Disruptive battery separator technology challenges polyolefins

A separator technology based on polyimide nanofibe promises to produce a breakthrough in electric vehicle lithium ion battery technology while causing concern among current producers of polyolefin separators according to a report from Eldib Engineering and Research Inc. (Berkeley Heights,  NJ). The study issued by Eldib describes the advantages of DuPont's new Energain lithium ion battery separator.

DuPont's (Wilmington, DE) Energain separators reportedly afford 15-30% in power gain through their high temperature polyimide nano-diameter non-woven mat construction. After extensive testing and evaluation by a substantial number of auto OEM's and battery producers, the evaluators conclude that this new development will enable the LIB's in autos to be much lighter for the power needs,  and get longer driving range. In addition, DuPont claims Energain will realize longer battery life. The fibers used are made by electro blown spinning and hot air blowing of a polyimide solution

While not specifically claimed by DuPont, the properties of the high temperature non-woven mat suggests additional benefits for the batteries produced with Energain separators. These include: improved mileage of the electric vehicles (EVs), hybrid electric vehicles (HEVs) and plug-in (HEVs) for the same battery power as a result of the battery pack being significantly lighter in weight.

According to the Eldib Report, the polyimide non-woven nanofiber should be able to tolerate faster charging, a major concern with owners of electric cars. Time consumed for charging along with the limited driving range have been deterrents to acceptance of EV's.

Additional benefits should arise from the lower raw material cost (especially lithium) resulting from fewer cells being needed to supply the power needs. The battery would be expected to have improved cold cranking and also to possess improved ability to capture power from regenerative braking.

All of these benefits come at a higher separator cost compared with the competitive separators made by the Celgard dry process and Exxon Mobil Tonen wet process, both using porous polyolefins as the separator sheets.

DuPont is investing in a plant capable of supplying 20% of the current global demand for LIB's in transportation. It iss clear that DuPont intends to be a major supplier for transportation batteries with a capacity able to provide enough separators for 100,000 to 200,00 hybrids and EVs according to Eldib.

Energain separators also are said to extend battery life. LiB battery depreciation may be of the order of 5¢/mi so that increased battery life would become a significant factor, in that longer  battery life serves to lower net operating costs for EVs and HEVs.

The Energain process for producing LIB separators is significantly more costly than the current wet or dry process producing polyolefin films  now in use, but the fewer cells needed for autos would lower cost of the battery pack. Eldib is analyzing the process cost for producing Energain non-woven nano fiber and in the analysis is taking into account the associated peripheral beneficial costs of the cells, and the total battery costs. In addition, the cost savings resulting from the lighter battery pack in the EV and PHEV is being examined.

The combination of benefits from a lighter weight battery for the same power serve to yield improved driving range, better acceleration and improved mileage. In effect this technology imparts the same benefits as targeted  by auto manufacturers as they strive to light weight their cars for improving mileage and performance.

Eldib sees Energain as a "break through technology" which could well be expected to slash LIB battery costs for transportation to the degree that would  kick start a current lagging interest in EVs and PHEVs in the US and Europe. At the same time Energain, could cause marketing concerns among current producers of polyolefin-type separators. The extent of impact will depend on DuPont's marketing practices as they begin marketing Energain non-woven separator mat from their new plant being completed in Spruance, VA.

For perspective, Andrew Eldib the researcher-in-chief of this study says it is interesting to note that a European battery manufacturer has been given $4.7 million by EU to achieve the similar goals of weight reduction, volume reduction, and cost reduction that are realized through Energain separator technology.-[email protected]