Languang Lu

Analysis of the heat generation of lithium-ion battery during charging and discharging considering different influencing factors

Operating temperature of lithium-ion battery is an important factor influencing the performance of electric vehicles. During charging and discharging process, battery temperature varies due to internal heat generation, calling for analysis of battery heat generation rate. The generated heat consists of Joule heat and reaction heat, and both are affected by various factors, including temperature, battery aging effect, state of charge (SOC), and operation current. In this article, a series of experiments based on a power-type lithium manganese oxide/graphite battery was implemented under different conditions. The parameters for Joule heat and reaction heat are determined, and the Joule heat, reaction heat as well as total heat generation rate is detailed and analyzed considering the influence of temperature, aging, SOC, and current. In order to validate the accuracy of heat generation rate, a lumped battery heat transfer model is applied to calculate the temperature variation, and the estimated temperature variation shows good correspondence with experimental results under different currents and aging conditions. Due to its simplicity, the temperature variation estimation method is suitable for real time applications.

Mechanism of the entire overdischarge process and overdischarge-induced internal short circuit in lithium-ion batteries.

Lithium-ion batteries connected in series are prone to be overdischarged. Overdischarge results in various side effects, such as capacity degradation and internal short circuit (ISCr). However, most of previous research on the overdischarge of a cell was terminated when the cell voltage dropped to 0 V, leaving the further impacts of overdischarge unclear. This paper investigates the entire overdischarge process of large-format lithium-ion batteries by discharging the cell to −100% state of charge (SOC). A significant voltage platform is observed at approximately −12% SOC, and ISCr is detected after the cell is overdischarged when passing the platform. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) results indicate that the overdischarge-induced ISCr is caused by Cu deposition on electrodes, suggesting possible Cu collector dissolution at the voltage platform near −12% SOC. A prognostic/mechanistic model considering ISCr is used to evaluate the resistance of ISCr (RISCr), the value of which decreases sharply at the beginning of ISCr formation. Inducing the ISCr by overdischarge is effective and well controlled without any mechanical deformation or the use of a foreign substance.

Equivalent Consumption Minimization Strategies of Series Hybrid City Buses

With ever growing concerns on energy crisis and environmental issues, alternative clean and energy efficient vehicles are favoured for public applications. Internal combustion engine(ICE)-powered series hybrid buses and fuel cell (FC) hybrid buses, respectively as a near-term and long-term strategy, have a very promising application prospect. The series hybrid vehicle utilizes an ICE/FC as the main power source and a battery/ultra capacity (UC) as the auxiliary power source. The main power source supplies the average vehicle power, and the auxiliary power source functions during accelerating and decelerating. Because the battery/UC fulfills the transient power demand fluctuations, the ICE/FC can work steadly. Thus, the durability of the fuel cell stack could be improved compared with a pure FC-powered bus in the FC series hybrid bus. And the PM and NOx can be greatly lowered in the ICE series hybrid bus compared with a traditional city bus. Besides, the ability of the energy storage source to recover braking energy enhances the fuel economy greatly. The hybrid configuration raises the question of energy management strategy, which chooses the power split between the two. The strategy is developed to achieve system-level objectives, e.g. fuel economy, low emission and battery charge-sustaining, while satisfying system constraints. Energy management strategies in the recent literature can be generally categorized into two types: rule-based strategies and optimal strategies. A rule based strategy can be easily implemented for the real-time applications based on heuristics (N.Jalil, N.A.Kheir & M.Salman, 1997). Such a strategy could be further improved by extracting optimal rules from optimal algorithms (S.Aoyagi, Y.Hasegawa & T.Yonekura, 2001). Optimal strategies differ from each other in the time range. Fuel consumption in a single control cycle is minimized in an instantaneous optimal strategy (G.Paganelli, S.Delprat & T.M.Guerra, 2002). And a global optimal strategy minimises it over a whole determined driving cycle using determined dynamic programming method (DDP) (Chan Chiao Lin et al., 2003), or over a undetermined driving cycle using stochastic dynamic programming method (SDP) (Andreas Schell et al., 2005). Other strategies minimize fuel consumption over an adaptive time span, which could be adjusted on the basis of vehicular speed, pedal 7

A comparative study of equivalent circuit models and enhanced equivalent circuit models of lithium-ion batteries with different model structures

Lithium-ion battery model is critical for voltage and state of charge (SOC) determination, and the equivalent circuit model (ECM) is frequently implemented in real -time cases due to low complexity, but the low-SOC-area performance requires improvement. This paper introduces an enhanced equivalent circuit model (EECM) based on electrochemical analysis, in which the surface SOC (SOCsurf) reflects the lithium concentration at the particle surface and is used to determine the terminal voltage. Five empirical based models with different model structures (in which two ECMs and three EECMs included) are selected to compare the model accuracy and complexity. Experiments were carried out on a battery test system with a temperature chamber, and a modified hybrid pulse power characterization (HPPC) profile was employed to measure the battery dynamic response. The genetic algorithm method is implemented in model parameterization, and the voltage estimation accuracy of the five empirical models is compared in SOC range 0~100%. The results show that the EECMs considering SOCsurf provides better accuracy than the traditional ECMs in low-SOC area, and the EECM with one RC component and one DS component provides the optimum performance considering accuracy and complexity.

Thermal Modeling of a LiFePO4/Graphite Battery and Research on the Influence of Battery Temperature Rise on EV Driving Range Estimation

Operating temperature of lithium-ion battery is an important factor strongly influencing the performance of electric vehicles. The battery temperature variation affects the remaining energy capacity, which in addition influences the remaining driving range of EV. An accurate range estimation method must take battery temperature rise into account, since the charge and discharge process leads to internal heat generation. In order to determine the battery temperature rise, we built a three-dimensional electrochemical-thermal model for a prismatic lithium-iron-phosphate/graphite cell, and calibrated its heat-transferring parameters. The accuracy of the 3-D model was verified by a series of discharge experiment, with the estimation error less than 1°C. Then a driving range estimation model was design for this battery on a pure electric vehicle. When considering or not-considering the battery temperature increase, a significant driving range estimation difference was found in Matlab/Simulink simulation, showing the importance of battery temperature prediction.

Thermal Runaway Propagation Within Module Consists of Large Format Li-Ion Cells

Thermal runaway (TR) propagation within a large format lithium ion battery module includes two stages: the Initiation Stage and the Propagation Stage. Experiments were conducted to investigate the mechanisms of TR initiation at single cell and TR propagation in a battery module. A lumped TR propagation model was built based on heat transfer theory, and was calibrated by experiment data. The calibrated TR propagation model can analyze the heat transfer amount through different paths during TR propagation. Base on analysis on the heat transfer paths, methods were proposed to prevent TR propagation within battery module. TR propagation can be successfully prevented according to the method proposed, which is verified by experiment.

Research on simplification of simulating the heat conduction in the lithium-ion battery core

This paper discusses the model simplifing issue in battery thermal simulation. The paper verifies that for the large power battery simplifying the multilayer battery core as a lumped cuboid is reasonable. So when doing simulation, building a multilayer core is unnecessary. And the calculation cost can be reduced by the lumped model. Specific power battetry of 70Ah is dissembled to be modeld. Thermal models of are established, including models with a lumped core and with multilayer cores. For the lumped core, the anisotropic thermal conductivities are got by equations calculating series and parallel equivalent thermal conductivity. While for the multilayer core models, the core contains numbers of unit cells and the volume of which is equal to that of the lumped. In addition, under the boundary conditions of inner heat source and surface heating, steady state simulations are performed. Simulation results indicate that the temperature distributions of the lumped model and the multilayer model are almost the same. For one thing, large number of multilayers and low shell thermal conductivity contribute to a uniform temperature distribution within the core, so it is reasonable to simplify the multilayer core as a lumped cuboid. For another, due to the size of the battery and the shell property, it is difficult to find a simple curve to fit the simulation temperature on the battery surface. Although minor differences still exist, the lumped core can well subsitute the multilayer core in battery thermal simulation.

Pattern matching and simulation research of extended range electric vehicle

Based on the foundation of determined system configuration and performance target of a miniature of extended range electric car, some pattern selection and matching research on the auxiliary power unit, the power battery and the traction motor are carried on. The vehicle model is established and the simulation result of dynamic performance and fuel economy of the whole vehicle is analyzed.

Simulation research of energy management strategy for range extended electric bus

Based on the analysis of configuration of Range Extended Electric Bus (REEB), the article studies two energy management strategy, which are Charge-Depleting Charge-Sustaining (CDCS) and blended type. On the foundation of creating a vehicle simulation model, the article takes a simulation analysis on the economy of Range Extended Electric Bus. Take the Chinese city bus driving cycle conditions of daily travel mileage 200km for example, the simulation results show that comparing with blended control strategy, Auxiliary Power Unit (APU) application load following control methods with CDCS management strategy have certain improvement on the electric consumption and fuel consumption.

State of Charge, State of Health and State of Function Co-Estimation of Lithium-Ion Batteries for Electric Vehicles

This paper proposed a co-estimation scheme of State of Charge (SOC), State of Health (SOH), and State of Function (SOF) for lithium-ion batteries. The Extended Kalman Filter is adopted to SOC estimation. Battery parameters are identified online by using Recursive Least Square Algorithm to further estimate battery SOH and SOF. The accuracy of the estimation is improved and the computation is reduced by making good use of the correlations among the states.