Cylindrical Lithium-ion Cells Research Articles

Estimating state of charge of cylindrical lithium-ion cells using multiple random convolutional kernel transform and low-frequency stress waves

Lithium-ion batteries (LIBs) represent an energy storage technology increasingly utilized across various fields. To maintain the safety and reliability of a LIB, monitoring the LIB state of charge (SoC) is essential. Currently, there are limited studies on SoC estimation of cylindrical LIBs using the low-frequency stress wave technique due to its limited sensitivity to internal changes of LIBs during the charging/discharging process. Here, we present the first demonstration of SoC estimation of cylindrical LIBs using low-frequency stress wave (5-50kHz). We adopt Pearson correlation coefficients (PCCs) to select sampling points relevant (>0.5) to the SoC from the response stress wave signals and then apply the multiple random convolutional kernel transform (Multi-Rocket) model to extract four types of features for SoC estimation. The SoC estimation performance of the developed method achieves similar accuracy in both original and down-sampled (low-resolution) signals, with estimation root mean square error of about 0.7%, 1.4%, 3.5%, and 5.3%, respectively in four scenarios. This new method based on low-frequency stress waves enables a drastic cost reduction compared to expensive high-frequency ultrasound methods, paving the way for low-cost, real-time SoC monitoring with excellent accuracy.

Coupled Electrochemical-Thermal Runaway Model of Lithium-Ion Cells Operating Under High Ambient Temperatures

The risk of thermal runaway (TR) in high energy density Lithium-ion batteries (LIBs), which may initiate at around 90 °C, is a critical safety concern, particularly in regions where summer temperatures can reach nearly 50 °C. While multiple exothermic reactions that cause TR and modeled using Arrhenius equations lead to good predictions in controlled oven tests, their use in practical applications is questionable as these do not consider internal electrochemical processes that cause temperature rise and trigger exothermic reactions. Further, limited literature focuses on coupling electrochemical thermal models with exothermic reactions. This study demonstrates a method to couple the electrochemical and thermal runaway models for a commercial cylindrical Lithium-ion cell. The proposed model averages pseudo-2D electrochemical heat and couples it to a two-dimensional, axisymmetric heat transfer model of 18650-type Lithium-ion cell. The jellyroll structure is approximated as a homogeneous and anisotropic domain for electrochemical and exothermic heating. Simulations are performed through several, uninterrupted charge-discharge cycles at different ambient temperatures and C-rates. We show that while cycling rate is critical in instigating and accelerating TR, parameters like ambient temperature, particle radii and initial electrolyte concentration also play a role in determining the core temperature and its rate of growth in the cell.

Design guidelines to prevent thermal propagation and maximize packing density within battery systems with tabless cylindrical lithium-ion cells

Large-format tabless cylindrical lithium-ion cells are a promising candidate to not only enhance performance and reduce cost of next generation vehicles but also increase safety compared to other cell formats. In this study, numerical models are developed and validated based on sophisticated mass-produced large-format tabless cylindrical cells that allow analyzing the thermal propagation resilience. Experiments are conducted to prove cylindrical cells may locally drastically exceed common trigger temperatures obtained from accelerating rate calorimetry. A thermal propagation risk map is introduced that establishes an understanding on the influence of the convective and conductive heat paths on different timescales. The influence of varying dimensions and housing materials is revealed and the minimal cell-to-cell spacing is determined that maximizes packing density while still obeying strict no-thermal propagation philosophy. Results show great emphasize must be put on design measures to prevent hot venting gas to introduce heat into the neighboring cells through convection. Afterwards, the cells mass loss and spacing should be optimized to counter the leftover conductive heat path and optimize packing density. The larger the diameter, the further the cells need to be positioned apart. Cells with aluminum housing require less spacing and enable tighter packing density compared to regular deep-drawn steel housings due to the ability to dissipate heat in circumferential and axial direction away from the critical area with highest active material temperatures.

Improving lithium battery cooling: analyzing the impact of air flow, nanofluid flow, and phase change materials

In this study, a finite element analysis is employed to numerically investigate the thermal behavior of a battery pack comprising cylindrical lithium-ion cells. The system incorporates air cooling with phase change material (PCM) surrounding the batteries and nanofluid (NFD) circulating within the PCM through tubes of varying diameters (ranging from 2 mm to 6 mm) at flow rates (FRT) spanning 5 mL/min to 20 mL/min. A two-phase mixture model is applied to analyze the behavior of the NFD as it changes phase. The transient simulation covers a 1-h period to assess temperature variations of the NFD, batteries, surrounding air, PCM, and the phase change process within the PCM. Our results indicate that variations in NFD flow rate (NFFR) do not significantly affect the PCM’s molten fraction during PCM melting, coinciding with an increase in battery temperature (TBT). However, during the PCM refreezing phase, a FRT of 15 mL/min results in the highest quantity of solid PCM. The outlet temperature (TOT) of the NFD demonstrates a cyclical pattern of increase and decrease over time. We observe that when the NFD temperature is elevated, the lowest TOT of the NFD is associated with a FRT of 5 mL/min. Conversely, when the NFD temperature is lowered, this FRT leads to the highest TOT of the NFD. The TBT exhibits some sensitivity to changes in FRT within the initial half-hour, with a subsequent decline, particularly with a FRT of 15 mL/min.

Parametric study of battery module cooling: Configuration optimization using response curve method

Recently, cylindrical lithium-ion battery cells have been widely used in electric vehicles due to efficient automated production and cheap kilowatt-hour capacity. For optimal operation of a cell, the internal temperature of the cell should be maintained within the range of 15–35 °C by employing suitable cooling mechanism. This study comprehensively compares multiple air-cooling configurations specifically designed for lithium-ion battery three-series and three-parallel (3S3P) modules using. The methodology involves an experimental phase to measure the parameters of Bernardi's equation, essential for calculating heat generation with consideration of both Joule's heat and entropic heat. Subsequently, a numerical simulation using Ansys Fluent examines battery heat generation within the 3S3P modules, employing diverse air-cooling configurations. Each configuration undergoes simulation with the aid of design of experiments and parametric analysis, allowing the observation of cooling behavior across various input parameters. To ensure reliability of simulation, the cooling of the unit cell module is simulated under similar conditions. The comparison between these simulated results and experimental values is conducted to validate the accuracy of the overall analysis methodology. The heat measurements indicated a unit cell heat output of 0.9028 W at an average rate of 0.85C. Among the investigated air-cooling configurations, the SIDO (Single Input Double Output) arrangement stood out as the most effective in maintaining a consistently lower average cell temperature, as determined through the application of the response curve method. This study emphasizes the importance of air-cooling design for improving the performance and safety of lithium-ion battery modules used in electric vehicles.

Extensive Experimental Thermal Runaway and Thermal Propagation Characterization of Large-Format Tabless Cylindrical Lithium-Ion Cells with Aluminum Housing and Laser Welded Endcaps

Large-format tabless cylindrical lithium-ion cells are expected to enhance performance and reduce cost of next generation vehicles. The influence of innovative new tab designs, increased dimensions and new housing materials are however still unexplored and must be revealed to unlock safe future battery systems. In this study, the thermal runaway and thermal propagation characteristics of sophisticated state-of-the-art large-format tabless cylindrical cells with aluminum housing and laser welded endcaps are extensively characterized. Multiple abuse test setups on cell and battery level are custom designed close to the true boundary conditions in real world applications. Results show cells with aluminum housing require careful choice of trigger methods as the low melting point and less mechanical strength compared to conventional nickel-plated steel housings introduce additional challenges. The tabless design was found to act as a strong mechanical connection that prevents shifting of the electrode assembly. Instead, axial ruptures of the jelly roll may occur. The leftover high density material conglomeration that is in tight contact with the inner housing wall transfers heat into the surroundings and is critical for thermal propagation safety. Strong interstitial potting compound with low thermal conductivity successfully prevented any major convective heat transfer into the neighboring cells by venting gas.

Characterization and energy storage performance assessment of repurposed 18650 cylindrical lithium-ion cells for second life application in battery energy storage systems

Characterization and energy storage performance assessment of repurposed 18650 cylindrical lithium-ion cells for second life application in battery energy storage systems

A lithium-ion battery equivalent circuit model based on a hybrid parametrization approach

This paper proposes an improved lithium-ion battery equivalent circuit model that can simulate the current-voltage characteristics of the battery under various operating conditions. Specifically, a hybrid parametrization approach is adopted by combining the electrochemical impedance spectroscopy and the hybrid pulse power characterization techniques for the identification and quantification of all loss contributions in a lithium-ion battery cell, for a wide operating frequency range. Moreover, the proposed equivalent circuit model considers the variation of the state of charge, the temperature and the charging-discharging current, and since it can be easily realized by utilizing the existing hardware for the cell equalization, it can be a useful tool for a wide range of real-time applications. The above are realized based on analytical equations of the battery performance with respect to the aforementioned operating parameters' variations. The effectiveness and feasibility of the proposed model is experimentally verified on a commercial, high energy capacity cylindrical lithium-ion battery cell of 3.25 Ah by comparing the model voltage performance with the real voltage of the cell during dynamic operating conditions and with variable surface temperature values.

Degradation behavior of 21700 cylindrical lithium-ion battery cells during overdischarge cycling at low temperatures

Lithium-ion battery (LIB) cells are prone to overdischarge or overcharge when connected in series or parallel as a module or pack for large-format applications, such as electric vehicles (EVs) because of variations in battery capacities and difficulty in maintaining similar state-of-charge (SOC) of every single battery. However, the thermo-electrochemical behavior of LIBs during overdischarge has not been investigated at low temperatures. This study unveils the thermo-electrochemical behavior of overdischarged 21700 cylindrical LIB cells at −20 °C and 25 °C. Also, a thermo-electrochemical model was built to explain the heat generation within the cells and correlate them with the observed electrochemical characteristics. It was found that contrary to the severe cell degradation observed in the overdischarged cell compared to the standard cell at 25 °C, both cells show similar degradation behavior under low temperature cycling conditions. Thus, at low temperatures, overdischarge does not adversely affect cell degradation as observed at room temperature. This was attributed to the significant increase in the internal temperature, which results in improved electrochemical characteristics of the cell.

Effects of control volume outlet variation on axial air cooling of lithium-ion batteries

This paper addresses cylindrical lithium-ion cells' heating and non-uniform cooling by simulating a simple battery pack design with 24 cells and axial airflow. Cooling a battery pack using forced air convection in a rectangular container causes non-homogeneous temperature distribution. The middle cells and the second half of the battery pack (near the exit) get less cooling compared to the cells near the inlet. To solve this issue of non-uniform cooling, in this paper, we propose an optimized Battery Thermal Management System (BTMS) which allows higher amounts of turbulent kinetic energy to be generated near the cells closer to the exit and farther away from the inlet. We attempted to create a narrow region in the middle of the pack which leads to an increase in mixing and turbulence in the airflow. This directs the flow precisely, hence getting rid of dead air flow zones behind the cells. The convergence functions like a nozzle, propelling the air flow into the second half of the battery pack. Using COMSOL Multiphysics, the mixing and turbulence of the airflow, as well as the temperature increase and homogeneity inside the battery pack, are investigated. Three separate investigations are conducted in order to determine the optimal shape for the BTMS control volume as well as to determine the effect of system's inlet pressure and outlet velocity on the cooling performance. Results indicated that the system's temperature decreased significantly by lowering the outlet dimensions and introducing convergence to the BTMS's central area. Increasing outlet velocity increased cooling in a case with a single fan significantly, whereas increasing pressure in a case with two fans increased cooling slightly.

Behaviours of thermal management system with micro channels for cylindrical Lithium-ion cells under Fuzzy-PID control strategy

Replacing conventional fuel vehicles with electric vehicles can effectively reduce pollution from fossil fuels. However, quick charging has been an urgently solved problem to promote the broad application of electric vehicles. A water-cooled battery thermal management system has been proposed, in which the cylindrical batteries were embedded into the cold plate with parallel microchannels in the height direction. It greatly enlarges the contact areas between the battery and the cold plate to strengthen the cooling capacity and improve the temperature uniformity in a high-rate charge. The charge experiments for the prototype of the battery module have been carried out at a 4C charge rate. the cooling behaviours of the system have been investigated including the heat dissipation, the response time, and the average state of charge under Switch, PID, and fuzzy PID control strategies. The fuzzy PID controller shows a desired control effect on the maximum module temperature and temperature difference at different ambient temperatures. Compared with the Switch and PID control strategies, the response time of the fuzzy PID controller is the shortest. At the same time, the average state of charge at the ambient temperature of 298.15 K, 308.15 K, and 323.15 K under fuzzy PID control can be improved to 94.3%, 94.2%, and 93.5 %, respectively. The cooling behaviours of the proposed battery thermal management system under fuzzy PID control are outstanding at a charge rate of 4C and the system is suitable for electric vehicles.

Thermal performance assessment for an array of cylindrical Lithium-Ion battery cells using an Air-Cooling system

Modern society depends on energy storage systems like Lithium-ion (Li-ion) batteries. Li-ion battery cells are delicate to changes in temperature. Extreme environmental conditions affect their life cycle and performance. Therefore, effective cell temperature management is a must for secure and dependable battery operation. Additionally, the high production costs of electric cars must be countered by the adaptability of the battery pack design for modern electric vehicles. As the chemical reactions generate more heat and raise the battery's temperature, it may cause the battery to explode and cause fires in the workplace. To address this issue, the present work attempts to numerically study a novel design of an efficient air-cooling system for improving the performance of lithium-ion batteries by reducing the operational temperatures under a different coolant flow rate. The main output of the presented study is the analysis of a novel design of an efficient air-cooling system for lithium-ion batteries. The study aims to reduce the operational temperatures of the batteries under different coolant flow rates to improve their performance and service life. The numerical simulations are carried out using a finite volume-based computing tool with the K-epsilon (k-ε) turbulence model. The analysis is performed for various pertinent parametric ranges, including the spacing between the batteries, Reynolds numbers, and average Nusselt numbers. The results indicate that increasing air inlet velocity (Re) substantially reduces the average air temperature of the cooling pack and temperature difference (ΔT) of the battery cells, and the cooling pack's average heat transfer rate (Nu) increases monotonically as the Re increases.

Influence of cell dimensions and housing material on the energy density and fast-charging performance of tabless cylindrical lithium-ion cells

The utilization of large-format cylindrical lithium-ion cells with innovative tab design has been confirmed by a number of automotive manufacturers for future vehicle generations. The cell dimensions and housing materials are however widely discussed and will vary depending on the application and vehicle class. In this study, geometrical models are developed that describe the properties of the cells structural components with regard to certain defining loadcases. The volume efficiency and energy density as a function of cell dimensions and housing material choices are explored. A thermo-electrical-electrochemical modeling framework is used to generate a deep understanding of the investigated variables on the key characteristics of fast-charging processes. A 3-stage coolant flow controlling procedure is proposed that ensures the best possible performance for all dimensions and material choices and enables a consistent basis for meaningful comparisons. Results show that cells with aluminum housings provide slightly less volumetric energy density of 3% - 4% compared to nickel plated steel housings while providing 9% - 11% more gravimetric energy density. The fast-charging performance of a 4695 cell with bottom cooling can be optimized by 15% from 13 min 45 s to 11 min 45 s when introducing an aluminum housing due to less heat generation and less thermal resistance in axial direction. The electrical and thermal resistances imposed by the connection between the tabless jelly roll and the cell ends are identified as having significant influence on the cells performance as a function of dimensions.

In-situ measurement of internal gas pressure within cylindrical lithium-ion cells

Internal gas pressure is a key parameter that varies depending on cell heating and gas formation over the lifetime of a lithium-ion cell under dynamic load conditions and ageing. In our research, for the first time, we present a methodology to directly measure internal gas pressure during pre-instrumentation, cell operation and ageing via an embedded sensor system. Cylindrical format cells (LG-INR21700M50) are instrumented using our proven instrumentation technique. Our study demonstrates that the performance and degradation of instrumented cells are not adversely affected by the instrumentation process. In this study, the effect of state-of-charge (SOC), degradation and temperature on internal gas pressure is evaluated. Initial results highlight a nonlinear relationship between gas pressure and SOC of the cells during charging and discharging and, gas pressure and temperature when the cells are operated under no-load conditions. Our study further highlights that gas pressure accumulation can be correlated with capacity fade or state-of-health (SOH). Monitoring of internal gas pressure could therefore become a useful additional indicator of SOC and SOH and provide new insights into degradation and the safety of lithium-ion cells.

Passive thermal management system of lithium-ion batteries employing metal foam/ pcm composite for the development of electric vehicles

ABSTRACT Electric vehicles with a pack of lithium-ion batteries (LIBs) are taking a significant place in the field of transportation. Since lithium-ion battery efficiency relies on battery pack temperature, the temperature of the battery pack must be maintained within the safe limits for proper working of the system. This paper proposes a novel experimental method to dissipate and maintain the thermal energy emitted by LIBs based on a nickel foam/paraffin composite and a composite of copper foam/paraffin for thermal management of Panasonic NCR 18650B cylindrical lithium-ion battery cells. The results indicate that the surface temperature of the battery is reduced by 30.95% by comparing with ambient air convection and 24% temperature reduction by comparing with PCM by the application of nickel foam at a 2C discharge rate. By using copper foam/paraffin composite 34% and 25% temperature reduction by comparing with ambient air convection and PCM (paraffin) accordingly was achieved at a 2C discharge rate. Additionally, the result of temperature uniformity on the thermal management of the battery pack was also studied.

Cycle Tests on the Influence of Different Charging Currents—A Case Study on Different Commercial, Cylindrical Lithium Ion Cells

On the way to a Precise Battery, the generation of measurement results and findings based on them play an important role. Although cycle life tests are time-consuming and expensive, they can provide support and important information. Especially in the current topic of accelerating the charging process, it is important to know how different charging currents affect different cell types. The CC CV charging method is still the most common, widely used method. Therefore, long-term cycle tests are carried out in this work in order to clarify the influence of different charging currents, as recommended by the cell manufacturers. Common high-energy and high-power cylindrical lithium ion cells are investigated and compared. In addition to the influence of the charging protocol on the aging, charging time and heating, the effects on the dispersion of the cells as well as the effects on the constant current and the constant voltage part of the charging process are considered. From the results it can be seen how different the investigated cells behave in response to increased charging currents. Even supposedly similar cells show significant differences in aging behavior.

Heat generation rates and anisotropic thermophysical properties of cylindrical lithium-ion battery cells with different terminal mounting configurations

This paper investigates the variation in the heat generation rates and anisotropic thermophysical properties of cylindrical 18,650 and 21,700 lithium-nickel-manganese-cobalt-oxide (NMC) battery cells when the negative terminal is mounted at different points on the cell surface. We developed a methodology that combines experimental data with a numerical inverse heat transfer (IHT) model to quantify the differences in these properties under two strategies for connecting the negative terminal to the cell surface. In the first, the negative terminal is connected at the top rim of the cell, adjacent to the positive terminal; in the second, the negative terminal is connected at the bottom of the cell, adjacent to the negative current collector. Applying this methodology, we found that the total heat generation over 1000 s for 18,650 and 21,700 cells with the negative terminal at the top rim is higher than that for batteries with the negative terminal at the bottom by up to 4.6 % and 10.7 %, respectively. The additional heat was concentrated in the cell canisters, resulting in non-uniform heat generation across the cell volume. Without considering this non-uniformity in the numerical IHT model, the characterization process yielded 15–22 % discrepancies in the predicted thermal conductivities. By considering the canister and jelly roll of the cell as separate heat generation domains, the discrepancies were reduced below 6 % and 7 % for 18,650 and 21,700 cells, respectively. This work developed an improved battery cell characterization methodology taking into account localized heat generation and extrinsic terminal mounting effects. The results underline the importance of high-fidelity cell characterization in the battery cell design process.

Influence of Breathing and Swelling on the Jelly-Roll Case Gap of Cylindrical Lithium-Ion Battery Cells

Cylindrical 18650 and 21700 lithium-ion batteries are produced with small gaps between the jelly roll and the case. The size of these gaps and the mechanical attachment of the jelly roll to the case can have a significant impact on the thermal and mechanical properties of cells. To investigate the influence of the state of charge (SOC) and state of health (SOH) on the size of the gap, computed tomography (CT) and gray-value analysis was conducted with various cell types at 0% and 100% SOC and after cycling. The results show a significant influence of the SOC on the gap for new cells and a substantial reduction in the gap during the first cycles.

Experimental investigation of parameters influencing battery life cycle of lithium-ion batteries at ambient cell surface temperature

Lithium-ion batteries and their usage have been dominating the industry for a decade. However, it has been found through the years that Lithium Nickel Manganese Cobalt Oxide (NMC), and Lithium Iron Phosphate (LFP) battery cells are widely preferred over the other types of cylindrical lithium-ion cells. The performance of NMC and LFP battery cells are compared experimentally using a 5 V 6A 8CH Cell tester, by studying the Ah charged and discharged, Wh charged and discharges as well as temperature variation in the charging and discharging cycles. 18650 NMC and LFP cells were set up, wherein 40 experimental trials were performed at the as per the voltage and cell chemistry at using a Constant Current Constant Voltage charging scheme. The aim was to determine the value of capacity degradation, its trend for both cells, and the predicted cycle life of these cells. The voltage parameters for LFP were (3.2 V to 2.5 V), Charging at 3.2 V, and discharging at 2.5 V, similarly for NMC it was (3.6 V to 2.8 V), charging at 3.6 V to 2.8 V respectively. A thorough analysis for 40 cycles for NMC and LFP wherein temperature variation and capacity degradation for cycles after 5 intervals has been explained in the report. Also, the Capacity degraded during the process was fit using a regression model, from which it was concluded which of the batteries has a greater cycle life.

Fast-charging performance and optimal thermal management of large-format full-tab cylindrical lithium-ion cells under varying environmental conditions

Various automobile manufacturers have announced utilization of large-format cylindrical lithium-ion cells with innovative tab design for future vehicle generations. In this study, a cylindrical lithium-ion cell with novel full-tab design, state-of-the-art Ni-rich cathode and SiOx-C anode made specifically for automotive high-performance applications is used to parameterize a modeling framework and investigate the performance of large-format cylindrical cells. Much attention is paid to accurately modeling and validating the internal heat path of the enhanced tab design that is crucial for effective thermal management and is one of the biggest advantages compared to former single-tab cells. The spatially-resolved physico-chemical model is extensively validated within the temperature range of −20 °C to 65 °C with experimental data from multiple different test setups. The validated model is used to investigate optimal fast-charging times and thermal management strategies based on local anode voltage and plating risk under varying environmental condition. The findings are summarized in a generalized cooling-and-heating-map that provides an outlook on the fast-charging performance of less than 12 minutes from 10% to 80% state of charge for large-format cylindrical cells.