A soft package battery three-electrode system, a preparation method and use thereof

Abstract

The present application relates to a kind of soft package battery three-electrode system and its preparation method and purposes, the soft package battery three-electrode system includes battery and shell, the battery includes positive plate, negative plate, diaphragm and reference electrode;The reference electrode is copper silicon composite wire material.The present application uses copper silicon composite material as reference electrode, so that soft package battery is plated lithium work step, silicon and lithium alloy reaction generates lithium silicon alloy, ensure that the lithium deposited on the surface exists stably during testing, reduce and electrolyte reaction;At the same time, copper silicon composite is wire material, reduce the active lithium loss caused by reference electrode plating lithium, avoid the hindrance to lithium ion transport between positive and negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery manufacturing technology, and relates to a three-electrode system for a soft-pack battery, its preparation method, and its applications. Background Technology

[0002] With the rapid development of emerging industries such as small electronic devices and new energy vehicles, lithium-ion batteries have become the mainstream energy storage system due to their high energy density and green, environmentally friendly, and pollution-free advantages. However, when batteries are charged at low temperatures or high rates, lithium ions may not be able to embed into the graphite layers in time after reaching the negative electrode, resulting in lithium plating. Therefore, during the battery pre-charge formation process, by introducing a reference electrode, the voltage changes of the positive and negative electrodes relative to a stable reference electrode can be obtained, enabling in-situ detection of the internal electrochemical reactions of the battery.

[0003] CN 113540404A provides an Ag / AgCl reference electrode and its fabrication method. A platinum electrode lead is disposed on a glass substrate, with a silver / silver chloride electrode layer disposed at its end. A silicon substrate is bonded to the glass substrate. The silicon substrate has a downward-opening cavity that at least encompasses the silver / silver chloride electrode layer, forming a reservoir with the glass substrate for storing a saturated potassium chloride solution. The top wall of the reservoir has multiple nanoscale conical micropores with large outer and small inner diameters etched by wet etching, forming a conical micropore array. Each conical micropore serves as a nanochannel for ion exchange with the external analyte. The glass substrate has an injection hole and is coated with sealant.

[0004] Existing technologies use gold, silver, and platinum wires as reference electrodes. However, the exposed metal wires can interfere with the battery signal in the electrolyte, and all of these wires are expensive, resulting in high system costs. Using pure lithium metal wires / sheets as reference electrodes may lead to lithium metal consumption or even dissolution during long-term charge-discharge processes. Furthermore, since the reference electrode only contains lithium and lacks other supporting metals, it is prone to breakage, making it difficult to continue using it as a reference electrode in experiments. In addition, lithium metal is highly reactive and reacts with oxygen and moisture when exposed to air, requiring the fabrication process to be completed in a glove box, which increases the manufacturing difficulty.

[0005] CN 115207504A discloses a reference electrode and its preparation method, as well as a three-electrode lithium-ion battery. The reference electrode includes: a first reference electrode tab, a winding structure, and a second reference electrode tab stacked sequentially. The winding structure includes a first metal foil and a second metal foil integrally connected, and a first copper wire and a second copper wire integrally connected. The first copper wire is wound on the first metal foil, and the first metal foil with the first copper wire wound on it is wound inside the second metal foil. The second copper wire is disposed away from the first reference electrode tab and the second reference electrode tab, and a lithium layer is provided at the end of the second copper wire away from the first copper wire.

[0006] Another existing technology uses copper as a reference electrode. However, lithium plating on copper results in significant loss of active lithium, causing a potential shift between the positive and negative electrodes and hindering the normal transport of lithium ions between them. Furthermore, after lithium plating on the copper surface, the deposited lithium readily reacts with the electrolyte, failing to maintain a stable state during cell cycling or storage, potentially leading to the short-term failure of the three-electrode system in the lithium-ion battery. On the other hand, during lithium-ion battery cycling, the reference electrode is prone to reacting with the electrolyte, damaging the lithium metal layer and causing the three-electrode system to fail.

[0007] Therefore, ensuring the stability of lithium, reducing its reaction with the electrolyte, and minimizing the loss of active lithium during the lithium plating process are urgent problems to be solved in the process of setting a reference electrode. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a three-electrode system for a soft-pack battery, its preparation method and application. A copper-silicon composite material is used as a reference electrode, so that when the lithium plating step is performed, silicon and lithium undergo an alloy reaction to form a lithium-silicon alloy, which ensures the stable existence of lithium deposited on the surface during the test and reduces the reaction with the electrolyte. At the same time, the copper-silicon composite is used as a wire material, which reduces the loss of active lithium caused by lithium plating of the reference electrode and avoids hindering the lithium ion transport between the positive and negative electrodes.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a three-electrode system for a pouch battery, the three-electrode system comprising a cell and a casing, the cell comprising a positive electrode, a negative electrode, a separator and a reference electrode; the reference electrode is a copper-silicon composite wire.

[0011] In this invention, a copper-silicon composite material is used as the reference electrode, which enables the silicon and lithium to undergo an alloy reaction to form a lithium-silicon alloy during the lithium plating step of the soft-pack battery. This ensures the stable existence of the lithium deposited on the surface during the test and reduces the reaction with the electrolyte. At the same time, the copper-silicon composite material is used as a wire, which reduces the loss of active lithium caused by lithium plating of the reference electrode and avoids hindering the lithium ion transport between the positive and negative electrodes.

[0012] Preferably, the diaphragm includes a first diaphragm and a second diaphragm.

[0013] Preferably, the battery cell includes a positive electrode, a first separator, a second separator, and a negative electrode stacked in sequence.

[0014] Preferably, the reference electrode is disposed between the first diaphragm and the second diaphragm.

[0015] Preferably, the area of ​​the second diaphragm is less than the area of ​​the first diaphragm, and the area of ​​the second diaphragm is greater than the area of ​​the reference electrode.

[0016] Preferably, the bottom of the reference electrode is located at the middle position of the bottom of the battery cell, and the top of the reference electrode is located on the side of the battery cell.

[0017] The purpose of placing the reference electrode at the bottom is to prevent the temperature rise at the top of the cell from being too high during charging, which would lead to an overestimation of the test results. Therefore, it is preferable to place the reference electrode at the bottom of the cell.

[0018] Preferably, a positive electrode tab is provided on the positive electrode plate, and a negative electrode tab is provided on the negative electrode plate.

[0019] Preferably, a reference tab is provided on the reference electrode.

[0020] Preferably, the positive electrode tab and the negative electrode tab are parallel to each other, and the reference electrode tab and the positive electrode tab are perpendicular to each other.

[0021] The purpose of extending the reference electrode from the side of the cell is to prevent the positive and negative tabs of the pouch cell from coming into contact with each other, thus avoiding the risk of a short circuit.

[0022] Preferably, the reference electrode is made of nickel.

[0023] Preferably, the diameter of the reference electrode is 0.05 to 0.2 mm, for example, it can be 0.05 mm, 0.08 mm, 0.1 mm, 0.15 mm or 0.2 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the copper content in the reference electrode is 70-80 wt%, for example, it can be 70 wt%, 72 wt%, 74 wt%, 76 wt%, 78 wt%, or 80 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the housing is any one of aluminum-plastic film, aluminum shell, steel shell or glass shell.

[0026] In a second aspect, the present invention provides a method for preparing a three-electrode system for a pouch cell according to the first aspect, characterized in that the preparation method includes the following steps:

[0027] (1) Provide copper-silicon composite wire as a reference electrode;

[0028] (2) Stack the positive electrode, the separator and the negative electrode in sequence, and place the reference electrode described in step (1) between the separator and the negative electrode to obtain the battery cell;

[0029] (3) The cell described in step (2) is encapsulated in a housing to obtain the three-electrode system of the soft-pack battery.

[0030] Preferably, the copper-silicon composite wire in step (1) is prepared in the following manner:

[0031] Copper powder and silicon powder are mixed and calcined under a protective atmosphere to obtain a composite material; the composite material is then rolled and drawn into wire to obtain the copper-silicon composite wire.

[0032] Preferably, the mass ratio of copper powder to silicon powder is (2-4):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the protective atmosphere includes an inert atmosphere, preferably helium.

[0034] Preferably, the calcination temperature is 800–1500°C, for example, 800°C, 1000°C, 1200°C, 1400°C or 1500°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the calcination time is 8 to 15 hours, for example, 8 hours, 10 hours, 12 hours, 14 hours or 15 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the diameter of the drawn wire is 0.05 to 0.2 mm, for example, it can be 0.05 mm, 0.08 mm, 0.1 mm, 0.15 mm or 0.2 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the diaphragm in step (2) is a first diaphragm.

[0038] Preferably, after setting the reference electrode in step (2), a second diaphragm is set between the reference electrode and the negative electrode.

[0039] Preferably, after encapsulation in step (3), liquid injection, formation and volume separation are also included.

[0040] Preferably, the process of separating the capacity further includes welding a reference electrode and a reference tab.

[0041] As a preferred embodiment of the preparation method described in the second aspect of the present invention, the preparation method includes the following steps:

[0042] (1) Copper powder and silicon powder are mixed in a mass ratio of (2-4):1 and calcined at 800-1500℃ for 8-15h in a helium atmosphere to obtain a composite material; the composite material is rolled and drawn into wires with a diameter of 0.05-0.2mm to obtain the copper-silicon composite wire, which is used as a reference electrode.

[0043] (2) Stack the positive electrode, the first separator and the negative electrode in sequence, place the reference electrode described in step (1) between the first separator and the negative electrode and fix it, and then place the second separator between the reference electrode and the negative electrode to obtain the battery cell;

[0044] (3) The cell described in step (2) is encapsulated in a housing, and after liquid injection, formation and capacity testing, the reference electrode is welded to the reference tab to obtain the three-electrode system of the soft pack battery.

[0045] Thirdly, the present invention provides an application of the three-electrode system of the pouch battery according to the first aspect, characterized in that the three-electrode system of the pouch battery is used in electronic devices or new energy vehicles.

[0046] Based on the above technical solutions, the beneficial effects of the present invention are as follows:

[0047] In this invention, a copper-silicon composite material is used as the reference electrode, which enables the silicon and lithium to undergo an alloy reaction to form a lithium-silicon alloy during the lithium plating step of the soft-pack battery. This ensures the stable existence of the lithium deposited on the surface during the test and reduces the reaction with the electrolyte. At the same time, the copper-silicon composite material is used as a wire, which reduces the loss of active lithium caused by lithium plating of the reference electrode and avoids hindering the lithium ion transport between the positive and negative electrodes. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the three-electrode system of the pouch cell.

[0049] Figure 2 This is a side view of the battery cell.

[0050] in:

[0051] 1-Battery cell, 2-Housing, 3-Reference electrode, 4-Reference tab, 5-Positive tab, 6-Negative tab, 7-Positive electrode plate, 8-Negative electrode plate, 91-First diaphragm, 92-Second diaphragm. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0053] Example 1

[0054] This embodiment provides a three-electrode system for a pouch cell, such as... Figure 1 As shown, the three-electrode system of the pouch battery includes a cell 1 and an aluminum-plastic film casing 2. A reference electrode 3, led out from inside the cell 1, is connected to the side of the aluminum-plastic film casing 2. The reference electrode 3 is welded to a nickel reference tab 4, which is located on the side of the casing 2. The reference electrode 3 is a copper-silicon composite wire with a copper mass percentage of 75%.

[0055] The battery cell 1 (structural schematic diagram as shown) Figure 2 (As shown) includes a positive electrode 7, a first separator 91, a reference electrode 3, a second separator 92, and a negative electrode 8 stacked sequentially. The area of ​​the second separator 92 is slightly larger than the area of ​​the reference electrode 3. The bottom of the reference electrode 3 is located in the middle of the bottom of the cell 1, and the top of the reference electrode 3 is located on the side of the cell 1, extending out from the side of the cell 1. A positive electrode tab 5 is provided on the positive electrode 7, and a negative electrode tab 6 is provided on the negative electrode 8. The positive electrode 7 and the negative electrode 8 are located on the top of the housing 2. The positive electrode tab 5 and the negative electrode tab 6 are parallel to each other, and the reference electrode tab 4 is perpendicular to the positive electrode tab 5.

[0056] The preparation method includes the following steps:

[0057] (1) Copper powder and silicon powder with a mass ratio of 3:1 are mixed and calcined at 1000°C for 10 hours under a helium atmosphere to obtain a composite material; the composite material is rolled and drawn into wires with a diameter of 0.1 mm to obtain the copper-silicon composite wire, which is used as reference electrode 3.

[0058] (2) Stack the positive electrode 7, the first separator 91 and the negative electrode 8 in sequence, place the reference electrode 3 described in step (1) between the first separator 91 and the negative electrode 8 and fix it, and then place the second separator 92 between the reference electrode 3 and the negative electrode 8 to obtain the battery cell 1.

[0059] (3) The cell 1 described in step (2) is encapsulated in the housing 2, and after liquid injection, formation and capacity testing, the reference electrode 3 is welded to the reference tab 4 to obtain the three-electrode system of the soft pack battery.

[0060] Example 2

[0061] This embodiment provides a three-electrode system for a pouch cell, such as... Figure 1 As shown, the three-electrode system of the pouch battery includes a cell 1 and an aluminum-plastic film casing 2. A reference electrode 3, led out from inside the cell 1, is connected to the side of the aluminum-plastic film casing 2. The reference electrode 3 is welded to a nickel reference tab 4, which is located on the side of the casing 2. The reference electrode 3 is a copper-silicon composite wire with a copper mass percentage of 70%.

[0062] The battery cell 1 (structural schematic diagram as shown) Figure 2 (As shown) includes a positive electrode 7, a first separator 91, a reference electrode 3, a second separator 92, and a negative electrode 8 stacked sequentially. The area of ​​the second separator 92 is slightly larger than the area of ​​the reference electrode 3. The bottom of the reference electrode 3 is located in the middle of the bottom of the cell 1, and the top of the reference electrode 3 is located on the side of the cell 1, extending out from the side of the cell 1. A positive electrode tab 5 is provided on the positive electrode 7, and a negative electrode tab 6 is provided on the negative electrode 8. The positive electrode 7 and the negative electrode 8 are located on the top of the housing 2. The positive electrode tab 5 and the negative electrode tab 6 are parallel to each other, and the reference electrode tab 4 is perpendicular to the positive electrode tab 5.

[0063] The preparation method includes the following steps:

[0064] (1) Copper powder and silicon powder with a mass ratio of 2.3:1 were mixed and calcined at 800°C for 15 hours in a helium atmosphere to obtain a composite material; the composite material was rolled and drawn into wires with a diameter of 0.05 mm to obtain the copper-silicon composite wire, which was used as reference electrode 3.

[0065] (2) Stack the positive electrode 7, the first separator 91 and the negative electrode 8 in sequence, place the reference electrode 3 described in step (1) between the first separator 91 and the negative electrode 8 and fix it, and then place the second separator 92 between the reference electrode 3 and the negative electrode 8 to obtain the battery cell 1.

[0066] (3) The cell 1 described in step (2) is encapsulated in the housing 2, and after liquid injection, formation and capacity testing, the reference electrode 3 is welded to the reference tab 4 to obtain the three-electrode system of the soft pack battery.

[0067] Example 3

[0068] This embodiment provides a three-electrode system for a pouch cell, such as... Figure 1 As shown, the three-electrode system of the pouch battery includes a cell 1 and an aluminum casing 2. A reference electrode 3, led out from inside the cell 1, is connected to the side of the aluminum casing 2. The reference electrode 3 is welded to a nickel reference tab 4, which is located on the side of the aluminum casing 2. The reference electrode 3 is a copper-silicon composite wire with a copper mass percentage of 80%.

[0069] The battery cell 1 (structural schematic diagram as shown) Figure 2(As shown) includes a positive electrode 7, a first separator 91, a reference electrode 3, a second separator 92, and a negative electrode 8 stacked sequentially. The area of ​​the second separator 92 is slightly larger than the area of ​​the reference electrode 3. The bottom of the reference electrode 3 is located in the middle of the bottom of the cell 1, and the top of the reference electrode 3 is located on the side of the cell 1, extending out from the side of the cell 1. A positive electrode tab 5 is provided on the positive electrode 7, and a negative electrode tab 6 is provided on the negative electrode 8. The positive electrode 7 and the negative electrode 8 are located on the top of the housing 2. The positive electrode tab 5 and the negative electrode tab 6 are parallel to each other, and the reference electrode tab 4 is perpendicular to the positive electrode tab 5.

[0070] The preparation method includes the following steps:

[0071] (1) Copper powder and silicon powder with a mass ratio of 4:1 were mixed and calcined at 1500°C for 8 hours under a helium atmosphere to obtain a composite material; the composite material was rolled and drawn into wires with a diameter of 0.2 mm to obtain the copper-silicon composite wire, which was used as reference electrode 3.

[0072] (2) Stack the positive electrode 7, the first separator 91 and the negative electrode 8 in sequence, place the reference electrode 3 described in step (1) between the first separator 91 and the negative electrode 8 and fix it, and then place the second separator 92 between the reference electrode 3 and the negative electrode 8 to obtain the battery cell 1.

[0073] (3) The cell 1 described in step (2) is encapsulated in an aluminum shell 2, and after liquid injection, formation and capacity testing, the reference electrode 3 is welded to the reference tab 4 to obtain the three-electrode system of the soft pack battery.

[0074] Example 4

[0075] This embodiment provides a three-electrode system for a soft-pack battery. The difference from Embodiment 1 is that the bottom of the reference electrode 3 is located at the middle of the top of the cell 1, the top of the reference electrode 3 is located on the side of the cell 1, and it is led out from the side of the cell 1. The reference tab 4 is perpendicular to the positive tab 5, and the reference tab 4 is located on the side of the housing 2.

[0076] Example 5

[0077] This embodiment provides a three-electrode system for a soft-pack battery. The difference from Embodiment 1 is that the bottom of the reference electrode 3 is located in the middle of the top of the cell 1, the top of the reference electrode 3 is located on the top of the cell 1, and it is led out from the top of the cell 1 and parallel to the positive electrode tab 5. The reference electrode tab 4 is located on the top of the housing 2.

[0078] Example 6

[0079] This embodiment provides a three-electrode system for a soft-pack battery. The difference from Embodiment 1 is that the reference electrode 3 is a copper-silicon composite wire with a copper mass percentage of 60% and the mass ratio of copper powder to silicon powder in step (1) of the preparation method is 1.5:1.

[0080] Example 7

[0081] This embodiment provides a three-electrode system for a soft-pack battery. The difference from Embodiment 1 is that the reference electrode 3 is a copper-silicon composite wire with a copper mass percentage of 90% and the mass ratio of copper powder to silicon powder in step (1) of the preparation method is 9:1.

[0082] Example 8

[0083] This embodiment provides a three-electrode system for a pouch cell, which differs from Embodiment 1 in that the diameter of the reference electrode 3 is 0.03 mm.

[0084] Example 9

[0085] This embodiment provides a three-electrode system for a pouch cell, which differs from Embodiment 1 in that the diameter of the reference electrode 3 is 0.25 mm.

[0086] Comparative Example 1

[0087] This comparative example provides a three-electrode system for a pouch cell, the difference from Example 1 being that the reference electrode 3 is replaced with a copper wire.

[0088] Comparative Example 2

[0089] This comparative example provides a three-electrode system for a pouch cell, the difference from Example 1 being that the reference electrode 3 is replaced with a platinum wire.

[0090] Comparative Example 3

[0091] This comparative example provides a three-electrode system for a pouch cell, the difference from Example 1 being that the reference electrode 3 is replaced with a lithium wire.

[0092] Comparative Example 4

[0093] This comparative example provides a pouch cell, which differs from Example 1 in that it does not contain a reference electrode 3.

[0094] The soft-pack battery obtained above was tested by charging and discharging it under a constant current of 0.33C. The active lithium loss and cycle time of the soft-pack battery at the end of the test were measured. The test results are shown in Table 1.

[0095] Table 1

[0096] Test number active lithium loss 0.33C cycle time Example 1 0.24％ 635h Example 2 0.25％ 616h Example 3 0.37％ 655h Example 4 0.32％ 592h Example 5 0.32％ 597h Example 6 0.74％ 404h Example 7 0.67％ 503h Example 8 0.41％ 91.2h Example 9 0.83％ 362h Comparative Example 1 0.75％ 470h Comparative Example 2 1.25％ 88.2h Comparative Example 3 0％ 479h

[0097] The following conclusions can be drawn from Table 1:

[0098] (1) As can be seen from Examples 1-3, the present invention uses copper-silicon composite material as reference electrode, so that when the soft-pack battery is lithium-plated, silicon and lithium undergo an alloy reaction to generate lithium-silicon alloy, ensuring that the lithium deposited on the surface is stable during the test and reducing the reaction with the electrolyte; at the same time, the copper-silicon composite is used as wire material, which reduces the loss of active lithium caused by lithium plating of the reference electrode and avoids the obstruction of lithium ion transport between the positive and negative electrodes.

[0099] (2) As can be seen from the comparison between Examples 4 and 5 and Example 1, when the reference electrode is not located at the bottom of the cell and is not led out from the side of the cell, it is not conducive to reducing the loss of active lithium caused by lithium plating of the reference electrode, and it is not conducive to avoiding the obstruction of lithium ion transmission between the positive and negative electrodes.

[0100] (3) As can be seen from the comparison between Examples 6-9 and Example 1, when the mass percentage of copper and the diameter of the reference electrode are not within the preferred range of the present invention, it is not conducive to reducing the loss of active lithium caused by lithium plating of the reference electrode, and it is not conducive to avoiding the obstruction of lithium ion transport between the positive and negative electrodes.

[0101] (4) As can be seen from the comparison between Comparative Examples 1-3 and Example 1, compared with the use of copper-silicon composite material, the loss of active lithium caused by lithium plating is greater when copper is used as the reference electrode, resulting in a shift in the positive and negative electrode potentials and hindering the transport of lithium ions between the normal positive and negative electrodes; when gold wire, silver wire and platinum wire are used as reference electrodes, the exposed metal wires will interfere with the battery signal in the electrolyte; when lithium wire is used as the reference electrode, lithium metal consumption or even dissolution may occur during long-term charging and discharging, and the reference electrode with only lithium and no other supporting metal is easy to break, making it difficult to continue to use as the reference electrode for experiments.

[0102] In summary, this invention uses a copper-silicon composite material as a reference electrode, which enables silicon and lithium to undergo an alloying reaction to form a lithium-silicon alloy during the lithium plating step of the soft-pack battery. This ensures the stable existence of lithium deposited on the surface during the testing process and reduces reactions with the electrolyte. At the same time, the copper-silicon composite material is used as a wire, which reduces the loss of active lithium caused by lithium plating of the reference electrode and avoids hindering the transport of lithium ions between the positive and negative electrodes.

[0103] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A three-electrode system for a pouch cell, characterized in that, The three-electrode system of the soft-pack battery includes a cell and a casing. The cell includes a positive electrode, a first separator, a second separator, and a negative electrode stacked in sequence. A reference electrode is disposed between the first separator and the second separator. The reference electrode is a copper-silicon composite wire. The reference electrode contains 70-80 wt% copper. The copper-silicon composite wire is prepared by mixing copper powder and silicon powder, calcining them under a protective atmosphere to obtain a composite material; and then rolling and drawing the composite material to obtain the copper-silicon composite wire.

2. The three-electrode system for a soft-pack battery according to claim 1, characterized in that, The area of ​​the second diaphragm is less than the area of ​​the first diaphragm, and the area of ​​the second diaphragm is greater than the area of ​​the reference electrode.

3. The three-electrode system for a soft-pack battery according to claim 1, characterized in that, The bottom of the reference electrode is located at the middle position of the bottom of the battery cell, and the top of the reference electrode is located on the side of the battery cell.

4. The three-electrode system for a soft-pack battery according to claim 1, characterized in that, The positive electrode plate is provided with a positive electrode tab, and the negative electrode plate is provided with a negative electrode tab.

5. The three-electrode system for a pouch cell according to claim 4, characterized in that, The reference electrode is provided with a reference tab.

6. The three-electrode system for a soft-pack battery according to claim 5, characterized in that, The positive electrode tab and the negative electrode tab are parallel to each other, and the reference electrode tab and the positive electrode tab are perpendicular to each other.

7. The three-electrode system for a soft-pack battery according to claim 5, characterized in that, The reference electrode is made of nickel.

8. The three-electrode system for a soft-pack battery according to claim 1, characterized in that, The diameter of the reference electrode is 0.05~0.2mm.

9. The three-electrode system for a soft-pack battery according to claim 1, characterized in that, The housing can be any one of aluminum-plastic film, aluminum shell, steel shell or glass shell.

10. A method for preparing a three-electrode system for a pouch cell according to any one of claims 1-9, characterized in that, The preparation method includes the following steps: (1) Provide copper-silicon composite wire as a reference electrode; the copper-silicon composite wire is prepared by mixing copper powder and silicon powder, calcining under a protective atmosphere to obtain a composite material; rolling and drawing the composite material to obtain the copper-silicon composite wire; (2) Stack the positive electrode, the separator and the negative electrode in sequence, and place the reference electrode described in step (1) between the separator and the negative electrode to obtain the battery cell; (3) The cell described in step (2) is encapsulated in a housing to obtain the three-electrode system of the soft-pack battery.

11. The preparation method according to claim 10, characterized in that, The mass ratio of copper powder to silicon powder is (2~4):

1.

12. The preparation method according to claim 10, characterized in that, The protective atmosphere includes an inert atmosphere.

13. The preparation method according to claim 12, characterized in that, The protective atmosphere is helium.

14. The preparation method according to claim 10, characterized in that, The calcination temperature is 800~1500℃.

15. The preparation method according to claim 10, characterized in that, The calcination time is 8-15 hours.

16. The preparation method according to claim 10, characterized in that, The diameter of the drawn wire is 0.05~0.2mm.

17. The preparation method according to claim 10, characterized in that, The diaphragm mentioned in step (2) is the first diaphragm.

18. The preparation method according to claim 10, characterized in that, Step (2) after setting the reference electrode further includes setting a second diaphragm between the reference electrode and the negative electrode.

19. The preparation method according to claim 10, characterized in that, Step (3) after encapsulation also includes liquid injection, formation and volume separation.

20. The preparation method according to claim 19, characterized in that, The process of separating the capacity also includes welding a reference electrode and a reference tab.

21. The preparation method according to claim 10, characterized in that, The preparation method includes the following steps: (1) Copper powder and silicon powder with a mass ratio of (2~4):1 are calcined at 800~1500℃ for 8~15h in a helium atmosphere to obtain a composite material; the composite material is rolled and drawn into wires with a diameter of 0.05~0.2mm to obtain the copper-silicon composite wire, which is used as a reference electrode; (2) Stack the positive electrode, the first separator and the negative electrode in sequence, place the reference electrode described in step (1) between the first separator and the negative electrode and fix it, and then place the second separator between the reference electrode and the negative electrode to obtain the battery cell; (3) The cell described in step (2) is encapsulated in a housing, and after liquid injection, formation and capacity testing, the reference electrode is welded to the reference tab to obtain the three-electrode system of the soft pack battery.

22. Use of a three-electrode system for a pouch cell according to any one of claims 1-9, characterized in that, The pouch battery three-electrode system is used in electronic devices or new energy vehicles.

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