NOVELTY - Thermal runaway suppression component (18) for interposition between cells (10) of multiple-cell battery pack comprises container (26) conforming to external surfaces of cells, such that container is in good thermal conductive relation with cells; and phase change material (28) comprising water in hydrogel form, disposed in container. In the event that one of cells overheats, heat is transferred to hydrogel, heating the water, such that water absorbs heat given off by overheated cell, and water can undergo phase change and be vaporized if sufficiently heated.    USE - Thermal runaway suppression component for interposition between the cells (i.e. of lithium-ion battery chemistry) of a multiple-cell battery pack, useful for suppressing thermal runaway of battery pack (claimed) e.g. for hybrid electric cars.    ADVANTAGE - The thermal runaway suppression component uses components that are simple, low in cost, and relatively easy to mass manufacture. The hydrated hydrogel of the thermal suppression component is retained in a pouch or other container adapted to fit closely between the cells of the battery pack. As the water is retained in the gel, it is not dispersed if the container is melted, torn, or ruptured, and thus retains its heat-absorptive qualities should a cell vent, melt, or rupture. As compared to waxes or paraffins used in the prior art, water exhibits higher specific heat, such that it is capable of absorbing more heat per unit mass than such materials without phase change. The amount of heating required to cause phase change in water, i.e. from liquid to gas, is much higher than that required to melt wax, i.e. much more heat is required to cause water to undergo phase change from liquid to gas than to melt wax. Water is not flammable; waxes can catch fire contrary to the goal of preventing thermal runaway. Even when prepared as a gel, water is much less expensive than waxes. Water has a relatively high specific heat, i.e. more heat (4.18 kJ/(kg.K)) is required to warm a given amount of water to a given degree than for wax (3.4 kJ/(kg.K)). Thus, a given amount of water can absorb more heat than an equal mass of wax. Particularly, because water comprised by the hydrogel must be heated from ambient temperature, typically 20 degrees C to its boiling point of 100 degrees C, before phase change, i.e. vaporization, takes place, far more total heat absorptive capacity is provided than is required to melt an equivalent amount of wax, which melts at 60 degrees C. The amount of energy required to melt paraffin wax is 195 kJ/kg, while that required to vaporize water is 2260 kJ/kg. Thus, use of water in lieu of wax provides more than 10 times the heat absorptive capability for equal weight of phase-change material used before phase change takes place. The thermal runaway suppression component effectively smoothes the peak temperatures reached by battery cells in pulsed-power applications by the provision of sensible heat storage in the superabsorbent polymer hydrogel. Service lifetime is increased.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a battery pack; and    (2) a method of suppressing thermal runaway of battery pack.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view showing thermal suppression components that can be assembled in a multi-cell battery pack.    Cells (10)    Circuit boards (12)    Thermal runaway suppression component (18)    Container (26)    Phase change material (28)