DESCRIPTION: As naval aircraft electrical power demands are increasing, the full potential of Li-ion battery technology must be realized to meet such demands. Li-ion battery technology has unique advantages – increased capacity (~3X) and decreased weight (~1/3) in comparison to the lead-acid and nickel-cadmium batteries currently used in aircraft. The power and energy demands of the aircraft system have increased significantly over the years and the systems have become more complex. There is a need for lithium-ion cells that allow higher capacity, smaller cells and innovative product designs. Lighter, high energy density batteries with more power capability have an overall positive impact on system complexity and reliability. Such Li-ion batteries use graphitic carbon with inherent, desirable properties such as large reversible Lithium (Li+) intercalation, good electrical conductivity, and stable solid electrolyte interface (SEI).  However, there are several drawbacks associated with the use of carbon including its relatively low specific capacity (372 mAh/g), poor rate capability in high-current applications, increasing internal resistance with cycling and age, as well as safety concerns due to thermal runaway conditions as a result of thermal exposure, overcharge and overheat conditions. Also, the formation of dendrites produced and grown during cycling, penetrate the separator causing an internal electrical short of the cells leading to battery fire accidents.  The current cost of Li-ion batteries at > $800/KWh is extremely high. Novel, higher capacity anode materials are needed that store more energy, exhibit longer cycle life for reduced total ownership cost, are lighter weight, and are safe to use for Navy applications.

Higher energy alloy anode materials provide distinct advantages. They significantly reduce the amount of material needed to make cells and the number of cells needed for building the complete battery module.  In addition, the amount of supporting hardware needed to construct the battery is reduced, resulting in SWAP-C benefits (space, weight and power - cooling) as well as reducing battery costs ($/KWh basis).

A number of potential alternatives to carbon have emerged recently.  Metal alloy anodes (ex. Si, Ge, Sn) with advancements (ex. nanostructures, composites) are promising anode materials for NGLB. For example, silicon has a theoretical capacity of 3590 mAh/g, almost ten times higher than graphite.  The higher working potential of silicon (0.5 V vs. Li/Li+) in comparison to that of carbon (0.05 Vs. Li+) prevents Li metal deposition and, ultimately, reduces the risk of safety incidents.  However, there are several technical challenges of Si; for example, during cycling; there are multiple amorphous phase transformations, which result in reduced cycling performance. Si suffers from huge volume changes (~ 400%) during the dealloying process, which leads to loss of electrical contact between the particles, resulting in rapid loss of capacity during cycling and reduced total life of the cell and the battery. If such drawbacks are overcome, then the use of this material as an alloy anode offers promise for higher capacity, higher energy density, and longevity. It will allow for the use of smaller, lighter cells and higher safety margin for the battery as well as the potential for reduced cost due to the abundance of the raw materials.

The benefit that metal alloys hold can be realized for NGLB if innovations with novel architectures that ensure extended battery life cycle are made.  Novel, high capacity anode alloys with innovative architectures with the following features are sought: 1) increase in energy density per volume and weight while maintaining extended cycle life with high Coulombic efficiency, 2) demonstrated improvement in safety, and 3) reduction in the overall battery cost, which will enable the development of NGLB.

The developed battery system, 28V/270VDC battery with the advanced high energy density anodes, must be compatible with current aircraft operational, electrical, and environmental requirements. The functional battery must meet the requirements called out in NAVSEA S9310-AQ-SAF-010 [4], and MIL-PRF-29595A [5] which are performance and safety specifications, respectively.

 For example, the requirements include sustained operation over a wide temperature range from - 40 to +71 degrees Celsius and exposure to +85 degrees Celsius. Other requirements that need to be met are the following: ability to withstand carrier based shock and vibration loads, altitude range up to 65,000 feet per MIL-STD-810G [6], and electromagnetic inference up to 200 V/m, per MIL-STD- 461 F [7].  The battery product developed must also meet additional requirements of low self-discharge (< 5% per month), extended cycle life (> 2000 cycles at 100% DOD), and long calendar life (> 6 years of service life).
 

PHASE I: Design and develop an innovative concept to realize high energy density for metal anode alloys and demonstrate the feasibility at full-cell level. Perform preliminary safety, electrical, and performance evaluations.
 

PHASE II: Develop a prototype and demonstrate the functionality of NGLB over a wide-temperature range, in harsh environments, including Navy unique salt fog, and extended life cycle (over > 1000 cycles). Develop a plan for future scale-up for large scale manufacturing of NGLBs.
 

PHASE III DUAL USE APPLICATIONS: Finalize the fully functional aircraft-worthy NGLB product. Consisting of battery modules/pack, battery management system, connectors, and control systems, with performance specifications satisfying the targeted acquisition requirements (ex. F/A-18, F-35, H-60). The batteries must pass qualification and certification testing. Commercialize the technology and develop a cost effective manufacturing process focusing on DOD and civilian market applications. The potential for commercial application and dual use is high. Beyond the Navy application, there are applications for electric vehicle, consumer portable electronics products, and commercial aviation sectors.
 

REFERENCES:

1.  McDowell, T.M., Lee, S.W., Nix, W.D., and Cui, Yi., (2013), Understanding the Lithiation of Silicon and other alloying anodes for Lithium-ion batteries, Advanced Materials, , 24, 4966-4985. DOI: 10.1002/adma.201301795.
 

2.  Liang, B., Liu, Y., and Xu, Y., (2014), Silicon-based materials as high capacity anodes for next generation lithium ion batteries, Journal of Power Sources, 267 469-490.
 

3.  Terranova, M.L., Orlanducci, S., Tamburri, E., and Guglielmott, V., and Ross, M., (2014), Si/C hybrid nanostructures for Li-ion anodes: An overview, Journal of Power Sources, 246 167-177.
 

4.  NAVSEA S9310-AQ-SAF-010, (15 July 2010), Navy lithium battery safety program responsibilities and procedures, Retrieved from http://everyspec.com/USN/nAVSEA/NAVSEA S9310-AQ-SAF-010 4137/.
 

5.  MIL-PRF-29595A- Performance Specification: Batteries and Cells, Lithium, Aircraft, General specification for (21 Apr 2011) [Superseding MIL-B-29595]. Retrieved from http://quicksearch.dla.mil/
 

6.  MIL-STD-810G – Department of Defense Test Method Standard: Environmental Engineering Considerations Laboratory Tests (31 Oct 2008). Retrieved from http://quicksearch.dla.mil/
 

7.  MIL-PRF-461F – Department of Defense Interface Standard: Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment (10 Dec 2007). http://quicksearch.dla.mil/ http://quicksearch.dla.mil/