Large Format Lithium Ion Battery Research Articles

Toward high-accuracy and high-efficiency battery electrothermal modeling: A general approach to tackling modeling errors

An accurate control-oriented electrothermal model is a prerequisite for efficient thermal management of battery-powered applications. Despite the great efforts made to pursue high-accuracy modeling of the heat generation and transfer processes inside lithium-ion batteries for control purposes, little work has shed light on the error sources in such electrothermal modeling for obtaining an optimal model. In this article, we propose a practical and general framework for investigating the potential error sources in computationally efficient electrothermal modeling of large-format lithium-ion batteries. The results demonstrate that the high-accuracy modeling of the thermal interplay between two tabs and the cell body and the optimization of the temperature sensor placements should be given high priority. Further, the overpotential-based method is preferred to calculate the local generation rates of the battery body for accuracy and generalizability. This study provides important insights into accurate and computationally efficient electrothermal modeling for large-format energy storage batteries.

Toward the flexible production of large-format lithium-ion batteries using laser-based cell-internal contacting

Lithium-ion battery cells are used for energy storage in many industrial sectors, such as consumer electronics or electromobility. Due to the diversity of these applications, the demand for tailored battery cells is increasing. Consequently, the technical development of the cells leads to numerous coexisting cell variants. Examples of such variants are altering cell materials, formats, and capacities. Different target capacities can be realized by changing the geometrical dimensions of the individual electrodes or the number of electrodes in the cell cores. The increasing quantity of variants poses challenges within battery cell manufacturing, such as the need to adapt the process parameters for the cell-internal contacting of a higher number of electrode sheets in the cell stack. Each new cell variant currently requires elaborate experimental parameter studies for its manufacture. An approach for selecting suitable process parameters for laser-based cell-internal contacting in terms of a modification of the cell properties is presented in this paper. A model was built to determine the weld depth in copper sheets using a millisecond pulsed laser welding strategy. The process parameters for welding stacks of electrode sheets to an arrester tab were calculated on the basis of this model. The necessary weld depth in the arrester tab for achieving suitable mechanical properties of the cell-internal joint was considered. The presented approach was validated by welding different numbers of foils to an arrester tab and varying the thickness of the foils. It was shown that the experimental effort for the selection of the process parameters for laser-based contacting can be reduced significantly.

Thermal performance evaluation of boiling cooling system for the high-rate large-format lithium-ion battery under coolant starvations

The boiling cooling system exhibits superior cooling capacity and temperature homogenization ability, which has great potential in managing the undesirable temperature spike and temperature gradient of the large-format lithium-ion batteries. However, in-depth experimental investigation to reveal the effects of harsh operation conditions and parameters on the cooling characteristics are still lacking. In this study, thermal control ability of the boiling cooling system using Novec 7000 as coolant is evaluated for a large-format 20-Ah lithium-ion battery, with special attentions to the cooling performance under harsh operation conditions such as high-rate cyclic and coolant starvation. The experimental results show that the boiling-cooling system with uninterrupted/small coolant flow exhibits superior cooling capacity and the battery temperature can be controlled around 35 ± 2 °C over the high-rate cycles. However, when the coolant starvation issue occurs in the static mode, the maximum temperature and temperature difference rise drastically up to 53.45 °C and 18.56 °C in the fourth discharge process, which are abnormally higher than the system without injecting liquid coolant. The incorporation of 20PPI copper foam filler can alleviate the coolant starvation issue to some extent, which reduces the peak values of battery temperature and temperature difference by 13.28 % and 39.33 % under the same condition.

Modeling the inhomogeneous lithium plating in lithium-ion batteries induced by non-uniform temperature distribution

Under fast-charging or low-temperature charging conditions, large-format lithium-ion batteries are prone to inhomogeneous lithium plating, resulting in localized degradation and even internal short circuit, thus requiring a thorough investigation. This study establishes a three-dimensional electrochemical model to analyze the inhomogeneous lithium plating behavior in lithium-ion batteries. The model is validated with the voltage profiles and temperature distributions of a 24Ah pouch lithium-ion battery during low-temperature charging. The inhomogeneous lithium plating induced by non-uniform temperature distribution and the underlying mechanism are investigated using the model. The local current density and overpotential turn out to be the key factors affecting the spatial distribution of plated lithium. Moreover, the effects of temperature gradients on the lithium plating and stripping behaviors are explored. In-plane temperature gradient shows little effect on the total amount of plated lithium, but leads to apparent inhomogeneity in the distribution of plated lithium, with the differences between the concentrations of plated lithium in the upper and lower half of battery reach 57.61%, 103.06% and 159.68% of the average concentration in the whole battery during 1C charging at -5, 5 and 10°C, respectively. The temperature gradient also significantly influences the battery voltage relaxation profile related to the lithium stripping process. The characteristic plateau in the battery voltage relaxation profile disappears when the temperature gradient increases to larger than 6°C, leading to difficulty in detecting inhomogeneous lithium plating in large-format lithium batteries. The results presented in this study can provide helpful guidance for the design and management of large-format lithium-ion batteries.

Inhomogeneous degradation induced by lithium plating in a large-format lithium-ion battery

With the demand for high-energy-density power sources for electric vehicles, large-format lithium-ion batteries are widely applied, considering their advantages in reducing the weight of inactive materials. However, large-format cells suffer from internal inhomogeneities, which become the bottleneck limiting their performance. Here, the inhomogeneous degradation in a large-format pouch cell is comprehensively investigated using a series of (non-)destructive techniques. Spatial-resolved deformation detection and ultrasonic diagnostics are utilized to study the evolution of inhomogeneity inside the large-format battery. Localized deformation and deposits are found to firstly appear at the tab-near regions and then propagate into central regions, which is identified by characterization tests to be induced by lithium plating. The inhomogeneous degradation mechanism inside the battery is summarized as an initiation-propagation process. During the process, lithium deposit is initiated by a local high current density, resulting in the local separator pore closure. Pore closure in the separator in return creates a high current density and overpotential in the adjacent area, leading to a continuous propagation of the lithium deposition area. Finally, an effective indicator—peak height in the differential voltage curve is proposed to detect the inhomogeneity in the battery, and thus offers guidance to the design and management of large-format cells.

Thermal-Switchable, Trifunctional Ceramic-Hydrogel Nanocomposites Enable Full-Lifecycle Security in Practical Battery Systems.

Thermal runaway (TR) failures of large-format lithium-ion battery systems related to fires and explosions have become a growing concern. Here, we design a smart ceramic-hydrogel nanocomposite that provides integrated thermal management, cooling, and fire insulation functionalities and enables full-lifecycle security. The glass-ceramic nanobelt sponges exhibit high mechanical flexibility with 80% reversible compressibility and high fatigue resistance, which can firmly couple with the polymer-nanoparticle hydrogels and form thermal-switchable nanocomposites. In the operating mode, the high enthalpy of the nanocomposites enables efficient thermal management, thereby preventing local temperature spikes and overheating under extremely fast charging conditions. In the case of mechanical or thermal abuse, the stored water can be immediately released, leaving behind a highly flexible ceramic matrix with low thermal conductivity (42 mW m-1 K-1 at 200 °C) and high-temperature resistance (up to 1300 °C), thus effectively cooling the TR battery and alleviating the devastating TR propagation. The versatility, self-adaptivity, environmental friendliness, and manufacturing scalability make this material highly attractive for practical safety assurance applications.

Explosion behavior investigation and safety assessment of large-format lithium-ion pouch cells

Large-format lithium-ion (Li-ion) batteries with high energy density for electric vehicles are prone to thermal runaway (or even explosion) under abusive conditions. In this study, overcharge induced explosion behaviors of large-format Li-ion pouch cells with Li[Ni0.8Co0.1Mn0.1]O2 cathode at different current rates (C-rates) (0.5C, 1C, 2C) were investigated. The explosion characteristics of the cells were elucidated by discussing the evolution of the cell voltage, the surface temperature and the shock wave pressure. Generally, the whole overcharge process could be divided into four stages according to the evolution of several key parameters and the overcharge behaviors; the overcharge C-rate has a great influence on cells’ thermal behaviors. The experimental results showed that the thermal runaway process of Li-ion cells caused by overcharging consisted of two kinds of explosions, physical explosion and chemical explosion. The existence of observable negative pressure zone in the pressure curves indicated that the Li-ion cells are not a self-supplying oxygen system during the explosion. Further, the explosion dynamics parameters were matched. An explosion TNT-equivalent conversion strategy that depended on the pressure of the shock wave was utilized to evaluate the released energy and its hazards. In addition, with respect to the overcharge of Li-ion pouch cells, a safety assessment method and a safety management method were proposed based on the explosion behaviors. From the perspective of battery safety, this study is of great significance for the safety design of Li-ion cells and can provide guidance for engineers to optimize the safety function of battery packs.

Thermal runaway propagation in large format lithium ion battery modules under inclined ceilings

Currently, the horizontal ceiling structure is widely adopted in large format battery systems. Thus systematically investigating the thermal runaway (TR) propagation behaviors features of large format lithium ion battery modules under different inclined ceilings is of importance for the safety design and protection of battery systems. This work focuses on the experimental phenomenon elucidation and theoretical analysis of the single cell TR and its propagation. Firstly, a single cell test is carried out to investigate the TR behavior features of target battery. Then, four sets of TR propagation tests with different ceiling angles (0°, 10°, 30°, 90°) are performed to explore the effect of inclined ceiling angle on TR propagation. Besides, a set of 0° ceiling angle experiment with fireproof barriers is conducted to study the blocking effect of barriers. Results show that a larger ceiling angle provides a better heat dissipation condition for modules, and the threshold value of ceiling angle at which TR stops propagating is between 10 and 30°. The barriers cannot block the TR propagation but great delay and weaken the propagation process. This study helps to enhance the insight of TR propagation behaviors and provides valuable guidance for the relative researchers and engineers.

Taming the chemical instability of lithium hexafluorophosphate-based electrolyte with lithium fluorosulfonimide salts

Undesired chemical degradation of lithium hexafluorophosphate (LiPF6) in non-aqueous liquid electrolytes is a Gordian knot in both science and technology, which largely impedes the practical deployment of large-format lithium-ion batteries (LIBs) in emerging applications (e.g., electric vehicles). From a fresh perspective that the decomposition of LiPF6 in non-aqueous liquid electrolyte is likely to be induced by hydrogen fluoride (HF) and other protic impurities, we herein report the incorporation of lithium fluorosulfonimide salts (LFSs) as an effective and practical applicable strategy for stabilizing LiPF6-based electrolytes. Our results show that LFSs can dramatically stabilize both LiPF6 and carbonate solvents in the electrolyte through chemically removing HF impurities. The HF-removing impact of LFSs to effectively improve the capacity resilience of LIBs is further demonstrated by superior cycling performances of graphite || LiCoO2 cells utilizing the LFS-added electrolytes.

A statistical analysis of thermal characteristics of 55-Ah large-format LIB pouch cell with different tab-type, tab size, and tab position

The non-uniform temperature distribution in large-format lithium-ion batteries (LIBs) can lead to thermal runaway or performance degradation. This study develops a three-dimensional electrochemical–thermal model of a 55-Ah large-format LiFePO4/graphite pouch cell and statistically analyzes the effects of width, height, and attachment positions of the nominal tab (NT), lateral tab (LT), and counter tab (CT) on the temperature distribution. The temperature difference that occurs across the cell is analyzed separately for each design factor through design of experiments (DOE) and analysis of variance (ANOVA). Accordingly, wider tabs reduce the maximum temperature and temperature difference irrespective of the tab type. Taller tabs yield higher maximum temperatures, resulting in a larger temperature difference. Attaching tabs to the edge of the cell increases the maximum temperature and temperature difference. The locations of the negative NTs and CTs do not affect the temperature difference. However, the location of the negative LT increases the minimum temperature, thereby decreasing the temperature difference. The ANOVA revealed that the p-value of the width, height, and attachment position of the positive tab is lower than 0.05 which means the factors strongly influence the temperature difference for all tab-types. Also, the attachment position of the negative tab affects only the LT-type.

Mitigating overcharge induced thermal runaway of large format lithium ion battery with water mist

• Overcharge induced thermal runaway can be efficiently prevented with water mist. • Over 80% of the total heat generation is released after the thermal runaway. • The battery flame can be suppressed within several seconds with water mist. • The maximum cooling power of water mist can reach 9.0 kW in the tests. Thermal runaway (TR) is one of the ringleaders of lithium ion battery (LIB) hazard, which has become a major safety concern. Especially to the large-scale LIBs, the TR has been intensified owing to the expanded capacity. Hence, effective countermeasures are urgently needed. In this study, the cooling control capacity of water mist (WM) on mitigating the overcharge induced TR for large-scale LIB is experimentally studied. The thermal hazard processes with and without WM have been comprehensively investigated. Results show that the battery flame experiences rapid increasing process from 0.02 m to 0.9 m, which intensifies the inhomogeneity of temperature distribution. The total heat accumulation of the LIB reaches 1971.0 kJ, over 80% of which is generated after TR. A critical inflection point during TR development has been identified, where the WM has been introduced to successfully suppress the TR. For cases with continuous overcharge current, the occurrence of TR is unstoppable, but the hazard has been significantly mitigated with the maximum temperature decreases to 122.1 °C, and over 1000 kJ heat has been dissipated during WM release. This work confirms the excellent cooling capacity of WM on the large-scale LIB, and the overcharge induced TR can be effectively mitigated.

Laser welding of current collector foil stacks in battery production\u2013mechanical properties of joints welded with a green high-power disk laser

The qualification of production systems that enable reliable and stable production processes is a major challenge in manufacturing large-format lithium-ion batteries. During cell assembly, the electrode sheets of the anode and the cathode are stacked, and are electrically contacted by a welding process. It was shown that laser beam welding employing a beam source in the green wavelength range is a promising joining approach in terms of high productivity. Therefore, the influence of the process parameters, such as the laser power, the welding speed, the pulse frequency, and the pulse duration, on the weld seam quality was investigated. Particular emphasis was placed on the mechanical strength of the weld seam. Statistically planned experiments were used to determine feasible parameter sets for welding the most common current collectors of lithium-ion battery electrodes, copper (Cu), and aluminum (Al). The influence of the individual process parameters on the tensile shear force was evaluated. Stacks of 40 metal foils were welded with a thin metal sheet in lap joint configuration. Based on an analysis of the requirements for minimum mechanical seam strengths, this study confirms that laser beam welding using a green high-power disk source is an auspicious process for the internal contacting of lithium-ion batteries.

Thermal runaway front in failure propagation of long-shape lithium-ion battery

Long, large-format lithium-ion batteries have become prominent in recent years in high-power application scenarios, such as in electrochemical energy storage stations, electric vehicles, and electric ships. In these batteries, failure is always initiated from a local point and then propagates to the full cell, requiring countermeasures to quench the in-cell thermal runaway propagation. This study investigates the thermal runaway propagation behaviors of long, large-format lithium-ion batteries. A thermal runaway front exists during the propagation of thermal runaway; it separates the failure zone and normal zone and carries significant information regarding the thermal runaway reactions. The characteristics of the thermal runaway front are investigated through experiments and simulations. The thermal runaway front moves forward with an average velocity of approximately 24.14 mm·s−1, driven by the large temperature gradient between the failure and intact zones. The velocity of the thermal runaway front is correlated with the thermophysical properties of the battery. A modeling analysis indicates that the velocity of the thermal runaway front in propagation has a square root correlation with the thermal conductivity and heat generation rate. This square root correlation links the failure process and the thermophysical properties of the battery and can contribute to the future safety design of large-format batteries.

Investigation of inhomogeneous degradation in large-format lithium-ion batteries

Large-format prismatic lithium-ion batteries (LIBs) with 52 Ah capacity and Verband Der Automobilindustrie (VDA) standard dimensions were cycled under a preloading force of 2.5 kN at 25 °C. When cycled, the LIBs exhibited a two-stage degradation behavior characterized by a first linear degradation stage and a second nonlinear degradation stage. The two-stage behavior which is also called rollover failure is investigated by post-mortem analysis. When the jelly roll was unfolded, lithium plating and delamination of cathode materials were found in the curved areas. From the scanning electron microscopy (SEM) images, the graphite particles in the curved areas were deformed and cracked. The LIB under a higher preloading force of 5.5 kN was found to have shorter cycle life, indicating mechanical force is one of the factors that lead to the rollover failure. The degradation mechanism was thoroughly illustrated by applying shift voltage-resistance voltage (SV-RV), differential voltage (DV) and electrochemical impedance spectroscopy (EIS) measurements. The SV-RV analysis suggests that lithium plating occurs after around 300 cycles. The shifting to low capacity and broadening of peaks in dV/dQ curves indicate that the second nonlinear degradation stage could be caused by combining loss of active materials (LAM) and loss of lithium inventory (LLI). In the nonlinear degradation stage, ohmic resistance (Rs) and charge transfer resistance (Rct) is dramatically increased as characterized by EIS measurement. The increased Rs and Rct further support the conclusion that LLI and LAM are the dominating degradation mechanism in the nonlinear degradation stage.

Thermal runaway model of high-nickel large format lithium-ion battery under thermal abuse conditions

Battery safe necessitates preventing thermal runaway and its propagation. Aiming at the thermal runaway problem of pure electric vehicle lithium-ion power battery, a thermal runaway model for large-capacity lithium-ion prismatic batteries is developed. Two thermal abuse conditions: hot box and single-side heating are considered in the simulation. Corresponding experiments are conducted to verify the accuracy of the model. The results show that the gas generated by the decomposition of the solid electrolyte interface (SEI) membrane and the anode-solvent reaction triggered the pressure relief valve. The thermal runaway process of single-side heating has a temperature difference of more than 200°C, and thermal runaway may have occurred when the local temperature of the battery is normal. This lays a foundation for subsequent research and system development.

Heating power effect on the thermal runaway characteristics of large-format lithium ion battery with Li(Ni1/3Co1/3Mn1/3)O2 as cathode

Overheat is one of the common safety issues for the large-scale application of lithium-ion batteries (LIBs), and is a potential risk that triggers thermal runaway (TR). In this work, the effects of the heating power and state of charge (SOC) on TR characteristics of large-format (Ni1/3Co1/3Mn1/3)O2 LIBs under overheat are investigated experimentally. The relationship between heating power, critical input thermal energy (Einput) and TR are identified firstly. The results show the Einput, critical internal energy, chemical heat and joule heat of batteries in critical TR state all decrease with increasing SOC. The heating power exhibits more significant impact on TR behavior than SOC dues to the rapid deterioration of TR as heating power ascends. The peak heat release rate of TR rises from 7.5 to 95.2 kW when heating power increases from 400 to 700 W. And the law the severity of TR deteriorates sharply with increasing heating power is more prominent in the TR propagation process. Besides, TR induced by higher heating power requires lower Einput. Einput decreases from 477.08 to 329.23 kJ as heating power ascends from 400 to 700 W. Furthermore, the relationship between internal short circuit and TR under different SOC and heating power are analyzed.

A multi scale multi domain model for large format lithium-ion batteries

A multi scale multi domain (MSMD) model for large format lithium-ion battery (LIB) cells is presented. In our approach the homogenization is performed on two scales (i) from the particulate electrodes to homogenized electrode materials using an extended Newman model and (ii) from individual cell layer materials to a homogenized battery material with anisotropic electrical and thermal transport properties. Both intertwined homogenizations are necessary for considering electrochemical-thermal details related to microstructural and material features of electrode and electrolyte layers at affordable computational costs. Simulation results validate the MSMD model compared to the homogenized Newman model for isothermal cases. The strength of the MSMD model is demonstrated for non-isothermal conditions, namely for a 120 Ah cell discharged with four different cooling concepts: (i) without cooling (ii) with a base plate cooling (iii) with a tab cooling and (iv) with a side cooling. As one result, temperature gradients cause a local peak discharge up to 2.8 C for a global 2 C discharge rate.

An experimental study on the mechanical characteristics of Li‐ion battery during overcharge‐induced thermal runaway

Lithium batteries are prone to swelling during overcharge, which leads to a huge external force in modules and poses a potential threat to electric vehicles. Therefore, it is extremely important to understand the swelling mechanism of lithium batteries in-depth. In this paper, expansion force evolution during overcharge-induced thermal runaway process for large format lithium-ion battery with Li(Ni0.5Co0.2Mn0.3)O2 cathode is investigated. The rupture of the battery shell due to huge swelling is proved as the trigger of the thermal runaway event. In detail, the expansion force increases dramatically with the state of charge, which can be up to 3400 N. And it is a highly dynamic quantity with four obvious inflection points during overcharge, indicating a strong relationship with failure mechanisms. The inherent failure mechanism behind expansion force is investigated using both in-situ and ex-situ measurement techniques. The results revealing that the early abnormal expansion of the battery is caused by lithium dendrite and lithium plating. The rapid expansion mainly caused by CO, which is produced by incomplete electrolyte oxidation, leads to the rupture of the battery shell and thermal runaway events. This paper aims to unravel the mystery of lithium battery swelling during overcharge and provide valuable guidance to mitigate the overcharge risk induced by battery swelling.

Non-destructive local degradation detection in large format lithium-ion battery cells using reversible strain heterogeneity

Heterogeneous degradation is a key challenge faced in the production of large format lithium-ion battery (LIB) cells, and is difficult to evaluate non-destructively. This study demonstrates that reversible strain heterogeneity has the potential of becoming a useful non-destructive tool for local degradation analysis of large format LIB cells. A commercial 59.5 Ah LIB cell with a Li[Ni0.6Co0.2Mn0.2]O2 (NCM622) cathode and graphite anode was degraded at 1.3C current with and without external constraint. The aged unconstrained cells experienced a sudden capacity drop and abnormal expansion at certain locations during discharging at 87% SOH (state of health), which was not observed for the constrained ones. Detailed post-mortem analysis was carried out to understand the capacity drop mechanism. The abnormal expansion was ascribed to the gas bubbles produced by localized severe side reactions between the graphite particles and electrolyte, and the significant heat in certain regions with high impedance. The quick spread of the defective regions was responsible for the sudden capacity drop. This work confirms that the reversible strain distribution contains useful information inside the battery and can help monitor battery degradation and capacity drop.

Experimental investigation on the characteristics of thermal runaway and its propagation of large-format lithium ion batteries under overcharging and overheating conditions

Overcharge and overheating are two common safety issues for the large-scale application of lithium-ion batteries (LIBs), and in-depth understanding of the thermal runaway (TR) and its propagation of LIBs induced by overcharging and overheating are strongly required to guide the safety design of battery system. In this paper, investigation on characteristics and mechanism of TR and its propagation of LIBs induced by overcharging and overheating are conducted experimentally. Besides, critical thermal energy triggering TR and chemical thermal contribution are identified. The normalized critical energy triggered by overcharging and overheating to TR are also determined. The results show compared with TR induced by overheating, TR induced by overcharging exhibits a more severe and catastrophic result due to their higher heat release, more combustible gases and mass loss. In addition, critical thermal energy triggering TR may be constant for fully charged batteries under the overheating of 300 W and 400 W, which is slightly affected by heating power (Ph). Moreover, Critical chemical heat shows a certain upward trend with increasing Ph. Critical electric energy triggering TR and critical self-generated heat slightly decrease with increasing overcharge rate. In open environment, TR induced by overheating propagates faster than that induced by overcharging.