Flammable Electrolytes Research Articles

Explosion characteristics of two-phase ejecta from large-capacity lithium iron phosphate batteries

When a thermal runaway accident occurs in a lithium-ion battery energy storage station, the battery emits a large amount of flammable electrolyte vapor and thermal runaway gas, which may cause serious combustion and explosion accidents when they are ignited in a confined space. With the gradual development of large-scale energy storage batteries, the composition and explosive characteristics of thermal runaway products in large-scale lithium iron phosphate batteries for energy storage remain unclear. In this paper, the content and components of the two-phase eruption substances of 340Ah lithium iron phosphate battery were determined through experiments, and the explosion parameters of the two-phase battery eruptions were studied by using the improved and optimized 20L spherical explosion parameter test system, which reveals the explosion law and hazards of the two-phase battery eruptions. Studies have shown that in a two-phase system explosion, EMC can make the two-phase system more explosive and more powerful, and the thermal runaway gas expands its explosion concentration range. The coupling explosion of the two enhanced the sensitivity and explosive power of the two-phase ejecta. Increasing the concentration of any combustible in a two-phase system will cause the explosion intensity parameters of the system to increase. However, when the combustible concentration exceeds the optimal explosion concentration, the explosion intensity parameters will decrease or even no explosion will occur. Both explosion intensity parameters and sensitivity parameters are more sensitive to EMC concentration, and the higher the EMC concentration, the stronger its dominant role in the explosion of the two-phase system. This work can lay the foundation for revealing the disaster-causing mechanism of explosion accidents in lithium-ion battery energy storage power stations, guide the safe design of energy storage systems and the prevention and control of explosion accidents, and provide theoretical and data support for the investigation of explosion accidents in energy storage power stations.

Dual-Anionic Coordination Manipulation Induces Phosphorus and Boron-Rich Gradient Interphase Towards Stable and Safe Sodium Metal Batteries.

High-voltage sodium metal batteries (SMBs) present a viable pathway towards high-energy-density sodium-based batteries due to the competitive cost advantage and abundant supply of sodium resources. However, they still suffer from severe capacity decay induced by the notorious decomposition of the electrolyte under high voltage and unstable cathode/electrolyte interphase (CEI). In addition, the high reactivity of Na metal and flammable electrolytes push SMBs to their safety limits. Herein, a special dual-anion aggregated Na+ solvation structure is designed in a nonflammable trimethyl phosphate-based localized high-concentration electrolyte, and a gradient CEI enriched with phosphorus and boron compounds is formed on the cathode. This thin and stable interphase effectively suppresses the parasitic reaction, improves the interfacial stability of the cathode, and facilitates Na+ transport through the interface by the synergistic effect of multi-components, thus optimizing the cycling stability and safety of SMBs. The Na0.95Ni0.4Fe0.15Mn0.3Ti0.15O2//Na batteries employing such electrolyte provide a discharge capacity of 167.5 mA h g-1 and high retention in the capacity of 85.2% after 800 cycles at 1 C. This approach offers a general strategy for the design of flame-retardant high-voltage electrolytes and the practical application of SMBs.

Electrospinning Fiber Membrane‐Derived Gel Polymer Electrolytes with High Mechanical Strength and Low Swelling Effect for High‐Safety Lithium Metal Batteries

AbstractThe practical application of lithium metal batteries (LMBs) is hindered by the issues of flammable electrolytes, lithium dendrites and the resulting thermal runaway. Designing flame‐retardant electrolytes with high performance is a valid strategy to break the current dilemma. In this work, the flame retardant of triphenyl phosphate (TPP) is elaborately encapsulated into the polymer shell of polyacrylonitrile (PAN) and polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) to realize the controllable release of TPP during the soaking process. The resulting TPP@PAN/PVDF‐HFP fiber membrane holds high thermal stability, high mechanical strength, and low swelling rate, which is essential for the preparation of flame‐retardant gel polymer electrolyte (GPE). As demonstrated, the TPP@PAN/PVDF‐HFP GPE can deliver high Li+ transference number of 0.877, low interfacial activation energy barrier of 26.6 kJ mol−1 and heterogeneous SEI composition of Li3PO4/Li2CO3/LiF. The corresponding Li||Li cells achieve stable voltage polarization over 1000 h, and the Li||Cu cells display high plating/stripping CE of 99.1%. Meanwhile, the optimized Li||LiFePO4 batteries exhibit high reversible capacity of 158 mAh g−1 after 200 cycles at 0.5 C, and present outstanding fire resistance through the thermal runaway and puncture test. This study will open window for the design of high‐safety electrolytes to promote the practical application of LMBs.

Perspective on eutectic electrolytes for next‐generation batteries

AbstractThe environmental challenges and growing energy demand have promoted the development of renewable energy, including solar, tidal, and wind. The next‐generation electrochemical energy storage (EES), incorporating flow battery (FB) and metal‐based battery (MB, Li, Na, Zn, Mg, etc.) received more attention. The flammable electrolytes in nonaqueous batteries have raised serious safety hazards and more unconventional electrolyte systems have been proposed recently. An emerging class of electrolytes, eutectic electrolytes have been reported in many batteries due to the facile preparation, concentrated states, and unique ion transport properties. In FB, eutectic electrolytes can significantly increase the energy density by promoting the molar ratio of redox active materials. In MB, eutectic electrolytes reduce the vapor pressure and toxicity, inhibit metal dendrites growth, and enlarge the electrochemical window. In this review, we summarize the progress status of different eutectic electrolytes on both FBs and MBs. We expect this review can supply the guidance for the application of eutectic electrolytes in EES.

Controlling the temperature build-up in electrode-sealed coin-shaped batteries via designing central heat dissipator

Nowadays, the ever-increasing demand for the computational power in the calculators, watches and LED lights require higher consumption rate from their portable energy source, which is typically coin-shaped batteries. The required power generates and accumulates a large amount of heat, which is a critical safety concern due to flammability of the included organic electrolytes. When heat dissipation is minimal from the electrode surface, the packaging boundary remains the sole heat transfer medium. In such case, although the center carries a minimal real estate compared to the rest of the electrode surface, the heat gets trapped, due to having the lowest reach to the heat-dissipating boundaries. For this purpose, a central heat sink component is anticipated for the coin-shaped batteries and the temperature profile across the cell is analytically derived. Subsequently, the role of the sink thermal conductivity and its scale as well as the thermal conduction of the boundary on the formation of steady state temperature profile has been analyzed. More specifically, the location of the maximum temperature rmax and its value Tmax is obtained and verified versus the extreme values of the thermal conductivities, the areal ratio of the heat sink, and the current density. The obtained results could be useful for the cost-effective design of the packaging materials (i.e. sustainable plastics and bio-degradable) with limited heat dissipation for the rechargeable batteries, particularly during the high power applications, in the presence of highly flammable electrolytes.

Revolutionizing Implantable Technology: Biocompatible Supercapacitors as the Future of Power Sources

AbstractAlmost all implantable electronic medical devices (IEMDs) are powered by bulky Li‐ion batteries (LIBs), limiting their miniaturization and lifespan advancements. In addition, LIBs contain toxic materials and flammable electrolytes that are dangerous if they leak into human organs. In this context, there is an urgent need to explore new approaches and concepts that can address the critical challenges of designing novel electrochemical energy storage systems and gain a mechanistic understanding of the phenomena taking place in diverse scenarios. This review summarizes recent advancements in biocompatible supercapacitors (B‐SCs) as a power source for various IEMDs, offering a potential solution to these challenges. Different types of IEMDs and their power requirements are briefly discussed, along with challenges arising from energy storage systems and their applications in IEMDs. Given the importance of electrode materials in determining the electrochemical performance of B‐SCs in terms of energy and power densities, different electrode materials and their developments are systematically reviewed. Finally, new insights are offered into potential opportunities and future prospects for the rational design of next‐generation B‐SCs.

Designing Advanced Electrolytes for High-Safety and Long-Lifetime Sodium-Ion Batteries via Anion-Cation Interaction Modulation.

Safety hazards caused by flammable electrolytes have been major obstacles to the practical application of sodium-ion batteries (SIBs). The adoption of nonflammable all-phosphate electrolytes can effectively improve the safety of SIBs; however, traditional low-concentration phosphate electrolytes are not compatible with carbon-based anodes. Herein, we report an anion-cation interaction modulation strategy to design low-concentration phosphate electrolytes with superior physicochemical properties. Tris(2,2,2-trifluoroethyl) phosphate (TFEP) is introduced as a cosolvent to regulate the ion-solvent-coordinated (ISC) structure through enhancing the anion-cation interactions, forming the stable anion-induced ISC (AI-ISC) structure, even at a low salt concentration (1.22 M). Through spectroscopy analyses and theoretical calculations, we reveal the underlying mechanism responsible for the stabilization of these electrolytes. Impressively, both the hard carbon (HC) anode and Na4Fe2.91(PO4)2(P2O7) (NFPP) cathode work well with the developed electrolytes. The designed phosphate electrolyte enables Ah-level HC//NFPP pouch cells with an average Coulombic efficiency (CE) of over 99.9% and a capacity retention of 84.5% after 2000 cycles. In addition, the pouch cells can operate in a wide temperature range (-20 to 60 °C) and successfully pass rigorous safety testing. This work provides new insight into the design of the electrochemically compatibility electrolyte for high-safety and long-lifetime SIBs.

Stable Photo-Rechargeable Al Battery for Enhancing Energy Utilization.

Photovoltaic cells (PVs) are able to convert solar energy to electric energy, while energy storage devices are required to be equipped due to the fluctuations of sunlight. However, the electrical connection of PVs and energy storage devices leads to increased energy consumption, and thus energy storage ability and utilization efficiency are decreased. One of the solutions is to explore an integrated photoelectrochemical energy conversion-storage device. Up to date, the integrated photo-rechargeable Li-ion batteries often suffer from unstable photo-active materials and flammable electrolytes under illumination, with concerns in safety risks and limited lifetime. To address the critical issues, here a novel photo-rechargeable aluminum battery (PRAB) is designed with safe ionic liquid electrolytes and stable polyaniline photo-electrodes. The integrated PRAB presents stable operation with an enhanced reversible specific capacity ≈191% under illumination. Meanwhile, a simplified continuum model is established to provide rational guidance for designing electrode structures along with a charging/discharging strategy to meet the practical operation conditions. The as-designed PRAB presents an energy-saving efficiency ≈61.92% upon charging and an energy output increment ≈31.25% during discharging under illumination. The strategy of designing and fabricating stable and safe photo-rechargeable non-aqueous Al batteries highlights the pathway for substantially promoting the utilization efficiency of solar energy.

Interfacial polymerization mechanisms assisted flame retardancy process of low-flammable electrolytes on lithium anode

Thermal runaway is a hazardous risk, occurring more readily in high-energy–density lithium-ion batteries (LIBs), which leads to a rapid temperature rise and even combustion or explosion when using flammable electrolyte systems. Flame retardants (FRs), such as trimethyl phosphate (TMPa) and triethyl phosphate (TEP), are commonly utilized due to their effective flame suppression, low toxicity, and excellent thermal stability. However, the lack of in-depth understanding of the flame retardancy mechanism and solid electrolyte interphase (SEI) formation process has made the development of functional electrolytes difficult at present. In this study, we clarified the flame retardancy and interfacial reaction mechanisms of low-flammable TMPa localized high-concentration electrolytes (LHCE) using hybrid ab initio and reactive force field (HAIR) schemes. Long-term HAIR simulation reveals that phosphorous radicals produced by the decomposition of TMPa capture carbon radicals, encouraging their polymerization into low-flammable oligomers, while fluorine-containing solvents in the electrolyte capture hydrogen radicals and produce nonflammable hydrofluoric acid (HF). This synergistic flame retardancy mechanism provides essential atomic-level insights for the rational design of high-safety electrolytes in the future.

(Invited) Investigating Microstructural Effects of Composite NCM811 Cathodes on ALL-Solid-State Li-Ion Batteries Performance Under Low Operation Stacking Pressure

All-solid-state lithium-ion batteries (ASSLIBs) have been considered suitable alternatives to commercial lithium-ion batteries (LIBs) in the aspect of safety issues that come from the use of inflammable solid electrolytes to replace organic flammable electrolytes. Nevertheless, there apparently remains much room for a better understanding of their properties and behaviors in order to upgrade their performance to reach the practical application level. Ni-rich layered oxides, LiNi1-x-yCoxMnyO2 (NCM), are promising cathodes for high-energy ASSLIBs because of their high capacities and redox potentials, and low material cost when compared with conventional LiCoO2. However, certain challenges associated with their use in ASSLIBs must be addressed for their effective use and industrialization. In particular, the structural integrity of the NCM electrodes during the long-term charge/discharge process suffers from the formation of an intergranular and/or intragranular cracking behavior. These microcracks are initiated at the grain boundaries from the anisotropic chemical strain of the randomly oriented polycrystal (PC) primary cathode particles. Solid evidence behind the electrochem-mechanical breakdown of an NCM cathode with liquid electrolytes has been well discussed and reported in the literature. However, the breakdown in ASSLIBs may not obey as same as in the liquid-electrolyte LIBs and display exclusive mechanics-oriented material damage in the presence of rigid solid-state electrolytes (SSEs). The primary objective of this research is to gain a deeper understanding of various cracking modes in ASSLIBs, which we believe is instrumental to improving the lifespan and cell performance as a whole. ForASSLIBs, stacking pressures greater than 100 MPa under battery operation are currently commonly used. The use of high stacking pressure increases manufacturing and usage difficulties and overall cost. Lowering the battery-operation stacking pressure, for example to the level of the liquid-electrolyte batteries, will certainly facilitate the wider applications of ASSLIBs. In this context, composite cathodes consisting of a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and brittle Li3InCl6 (LIC) SSE have been assessed for ASSLIB applications under low operation stacking pressure (coin-cell configuration; ~2.0 MPa). The study reveals the effects of material and structural characteristics of the composite cathode, including the NCM particle size and size distribution, active-material spatial distribution, particle crystallinity (polycrystal or single-crystal), and electrochemical operation parameters (voltage range, current rates) on the cycle stability of the ASSLIBs as a result of the electrochem-mechanical behaviors of the oxide cathode. Meanwhile, a novel solvent-based synthesis process of LIC for achieving high-density cathodes is introduced.

Flame-Retardant Nonaqueous Electrolytes for High-Safety Potassium-Ion Batteries.

Potassium-ion batteries (PIBs) with conventional organic-based flammable electrolytes suffer from serious safety issues with a high risk of ignition and burning especially under harsh conditions, which significantly limits their widespread applications. Flame-retardant electrolytes (FREs) are considered as one of the most effective strategies to address these safety issues. Therefore, it's much necessary to summarize the challenges, recent progress, and design principles of flame-retardant nonaqueous electrolytes for PIBs to guide their development and future applications. In this review, an in-depth introduction and explanation of the origins of electrolyte flammability are first presented. Particularly, the state-of-the-art design principles of FREs for PIBs are extensively summarized and emphasized, including the electrolyte flame-retardant solvents/additives, highly concentrated electrolytes (HCEs), localized high-concentration electrolytes (LHCEs), ionic liquids-based electrolytes and solid-state electrolytes. Moreover, the advantages and drawbacks of each approach are systematically presented and discussed, following by proposed perspectives to guide the rational development of next-generation high-safety PIBs for practical applications.

Recent Progress in Flame-Retardant Polymer Electrolytes for Solid-State Lithium Metal Batteries

Lithium-ion batteries (LIBs) have been widely applied in our daily life due to their high energy density, long cycle life, and lack of memory effect. However, the current commercialized LIBs still face the threat of flammable electrolytes and lithium dendrites. Solid-state electrolytes emerge as an answer to suppress the growth of lithium dendrites and avoid the problem of electrolyte leakage. Among them, polymer electrolytes with excellent flexibility, light weight, easy processing, and good interfacial compatibility with electrodes are the most promising for practical applications. Nevertheless, most of the polymer electrolytes are flammable. It is urgent to develop flame-retardant solid polymer electrolytes. This review introduces the latest advances in emerging flame-retardant solid polymer electrolytes, including Polyethylene oxide (PEO), polyacrylonitrile (PAN), Poly (ethylene glycol) diacrylate (PEGDA), polyvinylidene fluoride (PVDF), and so on. The electrochemical properties, flame retardancy, and flame-retardant mechanisms of these polymer electrolytes with different flame retardants are systematically discussed. Finally, the future development of flame-retardant solid polymer electrolytes is pointed out. It is anticipated that this review will guide the development of flame-retardant polymer electrolytes for solid-state LIBs.

Shock-tube CO measurements during the pyrolysis of ethylene carbonate

Ethylene carbonate (EC) is a key component of the flammable electrolyte in lithium-ion batteries. In this study, the pyrolysis of ethylene carbonate was investigated by measuring CO time histories near atmospheric pressure and in highly diluted conditions (0.999 He/Ar). The performance of a recent detailed chemical kinetics mechanism from Kanayama et al., 2022, was evaluated, and noticeable discrepancies were found, possibly indicating missing reaction pathways. A tentative model was proposed by merging the EC sub-mechanism from the Kanayama study with a recent model for linear carbonate pyrolysis from the authors (Grégoire et al., 2023). This tentative model includes the addition of several missing reactions for oxirane pyrolysis, and a couple of reactions for acetaldehyde and EC thermal decomposition were modified within their error uncertainties. The resulting model presents better predictions overall, but room for improvement remains. This study highlights the need to further study the pyrolysis chemistry of EC as well as acetaldehyde, which is a major intermediate component from EC pyrolysis under our conditions.

Tunning solvation structure in non-flammable, localized high-concentration electrolytes with enhanced stability towards all aluminum substrate-based K batteries

Although metallic potassium or graphite anode with low redox potentials are desirable for potassium-ion batteries (PIBs), the severe capacity decay caused by consecutive reduction reactions on the aggressively reactive anode surface is inevitable because of the scarcity of an effective passivation layer. Additionally, the development of PIBs faces potential safety hazards due to the usage of reactive anodes with flammable electrolytes. Herein, a fire-retardant localized high-concentration electrolyte (LHCE) is formulated by adding a low-polarity co-solvent of highly fluorinated ether into the concentrated potassium bis(fluorosulfonyl)imide/trimethyl phosphate. A unique electrolyte solvation environment with the enhanced anion-cation interaction in an LHCE facilitates a durable anion-derived solid electrolyte interphase (SEI) with self-accelerated interfacial kinetics and minimizes the SEI dissolution compared to the conventional carbonate-based electrolyte. Consequently, the unmodified Al substrate could sustain stable potassium metal cycling above 3400 h (over 800 cycles) with high reversibility (98%), and the graphite anode retains prolonged cyclic stability (over 300 cycles) with a high reversible capacity (257.6 mAh g−1) and capacity retention (92.6 % at 0.2 C). Meanwhile, Al corrosion at high voltage is significantly suppressed, and the electrochemical window is extended due to less free solvents in an LHCE, enabling good electrolyte compatibility with high-voltage cathodes. Coupling non-flammable solvents and the concept of LHCE could facilitate a better understanding of electrolyte chemistry and offer more opportunities to use K or graphite anode for all Al substrate-based PIBs highlighted with high performance and superb safety.

Nonflammable electrolyte with low exothermic design for safer lithium-based batteries

Battery safety has always been a concern for high-energy-density configurations with nickel-rich cathode (Ni>0.6). Tremendous heat released from the reaction between highly flammable electrolyte and cathode under mechanical, thermal or electrical abuse may cause thermal runaway. Herein, we explore the heat release of various solvents with fully charged cathodes and summarized the solvent/heat release phase diagram. On this basis, we select fluorinated bis(2,2,2-trifluoroethyl) carbonate to prepare a nonflammable, low exothermic electrolyte. This electrolyte significantly reduces the maximum temperature by one-third and decreases the maximum heating rate from 206.0 °C s−1 to 82.6 °C s−1 during the thermal runaway process of commercial lithium-ion pouch cell. Moreover, it demonstrates remarkable compatibility with lithium metal anode. Benefited from the uniform solid-electrolyte interphase (SEI) rich in -CF3 organic layer, the Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) full cell exhibits a capacity retention rate of 80% after 240 cycles. Notably, a 1.5 Ah Li metal pouch cell with a high energy density of 365 Wh kg−1 displays an excellent capacity retention of 90.02% after 98 cycles under realistic conditions. This work provides a novel approach to construct safer and longer-lasting lithium-based batteries by designing nonflammable and low exothermic electrolyte.

A Non‐Volatile, Thermo‐Reversible, and Self‐Protective Gel Electrolyte Providing Highly Precise and Reversible Thermal Protection for Lithium Batteries

AbstractThe safety issue represents a long‐standing obstacle that retards large‐scale applications of high‐energy lithium batteries. Among different causes, thermal runaway is the most prominent one. To date, various approaches have been proposed to inhibit thermal runaway; however, they suffer from some intrinsic drawbacks, either being irreversible (one‐time protection), using volatile and flammable electrolytes, or delayed thermal protection (140–150 °C). Herein, this work exploits a non‐volatile, non‐flammable, and thermo‐reversible polymer/ionic liquid gel electrolyte as a built‐in safety switch, which provides highly precise and reversible thermal protection for lithium batteries. At high temperature, the gel electrolyte experiences phase separation and deposits polymer on the electrode surfaces/separators, which blocks Li+ insertion reactions and thus prevents thermal runaway. When the temperature decreases, the gel electrolyte restores its original properties and battery performance resumes. Notably, the optimal protection effect is achieved at 110 °C, which is the critical temperature right before thermal runaway. More importantly, such a thermal‐protection process can repeat multiple times without compromising the battery performance, indicating extraordinary thermal reversibility. To the authors' knowledge, such a precise and reversible protection effect has never been reported in any electrolyte systems, and this work opens an exciting avenue for safe operation of high‐energy Li batteries.

Brominated flame retardants coated separators for high-safety lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have become highly promising next-generation secondary lithium batteries owing to their high theoretical energy density and abundance of sulfur. Nevertheless, the large-scale application of LSBs is still restricted by the shuttle effect of lithium polysulfide (LiPSs) and the potential fire hazard caused by flammable electrolytes. Herein, three electrolyte-insoluble brominated flame retardants (BFRs) are selected and coated on both sides of commercial polypropylene separators by a facile slurry coating method. The effects of the three BFRs on the safety and electrochemical properties of LSBs are characterized and compared. The coating modification separators greatly improves the flame retardancy of LSBs through radical elimination mechanism. The self-extinguishing time of the electrolyte is reduced from 0.66 s/mg to 0.20 s/mg. Moreover, it is demonstrated that the oxygen (O)-containing BFRs exert a significant adsorption capacity and are more advantageous than O-free BFRs in LSBs. In addition, octabromoether (BDDP) coated separator is more effective in trapping LiPSs than decabromodiphenyl ether (DBDPO) due to higher O content, which can mitigate the shuttle effect and enhance the cycle and rate performance of LSBs. This simple coating strategy for separators with BFRs offers a strongly competitive option for the large-scale production of high-safety LSBs.

Non-flammable Phosphate-Grafted Nanofiber Separator Enabling Stable-Cycling and High-Safety Lithium Metal Batteries

Lithium metal batteries (LMBs) are promising rechargeable energy storage devices with high energy densities and long lifetimes. Nevertheless, safety concerns constitute a severe impediment to the commercial demand for LMBs, including uncontrollable lithium dendrites, heat-intolerant separators, and flammable electrolytes. Herein, a novel separator (PSVHM) containing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), poly(methyl methacrylate) (PMMA) and cage silsesquioxanes, phosphorous-containing acrylate monomers is fabricated by electrospinning with in situ ultraviolet-irradiation grafting polymerization. Attributed to the presence of phosphate groups in the membrane with flame retardant properties, the PSVHM separators have outstanding self-extinguish capabilities. In addition, the 3D-crosslinked PSVHM separator possesses high ion conductivity, and excellent mechanical strength, thus suppressing the uneven lithium dendrites and constructing a stable solid electrolyte interface (SEI). Moreover, cell assembled with the PSVHM separator exhibits an ultra-capacity retention of 98% after 200 cycles at a high current density of 2 C. This work provides a guideline for the preparation of high-safety and high-performance lithium metal batteries.

Non‐Flammable Electrolyte with Lithium Nitrate as the Only Lithium Salt for Boosting Ultra‐Stable Cycling and Fire‐Safety Lithium Metal Batteries

AbstractLithium metal batteries (LMBs) attract considerable attention for their incomparable energy density. However, safety issues caused by uncontrollable lithium dendrites and highly flammable electrolyte limit large‐scale LMBs applications. Herein, a low‐cost, thermally stable, and low environmentally‐sensitive lithium nitrate (LiNO3) is proposed as the only lithium salt to incorporate with nonflammable triethyl phosphate and fluoroethylene carbonate (FEC) co‐solvent as the electrolyte anticipated to enhance the performance of LMBs. Benefiting from the presence of NO3− and FEC with strong solvation effect and easily reduced ability, a Li3N–LiF‐rich stable solid electrolyte interphase is constructed. Compared to commercial electrolytes, the proposed electrolyte has a high Coulombic efficiency of 98.31% in Li‐Cu test at 1 mA cm−2 of 1.0 mAh cm−2 with dendrite‐free morphology. Additionally, the electrolyte system shows high voltage stability and cathode electrolyte interphase film‐forming properties with stable cycling performances, which exhibit outstanding capacity retention rates of 96.39% and 83.74% after 1000 cycles for LFP//Li and NCM811//Li, respectively. Importantly, the non‐flammable electrolyte delays the onset of combustion in lithium metal soft pack batteries by 255 s and reduces the peak heat release by 21.02% under the continuous external high‐temperature heating condition. The novel electrolyte can contribute immensely to developing high‐electrochemical‐performance and high‐safety LMBs.

Understanding Surface and Bulk Electronic Structure of Li-ion Battery Cathodes Operated at Extreme Environment

Li-ion and Li metal batteries are widely used for portable devices due to their high gravimetric and volumetric energy densities and cyclability. However, overcharging and extreme discharging of the battery can lead to overheating and thermal runaway, while improper use can lead to fires and explosions. The volatility and flammability of the organic solvents (ethylene carbonate/dimethyl carbonate) used as electrolytes are the major sources of these thermal stability issues. Therefore, an alternative to flammable electrolytes, room temperature ionic liquids (RTILs) electrolyte chemistry is investigated due to its high thermal and electrochemical stability. Here, the fundamental understanding of developing high temperature Liion battery materials is evaluated using electrochemistry and depth-dependent the X-ray spectroscopy techniques.