KR101106359B1 - Method for manufacturing lithium ion secondary battery - Google Patents

Abstract

The present invention is to provide a method for manufacturing a lithium ion secondary battery that can increase the capacity of the battery by improving the chemical conversion process of the lithium secondary battery manufacturing process.

In the method of manufacturing a lithium ion secondary battery of the present invention, a room temperature aging step of aging a battery into which an electrolyte is injected is performed at room temperature, a precharge step of precharging a room temperature aged battery, and a high temperature aging step of aging a precharged battery at a temperature higher than room temperature. Characterized in that it comprises a step.

Lithium Ion Secondary Battery, Capacity, Precharge, SEI

Description

Method for manufacturing a lithium ion secondary battery {METHOD FOR MANUFACTURING LITHIUM ION SECONDARY BATTERY}

The present invention relates to a method for producing a lithium ion secondary battery.

A lithium ion secondary battery is a battery that exhibits a high energy density by using an organic electrolyte and exhibiting a discharge voltage two times higher than that of a battery using a conventional aqueous alkali solution.

The lithium ion secondary battery is manufactured through a series of processes including a pole plate manufacturing process, an assembly process, and a chemical conversion process. Here, the chemical conversion process is a process of stabilizing the battery structure and making it usable through a series of processes such as charging, aging, and discharging of the assembled battery.

Portable electronic devices become smaller and smaller, but their functions are added more and more. Therefore, the capacity of batteries used in portable electronic devices must also be increased.

The present invention is to provide a method for manufacturing a lithium ion secondary battery that can increase the capacity of the battery by improving the chemical conversion process of the lithium secondary battery manufacturing process.

Problems to be solved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above may be clearly understood by those skilled in the art from the following description. There will be.

In the method of manufacturing a lithium ion secondary battery of the present invention, a room temperature aging step of aging a battery into which an electrolyte is injected is performed at room temperature, a precharge step of precharging a room temperature aged battery, and a high temperature aging step of aging a precharged battery at a temperature higher than room temperature. Characterized in that it comprises a step.

Here, the room temperature aging step, the aging time may be 22 hours to 26 hours.

In addition, the pre-charging step, the charging voltage may be carried out under the conditions of 2.0 ~ 2.4 V, charging current of 0.045 ~ 0.055 C and charging time 5 ~ 7 minutes.

In addition, in the high temperature aging step, the aging temperature is 40 to 50 ℃ and the aging time is 43 to 53 hours of aging first aging step and the aging temperature is 70 to 80 ℃ and the aging time is 2.3 to 2.8 hours And a second aging step of aging.

In addition, after the room temperature aging step, it may further include a degassing step for removing the gas inside the battery.

The method may further include a pressing step of pressurizing the battery after the high temperature aging step.

According to the lithium ion secondary battery manufacturing method of the present invention, the battery is activated by normal temperature aging at room temperature, the reversible capacity is increased by precharging, and the SEI (Solid) generated during precharging by high temperature aging at high temperature. Electrolyte Interface) By stabilizing and uniformizing the membrane, the capacity of the lithium ion secondary battery can be increased.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a process flowchart of the chemical conversion process of the present invention.

As shown in Figure 1, the chemical conversion process of the present invention is the normal temperature aging step (S10), degassing step (S20), pre-charging step (S30), high temperature aging step (S40), pressurization step (S50), formation A step S60, a third aging step S70, a fourth aging step S80, a second full discharge step 90, and a half charge step S100 may be included.

Here, the degassing step (S20), the pressing step (S50), the formation step (S60), the third aging step (S70), the fourth aging step (S80), the second full discharge step (90) and the semi-charge step S100 may be selectively implemented.

The normal temperature aging step (S10) is a step of stabilizing the battery by leaving the battery in which the electrolyte is injected.

In general, lithium ion secondary batteries have a risk of accelerating the decomposition of the electrolyte solution at a high temperature or reducing the charge / discharge capacity. Therefore, it is preferable to proceed with aging primarily at room temperature. In addition, it is preferable to remove the gas that may occur at a high temperature in advance with the multigasing step (S20).

The room temperature aging step (S10) is preferably performed for 22 hours to 26 hours. If the room temperature aging is less than 22 hours, the electrolyte is not evenly impregnated to inhibit the formation of a uniform SEI film in the precharge step 30. On the contrary, if the aging proceeds for longer than 26 hours, there is a problem that the manufacturing process is delayed.

In addition, IR / OCV (Internal Resistance / Open Circuit Voltage) of the room temperature aged battery may be measured by a multimeter having a resolution of 0.001 or less. On the basis of the measured values, batteries with poor welding and electrolyte impregnation can be selected.

The degassing step 20 is a step of removing the gas generated in the room temperature aging step (S10).

The gas generated in the room temperature aging step S10 may cause a swelling phenomenon of the battery. Therefore, it is preferable to proceed with the degassing step (S20) to remove the gas.

The precharging step (S30) is a step for forming an SEI film on the surface of the cathode.

SEI membranes are insulators formed when the amount of ion transport in a battery increases. Once formed, the SEI film prevents lithium ions and other materials from reacting at the cathode during subsequent battery charging. SEI membranes also function as a kind of ion tunnel. In other words, it serves to pass only lithium ions. The ion tunnel effect prevents large molecular weight organic solvents traveling with lithium ions from reacting with the negative electrode to disrupt the negative electrode structure. That is, after the SEI film is formed, lithium ions do not react side-by-side with the negative electrode or other materials, and thus the amount of lithium ions can be reversibly maintained. In addition, the organic solvents are inserted together with lithium ions to prevent the structure of the negative electrode from collapsing, thereby maintaining charge and discharge of the lithium ion polymer secondary battery reversibly, thereby improving battery life. In addition, since the SEI film is not easily collapsed even when it is left at high temperature or repeats charging and discharging, the SEI film has less thickness increase at high temperature and maintains the initial charge capacity. As a result, the SEI film formed by precharging ensures the battery capacity.

In other words, the precharge induces a non-responsive gas by charging before high temperature aging, thereby reducing the uncharged area. Thereby, the substantial reversible capacity of the unfilled area can be increased.

Precharge charges the battery to 10-40% of the battery capacity.

The preliminary charging step (S30) is preferably carried out with a charging voltage of 2.0 ~ 2.4 V, a charging current of 0.045 ~ 0.055 C, the charging time in the above charging conditions takes about 5 ~ 7 minutes. If precharge is performed at a charge voltage of 2.0 V or a charge current of less than 0.045 C, a sufficient SEI film cannot be produced and a long time of precharge is not suitable for mass production processes. On the other hand, if the charging voltage is precharged at 2.4 V or the charging current at 0.055 C, the battery needs to be charged at a high rate in order to meet a predetermined capacity, so that the battery is overloaded and easily causes an overvoltage. In addition, even SEI film cannot be produced and deformation of the battery is likely to occur, which is not preferable.

The high temperature aging step (S40) is a step of aging the pre-charged battery at a temperature higher than room temperature.

Aging at high temperatures causes the SEI film to be more stabilized by thermal and electrochemical energy and reshaped to an even and uniform thickness without partial bias. As described above, the SEI film thus formed is not easily collapsed even when left at a high temperature or rotated cycles, thereby reducing the increase in thickness during the high temperature and maintaining the capacity at the initial stage of charging.

Here, the high temperature aging may be divided into a first aging and a second aging.

The first aging may be carried out at a temperature of 40 to 50 ℃. The first aging improves the unfilled area, improves the full charge thickness, and stabilizes the SEI film. If the first aging temperature is less than 40 ° C, thermal energy is insufficient to stabilize the SEI film. In addition, when the first aging temperature is 50 ° C. or more, the SEI film may be exposed to a high temperature in a state where the SEI film is not stabilized, thereby causing the SEI film to collapse.

The time for which the first aging proceeds can be appropriately adjusted depending on the type of the active material, the electrolyte, and other materials and battery models. For example, when the negative electrode active material is KPL3, the solvent of the negative electrode active material is pure, the binder of the negative electrode active material is SBR + CMC, the positive electrode active material is KD10, the binder of the positive electrode active material is PVdF, and the conductive material of the positive electrode active material is Solef6020. 43 to 53 hours is preferable.

 The second aging may proceed at a temperature of 70-80 ° C. The second aging may promote thermal polymerization of the monomer, impregnate the electrolyte, and improve swelling characteristics without degrading the performance of the battery. If the second aging temperature is less than 70 ℃ swelling effect may be insignificant. In addition, when the second aging temperature is 80 ° C. or higher, there is a possibility that the packaging material may be destroyed or the battery may ignite due to evaporation of the electrolyte solution.

The time for which the second aging proceeds can be appropriately adjusted depending on the type of the active material, the electrolyte solution, other materials and the battery model. For example, when the negative electrode active material is KPL3, the solvent of the negative electrode active material is pure, the binder of the negative electrode active material is SBR + CMC, the positive electrode active material is KD10, the binder of the positive electrode active material is PVdF, and the conductive material of the positive electrode active material is Solef6020. Is preferably 2.3 to 2.8 hours.

The pressing step (S50) is a step of pressing the high temperature aged battery.

Pressurization in the pressurizing step (S50) may be carried out to 680 ~ 820 kgf, pressurization time is 4 ~ 6 seconds. In the case of a lithium ion polymer battery using a pouch as an exterior material, thickness expansion may occur due to a gas generated as the chemical conversion process proceeds. Therefore, it is desirable to improve the thickness of the cell through the press to match the thickness of the cell on the customer's spec.

The formation step (S60) is a step of repeatedly charging and discharging the pressurized battery. At this time, the forming step is to charge with a charging time of 54 to 66 minutes at a charge current of 0.18 ~ 0.22 C, a charge voltage of 3.8 ~ 4.6 V, a charge current of 0.63 ~ 0.77 C, a charge voltage of 3.8 ~ 4.6 V At full charge, cut-off charging at a charge current of 0.09 to 0.11 C, discharge current of 0.9 to 1.1 C, first full discharge at a discharge voltage of 2.5 to 2.9 V, and charging current of 0.9 to 1.1 C, At a charging voltage of 3.8 to 4.6 V, the charging time may include a recharging step of 4.5 to 5.5 minutes.

The third aging step (S70) is a step of aging the formed battery at room temperature. At this time, the third aging can be carried out with the battery having an aging time of 11 to 13 hours and an aging temperature of room temperature. The third aging may stabilize the battery voltage before and after replenishment.

In addition, the IR / OCV of the third aged battery may be measured by a multimeter having a resolution of 0.001 or less. This provides a reference voltage of ΔV when measuring the IR / OCV of the fourth aged cell, described below. The measured OCV is called OCV2.

The fourth aging step (S80) is a step of aging the third aged battery at room temperature. At this time, the fourth aging can be performed at an aging time of 6 to 8 days and at an aging temperature of room temperature. Fine short voltage may be induced through the fourth aging.

In addition, the IR / OCV of the fourth aged battery may be measured by a multimeter having a resolution of 0.001 or less. This allows the screen to generate fine short and to screen for IR defects. In this case, the measured OCV is called OCV3. ΔV = OCV2-OCV3. ΔV can be used to select cells with microshorts.

The second full discharge step 90 is a step of full discharge of the fourth aged battery. At this time, the second full discharge can be performed with a discharge current of 0.9 to 1.1 C and a discharge voltage of 2.5 to 2.9 V.

The half charging step (S100) is a step of charging the second full discharged battery to a capacity corresponding to 50%. At this time, the half charge can be carried out with a charging current of 0.9 to 1.1C. At this time, it can be charged to customer's required voltage.

Here, the IR / OCV of the half-charged battery can be measured with a multimeter having a resolution of 0.001 or less. At this time, the battery can be selected to meet the customer shipping conditions.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

First, the battery targeted by the chemical conversion process is as follows. The battery is a lithium ion polymer battery. The electrolyte is of gel type and formed of film type. The thickness is about 0.137 mm, the width is about 41 mm, and the height is about 67 mm. The rated voltage is about 3.7 V and the rated capacity is about 1230 mAh.

The negative electrode active material is about 97.5% of KPL3, the solvent of the negative electrode active material is pure, the binder of the negative electrode active material is about 1.5% of SBR (Styrene Butadiene Rubber) + about 1% CMC, and there is no conductive material of the negative electrode active material. The cathode active material is about 96% KD10, the binder of the cathode active material is about 2% polyvinylidene flouride (PVDF), and the conductive material of the cathode active material is about 2% Solef6020. HSPG (High Strength Polymer Gel) is added to the electrolyte.

The chemical conversion process was carried out as follows.

First, aging was performed at room temperature for about 24 hours, and IR / OCV was measured by a multimeter having a resolution of about 0.001 or less, and a battery was selected for poor welding or abnormal electrolyte impregnation.

The degassing process was then carried out in vacuo for about 15 seconds.

Then, precharging was performed for about 6 minutes at a condition of about 2.2 V and about 0.05 C.

Then, the first aging was carried out at about 45 ° C. for about 48 hours.

Then, the second aging was carried out at about 75 ° C. for about 2.5 hours.

Then, the pressurization process was performed at about 750 kgf.

Then, charge for about 60 minutes at about 0.2 C, about 4.2 V, full charge at about 0.7 C, about 4.2 V, cut-off charge at about 0.1 C, first full discharge at about 1 C, about 2.75 V, The formation was progressed by replenishment in turn at about 1 C and 4.2 V for about 5 minutes.

Then, the third aging was carried out at room temperature for about 12 hours.

Then, the hard short cell was selected by measuring IR / OCV with a multimeter having a resolution of about 0.001 or less. The measured OCV is called OCV2.

Then, the fourth aging process was performed at room temperature for about 7 days.

Subsequently, IR / OCV was measured with a multimeter having a resolution of about 0.001 or less to select a cell having a micro short and an IR defect. The measured OCV is called OCV3. ΔV = OCV2-OCV3. ΔV can be used to select cells with microshorts.

Then, the second full discharge was performed at a condition of about 1 C and about 2.75, and was half charged to about 50% based on the charging capacity at about 1 C. Half charge took about 30 minutes.

Then, the cells were selected by measuring IR / OCV with a multimeter having a resolution of about 0.001 or less.

(Comparative Example 1)

In order to see the effect of precharging, the process is the same except for precharging.

As a result of comparing Example 1 with Comparative Example 1, it was confirmed that Example 1 is 30 mAh higher than the comparative example.

(Example 2)

First, the battery targeted by the chemical conversion process is as follows. The battery is a lithium ion polymer battery. The electrolyte is of gel type and formed of film type. The thickness is about 0.165 mm, the width is about 45 mm, and the height is about 68 mm. The rated voltage is about 3.7 V and the rated capacity is about 2400 mAh.

The negative electrode active material is about 97.5% of KPL3, the solvent of the negative electrode active material is pure, the binder of the negative electrode active material is SBR about 1.5% + CMC about 1% and there is no conductive material of the negative electrode active material. The cathode active material is about 96% KD10, the binder of the cathode active material is about 2% PVdF, and the conductive material of the cathode active material is about 2% Solef6020.

The chemical conversion process was carried out as follows.

First, aging was performed at room temperature for about 24 hours, and IR / OCV was measured by a multimeter having a resolution of about 0.001 or less, and a battery was selected for poor welding or abnormal electrolyte impregnation.

The degassing process was then carried out in vacuo for about 15 seconds.

Then, precharging was performed for about 6 minutes at a condition of about 2.2 V and about 0.05 C.

Then, the first aging was carried out at about 45 ° C. for about 48 hours.

Then, the second aging was carried out at about 75 ° C. for about 2.5 hours.

Then, the pressurization process was performed at about 750 kgf.

Then, charge for about 60 minutes at about 0.2 C, about 4.2 V, full charge at about 0.7 C, about 4.2 V, cut-off charge at about 0.1 C, first full discharge at about 1 C, about 2.75 V, At about 1 C and 4.2 V, the formation was progressed by replenishment for 5 minutes in sequence.

Then, the third aging was carried out at room temperature for about 12 hours.

Then, the hard short cell was selected by measuring IR / OCV with a multimeter having a resolution of about 0.001 or less. The measured OCV is called OCV2.

Then, the fourth aging process was performed at room temperature for about 7 days.

Subsequently, IR / OCV was measured with a multimeter having a resolution of about 0.001 or less to select a cell having a micro short and an IR defect. The measured OCV is called OCV3. ΔV = OCV2-OCV3. ΔV can be used to select cells with microshorts.

Then, the second full discharge was performed at a condition of about 1 C and about 2.75, and was half charged to about 50% based on the charging capacity at about 1 C. Half charge took about 30 minutes.

Then, the cells were selected by measuring IR / OCV with a multimeter having a resolution of about 0.001 or less.

(Comparative Example 2)

In order to see the effect of precharging, the process is the same except for precharging.

Figure 2 is a frequency / capacity graph showing the capacity distribution of the cells prepared in Example 2 and Comparative Example 2.

The pink line in the graph is the result for Example 2 and the blue line is the result for Comparative Example 2.

As shown in FIG. 2, the average capacity of Example 2 is about 2420 mAh and the comparative capacity of Comparative Example 2 is about 2300 mAh. Thus, when comparing Example 2 with Comparative Example 2, it can be seen that Example 2 has an average capacity of about 120 mAh higher.

That is, the capacity of the battery is improved through precharging as seen in Examples 1 and 2.

In addition, the present invention can improve the OCV dispersion through the measurement of the IR / OCV in the chemical conversion process, it can present an optimized chemical conversion process conditions.

1 is a process flowchart of the chemical conversion process of the present invention.

Figure 2 is a frequency / capacity graph showing the capacity distribution of the cells prepared in Example 2 and Comparative Example 2.

Claims (6)

Room temperature aging step of aging the battery in which the electrolyte is injected at room temperature; Degassing the gas inside the room temperature aged cell; A precharge step of precharging the battery from which the gas has been removed; And And a high temperature aging step of aging the precharged battery at a temperature higher than the room temperature. The method of claim 1, The room temperature aging step, An aging time is 22 hours to 26 hours, characterized in that the lithium ion secondary battery manufacturing method. The method of claim 1, The precharge step, A method for producing a lithium ion secondary battery, characterized in that the charging voltage is carried out under the conditions of 2.0 to 2.4 V, charging current of 0.045 to 0.055 C, and charging time of 5 to 7 minutes. The method of claim 1, The high temperature aging step, A first aging step of aging at an aging temperature of 40 to 50 ° C. and an aging time of 43 to 53 hours; And And a second aging step of aging at an aging temperature of 70 to 80 ° C. and an aging time of 2.3 to 2.8 hours. delete The method of claim 1, After the high temperature aging step, A method of manufacturing a lithium ion secondary battery further comprising a pressurizing step of pressurizing the battery.

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