Dual cation metal battery and method for charging and discharging the same

Abstract

To provide a dual-cation metal battery and a charging and discharging method thereof, capable of reducing the cost of materials, maintaining the long-term service life and providing multiple varied applications.SOLUTION: A dual-cation metal battery includes a positive electrode, a negative electrode, an electrolyte solution and a separator. The positive electrode includes a positive electrode material comprising one selected from the group consisting of iron phosphate (heterosite, FePO4), lithium iron phosphate (LiFePO4) and LixNa1-xFePO4 where 0<x<1. The negative electrode includes a metal mixture comprising lithium metal and sodium metal, a weight ratio of the lithium metal to the sodium metal being 1:3. The electrolyte solution is disposed between the positive electrode and the negative electrode. The separator is disposed in the electrolyte solution, and the positive electrode and the negative electrode are separated from each other by the separator. By selecting different charging and discharging modes, different electrochemical characteristics are presented in the dual-cation metal battery.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a secondary battery, and more particularly to a dual cation metal battery capable of reducing material costs, maintaining a long service life, and enabling multiple changes in use, and a method for charging and discharging the same. [Background technology]

[0002] A lithium-ion battery is a secondary battery that can be repeatedly charged and discharged. Lithium ions move between the positive and negative electrodes to achieve charging and discharging. Therefore, lithium-ion batteries must use lithium compounds as electrode materials. The positive electrode materials used in conventional lithium-ion batteries are mainly lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4). Among them, lithium iron phosphate batteries are widely used in electric vehicles and energy storage devices due to their good safety, large specific capacity, long cycle life, high temperature resistance, and low cost.

[0003] In recent years, with the application of lithium-ion batteries in electric vehicles and energy storage devices, the prices of related raw materials have fluctuated significantly. Considering that future demand will continue to increase, it is important to find alternatives to lithium-ion. In this case, when looking for a substitute for lithium-ion in lithium-ion batteries, it is necessary to consider the impact of the difference in plateau voltage on ease of use, product life, and battery stability.

[0004] The present invention has been made in view of the above circumstances, and in order to solve the problems faced by the conventional technology, provides a dual cation metal battery and a method for charging and discharging the same, which can reduce material costs, maintain a long service life, and allow multiple changes in use. Summary of the Invention [Problem to be solved by the invention]

[0005] The objective of the present invention is to provide a dual cation metal battery and a method for charging and discharging the same, which can reduce material costs, maintain a long service life, and allow multiple uses. Lithium iron phosphate and iron phosphate with an olivine structure have lithium ions and sodium ions stored and released simultaneously in the structure, and the Li x Na 1-x A dual cation cathode material can be formed, which allows the metal battery to provide two different plateau voltages, LiFePO4 and NaFePO4. The present invention uses sodium ions to replace some of the lithium ions, resulting in a LiFePO4 dual cation cathode material. x Na 1-x The dual cation cathode material of the present invention is formed by using FePO4, which is different from single cation cathode materials such as conventional lithium ion cathode materials and sodium ion cathode materials. The dual cation metal battery of the present invention also uses sodium ions, which are more abundant in the earth's crust, to replace some of the lithium ions, making the secondary battery material more sustainable and providing higher plateau voltage, capacity and more diverse applications than sodium iron phosphate cathode materials.

[0006] Another object of the present invention is to provide a dual cation metal battery and a method for charging and discharging the same. In the dual cation metal battery, lithium metal and sodium metal are mixed and used as a composite negative electrode. Lithium metal (lithium metal has a theoretical capacity per gram of 3840 mAh / g) and sodium metal (sodium metal has a theoretical capacity per gram of 1166 mAh / g) have high capacitance per gram, which can help reduce the thickness of the negative electrode and increase the energy density of the battery.

[0007] Another object of the present invention is to provide a dual cation metal battery and a method for charging and discharging the same. x Na 1-xDual cation metal batteries, which are made up of a positive electrode material such as FePO4 and a mixture of lithium metal and sodium metal, have two different plateau voltages during the charge and discharge process: LiFePO4 and NaFePO4. x Na 1-x When the FePO4 dual cation cathode material is matched with the lithium-sodium metal anode, it can exhibit different electrical properties by using different charge and discharge modes. When the dual cation metal battery is discharged in a ramp voltage mode, the ratio of lithium ions and sodium ions stored in the structure can be controlled by controlling the voltage drop rate. In addition, when the dual ion cathode metal battery is used for energy storage applications that do not require a large discharge current output, such as when used in a solar power generation system, when solar power is generated by sunlight during the day, the battery is charged slowly with the current from the solar panel and discharged at night, when larger power is required, it can be discharged using a constant current-constant voltage discharge mode. That is, it is discharged by the LiFePO4 plateau voltage. On the other hand, when a large power output is not required, the dual cation metal battery can be discharged using a ramp voltage discharge mode and the power released by the NaFePO4 plateau voltage can be used. This allows the selection of the ramp voltage mode or the constant current-constant voltage mode according to actual demand. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a dual cation metal battery comprising a positive electrode, a negative electrode, an electrolyte solution and a separator. The positive electrode comprises a positive electrode material, the positive electrode material being selected from the group consisting of iron phosphate (heterosite, FePO4), lithium iron phosphate (LiFePO4) and Li x Na 1-xIt is one selected from the group consisting of FePO4 and 0 < x < 1. The negative electrode contains a metal mixture, and the metal mixture is composed of lithium metal and sodium metal, and the weight ratio of lithium metal to sodium metal is 1:3. An electrolyte solution is installed between the positive electrode and the negative electrode. The separator is installed in the electrolyte solution, and the positive electrode and the negative electrode are separated from each other through the separator. By selecting different charge and discharge modes, the dual cation metal battery has different electrical characteristics (showing the results of different electrical characteristics). Preferably, the dual cation metal battery is charged and discharged in a constant current-constant voltage mode, and the constant current-constant voltage mode is a 0.1C constant current-constant voltage mode. Preferably, the dual cation metal battery is charged and discharged in a mixed mode of a constant current-constant voltage mode and a ramp voltage mode. The constant current-constant voltage mode is a 0.1C constant current-constant voltage mode, and the ramp voltage mode has a charge and discharge interval range of 2.0 V to 4.0 V and a charge and discharge rate of ±0.2 mV / s. Preferably, when the positive electrode material is Li x Na 1-x FePO4, the dual cation metal battery is charged in a constant current-constant voltage mode and discharged in a ramp voltage mode. The constant current-constant voltage mode is a 0.1C constant current-constant voltage mode, and the ramp voltage mode has a discharge interval range of 4.0 V to 2.0 V and a discharge rate of -0.2 mV / s. Preferably, the ramp voltage mode has a discharge interval range of 2.8 V to the cut-off voltage of 2.0 V.

[0009] To achieve the above object, the present invention provides a dual cation metal battery, which includes a positive electrode, a negative electrode, an electrolyte solution, and a separator. The positive electrode contains a positive electrode material, and the positive electrode material includes iron phosphate, lithium iron phosphate, and Li x Na 1-xIt is one selected from the group consisting of FePO4, and 0 < x < 1. The negative electrode contains a metal mixture, and the metal mixture is composed of lithium metal and sodium metal, and the weight ratio of lithium metal to sodium metal is 1:3. An electrolyte solution is installed between the positive electrode and the negative electrode, a separator is installed in the electrolyte solution, and the positive electrode and the negative electrode are separated from each other through the separator in step (a); and step (b) of selecting a constant current-constant voltage mode or a ramp voltage mode to charge or discharge the dual-cation metal battery is included, and a charge-discharge method for the dual-cation metal battery is provided. Preferably, in step (b), charging and discharging are performed in a constant current-constant voltage mode, and the constant current-constant voltage mode is a 0.1C constant current-constant voltage mode. Preferably, in step (b), charging and discharging are performed in a mixed mode of a constant current-constant voltage mode and a ramp voltage mode. The constant current-constant voltage mode is a 0.1C constant current-constant voltage mode, and the ramp voltage mode has a charge-discharge interval range of 2.0 V to 4.0 V and a charge-discharge rate of ±0.2 mV / s. Preferably, when the positive electrode material is Li x Na 1-x FePO4, in step (b), charging is performed in a constant current-constant voltage mode and discharging is performed in a ramp voltage mode. The constant current-constant voltage mode is a 0.1C constant current-constant voltage mode, and the ramp voltage mode has a discharge interval range of 4.0 V to 2.0 V and a discharge rate of -0.2 mV / s. Preferably, the ramp voltage mode has a discharge interval range of 2.8 V to a cut-off voltage of 2.0 V.

Brief Description of the Drawings

[0010] [Figure 1] It is a structural conceptual diagram of a dual-cation metal battery in a preferred embodiment of the present invention. [Diagram 2] It shows the comparison results obtained by scanning the dual-cation positive electrode materials, LiFePO4 and NaFePO4, in the dual-cation metal battery in a preferred embodiment of the present invention by cyclic voltammetry. [Diagram 3]1 shows cyclic voltammetry scans with different cutoff voltages for a dual cation metal battery containing Li0.25Na0.75FePO4 cathode material in a preferred embodiment of the present invention. [Figure 4] 1 shows measurement results of charging and discharging a dual cation metal battery containing a Li0.25Na0.75FePO4 positive electrode material in a 0.1 C constant current-constant voltage (CC-CV) mode in a preferred embodiment of the present invention. [Diagram 5] 1 shows measurement results of charging and discharging a dual cation metal battery containing a Li0.25Na0.75FePO4 cathode material in a preferred embodiment of the present invention in a ramp voltage mode. [Figure 6] The results of charging and discharging an iron phosphate / sodium metal negative electrode coin cell in ramp voltage mode are shown. [Figure 7] 1 shows the measurement results obtained by charging and discharging a dual cation metal battery containing Li0.25Na0.75FePO4 cathode material in a preferred embodiment of the present invention using a mixed constant current-constant voltage mode and a ramp voltage mode. [Figure 8] A dual cation metal battery containing Li0.25Na0.75FePO4 cathode material in a preferred embodiment of the present invention shows results measured by charging in constant current-constant voltage mode and discharging in ramp voltage mode. [Figure 9] Dual cation metal batteries containing the iron phosphate cathode material of the preferred embodiment of the present invention have been measured by charging and discharging in a mixed constant current-constant voltage mode and a ramp voltage mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Some exemplary embodiments embodying the features and advantages of the present invention will be described in detail in the following. The present invention can be modified in various ways without departing from the scope of the present invention, and the following description and drawings are used to describe the present invention and are not intended to limit the present invention. In addition, in the detailed description of the present invention, the term "a first feature is disposed on or above a second feature" includes an embodiment in which the disposed first feature and the second feature are directly connected to each other, and an embodiment in which the first feature and the second feature are not directly connected to each other through another structure between the first feature and the second feature. Furthermore, in the description of different embodiments in this specification, symbols and / or symbols may be used repeatedly. Such repetition is for the purpose of brevity and clarity, and is not intended to limit the relationship between the various embodiments and / or the exterior structures described. In addition, in the figures, spatial terms such as "inside", "outside", "high", and "low" are described to facilitate the description of the relationship between one component or feature and other (several) components or features. These descriptions are spatially relative terms and are intended to encompass different orientations of the device during use or operation in addition to the orientations shown in the schematic. The device may also be placed in other configurations (e.g., rotated 90 degrees or at other orientations) and may be interpreted according to the context in which it is used. When a component is described as being "connected" or "coupled" to another component, it may be directly connected or coupled to the other component or may be connected or coupled through the other component. Although the numerical ranges and parameters indicating the broad scope of the present specification are approximations, the numerical values ​​set forth in the specific examples are described as being as precise as possible. In addition, the terms "first", "second", "third", etc. are used to describe different configurations described in the claims, and these configurations are not limited to these terms, and in the context of the embodiments, although the corresponding configurations are indicated by different symbols, the first configuration may be indicated as the second configuration and the second configuration may be indicated as the first configuration, without departing from the embodiments of the present invention. In addition, the term "and / or" means one and / or a combination of the associated elements or all of them.Unless expressly defined in the embodiments relating to operation / operation, all numerical ranges, amounts, values, percentages, etc. described herein (e.g., angles, durations, temperatures, operating conditions, ratios and corresponding percentages, etc.) should be understood in all embodiments by the terms "about" or "substantially". In addition, unless otherwise stated in the content, all numerical values ​​in the present invention and claims can be taken as approximations that can be varied as necessary. For example, each parameter may be interpreted in light of at least the number of significant digits described, applying ordinary rounding rules. In addition, numerical ranges herein can be expressed as ranges from one endpoint to the other endpoint or between two endpoints. It should be noted that all ranges described herein include the endpoints unless otherwise defined.

[0012] 1 is a structural conceptual diagram of a dual cation metal battery according to a preferred embodiment of the present invention. In this embodiment, a dual cation metal battery (hereinafter referred to as a metal battery) 1 provided by the present invention comprises a positive electrode 10, a negative electrode 20, an electrolyte solution 30, and a separator 40. The positive electrode 10 comprises a positive electrode material 11, which is composed of iron phosphate (heterosite, FePO4), lithium iron phosphate (lithium iron phosphate ion, LiFePO4), and Li x Na 1-xIt is one selected from the group consisting of FePO4, where 0 < x < 1. The negative electrode 20 contains a metal mixture 21, and the metal mixture 21 is composed of lithium metal and sodium metal, and the weight ratio of lithium metal to sodium metal is 1:3. The electrolyte solution 30 includes, for example, a 1.0 M lithium hexafluorophosphate (LiPF6) / sodium hexafluorophosphate (NaPF6) propylene carbonate (PC) solution, but the present invention is not limited thereto. Also, the electrolyte solution 30 is installed between the positive electrode 10 and the negative electrode 20. In another embodiment, the selection of the electrolyte solution 30 can be adjusted according to actual application requirements, and the present invention is not limited thereto. The separator 40 includes, for example, glass fiber filter paper, but is not limited thereto. Also, the separator 40 is installed in the electrolyte solution 30, and separates the positive electrode 10 and the negative electrode 20 from each other through the separator 40. Thereby, the metal battery 1 can achieve the purpose of providing two voltage plateaus of LiFePO4 and NaFePO4, reducing material costs, maintaining a long service life, and providing multiple application changes.

[0013] In this embodiment, the Li contained in the positive electrode material 11 x Na 1-x The FePO4 dual-cation positive electrode material can store Li + ions or Na + ions simultaneously during the charge and discharge process, meaning that two types of positive electrode materials, LiFePO4 and olivine (Olivine) NaFePO4, are provided on the same positive electrode 10. When lithium ions are removed from the structure of lithium iron phosphate with an olivine structure, it changes to a heterosite FePO4 structure, and the structure of heterosite can exist stably in the atmospheric environment, so no structural destruction occurs due to the removal of cations. In an embodiment, when heterosite is applied to the positive electrode material 11 of the metal battery 1, lithium cations or sodium cations can be provided, for example, by the metal mixture 21 of the negative electrode 20. Note that the present invention is not limited thereto.

[0014] In this embodiment, the positive electrode 10 forms a positive electrode sheet with a ratio of, for example, positive electrode material 11:carbon conductive assistant:adhesive=8:1:1. The electrolyte 30 is a 1.0 M propylene carbonate (PC) solution of lithium hexafluorophosphate (LiPF6) / sodium hexafluorophosphate (NaPF6). Glass fiber filter paper is used as the separator 40. The negative electrode 20 of the metal mixture 21 containing lithium and sodium is manufactured by, for example, mixing lithium metal and sodium metal in a weight ratio of 1:3, rolling the lithium-sodium mixed metal to a thickness of 200 μm, and preparing a circular lithium-sodium metal negative electrode sheet with a diameter of 12 mm, which is used as the negative electrode 20 for measurement. Note that in one embodiment, Li is used as the positive electrode 10 of the positive electrode material 11. 0.25 Na 0.75 The LiFePO4 was used, and the preparation method was as follows: LiFePO4 positive electrode sheet, lithium foil, separator and 1.0 M LiPF6 ethylene carbonate (EC) / dimethyl carbonate (DMC) electrolyte were assembled into a Swagelok type 3-electrode battery, and 75% of the lithium ions were removed by slow charging at 0.1 C and controlling the charging time. Then, the positive electrode sheet containing 25% lithium ions was taken out from the Swagelok type battery, and the excess electrolyte was removed by washing twice with dimethyl carbonate (DMC) solvent, and the Li 0.25The FePO4 material can be obtained and pretreated to form the positive electrode 10 of the positive electrode material 11. Thereafter, the positive electrode 10 after the rinsing treatment, the electrolyte solution 30 of 1.0 M LiPF6 / NaPF6 in propylene carbonate (PC), the glass fiber separator 40, and the lithium-sodium metal negative electrode 20 are assembled into a button battery to form a measurement metal battery 1 of the dual cation positive electrode material 11. In this embodiment, in order to ensure that sodium ions are stored (embedded) in the structure of the positive electrode material 11, the measurement half cell described above is, for example, first discharged in a ramp voltage (Vramp) mode, i.e., at a rate of -0.2 mV / sec, from 2.8 V to a cutoff voltage of 2.0 V, so that sodium ions are stored in the structure of the positive electrode material 11 and Li is discharged. 0.25 Na 0.75 In another embodiment, the iron phosphate (heterosite, FePO4), lithium iron phosphate (LiFePO4), or Li x Na 1-x The positive electrode material 11 made of FePO4 can be adjusted according to the requirements of actual applications, and the present invention is not limited thereto.

[0015] In this embodiment, the dual cation cathode material 11 in the metal battery 1 can be further analyzed for electrochemical properties by cyclic voltammetry. 0.25 Na 0.75 Taking the dual cation cathode material 11 composed of FePO4 as an example, the oxidation peak and reduction peak of the dual cation cathode material 11 obtained after slow scanning at a scanning rate of 0.1 mV / s by cyclic voltammetry are shown in Figure 2. 0.25 Na 0.75The oxidation peak of the positive electrode material 11 made of FePO4 has a maximum value of 3.7 V, which is higher than the oxidation peaks of LiFePO4 and NaFePO4. In this embodiment, the electrolyte solvent used in the measurement metal battery 1 is PC, and unlike the electrolyte resistance of the electrolyte solvent used in the measurement of LiFePO4 and NaFePO4, the resistance of the electrolyte in the electrolyte solution 30 of the present invention is relatively high, so the oxidation peak delay phenomenon occurred. By optimizing the electrolyte, it is possible to reduce the occurrence of the oxidation peak delay phenomenon due to high resistance, and the details will be omitted. In the reduction peak region, within the range from 3.3 V for LiFePO4 to 2.6 V for NaFePO4, Li 0.25 Na 0.75 All of the positive electrode materials 11 made of FePO4 have a reduction peak. x Na 1-x It can be seen that lithium ions and sodium ions exist simultaneously in the positive electrode material 11 composed of FePO4. Note that the ionic radius of the lithium ion is 0.76 Å, the ionic radius of the sodium ion is 1.02 Å, the volume of the sodium ion is 34% larger than that of the lithium ion, and the diffusion speed of the sodium ion is 1 / 10 that of the lithium ion. Therefore, the metal battery 1 can change the storage results of the lithium ions and sodium ions in the positive electrode material 11 by selecting an appropriate charge and discharge mode.

[0016] FIG. 3 shows a Li 0.25 Na 0.75 1 shows cyclic voltammetry scans with different cutoff voltages for a dual cation metal battery containing FePO4 cathode material. In this embodiment, Li 0.25 Na 0.75The dual cation metal battery 1 containing the FePO4 cathode material 11 was measured at four oxidation reaction cutoff voltages of 3.6 V, 3.8 V, 4.0 V, and 4.2 V and a scan rate of 0.2 mV / s. The measurement results of cyclic voltammetry using different cutoff voltages are shown in Figure 3. As shown in Figure 3, in the region of the oxidation peak, when the cutoff voltages are set to 3.6 V and 3.8 V, the maximum values ​​of the oxidation peaks are close (approximately coincident), and when the cutoff voltages are set to 4.0 V and 4.2 V, the maximum values ​​of the two oxidation peaks are also close (approximately coincident). The higher the cutoff voltage is set, the larger the area of ​​the oxidation peak, and the larger the area of ​​the oxidation peak, the more lithium ions or sodium ions tend to move out of the structure of the cathode material 11. In addition, in the region of the reduction peak, different degrees of response current appear in the reduction reaction potential reflected in the LiFePO4 plateau voltage and the NaFePO4 plateau voltage due to the difference in the charge cutoff voltage. When the cutoff voltage of the oxidation reaction is 3.6 V, judging from the size of the area of ​​the oxidation peak, the number of cations that have moved out of the structure of the positive electrode material 11 is small, and the number of vacant positions (locations) in the structure is also relatively small. Therefore, when a reduction reaction is performed, in the reduction voltage range (3.2 to 3.5 V) of LiFePO4, lithium ions are stored in the structure first, and a relatively high response current is formed in this range. When the cutoff voltage of the oxidation reaction is set to 3.8 V, 4.0 V, and 4.2 V, the area of ​​the oxidation peak gradually increases, that is, the amount of cations that move out of the structure of the positive electrode material 11 gradually increases, and when a reduction reaction scan is performed, the change in the response current generated at the reduction reaction potential of the LiFePO4 plateau voltage and the NaFePO4 plateau voltage is different. As a result, the metal battery 1 of the present invention can adjust the amount of lithium ions or sodium ions into the structure of the positive electrode material 11 according to different oxidation reaction scan cutoff voltages and scan rates. It should be noted that the present invention is not limited thereto.

[0017] FIG. 4 shows a Li 0.25 Na 0.75The results of charge / discharge measurements in constant current-constant voltage (CC-CV) mode at 0.1 C for a dual cation metal battery containing FePO4 positive electrode material are shown. 0.25 Na 0.75 When the dual cation metal battery 1 containing the FePO4 positive electrode material 11 is charged and discharged in a constant current-constant voltage mode, two charging plateaus of NaFePO4 are observed in the first cycle of charging, and discharge plateaus of LiFePO4 and NaFePO4 are observed in the first cycle of discharging. Since the discharge capacity of NaFePO4 accounts for a relatively high proportion, 0.25 Na 0.75 It can be seen that in the first cycle of charging and discharging FePO4, the proportion of sodium ions is relatively high, and the amount of charge released during discharging is mainly the amount of charge released by NaFePO4. In the second cycle of charging, the proportion of the charge plateau voltage of NaFePO4 decreases, and in the second cycle of discharging, the discharge plateau voltage of NaFePO4 also tends to decrease. Meanwhile, the discharge plateau voltage of LiFePO4 gradually increases, and when the third to fifth cycles of charging and discharging are performed, the discharge plateau voltage and discharge voltage of NaFePO4 gradually disappear. The charge and discharge capacities of the first to fifth cycles are shown in Table 1. From the charge and discharge capacity table, it can be seen that the 0.1 C discharge capacity of NaFePO4 is about 120 to 125 mAh / g, and 25% of the sodium ions in the structure are replaced by lithium ions to become LiFePO4. 0.25 Na 0.75 When FePO4 is produced, the 0.1 C discharge capacity is higher than that of NaFePO4. x Na 1-x FePO4 can provide a higher discharge capacity than NaFePO4, and Li x Na 1-x Since FePO4 has two discharge plateau voltages, LiFePO4 and NaFePO4, it can provide higher discharge efficiency than the single discharge plateau of NaFePO4. In addition, from the viewpoint of the charge / discharge plateau voltage and the tendency of capacity change, when using the constant current-constant voltage mode, Li 0.25 Na 0.75The dual cation metal battery 1 containing the FePO4 positive electrode material 11 can be applied to cases where a relatively high discharge capacity of LiFePO4 and a relatively high discharge power are required. Since the diffusion rate of sodium ions is 1 / 10 of the diffusion rate of lithium ions, the discharge voltage of NaFePO4 is relatively low during constant current discharge, so that the lithium ions are stored in the structure of the positive electrode material 11 under a relatively high voltage. Note that the charge and discharge mode of the metal battery 1 of the present invention is not limited to this. JPEG0007644166000001.jpg44161

[0018] FIG. 5 shows a Li 0.25 Na 0.75 The results of charge / discharge measurements in ramp voltage mode for a dual cation metal battery containing FePO4 cathode material are shown. 0.25 Na 0.75 The dual cation metal battery 1 containing the FePO4 positive electrode material 11 controls the rate of voltage rise and fall in the charge and discharge operation in a ramp voltage (Vramp) mode, the ramp voltage charge and discharge section is set to 2.0 V to 4.0 V, and the ramp voltage charge and discharge rate is set to ±0.2 mV / s. The obtained results are shown in FIG. 5. When charging is performed in the ramp voltage mode, a relatively large response current peak appears in the voltage section of 3.2 V to 3.8 V, and the maximum value of the response current is about 0.7 mA, so charging is performed at about 0.6 C. When discharging is performed in the ramp voltage mode, the maximum value of the response current is about 0.75 mA, so discharging is performed at about 0.7 C. When discharging in the ramp voltage mode, there is a turning point near the discharge voltage of 2.7 V, so discharging can be performed by using the ramp voltage mode. In other words, when the discharge conditions are set appropriately, Li 0.25 Na 0.75 The dual cation metal battery 1 containing the FePO4 cathode material 11 can provide the discharge plateau voltage of NaFePO4 and also the discharge capacity thereof.

[0019] Table 2 shows the results of the Li 0.25 Na 0.75The charge and discharge capacity obtained by charging and discharging the dual cation metal battery 1 containing the FePO4 positive electrode material 11 is shown. As shown in the data in Table 2, the voltage range corresponding to the charge and discharge capacity and the response current was close to the charge and discharge capacity and the charge and discharge plateau voltage of LiFePO4, so that the charge and discharge mode of the ramp voltage was used to charge and discharge LiFePO4. 0.25 Na 0.75 It can be seen that the charge / discharge capacity obtained by charging and discharging FePO4 is mainly provided by LiFePO4. JPEG0007644166000002.jpg44160

[0020] Using the lamp voltage mode, the Li 0.25 Na 0.75 From the results obtained by charging and discharging the dual cation metal battery 1 containing the FePO4 cathode material 11, it can be seen that lithium ions and sodium ions are stored in the cathode material 11 structure during the same discharge process. FIG. 6 shows the results of charging and discharging the iron phosphate / sodium metal anode button battery in ramp voltage mode. In order to more clearly understand the relationship between the corresponding voltage and current when sodium ions are stored and transferred out of the iron phosphate (heterosite, FePO4) structure when charging and discharging using a ramp voltage, a comparative button battery with iron phosphate (heterosite, FePO4) as the cathode and sodium metal as the anode is charged and discharged in ramp voltage mode and measured to evaluate the relative relationship between voltage and current. The charge / discharge range during the measurement was set to 2.0 V to 3.6 V, and the ramp voltage charge / discharge rate was set to ±0.2 mV / s. During the charging process, two relatively large response current peaks appeared, which is the same as the two plateau voltages that appeared when charging / discharging using the constant current-constant voltage mode. In other words, it can be seen that there are two phase transition points in the structure of olivine NaFePO4. In other words, the phases that appeared during the oxidation-reduction process of olivine NaFePO4 were FePO4, Na 0.7Since there are three phases, such as FePO4, NaFePO4, etc., two plateau voltages appear during the charging process. In the case of discharging, the maximum response current appears when the discharge voltage ranges from 3.0 V to 2.6 V, which is close to the discharge voltage of 2.75 V for olivine NaFePO4 when charging and discharging using the constant current-constant voltage mode. JPEG0007644166000003.jpg39158

[0021] FIG. 7 shows the Li in a preferred embodiment of the present invention using a mixed mode of constant current-constant voltage mode and ramp voltage mode. 0.25 Na 0.75 The results are shown in Table 1. The results are obtained by charging and discharging a dual cation metal battery containing a FePO4 positive electrode material. 0.25 Na 0.75 The dual cation metal battery 1 containing the FePO4 positive electrode material 11 may be charged and discharged in a mixed mode of a constant current-constant voltage mode and a ramp voltage mode. The metal battery 1 uses a ramp voltage charging mode in the charging stage, the charging voltage range is set to 2.0 V to 4.2 V, the charging rate is set to 0.2 mV / s, and the metal battery 1 is discharged in a constant current discharging mode of 0.1 C in the discharging stage, and the corresponding relationship between the current, the voltage, and the charge and discharge capacity is measured. The measurement results are shown in FIG. 7. According to the measurement results, when the charging voltage reaches 3.4 V to 3.8 V, a response current appears, and at this time, the sodium ions and lithium ions in the structure of the positive electrode material 11 begin to migrate out of the structure. When discharge begins, since the constant current discharge mode was used for discharge during the experiment, when constant current discharge begins in a voltage range with a relatively high discharge voltage of 3.4 V, lithium ions are stored in the positive electrode material 11, and as shown in the figure, the discharge plateau is maintained at 3.3 to 3.4 V, which is the discharge voltage range of the LiFePO4 plateau voltage.

[0022] Table 4 shows the Li-ion battery charging and discharging mode using a combination of constant current-constant voltage mode and ramp voltage mode. 0.25 Na 0.75The charge and discharge capacity obtained by charging and discharging the dual cation metal battery 1 containing the FePO4 positive electrode material 11 is shown. As shown in Table 4, the charge and discharge capacity obtained after the measurement was determined based on the charge capacity, discharge capacity, and current-voltage relationship diagram. x Na 1-x This should be the charge / discharge capacity provided by the LiFePO4 plateau voltage of FePO4. JPEG0007644166000004.jpg44161

[0023] As can be seen from the above, Li 0.25 Na 0.75 In the dual cation metal battery 1 containing the FePO4 positive electrode material 11, sodium ions or lithium ions are transferred out of the positive electrode material 11 structure during charging, and sodium ions or lithium ions are transferred from the negative electrode 20 to the positive electrode 10 during discharging. Since sodium ions or lithium ions are sequentially stored in the positive electrode material 11 structure to complete the discharging operation, it can be seen from the above that the voltage at which sodium ions or lithium ions are stored in the positive electrode material 11 structure is different, and voltage control is an important factor. In one embodiment, the charging process is charged in a constant current-constant voltage mode, and the discharging process is discharged in a ramp voltage mode, and the results are shown in FIG. 8. As shown in the figure, when discharging using the ramp voltage discharge mode, two different response current peaks are detected in the discharging section of LiFePO4 and NaFePO4, respectively. Therefore, in the mixed mode of charging in a constant current-constant voltage mode during the charging process and discharging in a ramp voltage discharge mode during the discharging process, Li x Na 1-x A dual cation metal battery 1 containing an FePO4 cathode material 11 is applied.

[0024] Table 5 shows the Li-ion battery life when charging and discharging using the constant current-constant voltage mode and ramp voltage discharge mode separately. 0.25 Na 0.75The charge and discharge capacity obtained by charging and discharging the dual cation metal battery 1 containing the FePO4 positive electrode material 11 is shown. As shown in Table 5, the charge capacity, discharge capacity, and the current and voltage obtained by the measurement show that the discharge capacity obtained after the measurement is Li 0.25 Na 0.75 It can be seen that the total discharge capacity provided by discharging at different stages of the discharge voltage of the LiFePO4 plateau voltage and the NaFePO4 plateau voltage in FePO4. JPEG0007644166000005.jpg30161

[0025] From the above, it can be seen that the positive electrode 10 of the lithium-sodium dual cation positive electrode material 11 of the present invention can be applied to the metal battery 1 together with the negative electrode 20 of the lithium-sodium metal mixture 21, and different discharge modes can be selected according to different usage situations to exhibit different properties of the metal battery 1.

[0026] In one embodiment, a metal battery 1 composed of a positive electrode material of the positive electrode 10 made of iron phosphate (heterosite FePO4) and a negative electrode 20 made of a lithium-sodium metal mixture 21 is measured in a mixed charge-discharge mode, and the measurement results are shown in FIG. 9. The first cycle is charged and discharged in a constant current-constant voltage mode at 0.1 C, and judged by the charge-discharge plateau voltage shown in the figure. The metal battery containing the dual cation positive electrode material 11 is charged and discharged using a constant current-constant voltage mode, and the obtained charge-discharge capacity is provided by the LiFePO4 plateau voltage in the dual cation positive electrode material 11, and the discharge capacity per gram is 138.9 mAh / g. The second cycle is charged in a constant current-constant voltage mode at 0.1 C, and discharged in a ramp voltage mode during discharge. As shown in the figure, in the discharge stage, the reduction peaks of the LiFePO4 plateau voltage and the NaFePO4 plateau voltage appear sequentially, which means that the phenomenon changes according to the voltage during discharge. Lithium ions and sodium ions are stored sequentially in the structure of the positive electrode 10, and the discharge capacity per gram is 121.8 mAh / g. The amount of charge discharged in the discharge voltage range of the LiFePO4 plateau voltage from 3.44 V to 3.0 V is 42.7 mAh / g, and the amount of charge discharged in the discharge voltage range of the NaFePO4 plateau voltage from 2.99 V to 2.0 V is 79.1 mAh / g. Since the discharge capacities of the LiFePO4 plateau voltage and the NaFePO4 plateau voltage are approximately 1:2, the Li x Na 1-x It can be inferred that the Li:Na ratio in the FePO4 positive electrode material 11 structure is 1:2. The structural formula of the positive electrode material 11 is Li 0.33 Na 0.66 It can be written as FePO4. JPEG0007644166000006.jpg30158

[0027] In this embodiment, the discharge mode of the ramp voltage achieves the purpose of discharge by controlling the voltage drop rate, so that the control of the voltage drop rate can adjust the ratio of lithium ions and sodium ions stored in the structure. When the dual ion positive electrode metal battery is used for energy storage applications that do not require a large discharge current output, for example, when used in a photovoltaic power generation system, when solar power generation is performed by sunlight during the day, the battery is slowly charged with the current from the solar panel and discharged at night, when a larger power output is required, the constant current-constant voltage discharge mode can be used for discharge. That is, the power released by the LiFePO4 plateau voltage can be used. When a large power output is not required, the discharge mode of the ramp voltage can be used for discharge. That is, the power released by more NaFePO4 plateau voltage can be used. This allows the two modes to be selected according to actual demand. However, the present invention is not limited to this, and details thereof will be omitted.

[0028] As described above, the present invention provides a dual cation metal battery and a method for charging and discharging the same, which can reduce material costs, maintain a long service life, and allow multiple uses. Lithium iron phosphate with olivine structure and iron phosphate have lithium ions and sodium ions stored and released simultaneously in the structure, and the Li x Na 1-x A dual cation cathode material can be formed, which allows the metal battery to provide two different plateau voltages for LiFePO4 and NaFePO4. The present invention uses sodium ions to replace some of the lithium ions, resulting in a LiFePO4 dual cation cathode material. x Na 1-xThe dual cation metal battery of the present invention uses sodium ions, which are more abundant in the earth's crust, to replace some of the lithium ions, making the secondary battery material more sustainable and providing higher plateau voltage, capacity and more diverse applications than sodium iron phosphate cathode materials. In the dual cation metal battery of the present invention, lithium metal and sodium metal are mixed as a composite anode. Lithium metal (lithium metal has a theoretical capacity per gram of 3840 mAh / g) and sodium metal (sodium metal has a theoretical capacity per gram of 1166 mAh / g) have high capacity per gram, which can help reduce the thickness of the anode and increase the energy density of the battery. In addition, iron phosphate (heterosite, FePO4), lithium iron phosphate (LiFePO4) or Li x Na 1-x Dual cation metal batteries, which are made up of a positive electrode material such as FePO4 and a mixture of lithium metal and sodium metal, have two different plateau voltages during the charge and discharge process: LiFePO4 and NaFePO4. x Na 1-xWhen the FePO4 dual cation cathode material is matched with the lithium-sodium metal anode, it can exhibit different electrical properties by using different charge and discharge modes. When the dual cation metal battery is discharged in a ramp voltage mode, the ratio of lithium ions and sodium ions stored in the structure can be controlled by controlling the voltage drop rate. In addition, when the dual ion cathode metal battery is used for energy storage applications that do not require a large discharge current output, such as when used in a solar power generation system, when solar power is generated by sunlight during the day, the battery is charged slowly with the current from the solar panel and discharged at night, when larger power is required, it can be discharged using a constant current-constant voltage discharge mode. That is, it is discharged by the LiFePO4 plateau voltage. On the other hand, when a large power output is not required, the dual cation metal battery can be discharged using a ramp voltage discharge mode and the power released by the NaFePO4 plateau voltage can be used. This allows the selection of the ramp voltage mode or the constant current-constant voltage mode according to actual demand.

[0029] The present invention can be modified or changed in various ways by those skilled in the art, but all such modifications and changes are included in the scope of the claims of the present invention without departing from the technical spirit of the present invention. [Explanation of symbols]

[0030] 1: Dual cation metal battery 10: Positive electrode 11: Cathode material 20: Negative electrode 21: Metal mixture 30: Electrolyte solution (electrolyte) 40: Separator

Claims

1. A dual cation metal battery comprising a positive electrode, a negative electrode, an electrolyte solution, and a separator, The positive electrode contains a positive electrode material, and the positive electrode material is selected from the group consisting of iron phosphate, lithium iron phosphate, and Li ｘ Na １－ｘ FePO ４ where 0<x<1; The negative electrode contains a metal mixture, the metal mixture being composed of lithium metal and sodium metal, and the weight ratio of the lithium metal to the sodium metal is 1:3; the electrolyte solution is disposed between the positive electrode and the negative electrode; a separator disposed within the electrolyte solution, the positive electrode and the negative electrode being separated from each other by the separator.

2. 2. The dual cation metal battery of claim 1, wherein the dual cation metal battery is charged and discharged in a constant current-constant voltage mode, the constant current-constant voltage mode being a 0.1C constant current-constant voltage mode.

3. 2. The dual cation metal battery of claim 1, wherein the dual cation metal battery is charged and discharged in a mixed mode of a constant current-constant voltage mode and a ramp voltage mode, the constant current-constant voltage mode being a 0.1 C constant current-constant voltage mode, the ramp voltage mode having a charge / discharge range of 2.0 V to 4.0 V, and a charge / discharge rate of ±0.2 mV / s.

4. The positive electrode material is Li ｘ Na １－ｘ FePO ４ 2. The dual cation metal battery according to claim 1, wherein the dual cation metal battery is charged in a constant current-constant voltage mode and discharged in a ramp voltage mode, the constant current-constant voltage mode being a 0.1C constant current-constant voltage mode, the ramp voltage mode having a discharge section range of 4.0 V to 2.0 V, and a discharge rate of -0.2 mV / s.

5. The dual cation metal battery of claim 4, wherein in the ramp voltage mode, the discharge section ranges from 2.8 V to a cutoff voltage of 2.0 V.

6. A method for charging and discharging a dual cation metal battery, comprising: A dual cation metal battery is provided, the dual cation metal battery comprising a positive electrode, a negative electrode, an electrolyte solution and a separator, the positive electrode comprising a positive electrode material, the positive electrode material being selected from the group consisting of iron phosphate, lithium iron phosphate and Li ｘ Na １－ｘ FePO ４ and 0<x<1, the negative electrode comprises a metal mixture, the metal mixture being composed of lithium metal and sodium metal, the weight ratio of the lithium metal to the sodium metal being 1:3, the electrolyte solution is disposed between the positive electrode and the negative electrode, the separator is disposed in the electrolyte solution, and the positive electrode and the negative electrode are separated from each other by the separator; and (b) selecting a constant current-constant voltage mode or a ramp voltage mode to charge or discharge the dual cation metal battery.

7. The method for charging and discharging a dual cation metal battery according to claim 6, characterized in that in step (b), the constant current-constant voltage mode is used for charging and discharging, and the constant current-constant voltage mode is a 0.1C constant current-constant voltage mode.

8. 7. The method of claim 6, wherein in step (b), the charge and discharge are performed in a mixed mode of the constant current-constant voltage mode and the ramp voltage mode, the constant current-constant voltage mode being a 0.1C constant current-constant voltage mode, the ramp voltage mode having a charge / discharge range of 2.0 V to 4.0 V, and a charge / discharge rate of ±0.2 mV / s.

9. The positive electrode material is Li ｘ Na １－ｘ FePO ４ 7. The method of claim 6, wherein, in step (b), the battery is charged in the constant current-constant voltage mode and discharged in the ramp voltage mode, the constant current-constant voltage mode being a 0.1C constant current-constant voltage mode, the ramp voltage mode having a discharge section range of 4.0 V to 2.0 V, and a discharge rate of -0.2 mV / s.

10. 10. The method of claim 9, wherein the ramp voltage mode has a discharge section range of 2.8 V to a cutoff voltage of 2.0 V.

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