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EV traction battery with thermal storage

The EU OPTEMUS (Optimized Energy Management and Use) project seeks to address the electric range limitation due to limited storage capacity of electric batteries by leveraging low energy consumption and energy harvesting through a holistic vehicle-occupant-centered approach, considering space, cost and complexity requirements.

Specifically, OPTEMUS intends to develop a number of innovative core technologies (Integrated thermal management system comprising the compact refrigeration unit and the compact HVAC unit, battery housing and insulation as thermal and electric energy storage, thermal energy management control unit, regenerative shock absorbers) and complementary technologies (localized conditioning, comprising the smart seat with implemented TED and the smart cover panels, PV panels) combined with intelligent controls (eco-driving and eco-routing strategies, predictive cabin preconditioning strategy with min. energy consumption, electric management strategy).

Among the OPTEMUS projects is a traction battery with thermal storage, which the Fraunhofer Institute for Structural Durability and System Reliability LBF has helped to design.

The phase change material composite system developed by the Fraunhofer LBF can be used to precondition the temperature-sensitive battery cells in cold weather and to keep them at this optimum operating temperature for longer using the thermally insulating housing. An active temperature control can thus usually be avoided.

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A novel phase change material composite is thermally decoupled from the environment by an insulating sandwich housing.

Conversely, it is possible to mitigate short-term, unwanted heat increases of the battery, which may occur during rapid charging.

In order to thermally decouple the PCM composite from the environment and thus make it easier to control, scientists from the Fraunhofer LBF have developed a method for producing a thermally insulating, high-strength battery housing.

This is based on a foam injection-molded integral polymer foam (SABIC PP15T1020), which is locally reinforced with high-strength thermoplastic fiber-plastic composites (TP-FKV) using the hybrid production process. Here, the foam ensures the insulating ability.

In order to be able to investigate and evaluate different polymer foams with regard to their foam morphologies and thus the isolation capability, the researchers designed a morphology analysis based on computer tomographic 3D images.

Since the polymer foam has only low strengths and stiffnesses, it is covered with TP-FKV in order to safely carry the operating loads on the battery. For this purpose, the LBF scientists made a laminate out of several 0.25 mm thin unidirectional tapes (UDMAX from SABIC) and deformed it in three dimensions before the integral foam was injected as a core between the laminate cover layers in the hybrid manufacturing process.

The resulting sandwich construction has several advantages: It has a high lightweight potential and leads to high specific bending properties and impact resistance. In addition, it offers a high level of protection against intrusion events, which play a major safety role especially in battery packs.

In order to do justice to the automotive application, both material and structural concepts have been developed so that they can also be used in large-scale production. For example, the production of the thermally insulating housing is realized by a hybrid foam injection molding process developed at the Fraunhofer LBF, which for the first time makes it possible to produce cost-efficient three-dimensional FRP sandwich components in short cycle times at comparatively low material costs.

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