Fast charging capable and weight optimized battery system

Leadership: Fraunhofer IISB

Contributing: AVL List, Mercedes Benz AG, Technische Universität Dresden, Valeo-Siemens

Objectives

• Optimization of automotive grade battery cells to enable ultra-fast charging capability (up to 350 kW charg-ing power at pack level)
• Adaption of an existing open-source BMS solution to the requirements of the battery and demonstration ve-hicle
• Development, assembly and test of the fast charging capable battery system of around 100 kWh at 800 V and less than 600 kg

Description This supply chain will provide the fast charging capable weight optimized battery system to the supply chain 3 being in charge of the vehicle integration and demonstration. The outcome of this supply chain will be a tested and ready to be integrated 800 V battery system providing around 100 kWh of energy storage and able to be charged at power rates up to 350 kW. A typical automotive battery system consists of several battery modules, the thermal management system, the battery management system (BMS) and a battery junction box (BJB) containing the nec-essary electrical safety components.

Battery Cells: To ensure the highest possible perfor-mance and the best mechanical and thermal configura-tion for the battery system to be developed for the demonstration vehicle, SAFT will use its pouch cell for-mat. The electrochemistry will be optimized for ultra-fast charging rates (i.e., between 2 to 4 C-rate). Rather than using a metallic casing, the li-ion pouch cell is made of conductive foil-tabs welded to the electrodes and brought to the outside in a fully sealed way. The pouch cell makes most efficient use of space and achieves 90–95% packaging efficiency, the highest among battery packs. Eliminating the metal enclosure reduces weight, but the cell needs mechanical support in the module. Pouch cells are widely used in consumer and automotive applications. There exists no standard format for pouch cells: each manufacturer designs its own, thus making it possible to fit the available vehicle compartment in the best way.

BMS and BJB: The battery management system that will be used in the 1000kmPLUS project will be based on the existing foxBMS plat-form initially released in 2016 and developed and maintained by the FhG. foxBMS is a free, open and flexible development environment for the design of complex and highly demanding battery management systems for mobile and stationary applications. It is worldwide the first universal BMS platform providing open source for both hardware and software, and is able to manage modern energy storage systems. The architecture of foxBMS is the result of more than 15 years of development in innovative hardware and software solutions for lithi-um-ion battery systems. The foxBMS hardware and software building blocks are used successfully in battery electric vehicles based on lith-ium-ion NMC/Graphite battery cells, where it has obtained a road homologation by TÜV Süd in Germany.

The hardware of foxBMS enables the management of high-performance prototypes of complex lithium-ion battery systems of any size (i.e., from one cell up to several hundreds of cells at up to 1600 V). The redundant hardware architecture of foxBMS is well suited to develop battery systems requiring a high level of safety and availability. The hardware is licensed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. The BMS consists of the BMS-Master board on which the software is running on two separated microcontrollers. The BMS-Master is connected over the BMS-Interface in a daisy-chain architecture to the BMS-Slaves, which are measuring the cell voltages and cell temperatures in each battery module. The BMS-Master together with the BMS-Extension controls all the components in the battery junction box (BJB), like the power contactors, current sensor, interlock, and the galvanic isolation monitoring.

The software implemented in foxBMS uses only specifically developed open source and free of charge software components, or free of charge third-party software. The entire source code of foxBMS is provided online on GitHub and includes its own development environment and configuration files based on Eclipse and GCC compil-er, thus enabling immediate use on Windows, Mac, and Linux operating systems. The software is licensed under the BSD 3-Clause license. All foxBMS parts can therefore be utilized unrestrictedly, including free and open source use, as well as closed source commercial use. The BMS hardware concept that will be used in the project will be derived.

Battery System: The 800 V battery system will provide around 100 kWh of energy with a total weight of less than 600 kg. It will be designed with a liquid cooling fitting the shape of the pouch cells. Thin pouch cells offer the best thermal conductivity, which provides an efficient cooling possibility during the fast charging phases. The cells will be assembled into battery modules, which will also contain the BMS-Slaves electronics to monitor the voltages and the temperatures, and to perform the cell balancing. The modules will be assembled in a battery pack and connected to the BJB to become the battery system. The housing of the battery system will be optimized on lightweight by TUD. Once assembled, the battery system will be tested electrically and thermally, especially at high charging rates, to ensure proper operation before it will be integrated into the demonstration vehicle in SC3.ed from the fox-BMS platform, with a specific focus on the 800V aspects to be realized by the BMS hardware.