Cylindrical battery

Abstract

The present application relates to the field of lithium battery, and specifically provides a cylindrical battery, aiming at solving the problem that the existing cylindrical battery has serious lithium precipitation phenomenon and the metal lithium and the negative pole ear cannot be effectively electrically connected, resulting in the problem that the initial efficiency of the battery cannot be truly improved. For this purpose, the cylindrical battery of the present application comprises a battery shell, an electric core, a lithium sheet and a lower insulating gasket, the battery shell contains electrolyte; the electric core is arranged in the battery shell, the outermost pole piece of the electric core is a positive pole foil tail; the lithium sheet is arranged in the battery shell and is located below the electric core, the negative pole ear of the electric core and the battery shell are electrically connected with the lithium sheet; the lower insulating gasket is arranged in the battery shell and is located between the electric core and the lithium sheet, and the lower insulating gasket covers the lithium sheet. After lithium ions enter the diaphragm and the surface of the pole piece in the electric core with the electrolyte, due to the potential difference between the lithium sheet and the negative pole, the lithium ions are uniformly embedded on the negative pole sheet to complete the prelithiation of the negative pole.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and specifically provides a cylindrical battery. Background Technology

[0002] Lithium-ion batteries can be mainly divided into three categories based on their casing: soft-pack batteries, aluminum-cased batteries, and cylindrical batteries. Cylindrical batteries consist of cylindrical cells housed in a steel casing. Originally, cylindrical batteries were represented by the 18650 model, where 18 represents a diameter of 18mm and 65 indicates a height of 65mm. With the increasingly widespread use of cylindrical batteries in electric vehicles, the market for models such as 21700 and 4680 is also expanding.

[0003] The initial discharge capacity of a lithium-ion battery is significantly lower than its initial charge capacity. This is because after lithium ions are embedded in the graphite layer during discharge, not all of them are completely extracted during subsequent charging. This is because when lithium ions first embed in graphite, an SEI film forms on the graphite surface. These lithium ions cannot return to the graphite anode, resulting in an initial discharge capacity less than the initial charge capacity, meaning the initial efficiency is less than 100%. Typically, the initial efficiency of a full cell with a graphite anode is between 86% and 92%. Low initial efficiency affects the battery's energy density. Currently, pre-lithiation technology is generally used to improve initial efficiency. Pre-lithiation refers to adding a lithium source to the battery before it begins operation. By replenishing the electrode material with lithium, the lithium ions for the SEI film formed during the initial charge and discharge process are provided by the lithium source, offsetting the irreversible lithium loss caused by the formation of the SEI film, thereby improving the battery's total capacity and energy density.

[0004] Chinese patent (CN111969266A) discloses a cylindrical lithium-ion battery capable of automatic pre-lithiation and its preparation method, specifically, as follows: Figure 1 As shown, the cell 10 has a central hole through which metallic lithium or a lithium-containing alloy is added to the bottom of the battery casing. The metallic lithium or lithium-containing alloy is electrically connected to the negative electrode tab. The lithium block 20 and the negative electrode electrolyte constitute a primary cell. Active lithium is replenished to the graphite through the lithium source in the central hole.

[0005] However, this method has the following problems: 1) The central hole contacts the innermost diaphragm, the innermost diaphragm directly contacts the innermost negative electrode, and then the diaphragm, positive electrode, and negative electrode are arranged outwards in sequence. Because the negative electrode is connected to the lithium block 20, the innermost negative electrode sheet and the lithium block 20 will form a strong electric field. Under the action of the strong electric field, most (more than 90%) of the metallic lithium will be embedded into the innermost negative electrode corresponding to the lithium block 20. Only a small part of the inner side of the negative electrode sheet at the center hole of the innermost ring receives most of the electric field lines, so metallic lithium will be over-embedded and deposited in this area, which will cause serious lithium plating. 2) The innermost negative electrode does not have a corresponding positive electrode sheet and does not participate in the normal electrochemical reaction of the battery. Therefore, this part of the pre-lithiated negative electrode cannot improve the battery's first efficiency. 3) Lithium is connected to the negative electrode tab in the center hole by gravity. However, the weight of lithium required for pre-lithiation is very small, generally only 0.5g-3g. The density of lithium itself is small, specifically 0.534g / cm3, while the density of the electrolyte is about 1.2g / cm3. Metallic lithium floats in the electrolyte. Therefore, relying solely on gravity, there will be problems with the metallic lithium connecting to the negative electrode tab at the bottom.

[0006] Therefore, there is an urgent need in this field for a cylindrical battery to solve the above-mentioned technical problems. Summary of the Invention

[0007] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem that existing cylindrical batteries have serious lithium plating and the inability to effectively conduct electricity between metallic lithium and the negative electrode tab, which makes it impossible to truly improve the battery's initial efficiency.

[0008] In a first aspect, the present invention provides a cylindrical battery comprising:

[0009] A battery casing containing an electrolyte;

[0010] The battery cell is disposed inside the battery casing, and the outermost electrode of the battery cell is a positive electrode foil tail;

[0011] A lithium sheet is disposed inside the battery casing, located below the battery cell, and both the negative electrode tab of the battery cell and the battery casing are electrically connected to the lithium sheet;

[0012] A lower insulating pad is disposed within the battery housing and located between the battery cell and the lithium sheet, the lower insulating pad covering the lithium sheet.

[0013] In the specific embodiment of the cylindrical battery described above, a first central hole is formed on the lithium sheet, and a second central hole is formed on the lower insulating pad. The inner diameter of the first central hole is larger than the inner diameter of the second central hole, and both the first central hole and the second central hole are coaxially arranged with the central hole of the battery cell.

[0014] In the specific embodiment of the cylindrical battery described above, the distance between the edge of the lithium sheet and the edge of the lower insulating pad is greater than a preset value.

[0015] In the specific embodiment of the cylindrical battery described above, the negative electrode tab passes through the first central hole and the second central hole and is fixed to the bottom wall of the battery casing.

[0016] In the specific embodiment of the cylindrical battery described above, the negative electrode tab is welded to the battery casing or bonded together with conductive adhesive.

[0017] In the specific embodiment of the cylindrical battery described above, the lithium sheet is attached to the bottom wall of the battery casing.

[0018] In a specific embodiment of the cylindrical battery described above, the cylindrical battery further includes an upper insulating pad, which is disposed inside the battery casing and covers the top of the battery cell.

[0019] In a specific embodiment of the cylindrical battery described above, the cylindrical battery further includes a cap that covers the top of the battery casing, and the positive electrode tab of the battery cell is electrically connected to the cap.

[0020] In the specific embodiment of the cylindrical battery described above, a through hole is formed on the upper insulating pad, and the positive electrode tab passes through the through hole and is fixed to the inside of the cap.

[0021] In the specific embodiment of the cylindrical battery described above, the positive electrode tab is welded to the cap or bonded together with conductive adhesive.

[0022] With the above technical solution, the lithium sheet of the present invention is located below the lower insulating pad, which is located below the battery cell. Under the weight of the battery cell, the lithium sheet will not float, ensuring that the lithium sheet remains in contact with the battery casing and maintaining good electrical conductivity between the lithium sheet and the negative electrode tab. Since there is no lithium block in the center hole of the battery cell, the innermost negative electrode and the lithium block will not form a strong electric field, preventing most of the lithium ions from being embedded in the innermost negative electrode and avoiding lithium deposition on the innermost negative electrode. The lower insulating pad covers the lithium sheet, preventing the negative electrode from contacting the lithium sheet and preventing the dissolved lithium ions from moving directly to the lower negative electrode, thus avoiding lithium deposition at the bottom of the battery cell. The outermost electrode of the battery cell is wrapped with positive electrode foil, preventing lithium deposition on the outermost edge of the battery cell.

[0023] The lithium sheet is located below the lower insulating pad. Lithium ions dissolved in the electrolyte move upwards from the center hole and periphery of the cell. Then, along with the electrolyte, the lithium ions enter the separator and electrode surface inside the cell. Due to the potential difference between the lithium sheet and the negative electrode, the lithium ions are uniformly embedded in the negative electrode, completing the pre-lithiation of the negative electrode. Because severe lithium plating does not occur, and the lithium ions are uniformly embedded in the negative electrode, an SEI film can be formed on the surface of the negative electrode, completing the pre-lithiation of the battery and improving the battery's initial efficiency. Attached Figure Description

[0024] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0025] Figure 1 This is a schematic diagram of the structure of a cylindrical battery in the prior art;

[0026] Figure 2 This is a schematic diagram of the cylindrical battery structure provided by the present invention;

[0027] Figure 3 This is a schematic diagram of the structure of the lower insulating pad provided by the present invention;

[0028] Figure 4 This is a schematic diagram of the structure of the lithium sheet provided by the present invention;

[0029] Figure 5 This is a schematic diagram of the structure of the lower insulating pad and lithium sheet provided by the present invention.

[0030] 10. Battery cell; 20. Lithium block;

[0031] 1. Battery casing; 2. Battery cell; 21. Negative electrode tab; 22. Positive electrode tab; 23. Positive electrode foil sheath;

[0032] 3. Lithium sheet; 31. First center hole; 4. Lower insulating pad; 41. Second center hole; 5. Upper insulating pad; 6. Cap. Detailed Implementation

[0033] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0034] It should be noted that in the description of this invention, terms such as "upper," "lower," "left," "right," "inner," and "outer," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection, an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0036] To address the problem that existing cylindrical batteries suffer from severe lithium plating and the inability of metallic lithium to effectively conduct electricity with the negative electrode tab, thus failing to truly improve the battery's initial efficiency.

[0037] like Figure 2 As shown, this embodiment discloses a cylindrical battery, which includes a battery casing 1, a battery cell 2, a lithium sheet 3, a lower insulating pad 4, an upper insulating pad 5, and a cap 6.

[0038] The cylindrical battery is cylindrical, and the cell 2 is a cylindrical core with a central hole inside. The battery casing 1 is a cylindrical steel casing, which serves as the negative electrode of the cylindrical battery.

[0039] The outermost electrode of cell 2 is a positive electrode foil tail 23, and a separator is wrapped on the outside of the positive electrode foil. That is, the outermost layer of cell 2 consists of a negative electrode, a separator, a positive electrode, and a separator from the inside to the outside.

[0040] The battery cell 2, lithium sheet 3, and lower insulating pad 4 are all disposed inside the battery casing. The lithium sheet 3 is located at the bottom and is attached to the bottom wall of the battery casing 1. The lower insulating pad 4 is located above the lithium sheet 3, and the battery cell 2 is located above the lower insulating pad 4. That is, the lower insulating pad 4 is located between the lithium sheet 3 and the battery cell 2, covering the lithium sheet 3 and isolating the battery cell 2 and the lithium sheet 3 to prevent them from contacting each other. The battery casing 1 contains electrolyte, and the battery cell 2 is immersed in the electrolyte. The negative electrode tab 21 of the battery cell 2 and the battery casing 1 are both electrically connected to the lithium sheet 3. The lithium sheet 3 and the battery cell 2 do not contact each other; they are electrically connected through the negative electrode tab 21. The lithium sheet 3 is specifically a metallic lithium sheet 3 or a lithium alloy lithium sheet 3.

[0041] The lithium sheet 3 is located below the lower insulating pad 4, which in turn is located below the battery cell 2. Under the weight of the battery cell 2, the lithium sheet 3 will not float, ensuring continuous contact between the lithium sheet 3 and the battery casing 1, and maintaining good electrical conductivity between the lithium sheet 3 and the negative electrode tab 21. Since there is no lithium block inside the central hole of the battery cell 2, the innermost negative electrode and the lithium block will not form a strong electric field, preventing most lithium ions from being embedded in the innermost negative electrode of the battery cell 2, thus avoiding lithium plating. The lower insulating pad 4 covers the lithium sheet 3, preventing contact between the negative electrode of the battery cell 2 and the lithium sheet 3, and preventing the dissolved lithium ions from directly moving to the lower negative electrode, thus avoiding lithium plating at the bottom of the battery cell 2. The outermost electrode of the battery cell 2 is wrapped with positive electrode foil, preventing lithium plating from occurring on the outermost edge of the battery cell 2.

[0042] The lithium sheet 3 is located below the lower insulating pad 4. Lithium ions dissolved in the electrolyte in the lithium sheet 3 move upwards from the center hole and the periphery of the cell 2. Then, the lithium ions enter the separator and electrode surface inside the cell 2 with the electrolyte. Due to the potential difference between the lithium sheet 3 and the negative electrode, the lithium ions are uniformly embedded in the negative electrode to complete the pre-lithiation of the negative electrode. Since severe lithium plating does not occur and the lithium ions are uniformly embedded in the negative electrode, an SEI film can be formed on the surface of the negative electrode, completing the pre-lithiation of the battery and improving the battery's first efficiency.

[0043] Reference Figure 3-5 A first central hole 31 is formed on the lithium sheet 3, and a second central hole 41 is formed on the lower insulating pad 4. The inner diameter of the first central hole 31 is larger than the inner diameter of the second central hole 41. Both the first central hole 31 and the second central hole 41 are coaxially arranged with the central hole of the battery cell 2. The negative electrode tab 21 passes through the first central hole 31 and the second central hole 41 and is fixed to the bottom wall of the battery casing 1. Specifically, the negative electrode tab 21 is welded to the bottom wall of the battery casing 1, specifically spot welded. This not only fixes the negative electrode tab 21 to the bottom wall of the battery casing 1, but also ensures that the negative electrode tab 21 is electrically conductive to the battery casing 1, and there is no poor contact.

[0044] Although welding is chosen in this embodiment, in other embodiments, those skilled in the art can bond the negative electrode tab 21 to the bottom wall of the battery casing 1 with conductive adhesive as needed.

[0045] The distance between the edge of the lithium sheet 3 and the edge of the lower insulating pad 4 is greater than a preset value. Specifically, the distance between the outer edge of the lower insulating pad 4 and the outer edge of the lithium sheet 3 is greater than the preset value, and the distance between the inner edge of the lower insulating pad 4 and the inner edge of the lithium sheet 3 is also greater than the preset value. This arrangement ensures that, even with some error during cylindrical battery assembly, the lithium sheet 3 will not directly contact the negative electrode of the cell 2. In this embodiment, the preset value is preferably 2mm. In other embodiments, those skilled in the art can choose other values ​​as needed, as long as the required lithium amount for pre-lithiation is met and the lithium sheet 3 does not directly contact the cell 2.

[0046] Continue to refer to Figure 2 An upper insulating gasket 5 is placed inside the battery casing 1 and covers the top of the battery cell 2. A cap 6 covers the top of the battery casing 1, and the cap 6 is fixed and sealed to the battery casing 1. An insulating gasket is provided between the cap 6 and the battery casing 1 to ensure that they are not electrically connected and to avoid short circuit between the positive and negative terminals. The positive electrode tab 22 of the battery cell 2 is electrically connected to the cap 6. Specifically, the upper insulating gasket 5 is provided with a through hole, which is coaxial with the center hole of the battery cell 2. The positive electrode tab 22 passes through the through hole and is fixed to the inside of the cap 6. Specifically, it is fixed to the inside of the cap 6 by laser welding, which can both fix the positive electrode tab 22 and make the cap 6 and the positive electrode tab 22 electrically connected.

[0047] Although in this embodiment, the positive electrode tab 22 is welded to the cap 6, in other embodiments, those skilled in the art may choose to connect the positive electrode tab 22 and the cap 6 by means of conductive adhesive.

[0048] After the cylindrical battery is assembled, lithium sheet 3 is gradually dissolved in the electrolyte. Lithium ions dissolved in the electrolyte move upwards from the center hole and periphery of cell 2. Then, the lithium ions enter the separator and electrode surface inside cell 2 along with the electrolyte. Due to the potential difference between lithium sheet 3 and the negative electrode, the lithium ions are uniformly embedded in the negative electrode, completing the pre-lithiation of the negative electrode. Since severe lithium plating does not occur, and the lithium ions are uniformly embedded in the negative electrode, an SEI film can be formed on the surface of the negative electrode, completing the pre-lithiation of the battery and improving its initial efficiency. As the pre-lithiation process continues, after approximately 0.5 to 7 days, lithium sheet 3 is gradually consumed, and the negative electrode gradually completes pre-lithiation.

[0049] Example 1

[0050] The cylindrical battery model is 18650, with a designed capacity of 3200mAh. The positive electrode is a ternary 8-series lithium-ion battery; the negative electrode is artificial graphite doped with silicon-oxygen, without any silicates added separately, containing 80% artificial graphite and 20% silicon-oxygen; the separator is a single-layer PE-coated ceramic. The positive electrode width is 57mm, the negative electrode width is 59mm, and the separator width is 61.5mm. The outer diameter of the lower insulating pad 4 is ΦA = 17.5mm, the inner diameter of the second central hole 41 is ΦB = 4mm, and the thickness is 0.15mm; the outer diameter of the lithium sheet 3 is ΦC = 15mm, the inner diameter of the first central hole 31 is ΦD = 6mm, and the thickness is 0.12mm.

[0051] The outermost ring of cell 2 is the positive electrode foil tail 23, that is, the outermost ring of cell 2 consists of negative electrode sheet, separator, positive electrode foil, and separator in sequence. After cell 2 is manufactured, the lower insulating pad 4 is placed at the center of the bottom of cell 2, and the second center hole 41 of the lower insulating pad 4 corresponds to the center hole of cell 2. Then, the lithium sheet 3 is placed at the center of the lower insulating pad 4, and then the negative electrode tab 21 is bent to fix the lithium sheet 3 and the lower pad. After bending, the negative electrode tab 21 will correspond to the center hole of cell 2. Cell 2 is installed into battery casing 1, and the rolling groove of battery casing 1, spot welding of negative electrode tab 21 and bottom of battery casing 1 are completed in sequence. Then, the upper insulating pad 5 is placed on top of cell 2, and the positive electrode tab 22 passes through the through hole of the insulating pad. Then, cell 2 is baked, liquid is injected, positive electrode tab 22 is bent and laser welded to battery cap 6, and battery is sealed. The battery was then left to stand for two days to allow the electrolyte to fully wet the cell 2. Simultaneously, lithium from the lithium sheet 3 continuously dissolved into the electrolyte. Due to the potential difference between the lithium sheet 3 and the primary cell, lithium was uniformly embedded on the surface of the negative electrode, completing the pre-lithiation of the negative electrode. Once the lithium sheet 3 was completely consumed, the battery's positive and negative electrode voltages were 2.5V-3.3V. Formation, capacity testing, and self-discharge testing were then performed, thus completing the fabrication of the pre-lithiated 18650 battery in Example 1.

[0052] Comparative Example 1

[0053] The cylindrical battery model is 18650, with a designed capacity of 3200mAh. The positive electrode is a ternary 8-series lithium-ion battery; the negative electrode is artificial graphite doped with silicon-oxygen, without any silicates added separately, consisting of 80% artificial graphite and 20% silicon-oxygen; the separator is a single-layer PE-coated ceramic layer. The positive electrode width is 57mm, the negative electrode width is 59mm, and the separator width is 61.5mm. The outer diameter of the lower insulating pad is ΦA = 17.5mm, the inner diameter of the center hole of the lower insulating pad is ΦB = 4mm, and the thickness is 0.15mm; there is no lithium sheet.

[0054] The outermost ring of the battery cell has a negative electrode tail structure, meaning the outermost ring consists of the negative electrode sheet and the separator. After the battery cell is manufactured, the lower insulating pad is placed at the center of the bottom of the battery cell, with the center hole of the lower insulating pad corresponding to the center hole of the battery cell. Then, the negative electrode tab is bent to fix the lithium sheet and the lower pad, and after bending, the negative electrode tab will correspond to the center hole of the battery cell. The battery cell is then installed into the battery casing, and the battery casing groove is completed in sequence, followed by spot welding of the negative electrode tab and the bottom of the battery casing. Next, the upper insulating pad is placed on top of the battery cell, and the positive electrode tab passes through the through hole of the insulating pad. Then, the battery cell is baked, electrolyte is injected, the positive electrode tab is bent and laser-welded to the battery cap, and the battery is sealed. The battery is then left to stand for 2 days to allow the electrolyte to fully wet the battery cell. At this time, the positive and negative electrode voltages of the battery are below 0.1V. Then, formation, capacity testing, and self-discharge testing are performed, thus completing the manufacture of the 18650 battery of Comparative Example 1.

[0055] Comparative Example 2

[0056] The cylindrical battery model is 18650, with a designed capacity of 3200mAh. The positive electrode is a ternary 8-series lithium-ion battery; the negative electrode is artificial graphite doped with silicon-oxygen, without any silicates added separately, containing 80% artificial graphite and 20% silicon-oxygen; the separator is a single-layer PE-coated ceramic. The positive electrode width is 57mm, the negative electrode width is 59mm, and the separator width is 61.5mm. The outer diameter of the lower insulating pad is ΦA = 17.5mm, the inner diameter of the center hole of the lower insulating pad is ΦB = 4mm, and the thickness is 0.15mm; the lithium block is a cylinder with a diameter of 3mm and a height of 2.15mm, with the same weight and volume as the lithium sheet in Example 1.

[0057] The outermost ring of the battery cell has a negative electrode tail structure, meaning the outermost ring consists of the negative electrode sheet and the separator. After the battery cell is manufactured, the lower insulating pad is first placed at the center of the bottom of the battery cell, with the center hole of the lower insulating pad corresponding to the center hole of the battery cell. Then, the negative electrode tab is bent to fix the lithium sheet and the lower pad, and after bending, the negative electrode tab will correspond to the center hole of the battery cell. The battery cell is installed into the battery casing, and then the cylindrical lithium block is installed into the center hole and pushed to the bottom of the center hole to contact the negative electrode tab. Then, the battery casing is grooved, and the negative electrode tab and the bottom of the battery casing are spot welded. Then, the upper insulating pad is placed on top of the battery cell, and the positive electrode tab passes through the through hole of the insulating pad. Then, the battery cell is baked, liquid is injected, the positive electrode tab is bent and laser welded to the battery cap, and the battery is sealed. The battery was then left to stand for 2 days to allow the electrolyte to fully wet the cell, and the negative electrode was pre-lithiated. At this time, the positive and negative electrode voltages of the battery were below 0.1V. Then, the formation, capacity and self-discharge tests were performed, thus completing the production of the 18650 battery of Comparative Example 2.

[0058] Comparative Example 3

[0059] The cylindrical battery model is 18650, with a designed capacity of 3200mAh. The positive electrode is a ternary 8-series lithium-ion battery; the negative electrode is artificial graphite doped with silicon-oxygen, without any silicates added separately, containing 80% artificial graphite and 20% silicon-oxygen; the separator is a single-layer PE-coated ceramic. The positive electrode width is 57mm, the negative electrode width is 59mm, and the separator width is 61.5mm. The outer diameter of the lower insulating pad is ΦA = 17.5mm, the inner diameter of the center hole of the lower insulating pad is ΦB = 4mm, and the thickness is 0.15mm; the lithium block is a cylinder with a diameter of 3mm and a height of 2.15mm, with the same weight and volume as the lithium sheet in Example 1.

[0060] The outermost ring of the battery cell has a negative electrode tail structure, meaning the outermost ring of the battery cell consists of the negative electrode sheet and the separator in sequence. After the battery cell is manufactured, the lower insulating pad is first placed at the center of the bottom of the battery cell, with the center hole of the lower insulating pad corresponding to the center hole of the battery cell. Then, the negative electrode tab is bent to fix the lithium sheet and the lower pad, and after bending, the negative electrode tab will correspond to the center hole of the battery cell.

[0061] The battery cell is installed into the battery casing, and then a cylindrical lithium block is inserted into the central hole and pushed to the bottom of the central hole to contact the negative electrode tab. A central pin is then inserted into the central hole to ensure that the lithium block remains on the surface after being immersed in the electrolyte and maintains contact with the negative electrode tab. Next, the battery casing is grooved, and the negative electrode tab and the bottom of the battery casing are spot-welded. The battery is then left to stand for 2 days to allow the electrolyte to fully wet the battery cell, and the negative electrode is pre-lithiated. At this point, the positive and negative electrode voltages are below 0.2V. Then, formation, capacity testing, and self-discharge testing are performed, thus completing the fabrication of the 18650 battery for Comparative Example 3.

[0062] The test included the first-efficiency, average capacity, and cycle data of the 18650 batteries in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, as well as the disassembly interface.

[0063] The data comparison table is as follows:

[0064] As can be seen from the table above, in Example 1, the voltage of the battery reached 3.125V after immersion. At this voltage, the negative electrode has formed an SEI film and some lithium is still intercalated. All lithium sheets 3 are consumed, the initial efficiency and capacity are significantly improved, the number of cycles is increased, and there is no lithium plating on the surface of the negative electrode after dissection.

[0065] Comparative Example 1 was not pre-lithiated.

[0066] Comparative Example 2 adopted the pre-lithiation method of Chinese patent CN111969266A. After the battery was immersed, the voltage did not change significantly compared with Comparative Example 1, indicating that the negative electrode was not significantly pre-lithiated. The first efficiency, capacity and cycle number were not significantly improved compared with Comparative Example 1. Disassembly revealed that the lithium block floated at the center hole and was no longer in electrical contact with the negative electrode tab. The lithium block was not significantly consumed and failed to play the role of pre-lithiation.

[0067] Comparative Example 3, based on Comparative Example 2, used a center pin to fix the lithium block to the negative electrode tab, preventing the lithium block from floating and maintaining electrical contact between the lithium block and the negative electrode. After immersion, the battery voltage reached 0.114V, slightly higher than Comparative Example 1; the initial efficiency and capacity also slightly increased compared to Comparative Example 1, but the improvement was not significant; the cycle life decreased considerably. Disassembly revealed that after the lithium block was completely consumed, severe lithium deposition occurred at the center hole of the inner ring of the negative electrode corresponding to the lithium sheet, with lithium dendrites covering the separator and surrounding area of ​​the negative electrode at this location; the battery exhibited a significant short circuit, which is likely the main reason for the poor cycle life.

[0068] In summary, the cylindrical battery used in this invention has a reliable structure, uniform lithium intercalation, and can effectively improve initial efficiency, capacity, and cycle life. It does not produce lithium plating and is a practical and efficient electrochemical pre-lithiation structure.

[0069] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A cylindrical battery, characterized in that, include: Battery casing (1), wherein the battery casing (1) contains electrolyte; The battery cell (2) is disposed inside the battery casing (1), and the outermost electrode of the battery cell (2) is a positive electrode foil tail; A lithium sheet (3) is disposed inside the battery casing (1) and located below the battery cell (2). The negative electrode tab (21) of the battery cell (2) and the battery casing (1) are both electrically connected to the lithium sheet (3). A lower insulating pad (4) is disposed inside the battery housing (1) and located between the battery cell (2) and the lithium sheet (3), the lower insulating pad (4) covering the lithium sheet (3).

2. The cylindrical battery according to claim 1, characterized in that, A first central hole (31) is formed on the lithium sheet (3), and a second central hole (41) is formed on the lower insulating pad (4). The inner diameter of the first central hole (31) is larger than the inner diameter of the second central hole (41). Both the first central hole (31) and the second central hole (41) are coaxially arranged with the central hole of the battery cell (2).

3. The cylindrical battery according to claim 2, characterized in that, The distance between the edge of the lithium sheet (3) and the edge of the lower insulating pad (4) is greater than a preset value.

4. The cylindrical battery according to claim 3, characterized in that, The negative electrode tab (21) passes through the first central hole (31) and the second central hole (41) and is fixed to the bottom wall of the battery casing (1).

5. The cylindrical battery according to claim 4, characterized in that, The negative electrode tab (21) is welded to the battery casing (1) or bonded with conductive adhesive.

6. The cylindrical battery according to any one of claims 1-5, characterized in that, The lithium sheet (3) is attached to the bottom wall of the battery casing (1).

7. The cylindrical battery according to any one of claims 1-5, characterized in that, The cylindrical battery also includes an upper insulating pad (5), which is disposed inside the battery housing (1) and covers the top of the cell (2).

8. The cylindrical battery according to claim 7, characterized in that, The cylindrical battery also includes a cap (6) which covers the top of the battery casing (1), and the positive electrode tab (22) of the cell (2) is electrically connected to the cap (6).

9. The cylindrical battery according to claim 8, characterized in that, A through hole is formed on the upper insulating pad (5), and the positive electrode tab (22) passes through the through hole and is fixed to the inside of the cap (6).

10. The cylindrical battery according to claim 9, characterized in that, The positive electrode tab (22) is welded to the cap (6) or bonded with conductive adhesive.

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