Separator for batteries and method for manufacturing the same

Abstract

A separator which is permeable to hydroxide ion contains at least one Dendrite Stopping Substance such as Ni(OH)2, or its precursor.

Claims

1. A method for preparing a separator, which is permeable to hydroxide ions, for use in an electrically rechargeable electrochemical cell with alkaline electrolyte between a zinc electrode and a counter electrode, wherein: (a) said separator is constituted by a porous or fibrous material defining cavities or pores, and at least one Dendrite Stopping Substance or DSS, said DSS being a metal-containing compound, said metal selected from the group consisting of Pt, Pd, Ni, Fe and Mn, and, (b) said DSS being in a form of particles, said method comprising: a first step of soaking a porous or fibrous material defining cavities or pores with a first solution comprising at least one DSS precursor, said DSS being a metal-containing compound, said metal being selected from the group consisting of Pt, Pd, Ni, Fe and Mn, and a second step of impregnating the resulting soaked material with a second solution, wherein said second solution allows the precipitation of the at least one DSS precursor in form of the DSS particle, wherein the material resulting from the second step contains the at least one DSS particle within its cavities or pores, and wherein the material resulting from the second step forms the separator.

2. The method according to claim 1, wherein the second solution is selected from the group comprising KOH solution, NaOH solution, Na.sub.2CO.sub.3 solution and K.sub.2CO.sub.3 solution.

3. The method according to claim 1, comprising: a third step of removing mechanically the excess of the at least one DSS particle from the surface of the separator.

Description

LEGEND TO THE FIGURE

(1) FIG. 1 shows a cross section view of a zinc-air battery cell with second reversible electrode and without auxiliary electrode, where (11) is an air electrode; (12) is a first reversible zinc electrode; (13) is a second reversible nickel-oxide electrode; (14) (15) are separators placed in between the neighboring electrodes; (16) is the casing of the battery.

EXAMPLES

Example 1

(2) In this first example the inventors prepare a separator according to the invention by: adding 7 g of 50-100 m Ni(OH).sub.2 particles to 100 ml ethanol C.sub.2H.sub.5OH and mixing with a magnetic stirrer 20 min. then 3.3 ml of PTFE suspension (DuPont Teflon PTFE TE-3893 with particle size 0.05 to 0.5 m, solid content 60%, density 1.5 g/cc) is added to the mixture and further mixed for 2 h. then the mixture is left to rest and decant. then the decanted solid mass is well kneaded and rolled 12 times to obtain separator layers of thickness down to 0.2 mm. finally, these separator layers are dried 48 h at 30 C. during which time the thickness of the separator increases from 0.2 mm up to 0.25 to 0.3 mm.

(3) The separator obtained has a very good dendrite stopping effect.

(4) It is to be noted that by using Ni(OH).sub.2 particles smaller than 50 m thinner layers can be rolled, thus permitting to obtain a separator final thickness of only 0.1 to 0.15 mm.

Example 2

(5) In this second example to prepare a separator according to the invention, the inventors use a microporous PVC separator having a thickness of 1.1 mm for use in lead-acid batteries manufactured by Microtex Energy P Ltd., Bengaluru560058, Karnataka, India. This material is first soaked during 1 hour with a 200 g/l NiSO.sub.4 solution (nickel sulfate NiSO.sub.4 is very soluble in water), then impregnated during 1 hour by strong alkaline solution, 100 g/l KOH, resulting in a precipitation of Ni(OH).sub.2 particles within the pores of the microporous separator. It is to be noted that Ni(NO3)2 and NiCl2 could be used instead of NiSO.sub.4 as DSS precursor, while NaOH, Na.sub.2CO.sub.3 or K2CO3 could be swapped for KOH. Also the concentrations of both the DSS precursor and alkaline electrolyte can vary in a range of 35% to 300%.

(6) Then the separator is well rinsed in water and dried, the excess of Ni(OH).sub.2 being removed from the separator's surface mechanically.

(7) As a result, the in-pore Ni(OH).sub.2 particles could occupy from 5 to 50% of pore volume with various particle-size distribution.

(8) Ni(OH).sub.2 particles are 5 to 10 weight percent from the final separator's weight.

(9) Such prepared separator possesses enhanced counter-dendrites properties.

Example 3

(10) In this third example one cell zinc-air battery is prepared including:

(11) 1a Zinc anode, an Air-Electrode and an auxiliary electrode as described in FIG. 2 of WO2013/110097. Briefly, the battery cell contains the components described below with an additional indifferent auxiliary electrode made of fine nickel mesh (such as 6 Tyler mesh), it could also be an Ni-coated iron grid, electrically connected to the nickel-oxide electrode during cell charge.

(12) A battery cell is prepared, and as shown in FIG. 1 contains the following components: an air electrode (11) produced by the company MEET (Korea, www.mee-t.com); a zinc electrode (12), having Ca 5 mm thickness and 5.5 Ah nominal capacity, prepared for example as described in PCT Application PCT/AM2010/000001; a nickel-oxide electrode (13) possessing 1.1 Ah nominal capacity such as one from NKBN 11 D NiCd accumulator of Lugansk accumulator production plant; all these electrodes having the same visible surface area of 4080 mm.sup.2;

(13) 2a porous separator (14) and (15) according to the invention (with DSS) used to wrap the Zinc electrode.

(14) The zinc anode, the separator, the counter electrode and the air-electrode are bathing, immersed in a strong 6M KOH electrolyte.

(15) This battery setup is submitted to cycles of 8 hours 20 mA/cm.sup.2 charging and 6 hours discharging at 25 mA/cm.sup.2.

(16) At first, a battery comprising the separator as described in Example 2 is carried out and no dendrite is piercing it after 50 cycles.

(17) Secondly, a battery comprising the separator used is the initial PVC microporous separator of example 2, but without the preparation according to this invention (i.e. without DSS) is carried out. When used without DSS this separator is pierced by dendrites after less than 5 cycles at the same charge-discharge conditions.

(18) This example shows that the separator of Example 2 possesses enhanced counter-dendrites properties.

(19) Specific embodiments of the invention have been described by the way of exemplary teachings however the scope of the present invention is not limited to the specific details and the illustrative examples shown and described. It will be apparent to persons skilled in the art that modifications and variations can be made without departing from the scope of the invention.