Sectional formation process and lithium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to a sectional formation process and a lithium ion battery. The sectional type formation process comprises the following steps: S01, a constant-current charging stage I, S02, a standing stage, S03, a constant-current charging stage II and S04, a constant-voltage charging stage. According to the technical scheme, the voltage safety is high, and the highest voltage is reduced to avoid the gas production voltage interval from the source; the process compatibility is good, existing production line equipment does not need to be transformed, and only charging program parameters are adjusted; the dynamic adaptability is high, the standing stage provides interface stabilization time for the lithium removal product in the first step, and the ultra-small current ensures that the platform reaction in the second step is completed in a near-equilibrium state; the cost benefit is increased, the electrolyte decomposition loss is reduced, the liquid supplementing cost of the square battery is reduced, gas production is inhibited, and the yield of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a segmented formation process and a lithium-ion battery. Background Technology

[0002] Lithium iron phosphate (LFP) batteries have become the mainstream choice in the power and energy storage fields due to their long cycle life, low cost, and high safety. Lithium replenishment agents can precisely compensate for the irreversible lithium consumption during the formation of the SEI film on the negative electrode, improving the initial coulombic efficiency. Simultaneously, due to their high specific capacity, they can significantly increase the battery's energy density, which is key to overcoming the technological bottleneck of LFP batteries. Furthermore, they provide additional lithium reserves, significantly extending the battery's cycle life. Positive electrode lithium replenishment agents (such as Li5FeO4) have been introduced into lithium-ion battery systems to improve energy density and cycle performance, reduce the cost per unit energy density and the total life cycle cost, becoming a common technological direction in the industry.

[0003] Currently, industrial production lines for lithium iron phosphate batteries generally employ a formation process of "constant current charging to above 4.2V." However, this process has revealed serious problems in application: uncontrolled gas generation at high voltage, catalytic electrolyte oxidation and decomposition at high potential, producing gases such as CO2 and CH4, leading to swelling and bulging of pouch batteries and an increased risk of pressure relief valve opening in prismatic batteries. One issue is insufficient activation of the lithium replenishing agent. Mainstream lithium-rich replenishing agents (such as Li5FeO4) require two delithiation reactions (Platform I: 3.5–3.6V; Platform II: 3.9–4.0V). In traditional formation processes, the first reaction is not fully completed when charging to 3.8V (requiring kinetic relaxation time); subsequently, the process jumps directly to the 4.2V high-voltage region, skipping the second reaction platform, resulting in residual lithium replenishing agent that has not been completely delithilated. Another issue is deteriorated interface stability. Electrolyte decomposition products in the high-voltage region cover the electrode surface, increasing interfacial impedance and accelerating capacity decay. Existing solutions mainly include: extending the constant pressure time, but this exacerbates high-pressure side reactions, leading to an increase in gas production of about 30%; adding antioxidants, which increases costs and may sacrifice low-temperature performance; and using physical pre-lithiation technology, which has high equipment complexity and poor compatibility. The core contradiction that remains unresolved is the fundamental conflict between "the lithium supplement agent needs ≥4.0V to be fully activated" and "the LFP system produces gas violently at ≥4.2V." There is an urgent need for an innovative formation method that can fully activate the lithium supplement agent within a safe voltage window below 4.2V. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a segmented formation process and a lithium-ion battery.

[0005] To achieve the above objectives, this application adopts the following solution:

[0006] A segmented formation process, characterized by comprising the following steps:

[0007] S01, Constant current charging stage one: Charge to the first target voltage V1 with the first charging current C1 at a constant current;

[0008] S02, Settling Stage: The first settling time is T1;

[0009] S03, Constant current charging stage two: Continue constant current charging with the second charging current C2 until the battery voltage reaches the second target voltage V2;

[0010] S04. Constant voltage charging stage: After reaching the second target voltage V2, it switches to constant voltage charging. The constant voltage voltage is V2, the low rate charging cutoff current is C3, the duration is T2, and it ends after resting.

[0011] Preferably, the first charging current C1 in step S01 is 0.05C to 0.2C; more preferably 0.1C to 0.15C. The current C1 is chosen because this current intensity can ensure a certain charging efficiency while avoiding excessively violent internal reactions in the battery due to excessive current. Charging with a small current is more conducive to the formation of a dense SEI film.

[0012] In step S01, the first target voltage V1 is greater than the first delithiation plateau of the lithium replenishing agent. Preferably, the first delithiation plateau is 3.5–3.6V; more preferably, V1 is 3.8V ± 0.1V; more preferably, V1 is 3.75–3.85V, and even more preferably, 3.8V. This allows for the initial activation of the lithium replenishing agent at a lower voltage, while preventing the battery from entering a high-voltage region and triggering excessive side reactions.

[0013] In step S02, the first settling time T1 is 2 to 30 minutes; preferably, the settling time is 5 to 15 minutes. This improves the uniformity of lithium ion migration and prepares the battery for the subsequent charging stage. If the settling time is too short, the lithium ion distribution will be uneven, affecting the subsequent charging effect; if the settling time is too long, it will reduce production efficiency.

[0014] In step S03, the second charging current C2 is 0.02C to 0.05C; preferably 0.03C to 0.04C, and more preferably 0.035C. Charging with a small current can slow down the reaction rate inside the battery and avoid generating too much gas due to excessive reaction when approaching the second delithiation plateau (3.9 to 4.0V) of the lithium replenishment agent.

[0015] In step S03, the second target voltage V2 is greater than the second delithiation plateau of the lithium replenishing agent, which is 3.9–4.0V; preferably, V2 is 4.05V ± 0.05V; more preferably, V2 is 4.02V–4.06V. This range matches the second delithiation plateau of the lithium replenishing agent, which can fully activate the lithium replenishing agent without causing excessively high voltage, which would lead to severe side reactions in the electrolyte and the generation of a large amount of gas.

[0016] In step S04, T2 is set to 0.5 hours to 2 hours; preferably 0.5 hours to 1 hour. Limiting the time can prevent the constant pressure stage from being too long, which could lead to severe overcharging side reactions.

[0017] Preferably, the third charging current C3 is 0.005C to 0.025C, more preferably 0.02C. C3 ≤ C2 ≤ C1. Constant voltage charging ensures that the battery continues to be charged in small amounts after reaching the upper limit voltage, allowing the internal reaction of the battery to be more complete and reducing battery polarization, thus fully activating the lithium replenisher and improving the battery's capacity and performance.

[0018] The present invention also includes a lithium-ion battery obtained by the segmented formation process described above, comprising a positive electrode, a negative electrode, and a separator; wherein the positive electrode comprises a positive electrode active material and a positive electrode lithium replenishing agent.

[0019] The positive electrode active material is lithium iron phosphate;

[0020] Preferably, the positive electrode lithium replenishing agent is an inorganic lithium replenishing agent, and the inorganic lithium replenishing agent is selected from at least one of Li5FeO4 and Li2NiO2;

[0021] Preferably, the inorganic lithium supplement agent accounts for 0.5%-10% of the positive electrode active material.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The technical solution of this application has high voltage safety by reducing the maximum voltage to avoid the gas generation voltage range at the source; it has good process compatibility, requiring no modification to existing production line equipment, only adjustment of charging program parameters; it has high kinetic adaptability, providing interface stabilization time for the first step of lithium removal products during the resting stage, and ensuring that the second step of the platform reaction is completed in a near-equilibrium state with ultra-low current; it increases cost-effectiveness by reducing electrolyte decomposition loss, lowering the cost of electrolyte replenishment for prismatic batteries, suppressing gas generation, and improving battery yield. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process flow for the segmented formation process of the present invention. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] The battery used in this invention is a pouch battery, with lithium iron phosphate as the positive electrode and graphite as the negative electrode. The positive electrode active material contains lithium ferrite (Li5FeO4) as a lithium replenishing agent, and the battery has a rated capacity of 3Ah.

[0027] The positive electrode material of the lithium-ion battery (battery to be formed) used in the following examples and comparative examples is lithium iron phosphate (LFP) and lithium ferrite (LFO) with a mass ratio of 98:2, and the negative electrode material is artificial graphite (C).

[0028] The positive electrode (LFP+LFO):SP:CNT:PVDF is mixed in a ratio of 97.5:0.5:0.5:1.5, and coated onto carbon-coated aluminum foil using NMP as a solvent to form a positive electrode sheet with an areal density of 360 g / m³. 2 .

[0029] The negative electrode is prepared by mixing C:SP:CMC:SBR in a ratio of 96.4:1.0:1.2:1.4, using water as a solvent, and coating it onto copper foil to form a negative electrode sheet with an areal density of 185 g / m³. 2 .

[0030] The electrolyte used was a solution of LiPF6 as the lithium salt, EC, DMC, and EMC (EC:DMC:EMC = 30:30:40). The battery to be formed was placed in the formation equipment, and the vacuum was evacuated to -50 kPa. The ambient dew point was -30°C, and the ambient temperature was 45°C.

[0031] Example 1: This example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent. Figure 1 (As shown), it includes the following steps:

[0032] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0033] S02: Second stage: Let stand for 5 minutes.

[0034] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0035] S04: Fourth stage: Constant voltage charging with a current of C3 = 0.02C for 1 hour.

[0036] Example 2: This example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0037] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.15C until the charging voltage reaches V1 = 3.8V.

[0038] S02: Second stage: Let stand for 5 minutes.

[0039] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0040] S04: Constant voltage charging is performed with a current of C3 = 0.02C for 1 hour.

[0041] Example 3: This example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0042] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.2C until the charging voltage reaches V1 = 3.8V.

[0043] S02: Second stage: Let stand for 5 minutes.

[0044] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0045] S04: Constant voltage charging is performed with a current of C3 = 0.02C for 1 hour.

[0046] Example 4

[0047] This embodiment provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0048] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.2C until the charging voltage reaches V1 = 3.8V.

[0049] S02: Second stage: Let stand for 30 minutes.

[0050] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0051] S04: Fourth stage: Constant voltage charging with a current of C3 = 0.02C for 1 hour.

[0052] Example 5: This example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0053] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0054] S02: Second stage: Let stand for 5 minutes.

[0055] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.02C until the charging voltage reaches V2 = 4.05V.

[0056] S04: Fourth stage: Constant voltage charging with a current of C3 = 0.02C for 1 hour.

[0057] Example 6: This example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0058] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0059] S02: Second stage: Let stand for 5 minutes.

[0060] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.05C until the charging voltage reaches V2 = 4.05V.

[0061] S04: Fourth stage: Constant voltage charging with a current of C3 = 0.02C for 1 hour.

[0062] Example 7: This example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0063] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0064] S02: Second stage: Let stand for 5 minutes.

[0065] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0066] S04: Fourth stage: Constant voltage charging with a current of C3 = 0.01C for 1 hour.

[0067] Example 8: This example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0068] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0069] S02: Second stage: Let stand for 5 minutes.

[0070] S03: Three-stage: The lithium-ion battery is continued to be charged at a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0071] S04: Fourth stage: Constant voltage charging with a current of C3 = 0.02C for 0.5 hours.

[0072] Comparative Example 1 (without lithium replenishing agent): The comparative example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent that is the same as that in Example 1, except that the positive electrode active material of the battery does not contain the lithium replenishing agent LFO.

[0073] Comparative Example 2 (One-step process): The comparative example provides a conventional formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps: First stage: The lithium-ion battery is charged with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 4.2V.

[0074] Comparative Example 3 (Conventional Upper Limit Voltage): This comparative example provides a conventional formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0075] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0076] S02: Second stage: Let stand for 5 minutes.

[0077] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.2V.

[0078] S04: Fourth stage: Constant voltage charging with a current of C3 = 0.02C for 1 hour.

[0079] Comparative Example 4 (without settling): This comparative example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0080] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0081] S02: Second stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0082] S03: Third stage: Constant voltage charging with a current of C3 = 0.02C for 1 hour.

[0083] Comparative Example 5 (without constant voltage section): This comparative example provides a low-voltage formation method for a lithium-ion battery containing a lithium replenishing agent, including the following steps:

[0084] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0085] S02: Second stage: Let stand for 5 minutes.

[0086] S02: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.035C until the charging voltage reaches V2 = 4.05V.

[0087] Comparative Example 6 (Current C2 > C1)

[0088] S01: First stage: Charge the lithium-ion battery with a constant current of C1 = 0.1C until the charging voltage reaches V1 = 3.8V.

[0089] S02: Second stage: Let stand for 5 minutes.

[0090] S03: Third stage: Continue charging the lithium-ion battery with a constant current of C2 = 0.15C until the charging voltage reaches V2 = 4.05V.

[0091] S04: Constant voltage charging is performed with a current of C3 = 0.02C for 1 hour.

[0092] Table 1 shows a comparison of the formation processes of the embodiments and comparative examples.

[0093] Table 1

[0094]

[0095] The results of relevant tests on the cells of the examples and comparative examples are shown in Tables 2-4 below: Based on the formation and charging capacity data of the lithium-ion batteries after formation in Examples 1-8 and Comparative Examples 1-5, the specific capacity of the lithium replenishment agent was calculated; the results are shown in Table 2.

[0096] Table 2

[0097]

[0098]

[0099] The gas production of lithium-ion batteries after formation in Examples 1-8 and Comparative Examples 1-5 was tested. The test conditions were that the gas production of the soft pack was measured by the water displacement method, the gas production data were obtained, and the volume expansion rate was calculated. The results are shown in Table 3.

[0100] Table 3

[0101] serial number Volume expansion rate (%) Gas production rate (mL / Ah) Example 1 1.4 0.36 Example 2 1.9 0.48 Example 3 2.3 0.52 Example 4 2.8 0.72 Example 5 2.0 0.49 Example 6 1.8 0.45 Example 7 3.2 0.82 Example 8 3.8 0.91 Comparative Example 1 0.5 0.11 Comparative Example 2 8.7 2.32 Comparative Example 3 8.1 2.01 Comparative Example 4 4.0 1.05 Comparative Example 5 4.8 1.22 Comparative Example 6 6.2 1.63

[0102] When the lithium-ion batteries of Examples 1-8 and Comparative Examples 1-5 were formed, the test conditions were: temperature 25°C, voltage range 2.5V-3.65V, and 1C charging-1C discharging mode was used; the results are shown in Table 4.

[0103] Table 4

[0104] serial number Week 600 capacity retention rate DCIR growth rate Example 1 98.3％ 0.92％ Example 2 97.9％ 1.12％ Example 3 97.0％ 1.45％ Example 4 97.2％ 1.37％ Example 5 97.7％ 1.21％ Example 6 97.6％ 1.19％ Example 7 96.9％ 1.59％ Example 8 96.8％ 1.62％ Comparative Example 1 92.4％ 1.03％ Comparative Example 2 94.5％ 3.24％ Comparative Example 3 96.3％ 2.51％ Comparative Example 4 97.1％ 1.73％ Comparative Example 5 96.9％ 1.95％ Comparative Example 6 95.3％ 2.94％

[0105] in conclusion:

[0106] 1. As can be seen from Table 2, the lithium replenishing agent in Example 1 (preferred parameters) performs close to that of one-step formation and conventional voltage, proving that the low-voltage process can fully activate the lithium replenishing agent; the lithium replenishing agent in Comparative Example 4 (no standing) performs poorly, indicating that standing is the key to ensuring the stability of the first-step delithiation product; the lithium replenishing agent in Comparative Example 5 (no constant voltage section) performs poorly because the absence of a low-rate constant voltage section leads to some LFO not reacting completely; the lithium replenishing agent in Comparative Example 6 (current C2 > C1) performs the least poorly because the high-rate current cannot ensure that the second-stage delithiation is insufficient.

[0107] 2. As can be seen from Table 3, the gas production of Example 1 (preferred parameters) is only 15.5% of that of Comparative Example 2 (one-step formation) and 18% of that of Comparative Example 3 (conventional high voltage), indicating that this preferred parameter combination can significantly reduce the gas production risk of high voltage. The gas production of Example 1 is higher than that of Comparative Example 4 (no settling), indicating that settling can reduce the side reactions in subsequent charging.

[0108] 3. As can be seen from Table 4, the battery of Example 1 (preferred parameters) exhibits better cycle stability compared to other examples and comparative examples. After 600 cycles, the capacity retention rate can be maintained above 98%, and the DCIR growth rate is the lowest.

[0109] 4. In summary, the battery performance of Example 1 (preferred parameters) is optimal, including more complete activation of the lithium replenishment agent, the least amount of gas production, and the highest cycle capacity retention.

[0110] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0111] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0112] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A segmented formation process, characterized in that, Includes the following steps: S01, Constant current charging stage one: Charge to the first target voltage V1 with the first charging current C1 at a constant current; S02, Settling Stage: The first settling time is T1; S03, Constant current charging stage two: Continue constant current charging with the second charging current C2 until the battery voltage reaches the second target voltage V2; S04. Constant voltage charging stage: After reaching the second target voltage V2, it switches to constant voltage charging. The constant voltage voltage is V2, the low rate charging cutoff current is C3, the duration is T2, and it ends after resting.

2. The segmented formation process according to claim 1, characterized in that, In step S01, the first charging current C1 is 0.05C to 0.2C; preferably 0.1C to 0.15C.

3. The segmented formation process according to claim 1, characterized in that, In step S01, the first target voltage V1 is greater than the first delithiation plateau of the lithium replenishing agent. Preferably, the first delithiation plateau is 3.5 to 3.6V; preferably, V1 is 3.8V ± 0.1V; preferably, V1 is 3.75 to 3.85V, and more preferably 3.8V.

4. The segmented formation process according to claim 1, characterized in that, In step S02, the first settling time T1 is 2 to 30 minutes; preferably, the settling time is 5 to 15 minutes.

5. The segmented formation process according to claim 1, characterized in that, In step S03, the second charging current C2 is 0.02C to 0.05C; preferably 0.03C to 0.04C, and more preferably 0.035C.

6. The segmented formation process according to claim 1, characterized in that, In step S03, the second target voltage V2 is greater than the second delithiation plateau of the lithium replenishing agent, wherein the second delithiation plateau is 3.9 to 4.0V; preferably, V2 is 4.05V ± 0.05V; more preferably, V2 is 4.02V to 4.06V, and even more preferably, 4.05V.

7. The segmented formation process according to claim 1, characterized in that, In step S04, T2 is set to 0.5 hours to 2 hours; preferably 0.5 hours to 1 hour. Preferably, the third charging current C3 is 0.005C to 0.025C, more preferably 0.02C.

8. The segmented formation process according to claim 1, characterized in that, The segmented formation process according to claim 1 is characterized in that C3≤C2≤C1.

9. A lithium-ion battery, characterized in that, The material is obtained by the segmented formation process according to any one of claims 1-8, and includes a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet includes a positive electrode active material and a positive electrode lithium supplement.

10. The lithium-ion battery according to claim 9, characterized in that, The positive electrode active material is lithium iron phosphate; Preferably, the positive electrode lithium replenishing agent is an inorganic lithium replenishing agent, and the inorganic lithium replenishing agent is selected from at least one of Li5FeO4 and Li2NiO2; Preferably, the inorganic lithium supplement agent accounts for 0.5%-10% of the positive electrode active material.

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