Resistance measurement method of anode of secondary battery, and secondary battery capable of measuring resistance of anode

Abstract

An anode included in a secondary battery, according to the present invention, comprises an anode active material and is a freestanding type without a separate current collector, the anode comprising a first anode tab and a second anode tab that extend in opposite directions of each other. In the secondary battery, the resistance of merely the anode can be measured alone without disassembly, and the resistance of the anode can be accurately measured. In addition, in the secondary battery, the degree of degradation of the anode can be determined by measuring the resistance of the anode.

Description

Method for measuring negative electrode resistance for secondary batteries and secondary batteries capable of measuring negative electrode resistance

[0001] The present invention relates to a method for measuring the resistance of a negative electrode for a secondary battery and a secondary battery capable of measuring the resistance of the negative electrode.

[0002] This application claims priority to Korean Application No. 10-2023-0112035, filed August 25, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] Secondary batteries, which can be repeatedly charged and discharged, are gaining attention as an alternative to fossil fuels. Secondary batteries have been primarily used in traditional handheld devices such as cell phones, video cameras, and power tools. However, their applications are increasingly expanding, encompassing electric vehicles (EVs, HEVs, PHEVs), large-capacity energy storage systems (ESSs), and uninterruptible power supply systems (UPSs).

[0004] Secondary batteries include an electrode assembly that includes a positive electrode, a negative electrode, and a separator interposed between them, and an electrolyte that electrochemically reacts with the active material coated on the positive electrode and the negative electrode. Lithium-ion secondary batteries are representative examples, in which lithium ions act as working ions during charging and discharging, inducing an electrochemical reaction at the positive and negative electrodes. In conventional lithium-ion secondary batteries, lamination is applied during the assembly process to ensure adhesion between the electrode and the separator within the electrode assembly. Lamination is a process that thermally bonds the separator and the electrode. Lamination heats and bonds the separator and electrode, which are stacked vertically, and as a result, increases the adhesion between the separator and the electrode. The rough surface of a conventional electrode composed of an active material, a conductive material, and a binder facilitates the formation of electrode-separator adhesion through lamination with the separator.

[0005] Recently, as part of efforts to improve the energy density of lithium-ion secondary batteries, the development of next-generation secondary batteries that utilize lithium metal films directly as anodes has received significant attention. Lithium metal not only has a high ionization tendency and low density, but also a very low standard electrode potential, resulting in a very high specific capacity. If issues such as internal battery short-circuiting due to lithium dendrite growth and the risk of explosion due to moisture exposure can be addressed, lithium metal offers the advantage of achieving the highest energy density, making it worthy of continued research.

[0006] For these lithium-ion secondary batteries, performance deteriorates over time compared to initial performance. Specifically, in lithium metal batteries that directly utilize a lithium metal film as the anode, the lithium metal readily forms large-area dendrites, which react with salts and additives in the electrolyte to form a solid electrolyte interphase (SEI), continuously consuming the electrolyte's salts and additives, ultimately accelerating battery degradation.

[0007] Accordingly, various studies are being conducted to estimate the lifespan or degradation of lithium metal batteries. It is known that lithium metal battery resistance increases due to changes in the chemical composition and physical structure of lithium metal. Using this correlation, it is believed that observing the cathode resistance of a lithium metal battery during operation can be used to estimate the degree of degradation in the battery. However, in the typical lithium metal battery structure, there is no technology to independently measure the resistance of the lithium metal cathode during operation, necessitating further development of this technology.

[0008] Accordingly, the problem to be solved by the present invention is to provide a secondary battery and a measuring method thereof capable of measuring the resistance of a negative electrode during operation of the secondary battery and determining the degree of deterioration.

[0009] According to one aspect of the present invention, secondary batteries of the following embodiments are provided.

[0010] The secondary battery according to the first embodiment is

[0011] comprising: an anode; a cathode; and a separator positioned between the anode and the cathode;

[0012] The above negative electrode is a free-standing type that includes a negative active material and does not have a separate current collector.

[0013] The above negative active material includes at least one lithium-based material among lithium metal and lithium alloy,

[0014] The cathode includes a first cathode tab and a second cathode tab extending in opposite directions, respectively.

[0015] The second embodiment is, in the first embodiment,

[0016] The above positive electrode has a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the positive electrode active material layer may include a sulfur-carbon complex and a binder polymer.

[0017] The third embodiment is, in the first embodiment or the second embodiment,

[0018] The above anode may include an anode tab.

[0019] The fourth embodiment is, in any one of the first to third embodiments,

[0020] The above negative electrode may be composed solely of at least one lithium-based material among lithium metal and lithium alloy.

[0021] The fifth embodiment is, in any one of the first to fourth embodiments,

[0022] The first negative electrode tab and the second negative electrode tab may extend outward from the ends of the direction of the width direction or the length direction of the negative electrode, respectively.

[0023] The sixth embodiment is, in any one of the first to fifth embodiments,

[0024] The first negative electrode tab and the second negative electrode tab may be positioned in an area symmetrical with respect to the negative electrode.

[0025] The seventh embodiment is, in any one of the first to sixth embodiments,

[0026] The first negative electrode tab and the second negative electrode tab may be positioned in an area that is symmetrical with respect to the negative electrode.

[0027] The eighth embodiment is, in any one of the first to seventh embodiments,

[0028] The first negative tab and the second negative tab may be configured to be connectable to a resistance measuring device for measuring the resistance of the negative electrode.

[0029] The ninth embodiment is, in any one of the first to eighth embodiments,

[0030] The secondary battery can observe the degree of electrical deterioration of the negative electrode and the secondary battery by connecting a resistance measuring device to the first negative electrode tab and the second negative electrode tab.

[0031] The tenth embodiment is, in any one of the first to ninth embodiments,

[0032] The positive electrode has a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the loading amount of the negative electrode may be 1 to 2.5 times the loading amount of the positive electrode active material.

[0033] The cathode resistance measurement method according to the 11th embodiment is:

[0034] A method for measuring the negative electrode resistance of a secondary battery according to any one of the first to tenth embodiments,

[0035] It includes a step of connecting a resistance measuring device to the first negative tab and the second negative tab and measuring the resistance of the negative electrode.

[0036] The 12th implementation example is, in the 11th implementation example,

[0037] The above resistance measurement can be performed using an electrochemical impedance analysis method.

[0038] The 13th embodiment is, in the 11th embodiment or the 12th embodiment,

[0039] The above resistance measurement can be performed at a voltage amplitude of 0.01 mV to 0.5 mV.

[0040] The 14th embodiment is any one of the 11th to 13th embodiments,

[0041] The above resistance measurement can be performed at a frequency of 100 Hz to 1000 Hz.

[0042] The 15th embodiment is any one of the 11th to 14th embodiments,

[0043] The above resistance measurement can be performed whenever the SOC (State Of Charge) of the secondary battery changes by 5% to 20%.

[0044] In the past, in order to measure the resistance of a negative electrode in a secondary battery, the secondary battery had to be disassembled to obtain the negative electrode separately. However, since the secondary battery according to one embodiment of the present invention includes a first negative electrode tab and a second negative electrode tab extending in opposite directions, the resistance of only the negative electrode can be measured without disassembling the secondary battery to separate the negative electrode.

[0045] In addition, according to one embodiment of the present invention, the secondary battery can measure the electrical resistance between the first negative electrode tab and the second negative electrode tab in both directions during operation to observe the degree of electrical degradation of the negative electrode, and from this, the degree of degradation of the secondary battery can be estimated. The method for measuring the resistance of the negative electrode for a secondary battery according to the present invention can measure the resistance of the negative electrode alone without disassembling the secondary battery.

[0046] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the matters described in these drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation.

[0047] Figure 1 is a schematic diagram of a negative electrode of a secondary battery according to conventional technology.

[0048] Figure 2 is a schematic diagram of a negative electrode of a secondary battery according to one embodiment of the present invention.

[0049] Figure 3 is a schematic diagram of a negative electrode of a secondary battery according to one embodiment of the present invention.

[0050] Figure 4 is a schematic diagram of a negative electrode of a secondary battery according to one embodiment of the present invention.

[0051] Figure 5 is a schematic diagram of the negative electrode and positive electrode of a secondary battery according to one embodiment of the present invention.

[0052] Figure 6 is a graph showing the change in resistance during one charge / discharge cycle of a secondary battery according to Example 1 of the present invention.

[0053] Figure 7 is a graph showing the capacity retention rate of a secondary battery according to Example 1 of the present invention.

[0054] Figure 8 is a graph showing the change in resistance of a secondary battery according to Example 1 of the present invention.

[0055] Hereinafter, the present invention will be described in detail with reference to the drawings. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted in the sense and concept consistent with the technical spirit of the present invention.

[0056] Accordingly, the embodiments described in this specification and the configurations described in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that there may be various equivalents and modified examples that can replace them at the time of filing this application.

[0057] Additionally, throughout the specification, whenever a part is said to “include,” “comprise,” “have,” or “have” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0058] Throughout this specification, references to 'A and / or B' mean 'A or B or both.'

[0059] Unless otherwise specified throughout this specification, temperature refers to Celsius temperature, and the unit is ℃.

[0060]

[0061] The first aspect of the present invention relates to a secondary battery.

[0062] A secondary battery according to one aspect of the present invention comprises: a positive electrode; a negative electrode; and a separator positioned between the positive electrode and the negative electrode;

[0063] The above negative electrode is a free-standing type that includes a negative active material and does not have a separate current collector.

[0064] The above negative active material includes at least one lithium-based material among lithium metal and lithium alloy,

[0065] The cathode includes a first cathode tab and a second cathode tab extending in opposite directions, respectively.

[0066]

[0067] In one embodiment of the present invention, the positive electrode may have a positive electrode active material layer formed on at least one surface of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material and a binder polymer, and optionally may further include a conductive material.

[0068]

[0069] In one embodiment of the present invention, the positive electrode active material may include a sulfur-carbon complex. The sulfur-carbon complex may be a sulfur-based material supported on a porous carbon material.

[0070] The above sulfur-based material may include at least one of sulfur (S8) and sulfur-based compounds. Here, the sulfur-based compound may be a general term for a material containing elemental sulfur (S). The sulfur-based compound may include, for example, all sulfur-containing compounds that can be formed through a reduction reaction of inorganic sulfur (S8) or an oxidation reaction of lithium sulfide (Li2S), and more specifically, lithium sulfide (Li2S), lithium polysulfide (Li2S). x , x is an integer of 2 ≤ x ≤ 8), disulfide compounds, carbon-sulfur polymers ((C2S y ) n , y = 2.5 to 50, n≥2), lithium sulfide (Li2S), or two or more thereof.

[0071] The porous carbon material may be a crystalline or amorphous carbon material, and may be a conductive carbon. The porous carbon material provides a framework capable of uniformly and stably fixing the sulfur-based material, and compensates for the low electrical conductivity of the sulfur-based material, thereby enabling the electrochemical reaction to proceed smoothly.

[0072] The above porous carbon material can be manufactured by carbonizing various carbon precursors, and can include irregularities and / or pores inside, and the average diameter of the pores can be 1 nm to 200 nm, and the porosity can be 10 vol% to 90 vol% of the total volume of the carbon material. When the average diameter of the carbon material satisfies the above range, the mechanical strength of the carbon material can be maintained.

[0073] The above porous carbon material can be used without limitation as long as it is commonly used in lithium sulfur batteries, such as spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped. In addition, the porous carbon material can have a high specific surface area. For example, the carbon material can be graphite, graphene, Super P, carbon black, Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, carbon nanofiber, carbon nanotube (SWCNT, MWCNT), carbon nanowire, carbon nanoring, carbon fabric, and fullerene (C). 60 ) may include at least one selected from the group consisting of.

[0074] The sulfur-carbon composite in which the sulfur-based material is supported on the porous carbon material may contain 60 to 90 wt% of the sulfur-based material relative to a total of 100 wt%. Since the content of the sulfur-based material is within the above range, the content of the sulfur-based material and the content of the porous carbon material are appropriately balanced, so that only an appropriate amount of the binder polymer for binding the sulfur-based material to the porous carbon material can be used. Accordingly, only an appropriate amount of the binder polymer that may cause an increase in resistance can be used, thereby improving battery performance.

[0075] In the above sulfur-carbon composite, the sulfur-based material may be positioned externally in a manner that at least partially fills the internal space (e.g., pores) of the porous carbon material, or covers at least a portion of the surface of the porous carbon material together with or independently of the internal space. In a specific embodiment, the sulfur-based material may be positioned on less than 100%, 1 to 95%, or 60 to 90% of the surface of the porous carbon material. When the sulfur-based material is present in the above range, wettability with respect to an electrolyte becomes excellent, and electrical conductivity becomes excellent.

[0076] The method for producing the above sulfur-carbon composite is not particularly limited and can be produced using a method commonly used in the art. For example, the sulfur-carbon composite can be produced by mixing sulfur (S8) with a porous carbon material and heat-treating it.

[0077] The above sulfur-carbon complex may be included in an amount of 50 to 95 wt%, 60 to 95 wt%, or 70 to 90 wt% relative to the total 100 wt% of the positive electrode active material layer. When the sulfur-carbon complex is included within the above range, the positive electrode can sufficiently cause an electrochemical reaction.

[0078] The above binder polymer maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to further enhance the bonding strength between them, and any binder polymer known in the art can be used. For example, the binder polymer may be a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butidiene rubber, or styrene-isoprene rubber; a cellulose binder including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyalcohol binder; a polyolefin binder including polyethylene or polypropylene; a polyimide binder; or a polyester binder. A mixture or copolymer of one or more selected from the group consisting of a polyacrylic binder and a silane binder may be used. The content of the binder polymer may be comprised in an amount of 0.5 to 30 wt% based on 100 wt% of the total weight of the positive electrode active material layer. When the content of the binder polymer satisfies this range, the physical properties of the positive electrode are improved, so that the phenomenon of the active material and conductive material in the positive electrode being detached can be prevented, and the ratio of the active material and conductive material in the positive electrode can be appropriately controlled, so that the battery capacity can be secured.

[0079] The conductive material electrically connects the electrolyte and the positive electrode active material, acts as a path for electrons to move from the positive electrode current collector to the positive electrode active material, and improves electrical conductivity or ionic conductivity. Any conductive material can be used without limitation. For example, the conductive material may be carbon black such as Super-P, Denka Black, acetylene black, Ketjen Black, channel black, furnace black, lamp black, summer black, carbon black; carbon derivatives such as carbon nanotubes, graphene, and fullerene; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum, and nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole, which can be used alone or in combination. The content of the conductive material may be 0.01 to 30 wt% based on 100 wt% of the total positive electrode active material layer. When the above-mentioned conductive material is included in the above range, electrons can move better from the positive electrode current collector to the positive electrode active material, and the ionic conductivity or electrical conductivity of the positive electrode can be appropriately maintained.

[0080]

[0081] In one embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0082]

[0083] In one embodiment of the present invention, the positive electrode may include one or more positive electrode tabs. The positive electrode tabs may include the same material as the positive electrode current collector, and may be composed solely of the same material as the positive electrode current collector.

[0084] The positive electrode tab may be formed on the positive electrode current collector. The positive electrode tab may be formed to extend outward from the positive electrode current collector.

[0085]

[0086] In one embodiment of the present invention, the positive electrode tab may be formed by extending the positive electrode current collector itself. Alternatively, the positive electrode tab may be formed by electrically connecting a separate metal (or alloy) to the positive electrode current collector.

[0087] For example, a separate metal (or alloy) may be welded to the positive electrode current collector to form the positive electrode tab. The separate metal (or alloy) is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. may be used.

[0088]

[0089] In one embodiment of the present invention, the loading amount of the cathode may be 1 to 2.5 times the loading amount of the positive electrode.

[0090] The loading amount of the positive electrode active material may be 1 to 2.5 times that of the negative electrode active material. When the loading amounts of the positive electrode active material and the negative electrode active material fall within the above range, the secondary battery can have sufficient energy density and lifespan. In addition, when the negative electrode active material falls within the above range, the range of change in the resistance of the negative electrode can be small, thereby increasing the accuracy of resistance measurement.

[0091]

[0092] The negative electrode according to the present invention is a freestanding type that includes a negative electrode active material and does not have a separate current collector. In one embodiment of the present invention, the negative electrode may be composed solely of the negative electrode active material.

[0093] Conventional secondary batteries use a negative electrode in which a negative electrode active material is coated on a negative electrode current collector. The negative electrode current collector is made of a material with excellent conductivity and does not induce chemical changes in the battery, such as copper or stainless steel. However, when voltage is applied to measure the resistance of the above-described negative electrode, the current flows to the negative electrode current collector with excellent conductivity. Therefore, the resistance measured at this time is actually the resistance of the negative electrode current collector with excellent conductivity. The degree of negative electrode degradation is greatly influenced by the negative electrode active material into which lithium is inserted / deintercalated. In the case of a negative electrode including a negative electrode current collector, as in conventional secondary batteries, even if the resistance of the negative electrode is measured, the resistance of the negative electrode active material is not measured, but rather the resistance of the negative electrode current collector. Therefore, the degree of negative electrode degradation cannot be determined based on the measured resistance. Therefore, the negative electrode included in the secondary battery according to the present invention is a freestanding type that does not have a separate current collector, and the degree of negative electrode degradation can be determined by measuring the resistance of the negative electrode.

[0094]

[0095] The negative active material of the negative electrode according to the present invention includes at least one lithium-based material selected from the group consisting of lithium metal and lithium alloy. The negative electrode may be composed solely of at least one lithium-based material selected from the group consisting of lithium metal and lithium alloy.

[0096] The above lithium alloy includes an element capable of alloying with lithium, and the elements capable of alloying with lithium include Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or alloys thereof.

[0097]

[0098] The cathode according to the present invention includes a first cathode tab and a second cathode tab.

[0099] Since the cathode of the present invention includes two or more cathode tabs, the resistance of the cathode can be measured by connecting a resistance measuring device to different cathode tabs. The resistance measurement is performed by applying current to one cathode tab and receiving current from the other cathode tab, thereby measuring the resistance of the cathode.

[0100]

[0101] However, when the negative tabs are close together, the current applied to one negative tab may flow directly to the other negative tab, or the current applied to one negative tab may pass only a portion of the negative electrode and flow out to the other negative tab. Therefore, when the negative tabs are close together, the resistance of the negative electrode may not be accurately measured.

[0102]

[0103] The first and second negative electrode tabs included in the cathode according to the present invention extend in opposite directions. Therefore, the current applied to one negative electrode tab can flow through as much of the cathode as possible while flowing out to the other negative electrode tab, enabling accurate measurement of the resistance of the cathode and accurate determination of the degree of cathode degradation.

[0104] The fact that the first negative electrode tab and the second negative electrode tab extend in opposite directions means that the second negative electrode tab is provided on the opposite side of the negative electrode that does not come into contact with the side on which the first negative electrode tab is provided. For example, when the negative electrode has a hexahedral structure, the first negative electrode tab may be provided on one side of the side of the hexahedron, and the second negative electrode tab may be provided on the opposite side that does not come into contact with the side on which the first negative electrode tab is provided and is opposite to each other.

[0105]

[0106] Figure 1 is a schematic diagram of a cathode according to the prior art. In Figure 1, arrows indicate the flow of current.

[0107] Referring to the above drawing 1, the first negative electrode tab (11) and the second negative electrode tab (12) extend in the same direction. In this case, the current applied to the first negative electrode tab (11) passes through only a portion of the negative electrode (10) when it flows out to the second negative electrode tab (12). Therefore, the resistance of the entire negative electrode (10) cannot be accurately measured, and the measured value may have a large deviation each time the resistance is measured.

[0108]

[0109] Fig. 2 is a schematic diagram of a cathode according to one embodiment of the present invention. In Fig. 2, arrows indicate the flow of current.

[0110] Referring to the above Fig. 2, the first negative electrode tab (11) and the second negative electrode tab (12) extend in opposite directions with the negative electrode (10) as the center. Therefore, the current applied to the first negative electrode tab (11) to measure the resistance of the negative electrode (10) can pass through the negative electrode (10) while flowing out to the second negative electrode tab (12). Therefore, in this case, the overall resistance of the negative electrode (10) can be accurately measured, and the measured value can have a small deviation each time the resistance is measured.

[0111]

[0112] In one embodiment of the present invention, the first negative electrode tab and the second negative electrode tab may extend outward from the ends in each direction at both width-wise ends or both length-wise ends of the negative electrode. The width-wise direction may refer to the short side of the negative electrode, and the length-wise direction may refer to the long side of the negative electrode.

[0113] For example, the cross-section of the cathode (specifically, the horizontal cross-section) may have a rectangular shape with an aspect ratio of 1 or more. Here, the shorter side of the two adjacent sides may be referred to as the width-direction side, and the longer side may be referred to as the length-direction side. In addition, the first cathode tab and the second cathode tab may extend outward from different width-direction sides, or may extend outward from different length-direction sides, respectively.

[0114]

[0115] Figures 3 and 4 are schematic diagrams showing that the first negative electrode tab (11) and the second negative electrode tab (12) are formed on different width directions of the negative electrode (10), respectively.

[0116] The widthwise sides of the above cathode (10) can be divided into two equal parts, one widthwise side being designated as region 10a and region 10b, and the other widthwise side being designated as region 10c and region 10d. Then, with the cathode (10) as the center, the region 10a and the region 10c are regions that are line-symmetrical to each other, and the region 10b and the region 10d are regions that are line-symmetrical to each other. In addition, the region 10a and the region 10d are regions that are point-symmetrical to each other, and the region 10b and the region 10c are regions that are point-symmetrical to each other.

[0117] The above line symmetry refers to a case where two areas of the sides in the width direction of the cathode can overlap when symmetrical about a straight line, and point symmetry refers to a case where two areas of the sides in the width direction of the cathode do not overlap when symmetrical about a straight line, but are at the same distance with one point between them.

[0118]

[0119] Referring to Fig. 3, the first negative electrode tab (11) is located in the 10a region, and the second negative electrode tab (12) is located in the 10c region. In this case, the first negative electrode tab (11) and the second negative electrode tab (12) are located in regions that are symmetrical with respect to the negative electrode.

[0120]

[0121] Referring to Fig. 4, the first negative electrode tab (11) is located in the 10a region, and the second negative electrode tab (12) is located in the 10d region. In this case, the first negative electrode tab (11) and the second negative electrode tab (12) are located in regions that are point-symmetrical with respect to the negative electrode.

[0122]

[0123] The above FIGS. 3 and 4 illustrate that the first negative electrode tab and the second negative electrode tab are positioned in point-symmetrical or line-symmetrical regions, exemplarily dividing the widthwise side into two equal parts, namely region 10a, region 10b, region 10c, and region 10d. In the present invention, the positions of the first negative electrode tab and the second negative electrode tab are not limited to regions 10a to 10d, and may be positioned at any location on the widthwise side or the lengthwise side. For example, the first negative electrode tab may be positioned in a region including the center portion of the widthwise side, and the second negative electrode tab may be positioned in a region including the center portion of the other widthwise side.

[0124]

[0125] In this way, in the negative electrode according to the present invention, the first negative electrode tab and the second negative electrode tab may be formed in a line-symmetrical region, or may be formed in a point-symmetrical region, respectively. In this way, when the first negative electrode tab and the second negative electrode tab are formed in a line-symmetrical or point-symmetrical region, the current can pass through a large portion of the negative electrode when measuring resistance, so the resistance of the negative electrode can be accurately measured.

[0126]

[0127] In one embodiment of the present invention, the first negative electrode tab and / or the second negative electrode tab may be formed by extending the lithium-based material itself from the lithium-based material negative electrode. That is, the first negative electrode tab and the second negative electrode tab may be composed of the same material as the negative electrode.

[0128]

[0129] In one embodiment of the present invention, the first negative electrode tab and / or the second negative electrode tab may be formed by electrically connecting a separate metal (or alloy) to a lithium-based material negative electrode.

[0130] For example, a separate metal may be welded to the negative electrode to form the first negative electrode tab and / or the second negative electrode tab. The separate metal is not particularly limited as long as it has high conductivity and does not cause a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. may be used.

[0131]

[0132] In one embodiment of the present invention, the first negative electrode tab and the second negative electrode tab may be configured to be connected to a resistance measuring device for measuring the resistance of the negative electrode between them. The degree of deterioration of the negative electrode and the degree of deterioration of the secondary battery including the negative electrode can be determined based on the resistance value of the negative electrode measured by the resistance measuring device.

[0133] For example, when the secondary battery according to the present invention is stored in a pouch case, the first negative electrode tab and the second negative electrode tab may protrude outside the pouch case. Alternatively, a separate electrode lead may be attached to the first negative electrode tab and / or the second negative electrode tab, and the attached electrode lead may protrude outside the pouch case. A resistance measuring device may be electrically connected to the protruding negative electrode tab or electrode lead to measure the resistance of the negative electrode.

[0134]

[0135] A second aspect of the present invention relates to a method for measuring the negative electrode resistance of a secondary battery according to one aspect of the present invention.

[0136] A cathode resistance measurement method according to one aspect of the present invention is:

[0137] According to one aspect of the present invention, a resistance measuring device is connected to the first negative electrode tab and the second negative electrode tab included in the negative electrode of a secondary battery, and the resistance of the negative electrode is measured. The resistance measuring device may be directly or indirectly connected to the first negative electrode tab and the second negative electrode tab. For example, a negative electrode lead may be attached to the first negative electrode tab and / or the second negative electrode tab, and the resistance measuring device may be connected to the negative electrode lead.

[0138]

[0139] In one embodiment of the present invention, resistance measurement can be performed using Electrochemical Impedance Spectroscopy (EIS). EIS is a method of measuring resistance by applying an AC voltage to a measurement target, and interprets the results when an AC voltage is applied to a sample at a certain frequency using a Nyquist pilot. EIS has the advantage of allowing for a wider range of analyses than constant current or constant voltage measurement methods.

[0140]

[0141] In one embodiment of the present invention, the amplitude range of the voltage when measuring the resistance may be 0.01 mV to 0.5 mV, or 0.01 mV to 0.2 mV, or 0.2 mV to 0.5 mV. When the amplitude of the voltage falls within the above range, the accuracy of the measured resistance may be excellent while not causing damage to the secondary battery.

[0142]

[0143] In one embodiment of the present invention, the frequency of the voltage when measuring the resistance may be 100 Hz to 1000 Hz.

[0144]

[0145] In one embodiment of the present invention, a secondary battery can be charged or discharged by connecting a charging / discharging device to one positive electrode tab and a first negative electrode tab. Furthermore, while charging / discharging the secondary battery, a resistance measuring device can be connected to the first negative electrode tab and the second negative electrode tab, thereby measuring the resistance of the negative electrode. That is, while charging or discharging the secondary battery, the resistance of the negative electrode can be measured simultaneously, and the degree of deterioration of the negative electrode and the secondary battery can be determined based on the measured resistance of the negative electrode.

[0146]

[0147] In one embodiment of the present invention, resistance can be measured whenever the State of Charge (SOC) of the secondary battery changes from 5% to 20%, from 5% to 10%, or from 10% to 20%.

[0148]

[0149] Figure 5 schematically illustrates a configuration in which a negative electrode, with two negative tabs formed in opposite directions, and a positive electrode, with one positive tab formed, are laminated with a separator in between. A charging / discharging device can be connected to one positive tab and one negative tab formed in the same direction to operate the secondary battery. Furthermore, a resistance measuring device can be connected to the two negative tabs formed in opposite directions to measure the resistance of the negative electrode.

[0150]

[0151] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0152]

[0153] Example 1

[0154] Loading capacity 5.16mAh / cm 2A lithium metal foil having a thickness of 50 μm was prepared, and the lithium metal foil was punched to form a first negative electrode tab and a second negative electrode tab. At this time, the first negative electrode tab and the second negative electrode tab were formed on each of the widthwise sides of the lithium metal foil, and were formed in an area that was point-symmetrical with respect to the lithium metal.

[0155] A sulfur-carbon composite, in which sulfur (S8) is loaded onto carbon nanotubes, was prepared as a positive electrode active material. The weight ratio of carbon nanotubes to sulfur was 3:7. The prepared sulfur-carbon composite and polyacrylic acid (PAA) as a binder polymer were mixed in a weight ratio of 96:4 and added to water to prepare a positive electrode slurry composition. The positive electrode slurry composition was applied to an aluminum current collector and then dried to prepare a positive electrode. The loading capacity of the prepared positive electrode was 3.3 mAh / cm 2 The above aluminum current collector was used with a positive electrode tab formed on one widthwise side.

[0156] An electrode assembly was manufactured by positioning the positive and negative electrodes so that they face each other and interposing a polyethylene separator having a thickness of 16 μm and a porosity of 46 vol% between them. The electrode assembly was placed in an aluminum pouch, and an electrolyte solution containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt% lithium nitrate (LiNO3) dissolved in a solvent containing 1,3-dioxolane (DOL) and dimethyl ether (DME) in a volume ratio of 1:1 was injected to manufacture a secondary battery.

[0157]

[0158] Experimental example

[0159] A charging / discharging device was connected to the positive electrode tab and the first negative electrode tab of the manufactured secondary battery, and the secondary battery was driven in a range of 1.8 V to 2.5 V in an environment of 25°C to measure the capacity. At this time, charging was performed in 0.2 C CC mode, and discharging was performed in 0.3 C CC mode.

[0160] In addition, a resistance measuring device was connected to the first negative tab and the second negative tab, and the resistance was measured whenever the SOC in the charge / discharge device changed by 10%. The resistance was measured using EIS in a frequency range of 100 Hz to 1000 Hz, and the voltage amplitude was 0.2 mV.

[0161]

[0162] Figure 6 is a graph showing the resistance change within one charge / discharge cycle of the secondary battery of Example 1. When charging from SOC 0% to SOC 100% and then discharging back to SOC 0%, the resistance was measured at 10% SOC intervals. The charging was performed in 0.2C CC mode at 25°C, and the discharging was performed in 0.3C CC mode at 25°C.

[0163] It was confirmed that the resistance decreased as the SOC approached 100%, and increased as the SOC approached 0%. This reflects the increase in resistance due to the decrease in the thickness of the lithium metal foil during discharge, and the decrease in resistance due to the increase in the thickness of the lithium metal foil during charge.

[0164]

[0165] Figure 7 shows the discharge capacity retention rate measured while continuing the charge / discharge cycle for the secondary battery of Example 1, and Figure 8 shows the change in resistance measured while continuing the charge / discharge cycle for the secondary battery of Example 1. The charging was performed in 0.2C CC mode at 25°C, and the discharging was performed in 0.3C CC at 25°C.

[0166] At this time, the discharge capacity retention rate was calculated by the following formula.

[0167] Discharge capacity retention rate (%) = [(discharge capacity of 1 cycle - discharge capacity of n cycles) / discharge capacity of 1 cycle] × 100

[0168]

[0169] Referring to FIGS. 7 and 8, it can be seen that as the cycle progresses, the peak resistance (resistance at the point where the SOC is 0% in each cycle) gradually increases. This is because the lithium metal foil of the negative electrode deteriorates and the resistance increases. In other words, by measuring the resistance of the lithium metal negative electrode using the negative electrode resistance measuring method according to the present invention, information on the deterioration state of the secondary battery can be obtained.

[0170]

[0171] As described above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. In a secondary battery including a positive electrode; a negative electrode; and a separator positioned between the positive electrode and the negative electrode; The above negative electrode is a free-standing type that includes a negative active material and does not have a separate current collector. The above negative active material includes at least one lithium-based material among lithium metal and lithium alloy, A secondary battery characterized in that the negative electrode includes a first negative electrode tab and a second negative electrode tab extending in opposite directions, respectively.

2. In paragraph 1, A secondary battery characterized in that the positive electrode has a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a sulfur-carbon complex and a binder polymer.

3. In paragraph 1, A secondary battery characterized in that the positive electrode includes a positive electrode tab.

4. In paragraph 1, A secondary battery characterized in that the above negative electrode is composed only of at least one lithium-based material among lithium metal and lithium alloy.

5. In paragraph 1 A secondary battery characterized in that the first negative electrode tab and the second negative electrode tab extend outward from the ends of the direction of the negative electrode, respectively, at both ends in the width direction or both ends in the length direction.

6. In paragraph 1 A secondary battery, characterized in that the first negative electrode tab and the second negative electrode tab are positioned in an area symmetrical with respect to the negative electrode.

7. In paragraph 1 A secondary battery, characterized in that the first negative electrode tab and the second negative electrode tab are located in an area that is point-symmetrical with respect to the negative electrode.

8. In paragraph 1, A secondary battery characterized in that the first negative tab and the second negative tab are configured to be connectable to a resistance measuring device for measuring the resistance of the negative electrode.

9. In paragraph 1, A secondary battery characterized in that the above secondary battery can observe the degree of electrical deterioration of the negative electrode and the secondary battery by connecting a resistance measuring device to the first negative electrode tab and the second negative electrode tab.

10. In paragraph 1, A secondary battery characterized in that the positive electrode has a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the loading amount of the negative electrode is 1 to 2.5 times the loading amount of the positive electrode active material.

11. In a method for measuring the negative electrode resistance of a secondary battery according to any one of clauses 1 to 10, A cathode resistance measuring method, characterized by comprising the step of connecting a resistance measuring device to the first cathode tab and the second cathode tab and measuring the resistance of the cathode.

12. In paragraph 11, A cathode resistance measurement method characterized in that the above resistance measurement is performed using an electrochemical impedance analysis method.

13. In paragraph 11, A cathode resistance measurement method characterized in that the above resistance measurement is performed at an amplitude of voltage of 0.01 mV to 0.5 mV.

14. In paragraph 11, A cathode resistance measurement method characterized in that the above resistance measurement is performed at a frequency of 100 Hz to 1000 Hz.

15. In paragraph 11, A cathode resistance measurement method characterized in that the above resistance measurement is performed every time the SOC (State Of Charge) of the secondary battery changes by 5% to 20%.

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