Electrolyte as the most flammable component of lithium ion battery is always considered to be closely related to its safety. Great efforts are made to optimize electrolyte since it is the ultimate ...means to improve the lithium ion battery safety. This article reviews the thermal risk of commercial electrolytes and the development of safer electrolytes. The main reason for the thermal instability of the traditional nonaqueous electrolyte is the thermal decomposition of lithium hexafluorophosphate (LiPF6) and highly flammable solvents. Substitution technique of the lithium salt is under developing and the electrolyte flame retardant additives are widely studied. Novel addition technologies like electrospinning and microcapsules are introduced to reduce the restrictions on physical properties of flame retardants and improve electrochemical performances. Overcharge protection additives are simply summarized according to their reaction mechanism. For the breakthrough of new generations of safer electrolytes, nonflammable solvents with new salts and solid state electrolytes are reviewed as well as their existing problems at present. This shall serve as a summary for the development of electrolytes and a reference for the design of next generation of safer electrolytes.
Lithium ion battery safety is widely concerned and using more stable electrolytes is an effective way to solve the safety problems. Efforts to design safer electrolytes is provided including stable lithium salts, electrolyte additives, nonflammable solvents and solid state electrolytes. These methods and technologies are becoming mature and advanced providing the possibility for future applications of high-safety lithium ion batteries. Display omitted
•The safety problems of lithium ion battery related to electrolytes are reviewed.•Various means to improve the safety of electrolytes are summarized.•The essentials and further directions of next generation electrolytes are pointed out.
Lithium ion batteries (LIBs) are booming due to their high energy density, low maintenance, low self-discharge, quick charging and longevity advantages. However, the thermal stability of LIBs is ...relatively poor and their failure may cause fire and, under certain circumstances, explosion. The fire risk hinders the large scale application of LIBs in electric vehicles and energy storage systems. This manuscript provides a comprehensive review of the thermal runaway phenomenon and related fire dynamics in singe LIB cells as well as in multi-cell battery packs. Potential fire prevention measures are also discussed. Mitigating the hazards associated with a growing number of LIB applications represents a significant new challenge for the fire safety engineering community. Some perspectives and outlooks on the future of LIB fire safety research and safety engineering are given.
Transition metal sulfides (TMSs) have been demonstrated as attractive anodes for potassium-ion batteries (KIBs) due to the high capacity, abundant resource, and excellent redox reversibility. ...Unfortunately, practical implementation of TMSs to KIBs is still hindered by the unsatisfactory cyclability and rate performance which result from the vast volume variation during charge/discharge processes. Herein, a uniform nitrogen-doped carbon coated Cu2S hollow nanocube (Cu2S@NC) is designed as an anode material for the KIB, which displays an outstanding cycle performance (317 mAh g–1 after 1200 cycles at 1 A g–1) and excellent rate capacity (257 mAh g–1 at 6 A g–1) in a half-cell. The hollow nanosized structure can both shorten the diffusion length of potassium ions/electrons and buffer the volume expansion upon cycling. Besides, the high concentration electrolyte is beneficial to form the stable solid electrolyte interphase (SEI) film, reducing the interface impedance and enhancing the cycling stability. Ex situ transmission electron microscopy (TEM) and ex situ X-ray diffraction (XRD) reveal the reaction mechanism of Cu2S@NC.
•Inhibition effect of interstitial materials on TR in battery modules is studied.•CFD model is used to analyze battery temperature under different conditions.•The simulation is experimentally ...compared and verified by basic safety units.•Composite graphite sheet and Al extrusion can effectively control the thermal path.
With the growing demand for high specific energy density of lithium-ion battery pack in electric vehicle to relieve range anxiety, thermal stability in abused conditions is becoming increasingly important in battery pack safety design. Most of the fire accidents are resulted from the thermal runaway (TR) of a single cell and then propagate to the battery modules and entire pack. This study focuses on the safety enhancement methods for battery module, which is filled with different interstitial materials. The basic safety unit is composed of 11 commercial 18,650 cylindrical cells, which is isolated from the electric vehicle pack as the test module. The test modules were intentionally triggered into TR by heating wire to evaluate the TR propagation resistance. A model based on finite volume method was established to simulate the TR propagation. The results of both simulation and experiments show that the protection of neighboring cells from different interstitial materials varies significantly. Graphite composite sheet and Al extrusion as interstitial materials could effectively suppress TR propagation. The results also indicate that for safety design of battery pack, thermal path should be effectively controlled, and particularly the combustion of expelled electrolyte must be directed away from adjacent cells.
Thermal degradation characteristics of rigid polyurethane (PUR) foam in both air and nitrogen gaseous environments were studied using thermogravimetry and differential scanning calorimetry (TG-DSC) ...hyphenated techniques. And in situ Fourier Transform Infrared (FTIR) was employed to investigate the characteristic functional groups of the decomposition residues at different temperatures. It is found that the thermal degradation of PUR material in air and N2 present a three-stage and a two-stage process, respectively. And the degradation reaction rate of PUR in air is accelerated significantly due to the presence of oxygen. The thermal degradation mechanism of PUR under non-oxidizing gaseous environment was evaluated using a TGA instrument coupled with Fourier Transform Infrared and mass spectrometer (TG-FTIR-MS). HCFC-141b served as blowing agent is detected at the initial stage. The urethane bond groups of PUR start to break up into isocyanates segments and polyols segments from about 200 °C. With an increase of temperature, the polyols decompose into some kinds of aliphatic ether alcohol. In the temperature range of 350–500 °C, the dominant volatile products are primary amines, secondary amines, vinyl ethers and CO2.
Propagation of thermal runaway when penetrated at different positions.
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•Fire behavior of the lithium ion battery induced by penetration is presented.•Influences of penetration ...position and depth on thermal response are analyzed.•Inner structure of internal short circuit within the jelly-roll is exhibited.•Failure mechanism of the lithium ion battery during nail penetration is proposed.
Nail penetration is one of the most important methods to study the internal short circuit safety of lithium ion batteries (LIBs). A series of penetration tests on LIBs under different conditions are conducted. The effects of the states of charge (SOC), penetration positions, depths and speeds are analyzed. As for different penetration positions, thermal runaway reaction is more severe when the battery is penetrated at center due to the faster propagation of thermal runaway. The battery surface temperature is not positively correlated with penetration depth, and the temperature distribution becomes more nonuniform with the increasing of penetration speed. All batteries get into thermal runaway if their temperatures exceed 233 °C due to the shrinkage of separator and trigger of reaction between cathode and electrolyte. The fire behavior of penetrated batteries is exhibited in this work. “Micro short-circuit cell” structure is proposed to interpret the mechanism of internal short circuit induced by penetration.
The essential demand for functional materials enabling the realization of new energy technologies has triggered tremendous efforts in scientific and industrial research in recent years. Recently, ...high-entropy materials, with their unique structural characteristics, tailorable chemical composition and correspondingly tunable functional properties, have drawn increasing interest in the fields of environmental science and renewable energy technology. Herein, we provide a comprehensive review of this new class of materials in the energy field. We begin with discussions on the latest reports on the applications of high-entropy materials, including alloys, oxides and other entropy-stabilized compounds and composites, in various energy storage and conversion systems. In addition, we describe effective strategies for rationally designing high-entropy materials from computational techniques and experimental aspects. Based on this overview, we subsequently present the fundamental insights and give a summary of their potential advantages and remaining challenges, which will ideally provide researchers with some general guides and principles for the investigation and development of advanced high-entropy materials.
An overview of high-entropy materials for energy applications, including H
2
catalysis and storage, CO
2
conversion, O
2
catalysis and electrochemical energy storage, is given and the challenges and opportunities within this field are discussed.
This paper systematically studies a new kind of PM machines with both stator and rotor PM excitations, namely, dual-PM excited machines. The key is to rely on the PM-iron structure in the machine to ...provide both PM excitation and flux modulation. Besides the fundamental field component in the air-gap, some other predominant harmonics introduced by the flux modulating effect can also contribute to the electromagnetic torque production. Therefore, this kind of machines can be designed with high torque density. Four dual-PM excited machine concepts with the same rotor configuration but different stator structures are comparatively studied, which include double-stator PM machine, stator multitooth-PM machine, stator slot-PM machine, and stator tooth-PM machine (STPM). Based on the flux modulating effect, the general design principle of the dual-PM machines is proposed in this paper. Through analytically investigating the air-gap field harmonics, the physical insight of the dual-PM machines is brought forward. All the four machines are optimized using an improved Tabu search coupled with finite element method, and their electromagnetic performances are comprehensively studied and compared. A prototype of STPM is manufactured. Experimental tests are conducted and the results well verify the electromagnetic design.
Because of the inconsistency in battery pack and failure of charging device, slight overcharging of lithium ion batteries appears and even causes to thermal runaway. The aging behavior and mechanisms ...of lithium ion battery under slight overcharging cycling are studied qualitatively and quantitatively based on incremental capacity analysis and electrochemical impedance spectroscopy in this work. The results show that slight overcharging accelerates battery aging because of the loss of active material. While, conductive loss influences capacity fading less. The effect of lithium density loss is in the middle level. So it is suggested that incremental capacity analysis and impedance estimation are used to detect overcharging cycling on-line. Furthermore, the thermal stability of aged batteries are studied using Extended Volume Accelerating Rate Calorimeter. The results show that the stability of aged batteries become worse. The anode plays a key role in the thermal stability changes because of lithium plating under overcharging. The cathode dominates the stability after 70% SOH because of structure damage of cathode.
•Thermal stability of aged battery caused by slight overcharging cycling is studied.•Aging behavior and mechanisms of slight overcharging cycling are revealed.•Cathode and anode play different roles in different aging stages.•Changes of thermal stability of aged battery are explained by aging mechanisms.
► This article is a wide-ranging review of the most up-to-date studies on lithium ion battery thermal safety. ► This review article surveys recent progress in the thermal runaway mechanism and ...thermal modeling of lithium ion battery. ► Various thermal runaway prevention techniques used and their applicability is discussed.
Lithium ion battery and its safety are taken more consideration with fossil energy consuming and the reduction requirement of CO2 emission. The safety problem of lithium ion battery is mainly contributed by thermal runaway caused fire and explosion. This paper reviews the lithium ion battery hazards, thermal runaway theory, basic reactions, thermal models, simulations and experimental works firstly. The general theory is proposed and detailed reactions are summarized, which include solid electrolyte interface decomposition, negative active material and electrolyte reaction, positive active material and electrolyte reaction, electrolyte decomposition, negative active material and binder reaction, and so on. The thermal models or electrochemical–thermal models include one, two and three dimensional models, which can be simulated by finite element method and finite volume method. And then the related prevention techniques are simply summarized and discussed on the inherent safety methods and safety device methods. Some perspectives and outlooks on safety enhancement for lithium ion battery are proposed for the future development.
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