Lithium Metal-based Batteries Research Articles

(Invited) Integration of Sulfide and Halide Based Solid-Electrolyte Membranes with Li-Ion Cathodes

Lithium metal-based batteries (LMBs) employ a Li-metal anode coupled with a conventional high voltage ceramic cathode. The higher capacity of Li vs. graphite (3861 mAh g-1 vs. 372 mAh g-1) combined with high voltage cathodes results in an over 50% increase in the specific energy versus conventional ion-insertion anodes. All-solid-state batteries (ASSBs) can achieve the sought-after high energies when employing cathodes such as LiNi0.8Mn0.1Co0.1O2 (NMC811) and LiNi0.5Mn1.5O4. Having the SEs be as thin as practically possible maximizes the energy density of the cells by both reducing the total weight and achieving voltage window closer to the theoretical limit due to reduced impedance. Likewise, a thin metal anode is sought-after since it reduces the cell weight as well as the risk associated with accidental ignition of the metal. Argyrodite SEs such as Li6PS5Cl (LPSCl) and Li6PS5Br (LPSBr) form terminal decomposition products such as Li3P and Li2S at the metal anode. However, it is the presence of halide-based decomposition products such as LiCl that kinetically stabilizes the interface. For example, substantially improved ASSB performance has been achieved with “sandwich” structures such as LPSCl/LGPS/LPSCl. The talk will focus on the recent approaches to improve interfacial stability of sulfide based solid electrolytes (SEs) with Li-metal and NMC based cathodes for SSB’s. A comparative evaluation of SSB performance between Argyrodite (Li6PS5X, X= Cl, Br) and halide-based SE (Li3ACl6, A = In, Y) using them as a separator and catholyte will be presented. Overall, these results demonstrate that incorporating oxidatively stable SEs in composite cathodes does not necessarily ensure the formation of robust NMC/SE interfaces, and cumulative irreversible capacity losses in such cells can yield rapid performance decline. Rather than SE decomposition, the dominant cause for capacity fade in SSBs is due to active material isolation resulting from repeated volume changes during cycling. Further, additional understanding of the mechanics of solid-solid interfaces and their dynamical evolution during SSB operation will be critical to address key performance bottlenecks for Li metal SSBs.

Acceleration of interfacial kinetics induced by regulation of Li+ desolvation process in lithium metal-based batteries

Lithium (Li) metal anode is the most promising anode for next-generation high-energy-density batteries due to the high theoretical specific capacity and the lowest redox potential. However, the uncontrollable growth of lithium dendrite and infinite volume expansion limit the development of Li metal-based batteries (LMBs). Introducing functional additives into electrolytes is considered as one of the efficient and economical strategies to suppress the Li dendrite growth and relieve the volume effect. Nevertheless, single-functional electrolyte additives can hardly comprehensively enhance the electrochemical performance of LMBs. Herein, boron-based anion receptor Tris(hexafluoroisopropyl) Borate (THFPB) is introduced into the electrolyte to weaken the interaction between the solvent and lithium ions, which regulates the lithium-ion desolvation process and enhance Li+ migration, resulting in the formation of smooth, dense, and rich-inorganic solid electrolyte interphase (SEI) film. Strikingly, with 2 wt % THFPB additive, the Li||Li cell shows an extremely long cycle life of 4200 h, and the Li||Cu cell affords a high Coulombic efficiency (CE) of 99.87 %. The THFPB-modified electrolyte shows superior universality, which enhances the cycling and rate performance of the Li||S and Li||LiFePO4 cells. Generally, this work provides a new perspective on the selection of new functional additives to achieve a long cycling life Li metal battery with great performance.

Functional Laminated Fiber Scaffold Based on Titanium Monoxide for Lithium Metal-Based Batteries.

Lithium metal-based rechargeable batteries are attracting increasing attention due to their high theoretical specific capacity and energy density. However, the dendrite growth leads to short circuits or even explosions and rapid depletion of active materials and electrolytes. Here, a functionalized and laminated scaffold (PVDF/TiO@C fiber) based on lithiophilic titanium monoxide is rationally designed to inhibit dendrite growth. Specifically, the bottom TiO@C fiber sublayer provides rich Li nucleation sites and facilitates the formation of stable solid electrolyte interphase. Together with the top lithiophobic PVDF sublayer, the prepared freestanding scaffold can effectively suppress the growth of Li dendrite and ensure stable Li plating/stripping. Based on the dendrite-free deposition, the Li/PVDF/TiO@ C fiber anode enables over 1000h at a current density of 1mA cm-2 in a symmetrical cell and delivers superior electrochemical performance in both Li || LFP and Li-S batteries. The functional laminated fiber scaffold design provides essential insights for obtaining high-performance lithium metal anodes.

Cathode Development for All Solid-State Lithium-Sulfur Batteries

With higher demand for alternative energy sources that are cleaner and more sustainable, research has shifted towards various lithium metal-based batteries with higher capacities than lithium-ion (LIBS). The study of lithium-sulfur energy storage systems has been heavily influenced due to the high gravimetric capacity of sulfur (1672 mA h g−1) and its abundance in the Earth’s crust. To increase the safety of lithium-sulfur batteries, solid state systems have been developed. These systems are also advantageous as the polysulfide shuttle effect normally seen in organic liquid electrolytes (OLEs) is eliminated, decreasing degradation due the irreversible reactions. Some of the most successful electrolytes found for lithium-sulfur all solid-state batteries (ASSLSBs) are ceramic based electrolytes. These electrolytes have high ionic conductivities (ranging 10-3-10-4 S cm-1) and do not pose any safety risks. However, one of the biggest bottlenecks of ASSLSBs is the utilization and accessibility of sulfur during cycling.To ensure these attributes are met, carbon materials have been used as supports; additionally, carbon also aids in electron transport due sulfur’s low electrical conductivity (10 -15 S m-1).Sulfur is typically dispersed or deposited on these carbon supports in different approaches before a full cathode composition is developed. Varying synthesis methods of sulfur deposition onto reduced graphene oxide are studied to determine which synthesis method provides the most accessibility for sulfur utilization. Utilization and accessibility will be analyzed through cyclic voltammetry, galvanostatic charge and discharge and impedance measurements to obtain characteristic voltammograms, specific capacity curves and Nyquist plots. Cells are assembled in PEEK Split cells using ceramic based electrolyte and lithium metal for the development of a noble ASSLSB.

Polyetherimide membrane with tunable porous morphology for safe lithium metal-based batteries

The separator is critical in ensuring the safety and improving the electrochemical performance of lithium metal batteries (LMBs). However, the weak thermal stability, common mechanical strength and the poor wettability towards electrolyte of the commercial polyolefin separator severely hamper its application in high-performance LMBs. Herein, a simple phase inversion technique could be used to design and scalably fabricate porous polyetherimide (PEI) membranes, which was used as LMB separators for the first time. The final morphology of PEI membranes can be finely tuned from finger-like voids to sponge-like pores by selecting an appropriate non-solvent. Combining experiments and density functional theory (DFT) simulations, it reveals that the optimal PEI membrane shows a sponge-like pore structure, which can induce the genuine deposition of the Li metal due to the homogeneously distributed pores in high density on the membrane and its good affinity towards the electrolytes. Consequently, the PEI based LMB show better performance than the commercial polypropylene (PP) based LMB. More importantly, the optimal PEI membrane shows a better mechanical strength and thermal stability than the PP membrane at the same thickness, which can ensure a higher safety for real applications. Since the non-solvent induced phase separation technique used to prepare PEI membrane is scalable in low cost, this work provides insightful route to overcome one of the main challenges, i.e. lack of high performance and high safety separator, for practical LMB application.

Printable Lithium - LIOVIXTM Assisted All Solid-State Lithium-Ion and Lithium-Metal Batteries for Enhanced Electrochemical Properties

All solid-state lithium-ion and lithium-metal batteries, which utilize a solid electrolyte in place of liquid electrolytes, are considered next-generation devices for energy storage due to their advantages in safety and potentially higher energy density. However, currently many solid-state lithium-ion and lithium-metal batteries are limited by their low Coulombic efficiency, poor power performance, and short cycling life due to the high resistance at the solid-state interfaces. Because of the diverse physical, chemical, and mechanical properties of various solid components in all solid-state batteries as well as the nature of solid-solid contact, many types of interfaces are present in a solid-state battery that can result in loose physical contact, formation of grain boundaries, and undesired chemical and electrochemical side reactions. All of these contribute to increasing resistance at the interface, which diminishes the cell performance, making solid state batteries not suitable for practical application.LIOVIXTM is a unique printable formulation of lithium metal and other specialty materials, which can be used in both lithium-ion and lithium metal-based rechargeable batteries. In the case of lithium-ion batteries, it can be printed on a range of anode materials including silicon-containing anodes for the pre-lithiation process to improve the first cycle columbic efficiency and cell performance. In the case of lithium metal-based batteries, LIOVIXTM can be printed directly onto the current collectors or solid electrolyte separators to fabricate all solid-state batteries utilizing printed lithium metal anodes. This approach has the potential to enable improved performance, safety, recyclability, and lower cost compared to the current advanced lithium-ion systems. In both categories, printable lithium formulation can reduce the interface resistance between the anode and solid electrolyte layer, which enhances the cell performance enabling practical application. The printable lithium formulation is easily scalable using industry standard coating and printing equipment and is adaptable to any anode or cathode chemistry where an independent source of lithium is required. In addition, the lithium loading can be accurately controlled based on the applications’ requirements. We have demonstrated improved electrochemical performance of silicon containing anodes with liquid electrolytes in a full cell format. The present work will demonstrate the concept of all solid-state batteries incorporating printable lithium with enhanced electrochemical properties compared to conventional solid-state batteries.

Modification of LiNi0.8Co0.1Mn0.1 cathode with AI-Screened LiPO3 to enhance interfacial stability and ionic dynamics

The application of LiNi0.8Co0.1Mn0.1 (NCM811) cathode is restricted with poor cycle stability and capacity fading. Artificial intelligence (AI) assisted high-throughput screening is performed to search for promising cathode coating materials. The screened LiPO3 is proposed, as it may have the potential of alleviating the phase transition of NCM811 cathode and enhancing the ionic diffusion. Hence, LiPO3 nanomaterial is adopted to enhance the cycle and rate performance of the NCM811 cathode. NCM811 cathode modified with LiPO3 exhibits lower interfacial impedance and charge transfer impedance in the in-situ EIS experiments. In the lithium metal-based batteries, the modified NCM811 cathode exhibits a specific capacity of 208.2 mAh g−1 at 0.2C/141.5 mAh g−1 at 5C. In addition, owing to the improvement in interfacial stability, NCM811 cathode keeps capacity retention of 80% after 150 cycles at 3C. After cycling at 3C rate, the TEM result confirms that LiPO3 modified NCM811 cathode suffers little structural change. Therefore, LiPO3 modified NCM811 cathode exhibits a wild prospect for commercialization.

Does Cell Polarization Matter in Single-Ion Conducting Electrolytes?

Single-ion conducting polymer electrolytes (SIPE) are particularly promising electrolyte materials in lithium metal-based batteries since theoretical considerations suggest that the immobilization of anions avoids polarization phenomena at electrode|electrolyte interfaces. SIPE in principle could allow for fast charging while preventing cell failure induced by short circuits arising from the growth of inhomogeneous Li depositions provided that SIPE membranes possess sufficient mechanical stability. To date, different chemical structures are developed for SIPE, where new compounds are often reported through electrochemical characterization at low current rates. Experimental counterparts to model-based assumptions and determination of system limitations by correlating both models and experiments are rare in the literature. Herein, Chazalviel's model, which is derived from ion concentration gradients, is applied to theoretically determine the limiting current density (JLim) of a SIPE. Comparison with the experimentally obtained JLim reveals a large deviation between the theoretical and practical values. Beyond that, charge-discharge profiles show a distinct arcing behavior at moderate current densities (0.5 to 1 mA cm-2), indicating polarization of the cell, which is not so far reported for SIPE. In this context, by application of various electrochemical and physiochemical methods, the details of cell polarization and the role of the solid electrolyte interphase in producing arcing behavior in the voltage profiles in stripping/plating experiments are revealed, which eventually also elucidate the inconsistency of JLim.

A mechanistic review of lithiophilic materials: resolving lithium dendrites and advancing lithium metal-based batteries

A review and the prospect of lithiophilic materials to highlight their versatility among the various forms of lithium metal-based batteries.

Effect of Surface Roughness Evolution of a Metal Current Collector Using a Pulse-Reverse Polarization Method on the Stability of the Anode-Free Lithium Metal Batteries

Recently, Lithium(Li) metal has been considered as a “ideal” anode material due to the extra-high capacity (3,860 mAh g-1), the lowest electrochemical equilibrium potential (-3.040 VSHE) and low density (0.534 g cm-3). Despite its ideal characteristics, Li metal anode(LMA) has a critical drawback that Li deposits grow in the form of dendrite due to its ununiform plating/stripping behaviors. The undesired dendritic growth of Li results in the detrimental effects on the cell performance, such as cell short-circuit, low coulombic efficiency(CE), and dead lithium, which have hampered widespread exploits of lithium metal-based batteries. Therefore, in recent years, numerous strategies to prevent or mitigate the problematic dendrite growth, including construction of artificial solid electrolyte interphase (SEI), lithiophilicity/morphology control of current collector, modification of electrolyte, and so forth [1,2].Meanwhile, by virtue of quite successful improvement in performance of LMAs, the battery system using in-situ formed LMAs, called anode-free lithium metal batteries (AFLMBs) have gained much interests [3]. In AFLMBs, the anode compartment has only a current collector at the initial state and then lithium metal anode is formed by electroplating with lithium ions provided from the cathode through initial charging step. The absence of corrosive/reactive Li metal in assembly process decreases the production cost and the energy density of a full-cell can be increased due to additional loading of cathode active materials. However, the dendritic growth of lithium could become more problematic because the cyclable lithium ions are fully limited to those provided from the cathode active materials. For solving notorious dendrite problem in AFLMBs, many strategies such as a use of highly concentrated salt electrolytes [3], the addition of functional electrolyte additives [4] and the introduction of lithiophilic elements on the current collector have been reported [5]. Unfortunately, however, it still seems difficult to nurture all strengths of AFLMBs related to the cost-effectiveness, simple cell design and high-energy density.One of the effective ways to regulate electroplating behavior of lithium is to introduce the surface-roughed metal current collector. Using such the structures, the charge accumulation sites on the microscopic structure of current collector can be randomly distributed, resulting in uniform electric field on the surface of current collector. Additionally, the localized current density can be reduced, and problematic volume changes of lithium can be buffered [2].In this context, we introduced the surface-roughed metal current collector as a substrate of AFLMBs to improve their stability. The surface roughness was controlled by an electrochemical method using a pulse-reverse polarization [6]. In particular, we focused on studying the effect of various pulse parameters on the morphological evolution of a metal current collector. To investigate their effects on the stability of AFLMBs, the CR 2032-type coin cells composed of the roughly surface-treated metal foil as a current collector and high-loading Li-Ni0.5Co0.2Mn0.3 (≈ 12.1 mg/cm2) as a cathode were assembled in an Ar-filled glove box. Figure 1-(a) presents an example of pulse signal used to modify roughness of metal surfaces. First, to investigate effect of pulse current density(iox=ire=i), we fixed the amount of metals, which were electrochemically oxidized and reduced by giving different pulse duration time (tox = tre = t,). Figure 1-(b) presents the effect of pulse current on the morphology of metal foils. After pulse with 0.5 mA/cm2, the surface of metal foil is covered by the clusters of metal/metal oxide particles. With increasing current density, the diameter of the clusters decreased and the number of clusters increased. Figure 2 shows the effect of surface-roughed metal surface on the electroplating behavior of lithium metals. As can be seen in Figure 2-(a), the morphology of electrodeposited lithium on the surface-treated metal foil has a denser and flatter Li deposit than that on pristine metal foil, where a needle-like dendritic structure is shown. Figure 2-(b) presents the CE of the repeated plating/stripping process of lithium metal. All the cells adopting the surface-treated foils showed a higher cycling stability compared to a pristine metal foil.Additionally, in this presentation, the correlation between pulse-reverse parameters and morphological evolution of a metal current collector, and the effect on the electrochemical long-term stability of AFLMBs will be discussed in more detail References [1] X.-B. Cheng et al., Chem. Rev, 117, 10403, 2017.[2] J. Zheng et al., Chem. Soc. Rev., 49, 2701, 2020.[3] J. Qian et al., Adv. Funct. Mater., 26, 7094, 2016.[4] N. A. Sahalie et al., J. Power Sources, 437, 226912, 2019.[5] S. S. Zhang et al., Electrochimica Acta, 258, 1201, 2017.[6]M. S. Chandrasekar and M. Pushpavanam, Eletrochimica Acta, 53, 3313, 2008 Figure 1

Effect of Thermally Evaporated Silver Nanoparticles on the Surface Morphology and Stability of Electrodeposited Lithium Metal Anode

Due to the extra-high capacity (3860 mAhg-1) and the lowest electrochemcial equilibrium potential (-3.040 VSHE), lithium metal has been considered as a promising candidate for high-energy lithium ion battery anode [1]. However, the undesired dendrite growth results in detrimental effects in the cell performance, such as cell short-circuit, low coulombic efficiency, and dead lithium, which have hampered widespread exploits of lithium metal-based batteries. Therefore, in recent year, numerous strategies to prevent or mitigate the problematic dendrite growth, including protective layers on Li metal surface, solid electrolytes, artificial solid electrolyte interphase (SEI) layer and so forth has been reported. Among them, one of the effective methods is to provide heterogeneous lithiophilic nucleation sites on the surface of current collectors as first suggested by Yan et al., [2]. They found that heterogeneous metal seeds, which have solubility of lithium in binary phase diagram, could induce selective deposition of lithium on its surface. Recently, Hou et al., reported lithiophilic Ag nanoparticles as nucleation sites by using electroless deposition for stable electrodeposition of lithium [3]. However, from a heterogeneous nucleation point of view, the morphology of electrodeposited lithium metal will be strongly affected by uniformity of nucleation seed layers, in other words, the more uniform distribution of nucleation seeds, the more stable morphology of lithium. In this study, we introduce a thermal evaporation method to deposit Ag nanoparticles as well-distributed nucleation sites. The Ag seeds with various evaporation thicknesses (1, 3 and 5 nm) were deposited on the commercial copper foils (thickness ≈ 25 um) to study the effect of evaporation thickness on the morphology of electrodeposited lithium metal. To electrodeposit lithium on Ag-seeded Cu foil and investigate the electrochemical properties of deposited Li metal electrodes, CR 2032-type coin cells were assembled in an Ar-filled glove box (CE: Li strip, WE: Ag-seeded Cu foil, and Celgard separator). We used 1M lithium bis(trifluoromethane)sulfonamide (LiTFSI) dissolved in 1,3-dioxolane/1,2-dimethoxyethane (DOL/DME, 1:1 by volume) as electrolyte without any additives. Figure 1 shows SEM surface morphologies of a pristine copper foil and Ag-seeded Cu foils with different evaporation thicknesses of Ag. After evaporation of Ag 1 nm on the pristine Cu foil (Fig. 1-(a)), it is showed that nano-sized Ag particles uniformly distributed on the surface of Cu foil (Fig. 1-(b)). In addition, from Fig. 1-(b) to Fig. 1-(d) it is clearly confirmed that the sizes of Ag particles increased with increasing evaporation thicknesses. Figure 2 shows the morphologies of electrodeposited lithium on Ag-seeded layers with different evaporation thickness. Figure 2-(a) shows SEM image of lithium metal deposited on a pristine Cu foil, which has well-known dendritic structure. In case of electrodeposited lithium on the Ag 1 nm-seeded Cu foil (Fig. 2-(b)), it also shows dendrites on its surface although heterogeneous nucleation sites are provided. However, the morphology of lithium on the Ag-3nm seeded Cu foil has distinct differences in shape and size of lithium deposits (Fig. 2-(c)). The width size of lithium deposits was smaller than those of Ag 1 nm-seeded Cu foil and pristine Cu foil, and they have interlacing vine-like structure. Further increased evaporation thickness of Ag nucleation layer to 5 nm leads to large morphological changes of electrodeposited lithium metal (Fig. 2-(d)). It shows highly dense structure with less pore and flat surface, meaning that dendrite-free lithium film was deposited. In summary, we used thermally evaporated Ag nanoparticles as heterogeneous nucleation sites to electroplate uniform lithium metal. From the results, it was concluded that through a facile thermal evaporation controllable and well-distributed heterogeneous nucleation metal seeds can be formed on the commercial Cu current collectors, leading to a dendrite-free deposition of lithium.

Phenothiazine-Based Redox Polymers As Cathode-Active Materials in Li/Organic Batteries

The rising demand for energy storage is increasing the research on so-called next generation or beyond lithium ion battery technologies.[1] The most promising candidates are lithium metal-based batteries (LMBs) with the Li/S battery as the most advanced example.[2] Even though LMBs show a high energy storage ability, the sluggish kinetics combined with safety concerns keeps the field open for alternative battery principles. One of these are organic-based materials which offer a great opportunity for the next generation of energy storage.[3] Their energy densities are mostly lower compared to their inorganic counterparts, but the ability of fast electron transfer and therefore high kinetics leads to an increased power density (e.g. 33.6 kW kg−1[4] vs. common battery materials, e.g. 4.75 kW kg−1[5]). Redox polymers are one of the most versatile organic-based materials for energy storage as they show decreased solubility and offer countless possibilities for modifications of the polymeric backbone and the side chains, while the polymer itself can be conjugated or non-conjugated.[6] Herein, we present a non-conjugated redox polymer with a substituted poly(vinylene) backbone.[7] The redox active side chain consists of a methyl phenothiazine moiety and undergoes an one-electron transfer process during oxidation and forms a radical cation. This oxidation is accompanied by an anion insertion into the polymeric structure. Due to a π-π-interaction between the side chains this polymer is able to enable long-term cycling with increased C-rates resulting in an ultra high cycling stability of 10,000 cycles with a capacity retention of 93%. In this work, we will describe these interactions and verify them with spectroscopic methods like EPR- and X-ray photoelectron spectroscopy (XPS). Additionally, density functional theory calculations (DFT) are shown which support the strong stabilizing effect of the π-π-interactions in this organic material.[7] Beside the mechanistic studies on molecular scale, we will comment further on the mechanism on the macroscopic electrode level. Here, we performed microscopic (SEM, LSM) and spectroscopic experiments (XPS, UV/Vis) to uncover the unique cycling behavior of PVMPT.[8] Finally, we will present an approach to increase the cycling capacity of the material and discuss the influence on the stabilizing interactions.[9]

Ultra-stable lithium plating/stripping in garnet-based lithium-metal batteries enabled by a SnO2 nanolayer

Owing to its high ionic conductivity (10−4 - 10−3 S cm−1), excellent stability toward lithium and a wide electrochemical window, the garnet-type solid-state electrolyte has been regarded as one of the most promising solutions to the viability of lithium metal-based batteries. However, the poor interfacial contact between the garnet and the lithium metal leads to an ultrahigh interfacial resistance (∼1000 Ω cm2) and uneven current distribution. In this work, the issue is effectively addressed by coating the garnet pellet with a SnO2 nanolayer. Attributed to the lithiation reaction between the lithium metal and SnO2, an ion-conducting interlayer is generated automatically between the garnet and lithium metal, which reduces their interfacial resistance from 1019 to 153 Ω cm2. A Li | SnO2-garnet | Li symmetric cell is then built and achieves a stable lithium plating/stripping for more than 900 h at 0.2 mA cm−2 without short circuit. Moreover, in a Li | SnO2-garnet | LiFePO4 full battery test, the SnO2 nanolayer enables the full battery to be stably operated for over 100 cycles at 0.3 C with a capacity retention of 98.6%, whereas the control group using bare garnet is unable to work at this high rate.

A comparative study of cellulose derived structured carbons on the electrochemical behavior of lithium metal-based batteries

Cellulose nanomaterials with different structures (i.e., cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC)) were carbonized to investigate the effect of morphology and crystallinity of cellulose-derived carbon nanomaterials on the overall electrochemical reactions in Li metal-based batteries. Carbonized CNF (c-CNF) and carbonized CNC (c-CNC) were coated separately on either a Cu current collector or a polypropylene (PP) separator for electrochemical tests. The resulting carbon derived from the amorphous region of CNF contributes to increasing the specific capacity of a cell but decreasing the overall electrical conductivity of the electrode. The c-CNF electrode delivered a relatively high capacity of 412 mAh g−1 at a low current density (0.2 A g−1) in comparison with the c-CNC (370 mAh g−1). In contrast, the c-CNC exhibited better rate capability than the c-CNF. When PP separators modified with c-CNF and c-CNC were employed in Li/Cu cells, it has shown remarkable improvements in Coulombic efficiency and cycle stability (over 120 cycles). This effect is ascribed to the substantially decreased local current density and the improved Li-ion storage in additional c-CNF and c-CNC layers. In addition, Li/LiFePO4 full-cell study tested with modified membranes further demonstrated the beneficial effect of cellulose-derived carbon nanomaterials on electrochemical reactions. Throughout this study, we explored the material characteristics of c-CNF and c-CNC, revealing the strong influence of the resulting carbon originated from the amorphous region of CNF on the electrochemical behaviors in Li-ion and Li-metal batteries.

Composite lithium electrode with mesoscale skeleton via simple mechanical deformation

Lithium metal-based batteries are attractive energy storage devices because of high energy density. However, uncontrolled dendrite growth and virtually infinite volume change, which cause performance fading and safety concerns, have limited their applications. Here, we demonstrate that a composite lithium metal electrode with an ion-conducting mesoscale skeleton can improve electrochemical performance by locally reducing the current density. In addition, the potential for short-circuiting is largely alleviated due to side deposition of mossy lithium on the three-dimensional electroactive surface of the composite electrode. Moreover, the electrode volume only slightly changes with the support of a rigid and stable scaffold. Therefore, this mesoscale composite electrode can cycle stably for 200 cycles with low polarization under a high areal current density up to 5 mA/cm2. Most attractively, the proposed fabrication process, which only involves simple mechanical deformation, is scalable and cost effective, providing a new strategy for developing high performance and long lifespan lithium anodes.

Nanoporous and lyophilic battery separator from regenerated eggshell membrane with effective suppression of dendritic lithium growth

Lithium metal-based batteries are attractive energy storage systems owing to the high theoretical capacity of lithium metal anode and the known lowest potential among existing anodes. However, lithium anodes usually suffer from severe growth of lithium dendrites, a main reason of safety concern. Engineering the structure of separators could be an effective solution for resolving this issue. Herein, we demonstrate that eggshell membrane (ESM) extracted from waste eggshell is a promising candidate as high-performance separator. Furthermore, we have developed a biomimetic and economic strategy to produce large-area and flat regenerated ESM (RESM) to overcome the size and shape limits of raw ESM. The ESM and RESM are highly lyophilic to electrolytes; their well-distributed pores and high electrolyte uptake allow fast ion-diffusion; and their high mechanical and thermal stability ensure the safety and cyclability of batteries. Most impressively, the nanoporous structure and the negatively-charged surface of ESM and RESM separators can effectively suppress the formation of lithium dendrites, even after long-term cycling under high rate. Lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries using RESM separators all show boosted rate capability and cycling retention, outperforming commercial separators on almost all fronts. Even at a high temperature (120 °C), lithium-ion batteries with RESM separators can still operate normally. Our findings indicate the nanoporous RESM film can meet most if not all requirements of an ideal separator for metal ion batteries.

Suppression of dendritic lithium growth in lithium metal-based batteries.

Lithium metal-based batteries offer promising prospects as alternatives to today's lithium-ion batteries, due to their ultra-high energy density. Unfortunately, the application of lithium metal is full of challenges and has puzzled researchers for more than 40 years. In this feature article, we describe the history of the development of lithium metal batteries and their existing key challenges, which include non-uniform electrodeposition, volume expansion, high reactivity of the lithium metal/unstable solid electrolyte interphase (SEI), and the shuttling of active cathode materials. Then, we focus on the growth mechanisms of uneven lithium electrodeposition and extend the discussion to the approaches to inhibit lithium dendrites. Finally, we discuss future directions that are expected to drive progress in the development of lithium metal batteries.

Nanodiamonds suppress the growth of lithium dendrites

Lithium metal has been regarded as the future anode material for high-energy-density rechargeable batteries due to its favorable combination of negative electrochemical potential and high theoretical capacity. However, uncontrolled lithium deposition during lithium plating/stripping results in low Coulombic efficiency and severe safety hazards. Herein, we report that nanodiamonds work as an electrolyte additive to co-deposit with lithium ions and produce dendrite-free lithium deposits. First-principles calculations indicate that lithium prefers to adsorb onto nanodiamond surfaces with a low diffusion energy barrier, leading to uniformly deposited lithium arrays. The uniform lithium deposition morphology renders enhanced electrochemical cycling performance. The nanodiamond-modified electrolyte can lead to a stable cycling of lithium | lithium symmetrical cells up to 150 and 200 h at 2.0 and 1.0 mA cm–2, respectively. The nanodiamond co-deposition can significantly alter the lithium plating behavior, affording a promising route to suppress lithium dendrite growth in lithium metal-based batteries.

Ultrathin Coating of Nitrogen and Sulfur Co-Doped Graphene Nanosheets on Polymer Separator for Suppressing Dendritic Lithium Growth in Lithium Metal Batteries

The advent of electric vehicles and other high energy density applications has intensified the research efforts on lithium metal-based batteries, as metallic lithium can provide a high specific capacity (~3,862 mAh g-1), enabling it as a promising negative electrode for next-generation battery systems [1,2]. However, the instability of lithium electrodes is one of the greatest challenges hindering the successful development of lithium metal batteries. Lithium metal is unstable against nearly all chemical species and reacts with organic solvents and salts in liquid electrolytes. Moreover, continuous deposition and stripping of lithium may induce uncontrollable dendritic Li growth, which in turn leads to internal short circuits, failure, and eventually explosions. In this work, we demonstrated that an ultrathin nitrogen and sulfur co-doped graphene (NSG) layer deposited on a PE separator could effectively stabilize the lithium electrode surface, suppress dendrite formation, and improve the cycling stability of lithium metal batteries. The NSG coating layer is very thin as compared to other ceramic coatings in micrometer scales, which can provide higher energy density of the cell with NSG separator. The incorporation of heteroatom dopants could induce structural deformations due to local strains induced in the carbon framework, thereby allowing for easy ionic migration while maintaining a uniform ionic flux on the Li metal surface. Moreover, the lone pair electrons in the heteroatom dopants led to the generation of negative charge, resulting in enhanced interfacial interactions between the NSG-coated separator and the lithium electrode. The NSG coating also imparted thermal stability to the PE separator, thus preventing thermal shrinkage of the separator at elevated temperature and enhancing battery safety. The cycling performance of the lithium metal cell employing a NSG coated separator was remarkably improved as compared to the cell with a pristine PE separator.

Ultrastrong Polyoxyzole Nanofiber Membranes for Dendrite-Proof and Heat-Resistant Battery Separators.

Polymeric nanomaterials emerge as key building blocks for engineering materials in a variety of applications. In particular, the high modulus polymeric nanofibers are suitable to prepare flexible yet strong membrane separators to prevent the growth and penetration of lithium dendrites for safe and reliable high energy lithium metal-based batteries. High ionic conductance, scalability, and low cost are other required attributes of the separator important for practical implementations. Available materials so far are difficult to comply with such stringent criteria. Here, we demonstrate a high-yield exfoliation of ultrastrong poly(p-phenylene benzobisoxazole) nanofibers from the Zylon microfibers. A highly scalable blade casting process is used to assemble these nanofibers into nanoporous membranes. These membranes possess ultimate strengths of 525 MPa, Young's moduli of 20 GPa, thermal stability up to 600 °C, and impressively low ionic resistance, enabling their use as dendrite-suppressing membrane separators in electrochemical cells. With such high-performance separators, reliable lithium-metal based batteries operated at 150 °C are also demonstrated. Those polyoxyzole nanofibers would enrich the existing library of strong nanomaterials and serve as a promising material for large-scale and cost-effective safe energy storage.