N131-020 TITLE: High Energy and Power Density Electrical Energy Storage Device

TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes, Electronics

ACQUISITION PROGRAM: NAVFAC Directed Energy Program

OBJECTIVE: The objective is to develop an energy storage device that has both high energy and power density. The device would be robust with a wide temperature range, long life, and exhibits minimal degradation under numerous recharge cycles. Energy storage per kW-h would have to be cost competitive with existing battery technology to be viable for infrastructure applications.

DESCRIPTION: Naval Facilities Engineering Command (NAVFAC) has a need for a robust electrical energy storage device. Traditionally chemical batteries have been the primary technology for powering portable devices, remote asset monitoring, electric vehicles, and small to large scale utility back up power supplies. Battery technology is limited by the need for an electrochemical reaction which is not completely reversible and is temperature dependent. Infrastructure applications have unique requirements different than consumer electronics which batteries are better suited for. These requirements include operation in harsh temperature ranges, and difficult to access locals that demand maintenance free, long life operation. Current Ultracapacitor technology offers all these advantages but have energy densities that are only 10-20% that of traditional batteries.

Commercially available Ultracapacitors or Supercapacitors employs an EDLC (Electrochemical Dual Layer Capacitor) architecture that maximizes the surface area and minimizes charge separation distances to achieve high capacitance. Maximum energy is a function of dielectric volume, permittivity, and dielectric strength per distance.

EDLC thus only maximizes the (A/d) geometric term, while the electrolytes used have low relative permittivity e, and break down voltages Vb. A materials solution is sought that would complement existing EDLC structures with significantly higher e and/or Vb, i.e. by using newer electrolyte solutions or coating the carbon powders, nanofibers, or aerogels with a high dielectric coating. Alternatively solid state ceramic dielectric materials could be used to maximize permittivity and break down voltages, though with a lower geometric factor.

Recent fabrication technologies for multilayer ceramic capacitors (MLC�s) have improved significantly, permitting both lower cost and higher quality devices with low defects. These MLC use high dielectric ceramics that theoretically are capable of very high breakdown voltages, but voids and other defects have limited the electrical break down. Submicron thick film and size powders with glass encapsulation have been shown to provide significantly higher break down voltages because of less voids and defects. It has been suggested that these materials can have Vb of 8MV/cm, which could translate to energy densities of greater than 500 W-h/L.

Advanced Ultracapacitor concepts are sought that would maximize both geometric and materials parameters to provide energy densities greater than current Li-ion batteries, have low maintenance, and long operational life spans of 10 years with greater than 100,000 recharge cycles. Materials selection and manufacturing processing should be compatible with cost restrictions, such that the final product should be price competitive with Li-ion storage, and practical for large scale infrastructure applications. Proposals should offer a conceptual architecture and provide a quick calculation of energy density to estimate feasibility of obtaining the objective energy density.

PHASE I: Develop the process and fabricate a small laboratory device for testing. Measure capacitance and material properties of the device to extrapolate expected energy density. Laboratory device should meet the following targets:
- Energy storage density of 200 Wh/L
- Power density of 5000 W/L
- 25,000 full charge/discharge cycles while maintaining 80% of initial performance
- operational at temperatures from -32F to 150F

PHASE II: Build and demonstrate a device capable of 1kW-h of energy storage. Measure device performance metrics i.e., recharge cycles, temperature range, current leakage, etc. Provide cost breakdown of device and path to a cost objective of under $500/kW-h.

PHASE III: Build a 5kW prototype that can be integrated into a modular system with capacity up to 500kW-h of energy storage. Target application will be in a micro-grid for power backup and power stabilization. Evaluate unit for reliability, operating thresholds, and integration issues.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial power utilities, telecom UPS, and electric vehicles are potential applications with similar energy capacity requirements. Smaller portable electronics, remote wireless devices, and portable lighting would also benefit from the quick charge, and robust operating life of these energy storage devices.

REFERENCES:
1. Ezzat G. Bakhoum, "New Mega-Farad Ultracapacitors", IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 56, no. 1, p.14, 2009.

2. Gordon R. Love, "Energy Storage in Ceramic Dielectrics", Journal of the American Ceramic Society Volume 73, Issue 2, p.323-328, February 1990

3. I. Burn and D. M. Smyth, "Energy storage in ceramic dielectrics", Journal of Materials Science, Volume 7, Number 3, p. 339-343, 1972.

4. N. H. Fletcher et al., "Optimization of energy storage density in ceramic capacitors", J. Phys. D: Appl. Phys., 29, p. 253, 1996.

5. US Patents #6078494, #7729811

KEYWORDS: Supercapacitor, ferroelectric, Ultracapacitor, EDLC, dielectrics, pseudocapacitor

** TOPIC AUTHOR (TPOC) **

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