## 4 Conclusions  
This study demonstrated a novel approach to enhancing the crashworthiness of lithium-ion cylindrical cell packs by incorporating spacers strategically placed between the cells. By transforming the initial line contacts into broader surface contacts, the proposed design effectively increased the overall stiffness of the pack, reducing radial deformation under compression. The concept was evaluated using finite element analysis (FEA), leveraging previously established material models to efficiently explore its potential before engaging in resource-intensive physical testing. To further validate the robustness of the homogenized cell material and its applicability in a full pack, a compression experiment was conducted on a pack of nine cells. The results from this experiment were compared against simulation data, showing strong alignment in the force-displacement curves, with almost perfect alignment in the pack without spacers and less displacement than the simulation at 20 kN accounting for an error of 20% with spacers, showing that the simulation is worse in stiffness, with spacers, than in reality. The FEA results showed that filling the interstitial spaces with appropriate spacer materials significantly reduced cell deformation and increased the force required to compress the pack. The study also explored the use of three different materials for the spacers: aluminum, printed PLA, and printed PLA conditioned at 60 \({}^{\circ}\)C. The simulation results demonstrated that the effectiveness of the spacers improves with increased material stiffness, as stiffer spacers more effectively distribute forces and minimize the deformation of the cells. The mass was also taken into consideration, as the aluminum spacers add 26% more mass, relative to the cells' mass, compared with the printed PLA 8%. However, even the printed PLA spacer conditioned at 60 \({}^{\circ}\)C--a material with relatively lower stiffness--exhibited a significant improvement in pack performance, reducing deformation and enhancing structural integrity. This highlights that while stiffness is a key factor, even moderately stiff  
Figure 20: Dynamic loading stress in V3 cell configuration at center cut: (**a**) no spacers; (**b**) aluminum; (**c**) printed PLA; (**d**) printed PLA at 60 \({}^{\circ}\)C.  
materials can yield substantial benefits in improving crashworthiness, making the concept versatile and adaptable to a range of material choices. In the quasi-static plate compression, V1 saw a 400% increase in stiffness with aluminum spacers and 360% with PLA, though the PLA spacer pack stiffness dropped by 12.5% at 60 \({}^{\circ}\)C. V2 and V3 also showed significant improvements, with stiffness increases of 363.3% and 308.3% for the aluminum and PLA spacers, respectively, in V2, and 193% and 192% for the aluminum and PLA spacers in V3. Temperature-induced reductions in the PLA spacer stiffness pack were observed, with 29.7% in V2 and 11% in V3. Similar trends were observed under cylinder loading, where aluminum spacers boosted stiffness by 571% in V1, 425% in V2, and 219% in V3, while PLA spacers saw reductions of 21% in V1, 33% in V2, and 9% in V3 at 60 \({}^{\circ}\)C. The dynamic impact tests demonstrated substantial reductions in intrusion, with V1 intrusion decreasing by 42% with aluminum and PLA spacers and slightly increasing with PLA at 60 \({}^{\circ}\)C. V2 and V3 also showed significant improvements, with intrusions reduced to 22% and 15%, respectively, with PLA spacers. The study validates the mechanical principle illustrated in Figure 1, demonstrating that the line of contact between cells expands into a surface, enhancing resistance to radial deformation and improving the overall stiffness of the battery pack. These results establish a good foundation for the practical application of the spacer concept in electric vehicle battery packs, showing potential in improving the overall stiffness and reducing the deformation in a crash without reducing the number of battery cells.