Anode interface construction method and application in lithium ion capacitor
By constructing an organic/inorganic composite CEI layer on the surface of the positive electrode of a lithium-ion capacitor, the problem of gas generation and expansion during overcharging of lithium-ion capacitors is solved, improving electrochemical stability and safety, and achieving good cycle stability and rate performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-03-27
AI Technical Summary
During long-term use, existing lithium-ion capacitors are prone to oxidation at the positive electrode interface and electrolyte decomposition, which can lead to gas expansion during overcharging, affecting system safety and stability.
By electrochemically treating the positive electrode in a specific electrolyte system, and micro-corroding the aluminum current collector using an electrolyte containing fluorinated lithium salts and cyclic carbonate solvents, a multifunctional CEI layer is constructed in situ. This CEI layer includes an organic/inorganic composite structure, including AlxOyFz and LiF, polyester or polycarbonate compounds.
It significantly suppressed overcharge gas generation, increased the upper limit of electrochemical stable voltage, and maintained good cycle stability and rate performance, thereby enhancing the safety and electrochemical performance of lithium-ion capacitors.
Smart Images
Figure CN121748183A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of capacitors, and particularly relates to a positive electrode interface construction method and application thereof in lithium ion capacitors. BACKGROUND
[0002] With the large-scale application of electrochemical energy storage technology, its safety and operation stability are increasingly important. In the long-term use process, the electrochemical energy storage system will inevitably age, leading to a decrease in consistency of the energy storage unit in charge and discharge behavior, and making some units prone to overcharging. When the capacitor is charged beyond its state of charge (SOC) limit, excessive energy input will trigger harmful electrochemical reactions, leading to decomposition of the electrolyte and generation of a large amount of gas products. With the accumulation of gas, the single device will swell and even rupture, thereby causing a series of thermal runaway reactions and seriously damaging the performance and safety of the system.
[0003] At the positive electrode interface, the decomposition of the electrolyte is mainly dominated by two pathways: in the chemical pathway, high-activity substances released from the positive electrode (such as functional groups contained in porous carbon) and other impurities will trigger a violent oxidation reaction on the traditional carbonate solvent; in the electrochemical pathway, when the local potential of the positive electrode exceeds the electrochemical stability window of the electrolyte, the electrolyte will directly decompose. Preventing direct contact between the electrode and the electrolyte is one of the most effective strategies to inhibit undesirable interfacial reactions. This strategy is generally achieved by two methods, including the addition of a positive electrode surface coating and the in-situ construction of a positive electrode / electrolyte interface phase (CEI). The addition of a surface coating is difficult to achieve uniform coverage on a high specific surface area substrate, while the in-situ construction of a CEI is a self-adaptive assembly process that can provide good protection effect even for nano-scale porous structures. Currently, researchers generally construct a CEI layer by adjusting the electrolyte formulation (such as replacing or adding solvents, lithium salts and other functional additives). The CEI construction process guided by electrolyte adjustment is often gradually completed in multiple charge and discharge cycles. However, as the cycle progresses, the continuous consumption and transformation of electrolyte components will change the positive electrode interface chemistry, leading to deviation of the CEI construction process from the set path and weakening of its protective effect. SUMMARY
[0004] The purpose of the present application is to provide a positive electrode interface construction method and its application. By pre-electrochemically treating the positive electrode in a specific electrolyte system, a multifunctional CEI is constructed on the surface of the activated carbon positive electrode using the micro-corrosion effect of the electrolyte on the aluminum current collector. In the lithium ion capacitor system using conventional carbonate electrolyte, compared with the original positive electrode, the lithium ion capacitor using the positive electrode after the construction of the CEI shows a higher upper limit of the electrochemical stability voltage, and the gas generation phenomenon under overcharging conditions is significantly inhibited. In addition, the positive electrode after the construction of the CEI still shows good cycle stability.
[0005] The technical solution of the present application is as follows:
[0006] A positive electrode interface construction method, comprising the following steps:
[0007] Assembling a non-liquid injected lithium ion capacitor, comprising an activated carbon positive electrode and a lithium ion battery negative electrode material;
[0008] Injecting a CEI construction electrolyte, the electrolyte comprising a fluorine-containing lithium salt and a cyclic carbonate solvent, the anion of the fluorine-containing lithium salt being capable of forming a soluble compound with aluminum ions;
[0009] Constant current charging the capacitor to a set capacity and then discharging, in-situ constructing a CEI layer on the surface of the activated carbon positive electrode;
[0010] Replacing the electrolyte and injecting a cycling electrolyte.
[0011] In the above technical solution, the fluorine-containing lithium salt is at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, or lithium (trifluoromethylsulfonyl)(pentafluoroethylsulfonyl)imide, with a concentration of 0.5-3 mol / L; the cyclic carbonate solvent is at least one of EC, PC, FEC, DFEC, FPC, or DFPC.
[0012] In the above technical solution, the set capacity is 150%-1500% of the nominal capacity, the charging rate is 0.01-10C, and the discharge termination voltage is 3.0-3.1 V.
[0013] In the above technical solution, the cycling electrolyte comprises: a lithium salt being at least one of LiPF6, LiBF4, or LiDFOB; and a solvent comprising a cyclic carbonate compound.
[0014] In the above technical solution, when the negative electrode material is lithium metal, the charging capacity is 150%-1500% of the nominal capacity; when the negative electrode material is a non-lithium metal material, the charging capacity is 150%-1500% of the nominal capacity.
[0015] A lithium ion capacitor, the positive electrode of which is constructed with a CEI layer by the method of any one of the above, the CEI layer comprising an organic / inorganic composite structure, wherein the inorganic phase is Al x O y F z and LiF, and the organic phase is a polyester or polycarbonate compound.
[0016] A device for preparing a lithium ion capacitor, comprising:
[0017] Electrolyte injection module, used for injecting electrolyte for CEI construction;
[0018] The electrochemical processing module performs constant current charging and discharging operations;
[0019] Electrolyte replacement module, used to replace the circulating electrolyte.
[0020] The above-mentioned lithium-ion capacitors are used in energy storage systems.
[0021] The above-mentioned lithium-ion capacitors are used to suppress gas generation during overcharging.
[0022] An electrochemical energy storage system comprising the aforementioned lithium-ion capacitor.
[0023] Beneficial effects:
[0024] Compared to CEIs that gradually form during multiple cycles by adjusting the electrolyte formulation, the CEI prepared by the method of this invention has a unique organic / inorganic composite structure, wherein the inorganic phase contains Al. x O y F z And LiF, the organic phase is polyester or polycarbonate compound. More importantly, the method of the present invention can achieve precise control of CEI thickness. The lithium-ion capacitor constructed with CEI by the method of the present invention exhibits excellent overcharge gas generation suppression ability, and can maintain good rate performance and cycle stability, effectively taking into account the electrochemical performance and safety of lithium-ion capacitors. These advantages come from the following technical points: (1) Utilizing the micro-corrosion effect of the electrolyte used for CEI construction on aluminum, an in-situ Lewis acidic Al is formed. x O y F z The components can catalyze the ring-opening polymerization of cyclic carbonates under high voltage conditions, thereby avoiding the oxidation and decomposition of cyclic carbonates to generate CO2 and significantly suppressing overcharge gas generation; (2) During the construction of CEI, fluorinated lithium salt anions are enriched on the positive electrode surface, promoting the in-situ generation of LiF components and ensuring the rapid transport of lithium ions; (3) The amount of CEI formation is positively correlated with the charging capacity during the CEI construction process, and the nanometer-level precise control of CEI thickness can be achieved by adjusting the charging capacity. Attached Figure Description
[0025] Figure 1 Transmission electron microscopy image of the activated carbon cathode surface of CEI constructed in Example 1;
[0026] Figure 2 Transmission electron microscopy image of the activated carbon cathode surface without CEI construction in Comparative Example 1;
[0027] Figure 3This is a comparison chart of the rate performance of lithium-ion capacitors in Example 1 and Comparative Example 1;
[0028] Figure 4 This is a comparison of the appearance of the lithium-ion capacitors of Example 1 and Comparative Example 1 after overcharging.
[0029] Figure 5 This is an ultrasonic transmission image of a lithium-ion capacitor before overcharging, as shown in Example 1.
[0030] Figure 6 The image shows the ultrasonic transmission diagram (gas production) of the lithium-ion capacitor after overcharging in Comparative Example 1.
[0031] Figure 7 The images show a comparison of the appearance of the lithium-ion capacitors of Example 2 and Comparative Example 2 after overcharging. Detailed Implementation
[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.
[0033] Assemble an unfilled lithium-ion capacitor, wherein the positive electrode material is activated carbon, and the negative electrode material includes, but is not limited to, lithium metal, graphite, hard carbon, soft carbon, silicon carbon, and other lithium battery negative electrode materials. Inject an electrolyte for CEI construction into the lithium-ion capacitor. The electrolyte for CEI construction is characterized by its lithium salt anion containing fluorine, and its ability to form a compound soluble in the electrolyte with aluminum ions, meaning it exhibits a certain degree of corrosivity to aluminum metal in the electrochemical system. Lithium salts meeting these conditions include, but are not limited to, fluorinated lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, or lithium (trifluoromethanesulfonyl)(pentafluoroethylsulfonyl)imide, with a lithium salt concentration of 0.5~3 mol / L. The electrolyte system contains cyclic carbonate compounds, including but not limited to EC, PC, FEC, DFEC, FPC, or DFPC. The lithium-ion capacitors are vacuum-sealed after electrolyte injection and allowed to stand for at least 8 hours.
[0034] For lithium-ion capacitor systems that do not require pre-intercalation of lithium (with lithium metal as the negative electrode and activated carbon as the positive electrode), a charge-discharge tester is used to perform constant current charging at a rate of 0.01~10 C. When the capacitor is charged to a certain capacity (the capacity range is 150%~1500% of the nominal capacity), it is then discharged to about 3.0 V, thus completing the CEI construction process.
[0035] For lithium-ion capacitor systems that require pre-lithiation (the negative electrode is a lithium-ion battery negative electrode material such as hard carbon or soft carbon, the positive electrode is activated carbon, and lithium metal is added as the negative electrode pre-lithiation counter electrode), the CEI construction process and the pre-lithiation process can be completed in two ways: (1) Using lithium metal as the negative electrode and activated carbon as the positive electrode, constant current charging is performed using a charge-discharge tester at a charging rate of 0.01~10 C. When the capacity is charged to a certain level (the capacity range is 150%~1500% of the nominal capacity), it is then discharged to about 3.0V, which completes the CEI construction process. Then, using lithium metal as the negative electrode and non-lithium metal lithium-ion battery negative electrode material as the positive electrode, constant current and constant voltage discharge is performed using a charge-discharge tester until the designed pre-lithiation capacity is reached, which completes the pre-lithiation process; (2) Using lithium-ion battery negative electrode material as the negative electrode and activated carbon as the positive electrode, constant current charging is performed using a charge-discharge tester at a charging rate of 0.01~10 C. C. When the battery is charged to a certain capacity (capacity range is 150%~1500% of the nominal capacity), it is then discharged to about 3.0 V for the positive electrode relative to lithium, which completes the CEI construction process. Then, with lithium metal as the negative electrode and the lithium-ion battery negative electrode material as the positive electrode, a constant current and constant voltage discharge is performed using a charge and discharge tester until a certain capacity is reached (discharge capacity = designed pre-intercalation capacity - charging capacity of the CEI construction process), which completes the pre-intercalation process.
[0036] The electrolyte in the lithium-ion capacitor constructed using the CEI method is poured out, and a circulating electrolyte is added. This process of rinsing and pouring out the electrolyte is repeated multiple times to complete the electrolyte replacement, resulting in a usable lithium-ion capacitor. The circulating electrolyte is characterized by low corrosivity to aluminum in the electrochemical environment, or its products with aluminum are poorly soluble in the electrolyte, thus forming a passivation layer that blocks further corrosion. For electrolytes meeting these conditions, the lithium salt includes, but is not limited to, fluorinated lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, or lithium (trifluoromethanesulfonyl)(pentafluoroethylsulfonyl)imide. The solvent should contain cyclic carbonate compounds. Conventional commercial electrolytes generally meet the characteristics of circulating electrolytes.
[0037] Example:
[0038] Example 1
[0039] S1. Using lithium metal and activated carbon as negative and positive electrode materials respectively, assemble a lithium-ion capacitor cell with a nominal capacity of 6 mAh, and inject it with CEI construction electrolyte (lithium salt is LiFSI, concentration is 1 mol / L, solvent is PC), vacuum seal and let stand for 12 h.
[0040] S2. Using soft carbon as the negative electrode and activated carbon as the positive electrode, the monomer was charged at a constant current using a charge-discharge tester at a charging rate of 1 C (1 C = 6 mA), resulting in a charging capacity of 78 mAh. After charging, the monomer was discharged at a constant current and constant voltage at a discharge rate of 1 C, with a final discharge voltage of 3.05 V, thus completing the CEI construction process.
[0041] S3. Pour out the electrolyte from the monomer, add circulating electrolyte (lithium salt is LiPF6, concentration is 1 mol / L, solvent is PC), thoroughly rinse the electrode, and then pour it out. Repeat the above process 3 times to complete the electrolyte replacement. After vacuum sealing, the final lithium-ion capacitor monomer 1 containing CEI is obtained.
[0042] Transmission electron microscopy image of the positive electrode surface of CEI construction as shown below Figure 1 As shown. From Figure 1 As can be seen from the above, the method of the present invention constructs a uniformly coated CEI on the surface of activated carbon with a thickness of about 10 nm.
[0043] Example 2
[0044] S1. Using soft carbon and activated carbon as negative and positive electrode materials respectively, assemble a lithium-ion capacitor cell with a nominal capacity of 650 mAh. Add metallic lithium as the negative electrode pre-intercalated lithium counter electrode, and inject CEI construction electrolyte (lithium salt is LiFSI, concentration is 1.2 mol / L, solvent is EC / PC / DEC, volume ratio is 3:1:4), vacuum seal and let stand for 12 h.
[0045] S2. Using soft carbon as the negative electrode and activated carbon as the positive electrode, the single cell was charged at a constant current using a charge-discharge tester at a charging rate of 1 C (1 C = 650 mA), resulting in a charging capacity of 1500 mAh. After charging, the single cell was discharged at a constant current and constant voltage at a discharge rate of 1 C, with a final discharge voltage of 3.1 V (vs. Li). + The CEI construction process is completed by using lithium metal as the negative electrode and soft carbon as the positive electrode. A constant current and constant voltage discharge tester was used, with the constant current set at 100 mA and the constant voltage at 0.01 V. Since the designed pre-intercalation capacity of this monomer is 2200 mAh, the pre-intercalation process is completed when the discharge capacity reaches 700 mAh.
[0046] S3. Remove the lithium metal, pour out the electrolyte from the monomer, add circulating electrolyte (lithium salt is LiPF6, concentration is 1.2 mol / L, solvent is EC / DEC / DMC, volume ratio is 1:1:1), thoroughly rinse the electrode, and then pour it out. Repeat the above process 3 times to complete the electrolyte replacement. After vacuum sealing, the final lithium-ion capacitor monomer 2 containing CEI is obtained.
[0047] Comparative example:
[0048] Comparative Example 1
[0049] The lithium-ion capacitor cell was prepared according to the method of Example 1, except that step S2 was skipped and the remaining operations were the same as in Example 1, and finally a lithium-ion capacitor cell 1 without CEI was obtained.
[0050] Transmission electron microscopy image of the cathode surface without CEI formation as shown below Figure 2 As shown. From Figure 2 As can be seen, no CEI was observed on the positive electrode surface.
[0051] Comparative Example 2
[0052] Lithium-ion capacitor cells were prepared according to the method in Example 2.
[0053] The difference is that step S2 is changed to using lithium metal as the negative electrode and soft carbon as the positive electrode, and performing constant current and constant voltage discharge using a charge-discharge tester, setting the constant current to 100 mA and the constant voltage to 0.01 V. Discharge until the discharge capacity reaches 2200 mAh, thus completing the pre-lithiation process.
[0054] The remaining operations are the same as in Example 2, and finally a lithium-ion capacitor cell 2 without CEI is obtained.
[0055] Application example:
[0056] Application Example 1
[0057] The lithium-ion capacitor cells obtained in Example 1 and Comparative Example 1 were placed on a charge-discharge tester for constant current charge-discharge testing. The voltage window was 2.2~3.8 V, and a series of current densities were set to test their rate performance.
[0058] The lithium-ion capacitor cells obtained in Example 1 and Comparative Example 1 were placed on a charge-discharge tester for constant current charging test. The initial voltage was about 3.05 V, the charging rate was 1 C, and the charging time was 24 h, in order to test their gas generation under overcharge conditions.
[0059] Figure 3 The graph shows the rate performance of the lithium-ion capacitor cells obtained in Example 1 and Comparative Example 1. Figure 4 The images shown are digital photographs of the lithium-ion capacitor cells obtained in Example 1 and Comparative Example 1 after overcharging. The corresponding ultrasonic transmission images before and after overcharging are shown below. Figure 5 and Figure 6 As shown. From Figure 3 It can be seen that, compared with the monomer of Comparative Example 1, the monomer of Example 1 exhibits higher discharge capacity at different rates, i.e., better rate performance. From Figures 4-6It can be seen that after overcharging under the same conditions, the outer packaging of the monomer in Comparative Example 1 was significantly deformed and a large amount of gas was detected inside, while the shape of the monomer in Example 1 remained basically unchanged and only a very small amount of gas was detected inside, demonstrating good overcharging gas generation suppression ability.
[0060] Application Example 2
[0061] The lithium-ion capacitor cells obtained in Example 2 and Comparative Example 2 were placed on a charge-discharge tester for constant current charging test. The initial voltage was about 3.1 V, the charging rate was 1 C, and the cutoff voltage was 4.8 V, in order to test their gas generation under overcharge conditions.
[0062] Figure 7 The images show digital photographs of the lithium-ion capacitor cells obtained in Example 2 and Comparative Example 2 after overcharging. As can be seen from the figures, under the same conditions, after overcharging, the outer packaging of the cell in Comparative Example 2 is significantly deformed, while the cell in Example 2 remains essentially unchanged in shape, demonstrating good overcharge gas generation suppression capability.
[0063] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.
Claims
1. A method for constructing a positive electrode interface, characterized in that, Includes the following steps: Assemble an unfilled lithium-ion capacitor, comprising an activated carbon positive electrode and lithium battery negative electrode materials; An electrolyte for CEI construction is injected, the electrolyte comprising a fluorinated lithium salt and a cyclic carbonate solvent, wherein the anion of the fluorinated lithium salt can form a soluble compound with aluminum ions; The capacitor is charged to a set capacity by constant current and then discharged to form an in-situ CEI layer on the surface of the activated carbon positive electrode. Replace the electrolyte and inject circulating electrolyte.
2. The method according to claim 1, characterized in that: The fluorinated lithium salt is at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, or lithium (trifluoromethanesulfonyl)(pentafluoroethylsulfonyl)imide, with a concentration of 0.5-3 mol / L; The cyclic carbonate solvent is at least one of EC, PC, FEC, DFEC, FPC, or DFPC.
3. The method according to claim 1, characterized in that: The set capacity is 150%-1500% of the nominal capacity, and the charging rate is 0.01-10 C; The discharge termination voltage is 3.0-3.1 V.
4. The method according to claim 1, characterized in that, The circulating electrolyte comprises: The lithium salt is at least one of LiPF6, LiBF4 or LiDFOB; The solvent contains cyclic carbonate compounds.
5. The method according to claim 1, characterized in that: When the negative electrode material is lithium metal, the charging capacity is 150%-1500% of the nominal capacity; When the negative electrode material is a non-lithium metal material, the charging capacity is 150%-1500% of the nominal capacity.
6. A lithium-ion capacitor, characterized in that, Its positive electrode is constructed with a CEI layer by the method described in any one of claims 1-5, wherein the CEI layer comprises an organic / inorganic composite structure, wherein the inorganic phase is Al. x O y F z And LiF, the organic phase is a polyester or polycarbonate compound.
7. An apparatus for manufacturing a lithium-ion capacitor, characterized in that, include: Electrolyte injection module, used for injecting electrolyte for CEI construction; The electrochemical processing module performs constant current charging and discharging operations; Electrolyte replacement module, used to replace the circulating electrolyte.
8. The application of the lithium-ion capacitor of claim 6 in an energy storage system.
9. The application of the lithium-ion capacitor of claim 6 in suppressing overcharge gas generation.
10. An electrochemical energy storage system, characterized in that, It includes the lithium-ion capacitor as described in claim 6.