用热量延长电池寿命

Don't go sticking your electronic devices in a toaster oven just yet, but for a longer-lasting battery, you might someday heat them up when not in use. Over time, the electrodes inside a rechargeable battery cell can grow tiny, branch-like filaments called dendrites, causing short circuits that kill the battery or even ignite it in flames. But thanks to new experiments and computer simulations, researchers from the California Institute of Technology have explored in detail how higher temperatures can break down these dendrites -- and possibly extend battery lifetimes. A battery cell consists of a positive and negative electrode, called the cathode and anode. As the battery produces electrical current, electrons flow from the anode through a circuit outside the battery and back into the cathode. Having lost the electrons that are generating the current, some of the atoms in the anode -- an electrically conductive metal like lithium -- become ions that then travel to the cathode, moving through a conductive liquid medium called an electrolyte.

Recharging the battery reverses the process, and the ions travel back and stick onto the anode. But when they do, the ions don't attach evenly. Instead, they form microscopic bumps that eventually grow into long branches after multiple recharging cycles. When these dendrites reach and contact the cathode, they form a short circuit. Electrical current now flows across the dendrites instead of the external circuit, rendering the battery useless and dead. 

The current also heats up the dendrites, and because the electrolyte tends to be flammable, the dendrites can ignite. Even if the dendrites don't short circuit the battery, they can break off from the anode entirely and float around in the electrolyte. In this way, the anode loses material, and the battery can't store as much energy.