Feng Guo

Bio: Feng Guo is an academic researcher from Hokkaido University. The author has contributed to research in topics: Combustion & Flammability. The author has an hindex of 4, co-authored 8 publications receiving 30 citations. Previous affiliations of Feng Guo include China University of Mining and Technology.

Experimental study on flammability limits of electrolyte solvents in lithium-ion batteries using a wick combustion method

Abstract: To quantify the flammability limits of organic electrolyte solvents used in lithium-ion batteries, a unique wick combustion system was developed in conjunction with limiting oxygen concentration (LOC) of candle-like flame, named wick-LOC method. By controlling the oxygen-nitrogen ratio of external flow of the wick diffusion flame, the flammability limits (LOC) of electrolyte solvents were determined experimentally. To provide reproducible results under specified conditions, the effects of axial flow velocity, exposed wick length and elapsed time after ignition on the wick-LOC were studied, and the proper experimental conditions were selected for further applications. To validate the reliability of wick-LOC in flammability evaluation, correlation analyses to other flammability properties (flash point, auto-ignition temperature, the heat of combustion and other types of LOC) were conducted. The wick-LOC method was then applied to quantify the flammability of mixed solvents. The linear changes of wick-LOC with mixing ratios were found in the mixture of linear and cyclic carbonates, while the non-linear trends were found in carbonate-ether mixed solvents. To evaluate the flame-retardant effectiveness of organophosphorus compounds (OPCs) as additives in electrolyte solvents, a series of tests were conducted. Results showed that small amounts of OPCs had significant flame-retardant effects, but the efficiency decreased with the higher OPC additions. The effectiveness of four OPCs was distinguished as well. The results of this work provided valuable information about the flammability limits of single and mixed electrolyte solvents, and it may be useful for designing electrolyte balanced in both performance and safety.

Influence of lithium salts on the combustion characteristics of dimethyl carbonate-based electrolytes using a wick combustion method

Abstract: Flammability studies of electrolytes are required for screening safer materials used in lithium-ion batteries. Besides the thermal stability, the effects of lithium salts on electrolyte combustion are important as well for fire safety of electrolytes. To clarify the influence of lithium salts on the electrolyte flammability, experimental analyses were conducted using a unique wick combustion system in conjunction with the limiting oxygen concentration (LOC) test, called wick-LOC method. The dimethyl carbonate (DMC)-based electrolytes with 1M addition of different lithium salts (LiPF6, LiBF4, and LiTFSI) were studied comparing with pure DMC and trimethyl phosphate (TMP)-added solvents. The three lithium salts gave unique and distinct flame behaviors including flame shapes, colors and the changes of wick surface until self-extinguishing. The wick-LOC results indicated a considerable flame-retardant effect of LiPF6, while other salts have minor effects on the flame extinction. Utilizing the flame spectrum and combustion residue analyses, the roles of salts during combustion were characterized. The PF6 anion played a similar role with the TMP additive in the gas phase flame inhibition. In the cases of LiPF6 and LiBF4, the solid products (LiF) accumulation blocked the fuel supply from the wick to the flame region. In the case of LiTFSI, the serious charring of the cotton wick was considered as a potential hazard on solid combustibles in the real fire scenarios.

Experimental study on flame stability limits of lithium ion battery electrolyte solvents with organophosphorus compounds addition using a candle-like wick combustion system

Abstract: To evaluate the fire-retardant effectiveness of organophosphorus compounds (OPC) added to Li-ion battery electrolyte solvents, the limiting oxygen concentration (LOC) method is used in conjunction with a wick combustion system, called as wick-LOC method. With the wick-LOC method, two modes of stabilized flame are found, namely, wake flame and full flame. When OPC is added to the electrolyte, two distinct branches of extinction processes occur according to the different flame modes near extinction with no transition from the full flame to the wake flame in the case of higher OPC addition. The flame stability limits are measured as a function of OPC addition for both flame modes. The wake flame is shown to be consistently more stable at low levels of OPC addition. However, once the OPC addition exceeds a critical amount, the full flame shows higher stability with a lower LOC than the wake flame. These phenomena in the two regimes are also found in other cases of high OPC addition (different type of OPC and electrolyte solvent). In the most stable flame mode, the regime switches from the wake flame to the full flame with increasing OPC addition, and they are defined correspondingly as “blow-off regime” and “quenching regime”. To explain the presence of these two regimes, the thermal balance effect is considered in the discussion of flame extinction mechanisms. The difference in flame volume near the extinction limit shows that the quenching mechanism dominates flame extinction under higher OPC addition. The thermal balance effect on flame stabilization or extinction can be the additional impact on the fire retardation abilities of OPC itself.

Experimental study of welding region effects on upward flame spread over textile membranes

Abstract: Textile membranes are used widely as a main architectural material in membrane structure buildings. However, very few studies have been conducted to investigate the flame spread characteristics of ...

Effect of DPK flame retardant on combustion characteristics and fire safety of PVC membrane

Abstract: In this work, the performances of PVC membrane with DPK flame retardant and without flame retardant were investigated under external radiation flux. The experimental results showed that the addition of DPK flame retardant can greatly reduce the peak heat release, total heat release of the material, and increase the time to peak heat release, time to ignition and the production of poisonous gas CO. By introducing the mathematical evaluation model and specifying the reliable evaluation indexes, the safety indexes of two kinds of materials are obtained. The results showed that by adding the flame retardant, the safety indexes of the PVC membranes were increased to 161% and 156% under 40 kw/m 2 and 50 kw/m 2 respectively, which is accordant to the result of experiments and suggest that the presence of DPK has a good flame retardant effect.

A review of battery fires in electric vehicles

Abstract: Over the last decade, the electric vehicle (EV) has significantly changed the car industry globally, driven by the fast development of Li-ion battery technology. However, the fire risk and hazard associated with this type of high-energy battery has become a major safety concern for EVs. This review focuses on the latest fire-safety issues of EVs related to thermal runaway and fire in Li-ion batteries. Thermal runaway or fire can occur as a result of extreme abuse conditions that may be the result of the faulty operation or traffic accidents. Failure of the battery may then be accompanied by the release of toxic gas, fire, jet flames, and explosion. This paper is devoted to reviewing the battery fire in battery EVs, hybrid EVs, and electric buses to provide a qualitative understanding of the fire risk and hazards associated with battery powered EVs. In addition, important battery fire characteristics involved in various EV fire scenarios, obtained through testing, are analysed. The tested peak heat release rate (PHHR in MW) varies with the energy capacity of LIBs ($$E_{B}$$ in Wh) crossing different scales as $$PHRR = 2E_{B}^{0.6}$$. For the full-scale EV fire test, limited data have revealed that the heat release and hazard of an EV fire are comparable to that of a fossil-fuelled vehicle fire. Once the onboard battery involved in fire, there is a greater difficulty in suppressing EV fires, because the burning battery pack inside is inaccessible to externally applied suppressant and can re-ignite without sufficient cooling. As a result, an excessive amount of suppression agent is needed to cool the battery, extinguish the fire, and prevent reignition. By addressing these concerns, this review aims to aid researchers and industries working with batteries, EVs and fire safety engineering, to encourage active research collaborations, and attract future research and development on improving the overall safety of future EVs. Only then will society achieve the same comfort level for EVs as they have for conventional vehicles.

Effects of chlorinated polyethylene and antimony trioxide on recycled polyvinyl chloride/acryl-butadiene-styrene blends: Flame retardancy and mechanical properties

Abstract: The effects of chlorinated polyethylene (CPE) and antimony trioxide (Sb2O3) on the flame retardancy and mechanical properties of the recycled polyvinyl chloride/acryl-butadiene-styrene (R–PVC/ABS) blends were investigated. The tensile strength of the blends with 40 wt% ABS, 35 wt% R–PVC and 25 wt% PVC was close to that of ABS. Both the limiting oxygen index and the vertical burning level were significantly improved, and the blends reached a flame retardant level. The notched impact strength was significantly improved with the addition of CPE. The SEM observed interpenetrating CPE network structure in the blends resulted in a significant ductile fracture of the blends. With the addition of Sb2O3, the limiting oxygen index and vertical burning grade of the blends were further improved; and the heat release rate, total heat of release and mass loss were significantly reduced. When the addition amount of CPE and Sb2O3 was 8 wt% and 6 wt% respectively, the tensile strength of the blends was 63.5 MPa, the notched impact strength was 9.2 kJ m−2, the limiting oxygen index was 31.3%, and the vertical burning grade reached V0 level. This study provides a way to reuse the polyvinyl chloride with enhanced properties.

Low-Concentrated Lithium Hexafluorophosphate Ternary-based Electrolyte for a Reliable and Safe NMC/Graphite Lithium-Ion Battery.

Abstract: Current commercial lithium-ion battery (LIB) electrolytes are heavily influenced by the cost, chemical instability, and thermal decomposition of the lithium hexafluorophosphate salt (LiPF6). This work studies the use of an unprecedently low Li salt concentration in a novel electrolyte, which shows equivalent capabilities to their commercial counterparts. Herein, the use of 0.1 M LiPF6 in a ternary solvent mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFE) (3EC/7EMC/20TFE, by weight) is investigated for the first time in LiNi1/3Mn1/3Co1/3O2 (NMC111)/graphite pouch cells. In solution, the Li+ transport number and diffusion are governed by the Grotthuss mechanism, with transport properties being independent of salt concentration. The proposed electrolyte operates in a wide temperature window (0-40 °C), is nonflammable (self-extinguishing under 2 s), and shows adequately fast wetting (4 s). When incorporated into the NMC/graphite pouch cell, it initially forms a solid electrolyte interphase (SEI) with minimal gas formation followed by a comparable battery performance to standard LiPF6 electrolytes, validated by a high specific capacity of 165 mAh g-1, Coulombic efficiencies of 99.3%, and capacity retention of 85% over 700 cycles.

Novel synthesis of renewable and green flame-retardant, antibacterial and reinforcement material for styrene–butadiene rubber nanocomposites

Abstract: Novel and facile method was developed for synthesis of cost-effective, green and smart flame-retardant material. Rice husk silica nanoparticles of an average size of 150 nm were prepared and coated with organic green molokhia extract. The developed nanomaterial was used as effective flame-retardant, reinforcement and antibacterial material for styrene–butadiene rubber nanocomposite. The thermal stability of the developed nanocomposite was enhanced by 55 °C. The flame retardancy properties of the new nanocomposites was improved and achieved 31 and 33% reduction in peak heat release rate and average heat release rate, respectively, compared to blank sample. This is in conjunction with significant reduction in average effective heat of combustion (57%) with high fire safety rank. Additionally, significant suppression of emission of CO2 and CO gases by 60% was achieved. The tensile strength of the smart nanocomposite was improved by 80% compared to blank rubber. The smart rubber nanocomposites achieved excellent inhibition for bacterial growth recorded 11.5 mm as inhibition zone compared to blank sample. This study opens new avenues for production of green, renewable and cost-effective reinforcement, flame-retardant and antibacterial material for various types of polymer and rubber nanocomposites for a variety of medical and industrial applications.

Glyme-based electrolytes: suitable solutions for next-generation lithium batteries

Abstract: The concept of green in a battery involves the chemical nature of electrodes and electrolytes as well as the economic sustainability of the cell. Although these aspects are typically discussed...