Temperature gradient reduction in high-power battery systems using prismatic cells combined with Phase-Change Sheets and Graphite foils

In lithium-ion battery systems thermal management has an important influence on performance, safety and service life. Especially in automotive applications short-term peak loads thermally stress the battery cells. Temperature inhomogeneities arise, effecting ageing rates and electrical properties with the consequences of a reduced system lifetime and diverging state-of-charge of the battery cells. By integration of Phase-Change-Material together with high thermally conductive Pyrolytic Graphite Sheets and graphite gap filler pads, thermal peak shaving and temperature homogenization are implemented to reduce temporal and spatial temperature gradients. In this paper a battery module with prismatic cells and advanced thermal materials was investigated on test-bench. Measurements of temperature rise, differences and distribution at different boundary conditions were performed to evaluate the designed concept. The measured temperature profiles were captured in all three spatial directions within the battery module. As a result, without increasing the volumetric overhead, the maximum rise in temperature was reduced by 13%, while the additional Phase Change Material has 5% of the cells mass. Furthermore the temperature difference on module level was kept below 5K at all conditions above zero degrees ambient temperature even at the maximum specified discharge current and continuous cycling

Investigation of gas sensing in large lithium-ion battery systems for early fault detection and safety improvement

Large lithium-ion battery systems rely on battery monitoring and management systems to ensure safe and efficient operation. Typically the battery current, the cell voltages, and the cell temperatures are monitored. This paper describes the use of gas sensors in large lithium-ion battery systems in addition to conventionally used means of battery monitoring. An undetected electrolyte leak in a cell can pose a serious threat to users and maintenance personnel. Experiments described in this paper show that a gas sensor can easily detect volatile organic compounds (VOC) from the leaking electrolyte, whereas standard cell monitoring methods can only detect a leak indirectly over premature cell performance degradation. Therefore, gas sensors offer a fast, simple, and cost efficient way to increase the safety of battery systems. This paper gives a description of a suitable gas sensor and its application in a battery system, followed by the identification of relevant use cases. In the experimental section the performance of the gas sensor in these use cases is investigated and evaluated. The paper ends with a summary of the results and a short outlook

Introduction and application of formation methods based on serial-connected lithium-ion battery cells

The process step of formation is one key process to guarantee high performance, long-lasting and safe automotive lithium-ion cells. Since the formation of the cell is the most expensive process in cell manufacturing, reducing process cost and time is advanced. The state-of-the-art formation process includes the cycling of lithium-ion cells each on its own power electronic channel which amounts to about 38% of the total formation costs. Therefore, this paper proposes an optimized formation method by serial-connected lithium-ion cells. Due to small resistance and capacity deviations conditioned by manufacturing tolerances, charge balancing is necessary for formation of serial-connected cells. This paper introduces several serial interconnection circuits for serial cell formation, like passive balancing or drop out system. Furthermore, the associated influences on the formation process parameters, e.g. the charging profile and the charge current control are investigated. T he comprehensive comparison of serial formation techniques reveals cost reduction potentials and challenges regarding the process control

Galvanically isolated differential data transmission using capacitive coupling and a modified Manchester algorithm for smart power converters

In this paper, a method for encoding and decoding digital data signals using a modified form of the standard Manchester code for the application in galvanically isolated data transmission in smart power electronics is described. The method includes a modified encoder circuit and a matching decoder circuit that is able to rebuild the original clock and data signal without a separate transmission of the clock signal. A capacitive coupling element with a corresponding signal conditioning circuit was placed between the encoder and decoder circuit to achieve a galvanic isolation between the primary side that processes the data signals and the secondary side that is responsible for the processing of power in smart power devices. After a description of basic principles of the transmission of data over a galvanic isolation and the state-of-the-art of Manchester code based data transmission, the encoding and decoding process of the modified Manchester code is elaborated and experimental results are presented

Hardware and software framework for an open battery management system in safety-critical applications

Lithium ion batteries are a common choice for many use cases, ranging from medical devices to automotive and airborne applications. Despite their widespread application, lithium ion batteries still remain an expensive, yet sensitive component within these systems. In order to maintain the operability of the battery system over its designated service life an appropriate battery management system (BMS) is required. The development of such a BMS is a challenging task, as various technological, environmental and application-specific aspects have to be considered. Especially safe and reliable operation of the battery system is an important and critical issue in this context. Besides these safety critical aspects, the BMS also includes extensive non safety related components and functions. Therefore, in order to fulfill safety-critical requirements, it is mandatory to keep the respective hardware and software components isolated. Redundancy, partitioning and the implementation of diagnostic functions at several software layers and different hardware partitions are the mechanisms for ensuring the integrity of the system. For performance and economical reasons, these techniques have to be tailored to the application. Based on a real-time operation system, a flexible and extensible strategy for a software framework with minimal code size, lean interfaces and few dependencies is introduced. The use of a dedicated BMS-Engine with a partitioned database enables the implementation of a stringent safety concept, which is discussed and demonstrated to be feasible

Aviation battery monitoring electronics in lithium-ion based battery systems for electrified sailplanes and aircrafts

This paper presents the hardware and software design of a battery monitoring circuit developed to be used in aviation applications employing lithium-ion batteries in their electrified powertrain. The considered aircraft is a manned sailplane able to take-off and climb by using its electric propulsion system supplied by NCA/Graphite lithium-ion batteries. The battery monitoring electronics was developed with the highest considerations in terms of fail-safe and fail-operational requirements. The electronic design of the battery monitoring circuit integrates the battery busbars and uses new passive balancing components with an innovative busbar cooling solution, thus increasing the reliability and the robustness of the whole battery system. The software also contributes to the high safety level by employing crosscheck and plausibility check mechanisms