KR20210031196A - Method for manufacturing aqueous lithium secondary battery - Google Patents

Abstract

The present invention relates to a method for manufacturing an aqueous lithium secondary battery, which includes a step of pre-charging and discharging under specific conditions, thereby improving the wettability between an electrode and an aqueous electrolyte to manufacture the aqueous lithium secondary battery with improved performance and lifespan characteristics. The present invention includes the following steps: (S1) injecting the aqueous electrolyte into the electrode assembly including the electrode and a separator; (S2) aging the electrode assembly prepared in the step (S1); and (S3) pre-charging/discharging the electrode assembly prepared in the step (S2) in a voltage range of 0.4 to 1.3 V.

Description

Manufacturing method of aqueous lithium secondary battery {METHOD FOR MANUFACTURING AQUEOUS LITHIUM SECONDARY BATTERY}

The present invention relates to a method of manufacturing an aqueous lithium secondary battery.

Recently, the miniaturization, weight reduction and high performance of electronic devices and communication devices are rapidly progressing, and the necessity of electric vehicles (EV) and electric storage systems (ESS) is required in relation to the depletion of petroleum resources and environmental problems. As it emerges largely, research on secondary batteries used as a power source for these products is being actively conducted. Among various secondary batteries, a lithium secondary battery that can be applied to a field requiring high capacity, high output characteristics and high stability is attracting attention.

In general, in order to achieve a high energy density, a lithium secondary battery mainly uses a non-aqueous (or organic) electrolyte containing a non-aqueous organic solvent that does not decompose even at a voltage of about 4 V.

However, the non-aqueous electrolyte has a high viscosity and low ionic conductivity compared to an aqueous electrolyte, so its application to applications requiring high output is limited. In addition, since the non-aqueous electrolyte _{contains a salt such as expensive LiPF 6} and must be manufactured in a dry space without moisture, the manufacturing cost is high, and the manufacturing process is complicated. In addition, the organic solvent used in the non-aqueous electrolyte is flammable, and there is a risk of ignition or explosion due to ignition or side reactions, so safety and stability are weak. In particular, in the case of an electric vehicle or a power storage device, it is important to ensure safety and stability along with high output. In the case of a lithium secondary battery using a non-aqueous electrolyte, it is difficult to satisfy the safety, stability, and reliability, so that commercialization is limited.

In view of the problem of such a non-aqueous electrolyte, various studies have been conducted on an aqueous electrolyte using an aqueous solvent.

An aqueous electrolyte is an aqueous solution obtained by dissolving a salt in an aqueous solvent such as water, and does not contain an organic solvent, so safety and stability are guaranteed, and a manufacturing process and cost are low. In addition, the aqueous electrolyte has a higher ionic conductivity than a non-aqueous electrolyte and has a low viscosity, so that the internal resistance of the electrolyte is small, so that the output characteristics of the lithium secondary battery can be improved.

The lithium secondary battery has a structure in which an electrolyte is impregnated in an electrode assembly in which a separator is interposed between a positive electrode and a negative electrode. In the case of the positive electrode and the negative electrode of such a lithium secondary battery, a conductive material and a binder are basically included in order to improve conductivity and durability. At this time, the conductive material and the binder used are materials with strong hydrophobicity, and since the electrode containing them exhibits hydrophobicity, there is a problem in that the electrode is not sufficiently impregnated or wetted when an aqueous electrolyte is used. . In addition, when the wettability between the electrode and the electrolyte is deteriorated in this way, the electrochemical reaction cannot proceed smoothly, and the performance of the lithium secondary battery is deteriorated.

Accordingly, several techniques have been proposed to improve the wettability of the electrode to the electrolyte.

For example, Korean Patent Application Publication No. 2017-0035565 includes a prewetting process in which charging and discharging is performed in a 0 to 70% SOC (State of Charge) region during the activation process of the battery, thereby improving the electrolyte impregnation property of the battery. It is disclosed that it can be.

In addition, Korean Patent Registration No. 10-1310553 applies electrical perturbation to the electrochemical device using the principle of electrowetting, thereby improving the wettability between the electrode constituting the electrochemical device and the electrolyte. Is being disclosed.

The prior literature has improved the wettability of the electrolyte to some extent, but mainly relates to a non-aqueous electrolyte, and does not consider the improvement of the wettability of the aqueous electrolyte at all. In addition, as a separate process is required, the manufacturing process becomes complicated and the manufacturing cost increases. Accordingly, there is a need for further development of a method for manufacturing a lithium secondary battery that can effectively improve the wettability of an aqueous electrolyte through a simple process.

Republic of Korea Patent Publication No. 2017-0035565 (2017.03.31), a method of manufacturing a secondary battery including a prewetting process Republic of Korea Patent Registration No. 10-1310553 (2013.09.12), Electrochemical device with improved wettability between electrode and electrolyte, and its manufacturing method

Accordingly, the inventors of the present invention conducted various studies to solve the above problem. As a result, when the manufacturing of an aqueous lithium secondary battery includes the step of pre-charging and discharging under specific conditions, the wettability of the electrode to the aqueous electrolyte is improved. The present invention was completed by confirming that the performance of the manufactured battery was also improved.

Accordingly, an object of the present invention is to provide a method of manufacturing an aqueous lithium secondary battery having excellent wettability to an aqueous electrolyte.

In order to achieve the above object, the present invention comprises the steps of: (S1) injecting an aqueous electrolyte into an electrode assembly including an electrode and a separator; (S2) aging the electrode assembly prepared in step (S1); And (S3) pre-charging and discharging the electrode assembly prepared in step (S2) in a voltage range of 0.4 to 1.3 V.

The pre-charging and discharging of the step (S3) may be performed under conditions of a current density of 1 to 5 A/g.

Pre-charging and discharging in step (S3) may be performed in 30 to 60 cycles.

The aging of step (S2) may be performed for 6 to 18 hours at a temperature of 20 to 40°C.

Between the step (S2) and step (S3), the step of removing the gas inside the electrode assembly may be further included.

The method of manufacturing an aqueous lithium secondary battery according to the present invention can greatly improve the wettability of the aqueous electrolyte with respect to the electrode by including a process of pre-charging and discharging under specific conditions. Accordingly, the aqueous lithium secondary battery manufactured according to the manufacturing method of the present invention is superior in impregnation to the aqueous electrolyte compared to the prior art, so that the high capacity characteristics of the aqueous lithium secondary battery are sufficiently exhibited, thereby exhibiting excellent performance and lifespan characteristics.

In addition, since the manufacturing method according to the present invention simplifies the process and shortens the time, it is possible to increase the economy and productivity of the entire manufacturing process.

1 is a graph showing a cycle stability evaluation result of the aqueous lithium secondary battery of Example 1 according to Experimental Example 1 of the present invention.
1 is a graph showing a cycle stability evaluation result of an aqueous lithium secondary battery of Comparative Example 1 according to Experimental Example 1 of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The terms used in the present invention are used only to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present invention, terms such as'include' or'have' are intended to designate the presence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof does not preclude in advance.

The term “wettability” as used herein refers to the degree to which an electrolyte penetrates into an electrode, particularly an electrode active material, and can be used interchangeably with the term “impregnability”.

Lithium secondary batteries have been applied to small-sized fields such as mobile phones and notebook computers, but in recent years, their application fields are expanding to mid- to large-sized fields such as electric vehicles and energy storage devices. In this case, unlike a small size, the operating environment is harsh, and the corresponding output must be maintained for a long time along with high output characteristics, so high capacity and high stability need to be secured together.

When an aqueous electrolyte is used in a lithium secondary battery, since it does not contain a non-aqueous organic solvent, there is no risk of ignition or explosion due to volatilization or decomposition reaction of the electrolyte, so it is not only safe, but also excellent in stability. In addition, since aqueous electrolytes have high ionic conductivity, high output is possible, manufacturing processes and manufacturing costs are inexpensive, and environmental aspects are also advantageous, they are in the spotlight as an energy source for mid- to large-sized devices such as electric vehicles.

The lithium secondary battery is manufactured in a state in which the electrode assembly is impregnated with an electrolyte, and at this time, it is preferable from the viewpoint of the performance and life of the battery only to be quickly and sufficiently impregnated into the electrode, that is, the electrode active material. However, in the manufacturing process of a lithium secondary battery, an electrolyte impregnation or wetting process of an electrode generally takes a lot of time. In addition, since the electrode generally contains a hydrophobic conductive material and a binder component that does not have a high affinity with the electrolyte, the wettability for the electrolyte, especially the aqueous electrolyte, is low. Movement is slowed so that the electrochemical reaction in the electrode cannot be performed smoothly, and as a result, the performance and life of the battery are deteriorated. In addition, as the electrode thickness or the loading amount of the active material is increased in recent years to increase the energy density, the electrode cannot be sufficiently impregnated by the electrolyte as the movement path of the electrolyte is lengthened, thereby reducing the electrochemical reaction, thus shortening the performance or lifespan of the battery. It is a big factor to let you do.

In order to improve the wettability between the electrode and the electrolyte, methods such as changing the structure of the electrode assembly, injecting the electrolyte under high temperature, pressure, or reduced pressure, or adding a separate process to promote electrolyte impregnation have been proposed, but mainly non-aqueous systems. It targets a lithium secondary battery using an electrolyte, and requires a lot of time and cost, so there is a problem that it is inefficient in terms of fairness, economy, and productivity.

Accordingly, the present invention provides a method of manufacturing an aqueous lithium secondary battery including a process of pre-charging and discharging under specific conditions in order to improve the wettability of an aqueous electrolyte of an electrode in a lithium secondary battery including an aqueous electrolyte.

Specifically, the method of manufacturing an aqueous lithium secondary battery according to the present invention includes the steps of: (S1) injecting an aqueous electrolyte into an electrode assembly including an electrode and a separator; (S2) aging the electrode assembly manufactured in step (S1); And (S3) pre-charging and discharging the electrode assembly prepared in step (S2) in a voltage range of 0.4 to 1.3 V.

Step (S1)

Step (S1) is a step of injecting an aqueous electrolyte into an electrode assembly including an electrode and a separator.

In the step (S1), the injection of the aqueous electrolyte is performed without a separate pressure change at room temperature (25° C.), and the injection method is not particularly limited, and may be performed by a conventional method known in the art.

In this case, the electrode assembly generally includes at least one unit cell having a basic structure including a positive electrode composed of a positive electrode active material and a positive electrode current collector, a negative electrode composed of a negative electrode active material and a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode. It was done.

In the electrode assembly of the present invention, the unit cell is a lithium secondary battery, and a detailed description thereof will be described later.

In the present invention, the electrode assembly may be manufactured by a conventional method known in the art, and the shape of the electrode assembly is not particularly limited, and may be, for example, a wound type, a stack type, or a stack/folding type.

The wound electrode assembly is coated with an electrode active material, etc. on a metal foil used as a current collector, dried and pressed, cut into a band of a desired width and length, and separated from the negative electrode and the positive electrode using a separator, and then spirally It is manufactured by winding it.

The stacked electrode assembly is a structure in which a plurality of anode and cathode unit cells are sequentially stacked, and has an advantage in that it is easy to obtain a square shape, but the manufacturing process is complicated and the electrode is pushed when an impact is applied, causing a short circuit. There are drawbacks.

The stack/folding type electrode assembly is an electrode assembly of a structure in which a conventional folding type and a stack type are combined, and a full cell or bi cell of a certain unit size is used as a continuous separation film of a long length. It is an electrode assembly of a folded structure.

The full cell is a unit cell composed of a unit structure of an anode/separator/cathode, and is a cell in which an anode and a cathode are respectively located on both sides of the cell. Such full cells include an anode/separator/cathode cell and an anode/separator/cathode/separator/anode/separator/cathode cell having the most basic structure. In order to construct an electrode assembly using such full cells, a plurality of full cells must be stacked so that the anode and the cathode face each other while the separator is interposed therebetween.

The bicell is a unit cell in which the same electrode is located on both sides of a cell, such as a unit structure of an anode/separator/cathode/separator/anode and a unit structure of a cathode/separator/anode/separator/cathode. In order to construct an electrochemical cell using such a bi-cell, a bi-cell of an anode/separator/cathode/separator/anode structure and a cathode/separator/anode/separator/cathode structure with a separator interposed therebetween. A plurality of bi-cells must be stacked so that the bi-cell (cathode bi-cell) face each other. In some cases, bicells with a larger number of stacks are also possible, for example, anode/separator/cathode/separator/anode/separator/cathode/separator/anode and cathode/separator/anode/separator/cathode/separator Bi-cell of /positive/separator/cathode structure is also possible.

Further details on the stack/folding structure of the electrode assembly are disclosed in Korean Patent Publication Nos. 2001-0082058, 2001-0082059 and 2001-0082060 of the applicant of the present invention. Incorporated by reference into the content.

The aqueous electrolyte includes an aqueous solvent and a lithium salt, and known in the art may be used, and a detailed description thereof will be described later.

Step (S2)

The step (S2) is a step of aging the electrode assembly manufactured in the step (S1).

The aging is a step of stabilizing the battery by leaving the electrode assembly injected with the aqueous electrolyte.

The aging may be performed at a temperature of 20 to 40°C, preferably 20 to 30°C. It is preferable to perform aging in the above-described temperature range from the viewpoint of electrolyte stability.

In addition, the aging may be performed for 6 to 18 hours, preferably 6 to 12 hours. If the aging is performed below the above range, it is difficult for the aqueous electrolyte to be evenly impregnated. Conversely, if the above range is exceeded, there is a problem that the manufacturing process is lengthened.

Gas may be generated in the aging step, which may cause swelling of the battery. Accordingly, a step of degassing may be additionally performed to remove the gas generated inside the battery and secure the workability of the subsequent step.

Step (S3)

The step (S3) is a step of pre-charging and discharging the electrode assembly prepared in the step (S2) in a voltage range of 0.4 to 1.3 V.

As described above, a lithium secondary battery uses an electrochemical reaction with an electrolyte in an electrode, and it is known that the wettability between the electrode and the electrolyte is very important in terms of securing the performance and life of the battery, but requires a long time. In the case of the prior art, in order to increase the wettability of the electrolyte and shorten the time required, there are many cases of using a method such as varying the temperature, pressure, SOC, etc. or having a separate process when injecting the electrolyte. The reality is that it takes time. Accordingly, the present invention can effectively increase the wettability of the electrode to the electrolyte as the aqueous electrolyte injected in the above step is more quickly and easily impregnated into the battery, specifically the electrode, by performing the pre-charging and discharging of the step (S3). have. Accordingly, the time for activation of the battery can be significantly shortened compared to the conventional manufacturing method. In addition, the pre-charge/discharge process for improving wettability of the present invention has the advantage that the process is simple and can be performed in a short time, so that it can be easily used in an actual mass production process.

The pre-charging and discharging of the step (S3) may be performed under conditions of a voltage of 0.4 to 1.3 V, preferably 0.4 to 1.25 V. When the voltage of the pre-charging/discharging is less than the above range, the effect of improving wettability cannot be sufficiently secured. Conversely, when the voltage exceeds the above range, a problem of performance degradation due to an imbalance between positive and negative charges may occur.

In addition, the pre-charging and discharging of the step (S3) may be performed under conditions of a current density of 1 to 5 A/g, preferably 3 to 5 A/g. If the current density of the pre-charge/discharge is less than the above range, there is a disadvantage that the prewetting time for impregnation of the electrolyte is prolonged. On the contrary, if the current density exceeds the above range, it is difficult to reach equilibrium between the positive electrode active material and the negative electrode active material due to high output. There is a loss problem, so it is not suitable for the actual mass production process.

In addition, the pre-charging and discharging of the step (S3) may be performed in 30 to 60 cycles, preferably 40 to 50 cycles. When the pre-charge/discharge cycle is less than the above range, the wettability improvement effect is insignificant.

After the step (S3), a step of degassing to remove the gas generated in the manufacturing process may be additionally performed.

According to the method of manufacturing an aqueous lithium secondary battery of the present invention, by including the step of pre-charging and discharging under specific conditions, it is possible to improve the wettability of the battery, specifically, the aqueous electrolyte with respect to the electrode. As the wettability of the aqueous electrolyte is improved as described above, when the aqueous lithium secondary battery is manufactured, sufficient impregnation of the aqueous electrolyte into the electrode is performed, so that a lithium secondary battery having excellent performance can be manufactured.

According to a preferred embodiment of the present invention, the aqueous lithium secondary battery manufactured by the above manufacturing method may exhibit an initial performance of 60% or more, preferably 80% or more of the theoretical capacity when first used.

In addition, the manufacturing method of an aqueous lithium secondary battery according to the present invention is not only simple in the process, but also can greatly shorten the time required for electrolyte impregnation and activation of the battery during the manufacturing process of the battery, thereby providing excellent productivity and economy.

In addition, the present invention provides an aqueous lithium secondary battery manufactured by the above-described method.

For example, the aqueous lithium secondary battery may be embedded in a battery case in a state in which an aqueous electrolyte is impregnated in an electrode assembly including a positive electrode and a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

In particular, the aqueous lithium secondary battery manufactured according to the manufacturing method of the present invention may exhibit excellent performance and lifespan characteristics as the wettability of the aqueous electrolyte to the battery is improved through a precharge/discharge process.

The positive electrode may include a positive electrode current collector and a positive electrode active material applied to one or both surfaces of the positive electrode current collector.

The positive electrode current collector supports a positive electrode active material, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, nickel, titanium, palladium, calcined carbon, aluminum or stainless steel surface treated with carbon, nickel, silver, or the like may be used.

The positive electrode current collector may form fine irregularities on its surface to enhance the bonding strength with the positive electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and nonwoven fabrics may be used.

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 as the positive electrode active material; Lithium manganese oxides such as formula Li _{1 + x} Mn _{2 - x} O ₄ (0≦x≦0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO _2; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O _7; Ni site type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga; 0.01≦x≦0.3); Formula LiMn _{2 - x} M _x O ₂ (M = Co, Ni, Fe, Cr, Zn or Ta; 0.01≤x≤0.1) or Li ₂ Mn ₃ MO ₈ (M = Fe, Co, Ni, Cu or Zn A lithium manganese composite oxide represented by ); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _{2 - x} O _4; LiCoPO ₄ ; LiFePO ₄ ; Elemental sulfur (S ₈ ); Li ₂ S _n (n≥1), an organosulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5 to 50, n≥2) may include sulfur-based compounds, such as, but these It is not limited to only.

The positive active material may include a positive active material and optionally a conductive material and a binder.

The conductive material is a material that acts as a path for electrons to move from a current collector to the positive electrode active material by electrically connecting the electrolyte and the positive electrode active material, and does not cause chemical changes in a lithium secondary battery, and has porosity and conductivity. If it is, you can use it without limitation.

For example, a carbon-based material having a porosity may be used as the conductive material, and examples of such a carbon-based material include carbon black, graphite, graphene, activated carbon, carbon fiber, and the like, and metallic fibers such as metal mesh; Metallic powders such as copper, silver, nickel, and aluminum; Or an organic conductive material such as a polyphenylene derivative. The conductive materials may be used alone or in combination.

Products currently marketed as conductive materials include acetylene black (Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC (Armak Company). Company), Vulcan XC-72 (made by Cabot Company) and Super P (made by MMM). For example, acetylene black, carbon black, graphite, etc. are mentioned.

In addition, the positive electrode may further include a binder, and the binder further enhances binding strength between components constituting the positive electrode and between them and a current collector, and any binder known in the art may be used.

For example, the binder may include a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; Polyalcohol-based binder; Polyolefin-based binders including polyethylene and polypropylene; Polyimide binders; Polyester binder; And a silane-based binder; one, two or more mixtures or copolymers selected from the group consisting of may be used.

The positive electrode can be manufactured by a conventional method known in the art. For example, after preparing a slurry by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a positive electrode active material, it is applied (coated) to a current collector of a metal material, compressed, and dried to prepare a positive electrode. have.

The negative electrode may include a negative electrode current collector and a negative active material disposed on the negative electrode current collector.

The negative electrode current collector is for supporting the negative electrode active material, as described for the positive electrode.

The negative active material includes ^{a material capable of reversibly intercalating or deintercalating lithium (Li +} ), and a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions.

For example, metal compounds such as metal oxides, metal sulfides, and metal nitrides may be mentioned. For example, as a metal oxide having a lithium element, for example, lithium vanadium oxide (Li _x VO ₂ (0<x≤1.0), LiV ₃ O ₈ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ )) ₃ (0<x<2, 0<y<3)), lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ), Li _{1 . 2} Cr _{0 . 2} Ti _{1 .8} (PO ₄ ) ₃ and the like. Moreover, as a metal nitride containing a lithium element, lithium cobalt nitride, lithium iron nitride, lithium manganese nitride, etc. are mentioned, for example. Moreover, a sulfur-based compound can also be illustrated. In addition to this, a metal such as iron or zinc may be used.

A polarizable material may be included as the negative active material, as described above for the positive active material. In addition, a material capable of occluding and releasing lithium ions may be included as an anode active material. For example, natural graphite or artificial graphite, activated carbon, carbon nanotubes, and carbon materials such as graphene may be included.

The negative electrode may further include the negative electrode active material and optionally a conductive material and a binder. At this time, the conductive material and the binder are as described in the positive electrode active material.

The method of forming the cathode is not particularly limited, and a layer or film forming method commonly used in the art may be used. For example, a method such as compression, coating, or evaporation may be used. In addition, a case in which a metal lithium thin film is formed on a metal plate by initial charging after assembling a battery without a lithium thin film in the current collector is also included in the negative electrode of the present invention.

The aqueous electrolyte contains lithium ions, and is intended to cause an electrochemical oxidation or reduction reaction in the positive electrode and the negative electrode through this.

The aqueous electrolyte includes a lithium salt and an aqueous solvent.

The lithium salt is not particularly limited as long as it is commonly used in an aqueous electrolyte for a lithium secondary battery. For example, the lithium salt is lithium hydroxide (LiOH), lithium oxide (Li ₂ O), lithium carbonate (LiCO ₃ ), lithium chloride (LiCl), lithium nitrate (LiNO ₃ ), lithium sulfate (Li ₂ SO ₄ ), lithium perchlorate (LiClO ₄ ), and lithium acetate (LiCH ₃ COO).

The concentration of the lithium salt may be appropriately determined in consideration of ionic conductivity, solubility, and the like, and may be, for example, 0.1 to 10 M, preferably 0.5 to 8 M. When the concentration of the lithium salt is less than the above range, it is difficult to secure an ionic conductivity suitable for driving the device.On the contrary, when the concentration of the lithium salt exceeds the above range, complete dissolution of the lithium salt is not achieved, and the performance of the battery is impaired by the lithium salt precipitated without dissolution. Since it may be lowered, it is appropriately adjusted within the above range.

The electrolyte according to the present invention includes an aqueous solvent as a medium through which ions involved in the electrochemical reaction of a battery, that is, lithium ions can move. Water is usually used as the aqueous solvent, and although not particularly limited, water may be included in an amount of 1% by weight or more based on the total weight of the aqueous solvent constituting the electrolyte. Therefore, the main solvent used in the aqueous electrolyte of the present invention is water. At this time, water may be used alone as a solvent, but a solvent miscible with water may be used in combination.

The water-miscible solvent may be a polar solvent, and may include, for example, one or more selected from the group consisting of C1 to C5 alcohols and C1 to C10 glycol ethers.

For example, the C1 to C5 alcohol is methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1 ,4-butanediol, glycerol, and 1,2,4-butanetriol may be one or more selected from the group consisting of, but is not limited thereto.

The glycol ethers of C1 to C10 are ethylene glycol monomethyl ether (MG), diethylene glycol monomethyl ether (MDG), triethylene glycol monomethyl ether (MTG), polyethylene glycol monomethyl ether (MPG), ethylene glycol monoethyl Ether (EG), diethylene glycol monoethyl ether (EDG), ethylene glycol monobutyl ether (BG), diethylene glycol monobutyl ether (BDG), triethylene glycol monobutyl ether (BTG), propylene glycol monomethyl ether ( MFG) and dipropylene glycol monomethyl ether (MFDG) may be one or more selected from the group consisting of, but is not limited thereto.

In addition to the above-described composition, the aqueous electrolyte may additionally include additives commonly used for the purpose of improving its function in the relevant technical field, if necessary. For example, a conventionally known overcharge prevention agent, a property improvement aid for improving capacity retention characteristics and cycle characteristics after high temperature storage, and the like may be mentioned.

A separator may be additionally included between the above-described anode and cathode. The separator is for physically separating both electrodes in a lithium secondary battery, and can be used without particular limitation as long as it is used as a separator in a general lithium interest battery. It is desirable.

The separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used in an electrochemical device, and for example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto. .

Examples of the polyolefin-based porous membrane include polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, alone or as a mixture of them. There is one membrane.

As the nonwoven fabric, in addition to the polyolefin nonwoven fabric, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide and polyethylene naphthalate, etc. Alternatively, a nonwoven fabric formed of a polymer obtained by mixing them may be mentioned. The structure of the nonwoven fabric may be a sponbond nonwoven fabric composed of long fibers or a melt blown nonwoven fabric.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 µm and 10 to 95%, respectively.

The shape of the aqueous lithium secondary battery according to the present invention is not particularly limited and may vary depending on the battery case. The battery case is for accommodating an electrode assembly including an aqueous lithium secondary battery having the above-described configuration and shape, and may have various shapes such as a cylindrical shape, a stacked type, and a coin type.

Hereinafter, a preferred embodiment is presented to aid in the understanding of the present invention, but it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the scope of the technical idea, but the following examples are only illustrative of the present invention, It is natural that such modifications and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

[Example 1]

_{A positive electrode slurry composition was prepared by mixing 90% by weight of LiMn 2} O ₄ as a positive electrode active material, 5% by weight of acetylene black as a conductive material, and 5% by weight of polyvinylidene fluoride (PVDF) as a binder. A positive electrode was prepared by applying the prepared positive electrode slurry composition to a 10 μm-thick nickel current collector at a loading density of 12 mg/cm 2 and then drying it.

_{Li 1} as a negative active material _{. 2} Cr _{0 . 2} Ti _{1 .8} (PO ₄ ) ₃ 88% by weight, 5% by weight of acetylene black as a conductive material, and 7% by weight of polyvinylidene fluoride (PVDF) as a binder were mixed to prepare a negative electrode slurry composition. The prepared negative electrode slurry composition was coated on a 10 µm-thick nickel current collector at a loading density of 14.5 mg/cm 2 and dried to prepare a negative electrode.

1.0 M lithium nitrate (LiNO ₃ ) was dissolved in water to prepare an aqueous electrolyte.

An aqueous lithium secondary battery was prepared by placing the prepared positive and negative electrodes facing each other, interposing a hydrophilic polyethylene separator having a thickness of 20 µm and a porosity of 45%, and injecting 10 µl of an electrolyte at room temperature and pressure. .

The prepared lithium secondary battery was aged at 25° C. for 8 hours.

Subsequently, pre-charging and discharging were performed for 50 cycles under conditions of 0.4 to 1.3 V and 5 A/g.

[Comparative Example 1]

A battery was manufactured in the same manner as in Example 1, except that pre-charging and discharging were not performed on the aqueous lithium secondary battery manufactured in the same manner as in Example 1.

Experimental Example 1. Cycle stability evaluation

Cycle stability was evaluated for the aqueous lithium secondary batteries of Examples and Comparative Examples using BCS-810, (manufactured by Neo Science). Specifically, capacity characteristics according to cycles were evaluated using a constant-current discharge method under charging/discharging conditions (constant current 5 A/g, voltage 0.4 to 2.1 V). The results obtained at this time are shown in FIGS. 1 to 3.

1 to 3, the aqueous lithium secondary battery according to the embodiment exhibits a capacity of 80% of the theoretical capacity from the beginning of the cycle, whereas the aqueous lithium secondary battery according to the comparative example has a capacity as the cycle progresses. It can be seen that it gradually increases and shows a capacity at the level of 80% of the theoretical capacity only after 1000 cycles.

From these results, it can be seen that the aqueous lithium secondary battery manufactured according to the present invention has improved wettability with respect to the aqueous electrolyte compared to the comparative example, and thus has excellent initial capacity characteristics.

Claims (7)

(S1) injecting an aqueous electrolyte into an electrode assembly including an electrode and a separator;
(S2) aging the electrode assembly prepared in step (S1); And
(S3) A method of manufacturing an aqueous lithium secondary battery comprising pre-charging and discharging the electrode assembly prepared in step (S2) in a voltage range of 0.4 to 1.3 V. The method of claim 1,
The pre-charging and discharging of the step (S3) is performed under conditions of a current density of 1 to 5 A/g. The method of claim 1,
The pre-charging and discharging of the step (S3) is performed under conditions of a voltage of 0.4 to 1.25. The method of claim 1,
The pre-charging and discharging of the step (S3) is performed in 30 to 60 cycles. The method of claim 1,
The aging of the step (S2) is performed for 6 to 18 hours at a temperature of 20 to 40° C., a method of manufacturing an aqueous lithium secondary battery. The method of claim 1,
Between the step (S2) and step (S3), further comprising the step of removing the gas inside the battery, a method of manufacturing an aqueous lithium secondary battery. An aqueous lithium secondary battery manufactured by the manufacturing method of claim 1 and having an initial performance of at least 60% of the theoretical capacity when used for the first time.

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