Lithium secondary battery that can be injected with additional electrolyte

Abstract

The present invention relates to a lithium secondary battery capable of additional electrolyte injection, comprising: an electrode assembly and a battery case accommodating the electrode assembly; an electrolyte replenishment unit having a pre-electrolyte filled within a packaging unit for replenishing the electrolyte; and a rupture member disposed adjacent to the electrolyte replenishment unit and thermally deformed by a temperature change to form a hole in the packaging member so as to inject the pre-electrolyte inside the replenishment unit.

Description

Technology Field

[0001] The present invention relates to a lithium secondary battery capable of additional electrolyte injection. 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 serving as power generation elements, and a liquid electrolyte is injected between the elements.

[0004] Commonly used pouch-type batteries are manufactured by housing an electrode assembly consisting of a positive electrode, separator, and negative electrode inside a pouch-type battery case made of a laminate sheet of polymer resin and aluminum, then combining the upper and lower laminate sheets with the electrode leads exposed at both ends of the battery case, and finally sealing them through heat compression.

[0005] Meanwhile, if the secondary battery continues to be charged and discharged, the electrolyte undergoes side reactions and deterioration, and the electrolyte within the battery becomes insufficient, which reduces the lifespan of the secondary battery.

[0006] Since prismatic or cylindrical lithium-ion rechargeable batteries have cell cases made of metallic materials, the cells must be disassembled to inject additional electrolyte. However, this process has disadvantages, such as the electrodes oxidizing if exposed to air during disassembly, and the difficulty of resealing the cells after injection.

[0007] Korean Published Patent Application No. 10-2018-0023706 discloses a technology that includes a sealing member for additional electrolyte injection formed in a part of a battery case to inject electrolyte into an electrolyte receiving portion of the battery case to replenish the electrolyte without disassembling the battery and to seal the injection site. However, the assembly process of the battery is complicated due to the sealing member, and there is a disadvantage that the electrolyte must be injected into each battery.

[0008] Therefore, there is a need to develop technology that can supply additional electrolyte in a safer and more convenient manner. Prior art literature

[0010] Korean Patent Publication No. 10-2018-0023706 The problem to be solved

[0011] The present invention aims to solve the aforementioned conventional problems, and the objective of the present invention is to provide a lithium-ion secondary battery with a novel structure capable of supplying additional electrolyte when the cell degrades in order to extend the lifespan of the lithium secondary battery.

[0012] In addition, the present invention provides a method for additionally supplying an electrolyte to the lithium-ion secondary battery. means of solving the problem

[0014] To achieve the above objectives, a lithium secondary battery according to one embodiment of the present invention comprises an electrode assembly and a battery case that accommodates the electrode assembly, and is characterized by comprising: an electrolyte replenishment unit in which a reserve electrolyte for replenishing the electrolyte is filled within a packaging unit; and a rupture member disposed adjacent to the electrolyte replenishment unit and which is thermally deformed by a temperature change to form a hole in the packaging member so that the reserve electrolyte inside the replenishment unit is injected.

[0015] The above electrolyte replenishment unit may be in the form of a pouch made of a thermoplastic synthetic resin film.

[0016] The above electrolyte replenishment unit may be made of polyethylene resin.

[0017] The above electrolyte replenishment unit may be laminated to the electrode assembly and positioned adjacent to the upper or lower surface of the electrode case.

[0018] The above electrolyte replenishment unit can be placed on the side wall of the battery case in the dead space near the end of the electrode assembly.

[0019] The above-mentioned rupture member can be thermally deformed at a temperature of 80°C to 120°C.

[0020] The above-mentioned rupture member may be a shape memory alloy.

[0021] The above-mentioned rupture member may be a bimetal.

[0022] The above-mentioned rupture member may be interposed between the electrolyte replenishment unit and the battery case.

[0023] The above-mentioned rupture member is laminated with an electrolyte replenishment unit, and can rupture the film of the electrolyte replenishment unit when the rupture member is thermally deformed.

[0024] The above-mentioned rupture member is joined to an electrolyte replenishment unit, and a weak portion may be formed in the film of the electrolyte replenishment unit along the edge direction of the above-mentioned rupture member.

[0025] The above-mentioned preliminary electrolyte may be a composition in which the main electrolyte composition injected into the above-mentioned lithium secondary battery does not include an SEI film-forming agent component.

[0026] The above-mentioned preliminary electrolyte may be identical to the main electrolyte composition, except that it does not contain an SEI film-forming agent.

[0027] A method for replenishing the electrolyte of a lithium secondary battery according to one embodiment of the present invention may include a step of applying heat to the lithium secondary battery of the present invention to cause thermal deformation of the ruptured member.

[0028] The temperature at which heat is applied to the above-mentioned ruptured member may be 80°C to 120°C. Effects of the invention

[0030] The present invention provides the effect of extending the lifespan of a lithium secondary battery by, when degradation of the capacity or resistance of the lithium secondary battery is observed, deforming a rupture member made of a shape memory alloy or bimetal through high-temperature heat treatment to form a hole in a packaging member containing a pre-electrolyte, thereby injecting additional electrolyte into the lithium secondary battery without opening the battery case. Brief explanation of the drawing

[0032] FIG. 1 is a cross-sectional view illustrating the structure of a pouch-type secondary battery according to one embodiment of the present invention. Figure 2 is a cross-sectional view of a lithium secondary battery with the electrolyte depleted. Figure 3 is a cross-sectional view of a lithium secondary battery in which the pre-electrolyte of the electrolyte replenishment unit is charged inside the battery. FIG. 4 is a graph showing the capacity retention rate according to the number of cycles for a lithium secondary battery according to one embodiment of the present invention. FIG. 5 is a graph showing the resistance increase rate according to the number of cycles for a lithium secondary battery according to one embodiment of the present invention. FIG. 6 is a graph showing the resistance according to the depth of charge for a lithium secondary battery according to one embodiment of the present invention and a secondary battery according to a comparative example. Specific details for implementing the invention

[0033] The present invention will be described in more detail below.

[0034] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0035] FIG. 1 is a cross-sectional view illustrating the structure of a pouch-type secondary battery according to one embodiment of the present invention.

[0036] The present invention provides a lithium secondary battery (100) comprising an electrode assembly (10) and a battery case (60) that accommodates the electrode assembly (10), an electrolyte replenishment unit (40) in which a preliminary electrolyte (45) for replenishing the electrolyte is filled within a packaging member (41); and a rupture member disposed adjacent to the electrolyte replenishment unit (40) and having a shape that changes due to a temperature change to form a hole in the packaging member so that the preliminary electrolyte inside the replenishment unit is injected.

[0037] The electrode assembly (10) comprises an anode plate (11), a cathode plate (12), and a separator (13) interposed between the anode plate (11) and the cathode plate (12). Additionally, an anode tab (31) is formed on one side of the anode plate (11), and a cathode tab (32) is formed on one side of the cathode plate (12), and the anode tab (31) and the cathode tab (32) are arranged side by side at a certain distance apart. The tabs are connected to an external circuit by being connected to the anode lead (21) and the cathode lead (22), respectively.

[0038] The electrode assembly (10), the positive lead (21), and the negative lead (22) are sealed by a pouch-type battery case (60). The battery case (60) typically has a form in which a heat-sealable material is laminated on the upper and lower surfaces of an aluminum film, and the interior is sealed by the heat-sealable material being bonded together. At this time, to ensure electrical connection with the outside of the electrode assembly (10), a portion of the positive lead (31) and the negative lead (32) is exposed to the outside and sealed by the pouch.

[0039] The above lithium secondary battery further includes a main electrolyte (15), and the main electrolyte (15) may be an aqueous electrolyte or a non-aqueous electrolyte. The aqueous electrolyte may include water and an electrolyte salt as solvents, and the non-aqueous electrolyte may use a non-aqueous solvent and an electrolyte salt as solvents.

[0040] The above-mentioned non-aqueous solvent may be selected from those generally used in the field of the art and is not specifically limited, but may be selected from the group consisting of carbonate-based, ester-based, ether-based, ketone-based, organosulfur-based, organophosphorous-based, non-protic solvents and combinations thereof, and specifically may be at least one of EC (Ethylene Carbonate), PC (Poly Carbonate), EMC (Ethylene Carbonate), DMC (Dimethyl Carbonate), DEC (Diethyl Carbonate), EA (Ethyl acetate), and EP (Ethyl Propionate).

[0041] The above-mentioned electrolytic salt may specifically be one or more of LiPF6, LiTFSI, and LiBOB.

[0042] The above main electrolyte (15) may include additives for forming SEI, such as VC (vinylene carbonate), FEC (fluoroethylene carbonate), PS (propane sulfone), ESA (ethylene sulfite), and LiBF4, in order to form a stable SEI (solid electrolyte interface) film on the surface of the negative electrode active material during the initial charging stage. The SEI film located on the surface of the negative electrode active material acts as a kinetic barrier that prevents further reduction reactions, thereby preventing or significantly reducing the degradation of the battery's lifespan. In particular, it can prevent an increase in cell resistance and a decrease in cycle life caused by the stacking of dead lithium and porous layers resulting from the repeated breakdown and formation of the SEI film.

[0043] The above electrolyte replenishment unit (40) is intended to fill with a preliminary electrolyte, and although there are no special limitations on its shape, it can be formed as a pouch-shaped packaging member (41). When the above electrolyte replenishment unit (40) is formed as a pouch-shaped packaging member (41), it is preferable to stack it on the electrode assembly (10) and place it adjacent to the upper or lower surface of the battery case (60) so that heat can be efficiently applied from the outside.

[0044] Additionally, although not shown in the drawing, the electrolyte replenishment unit (40) may be interposed on the side wall of the battery case (60) in the unused dead space (A) near the end of the electrode assembly (10), and in this case, the electrolyte replenishment unit (40) may be formed in one or more air cap shapes rather than a pouch shape.

[0045] FIG. 3 is a perspective view illustrating the structure of a lithium secondary battery according to one embodiment of the present invention. When the electrolyte replenishment unit (40) is formed in a pouch shape, it can be formed with a large cross-sectional area similar to the electrode assembly (10), so that a sufficient amount of reserve electrolyte can be contained and the thickness of the electrolyte replenishment unit can be formed thinly.

[0046] The above electrolyte replenishment unit (40) can be formed from a thermoplastic synthetic resin film, and among them, it is preferable to form it from a polyethylene film, because the polyethylene film is easily destroyed by physical pressure.

[0047] It is preferable that the pre-electrolyte (45) contained in the electrolyte replenishment unit (40) does not contain an additive for SEI formation. Since the additive for SEI formation is added to form an SEI film during initial charging, the additive for SEI film formation is not required in the pre-electrolyte for additional replenishment, and if the additive for SEI film formation is included, it may have a negative effect on the battery due to the decomposition reaction of these components.

[0048] The above-mentioned 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. A shape memory alloy is a metal that causes stress-induced martensitic deformation or pseudoelasticity or suprerelasticity deformation when heat is applied, and a representative example is a nickel-titanium alloy. The above-mentioned bimetal is in the form of two metals joined with different coefficients of thermal expansion, and when heat is applied, the bimetal bends in the direction of the metal with the lower coefficient of thermal expansion.

[0049] The rupture member (50) may be positioned adjacent to one side of the electrolyte replenishment unit, so that when heat is applied from the outside and the rupture member (50) is thermally deformed, the thermally deformed end portion (51) of the rupture member can apply physical pressure to form a hole in the electrolyte replenishment unit (40). The rupture member (50) and the electrolyte replenishment unit (40) may have a simply stacked structure or a bonded structure. In the case where the rupture member (50) and the electrolyte replenishment unit (40) have a simply stacked structure, it is preferable to form a hole by rupturing the film (41) of the electrolyte replenishment unit (40) by 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. In the case where the above-mentioned rupture member (50) and the above-mentioned electrolyte replenishment unit (40) are joined, a weak point (not shown) is formed in the film (41) of the electrolyte replenishment unit (40) along the edge direction of the rupture member (50), so that when the rupture member is thermally deformed, the film is destroyed along the weak point, thereby facilitating the leakage of the electrolyte.

[0050] The rupture member (50) is not specifically limited in shape, but it is preferable to form it in the form of a thin film to reduce volume and weight. Additionally, it is preferable that the rupture member (50) be interposed between the electrolyte replenishment unit (50) and the battery case (60) so that heat can be easily applied from the outside.

[0051] It is preferable that the rupture member undergoes thermal deformation in a temperature range of 80°C to 120°C, preferably 85°C to 110°C. If the rupture member undergoes thermal deformation at a temperature below 80°C, unintended thermal deformation of the rupture member may occur during the routine charging and discharging of the lithium secondary battery. If the rupture member undergoes thermal deformation at a temperature exceeding 120°C, excessive heat must be applied to the lithium secondary battery, which may cause the battery to degrade or adversely affect the cycle characteristics of the battery, and may lead to thermal runaway, which is undesirable.

[0052] A method for replenishing the electrolyte of a lithium secondary battery according to one embodiment of the present invention may include a step of applying heat to the lithium secondary battery of the present invention to cause thermal deformation of the ruptured member.

[0053] Figure 2 shows a cross-sectional view of a lithium secondary battery with the electrolyte depleted, and Figure 3 shows a cross-sectional view of a lithium secondary battery in which the reserve electrolyte of the electrolyte replenishment unit is charged inside the battery.

[0054] As seen in FIG. 2, the electrolyte in the lithium secondary battery is depleted due to continuous charging and discharging, and as seen in FIG. 3, when the user applies heat to the outside at an appropriate time, the rupture member (50) undergoes thermal deformation, and as a result, a hole is formed in the electrolyte replenishment unit (40), causing the reserve electrolyte (45) contained in the electrolyte replenishment unit (40) to flow out and be injected into the battery.

[0055] As the above-mentioned rupture member (50) undergoes thermal deformation in a temperature range of 80°C to 120°C as described above, the temperature at which heat is applied is preferably in the range of 80°C to 120°C.

[0057] Examples

[0058] <Manufacturing of Electrode Assembly>

[0059] A stacked electrode assembly was manufactured by stacking eight basic units of anode-separator-cathode-separator.

[0060] <Preparation of Main Electrolyte>

[0061] An electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 30:70 volume ratio and dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent, and adding 1.0 wt% vinylene carbonate (VC) and 0.5 wt% propanesulfone (PS) as SEI film-forming additives.

[0062] <Preparation of Electrolyte Replenishment Unit and Rupture Member>

[0063] As an electrolyte to be filled into the electrolyte replenishment unit, an electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 and dissolving LiPF6 to a concentration of 1.0 M.

[0064] As a packaging material for the electrolyte replenishment unit, a pouch made of polyethylene resin was prepared, the electrolyte was filled inside the pouch, and the electrolyte was sealed to manufacture the electrolyte replenishment unit.

[0065] As a rupture member, a shape memory alloy was prepared that undergoes thermal deformation at 90°C and has needle-shaped ends.

[0066] Assembly of secondary batteries

[0067] The electrode assembly, the electrolyte replenishment unit, and the rupture member are housed in a pouch-type battery case laminated with PP / Al / Nylon as shown in FIG. 1, and the main electrolyte is injected to complete the manufacture of a secondary battery.

[0069] Comparative example

[0070] In the above embodiment, when assembling the secondary battery, the electrolyte replenishment unit and the rupture member were not housed, and a secondary battery was manufactured by housing the electrode assembly of the embodiment and the main electrolyte.

[0072] Experimental Example 1: Capacity retention rate according to charge / discharge cycles

[0073] The secondary battery of the example was charged at 25°C under conditions of 0.33C / 4.2V constant current / constant voltage (CC / CV) 4.2V / 0.05C and discharged at 0.33C / 2.5V constant current, and the discharge capacity was measured using a PNE-0506 charge / discharger (Manufacturer: PNE Solution Co., Ltd., 5V, 6A). At this time, the measured discharge capacity was defined as the initial capacity.

[0074] The charge and discharge cycles were repeated 1,400 times under the above charge and discharge conditions, and then the secondary battery was heated to a temperature of 90°C to 100°C for 10 minutes. Afterward, the charge and discharge cycles were repeated 200 more 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 equation (1), and the result is shown in FIG. 4.

[0075] Equation (1): Capacity retention rate (%) = (Discharge capacity per cycle / Initial capacity) × 100

[0077] Experimental Example 2: Resistance increase rate according to charge / discharge cycles

[0078] The secondary battery of the example was charged using a PNE-0506 charge / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A) under conditions of 0.33C / 4.2V constant current and 4.2V / 0.05C constant voltage, and discharged at 0.33C to adjust the battery's charge state to 50% SOC. Then, the voltage drop observed while applying a discharge pulse at a constant current of 2.5C for 10 seconds was measured to obtain the resistance value. This was defined as the initial resistance.

[0079] The secondary battery was charged and discharged 1,400 times under the above charging and discharging conditions, and then heated to a temperature of 90°C to 100°C for 10 minutes. Afterward, the secondary battery was charged and discharged 200 more times under the above charging and discharging conditions. The resistance increase rate (%) for the secondary battery was calculated from the ratio of resistance according to the above charging and discharging cycles, and this is shown in FIG. 5.

[0080] Equation (2): Resistance increase rate (%) = {(Resistance different in cycle - Initial resistance) / Initial resistance} x 100

[0082] Experimental Example 3: Resistance measurement according to charging depth after long-term cycling

[0083] The secondary batteries of the example and comparative example were charged at 25°C under a constant current / constant voltage (CC / CV) condition of 0.33C / 4.2V and discharged under a constant current condition of 0.33C / 2.5V, and the charge / discharge was repeated 1,400 times with the charge / discharge being one cycle.

[0084] For the secondary battery of the example, it was heated at a temperature of 90°C to 100°C for 10 minutes. For the secondary battery of the comparative example, the above heating process was not performed.

[0085] Subsequently, for the secondary batteries of the examples and comparative examples, the charge state of the battery was adjusted to a state of charge (SOC) of 5% by charging under conditions of 0.33C / 4.2V constant current and constant voltage of 4.2V / 0.05C and discharging at 0.33C, and then the voltage drop observed while applying a discharge pulse at a constant current of 2.5C for 10 seconds was measured to obtain the resistance value. At points where the state of charge was 10%, 15%, 20%, 35%, 50%, 65%, 80%, and 95%, the respective resistance values ​​were measured in the same manner as above, and the results are shown in FIG. 6.

[0087] Referring to Fig. 4, as the charge-discharge cycle of the lithium secondary battery progresses, the battery degrades and the capacity retention rate continuously decreases. In particular, at 1200 to 1400 cycles, the capacity retention rate drops sharply from 83% to 75%, indicating that the degradation of the battery intensifies in that range. Referring to Fig. 5, as the charge-discharge cycle of the lithium secondary battery progresses, the resistance of the lithium secondary battery continuously increases. In particular, at 1200 to 1400 cycles, it increases significantly from 40% to 59% compared to the initial resistance. This is presumed to be due to the depletion of the electrolyte inside the lithium secondary battery and the degradation of the active material. However, in the lithium secondary battery according to the present invention, additional electrolyte is injected by an electrolyte replenishment unit at 1400 cycles, and in subsequent charge-discharge cycles, the slope of the capacity retention rate decreases and the resistance increase rate decreases sharply from about 59% to about 18%, and no increase in resistance is observed even after 200 additional charge-discharge cycles.

[0088] Referring to FIG. 6, the lithium secondary battery according to the comparative example showed a significantly higher cell resistance at all charging depths compared to the lithium secondary battery according to the embodiment.

[0089] In this way, when degradation is observed in the secondary battery according to the present invention, through high-temperature heat treatment, the rupture member causes a rupture on the surface of the electrolyte replenishment unit, allowing additional electrolyte to be injected, thereby extending the lifespan of the battery. Explanation of the symbols

[0091] 100 : Lithium secondary battery 10 : Electrode assembly 11: Positive plate 12: Cathode plate 13 : Separator 21: Positive lead, 22: Negative lead 31: Positive tab, 32: Negative tab 40: Electrolyte replenishment unit 50: Rupture absence 60 : Battery case A : Private space

Claims

Claim 1 A lithium secondary battery comprising: an electrode assembly and a battery case accommodating the electrode assembly; an electrolyte replenishment unit having a pre-electrolyte filled within a packaging member for replenishing the electrolyte; and a rupture member disposed adjacent to the electrolyte replenishment unit and thermally deformed by a temperature change to form a hole in the packaging member so as to inject the pre-electrolyte inside the electrolyte replenishment unit; wherein the electrode assembly, the main electrolyte, the electrolyte replenishment unit, and the rupture member are accommodated within the battery case, and the rupture member is interposed between the electrolyte replenishment unit and the battery case. Claim 2 A lithium secondary battery according to claim 1, wherein the electrolyte replenishment unit is in the form of a pouch made of a thermoplastic synthetic resin film. Claim 3 A lithium secondary battery according to paragraph 2, wherein the electrolyte replenishment unit is made of polyethylene resin. Claim 4 A lithium secondary battery according to claim 1, characterized in that the electrolyte replenishment unit and the rupture member are laminated to the electrode assembly and disposed adjacent to the upper or lower surface of the battery case. Claim 5 A lithium secondary battery according to claim 1, characterized in that the electrolyte replenishment unit and the rupture member are disposed on the side wall of the battery case in a dead space near the end of the electrode assembly. Claim 6 A lithium secondary battery according to claim 1, characterized in that the rupture member undergoes thermal deformation at a temperature of 80°C to 120°C. Claim 7 A lithium secondary battery according to claim 1, characterized in that the rupture member is a shape memory alloy. Claim 8 A lithium secondary battery according to claim 1, characterized in that the rupture member is a bimetal. Claim 9 delete Claim 10 A lithium secondary battery according to claim 1, wherein the rupture member is laminated with an electrolyte replenishment unit, and the film of the electrolyte replenishment unit is ruptured upon thermal deformation of the rupture member. Claim 11 A lithium secondary battery according to claim 1, wherein the rupture member is joined to an electrolyte replenishment unit, and a weak portion is formed in the film of the electrolyte replenishment unit along the edge direction of the rupture member. Claim 12 A lithium secondary battery according to claim 1, characterized in that the above-mentioned preliminary electrolyte is a composition in which the main electrolyte composition injected into the lithium secondary battery does not include a SEI film-forming agent component. Claim 13 A lithium secondary battery characterized in that, in claim 12, the above-mentioned preliminary electrolyte is identical to the main electrolyte composition except that it does not contain an SEI film-forming agent. Claim 14 A method for replenishing the electrolyte of a lithium secondary battery, comprising the step of applying heat to the lithium secondary battery of claim 1 to cause thermal deformation of the ruptured member. Claim 15 A method for replenishing electrolyte of a secondary battery according to claim 14, characterized in that the temperature at which heat is applied to the ruptured member is 80℃ to 120℃.

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