A metal oxide-based lithium ion capacitor formation aging method

Abstract

The present invention relates to a formation aging method for metal oxide-based lithium ion capacitors, comprising: S1 applying pressure to the lithium ion capacitor at room temperature; S2 constant current charging the capacitor with a first current I1 to a first voltage U1, performing constant voltage charging at the first voltage U1, and discharging the capacitor with the first current I1 to a second voltage U2, and repeating the above process; S3 constant current charging the lithium ion capacitor with a second current I2 to a third voltage U3, and discharging the capacitor with the second current I2 to the second voltage U2, and repeating the above process; S4 constant current charging with the first current I1 to a third voltage U3, and performing constant voltage charging at the third voltage U3; S5 aging the capacitor at 45 to 60°C for 48 to 120 hours under the pressure state of S1; S6 aging the capacitor at room temperature for 6 to 12 hours under the pressure state of S1; and S7 venting and secondary packaging. The present invention has the advantages of optimizing the performance and stability of lithium ion capacitors.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion capacitors, and in particular relates to a formation aging method for metal oxide-based lithium ion capacitors. Background Art

[0002] Lithium-ion capacitors (LICs) are energy storage devices that combine the advantages of LIBs and supercapacitors (EDLCs), exhibiting high energy density, high power density, and a long cycle life. These characteristics have led to their widespread application in a variety of fields, including automotive start-stop systems, grid energy recovery, and wind and solar power generation.

[0003] Titanium- or niobium-based metal oxides, such as lithium titanate, titanium niobium oxide, lithium niobate, lithium-containing titanium niobium oxide, niobium pentoxide, and titanium dioxide, have attracted widespread attention as negative electrode materials for lithium-ion capacitors due to their cycling stability, high-rate performance, and safety. However, these materials may experience expansion issues when used in lithium-ion capacitors, resulting in reduced performance and limiting their further market application.

[0004] The main approach to addressing this issue is to modify the metal oxide raw materials, optimize the electrolyte, and improve the formation and aging process to reduce expansion and extend the life of the capacitor. Therefore, optimizing the formation and aging process of titanium or niobium metal oxide-based lithium-ion capacitors to reduce expansion and extend capacitor life is of great practical significance.

[0005] At present, commonly used formation aging methods include low-current charging and discharging and high-temperature aging technologies. For example, Chinese patent CN201710719582.2 discloses a formation method for activated carbon lithium titanate lithium ion capacitors, which activates the capacitor by charging and discharging with a small current, and then consumes internal moisture and oxygen-containing functional groups on the surface of the activated carbon through multiple cycles of charging and discharging with a large current, and finally performs room temperature aging and decompression exhaust. However, during the formation stage, the capacitor may produce a large amount of gas. If these gases are not under pressure, they will reduce the contact between the active material and the current collector, thereby increasing the electrode sheet resistance. Although these methods can reduce the generation of gas, they may cause the electrode sheet resistance to increase, thereby affecting the service life of the capacitor.

[0006] Other patents, such as CN201711491280.0, CN202110314513.X and CN201710936518.X, propose methods for forming lithium titanate batteries using multi-stage step charging and low-current charging. Although these methods can improve the performance of capacitors, the formation time is long, which is not conducive to improving actual production efficiency. In addition, these methods are mainly aimed at lithium-ion batteries with lithium titanate as the negative electrode, and the operating current of lithium-ion batteries is much smaller than the current required by lithium-ion capacitors. At the same time, the amount of gas generated during the formation and recycling of titanium or niobium metal oxide negative electrode materials and porous carbon positive electrode materials in lithium-ion capacitors is also much higher than that of lithium-ion batteries. Therefore, the formation aging method of lithium-ion batteries cannot be simply applied directly to lithium-ion capacitors. Summary of the Invention

[0007] To solve the problems of the prior art, the present invention provides a metal oxide-based lithium ion capacitor formation aging method. This method is used to address the technical problem that lithium ion capacitors constructed with titanium or niobium metal oxide negative electrode materials and porous carbon positive electrode materials produce gas during actual use, resulting in unsatisfactory cycle life. A metal oxide-based lithium ion capacitor formation aging method is provided to reduce the flatulence of lithium ion capacitors based on titanium or niobium metal oxide negative electrodes during subsequent use, improve the cycle life of lithium ion capacitors, and promote the practical application of lithium ion capacitors based on titanium or niobium metal oxide negative electrodes. The specific technical solutions of the present invention are as follows:

[0008] The present invention provides a formation aging method for metal oxide-based lithium ion capacitors, comprising: S1. applying pressure to the lithium ion capacitor at room temperature, the pressure range being 0.1 to 1 MPa, and maintaining the pressure throughout the formation aging process; S2. charging the lithium ion capacitor with a first current I1 to a first voltage U1, performing constant voltage charging at the first voltage U1 for a period of 0.1 to 1 hour, and then discharging the capacitor with the first current I1 to a second voltage U2, repeating the above charging and discharging process 2 to 5 times; S3. The lithium ion capacitor is charged with a second current I2 at a constant current to a third voltage U3, and discharged with the second current I2 at a constant current to the second voltage U2, and the above charging and discharging process is repeated 10 to 50 times; S4. The lithium ion capacitor is charged with a first current I1 at a constant current to a third voltage U3, and constant voltage charging is performed at the third voltage U3, and the charging time is 0.1 to 1 hour; S5. While maintaining the pressurized state of step s1, the lithium ion capacitor is aged at 45 to 60° C. for 48 to 120 hours; S6. While maintaining the pressurized state of step s1, the lithium ion capacitor is aged at room temperature for 6 to 12 hours; S7. The lithium ion capacitor is degassing and re-encapsulated.

[0009] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the first current I1 in step s2 and step s4 is in the range of 0.5~3C.

[0010] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the second current I2 in step s3 is 3~30C.

[0011] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the voltage difference between the first voltage U1 and the third voltage U3 is 0.1 to 0.2 V, and the first voltage U1 is 0.1 to 0.2 V higher than the third voltage U3.

[0012] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the third voltage U3 is the rated voltage of the lithium ion capacitor.

[0013] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the second voltage U2 ranges from 1 to 1.5 V, and the second voltage U2 is not higher than the lower operating limit voltage of the lithium ion capacitor.

[0014] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the negative electrode active material of the lithium ion capacitor in the metal oxide-based lithium ion capacitor is a titanium or niobium metal oxide, and the titanium or niobium metal oxide comprises one or more of the following combinations: lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide and titanium dioxide.

[0015] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the positive electrode active material of the lithium ion capacitor in the metal oxide-based lithium ion capacitor is a porous carbon material, and the porous carbon material includes one or a combination of activated carbon, mesoporous carbon, carbon nanotubes, onion carbon, carbon aerogel, activated carbon fiber, skeleton carbon or graphene.

[0016] Compared with the prior art, the present invention has the following better technical effects:

[0017] The present invention optimizes the performance and stability of lithium-ion capacitors through a series of refined charging and discharging processes. First, a small current is used for charging and discharging under conditions slightly higher than the rated voltage of the capacitor. This step helps to consume moisture and unstable chemical functional groups inside the capacitor and form a protective film at the electrode interface. Then, by using a large current for charging and discharging at the rated voltage, the side reactions that may occur under high-rate charging and discharging conditions are effectively suppressed. Finally, the capacitor is charged to a fully charged state and aged under high temperature and high pressure conditions to promote the full side reactions inside the capacitor and further stabilize the electrode interface. This formation aging method significantly reduces the possibility of side reactions occurring during the use of lithium-ion capacitors based on titanium or niobium metal oxide negative electrode materials, reduces gas generation, and thus extends the cycle life of the capacitor. In addition, the method is simple to operate and easy to implement, which helps to promote the technical solution of the present invention into actual production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of the method of the present invention;

[0019] Figure 2 It is a schematic diagram of the results of Example 1, Example 5, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0020] The terms used in the present invention generally have the meanings commonly understood by those skilled in the art unless otherwise specified.

[0021] In the following examples, various processes and methods not described in detail are conventional methods well known in the art.

[0022] The reagents used in the following examples were purchased from common commercial channels. The experimental operations and experimental conditions not specified were based on conventional operations and conditions in the art.

[0023] The specific implementation of the present invention is described below with reference to the embodiments and drawings.

[0024] <Example 1>

[0025] The present invention adopts the following technical solutions, see Figure 1 :

[0026] Step 1: Pressurize the lithium-ion capacitor at room temperature to a pressure of 0.1-1 MPa. Maintain the pressurized state throughout the formation aging process. Apply pressure throughout the formation aging process to prevent the gases generated by formation aging from reducing the contact between the active material and the current collector and increasing the electrode sheet resistance.

[0027] Step 2: Charge the lithium-ion capacitor at a constant current of I1 to a first voltage of U1. Continue charging at this constant voltage for 0.1 to 1 hour. Then, discharge the capacitor at the same constant current of I1 to a second voltage of U2. Repeat this charge-discharge cycle 2 to 5 times. This step consumes moisture and unstable functional groups within the capacitor, forming a protective film on the interface.

[0028] Step 3: Charge the lithium-ion capacitor with a second constant current I2 to a third voltage U3, and discharge it with the second constant current I2 to a second voltage U2, cycling this charge-discharge cycle 10-50 times. Performing charge and discharge at high current and rated voltage eliminates side effects of the lithium-ion capacitor at high rates.

[0029] Step 4: Charge the lithium-ion capacitor with a first constant current I1 to a third voltage U3, and then charge at a constant voltage for 0.1 to 1 hour at the first voltage U3. This step uses a small current to charge the lithium-ion capacitor to a fully charged state, allowing the capacitor to age in the fully charged state.

[0030] Step 5: While maintaining the pressurized state from step 1, age the lithium-ion capacitor at 45-60°C for 48-120 hours. Aging the lithium-ion capacitor at high temperature and high pressure in a fully charged state allows the internal side reactions of the lithium-ion capacitor to fully proceed and form a stable interface.

[0031] Step 6: Keep the lithium-ion capacitor pressurized as in step 1 and age it at room temperature for 6 to 12 hours.

[0032] Step 7: Exhaust and reseal the lithium-ion capacitor.

[0033] It is worth noting that the first current I1 described in steps 2 and 4 is 0.5-3C. While the first current I1 is low relative to the second current I2, it is high relative to the lithium-ion battery. The second current I2 described in step 3 is 3-30C. U1-U3 = 0.1-0.2V; that is, the first voltage U1 is 0.1-0.2V higher than the third voltage U3; the third voltage U3 is the rated voltage of the lithium-ion capacitor; the second voltage U2 is 1-1.5V; the second voltage U2 is not higher than the lower operating voltage limit of the lithium-ion capacitor (i.e., U2 ≤ lower operating voltage limit);

[0034] Among them, the metal oxide-based lithium ion capacitor, the negative electrode active material is a titanium or niobium metal oxide, and the titanium or niobium metal oxide includes one or a combination of lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide, and titanium dioxide; the positive electrode active material is a porous carbon material, and the porous carbon material includes one or a combination of activated carbon, mesoporous carbon, carbon nanotubes, onion carbon, carbon aerogel, activated carbon fiber, skeleton carbon or graphene.

[0035] Specifically,

[0036] The battery uses activated carbon as the positive electrode material, lithium titanate as the negative electrode material, and a 1M LiBF4 acetonitrile solution as the electrolyte. The rated voltage is 2.7V, and the operating lower limit voltage is 1.5V.

[0037] Step 1: Apply 0.5MPa pressure to the lithium-ion capacitor at room temperature of 25°C, and keep the pressure state throughout the entire formation and aging process;

[0038] Step 2: Charge the lithium-ion capacitor at a constant current of 1C to 2.85V, charge at a constant voltage of 2.85V for 0.2h, and discharge at a constant current of 1C to 1.2V. This charge and discharge cycle is repeated three times.

[0039] Step 3: Charge the lithium-ion capacitor at a constant current of 5C to 2.7V, and discharge it at a constant current of 5C to 1.2V, and cycle this charge and discharge cycle 20 times.

[0040] Step 4: Charge the lithium-ion capacitor to 2.7V at a constant current of 1C, and charge at a constant voltage of 2.7V for 0.2h;

[0041] Step 5: The lithium-ion capacitor is aged at 50°C for 60 hours while maintaining the pressurized state of step 1;

[0042] Step 6: The lithium-ion capacitor is aged at room temperature of 25°C for 8 hours while maintaining the pressurized state in step 1;

[0043] Step 7: Exhaust and reseal the lithium-ion capacitor.

[0044] <Example 2>

[0045] The only difference from Example 1 is the charging voltage in step 2.

[0046] Step 2: Charge the lithium-ion capacitor to 2.7V at a constant current of 1C, charge it at a constant voltage of 2.7V for 0.2h, and discharge it to 1.2V at a constant current of 1C. This charge-discharge cycle is repeated three times.

[0047] The other steps are the same as those in Example 1.

[0048] <Example 3>

[0049] The only difference from Example 1 is the discharge voltage in steps 2 and 3.

[0050] Step 2: Charge the lithium-ion capacitor at a constant current of 1C to 2.85V, charge at a constant voltage of 2.85V for 0.2h, and discharge at a constant current of 1C to 1.8V. Cycle this charge and discharge regime three times.

[0051] Step 3: Charge the lithium ion capacitor to 2.7V at a constant current of 5C, and discharge it to 1.8V at a constant current of 5C, and cycle this charge and discharge regime 20 times; other steps are the same as in Example 1.

[0052] <Example 4>

[0053] The only difference from Example 1 is the charge and discharge current in step 2.

[0054] Step 2: Charge the lithium-ion capacitor at a constant current of 10C to 2.85V, charge at a constant voltage of 2.85V for 0.2h, and discharge at a constant current of 10C to 1.2V. This charge and discharge cycle is repeated three times.

[0055] The other steps are the same as those in Example 1.

[0056] <Example 5>

[0057] The battery uses activated carbon as the positive electrode material, niobium pentoxide as the negative electrode material, and a 1M LiBF4 acetonitrile solution as the electrolyte. The rated voltage is 2.7V, and the operating lower limit voltage is 1.0V.

[0058] Step 1: Apply 0.5MPa pressure to the lithium-ion capacitor;

[0059] Step 2: Charge the lithium-ion capacitor at a constant current of 1C to 2.85V, charge at a constant voltage of 2.85V for 0.2h, and discharge at a constant current of 1C to 1.0V. Cycle this charge and discharge regime three times.

[0060] Step 3: Charge the lithium-ion capacitor at a constant current of 5C to 2.7V, and discharge it at a constant current of 5C to 1.0V, and cycle this charge and discharge cycle 20 times.

[0061] Step 4: Charge the lithium-ion capacitor to 2.7V at a constant current of 1C, and charge at a constant voltage of 2.7V for 0.2h;

[0062] Step 5: The lithium-ion capacitor is aged at 50°C for 60 hours while maintaining the pressurized state of step 1;

[0063] Step 6: Keep the lithium-ion capacitor pressurized as in step 1 and let it stand at room temperature for 8 hours;

[0064] Step 7: Exhaust and reseal the lithium-ion capacitor.

[0065] Comparative Example 1

[0066] The only difference from Example 1 is that there is no step 1, and no pressure is applied during the entire formation and aging process. The other steps are the same as in Example 1.

[0067] Comparative Example 2

[0068] The only difference from Example 1 is that there is no step 2, and the other steps are the same as Example 1.

[0069] Comparative Example 3

[0070] The only difference from Example 1 is that there is no step 3, and the other steps are the same as Example 1.

[0071] Comparative Example 4

[0072] The only difference from Example 1 is that step 4 is omitted, and the other steps are the same as those in Example 1.

[0073] <Comparison of technical effects of embodiments and comparative examples>

[0074] According to the current of 40C, within the voltage range from the working lower limit voltage to the rated voltage, the lithium ion capacitors aged by the above-mentioned embodiment and comparative example methods were subjected to 5000 cycles of charge and discharge test. The test results are shown in Table 1. Figure 2 As shown:

[0075]

[0076] Table 1: Test results of 5000 charge and discharge cycles;

[0077] Examples 1 and 5 illustrate that for titanium and niobium metal oxides, a good cycle life can be achieved at a high rate of 40C according to the above-mentioned chemical aging method.

[0078] Comparing Examples 1 and 2, since the maximum charging voltage is relatively low during the low current formation stage, some moisture and unstable functional groups inside the capacitor cannot be eliminated, resulting in reduced cycle performance.

[0079] Comparing Examples 1 and 3, since the minimum discharge voltage is relatively high during the low current formation stage, some unstable functional groups inside the capacitor cannot be eliminated, resulting in reduced cycle performance.

[0080] Comparing Examples 1 and 4, since the formation current is relatively large in the initial stage of formation, the cycle life is slightly reduced.

[0081] Comparing Example 1 with Comparative Example 1, since a large amount of gas is generated during the formation stage, when no pressure is applied, the generated gas will reduce the contact between the active material and the current collector, increase the electrode resistance, and thus affect the life.

[0082] Comparing Example 1 and Comparative Example 2, due to the lack of small current and charging and discharging at a voltage slightly higher than the rated voltage, a portion of the moisture and unstable functional groups inside the capacitor could not be eliminated, resulting in reduced cycle performance.

[0083] Comparing Example 1 and Comparative Example 3, due to the lack of large current and charging and discharging at rated voltage, the side reactions of the capacitor at high rates could not be eliminated, resulting in reduced cycle performance.

[0084] Comparing Example 1 and Comparative Example 4, since the capacitor ages at low voltage, a stable interface cannot be formed, resulting in poor cycle performance.

[0085] The above is a detailed description of the embodiments to facilitate proper understanding and application of the present invention by those skilled in the art. Any improvements or modifications to the technical solutions derived by those skilled in the art based on the present invention, without inventive effort, solely through analysis, analogy, or limited enumeration, should be within the scope of protection defined by the claims.

Claims

1. A metal oxide based lithium ion capacitor formation aging method, characterized in that The method comprises S1. Apply pressure to the lithium-ion capacitor at room temperature, with a pressure range of 0.1 to 1 MPa, and maintain the pressure throughout the formation and aging process; S2. The lithium ion capacitor is charged with a constant current to a first voltage U1 at a first current I1, and is charged at a constant voltage at the first voltage U1 for a charging time of 0.1 to 1 hour, and is discharged with a constant current to a second voltage U2 at a first current I1, and the above charge and discharge process is repeated 2 to 5 times; S3. The lithium ion capacitor is charged with a second constant current I2 to a third voltage U3, and discharged with a second constant current I2 to a second voltage U2, and the charge and discharge process is repeated 10 to 50 times; S4. The constant current I1 is charged to a third voltage U3, and the constant voltage charging is performed at the third voltage U3, and the charging time is 0.1 to 1 hour; S5. While maintaining the pressurized state in step s1, the lithium ion capacitor is aged at 45 to 60 ℃ for 48 to 120 hours; S6. While maintaining the pressurized state in step s1, the lithium ion capacitor is aged at room temperature for 6 to 12 hours; S7. Exhaust the lithium-ion capacitor and perform secondary packaging; In the steps s2 and s4, the first current I1 is in the range of 0.5 to 3C, the second current I2 in the step s3 is in the range of 3 to 30C, the voltage difference between the first voltage U1 and the third voltage U3 is 0.1 to 0.2 V, the first voltage U1 is 0.1 to 0.2 V higher than the third voltage U3, and the third voltage U3 is the rated voltage of the lithium ion capacitor.

2. A metal oxide-based lithium ion capacitor formation aging method as claimed in claim 1, characterized in that The second voltage U2 is in the range of 1 to 1.5 V, and the second voltage U2 is not higher than the lower limit operating voltage of the lithium ion capacitor.

3. A metal oxide-based lithium ion capacitor formation aging method as claimed in claim 1, characterized in that The negative electrode active material of the lithium ion capacitor in the metal oxide-based lithium ion capacitor is a titanium or niobium metal oxide, and the titanium or niobium metal oxide includes one or a combination of the following: lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide and titanium dioxide.

4. A metal oxide-based lithium ion capacitor formation aging method as claimed in claim 1, characterized in that The positive active material of the lithium ion capacitor in the metal oxide-based lithium ion capacitor is a porous carbon material, and the porous carbon material includes one or a combination of activated carbon, mesoporous carbon, carbon nanotubes, onion carbon, carbon aerogel, activated carbon fiber, skeleton carbon or graphene.

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