Lithium ion capacitor high-temperature pressure formation process

Abstract

The invention discloses a high-temperature pressure formation process for a lithium ion capacitor in the technical field of preparation of lithium ion capacitors, which comprises the following steps: (1) charging a battery after liquid injection and standing for the first time, charging a battery core for the first time to 40% SOC (State of Charge), the pressure of the first charging being 3000-4000 N, the current being 0.02-0.1 C and the temperature being 30-40 DEG C; (2) carrying out secondary charging on the battery cell after the first charging to 60% SOC (State of Charge), wherein the pressure of the secondary charging is 1500-2500N, the current is 0.1-0.2 C, and the temperature is 30-40 DEG C; and (3) carrying out third-time charging on the battery cell after the secondary charging and charging to 80% SOC (State of Charge), wherein the pressure of the third-time charging is 500-1000N, the current is 0.2-0.4 C, and the temperature is 40-50 DEG C. The process can significantly improve the cycle life and rate capability of the lithium ion capacitor.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion capacitor preparation, and in particular relates to a high-temperature pressure formation process for lithium ion capacitors. Background Art

[0002] Lithium-ion capacitor (LIC) is a new type of energy storage device. Compared with lithium-ion batteries, it has a relatively higher specific power; compared with traditional supercapacitors, it has a relatively higher specific energy, so it has excellent application prospects. Lithium-ion capacitors, a hybrid energy storage device that combines the advantages of lithium-ion batteries and supercapacitors, have received widespread attention.

[0003] Lithium-ion capacitors need to go through a formation step before use. The formation of lithium-ion capacitors has two main functions. On the one hand, it activates the active substances in the positive and negative electrodes so that the lithium-ion capacitor reaches the optimal charge and discharge state. On the other hand, during the formation process of lithium-ion capacitors, a SEI film (solid electrolyte interface film) will form on the surface of the negative electrode. Since the insertion / extraction process of lithium ions must pass through the SEI film covering the negative electrode, the uniformity and stability of the SEI film will affect the capacity, cycle life, high and low temperature performance, self-discharge performance, stability and safety of lithium-ion capacitors, and is one of the important factors that determine the electrical performance of lithium-ion capacitors. The traditional high-temperature pressure formation process usually uses high temperature (>35°C) and constant current (≥0.2C) to charge the battery to 100% SOC for formation. Although this formation process can increase the electrochemical reaction rate and SEI film formation rate, the formed SEI film is not consistent, loose and unstable. It will significantly affect the cycle life, rate performance and first coulomb efficiency of the capacitor. Summary of the invention

[0004] The present invention aims to provide a high temperature pressure formation process for lithium ion capacitors to improve the cycle life and rate performance of lithium ion capacitors.

[0005] A high temperature pressure formation process for lithium ion capacitors in this scheme includes the following steps:

[0006] (1) Placing the battery after injection and standing still on a high temperature pressure formation device for the first charge, the battery cell is charged to 40% SOC for the first time, the pressure of the first charge is 3000-4000N, the current is 0.02C-0.1C, and the temperature is 30-40°C;

[0007] (2) The battery cell after the initial charge is recharged to 60% SOC, the pressure of the secondary charge is 1500-2500N, the current is 0.1C-0.2C, and the temperature is 30-40°C;

[0008] (3) The battery cell after the secondary charge is charged three times and charged to 80% SOC. The pressure of the three charges is 500-1000N, the current is 0.2C-0.4C, and the temperature is 40-50°C.

[0009] Beneficial effects of this scheme: By optimizing parameters such as pressure, current and charging degree, this scheme enables the prepared lithium ion capacitor to exhibit excellent coulombic efficiency, rate performance and extreme pulse discharge capability.

[0010] Furthermore, the battery cell is injected with electrolyte under the conditions of 10-100 Pa and 30-50° C., and maintained under the conditions for 20-50 minutes after the injection is completed, so that the electrolyte can quickly infiltrate the surface of the diaphragm and the electrode.

[0011] Furthermore, the battery cell after the injection is placed in an environment of 30-50°C for 4-8 hours before the first charge is performed, so that the electrolyte and the microscopic pores of the electrode can be completely infiltrated.

[0012] Furthermore, after the battery cell completes the first charge, the lithium-rich electrolyte is supplemented, and the amount of the lithium-rich electrolyte supplemented is 9% to 15% of the amount of electrolyte injected when the battery cell is filled.

[0013] Furthermore, after the battery cell completes secondary charging, the lithium-rich electrolyte is supplemented, and the amount of the lithium-rich electrolyte supplemented is 5% to 10% of the amount of electrolyte injected when the battery cell is injected.

[0014] Because the hard carbon negative electrode material used in lithium-ion capacitors has a large irreversible capacity, a large amount of lithium ions will be consumed during the first charging process. Therefore, in order to make up for the irreversible capacity of the negative electrode, it is necessary to add lithium-rich electrolyte during the formation process of the lithium-ion capacitor to make up for the irreversible loss of lithium ions and improve the initial coulombic efficiency and capacity of the lithium-ion capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a comparison diagram of the positive electrode of an ion capacitor. DETAILED DESCRIPTION

[0016] The following is further described in detail through specific implementation methods:

[0017] Hard carbon is used as the negative electrode, lithium cobalt oxide is used as the positive electrode, Celgard 2300 membrane (made in the United States) is used as the separator, 1mol / LLiPF6 / EC+DMC+EMC (made in Shenzhen, 1:1:1) is used as the electrolyte, and then the battery cells are assembled and finally assembled into a soft-pack lithium-ion capacitor. The battery cell shape is designed to be square.

[0018] Example 1

[0019] (1) The battery cell was injected with 1 mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1) electrolyte under negative pressure (100 Pa) and high temperature (40°C) conditions and maintained under these conditions for 50 min.

[0020] (2) The battery cell after the injection is placed in a 40°C environment for 8 hours.

[0021] (3) First charge: After the resting, the battery is placed on a high-temperature pressure formation device and the battery cell is charged to 40% SOC using a certain pressure, current and temperature. The pressure at this stage is 3000N, the current is 0.02C, the temperature is 40°C, and the charging time is 4h. Then, 4g of LiPF6 lithium-rich electrolyte (2mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1)) is added.

[0022] (4) Secondary charging: Continue charging the battery cell to 60% SOC. The pressure at this stage is 2000N, the current is 0.1C, the temperature is 40°C, the charging time is 1h, and then 2.5g LiPF6 lithium-rich electrolyte (2mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1)) is added.

[0023] (5) Three-time charging: Increase the temperature and current to charge the battery to 80% SOC, the pressure is set to 1000N, the current is 0.2C, the temperature is 40℃, and the charging time is 20min.

[0024] Example 2

[0025] (1) The battery cell was injected with 1 mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1) electrolyte under negative pressure (100 Pa) and high temperature (40°C) conditions and maintained under these conditions for 50 min.

[0026] (2) The battery cell after the injection is placed in a 40°C environment for 8 hours.

[0027] (3) After the resting, the battery is placed on a high-temperature pressure formation device and the battery cell is charged to 50% SOC using a certain pressure, current and temperature. The pressure at this stage is 4500N, the current is 0.15C, the temperature is 40°C, and the charging time is 3h.

[0028] (4) Continue charging and charge the battery cell to 65% SOC. The pressure at this stage is 3000N, the current is 0.2C, the temperature is 40°C, and the charging time is 1h.

[0029] (5) Reduce the pressure. Increase the temperature and current to charge the cell to 85% SOC, with the pressure set to 1500N, the current to 0.25C, the temperature to 40°C, and the charging time to 15min.

[0030] Example 3

[0031] (1) The battery cell was injected with 1 mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1) electrolyte under negative pressure (100 Pa) and high temperature (40°C) conditions and maintained under these conditions for 50 min.

[0032] (2) The battery cell after the injection is placed in a 40°C environment for 8 hours.

[0033] (3) First charge: After the resting, the battery is placed on a high-temperature pressure formation device and charged to 40% SOC using a certain pressure, current and temperature. The pressure at this stage is 3000N, the current is 0.02C, the temperature is 40°C, and the charging time is 4h.

[0034] (4) Secondary charging: Continue charging the battery to 60% SOC. The pressure at this stage is 2000N, the current is 0.1C, the temperature is 40°C, and the charging time is 1h.

[0035] (5) Three-time charging: Increase the temperature and current to charge the battery to 80% SOC, the pressure is set to 1000N, the current is 0.2C, the temperature is 40℃, and the charging time is 20min.

[0036] Comparative Example 1

[0037] The traditional high temperature pressure formation process usually uses high temperature (>35°C) and constant current (≥0.2C) to charge the battery to 100% SOC for formation, as follows:

[0038] (1) The battery cell was injected with 1 mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1) electrolyte under negative pressure (100 Pa) and high temperature (40°C) conditions and maintained under these conditions for 50 min.

[0039] (2) The battery cell after the injection is placed in a 40°C environment for 8 hours.

[0040] (3) After the resting, the battery is placed on a high-temperature pressure formation device and the battery cell is charged to 100% SOC using a certain pressure, current and temperature. The pressure in this stage is 3000N, the current is 0.2C, the temperature is 40°C, and the charging time is 8h.

[0041] Comparative Example 2

[0042] (1) The battery cell was injected with 1 mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1) electrolyte under negative pressure (100 Pa) and high temperature (40°C) conditions and maintained under these conditions for 50 min.

[0043] (2) The battery cell after the injection is placed in a 40°C environment for 8 hours.

[0044] (3) First charge: After the resting, the battery is placed on a high-temperature pressure formation device and the battery cell is charged to 40% SOC using a certain pressure, current and temperature. The pressure at this stage is 3000N, the current is 0.02C, the temperature is 40°C, and the charging time is 4h. Then, 4g of LiPF6 lithium-rich electrolyte (2mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1)) is added.

[0045] (4) Secondary charging: Continue charging the battery cell to 60% SOC. The pressure at this stage is 2000N, the current is 0.1C, the temperature is 40°C, the charging time is 1h, and then 2.5g LiPF6 lithium-rich electrolyte (2mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1)) is added.

[0046] (5) Three-time charging: Increase the temperature and current to charge the battery cell to 80% SOC, the pressure is set to 2000N, the current is 0.1C, the temperature is 40℃, and the charging time is 1h.

[0047] (6) Four-time charging: Use a certain pressure, current and temperature to charge the battery cell to 100% SOC. The pressure in this stage is 3000N, the current is 0.2C, the temperature is 40℃, and the charging time is 8h.

[0048] Comparative Example 3

[0049] (1) The battery cell was injected with 1 mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1) electrolyte under negative pressure (100 Pa) and high temperature (40°C) conditions and maintained under these conditions for 50 min.

[0050] (2) The battery cell after the injection is placed in a 40°C environment for 8 hours.

[0051] (3) First charge: Continue charging the battery cell to 60% SOC. The pressure at this stage is 2000N, the current is 0.1C, the temperature is 40°C, the charging time is 1h, and then 2.5g LiPF6 lithium-rich electrolyte (2mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1)) is added.

[0052] (4) Secondary charging: Increase the temperature and current to charge the cell to 80% SOC, with the pressure set to 1000N, the current to 0.2C, the temperature to 40°C, and the charging time to 20min.

[0053] Comparative Example 4

[0054] (1) The battery cell was injected with 1 mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1) electrolyte under negative pressure (100 Pa) and high temperature (40°C) conditions and maintained under these conditions for 50 min.

[0055] (2) The battery cell after the injection is placed in a 40°C environment for 8 hours.

[0056] (3) First charge: After the resting, the battery is placed on a high-temperature pressure formation device and the battery cell is charged to 40% SOC using a certain pressure, current and temperature. The pressure at this stage is 3000N, the current is 0.02C, the temperature is 40°C, and the charging time is 4h. Then, 4g of LiPF6 lithium-rich electrolyte (2mol / L LiPF6 / EC+DMC+EMC (produced in Shenzhen, 1:1:1)) is added.

[0057] (4) Secondary charging: Increase the temperature and current to charge the cell to 80% SOC, with the pressure set to 1000N, the current to 0.2C, the temperature to 40°C, and the charging time to 20min.

[0058] Figure 1 The following are photos of the positive electrodes of lithium ion capacitors obtained by two formation methods. The positive electrode in the left picture is prepared by Example 1, and the positive electrode in the right picture is prepared by Comparative Example 1. Figure 1 It can be seen that the surface of the positive electrode obtained by the formation process of Example 1 did not show obvious changes, while the surface of the electrode obtained by the formation process of Comparative Example 1 showed mottled marks, and the color turned light yellow, indicating that there was a mixed phase on the surface of the positive electrode, which may be related to the delithiation of the positive electrode, indicating that the proportion of active lithium loss in the battery gradually increased. This shows that although the use of traditional formation processes can increase the electrochemical reaction rate and SEI film formation rate, it will significantly affect the cycle life, rate performance and first coulomb efficiency of the capacitor.

[0059] Performance Verification

[0060] Lithium Ion Capacitor Coulomb Efficiency Test

[0061] The coulombic efficiency test was performed on the lithium ion capacitors prepared in Example 1, Example 2 and Comparative Example 1. The results are shown in Table 1:

[0062] Table 1 Coulombic efficiency test of lithium ion capacitor

[0063]

[0064]

[0065] It can be seen from Table 1 that the battery prepared by Example 1 of the present invention exhibits excellent first efficiency. Compared with the prior art (Comparative Example 1), the formation process can improve the coulombic efficiency of the lithium ion capacitor by about 15.5%.

[0066] Lithium Ion Capacitor Cycle Life Test

[0067] The lithium ion capacitors prepared in Example 1, Example 2 and Comparative Example 1 were subjected to cycle life tests, and the results are shown in Table 1:

[0068] Table 2 Lithium ion capacitor cycle life test

[0069] Cycle times Capacity retention rate (%) Example 1 3568 80.4 Example 2 2905 80.2 Example 3 3362 80.4 Comparative Example 1 2301 80.3 Comparative Example 2 2856 80.3 Comparative Example 3 2537 80.2 Comparative Example 4 2692 80.3

[0070] It can be seen from Table 2 that, compared with the prior art (Comparative Example 1), the cycle life of the lithium ion capacitor prepared by the formation process of Example 1 of the present invention is significantly improved, with the cycle life being improved by 55.1%.

[0071] Lithium Ion Capacitor Internal Resistance Test

[0072] The internal resistance of the lithium ion capacitors prepared in Example 1, Example 2 and Comparative Example 1 was tested, and the results are shown in Table 1:

[0073] Table 3 Lithium Ion Capacitor Internal Resistance Test

[0074]

[0075]

[0076] Lithium Ion Capacitor Rate Performance Test

[0077] The rate performance test of the lithium ion capacitors prepared in Example 1, Example 2 and Comparative Example 1 was performed, and the results are shown in Table 3:

[0078] Table 4 Lithium Ion Capacitor Rate Performance Test

[0079]

[0080] It can be seen from Tables 3 and 4 that the internal resistance of the lithium ion capacitor prepared in Example 1 is significantly reduced, and the rate performance is greatly improved. The capacity retention rate is as high as 86.4% under the 200C rate condition, while the capacity retention rate using the traditional formation process is only 75.3%.

[0081] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A high temperature pressure formation process for lithium ion capacitors, characterized in that: The following steps are involved: (1) Placing the battery after injection and standing still on a high temperature pressure formation device for the first charge, the battery cell is charged to 40% SOC for the first time, the pressure of the first charge is 3000-4000N, the current is 0.02C-0.1C, and the temperature is 30-40°C; (2) The battery cell after the initial charge is recharged to 60% SOC, the pressure of the secondary charge is 1500-2500N, the current is 0.1C-0.2C, and the temperature is 30-40°C; (3) The battery cell after the secondary charge is charged three times and charged to 80% SOC. The pressure of the three charges is 500-1000N, the current is 0.2C-0.4C, and the temperature is 40-50°C.

2. A high temperature pressure formation process for lithium ion capacitors according to claim 1, characterized in that: The battery cell is injected with liquid under the conditions of 10-100 Pa and 30-50 ° C, and maintained under the conditions for 20-50 minutes after the injection is completed.

3. A high temperature pressure formation process for lithium ion capacitors according to claim 2, characterized in that: After the injection, place the battery cell in an environment of 30-50℃ for 4-8 hours before charging it for the first time.

4. A high temperature pressure forming process for lithium ion capacitors according to any one of claims 1 to 3, characterized in that: After the battery cell completes the first charge, add an appropriate amount of lithium-rich electrolyte.

5. A high temperature pressure formation process for lithium ion capacitors according to claim 4, characterized in that: After the battery cell completes secondary charging, add an appropriate amount of lithium-rich electrolyte.

Images