A three-electrode sodium ion battery and a method for preparing the same

Abstract

The present invention relates to the technical field of sodium ion batteries, and discloses a three-electrode sodium ion battery and a preparation method thereof, wherein the three-electrode sodium ion battery comprises a positive electrode ear, a negative electrode ear, a conductor, and a battery cell, wherein the positive electrode ear, the negative electrode ear, and the conductor are electrically connected to the battery cell respectively. The present invention solves the problems of low safety and stability, complex operation, and high production cost existing in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a three-electrode sodium ion battery and a preparation method thereof. Background Art

[0002] Sodium-ion batteries have the characteristics of low material cost, good low-temperature performance, long cycle life and good safety performance. In recent years, their industrialization has developed rapidly and have become a research hotspot.

[0003] Generally, sodium-ion batteries have positive and negative tabs. The positive tab is connected to the positive electrode sheet as the working electrode, and the negative tab is connected to the negative electrode sheet as the counter electrode. During the charge and discharge process of sodium-ion batteries, the potentials of the positive and negative electrodes change synchronously. By measuring the voltage, only the relative potential difference between the positive and negative electrodes can be obtained, but the absolute potential of the positive and negative electrodes cannot be obtained, which makes it impossible to analyze the potential changes.

[0004] Therefore, it is necessary to implant a third electrode with a constant potential inside the sodium ion battery as a reference electrode. The patent with application publication number CN115241553A proposes a sodium ion battery three-electrode structure and a manufacturing method thereof. The specific method is to open grooves on the side surfaces of the positive electrode sheet and the negative electrode sheet to form a reference electrode cavity, and then melt the sodium powder in the foam metal skeleton. The foam metal skeleton is wrapped with a diaphragm and placed in the reference electrode cavity, and then welded to the foam metal skeleton through the pole ear or copper wire and led to the outside. Although the above method can use the high porosity of the foam metal skeleton to hold more sodium metal and form a more stable reference electrode, sodium metal is extremely active and there are safety hazards in the preparation process. In addition, the processing flow of the reference electrode cavity is very complicated and requires high dimensional accuracy, which greatly increases the difficulty of production. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a three-electrode sodium ion battery and a preparation method thereof, which solve the problems of low safety and stability, complex operation, high production cost, etc. in the prior art.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] A three-electrode sodium ion battery comprises a positive electrode ear, a negative electrode ear, a conductor and a battery cell, wherein the positive electrode ear, the negative electrode ear and the conductor are electrically connected to the battery cell respectively.

[0008] As a preferred technical solution, the potential of the conductor is constant.

[0009] As a preferred technical solution, the conductor is bent, and the bent portion is arranged inside the battery core.

[0010] As a preferred technical solution, the material of the conductor is copper.

[0011] As a preferred technical solution, the purity of the conductor is ≥99.95%.

[0012] As a preferred technical solution, the diameter range of the conductor is [20um, 50um].

[0013] The method for preparing a three-electrode sodium ion battery comprises the following steps:

[0014] S1, stacking or winding the positive electrode sheet, the negative electrode sheet, and the separator into a stacked core or a wound core;

[0015] S2, implanting the conductor into the stacked core or the wound core;

[0016] S3, packaging the stacked core or rolled core to manufacture the battery cell;

[0017] S4, charging and sodium plating operation is performed on the conductor: the positive electrode of the charging and discharging device is connected to the positive electrode ear, and the negative electrode of the charging and discharging device is connected to the conductor, so as to realize sodium plating on the positive electrode side of the conductor close to the positive electrode ear; and, the positive electrode of the charging and discharging device is connected to the negative electrode ear, and the negative electrode of the charging and discharging device is connected to the conductor, so as to realize sodium plating on the negative electrode side of the conductor close to the negative electrode ear.

[0018] As a preferred technical solution, in step S2, after pre-treating the stacked core or the wound core, the conductor is implanted into the stacked core or the wound core; wherein the pre-treatment method is: soaking in dilute hydrochloric acid or dilute sulfuric acid for a set time to remove the oxide film on the surface of the conductor, and then rinsing with anhydrous ethanol and drying.

[0019] As a preferred technical solution, in step S4, when the battery cell is charged and sodium-plated, the charging and discharging device charges the conductor with a current of 20uA to 100uA.

[0020] As a preferred technical solution, in step S4, when the battery cell is charged for sodium plating, the charging time is 2 to 20 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention adopts the method of folding the copper wire and implanting it to form the third electrode, which is not easy to pierce the diaphragm, and the two copper wires are packaged in parallel, which does not affect the packaging effect and greatly improves the success rate of the three-electrode production;

[0023] (2) The present invention adopts a reasonable sodium plating process to form a uniform, stable and dense sodium plating layer, which can accurately monitor the independent potential changes of the positive and negative electrodes during the charging and discharging process of the sodium ion battery;

[0024] (3) The three-electrode sodium ion battery of the present invention has the characteristics of simple structure, low cost, convenient operation, strong compatibility, safety and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of a three-electrode sodium ion battery according to the present invention;

[0026] Figure 2 It is the sodium plating stability curve diagram of Example 2;

[0027] Figure 3 This is a 0.5C charge and discharge curve diagram of the sodium ion battery of Example 2.

[0028] The marks and their corresponding names in the accompanying drawings are: 101 - positive electrode ear, 102 - negative electrode ear, 103 - conductor, 104 - battery cell. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0030] Example 1

[0031] like Figures 1 to 3 As shown, in order to solve the problems existing in the prior art, the present invention discloses a three-electrode sodium ion battery and a preparation method thereof, which has the characteristics of simple structure, low cost, convenient operation, strong compatibility, safety and stability.

[0032] The three-electrode sodium ion battery described in the present invention introduces a third electrode on the basis of a traditional battery structure. The potential of the third electrode is constant, so the potential difference between the positive electrode and the third electrode and the potential difference between the negative electrode and the third electrode can be measured separately, thereby analyzing the independent potential changes of the positive and negative electrodes, and then guiding the processes of battery cell design, charging strategy formulation, material evaluation, failure analysis, etc.

[0033] Specifically, the above technical solution is implemented through the following steps:

[0034] S1, stacking or winding the positive electrode sheet, the negative electrode sheet, and the separator into a stacked core or a rolled core (the positive electrode sheet, the negative electrode sheet, the separator layer, the stacked core or the rolled core are all encapsulated inside the battery cell 104, Figure 1 The middle view is not shown, the positive electrode sheet is electrically connected to the positive electrode ear 101, and the negative electrode sheet is electrically connected to the negative electrode ear 102);

[0035] S2, pre-treating a high-purity copper wire (i.e., the conductor 103, the copper wire used in this embodiment has the advantages of good conductivity and easy attachment of sodium during charging and sodium plating) and then folding it in half (preferably folding it in half, but not limited to bending it in half length) and embedding it into a stacked core or a coiled core;

[0036] S3, after packaging the stacked core or the wound core, the conventional cell manufacturing process is followed to complete the processes of baking, liquid injection, chemical formation, and capacity division to form a cell 104;

[0037] S4, performing a charging and sodium plating operation on the copper wire (the copper wire after the charging and sodium plating is the third electrode): connecting the positive electrode of the charging and discharging device to the positive electrode ear 101, and connecting the negative electrode of the charging and discharging device to the copper wire, so as to achieve sodium plating on the positive electrode side of the copper wire close to the positive electrode ear 101; and connecting the positive electrode of the charging and discharging device to the negative electrode ear 102, and connecting the negative electrode of the charging and discharging device to the copper wire, so as to achieve sodium plating on the negative electrode side of the copper wire close to the negative electrode ear 102;

[0038] S5: Testing the three-electrode sodium-ion battery after sodium plating.

[0039] The copper wire mentioned above is made of red copper with a purity of not less than 99.95%, excellent electronic conductivity, and a diameter range of 20-50um. If the diameter is too small, the physical strength of the copper wire is too low and it is easy to break during the packaging process. If the diameter is too large, it is easy to leak during the packaging process.

[0040] The copper wire should be pretreated before implantation. The specific treatment method is to soak it in dilute hydrochloric acid or dilute sulfuric acid for about 10 minutes to remove the oxide film on the surface of the copper wire, then rinse it with anhydrous ethanol and dry it for use. Otherwise, the oxide film on the surface of the copper wire will cause the sodium plating layer to be unstable.

[0041] The copper wire is implanted after being folded in half. On the one hand, the folded position forms an arc, there are no burrs, and it is not easy to pierce the diaphragm. On the other hand, the number of copper wires led out after folding in half is two, and the two copper wires are packaged in parallel, which does not affect the packaging effect and greatly improves the success rate of three-electrode production. The inventor found in the actual production process that if one copper wire is implanted, the end of the copper wire is relatively sharp and it is very easy to pierce the diaphragm, thereby causing a short circuit between the positive and negative electrodes, and the copper wire is easily broken by the head during the packaging process, causing a short circuit. The success rate of preparing three electrodes is only about 20%. After the present invention adopts the copper wire folding implantation scheme, the success rate of preparing three electrodes exceeds 80%.

[0042] After the copper wire is implanted into the stacked core or the wound core, an independent diaphragm needs to be added to insulate the copper wire from the positive electrode sheet or the negative electrode sheet (the portion of the copper wire located inside the battery cell 104 is insulated from the positive electrode sheet or the negative electrode sheet, and the portion of the copper wire extending outside the battery cell 104 does not need to be insulated by a diaphragm) to avoid direct contact and short circuit between the two. The newly added diaphragm should extend beyond the edge of the stacked core or the wound core by 0.5 to 2 mm, thereby completely ensuring that the copper wire will not come into direct contact with the positive electrode sheet or the negative electrode sheet at any position.

[0043] The sodium plating process includes two steps: sodium plating on the positive electrode side and sodium plating on the negative electrode side. First, the positive and negative electrodes of the charging and discharging equipment are connected to the positive electrode ear of the sodium ion battery and the copper wire respectively, and then charged with a current of 20uA to 100uA for 2h to 20h. The sodium ions released from the positive electrode migrate to the surface of the copper wire under the action of the electric field and are reduced to sodium element to form a sodium plating layer on the positive electrode side. Then, the positive and negative electrodes of the charging and discharging equipment are connected to the negative electrode ear of the sodium ion battery and the copper wire respectively, and sodium plating is performed on the negative electrode side according to the same sodium plating process. In the sodium plating process, in order to form a uniform and dense sodium plating layer, it is advisable to use a smaller current for charging, but the current should not be too small, otherwise the charging time is too long, affecting the sodium plating efficiency.

[0044] Example 2

[0045] like Figures 1 to 3 As shown, as a further optimization of Example 1, based on Example 1, this embodiment also includes the following technical features:

[0046] Sodium iron phosphate pyrophosphate is used as the positive electrode active material of the sodium ion battery, and the positive electrode sheet coating surface density is 400g / m 2 After cold pressing, the thickness of the positive electrode sheet is 202um.

[0047] Hard carbon is used as the negative electrode active material for sodium ion batteries, and the negative electrode sheet coating surface density is 151g / m 2 After cold pressing, the thickness of the negative electrode sheet is 171um.

[0048] The cold-pressed positive electrode sheet, negative electrode sheet and separator are stacked to form a stacked core;

[0049] Take a high-purity copper wire of appropriate length and immerse it in 20% volume concentration of dilute hydrochloric acid for 10 minutes. The purity of the copper wire is 99.99% and the diameter of the copper wire is 40um. Then rinse it with anhydrous ethanol three times and bake it in a 45℃ oven for 2 hours.

[0050] Take out the baked copper wire, fold it in half and then embed it into the stacked core. First, cut a piece of diaphragm of appropriate size to fix the stacked core without misalignment, then put the copper wire in the preset position, and then completely cover the surface of the copper wire with the diaphragm. The newly added diaphragm extends 1mm beyond the edge of the stacked core, thus completely ensuring that the copper wire will not come into direct contact with the positive or negative electrode sheet at any position.

[0051] The stacked core with implanted copper wires is placed in an aluminum-plastic film shell for packaging. During the packaging process, care should be taken not to overlap the two copper wires to avoid increasing the thickness of the overlapping area and causing packaging leakage.

[0052] Preferably, the two copper wires exposed outside the battery cell can be soldered to the nickel sheet using a soldering process to maintain good electrical contact between the nickel sheet and the copper wire. This can ensure that the test fixture clamps the nickel sheet to obtain more accurate test results. Otherwise, since the copper wire is too thin, the test fixture may have poor contact with the copper wire.

[0053] Then, the conventional cell manufacturing process is followed to complete the baking, liquid injection, formation, and capacity division processes. It should be noted that after formation and capacity division, since some sodium ions have been embedded in the negative electrode, and only some sodium ions have been released from the positive electrode, there are sodium sources in both the positive and negative electrodes, which can provide sodium sources for subsequent sodium plating on the positive and negative electrode sides.

[0054] The battery after capacity division is plated with sodium using a charging and discharging device. Specifically, the sodium ions in the positive and negative electrodes are deposited on the surface of the copper wire to form a third electrode. First, the positive and negative electrodes of the charging and discharging device are connected to the positive ear and copper wire of the sodium ion battery respectively, and charged at a current of 50uA for 10 hours to complete the sodium plating on the positive electrode side. Then, the positive and negative electrodes of the charging and discharging device are connected to the negative ear and copper wire of the sodium ion battery respectively, and charged at a current of 50uA for 10 hours to complete the sodium plating on the negative electrode side.

[0055] Finally, the three-electrode sodium-ion battery was tested after sodium plating.

[0056] from Figure 2 It can be seen that the sodium ion battery voltage, positive electrode potential and negative electrode potential after sodium plating remain stable after 45 hours, indicating that sodium plating using the technical solution of the present invention has excellent stability, wherein the battery voltage is the difference between the positive electrode potential and the negative electrode potential.

[0057] from Figure 3 It can be seen that the three-electrode sodium ion battery of the present invention can synchronously display the battery voltage, positive electrode potential and negative electrode potential, and the dynamic changes of the positive and negative electrode potentials can be clearly observed. Taking this embodiment as an example, during the charging process, the lowest potential of the negative electrode material is 0.0175V, while the sodium precipitation potential is theoretically 0V, indicating that the negative electrode material has not reached the sodium precipitation potential and there is no risk of sodium precipitation. In addition, the potential range of the positive and negative electrode materials during the discharge process can also be observed, which can guide the capacity design process of the battery cell.

[0058] As described above, the present invention can be preferably implemented.

[0059] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or expanded or replaced in any manner.

[0060] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. According to the technical essence of the present invention, within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A three-electrode sodium ion battery, characterized in that: It comprises a positive electrode ear (101), a negative electrode ear (102), a conductor (103), and a battery cell (104); the positive electrode ear (101), the negative electrode ear (102), and the conductor (103) are electrically connected to the battery cell (104) respectively; The conductor (103) is folded in half, and the folded portion is arranged in the battery core (104). After the fold, the number of conductors (103) leading out is two; The conductor (103) is made of copper; The purity of the conductor (103) is ≥ 99.95%; The diameter of the conductor (103) is in the range of [20um, 50um].

2. A three-electrode sodium ion battery according to claim 1, characterized in that: The electric potential of the conductor (103) is constant.

3. A method for preparing a three-electrode sodium ion battery according to claim 1 or 2, characterized in that: The following steps are involved: S1, stacking or winding the positive electrode sheet, the negative electrode sheet, and the separator into a stacked core or a wound core; S2, implanting the conductor (103) into the stacked core or the wound core; S3, packaging the stacked core or the rolled core to form a battery cell (104); S4, performing a charging sodium plating operation on the conductor (103): connecting the positive electrode of the charging and discharging device to the positive electrode ear (101), and connecting the negative electrode of the charging and discharging device to the conductor (103), so as to achieve sodium plating on the positive electrode side of the conductor (103) close to the positive electrode ear (101); and connecting the positive electrode of the charging and discharging device to the negative electrode ear (102), and connecting the negative electrode of the charging and discharging device to the conductor (103), so as to achieve sodium plating on the negative electrode side of the conductor (103) close to the negative electrode ear (102).

4. The method for preparing a three-electrode sodium ion battery according to claim 3, characterized in that: In step S2, after pre-treating the stacked core or the wound core, the conductor (103) is implanted into the stacked core or the wound core; wherein the pre-treating method is: soaking in dilute hydrochloric acid or dilute sulfuric acid for a set time to remove the oxide film on the surface of the conductor (103), and then rinsing with anhydrous ethanol and drying.

5. The method for preparing a three-electrode sodium ion battery according to claim 3, characterized in that: In step S4, when the battery cell (104) is charged and sodium-plated, the charging and discharging device charges the conductor (103) with a current of 20uA to 100uA.

6. The method for preparing a three-electrode sodium ion battery according to claim 5, characterized in that: In step S4, when the battery cell (104) is charged and sodium-plated, the charging time is 2 to 20 hours.

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