Formation process of lithium ion battery and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a formation process of a lithium ion battery and the lithium ion battery. And high and low temperature aging is carried out after liquid injection to promote infiltration of the electrolyte. And normal-temperature pulse formation promotes the formation of an inorganic SEI film, so that the internal resistance of the battery is reduced, the polarization of the battery is reduced, and the cycle performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a formation process of a lithium ion battery and a lithium ion battery. Background Art

[0002] With the depletion of non-renewable energy sources such as oil and natural gas, electric energy as a renewable clean energy will become the cornerstone of future social development. Lithium-ion batteries have the advantages of energy density, small weight per unit volume, and long cycle life. Lithium-ion batteries have become a necessity in people's lives. However, there are many manufacturing procedures for lithium-ion batteries, and the manufacturing process has a great influence on the performance of lithium-ion batteries. Among them, formation is one of the most important preparation processes. The purpose of formation is to form a layer of solid electrolyte interface film (SEI film) on the internal electrode material of the battery during the first charge and discharge process. The quality of the formation process directly affects the battery's capacity, cycle life, high-temperature storage and other performance.

[0003] The existing formation process uses a small current to charge to form the SEI film, but this can easily cause the SEI film to be unstable, take a long time to form, and have poor rate performance.

[0004] How to improve the stability of the SEI film, reduce the formation time of lithium-ion batteries, and improve rate performance has become an urgent problem to be solved by technicians in this field. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a lithium ion battery formation process and a lithium ion battery, which are helpful to form a uniform SEI film and improve the performance of the lithium ion battery. The lithium ion battery formation process comprises:

[0006] Charging with a first constant current until the SOC value of the lithium-ion battery reaches a preset SOC; the preset SOC value is 10-20%;

[0007] Charging with a second constant current until the voltage of the lithium-ion battery is not less than a preset voltage; the second current is greater than the first current, and the preset voltage is 3.9V to 4.6V;

[0008] Charging with a third constant current and constant voltage until the charging current is lower than a fourth charging current, and the fourth current is lower than the second current;

[0009] Discharging at a fifth constant current to a cut-off voltage, wherein the cut-off voltage is no higher than 3.0 V;

[0010] Charging with a sixth constant current until the charging voltage of the lithium ion battery reaches 3.9V;

[0011] The lithium-ion battery is left to stand for a first preset time period.

[0012] Optionally, the step of charging with a second constant current until the voltage of the lithium-ion battery is not lower than a preset voltage comprises:

[0013] Charging with the second constant current for a second preset time and then leaving it to stand;

[0014] After being left to stand for a third preset time, charging again with the second constant current for the second preset time;

[0015] When the voltage of the lithium-ion battery is not lower than a preset voltage, constant current charging is stopped.

[0016] Optionally, the step of charging with a sixth constant current until the charging voltage of the lithium-ion battery reaches 3.9V comprises:

[0017] Charging with the sixth constant current for a fourth preset time and then leaving it to stand;

[0018] After being left to stand for a fifth preset time, charging again with the sixth constant current for the fourth preset time;

[0019] When the voltage of the lithium ion battery reaches 3.9V, constant current charging is stopped.

[0020] Optionally, it is characterized in that the first current is 0.01C to 0.03C.

[0021] Optionally, it is characterized in that the second current is 0.2C to 0.5C.

[0022] Optionally, the fourth charging current is 0.02C.

[0023] Optionally, the fifth current is 0.1C to 0.5C.

[0024] Optionally, the sixth current is 0.2C-0.5C.

[0025] Optionally, the second preset time length is 2 to 30 minutes, the third preset time length is 1 to 5 minutes; the fourth preset time length is 2 to 30 minutes, and the fifth preset time length is 1 to 5 minutes.

[0026] Furthermore, the present invention also provides a lithium-ion battery formed by any of the above-mentioned formation processes.

[0027] Optionally, the lithium-ion battery further comprises, before the formation process:

[0028] Drying to remove moisture from the battery cells;

[0029] injecting electrolyte into the battery cell;

[0030] After the chemical formation process, the method further comprises:

[0031] The lithium-ion battery is evacuated and sealed.

[0032] Optionally, the positive electrode material of the lithium-ion battery is lithium cobalt oxide, the negative electrode material is graphite, the separator is a commercial PP separator, the electrolyte is 1M LiPF6, 0.6M LIFSI, EC:DMC (v:v=1:1), and vinylene carbonate VC, fluoroethylene carbonate FEC and ethyl difluoroacetate (EDFA) are used as additives.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The repeated high and low temperature aging mechanism after injection is conducive to the infiltration of electrolyte.

[0035] (2) Pulse formation at room temperature is conducive to the formation of inorganic SEI, thereby reducing the internal resistance of the battery, reducing battery polarization, and improving the cycle performance of lithium-ion batteries.

[0036] Based on the following detailed description of specific embodiments of the present invention, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. DETAILED DESCRIPTION

[0037] The following describes a formation process of a lithium-ion battery and a lithium-ion battery according to an embodiment of the present invention. In the description of this embodiment, it should be understood that the terms "first" and "second" are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features, that is, include one or more of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. When a feature "includes or contains" one or some of the features it covers, unless otherwise specifically described, this indication does not exclude other features and may further include other features.

[0038] In the description of the present embodiment, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0039] The present invention provides a formation process for a lithium ion battery, the formation process comprising:

[0040] Step S10, charging with a first constant current until the SOC value of the lithium-ion battery reaches a preset SOC; the preset SOC value is 10-20%;

[0041] Step S20, charging with a second constant current until the voltage of the lithium-ion battery is not less than a preset voltage; the second current is greater than the first current, and the preset voltage is 3.9V to 4.6V;

[0042] Step S30, charging with a third constant current and constant voltage until the charging current is lower than a fourth charging current, and the fourth current is lower than the second current;

[0043] Step S40, discharging with a fifth constant current to a cut-off voltage, wherein the cut-off voltage is not higher than 3.0V;

[0044] Step S50, charging with a sixth constant current until the charging voltage of the lithium-ion battery reaches 3.9V;

[0045] Step S60, leaving the lithium-ion battery to rest for a first preset time period.

[0046] Specifically, in the present embodiment, the formation of the lithium-ion battery includes a first charging stage, a discharging stage, a second charging stage and a rest stage. In the first charging stage, the lithium-ion battery is first charged with a first current at a constant current; then, the lithium-ion battery is charged with a second current at a constant current value that is not lower than a preset voltage; finally, the third current is used for constant current and constant voltage charging until the charging current is reduced to a fourth current. In the discharging stage, the fifth current is used for constant current discharge until the lithium battery voltage is no higher than 3.0V. In the second charging stage, the sixth current is used for constant current charging until the lithium-ion battery voltage reaches 3.9V. The rest stage lasts for a first preset duration. It should be noted that the preset voltage can be any value between 3.9V and 4.6V, such as 3.9V, 4.2V, 4.5V, 4.6V, etc.

[0047] In this embodiment, the aging mechanism is repeated, which is beneficial to the infiltration of the electrolyte.

[0048] In some embodiments of the present invention, the above-mentioned constant current charging with the second current until the voltage of the lithium-ion battery is not lower than the preset voltage includes:

[0049] Step S11, charging with a second constant current for a second preset time and then standing still;

[0050] Step S12, after standing for a third preset time, charging again with a second constant current for a second preset time;

[0051] Step S13, when the voltage of the lithium-ion battery is not lower than the preset voltage, the constant current charging is stopped.

[0052] In this embodiment, room temperature pulse formation is beneficial to the formation of inorganic SEI, which is beneficial to reducing the internal resistance of the battery, reducing the polarization of the battery, and improving the cycle performance of the lithium-ion battery.

[0053] In some embodiments of the present invention, the above-mentioned constant current charging with the sixth current until the charging voltage of the lithium-ion battery reaches 3.9V includes:

[0054] Step S51, charging with a sixth constant current for a fourth preset time and then standing still;

[0055] Step S52, after standing for a fifth preset time, charging again with a sixth constant current for a fourth preset time;

[0056] Step S53, when the voltage of the lithium-ion battery reaches 3.9V, the constant current charging is stopped.

[0057] In this embodiment, the fourth preset time length may be equal to the second preset time length, and the fifth preset time length may be equal to the third preset time length.

[0058] In some embodiments of the present invention, the first current is 0.01C-0.03C.

[0059] In some embodiments of the present invention, the second current is 0.2C-0.5C.

[0060] In some embodiments of the present invention, the fourth charging current is 0.02C.

[0061] In some embodiments of the present invention, the fifth current is 0.1C-0.5C.

[0062] In some embodiments of the present invention, the sixth current is 0.2C-0.5C.

[0063] In some embodiments of the present invention, the first preset time length is 2 to 30 minutes, and the second preset time length is 1 to 5 minutes; the first preset time length is 2 to 30 minutes, and the second preset time length is 1 to 5 minutes.

[0064] The present invention also provides a lithium ion battery, which is formed by the formation process in any of the above embodiments.

[0065] In this embodiment, the lithium ion battery obtained by the formation method in any of the above embodiments has good cycle performance.

[0066] In some embodiments of the present invention, the process includes drying to remove moisture from the battery cell before the formation process, injecting electrolyte into the battery cell, and evacuating and sealing the lithium-ion battery after the formation process.

[0067] In some embodiments of the present invention, the positive electrode material of the lithium-ion battery is lithium cobalt oxide, the negative electrode material is graphite, the separator is a commercial PP separator, the electrolyte is 1M LiPF6, 0.6M LIFSI, EC:DMC (v:v=1:1), and vinylene carbonate VC, fluoroethylene carbonate FEC and ethyl difluoroacetate (EDFA) are used as additives.

[0068] The present invention is specifically explained below using several embodiments, and the technical solutions in the embodiments of the present invention are clearly and completely described. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0069] Example 1

[0070] A method for preparing a lithium ion battery comprises the following steps:

[0071] Step S101, placing the battery cell in an oven to remove moisture from the lithium-ion battery.

[0072] Step S102, after injecting the electrolyte into the soft-pack lithium-ion battery, first let it stand at 45°C for 12 hours, then let it stand at -20°C for 2 hours, and finally let it stand at 45°C for 8 hours.

[0073] Step S103, pre-pressing the lithium-ion battery after standing at 45° C. for 0.5 h.

[0074] Step S104, using a constant current of 0.02C, constant current charging to 10% SOC.

[0075] Step S105, charging at a constant current of 0.2C at 0°C for 10 minutes, with an interval of 1 minute, and repeating for multiple times until the constant current charging voltage is greater than 3.9V;

[0076] Step S106, perform constant current and constant voltage charging at 4.2V until the charging current is lower than 0.02C.

[0077] Step S107, using a 0.5C constant current, constant current discharge to a cut-off voltage, the cut-off voltage is 3V.

[0078] Step S108, charge at a constant current of 0.5C at 0°C for 30 minutes, with an interval of 5 minutes, and cycle multiple times until the constant current charging voltage reaches 3.9V, and charge at a constant current and voltage of 0.5C to 4.2V, with a cut-off current of 0.02C.

[0079] Step S109, leaving the formed battery at 45° C. for 24 hours.

[0080] Step S110, evacuating and sealing the lithium-ion battery.

[0081] Example 2

[0082] A method for preparing a lithium ion battery comprises the following steps:

[0083] Step S201, placing the battery cell in an oven to remove moisture from the lithium-ion battery.

[0084] Step S202, after injecting the electrolyte into the soft-pack lithium-ion battery, first let it stand at 45°C for 12 hours, then let it stand at -20°C for 2 hours, and finally let it stand at 45°C for 8 hours.

[0085] Step S203, pre-pressing the lithium-ion battery after standing at 45° C. for 0.5 h.

[0086] Step S204, using a constant current of 0.02C, constant current charging to 10% SOC.

[0087] Step S205, charging at a constant current of 0.2C at 25°C for 10 minutes, with an interval of 1 minute, and repeating for multiple times until the constant current charging voltage is greater than 3.9V;

[0088] Step S206, constant current and constant voltage charging to 4.2V, until the charging current is lower than 0.02C.

[0089] Step S207, using a 0.5C constant current, constant current discharge to a cut-off voltage of 3.0V.

[0090] Step S208, charging at a constant current of 0.5C at 25°C for 30 minutes, with an interval of 5 minutes, and repeating multiple times until the constant current charging voltage reaches 3.9V, and charging at a constant current and voltage of 0.5C to 4.2V, with a cut-off current of 0.02C.

[0091] Step S209, leaving the formed battery at 45° C. for 24 hours.

[0092] Step S210, evacuating and sealing the lithium-ion battery.

[0093] Example 3

[0094] A method for preparing a lithium ion battery comprises the following steps:

[0095] Step S301, placing the battery cell in an oven to remove moisture from the lithium-ion battery.

[0096] Step S302, after injecting the electrolyte into the soft-pack lithium-ion battery, first let it stand at 45°C for 12 hours, then let it stand at -20°C for 2 hours, and finally let it stand at 45°C for 8 hours.

[0097] Step S303, pre-pressing the lithium-ion battery after standing at 45°C for 0.5h.

[0098] Step S304, using a constant current of 0.02C, constant current charging to 10% SOC.

[0099] Step S305, charging at a constant current of 0.2C at 45°C for 10 minutes, with an interval of 1 minute, and repeating for multiple times until the constant current charging voltage is greater than 3.9V;

[0100] Step S306, constant current and constant voltage charging to 4.2V, until the charging current is lower than 0.02C.

[0101] Step S307, using a 0.5C constant current, constant current discharge to a cut-off voltage of 3.0V.

[0102] Step S308, charge at a constant current of 0.5C at 45°C for 30 minutes, with an interval of 5 minutes, and repeat multiple times until the constant current charging voltage reaches 3.9V, and charge at a constant current and voltage of 0.5C to 4.2V, with a cut-off current of 0.02C.

[0103] Step S309, leaving the formed battery at 45° C. for 24 hours.

[0104] Step S310, evacuating and sealing the lithium-ion battery.

[0105] Example 4

[0106] A method for preparing a lithium ion battery comprises the following steps:

[0107] Step S401, placing the battery cell in an oven to remove moisture from the lithium-ion battery.

[0108] Step S402, after injecting the electrolyte into the soft-pack lithium-ion battery, first let it stand at 45°C for 12 hours, then let it stand at -20°C for 2 hours, and finally let it stand at 45°C for 8 hours.

[0109] Step S403, pre-pressing the lithium-ion battery after standing at 45°C for 0.5h.

[0110] Step S404, using a constant current of 0.02C, constant current charging to 10% SOC.

[0111] Step S405, charging at a constant current of 0.2C at 25°C for 10 minutes, with an interval of 2 minutes, and repeating for multiple times until the constant current charging voltage is greater than 3.9V;

[0112] Step S406, perform constant current and constant voltage charging at 4.2V until the charging current is lower than 0.02C.

[0113] Step S407, use 0.5C constant current, constant current discharge to 2.0V.

[0114] Step S408, charge at a constant current of 0.5C at 25°C for 30 minutes, with an interval of 10 minutes, and cycle multiple times until the constant current charging voltage reaches 3.9V, and charge at a constant current and voltage of 0.5C to 4.2V, with a cut-off current of 0.02C.

[0115] Step S409, leaving the formed battery at 45° C. for 24 hours.

[0116] Step S410, evacuating and sealing the lithium-ion battery.

[0117] Comparative Example 1

[0118] This embodiment provides a formation process for a lithium-ion battery, comprising the following steps:

[0119] A method for preparing a lithium ion battery comprises the following steps:

[0120] Step S501, placing the battery cell in an oven to remove moisture from the lithium-ion battery.

[0121] Step S502, after injecting the electrolyte into the soft-pack lithium-ion battery, first let it stand at 45°C for 12 hours, then let it stand at -20°C for 2 hours, and finally let it stand at 45°C for 8 hours.

[0122] Step S503, pre-pressing the lithium-ion battery after standing at 45°C for 0.5h.

[0123] Step S504, using a constant current of 0.02C, constant current charging to 10% SOC.

[0124] Step S505, charging at 0.2C constant current at 25°C to 3.9V;

[0125] Step S506, perform constant current and constant voltage charging at 4.2V until the charging current is lower than 0.02C.

[0126] Step S507, use 0.5C constant current, constant current discharge to 2.0V.

[0127] Step S508, charging to 4.2V at a constant current and constant voltage of 0.5C at 25°C, with a cut-off current of 0.02C.

[0128] Step S509, leaving the formed battery at high temperature for 24 hours.

[0129] Step S510, evacuating and sealing the lithium-ion battery.

[0130] Comparative Example 2

[0131] A method for preparing a lithium ion battery comprises the following steps:

[0132] Step S601, placing the battery cell in an oven to remove moisture from the lithium-ion battery.

[0133] Step S602, after injecting the electrolyte into the soft-pack lithium-ion battery, first let it stand at 45°C for 12 hours, then let it stand at -20°C for 2 hours, and finally let it stand at 45°C for 8 hours.

[0134] Step S603, pre-pressing the lithium-ion battery after standing at 45°C for 0.5h.

[0135] Step S604, using a constant current of 0.02C, constant current charging to 10% SOC.

[0136] Step S605, charging at 45°C with a constant current of 0.2C to 3.9V;

[0137] Step S606, perform constant current and constant voltage charging at 4.2V until the charging current is lower than 0.02C.

[0138] Step S607, use 0.5C constant current, constant current discharge to 2.0V.

[0139] Step S608, charging to 4.2V at a constant current and constant voltage of 0.5C at 45°C, with a cut-off current of 0.02C.

[0140] Step S609, leaving the formed battery at high temperature for 24 hours.

[0141] Step S610, evacuating and sealing the lithium-ion battery.

[0142] The performance of the lithium ion batteries obtained in Examples 1 to 4, Comparative Examples 1 and 2 was tested to measure the maximum voltage reached after applying current for 5 minutes and the voltage difference after charging was stopped, the battery internal resistance and the capacity retention rate of 500 normal temperature cycles. The results are shown in Table 1.

[0143] Table 1 Battery performance measurement

[0144] plan Voltage difference after applying current for 5 minutes (mV) Internal resistance(mΩ) 500 cycles at room temperature Capacity retention rate (%) Example 1 90 34.6 84.5％ Example 2 83 30.8 87.3％ Example 3 100 37.6 83.3％ Example 4 72 28.1 89.2％ Comparative Example 1 94 38.2 82.4％ Comparative Example 2 108 42.4 78.5％

[0145] As can be seen from the above table, the lithium-ion battery formed by room temperature pulse has smaller internal resistance, smaller battery polarization, and better cycle capacity retention rate than the control battery.

[0146] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all these other variations or modifications.

Claims

1. A formation process for a lithium ion battery, characterized in that: The following steps are involved: Charging with a first constant current until the SOC value of the lithium-ion battery reaches a preset SOC; The preset SOC value is 10-20%; Charging with a second constant current until the voltage of the lithium-ion battery is not lower than a preset voltage; The second current is greater than the first current, and the preset voltage is 3.9V to 4.6V; Charging with a third constant current and constant voltage until the charging current is lower than a fourth charging current, and the fourth current is lower than the second current; Discharging at a fifth constant current to a cut-off voltage, wherein the cut-off voltage is no higher than 3.0 V; Charging with a sixth constant current until the charging voltage of the lithium ion battery reaches 3.9V; The lithium-ion battery is left to stand for a first preset time period.

2. The formation process of a lithium ion battery according to claim 1, characterized in that: The method of charging the lithium-ion battery with a second constant current until the voltage of the lithium-ion battery is not lower than a preset voltage includes: Charging with the second constant current for a second preset time and then leaving it to stand; After being left to stand for a third preset time, charging again with the second constant current for the second preset time; When the voltage of the lithium-ion battery is not lower than a preset voltage, constant current charging is stopped.

3. The formation process of a lithium ion battery according to claim 1, characterized in that: The step of charging the lithium-ion battery with a sixth constant current until the charging voltage of the lithium-ion battery reaches 3.9V comprises: Charging with the sixth constant current for a fourth preset time and then leaving it to stand; After being left to stand for a fifth preset time, charging again with the sixth constant current for the fourth preset time; When the voltage of the lithium ion battery reaches 3.9V, constant current charging is stopped.

4. The formation process of a lithium ion battery according to any one of claims 1 to 3, characterized in that: The first current is 0.01C to 0.03C.

5. The formation process of a lithium ion battery according to any one of claims 1 to 3, characterized in that: The second current is 0.2C to 0.5C.

6. The formation process of a lithium ion battery according to any one of claims 1 to 3, characterized in that: The fourth charging current is 0.02C.

7. The formation process of a lithium ion battery according to any one of claims 1 to 3, characterized in that: The fifth current is 0.1C to 0.5C.

8. The formation process of a lithium ion battery according to any one of claims 1 to 3, characterized in that: The sixth current is 0.2C to 0.5C.

9. The formation process of a lithium ion battery according to any one of claims 1 to 3, characterized in that: The second preset time length is 2 to 30 minutes, and the second preset time length is 1 to 5 minutes; the fourth preset time length is 2 to 30 minutes, and the fifth preset time length is 1 to 5 minutes.

10. A lithium ion battery, formed by the formation process according to any one of claims 1 to 9, characterized in that: The positive electrode material of the lithium-ion battery is lithium cobalt oxide, the negative electrode material is graphite, the diaphragm is a commercial PP diaphragm, the electrolyte is 1MLiPF6, 0.6M LIFSI, EC:DMC (v:v=1:1), and vinylene carbonate VC, fluoroethylene carbonate FEC and ethyl difluoroacetate (EDFA) are used as additives.