Lithium metal batteries, battery modules and battery packs containing the same.

Abstract

A lithium metal battery according to one embodiment of the present invention includes an electrode assembly comprising a negative electrode, a positive electrode, and a separation membrane interposed between the negative electrode and the positive electrode; an electrolyte impregnating the electrode assembly; and a battery case containing the electrode assembly and the electrolyte, wherein the negative electrode comprises 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 has a charge of 2 kgf / cm². 2 More than 30kgf / cm 2 The following pressures are applied during charging and discharging.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights based on Korean Patent Application No. 10-2023-0073022 dated June 7, 2023, and Korean Patent Application No. 10-2024-0073720 dated June 5, 2024, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] The present invention relates to a lithium metal battery, a battery module including the same, and a battery module including a battery pack, and more particularly to a lithium metal battery, a battery module including the same, and a battery pack characterized in that a predetermined pressure is applied to the lithium metal battery during charging and discharging of the lithium metal battery. [Background technology]

[0003] Demand for rechargeable batteries as an energy source is rapidly increasing, and among such batteries, lithium-ion batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Typically, from the perspective of battery shape, there is high demand for prismatic and pouch-type rechargeable batteries that are thin and can be applied to products such as mobile phones. From the perspective of materials, there is high demand for lithium-ion batteries and lithium-ion polymer batteries, which have high energy density, discharge voltage, and output stability.

[0005] Generally, lithium secondary batteries have a structure in which a non-aqueous electrolyte is impregnated into an electrode assembly consisting of a positive electrode, a negative electrode, and a porous separation membrane. Generally, the positive electrode is manufactured by coating aluminum foil with a positive electrode mixture containing a positive electrode active material, and the negative electrode is manufactured by coating copper foil with a negative electrode mixture containing a negative electrode active material.

[0006] While lithium transition metal oxides have traditionally been used as the positive electrode active material and carbon-based materials as the negative electrode active material, lithium metal batteries that use lithium metal itself, which exhibits high energy density, as the negative electrode active material have recently been commercialized.

[0007] At this time, the lithium metal used as the negative electrode has a density of (0.54 g / cm³). 3 Because of its low saturation and extremely low standard reduction potential (-3.045V SHE), it is the most sought-after material for anodes in high-energy-density batteries. Furthermore, despite the problems arising from its extremely high chemical reactivity, the need for lithium metal anodes is also emerging due to the increasing demand for the development of high-energy-density secondary batteries, driven by the sustained increase and rapid development of mobile communications and portable electronic devices.

[0008] In this case, when a lithium metal electrode is used as the negative electrode, unlike lithium-ion batteries, the lithium metal is deposited or removed during charging and discharging, resulting in a greater change in the thickness of the battery cell compared to lithium-ion batteries. When lithium is charged, a porous layer may be formed due to the localized concentration of electrodeposited lithium, creating needle-shaped lithium deposits. This can increase the battery's resistance and even lead to internal short circuits, potentially reducing the battery's stability. When lithium is discharged, the distance between the separator membrane and the negative electrode interface increases, increasing resistance. Repeated deformation due to charging and discharging can cause internal elements to deteriorate, leading to problems such as a shortened charge-discharge cycle life.

[0009] Therefore, the development of lithium metal batteries, battery modules, and battery packs containing them is necessary to solve these problems. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention aims to provide a lithium metal battery with improved stability during driving and an increased lifespan, a battery module including the same, and a battery pack.

[0011] However, the problems to be solved by the embodiments of the present invention are not limited to the above-mentioned problems, and can be variously extended within the scope of the technical idea included in the present invention.

Means for Solving the Problems

[0012] A lithium metal battery according to an embodiment of the present invention includes an electrode assembly including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode; an electrolytic solution impregnating the electrode assembly; and a battery case containing the electrode assembly and the electrolytic solution. 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. The lithium metal battery may be charged and discharged while a pressure of 2 kgf / cm 2 or more and 30 kgf / cm 2 or less is applied. <00001​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0017] The equivalent spring constant of the elastic member applied to the constant-variable pressure pressurization method may be 60 kgf / mm or more and 1000 kgf / mm or less.

[0018] Pressure is applied to the lithium metal battery using a constant pressure pressurization method, and the pressure applied to the lithium metal battery is 10 kgf / cm². 2 More than 30kgf / cm 2 The following is also acceptable.

[0019] Pressure is applied to the lithium metal battery using a constant pressure pressurization method, and the pressure applied to the lithium metal battery is 10 kgf / cm². 2 More than 25kgf / cm 2 The following is also acceptable.

[0020] The lithium metal battery may be a pouch-type lithium metal battery.

[0021] The lithium metal battery may be mounted on a pressurizing jig, and the pressure may be applied by the pressurizing jig.

[0022] 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 houses the battery cell stack, wherein the battery cells may be lithium metal batteries according to the above-described embodiment.

[0023] If the method of pressurizing the lithium metal battery is a constant-pressure pressurization method, the battery module may further include, within the module case, a pressurizing unit provided at a variable distance from the large surface area of ​​the battery cells, a drive unit capable of moving the pressurizing unit, a measuring unit for measuring the pressure applied to the pressurizing member, and a control unit that receives data measured from the measuring unit and adjusts the pressure applied to the pressurizing member to a constant value.

[0024] If the method of pressurizing the lithium metal battery is a constant-voltage pressurizing method, the battery module may further include an elastic member within the module case.

[0025] A battery pack according to one embodiment of the present invention may include a battery module according to the above-described embodiment and a pack case for housing the battery module. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a lithium metal battery in which the stability during operation is improved and the lifespan is extended by the pressurized conditions during charging and discharging, as well as a battery module and battery pack containing the same.

[0027] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned should be clearly understood by those skilled in the art from the claims. [Brief explanation of the drawing]

[0028] [Figure 1] This diagram provides a schematic explanation of the localized pressure system. [Figure 2] This diagram provides a schematic explanation of the constant-pressure pressurization method. [Figure 3] This diagram provides a schematic explanation of the constant-pressure pressurization system. [Figure 4] This graph shows the discharge capacity and C / E (coulombic efficiency) measured each time for each charge-discharge cycle, when the pressure applied to the battery cell is changed in Example 1 and Comparative Example 1 of the present invention. [Figure 5] This graph shows the results of measuring the voltage between the positive and negative electrodes of a battery cell based on its discharge capacity after varying the number of charge and discharge cycles. [Figure 6] In the case of the stationary pressure method, the graph shows the results of tests conducted by changing the pressure applied to the battery cell. [Figure 7]In the case of the stationary pressure method, the graph shows the results of tests conducted by changing the pressure applied to the battery cell. [Figure 8] In the case of the stationary pressure method, the graph shows the results of tests conducted by changing the pressure applied to the battery cell. [Figure 9] In the case of the constant-voltage pressurization method, the graph shows the results of tests conducted by changing the pressure applied to the battery cells. [Figure 10] In the case of the constant-voltage pressurization method, the graph shows the results of tests conducted by changing the pressure applied to the battery cells. [Figure 11] In the case of the constant-voltage pressurization method, the graph shows the results of tests conducted by changing the pressure applied to the battery cells. [Figure 12] In the case of the constant-pressure pressurization method, the graph shows the results of tests conducted by varying the pressure applied to the battery cells. [Figure 13] In the case of the constant-pressure pressurization method, the graph shows the results of tests conducted by varying the pressure applied to the battery cells. [Figure 14] In the case of the constant-pressure pressurization method, the graph shows the results of tests conducted by varying the pressure applied to the battery cells. [Modes for carrying out the invention]

[0029] The following description, with reference to the attached drawings, will detail various embodiments of the present invention so that those with ordinary skill in the art to which the present invention pertains can easily implement them. The present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0030] Furthermore, when the specification as a whole states that a certain part "includes" a certain component, unless otherwise stated, this means that it may include other components, not exclude other components.

[0031] A lithium metal battery according to one embodiment of the present invention includes an electrode assembly comprising a negative electrode, a positive electrode, and a separation membrane interposed between the negative electrode and the positive electrode; an electrolyte impregnating the electrode assembly; and a battery case containing the electrode assembly and the electrolyte. The negative electrode comprises a negative electrode current collector and a lithium metal layer formed on at least one surface of the negative electrode current collector.

[0032] As mentioned above, conventional lithium metal batteries can develop needle-shaped lithium deposits during charging due to localized electrodeposition, and during discharge, the distance between the separator membrane and the negative electrode interface increases, leading to increased resistance and reduced discharge capacity. Repeated deformation due to charging and discharging causes internal components to deteriorate, resulting in problems such as a shortened charge-discharge cycle life.

[0033] To address these issues, the lithium metal battery of the present invention is charged and discharged under a predetermined pressure. The performance of the lithium metal battery is improved when the pressure is adjusted to match the rate at which the lithium metal grows and disappears.

[0034] The lithium metal battery of the present invention exhibits a charge and / or discharge rate of 2 kgf / cm². 2 More than 30kgf / cm 2 The following pressures are applied to the battery cells.

[0035] In the case of the fixed-position pressurization method, the pressure applied to the lithium metal battery is 7 kgf / cm². 2 More than 12kgf / cm 2 Less than 8 kgf / cm² 2 More than 11kgf / cm 2 The following is also acceptable.

[0036] In the case of a constant-voltage pressurization system, the pressure applied to the lithium metal battery is 4 kgf / cm². 2 More than 30kgf / cm 2 The following, or 5 kgf / cm² 2 More than 25kgf / cm 2The following is also possible: The spring constant of the elastic member applied to the constant-pressure pressurization system may be 60 kgf / mm or more and 1000 kgf / mm or less.

[0037] In the case of a constant-pressure pressurization method, the pressure applied to the lithium metal battery is 10 kgf / cm². 2 More than 30kgf / cm 2 The following, or 10 kgf / cm² 2 More than 25kgf / cm 2 The following is also acceptable.

[0038] In this specification, when pressure is applied to a lithium metal battery, it means that pressure is applied in the thickness direction of the lithium metal battery or across a large surface area. Maintaining a certain level of pressure is necessary during both charging and discharging of lithium metal batteries. During charging, pressure is necessary to prevent the formation and growth of lithium metal, thus preventing it from becoming porous. During discharging, lithium metal is consumed and can locally become porous; therefore, pressure is also applied to the lithium metal battery in this case.

[0039] On the other hand, when the pressure applied to the battery cell during charging satisfies the conditions according to the embodiment of the present invention, it is possible to effectively prevent localized electrodeposition of lithium that may occur during charging, while also ensuring battery cell safety by preventing leakage of electrolyte due to excessive pressure, increase in battery cell resistance, and compression of the separation membrane.

[0040] Furthermore, when the pressure applied to the battery cell during discharge satisfies the conditions according to the embodiment of the present invention, the space between the separation membrane and the negative electrode interface can be minimized, reducing the resistance of the battery cell and preventing a decrease in discharge capacity.

[0041] The charging and discharging described herein refers not only to the charging and discharging that occurs during the battery cell manufacturing process (e.g., the activation process), but also to the charging and discharging that occurs during the actual use of the product containing the battery cells after the product has been shipped.

[0042] There are three methods for pressurizing lithium metal batteries: fixed-position pressurization, constant-pressure pressurization, and constant-variable-pressure pressurization. These can be implemented using pressurization jigs, battery modules, and / or battery packs. Figures 1, 2, and 3 schematically illustrate the fixed-position, constant-pressure, and constant-variable-pressure pressurization methods, respectively.

[0043] The positional pressurization method shown in Figure 1 is a method that maintains a constant distance (spacing) between the pressurizing members 110 on both sides of the battery cell 10. For example, in the battery cell manufacturing process, the distance between the pressurizing jigs may be constant. Alternatively, it may be a normal battery module case and / or battery pack case. In this case, during actual use of the product with the battery cell installed, it corresponds to a situation where the distance between the frames (housings) of the battery module or battery pack in which the battery cell is housed is constant.

[0044] Since the distance between the pressurizing members 110 is kept constant, the lithium metal battery expands during charging, which may, in some cases, apply a large pressure to the battery cell 10. Alternatively, even though the distance between the separation membrane 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, which may result in a situation where it is not possible to apply enough pressure during discharge. Therefore, while it is possible to apply only the constant-position pressurizing method during charging and discharging, it is also possible to apply a mixture of the constant-pressure pressurizing method and the constant-variable-pressure pressurizing method, which will be described later, as methods with less pressure change.

[0045] The constant-pressure pressurization method shown in Figure 2 is a method of controlling the pressure applied by the pressurizing member 110 to maintain a constant pressure. In other words, it is a method in which a constant pressure is applied to the battery cell 10 by the pressurizing member 110. For example, in the manufacturing process of battery cells, a constant pressure may be applied to the pressurizing jig. During actual use of a product with battery cells installed, a constant pressure may be applied to the battery cells from inside and / or outside the frame (housing) of the battery module or battery pack in which the battery cells are housed.

[0046] When a constant-pressure pressurization method is applied, a mechanical device is included that adjusts the pressure according to the degree of tightening in order to maintain a constant pressure. During charging, the pressure is maintained by releasing the tightening at the pressurized position on the battery cell 10, and during discharge, the pressure is maintained by increasing the degree of tightening at the pressurized position on the battery cell 10 to further apply pressure. For example, the battery module and / or battery pack according to the present invention may include a pressurizing unit 110 provided on both sides of the battery cell 10, with the battery cell 10 in between, and the distance from the large area of ​​the battery cell 10 is variable; a drive unit 120 that can move the pressurizing unit 110; a measuring unit 130 that measures the pressure applied to the pressurizing member; a control unit (not shown) that receives data measured from the measuring unit and adjusts the pressure applied to the pressurizing member to a constant value. The drive unit 120 may be, for example, a motor (servo motor, etc.), and the measuring unit 130 may be, for example, a rod (load) cell.

[0047] The constant-voltage pressurization method shown in Figure 3 is a modified version of the fixed-position pressurization method, in which the distance (spacing) between the pressurizing members 110 on both sides of the battery cell 10 is kept constant, and an elastic member 140 is interposed between one or both sides of the pressurizing member 110 and the battery cell 10. In other words, the sum of the pressure applied by the pressurizing member 110 and the elastic force applied by the elastic member 140 is applied to the battery cell 10.

[0048] The elastic member 140 may be, for example, a spring. To obtain the desired elastic force, an elastic member 140 having a suitable elastic modulus can be used, or a method of changing the number of elastic members 140 attached can be applied, or a combination of these is also possible.

[0049] The equivalent spring constant of the elastic member 140 may be, for example, 60 kgf / mm or more and 1000 kgf / mm or less.

[0050] 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 60 kgf / mm or more and 200 kgf / mm or less, or for example, 160 kgf / mm. For example, an equivalent spring constant of 160 kgf / mm can be achieved by arranging four elastic members 140 with a spring constant of 40 kgf / mm at each corner of one side of a battery cell, battery module, or battery pack and connecting them in parallel (40 kgf / mm × 4 = 160 kgf / mm).

[0051] In the case of medium to large 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 300 kgf / mm or more and 1000 kgf / mm or less, or it may be, for example, 480 kgf / mm. For example, if the size of the battery cell is 100 mm × 300 mm, the equivalent spring constant may be, for example, 480 kgf / mm.

[0052] The spring constant may be selected to be appropriate for the environment in which the present invention is realized, such as the size of the battery cell.

[0053] Furthermore, while the elastic member 140 can directly contact the battery cell 10, an auxiliary pressurizing member 110 may be provided between the elastic member 140 and the battery cell 10, with the auxiliary pressurizing member 110 in contact with the battery cell 10 and the auxiliary pressurizing member 110 being variable by the elastic force of the elastic member 140.

[0054] When using a constant-pressure pressurization method and / or a constant-variable-pressure pressurization method, there is an advantage in that it can compensate for phenomena that may occur in a fixed-position pressurization method. For example, it can compensate for the increase in internal battery resistance caused by the compression of the separation membrane, the micro-short phenomenon caused by the needle-shaped electrodeposited lithium metal penetrating the separation membrane, and the crack phenomenon caused by the cracking of the positive electrode active material.

[0055] When a constant-pressure jig, battery module, and / or battery pack equipped with a mechanical device to maintain constant pressure is unavailable, a constant-voltage jig, battery module, and / or battery pack can be used, and when a constant-voltage system is also difficult to apply, a positioning jig, battery module, and / or battery pack can be used.

[0056] On the other hand, it can also be achieved using a combination of at least two of the following methods: fixed position, constant pressure, and constant variable pressure pressurization.

[0057] Furthermore, the present invention is not limited to those described above, and the pressurization method may be not only a jig pressurization method but also a magnetic pressurization method or a combination thereof, depending on the type of pressurizing member, and may be applied in a variety of ways in a variety of environments.

[0058] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples described later.

[0059] First, the lithium metal batteries used in the examples and comparative examples of the present invention are as follows.

[0060] Lithium metal battery Approximately 95 parts by weight of LiFePO4 as the positive electrode active material, approximately 0.5 parts by weight of CNT as the conductive agent, and approximately 3 parts by weight of polyvinylidene fluoride (PVDF) as the binder were added to N-methylpyrrolidone (NMP) as the solvent to produce a positive electrode active material slurry. Then, the positive electrode active material slurry was coated to a thickness of 90 μm or more on both sides of an aluminum current collector with a thickness of 10 to 20 μm. After drying and rolling, the material was cut to a certain size to produce a positive electrode sheet. A single-sided positive electrode sheet was also produced in the same manner as described above, except that the positive electrode active material slurry was coated on only one side.

[0061] Furthermore, a negative electrode sheet was manufactured by attaching lithium metal foil with a thickness of 30 μm or less to both sides of a copper current collector with a thickness of 5 to 15 μm.

[0062] Furthermore, an electrode assembly was manufactured using 20 separation membranes (a porous coating layer formed on both sides of a polyethylene-based porous polymer substrate using a mixture of alumina and PVDF binder), 9 of the aforementioned double-sided positive electrode sheets, and 10 double-sided negative electrode sheets, with 2 double-sided negative electrode sheets on the outermost surface.

[0063] Subsequently, an electrolyte prepared by dissolving 1-4M LiFSI, LiTFSI, etc., in ether, carbonate, and THP solvents, and then adding a non-solvent, was injected into the battery cell pouch. The lithium metal battery was then manufactured by completely sealing the pouch.

[0064] Evaluation of the cycle characteristics of lithium metal batteries Under constant current / constant voltage (CC / CV) conditions, 1-10 mA / cm 2 The battery was charged to 3.6-3.8V with a constant current. After charging was completed with a 0.05C cutoff, the current density was 1-10mA / cm². 2 The lithium metal battery was discharged to 2.6-2.8V under constant current (CC) conditions (discharge temperature 25°C). At this time, the lithium metal battery was (a) 8 kgf / cm² in the case of Example 1. 2 (b) At a pressure of 1 kgf / cm², and in the case of Comparative Example 1, 2 Each was pressurized with the specified pressure.

[0065] Under these conditions, the charge-discharge process was repeated several times, and the discharge capacity and C / E ratio were measured and shown in Figure 4. However, in Comparative Example 1, after about 30 cycles, the process was interrupted due to a rapid deterioration in the performance of the battery cell. On the other hand, in Example 1 of the present invention, the discharge capacity and C / E ratio were measured while repeating the charge-discharge process for 130 or more cycles.

[0066] Figure 4 is a graph showing the discharge capacity and C / E (coulombic efficiency) measured for each charge-discharge cycle in Example 1 and Comparative Example 1 of the present invention, where the pressure applied to the battery cell under constant pressure conditions was varied.

[0067] Figure 4(a) shows Comparative Example 1, with a value of 1 kgf / cm². 2 This graph shows the measurements taken when a pressure of 8 kgf / cm² is applied to a battery cell. Figure 4(b) shows 8 kgf / cm² as Example 1 of the present invention. 2 This graph shows the measurements taken when the pressure applied to the battery cell. Figure 4(c) shows a comparison of Example 1 and Comparative Example 1 of the present invention in a single graph.

[0068] In the graphs (a) and (c) of Figure 4, the x-axis represents the number of charge / discharge cycles, the left y-axis represents the discharge capacity, and the right y-axis represents the C / E (coulombic efficiency), that is, the ratio of discharge capacity to charge capacity. The discharge capacity in Figure 4 represents the discharge capacity, which is the capacity exhibited when going from SOC100 (fully charged) to SOC0 (completely discharged). In the case of C / E, it indicates whether the discharge capacity is commensurate with the charge capacity of the nth cycle, and C / E = (discharge capacity of the nth cycle) / (charge capacity of the nth cycle), where n is a natural number. The values ​​in the upper part of the graph represent the measured discharge capacity values, and the values ​​in the lower part represent the measured C / E values.

[0069] 8 kgf / cm² 2 In Example 1 shown in Figure 4(b), where the battery cell was pressurized with a certain pressure, the discharge capacity and C / E ratio were measured to be high, and these values ​​were substantially maintained even after repeated charge-discharge cycles.

[0070] In contrast, 1 kgf / cm² 2In Comparative Example 1, shown in Figure 4(a), where the battery cell was pressurized with a certain pressure, it can be seen that the discharge capacity and C / E were measured as values ​​with large deviations from cycle to cycle as 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. At the same time, it can be seen that the discharge capacity value is also even lower overall compared to Example 1 in Figure 4(b).

[0071] Furthermore, in Comparative Example 1 (a) in Figure 4, the number of cycles is significantly lower compared to Example 1 (b) in Figure 4, due to reasons such as battery cell degradation. This means that the battery life in Comparative Example 1 (a) in Figure 4 is significantly shorter than that in Example 1 (b) in Figure 4.

[0072] In summary, as can be seen from the comparison graph between Example 1 and Comparative Example 1 in Figure 4(c), Example 1 not only has a higher discharge capacity value compared to Comparative Example 1, but also maintains a constant discharge capacity and C / E value even after repeated charge-discharge cycles (i.e., the battery's stability is significantly improved), and can withstand a greater number of charge-discharge cycles (i.e., has a longer battery life).

[0073] For reference, in Comparative Example 1 in Figure 4(a), some measurements showed a high range of variation in the C / E value. This indicates that a micro-short circuit may occur or deposition may occur on the positive electrode during discharge.

[0074] Figure 5 is a graph showing the results of measuring the voltage between the positive and negative electrodes of a battery cell based on its discharge capacity, under the same measurement conditions as in Figure 4, but with a different number of charge-discharge cycles. This makes it easy to check for abnormalities when reviewing the charge-discharge profile.

[0075] In Comparative Example 1 in Figure 5(a), the load is 1 kgf / cm². 2 This is the case when the battery cell is pressurized with a pressure of 8 kgf / cm², and in the example shown in Figure 5(b), the pressure is 8 kgf / cm². 2This is the case when the battery cell is pressurized with the specified pressure. In the graphs of Figure 5(a) and (b), the x-axis represents discharge capacity and the y-axis represents voltage. On the x-axis, the value of discharge capacity increases from left to right. In Figure 5(a) and (b), the values ​​shown in the upper row are the values ​​measured during charging, and the values ​​shown in the lower row are the values ​​measured during discharging.

[0076] In Comparative Example 1 in Figure 5(a), instead of showing the values ​​measured in each cycle on the graph, for readability, the graph shows the values ​​measured after 1, 7, 12, 15, and 18 charge-discharge cycles, as representative examples. In the example in Figure 5(b), the graph shows the values ​​measured after 2, 5, 10, 15, 20, 25, 35, 40, 45, and 50 charge-discharge cycles, as representative examples. As mentioned above, in the example in Figure 5(b), the battery cell life is longer than in Comparative Example 1 in Figure 5(a), so the number of charge-discharge cycles is greater.

[0077] In the example shown in Figure 5(b), as can be seen from the area represented by the dotted circle, the voltage value relative to the discharge capacity is measured to be almost constant regardless of the number of charge and discharge cycles. In contrast, in Comparative Example 1 shown in Figure 5(a), as can be seen from the area represented by the dotted circle, the voltage value varies depending on the number of charge and discharge cycles. This means that the stability of the battery cell is significantly improved in the example shown in Figure 5(b) compared to Comparative Example 1 shown in Figure 5(a).

[0078] Figures 6 through 8 show graphs of the results of tests conducted using the stationary pressure method, where different pressures were applied to the battery cells and the number of charge-discharge cycles was increased. The tests were conducted under the same measurement conditions as in Figure 4. In the stationary pressure method, lower pressure is more advantageous for the realization and design of actual battery packs, so tests were conducted to find the optimal (minimum) pressure condition.

[0079] Figures 6 and 7 show graphs of discharge capacity and capacity retention measured for each charge-discharge cycle, respectively. The x-axis represents the number of charge-discharge cycles, the left y-axis represents discharge capacity, and the right y-axis represents capacity retention. Capacity retention is an indicator that shows how much the capacity changes relative to the capacity expressed in the first cycle.

[0080] The pressure applied to each battery cell is 1 kgf / cm². 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. In the graph, the upper values ​​show the measured discharge capacity, and the lower values ​​show the measured capacity retention rate.

[0081] First, the pressure applied is 1 kgf / cm². 2 In this case, the result is the same as the upper graph of Comparative Example 1 in Figure 4(a), and the pressurized force is 8 kgf / cm². 2 In this case, it is the same as the upper graph of Example 1 in Figure 4(b). 1 kgf / cm 2 When the battery cell was pressurized with a pressure of 4 kgf / cm², as mentioned earlier in Figure 4(a), it can be seen that when charging and discharging were repeated, the discharge capacity and capacity retention rate were measured as values ​​with large deviations from each cycle. In other words, a fluctuating graph is shown. This means that the stability of the battery cell becomes significantly low. 2 If this is the case, both normal and abnormal operation will be observed, and the load will be 1 kgf / cm². 2 This can be interpreted as showing slightly better results than in the previous case, but the C / E fluctuation range became larger and premature degradation occurred.

[0082] The pressure applied is 6 kgf / cm². 2In this case, when charging and discharging are repeated, the discharge capacity and capacity retention rate values ​​were measured to be relatively constant for each cycle, but it can be seen that the battery life is shortened due to the phenomenon of premature degradation.

[0083] The pressure applied is 12 kgf / cm². 2 Even in this case, it can be seen that when charging and discharging are repeated, the discharge capacity and capacity retention rate values ​​were measured as having large deviations from each cycle. The pressurized force was 15 kgf / cm². 2 In this case, it can be seen that the number of effective charge-discharge cycles becomes significantly lower. This is because if the pressurizing force becomes excessively high, the separation membrane is compressed, reducing the amount of residual electrolyte and negatively affecting performance. In addition, the possibility of a short circuit also increases.

[0084] In contrast, the pressurizing force is 8 kgf / cm². 2 In the case of 10 kgf / cm² 2 This shows excellent results. Even after repeated charge-discharge cycles, the discharge capacity and capacity retention rate remain constant, indicating that the battery cell's discharge capacity is even higher. (Pressure applied: 8 kgf / cm²) 2 If this is the case, please refer to the explanation in Figure 4(b) as it overlaps with the previous explanation.

[0085] Figure 8 shows a graph of C / E (Coulomb efficiency) measured for each charge-discharge cycle. The pressure applied to the battery cell was 1 kgf / cm². 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, the pressure applied is 1 kgf / cm². 2 In this case, it is the same as the lower graph of Comparative Example 1 in Figure 4(a), and the pressurized force is 8 kgf / cm 2 In this case, it is the same as the lower graph of Example 1 in Figure 4(b).

[0086] In Figure 8, the pressure applied is 1 kgf / cm². 2 , 4 kgf / cm 2 If this is the case, it indicates that when charging and discharging are repeated, the C / E ratio is measured as a value with a large deviation from the previous cycle. In other words, it shows a fluctuating graph. This means that the stability of the battery cell is significantly low.

[0087] The pressure applied is 6 kgf / cm². 2 In this case, while the C / E ratio remains relatively stable with each charge / discharge cycle, it can be seen that the battery life is shortened due to premature degradation.

[0088] Furthermore, the pressure applied is 12 kgf / cm². 2 Even in this case, it can be seen that when charging and discharging are repeated, the measured value shows a large deviation in C / E for each cycle. In other words, it shows a fluctuating graph. This means that the stability of the battery cell is significantly low. Also, the pressurized force was 15 kgf / cm². 2 In this case, it can be seen that the number of effective charge-discharge cycles becomes significantly lower. This is because if the pressurizing force becomes excessively high, the separation membrane is compressed, reducing the amount of residual electrolyte and negatively affecting performance. In addition, the possibility of a short circuit also increases.

[0089] In contrast, the pressurizing force is 8 kgf / cm². 2 , and 12 kgf / cm² 2 In this case, the C / E value remained constant even after repeated charge-discharge cycles. In particular, the pressurized force was 8 kgf / cm². 2 , and 12 kgf / cm² 2 In this case, the number of effective charge-discharge cycles also increases, demonstrating superior results.

[0090] Referring to the results shown in Figures 6, 7, and 8, in the case of the stationary pressurization method, the pressure applied to the battery cell during charging and discharging of the lithium metal battery is 7 kgf / cm². 2 More than 12kgf / cm 2 Less than 8 kgf / cm² 2 More than 11kgf / cm 2 It can be seen that the following is appropriate.

[0091] Figures 9 through 11 show graphs illustrating the results of tests conducted using a constant-voltage pressurization method, where different pressures were applied to the battery cells and the number of charge-discharge cycles was increased. In the constant-voltage pressurization method, lower pressure is more advantageous for the actual realization and design of the battery pack; therefore, tests were conducted to find the optimal (minimum) pressurization conditions.

[0092] In the cases shown in Figures 9 to 11, the tests were conducted under the same measurement conditions as those in Figure 4, except that a constant-variable-pressure method was used. As mentioned above, the constant-variable-pressure method is a modified version of the constant-position pressurization method, and the elastic member 140 (see Figure 3) was interposed, with the spring constant of the elastic member (i.e., the spring) used in this test being 160 kgf / mm (40 kgf / mm × 4 = 160 kgf / mm).

[0093] Figures 9 and 10 show graphs of discharge capacity and capacity retention measured for each charge-discharge cycle, respectively. The x-axis represents the number of charge-discharge cycles, the left y-axis represents discharge capacity, and the right y-axis represents capacity retention. Capacity retention is an indicator that shows how much the capacity changes relative to the capacity expressed in the first cycle.

[0094] The pressure applied to each battery cell is 1 kgf / cm². 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. In the graph, the upper values ​​show the measured discharge capacity, and the lower values ​​show the measured capacity retention rate.

[0095] First, the pressure applied is 1 kgf / cm². 2In the case where it is so, it shows the result that each of the discharge capacity and the capacity retention rate for each cycle in which charge and discharge are repeated is not relatively stable. This is interpreted as having brought about the results shown in FIGS. 9 and 10 because the interface between the positive electrode / separator / negative electrode of the lithium metal battery is not properly pressed.

[0096] On the other hand, when the applied pressure is 5 kgf / cm 2 , 10 kgf / cm 2 , 15 kgf / cm 2 , 20 kgf / cm 2 in this case, even if the number of charge and discharge cycles is repeated, the discharge capacity and the capacity retention rate values are measured constantly, showing very excellent results.

[0097] FIG. 11 shows a graph of C / E (coulomb efficiency) measured for each charge and discharge cycle. The test results in the case where 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 are respectively shown in the graph.

[0098] When the applied pressure is 1 kgf / cm 2 , it can be seen that when charge and discharge are repeated, C / E is measured as a value having a large deviation for each cycle. That is, it shows a fluctuating graph. This means that the stability of the battery cell is significantly reduced. On the other hand, when the applied pressure is 5 kgf / cm 2 , 10 kgf / cm 2 , 15 kgf / cm 2 , 20 kgf / cm 2 , the C / E value was measured constantly even when the number of charge and discharge cycles was repeated. Referring to the results of FIGS. 9 to 11 as described above, in the case of the constant variable pressure application method, the pressure applied to the battery cell during charge and discharge of the lithium metal battery is 4 kgf / cm 2 or more and 30 kgf / cm 2 or less, or 5 kgf / cm 2 or more and 25 kgf / cm 2It can be seen that the following is appropriate. For reference, 20 kgf / cm² 2 In this case, it should be noted that the increase in the value from 0 in the first cycle of C / E does not necessarily mean a statistically significant value. In other words, it should be noted that the increase in the value in the first cycle can vary depending on the degree of activation and does not necessarily mean a large range of fluctuation.

[0099] Figures 12 to 14 show graphs of the results of tests conducted using the constant-pressure method, where different pressures were applied to the battery cells and the number of charge-discharge cycles was increased. The tests were conducted under the same measurement conditions as in Figure 4. In the constant-pressure method, lower pressure is more advantageous for the realization and design of actual battery packs, so tests were conducted to find the optimal (minimum) pressure condition.

[0100] In the cases of Figures 12 to 14, the tests were conducted under the same measurement conditions as in Figure 4, except that a constant-pressure pressurization method was used.

[0101] Figures 12 and 13 show graphs of discharge capacity and capacity retention measured for each charge-discharge cycle, respectively. The x-axis represents the number of charge-discharge cycles, the left y-axis represents discharge capacity, and the right y-axis represents capacity retention. Capacity retention is an indicator that shows how much the capacity changes relative to the capacity expressed in the first cycle.

[0102] The pressure applied to each battery cell is 1 kgf / cm². 2 , 3 kgf / cm 2 , 5 kgf / cm 2 , 10 kgf / cm 2 The test results for each case are shown in the graph. In the graph, the upper values ​​show the measured discharge capacity, and the lower values ​​show the measured capacity retention rate.

[0103] First, the pressure applied is 1 kgf / cm². 2 In this case, and with a pressure of 3 kgf / cm²,2 In each of these cases, premature degradation occurred. This means that the discharge capacity and capacity retention rate for each charge-discharge cycle could not be maintained for long, resulting in a shortened battery life. This is interpreted as the interface between the positive electrode / separator membrane / negative electrode of the lithium metal battery not being properly pressurized, leading to the results shown in Figures 12 and 13.

[0104] Pressurized force of 5 kgf / cm² 2 In this case, premature deterioration will not occur, and the pressure will be 1 kgf / cm². 2 In this case, and with a pressure of 3 kgf / cm², 2 While the cycle lasted longer than in the previous case, it was observed that the discharge capacity decreased and performance degraded as the number of charge-discharge cycles increased.

[0105] In contrast, the pressurizing force is 10 kgf / cm². 2 In this case, the discharge capacity and capacity retention rate values ​​were measured to be relatively constant even after repeated charge-discharge cycles.

[0106] Figure 14 shows a graph of C / E (Coulomb efficiency) measured for each charge-discharge cycle. The pressure applied to the battery cell was 1 kgf / cm². 2 , 3 kgf / cm 2 , 5 kgf / cm 2 , 10 kgf / cm 2 The test results for each case are shown in the graph.

[0107] In Figure 14, the pressure applied is 1 kgf / cm². 2 , 3 kgf / cm 2 In this case, it was measured that a large fluctuation range in C / E occurs, which means that a micro-short occurs or deposition occurs on the positive electrode during discharge. This means that it can have a serious impact on the battery cell or shorten the battery cell's lifespan.

[0108] Pressurized force of 5 kgf / cm² 2 Even in this case, the pressure is 1 kgf / cm². 2In this case, and with a pressure of 3 kgf / cm², 2 While this is better than the previous case, it can be seen that there are instances where the C / E ratio fluctuates significantly.

[0109] In contrast, the pressurizing force is 10 kgf / cm². 2 In this case, the C / E value remained relatively constant even after repeated charge-discharge cycles.

[0110] Referring to the results shown in Figures 12 to 14, in the case of a constant pressure pressurization method, the pressure applied to the battery cell during charging and discharging of a lithium metal battery is 10 kgf / cm². 2 More than 30kgf / cm 2 The following, or 10 kgf / cm² 2 More than 25kgf / cm 2 It can be seen that the following is appropriate.

[0111] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto. Various modifications and improvements that a person skilled in the art can make using the basic concepts of the present invention, as defined in the following claims, also fall within the scope of the present invention. [Explanation of Symbols]

[0112] 10: Battery cell 110: Pressurizing member 120: Drive Unit 130: Measurement Unit 140: Elastic member

Claims

1. An electrode assembly comprising a negative electrode, a positive electrode, and a separator membrane interposed between the negative electrode and the positive electrode; An electrolyte solution impregnating the electrode assembly; and A lithium metal battery comprising a battery case containing 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. The lithium metal battery is supplied with 2 kgf / cm². ２ More than 30kgf / cm ２ A lithium metal battery that is charged and discharged under the following pressures.

2. Pressure is applied to the lithium metal battery using a fixed-position pressurization method. The pressure applied to the lithium metal battery is 7 kgf / cm². ２ More than 12kgf / cm ２ A lithium metal battery according to claim 1, wherein the value is less than [value missing].

3. The pressure applied to the lithium metal battery is 8 kgf / cm². ２ More than 11kgf / cm ２ The lithium metal battery according to claim 2, which is as follows:

4. Pressure is applied to the lithium metal battery using a constant-voltage pressurization method. The pressure applied to the lithium metal battery is 4 kgf / cm². ２ More than 30kgf / cm ２ The lithium metal battery according to claim 1, which is as follows:

5. The pressure applied to the lithium metal battery is 5 kgf / cm ２ or more and 25 kgf / cm ２ or less. The lithium metal battery according to claim 4.

6. The lithium metal battery according to claim 4 or claim 5, wherein the equivalent spring constant of the elastic member applied to the constant variable pressure pressurization method is 60 kgf / mm or more and 1000 kgf / mm or less.

7. Pressure is applied to the lithium metal battery using a constant pressure pressurization method. The pressure applied to the lithium metal battery is 10 kgf / cm². ２ More than 30kgf / cm ２ The lithium metal battery according to claim 1, which is as follows:

8. Pressure is applied to the lithium metal battery using a constant pressure pressurization method. The pressure applied to the lithium metal battery is 10 kgf / cm². ２ More than 25kgf / cm ２ The lithium metal battery according to claim 7, which is as follows:

9. The lithium metal battery according to claim 1, wherein the lithium metal battery is a pouch-type lithium metal battery.

10. The lithium metal battery according to claim 1, wherein the lithium metal battery is attached to a pressurizing jig and the pressure is applied by the pressurizing jig.

11. The system includes a battery cell stack in which multiple battery cells are stacked, and a module case that houses the battery cell stack. A battery module wherein the battery cell is a lithium metal battery according to any one of claims 1 to 5 or 7 to 10.

12. The battery module according to claim 11, further comprising, when the method of pressurizing the lithium metal battery is a constant-pressure pressurizing method, a pressurizing unit provided within the module case at a variable distance from the large area of ​​the battery cell, a drive unit capable of moving the pressurizing unit, a measuring unit for measuring the pressure applied to the pressurizing member, and a control unit that receives data measured from the measuring unit and adjusts the pressure applied to the pressurizing member to a constant level.

13. The battery module according to claim 11, wherein the method of pressurizing the lithium metal battery is a constant-voltage pressurizing method, and the module case further includes an elastic member.

14. A battery pack comprising a battery module according to claim 11 and a pack case for housing the battery module.

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