmetric Li//Li cell that exhibits an ultra-long cycling for over 1850 h with no Li dendrite formation.

Photo-crosslinked lignin/PAN electrospun separator for safe lithium-ion batteries

A novel crosslinked electrospun nanofibrous membrane with maleated lignin (ML) and poly(acrylonitrile) (PAN) is presented as a separator for lithium-ion batteries (LIBs). Alkali lignin was treated with an esterification agent of maleic anhydride, resulting in a substantial hydroxyl group conversion to enhance the reactivity and mechanical properties of the final nanofiber membranes. The maleated lignin (ML) was subsequently mixed with UV-curable formulations (up to 30% wt) containing polyethylene glycol diacrylate (PEGDA), hydrolyzed 3-(Trimethoxysilyl)propyl methacrylate (HMEMO) as crosslinkers, and poly(acrylonitrile) (PAN) as a precursor polymer. UV-electrospinning was used to fabricate PAN/ML/HMEMO/PEGDA (PMHP) crosslinked membranes. PMHP membranes made of electrospun nanofibers feature a three-dimensional (3D) porous structure with interconnected voids between the fibers. The mechanical strength of PMHP membranes with a thickness of 25 µm was enhanced by the variation of the cross-linkable formulations. The cell assembled with PMHP2 membrane (20 wt% of ML) showed the maximum ionic conductivity value of 2.79*10−3 S cm−1, which is significantly higher than that of the same cell with the liquid electrolyte and commercial Celgard 2400 (6.5*10−4 S cm−1). The enhanced LIB efficiency with PMHP2 membrane can be attributed to its high porosity, which allows better electrolyte uptake and demonstrates higher ionic conductivity. As a result, the cell assembled with LiFePO4 cathode, Li metal anode, and PMHP2 membrane had a high initial discharge specific capacity of 147 mAh g−1 at 0.1 C and exhibited outstanding rate performance. Also, it effectively limits the formation of Li dendrites over 1000 h. PMHP separators have improved chemical and physical properties, including porosity, thermal, mechanical, and electrochemical characteristics, compared with the commercial ones.

Stabilization of garnet/Li interphase by diluting the electronic conductor.

The high interfacial resistance and lithium (Li) dendrite growth are two major challenges for solid-state Li batteries (SSLBs). The lack of understanding on the correlations between electronic conductivity and Li dendrite formation limits the success of SSLBs. Here, by diluting the electronic conductor from the interphase to bulk Li during annealing of the aluminium nitride (AlN) interlayer, we changed the interphase from mixed ionic/electronic conductive to solely ionic conductive, and from lithiophilic to lithiophobic to fundamentally understand the correlation among electronic conductivity, Li dendrite, and interfacial resistance. During the conversion-alloy reaction between AlN and Li, the lithiophilic and electronic conductive LixAl diffused into Li, forming a compact lithiophobic and ionic conductive Li3N, which achieved an ultrahigh critical current density of 2.6/14.0 mA/cm2 in the time/capacity-constant mode, respectively. The fundamental understanding on the effect of interphase nature on interfacial resistance and Li dendrite suppression will provide guidelines for designing high-performance SSLBs.

Analysis of Li Dissolution/Deposition Behavior in LiNO3 Electrolytic Solution for Li-Air Battery

Li-air batteries (LAB) have been attracting much attention because of their theoretical energy density of 3500 Wh kg−1, which is five times as high as that of Li-ion batteries. However, many problems remain to be challenged in every component of the battery: air electrodes, electrolytic solutions, Li electrodes, etc. As for the Li electrode, we have reported some results on the reversibility of the Li dissolution/deposition reaction by using Li | Li symmetric cells with tetraglyme (G4) -based electrolytic solution [1, 2]. In particular, it has been confirmed that in the 1.0 M LiNO3/G4 electrolyte under an O2 atmosphere, a Li2O protective layer is efficiently formed on the Li electrode at a current density of 0.4 mA cm-2, and Li dendrite formation is suppressed. In this study, we expanded test conditions in current densities up to 2.0 mA cm-2 and temperatures at 10 °C to 50 °C to reveal whole picture of dissolution/deposition behavior of the Li electrode.A Li | Li symmetric cell was assembled using a pair of Li foils inserted by a separator (Celgard 2400) and 1.0 M LiNO3/G4 or 1.0 M LiTFSI / G4 as the electrolytic solutions in an Ar-filled glove box. The Li dissolution/deposition cycle tests by the cells were carried out at 10, 30 and 50℃ at a constant current density between 0.2 to 2.0 mA cm-2 regulated by a constant capacity of 0.5 mAh cm− 2. After the tests, the Li electrodes were taken out of the cells followed by rinsing in G4 in the glove box, the surfaces of which were observed by SEM and analyzed by XPS. Figure 1 showed Li | Li cell test results at 0.4 mA cm−2 and 30 ℃ in different electrolytic solutions. Fig ure 1a for that in 1.0 M LiTFSI/G4 showed gradual decrease in overvoltages and unstable polarization curves. These two features suggested that the Li electrode protection by the Li2O layer from O2 gas could not withstand the current density and the exposed Li metal reacted with the solvent and electrolyte, resulting in growing Li dendrite deposition. On the other hand, Figure 1B for that in the 1.0 M LiNO3 / G4 overvoltages, suggesting suppressed Li-electrolytic solution showed very flat polarization plateaus and slightly growing dendrite formation. The difference between Figure 1a and 1b demonstrated the effect of Li2O protective layer of Li surface formed by the reaction between Li and NO3 −. Figure 2 showed the SEM image of the Li electrode after the dissolution/deposition test for 15 cycles and the surface analysis by C1s XPS. Figure 2a for LiTFSI/G4 electrolytic solution showed bulky surface layer as thick as 30 µm accompanied by a large dent. Figure 2b suggested various kind of C-containing deposits on the Li surface, which was presumably decomposed products of electrolytic solution. Therefore, Figure 2a and 2b were well consistent with Figure 1a which suggested successive surface reactions. Figure 2c and 2d for LiNO3/G4 electrolytic solution, on the contrary, showed thin surface layer and poor amount of surface products, even though the current density, 0.6 mA cm−2, was higher than that in Figure 2a, 0.4 mA cm−2. These results suggested steady surface protected by Li2O layer and were also consistent with Figure 1b.Other results presenting the effect of current densities and temperatures will be reported in our presentation to clarify the whole picture of Li dissolution/deposition reaction mechanism.

Li Morphology Evolution during Initial Cycling in a Gel Composite Electrolyte

Li metal anodes are the potential solution for high-energy batteries. One of the challenges of applying such a high-energy anode is Li dendrite growth, which results in short-circuit and thermal runaway. Current battery research focuses on developing solid electrolytes to serve as a physical barrier to prevent dendrite growth. However, the Li morphology change during plating and stripping, and the mechanisms of how Li dendrite grows and propagates into a complex composite solid electrolyte are poorly understood. Understanding and controlling Li morphology evolution, dendrite formation, and growth during cycling are crucial to developing dendrite suppression strategies for solid electrolytes and enabling high-energy lithium metal batteries.In this work, Li morphology evolution during initial cycling in a crosslinked PEO-based gel composite electrolyte full cell with NMC 811 cathode is monitored via post-mortem SEM. The results show that severe surface pitting occurs as early as the second stripping cycle. Pit formation and continuous dissolution is the main cause of Li surface roughening and dendrite growth mechanism in the model gel composite electrolyte. Comparing Li dendrite growth mechanisms in liquid, polymer, and solid electrolytes, the observed dendrite growth mechanism resembles that of the liquid electrolyte the most. This study suggests that strategies to improve the electrochemical reversibility of electrodeposited Li reported in liquid electrolytes to control Li morphology and prevent dendrite growth may be transferrable in a gel electrolyte.This work is sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. Part of the measurements was performed at the Center for Nanophase Materials Sciences (CNMS), which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences.

Mechanistic Understanding of Lithium Plating/Stripping Processes on the 3D Conductive Host Based on Vertically Aligned Carbon Nanofibers for Li Metal Anode

The highest theoretical capacity (3860 mAh/g) and lowest redox potential (-3.04 V vs standard hydrogen electrode) makes lithium metal as a promising anode for next generation high energy density batteries.1 Despite theoretical advantages, there are challenges in commercializing Li metal anodes such as low coulombic efficiency, dendrite formation and poor cycling life. Dendrite formation can cause short circuit and thermal runaway, which is a safety concern. Among the various ways to mitigate the Li dendrite formation, using three-dimensional (3D) current collectors with lithiophilic properties and low tortuous pore architecture is an effective way. It would decrease the local current density owing to high active surface area while accommodating the large volume change during prolonged charge/discharge cycles.Vertically aligned carbon nanofibers (VACNF) have been demonstrated as a promising candidate as a lithiophilic 3D host for lithium metal anodes as they possess unique conically stacked lithiophilic graphitic edges with O containing functional groups and high N doping (~6.5 at%).2 However, a fundamental, deeper understanding of the Li plating/stripping processes on such 3D electrodes has not been developed yet. Here in, we investigate the lithium nucleation and growth processes and its morphological changes using ex-situ structural characterization techniques such as SEM and cryo-TEM. The composition of the solid electrolyte interface is investigated using XPS. In-situ Raman spectroscopic studies provided further information about the changes that occur in the VACNFs during Li plating/stripping processes and Li intercalation/deintercalation processes. Ion-beam sputtering of an ultrathin gold layer onto the VACNFs was found to further improve the lithiophilicity of the 3D electrode and lead to more reversible Li metal plating/stripping. The new insights on the electrodeposition of lithium in 3D electrodes and its relationship with the enhanced cycle life acquired using various analytical tools will be discussed.Reference:(1) Manthiram, A.; Chung, S.-H.; Zu, C. Lithium–Sulfur Batteries: Progress and Prospects. Advanced Materials 2015, 27 (12), 1980–2006.(2) Chen, Y.; Elangovan, A.; Zeng, D.; Zhang, Y.; Ke, H.; Li, J.; Sun, Y.; Cheng, H. Vertically Aligned Carbon Nanofibers on Cu Foil as a 3D Current Collector for Reversible Li Plating/Stripping toward High-Performance Li–S Batteries. Advanced Functional Materials 2020, 30 (4), 1906444.

(Invited) U.S. DOE Lithium Metal Solid-State Battery R&D

Decarbonizing transportation through electrification requires less expensive, higher energy density batteries made from earth-abundant materials to displace internal combustion engines. Suitable solid-state electrolytes (SSEs) that facilitate lithium metal anodes by blocking Li dendrite formation represent a promising pathway to high-energy density cells. In a similar manner, SSEs that block the polysulfide shuttle could facilitate sulfur cathodes with even higher energy density that avoid issues of critical materials and supply chain constraints coupled to transition metal oxide-based cathodes.Interest in solid-state batteries has increased rapidly in recent years. There are examples of solid-state batteries (SSBs) in commercial automotive applications; however, achieving wider adoption requires SSBs operating without the need for heating or excessive applied cell pressure. Several solid-state electrolyte chemistries (e.g., sulfides, ceramics, polymers, halides) are under development, but key issues remain unresolved in the case of each electrolyte chemistry.The U.S. Department of Energy Vehicle Technologies Office supports R&D encompassing all of these candidate electrolytes for solid-state batteries through the Advanced Battery Materials Research program. The R&D portfolio prioritizes: improving electrolytes through modified composition or synthesis to increase room-temperature Li+ conductivity and mitigate Li dendrite penetration; improving interfaces to address chemical or electrochemical reactivity, to decrease impedance, and to improve Li plating and stripping; and improving suitability for high-volume manufacturing of solid-state lithium metal batteries by improving mechanical properties and demonstrating thin, defect-free, large-area SSE layers.This presentation comprises solid-state lithium metal battery R&D priorities and accomplishments in the context of meeting DOE targets for energy density, cycle life, and cost. It will also emphasize the importance of SSBs to U.S. DOE strategy for increasing domestic lithium-based battery manufacturing and securing the U.S. position in next-generation battery innovation.

(Invited) Garnet Solid Electrolytes for Advanced All-Solid-State Li Metal Batteries

These days, Li metal anode-based battery has been arisen as one of the key energy storage technologies due to its high theoretical energy density compared to conventional lithium and sodium ion-based batteries. The present Li-S batteries suffer due to Li dendrite formation and capacity decay due to polysulfide dissolution effect, because of organic electrolytes used in the current research. Solid state (ceramic) electrolytes are promising to prevent Li dendrite growth and polysulfide dissolution. Among different ceramic electrolytes garnet-type structure solid inorganic electrolytes are very promising because of its high lithium-ion conductivity and stability with elemental Li. However, the high interfacial resistance with the electrode is the major bottleneck for the practical use of ceramic electrolyte. Polymer and ceramic hybrid electrolytes exhibit low interfacial resistance. In this talk, we will present development of electrolytes for all-solid-state Li metal batteries.