Storing a possibly damaged Li-Ion battery
The battery is likely less dangerous than the low internal resistance batteries used in RC models. Nevertheless, there is still a very small chance that it will short out internally, puff up, rupture, and burn the place to the ground, even spontaneously after some time. LiPo- and Li-Ion batteries can be rendered inert (chemically unable to enter thermal runaway) by discharging all cells to 0V.

In order to safely dispose of the battery, just submerge it in salt water. The conductive water will then find its way into and short out the terminals of each cell in the pack. After a few hours each cell should reach a potential of 0V, at which point the battery is completely safe.

For a less messy approach, you can connect a power resistor of a few ohms or even a flashlight bulb across each cell, for the same effect.