Lithium-supplementing positive pole piece, cylindrical battery cell and battery

Abstract

The utility model provides a lithium-supplementing positive pole piece, a cylindrical battery cell and a battery. The lithium-supplementing positive pole piece comprises a positive pole current collector, a positive pole layer and two lithium-supplementing layers are arranged on the surface of the positive pole current collector, and the two lithium-supplementing layers are located on the two sides of the positive pole layer respectively and close to a blank area, in the width direction, of the positive pole current collector. Compared with the prior art, the lithium supplementing layers of the lithium supplementing positive pole piece provided by the utility model are distributed on the two sides of the positive pole layer and are close to the blank area of the positive pole current collector along the width direction, so that the performances of the lithium supplementing layers and the positive pole layer can be exerted to the maximum extent; meanwhile, the lithium supplementing layer is distributed on the edge, and gas generated after the lithium supplementing layer is separated can be quickly charged and discharged from the lithium supplementing layer, so that purple spots are prevented from being generated during formation and capacity grading.

Description

Technical Field

[0001] This utility model relates to the field of lithium-ion battery technology, and in particular to a lithium-replenishing positive electrode, a cylindrical cell, and a battery. Background Technology

[0002] With the increasing demand for electric vehicles and large-scale energy storage, next-generation power batteries and energy storage batteries face higher requirements for energy density and cycle life. To address this challenge, lithium replenishment technology is considered an effective solution.

[0003] Lithium replenishment technologies mainly include various methods such as anode electrochemical methods, anode chemical methods, and cathode pre-lithiation methods. Among them, cathode pre-lithiation methods have attracted much attention from researchers in recent years due to their simple process, perfect compatibility with existing battery processes, and ability to effectively improve the energy density of the entire battery. Cathode pre-lithiation methods involve adding a pre-lithiation reagent to the cathode material. During the first charge, the pre-lithiation reagent, which has a high lithium-ion content, irreversibly releases active lithium ions to compensate for the initial irreversible lithium consumption of the anode material, thereby improving the battery's energy density. The pre-lithiation reagent can be blended with the cathode material using existing production processes, allowing for precise control of the replenishment capacity based on the added content. This high level of safety makes it highly suitable for large-scale commercial applications.

[0004] A common cathode lithium replenishment method involves blending the lithium replenishing agent with the cathode material during the slurry mixing stage. This utilizes the excess lithium ions released during the initial charging of the lithium replenishing agent to compensate for the loss of active lithium ions in the cell, thereby improving the cell's energy density and cycle life. However, current cathode lithium replenishment technology still faces some challenges. Most cathode lithium replenishing agents, such as Li5FeO4 and Li2NiO2, suffer from poor conductivity. They must be combined with a relatively high proportion of conductive agents to effectively release their contained lithium ions. Simply blending the cathode lithium replenishing agent with the cathode active material often results in a lower lithium ion release capacity than the theoretical capacity, severely impacting the improvement of battery energy density. In addition, lithium replenishing agents such as Li5FeO4 and Li2NiO2 generate oxygen during the lithium replenishment process, which leads to severe purple spots at the interface after formation and capacity testing, further affecting the battery performance. At the same time, the low conductivity of the residual low-conductivity substances after lithium replenishment reagents delithiize increases the resistance of the positive electrode sheet, deteriorates the specific capacity of the positive electrode active material itself, and makes the improvement of the energy density of the cell unsatisfactory. Utility Model Content

[0005] In view of this, the present invention proposes a lithium-replenishing positive electrode sheet, a cylindrical cell, and a battery to maximize the performance of the lithium replenishing agent and the positive electrode active material, and to avoid the capacity utilization of the lithium replenishing agent and the positive electrode active material being degraded due to the poor conductivity of the lithium replenishing agent.

[0006] In a first aspect, the present invention provides a lithium-supplemented positive electrode sheet, comprising a positive current collector, wherein a positive electrode layer and a lithium-supplemented layer are disposed on the surface of the positive current collector, characterized in that: the lithium-supplemented layer comprises two layers, respectively located on both sides of the positive electrode layer and close to the blank area along the width direction of the positive current collector.

[0007] Based on the above technical solutions, preferably, the raw materials constituting the positive electrode layer include: positive electrode active material, conductive agent and binder.

[0008] Based on the above technical solutions, preferably, the thickness of the positive electrode layer is 40-120 μm.

[0009] Based on the above technical solutions, preferably, the thickness of the lithium replenishment layer at both ends is 4% to 10% thinner than the thickness of the positive electrode layer.

[0010] More preferably, the thicknesses of the lithium replenishment layers at both ends are equal or unequal.

[0011] Based on the above technical solutions, preferably, the width of the lithium replenishment layers at both ends is 1 to 8 mm.

[0012] More preferably, the widths of the lithium replenishment layers at both ends are equal or unequal.

[0013] Based on the above technical solutions, preferably, the raw materials of the lithium replenishment layer include: lithium replenishing agent, conductive agent and binder.

[0014] Secondly, this utility model relates to a cylindrical battery cell, comprising a positive electrode, a negative electrode, and a separator spaced between the positive and negative electrodes. The positive and negative electrodes and the separator are wound together, and the positive electrode is the aforementioned lithium-filled positive electrode.

[0015] Based on the above technical solutions, preferably, the negative electrode sheet includes a negative electrode layer and a negative electrode current collector.

[0016] Based on the above technical solutions, preferably, the cylindrical battery cell, from the inside out, consists of: a positive current collector, a positive electrode layer, a separator, a negative electrode layer, and a negative current collector.

[0017] Based on the above technical solutions, preferably, the widths of the lithium replenishment layers on both sides of the positive electrode layer are equal or unequal in value.

[0018] Thirdly, this utility model relates to a battery, which includes the aforementioned cylindrical cell.

[0019] Compared with the prior art, the lithium replenishment layer of this invention is distributed on both sides of the positive electrode layer. This method allows the active material of the positive electrode layer and the lithium replenishment agent of the lithium replenishment layer to be homogenized separately, thereby maximizing the performance of the lithium replenishment agent and the positive electrode active material and avoiding the deterioration of the capacity performance of the lithium replenishment agent and the positive electrode active material due to the poor conductivity of the lithium replenishment agent. At the same time, because the lithium replenishment layer is distributed at the edge, the gas generated after the lithium replenishment layer is desorbed can be quickly discharged from the lithium replenishment layer, avoiding the formation and capacity separation of purple spots. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A cross-sectional view of the positive electrode sheet provided by this utility model;

[0022] Figure 2 A cross-sectional view of the cylindrical battery cell provided by this utility model;

[0023] In the figure, 1 is the positive electrode, 11 is the positive current collector, 12 is the positive electrode layer, and 13 is the lithium replenishment layer; 2 is the separator; 3 is the negative electrode, 31 is the negative electrode layer, and 32 is the negative current collector. Detailed Implementation

[0024] The technical solutions of this utility model will be clearly and completely described below with reference to the embodiments of this utility model. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this utility model.

[0025] like Figure 1 As shown, the lithium-supplemented positive electrode 1 of this invention includes a positive electrode layer 12 and a lithium-supplemented layer 13 disposed on the surface of a positive electrode current collector 11. The lithium-supplemented layer 13 has two layers, located on both sides of the positive electrode layer 12 and close to the blank area along the width direction of the positive electrode current collector 11. The side of the lithium-supplemented layer 13 closest to the positive electrode layer 12 is the longer side, and both the lithium-supplemented layer 13 and the positive electrode layer 12 have their wider sides close to the positive electrode current collector 11.

[0026] In this invention, the positive electrode layer 12 is composed of a positive electrode active material, a conductive agent, and a binder. Preferably, the positive electrode active material includes, but is not limited to, LiFePO4; the conductive agent includes, but is not limited to, carbon black; and the binder includes, but is not limited to, polytetrafluoroethylene (PVDF).

[0027] In the positive electrode layer 12 of this invention, the mass ratio of the positive electrode active material, the conductive agent and the binder is 97:2:1.

[0028] In this invention, the width (X3 and X5) of each lithium replenishment layer 13 is independently 1 to 8 mm, and the width of each lithium replenishment layer 13 can be equal or unequal in value; the thickness (X1) of the positive electrode layer 12 is 40 to 120 μm, and the thickness (X2 and X4) of each lithium replenishment layer 13 is independently 4% to 10% thinner than the thickness (X1) of the positive electrode layer 12, and the thickness of each lithium replenishment layer can be equal or unequal in value.

[0029] In this invention, the lithium replenishing layer 13 is composed of a lithium replenishing agent, a conductive agent, and a binder. Preferably, the lithium replenishing agent is selected from Li5FeO4 and / or Li2NiO2, the conductive agent is selected from carbon black, and the binder is selected from polytetrafluoroethylene (PVDF).

[0030] The lithium replenishing layer 13 of this invention comprises, by mass percentage: 96% lithium replenishing agent, 2.5% conductive agent, and 1.5% binder.

[0031] In this invention, the lithium-supplemented positive electrode sheet is prepared by separately homogenizing the positive electrode active material and the lithium-supplementing agent, matching different formulations according to their respective characteristics, and then coating the positive electrode slurry and the lithium-supplementing slurry onto the current collector. The lithium-supplementing layer is distributed on both sides of the positive electrode layer. After baking, it is assembled with the negative electrode separator to form a battery. This method allows the active material of the positive electrode layer and the lithium-supplementing agent of the lithium-supplementing layer to be homogenized separately, thereby maximizing the performance of the lithium-supplementing agent and the positive electrode active material, and avoiding the deterioration of the capacity performance of the lithium-supplementing agent and the positive electrode active material due to the poor conductivity of the lithium-supplementing agent. At the same time, because the lithium-supplementing layer is distributed at the edge, the gas generated after the lithium-supplementing layer is desorbed can be quickly discharged from the lithium-supplementing layer, avoiding purple spots during formation and capacity testing.

[0032] like Figure 2 As shown, the cylindrical battery cell of this invention includes a positive electrode 1, a negative electrode 3, and a separator 2 spaced between the positive and negative electrodes, wherein the positive electrode 1 is the aforementioned lithium-filled positive electrode 1. The cylindrical battery cell, from the inside out, consists of: a positive current collector 11, a positive electrode layer 12, a separator 2, a negative electrode layer 31, and a negative current collector 32. Lithium-filled layers 13 are disposed on both sides of the positive electrode layer 12, and are close to the blank area along the width direction of the positive current collector 11. The widths of the lithium-filled layers 13 at both ends may be equal or unequal in numerical value.

[0033] In this invention, the negative electrode layer 31 is composed of a negative electrode active material, a conductive agent, and a binder; as a preferred embodiment of this invention, the negative electrode active material includes, but is not limited to, graphite, the conductive agent includes, but is not limited to, conductive carbon black Super-P, and the binder includes, but is not limited to, styrene-butadiene rubber and / or sodium carboxymethyl cellulose.

[0034] In the negative electrode layer 31 of this invention, the mass ratio of negative electrode active material, conductive agent and binder is 96.5:1:2.5; more preferably, the binder is a mixture of styrene-butadiene rubber and sodium carboxymethyl cellulose, and the mass ratio of styrene-butadiene rubber to sodium carboxymethyl cellulose is 1.2:1.3.

[0035] Example 1

[0036] Preparation of positive electrode 1

[0037] Under stirring conditions, positive electrode active material LiFePO4, conductive carbon black Super-P, and binder PVDF are dissolved in an N-methylpyrrolidone (NMP) solvent system at a mass ratio of 97:2:1 to obtain a positive electrode slurry. Simultaneously, according to mass percentage, 96% of lithium supplementer (Li5FeO4 or Li2NiO2), 2.5% of conductive carbon black Super-P, and 1.5% of binder PVDF are added to the NMP solvent system and thoroughly stirred using a vacuum mixer to obtain a lithium supplement slurry. The positive electrode slurry and the lithium supplement slurry are simultaneously coated on both surfaces of a 12μm thick Al foil substrate, and then dried to form a positive electrode layer 12 and a lithium supplement layer 13. The thickness (X1) of the positive electrode layer 12 is 100 μm, and the thickness (X2 = X4) of the lithium replenishment layer 13 is 90 μm; the width (H1) of the positive electrode layer 12 is 82 mm; the width (X3 = X5) of the lithium replenishment layer 13 is 1 mm; then, the positive electrode sheet 1 is obtained by drying, cold pressing, slitting and cutting in sequence.

[0038] Preparation of negative electrode 3

[0039] The negative electrode active material - graphite, conductive agent, binder - styrene-butadiene rubber and - sodium carboxymethyl cellulose were dissolved in deionized water in a weight ratio of 96.5:1:1.2:1.3, and the mixture was stirred and mixed thoroughly to obtain a slurry containing the first negative electrode active material.

[0040] The negative electrode slurry containing the negative electrode active material is coated onto the surface of a 6μm thick Cu foil of the negative electrode current collector using an extrusion coating machine. After drying, cold pressing and cutting, the negative electrode sheet 3 with a double active material layer is obtained.

[0041] Preparation of electrolyte

[0042] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0043] Preparation of diaphragm

[0044] The diaphragm substrate is made of 9μm thick polyethylene (PE). A 2μm alumina ceramic layer is coated on each side of the diaphragm substrate. Finally, 0.5mg of polyvinylidene fluoride (PVDF) binder is coated on each side of the ceramic layer and then dried.

[0045] Preparation of cylindrical battery cells

[0046] The positive electrode 1, separator 2, and negative electrode 3 are stacked in sequence, with the separator 2 positioned between the positive and negative electrode 3 to provide isolation. The cells are then wound to obtain a bare cell. The qualified bare cell is installed into a cylindrical shell, and the tabs are welded to the top cover current collector. After drying, electrolyte is injected. The battery undergoes a series of processes including settling, formation, aging, and sealing nail welding to obtain a lithium-ion cylindrical battery with a diameter of 46 mm and a height of 95 mm.

[0047] Example 2

[0048] The difference between Example 2 and Example 1 is that the thickness of the positive electrode layer and the thickness and width of the lithium replenishment layer are different; the rest are the same as in Example 1.

[0049] The thickness (X1) of the positive electrode layer 12 is 40 μm, and the thicknesses (X2 and X4) of the lithium replenishment layer 13 are different, with X2 being 34.8 μm and X4 being 38 μm; the width (H1) of the positive electrode layer 12 is 82 mm; the widths (X3 and X5) of the lithium replenishment layer 13 are different, with X3 being 6 mm and X5 being 8 mm.

[0050] Example 3

[0051] The difference between Example 3 and Example 1 is that the thickness of the positive electrode layer and the thickness and width of the lithium replenishment layer are different, while the rest are the same as in Example 1.

[0052] The thickness (X1) of the positive electrode layer 12 is 120 μm, and the thickness (X2 = X4) of the lithium replenishment layer 13 is 110 mm; the width (H1) of the positive electrode layer 12 is 82 mm; and the width (X3 = X5) of the lithium replenishment layer 13 is 5 mm.

[0053] Comparative Example 1

[0054] Preparation of positive electrode plate 1:

[0055] The positive electrode active material LiFePO4, lithium supplement (Li5FeO4, Li2NiO2), conductive carbon black Super-P, and binder PVDF were mixed in an NMP solvent system at a mass ratio of 95:2:2:1 and thoroughly stirred using a vacuum mixer to obtain a positive electrode slurry. The positive electrode slurry was then continuously coated onto both surfaces of a 12μm thick Al foil substrate. The substrate was then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet 1.

[0056] Preparation of negative electrode plate 3:

[0057] The negative electrode active material - graphite, conductive agent, binder - styrene-butadiene rubber and - sodium carboxymethyl cellulose were dissolved in deionized water in a mass ratio of 96.5:1:1.2:1.3, and the mixture was stirred and mixed thoroughly to obtain a slurry containing the first negative electrode active material.

[0058] The thermally conductive material 1-aluminum nitride, conductive carbon black, binder styrene-butadiene rubber and sodium carboxymethyl cellulose were dissolved in deionized water in a weight ratio of 80:17:1.6:1.4, and the mixture was stirred and mixed thoroughly to obtain the thermally conductive slurry containing the above.

[0059] The negative electrode slurry containing negative electrode active material and the thermal conductive slurry are coated onto the surface of the negative electrode current collector 6μm Cu foil using a specially designed extrusion coating machine. After drying, cold pressing and cutting, the negative electrode sheet 3 with a double active material layer is obtained.

[0060] Electrolyte preparation:

[0061] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0062] Preparation of diaphragm 2:

[0063] The substrate of diaphragm 2 is 9μm thick polyethylene (PE). A 2μm thick alumina ceramic layer is coated on both sides of the substrate of diaphragm 2. Finally, 0.5mg of polyvinylidene fluoride (PVDF) binder is coated on both sides of the ceramic layer and then dried.

[0064] Fabrication of cylindrical batteries:

[0065] The positive electrode 1, separator 2, and negative electrode 3 are stacked in sequence, with separator 2 positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The qualified bare cell is installed into a cylindrical shell, and the tabs are welded to the top cover current collector. After drying, electrolyte is injected. The battery undergoes a series of processes including settling, formation, aging, and sealing nail welding to obtain a lithium-ion cylindrical battery with a diameter of 46 mm and a height of 95 mm.

[0066] Table 1 Performance tests of batteries prepared in the examples and comparative examples

[0067] Capacity / Ah Capacity after 1000 cycles / Ah Example 1 33.5 29.1 Example 2 33 28.7 Example 3 33.3 28.9 Comparative Example 1 32 28.1

[0068] Table 1 shows that the capacities of Examples 1-3 are 33 Ah to 33.5 Ah, while the capacity of Comparative Example 1 is 32 Ah. The capacities of the Examples are 1 to 1.5 Ah higher than those of the Comparative Example. The average capacity of Examples 1-3 after 1000 cycles is 28.9 Ah, while that of Comparative Example 1 after 1000 cycles is 28.1 Ah. Therefore, the cylindrical cell prepared by this invention can maximize the performance of the lithium replenishing agent and the positive electrode active material, avoiding the deterioration of the capacity performance of the lithium replenishing agent and the positive electrode active material due to the poor conductivity of the lithium replenishing agent. At the same time, since the lithium replenishing layer 13 is distributed at both ends of the positive electrode layer 12, the gas generated after the lithium replenishing layer 13 is removed can be quickly discharged from the lithium replenishing layer 13, avoiding the problem of purple spots during formation and capacity testing.

[0069] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A lithium-supplemented positive electrode sheet, comprising a positive current collector (11), wherein a positive electrode layer (12) and a lithium-supplemented layer (13) are disposed on the surface of the positive current collector (11), characterized in that: The lithium replenishment layer (13) has two layers, located on both sides of the positive electrode layer (12) and close to the blank area along the width direction of the positive electrode current collector (11).

2. The lithium-added positive electrode sheet as described in claim 1, characterized in that, The thickness of the positive electrode layer (12) is 40-120 μm.

3. The lithium-added positive electrode sheet as described in claim 2, characterized in that, The thickness of the lithium replenishment layer (13) is 4% to 10% thinner than the thickness of the positive electrode layer (12).

4. The lithium-added positive electrode sheet as described in claim 3, characterized in that, The width of each of the lithium replenishment layers (13) at both ends is 1 to 8 mm, and the length is the same as that of the positive electrode layer (12).

5. A cylindrical battery cell, comprising a positive electrode (1), a negative electrode (3), and a separator (2) spaced between the positive electrode (1) and the negative electrode (3), wherein the positive electrode (1), the negative electrode (3), and the separator (2) are wound structures, characterized in that, The positive electrode (1) is selected from the lithium-filled positive electrode as described in any one of claims 1 to 4.

6. The cylindrical battery cell as described in claim 5, characterized in that, The negative electrode sheet (3) includes a negative electrode layer (31) and a negative electrode current collector (32).

7. The cylindrical battery cell as described in claim 6, characterized in that, The cylindrical battery cell, from the inside out, consists of: a positive current collector (11), a positive electrode layer (12), a separator (2), a negative electrode layer (31), and a negative current collector (32).

8. The cylindrical battery cell as described in claim 7, characterized in that, The widths of the lithium replenishment layers (13) on both sides of the positive electrode layer (12) are numerically equal or unequal.

9. A battery, characterized in that, The battery comprises a cylindrical cell as described in any one of claims 5 to 7.

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