A silicon-carbon-graphite composite negative electrode battery formation process

Abstract

The invention discloses a silicon-carbon-graphite composite negative electrode battery formation process, wherein the battery cell is pre-formed before formation, the temperature is 60°C, the charging power is 20-25%, and the battery cell is vacuum-extracted and pre-packaged after being placed in a lower cabinet at room temperature for 6-7 hours; the pre-packaged battery cell is further formed in a pressurized formation cabinet, the temperature is 75°C, and the charging power is 50-55%, and the total charging power is 70-80%; and finally, the second sealing and subsequent processes are performed. The present invention is formed in two times, and the two charges are 70% in total. The pre-formation can produce gas better without affecting the gel, and the battery capacity is improved at the same time. During the formation, it is beneficial to the high-temperature gelation of the gel diaphragm, so that the negative electrode silicon-carbon material is closely bonded to the diaphragm, the internal tension of the battery is reduced, the thickness expansion during the charging process is reduced, and the high-temperature formation time is shortened, thereby reducing the effect of the high-temperature formation on the electrolyte, and improving the battery capacity and cycle life.

Description

Technical Field

[0001] The invention relates to a silicon-carbon-graphite composite negative electrode battery formation process, belonging to the technical field of lithium battery preparation. Background Art

[0002] With the opening of the policy of low-altitude economic development, the development of the drone industry has sprung up. Drones are widely used in a wide range of fields, including agricultural plant protection, surveying and mapping, logistics, aerial photography, firefighting and other types. The characteristics of these drones are that they require power sources with instantaneous high magnification, long endurance and high cycle life. At present, more than 90% of the energy system of drones is a silicon-carbon-graphite composite negative electrode lithium battery power supply. Silicon-carbon has a high gram capacity. For example, the porous silicon-carbon used now can reach more than 1800mAh / g in actual full battery gram capacity. The comprehensive gram capacity after composite artificial graphite reaches 600mAh / g, and the traditional graphite negative electrode battery graphite gram capacity is only 350mAh / g. The silicon-carbon-graphite composite negative electrode has increased its energy density by nearly 71%, making it a preferred material for high-energy-density batteries. However, silicon expands greatly during the charging and discharging process. At present, the comprehensive expansion rate of the silicon-carbon-graphite negative electrode battery that is well-made in the industry has reached 20% after 300 cycles, while the conventional graphite negative electrode is within 8%. The continuous expansion and contraction of silicon-carbon during the charge and discharge process can easily cause the negative electrode to become powdered, seriously affecting the battery cycle performance. How to solve the expansion of silicon-carbon-graphite composite negative electrode batteries during the charge and discharge cycle has become a technical barrier that lithium battery manufacturers need to overcome. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a silicon-carbon-graphite composite negative electrode battery formation process that reduces the expansion of the silicon-carbon-graphite negative electrode composite full battery after cycling.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A silicon-carbon-graphite composite negative electrode battery formation process, characterized by comprising the following steps:

[0006] a. Place the cell that has been aged and soaked after injection in a pressurized forming cabinet for pre-forming. The pre-forming parameters are temperature 60°C and pressure 1-3KG / CM 2 , charging capacity 20-25%;

[0007] b. Place the battery cells under the cabinet at room temperature for 6-7 hours;

[0008] c. Pre-package the set-aside cells by vacuum evacuation;

[0009] d. Place the pre-packaged cells in the pressurized forming cabinet for forming at a temperature of 75°C and a pressure of 1-3KG / CM. 2, recharge 50-55%, total charge 70-80%;

[0010] e. The charged cells are re-sealed and the cells undergo subsequent processes.

[0011] The pre-forming charging process of step a of the present invention is divided into two steps:

[0012] Charging process 1 is 0.05C CC 4.2V, 60min, and charging process 2 is 0.1C CC 4.2V, 90-120min.

[0013] The formation charging process of step d of the present invention is the third time:

[0014] Charging process 3 is 0.3C CC 4.2V, 120min.

[0015] Further preferably, there is an air bag between the pre-seal and a sealing edge of the pre-packaged battery cell, and the distance between the pre-seal and the battery cell body is not less than 30 mm, leaving room for two seals.

[0016] In the present invention, the packaging parameters of the pre-sealed edge are:

[0017] Temperature 170-180℃, packaging time 3-4S, pressure 0.2-0.3Mpa.

[0018] In the present invention, the second packaging parameters are:

[0019] Temperature 195-205℃, packaging time 4-5s, pressure 0.3-0.5MPa, vacuum degree ≤-85KPa, time to reach vacuum degree 10-12s.

[0020] The cells that have completed double sealing are put on the cabinet for capacity separation. After the capacity separation is completed, the cells are stored at 50℃ and 90% relative humidity, and the cells with poor packaging are selected.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The present invention is divided into two formations, and a low-temperature 60°C pre-formation is first performed before a high-temperature 75°C formation. The pre-formation temperature is low, and gas can be produced better without affecting the gel, while the battery capacity is improved. During the secondary formation, only the diaphragm gel layer needs to be activated, and the high-temperature formation time can be shortened, thereby reducing the effect of the high-temperature formation on the electrolyte and improving the battery capacity and cycle life.

[0023] The pre-charging amount of 20-25% is enough to form the SEI film without excessive gas production. The polarization of the charging process is dissipated by leaving it at room temperature, and further electrolyte absorption is achieved. The present invention performs a pre-sealing before the second sealing to extract the gas produced by the formation and excess free electrolyte, so that the positive electrode, the diaphragm and the negative electrode are in closer contact, which is beneficial to the high-temperature gelation of the gel diaphragm, so that the negative electrode silicon-carbon material is tightly bonded to the diaphragm, the internal tension of the battery is reduced, and the thickness expansion during the charging process is reduced. The formation temperature of the present invention does not exceed 80°C, so as to avoid partial decomposition of the electrolyte, reduce the function of the electrolyte, and facilitate battery circulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the packaging process of soft-pack lithium batteries;

[0025] The structures represented by the serial numbers are: 1-battery cell, 2-pre-sealed edge, 3-first-sealed edge, 4-airbag, 5-second-sealed edge. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] A silicon-carbon-graphite composite negative electrode battery formation process comprises the following steps:

[0028] a. Place the cell that has been aged and soaked after injection in a pressurized forming cabinet for pre-forming. The pre-forming parameters are temperature 60°C and pressure 1-3KG / CM 2 , charging process 1 is 0.05C CC4.2V, 60min, charging process 2 is 0.1C CC 4.2V, 90-120min, charging capacity is 20-25%;

[0029] b. Place the battery cells under the cabinet at room temperature for 6-7 hours to allow the polarization of the charging process to dissipate and the electrolyte to absorb;

[0030] c. Pre-package the battery cell 1 by vacuum evacuation, and reserve an air bag 4 between the pre-sealed edge 2 and the sealed edge 3 of the pre-package. The distance between the pre-sealed edge 2 and the battery cell 1 shall not be less than 30 mm. Figure 1 As shown, the packaging parameters of the pre-sealed edge are:

[0031] Temperature 170-180℃, packaging time 3-4S, pressure 0.2-0.3Mpa;

[0032] d. Place the pre-packaged cells in the pressurized forming cabinet at a temperature of 75°C and a pressure of 1-3KG / CM. 2 , Charging process 3 is 0.3C CC 4.2V, 120min;

[0033] e. The formed and charged battery cell is double-sealed to form a double-sealed edge 5. After the double-sealing, the battery cell is subjected to subsequent processes. The double-sealing packaging parameters are: temperature 195-205°C, packaging time 4-5s, pressure 0.3-0.5MPa, vacuum degree ≤-85KPa, and time to reach vacuum degree 10-12s.

[0034] Preparation and testing of embodiments and comparative examples:

[0035] A 27AH battery cell was designed, and the same composite silicon-carbon-graphite negative electrode, PMMA gel diaphragm and high-temperature electrolyte were selected to form the battery according to the different positive electrode materials and parameters in Table 1. After capacity division, the battery was made and then tested.

[0036] The preparation method of Example 1-2 is:

[0037] S1. Place the cell that has been aged and soaked after injection in a pressurized forming cabinet at 60°C for pre-forming. Charging process 1 is 0.05C CC 4.2V, 60min, and charging process 2 is 0.1C CC 4.2V, 90-120min.

[0038] S2. Place the battery cells under the cabinet at room temperature for 6-7 hours, and then perform vacuum pre-packaging. The pre-sealing edge packaging parameters are:

[0039] Temperature 175℃, packaging time 3-4S, pressure 0.2-0.3Mpa;

[0040] S3, the pre-packaged battery cells are placed in a pressurized forming cabinet at 75°C for forming, and the charging process 3 is 0.3C CC4.2V, 120min;

[0041] S4, the charged cell is subjected to secondary sealing to form secondary sealing edge 5, and the cell after secondary sealing is subjected to subsequent process, and the secondary sealing parameters are: temperature 200°C, sealing time 4-5s, pressure 0.4MPa, vacuum degree ≤-85KPa, and time to reach vacuum degree 10-12s;

[0042] S5. Put the cells after the second sealing into the cabinet for capacity division and storage, and select and package them to make batteries.

[0043] The preparation method of Comparative Example 1-2 is:

[0044] S1. Place the battery cells that have been aged and soaked after injection in a pressurized forming cabinet at 75°C for forming. Charging process 1 is 0.05C CC 4.2V, 60min, charging process 2 is 0.1C CC 4.2V, 90-120min, and charging process is 0.3C CC 4.2V, 120min.

[0045] S2, the battery cell after formation and charging is double-sealed to form a double-sealed edge 5 (Comparative Example 1-2 does not have a pre-sealed edge 2), and the battery cell after the double sealing is carried out to the subsequent process, and the double sealing packaging parameters are: temperature 200°C, packaging time 4-5s, pressure 0.4MPa, vacuum degree ≤-85KPa, and vacuum time 10-12s;

[0046] S3, put the cells after double sealing into cabinets for capacity division and storage, and select and package them to make batteries.

[0047] Table 1:

[0048]

[0049] As can be seen from Table 1, Examples 1 and 2 of the present invention have high capacity utilization, high cycle retention, and low cycle expansion, while Comparative Examples 1-2 have low capacity utilization, low cycle retention, and large cycle expansion.

Claims

1. A silicon-carbon-graphite composite negative electrode battery formation process, characterized in that The following steps are involved: a. Place the cell that has been aged and soaked after injection in a pressurized forming cabinet for pre-forming. The pre-forming parameters are temperature 60°C and pressure 1-3KG / CM 2 , charging capacity 20-25%; b. Place the battery cells under the cabinet at room temperature for 6-7 hours; c. Pre-package the set-aside cells by vacuum evacuation; d. Place the pre-packaged cells in the pressurized forming cabinet for forming at a temperature of 75°C and a pressure of 1-3KG / CM. 2 , recharge 50-55%, total charge 70-80%; e. The charged cells are re-sealed and the cells undergo subsequent processes.

2. A silicon-carbon-graphite composite negative electrode battery formation process according to claim 1, characterized in that The pre-formation charging process of step a is as follows: Charging process 1 is 0.05C CC 4.2V, 60min, and charging process 2 is 0.1C CC 4.2V, 90-120min.

3. A silicon-carbon-graphite composite negative electrode battery formation process according to claim 1, characterized in that The formation charging process of step d is: Charging process 3 is 0.3C CC 4.2V, 120min.

4. A silicon-carbon-graphite composite negative electrode battery formation process according to claim 1, characterized in that There is an air bag between the pre-seal and a sealing edge of the pre-packaged battery cell, and the distance between the pre-seal and the battery cell body is not less than 30 mm.

5. A silicon-carbon-graphite composite negative electrode battery formation process according to claim 4, characterized in that The packaging parameters of the pre-sealed edge are: Temperature 170-180℃, packaging time 3-4S, pressure 0.2-0.3Mpa.

6. A silicon-carbon-graphite composite negative electrode battery formation process according to claim 1, characterized in that The two-seal packaging parameters are: Temperature 195-205℃, packaging time 4-5s, pressure 0.3-0.5MPa, vacuum degree ≤-85KPa, time to reach vacuum degree 10-12s.

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