KR102315177B1 - Hybrid Electrolyte comprising Lithium Phosphates and Polymer For Li Batteries Operable At Room Temperatures And Li Batteries comprising The Same - Google Patents

Abstract

The present invention relates to a lithium secondary battery including an electrolyte in the form of a film and a method for manufacturing the same. The present _{invention, Li 1 + x M 2 -} x M 'x (PO 4) 3 ( where, x≥0 and, M is at least one element selected from the group consisting of Ti, Ge, and Hf, M' is at least one element selected from the group consisting of Al, B and Sn); at least one polymer selected from the group consisting of polyethylene oxide and polypropylene oxide (PPO); polymer plasticizers; and a composite electrolyte in the form of a film containing a lithium salt, wherein the weight ratio of the lithium phosphate powder and the polymer in the composite electrolyte is in the range of 60:40 to 90:10.

Description

Lithium Phosphate-Polymer Composite Electrolyte and Secondary Battery Containing Same

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including a film-type electrolyte capable of being driven at room temperature and a method for manufacturing the same.

A lithium secondary battery is largely composed of a positive electrode, an electrolyte, and a negative electrode. Universal lithium secondary batteries commercially available are as when is in an organic solvent and a lithium salt in a liquid electrolyte with added polymer membrane of 15 ~ 25 ㎛ thickness structure in consisting of, discharged, moved to the positive electrode in a Li ⁺ ion the negative electrode and Li is ionized The generated electrons also move from the cathode to the anode, and vice versa during charging. The driving force of such Li ⁺ ion migration is generated by chemical stability according to the potential difference between the two electrodes. ^{The amount of Li +} ions moving from the negative electrode to the positive electrode and from the positive electrode to the negative electrode determines the capacity (Ah) of the battery. On the other hand, since ^{the movement of Li +} ions is done through the electrolyte, the Li ⁺ ion conductivity of the electrolyte affects the charge/discharge rate of the battery.

An all-solid-state battery refers to a liquid electrolyte replaced with a solid electrolyte among the above battery components. Compared to liquid electrolytes, all-solid-state secondary batteries are attracting attention as next-generation secondary batteries because they do not have the risk of explosion or fire, simplify the manufacturing process, and increase energy density. However, while the all-solid-state secondary battery has higher safety and the like compared to liquid electrolyte, there is a problem in that the ion conductivity decreases because the ion conduction path is small due to the decrease in interfacial contact with the electrode.

In addition, in recent years, lithium ion secondary batteries using a polymer electrolyte made of a polymer have received more attention than batteries using the electrolyte using an electrolyte solution. These polymer cells use a gel type electrolyte. This battery has no risk of leakage and has improved safety because it contains less flammable organic solvent. Further, such a cell has the advantage of having an improved degree of freedom in the shape it can take. However, this type of polymer electrolyte has a problem in that it has a lower lithium ion conductivity than an electrolyte type electrolyte and mechanical strength is also reduced, resulting in a short circuit between the positive electrode and the negative electrode due to damage to the polymer electrolyte during the manufacturing process.

US 10-1997-18826 A

In order to solve the problems of the prior art, 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 having an optimized composition for improving electrical conductivity.

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

Another object of the present invention is to provide a method for manufacturing the above-described lithium secondary battery.

Another object of the present invention is to provide a lithium secondary battery comprising a composite electrolyte composed of a polymer and an ion conductive lithium phosphate and capable of operating at room temperature.

Another object of the present invention is to provide a composite electrolyte composition that is easily molded into a film-type electrolyte.

The present invention to achieve the above-mentioned technical problems _{is, Li 1 + x M 2 -} x M 'x (PO 4) 3 ( where, x≥0 and, M is at least selected from the group consisting of Ti, Ge and Hf 1 a multicomponent lithium phosphate powder represented by an element of a species, and M' is at least one element selected from the group consisting of Al, B and Sn); at least one polymer selected from the group consisting of polyethylene oxide and polypropylene oxide (PPO); polymer plasticizers; and a composite electrolyte in the form of a film containing a lithium salt, wherein the weight ratio of the lithium phosphate powder and the polymer in the composite electrolyte is in the range of 60:40 to 90:10.

In the present invention, the weight ratio of the polymer and the plasticizer is preferably in the range of 99:1 to 70:30.

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

In the present invention, the polymer is preferably polyethylene oxide, and the plasticizer is preferably succinonitrlie (SN).

The lithium phosphate powder in the present invention may include _{Li 1 .5 Al 0 .5 Ge 1} .5 (PO4) 3 composition.

In the present invention, the polymer plasticizer is preferably included in an amount of 2 to 6% by weight based on the total weight of the composite electrolyte.

In addition, the present invention in order to achieve the above-mentioned technical problems is, Li _{1 + x} M _{2 -} and _x M _'x (PO ₄₎ multi-component system lithium phosphate powder (where, x≥0 represented by the _3, M is Ti, Ge, and at least one element selected from the group consisting of 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 so that the weight ratio of the lithium phosphate powder and the polymer powder is within the range of 60:40 to 90:10. blending; preparing a slurry by mixing the blended powder with an organic solvent; forming a film by applying the prepared slurry on a substrate; and evaporating the organic solvent from the applied slurry to dry it, wherein the slurry contains a polymer plasticizer in an amount of 9:1 to 7:3 based on the weight of the polymer powder.

In the present invention, the compounding step may further include adding a lithium salt.

Also the present invention to an aspect, the polyethylene oxide matrix Li _{1 + x} M ₂ on _- and _x M _'x (PO ₄₎ multi-component system lithium phosphate powder (where, x≥0 represented by the _3, M is At least one element selected from the group consisting of Ti, Ge and Hf, M' is at least one element selected from the group consisting of Al, B and Sn) is dispersed, and the weight ratio to the polyethylene oxide is 99: It provides a composite electrolyte film, characterized in that it contains a plasticizer in a ratio of 1 to 70:30.

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

In addition, according to the present invention, it is possible to solve the problem of low mechanical strength of the polymer electrolyte while having the advantage of a polymer electrolyte with easy moldability, and has the advantage of not requiring other complicated processes for molding.

In addition, the secondary battery having the composite electrolyte according to the present invention exhibits high ionic conductivity at room temperature as well as high charge/discharge capacity and stable charge/discharge characteristics.

1 is a flowchart showing a manufacturing procedure of a composite electrolyte film according to a preferred embodiment of the present invention.
2 is a plan view of a film sample prepared according to a preferred embodiment of the present invention.
3 is an electron micrograph of a cross-sectional structure of a film sample prepared according to a preferred embodiment of the present invention.
4 is a graph showing the ionic conductivity measurement result of the composite electrolyte film prepared according to a preferred embodiment of the present invention.
5 is a graph showing the ionic conductivity according to the temperature of the composite electrolyte film prepared according to a preferred embodiment of the present invention.
6 is a graph showing the results of a charge/discharge test of an all-solid-state lithium battery manufactured according to a preferred embodiment of the present invention.

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the drawings.

The present invention provides a composite solid electrolyte comprising the multi-component lithium phosphate represented and a polymer.

(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 above-mentioned compound is also expressed as LISICON (Li Super Ion Conductivity), and due to its structural characteristics, lithium and sodium can move very quickly in the structure, and thus the ionic conductivity is very good.

In addition, the compounds of the lysicone structure are polyanionic compounds that strongly hold the structure like olivine-type compounds, and have excellent thermal stability and lifespan characteristics. Lithicon-structured solid electrolytes have a three-dimensional interstitial structure, so lithium ions can move easily in all directions, so high ionic conductivity can be expected. have an advantage

In LISICON, Li or other metals can be substituted for metal ions. LAGP (lithium-aluminum-), which is known to improve the high grain boundary resistance of the lysicon structure through metal substitution, and exhibits strong covalent bonding of Ge-O by substitution of Ge metal, is known to have better stability at electrochemical reduction potentials. germanium-phosphate). For _{example, Li 1 .5 Al 0 .5 Ge} 1 For the electrolyte having _.5 (PO4) ₃ composition has a high ionic conductivity of 2.18x10 ^-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) and polypropylene oxide (PPO). Preferably, polyethylene oxide is used as the polymer of the composite electrolyte.

In the present invention, the composite solid electrolyte includes a lithium salt. The lithium salt may serve as a source of lithium ions in the electrolyte. As the lithium salt, LiTFSI, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li(CF ₃ SO ₂ ) ₃ C , and LiBPh ₄ At least one compound selected from the group consisting of may be used.

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

Hereinafter, a method of manufacturing the composite electrolyte film will be described with reference to FIG. 1 .

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

Additionally, a plasticizer is used for the production of the composite electrolyte film in the present invention. The plasticizer is at least one selected from the group consisting of succinonitrlie (SN), ethylene carbonate (EC), propylene carbonate {Propylene Carbonate, PC}, γ-butyrolactone, and a polymer-based plasticizer of plasticizers may be used. As the polymer-based plasticizer, for example, polyethylene glycol dimethyl ether (PEGDME) or low molecular weight PEG may be used. The plasticizer improves the room temperature ionic conductivity of the composite electrolyte film.

Then, the above-mentioned powders, lithium salt and plasticizer are stirred and mixed in an organic solvent to prepare a mixed slurry (S110). Next, the prepared mixed slurry is applied on a predetermined substrate such as a glass substrate to form a film (S120). An electrolyte film is prepared by drying the organic solvent contained in the coated film (S130) and removing the substrate (S140).

Through the above manufacturing process, the electrolyte film has a form in which ion conductive lithium phosphate is dispersed on a polymer matrix as shown in FIG. 3 .

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

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention.

lithium phosphate powder ( LAGP ) manufacturing

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

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. Calcination results, the boron (B) doped LAGP (Li Ge _{1 .5 1 .5 0 .5} Al (PO _{4) 3)} of this powder was synthesized. The ionic conductivity of the synthesized LAGP at room temperature was 2.18*10 ^-4 S/cm.

Preparation of Electrolyte Film

(Example 1)

Polyethylene oxide in the solid electrolyte: LAGP weight ratio of 100: 0 to 10: 90 by varying the weights of polyethylene oxide and LAGP to prepare electrolyte film samples of each composition. Polyethylene oxide having a molecular weight (Mn) of 200,000 was used as the polyethylene oxide.

First, using ACN (acetonitrile) as an organic solvent, lithium salt (LiClO ₄ ) was dissolved. At this time, the content of the dissolved lithium salt was such that the molar ratio to polyethylene oxide was 1/18. Then, polyethylene oxide powder (Aldrich) and the previously prepared LAGP were added to the organic solvent in which the lithium salt was dissolved according to the mixing ratio, and stirred to prepare a slurry.

The prepared slurry was thinly cast on a Teflon plate with a doctor blade, dried at room temperature in an Ar gas atmosphere for 24 hours, and then dried in a vacuum for 24 hours. The dried film exhibited a thickness of several tens to several hundreds of μm. The prepared electrolyte film was punched out in a circle.

2 is a planar photograph of a circular film, and FIG. 3 is an electron microscope photograph of a cross-section of a sample having a LAGP content of 70 wt%.

(Example 2)

The effect of adding a plasticizer was observed based on a case where the weight ratio of LAGP:PEO was 70:30.

The content of the plasticizer in the solid electrolyte was maintained at 0 to 30 parts by weight based on 100 parts by weight of the sum of the polyethylene oxide and the plasticizer. The LAGP content was maintained to be 70:30 with respect to the sum of polyethylene oxide and plasticizer. As the polyethylene oxide, polyethylene oxide having a molecular weight (Mn) of 200,000 was used.

First, using ACN (acetonitrile) as an organic solvent, lithium salt (LiClO ₄ ) was dissolved. The content of the dissolved lithium salt was such that the molar ratio to polyethylene oxide was 1/10.

Then, polyethylene oxide powder (Aldrich), succinonitrile (Succinonitrile), and LAGP prepared above were added to the organic solvent in which the lithium salt was dissolved according to the mixing ratio and stirred to prepare a slurry. The mixing ratio (weight ratio) of each raw material is shown in Table 1.

Psalter LAGP PEO (200K) LiClO ₄ Succinonitrile 70-C-10 1.4 0.6 0.145 - 70-C-10-SN10 1.4 0.54 0.131 0.06 70-C-10-SN20 1.4 0.48 0.116 0.12 70-C-10-SN30 1.4 0.42 0.101 0.18

The prepared slurry was thinly cast on a flat substrate with a doctor blade, dried at room temperature in an Ar gas atmosphere for 24 hours, and then dried in a vacuum for 24 hours. The dried film exhibited a thickness of several tens to several hundreds of μm. The prepared electrolyte film was punched out in a circle.

Measurement of ionic conductivity

The punched ^{round film of 1.54 cm 2} was laminated in the order of stainless steel/film/stainless steel to construct a cell, and the AC impedance of the cell was measured. Impedance was repeated by varying the cell temperature (25°C to 75°C), and was performed under the condition of a frequency range of ^{0.1 to 10 5 Hz and an amplitude of 100 mV.} The ionic conductivity was calculated from the measured impedance.

4 is a graph showing the measurement results of the ion conductivity of each sample prepared in Example 1. As shown, it can be seen that the ionic conductivity increases as LAGP replaces polyethylene oxide. In addition, when LAGP replaces 60-80% by weight of polyethylene oxide, the electrical conductivity can be seen at the maximum value.

In addition, the composite solid electrolyte composed of LAGP and polyethylene oxide exhibits a higher ionic conductivity value than that of a pure polymer electrolyte in a relatively very wide mixing range. That is, when 60 wt% or more of LAGP is included with respect to the total weight of the solid electrolyte (LAGP + PEO), preferably 60 to 90 wt%, more preferably 60 to 80 wt%, relatively high ionic conductivity can be seen to indicate

5 is a graph showing the ionic conductivity measurement results of each sample prepared in Example 2.

Referring to FIG. 5 , each specimen exhibits a tendency to decrease in ionic conductivity as the temperature decreases. In the case of the sample to which no plasticizer was added, the ionic conductivity decreased sharply with temperature, whereas the sample to which the plasticizer was added showed a gradual decrease.

In particular, it can be seen that the specimen to which the plasticizer is added at room temperature exhibits high ionic conductivity according to the amount of the plasticizer added. Table 2 below shows the ionic conductivity (S/cm) of each specimen.

division 25 ℃ 35 ℃ 45 ℃ 55 ℃ 65 ℃ 75 ℃ 70-C-10 9.9×10 ^-6 2.4×10 ^-5 5.0×10 ^-5 8.9×10 ^-5 1.3×10 ^-4 1.7×10 ^-4 70-C-10-SN10 1.3×10 ^-5 3.0×10 ^-5 5.7×10 ^-5 1.0×10 ^-4 1.5×10 ^-4 1.9×10 ^-4 70-C-10-SN20 2.7×10 ^-5 5.8×10 ^-5 1.1×10 ^-4 2.0×10 ^-4 2.9×10 ^-4 3.5×10 ^-4 70-C-10-SN30 4.6×10 ^-5 1.0×10 ^-5 1.8×10 ^-4 3.1×10 ^-4 4.3×10 ^-4 5.6×10 ^-4

6 is a graph showing the results of the charging and discharging test for the specimen of Example 2.

In the charge/discharge test, the charging conditions were 0.2C (C-rate) and cut-off voltage (25°C) of 4.0V, and the discharging conditions were 0.2C (C-rate) and cut-off volage (25°C) of 2.6V.

Referring to FIG. 6 , the plasticizer-added specimen 70-C-10-SN30 exhibits higher discharge capacity at room temperature than the plasticizer-free specimen 70-C-10.

Claims (10)

Multi-component lithium phosphate powder represented by Li _1+x M _2-x M' _x (PO ₄ ) ₃ , wherein x≥0, and 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); at least one polymer selected from the group consisting of polyethylene oxide and polypropylene oxide (PPO); polymer plasticizers; And a composite electrolyte in the form of a film containing a lithium salt,
The weight ratio of the lithium phosphate powder and the polymer in the composite electrolyte is within the range of 60:40 to 80:20,
The plasticizer includes succinonitrlie,
A lithium secondary battery, characterized in that the weight ratio of the polymer to the plasticizer is 90:10 to 70:30. delete delete According to claim 1,
The polymer is a lithium secondary battery, characterized in that the polyethylene oxide. According to claim 1,
The lithium phosphate powder was _{Li 1 .5 Al 0 .5 Ge 1} .5 (PO4) a lithium secondary battery, comprising a step of including _three compositions. delete delete Multi-component lithium phosphate powder represented by Li _1+x M _2-x M' _x (PO ₄ ) ₃ , wherein x≥0, and 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 blending at least one polymer powder selected from the group consisting of polyethylene oxide and polypropylene oxide (PPO) so that the weight ratio of the lithium phosphate powder and the polymer powder is in the range of 60:40 to 80:20;
preparing a slurry by mixing the blended powder with an organic solvent;
forming a film by applying the prepared slurry on a substrate; and
and evaporating the organic solvent from the applied slurry to dry it,
The slurry contains 80:20 to 70:30 of a polymer plasticizer based on the weight of the polymer powder,
The plasticizer is a method of manufacturing a composite electrolyte film for a lithium secondary battery, characterized in that it comprises succinosuccinonitrile (succinonitrlie). 9. The method of claim 8,
A method of manufacturing a composite electrolyte film for a lithium secondary battery, characterized in that further adding a lithium salt in the mixing step. _{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 selected from the group consisting of Ti, Ge and Hf. In the composite electrolyte film in which M' is at least one element selected from the group consisting of Al, B and Sn) is dispersed,
The weight ratio of the lithium phosphate powder and the polymer in the composite electrolyte of the composite electrolyte film is in the range of 60:40 to 80:20,
The composite electrolyte film further comprises a plasticizer,
The composite electrolyte film, characterized in that the plasticizer contains succinonitrile in a weight ratio of 80:20 to 70:30 compared to the polyethylene oxide.

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