A formation method for a long-life lithium-ion battery and the resulting long-life lithium-ion battery

Abstract

This invention discloses a formation method for a long-life lithium-ion battery and the resulting long-life lithium-ion battery, belonging to the field of lithium-ion battery technology. The formation method is as follows: charging with a first preset current C1 at a constant current until a first preset state of charge (SOC1) is reached, then resting; charging with a second preset current C2 at a constant current until a second preset state of charge (SOC2) is reached, then resting; charging with a third preset current C3 at a constant current until a first preset voltage U1 is reached, then resting; charging with a fourth preset current C4 at a constant current until a second preset voltage U2 is reached, then resting; charging with a fifth preset current C5 at a constant current until a third preset voltage U3 is reached, then resting, and finally ending the process. This invention uses a stepped current formation method for long-life lithium-ion batteries containing lithium iron phosphate supplements, resulting in batteries with low DC internal resistance, good stability, and good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a formation method for a long-life lithium-ion battery and the resulting long-life lithium-ion battery. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In the production of lithium-ion batteries, formation, as the initial charging process, is an indispensable step. After battery manufacturing, the positive and negative electrode materials inside are activated through a specific charging and discharging method, forming a solid electrolyte interphase (SEI) film on the negative electrode side of the lithium battery. This improves the battery's charge-discharge performance, as well as its overall performance in terms of self-discharge, cycle life, and storage. The formation process directly affects the quality of the SEI film.

[0004] Currently, the formation method used for lithium iron phosphate (LFP) batteries is the traditional low-current pre-charging method. However, prolonged low-current charging leads to increased SEI film impedance and defects, resulting in high DC internal resistance and affecting cycle performance. Adding lithium additives can significantly improve the cycle performance of LFP batteries, extending their lifespan. Since different battery systems employ different formation methods, most existing lithium-ion battery formation methods are not directly applicable to LFP batteries with added lithium additives. Therefore, providing a formation method for LFP batteries with added lithium additives to improve SEI film stability, reduce DC internal resistance, and enhance cycle performance is a pressing issue. Summary of the Invention

[0005] In view of this, the present invention provides a formation method for a long-life lithium-ion battery and the resulting long-life lithium-ion battery. Compared with the traditional formation method, the formation method provided by the present invention significantly improves the stability of the SEI film, and the SEI film has fewer defects and higher uniformity, which is beneficial to improving the interface performance of the negative electrode, increasing the energy density and cycle performance of the battery, and improving the stability of the battery.

[0006] In a first aspect, the present invention provides a method for forming a long-life lithium-ion battery, comprising the following steps:

[0007] S1. Charge the battery with a constant current C1 until the first preset state of charge SOC1 is reached, and then let it stand.

[0008] S2. Charge the battery with a constant current C2 until the second preset state of charge SOC2 is reached, and then let it stand.

[0009] S3. Charge the battery to the first preset voltage U1 using the third preset current C3, and then let it stand.

[0010] S4. Charge the battery to the second preset voltage U2 using the fourth preset current C4, and then let it stand.

[0011] S5. Charge the battery to the third preset voltage U3 using the fifth preset current C5 at a constant current, and then let it stand before stopping.

[0012] Among them, 3%≤SOC1≤5%, 38%≤SOC2≤42%, U1<U2<U3, C5<C1<C2<C3; the positive electrode material of the long-life lithium-ion battery includes lithium iron phosphate and lithium replenishment agent.

[0013] Secondly, the present invention provides a long-life lithium-ion battery, which is manufactured by the above-described formation method.

[0014] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0015] (1) The present invention adopts a stepped current step formation for lithium iron phosphate long-life lithium-ion batteries containing lithium replenishment agents, and controls the state of charge and charging voltage. Compared with the traditional formation process using constant small current, the stability of SEI film is greatly improved, and there are fewer defects and higher uniformity, which is conducive to improving the interface performance of the negative electrode and improving the cycle performance of the battery.

[0016] (2) The lithium-ion battery obtained by the formation method provided by the present invention has a low DC internal resistance, which is below 25mΩ; at the same time, it has good cycle stability. In the range of 25℃ and 2.5-3.65V, with stepped charging and 1C discharge, it can cycle for 4000 cycles and the capacity retention rate can still be maintained above 88%; even if it is stored in a high temperature environment of 55℃ for 28 days, its capacity recovery rate can still reach more than 98%, and the battery has good stability. Detailed Implementation

[0017] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0018] This invention provides a method for forming a long-life lithium-ion battery, comprising the following steps:

[0019] S1. Charge the battery with a constant current C1 until the first preset state of charge SOC1 is reached, and then let it stand.

[0020] S2. Charge the device with a constant current C2 until it reaches the second preset state of charge SOC2, and then let it stand.

[0021] S3. Charge the battery to the first preset voltage U1 using the third preset current C3, and then let it stand.

[0022] S4. Charge the battery to the second preset voltage U2 using the fourth preset current C4, and then let it stand.

[0023] S5. Charge the battery to the third preset voltage U3 using the fifth preset current C5 at a constant current, and then let it stand before stopping.

[0024] Among them, 3%≤SOC1≤5%, 38%≤SOC2≤42%, U1<U2<U3, C5<C1<C2<C3; the positive electrode material of the long-life lithium-ion battery includes lithium iron phosphate and lithium replenishment agent.

[0025] This invention employs a multi-step, stepped formation process for long-life lithium-ion batteries. Stage S1 primarily involves charging with a low current to a low state of charge (SOC) for initial film formation. Stage S2 further increases the current and SOC to ensure more complete side reactions and a denser film. Stages S3, S4, and S5 utilize the voltage window of the lithium replenishment agent to allow lithium to fully intercalate into the negative electrode, replenishing the irreversible capacity of the lithium iron phosphate during its initial charge and thus increasing the cell's capacity. Overall, by controlling the state of charge and charging voltage, compared to traditional formation processes using a constant low current, the stability of the SEI film is significantly improved, with fewer defects and higher uniformity. This is beneficial for improving the interface performance of the negative electrode and enhancing the battery's energy density and cycle performance.

[0026] In this invention, the first preset current C1 is 0.05C to 0.12C, for example, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, 0.1C, etc.; the second preset current C2 is 0.12C to 0.16C, for example, 0.12C, 0.13C, 0.14C, 0.15C, etc.; the third preset current C3 is 0.16C to 0.25C; the fourth preset current C4 is 0.15C to 0.3C; and the fifth preset current C5 is 0.02C to 0.05C. The fifth preset current C5 is the smallest in this invention, mainly to eliminate battery polarization and make side reactions more complete.

[0027] In this invention, the first preset voltage U1 is 3.6 to 3.7V, more preferably 3.65V; the second preset voltage U2 is 3.75 to 3.85V, more preferably 3.8V; and the third preset voltage U3 is 4.15 to 4.25V, more preferably 4.2V.

[0028] In this invention, the settling time for steps S1 to S5 is 2 to 10 minutes, more preferably 3 to 5 minutes. The settling process is to ensure that the gas generated during the formation process can be fully discharged from the battery.

[0029] In this invention, steps S1 to S5 are performed under vacuum conditions, with a charging temperature of 40–50°C and an ambient dew point ≤ -30°C. The high temperature and negative pressure conditions promote more thorough battery side reactions and more complete venting. Further, the vacuum conditions are: negative pressure -85 to -75 kPa; charging temperature 42–48°C; and ambient dew point -45 to -35°C. These environmental conditions are provided by the formation equipment, and this invention does not impose any special restrictions on the model of the formation equipment.

[0030] In this invention, the mass ratio of lithium iron phosphate to lithium replenishing agent is (95-99):(1-5), for example, 95:5, 96:4, 96:4, 97:3, 98:2, 99:1, etc. The formation method of this invention serves two main purposes: firstly, it pre-lithiation, extracting lithium from the lithium replenishing agent and adding lithium sources to the electrode before the lithium-ion battery operates normally, thereby replenishing lithium ions, compensating for irreversible lithium loss caused by the formation of the SEI film, and improving battery performance. Secondly, and importantly, the excess lithium source is embedded in the negative electrode material, increasing the battery capacity, reducing the capacity decay rate of the lithium-ion battery, and thus improving the lifespan of the lithium-ion battery.

[0031] In this invention, the lithium replenishing agent is preferably lithium iron phosphate. The introduction of lithium iron phosphate can significantly improve the cycle life of lithium iron phosphate batteries.

[0032] In this invention, the negative electrode material of the long-life lithium-ion battery is selected from one or more of artificial graphite, natural graphite, soft carbon, or hard carbon. This invention does not impose any special limitations on the preparation method of the long-life lithium-ion battery; commonly used methods in the art for preparing long-life lithium-ion batteries can be employed.

[0033] This invention also provides a long-life lithium-ion battery, manufactured using the above-described formation method. The lithium-ion battery obtained using the formation method provided by this invention exhibits low DC internal resistance, below 25 mΩ; it also demonstrates excellent cycle stability, maintaining a capacity retention of over 88% after 4000 cycles under stepped charging conditions of 25°C and 2.0-3.65V, and 1C discharge conditions; furthermore, even after storage at 55°C for 28 days, its capacity recovery rate still reaches over 98%, demonstrating excellent battery stability.

[0034] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0035] In the following examples, the long-life lithium-ion battery (battery to be formed) uses lithium iron phosphate (LFP) and lithium ferrite (LFO) in a mass ratio of 98:2 as the positive electrode material and artificial graphite (C) as the negative electrode material. The positive electrode is prepared by mixing (LFP+LFO):SP:CNT:PVDF = 97:0.5:0.5:2, using NMP as a solvent, and coating it onto aluminum foil to form a positive electrode sheet with an areal density of 375 g / m³. 2 The negative electrode is prepared by mixing C:SP:CMC:SBR in a ratio of 95.6:1.0:1.4:2.0, using water as a solvent, and coating it onto copper foil to form a negative electrode sheet with an areal density of 242 g / m³. 2 The electrolyte is a 1 mol / L solution of LiPF6 EC, DMC and EMC (volume ratio 1:1:1).

[0036] Example 1

[0037] This embodiment provides a formation method for a long-life lithium-ion battery.

[0038] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0039] (2) Charge at a constant current of C1 = 0.05C to SOC1 = 4%, taking a total of 48 minutes, and then let stand for 4 minutes.

[0040] (3) Charge at a constant current of C2 = 0.12C to SOC2 = 40%, taking a total of 180 minutes, and then let stand for 4 minutes.

[0041] (4) Charge the battery with a constant current of C3 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0042] (5) Charge the battery with a constant current of C4 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0043] (6) Charge the battery with a constant current of C5 = 0.035C until U3 = 4.2V, and then let it stand for 4 minutes.

[0044] Example 2

[0045] This embodiment provides a formation method for a long-life lithium-ion battery.

[0046] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0047] (2) Charge at a constant current of C1 = 0.05C to SOC1 = 4%, taking a total of 48 minutes, and then let stand for 4 minutes.

[0048] (3) Charge at a constant current of C2 = 0.14C to SOC2 = 40%, taking a total of 154.28 minutes, and then let stand for 4 minutes.

[0049] (4) Charge the battery with a constant current of C3 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0050] (5) Charge the battery with a constant current of C4 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0051] (6) Charge the battery with a constant current of C5 = 0.035C until U3 = 4.2V, and then let it stand for 4 minutes.

[0052] Example 3

[0053] This embodiment provides a formation method for a long-life lithium-ion battery.

[0054] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0055] (2) Charge at a constant current of C1 = 0.05C to SOC1 = 4%, taking a total of 48 minutes, and then let stand for 4 minutes.

[0056] (3) Charge at a constant current of C2 = 0.16C to SOC2 = 40%, taking a total of 135 minutes, and then let stand for 4 minutes.

[0057] (4) Charge the battery with a constant current of C3 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0058] (5) Charge the battery with a constant current of C4 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0059] (6) Charge the battery with a constant current of C5 = 0.035C until U3 = 4.2V, and then let it stand for 4 minutes.

[0060] Example 4

[0061] This embodiment provides a formation method for a long-life lithium-ion battery.

[0062] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0063] (2) Charge at a constant current of C1 = 0.1C to SOC1 = 4%, taking a total of 24 minutes, and then let stand for 4 minutes.

[0064] (3) Charge at a constant current of C2 = 0.12C to SOC2 = 40%, taking a total of 180 minutes, and then let stand for 4 minutes.

[0065] (4) Charge the battery with a constant current of C3 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0066] (5) Charge the battery with a constant current of C4 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0067] (6) Charge the battery with a constant current of C5 = 0.035C until U3 = 4.2V, and then let it stand for 4 minutes.

[0068] Example 5

[0069] This embodiment provides a formation method for a long-life lithium-ion battery.

[0070] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0071] (2) Charge at a constant current of C1 = 0.1C to SOC1 = 4%, taking a total of 24 minutes, and then let stand for 4 minutes.

[0072] (3) Charge at a constant current of C2 = 0.14C to SOC2 = 40%, taking a total of 154.28 minutes, and then let stand for 4 minutes.

[0073] (4) Charge the battery with a constant current of C3 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0074] (5) Charge the battery with a constant current of C4 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0075] (6) Charge the battery with a constant current of C5 = 0.035C until U3 = 4.2V, and then let it stand for 4 minutes.

[0076] Example 6

[0077] This embodiment provides a formation method for a long-life lithium-ion battery.

[0078] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0079] (2) Charge at a constant current of C1 = 0.1C to SOC1 = 4%, taking a total of 24 minutes, and then let stand for 4 minutes.

[0080] (3) Charge at a constant current of C2 = 0.16C to SOC2 = 40%, taking a total of 135 minutes, and then let stand for 4 minutes.

[0081] (4) Charge the battery with a constant current of C3 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0082] (5) Charge the battery with a constant current of C4 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0083] (6) Charge the battery with a constant current of C5 = 0.035C until U3 = 4.2V, and then let it stand for 4 minutes.

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 1 is that the formation method is to use a constant current charging at 0.02C for 20 hours.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 1 is that this comparative example does not include step (2). The specific steps are as follows:

[0088] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0089] (2) Charge at a constant current of C1 = 0.12C to SOC = 40%, taking a total of 200 minutes, and then let stand for 4 minutes.

[0090] (3) Charge the battery with a constant current of C2 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0091] (4) Charge the battery with a constant current of C3 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0092] (5) Charge the battery with a constant current of C4 = 0.035C until U3 = 4.2V, and then let it stand for 4 minutes.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, the device is charged to SOC1 = 10% using a constant current. The specific steps are as follows:

[0095] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0096] (2) Charge at a constant current of C1 = 0.05C to SOC1 = 10%, taking a total of 120 minutes, and then let stand for 4 minutes.

[0097] (3) Charge at a constant current of C2 = 0.12C to SOC2 = 46%, taking a total of 180 minutes, and then let stand for 4 minutes.

[0098] (4) Charge the battery with a constant current of C3 = 0.2C until U1 = 3.65V, and then let it stand for 4 minutes.

[0099] (5) Charge the battery with a constant current of C4 = 0.25C until U2 = 3.8V, and then let it stand for 4 minutes.

[0100] (6) Charge the U3 to 4.2V with a constant current of C5 = 0.035C, and then let it stand for 4 minutes.

[0101] Comparative Example 4

[0102] The difference between this comparative example and Example 1 is that C5 = 0.1C in step (6) of this comparative example.

[0103] Comparative Example 5

[0104] The conversion method for this comparative example is as follows:

[0105] (1) Place the battery to be formed into the formation equipment, evacuate to -80kPa, the ambient dew point is -40℃, and the ambient temperature is 45℃.

[0106] (2) Charge the battery with a constant current of C1 = 0.05C until U1 = 3.65V, and then let it stand for 4 minutes.

[0107] (3) Charge the battery with a constant current of C2 = 0.1C until U2 = 3.8V, and then let it stand for 4 minutes.

[0108] (4) Charge the battery with a constant current of C3 = 0.2C until U3 = 4.2V, and then let it stand for 4 minutes.

[0109] Test case

[0110] 1. Stability determination at different temperatures:

[0111] The lithium-ion batteries formed in Examples 1-6 and Comparative Examples 1-5 were stored in different temperature environments (25°C, 45°C, 55°C) for 28 days, and charge-discharge tests (1 / 3C charge-discharge) were conducted. The battery capacity was measured and the capacity recovery rate was calculated to compare the storage performance of the batteries. The results are shown in Table 1.

[0112] Table 1. Battery capacity recovery rates after formation in Examples 1-6 and Comparative Examples 1-5.

[0113]

[0114]

[0115] As can be seen from Table 1, the battery storage performance of the embodiments is better than that of the comparative examples. The storage performance of different embodiments is not significantly different. The capacity recovery rate decreases slightly with increasing temperature. However, after being stored at 55°C for 28 days, the capacity recovery rate of the battery in the embodiments can still be maintained above 98%, indicating that the battery formed by the formation method provided in the embodiments has good storage performance, slow decay, and good stability.

[0116] 2. DC internal resistance measurement

[0117] The DC internal resistance of the lithium-ion batteries formed in Examples 1-6 and Comparative Examples 1-5 was measured (50% SOC, 5C10s). The results are shown in Table 2.

[0118] Table 2 DC internal resistance of batteries after formation in Examples 1-6 and Comparative Examples 1-5 Table 2 DC internal resistance of batteries after formation in Examples 1-6 and Comparative Examples 1-5

[0119]

[0120]

[0121] It can be seen that the DC internal resistance of the batteries in the embodiments is lower than that in the comparative examples, all below 25mΩ. The storage performance of the different embodiments is not significantly different, indicating that the batteries formed by the formation method provided in the embodiments have low DC internal resistance, slow decay, and good cycle stability.

[0122] 3. Cyclic performance testing

[0123] The cycle performance of the lithium-ion batteries formed in Examples 1-6 and Comparative Examples 1-5 was measured under the following conditions: 25°C, stepped charging in the range of 2.5-3.65V, and 1C discharge. The results are shown in Table 3.

[0124] Table 3. Cycle performance of lithium-ion batteries after formation in Examples 1-6 and Comparative Examples 1-5.

[0125]

[0126]

[0127] As can be seen from Table 3, the battery in the embodiment exhibits better cycle stability compared to the battery in the comparative example, and the capacity retention rate can be maintained at more than 88% after 4000 cycles.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A formation method of a long-life lithium-ion battery, characterized by, Comprising the following steps: S1, constant current charging to reach a first preset state of charge SOC1 with a first preset current C1, and standing; S2, constant current charging to reach a second preset state of charge SOC2 with a second preset current C2, and standing; S3, constant current charging to a first preset voltage U1 with a third preset current C3, and standing; S4, constant current charging to a second preset voltage U2 with a fourth preset current C4, and standing; S5, constant current charging to a third preset voltage U3 with a fifth preset current C5, and standing, and ending; Wherein, 3%≤SOC1≤5%, 38%≤SOC2≤42%, U1 The steps S1-S5 are carried out under vacuum conditions, the temperature during charging is 40-50℃, and the environmental dew point is ≤-30℃.

2. The formation method of claim 1, wherein, The standing time of the steps S1-S5 is 2-10min.

3. The formation method of claim 1, wherein, The vacuum condition is: negative pressure-85--75kPa; the temperature during charging is 42-48℃; and the environmental dew point is-45--35℃.

4. The formation method of claim 1, wherein, The mass ratio of the lithium iron phosphate and the lithium supplement agent is (95-99):(1-5).

5. The formation method of claim 1, wherein, The lithium supplement agent is lithium ferrite.

6. The formation method of claim 1, wherein, The negative electrode material of the long-life lithium ion battery is selected from one or more of artificial graphite, natural graphite, soft carbon or hard carbon.

7. A long-life lithium-ion battery, characterized by, Made by the formation method according to any one of claims 1-6.

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