Lithium secondary battery and manufacturing method thereof

Abstract

One aspect of the present invention relates to a lithium secondary battery comprising a protective layer and a volume expansion layer, a method for manufacturing the lithium secondary battery, and a safety evaluation system for the lithium secondary battery. One aspect of the present invention can primarily suppress dendrite growth by including a protective layer and secondarily suppress dendrite growth by including a volume expansion layer. Accordingly, a lithium secondary battery in which a short circuit is fundamentally prevented can be provided.

Description

Technology Field

[0001] The present invention relates to a lithium secondary battery and a method for manufacturing a lithium secondary battery. Background Technology

[0002] The importance of lithium-ion batteries is increasing due to the growing use of vehicles, computers, and mobile devices. Among these, there is a particular demand for the development of lithium-ion batteries that can achieve high energy density while being lightweight.

[0003] Such lithium secondary batteries can be manufactured by injecting a liquid electrolyte after interposing a separator between the positive and negative electrodes, or by interposing a separator made of a solid electrolyte instead of a liquid electrolyte between the positive and negative electrodes.

[0004] Meanwhile, depending on usage conditions, lithium metal can precipitate on the negative electrode of a lithium secondary battery and grow into a dendrite shape. If these dendrites continue to grow, they can come into contact with the positive electrode and cause an internal short circuit in the battery. In particular, when lithium metal is used as the negative electrode to achieve high energy density, lithium ions present in the lithium metal negative electrode meet with electrons and are plated onto the surface of the lithium metal negative electrode. This makes it easier for lithium dendrites to grow compared to cases where a negative electrode active material other than lithium metal is used, which becomes an even greater problem.

[0005] The present invention is intended to fundamentally solve the problem of lithium dendrites formed from the negative electrode growing and coming into contact with the positive electrode during battery operation, thereby causing a short circuit. The problem to be solved

[0006] One aspect of the present invention is to solve the aforementioned technical problem by fundamentally suppressing the growth of lithium dendrites so as not to cause a short circuit.

[0007] In addition, it is intended to provide a lithium secondary battery with improved safety that does not experience internal short circuits.

[0008] In addition, it is intended to provide a lithium secondary battery having high energy density.

[0009] Meanwhile, other objects and advantages of the present invention will be understood from the following description. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means or methods described in the claims and combinations thereof. means of solving the problem

[0010] One aspect of the present invention provides a lithium secondary battery according to the following embodiments.

[0011] The first embodiment is,

[0012] As a lithium secondary battery,

[0013] The above lithium secondary battery comprises: a negative electrode; a protective layer located on the negative electrode; a volume expansion layer located on the protective layer; a separator layer located on the volume expansion layer; a positive electrode located on the separator layer; and an electrolyte.

[0014] The above volume expansion layer comprises a binder polymer (a); and inorganic particles (b) capable of adsorbing lithium ions or lithium (intercalation); and

[0015] The present invention relates to a lithium secondary battery characterized in that the above-mentioned inorganic particles (b) react physically, chemically, or electrochemically with lithium ions or lithium to become lithiated, and include a metal, a metal oxide, or both thereof that expands in volume upon lithiation.

[0016] The second embodiment is, in the first embodiment,

[0017] The present invention relates to a lithium secondary battery characterized in that the above-mentioned inorganic particles (b) have a volume expansion rate of 10% to 1000% after lithiation compared to before lithiation.

[0018] A third embodiment is, in any one of the aforementioned embodiments,

[0019] The present invention relates to a lithium secondary battery characterized in that the above-mentioned inorganic particles (b) include Si, Sn, SiO, SnO, MnO2, Fe2O3, or two or more of these.

[0020] The fourth embodiment is, in any one of the aforementioned embodiments,

[0021] The present invention relates to a lithium secondary battery characterized in that the above-mentioned inorganic particles (b) are present in an amount of 10 to 99 parts by weight based on 100 parts by weight of the volume expansion layer.

[0022] The fifth embodiment is, in any one of the aforementioned embodiments,

[0023] The present invention relates to a lithium secondary battery characterized in that the protective layer is a polymer layer.

[0024] The sixth embodiment is, in the fifth embodiment,

[0025] The present invention relates to a lithium secondary battery characterized in that the above-mentioned polymer layer comprises a polymer having electrical insulating properties.

[0026] The seventh embodiment is, in the sixth embodiment,

[0027] The above polymers are polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylidene fluoride, polyvinylacetate, polyethylene, polypropylene, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide, The present invention relates to a lithium secondary battery characterized by comprising any one selected from the group consisting of polypropylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxymethylcellulose, or a mixture of two or more of these.

[0028] The eighth embodiment is, in any one of the aforementioned embodiments,

[0029] The present invention relates to a lithium secondary battery characterized in that the thickness of the volume expansion layer is 10 nm to 50 μm.

[0030] The ninth embodiment is, in any one of the aforementioned embodiments,

[0031] The present invention relates to a lithium secondary battery characterized in that the above electrolyte is a solid electrolyte or a liquid electrolyte.

[0032] The 10th embodiment is, in any one of the aforementioned embodiments,

[0033] The present invention relates to a lithium secondary battery characterized in that the pores within the protective layer, volume expansion layer, and separator layer are impregnated with the solid electrolyte or the liquid electrolyte.

[0034] The 11th embodiment is, in any one of the aforementioned embodiments,

[0035] The binder polymer (a) is polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylfluran The present invention relates to a lithium secondary battery characterized by comprising cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose alone or two or more of these.

[0036] The 12th embodiment is, in any one of the aforementioned embodiments,

[0037] The present invention relates to a lithium secondary battery characterized in that the above-mentioned separator comprises a porous polymer film substrate or a porous polymer nonwoven fabric substrate.

[0038] Another aspect of the present invention provides a method for manufacturing a lithium secondary battery according to the following embodiment.

[0039] The 13th embodiment is,

[0040] A method for manufacturing a lithium secondary battery comprising: a negative electrode; a protective layer located on the negative electrode; a volume expansion layer located on the protective layer; a separator layer located on the volume expansion layer; a positive electrode located on the separator layer; and an electrolyte.

[0041] Step of placing a protective layer on the above cathode;

[0042] A step of placing the volume expansion layer on the separation layer;

[0043] The method includes the step of sequentially interposing the above-mentioned cathode, protective layer, volume expansion layer, separator layer, and anode;

[0044] The volume expansion layer comprises a binder polymer (a); and inorganic particles (b) capable of adsorbing lithium ions or lithium (intercalation); and

[0045] The present invention relates to a method for manufacturing a lithium secondary battery, characterized in that the above-mentioned inorganic particles (b) react physically, chemically, or electrochemically with lithium ions or lithium to become lithiated, and include a metal, a metal oxide, or both thereof that expands in volume upon lithiation. Effects of the invention

[0046] According to one aspect of the present invention, lithium dendrite growth can be primarily suppressed by forming a protective layer on the cathode.

[0047] According to one aspect of the present invention, dendrite growth can be secondarily suppressed by separating the separation layer and the protective layer by inorganic particles contained within the volume expansion layer. Accordingly, internal short circuits between the anode and the cathode can be fundamentally suppressed.

[0048] In addition, according to one aspect of the present invention, a lithium secondary battery having high energy density by using a lithium metal anode and improved safety by using a solid electrolyte can be provided.

[0049] Meanwhile, one aspect of the present invention may provide a method for manufacturing the lithium secondary battery. Brief explanation of the drawing

[0050] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to help to better understand the technical concept of the present invention together with the description of the invention above; therefore, the present invention is not to be interpreted as being limited only to the matters described in such drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation. Figure 1 schematically illustrates the problem of lithium dendrites growing from the negative electrode of a conventional lithium secondary battery, which causes a short circuit. FIGS. 2 and 3 relate to a lithium secondary battery including a volume expansion layer according to one embodiment of the present invention, schematically illustrating a reaction in which lithium dendrite growth is inhibited by inorganic particles or a volume expansion layer containing the same. Specific details for implementing the invention

[0051] Embodiments of the present invention will be described in detail below. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe their invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, the configurations described in the embodiments of this specification are merely one preferred embodiment of the present invention and do not represent all aspects of the technical spirit of the present invention. It should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0053] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0055] Additionally, terms such as “about,” “substantially,” as used throughout this specification, are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding this invention.

[0057] Throughout this specification, the description “A and / or B” means “A or B or both.”

[0059] Specific terms used in the following detailed description are for convenience only and are not restrictive. The words 'right', 'left', 'top', and 'bottom' indicate directions in the referenced drawings. The words 'inward' and 'outward' indicate directions toward or away from the geometric center of the specified device, system, and its components, respectively. 'Forward', 'rear', 'upward', 'downward', and related words and phrases indicate positions and orientations in the referenced drawings and should not be restrictive. These terms include the words listed above, their derivatives, and words of similar meaning.

[0061] The present invention relates to a lithium secondary battery and a method for manufacturing a lithium secondary battery. The lithium secondary battery according to the present invention primarily suppresses dendrite growth by providing a protective layer on the negative electrode, and secondarily suppresses dendrite growth by including inorganic particles that are lithiated with lithium or lithium ions in a volume expansion layer, thereby fundamentally preventing internal short circuits and providing a lithium secondary battery and a method for manufacturing a lithium secondary battery with improved safety.

[0063] FIG. 1 schematically illustrates the problem of lithium dendrite growth from the negative electrode of a conventional lithium secondary battery, which causes a short circuit. FIG. 2 and FIG. 3 relate to a lithium secondary battery according to an embodiment of the present invention, schematically illustrating a reaction in which lithium dendrite growth is suppressed by a volume expansion layer containing inorganic particles. The present invention will be described in more detail below with reference to the drawings.

[0065] Referring to FIG. 1, a conventional lithium secondary battery (100) is typically formed into a layered structure by integrating particulate ion-conducting inorganic materials. At this time, a large number of pores are contained due to the interstitial volume between the particles. Through the space provided by the pores, lithium dendrites grown from the negative electrode (10) come into contact with the positive electrode (20), causing a short circuit.

[0066] On the other hand, a lithium secondary battery (200) according to one aspect of the present invention can fundamentally suppress short circuits caused by lithium dendrite growth during battery operation by including a protective layer (40) and a volume expansion layer (50). This is illustrated in FIGS. 2 and FIGS. 3.

[0067] Specifically, referring to FIG. 2 and 3, a lithium secondary battery (200) according to one aspect of the present invention comprises a negative electrode (10); a protective layer (40) located on the negative electrode (10); a volume expansion layer (50) located on the protective layer (40); a separator layer (30) located on the volume expansion layer (50); a positive electrode (20) located on the separator layer (30); and an electrolyte (not shown).

[0068] That is, in one aspect of the present invention, a lithium secondary battery comprising a protective layer and a volume expansion layer is provided.

[0070] In the present invention, the protective layer (40) is located on the negative electrode. Lithium dendrites may grow from the negative electrode during battery operation. The present invention can primarily suppress the growth of lithium dendrites by providing the protective layer on the negative electrode. The protective layer also performs the role of preventing the volume expansion layer from coming into direct contact with the negative electrode. If the protective layer is absent and the volume expansion layer comes into direct contact with the negative electrode, inorganic particles present in the volume expansion layer may react directly with the negative electrode, thereby promoting the growth of lithium dendrites, or the inorganic particles may be lithiated, causing uncontrollable reactions such as explosions. In other words, the protective layer according to the present invention suppresses direct contact between the negative electrode and the volume expansion layer, and by forming it directly on the negative electrode to lower the interfacial resistance, the lifespan characteristics of the battery can be improved.

[0071] The above protective layer may be directly coated or applied to the cathode.

[0072] In a specific embodiment of the present invention, the protective layer is a porous polymer layer. The porous polymer layer may include a polymer, and the polymer may be polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylidene fluoride, polyvinylacetate, polyethylene, polypropylene, or ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide, polypropylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose,It may include any one selected from the group consisting of pullulan and carboxymethyl cellulose, or a mixture of two or more of these.

[0073] By providing a polymer layer made of polymer in this way, it is possible to manufacture it as a thin film and obtain a battery with high energy density.

[0075] Next, according to one aspect of the present invention, a lithium secondary battery (200) includes a volume expansion layer (50) between the protective layer (40) and the separating layer (30).

[0076] The above volume expansion layer comprises a binder polymer (a) and inorganic particles (b).

[0077] The above-mentioned inorganic particles (b) are capable of adsorbing lithium ions or intercalating lithium ions. The aforementioned inorganic particles come into direct contact with lithium dendrites generated at the negative electrode during battery operation, thereby becoming electrically connected to the negative electrode, and the inorganic particles exhibit a negative electrode potential. Accordingly, the inorganic particles can function as a negative electrode active material. Subsequently, as the battery operates, the lithium ions supplied from the positive electrode or lithium grown from lithium dendrites react physically, chemically, or electrochemically with the above-mentioned inorganic particles to become lithiated.

[0078] At this time, the lithium may be the lithium atom itself. The lithium is electrically conductive when in contact with inorganic particles via lithium dendrites and can exhibit a negative potential, so it can be lithiated by contacting inorganic particles.

[0080] As shown in Fig. 3, lithiated inorganic particles expand in volume, creating a dead space or void between the protective layer and the separator layer. Ion transfer becomes impossible through the generated dead space or void, causing the resistance within the lithium secondary battery to increase rapidly and stopping the growth of lithium dendrites. Consequently, a short circuit between the anode and the cathode can be fundamentally suppressed. This effect can be even more effective, particularly when using a solid electrolyte, as there is no movement of the electrolyte. Meanwhile, even when using a liquid electrolyte, since the residual electrolyte inside the battery must be minimized to achieve high energy density, the voids generated when lithium dendrites grow as described above cannot all be filled, so a short circuit between the cathode and the anode can still be suppressed.

[0082] In a specific embodiment of the present invention, the inorganic particle (b) is capable of accommodating lithium ions or lithium. In this case, the lithium ions or lithium react physically, chemically, or electrochemically with the inorganic particle to form a complex within the inorganic particle.

[0083] Accordingly, the inorganic particle (b) is a lithium ion or lithium that, once lithiated, cannot have the lithium ion or lithium removed, and cannot be restored to its state before lithiation. In other words, as ion transfer becomes impossible due to the occurrence of voids or dead spaces, or as the lithium dendrite becomes separated from the inorganic particle due to discharge and becomes electrically insulated, the lithiated inorganic particle cannot have lithium removed and cannot be restored to its state before lithiation.

[0084] The inorganic particles (b) according to the present invention are lithiated by reacting physically, chemically, or electrochemically with lithium ions or lithium, and may include metals, metal oxides, or both.

[0085] Specifically, in the case where the inorganic particles are metal, the above lithiation may involve the metal inorganic particles being lithiated in the form of lithium ions or an alloy with lithium.

[0086] Specifically, in the case where the inorganic particles are metal oxides, the lithiation may involve the metal oxide inorganic particles being complexed with lithium ions or lithium and chemically bonded with lithium. More specifically, the lithiation may involve the inorganic particles reacting as shown in Formula 1:

[0087] [Equation 1]

[0088] X(Li) + Y(M) -> LixMy

[0089] At this time, M includes Si, Sn, SiO, SnO, MnO2, or two or more of these, and x and y are determined according to the oxidation number of M, and X and Y are integers greater than or equal to 1.

[0090] The above reaction can be applied in the same way even if the above inorganic particles include both metal and metal oxide.

[0091] The inorganic particle (b) according to the present invention expands in volume by being lithiated with lithium ions or lithium.

[0092] In other words, the present invention utilizes volume-expandable inorganic particles to create a void between the protective layer and the separator layer as the battery operates. This void creation can fundamentally restrict the movement of lithium ions or lithium, and as the battery's resistance increases, the battery can be degraded without micro short circuits. Thus, according to one aspect of the present invention, safety issues caused by short circuits can be fundamentally prevented in advance.

[0093] To this end, the inorganic particles (b) according to the present invention are positioned so as not to come into direct contact with the electrode. In other words, the inorganic particles are positioned between the protective layer and the separating layer, thereby fundamentally suppressing the growth of lithium dendrites generated as the battery operates.

[0094] Meanwhile, in one aspect of the present invention, it is preferable that the inorganic particles be densely packed so that they expand in volume within the volume expansion layer to generate voids.

[0095] In a specific embodiment of the present invention, the volume expansion rate of the inorganic particles after lithiation compared to before lithiation may be 10 to 1000%, or 20 to 500%, or 50 to 300%. That is, when the inorganic particles (b) according to the present invention are lithiated with lithium ions or lithium, they become lithiated inorganic particles (c), and the volume of the lithiated inorganic particles (c) is significantly larger than that of the inorganic particles (b).

[0096] At this time, the lithiated inorganic particle (c) may be as in Equation 2:

[0097] [Equation 2]

[0098] LixMy

[0099] At this time, the above M includes Si, Sn, SiO, SnO, MnO2, or two or more of these, and the above x and y are determined according to the oxidation number of M.

[0100] In one embodiment of the present invention, the inorganic particles (b) comprise a metal or a metal oxide. Specifically, the inorganic particles may comprise Si, Sn, SiO, SnO, MnO2, Fe2O3, or two or more of these.

[0101] In particular, Si is suitable for solving the problem according to one aspect of the present invention in that the volume expansion rate after lithiumization reaches about 300% compared to before lithiumization.

[0102] In a specific embodiment of the present invention, the inorganic particles (b) may be included in an amount of 10 to 99 parts by weight, 15 to 95 parts by weight, or 20 to 90 parts by weight based on 100 parts by weight of the volume expansion layer.

[0103] In a specific embodiment of the present invention, the thickness of the volume expansion layer may be formed to be less than 50 μm, preferably 10 μm or less, for example, 1 μm or less, 100 nm or less, or on a nanometer scale of 10 nm or less.

[0104] In one embodiment of the present invention, the volume expansion layer may be coated to less than 90%, less than 50%, or less than 30% of the surface area of ​​the separation layer. As the volume expansion layer is coated within the above numerical range, the reduction in ion conductivity can be minimized while maximizing the safety improvement effect of the present invention.

[0106] In a specific embodiment of the present invention, the binder polymer (a) faithfully performs the role of a binder that connects and stably fixes the inorganic particles, thereby contributing to preventing the deterioration of the mechanical properties of the volume expansion layer.

[0107] In addition, the binder polymer does not necessarily have ion conductivity, but using a polymer with ion conductivity can further improve the performance of the electrochemical device. Therefore, the binder polymer may have a high possible dielectric constant. In fact, since the degree of dissociation of a salt in an electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the binder polymer, the better the degree of salt dissociation in the electrolyte can be improved. The dielectric constant of such a binder polymer can be used in the range of 1.0 to 100 (measurement frequency = 1 kHz), and in particular, it can be 10 or higher.

[0108] In addition to the aforementioned functions, the binder polymer may have the characteristic of exhibiting a high degree of electrolyte swelling by gelling upon impregnation with a liquid electrolyte. Accordingly, the solubility index of the binder polymer, namely the Hildebrand solubility parameter, is 15 to 45 MPa 1 / 2 or 15 to 25 MPa 1 / 2 and 30 to 45 MPa 1 / 2 It is within the range. Therefore, hydrophilic polymers having many polar groups can be used more than hydrophobic polymers such as polyolefins. The above solubility index is 15 MPa 1 / 2 Less than and 45 MPa 1 / 2 This is because if it exceeds, it may be difficult to swell with a conventional liquid electrolyte for batteries.

[0109] The above binder polymer attaches the inorganic particles to each other so that they can maintain a bonded state, for example, the binder polymer connects and fixes the inorganic particles together.

[0110] As for the binder polymer that can be included within the volume expansion layer in this manner, any polymer commonly used in the relevant technical field may be applied without limitation; examples include polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, and cellulose acetate butyrate. Examples include butyrate), cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, but are not limited thereto.

[0112] In a specific embodiment of the present invention, the separating layer (30) is a porous membrane capable of electrically insulating the anode and cathode to prevent short circuits while providing a path for the movement of lithium ions, and can be used without special limitations as long as it is a separator material that can be used in an electrochemical device.

[0113] The above separation layer may specifically be a porous polymer film substrate or a porous polymer nonwoven fabric substrate, or a film capable of swelling by an electrolyte.

[0114] The above porous polymer film substrate may be a porous polymer film composed of polyolefins such as polyethylene, polypropylene, polybutene, and polypentene, and such a polyolefin porous polymer film substrate exhibits a shutdown function at a temperature of, for example, 80°C to 130°C.

[0115] At this time, the polyolefin porous polymer film substrate can be formed as a polymer by using polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutylene, and polypentene, either individually or by mixing two or more of these.

[0116] In addition, the porous polymer film substrate may be manufactured by forming it into a film shape using various polymers such as polyester in addition to polyolefin. Furthermore, the porous polymer film substrate may be formed in a structure in which two or more film layers are laminated, and each film layer may be formed from the aforementioned polymers such as polyolefin and polyester alone, or from a polymer in which two or more of these are mixed.

[0117] In addition, the porous polymer film substrate and porous nonwoven fabric substrate may be formed from polymers other than the polyolefin-based materials mentioned above, such as polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, either individually or in a mixture thereof.

[0118] The thickness of the separator layer is not particularly limited, but specifically 1 to 100 μm, more specifically 2 to 50 μm, and as the high power and high capacity of batteries have recently progressed, it is advantageous to use a thin film for the separator layer. The pore diameter present in the separator layer is 10 nm to 100 nm, or 10 nm to 70 nm, or 10 nm to 50 nm, or 10 nm to 35 nm, and the porosity can be formed to be 5% to 90%, preferably 20% to 80%. However, in the present invention, these numerical ranges can be easily modified according to specific embodiments or as needed.

[0119] The pores of the above separation layer have various types of pore structures, and if any one of the average pore size measured using a porosimeter or observed on an FE-SEM satisfies the conditions presented above, it is included in the present invention.

[0120] Here, in the case of a generally known uniaxially stretched dry separation layer, the central pore size is based on the pore size in the TD direction rather than the MD direction on the FE-SEM, and in other cases, a separation layer having a mesh structure (e.g., a wet PE separator) can be based on the pore size measured with a porosimeter.

[0121] Meanwhile, if the electrolyte is a swelling film, it may not contain pores or may have less than 50% pores. Since ion transfer can occur as the electrolyte is impregnated between polymer chains, it can operate as a battery even without pores. Examples of such materials include polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyacetonitrile (PAN), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF).

[0123] In a specific embodiment of the present invention, the electrolyte may be a solid electrolyte or a liquid electrolyte. In this case, the electrolyte may be impregnated into the pores within the protective layer, the volume expansion layer, and the separating layer. Of course, the electrolyte is also present in the electrode active material layer within the electrode of the present invention.

[0124] When the above electrolyte is a solid electrolyte, the solid electrolyte comprises an ion-conducting solid electrolyte material and can be applied, for example, as an ion-conducting electrolyte in an all-solid-state battery that does not use a liquid electrolyte. The ion-conducting solid electrolyte material is 10 at the battery operating temperature. -5 It may have an ionic conductivity of S / cm or higher.

[0125] The above solid electrolyte material may include a polymer-based solid electrolyte, an inorganic solid electrolyte, or a mixture of both.

[0126] In one embodiment of the present invention, the polymer-based solid electrolyte comprises a polymer resin and a lithium salt, and may be a solid polymer electrolyte having the form of a mixture of a solvated lithium salt and a polymer resin, or a polymer gel electrolyte having an organic electrolyte containing an organic solvent and a lithium salt contained in a polymer resin.

[0127] In one embodiment of the present invention, the solid polymer electrolyte may include, for example, a polymer resin comprising a polyether-based polymer, a polycarbonate-based polymer, an acrylate-based polymer, a polysiloxane-based polymer, a phosphazene-based polymer, a polyethylene derivative, an alkylene oxide derivative, a phosphate ester polymer, a polyagitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, a polymer containing an ionic dissociator, or two or more of these, but is not limited thereto.

[0128] In a specific embodiment of the present invention, the solid polymer electrolyte may include a branched copolymer, a comb-like polymer, a cross-linked polymer resin, or two or more of the above, in which an amorphous polymer such as PMMA, polycarbonate, polysiloxane (PDMS), and / or phosphazene is copolymerized as a comonomer to a polyethylene oxide (PEO) main chain.

[0129] In addition, in a specific embodiment of the present invention, the polymer gel electrolyte comprises an organic electrolyte containing a lithium salt and a polymer resin, wherein the organic electrolyte may comprise 60 to 400 parts by weight per 100 parts by weight of the polymer resin. The polymer resin applied to the gel electrolyte is not limited to a specific component, but may include, for example, PVC (Polyvinyl chloride)-based, PMMA (Poly(methyl methacrylate))-based, polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), poly(vinylidene fluoride-hexafluoropropylene (PVdF-HFP), or a mixture of two or more of these, but is not limited thereto.

[0130] In the electrolyte of the present invention, the aforementioned lithium salt is an ionizable lithium salt, Li + X - It can be expressed as. The anion (X) of such lithium salt is not particularly limited, but F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C -, (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - Examples of the back can be given.

[0131] Meanwhile, in a specific embodiment of the present invention, the polymer solid electrolyte may further comprise an additional polymer gel electrolyte. The polymer gel electrolyte has excellent ionic conductivity (or 10 -4 It has binding characteristics (e.g., S / cm or higher), and can provide not only the function of an electrolyte but also the function of an electrode binder resin that provides binding force between electrode active materials and binding force between the electrode layer and the current collector.

[0132] Meanwhile, in the present invention, the inorganic solid electrolyte may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or both.

[0133] In a specific embodiment of the present invention, the sulfide-based solid electrolyte comprises a sulfur atom among the electrolyte components and is not limited to a particularly specific component, but may include one or more of a crystalline solid electrolyte, an amorphous solid electrolyte (glassy solid electrolyte), and a glass ceramic solid electrolyte. Specific examples of the sulfide-based solid electrolyte include LPS-type sulfides containing sulfur and phosphorus, and Li 4-x Ge 1-x P x S4(x is 0.1 to 2, specifically x is 3 / 4, 2 / 3), Li 10±1 MP2X 12 (M=Ge, Si, Sn, Al, X=S, Se), Li 3.833 Sn 0.833 As 0.166 S4, Li4SnS4, Li 3.25 Ge 0.25 P 0.75Examples include S4, Li2S-P2S5, B2S3-Li2S, xLi2S-(100-x)P2S5(x is 70 to 80), Li2S-SiS2-Li3N, Li2S-P2S5-LiI, Li2S-SiS2-LiI, Li2S-B2S3-LiI, but are not limited thereto.

[0134] In a specific embodiment of the present invention, the oxide-based solid electrolyte is, for example, Li 3x La 2 / 3-x LLT systems with perovskite structures such as TiO3, Li 14 LISICON, such as Zn(GeO4)4, Li 1.3 Al 0.3 Ti 1.7 LATP systems such as (PO4)3, (Li 1+x Ge 2-x Al x LAGP-based materials such as (PO4)3) and phosphate-based materials such as LiPON can be appropriately selected and used, but are not specifically limited thereto.

[0136] If the above electrolyte is a liquid electrolyte, A + B - As a salt with a structure like that, A + is Li + , Na + , K + It includes alkali metal cations such as or ions composed of combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 -Salts containing anions such as or combinations thereof are dissolved or dissociated in organic solvents composed of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or mixtures thereof, but are not limited thereto.

[0138] In a specific embodiment of the present invention, the cathode may include a current collector in contact with the cathode active material layer to support the cathode active material layer and to transfer electrons between the cathode active material and the wire. In addition, in a specific embodiment of the present invention, the cathode may consist only of a current collector without a cathode active material layer.

[0139] The above current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, various forms may be used, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics, with or without fine grooves formed on the surface.

[0140] The thickness of the current collector may be 5 to 30 μm. In a specific embodiment of the present invention, the lower limit of the current collector thickness may be 5 μm, 7 μm, or 10 μm or more, and the upper limit of the current collector thickness may be 30 μm, 25 μm, or 20 μm or less, or any combination thereof. Within the above numerical range, the negative electrode active material layer may be supported by the current collector, and the problem of reduced energy density per negative electrode volume is minimized.

[0141] In a specific embodiment of the present invention, the cathode may include a cathode active material layer located on a current collector. The cathode active material layer may include lithium metal as the cathode active material. In a specific embodiment of the present invention, the cathode active material layer may include one or more of a metal thin film, a metal alloy, and a powder thereof.

[0142] In a specific embodiment of the present invention, the negative electrode active material comprises lithium metal and may additionally include one or more of the group consisting of lithium alloys, lithium metal composite oxides, lithium-containing titanium composite oxides (LTO), and combinations thereof. In this case, the lithium alloy comprises an element capable of alloying with lithium, and the elements capable of alloying with lithium may include Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or alloys thereof.

[0143] The thickness of the above negative electrode active material layer may be 5 to 40 μm. In a specific embodiment of the present invention, the thickness of the negative electrode active material layer may be 5 μm, 7 μm, or 10 μm or more within the above numerical range, and the thickness of the negative electrode active material layer may be 40 μm, 30 μm, or 20 μm or less within the above numerical range. For example, the thickness may be 5 μm to 30 μm, or 7 μm to 40 μm. Within the above numerical range, lithium ions can sufficiently diffuse into the interior of the negative electrode active material layer.

[0144] In a specific embodiment of the present invention, the negative active material layer may be manufactured by coating, bonding, rolling, or depositing a metal foil onto a planar current collector. Alternatively, it may be manufactured by applying metal powder onto the current collector. Meanwhile, the negative active material layer may consist solely of a lithium metal thin film or a lithium metal alloy without a current collector. In a specific embodiment of the present invention, the negative active material layer may be manufactured by physically bonding or rolling lithium metal onto a current collector. In a specific embodiment of the present invention, the negative active material layer may be manufactured by electrodepositing or chemical vapor deposition of lithium metal onto a current collector.

[0145] The positive electrode to be applied together with the negative electrode for the lithium metal battery of the present invention is not particularly limited, and the positive active material can be manufactured in a state in which it is bound to a positive current collector according to conventional methods known in the art. Non-limiting examples of the positive active material include conventional positive active materials that can be used in the positive electrodes of conventional electrochemical devices, and it is particularly preferable to use lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide formed by combining these.

[0147] In one aspect of the present invention, a method for manufacturing a lithium secondary battery as described above is provided.

[0148] First, a protective layer is placed on the cathode.

[0149] The method of placing the above protective layer is not particularly limited, and methods commonly used in the industry may be used without limitation depending on the material of the protective layer. For example, general methods for forming a layer such as the doctor blade method, solution casting method, dip coating method, spray coating method, spin coating method, sputtering method of physical vapor deposition (PVD), and atomic layer deposition (ALD) method of chemical vapor deposition (CVD) may be used.

[0150] Next, a volume expansion layer is placed on the separation layer.

[0151] Specifically, a polymer solution is prepared by dissolving the aforementioned polymer in a solvent, and a composition for forming a volume expansion layer is prepared by adding the inorganic particles to the polymer solution. A stirring process may be applied to the polymer solution and the composition to ensure uniform dispersion of the components added in the solvent. The solvent may include one or more selected from ethanol, toluene, tetrahydrofuran, ethylene, acetone, chloroform, and dimethylformamide (DMF).

[0152] Next, the composition for forming the volume expansion layer is coated onto the prepared separation layer. At this time, the method of placing the volume expansion layer is not particularly limited, and any method commonly used in the industry can be used without limitation. For example, general methods for forming a layer such as the doctor blade method, solution casting method, dip coating method, spray coating method, spin coating method, sputtering method of physical vapor deposition (PVD), and atomic layer deposition (ALD) method of chemical vapor deposition (CVD) may be used.

[0153] Subsequently, an electrode assembly is manufactured by sequentially interposing a cathode, a protective layer, a volume expansion layer, a separator, and an anode so that the cathode equipped with the protective layer and the separator equipped with the volume expansion layer come into contact.

[0154] The methods described above are not particularly limited, and methods commonly used in the industry may be used without restriction.

[0155] Meanwhile, when a liquid electrolyte is applied to the manufactured electrode assembly, the liquid electrolyte can be injected after the manufactured electrode assembly is placed in a pouch. On the other hand, when a solid electrolyte is applied, since the separation layer is a solid electrolyte, an additional process of introducing the electrolyte is not required.

[0157] The present invention provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool that moves by receiving power from a battery motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; an electric two-wheeled vehicle including an electric bicycle (E-bike) or an electric scooter (E-scooter); an electric golf cart; and a power storage system.

[0159] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0161] Example 1

[0162] 1. Manufacturing of a separation layer where the volume expansion layer is located

[0163] A slurry was prepared by stirring overnight at a concentration of 10 wt% in N-methyl-2-pyrrolidone solvent with Si (Sigma-Aldrich, <100 nm) inorganic particles in an 8:2 weight ratio with a PVDF-HFP (5% HFP, Mw 800,000) binder. The prepared slurry was spin-coated onto a separation layer (polyethylene porous polymer substrate, Asahi, ND307B) at a speed of 1000 ppm for 1 minute. Subsequently, the separation layer was vacuum-dried at 80 °C for 12 hours to produce a separation layer with a volume expansion layer. At this time, the thickness of the volume expansion layer was 0.5 μm and the content was 0.99 g / m². 2Accordingly, the air permeability of the separation layer equipped with a volume expansion layer exhibited a physical property of 273 sec / 100cc. At this time, the volume expansion rate of the inorganic particles Si after lithiation was 300% compared to before lithiation. In addition, the inorganic particles were 80 parts by weight based on 100 parts by weight of the volume expansion layer.

[0165] 2. Manufacturing of a cathode equipped with a protective layer

[0166] A Li metal cathode with a protective layer was prepared by spin-coating a pre-prepared 5wt% PVDF-HFP (5% HFP, Mw 800,000) binder solution onto Honjo Li metal (20㎛ thickness) at a speed of 2000 ppm for 1 minute, and then drying at room temperature for 12 hours.

[0168] 3. Anode manufacturing

[0169] For slurry preparation, the cathode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), FX35 conductive material, and PVDF binder were mixed in a ratio of 96:2:2 wt%, added to N-methyl-2-pyrrolidone solvent, and stirred. This mixture was applied to a 20 µm thick aluminum current collector using a doctor blade, and the resulting product was vacuum dried at 120°C for 4 hours. Subsequently, the vacuum-dried product was subjected to a rolling process using a roll press to achieve 3 mAh / cm² 2 The anode slurry was loaded, and an anode with a porosity of 22% was obtained.

[0171] 4. Battery manufacturing

[0172] The anode manufactured above is 1.4875 cm 2 It was prepared by stamping into a circular shape. 1.7671cm 2A lithium metal thin film coated with a protective layer and cut into a circular shape was prepared as the negative electrode. A separator layer equipped with a volume expansion layer was interposed between these two electrodes, and a coin-type half-cell was manufactured by injecting a liquid electrolyte (EC : EMC = 3 : 7 (vol.%), LiPF6 1M, vinylene carbonate 0.5 wt, FEC 1 wt%). At this time, the separator layer without the volume expansion layer coating was manufactured to face the positive electrode.

[0173] The above-mentioned battery was charged and discharged under room temperature conditions to measure the initial discharge capacity.

[0175] Charging conditions: CC / CV (4.0V, 0.1C-rate, 0.05C current cut-off)

[0176] Discharge conditions: CC (3V, 0.1C-rate)

[0177] In addition, after evaluating the initial discharge capacity, lifespan was evaluated by performing charge (0.3C-rate) and discharge (0.5C-rate) cycles. The timing of Li dendrite formation was determined by analyzing the voltage drop caused by short circuits through the charging profile.

[0179] Example 2.

[0180] The separation layer and cell were fabricated and evaluated as in Example 1, except that the volume expansion layer composition was Si:PVDF = 9:1. In this case, the thickness of the volume expansion layer was 0.5 μm and the content was 1.01 g / m². 2 As such, the air permeability of the separation layer equipped with a volume expansion layer was 258 sec / 100cc. At this time, the inorganic particles were 90 parts by weight based on 100 parts by weight of the volume expansion layer.

[0182] Example 3.

[0183] The thickness of the volume expansion layer is 1 µm and the content is 1.98 g / m² 2Except for the air permeability of the separation layer equipped with a volume expansion layer being 281 sec / 100cc, the separation layer and cell were fabricated and evaluated as in Example 1.

[0185] Example 4.

[0186] A lithium secondary battery was manufactured using the same method as in Example 1, except that the volume expansion layer was prepared by the following method. Specifically, it was prepared as in Example 1, except that SnO2 (Sigma-Aldrich, <100 nm) was used instead of Si (Sigma-Aldrich, <100 nm) as the inorganic particles. At this time, the thickness of the volume expansion layer was 0.5 μm and the content was 2.66 g / m² 2 The air permeability of the separation layer equipped with a volume expansion layer was 265 sec / 100cc.

[0188] Comparative Example 1.

[0189] A lithium secondary battery was fabricated using a separator layer equipped with a porous coating layer containing Al2O3 as an inorganic particle and PVDF as a binder polymer in a ratio of 20:80, instead of a volume expansion layer. In this case, the thickness of the porous coating layer was 2.5 μm and the content was 8.1 g / m². 2 The air permeability of the separation layer equipped with a volume expansion layer was 260 sec / 100cc.

[0191] Comparative Example 2.

[0192] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode was not provided with a protective layer.

[0193] That is, a Honjo Li metal (20 μm thick) negative electrode was prepared. A lithium secondary battery was manufactured by sequentially stacking a separator layer containing a volume expansion layer according to Example 1 and a positive electrode on the prepared negative electrode.

[0195] Comparative Example 3.

[0196] A lithium secondary battery was manufactured in the same manner as in Example 3, except that a porous inorganic layer was provided instead of a protective layer.

[0197] Specifically, a porous inorganic layer was prepared using the following method.

[0198] A binder polymer solution was prepared by adding PVDF-HFP as a binder polymer to N-methyl-2-pyrrolidone solvent and dissolving it at 50 °C for approximately 4 hours. Al2O3 (particle size: 500 nm, US Research Nanomaterials, Inc.) was added as an inorganic particle to the prepared binder polymer solution, and the inorganic particles were crushed and dispersed using a ball milling method for 12 hours to prepare a slurry for forming a porous coating layer. At this time, the weight ratio of inorganic particles to binder polymer was 80:20.

[0199] The above slurry for forming a porous coating layer was applied onto a release film and dried, and then the release film was removed. The thickness of the obtained porous coating layer was approximately 3 μm.

[0200] Charging capacity (mAh / g, 4.25V) Discharge capacity (mAh / g, 4.25V) Efficiency (%) Short occurrence point (number of cycles) Battery characteristics after the point of short circuit occurrence Example 1 225.1 201.8 89.6 42 Not running Example 2 225.8 203.3 90.0 44 Not running Example 3 225.3 201.9 89.6 45 Not running Example 4 224.5 202.5 90.2 50 Not running Comparative Example 1 225.2 202.4 89.9 48 Future events (vent, ignition, or explosion, etc.) are possible Comparative Example 2 218.5 182.2 83.4 14 Not running Comparative Example 3 221.7 198.2 89.4 38 Not running

[0201] As shown in Table 1 above, it can be seen that when the same electrode is used and a volume expansion layer is provided in the separator, there is a difference in the timing of short circuit occurrence. In the battery of Comparative Example 1, a micro-short circuit occurs due to lithium dendrites after 48 cycles, posing a risk of ignition or explosion during subsequent operation. On the other hand, in the case of the Example, it was confirmed that the lithium dendrites, instead of encountering the anode to cause a micro-short circuit, encounter the volume expansion material to degrade performance, thereby preventing subsequent events in advance. In the case of Comparative Example 2, some inorganic particles (b) exposed on the surface of the separator came into direct contact with the Li metal anode without a protective layer, causing charging and discharging to proceed with high resistance from the beginning. Consequently, significantly lower capacity and efficiency were obtained. Furthermore, lifespan characteristics were significantly reduced, and a problem arose where the battery did not last long due to the high initial resistance. In the case of Comparative Example 3, when inorganic particles are applied, the relationship between the volume expansion layer and the current collector is electrically or physically suppressed, but the problem of increased resistance and low capacitance development due to increased thickness and tortuosity appeared.

[0203] Experimental Example

[0204] (1) Initial charge and discharge capacity measurement

[0205] The above-mentioned battery was charged and discharged under room temperature conditions to measure the initial discharge capacity.

[0207] Charging conditions: CC / CV (4.0V, 0.1C-rate, 0.05C current cut-off)

[0208] Discharge conditions: CC (3V, 0.1C-rate)

[0210] (2) Battery horizontal evaluation

[0211] After evaluating the initial discharge capacity, the lifespan was evaluated by performing charge (0.3C-rate) and discharge (0.5C-rate) cycles.

[0213] (3) Short occurrence time

[0214] The voltage drop caused by the short was analyzed by checking the charging profile to identify the point at which the short occurred.

[0216] (4) Measurement of air permeability of a separation layer equipped with a volume expansion layer

[0217] For the separation layer equipped with a volume expansion layer, air permeability was measured using a Gurley-type air permeability meter in accordance with JIS P-8117.

[0219] (5) Measurement of volume expansion rate

[0220] Since it is difficult to determine the direct volume expansion rate of inorganic particles, the size of the inorganic particles after lithiation was measured relative to before lithiation, and calculated as follows:

[0221] Volume expansion rate: (Thickness of electrode with inorganic particles after lithiation - Thickness of electrode with inorganic particles before lithiation) / (Thickness of electrode with inorganic particles before lithiation) X 100%. Explanation of the symbols

[0223] 100, 200: Lithium secondary battery 10: Cathode 20: Anode 21: Positive current collector 22: Positive active material 23: Challenger 24; solid electrolyte 30: Separation layer 40: Protection layer 50: Volume expansion layer 51: Inorganic particles 52: Lithium or lithium ions and lithiated inorganic particles

Claims

Claim 1 As a lithium secondary battery, the lithium secondary battery comprises: a negative electrode; a protective layer located on the negative electrode; a volume expansion layer located on the protective layer; a separator layer located on the volume expansion layer; a positive electrode located on the separator layer; and an electrolyte; wherein the protective layer is a binder layer directly coated or applied on the negative electrode, and the volume expansion layer comprises a binder polymer (a); and inorganic particles (b) capable of adsorbing lithium ions or lithium (intercalation); A lithium secondary battery comprising, wherein the inorganic particles (b) comprise Si, Sn, SiO, SnO, MnO2, Fe2O3 or two or more of these, and wherein the inorganic particles react physically, chemically, or electrochemically with lithium ions or lithium to become lithiated, and are characterized by expanding in volume by 20 to 500% to create a dead space or void between the protective layer and the separator layer. Claim 2 delete Claim 3 delete Claim 4 A lithium secondary battery according to claim 1, characterized in that the inorganic particles (b) are in an amount of 10 to 99 parts by weight based on 100 parts by weight of the volume expansion layer. Claim 5 A lithium secondary battery according to claim 1, characterized in that the protective layer is a polymer layer. Claim 6 A lithium secondary battery according to claim 5, wherein the polymer layer comprises a polymer that is electrically insulating. Claim 7 In claim 6, the polymer is polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylidene fluoride, polyvinylacetate, polyethylene, polypropylene, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide A lithium secondary battery characterized by comprising any one selected from the group consisting of polyethylene oxide, polypropylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxymethylcellulose, or a mixture of two or more of these. Claim 8 A lithium secondary battery according to claim 1, characterized in that the thickness of the volume expansion layer is 10 nm to 50 μm. Claim 9 A lithium secondary battery according to claim 1, characterized in that the electrolyte is a solid electrolyte or a liquid electrolyte. Claim 10 A lithium secondary battery according to claim 9, characterized in that the pores within the protective layer, volume expansion layer, and separator layer are impregnated with the solid electrolyte or the liquid electrolyte. Claim 11 In claim 1, the binder polymer (a) is polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, A lithium secondary battery characterized by comprising cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose alone or two or more of these. Claim 12 A lithium secondary battery according to claim 1, characterized in that the separating layer comprises a porous polymer film substrate or a porous polymer nonwoven fabric substrate. Claim 13 A method for manufacturing a lithium secondary battery according to claim 1, comprising: a negative electrode; a protective layer located on the negative electrode; a volume expansion layer located on the protective layer; a separator layer located on the volume expansion layer; a positive electrode located on the separator layer; and an electrolyte, wherein the method comprises the steps of: placing a protective layer on the negative electrode; placing the volume expansion layer on the separator layer; and sequentially interposing the negative electrode, the protective layer, the volume expansion layer, the separator layer, and the positive electrode; wherein the volume expansion layer comprises a binder polymer (a); and inorganic particles (b) capable of adsorbing lithium ions or lithium (intercalation); wherein the inorganic particles (b) comprise Si, Sn, SiO, SnO, MnO2, Fe2O3, or two or more of these, and wherein the inorganic particles react physically, chemically, or electrochemically with lithium ions or lithium to become lithiated, and upon lithiation, expand in volume by 20 to 500% to create a dead space or void between the protective layer and the separator layer.

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