Nano scale solution for large scale storage

Nanophosphate® is a cathode material for lithium ion batteries. It was originally developed by Professor Yet-Ming Chiang and his team at MIT. Over 100 MW of grid-scale storage systems using this patented technology have now been installed around the world exclusively by A123 Energy Solutions, including six recent projects in the UK with energy storage capacities ranging from 100 kWh to 5 MWh. The photograph below shows a 2.5 MVA/5 MWh system installed at a primary substation.

Nanophosphate-based batteries employ lithium iron phosphate (LiFePO4) chemistry but should not be confused with standard lithium iron phosphate, which has a lower power output and poorer durability. Nanophosphate is an engineered nanoscale material with specific structural and chemical properties designed to maximise the performance of lithium ion batteries. Traditional lithium ion batteries have high energy but low power. Nanophosphate technology greatly increases the cathode surface area in contact with the electrolyte, which allows greater power output capability while still delivering all the energy stored in the battery.

Another significant advantage of Nanophosphate as compared with traditional lithium ion systems is that it is much more stable chemically. When subjected to abusive conditions, such as high temperature or over voltage, traditional lithium ion cathode materials can degrade, producing an exothermic reaction that releases gaseous oxygen. This heat and oxygen can then combine with flammable electrolyte to support oxidation or combustion within the cell, known in the industry as thermal runaway. In contrast, Nanophosphate releases only a small amount of heat and oxygen under similar conditions and cells manufactured using Nanophosphate do not exhibit the thermal runaway that metal oxide lithium ion cells can experience.

Cycle life and calendar life are key metrics for any energy storage technology because they affect the overall usability, total cost of ownership and return on investment over time. Traditional battery chemistries require systems to be oversized so that, as the cells degrade and lose power, they still meet performance requirements at the end of use. Nanophosphate cells have low capacity loss and impedance growth over time allowing the battery storage systems to meet end-of-life power and energy requirements with minimal oversizing, saving on upfront cost. The technology can be charged to full state of charge with minimal impact on battery life unlike many alternatives, decreasing the total cost of ownership over time. In addition, the power capability is excellent at low state of charge resulting in more available useable energy.

Combining the advantages of high power capability across the entire state of charge range, cycle life and durability, and excellent safety characteristics, this nanoscale technology can now be applied to the grid, and is found exclusively in A123 Energy Solutions' multi-megawatt-scale Grid Storage SolutionTM (GSSTM). GSS can help integrate renewables into the existing grid infrastructure by performing ramp rate management or capacity firming. It can also be used to lower emissions from traditional power generation plant, reduce maintenance and capital costs, and increase asset value by enabling generators to sell power to the grid that was previously set aside for primary reserve or frequency control. It improves the reliability of the grid by performing highly accurate fast-response frequency regulation and other ancillary services. In addition, it can increase the utilisation factor of not only generation but also transmission and distribution assets.

A123 Energy Solutions is now a wholly owned subsidiary of the Wanxiang Group. The Wanxiang Group, which acquired nearly all of A123's businesses in January 2013, is one of China's largest non-state-owned enterprises, with about $16 billion in annual sales. The operational scale and financial strength of Wanxiang has provided the stability necessary for A123 to grow during a period of consolidation within the energy storage industry.

Author notes

Mark Moreton, sales director EMEA, A123 Energy Solutions, Stafford, UK