Aqueous electrolyte for proton battery and proton battery

Abstract

This aqueous electrolyte solution for proton batteries has pyrophosphoric acid (H4P2O7) dissolved in water at a concentration of 6 mol or more per 1 kg of water, and does not have a freezing point at-60 DEG C or more. In addition, the proton battery disclosed by the invention is provided with the aqueous electrolyte disclosed by the invention. In addition, the proton battery disclosed by the invention is provided with the aqueous electrolyte disclosed by the invention.

Description

Technical Field

[0001] The present disclosure relates to a water electrolyte for a proton battery and a proton battery. Background Art

[0002] The number of components of a non-aqueous battery with a flammable non-aqueous electrolyte increases, and as a result, there is a problem that the energy density per unit volume of the battery as a whole becomes lower. In contrast, an aqueous battery with a non-flammable aqueous electrolyte has various advantages such as being able to increase the energy density per unit volume. Therefore, an aqueous battery with an aqueous electrolyte has been developed.

[0003] Japanese Patent Application Laid-Open No. 2007-194105 discloses a proton conductive polymer battery comprising a positive electrode, a negative electrode and an electrolyte. The electrolyte is an aqueous solution with sulfuric acid as an electrolyte. Part of the water contained in the electrolyte is replaced by at least one of phosphoric acid and diphosphoric acid. The sulfuric acid concentration in the electrolyte is 3 to 35% by weight, and the water concentration is 65% by weight or less.

[0004] Japanese Patent Application Laid-Open No. 2019-220294 discloses an aqueous electrolyte, which is an aqueous electrolyte for an aqueous potassium ion battery and contains water and potassium pyrophosphate dissolved at a concentration of 2 mol or more per 1 kg of water.

[0005] Japanese Patent Application Laid-Open No. 2006-164945 discloses a liquid electrolyte composed of an alkali A and a phosphoric acid B, wherein the molar ratio of A to B is in the range of 1:3 to 1:50 and the solidification temperature is lower than -30°C. Summary of the invention

[0006] In recent years, proton batteries, in which protons move between the positive electrode and the negative electrode through an electrolyte, have been developed as secondary batteries to replace lithium-ion secondary batteries. Such proton batteries use aqueous electrolytes, and low-temperature stability is required in order to be able to use the batteries even in extremely low temperatures such as in cold regions.

[0007] An object of the present invention is to provide an aqueous electrolyte for a proton battery having excellent low-temperature stability and a proton battery having such an aqueous electrolyte.

[0008] The inventors of the present invention have found that the above-mentioned problems can be solved by the following means.

[0009] Method 1

[0010] A water-based electrolyte for a proton battery, comprising water and pyrophosphoric acid dissolved in the water at a concentration of 6 mol or more per 1 kg of the water, and

[0011] The aqueous electrolyte has no freezing point above -60°C.

[0012] Method 2

[0013] The aqueous electrolyte as described in method 1 has the pyrophosphate dissolved in the water at a concentration of more than 6 mol and less than 25 mol per 1 kg of the water, or has the pyrophosphate and potassium salt dissolved in the water at a concentration of more than 25 mol per 1 kg of the water.

[0014] Method 3

[0015] In the aqueous electrolyte according to Embodiment 2, the potassium salt is potassium phosphate.

[0016] Method 4

[0017] In the aqueous electrolyte according to Embodiment 3, the potassium phosphate is potassium pyrophosphate.

[0018] Method 5

[0019] A proton battery comprising the aqueous electrolyte according to any one of aspects 1 to 4.

[0020] According to the present disclosure, it is possible to provide an aqueous electrolyte for a proton battery having excellent low-temperature stability and a proton battery having the aqueous electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a phase diagram showing the state of the aqueous electrolyte of each example after being stored in a thermostatic bath at -60°C for a predetermined period of time;

[0022] Figure 2 The DSC graph shows the results of DSC measurements of water (reference example), an aqueous electrolyte solution containing 10 mol of pyrophosphoric acid per 1 kg of water (Example 5), and an aqueous electrolyte solution containing 40 mol of pyrophosphoric acid per 1 kg of water (Comparative Example 27). DETAILED DESCRIPTION

[0023] The following detailed description of the embodiments of the present disclosure is provided with reference to the accompanying drawings to illustrate the technical features and industrial significance of the present invention. In addition, the same symbols represent the same components, and the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the main idea of ​​the disclosure.

[0024] Proton batteries use aqueous electrolytes

[0025] The aqueous electrolyte for the proton battery of the present disclosure contains water and pyrophosphoric acid (H4P2O7) dissolved in water at a concentration of 6 mol or more per kg of water, and has no freezing point above -60°C.

[0026] The present inventors have found that the aqueous electrolyte for proton batteries has improved low-temperature stability by having pyrophosphoric acid dissolved in water at a concentration of 6 mol or more per 1 kg of water. Although not wishing to be bound by any theory, it is believed that this is because pyrophosphoric acid forms a strong hydrogen bond with water, which can inhibit the freezing of water in the aqueous electrolyte.

[0027] The aqueous electrolyte solution of the present disclosure may contain pyrophosphoric acid dissolved in water at a concentration of 6 mol to 25 mol per 1 kg of water.

[0028] The aqueous electrolyte of the present disclosure may include a potassium salt and pyrophosphoric acid dissolved in water at a concentration of more than 25 mol per 1 kg of water.

[0029] The present disclosure et al. have found that when an aqueous electrolyte contains pyrophosphoric acid dissolved in water at a concentration greater than 25 mol per 1 kg of water, the water in the aqueous electrolyte is prone to freezing. As a reason for this, although I do not want to be bound by any theory, it can be considered that when the concentration of pyrophosphoric acid becomes high, pyrophosphoric acid easily forms a eutectic with water. In response to this, the present disclosure et al. have found that by further having a potassium salt in the aqueous electrolyte, the freezing of water in the aqueous electrolyte can be suppressed. As a reason for this, although I do not want to be bound by any theory, it can be considered that due to the presence of potassium salt, the entropy of the aqueous electrolyte increases, making it difficult to form a eutectic of a mixed solution of pyrophosphoric acid and water.

[0030] In the aqueous electrolyte of the present disclosure, the potassium salt may be a potassium phosphate. The potassium phosphate is not particularly limited, and examples thereof include potassium pyrophosphate (K4P2O7), tripotassium phosphate (K3PO4), and potassium triphosphate (K5P3O 10 )wait.

[0031] When the aqueous electrolyte disclosed in the present invention has pyrophosphate dissolved in water at a concentration greater than 25 mol per 1 kg of water, the concentration of the potassium salt converted into potassium ions is greater than 0 mol / L, and preferably lower than the minimum concentration of potassium salt saturation in the aqueous electrolyte. Since the saturated concentration of potassium salt in the aqueous electrolyte is affected by the concentration of pyrophosphate, the concentration of potassium salt as potassium ion can be determined according to the concentration of pyrophosphate.

[0032] The following represents the potassium ion concentration when the potassium salt is potassium pyrophosphate. When the aqueous electrolyte has pyrophosphate dissolved in water at a concentration of 25mol per 1kg of water, the potassium ion concentration can be greater than 0mol / L and less than 3.5mol / L. When the aqueous electrolyte has pyrophosphate dissolved in water at a concentration of 30mol per 1kg of water, the potassium ion concentration is preferably greater than 0mol / L and less than 1.6mol / L. When the aqueous electrolyte has pyrophosphate dissolved in water at a concentration of 35mol per 1kg of water, the potassium ion concentration is preferably greater than 0mol / L and less than 1.2mol / L. When the aqueous electrolyte has pyrophosphate dissolved in water at a concentration of 40mol per 1kg of water, the potassium ion concentration is preferably greater than 0mol / L and less than 1.0mol / L.

[0033] The potassium ion concentration can be analyzed by using an emission spectrometer (ICP) by taking 20 μL of each solution, adding 1.5 mL of hydrochloric acid, and then adding 100 mL of ultrapure water to dilute the solution 5000 times. As the ICP, ICPS-8100 manufactured by Shimadzu Corporation can be used.

[0034] The aqueous electrolyte disclosed in the present invention does not have a freezing point above -60°C, which can be confirmed by appearance observation and measurement using a differential scanning calorimeter (DSC). That is, for example, it can be confirmed by evaluating the presence or absence of freezing in the appearance observation of the aqueous electrolyte after being kept in a constant temperature bath at -60°C for a predetermined time. In addition, for example, it can be confirmed by measuring the aqueous electrolyte with DSC and evaluating the generation of differential heat before reaching -60°C. In addition, as DSC, DSC200F3Maia of NETZSCH can be used.

[0035] As a method for preparing an aqueous electrolyte solution, there can be exemplified a method in which water and pyrophosphoric acid are weighed so as to have a predetermined concentration, these are mixed, and if necessary, a potassium salt is further added and mixed.

[0036] The aqueous electrolyte disclosed in the present invention is used in a proton battery.

[0037] Proton battery

[0038] The proton battery of the present disclosure has the aqueous electrolyte of the present disclosure. Regarding the aqueous electrolyte, reference can be made to the above description regarding the aqueous electrolyte used in the proton battery of the present disclosure.

[0039] The proton battery of the present disclosure may include a current collector and an electrode active material layer formed on the current collector.

[0040] The current collector has the function of supplying charge to the electrode active material layer and recovering charge from the electrode active material layer while maintaining the electrode active material layer. The current collector is not particularly limited as long as it is acid-resistant and conductive, and can be composed of metal foil or metal plate. Specifically, the current collector can be aluminum, an alloy with aluminum as the main component, nickel, titanium, SUS and copper, etc. In addition, the current collector can be a carbon plate and a current collector formed by mixing carbon materials in a resin, etc. The current collector can also be plated with the above-mentioned materials on substrates such as iron, or the above-mentioned materials can be coated on the surface, etc.

[0041] As electrode active materials, manganese oxide, tungsten oxide, and molybdenum oxide can be listed. In addition, as electrode active materials, Prussian blue derivatives, MXene, polyaniline, polythiophene, polypyrrole, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyperinaphthalene, polyfuran, polyfluorene, polythiophene, polypyridine diyl, polyisothionaphthene, polyquinoxaline, polypyridine, polypyrimidine, polyindole, polyaminoanthraquinone, polyimidazole and its derivatives and other π conjugated polymers, and indole trimers and other indole conjugated compounds, quinone compounds such as benzoquinone, naphthoquinone, and anthraquinone, polyanthraquinone, polynaphthoquinone, polybenzoquinone and other quinone polymers (compounds obtained by conjugating quinone oxygen into hydroxyl). Furthermore, as electrode active materials, proton conductive polymers obtained by copolymerizing two or more monomers that can obtain the above-mentioned polymers can be listed. By doping these compounds, redox pairs are formed to show conductivity. These compounds are selected and used as the positive electrode active material and the negative electrode active material by appropriately adjusting the difference in their redox potentials.

[0042] The proton battery disclosed herein may also have a separator. The separator may be impregnated with an aqueous electrolyte and disposed between the positive electrode active material layer and the negative electrode active material layer. The separator is acid-resistant and is not particularly limited as long as it can insulate the positive electrode active material layer and the negative electrode active material layer and has ion permeability. The separator may be, for example, a polyolefin material such as polyethylene, polypropylene, polytetrafluoroethylene (PTFE), a cellulose material, an aromatic polyamide material, an amide material, and a glass fiber material.

[0043] In addition, in this disclosure, the so-called proton battery refers to a proton (H + ) A secondary battery in which protons move between a positive electrode active material layer and a negative electrode active material layer, and are charged and discharged by inserting and desorbing protons in the positive electrode active material layer and the negative electrode active material layer.

[0044] In a proton battery, protons move as follows. That is, during discharge, protons are separated from the negative electrode active material layer, and the separated protons move from the negative electrode active material layer to the positive electrode active material layer in the electrolyte, so that the protons are inserted into the positive electrode active material layer. On the other hand, during charge, protons are separated from the positive electrode active material layer, and the separated protons move from the positive electrode active material layer to the negative electrode active material layer in the electrolyte, so that the protons are inserted into the negative electrode active material layer.

[0045] Aqueous electrolyte preparation

[0046] Water and pyrophosphoric acid are weighed in a manner to obtain the concentrations described in Table 1 below, placed in a container, and the container is shaken for stirring. When the concentration of pyrophosphoric acid is greater than 25 mol per 1 kg of water, potassium pyrophosphate is weighed in a manner to obtain the potassium ion concentration described in Table 1 below, and added to the mixture of water and pyrophosphoric acid for stirring. After stirring, the aqueous electrolyte of each example is prepared by standing in a thermostatic bath at 25° C. for more than 3 days. In addition, the potassium ion concentration is analyzed using an emission spectrometer (ICP). Specifically, using ICPS-8100 from Shimadzu Corporation, 20 μL of each solution is collected, 1.5 mL of hydrochloric acid is added, 100 mL of ultrapure water is added, and the dilution is adjusted to 5000 times, thereby analyzing the potassium ion concentration.

[0047] Low temperature stability evaluation

[0048] After the aqueous electrolyte solution of each example was kept in a thermostatic chamber at -60°C for 8 hours or more, the appearance was visually observed to confirm whether or not there was freezing.

[0049] DSC evaluation

[0050] For water (reference example), an aqueous electrolyte having 10 mol of pyrophosphoric acid per 1 kg of water (Example 5), and an aqueous electrolyte having 40 mol of pyrophosphoric acid per 1 kg of water (Comparative Example 27), DSC evaluation was performed according to the following steps. That is, first, the temperature was lowered from room temperature to -120°C at a rate of 1°C / min. Then, the temperature was raised from -120°C to 30°C at a rate of 1°C / min. Thus, a DSC chart was obtained. The measurement was performed using a DSC 200F3Maia of NETZSCH and a container made of gold (Au).

[0051] result

[0052] The results of appearance evaluation are shown in Table 1 and Figure 1 The evaluation results of DSC are shown in Figure 2 shown.

[0053] Table 1

[0054]

[0055] Figure 1 The phase diagram shows the state of the aqueous electrolyte of each example after being stored in a constant temperature bath at -60°C for a predetermined time. Figure 1 As shown, an aqueous electrolyte having pyrophosphate dissolved in water at a concentration of 6 mol or more and 25 mol or less per kg of water has a non-freezing region (non-freezing region) at -60°C. On the other hand, when the concentration of pyrophosphate is 30 mol or more and 40 mol or less per kg of water, an aqueous electrolyte without potassium pyrophosphate freezes at -60°C. In contrast, in the case where the aqueous electrolyte has potassium pyrophosphate, the aqueous electrolyte will not freeze at -60°C even if the concentration of pyrophosphate is 30 mol or more and 40 mol or less per kg of water. The above suggests that by having a potassium salt in the aqueous electrolyte, the concentration range of pyrophosphate that can prepare an aqueous electrolyte that does not have a freezing point at -60°C can be expanded to the high concentration side.

[0056] Figure 2 The DSC graphs show the results of DSC measurements of water (reference example), an aqueous electrolyte having 10 mol of pyrophosphoric acid per 1 kg of water (Example 5), and an aqueous electrolyte having 40 mol of pyrophosphoric acid per 1 kg of water (Comparative Example 27). Figure 2 As shown, the aqueous electrolyte solution of Example 5 does not have a freezing differential heat at -60°C or higher. That is, the aqueous electrolyte solution does not have a freezing point up to -60°C. In addition, the aqueous electrolyte solution does not have a freezing differential heat even at -100°C.

[0057] Next, the aqueous electrolyte solutions of each example were prepared in the same manner as in the case of using potassium pyrophosphate, except that the potassium salt was changed from potassium pyrophosphate to tripotassium phosphate and the concentrations were as shown in Table 2 below. The appearance of the obtained aqueous electrolyte solutions was evaluated in the same manner as above. The results are shown in Table 2.

[0058] Table 2

[0059]

[0060] As shown in Table 2, when tripotassium phosphate is used as the potassium salt, the aqueous electrolyte of the example having 30 mol of pyrophosphoric acid per 1 kg of water does not freeze at -60°C. In contrast, the aqueous electrolyte of the comparative example having 10 mol of pyrophosphoric acid per 1 kg of water or 20 mol of pyrophosphoric acid per 1 kg of water freezes at -60°C even if it contains tripotassium phosphate. It is considered that this result supports the above inference that the concentration range of pyrophosphoric acid that can prepare an aqueous electrolyte having no freezing point at -60°C can be expanded to the high concentration side by having a potassium salt in the aqueous electrolyte.

[0061] Furthermore, the aqueous electrolyte solutions of each example were prepared in the same manner as when potassium pyrophosphate was used, except that the potassium salt was changed from potassium pyrophosphate to potassium triphosphate and the concentrations were as shown in Table 3 below. The appearance of the obtained aqueous electrolyte solutions was evaluated in the same manner as above. The results are shown in Table 3.

[0062] Table 3

[0063]

[0064] As shown in Table 3, when potassium triphosphate is used as the potassium salt, the aqueous electrolyte of the embodiment having 20 mol to 40 mol of pyrophosphoric acid per 1 kg of water does not freeze at -60°C. In contrast, the aqueous electrolyte of the comparative example having 10 mol of pyrophosphoric acid per 1 kg of water freezes at -60°C even if it contains potassium triphosphate. This result is the same as the case of using tripotassium phosphate as the potassium salt, and it is considered that this supports the following inference, that is, by having a potassium salt in the aqueous electrolyte, the concentration range of pyrophosphoric acid that can prepare an aqueous electrolyte that does not have a freezing point at -60°C can be expanded to the high concentration side.

Claims

1. An aqueous electrolyte for a proton battery, comprising water and pyrophosphoric acid dissolved in the water at a concentration of 6 mol or more per 1 kg of the water, and The aqueous electrolyte has no freezing point above -60°C.

2. The aqueous electrolyte according to claim 1, comprising the pyrophosphoric acid dissolved in the water at a concentration of 6 mol or more and 25 mol or less per 1 kg of the water, or comprising the pyrophosphoric acid and a potassium salt dissolved in the water at a concentration of more than 25 mol per 1 kg of the water.

3. The aqueous electrolyte according to claim 2, wherein the potassium salt is potassium phosphate.

4. The aqueous electrolyte according to claim 3, wherein the potassium phosphate is potassium pyrophosphate. 5 . A proton battery comprising the aqueous electrolyte according to claim 1 .

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