Method for activating lithium secondary battery

Abstract

The present invention relates to a method for activating a lithium secondary battery, the method comprising: (1) an initial charging step of charging at a first C-rate to a first state of charge (SOC); (2) an intermediate charging step of charging at a second C-rate lower than the first C-rate to a second SOC higher than the first SOC after the initial charging step; and (3) a final charging step of completing charging by charging at a third C-rate lower than the second C-rate to a third SOC higher than the second SOC after the intermediate charging step, wherein, through the method for activating a lithium secondary battery performed at a temperature in the range of 50°C to 60°C, the activation time of the lithium secondary battery can be shortened, and the lithium plating problem can be solved.

Description

Activation method for lithium secondary batteries

[0001] Cross-citation with related application(s)

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2025-0005335 filed January 14, 2025 and Korean Patent Application No. 10-2026-0003623 filed January 8, 2026, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of the specification.

[0003] The present invention relates to a method for activating a lithium secondary battery, and more specifically, to a method for activating a lithium secondary battery capable of shortening the activation time and reducing the amount of lithium precipitated.

[0004] Recently, as the demand for technology development and ESS (Energy Storage System) for portable devices such as portable computers, mobile phones, and cameras has increased, the demand for secondary batteries as an energy source has been rapidly increasing. Among these secondary batteries, a lot of research has been conducted on environmentally friendly lithium secondary batteries that exhibit high charge / discharge characteristics and lifespan characteristics, and they have also been commercialized and are widely used.

[0005] Furthermore, while active research is being conducted on materials capable of securing high energy density per unit volume as cathode active materials for lithium-ion batteries, some of these high-energy-density materials require a lengthy activation process to form a stable Solid Electrolyte Interphase (SEI) film on the anode surface, which leads to increased process costs. Moreover, performing the activation process under high voltage conditions can cause the SEI film formed on the anode surface to become non-uniform or unstable, thereby increasing the likelihood of lithium precipitation.

[0006] Therefore, there is a need to develop an activation method that can form a uniform and stable SEI film on the cathode surface during the activation process, while simultaneously shortening the activation time and reducing the amount of lithium precipitation.

[0007] The present invention aims to provide an activation process for a lithium secondary battery that suppresses lithium precipitation by forming a stable SEI film and simultaneously shortens the activation time.

[0008] The present invention is a method for activating a lithium secondary battery, wherein

[0009] (1) Initial charging step of charging at a first C-rate up to a first SOC (State of Charge);

[0010] (2) After the initial charging step, an intermediate charging step of charging to a second SOC higher than the first SOC at a second C-rate lower than the first C-rate; and

[0011] (3) A final charging step in which, after the intermediate charging step, charging is completed by charging to a third SOC higher than the second SOC at a third C-rate lower than the second C-rate; and

[0012] A method for activating a lithium secondary battery is provided, which is performed at a temperature in the range of 50℃ to 60℃.

[0013] The present invention relates to a method for activating a lithium secondary battery, wherein the activation time can be shortened and the precipitation of lithium can be suppressed by including three or more charging steps in which the C-rate is lowered stepwise as the SOC increases.

[0014] In addition, since the activation method of the present invention is performed at a temperature in the range of 50°C to 60°C, a more uniform and stable SEI film can be formed.

[0015] Figure 1 shows the C-rate and SOC at the activation stages of the examples and comparative examples according to the experimental example.

[0016] Figure 2 shows a photograph of cell decomposition after activation of the example and comparative example according to the experimental example.

[0017] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0018] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0019] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020]

[0021] The present invention will be described in more detail below.

[0022]

[0023] Activation method for lithium secondary batteries

[0024] The method for activating a lithium secondary battery according to the present invention is,

[0025] (1) Initial charging step of charging at a first C-rate up to a first SOC (State of Charge);

[0026] (2) After the initial charging step, an intermediate charging step of charging to a second SOC higher than the first SOC at a second C-rate lower than the first C-rate; and

[0027] (3) A final charging step in which, after the intermediate charging step, charging is completed by charging to a third SOC higher than the second SOC at a third C-rate lower than the second C-rate; and

[0028] It is characterized by being performed at a temperature in the range of 50℃ to 60℃.

[0029] First, the above C-rate is an abbreviation of Current rate, which refers to the speed at which a battery is charged or discharged, and the unit used is C, and it can be defined as shown in Equation 1 below.

[0030] [Mathematical Formula 1]

[0031] C-rate (C) = Charge / Discharge Current / Battery Rated Capacity

[0032] After in-depth research, the inventors of the present application confirmed that by applying a charging process of three or more stages in which the C-rate is gradually reduced as the SOC increases, as in the activation method of the lithium secondary battery of the present invention, the activation time can be shortened while simultaneously suppressing lithium precipitation.

[0033] In the activation process, a Solid Electrolyte Interphase (SEI) film is formed on the cathode surface by a decomposition reaction between the cathode surface and the electrolyte, and the formation rate, stability, and uniformity of the SEI film affect the activation process rate and the occurrence of lithium precipitation.

[0034] Specifically, by applying a relatively high C-rate during the initial charging phase, the initiation of SEI film formation on the cathode surface is rapidly induced, and by gradually decreasing the C-rate during subsequent charging phases, the SEI film can be grown and stabilized uniformly and densely. Furthermore, by applying a low C-rate in the high SOC range, the rapid drop in cathode potential is suppressed, thereby effectively inhibiting lithium precipitation.

[0035] Through this stepwise charging process, the SEI film can be stably formed while simultaneously shortening the activation process time.

[0036] The activation method of the present invention is performed in the entire process of steps (1) to (3) at a temperature in the range of 50°C to 60°C.

[0037] Specifically, the activation method of the present invention can be performed at a temperature in the range of 50°C to 60°C, more specifically 53°C to 57°C, and even more specifically 54°C to 56°C. When the temperature of the activation process satisfies the above range, the electrolyte decomposition reaction and lithium ion diffusion are balanced, allowing a uniform and dense SEI film to be rapidly formed across the entire surface of the cathode. Accordingly, the effects of reducing lithium precipitation and shortening activation time are more effectively realized.

[0038] The activation method of the present invention performs an initial charging step of charging to a first SOC at a first C-rate.

[0039] At this time, the first C-rate may be 1.1C or higher, specifically 1.1C to 1.4C, and more specifically 1.3C. When the first C-rate satisfies the above range, the initiation of SEI film formation can be rapidly induced during the initial charging stage, and the possibility of lithium precipitation occurring due to excessive current application can be reduced.

[0040] In addition, the first SOC may be 20% to 30%, specifically 25% to 30%.

[0041] An activation method according to one embodiment of the present invention performs an initial charging step, and then performs an intermediate charging step in which the device is charged to a second SOC at a second C-rate lower than the C-rate of the initial charging step. In this way, during the intermediate charging step in which a second C-rate lower than the first C-rate is applied, the electrolyte decomposition reaction proceeds at an appropriate rate, thereby forming a uniform and dense SEI film across the entire surface of the cathode, and consequently, the structural stability of the SEI film is improved.

[0042] The second C-rate can be selected from 0.6C to 1.3C as a value lower than the first C-rate, and the second SOC can be 30% to 90%, more specifically 60% to 90%, and even more specifically 80% to 90%.

[0043] Furthermore, the above intermediate charging step may include two or more steps.

[0044] Specifically, the method may include two or more steps of charging while gradually decreasing the C-rate as the SOC increases, and more specifically, the intermediate charging step may include two to eight steps of charging while decreasing the C-rate by 0.1C each time the SOC increases by 5% to 20%. In this way, by gradually decreasing the C-rate as the SOC increases, the activation time can be further shortened and the lithium precipitation problem can be resolved.

[0045] According to one embodiment of the present invention, the intermediate charging step may include: a step of charging at a C-rate of 1.2C up to 30% to 40% SOC; a step of charging at a C-rate of 1.1C up to 40% to 50% SOC; a step of charging at a C-rate of 1.0C up to 50% to 60% SOC; a step of charging at a C-rate of 0.9C up to 60% to 70% SOC; a step of charging at a C-rate of 0.8C up to 70% to 80% SOC; and a step of charging at a C-rate of 0.7C up to 80% to 90% SOC.

[0046] The activation method of the present invention performs a final charging step after the intermediate charging step, in which charging is completed by charging to a third SOC higher than the second SOC at a third C-rate lower than the second C-rate.

[0047] At this time, the third C-rate can be selected from 0.5C to 0.7C as a value lower than the second C-rate, and specifically 0.6C, and the third SOC can be 90% to 100%, and specifically 95% to 100%.

[0048] In addition, the activation method of the present invention may further include a step of charging up to 4.4V to 4.7V. Specifically, after the final charging step is performed, CC (Constant Current) charging may be performed until 4.4V to 4.7V is reached, and then CV (Constant Voltage) charging may be performed. More specifically, after the final charging step is performed, CC (Constant Current) charging may be performed at approximately 0.4C to 0.8C until 4.4V to 4.7V is reached, and then CV (Constant Voltage) charging may be performed up to 0.1C to 0.2C. By performing such CC-CV charging in the final step, the reaction inside the battery can be stabilized and the initial charging capacity can be secured.

[0049] An activation method according to one embodiment of the present invention can be applied to a lithium secondary battery comprising a lithium transition metal oxide as a positive active material, comprising lithium and one or more transition metals selected from the group consisting of nickel, manganese, cobalt, iron, and phosphorus.

[0050] Specifically, the activation method according to one embodiment of the present invention can be applied to a lithium secondary battery that must be charged up to 100% SOC. Such a lithium secondary battery may include a lithium iron phosphate compound, lithium iron oxide, etc., as a positive electrode active material.

[0051] In addition, the activation method according to one embodiment of the present invention can be applied to a lithium secondary battery comprising a positive electrode active material comprising a lithium manganese-rich oxide containing 50 mol% or more and less than 100 mol% of manganese based on the total metal content excluding lithium.

[0052] The above-mentioned lithium manganese-rich oxide has a structure in which a layered phase (LiM'O2) and a rock salt phase (Li2MnO3) are mixed. Since high capacity can be achieved by activating the rock salt phase through a potential flattening region that occurs when charging at a high voltage of 4.4V or higher, a long activation process is required, which increases process costs. Additionally, when carbon-based materials such as natural graphite are used as the negative electrode active material to reduce material costs, there was a problem of lithium precipitation during the high-voltage activation process. Therefore, when the activation method of the present invention is applied to a lithium secondary battery containing lithium manganese-rich oxide as the positive electrode active material, the aforementioned problems can be resolved.

[0053] The above-mentioned lithium manganese-rich oxide may include a compound represented by the following chemical formula 1:

[0054] [Chemical Formula 1]

[0055] Li a [Ni b Co c Mn d M e ]O2

[0056] In the above chemical formula 1, M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 1 <a, 0≤b≤0.5, 0≤c≤0.1, 0.5≤d<1, 0≤e≤0.2이다.

[0057] Meanwhile, a is the molar ratio of Li in the lithium-over-manganese-rich oxide, 1 <a, 1.1≤a≤1.5, 또는 1.12≤a≤1.18일 수 있다. a가 상기 범위를 만족할 때, 고용량 특성 및 단위부피당 높은 에너지 밀도를 구현할 수 있다.

[0058] The above b is the molar ratio of Ni in the lithium manganese-rich oxide, and may be 0≤b≤0.5, 0.1≤b≤0.4, or 0.24≤b≤0.36.

[0059] The above c is the molar ratio of Co in the lithium-rich manganese oxide, and may be 0≤c≤0.1 or 0≤c≤0.05. If c exceeds 0.1, it is difficult to secure high capacity, and gas generation and degradation of the cathode active material may be exacerbated, which may lead to a decrease in lifespan characteristics.

[0060] The above d is the molar ratio of Mn in the lithium-rich manganese oxide, and may be 0.5≤d<1, 0.5≤d≤0.8, or 0.5≤d≤0.63. If d is less than 0.5, the proportion of rock salt phase becomes too small, so the effect of improving capacity is negligible.

[0061] The above e is the molar ratio of additional element M in the lithium-rich manganese oxide, and may be 0≤e≤0.2, 0≤e≤0.1, or 0≤e≤0.05. If the content of the additional element is too high, it may have an adverse effect on the capacity of the active material.

[0062] Meanwhile, the above-mentioned lithium manganese-rich oxide may be represented more specifically by the following chemical formula 2.

[0063] [Chemical Formula 2]

[0064] X Li2MnO3· (1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0065] In the above chemical formula 2,

[0066] M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, and 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, 0≤w≤0.2.

[0067] The above X represents the ratio of the rock salt phase (Li2MnO3) in the lithium-over-manganese-rich oxide, and may be 0.2≤X≤0.5, 0.25≤X≤0.5, or 0.25≤X≤0.4. When the ratio of the rock salt phase (Li2MnO3) in the lithium-over-manganese-rich oxide satisfies the above range, high capacity characteristics can be achieved.

[0068] The above y is the molar ratio of Mn in the layer (LiM'O2), and may be 0.4≤y<1, 0.4≤y≤0.8, or 0.4≤y≤0.7.

[0069] The above z is the molar ratio of Co in the layered structure (LiM'O2), and may be 0≤z≤0.1, 0≤z≤0.08, or 0≤z≤0.05. If z exceeds 0.1, gas generation and degradation of the cathode active material may be exacerbated, which may lead to a decrease in lifespan characteristics.

[0070] The above w is the molar ratio of additional element M in the layer (LiM'O2), and may be 0≤w≤0.2, 0≤w≤0.1, or 0≤w≤0.05.

[0071] The above lithium transition metal oxide and lithium-rich manganese oxide can be manufactured according to manufacturing methods known in the art, and a positive electrode of a lithium secondary battery can be manufactured using a positive electrode active material comprising the above lithium transition metal oxide and lithium-rich manganese oxide.

[0072] In addition, a lithium secondary battery to which the activation method of the present invention is applied may include a carbon-based material as a negative electrode active material. Specific examples of the carbon-based material include artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon. Furthermore, both low-crystallinity carbon and high-crystallinity carbon may be used as the carbon-based material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbon such as petroleum or coal tar pitch-derived cokes. A negative electrode of a lithium secondary battery can be manufactured using a negative electrode active material containing the above carbon-based material.

[0073]

[0074] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily practice the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0075]

[0076] [Experimental Example]

[0077] Example of preparation. Preparation of a lithium secondary battery

[0078] Lithium over-manganese-rich oxide (Li 1.3 [Ni 0.35 Mn 0.65An anode slurry was prepared by adding CNT as a conductive material, PVDF (polyvinylidene fluoride) as a binder, and an acrylonitrile butadiene rubber solution as a dispersant to NMP (N-methyl-2-pyrrolidone), a solvent, in a weight ratio of 97.46:0.62:1.7:0.22. An anode was prepared by coating the anode slurry onto an aluminum (Al) film with a thickness of 12 μm and drying it.

[0079] A cathode slurry was prepared by adding natural graphite as a cathode active material, carbon black and CNT (carbon black weight:CNT weight = 98.5:1.5) as conductive materials, SBR (styrene-butadiene rubber) as a binder, and CMC (carboxymethyl cellulose) as a thickener to water as a solvent in a weight ratio of 95.63:1.0:2.3:1.07. The cathode slurry was coated onto a copper (Cu) thin film with a thickness of 8 μm and dried to produce a cathode.

[0080] A cell was manufactured by interposing an SRS separator with ceramic coatings on both sides as a separator between the anode and cathode prepared above, mixing EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DEC (diethyl carbonate) as electrolytes in a volume ratio of 1:2:2, and then adding 1.2M LiPF6 as a lithium salt.

[0081]

[0082] Comparative Example 1.

[0083] The cell manufactured in the above manufacturing example was charged at 1.0C to 60% SOC at 45℃, then CC (Constant Current) charged at 0.4C to 4.6V, and subsequently CV (Constant Voltage) charged to 0.05C.

[0084]

[0085] Comparative Example 2.

[0086] The cell manufactured in the above manufacturing example was charged at 1.0C to 60% SOC at 55℃, then CC (Constant Current) charged at 0.6C to 4.6V, and subsequently CV (Constant Voltage) charged to 0.16C.

[0087]

[0088] Example.

[0089] After charging the cell manufactured in the above manufacturing example to 25% SOC at 1.3C at 55℃, charging to 35% SOC at 1.2C, charging to 45% SOC at 1.1C, charging to 55% SOC at 1.0C, charging to 65% SOC at 0.9C, charging to 75% SOC at 0.8C, and charging to 85% SOC at 0.7C was performed in stages, and then CC (Constant Current) charging was performed at 0.6C to 4.6V, and then CV (Constant Voltage) charging was performed to 0.16C.

[0090]

[0091] The C-rate and SOC at the activation stages of Comparative Example 1, Comparative Example 2, and the Example above are shown in FIG. 1, and a photograph taken after disassembling the cell following activation is shown in FIG. 2. In addition, the activation temperature, activation charge time, and presence or absence of lithium precipitation of the Comparative Example and the Example are shown in Table 1 below.

[0092] Experiment Example Activation Temperature Activation Charging Protocol Activation Charging Time Presence or Absence of Lithium Precipitation Comparative Example 145℃ 4.6V 1.0C / 0.4C (CC-CV 5% cut) 152 min O Comparative Example 255℃ 4.6V 1.0C / 0.6C (CC-CV 16% cut) 97 min X Example 55℃ 4.6V 1.3C / 0.6C (CC-CV 16% cut) 81 min X

[0093]

[0094] As can be seen from Table 1 above, the activation method of the lithium secondary battery of the present invention can significantly shorten the activation charging time, and it can be confirmed that no lithium precipitation occurs even after activation is completed. On the other hand, in Comparative Example 1, which is a conventional activation method, the activation time was long and the problem of lithium precipitation occurred. In addition, Comparative Example 2, in which activation was performed by increasing the activation temperature and the secondary charging C-rate compared to Comparative Example 1, solved the problem of lithium precipitation and shortened the activation time, but it can be confirmed that the effect of shortening the activation time of the example is much superior.

[0095] Figure 2 shows the decomposed separator of Comparative Example 1, and the decomposed cathode (top) and separator (bottom) of Comparative Example 2 and the Example. When examining the surface of the separator of Comparative Example 2 and the Example after activation is complete, it can be seen that no lithium was deposited. On the other hand, in Comparative Example 1, it can be seen that lithium was deposited, forming a black and cloudy pattern on the cross-section of the separator.

[0096] From these results, it was confirmed that applying the lithium secondary battery activation method of the present invention can shorten the activation time of the lithium secondary battery and solve the problem of lithium precipitation.

Claims

1. As a method for activating a lithium secondary battery, (1) Initial charging step of charging at a first C-rate up to a first SOC (State of Charge); (2) After the initial charging step, an intermediate charging step of charging to a second SOC higher than the first SOC at a second C-rate lower than the first C-rate; and (3) A final charging step in which, after the intermediate charging step, charging is completed by charging to a third SOC higher than the second SOC at a third C-rate lower than the second C-rate; and A method for activating a lithium secondary battery, which is performed at a temperature in the range of 50℃ to 60℃.

2. In Paragraph 1, A method for activating a lithium secondary battery in which the first C-rate is 1.1C or higher.

3. In Paragraph 1, A method for activating a lithium secondary battery, wherein the third C-rate is selected from 0.5C to 0.7C.

4. In Paragraph 1, A method for activating a lithium secondary battery, wherein the above intermediate charging step includes two or more steps of charging while gradually decreasing the C-rate as the SOC increases.

5. In Paragraph 4, A method for activating a lithium secondary battery, wherein the above intermediate charging step comprises 2 to 8 steps of charging while decreasing the C-rate by 0.1C each time the SOC increases by 5% to 20%.

6. In Paragraph 1, A method for activating a lithium secondary battery in which the first SOC is 20% to 30%.

7. In Paragraph 1, A method for activating a lithium secondary battery in which the above-mentioned third SOC is 90% to 100%.

8. In Paragraph 1, The above activation method is a method for activating a lithium secondary battery, which further includes the step of charging to 4.4V to 4.7V.

9. In Paragraph 1, A method for activating a lithium secondary battery, wherein the lithium secondary battery comprises a positive electrode active material comprising a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium.

10. In Paragraph 9, A method for activating a lithium secondary battery in which the above-mentioned lithium manganese-rich oxide comprises a compound represented by the following chemical formula 1: [Chemical Formula 1] Li a [Ni b Co c Mr d M e ]O2 In the above chemical formula 1, M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 1 <a, 0≤b≤0.5, 0≤c≤0.1, 0.5≤d<1, 0≤e≤0.2이다.

11. In Paragraph 9, A method for activating a lithium secondary battery in which the above-mentioned lithium manganese-rich oxide comprises a compound represented by the following chemical formula 2: [Chemical Formula 2] X Li2MnO3· (1-X)Li[Ni 1-y-z-w Mr y Co z M w ]O2 In the above chemical formula 2, M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, and 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, 0≤w≤0.

2.

12. In Paragraph 1, A method for activating a lithium secondary battery in which the above lithium secondary battery includes a carbon-based material as a negative electrode active material.

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