KR20190009242A - Cathode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides an anode for a lithium secondary battery and a lithium secondary battery including the same for ensuring the safety of the lithium secondary battery in an overcharged state. The anode for a lithium secondary battery according to the present invention comprises: an anode current collector; an anode active material coating portion formed on at least one surface of the anode current collector; and a gas generating layer formed only on the uncoated portion of the anode in which the anode active material coating portion is not formed in the anode current collector and including gas generating agent particles, a binder polymer, and a conductive material.

Description

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same,

The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a positive electrode for a lithium secondary battery capable of improving the safety of the lithium secondary battery by generating a gas at a specific voltage, .

The use of portable electronic products such as camcorders, mobile phones, and notebook PCs has become common due to the small size, light weight, and high functionality of devices due to rapid development of electronics, communication, and computer industries. Demand is rising. In particular, the rechargeable lithium secondary battery has a high energy density per unit weight and can be rapidly charged as compared with conventional lead batteries, nickel-cadmium batteries, nickel-hydrogen batteries and nickel-zinc batteries, .

In recent years, overcharging has been a problem due to the development and application of high capacity active material, thin separator, and high voltage driving technology for high energy density and low cost of lithium secondary batteries. In the overcharging situation, A solution is needed. In particular, since lithium secondary batteries use an organic solvent which is flammable, it is necessary to secure safety when the battery becomes abnormal due to overcharging or the like.

To this end, a safety device inside the battery, such as a pressure CID (Current Interrupt Device), which is operated by an increase in the battery internal pressure, is provided at the overcharge end voltage, and lithium carbonate (Li ₂ CO ₃ ) A technique for raising the internal pressure of the battery to such an extent that it can be made is proposed in various documents including Patent Document 1.

However, in Patent Document 1, lithium carbonate is uniformly present in the positive electrode active material layer. Here, lithium carbonate acts as a resistor in a normal charge / discharge cycle. Therefore, the battery described in Patent Document 1 has a problem of causing an increase in internal resistance at the time of normal charge / discharge.

Moreover, in Patent Document 1, there arises a problem that the resistance increases after the cycle. When the resistance increases after the cycle, gas is locally generated and accumulated in the pores of the electrode, and as a result, there is a possibility that cycle performance may be deteriorated as the interfacial resistance increases.

Even if the patent document 1 is improved, it takes a long time to generate sufficient gas from the lithium carbonate, or the anode resistance does not increase much more than expected, and it takes a long time to reach the overcharge end voltage, .

In addition, since lithium carbonate is present in the positive electrode active material layer in the prior art, there is a problem that the active material content causing the battery capacity is reduced and the energy density is reduced.

Japanese Patent Application Laid-Open No. 2008-186792

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a positive electrode for a lithium secondary battery securing the safety of a lithium secondary battery in an overcharged state.

Another object to be solved by the present invention is to provide a lithium secondary battery including such a positive electrode.

A positive electrode for a lithium secondary battery according to the present invention includes: a positive electrode collector; A cathode active material coating portion formed on at least one surface of the cathode current collector; And a gas generating layer formed only on the cathode uncoated portion where the cathode active material coating portion is not formed in the cathode current collector and including the gas generating agent particles, the binder polymer, and the conductive material.

The gas generating layer may be spaced apart from the cathode active material coating portion.

The gas generating agent particles may include lithium carbonate (Li ₂ CO ₃ ), calcium carbonate (CaCO ₃ ), lithium oxalate (C ₂ Li ₂ O ₄ ), or a mixture of two or more thereof.

It is preferable that the gas generating layer is a porous structure having the pores formed by the void spaces between the gas generating agent particles and the gas generating agent particles being connected and fixed to each other by the binder polymer.

The gas generating layer may have a concavo-convex structure formed integrally with the surface and being integrally formed on the surface, or may be a layer patterned to partially expose the positive electrode uncoated portion to form a gas movement path.

In one embodiment, the cathode current collector is a sheet longer than the width, and the cathode active material coating portion includes a first cathode active material layer formed on one surface of the cathode current collector; And a second cathode active material layer formed on the other surface of the cathode current collector on the opposite side of the first cathode active material layer and being formed longer than the first cathode active material layer in the longitudinal direction of the cathode current collector, And a first gas generating layer formed on a positive electrode uncoated portion where the first positive electrode active material layer is not formed on one surface of the current collector.

In this case, the first gas generating layer is formed in the first cathode active material layer in the longitudinal direction of the cathode current collector, and is formed to have the same width as the first cathode active material layer in the width direction of the cathode current collector Can be. The first gas generating layer may be formed to correspond to a position where the second cathode active material layer is terminated.

In another embodiment, the gas generating layer further includes a second gas generating layer formed on the other surface of the cathode current collector on the anode uncoated portion where the second cathode active material layer is not formed.

In this case, the second gas generating layer is formed adjacent to the second cathode active material layer in the longitudinal direction of the cathode current collector, and is formed to have the same width as the second cathode active material layer in the width direction of the cathode current collector Can be. The second gas generating layer may be formed to correspond to a position where the first gas generating layer is terminated.

The lithium secondary battery according to the present invention is a positive electrode for a lithium secondary battery according to the present invention; A negative electrode including a negative electrode current collector and a negative electrode active material coating portion formed on at least one side of the negative electrode current collector; And an electrode assembly including a separator interposed between the anode and the cathode.

In a preferred embodiment, the positive electrode includes a positive electrode collector of a sheet longer than the width as in the embodiment of the positive electrode for a lithium secondary battery according to the present invention. And the negative electrode includes a negative electrode current collector of the sheet corresponding to the positive electrode current collector. An anode active material coating portion is formed on at least one surface of the anode current collector. The electrode assembly is wound between the positive electrode and the negative electrode with the separator interposed therebetween and wound from one side of the positive electrode collector and the negative electrode collector along the longitudinal direction of the positive electrode collector and the negative electrode collector.

In particular, the electrode assembly may be a wound electrode assembly, and the gas generating layer of the anode may be located at an outermost portion of the electrode assembly. The electrode assembly may be a wound type, a stack type, a stack and a folding type, .

According to the present invention, in a situation where the lithium secondary battery is overcharged, the lithium secondary battery quickly reaches the overcharge end voltage due to the gas generated in the gas generating layer formed in the positive electrode uncoated portion of the positive electrode collector, Can be secured.

Further, since the battery internal pressure increases quickly, the safety device inside the battery such as the pressure CID operates, thereby effectively limiting overcharging.

In addition, the time required for reaching the overcharge end voltage is shortened, thereby providing a lithium secondary battery improved in safety.

Further, since the gas generating layer is further formed only on the positive electrode uncoated portion of the positive electrode current collector, there is an advantage that the amount of the positive electrode active material loaded for realizing the desired capacity is not reduced.

In the present invention, the gas generating layer may be formed apart from the cathode active material coating portion. Therefore, the gas generating layer does not act as a resistor at the time of normal charge / discharge. Therefore, the gas generating layer does not increase the internal resistance at the time of normal charge / discharge. In addition, the resistance does not increase after the cycle.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a perspective view of a positive electrode for a lithium secondary battery according to an embodiment of the present invention.
2 is a longitudinal sectional view of the positive electrode for a lithium secondary battery shown in Fig.
3 is a longitudinal cross-sectional view of a positive electrode for a lithium secondary battery according to another embodiment of the present invention.
4 is a longitudinal cross-sectional view of a positive electrode for a lithium secondary battery according to another embodiment of the present invention.
5 is a view showing an example of a gas generating layer included in a positive electrode for a lithium secondary battery of the present invention.
6 is a view showing another example of the gas generating layer included in the positive electrode for a lithium secondary battery of the present invention.
7 and 8 are views for explaining an electrode assembly of a lithium secondary battery according to the present invention.
Figs. 9 and 10 are graphs showing the electrode resistance evaluation results of Examples and Comparative Examples. Fig.
11 is a graph showing the results of AC resistance evaluation of Examples and Comparative Examples.
12 is a graph showing the charging / discharging profile of the embodiment and comparison battery.
13 is a graph for evaluating overcharge safety of Examples and Comparative Examples.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the embodiments of the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

In addition, the shapes and the like of the elements in the drawings are exaggerated in order to emphasize a clearer description, and the same reference numerals denote the same elements. Throughout the specification, when an element is referred to as " comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

The lithium secondary battery mainly uses a lithium oxide and a carbonaceous material as a cathode active material and an anode active material, respectively. The lithium secondary battery includes an electrode assembly in which a cathode in which such a cathode active material is coated on a cathode current collector and a cathode in which a cathode active material is coated on an anode current collector are disposed with a separation membrane interposed therebetween, (Outer case). Normally, the electrode assembly is impregnated with a lithium salt-containing electrolytic solution and sealed in a battery case.

The type of the battery is divided into a cylindrical battery or a prismatic battery according to the outer shape of the battery case, and the types of the electrode assembly are a winding type, a stack type, a stack and a folding type, and the like. Normally, the active material is coated on both sides of the current collector. At this time, the current collector is formed with an uncoated portion which is not coated with the active material, and the tab may be attached to the uncoated portion. Embodiments in which the cathode active material coated on both sides of the anode current collector in various aspects are terminated at different points is shown in Figs.

FIG. 1 is a perspective view of a positive electrode for a lithium secondary battery according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of the positive electrode for a lithium secondary battery shown in FIG. 2 corresponds to A-A 'in Fig.

1 and 2, the anode 100 includes a cathode current collector 110 and a cathode active material coating portion 120 having cathode active material layers 121 and 122 formed on the cathode current collector 110. The positive electrode collector 110 is a sheet having a length L longer than the width W and the positive electrode active material coating portion 120 is coated on a part of the positive electrode collector 110 as shown in the figure. A first cathode active material layer 121 is formed on one surface 111 of the cathode current collector 110 and a second cathode active material layer 122 is formed on the other surface 112 opposite to the first surface 111 of the cathode current collector 110. [ Respectively. The positive electrode uncoated portion 130 in which the positive electrode active material coating portion 120 is not formed in the positive electrode current collector 110 is located on both sides 111 and 112 of the positive electrode current collector 110.

The cathode active material coating part 120 is formed by preparing a cathode active material slurry in which a cathode active material, a binder polymer, a conductive material and the like are dispersed or dissolved in an organic solvent, coating the anode current collector 110 using a slot die or the like, . The first cathode active material layer 121 has a shorter coating length than the second cathode active material layer 122 in the length L direction of the cathode current collector 110. That is, the first positive electrode active material layer 121 is terminated faster than the second positive electrode active material layer 122 in the direction of the length L so that the positive electrode uncoated portion 130 contacts both surfaces 111 and 112 of the positive electrode collector 110 ) Have different lengths. In other words, the positive electrode uncoated portion 131 formed on one surface 111 of the positive electrode current collector 110 is longer than the positive electrode uncoated portion 132 formed on the other surface 112 of the positive electrode current collector 110 by a length L ) Direction. For example, in the case of constructing a wound-type electrode assembly in a cylindrical or prismatic battery, it is difficult to say that the positive electrode active material layer outside the outermost winding portion contributes to the actual cell reaction because there is no corresponding negative electrode active material layer. Therefore, the cathode active material layer outside the outermost winding portion may have a shorter coating length than the inner cathode active material layer, that is, the second cathode active material layer 122, like the first cathode active material layer 121 of the present embodiment.

The anode 100 has a configuration in which the safety of the lithium secondary battery is ensured without changing the configuration of the cathode active material coating portion 120, that is, without adversely affecting the battery capacity, . The gas generating layer 140 may include gas generating agent particles, a conductive material, and a binder polymer. The gas generating layer 140 may be formed by preparing a gas generating agent slurry in which the gas generating agent particles, the conductive material and the binder polymer are dispersed or dissolved in an organic solvent, coating the coated layer on the cathode current collector 110, and drying the same.

The gas generating layer 140 is a first gas generating layer 141 formed on the positive electrode uncoated portion 131 formed on one surface 111 of the positive electrode collector 110. In this embodiment, That is, the case where the gas generating layer 140 is formed only in the larger uncoated region 131 among the uncoated region 130 formed on both surfaces 111 and 112 of the positive electrode collector 110. The first gas generating layer 141 is formed adjacent to the first cathode active material layer 121 but separated from the first cathode active material layer 121 by an interval G, for example. That is, the first gas generating layer 141 and the first cathode active material layer 121 are separated from each other so that they are not formed to have side faces and are not formed to overlap each other.

The anode 100 is formed by coating the cathode active material coating portion 120 and the gas generating layer 140 on the cathode current collector 110 by coating the respective slurries and then drying the anode active material coating portion 120 and the gas generating layer 140 as a whole, ). However, it is not necessarily limited to the production method of this order.

Since the gas generating layer 140 is formed on the anode uncoated portion 130 on which the cathode active material coating portion 120 is not formed as long as it is in accordance with the purpose of the present invention, 1, for example, the first gas generating layer 141 may be formed in a region of the first positive electrode active material layer (not shown) of the positive electrode collector 110, 121 may be formed adjacent to each other in the direction of the length L of the positive electrode collector 110 and may be formed to have the same width as the width of the first positive electrode active material layer 121 in the direction of the width W of the positive electrode collector 110 have. The positive electrode uncoiled portion 131 of the positive electrode current collector 110 in which the first positive electrode active material layer 121 and the first gas generating layer 141 are not formed may exist at the end in the length L direction. As shown in FIG. 2, the first gas generating layer 141 may be formed to correspond to a position where the second cathode active material layer 122 is terminated. As a result, the symmetry of the both surfaces 111 and 112 of the electrode collector 110 can be secured to a certain degree when viewed from the whole of the anode 100, which is structurally advantageous. For example, there is no problem such as bending in one plane direction.

The gas generating layer 140 is not limited to the structures shown in FIGS. 1 and 2, but may have a structure as shown in FIG. 3 and FIG. FIG. 3 is a longitudinal cross-sectional view of a positive electrode for a lithium secondary battery according to another embodiment of the present invention, and FIG. 4 is a longitudinal sectional view of a positive electrode for a lithium secondary battery according to another embodiment of the present invention.

Referring to FIG. 3, the anode 100 'has a second gas generating layer 142 formed on the cathode uncoated portion 132 formed on the other surface 112 of the cathode current collector 110. That is, in this embodiment, the gas generating layer 140 is the second gas generating layer 142 formed on the cathode uncoated portion 132 formed on the other surface 112 of the cathode current collector 110. In other words, the case where the gas generating layer 140 is formed only in the narrower unoccupied plain portion 132 among the positive electrode uncoated portions 130 formed on both surfaces 111 and 112 of the positive electrode collector 110. The second gas generating layer 142 is formed adjacent to the second cathode active material layer 122, but spaced apart from the second cathode active material layer 122 by an interval G, for example. That is, the second gas generating layer 142 and the second positive electrode active material layer 122 are separated from each other so that they are not formed to have side faces and are not formed to overlap each other.

4, the anode 100 " includes a gas generating layer 140 including both a first gas generating layer 141 as shown in FIG. 2 and a second gas generating layer 142 as shown in FIG. 3 The gas generating layer 140 is formed on both of the positive electrode uncoated portions 130 formed on both surfaces 111 and 112 of the positive electrode collector 110. In this case,

3 and 4, the gas generating layer 140 may be formed on either side of the positive electrode collector 110 as long as the positive electrode uncoated portion 130 is formed. Since the gas is generated by the decomposition reaction of the gas generating agent in the gas generating layer 140, it is preferable to secure a large area of the gas generating layer 140 to contain a large amount of the gas generating agent, It will be advantageous. Therefore, it is preferable that the case of FIG. 4 in which the gas generating layer 140 is formed as wide as possible in the cathode uncooled portion 130 of the cathode current collector 110 as far as possible is considered only in the gas generating side.

3 and 4, the second gas generating layer 142 is formed on the second positive electrode active material layer 122 in the direction of the length L of the positive electrode collector 110, similarly to the first gas generating layer 141 And may be formed to have the same width as that of the second cathode active material layer 122 in the direction of the width W of the cathode current collector 110. The positive electrode uncoated portion 132 of the positive electrode current collector 110 in which the second positive electrode active material layer 122 and the second gas generating layer 142 are not formed may exist at the end in the length L direction. As shown in FIG. 4, the second gas generating layer 142 may be formed to correspond to a position where the first gas generating layer 141 is terminated. As a result, the symmetry of the both surfaces 111 and 112 of the electrode current collector 110 can be secured to a certain extent when viewed from the whole of the anode 100 ", which is structurally advantageous.

2 to 4, the gas generating layer 140 is formed to have the same thickness or height h as the cathode active material coating portion 120. The gas generating layer 140 may have a thickness smaller than that of the cathode active material coating portion 120 or may be formed to have the same thickness or height as the cathode active material coating portion 120 adjacent to the cathode active material coating portion 120 And an aspect in which it is formed so as to become gradually thinner may be included. According to this embodiment, when rolling the entire anode 100, 100 ', 100 ", rolling is performed from one side of the cathode active material coating portion 120 with the rolling roll to finish rolling near the gas generating layer 140, 100 ', 100 " due to the occurrence of a minute pressure difference due to the difference in thickness at the time of termination.

2 to 4, the first gas generating layer 141 is formed only in the positive electrode uncoated portion 131 in which the first positive active material layer 121 is not formed, and the second gas generating layer 142 is formed in the non- Only the positive electrode uncoated portion 132 on which the two positive electrode active material layers 122 are not formed. That is, in the present invention, the gas generating layer 140 is formed only on the cathode uncoated portion 130 where the cathode active material coating portion 120 is not formed. Therefore, instead of forming the gas generating layer 140 in the anode uncoated portion 130, the gas generating agent 140 may be mixed in the cathode active material coating portion 120 by coating the cathode active material slurry with the gas generating agent. Or the gas generating layer 140 may be formed on the cathode uncoated portion 130 but may penetrate to the cathode active material coating portion 120 so that the gas generating layer 140 contacts the cathode active material coating portion 120 As compared with the case where they are formed in a superposed manner, they have a number of advantages as follows. It is possible to quickly reach the overcharge end voltage due to the generation of the gas generated by decomposition of the gas generating agent at the time of overcharging. It does not affect the positive electrode active material layer, so that the electrode resistance and the battery resistance can be reduced. The energy density of the battery can be increased since the amount of the active material loaded in the cathode active material layer is not reduced as compared with the case where the gas generating layer 140 is formed in the cathode active material coating portion 120. Since the thickness and height of the gas generating layer 140 are not increased compared with the case where the gas generating layer 140 is formed to overlap with the cathode active material coating portion 120, the tearing of the separator can be prevented during manufacturing of the battery.

In particular, the gas generating layer 140 is formed apart from the cathode active material coating portion 120. As a result, the battery including such a positive electrode can generate a gas upon overcharging and smoothly diffuse into the battery case, so that the battery internal pressure can be rapidly increased. Since the gas generating layer 140 does not affect the structure of the cathode active material coating portion 120 at all, the battery characteristics can be kept excellent. When the gas generating layer 140 is attached to or overlapped with the cathode active material coating portion 120, the gas generating layer 140 acts as a resistor, which may cause electrode resistance or battery resistance to increase. In the case where the gas generating layer 140 is formed to overlap with the cathode active material coating portion 120, the tearing of the separator occurs due to the height difference from the non-overlapping portion, or the stress at the time of rolling increases There is a risk that the positive electrode collector 110 is cut off. In order to quickly generate gas in the gas generating layer 140, electrons from the cathode current collector 110 must move fast. The gas generating layer 140 may be spaced apart from the cathode active material coating portion 120 to form the anode uncoated portion 130 as in the case of the present invention where the gas generating layer 140 is attached to or overlapped with the cathode active material coating portion 120, The electrons move rapidly from the anode current collector 110 and the reaction occurs, so that the gas can be generated in a short time.

The gas generating layer 140 does not contain a cathode active material. Therefore, even if the gas generating layer 140 is disposed facing the negative electrode, the positive active material may be dropped from the gas generating layer 140 to cause a short circuit of the battery. The gas generating layer 140 includes gas generating agent particles, a binder polymer, and a conductive material. The gas generating layer 140 may be composed of only the gas generating agent particles, the binder polymer, and the conductive material, and may further include additives commonly used in the art if necessary.

The cathode active material coating portion 120 does not contain the gas generating agent particles. Therefore, the resistance of the cathode active material coating portion 120 is not affected by gas generation by the gas generating agent particles. The cathode active material coating portion 120 includes cathode active material particles, a binder polymer, and a conductive material. The cathode active material coating portion 120 may be formed only of the cathode active material, the binder polymer, and the conductive material, and may further include additives commonly used in the art if necessary.

As described above, the cathode active material coating portion 120 and the gas generating layer 140 may be formed of a binder polymer, a conductive material, an organic solvent, and a coating method, except that the cathode active material particles or the gas generating agent particles exclusively include each other. May be the same or similar. Accordingly, the gas generating layer 140 of the present invention can be used as it is while using the conventional binder polymer, conductive material, and organic solvent used in the production of the cathode active material slurry for forming the cathode active material coating portion 120, The gas generating agent slurry containing the gas generating agent particles may be prepared separately from the cathode active material slurry and separately coated in place of the cathode active material particles in the slurry of the cathode active material while using the coating method as it is. Since the method of preparing and coating the gas generating agent slurry containing the gas generating agent particles is not known at present, the method of manufacturing the anode of the present invention differs from that of the conventional anode manufacturing method.

The positive electrode collector 110 is generally made to have a thickness of 3 to 500 μm. As the material of the positive electrode collector 110, aluminum is mainly used. Alternatively, the cathode current collector 110 may be made of stainless steel, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Further, if the secondary battery is made of a material having high conductivity without causing a chemical change, there is no limit to the use as the positive electrode collector 110. The anode current collector 110 may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and may have various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The cathode active material is a lithium-based active material, and typical examples thereof include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO _4, or Li _{1 + z} Ni _{1 -x- y} Co _x M _y O ₂ 1, 0? Y? 1, 0? X + y? 1, 0? Z? 1, and M is a metal such as Al, Sr, Mg, La, or Mn).

The binder polymer plays a role of attaching the positive electrode active material particles to each other well and attaching the positive electrode active material to the positive electrode collector 110 well. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl Examples of the binder include cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, tetrafluoroethylene, polyvinylidene (EPDM), sulfonated EPDM, epoxy resin, nylon, and the like can be used, but the present invention is not limited thereto, and examples thereof include, but are not limited to, polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, fluorinated polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, no.

The conductive material is used for imparting conductivity to the anode 100. Any conductive material can be used without causing any chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives; Or a conductive material containing a mixture of two or more thereof.

The cathode active material coating portion 120 may further include a filler. The filler is optionally used as a component for suppressing expansion of the anode 100 and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene ; Fibrous materials such as glass fibers and carbon fibers are used.

The cathode active material particles, the conductive material, the binder polymer, and the filler are dispersed or dissolved in an organic solvent to prepare a cathode active material slurry. In this case, the content of the solid content in the organic solvent is not particularly limited as long as it is a slurry having a viscosity that can not easily be flowed while being coated. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), methoxypropyl acetate, butyl acetate, glycolic acid esters, butyl esters, butyl glycols, methylalkylpolysiloxanes, alkylbenzenes, propylene glycols, But are not limited to, polyglycidyl polysiloxane copolymers, polyether modified dimethylpolysiloxane copolymers, polyacrylate solutions, alkylbenzenes, diisobutyl ketones, organic modified polysiloxanes, butanol, isobutanol, modified poly Acrylate, a modified polyurethane, and a polysiloxane-modified polymer may be preferably used.

The gas generating agent particles of the gas generating layer 140 may be lithium carbonate (Li ₂ CO ₃ ), calcium carbonate (CaCO ₃ ), lithium oxalate (C ₂ Li ₂ O ₄ ), or a mixture thereof. The gas generating agent is selected according to the battery model, which can be decomposed and vaporized at a specific voltage set as an overcharge voltage. For example, if it is more than 4.5 V, which is usually regarded as an overcharged state, the current must be cut off to stop charging. Of the substances to be vaporized, lithium carbonate, for example, is suitable because it decomposes above 4.8 V.

The gas generating agent particles, especially lithium carbonate particles, may have shapes such as spheres, ellipses, polygons, but are not limited thereto. Also, in the present specification, when it is referred to as 'spherical shape' or 'elliptical shape', it does not mean a complete 'spherical shape' or 'elliptical shape' but means a spherical shape or an elliptical shape It is a broad sense. Such lithium carbonate particles may have a particle diameter of 0.1 to 50 탆.

The binder polymer of the gas generating layer 140 is a component that assists in bonding between the gas generating agent particles and the conductive material and bonding to the cathode current collector 110. The binder polymer may be the same as the binder polymer contained in the cathode active material coating portion 120. The same material as the conductive material contained in the cathode active material coating portion 120 of the gas generating layer 140 may be used. The organic solvent for the slurry for forming the gas generating layer 140 may be the same as the organic solvent for the cathode active material slurry. Therefore, the process of forming the gas generating layer 140 is compatible with the process of forming the existing cathode active material coating portion 120 and can be easily introduced into an existing process.

The gas generating layer 140 should contain gas generating agent particles sufficient to ensure the safety of the lithium secondary battery in an overcharged state. For example, 0.1 to 99.9% by weight of the gas generating agent particles may be included based on the combined weight of the gas generating agent particles, the conductive material and the binder polymer. Preferably, 1 to 10% by weight of the gas generating agent particles may be included based on the combined weight of the gas generating agent particles, the conductive material and the binder polymer. In the gas generating layer 140, the conductive material may be contained in an amount of 0.1 to 10% by weight based on the combined weight of the gas generating agent particles, the conductive material, and the binder polymer.

For example, 0.1 to 99.9% by weight of lithium carbonate particles may be included based on the combined weight of lithium carbonate, conductive material, and binder polymer. Preferably, lithium carbonate particles of 1 to 10% by weight, based on the combined weight of lithium carbonate, conductive material and binder polymer, may be included.

The gas generating layer 140 may be formed of a porous structure that is sustained by the gas generating agent particles. That is, the gas generating agent particles are connected and fixed to each other by the binder polymer, that is, they are bonded, and the void space between the gas generating agent particles can act as pores. The porous structure with the pores thus formed increases the area of reaction with the electrolyte, especially the electrolyte, in the assembled battery. Therefore, gas generation is more actively performed. Pores that are not filled with electrolyte may form a path of travel through which the generated gas is spread. In order for the gas generating layer 140 to function efficiently, it is important to widen the reaction area of the gas generating layer 140. To this end, the gas generating layer 140 may be formed as wide as possible in the cathode uncoated portion 130, but it may be formed to have a large surface area even if it is formed in a narrow area. For this purpose, a large number of small pores may be formed in the gas generating layer 140. For example, the desired result can be achieved by controlling the size of the gas generating agent particles.

1 to 4 illustrate a case where the gas generating layer 140 is entirely coated on the cathode uncoated portion 130, that is, one integrated layer. Here, "integration" means that it is a chunk or a continuous form. However, it is also possible to form a pattern such as a stripe, a dot, and a wave pattern as well as such an embodiment. Also, an aspect may be included in which another functional layer is disposed between the patterns.

FIG. 5 shows a case in which a stripe pattern is formed and coated. Referring to FIG. 5, for example, the first gas generating layer 141 is patterned in a line-and-space type so as to partially expose the anode uncoated portion of the cathode current collector 110, The space forms a gas movement path. A gas is generated at the time of overcharging and is smoothly diffused into the battery case, so that the battery internal pressure can be rapidly increased.

Various methods can be used to form such a pattern. For example, it is possible to use an apparatus or a method capable of coating the gas generating agent slurry in a pattern shape when coating the slurry. For example, it is possible to make a line coating or a point coating or a method of shaking the proceeding direction of the coating to the left or right. Alternatively, it is possible to perform patterning in a desired shape after collectively coating the entire surface.

1 to 4 illustrate that the gas generating layer 140 is a single integrated layer and has a smooth surface. Depending on the particle size or coating state of the gas generating agent particles constituting the gas generating layer 140, It is obvious that it will have a predetermined surface roughness, and may be formed with an uneven structure intentionally by a method such as stamping.

Referring to FIG. 6, for example, the gas generating layer 140 including the first gas generating layer 141 has a concave portion C and a convex portion V on its surface. The concave and convex portions formed by the concave portion C and the convex portion V not only enlarge the surface area of the first gas generating layer 141 but also form a gas movement path if the concave portion C is connected in one direction none. Therefore, gas is generated during overcharging and is smoothly diffused into the battery case, so that the battery internal pressure can be rapidly increased.

Various methods can be used for the method of obtaining such a concavo-convex structure. For example, a stamping method in which a pressure is applied directly to the surface of the gas generating layer 140 by using a pattern mold having recesses and protrusions is possible. It is possible to form a concave and convex structure while being rolled. Otherwise, a concave-convex structure may be formed by a scratch technique using a fine needle.

In the above embodiments, the cathode active material coating portion starts coating from one end of the cathode current collector and is formed on both sides of the cathode current collector with different coating lengths, but the present invention is not limited thereto. The cathode active material coating portion may be formed on both sides of the anode current collector with the same coating length. The cathode active material coating portion may be formed on only one side of the positive electrode current collector. Also, when forming the cathode active material coating portion, when coating is started while leaving a predetermined length at one end of the cathode current collector, the cathode active material coating portion is formed at the center and the unoccluded portions are formed at both ends of the cathode current collector. In either case, the gas generating layer is formed only in the positive electrode uncoated portion.

7 and 8 are views for explaining an electrode assembly of a lithium secondary battery according to the present invention. Fig. 7 is an exploded perspective view of the electrode assembly before the electrode assembly is wound, and Fig. 8 is a perspective view of the electrode assembly after the winding of Fig.

7 and 8, a lithium secondary battery according to the present invention includes an anode 100 for a lithium secondary battery, an anode 200, and an electrode assembly 400 wound with separators 300 and 310 . That is, the electrode assembly 400 includes the anode 100, the cathode 200, and the separators 300 and 310, and the separators 300 and 310 are interposed between the anode 100 and the cathode 200. The anode 100, the separator 300, the cathode 200 and the other separator 310 are formed into a sheet, stacked in order, and then wound from one side to form an electrode assembly 400.

The anode 100 has been described in detail with reference to FIGS. 1 and 2 and the like. The positive electrode tab 150 may be attached to the positive electrode uncoated portion 130 of the positive electrode 100.

The cathode 200 also includes a cathode current collector 210 of a sheet corresponding to the cathode current collector 110. An anode active material coating portion 220 is formed on both surfaces of the anode current collector 210. And the negative electrode uncoated portion 230 which is a portion where the negative electrode active material layer is not formed in the negative electrode current collector 210. In this embodiment, the negative electrode uncoated portion 230 has the same length on both sides of the negative electrode collector 210, but the present invention is not limited thereto. The negative electrode tab 250 may be attached to the negative electrode uncoated portion 230 of the negative electrode 200.

The uncoated portions 130 and 230 to which the tabs 150 and 250 are attached are spaced apart from each other by a length L of the positive electrode 100 and the negative electrode 200, It is preferable to place them on opposite sides when viewed in the direction.

As described above, the anode 100 is manufactured by coating, drying and rolling the cathode active material slurry on the cathode current collector 110. The cathode 200 can also be manufactured by coating, drying and rolling the anode active material slurry on the anode current collector 210. With respect to the production of the negative electrode active material slurry, the preparation of the positive electrode active material slurry described above can be referred to.

The anode current collector 210 is also generally made to a thickness of 3 to 500 μm. The anode current collector 210 is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. The cathode current collector 210 is mainly made of copper, but may be made of stainless steel, aluminum, nickel, titanium, A surface treated with carbon, nickel, titanium, or silver on the surface of stainless steel, an aluminum-cadmium alloy, or the like may be used. Further, similarly to the cathode current collector 110, fine unevenness may be formed on the surface to enhance the bonding force of the anode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, .

The negative electrode active material is a carbon-based active material, and examples of the negative electrode active material include a carbon material such as crystalline carbon, amorphous carbon, carbon composite, and carbon fiber, lithium metal, and lithium alloy. For example, carbon; Li _x Fe ₂ O ₃ (0 _x 1), Li _x WO ₂ (0 _x 1), Au _x Me _{1 -x} Me _y O _z (Me: Mn, Fe, Pb, : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x < Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{AuO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide and the like can be used.

However, the types and chemical compositions of the cathode active material and the anode active material may vary depending on the type of the secondary battery. Therefore, it should be understood that the specific examples given above are only examples.

The separators 300 and 310 are interposed between the anode 100 and the cathode 200 and use an insulating thin film having high ion permeability and mechanical strength. The pore diameters of the separators 300 and 310 are generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. The separators 300 and 310 include, for example, olefin-based polymers such as polypropylene, which is chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The separators 300 and 310 are not particularly limited as long as they have a porous material. The separators 300 and 310 may be formed of a porous polymer membrane such as a porous polyolefin membrane, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichlorethylene, polymethyl methacrylate, Polyvinyl pyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyano But are not limited to, ethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose, acrylonitrile styrene butadiene copolymer polyimide, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polyetheretherketone, Polyethersulfone, poly Phenyl with alkylene oxide, polyphenylene sulfide, polyethylene may be formed of a naphthalene, a non-woven film, a porous web (web) or a mixture film having a structure like.

At the end face or both faces of the separation membranes 300 and 310, inorganic particles may be bonded. The inorganic particles are preferably inorganic particles having a high dielectric constant of 5 or more, more preferably inorganic particles having a dielectric constant of 10 or more and a low density. This is because it can easily transfer lithium ions moving in the cell. Non-limiting examples of inorganic particles having a high dielectric constant of 5 or more is _{Pb (Zr, Ti) O 3} (PZT), Pb 1 - x La x Zr 1 -y Ti y O 3 (PLZT), PB (Mg 3 Nb _{2/3) O 3 -PbTiO 3 (PMN} -PT), BaTiO 3, HfO 2, SrTiO 3, TiO 2, Al 2 O 3, ZrO 2, SnO 2, CeO 2, MgO, CaO, ZnO, Y 2 O _3, or a mixture thereof.

7, the electrode assembly 400 may include a separator 300 and a separator 300 between the anode 100 and the cathode 200. The separator 300 may be disposed between the anode 100 and the cathode 200, Is wound in a direction of an arrow along the direction of the length L of the positive electrode collector 110 and the negative electrode collector 210 from one side (winding center). In this case, the gas generating layer 140 of the anode 100 may be located at the outermost part of the electrode assembly 400 as shown in FIG. The gas generating layer 140 is provided perpendicularly to the direction of the length L in the winding direction. In other words, the gas generating layer 140 is formed at the outermost portion of the electrode assembly 400 in the longitudinal direction. The gas generating layer 140 is formed on the outer periphery of the outermost portion of the electrode assembly 400, that is, the cathode uncoated portion 131 of the positive electrode collector 110 that does not face the negative electrode 200, The positive electrode current collector 110 forming the positive electrode uncoated portion 131 is formed.

The lithium secondary battery includes such an electrode assembly 400 and a battery case sealingly accommodates the electrode assembly 400 together with the electrolyte. As the electrolyte, an electrolyte solution containing a lithium salt is typical. The electrode assembly 400 is placed in a cylindrical battery case (can) to inject electrolyte, and then sealed to form a lithium secondary battery. The structure after assembly can be referenced, for example, to Korean Patent No. 10-1803528 of the present applicant, and also includes a cap assembly provided with the CID as described above, so that the lithium secondary The stability of the battery can be ensured.

The electrolyte solution containing a lithium salt is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, Tetrahydrofuran, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyltetrahydrofuran, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, methyl ethyl ketone, , Ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

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

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

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In a preferred _{embodiment, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

The present invention can also be used to provide a battery module including the secondary battery as a unit battery and to provide a battery pack including the battery module. The battery pack can be used as a power source for a medium and large-sized device requiring high temperature stability, long cycle characteristics, and high rate characteristics. Preferred examples of the above medium and large-sized devices include a power tool which is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; A power storage system (ESS), and the like, but the present invention is not limited thereto.

Hereinafter, the present invention will be further described with reference to experimental examples, but the scope of the present invention is not limited thereto.

Example  One

3, a positive electrode was fabricated to include a gas generating layer in a narrow unoccupied area, and a battery including the wound electrode assembly was manufactured using the positive electrode. Lithium carbonate was used as the gas generating agent.

Specifically, 2 g of polyvinylidene fluoride as a binder polymer was dissolved in NMP, and then 50 g of lithium carbonate (Li ₂ CO ₃ ) having a particle diameter of 5.0 탆 and 4 g of Super-P, which is a conductive material, A slurry was prepared.

Subsequently, LiCoO2 having a D50 of approximately 15 to 20 mu m, Super P as a conductive material, and polyvinylidene fluoride as a binder were mixed at a weight ratio of 92: 4: 4, and then NMP was added to prepare a slurry for forming a cathode active material layer Respectively.

An aluminum current collector having a length of 100 to 200 cm and a width of 5 to 7 cm was prepared as a positive electrode current collector, and a slurry for forming a cathode active material layer and a slurry for forming a gas generating layer were respectively applied. In order to prevent the slurry for forming the cathode active material layer and the slurry for forming the gas generating layer from being mixed in the regions adjacent to each other, the slurry for forming the cathode active material layer is applied and dried, and then the slurry for forming the gas generating layer is applied and dried . At this time, a slot die coating method was used for slurry application, and drying was performed in a vacuum oven at 120 ° C. The gas generating layer thus prepared was applied to the positive electrode collector at a loading amount of 0.03 g / cm ² , and had a thickness of 20 탆.

As a cathode, MCMB (mesocarbon microbead) was used as an active material, super P as a conductive material and PVdF as a binder were mixed at a ratio (weight ratio) of 92: 2: 6 and dispersed in NMP and coated on a copper foil To prepare a negative electrode.

Each of the tabs was connected to the positive electrode and the negative electrode, and then a wound electrode assembly was manufactured using the polyethylene separator between the negative electrode and the positive electrode. The electrode assembly was placed in a cylindrical battery case (can), and ethylene carbonate (EC) and dimethyl carbonate (DMC) solutions having a 1: 1 volume ratio in which 1 M of LiPF6 was dissolved were injected into the electrolyte, Assembled.

Example  2

4, a positive electrode was fabricated so as to include a gas generating layer in a narrow positive electrode non-coated portion and a wide positive electrode non-coated portion, and a battery including the wound electrode assembly was manufactured using the positive electrode. All the conditions were the same as in Example 1.

Comparative Example  One

Instead of the gas generating layer as in Example 1 or Example 2, lithium carbonate was mixed in the positive electrode active material layer as in Patent Document 1 to prepare a positive electrode, and a battery including the wound electrode assembly was manufactured using the positive electrode. The gas generating layer was not formed separately from the positive electrode active material layer, and the amount of lithium carbonate was set to be the same as that in Example 1, and all the conditions were the same as those in Example 1.

Evaluation example : Electrode resistance evaluation result

Figs. 9 and 10 are graphs showing the results of the electrode resistance evaluation of the embodiment and the comparative example, where Fig. 9 is the volume resistance and Fig. 10 is the sheet resistance. The electrode resistance was obtained by measuring the portion of the positive electrode active material layer on the positive electrode of each experimental example. The current and voltage on the surface of the positive electrode active material layer were measured with four probes by the commonly used 4-probe method, And the correction factor considering the pressurized pressure was applied.

Referring to FIGS. 9 and 10, the volume resistivity and sheet resistance of Examples 1 and 2 are low compared to Comparative Example 1. In Comparative Example 1, since the cathode active material was mixed with lithium carbonate, the electrode resistance was higher than those of Examples 1 and 2 in which the gas generating layer was formed in the cathode uncoated portion and the cathode active material layer was left intact. In Example 1 and Example 2, except for the gas generating layer forming area, the cathode active material layers were the same, so that the electrode resistances were not different from each other.

Evaluation example : Evaluation results of cell resistance

11 is a graph showing the results of AC resistance evaluation of Examples and Comparative Examples. The AC impedance was measured by applying a current of 1 kHz alternating current using a generally used AC impedance meter.

As can be seen from Fig. 11, it was confirmed that 1.4 mhm resistance reduction occurred in Examples 1 and 2 compared to Comparative Example 1. [ The case of the present invention is reduced by about 3%. The AC resistance of the battery is a major factor in resistance of the active material layer. In Comparative Example 1, since the cathode active material was mixed with lithium carbonate, the gas generating layer was formed on the cathode uncoated portion and the resistance was higher than in Examples 1 and 2 in which the cathode active material layer was left intact. In Examples 1 and 2, since the gas generating layer was formed on the cathode uncoated portion and the resistance of the active material layer was not changed, the AC resistance also showed no difference.

Evaluation example : Charging and discharging  Evaluation results

The lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Example 1 were subjected to a constant current (CC) -constant voltage (CV) charge and then a constant current (CC) discharge to obtain a charge / discharge profile as shown in FIG.

In FIG. 12, the difference between Examples 1 and 2 and Comparative Example 1 is clearly shown, which is a result of a smaller charging voltage at the time of constant current charging because the resistances of Examples 1 and 2 are small.

Evaluation example : Overcharge evaluation result

The overcharge test proceeded to two steps. First, CC-CV was charged at room temperature (25 ℃) and atmospheric pressure to make 100% state of SOC. For overcharge test, CC charging was started from SOC 100% at room temperature and normal pressure and 1.5 times of 1 hour or maximum voltage And terminated upon overcharging (second step: overcharging). Charge / discharge test equipment was used for overcharge evaluation.

Overcharging characteristics were carried out for Examples 1 and 2 and Comparative Example 1 under the same conditions as above, and the results are shown in FIG. As can be seen from Fig. 13, in Example 1, overcharge safety is secured at a level similar to that of Comparative Example 1, and in Example 2, overcharge safety is secured at a level higher than Comparative Example 1.

In the case of Example 1 in which the same amount of lithium carbonate as in Comparative Example 1 was added, the voltage was increased in the same manner as in Comparative Example 1, but the lithium carbonate of Example 1 was located in the positive electrode non- The gas is generated somewhat faster and the overcharge end timing is slightly faster. It was confirmed that the overcharging was completed at a faster time point than that of Comparative Example 1 and Example 1 in the case of Example 2 in which a large amount of lithium carbonate was contained compared to Comparative Example 1 and Example 1 since the gas generating layer formation area was wider than Example 1 .

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the general inventive concept as defined by the appended claims. It is to be understood that modifications are possible and that such modifications are within the scope of the claims.

100, 100 ', 100 ": positive
110: positive electrode collector
120: cathode active material coating part
130: positive uncoated portion
140: gas generating layer
150: positive electrode tab
200: cathode
210: cathode collector
220: Negative electrode active material coating part
230: negative electrode non-
250: negative electrode tab
300, 310: separator
400: electrode assembly

Claims (9)

Anode collector;
A cathode active material coating portion formed on at least one surface of the cathode current collector; And
And a gas generating layer formed only on a cathode uncoated portion where the cathode active material coating portion is not formed on the cathode current collector, the gas generating layer comprising a gas generating agent particle, a binder polymer, and a conductive material. The positive electrode for a lithium secondary battery according to claim 1, wherein the gas generating layer is spaced apart from the cathode active material coating portion. The method of claim 1, wherein the gas generating agent particles comprise lithium carbonate (Li ₂ CO ₃ ), calcium carbonate (CaCO ₃ ), lithium oxalate (C ₂ Li ₂ O ₄ ), or a mixture of two or more thereof And a positive electrode for a lithium secondary battery. The gas generating apparatus according to claim 1, wherein the gas generating layer is a porous structure having the pores formed by the void spaces between the gas generating agent particles and the gas generating agent particles being connected and fixed to each other by the binder polymer For a lithium secondary battery. The gas generating layer according to claim 1, wherein the gas generating layer has a concavo-convex structure that is an integrated layer and is deliberately formed on the surface, or is a layer patterned to partially expose the positive electrode uncoated portion to form a gas moving path Anode for lithium secondary battery. The positive electrode collector according to claim 1, wherein the positive electrode collector is a sheet having a length longer than the width,
Wherein the cathode active material coating portion comprises: a first cathode active material layer formed on one surface of the cathode current collector; And a second cathode active material layer formed on the other surface of the cathode current collector on the opposite side of the first cathode active material layer and formed longer than the first cathode active material layer in the longitudinal direction of the cathode current collector,
Wherein the gas generating layer comprises a first gas generating layer formed on one surface of the cathode current collector and on a cathode uncoated portion in which the first cathode active material layer is not formed. 7. The lithium secondary battery according to claim 6, wherein the gas generating layer further comprises a second gas generating layer formed on the other surface of the positive electrode current collector at a positive electrode uncoated portion in which the second positive electrode active material layer is not formed Anode for secondary battery. A positive electrode for a lithium secondary battery according to any one of claims 1 to 7;
A negative electrode including a negative electrode current collector and a negative electrode active material coating portion formed on at least one side of the negative electrode current collector; And
And an electrode assembly including a separator interposed between the positive electrode and the negative electrode. The lithium secondary battery of claim 8, wherein the electrode assembly is a wound electrode assembly and the gas generating layer of the anode is located at an outermost portion of the electrode assembly.

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