A lithium secondary battery that allows for additional electrolyte injection

Abstract

The present invention relates to a technology relating to a lithium secondary battery capable of injecting additional electrolyte, and includes an electrolyte refill unit having a packaging material filled with spare electrolyte, and a rupture member disposed adjacent to the electrolyte refill unit and configured to deform in response to a temperature change to form a hole in the packaging material and inject the spare electrolyte from inside the electrolyte refill unit.

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0163410, filed November 24, 2021.

[0002] The present invention relates to a lithium secondary battery that allows additional injection of an electrolyte. [Background technology]

[0003] Generally, a lithium secondary battery has a structure in which a separator is interposed between a positive electrode and a negative electrode as power generating elements, and a liquid electrolyte is injected between the elements.

[0004] A commonly used pouch-type battery is manufactured by accommodating an electrode assembly consisting of a positive electrode, a separator, and a negative electrode in a pouch-type battery case made of a polymer resin and aluminum laminate sheet, bonding an upper laminate sheet and a lower laminate sheet in a state in which the electrode leads are exposed at both ends of the battery case, and then sealing the battery case by thermocompression.

[0005] On the other hand, when a secondary battery continues to be repeatedly charged and discharged, the electrolyte undergoes side reactions and other such changes, causing a shortage of electrolyte in the battery, which shortens the life of the secondary battery.

[0006] Prismatic or cylindrical lithium-ion secondary batteries have cell casings made of metallic materials, so the cells must be disassembled to inject additional electrolyte. However, if the electrodes are exposed to air when the cells are disassembled, they may be oxidized. In addition, there are disadvantages in that it is difficult to reseal the cells after injecting additional electrolyte.

[0007] Korean Patent Publication No. 10-2018-0023706 discloses a technology for refilling electrolyte without disassembling a battery, which includes a sealing member for refilling electrolyte formed in a part of the battery case to inject electrolyte into an electrolyte container of the battery case and seal the injection site. However, the sealing member makes the battery assembly process complicated, and electrolyte must be injected for each battery. This is a drawback.

[0008] Therefore, there is a need to develop a technology that can supply additional electrolyte in a safer and more convenient manner. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a lithium ion secondary battery having a novel structure that can supply additional electrolyte when the cell deteriorates in order to extend the life of the lithium secondary battery.

[0010] The present invention also provides a method for additionally supplying an electrolyte to the lithium ion secondary battery. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, a lithium secondary battery according to one embodiment of the present invention is a lithium secondary battery that accommodates an electrode assembly and a main electrolyte inside a battery case, and includes an electrolyte refill unit in which a spare electrolyte is filled inside a packaging material, and a rupture member that is disposed adjacent to the electrolyte refill unit and is configured to deform due to a change in temperature to form a hole in the packaging material and inject the spare electrolyte inside the electrolyte refill unit.

[0012] In the lithium secondary battery according to one embodiment of the present invention, the packaging member may be a pouch-type material made of a thermoplastic synthetic resin film.

[0013] In the lithium secondary battery according to one embodiment of the present invention, the packaging member may be made of a polyethylene resin film.

[0014] In the lithium secondary battery according to an embodiment of the present invention, the electrolyte refill unit and the rupture member may be stacked on the electrode assembly and disposed adjacent to an upper surface or a lower surface of the battery case.

[0015] In the lithium secondary battery according to an embodiment of the present invention, the electrolyte refill unit and the rupture member may be disposed in a side wall of the battery case, which is a dead space near an end of the electrode assembly.

[0016] In the lithium secondary battery according to one embodiment of the present invention, the rupture member may be disposed between the electrolyte refill unit and the battery case.

[0017] In the lithium secondary battery according to one embodiment of the present invention, the rupture member can be thermally deformed at a temperature of 80°C to 120°C.

[0018] In the lithium secondary battery according to one embodiment of the present invention, the rupture member may be a shape memory alloy.

[0019] In the lithium secondary battery according to an embodiment of the present invention, the rupture member may be a bimetal.

[0020] In the lithium secondary battery according to an embodiment of the present invention, the rupture member may be joined to an electrolyte refill unit, and the packaging member may be formed with a fragile portion along an edge direction of the rupture member.

[0021] In the lithium secondary battery according to one embodiment of the present invention, the spare electrolyte does not need to contain an additive for forming an SEI film.

[0022] In the lithium secondary battery according to one embodiment of the present invention, the battery case may be a cylindrical metal can or a rectangular metal can.

[0023] A method for refilling an electrolyte in a lithium secondary battery according to an embodiment of the present invention includes applying heat to the lithium secondary battery to cause thermal deformation of the rupture member.

[0024] In the method for refilling an electrolyte for a lithium secondary battery according to one embodiment of the present invention, the temperature at which heat is applied to the rupture member may be 80°C to 120°C. Effect of the Invention

[0025] The lithium secondary battery according to the present invention includes an electrolyte refill unit filled with spare electrolyte in preparation for depletion of the electrolyte, and a rupture member that can deform within a predetermined temperature range to form a hole in the surface of the electrolyte refill unit. When a decrease in capacity or a sudden increase in resistance is observed due to repeated charging and discharging of the lithium secondary battery, the rupture member penetrates the surface of the electrolyte refill unit through heat treatment of the lithium secondary battery, and additional electrolyte is replenished inside the electrolyte refill unit, thereby extending the life of the secondary battery.

[0026] Furthermore, the lithium secondary battery according to the present invention has an advantage that it is not necessary to disassemble the secondary battery in order to replenish the electrolyte. [Brief description of the drawings]

[0027] [Figure 1] 1 is a cross-sectional view illustrating a structure of a pouch-type secondary battery according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a cross-sectional view of a lithium secondary battery in which the electrolyte has been depleted. [Diagram 3] 1 is a cross-sectional view of a lithium secondary battery in which a spare electrolyte from an electrolyte refill unit is charged inside the battery; [Figure 4] 4 is a graph showing the capacity retention rate as a function of the number of cycles for a lithium secondary battery according to an embodiment of the present invention. [Diagram 5] 4 is a graph showing a resistance increase rate according to the number of cycles for a lithium secondary battery according to an embodiment of the present invention. [Figure 6]4 is a graph showing resistance according to the depth of charge for a lithium secondary battery according to an embodiment of the present invention and a secondary battery according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Since the present invention can be modified in various ways and has various embodiments, a specific embodiment will be illustrated and described in detail in the detailed description. However, this is not intended to limit the present invention to the specific embodiment, and should be understood as including all modifications, equivalents, or alternatives within the spirit and technical scope of the present invention.

[0029] The terms used in the present invention are merely used to describe certain embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise. In the present invention, the terms "include" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0030] The lithium secondary battery of the present invention includes an electrode assembly and a main electrolyte inside a battery case.

[0031] The electrode assembly is a power generating element capable of charging and discharging and has a laminated structure of a positive electrode / separator / negative electrode, and may be any one of a folding type electrode assembly (jelly roll) in which a separator is interposed between a long sheet-like positive electrode and a negative electrode coated with an active material and then wound up, a stack type electrode assembly in which a number of positive electrodes and negative electrodes of a predetermined size are sequentially stacked with a separator interposed therebetween, a stack and folding type electrode assembly, and a stack and lamination electrode assembly.

[0032] The battery case may be a cylindrical or rectangular metal can or a pouch-type battery case made of an aluminum laminate sheet.

[0033] FIG. 1 is a cross-sectional view illustrating the structure of a lithium secondary battery according to one embodiment of the present invention, illustrating a pouch-type lithium secondary battery having a stack-type electrode assembly built into a pouch-type battery case made of an aluminum laminate sheet.

[0034] The lithium secondary battery 100 according to an embodiment of the present invention includes an electrode assembly 10 and a battery case 60 that houses the electrode assembly 10, and includes an electrolyte refill unit 40 in which a spare electrolyte 45 for refilling an electrolyte is filled within a packaging member 41, and a rupture member 50 that is disposed adjacent to the electrolyte refill unit 40 and deforms in shape due to a change in temperature to form a hole in the packaging member 41 to allow the spare electrolyte 45 inside the electrolyte refill unit 40 to be injected.

[0035] In one embodiment, the electrode assembly 10 includes a positive electrode plate 11, a negative electrode plate 12, and a separator 13 interposed between the positive electrode plate 11 and the negative electrode plate 12. A positive electrode tab 31 is formed on one side of the positive electrode plate 11, and a negative electrode tab 32 is formed on one side of the negative electrode plate 12, and the positive electrode tab 31 and the negative electrode tab 32 may be arranged side by side with a certain interval between them. The tabs may be connected to an external circuit by being connected to a positive electrode lead 21 and a negative electrode lead 22, respectively.

[0036] The electrode assembly 10, the positive electrode lead 21, and the negative electrode lead 22 are sealed by a pouch-type battery case 60. The pouch-type battery case 60 is typically a laminate sheet of an inner coating layer / metal layer / outer layer, and the inside is sealed by heat-pressing the sealing portions of the upper case and the lower case using a sealing member, and the inner coating layers of the upper case and the lower case are heat-sealed. At this time, the electrode assembly 10 may be sealed by the battery case with a portion of the positive electrode lead 21 and the negative electrode lead 22 exposed to the outside for electrical connection with the outside.

[0037] The lithium secondary battery 100 further includes a main electrolyte 15 therein, which may be an aqueous electrolyte or a non-aqueous electrolyte. The aqueous electrolyte may include water and a lithium salt as a solvent, and the non-aqueous electrolyte may include a non-aqueous solvent and a lithium salt as a solvent.

[0038] The non-aqueous solvent may be any solvent without particular limitation, so long as it can function as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the non-aqueous solvent that can be used include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, ether-based solvents such as dibutyl ether and tetrahydrofuran, ketone-based solvents such as cyclohexanone, aromatic hydrocarbon-based solvents such as benzene and fluorobenzene, and carbonate-based solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0039] Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and low-viscosity linear carbonate-based compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferred.

[0040] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 The lithium salt is preferably contained in the main electrolyte solution 15 at a concentration of about 0.6 mol % to 2 mol %.

[0041] In addition to the above-mentioned components, the main electrolyte solution 15 may further contain one or more additives such as pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purposes of improving the battery's life characteristics, suppressing a decrease in battery capacity, and improving the battery's discharge capacity.

[0042] In addition, the main electrolyte 15 is made of VC (vinylene carbonate), FEC (fluoroethylene carbonate), PS (propane sultone), ESA (ethylene sulfite) and LiBF in order to form a stable SEI (Solid electrolyte interface) film on the surface of the negative electrode active material in the initial charging stage. 4 The SEI film forming additives may be included.

[0043] The electrolyte refill unit 40 is for replenishing the insufficient electrolyte when the main electrolyte is depleted due to repeated charging and discharging of the lithium secondary battery, and may be in the form of a pouch-shaped packaging member 41 filled with spare electrolyte 45. However, the form of the electrolyte refill unit is not limited thereto.

[0044] When it is necessary to replenish the electrolyte, the packaging member 41 of the electrolyte refill unit 40 is ruptured by the rupture member 50 described later, and the spare electrolyte 45 contained inside the packaging member 41 replenishes the depleted main electrolyte of the secondary battery.

[0045] In one embodiment, the packaging member 41 may be made of a thermoplastic synthetic resin film, and among them, a polyethylene resin film is preferable because the polyethylene resin film is easily ruptured by physical pressure.

[0046] It is preferable that the spare electrolyte 45 held in the electrolyte refill unit 40 does not contain an additive for forming an SEI film. Since the additive for forming an SEI film is added to form an SEI film during initial charging, the additive is not necessary in the spare electrolyte for additional refilling, and if the additive for forming an SEI film is contained, it may have a negative effect on the battery due to the decomposition reaction of these components.

[0047] 3 is a perspective view illustrating the structure of a lithium secondary battery according to an embodiment of the present invention. When the electrolyte refill unit 40 is formed in a pouch shape, it can be formed with a large cross-sectional area similar to that of the electrode assembly 10, so that it can hold a sufficient amount of spare electrolyte, and the electrolyte refill unit can be formed with a thin thickness.

[0048] The rupture member 50 may be a thermally deformable member that is deformed by heat, and the thermally deformable member is preferably a shape memory alloy or a bimetal.

[0049] A shape memory alloy is a metal that undergoes stress-induced martensite deformation, pseudoelasticity, or superelasticity deformation when heat is applied. A typical example is a nickel-titanium alloy.

[0050] A bimetal is made by bonding two metals that have different thermal expansion coefficients. Since each metal has a different inherent thermal expansion coefficient, it expands differently in response to changes in temperature, and so has the property of bending in one direction.

[0051] Of the two metals that make up the bimetal, it is preferable that the upper metal be made of a first metal with a small thermal expansion coefficient, and the lower metal be made of a second metal with a larger thermal expansion coefficient than that of the first metal. During thermal expansion, the first metal expands relatively less and the second metal expands relatively more, causing the bimetal to bend in one direction.

[0052] The rupture member 50 may be disposed adjacent to one side of the electrolyte refill unit so that when heat is applied from the outside to thermally deform the rupture member 50, the thermally deformed end portion 51 of the rupture member applies physical pressure to form a hole in the electrolyte refill unit 40.

[0053] The rupture member 50 and the electrolyte refill unit 40 may have a simply stacked structure or a joined structure. When the rupture member 50 and the electrolyte refill unit 40 have a simply stacked structure, it is preferable to form a hole by rupturing the packaging material 41 of the electrolyte refill unit 40 with the end of the rupture member 50, and in this case, it is preferable to form the end portion 51 of the rupture member 50 sharply.

[0054] In the case where the rupture member 50 and the electrolyte refill unit 40 are joined together, a fragile portion (not shown) may be formed in the packaging material along the edge direction of the rupture member 50, so that when the rupture member is thermally deformed, the packaging material may be broken along the fragile portion, facilitating the leakage of the electrolyte.

[0055] The shape and size of the rupture member 50 are not particularly limited as long as it can form a hole in the packaging member 41 of the electrolyte refill unit 40, and it is preferable that the rupture member 50 reduces the volume and weight. In addition, the rupture member 50 is preferably interposed between the electrolyte refill unit 40 and the battery case 60 so that heat can be easily applied from the outside.

[0056] The rupturable member is preferably thermally deformed in a temperature range of 80° C. to 120° C., preferably 85° C. to 110° C. If the rupturable member is thermally deformed at a temperature below 80° C., unintended thermal deformation of the rupturable member may occur during daily charging and discharging of the lithium secondary battery, whereas if the rupturable member is thermally deformed at a temperature above 120° C., excessive heat must be applied to the lithium secondary battery to replenish the electrolyte, which may deteriorate the battery or adversely affect the cycle characteristics of the battery and may cause thermal runaway, which is undesirable.

[0057] The electrolyte refill unit 40 and the rupture member 50 are disposed in the space between the electrode assembly 10 and the battery case 60 .

[0058] When the electrolyte refill unit 40 is formed of a pouch-type packaging member 41, it may be stacked on the electrode assembly 10 and disposed adjacent to the upper or lower surface of the battery case 60. In this case, it is preferable because heat can be efficiently applied to the rupture member from the outside.

[0059] Although not shown in the drawings, the electrolyte refill unit 40 and the rupture member 50 may be interposed in the side wall of the battery case 60, which is the dead space A near the end of the electrode assembly 10. However, since the rupture member 50 may be conductive, if the conductive rupture member 50 comes into contact with an electrode lead, it may induce an internal short circuit. Therefore, if the rupture member 50 is conductive, it would be preferable that the electrolyte refill unit 40 and the rupture member 50 are stacked on the electrode assembly 10 and disposed adjacent to the upper or lower surface of the battery case 60.

[0060] The method for refilling an electrolyte in a lithium secondary battery according to an embodiment of the present invention may include applying heat to the lithium secondary battery to cause thermal deformation of the rupture member.

[0061] FIG. 2 shows a cross-sectional view of a lithium secondary battery in which the electrolyte has been depleted, and FIG. 3 shows a cross-sectional view of a lithium secondary battery in which spare electrolyte from an electrolyte refill unit has been charged into the battery.

[0062] As shown in FIG. 2, the main electrolyte in the lithium secondary battery is depleted due to repeated charging and discharging, and as shown in FIG. 3, when a user applies heat to the outside at a suitable time, the rupture member 50 undergoes thermal deformation, which forms a hole in the surface of the electrolyte refill unit 40, causing the spare electrolyte 45 held in the electrolyte refill unit 40 to flow out and be injected into the battery.

[0063] Since the rupturable member 50 is thermally deformed in the temperature range of 80°C to 120°C as described above, the temperature to which heat is applied is preferably in the range of 80°C to 120°C.

[0064] As described above, in the lithium secondary battery according to the present invention, when the main electrolyte injected at the time of shipment is depleted due to repeated charging and discharging, and the battery performance is deteriorated, the spare electrolyte stored inside the electrolyte refill unit is additionally injected through a heat treatment, thereby extending the life of the battery.

[0065] In addition, since there is no need to disassemble the battery to inject additional electrolyte, the present invention is particularly useful for prismatic or cylindrical lithium secondary batteries that use a metal can-shaped battery case, which is difficult to disassemble after manufacture.

[0066] (Example) <Manufacturing of electrode assembly> A stack-type electrode assembly was manufactured by stacking eight basic units of positive electrode-separator-negative electrode-separator.

[0067] <Preparation of main electrolyte> Ethylene carbonate (EC): ethyl methyl carbonate (EMC) was mixed in a volume ratio of 30:70, and LiPF 6 An electrolyte solution was prepared by adding 1.0 wt% vinylene carbonate (VC) and 0.5 wt% propane sultone (PS) as additives for forming the SEI film to a non-aqueous organic solvent in which 1.0 wt% of ethylenediaminetetraacetate (EDTA) had been dissolved to a concentration of 1.0 M.

[0068] <Preparation of electrolyte refill unit and rupture material> The spare electrolyte to be filled in the electrolyte refill unit is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70, and LiPF 6 An electrolyte solution was prepared by dissolving ZnO in a solution at a concentration of 1.0 M.

[0069] A pouch-shaped polyethylene resin film was prepared as a packaging member for the electrolyte refill unit, and the above-mentioned spare electrolyte was filled inside the packaging member and sealed to produce an electrolyte refill unit.

[0070] As the rupture member, a shape memory alloy with a needle-shaped end that thermally deforms at 90°C was prepared.

[0071] <Assembling secondary batteries> The electrode assembly, the electrolyte refill unit and the rupture member were placed in a pouch-type battery case laminated with PP / Al / Nylon as shown in FIG. 1, and the main electrolyte was injected to complete the manufacture of a secondary battery.

[0072] (Comparative Example) In the above embodiment, the electrolyte refill unit and the rupture member were not included when assembling the secondary battery, but the electrode assembly and the main electrolyte of the embodiment were included to manufacture the secondary battery.

[0073] (Experimental Example 1: Capacity retention rate according to charge / discharge cycle) The secondary battery of the embodiment was charged at 25° C. under the condition of 0.33 C / 4.2 V constant current / constant voltage (CC / CV) 4.2 V / 0.05 C, and discharged at a constant current of 0.33 C / 2.5 V, and the discharge capacity was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5 V, 6 A). The measured discharge capacity was defined as the initial capacity.

[0074] The secondary battery was repeatedly charged and discharged 1,400 times under the above charge and discharge conditions, and then heated at a temperature of 90°C to 100°C for 10 minutes.The battery was then repeatedly charged and discharged 200 times under the above charge and discharge conditions.The capacity retention rate according to the above charge and discharge cycles was calculated by substituting it into the following formula (1), and the results are shown in Figure 4.

[0075] Formula (1): Capacity retention rate (%) = (discharge capacity by cycle / initial capacity) x 100

[0076] (Experimental Example 2: Resistance increase rate according to charge / discharge cycle) The secondary battery of the embodiment was charged at a constant current-constant voltage (CC / CV) of 0.33C / 4.2V using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A) at 4.2V / 0.05C, and discharged at 0.33C to adjust the battery's state of charge to about 50% SOC. Then, a discharge pulse was applied at a constant current of 2.5C for 10 seconds, and the voltage drop was measured to obtain the resistance value. This was defined as the initial resistance.

[0077] The secondary battery was repeatedly charged and discharged 1400 times under the above charge and discharge conditions, and then heated at a temperature of 90°C to 100°C for 10 minutes.The secondary battery was then repeatedly charged and discharged 200 times under the above charge and discharge conditions.The resistance increase rate (%) for the secondary battery was calculated from the resistance ratio according to the above charge and discharge cycles, and is shown in Figure 5.

[0078] Equation (2): Resistance increase rate (%) = {(resistance according to cycle - initial resistance) / initial resistance} x 100

[0079] (Experimental example 3: Resistance measurement according to charge depth after long-term cycle) The secondary batteries of the examples and comparative examples were charged at 25°C under conditions of a constant current-constant voltage (CC / CV) of 0.33C / 4.2V and 4.2V / 0.05C, and then discharged under a constant current condition of 0.33C / 2.5V. This cycle was counted as one cycle, and the batteries were repeatedly charged and discharged 1,400 times.

[0080] The secondary battery of the example was heated for 10 minutes at a temperature of 90° C. to 100° C. The secondary battery of the comparative example was not subjected to the above heating process.

[0081] Thereafter, the secondary batteries of the example and comparative examples were charged under the condition of a constant current of 0.33C / 4.2V-constant voltage of 4.2V / 0.05C, and discharged at 0.33C to adjust the state of charge of the battery to about 5% SOC, and then a discharge pulse was applied for 10 seconds at a constant current of 2.5C to measure the voltage drop and obtain the resistance value. The resistance value was measured at the SOC of 10%, 15%, 20%, 35%, 50%, 65%, 80%, and 95% using the same method as above, and the results are shown in Figure 6.

[0082] Referring to FIG. 4, as the charge / discharge cycle of the lithium secondary battery increases, the battery is altered and the capacity storage rate continues to decrease. In particular, the capacity storage rate rapidly decreased from 83% to 75% in the 1200 to 1400 cycles, indicating that the battery deterioration became more severe in this range.

[0083] 5, the resistance of the lithium secondary battery continues to increase as the charge / discharge cycle of the lithium secondary battery is repeated, and in particular, the resistance significantly increases from 40% to 59% compared to the initial resistance at cycles 1200 to 1400, which is presumed to be due to depletion of electrolyte inside the lithium secondary battery and deterioration of the active material. However, in the lithium secondary battery according to the present invention, electrolyte is additionally injected by the electrolyte refill unit at cycle 1400, and the slope of the capacity retention rate decreases in the subsequent charge / discharge cycles, and the resistance increase rate rapidly decreases from about 59% to about 18%, and no increase in resistance is observed even after 200 additional charge / discharge cycles thereafter.

[0084] Referring to FIG. 6, the lithium secondary battery according to the comparative example had a large cell resistance at all depths of charge, compared to the lithium secondary battery according to the example.

[0085] In this way, when deterioration is observed in the secondary battery according to the present invention, the rupture member ruptures on the surface of the electrolyte refill unit through high-temperature heat treatment, so that additional electrolyte can be injected, thereby extending the life of the battery. [Explanation of symbols]

[0086] 100: Lithium secondary battery 10: Electrode assembly 11: Positive electrode plate 12: Negative plate 13: Separation membrane 21: Positive electrode lead, 22: Negative electrode lead 31: Positive electrode tab, 32: Negative electrode tab 40: Electrolyte refill unit 50: Bursting member 60: Battery case A: Dead Space

Claims

1. An electrode assembly, The main electrolyte; an electrolyte refill unit having a packaging member filled with spare electrolyte; a rupture member disposed adjacent to the electrolyte refill unit and configured to deform in response to a temperature change to form a hole in the packaging member and to inject the spare electrolyte inside the electrolyte refill unit; a battery case that accommodates the electrode assembly, the main electrolyte, the electrolyte refill unit, and the rupture member therein; A lithium secondary battery comprising:

2. 2. The lithium secondary battery according to claim 1, wherein the packaging member is a pouch-shaped member made of a thermoplastic synthetic resin film.

3. 3. The lithium secondary battery according to claim 2, wherein the packaging material is made of a polyethylene resin film.

4. The lithium secondary battery according to claim 1 , wherein the electrolyte refill unit and the rupture member are disposed in a space between the electrode assembly and the battery case.

5. The lithium secondary battery according to claim 1 , wherein the electrolyte refill unit and the rupture member are stacked on the electrode assembly and disposed adjacent to an upper surface or a lower surface of the battery case.

6. 2. The lithium secondary battery according to claim 1, wherein the electrolyte refill unit and the rupture member are disposed on a side wall of the battery case in a dead space near an end of the electrode assembly.

7. 7. The lithium secondary battery according to claim 4, wherein the rupture member is disposed between the electrolyte refill unit and the battery case.

8. 2. The lithium secondary battery according to claim 1, wherein the rupture member is thermally deformed at a temperature of 80°C to 120°C.

9. 2. The lithium secondary battery according to claim 1, wherein the rupture member is a shape memory alloy.

10. 2. The lithium secondary battery according to claim 1, wherein the rupture member is a bimetal.

11. The bursting member is joined to an electrolyte refill unit; The lithium secondary battery according to claim 1 , wherein the packaging member has a fragile portion formed along an edge direction of the rupture member.

12. The lithium secondary battery according to claim 1 , wherein the spare electrolyte does not contain an additive for forming an SEI film.

13. 2. The lithium secondary battery according to claim 1, wherein the battery case is a cylindrical metal can or a rectangular metal can.

14. 2. A method for refilling an electrolyte in a lithium secondary battery, comprising the step of applying heat to the lithium secondary battery according to claim 1 to cause thermal deformation of the rupture member.

15. 15. The method for refilling electrolyte in a secondary battery according to claim 14, wherein the temperature at which heat is applied to the rupture member is 80°C to 120°C.

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