KR101001324B1 - Electrolyte with Improved Wetting Properties and Lithium Secondary Battery Having the Same - Google Patents

Abstract

The present invention provides an electrolyte solution in which a material in which a perfluorinated sulfonamide substituent is bonded to one or both ends of a block copolymerization structure of polyethylene oxide (PEO) and polypropylene oxide (PPO) is included to improve the wetting property on the negative electrode. to provide.

Electrolyte solution of the present invention is unlikely to immerse the negative electrode in the electrolyte for a long time in the manufacturing process of the battery due to the property that the hydrophilic electrolyte does not easily penetrate into the hydrophobic negative electrode to ensure the wettability (wetting properties), it does not undergo a long immersion process There is a very economical effect, such as wettability is improved without saving the manufacturing time.

Description

Electrolyte with improved wettability and lithium secondary battery comprising same {Electrolyte with Improved Wetting Properties and Lithium Secondary Battery Having the Same}

1 is a graph showing the experimental results of the life characteristics of the battery of Example 1 and the batteries of Comparative Examples 1 and 2 according to the present invention.

The present invention relates to an electrolyte with improved wettability and a lithium secondary battery including the same, and more particularly, due to a property that hydrophilic electrolyte does not easily penetrate into a hydrophobic anode, the anode is immersed in the electrolyte for a long time in a conventional battery manufacturing process. Unlike securing wettability, the present invention relates to an electrolyte having a very economical effect such as improved wettability without saving a long immersion step and saving manufacturing time, and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing, and lithium secondary batteries having high energy density and voltage are commercially used in such secondary batteries.

The lithium secondary battery is manufactured by using a metal oxide such as LiCoO ₂ as a cathode active material and a carbon material as an anode active material, a polyolefin-based porous separator between the anode and the cathode, and a non-aqueous electrolyte containing lithium salt such as LiPF ₆ . Done. During charging, lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode, and during discharge, lithium ions of the negative electrode carbon layer are released and inserted into the positive electrode active material, wherein the non-aqueous electrolyte solution is lithium ions between the negative electrode and the positive electrode. It acts as a medium for moving the. Such a lithium secondary battery should basically be stable in the operating voltage range of the battery and have a performance capable of transferring ions at a sufficiently high speed.

The non-aqueous electrolyte is introduced into the battery at the end of the lithium secondary battery manufacturing. At this time, the electrode needs to be wetted quickly and completely by the electrolyte to shorten the time required for manufacturing the battery and to optimize battery performance.

As a non-aqueous electrolyte of a lithium secondary battery, an aprotic organic solvent, such as ethylene carbonate, diethyl carbonate, and 2-methyl tetrahydrofuran, is mainly used. These electrolytes are polar solvents that are polar enough to effectively dissolve and dissociate electrolyte salts, and are aprotic solvents without active hydrogen, and are often high in viscosity and surface tension due to extensive interactions within the electrolyte. Therefore, the non-aqueous electrolyte of the lithium secondary battery has little affinity with the electrode material containing the polytetrafluoroethylene, polyvinylidene fluoride binder, and the like, and does not easily wet the electrode material. This is one of the main causes of inefficiently increasing the manufacturing process time of the battery, as will be described later.

In general, the negative electrode used in the lithium secondary battery has a strong lipophilic property, and thus the wettability of the electrolyte having a hydrophilic property is not good. When the activation of the battery proceeds while the electrolyte is not sufficiently wet with the electrode, the SEI film (solid electrolyte interface film, solid electrolyte interface film) of the negative electrode is not properly formed, there is a problem that the life characteristics of the battery is reduced.

Therefore, conventionally, in order to promote wetting of the electrolyte solution to the battery, an additional process such as aging, which is stored for a predetermined time so that the negative electrode is sufficiently wetted with the electrolyte after injection of the electrolyte, is added, or a vacuum or pressure is applied. Special process techniques were used to solve this problem. However, this method leads to the cost of a separate additional process and to the long production time.

Therefore, there is a high need for a technology capable of shortening the manufacturing time of the battery and improving the performance of the battery by increasing the wettability of the electrode with respect to the electrolyte in the manufacturing process of the battery.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

The inventors of the present application have continued in-depth studies and various experiments, and a substance in which a perfluorinated sulfonamide substituent is bonded to one side of a block copolymer structure of polyethylene oxide (PEO) and polypropylene oxide (PPO) is added to the electrolyte solution. In addition, the wettability of the electrolyte solution to the negative electrode was greatly improved, and the present invention was completed by confirming that the performance deterioration of the battery did not occur even after the step of immersion for a predetermined time after the injection of the electrolyte solution.

Accordingly, the present invention includes a material in which a perfluorinated sulfonamide substituent is bonded to one or both ends of a block copolymerization structure of polyethylene oxide (PEO) and polypropylene oxide (PPO) to improve the wetting characteristics of the negative electrode. Provide an electrolyte solution.

The PEO-PPO block copolymer structure is a structure in which hydrophilic polyethylene oxide (PEO) and hydrophobic polypropylene oxide (PPO) chains are repeatedly combined in a constant unit, and have a very low influence on the operation mechanism of the battery, and have a hydrophilic property in the molecule. And having a hydrophobic portion together, it is possible to improve the wetting characteristics of the electrolyte solution to the electrode. The electrolyte additive used in the present invention has a lower surface compared to the use of PEO-PPO block copolymers alone by combining perfluoro sulfonamide substituents having a large number of fluoroins with very low surface energy at the ends of such block copolymer structures. You have energy. This type of bond can change the surface energy gradient of the surfactant to maximize the wetting properties of the electrolyte, including this to the cathode of the electrolyte.

The PEO content in the PEO-PPO block copolymer is preferably 30 to 80% by weight based on the total weight of the copolymer.

The material in which the perfluorinated sulfonamide substituent is bonded to one or both ends of the PEO-PPO block copolymer structure is preferably included in an amount of 0.01 to 10% by weight based on the total weight of the electrolyte. When the content is too small, it is difficult to expect the effect of the addition, on the contrary, when too much, the viscosity of the electrolyte is increased, which is not preferable to cause problems in the pouring process.

In addition, the perfluorinated sulfonamide substituent is preferably bonded to the block copolymer in an amount of less than 1% in the electrolyte additive.

The number of PEO blocks and PPO blocks in the PEO-PPO block copolymer is not particularly limited, and the perfluorinated sulfonamide substituents may be used on one or both ends of the copolymer, regardless of which block the ends of the copolymer consist of. It may be bonded to the terminal and added to the electrolyte.

However, when the copolymer is composed entirely of PEO blocks and PPO blocks to constitute both ends thereof, a structure in which the perfluorinated sulfonamide substituent is bonded to the ends of the PEO blocks is more preferable. This is because when the perfluorinated sulfonamide substituent is bonded to the terminal of the PPO block, the energy gradient of the surfactant is biased to one side, so that the effect is reduced. In other words, when both of the surfactants have a hydrophobic functional group, the surfactant acts in the V-shape to form two anchors connecting the hydrophilic group and the hydrophobic group, but when bound to the end of the PPO block, the surfactant is I-shaped. Since only one anchor acts as a, the efficiency is reduced.

In one preferred embodiment, the material may be represented by the following formula (1).

[Formula 1]

FC4430 (manufactured by 3M Co., Ltd.) is commercially available for having the material of Formula 1 above.

The compound according to the present invention may be added to the components of the battery by itself, or in some cases dissolved in a solvent or the like or dispersed.

The present invention also provides a lithium secondary battery comprising the electrolyte solution containing the additive and a carbon-based negative electrode active material.

Other components of the lithium secondary battery according to the present invention will be described below.

The positive electrode for a lithium secondary battery is prepared by, for example, applying a mixture of a positive electrode active material, a conductive agent, and a binder in the form of a slurry on a positive electrode current collector, and then drying and compressing the filler. Also add more.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive agent is typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like.

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

The negative electrode for a lithium secondary battery is manufactured by coating, drying, and compressing a negative electrode material on a negative electrode current collector, and if necessary, components of the positive electrode (binder, conductive agent, filler, etc.) as described above may be further included.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator for a lithium secondary battery is interposed between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The nonaqueous electrolyte for lithium secondary batteries consists of a nonaqueous electrolyte and lithium. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

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

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

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

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The content of the present invention will be described below with reference to Examples and Comparative Examples, but the scope of the present invention is not limited thereto.

Example 1

A lithium secondary battery was prepared as follows. At this time, the electrolyte was injected and then granulated without undergoing a aging step.

1-1. Manufacture of anode

LiCoO ₂ was used as the cathode active material, and was added to N-methyl-2-pyrrolidone (NMP) as a composition of 95% by weight of LiCoO ₂ , 2.5% by weight of Super-P (conductor) and 2.5% by weight of PVDF (binder). To prepare a positive electrode mixture slurry, and then coated, dried and pressed on an aluminum current collector to prepare a positive electrode.

1-2. Preparation of Cathode

Artificial negative electrode was used as the negative electrode active material, and the negative electrode mixture slurry was prepared by adding 95.3% by weight of artificial graphite, 0.7% by weight of Super-P (conductive agent) and 4% by weight of PVDF (binder) to NMP as a solvent. The negative electrode was prepared by coating, drying, and pressing on a copper current collector.

1-3. Preparation of Electrolyte

As an electrolyte, an EC / EMC solution was used in 1M LiPF ₆ , and 0.5 wt% of FC4430 (3M product) was added as a PEO-PPO block copolymer substituted with perfluorinated sulfonamide to prepare an electrolyte for a lithium secondary battery. It was.

1-4. Manufacture of batteries

A porous separator (trademark: Celgard) was placed between the positive electrode and the negative electrode prepared in 1-1 and 1-2, respectively, and a lithium secondary battery was prepared by injecting the non-aqueous electrolyte prepared in 1-3.

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the PEO-PPO block copolymer having a perfluorinated sulfonamide group substituted therein was not added to the electrolyte.

Comparative Example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the PEO-PPO block copolymer having a perfluorinated sulfonamide group substituted therein was added to the electrolyte and aged for 3 hours at room temperature.

Experimental Example: Measurement of Lifetime Characteristics

Experiments on the life characteristics of the batteries prepared in Example 1 and Comparative Examples 1 and 2, respectively, and the results are shown in Table 1 and Figure 1, respectively.

As shown in Table 1 and Figure 1 attached, it was confirmed that the battery of Example 1, the life characteristics improved compared to the battery of Comparative Example 1. In addition, it can be seen that compared with Comparative Example 2 subjected to the aging process, the equivalent level.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

As described above, the electrolytic solution with improved wettability according to the present invention and a lithium secondary battery comprising the same, by adding an additive that improves the wettability to a general electrolyte solution, unlike the conventional aging process for storing a certain time after the electrolyte solution injection of the battery Since it can be omitted, the process cost is reduced, further reducing the cost of manufacturing the product.

Claims (6)

An electrolyte solution in which a material having a perfluorinated sulfonamide substituent bonded to one or both ends of a block copolymerization structure of polyethylene oxide (PEO) and polypropylene oxide (PPO) is included to improve the wettability to the negative electrode. The electrolyte of claim 1, wherein the material is included in an amount of 0.01 to 10 wt% based on the total weight of the electrolyte. According to claim 1, wherein when the PEO-PPO block copolymer is composed entirely of PEO block and PPO block constituting both ends thereof, the perfluorinated sulfonamide substituent is bonded to the end of the PEO block Electrolyte solution. The electrolyte of claim 1, wherein the material is represented by the following Chemical Formula 1.

(One) The electrolyte of claim 1, wherein the PEO content in the PEO-PPO block copolymer is 30 to 80% by weight based on the total weight of the copolymer. A lithium secondary battery comprising the electrolyte according to any one of claims 1 to 5 and a carbon-based negative electrode active material.

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