KR20150138497A - Hybrid Electrolyte comprising Lithium Phosphates and Polymer Systems For Li Batteries And Li Ion Batteries comprising The Same - Google Patents

Abstract

The present invention relates to a lithium secondary battery including a film shaped electrolyte, and to a method for manufacturing the same. The lithium secondary battery of the present invention comprises the film shaped composite electrolyte which includes at least one kind of polymer selected from the group consisting of multi-component lithium phosphate powder, polyethylene oxide, polypropylene oxide (PPO), and glycidol. A weight ratio of the lithium phosphate powder and the polymer inside the composite electrolyte is within a range of 60:40-90:10. According to the present invention, a lithium secondary battery, which has a high mechanical strength and a high ion conductivity and is easily formed, can be manufactured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium phosphate-polymer composite electrolyte for a lithium secondary battery, and a secondary battery comprising the lithium phosphate-

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including a film-like electrolyte and a method of manufacturing the same.

Lithium secondary batteries are largely composed of an anode, an electrolyte and a cathode. As a general lithium secondary battery is commercialized as moved to an organic solvent and a 15 ~ 25㎛ thickness in the liquid electrolyte consisting of a lithium salt is in a structure added to the polymer membrane, the anode in Li ⁺ ions to the negative electrode during discharge and Li ionization The generated electrons move from the cathode to the anode, and when charged, move backward. The driving force of this Li ⁺ ion movement is generated by the chemical stability depending on the potential difference between the two electrodes. The capacity (capacity, Ah) of the battery is determined by the amount of Li ⁺ ions moving from the cathode to the anode and from the anode to the cathode. On the other hand, since the migration of Li ⁺ ions occurs through the electrolyte, the Li ⁺ ion conductivity of the electrolyte affects the charge / discharge rate of the battery.

All solid-state batteries refer to the replacement of liquid electrolytes with solid electrolytes among the above battery components. The solid secondary battery has less risk of explosion or fire than the liquid electrolyte, simplifies the manufacturing process, and is attracting attention as a next generation secondary battery because of high energy density. However, since the solid secondary battery has higher safety than the liquid electrolyte, the ion conductivity is reduced due to the lower ion conduction path due to the lowered interface contact with the electrode.

Further, in recent years, a lithium ion secondary battery using a polymer electrolyte made of a polymer has received more attention than a battery utilizing the electrolyte using an electrolyte. Such a polymer battery uses a gel-type electrolyte. This battery has no fear of leaking, does not contain a combustible organic solvent, improves the safety of the battery, and further has such an advantage that the battery has an increased degree of freedom in a shape that can be taken. However, this type of polymer electrolyte has a lower lithium ion conductivity and lower mechanical strength than an electrolyte type electrolyte, resulting in a short circuit between the positive electrode and the negative electrode due to damage of the polymer electrolyte during the manufacturing process.

In order to solve the problems of the prior art described above, it is an object of the present invention to provide a lithium secondary battery including a composite electrolyte composed of a polymer and an ion conductive lithium phosphate.

Another object of the present invention is to provide a lithium secondary battery having a composite electrolyte of a composition optimized for improving electrical conductivity.

Another object of the present invention is to provide a lithium secondary battery having a composite electrolyte capable of compensating for a low mechanical strength of a polymer electrolyte.

It is another object of the present invention to provide a method of manufacturing the above-mentioned lithium secondary battery.

In order to accomplish the above object, the present invention provides a multi-component lithium phosphate powder represented by the following formula

Li _{1 + x} M _{2 - x} M ' _x (PO ₄ ) ₃

(Where x? 0, M is at least one element selected from the group consisting of Ti, Ge and Hf, and M 'is at least one element selected from the group consisting of Al, B and Sn); And a composite electrolyte in the form of a film comprising at least one polymer selected from the group consisting of polyethylene oxide, polypropylene oxide (PPO) and glycidol,

Wherein the weight ratio of the lithium phosphate powder to the polymer in the composite electrolyte is in the range of 60:40 to 90:10.

In the present invention, the composite electrolyte may further include a lithium salt.

In the present invention, the weight ratio of the lithium phosphate powder to the polymer in the composite electrolyte is preferably in the range of 60:40 to 80:20.

Further, the polymer is preferably polyethylene oxide.

In the present invention, the lithium phosphate powder may include a composition of Li _{1 .5} Al _{0 .5} Ge _{1 .5} (PO ₄ ) ₃ .

The present invention also provides a multicomponent lithium phosphate powder represented by Li _{1 + x} M _{2 - x} M ' _x (PO ₄ ) ₃ , wherein x≥0, M represents Ti, Ge, Hf and M 'is at least one element selected from the group consisting of Al, B and Sn); And at least one polymer powder selected from the group consisting of polyethylene oxide, polypropylene oxide (PPO) and glycidol is mixed with the lithium phosphate powder and the polymer powder in a weight ratio of 60:40 to 90:10 Blending; Mixing the blended powder with an organic solvent to prepare a slurry; Applying the prepared slurry on a substrate to form a film; And drying and evaporating the organic solvent in the coated slurry. The present invention also provides a method for producing a composite electrolyte film for a lithium secondary battery.

In the present invention, a lithium salt may be further added in the compounding step.

Further, the lithium phosphate powder in the blending step may include _{Li 1 .5 Al 0 .5 Ge 1} .5 (PO 4) 3 composition.

The present invention also provides a multicomponent lithium phosphate powder represented by Li _{1 + x} M _{2 - x} M ' _x (PO ₄ ) ₃ on a polyethylene oxide matrix wherein x is 0 and M is selected from Ti, Ge and Hf , And M 'is at least one element selected from the group consisting of Al, B, and Sn). The present invention also provides a composite electrolyte film in which lithium phosphate powder having a composition of at least one element selected from the group consisting of Al, B and Sn is dispersed.

According to the present invention, by using a composite electrolyte composed of a polymer and an ion conductive lithium phosphate as an electrolyte of a lithium secondary battery, ion conductivity can be improved.

In addition, according to the present invention, it is possible to solve the low mechanical strength problem of the polymer electrolyte having the advantage of the polymer electrolyte which is easy to form.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing a manufacturing procedure of a composite electrolyte film according to a preferred embodiment of the present invention; FIG.
2 is a plan view photograph of a film sample manufactured according to a preferred embodiment of the present invention.
3 is an electron micrograph of a cross-sectional structure of a film sample produced according to a preferred embodiment of the present invention.
4 is a graph showing ion conductivity measurement results of a sample manufactured according to a preferred embodiment of the present invention.
5 is a graph showing the current density according to the applied voltage measured by the oxidation potential scanning method of the sample manufactured according to the preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the drawings.

The present invention provides a composite solid electrolyte comprising a multicomponent lithium phosphate and a polymer to be represented.

(Formula 1)

Li _{1 + x} M _{2 - x} M ' _x (PO 4) ₃

Here, x? 0, M is at least one element selected from the group consisting of Ti, Ge and Hf, and M 'is at least one element selected from the group consisting of Al, B and Sn.

The aforementioned compounds are sometimes expressed as LISICON (Li Super Ion Conductivity), and due to their structural characteristics, lithium and sodium can migrate very rapidly in the structure. The ionic conductivity is very good.

In addition, the ricicon compound is a polyanion compound that holds the structure strongly like olivine-type compounds, and is excellent in thermal stability and lifetime characteristics. Since the solid electrolyte having a ricicon structure has a three-dimensional interstitial structure, migration of lithium ions is facilitated in all directions and a high ion conductivity can be expected. It is easier to handle than a sulfide-based solid electrolyte and excellent in thermal stability and chemical stability .

LISICON can substitute other metals for Li or metal ion sites. It is known that LAGP (lithium-aluminum-zirconium oxide), which is known to improve the grain boundary resistance of the ricicon structure through metal substitution and exhibits strong covalent bond of Ge-O due to the substitution of Ge metal, Germanium-for-state). For example, in the case of an electrolyte having a composition of Li _{1 .5} Al _{0 .5} Ge _{1 .5} (PO 4) ₃ , it has a high ionic conductivity of 2.18 × 10 ^-4 S / cm.

In the present invention, the polymer constituting the composite electrolyte may include at least one polymer selected from the group consisting of polyethylene oxide (PEO), polypropylene oxide (PPO), and glycidol. Preferably, polyethylene oxide is used as the polymer of the composite electrolyte.

In the present invention, the complex solid electrolyte includes a lithium salt. The lithium salt may act as a source of lithium ions in the electrolyte. The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) 2N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , At least one compound selected from the group consisting of LiAlCl ₄ , LiF, LiBr, LiCl, and LiI may be used.

In the present invention, the composite electrolyte is preferably provided in the form of a film.

Hereinafter, a method for producing a composite electrolyte film will be described with reference to FIG.

The above-mentioned polymer powder, lithium phosphate powder and lithium salt and an organic solvent for dissolving them are prepared. As the organic solvent, acetonitrile (ACN) is preferably used. However, the present invention is not limited thereto, and various solvents capable of dissolving the above-mentioned polymer powder and lithium salt can be used. For example, a carbonate-based, ester-based, ether-based, ketone-based, organosulfur-based solvent, organophosphorous-based solvent or aprotic solvent may be used.

Subsequently, the above-mentioned powders and the lithium salt are stirred and mixed in an organic solvent to prepare a mixed slurry (S110). Next, the prepared mixed slurry is coated on a predetermined substrate such as a glass substrate to form a film (S120). The organic solvent contained in the applied film is dried (S130), and the substrate is removed to produce an electrolyte film (S140).

Through the above manufacturing process, the electrolyte film has a form in which the ion conductive lithium phosphate is dispersed on the polymer matrix as shown in FIG.

By punching the produced film, the film can be processed into a shape suitable for being received inside the cell.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to preferred embodiments of the present invention.

Lithium phosphate  powder( LAGP )

A small amount (0.05 wt%) of B (Sigma-Aldrich), Al ₂ O ₃ (Sigma-Aldrich), GeO ₂ (Alfa aeser) and ammonium phosphate (NH ₄ H ₂ PO ₄ ; ₂ O ₃ (Sigma-Aldrich) was mixed with isopropyl alcohol as a dispersion medium in a ball mill for 24 hours with stirring.

The mixed raw materials were dried at room temperature for 24 hours and calcined at a temperature of 700 to 850 ° C in an Ar atmosphere. As a result of calcining, LAGP (Li _{1 .5} Al _{0 .5} Ge _{1 .5} (PO ₄ ) ₃ ) powder doped with boron (B) was synthesized. The ionic conductivity of synthesized LAGP at room temperature was 2.18 * 10 ^-4 S / cm.

Preparation of electrolyte film

Electrolyte film samples of each composition were prepared by varying the weight of polyethylene oxide and LAGP in the range of polyethylene oxide: LAGP weight ratio of 100: 0 to 10: 90 in the solid electrolyte.

First, a lithium salt (LiClO ₄ ) was dissolved by using ACN (acetonitrile) as an organic solvent. At this time, the molar ratio of the dissolved lithium salt to the polyethylene oxide was 1/15. Then, polyethylene oxide powder (Aldrich) and LAGP prepared above were added to the organic solvent in which the lithium salt was dissolved, and the mixture was stirred to prepare a slurry.

The prepared slurry was cast on a Teflon plate and dried at room temperature while evaporating the solvent. The dried film had a thickness of several tens to several hundreds of 탆 in thickness. The prepared electrolyte film was circularly punched.

FIG. 2 is a plan view photograph of the circular film, and FIG. 3 is an electron micrograph of a cross section of a sample having a LAGP content of 70% by weight.

Measurement of ion conductivity

A 1.54 cm ² punched circular film was laminated in the order of stainless steel / film / stainless steel in this order to form a cell, and the alternating current impedance of the cell was measured. Impedance measurements were repeated at different cell temperatures, and impedance measurements were performed at a frequency range of 10 ⁵ to 0.1 Hz and an amplitude of 100 mV. The ionic conductivity was calculated from the measured impedance.

4 is a graph showing the ion conductivity measurement results of the respective samples. As shown, it can be seen that ion conductivity is increased by replacing polyethylene oxide with LAGP. Further, when LAGP replaces 60 to 80% by weight of the polyethylene oxide, the electric conductivity can be named as the maximum value.

In addition, the composite solid electrolyte consisting of LAGP and polyethylene oxide exhibits a higher ion conductivity value than a pure polymer electrolyte in a relatively wide mixing range. That is, when the LAGP is contained in an amount of 60% by weight or more, preferably 60 to 90% by weight, and more preferably 60 to 80% by weight based on the total weight of the solid electrolyte (LAGP + PEO) .

LSV  Measure

Stainless steel, an electrolyte film and a lithium metal were stacked in this order, and were mounted in a 2032 coin cell to measure a linear sweep volatmmetry (LSV). The laminated structure in the coin cell was pressed using a spring. The voltage range was from 3V to 6V and measured at a scan rate of 1 mVs ^-1 . The measurement temperature was maintained at 55 占 폚.

5 is a graph showing the current density according to the applied voltage measured by the LSV test.

Claims (9)

A multicomponent lithium phosphate powder represented by the following formula
Li _{1 + x} M _{2 - x} M ' _x (PO ₄ ) ₃
(Where x? 0, M is at least one element selected from the group consisting of Ti, Ge and Hf, and M 'is at least one element selected from the group consisting of Al, B and Sn); And
A composite electrolyte in the form of a film comprising at least one polymer selected from the group consisting of polyethylene oxide, polypropylene oxide (PPO) and glycidol,
Wherein the weight ratio of the lithium phosphate powder to the polymer in the composite electrolyte is in the range of 60:40 to 90:10. The method according to claim 1,
Wherein the composite electrolyte further comprises a lithium salt. The method according to claim 1,
Wherein the weight ratio of the lithium phosphate powder to the polymer in the composite electrolyte is in the range of 60:40 to 80:20. The method according to claim 1,
Wherein the polymer is polyethylene oxide. The method according to claim 1,
The lithium phosphate powder was _{Li 1 .5 Al 0 .5 Ge 1} .5 (PO 4) The lithium secondary battery characterized in that it comprises _three composition. Li _{1 + x} M _{2 -} and _x M _'x (PO ₄₎ multi-component system lithium phosphate powder (where, x≥0, which is represented by the _3, M is an element of at least one selected from the group consisting of Ti, Ge, and Hf And M 'is at least one element selected from the group consisting of Al, B, and Sn); And at least one polymer powder selected from the group consisting of polyethylene oxide, polypropylene oxide (PPO) and glycidol is mixed with the lithium phosphate powder and the polymer powder in a weight ratio of 60:40 to 90:10 Blending;
Mixing the blended powder with an organic solvent to prepare a slurry;
Applying the prepared slurry on a substrate to form a film; And
And drying and evaporating the organic solvent in the coated slurry. The method for producing a composite electrolyte film for a lithium secondary battery according to claim 1, The method according to claim 6,
Wherein the lithium salt is further added in the mixing step. The method according to claim 6,
Wherein the lithium phosphate powder comprises a composition of Li _{1 .5} Al _{0 .5} Ge _{1 .5} (PO ₄ ) ₃ in the mixing step. A multi-component lithium phosphate powder represented by Li _{1 + x} M _{2 - x} M ' _x (PO ₄ ) ₃ on a polyethylene oxide matrix wherein x≥0 and M is at least one selected from the group consisting of Ti, Ge and Hf And M 'is at least one element selected from the group consisting of Al, B and Sn).

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