Application Of Li Metal Batteries Research Articles

Multifunctional covalent organic frameworks for high capacity and dendrite-free lithium metal batteries

For its high specific capacity of 3860 mAh g−1 and low redox potential of −3.04 V (vs. SHE), lithium (Li) metal has been regarded as one of the most promising anode materials for the next-generation batteries. However, the limited Li utilization and the detrimental dendrite growth severely impede the practical application of Li metal batteries. Herein, the covalent organic frameworks LZU1 (COF-LZU1) is introduced to serve as a protective layer in-between the Li anode and separator. Because of the interaction between bis(trifluoromethanesulonyl)imide (TFSI) anions and aldehyde functional groups in COF-LZU1, TFSI− are immobilized on the COF-LZU1, alleviating the impact of space charge and hence suppressing the dendrite growth. Furthermore, the imine-linked COF-LZU1 is lithiophilic and electrolyte wettable, enabling a homogenous Li ions flux distribution and transport and hence resulting in a low voltage hysteresis. With the dendrite-free anode, the utilization of Li achieves >99% in Li–Cu cell and the life-span is over 2000 h in Li–Li symmetric cell with a low voltage hysteresis of ≈35 mV. Moreover, Li-Sulfur batteries with COF-LZU1 layer present significantly better stability and rate properties than the ones without COF-LZU1. Therefore, utilization of the COF-LZU1 protective layer has been successfully demonstrated to be an effective approach to enable safe and high power/energy density Li metal batteries.

Towards high-performance lithium metal anodes via the modification of solid electrolyte interphases

Abstract Li metal has been regarded as one of the most promising anodes for high-energy-density storage systems due to its high theoretical capacity and lowest electrochemical potential. Unfortunately, an unstable and non-uniform solid electrolyte interphase (SEI) deriving from the spontaneous reaction between Li metal anode and electrolyte causes uneven Li deposition, resulting in the growth of Li dendrites and low Coulombic efficiency, which have greatly hindered the practical application of Li metal batteries. Thus, the construction of a stable SEI is an effective approach to suppress the growth of Li dendrites and enhance the electrochemical performances of Li metal anode. In this review, we firstly introduce the formation process of inferior SEI of Li metal anode and the corresponding challenges caused by the unstable SEI. Next, recent progresses to modify SEI layer through the regulation of electrolyte compositions and ex-situ protective coating are summarized. Finally, the remained issues, challenges, and perspectives are also proposed on the basis of current research status and progress.

Controlling Li Ion Flux through Materials Innovation for Dendrite‐Free Lithium Metal Anodes

AbstractLithium (Li) metal with high theoretical capacity and the lowest electrochemical potential has been proposed as the ideal anode for high‐energy‐density rechargeable battery systems. However, the practical commercialization of Li metal anodes is precluded by a short lifespan and safety problems caused by their intrinsically high reductivity, infinite volume change, and uncontrollable dendrite growth during deposition and dissolution processes. Plenty of strategies have been introduced to solve the above‐mentioned problems. Among these, controlling Li+ flux plays a vital role to directly influence the plating and stripping process. In this work, the fundamental effect of Li+ flux distribution on Li nucleation and early dendrite growth is discussed. Then, recent strategies of controlling Li+ flux to suppress dendrite formation and growth through materials design are summarized, including homogenizing Li+ flux, localizing Li+ flux, and guiding gradient Li+ distribution. Finally, underexplored materials are proposed and explored to control Li+ flux and further directions for dendrite‐free Li anodes. It is expected that this progress report will help to deepen the understanding of Li+ flow tuning and morphology control of Li anodes and eventually facilitate the practical application of Li metal batteries.

A Coaxial‐Interweaved Hybrid Lithium Metal Anode for Long‐Lifespan Lithium Metal Batteries

AbstractLithium (Li) metal is one of the most promising anode materials to construct next‐generation rechargeable batteries owing to its ultrahigh theoretical capacity and the lowest electrochemical potential. Unfortunately, practical application of Li metal batteries is severely hindered by short lifespan and safety concerns caused by Li dendrite growth during cycling. Herein, a coaxial‐interweaved hybrid Li metal anode is proposed for dendrite inhibition that significantly improves the cycling stability of Li metal batteries. The hybrid Li metal anode is fabricated by Li composition into a 3D interweaved scaffold, where each fiber of the interwoven scaffold is composed of a conductive skeleton and a coaxial lithiophilic layer modified on the surface. The coaxial‐interweaved structure endows the hybrid anode with favored Li affinity to guide uniform Li deposition, sufficient channels for ion transportation and electron conduction, and enhanced stability during Li plating and stripping. Consequently, the hybrid Li metal anode affords high Coulombic efficiency over 98.5% for 750 cycles with dendrite‐free morphologies in half cells and improved capacity retention of 80.1% after 100 cycles in LiFePO4 full cells. The innovative coaxial‐interweaved hybrid Li metal anode demonstrates multiscale design strategy from lithiophilic modification to scaffold construction and promises the prospect of Li metal batteries for future applications.

Multifunctional Gel Polymer/Microspheres Composite Electrolyte Coated Separator for Lithium Metal Batteries

Lithium (Li) metal has received much attention as a promising anode candidate in recent years with the increasing demand for high-energy-density rechargeable batteries in industrial fields. However, unlike current graphite anodes where Li ions are intercalated, metallic Li anodes generate Li deposition forming an uneven anode surface and have high reactivity toward organic electrolytes. This can cause safety concerns including cycling instability. Thus, developing a stable electrolyte and its corresponding separator is widely recognized as a major challenge to the practical application of Li metal batteries. Although there remains a need for improving the separator performance because of poor separator wettability for highly viscous electrolytes, little work has been done about the separator structure design to ensure proper wettability and stability [1]. In this study, we propose a high performance composite coated separator for Li metal batteries. A commercial separator was thinly coated with a mixture of block copolymer, ionic liquid, and microspheres. The composite electrolyte coated separator showed significantly enhanced wettability which is sufficient to adsorb highly viscous electrolytes. To improve the mechanical properties of the separator, microspheres with high rigidity and stability to organic electrolyte [2] were used. The tensile strength and thermal stability of the separator were improved by microspheres and block copolymer. This approach appears to be effective in improving battery safety by inhibiting the growth of Li dendrites. Due to the increased wettability and enhanced mechanical properties, the cycle life of the cell was greatly improved when our separator was applied. In addition, unlike the ceramic component with a poor dispersion in the coating solution, our novel coating blend enables cost-effective production with rapid and uniform coatings with its excellent dispersion stability. [1] M. H. Ryou, Y. M. Lee, J. K. Park, and J. W. Choi, Adv. Mater., 23, 27 (2011). [2] Y. G. Lee, S. Ryu, T. Sugimoto, T. Yu, W. S. Chang, Y. Yang, C. Jung, J. Woo, S. G. Kang, H. N. Han, S. G Doo, Y. Hwang, H. Chang, J. M. Lee, and J. Y. Sun, Chem. Mater., 29, 14 (2017).

Stable lithium metal anode enabled by lithium metal partial alloying

The practical application of lithium (Li) metal anodes is critical for the next generation high energy density batteries. However, the mainstream challenge of Li dendrites formation that affects the cycle performance and safety of the battery still needs to be addressed. Here, Li/LixC/LiySn (Li/C/Sn) composites with uniform distribution of Li metal alloys are fabricated and applied to a Li metal anode. Electrochemical measurements and post-mortem analysis reveals the effectiveness of the Li alloy phases for promoting uniform Li deposition and inhibiting Li dendrite growth. The Li/C/Sn composite electrode delivers enhanced cycle stability over 1800 and 1200 h at the current densities of 1 and 2 mA cm−2, respectively. Moreover, the full cells of the Li/C/Sn electrode paired with LiFePO4 exhibited significantly enhanced rate performance and cycle stability. The effective and scalable method for modifying Li metal anodes represents an essential step to promote the commercial application of Li metal batteries.

Non-destructive characterization of lithium deposition at the Li/separator and Li/carbon matrix interregion by synchrotron X-ray tomography

Inherently uncontrollable Li electrodeposition has significantly hindered the practical application of Li metal batteries largely due to a dendritic deposition which can initiate an internal short circuit and gives rise to severe safety issues. The understanding of the fundamental electrodeposition mechanism is, however, elusive and limited due to a lack of feasible in situ characterization techniques. Here synchrotron X-ray tomography was employed to noninvasively visualize Li deposition at the lithium/separator and lithium/carbon matrix interregion. A higher concentration of widely distributed deposition sites was observed under an increased current density. The 3D morphology and distribution of deposited Li within the widely used Celgard® 2325 polyolefin separator are, for the first time, visualized in situ, thus promoting the understanding of the short-circuiting process of Li metal batteries. In addition, we also visualized and quantified the spatial distribution of Li depositions inside a porous carbon host to unravel the deposition behavior that can hardly be probed by surface imaging techniques. The Li electrodeposition behavior found here could help to promote the understanding and development of surface modifications related to Li anodes, separators as well as novel 3D geometry electrode designs for accommodation of Li depositions and alleviation of volumetric changes.

Hybrid Polymer Electrolytes for Lithium Metal Batteries

The use of lithium (Li) metal as anode in rechargeable batteries has been revived recently because Li metal has the potential to double the specific energy density of the state-of-the-art Li ion batteries. However, Li dendrite growth and low Coulombic efficiency still hinder the application of Li metal batteries. The urgent and most important thing is to develop an electrolyte which can enable Li metal to be used as anode with high safety and good stability. Solid polymer electrolytes (SPEs) have attracted much attention due to their outstanding advantages over conventional liquid electrolytes, including no leakage of electrolytes, good flexibility, low flammability, high safety and stable contact with the electrodes. As the most widely studied polymer in SPEs, polyethylene oxide (PEO) still faces some challenges, including the low ionic conductivity (σ < 10-5 S cm-1) at room temperature (RT) and instability when charged to above 4 V vs. Li/Li+. In this work, we developed a hybrid polymer electrolyte (HPE) which exhibits high oxidation voltage and high ionic conductivity. The HPE shows an oxidation stability above 4.5 V vs. Li/Li+ when platinum was used as the working electrode in a three-electrode cell. The pure HPE has an ionic conductivity of 0.46 mS cm-1 and 2.8 mS cm-1 at 30 °C and 60 °C, respectively. The increased electrochemical window and the high conductivity of the HPE enable the Li||LiNi1/3Mn1/3Co1/3O2 cells (with an areal capacity loading of 2 mAh cm-2) to show a stable cycling in the voltage range of 3.0 – 4.2 V, having a high capacity retention of 84.2% after 170 cycles under charge rate of C/5 and discharge rate of C/3 at 60 °C. More details will be reported during the presentation at the meeting. Acknowledgement This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, the Advanced Battery Materials Research (BMR) Program of the U.S. Department of Energy (DOE) under contract no. DE-AC02-05CH11231.

Mixed Ion and Electron‐Conducting Scaffolds for High‐Rate Lithium Metal Anodes

AbstractLi metal batteries are considered a promising candidate for next‐generation rechargeable batteries. However, the practical application of Li metal batteries has been hindered by many challenges, especially the cycling stability of Li anodes due to their uncontrollable dendrite growth, volume fluctuation, and side reactions. These problems are more severe under high‐rate charge/discharge process. Therefore, the realization of stable cycling of Li anodes under high current density is crucial for the practical application of Li metal batteries. In this Progress Report, the authors focus on the stability of metallic Li through interphase design or microstructure construction. The advantages and drawbacks of the first‐generation 3D scaffolds are summarized, and a review of recent research progress in this area is generated. As high‐rate cycling of metallic Li is a complex dynamic problem, a scaffold with high mixed ionic and electronic conductivity may be a promising approach. The different design strategies of mixed ion and electron‐conductive scaffolds working with liquid and solid electrolytes are discussed, along with their technical challenges. Further directions of mixed ion and electron‐conductive scaffolds are also proposed.

Three-dimensional carbon material as stable host for dendrite-free lithium metal anodes

For its low redox potential (−3.04 V vs. SHE) and the high theoretical specific capacity (3860 mA h g−1), lithium metal is regarded as one of the most promising anode materials for next-generation batteries. However, the poor cycling performances and serious safety hazards caused by the inhomogeneous lithium deposition severely hinder the practical applications of Li metal batteries. Here, we introduce 3-D carbon materials which are subsequently in-situ transformed into LiC6 as electrode scaffold. Such lithiophilic 3-D structure with a high specific surface area enables dendrite-free deposition of Li metal, resulting in a high coulombic efficiency up to 97% after 300 cycles. We propose that besides 3-D structure, LiC6 intermediate may be responsible for the dendrite-free growth of Li, offering a potential new strategy to design high performance anodes for Li metal batteries.

An ion redistributor for dendrite-free lithium metal anodes.

Lithium (Li) metal anodes have attracted considerable interest due to their ultrahigh theoretical gravimetric capacity and very low redox potential. However, the issues of nonuniform lithium deposits (dendritic Li) during cycling are hindering the practical applications of Li metal batteries. Herein, we propose a concept of ion redistributors to eliminate dendrites by redistributing Li ions with Al-doped Li6.75La3Zr1.75Ta0.25O12 (LLZTO) coated polypropylene (PP) separators. The LLZTO with three-dimensional ion channels can act as a redistributor to regulate the movement of Li ions, delivering a uniform Li ion distribution for dendrite-free Li deposition. The standard deviation of ion concentration beneath the LLZTO composite separator is 13 times less than that beneath the routine PP separator. A Coulombic efficiency larger than 98% over 450 cycles is achieved in a Li | Cu cell with the LLZTO-coated separator. This approach enables a high specific capacity of 140 mAh g-1 for LiFePO4 | Li pouch cells and prolonged cycle life span of 800 hours for Li | Li pouch cells, respectively. This strategy is facile and efficient in regulating Li-ion deposition by separator modifications and is a universal method to protect alkali metal anodes in rechargeable batteries.

Localized High-Concentration Sulfone Electrolytes for High-Efficiency Lithium-Metal Batteries

Summary To enable next-generation high-energy-density lithium (Li)-metal batteries (LMBs), an electrolyte that has simultaneous high Li-metal Coulombic efficiency (CE) and high anodic stability on cathodes is of significant importance. Sulfones are known for strong resistance against oxidation, yet their application in LMBs is restricted because of their poor compatibility with Li-metal anodes, high viscosity, and poor wettability. Here, we demonstrate that a high Li CE over 98% can be achieved in concentrated sulfone-based electrolytes. Furthermore, the viscosity and wettability issues of sulfones are resolved by the addition of a fluorinated ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, to form a localized high-concentration electrolyte (LHCE), which not only provides further improvement in Li CE (98.8%) but also remains anodically stable with high-voltage cathodes, suppresses Al corrosion, and enables LMBs to operate in a wide temperature range. As a result, significantly improved cycling performance of LMBs has been realized with sulfone-based LHCE.

Sulfone-Based Electrolytes for Highly-Efficient and Stable Lithium Metal Anode

Lithium (Li) metal batteries (LMBs) have been regarded as a very promising next-generation energy storage system because of the high theoretical specific capacity, the lowest electrochemical potential and the very low gravimetric density of the Li metal anode. Electrolytes that have high Li metal Coulombic efficiency (CE) and high anodic stability on cathodes play a major role to enable the long-term cycling stability of LMBs. Sulfones are known for their high dielectric constants, low flammability and good oxidation stability, but their application in LMBs is restricted due to their poor compatibility with Li metal anode. Uncontrolled Li platting can result in poor Li CE and induce battery short-circuit. Moreover, their high viscosity and poor wettability towards electrodes and separators are serious issues for practical applications. Here, we demonstrate that nodule-shaped instead of dendritic Li deposition and stable Li plating/stripping cycles can be achieved in concentrated sulfone-based electrolytes with a high CE over 98%. Furthermore, with the addition of selected co-solvents, not only the Li metal CE can be further improved, but also the viscosity and wettability issues are solved, enabling high rate Li||NMC cells cycling at a wide temperature range. As a result, improved cycling performance of Li||NMC cells using sulfone-based electrolytes has been realized.

Continuous plating/stripping behavior of solid-state lithium metal anode in a 3D ion-conductive framework.

The increasing demands for efficient and clean energy-storage systems have spurred the development of Li metal batteries, which possess attractively high energy densities. For practical application of Li metal batteries, it is vital to resolve the intrinsic problems of Li metal anodes, i.e., the formation of Li dendrites, interfacial instability, and huge volume changes during cycling. Utilization of solid-state electrolytes for Li metal anodes is a promising approach to address those issues. In this study, we use a 3D garnet-type ion-conductive framework as a host for the Li metal anode and study the plating and stripping behaviors of the Li metal anode within the solid ion-conductive host. We show that with a solid-state ion-conductive framework and a planar current collector at the bottom, Li is plated from the bottom and rises during deposition, away from the separator layer and free from electrolyte penetration and short circuit. Owing to the solid-state deposition property, Li grows smoothly in the pores of the garnet host without forming Li dendrites. The dendrite-free deposition and continuous rise/fall of Li metal during plating/stripping in the 3D ion-conductive host promise a safe and durable Li metal anode. The solid-state Li anode shows stable cycling at 0.5 mA cm-2 for 300 h with a small overpotential, showing a significant improvement compared with reported Li anodes with ceramic electrolytes. By fundamentally eliminating the dendrite issue, the solid Li metal anode shows a great potential to build safe and reliable Li metal batteries.

Artificial Soft–Rigid Protective Layer for Dendrite‐Free Lithium Metal Anode

AbstractLithium (Li) metal has been pursued as “Holy Grail” among various anode materials due to its high specific capacity and the lowest reduction potential. However, uncontrolled growth of Li dendrites and extremely unstable interfaces during repeated Li plating/stripping ineluctably plague the practical applications of Li metal batteries. Herein, an artificial protective layer with synergistic soft–rigid feature is constructed on the Li metal anode to offer superior interfacial stability during long‐term cycles. By suppressing random Li deposition and the formation of isolated Li, such a protective layer enables a dendrite‐free morphology of Li metal anode and suppresses the depletion of Li metal and electrolyte. Additionally, sufficient ionic conductivity is guaranteed through the synergy between soft and rigid structural units that are uniformly dispersed in the layer. Dendrite‐free and dense Li deposition, as well as a greatly reduced interfacial resistance after cycling, is achieved owing to the stabilized interface, accounting for significantly prolonged cycle life of Li metal batteries. This work highlights the ability of synergistic organic/inorganic protective layer in stabilizing Li metal anode and provides fresh insights into the energy chemistry and mechanics of anode in a working battery.

Trapping Lithium into Hollow Silica Microspheres with a Carbon Nanotube Core for Dendrite-Free Lithium Metal Anodes.

Li metal anodes, which have attracted much attention for their high specific capacity and low redox potential, face a great challenge in realizing their practical application. The fatal issue of dendrite formation gives rise to internal short circuit and safety hazards and needs to be addressed. Here we propose a rational strategy of trapping Li within microcages to confine the deposition morphology and suppress dendrite growth. Microcages with a carbon nanotube core and porous silica sheath were prepared and proved to be effective for controlling the electrodeposition behavior. In addition, the insulative coating layer prevents concentrated electron flow and decreases the possibility of "hot spots" formation. Because of the Li trapper and uniform electron distribution, the electrode with delicate structure exhibits a dendrite-free morphology after plating 2 mA h cm-2 of Li. As the dendrite growth is suppressed, the as-obtained electrode maintains a high plating/stripping efficiency of 99% over 200 cycles. This work delivers new insights into the design of rational Li metal anodes and hastens the practical application of Li metal batteries.

Three-dimensional pie-like current collectors for dendrite-free lithium metal anodes

Lithium (Li) metal possesses very high specific capacity and low electrochemical potential, which shows great advantages to be used in next generation rechargeable Li metal batteries (LMBs). However, poor cyclability of Li metal anodes caused by inhomogeneous and uncontrolled Li deposition hinders the practical applications of rechargeable LMBs. Here, in order to effectively suppress Li dendrite growth without degrading the specific capacity, a three-dimensional (3D) pie-like porous current collector was prepared based on copper nanowires (CuNWs) and graphene (GE). The inter-spaces inside the CuNWs framework efficiently accommodate Li deposition. Meanwhile, the GE layer wrapped outside CuNWs functions as flexible interfacial protective layer that could protect extra Li deposition. Furthermore, the GE shell can also decelerate the oxidation of CuNWs in ambient atmosphere. The CuNWs@GE current collectors demonstrated several merits to achieve better Li metal anodes with significantly improved Coulombic efficiency and cyclability for rechargeable LMBs.

Garnet/polymer hybrid ion-conducting protective layer for stable lithium metal anode

Rechargeable Li metal batteries using Li metal anodes have attracted worldwide interest because of their high energy density. The critical barriers limiting their commercial application include uncontrolled dendritic Li growth and the unstable Li–electrolyte interface. Considerable efforts have been directed towards solving these problems, e.g., modifying the electrolyte, creating artificial interfacial layers for the Li metal, and constructing three-dimensional structures for the Li metal. However, stabilizing the Li metal interface remains challenging because of the highly reactive nature of the Li metal. In this study, we utilize a Li-ion conducting hybrid film comprising a garnet-type ion conductor and a poly(ethylene oxide)-based polymer electrolyte as a protective layer to stabilize the Li–electrolyte interface and mitigate the growth of Li dendrites. The hybrid ion-conducting layer can block Li dendrites from proliferating and accommodate Li volume expansion because of its robust mechanical properties. Moreover, the ion-conducting layer allows Li deposition only underneath it, rather than on the surface, functioning as a permanent protective layer to ensure the stability of the Li metal over a long cycling life. The dendrite-inhibiting effect of the ion-conducting protective layer is visually evidenced by in situ microscopy using planar batteries. The protective Li metal anode exhibits excellent cycling stability and low voltage hysteresis (~15 mV at 0.2 mA·cm–2) for a cycle life as long as 1,000 h. It also shows a high Coulombic efficiency (~99.5%) in a full cell against a LiFePO4 cathode, exhibiting promise for application in Li metal batteries. Our results imply that the ion-conducting protective layer markedly improves the metal anode, yielding safe, long-life, and high-energy-density batteries. Open image in new window

Lithiophilic Sites in Doped Graphene Guide Uniform Lithium Nucleation for Dendrite‐Free Lithium Metal Anodes

AbstractLithium (Li) metal is the most promising electrode for next‐generation rechargeable batteries. However, the challenges induced by Li dendrites on a working Li metal anode hinder the practical applications of Li metal batteries. Herein, nitrogen (N) doped graphene was adopted as the Li plating matrix to regulate Li metal nucleation and suppress dendrite growth. The N‐containing functional groups, such as pyridinic and pyrrolic nitrogen in the N‐doped graphene, are lithiophilic, which guide the metallic Li nucleation causing the metal to distribute uniformly on the anode surface. As a result, the N‐doped graphene modified Li metal anode exhibits a dendrite‐free morphology during repeated Li plating and demonstrates a high Coulombic efficiency of 98 % for near 200 cycles.

Lithiophilic Sites in Doped Graphene Guide Uniform Lithium Nucleation for Dendrite-Free Lithium Metal Anodes.

Lithium (Li) metal is the most promising electrode for next-generation rechargeable batteries. However, the challenges induced by Li dendrites on a working Li metal anode hinder the practical applications of Li metal batteries. Herein, nitrogen (N) doped graphene was adopted as the Li plating matrix to regulate Li metal nucleation and suppress dendrite growth. The N-containing functional groups, such as pyridinic and pyrrolic nitrogen in the N-doped graphene, are lithiophilic, which guide the metallic Li nucleation causing the metal to distribute uniformly on the anode surface. As a result, the N-doped graphene modified Li metal anode exhibits a dendrite-free morphology during repeated Li plating and demonstrates a high Coulombic efficiency of 98 % for near 200 cycles.