WO2016030565A1

WO2016030565A1 - Battery with polymer electrolyte

Info

Publication number: WO2016030565A1
Application number: PCT/ES2015/070633
Authority: WO
Inventors: Pedro Luis GARCÍA YBARRA; José Luis CASTILLO GIMENO; Beatriz MARTÍNEZ VÁZQUEZ
Original assignee: Universidad Nacional De Educación A Distancia
Priority date: 2014-08-28
Filing date: 2015-08-26
Publication date: 2016-03-03
Also published as: ES2561705A1; ES2561705B2

Abstract

The invention relates to a battery with a polymer electrolyte (PEM), comprising at least one unipolar plate that separates two electrolytic cells, wherein said unipolar plate has a groove passing through same, via which a reactive fluid circulates, said reactive fluid simultaneously supplying the two adjacent electrodes arranged one on each side of the plate. The substitution of the bipolar plates of prior art with unipolar plates comprising through-channels operating as an anode or cathode at the same time in two adjacent electrolytic cells mounted in parallel, improves the operability of the current electrolytic batteries, reducing the weight and size of the material.

Description

BATTERY WITH POLYMER ELECTROLYTE

Field of the Invention

The present invention relates to an improved polymer electrolyte fuel cell with application in the energy sector, for example for automotive and portable systems, and in particular in direct small and medium scale power generation.

Background of the invention

Fuel cells are electrochemical devices formed by the connection of unit cells, each consisting basically of two electrodes separated by an electrolyte.

Polymeric electrolyte (PEM) batteries incorporate at least two reactive fluids, liquid or gaseous, that act as fuel and oxidizer. The electrolyte used is impermeable to the passage of the reagents and these are fed separately through the porous electrodes, anode and cathode, respectively. For this, each of the electrodes is in contact with a system of channels that distribute the fluid along the surface of the electrode.

The plate material that distributes the reactive fluids and on which said channels are printed is a good electronic conductor. This allows the serial connection of adjacent cells to be made, so that the channel system of an electrode is connected to the opposite sign electrode channel system of the adjacent cell. Both reactive fluid distribution systems are therefore part of the same component, called bipolar plate. The two independent channel systems have been engraved on opposite sides of the bipolar plate, typically reducing the material with a milling machine. Therefore, the thickness "e" of a bipolar layer turns out to be equal to the sum of the depths of the channels on both sides plus the thickness of the remaining material between them (Fig. 1).

On the other hand, the battery is closed at both ends with monopolar plates with channels printed only on the operating side in the corresponding cell, called collector end plates. These collector plates confine the battery and typically subject it to a certain pressure to ensure the tightness of the entire assembly. Thus, a single cell cell is composed of the electrodes, anode A and cathode C, separated by electrolyte E and closed by monopolar plates M, being able to be represented by the MAECM sequence. In the current technique there are membrane-electrode assemblies (MEA, Membrane Electrode Assembly) that consist of a porous body joined in solidarity with the polymer electrolyte, which in turn is attached to another porous body, each of said porous bodies acting as cathode or anode respectively according to its design in terms of catalytic content, structure, etc. Thus, the previous AEC succession would constitute an MEA.

The serial connection of the cells is made through a bipolar plate B, so that it would be represented by the MAECBAECM sequence. The model can represent batteries of more units without juxtaposing them by means of bipolar plates, that is: MAECBAECBAECB BAECM

This arrangement however has the disadvantage of the large amount of material necessary for the manufacture of batteries in series, and the size and weight of the resulting battery.

US Patent 7585577 B2 describes PEM methanol batteries as a liquid reagent made of monopolar plates, the structure of which involves a particular assembly of individually sealed unit cells. The plates that close these individual batteries on each side are monopolar plates grooved only on one side and in contact with the anode or cathode, respectively. The distribution sequence would then be MAECM.

The problem of the technique is the need to improve the operability of the current electrolytic batteries by lightening the material and reducing its size. The solution proposed by the present invention is the replacement of bipolar plates with monopolar plates with through channels that open the plate from side to side operating either as an anode or as a common cathode to two adjacent electrolytic cells that are connected in parallel. Description of the invention

The present invention is a PEM, comprising at least one monopolar plate separating two electrolytic cells, wherein said monopolar plate has a through slot through which a reactive fluid circulates, said reactive fluid feeding at the same time the two juxtaposed electrodes, one on each side of the plate. This monopolar plate can be said to have dual functionality. In one aspect of the invention, said monopolar plate has more than one through slot. In another aspect of the invention, said monopolar plate is connected to the anodic terminal, and in one more aspect is connected to the cathodic terminal.

The "dual monopolar plate" of the present invention simultaneously serves two juxtaposed electrodes of two adjacent unit cells leading naturally to the parallel connection of the unit cells. On the other hand, the concept of a battery in which these monopolar plates are integrated is the classic one, in the sense that the unit cells are distributed one after the other, forming among all a battery that ends up being compressed with collector end plates, that provide solidity and tightness to the whole.

The invention replaces the bipolar plates of the technique with monopolar plates that connect electrodes of the same sign from adjacent cells. In the monopolar plates of the invention the channels are grooves that open the plate from side to side, allowing the reactive fluid to feed the two juxtaposed electrodes at the same time. Within the scope of the present invention, these unipolar plates are called dual D plates. With this arrangement the cells must be connected in parallel, so that in the operating mode of a battery consisting of two cells, the dual plate D would be connected and the Porous electrodes adjacent C to the cathodic terminal, and to the anodic terminal would be the final monopolar plates M and adjacent porous electrodes A previously interconnected, as follows:

Cathode

r

A preferable embodiment of the invention is a three cell stack constituted analogously according to the scheme:

Cathode

, í,

MAECDCEADAECM

Anode In which the first dual plate together with the adjacent porous electrodes C are connected with the cathodic end plate, and the second dual plate with the adjacent porous electrodes A are connected with the anodic end plate.

In a more preferred embodiment of the invention, a four cell stack would respond to the following scheme:

Cathode

t

MAECDCEADAECDCEAM

and so on.

So that a very preferable aspect of the invention is a PEM comprising "n" electrolytic cells, in which each of said cells is separated from the adjacent cell by a monopolar plate, said monopolar plate having a slot through the a reactive fluid circulating that feeds at the same time the two electrodes juxtaposed one on each side of the plate, in which said monopolar plates are successively of opposite sign and in which "n" is an integer between 2 and 150, more preferably between 2 and 100, more preferably between 50 and 100, even more preferable between 75 and 100, most preferably 100. In another aspect, said monopolar plate has more than one through slot. The number of electrolytic cells will depend on the application of said battery depending on the total power to be developed and the geometry of the available volume.

In a further aspect of the invention said monopolar plate is of a unique coil and in another aspect it is of parallel coils. In the latter case, there cannot be a single reagent input common to the different channels, but the input of each must be separated from the others so that the spacing between them serves as support for the material between channels. The invention also comprises the single-coil single-pole plate itself and the parallel-coil monopolar plate, respectively. A further aspect is the PEM of the invention in which said monopolar plate is a corrugated plate.

In the plates of the invention, the typical topology of several parallel channels in coil is translated into a series of parallel grooves separated by strips of material, also in the form of a coil or two combs interspersed in the case of a single channel. Preferably, the plates of the invention are made of stainless steel because their strength and toughness allow processing by die cutting or laser cutting or water. Another preferable material of the invention is the electrically conductive plastics, which allow easy manufacturing of the monopolar plates by molding and imply a substantial reduction in the weight of the battery. Another preferable material would be a composite of graphite or carbon fiber, whose possible porous consistency does not in this case have any difficulty being a monopolar plate.

The present invention is conceptualized for PEM or polymer electrolyte fuel cells and gaseous or liquid reagents. It proposes the use of dual monopolar plates, which are essentially grooved plates, replacing the bipolar plates common in the art.

The main advantage therefore of the invention over the technique is a faster and cheaper manufacturing of the electrolytic cell. The high costs of the battery components are one of the main problems that prevent their implementation on a large scale. Among these components, bipolar plates are one of the most expensive because the most common manufacturing procedure consists in roughing the chosen material, typically graphite or steel, by precision milling to mold the distribution channels of reactive fluids on both sides. of the plate. In the dual unipolar plate of the present invention the reagent distribution channels are grooves that slide the plate from one side to the other, so that they can be manufactured by simple die cutting or mechanical cutting, laser or water depending on the material and the accuracy required. The result is that the difference in the cost of the cell of the invention in the proportional part corresponding to the monopolar plates is of the order of ten times less than the cost of the bipolar plates of a conventional PEM battery. Another advantage over the technique is the reduction of the size and weight of the cell of the invention. The length of a pile, not counting the collector plates of the ends, is given by the sum of the thicknesses of the MEAs and mainly of the plates bipolar, which are the ones that contribute most to the total length. The thickness of these bipolar plates is typically about 3 mm, the channels on each side being for the passage of reactive fluids 1 mm deep. The thickness of a dual monopolar plate according to the present invention is the depth of the channel, which typically becomes 1 mm, that is, one third of the thickness of a bipolar plate of the art. Most of the weight of the battery is due to the weight of the bipolar plates, therefore also the weight of the battery is markedly reduced if dual monopolar plates are used. The PEM battery of the invention maintains the technical performance of the conventional batteries of the technique of similar characteristics. In particular, with the same active surface per electrode and the same number of unit cells it develops the same electrical power, although with a current of greater amperage and lower voltage as a result of the parallel connection of the unit cells. If we take as a reference a battery formed by a single cell of electromotive force ε and internal resistance R¡ and we assume for simplicity that its behavior is purely ohmic, when it generates a current of intensity I the voltage drop in terminals of battery V is V = ε - IR¡ giving an electric power P that is equal to

P = l V = I ε - I ² R¡

In terms of the current intensity, this power is in the form of an inverted parabola presenting a maximum value P _m = ε l _m / 2 when the current is l _m = s / 2R¡, so that the power curve can be written as P / P _m = 2 (l / l _m ) - (l / l _m ) ² as shown in curve 1 of Figure 4. In a conventional cell formed by the serial connection of two unit cells, The resulting electromotive force is 2ε and the internal resistance is 2R¡, so that the power curve is

P / P _m = 4 (l / l _m ) - 2 (l / l _m ) ² as curve 2 of Figure 4. That is, this battery offers twice the power with the same current values as the total potential in the battery terminals is doubled. On the other hand, if the two unit cells are connected in parallel, the resulting battery has the same electromotive force ε as each of the unit cells and an internal resistance R¡ / 2, which turns out to be half of the internal resistance of a cell unity. Under these conditions, the power of the resulting battery is

P / Pm = 2 (l / l _m ) - (l / l _m ) ^2/2 represented in curve 3 of Figure 4. As can be seen, as in the case of the conventional battery, also the maximum of power is twice that produced by a unit cell, although in the case of the present invention the maximum is obtained at a double current intensity and with the same voltage as the unit cell. As for the dynamic dynamics of the distribution channels of the dual plate, each channel now serving a double electrode surface must also carry twice the flow rate, which multiplies by 2 the average speed of the reactive fluid in the channel. Typically, this increase will not lead to a significant change of flow regime. On the other hand, a greater speed of the reactive fluid implies a greater viscous effort on the walls and, therefore, a better evacuation of the water that can condense on them.

Brief description of the figures

Figure 1: Schematic of a cross section of a bipolar parallel channel plate used in the art, "e": Total thickness.

Figure 2a: Dual monopolar plate with single coil type channel.

Figure 2b: Enlargement in three dimensions of the circumferential detail of Figure 2a.

Figure 3: Dual monopolar plate with parallel coil type channels.

Figure 4: Comparative scheme of the power generated by an individual unit cell (line 1) and that of a battery composed of two unit cells, either connected in series (line 2) as in the current technique or connected in parallel (line 3 ) according to the present invention.

Figure 5: Particular embodiment of the monopolar plate of Figure 2, with lateral widening for interconnection. The dimensions are in millimeters.

Examples

With the intention of showing the present invention in an illustrative way but not in any way limiting, the following examples are provided. Example 1: Characteristics of monopolar steel plate.

It is considered a monopolar plate according to Figure 5. The material is a 1 mm thick stainless steel sheet with good corrosion resistance. The weight is Mm = 60.6 g. Since the density of steel is approximately 8 g / cm ³ , this mass results from an approximate volume of material of 7.6 cm ³ . On the other hand, if the plate were a bipolar plate of the same dimensions, its mass would be a mass equal to Mm for each of the two grooves on each side plus the mass of the solid material between them, resulting approximately equal to Mb = 204 g ; that is, more than 3 times greater than that of the monopolar plate and in addition to a thickness 3 times greater. Even in spite of its fragility, graphite is usually preferred for the manufacture of bipolar plates given its reduced density, 2.2 g / cm ³ , which in the case considered would lead to a bipolar plate of mass Mbg = 56.3 g. However, when this value is compared with that of a monopolar steel plate according to the present invention, the latter's mass turns out to be greater only by a little more than 4 g. The result is that the monopolar steel plate turns out to have a very similar weight, a thickness 3 times lower and a cost about 9 times lower compared to a bipolar graphite plate of the technique, also avoiding the fragility of graphite, of utmost importance for industrial applications

Example 2:

Another embodiment of monopolar plate can be achieved with a corrugated metal plate, this case corresponding to a distribution of reactive fluids in parallel channels. WO 201 1/154576 A1 describes the use of corrugated metal plates as bipolar plates. The concept of corrugated plate, which forms a series of parallel channels alternating on both sides of the plate, turns out to be a very suitable configuration for use as a dual monopolar plate. The corrugated plate, made of a corrosion-resistant steel, is attached to a frame of conductive material where through holes have been made for reactive fluids, two of which connect to the internal cavity where the corrugated plate is located to feed , with the corresponding reagent, the electrodes of the adjacent MEAs to be juxtaposed to the monopolar plate, as indicated in the general description of the invention.

Claims

one . Polymeric electrolyte cell, characterized in that it comprises at least one monopolar plate that separates two electrolytic cells, in which said monopolar plate has a through slot through which a reactive fluid circulates, said reactive fluid feeding at the same time the two electrodes juxtaposed one on each side of the plate.

2. A polymer electrolyte cell according to claim 1, characterized in that said monopolar plate is connected to the anodic terminal.

3. A polymer electrolyte cell according to claim 1, characterized in that said monopolar plate is connected to the cathodic terminal.

4. A polymer electrolyte cell according to any one of claims 1 to 3, characterized in that said monopolar plate is single coil.

5. A polymer electrolyte cell according to any one of claims 1 to 3, characterized in that said monopolar plate is of parallel coils.

A polymer electrolyte cell according to any one of claims 1 to 3, characterized in that said monopolar plate is a corrugated plate.

7. A polymer electrolyte cell according to any one of claims 1 to 6, comprising "n" electrolytic cells, characterized in that each of said cells is separated from the adjacent cell by a monopolar plate, said monopolar plate having a through slot through which a reactive fluid circulates that feeds at the same time the two electrodes juxtaposed one on each side of the plate, in which said monopolar plates are successively of opposite sign and in which "n" is an integer between 2 and 150.

8. A polymer electrolyte cell according to claim 7, characterized in that "n" is 100.

9. Single coil monopolar plate.

10. Monopolar plate of parallel coils.