Electrode assembly and secondary battery including the same

Abstract

Disclosed is an electrode assembly and a secondary battery including the same, which can comprehensively solve the problems of lithium deposition caused by an electrode sliding phenomenon, the problem that the outer separator of the half cell is easily folded or torn to expose the electrode, and the problem that it is difficult to check whether the electrode is damaged because the outer separator of the half cell is opaque, by changing the outer separator of the half cell located at the outermost corner of the electrode assembly to a specific shape and material.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0144435 dated October 27, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated as part of this specification.

[0002] The present invention relates to an electrode assembly and a secondary battery including the same, and more particularly, to an electrode assembly and a secondary battery including the same, which can comprehensively solve the problems of lithium deposition caused by an electrode sliding phenomenon, the problem that the outer separator of the half cell is easily folded or broken to expose the electrodes, and the problem that it is difficult to check whether the electrodes are damaged because the outer separator of the half cell is opaque, by changing the shape and material of an outer separator of a half cell located at the outermost corner of the electrode assembly. [Background technology]

[0003] Due to the explosive increase in technological development and demand for mobile devices and automobiles, much research is being conducted on secondary batteries with high energy density, discharge voltage, and excellent output stability. Examples of such secondary batteries include lithium secondary batteries such as lithium-sulfur batteries, lithium ion batteries, and lithium ion polymer batteries. At the same time, such secondary batteries can be classified into cylindrical, rectangular, pouch-type, etc. depending on their shape, and among them, interest and demand for pouch-type battery cells is gradually increasing. Pouch-type battery cells can be stacked with a high degree of integration, have a high energy density per weight, are inexpensive, and are easily modified. Therefore, pouch-type battery cells can be manufactured in shapes and sizes applicable to various mobile devices and automobiles.

[0004] In a typical secondary battery, an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is stacked and housed in a battery case. The electrode assemblies housed in the battery case can be specifically classified into a jelly-roll type (or a winding type) in which a separator is interposed between a sheet-type positive electrode and a negative electrode coated with an active material and the electrode is wound up, a stack type in which a number of positive electrodes and negative electrodes are stacked in sequence with a separator interposed therebetween, and a stack / folding type in which a stack type unit cell is wound up with a long separator.

[0005] Among them, the stack type electrode assembly is manufactured by attaching the cut electrodes to the separator through the lamination process with strong heat and pressure to make a mono cell, stacking them in order, and finally providing a half cell on the top. At the same time, a process of attaching tape at regular intervals can also be performed to fix the stacked mono cell and half cell as one unit.

[0006] However, the stack-type electrode assembly currently being used has a problem that lithium (Li) is deposited in the sliding portion due to the difference in contact area between the positive and negative electrodes caused by the electrode sliding phenomenon. This lithium deposition problem can lead to a decrease in the life span of the battery and can even cause explosions and fires. Therefore, there is a strong demand for the development of a new stack-type electrode assembly that can solve the above problems.

[0007] At the same time, the outer separator of the half cell located at the outermost corner of the electrode assembly is easily bent by equipment or human hands due to its stiffness like a piece of cloth, and can be torn if rubbed against a hard or sharp part, exposing the electrodes. In addition, since the outer separator of the half cell is opaque (i.e., it does not transmit light), it is difficult to check whether the electrodes are damaged. Therefore, it is necessary to change the outer separator of the half cell located at the outermost corner of the electrode assembly to a material that (1) has tensile strength that does not easily break without bending, (2) transmits light well, (3) is easy to supply and is cost competitive, (4) does not chemically react when the electrolyte penetrates, (5) has excellent thermal stability to withstand high temperatures during charging, and (6) is light and does not harm the competitiveness of capacity per weight. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide an electrode assembly and a secondary battery including the same, which can comprehensively solve the problems of lithium deposition caused by an electrode sliding phenomenon, the problem that the outer separator of the half cell is easily folded or broken to expose the electrodes, and the problem that it is difficult to check whether the electrodes are damaged because the outer separator of the half cell is opaque, by changing the shape and material of the outer separator of the half cell located at the outermost corner of the electrode assembly. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides an electrode assembly including: a mono cell formed by sequentially stacking a unit cell in which a separator and a negative electrode are stacked, and a unit cell in which a separator and a positive electrode are stacked; a half cell in which a separator, a negative electrode or a positive electrode, and a pressure plate are stacked; and a wrapping member in which the mono cell and the half cell are stacked and then wound and fixed in a width direction, the half cells being stacked such that a separator is located on an upper surface of the negative electrode or the positive electrode exposed to the outside of the mono cell, different electrodes are located on either side of the separator, and the pressure plate of the half cell includes an inclined portion inclined toward the electrode at both ends in a longitudinal direction of the electrode facing portion.

[0010] The present invention also provides a secondary battery including the electrode assembly; and a housing case that houses the electrode assembly. Effect of the Invention

[0011] According to the electrode assembly and the secondary battery including the same according to the present invention, by changing the outer separator of the half cell located at the outermost corner of the electrode assembly to a specific shape and material, it has an advantage that it is possible to comprehensively solve the problems of lithium deposition caused by the electrode sliding phenomenon, the problem that the outer separator of the half cell is easily folded or broken to expose the electrode, and the problem that it is difficult to check whether the electrode is damaged because the outer separator of the half cell is opaque. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic side view showing an electrode sliding phenomenon that occurs in a conventional stack-type electrode assembly. [Diagram 2] 1 is a schematic side view showing that the contact area with a separator changes depending on the difference in the degree to which one end of a positive electrode active material and one end of a negative electrode active material are slid in one mono-cell. FIG. [Diagram 3] FIG. 2 is a schematic side view showing a state in which one end of a positive electrode active material and one end of a negative electrode active material are slid against each other in one mono-cell, and at the same time, the negative electrode active material and a separator are separated from each other. [Figure 4] 1 is a schematic diagram of a conventional stack-type electrode assembly in which a negative electrode active material is designed to be longer than a positive electrode active material. [Diagram 5] 1 is a schematic side view showing a problem that the contact area between the positive electrode active material and the separator is larger than the contact area between the negative electrode active material and the separator even if the negative electrode active material is designed to be longer than the positive electrode active material. FIG. [Figure 6] FIG. 2 is a schematic diagram showing a state in which a conventional stack-type electrode assembly is fixed and compressed with tape. [Figure 7] 1 is a schematic side view of an electrode assembly according to an embodiment of the present invention; [Figure 8]4 is a schematic side view of a pressure plate provided at the outermost corner of a half cell of an electrode assembly according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will now be described in detail with reference to the accompanying drawings.

[0014] Fig. 1 is a schematic side view showing the electrode sliding phenomenon that occurs in a conventional stack-type electrode assembly. In a conventional stack-type electrode assembly, as shown in Fig. 1, a viscous liquid electrode active material 20 is applied to one side of a metal current collector 10 (e.g., the positive electrode may be aluminum and the negative electrode may be copper), and at this time, a slope S having a length of several mm to several tens of mm is formed on each end (the direction where the tabs are located) of the electrode active material 20 due to surface tension or uneven heat during the process, and this is called the electrode sliding phenomenon.

[0015] 2 is a schematic side view showing that the contact area with the separator changes depending on the difference in the degree of sliding of one end of the positive and negative active materials in one monocell, where FIG. 2a corresponds to the case where the contact area between the negative active material 30 and the separator 50 is larger than the contact area between the positive active material 40 and the separator 50, and FIG. 2b corresponds to the case where the contact area between the positive active material 40 and the separator 50 is larger than the contact area between the negative active material 30 and the separator 50 (the vertical line in the active materials 30, 40 indicates the point where the inclination begins). As described above, when the electrode active material is applied, a sliding phenomenon occurs, and at this time, as shown in FIG. 2b, if the contact area between the negative active material 30 and the separator 50 is narrower than the contact area between the positive active material 40 and the separator 50, lithium is inevitably precipitated in the narrowed area. Therefore, the contact area between the negative electrode active material 30 and the separator 50 needs to be larger than the contact area between the positive electrode active material 40 and the separator 50 .

[0016] FIG. 3 is a schematic side view showing a state in which one end of a positive active material and one end of a negative active material are slid together in one monocell, and at the same time, the negative active material and the separator are separated from each other. At the same time, as shown in FIG. 3, when the negative active material 30 and the separator 50 are separated from each other, lithium deposition may occur as in the case of the difference in contact area between the active material and the separator. Therefore, there should be no empty space (G) between the negative active material 30 and the separator 50. FIG. 3 is an example, and when the positive active material 40 and the separator 50 are separated from each other, lithium may be deposited, so that there should be no empty space between the negative active material 30 and the separator 50 and between the positive active material 40 and the separator 50.

[0017] 4 is a schematic diagram of a conventional stack-type electrode assembly in which the negative active material is designed to be longer than the positive active material. For the above reasons, in the industry, as shown in FIG. 4, the contact area between the negative active material 30 and the separator 50 is larger than the contact area between the positive active material 40 and the separator 50, and an electrolyte is injected and pressed so that there is no empty space between the negative active material 30 and the separator 50 and between the positive active material 40 and the separator 50.

[0018] 5 is a schematic side view showing a problem that the contact area between the positive active material and the separator is wider than the contact area between the negative active material and the separator even if the negative active material is designed to be longer than the positive active material. As described above, in the industry, the contact area between the negative active material 30 and the separator 50 is wider than the contact area between the positive active material 40 and the separator 50, and an electrolyte is injected and pressed so that there is no empty space between the negative active material 30 and the separator 50 and between the positive active material 40 and the separator 50. However, even if manufactured in this way, a problem occurs in that the contact area between the positive active material 40 and the separator 50 is wider than the contact area between the negative active material 30 and the separator 50 as shown in FIG. 5. That is, even if the negative electrode active material 30 is designed to be longer than the positive electrode active material 40, the slope of the negative electrode active material 30 formed during sliding is gentler than the slope of the positive electrode active material 40, so that the contact area between the negative electrode active material 30 and the separator 50 is smaller than the contact area between the positive electrode active material 40 and the separator 50. In addition, as shown in FIG 5, this problem is difficult to solve even by squeezing.

[0019] FIG. 6 is a schematic diagram showing a state where a conventional stacked electrode assembly is fixed and compressed with tape. In addition, in order to solve the above problem, that is, the contact area between the negative active material 30 and the separator 50 is narrower than the contact area between the positive active material 40 and the separator 50 even if the negative active material 30 is designed to be longer than the positive active material 40, the industry has used a method of fixing and compressing the electrode assembly (half cell + mono cell) with tape 60 (halogen free) in addition to squeezing as shown in FIG. 6. However, because it is difficult to attach tape to both ends of the electrode sliding due to the structure of the stacked electrode assembly, tape is attached only to the center and its periphery as shown in FIG. 6 (for example, 3 to 5 pieces of tape are attached with a width of 20 to 30 mm excluding both ends of the electrode assembly). Therefore, both ends of the electrode assembly where the electrode sliding phenomenon occurs and the inclined parts are formed cannot bear the force of the tape at all, and ultimately, this case also leads to explosion and fire due to lithium deposition.

[0020] Therefore, the applicant has developed a stack-type electrode assembly in which there is no or minimal empty space between the negative active material and the separator and between the positive active material and the separator, and in which the contact area between the negative active material and the separator is larger than the contact area between the positive active material and the separator even when the electrode assembly is fixed and compressed with a wrapping member.

[0021] The present invention will now be described in more detail with reference to the accompanying drawings.

[0022] FIG. 7 is a schematic side view of an electrode assembly according to an embodiment of the present invention, and FIG. 8 is a schematic side view of a pressure plate provided at the outermost corner of a half cell of the electrode assembly according to an embodiment of the present invention. 7 and 8, an electrode assembly 100 according to an embodiment of the present invention includes a mono-cell 120 formed by sequentially stacking a unit cell in which a separator and a negative electrode 112 are stacked, and a unit cell in which a separator 114 and a positive electrode 116 are stacked, a half-cell 130 in which a separator 134b, an electrode 132 (negative electrode or positive electrode), and a pressure plate 134a are stacked, and a wrapping member 150 in which the mono-cell 120 and the half-cell 130 are stacked and then wound and fixed in the width direction, the half-cell 130 is stacked such that the separator 134b is located on the upper surface of the negative electrode or positive electrode exposed to the outside of the mono-cell 120, different electrodes are located with the separator 134b as a boundary, and the pressure plate 134a of the half-cell 130 includes an inclined portion P inclined toward the electrode at both ends of the electrode facing portion in the longitudinal direction.

[0023] The most distinctive feature of the present invention is the shape of the pressure plate 134a provided at the outermost corner of the half cell 130 of the electrode assembly 100. That is, as shown in Fig. 7 and Fig. 8, the surface (i.e., electrode facing portion) of the pressure plate 134a located at the outermost corner of the half cell 130 facing the negative electrode (electrode 132) has an inclined portion P inclined toward the electrode and is closer to the electrode 132 (negative electrode or positive electrode) as it approaches both ends in the longitudinal direction, in order to increase the contact area between the electrode 132 included in the half cell 130 and the pressure plate 134a through the inclined portions S formed at both ends of the electrode active material included in the electrode when it is applied to the metal collector, which is a sliding phenomenon that occurs when a viscous electrode active material is applied to a metal collector.

[0024] More ultimately, the surface of the pressure plate 134a located at the outermost corner of the half cell 130 facing the electrode 132 is configured to become closer to the electrode 132 toward both ends in the longitudinal direction in order to make the contact area between the negative electrode 112 and the separator 114 in each unit mono-cell 110 located at the bottom of the half cell 130 larger than the contact area between the positive electrode 116 and the separator 114 (thus, the contact area between the negative electrode and the separator in the electrode assembly is larger than the contact area between the positive electrode and the separator).

[0025] That is, when the wrapping member 150 surrounds, fixes, and compresses the outer peripheral surfaces of the mono-cell 120 and the half-cell 130 together in the width direction, the sloped portions P at both ends of the pressure plate 134a included in the half-cell 130 are in close contact with the electrode 132. At the same time, both ends of the separator 134b included in the half-cell 130 and both ends of the electrode and separator included in the mono-cell 120 are pulled downward together, so that the contact area between the negative electrode 112 and the separator 114 in each unit mono-cell 110 becomes larger than the contact area between the positive electrode 116 and the separator 114. In other words, both ends of the sloped portions of the negative electrode active material included in the negative electrode 112 in each unit mono-cell 110 are matched with both ends of the separator 114 facing the both ends.

[0026] 2, 3 and 5, the inclined portion formed by the sliding of the negative active material 30 faces upward, while the inclined portion formed by the sliding of the positive active material 40 faces downward. In other words, when both ends of the separator 114 of the unit mono-cell 110 are pulled by the wrapping member 150, it matches the shape of the negative electrode 112 having an upward inclined portion, but does not match the shape of the positive electrode 116 having a downward inclined portion. That is, the inclined portions of both ends of the negative active material included in the negative electrode 112 of the unit mono-cell 110 face upward and match both ends of the separator 114 facing thereto, and the inclined portions of both ends of the positive active material included in the positive electrode 116 of the unit mono-cell 110 face downward and do not match both ends of the separator 114 facing thereto. For this reason, the contact area between the negative electrode 112 and the separator 114 in each unit monocell 110 is larger than the contact area between the positive electrode 116 and the separator 114. At this time, it goes without saying that there is no or minimal empty space between the negative electrode and the separator and between the positive electrode and the separator in the electrode assembly.

[0027] At the same time, the separator located to face the upper surface of the negative electrode 112 among the separators included in the mono-cell 120 may have a shape in which the surface facing the negative electrode 112 contacts the negative electrode 112 toward both ends in the longitudinal direction, similar to the pressure plate 134a included in the half-cell 130 (i.e., similar to the shape shown in FIG. 7). That is, the both ends may have a larger thickness than the center (i.e., may have a slope).

[0028] Meanwhile, each of both ends of the pressure plate 134a included in the half cell 130 is close to the electrode 132 included in the half cell 130 as described above. Therefore, each of both ends of the pressure plate 134a included in the half cell 130 has a thickness greater than the center of the pressure plate 134a included in the half cell 130. For example, the thickness of each of both ends of the pressure plate 134a included in the half cell 130 may be about 30 μm to 50 μm thicker than the thickness of the center (gradually becoming thicker toward the end), and when this is applied to an electrode assembly including about 20 (stack) unit mono cells, the negative electrode can contact the separators included in all the unit mono cells with the maximum area.

[0029] Therefore, the pressure plate 134a must include an inclined portion P in which the electrode facing portion at both ends in the longitudinal direction is inclined toward the electrode. In this case, the pressure plate 134a may have a plate shape in which both ends in the longitudinal direction are curved toward the electrode. Also, the curved portion of the pressure plate 134a may be in a straight line shape or in a curved surface shape curved toward the electrode. Meanwhile, as shown in FIG. 8, the pressure plate 134a may have a flat plate shape as a basic structure, and an inclined surface structure that gradually becomes thicker toward the end portion may be added to the electrode facing surface at both ends in the longitudinal direction. In this case, the inclined surface may be in a straight line shape or in a curved surface shape curved toward the electrode. In addition, the pressure plate 134a may have an electrode facing surface that is concave and curved in the longitudinal direction, and there is no particular restriction on the shape as long as the thickness of both ends is thicker than the center.

[0030] If the pressure plate 134a included in the half cell 130 has excellent bending strength and hardness, the above-described effects can be more pronounced. For this reason, the pressure plate 134a may contain polypropylene resin, and preferably may be made of only polypropylene resin. The melting point of the pressure plate 134a containing polypropylene resin is about 170° C., and the specific gravity is about 0.91 g / cm.3 At the same time, the temperature of the heater rises to about 80°C during the related process, but if the pressure plate 134a contains polypropylene resin, which has a high melting temperature of about 135°C to 160°C, as described above, there is an advantage that the pressure plate 134a does not melt at all even if the heater temperature rises to the maximum value.

[0031] Usually, the outer separator (corresponding to the pressure plate of the present invention) of the half cell located at the outermost corner of the electrode assembly is often touched by equipment and human hands, and even if it is as rigid as a piece of cloth, it is easily bent, and if it is scratched by a hard or sharp part, it can be torn, exposing the electrode. Such problems can reduce the performance of the battery and even cause a fire. Therefore, the applicant has changed the material to a stabilized polypropylene resin that has not only rigidity (excellent bending strength and hardness) but also does not deform even with electrolyte (i.e., excellent chemical stability (acidity and alkalinity at room temperature)) instead of the existing general material, focusing on the fact that the outer surface of the outer separator included in the half cell is not related to the battery reaction, and thereby it is possible to solve the problems that the existing material had. Furthermore, if the pressure plate 134a is made of transparent polypropylene resin and a transparent adhesive (e.g., epoxy adhesive) is used, it is even possible to check the condition of the electrode 132 in the half cell 130, such as knowing if it will break due to an external impact.

[0032] The wrapping member 150 surrounds the outer periphery of the mono-cell 120 and the half-cell 130 together in the width direction and serves to pull both ends of the pressure plate 134a included in the half-cell 130 with a stronger force. Therefore, the wrapping member 150 should be located at least one at each end of the electrode assembly 100 to surround the outer periphery of the mono-cell 120 and the half-cell 130. However, it is preferable that the center of the electrode assembly 100 is also surrounded by the wrapping member 150 so that the contact area between the electrodes and the separator is increased. In addition, there is no particular limit to the number of wrapping members 150 installed as long as the contact area between the electrodes and the separator can be increased to the maximum.

[0033] Examples of the wrapping member 150 include an adhesive member provided with an adhesive component and a non-adhesive member that does not. The adhesive member provided with an adhesive component may be a tape or a member that does not break to an appropriate level even when a tensile force is applied to it, to which an adhesive component is separately applied. And, the non-adhesive member may be a member that does not break to an appropriate level even when a tensile force is applied to it, in which case, since adhesion is not possible, it can be fixed in place by various methods such as surrounding the electrode assembly and tying both ends.

[0034] Meanwhile, according to another embodiment of the present invention, a groove (or engraved pattern, G) capable of receiving and fixing the wrapping member 150 may be formed in the width direction on the opposite surface (i.e., outer surface) of the pressure plate 134a provided at the outermost corner of the half cell 130, which is not opposed to the electrode 132, as shown in Figs. 7 and 8. This is for more stable fixing and compression, and the groove G may be formed at least at both ends of the opposite surface of the pressure plate 134a provided at the outermost corner of the half cell 130, which is not opposed to the electrode 132. In addition, it is preferable that the groove G is formed up to the center of the opposite surface of the pressure plate 134a provided at the outermost corner of the half cell 130, which is not opposed to the negative electrode (electrode 132). At the same time, as long as the effect of the wrapping member 150 received and fixed in the groove G can be maximized, the number of the grooves G is not particularly limited, and for example, two to five grooves G may be formed as described above. As described above, the wrapping member 150 is characterized by being wound so as to be accommodated in the groove portion G.

[0035] Also, there is no particular limitation on the width and depth of the groove G since the width and depth of the groove G can be variously set according to the width and depth of the wrapping member 150. However, as an example, when the thickness of each end of the pressure plate 134a included in the half cell 130 is about 30 μm to 50 μm thicker than the thickness of the center (as an extreme example, when the thickness of each end of the pressure plate 134a is 210 μm to 230 μm and the thickness of the center of the pressure plate 134a is 180 μm), it is preferable that the depth of the groove G is about 22 μm.

[0036] Next, a secondary battery according to the present invention will be described. The secondary battery includes the electrode assembly of the present invention described above and a storage case that stores the electrode assembly. The secondary battery is not particularly limited in its use, but is preferably a battery for automobiles. The secondary battery may be any battery that can store the electrode assembly inside a storage case such as a pouch, but is preferably a lithium-based secondary battery. The lithium-based secondary battery may be any lithium-based secondary battery that has a lithium precipitation problem, and more specifically, may be a lithium ion battery.

[0037] When the secondary battery of the present invention is a lithium ion battery, examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compound (LiFePO4), and lithium nickel cobalt manganese-based positive electrode active material (or lithium NCM-based positive electrode active material, or NCM-based lithium composite transition metal oxide, or high Ni positive electrode material), etc. In addition to the positive electrode active material, the positive electrode further includes a binder and a conductive material, etc.

[0038] The binder is a component useful for binding the positive electrode material (positive electrode active material) to the conductive material and the current collector, and may be, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof, but is not necessarily limited thereto.

[0039] The binder is typically added in an amount of 1 to 50 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the binder is less than 1 part by weight, the adhesive strength between the positive electrode material and the current collector may be insufficient, and if the content of the binder exceeds 50 parts by weight, the adhesive strength is improved, but the content of the positive electrode material is reduced accordingly, resulting in a low battery capacity.

[0040] The conductive material contained in the positive electrode is not particularly limited as long as it has excellent electrical conductivity without causing side reactions in the internal environment of the battery and without causing chemical changes in the battery. Representative examples include graphite or conductive carbon. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, dengue black, thermal black, channel black, furnace black, and lamp black; carbon-based materials having a graphene or graphite crystal structure; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination, but are not necessarily limited thereto.

[0041] The conductive material is usually added in an amount of 0.5 to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the conductive material is too low, such as less than 0.5 parts by weight, it is difficult to expect an effect of improving electrical conductivity or the electrochemical characteristics of the battery may be reduced, and if the content of the conductive material is too high, such as more than 50 parts by weight, the amount of the positive electrode material may be relatively small, and the capacity and energy density may be reduced. The method of incorporating the conductive material into the positive electrode is not greatly limited, and a conventional method known in the art, such as coating on the positive electrode material, may be used. In addition, if necessary, a conductive second coating layer may be added to the positive electrode material to replace the addition of the conductive material as described above.

[0042] In addition, a filler may be selectively added to the positive electrode as a component for suppressing the expansion of the positive electrode. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and examples of such a filler include polyolefin polymers such as polyethylene and polypropylene, and fibrous materials such as glass fiber and carbon fiber.

[0043] The cathode material, binder, conductive material, etc. are dispersed and mixed in a dispersion medium (solvent) to prepare a slurry, which is then coated on a cathode current collector, and then dried and rolled to manufacture the cathode. The dispersion medium may be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or a mixture thereof.

[0044] The positive electrode current collector may be, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, and aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The positive electrode current collector may be in the form of a foil, a film, a sheet, a punched piece, a porous body, a foam, or the like.

[0045] The negative electrode may be manufactured by a conventional method known in the art. For example, a negative electrode active material, a conductive material, a binder, and optionally a filler may be dispersed and mixed in a dispersion medium (solvent) to prepare a slurry, which may then be applied onto a negative electrode current collector, and then dried and rolled to manufacture the negative electrode. The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; SiO β(0<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, among which one or a mixture of two or more may be used. Also, a metallic lithium thin film may be used as the negative electrode active material. Also, both low crystalline carbon and high crystalline carbon may be used as the carbon material. Representative examples of low crystalline carbon include soft carbon and hard carbon, while representative examples of high crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature plastic carbon such as petroleum or coal tar pitch derived cokes.

[0046] The binder and conductive material used in the negative electrode may be the same as those described in the positive electrode. The negative electrode current collector may be made of platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, and copper (Cu) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not limited thereto. The negative electrode current collector may be in the form of a foil, a film, a sheet, a punched piece, a porous body, a foam, or the like.

[0047] The inner separators other than the pressure plate 134a located at the outermost corner of the half cell in the electrode assembly may be made of olefin polymers such as polyethylene and polypropylene, glass fiber, etc. in the form of a sheet, multi-layer film, microporous film, woven fabric, nonwoven fabric, etc., but are not necessarily limited thereto. However, it is preferable to use porous polyethylene or porous glass fiber nonwoven fabric as the separator, and it is more preferable to use porous glass filter (glass fiber nonwoven fabric) as the separator.

[0048] On the other hand, when a solid electrolyte such as a polymer (e.g., an organic solid electrolyte, an inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte can also serve as the separation membrane. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separation membrane may generally be in the range of 0.01 μm to 10 μm, and the thickness may generally be in the range of 5 μm to 300 μm, but is not limited thereto.

[0049] In the electrolyte or electrolytic solution, a carbonate, an ester, an ether or a ketone may be used alone or in combination as a non-aqueous electrolytic solution (non-aqueous organic solvent), but is not necessarily limited thereto. For example, aprotic organic solvents such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydrofuran derivatives such as 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate may be used, but are not necessarily limited thereto.

[0050] The electrolyte may further contain a lithium salt (so-called lithium salt-containing non-aqueous electrolyte). The lithium salt may be a known substance that is easily dissolved in a non-aqueous electrolyte, such as LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiPF3(CF2CF3)3, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, lithium imide, etc., but are not necessarily limited thereto. For the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, glyme-based compounds, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added to the (non-aqueous) electrolyte. If necessary, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further added to impart non-flammability, and carbon dioxide (carbon dioxide gas) may be further added to improve high-temperature storage properties.

[0051] Meanwhile, the secondary battery may be manufactured by a conventional method in the art. For example, the secondary battery may be manufactured by inserting a porous separator between a positive electrode and a negative electrode, and then introducing a non-aqueous electrolyte. The lithium secondary battery according to the present invention may be applied to a battery cell used as a power source for a small device, and may be particularly suitable for use as a unit battery of a battery module that is a power source for a medium- to large-sized device. In this respect, the present invention also provides a battery module including two or more secondary batteries electrically connected (in series or parallel). Of course, the number of secondary batteries included in the battery module may be variously adjusted in consideration of the use and capacity of the battery module.

[0052] The present invention further provides a battery pack in which the battery modules are electrically connected according to a conventional technique in the art. The battery modules and the battery pack can be used as a power source for one or more medium- to large-sized devices including, but not limited to, power tools, electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric trucks, electric commercial vehicles, or power storage systems.

[0053] Although the present invention has been described through preferred embodiments as described above, the present invention is not limited thereto, and those skilled in the art to which the present invention pertains can easily understand that various modifications and variations are possible without departing from the concept and scope of the claims below. [Explanation of symbols]

[0054] 10: Metal current collector 20: Electrode active material 30: Negative electrode active material 40: Positive electrode active material 50: Separation membrane 60: Tape 100: Electrode assembly 110: Unit Monocell 112: Negative electrode 114: Separation membrane 116: Positive electrode 120: Monocell 130: Half cell 132: Electrode 134a: Pressure plate 134b: Separation membrane 150: Wrapping material S: Inclined part G:Groove

Claims

1. a monocell formed by sequentially stacking a unit cell in which a separator and a negative electrode are stacked and a unit cell in which the separator and a positive electrode are stacked; A half cell in which the separator, the negative electrode, and a pressure plate are stacked; and The mono-cell and the half-cell are laminated together, and then the mono-cell and the half-cell are wrapped and fixed in a width direction by a wrapping member. The half-cell is stacked such that the separator is located on an upper surface of the positive electrode exposed to the outside of the mono-cell, and different electrodes are located on either side of the separator, The pressure plate of the half cell includes an inclined portion inclined toward the electrode at both ends in the longitudinal direction of the electrode facing portion, The pressure plate comprises a polypropylene resin. Electrode assembly.

2. 2. The electrode assembly according to claim 1, wherein the pressure plate has a thickness at each end that is 30 to 50 [mu]m thicker than the thickness at the center.

3. 2. The electrode assembly according to claim 1, wherein the pressure plate has a plate shape with both ends in a longitudinal direction bent toward the electrode.

4. 4. The electrode assembly according to claim 3, wherein the curved portion of the pressure plate is in a straight line shape or in a curved shape curved toward the electrode.

5. 2. The electrode assembly of claim 1, wherein the pressure plate has a flat plate shape as a basic structure, and has an inclined surface structure that becomes gradually thicker toward the end on the electrode facing surface at both ends in the longitudinal direction.

6. The electrode assembly according to claim 5 , wherein the inclined surface forming structure is a straight line or a curved surface bent toward the electrode.

7. 2. The electrode assembly according to claim 1, wherein the pressure plate has a curved surface that is concavely curved in the longitudinal direction on a surface facing the electrode.

8. 2. The electrode assembly according to claim 1, wherein the pressure plate has a groove formed in an outer surface thereof in a width direction thereof for receiving the wrapping member.

9. The electrode assembly of claim 8 , wherein the number of the grooves is two to five.

10. The electrode assembly of claim 8 , wherein the wrapping member is wound to be received in the groove.

11. The electrode assembly of claim 1 , wherein a contact area between the negative electrode and the separator in the electrode assembly is larger than a contact area between the positive electrode and the separator.

12. 2. The electrode assembly according to claim 1, wherein the pressure plate is made solely of polypropylene resin.

13. A secondary battery comprising: the electrode assembly according to claim 1 ; and a storage case that houses the electrode assembly.

14. The secondary battery according to claim 13 , wherein the secondary battery is a lithium-based secondary battery.

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