KR102739920B1 - Polymeric electrolyte composition and polymeric solid electrolyte prepared from the same, and lithium secondary battery comprising the polymeric solid electrolyte - Google Patents

Abstract

The present invention relates to a polymer electrolyte composition capable of producing a polymer solid electrolyte having uniform particles, low viscosity, and excellent ionic conductivity and lifespan characteristics, a polymer solid electrolyte produced therefrom and a method for producing the same, and a lithium secondary battery including the polymer solid electrolyte.

Description

Polymeric electrolyte composition and polymeric solid electrolyte prepared from the same, and lithium secondary battery comprising the polymeric solid electrolyte

The present invention relates to a polymer electrolyte composition capable of producing a polymer solid electrolyte having uniform particles, low viscosity, and excellent ionic conductivity and lifespan characteristics, a polymer solid electrolyte produced therefrom and a method for producing the same, and a lithium secondary battery including the polymer solid electrolyte.

Lithium secondary batteries have a large electrochemical capacity, high operating potential, and excellent charge/discharge cycle characteristics, and are therefore increasingly in demand for portable information terminals, portable electronic devices, small household power storage devices, motorcycles, electric vehicles, and hybrid electric vehicles. As these applications expand, there is a demand for improved safety and higher performance of lithium secondary batteries.

Lithium secondary batteries can generally be manufactured using a positive electrode and a negative electrode including electrode active materials capable of inserting/releasing lithium ions, and an electrolyte which is a medium for transferring lithium ions. Conventionally, a liquid electrolyte, particularly an ion-conductive organic liquid electrolyte in which a salt is dissolved in a non-aqueous organic solvent, has been mainly used as the electrolyte. However, such liquid electrolytes have concerns of leakage during operation, and there are problems such as ignition and explosion due to the high flammability of the non-aqueous organic solvent used. Furthermore, the liquid electrolyte can generate gas inside the battery due to the decomposition of the carbonate-based organic solvent or a side reaction with the electrode during charging and discharging of the lithium secondary battery, and such decomposition reaction or side reaction can be further accelerated at high temperatures, which can increase the amount of gas generated.

Gases continuously generated in this way can cause an increase in the internal pressure of the battery, which can cause deformation of the battery, such as expansion of the thickness of the battery, and can also cause local differences in adhesion at the electrode surface within the battery, which can cause the electrode reaction not to occur equally across the entire electrode surface.

Accordingly, in order to overcome the stability problem of the liquid electrolyte, a method using a solid electrolyte without concerns about leakage, etc. has been proposed recently. As an example of such a solid electrolyte, a polymer-based solid electrolyte has been proposed that is manufactured by impregnating a polymer matrix formed by a crosslinking reaction with an electrolyte solution containing an electrolyte salt and a non-aqueous organic solvent, and then gelling the polymer matrix (Korean Patent Publication No. 10-2000-0003090).

Until recently, many studies have been conducted focusing on improving the performance of polymer-based solid electrolytes, and polymer-based solid electrolytes with improved ionic conductivity and life characteristics have been developed ( ACS Appl. Energy Mater. 2020, 3, 1, 1099-1110). However, these polymer-based solid electrolyte compositions have too high a viscosity, making it difficult to manufacture a polymer-based solid electrolyte so that the particles are uniformly dispersed when using these compositions. In addition, the process of impregnating the electrolyte after forming the polymer matrix increases the time required to manufacture the polymer-based solid electrolyte, which reduces productivity and mass production.

Therefore, there is a need for the development of a polymer electrolyte composition capable of ensuring productivity/mass production while maintaining uniform particle distribution and excellent electrolyte properties, and a method for manufacturing a polymer-based solid electrolyte using the same.

The present invention aims to solve the problems of the prior art described above, and to provide a polymer electrolyte composition capable of improving particle uniformity in a polymer electrolyte composition, maintaining excellent electrolyte properties while shortening the time required for a drying process during the production of a polymer-based solid electrolyte, thereby improving productivity and mass production, a polymer-based solid electrolyte produced therefrom and a production method therefor, and a lithium secondary battery including the polymer-based solid electrolyte.

In order to solve the above-mentioned problems, the present invention provides a polymer electrolyte composition comprising: a polymer resin; a lithium salt; an electrolyte component including a carbonate-based compound and a nitrile-based compound; inorganic particles; and an organic solvent; wherein, based on 100 parts by weight of the total polymer electrolyte composition, the content of the polymer resin is 2.1 to 7.5 parts by weight, the content of the lithium salt is 2.1 to 7.5 parts by weight, the content of the inorganic particles is 0.1 to 5.1 parts by weight, and a molar ratio of nitrile groups (-C≡N) in the nitrile-based compound per 1 mol of carbonyl groups (-C(=O)-) in the carbonate-based compound in the electrolyte component is 0.38 to 2.30.

Another aspect of the present invention provides a method for producing a polymer-based solid electrolyte, comprising: (1) a step of coating a polymer electrolyte composition according to the present invention on a substrate; and (2) a step of drying the coated polymer electrolyte composition.

Another aspect of the present invention provides a polymer-based solid electrolyte manufactured by a method for manufacturing a polymer-based solid electrolyte according to the present invention.

Another aspect of the present invention provides a lithium secondary battery comprising a polymer-based solid electrolyte according to the present invention.

The polymer electrolyte composition according to the present invention can form a solid electrolyte film having a desired thickness level, and by appropriately lowering the viscosity of the composition to facilitate dispersion of inorganic particles within the composition, the uniformity of particles within the composition can be improved without performing an additional ball milling process, thereby improving mechanical properties such as tensile strength.

In addition, according to the method for manufacturing a polymer-based solid electrolyte according to the present invention, unlike conventional methods for manufacturing a polymer-based solid electrolyte (e.g., Korean Patent Publication No. 10-2000-0003090 and ACS Appl. Energy Mater. 2020, 3, 1, 1099-1110), a polymer-based solid electrolyte can be manufactured only by a simple drying process without impregnation of an electrolyte solution instead of impregnating an electrolyte solution after vacuum drying, thereby minimizing the loss of raw materials and increasing the reproducibility of the excellent performance of the electrolyte.

In addition, in the method for manufacturing a polymer-based solid electrolyte according to the present invention, if the drying step is performed by a thermal drying method instead of a vacuum drying method, a continuous process in a roll-to-roll manner is possible, thereby shortening the manufacturing time of the polymer-based solid electrolyte and improving productivity/mass production.

In addition, the polymer solid electrolyte manufactured according to the present invention can improve ionic conductivity and capacity retention rate (life retention rate) compared to the polymer solid electrolyte manufactured by a conventional manufacturing method.

Hereinafter, the present invention will be described in detail.

The polymer electrolyte composition of the present invention comprises: a polymer resin; a lithium salt; an electrolyte component including a carbonate-based compound and a nitrile-based compound; inorganic particles; and an organic solvent; wherein, based on 100 parts by weight of the total polymer electrolyte composition, the content of the polymer resin is 2.1 to 7.5 parts by weight, the content of the lithium salt is 2.1 to 7.5 parts by weight, the content of the inorganic particles is 0.1 to 5.1 parts by weight, and a molar ratio of nitrile groups (-C≡N) in the nitrile-based compound per 1 mol of carbonyl groups (-C(=O)-) in the carbonate-based compound in the electrolyte component is 0.38 to 2.30.

Polymer resin

The polymer resin included in the polymer electrolyte composition of the present invention is a component that forms the matrix of a polymer electrolyte membrane.

In one specific example, the polymer resin can perform a gelling function by forming a matrix of a polymer electrolyte membrane through partial cross-linking within the polymer resin during a drying step (preferably a drying step under normal pressure (atmospheric pressure)) during the production of a polymer-based solid electrolyte.

In addition, in one specific example, if the polymer resin contains an atom with high electronegativity (e.g., a nitrogen atom, an oxygen atom, or a sulfur atom) in the main chain or terminal of the polymer resin, it can bind to lithium ions and move lithium ions, which can help improve ion conductivity.

In one specific example, the polymer resin may be selected from the group consisting of polyacrylonitrile (PAN)-based polymers, polyimide-based polymers, polyalkylene oxide-based polymers, polyarylene oxide-based polymers, polysulfone-based polymers, siloxane-based polymers, polyacrylate-based polymers, or combinations thereof.

More specifically, the polyacrylonitrile-based polymer may be selected from the group consisting of polyacrylonitrile, poly(acrylonitrile-co-methylacrylate), poly(acrylonitrile-co-methylmethacrylate), or a combination thereof, the polyimide-based polymer may be selected from the group consisting of polyetherimide, polyimide, or a combination thereof, the polyalkylene oxide-based polymer may be selected from the group consisting of polyethylene oxide, polypropylene oxide, or a combination thereof, the polyarylene oxide-based polymer may be polyphenylene oxide, the polysulfone-based polymer may be selected from the group consisting of polyethersulfone, polysulfone, or a combination thereof, the siloxane-based polymer may be polysiloxane, and the polyacrylate-based polymer may be, but is not limited to, polymethylmethacrylate (PMMA).

The weight average molecular weight (Mw) of the above polymer resin is not particularly limited as long as it can form a matrix film, and specifically, the weight average molecular weight may be 5,000 to 600,000, more specifically, 10,000 to 400,000, and even more specifically, 100,000 to 300,000, but is not limited thereto. However, if the weight average molecular weight of the polymer resin is too lower than the above level, the physical properties of the solid electrolyte membrane may deteriorate.

The polymer electrolyte composition of the present invention contains the polymer resin in an amount of 2.1 to 7.5 parts by weight within a total of 100 parts by weight. If the polymer resin content within the total of 100 parts by weight of the polymer electrolyte composition is less than 2.1 parts by weight, a polymer electrolyte membrane may not be formed, and conversely, if it exceeds 7.5 parts by weight, the viscosity of the polymer electrolyte composition rapidly increases and the polymer resin partially does not dissolve, so that the properties of a polymer electrolyte membrane manufactured therefrom may not be uniform.

In one specific example, the content of the polymer resin in the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 2.1 parts by weight or more, 2.3 parts by weight or more, 2.5 parts by weight or more, 3.0 parts by weight or more, 3.5 parts by weight or more, or 4.0 parts by weight or more, and may also be 7.5 parts by weight or less, 7.3 parts by weight or less, 7.1 parts by weight or less, 7.0 parts by weight or less, 6.9 parts by weight or less, or 6.8 parts by weight or less.

More specifically, the content of the polymer resin within the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 2.5 to 7.1 parts by weight, more specifically 3.0 to 7.0 parts by weight, and even more specifically 4.0 to 6.8 parts by weight.

Lithium salt

The lithium salt included in the polymer electrolyte composition of the present invention plays a role in generating lithium ions, and any lithium salt commonly used in the art can be used without limitation.

In one specific example, the lithium salt may be selected from the group consisting of, but is not limited to, LiClO ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiBF ₄ , LiAsF ₆ , LiAlO ₄ , LiAlCl ₄ , LiBOB, _LiB (C ₂ O ₄ ) ₂ , LiN(C ₂ F ₅ SO 3 ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ or combinations thereof.

The polymer electrolyte composition of the present invention contains the lithium salt in an amount of 2.1 to 7.5 parts by weight within a total of 100 parts by weight. If the lithium salt content within the total of 100 parts by weight of the polymer electrolyte composition is less than 2.1 parts by weight, the polymer electrolyte membrane may not be formed and the desired level of ionic conductivity may not be achieved at room temperature. On the other hand, if it exceeds 7.5 parts by weight, the viscosity of the polymer electrolyte composition rapidly increases and the composition may harden before being coated on a substrate.

In one specific example, the lithium salt content in the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 2.1 parts by weight or more, 2.3 parts by weight or more, 2.5 parts by weight or more, 3.0 parts by weight or more, 3.5 parts by weight or more, or 4.0 parts by weight or more, and may also be 7.5 parts by weight or less, 7.3 parts by weight or less, 7.1 parts by weight or less, 7.0 parts by weight or less, 6.9 parts by weight or less, or 6.8 parts by weight or less.

More specifically, the lithium salt content within the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 2.5 to 7.1 parts by weight, even more specifically 3.0 to 7.0 parts by weight, and even more specifically 4.0 to 6.8 parts by weight.

Electrolyte components

The electrolyte component included in the polymer electrolyte composition of the present invention helps improve ion conductivity by dissolving a lithium salt in the polymer electrolyte composition and allowing 4 to 6 electrolyte component particles to bind around lithium ions to move lithium ions. In addition, the electrolyte component reduces the cohesion of the polymer resin in the polymer electrolyte composition and lowers the melt viscosity of the polymer electrolyte composition, thereby facilitating coating when coating the polymer electrolyte composition on a substrate.

In one specific embodiment, the electrolyte component may have a higher flash point and/or boiling point than conventional liquid electrolytes to ensure ignition stability. For example, the flash point of the electrolyte component may be 100°C or higher, and more specifically, 110°C or higher.

The electrolyte component included in the polymer electrolyte composition of the present invention includes a carbonate-based compound and a nitrile-based compound.

In one specific embodiment, the carbonate compound may be selected from the group consisting of, but not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinylene carbonate, vinylethylene carbonate, or combinations thereof.

In one specific example, the nitrile compound may be selected from the group consisting of, but is not limited to, succinonitrile (SN), glutaronitrile (GN), adiponitrile (AN) or a combination thereof.

The carbonyl group (-C(=O)-) included in the above carbonate compounds has a stable oxidation/reduction ability, and thus can realize insertion and removal of lithium ions during the oxidation and reduction processes, and can be reduced by accepting one lithium ion during discharge and generating a lithium coordination compound. Since the reduction reaction has a fast reaction rate, the carbonate compounds have high reversibility of electrochemical reactions. Accordingly, the carbonate compounds can combine with and move lithium ions, and then dissociate lithium ions, and by repeating the combination and dissociation with the lithium ions, they allow the lithium ions to move between the positive and negative electrodes.

In addition, the nitrile group (-C≡N) in the above nitrile compound has a high dielectric constant and can increase the oxidation potential of the electrolyte through interaction with lithium ions.

In the polymer electrolyte composition of the present invention, the molar ratio of the nitrile group (-C≡N) in the nitrile compound per 1 mol of the carbonyl group (-C(=O)-) in the carbonate compound in the electrolyte component is 0.38 to 2.30. If the molar ratio of the nitrile group (-C≡N) in the nitrile compound per 1 mol of the carbonyl group (-C(=O)-) in the carbonate compound is less than 0.38, the oxidation potential of the electrolyte may be lowered, and conversely, if it exceeds 2.30, the solubility of the polymer resin may be reduced.

In one specific example, the molar ratio of the nitrile group (-C≡N) in the nitrile compound per 1 mole of the carbonyl group (-C(=O)-) in the carbonate compound in the electrolyte component may be 0.38 or more, 0.39 or more, 0.40 or more, 0.45 or more, 0.50 or more, 0.55 or more, 0.56 or more, 0.60 or more, 0.65 or more, 0.70 or more, or 0.80 or more, and may also be 2.30 or less, 2.29 or less, 2.28 or less, 2.25 or less, 2.20 or less, 2.15 or less, 2.10 or less, 2.05 or less, 2.0 or less, 1.95 or less, or 1.92 or less.

More specifically, the molar ratio of the nitrile group (-C≡N) in the nitrile compound per 1 mol of the carbonyl group (-C(=O)-) in the carbonate compound in the electrolyte component may be 0.40 to 2.20, more specifically 0.60 to 2.0, and even more specifically 0.80 to 1.95.

The content of the electrolyte component within 100 parts by weight of the polymer electrolyte composition of the present invention may be, for example, 5 to 75 parts by weight. If the content of the electrolyte component within the polymer electrolyte composition is too low compared to the above level, the polymer resin may not be easily dissolved within the polymer electrolyte composition, and the ion conductivity of the polymer-based solid electrolyte manufactured using the same may be reduced. On the other hand, if the content is too high compared to the above level, the content of the polymer resin may be relatively reduced, making it difficult to form a polymer electrolyte membrane.

In one specific embodiment, the content of the electrolyte component within the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 5 parts by weight or more, 10 parts by weight or more, 13 parts by weight or more, 15 parts by weight or more, 18 parts by weight or more, 20 parts by weight or more, 23 parts by weight or more, 25 parts by weight or more, 28 parts by weight or more, or 30 parts by weight or more, and may also be 75 parts by weight or less, 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, 55 parts by weight or less, or 50 parts by weight or less.

More specifically, the content of the electrolyte component within the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 18 to 60 parts by weight, even more specifically 20.1 to 58.9 parts by weight, even more specifically 23 to 55 parts by weight, and even more specifically 28 to 50 parts by weight.

Weapon particles

The inorganic particles included in the polymer electrolyte composition of the present invention can assist in the dissociation and movement of lithium salts in a polymer-based solid electrolyte membrane, thereby further improving ion conductivity.

Any inorganic particle that can improve ion conductivity may be used without limitation, and for example, metal oxide particles may be used.

In one specific example, the metal oxide particles may be selected from the group consisting of SiO ₂ , TiO ₂ , Al ₂ O ₃ , BaTiO ₃ or a combination thereof, but are not limited thereto.

In one specific example, the average particle size of the inorganic particles may be 10 to 500 nm, more specifically 10 to 100 nm, and even more specifically 10 to 50 nm. If the average particle size of the inorganic particles is excessively smaller than the above level, the inorganic particles may exhibit severe agglomeration due to mutual attraction, making dispersion difficult. On the other hand, if the average particle size is excessively larger than the above level, the lithium ion transfer path may become longer, which may lower the ion conductivity.

The polymer electrolyte composition of the present invention contains the inorganic particles in an amount of 0.1 to 5.1 parts by weight within a total of 100 parts by weight. If the inorganic particle content within the total of 100 parts by weight of the polymer electrolyte composition is less than 0.1 parts by weight, the above-described effect due to the inorganic particles may not be obtained, and conversely, if it exceeds 5.1 parts by weight, the ion conductivity may decrease and formation of a polymer electrolyte membrane may be difficult.

In one specific embodiment, the content of the inorganic particles in the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.40 parts by weight or more, 0.5 parts by weight or more, or 1.0 parts by weight or more, and may also be 5.1 parts by weight or less, 5.0 parts by weight or less, 4.9 parts by weight or less, 4.8 parts by weight or less, 4.5 parts by weight or less, or 4.0 parts by weight or less.

More specifically, the content of the inorganic particles within 100 parts by weight of the polymer electrolyte composition of the present invention may be 0.3 to 5.0 parts by weight, and even more specifically, 0.5 to 4.8 parts by weight.

Organic solvent

The organic solvent included in the polymer electrolyte composition of the present invention is used as a process aid for improving the process in a method for producing a polymer-based solid electrolyte using the polymer electrolyte composition of the present invention, and is a volatile component that is easy to remove after the process.

As the organic solvent, a solvent having a lower boiling point and greater volatility than the electrolyte component described above can be preferably used.

In one specific embodiment, the organic solvent may be selected from the group consisting of, but is not limited to, dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), or a combination thereof.

Since the organic solvent is removed by volatilization during the manufacturing process of the polymer-based solid electrolyte described below, there is no particular limitation on its content in the polymer electrolyte composition, and a content that can provide the polymer electrolyte composition with a viscosity at a level that enables it to be smoothly coated on a substrate is sufficient.

In one specific example, the content of the organic solvent in the total 100 parts by weight of the polymer electrolyte composition of the present invention may be, for example, 5 to 75 parts by weight. If the content of the organic solvent in the polymer electrolyte composition is too low compared to the above level, the viscosity of the polymer electrolyte composition may become too high, making it difficult to coat the substrate, and conversely, if it is too high compared to the above level, the polymer electrolyte membrane may not be formed properly.

In one specific embodiment, the organic solvent content within the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 5 parts by weight or more, 10 parts by weight or more, 13 parts by weight or more, 15 parts by weight or more, 18 parts by weight or more, 20 parts by weight or more, 23 parts by weight or more, 25 parts by weight or more, 28 parts by weight or more, or 30 parts by weight or more, and may also be 75 parts by weight or less, 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, 55 parts by weight or less, or 50 parts by weight or less.

More specifically, the content of the organic solvent within the total 100 parts by weight of the polymer electrolyte composition of the present invention may be 10 to 75 parts by weight, even more specifically 20 to 74.5 parts by weight, and even more specifically 24.3 to 74.2 parts by weight.

The polymer electrolyte composition of the present invention may further include, in addition to the components described above, additional components commonly used in electrolyte compositions (more specifically, electrolyte compositions for lithium secondary batteries).

In one specific example, the polymer electrolyte composition of the present invention may be manufactured by a method including, but not limited to, a step of preparing a solution in which the above-described electrolyte component and the above-described lithium salt are dissolved in an organic solvent; a step of dissolving the above-described polymer resin in the solution; and a step of dispersing the above-described inorganic particles in the solution in which the above-described polymer resin is dissolved.

Polymer solid electrolyte and its manufacturing method

According to another aspect of the present invention, a method for producing a polymer-based solid electrolyte, and a polymer-based solid electrolyte produced by the method, are provided, comprising: (1) a step of coating a polymer electrolyte composition according to the present invention on a substrate; and (2) a step of drying the coated polymer electrolyte composition.

In one specific example, the coating method of step (1) may be used without limitation as long as it is a known method capable of uniformly coating the polymer electrolyte composition on a substrate, and examples thereof include, but are not limited to, casting or spin coating.

In one specific example, the type of the substrate in the coating step (1) is not particularly limited, and may be, for example, a support (e.g., inorganic fibers, organic fibers, or a combination thereof), a release film (e.g., a metal thin film such as a Teflon sheet, aluminum foil, or a combination thereof), or a combination thereof.

When a support is used as the substrate when manufacturing a polymer-based solid electrolyte using the polymer electrolyte composition of the present invention, the polymer-based solid electrolyte may include a support and a polymer-based solid electrolyte membrane formed from the polymer electrolyte composition of the present invention on the support.

In addition, when a release film is used as the substrate when manufacturing a polymer-based solid electrolyte using the polymer electrolyte composition of the present invention, the polymer electrolyte composition of the present invention is coated on the release film and dried to form a polymer-based solid electrolyte membrane, and then the polymer-based solid electrolyte membrane can be separated from the release film for use.

In addition, when a combination of a support and a release film is used as the substrate when manufacturing a polymer-based solid electrolyte using the polymer electrolyte composition of the present invention, a laminate in which the release film; support; and polymer-based solid electrolyte membrane are laminated in that order can be obtained, and at this time, the support; and polymer-based solid electrolyte membrane can be separated from the release film and used.

In one specific example, the coating step (1) may be performed at a temperature of 25° C. to 100° C., and more specifically, may be performed at a temperature of 30° C. to 80° C. If the temperature of the coating step (1) is too low compared to the above level, the polymer electrolyte membrane may harden at the start of coating, making it difficult to obtain a uniform membrane. On the other hand, if the temperature is too high compared to the above level, the organic solvent in the polymer electrolyte composition may volatilize, which may deteriorate the uniformity of the polymer electrolyte membrane.

In one specific example, the coating step (1) can be performed under normal pressure (atmospheric pressure).

In one specific example, the drying step (2) is performed to remove an organic solvent in the polymer solid electrolyte composition coated on the substrate, and, like a conventional drying process, may be performed under a vacuum pressure condition, or may be performed under a normal pressure (atmospheric pressure) or higher pressure condition, and preferably may be performed under a vacuum or normal pressure condition. If the pressure is too high during drying, the drying time may be prolonged, and thus the amount of raw material loss may increase, which may deteriorate the ion conductivity and life maintenance characteristics of the polymer-based solid electrolyte.

In one specific example, the pressure range of the drying step (2) may be more than 1 mmHg and less than 1,000 mmHg, and more specifically, may be 380 mmHg to 910 mmHg. When the pressure range of the drying step (2) is less than or equal to 1 mmHg or more than 1,000 mmHg, the amount of raw material loss of the polymer electrolyte composition during drying may increase, thereby deteriorating the ionic conductivity and lifespan characteristics of the polymer-based solid electrolyte.

When a polymer solid electrolyte is manufactured using the polymer electrolyte composition of the present invention, the time for the drying step (2) can be reduced to minimize the loss of raw materials, thereby increasing cost efficiency and improving the reproducibility of electrolyte performance.

According to one specific example, the temperature range of the drying step (2) may be a temperature that is lower than the boiling point of the electrolyte component and lower than the boiling point of the organic solvent. Specifically, the drying step may be performed at a temperature range of 30° C. to 150° C., more specifically, 40° C. to 100° C.

If the temperature of the drying step (2) above is higher than the boiling point of the organic solvent, the organic solvent volatilizes and evaporates, and components combined with the organic solvent (e.g., electrolyte components, etc.) are also removed, which may result in increased loss of raw materials. Furthermore, if the temperature of the drying step (2) above is higher than the boiling point of the electrolyte component, loss due to evaporation of the electrolyte component may occur.

In addition, (2) when the temperature of the drying step is below room temperature, it is not easy to remove the organic solvent used as a process aid, making it difficult to form a polymer solid electrolyte film of the desired composition, and the drying time may be long, which may reduce mass production/productivity.

According to one specific example, the drying time of the drying step (2) may be variously selected depending on the temperature and pressure conditions. For example, the drying time may be 5 minutes to 120 minutes, specifically 5 minutes to 90 minutes, and more specifically 5 minutes to 60 minutes. Depending on the drying temperature and pressure conditions, if the drying time is too short, the removal of the organic solvent may not be sufficient, which may affect the properties of the polymer-based solid electrolyte, and conversely, if the drying time is too long, the amount of raw material loss may increase accordingly, which may deteriorate the ionic conductivity and life maintenance characteristics of the polymer-based solid electrolyte.

Lithium secondary battery

According to another aspect of the present invention, a lithium secondary battery is provided including a polymer solid electrolyte manufactured by the polymer solid electrolyte manufacturing method of the present invention described above.

The lithium secondary battery of the present invention is characterized by including a polymer-based solid electrolyte manufactured by the method for manufacturing a polymer-based solid electrolyte of the present invention, and other lithium secondary battery components, such as a positive electrode and a negative electrode, may include, without limitation, those commonly used for lithium secondary batteries.

In one specific embodiment, the lithium secondary battery of the present invention includes a positive electrode; a negative electrode; and the polymer-based solid electrolyte between the positive electrode and the negative electrode.

In one specific example, the negative electrode (anode) may include lithium metal or a lithium alloy (e.g., an alloy of Li with Si, Sn, In, etc.), and the positive electrode (cathode) may be a porous current collector supporting a composite metal oxide catalyst.

As the above negative electrode material, a material capable of doping or dedoping lithium ions may be used, and specific examples thereof include, but are not limited to, carbon compounds such as graphite, pyrolytic carbons, cokes, glassy carbons, sintered bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, and activated carbon.

The above positive electrode may include a composite metal oxide (e.g., metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNiCoO ₂ , manganese dioxide, vanadium pentoxide, and chromium oxide, or metal sulfides such as titanium disulfide and molybdenum disulfide), and a conductive agent (e.g., flake-shaped graphite, carbon black, acetylene black, etc.) or a binder (e.g., polyvinylidene fluoride, polytetrafluoroethylene, etc.) may be used as needed, and the material of the porous current collector supporting the composite metal oxide may be, but is not limited to, aluminum, nickel, iron, titanium, etc.

The lithium secondary battery of the present invention may include a separator made of a porous film or non-woven material such as polyethylene or polypropylene between the negative electrode and the positive electrode, but the polymer solid electrolyte of the present invention can replace such a separator.

Therefore, according to a preferred specific embodiment, the lithium secondary battery of the present invention may not include a separator between the negative electrode and the positive electrode, and the omission of the separator can simplify the configuration and manufacturing process of the lithium secondary battery.

As a case for the lithium secondary battery of the present invention, a case of a conventional shape such as a coin shape, a flat plate shape, a cylindrical shape, or a laminate shape can be applied.

Hereinafter, the present invention will be described in more detail through examples and comparative examples. However, the scope of the present invention is not limited thereto.

[Example]

<Preparation of polymer electrolyte composition>

Example A1

24.6 parts by weight of ethylene carbonate (EC) was added to a round-bottom flask, 4.6 parts by weight of LiPF ₆ and 48.9 parts by weight of dimethyl formamide (DMF) were added thereto, the temperature was raised to 60°C, and the mixture was stirred for 30 minutes so that the LiPF ₆ was dissolved in the solvent. Next, 4.6 parts by weight of polyacrylonitrile (PAN) resin was added to the round-bottom flask, the temperature was raised to 120°C, and the mixture was stirred for about 2 hours until the solution became transparent so that the PAN resin was dissolved in the solvent. 15.1 parts by weight of glutaronitrile (GN) was added to the transparent electrolyte mixture solution, and the mixture was stirred at 120°C for about 1 hour. 2.2 parts by weight of Al ₂ O ₃ was added to the above mixture solution, stirred at 700 rpm for 1 hour to evenly disperse Al ₂ O ₃ in the electrolyte mixture solution, and a polymer electrolyte composition was prepared. At this time, the total content of the electrolyte component (mixture of EC and GN), lithium salt (LiPF ₆ ), polymer resin (PAN resin), inorganic particles (Al ₂ O ₃ ), and organic solvent (DMF) was 100 parts by weight, and the molar ratio of nitrile groups in glutaminyl per 1 mol of carbonyl groups in ethylene carbonate (molar ratio of nitrile groups / carbonyl groups) was 1.14.

Examples A2 to A18 and Comparative Examples A1 to A11

Polymer electrolyte compositions of Examples A2 to A18 and Comparative Examples A1 to A11 were prepared by the same method as Example A1, except that the components and contents of the polymer electrolyte compositions were changed as described in Table 1 below.

[Raw material components used in the manufacture of polymer electrolyte composition]

- PAN 150K: Polyacrylonitrile with a weight average molecular weight of 150,000

- PAN 230K: Polyacrylonitrile with a weight average molecular weight of 230,000

- PEO: Polyethylene oxide with a weight average molecular weight of 600,000

- PPS: Polyphenylene sulfide with a weight average molecular weight of 100,000

- EC: Ethylene carbonate

- PC: Propylene carbonate

- GN: Glutaronitrile

- AN: Adiponitrile

- DMF: Dimethylformamide

- DMAc: Dimethylacetamide

[Table 1]

[Table 1]

The physical properties of the polymer electrolyte compositions manufactured in Examples A1 to A18 and Comparative Examples A1 to A11 were measured by the following methods, and the results are shown in Table 2 below.

<Method of Measuring Physical Properties>

(1) Viscosity

The viscosity of the polymer electrolyte compositions manufactured in each example and comparative example was measured using a Brookfield viscometer (DV2TL VCJ0). At this time, 500 μL was collected as a sample from the polymer electrolyte compositions manufactured in each example and comparative example, and the viscosity measurement temperature was 25°C.

(2) Particle uniformity

A drop of a sample collected from the polymer electrolyte composition manufactured in each example and comparative example was dropped on a glass plate and observed through an optical microscope, and the maximum size of the particles was measured to select uniformity by size according to the following criteria.

A: When the maximum particle size is less than 50 nm (excellent)

B: When the maximum particle size is greater than 50 nm and less than 1 μm (good)

C: When the maximum particle size is 1㎛ or more and less than 2㎛ (normal)

D: When the maximum particle size is 2㎛ or more (poor)

[Table 2]

[Table 2]

As shown in Table 2 above, in the case of the polymer electrolyte compositions of Examples A1 to A18 according to the present invention, the viscosity of the polymer electrolyte composition was appropriate enough to facilitate casting, and the inorganic particles were uniformly dispersed, so that the particle uniformity was excellent.

On the other hand, in the case of polymer electrolyte compositions in which lithium salt was used in excess (Comparative Example A1) or polymer resin was used in excess (Comparative Example A3), the viscosity of the composition was high, making it difficult to coat the substrate, and the uniformity of the inorganic particles was poor. In the case of polymer electrolyte compositions in which lithium salt was used in small amounts (Comparative Example A2) or polymer resin was used in small amounts (Comparative Example A4), the viscosity of the composition was too low, making it difficult to coat the substrate, and thus making it difficult to form a polymer-based solid electrolyte membrane. In addition, in the case of polymer electrolyte compositions in which inorganic particles were not used (Comparative Example A5), the viscosity was too low, making it difficult to coat the substrate, and thus making it difficult to form a polymer-based solid electrolyte membrane. In the case of polymer electrolyte compositions in which inorganic particles were used in excess (Comparative Example A6), the inorganic particles in the composition were not uniformly dispersed, and thus the uniformity of the inorganic particles was very poor. In addition, in the case of polymer electrolyte compositions in which no organic solvent was used (Comparative Example A9) or in which a small amount of organic solvent was used (Comparative Example A10), the viscosity was very high, making it difficult to coat the substrate, and the uniformity of the inorganic particles was very poor. In the case of polymer electrolyte compositions in which an excessive amount of organic solvent was used (Comparative Example A11), the viscosity was too low, making it difficult to coat the substrate, and thus making it difficult to form a polymer-based solid electrolyte membrane.

In particular, in the case of the polymer electrolyte compositions of Comparative Examples A1, A3, and A9, the viscosity of the compositions was too high, making it difficult to coat the substrate during the manufacture of the polymer-based solid electrolyte described later, making it difficult to form the polymer-based solid electrolyte; in the case of the polymer electrolyte composition of Comparative Example A6, the uniformity of the inorganic particles was very poor, making it difficult to uniformly coat the substrate during the manufacture of the polymer-based solid electrolyte, making it difficult to form the polymer-based solid electrolyte; and in the case of the polymer electrolyte composition of Comparative Example A11, the viscosity of the composition was too low, making it flow down when coated on the substrate during the manufacture of the polymer-based solid electrolyte, making it difficult to form the polymer-based solid electrolyte.

<Manufacture of polymer-based solid electrolyte>

Example B1

The polymer electrolyte composition obtained in Example A1 was cast with a uniform thickness on a substrate (aluminum foil) preheated to 40°C using a doctor blade, and then the polymer electrolyte composition was dried for 30 minutes under conditions of a pressure of 760 mmHg and a temperature of 60°C to remove dimethylformamide (DMF), thereby producing a polymer-based solid electrolyte.

Examples B2 to B18 and Comparative Examples B1 to B6

Polymer solid electrolytes of Examples B2 to B18 and Comparative Examples B1 to B6 were manufactured by performing the same method as in Example B1, except that the type of polymer electrolyte composition and the conditions of the drying step were changed as described in Table 3 below.

[Table 3]

[Table 3]

<Manufacturing of lithium secondary batteries>

Manufacturing of the anode

A positive electrode mixture composition was prepared by adding 40 parts by weight of a positive electrode active material to 100 parts by weight of N-methyl-2-pyrrolidone (NMP), a solvent. The positive electrode mixture composition was then applied to a positive electrode current collector (aluminum thin film) having a thickness of 100 μm, dried, and roll pressed to prepare a positive electrode. At this time, the positive electrode mixture was prepared by mixing a positive electrode active material (lithium nickel/cobalt/aluminum (NCA)), a conductive material (carbon black), and a binder (polyvinylidene fluoride (PVDF)) in a weight ratio of 94:3:3.

Manufacturing of cathode

A negative electrode mixture composition was prepared by adding 90 parts by weight of a negative electrode agent to 100 parts by weight of a solvent, N-methyl-2-pyrrolidone (NMP). The negative electrode mixture composition was then applied to a negative electrode current collector (copper film) having a thickness of 90 μm, dried, and roll pressed to prepare a negative electrode. At this time, the negative electrode mixture was prepared by mixing natural graphite, a conductive agent (carbon black), a thickener (carboxymethyl cellulose), and a binder (PVDF) in a weight ratio of 96:1:1:2.

Manufacturing of lithium secondary batteries

A lithium secondary battery was manufactured by laminating the positive and negative electrodes manufactured by the above-described method together with the polymer-based solid electrolytes obtained in Examples B1 to B18 and Comparative Examples B1 to B6. The physical properties of the polymer-based solid electrolytes manufactured in Examples B1 to B18 and Comparative Examples B1 to B6 were measured by the following methods, and the results are shown in Table 4 below.

<Method of Measuring Physical Properties>

(1) Ionic conductivity

In the examples and comparative examples, the polymer solid electrolytes manufactured were punched to a size of Ø19, as in the coin cell battery manufacturing process, and then assembled in the order of Sus/polymer solid electrolyte/Sus and mounted in a coin cell, and the bulk resistance was measured using an impedance meter (VSP-240). At this time, the bulk resistance was measured by applying the same measurement frequency of 0.1 to 1 MHz. The ionic conductivity value was calculated from the measured bulk resistance using Equation 1 below. The Sus is an abbreviation for Stainless Use Steel, a term used to indicate the specifications of stainless steel, and the size of the Sus is Ø.

[Formula 1]

Here, σ represents the ionic conductivity (S/cm), d is the thickness of the polymer-based solid electrolyte (cm), Rb is the bulk resistance (ohm), and S represents the area of the polymer-based solid electrolyte (cm ² ).

(2) Room temperature life maintenance evaluation (Discharge Capacity)

The room temperature life maintenance evaluation was performed on the lithium secondary batteries manufactured in the examples and comparative examples. Specifically, the manufactured lithium secondary batteries were charged in constant current-constant voltage mode at room temperature (25°C) until the voltage reached 4.2 V at 500 mAh, and charging was completed when the charge capacity dropped to 50 mAh. Ten minutes after the completion of charging, discharge was performed in constant current mode until the voltage reached 3.0 V at 500 mAh. One charge and one discharge were defined as one cycle, and the maintenance rate (life maintenance rate) compared to the initial charge capacity at room temperature was measured while performing 100 cycles of the charge and discharge.

[Table 4]

[Table 4]

As shown in Table 4 above, in the case of the polymer-based solid electrolytes of Examples B1 to B18 manufactured using the polymer electrolyte composition according to the present invention, it was confirmed that the polymer-based solid electrolyte membrane was easily formed, and the ion conductivity was 1.0 x 10 ^-3 S/cm or higher, while the initial charge capacity retention rate was significantly improved to 88% or higher after 100 charge/discharge cycles.

On the other hand, in the case of comparative compositions, it can be confirmed that the viscosity is lowered to a level that makes casting difficult, or conversely, the viscosity is higher and the uniformity level of the inorganic particles is lowered. In addition, even if the viscosity and the uniformity level of the inorganic particles are appropriate, it can be confirmed that the ion conductivity is lowered to less than 1.0 x 10 ^-3 S/cm after the formation of the polymer solid electrolyte film, or the capacity retention rate (life retention rate) is significantly reduced.

Claims (12)

As a polymer electrolyte composition,
polymer resin;
lithium salt;
An electrolyte component comprising a carbonate compound and a nitrile compound;
inorganic particles; and
organic solvents;
Here, based on 100 parts by weight of the total polymer electrolyte composition,
The content of the polymer resin is 2.1 to 7.5 parts by weight,
The content of the above lithium salt is 2.1 to 7.5 parts by weight,
The content of the above inorganic particles is 0.1 to 5.1 parts by weight,
The content of the above electrolyte component is 18 to 60 parts by weight,
The molar ratio of the nitrile group (-C≡N) in the nitrile compound per 1 mol of the carbonyl group (-C(=O)-) in the carbonate compound in the electrolyte component is 0.38 to 2.30.
Polymer electrolyte composition. A polymer electrolyte composition in claim 1, wherein the polymer resin is selected from the group consisting of polyacrylonitrile (PAN)-based polymers, polyimide-based polymers, polyalkylene oxide-based polymers, polyarylene oxide-based polymers, polysulfone-based polymers, siloxane-based polymers, polyacrylate-based polymers, or combinations thereof. In the second paragraph,
The above polyacrylonitrile polymer is selected from the group consisting of polyacrylonitrile, poly(acrylonitrile-co-methylacrylate), poly(acrylonitrile-co-methylmethacrylate), or a combination thereof,
The above polyimide polymer is selected from the group consisting of polyetherimide, polyimide, or a combination thereof,
The above polyalkylene oxide polymer is selected from the group consisting of polyethylene oxide, polypropylene oxide or a combination thereof,
The above polyarylene oxide polymer is polyphenylene oxide,
The above polysulfone polymer is selected from the group consisting of polyethersulfone, polysulfone, or a combination thereof,
The above siloxane polymer is polysiloxane,
The above polyacrylate polymer is polymethyl methacrylate.
Polymer electrolyte composition. A polymer electrolyte composition in claim 1, wherein the lithium salt is selected from the group consisting of LiClO ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiBF ₄ , LiAsF ₆ , LiAlO ₄ , LiAlCl ₄ , LiBOB, LiB(C ₂ O ₄ ) ₂ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ or a combination thereof. In the first paragraph,
The above carbonate compound is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate or a combination thereof,
The above nitrile compound is selected from the group consisting of succinonitrile, glutaronitrile, adiponitrile or a combination thereof.
Polymer electrolyte composition. A polymer electrolyte composition in claim 1, wherein the inorganic particles are metal oxide particles. A polymer electrolyte composition in claim 6, wherein the metal oxide particles are selected from the group consisting of SiO ₂ , TiO ₂ , Al ₂ O ₃ , BaTiO ₃ or a combination thereof. A polymer electrolyte composition in claim 1, wherein the organic solvent is a volatile solvent having a lower boiling point than the electrolyte component. A polymer electrolyte composition in claim 8, wherein the organic solvent is selected from the group consisting of dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, or a combination thereof. (1) a step of coating a polymer electrolyte composition according to any one of claims 1 to 9 on a substrate; and
(2) a step of drying the coated polymer electrolyte composition; comprising;
Method for producing a polymer-based solid electrolyte. A polymer solid electrolyte manufactured by the method according to Article 10. A lithium secondary battery comprising a polymer solid electrolyte according to claim 11.