Positive electrode active material for proton-conducting secondary batteries and proton-conducting secondary batteries equipped therewith

Abstract

According to the present invention, a compound which is a solid solution that has a composition containing Mn is used as a positive electrode active material of a proton conducting secondary battery. For example, the positive electrode active material may be a compound which has a composition represented by formula (1) MnaM1-aOxHy (wherein M represents a metal element other than Mn or a combination of metal elements other than Mn; 0 < a ≤ 1; 1 ≤ x ≤ 4; and 0 ≤ y ≤ 7); and M in formula (1) may be one element or a combination of elements that is / are selected from the group consisting of Co, Ni, Li and Bi.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a proton-conducting secondary battery and a proton-conducting secondary battery including the same.

Background Art

[0002] Alkali metals with a small electrochemical equivalent such as lithium are particularly useful as battery constituent materials. By using lithium, the energy per weight can be increased compared to nickel and cadmium that have been conventionally used. However, in the development of rechargeable lithium metal batteries, an effective charge-discharge cycle is an important development issue. When charging and discharging are repeated, "dendrites" of lithium are gradually generated on the surface of the lithium metal electrode, and these grow to the extent of finally contacting the positive electrode, causing an internal short circuit of the battery, and there is a possibility that the battery becomes unusable after a relatively small number of cycles. On the other hand, since silicon, which is generally used as a negative electrode material for lithium ion batteries, has a very high theoretical specific capacity (4000 mAh / g), it causes a remarkable volume lattice expansion of 400% when cycled with lithium. This volume expansion further shortens the cycle life and makes it impossible to effectively use the material in many systems.

[0003] Therefore, as an alternative technology for secondary batteries, it is promising to circulate hydrogen atoms with an extremely low molecular weight. Some materials such as metal hydride alloys like nickel hydroxide are known to be able to absorb and release hydrogen. By combining with an appropriate negative electrode material, these hydrogen storage materials can be used in fuel cells and metal hydride batteries (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] However, the cathode active material commonly used in the above-mentioned metal hydroxide batteries has traditionally been a hydroxide mixture of transition metals with nickel as the main component. When such a cathode active material is used, the charge and discharge capacity of the resulting battery is not considered sufficient.

[0006] The objective of the present invention is to provide a positive electrode active material that can improve the charge-discharge capacity characteristics of a proton-conducting secondary battery in order to solve the above problems. [Means for solving the problem]

[0007] To achieve the aforementioned objectives, the positive electrode active material for a proton-conducting secondary battery according to the present invention is a positive electrode active material used in a proton-conducting secondary battery, and consists of a compound that is a solid solution containing Mn in its composition.

[0008] This configuration dramatically improves the discharge capacity and charge-discharge cycle characteristics of a proton-conducting secondary battery using the positive electrode active material.

[0009] In a positive electrode active material according to one embodiment of the present invention, the active material is, for example, the following formula (1) [ka] (However, in the formula, M is a metal element other than Mn or a combination of metal elements, 0 <a≦1,1≦x≦4,および0≦y≦7) The compound may have a composition represented by formula (1). In formula (1), M may be, for example, one element or a combination of elements selected from the group consisting of Co, Ni, Li, and Bi.

[0010] In a positive electrode active material according to one embodiment of the present invention, in formula (1), for example, a > 0.5 may be, more specifically, a > 0.8 may be, furthermore, a > 0.9 may be, and a > 0.95 may be.

[0011] The proton-conducting secondary battery according to the present invention comprises a positive electrode containing the positive electrode active material, a negative electrode containing a negative electrode active material capable of intercalating and releasing hydrogen, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode.

[0012] This configuration dramatically improves the discharge capacity and charge-discharge cycle characteristics of proton-conducting secondary batteries.

[0013] Any combination of at least two configurations disclosed in the claims and / or specification and / or drawings is included in the present invention. In particular, any combination of two or more of each claim in the claims is included in the present invention. [Brief explanation of the drawing]

[0014] This invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustrative and explanatory purposes only and should not be used to define the scope of this invention. The scope of this invention is defined by the accompanying claims. In the accompanying drawings, the same reference numerals in multiple drawings indicate the same or corresponding parts. [Figure 1] This is a schematic cross-sectional view showing a test cell for testing the properties of an electrolyte according to one embodiment of the present invention. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments.

[0016] The positive electrode active material used in the proton-conducting secondary battery according to this embodiment consists of a compound that is a solid solution containing Mn in its composition. As will be described in detail later, it has been found that using such a material as the positive electrode active material of a proton-conducting secondary battery dramatically improves the discharge capacity and charge-discharge cycle characteristics of the proton-conducting secondary battery.

[0017] The positive electrode active material may be, for example, a compound having a composition represented by the following formula (1): [Chemical formula] (where M is a metal element other than Mn or a combination of metal elements, 0 < a ≤ 1, 1 ≤ x ≤ 4, and 0 ≤ y ≤ 7) In the formula (1), M may be, for example, one element selected from the group consisting of Co, Ni, Li, and Bi or a combination of a plurality of elements.

[0018] In the formula (1), for example, a > 0.5 may be satisfied, more specifically, a > 0.8 may be satisfied, further, a > 0.9 may be satisfied, and a > 0.95 may also be satisfied.

[0019] The proton-conducting secondary battery according to this embodiment includes a positive electrode containing a positive electrode active material made of the above-described materials, a negative electrode containing a negative electrode active material capable of storing and releasing hydrogen, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode.

[0020] The "proton-conducting secondary battery" in this specification is different from a conventional battery using a metal hydride in many aspects, such as not using an aqueous electrolyte. This new type of proton-conducting secondary battery operates by circulating hydrogen between the negative electrode and the positive electrode, similar to a conventional battery. As a result, in the negative electrode, hydrides of one or more elements are formed during charging. This hydride is a reversible product, and during discharging, it generates both protons and electrons as part of the active material of the negative electrode.

[0021] In this specification, the "negative electrode" refers to the electrode side containing a substance that electrochemically receives electrons during charging, and the "positive electrode" refers to the electrode side containing a substance that electrochemically releases electrons during charging.

[0022] The reaction occurring in the negative electrode of the proton-conducting secondary battery is represented by the following half-reaction formula. [ka] The negative electrode active material M in this equation will be discussed later.

[0023] The reaction that occurs at the positive electrode corresponding to the above reaction is represented by the following half-reaction equation. [ka] M in this equation C These are the metallic elements in the positive electrode active material as exemplified above.

[0024] The negative electrode active material is, for example, a hydrogen storage alloy that can absorb hydrogen electrochemically generated in the electrolyte during charging and readily release the absorbed hydrogen during discharge. Such a hydrogen storage alloy may have a structure represented as ABx type, where A is a hydride-forming element, B is a non-hydride-forming element, and x is a real number from 1 to 5. The hydride-forming element (A) includes, but is not limited to, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, yttrium, titanium, zirconium or combinations thereof, or other metals such as mischmetal. The non-hydride-forming element includes, but is not limited to, metals such as aluminum, nickel, cobalt, copper, manganese or combinations thereof. More specific examples of hydrogen storage alloys include, but are not limited to, AB5 type systems such as LaNi5 and MmNi5 (where Mm is mischmetal), AB3 type systems such as rare earth-magnesium-nickel systems, A2B7 type systems such as rare earth-magnesium-nickel systems forming a superlattice structure, and AB2 type systems such as (Zr,Ti)Ni2. Other examples of negative electrode active materials include Group 14 elements, or compounds or alloys consisting of multiple Group 14 elements, specifically, for example, carbon, silicon, silicon carbide (C x Si 1-x ), silicon germanium alloy (Si x Ge 1-x ) are some examples.

[0025] The negative electrode active material and / or the positive electrode active material may be in powder or granular form. The particles may be held together by a binder and formed in layers on a current collector in the formation of the negative or positive electrode. Any binder known in the art may be used as the binder, as long as it is suitable for use in forming the negative electrode, positive electrode, or both, and is suitable for proton conduction.

[0026] Examples of binders used in the formation of the negative electrode include, but are not limited to, polymer binder materials. Specific examples of binder materials include elastomer materials, more specifically, styrene-butadiene (SB), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and styrene-ethylene-butadiene-styrene block copolymer (SEBS). More specific examples of binders include, but are not limited to, polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), Teflon®-polymerized acetylene black (TAB-2), styrene-butadiene binder materials, or carboxymethylcellulose (CMC).

[0027] The positive electrode and / or the negative electrode may further contain one or more types of additives in the active material. These additives are, for example, conductive materials. Preferably, the conductive material is conductive carbon. Examples of conductive carbon include graphite or graphitized carbon such as graphitized coke. Further examples of conductive carbon include amorphous or non-graphitized carbon, such as petroleum coke or carbon black. The conductive material is included in the positive or negative electrode in amounts ranging from, for example, 0.1% to 20% by weight.

[0028] The negative and positive electrodes can be formed by any method known in the art. For example, a layer of the active material can be formed on the surface of a current collector by mixing the active material of the negative electrode or the active material of the positive electrode with a binder and optionally a conductive material in a suitable solvent to form a slurry, coating the current collector with the slurry, and drying it to evaporate some or all of the solvent.

[0029] The current collector may be in the form of a mesh, foil, or other suitable form. For example, the current collector may be made of materials such as aluminum alloys or other aluminum-based metals, nickel or nickel alloys, steel such as stainless steel, copper or copper alloys. The current collector may be, for example, in the form of a sheet, and further may be foil, solid substrate, porous substrate, grid, foam, or a form known in the art. The current collector may be any suitable electronically conductive and selectively impermeable or substantially impermeable material, such as copper, stainless steel, titanium, or carbon paper / film, non-perforated metal foil, aluminum foil, clad materials containing nickel and aluminum, clad materials containing copper and aluminum, nickel-plated steel, nickel-plated copper, nickel-plated aluminum, gold, silver, or any suitable combination thereof.

[0030] The electrolyte used in the proton-conducting secondary battery according to this embodiment is a non-aqueous electrolyte, and for example, comprises an ionic liquid.

[0031] The ionic liquid contained in the electrolyte may, for example, include an aprotic liquid and one or more acids added to the aprotic liquid as a proton source. The aprotic liquid may be any compound suitable as a composition in the electrolyte and which does not undergo harmful reactions with other compounds in the battery. Examples of compounds constituting the aprotic liquid include ammonium or phosphonium compounds, which optionally include one or more linear, branched, cyclically substituted, or unsubstituted alkyl groups bonded to nitrogen or phosphorus.

[0032] The aprotic compound may be, for example, an ammonium or phosphonium compound containing a linear, branched, or cyclic substituted or unsubstituted alkyl group bonded to one or more linear, positively charged nitrogen or phosphorus atoms. The nitrogen or phosphorus may be a constituent element of a five- or six-membered ring structure that may have one or more pendant groups extending from the central ring. Specifically, the ammonium ion may be an imidazolium ion, and the phosphonium ion may be a pyrrolidinium ion.

[0033] Ammonium or phosphonium contains one or two linear or cyclic, substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms. Optionally, the alkyl group contains 2 to 6 carbon atoms. The substituted elements of the alkyl group may be, for example, nitrogen, oxygen, or sulfur.

[0034] Specific examples of aprotic compounds for use as electrolytes include, but are not limited to, 1-butyl-3-methylimidazolium (BMIM), 1-ethyl-3-methylimidazolium (EMIM), 1,3-dimethylimidazolium, 1,2,3-trimethylimidazolium, tris(hydroxyethyl)methylammonium, 1,2,4-trimethylpyrazolium, or combinations thereof.

[0035] Aprotic compounds may contain one or more anions in combination with other aprotic compounds as needed. Examples of anions include, but are not limited to, methides, nitrates, carboxylates, imides, halides, borates, phosphates, phosphinates, phosphonates, sulfonates, sulfates, carbonates, and aluminates. More specifically, anions may include carboxylates such as acetates, phosphates such as hydrogen, alkyl, or fluorophosphates, and phosphinates such as alkyl phosphinates. Examples of such aprotic compounds include, but are not limited to, acetates, sulfonates, or borates of 1-butyl-3-methylimidazolium (BMIM), 1-ethyl-3-methylimidazolium (EMIM), 1,3-dimethylimdiazolium, 1,2,3-trimethylimidazolium, tris(hydroxyethyl)methylammonium, 1,2,4-trimethylpyrazolium, or combinations thereof. Specific examples of such compounds include diethylmethylammonium trifluoromethanesulfonate (DEMA / TfO), 1-ethyl-3-methylimidazolium acetate (EMIM / AC), or 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM / TFSI).

[0036] The ionic liquid electrolyte may, if necessary, have a salt added as a pH buffer. The added salt may be an organic or inorganic salt. Examples of organic salts include, but are not limited to, potassium or sodium citrate, potassium or sodium oxalate, and examples of inorganic salts include, potassium or sodium phosphate, carbonate, or sulfate. The acid dissociation constant (pKa) of these salt additives in aqueous solution may be in the range of 1 to 14. The pKa value of the salt may be lower than 7, lower than 3, and lower than 1.5.

[0037] A proton-conducting secondary battery may include a separator between the negative and positive electrodes. The separator can be permeable to hydrogen ions, allowing or not restricting ion movement between the negative and positive electrodes to an unacceptable degree. Examples of materials that can be used for the separator include, but are not limited to, nylon, polyester, polyvinyl chloride, glass fiber, and cotton. More specifically, the separator may be polyethylene or polypropylene.

[0038] The negative electrode, positive electrode, separator, and ionic liquid used as the electrolyte are housed in an outer casing. The outer casing may be, for example, a metal or polymer can, or a heat-sealable laminate film such as aluminum foil or an aluminum-coated polypropylene film. Thus, the electrochemical battery provided herein may be any known form, such as a button cell, pouch cell, cylindrical cell, or prismatic cell.

[0039] The current collector and / or substrate may have one or more tabs for allowing electrons to move from the current collector to the outside of the battery and for connecting the current collector to a device such as a circuit. The tabs may be formed of any suitable conductive material (e.g., nickel, aluminum, or other metals) and may be connected to the current collector by, for example, welding.

[0040] The present invention will be further described by the following examples, but the present invention is not limited thereto. [Examples]

[0041] Reference example The positive electrode active material related to 1-1 was prepared according to the procedure shown in (1) to (6) below (hereinafter referred to as "procedure (1-1)"). (1) 10 g of NiSO4·6H2O, 10.7 g of CoSO4·7H2O, and 6.4 g of MnSO4·H2O were each dissolved independently in 100 ml of distilled water. These aqueous solutions were then mixed, and water was added until the total volume reached 500 ml. (2) 60 g of NaOH and 15.6 g of Na2CO3 were dissolved in 500 ml of distilled water. (3) After dissolving 6.4 g of NH4Cl in 100 ml of distilled water, NH3·H2O was added until the pH value reached 10. (4) The aqueous solutions of (1) and (2) were added to the aqueous solution of (3) while adjusting them so that the pH value was maintained within the range of 10-10.2. After the entire volume of aqueous solution of (1) had been added, more aqueous solution of (2) was added to raise the pH value to 11.0-11.2. The aqueous solutions from (5) and (4) were stirred continuously at room temperature for 5 hours, and then left at 60°C for 8 hours. The final pH value was 11.0-11.4. (6) After filtering the aqueous solution from (5), it was washed with distilled water and then dried at 60°C for 5 hours.

[0042] Reference example The positive electrode active material related to 1-2 was prepared according to the procedure shown in (1) to (3) below (hereinafter referred to as "procedure (1-2)"). (1) 3g of the material obtained in procedure (1-1) was heated in a warming furnace at 120°C for 3 hours. (2) The temperature of the warming furnace was increased from 120°C to 550°C at a rate of 10°C / min, and then heated at 550°C for 8 hours. (3) Heating in the warming furnace was stopped and natural cooling was allowed.

[0043] Reference example The positive electrode active material related to 1-3 was prepared according to the procedure shown in (1) to (3) below (hereinafter referred to as "procedure (1-3)"). (1) 5g of the material obtained in procedure (1-1) was mixed with 2g of LiOH·H2O. (2) 9g of KOH was dissolved in 21g of distilled water. (3) The solution prepared by adding the powder from (1) to the aqueous solution from (2) was heated in a solution tank at 70°C for 8 hours. (4) The solution from (3) was heated in a warming furnace at 120°C for 3 hours. (5) The temperature of the warming furnace was increased from 120°C to 800°C at a rate of 10°C / min, and then heated at 800°C for 8 hours. (6) Heating in the warming furnace was stopped and natural cooling was allowed.

[0044] Except for using 10g NiSO4·6H2O, 10.7g CoSO4·7H2O, 16.0g MnSO4·H2O, and 8.6g LiOH·H2O as raw materials, the procedure was the same as in (1-1). Reference example The positive electrode active material related to 2-1 was prepared. Furthermore, the procedure was the same as in procedure (1-2), except that the raw materials were as described above. Reference example The positive electrode active material related to 2-2 was prepared. Furthermore, the same procedure as in procedure (1-3) was used, except that the raw materials were as described above. Reference example The positive electrode active material related to 2-3 was prepared.

[0045] Except for adding an additional 2g of MnO2 to the aqueous solution in (1) in procedure (1-1), the procedure is the same as in procedure (1-1). Reference example The positive electrode active material related to 3-1 was prepared. Furthermore, the procedure was the same as in procedure (1-2), except for the points mentioned above. Reference example The positive electrode active material related to 3-2 was prepared. Furthermore, except for the points mentioned above, the procedure was the same as in procedure (1-3). Reference example The positive electrode active material related to 3-3 was prepared.

[0046] Reference example The positive electrode active material related to 4 was prepared according to the procedure shown in (1) to (4) below (hereinafter referred to as "procedure (4)"). (1) 50 g of Mn(NO3)2·4H2O was dissolved in 80 ml of distilled water, and then mixed with 6.4 ml of HNO3 solution. (2) The aqueous solution from (1) was heated to 125°C at a rate of 5°C / min while being stirred, and then left in a vacuum at 125°C for 12 hours. (3) The aqueous solution from (2) was further heated in a warming furnace at 325°C for 5 hours. (4) After that, it was ground using a mortar and pestle.

[0047] The positive electrode active material according to Example 5 was prepared in the same manner as in Procedure (4), except that 4.27 g of Bi(NO3)3·5H2O was dissolved in a mixture of 18.6 ml of distilled water and 6.4 ml of HNO3 solution instead of the 6.4 ml of HNO3 solution used in Procedure (4).

[0048] As a comparative example of a positive electrode active material that does not contain Mn in its composition, Ni was obtained by coprecipitation. 0.87 Co 0.08 Zn 0.05 (OH)2 was prepared, and the powder was obtained by coating this powder with 2% by weight of cobalt oxyhydroxide (CoOOH).

[0049] Table 1 shows the composition of each positive electrode active material prepared in this manner. [Table 1]

[0050] Each of the above positive electrode active material powders was mixed with a dry TAB-2 binder in a weight ratio of 1:3, and then press-molded onto a nickel mesh substrate, which served as the current collector, to produce each positive electrode.

[0051] As the negative electrode active material, a commercially available superlattice hydrogen storage alloy (A2B7 type) prepared using a standard method was used.

[0052] As the electrolyte, EMIM / AC (purity >95%) containing 3.33 mg of acetic acid was used.

[0053] Each of the above Reference example,To perform comparative electrochemical properties tests on the positive electrode active materials of the examples and comparative examples, a test electrochemical cell was fabricated in a Teflon Swagelok tee. The structure of the test cell T used in this charge-discharge test is shown in Figure 1. This test cell T is equipped with a central gland 1, which is covered with a ferrule 2 fixed at both ends by collars 3. The test sample 4 is sandwiched between two current collector rods 5 made of Ni-plated steel (NS) inserted into the central gland 1. The upper channel of the test cell T is covered with Parafilm 6, which is a pressure venting device. The test sample 4 was formed by stacking the above-mentioned negative electrode and positive electrode via a standard separator. The above-mentioned electrolyte was filled into this test cell T.

[0054] (Test results) Regarding the test cells prepared in this manner, • Charging conditions: charging rate 500mA / g, charging termination voltage 3V, charging time 3 hours (2 hours for the 11th cycle). • Discharge conditions: Discharge rates in the order of 50mA / g → 10mA / g → 2mA / g, with a discharge termination voltage of 0V for each. A charge-discharge cycle test was conducted under the specified charge-discharge conditions. The above charge rate and discharge rate are values ​​per unit weight (g) of the positive electrode active material. The results are shown in Table 2. [Table 2]

[0055] As is clear from Table 2, all example cells using manganese-containing materials as the positive electrode active material showed superior discharge capacity compared to comparative example cells using conventional, typical positive electrode active materials that do not contain manganese. More specifically, Reference example cells and The example cell showed superior discharge capacity compared to the comparative example cell in both the total discharge capacity across the three discharge rates and the discharge capacity at the first stage (50 mA / g), which had the highest discharge rate.

[0056] In particular, it contains 100% manganese as a metallic element. Reference example In 4, Reference examples and This cell exhibited the best discharge characteristics among the examples, showing a significant improvement in total discharge capacity of approximately 3.8 times compared to the comparative example cell.

[0057] Furthermore, in Example 5, which contains 95% manganese as a metallic element, in the first stage of high-rate discharge, Reference example It exhibited excellent discharge capacity, comparable to that of 4.

[0058] Thus, by using manganese-containing materials as the positive electrode active material for proton-conducting secondary batteries, the discharge capacity and charge-discharge cycle characteristics of the proton-conducting secondary battery can be significantly improved.

[0059] As described above, preferred embodiments of the present invention have been explained with reference to the drawings, but various additions, modifications, or deletions are possible without departing from the spirit of the invention. Therefore, such additions, modifications, or deletions are also included within the scope of the present invention.

Claims

1. A positive electrode active material used in a proton-conducting secondary battery, It consists of a compound that contains Mn in its composition, The following equation (1) Mn ａ M １－ａ O ｘ H ｙ (1) (However, in the formula, M is one or a combination of elements selected from the group consisting of Co, Ni, Li, and Bi, and 0.5 < a < 1, 1 ≤ x ≤ 4, and 0 ≤ y ≤ 7) A compound having the composition represented by, In equation (1), a > 0.8, Positive electrode active material for proton-conducting secondary batteries.

2. In the positive electrode active material according to claim 1, In equation (1), a > 0.9, Positive electrode active material for proton-conducting secondary batteries.

3. In the positive electrode active material according to claim 1, In equation (1), a > 0.95, Positive electrode active material for proton-conducting secondary batteries.

4. A positive electrode containing a positive electrode active material, A negative electrode containing a negative electrode active material capable of hydrogen absorption and release, A non-aqueous electrolyte interposed between the positive electrode and the negative electrode, Equipped with, The positive electrode active material is, It consists of a compound that contains Mn in its composition, The following equation (1) Mnal １－ａ O8Hy (1) (However, in the formula, M is one or a combination of elements selected from the group consisting of Co, Ni, Li, and Bi, and 0.5 < a < 1, 1 ≤ x ≤ 4, and 0 ≤ y ≤ 7) A proton-conducting secondary battery, which is a compound having the composition represented by [formula].

Images