Method for eliminating lithium precipitation on surface of negative electrode of lithium ion capacitor

Abstract

The invention discloses a method for eliminating lithium precipitation on the surface of a negative electrode of a lithium ion capacitor, and belongs to the technical field of lithium ion capacitors, and the method comprises the following steps: 1, adjusting a lithium precipitation monomer to be in an SOC state of-100% to 0%; step 2, adding an additive accounting for 0.01-10% of the injection mass of the original electrolyte into the monomer, and standing for 1-30 days; step 3, adjusting the voltage of the single body to 50%-200% of the SOC state, and quenching the additive; and step 4, carrying out degas operation on the monomers. By adopting the method, lithium precipitated on the surface of the negative electrode can be effectively eliminated, potential safety hazards caused by the lithium can be eliminated, and the additive activates the lithium precipitated on the surface of the negative electrode and returns to the positive electrode after being oxidized on the surface of the positive electrode, so that the potential of the negative electrode can be reduced, the monomer capacity is improved, and the cycling stability of the monomer is recovered.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion capacitors, and in particular relates to a method for eliminating lithium deposition on the negative electrode surface of a lithium ion capacitor. Background Art

[0002] Lithium-ion capacitors combine the double-layer energy storage mechanism of traditional capacitors with the ion embedding / de-embedding energy storage mechanism of lithium-ion batteries. Therefore, they not only have the high power density and fast response capability of traditional capacitors, but also the high energy density of lithium-ion batteries. On the one hand, thanks to the stable ion adsorption and desorption characteristics of the positive electrode material, hundreds of thousands or even millions of cycles can be achieved; on the other hand, thanks to the stable potential of ion embedding / de-embedding of the negative electrode material, it can store more energy at the same volume or weight, and the energy density is significantly improved compared to double-layer capacitors.

[0003] However, it is precisely because of this configuration that the kinetic mismatch between the positive and negative electrode materials occurs. Specifically, the rate of ion extraction from the negative electrode is significantly slower than the rate of ion adsorption and extraction from the positive electrode material. Therefore, when the lithium-ion capacitor works for a long time at a charge and discharge rate exceeding its allowable rate, the kinetic rate of lithium ion insertion and extraction on the negative electrode surface is slow, and it usually undergoes great surface polarization. Therefore, it is easy to cause lithium precipitation on the negative electrode surface during charging, causing the negative electrode potential to gradually shift to a high potential.

[0004] On the one hand, this phenomenon will lead to a synchronous rise in the positive electrode potential, causing the electrolyte to decompose violently on the positive electrode surface, resulting in serious attenuation such as blockage of positive electrode pores, decrease in specific capacitance, increase in interface resistance, and electrolyte drying up. On the other hand, the lithium precipitated on the negative electrode surface usually exists in the form of moss or dendrites, which can easily develop rapidly with the progress of charging and discharging, leading to more serious lithium precipitation, and may even cause dendrites to pierce the diaphragm, causing safety problems.

[0005] Therefore, timely eliminating the precipitated lithium on the negative electrode surface of the lithium ion capacitor and inhibiting the further deterioration of the positive and negative electrode materials due to lithium precipitation are particularly important for improving the cycle performance and safety of the lithium ion capacitor. Summary of the invention

[0006] In view of the problem of lithium precipitation on the negative electrode surface of a lithium ion capacitor, the present invention provides a method for eliminating lithium precipitation on the negative electrode surface of a lithium ion capacitor.

[0007] The technical solution of the present invention is as follows:

[0008] A method for eliminating lithium precipitation on the negative electrode surface of a lithium ion capacitor comprises the following steps:

[0009] Step 1: Use the charging and discharging equipment to adjust the voltage of the monomer that has been lithium-deposited to a SOC state of -100% to 0%.

[0010] Step 2: Add additives equivalent to 0.01-10% of the original electrolyte injection mass to the monomer in step 1, and leave it for 1-30 days. During this process, the additives will fully dissolve in the electrolyte, diffuse to the surface of the precipitated lithium, and react with the precipitated lithium to completely dissolve the lithium precipitated due to charging and discharging.

[0011] Step 3: After the storage is completed, the cell voltage is adjusted to a SOC state of 50%-200% through the charge and discharge equipment, so that the additives that have reacted are oxidatively polymerized on the positive electrode surface to form insoluble SEI components, thereby eliminating the additive components in the electrolyte.

[0012] Step 4: Finally, after the charge quenching additive is completed, the monomer is subjected to a degas operation to eliminate the gas components generated during the charging process, thereby obtaining the final monomer from which lithium precipitation has been eliminated.

[0013] In the above technical solution, in step 1, the negative electrode is at a higher potential than in normal use (0-100% SOC), and the positive electrode is at a lower potential than in normal use (0-100% SOC) to avoid reaction with the additive to be added in the next step.

[0014] In the above technical solution, in step 2, the additive is naphthalene, biphenyl, 4,4'-dimethylbiphenyl, 2-fluoro-5-iodopyridine, 2,2,6,6-tetramethylpiperidinoxide or a solution formed by dissolving these substances in a lithium-ion battery electrolyte solvent.

[0015] Beneficial effects:

[0016] The present invention discloses a method for eliminating lithium precipitated on the negative electrode surface of a lithium ion capacitor. The method can effectively eliminate the lithium precipitated on the negative electrode surface and eliminate the potential safety hazard caused thereby. Moreover, since the lithium precipitated on the negative electrode surface is activated by an additive, the lithium precipitated on the positive electrode surface is oxidized and returns to the positive electrode, thereby reducing the negative electrode potential, improving the monomer capacity and restoring the cycle stability of the monomer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Comparison of the negative electrode surface morphology before and after treatment.

[0018] Figure 2 Comparison of negative electrode potential under 3.0V conditions before and after treatment.

[0019] Figure 3 Comparison of the optical morphology of the negative electrode surface before and after treatment.

[0020] Figure 4 Comparison of the capacity of the monomer before and after treatment. DETAILED DESCRIPTION

[0021] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. However, the following embodiments are limited to explaining the present invention, and the protection scope of the present invention should include the entire contents of the claims, and through the description of the following embodiments, those skilled in the art can fully implement the entire contents of the claims of the present invention.

[0022] Embodiment 1:

[0023] Take a 1100F soft-pack lithium-ion capacitor that has undergone severe lithium precipitation, adjust the cell voltage to -50% SOC (corresponding to about 3.0V), cut it, add naphthalene particles with a mass equivalent to 0.5% of the injection volume, and seal it. Leave it at room temperature for 3 days. Then charge the cell, control the SOC to 120%, and keep the voltage constant for 1h. Vacuum seal the charged cell to obtain a soft-pack lithium-ion capacitor that eliminates lithium precipitation. By observing the morphology of the electrode surface before and after treatment, it can be seen that the lithium content on the negative electrode surface is significantly reduced after treatment.

[0024] Embodiment 2:

[0025] Take a 3300F wound aluminum shell lithium ion capacitor that has suffered severe lithium precipitation, adjust the monomer voltage to 0% SOC, add a saturated solution of DMC / EC / DEC (1:1:1, V:V) with a mass equivalent to 0.1% of the injection volume of biphenyl through the reserved injection port and seal it. Leave it at room temperature for 7 days. Then charge the monomer, control the SOC to 110%, and keep the voltage constant for 1h. The charged monomer is sealed to obtain a soft-pack lithium ion capacitor with lithium precipitation eliminated. By observing the negative electrode potential at 3.0V voltage, it can be found that after treatment, the negative electrode potential is reduced by about (6) mV, indicating that some of the precipitated lithium dissolves and returns to the negative electrode.

[0026] Embodiment 3:

[0027] Take a removable button-type lithium-ion capacitor that has undergone severe lithium deposition, adjust the voltage to -100% SOC, disassemble and observe the surface state of the negative electrode, then add a saturated solution of DMC / EC / DEC (1:1:1, V:V) of 4,4'-dimethylbiphenyl equivalent to 1% of the injection volume and seal it. Leave it at room temperature for 30 days. Then charge the monomer, control the SOC to 100%, and keep the constant voltage for 1h. Disassemble the charged monomer and observe the state of the negative electrode surface.

[0028] Embodiment 4:

[0029] Take a 1100F lithium-ion capacitor that has undergone severe lithium deposition, adjust the voltage to -100% SOC, then add a saturated solution of DMC / EC / DEC (1:1:1, V:V) of 2-fluoro-5-iodopyridine (5% of the injection volume) and 5% of DMC / EC / DEC (1:1:1, V:V) of 2,2,6,6-tetramethylpiperidinoxide to it and seal it. Leave it at room temperature for 1 day. Then charge the monomer, control the SOC to 150%, and keep the voltage constant for 1h. Comparing the charge and discharge curves of the treated monomer, it can be found that after treatment, the capacity of the monomer is significantly restored and the cycle stability is improved.

[0030] Results and Analysis: Figure 1 Comparison of the negative electrode surface morphology before and after treatment; a is before treatment, b is after treatment. Figure 2 Comparison of negative electrode potential at 3.0V before and after treatment; Figure 3 Comparison of the optical morphology of the negative electrode surface before and after treatment; a is before treatment, and b is after treatment. Figure 4 The capacity of the monomers before and after treatment is compared. The principle of the present invention is as follows: naphthalene, biphenyl, 4,4'-dimethylbiphenyl, 2-fluoro-5-iodopyridine, and 2,2,6,6-tetramethylpiperidin oxide do not participate in the reaction at a low SOC state because the negative electrode is at a higher potential. In contrast, due to the high reduction activity of lithium precipitated on the surface of the negative electrode of the monomer, these additives react with specific metallic lithium to generate lithium-containing compounds, such as naphthyl lithium, biphenyl lithium, etc., thereby eliminating the precipitated lithium caused by the degradation and abuse of the monomer performance. At the same time, the lithium-containing organic compounds produced by these reactions have high reducibility and will decompose on the surface of the positive electrode during the charging process. Part of the lithium element in the compound returns to the negative electrode in the form of active lithium, activating the dead lithium caused by lithium precipitation, and inhibiting the further degradation of the lithium ion capacitor.

[0031] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for eliminating lithium precipitation on the negative electrode surface of a lithium ion capacitor, characterized in that: The steps include: Step 1: Adjust the voltage of the monomer that has been lithium-deposited to a SOC state of -100% to 0% through a charging and discharging device; Step 2, adding an additive equivalent to 0.01-10% of the original electrolyte injection mass to the monomer in step 1, and leaving it aside for 1-30 days; Step 3: After the storage is completed, the cell voltage is adjusted to a SOC state of 50%-200% by a charge and discharge device to quench the additive; Step 4: Finally, after the charge quenching additive is completed, the monomer is subjected to a degas operation to eliminate the gas components generated during the charging process, thereby obtaining the final monomer from which lithium precipitation has been eliminated.

2. A method for eliminating lithium precipitation on the negative electrode surface of a lithium ion capacitor according to claim 1, characterized in that: In step 1, the negative electrode is at a higher potential than that in a normal SOC state (0-100%), and the positive electrode is at a lower potential than that in a normal SOC state (0-100%).

3. A method for eliminating lithium precipitation on the negative electrode surface of a lithium ion capacitor according to claim 1, characterized in that: In step 2, the additive is naphthalene, biphenyl, 4,4'-dimethylbiphenyl, 2-fluoro-5-iodopyridine, 2,2,6,6-tetramethylpiperidinoxide, or a solution formed by dissolving these substances in a lithium-ion battery electrolyte solvent.

Images