Solid electrolytes thickness

Effects of the Electrode Asymmetry and Solid-Electrolyte Thickness... 

Fig. 9.4 Potential difference between the working and reference electrodes (a) and relative error in the determination of WE polarization resistance (b) as functions of misalignment between the WE and CE normalized by the solid-electrolyte thickness (s/d), as calculated by the finite-element analysis assuming linear electrode kinetics [8, 25]. At high s/d ratios, the experimentally measured value stabilizes at a small Nemst potential due to gas-phase polarization of the working electrode,...

Fig. 9.7 Examples of thick pellet-based cell geometries with a small working electrode and essentially radial distribution of equipotential surfaces, as shown by solid lines in (b) [26, 35]. Lwe is the width of the working electrode, is the distance between WE and RE, and d is the solid-electrolyte thickness, (a), (c) and (d) illustrate the configurations with small WE and RE having similar sizes, an axially symmetric configuration, and point WE, respectively. The advantages and disadvantages of these configurations are discussed in the text...

Fig. 9.8 Schematic diagram showing the domain of possible ccnnbinations of the reftaence electrode width (Lre), distance between working and reference electrodes ( ), and solid-electrolyte thickness (d) in the planar cells with symmetric WE and CE, illustrated in the inset [8]. Solid line corresponds to the condition A.Uj / Ra 1) = 10 where A /re is the potential differtaice along the RE, Rci is the total ohmic resistance of the cell, and I is the total electrical cumait. Bine area corresponds to the region where normalized A17re does not introduce any significant error in the measurements...

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

The equivalent circuit of a section of this SEI is presented in Fig. 13(b). It was recently found [123, 124] that at temperatures lower than 90 °C, the grain-boundary resistance of composite polymer electrolytes and composite solid electrolytes based on Lil-A Ojis many times larger than their ionic resistance. At 30 °C / GB is several orders of magnitude larger than (the ionic resistance) and for 100 pm-thick CPE foils or Lil-A Oj pellets it reaches [125] 105-106Qcm2 (depending on CPE composition). 

A value of Rqb for an SEI lOnm thick can be estimated from its values for CPE and CSE by assuming that these solid electrolytes consist of nanometer-sized particles. Thus the expected value for / GB at 30 °C for a lOnm SEI is in the range 10-lOOQcm2, i.e., it cannot be neglected. In some cases it may be larger than the ionic (bulk) resistance of the SEI. This calculation leads us to the conclusion that 7 GB and CGB must be included in the equivalent circuits of the SEI, for both metallic lithium and for LixC6 electrodes. The equivalent circuit for a mosaic-type... 

The tape-casting method makes possible the fabrication of films in the region of several hundred micrometers thick. The mechanical strength allows the use of such a solid electrolyte as the structural element for devices such as the high-temperature solid oxide fuel cell in which zirconia-based solid electrolytes are employed both as electrolyte and as mechanical separator of the electrodes. 

In solid-state batteries, it is extremely favorable to use the solid electrolyte for mechanical support. Despite the larger thickness, which lowers the relative amount for active material in the battery, the advantages are the absence of pinholes of the solid electrolyte, high electronic resistance, and simple multistack fabrication, since the individual cells may be contacted by their electronically conducting current collectors. 

An important question frequently raised in electrochemical promotion studies is the following How thick can a porous metal-electrode deposited on a solid electrolyte be in order to maintain the electrochemical promotion (NEMCA) effect The same type of analysis is applicable regarding the size of nanoparticle catalysts supported on commercial supports such as Zr02, Ti02, YSZ, Ce02 and doped Zr02 or Ti02. What is the maximum allowable size of supported metal catalyst nanoparticles in order for the above NEMCA-type metal-support interaction mechanism to be fully operative ... 

Most of the electrochemical promotion studies surveyed in this book have been carried out with active catalyst films deposited on solid electrolytes. These films, typically 1 to 10 pm in thickness, consist of catalyst grains (crystallites) typically 0.1 to 1 pm in diameter. Even a diameter of 0.1 pm corresponds to many (-300) atom diameters, assuming an atomic diameter of 3-10 10 m. This means that the active phase dispersion, Dc, as already discussed in Chapter 11, which expresses the fraction of the active phase atoms which are on the surface, and which for spherical particles can be approximated by ... 

The conductivity ofthe film was calculated for 30 monolayers. The film was deposited onto a Ag microelectrode array with a 1-mm distance between fingers. The thickness ofthe monolayer was taken to be 2 x 10"7 cm. For an air humidity value of 60% the conductivity equals 1.3 x 10"6 (Q/cm)-1 The current through the film has an ionic character, and there is apparently layered solid electrolyte... 

Figure 8.12 (a) Nyquist plot obtained for the all-solid-state cell, ITOAVO3/PEO-H3PO4/ ITO(H) at 8°C, with the electrolyte being unplasticized. The WO3 layer was 0.3 pm in thickness (as gauged during vacuum evaporation with a thin-film monitor), while the electrolyte thickness was 0.24 mm (achieved by using 0.3 mm spacers of inert plastic placed between the two ITO electrodes), (b) Schematic representation of the equivalent circuit for this cell. 

Electrochemical cells are of two types power cells and sensors. In an ideal power cell, the ionic current through the electrolyte inside the cell matches an electronic current through an external load. The solid electrolyte is in the form of a membrane of thickness L and area A that separates electronically the two electrodes of the cell. Any internal electronic current across the electrolyte reduces the power output. The internal resistance to the ionic current is... 

While the amount of electricity that can be conducted by polymer films and wires is limited, on a weight basis the conductivity is comparable with that of copper. These polymeric conductors are lighter, some are more flexible, and they can be laid down in wires that approach being one-atom thick. They are being used as cathodes and solid electrolytes in batteries, and potential uses include in fuel cells, smart windows, nonlinear optical materials, LEDs, conductive coatings, sensors, electronic displays, and in electromagnetic shielding. 

Other developments in the area of solid state lithium batteries include prototype production and testing of thin-film microbatteries at Oak Ridge National Laboratory in the USA. The fabrication involves electrode and electrolyte film deposition to form compact layers of thickness of the order of few microns. The cell uses a lithium anode, an amorphous Li3 3PO3.9N0.17 solid electrolyte and an amorphous V205 cathode ... 

Arranged in layered fashion on the alumina substrate are the zirconia underlayer, the platinum reference electrode, the zirconia solid electrolyte stabilized with 5.1 mole % Y2O3, the platinum measurement electrode, and finally,the protective spinel (A203 Mg0) layer. The zirconia layer is Umm long, 1+mm wide and 30pm thick. 

O2 gas is generated electrolytically at the interface between the reference electrode and the solid electrolyte layer. The mass of the O2 gas is equal to the mass of O2 gas which diffuses through the porous thick film zirconia, plus the mass of O2 gas which reacts with CO gas at the reference electrode. 

At the reference electrode/solid electrolyte layer interface, the mass of the CO gas which diffuses from the porous thick film zirconia is equal to the mass of CO2 gas which diffuses into the porous thick film zirconia. 

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