Patent Application
20240097221
The present disclosure relates to a nickel-zinc secondary battery.
It is known that in zinc secondary batteries such as a nickel-zinc secondary battery and an air-zinc secondary battery, metallic zinc in a dendrite form precipitates from a negative electrode upon charge, penetrates voids of a separator such as a nonwoven fabric, and reaches a positive electrode, resulting in occurrence of a short circuit. This short circuit due to such zinc dendrites leads to shorten repeated charge/discharge life. In order to deal with the problems described above, a battery comprising a layered double hydroxide (LDH) separator that blocks the penetration of zinc dendrite while selectively permeating hydroxide ions has been proposed (see, for example, Patent Literature 1 (WO2016/076047), and Patent Literature 2 (WO2019/124270)). Moreover, LDH-like compounds have being known as hydroxides and/or oxides with a layered crystal structure that cannot be called LDH but are analogous thereto, which exhibit hydroxide ion conductive properties similar to those of a compound to an extent that it can be collectively referred to as hydroxide ion conductive layered compounds together with LDH. For example, Patent Literature 3 (WO2020/255856) discloses a hydroxide ion conductive separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that clogs up pores in the porous substrate. Patent Literature 4 (WO2019/069760) and Patent Literature 5 (WO2019/077953) have proposed a zinc secondary battery having a configuration in which the whole of a negative electrode active material layer is covered or wrapped up with an electrolyte retention member and an LDH separator, and a positive electrode active material layer is covered or wrapped up with an electrolyte retention member. A nonwoven fabric is used as the electrolyte retention member. It is described that according to such a configuration, complicated sealing and bonding between the LDH separator and a battery container is unnecessary, and hence a zinc secondary battery (especially a stacked-cell battery thereof) capable of preventing zinc dendrite propagation can be produced extremely easily and with high productivity.
By the way, vinylon nonwoven fabrics and separators are commercially available. In particular, a vinylon separator is used in alkaline batteries such as an alkaline manganese battery (alkaline dry battery). Vinylon is a generic term for polyvinyl alcohol (PVA)-based synthetic fibers, and generally refers to synthetic fibers obtained using PVA as a raw material. On the other hand, polyvinyl alcohol used in vinylon is known to deteriorate in air by heating at 200° C. or more, or deteriorate in an alkaline aqueous solution. For example, Non-Patent Literature 1 (see Kiyokazu Imai, “Polyvinyl Alcohol no Rekka (Deterioration of Polyvinyl Alcohol)”, Polymer, 1962, Vol. 11, No. 6, p. 426-430, published on 2011 Sep. 21) describes, about thermal deterioration of PVA in air at 200° C. or more, together with reaction formulas of deterioration mechanisms, that main deterioration reactions are generation of a carbonyl group (oxidation), a double bond (dehydration) (a conjugated enone structure or a polyene structure), a crosslinking bond or branched bond, and split of the main chain. Besides, this literature describes that PVA splits in an alkaline aqueous solution and in the presence of air, but does not split in nitrogen, and that this is because PVA is oxidized by air to generate a carbonyl group in the main chain, and is subsequently split by a retroaldol reaction. Besides, Non-Patent Literature 2 (Shuji Matsuzawa, “Polyvinyl Alcohol no Bunkai to Hashikake (Decomposition and Crosslinking of Polyvinyl Alcohol)”, Polymer, 1963, Vol. 12, No. 4, P. 283-287, published on 2011 Sep. 21) describes that PVA is decomposed when heated at 200° C. or more in air, and describes, together with reaction formulas, a reaction mechanism in which when a ketone group is once formed by oxidation in air, PVA is decomposed, an aldehyde group is formed in the decomposed portion, and PVA having this aldehyde group is further decomposed. Besides, this literature also describes, together with reaction formulas, that when PVA is boiled in an alkaline aqueous solution, a retroaldol reaction is caused, and the thus generated end group would be an aldehyde group, and that PVA having a carbonyl group introduced into the main chain excluding ends is decomposed completely similarly through a retroaldol reaction.
By providing the above-described countermeasures against dendrite, cycle life of a nickel-zinc secondary battery can be elongated. The life of a nickel-zinc secondary battery depends, however, not only on the cycle life but also on calendar life. Therefore, improvement of calendar life of a nickel-zinc secondary battery is demanded.
The inventors have now found that calendar life can be significantly improved by providing an oxygen absorber inside a nickel-zinc secondary battery.
Accordingly, an object of the present invention is to provide a nickel-zinc secondary battery having significantly improved calendar life.
The present invention provides the following aspects.
A nickel-zinc secondary battery, comprising, in a sealed container, a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, and an electrolytic solution, wherein an oxygen absorber is provided in a position where oxygen generated in the positive electrode in the sealed container is absorbable.
The nickel-zinc secondary battery according to aspect 1, wherein the position where oxygen generated in the positive electrode is absorbable is at least one selected from the group consisting of a surface or surrounding of the positive electrode, a surface or surrounding of the negative electrode, a position between the positive electrode and the negative electrode, a surface or surrounding of the separator, an inner wall of the sealed container, a surface of a positive electrode current collector tab extending from the positive electrode, a surface of a negative electrode current collector tab extending from the negative electrode, and an extra space in the sealed container.
The nickel-zinc secondary battery according to aspect 1 or 2, wherein the oxygen absorber is at least one selected from the group consisting of a metal powder, titanium dioxide, cerium oxide, a transition metal salt, a ferrous salt, a dithionite salt, zeolite, vinylon, benzenetriol, a polyhydric phenol compound, a polyhydric alcohol compound, an ascorbic acid compound, a cyclohexene compound, a polyene-based polymer having an unsaturated double bond, and an ethylene-vinyl alcohol copolymer.
The nickel-zinc secondary battery according to any one of aspects 1 to 3, wherein the oxygen absorber is in the form of a nonwoven fabric, and the positive electrode and/or the negative electrode is covered with the nonwoven fabric.
The nickel-zinc secondary battery according to aspect 4, wherein the nonwoven fabric contains vinylon.
The nickel-zinc secondary battery according to any one of aspects 1 to 5, wherein the positive electrode contains nickel hydroxide and/or nickel oxyhydroxide, and the negative electrode contains zinc and/or zinc oxide.
2NiOOH+H2O→2Ni(OH)2+1/2O2↑ (a1)
2NiOOH+H2→2Ni(OH)2 (a2)
Zn+H2O→ZnO+H2↑(b1)
Zn+1/2O2→ZnO (b2)
In this self-discharge, the amount of consumption of negative electrode discharge capacity is larger than the amount of consumption of positive electrode discharge capacity during the storage, and therefore, residual capacity is decreased in a larger amount in the negative electrode than in the positive electrode. This is because, as illustrated in
Thus, a factor most largely affecting calendar life reduction is probably consumption of the negative electrode discharge capacity larger than consumption of the positive electrode discharge capacity due to a self-discharge reaction. In this regard, a cause of the consumption of the negative electrode discharge capacity can be that although oxygen and hydrogen are generated respectively in the positive electrode and the negative electrode through electrolysis of water, the reaction of absorbing, by the negative electrode, the oxygen generated in the positive electrode (formula (b2)) has not been conventionally dealt with. As a result, a state where the generation and absorption of oxygen through the formulas (a1) and (b2) proceeds faster than the generation and absorption of hydrogen through the formulas (b1) and (a2) is left unresolved, which reduces calendar life. Therefore, in the present invention, the oxygen absorber 17 is provided within the nickel-zinc secondary battery 10 as illustrated in
The oxygen absorber 17 is provided in a position where oxygen generated in the positive electrode 12 in the sealed container 20 is absorbable. Accordingly, the oxygen absorber 17 is provided to cover the surfaces or surroundings of the positive electrode 12 and the negative electrode 14 in
The oxygen absorber 17 is not especially limited as long as it is a material capable of absorbing, adsorbing or capturing oxygen, and may be any of various known materials. Examples of the oxygen absorber 17 include a metal powder, titanium dioxide, cerium oxide, a transition metal salt, a ferrous salt, a dithionite salt, zeolite, vinylon, benzenetriol, a polyhydric phenol compound, a polyhydric alcohol compound, an ascorbic acid compound, a cyclohexene compound, a polyene-based polymer having an unsaturated double bond, an ethylene-vinyl alcohol copolymer, and a combination thereof. Specific examples of these oxygen absorbers 17 include those shown in the following table.
The form of the oxygen absorber 17 is not especially limited and may be appropriately selected in accordance with the form and type of the oxygen absorber to be used, and can be any of various forms including a fabric product such as a nonwoven fabric, a powder, a paste, a coating, a film, a plate, a tablet, and a bulk.
The oxygen absorber 17 is preferably in the form of a nonwoven fabric. It is noted that the term “nonwoven fabric” used herein refers to a sheet-shaped product obtained by entangling, without weaving, fibers with one another, and encompasses not only those designated as nonwoven fabrics but also those designated as paper, namely, how it is called does not matter. In addition, it is preferable that the positive electrode 12 and/or the negative electrode 14 is covered with the oxygen absorber 17 in the form of a nonwoven fabric as illustrated in
The positive electrode 12 contains a positive electrode active material. The positive electrode active material preferably contains nickel hydroxide and/or nickel oxyhydroxide. Representatively, it is preferable that the positive electrode 12 further includes a positive electrode current collector (not shown), and that the positive electrode current collector has the positive electrode current collector tab 13 extending from an end (for example, an upper end) thereof. A preferred example of the positive electrode current collector includes a nickel porous substrate such as a foam nickel plate. In this case, for example, when a paste containing an electrode active material such as nickel hydroxide is uniformly applied on a nickel porous substrate, and the resultant is dried, a positive electrode plate including a positive electrode/positive electrode current collector can be favorably produced. At this point, it is also preferred that the dried positive electrode plate (namely, the positive electrode/positive electrode current collector) is subjected to pressing to prevent the electrode active material from coming off and to improve electrode density. Although the positive electrode 12 illustrated in
The positive electrode 12 may contain an additive that is at least one selected from the group consisting of a silver compound, a manganese compound, and a titanium compound, and thus, a positive electrode reaction for absorbing hydrogen gas generated through self-discharge reaction can be accelerated. Besides, the positive electrode 12 may further contain cobalt. Cobalt is contained in the positive electrode 12 preferably in the form of cobalt oxyhydride. In the positive electrode 12, cobalt functions as a conductive auxiliary agent to contribute to improvement of charge/discharge capacity.
The negative electrode 14 includes the negative electrode active material. The negative electrode active material preferably contains zinc and/or zinc oxide. The zinc may be contained in any form of a zinc metal, a zinc compound, and a zinc alloy as long as it has electrochemical activity suitable for the negative electrode. Preferred examples of the negative electrode material include zinc oxide, a zinc metal, and calcium zincate, and a mixture of a zinc metal and zinc oxide is more preferred. The negative electrode active material may be in the form of a gel, or may be mixed with the electrolytic solution 18 to obtain a negative electrode mixture. For example, a gelled negative electrode can be easily obtained by adding an electrolytic solution and a thickener to a negative electrode active material. Examples of the thickener include polyvinyl alcohol, polyacrylate, CMC, and alginic acid, and polyacrylic acid is preferred because of excellent chemical resistance to strong alkali.
As the zinc alloy, a zinc alloy containing neither mercury nor lead, known as mercury-free zinc alloy, can be used. For example, a zinc alloy containing 0.01 to 0.1% by mass of indium, 0.005 to 0.02% by mass of bismuth, and 0.0035 to 0.015% by mass of aluminum is preferred because it has an effect of inhibiting hydrogen gas generation. In particular, indium and bismuth are advantageous in improving discharge performance. When a zinc alloy is used in the negative electrode, a self-dissolution rate in an alkaline electrolytic solution is decreased to inhibit hydrogen gas generation, and thus, safety can be improved.
The shape of the negative electrode material is not especially limited, and is preferably a powder shape, and thus, the surface area is increased to cope with large current discharge. A preferred average particle size of the negative electrode material is, in using a zinc alloy, in a range of 3 to 100 μm in minor axis, and when the average particle size is within this range, the surface area is so large that large current discharge can be suitably coped with, and in addition, the material can be easily homogeneously mixed with an electrolytic solution and a gelling agent, and handleability in assembling the battery is favorable.
It is preferable that the negative electrode 14 further includes a negative electrode current collector 15, and that the negative electrode current collector 15 has the negative electrode current collector tab 15a extending from an end (for example, an upper end) of the negative electrode 14. The negative electrode current collector tab 15a is provided preferably in a position not overlapping with the positive electrode current collector tab 13. The nickel-zinc secondary battery 10 preferably further includes a negative electrode current collector plate connected to a tip of the negative electrode current collector tab 15a, and more preferably, a plurality of negative electrode current collector tabs 15a are connected to one negative electrode current collector plate. In this manner, current collection can be space efficiently conducted with a simple configuration, and connection to a negative electrode terminal 28 is also eased. Besides, the negative electrode current collector plate itself may be used as the negative electrode terminal 28.
Preferable examples of the negative electrode current collector 15 include a copper foil, a copper expanded metal, and a copper punched metal, and a copper expanded metal is more preferred. In this case, for example, a negative electrode plate including a negative electrode/negative electrode current collector can be favorably produced by applying, on a copper expanded metal, a mixture containing a zinc oxide powder and/or a zinc powder, and optionally a binder (for example, a polytetrafluoroethylene particle). At this point, it is also preferred that the dried negative electrode plate (namely, the negative electrode/negative electrode current collector) is subjected to pressing to prevent the electrode active material from coming off and to improve electrode density.
An electrolyte retention member may be provided to cover or wrap up the positive electrode 12 and/or the negative electrode 14. In this manner, the electrolytic solution 18 can be uniformly present between the positive electrode 12 and/or the negative electrode 14, and the separator 16. Accordingly, hydroxide ions can be efficiently transferred between the positive electrode 12 and the separator 16, and/or between the negative electrode 14 and the separator 16. The electrolyte retention member is not especially limited as long as it is a member capable of retaining the electrolytic solution 18, and is preferably a sheet-shaped member. Preferable examples of the electrolyte retention member include a nonwoven fabric, a water-absorbent resin, an electrolyte retention resin, a porous sheet, and various spacers, and a nonwoven fabric is particularly preferable because a high performance negative electrode structure can be thus produced at low cost. Accordingly, it is most preferable that a nonwoven fabric (for example, a vinylon nonwoven fabric) used as the oxygen absorber 17 is used as the electrolyte retention member. As described above, the term “nonwoven fabric” used herein refers to a sheet-shaped product obtained by entangling, without weaving, fibers with one another, and encompasses not only those designated as nonwoven fabrics but also those designated as paper, namely, how it is called does not matter.
The electrolyte retention member or the nonwoven fabric (that can be the oxygen absorber 17) has a thickness of preferably 10 to 200 μm, more preferably 20 to 200 μm, further preferably 20 to 150 μm, particularly preferably 20 to 100 μm, and most preferably 20 to 60 μm. When the thickness falls in the above-described range, with the entire size of the negative electrode structure efficiently suppressed to be compact, a sufficient amount of the electrolytic solution 18 can be retained in the electrolyte retention member.
The separator 16 is provided to be interposed between the positive electrode 12 and the negative electrode 14. As the separator 16, any separator generally used in an alkaline secondary battery or a zinc secondary battery may be used, a microporous film separator (made of, for example, a polyolefin such as polyethylene, or polypropylene) may be used, and a hydroxide ion conductive separator such as an LDH separator is preferably used because penetration of zinc dendrite can be blocked while selectively permeating hydroxide ions. When a hydroxide ion conductive separator is used, it is preferable to employ a configuration in which both or one of the positive electrode 12 and the negative electrode 14 are covered or wrapped up with the hydroxy ion conductive separator 16 as illustrated in
The hydroxide ion conductive separator 16 is not especially limited as long as it is a separator capable of separating the positive electrode 12 and the negative electrode 14 such that hydroxide ions can be conducted, and representatively is a separator that contains a hydroxide ion conductive solid electrolyte, and selectively allows hydroxide ions to pass by solely utilizing hydroxide ion conductivity. A preferred hydroxide ion conductive solid electrolyte is a layered double hydroxide (LDH) and/or an LDH-like compound. Accordingly, the hydroxide ion conductive separator 16 is preferably an LDH separator. The “LDH separator” herein is a separator containing an LDH and/or an LDH-like compound, and is defined as a separator that selectively allows hydroxide ions to pass by solely utilizing hydroxide ion conductivity of the LDH and/or the LDH-like compound. The “LDH-like compound” herein is a hydroxide and/or oxide having a layered crystal structure analogous to LDH but is a compound that may not be called LDH, and it can be said to be an equivalent of LDH. However, according to a broad sense of definition, it can be appreciated that “LDH” encompasses not only LDH but also LDH-like compounds. The LDH separator is preferably composited with a porous substrate. Accordingly, it is preferred that the LDH separator further includes a porous substrate, and is composited with the porous substrate with the LDH and/or the LDH-like compound filled in pores in the porous substrate. In other words, in a preferred LDH separator, the LDH and/or the LDH-like compound clogs up pores in the porous substrate so that hydroxide ion conductivity and gas impermeability can be exhibited (thereby the LDH separator can function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymer material, and the LDH is particularly preferably incorporated over the entire area in the thickness direction of the porous substrate made of a polymer material. For example, known LDH separators disclosed in Patent Literatures 1 to 5 can be used. The thickness of the LDH separator is preferably 5 to 100 μm, more preferably 5 to 80 μm, further preferably 5 to 60 μm, and particularly preferably 5 to 40 μm.
When the positive electrode 12 and/or the negative electrode 14 are covered or wrapped up with the electrolyte retention member (that can be the oxygen absorber 17) and/or the separator 16, outer edges thereof (excluding a side on which the positive electrode current collector tab 13 or the negative electrode current collector tab 15a is extended) are preferably closed. In this case, closed sides of the outer edges of the electrolyte retention member and/or the separator 16 are preferably realized by bending the electrolyte retention member and/or the separator 16, or sealing the edges of the electrolyte retention member and/or the edges of the separator 16. Preferred examples of the sealing method include an adhesive, thermal welding, ultrasonic welding, an adhesive tape, a sealing tape, and a combination thereof. In particular, an LDH separator including a porous substrate made of a polymer material has flexibility, and hence is advantageously easily bent, and therefore, it is preferred that the LDH separator formed into a rectangular shape is bent to obtain a state where one side of the outer edges is closed. For thermal welding and ultrasonic welding, a commercially available heat sealer or the like may be used, and in sealing the edges of an LDH separator, it is preferred to perform the thermal welding and the ultrasonic welding with an outer circumferential portion of the electrolyte retention member sandwiched between outer circumferential portions of the LDH separator because the sealing can be thus more effectively performed. On the other hand, as an adhesive, an adhesive tape, and a sealing tape, commercially available products may be used, and in order to prevent deterioration otherwise caused in an alkaline electrolytic solution, one containing an alkali resistant resin is preferred. From this point of view, preferred examples of the adhesive include an epoxy resin-based adhesive, a natural resin-based adhesive, a modified olefin resin-based adhesive, and a modified silicone resin-based adhesive, among which an epoxy resin-based adhesive is more preferred because of excellent alkali resistance. An example of products of the epoxy resin-based adhesive includes an epoxy adhesive, Hysol® (manufactured by Henkel).
The electrolytic solution 18 preferably contains an alkali metal hydroxide aqueous solution. Although the electrolytic solution 18 is merely locally illustrated in
The battery components 11 are preferably formed, as illustrated in
The sealed container 20 is preferably made of a resin. The resin constituting the sealed container 20 is preferably a resin having resistance to an alkali metal hydroxide such as potassium hydroxide, more preferably a polyolefin resin, an ABS resin, or modified polyphenylene ether, and further preferably an ABS resin or modified polyphenylene ether. The sealed container 20 has a top cover 20a. The sealed container 20 (for example, the upper cover 20a) may have a pressure release valve for releasing a gas. Besides, a container group in which two or more sealed containers 20 are arranged may be housed in an outer frame to obtain a configuration of a battery module.
The present invention will be further specifically described with reference to the following examples.
A positive electrode plate, a negative electrode plate, an LDH separator, a nonwoven fabric, a battery case, and an electrolytic solution as follows were prepared.
The positive electrode plate was wrapped up from the both surfaces with the nonwoven fabric in such a manner as to cause the nonwoven fabric to slightly protrude from three sides excluding a side on which a positive electrode current collector tab extended. Excessive portions of the nonwoven fabric thus protruded from the three sides of the negative electrode plate were thermally welded with a heat seal bar to obtain a positive electrode structure. Besides, the negative electrode plate was wrapped up from the both surfaces successively with the nonwoven fabric and the microporous separator in such a manner as to cause the nonwoven fabric and the microporous film separator to slightly protrude from three sides excluding a side on which a negative electrode current collector tab extended. Excessive portions of the nonwoven fabric and the microporous film separator thus protruded from the three sides of the positive electrode plate were thermally welded with a heat seal bar to obtain a negative electrode structure. In this manner, 25 electrode structures in total including 12 positive electrode structures and 13 negative electrode structures were prepared. The positive electrode structures and the negative electrode structures were alternately stacked to be arranged in the battery case. A positive electrode current collector and a negative electrode current collector were respectively connected to a positive electrode current collector terminal and a negative electrode current collector terminal, and the resin case and a resin cover were integrated with each other by thermal welding. Thereafter, the electrolytic solution was added through an electrolyte inlet, and was sufficiently impregnated in the positive electrode plates and the negative electrode plates by evacuation or the like. Thereafter, the electrolyte inlet was closed to obtain a sealed cell.
A charge/discharge system (manufactured by Toyo System Co., Ltd., TOSCAT 3100) was used to subject the sealed cell to chemical conversion by 0.1 C charge and 0.2 C discharge. Thereafter, 0.5 C charge/discharge was conducted, and initial discharge capacity was measured at 25° C. After the measurement of the discharge capacity, the sealed cell was charged to 50% SOC, the cell in this charged state was stored for 30 days under an environment of 65° C., and then the discharge capacity was measured in the same manner as described above. Here, a ratio of the discharge capacity after the storage to the initial discharge capacity was calculated as a discharge capacity retention (%). This series of operations were repeated until the discharge capacity retention was lowered to 70% or less. The number of days elapsed until the discharge capacity retention was lowered to 70% or less was evaluated as an index corresponding to calendar durability performance. Higher calendar durability performance means longer calendar life. The temperature during the storage was set to a high temperature of 65° C. in order to acceleratedly evaluate the calendar durability performance and the calendar life.
A battery was produced and evaluated in the same manner as in Example 1 except that the following LDH separator was used as a separator instead of the microporous film.
A battery was produced and evaluated in the same manner as in Example 2 except that a vinylon nonwoven fabric (product name: BFN No. 2, manufactured by Kuraray Co., Ltd., thickness: 84 μm) was used, instead of the polyolefin nonwoven fabric, as an oxygen absorber in the form of a nonwoven fabric covering the positive electrode plate and the negative electrode plate.
Table 2 shows results obtained in Examples 1 to 3. Calendar life of each example was calculated as a relative value to the calendar life (the number of days elapsed until the discharge capacity retention was lowered to 70% or less) obtained in Example 1.
It is understood, based on the results shown in Table 2, that the calendar durability performance, namely, calendar life, is improved by 1.5 times in Example 3 (Example) using an oxygen absorber of vinylon as compared with in Examples 1 and 2 (Comparative Examples) not using an oxygen absorber of vinylon.
Besides,
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-098351 | Jun 2021 | JP | national |
This application is a continuation application of PCT/JP2022/022988 filed Jun. 7, 2022, which claims priority to Japanese Patent Application No. 2021-098351 filed Jun. 11, 2021, the entire contents all of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/022988 | Jun 2022 | US |
| Child | 18524808 | US |
