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Increasing the areal capacity or electrode thickness in lithium ion batteries is one possible means to increase pack level energy density while simultaneously lowering cost. The physics that limit use of high areal capacity as a function of battery power to energy ratio are poorly understood and thus most currently produced automotive lithium ion cells utilize modest loadings to ensure long life over the vehicle battery operation. Here we show electrolyte transport limits the utilization of the positive electrode at critical C-rates during discharge; whereas, a combination of electrolyte transport and polarization lead to lithium plating in the graphite electrode during charge. Experimental measurements are compared with theoretical predictions based on concentrated solution and porous electrode theories. An analytical expression is derived to provide design criteria for long lived operation based on the physical properties of the electrode and electrolyte. Finally, a guideline is proposed that graphite cells should avoid charge current densities near or above 4 mA/cm2 unless additional precautions have been made to avoid deleterious side reaction.

Gadolinium-doped ceria (GDC) deposited by radio frequency magnetron sputtering is utilized as the anode interlayer for low-temperature solid oxide fuel cells (LT-SOFCs) with a nanothin yttria-stabilized zirconia (YSZ) electrolyte and Ni/Pt electrodes. When the thickness ratio of YSZ electrolyte versus 100 nm GDC anode interlayer is at or below 1.5, the electrochemical performance of the LT-SOFC is severely poor due to the microstructural instability of the GDC anode interlayer under high-temperature reducing atmospheric conditions. At 500 °C, the peak power density of the LT-SOFC with a Ni anode and a 20 nm GDC anode interlayer is ~ 30% higher than that without the GDC anode interlayer due to faster reaction kinetics on the anode side.

This paper presents the architecture of a nano thin-film yttrium-doped barium zirconate (BYZ) solid-oxide fuel cell that uses nanoporous anodic aluminum oxide (AAO) as a supporting and gas-permeable substrate. The anode was fabricated by sputtering 300 nm platinum thin film that partially covered the AAO surface pores, followed by an additional conformal platinum coating to tune the pore size by atomic layer deposition. Two different nano-porous anode structures with a pore size of 10 nm or 50 nm were deposited. Proton-conducting BYZ ceramic electrolyte with increasing thicknesses of 300, 600, and 900 nm was deposited on top of the platinum anode by pulsed laser deposition, followed by a 200 nm layer of porous Pt sputtered on BYZ electrolyte as a cathode. The open circuit voltage (OCV) of the fuel cells was characterized at 250 °C with 1:1 volumetric stoichiometry of a methanol/water vapor mixture as the fuel. The OCVs were 0.17 V with a 900 nm-thick BYZ electrolyte on 50 nm pores and 0.3 V with a 600 nm-thick BYZ electrolyte on 10 nm pores, respectively, but it increased to 0.8 V for a 900 nm-thick BYZ electrolyte on 10 nm pores, indicating that increasing the film thickness and decreasing a surface pore size help to reduce the number of electrolyte pinholes and the gas leakage through the electrolyte. A maximum power density of 5.6 mW/cm 2 at 250 °C was obtained from the fuel cell with 900 nm of BYZ electrolyte using methanol vapor as a fuel.

A novel processing sequence for the formation of gated diamond field emitter array (triode system) is proposed and the feasibility is tested by investigating the field emission property. The processing scheme is based on the selective deposition of diamond by using the well established nucleation enhanced process on substrate, so callled bias enhanced nucleation (BEN). The structure of substrate was patterned [SiO 2 /Mo(gate)SiO 2 (insulator)Si(100). Our preliminary results show that the diamond field emitter is turned on at around 87 V/μm with the current level of about several μA.