Multicell Lithium-ion Batteries Research Articles

A novel voltage protection method for multi-cell lithium-ion battery protection IC

Lithium batteries have been widely used in portable electronic devices and other electric products. To ensure safety and long life, a lithium battery needs to be equipped with a protection chip. A novel voltage protection method for three-cell lithium-ion battery protection IC (Integrated Circuit) is proposed in this paper. A new voltage protection circuit structure and a three-cell lithium battery voltage sampling circuit are presented to improve the circuit performance of the chip and reduce the dynamic power consumption and chip area of the system. With a new time-division multiplexing circuit structure, the area and power consumption of the chip are greatly reduced. Moreover, this solution can be extended to any number of lithium battery packs connected in series for voltage protection. Testing results show that the overcharge detection accuracy can achieve better than ±15mV, the over-discharge detection accuracy can achieve ±7.5mV, the power consumption of the voltage protection module is 1.7μA, and the area is 300μm×500μm2.

Ultrasonic reflection characteristics of Lithium-ion battery based on Legendre orthogonal polynomial method

Mechanical properties such as density and Young's modulus of lithium-ion battery electrodes are related to the state of charge (SOC). Characterizing the battery SOC by means of ultrasonic non-destructive testing can obtain the relationship between wave propagation information and the SOC. During the battery charging process, the Young’s modulus and density of the internal electrode material will change, which will affect the propagation of ultrasonic waves in the battery. In this research, a clear and more comprehensive description of the reflection characteristics of ultrasonic waves in lithium-ion batteries have been presented. The Legendre orthogonal polynomial method (LOPM) was first introduced to solve the reflection coefficients of single- and multi-cell lithium-ion batteries. The angular spectrum and frequency spectrum of which were regularly shifted with the SOC, so the SOC could be characterized accordingly. The results obtained by finite element simulation were highly consistent with the method used. Moreover, an ultrasonic reflection experiment system was built, which the result matched with theoretical calculation in a customized battery, further verified the feasibility of the method.

Dynamic battery equalization scheme of multi-cell lithium-ion battery pack based on PSO and VUFLC

Aiming at three problems of over equalization, energy loss and time consumption, a dynamic equalization scheme is designed to control the equalization process of multi-cell Lithium-ion battery pack. First, a modified Buck-Boost circuit using inductor to transfer energy is proposed, which improves the equalization speed and is easy to realize in hardware modules. Then, for the problem of over equalization, state of charge is estimated by extreme learning machine based on genetic algorithm and used as the equalization variable. In order to improve energy utilization, particle swarm optimization is used to dynamically optimize the equalization process to obtain the optimal equalization energy path. On the basis of the optimal equalization energy path, variable universe fuzzy logic control based on fuzzy inference is used to achieve dynamic adjustment of the equalization current and reduce the time consumption. Finally, the simulation results show that the proposed equalization scheme can reduce the energy loss by 2.39%, improve the equalization speed by 36%, and effectively reduce the inconsistency of multi-cell Lithium-ion battery pack.

Fire blanket and intumescent coating materials for failure resistance

There is major fire safety concern about failure propagation of thermal runaway in multicell lithium-ion batteries. This article overviews the passive fire-protection approach based on thermal insulation by intumescent coating materials and fire blankets for viable failure resistance. The intumescent coating will expand (up to 100× on heating) to form a thick, porous char layer and act as a thermal barrier to insulate the substrate. It is also used to seal around openings in a wall or floor to impede the spread of fire and smoke. High-temperature fire blankets are made of noncombustible or flame-resistant fabric materials (e.g., aramids, fiberglass, amorphous silica, preoxidized carbon, and mineral fibers). Both working intumescent coating and fire blankets can block a significant portion (typically 60 to 90%) of the incident heat. Impact-resistant high-strength fabrics, in either soft or rigid forms, can also be used as parts of multilayer protection assembly. Thus, multilayer assemblies can be used for various commercial products, including passive and active fire-protection blankets, battery-cell partitions, confinement bags and containers, packaging materials, and personal protective equipment.

Passive Mitigation of Cascading Propagation in Multi-Cell Lithium Ion Batteries

The heat generated during a single cell failure within a high energy battery system can force adjacent cells into thermal runaway, creating a cascading propagation effect through the entire system. This work examines the response of modules of stacked pouch cells after thermal runaway is induced in a single cell. The prevention of cascading propagation is explored on cells with reduced states of charge and stacks with metal plates between cells. Reduced states of charge and metal plates both reduce the energy stored relative to the heat capacity, and the results show how cascading propagation may be slowed and mitigated as this varies. These propagation limits are correlated with the stored energy density. Results show significant delays between thermal runaway in adjacent cells, which are analyzed to determine intercell contact resistances and to assess how much heat energy is transmitted to cells before they undergo thermal runaway. A propagating failure of even a small pack may stretch over several minutes including delays as each cell is heated to the point of thermal runaway. This delay is described with two new parameters in the form of gap-crossing and cell-crossing time to grade the propensity of propagation from cell to cell.

Numerical Investigation of Thermal Management for Lithium-Ion Battery Pack Under Thermal Abuse Condition

Thermal runaway and its propagation is a big concern for the application of lithium-ion battery. [1] In order to control the propagation in a battery pack, different types of passive cooling have been used as the heat sink of lithium-ion battery packs, such as phase change materials [2] or metal plates. [3] Aluminum has been used widely as it is a relatively light and common material with high thermal conductivity and specific heat. However, how to optimize the configuration of aluminum heat sinks to prevent thermal runaway propagation is still unclear. Recently, Sandia National laboratories [4] assembled modules with aluminum plates of different thicknesses between pouch cells, and investigated experimentally the effect of plate thickness on thermal runaway propagation in a battery module. In the present study, NREL co-investigated these results from Sandia National Laboratories using numerical simulations. [5] This talk addresses the mechanism of thermal runaway propagation in detail. The dominant parameters to prevent propagation are identified. Moreover, an optimum configuration for the aluminum heat sink is proposed. The study provides further insights into the optimization of aluminum heat sink design for lithium-ion battery packs. Acknowledgement This study was supported by Computer Aided Engineering for Batteries (CAEBAT) project of the Vehicle Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. The research was performed using computational resources sponsored by the Department of Energy's Office of Energy Efficiency and Renewable Energy, located at the National Renewable Energy Laboratory. Reference [1] T. Reddy, Linden’s Handbook of Batteries, McGraw-Hill Professional (2010). [2] S.A. Khateeb, M.M. Farid, J.R. Selman, and S. Al-Hallaj, Design and simulation of a lithium-ion battery with a phase change material thermal management system for an electric scooter, Journal of Power Sources. Vol. 128(2), pp: 292-307 (2004) [3] E. Darcy, Passively Thermal Runaway Propagation Resistant Battery Module that Achieves > 190 Wh/kg, Sustainable Aircraft Symposium. Retrieved from https://ntrs.nasa.gov/search.jsp?R=20160003490 2017-11-16T22:50:41+00:00Z [4] J. Lamb, C.J. Orendorff, L.M. Steele, S.W. Spangler, Failure propagation in multi-cell lithium ion batteries, Journal of Power Sources, Vol. 283, PP:517-235, (2015) [5] G. H. Kim, K. Smith, K. J. Lee, S. Santhanagopalan, and A. Pesaran, Multi-domain modeling of lithium-ion batteries encompassing multi-physics in varied length scales, J Electrochem Soc, 158(8), pp: 955-969 (2011). Figure 1

Mitigation of Failure Propagation in Multi-Cell Lithium Ion Batteries

Lithium ion batteries are one of the main energy storage devices that have the potential to be fully integrated in electric grid applications and electric vehicles. Despite years of research in battery safety, there are still challenges associated with the complexity of system-level safety for large battery systems. There is a major gap of safety knowledge at the module or pack level on the effects on adjacent cells in a large-scale battery pack as one cell experiences failure. After the impacts and consequences are identified it is also important to determine mechanisms to mitigate the effects of a single cell failure to the entire pack. In this study, we analyze the failure behavior of small battery packs with 5 stacked pouch cells (LiCoO2 cathode, 3Ah) after thermal runaway is induced to a single cell with nail penetration as the failure initiation method. The first part of the study was to determine the SOC in which full propagation was identified. Different states of charge were tested, including 50%, 75%, 80% and 100% SOC. Complete propagation was observed for 80% and 100 % SOC as shown in Figure 1. The second part of the investigation focused on identifying passive thermal management approaches to mitigating failure propagation. Figure 2 presents the preliminary results using an aluminum heat sink, in which partial propagation was achieved. The results of this study could provide insightful information of the impacts of single battery failure in a pack and a base for future battery designs. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. Figure 1

System state estimation and optimal energy control framework for multicell lithium-ion battery system

Cell variations caused by the inevitable inconsistency during manufacture and use of battery cells have significant impacts on battery capacity, security and durability for battery energy storage systems. Thus, the battery equalization systems are essentially required to reduce variations of in-pack cells and increase battery pack capability. In order to protect all in-pack cells from damaging, estimate battery state and reduce variations, a system state estimation and energy optimal control framework for multicell lithium-ion battery system is proposed. The state-of-charge (SOC) values of all in-pack cells are firstly estimated using a dual-scale extended Kalman filtering (EKF) to improve estimation accuracy and reduce computation simultaneously. These estimated SOC values provide specific details of battery system, which cannot only be used to protect cells from over-charging/over-discharging, but also be employed to design state-feedback controller for battery equalization system. A two-stage hybrid state-feedback and output-feedback equalization algorithm is proposed. The state-feedback controller is firstly employed for coarse-grained adjustment to reduce equalization time cost with large current. However, due to the inevitable SOC estimation errors, the output-feedback controller is then used for fine-grained adjustment with trickle current. Experimental results show that the proposed framework can provide an effectively estimation and energy control for multicell battery systems. Finally, the implementation of the proposed method is further discussed for the real applications.

Discharge characteristics of multicell lithium-ion battery with nonuniform cells

This paper addresses the discharge characteristics of a multicell lithium-ion battery with nonuniform cells. By using a multicell battery with two different types of cell, we experimentally investigate the relationship between discharge capacity and battery topology. In the series connection of nonuniform cells, the total capacity of the battery is governed by a cell with the smallest capacity. In the parallel connection, the total capacity becomes the sum of cells in parallel. In a multicell battery with the series–parallel connection, the discharge capacity depends on its configurations such as connection and number of nonuniform cells. Also, we derive a mathematical model for discharge characteristics of the multicell battery based on the equivalent circuit model of an individual cell. For a multicell battery with a general configuration, the discharge capacity is successfully evaluated by numerical simulations of the mathematical model.