N151-073 TITLE: Enhanced Cell Designs for Improved Internal Heat Transfer for High Rate and Power Capable, Large-Format Batteries

TECHNOLOGY AREAS: Materials/Processes, Electronics, Weapons

ACQUISITION PROGRAM: Multi-Mission Energy Storage FNC, Railgun INP

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 5.4.c.(8) of the solicitation. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Optimize heat transfer and cell design for large, high rate Lithium (Li)-ion cells for supporting pulsed power applications.

DESCRIPTION: Energy storage is a key enabling subsystem for supporting future shipboard loads. To date, industry and academia have performed substantial innovative work that has resulted in a continuous improvement in energy density of batteries destined for high energy applications. However, the capability of the high energy cells and chemistries developed do not necessarily apply to the rates and modes of operations required for shipboard applications. High power batteries have also undergone beneficial development and improvement; however, these improvements have generally focused on new chemistries or battery designs which reduce impedance and increase energy density while retaining power. The missing developmental area in the space of large-format high power batteries is internal, cell-level thermal management. This has typically been a challenge in the large-format battery space because of the increased length scale over which thermal energy must transfer. However, large-format batteries are essential for simplified, more manageable large-scale systems. Within large-scale shipboard energy storage systems, reduction of the number of components and connectors will be key for ensuring reliability while minimizing Direct Current (DC) losses, particularly at high rate and deep discharge (high current). Large-format storage offers the potential for maximizing reliability and reducing maintenance requirements by minimizing connectivity and monitoring points. To reduce the number of components, the cell format must be increased beyond commercially available 18650 or 26650 cylindrical cells, while retaining or improving upon performance, density and thermal character, and focusing upon safer yet well-characterized chemistries, preferably phosphate or titanate-based approaches.

Increased scale of cells present unique challenges, particularly as operational rate and depth of discharge increases. Larger designs can present thermal resistance issues due to design attributes that impede heat flow in certain directions. As the operational rate increases to 10C or higher to support pulsed power and directed energy applications, these challenges are manifested further. The greater rate of heat generation and higher inefficiency (losses) cannot be easily removed from within the cell. Thus, as cell format increases, the pathway for thermal conduction outward from the cell becomes more resistive (as diameter and length increase). Reduction of the conduction pathway in large format cells is thus an important and desirable trait that requires innovative approaches and investment. This is the case for both cylindrical as well as prismatic designs.

Innovative approaches are desired to enable larger and higher capacity cells capable of performance and efficiency at rate (>10C). The intent is to minimize thermal resistance either through improved cell construction materials (not electrochemical couples or electrolytes), improved material interfaces, improved cell design/construction, or a combination thereof. Specifically, this is a hardware-oriented effort, and so emphasis is made on innovation in the hardware design approaches, as well as on the ability to prove the innovative hardware in a practical manner as early as Phase I. The end intent is reduced conduction path resistance within a large format cell of over 20Ah. Innovation is also necessary such that the cell energy density is minimally impacted with such re-design, so that the benefits at the system-level can be manifested.

PHASE I: Develop proof of concept of a large-format battery cell with innovative thermal approaches. This includes a workable chemistry and electrode approach at a reasonable hardware scale to demonstrate performance at rate. Such a demonstration cell shall include relevant conduction path lengths and support detailed modeling and simulation, or other approaches to indicate the performance of cells at scale, in accordance with the Phase II requirements. The Phase I goal is to deliver a small number of these innovative cells for abuse testing by either the vendor or the Navy in order to help identify weaknesses in the design.

In the Phase I Option, if awarded, a detailed design of the full scale cell shall be completed, based upon cell test results.

PHASE II: Develop, fabricate and demonstrate a cell and battery design suitable for operation at 1000V and 10C (thr) to 30C (obj), using 40�C liquid cooling only. The design shall be suitable for compact racking and operation in tight applications and in spaces with ambient temperatures up to 60�C. The design should be able to transfer heat to the cooling media in such a manner that upon completion of a full discharge (=80% DOD) at rated conditions, the cells can immediately undergo charge at a 2C rate (thr) or higher (15C, obj), and repeat this continually. The effort will deliver cells and modules to support safety evaluation of the approach, and will deliver a battery pack of minimum 20Ah, 1000V, including Battery Management System BMS and any necessary balance of plant for a system demonstration.

PHASE III: Perform sufficient engineering to support evaluation of safety for fully racked and enclosed batteries under the necessary Navy safety test efforts. Provide battery systems for evaluation under shock, vibration and thermal propagation scenarios. Deliver full packaged battery string with suitable design basis to build and integrate into future applications.

The small business will support the Navy with certifying and qualifying the batteries for Navy use on the appropriate platforms. When appropriate the small business will focus on scaling up manufacturing capabilities and commercialization plans for domestic cell manufacture and modularization.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The electric utility industry uses large battery bank installations in lieu of "peaker plants" in order to level load the power generation requirements during peak time of day. The automotive and marine industries are transitioning to electric drive. These large-format high-power batteries would be directly relevant for these applications and would furthermore reduce Department of Defense (DoD) procurement costs with the economy of scale of manufacturing for multiple industrial sectors.

REFERENCES:
1. Drake, S. J., Wetz, D. A., Ostanek, J. K., Miller, S. P., Heinzel, J. M., & Jain, A. (2014). Measurement of anisotropic thermophysical properties of cylindrical Li-ion cells. Journal of Power Sources, 252, 298-304.

2. Al Hallaj, S., Maleki, H., Hong, J. S., & Selman, J. R. (1999). Thermal modeling and design considerations of lithium-ion batteries. Journal of Power Sources, 83(1), 1-8.

3. Smith, K., & Wang, C. Y. (2006). Power and thermal characterization of a lithium-ion battery pack for hybrid-electric vehicles. Journal of Power Sources, 160(1), 662-673.

4. Analysis of Heat Dissipation in Li-Ion Cells & Modules for Modeling of Thermal Runaway Accessed 25 July 2014, www.nrel.gov/vehiclesandfuels/energystorage/pdfs/41531.pdf

KEYWORDS: Energy storage; Electrochemistry; thermal design; large-format cell design; high power battery; Li-ion battery; heat transfer

** TOPIC AUTHOR (TPOC) **

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