Search

Electrolyte poisons comprised of diols and diamines are investigated for the intended function of exacerbating internal resistance in lithium-ion batteries upon short circuit failure, to quickly arrest uncontrolled joule heat generation in the earliest stages. The competing dynamics of powerful short circuit currents and electrolyte poisoning interactions are evaluated via simultaneous nail penetration and poison injection of LIR2450 format LiCoO2/graphite 120 mAh coin cells. To forcibly increase electrolyte impedance, diols serve to hinder charge-carrying ion mobility by raising solution viscosity, while diamines disrupt solvent permittivity by rapidly polymerizing the ethylene carbonate solvent. Diamines demonstrate great potency, and are suitable for integration into battery cells within chemically-inert, breakable containers, rigged for release upon mechanical activation. Mixtures of 1,2-ethanediol and 1,2-ethanediamine show synergistic poisoning effects, decreasing peak temperature accrued by 70% when introduced simultaneously upon nail penetration. With the innate presence and abundance of diols and diamines in electric vehicle heat exchangers, they may be employed for multifunctional applications.

Internal resistance and temperature measurements are made for LIR2450 format LiCoO2/graphite 120 mA h coin cells upon abusive discharge conditions. The dynamic contributions of electrical and ionic resistances to joule heat generation are investigated in the earliest stages of battery failure. It is shown that while ohmic, primarily electrical resistances initially dictate the joule heating rates, polarization, primarily ionic resistances become dominant as time progresses. Ionic conductivity and resistance of LiPF6 salt in ethylene carbonate/ethyl methyl carbonate solvent are examined through concurrent concentration, viscosity, and temperature measurements to elucidate the intricacies of electrolyte polarization. Comparative analysis suggests that upon polarization at high discharge rates, resistance is concentrated in the electrolyte within the cathode region due to rapid depletion of lithium-ions available to facilitate charge transfer. Expected consequences are corroborated in external shorting and nail penetration experiments. The findings are used to predict how a cell would respond if electrical or ionic resistances are exacerbated upon shorting, so as to identify effective thermal runaway mitigation strategies.

Summary We investigate the effects of thermally sensitive binder (TSB) on the temperature increase of lithium-ion battery (LIB) coin cell subjected to severe mechanical abuse. The TSB is poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP), similar to conventional poly(vinylidenefluoride) (PVDF) binder but with a significant hexafluoropropylene (HFP) content. The testing data show that by using TSB, the peak temperature increase of nail-penetrated LIB coin cell can be reduced by 20% to 40%, attributed to the softening of TSB that begins from ~80°C. The cycling performance of the LIB cells is also characterized. This research sheds light on the development of thermal-runaway mitigation techniques.

Tuckeroo (Cupaniopsis anacardioides) is an Australian native tree, possessing high level bioactivity and antioxidant activity. To prevent deterioration of active constituents, appropriate drying practices must be determined. This study comparatively evaluates the impact of a range of drying methods including freeze-, microwave-, vacuum-, hot air- and sun-drying on the physical, phytochemical and antioxidant characteristics of Tuckeroo fruit. Experimental results showed that the five drying methods had significant impact on the physicochemical properties and antioxidant activity of the fruits. Of the drying methods assessed, freeze drying best preserved Tuckeroo activity, recording higher total phenolic content (TPC) (81.88 mg gallic acid equivalent (GAE)/g), total flavonoids (TFC) (107.71 mg catechin equivalent (CAE)/g), proanthocyanidins (TPro) (83.86 mg CAE/g) and exhibited the strongest antioxidant capacity. However, vacuum drying at 65 kPa, 100 &deg, C for 5 h is recommended for drying Tuckeroo fruits for further processing in a large scale as it also retained high levels of TPC, TFC and TPro (58 mg GAE/g, 91 mg CAE/g and 74 mg CAE/g, respectively).

By adding 1 wt% damage homogenizer (DH), i.e. carbon black microparticles, into the electrodes of lithium-ion batteries, thermal runaway can be mitigated as the battery cells are subjected to impact loadings. In a drop tower test, the generated heat of the modified cells is reduced by nearly 40%, compared with the reference cells. This phenomenon may be attributed to the weakening effect of the carbon black fillers. The shape of the filler grains does not have a pronounced influence on the temperature profile.

A thermal-runaway retardant (TRR) of lithium-ion batteries (LIBs), dibenzylamine (DBA), is investigated. In a TRR-modified LIB, DBA can be encapsulated in packages made of inert materials. When the LIB is subjected to mechanical abuse, the packages would be broken apart and the TRR is released. In nail penetration and impact tests, addition of 4 wt% DBA reduces the temperature increase of fully charged LIR-2450 cells by nearly 50%. The influence of TRR packages on the cycling performance of LIBs is negligible. The working mechanism of DBA is associated with the decrease in electrolyte conductivity, the increase in charge transfer resistance, and the reduction in lithium ion (Li + ) transference numbers.

Gac (Momordica cochinchinensis Spreng.) seeds contain bioactive compounds with medicinal properties. This study aimed to determine a suitable solvent and extraction technique for recovery of important compounds, namely, trypsin inhibitors, saponins, and phenolics. The antioxidant capacity and total solids of derived extracts were also measured. Water with conventional extraction method gave the highest value of trypsin inhibitor activity (118.45 &plusmn, 4.90 mg trypsin g&minus, 1) while water-saturated n-butanol and methanol extracts were characterized by their highest content of saponins (40.75 &plusmn, 0.31 and 38.80 &plusmn, 2.82 mg AE g&minus, 1, respectively). Aqueous extract with microwave assistance achieved the highest phenolics (3.18 &plusmn, 0.04 mg GAE g&minus, 1). As a measure of antioxidant capacity, the 2,2&prime, azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assay gave highest value to the aqueous microwave extract (23.56 &plusmn, 0.82 &mu, mol TE g&minus, 1) while the ferric reducing antioxidant power (FRAP) assay gave highest values to water-saturated n-butanol and 70% ethanol extracts (5.25 &plusmn, 0.04 and 4.71 &plusmn, 0.39 &mu, 1, respectively). The total solids value was highest using water with microwave assistance (141.5 g kg&minus, 1) while ultrasound treatment did not improve any extractions. Therefore, trypsin inhibitors are suitably recovered using water while water-saturated n-butanol or methanol is for saponins, both using a conventional method. Microwave extraction is suitable for phenolics recovery. These conditions are recommended for an efficient recovery of bioactive compounds from defatted Gac seeds.

In the current study, through a set of nail penetration and impact tests on modified lithium-ion battery coin half-cells, we examine the effects of electrode pattern on the heat generation behaviors associated with internal shorting. The results show that the temperature profile is quite insensitive to the openings in cathode layer, which may be attributed to the high specific energy as well as the secondary conductive paths. This finding will considerably influence the study in the area of thermal runaway mitigation of energy storage systems.

In this paper, we study expanding phenomena in the setting of matrix rings. More precisely, we will prove that If $A$ is a set of $M_2(\mathbb{F}_q)$ and $|A|\gg q^{7/2}$, then we have \[|A(A+A)|, ~|A+AA|\gg q^4.\] If $A$ is a set of $SL_2(\mathbb{F}_q)$ and $|A|\gg q^{5/2}$, then we have \[|A(A+A)|, ~|A+AA|\gg q^4.\] We also obtain similar results for the cases of $A(B+C)$ and $A+BC$, where $A, B, C$ are sets in $M_2(\mathbb{F}_q)$., Comment: 31 pages

Mechanical abuse often causes thermal runaway of lithium-ion battery (LIB). When a LIB cell is impacted, radial cracks can be formed in the current collector, separating the electrode into petals. As separator ruptures, the petals on positive and negative electrodes may contact each other, forming internal short circuit (ISC). In this study, we conducted an experimental investigation on LIB coin cells with current collectors modified by surface notches. Our testing results showed that as the current collector contained appropriate surface notches, the cracking mode of electrode in a damaged LIB cell could be adjusted. Particularly, if a complete circumferential crack was generated, the petals would be cut off, which drastically reduced the area of electrode involved in ISC and the associated heat generation rate. A parameterized study was performed to analysis various surface-notch configurations. We identified an efficient surface-notch design that consistently led to trivial temperature increase of ISC.

Alkanes are investigated as thermal-runaway retardants (TRR) for lithium-ion battery (LIB). TRR is a chemical that can rapidly terminate exothermic reactions in LIB. Under normal working conditions, TRR is sealed in separate packages in the LIB cell, and upon mechanical abuse, it is released to suppress heat generation. The alkanes under investigation include octane, pentadecane, and icosane, among which pentadecane has the highest thermal-runaway mitigation (TRM) efficiency. In nail penetration test on coin cells, ∼4 wt. % pentadecane reduced the maximum temperature by ∼60%; in impact test on pouch cells, ∼5 wt. % pentadecane reduced the maximum temperature by ∼90%. The high TRM efficiency of pentadecane is attributed to its high wettability to separator and its immiscibility with electrolyte. By forming a physical barrier between the cathode and anode, pentadecane interrupts lithium ion (Li+) transport and increases the charge transfer resistance by nearly two orders of magnitude. The diffusion rate of pentadecane in the electrode layer stack was measured to be ∼580 μm/s.

The safety of lithium-ion battery (LIB) becomes increasingly critical as the specific energy and cell capacity rapidly increase. Based on the modified current collector technique recently developed for nickel–cobalt–manganese active materials, here we investigate high-energy LIBs based on functional current collectors (FCC). Two high-voltage active materials were tested in our experiments: lithium-rich layered oxide (LRLO) and lithium nickel manganese oxide (LNMO). At the same time as a fully charged LIB cell is damaged, FCC isolates the internal short circuit (ISC) from the undamaged area; hence, the ISC-induced heat generation is drastically reduced to a negligible level. The electrochemical performance of FCC-based cells is nearly identical to that of reference cells.

Benzylamine (BA), dibenzylamine (DBA), and trihexylamine (THA) are investigated as thermal-runaway retardants (TRR) for lithium-ion batteries (LIBs). In a LIB, TRR is packaged separately and released when internal shorting happens, so as to suppress exothermic reactions and slow down temperature increase. THA is identified as the most efficient TRR. Upon nail penetration, 4 wt % THA can reduce the peak temperature by nearly 50%. The working mechanisms of the three amines are different: THA is highly wettable to the separator and immiscible with the electrolyte, and therefore, it blocks lithium-ion (Li+) transport. BA and DBA decrease the ionic conductivity of electrolyte and increase the charge transfer resistance. All three amines react with charged electrodes; the reactions of DBA and THA do not have much influence on the overall heat generation, while the reaction of BA cannot be ignored.

Formation of internal short circuit (ISC) may result in catastrophic thermal runaway of lithium-ion battery (LIB). Among LIB cell components, direct contact between cathode and anode current collectors is most critical to the ISC behavior, yet is still relatively uninvestigated. In the current study, we analyze the effect of heterogeneity of current collector on the temperature increase of LIB cells subjected to mechanical abuse. The cathode current collector is modified by surface notches, so that it becomes effectively brittle and the ISC site can be isolated. Results from impact tests on LIB cells with modified current collectors suggest that their temperature increase can be negligible. The critical parameters include the failure strain and the failure work of modified current collector, both of which are related to the notch depth.

In a lithium-ion battery (LIB), mechanical abuse often leads to internal short circuits (ISC) that trigger thermal runaway. We investigated a thermal-runaway mitigation (TRM) technique using a modified current collector. By generating surface grooves on the current collector, the area of electrodes directly involved in ISC could be largely reduced, which decreased the ISC current. The TRM mechanism took effect immediately after the LIB was damaged. The testing data indicate that the groove width is a critical factor. With optimized groove width, this technique may enable robust and multifunctional design of LIB cells for large-scale energy-storage units.

Thermally sensitive binder (TSB) is developed as an internal safety mechanism of lithium-ion battery (LIB). The TSB is a polymer blend of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). Compared with regular PVDF binder, the softening and swelling of TSB are more pronounced when temperature is above 110 °C. With the TSB, the cycling performance of LIB cell is not affected; upon nail penetration, the heat generation rate is significantly reduced. The crystallinity of TSB is an important factor. This technology may lead to the development of thermal-runaway-mitigating LIB cells. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45737.

Author(s): Le, Anh V; Wang, Meng; Noelle, Daniel J; Shi, Yang; Yoon, Hyojung; Zhang, Minghao; Meng, Y Shirley; Qiao, Yu

Current collector accounts for more than 90% of the electric conductivity and ∼90% of the mechanical strength of the electrode in lithium-ion battery (LIB). Usually, current collectors are smooth metallic thin films. In the current study, we show that if the current collector is heterogeneous, the heat generation becomes negligible when the LIB cell is subjected to mechanical abuse. The phenomenon is attributed to the guided strain concentration, which promotes the separation of the forward and the return paths of internal short circuit. As the internal impedance drastically increases, the stored electric energy cannot be dissipated as thermal energy. The modification of current collector does not affect the cycling performance of the LIB cell. This finding enables advanced thermal-runaway mitigation techniques for high-energy, large-scale energy storage systems.

In the current study, we investigated sigmoidal current collector in lithium-ion battery (LIB). Traditionally, the active material in an LIB electrode is coated on a flat current collector. By rendering the current collector sigmoidal-shaped, cracking and debonding of active material layer could be promoted, which would considerably increase the internal impedance, as the LIB is mechanically abused, beneficial to thermal-runaway mitigation. The energy absorption capacity is also improved, enabling multifunctional LIB cell design. This technique has important relevance to large-sized LIB systems, for which cell robustness and fire safety are prioritized.

This work introduces a new mechanically triggered thermal runaway mitigation mechanism. The homogenizer of electrode failure (HEF), multiwall carbon nanotube (MWCNT), was added into LiNi0.5Mn0.3Co0.2O2 (NMC532) battery electrodes. We have studied the effect of the HEF additive on the internal electrical resistance and the mechanical impact resistance of the electrodes. The additional MWCNTs reduced the internal electrical resistance of electrodes before mechanical abuse. Upon mechanical abuse, they could mitigate internal shorting and thermal runaway at normal battery working temperature.

In the current study, we experimentally investigated the effects of carbon black micro-particulates (CBMP) on the temperature increase of lithium-ion battery coin cells subjected to nail penetration and blunt impact. The major difference between CBMP and regular carbon black additives is in particle size. The testing data showed that addition of 1 wt% of CBMP in the cathode and anode does not influence the cycle life, while can reduce the heat generation rate by nearly 50%, after the peak temperature is reached. Thermal treatment of the modified cells at 100 °C would further reduce the heat generate rate. The initial temperature increase rate, the maximum temperature, as well as the total energy dissipation are not affected. These findings shed light on thermal runaway mitigation of high-energy batteries.