Lithium secondary battery and method for manufacturing same

Abstract

This lithium secondary battery (100) is provided with: a positive electrode (5) that contains MnO2; a negative electrode (6) that contains a negative electrode active material in which lithium ions are absorbed; and an electrolyte solution that is impregnated in the positive electrode (5) and the negative electrode (6) and that contains a mixed solvent of a cyclic carbonate and a chain carbonate. The negative electrode active material contains, for example, at least one selected from the group consisting of graphite and silicon. The cyclic carbonate contains, for example, at least one selected from the group consisting of ethylene carbonate and vinylene carbonate. The chain carbonate contains, for example, methyl ethyl carbonate.

Description

Technical Field

[0001] The present disclosure relates to a lithium secondary battery and a method for manufacturing the same. Background Art

[0002] The most well-known material for the positive electrode active material of lithium secondary batteries is a composite oxide containing cobalt. However, the estimated reserves of cobalt are not necessarily large, so there is a concern that it will be exhausted in the near future. As positive electrode active materials that do not contain rare metals such as cobalt, manganese dioxide and transition metal phosphates can be cited. Transition metal phosphates, such as lithium iron phosphate, have been put into practical use. On the other hand, manganese dioxide has a capacity density that greatly exceeds that of transition metal phosphates and is inexpensive, so it is highly anticipated as the next generation of positive electrode active materials.

[0003] Patent document 1 describes a non-aqueous secondary battery having a positive electrode using manganese dioxide as an active material and a negative electrode using lithium or a lithium alloy as an active material, wherein the positive electrode further contains Li2MnO3. As an electrolyte, an electrolyte in which lithium perchlorate is dissolved at a concentration of 1 mol / L in a mixed solvent of propylene carbonate (PC) and dimethoxyethane (DME) is used.

[0004] Prior Art Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 63-114064

[0006] Patent Document 2: International Publication No. 2022 / 118545 Summary of the invention

[0007] Problems to be solved by the invention

[0008] The present disclosure provides a technology for improving the capacity density of a lithium secondary battery using MnO 2 as a positive electrode.

[0009] Means for solving problems

[0010] The present invention provides a lithium secondary battery, which comprises a positive electrode, a negative electrode and an electrolyte.

[0011] The positive electrode comprises MnO2,

[0012] The negative electrode includes a negative electrode active material that absorbs lithium ions.

[0013] The electrolyte solution is impregnated into the positive electrode and the negative electrode, and contains a mixed solvent of cyclic carbonate and chain carbonate.

[0014] Effects of the Invention

[0015] According to the present disclosure, the capacity density of a lithium secondary battery using MnO 2 as a positive electrode can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a cross-sectional view of a lithium secondary battery according to one embodiment of the present disclosure.

[0017] Figure 2 This is a process diagram showing a method for manufacturing a lithium secondary battery.

[0018] Figure 3A This is a cross-sectional view showing an example of the positional relationship among the container, the Li metal foil, and the electrode group.

[0019] Figure 3B It is a perspective view showing an example of the positional relationship among the container, the Li metal sheet, and the electrode group.

[0020] Figure 4 This is a graph showing the initial charge and discharge curves of the lithium secondary batteries of Example 1 and Comparative Example 1.

[0021] Figure 5 This is a graph showing the initial charge and discharge curves of the lithium secondary batteries of Example 1 and Example 2.

[0022] Figure 6 This is a graph showing the results of the charge and discharge cycle test of the lithium secondary battery of Example 1.

[0023] Fig. 7A This is a graph showing the charge and discharge curve of the lithium secondary battery of Example 1 in the charge and discharge test 2.

[0024] Figure 7B This is a graph showing the charge and discharge curve of the lithium secondary battery of Example 3 in the charge and discharge test 2. DETAILED DESCRIPTION

[0025] (Insights that form the basis of this disclosure)

[0026] Since MnO2 does not contain lithium, a lithium secondary battery using MnO2 as a positive electrode active material must be in a charged state when assembled. For example, in the non-aqueous secondary battery of Patent Document 1, Li metal is used as a negative electrode active material.

[0027] As known to those skilled in the art, lithium secondary batteries using Li metal as negative electrode active materials have poor reversibility. When Li alloys such as LiAl alloys are used instead of Li metal, the cycle characteristics at a shallow depth are good. However, if the charge and discharge are repeated at a deep depth, the battery will reach the end of its life with fewer charge and discharge times. Therefore, lithium secondary batteries using MnO2 as positive electrode active materials are limited to practical uses such as memory backup uses where the charge and discharge are repeated at a shallow depth. There is also the problem that Li alloys are hard and are not suitable for batteries with a winding structure.

[0028] In addition, in Patent Document 1, a mixed solvent of propylene carbonate (PC) and dimethoxyethane (DME) is used as a solvent for the non-aqueous electrolyte. However, the withstand voltage of this mixed solvent is low, so according to the battery of Patent Document 1, only about half of the theoretical capacity of the positive electrode (MnO2) can be utilized.

[0029] As described in Patent Document 2, it is also conceivable to use MnO2 that absorbs lithium as a positive electrode active material. However, it is not easy to prepare such a material.

[0030] Therefore, a technology for improving the capacity density of lithium secondary batteries using MnO2 as positive electrodes is needed. While improving the capacity density, lithium secondary batteries are also required to have practical reversibility. Specifically, lithium secondary batteries are required to show good cycle characteristics even when charged and discharged at a deep depth.

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0032] (Implementation Method)

[0033] Figure 1 1 is a cross-sectional view of a lithium secondary battery according to an embodiment of the present disclosure. The lithium secondary battery 100 includes a container 1 and an electrode group 4. The electrode group 4 has a winding structure. The electrode group 4 is accommodated in the container 1. The electrode group 4 includes a positive electrode 5, a negative electrode 6, and a pair of separators 7. The electrode group 4 is impregnated with an electrolyte. The opening of the container 1 is sealed by a sealing plate 2. The positive electrode 5 includes a positive electrode collector 5a and a positive electrode active material layer 5b. One end of the positive electrode lead 5c is connected to the positive electrode 5. The other end of the positive electrode lead 5c is connected to the back of the sealing plate 2. An insulating filler 3 is arranged around the sealing plate 2. The negative electrode 6 includes a negative electrode collector 6a and a negative electrode active material layer 6b. One end of the negative electrode lead 6c is connected to the negative electrode 6. The other end of the negative electrode lead 6c is connected to the bottom surface of the container 1. Insulating rings 8 are arranged on the upper surface and the lower surface of the electrode group 4, respectively.

[0034] In this embodiment, the container 1 has a negative polarity and the sealing plate 2 has a positive polarity. However, the container 1 may have a positive polarity and the sealing plate 2 may have a negative polarity.

[0035] As the positive electrode current collector 5a, a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are cheap and easy to be made into thin films, so they are suitable as the material of the positive electrode current collector 5a. The sheet or film can be porous or non-porous. As the sheet or film, a metal foil, a metal mesh, etc. can be used. A carbon material such as carbon can be coated on the surface of the positive electrode current collector 5a as a conductive auxiliary material.

[0036] The positive electrode active material layer 5b contains MnO2 as a positive electrode active material. In detail, when the assembly of the lithium secondary battery 100 is completed, the positive electrode active material layer 5b contains MnO2. The lithium secondary battery 100 is in a charged state when the assembly is completed. Therefore, the lithium secondary battery 100 can start from discharge after assembly. "When the assembly is completed" refers to any time during the period from the moment when the production of the lithium secondary battery 100 is completed to the time when the external power supply is connected to the lithium secondary battery 100 and the charge and discharge process is performed.

[0037] As MnO2, electrolytic manganese dioxide can be used. Electrolytic manganese dioxide is manganese dioxide produced by electrolysis. Electrolytic manganese dioxide is known as a material for primary batteries and is inexpensive. Electrolytic manganese dioxide can be heat-treated at a temperature of 150°C to 430°C. In addition, manganese dioxide is represented as "MnO2" in the chemical formula, but is actually an indefinite compound.

[0038] There is no particular limitation on the crystal structure of MnO2. MnO2 with various crystal structures such as α-MnO2, β-MnO2, γ-MnO2, ε-MnO2, λ-MnO2, δ-MnO2, γ-β-MnO2, and R-MnO2 (ramsdellite-type manganese dioxide) can be used. MnO2 may contain multiple crystalline phases or may be a mixed crystal. MnO2 may contain at least one selected from γ-β-MnO2, ramsdellite, and β-MnO2. Ramsdellite, γ-β-MnO2, which can be made from electrolytic manganese dioxide, and β-MnO2, which can also be made from electrolytic manganese dioxide, all have tunnel structures, are cheap, and are easily available. In particular, γ-β-MnO2 shows the highest discharge capacity density when used as an active material. In other words, Mn is easily reduced. Therefore, γ-β-MnO2 is also suitable as an active material for lithium secondary batteries 100. In addition, γ-β-MnO 2 represents a mixed crystal of γ-MnO 2 and β-MnO 2.

[0039] The positive electrode active material layer 5 b may contain a positive electrode active material other than MnO 2 , or may contain only MnO 2 as the positive electrode active material.

[0040] The positive electrode active material layer 5 b may contain other materials such as a conductive auxiliary agent and a binder.

[0041] The conductive auxiliary agent is used to reduce the resistance of the positive electrode 5. Examples of the conductive auxiliary agent include carbon materials, conductive polymer compounds, etc. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, graphite oxide, etc. Examples of the conductive polymer compound include polyaniline, polypyrrole, polythiophene, etc.

[0042] The binder is used to improve the binding property of the material constituting the positive electrode 5. As the binder, a polymer material such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, polyimide, etc. can be used.

[0043] As the negative electrode current collector 6a, a sheet or film made of a metal material such as stainless steel, nickel, copper, or an alloy thereof can be used. The sheet or film can be porous or non-porous. As the sheet or film, a metal foil, a metal mesh, etc. can be used. A carbon material such as carbon can be coated on the surface of the negative electrode current collector 6a as a conductive auxiliary material.

[0044] The negative electrode active material layer 6 b contains a negative electrode active material that absorbs lithium ions. Specifically, when the lithium secondary battery 100 is assembled, the negative electrode active material layer 6 b contains lithium ions. When the lithium secondary battery 100 is assembled, it is in a charged state.

[0045] The negative electrode active material is a material that can reversibly absorb and release lithium ions. The negative electrode active material, for example, includes at least one selected from a carbon material and a material that can form an alloy with lithium. As a carbon material, graphite can be cited. As a material that can form an alloy with lithium, silicon, silicon-containing oxides, tin, zinc alloys, bismuth, germanium, etc. can be cited. One selected from these negative electrode active materials can be used, and two or more can be used in combination.

[0046] The negative electrode active material layer 6b may contain at least one selected from graphite and silicon as the negative electrode active material. As the negative electrode active material, only graphite may be contained in the negative electrode active material layer 6b. Graphite is not easily degraded even when repeatedly charged and discharged at a deep depth, so it is recommended. Carbon materials other than graphite may also be used as negative electrode active materials. Silicon shows a larger capacity than graphite, and therefore is conducive to increasing the capacity of the lithium secondary battery 100.

[0047] In this embodiment, the lithium secondary battery 100 is in a charged state when the assembly is completed, and can be started from discharge. When graphite is used as the negative electrode active material, the negative electrode 6 can contain LiC6 when the assembly of the lithium secondary battery 100 is completed. When silicon is used as the negative electrode active material, the negative electrode 6 can contain Li 22 Si5.

[0048] The negative electrode active material layer 6b may contain a conductive additive, a binder, etc. As the conductive additive and the binder, the same materials as those used in the positive electrode active material layer 5b can be used in the negative electrode active material layer 6b.

[0049] The electrolyte is a non-aqueous electrolyte that is impregnated into the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte can fill the internal space of the container 1. Lithium ions can move between the positive electrode 5 and the negative electrode 6 through the action of the electrolyte.

[0050] The electrolyte contains a non-aqueous solvent and a lithium salt.

[0051] As the non-aqueous solvent, a mixed solvent of cyclic carbonate and chain carbonate is used. The mixed solvent of cyclic carbonate and chain carbonate has excellent withstand voltage. Therefore, by using a mixed solvent of cyclic carbonate and chain carbonate, MnO2 can be charged to a high charging voltage. In other words, MnO2 can be fully utilized to increase the capacity of the lithium secondary battery 100. In addition, since the negative electrode 6 contains a negative electrode active material that has absorbed lithium ions, the lithium secondary battery 100 also shows good cycle characteristics even when charging and discharging at a deep depth.

[0052] Cyclic carbonate is typically 5-membered ring cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate. Cyclic carbonate can contain at least one selected from ethylene carbonate and vinylene carbonate. By combining these cyclic carbonates with linear carbonate, it is possible to obtain an electrolyte having a high withstand voltage.

[0053] At least one hydrogen atom of cyclic carbonate can be replaced by halogen atom.That is to say, can be combined with halogen atom on contained carbon atom in cyclic carbonate.Cyclic carbonate with halogen atom shows higher withstand voltage, excellent stability.As cyclic carbonate with halogen atom, can enumerate fluoroethylene carbonate, chloroethylene carbonate etc.The number of contained halogen atom in cyclic carbonate can be 1, also can be a plurality of.

[0054] The cyclic carbonate is represented by, for example, the following formula (1) or formula (2). In formula (1), R 1 , R 2 , R 3 and R 4 In formula (2), R 5 and R 6 Independently of each other, they represent a hydrogen atom or a halogen atom. As shown in formula (1) or formula (2), the halogen atom may be bonded to the carbon atom at the 3-position or the carbon atom at the 4-position of the 5-membered cyclic carbonate. The halogen atom may be F or Cl.

[0055]

[0056] As the linear carbonate, at least one selected from ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate can be used. By combining these linear carbonates with cyclic carbonates, an electrolyte having a high withstand voltage can be obtained. Among them, ethyl methyl carbonate is recommended.

[0057] As lithium salts, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethylsulfonyl)imide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, lithium difluoro(oxalate)borate, etc. can be used. One selected from these lithium salts can be used, or two or more can be used in combination.

[0058] The diaphragm 7 has lithium ion conductivity. As long as lithium ions are allowed to pass through, the material of the diaphragm 7 is not particularly limited. The material of the diaphragm 7 can be at least one selected from a gel electrolyte, an ion exchange resin membrane, a semipermeable membrane and a porous membrane. If the diaphragm 7 is made of these materials, the safety of the lithium secondary battery 100 can be fully ensured. As a gel electrolyte, a gel electrolyte containing a fluororesin such as PVdF can be cited. As an ion exchange resin membrane, a cation exchange membrane, an anion exchange membrane, etc. can be cited. As a porous membrane, a porous membrane made of a polyolefin resin, a porous membrane containing a cellophane obtained by weaving glass fibers into a non-woven fabric, etc. can be cited.

[0059] The container 1 is a container made of metal such as aluminum or stainless steel, etc. The container 1 may have a cylindrical shape or a square cylindrical shape.

[0060] The electrode group 4 can be rolled into a cylindrical shape or an elliptical shape.

[0061] There is no particular limitation on the shape of the lithium secondary battery 100. The lithium secondary battery 100 may be in various shapes such as a cylindrical shape or a square cylindrical shape.

[0062] Next, a method for manufacturing the lithium secondary battery 100 will be described. Figure 2 1 is a process diagram showing a method for manufacturing the lithium secondary battery 100 .

[0063] In step S1, the electrode group 4 is prepared. Specifically, after the positive electrode 5 and the negative electrode 6 are prepared, the positive electrode 5, the negative electrode 6 and a pair of separators 7 are stacked and wound to form the electrode group 4 wound in a spiral shape. In this way, the electrode group 4 is obtained.

[0064] The positive electrode 5 can be prepared by coating a positive electrode mixture on one or both sides of a positive electrode current collector 5a, drying and rolling. The positive electrode 5 has a thickness of, for example, 30 μm to 200 μm, and is preferably flexible. The positive electrode mixture is obtained by kneading and uniformly dispersing materials such as a positive electrode active material, a binder, and a conductive aid using a dispersion medium.

[0065] There is no particular limitation on the method for coating the positive electrode mixture on the positive electrode collector 5a. A slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, a dip coater, etc. can be used to coat the positive electrode mixture in a slurry state on the positive electrode collector 5a. The coated positive electrode mixture can be dried naturally or by using a drying device.

[0066] After drying, the positive electrode 5 is rolled to make the positive electrode active material layer 5b have a predetermined thickness. Rolling can be performed multiple times using a roller press, or multiple times while changing the pressing pressure of the roller press. After rolling, the positive electrode lead 5c for extracting electricity is welded to the positive electrode collector 5a.

[0067] The negative electrode 6 can be made by applying a negative electrode mixture on one or both sides of a negative electrode collector 6a, drying and rolling. After rolling, a negative electrode lead 6c for extracting power is welded to the negative electrode collector 6a. The negative electrode 6 has a thickness of, for example, 30 μm to 210 μm, and is preferably flexible. The negative electrode mixture is obtained by kneading and uniformly dispersing materials such as a negative electrode active material, a binder, and a conductive aid using a dispersion medium.

[0068] As a method for making the negative electrode 6, a dry method can also be used instead of the above-mentioned wet method. As dry film-forming methods, evaporation method, sputtering method, CVD method (chemical vapor deposition method) and the like can be cited. These methods can all be implemented in a vacuum. From the viewpoint of effectively forming the negative electrode active material layer 6b, evaporation method is preferred. As an evaporation method, any one of electron beam evaporation and resistance heating evaporation can be used. In the case of evaporation of oxides, nitrides or oxynitrides, oxides and / or nitrides can be used as evaporation materials. While evaporating negative electrode active materials such as silicon and tin from an evaporation source, oxygen, nitrogen or ions or radicals containing elements constituting these gases can be introduced between the negative electrode collector 6a and the evaporation source, thereby performing reactive evaporation.

[0069] In step S2, Li metal foil is wound on the electrode group 4. When the negative electrode active material is graphite, the amount of Li in the Li metal foil is adjusted to satisfy the molar ratio of lithium: carbon = 1: 6, for example. When the negative electrode active material is silicon, the amount of Li in the Li metal foil is adjusted to satisfy the molar ratio of lithium: silicon = 22: 5, for example.

[0070] In step S3, the electrode group 4 is placed in the container 1. Specifically, the electrode group 4 and the Li metal foil are arranged inside the container 1 in such a manner that the negative electrode 6 of the electrode group 4 is electrically connected to the Li metal foil and the Li metal foil is located between the electrode group 4 and the inner surface of the container 1. According to such a structure, lithium ions can be supplied to the negative electrode 6 by injecting an electrolyte and can be absorbed.

[0071] Figure 3A 1 is a cross-sectional view showing an example of the positional relationship among the container 1, the Li metal foil 9, and the electrode group 4. Figure 3A In the example shown, the container 1 is a cylindrical container. By placing the electrode group 4 wound with the Li metal foil 9 in the container 1, the Li metal foil 9 can be arranged between the electrode group 4 and the inner surface of the container 1. In the radial direction of the container 1, the electrode group 4, the Li metal foil 9 and the container 1 are arranged in this order. The Li metal foil 9 is in contact with the container 1 and is electrically connected to the negative electrode 6 via the container 1. According to such a structure, lithium ions can be supplied to the negative electrode 6 by injecting an electrolyte and can be absorbed.

[0072] The lithium ion supply source is not limited to Figure 3A The Li metal foil 9 is shown. Figure 3B 1 is a perspective view showing an example of the positional relationship among the container 1, the Li metal sheet 19, and the electrode group 4. Figure 3B In the example shown, the supply source of lithium ions is at least one Li metal sheet 19. The container 1 is a square cylindrical container. The Li metal sheet 19 is arranged at at least one of the four corners of the container 1. Thus, the Li metal can be arranged between the electrode group 4 and the inner surface of the container 1. The Li metal sheet 19 is in contact with the container 1 and is electrically connected to the negative electrode 6 via the container 1. According to such a structure, lithium ions can be supplied to the negative electrode 6 and absorbed by injecting an electrolyte. When the square cylindrical container 1 is combined with the cylindrical electrode group 4, dead spaces are generated at the four corners. According to this embodiment, the dead spaces at the four corners of the square cylindrical container 1 can be effectively utilized. In addition, the four corners of the square cylindrical container 1 can also be formed into a curved surface.

[0073] When the Li metal sheet 19 is used as a lithium ion supply source, the above step S2 is not necessary. In step S3, the Li metal sheet 19 may be placed inside the container 1 after the electrode group 4 is placed in the container 1, or the Li metal sheet 19 and the electrode group 4 may be placed in the container 1 together. Alternatively, the Li metal sheet 19 may be placed in the container 1 first, and then the electrode group 4 may be placed in the container 1.

[0074] The Li metal sheet 19 may be disposed at each of the four corners of the container 1 .

[0075] according to Figure 3A In the example shown, the step of placing the electrode group 4 in the container 1 also serves as the step of placing the Li metal between the electrode group 4 and the inner surface of the container 1. Figure 3B In the example shown, the step of placing the electrode group 4 in the container 1 may also serve as the step of disposing the Li metal between the electrode group 4 and the inner surface of the container 1 , or may be a separate step.

[0076] In step S4, the electrolyte is injected into the container 1. Since the negative electrode 6 is electrically connected to the Li metal foil 9 or the Li metal sheet 19, when the electrolyte is injected, the Li metal foil 9 or the Li metal sheet 19 dissolves and supplies lithium ions to the electrolyte. The lithium ions move to the negative electrode 6 through the electrolyte and are absorbed by the negative electrode 6. According to such a structure, the lithium ions can be easily absorbed in the negative electrode 6.

[0077] In step S5, the container 1 is sealed.

[0078] After the above processes, we get Figure 1 A lithium secondary battery 100 is shown.

[0079] After the assembly is completed, the electrode group 4 can be discharged and charged. In one example, the charge termination voltage during charging is 4.2 V or more. The electrolyte used in this embodiment has excellent withstand voltage, so the lithium secondary battery 100 can be charged to a termination voltage of 4.2 V or more. According to this embodiment, the capacity density of MnO2 can be fully utilized.

[0080] Even if Li metal is not completely absorbed by the negative electrode 6 after the electrolyte is injected into the container 1, the Li metal dissolves in the electrolyte by discharging the lithium secondary battery 100 to supply lithium ions to the positive electrode 5. Then, when the lithium secondary battery 100 is charged, the lithium ions are absorbed by the active material such as graphite in the negative electrode 6.

[0081] (Other embodiments)

[0082] (Note)

[0083] Based on the description of the above embodiments, the following technical solutions are disclosed.

[0084] (Technical Solution 1)

[0085] A lithium secondary battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises MnO2, the negative electrode comprises a negative electrode active material that absorbs lithium ions, and the electrolyte is impregnated in the positive electrode and the negative electrode and comprises a mixed solvent of a cyclic carbonate and a chain carbonate.

[0086] According to such a structure, MnO2 can be charged to a high charging voltage. In other words, MnO2 can be fully utilized to increase the capacity of the lithium secondary battery. In addition, since the negative electrode contains a negative electrode active material that absorbs lithium ions, the lithium secondary battery shows good cycle characteristics even when charging and discharging at a deep depth.

[0087] (Technical Solution 2)

[0088] According to the lithium secondary battery described in technical solution 1, the negative electrode active material includes at least one selected from graphite and silicon. Graphite is not easily degraded even if it is repeatedly charged and discharged at a deep depth, so it is recommended. Silicon shows a larger capacity than graphite, so it is conducive to increasing the capacity of the lithium secondary battery.

[0089] (Technical Solution 3)

[0090] According to the lithium secondary battery of claim 1 or 2, the cyclic carbonate comprises at least one selected from ethylene carbonate and vinylene carbonate. By combining these cyclic carbonates with chain carbonates, an electrolyte having a high withstand voltage can be obtained.

[0091] (Technical Solution 4)

[0092] According to the lithium secondary battery of claim 1 or 2, a halogen atom is bonded to a carbon atom contained in the cyclic carbonate. The cyclic carbonate having a halogen atom exhibits a higher withstand voltage and is excellent in stability.

[0093] (Technical Solution 5)

[0094] According to any one of claims 1 to 4, the chain carbonate comprises ethyl methyl carbonate. By combining ethyl methyl carbonate and cyclic carbonate, an electrolyte having a high withstand voltage can be obtained.

[0095] (Technical Solution 6)

[0096] According to any one of technical solutions 1 to 5, the MnO2 contains electrolytic manganese dioxide. Electrolytic manganese dioxide is a known material for primary batteries and is inexpensive.

[0097] (Technical Solution 7)

[0098] A method for manufacturing a lithium secondary battery comprises: electrically connecting Li metal to the negative electrode of an electrode group having a positive electrode containing MnO2 and a negative electrode containing a negative electrode active material, and arranging the electrode group and the Li metal inside the container in such a way that the Li metal is located between the electrode group and the inner surface of the container; and injecting an electrolyte solution containing a mixed solvent of a cyclic carbonate and a chain carbonate into the container.

[0099] According to such a technical configuration, lithium ions can be supplied to the negative electrode and stored by injecting an electrolyte solution.

[0100] (Technical Solution 8)

[0101] According to the method for manufacturing a lithium secondary battery according to technical solution 7, the container is a cylindrical container, and the electrode group wound with the Li metal is placed in the container, and the electrode group and the Li metal are arranged inside the container. According to such a technical structure, lithium ions can be supplied to the negative electrode and absorbed by injecting an electrolyte.

[0102] (Technical Solution 9)

[0103] According to the method for manufacturing a lithium secondary battery described in technical solution 7, the container is a square cylindrical container, and the Li metal is arranged at at least one of the four corners of the container. According to such a technical structure, by injecting an electrolyte, lithium ions can be supplied to the negative electrode and absorbed. In addition, the dead space at the four corners of the square cylindrical container can be effectively utilized.

[0104] (Technical Solution 10)

[0105] According to the method for manufacturing a lithium secondary battery according to any one of claims 7 to 9, the Li metal is electrically connected to the negative electrode via the container. According to such a technical configuration, lithium ions can be easily absorbed into the negative electrode 6 .

[0106] (Technical Solution 11)

[0107] The method for manufacturing a lithium secondary battery according to any one of technical solutions 7 to 10 further includes discharging and charging the electrode group, wherein the charge termination voltage during charging is 4.2 V or more. According to such a technical configuration, the capacity density of MnO2 can be fully utilized.

[0108] Example

[0109] (Example 1)

[0110] A binder, a conductive aid, γ-β-MnO2 powder and a solvent are mixed to prepare a positive electrode mixture. The positive electrode mixture is applied to an Al current collector to form a coating. The coating is dried and rolled to obtain a positive electrode. PVdF is used as a binder. Acetylene black is used as a conductive aid. N-methylpyrrolidone is used as a solvent. The ratio of the binder, the conductive aid and the γ-β-MnO2 powder is 10:5:85 by mass.

[0111] A binder, graphite powder and solvent are mixed to prepare a negative electrode mixture, the negative electrode mixture is coated on a Cu current collector to form a coating film, the coating film is dried and rolled to obtain a negative electrode.

[0112] The positive electrode lead and the negative electrode lead were welded to the positive electrode and the negative electrode, respectively. Then, the positive electrode and the negative electrode were used to make an electrode group having a wound structure. A microporous film made of polyolefin was used as a separator.

[0113] Next, a Li metal foil was wound around the electrode group. The amount of Li in the Li metal foil was adjusted so as to satisfy a molar ratio of lithium:carbon=1:6.

[0114] Next, the electrode group is placed in a cylindrical container in such a way that the Li metal foil is connected to the negative electrode through the container. Then, an electrolyte is injected into the container. The electrolyte is prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1. A sealing plate is installed on the container to obtain a Figure 1 A lithium secondary battery with the structure shown.

[0115] (Example 2)

[0116] The lithium secondary battery of Example 2 was prepared in the same manner as in Example 1 except that a mixed solvent containing vinylene carbonate (VC) and methyl ethyl carbonate (MEC) in a volume ratio of 1:1 was used to prepare the electrolyte.

[0117] (Example 3)

[0118] A lithium secondary battery of Example 3 was prepared in the same manner as in Example 1, except that a mixed solvent containing fluoroethylene carbonate (FEC) and methyl ethyl carbonate (MEC) in a volume ratio of 1:1 was used to prepare the electrolyte.

[0119] (Comparative Example 1)

[0120] A lithium secondary battery of Comparative Example 1 was prepared in the same manner as in Example 1 except that a mixed solvent containing propylene carbonate (PC) and dimethoxyethane (DME) in a volume ratio of 1:1 was used to prepare the electrolyte.

[0121] (Charge and discharge test 1)

[0122] The lithium secondary batteries of Example 1, Example 2 and Comparative Example 1 were subjected to charge and discharge tests. First, the lithium secondary batteries were discharged, and then the initial charge capacity and the initial discharge capacity were measured. In Example 1 and Example 2, the charge and discharge current was 0.025C, the charge end voltage was 4.2V, and the discharge end voltage was 2.0V. In Comparative Example 1, the charge and discharge current was 0.025C, the charge end voltage was 3.6V, and the discharge end voltage was 2.0V.

[0123] Figure 4 1 is a graph showing the initial charge and discharge curves of the lithium secondary batteries of Example 1 and Comparative Example 1. The horizontal axis represents the capacity density (mAh / g). The vertical axis represents the voltage (V). Figure 4 As shown, the lithium secondary battery of Example 1 showed a capacity density of about 270 mAh / g. In Example 1, no significant decomposition of the electrolyte was found until the charging voltage of 4.2 V. In contrast, the capacity density of the lithium secondary battery of Comparative Example 1 was about 150 mAh / g. In Comparative Example 1, since the electrolyte was significantly decomposed, it was impossible to charge at a voltage higher than 3.6 V.

[0124] Figure 5 It is a graph showing the initial charge and discharge curves of the lithium secondary batteries of Examples 1 and 2. Even when the cyclic carbonate in the mixed solvent is changed from ethylene carbonate (Example 1) to vinylene carbonate (Example 2), charging at a voltage of 4.2 V can be achieved, and a high capacity density of 250 mAh / g or more can be achieved.

[0125] (Charge and discharge cycle test)

[0126] The charging and discharging of the lithium secondary battery of Example 1 was repeated 10 times. The charging and discharging conditions were as described in the charging and discharging test column. The results are shown in Figure 6 .

[0127] Figure 6 1 is a graph showing the results of the charge and discharge cycle test of the lithium secondary battery of Example 1. The horizontal axis represents the number of cycles as the number of charge and discharge times. The vertical axis represents the discharge capacity density (mAh / g). Figure 6 As shown, the lithium secondary battery of Example 1 maintained a discharge capacity density of 200 mAh / g or more even when charge and discharge were repeated 10 times at a deep charge depth.

[0128] (Charge and discharge test 2)

[0129] The lithium secondary batteries of Example 1 and Example 3 were subjected to charge and discharge tests. First, the lithium secondary batteries were subjected to discharge treatment, and then the initial charge and discharge treatment was performed. Then, the second charge and discharge treatment was performed to measure the charge capacity and discharge capacity. In the charge and discharge test 2, the charge and discharge current was 0.015C, the charge end voltage was 4.2V, and the discharge end voltage was 2.0V.

[0130] Fig. 7A This is a graph showing the charge and discharge curve of the lithium secondary battery of Example 1 in the charge and discharge test 2. Figure 7B Graph showing the charge and discharge curve of the lithium secondary battery of Example 3 in the charge and discharge test 2. Fig. 7A and Figure 7B As shown, in charge and discharge test 2, the lithium secondary battery of Example 1 exhibits a capacity density of about 180 mAh / g. The lithium secondary battery of Example 3 exhibits a capacity density of about 160 mAh / g. The current value in charge and discharge test 2 is about 0.6 times the current value in charge and discharge test 1. Even under such conditions, the lithium secondary batteries of Examples 1 and 3 exhibit a capacity density greater than the capacity density of the lithium secondary battery of Comparative Example 1 in charge and discharge test 1 (about 150 mAh / g). In addition, the lithium secondary battery of Example 3 has a capacity density comparable to that of the lithium secondary battery of Example 1.

[0131] Industrial Availability

[0132] The technology disclosed in the present disclosure can be used for lithium secondary batteries.

Claims

1. A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, The positive electrode comprises MnO2, The negative electrode includes a negative electrode active material that absorbs lithium ions. The electrolyte solution is impregnated into the positive electrode and the negative electrode, and contains a mixed solvent of cyclic carbonate and chain carbonate.

2. The lithium secondary battery according to claim 1, The negative electrode active material includes at least one selected from graphite and silicon.

3. The lithium secondary battery according to claim 1, The cyclic carbonate includes at least one selected from ethylene carbonate and vinylene carbonate.

4. The lithium secondary battery according to claim 1, A halogen atom is bonded to a carbon atom contained in the cyclic carbonate.

5. The lithium secondary battery according to claim 1, The chain carbonate includes ethyl methyl carbonate.

6. The lithium secondary battery according to claim 1, The MnO2 comprises electrolytic manganese dioxide.

7. A method for manufacturing a lithium secondary battery, comprising: The electrode group having a positive electrode containing MnO2 and a negative electrode containing a negative electrode active material is electrically connected to the negative electrode of the electrode group, and the electrode group and the Li metal are arranged inside the container in such a way that the Li metal is located between the electrode group and the inner surface of the container; as well as An electrolyte solution containing a mixed solvent of a cyclic carbonate and a chain carbonate is injected into the container.

8. The method for manufacturing a lithium secondary battery according to claim 7, The container is a cylindrical container, The electrode group in which the Li metal is wound is placed in the container, so that the electrode group and the Li metal are arranged inside the container.

9. The method for manufacturing a lithium secondary battery according to claim 7, The container is a square cylindrical container. The Li metal is disposed at at least one of the four corners of the container.

10. The method for manufacturing a lithium secondary battery according to claim 7, The Li metal is electrically connected to the negative electrode via the container.

11. The method for manufacturing a lithium secondary battery according to claim 7, Also includes discharging and charging the electrode group, The charge termination voltage during charging is 4.2V or above.

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