Formation and aging method for metal oxide-based lithium ion capacitor

Abstract

The invention relates to a formation and aging method for a metal oxide-based lithium ion capacitor. The method comprises the following steps: S1, applying pressure to the lithium ion capacitor at normal temperature; s2, performing constant-current charging on the capacitor with the first current I1 to a first voltage U1, performing constant-voltage charging under the first voltage U1, performing constant-current discharging with the first current I1 to a second voltage U2, and repeating the process; s3, carrying out constant-current charging on the lithium ion capacitor with a second current I2 to a third voltage U3, carrying out constant-current discharging with the second current I2 to a second voltage U2, and repeating the above process; s4, carrying out constant-current charging at the first current I1 to a third voltage U3, and carrying out constant-voltage charging at the third voltage U3; s5, aging for 48 to 120 hours at 45 to 60 DEG C in a pressurized state of s1; s6, aging for 6-12 hours at normal temperature in a pressurized state of s1; and S7, exhausting and secondary packaging are carried out. The lithium ion capacitor has the advantage that the performance and the stability of the lithium ion capacitor are optimized.

Description

Technical Field

[0001] The 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 are innovative energy storage devices that combine the advantages of lithium-ion batteries and supercapacitors (double-layer capacitors), showing characteristics such as high energy density, high power density and long cycle life. These characteristics make lithium-ion capacitors widely used in many fields such as automotive start-stop systems, power grid energy recovery, wind power generation and solar power generation.

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

[0004] The main method to solve this problem is to modify the metal oxide raw materials, optimize the electrolyte and improve the formation aging process to reduce the expansion phenomenon and extend the service life of the capacitor. Therefore, it is of great practical significance to optimize the formation aging process of titanium or niobium metal oxide-based lithium ion capacitors to reduce expansion and increase the life of the capacitor.

[0005] At present, commonly used formation aging methods include low-current charging and discharging and high-temperature aging technology. 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 the 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, which, if no pressure is applied, will reduce the contact between the active material and the current collector, thereby increasing the pole sheet resistance. Although these methods can reduce the generation of gas, they may cause the pole 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 working 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 by titanium or niobium metal oxide negative electrode materials and porous carbon positive electrode materials during the formation and recycling of 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] In order to solve the problems of the prior art, the present invention provides a metal oxide-based lithium ion capacitor formation aging method, which is used to solve 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: The present invention provides a metal oxide-based lithium ion capacitor formation aging method, the method comprising S1. applying pressure to the lithium ion capacitor at room temperature, the pressure range is 0.1 to 1 MPa, and the entire formation aging process is kept in a pressurized state; S2. charging the lithium ion capacitor with a first current I1 to a first voltage U1, charging at a constant voltage under the first voltage U1, the charging time is 0.1 to 1 hour, discharging with the first current I1 to a second voltage U2, and 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 a second current I2 at a constant current to a 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 exhausted and repackaged.

[0008] Preferably, the metal oxide-based lithium ion capacitor formation aging method provided by the present invention also includes other technical features, wherein the range of the first current I1 in step s2 and step s4 is 0.5~3C.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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 working lower limit 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 negative electrode active material of the lithium ion capacitor in the metal oxide-based lithium ion capacitor is a metal oxide, and the metal oxide comprises one or a combination of the following: lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide and titanium dioxide.

[0014] 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.

[0015] Compared with the prior art, the present invention has the following better technical effects: 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. Next, 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 during 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

[0016] Figure 1 is a flow chart of the method of the present invention; Figure 2 It is a schematic diagram of the results of Example 1, Example 5, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0017] The terms used in the present invention, unless otherwise specified, generally have the meanings that are commonly understood by those of ordinary skill in the art.

[0018] In the following examples, various processes and methods not described in detail are conventional methods well known in the art.

[0019] The reagents used in the following examples were purchased from common commercial sources, and the experimental operations and experimental conditions not specified were referred to the conventional operations and conventional conditions in the art.

[0020] The specific implementation of the present invention is described below in conjunction with embodiments and drawings.

[0021] <Example 1> The present invention adopts the following technical solutions, see Figure 1 : Step 1: Pressurize the lithium-ion capacitor at room temperature with a pressure of 0.1~1Mpa, and keep the pressurized state throughout the formation aging process. Apply pressure throughout the formation aging process to prevent the gas generated by formation aging from reducing the contact between the active material and the current collector and increasing the electrode sheet resistance.

[0022] Step 2: Charge the lithium ion capacitor with a first current I1 to a first voltage U1, charge at a constant voltage for 0.1 to 1 hour at the first voltage U1, discharge at a constant current of the first current I1 to a second voltage U2, and cycle the charge and discharge regime 2 to 5 times. This step consumes the water and unstable functional groups inside the capacitor and forms a protective film on the interface.

[0023] Step 3: Charge the lithium ion capacitor with the second current I2 to the third voltage U3, and discharge it with the second current I2 to the second voltage U2, and cycle the charge and discharge system 10 to 50 times. Charge and discharge at high current and rated voltage to eliminate the side reactions of the lithium ion capacitor at high rates.

[0024] Step 4: Charge the lithium ion capacitor with a first current I1 to a first voltage U3, and charge at a constant voltage for 0.1 to 1 hour at the first voltage U3. This step charges the lithium ion capacitor to a fully charged state with a small current, so that the lithium ion capacitor ages in a fully charged state.

[0025] Step 5: The lithium ion capacitor is aged at 45-60°C for 48-120 hours while maintaining the pressurized state of step 1. The lithium ion capacitor is aged at high temperature and high pressure in a fully charged state so that the side reactions inside the lithium ion capacitor can be fully carried out and a stable interface can be formed.

[0026] Step 6: The lithium-ion capacitor is aged at room temperature for 6 to 12 hours while maintaining the pressurized state in step 1.

[0027] Step 7: Exhaust and reseal the lithium-ion capacitor.

[0028] It is worth noting that: the first current I1 described in step 2 and step 4 is 0.5~3C, the first current I1 is a small current relative to the second current I2, but the first current I1 is a large current 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 limit voltage of the lithium-ion capacitor (that is, U2≤lower limit voltage); Among them, the metal oxide-based lithium ion capacitor, the negative electrode active material is a metal oxide, and the 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.

[0029] In this embodiment 1, specifically The positive electrode material is activated carbon, the negative electrode material is lithium titanate, and the electrolyte is 1M LiBF4 acetonitrile solution. The rated voltage is 2.7V and the lower limit voltage is 1.5V.

[0030] Step 1: Apply 0.5MPa pressure to the lithium-ion capacitor at room temperature of 25°C, and keep the pressure state during the entire formation and aging process; Step 2: Charge the lithium ion capacitor to 2.85V at 1C constant current, charge at 2.85V at constant voltage for 0.2h, discharge at 1C constant current to 1.2V, and cycle this charge and discharge system 3 times; Step 3: Charge the lithium-ion capacitor to 2.7V at 5C constant current, and discharge it to 1.2V at 5C constant current, and cycle this charge and discharge system 20 times; 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; Step 5: The lithium-ion capacitor is aged at 50°C for 60 hours while maintaining the pressurized state of step 1; Step 6: The lithium-ion capacitor is aged at room temperature of 25°C for 8 hours while maintaining the pressurized state of step 1; Step 7: Exhaust and reseal the lithium-ion capacitor.

[0031] <Example 2> The only difference from Example 1 is the charging voltage in step 2. Step 2: Charge the lithium ion capacitor to 2.7V at 1C constant current, charge at 2.7V at constant voltage for 0.2h, discharge at 1C constant current to 1.2V, and cycle this charge and discharge system 3 times; The other steps are the same as those in Example 1.

[0032] <Example 3> The only difference from Example 1 is the discharge voltage in step 2 and step 3. Step 2: Charge the lithium ion capacitor to 2.85V at 1C constant current, charge at 2.85V at constant voltage for 0.2h, discharge at 1C constant current to 1.8V, and cycle this charge and discharge system 3 times; 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 the charge and discharge system 20 times; the other steps are the same as those in Example 1.

[0033] <Example 4> The only difference from Example 1 is the charge and discharge current in step 2. Step 2: Charge the lithium ion capacitor to 2.85V at a constant current of 10C, charge at a constant voltage of 2.85V for 0.2h, discharge at a constant current of 10C to 1.2V, and cycle this charge and discharge regime 3 times; The other steps are the same as those in Example 1.

[0034] <Example 5> The positive electrode material is activated carbon, the negative electrode material is niobium pentoxide, and the electrolyte is 1M LiBF4 acetonitrile solution. The rated voltage is 2.7V and the lower limit voltage is 1.0V.

[0035] Step 1: Apply 0.5MPa pressure to the lithium-ion capacitor; Step 2: Charge the lithium ion capacitor to 2.85V at 1C constant current, charge at 2.85V at constant voltage for 0.2h, discharge at 1C constant current to 1.0V, and cycle this charge and discharge system 3 times; Step 3: Charge the lithium ion capacitor to 2.7V at 5C constant current, and discharge it to 1.0V at 5C constant current, and cycle this charge and discharge system 20 times; 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; Step 5: The lithium-ion capacitor is aged at 50°C for 60 hours while maintaining the pressurized state of step 1; Step 6: Keep the lithium-ion capacitor under the pressurized state of step 1 and let it stand at room temperature for 8 hours; Step 7: Exhaust and reseal the lithium-ion capacitor.

[0036] <Comparative Example 1> 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 Example 1.

[0037] <Comparative Example 2> The only difference from Example 1 is that there is no step 2, and the other steps are the same as Example 1.

[0038] <Comparative Example 3> The only difference from Example 1 is that there is no step 3, and the other steps are the same as Example 1.

[0039] <Comparative Example 4> The only difference from Example 1 is that there is no step 4, and the other steps are the same as Example 1.

[0040] <Comparison of technical effects of embodiments and comparative examples> 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 tests. The test results are shown in Tables 1, Figure 2 As shown: Table 1 5000 times charge and discharge test results; Through Examples 1 and 5, it is shown that for titanium and niobium metal oxides, according to the above-mentioned chemical formation aging method, a good cycle life can be achieved at a high rate of 40C.

[0041] Compared with Examples 1 and 2, since the maximum charging voltage is relatively low during the low current formation stage, part of the moisture and unstable functional groups inside the capacitor cannot be eliminated, resulting in reduced cycle performance.

[0042] Compared with 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.

[0043] Compared with Examples 1 and 4, since the formation current is relatively large at the initial stage of formation, the cycle life is slightly reduced.

[0044] Compared with Example 1 and Comparative Example 1, since a large amount of gas will be 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 sheet resistance, and thus affect the life.

[0045] 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 cannot be eliminated, resulting in reduced cycle performance.

[0046] 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.

[0047] Compared with Example 1 and Comparative Example 4, since the capacitor ages at low voltage, a stable interface cannot be formed, resulting in poor cycle performance.

[0048] The above is a detailed description of the embodiments, which is convenient for those skilled in the art to correctly understand and use the present invention. Any improvements or modifications to the technical solutions obtained by those skilled in the art based on the present invention on the basis of the prior art, without innovative work, only through analysis, analogy or limited enumeration, etc., should be within the scope of protection determined 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 keep the pressure state during the entire formation and aging process; S2. The lithium ion capacitor is charged with a first current I1 to a first voltage U1 at a constant current, 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 first current I1 at a constant current to a second voltage U2, and the above charging and discharging process is repeated 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 a second current I2 at a constant current to a second voltage U2, and the charging and discharging process is repeated 10 to 50 times; S4. The first current I1 is charged 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 in step s1, aging the lithium ion capacitor at 45 to 60 ° C 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.

2. A metal oxide based lithium ion capacitor formation aging method as claimed in claim 1, characterized in that The range of the first current I1 in step s2 and step s4 is 0.5-3C.

3. A metal oxide based lithium ion capacitor formation aging method as claimed in claim 1, characterized in that In step s3, the second current I2 is 3-30C.

4. A metal oxide based lithium ion capacitor formation aging method as claimed in claim 1, characterized in that 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.

5. A metal oxide based lithium ion capacitor formation aging method as claimed in claim 1 or 4, characterized in that The third voltage U3 is the rated voltage of the lithium ion capacitor.

6. 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 voltage of the lithium ion capacitor.

7. 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 metal oxide, and the metal oxide comprises one or a combination of the following: lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide and titanium dioxide.

8. 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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