KR102663579B1 - Doping method of polymer for solid electrolyte - Google Patents

Abstract

The present invention relates to a method for doping polymers for solid electrolytes using a ball milling method. Specifically, the method consists of ball milling a mixture of polymer and dopant, and washing and drying the ball milled mixture to obtain a polymer doped with a dopant.

Description

Doping method of polymer for solid electrolyte {DOPING METHOD OF POLYMER FOR SOLID ELECTROLYTE}

The present invention relates to a method of doping a polymer for a solid electrolyte, and more specifically, to a method of doping a polymer for a solid electrolyte using a ball milling method.

Various batteries that can overcome the limitations of current lithium secondary batteries are being researched in terms of battery capacity, safety, output, larger size, and ultra-miniaturization.

Representative examples include a metal-air battery with a very large theoretical capacity compared to lithium secondary batteries, an all-solid-state battery with no risk of explosion in terms of safety, and a super capacitor in terms of output. Continuous research is being conducted in academia and industry on supercapacitors, NaS batteries or RFBs (redox flow batteries) in terms of large size, and thin film batteries in terms of miniaturization.

An all-solid-state battery refers to a battery in which the liquid electrolyte used in existing lithium secondary batteries has been replaced with a solid one. Since flammable solvents are not used in the battery, ignition or explosion due to the decomposition reaction of the conventional electrolyte solution does not occur at all, thereby ensuring safety. It can be greatly improved. In addition, since Li metal or Li alloy can be used as the cathode material, there is an advantage in dramatically improving the energy density relative to the mass and volume of the battery.

In an all-solid-state battery, the electrolyte is in a solid phase rather than a liquid phase, so the interface where the electrode and the solid electrolyte contact is very important. In other words, if a problem occurs at the interface or the amount of contact at the interface is insufficient, the characteristics of the battery are greatly reduced, so its control is important. All _- solid-state batteries _{use solid electrolytes such as polymer solid electrolytes such as polystyrene-polyethylene oxide block copolymers, crystalline solid electrolytes such as LLT (Li 0.35 La 0.55} TiO ₃ ) _, and silica _- based amorphous solid electrolytes, thio- There are sulfide-based solid electrolytes such as LISICON.

The solid electrolyte material of the all-solid-state battery itself often has difficulty satisfying the physical properties required for the all-solid-state battery, and to supplement this, a material with functionality can be added to the solid electrolyte material. In this regard, the physical properties of the polymer solid electrolyte can be improved by doping with a functional dopant. However, due to the nature of the polymer, the functional dopant cannot be uniformly and easily doped in the polymer solid electrolyte by simply mixing the functional dopant and the polymer solid electrolyte. . In this situation, in order to uniformly dope the functional dopant into the polymer solid electrolyte, doping was conventionally performed under high temperature conditions. However, in order for doping to proceed under high temperature conditions, a separate heat source is needed in the device, and energy must be continuously supplied to this heat source to maintain the inside of the device at a high temperature during the doping time. In particular, polymers, which are the material of solid electrolytes, have the possibility of being deformed by heat, so the properties of existing materials may not be maintained as is. In this respect, improved doping methods are still required in the field of technology.

Shizuo Tokito. Et al., Electrical Conductivity and Optical Properties of Poly(p-phenylene sulfide) Doped with Some Organic Acceptor, Polymer Journal, Vol. 17, No. 8, pp 959-968 (1985)

In order to solve the above problems, the present invention seeks to provide a doping method for a polymer for a solid electrolyte that can dope a polymer for a solid electrolyte with a functional dopant using only a ball milling method without increasing the temperature.

According to the first aspect of the present invention,

The present invention includes the steps of ball milling a mixture of polymer and dopant; and

A method for doping a polymer for a solid electrolyte is provided, which consists of washing and drying the ball milled mixture to obtain a polymer doped with a dopant.

In one embodiment of the present invention, the polymer is selected from the group consisting of polyphenylene sulfide, polyphenylene oxide, polyether ketone, polysulfone, polyvinylidene fluoride, and combinations thereof.

In one embodiment of the present invention, the dopant is selected from the group consisting of tetra-cyanoethylene, dicyanodichlorobenzoquinone, chloranyl, and combinations thereof.

In one embodiment of the present invention, the weight ratio of polymer and dopant in the mixture is 1:1 to 3:1.

In one embodiment of the present invention, the ball milling is performed using balls with a particle diameter of 5 to 20 mm, and the weight ratio of the balls to the mixture is 10:1 to 30:1.

In one embodiment of the present invention, the ball milling is performed for 10 to 30 hours at a rotation speed of 300 to 700 rpm.

In one embodiment of the present invention, the ball milling is performed under temperature conditions of 20 to 50°C.

According to the second aspect of the present invention,

The present invention provides a solid electrolyte for a lithium secondary battery containing a polymer doped with a dopant prepared by the polymer doping method described above.

According to the third aspect of the present invention,

The present invention provides a lithium secondary battery containing the above-described solid electrolyte.

The method of doping a polymer for a solid electrolyte according to the present invention can introduce a dopant into the polymer simply by ball milling without particularly increasing the temperature at room temperature, thereby minimizing deformation of the polymer that may occur during doping. In addition, using the above method, doping is possible without heating, which simplifies the doping process and increases energy efficiency. In addition, since the doped dopant has a similar level of uniformity compared to the conventional doping method by heating, it can be directly applied as a solid electrolyte for an all-solid-state battery.

Figure 1 is a graph showing the results of FT-IR analysis for each sample before and after doping according to Example 1 and Comparative Example 1.
Figure 2 is a photographic image of polyphenylene sulfide according to Example 1 and Comparative Example 2.

The embodiments provided according to the present invention can all be achieved by the following description. It should be understood that the following description describes preferred embodiments of the present invention, and that the present invention is not necessarily limited thereto.

Doping Methods for Polymers

The present invention provides a method for doping a polymer for a solid electrolyte, comprising the steps of ball milling a mixture of a polymer and a dopant and washing and drying the ball milled mixture to obtain a polymer doped with a dopant. Since the polymer is substantially doped with a dopant by the ball milling step in the above method, the present invention does not include steps for doping other than the ball milling step. Below, the two steps that constitute the polymer doping method according to the present invention will be described in detail.

To dope a polymer with a dopant, the polymer and the dopant are first put into a ball milling device. Here, the ball milling device can be used without particular restrictions as long as it is commonly used in the relevant technical field. However, in the ball milling device, the balls are made of zirconia (ZrO ₂ ) having a particle diameter of 5 to 20 mm, preferably 10 to 15 mm. It may be desirable to use a ball. Additionally, the weight ratio of the ball and the mixture may preferably be 10:1 to 30:1, preferably 20:1 to 30:1. When zirconia balls of the above-described particle size range are used and the weight ratio of the balls and the mixture is adjusted within the above-described range, ball milling can have functionality for crushing, mixing, and doping within an appropriate range. The polymer may be selected without particular limitation, but considering the usability of the present invention, a polymer that can be used as a solid electrolyte in an all-solid-state battery may be preferable. In the all-solid-state battery, the solid electrolyte is required to have ionic conductivity above a certain level due to the characteristics of the battery, and this requirement is satisfied by doping the polymer with a dopant. According to an embodiment of the present invention, the polymer is polyphenylene sulfide, polyphenylene oxide, polyetherketone, polysulfone, polyvinylidene fluoride. ) and combinations thereof, and is preferably polyphenylene sulfide. Additionally, the dopant acts to release ions for ion transport and mobility, and it may be useful to use an electron acceptor or oxidizing agent. According to an embodiment of the present invention, the dopant may be selected from the group consisting of tetra-cyanoethylene, dicyanodichlorobenzoquinone, chloranil, and combinations thereof, and is preferably It may be chloranil.

According to an embodiment of the present invention, it may be desirable to add the polymer and the dopant at a weight ratio of 1:1 to 3:1, preferably 1.5:1 to 2.5:1. Since the doping method according to the present invention has a lower probability of dopant being doped into the polymer compared to the doping method using heating, the content of dopant compared to the polymer may be relatively high compared to the doping method using heating. However, the dopant can be recovered and recycled later through washing. If the weight ratio of the polymer to the dopant is less than 1, even if the ratio of the dopant added exceeds the content that the polymer can accommodate, the amount of dopant doped into the polymer increases slightly, and the weight ratio of the polymer to the dopant is 3. If it is excessive, the amount of dopant doped into the polymer may be significantly reduced.

In the ball milling step, rotational speed may be an important factor in determining mixing, doping, or crushing of polymers and dopants. Mixing is the process that can occur most easily, but in comparison, doping is a process that requires a greater force than mixing to be applied to the polymer and dopant. However, if an infinitely large force is applied to the polymer and dopant, the polymer and dopant may be broken, so the force must be adjusted within an appropriate range. The rotation speed can determine the force applied to the polymer and dopant. According to an embodiment of the present invention, the ball milling step may be performed at a rotation speed of 300 to 700 rpm, preferably 400 to 600 rpm. When the rotation speed is less than 300 rpm, the polymer and dopant are simply mixed and the amount of dopant doped into the polymer is not large. On the other hand, when the rotation speed exceeds 700 rpm, the amount of dopant doped into the polymer may increase, but the polymer and dopant may be broken. The time for performing the ball milling must be sufficiently secured so that the dopant can be evenly doped throughout the added polymer. According to an embodiment of the present invention, the ball milling step may be performed for 10 to 30 hours, preferably 15 to 25 hours. If the ball milling time is less than 10 hours, the amount of dopant doped into the polymer is small or it is difficult to dope the dopant evenly throughout the added polymer. Additionally, if the time for performing ball milling exceeds 30 hours, it is difficult to expect an increase in the doping effect over time.

Ball milling according to the present invention can be performed under temperature conditions of 20 to 50°C. According to the method according to the present invention, since the dopant can be doped into the polymer even at room temperature, deformation of the polymer structure can be minimized during the doping process, and by using a ball milling device that can be used for mixing without a separate heating device. You can simply dope with a dopant.

The polymer doped with a dopant by the ball milling step described above can be separated from the undoped dopant through washing. The solvent used for cleaning is not particularly limited as long as it is commonly used in the relevant technical field, but a solvent with a higher affinity for the dopant than the polymer and a low boiling point may be used. According to an embodiment of the present invention, the solvent may preferably be acetone. The dopant separated with acetone by washing can be dried and recycled. Additionally, after washing, the dopant-doped polymer can be dried at a temperature of 60 to 80°C to remove the cleaning solvent that may be present on the surface. After drying, a final dopant-doped polymer can be obtained.

Solid electrolyte and containing it All solid battery

The dopant-doped polymer obtained by the above-described method can be used as a material for a solid electrolyte. In an all-solid-state battery, the solid electrolyte is interposed between the anode and the cathode, and the method of introducing the solid electrolyte into the all-solid-state battery is a method known in the art. Below, the solid electrolyte, anode, and cathode in the all-solid-state battery will be described in detail.

The negative electrode of the all-solid-state battery uses lithium metal alone or lithium metal laminated on a negative electrode current collector. More specifically, the negative electrode active material may be lithium metal or lithium alloy. The lithium alloy may be an alloy made of lithium and at least one metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn. In addition, the negative electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the all-solid-state battery. For example, it may be used on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. Like the positive electrode current collector, the negative electrode current collector may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics with fine irregularities formed on the surface.

The positive electrode of the all-solid-state battery is not particularly limited and may be any material used in known all-solid-state batteries. If the electrode is a positive electrode, it is a positive electrode current collector, and if the electrode is a negative electrode, it is a negative electrode current collector. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon or nickel on the surface of aluminum or stainless steel. , titanium, silver, etc. can be used.

The _positive electrode active material may vary depending on the _use of _the all _- solid- _state battery, LiNi _{0.8- x Co 0.2} AlxO ₂ , _{LiCo x} Mn _{y O 2} , _LiNi Lithium transition metal oxides such as Mn _z O ₂ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ and Li ₄ Ti ₅ O ₁₂ ; Chalcogenides such as Cu ₂ Mo ₆ S ₈ , FeS, CoS and MiS, and oxides, sulfides or halides such as scandium, ruthenium, titanium, vanadium, molybdenum, chromium, manganese, iron, cobalt, nickel, copper and zinc. It may be used, and more specifically, TiS ₂ , ZrS ₂ , RuO ₂ , Co ₃ O ₄ , Mo ₆ S ₈ , V ₂ O ₅ , etc. may be used, but it is not limited thereto.

The shape of the positive electrode active material is not particularly limited, and may be particle-shaped, for example, spherical, oval, or rectangular parallelepiped. The average particle diameter of the positive electrode active material may be in the range of 1 to 50 ㎛, but is not limited thereto. The average particle diameter of the positive electrode active material can be obtained, for example, by measuring the particle diameter of the active material observed using a scanning electron microscope and calculating the average value.

The binder included in the positive electrode is not particularly limited, and fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) may be used. The content of the binder is not particularly limited as long as it can fix the positive electrode active material, and may be in the range of 0 to 10% by weight based on the entire positive electrode.

The anode may additionally contain a conductive material. The conductive material is not particularly limited as long as it can improve the conductivity of the anode, and examples include nickel powder, cobalt oxide, titanium oxide, and carbon. Carbon may include any one selected from the group consisting of Ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene, or one or more types thereof. The content of the conductive material may be selected in consideration of other battery conditions, such as the type of conductive material, and may be, for example, in the range of 1 to 10% by weight based on the entire positive electrode.

As a material for the solid electrolyte, a dopant obtained by the above-described method is used as a doped polymer, and the solid electrolyte is applied to the anode in the form of a pellet or film. The solid electrolyte may further include an electrolyte salt, and the electrolyte salt may be a lithium salt. The lithium salt serves as a source of lithium ions and enables basic lithium battery operation. Any lithium salt commonly used in lithium batteries can be used, but preferably LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC(CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, It may include one selected from lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate, imide, and combinations thereof, but more preferably LiFSI (Lithium bis() represented by (FSO ₂ ) ₂ NLi. fluorosulfonyl)imide) is possible.

The present invention provides a method for simply doping a dopant into a polymer without separate heating, and the dopant-doped polymer produced by the above method can be used as a material for a solid electrolyte. When doping a dopant using the method of the present invention, the dopant can be doped uniformly within the polymer and doping is possible at room temperature, thereby minimizing deformation of the polymer, so when applying the polymer to a solid electrolyte, it is possible to use the conventional method. Compared to , equivalent or better battery performance can be expected.

Hereinafter, preferred examples are presented to aid understanding of the present invention, but the following examples are provided to facilitate understanding of the present invention and do not limit the present invention thereto.

Example

Example One

2 g of polyphenylene sulfide (manufactured by Sigma Aldrich) and 1 g of chloranil (manufactured by Sigma Aldrich) were added to a ball milling device (FRITSCH, Planetary ball mill). The ball milling device includes a total of 60 g of ZrO ₂ balls with a particle diameter of 10 mm. The ball milling device containing polyphenylene sulfide and chloranil was operated at room temperature at a rotation speed of 500 rpm for 20 hours. The material inside the ball milling device was washed with acetone to remove residual chloranyl, and then dried at 80°C to obtain 2 g of polyphenylene sulfide doped with chloranyl.

Example 2

The experiment was conducted in the same manner as Example 1, except that a total of 90 g of ZrO ₂ balls were used in the ball milling device.

Comparative example One

Polyphenylene sulfide (manufactured by Sigma Aldrich) was compressed at a temperature of 300°C to prepare a polyphenylene sulfide film (width: 1 cm, length: 3 cm, thickness: 200 μm, weight: 0.1 to 0.2 g). After placing the polyphenylene sulfide film and 1 g of chloranil in an autoclave device (high pressure reactor), the autoclave device was operated at a temperature of 200° C. for 1 hour in an air atmosphere. The material inside the autoclave was washed with acetone to remove residual chloranyl, and then dried at 80°C to obtain polyphenylene sulfide doped with chloranyl.

Comparative example 2

The experiment was conducted in the same manner as Example 1, except that the ball milling device was operated at a rotation speed of 100 rpm.

Experiment example

Experiment example 1: FT-IR analysis

The chloranyl-doped polyphenylene sulfide prepared in Examples and Comparative Examples was subjected to FT-IR analysis (Agilent), and the results are shown in Figure 1. According to Figure 1, the polyphenylene sulfide doped according to Examples 1 and 2 and the polyphenylene sulfide doped according to Comparative Example 1 showed similar FT-IR analysis peaks, and accordingly, the ball of Example 1 It was confirmed that polyphenylene sulfide can be doped with chloranyl through the milling method. On the other hand, the peak for chloranyl could not be confirmed in the polyphenylene sulfide doped according to Comparative Example 2, which means that chloranyl could not be sufficiently doped using the method of Comparative Example 2.

Experiment example 2

Polyphenylene sulfide according to Example 1 and Comparative Example 2 was photographed, and the image is shown in FIG. 2. According to Figure 2, in the case of Comparative Example 2, white polyphenylene sulfide and yellow chloranyl were simply mixed, resulting in a light yellow color. However, in Example 1, chloranyl was completely doped to form a charge transfer complex. It was confirmed that black color appears because it forms a charge transfer complex.

All simple modifications or changes of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims (9)

Ball milling the mixture of polymer and dopant; and
It consists of washing and drying the ball milled mixture to obtain a polymer doped with a dopant,
The polymer is selected from the group consisting of polyphenylene sulfide, polyphenylene oxide, polyether ketone, polysulfone, polyvinylidene fluoride, and combinations thereof,
The dopant is selected from the group consisting of tetra-cyanoethylene, dicyanodichlorobenzoquinone, chloranyl, and combinations thereof,
The ball milling is performed using balls with a particle diameter of 5 to 20 mm, and the weight ratio of the balls to the mixture is 10:1 to 30:1,
The ball milling is a method of doping a polymer for a solid electrolyte in which the ball milling is performed for 10 to 30 hours at a rotation speed of 300 to 700 rpm under temperature conditions of 20 to 50 ° C. delete delete In claim 1,
A method of doping a polymer for a solid electrolyte, characterized in that the weight ratio of the polymer and the dopant in the mixture is 1:1 to 3:1. delete delete delete A solid electrolyte for a lithium secondary battery comprising a polymer doped with a dopant prepared by the polymer doping method according to claim 1. A lithium secondary battery comprising the solid electrolyte according to claim 8.