Stability Of Li Metal Anode Research Articles

Application of artificial SEI layers for lithium metal battery anodes

Unpredictable lithium dendrite growth on the metal anode and repeated destruction and creation of the solid electrolyte interphase (SEI) layer result in hidden risks and low Coulombic efficiencies (CEs). Researchers have found that designing a high-quality SEI layer can prevent the growth of dendrite. However, designing and forming a high-quality SEI layer is still a problem. Making trade-off between capacity reduction caused by the SEI layer and better cycle stability significantly limits the general performance of lithium metal batteries. In this research, characteristics of SEI layers and some significant advancements made in SEI formation are outlined. Some designs for the SEI layers on the lithium metal anodes include designing hybrid polymer SEI layers, producing synthetic SEI layers. By controlling the behaviours of Li ions throughout the stripping and depositing processes, the capacity and stability of Li metal anodes may be improved. Finally, some case studies of the applying of SEI in lithium metal battery systems are introduced.

Dynamic Adaptive Porous Cu Current Collector for Low N/P Ratio Li Metal Batteries

AbstractPorous copper (Cu) current collectors effectively suppress the growth of lithium (Li) dendrites and enhance the stability of Li metal anodes. However, the current development of porous Cu hosts generally involves a high proportion of Cu, mostly rigid structures, small pore volumes, and low Li utilization. Here, we propose a dynamic adaptive porous Cu (DAP−Cu) host, which is lightweight with a high pore volume, fabricated using a large aspect ratio of Cu nanowires as the building blocks. This DAP−Cu allows for the precise loading of metallic Li, and the symmetric battery assembled with Li/DAP−Cu electrode operates at the high current density of 5 mA cm−2 for 4000 hours while exhibiting a low polarization voltage of ~60 mV. The Li/DAP−Cu anode achieves high‐performance compatibility with LiFePO4 and sulfur cathodes, with optimal N/P ratios of 1.20 : 1 and 4.0 : 1, respectively. Full and pouch cells with low N/P ratios exhibit exceptionally high specific capacities and long‐term cycling life. The establishment of standards for the matching of anodes and cathodes provides a reference for the quantitative preparation of electrode materials and is of significant guidance for enhancing the efficient utilization of metallic Li.

A novel cathode interphase formation methodology by preferential adsorption of a borate-based electrolyte additive.

The coupling of high-capacity cathodes and lithium metal anodes promises to be the next generation of high-energy-density batteries. However, the fast-structural degradations of the cathode and anode challenge their practical application. Herein, we synthesize an electrolyte additive, tris(2,2,3,3,3-pentafluoropropyl) borane (TPFPB), for ultra-stable lithium (Li) metal||Ni-rich layered oxide batteries. It can be preferentially adsorbed on the cathode surface to form a stable (B and F)-rich cathode electrolyte interface film, which greatly suppresses the electrolyte-cathode side reactions and improves the stability of the cathode. In addition, the electrophilicity of B atoms in TPFPB enhances the solubility of LiNO3 by 30 times in ester electrolyte to significantly improve the stability of the Li metal anode. Thus, the Li||Ni-rich layered oxide full batteries using TPFPB show high stability and an ultralong cycle life (up to 1500 cycles), which also present excellent performance even under high voltage (4.8V), high areal mass loading (30mg cm-2) and wide temperature range (-30∼60°C). The Li||LiNi0.9Co0.05Mn0.05O2 (NCM90) pouch cell using TPFPB with a capacity of 3.1Ah reaches a high energy density of 420Wh kg-1 at 0.1C and presents outstanding cycling performance.

Co@CoO core–shell cross-linked framework modified 3D Cu for dendrite-free lithium anode

Lithium metal anode with high energy density is important for developing next-generation batteries. However, low coulombic efficiency, short cycle life, internal short circuits caused by the growth of lithium dendrites, and the high reactivity with the electrolyte have seriously hindered the practical application of lithium metal anode. Herein, we constructed a core–shell cross-link matrix on copper, Co@CoO/3D Cu, for Li metal anode optimization. Various characterizations and DFT simulations jointly reveal the great effects of the special structural features of Co@CoO/3D Cu on enhancing the coulombic efficiency and cyclic stability of Li metal anodes. As a result, the modified half-cell could cycle stably for 240 cycles at 1 mA cm−2 and 1 mA h cm−2 with a coulombic efficiency as high as 98 %. The modified symmetric cell could cycle stably for 1400 h at 1 mA cm−2 and 1 mA h cm−2 with a very low polarization of 22 mV. The modification method proposed in this paper provides a novel path for Li metal anode optimizations.

Rational construction Ag/LiF/sulfide rich protective layer for remarkably enhancing the stability of Li metal anodes

Li metal is a promising anode material for high-energy–density batteries due to its high theoretical capacity and low redox potential. However, both the uncontrolled Li dendrite growth and unstable solid electrolyte interphase (SEI) layer restricts its large-scale practical applications. Herein, an artificial protective layer consisting of Ag nanoparticles, lithium fluoride (LiF) and sulfide are innovatively designed and fabricated via the in-situ chemical reaction between Ag(I) trifluoromethylthiolate (AgSCF3) and Li metal. Density functional theory (DFT) results indicate that Ag nanoparticles have a high binding energy with Li atom and LiF/sulfide have wide band gap, which would provide plenty of nucleation sites for Li+ and reduce the direct contact between inner Li metal and the electrolyte. The co-existence of Ag and LiF/sulfide results in a strong synergistic effect, and this is confirmed by the systematical comparison with single modified Ag-Li and double modified F/S-Li anodes. Benefitting from this synergistic effect, the Ag/F/S-Li symmetrical cells can stably work for 2000 h with low-voltage hysteresis at current density of 1 mA cm−2. Full cells assembled with LiCoO2 (LCO) and LiFePO4 (LFP) cathodes displays much better long‐term cycle performance when the Ag/F/S-Li anode is applied. Furthermore, this Ag/F/S-Li modification can significantly enhance discharge capacity, rate performance, as well as energy density of Li(or LiB alloy)||MnO2 primary cells. This promising work promotes the practical application of Li metal and provides new insight into the protective layer design in stable Li metal batteries.

Effect of Water As an Electrolyte Additive for Lithium Plating

Li metal anode is generally referred to as the “holy grail” of battery technology as it can deliver the highest possible energy density, which double the capacity of state of art graphite based cells1. At the heart of this advanced technology is the process of continuous plating and stripping of lithium during the cycling of the battery. Owing to the highly reactive nature of Li, this is a complicated process with several challenges2 during both plating (for e.g., dendrite formation and growth, dead lithium, continuous interface/interphase change, short circuit etc.) and stripping (void formation, pitting, broken interface/interphase layers etc.). The electrode architecture, choice of electrolyte, solid electrolyte interphase (SEI) formation, operating conditions etc. are key factors that determine overall stability of Li metal anodes. These issues get magnified when using liquid electrolytes, where continuous SEI formation leads to dead Lithium (electrically insulating) accumulation.In general, most solvents and salts employed for Li ion cells contain some amount of water as impurity even after maintaining strict conditions to keep them anhydrous. The presence of trace amount of water in combination with fluorine from either salt (LiPF6. LiTFSI, LiFSI) or solvent additives FEC can then lead to in-situ formation of HF, which has detrimental effects on Li plating. However, recently many groups have shown the beneficial effect of small amount of water as additives for Li metal anodes3,4. However, the exact mechanism of functioning of H2O as an additive is not very clear. This is partly because the formation of SEI is quite complex, especially when film forming type solvents/additives are present in the electrolyte addition to trace amounts of water.It is thus important to investigate the nucleation and growth of Li during the initial stages of plating and understand how the presence of H2O in the electrolyte affects the morphology andthe chemical nature of the deposited Li metal films. In this direction, we choose tetraglyme (4G), which is a relatively non-labile solvent towards Li plating conditions (reduction potential ~ 1.49 vs Li+/Li), as the solvent to avoid any contribution from the solvent itself on SEI formation. We then systematically study the effect of H2O on Li plating; both stand alone and in presence of various film forming additives. We show that water can indeed drastically affect the morphology and electrochemical properties of the deposited Li. Acknowledgement: This work is part of FUGELS (Functionally Graded Electrodes for Long-Life Lithium-Sulfur Batteries) project, which is a cconsortium of researchers from University of Hasselt, University of Gent, University of Antwerp, VITO, IMEC and IMOMEC.

Enhanced stability of Li metal anodes enabled with iron oxides modified Cu foil

Li metal is widely regarded as the ideal material for anodes in high energy density batteries. Nonetheless, the growth of dendrites and its limited stability significantly hinder the practical use of Li anodes in commercial applications. Herein, we have successfully prepared iron oxides on the Cu current collector by the combination of vacuum evaporation coating and annealing under O2 atmosphere. During the charge/discharge processes, the iron oxides of the oxidized-Fe/Cu foil can react with lithium to generate Li2O, which is beneficial for both the deposition behavior and the ions conduction of Li. Therefore, the oxidized-Fe/Cu foil shows an excellent cycling stability, even when increasing total Li content up to 4 mA h cm−2, the oxidized-Fe/Cu foil can still be steady for 120 cycles. The LiFePO4||oxidized-Fe/Cu-Li full-cell demonstrated improved cycling stability and exceptional rate performance, allowing it to achieve a high specific capacity of 107.7 mA h g−1 at a rate of 10C. This work presents a straightforward approach to creating lithium batteries with extended lifespan and increased capacity.

Ag/microcrystalline-Cu2O composite film as an interfacial regulator for highly reversible lithium metal anode

Lithium (Li) metal is a promising anode material for high-energy–density batteries, yet its low average Coulombic efficiency (CE) results in poor cycling stability. Although significant progress has been made in addressing these issues, the stability of Li metal anode at high rates and large capacities falls short of meeting the practical application requirements. Herein, we develop a microcrystalline (MC)-Cu2O/Ag composite film on Cu current collector to regulate the interfacial properties for achieving even and dense Li deposition. The MC-Cu2O can be lithiated to form a ternary Li-Cu–O phase which possesses strong Li+ trapping capability. Besides, the MC-Cu2O can activate the electrochemical activity of Ag film, inducing a single-phase transition solid solution (alloying) reaction with high reversibility. As a result, the Ag/MC-Cu2O foam enables an even and dense Li plating/stripping behavior with high CE at a high rate and large capacity. When Ag/MC-Cu2O@Li anode is coupled with LiFePO4 cathode, the yielded full cell exhibits superior cycling stability and rate performance. Our results provide a facile approach to constructing lithiophilic current collector for a practical Li anode.

Organic Nitrate Additive for High-Rate and Large-Capacity Lithium Metal Anode in Carbonate Electrolyte.

Lithium nitrate has been widely used to improve the interfacial stability of Li metal anode in ether electrolyte. However, the low solubility limits its application in carbonate electrolytes for high-voltage Li metal batteries. Herein, nitrated polycaprolactone (PCL-ONO2 ), which is prepared via the acylation of polycaprolactone diol (PCL-diol) followed by the grafting of nitrate group, has been proposed as an electrolyte additive to introduce high-concentration NO3 - into carbonate electrolytes for the first time. The theoretical calculations and X-ray photoelectron spectroscopy depth profiling demonstrate that the PCL-ONO2 additive preferentially reacts with Li metal and in situ constructs a stable dual-layered solid electrolyte interphase film, presenting an inner nitride-rich layer and an outer flexible PCL-based layer on the surface of Li metal anode. As a result, the Li metal anode delivers an impressive long-term cycling performance over 1400h at an elevated area capacity of 10.0mAhcm-2 and an ultrahigh current density of 10.0mAcm-2 in the Li symmetrical cells. Moreover, the PCL-ONO2 additive enables the full cells constructed by coupling high-loading LiFePO4 (20.0mgcm-2 ) or LiNi0.5 Co0.2 Mn0.3 (16.5mgcm-2 ) cathode and thin Li metal anode (≈50µm) to demonstrate greatly improved cycling stability and rate capability.

Integrated Gradient Cu Current Collector Enables Bottom-Up Li Growth for Li Metal Anodes: Role of Interfacial Structure.

3D Cu current collectors have been demonstrated to improve the cycling stability of Li metal anodes, however, the role of their interfacial structure for Li deposition pattern has not been investigated thoroughly. Herein, a series of 3D integrated gradient Cu-based current collectors are fabricated by the electrochemical growth of CuO nanowire arrays on Cu foil (CuO@Cu), where their interfacial structures can be readily controlled by modulating the dispersities of the nanowire arrays. It is found that the interfacial structures constructed by sparse and dense dispersion of CuO nanowire arrays are both disadvantageous for the nucleation and deposition of Li metal, consequently fast dendrite growth. In contrast, a uniform and appropriate dispersity of CuO nanowire arrays enables stable bottom Li nucleation associated with smooth lateral deposition, affording the ideal bottom-up Li growth pattern. The optimized CuO@Cu-Li electrodes exhibit a highly reversible Li cycling including a coulombic efficiency of up to ≈99% after 150 cycles and a long-term lifespan of over 1200h. When coupling with LiFePO4 cathode, the coin and pouch full-cells deliver outstanding cycling stability and rate capability. This work provides a new insight to design the gradient Cu current collectors toward high-performance Li metal anodes.

Ion modulation engineering toward stable lithium metal anodes.

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

Protecting lithium metal anodes in lithium–sulfur batteries: A review

Lithium–sulfur (Li–S) batteries are considered as one of the most promising next-generation energy storage devices because of their ultrahigh theoretical energy density beyond lithium-ion batteries. The cycling stability of Li metal anode largely determines the prospect of practical applications of Li–S batteries. This review systematically summarizes the current advances of Li anode protection in Li–S batteries regarding both fundamental understanding and regulation methodology. First, the main challenges of Li metal anode instability are introduced with emphasis on the influence from lithium polysulfides. Then, a timeline with 4 stages is presented to afford an overview of the developing history of this field. Following that, 3 Li anode protection strategies are discussed in detail in aspects of guiding uniform Li plating/stripping, reducing polysulfide concentration in anolyte, and reducing polysulfide reaction activity with Li metal. Finally, 3 viewpoints are proposed to inspire future research and development of advanced Li metal anode for practical Li–S batteries.

Cellulose-based gel-type electrolyte fabricated by lyophilization to enable uniform Li+ ion flux distribution for stable Li metal anodes with high-rate capability

Lithium metal has been extensively investigated as the optimal anode for the next-generation rechargeable batteries. However, the high reactivity of Li with liquid electrolytes and the undesired dendrite growth predisposes the battery to destruction and even safety problems. Herein, a methyl cellulose-based gel polymer electrolyte (MC-GPE) with three-dimensional (3D) networks fabricated via lyophilization is implemented to guide the uniform Li+ deposition and suppress dendrite growth. Owing to the high absorption to LiPF6-based liquid electrolyte, the ionic conductivity of MC-GPE can reach up to around 0.7 mS cm–1 at ambient temperature, almost twice as large as the Polyethylene (PE) separator (Celgard 2730) immersed by the same electrolyte (0.43 mS cm–1). Accordingly, highly reversible Li plating/stripping with a stable polarization (< 40 mV), high coulombic efficiency (CE) (99%) and long lifespan (>400 h) can be obtained (1 mA cm−2, 1 mAh cm−2). The assembled Li-metal cells coupled with LiFePO4 cathodes show remarkable cycling stability and rate performance (157 mAh g–1 after 200 cycles at 1 C and 115 mAh g–1 after 400 cycles at 5 C) with high CE (∼100%). These results indicate the obtained MC-GPE can promote uniform Li+ ion flux distribution, suppress growth of Li dendrite and improve the cycle stability of Li metal anodes. This work paves a way for the application of the cellulose-based GPEs in the future Li-metal batteries.

Mechanistic Insight into Li–Host Interactions in Carbon Hosts for Reversible Li Metal Storage

In recent years, the industrial requirements for rechargeable batteries in terms of energy density have continuously increased owing to the widespread adoption of portable electronic devices and electric vehicles. Li metal has been identified as a promising anode material to meet the ever-increasing demand for rechargeable batteries with high energy densities because of its low redox potential (−3.04 V vs. standard hydrogen electrode)and high specific capacity (3860 mAh g−1) [1]. Despite these advantages, the commercial use of Li metal anodes has been hindered by unresolved critical issues, such as the uncontrollable growth of Li dendrites and the severe volume changes during cycling. In practice, the dendritic growth of Li deposits causes the formation of dead Li species and triggers internal short-circuiting of batteries during cycling, leading to a significant loss of reversibility and raising safety concerns. Moreover, large volume changes in the Li metal anode during Li plating–stripping, which originate from the “hostless” character of the Li metal, impose severe stresses on the solid–electrolyte interphase (SEI) layers, and thus reducing the mechanical stability of SEIs. Once the SEI layers are cracked or fractured, bare Li metal is exposed to the electrolyte, leading to the continuous formation of thick SEI layers on the anode surface. This is mainly responsible for the continuous, irreversible loss of active Li, i.e., low Coulombic efficiency and short cycle lifetimes.3D “host” architectures are beneficial for securing the dimensional stability of Li metal anodes by utilizing internal pores (i.e., free-spaces) as reservoirs for Li storage. Moreover, they provide large active surface areas and hence reduce the effective current densities, suppressing uneven Li plating (dendritic growth) during high-rate operations. Metal-organic framework (MOF)-derived carbon offers many advantages over conventional carbon materials in terms of specific surface area, pore volume, and structural tunability. Furthermore, the critical role of atomically dispersed heteroatoms has been verified in reducing the energy barriers for the nucleation and growth of Li [2].Herein, we report MOF-derived porous carbon hosts with strong Li–host interactions achieved by galvanically displaced lithiophilic seeds. Owing to the distinctive chemical and structural nature of zeolitic imidazolate frameworks (ZIF-8), atomically dispersed Zn can be spontaneously replaced by Ag with a strong lithiophilicity via a galvanic displacement (GD) reaction. Based on a comparative study of carbon hosts with different sizes, morphologies, and distributions of Ag, in particular, we assess the efficacy of lithiophilic Ag in promoting reversible Li storage inside porous carbon hosts. The strong Li–host interactions enabled by lithiophilic Ag effectively reduce the overpotentials for nucleation and growth of Li, and more importantly, the role of lithiophilic Ag in governing the reversibility of Li plating–stripping is discussed in terms of the spatial distribution characteristics of Ag. The atomically dispersed Ag triggers the outward growth of Li from the internal pores of the carbon host, showing a stable cycling performance (>745 cycles). Contrarily, the surface-anchored Ag nanoparticles induce uneven Li plating on the outer surface of the carbon host, resulting in a rapid performance drop (~305 cycles) during cycling. This work provides new insights into the development of advanced 3D host materials for reversible Li metal anodes by utilizing strong Li–host interactions.

Metal Nitrate Embedded Polymeric Interlayer for Improving Cycling Stability of Li Metal Anode

Among secondary batteries using lithium, the use of lithium metal anodes for high capacity has become a hot topic. However, in lithium metal anodes, there is a major problem of dendritic growth and research are actively underway to address the issue. And it is reported that it is possible to improve the stability of Li metal anode by facilitating the movement of lithium ions through various additives to suppress dendritic growth and to make robust and stable SEI layer. To address the issue of dendritic growth of Li, using cesium nitrate is selected to improve the stability of the anode based on a mechanism by which a nitrogen-rich compounds lithiophilic to transport Li ion uniformly are formed in the SEI layer. And also the cesium element induces an cation electrostatic shielding effect while lithium metal is deposited and grown in the anode. In addition, since metal nitrates have very low solubility in carbonate-based electrolytes, polymer nanofiber-interlayer is synthesized by electrospinning to support metal nitrate and supply nitrate continuously and stably, while interlayer does not interfere with the movement of lithium ions through the nanofiber layer. In summary, a metal nitrate embedded polymer nanofiber layer is synthesized through an electrospinning method, then stabilization of a lithium surface and stability of a lithium metal anode are obtained by using an intermediate layer, and a relationship between an additive and SEI formation is identified at a limited solubility in carbonate electrolytes. The study result demonstrates that the lifetime of symmetric Li-Li cells and full cell with LCO cathodes improved greatly. And the deposition morphology of Li become dendrite-free and more uniform.

Stabilizing Li-O2 Batteries with Multifunctional Fluorinated Graphene.

As a full cell system with attractive theoretical energy density, challenges faced by Li-O2 batteries (LOBs) are not only the deficient actual capacity and superoxide-derived parasitic reactions on the cathode side but also the stability of Li-metal anode. To solve simultaneously intrinsic issues, multifunctional fluorinated graphene (CFx, x = 1, F-Gr) was introduced into the ether-based electrolyte of LOBs. F-Gr can accelerate O2- transformation and O2--participated oxygen reduction reaction (ORR) process, resulting in enhanced discharge capacity and restrained O2--derived side reactions of LOBs, respectively. Moreover, F-Gr induced the F-rich and O-depleted solid electrolyte interphase (SEI) film formation, which have improved Li-metal stability. Therefore, energy storage capacity, efficiency, and cyclability of LOBs have been markedly enhanced. More importantly, the method developed in this work to disperse F-Gr into an ether-based electrolyte for improving LOBs' performances is convenient and significant from both scientific and engineering aspects.

Hollow spherical organic polymer artificial layer enabled stable Li metal anode

Li metal is regarded as one of the most promising anodes in rechargeable battery systems for its high theoretical specific capacity, low redox potential and light weight. However, Li dendritic formation and low Coulombic efficiency (CE) triggered by the nonuniform Li+ deposition restrict the further step to the commercialization of lithium metal batteries. Herein, a fantastic hollow spherical porous organic polymer (HS-POP) with concentrated lithiophilic functional groups of –C=N, –OH has been synthesized and utilized as an artificial solid electrolyte interphase (SEI) to regulate the interfacial stability of Li metal anode. The compelling evidences of density functional theory (DFT) calculations and Fourier-transform infrared spectra verified the energetical lithiophilic property, which facilitates Li+ uniform transfer and nucleation with decreased energy barriers. The large cavities and well-flexible shell structure not only provide enlarged lithium storage capacity, but also act as a buffer layer during repeated Li deposition and dissolution protocols. The HS-POP modified Li anode delivered a higher CE at high current density of 2 mA cm−2, and the HS-POS@Li|S full cell demonstrates excellent performance with high reversible capacity for 400 cycles at 0.5 C.

Electronic Localization Derived Excellent Stability of Li Metal Anode with Ultrathin Alloy.

Lithium metal is an ideal anode for next‐generation high‐energy‐density batteries. However, lithium dendrite growth has impeded its commercial application. Herein, fabricating Li‐based ultrathin alloys with electronic localization and high surface work function via depositing Bi, Al, or Au metals on the surface of copper foil for in situ alloying with lithium is proposed. It is discovered that the electronic localization can induce self‐smoothing effect of Li ions, as a result, significantly suppressing the growth of dendritic lithium. Meanwhile, the high surface work function can effectively alleviate side reactions between the electrolyte and lithium. With the as‐obtained ultrathin alloys as anodes, excellent cycling performance is achieved. The half cells run stably after more than 120 cycles under high capacity of 4 mAh cm−2. The S||Bi/Cu‐Li full cell delivers a specific capacity of 736 mAh g−1 after 200 cycles. This work provides a new strategy for fabricating long‐life and high‐capacity lithium batteries.

Sulfonated poly(vinyl alcohol) as an artificial solid electrolyte interfacial layer for Li metal anode

The cycle performance of Li metal batteries with high energy-density is hindered by the stability of Li metal anode. In this manuscript, sulfonated poly(vinyl alcohol) (SPVA) was synthesized and used as an artificial solid electrolyte interfacial (SEI) layer to construct stable Li metal anode interface. The ionic conductivity of SPVA coating layer in liquid electrolyte was calculated according to the theories of interfacial polarization in heterogeneous systems by dielectric method. In the Li|PE|SPVA/Cu or Li/SPVA|PE|SPVA/Li cells, Li deposits beneath the SPVA layer, surviving from the corrosion of liquid electrolyte and excessive volume expansion. Benefited from the constructed stable artificial SEI layer, the interfacial polarization and internal resistance in the symmetric cells are reduced. The cycle performance of LiFePO4|PE|SPVA/Li cell has been greatly improved, which could be stably cycled for more than 500 cycles.

Supramolecular “flame-retardant” electrolyte enables safe and stable cycling of lithium-ion batteries

Although energy densities of lithium-ion batteries (LIBs) continue to increase, safety problems such as fires and explosions have significantly hindered their large-scale applications. Conventional wisdom tells us the fire of LIBs largely originated from the flammable liquid carbonate solvents, and thus the research on additives with properties of suppressing “liquid-type fire” is the way to fabricate nonflammable batteries. However, the outcome has been proven to be inferior. Here, we carefully examined the evolution of battery fire under thermal abuse condition and found that the “jet fire” caused by flammable gases inside batteries is critical for the fire hazard, and the research effort should be redirected to search proper additives with “gaseous-type fire” suppressing properties. Unfortunately, conventional “gaseous-type fire suppressant” shows poor compatibility with battery electrolytes. Thus, we rationally designed a new kind of supramolecular electrolyte, where the molecules of “gaseous-type fire suppressant” and “SEI&CEI improver” are self-assembled together by intermolecular interactions. Due to this design, the supramolecular electrolyte produces improved cycling stability of Li metal anode and high voltage LiCoO2 cathode (up to 4.4 V). More importantly, it sharply decreases the self-extinguish time of carbonate-based electrolyte from ∼100 s/g to ∼0 s/g, which is unprecedented and can effectively suppress the “jet fire”, thus preventing the further combustion of commercial pouch cell during thermal runaway. Our work is providing the criteria required to overcome this challenge via supramolecular engineering of the electrolyte, which provides a new way to tune electrolyte functions and may bring numerous new possibilities.