Lithium-ion supercapacitor cell and formation method therefor

Abstract

The present invention relates to the technical field of lithium-ion batteries, in particular to a lithium-ion supercapacitor cell and a formation method therefor. The negative / positive ratio of a lithium-ion supercapacitor is (1.1-2.2):1. The calculation formula for the negative / positive ratio is (AC×Ad×AL) / (Cc×Cd×CL). In the present invention, by means of a stepped low-current formation charging process, a uniform and stable SEI film is formed on a surface of an amorphous carbon negative electrode, and by means of increasing a formation cut-off voltage, the minimal potential of an anode reaches approximately 0.06 V at the end of the initial charging of a battery, thereby consuming some of irreversible active sites. Furthermore, due to the over-capacity design of the anode, the phenomenon of lithium plating on a surface of the anode can also be prevented when a battery cell is at a high cut-off voltage, thereby greatly improving the safety performance of the battery. In addition, the over-capacity anode also ensures the cycle life of the lithium-ion supercapacitor under high-rate charging and discharging.

Description

Lithium-ion supercapacitor cells and their formation methods Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to a lithium-ion supercapacitor cell and its formation method. Background Technology

[0002] Lithium-ion supercapacitors (hereinafter referred to as lithium supercapacitors) are hybrid energy storage devices that combine high energy density, high power density, and long cycle life. Their energy storage mechanism integrates the Faraday storage of lithium-ion batteries and the non-Faraday storage of supercapacitors, while also possessing, to a certain extent, the advantages of both.

[0003] Currently, the anode material for lithium supercapacitors is a mixture of the active material of lithium-ion batteries and the carbon material commonly used in supercapacitors. The anode material is amorphous carbon, and the electrolyte composition is basically the same as that of lithium-ion batteries. Therefore, similar to lithium-ion batteries, lithium supercapacitors also require formation charging after assembly to activate the positive and negative electrode active materials and form an SEI film on the negative electrode surface. However, unlike lithium-ion batteries, lithium supercapacitors, as a high-power-density, long-cycle-life hybrid energy storage device, need to complete at least 10,000 cycles under a ≥5C cycling current. Therefore, it is necessary to explore suitable cell formation processes to achieve a series of objectives, including activating electrode materials, improving cell interfaces, self-discharge, and the hardness of pouch cells.

[0004] Hard carbon, an amorphous carbon material commonly used as an anode in lithium supercapacitors, suffers from irreversible capacity due to its functional groups, impurities, and microporous defects, resulting in low initial formation efficiency. Furthermore, if the irreversible active sites of hard carbon cannot be fully consumed during formation to form a stable SEI (interface electrolyte membrane), lithium supercapacitors will face rapid capacity decay and significantly reduced cycle life during subsequent 5C high-rate cycling.

[0005] In the prior art, CN102916224A discloses a method for forming a lithium-ion battery with an active material comprising amorphous carbon material. The formation process includes at least two steps: charging and resting. The characteristic feature is that the battery balance ratio of the lithium-ion battery is (1.04-1):1, and the anode potential at the end of formation is between 0.03-0V. CN110676514A discloses a lithium-ion battery cell and its formation method, wherein the lithium-ion battery cell includes an anode, an anode (containing amorphous carbon material), a separator, an electrolyte, and an encapsulation material, and the ratio of anode capacity A to anode capacity B is 0.7-1. CN109560282A discloses an electrode active composition (including amorphous carbon, polyvinyl alcohol, and N-methylpyrrolidone) wherein the electrode active composition accounts for 0.1-0.5% of the electrode material by weight. An electrode sheet and its preparation method are also provided, as well as a low-temperature formation method, which involves placing the electrode sheet in an electrolyte and charging it at 0.005C to 0.02C for 30 hours at -25 to -15°C.

[0006] However, the technical solutions in the aforementioned patent applications mostly employ a battery design balance ratio of around 1. While this approach effectively addresses lithium plating prevention and production process capabilities in graphite anode battery systems, the balance ratio can be appropriately relaxed due to the inherent resistance to lithium plating in hard carbon materials. Furthermore, hard carbon is prone to capacity decay at high rates, particularly a decrease in the capacity contribution from the pore adsorption region, which negatively impacts cycle life. Therefore, increasing the N / P ratio to allow the anode to operate in a shallow charge-discharge state is beneficial for maintaining a lifespan of tens of thousands of cycles and improving charge performance. Summary of the Invention

[0007] Hard carbon, as an amorphous form of carbon, has an interlayer spacing d 002 Larger than graphite, amorphous carbon has a higher lithium insertion / extraction potential and excellent rate charge / discharge and low-temperature performance. However, due to its low heat treatment temperature and large specific surface area, when combined with lithium iron phosphate or lithium nickel cobalt manganese oxide batteries, it consumes a large number of lithium ions at the anode during the first formation charge, resulting in a low initial efficiency and affecting battery capacity. Current formation processes that widely utilize amorphous carbon tend to control the battery's balance ratio between 0.7 and 1.04, with the designed anode capacity being basically consistent with, or even lower than, the original anode capacity. However, this has not significantly improved the cell lifespan during high-rate cycling or its high-temperature charging capability.

[0008] The present invention has discovered that by further increasing the balance ratio of the battery, the cycle stability and charging capacity of high-rate cycling devices can be improved.

[0009] Based on this, the present invention has the following technical solution:

[0010] In a first aspect, the present invention provides a lithium-ion supercapacitor cell with a lithium supercapacitor balance ratio of (1.1 to 2.2):1;

[0011] The formula for calculating the balance ratio is: (A) c ×A d ×A L ) / (C c ×C d ×C L );

[0012] Among them, A c The discharge specific capacity of the anolyte is expressed in mAh / g.

[0013] A d The areal density of the anode material, in g / m³. 2 ;

[0014] A L This represents the percentage of the anolyte active material loaded in the overall anode.

[0015] C c The discharge specific capacity of the cathode active material is expressed in mAh / g.

[0016] C d The areal density of the cathode material, in g / m³. 2 ;

[0017] C L This represents the percentage of the cathode active material loaded in the overall cathode.

[0018] In this invention, the balance ratio of lithium supercapacitor can be 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1 or 2.2:1, etc.

[0019] In this invention, the lithium-ion supercapacitor cell includes an anode, a cathode, a separator, an electrolyte, structural components, and auxiliary materials.

[0020] Preferably, the anode active material includes one or more of graphite, silicide, amorphous carbon, activated carbon, and carbon microspheres; wherein the amorphous carbon accounts for 5-95% of the total mass of the anode active material.

[0021] More preferably, the amorphous carbon accounts for 5 to 50% of the total mass of the anode active material; even more preferably, the amorphous carbon accounts for 5 to 30% of the total mass of the anode active material; for example, values ​​such as 5%, 10%, 15%, 20%, 25%, or 30%.

[0022] Preferably, the cathode active material includes one or more of lithium nickel cobalt manganese, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, and lithium vanadium phosphate, wherein lithium iron phosphate accounts for 10-95% of the total mass of the cathode active material.

[0023] More preferably, lithium iron phosphate accounts for 50% to 95% of the total mass of the cathode active material; for example, values ​​such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%.

[0024] In this invention, the diaphragm allows ions to move freely in the electrolyte to maintain the charging and discharging process of the capacitor. Those skilled in the art can choose conventional diaphragms that have been disclosed in the art as needed, and no further limitations are imposed here.

[0025] In this invention, structural components include the capacitor's casing, terminals, connectors, etc., providing mechanical support and protection for the capacitor. Auxiliary materials include adhesives, conductive agents, electrolyte additives, etc., used to improve the capacitor's performance and stability.

[0026] Secondly, the present invention provides a method for the formation of a lithium-ion supercapacitor cell, comprising:

[0027] S1: Constant current charging until the cell's charging capacity reaches 5-15%;

[0028] S2: After resting, charge at a constant current until the cell's charging capacity reaches 25-35%;

[0029] S3: After resting, constant current charging is performed until the cutoff voltage of 3.65V is reached;

[0030] S4: After resting, charge at a constant current until the cutoff voltage of 3.75~3.85V, then stop charging.

[0031] In this invention, on the one hand, a uniform and stable SEI film is formed on the surface of the amorphous carbon anode through a step-like low-current formation charging process. By increasing the formation cutoff voltage, the lowest anode potential reaches approximately 0.06V at the end of the first charge, thereby consuming some irreversible active sites. On the other hand, due to the excessive anode capacity design, lithium plating on the anode surface is prevented even at a high cutoff voltage, thus greatly improving the battery's safety performance. Simultaneously, the excessive anode capacity also ensures the cycle life of the lithium supercapacitor under high-rate charge-discharge conditions.

[0032] Preferably, the charging current in S1 is 0.01 to 0.05C, for example, 0.01C, 0.02C, 0.03C, 0.04C, and 0.05C.

[0033] Preferably, the charging current in S2 is 0.1 to 0.2C, for example, 0.1C, 0.2C, 0.3C, 0.4C, and 0.5C.

[0034] Preferably, the charging method in S3 is constant current and constant voltage charging, with a cutoff current of 0.05C.

[0035] Preferably, the settling time is 3 to 5 minutes, for example, 3 minutes, 4 minutes or 5 minutes.

[0036] Preferably, the formation temperature is 30 to 45°C, for example, 30°C, 35°C, 40°C, and 45°C.

[0037] This invention, on the one hand, utilizes a stepped, low-current formation and charging process to form a uniform and stable SEI film on the surface of the amorphous carbon anode. By increasing the formation cutoff voltage, the anode potential reaches a minimum of approximately 0.06V at the end of the first charge, thereby consuming some irreversible active sites. On the other hand, the excessive anode capacity design prevents lithium plating on the anode surface even at high cutoff voltages, significantly improving battery safety. Simultaneously, the excessive anode capacity also ensures the cycle life of the lithium supercapacitor under high-rate charge-discharge conditions. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 is a comparison chart of cycle life of the embodiments and comparative examples provided by the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0042] The formation temperature for the following examples and comparative examples is 45°C.

[0043] Example 1

[0044] This embodiment uses a soft-pack lithium supercapacitor with a capacity of approximately 2.6 Ah. The cathode active material is a mixture of LFP and activated carbon (the mass ratio of the two is 9:1), and the anode active material is hard carbon. The battery balance ratio in this embodiment is 2.2:1.

[0045] This embodiment provides a formation method, which specifically includes the following steps: first, charge the battery with a constant current of 0.05C to 10% of the battery formation charging capacity, let it stand for 5 minutes, then charge it with a constant current of 0.1C to 30% of the battery formation charging capacity, let it stand for 5 minutes, then charge it with a constant current of 0.2C to 3.65V, let it stand for 5 minutes, and finally charge it with a constant current of 0.2C to the cutoff voltage of 3.8V, thus completing the formation.

[0046] The battery in this embodiment was subjected to capacity testing: the test voltage range was 3.65-2.2V. After formation, the capacity was first tested by charging and discharging at 1C / 1C, and the test capacity was recorded as 2.49-2.517Ah. After the capacity was tested, the cycle test was performed by charging and discharging at 5C / 5C. After 1400 cycles at room temperature, the capacity retention rate was 97.82%, which was recorded as S1.

[0047] Example 2

[0048] This embodiment uses a soft-pack lithium supercapacitor of about 2.4Ah. The cathode active material is a mixture of LFP and activated carbon (mass ratio of 9:1), and the anode active material is a mixture of hard carbon and graphite (mass ratio of 75:25). The battery balance ratio in this embodiment is 2.2:1.

[0049] The formation method in this embodiment is the same as the formation method in Embodiment 1.

[0050] The battery in this embodiment was subjected to capacity testing: the test voltage range was 3.65-2.2V. After the formation was completed, the capacity was first tested by charging and discharging at 1C / 1C, and the test capacity was recorded as 2.37-2.43Ah. After the capacity was tested, the cycle test was performed by charging and discharging at 5C / 5C. After 1400 cycles at room temperature, the capacity retention rate was 91%, which was recorded as S2.

[0051] Comparative Example 1

[0052] This comparative example uses a pouch lithium supercapacitor of approximately 2.6 Ah, a mixture of LFP and activated carbon as the cathode active material (mass ratio of 9:1), hard carbon as the anode active material, and a battery balance ratio of 2.2:1 in this embodiment.

[0053] This comparative example provides a formation method, which specifically includes the following steps: first, charge the battery with a constant current of 0.05C to 10% of the battery's formation charging capacity, let it stand for 5 minutes, and the formation is complete.

[0054] Capacity testing was performed on the battery in this comparative example: the test voltage range was 3.65-2.2V. After formation, the capacity was first tested by charging and discharging at 1C / 1C, and the test capacity was recorded as 2.648-2.665Ah. After the capacity was tested, the cycle test was performed by charging and discharging at 5C / 5C. After 1400 cycles at room temperature, the capacity retention rate was 94.72%, which was recorded as D1.

[0055] Comparative Example 2

[0056] This comparative example uses a pouch lithium supercapacitor of approximately 2.6 Ah, a mixture of LFP and activated carbon as the cathode active material (mass ratio of 9:1), hard carbon as the anode active material, and a battery balance ratio of 2.2:1 in this embodiment.

[0057] This comparative example provides a formation method, which specifically includes the following steps: first, charge the battery with a constant current of 0.05C to 10% of the battery formation charge capacity, let it stand for 5 minutes, then charge it with a constant current of 0.1C to 30% of the battery formation charge capacity, let it stand for 5 minutes, and the formation is completed.

[0058] Capacity testing was performed on the battery in this comparative example: the test voltage range was 3.65-2.2V. After formation, the capacity was first tested using a 1C / 1C charge / discharge method, and the test capacity was recorded as 2.655-2.672Ah. After the capacity was tested, a cyclic test was performed using a 5C / 5C charge / discharge method. After 1400 cycles at room temperature, the capacity retention rate was 93.25%, which was recorded as D2.

[0059] Comparative Example 3

[0060] This comparative example uses a pouch lithium supercapacitor of approximately 2.6 Ah, a mixture of LFP and activated carbon as the cathode active material (mass ratio of 9:1), hard carbon as the anode active material, and a battery balance ratio of 2.2:1 in this embodiment.

[0061] This comparative example provides a formation method, which specifically includes the following steps: first, charge the battery with a constant current of 0.05C to 10% of the battery formation charge capacity, let it stand for 5 minutes, then charge it with a constant current of 0.1C to 30% of the battery formation charge capacity, let it stand for 5 minutes, and finally charge it with a constant current of 0.2C to the cutoff voltage, let it stand for 5 minutes, and the formation is completed.

[0062] The battery in this embodiment was subjected to capacity testing: the test voltage range was 3.65-2.2V. After formation, the capacity was first tested by charging and discharging at 1C / 1C, and the test capacity was recorded as 2.55-2.559Ah. After the capacity was tested, the cycle test was performed by charging and discharging at 5C / 5C. After 1400 cycles at room temperature, the capacity retention rate was 94.65%, which was recorded as D3.

[0063] Experimental Example 1

[0064] The first-efficiency / high-temperature charging performance of the above embodiments / comparative examples is shown in Table 1, and the cycle life comparison chart is shown in Figure 1.

[0065] Table 1

[0066] As shown in Table 1, compared to the more commonly used low-SOC formation method, the formation method of this invention significantly improves the initial efficiency of lithium supercapacitors with amorphous carbon in the anode. Simultaneously, this method also improves the high-temperature storage performance of lithium supercapacitors, and no anode lithium plating was observed during the disassembly of the fully charged cells after formation. From the comparison chart of 5C cycle life across the entire voltage range for each embodiment / comparative example, the cells prepared using the method of this invention effectively improve battery cycle life, achieving a capacity retention rate as high as 97.82% after 1400 cycles under optimal conditions.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion supercapacitor cell, characterized in that, The balance ratio of lithium supercapacitance is (1.1~2.2):1; The formula for calculating the balance ratio is: (A) C ×A d ×A L ) / (C c ×C d ×C L ); Among them, A C The discharge specific capacity of the anolyte is expressed in mAh / g. A d The areal density of the anode material, in g / m³. 2 ; A L This represents the percentage of the anolyte active material loaded in the overall anode. C C The discharge specific capacity of the cathode active material is expressed in mAh / g. C d The areal density of the cathode material, in g / m³. 2 ; C L This represents the percentage of the cathode active material loaded in the overall cathode.

2. The lithium-ion supercapacitor cell according to claim 1, characterized in that, The anode active material includes one or more of graphite, silicide, amorphous carbon, activated carbon, and carbon microspheres; wherein the amorphous carbon accounts for 5-95% of the total mass of the anode active material.

3. The lithium-ion supercapacitor cell according to claim 2, characterized in that, The amorphous carbon accounts for 5-50% of the total mass of the anode active material; preferably, the amorphous carbon accounts for 5-30% of the total mass of the anode active material.

4. The lithium-ion supercapacitor cell according to claim 2, characterized in that, The cathode active material includes one or more of lithium nickel cobalt manganese, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, and lithium vanadium phosphate, wherein lithium iron phosphate accounts for 10-95% of the total mass of the cathode active material.

5. The lithium-ion supercapacitor cell according to claim 4, characterized in that, Lithium iron phosphate accounts for 50-95% of the total mass of the cathode active material.

6. A method for the formation of a lithium-ion supercapacitor cell, characterized in that, include: S1: Constant current charging until the cell's charging capacity reaches 5-15%; S2: After resting, charge at a constant current until the cell's charging capacity reaches 25-35%; S3: After resting, constant current charging is performed until the cutoff voltage of 3.65V is reached; S4: After resting, charge at a constant current until the cutoff voltage of 3.75~3.85V, then stop charging.

7. The method for forming a lithium-ion supercapacitor cell according to claim 6, characterized in that, The charging current in S1 is 0.01 to 0.05C; and / or, the charging current in S2 is 0.1 to 0.2C.

8. The method for forming a lithium-ion supercapacitor cell according to claim 6, characterized in that, The charging method in S3 is constant current and constant voltage charging, with a cutoff current of 0.05C.

9. The method for forming a lithium-ion supercapacitor cell according to claim 6, characterized in that, The settling time described in S2 to S4 is 3 to 5 minutes.

10. The method for forming a lithium-ion supercapacitor cell according to claim 6, characterized in that, The formation temperature is 30–45°C.

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