Three-electrode pouch cell and method of manufacturing the same

Abstract

The application discloses a three-electrode soft package battery and a preparation method thereof. The three-electrode soft package battery comprises a soft package shell, an electrolyte, a diaphragm, a positive electrode sheet, a negative electrode sheet and a reference electrode. The electrolyte is sealed in the soft package shell, and the positive electrode sheet, the diaphragm, the reference electrode, the diaphragm and the negative electrode sheet are sequentially stacked and immersed in the electrolyte. The positive electrode sheet, the negative electrode sheet and the reference electrode are respectively connected with the positive electrode tab, the negative electrode tab and the reference electrode tab outside the soft package shell. The surface of the reference electrode is coated with lithium iron phosphate, and the area ratio of the reference electrode to the positive electrode sheet is 0.001-0.01. The three-electrode soft package battery is simple in structure and easy to quickly prepare. The reference electrode has little influence on the capacity of the full battery. The reference electrode is stable and suitable for real-time monitoring of the positive and negative electrode voltage in a long cycle process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a three-electrode soft package battery and a preparation method thereof. BACKGROUND

[0002] With the popularization of new energy vehicles, the performance of lithium ion batteries is also required to be higher and higher, and the update iteration speed of lithium ion power batteries is faster and faster, so it is particularly important to improve the system evaluation efficiency of power batteries. In the system evaluation method and evaluation means of lithium ion power batteries, soft package laminated batteries are particularly suitable for early system evaluation because of their simple preparation and the ability to basically simulate the actual performance of full battery systems, which is conducive to shortening the test and evaluation period and improving test efficiency.

[0003] In recent years, the use of three-electrode batteries to study the potential change, impedance change, lithium precipitation behavior, etc. of lithium ion batteries under different conditions has become an important evaluation method.

[0004] Among the widely used reference electrodes, copper wire reference electrodes have the advantages of simple preparation and low cost. However, in actual use, the metal lithium plated on the copper wire of the reference electrode is extremely active and will dissolve in the battery system in a short time at high temperature, affecting the judgment of the battery data in the test, and the copper wire also needs to be re-plated with lithium, which is not suitable for monitoring the positive and negative electrode voltages of long cycle batteries. Lithium iron phosphate can be used as a stable reference electrode due to its relatively stable lithium extraction voltage platform, and it has obvious advantages for monitoring the positive and negative electrode voltages of long cycle batteries. SUMMARY

[0005] The purpose of the present application is to provide a three-electrode soft package battery and a preparation method thereof.

[0006] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0007] The first aspect of the application discloses a three-electrode soft package battery, characterized in that it comprises a soft package shell, an electrolyte, a separator, a positive electrode sheet, a negative electrode sheet and a reference electrode; the electrolyte is sealed in the soft package shell, the positive electrode sheet, the separator, the reference electrode, the separator and the negative electrode sheet are sequentially stacked and immersed in the electrolyte; the positive electrode sheet, the negative electrode sheet and the reference electrode are respectively connected with the positive electrode tab, the negative electrode tab and the reference electrode tab outside the soft package shell; wherein the reference electrode is coated with lithium iron phosphate on both sides, and the area ratio of the reference electrode to the positive electrode sheet is 0.001-0.01. It should be noted that the three-electrode soft package battery of the application has a simple structure, the reference electrode contains lithium iron phosphate, and the lithium iron phosphate has a relatively stable lithium extraction voltage platform, so it is more stable when used as a reference electrode, especially for battery positive and negative voltage monitoring in long cycle. In addition, the reference electrode is relatively small in the application, so the amount of lithium iron phosphate on the reference electrode is sufficient, so that the reference electrode does not have too much impact on the capacity balance of the whole battery.

[0008] In an implementation manner of the application, the three-electrode soft package battery is subjected to activation treatment, and the activation treatment refers to charging and discharging cycle of the three-electrode soft package battery, so that the state of charge of the battery is finally 40%-60%. It should be noted that the three-electrode soft package battery of the application needs to be activated after assembly. Through activation, the reference electrode can be activated, and the activated three-electrode soft package battery can be used for various system tests. It should also be noted that the battery is finally in a half-electric state, which can make the battery system more stable.

[0009] In an implementation manner of the application, the area ratio of the separator to the negative electrode sheet is 1.06-1.2, and the area ratio of the negative electrode sheet to the positive electrode sheet is 1.05-1.1. It should be noted that the separator should completely cover the negative electrode sheet, and the negative electrode sheet should completely cover the positive electrode sheet, which can ensure that the electrodes are completely separated by the separator to prevent short circuit caused by the contact of the positive and negative electrodes. In addition, the area ratio of the negative electrode to the positive electrode is larger, which is beneficial to make the lithium ion insertion process more uniform, and will not cause uneven potential and error.

[0010] In an implementation manner of the application, the reference electrode is located at the center of the positive electrode sheet and / or the negative electrode sheet. It should be noted that because the area ratio of the negative electrode sheet to the positive electrode sheet is larger, in most cases, the edge of the negative electrode sheet is not directly opposite to the positive electrode sheet, which causes uneven edge in the lithium ion insertion process, which will cause uneven potential. In order to avoid the problem of error caused by uneven potential, the reference electrode is selected to be placed at the center of the positive electrode sheet. The material at the center reacts more uniformly when lithium ions are inserted and extracted, so the potential is more real and the error is relatively small.

[0011] In an implementation form of the application, the reference electrode is connected to the reference electrode tab through a reference electrode blank area, the reference electrode blank area being an area not containing lithium iron phosphate material; and an area ratio of the reference electrode to the reference electrode blank area is 0.1 to 0.5.

[0012] A second aspect of the application discloses a preparation method of a three-electrode soft package battery, comprising: assembling: welding the positive electrode tab, the negative electrode tab and the reference electrode tab to the positive electrode sheet, the negative electrode sheet and the reference electrode respectively, sequentially stacking the positive electrode sheet, the diaphragm, the reference electrode, the diaphragm and the negative electrode sheet, and then packaging in a soft package shell, injecting electrolyte, and sealing; activation treatment: performing charge and discharge cycles, and finally making the state of charge of the battery 40% to 60%.

[0013] In an implementation form of the application, the activation treatment comprises: activating the battery: taking the positive electrode sheet as the positive electrode and the negative electrode sheet as the negative electrode, performing charge and discharge cycles, and finally making the state of charge of the battery 40% to 60%; activating the reference electrode: taking the reference electrode as the positive electrode and the negative electrode sheet as the negative electrode, performing charge and discharge cycles, and finally making the state of charge of the battery 40% to 60%; and taking the positive electrode sheet as the positive electrode and the reference electrode as the negative electrode, performing charge and discharge cycles, and finally making the state of charge of the battery 40% to 60%. It should be further noted that the positive electrode sheet and the negative electrode sheet of the application can be single-sidedly coated with active paste.

[0014] In an implementation form of the application, the activating the battery comprises: using a 0.08 to 0.12 C current size to perform constant current charging to the cut-off voltage, then using constant voltage charging to the cut-off voltage after the current is less than 0.05 C, then using 0.1 C current size to perform constant current discharging to the cut-off voltage, then stopping charging after using 0.05 C current size to perform constant current charging to the cut-off voltage, and then stopping discharging after using 0.05 C current size to perform constant current discharging to the cut-off voltage, taking the discharging capacity of the last cycle as a reference, and using 0.05 C current size to charge the battery to a state of charge of 40% to 60%. It should be noted that in the application, 0.05 C current value is used for activation, which is small enough to significantly reduce polarization, and helps to form a stable SEI film on the negative electrode of the battery during the first cycle of charge and discharge, facilitating later testing.

[0015] In an implementation form of the application, the activation of the reference electrode comprises: making the reference electrode a positive electrode, the negative electrode tab a negative electrode, and first charging and then discharging at a current of 0.05C, wherein the charging is stopped after 18 hours, the discharging is stopped after 18 hours, the charging and discharging cycle is repeated three times, and the reference electrode is charged to a state of charge of 40% to 60% using a current of 0.05C based on the capacity of the last cycle of discharging; making the positive electrode tab a positive electrode, and the reference electrode a negative electrode, and first discharging and then charging at a current of 0.05C, wherein the discharging is stopped after 18 hours, the charging is stopped after 18 hours, the charging and discharging cycle is repeated three times, and the reference electrode is discharged to a state of charge of 40% to 60% using a current of 0.05C based on the capacity of the last cycle of charging.

[0016] With regard to the activation process of the application, it should be noted that, in the application, the battery is first activated so that the battery can be in a semi-electric state. The semi-electric battery system is relatively stable, which facilitates the subsequent activation of the reference electrode. Then, the lithium iron phosphate material on the side of the reference electrode opposite to the positive electrode tab and the lithium iron phosphate material on the side of the reference electrode opposite to the negative electrode tab are activated, respectively, thereby achieving the activation of the reference electrode. The reference electrode is activated to a semi-electric state because the voltage platform of the lithium iron phosphate material is very stable when the state of charge is 40% to 60%. Therefore, the voltage stability of the lithium iron phosphate material at a state of charge of about 50% is utilized, so that the reference electrode can exist relatively stably.

[0017] In an implementation form of the application, the state of charge of the battery after the activation process is 50%.

[0018] The application has the following beneficial effects:

[0019] The three-electrode soft package battery of the application has a simple structure and is easy to prepare quickly. The reference electrode is activated in advance, and the reference electrode is small, which has little effect on the capacity of the full battery. The reference electrode of the application is stable and suitable for real-time monitoring of the voltage of the positive and negative electrodes in the long cycle process. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 FIG. 1 is a structural schematic diagram of a three-electrode soft package battery according to the application.

[0021] Figure 2 FIG. 2 is a position schematic diagram of a soft package shell, a positive electrode tab, a negative electrode tab, a reference electrode, and a film according to the application.

[0022] Figure 3 FIG. 3 is an appearance diagram of a single-layer laminated soft package battery according to Embodiment 1 of the application.

[0023] Figure 4 FIG. 4 is a time-voltage change diagram of the single-layer laminated soft package battery according to Embodiment 1 of the application in a long cycle. DETAILED DESCRIPTION

[0024] The application will be described in further detail below with reference to the drawings. In the following embodiments, many specific details are described in order to provide a more thorough understanding of the application. However, it will be apparent to one skilled in the art that the present application can be practiced without some or all of these details. In other instances, well known features have not been described in detail or have been described only briefly in order not to obscure the core of the application. In addition, the description of the application is not intended to limit the application to the described embodiments. Various embodiments of the application can be implemented in a variety of ways.

[0025] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various embodiments. At the same time, the steps or actions in the method description can also be sequentially adjusted or adjusted in a manner that can be easily seen by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for the purpose of clearly describing a certain embodiment, and do not mean that the sequence is necessary, unless otherwise stated that a certain sequence must be followed.

[0026] The serial numbers of the components in this paper, such as "first", "second", etc., are only used to distinguish the described objects, and do not have any sequence or technical meaning.

[0027] With the popularization of new energy vehicles, the performance of lithium ion batteries is also required to be higher and higher, and the update iteration speed of lithium ion power batteries is faster and faster, so it is particularly important to improve the efficiency of the system evaluation of power batteries. In the system evaluation method and evaluation means of lithium ion power batteries, soft pack laminated batteries are particularly suitable for early system evaluation because of their simple preparation and the ability to basically simulate the actual performance of the full battery system, which is conducive to shortening the test and evaluation period and improving test efficiency. In recent years, the use of three-electrode batteries to study the potential change, impedance change, lithium precipitation behavior, etc. of lithium ion batteries under different conditions has become an important evaluation method.

[0028] In the currently widely used reference electrode, the copper wire reference electrode has the advantages of simple preparation and low cost. However, in the actual use process, the metal lithium plated on the reference electrode copper wire is extremely active and will dissolve in the battery system at high temperature for a short time, which will affect the judgment of the battery data in the test, and the copper wire also needs to be plated with lithium again, which is not suitable for the positive and negative electrode voltage monitoring of the long cycle battery. Lithium iron phosphate can be used as a stable reference electrode due to its relatively stable delithiation voltage platform, especially for the positive and negative electrode voltage monitoring of the long cycle battery. At present, there is also a lithium iron phosphate reference electrode, but the preparation process of the reference electrode is relatively complex. After the full battery is assembled, it needs to be charged and discharged, then the lithium iron phosphate sheet is taken out for rinsing, drying, and cutting to obtain the reference electrode. Then the reference electrode is embedded in a fresh battery, and then it can be directly used for testing. However, in the preparation process of the reference electrode, rinsing, drying, drying, and cutting operations can easily cause the reference material on the electrode to fall off. And because the reference electrode is very thin, plus the brittleness of the material lithium iron phosphate sheet itself, it is difficult to get a complete sheet after cutting, because the activated lithium iron phosphate material will fall off from the aluminum foil current collector during cutting. At the same time, the manual cutting process has burrs, which can easily pierce the separator, and there are certain difficulties in scaling up.

[0029] Therefore, the application creatively proposes a three-electrode soft package battery and a preparation method thereof, which has the following advantages:

[0030] The application is a single-layer laminated soft package battery, which is convenient and simple to prepare, can quickly prepare a full battery, and is convenient for later testing and analysis. It does not need to be wound in multiple layers, and the process of slot welding and other complex and high-cost processes is not needed.

[0031] In the application, the fresh and prepared reference electrode is assembled into a full battery and activated, and the activated battery can be used for testing. The application has the advantages of simple preparation method and strong operability for the battery material system to be evaluated, and the lithium iron phosphate reference electrode does not need to be operated too much during the preparation and activation process, thereby causing the reference electrode to drop material and the preparation process to be complicated.

[0032] In the application, the full battery is activated in advance in a half-electric state, and the lithium iron phosphate material on the reference electrode is sufficient, so that it does not have too much influence on the capacity balance of the full battery as a whole.

[0033] The reference electrode of the application is stable and suitable for real-time monitoring of the positive and negative electrode voltages during long cycle.

[0034] The application will be described below in conjunction with the drawings and specific embodiments.

[0035] The present application relates to a three-electrode soft-pack battery (hereinafter sometimes referred to as "battery" or "soft-pack battery") and a preparation method of a three-electrode soft-pack battery (hereinafter sometimes referred to as "preparation method").

[0036] Figure 1 is a structural schematic diagram of the three-electrode soft-pack battery involved in the present application.

[0037] As shown in Figure 1 , in a specific embodiment, the three-electrode soft-pack battery can include: a positive electrode tab 1, a negative electrode tab 2, a tab adhesive 3, a diaphragm 4, a positive electrode sheet 5, a negative electrode sheet 6, a reference electrode tab 7, a reference electrode blank area 8, a reference electrode 9, an aluminum plastic film 10 (i.e. soft-pack shell), a positive electrode sheet blank area 11, and a negative electrode sheet blank area 12.

[0038] In a specific embodiment, the positive electrode sheet 5 is an aluminum foil coated with a positive electrode sheet slurry.

[0039] In a specific embodiment, the positive electrode sheet 5 is a single-sided coated aluminum foil, i.e. the side facing the negative electrode sheet 6 is coated with a positive electrode sheet slurry.

[0040] In a specific embodiment, the positive electrode sheet 5 has an area density of 18.5-22.5 mg / cm 2 .

[0041] In a specific embodiment, the positive electrode sheet slurry is obtained by mixing a positive electrode active material, a conductive agent, polyvinylidene fluoride (PVDF), and a nitrogen methyl pyrrolidone (NMP) material.

[0042] In a specific embodiment, the positive electrode active material can be one or more of lithium iron phosphate, NCM (nickel-cobalt-manganese ternary material), NCMA (nickel-cobalt-manganese-aluminum quaternary material), NCA (nickel-cobalt-aluminum ternary material), lithium manganese iron phosphate, lithium manganate, etc.

[0043] In a specific embodiment, the conductive agent can be super-conductive carbon (Super-C or carbon nanotube).

[0044] In a specific embodiment, in the positive electrode sheet slurry, the positive electrode active material is 100 parts, the conductive agent is 2.0-3.0 parts, the polyvinylidene fluoride is 1-2 parts, and the NMP is 55-65 parts by weight.

[0045] In a specific embodiment, in the positive electrode sheet slurry, the lithium iron phosphate: conductive agent: polyvinylidene fluoride: NMP = 100:2.5:1.3:62 by weight.

[0046] In a specific embodiment, the negative electrode sheet 6 is a copper foil coated with a negative electrode sheet slurry.

[0047] In one embodiment, the negative electrode sheet 6 is single-sided coated, i.e. the side facing the positive electrode sheet 5 is coated with the negative electrode sheet slurry.

[0048] In one embodiment, the negative electrode sheet 6 has an area density of 8-11 mg / cm 2 .

[0049] In one embodiment, the negative electrode slurry is composed of a negative electrode active material, a conductive agent, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), H2O (water), and N-methyl pyrrolidone (NMP).

[0050] In one embodiment, the negative electrode active material is one or more of graphite, silicon-oxygen, silicon-carbon, soft carbon, and hard carbon.

[0051] In one embodiment, in the negative electrode slurry, the negative electrode active material is 100 parts, the conductive agent is 0.8-1.5 parts, the CMC is 1.2-1.5 parts, the SBR is 3-3.5 parts, the H2O is 80-90 parts, and the NMP is 1 part, by weight.

[0052] In one embodiment, in the negative electrode slurry, the graphite: conductive agent: CMC: SBR: H2O: NMP = 100:1:1.3:3.2:85:1, by weight.

[0053] In one embodiment, the reference electrode 9 is an aluminum foil coated with a reference electrode slurry.

[0054] In one embodiment, the reference electrode slurry is the same as the positive electrode sheet slurry.

[0055] In one embodiment, the reference electrode 9 has an area density of 38-45 mg / cm 2 .

[0056] In one embodiment, the tab is an aluminum foil or a copper foil.

[0057] In one embodiment, the tab adhesive 3 is an epoxy resin or an acrylic ester.

[0058] In one embodiment, the separator 4 is a polyolefin-based separator, a polyester-based separator, a non-woven fabric separator, or a ceramic separator.

[0059] In one embodiment, the positive electrode sheet blank area 11 is an aluminum foil that is not coated with the positive electrode sheet slurry.

[0060] In one embodiment, the negative electrode sheet blank area 12 is a copper foil that is not coated with the negative electrode sheet slurry.

[0061] In one embodiment, the reference electrode blank area 8 is an aluminum foil that is not coated with the reference electrode slurry.

[0062] Figure 2 is a schematic diagram of the positions of the soft package shell, the positive electrode sheet, the negative electrode sheet, the reference electrode and the film involved in the present application.

[0063] In a specific embodiment, as shown in Figure 2 , the positive electrode sheet 5, the separator 4, the reference electrode 9, the separator 4 and the negative electrode sheet 6 are sequentially laid and arranged in the middle of the two layers of the aluminum plastic film 10.

[0064] In a specific embodiment, the three-electrode soft package battery is a single-layer laminated soft package battery.

[0065] In a specific embodiment, the length and width of the separator 4 are respectively greater than the length and width of the negative electrode sheet 6, the length and width of the negative electrode sheet 6 are respectively greater than the length and width of the positive electrode sheet 5, and the length and width of the positive electrode sheet 5 are respectively greater than the length and width of the reference electrode 9.

[0066] In a specific embodiment, the area ratio of the separator 4 and the negative electrode sheet 6 is 1.06-1.2.

[0067] In a specific embodiment, the area ratio of the separator 4 and the negative electrode sheet 6 is 1.08.

[0068] In a specific embodiment, the area ratio of the negative electrode sheet 6 and the positive electrode sheet 5 is 1.05-1.1.

[0069] In a specific embodiment, the area ratio of the negative electrode sheet 6 and the positive electrode sheet 5 is 1.08.

[0070] In a specific embodiment, the reference electrode 9 accounts for 0.001-0.01 of the area of the positive electrode sheet 5. For example, the reference electrode 9 accounts for 0.001, 0.002, 0.004, 0.005, 0.006, 0.008 or 0.01 of the area of the positive electrode sheet 5.

[0071] In a specific embodiment, the reference electrode 9 accounts for 0.002-0.05 of the area of the positive electrode sheet 5.

[0072] In a specific embodiment, the positive electrode sheet 5, the negative electrode sheet 6 and the reference electrode 9 are respectively connected with the positive electrode tab 1, the negative electrode tab 2 and the reference electrode tab 7 by ultrasonic welding or electric welding through the positive electrode sheet blank area 11, the negative electrode sheet blank area 12 and the reference electrode blank area 8.

[0073] In a specific embodiment, the area ratio of the reference electrode 9 and the reference electrode blank area 8 is 0.1-0.5. For example, the area ratio of the reference electrode 9 and the reference electrode blank area 8 is 0.1, 0.2, 0.3, 0.4 or 0.5.

[0074] In one embodiment, the positive electrode sheet 5 is located in the middle of the negative electrode sheet 6, the negative electrode sheet 6 is located in the middle of the separator 4, and the reference electrode 9 is located in the middle of the separator 4 in the soft package battery.

[0075] In one embodiment, the positive electrode tab 1 and the negative electrode tab 2 are respectively located on the left and right sides of the outside of the aluminum plastic film 10.

[0076] In one embodiment, the positive electrode sheet margin 11, the negative electrode sheet margin 12, and the reference electrode margin 8 can be respectively pasted to the thin film 4 and the aluminum plastic film 10 using insulating tapes, so that the positive electrode sheet 5, the negative electrode sheet 6, the separator 4, and the reference electrode 9 are fixed to the center of the aluminum plastic film 10.

[0077] In one embodiment, the tab adhesive 3 is respectively sleeved on the positive electrode tab 1, the negative electrode tab 2, and the reference electrode tab 7.

[0078] In one embodiment, the aluminum plastic film 10 is injected with electrolyte.

[0079] In one embodiment, the solvent in the electrolyte is three or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0080] In one embodiment, the lithium salt in the electrolyte is one or more of LiBF4, LiPF6, and LiBOB.

[0081] In one embodiment, the concentration of the lithium salt in the electrolyte is 1-1.25 mol / L.

[0082] In one embodiment, the electrolyte contains an additive, which can be FEC (fluoroethylene glycol carbonate).

[0083] In one embodiment, the mass percentage of the additive in the electrolyte is 1%-5% (w / w).

[0084] In one embodiment, the length or width of the positive electrode sheet 5 is 30-60 mm.

[0085] In one embodiment, the length or width of the negative electrode sheet 6 is 32-62 mm.

[0086] In one embodiment, the length or width of the separator 4 is 34-64 mm.

[0087] In one embodiment, the soft package battery is subjected to an activation process.

[0088] In one embodiment, the activation process includes activating the battery and activating the reference electrode.

[0089] In a specific embodiment, the activation of the battery comprises: using a current size of 0.08-0.12C to charge the battery to the cut-off voltage, then using the cut-off voltage to charge to the cut-off after the current is less than 0.05C, then using a current size of 0.1C to discharge to the cut-off voltage, then stopping discharging after discharging to the cut-off voltage, and then using a current size of 0.05C to charge the battery to the cut-off voltage, and then stopping charging after charging to the cut-off voltage, and then using a current size of 0.05C to discharge to the cut-off voltage, and then stopping discharging after discharging to the cut-off voltage, and then using a current size of 0.05C to charge the battery to a state of charge of 40%-60% based on the discharge capacity of the last cycle.

[0090] In a specific embodiment, the activation of the reference electrode 9 comprises:

[0091] charging and then discharging using a current of 0.05C, wherein the charging is stopped after 18 hours and the discharging is stopped after 18 hours, and the charging and discharging cycle is repeated three times, and then using a current of 0.05C to charge the reference electrode to a state of charge of 40%-60% based on the discharge capacity of the last cycle;

[0092] charging and then discharging using a current of 0.05C, wherein the charging is stopped after 18 hours and the discharging is stopped after 18 hours, and the charging and discharging cycle is repeated three times, and then using a current of 0.05C to charge the reference electrode to a state of charge of 40%-60% based on the discharge capacity of the last cycle;

[0093] In a specific embodiment, the specific preparation method of the three-electrode soft-pack battery can be: the positive electrode sheet 5, the negative electrode sheet 6, and the reference electrode 9 are connected to the positive electrode tab 1, the negative electrode tab 2, and the reference electrode tab 7, respectively, through the positive electrode sheet blank area 11, the negative electrode sheet blank area 12, and the reference electrode blank area 8 using ultrasonic welding. The positive electrode sheet 5, the negative electrode sheet 6, and the reference electrode 9 are placed in the middle of the two layers of aluminum plastic film 10 in the order of positive electrode sheet 5-separator 4-reference electrode 9-separator 4-negative electrode sheet 6, so that the positive electrode sheet 5 is located in the middle of the negative electrode sheet 6, the negative electrode sheet 6 is located in the middle of the separator 4, and the reference electrode 9 is located in the middle of the separator 4, and the positive electrode tab 1 and the negative electrode tab 2 are respectively placed on the left and right sides of the aluminum plastic film, and finally the positive electrode sheet blank area 11, the negative electrode sheet blank area 12, and the reference electrode sheet blank area 8 are respectively pasted with insulating tape, so that the positive electrode sheet 5, the negative electrode sheet 6, the separator 4, and the reference electrode 9 are fixed in the center of the aluminum plastic film 10. After injecting electrolyte, the edges of the two layers of aluminum plastic film 10 are bonded together by vacuum heat sealing, forming a closed soft-pack battery. Subsequently, activation treatment is performed.

[0094] The application will be further described in detail below through specific examples. The following examples are only for further description of the application and should not be understood as limiting the application. It should be noted that the reagents, kits, instruments, etc. used in the examples are all commercially available, and the operation steps are carried out according to the instructions or general operation steps in the art.

[0095] Example 1:

[0096] (1) Material preparation:

[0097] The positive electrode sheet is an aluminum foil coated with a positive electrode sheet slurry on one side, and the positive electrode sheet slurry is prepared by mixing lithium iron phosphate, a conductive agent (carbon nanotube), polyvinylidene fluoride (PVDF), and N-methyl pyrrolidone (NMP), wherein the ratio of lithium iron phosphate: graphite: PVDF: NMP is 100:2.5:1.3:62; the area density of the positive electrode sheet is 20 mg / cm 2 After rolling, the hydraulic press is used to die-cut into a length of 54 mm and a width of 48 mm. The white space of the positive electrode sheet refers to the aluminum foil that is not coated with the positive electrode sheet slurry, and both the length and the width are 10 mm.

[0098] The negative electrode sheet is a copper foil coated with a negative electrode sheet slurry on one side, and the negative electrode sheet slurry is prepared by mixing graphite, a conductive agent (carbon nanotube), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), water, and N-methyl pyrrolidone (NMP), wherein the ratio of graphite: carbon black: CMC: SBR: water: NMP is 100:1:1.3:3.2:85:1; the area density of the negative electrode sheet is 10 mg / cm 2 After rolling, the hydraulic press is used to die-cut into a length of 56 mm and a width of 50 mm. The white space of the negative electrode sheet refers to the aluminum foil that is not coated with the negative electrode sheet slurry, and both the length and the width are 10 mm.

[0099] The separator is a polyethylene film with a length of 58 mm and a width of 52 mm;

[0100] The reference electrode is an aluminum foil coated with a reference electrode slurry on both sides, and the reference electrode slurry is prepared by mixing lithium iron phosphate, a conductive agent (carbon nanotube), polyvinylidene fluoride (PVDF), and N-methyl pyrrolidone (NMP), wherein the ratio of lithium iron phosphate: graphite: PVDF: NMP is 100:2.5:1.3:62; only part of the area of the aluminum foil is coated; after rolling, the hydraulic press is used to die-cut into an aluminum foil with a length of 38 mm and a width of 1 mm, wherein the area coated with the reference electrode slurry has a length of 8 mm and a width of 1 mm; the area not coated with the reference electrode slurry (reference electrode white space) has a length of 30 mm and a width of 1 mm.

[0101] The soft package shell is an aluminum plastic film with a length of 110 mm and a width of 80 mm.

[0102] Electrolyte: EC (ethylene glycol carbonate): DMC (diethyl carbonate): EMC (ethyl methyl carbonate) = 2:3:5 (volume ratio); lithium salt is LiPF6, concentration is 1 mol / L; additive FEC (fluoroethylene glycol carbonate) is 3% of the total mass of electrolyte.

[0103] (2) Battery assembly:

[0104] The positive electrode, negative electrode, and reference electrode are ultrasonically welded to the corresponding tabs using the reserved areas of the positive electrode, negative electrode, and reference electrode, respectively. Then, they are laid flat and stacked between two layers of aluminum-plastic film in the order of positive electrode - separator - reference electrode - separator - negative electrode (note that the side of the positive electrode coated with the active material is opposite to the side of the negative electrode coated with the active material), so that the positive electrode is in the center of the negative electrode, the negative electrode is in the center of the separator, and the reference electrode is in the center of the separator. The positive and negative electrode tabs are placed on the left and right sides of the aluminum-plastic film, respectively. Insulating tape is then applied to the reserved areas of the positive electrode, negative electrode, and reference electrode, fixing the positive electrode, negative electrode, separator, and reference electrode to the center of the aluminum-plastic film. Finally, 1.2g of electrolyte is injected. Finally, the tab adhesive is applied to the positive electrode tab, negative electrode tab, and reference electrode tab, respectively. The tab adhesive is 10mm long and its width is the same as that of the positive electrode tab, negative electrode tab, and reference electrode tab, respectively. The upper edge of the tab adhesive is attached to the upper edge of the aluminum-plastic film to protect the tabs and provide insulation. The four edges of the two layers of aluminum-plastic film are then vacuum heat-sealed together to form a sealed soft-pack battery.

[0105] (3) Activation of the reference electrode:

[0106] First, using the positive terminal of the full battery as the positive terminal and the negative terminal as the negative terminal, the full battery is charged at a constant current of 0.1C to 3.6V, then charged at a constant voltage of 3.6V until the current is less than 0.05C and then the charging is stopped. Then, the battery is discharged at a constant current of 0.1C to 2.0V and then the discharge is stopped. This charge-discharge cycle is repeated three times. Then, the full battery is charged at a constant current of 0.05C to 3.6V and then discharged at a constant current of 0.05C to 2.0V and then the discharge is stopped. Based on the discharge capacity of the last cycle, the battery is finally charged at a constant current of 0.05C until the state of charge (SoC) is adjusted to 50%.

[0107] Then, with the reference side of the full battery as the positive electrode and the negative side of the full battery as the negative electrode, it is charged and then discharged with a current of 0.05C. The charging is stopped when the voltage reaches 3.6V and the discharging is stopped when the voltage reaches 2.0V. The charge and discharge cycle is repeated three times. Based on the discharge capacity of the last cycle, it is finally charged again with a current of 0.05C until the state of charge (SoC) is adjusted to 50%.

[0108] Finally, with the positive side of the full battery as the positive terminal and the reference side as the negative terminal, discharge and then charge at a current of 0.05C. The discharge is stopped at -0.35V and the charging is stopped at 1.4V. The discharge and charge cycles are repeated three times. Based on the charging capacity of the last cycle, the battery is discharged again at a current of 0.05C until the state of charge (SoC) is adjusted to 50%.

[0109] Figure 3 This is an external view of the single-layer stacked soft-pack battery of Embodiment 1 of this application. Figure 4 This is a time-voltage variation diagram of a single-layer laminated pouch cell from Embodiment 1 of this application undergoing long-cycle operation. Figure 4 It can be seen that the single-layer stacked soft-pack battery of Example 1 has extremely high stability of the reference electrode detection potential.

[0110] Example 2:

[0111] The positive electrode is 48mm long and 44mm wide; the negative electrode is 50mm long and 46mm wide; the separator is 52mm long and 48mm wide; the aluminum-plastic film is 106mm long and 76mm wide; the reference electrode is 5mm long and 1mm wide; the blank areas of the positive and negative electrodes are both 8mm long and wide; the blank area of ​​the reference electrode is 30mm long and 1mm wide; the positive and negative electrode tabs are both 45mm long and 10mm wide; the reference electrode tab is 25mm long and 5mm wide.

[0112] The remaining parameters or steps are the same as in Example 1.

[0113] Example 3:

[0114] The positive electrode is 50mm long and 46mm wide; the negative electrode is 52mm long and 48mm wide; the separator is 54mm long and 50mm wide; the aluminum-plastic film is 106mm long and 76mm wide; the reference electrode is 6mm long and 2mm wide; the blank areas of the positive and negative electrodes are both 10mm long and wide; the blank area of ​​the reference electrode is 30mm long and 2mm wide; the positive and negative electrode tabs are both 46mm long and 8mm wide; the reference electrode tab is 28mm long and 8mm wide.

[0115] The remaining parameters or steps are the same as in Example 1.

[0116] The above description, in conjunction with specific embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. Those skilled in the art to which this application pertains can make several simple deductions or substitutions without departing from the concept of this application.

Claims

1. A method for manufacturing a three-electrode pouch battery, characterized by, The application relates to a three-electrode soft package battery. Assembling: welding positive electrode tabs, negative electrode tabs and reference electrode tabs with positive electrode sheets, negative electrode sheets and reference electrodes respectively, sequentially stacking the positive electrode sheets, a diaphragm, the reference electrodes, the diaphragm and the negative electrode sheets, and then packaging in a soft package shell, injecting electrolyte, and sealing; wherein the reference electrodes are coated with lithium iron phosphate on both sides, and the area ratio of the reference electrodes to the positive electrode sheets is 0.001-0.01; Activation treatment: the activation treatment includes activating the battery and activating the reference electrode; The activation of the battery includes: taking the positive electrode sheet as the positive electrode, taking the negative electrode sheet as the negative electrode, performing charge-discharge cycles, and finally making the state of charge of the battery 40%-60%; The activation of the reference electrode includes: Taking the reference electrode as the positive electrode and the negative electrode sheet as the negative electrode, first charging and then discharging at a current of 0.05C, wherein the charging is stopped after 18 hours, the discharging is stopped after 18 hours, the charge-discharge cycle is three times, and the reference electrode is charged to a state of charge of 40%-60% using a current of 0.05C as a reference. Taking the positive electrode sheet as the positive electrode and the reference electrode as the negative electrode, first discharging and then charging at a current of 0.05C, wherein the discharging is stopped after 18 hours, the charging is stopped after 18 hours, the charge-discharge cycle is three times, and the reference electrode is discharged to a state of charge of 40%-60% using a current of 0.05C as a reference.

2. The production method according to claim 1, characterized by, The state of charge of the battery after the activation treatment is 50%.

3. A three-electrode pouch cell, characterized by, The three-electrode soft package battery is prepared by the preparation method in any one of claims 1-2, and the three-electrode soft package battery comprises a soft package shell, electrolyte, a diaphragm, a positive electrode sheet, a negative electrode sheet and a reference electrode; the electrolyte is sealed in the soft package shell, the positive electrode sheet, the diaphragm, the reference electrode, the diaphragm and the negative electrode sheet are sequentially stacked and arranged and immersed in the electrolyte; the positive electrode sheet, the negative electrode sheet and the reference electrode are respectively connected with positive electrode tabs, negative electrode tabs and reference electrode tabs outside the soft package shell; wherein the reference electrode is coated with lithium iron phosphate on both sides, and the area ratio of the reference electrode to the positive electrode sheet is 0.001-0.

01. 4.The three-electrode soft-pack battery of claim 3, wherein, The area ratio of the diaphragm to the negative electrode sheet is 1.06-1.2, and the area ratio of the negative electrode sheet to the positive electrode sheet is 1.05-1.

1. 5.The three-electrode soft-pack battery of claim 3, wherein, The reference electrode is located in the middle of the positive electrode sheet and / or the negative electrode sheet. 6.The three-electrode soft-pack battery of claim 5, wherein, The reference electrode is connected with the reference electrode tab through a reference electrode blank area, the reference electrode blank area refers to an area without lithium iron phosphate material; and the area ratio of the reference electrode to the reference electrode blank area is 0.1-0.5.

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