> To make a battery safer, you reduce the ways it can give up that energy. well, not exactly: > [...] some batteries will give up their energy if they are pen

> To make a battery safer, you reduce the ways it can give up that energy. well, not exactly: > [...] some batteries will give up their energy if they are penetrated with a sharp object. Some won't. and your options for surviving punctures are essentially either: * make the battery store less energy, or * don't stack/roll the battery layers. the first is clearly a non-starter, the latter necessitates very flat & space wasting batteries. > [...] Some tolerate high temperatures, some don't. lithium based batteries chemistries are completely unfavorable to high temperatures. there is no way around this, without changing the chemistry of battery (which is likely an energy density decrease), or adding thermal mass to soak up extra heat for some finite duration. > Energy density is only loosely correlated with safety. ok, consider this scenario: say we found a battery chemistry is resilient to puncture. can tolerate hundreds of degrees of heat without issue, and can sustain the power required to drive an electric car. ultimately you have 50kwh battery with a positive and negative terminal. you could put a bar of copper over those terminals. one of two things is going to happen; * the copper will rapidly heat up and explode * the battery will rapidly heat up and its container will explode this battery is still very dangerous.