|For PHEV20 batteries, TIAX found significant overlap in battery costs among five cathode classes, with wider variation within each chemistry based on the electrode design than between chemistries. Source: TIAX. Click to enlarge.|
At the Department of Energy’s 2011 Hydrogen and Fuel Cells and Vehicle Technologies Programs combined annual merit review being held this week in Washington, DC, researchers presented results of two ongoing studies exploring the costs of three classes of battery packs: LEESS (Lower-Energy Energy Storage Systems—i.e., for power-assisted hybrids, earlier post) and PHEV20 (plug-in hybrid with 20-mile electric range) (study led by TIAX, LLC); and PHEV40 (plug-in hybrid with 40-mile electric range) (study led by Argonne National Laboratory).
PHEV20. TIAX employed a parametric approach in which it applied its cost model many times with different sets of input parameters, including pack energy requirements; power input/output; battery chemistries and material performance; electrode designs; fade and SOC (state of charge) range; and sufficiently high production volume.
For PHEV20, the program focused on both commercially available and emerging cathode materials aimed for use in a 20-mile PHEV battery pack. Costs were modeled for a 300V PHEV battery pack that could provide 5.5 kWh of usable energy storage, satisfying drive cycle requirements over the 20-mile urban drive cycle. Cells were designed for a range of electrode loadings (1.5–3 mAh/cm2) and fade characteristics (0 and 30%), assuming an 80% operating SOC range.
TIAX considered five classes of cathode materials: NCA (lithium nickel-cobalt-aluminum oxide); NCM (lithium nickel-cobalt-manganese oxide); LMO (lithium manganese spinel); LFP (lithium iron phosphate); and LL-NMC (layered-layered lithium nickel manganese cobalt oxide).
They found that there is significant overlap in battery costs among the five cathode classes, with wider variation within each chemistry based on the electrode design than between chemistries. Systems costs ranged from about 250 – 700 $/kWh.
Other findings of the study include:
Materials account for 60-70% of the final PHEV battery pack cost, with the cathode active material contributing 15-30%.
Cell formation and aging, anode and cathode coating and drying, and winding account for as much as 70% of the total processing costs.
TIAX concluded that the results point to a three-pronged approach in emphasizing specific areas of research with potential for reductions in battery cost:
Materials. Materials that support high power, and a wide SOC range; that provide minimal fade, impedance growth and calendar aging; and with higher specific capacity and higher average cell voltage.
Cell/electrode. New chemistry, electrolytes, and electrode designs permitting shorter, thicker electrodes. In general, chemistries and designs that enable lower overall electrode area per battery and minimize battery size will reduce cost.
Manufacturing. Identification and adoption of advanced processing technologies to significantly increase coater/dryer speed and/or other unit operations significantly, as well as fundamentally different electrode preparation processes. (The last a point further elaborated upon in subsequent technology presentations.)
LEESS. In 2009, USABC outlined requirements for a Lower-Energy Electric Storage System for power-assisted hybrid electric vehicles (PAHEV) that resulted in generally higher power, with significant reductions in system weight, volume and energy. The (LEESS) targets added 2-second discharge and regen pulses, and significantly increased the 10-second regen pulse requirement. The new targets generally involve substantial increases in power to energy ratio for the batteries.
This requirement, in turn, leads to the need for utilization of very thin electrodes with low active material loadings. TIAX took three approaches to defining batteries it could model for this project.
Parametric. TIAX modelled several candidate energy window ranges over which power requirements can be met and investigate consequences for selected chemistries and electrode designs.
Experimental. TIAX selected candidate alternative chemistries and electrode designs and determined appropriate energy window ranges over which power goals can be met.
Benchmark/extrapolation of commercial systems. TIAX selected candidate commercial systems and used their specifications to size them for LEESS applications.
One issue for LEESS, TIAX noted, is the extent to which the battery must be over-sized with respect to energy in order to deliver the required power and life. For the exercise, the company selected two material combinations were selected one representing lower power, higher energy (NCA and hard carbon) and one representing higher power, lower energy (LMO/LTO).
For all cell designs considered, total cell weight ranged between 6 and 25kg and total cell volume ranges between 4 and 14L, thereby generally meeting the LEESS weight and volume targets.
|Modelled costs of LEESS systems. Source: TIAX. Click to enlarge.|
For cell designs considered, TIAX found that the modeled “high volume” LEESS system costs range between $675 and $1,575.
Unlike for PHEV batteries, the cost of the LEESS batteries are dominated by battery management electronics and cell formation and aging operation, TIAX noted. Battery management electronics components account for 30-60% of materials costs, for example.
TIAX experimental data show that the likely energy window operating range is between 17% and 36%, necessitating substantial over-sizing of LEESS packs.
|Modelling battery cost. Source: ANL. Click to enlarge.|
PHEV 40. The orientation of the Argonne project was a bit different, in that its objective was to develop an efficient available simulation and design tool to predict:
- Precise overall (and component) mass and dimensions
- Cost and performance characteristics
- Battery pack values from bench-scale results
They developed a fully integrated model to design and predict high volume costs for PHEVs, as well as HEVs & EVs, based on user-defined requirements (pack voltage, power, efficiency, cell chemistry). They also documented the design and cost calculation methodology to support peer-review and free and open distribution of the Li-ion battery design and cost model. The model will be rolled out to the public this summer.
Applying the model to a PHEV40, the team assumed a 17 kWh pack, with 40 kW max power achieved at 80% of open-circuit voltage (OCV) and 70% useable capacity. Pack OCV at 50% state of charge would be 360 ± 15V (80-144 cells in series). Maximum electrode thickness was µm100.
|Path forward for Li-based batteries. Source: ANL. Click to enlarge.|
The model determined that the cost to an OEM of the pack could range from 222–301 $/kWhtotal for established chemistries and from 183–193 $/kWhtotal for advanced Li-ion chemistries. Given the pack specification, this worked out to a pack cost to OEM ranging from $3,112 to $5,125.
The Argonne team noted that large format cells and large electrode thicknesses reduce the contribution of inactive materials to total cost of PHEV batteries.
The researchers noted that if high-risk research is successful, then a 60% reduction in battery cost and 260% increase in energy density is possible from materials advances by 2025.
(Presentations from the Merit Review will be available online in several weeks.)
Brian Barnett, Jane Rempel, Chris McCoy, Sharon Dalton-Castor, Suresh Sriramulu (TIAX) PHEV and LEESS Battery Cost Assessment (ES001)
Kevin G. Gallagher, Dennis Dees and Paul Nelson (ANL) PHEV Battery Cost Assessment (ES111)