A method for injecting electrolyte into a lithium battery casing.

Abstract

This invention relates to the technical field of lithium battery casing and electrolyte injection methods, and particularly to a method for injecting electrolyte without vacuuming. The battery casing is provided with an injection hole and an vent hole communicating with its internal cavity. The diameter of the injection hole is defined as D1, and the diameter of the vent hole is defined as D2, where D1 = K·D2, D1 = 1.5–8 mm, and K = 3–6. The injection method includes: (S1) pretreatment: drying the battery cell and assembling it with the battery casing; (S2) coordinated positive pressure injection; (S3) gradient pressure holding impregnation; (S4) pressure replenishment, injection, and venting; (S5) welding and sealing. This invention discloses a lithium battery casing and electrolyte injection method that reduces the probability of battery cell damage and improves the injection effect.

Description

Technical Field

[0001] This invention relates to the technical field of lithium battery casing and electrolyte injection methods, and particularly to a method for injecting electrolyte without the need for vacuuming. Background Technology

[0002] Lithium-ion battery electrolyte filling is a crucial step connecting cell assembly and formation processes. Its core requirements are rapid and uniform electrolyte wetting while minimizing residual air bubbles. Current electrolyte filling processes generally rely on vacuum technology, creating a negative pressure environment by extracting gas from inside the battery to aid electrolyte penetration and expel gas from pores. However, this process has significant drawbacks: First, vacuum equipment is costly and energy-intensive, and requires stringent vacuum control precision, increasing production costs. Second, the sudden drop in internal pressure during vacuuming can easily lead to electrode coating detachment and separator shrinkage and deformation, especially damaging thick electrodes and high-density cells. Third, electrolyte is prone to evaporation under vacuum, affecting the accuracy of the filling volume and potentially causing electrolyte composition imbalance due to solvent evaporation, thus reducing battery performance. Fourth, the switching process between vacuuming and electrolyte filling can easily introduce external air, increasing the risk of residual air bubbles.

[0003] Some existing technologies attempt to simplify the vacuuming process, but most simply eliminate the vacuum step without establishing an effective alternative to the venting and wetting drive mechanism. This results in slow electrolyte penetration, difficulty in removing air bubbles, high battery internal resistance, and poor consistency.

[0004] Therefore, there is an urgent need to develop an electrolyte injection method that does not require vacuuming. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a method for injecting electrolyte into a lithium battery casing. This method achieves efficient electrolyte injection through coordinated control of positive pressure and venting, reducing production complexity and cost while ensuring battery performance.

[0006] One of the objectives of this invention is to provide a lithium battery casing, wherein the battery casing is provided with an injection hole and an exhaust hole communicating with its inner cavity, the diameter of the battery casing is defined as D, the diameter of the injection hole is defined as D1, and the diameter of the exhaust hole is defined as D2, wherein D=T·D1, and D1=K·D2, where D1=1.5~8mm, T=0.08~0.12, and K=3~6.

[0007] The second objective of this invention is to provide a method for injecting electrolyte, comprising the following steps: (S1) Pretreatment: After drying the bare cells, they are installed into the battery casing. After the terminal assembly is completed, the battery casing is pre-sealed by laser welding. The liquid injection hole is connected to the positive pressure liquid injection assembly, and the vent hole is connected to the directional vent assembly. (S2) Coordinated positive pressure injection: Control the positive pressure of the injection hole to P1 and control the venting pressure of the venting hole to P2, where P1 = 20~50kPa, P2 ≥ 5kPa, P1-P2 = 30kPa. The first injection is completed in stages. The total amount of electrolyte to be injected is defined as V, and the amount of the first injection is V1, where V1 < V. (S3) Gradient pressure holding impregnation: The impregnation stage is divided into a first stage impregnation and a second stage impregnation. After the first stage impregnation is completed, the pressure holding time is t1. During this stage, the positive pressure of the injection hole is P1' and the venting pressure of the venting hole is P2'. After the second stage impregnation is completed, the pressure holding time is t1. During this stage, the positive pressure of the injection hole is P1'' and the venting pressure of the venting hole is P2''. (S4) Replenishing and venting electrolyte; The amount of electrolyte replenished is V2, where V1+V2=V. When replenishing electrolyte, the positive pressure of the injection hole is P1''' and the venting pressure of the venting hole is P2'''. After the electrolyte replenishment is completed, the positive pressure of the injection hole (101) is maintained, and venting continues. The venting time is t3. (S5) Welding seal: Laser welding seals are used for the injection hole and the vent hole.

[0008] Preferably, in step (S1), the moisture content of the bare cell is 42 ppm when it is transferred into the battery casing.

[0009] Preferably, in step (S2), the positive pressure of the injection hole P1 = 45 kPa and the venting pressure of the venting hole P2 = 15 kPa.

[0010] Preferably, in step (S2), the first electrolyte injection is completed in three stages. In the first stage, the electrolyte flow rate is 18 mL / s and the injection volume is 92% V. In the second stage, the electrolyte flow rate is 8 mL / s and the injection volume is 95% V. In the third stage, the electrolyte flow rate is 4 mL / s and the injection volume is 97-98%. Finally, 2-3% is added to complete the first electrolyte injection.

[0011] Preferably, in step (S3), during the first stage of immersion, the positive pressure of the injection hole P1'=35kPa, the venting pressure of the venting hole P2'=12kPa, the holding temperature is 45℃, and the holding time t1 is 12min; during the second stage of immersion, the positive pressure of the injection hole P''=25kPa, the venting pressure of the venting hole P2''=8kPa, the holding temperature is 48℃, and the holding time t1 is 15min.

[0012] Preferably, in step (S4), the positive pressure P1''' of the injection hole is 15 kPa, the venting pressure P2''' of the venting hole is 6 kPa, the flow rate is 3 mL / s, and after the electrolyte is replenished, the positive pressure of the injection hole is maintained at 8 kPa, and venting is continued for 40 s.

[0013] The present invention has the following technical effects: (1) No need for vacuuming, reducing production costs: saving investment in vacuum equipment and energy consumption, simplifying the production process.

[0014] (2) The risk of cell damage is extremely low: there is no pressure drop process, and with the combination of pre-drying treatment and gradient pressure holding process, the electrode coating peeling rate is ≤0.1%, the diaphragm damage rate is close to 0, and the cell qualification rate is increased to more than 99.7%.

[0015] (3) Excellent wetting efficiency and uniformity: The synergistic effect of positive pressure drive and directional exhaust, combined with the staged flow rate and gradient pressure holding design, increases the electrolyte wetting speed by more than 30% compared with traditional vacuum injection, the wetting uniformity is ≥0.92, and the battery internal resistance is reduced by 10-15%.

[0016] (4) Thorough air bubble retention: Through a three-stage venting mechanism (directional venting during injection, venting during pressure holding and wetting, and continuous venting after replenishment), the air bubble retention rate is ≤0.2%, avoiding capacity decay and safety hazards caused by air bubbles.

[0017] (5) High injection accuracy: High-precision pressure and flow control, injection volume deviation is controlled within ±0.06g, battery capacity consistency is improved by 20%, and cycle life is extended by 15-25%. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the battery casing in this invention; Figure 2 This is a schematic diagram of the liquid injection system in this invention; In the diagram: 100. Battery casing; 101. Injection port; 102. Drain port; 103. Battery cell; 104. Terminals; 200. Liquid injection system; 201. Liquid storage tank; 202. Liquid injection pump; 203. Pressure controller; 204. Flow sensor; 205. Exhaust valve; 206. Gas storage tank. Detailed Implementation

[0019] The principles and features of the present invention are described below with reference to the accompanying drawings and embodiments; the examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0020] Example 1 This embodiment provides a lithium battery casing, as shown in the attached image. Figure 1 As shown, the battery casing 100 is an improvement on the existing battery casing. Specifically, a liquid injection hole 101 and a vent hole 102 communicating with its inner cavity are provided on one end face of the battery casing 100. The liquid injection hole 101 is located at the center of the end face of the battery casing 100, and the vent hole 102 is located at a non-center location of the battery casing 100.

[0021] The diameter of the battery casing is defined as D, the diameter of the injection hole 101 as D1, and the diameter of the vent hole 102 as D2. D = T·D1, D1 = K·D2, T = 0.08–0.12, and K = 3–6. When D1 < 3D2, venting will be too fast, making it difficult to maintain the pressure difference between the injection hole 101 and the vent hole 102. When D1 > 6D2, venting will be obstructed, causing internal pressure buildup and preventing air bubbles from escaping. In this embodiment, the diameter of the battery casing 100 is 46 mm, the height is 120 mm, the diameter of the injection hole 101 is 8 mm, the diameter of the vent hole 102 is 2 mm, and the distance between the center of the injection hole 101 and the center of the vent hole 102 is 20 mm.

[0022] Example 2 This embodiment provides a method for injecting electrolyte, and the schematic diagram of the injection system 200 used in this method is attached. Figure 2 As shown, the battery casing 100 includes an injection branch and an venting branch. The injection branch includes a storage tank 201, an injection pump 202, a pressure controller 203, and a flow sensor 204 connected in sequence. The venting branch includes an venting valve 205 and a gas storage tank 206. The injection branch is connected to the injection port 101 of the battery casing 100, and the venting branch is connected to the venting port 102 of the battery casing 100. The pressure controller 203 is used to control the pressure at the injection point, and the venting valve 205 is used to control the pressure at the venting point. The battery casing 100 in this embodiment is the same as the battery casing 100 described in Embodiment 1.

[0023] The electrolyte injected in this embodiment is ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 18:42:40, with the addition of 1.2 wt% lithium bis(fluorosulfonyl)imide and 0.6 wt% ethylene carbonate. The electrolyte has a viscosity of 2.3 mPa·s and a conductivity of 13.5 mS / cm at 25°C. The battery casing 100 is a 46120 battery casing (with an injection port 101 and a vent port 102). The specific injection steps include: (S1) Pretreatment: The cell 103 is pre-dried at 85℃ for 2.5 hours until the moisture content is reduced to 42ppm. It is then installed into the battery casing 100. After the terminal post 104 is assembled, the battery casing 100 is pre-sealed by laser welding. In a drying room with a dew point ≤-35℃, the injection needle of the liquid injection branch is connected to the injection hole 101 via an interference fit and a fluororubber sealing ring. The venting branch is connected to the venting hole 102 via a conical interference seal structure. The airtightness test result is 5×10⁻⁶. -4 Pa·m³ / s, the initial internal pressure of the battery is standard atmospheric pressure.

[0024] (S2) Coordinated positive pressure injection: Start the positive pressure pump, control the positive pressure of injection port 101 to P1, where P1 = 45 kPa, and control the exhaust pressure of exhaust port 102 to P2, where P2 = 15 kPa. While maintaining a stable driving pressure difference, avoid excessive positive pressure to prevent damage to the cell, shell and sealing structure, and ensure smooth injection of electrolyte and smooth directional exhaust. Complete the first injection in stages. Define the total amount of electrolyte to be injected as V, and the amount of the first injection as V1, where V1 < V. Specifically, complete the first injection in three stages. In the first stage, the electrolyte flow rate is 18 mL / s and the injection volume is 92% V. In the second stage, the electrolyte flow rate is 8 mL / s and the injection volume is 95% V. In the third stage, the electrolyte flow rate is 4 mL / s to complete the first injection.

[0025] (S3) Gradient pressure holding impregnation: The impregnation stage is divided into a first stage impregnation and a second stage impregnation. During the first stage impregnation, the positive pressure of injection hole 101 is P1'=35kPa, the venting pressure of vent hole 102 is P2'=12kPa, the pressure holding temperature is 45℃, and the pressure holding time is t1=12min. During the second stage impregnation, the positive pressure of injection hole 101 is P''=25kPa, the venting pressure of vent hole 102 is P2''=8kPa, the pressure holding temperature is 48℃, and the pressure holding time is t1=15min.

[0026] (S4) Replenishment and venting; The amount of electrolyte replenished is V2, where V1+V2=V. When replenishing electrolyte, the positive pressure of injection hole 101 is P1''', where P1'''=15kPa; the venting pressure of venting hole 102 is P2''', where P2'''=6kPa, and the replenishment flow rate is 3mL / s; After the electrolyte replenishment is completed, maintain the positive pressure of injection hole 101 at 8kPa and continue venting. The venting time is t3, which is 40s.

[0027] (S5) Welding seal: Laser welding seal is used for injection hole 101 and vent hole 102.

[0028] The difference between Example 3 and Example 2 is that the center distance between the injection hole 101 and the vent hole 102 in this example is 32mm.

[0029] Example 4 The difference between Example 4 and Example 3 is that in this example, the pressure holding temperature of the first stage of immersion in the injection step (S3) is 48°C and the pressure holding time is 8 min; the pressure holding temperature of the second stage of immersion is 50°C and the pressure holding time is 10 min.

[0030] Comparative Example 1 Comparative Example 1 also uses a battery casing of model 46120 (with only injection hole 101), vacuumed to -90kPa, injected under negative pressure, allowed to stand and soak, and had no coordinated venting.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 is that the diameter of the liquid injection hole in the battery casing is 4mm.

[0032] Comparative Example 3 The difference between this comparative example and Example 1 is that the diameter of the liquid injection hole in the battery casing is 14 mm.

[0033] Table 1. Test results of Examples 1 to 3 and Comparative Examples 1 to 3 Internal resistance (mΩ) 3.2 3.1 3.0 4.0 3.8 4.2 Liquid injection deviation (g) ±0.08 ±0.07 ±0.08 ±0.35 ±0.22 ±0.29 Immersion time (min) 28 26 24 45 36 52 Cycle life (times) 1400 1450 1500 1150 1200 1050 Cell pass rate (%) 99.7 99.8 99.8 96.8 97.2 95.5 Electrode coating peeling rate (%) ≤0.1 ≤0.1 ≤0.1 0.8 0.6 1.1 Diaphragm breakage rate (%) ≈0 ≈0 ≈0 0.3 0.2 0.5 Bubble residue rate (%) ≤0.2 ≤0.2 ≤0.2 1.2 0.9 2.3 The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium battery casing, characterized in that, The battery casing (100) is provided with an injection hole (101) and an exhaust hole (102) communicating with its inner cavity. The diameter of the casing (100) is defined as D, the diameter of the injection hole (101) is defined as D1, and the diameter of the exhaust hole (102) is defined as D2. D = T·D1, D1 = K·D2, D1 = 1.5~8mm, T = 0.08~0.12, K = 3~6.

2. A method for injecting electrolyte, characterized in that, Includes the following steps: (S1) Pretreatment: After drying the cell (103), it is installed into the battery casing (100). After the electrode post (104) is assembled, the battery casing (100) is pre-sealed by laser welding. The injection hole (101) is connected to the positive pressure injection assembly, and the vent hole (102) is connected to the directional vent assembly. (S2) Coordinate positive pressure injection: control the positive pressure of injection hole (101) to P1, control the venting pressure of vent hole (102) to P2, where P1=20~50kPa, P2≥5kPa, P1-P2=30kPa, complete the first injection in stages, define the total amount of electrolyte to be injected as V, and the amount of the first injection as V1, where V1<V; (S3) Gradient pressure holding impregnation: The impregnation stage is divided into a first stage impregnation and a second stage impregnation. After the first stage impregnation is completed, the pressure holding time is t1. During this stage, the positive pressure of the injection hole (101) is P1', and the venting pressure of the vent hole (102) is P2'. After the second stage impregnation is completed, the pressure holding time is t1. During this stage, the positive pressure of the injection hole (101) is P1'', and the venting pressure of the vent hole (102) is P2''. (S4) Replenishment and venting; The amount of electrolyte replenished is V2, where V1+V2=V. When replenishing electrolyte, the positive pressure of the injection hole (101) is P1''' and the venting pressure of the venting hole (102) is P2'''. After the electrolyte replenishment is completed, the positive pressure of the injection hole (101) is maintained, and venting continues. The venting time is t3. (S5) Welding seal: Laser welding seal is used for the injection hole (101) and the vent hole (102).

3. The electrolyte injection method according to claim 2, characterized in that, In step (S1), the water content of the cell (103) is 42 ppm when it is transferred into the battery casing (100).

4. The electrolyte injection method according to claim 2, characterized in that, In step (S2), the positive pressure of the injection hole (101) is P1=45kPa, and the venting pressure of the vent hole (102) is P2=15kPa.

5. The electrolyte injection method according to claim 2, characterized in that, In step (S2), the first electrolyte injection is completed in three stages. In the first stage, the electrolyte flow rate is 18 mL / s and the injection volume is 92% V. In the second stage, the electrolyte flow rate is 8 mL / s and the injection volume is 95% V. In the third stage, the electrolyte flow rate is 4 mL / s and the injection volume is 97-98%. Finally, 2-3% is added to complete the first electrolyte injection.

6. The electrolyte injection method according to claim 2, characterized in that, In step (S3), during the first stage of immersion, the positive pressure of the injection hole (101) is P1'=35kPa, the venting pressure of the vent hole (102) is P2'=12kPa, the holding temperature is 45℃, and the holding time is t1=12min; during the second stage of immersion, the positive pressure of the injection hole (101) is P''=25kPa, the venting pressure of the vent hole (102) is P2''=8kPa, the holding temperature is 48℃, and the holding time is t1=15min.

7. The electrolyte injection method according to claim 2, characterized in that, In step (S4), the positive pressure P1''' of the injection hole (101) is 15 kPa, the venting pressure P2''' of the venting hole (102) is 6 kPa, the flow rate is 3 mL / s, and after the electrolyte is replenished, the positive pressure of the injection hole (101) is maintained at 8 kPa, and the venting continues for 40 s.

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