JP2014531720A - Lithium ion secondary battery with suppressed internal short circuit - Google Patents

Abstract

The present invention provides a lithium ion secondary battery characterized in that a compound containing one or more intramolecular thiol (-SH) groups is provided inside the unit cell of the battery. In the present invention, by using a thiol group-containing compound that is excellent in reactivity with copper or copper ions, the dendrite produced by reduction on the negative electrode surface of the copper ions existing inside the battery or generated during the operation of the battery can be obtained. It is possible to prevent the formation and the internal short phenomenon between both electrodes due to such dendrite. [Selection figure] None

Description

  The present invention relates to a lithium ion secondary battery in which short circuit inside a battery caused by dendrite formation in the battery is suppressed, and the manufacturing quality and safety of the battery are ensured.

  Unlike primary batteries that cannot be recharged, rechargeable batteries that can be recharged and discharged are actively researched as developments in advanced fields such as digital cameras, mobile phones, laptop computers, and hybrid vehicles. .

  Examples of the secondary battery include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among these, the lithium secondary battery is used as a power source for portable electronic devices having an operating voltage of 3.6 V or higher, or is used in a high-output hybrid vehicle by connecting several in series, but a nickel-cadmium battery or Compared to nickel-metal hydride batteries, the operating voltage is three times higher and the energy density per unit weight tends to be excellent and tend to be used rapidly.

In addition to manufacturing quality of such a lithium secondary battery, in order to use the battery safely in the long term, copper ions (Cu ²⁺ ) generated by oxidizing foreign substances in the battery are negative electrode surfaces. It is necessary to form dendrite by reduction in the above and suppress the internal short circuit of the battery caused by such dendrite. Further, from the viewpoint of cell production quality, the dendrite generated by reduction of such metal ions during charge and discharge in the cell production process increases the defective rate during cell production.

  In addition, if the dendrite generated during the manufacturing process electrically connects the positive electrode and the negative electrode to each other by external pressure or vibration, it may cause problems in the safety and stability of the cell even during use. The reduction of metal ions that occurs further during use of the cell also induces the formation of dendrites, greatly impairing the safety and stability of the cell. Therefore, in the lithium secondary battery as described above, it is necessary to suppress the formation of dendrite in which the positive electrode and the negative electrode can be electrically connected inside the battery.

  In the present invention, the present invention has the following advantages: (i) effectively capping copper ions present inside the battery or generated during the operation of the battery, or (ii) reactivity with copper ions. The present invention has been completed by recognizing that the formation of dendrite by reduction of copper and the internal short-circuit phenomenon of the battery due to the formed dendrite can be remarkably suppressed if an excellent material is provided.

  Therefore, the present invention provides a lithium ion secondary battery in which the internal short circuit phenomenon of the battery is suppressed and the manufacturing quality of the cell is improved by providing a substance having excellent reactivity with copper ions inside the unit cell. There is a purpose to provide.

  The present invention provides a lithium ion secondary battery characterized in that a compound containing one or more intramolecular thiol (-SH) groups is provided inside a unit cell of the battery.

  According to one embodiment of the present invention, the compound containing at least one intramolecular thiol (-SH) group is selected from the group consisting of components constituting a battery, such as an electrode, a separation membrane, and an electrolyte. In addition, it is preferably contained in at least one component.

  The electrode may include a compound containing one or more intramolecular thiol (—SH) groups as an electrode mixture layer component or an electrode coating component.

  In addition, the electrolytic solution includes a lithium salt, an electrolytic solution solvent, and a compound including one or more intramolecular thiol (-SH) groups, and the compound including one or more intramolecular thiol groups includes 100 parts by weight of the electrolytic solution. It is preferably contained in the range of 0.01 to 10 parts by weight.

  The separation membrane may contain a compound containing one or more intramolecular thiol (-SH) groups as a constituent component or a coating component of the separation membrane.

  In the present invention, by using a thiol group-containing compound excellent in reactivity with copper ions inside the unit cell where the battery reaction occurs, the formation of dendrite and the resulting internal short circuit of the battery can be prevented, and the battery safety can be improved. Improvements can be realized.

  Hereinafter, the present invention will be described in detail.

The lithium ion secondary battery can include a plurality of metal components as foreign substances, and among them, a copper component or a copper-containing alloy component can be included. Such foreign substances of copper may be oxidized during operation of the battery to become copper ions (Cu ²⁺ ), or the generated copper ions may be reduced on the negative electrode surface and deposited on copper components. There is also.

  On the other hand, since copper (Cu) does not generate an oxide that is self-passivated, it tends to generate dendritic growth that can be regrown. Thus, the needle-like copper deposited on the negative electrode surface penetrates the separation membrane and causes an internal short-circuit phenomenon that electrically connects the positive electrode and the negative electrode, resulting in a decrease in battery safety. At the same time, the defect rate is increased in terms of cell manufacturing quality.

  Therefore, in the present invention, by providing a substance having high reactivity with copper or copper ions inside the unit cell of the lithium ion secondary battery, the formation of dendrite and the internal short circuit phenomenon of the battery due to this will be fundamentally prevented. It is what.

  In accordance with the present invention, the compound provided inside the lithium ion secondary battery, preferably inside the unit cell, may be a compound containing one or more intramolecular thiol (—SH) groups.

  The compound containing a thiol (—SH) group in the molecule has high selectivity for copper ions that are present inside the battery or generated during the operation of the battery. Therefore, under normal conditions, it remains in its original form and does not affect the operation of the battery at all. However, when copper or copper ions are present, they first react spontaneously before they are reduced on the negative electrode surface. It plays the role of capturing or capturing.

  Examples of the compound containing a thiol (—SH) group in the molecule include one or two aliphatic thiols selected from the group consisting of methanethiol and ethanethiol; thiophenol, 4-fluorothiophenol, 1 or 2 aromatic thiols selected from the group consisting of 2-chlorothiophenol, 4-t-butylthiophenol and 4-t-butyl-1,2-benzenethiol; 2- (butylamino) ethane Thiol (2- (Butylamino) ethanethiol); 3- (Methylthio) propylamine (3- (methylthio) propylamine); and [2- (Diisopropylamino) ethyl]-(2-mercaptoethyl) sulfite ([2- ( diisopropylamino) ethyl]-(2-mercaptoethyl) sulf ide) may be a single substance or a mixture of two or more selected from the group consisting of ide).

  The content of the compound containing one or more intramolecular thiol (-SH) groups is determined depending on the type of components of the lithium secondary battery to be applied, such as an electrode active material, an electrode, a separation membrane, an electrolytic solution, a battery case, and It can be adjusted as appropriate according to the other empty space inside the battery, and is not particularly limited.

  The above-described thiol (—SH) group-containing compound can be applied regardless of this application, the position of introduction, and the like as long as it is provided inside the unit cell of the battery. As an example, a component of a lithium ion secondary battery, for example, an electrode active material, an electrode, a separation membrane, an electrolytic solution, a device case, or a component other than an empty space inside the device, or a coating thereof It can also be used as a component.

  A lithium ion secondary battery provided with a compound containing one or more thiol groups in the molecule inside the unit cell of the battery can have roughly five embodiments. However, it is not particularly limited to this.

[Electrode containing a compound containing one or more thiol groups in the molecule]
1) A first embodiment of a lithium ion secondary battery containing a thiol (—SH) group-containing compound according to the present invention is used as a component of an electrode mixture layer, specifically, a coating component of an electrode active material. That is.

  A method for producing an electrode active material coated with a thiol (—SH) group-containing compound is not particularly limited, but when this preferred embodiment is exemplified, (a) a thiol (—SH) group-containing compound is added to a binder solution or a solvent. Dispersing and producing a coating solution containing a thiol (-SH) group-containing compound; (b) coating by adding and agitating electrode active material particles to the coating solution produced in the step (a); and (c) The method may include a step of heat-treating the electrode active material coated in the step (b).

As the above-described positive electrode active material that can be coated with a compound containing a thiol (—SH) group in the molecule, a normal positive electrode active material that can be used for a positive electrode of a conventional lithium ion secondary battery can be used. Non-limiting examples of positive electrode active materials that can be used include lithium transition metal composite oxides such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) (for example, LiMn ₂ 0 Lithium manganese composite oxide such as ₄ , lithium nickel oxide such as LiNiO ₂ , lithium cobalt oxide such as LiCoO ₂ and manganese, nickel, and a part of these oxides substituted with other transition metals, Or vanadium oxide containing lithium) or a chalcogen compound (eg, manganese dioxide, titanium disulfide, molybdenum disulfide). Preferably, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1 ), LiNi _1-Y Co _{Y 2} O ₂ , LiCo _1-Y Mn _{Y 2} O ₂ , LiNi _1-Y Mn _{Y 2} O ₂ (where 0 ≦ Y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2,0 <b <2,0 <c <2, a + b + c = 2), LiMn 2-Z Ni Z O 4, LiMn 2-Z Co Z O 4 ( where, 0 <Z <2 ), LiCoPO ₄ , LiFePO ₄ or a mixture thereof.

  As the negative electrode active material that can be coated with a thiol (—SH) group-containing compound in the molecule, a normal negative electrode active material that can be used for a negative electrode of a conventional lithium ion secondary battery can be used. Non-limiting examples of negative electrode active materials that can be used include lithium metal and lithium alloys, carbon, petroleum coke, activated carbon, graphite, silicon-based, tin-based or other carbon There are lithium adsorbents such as active materials and active materials used for negative electrodes. Non-limiting examples of positive current collectors include foils made from aluminum, nickel or combinations thereof, and non-limiting examples of negative current collectors include copper, gold, nickel or There are foils made of copper alloys or combinations thereof.

  At this time, the coating process can use a general coating method usually used in the art, for example, solvent evaporation, co-precipitation method, precipitation method, sol-gel method, filter method after adsorption, Sputtering, CVD, etc.

  2) According to the second embodiment of the lithium ion secondary battery containing a thiol (—SH) group-containing compound based on the present invention, the thiol (—SH) group-containing compound is used as a component of the electrode mixture layer, specifically Use as a component of the electrode and / or 3) A third embodiment is to use it as a coating component of an already manufactured electrode.

  A method for producing an electrode containing a thiol (-SH) group-containing compound as a constituent component of the electrode is not particularly limited. When this preferred embodiment is exemplified, (a) a thiol (-SH) group-containing compound is used as an electrode material, For example, an electrode slurry is prepared by mixing with an electrode active material, if necessary, a conductive agent, a binder, etc., and then coated on a current collector or coated on the surface of an already manufactured electrode; and ( b) may include drying the electrode.

  Hereinafter, an example of a method for dispersing the thiol (—SH) group-containing compound in the electrode will be described in detail.

  First, i) a binder (for example, PVDF (polyvinylidene fluoride)) is charged into a solvent or a dispersion medium (for example, NMP (N-methyl pyrrolidone)) to produce a binder solution.

  As the solvent or dispersion medium used for producing the binder solution, all common solvents used in the art can be used. For example, N-methylpyrrolidone, acetone, dimethylacetamide Or an organic solvent such as dimethylformaldehyde, an inorganic solvent such as water, or a mixture thereof. The amount of the solvent used is sufficient if it can dissolve and disperse the active material, the conductive agent, the electrode binder, and the adhesive additive in consideration of the coating thickness of the electrode slurry and the production yield. It is. The solvent and the like are removed by drying after coating the electrode slurry on the current collector.

  ii) An electrode active material and a thiol (-SH) group-containing compound are added to the produced binder solution, mixed, and dispersed completely. Then, this is applied onto a current collector and dried to obtain the electrode. Manufacturing is complete.

  As described above, the electrode active material and the conductive agent are added to the binder solution containing the thiol (—SH) group-containing compound, and the slurry for the electrode is produced with a mixer. The drying process of the electrode can also be performed by a common method well known in the art, for example, hot air drying.

  As the binder, an ordinary binder can be used, and non-limiting examples thereof include PVDF (polyvinylidene fluoride), SBR (styrene butadiene rubber), Teflon (registered trademark), or a mixture thereof.

  The conductive agent is not particularly limited as long as it can improve conductivity, and non-limiting examples include acetylene black or graphite.

  A method for producing an electrode using the thiol (-SH) group-containing compound as a coating component of the electrode can also be produced by a conventional method well known in the art. For example, a binder solution or a solvent After a thiol (-SH) group-containing compound is dispersed in a thiol (-SH) group-containing compound-containing dispersion, the surface of the electrode already manufactured may be coated and dried.

  The content of the compound containing one or more thiol (—SH) groups in the molecule in the present invention may be in the range of 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode mixture, but is not particularly limited thereto.

  In the electrode manufactured according to the two embodiments, a compound coating layer including one or more thiol (-SH) groups is formed on a part or all of the surface. As described above, the electrode on which the thiol (-SH) group-containing compound coating layer is formed selectively captures or reacts with the copper ions before the copper ions are reduced on the negative electrode surface. . Therefore, formation of copper dendrite by reduction on the negative electrode surface can be prevented.

[Electrolytic solution containing a compound containing one or more thiol groups in the molecule]
4) According to the fourth embodiment of the lithium ion secondary battery containing a thiol (—SH) group-containing compound based on the present invention, the thiol (—SH) group-containing compound is introduced into an ordinary battery electrolyte. It is.

  The battery electrolyte to which the thiol (-SH) group-containing compound is added contains a common electrolyte component known in the art, such as a lithium salt and a non-aqueous organic solvent.

The lithium salt is a material suitable for dissolving in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO _2. , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, etc. Can be used.

  Non-limiting examples of non-aqueous organic solvents that can be used include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, Tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, Sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, Non-protonic organic solvents such as ethyl propionate.

  For non-aqueous electrolytes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide for the purpose of improving charge / discharge characteristics and flame retardancy. Nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like may be added. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart incombustibility, and a carbon dioxide gas may be further included to improve high-temperature storage characteristics. it can.

  At this time, the content of the compound containing one or more intramolecular thiol groups can be appropriately adjusted in consideration of the safety of the battery and the manufacturing quality of the cell. To 10 parts by weight.

[Separation membrane containing a compound containing one or more thiol groups in the molecule]
5) According to the present invention, the fifth embodiment of the lithium ion secondary battery containing a thiol (—SH) group-containing compound is used as one component of a battery separation membrane, or a normal battery separation membrane It is used as a coating component.

  As an example of this, as is well known in the art, a polyolefin-based separation membrane substrate is impregnated with a coating solution containing a thiol (-SH) group-containing compound, or is coated according to a normal coating method and then dried. Can be completed.

  At this time, the separation membrane into which the thiol (-SH) group-containing compound can be introduced is not particularly limited as long as it is a porous substance that plays a role of blocking the internal short circuit between both electrodes and impregnating the electrolytic solution. The pore size of the separation membrane is generally from 0.01 to 10 μm and the thickness can generally be in the range from 5 to 300 μm. Examples of such a separation membrane include olefin-based polymers such as chemically resistant and hydrophobic polypropylene; composite porous separation membranes in which an inorganic material is added to a porous separation membrane substrate; glass fibers, polyethylene, or the like. A sheet or a non-woven fabric is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as a separation membrane.

  In addition, the same effect can be achieved by introducing the above-described thiol (—SH) group-containing compound into an empty space inside a lithium ion secondary battery such as a mandrel, center pin, or PTC.

  On the other hand, in the present invention, only a compound containing a thiol group is specifically exemplified, but any other substance having high reactivity with copper ions can be used regardless of this component, content, form, etc. It belongs to the category of the present invention.

  The lithium ion secondary battery according to the present invention can be manufactured based on a conventional method well known in the art, and in one embodiment, the lithium ion secondary battery is assembled with a separation membrane interposed between the positive electrode and the negative electrode. Then, it can manufacture by inject | pouring electrolyte solution. At this time, at least one of the electrode, the electrolytic solution, the separation membrane, and the case may be one into which the thiol (-SH) group-containing compound described above is introduced. At this time, at least one of the electrode active material, the electrode, the electrolytic solution, the separation membrane, the core, the center pin, and the inner space of the element case is introduced with the thiol (-SH) group-containing compound described above. Can be.

  The foregoing detailed description of the invention has been described with reference to specific embodiments. However, various modifications can be made without departing from the scope of the present invention. The technical idea of the present invention should not be limited to the described embodiments of the present invention, but should be determined not only by the claims but also by the equivalents of the claims. .

[Example]
Example 1
A slurry was prepared by adding 90% by weight of LiCoO ₂ as a positive electrode active material; 6% by weight of Denka Black as a conductive agent; and 4% by weight of PVDF as a binder to NMP. This was coated on an aluminum (Al) foil as a positive electrode current collector, rolled and dried to produce a positive electrode.

  A slurry was prepared by adding 90% by weight of graphite as a negative electrode active material; 6% by weight of Denka black as a conductive agent; and 4% by weight of PVDF as a binder to NMP. This was coated on a copper (Cu) foil as a negative electrode current collector, rolled, and dried to produce a negative electrode.

An electrode assembly was manufactured by interposing a porous polyethylene separation membrane between the positive electrode and the negative electrode manufactured as described above. After the electrode assembly is put in a case and electrode leads are connected, a 1: 1 ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) in which 1 M LiPF ₆ is dissolved is added to methanethiol (Methanthiol) 1. After injecting an electrolyte solution with a% added, it was sealed to produce a lithium ion secondary battery.

(Example 2)
A slurry was prepared by adding 90% by weight of LiCoO ₂ as a positive electrode active material; 6% by weight of Denka Black as a conductive agent; and 4% by weight of PVDF as a binder to NMP. This was coated on an aluminum (Al) foil as a positive electrode current collector, rolled and dried to produce a positive electrode.

  A slurry was prepared by adding 90% by weight of graphite as a negative electrode active material; 6% by weight of Denka black as a conductive agent; and 4% by weight of PVDF as a binder to NMP. This was coated on a copper (Cu) foil as a negative electrode current collector, rolled and dried to produce a negative electrode.

A separation membrane was prepared by dispersing and coating 99% by weight of Al ₂ O ₃ and 1% by weight of methanethiol on the surface of a porous polyethylene separation membrane coated with an inorganic substance.

An electrode assembly was manufactured with a separation membrane coated between the positive electrode and the negative electrode manufactured as described above. After the electrode assembly is put in a case and electrode leads are connected, a 1: 1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) electrolyte in which 1M LiPF ₆ is dissolved is injected, and then sealed. A lithium ion secondary battery was manufactured.

(Comparative Example 1)
A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that methanethiol was not added to the electrolyte.

(Comparative Example 2)
A lithium ion secondary battery was manufactured in the same manner as in Example 2 except that methanethiol was not added to the coated separation membrane.

[Experimental Example 1]
The voltage drop for 2 weeks was measured for 10,000 cells of the lithium ion secondary battery produced by the methods of Example 1 and Comparative Example 1, respectively, and the results are shown in Table 1 below.

[Experiment 2]
Table 1 below shows the voltage drop measured for two weeks with respect to 1,000 cells of the lithium ion secondary battery produced by the methods of Example 2 and Comparative Example 2, respectively.

Claims (11)

  A lithium ion secondary battery, wherein a compound containing one or more intramolecular thiol (-SH) groups is provided inside a unit cell of the battery.   The compound containing one or more intramolecular thiol (-SH) groups is one or more aliphatic thiols selected from the group consisting of methanethiol and ethanethiol; thiophenol, 4-fluorothiophenol, 2-chloro One or more aromatic thiols selected from the group consisting of thiophenol, 4-t-butylthiophenol and 4-t-butyl-1,2-benzenethiol; 2- (butylamino) ethanethiol; A single substance or a mixture of two or more selected from the group consisting of (methylthio) propylamine; and [2- (diisopropylamino) ethyl]-(2-mercaptoethyl) sulfite. 2. The lithium ion secondary battery according to 1.   3. The lithium ion secondary battery according to claim 1, wherein the compound containing one or more intramolecular thiol (—SH) groups is present in at least one of the components constituting the battery. 4.   The compound containing one or more intramolecular thiol (-SH) groups is contained in at least one battery component selected from the group consisting of an electrode, a separation membrane, and an electrolytic solution. The lithium ion secondary battery as described.   5. The lithium ion secondary battery according to claim 4, wherein the electrode includes a compound containing one or more intramolecular thiol (—SH) groups as an electrode mixture layer component or an electrode coating component.   The lithium ion secondary according to claim 5, wherein the compound containing one or more intramolecular thiol (-SH) groups is contained in an amount of 0.01 to 10 parts by weight relative to 100 parts by weight of the electrode mixture layer. battery.   The compound containing one or more intramolecular thiol (-SH) groups reacts with copper ions generated during operation of the battery to prevent dendrite formation due to reduction of copper on the negative electrode surface. The lithium ion secondary battery according to any one of claims 1 to 6.   The electrolytic solution includes a lithium salt, an electrolytic solution solvent, and a compound including one or more intramolecular thiol (-SH) groups, and the compound including one or more intramolecular thiol groups is compared with 100 parts by weight of the electrolytic solution. The lithium ion secondary battery according to claim 4, wherein the lithium ion secondary battery is contained in an amount of 0.01 to 10 parts by weight.   The lithium ion according to any one of claims 4 to 6, wherein the separation membrane contains a compound containing one or more intramolecular thiol (-SH) groups as a constituent component or a coating component of the separation membrane. Secondary battery.   A battery module comprising the lithium ion secondary battery according to any one of claims 1 to 9 as a unit battery.   A battery pack comprising the lithium ion secondary battery according to any one of claims 1 to 9 as a unit battery.