Deteriorated monomer production method and deteriorated monomer evaluation method

Abstract

The present invention relates to a method for manufacturing a deteriorated cell, and a method for evaluating a deteriorated cell including the same, the method for manufacturing a deteriorated cell including: preparing a battery cell having a structure in which an electrode assembly in which a negative electrode, a positive electrode, and a separator are stacked is accommodated in a battery case and an electrode lead is drawn outside the battery case; and causing lithium metal to be deposited on a predetermined region between the negative electrode and the separator by performing charging and discharging under predetermined temperature, pressure, and charging and discharging mode conditions.

Description

Technical Field

[0001] This application claims the benefit based on priority of Korean Patent Application No. 10-2020-0100842, filed on August 12, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing degraded monomers and a method including the method for evaluating degraded monomers. Background Technology

[0003] Recently, rechargeable and discharging secondary batteries have been widely used as power sources for wireless mobile devices. Furthermore, secondary batteries have attracted attention as power sources for electric vehicles, hybrid electric vehicles, and other applications, and have been proposed as a solution to air pollution from existing gasoline and diesel vehicles using fossil fuels. Therefore, due to the advantages of secondary batteries, their applications are currently diversified, and they are expected to be used in many fields and products in the future.

[0004] Based on the composition of the electrodes and electrolyte, these secondary batteries can be classified as lithium-ion batteries, lithium-ion polymer batteries, lithium polymer batteries, etc., among which the use of lithium-ion polymer batteries, which are less likely to leak electrolyte and are easier to manufacture, is increasing. Generally, secondary batteries are classified according to the shape of the battery casing into cylindrical and prismatic batteries, in which the electrode components are embedded in a cylindrical or rectangular metal can, and pouch batteries, in which the electrode components are embedded in a pouch-shaped casing with aluminum laminates. The electrode components built into the battery casing consist of a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes, and are power generation elements capable of charging and discharging. Electrode components are classified into wound types, in which a separator is placed between a long sheet-shaped positive and negative electrode coated with active material, and stacked types, in which multiple positive and negative electrodes of predetermined size are stacked sequentially with separators placed between them.

[0005] This type of secondary battery can be used as a single unit, a modular unit formed by connecting multiple units, or a group unit formed by connecting multiple modules.

[0006] Figure 1 It is a photograph showing lithium metal deposited when degradation occurs in a battery cell.

[0007] like Figure 1 As shown, if a secondary battery is repeatedly charged and discharged, lithium deposits on the negative electrode, resulting in battery performance degradation, such as a decrease in voltage and capacity. In particular, when batteries are used in modules and cell packs, the level of degradation varies between batteries depending on the repeated charging / discharging.

[0008] Therefore, degradation behavior must be ensured based on the actual charging / discharging of individual cells, and the behavior of modules or groups of cells should be analyzed, rather than the behavior of a single battery cell.

[0009] In this regard, Korean Patent No. 10-1293635 discloses an apparatus and method for managing a battery pack that reflects the degree of degradation of individual secondary battery cells. This method can more effectively generate and control various parameters that indicate the characteristics of the battery pack by effectively reflecting the degradation state of the individual secondary battery cells, thereby minimizing the performance degradation of the battery pack and allowing electric vehicles with the battery pack mounted thereon to operate more safely. The method also includes a battery pack.

[0010] In addition, Korean Patent Publication No. 10-2016-0136045 discloses a monomer manufacturing kit for analyzing the degradation of an electrode-symmetric monomer.

[0011] However, to determine the state of degradation, individual cells typically degrade through repeated charging / discharging, much like actual battery use, and it is difficult to measure the form of degradation based on the specific usage conditions of batteries, such as those exhibiting lithium deposition. Furthermore, since repeated charging / discharging must continue until the battery degrades, measurements are time-consuming.

[0012] Therefore, there is a need for a technology that can identify the form of battery degradation based on the battery's charging / discharging conditions. Summary of the Invention

[0013] [Technical Issues]

[0014] It is believed that the present invention solves at least some of the above-mentioned problems. For example, one aspect of the present invention provides a method for manufacturing degraded monomers, and a method for evaluating degraded monomers including the method for manufacturing degraded monomers, which is capable of modeling lithium deposition according to charge / discharge conditions, and thus evaluating the behavior of degraded monomers by depositing lithium metal on a desired region of the negative electrode.

[0015] [Technical Solutions]

[0016] The method for manufacturing a degraded cell according to the present invention includes: preparing a battery cell having an electrode assembly formed by stacking a negative electrode, a positive electrode and a separator, which is housed in a battery casing and electrode leads are led out to the outside of the battery casing; and depositing lithium metal in a predetermined region between the negative electrode and the separator by performing charging and discharging under predetermined temperature, pressure and charging and discharging mode conditions.

[0017] In a specific example, the initial state of charge (SOC) of a single battery cell corresponds to 20% to 50%.

[0018] In one example, charging and discharging are performed at temperatures ranging from -10°C to 0°C.

[0019] In one example, charging and discharging can be performed at pressures ranging from 120 to 200 kgf / cm.

[0020] At this point, pressure can be applied to the edge portion of the battery cell, and electrode leads are drawn out from the edge portion.

[0021] In addition, pressure can be applied to the central part of the battery cell.

[0022] In one example, the charging and discharging modes include charging a battery cell with a constant current (CC) until a predetermined voltage is reached, charging a battery cell that has reached the predetermined voltage with a constant voltage (CV) until a predetermined cutoff current is reached, and discharging a battery cell that has been charged with CV with a constant current (CC).

[0023] At this time, CC charging and CC discharging can be performed at a C rate in the range of 0.5 to 1.5C.

[0024] In a specific example, charging and discharging can be performed two or more times depending on the charging and discharging mode.

[0025] Furthermore, the present invention provides a method for evaluating degraded monomers, the method comprising: manufacturing degraded monomers according to the above-described method for manufacturing degraded monomers; determining: whether lithium metal has precipitated in the degraded monomers; the precipitation region of lithium metal; and the amount of lithium metal precipitated.

[0026] In a specific example, determining whether lithium metal has precipitated in the degraded monomer, the precipitation area of ​​lithium metal, and the amount of lithium metal precipitation involves establishing a database based on information about whether lithium metal has precipitated in the degraded monomer, the precipitation area of ​​lithium metal, and the amount of lithium metal precipitation, according to temperature, pressure, and charging and discharging modes.

[0027] Furthermore, the method for evaluating degraded monomers according to embodiments of the present invention may also include performing safety tests on the degraded monomers.

[0028] At this point, safety testing can be performed after the degraded cell has been charged to show a predetermined state of charge (SOC).

[0029] Furthermore, according to another embodiment of the present invention, the method for evaluating degraded monomers further includes preparing a module by connecting the degraded monomers and normal monomers that have not degraded in series or in parallel, and performing a safety test on the module.

[0030] At this point, safety testing can be performed after the degraded cell has been charged to show a predetermined state of charge (SOC).

[0031] [Beneficial Effects]

[0032] According to the degraded monomer manufacturing method and degraded monomer evaluation method of the present invention, lithium deposition based on charge / discharge conditions can be modeled, and thus lithium metal can be deposited on the desired portion of the negative electrode, thereby evaluating the behavior of the degraded monomer.

[0033] Furthermore, according to the present invention, degraded monomers can be manufactured with only a small number of repeated charge / discharge cycles.

[0034] Furthermore, according to the present invention, by simulating a battery module or pack by connecting a degraded cell to a normal cell, the impact of a degraded cell on a battery module or pack can be evaluated. Attached Figure Description

[0035] Figure 1 It is a photograph showing lithium metal deposited when degradation occurs in a battery cell.

[0036] Figure 2 This is a flowchart illustrating the sequence of the degraded monomer manufacturing method according to the present invention.

[0037] Figure 3 This is a schematic diagram illustrating the shape of a clamp for pressing a battery cell in a method for manufacturing a degraded cell according to an embodiment of the present invention.

[0038] Figure 4 This is a schematic diagram illustrating the shape of a clamp for pressing a battery cell in a method for manufacturing a degraded cell according to another embodiment of the present invention.

[0039] Figure 5 This is a flowchart illustrating the process of a degraded monomer evaluation method according to an embodiment of the present invention.

[0040] Figure 6 This is a flowchart illustrating the process of a degraded monomer evaluation method according to another embodiment of the present invention.

[0041] Figures 7 to 10 These are photographs showing whether lithium metal has been deposited in the negative electrode of the example and comparative examples. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings. The terms and words used in this specification and claims should not be construed as limited to common or dictionary terms, and the inventors may appropriately define the concepts of the terms in order to best describe their invention. Terms and words should be interpreted as having meanings and concepts consistent with the technical concept of the present invention.

[0043] In this application, it should be understood that terms such as "comprising" or "having" are intended to indicate that features, numbers, steps, operations, components, parts, or combinations thereof are described in the specification, and these terms do not preclude the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts, or combinations thereof. Furthermore, when a portion such as a layer, film, region, plate, etc., is referred to as being "on" another portion, this includes not only the case where the portion is "directly located" on the other portion, but also the case where other portions are placed between the portion and the other portion. On the other hand, when a portion such as a layer, film, region, plate, etc., is referred to as being "below" another portion, this includes not only the case where the portion is "directly located" below the other portion, but also the case where other portions are placed between the portion and the other portion. Additionally, in this application, being "on" can include being located at the bottom and at the top.

[0044] The present invention will now be described in detail with reference to the accompanying drawings.

[0045] Figure 2 This is a flowchart illustrating the sequence of the degraded monomer manufacturing method according to the present invention.

[0046] refer to Figure 2 The method for manufacturing a degraded cell according to the present invention includes: preparing a battery cell having an electrode assembly formed by stacking a negative electrode, a positive electrode and a separator, which is housed in a battery casing and electrode leads are led out to the outside of the battery casing (S10); and depositing lithium metal on a predetermined region between the negative electrode and the separator by performing charging and discharging under predetermined temperature, pressure and charging and discharging mode conditions (S20).

[0047] As mentioned above, in the past, there was no way to examine the lithium metal deposition pattern in degraded cells. Even when evaluating the performance of degraded batteries, the common method was to degrade the cells by repeatedly charging / discharging the battery. In this case, the repeated charging / discharging of the battery cells took a long time, and lithium was not deposited on the desired areas.

[0048] According to the method for manufacturing degraded monomers of the present invention, lithium deposition based on charge / discharge conditions can be modeled, and thus lithium metal can be deposited on a desired portion of the negative electrode, thereby evaluating the behavior of the degraded monomer. In this way, by performing short-circuit assessments on specific regions of the negative electrode, etc., monomers with enhanced safety can be manufactured.

[0049] Furthermore, according to the present invention, degraded monomers can be manufactured with only a small number of repeated charge / discharge cycles.

[0050] The method for manufacturing degraded monomers according to the present invention will be described in detail below.

[0051] To manufacture a degraded cell according to the present invention, a battery cell is first prepared. Here, a battery cell refers to a battery cell that has normal performance before deterioration. Furthermore, a degraded cell refers to a battery cell in a state where lithium metal has been deposited in the negative electrode of the battery cell.

[0052] Specifically, the battery cell has an electrode assembly formed by stacking a negative electrode, a positive electrode, and a separator, which is housed in a battery casing and electrode leads are led out to the outside of the battery casing. The negative electrode is obtained by coating a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector, and the positive electrode is obtained by coating a positive electrode slurry containing a positive electrode active material onto a positive electrode current collector.

[0053] The electrode according to the invention can be formed from a conductive component made of a metal with good conductivity. There are no particular limitations on such a conductive component, as long as it has high conductivity without causing chemical changes in the secondary battery. When the electrode is the positive electrode, stainless steel, aluminum, nickel, titanium, carbon plastic, or a material obtained by surface-treating aluminum or stainless steel with carbon, nickel, titanium, silver, etc., can be used as the positive electrode current collector. The current collector can have fine irregularities on its surface to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc., are possible. The positive electrode current collector typically has a thickness of 3 to 500 micrometers.

[0054] In the case of negative electrode current collectors, copper, stainless steel, aluminum, nickel, titanium, plastic carbon, substances obtained by surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys can be used as negative electrode current collectors. Negative electrode current collectors typically have a thickness of 3 to 500 micrometers.

[0055] In addition, the electrode active material layer may include an electrode active material, a conductive material, and a binder. The electrode active material can be a positive electrode active material and a negative electrode active material. The positive electrode active material can be a lithium-containing oxide and may be the same or different. Lithium-containing transition metal oxides can be used as lithium-containing oxides.

[0056] For example, lithium-containing transition metal oxides can be selected from Li x CoO2 (0.5 < x < 1.3), Li x NiO2 (0.5 < x < 1.3), Li x MnO2 (0.5 < x < 1.3), Li x Mn₂O₄ (0.5 < x < 1.3), Li x (Ni a Co b Mn c)O2 (0.5 < x < 1.3, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), Li x Ni 1-y Co y O2 (0.5 < x < 1.3, 0 < y < 1), Li x Co 1-y Mn y O2 (0.5 < x < 1.3, 0 ≤ y < 1), Li x Ni 1-y Mn y O2 (0.5 < x < 1.3, 0 ≤ y < 1), Li x (Ni a Co b Mn c )O4 (0.5 < x < 1.3, 0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), Li x Mn 2-z Ni z O4 (0.5 < x < 1.3, 0 < z < 2), Li x Mn 2-z Co z O4 (0.5 < x < 1.3, 0 < z < 2), Li x CoPO4 (0.5 < x < 1.3) and Li x FePO4 (0.5 < x < 1.3), or a mixture of any one or two or more of the components in the group. In addition, the lithium-containing transition metal oxide may be coated with a metal or metal oxide such as aluminum (Al). In addition, in addition to the lithium-containing transition metal oxide, one or more of sulfides, selenides, and halides may be used.

[0057] The negative electrode active material may include a carbon material, lithium metal, silicon, or tin. When a carbon material is used as the negative electrode active material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon typically include soft carbon and hard carbon. Representative examples of high-crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, and high-temperature calcined carbon—such as coke derived from petroleum or coal tar pitch.

[0058] In addition, the negative electrode paste and the positive electrode paste may further include a conductive material and an adhesive.

[0059] Based on the total weight of the mixture including the positive electrode active material, conductive material is typically added in an amount ranging from 1% to 30% by weight. There are no particular limitations on such conductive material, as long as it is conductive without causing chemical changes in the battery, and examples include graphite, such as natural and artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; metal powders, such as fluorinated carbon, aluminum, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives, etc.

[0060] Based on the total weight of the mixture containing the positive electrode active material, a binder is added in an amount of 1% to 30% by weight as a component that helps to bond the active material to the conductive material and to the current collector.

[0061] Non-aqueous polymers that are soluble in organic solvents but insoluble in water, or water-soluble polymers that are insoluble in organic solvents but soluble in water, can be used as adhesives. The non-aqueous polymer can be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), ethylene oxide-propylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene-butadiene rubber (SBR), polyacrylates, and their derivatives.

[0062] The water-soluble polymer may be one or more of the group consisting of various cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), hydroxypropyl methyl cellulose (HPMC), and hydroxypropyl methyl cellulose phthalate (HPMCP).

[0063] The battery casing is not particularly restricted, as long as it is used as the outer material for packaging the battery, and it can be cylindrical, square or pouch-shaped, and specifically pouch-shaped battery casings can be used.

[0064] When the electrode assembly is housed in the battery casing, the electrolyte solution can be injected into the battery casing and sealed, thereby manufacturing a single battery cell. At this point, the battery cell can be activated through an activation process.

[0065] Similarly, battery cells that have already undergone activation treatment can be charged to a specific SOC level before deterioration. This is to embed a certain level of lithium ions into the negative electrode of the battery cell and to ensure that the battery cell is in the same condition as before the charging / discharging steps.

[0066] There is no limit to the initial SOC before degradation. However, for example, it can be the SOC during normal transport charging, specifically in the range of 20 to 50%, and more specifically in the range of 30 to 50%.

[0067] Battery cells that have undergone activation treatment after manufacturing are degraded by charging / discharging to deposit lithium. Specifically, the battery cells are charged and discharged under predetermined temperature, pressure, and charge / discharge mode conditions. Preferably, the battery cells are charged under harsh conditions to rapidly deposit lithium within the battery cells.

[0068] Specifically, regarding temperature conditions, charging / discharging can be performed within a temperature range of -10 to 0°C. More specifically, charging / discharging can be performed within a temperature range of -5 to 0°C. When charging / discharging is performed within this range, lithium deposition in the negative electrode may be easier. If charging / discharging is performed above 0°C, lithium deposition may occur slowly due to the high temperature, and if charging / discharging is performed below -10°C, lithium may even deposit in undesirable areas due to the harsh conditions.

[0069] Furthermore, regarding pressure conditions, charging / discharging can be carried out at pressures ranging from 120 to 200 kgf / cm. Specifically, charging / discharging can be carried out at pressures ranging from 120 to 180 kgf / cm, and more specifically, at pressures ranging from 120 to 160 kgf / cm. In this case, pressure is applied to deposit lithium only in the portion where no pressure is applied. When charging / discharging is carried out within the above range, lithium deposition in the negative electrode may be easier. If the pressure applied during charging / discharging is less than the above range, lithium deposition in the desired portion will be difficult due to the low pressure, and if the pressure is above this range, the battery cell may rupture due to excessive pressure.

[0070] Furthermore, in the method for manufacturing degraded cells according to the invention, pressure can be applied to the front surface of the cell or only to a portion of the cell. In this case, no pressure is applied to the portion where lithium deposition is desired. Similarly, by applying pressure only to a portion of the cell, lithium metal can be deposited only on the desired portion of the negative electrode.

[0071] Figure 3 This is a schematic diagram illustrating the shape of a clamp for pressing a battery cell in a method for manufacturing a degraded cell according to an embodiment of the present invention.

[0072] Reference Figure 3 , Figure 3 (a) is a top view of the battery cell 10 being mounted on the clamp 20, and Figure 3(b) is a side view of the battery cell 10 being mounted on the clamp 20. Figure 3 In this design, the clamp 20 for pressing the battery cell 10 consists of a lower plate 22 in which the battery cell 10 is placed and an upper plate 21 for pressing the battery cell 10 from above. The battery cell 10 is a pouch-type battery cell, and the electrode leads 12 extend from both ends of the battery casing 11.

[0073] Reference Figure 3 Pressure can be applied to the edge portion of the battery cell, from which electrode leads 12 are led out. This allows lithium deposition to be regulated to occur at the center of the negative electrode. Furthermore, when pressure is applied to the battery cell, damage to the cell can be prevented, and to apply uniform pressure to the pressing surface, a resilient silicon pad 23 can be mounted on the lower surface of the upper plate 21.

[0074] Figure 4 This is a schematic diagram illustrating the shape of a clamp for pressing a battery cell in a method for manufacturing a degraded cell according to another embodiment of the present invention.

[0075] Reference Figure 4 , Figure 4 (a) is a top view of the battery cell 10 being mounted on the clamp 30, and Figure 4 (b) is a side view showing the battery cell 10 mounted on the clamp 30. Figure 4 In this design, the clamp 30 for pressing the battery cell 10 consists of a lower plate 32 in which the battery cell 10 is placed and an upper plate 31 for pressing the battery cell 10 from above. The battery cell 10 is a pouch-type battery cell, and the electrode leads 12 extend from both ends of the battery casing 11.

[0076] Reference Figure 4 Pressure can be applied to the central portion of the battery cell 10. This allows lithium deposition to be regulated to occur at the edge of the negative electrode. Furthermore, when pressure is applied to the battery cell 10, damage to the battery cell can be prevented, and in order to apply uniform pressure to the pressing surface, a resilient silicon pad 33 can be mounted on the lower surface of the upper plate 31.

[0077] In addition, Figure 3 and Figure 4 The clamp may also include a pressing member (not shown) that transmits a pressing force to lower the upper plate, thereby pressing the battery cell by lowering the upper plate. This pressing member may have a threaded shape, and when the threaded pressing member is rotated by a torque wrench or the like, the pressing member can lower the upper plate as the pressing member lowers. In this case, the pressure applied to the battery cell can be defined as the torque tightening pressure applied to the pressing member when it is lowered.

[0078] In addition, when charging and discharging a battery cell, the charging and discharging modes may include charging the battery cell with a constant current (CC) until a predetermined voltage is reached, charging the battery cell that has reached the predetermined voltage with a constant voltage (CV) until a predetermined cutoff current is reached, and discharging the battery cell that has been charged with CV with a constant current (CC).

[0079] When a battery cell is CC-charged, the current gradually decreases as it approaches the termination voltage, and charging stops when the current reaches the predetermined termination voltage. The secondary battery is then CV-charged. The termination voltage can be, for example, 3 to 4.2V. CV charging of a battery cell can be performed by charging the cell using the termination voltage until a predetermined cutoff current value is reached. During CV charging, the current value gradually decreases while maintaining the voltage. The current value at which charging stops is called the cutoff current. Similarly, by performing CV charging after CC charging, more lithium ions can be inserted into the negative electrode, which affects lithium deposition.

[0080] Furthermore, CC charging and CC discharging are performed by applying a constant current with a predetermined C rate to the battery cells. This accelerates the charging and discharging speed for lithium deposition. Specifically, CC charging and CC discharging can be performed at a C rate of 0.5 to 1.5C—specifically, at a C rate of 1 to 1.5C. When the charging / discharging rate is less than the above range, lithium may be difficult to deposit in the negative electrode in a short time, and when the charging / discharging rate exceeds the above range, lithium may deposit in undesirable areas due to excessive speed.

[0081] Furthermore, in the degraded monomer manufacturing method according to the present invention, lithium metal in the negative electrode can be stably deposited through two or more repeated charge / discharge cycles.

[0082] Furthermore, the present invention provides a method for evaluating degraded monomers, including the above-described method for manufacturing degraded monomers.

[0083] Figure 5 This is a flowchart illustrating the process of a degraded monomer evaluation method according to an embodiment of the present invention.

[0084] Reference Figure 5The method for evaluating a degraded cell includes: manufacturing a degraded cell according to the above-described method for manufacturing a degraded cell; determining whether lithium metal has been deposited in the degraded cell; the deposited area of ​​lithium metal; and the amount of lithium metal deposited. Therefore, the method for evaluating a degraded cell according to the present invention includes: preparing a battery cell having a structure in which an electrode assembly produced by stacking a negative electrode, a positive electrode, and a separator is housed in a battery casing and electrode leads are led out to the outside of the battery casing (S10); depositing lithium metal in a predetermined area between the negative electrode and the separator by performing charging and discharging under predetermined temperature, pressure, and charging and discharging mode conditions (S20); and determining whether lithium metal has been deposited in the degraded cell; the deposited area of ​​lithium metal; and the amount of lithium metal deposited (S30).

[0085] According to the degraded monomer evaluation method of the present invention, lithium deposition based on charge / discharge conditions can be modeled, thus allowing lithium metal to be deposited on desired portions of the negative electrode, thereby evaluating the behavior of degraded monomers. In this way, by conducting short-circuit assessments of specific regions of the negative electrode, etc., monomers with enhanced safety can be manufactured.

[0086] In a specific example, determining whether lithium metal has precipitated in the degraded cell, the precipitation area of ​​lithium metal, and the amount of lithium metal precipitation involves: manufacturing the degraded cell while varying temperature, pressure, and charge / discharge mode conditions, and establishing a database based on temperature, pressure, and charge / discharge modes using information about whether lithium metal has precipitated in the degraded cell, the precipitation area of ​​lithium metal, and the amount of lithium metal precipitation. In this case, the amount of lithium metal precipitation can be obtained, for example, by measuring the change in weight of the electrode or battery cell before and after charging / discharging.

[0087] In this context, data on lithium deposition patterns can be obtained, such as whether lithium metal has precipitated in the degraded monomer, the area where lithium metal has precipitated, and the amount of lithium metal deposited. This can be achieved by varying at least one of three variables: temperature, pressure, and charge / discharge pattern. Furthermore, the correlation between charge / discharge conditions and lithium deposition patterns can be derived from the data. Specifically, after identifying information on lithium deposition patterns based on charge / discharge conditions, this information can be accumulated in a storage system such as a memory, and such data can be recorded as visual data such as tables or graphs.

[0088] Furthermore, according to the deteriorated monomer evaluation method of the present invention, by adjusting the SOC of the deteriorated monomer and establishing a database of information regarding temperature, pressure, charge / discharge mode conditions, where lithium metal has precipitated based on the SOC of the deteriorated monomer, the area of ​​lithium metal precipitation, and the amount of lithium metal precipitation, the correlation between the SOC of the deteriorated monomer and the lithium precipitation mode can be derived under the same charge / discharge conditions. The details regarding the establishment of the database are the same as described above.

[0089] In addition, refer to Figure 5 The method for evaluating degraded cells according to embodiments of the present invention may further include performing a safety test (S40) on the degraded cells. Examples of safety tests include external short-circuit tests, which include a nail test allowing a nail-like conductor to penetrate the degraded cell, or a drop test to determine whether a short circuit occurs due to a drop impact caused by a falling cell. Specifically, by performing an external short-circuit test on a lithium deposition pattern, vulnerable portions can be identified. Safety can also be evaluated by simulating various degraded cell patterns.

[0090] At this point, a safety test can be performed after the degraded cell has been charged to exhibit a predetermined state of charge (SOC). In other words, a safety test can be performed while changing the SOC of the degraded cell. Based on the charging / discharging conditions and SOC of the degraded cell, the safety risks and short-circuit risk locations of each SOC of the degraded cell can be verified through safety testing. Similarly, the degraded cell evaluation method according to the present invention can be used as a basis for manufacturing cells with improved safety through short-circuit evaluation, etc.

[0091] Figure 6 This is a flowchart illustrating the process of a degraded monomer evaluation method according to another embodiment of the present invention.

[0092] Reference Figure 6 According to another embodiment of the present invention, the method for evaluating a degraded cell further includes preparing a module by connecting the degraded cell and a normal cell that has not degraded in series or in parallel, and performing an external short-circuit test on the module. Specifically, the method for evaluating a degraded cell includes: preparing a battery cell having an electrode assembly formed by stacking a negative electrode, a positive electrode, and a separator housed in a battery casing and electrode leads extended to the outside of the battery casing (S10); depositing lithium metal in a predetermined region between the negative electrode and the separator by performing charging and discharging under predetermined temperature, pressure, and charging and discharging mode conditions (S20); and determining: whether lithium metal has been deposited in the degraded cell; the area of ​​lithium metal deposition; the amount of lithium metal deposition (S30); connecting the degraded cell with a normal cell to prepare a module and performing a safety test on the module (S40).

[0093] Specifically, after assembling degraded and undegraded normal cells in a module or unit group, performance and short-circuit tests can be performed. This test can be performed while varying the number of degraded and undegraded normal cells. Safety can also be assessed by simulating various degraded cell patterns.

[0094] At this point, a safety test can be performed after the degraded cell has been charged to show a predetermined state of charge (SOC). In other words, a safety test can be performed while changing the SOC of the degraded cell.

[0095] According to the method for evaluating degraded cells of the present invention, the impact of degraded cells on battery modules or groups can be assessed by simulating battery modules or groups degraded under actual use by connecting multiple degraded cells and normal cells that have not degraded in series or in parallel. Furthermore, based on the SOC of the degraded cells, external short-circuit tests can be conducted to verify the safety risks and short-circuit risk locations of each SOC of the degraded cells in the assembled module or group state.

[0096] The present invention will now be described in detail with reference to examples. However, embodiments of the invention can be modified in various other forms, and the scope of the invention should not be construed as limited to the examples described below. Examples of the invention are provided to more fully describe the invention to those skilled in the art.

[0097] Preparation Example

[0098] The positive electrode mixture is prepared by mixing 96.7 parts by weight of Li[Ni] as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 The cathode was prepared by mixing O2, 1.3 parts by weight of graphite used as a conductive material, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) used as a binder. The cathode slurry was prepared by dispersing the obtained cathode mixture in 1-methyl-2-pyrrolidone used as a solvent. The cathode was prepared by coating, drying, and pressing the slurry onto both sides of an aluminum foil with a thickness of 20 μm.

[0099] The negative electrode mixture was prepared by mixing 97.6 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) as the negative electrode active material, 1.2 parts by weight of styrene-butadiene rubber (SBR) as the binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC). The negative electrode slurry was prepared by dispersing the negative electrode mixture in deionized water as the solvent. The negative electrode was prepared by coating, drying, and pressing the slurry onto both sides of a 20 μm thick copper foil.

[0100] The non-aqueous electrolyte solution was prepared by dissolving LiPF6 in an organic solvent, wherein ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a 3:3:4 (volume ratio). Here, LiPF6 was dissolved in the organic solvent to a concentration of 1.0 M.

[0101] A battery cell is prepared by laminating porous polyethylene separators between the positive and negative electrodes prepared above, storing them in a bag, and then injecting an electrolyte solution.

[0102] Example

[0103] Activate the battery cells prepared in the above preparation example to adjust the SOC to 30%. In use... Figure 4 With the pressing clamp pressing down on the center of the battery cell, the battery cell is charged under specific temperature, pressure, and charging / discharging modes.

[0104] Specifically, the charging / discharging temperature is -5°C, and the pressure is 120 kgf / cm². At this time, the pressure is determined by factors including... Figure 4 The torque fastening pressure received by the pressing component in the pressing clamp.

[0105] Furthermore, during charging / discharging, the battery cells are charged at a 1C rate (C) until the voltage reaches 4.2V. Once the voltage reaches 4.2V, charging continues while maintaining the voltage until the battery cell's current reaches 0.95C. When the battery cell's current reaches the cutoff current, the battery cell discharges at a 1C rate (C). This charging / discharging mode described above is executed once.

[0106] Comparative Example 1

[0107] Activate the battery cells prepared in the above preparation example to adjust the SOC to 30%. In use... Figure 4 With the pressing clamp pressing down on the center of the battery cell, the battery cell is charged under specific temperature, pressure, and charging / discharging modes.

[0108] Specifically, the charging / discharging temperature is -15°C, and the pressure is 120 kgf / cm². At this time, the pressure is determined by factors including... Figure 4 The torque fastening pressure received by the pressing component in the pressing clamp.

[0109] Furthermore, during charging / discharging, the battery cells are charged at a 1C rate (C) until the voltage reaches 4.2V. Once the voltage reaches 4.2V, charging continues while maintaining the voltage until the battery cell current reaches 0.05C. When the battery cell current reaches the cutoff current, the battery cell discharges at a 1C rate (C). This charging / discharging mode described above is executed once.

[0110] Comparative Example 2

[0111] Activate the battery cells prepared in the above preparation example to adjust the SOC to 30%. In use... Figure 4 With the pressing clamp pressing down on the center of the battery cell, the battery cell is charged under specific temperature, pressure, and charging / discharging modes.

[0112] Specifically, the charging / discharging temperature is -15°C, and the pressure is 120 kgf / cm². At this time, the pressure is determined by factors including... Figure 4 The torque fastening pressure received by the pressing component in the pressing clamp.

[0113] Furthermore, during charging / discharging, the battery cells are charged at a constant power (CP) while maintaining an output of 1W, and the current is reduced until the voltage of the battery cell reaches 4.2V. Thereafter, when the voltage of the battery cell reaches 4.2V, the battery cell is discharged at CP while maintaining an output of 1W. This charging / discharging mode described above is executed four times.

[0114] Comparative Example 3

[0115] Activate the battery cells prepared in the above preparation example to adjust the SOC to 30%. In use... Figure 4 With the pressing clamp pressing down on the center of the battery cell, the battery cell is charged under specific temperature, pressure, and charging / discharging modes.

[0116] Specifically, the charging / discharging temperature is 25°C (room temperature), and the pressure is 120 kgf / cm. At this time, the pressure is determined by factors including... Figure 4 The torque fastening pressure received by the pressing component in the pressing clamp.

[0117] Furthermore, during charging / discharging, the battery cells are charged at a constant power (CP) while maintaining an output of 1W, and the current is reduced until the voltage of the battery cell reaches 4.2V. Thereafter, when the voltage of the battery cell reaches 4.2V, the battery cell is discharged at CP while maintaining an output of 1W. This charging / discharging mode described above is executed four times.

[0118] Experimental Example

[0119] After disassembling the battery cells for charging / discharging, check whether lithium has deposited in the negative electrode. The results are as follows: Figures 7 to 10 As shown.

[0120] Reference Figure 7It can be confirmed that, when the battery cell is charged and discharged according to the example, lithium deposits on the unpressed area (the edge portion of the battery cell). That is, in the degraded cell manufacturing method according to the present invention, lithium can be deposited on the desired portion by pressing a specific portion of the battery cell under specific charging / discharging conditions.

[0121] However, refer to Figure 8 In a comparative example where the charging / discharging temperature was adjusted to -15°C, lithium even deposited on the pressed center portion, thus lithium metal even deposited on unwanted parts.

[0122] Furthermore, in Comparative Example 2, where the charging / discharging temperature was adjusted to -15°C and the battery cells underwent CP charging and CP discharging, lithium metal precipitated on the front surface of the negative electrode. Therefore, lithium metal even precipitated on undesirable areas, such as... Figure 9 As shown.

[0123] Furthermore, in Comparative Example 2, where the battery cells were charged and discharged at room temperature, it was confirmed that, despite... Figure 10 The process performed CP charging and CP discharging four times, but no lithium metal was deposited.

[0124] That is, according to the degraded monomer manufacturing method and the degraded monomer evaluation method including the degraded monomer manufacturing method of the present invention, lithium metal can be deposited on the desired portion by performing charging / discharging under predetermined conditions.

[0125] The above description merely illustrates the technical concept of the present invention, and those skilled in the art can make various modifications and variations without departing from the essential characteristics of the invention. Therefore, the accompanying drawings disclosed herein are not intended to limit the technical concept of the invention, but rather to describe it, and the scope of the technical concept of the invention is not limited by these drawings. The scope of protection of the present invention should be interpreted by the appended claims, and all technical concepts within the scope of the appended claims should be interpreted as being included within the scope of the present invention.

Claims

1. A method for manufacturing degraded monomers, the method comprising: A battery cell with the following structure is prepared: an electrode assembly, formed by stacking a negative electrode, a positive electrode, and a separator, is housed in a battery casing and electrode leads are led out to the outside of the battery casing; as well as By performing charging and discharging under predetermined temperature, pressure, and charging and discharging mode conditions, lithium metal is deposited on a predetermined region between the negative electrode and the separator. In this method, no pressure is applied to the predetermined area, thereby depositing lithium metal only in the predetermined area. The charging and discharging are performed at temperatures ranging from -10°C to 0°C. The charging and discharging are performed under pressures ranging from 120 to 200 kgf / cm. The charging and discharging modes include constant current charging of the battery cells and constant current discharging of the battery cells, wherein the constant current charging and constant current discharging are performed at a C rate in the range of 0.5C to 1.5C.

2. The method according to claim 1, wherein, The initial state of charge of the battery cell corresponds to 20% to 50%.

3. The method according to claim 1, wherein, The pressure is applied to the edge portion of the battery cell, from which the electrode leads are led out.

4. The method according to claim 1, wherein, The pressure is applied to the central portion of the battery cell.

5. The method according to claim 1, wherein, The charging and discharging modes include charging the battery cells with the constant current until a predetermined voltage is reached, charging the battery cells that have reached the predetermined voltage with the constant voltage until a predetermined cutoff current is reached, and discharging the battery cells that have been charged with the constant voltage with the constant current.

6. The method according to claim 5, wherein, The charging and discharging according to the charging and discharging mode is performed two or more times.

7. A method for evaluating deteriorating monomers, said method include: The method for manufacturing degraded monomers according to claim 1 manufactures degraded monomers; and Determine whether lithium metal has precipitated in the degraded monomer; the precipitation area of ​​lithium metal; and the amount of lithium metal precipitated.

8. The method according to claim 7, wherein, Whether lithium metal has precipitated in the deteriorated monomer; the precipitation area of ​​lithium metal; The determination of the amount of lithium metal precipitation includes: establishing a database based on temperature, pressure, and charging and discharging modes, using information about whether lithium metal has precipitated in the degraded monomer, the precipitation area of ​​lithium metal, and the amount of lithium metal precipitation.

9. The method of claim 7, further comprising performing a safety test on the degraded monomer.

10. The method according to claim 9, wherein, The safety test is performed after the degraded cell is charged to show a predetermined charging state.

11. The method of claim 7, further comprising: Modules are fabricated by connecting degraded monomers and normal monomers that have not degraded in series or in parallel, and safety tests are performed on the modules.

12. The method according to claim 11, wherein, The safety test is performed after the degraded cell is charged to show a predetermined charging state.

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