Localized impact-resistant battery enclosures for electric vehicles: crashworthy lightweight design, mechanical–thermal safety, and validation pathways

1 Introduction

Battery electric vehicles place a large, dense, and safety-sensitive energy storage system in the underfloor region. This layout lowers the centre of gravity and improves packaging, but it also exposes the pack to road debris, ground strike, curb contact, lateral intrusion, sealing loss, vibration, and fire-related hazards. The battery enclosure is therefore not a passive cover. It is a load-bearing shell, environmental barrier, and mechanical safety device that must keep local deformation away from cells while remaining light enough for range and cost targets. Cell-level studies have shown that mechanical abuse can progress from indentation and separator damage to internal short circuit and thermal consequences, so enclosure design has to be interpreted through cell safety as well as structural mass (Liu et al., 2020; Pan et al., 2020).

Bottom strike and side-pole collision are especially demanding because they act through narrow contact zones. Localized underbody loading can occur when a stone, hump, curb, or ground surface drives a concentrated load into the lower shield and tray. Side-pole collision can drive a narrow lateral intrusion path through the rocker, sill, battery side wall, and module boundary. In both cases, global vehicle crash metrics can look acceptable while a small group of cells experiences damaging strain. Ground-impact work by Xia et al. (2014) and later studies on undercarriage collision mitigation show that pack architecture, cell orientation, and enclosure stiffness must be considered together (Chen et al., 2024).

Recent reviews have broadened the field from simple battery-box lightweighting to mechanical reliability, safety standards, and integrated pack protection (Arslan et al., 2026; Kawsar et al., 2025; Abdisobbouhi et al., 2026). This Mini Review differs by treating the enclosure as a staged mechanical-thermal protection system under two localized crash scenarios: bottom strike and side-pole collision. The central contribution is a mechanism-based framework that links load paths, puncture resistance, intrusion control, energy absorption, cell-level deformation, manufacturability, and post-impact thermal safety. Whereas recent reviews mainly summarize battery-box materials, structural optimization, or pack-level reliability, this Mini Review uses localized impact scenarios as the organizing axis and evaluates enclosure concepts according to their role in interrupting the load-to-hazard chain. This focus is also consistent with the current regulatory direction in China. GB 38031-2025, which came into force on 1 July 2026, places stronger emphasis on traction-battery system safety and makes realistic mechanical and thermal-abuse validation more relevant to enclosure design (GB 38031-2025, 2025).

Recent reviews have addressed battery-box lightweighting, structural optimization, mechanical reliability, or battery safety from broad pack-level perspectives. In contrast, the present Mini Review is intentionally scenario-oriented. It focuses specifically on localized bottom strike and side-pole collision, where concentrated intrusion can threaten only a small region of the enclosure while directly endangering nearby cells. A second distinction is that enclosure concepts are not classified primarily by material type, but by their mechanical function in the protection chain, including puncture resistance, load spreading, progressive crushing, intrusion control, and preservation of post-impact thermal and electrical functions. A third distinction is the explicit linkage between enclosure deformation, cell-level abuse indicators, and post-impact validation requirements. This scope therefore complements, rather than duplicates, recent broader reviews of battery-box lightweighting and battery-pack mechanical safety.

2 Review scope and mechanism-based framework

This study was conducted as a focused Mini Review rather than a systematic review or meta-analysis. Literature searches were performed in Web of Science, Scopus, ScienceDirect, SpringerLink, and IEEE Xplore. The search strategy combined three groups of terms: (1) application terms, including “electric vehicle”, “EV”, “battery pack”, “battery enclosure”, and “battery box”; (2) loading and safety terms, including “crashworthiness”, “bottom impact”, “ground impact”, “undercarriage collision”, “road debris”, “side pole”, “lateral impact”, and “mechanical abuse”; and (3) structural-design terms, including “lightweight”, “honeycomb”, “sandwich”, “auxetic”, “foam-filled”, “composite”, and “energy absorption”. Boolean combinations of these groups were used to identify studies relevant to localized battery-enclosure protection. The search covered publications from 2014 to July 2026, with particular attention to studies published after 2020.

Studies were included when they addressed at least one of the following topics: (i) EV battery-enclosure or battery-pack structural protection; (ii) bottom strike, ground impact, side-pole collision, or another localized mechanical loading condition relevant to vehicle batteries; (iii) lightweight or energy-absorbing enclosure architecture; (iv) quantitative crashworthiness or intrusion metrics; or (v) relationships between mechanical deformation and cell-, module-, thermal-, or electrical-safety outcomes. Studies focusing exclusively on electrochemical materials, charging strategies, BMS algorithms, stationary energy storage, or normal-operation thermal management were excluded unless they provided evidence directly relevant to post-impact battery safety.

Records were screened sequentially by title, abstract, and full text. The initial search identified 214 records across Web of Science, Scopus, ScienceDirect, SpringerLink, and IEEE Xplore. After removal of 58 duplicate records, 156 records remained for title and abstract screening. Of these, 101 records were excluded because they were outside the EV battery-enclosure scope or lacked direct relevance to enclosure crashworthiness, localized mechanical protection, or mechanical–thermal safety. The remaining 55 articles underwent full-text assessment. Following full-text screening, 23 articles were excluded because they did not provide enclosure-level design information, mechanical-response data, cell-level abuse interpretation, or standards-relevant validation evidence. Finally, 32 studies were retained for qualitative synthesis and categorized according to load case, structural concept, validation scale, and reported performance metric.

The synthesis uses four protection stages (Figure 1). The first stage is the external load, including road-debris strike, ground impact, and side-pole intrusion. The second is enclosure response: puncture resistance, load spreading, progressive crushing, and joint retention. The third is the battery safety indicator set, including local intrusion, cell strain, separator damage, internal short-circuit risk, and module displacement. The final stage is post-crash function, including venting space, thermal path integrity, electrical isolation, water sealing, inspection, and repairability. This staging matters because a design can absorb energy efficiently yet remain unsafe if it transfers a high local load into cells or loses thermal and sealing functions after the crash.

For each included study, the synthesis extracted the design family, load case, scale of validation, and reported performance metric when available. The most useful metrics were mass reduction, maximum intrusion, peak force, specific energy absorption, modal frequency, local cell deformation, and thermal response after mechanical abuse. Because the included studies use different vehicle geometries, cell formats, impactors, boundary conditions, and optimization objectives, direct numerical normalization across all studies is not appropriate. Quantitative results are therefore reported in their original study-specific context, while cross-study comparisons emphasize relative changes against the corresponding baseline designs.

3 Localized crash scenarios: bottom strike and side-pole collision

Localized underbody loading is used here as an umbrella term that includes dynamic road-debris impact, bottom strike, and lower-speed ground or curb contact. Although these events differ in loading rate, they share a localized contact feature: the lower shield and tray must spread the load before the module floor or cell group becomes the effective hard stop. The lower shield, tray floor, ribs, cross members, module base, and cell layout determine whether a small contact load is spread into a broad structural path or concentrated into a few cells. Xia et al. (2014) showed that ground impact can damage cells and packs through localized indentation and load transfer, while dynamic cell-impact tests demonstrate that loading rate and format affect the onset of failure (Kisters et al., 2017). For enclosure design, this means that a thick plate is not always the best answer. A better bottom protector combines a hard contact face, a crushable or load-spreading core, and an upper boundary that keeps cell strain below damaging levels.

Side-pole collision is a lateral intrusion and load-path problem. A pole can bypass broad frontal crash structures and push loads through the rocker, sill, side rail, battery wall, and module edge. Setiawan and Salim (2017) showed how side-pole crashworthiness design can reduce deformation in an electric city car, and Moghaddam et al. (2023) proposed an integrated energy-absorbing module for battery protection under lateral pole impact. The design difficulty is that added side protection must start crushing early enough to absorb energy, but not so stiffly that it creates a hard point near the cells. Lateral protectors therefore need progressive folding, stable interaction with body-side members, and compatibility with service access. Relevant assessment outputs include lateral intrusion at the enclosure wall, energy absorbed before module contact, load transferred through the rocker and cross members, peak acceleration or force transmitted to the module edge, and residual clearance after deformation.

The two scenarios should not be merged into a generic crashworthiness target. Bottom strike and localized underbody loading need puncture resistance, distributed bearing, local crush management, and tolerance to repeated underbody events. Side-pole collision needs lateral crush distance, sill and cross-member load sharing, and intrusion control before deformation reaches the module boundary. A common enclosure can serve both roles only if its geometry is locally tuned: stiff where penetration must be blocked, ductile where energy must be dissipated, and inspectable where post-impact damage decisions are needed. This is why recent enclosure concepts increasingly use graded ribs, foam-filled or cellular inserts, and hybrid side structures rather than uniform wall thickening.

Vehicle architecture also changes the feasible design space. A skateboard platform may provide broad underfloor area but little vertical clearance, whereas a body-integrated pack may use cross members and side sills as part of the enclosure load path. For bottom strike, the critical question is whether the lower protector can spread a concentrated load before the module floor becomes the hard stop. For side-pole collision, the question is whether the side protection can cooperate with the rocker and floor without forcing an early load peak into the module edge. This architecture dependence explains why enclosure results should not be transferred between vehicle platforms without checking boundary conditions.

4 Lightweight enclosure solutions and energy-absorbing architectures

Aluminum alloys remain the most practical lightweight baseline because extrusion, casting, forming, welding, and adhesive bonding are mature in automotive production. Aluminum trays and side profiles can place material along load paths, while hollow members can be tuned for progressive collapse. The weakness is local indentation and joint sensitivity. Adhesively bonded aluminum structures depend strongly on surface preparation, ageing, and service exposure (Cavezza et al., 2020). High-strength steel and advanced high-strength steel should not be excluded from lightweight enclosure design, especially in local puncture-resistant shields, side rails, and hybrid metal frames where ductility, cost, and joining robustness may outweigh density alone (Pan et al., 2021). Foam-filled aluminum concepts address this by stabilizing crushing. Yay et al. (2025) reported improved specific energy absorption and reduced peak crushing force in optimized aluminum foam-filled battery boxes, and Farzaneh et al. (2024) used aluminum tubes filled with phase-change material to combine energy absorption with temperature reduction.

Composite enclosures can reduce mass when stiffness, intrusion, and joint requirements are satisfied under equivalent boundary conditions, but their safety value depends on controlled failure rather than material density alone. Finite element studies of carbon-fiber enclosures reported strong mass-saving potential relative to aluminum baselines (Kulkarni et al., 2023), and machine-learning-assisted organosheet design has been used to explore crashworthy composite layouts efficiently (Shaikh et al., 2024). Ma et al. (2024) further connected carbon-fiber battery-pack design with manufacturing optimization, which is important because layup, forming, trimming, inserts, and joining often determine industrial feasibility. The main risks are brittle fracture, delamination, bolt-hole failure, difficult repair, and uncertain end-of-life routes. Life-cycle assessment of a composite battery enclosure prototype confirms that lightweighting should be judged together with embodied impact and recyclability, not by mass alone (De Sio et al., 2025).

Sandwich, honeycomb, lattice, and bio-inspired structures are attractive because geometry can tune stiffness, force level, and crush distance. Honeycomb enclosure studies show that mass and vibration behavior can be improved when the core is designed around the battery-pack load path (Dhoke and Dalavi, 2024). Nature-inspired cellular compartments and broader reviews of bio-inspired energy absorbers also show that graded or hierarchical structures can produce stable crushing without excessive mass (Mudassir et al., 2020; Ha and Lu, 2020). For bottom strike, the lower face sheet should resist puncture, the core should crush progressively, and the upper face sheet should distribute residual load away from cells. For side-pole collision, the same logic shifts to side rails or side walls, where the core must crush laterally while preserving the joint line.

Auxetic and negative-Poisson-ratio structures can promote lateral densification and improve resistance to localized intrusion, but this benefit is sensitive to unit-cell orientation, boundary confinement, strain-rate effects, and manufacturing defects. Biharta et al. (2022) designed lightweight protectors with 3D auxetic meta-structures, Scurtu et al. (2023) studied an auxetic auxiliary battery-case structure, and Wang et al. (2021) proposed a negative-Poisson-ratio pack system that considered crashworthiness and heat dissipation together. Hybrid honeycomb-auxetic side profiles have also been optimized for battery-box lightweighting and crashworthiness (Arslan and Karamangil, 2025). These concepts are promising, but they should be judged by manufacturable cell size, crush repeatability, strain-rate sensitivity, debris clogging, and repair after a non-catastrophic strike.

A practical material ranking should therefore begin with the expected deformation mode rather than with density alone. If the design goal is to block puncture, a hard lower face and local reinforcement may matter more than a low average mass. If the goal is to reduce peak side intrusion, a ductile crush member or foam-filled profile may be preferable to a very stiff composite wall. If the goal is to save mass in broad areas away from severe contact, sandwich or composite panels may be efficient. The strongest enclosure concepts combine these roles locally, using different structural mechanisms at the bottom shield, side rail, cross member, and module interface. Table 1 summarizes the main design routes in terms of preferred load case, protection mechanism, key risk, and required validation.

TABLE 1. Lightweight enclosure design routes and validation focus under bottom strike and side-pole collision.

Table 2 highlights the different performance trade-offs among representative enclosure concepts. Metallic optimization provides moderate mass reduction while retaining mature manufacturing routes, whereas auxetic, hybrid, and foam-filled structures offer greater opportunities for localized intrusion control and energy absorption. For example, the foam-filled design reported by Yay et al. increased SEA by 40.76%–50.71% while reducing peak crushing force by 8.45%–11.56%. However, these values cannot be ranked directly because the studies adopted different impact conditions, geometries, and baseline designs. The comparison therefore emphasizes the need to evaluate lightweighting together with intrusion, energy absorption, peak force, and cell-clearance requirements.

TABLE 2. Representative quantitative performance of lightweight and crashworthy battery-enclosure concepts.

5 Crash-thermal coupling, validation and manufacturability

Mechanical deformation is relevant because it can trigger electrical and thermal hazards. Cell abuse reviews link indentation, bending, separator damage, and internal short circuit to heat generation and possible thermal runaway (Liu et al., 2020). At the electrode-material level, battery durability and safety are also governed by coupled structural, interfacial, and mechanical degradation, including lattice instability, interfacial side reactions, oxygen loss, and particle cracking (Liu et al., 2026). Battery fire and crash-safety reviews further show that propagation, suppression, occupant hazards, and incident handling depend on how damage evolves after the initiating event (Sun et al., 2020; Gong et al., 2022). In this review, thermal coupling refers mainly to post-abuse thermal safety rather than normal-operation battery thermal management. The key question is whether the enclosure still preserves venting, heat-spreading, and isolation functions after mechanical deformation. For an enclosure, the implication is direct: maximum tray displacement is not enough. A bottom shield or side wall should also preserve venting clearance, heat-spreading paths, isolation distance, sealing, and inspection access after deformation. Multifunctional concepts such as phase-change-filled aluminum tubes are promising because they suggest that the same protective volume may contribute to both crash absorption and thermal moderation, provided that post-impact integrity is retained (Farzaneh et al., 2024).

Validation should be hierarchical. Full-vehicle models are needed to obtain realistic boundary conditions for bottom and side impacts; pack submodels resolve enclosure ribs, joints, inserts, and module motion; cell or module models translate local deformation into safety indicators. Cell-level criteria should be calibrated with mechanical-abuse data that specify state of charge, temperature, loading rate, cell format, and failure definition, because these variables strongly affect the transition from deformation to internal short-circuit risk. Optimization studies have already used structural mass, intrusion, modal frequency, energy absorption, and crash responses as competing objectives (Shui et al., 2018; Pan et al., 2022; Lian et al., 2024). The next step is to align those objectives with abuse-test evidence and standards. Kotak et al. (2021) argued that battery crush procedures require augmentation and harmonisation, and Abdisobbouhi et al. (2026) made a broader call for harmonized lithium-ion battery safety testing. GB 38031-2025 adds a timely regulatory anchor for traction battery safety in China (GB 38031-2025, 2025).

Manufacturability can overturn an otherwise attractive design. Large castings, extruded rails, stamped shields, pultruded profiles, organosheets, bonded joints, and printed lattices differ in tolerance control, cycle time, corrosion behavior, cost, and repairability. A topology that performs well in simulation but needs slow additive manufacturing or inaccessible bonding surfaces may be unsuitable for mass production. For liquid-cooled packs, post-impact coolant leakage and sealing degradation should be treated as safety-relevant outcomes, because coolant loss or ingress can interact with electrical isolation and delayed thermal hazards. The most credible enclosure concepts are therefore hybrid and modular: metallic load paths for ductile crash response and joining, local composite or sandwich panels for mass reduction, and replaceable protectors where road-debris damage is expected. Such systems should be validated not only for the first impact, but also for residual stiffness, leakage, electrical isolation, and post-impact service decisions.

The same point applies to numerical modeling. Many enclosure papers use simplified battery modules or rigid cell blocks to reduce model size, which is reasonable during concept screening. However, final design decisions need a traceable link between structural response and cell safety. A useful workflow is to start with full-vehicle boundary conditions, extract critical pack deformation, refine a pack submodel around the impact region, and then use calibrated cell or module criteria to interpret the risk. This avoids two common errors: optimizing a tray without realistic vehicle load paths, and declaring a cell-safe design from a shell displacement metric alone. For liquid-cooled packs, the same validation chain should also check coolant leakage and insulation degradation after mechanical loading.

6 Discussion and future directions

Four gaps limit current enclosure research. First, metrics remain uneven across studies. One paper reports mass reduction, another reports peak force, another reports specific energy absorption, and another reports cell damage. These metrics are useful, but they are not interchangeable. A bottom-impact design should report local indentation, penetration resistance, residual module clearance, and cell strain risk. A side-pole design should report lateral intrusion, load transfer through body-side members, crush mode stability, and module boundary deformation. Without scenario-specific metrics, lightweighting can be mistaken for safety improvement. A minimum reporting set is needed for enclosure studies: mass change relative to baseline, local intrusion, residual module clearance, energy absorbed before module contact, maximum cell or module deformation indicator, leakage or sealing status, electrical isolation, and post-impact thermal-safety check.

Second, crash and thermal safety are still too often validated in separate silos. Battery enclosures experience coupled abuse: a mechanical strike may damage cells, distort venting paths, reduce insulation distance, and create delayed thermal risk. Future studies should therefore report mechanical deformation together with thermal propagation indicators, electrical isolation, and post-impact inspection criteria. This does not require every study to build a full electrochemical-thermal model. It does require clear thresholds that connect enclosure deformation to cell or module safety evidence.

Third, advanced architectures need production realism. Auxetic lattices, graded honeycombs, and bio-inspired cores can look compelling in a unit-cell study, but vehicle enclosures need meter-scale repeatability, corrosion control, debris tolerance, joining reliability, and repair routes. Hybrid designs are likely to be more deployable than single exotic materials: aluminum or steel frames can carry global loads, while composite, foam, honeycomb, or auxetic inserts can be placed only where local bottom or side intrusion risk is high. This approach also supports modular replacement after a minor underbody strike.

Finally, standards-based validation must move closer to realistic localized loading. Simplified cell blocks are useful during conceptual optimization, but they cannot directly predict separator damage, internal short circuit, or delayed thermal failure. Future studies should establish calibrated multiscale criteria that connect enclosure intrusion and module deformation with experimentally validated cell-level failure thresholds. Although new material and topology concepts remain valuable, the more urgent bottleneck is scenario-level validation that proves a design remains safe across localized mechanical loading and post-impact functional requirements. A useful future benchmark would pair a mechanical load case with cell-level safety criteria and post-impact functional checks. That benchmark would help distinguish a light enclosure that merely survives a simulation from a protective system that remains safe, inspectable, and manufacturable.

7 Conclusion

Lightweight battery enclosure design for electric vehicles is best framed as staged protection under localized impact. Bottom strike requires puncture resistance, load spreading, and controlled local crush before deformation reaches cells. Side-pole collision requires lateral load paths, stable progressive absorption, and early intrusion arrest around the module boundary. Aluminum alloys, composites, foam-filled members, sandwich panels, honeycomb cores, auxetic lattices, and bio-inspired structures can all help, but none is sufficient by itself. The next-generation of enclosure design should combine manufacturable hybrid structures with cell-aware deformation limits, thermal propagation mitigation, electrical isolation, and post-impact repair or inspection logic. Progress toward practical adoption therefore depends less on identifying another isolated lightweight material and more on establishing comparable scenario-specific metrics, calibrated cell-level failure criteria, manufacturable hybrid architectures, and standards-linked post-impact validation.

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Footnotes

Edited by: Adel Razek, UMR8507 Laboratoire Génie électrique et électronique de Paris (GeePs), France

Reviewed by: Pankaj Shrivastava, University of South Africa, South Africa

Fady A. Elshazly, Independent, Sacramento, United States