KR102282925B1 - Method for Electrolyte Injection of Two-step Vacuum - Google Patents

Abstract

The present invention is a method of injecting an electrolyte into a battery cell in which an electrode assembly is embedded in a receiving part of a battery case and an electrolyte injection port is not sealed in a battery cell manufacturing process,
(a) an arrangement process of disposing the unsealed battery cell in an injection chamber connected to an injection tank for storing an electrolyte;
(b) a first decompression process of vacuum suction until the pressure in the injection chamber becomes a first vacuum state;
(c) a second decompression process of increasing the pressure until the pressure in the injection chamber becomes a second vacuum state;
(d) an injection process of injecting the electrolyte of the injection tank through the injection port of the unsealed battery cell while maintaining the second vacuum state; and
(e) a venting process of releasing the vacuum state of the injection chamber so that the pressure in the injection chamber is in equilibrium with the atmospheric pressure;
It relates to an electrolyte injection method comprising a.

Description

{Method for Electrolyte Injection of Two-step Vacuum}

The present invention relates to a method for injecting an electrolyte in a two-stage vacuum.

With the increase in technology development and demand for mobile devices, the demand for secondary batteries is also rapidly increasing. Among them, lithium secondary batteries with high energy density and operating voltage and excellent preservation and lifespan characteristics are used in various electronic products as well as various mobile devices. It is widely used as an energy source.

A lithium secondary battery has a structure in which an electrolyte containing lithium salt is impregnated in an electrode assembly with a porous separator interposed between a positive electrode and a negative electrode, each of which is coated with an active material on a current collector. The positive active material is mainly composed of lithium cobalt-based oxide, lithium manganese-based oxide, lithium nickel-based oxide, lithium composite oxide, and the like, and the negative active material is mainly composed of carbon-based material. During charging, lithium ions from the positive electrode active material are released and inserted into the carbon layer of the negative electrode. On the contrary, during discharging, lithium ions from the negative electrode carbon layer are released and inserted into the positive electrode active material. At this time, the electrolyte moves lithium ions between the negative electrode and the positive electrode. It acts as a facilitating medium.

Therefore, in order for the secondary battery including the electrode assemblies as described above to have high capacity and high energy density and to maintain a long lifespan, the electrode assembly interposed inside the battery is completely immersed in the electrolyte so that the electrode reaction between the electrodes can occur actively. When the electrode assembly is incompletely impregnated with the electrolyte, the reaction between the electrodes is not smooth, so the resistance increases and the output characteristics and the capacity of the battery rapidly drop, which causes deterioration of battery performance and shortening of lifespan, as well as high resistance. is exposed to the risk of battery deterioration or explosion.

The electrolyte is injected into the battery in the last stage of manufacturing a lithium secondary battery, and in general, the electrolyte is a polar solvent having a polarity capable of effectively dissolving and dissociating electrolyte salts, and is an aprotic solvent that does not have active hydrogen. These electrolytes often have high viscosity and surface tension due to extensive interactions within the electrolyte, so it is difficult to penetrate into the electrode assembly stacked at high density or wound in a stacked state, and thus a long time is required to impregnate the electrolyte do it with

Therefore, in order to improve the performance and safety of the secondary battery, research on various methods for increasing the electrolyte impregnation property of the electrode assembly has been continuously conducted.

1 illustrates a process for a process of impregnating an electrolyte in a conventional vacuum chamber.

Referring to FIG. 1 , in the process (a), an unsealed battery cell 20 in which an electrolyte injection port having an electrode assembly (not shown) embedded in the battery case is not mounted is placed in a chamber 30, and the pressure in the chamber is reduced to 40 to 100 Torr, and the internal pressure of the unsealed battery cell 20 is maintained until equilibrium with the pressure in the chamber, and then the electrolyte is introduced into the battery case of the unsealed battery cell 20 in the process (b). When the injection is completed, the vent is vented to release the vacuum state of the chamber 30 in step (c) and pressure is applied to induce the electrolyte to be evenly impregnated into the electrode active material in the unsealed battery cell.

However, in this conventional injection method, the process (a) proceeds at a pressure within the above range in consideration of electrolyte evaporation, etc. In the above range, the pressure in the chamber and the pressure inside the unsealed battery cell are approximately equal to each other. Since it takes more than 1 minute, there is a problem in that the overall process time of the electrolyte injection is lengthened by such a process.

In addition, in order to shorten the process time, when the interval between the vacuum decompression process (a) and the injection process (b) is shortened in terms of process equipment, a large number of gases in the unsealed battery cell exist, so that the electrolyte impregnation is difficult. This is not easily achieved, so there is a limit to the impregnation of the electrolyte into the electrode elements.

Accordingly, there is a high need for a technology capable of improving the electrolyte impregnation property while shortening the process time in the battery cell manufacturing process.

An object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, it is an object of the present invention to provide an electrolyte injection method capable of improving electrolyte impregnation while shortening the electrolyte injection process time by applying a two-stage vacuum decompression process before injecting the electrolyte in the electrolyte injection method will do

The electrolyte injection method according to the present invention for achieving this object,

A method of injecting an electrolyte into a battery cell in which an electrode assembly is embedded in a receiving part of a battery case and an electrolyte injection port is not sealed in the manufacturing process of a battery cell,

(a) an arrangement process of disposing the unsealed battery cell in an injection chamber connected to an injection tank for storing an electrolyte;

(b) a first decompression process of vacuum suction until the pressure in the injection chamber becomes a first vacuum state;

(c) a second decompression process of increasing the pressure until the pressure in the injection chamber becomes a second vacuum state;

(d) an injection process of injecting the electrolyte of the injection tank through the injection port of the unsealed battery cell while maintaining the second vacuum state; and

(e) a venting process of releasing the vacuum state of the injection chamber so that the pressure in the injection chamber is in equilibrium with the atmospheric pressure;

It is characterized in that it includes.

In general, the gas flow rate is affected by pressure. Specifically, as shown in the following chemical formula, the gas flow rate is inversely proportional to the viscosity, and the viscosity is proportional to the pressure, and the gas flow rate is also inversely proportional to the pressure. The flow rate slows down.

Therefore, when vacuum pressure reduction is attempted or the pressure is increased by injecting gas to remove gases such as air present in the unsealed battery cell, the rate at which the gas flows out or the rate at which the gas flows into the cell is low. In particular, as the pressure outside the unsealed battery cell is lower, the gas present inside the unsealed battery cell escapes faster, and the pressure equilibration time between the outside and the inside of the unsealed battery cell is shortened.

As such, when the equilibration time of the unsealed battery cell is shortened, the time of the vacuum decompression process in the step for injecting the entire electrolyte is also shortened, thereby increasing the manufacturing efficiency.

In addition, when the manufacturing time is set to be short, the higher the pressure in the chamber, the longer the pressure equilibration time inside and outside the unsealed battery cell. Since the electrolyte is injected with more gas present in Since the vacuum state can be sufficiently reached to the inside of the sealing battery cell, there is an effect of improving the electrolyte impregnation property.

However, as the external pressure is lower, the vapor pressure point of the electrolyte is lowered, so that when the pressure is too low, for example, ^{when the pressure is 1x10 -3} to 1 Torr, evaporation of the electrolyte may occur. This is because, in general, evaporation starts at 30 to 80 Torr depending on the type of electrolyte at room temperature.

Therefore, conventionally, in consideration of electrolyte evaporation, mass-production was applied at a low vacuum level of 40 to 100 Torr. In the above range, the gas flow rate fell, and the equilibration time of the external and internal pressures of the unsealed battery cell was about 1 minute, so the impregnation effect The decompression process was carried out for 30 to 90 seconds to maximize

Accordingly, the inventors of the present application developed a two-stage vacuum electrolyte injection method as described above after repeated in-depth research.

Specifically, the pressure in the first vacuum state in the process (b) may be 1x10 ^-3 to 1 Torr, and the pressure in the second vacuum state in the process (c) may be 40 to 100 Torr.

That is, first, the pressure is ^{greatly reduced to 1x10 -3} to 1 Torr to speed up the gas flow rate, thereby greatly reducing the time required to reach the pressure equilibrium to the inside of the unsealed battery cell, while increasing the pressure to 40 to 100 Torr before injecting the electrolyte. This is to prevent the electrolyte from evaporating.

Out of the above range, if the pressure in the first vacuum state is too low, a high-spec pump must be used to further lower it even though the pressure equilibrium time is sufficiently shortened within the above range, so the cost-effectiveness is not good, and if it is too high, the time to reach the pressure equilibrium state If the pressure in the second vacuum state is too low, it takes time to evaporate the electrolyte, and if it is too high, it takes time to reach the equilibrium state again, and the gas remains inside the unsealed battery cell, so that the electrolyte injection is difficult. Not easy.

Specifically, by setting the pressure of the second vacuum to be equal to or greater than the vapor pressure of the electrolyte at the temperature of the injection process, and more specifically, 105% to 120% of the vapor pressure of the electrolyte at the temperature of the injection process, thereby preventing the evaporation of the electrolyte to facilitate the electrolyte solution It can be made to be impregnated.

Here, the temperature of the electrolyte in the pouring process may be room temperature, specifically, 20 to 25 degrees Celsius.

In this way, when the decompression process before the electrolyte injection process is applied as a two-stage vacuum process, the time to reach the pressure equilibrium state inside/outside the unsealed battery cell can be greatly reduced while preventing the electrolyte from evaporating during the electrolyte injection.

The decompression process in the general mass production process is performed at a pressure of 40 to 100 Torr, and since it takes a considerable amount of time for the pressure inside the unsealed battery cell and the injection chamber to reach an equilibrium state, it is finished before this, and the injection this begins

However, according to the injection method of the present invention, since the pressure in the first vacuum state in the first decompression process is very low and the flow rate of the gas is very fast, the process (b) is the internal pressure of the unsealed battery cell in the injection chamber. It may include a process of maintaining the first vacuum state until it reaches the equilibrium state with the pressure, at this time, the time it takes for the internal pressure of the unsealed battery cell and the pressure in the injection chamber to reach the equilibrium state is less than 3 seconds , in detail, it can be done within 1 second.

Similarly, the process (c) may also include a process of maintaining the second vacuum state until the internal pressure of the unsealed battery cell reaches an equilibrium state with the pressure in the injection chamber.

The pressure of the second vacuum state proceeds to a pressure of 40 to 100 Torr, as in the conventional method, but is not reduced from atmospheric pressure, but ^{by raising the pressure from 1x10 -3} to 1 Torr, the pressure of the first vacuum state. , since the pressure inside the unsealed battery cell also reaches the pressure of the second vacuum state from the pressure of the first vacuum state, a lot of time is not required to reach the equilibrium state again.

Specifically, the time it takes for the internal pressure of the unsealed battery cell and the pressure in the injection chamber to reach an equilibrium state in the process (c) may be made within 3 seconds, specifically within 1 second.

Therefore, according to the present invention, the time required for the entire depressurization process can be within 10 seconds, specifically within 5 seconds, so that the entire process time can be significantly reduced, thereby reducing and maintaining the pressure inside the existing chamber. Even when applied to the mass production process set within 5 seconds, the electrolyte injection is performed in a state in which the first vacuum state and the second vacuum state are sufficiently reached to the inside of the unsealed battery cell, so that the electrolyte impregnation property can be maximized.

On the other hand, this electrolyte injection, for mass production, can proceed to a large amount of unsealed battery cells at a time, specifically, two or more unsealed battery cells are arranged in the injection chamber, and can be injected simultaneously.

The configuration of the electrolyte injection chamber and the method of injecting the electrolyte may include all configurations disclosed in the art, and detailed descriptions thereof will be omitted herein.

The electrolyte used in the method may also include all of the components disclosed in the art, for example, may be a lithium salt-containing non-aqueous electrolyte, and specifically, the lithium salt-containing non-aqueous electrolyte is a polar organic electrolyte and a lithium salt consists of As the electrolyte, a non-aqueous liquid electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous liquid electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo An aprotic organic solvent such as a nate derivative, a tetrahydrofuran derivative, an ether, methyl pyropionate, or ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymer containing an ionic dissociation group or the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _{2 and the like may be used.}

The lithium salt is a material easily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide there is.

In addition, for the purpose of improving charge/discharge characteristics, flame retardancy, etc. in the non-aqueous electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide , nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. may be In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics.

When the injection of the electrolyte is completed, the vacuum state of the injection chamber may be released so that the pressure in the injection chamber is in equilibrium with the atmospheric pressure.

This release method may include all of the previously disclosed methods, for example, may be performed to introduce external air by including a vent part of the chamber, or may be performed by removing a vacuum hose for decompression.

When vented in this way, external air is introduced into the chamber to apply pressure to the unsealed battery cell, and by this pressure, the electrolyte can be more evenly impregnated into the electrode elements inside the unsealed battery cell.

In addition, in the injection method of the present invention, in order to further improve the electrolyte impregnation property inside the unsealed battery cell, after the process (e),

(f) vacuum suction and maintaining the pressure in the injection chamber to be in a third vacuum state of a pressure lower than atmospheric pressure; and

(g) a gas injection process of injecting gas into the unsealed battery cell;

may further include.

At this time, the pressure of the third vacuum state of the process (f) may be 40 Torr to 760 Torr, and the gas of the process (g), a separate gas may be injected, but in detail, the process of venting It may be air that is naturally introduced through the

That is, the process of reducing the pressure and venting may be repeated. This is called a vacuum impregnation process.

By repeating the above processes (f) and (g), the electrolyte can penetrate more deeply into the electrode elements in the unsealed battery cell to improve the electrolyte impregnability.

After the above process, the battery cell can be manufactured by finally sealing the electrolyte injection port of the unsealed battery cell.

Accordingly, the present invention provides a battery cell manufactured through the electrolyte injection method.

As described above, the battery cell has a structure in which the electrode assembly is embedded in the receiving part of the battery case, and then the electrolyte is impregnated by injecting the electrolyte.

The electrode assembly includes all of the configurations disclosed in the art, but for example, a plurality of positive electrodes, negative electrodes and separators are stacked, or laminated and wound so that a separator is interposed between the positive electrode, the negative electrode and the positive electrode and the negative electrode. manufactured by doing

In this case, the positive electrode, for example, is prepared by coating a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector and then drying, and, if necessary, further adding a filler to the mixture.

The positive electrode current collector is generally made to have a thickness of 3 micrometers or more and 500 micrometers or less. The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. Carbon, nickel, titanium, silver or the like surface-treated may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven body are possible.

The cathode active material may _{include a layered compound such as lithium cobalt oxide (LiCoO 2} ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO _{2 ;} lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, lithium manganese composite oxide represented by Ni, Cu or Zn; _{LiMn 2} O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; And the like Fe ₂ (MoO _{4) 3,} but is not limited to these.

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; A conductive material such as a polyphenylene derivative may be used.

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 , polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluororubber, various copolymers, and the like.

The filler is optionally used as a component for inhibiting the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. For example, an olipine-based polymer such as polyethylene or polypropylene; A fibrous material such as glass fiber or carbon fiber is used.

The negative electrode is manufactured by coating and drying the negative electrode active material on the negative electrode current collector, and if necessary, the above-described components may be optionally further included.

The negative electrode current collector is generally made to have a thickness of 3 micrometers or more and 500 micrometers or less. Such a negative current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, etc. on the surface, an aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding force 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 film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

Examples of the negative electrode active material include 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 ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as _{Bi 2} O _{5 ;} conductive polymers such as polyacetylene; A Li-Co-Ni-based material or the like can be used.

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-resistant 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.

The battery case may be a pouch-type case having a laminate structure including a metal layer and a resin layer.

As a specific example of the battery case, the battery case is composed of a laminate sheet including an excellent durable resin outer layer, a barrier metal layer, and a heat meltable resin sealant layer, and the resin sealant layers are thermally fused to each other. can

Since the resin outer layer has to have excellent resistance from the external environment, it is necessary to have a tensile strength and weather resistance of at least a predetermined level. In this respect, polyethylene terephthalate (PET) and a stretched nylon film may be preferably used as the polymer resin of the outer resin layer.

Preferably, aluminum may be used for the barrier metal layer to exhibit a function of improving the strength of the battery case in addition to the function of preventing the inflow or leakage of foreign substances such as gas and moisture.

The resin sealant layer has heat-sealing properties (thermal adhesive properties), low hygroscopicity to suppress the penetration of the electrolyte, and a polyolefin-based resin that is not expanded or eroded by the electrolyte may be preferably used, and more Preferably, unstretched polypropylene (CPP) may be used.

As described above, in the electrolyte injection method according to the present invention, in depressurizing the unsealed battery cell in the injection chamber before injecting the electrolyte, a two-stage vacuum decompression process of performing a low vacuum after a medium vacuum is applied. By significantly reducing the time it takes for the pressure inside and outside the unsealed battery cell to reach an equilibrium state, the time of the entire electrolyte injection process can be shortened, and the electrolyte impregnation property can be improved.

1 is a schematic diagram of a process of impregnating an electrolyte in a conventional vacuum chamber;
Figure 2 is a graph showing the process of the electrolyte injection method according to Example 1 of the present invention;
3 is a graph showing the process of the electrolyte injection method according to Comparative Example 1 of the present invention;
4 is a graph showing the process of the electrolyte injection method according to Comparative Example 2 of the present invention.

Hereinafter, it will be described in more detail with reference to embodiments according to the present invention, but the scope of the present invention is not limited thereto.

<Production Example 1>

Anode active material (Graphite), conductive material (Denka black), and binder (PVdF) were put into NMP in a weight ratio of 92: 3: 5 and mixed to prepare a negative electrode mixture, and the negative electrode mixture was coated on 8 μm thick copper foil Then, the negative electrode was prepared by rolling and drying.

In addition, as a positive electrode, LiNi _0.4 Mn _0.3 Co _0.3 O ₂ was used as a positive electrode active material, and a conductive material (Denka black) and a binder (PVdF) were put into NMP in a weight ratio of 88: 8.5: 3.5, respectively, and mixed, followed by mixing. It was coated on aluminum foil, rolled and dried to prepare a positive electrode.

An electrode assembly was prepared by interposing a polyethylene porous membrane (Asahi, thickness: 16 μm) as a separator between the prepared negative electrode and the positive electrode, and this was embedded in a battery case.

<Experimental Example 1>

In order to measure the time to reach equilibrium, after placing the battery case in which the electrode assembly is embedded in the injection chamber, the external pressure in the injection chamber and the internal pressure of the battery case reach equilibrium while varying the pressure in the injection chamber. The time required for the amount of electrolyte impregnation to converge and no longer increase was measured, and the results are shown in Table 1 below.

0.1 Torr 80 Torr 230 Torr 380 Torr Time required (s) ≤1 60 180 300

Referring to Table 1, it can be seen that as the pressure of the injection chamber is lowered, the time required until the internal pressure and the external pressure of the battery case are balanced is much shorter. Therefore, it can be seen that, in order to maximize the electrolyte impregnation property before injection of the electrolyte, when the internal and external pressures of the battery case are maintained until the equilibrium is reached, the lower the pressure, the shorter the process time.

<Example 1>

Propylene carbonate (PC): dimethyl carbonate (DMC): ethylmethyl carbonate (EMC) 20: 40: _{Prepare a liquid electrolyte in which LiPF 6} is dissolved at 1M in a solvent mixed at 40 vol% and stored in the injection tank connected to the injection chamber and prepared.

As in the schematic diagram of the injection method of FIG. 2, after placing the battery case in which the electrode assembly is embedded in the injection chamber, 1-0.1 After reducing the pressure inside the injection chamber by setting the pressure of Torr, the pressure was raised so that the pressure in the injection chamber became 40 to 100 Torr after about 1 second, and after about 1 second, the electrolyte stored in the injection tank was injected into the battery case. The time taken from the decompression to the start of the injection was made to be less than 5 seconds in total.

When the injection was completed, the vacuum state of the injection chamber was released, the pressure in the injection chamber was increased to atmospheric pressure, and the injection process was completed by leaving it to stand for 1 minute.

<Comparative Example 1>

As in the schematic diagram of the injection method of FIG. 3 , in Example 1, after placing the battery case in which the electrode assembly is embedded in the injection chamber, 40 to 100 After reducing the pressure inside the injection chamber by setting the pressure of Torr, the electrolyte stored in the injection tank was injected into the battery case after about 3 seconds. The injection process was completed in the same way, except that the time taken from decompression to starting injection was less than 5 seconds in total.

<Comparative Example 2>

As in the schematic diagram of the injection method of FIG. 4, after placing the battery case in which the electrode assembly is embedded in the first embodiment in the injection chamber, 1-0.1 After depressurizing the inside of the injection chamber by setting the pressure of Torr, the electrolyte stored in the injection tank was injected into the battery case after 3 seconds. The injection process was completed in the same way, except that the time taken from decompression to starting injection was less than 5 seconds in total.

<Experimental Example 2>

The amount of injection was confirmed by measuring the weight before and after injection of the battery cases in which the electrolyte injection of Example 1 and Comparative Examples 1 and 2 was completed, and thereafter, secondary batteries were manufactured by sealing the injection port, and the remaining after being impregnated for each waiting time. The amount of impregnation was confirmed by discharging the electrolyte, and the results are shown in Table 1 below.

Injection amount (g) 1 hour standby impregnation amount (g) 10 hours standby impregnation amount (g) Example 1 8.2g 4.5g 7.2g Comparative Example 1 8.2g 3.2g 6.0g Comparative Example 2 6.8g 4.2g 6.1g

Referring to Table 2, the battery of Example 1 according to the present invention had an impregnation amount of 4.5 g for 1 hour, while the battery of Comparative Example 1 had an impregnation amount of 3.2 g, showing a decrease in the amount of electrolyte impregnation by about 1.3 g. In addition, the 10 hours atmospheric impregnation amount also shows a similar difference in the electrolyte impregnation amount.

This is, as shown in Table 1, the higher the pressure, the slower the gas flow rate, and in Comparative Example 1, it takes about 1 minute for the pressure inside the unsealed battery cell to equilibrate with the external pressure, In fact, in order to reduce the electrolyte injection time, the electrolyte is injected in a state where equilibrium is not achieved, that is, the gas inside the unsealed battery cell is not completely removed, so the electrolyte impregnation property is poor.

On the other hand, the injection amount of Comparative Example 2 is 6.8 g, and the injection amount itself is 1.4 g lower than that of Example 1 and Comparative Example 1. This is because the pressure of 1 to 0.1 Torr is lower than the vapor pressure of the electrolyte, so the electrolyte is injected at this pressure This is because the electrolyte evaporates.

Those of ordinary skill in the art to which the invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (14)

A method of injecting an electrolyte into a battery cell in which an electrode assembly is embedded in a receiving part of a battery case and an electrolyte injection port is not sealed in the manufacturing process of a battery cell,
(a) an arrangement process of disposing the unsealed battery cell in an injection chamber connected to an injection tank for storing an electrolyte;
(b) a first decompression process of vacuum suction until the pressure in the injection chamber becomes a first vacuum state;
(c) a second decompression process of increasing the pressure until the pressure in the injection chamber becomes a second vacuum state;
(d) an injection process of injecting the electrolyte of the injection tank through the injection port of the unsealed battery cell while maintaining the second vacuum state; and
(e) including a venting process of releasing the vacuum state of the injection chamber so that the pressure in the injection chamber is in equilibrium with atmospheric pressure,
The pressure in the first vacuum state of the process (b) is 1x10 ^-3 to 1 Torr, the pressure in the second vacuum state of the process (c) is 40 to 100 Torr,
After process (e),
(f) vacuum suction and maintaining the pressure in the injection chamber to be in a third vacuum state of a pressure lower than atmospheric pressure; and
(g) a gas injection process of injecting gas into the unsealed battery cell;
Electrolyte injection method, characterized in that it further comprises. delete The method according to claim 1, wherein the pressure in the second vacuum state is equal to or higher than the vapor pressure of the electrolyte at the temperature of the pouring process. The electrolyte injection method according to claim 3, wherein the pressure in the second vacuum state is 105% to 120% of the vapor pressure of the electrolyte at the temperature of the injection process. [4] The method of claim 3, wherein the temperature of the electrolyte in the pouring process is 20 to 25 degrees Celsius. The electrolyte injection method according to claim 1, wherein the step (b) comprises maintaining the first vacuum state until the internal pressure of the unsealed battery cell reaches an equilibrium state with the pressure in the injection chamber. [Claim 7] The method according to claim 6, wherein in the step (b), the time required for the internal pressure of the unsealed battery cell and the pressure in the injection chamber to reach an equilibrium state is within 3 seconds. The method of claim 1, wherein the step (c) comprises maintaining the second vacuum state until the internal pressure of the unsealed battery cell reaches an equilibrium state with the pressure in the injection chamber. The method of claim 8, wherein in the step (c), the time required for the internal pressure of the unsealed battery cell and the pressure in the injection chamber to reach an equilibrium state is within 3 seconds. The electrolyte injection method according to claim 1, wherein two or more unsealed battery cells are disposed in the injection chamber to simultaneously inject the electrolyte. delete The method according to claim 1, wherein the pressure in the third vacuum state in step (f) is 40 Torr to 760 Torr. The method of claim 1, wherein the gas in step (g) is air. delete

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