Bipolar Architectures

A suitable architecture for putting electrochemical cells in series, without interfering with the mass and the volume of the resulting accumulator, is the so-called bipolar architecture (37). This design consists of stacking several electrochemical cells separated from 

This type of architecture allows a reduction in the electrical resistance of the assembly as compared with one accumulator, which would consist of a plurality of cells connected together through external connectors. The bipolar architecture also allows a limitation of unnecessary masses and volumes. 

However, this type of architecture may have drawbacks in terms of charging, since the electrochemical cells, because of their positioning in the stack, have different characteristics in terms of internal resistance and capacitance, which causes different charging times for identical electrochemical materials (37). 

It has been discovered that by adding a specific additive into the electrolyte of the electrochemical cells of a lithium accumulator with a bipolar architecture, it is possible to find a remedy to the charging problems of this cell t5 e. Each cell in the structure has a positive electrode and a negative electrode, separated by an electrolyte. To the electrolyte a lithium polysulfide 0285 is added. Li2S6 can be prepared by the reaction of lithium and sulfur in tetraethylene glycol dimethyl ether. 

The lithium polysulfide ensures the role of a redox shuttle. So this additive will undergo, at a determined potential, an oxidation at one of the electrodes of the cell in order to give an oxidized form of the additive. This oxidized form in turn imdergoes reduction at the electrode of the opposite sign of the same cell in order to give a reduced form. The reduced form is then capable of being oxidized at the electrode with reverse polarity. 

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Applied to lithium-ion technology, this bipolar architecture necessitates the use of a negative electrode that is compatible with an aluminum current collector. Such is the case of Li4Ti50i2. Replacing graphite with this titanium oxide enables us to use the same metal collector as the positive electrode. 

Probably one of the most interesting properties of the new composite membranes is their ability to reject di- and multivalent ions more strongly than monovalent ones. This property can be ascribed to the multi-bipolar architecture of the self-assembled polyelectrolyte membrane, which enables the rejection of ions by electrostatic repulsive forces [8, 11]. Some time ago, the effect has already been studied in solution-cast bipolar polyelectrolyte membranes of macroscopic thickness, and has been ascribed to the fact that divalent cations receive a much stronger repulsive force from a positively charged polyelectrolyte layer than the monovalent... 

C. Barchasz, M. Chami, and S. Patoux, Electrochemical lithium accumulator with a bipolar architecture comprising a specific electrolyte additive, US Patent 9337508, assigned to Commissariat a I Energie atomique et aux energies alternatives (Paris, PR), May 10, 2016. 

In 2001, Chen and coworkers prepared another interesting series of tetra-phenylmethane-based tetrahedral compounds. The initial step of the synthetic scheme involves the preparation of the tetrazole derivative 8 from the corresponding tetranitrile and its subsequent condensation with various benzoyl chlorides to give the cruciforms 9-11 depicted in Scheme 3.6. A modified procedure was developed to obtain the bipolar tetramers 16 and 17, as shown in Scheme 3.7. The acyl chloride functional group was this time attached to the tetrahedral core unit and the tetrazole function was attached to the triphenylamine component. Once again DSC measurements illustrated the effectiveness of this architecture in inducing a stable glassy state in these cruciform materials. 

The design of BP for PEMFCs is dependent on the cell architecture, on the fuel to be used, and on the method of stack cooling (e.g., water or air-cooling). To date, most of the fuel cells have employed traditional filter-press architecture, so that the cells are planar and reactant flow distribution to the cells is provided by the bipolar plate. The bipolar plate therefore incorporates reactant channels machined or etched into the surface. These supply the fuel and oxidant and also provide... 

A further interest in dendrimers for EL applications is the possibility of assigning different functional properties to the individual components of the macromo-lecular structure. For instance, it is conceivable to attach moieties with hole-transporting properties to the core region and electron-transporting properties to the dendrons, or even to integrate bipolar transport functionality in one molecule by virtue of asymmetric dendronization [41, 70]. Many of the fundamental aspects relating to the physical structure and architecture of dendrimers can be mapped... 

Similarly, research conducted on materials and fabrication methods for GDL and bipolar plates aim to tune their properties in order to improve the fuel cell performance. It is clear that the current trend is the integration of the MEA components in order to improve the architecture of the triple phase boundary region and, consequently, the mass and charge transport. 

Figure 16.16 Chemical structure of the semiconducting polymers P(NDI20DT2) and rr-P3HT and illustration of the bottom-gate/bottom-contact bipolar FET architecture. (Reprinted with permission from Ref. [15]).

Figure 1 Possible molecular architectures of monomeric amphiphiles classical amphi-philes (a) bolaform, bipolar amphiphiles (b) multipolar (c) and amphotropic (d) amphiphiles. The circles represent the ionic head-groups and the hydrophobic chains are depicted by the wavy lines. (Adapted from Ref. 1.)...

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