KR20120087724A - Polysiloxane resin containing single-ion conductor and a film for lithium secondary battery using the same - Google Patents

Abstract

PURPOSE: A polysiloxane polymer resin containing a mono-ionic conductor and a film for lithium secondary batteries are provided to maintain high portability and ion conductivity and enhance electro chemical stability of polyelectrolytes. CONSTITUTION: A polysiloxane polymer resin containing a mono-ionic conductor comprises a polysiloxane precursor, polyfunctional polyethylene oxide, mono-ionic monomers and lithium salt. The polysiloxane is manufactured by a coupling reaction and hydrogen removal polyethylhydrosiloxane and allyl polyether under a platinum catalyst. The polymethylhydrosiloxane has a molecular weight of 1,700-10,000 g/mole and the allyl polyether has a molecular weight of 230-400 g/mole.

Description

Polysiloxane resin containing single-ion conductor and a film for lithium secondary battery using the same}

The present invention relates to an ultraviolet curable polysiloxane polymer electrolyte containing a single ion conductor, a film for a lithium secondary battery using the same, and a lithium secondary battery comprising the same, and more particularly, to provide a high electrochemical stability by containing a single ion conductor. By using an ultraviolet curing process, it can be easily produced into a film, and a polyelectrolyte capable of securing high ion conductivity even after curing using polysiloxane as a substrate, and a film for a lithium secondary battery using the same and a lithium secondary battery comprising the same will be.

The solid polymer electrolyte is being developed as an alternative to greatly improve the safety of the lithium secondary battery, but is still in the research stage because it has not solved the low temperature ion conductivity, the occurrence of polarization due to the concentration gradient of the lithium salt and the improvement of the film properties.

The room temperature ion conductivity and the film properties are mutually opposite requirements. When using a polymer electrolyte of a liquid-like physical property, high room temperature ion conductivity can be obtained, but film formation itself is difficult, and in the opposite case, room temperature ion conductivity is required for excellent film properties. Must sacrifice the As a result, it is necessary to develop a solid electrolyte that can satisfy both requirements simultaneously.

Polarization due to the concentration gradient of lithium salts is a fundamental problem that occurs in solid polymer electrolytes in which lithium salts do not move smoothly. Currently, in order to secure long-term life characteristics of lithium secondary batteries, introduction of giant lithium salts that limit the movement of anions, introduction of additives forming complexes with anions, and introduction of monoion conductive monomers have been studied. Introduction of monomeric monoion conductors is the best means for suppressing polarization, but there is a problem that monomers forming monoions are not dissolved in a general organic solvent. In recently applied patent No. 2010-0140465, monomers having greatly increased solubility by introducing Lewis acid were synthesized, and the polymer synthesis was successfully performed in general organic solvents.

Therefore, an object of the present invention is to solve the problems of the prior art as described above,

To provide a method for producing a suitable film for lithium secondary batteries through the ultraviolet curing process after preparing a polymer resin by using a polysiloxane precursor having a low glass transition temperature as a substrate, by adding polyfunctional polyethylene oxide (meth) acrylate. The purpose is. Accordingly, the present invention can provide a solid electrolyte that simultaneously realizes excellent film properties and high ionic conductivity by soft polymers as a structure in which a polysiloxane precursor is trapped in a crosslinked polymer chain by polyfunctional polyethylene oxide (meth) acrylate. .

Another object of the present invention is to provide a polymer electrolyte for a lithium secondary battery having excellent electrochemical stability and high ion conductivity by low glass transition temperature by introducing a single ion monomer having improved solubility in an existing ultraviolet curable film.

Still another object of the present invention is to provide a lithium secondary battery including the polymer electrolyte.

In order to accomplish the object of the present invention as described above,

A polysiloxane polymer resin is provided that contains a monoionic conductor comprising a polysiloxane precursor, a polyfunctional polyethylene oxide, a monoionic monomer, and a lithium salt.

The polysiloxane may be prepared by hydrogenation and coupling reaction between poly (methylgydrosiloxane) and allylpolyether under a platinum catalyst, and the ratio of the polymethylhydrosiloxane and allylpolyether may be represented by molecular weight. It is preferable to set it as the ratio of 230-400 g / mol allyl polyether with respect to 1,700-10,000 g / mol polymethylhydrosiloxane, Preferably it is 2,400 g / mol, and a platinum catalyst is 0.1-0.5% of a weight of a polymer. It is preferably added with the reaction temperature is preferably 0 ~ 60 ℃.

If the molecular weight of the polymethylhydrosiloxane is less than 1,700g / mole is difficult to secure physical properties due to the low viscosity, when the molecular weight of more than 10,000g / mole, the viscosity is too high, the fluidity is inferior. In addition, when the molecular weight of allyl polyether is 230g / mol or less, there is a problem in ion conductivity due to low content of ethylene oxide, and when it is 400g / mol or more, the solubility of allylpolyether decreases, making it difficult to remove unreacted allylpolyether. It is set as said range.

In addition, the platinum catalyst is required at least 0.1% in order to show the activity of the platinum catalyst, the use of more than 0.5% of the expensive reagent is added to more than the required amount and fall in the economic range is in the above range. The polymer also represents the total amount of both materials. In addition, when the reaction temperature is 0 degrees or less, the reaction rate is too slow, and since the reaction is a large amount of heat generated by itself, when it is raised above 60 degrees, a side reaction such as crosslinking may occur, so the temperature range is preferable. The reaction time takes about 8 to 11 hours because it is unreacted at 8 hours or less, and after 11 hours, there is no reaction.

The polysiloxane precursor may be represented by the following Chemical Formula 1.

In addition, the polyfunctional polyethylene oxide (meth) acrylate may be used one or more selected from the group consisting of two to six chain terminal double bonds.

When the double bonds are two or more in the above, crosslinking is possible, and when the number exceeds 6, the crosslinking density is so high that the physical properties become hard and the double bonds are difficult.

The monoionic monomer may be used at least one selected from the group consisting of lithium acrylate, lithium methacrylate, lithium styrenesulfonate, lithium acrylamide propanesulfonate combined with BF ₃ , ZnCl _2, and the like.

The polymer resin may be additionally introduced with a lithium salt to improve the mobility of lithium ions, and may be used at least one selected from the group of lithium hexyfluorophosphate, lithium perchlorate, and lithium trifluorosulfonylimide.

The polymer resin is preferably composed of a polysiloxane precursor of 70%, a monoionic monomer of 10%, and a polyfunctional polyethylene oxide (meth) acrylate of 30%, as calculated by weight ratio. More preferably, it contains 15-25 weight part of polyfunctional polyethylene oxide (meth) acrylates, 10-20 weight part of monoionic monomers, and 1-50 weight part of lithium salts with respect to 100 weight part of polysiloxane precursors, As a solvent Acetonitrile may be used, in which case it is preferred to use 0.2-2 ml of solvent for 1 g of polysiloxane precursor.

The weight part is in the range of 25% because the polyfunctional polyethylene oxide needs more than 15% for crosslinking, and when too much, the ion conductivity is lowered. In addition, the monoionic monomer has a minimum ratio of 10% to increase the electrochemical stability, and the upper limit is 20% for a suitable lithium ion ratio. In addition, other lithium salts require at least 1% to improve the ionic conductivity, and when the maximum exceeds 50%, the physical properties of the polymer electrolyte are deteriorated as described above.

In addition, the solvent was introduced to dissolve the lithium salt, a minimum of 0.1ml is required, the use of more than 2ml is no problem, but it takes a lot of time to dry. Therefore, the optimum value is found through the embodiment of the present invention.

The polymer resin may be represented by the following formula (2).

The present invention also provides a lithium secondary battery film prepared by curing the polymer resin, wherein the UV curing agent used in the curing can be selected from the species having an activity at 254nm or 365nm, where the active range Is a range that is used a lot in the curing reaction.

The ultraviolet curing agent is preferably added in 2 to 5% by weight of the entire polymer resin.

The polymer resin has a semi-Interpenetration Polymer Network (semi-IPN) structure in which a polysiloxane precursor is freely present in crosslinking of a multifunctional polyethylene oxide (meth) acrylate through a photocuring reaction.

The semi-IPN structure may be represented by the following structural formula.

According to another embodiment of the present invention, the polymer electrolyte; Positive electrode active material; It provides a lithium secondary battery comprising a negative electrode active material.

Since the polysiloxane polymer of the present invention does not participate in crosslinking by itself, it has excellent mobility and can maintain high ion conductivity.

The monoionic monomer of the present invention improves the electrochemical stability of the polymer electrolyte and can reduce the polarization phenomenon in the long life, the polymer electrolyte for lithium secondary battery using the same can be manufactured into a film using an ultraviolet curing process Therefore, there is an effect that can simplify the entire battery manufacturing process.

1 is a cutaway perspective view of a lithium secondary battery.
2 is a graph showing a charge voltage curve and a discharge voltage curve at high temperature.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are merely intended to assist those skilled in the art, but are not intended to limit the invention.

Example 1 Preparation of Polysiloxane Precursor

A thin brown polysiloxane precursor was synthesized by stirring a polymethylhydrosiloxane having a molecular weight of 2,400 g / mol and an allyl polyether having a molecular weight of 230 g / mol at 25 ° C. for 10 hours under 0.05 g of a platinum catalyst in a round flask in a nitrogen atmosphere. The number average molecular weight of the precursor was 18,000 g / mol.

Example 2 Polysiloxane Polymer Resin and Film Preparation

A polymer resin was prepared by adding 1 g of a polysiloxane precursor, 0.16 g of borontrifluoride lithium methacrylate complex, 0.46 g of lithium perchlorate salt, and 0.2 g of polyethylene oxide diacrylate to 2 ml of acetonitrile. 0.05 g of methylbenzoylformate, an ultraviolet curing agent, was added to the resin and irradiated with ultraviolet light at 365 nm for 30 seconds to prepare a film. At this time, the concentration ratio of ethylene oxide and lithium ions, [EO]: [Li] is 4: 1.

Example 3 Polysiloxane Polymer Resin and Film Preparation

1 ml of acetonitrile and 0.25 g of lithium perchlorate salt were used, and other compositions were added in the same amount as in Example 2, and an ultraviolet curing film for a lithium secondary battery was prepared through ultraviolet curing. At this time, the concentration ratio of ethylene oxide and lithium ions, [EO]: [Li] is 6: 1.

Example 4 Polysiloxane Polymer Resin and Film Preparation

0.8 ml of acetonitrile and 0.15 g of lithium perchlorate salt were used, and other compositions were added in the same amount as in Example 2, and an ultraviolet cured film for a lithium secondary battery was prepared through ultraviolet curing. At this time, the concentration ratio of ethylene oxide and lithium ions, [EO]: [Li] is 9: 1.

Example 5 Polysiloxane Polymer Resin and Film Preparation

0.6 ml of acetonitrile and 0.11 g of lithium perchlorate salt were used, and other compositions were added in the same amount as in Example 2, and an ultraviolet cured film for a lithium secondary battery was prepared through ultraviolet curing. At this time, the concentration ratio of ethylene oxide and lithium ions, [EO]: [Li] is 10: 1.

Example 6 Polysiloxane Polymer Resin and Film Preparation

0.4 ml of acetonitrile and 0.09 g of lithium perchlorate salt were used, and other compositions were added in the same amount as in Example 2, and an ultraviolet curing film for a lithium secondary battery was prepared through ultraviolet curing. At this time, the concentration ratio of ethylene oxide and lithium ions, [EO]: [Li] is 11: 1.

Example 7 Polysiloxane Polymer Resin and Film Preparation

0.3 ml of acetonitrile and 0.07 g of lithium perchlorate salt were used, and the other composition was added in the same amount as in Example 2, and an ultraviolet curing film for a lithium secondary battery was prepared through ultraviolet curing. At this time, the concentration ratio of ethylene oxide and lithium ions, [EO]: [Li] is 13: 1.

Example 8 Polysiloxane Polymer Resin and Film Preparation

0.2 ml of acetonitrile and 0.02 g of lithium perchlorate salt were used, and other compositions were added in the same amount as in Example 2, and an ultraviolet cured film for a lithium secondary battery was prepared through ultraviolet curing. At this time, the concentration ratio of ethylene oxide and lithium ion, [EO]: [Li] is 17: 1.

Example 9 Fabrication of Composite Electrode

The polymer resin prepared in Example 5 was coated on a LiMn 2 O 4 positive electrode plate at a concentration of 0.3 g / ml, and dried at 80 ° C. for 10 hours, followed by UV curing in the same manner as in the above example, to form a composite electrode of a positive electrode active material / electrolyte. Was prepared.

Example 10 Preparation of Coin Cell

A coin cell was prepared using the composite electrode prepared in Example 9 as an anode, and using ethylene carbonate / diethyl carbonate containing lithium hexafluorophosphate 1M as a lithium metal as a cathode and a liquid electrolyte.

Example 11 Ion Conductivity Measurement

The room temperature ion conductivity of the ultraviolet curable film prepared according to Examples 2, 3, 4, 5, 6, 7, 8 was measured and the results are shown in Table 1.

Example S / cm (25 ℃) [EO]: [Li] 2 1.4 □ 10 ^-6 4: 1 3 6.6 □ 10 ^-6 6: 1 4 1.010 ^-5 9: 1 5 2.6 □ 10 ^-5 10: 1 6 2.3 □ 10 ^-5 11: 1 7 2.6 □ 10 ^-5 13: 1 8 2.2 □ 10 ^-5 17: 1

Referring to Table 1, in the case of the UV cured films prepared in Example [EO]: [Li] As the ratio is increased that is to lower the concentration of lithium increases the room temperature ionic conductivity. 9: 1.0 at least 1 □ 10 ^{- It} has a high value of ⁵ S / cm.

Example 12 Linear sweep voltammetry

The reverse potential of the ultraviolet curable film prepared according to Example 5 was measured by a linear sweep voltammetry method at a scan rate of 1 s / sec in a coin cell composed of a stainless steel working electrode, a lithium metal reference electrode, and a counter electrode. The results are shown in FIG.

As shown in FIG. 1, the UV-curable film prepared according to the embodiment does not undergo oxidation up to 4.5V, and a small amount of decomposition current generated thereafter is also electrochemically at a level of 1/100 when compared with a value of a general electrolyte. It can be seen that shows excellent stability.

 Example 13 Charging and Discharging Characteristics

The 2016 coin cell prepared according to Example 10 was charged and discharged at a high temperature of 80 ° C., and the results are shown in FIG. 2.

As shown in FIG. 2, even when measured at a high temperature of 80 ° C., a gentle charge voltage curve and a discharge voltage curve can be obtained. The discharge capacity is 93 mAh / g, and a value corresponding to 93% of the value using the liquid electrolyte at room temperature can be obtained. have.

When the experiments under the above conditions using the liquid electrolyte alone, it can be said to be a battery that ensures excellent capacity characteristics, especially at high temperatures, as compared with deterioration of the battery to generally 50 mAh / g or less.

Claims (16)

As a polysiloxane polymer resin containing a monoion conductor for manufacturing a film for lithium secondary batteries,
A polysiloxane polymer resin comprising a polysiloxane precursor, a polyfunctional polyethylene oxide, a monoionic monomer and a lithium salt. The polysiloxane polymer resin of claim 1, wherein the polysiloxane is prepared by hydrogenation and coupling reaction between polyethylhydrosiloxane and allyl polyether under a platinum catalyst. The polysiloxane polymer resin of claim 2, wherein the polymethylhydrosiloxane has a molecular weight of 1,700 to 10,000 g / mol and an allyl polyether has a molecular weight of 230 to 400 g / mol. The polysiloxane polymer resin of claim 2, wherein the platinum catalyst is 0.1 to 0.5% by weight of the polymer, and the reaction temperature is 0 to 60 ° C. The polysiloxane polymer resin according to claim 1, wherein the polyfunctional polyethylene oxide (meth) acrylate is at least one member selected from the group consisting of 2 to 6 chain terminal double bonds. The method of claim 1, wherein the monoionic monomer is at least one selected from lithium acrylate, lithium methacrylate, lithium styrene sulfonate and lithium acrylamide propane sulfonate bonded with BF ₃ , ZnCI ₂ . Polysiloxane polymer resin. The polysiloxane polymer resin of claim 1, wherein the lithium salt is at least one selected from lithium hexoxyphosphate, lithium perchlorate, and lithium trifluorosulfonylimide. The method of claim 1, wherein the polysiloxane precursor; Polyfunctional polyethylene oxide; Monoionic monomers; The proportion of the lithium salt is based on 100 parts by weight of the polysiloxane precursor; 15-25 parts by weight; 10-20 parts by weight; Polysiloxane polymer resin, characterized in that composed of 1 to 50 parts by weight. The polysiloxane polymer resin according to claim 1, wherein the polysiloxane polymer resin is used in an amount of 0.1 to 2 ml with respect to 1 g of the polysiloxane precursor. 10. The polysiloxane polymer resin according to claim 9, wherein the solvent is acetonitrile. A lithium secondary battery film, which is prepared by curing the polysiloxane polymer resin according to any one of claims 1 to 10. The film for lithium secondary battery according to claim 11, wherein the curing reaction is at least one selected from chemical species having an activity at 254 to 365 nm as an ultraviolet curing agent. The film for a lithium secondary battery according to claim 12, wherein the curing agent is methylbenzoylformate. The film for lithium secondary battery according to claim 12 or 13, wherein the ultraviolet curing agent is added in an amount of 2 to 5% by weight of the entire polymer resin. A lithium secondary battery comprising the polysiloxane polymer resin according to any one of claims 1 to 10. A lithium secondary battery, wherein the film according to any one of claims 11 to 14 is used.

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