KR20220045330A - Composite electrolyte laminated film for lithium secondary battery and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a composite electrolyte stacked membrane for a lithium secondary battery and a method for manufacturing the same. The composite electrolyte stacked membrane for a lithium secondary battery includes: a composite electrolyte membrane including a solid electrolyte and a polymer electrolyte; and a porous protective film stacked on the composite electrolyte membrane, wherein the porous protective film is an insulating film having a shape of a honeycomb structure.

Description

Composite electrolyte laminated film for lithium secondary battery and method of manufacturing the same

The present invention relates to a composite electrolyte laminated membrane for a lithium secondary battery and a method for manufacturing the same, and in detail, the composite electrolyte laminated membrane is a laminate of a composite electrolyte membrane and a porous protective membrane having a honeycomb structure.

Lithium secondary batteries are used as representative energy storage devices due to their high energy density and long cycle life. Recently, it has been used as a representative energy source for IT devices that require portability and movement of mobile phones, laptops, and electric vehicles.

Although the liquid electrolyte currently used in lithium secondary batteries has excellent lithium ion activation and electrochemical properties, the energy density has reached its limit because the charge/discharge voltage range is relatively limited. Furthermore, as it is vulnerable to external impact, stability problems such as explosion and water leakage are pointed out, and there is a limitation in application to IT devices.

Accordingly, there is a need for a solid-state electrolyte that is safe against external impact, and a typical example is a ceramic solid electrolyte. Ceramic-based electrolytes exhibit ionic conductivity of up to 10 ^-2 S/cm and have excellent chemical and mechanical stability, but require a high pressure/heating process, and are relatively brittle and inflexible. There is a problem in that the interface resistance due to contact is high.

Polymer-based electrolytes have disadvantages in that low ionic conductivity and elasticity at room temperature are reduced, and in particular, there is a problem of cycle stability due to a short circuit due to lithium dendrite growth in a lithium secondary battery.

Therefore, it is necessary to develop a solid electrolyte capable of simultaneously solving the problems present in ceramic or polymer-based solid electrolytes, while maximally maintaining the advantages of each single material, and in particular, improving cycle stability by inhibiting lithium dendrite growth. am.

KR 10-2003296 B1 (2019.07.18)

An object of the present invention is to provide a composite electrolyte laminate for a lithium secondary battery having high ionic conductivity, high mechanical strength, safe from external impact, and excellent electrochemical properties.

Another object of the present invention is to provide a composite electrolyte laminate for a lithium secondary battery capable of improving cycle stability by suppressing the growth of lithium dendrites while having the excellent mechanical and electrochemical properties.

the present invention

a composite electrolyte membrane including a solid electrolyte and a polymer electrolyte; and

It includes a porous protective film laminated on the composite electrolyte membrane,

The porous protective film provides a composite electrolyte laminate for a lithium secondary battery, which is an insulating film having a honeycomb structure.

In one embodiment according to the present invention, the honeycomb structure may be a polygonal honeycomb structure.

In one embodiment according to the present invention, the distance between the center of the polygon and the side closest to the center may be 200 nm or less.

In one embodiment according to the present invention, the proportion of hexagonal and pentagonal structures among the polygonal honeycomb structures may be 80% or more.

In one embodiment according to the present invention, the pore size of the porous protective film may include pores having an average size of 200 to 300 nm.

In one embodiment according to the present invention, the average thickness of the porous protective film may be 2 to 15㎛.

In one embodiment according to the present invention, the porous protective film may include aluminum oxide.

In one embodiment according to the present invention, the solid electrolyte may be represented by the following formula (1).

[Formula 1]

Li _x Sr _y Zr _2-y (PO ₄ ) ₃

(0<x<2, 0<y<1 in Formula 1).

In one embodiment according to the present invention, the polymer electrolyte may include one or more selected from the group consisting of polyethylene oxide (poly(ethylene oxide); PEO) and polypropylene oxide (poly(propylene oxide); PPO). there is.

In one embodiment according to the present invention, the polymer electrolyte is polyethylene glycol diacrylate (polyethyleneglycol diacrylate), triethyleneglycol diacrylate (triethyleneglycol diacrylate), trimethylolpropaneethoxylate triacrylate (trimethylolpropaneethoxylate triacrylate), and A crosslinking agent including at least one selected from the group consisting of bisphenol A ethoxylate dimethacrylate may be further included.

In one embodiment according to the present invention, the composite electrolyte membrane may contain 20 to 60 parts by weight of the solid electrolyte based on 100 parts by weight of the polymer electrolyte.

The present invention also

lithium electrode; and

Including; a composite electrolyte laminated film positioned on the electrode;

The composite electrolyte laminated membrane may include a composite electrolyte membrane including a solid electrolyte and a polymer electrolyte; and a porous protective film laminated on the composite electrolyte membrane,

The porous protective film provides a lithium secondary battery that is an insulating film having a shape of a honeycomb structure.

The present invention also

a) preparing a composite electrolyte precursor by mixing a solid electrolyte powder and a polymer electrolyte;

b) preparing a composite electrolyte membrane by thermosetting the precursor; and

c) laminating the composite electrolyte membrane and the porous protective membrane;

The porous protective film provides a method for manufacturing a composite electrolyte laminate for a lithium secondary battery, which is an insulating film having a honeycomb structure.

In one embodiment according to the present invention, the solid electrolyte powder may be synthesized by a sol-gel method.

In one embodiment according to the present invention, the thermosetting temperature of step b) may be 50 to 150 ℃.

The composite electrolyte laminated membrane for a lithium secondary battery according to the present invention has the advantage of exhibiting excellent mechanical stability and high ionic conductivity.

In addition, the composite electrolyte laminated membrane for a lithium secondary battery according to the present invention includes nanopores, thereby providing a passage for the smooth movement of lithium ions, which are ion conductive materials, thereby improving charge/discharge performance.

In addition, the composite electrolyte laminated membrane for a lithium secondary battery according to the present invention can inhibit the growth of lithium dendrites on the electrode surface or induce the growth of the formed dendrites into a specific shape, thereby preventing an internal short circuit, and furthermore, excellent cycle stability There are advantages to indicate.

Even if the effects are not explicitly mentioned in the present invention, the effects described in the specification expected by the technical features of the present invention and the inherent effects thereof are treated as if they were described in the specification of the present invention.

1 is a view for explaining the principle of suppressing the growth of lithium dendrites by the composite electrolyte laminate according to the present invention.
2 is a view showing a scanning electron microscope (SEM) image of a porous protective film having a polygonal honeycomb structure according to an embodiment of the present invention.
3 is a view showing an SEM image of a porous protective film having a circular honeycomb structure according to an embodiment of the present invention.
4 and 5 are diagrams showing the charging and discharging performance of a lithium secondary battery according to an embodiment of the present invention.
6 is a view showing the charging and discharging performance of the lithium secondary battery according to Comparative Example 1.

Unless otherwise defined in technical terms and scientific terms used in this specification, those of ordinary skill in the art to which this invention belongs have the meanings commonly understood, and in the following description and accompanying drawings, the subject matter of the present invention Descriptions of known functions and configurations that may unnecessarily obscure will be omitted.

Also, the singular form used herein may be intended to include the plural form as well, unless the context specifically dictates otherwise.

In addition, in the present specification, the unit used without special mention is based on the weight, for example, the unit of % or ratio means weight % or weight ratio, and the weight % means any one component of the entire composition unless otherwise defined. It means the weight % occupied in the composition.

In addition, the numerical range used herein includes the lower limit and upper limit and all values within the range, increments logically derived from the form and width of the defined range, all values defined therein, and the upper limit of the numerical range defined in different forms. and all possible combinations of lower limits. Unless otherwise defined in the specification of the present invention, values outside the numerical range that may occur due to experimental errors or rounding of values are also included in the defined numerical range.

As used herein, the term 'comprising' is an open-ended description having an equivalent meaning to expressions such as 'comprising', 'containing', 'having' or 'characterized', and elements not listed in addition; Materials or processes are not excluded.

In addition, as used herein, the term 'substantially' means that other elements, materials, or processes not listed together with the specified element, material or process are unacceptable for at least one basic and novel technical idea of the invention. It means that it can be present in an amount or degree that does not significantly affect it.

The present invention provides a composite electrolyte membrane comprising a solid electrolyte and a polymer electrolyte; and a porous protective film laminated on the composite electrolyte film, wherein the porous protective film is an insulating film having a honeycomb structure.

The biggest problem in the charging and discharging process of a lithium secondary battery is the growth of dendrites. In particular, in the case of a lithium secondary battery using lithium as an anode material, lithium dendrites generated on the electrode surface during the charging and discharging process grow and contact the positive electrode, causing an internal short circuit. This phenomenon is ultimately the cycle life of the lithium secondary battery directly related to the decline. As described above, in the case of a polymer-based electrolyte, there is a problem that the cycle stability degradation problem due to the above-described lithium dendrite growth is seriously generated. On the other hand, the ceramic-based solid electrolyte has a problem in that charge/discharge performance is reduced due to very high interfacial resistance due to interfacial contact due to low flexibility.

However, the composite electrolyte laminated membrane according to the present invention can simultaneously solve the above-mentioned problems existing in a single material solid or polymer electrolyte through the composite of the dissimilar materials and the porous protective membrane laminated on the composite electrolyte membrane, and Indicates cycle stability.

Specifically, the porous protective film is an insulating film having a porous shape of a honeycomb structure, has a porosity of 60% or more, preferably 70% to 80%, and may have a honeycomb structure in which pores are developed in a vertical direction. Through the composite electrolyte membrane in which the porous protective layer is laminated, the mechanical strength and chemical resistance of the composite electrolyte layered membrane may be increased. In this case, the honeycomb structure is a polygonal honeycomb structure, and the distance between the center of the polygon and the side closest to the center may be 200 nm or less, preferably 25 to 100 nm, more preferably 25 to 50 nm. In the above range, it is possible to induce dendrites generated by repeated charging and discharging of the lithium secondary battery to grow in the columnar shape of the honeycomb structure, preventing direct contact between the dendrites and the electrodes, effectively preventing the occurrence of internal short circuits. can be prevented

A proportion of the hexagonal and pentagonal structures among the polygonal honeycomb structures may be 80% or more, preferably 85%, more preferably 90%. Through the porous protective film including the above-described polygonal honeycomb structure, a uniform lithium ion flux is created to prevent unbalanced lithium metal deposition and growth, that is, the formation of dendrites due to the non-uniform movement of lithium ions on the electrode surface. can be significantly reduced.

The pillar wall of the honeycomb structure may include pores having an average size of 50 to 300 nm, preferably 100 to 300 nm, and more preferably 200 to 300 nm. The porous protective film has the shape of a honeycomb structure including the nanoporous column wall within the above range, thereby creating an efficient passageway for lithium ions, which are ion-conducting materials that move in the charging/discharging process of a lithium secondary battery, thereby improving ion conductivity can represent In this case, the porosity of the column wall may be 40 to 80%, preferably 50 to 80%.

The porous protective film is not reactive with lithium, and may include aluminum oxide in terms of pore size of the pillar wall and easy control of the thickness of the protective film. Specifically, the protective layer may have an average thickness of 2 to 20 μm, preferably 2 to 18 μm, and more preferably 2 to 15 μm. In the above range, it is possible to reduce the interfacial resistance of the composite electrolyte membrane and the porous protective layer, and at the same time, it is possible to effectively suppress the growth of lithium dendrites.

The composite electrolyte membrane may be in a state in which a solid electrolyte and a polymer electrolyte represented by the following Chemical Formula 1 are complexed, and specifically, based on 100 parts by weight of the polymer electrolyte, 20 to 60 parts by weight of the solid electrolyte, preferably 20 to 50, more Preferably, it may contain 20 to 40 parts by weight.

[Formula 1]

Li _x Sr _y Zr _2-y (PO ₄ ) ₃

(0<x<2, 0<y<1 in Formula 1).

The polymer electrolyte may be a hydrophilic polymer, preferably poly(alkylene oxide). As a specific example, it may be one or more selected from the group consisting of polyethylene oxide (poly(ethylene oxide); PEO) and polypropylene oxide (poly(propylene oxide); PPO).

Specifically, the phosphate-based solid electrolyte and the polymer electrolyte may exist in a cross-linked state in the composite electrolyte membrane, and in this case, the polymer electrolyte is polyethylene glycol diacrylate (polyethyleneglycol diacrylate), triethylene glycol diacrylate ( triethyleneglycol diacrylate), trimethylolpropaneethoxylate triacrylate, and bisphenol A ethoxylate dimethacrylate may further include a crosslinking agent comprising at least one selected from the group consisting of can

The present invention also relates to a lithium electrode; and a composite electrolyte laminated membrane positioned on the electrode, wherein the composite electrolyte laminated membrane includes: a composite electrolyte membrane including a solid electrolyte and a polymer electrolyte; and a porous protective film laminated on the composite electrolyte membrane, wherein the porous protective film is an insulating film having a honeycomb structure.

Specifically, the lithium electrode may be a negative electrode of a lithium secondary battery, and may include a composite electrolyte laminate layer on the negative electrode. As shown in FIG. 1 , when a solid-state electrolyte, for example, a single-material-based solid-state electrolyte such as a ceramic or polymer-based electrolyte, is included on the lithium electrode, lithium dendrites generated on the surface of the anode according to repeated charging and discharging are The problem of irregular growth is caused by crystals in the shape of branches. Such abnormal crystal growth eventually causes volume expansion of the electrode, which reduces the safety of the battery, and further, significantly reduces the lifespan of the battery due to an internal short circuit.

However, in the case of including a composite electrolyte membrane including a solid electrolyte and a polymer electrolyte according to the present invention and a composite electrolyte laminated membrane including a porous protective membrane laminated on the composite electrolyte membrane, superior electrochemical and As well as mechanical stability, it is possible to suppress the formation of dendrites on the electrode surface, and further, even if dendrites are formed, it can be induced to grow in the columnar shape of the honeycomb structure, thereby remarkably improving cycle stability.

The lithium electrode may be a lithium metal or a lithium alloy, specifically, a lithium-aluminum alloy.

The lithium secondary battery may further include a positive electrode disposed to be spaced apart from the lithium electrode with the composite electrolyte stacked film interposed therebetween. The positive electrode may include lithium transition metal oxide as a positive electrode active material, and specifically, as long as it is a compound capable of reversible intercalation and deintercalation of lithium, it is not particularly limited, but as a non-limiting example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c )O ₂ (0<a<1, 0<b<1, 0<c<1, a+b+c=1), LiNi _{1- y} Co _y O ₂ , LiCo _1-y Mn _y O ₂ , LiNi _1-y Mn _y O ₂ (0≤y<1), Li(Ni _a Co _b Mn _c )O ₄ (0<a<2, 0 <b<2, 0<c<2, a+b+c=2), LiMn _2-z Ni _z O ₄ , LiMn _2-z Co _z O ₄ (0<z<2), LiCoPO ₄ and LiFePO ₄ can be heard

The present invention also comprises the steps of: a) mixing a solid electrolyte powder and a polymer electrolyte to prepare a composite electrolyte precursor; b) preparing a composite electrolyte membrane by thermosetting the precursor; And c) laminating the composite electrolyte membrane and the porous protective film; includes, wherein the porous protective film is an insulating film having a shape of a honeycomb structure It provides a method of manufacturing a composite electrolyte laminated membrane for a lithium secondary battery.

Step a) is a step of preparing a composite electrolyte precursor, and may be prepared by mixing a solid electrolyte powder and a polymer electrolyte at room temperature. Specifically, the weight ratio of the solid electrolyte powder and the polymer electrolyte may be 1: 0.2 to 1: 0.8, preferably 1: 0.2 to 1: 0.6. In this case, the polymer electrolyte may be a hydrophilic polymer, preferably polyalkylene oxide (poly(alkylene oxide)). As a specific example, it may be one or more selected from the group consisting of polyethylene oxide (poly(ethylene oxide); PEO) and polypropylene oxide (poly(propylene oxide); PPO).

The polymer electrolyte is, based on 100 parts by weight of the polymer electrolyte, polyethylene glycol diacrylate, triethylene glycol diacrylate, trimethylolpropaneethoxylate triacrylate, and bisphenol It may include one or more crosslinking agents selected from the group consisting of ethoxylate dimethacrylate (Bisphenol A ethoxylate dimethacrylate).

In addition, the solid electrolyte powder of step a) may be synthesized by a sol-gel method. Specifically, the solid electrolyte powder may be a phosphate-based solid electrolyte represented by Formula 1 below.

[Formula 1]

Li _x Sr _y Zr _2-y (PO ₄ ) ₃

(0<x<2, 0<y<1 in Formula 1).

Specifically, the method for preparing the solid electrolyte powder includes a first step of reacting a lithium salt, a strontium (Sr) and a zirconium (Zr) precursor, and a solvent to obtain a solid electrolyte precursor; and a second step of heat-treating the precursor to obtain a solid electrolyte powder.

The heat treatment may be performed under oxygen conditions and at 200 to 1200° C. for 2 to 30 hours. Specifically, after performing the first heat treatment for 2 to 10 hours, preferably 2 to 8 hours at 200 to 800 ° C., preferably 300 to 600 ° C., 15 to 30 at 600 to 1200 ° C., preferably 800 to 1200 ° C. Time, preferably, the secondary heat treatment may be performed for 20 to 30 hours, and the temperature increase rate may be 2 to 10 °C/min.

In this case, the lithium salt is LiNO ₃ , LiCH ₃ COO, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(SO ₂ C2F ₅ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , may be at least one selected from the group consisting of LiCl and LiI, but is not limited thereto. In addition, the solvent may be an organic acid or an ethanol solvent, and specific examples thereof may include at least one selected from the group consisting of citric acid and 2-methoxyethanol, but is not limited thereto.

Step b) is a step of preparing a composite electrolyte membrane, and the composite electrolyte precursor prepared in step a) is heated at 50 to 150° C., preferably 80 to 150° C., more preferably 80 to 130° C. for 2 to 10 hours, preferably can be made through heat curing for 2 to 8 hours.

Step c) is a step of stacking the composite electrolyte membrane and the porous protective membrane prepared, specifically, placing the porous protective membrane as a base membrane so as to be in direct contact with the lithium electrode, and stacking the composite electrolyte membrane prepared in step b) on it. After that, excellent contact between the laminated porous protective membrane and the composite electrolyte membrane interface can be induced by pressurizing in an inert atmosphere and 80 to 200 ° C, preferably 80 to 150 ° C, for 0.5 to 3 hours, preferably 0.5 to 2 hours. can Under the above conditions, it is possible to significantly reduce the interfacial resistance between the porous protective membrane and the composite electrolyte membrane, thereby significantly increasing cycle stability as well as high ionic conductivity. In this case, the porous protective film may be an insulating film having a shape of a honeycomb structure, and specifically, it may include aluminum oxide in terms of not being reactive with lithium and easy to control the pore size of the pillar wall and the thickness of the protective film. More specifically, the pillar wall of the honeycomb structure includes pores having an average size of 50 to 300 nm, preferably 100 to 300 nm, more preferably 200 to 300 nm, and the average thickness of the protective film is 2 to 20 μm, preferably may be 2 to 18 μm, more preferably 2 to 15 μm.

Hereinafter, the present invention will be described in detail with reference to Examples, but these are for describing the present invention in more detail, and the scope of the present invention is not limited by the Examples below.

Step 1: Preparation of Solid Electrolyte

A solvent prepared by adding 10.51 g of citric acid to 250 ml of distilled water was heated to 80°C. Next, 0.84 g of lithium nitrate, 0.22 g of strontium nitrate, 6.31 g of zirconium oxychloride octahydrate, and 3.49 g of ammonium phosphate were added and stirred for 10 minutes. Then, 2.79 ml of ethylene glycol was added for gelation, followed by reaction for an hour and a half. Next, the powder obtained by drying the solution at 150° C. was put into an alumina boat, and using an oxidation furnace, the temperature was increased at a rate of 5° C./min. at 500° C. for 6 hours, and at 1000° C. for 24 hours in an oxygen atmosphere. Heat treatment was performed to prepare (Li _1.2 Sr _0.1 Zr _1.9 (PO ₄ ) ₃ ).

Step 2: Preparation of Polyelectrolyte

Number of moles of ethylene oxide of (poly(ethylene glycol) dimethyl ether and bisphenol-A ethoxylate diacrylate in 0.6 g of poly(ethylene glycol) dimethyl ether) having a number average molecular weight of 500: lithium Bis(trifluoromethanae)sulfonamide lithium salt) was added so that the number of moles of ions = 20: 1), and the solution was sufficiently dissolved and stirred at 60° C. until the lithium salt was completely dissolved.

When the temperature of the solution dropped to room temperature, 0.4 g of bisphenol A ethoxylate diacrylate having a number average molecular weight of 688 and 0.04 g of an initiator were added and sufficiently stirred to prepare a polymer electrolyte solution. At this time, the initiator contains 75% by weight of Tert-Butyl peroxyneodecanoate, naphtha (petroleum), and 25% by weight of hydrotreated heavy.

Step 3: Preparation of composite electrolyte solution

A composite electrolyte solution was prepared by mixing 40 parts by weight of the solid electrolyte prepared in step 1 with respect to 100 parts by weight of the mixture in which the polymer electrolyte and the crosslinking agent prepared in step 2 were mixed in a 60:40 weight ratio. In this case, the crosslinking agent is poly(ethylene glycol) dimethyl ether: bisphenol A ethoxylate diacrylate in a 6: 4 weight ratio mixed state.

Step 4: Preparation of composite electrolyte membrane

The composite electrolyte solution prepared in step 3 was poured into a Teflon petri dish, and then cured at 100° C. for 3 hours to prepare a composite electrolyte membrane having an average thickness of 500 μm.

Step 5: Preparation of a porous protective film

An aluminum oxide film having a honeycomb structure was formed on the surface of the aluminum foil by anodizing the polished aluminum foil having a purity of 99.999% under the conditions shown in Table 1 below.

electrolyte 0.3M phosphoric acid Voltage 130 V voltage application time 3 hours temperature 0 ℃

Next, after forming a protective layer by applying poly methyl methacrylate (PMMA) to the surface of the aluminum oxide film formed on the upper surface of the aluminum foil, water: phosphoric acid: chromium trioxide (CrO ₃ ) 100 ㎖ : The aluminum oxide film formed on the lower surface of the aluminum foil was removed using a mixed solution in a ratio of 10 ml: 1 g to expose aluminum.

The exposed aluminum was etched using a mixture of 100 ml: 100 ml: 3.4 g of water: hydrochloric acid: copper (II) chloride, and only the aluminum oxide film on which the protective layer was formed was separated. Thereafter, the separated aluminum oxide film was immersed in a 5% phosphoric acid solution and a condition of 40° C. for 1 hour to form a polygonal honeycomb structure, and the protective layer was removed using acetone to finally have an average thickness of 5 A porous protective film having a ㎛ and polygonal honeycomb structure was prepared. In this case, the average distance between the center of the polygon and the side closest to the center is 150 nm, and pores having an average size of 200 nm are included in the pore wall of the honeycomb structure.

Step 6: Preparation of composite electrolyte laminated membrane

After laminating the composite electrolyte membrane prepared in step 4 and the porous protective film film prepared in step 5, pressurization was performed for 1 hour in an inert atmosphere and 100° C. conditions to prepare a composite electrolyte laminate.

As shown in FIG. 3 by performing anodization treatment in step 5 of Example 1 under the conditions shown in Table 2 below, a porous protective film having a circular honeycomb structure with an average diameter of 80 nm and an average thickness of 10 μm was prepared, , except that a composite electrolyte laminate was prepared using the porous protective film film prepared above in step 6, and the same procedure was performed.

Specifically, after the first anodization treatment, a solution in which water: phosphoric acid: chromium trioxide (CrO ₃ ) was mixed in a ratio of 100 ml: 10 ml: 1 g was applied, and then secondary anodization was performed.

Primary anodization treatment Secondary anodization treatment electrolyte 0.3M phosphoric acid 0.3M phosphoric acid Voltage 50 V 50 V voltage application time 6 hours 2 hours temperature 0 ℃ 0 ℃

The same procedure was performed except that in step 6 of Example 1, the porous protective film and the composite electrolyte membrane were physically laminated without pressure and lamination in an inert atmosphere and 100° C. conditions for 1 hour.

(Comparative Example 1)

The same procedure was performed except that step 6 of Example 1 was not performed.

Experimental Example: Evaluation of charge/discharge cycle stability of lithium secondary batteries

A lithium secondary battery was prepared by punching the composite electrolyte laminated membrane (in the case of the comparative example, the composite electrolyte membrane) prepared according to Examples 1 to 3 and Comparative Example to a diameter of 18 mm and placing it between the positive electrode and the negative electrode. Specifically, LiFePO ₄ was used as the positive electrode, lithium metal was used as the negative electrode, and the porous protective film of the composite electrolyte laminate was disposed to face the negative electrode.

Next, the prepared lithium secondary battery was charged and discharged for 1 cycle at 0.1 C, 10 cycles at 0.2 C, 189 cycles at 1 C, for a total of 200 cycles, the results of which are shown in FIGS. 4 to 6, 0.1 C , the average discharge capacity at 0.2 C and 1 C is summarized in Table 3 below.

at 0.1 C
Discharge capacity (mA hg ^-1 ) average at 0.2 C
Discharge capacity (mA hg ^-1 ) average at 1 C
Discharge capacity (mA hg ^-1 ) Example 1 152 141 35 Example 2 143 131 9 Example 3 145 125 5 Comparative Example 1 142 118 0

As can be seen in Table 3, Examples 1 and 2 showed a constant discharge capacity for 200 cycles, and in the case of Example 3, the discharge capacity showed a tendency to decrease, and in the case of Comparative Example 1, after 12 cycles, It can be seen that the discharge capacity has dropped to 0. In addition, when a porous protective film having a polygonal honeycomb structure compared to a circular honeycomb structure is included, dendrite formation can be significantly suppressed, and it can be seen that a relatively stable cycle life is exhibited.

Claims (15)

a composite electrolyte membrane including a solid electrolyte and a polymer electrolyte; and
It includes a porous protective film laminated on the composite electrolyte membrane,
The porous protective film is an insulating film having a honeycomb structure, a composite electrolyte laminate for a lithium secondary battery. According to claim 1,
The honeycomb structure is a composite electrolyte laminated membrane having a polygonal honeycomb structure. 3. The method of claim 2,
A composite electrolyte laminated membrane wherein the center of the polygon and the distance from the center to the closest side are 200 nm or less. 3. The method of claim 2,
The composite electrolyte laminated membrane, wherein the ratio of hexagonal and pentagonal structures among the polygonal honeycomb structures is 80% or more. According to claim 1,
The composite electrolyte laminated membrane comprising pores having an average size of 200 to 300 nm on the pore walls of the porous protective membrane. According to claim 1,
The average thickness of the porous protective film is a composite electrolyte laminated film of 2 to 15 ㎛. According to claim 1,
The porous protective film is a composite electrolyte laminated film comprising aluminum oxide. According to claim 1,
The solid electrolyte is a composite electrolyte laminated membrane that is a phosphate-based solid electrolyte represented by the following Chemical Formula 1:
[Formula 1]
Li _x Sr _y Zr _2-y (PO ₄ ) ₃
(0<x<2, 0<y<1 in Formula 1). According to claim 1,
The polymer electrolyte is a composite electrolyte laminated membrane comprising at least one selected from the group consisting of polyethylene oxide (poly(ethylene oxide); PEO) and polypropylene oxide (poly(propylene oxide); PPO). According to claim 1,
The polymer electrolyte is polyethylene glycol diacrylate (polyethyleneglycol diacrylate), triethyleneglycol diacrylate (triethyleneglycol diacrylate), trimethylolpropaneethoxylate triacrylate (trimethylolpropaneethoxylate triacrylate), and bisphenol ethoxylate dimethacrylate ( Bisphenol A ethoxylate dimethacrylate) composite electrolyte laminated membrane further comprising a crosslinking agent comprising at least one selected from the group consisting of. According to claim 1,
The composite electrolyte membrane is a composite electrolyte laminated membrane comprising 20 to 60 parts by weight of the solid electrolyte based on 100 parts by weight of the polymer electrolyte. lithium electrode; and
Including; a composite electrolyte laminated film positioned on the electrode;
The composite electrolyte layered membrane may include a composite electrolyte membrane including a solid electrolyte and a polymer electrolyte; and a porous protective film laminated on the composite electrolyte membrane,
The porous protective film is a lithium secondary battery that is an insulating film having a shape of a honeycomb structure. a) preparing a composite electrolyte precursor by mixing a solid electrolyte powder and a polymer electrolyte;
b) preparing a composite electrolyte membrane by thermosetting the precursor; and
c) laminating the composite electrolyte membrane and the porous protective membrane;
The porous protective film is an insulating film having a shape of a honeycomb structure. 14. The method of claim 13,
The solid electrolyte powder is a method of manufacturing a composite electrolyte laminated membrane synthesized by a sol-gel method. 14. The method of claim 13,
The thermosetting temperature of step b) is 50 to 150 ℃ method of manufacturing a composite electrolyte laminated membrane.

Images