Side-impact protection of floor-mounted battery packs in electric vehicles: a review of load-path design, energy absorption, and lightweight optimisation

Floor-mounted battery packs improve packaging efficiency and lower the centre of gravity of battery electric vehicles, but the limited lateral crush space leaves the cells vulnerable to localised lateral intrusion. Side-pole and low-height obstacle impacts are therefore particularly demanding crash scenarios because localised deformation can propagate from the rocker or sill into the pack perimeter, compress cells, damage separators, initiate internal short circuits, and potentially trigger thermal runaway. This review synthesises recent work on side-impact protection from a structural mechanics perspective and organises the literature into three sequential protection functions: redirecting concentrated loads through the body-in-white, absorbing residual energy at the pack perimeter, and redistributing the remaining load before it becomes localised in vulnerable cells. Particular emphasis is placed on linking conventional crash metrics — including intrusion, peak force, residual deformation, acceleration, and energy absorption — to battery-relevant failure indicators rather than treating these metrics as interchangeable proxies. Lightweight optimisation and cell-to-body integration are discussed as cross-cutting design problems with trade-offs in mass, occupant loading, repairability, and life-cycle cost. The synthesis indicates that effective battery protection depends on coordinated action across the vehicle, enclosure, and internal pack architecture, whereas improvements in numerical crash metrics alone do not establish cell safety.