Electrode structure for measuring current distribution in thickness direction of battery cell and measuring method

Abstract

The invention discloses an electrode structure and method for measuring current distribution in the thickness direction of a battery cell, and relates to the technical field of batteries. The positive pole piece is composed of an iron-lithium layer and a positive current collector; the negative pole piece comprises a plurality of layers of sub-negative pole pieces; each sub-negative pole piece is composed of a graphite layer and a negative current collector; and a diaphragm is arranged between the positive pole piece and the negative pole piece. The negative pole piece of the electrode structure is divided into a plurality of layers of sub-negative pole pieces, and the current distribution in the thickness direction of the electrode can be decomposed through the design of the layered structure, so that the current density distribution in the thickness direction of the pole pieces can be accurately measured, and the evaluation of the reaction uniformity in the thickness direction of a battery cell is facilitated.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrode structure and a measurement method for measuring current distribution in a thickness direction of a battery cell. Background Art

[0002] The development of new energy vehicles has become a trend. As the energy source of new energy vehicles, the development of fast charging cells for power batteries has become the development of various OEMs. The main difficulty in the fast charging process is that lithium deposition is prone to occur on the surface of graphite negative electrodes or mixed negative electrodes. In the process of cell design, the N / P ratio of the cell is guaranteed to be between 1.05-1.2. In theory, the lithium ions released from the iron-lithium or ternary positive electrode have enough embedding points in the graphite negative electrode. However, at present, when lithium deposition occurs on the surface of the graphite negative electrode, the graphite near the current collector is not fully embedded with lithium. Therefore, the lithium deposition on the graphite surface is mainly caused by the different polarization conditions in the thickness direction of the graphite during charging, resulting in inconsistent current size distribution in the thickness direction of the graphite.

[0003] However, in the traditional electrode structure, the impedance of each layer in the thickness direction of the pole piece in the lithium battery and the polarization voltage difference during the charge and discharge process are uncontrollable and equivalent, making it difficult to measure the current distribution in the thickness direction of the lithium battery pole piece. In addition, the traditional method of measuring current distribution is generally to arrange a magnetic field acquisition unit and calculate the distribution of current density by the magnetic field strength. However, the current measurement accuracy of the magnetic field acquisition unit is in millimeter pole pieces. Generally, the thickness of the double-sided negative electrode in a lithium battery is within 200um, and the thickness of the single-sided pole piece is within 100um. Therefore, the current method of arranging electromagnetic acquisition units cannot meet the accuracy requirements and cannot achieve the measurement of current distribution in the thickness direction of the lithium-ion battery pole piece. Summary of the invention

[0004] The main purpose of the present application is to provide an electrode structure and a measurement method for measuring the current distribution in the thickness direction of a battery cell, aiming to solve the technical problem that the current distribution in the thickness direction of a lithium-ion battery electrode is difficult to measure by the current method of arranging electromagnetic acquisition units.

[0005] To achieve the above objectives, the present application proposes an electrode structure for measuring current distribution in the thickness direction of a battery cell, the electrode structure comprising:

[0006] Positive electrode sheet and negative electrode sheet;

[0007] The positive electrode plate is composed of an iron-lithium layer and a positive electrode current collector;

[0008] The negative electrode sheet comprises a multi-layer negative electrode sub-sheet, and the negative electrode sub-sheet is composed of a graphite layer and a negative electrode current collector;

[0009] A separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0010] In one embodiment, the negative electrode current collector of the sub-negative electrode sheet in the inner layer of the negative electrode sheet is a porous negative electrode current collector.

[0011] In one embodiment, a separator is provided between each layer of negative electrode plates.

[0012] In one embodiment, the graphite layer of each layer of the negative electrode plate is coated and rolled by the single-layer coating of the plate.

[0013] In one embodiment, after the graphite layer is coated with a single layer of the pole piece and rolled, the pore size of the porous negative electrode current collector is 50-200 um, and the pore spacing is 80-250 um.

[0014] In one embodiment, the positive electrode plate comprises a plurality of layers of sub-positive electrode plates, and each layer of the sub-positive electrode plates is composed of an iron-lithium layer and a positive electrode current collector.

[0015] In one embodiment, the thickness of the graphite layer of each layer of the negative electrode plate is the same.

[0016] In one embodiment, when the multi-layer negative electrode sub-pole sheet is a two-layer negative electrode sub-pole sheet or a three-layer negative electrode sub-pole sheet, the thickness of the graphite layer of each layer of the negative electrode sub-pole sheet is 20 um.

[0017] In addition, to achieve the above-mentioned purpose, the present application also proposes a method for measuring the current distribution in the thickness direction of a battery cell, characterized in that the method is applied to the electrode structure for measuring the current distribution in the thickness direction of the battery cell as described above, and the method comprises:

[0018] Connecting the graphite layers of each layer of negative electrode plates through wires;

[0019] A Hall sensor is used to perform a charge and discharge test on the graphite layer to obtain current data of the negative electrode plates of each layer;

[0020] The current density distribution in the thickness direction of the battery cell is determined according to the current data.

[0021] In one embodiment, after the step of determining the current density distribution in the thickness direction of the battery cell according to the current data, the method further includes:

[0022] Determine the specification capacity of the graphite layer of each layer of the negative electrode plate;

[0023] Determining the charging capacity of each layer of the negative electrode sheet according to the current data of each layer of the negative electrode sheet;

[0024] The specification capacity is compared with the charging capacity to determine the surface lithium deposition condition.

[0025] One or more technical solutions proposed in this application have at least the following technical effects: This application proposes an electrode structure for measuring the current distribution in the thickness direction of a battery cell, the electrode structure comprising: a positive electrode sheet and a negative electrode sheet; the positive electrode sheet is composed of an iron-lithium layer and a positive current collector; the negative electrode sheet comprises a multi-layer sub-negative electrode sheet, the sub-negative electrode sheet is composed of a graphite layer and a negative current collector; a separator is provided between the positive electrode sheet and the negative electrode sheet. Since this application divides the negative electrode sheet of the electrode structure into multi-layer sub-negative electrode sheets, the design of the layered structure can decompose the current distribution in the thickness direction of the electrode, so that the current density distribution in the thickness direction of the electrode sheet can be accurately measured, which is conducive to evaluating the uniformity of the reaction in the thickness direction of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 A schematic diagram of the structure provided for the first embodiment of the electrode structure for measuring the current distribution in the thickness direction of the battery cell of the present application;

[0029] Figure 2 A schematic diagram of current measurement provided in Example 1 of the present application;

[0030] Figure 3 A schematic diagram of current measurement without a diaphragm between the upper and lower graphite layers provided in Example 2 of the present application;

[0031] Figure 4 A schematic diagram of the structure of a multi-layered positive electrode sheet provided in Example 2 of the present application;

[0032] Figure 5 A schematic diagram of current measurement of a multi-layered positive electrode sheet provided in Example 2 of the present application;

[0033] Figure 6 A schematic diagram of current measurement of a two-layer negative electrode sub-electrode provided in Example 2 of the present application;

[0034] Figure 7 A schematic flow chart of the first embodiment of the method for measuring the current distribution in the thickness direction of a battery cell of the present application.

[0035] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0036] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] It should be noted that all directional indications in the embodiments of the present application (such as up, down, close, far...) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0039] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0040] The present application embodiment provides an electrode structure for measuring the current distribution in the thickness direction of a battery cell, referring to Figure 1 , Figure 1 A schematic diagram of the structure of the electrode structure embodiment 1 for measuring the current distribution in the thickness direction of the battery cell provided in this application. Figure 1 , a first embodiment of the electrode structure for measuring the current distribution in the thickness direction of the battery cell is proposed in the present application.

[0041] In this embodiment, the electrode structure includes:

[0042] A positive electrode sheet 10 and a negative electrode sheet 20;

[0043] The positive electrode sheet 10 is composed of an iron-lithium layer 11 and a positive electrode current collector 12;

[0044] The negative electrode sheet 20 includes a multi-layer negative electrode sub-sheet 21, and the negative electrode sub-sheet 21 is composed of a graphite layer 211 and a negative electrode current collector 212;

[0045] A separator 30 is disposed between the positive electrode sheet 10 and the negative electrode sheet 20 .

[0046] It should be noted that the positive electrode is the electrode part of the battery cell where oxidation reaction occurs, and outputs electrons during discharge. The negative electrode is the electrode part of the battery cell where reduction reaction occurs, and receives electrons from the positive electrode during discharge. The two electrodes work together to achieve functions such as storage and release of electrical energy through chemical reactions and electron transfer.

[0047] It should be noted that the iron-lithium layer is the part of the positive electrode plate that contains positive electrode active materials such as lithium iron phosphate. The iron-lithium layer is a key part for electrochemical reactions, storage and release of electrical energy.

[0048] The positive electrode current collector is a component that collects and conducts current. It is generally a metal foil (such as aluminum foil), etc. It can collect the current generated by the positive electrode active material and conduct it out to achieve the transmission and utilization of electrical energy.

[0049] It should be noted that the multi-layer sub-negative electrode sheet is a structure obtained by layering the negative electrode sheet, and the layered structure can be designed as a two-layer design, a three-layer design or more, and can be layered according to needs, which is not limited in this embodiment.

[0050] It is understandable that because the traditional electrode structure is a single layer, when measuring the current distribution in the thickness direction of the electrode, only the current distribution of one layer can be measured. However, through layered design, the current distribution in the thickness direction of the electrode can be decomposed, which is conducive to analyzing the causes of cell non-uniformity and assisting in identifying local lithium deposition risk points on the large surface of the cell.

[0051] Exemplarily, the layered design is not only applicable to lithium-ion batteries, but also to sodium-ion batteries and aqueous zinc-ion batteries, which is not limited in this embodiment.

[0052] It should be noted that the graphite layer is the active material part of the negative electrode, which plays the role of storing and releasing lithium ions during the charge and discharge process. Graphite is suitable as a negative electrode material because of its good conductivity and stability.

[0053] The negative electrode current collector is similar to the positive electrode current collector, which is used to collect and conduct current and is usually made of metal (such as copper foil). It can collect and transmit the electrons generated by the reaction of the graphite layer to ensure the smooth flow of current.

[0054] It should be noted that the separator is used to isolate the positive and negative electrodes to prevent direct contact between the positive and negative electrodes and cause a short circuit.

[0055] Exemplarily, the diaphragm material may include PP, PE and rubber-coated diaphragm, which is not limited in this embodiment.

[0056] In this embodiment, if Figure 1 As shown, the thickness direction of the negative electrode sheet is divided into three layers (three layers are used as an example for explanation, and this scheme is not limited). By testing the current distribution of the upper, middle and lower layers, the current distribution in the thickness direction of the graphite negative electrode can be achieved, so as to evaluate the uniformity of the reaction in the thickness direction of the battery cell and judge the information such as surface lithium deposition.

[0057] In a possible implementation, Figure 1 As shown, the negative electrode current collector 212 of the sub-negative electrode sheet 21 in the inner layer of the negative electrode sheet 20 is a porous negative electrode current collector 2121 .

[0058] It should be noted that the porous negative electrode current collector is a negative electrode current collector having a structure with many tiny holes.

[0059] It is understandable that the porous negative electrode current collector can increase the contact area between the current collector and the negative electrode active material (such as graphite, etc.), making electron conduction more efficient; the porous structure can also provide more space and active sites for electrode reactions, which is beneficial to improving battery performance; at the same time, the porous structure may also help the electrolyte to better infiltrate and penetrate, further optimizing the working state of the battery, which not only ensures the independence and safety of the sub-negative electrode sheet, but also provides a specific channel for the flow of ions.

[0060] In a feasible implementation manner, in this embodiment, the graphite layer of each layer of the sub-negative electrode sheet 21 is coated and rolled by the electrode sheet single layer.

[0061] It should be noted that the single-layer coating of the electrode is a process of uniformly coating a slurry containing active materials such as graphite on the current collector to form a coating. Through coating, materials such as graphite can be evenly distributed on the current collector to form the initial structure of the electrode.

[0062] Currently, industrial lithium-ion batteries generally use double-sided coated graphite negative electrodes, while the purpose of single-layer coating in this embodiment is to expose the copper current collector on the back so that the copper current collector can be laser-drilled to form a porous negative electrode current collector.

[0063] It should be noted that rolling is an operation performed after the above coating. The purpose of using a roller press to squeeze the coated electrode sheet is to improve the density of the coating, reduce the pores in the coating, make the active material better contact with the current collector, enhance the conductivity and mechanical strength, and also control the thickness of the electrode sheet to meet the design requirements.

[0064] In a feasible implementation manner, in this embodiment, after the graphite layer 211 is coated with a single layer of the pole piece and rolled, the pore size of the porous negative electrode current collector 2121 is 50-200 um, and the pore spacing is 80-250 um.

[0065] In this embodiment, after the graphite layer of the inner layer of the negative electrode sheet is coated and rolled, laser drilling can be selected to punch holes in the negative electrode current collector, keeping the pore size between 50-200um and the pore spacing between 80-250um, so as to keep the porous current collector with a high gap. If the coating is directly applied on the porous current collector, it will have a greater impact on the subsequent rolling process, and it is difficult to control the thickness during rolling.

[0066] For easier understanding, refer to Figure 2 , Figure 2 A schematic diagram of current measurement provided for the first embodiment of the present application. Graphite 1 is the upper graphite, and the corresponding current is the upper current A1; graphite 2 is the middle graphite, and the corresponding current is the middle current A2; graphite 3 is the bottom graphite, and the corresponding current is the bottom graphite A3. The novel electrode structure of this embodiment realizes the design of conducting ionic current and isolating electronic current in the thickness direction of the pole piece, and separates the ionic path and the electronic path in the porous electrode of the lithium battery (wherein the ionic current is formed by the directional movement of lithium ions in the electrolyte, and after the lithium ions are released from the iron-lithium positive electrode, they are mainly embedded in graphite 1, graphite 2 and graphite 3 through mass transfer in the porous graphite layer and the pores in the current collector, wherein the total electronic current passes through the wire A4 and then is shunted, and A1, A2 and A3 are all connected by metal wires). The electronic current is measured by a Hall meter, and the distribution of current in the thickness direction of the pole piece can be measured. The upper layer current is A1, the middle layer current is A2, the bottom layer current is A3, and the total current is A4. The currents satisfy the following relationship: A1+A2+A3=A4.

[0067] This embodiment proposes an electrode structure for measuring the current distribution in the thickness direction of a battery cell, the electrode structure comprising: a positive electrode sheet and a negative electrode sheet; the positive electrode sheet is composed of an iron-lithium layer and a positive current collector; the negative electrode sheet comprises a multi-layer sub-negative electrode sheet, the sub-negative electrode sheet is composed of a graphite layer and a negative current collector; a separator is provided between the positive electrode sheet and the negative electrode sheet. Since this embodiment divides the negative electrode sheet of the electrode structure into a multi-layer sub-negative electrode sheet, the design of the layered structure can decompose the current distribution in the thickness direction of the electrode, so that the current density distribution in the thickness direction of the electrode sheet can be accurately measured, which is conducive to evaluating the uniformity of the reaction in the thickness direction of the battery cell.

[0068] Based on the above first embodiment, a second embodiment is proposed.

[0069] In this embodiment, if Figure 1 As shown, a separator 30 is provided between each layer of the negative electrode sheets 21 .

[0070] It should be noted that the separator serves to isolate the layers of negative electrode plates, preventing the layers of negative electrode plates from direct contact and making it difficult to measure the current density distribution in the thickness direction of the plates.

[0071] For easier understanding, refer to Figure 3 , Figure 3 A schematic diagram of current measurement without a diaphragm between the upper and lower graphite layers provided in Example 2 of the present application. As shown in the figure, there is no electronic isolation between the upper and lower graphite layers, graphite 1 is the upper graphite layer, and the corresponding current is the upper layer current A1, graphite 2 is the middle layer graphite, and the corresponding current is the middle layer current A2, and graphite 3 is the bottom layer graphite, and the corresponding current is the bottom layer graphite A3.

[0072] Because there is no electronic isolation between the upper, middle and lower graphite layers, all electron currents and ion currents in the thickness direction go inside at this time, so the test results are A1=A2=0, A3=A4=total charge and discharge current. In this configuration, the battery cannot test the current distribution in the thickness direction. Therefore, setting a diaphragm between each layer of negative electrode sheets is conducive to testing the current distribution in the thickness direction.

[0073] In one possible implementation, reference Figure 4 , Figure 4 The structure diagram of the multi-layered sub-positive electrode sheet provided in the second embodiment of the present application is as follows: The positive electrode sheet 10 comprises a multi-layered sub-positive electrode sheet 13 , each layer of which is composed of an iron-lithium layer 11 and a positive current collector 12 .

[0074] In a feasible implementation manner, the thickness of the graphite layer 211 of each layer of the negative electrode sheet 21 is the same.

[0075] It should be noted that if Figure 4 As shown, the positive electrode current collector of the sub-positive electrode sheet in the inner layer of the positive electrode sheet is a porous positive electrode current collector 121. A separator is provided between each layer of the sub-positive electrode sheet. Similar to the above-mentioned negative electrode sheet, the positive electrode sheet can also be provided with the same electrode structure, which will not be repeated here.

[0076] For easier understanding, refer to Figure 5 , Figure 5 A schematic diagram of current measurement of a multi-layered sub-positive electrode sheet provided in Example 2 of the present application. Both positive and negative electrodes can detect the current in the thickness direction of the electrode sheet, where A1+A2+A3=A4, A5+A6+A7=A8, and A4=A8 are equal to the charge and discharge current in the test cabinet.

[0077] For ease of understanding, the current density distribution in the thickness direction of the graphite negative electrode is measured at different temperatures. Figure 2 As shown, the thickness and compaction of the three-layer graphite are the same, the compaction is 1.56g / cm3, the thickness is 20um, and the charging conditions are shown in Table 1, and the current distribution ratio of 10% SOC is recorded.

[0078] Table 1: Distribution of current density in the thickness direction at different temperatures

[0079] Test conditions Upper current A1 Middle layer current A2 Lower current A3 Case 1 -10℃-1C 72％ 25％ 3％ Case 2 25℃-1C 40％ 35％ 25％ Case 3 25℃-2.5C 48％ 34％ 18％ Case 4 45℃-2.5C 42％ 38％ 20％

[0080] In a possible implementation, Figure 1 and Figure 6 As shown, Figure 6 Schematic diagram of current measurement of a two-layer negative electrode sheet provided in Embodiment 2 of the present application. When the multi-layer negative electrode sheet 21 is a two-layer negative electrode sheet or a three-layer negative electrode sheet, the thickness of the graphite layer 211 of each layer of the negative electrode sheet 21 is 20 um.

[0081] For ease of understanding, the structural design of the battery cell is as follows Figure 6 Shown is a two-layer design where both graphite layers have the same thickness of 20 um and the compaction of each layer is different.

[0082] Taking the different compaction conditions of the upper coating as an example, the influence of different graphite electrode designs on the current density distribution in the thickness direction of graphite was measured.

[0083] As shown in Table 2, the compaction of the two layers of cells in Case 5 is the same, 1.56g / cm3; in Case 6, the upper layer is compacted 1.62g / cm3 and the lower layer is compacted 1.50g / cm3; in Case 7, the upper layer is compacted 1.50g / cm3 and the lower layer is compacted 1.62g / cm3. The test conditions are room temperature 25℃, 2C charging condition at 20% SOC, the current distribution of the upper and lower layers is shown in Table 2, the upper and lower current distribution of Case 6 is the most uniform, and the high compaction of the upper layer and the low compaction of the lower layer in Case 6 are the best.

[0084] Table 2: Effect of double-layer coating process on current density distribution of upper and lower layers of graphite negative electrode

[0085]

[0086] Among them, the upper layer current of case 6 accounts for 65% and the lower layer current accounts for 35% (the difference between the two data is the smallest), which has the best uniformity than case 5 (71.5% vs. 28.5%) and case 7 (82% vs. 12%). There is a difference in the fast charging ability between the upper layer high voids and the lower layer high voids, or the upper layer small particles and the lower layer large particles, and the upper layer large graphite particles and the lower layer lower graphite particles. Therefore, the current distribution percentage in the thickness direction of the battery cell pole piece can be used to more accurately evaluate the double-layer coating.

[0087] This embodiment realizes the conduction of ion current and isolation of electron current in the thickness direction of the pole piece by constructing a new type of electrode structure, and separates the ion path and electron path in the porous electrode of the lithium battery. By measuring the electron current through the Hall instrument, the distribution of current in the thickness direction of the pole piece can be measured. At the same time, it can also be used to evaluate the impact of different electrode structure designs on the current distribution in the thickness direction of the battery cell pole piece. A more uniform current distribution in the thickness direction of the electrode is conducive to achieving better fast charging capabilities.

[0088] To achieve the above purpose, the present application also proposes a method for measuring the current distribution in the thickness direction of a battery cell, which is based on the electrode structure for measuring the current distribution in the thickness direction of a battery cell as described above. Figure 7 , Figure 7 A schematic flow chart of the first embodiment of the method for measuring the current distribution in the thickness direction of a battery cell of the present application.

[0089] In this embodiment, the method for measuring the current distribution in the thickness direction of the battery cell includes steps S10 to S30:

[0090] Step S10: connecting the graphite layers of each layer of the negative electrode plates through a wire.

[0091] Step S20: using a Hall sensor to perform a charge and discharge test on the graphite layer to obtain current data of the negative electrode plates of each layer.

[0092] It should be noted that the Hall sensor is a device used to measure the current of the pole piece.

[0093] It should be noted that the current data refers to the output current of each layer of the negative electrode plate, such as A1, A2 and A3 mentioned above.

[0094] Step S30: determining the current density distribution in the thickness direction of the battery cell according to the current data.

[0095] It should be noted that the current density distribution refers to the distribution of current in different thickness directions of the electrode.

[0096] In this embodiment, if Figure 2 The specific test process is as follows:

[0097] 1. According to Figure 2 Construct a soft-pack battery, which now has one positive electrode current collector and three negative electrode current collectors.

[0098] 2. According to Figure 2 As shown, graphite 1, graphite 2 and graphite 3 are connected with round wires.

[0099] 3. Turn on the Hall sensor, open four of the channels and clamp them at A1, A2 and A3 respectively, keep the current direction of the clamps consistent, reset the device, select the range, and start testing the current.

[0100] 4. Perform charge and discharge tests on the positive electrode of the soft-pack battery and the total negative electrode at A4. At this time, the implementation current is displayed at A1, A2, A3, and A4.

[0101] 5. The current tested by the Hall instrument satisfies A1+A2+A3=A4, where A4 is equal to the total charge and discharge current.

[0102] In a feasible implementation manner, after step S30 of this embodiment, the steps may also be included: determining the specification capacity of the graphite layer of each layer of the negative electrode sheet; determining the charging capacity of each layer of the negative electrode sheet according to the current data of each layer of the negative electrode sheet; comparing the specification capacity with the charging capacity to determine the surface lithium deposition condition.

[0103] It should be noted that the specification capacity refers to the ability of the graphite layer of each layer of the negative electrode plate to accommodate or store the amount of charge.

[0104] It should be noted that the charge capacity is the amount of charge achieved by the insertion or accumulation of lithium ions.

[0105] In this embodiment, the surface lithium in the graphite electrode can be judged by the above electrode structure. Figure 6 Taking the upper and lower two-layer structure as an example, a soft-pack battery is assembled. The overall capacity of the soft-pack battery is 120mAh, of which the capacity of the upper graphite layer is 60mAh and the capacity of the lower graphite layer is 60mAh. This soft-pack battery is Case 8. The battery cell in Case 8 is charged at a rate of 3C (360mA). When charging for 15 minutes, considering that the overall capacity of the negative electrode is 90mAh, it reaches 50% SOC. The upper Hall instrument monitors the real-time current and time integration, and it is found that the upper graphite charging capacity is 68mAh and the lower graphite charging capacity is 22mAh. The upper graphite charging capacity of 68mAh is greater than the designed capacity of 60mAh, so the extra capacity is the lithium metal formed on the surface of the lithium-embedded graphite, so it is believed that obvious surface lithium precipitation has occurred.

[0106] This embodiment can accurately identify the current distribution in the thickness direction of the battery cell pole piece, which is conducive to analyzing the cause of the battery cell non-uniformity. At the same time, by comparing the total capacity of the surface current and time integration with the design capacity of the surface graphite, it can assist in identifying the risk points of local lithium deposition on the large surface of the battery cell. It can be used to predict the situation in which the electrode lithium deposition mainly occurs on the surface in the fast charging scenario.

[0107] It should be noted that the above examples are only used to understand the present application and do not constitute a limitation on the method for measuring the current distribution in the thickness direction of the battery cell of the present application. More simple transformations based on this technical concept are all within the scope of protection of the present application.

[0108] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0109] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. An electrode structure for measuring current distribution in the thickness direction of a battery cell, characterized in that: The electrode structure comprises: Positive electrode sheet and negative electrode sheet; The positive electrode plate is composed of an iron-lithium layer and a positive electrode current collector; The negative electrode sheet comprises a multi-layer negative electrode sub-sheet, and the negative electrode sub-sheet is composed of a graphite layer and a negative electrode current collector; A separator is arranged between the positive electrode sheet and the negative electrode sheet.

2. The electrode structure according to claim 1, characterized in that: The negative electrode current collector of the sub-negative electrode sheet in the inner layer of the negative electrode sheet is a porous negative electrode current collector.

3. The electrode structure according to claim 2, characterized in that: A separator is arranged between each layer of negative electrode plates.

4. The electrode structure according to claim 3, characterized in that: The graphite layers of each layer of the negative electrode plates are coated and rolled by the single-layer coating of the plates.

5. The electrode structure according to claim 4, characterized in that: After the graphite layer is coated with a single layer of the pole piece and rolled, the pore size of the porous negative electrode current collector is 50-200 um, and the pore spacing is 80-250 um.

6. The electrode structure according to any one of claims 1 to 5, characterized in that: The positive electrode plate comprises a plurality of layers of sub-positive electrode plates, and each layer of the sub-positive electrode plates is composed of an iron-lithium layer and a positive electrode current collector.

7. The electrode structure according to any one of claims 1 to 5, characterized in that: The thickness of the graphite layer of each layer of the negative electrode sheet is the same.

8. The electrode structure according to claim 7, characterized in that: When the multi-layer negative electrode sub-pole sheet is a two-layer negative electrode sub-pole sheet or a three-layer negative electrode sub-pole sheet, the thickness of the graphite layer of each layer of the negative electrode sub-pole sheet is 20 um.

9. A method for measuring current distribution in the thickness direction of a battery cell, characterized in that: The method is applied to an electrode structure for measuring current distribution in a thickness direction of a battery cell according to any one of claims 1 to 8, and the method comprises: Connecting the graphite layers of each layer of negative electrode plates through wires; A Hall sensor is used to perform a charge and discharge test on the graphite layer to obtain current data of the negative electrode plates of each layer; The current density distribution in the thickness direction of the battery cell is determined according to the current data.

10. The method according to claim 9, characterized in that After the step of determining the current density distribution in the thickness direction of the battery cell according to the current data, the method further includes: Determine the specification capacity of the graphite layer of each layer of the negative electrode plate; Determining the charging capacity of each layer of the negative electrode sheet according to the current data of each layer of the negative electrode sheet; The specification capacity is compared with the charging capacity to determine the surface lithium deposition condition.

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