Method for testing four-electrode cell, battery and charging window

Abstract

The invention discloses a four-electrode cell, a battery and a charging window test method. The four-electrode cell comprises a positive electrode, a negative electrode, a diaphragm, a reference electrode and an auxiliary electrode, the diaphragm is arranged between the positive electrode and the negative electrode; the auxiliary electrode is in contact with the surface of the negative electrode; the reference electrode is respectively isolated from the positive electrode, the negative electrode and the auxiliary electrode through diaphragms; the positive electrode, the negative electrode, the reference electrode and the auxiliary electrode are respectively led out to form electrode leading-out ends. The four-electrode cell provided by the invention can solve the problems that the lithium precipitation critical potential of charging at different temperatures and different multiplying powers is difficult to obtain, and the potentials of the negative electrode surface and the reference electrode cannot be determined, and the lithium precipitation critical potential at the required temperature and multiplying power can be determined without disassembling the cell.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and in particular to a testing method for a four-electrode battery cell, a battery and a charging window. Background Art

[0002] With the commercial development of lithium-ion batteries and the continuous expansion of the demand in the new energy market, people have higher and higher demands for the fast charging performance, energy density and safety performance of lithium-ion batteries. Fast charging has become an inevitable trend in the new energy market, which has improved the efficiency of energy replenishment and greatly solved the endurance anxiety of new energy. However, under the condition of high-rate current charging, the electrode polarization increases rapidly to reach the lithium metal precipitation potential, which leads to lithium precipitation and lithium dendrite growth on the negative electrode surface, and in severe cases, it can lead to safety risks such as internal short circuit and thermal runaway.

[0003] The current existing charging window test method is the disassembly observation method, which determines the charging lithium deposition window at different rates and temperatures by disassembling a large number of batteries and observing the lithium deposition state of the negative electrode. This includes the three-electrode method, which is to add a metal lithium reference electrode inside the battery cell and monitor the potential of the negative electrode and the lithium reference electrode to determine the critical potential value of lithium deposition. Among them, CN202949008U discloses a three-electrode device for a lithium-ion battery, which uses a metal lithium sheet with a diameter of 10-20mm and a thickness of 0.2mm as a reference electrode, and the positive electrode, negative electrode and reference electrode are led out from different sides of the shell respectively. The patent effectively solves the problems of poor sensitivity, poor sealing, leakage, and reference electrode lithium removal of the three-electrode device. CN 206976495U discloses a three-electrode battery, in which the reference electrode is a copper wire placed between the positive electrode and the negative electrode, and the reference electrode is lithium-plated before testing. The patent ensures the transmission of lithium ions between the positive and negative electrodes, and significantly improves the accuracy of the positive electrode potential, the negative electrode potential and the impedance. Although the three electrodes can effectively monitor the potential of the negative electrode and the lithium reference electrode, the three electrodes cannot obtain the critical potential for lithium deposition due to the polarization of the negative electrode during the charging process, especially under low temperature and high rate charging conditions (theoretically, the lithium deposition potential is 0V). It is also necessary to disassemble the battery cell to confirm the critical potential for lithium deposition (charging window) at different temperatures and rates.

[0004] Therefore, it is necessary to develop a four-electrode battery cell that can solve the problems of difficulty in obtaining the critical potential of lithium deposition when charging at different temperatures and different rates, and the inability to determine the potential of the negative electrode surface and the reference electrode. Summary of the invention

[0005] The purpose of the present invention is to provide a four-electrode battery cell to address the deficiencies in the prior art, which can solve the problems of difficulty in obtaining the critical potential for lithium deposition when charging at different temperatures and different rates, and inability to determine the potential of the negative electrode surface and the reference electrode.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A four-electrode battery cell, comprising a positive electrode, a negative electrode, a separator, a reference electrode and an auxiliary electrode;

[0008] The separator is disposed between the positive electrode and the negative electrode; the auxiliary electrode is in contact with the surface of the negative electrode;

[0009] The reference electrode is isolated from the positive electrode, the negative electrode and the auxiliary electrode respectively by a diaphragm;

[0010] The positive electrode, the negative electrode, the reference electrode and the auxiliary electrode are respectively led outward to form electrode lead-out terminals.

[0011] Preferably, the reference electrode is selected from a metal lithium sheet whose surface oxide layer has been removed or a metal wire that has been plated with lithium.

[0012] Preferably, the diameter of the metal lithium sheet is 5-25 mm, and the thickness of the metal lithium sheet is ≤0.5 mm.

[0013] Preferably, the metal wire is selected from any one of copper wire, platinum wire, manganese wire, iron wire, aluminum wire or nickel wire;

[0014] And / or, the diameter of the metal wire is 0.02-0.2 mm.

[0015] Preferably, the auxiliary electrode is selected from any one of copper wire, platinum wire, manganese wire, iron wire, aluminum wire or nickel wire that has not been plated with lithium.

[0016] In addition, the present invention also provides a four-electrode battery, including a shell, and a battery cell and an electrolyte disposed in the shell, wherein the battery cell is the above-mentioned four-electrode battery cell.

[0017] Preferably, the shell is a hard shell, and the electrode lead-out ends of the reference electrode and the auxiliary electrode extend outward through openings of the battery top cover respectively.

[0018] Preferably, the shell is a soft-package shell, and the electrode lead-out ends of the reference electrode and the auxiliary electrode extend outward through the soft-package shell respectively.

[0019] In addition, the present invention also provides a charging window test method for a four-electrode battery, comprising the following steps:

[0020] 1) Under the preset temperature and different charging rate conditions, monitor the potential difference between the auxiliary electrode and the reference electrode to obtain the potential data under different charge states;

[0021] 2) Establishing a relationship between the state of charge, test temperature, charging rate and lithium deposition based on the potential data, and determining the lithium deposition charging window.

[0022] Compared with the prior art, the beneficial effect of the present invention is that the four-electrode battery cell provided by the present invention can solve the problem that it is difficult to obtain the critical potential of lithium deposition when charging at different temperatures and different rates, and the potential of the negative electrode surface and the reference electrode cannot be determined. Among them, the auxiliary electrode is drawn out on the negative electrode surface, which solves the problem that the polarization of the current collector to the negative electrode causes the potential offset of the negative electrode and the reference electrode. The liquid phase potential of the auxiliary electrode drawn out from the negative electrode surface is approximately equal to the liquid phase potential of the reference electrode, that is, the theoretical lithium deposition potential is 0V as the critical lithium deposition potential, and the critical potential of lithium deposition at the required temperature and rate can be confirmed without disassembling the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic cross-sectional exploded structure diagram of a four-electrode battery cell according to an embodiment of the present invention;

[0024] Figure 2 It is a schematic structural diagram of a four-electrode battery according to an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of a four-electrode battery structure according to another embodiment of the present invention;

[0026] Figure 4 This is a potential data diagram of Example 1 of the present invention at different charge states;

[0027] Figure 5 This is a diagram showing the relationship between the lithium plating charging window of Example 1 of the present invention.

[0028] Among them, 1-positive electrode; 2-negative electrode; 3-diaphragm; 4-reference electrode; 5-auxiliary electrode. DETAILED DESCRIPTION

[0029] In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] According to a first aspect of the present application, the present application provides a four-electrode battery cell, including a positive electrode 1, a negative electrode 2, a separator 3, a reference electrode 4 and an auxiliary electrode 5;

[0031] The separator 3 is arranged between the positive electrode 1 and the negative electrode 2; the auxiliary electrode 5 is in contact with the surface of the negative electrode 2;

[0032] The reference electrode 4 is isolated from the positive electrode 1, the negative electrode 2 and the auxiliary electrode 5 by a diaphragm;

[0033] The positive electrode 1, the negative electrode 2, the reference electrode 4 and the auxiliary electrode 5 are respectively led outward to form electrode lead-out terminals.

[0034] In some embodiments, the reference electrode 4 is selected from a metal lithium sheet with its surface oxide layer removed or a metal wire that has been plated with lithium.

[0035] In some embodiments, the thickness of the metal lithium sheet is ≤0.5 mm, for example, it may be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm or 0.5 mm, preferably 0.2 mm.

[0036] In some embodiments, the metal wire is selected from any one of copper wire, platinum wire, manganese wire, iron wire, aluminum wire or nickel wire, preferably copper wire and platinum wire;

[0037] And / or, the diameter of the metal wire is 0.02-0.2 mm, for example, it can be 0.02 mm, 0.05 mm, 0.1 mm, 0.15 mm or 0.2 mm, preferably 0.05 mm.

[0038] In some embodiments, the metal lithium sheet is round or square, with a diameter or length and width of 5-25 mm, for example, 5 mm, 10 mm, 15 mm, 20 mm or 25 mm, preferably 10 mm.

[0039] In some embodiments, the auxiliary electrode is selected from any one of copper wire, platinum wire, manganese wire, iron wire, aluminum wire or nickel wire that has not been plated with lithium, preferably copper wire and platinum wire.

[0040] According to a second aspect of the present application, the present application provides a four-electrode battery, comprising a shell, and a battery cell and an electrolyte disposed in the shell, wherein the battery cell is the above-mentioned four-electrode battery cell.

[0041] In some embodiments, the shell is a hard shell, and the electrode lead ends of the reference electrode and the auxiliary electrode extend outward through the openings of the battery top cover respectively.

[0042] In some embodiments, the shell is a soft-package shell, and the electrode lead ends of the reference electrode and the auxiliary electrode extend outward through the soft-package shell respectively.

[0043] According to a third aspect of the present application, the present application provides a charging window test method for a four-electrode battery, comprising the following steps:

[0044] 1) Under the preset temperature and different charging rate conditions, monitor the potential difference between the auxiliary electrode and the reference electrode to obtain the potential data under different charge states;

[0045] 2) Establishing a relationship between the state of charge, test temperature, charging rate and lithium deposition based on the potential data, and determining the lithium deposition charging window.

[0046] In some embodiments, in step 2, the test temperature is -30-60°C, for example, it can be -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 40°C, 50°C or 60°C; the charging rate is 0.1-10C, for example, it can be 0.1C, 1C, 5C or 10C.

[0047] In some embodiments, the reference electrode is a metal wire plated with lithium or a metal lithium sheet, and the potential difference between the positive electrode and the reference electrode ranges from 2.0-4.8V; the potential difference between the negative electrode and the reference electrode ranges from 0-1.0V; the potential difference between the positive electrode and the auxiliary electrode ranges from 2.0-4.8V, and the potential difference between the negative electrode and the auxiliary electrode ranges from 0V.

[0048] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may include but is not limited to a chemical formula such as Li a Ni x Co y M z O 2-b N b (wherein 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from a combination of one or more of Mn and Al, and N is selected from a combination of one or more of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc. The positive active material may also be modified. The method of modifying the positive active material should be known to those skilled in the art. For example, the positive active material may be modified by coating, doping, etc. The material used for the modification may include but is not limited to a combination of one or more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive current collector is usually a structure or part for collecting current. The positive current collector may be various materials suitable for use as a positive current collector for lithium-ion batteries in the art. For example, the positive current collector may include but is not limited to metal foil, etc., and more specifically may include but is not limited to aluminum foil, etc.

[0049] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer may include but is not limited to one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium. Among them, graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; silicon-based materials can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is usually a structure or part that collects current. The negative electrode current collector can be various materials in the art that are suitable for use as a negative electrode current collector for lithium-ion batteries. For example, the negative electrode current collector can be, but is not limited to, metal foil, and more specifically, can be, but is not limited to, copper foil.

[0050] In some embodiments, the separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be a combination of one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers, etc., but not limited to.

[0051] In some embodiments, the battery further comprises an electrolyte, and the electrolyte comprises an organic solvent, an electrolyte lithium salt and an additive. Among them, the electrolyte lithium salt may be LiPF6 and / or LiBOB used in a high-temperature electrolyte; it may also be at least one of LiBF4, LiBOB, and LiPF6 used in a low-temperature electrolyte; it may also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in an anti-overcharge electrolyte; it may also be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent may be a cyclic carbonate, including PC and EC; it may also be a chain carbonate, including DFC, DMC, or EMC; it may also be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include but are not limited to at least one of a film-forming additive, a conductive additive, a flame retardant additive, an anti-overcharge additive, an additive for controlling the content of H2O and HF in the electrolyte, an additive for improving low-temperature performance, and a multifunctional additive.

[0052] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be described in further detail below in conjunction with specific implementation methods and accompanying drawings, but the implementation methods of the present invention are not limited thereto.

[0053] Experimental Example 1

[0054] Preparation of four-electrode cell

[0055] The positive electrode, diaphragm, reference electrode, diaphragm, auxiliary electrode and negative electrode are wound in sequence, one end of the reference electrode is tightly fixed between the diaphragms, one end of the auxiliary electrode is tightly fixed on the active material of the negative electrode plate, the other ends of the reference electrode and the auxiliary electrode are insulated and then led out through the side holes of the explosion-proof valve, fixed and sealed, and then welded to the reference electrode and auxiliary electrode ears respectively to obtain a four-electrode battery cell.

[0056] Among them, the rated capacity of the battery cell is 100Ah, the voltage platform is 3.2V, the internal resistance is 0.3mΩ, and the reference electrode and the auxiliary electrode are selected from two copper wires with a length of 15cm and a diameter of 0.05mm.

[0057] Preparation of four-electrode battery

[0058] After the four-electrode cell is fixed and sealed, an electrolyte is injected to obtain a four-electrode battery.

[0059] Wherein, the shell is a hard shell.

[0060] Charging window test

[0061] 1) At 25℃±2℃, charge at 2C, 3C, 4C, and 5C current densities, monitor the potential difference between the auxiliary electrode and the reference electrode, and obtain the potential data under different charge states (such as Figure 4 shown);

[0062] 2) Establishing the relationship between the state of charge, test temperature, charging rate and lithium deposition based on the potential data, and determining the lithium deposition charging window (such as Figure 5 shown).

[0063] Experimental Example 2

[0064] The difference from Experimental Example 1 is that the rated capacity of the battery cell in this experimental example is 4Ah, and the shell is a soft shell.

[0065] The rest is the same as Experimental Example 1 and will not be described again here.

[0066] Experimental Example 3

[0067] The difference from Experimental Example 2 is that in this experimental example, the reference electrode is selected from a metal lithium sheet with a diameter of 10 mm and a thickness of 0.2 mm, after the surface oxide layer is removed and rolled flat, and the auxiliary electrode is selected from a copper wire with a length of 15 cm and a diameter of 0.05 mm. One end of the copper wire is tightly fixed on the active material of the negative electrode plate, and the other end of the auxiliary electrode is insulated and welded to the auxiliary electrode ear. The electrolyte is supplemented to make the reference electrode fully contact with the winding core, and the reference electrode ear and the auxiliary electrode ear are insulated and led out from the lower end of the aluminum-plastic film of the lithium-ion battery cell.

[0068] The rest is the same as Experimental Example 1 and will not be described again here.

[0069] Experimental Example 4

[0070] The difference from Experimental Example 1 is that in this Experimental Example, the reference electrode is selected from a platinum wire with a diameter of 0.05 mm, and the auxiliary electrode is selected from a platinum wire with a diameter of 0.05 mm.

[0071] The rest is the same as Experimental Example 1 and will not be described again here.

[0072] The four-electrode battery cell provided by the present invention can solve the problems of difficulty in obtaining the critical potential for lithium deposition when charged at different temperatures and different rates, and inability to determine the potential of the negative electrode surface and the reference electrode. Among them, an auxiliary electrode is drawn out on the surface of the negative electrode, which solves the problem of the potential offset between the negative electrode and the reference electrode caused by the polarization of the current collector to the negative electrode. The liquid phase potential of the auxiliary electrode drawn out on the surface of the negative electrode is approximately equal to the liquid phase potential of the reference electrode, that is, the theoretical lithium deposition potential is 0V as the critical lithium deposition potential. According to the potential data under different states of charge, the relationship between the state of charge, the test temperature and the charging rate and the lithium deposition is established to determine the lithium deposition charging window, and the critical potential for lithium deposition at the required temperature and rate can be confirmed without disassembling the battery cell.

[0073] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A four-electrode battery cell, characterized in that: It includes positive electrode, negative electrode, diaphragm, reference electrode and auxiliary electrode; The separator is disposed between the positive electrode and the negative electrode; the auxiliary electrode is in contact with the surface of the negative electrode; The reference electrode is isolated from the positive electrode, the negative electrode and the auxiliary electrode respectively by a diaphragm; The positive electrode, the negative electrode, the reference electrode and the auxiliary electrode are respectively led outward to form electrode lead-out terminals.

2. The four-electrode battery cell according to claim 1, characterized in that: The reference electrode is selected from a metal lithium sheet after removing the surface oxide layer or a metal wire after lithium plating.

3. The four-electrode battery cell according to claim 2, characterized in that: The diameter of the metal lithium sheet is 5-25 mm, and the thickness of the metal lithium sheet is ≤0.5 mm.

4. The four-electrode battery cell according to claim 2, characterized in that: The metal wire is selected from any one of copper wire, platinum wire, manganese wire, iron wire, aluminum wire or nickel wire.

5. The four-electrode battery cell according to claim 4, characterized in that: The diameter of the metal wire is 0.02-0.2 mm.

6. The four-electrode battery cell according to claim 1, characterized in that: The auxiliary electrode is selected from any one of copper wire, platinum wire, manganese wire, iron wire, aluminum wire or nickel wire that has not been subjected to lithium plating.

7. A four-electrode battery, comprising a housing, a battery cell and an electrolyte disposed in the housing, characterized in that: The battery cell is a four-electrode battery cell as described in any one of claims 1 to 6.

8. The four-electrode battery according to claim 7, characterized in that: The shell is a hard shell, and the electrode lead-out ends of the reference electrode and the auxiliary electrode extend outward through the openings of the battery top cover respectively.

9. The four-electrode battery according to claim 7, characterized in that: The shell is a soft-package shell, and the electrode lead-out ends of the reference electrode and the auxiliary electrode extend outward through the soft-package shell respectively.

10. A charging window test method for a four-electrode battery according to any one of claims 7 to 9, characterized in that: The following steps are involved: 1) Under the preset temperature and different charging rate conditions, monitor the potential difference between the auxiliary electrode and the reference electrode to obtain the potential data under different charge states; 2) Establishing a relationship between the state of charge, test temperature, charging rate and lithium deposition based on the potential data, and determining the lithium deposition charging window.

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