11. TECHNOLOGIES RELATED TO ENERGY STORAGE FOR HYBRID AND PLUG-IN HYBRID ELECTRIC VEHICLES

 

Energy storage technology (batteries and/or electrochemical capacitors) represents one of the critical barriers to the development and marketing of cost-competitive hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs).   The energy storage requirements for these two types of vehicles are somewhat different:

 

 

 

All of these devices must be able to accept high power recharging pulses from regenerative braking.  For all systems, the materials to be utilized should be plentiful, have low cost (< $10/kg), be environmentally benign, and be easily recycled.  Evaluation of the technology with regard to the above criteria should be performed in accordance with applicable U.S. Advanced Battery Consortium test procedures or Society of Automotive Engineers recommended practices (see references that follow).  Grant applications must show how proposed innovations would result in significant advances in performance and cost reduction over state-of-the-art technologies. 

 

Grant applications are sought only in the following subtopics:

 

 

a. Technologies that Result in Cells with Increased Energy Density—Grant applications are sought to increase the energy density and specific energy of HEV and PHEV batteries by developing technology that will “stabilize” the surface of a lithium metal electrode in a rechargeable system.  The stabilization technology must allow the electrode to be deeply cycled at least a thousand times, without significant loss of active lithium and without the formation of lithium dendrites that might short the cell.  Possible approaches to this stabilization might include adding a “coating” on the surface of the lithium or an “additive” to the electrolyte in contact with the lithium.  The technical effort should focus on stabilizing the lithium surface under electrochemical cycling conditions that would be found in a vehicular battery.  It should be noted that the energy density and specific energy required of a battery designed for a PHEV application are greater than those for an HEV.  (The electrode must be able to charge and discharge at rates that are appropriate for a PHEV application.)  

 

Grant applications must:  (1) identify the nature of the electrochemical couple in which the electrode would be used (i.e., identify the positive electrode and electrolyte); (2) provide a theoretical basis for the research; (3) address the probable cost of using the technology in vehicular batteries; (4) address the impact of the technology on all performance parameters and assure that other performance requirements (e.g., cost, cycle life, calendar life, or abuse tolerance) will not be compromised; and (5) propose a Phase I project to demonstrate the technology by cycling a lithium metal electrode in a laboratory cell (whereas in Phase II, the cycling would be demonstrated on a scale and under conditions appropriate to a vehicular battery).  Grant applications dealing with lithium-ion systems or materials designed for use in a lithium-ion battery, or dealing with conductive polymer electrolytes designed to be used with a lithium metal electrode, are not of interest and will be declined.

 

Questions - contact James Barnes (james.barnes@ee.doe.gov) 

 

 

b. Development of Separators for Lithium-Ion Cells with High Temperature Melt Integrity —One of the concerns associated with the use of lithium-ion batteries in HEVs and PHEVs is the possibility of an internal short-circuit caused by the shrinkage of the separator at high temperatures.  This short-circuit mechanism has been postulated as follows:  (1) the battery becomes hot, causing (2) the separator in the cells begins to melt and shrink, which (3) allows the electrodes to short circuit, leading to (4) the cell going into thermal and/or electrochemical runaway and exhibiting unacceptable behavior.  Grant applications are sought to develop separators that will retain their integrity at temperatures of 200 degrees C or higher.  Proposed materials must meet all of the requirements for a lithium-ion separator (thickness, porosity, cost, etc.) at room temperature.  Grant applications must clearly define how “melt integrity” and other relevant properties will be evaluated and what performance will be expected in each area.  Also, a Phase I project should be proposed in which “coupon” size samples (10 cm2 or larger) of the new separator are prepared and evaluated .  In Phase II, the material would be refined, fully characterized, and prepared in quantities sufficient to allow the production of at least 100 vehicle-size cells using automated production equipment.  (The actual production of these cells is required under this development effort, but acceptance of the new separator for testing by a production company must be confirmed.)

 

Questions - contact James Barnes (james.barnes@ee.doe.gov)

 

 

c.  Development of “High Voltage” Electrolytes for Use in Advanced Lithium-Ion Cells—Batteries in PHEVs should have increased energy density and specific energy relative to the batteries now being used in HEVs.  For a lithium-ion cell, one approach to increasing these parameters is to use active materials in the positive electrode that undergo redox reactions relative to a lithium (or carbon) negative electrode at voltages significantly above 4 V.  However, state-of-the-art lithium-ion systems are rarely charged above about 4.2 V, because of undesirable side reactions.  At these voltages, currently-available electrolytes may decompose, even though the electrode materials remain stable.  Therefore, grant applications are sought to develop electrolytes (i.e., solvent mixtures plus conductive salts), for use in lithium-ion cells, that would operate at voltages of more that 4.8 V relative to lithium metal.  In Phase I, the stability of the new electrolytes must be confirmed instrumentally.  In Phase II, the electrolytes should be evaluated in lithium-ion cells of at least 1 Ah in size, using a positive electrode material that functions at more than 4.4 V relative to lithium metal.

 

Questions - contact James Barnes (james.barnes@ee.doe.gov)

 

 

d.  Development of “High Voltage” Positive Electrode Materials for Use in Advanced Lithium-Ion Cells—Batteries in PHEVs  have increased energy density and specific energy relative to the batteries now being used in HEVs.  For a lithium-ion cell, one approach to increasing these parameters is to use active materials in the positive electrode that undergo redox reactions relative to a lithium (or carbon) negative electrode at voltages significantly above 4 V.  However, state-of-the-art lithium-ion systems are rarely charged above about 4.2 V because of undesirable side reactions.  Many currently-available positive electrode materials are unstable at these higher voltages.  Therefore, grant applications are sought to develop positive electrode materials that would operate in a rechargeable cell at voltages of more that 4.8 V relative to lithium metal.  In Phase I, the stability and performance of the new material shall be confirmed in laboratory cells.  In Phase II, the materials should be evaluated in lithium-ion cells of at least 1 Ah in size, using an electrolyte that is stable enough to allow the assessment of the properties of the electrode material.  This electrolyte does not have to meet the requirements for use in a vehicle, such as calendar or cycle life.

 

Questions - contact James Barnes (james.barnes@ee.doe.gov) 

 

 

References:

 

1        Links to the following Manuals are available at: http://avt.inl.gov/energy_storage_lib.shtml.  These documents provide a good general basis for understanding the performance requirements for electric and hybrid electric vehicle energy storage devices.
· FreedomCAR 42V Battery Test Manual
· FreedomCAR Battery Test Manual for Power Assist Hybrid Electric Vehicles
· PNGV Battery Test Manual, Revision 3
· Electric Vehicle Capacitor Test Procedures
· USABC Electric Vehicle Battery Test Procedure Manual, Revision 2

 

2        The internet site for the Batteries for Advanced Transportation Technologies (BATT) program at http://berc.lbl.gov/BATT/BATT.html includes quarterly and annual reports. This program addresses many long-term issues related to lithium batteries, including new materials and basic issues related to abuse tolerance.

 

3        This site contains multiple references that summarize work supported by the FreedomCAR and Vehicle Technologies Program related to energy storage.  Prior to 2002, there are separate publications for the Energy Storage Effort and for Advanced Technology Development.  In more recent years, there is a combined report for Energy Storage.  These reports include information about cell chemistries that have proven to be useful model systems for these applications along with discussions of issues related to abuse tolerance and cell life.   http://www.eere.energy.gov/vehiclesandfuels/resources/ .

 

4        Information about requirements for vehicular batteries, separators for lithium-ion batteries, and abuse testing can all be found at the USABC section of the USCAR internet site.  Go to http://www.uscar.org/; click on “Teams”; under the USCAR Consortia section, click on “United States Advanced Battery Consortium (USABC)”. This site provides a second source for many of the documents found at reference 1.

 

5        Information on the FreedomCAR goals and test procedures for lithium-ion battery separators are available by email from Jim Barnes, e-mail: James.Barnes@ee.doe.gov.  If your email system will not accommodate files attached to a message, these documents can also be provided by fax.