Start-up looks to extend battery life

Intel-backed start-up ZPower may be the first to introduce an alternative to the ubiquitous lithium-ion laptop battery, with a silver-zinc technology the company says will make its debut with a large laptop maker in 2009.

The company promises up to 40 percent more run time than current lithium-ion batteries, and says its batteries are 95 percent recyclable.

ZPower made the announcement ahead of the Batteries 2008 conference in Nice, France, which began on Wednesday, and where ZPower's chief executive and president, Dr Ross E Dueber, will be presenting ZPower's take on silver-zinc technology, also known as silver-oxide.

Silver-zinc batteries were initially developed for aircraft, and were used to power the Apollo spacecraft, as well as finding their way into torpedoes and the US Alfa class submarine.

ZPower has also improved the batteries to be good for more than 200 cycles at full discharge. While this is an improvement over older silver-zinc technology, it is still lower than lithium-ion batteries, which laptop makers say should last for 300 to 500 cycles at full discharge. However, the charge silver-zinc retains is longer, so you can the battery for longer before it needs a recharge.

The lack of lithium and a water-based chemistry means silver-zinc batteries are not susceptible to the inflammability issues that have plagued some lithium-ion batteries, and that caused widespread laptop battery recalls last year, ZPower said.

Due to the high cost of silver, silver-zinc batteries have never come into large-scale consumer use except for in small 'button' cells, for example watch batteries. ZPower said it plans to offset this cost through a trade-in policy that will reduce the need to mine for new materials. Ninety-five percent of the key materials in the batteries are recyclable and reusable, and the raw materials recovered in the recycling process are of the same quality as those used to create the battery, ZPower said.

Another traditional concern with silver-zinc batteries is mercury leakage. Mercury has been traditionally used in the batteries to suppress zinc corrosion, which leads to hydrogen production and deformation of the shape of the battery. The poisonous mercury left in such cells at the end of their useful lives is a serious ecological concern.

ZPower said it has addressed shape-change problems with its zinc anode, a composite polymer electrode that inhibits both shape change and the growth of dendrites, a problem for silver-zinc batteries as well as other battery technologies.

Other innovations in the batteries are a new separator stack that resists dendrite growth and silver cathode degradation, and a nano particle coating on the silver cathode that is designed to enhance conductivity, ZPower said.

ZPower, which counts Intel as one of its main financial backers, first demonstrated its technology at the Intel Developer Forum in August.

Battery life has remained a major issue for powering laptops and consumer electronics, with electronics makers looking to extend the length of a charge via techniques such as silicon nanowires or simply by making other parts of the device, such as the screen and the disk drive, more efficient.

Environmental impact has also been a serious concern, since most batteries end up in a landfill; currently less than two percent of consumer batteries are collected when they become waste, according to Defra. The EU is attempting to encourage battery recycling via a revised Batteries Directive, which became law in EU member states in late September.