Secondary battery

Abstract

To provide a secondary battery structure which employs a metal other than aluminum as a negative electrode, has a low manufacturing cost, and is manufactured by a simple process.SOLUTION: A secondary battery uses copper as a material that constitutes a positive electrode 1, iron, nickel, or cobalt as a material that constitutes a negative electrode 2, and a non-aqueous electrolyte solution as an electrolyte, in which copper ions (Cu2+) move from the positive electrode to the negative electrode in the non-hydrogen electrolyte during charging, form a solid solution of iron, nickel, or cobalt and copper, and move in the opposite direction to the direction when charging when discharging.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention is directed to a secondary battery that includes a non-aqueous electrolyte and a separator between a positive electrode and a negative electrode, is small and high-capacity like a lithium-ion battery, and can be repeatedly charged and discharged.

Background Art

[0002] Small and high-capacity lithium-ion secondary batteries are used as power sources for portable electronic devices such as notebook personal computers and smartphones. In recent years, they have also been adopted as secondary batteries for renewable energy storage batteries and electric vehicles from the perspective of global environmental issues and decarbonization.

[0003] In lithium-ion secondary batteries, lithium compounds such as lithium cobalt oxide (LiCoO2), ternary systems (Li(Ni,Co,Mn)O2), lithium manganate (LiMn2O4), and lithium iron phosphate (LiFePO4) are adopted as positive electrode active materials, and carbon materials such as hard carbon and graphite, silicon oxide (SiO), and silicon (Si) are adopted as negative electrode active materials. However, since lithium, cobalt, and nickel are rare metals, the manufacturing cost is high. Moreover, compared with iron, aluminum, etc., the mining volume is scarce, and there is a risk of a shortage of raw materials due to a significant increase in demand.

[0004] Furthermore, it is essential that the positive electrode active material and the negative electrode active material be applied to the positive electrode current collector and the negative electrode current collector, that is, the terminals that transmit the current generated by the positive electrode active material and the negative electrode active material to the outside of the battery. However, the manufacturing process by such application is by no means simple but complicated. Incidentally, in a typical lithium-ion battery, lithium cobalt oxide powder, which is a positive electrode active material, is applied to an aluminum foil, which is a positive electrode current collector, and graphite powder, which is a negative electrode active material, is applied to a copper foil, which is a negative electrode current collector. These coating operations are quite complicated.

[0005] In consideration of the situation of such lithium-ion batteries, the applicants have filed a patent application for a secondary battery that uses copper as the positive electrode active material, aluminum as the negative electrode active material, and a non-aqueous electrolyte as the electrolyte (Japanese Patent Application No. 2022-047894), and based on this application, a patent right has been established according to Patent Document 1 (hereinafter, the invention according to the configuration of Patent Document 1 is abbreviated as the "prior application invention"). The prior application invention is based on the following configuration. Description A secondary battery that uses copper as the positive electrode active material, aluminum as the negative electrode active material, a non-aqueous electrolyte as the electrolyte, and in which copper ions (Cu 2+ ) move from the positive electrode to the negative electrode during charging, and copper ions (Cu 2+ ) move in the opposite direction to that during charging during discharging.

[0006] The prior application invention based on the above basic configuration can exhibit a technical merit that the manufacturing cost is lower than that of lithium-ion batteries.

[0007] However, for a secondary battery in which copper ions (Cu 2+ ) move during charging and discharging, it is not necessary to limit the metal used as the negative electrode active material to aluminum.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a configuration of a secondary battery that has a lower manufacturing cost than lithium-ion batteries, uses copper as the positive electrode active material, and uses a metal other than aluminum as the negative electrode active material.

Means for Solving the Problems

[0010] For the purpose of solving the above problems, the basic configurations conceivable by the inventor are as follows: (1) A secondary battery characterized in that copper is used as a positive electrode active material, iron or nickel or cobalt is used as a negative electrode active material, a non-aqueous electrolyte is used as an electrolyte, and copper ions (Cu 2+ ) move from the positive electrode to the negative electrode during charging, and copper ions (Cu 2+ ) move in the opposite direction to that during charging during discharging; (2) The secondary battery according to (1) above, characterized in that copper acts as both a positive electrode active material and a positive electrode current collector, and iron or nickel or cobalt acts as both a negative electrode active material and a negative electrode current collector; That is.

[0011] The basic configuration (1) encompasses the configuration of the basic configuration (2) in which copper and iron or nickel or cobalt act as a positive electrode current collector and a negative electrode current collector, respectively. However, it encompasses not only this configuration but also configurations such as using a silver foil or an aluminum foil as the positive electrode current collector and a silver foil or a copper foil as the negative electrode current collector. However, the above configuration is exceptional, and most of the embodiments of the basic configuration (1) are based on the basic configuration (2). In addition, the "non-aqueous electrolyte" in the above basic configuration means an electrolyte that does not contain water and allows cations (copper ions in the cases of the basic configurations (1) and (2)) to be conductive during charge and discharge.

Advantages of the Invention

[0012] As is apparent from the above basic configurations (1) and (2), the present invention is composed of three elements, namely, a separator that forms an integral state with copper, iron or nickel or cobalt, and a non-aqueous electrolyte. Since it does not use rare metals like a lithium-ion battery, the manufacturing cost is low as in the case of the prior application invention. In particular, when iron is selected as the negative electrode active material, the manufacturing cost can be made even lower than that of the prior application invention.

[0013] Moreover, in the case of the basic configuration (2), since all the materials of the positive electrode are copper and all the materials of the negative electrode are iron or nickel or cobalt, the coating process as in the case of a lithium-ion battery is unnecessary, and the manufacturing process is extremely simple.

[0014] The operation of the basic configuration with such an effect is as follows.

[0015] In the basic configurations (1) and (2), charging can be achieved by copper acting as the positive electrode active material and iron or nickel or cobalt acting as the negative electrode active material. At the stage of the said charging, at the positive electrode, Cu→Cu 2+ +2e - the ionization reaction as such is realized, copper ions (Cu 2+ ) move to the negative electrode side from the positive electrode, and electrons (e - ) move to the positive electrode side.

[0016] On the other hand, at the negative electrode, Cu 2+ +xFe+2e - → CuFe x or Cu 2+ +xNi+2e - → CuNi x or Cu 2+ +xCo+2e - → CuCo x As such, an alloy is formed by copper and iron or nickel or cobalt solid-solifying with each other to exhibit a crystal structure, and it is attributed to the release of electrons (e - ).

[0017] In addition, one copper ion (Cu 2+For the single entity of , the formation of an alloy with a solid solution of any number X (where usually X is an integer of 5 or less) of iron or nickel or cobalt is due to the fact that copper and iron or nickel or cobalt can form a stable crystal structure in a predetermined ratio.

[0018] Conversely, in the case of discharging, at the positive electrode, Cu 2+ +2e - → Cu The bonding reaction between copper ions and electrons as such occurs, and at the negative electrode, CuFe x → Cu 2+ +Fe x +2e - or CuNi x → Cu 2+ +Ni x +2e - or CuCo x → Cu 2+ +Co x +2e - The ionization reaction between copper and electrons as such is realized.

[0019] Therefore, regarding the overall reaction by the charge and discharge, Cu+Fe x ⇔ CuFe x or Cu+Ni x ⇔ CuNi x or CU 2+ +Co x ⇔ CuCox It is attributed to the realization of alloying between copper and iron or nickel or cobalt and the separation of both being realized.

[0020] In the basic configuration (1), copper acts as the positive electrode active material, and iron or nickel or cobalt acts as the negative electrode active material. However, as in the basic configuration (2), when copper is adopted as the positive electrode current collector and iron or nickel or cobalt is adopted as the terminal of the negative electrode current collector, the positive electrode and the negative electrode are each composed of copper and iron or nickel or cobalt, and an extremely simple manufacturing process can be realized.

[0021] The theoretical capacity of copper, which is the positive electrode active material, is about 850 mAh / g. However, as will be described later, when the operating voltage in discharge is 3.5 V, the weight energy density is 850×3.5 = 2,975 Wh / kg, and when the density is 8.91, the volume energy density is about 56,500 Wh / L.

[0022] When the numerical values of the above densities are compared with the positive electrode material Li(Ni,Co,Mn)O2 of an existing lithium-ion secondary battery, the values are about 4 times in weight energy density and about 8 times in volume energy density. Therefore, the weight energy density of about 3 times and the volume energy density of about 6 times in the prior application invention are further improved.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4(a)

Figure 4(b)

Figure 4(c)

Embodiments for Carrying Out the Invention

[0024] As shown in FIG. 1, the basic configuration (1) is a secondary battery that uses copper as the material for the positive electrode 1, uses iron or nickel or cobalt as the material for the negative electrode 2, and uses a non-aqueous electrolyte as the electrolyte. The basic configuration (2) is the secondary battery of (1) characterized in that copper acts as the positive electrode active material and the positive electrode current collector, and iron or nickel or cobalt acts as the negative electrode active material and the negative electrode current collector.

[0025] The basic configuration (1) generally stands on the basis of the basic configuration (2). Exceptionally, as for the fact that a copper foil of a metal other than copper can be adopted as the positive electrode current collector and a metal foil other than iron or nickel or cobalt can be adopted as the negative electrode current collector, it is as pointed out in the section of the means for solving the problems.

[0026] When compared with the configuration of a typical lithium-ion battery shown in FIG. 2, in the basic configuration (1), copper is adopted instead of a lithium-containing oxide or the like as the positive electrode active material 4 in the positive electrode, and iron or nickel or cobalt is adopted instead of graphite or the like as the negative electrode active material 5 in the negative electrode. In the basic configuration (2), in the case of a lithium-ion battery, instead of the current collector 6 made of an aluminum foil coated with the oxide 4, the positive electrode active material made of copper also serves as the positive electrode current collector, and instead of the current collector 7 made of a copper foil coated with lithium carbide or the carbon material 5, the negative electrode active material made of iron or nickel or cobalt also serves as the negative electrode current collector.

[0027] Due to such compositional differences, in the case of the basic configuration (1), the manufacturing cost of the lithium-ion secondary battery is low, and especially when iron is used as the negative electrode active material, it is even lower than the prior invention. In the case of the basic configuration (2), as already pointed out, the manufacturing process is simpler compared to the lithium-ion secondary battery.

[0028] In both the basic configurations (1) and (2), similar to the case of the lithium-ion secondary battery, a separator 3 formed integrally with the non-aqueous electrolyte is provided between the positive electrode 1 and the negative electrode 2.

[0029] However, the separator 3 in the basic configurations (1) and (2) is necessarily in a porous state that allows the permeation of copper ions (Cu 2+ ).

[0030] Typical examples of non-aqueous electrolytes are ionic liquids and organic electrolytes, and in either case, copper ions (Cu 2+ ) and electrons (e - ) can flow during charge and discharge.

[0031] Ionic liquids are usually defined as liquids in which cations and anions exist at 100 °C or lower.

[0032] Depending on the type of cation, from the basic skeleton of the cation, imidazolium salts, pyrrolidinium salts, pyridinium salts, piperidinium salts, ammonium salts, and phosphonium salts can be mentioned, and any of these cations can be adopted.

[0033] Examples of anions coexisting with the cation include halogen-based such as bromide ions and triflate, boron-based such as tetraphenylborate, and phosphorus-based such as hexafluorophosphate.

[0034] Since ionic liquids are non-flammable and non-volatile, when an ionic liquid is adopted as the non-aqueous electrolyte, a safe secondary battery can be obtained.

[0035] An organic electrolyte is defined as an electrolyte solution in which a salt of an electrolyte, that is, both a cation and an anion, is dissolved in an organic solvent.

[0036] Examples of the organic solvent include acetonitrile, dioxolane, 1,2-dimethoxyethane, tetrahydrofuran, γ-butyrolactone, propylene carbonate, ethylene carbonate, etc. Examples of the electrolyte salt include alkali metal ions such as lithium ions, quaternary alkylammonium, cations, and anions such as halogen ions, sulfate ions, perchlorate ions, etc.

[0037] However, organic electrolytes tend to be inferior in terms of non-flammability and non-volatility compared to ionic liquids.

[0038] In the basic configurations (1) and (2), a separator 3 impregnated with a non-aqueous electrolyte is employed between the positive electrode 1 and the negative electrode 2. Separators are also used in ordinary lithium-ion secondary batteries to prevent short circuits between the positive and negative electrodes.

[0039] The following will be described with reference to each graph.

[0040] A rectangular plate made of copper with a thickness of 0.1 mm and dimensions of 50 mm × 70 mm was adopted as the positive electrode 1, and a rectangular plate made of iron or nickel or cobalt or aluminum with a thickness of 0.1 mm and dimensions of 50 mm × 70 mm was adopted as the negative electrode 2. A sulfolane-based electrolyte was used as the electrolyte, and glass filter paper was used as the separator.

[0041] A cell was assembled according to the above design dimensions, and was vacuum-sealed with an aluminum laminate film with a thickness of 0.1 mm as the exterior to fabricate a secondary battery.

[0042] A charge-discharge cycle test was conducted by repeating charging under the conditions of a current of 40 mA and a cut-off voltage of 4.5 V, and discharging under the conditions of a current of 10 mA and a cut-off voltage of 2.5 V at an environmental temperature of 25°C.

[0043] Regarding the results of the charge-discharge cycle test, when iron, nickel, cobalt, and aluminum are used as the negative electrode active materials, they are respectively shown by the charge-discharge curves in FIGS. 3(a), 3(b), 3(c), and 3(d).

[0044] In the discharge curve, a voltage value due to a plateau, that is, a voltage value in a relatively stable state, could be observed near 3.5V.

[0045] Based on such observation results, it can be confirmed that the secondary battery according to the present invention is a secondary battery rather than a mere discharge capacitor, similar to the case of the prior application invention. Incidentally, in the case of a capacitor, the voltage value due to discharge decays exponentially, and it is impossible to realize the voltage value due to the plateau as described above.

[0046] Furthermore, as is clear from the comparison between the charge-discharge curves shown in FIGS. 3(a), (b), (c) and the charge-discharge curve shown in FIG. 3(d), in the case of the secondary battery in the simple cell state according to the present invention as well, similar to the case of the prior application invention, it can be confirmed that it is possible to charge and discharge at least up to 15 cycles, and moreover, the same charge and discharge as the prior application invention is possible.

[0047] Hereinafter, an explanation will be given in accordance with a specific comparison with the prior application invention. As shown in FIG. 4(a), when paying attention to the cycle characteristics in the case of using iron or nickel as the negative electrode compared to the prior application invention using aluminum as the negative electrode, the discharge current capacity of the present invention, compared to the prior application invention, as the number of cycles increases, in the case of the iron negative electrode, the number of cycles is slightly inferior, in the case of the nickel negative electrode, it is considerably inferior, and in the case of the cobalt negative electrode, it is in an intermediate state between iron and nickel. However, even in the case of the nickel negative electrode, at the cycle number of 15, it exhibits about 3 mAh, and even in the case of the cobalt negative electrode, at the cycle number of 15, it exhibits about 11 mAh. Therefore, even if the differences from the prior application invention as described above are observed, there are definitely no significant defects in the nickel negative electrode and the cobalt electrode. As is also clear from the graph of FIG. 4(b), it is found that the iron negative electrode and the nickel negative electrode can achieve a higher discharge voltage under the same conditions compared to the case of the prior invention. As is also clear from FIG. 4(c), while the charging voltage in the 10-cycle stage is substantially the same, the negative electrodes of the iron negative electrode, the nickel negative electrode, and the cobalt negative electrode enable the realization of a considerably higher discharge voltage compared to the prior invention.

Industrial Applicability

[0048] The secondary battery according to the present invention, like the prior invention, has a low manufacturing cost and a simple configuration. On the other hand, it can form a higher discharge voltage than the prior invention, and in the case of the iron negative electrode, a secondary battery can be realized at a lower cost than the prior invention.

[0049] Thus, the secondary battery according to the present invention can be used in a wider range of industrial fields such as power sources for various portable devices, power sources for electric vehicles, and energy storage facilities for standardizing the power of renewable energy, more so than the prior invention.

Explanation of Reference Numerals

[0050] 1 Positive electrode made of copper 2 Negative electrode made of iron or nickel 3 Separator impregnated with non-aqueous electrolyte 4 Positive electrode active material in a lithium-ion battery 5 Negative electrode active material in a lithium-ion battery 6 Positive electrode current collector made of iron or nickel in a lithium-ion battery 7 Negative electrode current collector made of copper in a lithium-ion battery

Claims

1. Copper is used as the positive electrode active material, iron, nickel, or cobalt is used as the negative electrode active material, and a non-aqueous electrolyte is used as the electrolyte. In addition, copper ions (Cu ２＋ ) moves from the positive electrode to the negative electrode, and during discharge, copper ions (Cu ２＋ ) moves in the opposite direction to that during charging.

2. 2. The secondary battery according to claim 1, wherein copper serves as a positive electrode active material and a positive electrode current collector, and iron, nickel or cobalt serves as a negative electrode active material and a negative electrode current collector.

3. 3. The secondary battery according to claim 1, wherein the positive and negative electrodes have an area of ​​50 mm x 70 mm, and the secondary battery can achieve a stable voltage with a plateau at about 3.5 V during the discharge stage by repeating a charge-discharge cycle in which charging is performed with a current of 40 mA and an end voltage of 4.5 V, and discharging is performed with a current of 10 mA and an end voltage of 2.5 V.

4. Cu in the negative electrode ２＋ +XFe+2e ⇔ CuFe ｘ Or C.U. ２＋ +xNi+2e ⇔ CuNi ｘ CuCox or Cu ２＋ 3. The secondary battery according to claim 1, wherein the alloying of copper with iron, nickel or cobalt is realized during charging, and the separation of copper from iron, nickel or cobalt is realized during discharging, based on the reaction formula: +Co+2e⇔CuCox.

Images