Power/Performance Bits: Jan. 27

Improving batteries
By digging into the complex science behind the formation of dendrites that cause lithium-ion batteries to fail, research by Purdue University engineers could bring safer, longer-lasting batteries capable of being charged within minutes instead of hours.

According to the researchers, dendrites form on anode electrodes and may continue to grow until causing an internal short circuit, which results in battery failure and possible fire. They discovered that dendrites that grow in needlelike shapes may breach the separating barrier, destroying the battery, and are using numerical modeling to find ways to understand the dendrites and to design better separators.

They said they are trying to define the fundamental science behind these complex objects so that in collaboration with experimentalists they can make batteries that do not have this problem.

Research shows how groups of dendrites form and evolve and how individual dendrites interact with each other; simulations depict how dendrites sometimes detach from battery electrodes and become floating deposits, another potentially dangerous scenario that can cause a battery to catch on fire.

As such, the researchers created a modeling tool to helps battery makers design better separators.

Setting a quantum speed limit
UC Berkeley scientists have proved a fundamental relationship between energy and time that sets a “quantum speed limit” on processes ranging from quantum computing and tunneling to optical switching.

They explained that the energy-time uncertainty relationship is the flip side of the Heisenberg uncertainty principle, which sets limits on how precisely you can measure position and speed, which has been the bedrock of quantum mechanics for nearly 100 years. It has become so well-known that it has infected literature and popular culture with the idea that the act of observing affects what we observe.

This new derivation of the energy-time uncertainty has application for any measurement involving time, particularly in estimating the speed with which certain quantum processes – such as calculations in a quantum computer – will occur. It limits how precise clocks can be, and in a quantum computer, it limits how fast you can go from one state to the other, so it puts limits on the clock speed of the computer.

The speed limit, that is, the minimal time to transition between two easily distinguishable states, such as the north and south poles representing up and down states of a quantum spin (top), is characterized by a well-known relationship. But the speed limit between two states not entirely distinguishable, which correspond to states of arbitrary latitude and longitude whether on or within the sphere of all possible states of a quantum spin (bottom), was unknown until two UC Berkeley chemical physicists calculated it. (Source: UC Berkeley)