A single cell capable of detecting the surface potential of an electrode sheet

Abstract

The present application provides a single cell capable of detecting the surface potential of an electrode sheet, comprising a shell and a battery cell located inside the shell, wherein the battery cell comprises a negative electrode sheet and a positive electrode sheet, and the surface of the electrode material layer of the negative electrode sheet or the positive electrode sheet is also provided with at least one surface electrode; wherein the surface electrode comprises a porous insulating film and a carbon nanotube conductive layer located on the surface of one side of the porous insulating film, and the carbon nanotube conductive layer is in contact with the electrode material layer; the surface electrode also comprises a metal conductor connected to the carbon nanotube conductive layer, the metal conductor extends in a direction parallel to the diaphragm, and the metal conductor does not cover the surface of the negative electrode sheet or the positive electrode sheet. The surface electrode can accurately test the potential difference between it and the electrode sheet where it is located, and obtain the surface potential of the electrode sheet, and the surface electrode does not affect the ion transmission between the positive and negative electrode sheets.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a single cell capable of detecting the surface potential of an electrode sheet. Background Art

[0002] The surface potential of the electrode sheet inside the battery is very important for monitoring the safety status of the battery. For example, for the negative electrode sheet, when its surface potential is low, lithium deposition may occur on its surface. If it is not detected in time and measures are not taken, it may cause safety problems such as puncture of the diaphragm and short circuit of the battery. However, there is currently no effective method to test the surface potential of the electrode sheet inside the battery. Summary of the invention

[0003] In view of this, the present application provides a battery that can accurately and conveniently test the surface potential of the electrode sheet inside the battery, so as to timely monitor the safety status of the battery.

[0004] Specifically, the present application provides a single cell battery that can detect the surface potential of an electrode sheet, the single cell battery comprising a shell and a battery cell located inside the shell, the battery cell comprising a negative electrode sheet and a positive electrode sheet, and at least one surface electrode is also provided on the surface of the electrode material layer of the negative electrode sheet or the positive electrode sheet; wherein the surface electrode comprises a diaphragm and a carbon nanotube conductive layer located on the surface of one side of the diaphragm, and the carbon nanotube conductive layer is in contact with the electrode material layer; the surface electrode also comprises a metal conductor connected to the carbon nanotube conductive layer, the metal conductor extends in a direction parallel to the diaphragm, and the metal conductor does not cover the surface of the negative electrode sheet or the positive electrode sheet.

[0005] In the present application, a porous insulating film with a carbon nanotube conductive layer is used as a surface electrode and is arranged on the surface of an electrode sheet. The carbon nanotube conductive layer has a conductive network with good air permeability, and the metal conductor connected to the carbon nanotube conductive layer does not cover the electrode sheet. This makes the overall surface electrode not affect the ion transmission between the positive and negative electrode sheets. The carbon nanotube conductive layer can form a conductive loop with the electrode material layer on the surface of the electrode sheet, and the potential of the carbon nanotubes is stable during the lithium removal / insertion of the negative electrode of the battery. Therefore, the carbon nanotube conductive layer can be used to accurately test the potential difference between the surface electrode and the electrode sheet where it is located, thereby obtaining the surface potential of the electrode sheet.

[0006] Optionally, the diameter of the carbon nanotube is 1 nm-50 nm. Preferably, the diameter of the carbon nanotube is 15 nm-25 nm.

[0007] Optionally, the thickness of the carbon nanotube conductive layer is 2 μm-10 μm. Further, the thickness of the carbon nanotube conductive layer is 1 / 8-1 / 2 of the thickness of the porous insulating film.

[0008] Optionally, the carbon nanotube conductive layer further comprises at least one of a binder and a dispersant. In some embodiments, in the carbon nanotube conductive layer, the mass percentage of the carbon nanotubes is 65%-80%, the mass percentage of the binder is 4%-11%, and the mass percentage of the dispersant is 15%-26%.

[0009] Optionally, the separator comprises a polyolefin separator substrate, and the porosity of the polyolefin separator substrate is 20%-60%.

[0010] In some embodiments, the surface of the carbon nanotube conductive layer away from the porous insulating film includes a first region and other regions except the first region, the first region is in direct contact with the electrode material layer, the other regions are separated from the electrode material layer by a diaphragm, and the other regions are close to the metal conductor. In this case, a plurality of surface electrodes may be provided on the surface of a positive electrode sheet or a negative electrode sheet, and they may not interfere with each other. Optionally, the first region is located at the edge of the carbon nanotube conductive layer and away from the metal conductor.

[0011] Optionally, the metal conductor includes a wire and a tab, the wire is embedded in the carbon nanotube conductive layer, the tab is connected to the carbon nanotube conductive layer through the wire, and the tab is located outside the shell. The wire can be made of aluminum, silver, platinum, copper, nickel, titanium, and alloys thereof.

[0012] Optionally, the surface electrode is disposed on the surface of the negative electrode sheet. Optionally, the battery cell has a plurality of negative electrode sheets, and one of the plurality of negative electrode sheets is provided with the plurality of surface electrodes at intervals. Further, the negative electrode sheet provided with the surface electrode is located in the middle of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1a A schematic diagram of the appearance of the lithium battery provided in this application (schematic diagram of the overall structure);

[0014] Figure 1b A schematic diagram of the exploded structure of the battery cell provided in this application;

[0015] Figure 1c A schematic diagram of the cross-sectional structure of the battery cell provided in this application;

[0016] Figure 2 The cyclic voltammetry curve of the half-cell composed of the carbon nanotube pole piece and the metal lithium sheet provided in this application;

[0017] Figure 3a Another schematic diagram of the structure of the surface electrode provided in this application;

[0018] Figure 3bAnother schematic structural diagram of a negative electrode sheet provided with a surface electrode provided in the present application. DETAILED DESCRIPTION

[0019] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0020] Please also read Figure 1a to Figure 1c The present application provides a single battery, which includes a housing 2 and a battery cell 100 located inside the housing 2. The battery cell 100 includes a negative electrode sheet 10, a positive electrode sheet 20, and a separator 30 located between the negative electrode sheet 10 and the positive electrode sheet 20. The surface of the electrode material layer of the negative electrode sheet 10 or the positive electrode sheet 20 is provided with at least one surface electrode 40 described below. In the following embodiments of the present application, the negative electrode sheet is provided with a surface electrode as an example for description.

[0021] See also Figure 1b and Figure 1c A surface electrode 40 is disposed on the surface of the negative electrode sheet 10, and the surface electrode 40 includes a porous insulating film 41 and a carbon nanotube conductive layer 42 disposed on one side of the porous insulating film 41, and the carbon nanotube conductive layer 42 is in contact with the surface of the negative electrode sheet 10 where the surface electrode 40 is located. Figure 1c , the negative electrode sheet 10 generally includes a negative electrode current collector 101 and a negative electrode material layer 102 arranged on the opposite sides of the negative electrode current collector 101, so the carbon nanotube conductive layer 42 is specifically in contact with the negative electrode material layer 102 of the negative electrode sheet 10. Among them, the surface electrode 40 also includes a metal conductor 43 connected to the carbon nanotube conductive layer 42, and the metal conductor 43 extends in a direction parallel to the porous insulating film 41, and the metal conductor 43 does not cover the surface of the negative electrode sheet 10 where the surface electrode 40 is located. It can be understood that in order for the surface electrode 10 to achieve the effect of testing the electrode potential, the metal conductor 43 should extend to expose the shell 2. For example, Figure 1a and Figure 1c As shown, the metal conductor 43 extends to the outside of the housing 2 .

[0022] In the present application, a porous insulating film with a carbon nanotube conductive layer is used as a surface electrode and is arranged on the surface of an electrode sheet (i.e., the surface of a positive electrode sheet or a negative electrode sheet), wherein the porous insulating film has a certain air permeability, and the carbon nanotube conductive layer arranged thereon does not affect its air permeability and ion transmission capacity, and the metal conductor connected to the carbon nanotube conductive layer does not cover the surface of the electrode sheet where the surface electrode is located, so that the surface electrode does not affect the ion deintercalation reaction between the positive and negative electrode sheets, and does not cause deformation of the electrode sheet. The carbon nanotube conductive layer can form a conductive loop with the electrode material layer on the surface of the electrode sheet, and the potential of the carbon nanotubes during lithium deintercalation / intercalation at the negative electrode of the battery is stable. Specifically, see the present application. Figure 2From the cyclic voltammetry curve of the half-cell composed of the provided carbon nanotubes and the metal lithium sheet, it can be seen that the lithium insertion potential of the carbon nanotubes is actually around 190mV, and the lithium de-insertion potential is actually around 550-580mV. The lithium insertion occurs before the lithium insertion of the graphite negative electrode, and the lithium de-insertion has basically not occurred after the lithium de-insertion of the graphite negative electrode (generally, the lithium de-insertion potential of the battery negative electrode will not be higher than 550mV). Therefore, during the battery cycle, in the potential range of graphite de-insertion / lithiation, the state of the carbon nanotubes is stable and can provide a stable potential. Therefore, the potential difference between the surface electrode and the electrode sheet where it is located can be accurately tested with the help of the carbon nanotube conductive layer, and the surface potential of the electrode sheet where the surface electrode is located can be obtained. Figure 1b Taking the potential on the surface of the negative electrode as an example, if the surface electrode is connected to the positive pole of the multimeter and the negative electrode is connected to the negative pole of the multimeter, the potential difference ΔV (i.e., V 表 -V 负极片 ), based on the potential V of carbon nanotubes during battery cycling 0 Stable and equal to its theoretical lithium deintercalation potential of 350V, the surface potential of the negative electrode V 负 =V 0 -ΔV.

[0023] In addition, the surface electrode has good flexibility and can be distributed at any position of the electrode sheet (negative electrode sheet or positive electrode sheet), which is convenient for fully understanding the surface potential of the electrode sheet surface and better ensuring the safe operation of the battery. In addition, considering that the surface of a certain electrode sheet can have at least one surface electrode, it can be understood that the porous insulating film 41 of the surface electrode 40 should partially cover the surface of the electrode sheet.

[0024] In the embodiment of the present application, in the carbon nanotube conductive layer 42, the diameter of the carbon nanotube can be 1nm-50nm. Carbon nanotubes with this diameter are conducive to forming a carbon nanotube conductive layer with good conductivity, so as to form a good electrical contact with the surface of the positive electrode sheet or the negative electrode sheet, and do not affect the air permeability of the porous insulating film 41. In some embodiments, the diameter of the carbon nanotube is 30nm-50nm. In other embodiments, the diameter of the carbon nanotube is 15nm-25nm, for example, 15nm-20nm. In some other embodiments, the diameter of the carbon nanotube is 1nm-10nm, for example, 6nm-10nm.

[0025] Preferably, the diameter of the carbon nanotube is 15nm-25nm. At this time, the diameter of the carbon nanotube is small and the tube length is long, so that a carbon nanotube conductive layer with a denser conductive network can be formed on the porous insulating film 41, and the distribution of carbon nanotubes in the carbon nanotube conductive layer is relatively uniform, so that the conductivity of the surface electrode 40 is good, and the polarization of the carbon nanotubes can be reduced, so as to ensure the accuracy of the potential test results, and to ensure the good air permeability of the porous insulating film 41 under the carbon nanotube conductive layer 42, without affecting the ion transmission between the positive and negative electrodes. In the embodiment of the present application, the aspect ratio of the carbon nanotube is greater than or equal to 1000, preferably greater than or equal to 3000, for example, 3000-10000. Carbon nanotubes with a longer aspect ratio are more convenient to intertwine with each other to form a conductive network with high conductivity.

[0026] In the embodiment of the present application, the thickness of the carbon nanotube conductive layer 42 is 2μm-10μm. At this time, the thickness of the carbon nanotube conductive layer 42 is appropriate, which can ensure the good conductivity of the carbon nanotube conductive layer 42, and does not affect the air permeability and ion transmission capacity of the porous insulating film 41, so that the surface electrode does not affect the ion transmission between the positive and negative electrodes. Exemplarily, the thickness of the carbon nanotube conductive layer 42 can be 2.5μm, 3μm, 4μm, 5μm, 6μm, 8μm or 9μm, etc. In some embodiments, the thickness of the carbon nanotube conductive layer 42 can be 2μm-5μm.

[0027] In the embodiment of the present application, there is no particular restriction on the thickness of the porous insulating film 41, which can be the common thickness of the separator in the battery, for example, 5μm-20μm. The porous insulating film with a thickness in this range can have sufficient structural strength and is not easy to crack under various mechanical deformations, ensuring that the surface electrode 40 can work normally. Exemplarily, the thickness can be specific but not limited to 8μm, 10μm, 12μm, 15μm, 18μm or 20μm. Furthermore, the thickness of the carbon nanotube conductive layer 42 can be 1 / 8-1 / 2 of the thickness of the porous insulating film 41. At this time, the thickness of the carbon nanotube conductive layer 42 will not be too thick or too thin.

[0028] In the embodiment of the present application, the porous insulating film 41 constituting the surface electrode may include a polyolefin diaphragm substrate. The polyolefin diaphragm substrate has good mechanical properties, such as good structural strength and tensile strength, so as to play a good supporting role. The holes on the porous insulating film 41 can ensure that lithium ions can be smoothly embedded or removed through the porous insulating film during the charging and discharging process of the battery. Among them, the polyolefin diaphragm substrate may include at least one of a polyethylene (PE) microporous diaphragm and a polypropylene (PP) microporous diaphragm, which may be a single-layer diaphragm, a double-layer diaphragm or a triple-layer diaphragm, such as a PE microporous membrane, a PP microporous membrane, a PE / PP double-layer microporous membrane, a PP / PP double-layer microporous membrane, and a PP / PE / PP three-layer microporous membrane.

[0029] In the embodiment of the present application, the porosity of the polyolefin separator substrate can be 20%-60%, for example, 20%, 30%, 40%, 50% or 55%. Suitable porosity can enable the separator to provide an effective ion transmission channel without affecting the transmission of lithium ions between the positive and negative electrodes, thereby not deteriorating the electrochemical performance of the battery. In addition, the air permeability of the polyolefin separator substrate is 250-600s / 100mL.

[0030] In the embodiment of the present application, the carbon nanotube conductive layer 42 further includes at least one of a binder and a dispersant. The presence of the adhesive can improve the adhesion strength of the carbon nanotube conductive layer 42 on the porous insulating film 41, and the dispersant can improve the uniform dispersion of the carbon nanotubes in the carbon nanotube conductive layer 42. Specifically, the dispersant and the binder can be types commonly used in the art, for example, the dispersant can be one or more of polyvinyl pyrrolidone (PVP), polyacrylamide (PAM), sodium carboxymethyl cellulose (CMC), etc. The binder can be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), acrylate, etc. In some embodiments of the present application, in the carbon nanotube conductive layer 42, the mass percentage of carbon nanotubes can be 65%-80%, the mass percentage of the binder can be 4%-11%, preferably 4.4%-10.7%, and the mass percentage of the dispersant can be 0%-26%, for example, 15%-26%.

[0031] The carbon nanotube conductive layer 42 can be obtained by coating a conductive layer slurry containing carbon nanotubes, a dispersant, a binder and a solvent on the porous insulating film 41, and then drying. In the conductive layer slurry, the mass percentage of carbon nanotubes can be 4%-5%. In the conductive layer slurry, the mass percentage of the binder in the conductive layer slurry can be 0.3%-0.6%. The mass percentage of the dispersant in the conductive layer slurry can be 1.0%-1.5%.

[0032] As described above in the present application, the metal conductor 43 extends in a direction parallel to the porous insulating film 41, and the metal conductor 43 does not cover the surface of the negative electrode sheet 10 where the surface electrode 40 is located. In other words, the metal conductor 43 is parallel to the surface of the carbon nanotube conductive layer 42 in contact with the porous insulating film 41; the orthographic projection of the metal conductor 43 on the diaphragm 30 does not cover the orthographic projection of the negative electrode sheet 10 on the diaphragm 30. At this time, the surface electrode 40 with the metal conductor 43 plays the role of testing the surface potential of the electrode sheet, and does not affect the lithium stripping / insertion reaction of the negative electrode sheet 10. In some embodiments, the metal conductor 43 is partially embedded in the carbon nanotube conductive layer 42. At this time, the connection between the metal conductor 43 and the carbon nanotube conductive layer 42 is relatively stable, and the quality reliability of the surface electrode 40 is relatively high.

[0033] In some embodiments of this application, see Figure 3a The metal conductor 43 includes a wire 431 and a tab 432 connected thereto, wherein the wire 431 is connected to the carbon nanotube conductive layer 42 (for example, the wire 431 is embedded in the carbon nanotube conductive layer 42), and the tab 432 is connected to the carbon nanotube conductive layer 42 through the wire 431, and the tab 432 is located outside the battery housing. The wire 431 may be made of a metal with good conductivity, such as aluminum, silver, platinum, copper, nickel, and titanium.

[0034] In addition, after the conductive layer slurry is coated on the porous insulating film 41, the conductive wire 431 can be inserted into the wet coating formed by the conductive layer slurry, so that after drying, the carbon nanotube conductive layer 42 partially embedded with the conductive wire 431 can be obtained, and then the conductive wire 431 can be connected to the pole ear to complete the production of the surface electrode. The dry coating formed by the conductive layer slurry after coating and drying can also be hot-pressed with the conductive wire 431 (note that the conductive wire 431 is placed outward as much as possible to ensure that the conductive wire 43 does not cover the surface of the electrode sheet in contact with the surface electrode in the formed surface electrode) to obtain the carbon nanotube conductive layer 42 connected with the conductive wire 43.

[0035] In order to obtain the above-mentioned single battery with the surface electrode 40, the surface electrode 40 can be placed on the surface of the negative electrode sheet or the positive electrode sheet, so that the carbon nanotube conductive layer 42 is in contact with the negative electrode material layer of the negative electrode sheet or the positive electrode material layer of the positive electrode sheet, and then the surface electrode 40 can be connected with the positive and negative electrode sheets by pressing. The pressing can be performed during the preparation of the electrode sheet or after the preparation of the electrode sheet is completed.

[0036] Please continue to see Figure 1aThe battery cell 100 of the present application also has a negative electrode tab 103 and a positive electrode tab 203 exposed outside the shell 2, wherein the negative electrode tab 103 is electrically connected to the negative electrode sheet 10, and the positive electrode tab 203 is electrically connected to the positive electrode sheet 20. The negative electrode tab 103 and the positive electrode tab 203 can be used as contact points when the battery is charged and discharged, and the negative electrode tab 103 and the tab of the surface electrode 40 can be used as contact points for the local potential test system of the negative electrode sheet composed of the negative electrode sheet 10 and the surface electrode 40, and the positive electrode tab 203 and the tab of the surface electrode 40 can be used as contact points for the local potential test system of the positive electrode sheet composed of the positive electrode sheet 20 and the surface electrode 40. Among them, the shell 2 of the battery can be made of aluminum-plastic composite film. The shell 2 also contains an electrolyte, and the above-mentioned battery cell 100 is immersed in the electrolyte.

[0037] It should be noted that the battery cell 100 may include a plurality of negative electrode sheets 10 and a plurality of positive electrode sheets 20, and the adjacent negative electrode sheets and positive electrode sheets are separated by a separator 30. The foregoing text of this application has been described by taking a surface electrode provided on a negative electrode sheet as an example, but in fact, the surface electrode 40 may be located on any one or more negative electrode sheets, or any one or more positive electrode sheets of the battery cell. Considering that in the actual use of the battery, lithium dendrites are generally prone to be generated on the surface of the negative electrode sheet, monitoring the surface potential of the negative electrode sheet is more meaningful for controlling the safety status of the battery. Therefore, generally, one of the negative electrode sheets located in the middle of the battery cell 100 has one or more surface electrodes 40, for example, surface electrodes may be provided on both side edges of the surface of the negative electrode sheet and / or its middle position. In this way, the situation of the single cell can be understood more quickly with a smaller number of surface electrodes.

[0038] The surface electrode 40 located on the surface of the electrode sheet may be longer sometimes, especially when it is located in the middle of a certain electrode sheet surface. In this case, the separator 44 may be used to shield a portion of the surface of the carbon nanotube conductive layer 42 away from the porous insulating film 41 (the portion not in contact with the negative electrode sheet), so that the surface electrode 40 can be connected to the negative electrode sheet 10 only through a smaller area of ​​the carbon nanotube conductive layer (see Figure 3b ). In this way, when the surface electrode 40 is testing the surface potential at the middle position of the electrode sheet, the carbon nanotube conductive layer with a larger area is partially blocked, and is only electrically connected to the negative electrode sheet through a small part, so that the potential at the middle position can be accurately measured. At this time, the metal conductor in the surface electrode still does not cover the surface of the negative electrode sheet, and does not affect the lithium ion transmission between the positive and negative electrodes. In addition, when multiple surface electrodes 40 are arranged on the surface of the negative electrode sheet, multiple such surface electrodes 40 will not be mistakenly connected, and their detection signals will not interfere with each other. Optionally, the area of ​​the carbon nanotube conductive layer that is not shielded by the diaphragm 44 is located at the edge of the carbon nanotube conductive layer 42.

[0039] In summary, the single cell provided in the present application has a surface electrode with the above-mentioned special structure, which will not affect the lithium ion transmission between the positive and negative electrodes of the single cell, and will not hinder the reaction between the positive and negative electrodes; the use of this surface electrode can realize accurate and convenient testing of the surface potential of the electrode sheet where it is located, thereby realizing timely control of the battery safety status and maintaining healthy operation of the battery.

[0040] The above-mentioned embodiments only express exemplary implementation methods of the present application, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A single cell capable of detecting the surface potential of an electrode sheet, characterized in that: The single battery comprises a shell and a battery cell located inside the shell, the battery cell comprises a negative electrode sheet and a positive electrode sheet, and at least one surface electrode is further provided on the surface of the electrode material layer of the negative electrode sheet or the positive electrode sheet; Among them, the surface electrode includes a porous insulating film and a carbon nanotube conductive layer located on the surface of one side of the porous insulating film, and the carbon nanotube conductive layer is in contact with the electrode material layer; the surface electrode also includes a metal conductor connected to the carbon nanotube conductive layer, the metal conductor extends in a direction parallel to the porous insulating film, and the metal conductor does not cover the surface of the negative electrode sheet or the positive electrode sheet.

2. The single cell according to claim 1, characterized in that: The diameter of the carbon nanotubes is 1nm-50nm.

3. The single cell according to claim 2, characterized in that: The diameter of the carbon nanotubes is 15nm-25nm.

4. The single cell according to claim 1, characterized in that: The thickness of the carbon nanotube conductive layer is 2 μm-10 μm.

5. The single cell according to claim 4, characterized in that: The thickness of the carbon nanotube conductive layer is 1 / 8 to 1 / 2 of the thickness of the porous insulating film.

6. The single cell according to any one of claims 1 to 5, characterized in that: The carbon nanotube conductive layer further comprises at least one of a binder and a dispersant.

7. The single cell according to claim 6, characterized in that: In the carbon nanotube conductive layer, the mass percentage of the carbon nanotubes is 65%-80%, the mass percentage of the binder is 4%-11%, and the mass percentage of the dispersant is 15%-26%.

8. The single cell according to claim 1, characterized in that: The porous insulating film comprises a polyolefin separator substrate, and the porosity of the polyolefin separator substrate is 20%-60%.

9. The single cell according to claim 1, characterized in that: The surface of the carbon nanotube conductive layer away from the porous insulating film includes a first region and other regions except the first region, the first region is in direct contact with the electrode material layer, the other regions are separated from the electrode material layer by a diaphragm, and the other regions are close to the metal conductor.

10. The single cell according to claim 1 or 9, characterized in that: The metal conductor comprises a wire and a tab, the wire is embedded in the carbon nanotube conductive layer, the tab is connected to the carbon nanotube conductive layer through the wire, and the tab is located outside the shell.

Images