advanced battery technology

NEI Corporation has revealed that it is developing a lithium-ion battery where the electrolytes are dissolved in water instead of an organic solvent. The aqueous-based lithium-ion battery has the potential to eliminate the risks associated with state of the art lithium-ion batteries, where the organic solvents are highly flammable.

The aqueous-based lithium-ion battery has the potential to eliminate the risks associated with state of the art lithium-ion batteries, where the organic solvents are highly flammable. In the event of a battery overcharge or a short circuit, the organic solvents pose serious safety hazards. A number of cases of lithium batteries catching fire have been reported in recent years. Aqueous-based lithium-ion batteries also have the potential to significantly reduce cost, measured in terms of US$/kWh.

While the concept of a lithium-ion cell using a water-based electrolyte has been known and studied, a major limitation is the narrow electrochemical stability window for water, which restricts the cell voltage. For example, the electrochemical stability window for water is within the range of 0 to 1.25V; electrolysis of water occurs outside this voltage range. In contrast, organic solvent-based electrolytes are stable up to at least 4V. The lower the cell voltage is, the lower the energy density is, and consequently, water-based lithium-ion batteries have had low energy densities. Recently, NEI Corporation has developed new materials concepts that can overcome the voltage stability issue of water-based lithium-ion systems. The innovations pertain to the composition and morphology of the materials used in the lithium-ion cell. The aqueous-based technology is being developed with funding from the US Environmental Protection Agency’s Small Business Innovation Research (SBIR) Program.

NEI adds that it welcomes the opportunity to partner with a battery manufacturer to co-develop, test and qualify the water-based lithium-ion batteries.

Germany’s ASD Automatic Storage Device is to present its new hybrid battery, combining the strengths of stand-alone and grid-tie storage systems, at Intersolar 2014. Compared to existing batteries, the new device significantly raises a household’s degree of self-sufficiency, frequently to over 80%, the company claims.

Furthermore, the small number of components means that ASD’s new battery system is particularly cheap to produce and supply, typically costing 20–30% less than other lithium-ion batteries on the market, they add.

“All the existing battery systems on the market have pros and cons. We have managed to combine all the advantages in one storage system and avoid the many disadvantages. Homeowners can therefore truly use the power generated on site entirely for themselves, which is not an option with other battery systems,” explains Wolfram Walter, managing director of ASD. “By introducing our hybrid technology, we have taken another huge step towards making battery systems more efficient, and above all more cost-effective – which is a real milestone for electricity storage.”

Previously, homeowners had to choose between grid-tied and stand-alone storage systems. Houses with grid-connected systems draw power from the grid almost continuously, even when their batteries are fully charged. Stand-alone storage systems, on the other hand, disconnect the house completely from the public grid as soon as sufficient power is stored and then supply the home with power produced on site. However, these systems have one big disadvantage: if the battery no longer furnishes enough power to supply all the appliances in the home, the storage system is shut down and the house draws 100% of its electricity from the grid again. Conventional stand-alone battery systems therefore only allow either fully battery-based or grid operation, but not both at the same time.

The hybrid battery system combines the operating principles and advantages of both technologies: it works like a stand-alone system and disconnects the house from the grid for as long as its batteries are able to furnish sufficient power. The house thus needs no further power from external supplies and operates autonomously. At times when the battery capacity is insufficient, the system automatically procures the additional quantity of energy required from the power grid. By design, the system therefore combines both energy sources and thus utilises the maximum amount of battery power directly on site. This flow of current is regulated via a computer-controlled filter developed by ASD for the hybrid battery.

The operating principle of ASD’s hybrid battery significantly increases a household’s degree of self-sufficiency compared to that achieved with existing systems, frequently topping 80%. It takes less than a millisecond to switch between the two operating modes.

The battery is suitable for both AC and DC coupling. This enables more flexible planning than previous storage types, which are specifically designed for either AC or DC operation. The battery can be charged by photovoltaic installations, CHP plants and small wind powered generators alike.