Lithium metal battery, and battery module and battery pack including same

Abstract

A lithium metal battery according to one embodiment of the present invention comprises: an electrode assembly including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode; an electrolyte impregnating the electrode assembly; and a battery case in which the electrode assembly and the electrolyte are embedded, wherein the negative electrode includes a negative electrode current collector and a lithium metal layer formed on at least one surface of the negative electrode current collector, and the lithium metal battery is charged and discharged in a state in which a pressure of 2 kgf / cm2 or more and 30 kgf / cm2 or less is applied thereto.

Description

Lithium metal battery, battery module and battery pack containing the same

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0073022, filed June 7, 2023, and Korean Patent Application No. 10-2024-0073720, filed June 5, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a lithium metal battery, a battery module including the same, and a battery module including the same, and more particularly, to a lithium metal battery characterized in that a predetermined pressure is applied to a lithium metal battery during charging and discharging of the lithium metal battery, and a battery module and battery pack including the same.

[0004] Currently, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, are being commercialized and widely used.

[0005] In terms of battery shape, there is a high demand for square secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones due to their thin thickness. In terms of materials, there is a high demand for lithium secondary batteries such as lithium-ion batteries and lithium-ion polymer batteries with high energy density, discharge voltage, and output stability.

[0006] Typically, lithium secondary batteries are structured to have an electrode assembly comprising a positive electrode, a negative electrode, and a porous separator, each impregnated with a non-aqueous electrolyte. Furthermore, the positive electrode is typically manufactured by coating a positive electrode mixture containing a positive electrode active material onto aluminum foil, while the negative electrode is typically manufactured by coating a negative electrode mixture containing a negative electrode active material onto copper foil.

[0007] The positive electrode active material is a lithium transition metal oxide, and the negative electrode active material has been using a carbon-based material, but recently, lithium metal batteries that use lithium metal itself, which exhibits high energy density, as the negative electrode active material have been commercialized.

[0008] At this time, the lithium metal used as the negative electrode has a density (0.54 g / cm 3 ) and a very low standard reduction potential (-3.045 V SHE), making it the most sought-after material as an anode material for high-energy-density batteries. In addition, despite the problems arising from its high chemical activity, the need for the development of high-energy-density secondary batteries continues to grow due to the continuous increase and rapid development of mobile communication and portable electronic devices, and thus the need for the use of lithium metal anodes continues to arise.

[0009] In this case, when a lithium metal electrode is used as the negative electrode, unlike a lithium ion battery, the thickness of the battery cell tends to change more than that of a lithium ion battery because the lithium metal is deposited or disappeared during charging and discharging. When lithium is charged, a porous layer may be formed due to the generation of lithium needles in which electrodeposition is concentrated locally. This may increase the resistance of the battery and even cause an internal short circuit, thereby lowering the stability of the battery. When lithium is discharged, the distance between the separator and the negative electrode interface increases, increasing the resistance. This repeated deformation due to charging and discharging deteriorates the internal elements, causing problems such as a shortened charge and discharge cycle life.

[0010] Therefore, there is a need to develop lithium metal batteries, battery modules and battery packs containing the same that address these problems.

[0011] The present invention aims to provide a lithium metal battery having improved stability during operation and an extended lifespan, and a battery module and battery pack including the same.

[0012] However, the problems to be solved by the embodiments of the present invention are not limited to the problems described above and can be expanded in various ways within the scope of the technical ideas included in the present invention.

[0013] According to one embodiment of the present invention, a lithium metal battery comprises an electrode assembly including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode; an electrolyte impregnating the electrode assembly; and a battery case housing the electrode assembly and the electrolyte, wherein the negative electrode includes a negative electrode current collector and a lithium metal layer formed on at least one surface of the negative electrode current collector, and a lithium metal battery having a density of 2 kgf / cm 2 More than 30 kgf / cm 2 It can be charged and discharged under the following pressure conditions:

[0014] Pressure is applied to the lithium metal battery in a positive pressure manner, and the pressure applied to the lithium metal battery is 7 kgf / cm 2 More than 12 kgf / cm 2 It may be less than.

[0015] The pressure applied to the above lithium metal battery is 8 kgf / cm 2 More than 11 kgf / cm 2 It could be as follows:

[0016] Pressure is applied to the lithium metal battery in a constant pressure manner, and the pressure applied to the lithium metal battery is 4 kgf / cm 2 More than 30 kgf / cm 2 It could be as follows:

[0017] The pressure applied to the above lithium metal battery is 5 kgf / cm 2 More than 25 kgf / cm 2 It could be as follows:

[0018] The equivalent spring constant of the elastic member applied to the above-mentioned constant pressure pressurization method may be 60 kgf / mm or more and 1000 kgf / mm or less.

[0019] Pressure is applied to the lithium metal battery in a constant pressure manner, and the pressure applied to the lithium metal battery is 10 kgf / cm 2 More than 30 kgf / cm 2 It could be as follows:

[0020] Pressure is applied to the lithium metal battery in a constant pressure manner, and the pressure applied to the lithium metal battery is 10 kgf / cm 2 More than 25 kgf / cm 2 It could be as follows:

[0021] The above lithium metal battery may be a pouch-type lithium metal battery.

[0022] The above lithium metal battery is mounted on a pressurizing jig so that pressure can be applied by the pressurizing jig.

[0023] A battery module according to one embodiment of the present invention includes a battery cell stack in which a plurality of battery cells are stacked and a module case that accommodates the battery cell stack, and may be a lithium metal battery according to the embodiments described above.

[0024] In the case where the pressurization method for the lithium metal battery is a constant pressure pressurization method, the battery module may further include a pressurization unit installed within the module case so that the distance from the large area of ​​the battery cell is variable, a driving unit capable of moving the pressurization unit, a measuring unit that measures the pressure applied to the pressurization member, and a control unit that receives data measured from the measuring unit and adjusts the pressure applied to the pressurization member to be constant.

[0025] If the pressurization method of the lithium metal battery is a constant pressure pressurization method, the battery module may further include an elastic member within the module case.

[0026] A battery pack according to one embodiment of the present invention may include a battery module according to the above-described embodiments and a pack case for storing the battery module.

[0027] According to the present invention, a lithium metal battery having improved stability during operation and an increased lifespan according to pressurization conditions during charging and discharging, and a battery module and battery pack including the same can be provided.

[0028] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0029] Figure 1 is a drawing schematically illustrating a stereotactic pressurization method.

[0030] Figure 2 is a drawing schematically illustrating a static pressure pressurization method.

[0031] Figure 3 is a drawing schematically explaining the constant pressure pressurization method.

[0032] FIG. 4 is a graph showing the discharge capacity and C / E (coulombic efficiency) measured each time per charge / discharge cycle by varying the pressure applied to the battery cell in Example 1 and Comparative Example 1 of the present invention.

[0033] Figure 5 is a graph showing the results of measuring the voltage value between the positive and negative electrodes of a battery cell according to the discharge capacity of the battery cell by varying the number of charge and discharge cycles.

[0034] Figures 6 to 8 are graphs showing the test results by varying the pressure applied to the battery cell in the case of the fixed pressure method.

[0035] Figures 9 to 11 are graphs showing the test results by varying the pressure applied to the battery cell in the case of the constant pressure pressurization method.

[0036] Figures 12 to 14 are graphs showing the test results by varying the pressure applied to the battery cell in the case of the constant pressure pressurization method.

[0037] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0038] Additionally, throughout the specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0039] A lithium metal battery according to one embodiment of the present invention comprises an electrode assembly including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, an electrolyte impregnating the electrode assembly, and a battery case housing the electrode assembly and the electrolyte. The negative electrode includes a negative electrode current collector and a lithium metal layer formed on at least one surface of the negative electrode current collector.

[0040] As described above, conventional lithium metal batteries have problems such as the formation of needle-like lithium in which electrodeposition is concentrated locally during charging, an increase in resistance and a decrease in discharge capacity due to a phenomenon in which the gap between the separator and the negative electrode interface increases during discharge, and a shortened charge / discharge cycle life due to deterioration of internal components caused by repeated deformation caused by such charging and discharging.

[0041] To address these issues, the lithium metal battery of the present invention is charged and discharged while pressurized to a predetermined pressure. When the pressure is adjusted to match the rate at which lithium metal grows and disappears, the performance of the lithium metal battery is improved.

[0042] The lithium metal battery of the present invention has a voltage of 2 kgf / cm during charging and / or discharging. 2 More than 30 kgf / cm 2 The following pressure is applied to the battery cell:

[0043] In the case of the positive pressure method, the pressure applied to the lithium metal battery is 7 kgf / cm 2 More than 12 kgf / cm 2 Less than or equal to 8 kgf / cm 2 More than 11 kgf / cm 2 It could be as follows:

[0044] In the case of the constant pressure pressurization method, the pressure applied to the lithium metal battery is 4 kgf / cm 2 More than 30 kgf / cm 2 or less, or 5 kgf / cm 2 More than 25 kgf / cm 2 The spring constant of the elastic member applied to the constant pressure pressurization method may be 60 kgf / mm or more and 1000 kgf / mm or less.

[0045] In the case of the constant pressure pressurization method, the pressure applied to the lithium metal battery is 10 kgf / cm 2 More than 30 kgf / cm 2 or less, or 10 kgf / cm 2 More than 25 kgf / cm 2 It could be as follows:

[0046] In this specification, applying pressure to a lithium metal battery means applying pressure in the thickness direction of the lithium metal battery or in a large-area surface. Maintaining a certain level of pressure is necessary during both charging and discharging of a lithium metal battery. During charging, lithium metal is created and grows, so pressure is required to prevent the lithium metal battery from growing into a porous shape. During discharging, lithium metal is consumed, which can locally become porous, so pressure is also applied to the lithium metal battery in this case.

[0047] Meanwhile, when the pressure applied to the battery cell during charging satisfies the conditions according to embodiments of the present invention, local lithium deposition that may occur during charging is effectively prevented, while leakage of electrolyte due to excessive pressure, increase in battery cell resistance, compression of the separator, etc. do not occur, thereby ensuring battery cell safety.

[0048] In addition, when the pressure applied to the battery cell during discharge satisfies the conditions according to embodiments of the present invention, the space between the separator and the negative electrode interface can be minimized to reduce the resistance of the battery cell and prevent a decrease in discharge capacity.

[0049] The charging and discharging mentioned here refers not only to charging and discharging performed during the manufacturing process of the battery cell (e.g., activation process, etc.), but also to charging and discharging performed during use of the product, including the actual battery cell, after the battery cell product is shipped.

[0050] There are three pressurization methods for lithium metal batteries: a positronic pressurization method, a constant pressure pressurization method, and a constant-variable pressurization method. These can be implemented as a pressurization jig, a battery module, and / or a battery pack. Figures 1, 2, and 3 are drawings schematically illustrating the positronic, constant pressure, and constant-variable pressurization methods, respectively.

[0051]

[0052] The positional pressurization method of Fig. 1 is a method of maintaining a constant distance (interval) between the pressing members (110) on both sides with the battery cell (10) in between. For example, in the manufacturing process of the battery cell, the distance between the pressing jigs may be constant. Alternatively, this may be the case of a typical battery module case and / or battery pack case. In this case, when a product equipped with battery cells is actually used, the distance between the frames (housings) of the battery module or battery pack in which the battery cells are housed is constant.

[0053] Since the distance between the pressurizing members (110) is maintained constant, when the lithium metal battery expands during charging, a large pressure may be applied to the battery cell (10) in some cases. Alternatively, even though the distance between the separator and the negative electrode interface gradually increases during discharge, the distance between the pressurizing members (110) on both sides of the battery cell remains constant, so a situation may arise where the pressure required during discharge is not applied. Therefore, only the positive pressure pressing method may be applied during charging and discharging, but as a method with a small degree of pressure change, the positive pressure pressing method or the positive variable pressure pressing method described below may be used in combination.

[0054] The constant pressure pressurization method of FIG. 2 is a method of controlling the pressure applied by the pressurizing member (110) to be maintained at a constant level. That is, it is a method in which a constant value of pressure is applied to the battery cell (10) by the pressurizing member (110). For example, in the manufacturing process of the battery cell, this may be the case in which a constant value of pressure is applied to the pressurizing jig. In the actual use of a product equipped with a battery cell, this may be the case in which a constant value of pressure is applied to the battery cell from the inside and / or outside of the frame (housing) of the battery module or battery pack in which the battery cells are stored.

[0055] When applying the constant pressure pressurization method, in order to maintain the constant pressure, a mechanical device that adjusts the pressure according to the degree of tightening is included, and when charging, the pressure is maintained by releasing the tightening at the position of pressing to the battery cell (10), and when discharging, the pressure can be maintained by increasing the degree of tightening at the position of pressing to the battery cell (10) to apply more pressure. For example, the battery module and / or battery pack according to the present invention may include a pressurization unit (110) that is provided on both sides of the battery cell (10) with the battery cell (10) interposed therebetween so that the distance from the large area of ​​the battery cell (10) can be variably installed, a drive unit (120) that can move the pressurization unit (110), a measurement unit (130) that measures the pressure applied to the pressurization member, a control unit (not shown) that receives data measured from the measurement unit and adjusts the pressure applied to the pressurization member to be constant, etc. The drive unit (120) may be, for example, a motor (servo motor, etc.), and the measurement unit (130) may be, for example, a load cell.

[0056] The static pressure pressurization method of FIG. 3 is a case where the static pressure pressurization method is partially modified, and the distance (interval) between the pressing members (110) on both sides with the battery cell (10) in between is kept constant, but an elastic member (140) is interposed between one or both sides of the pressing member (110) and the battery cell (10). That is, the sum of the pressing force by the pressing member (110) and the elastic force by the elastic member (140) is applied to the battery cell (10).

[0057] The elastic member (140) may be, for example, a spring. To obtain a desired elastic force, an elastic member (140) having an appropriate elastic coefficient may be used, or a method of changing the number of elastic members (140) installed may be applied, or a combination thereof is also possible.

[0058] The equivalent spring constant of the elastic member (140) may be, for example, 60 kgf / mm or more and 1000 kgf / mm or less.

[0059] More specifically, in the case of a small battery cell, the equivalent spring constant of the elastic member (140) may be, for example, 60 kgf / mm or more and 300 kgf / mm or less, or 60 kgf / mm or more and 200 kgf / mm or less, or, for example, 160 kgf / mm. For example, four elastic members (140) having a spring constant of 40 kgf / mm may be arranged at each corner of one side of a battery cell, a battery module, or a battery pack and connected in parallel, so that the equivalent spring constant may be 160 kgf / mm (40 kgf / mm × 4 = 160 kgf / mm).

[0060] In the case of medium- to large-sized battery cells, the equivalent spring constant of the elastic member (140) may be, for example, 200 kgf / mm or more and 1000 kgf / mm or less, or 300 kgf / mm or more and 1000 kgf / mm or less, or, for example, 480 kgf / mm. For example, when the size of the battery cell is 100 mm x 300 mm, the equivalent spring constant may be, for example, 480 kgf / mm.

[0061] The spring constant can be selected appropriately according to the environment in which the present invention is implemented, such as the size of the battery cell.

[0062] In addition, the elastic member (140) may be in direct contact with the battery cell (10), but an auxiliary pressure member (110) may be additionally provided between the elastic member (140) and the battery cell (10), so that the auxiliary pressure member (110) is in contact with the battery cell (10), and the auxiliary pressure member (110) may be variable depending on the elastic force of the elastic member (140).

[0063] When using the constant-pressure pressurization method and / or the constant-variable pressurization method, there are advantages in that they can compensate for phenomena that may occur in the constant-pressurization method. For example, they can compensate for increased internal battery resistance caused by the compression of the separator, micro-shorts caused by needle-shaped lithium metal piercing the separator, and cracks caused by the breakdown of the positive electrode active material.

[0064] In the case where there is no static pressure jig, battery module and / or battery pack having a mechanical device for maintaining static pressure, a static transformation jig, battery module and / or battery pack can be used, and in the case where it is difficult to apply even with a static transformation method, a static position jig, battery module and / or battery pack can be used.

[0065] Meanwhile, it can also be implemented as a composite method of at least two of the static, static pressure, and static transformation pressurization methods.

[0066] In addition, the present invention is not limited to the above-described method, and the pressurizing method can be applied in various environments, such as by a jig pressurizing method, a magnetic pressurizing method, or a mixed method thereof, depending on the type of the pressurizing member.

[0067]

[0068] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below.

[0069]

[0070] First, the lithium metal batteries used in the embodiments and comparative examples of the present invention are as follows.

[0071] lithium metal battery

[0072] A slurry of positive electrode active material (LiFePO495) was prepared by adding about 0.5 parts by weight of CNT as a conductive material, and about 3 parts by weight of polyvinylidene fluoride (PVDF) as a binder to N-methylpyrrolidone (NMP) as a solvent, and then the positive electrode active material slurry was coated on both sides of an aluminum current collector having a thickness of 10 to 20 μm to a thickness of 90 μm or more, dried and rolled, and then cut into a certain size to prepare a positive electrode sheet. In addition, a single-sided positive electrode sheet was prepared in the same manner as described above, except that the positive electrode active material slurry was coated on only one side.

[0073] Additionally, a negative electrode sheet was manufactured by attaching a lithium metal foil having a thickness of 30 ㎛ or less to each side of a copper current collector having a thickness of 5 to 15 ㎛.

[0074] In addition, an electrode assembly was manufactured using 20 separators (a porous coating layer formed of a mixture of alumina and PVDF binder on both sides of a polyethylene porous polymer substrate), 9 double-sided positive electrode sheets and 10 double-sided negative electrode sheets as described above, and 2 double-sided negative electrode sheets at the outermost end.

[0075] Afterwards, the electrolyte solution prepared by dissolving 1-4 M LiFSI, LiTFSI, etc. in Ether, Carbonate, and THP solvents and adding a non-solvent was injected into the pouch of the battery cell. Then, the lithium metal battery was manufactured by completely sealing it.

[0076]

[0077] Evaluation of cycle characteristics of lithium metal batteries

[0078] 1 to 10 mA / cm under constant current / constant voltage (CC / CV) conditions 2 Charge to 3.6 to 3.8 V with constant current, then charge and terminate with 0.05C current cut, and current density 1 to 10 mA / cm 2Discharge was performed to 2.6 to 2.8 V under constant current (CC) conditions (discharge temperature 25 ℃). At this time, the lithium metal battery was (a) 8 kgf / cm in the case of Example 1 2 At a pressure of 1 kgf / cm and (b) for comparative example 1 2 Each was pressurized with pressure of .

[0079] Under these conditions, the charge / discharge process was repeated several times, and the discharge capacity and C / E were measured, respectively, and are shown in Fig. 4. However, in Comparative Example 1, after approximately 30 cycles, the operation was stopped and no longer possible due to reasons such as rapid performance degradation of the battery cell. Meanwhile, in Example 1 of the present invention, the discharge capacity and C / E were measured while repeating the charge / discharge process for more than 130 cycles.

[0080] FIG. 4 is a graph showing the discharge capacity and C / E (coulombic efficiency) measured at each charge / discharge cycle by varying the pressure applied to the battery cell under the positive pressure condition in Example 1 and Comparative Example 1 of the present invention.

[0081] Figure 4 (a) is comparative example 1, 1 kgf / cm 2 This is a graph measured when a pressure of 8 kgf / cm is applied to a battery cell, and (b) of FIG. 4 is Example 1 of the present invention. 2 This is a graph measured when pressure is applied to a battery cell. Fig. 4 (c) is a graph showing the case in which Example 1 and Comparative Example 1 of the present invention are compared.

[0082] In each of the graphs (a) to (c) of FIG. 4, the x-axis represents the number of charge / discharge cycles, the y-axis on the left represents the discharge capacity, and the y-axis on the right represents C / E (coulombic efficiency), that is, the ratio of discharge capacity to charge capacity. Capacity in FIG. 4 represents the discharge capacity, which means the developed capacity when SOC 100 (fully charged) becomes SOC 0 (fully discharged). C / E represents whether the discharge capacity is properly output as charged in the nth cycle, and C / E = (nth cycle discharge capacity) / (nth cycle charge capacity), where n is a natural number. In addition, the value at the top of the graph represents the measured discharge capacity value, and the value at the bottom represents the measured C / E value.

[0083] 8 kgf / cm 2 In Example 1 of Fig. 4 (b), where the battery cell was pressurized with a pressure of , it was measured that the discharge capacity and C / E had high values ​​and that the values ​​were substantially maintained even when the charge and discharge cycles were repeated.

[0084] On the other hand, 1 kgf / cm 2 In Comparative Example 1 of Fig. 4 (a), where the battery cell was pressurized with a pressure of , it can be seen that the discharge capacity and C / E were measured as values ​​with a large deviation for each cycle when charge and discharge were repeated. In other words, a fluctuating graph is shown. This means that the stability of the battery cell is significantly lower. In addition, it can be seen that the discharge capacity values ​​are also lower overall compared to Example 1 of Fig. 4 (b).

[0085] In addition, it can be seen that in Comparative Example 1 of Fig. 4 (a), the number of cycles is significantly lower than in Example 1 of Fig. 4 (b) due to reasons such as deterioration of the battery cell. This means that the lifespan of the battery in Comparative Example 1 of Fig. 4 (a) is significantly lower than in Example 1 of Fig. 4 (b).

[0086] In summary, as can be seen from the comparison graph between Example 1 and Comparative Example 1 in (c) of FIG. 4, not only is the discharge capacity value higher in Example 1 than in Comparative Example 1, but the discharge capacity and C / E value are constant even when the number of charge / discharge cycles is repeated (i.e., the stability of the battery is significantly improved), and the number of charge / discharge cycles is greater (i.e., the lifespan of the battery is longer).

[0087] For reference, in some cases where the variation range of the C / E value in Comparative Example 1 of Fig. 4 (a) was high, this means that a micro-short occurred or deposition occurred on the anode during discharge.

[0088] Figure 5 is a graph showing the results of measuring the voltage value between the positive and negative electrodes of a battery cell according to the discharge capacity of the battery cell by varying the number of charge and discharge cycles under the same measurement conditions as Figure 4. It is easy to check for abnormalities when checking the charge and discharge profile.

[0089] In Comparative Example 1 of Fig. 5 (a), 1 kgf / cm 2 In the case where the battery cell is pressurized with a pressure of 8 kgf / cm in the embodiment of (b) of Fig. 5 2 This is when the battery cell is pressurized with a pressure of . In each of the graphs (a) and (b) of Fig. 5, the x-axis represents the discharge capacity and the y-axis represents the voltage. The value of the discharge capacity increases from left to right on the x-axis. In each of (a) and (b) of Fig. 5, the value indicated at the top is the value measured in the case of charging, and the value indicated at the bottom is the value measured in the case of discharging.

[0090] In Comparative Example 1 of Fig. 5 (a), instead of displaying the values ​​measured in each cycle on the graph, for readability, the values ​​measured when charging and discharging were performed 1, 7, 12, 15, and 18 times are displayed on the graph, and in the embodiment of Fig. 5 (b), the values ​​measured when charging and discharging were performed 2, 5, 10, 15, 20, 25, 35, 40, 45, and 50 times are displayed on the graph. As described above, in the embodiment of Fig. 5 (b), the number of cycles (charge and discharge) is greater than in Comparative Example 1 of Fig. 5 (a) because the lifespan of the battery cell is longer.

[0091] In the embodiment of Fig. 5 (b), as can be seen from the part indicated by the dotted circle, it can be seen that the voltage value for the discharge capacity is measured almost constantly regardless of the number of charge / discharge cycles. On the other hand, in Comparative Example 1 of Fig. 5 (a), as can be seen from the part indicated by the dotted circle, it can be seen that the voltage value is different depending on the number of charge / discharge cycles. This means that the stability of the battery cell is significantly improved in the embodiment of Fig. 5 (b) compared to Comparative Example 1 of Fig. 5 (a).

[0092] Figures 6 to 8 are graphs showing the results of tests conducted while varying the pressure applied to the battery cells and increasing the number of charge / discharge cycles in the case of the stationary pressurization method. The tests were conducted under the same measurement conditions as those in Figure 4. In the case of the stationary pressurization method, since a lower pressurization force is more advantageous for the implementation and design of the actual battery pack, tests were conducted to find the optimal (lowest) pressurization conditions.

[0093] Figures 6 and 7 respectively show graphs of discharge capacity and capacity retention measured at each charge / discharge cycle. The x-axis represents the number of charge / discharge cycles, the y-axis on the left represents discharge capacity, and the y-axis on the right represents capacity retention. Capacity retention is an indicator of how much the capacity changes based on the capacity developed in the first cycle.

[0094] The pressure applied to each battery cell is 1 kgf / cm 2 , 4 kgf / cm 2 , 6 kgf / cm 2 , 8 kgf / cm 2 , 10 kgf / cm 2 , 12 kgf / cm 2 , 15 kgf / cm 2 The test results for each case are shown in the graph. The upper value in the graph represents the measured discharge capacity, and the lower value represents the measured capacity retention.

[0095] First, the pressure is 1 kgf / cm 2 In this case, it is the same as the upper graph of Comparative Example 1 of Fig. 4(a), and the pressing force is 8 kgf / cm 2 In this case, it is the same as the upper graph of Example 1 of Fig. 4(b). 1 kgf / cm 2 When the battery cell was pressurized with a pressure of 4 kgf / cm, it can be seen that the discharge capacity and capacity retention rate were measured as values ​​with a large deviation for each cycle when charge and discharge were repeated as described above in Fig. 4(a). In other words, the graph shows fluctuations. This means that the stability of the battery cell is significantly reduced. When the pressing force is 4 kgf / cm 2 In this case, it was observed both in normal operation and in non-normal operation, so 1 kgf / cm 2 It can be interpreted that the results are slightly superior to those of the previous case, but as the C / E fluctuation range increased, early degradation occurred.

[0096] The pressure is 6 kgf / cm 2 In this case, when charge and discharge are repeated, the discharge capacity and capacity retention rate values ​​are measured relatively consistently for each cycle, but it can be seen that the battery life is shortened due to early degradation.

[0097] The pressure is 12 kgf / cm 2 Even in this case, when charge and discharge are repeated, it can be seen that the discharge capacity and capacity retention rate values ​​are measured as values ​​with a large deviation for each cycle. When the pressure is 15 kgf / cm 2 In this case, the effective charge / discharge cycle count is significantly reduced. This is because if the applied pressure is too high, the separator is compressed, reducing the amount of residual electrolyte, which has a negative impact on performance. In addition, the possibility of short circuits also increases.

[0098] On the other hand, the pressing force is 8 kgf / cm 2 If and 10 kgf / cm 2 In this case, it shows quite excellent results. Even after repeated charge and discharge cycles, the discharge capacity and capacity retention rate values ​​were measured to be constant, and it can be seen that the discharge capacity value of the battery cell is also higher. When the pressure is 8 kgf / cm 2 In this case, it overlaps with the explanation in Fig. 4(b), so refer to the above.

[0099] Figure 8 shows a graph of C / E (Coulombic efficiency) measured at each charge / discharge cycle. The pressure applied to the battery cell was 1 kgf / cm each. 2 , 4 kgf / cm 2 , 6 kgf / cm 2 , 8 kgf / cm 2 , 10 kgf / cm 2 , 12 kgf / cm 2 , 15 kgf / cm 2 The test results for each case are shown in the graph. Similarly, when the pressure is 1 kgf / cm 2In this case, it is the same as the lower graph of Comparative Example 1 of Fig. 4(a), and the pressing force is 8 kgf / cm 2 In this case, it is the same as the lower graph of Example 1 of Fig. 4(b).

[0100] In Fig. 8, the pressing force is 1 kgf / cm 2 , 4 kgf / cm 2 In this case, it can be seen that the C / E is measured as a value with a large deviation for each cycle when charge and discharge are repeated. In other words, the graph shows fluctuations. This means that the stability of the battery cell is significantly reduced.

[0101] The pressure is 6 kgf / cm 2 In this case, although the C / E maintains a relatively stable value for each cycle when charging and discharging are repeated, the battery life is shortened due to premature degradation.

[0102] Also, the pressing force is 12 kgf / cm 2 Even in this case, when charge and discharge are repeated, it can be seen that the C / E is measured as a value with a large deviation for each cycle. In other words, the graph shows fluctuations. This means that the stability of the battery cell is significantly reduced. In addition, when the pressure is 15 kgf / cm 2 In this case, the effective charge / discharge cycle count is significantly reduced. This is because if the applied pressure is too high, the separator is compressed, reducing the amount of residual electrolyte, which has a negative impact on performance. In addition, the possibility of short circuits also increases.

[0103] On the other hand, the pressing force is 8 kgf / cm 2 , and 12 kgf / cm 2 In this case, the C / E value was measured consistently even after repeated charge and discharge cycles. In particular, when the applied pressure was 8 kgf / cm 2 , and 12 kgf / cm 2 In this case, it shows excellent results, such as increasing the number of effective charge / discharge cycles.

[0104] Even with reference to the results of FIGS. 6, 7, and 8, in the case of the positive pressure method, the pressure applied to the battery cell during charging and discharging of the lithium metal battery is 7 kgf / cm. 2 More than 12 kgf / cm 2 Less than or equal to 8 kgf / cm 2 More than 11 kgf / cm 2 It can be seen that the following is suitable.

[0105] Figures 9 to 11 graphically illustrate the results of tests conducted while varying the pressure applied to the battery cells and increasing the number of charge / discharge cycles in the case of the constant-pressure pressurization method. In the case of the constant-pressure pressurization method, lower pressures are more advantageous for the implementation and design of actual battery packs, so tests were conducted to determine the optimal (minimum) pressurization conditions.

[0106] In the case of Figs. 9 to 11, tests were performed under the same measurement conditions as those of Fig. 4, except that the constant pressure pressurization method was used. In addition, as described above, the constant pressure pressurization method is a case where the constant pressure pressurization method is partially modified, and an elastic member (140, see Fig. 3) is interposed, and the spring constant of the elastic member (i.e., spring) used in this test is 160 kgf / mm (40 kgf / mm × 4 = 160 kgf / mm).

[0107] Figures 9 and 10 respectively show graphs of discharge capacity and capacity retention measured at each charge / discharge cycle. The x-axis represents the number of charge / discharge cycles, the y-axis on the left represents discharge capacity, and the y-axis on the right represents capacity retention. Capacity retention is an indicator of how much the capacity changes based on the capacity developed in the first cycle.

[0108] The pressure applied to each battery cell is 1 kgf / cm 2 , 5 kgf / cm 2 , 10 kgf / cm 2 , 15 kgf / cm2 , 20 kgf / cm 2 The test results for each case are shown in the graph. The upper value in the graph represents the measured discharge capacity, and the lower value represents the measured capacity retention.

[0109] First, the pressure is 1 kgf / cm 2 In this case, the discharge capacity and capacity retention rate for each cycle of repeated charge and discharge are relatively unstable. This is interpreted as being due to the interface between the positive electrode / separator / negative electrode of the lithium metal battery not being properly pressed, resulting in the results shown in Figures 9 and 10.

[0110] On the other hand, the pressure is 5 kgf / cm 2 , 10 kgf / cm 2 , 15 kgf / cm 2 , 20 kgf / cm 2 In this case, the discharge capacity and capacity retention rate values ​​were measured to be constant even after repeated charge and discharge cycles, showing considerably excellent results.

[0111] Figure 11 shows a graph of C / E (Coulombic efficiency) measured at each charge / discharge cycle. The pressure applied to the battery cell is 1 kgf / cm. 2 , 5 kgf / cm 2 , 10 kgf / cm 2 , 15 kgf / cm 2 , 20 kgf / cm 2 The test results for each case are shown in the graph.

[0112] The pressure is 1 kgf / cm 2 In this case, it can be seen that the C / E is measured as a value with a large deviation for each cycle when the charge and discharge are repeated. In other words, the graph shows fluctuations. This means that the stability of the battery cell is significantly reduced. On the other hand, when the pressure is 5 kgf / cm 2 , 10 kgf / cm 2 , 15 kgf / cm2 , 20 kgf / cm 2 In this case, the C / E value was measured consistently even after repeating the number of charge and discharge cycles. Even with reference to the results of Figs. 9 to 11, in the case of the constant-pressure pressurization method, the pressure applied to the battery cell during charge and discharge of the lithium metal battery is 4 kgf / cm. 2 More than 30 kgf / cm 2 or less, or 5 kgf / cm 2 More than 25 kgf / cm 2 It can be seen that the following is suitable. For reference, 20 kgf / cm 2 Note that the increase in numerical value from 0 in the first cycle of C / E does not imply a significant value. That is, the increase in numerical value in the first cycle may vary depending on the degree of activation, and does not imply a large fluctuation.

[0113] Figures 12 to 14 are graphs showing the results of tests conducted while varying the pressure applied to the battery cells and increasing the number of charge / discharge cycles in the case of the constant-pressure pressurization method. The tests were conducted under the same measurement conditions as those in Figure 4. In the case of the constant-pressure pressurization method, since a lower pressurization force is more advantageous for the implementation and design of the actual battery pack, tests were conducted to find the optimal (lowest) pressurization conditions.

[0114] In the cases of Figs. 12 to 14, tests were performed under the same measurement conditions as those of Fig. 4, except that the method was a constant pressure pressurization method.

[0115] Figures 12 and 13 respectively show graphs of discharge capacity and capacity retention measured at each charge / discharge cycle. The x-axis represents the number of charge / discharge cycles, the y-axis on the left represents discharge capacity, and the y-axis on the right represents capacity retention. Capacity retention is an indicator of how much the capacity changes based on the first cycle development capacity.

[0116] The pressure applied to each battery cell is 1 kgf / cm 2 , 3 kgf / cm 2 , 5 kgf / cm 2 , 10 kgf / cm 2 The test results for each case are shown in the graph. The upper value in the graph represents the measured discharge capacity, and the lower value represents the measured capacity retention.

[0117] First, the pressure is 1 kgf / cm 2 If the pressure is 3 kgf / cm 2 In each case, premature degradation occurred. This means that the discharge capacity and capacity retention rate for each cycle of repeated charge and discharge were not maintained for a long time, shortening the battery life. This is interpreted as being due to the interface between the positive electrode / separator / negative electrode of the lithium metal battery not being properly pressed, resulting in the results shown in Figures 12 and 13.

[0118] The pressure is 5 kgf / cm 2 In this case, premature deterioration does not occur, and the pressure is 1 kgf / cm 2 If the pressure is 3 kgf / cm 2 Although the cycle lasted longer than in the case of , it can be seen that as the number of charge and discharge cycles increased, the value of the discharge capacity decreased and the performance deteriorated.

[0119] On the other hand, the pressure is 10 kgf / cm 2 In this case, the discharge capacity and capacity retention rate values ​​were measured to be relatively constant even after repeated charge and discharge cycles.

[0120] Figure 14 shows a graph of C / E (Coulombic efficiency) measured at each charge / discharge cycle. The pressure applied to the battery cell was 1 kgf / cm each. 2 , 3 kgf / cm 2 , 5 kgf / cm 2 , 10 kgf / cm2 The test results for each case are shown in the graph.

[0121] In Fig. 14, the pressing force is 1 kgf / cm 2 , 3 kgf / cm 2 In this case, it was measured that there were cases where the C / E fluctuation range was large, which means that micro-shorts occurred or deposition occurred on the positive electrode during discharge. This means that the battery cell is seriously affected or the life of the battery cell is shortened.

[0122] The pressure is 5 kgf / cm 2 Even if the pressure is 1 kgf / cm 2 If the pressure is 3 kgf / cm 2 Although it is better than this case, we can see that there are cases where the C / E fluctuation range is large.

[0123] On the other hand, the pressure is 10 kgf / cm 2 In this case, the C / E value was measured to be relatively constant even after repeated charging and discharging.

[0124] Even with reference to the results of Figs. 12 to 14, in the case of the constant pressure pressurization method, the pressure applied to the battery cell during charging and discharging of the lithium metal battery is 10 kgf / cm. 2 More than 30 kgf / cm 2 or less, or 10 kgf / cm 2 More than 25 kgf / cm 2 It can be seen that the following is suitable.

[0125] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0126] [Explanation of symbols]

[0127] 10: Battery cell

[0128] 110: Pressurized member

[0129] 120: Drive unit

[0130] 130: Measurement unit

[0131] 140: Elastic member

Claims

1. An electrode assembly comprising a cathode, an anode, and a separator interposed between the cathode and the anode; An electrolyte solution impregnating the electrode assembly; and It includes a battery case containing the electrode assembly and the electrolyte, The above negative electrode includes a negative electrode current collector and a lithium metal layer formed on at least one surface of the negative electrode current collector, 2 kgf / cm for the above lithium metal battery 2 More than 30 kgf / cm 2 A lithium metal battery that is charged and discharged under the following pressure conditions.

2. In paragraph 1, Pressure is applied to the lithium metal battery in a positive pressure manner, The pressure applied to the above lithium metal battery is 7 kgf / cm 2 More than 12 kgf / cm 2 Lithium metal battery, less than.

3. In paragraph 2, The pressure applied to the above lithium metal battery is 8 kgf / cm 2 More than 11 kgf / cm 2 Lee Ha-in, lithium metal battery.

4. In paragraph 1, Pressure is applied to the above lithium metal battery by a constant pressure pressurization method, The pressure applied to the above lithium metal battery is 4 kgf / cm 2 More than 30 kgf / cm 2 Lee Ha-in, lithium metal battery.

5. In paragraph 4, The pressure applied to the above lithium metal battery is 5 kgf / cm 2 More than 25 kgf / cm 2 Lee Ha-in, lithium metal battery.

6. In paragraph 4 or 5, A lithium metal battery, wherein the equivalent spring constant of the elastic member applied to the above-mentioned constant pressure pressurization method is 60 kgf / mm or more and 1000 kgf / mm or less.

7. In paragraph 1, Pressure is applied to the above lithium metal battery by a constant pressure pressurization method, The pressure applied to the above lithium metal battery is 10 kgf / cm 2 More than 30 kgf / cm 2 Lee Ha-in, lithium metal battery.

8. In paragraph 7, Pressure is applied to the above lithium metal battery by a constant pressure pressurization method, The pressure applied to the above lithium metal battery is 10 kgf / cm 2 More than 25 kgf / cm 2 Lee Ha-in, lithium metal battery.

9. In paragraph 1, The above lithium metal battery is a pouch-type lithium metal battery.

10. In paragraph 1, A lithium metal battery, wherein the lithium metal battery is mounted on a pressurizing jig and pressure is applied by the pressurizing jig.

11. A battery cell stack having a plurality of battery cells stacked thereon and a module case for storing the battery cell stack, A battery module, wherein the battery cell is a lithium metal battery according to claim 1.

12. In paragraph 11, A battery module further comprising, when the pressurization method for the lithium metal battery is a constant pressure pressurization method, a pressurization unit installed within the module case so that the distance from the large area of ​​the battery cell can be variably set, a driving unit capable of moving the pressurization unit, a measuring unit for measuring the pressure applied to the pressurization member, and a control unit for receiving data measured from the measuring unit and adjusting the pressure applied to the pressurization member to be constant.

13. In paragraph 11, A battery module further comprising an elastic member within the module case, when the pressurization method for the lithium metal battery is a constant pressure pressurization method.

14. A battery pack comprising a battery module according to Article 11 and a pack case for storing the battery module.

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