CA1238682A

CA1238682A - Battery plate containing filler with conductive coating

Info

Publication number: CA1238682A
Application number: CA000465369A
Authority: CA
Inventors: John J. Rowlette
Original assignee: California Institute of Technology
Current assignee: California Institute of Technology
Priority date: 1983-11-14
Filing date: 1984-10-12
Publication date: 1988-06-28
Also published as: NO844367L; DE3481881D1; EP0142288A3; EP0142288A2; BR8405800A; US4510219A; JPS60175376A; DK537884D0; EP0142288B1; DK537884A

Abstract

Abstract BATTERY PLATE CONTAINING FILLER WITH CONDUCTIVE COATING The plate (10) comprises a matrix or binder resin phase (12) in which is dispersed particulate, conductive tin oxide such as tin oxide coated glass fibers (14). A monopolar plate (11) is prepared by coating a layer (18) of electrolytically active material onto a surface of the plate (10). Tin oxide is prevented from reduction by coating a surface of the plate (10) with a conductive, impervious layer resistant to reduction such as a thin film (22) of lead adhered to the plate with a layer (21) of con-ductive adhesive. The plate (10) can be formed by casting a molten dispersion from mixer (36) onto a sheet (30) of lead foil or by passing an assembly of a sheet (41) of resin, a sheet (43) of fiberglass and a sheet (45) of lead between the nip of heated rollers (48, 503.

Description

JPI. C~s~ ~. 16169 C:[T Case ~lo. 1756 ~.~3~68;2 Description BATTERY PLATE CONTAI N ING
E'ILLER WITH COMDUCTIVE COATING

Ori~in of the Invention The invention described herein was made in the performance of work under a NASA contract and is sub-ject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 83-568 (72 Stat 435; 42 USC 2457).

Technical Field The present invention relates to secondary batteries o~ the bipolar plate type and, more parti-cularly, to an improved lightweight battery plate for use in fabricating bipolar or monopolar plates for lead-acid batteries.
Background Art _ Even though there has been considerable study of alternative electrochemical systems, the lead~acid battery is still the battery-of-choice for general purpose uses such as startin~ a vehicle, boat or air-plane engine, emergency lightiny, electric vehicle motive power, energy buffer storage.for solar-electric energy, and field hardware whether industrial or military. These batteries may be periodically cha~ged from a generator.
The conventional lead-acid battery is a multi-cell structure. Each cell contains a plurality of vertical positive and negative plates formed of lead-based alloy grids containing layers of electrochemi-cally active pastes. The paste on the positive pla~ewhen charged contains lead dioxide which is the posi-tive active material and the negative plates contain .. ..

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2, a negative active material such as sponge lead. This battery has been widely used in the automotive industry for many years, and there is substantial experie~ce and tooling in place for manufacturing this battery and its components, and the battery is based on readily availa~le materials, is inexpensive to manufacture and is widely accepted by consumers.
The open circuit potential developed between each positive and ne~ative plate is about 2 volts.
Since the plates are connected in parallel, the com-bined potential for each cell will also be about 2 volts regardless of the number of plates utilized in the cell.
One or more cells are then connected in series to pro-vide a battery of desired voltage. Common low voltage ba~teries of 6 volts have 3 serially connected cells, 12 volt batteries include 6 serially connected cells and 24 volt batteries contain 12 serially connected cells. The bus bars and top straps used for intercell connection add to the wei~ht and the cost of the battery and often are subject to atmospheric or electrochemical corrosion at or near the terminals.
Another problem with lead-acid batteries is their limited lifetime due to shedding of the active materials ~rom the vertically oriented positive and negative plates. During operation, these electrode materials shed and flake and fall down between the vertically oriented plates and accumulate at the bottom of the battery. After a period of operation, sufficient flakes accumulate to short circuit the grids resulting in a dead battery cell and shortened battery life.
Lead-acid batteries are inherently heavy due to use of the heavy metal lead in constructing the plates. Modern attempts to produce lightweight lead-acid batteries, especially in the aircraft/ electric ~23~

car and vehicle fields, have placed theix emphasis on produci~g thinner plates from lighter weight materials u~ed in place of and in combinat:ion with lead. The thinner plates allow the use of rnore plates for a given volume, thus increasing the power density.
Some of these attempts have included battery ~tructures in which the plates are stacked :in horizontal conigur-ations. Highex voltages are provided in a bipolar bat-tery including bipolar plates capable of through~plate conduction to serially connect e;Lectrodes or cells.
The horizontal orientation of the gxids prevents the accumulation o~ ~lake lead compounds at the battery bottom. Downward movement of electrolyte can be blocked by use o~ glass or porous polypropylene ma~s to contain the electrolyte, Also, stratification o~ electrolyte is preventedsince the electrolyte is confined and con-tained within the acid resi~tant mats ~y capillary action.
The bipolar plates mu8t be impervious to elec-trolyte and be electrically conductive to provide a serial connection between cells. The bipolax plates also provide a continuous surface to prevent loss o~
active materials.
Most prior bipolar plates have utilized metallic substrates such as lead or lead alloy~. The use of lead allcys, such as lead antimony, gives strength to the substrate but causes increased corrosion and gassing.
Alternate approaches h~v,e included plates formed by dispersing conductive particles or filamen~s such as carbon, graphite or metal in a resin binder such as 30 polystyrene ~U.S.Paten~ 3,202,545), a plastic frame of polyvinyl chlcride with openings carrying a battery active paste mixed with nonconductive fibers and shoxt noncontacting lead fibexq ~or strengthening the sub-.
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strate (U.S. Patent3,466,193), a biplate having a layer of zinc and a polyisobutylene mixed with acety~
lene black and graphite particles for conductivity of the plate (U.S.Patent 3,565,694), a substrate for a bipolar plateincluding polymeric material and ~er-micular expanded graphite (V.S.Patent 3,573,122), a rigid polymer plastic frame havin~ a grid entixely o~ lead filled with battery paste (U.S.Patent 3,738,a71), a thin, plastic substrate having lead strips on opposite 10 faces, the lead strips being interconnected through an opening in the substrate and r~ained by plas-kic re-tention strips (U.S.Patent 3/819,412), and a biplate having a ~ubstrate of thermoplastia material i~1ed with finely divided vitreous carbon and a layer of lead-antimony foil bonded to the ~ubstrate for adheri~gactive materials (U.S. Patent 4,098,967).
Some more recent examples of batteries contain-ing bipolar plates are U.S. Patent No. 4,275,130 in which the biplate construction comprises a thin compo-site o randomly oriented conductive graphife, carbonox metal fibers imbedded in a re~in matrix with strips of lead plated on opposite surface~ thereof.
U.S.Patent No. 4,539,268disclo~es a biplate formed of a thin sheet of titanium covered with a con-ductive,protective layer of epoxy resin containinggraphite powder.
Dispersed, conductive fibexs form a conduction path by point-to-point contact of particles or fibers dispersed in an insulating matrix resin, and the through-plate serial conductivity is usually lower than desired.Fibrous illers do increase the strength o the plate by forming a fiber reinfo~ced composite.
It has been attempted to increase the conducti-vity and strength of bipolar plAtes by adding a con-"

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ductive filler such as g~aphite. Graphite haR been used successfully as a conductive filler in other electrochemical cells, ~uch as in the manganese di-oxide, positive active paste o~ the common carb~n-zinc cell, and it has been mixed with sul~ur ln sodium-sul-fur cells. However, even though graphlte is usually a fairly inert material, it i~ oxidized in ~he agressive electrochemical environment of the lead-acid cell to acetic acid. The acetate ions combine with the lead 10 ion to form lead acetate, a weak salt readily soluble in the sulfuric acid eleatrolyte. This reaction de-pletes the active material ~rom the pa~te and ties up the lead as a salt which does not contribute to pro~
duction or storage or electricity. Acetic acid also attacks the lead grids of the positive electrodes during charge, ultimatel~ causing them to disintegrate.
Highly conductive metals such as copper or silver are not capable of withstanding the high potential and strong acid environment present at the positive plate of a lead-acid bat~eryO A few electrochemically-inert metals such as platinum are reasonably stable. But the scarcity and high C05t 0~ ~uch metals prevent their use in high volume commercial applications such as the lead-acid battery. Platinum .would be a poor choi~e even if i~ could be afforded, because of its low gassing ovarpotentials.
A low cost, lightweight, stable bipolar plate is disclosed in my U.S. Patent 4,542,08~, entitled -- - BIPOLAR BATTERY
PLATE. The plate is produced by placing lead pellets into apertures ~ormed in a thermoplastic sheet and rolling or pressing the sheet with a heated platen to compress the pallets and seal them into the sheet.
Thi~ method involves several mechanical operations and requires that every aperture be filled with a pellet ' .

.~ 3 before heating and pressing in order to ~orm a fluid-impervious plate.
, Disclosure of the Invention . . _ .
An improved, lightweight conductive plate ~or a lead-acid battery is provided by the present invention~
The plate is resistant to the electrochemical environ-ment of the cell. The plate is prepared in a simple, xeliable manner to orm a low-resistance, fluid-impervious, through-conductive plate.
Theconductiveplate of the invention contains a dispersion in a matrix resin of a conductivity additive that is thermodynamically stable to the electrochemical en~iron~ent of the lead acid cell, both with respect to the strong sul~uric acid electrolyte and to species generated under oxidation and reduction condi~ions ex-perienced during charge and discharge of the batteryr A preferred conductivity additive for the plate of the present invention is conductive tin di-oxide (SnO2). SnO2 can be present as a powder or coated onto a ~articulate or fibr~us substrate such as glass powder or glass wool as disclo~ed in U.S.
Patent No. 4,507,372 ~
entitled IMPROVED POSITIVE BATTERY P~ATE, Stannic oxide has a conductivity several times that of graphite. SnO~ (doped) has a conducti-vity of 300 to 400 micro ohm cm vs. 1373 micro ohm-cm for graphite.
Stannic oxide is thermodynamically stable to the oxidation/reduction potential in ~he elactro-chemical environment of the positive plate of a lead-acid battery, has about the same resi~tivity as PbO~
when SnO2 is doped with a ~3uitabïe dopant such as fluoxide ion, and refractory or baked type of SnO2 is quite insoluble ~ ' . . .

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in sulfuric acid. The stannic oxide conductivity ad-ditive will remain unchanged during the course of charge and discharge of the battery.
These and many other features and attendant advantages of the invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawing~.

Brief Description of the Drawings Figure l is a sec~ional view o a bipol~r plate in accordance with the invention;
Figure 2 is a view in section of a monopolar plate prepared in accordance with the invention;
Figure 3 is a schematic view of an apparatus for forming a bipolar plate in accordance with the invention;
Figure 4 is a schematic view o an alternate method for forming a bipolar plate in accordance with the invention;
Figure 5 is a section taken on line 5-5 of Figure 4; and Figure 6 is a view in section of a stack of planar plates forming a battery cell Description of the Preferred Embodiments Referring now to Figure 1, the plate 10 is formed of a composite of a~ organic synthetic resin 12 in which is dispersed a sufficient amount of a stable filler 14 to provide through-plate conductivity. The preferred material is tin oxide in particulate form, preferably coated onto a particulate support such as glass fibers or glass particles. The glass fibers can be in roving, chopped or glass wool form. In one . .

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emkodiment, the glass particles are pref~rably sintered into a solid sheet having a porosity rom about 60 to about 90 percent. The plate 10 preferably has a thick-ness from about 1 to about 20 mils, more preferably from about 4 to about 10 mils.
The coating of stannic oxide onto glass to form a conductive coating was developed over 30 yeArs a~o and has be~n widely practiced to defros~ windshields in aircraft and automobiles. The conductive coating is applied to heated glass fiber~ or powder or qlass wool ~rom a solution of stannic chloride in hydro-chloric acid as disclosed in U.S. Patent No. 2,564,707, ~ he solution can ~e spxayed onto the heated fibers.
The diameter of the glass fibers i8 preferably very small such as from about 1 to about 20 microns.
Very fine fibers are too hard to handle and large diameter fiber~ have too small a surface to provide adequate conductive surface. The fibers preferably contain a conductive coating of stannic oxide ranging in thickness from a monolayer ùp to about 10 micron~, more preferably from 0.2 micron to 2 microns.
Referring now to Figure 2, the through-conduc-tive plate 10 can be used as the central ~ubstrate toform a monolayer plate 11 such as a positive plate containing a layer 18 of positive active material ueh as lead oxide paste.
Referring back to Figure 1, since tin oxide is not ~table in the reducing environment of a negative electrode, the surface 15 ~acing the negativ~ electrode must contain a layer 20 that is conductive and stable under reducin~ conditions. The layer 20 can be a composite of a synthetic or~anic resin such as epoxy ~.

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g or po].ypropylene containing a dispersion of about 20 to about 70 percent by weight of conductive fibers which are stable under reducing conditions such a~
graphite fibers or lead fibers. The layer 20 can also be a thin film or foil of lead having a thickness from about 0.5 to about 5 mils, preferably from about 1 to about 5 mils. The layer 20 can be adhered to the plate 10 by a conductive adhesive such as a film 21 of graphite-filled epoxy adhesive. The lead foil may be omitted if the conductive layer of epoxy or poly-propylene is suf~iciently thick to form a good elec-trolyte barrier. Electrical contact may be improved by applying an electrical current to the foil to slightly melt the foil so that it flows and forms a better contact with the ~in oxide coated glass fibers.
The fabrication of the bipolar plate is completed by depositing a layer 22 of negative active material such as lead paste onto the layer 20.
The synthetic organic resin 12 can be a thermo-plastic or thermosetting resin. Representative thermo-setting resins are epoxies and polyesters. Preferred thermoplastics are the polyolefins such as polyethylene or polypropylene, and the fluorocarbon resins. Poly-propylene is the resin of choice sin~e it has demon-strated long-term s~ability in lead-acid battery applications.
The conductive plate of the invention can be readily fabricated by casting or roll molding techni-ques. Referring now to Figure 3, the plate is fabri-cated by placing a sheet 30 of lead foil on the bottomsurface 32 of the casting cavity 34. A mixture of molten resin containing at least 20 to 80% by weight of ~3~

tin oxide coated glass fibers is then poured from mix-ing kettle 36 onto the cavity. After the resin cools, a conductive layer 38 attached to the lead foil 30 is formed.
Referring now to Figure 4, another apparatus for forming a conductive plate includes a supply roll 40 of a thermoplastic resin 41 such as polypropylene, a supply roll 42 of tin oxide coated fiberglass fabric 43 and a supply roll 44 of lead foil 45 having an upper surface coated with a layer 46 of a heat curable, con-ductive adhesive such as an epoxy filled with yraphite fibers and/or powder. The sheek 43 of fiberglass has a thickness slightly less than that of the sheet 41 of polypropylene. When the three sheets are drawn through heated rollers 48, 50, the polypropylene 41 softens.
The fabric is pressed onto the softened resin to form a composite layer 49 and also attaches the foil 45 to form the assembly as shown in Figure 5.
The following experiments were conducted to evaluate the performance of thin films of stannic oxide in the environment of a lead-acid battery.
Example 1 Gla~s plates were coated with a conductive coating of stannic oxide following the procedure of U.S. Patent No. 3,564,707.

Example 2 The stannic oxide coated glass plates of Example 1 were immersed in 5.3 M H2SO4 at both 20C
and 50C. The plates were withdrawn periodically and the resistance of the thin film coating was measured.
The results of measurements during 33 days are shown in Table 1.

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TABLE l Chemical corrosion of stannic oxide thin film in 5.301 M H2SO4.

. -~--- d 50 C ELECTRODE 20C ~LEcTRoDE
TIME RESIST~NCE RESIST~NCE
( DAYS ,? _ ~J~!~. ~9~
0 10.95 10.~4 ______.
l 10.94 10.~4 .,.. . ~_ .. _.. . ~ _ .. ~ ~ . ... . ~
~ 10.95 10.aq . . . ~ ~ _ .,._ __ ~
16 l0.9~ 10.8~
10.94 10. a3 __ _A__ _ , ~ _ _ __ __ _ 26 10.93 10.~2 _ ~
10.93 10.Bl .._ _ 33 10.93 . 10.~1 -_ _~

During tha~ time at both ~emperatures li~ted, the resi~tance ohange was less than 1/1000 of the film's original condition (day-0). .The two s~mples described in the Table started with different resi~-tance values for the reason that the plate~ do not have identical dimensions.
Electrochemical corrosion tests were run utilizing a PAR~ potentiostat, Model 173, to apply a constant potential to either the cathode or anode in the electrochemical cell. This was done by setting the poten~ial of one o~ the electrodes relative to a saturated calomel reference electrode (SCE). Two tests were run ~imultaneously in separate cells. One case corresponded to the SOTF used as an anode (positive .
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terminal) with a fixed potential. The counter electrode was a Pt foil. The second case has the SOTF situated .as ~he cathode, again using the Pt foil as the counter electrode.
5Shown in Table 2 is the data for ten days of electrochemical tests using SOTF as the anode.
TABLE :2 Potentiostatic corrosion of stannic oxide thin ~ilm Anode potential -.1.058 V vs S C E
10Platinum cathode in 5.301 M H2S04 at 22C

TIME RESISTANC~
(DAYS) Q ~20C) 8.12 . ~ 8.11 15 7- -- ~.11 ~.12 With a potential of +1.06 V relative to a calomel electrode, the stannic oxide film did not show a change in resistance wit.hin the measurement uncertainty of the experimental apparatus.
~ he results of using the stannic oxide film as the cathode in the electrochemical aell are shown in Tables 3, 4 and 5.

~J"qf~38682d Potentlostatic corrosion of stannic oxide thin film Cathodic potential - 0~695 V V5 S C E
Platinum anode in 5.301 M H2SO~ at room temperature TIME RESISTAoCE R ~Ro ~HRS) ~rL (20 C) 0 7.85 1.00 1/2 10.65 1.35 . 1-1/2 116.5~ 2.10 TA~LE 4 Potentiostatlc corroslon of stannic oxide thin film Cathodic potential - 0.1 V vs S.C.E.
Platinum anode in 5.301M H2SO4 at room temperature.

TIME ¦ RESISTANCE RT~R
~HRS) ~L ~20C) .. .
7.745 1.000 66 7.756 1.~01 _ . . _ _ . . _~ ~ -T
90 _ 7.754 1.001 130 . 7.753 _ I 1 001 ,..

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Potentiostatic corrosion of ~stannic oxide thin film Cathodic potential - 0O350 V v~ S C E
Platinum anode in 5.301 M H2SO4 at xoom temperatuxe TII~E RESISTANCE Rl,/R
~HRS) Q (20 C) o ..
0 7.599 1.000 . . .
1/27.622 1.003 _~ . . .... . __ 1 7.~41 1.005 _ . . . ~
1.0 2 7.667 1.009 3 7.67~ 1.010 _ _ 7.868 1.011 _ ~ 7.~96 1.012 . . . _ 7.863 = 1.034 i0 7.933 1.0~3 ! 9.589 ___ 1.261 115 I 9.981 1.313 . _ .
163 I 10.873 I 1.430 .

It was found that significant deterioration occurs at both -0.70 V and -0.35 V. Reducing the potential to -0.10 V stopped the electrochemical corrosion. Over a five day period, there was no measureable change in film resiskance.
After 33 days of conducting chemical corrosion ~5 testing, uslng electrical reslstance as the criteria, .

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less than 1/1000 change was detected in the measure-ments, i.e., the standard deviation is less than 1/1000. Since the error bar in the measurement may be a maximum 2/1000, a conservative approach to extrapolating the data is to assume an increase of 2/1000 in the film resistance every 30 days. At this rate of degradation, the SOTF (stannic oxide thin film) would take 20 years to double the initial electrical resistance.
The electrochemical corrosion resistance o~
the SOTF was determined in an electrochemical cell using the SOTF as either the positive or negative electrode and with Pt foil as th0 counter electrode.
The ce11 was set up with a saturated calomel reference electrode (SCE) which was used to fix the potential of the SOTF electrode. As before, 5.3 M sulfuric acid was used and all electrochemical tests were run at 20C. The SOTF electrode (coated glass plate) was removed periodically from the electrochemical cell and measurements were made of the films. Using the SOTF as the anode (positiv~ electrode with a potential of ~1.06 V versus SCE), less than 1/1000 change in electrical resistance was measured a~ter 10 days of continuous running. Given this limited data, it would take approximately seven years for the SOTF to double the initial resistance value~
Another series of experiments were run using SOTF as the cathode tnegative electrode) and Pt foil as the anode at 20C. Initial runs, where the SOTF
potential was set to -1.2 V relative ~o a SCE reference electrode, resulted-in a complete degradation or corro-sion of the thin film within a time frame of five to ten minutes. Running the electrochemical cell with SOTF at -0.70 V versus SCE and -0.35 V versus SCE
resulted in a sign~ficant increase in film electrical .~

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resistance with time. For the case o~ -0.70 V, the resistance doubled with a time of 1 hour while for -0.35 V the time for doubling of resistance is esti-mated to be 14 days. Reducing the SOTF potential further to -0.10 V versus SCE resulted in no notice-able resistance change during five days. Consequently, the threshold potential for degradation o~ SOTF appears to be between -0.10 V& -0.35V versu~ SCE. Polarity reversal below -0.10 V must be avo:ided.
The plate of the invention is a li~uid im-pervious, low resistance, through-plate conc~uctor having application in any stacked electrochemical cell in which it i8 desired to provide conduction to an ad-jacent electrode or an adjacent cell. The plate can be used in batteries, elec~rolysi~ cellq, fuel cells, electrophore~is cells, etc. The pla~e can be used in cells with vertically ox horizontally diqposed cell5.
The preferred cell configuration is horizontal since horizontal disposition of a cell prevents electrolyte stratification and the continuous, flat surface of the bipolar plate of the invention will prevent shedding of active electrode material, the most prominent failur~
mode for lead-acid cells.
A particular, efficient~ horizontal battery con-figuration is disclosed isU.S. Patent 4,539,268 entitled BIPOL~R
SEPARATE CELL BATTERY FOR HIGH OR LOW VOLTAGE, In that patent, bipolar plate groupings are placed betwaen monopolar plates to increase avail-able potantial voltage. The conductive plate of the inven~ion can be utilized as a substrate to form either the bipolar plate or a positive monopolar plate of such a battery. A monopolar plate will differ in haviny the same polarity materlal provided on each ~, .
' ~17-surface thereof, and means to provide lateral conduction to provide for parallel connection to cell yrouping~
Referring now to Figure 6, a biplate grouping 90 can be assembled surroundiny a through~conductive plate 92 of the invention by supporting a layer 94 o~
positive active lead dioxide material on a first ylass scrim sheet 96 and a layer 98 of negative active sponge lead on a second sheet 100 of glass scrim. These sheets 96, 100 are then placed againsk the plate 92 with the active layers 94, 98 in contact with the sur-faces oE the plate 92. The scrim sheets are in turn faced with a porous, fibrous mak 104 æuitably formed from glass fibers. The porous mat is capable o~ releas-ing any gases formed during operation of the cell and holds the electrolyte. The sheets of scrim fabric 98~
lS 100 may be bonded to the mats 104. ~y bonding an oppo-site polarity scrim sheet 106, 108 to each mat 104, a bipolar grouping can be assembled by alternating layers of plates 92 with bipolar porou~ mat assemblies 110, 112.
The bipolar groupings can be interspersed with monopolar plates connected by bus bars to battery term-inals. Alternately, the electrode materials can be plated diractly onto ~he through-conductive substrate plate of the inve~tion. For example, sponge lead can be coated onto one sur~ace and lead dioxide can be coated directly onto the other surace or indirectly onto lead strips coated onto the opposite surface.
Bipolar groupings are formed simply by intersper3ing a porous electroly~e-separator plate between the active material coated bipolar plate. The active materials can be applied as pastes and cured on the scrim or pla~e according to state of the art procedures. The ~S
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active materials can also be formed in situ according to the state of the art by applying lead to each sur face and then placing the electrode materials in elec-trolyte and connecting them to a source of potential.
It is to be realized ~hat only preferred embod-iments of the invention have been described and that numerous substitutions, modifi.cations and alterations are permissible without departing from the spirit and scope of the invention as defined in the following claims.

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Claims

WE CLAIM:

1. A through-conductive plate for a lead-acid bat-tery comprising:
a substrate of matrix resin containing a dispersion of particles containing a coating of conductive tin oxide that is insoluble in sulfuric acid electrolyte, has a high conduc-tivity, and is thermodynamically stable during charge and discharge of said battery.

2. A plate according to claim 1 in which the sub-strate is in powder, filamentary, or fiber form.

3. A plate according to claim 2 in which the sub-strate is a glass fiber having a diameter from about 1 to about 20 microns.

4. A plate according to claim 3 in which the tin oxide is present as a coating having a thickness from a mono-layer to about 10 microns.

5. A plate according to claim 4, in which the coated fibers are present in the resin substrate in an amount from about 20 to about 80 percent by weight.

6. A plate according to claim 5 in which the resin substrate is a polyolefin.

7. A plate according to claim 6 in which the resin substrate is polypropylene.

8. A plate according to claim 1 having a thickness from about 1 to about 20 mils.

9. A plate according to claim 1 having at least one electrode layer on a first surface thereof.

10. A plate according to claim 9 in which the elec-trode layer comprises a positive active paste.

11. A plate according to claim 10 in which the paste contains lead oxide.

12. A plate according to claim 9 in which the elec-trode layer comprises a negative active paste.

13. A plate according to claim 12 further including a protective conductive layer interposed between the surface of the plate and the negative active paste.

14. A plate according to claim 13 in which the prot-ective layer is selected from thin films of metal and a film of resin containing a dispersion of conductive particles.

15. A plate according to claim 14 in which the part-icles are fibers selected from lead or graphite.

16. A plate according to claim 13 in which the neg-ative active paste contains lead.

17. A plate according to claim 1 in which the coat-ing is in the form of a sheet of tin oxide coated glass.