Title of Invention: Battery cell for evaluation of lithium precipitation behavior and manufacturing method thereof
technical field
[One]
This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0043731 dated April 10, 2020, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[2]
The present invention relates to a battery cell for evaluating lithium precipitation behavior in which a viewing window is provided in a battery case to evaluate lithium precipitation behavior occurring in an overhang region in real time while charging and discharging, and a method for manufacturing the same.
background
[3]
In recent years, as the demand for portable electronic products such as laptops and mobile phones has rapidly increased and the demand for electric carts, electric wheelchairs, and electric bicycles has also increased, research on high-performance secondary batteries capable of repeatedly charging and discharging is actively conducted. is becoming In addition, in recent years, as carbon energy is gradually depleted and interest in the environment is increasing, the demand for hybrid electric vehicles (HEV) and electric vehicles (EV) is gradually increasing worldwide. Accordingly, more attention and research are being focused on secondary batteries for vehicles, which are core components of HEVs and EVs.
[4]
As such a high-performance secondary battery and a secondary battery for a vehicle, a lithium-ion secondary battery is the most realistic technology. Lithium ion secondary batteries act as batteries by repeating insertion and desorption of lithium ions from the negative electrode and the positive electrode. Between these electrodes, lithium ions move but electrons do not have lithium salt-containing electrolytes.
[5]
In particular, it is necessary to prevent lithium from being deposited on the surface of the anode, so-called lithium-plating. When lithium is precipitated, it causes a side reaction with the electrolyte and changes the kinetic balance of the secondary battery, which causes secondary battery deterioration such as capacity loss, and also affects the lifespan of secondary batteries and a safety problem in which overcharge control function is lost. because there is
[6]
In order to prevent lithium precipitation as described above, it is generally manufactured so that the area of ​​the anode active material layer is expanded to a larger area than the area of ​​the cathode active material layer when the electrode assembly is manufactured. However, due to a process problem, in some electrode assemblies, the area of ​​the anode active material layer does not cover all of the area of ​​the cathode active material layer, and thus a part of the cathode active material layer may have a structure in which it protrudes from the anode active material layer. This is referred to as mismatch or overhang between the positive and negative electrodes, and lithium is precipitated in the overhang region during charging, and safety is a problem in a battery in which such an overhang occurs.
[7]
Accordingly, there is a continuous need to analyze the behavior of lithium precipitates, such as the pattern of lithium-plating occurring in the overhang region, and the electrochemical evaluation.
[8]
However, it is very difficult to know whether lithium is precipitated in real time with respect to the secondary battery. Conventionally, as a technique for non-destructively detecting whether lithium is precipitated in an anode, there are discharge at a low temperature, heat capacity analysis, thickness increase analysis, and the like. However, these are not all measured in the environment in which the secondary battery is used. Therefore, it is necessary to secure evaluation and analysis technology according to the lithium precipitation behavior in real time non-destructively in the environment in which the secondary battery is actually used.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[9]
Accordingly, the present invention has been devised to solve the above problems, and a battery cell for evaluating lithium precipitation behavior capable of electrochemical evaluation according to lithium deposition behavior in real time in an environment in which a secondary battery is actually used, a manufacturing method thereof, and further It is intended to provide a technique for electrochemically evaluating and analyzing a secondary battery according to the lithium precipitation behavior used.
means of solving the problem
[10]
The manufacturing method of the battery cell for evaluation of lithium precipitation behavior of the present invention for achieving the above object includes: an electrode assembly manufacturing step (S10) of manufacturing an electrode assembly in which an overhang region protruding from a negative electrode is introduced; A battery cell manufacturing step (S20) of accommodating the electrode assembly in a first pouch, injecting an electrolyte, and then sealing the battery cell; a secondary sealing step (S30) of accommodating the battery cell in a second pouch and performing secondary sealing; a second pouch removing step (S40) of forming the secondary sealed battery cell and removing the second pouch; a gas pocket removing step (S50) of degassing and re-sealing the battery cell from which the second pouch is removed, and removing the gas pocket of the first pouch; and a completion step (S60) of accommodating and sealing the battery cell from which the gas pocket part has been removed in a third pouch provided with a viewing window.
[11]
In an embodiment of the present invention, the electrode assembly includes one or a plurality of bi-cell units having a positive/negative electrode/anode structure or a mono-cell unit having a positive/negative electrode structure.
[12]
In one embodiment of the present invention, the positive lead and the negative lead included in the electrode assembly are each wrapped with three lead films, and the third lead film, the second lead film, and the first lead film are in the order closest to the electrode assembly. may be
[13]
In one embodiment of the present invention, in the battery cell manufacturing step (S20), the first pouch and the third lead film are sealed together.
[14]
In one embodiment of the present invention, in the second sealing step (S30), the second pouch and the first lead film are sealed together.
[15]
In an embodiment of the present invention, in the completion step (S60), the third pouch and the second lead film are sealed together.
[16]
In one embodiment of the present invention, the first pouch is a pouch made of polyethylene terephthalate or polypropylene material in which the electrode assembly housed therein is visible.
[17]
In one embodiment of the present invention, the second pouch is a pouch of a laminate sheet including a barrier layer of aluminum.
[18]
In one embodiment of the present invention, the third pouch is a laminate sheet pouch including a barrier layer of aluminum, and in the third pouch, a through hole is formed in a portion corresponding to the overhang region, The viewing window may be formed by covering the through hole with an acrylic film.
[19]
Lithium precipitation behavior evaluation method according to the present invention, manufacturing a battery cell for lithium precipitation behavior evaluation; and charging and discharging the prepared battery cell for evaluating the lithium precipitation behavior, and observing the lithium precipitation behavior in the overhang region in real time through the viewing window.
[20]
The battery cell for evaluating lithium precipitation behavior of the present invention is a battery cell in which an electrode assembly in which an overhang region protruding from a negative electrode plate is introduced in a transparent pouch and a battery cell sealed by accommodating an electrolyte solution is sealed with a pouch of an aluminum laminate sheet, The pouch of the aluminum laminate sheet is provided with a viewing window at a portion corresponding to the overhang region, and electrochemical evaluation is performed while confirming the precipitation behavior of lithium in the overhang region through the viewing window.
[21]
In one embodiment of the present invention, the transparent pouch is a pouch made of polyethylene terephthalate or polypropylene material.
[22]
In one embodiment of the present invention, the viewing window is formed by covering a transparent film on a through hole formed in a portion corresponding to the overhang region among the pouches of the aluminum laminate sheet.
[23]
In one embodiment of the present invention, the transparent film is an acrylic film.
[24]
In one embodiment of the present invention, the transparent film is attached to the pouch of the aluminum laminate sheet using a polyimide-based adhesive tape.
Effects of the Invention
[25]
The manufacturing method of the battery cell for evaluation of lithium precipitation behavior of the present invention and the battery cell for evaluation can observe the lithium precipitation behavior in real time through a viewing window while charging and discharging, and lithium according to the electrochemical state of the battery cell Precipitation behavior can be confirmed.
Brief description of the drawing
[26]
1 is a flowchart of a method of manufacturing a battery cell for evaluation of lithium precipitation behavior according to the present invention.
[27]
2 is a schematic diagram of an electrode assembly according to an embodiment of the present invention.
[28]
3 is a schematic diagram showing an embodiment of a battery cell manufactured according to the battery cell manufacturing step (S20) of the present invention.
[29]
4 is a schematic diagram showing an embodiment of the battery cell after the secondary sealing step (S30) of the present invention.
[30]
5 is a schematic diagram showing a battery cell from which the second pouch is removed according to the second pouch removal step (S40) of the present invention.
[31]
6 is a schematic diagram of a third pouch according to an embodiment of the present invention.
[32]
7 is a schematic diagram of a battery cell for evaluating lithium precipitation behavior according to an embodiment of the present invention.
[33]
8 is a capacity-potential profile showing charging conditions of an experimental example for evaluating lithium precipitation behavior using a battery cell for evaluating lithium precipitation behavior according to an embodiment of the present invention.
[34]
9 is a photograph of lithium precipitation behavior occurring in the overhang region for each section of FIG. 8 .
Best mode for carrying out the invention
[35]
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention.
[36]
Therefore, the configuration shown in the embodiments and drawings described in the present specification is only the most preferred embodiment of the present invention and does not represent all the technical spirit of the present invention, so at the time of the present application, various It should be understood that there may be equivalents and variations.
[37]
Throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components unless otherwise stated.
[38]
[39]
1 is a flowchart of a method of manufacturing a battery cell for evaluation of lithium precipitation behavior according to the present invention. Referring to FIG. 1 , the method of manufacturing a battery cell for evaluating lithium precipitation behavior according to the present invention includes an electrode assembly manufacturing step (S10) of manufacturing an electrode assembly in which an overhang region protruding from a negative electrode is introduced; A battery cell manufacturing step (S20) of accommodating the electrode assembly in a first pouch, injecting an electrolyte, and then sealing the battery cell; a secondary sealing step (S30) of accommodating the battery cell in a second pouch and performing secondary sealing; a second pouch removing step (S40) of forming the secondary sealed battery cell and removing the second pouch; a gas pocket removing step (S50) of degassing and re-sealing the battery cell from which the second pouch is removed, and removing the gas pocket of the first pouch; and a completion step (S60) of accommodating and sealing the battery cell from which the gas pocket part has been removed in a third pouch provided with a viewing window.
[40]
In the battery cell for evaluating lithium precipitation behavior according to the manufacturing method of the present invention, an overhang region is introduced into the electrode assembly housed inside the battery case of the pouch, and a viewing window is provided in the pouch so that the electrode assembly inside the pouch can be observed. is equipped, it is possible to check the lithium precipitation behavior occurring in the overhang region through the transparent viewing window in real time while charging and discharging the battery cell without disassembling the battery cell, and electrochemical evaluation according to the lithium precipitation behavior There is an effect that can be done.
[41]
The electrode assembly manufacturing step ( S10 ) is a step of manufacturing the electrode assembly in which the overhang region is introduced. In general, in manufacturing the electrode assembly, in order to prevent lithium precipitation, the horizontal / vertical length of the negative active material layer is cut to be longer than the horizontal / vertical length of the positive active material layer, respectively, the negative electrode active material layer is a positive electrode material layer An electrode assembly is being manufactured to cover it. In the present invention, in order to artificially induce lithium precipitation so that lithium precipitation behavior can be observed, the positive electrode and the negative electrode are manufactured so that the area of ​​the negative electrode active material layer is smaller than the area of ​​the positive electrode active material layer, unlike the general electrode assembly manufacturing method. It is characterized in that an overhang region protruding from the cathode is introduced.
[42]
The overhang region may be formed by cutting the anode so that the horizontal or vertical length of the positive electrode is smaller than the horizontal or vertical length of the negative electrode in manufacturing the positive electrode and the negative electrode, and the area of ​​the overhang region can be appropriately adjusted according to the evaluation purpose. can
[43]
In one specific example, the electrode assembly may include one or a plurality of bi-cell units having a positive/negative electrode/anode structure or a mono-cell unit having a positive/negative electrode structure.
[44]
2 shows an electrode assembly according to an embodiment of the present invention. Referring to FIG. 2 , in one specific example, the electrode assembly 110 of the present invention may be a monocell of the positive electrode 112 / separator 113 / negative electrode 111 . In the monocell, a separator 113 is interposed between the anode 112 and the cathode 111 , and the separator 113 has a larger area than the anode 112 and the cathode 111 , and thus the anode 112 and the cathode It protrudes from (111). In addition, the vertical length of the positive electrode 112 is longer than that of the negative electrode 111 , so that the positive electrode 112 has an overhang region A protruding downward from the end of the negative electrode 111 . When charging or discharging the battery cell including the electrode assembly is repeated, lithium is precipitated in the overhang region.
[45]
Referring to FIG. 2 , the positive electrode tab 116 extends and protrudes from the positive electrode 112 of the electrode assembly 110 , and the negative electrode tab 115 extends and protrudes from the negative electrode 111 , and the positive electrode tab ( 116) and the negative electrode tab 115 are drawn out of the pouch, which is a battery case, respectively. In addition, the positive electrode tab 116 is surrounded by three lead films, and the negative electrode tab 115 is also surrounded by three lead films. Herein, in order to describe the three lead films, the third lead film 143 , the second lead film 142 , and the first lead film 141 will be referred to in the order closest to the electrode assembly for convenience. The first to third lead films are interposed between the electrode tabs 115 and 116 and the pouch, which is the battery case, and are sealed in such a way that the electrode tab and the pouch are integrally fused during sealing of the pouch. will be. That is, the pouch can be more firmly fusion-bonded to the electrode tab through the lead films.
[46]
In the present invention, the positive electrode and the negative electrode may be manufactured by applying an electrode mixture containing an electrode active material on a current collector, respectively, and then drying the electrode mixture, and the electrode mixture may optionally further include a binder, a conductive material, a filler, etc. have.
[47]
As the current collector, both a metal ultra-thin of a weak magnetic material or a non-magnetic material may be used. In the case of a positive electrode current collector, it is generally made to a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, or carbon, nickel on the surface of aluminum or stainless steel. , titanium, silver, etc. surface-treated may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine concavities and convexities on the surface thereof, and various forms such as a sheet, a foil, and a net are possible.
[48]
In the case of the negative electrode current collector, it is generally made to a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a sheet, a foil, a net, and the like.
[49]
The positive active material is a material capable of causing an electrochemical reaction, and as a lithium transition metal oxide, includes two or more transition metals, for example, lithium cobalt oxide (LiCoO 2 ) substituted with one or more transition metals (LiCoO 2 ), lithium layered compounds such as nickel oxide (LiNiO 2 ); lithium manganese oxide substituted with one or more transition metals; Formula LiNi 1-y M y O 2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga and includes at least one of the above elements, 0.01≤y≤0.7) Lithium nickel-based oxide represented by; Li 1+z Ni 1/3 Co 1/3 Mn 1/3 O 2 , Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O 2Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (where -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤, etc.) 0.8, 0≤d≤0.2, 0≤e≤0.2, b+c+d<1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl) lithium nickel cobalt manganese composite oxide; Formula Li 1+x M 1-y M' y PO 4-z X z where M = transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, and -0.5≤x≤+0.5, 0≤y≤0.5, 0≤z≤0.1 olivine-based lithium metal phosphate represented by), but is not limited thereto.
[50]
The negative electrode active material includes, for example, carbon such as non-graphitizable carbon and graphitic carbon; Li x Fe 2 O 3 (0≤x≤1), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me' : metal composite oxides such as Al, B, P, Si, elements of Groups 1, 2 and 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; SnO, SnO 2 , PbO, PbO 2 , Pb 2 O 3 , Pb 3 O 4 , Sb 2 O 3 , Sb metal oxides such as 2 O 4 , Sb 2 O 5 , GeO, GeO 2 , Bi 2 O 3 , Bi 2 O 4 , and Bi 2 O 5 ; conductive polymers such as polyacetylene; A Li-Co-Ni-based material or the like can be used.
[51]
The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.
[52]
The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, poly propylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluororubber, various copolymers, and the like.
[53]
The filler is optionally used as a component for inhibiting the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. A fibrous material such as glass fiber or carbon fiber is used.
[54]
Other components such as viscosity modifiers and adhesion promoters may be further included optionally or as a combination of two or more. The viscosity modifier is a component that adjusts the viscosity of the electrode mixture to facilitate the mixing process of the electrode mixture and the application process on the current collector thereof, and may be added up to 30% by weight based on the total weight of the negative electrode mixture. Examples of such a viscosity modifier include, but are not limited to, carboxymethylcellulose, polyvinylidene fluoride, and the like. In some cases, the solvent described above may serve as a viscosity modifier in parallel.
[55]
The adhesion promoter is an auxiliary component added to improve the adhesion of the active material to the current collector, and may be added in an amount of 10% by weight or less relative to the binder, for example, oxalic acid, adipic acid, formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.
[56]
The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 300 μm. As such a separation membrane, For example, olefin polymers, such as chemical-resistance and hydrophobic polypropylene; A sheet or nonwoven fabric made of glass fiber or polyethylene is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.
[57]
[58]
The battery cell manufacturing step ( S20 ) is a step including a step of accommodating the electrode assembly to which the overhang region is introduced in a first pouch, and sealing the electrode assembly by injecting the electrolyte together.
[59]
The first pouch is a pouch made of a transparent material so that the electrode assembly to be accommodated inside the first pouch can be seen from the outside of the first pouch. or polypropylene.
[60]
The electrolyte is a general non-aqueous electrolyte used in the manufacture of secondary batteries, and may specifically include an organic solvent and optionally a lithium salt.
[61]
The organic solvent is not limited as long as it can minimize decomposition due to oxidation reaction during the charging and discharging process of the secondary battery, and can exhibit desired properties together with the additive, for example, carbonate-based and propionate-based It may be . These may be used alone, or two or more may be used in combination.
[62]
Among the non-aqueous organic solvents, carbonate-based compounds include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and any one selected from the group consisting of vinylene carbonate (VC), or a mixture of two or more thereof.
[63]
Further, examples of the propionate-based compound include ethyl propionate (EP), propyl propionate (PP), n-propyl propionate, iso-propyl propionate, n-butyl propionate, and iso-butyl propionate. any one selected from the group consisting of cypionate and tert-butyl propionate, or a mixture of two or more thereof.
[64]
In addition, as the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, 1,2 -Dimethoxyethane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester , trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. A magnetic organic solvent may be used.
[65]
The lithium salt included in the electrolyte of the present invention may be used without limitation, those commonly used in the electrolyte for a lithium secondary battery. For example, the lithium salt includes Li + as a cation, and F - , Cl - as an anion. , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , AlO 4 - , AlCl 4 - , PF 6 - , SbF 6 - , AsF 6 - , BF 2 C 2O 4 -, BC 4 O 8 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , C 4 F 9 SO 3 - , F 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (F 2 SO 2 ) 2 N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) ) 2 CH - , CF 3(CF 2 ) 7 SO 3 — , CF 3 CO 2 — , CH 3 CO 2 — , SCN — and (CF 3 CF 2 SO 2 ) 2 N — may include at least one selected from the group consisting of. The lithium salt may be used alone or as a mixture of two or more as needed. The lithium salt may be appropriately changed within the range that can be used in general, but may be included in the electrolyte at a concentration of 0.8 M to 1.5 M in order to obtain an optimal effect of forming a film for preventing corrosion of the electrode surface.
[66]
3 shows a battery cell manufactured according to the battery cell manufacturing step (S20) according to an embodiment of the present invention. Referring to FIG. 3 , the first pouch 120 may be divided into an accommodating part (not shown) for accommodating the electrode assembly and a gas pocket part 122 , and a accommodating part (not shown) of the first pouch 120 . The electrode assembly 110 is accommodated in the. The electrode assembly has an overhang region (A) introduced therein, and the first pouch is transparent, so that the electrode assembly accommodated inside the first pouch can be visually confirmed. In addition, the positive electrode tab and the negative electrode tab are drawn out of the first pouch 120 while being connected to the positive electrode lead 132 and the negative electrode lead 131 , respectively, and the positive electrode lead 132 is formed of three lead films. 141 , 142 , and 143 , and the negative lead 131 is also surrounded by three lead films 141 , 142 , 143 . And, since the battery cell manufacturing step (S20) includes a process of sealing the first pouch and the third lead film together, the first pouch 120 is heat-sealed together with the third lead film 143 to form the battery cell. is sealed.
[67]
The secondary sealing step (S30) includes a process of accommodating the battery cell in a second pouch and sealing the second pouch. Since the first pouch is used for observing the electrode assembly from the outside, it does not include a barrier layer due to the constraint to select a transparent material. Therefore, a certain amount of sealing force can be maintained with the first pouch, but since some of the internal gas or electrolyte generated during formation may leak out of the pouch, the battery cell sealed with the first pouch before proceeding with the formation process. A secondary sealing step of sealing with a second pouch is required.
[68]
In one specific example, the second pouch is a pouch of a laminate sheet including a barrier layer of aluminum. The second pouch has a structure including a material barrier aluminum barrier layer, a heat-sealable first resin layer, and a second resin layer as an outer coating layer. The second resin layer insulates the barrier layer from the outside and is formed of a material having excellent durability or rigidity to protect the laminate sheet pouch from the outside. The first resin layer is a polypropylene-based resin layer having excellent repeated fatigue resistance and chemical resistance, and may have a structure including unstretched polypropylene.
[69]
In one specific example, the second sealing step ( S30 ) includes sealing the second pouch and the first lead film together. By sealing the second pouch and the first lead film together, the sealing force between the electrode lead and the second pouch can be improved.
[70]
4 is a perspective view showing an embodiment of the battery cell after the secondary sealing step (S30) of the present invention. Referring to FIG. 4 , the battery cell after the secondary sealing step ( S30 ) is in a form in which the electrode assembly and the electrolyte are accommodated together in the first pouch, and the sealed battery cell is accommodated in the second pouch 150 . Therefore, the second pouch preferably has a volume by adding a little extra to the volume of the battery cells sealed by the first pouch so as to accommodate the battery cells sealed by the first pouch. The negative lead 131 and the positive lead 132 are drawn out of the second pouch 150 , respectively, and the negative lead 131 and the positive lead 132 are formed through the first lead film 141 . 2 is tightly sealed in the pouch (150).
[71]
The second pouch removal step (S40) is a step of forming the battery cell sealed with the second pouch, and removing the second pouch after the formation process. Formation herein refers to an initial charging process of charging at a predetermined state of charge (SOC) in order to activate a battery cell, and optionally pressurizing a battery cell to a predetermined pressure before or during initial charging or after initial charging. It should be understood as including the process. In addition, the predetermined filling rate may be SOC 10% to 70%, SOC 15% to 60%. The formation process may prevent a gas trap in which gas generated during initial charging is trapped inside the electrode assembly by performing pressurization at the same time as initial charging or before/after initial charging. When the formation process is completed, the first lead film is removed together with the second pouch.
[72]
The step of removing the gas pocket portion of the first pouch (S50) is a process of degassing and re-sealing the battery cell from which the second pouch is removed, and removing the gas pocket portion of the first pouch. includes
[73]
5 is a schematic diagram illustrating a battery cell from which a second pouch is removed according to the second pouch removal step ( S40 ). Referring to FIG. 5 , as the second pouch is removed, a battery cell sealed with the first pouch is obtained. Since the inside of the first pouch contains gas generated during the formation process, a degassing process is performed to discharge the internal gas to the outside of the battery cell. The internal gas generated during the formation process is collected by the gas pocket part. In the degassing process, a through-hole communicating with the inside is punched in the gas pocket part of the first pouch in order to discharge the captured gas to the outside, and the gas is passed through the through-hole. It includes the process of releasing When the exhaust of the gas is completed, the first pouch is re-sealed by a heat-sealing method along BB' between the receiving part and the gas pocket part, and the gas pocket part is cut and removed.
[74]
After the gas pocket portion of the first pouch is removed, the battery cell from which the gas pocket portion has been removed is accommodated in the third pouch and a completion step (S60) of sealing is performed. The completion step (S60) includes a process of accommodating and sealing the battery cell from which the gas pocket part of the first pouch has been removed in the inside of the third pouch provided with the viewing window.
[75]
The third pouch is the same as the second pouch, which is a laminate sheet pouch including an aluminum barrier layer. Since the material of the third pouch is the same as the material of the second pouch, a detailed description of the material of the second pouch is the same as described above, and thus a detailed description of the material of the third pouch will be omitted.
[76]
6 is a schematic diagram of a third pouch according to an embodiment of the present invention. The third pouch is characterized in that it is provided with a viewing window. Referring to FIG. 6 , the third pouch 160 is in the form of a pouch of a laminate sheet including a barrier layer of aluminum, a through hole is formed in a portion corresponding to the overhang region, and the through hole is a viewing window ( 162) becomes. In order to block the through hole serving as a sight window from the outside, a transparent film capable of covering the through hole area is covered. At this time, the transparent film is positioned inside the transparent film so that the entire area of ​​the through hole is included. The transparent film is preferably an acrylic film having excellent visibility. In addition, in order to fix the transparent film to the third pouch, the viewing window may be manufactured by attaching it to the third pouch using an adhesive tape or an adhesive along the edge of the transparent film. The shape of the viewing window may be rectangular or circular as shown in FIG. 6, but it is preferable to have a rectangular shape according to the shape of the battery cell.
[77]
The present invention provides a battery cell for evaluation of lithium precipitation behavior manufactured according to the manufacturing method. 7 shows a battery cell for evaluation of lithium precipitation behavior manufactured through the completion step (S60). Referring to FIG. 7 , a battery cell sealed by accommodating an electrode assembly in which an overhang region (A) in which the positive plate protrudes from the negative plate is introduced into the transparent pouch 120 and the electrolyte is sealed with a pouch 160 of an aluminum laminate sheet. As a cell, the pouch of the aluminum laminate sheet is provided with a viewing window at a portion corresponding to the overhang region. Specifically, the battery cell sealed by the first pouch 120 is accommodated in the third pouch 160 , and the third pouch 160 is formed with a positive lead 131 and a negative electrode by a second lead film 142 . It is sealed together with the lid 132 . In addition, the electrode assembly 110 having the overhang (A) region is visible from the outside of the third pouch through the look-ahead window 162 provided in the third pouch. Therefore, it is possible to perform electrochemical evaluation of the battery cell in real time while confirming the precipitation behavior of lithium in the overhang region through the viewing window.
[78]
In one specific example, the transparent pouch may be a pouch made of polyethylene terephthalate or polypropylene material.
[79]
In one specific example, the viewing window is formed by covering a through hole formed in a portion corresponding to the overhang region of the pouch of the aluminum laminate sheet with a transparent film, and the transparent film is preferably an acrylic film. The transparent film has a structure attached to the pouch of the aluminum laminate sheet using a polyimide-based adhesive tape.
[80]
[81]
[Example]
[82]
An electrode assembly (monocell) laminated with a separator interposed between the positive electrode and the negative electrode was prepared. At this time, the vertical length of the positive electrode was longer than the vertical length of the negative electrode, so that the overhang region in which the positive electrode protruded from the negative electrode was introduced.
[83]
A transparent pouch made of polyethylene terephthalate material is selected as the first pouch, the electrode assembly having the overhang area introduced therein is accommodated in the first pouch, and after injecting the electrolyte, 1/ the length of the electrode tab extending from the electrode assembly The first pouch was sealed with the third lead film covering the three points.
[84]
After selecting an aluminum laminate sheet of nylon/aluminum/polyethylene as the second pouch, and accommodating the sealed battery cell in the second pouch, the first lead film surrounding the upper end point of the length of the electrode tab extended from the electrode assembly The second pouch was sealed with
[85]
Then, after performing a formation process including primary charging of the battery cells for 3 hours at a charging rate of 0.1C, the second pouch together with the first lead film was removed.
[86]
After performing a degassing process for discharging the internal gas of the battery cell from which the second pouch has been removed, and re-sealing the boundary between the electrode assembly accommodating part and the gas pocket part of the first pouch, the gas of the first pouch The pocket part was removed.
[87]
A third pouch provided with a viewing window shown in FIG. 6 was prepared. The third pouch has a through hole formed in a part of the same laminate sheet as the second pouch, and after covering the transparent acrylate film on the through hole, the transparent film is attached to the third pouch using a polyimide adhesive tape. made to be fixed.
[88]
The battery cell from which the gas pocket part was removed was accommodated in the third pouch, but the overhang area could be observed through the viewing window. Thereafter, the third pouch was sealed together with the second lead film covering 2/3 of the length of the electrode tab extended from the electrode assembly to complete the manufacture of the battery cell for evaluation of lithium precipitation behavior.
[89]
[90]
[Experimental example]
[91]
The lithium precipitation behavior of the overhang region was observed in real time through the viewing window while charging the battery cell for evaluation of the lithium precipitation behavior prepared in the above example (CC charging at 0.1 C, 8.25 mA, 4.3 V). is shown in FIGS. 8 to 9 .
[92]
8 shows that the profile of potential and capacity according to the charging condition is divided into sections (A) to (D), and FIG. 9 is an overhang area for each section of (A) to (D) of FIG. 8 . it's one picture
[93]
8 to 9 , lithium was not precipitated until section (A), but in (B), a trace amount of lithium started to precipitate, and in section (C), lithium was continuously released at the point where the lithium was deposited. was precipitated, and in the section (D), it was observed that the lithium precipitation amount was larger than that in (C).
[94]
In the battery cell for evaluating lithium precipitation behavior of the present invention, while charging and discharging the battery cell for evaluating lithium precipitation behavior, the lithium precipitation behavior can be observed in real time through a viewing window, and according to the electrochemical state of the battery cell Lithium precipitation behavior can be confirmed.
Claims
[Claim 1]
An electrode assembly manufacturing step (S10) of manufacturing an electrode assembly in which an overhang region in which the positive electrode protrudes from the negative electrode is introduced; A battery cell manufacturing step (S20) of accommodating the electrode assembly in a first pouch, injecting an electrolyte, and then sealing the battery cell; a secondary sealing step (S30) of accommodating the battery cell in a second pouch and performing secondary sealing; a second pouch removing step (S40) of forming the secondary sealed battery cell and removing the second pouch; a gas pocket removing step (S50) of degassing and re-sealing the battery cell from which the second pouch is removed, and removing the gas pocket of the first pouch; and a completion step (S60) of accommodating and sealing the battery cell from which the gas pocket part has been removed in a third pouch having a viewing window.
[Claim 2]
The lithium according to claim 1, wherein the electrode assembly includes one or a plurality of bi-cell units having a positive/negative electrode/anode structure or a mono-cell unit having a positive/negative electrode structure. A method of manufacturing a battery cell for evaluation of precipitation behavior.
[Claim 3]
The method according to claim 1, wherein the positive lead and the negative lead included in the electrode assembly are each wrapped with three lead films, and the third lead film, the second lead film, and the first lead film are in the order closest to the electrode assembly. A method of manufacturing a battery cell for evaluation of phosphorus lithium precipitation behavior.
[Claim 4]
The method of claim 3, wherein in the battery cell manufacturing step (S20), the first pouch and the third lead film are sealed together.
[Claim 5]
The method of claim 3, wherein in the secondary sealing step (S30), the second pouch and the first lead film are sealed together.
[Claim 6]
The method of claim 3, wherein in the completion step (S60), the third pouch and the second lead film are sealed together.
[Claim 7]
The method of claim 1 , wherein the first pouch is a pouch made of polyethylene terephthalate or polypropylene in which the electrode assembly housed therein is visible.
[Claim 8]
The method of claim 1, wherein the second pouch is a pouch of a laminate sheet including a barrier layer of aluminum.
[Claim 9]
The method of claim 1, wherein the third pouch is a laminate sheet pouch including a barrier layer of aluminum, and in the third pouch, a through hole is formed in a portion corresponding to the overhang region to form the through hole. A method of manufacturing a battery cell for evaluating lithium precipitation behavior, characterized in that the viewing window is formed by covering the acrylic film.
[Claim 10]
Preparing a battery cell for evaluation of lithium precipitation behavior according to claim 1; and charging and discharging the prepared battery cell for evaluating lithium precipitation behavior, and observing the lithium precipitation behavior in the overhang region through the viewing window in real time.
[Claim 11]
A battery cell in which an electrode assembly in which an overhang region in which a positive electrode plate protrudes from a negative electrode plate is introduced into a transparent pouch and a battery cell sealed by accommodating an electrolyte solution is sealed with a pouch of an aluminum laminate sheet, wherein the pouch of the aluminum laminate sheet is in the overhang region A battery cell for evaluating lithium precipitation behavior, which is provided with a viewing window at a corresponding part, and performs electrochemical evaluation while confirming lithium deposition behavior in an overhang region through the viewing window.
[Claim 12]
The battery cell for evaluating lithium precipitation behavior according to claim 11, wherein the transparent pouch is a pouch made of polyethylene terephthalate or polypropylene material.
[Claim 13]
The battery cell for evaluating lithium precipitation behavior according to claim 11, wherein the viewing window is formed by covering a transparent film on a through hole formed in a portion corresponding to the overhang region in the pouch of the aluminum laminate sheet.
[Claim 14]
The battery cell for evaluating lithium precipitation behavior according to claim 13, wherein the transparent film is an acrylic film.
[Claim 15]
The battery cell for evaluating lithium precipitation behavior according to claim 13, wherein the transparent film is attached to the pouch of the aluminum laminate sheet using a polyimide-based adhesive tape.