Although lithium-ion will become the preferred battery technology at some point in the future, there are still important risks and challenges in the short term that will keep overall penetration of the chemistry to less than 5% of the hybrid vehicle market by 2009, according to Menahem Anderman, president of Advanced Automotive Batteries.
Anderman was speaking at the SAE Hybrid Vehicle Technologies 2007 Symposium in San Diego to provide an overview of the opportunities and challenges for li-ion in the hybrid electric vehicle market. Last week, Anderman testified before the US Senate Committee on Energy and Natural resources in a hearing on Transportation Sector Fuel Efficiency.
Lithium-ion batteries offer higher power and energy per unit weight and volume, and better charge efficiency than NiMH batteries. Thus, if they can maintain performance over life, smaller and lighter batteries can be used in given applications. These attributes allowed them to capture a major part of the portable rechargeable battery market—which requires a battery life of only 2 to 3 years—within a few years of their introduction, and to generate global sales estimated at $5 billion in 2006. Nevertheless, the reliability of lithium-ion technology for automotive applications is not proven—unfriendly failure modes, for example, are a concern—and its current cost is higher than that of NiMH.
Cost is a major concern of the industry, and one expressed by other speakers at the Symposium. Anderman listed four primary challenges for lithium-ion batteries for the HEV market, all coming back to cost: cost of the battery at initial manufacturing volumes, safety, manufacturing reliability and life.
There are four major questions that manufacturers need to address, according to Anderman: cathode material, cell structure, manufacturing, and pack design and application.
Cathode selection. While LiNiCoAlO2 is the most proven cathode material, it is also the most thermally unstable at high states of charge. LiNoCoMnO2 is gaining momentum, but there is not much durability data yet. The newer LiMn2O4 materials are better, according to Anderman, but the issue of life at elevated temperatures has not been solved. LiFePO4 materials are the most thermally stable, yet deliver lower voltage and lower energy. Cost and life are not clear yet.
The latest trend is to use blends of materials—more than 50% of new cathode materials emerging are using some form of blended material, Anderman said, hoping that 0.5 + 0.5 is greater than 1.0.
Cell structure. Cell makers use either a spirally wound cylindrical structure which offers the best manufacturability; a spirally wound elliptic structure, which is easier to package and to cool; or stacked plates, which enable uniform compression but require more handling.
In addition there is the packaging issue: hard can versus pouch (soft). There is some question, according to Anderman, as to the ability of pouch packaging to support the life required of the battery in a vehicular application.
Manufacturing. The latest concern among manufacturers has been metal impurities in the cell—the cause of the recent $450-million recall of li-ion batteries. To guarantee power, cell makers need to use long, thin electrodes. To guarantee safety, yield and reliability, manufacturers must be conservative in terms of coating specifications, thickness of separators, winding, welding, filling and closing. Furthermore, batteries for the hybrid applications are required to have a much longer life than batteries targeted at consumer applications. This all translates to high initial manufacturing costs.
Pack design and application. A number of questions emerge in this area, including cell balancing, overcharge protection, crush protection and temperature range.
What the automotive industry is looking for in a battery supplier, according to Anderman, is someone with large cell design competence, with high-volume production experience, a significant amount of life data available, automotive supply experience, and deep pockets.
All those attributes are not always found in a single provider. The auto industry’s experience with getting packs from cell makers has not been great, according to Anderman. As a result, some automakers are looking to partnerships between cell developers and pack developers.
A good recent example of this is the partnership between cell developer A123 Systems and pack developers Cobasys that is now supplying li-ion packs to GM for use in the Saturn VUE plug in work. (Earlier post.)
Anderman projects that some 783,000 hybrid vehicles will be sold in 2009, with more than 95% of those using NiMH battery systems—leaving about 38,000 units for lithium-ion. As a result, he projects that hybrid vehicle applications will represent more than 50% of the total NiMH battery market by then.