Coordination structure regulation in non-flammable electrolyte enabling high voltage lithium electrochemistry

High-voltage battery systems bring significant increases in energy density but are also accompanied by fast degradation of electrochemical performance and serious safety issues.Herein,Li^(+)coordination structure regulation was conducted to formulate a non-flammable electrolyte,which consists of 1.5 M lithium bis(fluor sulfonyl)imide(LiFSI)in triethyl phosphate and methyl 2,2,2-trifluoromethyl carbonate(FEMC).The renamed TEP-FEMC-FEC(TFF)electrolyte exhibits an FSI^(−)-dominated solvation structure contributed by the weakly-solvating ability of FEMC.The generated inorganic-rich interfacial layers are conducive to stabilizing the phase transition of high-voltage cathodes while suppressing the dendritic growth on lithium metal or co-intercalation behavior in graphite anode.This TFF electrolyte enables LiCoO_(2)||Li batteries to achieve capacity maintenance over 79%after 400 cycles with high-rate of 5 C at an ultra-high voltage of 4.6 V,and an outstanding capacity exceeding 100 mA h g^(−1)even at a super-high current density of 20 C.Additionally,the Ah-level LiCoO_(2)||graphite pouch cells also exhibit high capacity retention and satisfactory safety performance even under fast charging.This work provides a novel research direction for the pursuit of high energy density non-flammable electrolytes.

Non-flammable long chain phosphate ester based electrolyte via competitive solventized structures for high-performance lithium metal batteries

Safety remains a persistent challenge for high-energy-density lithium metal batteries(LMBs).The development of safe and non-flammable electrolytes is especially important in harsh conditions such as high temperatures.Herein,a flame-retardant,low-cost and thermally stable long chain phosphate ester based(tributyl phosphate,TBP)electrolyte is reported,which can effectively enhance the cycling stability of highly loaded high-nickel LMBs with high safety through co-solvation strategy.The interfacial compatibility between TBP and electrode is effectively improved using a short-chain ether(glycol dimethyl ether,DME),and a specially competitive solvation structure is further constructed using lithium borate difluorooxalate(LiDFOB)to form the stable and inorganic-rich electrode interphases.Benefiting from the presence of the cathode electrolyte interphase(CEI)and solid electrolyte interphase(SEI)enriched with LiF and Li_(x)PO_(y)F_(z),the electrolyte demonstrates excellent cycling stability assembled using a 50μm lithium foil anode in combination with a high loading NMC811(15.4 mg cm^(-2))cathode,with 88%capacity retention after 120 cycles.Furthermore,the electrolyte exhibits excellent high-temperature characteristics when used in a 1-Ah pouch cell(N/P=0.26),and higher thermal runaway temperature(238℃)in the ARC(accelerating rate calorimeter)demonstrating high safety.This novel electrolyte adopts long-chain phosphate as the main solvent for the first time,and would provide a new idea for the development of extremely high safety and high-temperature electrolytes.

The Non-flammable Skin of Our Textiles

Do you know that even our curtains and table clothes have skins? They might be invisible to our naked eyes, however they do exist, and also, protect us.

“In-N-out” design enabling high-content triethyl phosphate-based non-flammable and high-conductivity electrolytes for lithium-ion batteries

Safety issues related to flammable electrolytes in lithium-ion batteries(LIBs) remain a major challenge for their extended applications.The use of non-flammable phosphate-based electrolytes has proved the validity in inhibiting the combustion of LIBs.However,the strong interaction between Li^(+) and phosphate leads to a dominant solid electrolyte interphase(SEI) with limited electronic shielding,resulting in the poor Li^(+) intercalation at the graphite(Gr) anode when using high-phosphate-content electrolytes.To mitigate this issue and improve Li^(+) insertion,we propose an “In-N-Out” strategy to render phosphates “noncoordinative”.By employing a combination of strongly polar solvents for a “block effect” and weakly polar solvents for a “drag effect”,we reduce the Li^(+)–phosphate interaction.As a result,phosphates remain in the electrolyte phase(“In”),minimizing their impact on the incompatibility with the Gr electrode(“Out”).We have developed a non-flammable electrolyte with high triethyl phosphate(TEP) content(>60 wt.%),demonstrating the excellent ion conductivity(5.94 mS cm^(-1) at 30 ℃) and reversible Li^(+) intercalation at a standard concentration(~1 mol L^(-1)).This approach enables the manipulation of multiple electrolyte functions and holds the promise for the development of safe electrochemical energy storage systems using non-flammable electrolytes.

Safe growth of graphene from non-flammable gas mixtures via chemical vapor deposition

Chemical vapor deposition has emerged as the most promising technique for the growth of graphene.However, most reports of this technique use either flammable or explosive gases, which bring safety concerns and extra costs to manage risk factors. In this article, we demonstrate that continuous monolayer graphene can be synthesized via chemical vapor deposition technique on Cu foils using industrially safe gas mixtures. Important factors, including the appropriate ratio of hydrogen flow and carbon precursor,pressure, and growth time are considered to obtain graphene films. Optical measurements and electrical transport measurements indicate graphene films are with comparable quality to other reports. Such continuous large area graphene can be synthesized under non-flammable and non-explosive conditions, which opens a safe and economical method for mass production of graphene. It is thereby beneficial for integration of graphene into semiconductor electronics.

Incombustible solid polymer electrolytes:A critical review and perspective

Since the advent of the solid-state batteries,employing solid polymer electrolytes(SPEs)to replace routine flammable liquid electrolytes is regarded to be one of the most promising solutions in pursing highenergy-density battery systems.SPEs with superior thermal stability,good processability,and high mechanical modulus obtain increasing attentions.However,SPE-based batteries are not impenetrable due to their decomposition and combustibility under extreme conditions.Researchers believe incorporating appropriate flame-retardant additives/solvents/fragments into SPEs can intrinsically reduce their flammability to solve the battery safety issues.In this review,the recent research progress of incombustible SPEs,with special emphasis on flame-retardant structural design,is summarized.Specifically,a brief introduction of flame-retardant mechanism,evaluation index for safety of SPEs,and a detailed overview of the latest advances on diverse-types SPEs in various battery systems are highlighted.The deep insight into thermal ru naway process,the free-standing incombustible GPEs,and the ratio nal design of pouch cell structures may be the main directions to motivate revolutionary next-generation for safety batteries.

Structural regulation chemistry of lithium-ion solvation in nonflammable phosphate-based electrolytes for high interfacial compatibility with graphite anode

With the booming development of lithium-ion batteries,safety has become one of the most primary focuses of current researches.Although there are various approaches to enhance the safety of lithiumion batteries,phosphate-based electrolyte holds the greatest potential for practical application due to their non-flammability.Nonetheless,its compatibility issue with the graphite anode remains a significant obstacle to its widespread use.Herein,an effective method is proposed to improve the compatibility of electrolyte with graphite(Gr)anode by rationally adjusting the proportion of lithium salt and solvent components to optimize the Li^(+)solvation structure.By slightly increasing the Li^(+)/triethyl phosphate(TEP)ratio,TEP alone cannot fully occupy the inner solvation sheath and therefore less polar ethylene carbonate(EC)has to be recruited,and the solvation structure gradually changes from Li^(+)–[TEP]_(4)to Li^(+)–[TEP]_(3)[EC]with the coexistence of EC and TEP.Simultaneously,EC molecules in the Li^(+)–[TEP]_(3)[EC]could be preferentially reduced on graphite compared to the TEP molecules,resulting in the formation of a uniform and durable solid-electrolyte interphase(SEI)layer.Benefiting from the optimized phosphate-based electrolyte,the Gr|Li battery exhibits a capacity retention rate of 96.8%after stable cycling at 0.5 C for 470 cycles which shows a longer cycle life than the battery with carbonate electrolyte(cycling at 0.5 C for 450 cycles).Therefore,this work provides the guidance for designing a non-flammable phosphate-based electrolyte for high-safety and long cycling-life lithium-ion batteries.

Dual-filler reinforced PVDF-HFP based polymer electrolyte enabling high-safety design of lithium metal batteries

Despite the high energy density of lithium metal batteries(LMBs),their application in rechargeable batteries is still hampered due to insufficient safety.Here,we present a novel flame-retardant solid-state electrolyte based on polyvinylidene fluoride-hexafluoropropylene(PVDF-HFP)with nano SiO_(2)aerogel as an inert filler but Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO)as an auxiliary component to enhance the ion conductivity.The introduction of SiO_(2)aerogels imparts the polymer electrolyte with exceptional thermal stability and flame retardancy.Simultaneously,the interaction between hydroxyl groups of SiO_(2)particles and PVDF-HFP creates a strong cross-linking structure,enhancing the mechanical strength and stability of the electrolyte.Furthermore,the presence of SiO_(2)aerogel and LLZTO facilitates the dissociation of lithium salts through Lewis acid-base interactions,resulting in a high ionic conductivity of 1.01×10^(−3)S·cm^(−1)and a wide electrochemical window of~5.0 V at room temperature for the prepared electrolytes.Remarkably,the assembled Li|Li cell demonstrates the excellent resistance to lithium dendrite and runs stablly for over 1500 h at a current density of 0.25 mA·cm^(−2).Thus,we prepare a pouch cell with high safety,which can work normally after short-circuiting under the external folding and cutting.

Stabilizing the cycling stability of rechargeable lithium metal batteries with tris(hexafluoroisopropyl)phosphate additive

The application of rechargeable lithium metal batteries(LMBs)has been hindered by the fast growth of lithium dendrites during charge and the limited cycling life because of the decomposition of the electrolyte at the interface.Here,we have developed a non-flammable triethyl phosphate(TEP)-based electrolyte with tris(hexafluoroisopropyl)phosphate(THFP)as an additive.The polar nature of the C–F bonding and the rich CF3 groups in THFP lowers its LUMO energy and HOMO energy to help form a stable,Li F-rich solid electrolyte interphase(SEI)layer through the reduction of THFP and increases the binding ability of the PF6-anions,which significantly suppresses lithium dendrite growth and reduces the electrolyte decomposition.Moreover,THFP participates in the formation of a thin,C–F rich electrolyte interphase(CEI)layer to provide the stable cycling of the cathode at a high voltage.The symmetric Li||Li and full Li/NCM622 cells with THFP additive have small polarization and long cycling life,which demonstrates the importance of the additive to the application of the LMBs.

Wide-temperature range and high safety electrolytes for highvoltage Li-metal batteries

Along with the keeping growing demand for high-energy-density energy storage system,high-voltage Li-metal batteries(LMBs)have attracted many attentions.In view of many defects of the commercial electrolytes,such as flammability,limited operation temperature range,and severe Li dendrite growth,non-flammable phosphate-based localized highly concentrated electrolytes(LHCE)have been explored as one of the safe electrolytes for LMBs.But until now there is rare report on wide-temperature range LMBs using phosphate-based electrolytes.Here,we prepare a wide-temperature LHCE,which is composed of lithium difluoro(oxalato)borate(LiDFOB),triethyl phosphate(TEP),and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(HFE),and explore the applicability in wide-temperature LMBs from−40 to 70℃.In the LHCE,both TEP and HFE are non-flammable,and Li^(+) is highly coordinated with TEP and DFOB^(−),which can effectively inhibit the TEP decomposition on anode,and facilitate the preferential reduction of DFOB^(−),thus obtain a robust solid electrolyte interphase(SEI)to suppress Li dendrite growth and side reactions.Therefore,this LHCE can not only endow Li/Cu and Li/Li cells with high Coulombic efficiency(CE)and long cycling lifespan,but also be applied to LiFePO_(4)(LFP)/Li and LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)(NCM523)/Li LMBs.Most importantly,the NCM523/Li LMBs with LHCE can deliver stable cycling performance at 4.5 V high-voltage and high-temperature(70℃),as well as excellent low-temperature capacity retention even though both charging and discharging process were carried out at−40℃.

Lithium(fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide for stabilizing cathode-electrolyte interface in sulfonamide electrolytes

Rechargeable lithium metal batteries(RLMBs)have been regarded as promising successors for contemporary lithium-ion batteries,in view of their high gravimetric and volumetric energy densities.Conventional non-aqueous liquid electrolytes containing organic carbonate solvents possess high chemical reactivities with metallic lithium anode and high flammability,which induces considerable safety threats under extreme conditions(e.g.,overcharging and thermal runaway).Herein,we propose the utilization of fluorinated sulfonamide(i.e.,N,N-dimethyl fluorosulfonamide(DMFSA))as solvent,together with lithium(fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide(LiFNFSI)as co-salt and/or electrolyte additive for accessing safer and highperforming RLMBs.Comprehensive physical(e.g.,thermal transition,viscosity,and ionic conductivity)and electrochemical(e.g.,anodic stability on different electrodes)characterizations have been performed,aiming to reveal the inherent characteristics of the sulfonamide-based electrolytes and the particular role of LiFNFSI on the stabilization of LiCoO_(2) cathode.It has been demonstrated that the sulfonamide-based electrolytes exhibit superior flame-retardant abilities and decent ionic conductivities(>1 mS·cm^(-1)at room temperature).The incorporation of LiFNFSI as co-salt and/or electrolyte additive could significantly suppress the side reactions occurring at the cathode compartment,through the preferential decompositions of the FNFSI-anion.This work is anticipated to give an in-depth understanding on the working mechanism of LiFNFSI in the sulfonamide-based electrolytes,and also spurs the development of high-energy and safer RLMBs.