Impact of Shock on Embedded Lithium-Ion Batteries in Automotive Structures

To reduce fuel consumption and greenhouse gas emissions, industries such as electric vehicles (EV), aerospace, and shipping are adopting two main approaches: electrification and structural lightweighting. Sandwich composites are increasingly used for structural components such as chassis and body panels to achieve lightweight design. In terms of electrification, lithium-ion batteries (LIB) are widely used in electric products and devices due to their excellent cycling performance and electrochemical energy storage characteristics. However, compared to traditional vehicles, electric vehicles require larger battery packs to increase range, often including bulky packaging materials, significantly increasing the overall structure’s weight and volume. One solution is to utilize structural energy storage composites to improve energy storage efficiency. These composites can serve as structural elements and distributed energy storage units within a single engineering structure, thus reducing the volume and mass of the entire system.

Currently, there are two main types of structural energy storage composites.

The first type involves modifying the reinforcement and matrix of the composite materials or the structure of lithium-ion batteries to achieve structural energy storage composites. These multifunctional composites can be designed to use carbon fiber reinforced materials and polymer matrices as electrodes and electrolytes, respectively, enhancing the load-bearing capacity of the battery. However, the energy density and power output of these structural energy storage composites have not yet reached practical requirements, and further research should focus on achieving high energy density and stable electrical performance of structural power composites.

The second type is to use multifunctional composite panels directly embedded with lithium-ion batteries to provide load-bearing and energy storage functions. Due to their high energy density and high charge/discharge rates, internal lithium-ion batteries exhibit relatively good electrochemical energy storage performance while being protected by the composite structure. This multifunctional structure is relatively easy to manufacture and has been applied in the aerospace and automotive industries, such as drones, CubeSats, artificial satellites, and Tesla Model Y.

The practical implementation of composite structures containing batteries requires an understanding of how the embedding of batteries affects the structural mechanical performance and safety behavior under mechanical load conditions. Previous works have studied these aspects.

Thomas et al. found that CFRP (carbon fiber reinforced polymer)/SAN (styrene-acrylonitrile) sandwich composites containing two lithium polymer batteries exhibited an increase in flexural modulus but a significant reduction in flexural strength.

On the other hand, Galos et al. reported that embedding small-sized lithium polymer batteries in the PVC foam core of sandwich composites did not significantly affect the stiffness and strength performance under bending loads, and the internal resistance and capacity of the soft-pack batteries remained unchanged.

Atalar et al. indicated that embedded batteries negatively affect the compressive stiffness, failure stress, and fatigue life of laminates. The force transfer paths of laminates and sandwich structures are different, thus replacing components with batteries has different effects on the mechanical performance of composite structures.

Patalakunanan et al. found that inserting one or more batteries reduces the tensile modulus and failure stress of CFRP laminates, while not changing the tensile stiffness and strength of foam core sandwich composites.

In certain scenarios, multifunctional composite panels may experience collision accidents during use, such as electric vehicles colliding, drones crashing, or portable electronic devices dropping. Therefore, impact resistance is a key factor in the structural integrity and safety design of multifunctional energy storage composite structures. In this regard, Patalakunanan et al. studied the impact damage tolerance of energy storage composite structures containing lithium-ion polymer batteries, finding that the capacity and internal resistance of batteries embedded within laminates and sandwich composites were not significantly affected under relatively low impact energy (below 6 J). For bare batteries, mechanical abuse loading can easily trigger internal short circuits (ISC) and thermal runaway (TR). The mechanical-electrochemical-thermal coupling behavior of batteries under mechanical abuse has been well predicted and studied. Zhang et al. used a proposed coupling model from a multidisciplinary perspective.

Although previous studies focused on the mechanical behavior of composite panels with embedded batteries under various mechanical conditions, the electromechanical coupling behavior and post-impact performance evolution of multifunctional composites under impact loads have not been studied. Furthermore, it is crucial to determine the remaining performance and evolution of embedded batteries under actual usage conditions, ensuring that these batteries do not cause internal short circuits or thermal runaway due to damage to the multifunctional structure and can continue to operate for future use.

To this end, this work designs and manufactures a multifunctional composite structure embedded with soft-pack lithium-ion batteries to achieve integrated design of energy storage structures. The mechanical-electrochemical coupling response and remaining performance of the multifunctional sandwich composite structure with embedded lithium-ion soft-pack batteries under low-speed impact loads were further studied. The rest of this paper is arranged as follows. Section 2 introduces the manufacturing process of multifunctional sandwich composites and the multidisciplinary characterization methods. Section 3 discusses the electromechanical coupling response during the impact loading process. Section 4 discusses the performance evolution of embedded batteries, then clarifies the capacity degradation mechanism caused by the impact on embedded batteries through charge/discharge cycles and damage characterization.

The results show that the embedded design can effectively protect the battery from severe internal short circuit effects, but performance may decline to varying degrees. The multifunctional composite structure embedded with lithium-ion batteries can still operate well after impact loads, demonstrating its potential application prospects in impact-resistant electrochemical energy storage integrated structures.

References:

Honggang Li, Dian Zhou, Junchao Cao, Zhihao Li, Chao Zhang (2023) “On the damage and performance degradation of multifunctional sandwich structure embedded with lithium-ion batteries under impact loading,” Journal of Power Sources, Volume 581 doi: 10.1016/j.jpowsour.2023.233509

Click “Read the original” at the bottom