Lithium ion battery formation method

Abstract

A lithium-ion battery formation method comprises the following steps: 2-3 cycles of low current density, low potential, constant current cyclic charge-discharge formation; 2-3 cycles of low current density, high potential, constant current cyclic charge-discharge formation; 2-3 cycles of high current density, high potential, constant voltage charging formation to a fully charged state; 2-4 cycles of high current density, high current density, pulse discharge formation; 2-4 cycles of medium current density, constant current discharge formation to a lower cutoff voltage; 2-5 cycles of high current density, pulse charge formation; 2-5 cycles of low current density, constant current charging formation to an upper cutoff voltage, and then constant voltage charging formation to a fully charged state; 2-6 cycles of high current density, high current density, pulse discharge formation; 2-6 cycles of low current density, constant current charging formation to an upper cutoff voltage, and then constant voltage charging formation to a fully charged state; 2-7 cycles of high current density, pulse discharge formation; 2-8 cycles of low current density, constant current charging formation to an upper cutoff voltage, and then constant voltage charging formation to a fully charged state; 2-9 cycles of high current density, pulse discharge formation; 3-5 hours of high current density, pulse discharge formation; and open circuit voltage, AC impedance, and discharge capacity sorting. The present invention selects different formation conditions based on the different characteristics of the positive and negative electrodes, making the SEI films on the positive and negative electrode surfaces more uniform and dense, achieving optimal formation effects for the positive and negative electrodes, and improving the battery's capacity performance. Furthermore, during the formation process, the hidden danger of micro-short circuits within the battery is eliminated, improving battery consistency, safety, and service life, and significantly increasing production capacity.

Description

Technical Field

[0001] The present invention relates to a lithium ion battery, and in particular to a lithium ion battery formation method. Background Art

[0002] Lithium-ion batteries offer a host of advantages, including high specific energy, high voltage, high output power, and rapid charge and discharge. However, complex manufacturing processes and safety concerns have hindered their rapid development. Before use, lithium-ion batteries undergo a formation process to activate the active materials at the positive and negative electrodes, allowing the battery to reach optimal charge and discharge conditions. This formation step is a core manufacturing process, and its results impact several key performance indicators, including capacity, cycle life, and safety.

[0003] Existing lithium-ion battery formation methods fail to tailor formation steps to the characteristics of the positive and negative electrode materials. To achieve rated capacity, they typically use a time-consuming, low-current formation process. This, coupled with long shelf aging times, results in a lengthy and complex process. The SEI film on the electrode surface also fails to achieve satisfactory results, resulting in a battery that is prone to short-circuiting when stored at low voltage, reducing safety. Furthermore, insufficient formation results in significant waste of positive electrode capacity, significant cell variability, long formation cycles, and low production efficiency.

[0004] In order to solve the above problems in the prior art, the present invention is provided. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium-ion battery formation method, which selects appropriate formation conditions for the different characteristics of the positive and negative electrodes, respectively, so that the SEI films formed on the surfaces of the positive and negative electrodes are more uniform and dense, and both the positive and negative electrodes can achieve optimal formation effects, which can significantly improve the battery's capacity performance and product consistency and significantly improve production efficiency.

[0006] Another purpose of the present invention is to effectively eliminate the hidden dangers of micro-short circuits that may exist inside the battery during the formation process, repair and activate individual defective batteries, and at the same time effectively improve the battery consistency, safety and service life;

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

[0008] A lithium ion battery formation method comprising the steps of:

[0009] S1, the battery is left to stand for T1 time after filling;

[0010] S2, charge and discharge the battery several times at a low current density, low potential, and constant current cycle;

[0011] S3, charge at a low current density and constant current to the upper cut-off voltage;

[0012] S4, with low current density, at medium and high potential, constant current cycle charge and discharge several times;

[0013] S5, charging the battery at a high potential constant voltage until it is fully charged;

[0014] S6, subjecting the battery to high current density pulse discharge for time t1;

[0015] S7, discharge the battery at a medium current density and constant current to the lower cut-off voltage;

[0016] S8, pulse charging the battery with high current density for t2 time;

[0017] S9, charge at a low current density and constant current to the upper cut-off voltage, then switch to constant voltage charging to the full charge state;

[0018] S10, placing the battery at an ambient temperature of 45-55°C for aging for a time period of T2;

[0019] S11, subjecting the battery to high current density pulse discharge for t3 time;

[0020] S12. After the battery is left to stand for T3 time, the battery is sorted by open circuit voltage, AC impedance and discharge capacity.

[0021] Preferably, the small current density is 0.01 to 0.2 times the rated current density of the battery, the medium current density is 0.5 to 1 times the rated current density of the battery, and the large current density is 10 to 20 times the rated current density of the battery;

[0022] Preferably, the low potential is 0% to 30% of the state of charge of the battery, the medium potential is 30% to 90% of the state of charge of the battery, and the high potential is 90% to 100% of the state of charge of the battery.

[0023] Preferably, the T1 time is not less than 8 hours; the T2 time is 24 to 72 hours; and the T3 time is 3 to 5 hours.

[0024] Preferably, the pulse discharge time t1, t3, and the pulse charging time t2 are both 10 to 20 seconds.

[0025] Preferably, except step S10, the ambient temperature of the remaining steps is 20-30°C.

[0026] Beneficial effects:

[0027] In secondary lithium-ion batteries, various graphite carbon materials are commonly used as negative electrode materials. During the charge and discharge process, lithium and some components in the electrolyte will be co-intercalated in a high-temperature environment, resulting in increased internal resistance and low capacity. The SEI film formed on the negative electrode surface is relatively fragile and easily falls off and decomposes in the later cycles. The re-formed SEI film will further consume the positive electrode active material. After multiple cycles, the battery capacity, life, rate and safety performance are greatly reduced.

[0028] Common cathode materials for secondary lithium-ion batteries include lithium iron phosphate, ternary lithium, lithium cobalt oxide, and lithium manganese oxide. These cathode materials exhibit spontaneous polarization and increased internal resistance during low-temperature charging and discharging, resulting in poor rate performance and reduced capacity. Choosing the right temperature for the cathode material formation is also crucial.

[0029] Therefore, the present invention purposefully proposes to form the positive and negative electrodes in stages according to their different film-forming mechanisms and formation conditions.

[0030] First, a temperature suitable for negative electrode formation is selected at 20-30°C for low-current and low-potential cyclic charge-discharge formation, which makes the SEI film formed on the negative electrode surface more dense and uniform than the traditional method. This cleverly avoids the common problems of uneven SEI film thickness and fragile structure caused by the rapid temperature rise inside the battery during the traditional formation process.

[0031] After multiple low-potential charge-discharge cycles, the internal temperature of the battery has risen. At this time, a small current density medium-to-high potential cycle step suitable for positive polarization is performed to fully participate in the formation of the active lithium in the positive electrode, effectively exerting the capacity of the material. At the same time, it also solves the problems of spontaneous polarization and increased internal resistance of the battery at low temperatures.

[0032] The multiple high-current pulse charge and discharge steps described in the present invention are the most important feature that is significantly different from traditional formation methods. The purpose is to:

[0033] (1) The internal temperature rise of the battery generated by high current charging and discharging is combined with high temperature aging for more than 24 hours to fully activate the positive electrode lithium at a suitable temperature and fully form it, maximizing the active capacity of the material and being more conducive to the formation of a stable and dense SEI film on the positive electrode surface;

[0034] (2) The potential micro-short circuit hazards inside the battery will be destroyed by local high-temperature ablation generated by the high current pulse charge and discharge, forming a cross-sectional area less than 0.03mm 2 The microscopic local collapse causes the short-circuit part to detach. This measure can effectively repair battery cells with safety hazards, and the capacity loss can be ignored. DETAILED DESCRIPTION

[0035] Example 1

[0036] This embodiment relates to a lithium ion formation method, comprising the following steps:

[0037] In this example, except for the ambient temperature that is separately marked in the operation steps, the ambient temperature is assumed to be 20±5℃;

[0038] Step 1: Take 10,000 26650 lithium iron phosphate cylindrical batteries, fill them with liquid, seal them, and let them stand for 8 hours;

[0039] Step 2: Charge the lithium-ion battery to 3.0V at a constant current of 0.7A, discharge it to 2.50V at a constant current, and cycle it twice;

[0040] Step 3, charge the lithium-ion battery to 3.65V at a constant current of 0.7A;

[0041] Step 4: discharge the lithium-ion battery to 3.3V at a constant current of 0.7A, charge it to 3.65V at a constant current, and cycle it twice;

[0042] Step 5, charging the lithium-ion battery at a constant voltage of 3.65V to 100% state of charge;

[0043] Step 6, pulse discharge the lithium-ion battery at a current of 35A for 10 seconds;

[0044] Step 7: Discharge the lithium-ion battery to 2.50V at 3.5A.

[0045] Step 8: Pulse charge the lithium-ion battery with a current of 35A for 10 seconds;

[0046] Step 9: Charge the lithium-ion battery to 3.65V at 0.7A, and then continue constant voltage charging to 100% state of charge;

[0047] Step 10, aging the batch of lithium-ion batteries at a temperature of 50±5°C for 48 hours;

[0048] Step 11, pulse discharge the lithium-ion battery with a current of 35A for 10 seconds;

[0049] Step 12: After the battery is left to stand for 3 hours, the battery is sorted by open circuit voltage (OCV), AC impedance (1kHz) and discharge capacity.

[0050] Comparative Example 1

[0051] This embodiment relates to a lithium ion formation method, comprising the following steps:

[0052] In this example, except for the ambient temperature that is separately marked in the operation steps, the ambient temperature is assumed to be 20±5℃;

[0053] Step 1: Take 10,000 26650 lithium iron phosphate cylindrical batteries, fill them with liquid, seal them, and let them stand for 8 hours;

[0054] Step 2: Charge the lithium-ion battery to 3.65V at a constant current of 0.7A.

[0055] Step 3: aging the batch of lithium-ion batteries at a temperature of 50±5°C for 48 hours;

[0056] Step 4: After the battery is left to rest for 3 hours, charge and discharge the battery at 0.7A for 2 cycles at 2.50-3.65V.

[0057] Step 5: sort the batteries by discharge capacity, open circuit voltage (OCV), and AC impedance (1kHz).

[0058] Table 1

[0059]

[0060] Example 2

[0061] In this example, except for the ambient temperature marked separately in the operation steps, the default ambient temperature is 20±5℃.

[0062] Step 1: Take 5000 26650 ternary lithium-ion cylindrical batteries, fill them with liquid, seal them, and let them stand for 8 hours;

[0063] Step 2: Charge the lithium-ion battery to 3.3V at a constant current of 1.1A, and discharge it to 2.75V at a constant current, and cycle it twice;

[0064] Step 3, charge the lithium-ion battery to 4.35V at a constant current of 1.1A;

[0065] Step 4: discharge the lithium-ion battery at a constant current of 1.1A to 3.90V, charge it at a constant current to 4.35V, and cycle it twice;

[0066] Step 5, charging the lithium-ion battery at a constant voltage of 4.35V to 100% state of charge;

[0067] Step 6, pulse discharge the lithium-ion battery at a current of 55A for 10 seconds;

[0068] Step 7: Discharge the lithium-ion battery to 2.75V at 5.5A.

[0069] Step 8: Pulse charge the lithium-ion battery with a current of 55A for 10 seconds;

[0070] Step 9: Charge the lithium-ion battery to 4.35V at 1.1A, and then continue charging at a constant voltage of 4.35V to 100% state of charge;

[0071] Step 10, aging the batch of lithium-ion batteries at a temperature of 50±5°C for 48 hours;

[0072] Step 11, pulse discharge the lithium-ion battery with a current of 55A for 10 seconds;

[0073] Step 12: After the battery is left to stand for 3 hours, the battery is sorted by open circuit voltage (OCV), AC impedance (1kHz) and discharge capacity.

[0074] Comparative Example 2

[0075] This embodiment relates to a lithium ion formation method, comprising the following steps:

[0076] In this example, except for the ambient temperature that is separately marked in the operation steps, the ambient temperature is assumed to be 20±5℃;

[0077] Step 1: Take 10,000 26650 ternary lithium cylindrical batteries, fill them with liquid, seal them, and let them stand for 8 hours;

[0078] Step 2: Charge the lithium-ion battery to 4.35V at a constant current of 1.1A.

[0079] Step 3: aging the batch of lithium-ion batteries at a temperature of 50±5°C for 48 hours;

[0080] Step 4: After the battery is left to rest for 3 hours, charge and discharge the battery at 1.1A for 2 cycles at 2.75-4.35V.

[0081] Step 5: sort the batteries by open circuit voltage (OCV), AC impedance (1kHz), and discharge capacity.

[0082] Table 2

[0083]

[0084] Comparing the data in Tables 1 and 2 shows that the formation method of the present invention achieves excellent product consistency, significantly improving discharge capacity, discharge performance, and cycling performance, while also enhancing safety to a higher level. The entire formation process is simple, significantly reducing the time required by traditional methods, significantly improving production efficiency, and generating significant economic benefits.

[0085] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any modifications made based on the spirit of the main technical solution of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A lithium ion battery formation method, characterized in that: Including steps: S1, the battery is left to stand for T1 time after filling; S2, charge and discharge the battery several times at a low current density, low potential, and constant current cycle; S3, charge at a low current density and constant current to the upper cut-off voltage; S4, with low current density, at medium potential and high potential, constant current cycle charge and discharge several times; S5, charging the battery at a high potential constant voltage until it is fully charged; S6, subjecting the battery to high current density pulse discharge for time t1; S7, discharge the battery at a medium current density and constant current to the lower cut-off voltage; S8, pulse charging the battery with high current density for t2 time; S9, charge at a low current density and constant current to the upper cut-off voltage, then switch to constant voltage charging to the full charge state; S10, placing the battery at an ambient temperature of 45-55°C for aging for T2 time; S11, subjecting the battery to high current density pulse discharge for t3 time; S12, after the battery is left to stand for T3 time, the battery is sorted by open circuit voltage, AC impedance and discharge capacity; The small current density is 0.01 to 0.2 times the rated current density of the battery, the medium current density is 0.5 to 1 times the rated current density of the battery, and the large current density is 10 to 20 times the rated current density of the battery; The low potential is 0-30% of the battery's state of charge, the medium potential is 30-90% of the battery's state of charge, and the high potential is 90-100% of the battery's state of charge; The T1 time is not less than 8 hours; the T2 time is 24 to 72 hours; and the T3 time is 3 to 5 hours; The pulse discharge time t1, t3 and the pulse charging time t2 are all 10~20s.

2. The lithium ion battery formation method according to claim 1, wherein Except step S10, the ambient temperature of the remaining steps is 20-30°C.

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