Electrolyte injection device, and electrolyte injection method for battery cells

Abstract

The present application provides an electrolyte injection device, and an electrolyte injection method for battery cells. The electrolyte injection device comprises: a pressing rod configured to be capable of moving towards a battery cell; and an injection mechanism having one end connected to the pressing rod and the other end provided with a pressing portion, wherein the pressing portion can be used for driving a sealing element, so that the sealing element is staggered from an electrolyte injection hole.

Description

Liquid injection device and liquid injection method for battery cell

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 2, 2023, with application number 202311455644.5. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a liquid injection device and a liquid injection method for a battery cell. Background Art

[0003] A battery pack includes multiple battery cells, each of which includes a shell, a top cover assembly, a negative electrode, a positive electrode, a diaphragm and an electrolyte. An injection hole is provided on the top cover assembly, and an injection device injects electrolyte into the interior of the battery cell through the injection hole. After the injection is completed, the injection hole is sealed by a sealing gasket and a sealing rubber particle. The electrolyte in the battery cell usually needs to be injected in multiple times or some battery packs are configured so that the electrolyte is replenishable. In the related art, removing the sealing gasket and sealing rubber particles used to seal the injection hole is often complicated, especially the sealing rubber particles need to be removed with the help of special tools and the operation is difficult, which leads to the problem of difficulty in secondary injection of the battery cell. SUMMARY OF THE INVENTION

[0004] The embodiments of the present application provide a liquid injection device and a liquid injection method for a battery cell, which can improve the technical problem of difficulty in secondary liquid injection of a battery pack.

[0005] In a first aspect, an embodiment of the present application provides a liquid injection device for injecting electrolyte into a battery cell, wherein the battery cell includes a top cover assembly and a liquid injection hole provided on the top cover assembly, the top cover assembly further including a sealing element for covering the liquid injection hole, and the liquid injection device includes:

[0006] a pressure rod, the pressure rod being configured to be movable toward a direction close to the battery cell;

[0007] An injection mechanism, one end of which is connected to a pressure rod, and the other end of which is provided with a pressing portion, which is configured to be inserted into the interior of the injection hole, and the pressing portion can be used to drive the sealing element so that the sealing element is staggered with the injection hole.

[0008] In a second aspect, an embodiment of the present application provides a method for injecting electrolyte into a battery cell using the above-mentioned injection device. The battery cell includes a top cover assembly, the top cover assembly includes an injection hole and a sealing element for sealing the injection hole, and the top cover assembly also includes an elastic mechanism connected to the sealing element. The injection method includes:

[0009] Inserting the injection mechanism of the liquid injection device into the liquid injection hole, and making the injection mechanism abut against one end of the sealing element;

[0010] Pressing the injection mechanism causes the sealing element to move from the first position to the second position, the injection hole opens, and the injection mechanism injects the electrolyte into the interior of the battery cell through the injection hole;

[0011] The injection is stopped, the injection mechanism is removed from the injection hole, and the sealing element is driven by the elastic mechanism to move from the second position to the first position, and the injection hole is closed. Beneficial effects

[0012] The beneficial effects of this application are:

[0013] In an embodiment of the present application, a pressing portion is provided at the end of the injection mechanism of the liquid injection device, the pressing portion of the injection mechanism is inserted into the liquid injection hole of the battery cell, and the sealing element on the top cover assembly is pressed by the pressing portion, so that the sealing element and the liquid injection hole can be staggered. That is, the liquid injection hole can be opened and the electrolyte can be injected into the interior of the battery cell in a simple step by pressing the injection mechanism, which is simple and convenient to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0015] FIG1 is a perspective view of a top cover assembly provided in an embodiment of the present application;

[0016] FIG2 is a cross-sectional view of a top cover assembly provided in an embodiment of the present application;

[0017] FIG3 is a partial enlarged view of FIG2;

[0018] FIG4 is a perspective view of a sealing element provided in an embodiment of the present application;

[0019] FIG5 is a schematic diagram of the three-dimensional structure of the liquid injection device provided in an embodiment of the present application;

[0020] FIG6 is a perspective view of an injection mechanism provided in one embodiment of the present application;

[0021] 7 is a cross-sectional view of a top cover assembly with a sealing element in a first position according to an embodiment of the present application;

[0022] FIG8 is a partial enlarged view of FIG7;

[0023] 9 is a cross-sectional view of a top cover assembly with a sealing element in a second position according to an embodiment of the present application;

[0024] FIG10 is a partial enlarged view of FIG9;

[0025] FIG11 is a perspective view of an injection mechanism provided in yet another embodiment of the present application;

[0026] 12 is a cross-sectional view of a top cover assembly with a sealing element in a first position according to yet another embodiment of the present application;

[0027] FIG13 is a partial enlarged view of FIG12;

[0028] Figure Number:

[0029] 100, battery cell; 10, top cover assembly; 11, upper plastic component; 12, cover plate; 121, outer surface; 122, inner surface; 13, insulating seat; 14, injection hole; 141, first portion; 142, second portion; 143, stepped surface; 15, sealing element; 151, main body; 152, boss portion; 153, first contact surface; 16, elastic mechanism;

[0030] 200, liquid injection device; 20, injection mechanism; 21, sleeve; 211, first chamber; 212, bottom wall; 213, opening; 22, pressing portion; 23, piston; 231, base; 232, bottom end surface; 233, second contact surface; 234, groove; 235, cylindrical portion; 2351, second chamber; 2352, liquid guide hole; 236, columnar portion;

[0031] 50. Base; 51. Support frame; 52. Top frame; 53. Cylinder; 54. Pressure rod; 55. Vacuum system. Modes for Carrying Out the Invention

[0032] In this application, unless otherwise specified, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the device in actual use or working state, specifically the direction of the drawings in the accompanying drawings; while "inside" and "outside" refer to the outline of the device.

[0033] An embodiment of the present application provides a battery pack, and the battery pack is applicable to electrical devices including mobile phones, portable devices, laptops, electric bicycles, electric cars, electric boats, electric toys, electric tools, etc.

[0034] The battery pack includes a box body, and multiple battery cells provided in the above embodiments are arranged in a matrix inside the box body. The multiple battery cells can be arranged in series, or in parallel, or in a mixed connection of series and parallel, so that the battery pack has a capacity and power suitable for use by electrical equipment.

[0035] An embodiment of the present application provides a battery cell, which includes a housing, a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0036] The positive electrode and the negative electrode are the main chemical reaction parts of the battery cell. The electrochemically active substance of the positive electrode usually contains a compound containing lithium, while the negative electrode usually contains carbon material or metal material.

[0037] The separator is an isolation layer located between the positive electrode and the negative electrode in the battery cell, which prevents direct contact between the positive electrode and the negative electrode, thereby preventing short circuits. The separator is usually configured as a specially formed polymer film.

[0038] The electrolyte is usually a solution that can conduct ions, which is used to provide the movement of positive and negative ions and promote the chemical reactions of the battery cell.

[0039] The positive electrode sheet, negative electrode sheet, separator and electrolyte together constitute the core assembly of the battery cell.

[0040] Depending on the electrolyte, the battery cells include lithium-ion batteries, lithium-sulfur batteries, nano-lithium-ion batteries, sodium-ion batteries, or magnesium-ion batteries. Depending on whether the electrolyte in the battery cell is replenishable, the battery cells include but are not limited to lithium-ion secondary batteries and lithium-ion primary batteries.

[0041] The housing typically consists of a shell and a top cover assembly. The shell is made of a metal material with a certain degree of mechanical strength and corrosion resistance. Suitable metal materials include nickel or steel. The shell is used to fix and protect the positive and negative electrodes, separator membrane, and electrolyte inside the battery cell from external physical damage. The shell can be wound into a cylindrical shape or configured as a block.

[0042] The top cover assembly is arranged at the top open end of the shell, and the top cover assembly is used to seal the open end of the battery cell and provide a contact point for the positive electrode of the battery cell or a contact point between the positive electrode and the negative electrode of the battery cell.

[0043] 1 , 2 and 3 , a structure of a top cover assembly 10 of a battery cell 100 is provided in one embodiment of the present application, which is described taking a square battery cell as an example. FIG1 is a three-dimensional view of the top cover assembly 10 , and FIG2 is a cross-sectional view of the top cover assembly 10 .

[0044] The top cover assembly 10 includes an upper plastic member 11 , a cover plate 12 and an insulating seat 13 stacked in sequence from top to bottom.

[0045] The cover plate 12 is the primary support member of the top cover assembly 10. It covers the top opening of the housing and supports other components. The cover plate 12 is made of a metal material with good electrical conductivity and mechanical strength. Suitable metal materials for the cover plate 12 include nickel and copper alloys.

[0046] The cover 12 includes an outer surface 121 and an inner surface 122 that are opposite to each other. The upper plastic component 11 is fixed on the outer surface 121 of the cover 12 , and the insulating seat 13 is fixed on the inner surface 122 of the cover 12 .

[0047] The cover plate 12 is further provided with a liquid injection hole 14 for the liquid injection device 200 to replenish electrolyte into the battery cell 100 . The upper plastic part 11 is fixed to one side of the cover plate 12 , and the liquid injection hole 14 is provided on the other side of the cover plate 12 .

[0048] The top cover assembly 10 also includes a sealing element 15 and an elastic mechanism 16. The sealing element 15 is used to seal a portion of the liquid injection hole 14. One end of the elastic mechanism 16 is connected to the sealing element 15. The sealing element 15 is configured to move in a first direction relative to the cover plate 12 between a first position and a second position. When the sealing element 15 is in the first position, the sealing element 15 can seal the liquid injection hole 14, the battery cell 100 is in a closed state, and the liquid injection device 200 cannot replenish electrolyte into the battery cell 100 through the liquid injection hole 14. When the sealing element 15 is in the second position, the sealing element 15 and the liquid injection hole 14 are offset, and the liquid injection device 200 can replenish electrolyte into the battery cell 100 through the liquid injection hole 14.

[0049] The sealing element 15 is made of a flexible silicone material or an elastic plastic material, so that the sealing element 15 is configured to be easily inserted into the liquid injection hole 14 .

[0050] As shown in Figure 4, the sealing element 15 is roughly in the shape of a cone. The sealing element 15 includes a main body portion 151 with a larger outer diameter and a boss portion 152 with a smaller outer diameter. The main body portion 151 abuts against the inner surface 122 of the cover plate, and the boss portion 152 is inserted into the interior of the injection hole 14, which helps the sealing element 15 to form a stable sealing effect on the injection hole 14.

[0051] The elastic mechanism 16 is connected to the main body 151 and can be configured as a spring or a lantern-shaped elastic member. When the sealing element 15 is in the first position, the elastic mechanism 16 is in a relaxed state, exerting a force on the boss portion 152 of the sealing element, causing the sealing element 15 to move in a first direction and thereby compressing the elastic mechanism 16 in the first direction. When the sealing element 15 is in the second position, the elastic mechanism 16 is in a compressed state, driving the sealing element 15 to move in a direction opposite to the first direction to the first position, thereby sealing the liquid injection hole 14.

[0052] In one embodiment of the present application, the structure of the injection mechanism 20 of the injection device 200 is optimized so that after the injection mechanism 20 is inserted into the injection hole 14, it can drive the sealing element 15 to move from the first position to the second position, thereby fully opening the injection hole 14. That is, by pressing the injection mechanism 20 of the injection device, the injection hole 14 can be opened and the electrolyte can be injected into the interior of the battery cell 100 through the injection hole 14. The operation is simple and convenient, and the injection efficiency is effectively improved.

[0053] Referring to Figure 5, in a specific implementation provided in the present application, the liquid injection device 200 includes a base 50, a support frame 51 and a top frame 52, wherein one end of the support frame 51 is fixed on the base 50, and the other end of the support frame 51 is fixed on the top frame 52, and the support frame 51 and the base 50 are arranged to be vertically connected, and the support frame 51 and the top frame 52 are arranged to be vertically connected.

[0054] The battery cell 100 that needs to be injected with electrolyte is fixed on the base 50 . A plurality of fixing grooves may be provided on the base 50 , and each fixing groove may be used to fix one battery cell 100 .

[0055] The liquid injection device 200 further includes a cylinder 53, which is suspended on the top frame 52. One end of the cylinder 53 is connected to a pressure rod 54, and the end of the pressure rod 54 facing away from the cylinder 53 is connected to the injection mechanism 20.

[0056] The liquid injection device 200 further includes a vacuum system 55 , which is connected to the cylinder 53 .

[0057] When the battery cell 100 needs to be injected with electrolyte, the battery cell 100 is fixed on the base 50, the vacuum system 55 is turned on, the cylinder 53 starts working, the pressure rod 54 connected to the cylinder 53 moves toward the direction close to the battery cell 100, and the injection mechanism 20 is configured to move toward the injection hole 14.

[0058] One end of the injection mechanism 20 is connected to the pressure rod 54, and the other end of the injection mechanism 20 is provided with a pressing portion 22. When the pressure rod 54 moves toward the direction close to the battery cell 100, the pressing portion 22 is configured to be inserted into the interior of the injection hole 14 and the pressing portion 22 can also be used to drive the sealing element 15 to move along the first direction so that the sealing element 15 is staggered with the injection hole 14.

[0059] The injection mechanism 20 includes a sleeve 21, which has a hollow first cavity 211. The top end of the sleeve 21 is configured as an open end, and the bottom end of the sleeve 21 is provided with a bottom wall 212. An opening 213 is provided on the bottom wall 212 of the sleeve. The electrolyte can be injected into the first cavity 211 through the open end and flow out through the opening 213.

[0060] The injection mechanism 20 further includes a piston 23 . A portion of the piston 23 extends inside the sleeve 21 , and another portion of the piston 23 extends to the outside of the sleeve 21 through the opening 213 . The piston 23 is movable relative to the sleeve 21 .

[0061] The piston 23 further includes a base 231 . The base 231 is disposed outside the sleeve 21 . The base 231 is configured as the pressing portion 22 of the injection mechanism 20 .

[0062] The outer diameter of the base 231 is smaller than the outer diameter of the sleeve 21, wherein the outer diameter of the sleeve 21 is larger than the minimum outer diameter of the injection hole 14, and the outer diameter of the base 231 is smaller than the minimum outer diameter of the injection hole 14, so that the base 231 can pass through the injection hole 14, while the sleeve 21 can only partially enter the injection hole 14, or the sleeve 21 can only abut against one end of the injection hole 14.

[0063] The bottom end surface 232 of the base 231 is used to form a stable contact with the top end surface of the sealing element 15, so that the bottom end surface 232 of the base and the top end surface of the sealing element 15 have a basically compatible contour shape. Referring to Figures 3 and 5, the top end of the sealing element 15 is provided with a first contact surface 153, and the bottom end of the base 231 is provided with a second contact surface 233, wherein the first contact surface 153 is configured as a circular plane, wherein the first contact surface 153 is provided on the boss portion 152 of the sealing element, and the second contact surface 233 is provided in the groove 234 of the base 231, and at least a portion of the boss portion 152 can be accommodated in the groove 234, which is conducive to forming a stable contact between the base 231 and the sealing element 15.

[0064] With further reference to Figures 6 to 10 , in one embodiment provided herein, the piston 23 further comprises a cylindrical portion 235 connected to one end of the base 231. The outer diameter of the cylindrical portion 235 is smaller than the outer diameter of the base 231, and the outer diameter of the cylindrical portion 235 is also smaller than the inner diameter of the opening 213. The cylindrical portion 235 can pass through the opening 213 and move axially along the sleeve 21. The cylindrical portion 235 and the base 231 can be integrally formed, or the base 231 can be fixed to one end of the cylindrical portion 235 by a snap connection or a threaded connection.

[0065] Furthermore, the injection hole 14 is configured as a stepped hole. Specifically, the injection hole 14 includes a first part 141 and a second part 142 connected to each other, wherein the inner diameter of the first part 141 is larger than the inner diameter of the second part 142, and a step surface 143 is formed between the first part 141 and the second part 142. The boss portion 152 of the sealing element is inserted into the second part 142, wherein the first part 141 is connected to the outside of the battery cell 100, and the second part 142 is connected to the inside of the battery cell 100, and the boss portion 152 is used to seal the second part 142 and its open end.

[0066] The outer diameter of the sleeve 21 is smaller than the inner diameter of the first portion 141 , while the outer diameter of the sleeve 21 is larger than the inner diameter of the second portion 142 , so that the bottom end surface of the sleeve 21 abuts against the step surface 143 .

[0067] The outer diameter of the cylindrical portion 235 is smaller than the inner diameter of the second portion 142 , so that the cylindrical portion 235 can pass through the liquid injection hole 14 and enter the interior of the battery cell 100 .

[0068] The sleeve 21 is provided with a first cavity 211, and the cylindrical portion 235 is provided with a second cavity 2351. At least a portion of the cylindrical portion 235 is disposed within the first cavity 211. The cylindrical portion 235 is further provided with a plurality of liquid guide holes 2352, which are evenly spaced along the circumference of the cylindrical portion 235. When the cylindrical portion 235 is located within the first cavity 211, the electrolyte stored within the first cavity 211 can flow into the second cavity 2351 through the plurality of liquid guide holes 2352. Furthermore, when a portion of the cylindrical portion 235 enters the interior of the battery cell 100 through the liquid injection hole 14, the electrolyte enters the interior of the battery cell 100 through the plurality of liquid guide holes 2352. The plurality of liquid guide holes 2352 are spaced along the circumference of the cylindrical portion 235, so that the electrolyte enters the interior of the battery cell 100 along the circumference of the cylindrical portion 235.

[0069] Compared with the related art, the electrolyte is injected into the interior of the battery cell 100 through a single injection hole 14. The fluid impact force formed by the electrolyte passing through the single injection hole 14 is relatively large, which will cause impact damage to the core assembly inside the battery cell 100. The electrolyte enters the interior of the battery cell 100 along the circumference of the cylindrical portion 235 through multiple liquid guide holes 2352, which will greatly reduce the impact damage caused by the electrolyte flowing into the interior of the battery cell 100 to the core assembly, and effectively protect the core assembly inside the battery cell.

[0070] Referring to Figures 7 and 8, when the sealing element 15 is in the first position, the pressure rod 54 pushes the injection mechanism 20 to move toward the direction close to the battery cell 100 until the injection mechanism 20 enters the interior of the injection hole 14. Furthermore, the bottom end surface of the sleeve 21 abuts against the step surface 143 inside the injection hole 14, and the piston 23 further enters the interior of the second part 142 of the injection hole. The base 231 located at the bottom of the piston 23 is in contact with the boss portion 152 of the sealing element, and the piston 23 is further pressed. The piston 23 pushes the sealing element 15 to move downward, so that the sealing element 15 further pushes the elastic mechanism 16 to move downward and then compresses the elastic mechanism 16 until the sealing element 15 moves to the second position.

[0071] Referring to Figures 9 and 10, when the sealing element 15 is in the second position, the elastic mechanism 16 is in a compressed state, the sealing element 15 is completely offset from the liquid injection hole 14, a portion of the piston 23 enters the interior of the battery cell 100, a portion of the electrolyte can flow into the interior of the battery cell 100 along the outer wall of the cylindrical portion 235 through the opening 213, and a portion of the electrolyte can enter the second cavity 2351 through multiple liquid guide holes 2352. The electrolyte entering the second cavity 2351 further flows into the interior of the battery cell 100 through multiple liquid guide holes 2352.

[0072] After the injection operation is completed, the injection mechanism 20 is removed from the inside of the injection hole 14 , and the sealing element 15 is driven by the elastic force of the elastic mechanism 16 to move upward until the sealing element 15 seals the injection hole 14 .

[0073] With further reference to Figures 11 to 13 , in yet another embodiment provided herein, an injection mechanism 20 includes a sleeve 21 and a piston 23 movable relative to the sleeve 21. Unlike the aforementioned embodiment, the piston 23 includes a base 231 and a columnar portion 236 connected to one end of the base 231, wherein a portion of the columnar portion 236 is disposed within the sleeve 21, and another portion of the columnar portion 236 extends outside the sleeve 21. The columnar portion 236 and the base 231 may be integrally formed, or the base 231 may be secured to one end of the columnar portion 236 via a snap-fit ​​or threaded connection.

[0074] The outer diameter of the base 231 is greater than the outer diameter of the columnar portion 236 , and the base 231 is configured as the pressing portion 22 of the injection mechanism 20 .

[0075] Different from the above embodiment, when the sealing element 15 is in the second position, the electrolyte can only flow into the interior of the battery cell 100 along the outer wall of the columnar portion 236 through the opening 213 .

[0076] Furthermore, the injection mechanism 20 is also equipped with a sensing device for monitoring the injection rate of the injection mechanism 20 and controlling the injection mechanism 20 to stop injection after the injection time reaches T, where the injection time T = the volume of electrolyte required to be injected into the battery cell / the injection rate of the injection mechanism. By controlling the injection time of the injection mechanism, the volume of the injected electrolyte is precisely controlled to prevent the injected electrolyte from exceeding the storage capacity of the battery cell, thereby causing inaccurate battery cell capacity and affecting the use of the battery cell.

[0077] In one embodiment of the present application, a method for injecting electrolyte into a battery cell is further provided. The battery cell includes a top cover assembly 10. The battery cell 100 uses the above-mentioned injection device 200 to inject electrolyte into the interior of the battery cell 100. The injection method includes:

[0078] Insert the injection mechanism 20 of the injection device 200 into the injection hole 14 and make the injection mechanism 20 abut against one end of the sealing element 15;

[0079] Press the injection mechanism 20, the sealing element 15 moves from the first position to the second position, the injection hole 14 opens, and the injection mechanism 20 injects the electrolyte into the interior of the battery cell through the injection hole 14;

[0080] The injection is stopped, and the injection mechanism 20 is removed from the injection hole 14 . The sealing element 15 is driven by the elastic mechanism 16 to move from the second position to the first position, and the injection hole 14 is closed.

[0081] Furthermore, the injection mechanism 20 is also equipped with a sensing device for monitoring the injection rate of the injection mechanism 20 and controlling the injection mechanism 20 to stop injection after the injection time reaches T, where the injection time T = the volume of electrolyte required to be injected into the battery cell / the injection rate of the injection mechanism. By controlling the injection time of the injection mechanism, the volume of the injected electrolyte is precisely controlled to prevent the injected electrolyte from exceeding the storage capacity of the battery cell, thereby causing inaccurate battery cell capacity and affecting the use of the battery cell.

[0082] The injection mechanism 20 includes a sleeve 21 and a piston 23 that can move relative to the sleeve 21. When the injection mechanism 20 is pressed, before the sealing element 15 moves from the first position to the second position, the sleeve 21 abuts on the top cover assembly 10, and the piston 23 enters the interior of the battery cell through the injection hole 14. An outlet for electrolyte is formed between the sleeve 21 and the piston 23. The electrolyte enters the interior of the injection hole 14 through the outlet and flows into the interior of the battery cell through the injection hole 14, which can effectively improve the introduction efficiency of the electrolyte.

Claims

1. A liquid injection device for injecting electrolyte into a battery cell, wherein the battery cell comprises a top cover assembly and a liquid injection hole provided on the top cover assembly, wherein the top cover assembly further comprises a sealing element for covering the liquid injection hole, and the liquid injection device comprises: A pressure rod, wherein the pressure rod is configured to be movable toward a direction close to the battery cell; An injection mechanism, one end of which is connected to a pressure rod, and the other end of which is provided with a pressing portion, wherein the pressing portion is configured to be inserted into the interior of the injection hole, and the pressing portion can be used to drive the sealing element so that the sealing element is staggered with the injection hole.

2. The liquid injection device according to claim 1, wherein: The injection mechanism includes a sleeve and a piston movable relative to the sleeve, a portion of the piston is located inside the sleeve, and another portion of the piston is located outside the sleeve.

3. The liquid injection device according to claim 2, wherein: The piston includes a base, the base is disposed outside the sleeve, and the base is configured as the pressing portion.

4. The liquid injection device according to claim 3, wherein: A groove is provided at the bottom end of the base, and the groove is used to accommodate a part of the sealing element.

5. The liquid injection device according to claim 2, wherein: The injection mechanism includes a base and a cylindrical portion connected to one end of the base, and the cylindrical portion extends from the inside of the sleeve to the outside of the sleeve.

6. The liquid injection device according to claim 5, wherein: The outer diameter of the base is larger than the outer diameter of the cylindrical portion.

7. The liquid injection device according to claim 5, wherein: The sleeve is provided with a first cavity, the cylindrical portion is provided with a second cavity, and the cylindrical portion is further provided with a plurality of liquid guide holes, and the plurality of liquid guide holes are used to connect the first cavity and the second cavity.

8. The liquid injection device according to claim 7, wherein: The plurality of liquid guide holes are distributed at intervals along the circumference of the cylindrical portion, and the plurality of liquid guide holes are used to guide the electrolyte to be injected into the interior of the battery core along the circumference of the cylindrical portion.

9. The liquid injection device according to claim 2, wherein: The piston includes a base and a columnar portion connected to one end of the base, and the columnar portion extends from the inside of the sleeve to the outside of the sleeve.

10. The liquid injection device according to any one of claims 1 to 9, wherein: The injection mechanism includes a sensing device for monitoring the injection rate of the injection mechanism.

11. A method for injecting electrolyte into a battery cell, wherein the battery cell uses the injection device according to any one of claims 1 to 10 to inject electrolyte into the battery cell, wherein the battery cell comprises a top cover assembly, wherein the top cover assembly comprises an injection hole and a sealing element for sealing the injection hole, wherein the top cover assembly further comprises an elastic mechanism connected to the sealing element, wherein the injection method comprises: Inserting the injection mechanism of the injection device into the injection hole, and making the injection mechanism abut against one end of the sealing element; Pressing the injection mechanism, the sealing element moves from the first position to the second position, the injection hole opens, and the injection mechanism injects the electrolyte into the interior of the battery cell through the injection hole; Stop the injection, remove the injection mechanism from the injection hole, and drive the sealing element from the second position to the first position under the drive of the elastic mechanism, so that the injection hole is closed.

12. The liquid injection method according to claim 11, wherein: The injection mechanism further includes a sensing device, and the sensing device is used to monitor the injection rate of the injection mechanism. The injection method also includes: The injection mechanism stops injecting after injection time T, and the injection time T is equal to the ratio of the capacity of the electrolyte required to be injected into the battery cell to the injection rate of the injection mechanism.

13. The liquid injection method according to claim 11, wherein: The injection mechanism includes a sleeve and a piston movable relative to the sleeve. The injection mechanism is pressed, and before the sealing element moves from the first position to the second position, it also includes: the sleeve abuts against the top cover assembly, and the piston enters the interior of the battery cell through the injection hole.

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