KR101640972B1 - Non aqueous electrolyte and lithium secondary battery comprising thereof - Google Patents

Abstract

The present invention relates to a non-aqueous liquid electrolyte for a lithium secondary battery containing a POS (POSS) compound, an ionizable lithium salt and an organic solvent, which has an effect of improving the high-temperature stability and lifespan characteristics of the battery, and a lithium secondary battery comprising the same . Accordingly, the non-aqueous liquid electrolyte has an effect of improving high-temperature stability and lifetime characteristics while maintaining a high-rate discharge capacity of an excellent level without deteriorating the high rate charge / discharge characteristics of the lithium secondary battery.

Description

[0001] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery comprising the same.

The present invention relates to a non-aqueous liquid electrolyte for a lithium secondary battery containing a POS (POSS) compound, an ionizable lithium salt and an organic solvent, which has an effect of improving the high-temperature stability and lifespan characteristics of the battery, and a lithium secondary battery comprising the same .

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. Electrochemical devices have attracted the greatest attention in energy storage technology, and among them, attention is focused on the development of rechargeable secondary batteries.

Of the currently applied secondary batteries, the lithium secondary battery generally has an average discharge voltage of about 3.6 V to 3.7 V, which is one of the merits that the discharge voltage is higher than other alkaline batteries and nickel-cadmium batteries. However, in order to achieve such a high driving voltage, an electrochemically stable electrolyte composition is required at a charge / discharge voltage range of 0 to 4.2 V.

On the other hand, when the lithium secondary battery is initially charged, the lithium ions in the non-aqueous liquid electrolyte are reduced to be inserted between the graphite constituting the negative electrode, and the lithium metal oxide constituting the positive electrode is dissolved in the non-aqueous liquid electrolyte, Concentration is maintained. In this process, the lithium ion and the anion of the organic solvent or the lithium salt are partially decomposed to form a thin solid electrolyte interface (SEI) on the surface of the electrode.

The solid electrolyte film serves as a barrier for preventing the collapse of the electrode structure by inserting an organic solvent having a large molecular weight between the graphite constituting the cathode and for facilitating the smooth movement of lithium ions. Therefore, the components and the structure of the solid electrolyte coating formed on the surface of the negative electrode at the time of initial charging of the battery greatly affect battery performance.

However, there arises a problem that the thickness of the battery expands during filling due to gases such as CO, CO ₂ , CH ₄ , C ₂ H ₆ and the like generated from the decomposition of the carbonate-based solvent during the formation reaction of the solid electrolyte film. As the time elapses from the full charge state to the full charge state, the solid electrolyte film gradually collapses due to the increased electrochemical energy and thermal energy, and side reactions are continuously generated. As a result, the thickness of the battery is increased, .

Therefore, studies have been made to change the composition of the solvent component of the carbonate organic solvent or to change the form of the solid electrolyte film formation reaction by mixing specific additives. However, as is known hitherto, when a solvent component is changed or a specific compound is added to an electrolyte solution to improve battery performance, some of the required battery characteristics are improved, but other characteristics are deteriorated.

Under the above circumstances, the inventors of the present invention have been studying a nonaqueous electrolyte solution for a lithium secondary battery capable of improving overall battery characteristics without adversely affecting some battery characteristics, and it has been found that by adding a phosgene compound to an electrolyte solution as an additive, It is possible to improve the high temperature stability and the life characteristic while maintaining the charge / discharge characteristics.

An object of the present invention is to provide a non-aqueous liquid electrolyte for a lithium secondary battery comprising a phos-based compound capable of improving battery life characteristics and high-temperature stability while maintaining excellent high rate charge / discharge characteristics.

Another object of the present invention is to provide a lithium secondary battery comprising the above non-aqueous liquid electrolyte, a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

In order to solve the above problems, the present invention provides a nonaqueous electrolyte solution for a lithium secondary battery containing a POS (POSS) compound, an ionizable lithium salt and an organic solvent.

The present invention also provides a lithium secondary battery comprising the above non-aqueous liquid electrolyte, a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

The non-aqueous liquid electrolyte containing the positive charge type compound or the positive charge type compound and the phosphate type compound according to the present invention improves the high temperature stability and the life characteristic while maintaining the high rate discharge capacity of the lithium secondary battery without lowering the high rate charge / .

1 is a graph showing a result of a high-rate discharge capacity analysis of a secondary battery including an electrolyte according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The nonaqueous electrolyte solution for a lithium secondary battery of the present invention is characterized by containing a POSS compound, an ionizable lithium salt and an organic solvent.

POSS refers to a polyhedral oligomeric silsesquioxane, and the term "POSS compound" used in the present invention refers to a substance having the above-mentioned fossa skeleton.

The phosphine compound according to the present invention may be a compound represented by the following general formula (1).

[Chemical Formula 1]

Wherein R, R may be an acrylate group (-OOCHC = H ₂ C), or is a polyethylene glycol _{(H (OCH 2 CH 2)} n OH). Preferably, R may be an acrylate group.

On the other hand, when R is polyethylene glycol (H (OCH ₂ CH ₂ ) _n OH), n may be 1 to 16. If n is less than 1, the function as a functional group may be lost. If n exceeds 16, the resistance as an additive becomes too large due to an increase in molecular weight, and entanglement between long functional groups occurs And problems such as increase in resistance and difficulty in dispersion may occur.

Specifically, the phos compound represented by Formula 1 may be a substance in which an acrylate group or polyethylene glycol is bonded to each of eight Si atoms located in eight directions in a force.

The phosgene compound to which the acrylate group or polyethylene glycol is bonded is not particularly limited and may be prepared by a commonly known production method in the art or may be used by being commercially available in the art.

When the above-mentioned phosphosilicate compound is prepared and used, it can be prepared by mixing and reacting a phosphosiloxane compound with an acrylate-based compound or polyethylene glycol. Acrylo-Phos (MA0736) manufactured by Hybrid- PEG-force, etc., and has the following characteristics.

The acrylo-foe is in the form of a colored oil having a molecular weight of 1321.75 g / mol and is soluble in solvents such as tetrahydrofuran (THF), chloroform, acetone, and acetonitrile, but not in water or methanol .

The PEG-force is a pale yellow liquid with a molecular weight of 5576.6 g / mol and has 13 repeating units. It is soluble in water and alcohols, but not in hexanes.

The acrylate compound may be at least one selected from the group consisting of cyclohexyl (meth) acrylate, benzyl (meth) acrylate, butoxyethyl (meth) acrylate, cetyl methacrylate, ethyl (meth) acrylate, glycerol (Meth) acrylate, hexafluoropropyl (meth) acrylate, isobutyl (meth) acrylate or t-butyl (meth) acrylate.

The phosphine compound according to the present invention may be contained in an amount of 0.5 to 2 wt% based on 100 wt% of the non-aqueous liquid electrolyte. If the non-aqueous liquid electrolyte contains less than 0.5% by weight of the phos-based compound, the desired effect may not be sufficiently obtained. On the other hand, when the amount of the electrolyte is more than 2% by weight, aggregation occurs due to the nano-sized particles of the POS compound, thereby failing to smoothly perform the original role and lowering the lithium ion permeability of the solid electrolyte coating, And the capacity and charge / discharge efficiency can be lowered.

Meanwhile, the non-aqueous liquid electrolyte of the present invention may further include a phosphate-based compound. The phosphate-based compound may be contained in an amount of 0.1% by weight to 0.3% by weight based on 100% by weight of the nonaqueous electrolyte solution. If the phosphate-based compound is contained outside the above range, not only the desired effect can be obtained but also the battery performance may be deteriorated.

The phosphate-based compound may be triacrylate phosphate.

Further, the non-aqueous liquid electrolyte according to the present invention may contain a phos-based compound and a phosphate-based compound at the same time. At this time, it is preferable that the phospho-based compound and the phosphate-based compound have a weight ratio of 0.5: 0.1 to 2: 0.3. If the weight ratio of the phosphine compound and the phosphate compound exceeds the above range and is contained in the electrolyte solution, it acts as a large resistance which interferes with the movement of lithium ions in the electrolyte solution, .

The phosphine compound according to the present invention may be contained in an amount of 0.5 to 2 wt% based on 100 wt% of the non-aqueous liquid electrolyte. If the non-aqueous liquid electrolyte contains less than 0.5% by weight of the phos-based compound, the desired effect may not be sufficiently obtained. On the other hand, when the amount of the electrolyte is more than 2% by weight, aggregation occurs due to the nano-sized particles of the POS compound, thereby failing to smoothly perform the original role and lowering the lithium ion permeability of the solid electrolyte coating, And the capacity and charge / discharge efficiency can be lowered.

That is, the non-aqueous liquid electrolyte according to an embodiment of the present invention may simultaneously contain a phos compound represented by Formula 1 and acrylate or triacrylate phosphate combined with polyethylene glycol. For example, it may be one containing a phosphorus compound bonded with an acrylate group and triacrylate phosphate at the same time. At this time, it is preferable that the acrylate-bonded phos compound and triacrylate phosphate have a weight ratio of 0.5: 0.1 to 2: 0.3.

As described in the Experimental Examples to be described later, when the lithium secondary battery comprising the non-aqueous liquid electrolyte of the present invention containing the above-mentioned positive system compound or the positive system compound and the phosphate system compound simultaneously contains the electrolytic solution of the comparative example , The high rate charge / discharge characteristics were maintained at an equivalent level, but it was remarkably improved in terms of high temperature stability and lifetime characteristics.

On the other hand, the lithium salt of the anion of the present invention is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CH 3) 2 _{^{PF 4 -, (CF 3)}} 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 _{^{-, (CF 3 SO 2)}} 2 N -, (FO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 6) 3 C -, (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- Or more.

The organic solvent may be a mixture of ethylene carbonate, propylene carbonate and ethyl propionate or a mixture of ethylene carbonate and ethyl propionate.

When the organic solvent is a mixture of ethylene carbonate, propylene carbonate and ethyl propionate, it may be preferable to mix the ethylene carbonate, propylene carbonate and ethyl propionate in a weight ratio of 3: 1: 6 to 3: 2: 5 .

When the organic solvent is a mixture of ethylene carbonate and ethyl propionate, it may be a mixture of ethylene carbonate and ethyl propionate in a weight ratio of 3: 7.

The present invention also provides a lithium secondary battery comprising a nonaqueous electrolyte solution containing the above-mentioned phosphine compound, a separator interposed between the anode and the cathode, and between the anode and the cathode.

The positive electrode of the present invention can be produced, for example, by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, followed by drying, and if necessary, a filler may be further added to the mixture.

The cathode active material is not limited as long as it is commonly used in the art, but may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxide (LiMnO ₂ ); Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxide; Nickel-situ type lithium nickel oxide; A lithium manganese composite oxide, a disulfide compound, or a composite oxide formed by combination of these compounds, and the like.

The cathode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. Examples of the cathode current collector include carbon, nickel, aluminum, nickel, titanium, Titanium, silver, or the like. The current collector may be formed in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, or the like by forming fine irregularities on the surface of the current collector to increase the adhesive force of the cathode active material.

The conductive material is not particularly limited as long as the conductive material does not cause a chemical change in the battery, and is conductive. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, and lamp black; Conductive fibers such as carbon fibers and metal fibers, and the like.

The binder is a component that assists in bonding between the active material and the conductive material, and bonding to the current collector, and is usually composed of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, carboxymethylcellulose, starch, hydroxypropylcellulose, Polypropylene, ethylene-propylene-diene terpolymer, sulfonated ethylene-propylene-diene terpolymer, styrene butylene rubber or fluorine rubber, and the like.

The negative electrode may be manufactured by applying a negative electrode active material on the negative electrode collector and drying the negative electrode active material. If necessary, the negative electrode may further include the above-described components.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include carbon, nickel, and the like on the surface of copper, stainless steel, aluminum, nickel, titanium, , Titanium, silver, or the like. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The separation membrane is not particularly limited, and an insulating thin film having high ion permeability and mechanical strength can be used. For example, polyethylene, polypropylene, polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and combinations thereof, having a microporous structure.

The lithium secondary battery according to the present invention is not particularly limited and can be manufactured by a conventional method known in the art.

For example, the electrode assembly may be fabricated by assembling an electrode assembly composed of an anode, a cathode, and a separator interposed between the anode and the cathode, and injecting a non-aqueous electrolyte containing the phosphorus compound into the electrode assembly.

The lithium secondary battery according to the present invention is not particularly limited in external appearance, but may be a cylindrical, square, or coin type using a pouch-type can.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. However, the following examples and experimental examples are provided for illustrating the present invention, and the scope of the present invention is not limited thereto.

[ Example  One]

Ethylene carbonate, propylene carbonate, and ethyl propionate were mixed in a weight ratio of 3: 1: 6, and 1 M LiPF ₆ was added to the mixed organic solvent. Thereafter, a force having an acrylate group of 2% by weight based on 100 parts by weight of the electrolytic solution was added to prepare a nonaqueous electrolytic solution. At this time, the acryl-group-containing force (MA0736) was purchased from Hybrid-Plastics Corporation.

The prepared electrolyte solution was uniformly injected into a pouch-shaped battery having a cathode having a LiCoO ₂ active material layer and a cathode having a synthetic graphite active material layer to prepare a battery.

[ Example  2]

A battery was prepared in the same manner as in Example 1 except that 0.5% by weight of a force having an acrylate group was added.

[ Example  3]

A battery was prepared in the same manner as in Example 1, except that 0.5% by weight of an acrylate group-containing catalyst and 0.2% by weight of triacrylate phosphate were added together.

[ Example  4]

A battery was prepared in the same manner as in Example 1 except that 2 wt% of polyethylene glycol-bonded force was added. At this time, the polyethylene glycol-bonded force was PEG-force (13 repetitive units) manufactured by Hybrid-Plastics Corporation.

[ Comparative Example ]

A mixed solvent of ethylene carbonate, propylene carbonate and ethyl propionate in a weight ratio of 3: 1: 6 was mixed with LiPF ₆ at a concentration of 1 M to prepare a nonaqueous electrolytic solution.

The prepared electrolyte solution was uniformly injected into a pouch-shaped battery having a cathode having a LiCoO ₂ active material layer and a cathode having a synthetic graphite active material layer to prepare a battery.

Experimental Example  1: High temperature safety evaluation

In order to comparatively analyze the high-temperature safety of each of the secondary batteries manufactured in Examples 1 to 4 and Comparative Examples, the degree of swelling of the battery at a high temperature was measured.

The cells of Examples 1 to 4 and Comparative Example were each heated for 1 hour from room temperature to 90 占 폚 and maintained at 90 占 폚 for 4 hours. Then, the temperature change of the battery was measured in real time while the temperature was reduced for 1 hour at 90 ° C. The results are shown in Table 1 below.

division Initial thickness (mm) Final thickness (mm) Thickness increase rate (%) Example 1 4.55 4.96 9.01 Example 2 4.42 5.60 26.70 Example 3 4.47 5.29 18.34 Example 4 4.47 5.88 31.54 Comparative Example 4.52 6.46 42.92

As shown in Table 1, the lithium secondary battery according to the present invention, which includes the lithium-based compound or the lithium-based compound and the phosphate-based compound at the same time, As compared with the control group. This means that the electrolytic solution containing the phosphine compound or the phosphine compound and the phosphate compound simultaneously according to the present invention has an effect of improving the high temperature stability of the battery.

Experimental Example  2: Evaluation of battery life characteristics

In order to compare the battery life characteristics of the lithium secondary battery including the electrolyte containing the phos compound of Example 3 and the lithium secondary battery of the comparative example, the battery capacity retention ratio was analyzed.

First, in order to measure the initial capacity, the lithium secondary batteries of Example 3 and Comparative Example were discharged until a current of 3 C at a rate of 0.2 C was reached, and the battery was charged at a constant current of 1 C After charging to 1/20 mA of current, discharge to 3 V was repeated 4 times with 1 C current. The discharge capacity at the last stage was measured.

After the initial capacity was measured, charging and discharging were carried out 100 times at 1.2 C / 1 C-rate at room temperature in the same voltage range, and the discharge capacity was measured 100 times. The results are shown in Table 2 below.

division Shipping Thickness after filling (mm) Initial capacity (mAh) Capacity retention after 100 times charge / discharge (%) Example 3 4.28 1349.3 89.3 Comparative Example 4.29 1345.7 77.8

As shown in Table 2, in comparison with the lithium secondary battery of the comparative example including the electrolytic solution containing no phospho-compound, the electrolytic solution containing the phospho-based compound and the phosphate- It was confirmed that the capacity retention rate of the lithium secondary battery was remarkably high. Accordingly, it has been confirmed that the electrolyte solution containing both the phosphine-based compound and the phosphate-based compound according to the present invention has an effect of improving the life characteristics of the battery.

Experimental Example  3: High rate Charging and discharging  Character rating

In order to compare the high rate charge reversal characteristics of the lithium secondary batteries of Examples 1 to 3 and Comparative Examples, a high rate charge / discharge test was performed as described below.

The lithium secondary batteries of Examples 1 to 3 and Comparative Examples were initially charged and discharged, and then subjected to 0.5 C charging / 1.0 C discharging, 0.5 C charging / 1.5 C discharging, and 0.5 C charging / 2.0 C discharging. The results are shown in Table 3 and FIG.

division High rate discharge capacity retention rate (%) 1.0 C 1.5 C 2.0 C Example 1 96.6 92.3 71.3 Example 2 96.9 93.3 71.1 Example 3 95.9 91.8 72.3 Comparative Example 96.8 93.0 70.9

As shown in Table 3 and FIG. 1, the lithium secondary batteries of Examples 1 to 3 comprising the lithium-based compound according to the present invention or the electrolyte containing both the phosphine-based compound and the phosphate- It was confirmed that the high rate discharge capacity retention ratio was equivalent to that of the battery.

As shown in the above Experimental Example, the non-aqueous liquid electrolyte containing the phos-type compound or the phos-system compound and the phosphate-based compound of the present invention can be obtained by adding the above-mentioned phos- and phosphate-based compounds as additives to the non- Temperature swelling phenomenon of the battery is suppressed while maintaining a high rate charge / discharge characteristic equivalent to that of an electrolyte solution containing no electrolyte, thereby improving the high-temperature stability of the battery and improving the lifetime characteristics of the battery.

In particular, a lithium secondary battery (Example 3) comprising a nonaqueous electrolyte solution containing a phosgene compound having an acrylate group and a triacrylate phosphate at a weight ratio of 0.5: 3 (Example 3) contains a nonaqueous electrolyte solution containing only a phos- (Examples 1, 2 and 4), which have relatively high temperature stability and life characteristics.

Claims (14)

POS (POSS) based compounds;
Ionizable lithium salts; And
An organic solvent,
Wherein the phos-based compound is a compound represented by the following formula (1).
[Chemical Formula 1]

(Wherein R is an acrylate group (-OOCHC = H ₂ C)
delete delete The method according to claim 1,
Wherein the phosphorus compound is contained in an amount of 0.5 to 2 wt% based on 100 wt% of the non-aqueous liquid electrolyte.
The method according to claim 1,
Wherein the non-aqueous liquid electrolyte further comprises a phosphate-based compound.
6. The method of claim 5,
Wherein the phosphate-based compound is triacrylate phosphate.
6. The method of claim 5,
Wherein the phosphate compound is contained in an amount of 0.1% by weight to 0.3% by weight based on 100% by weight of the non-aqueous liquid electrolyte.
The method according to claim 1,
Wherein the non-aqueous liquid electrolyte comprises a phos-based compound and a phosphate-based compound in a weight ratio of 0.5: 0.1 to 2: 0.3.
delete delete The method according to claim 1,
The anion of the lithium salt may be selected from the group consisting of F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CH ₃ ) ₂ PF ₄ ^{- _{CF 3) 3 PF 3 -,}} (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 ^{_{SO 2) 2 N -, (}} FO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 6) 3 C -, (CF 3 SO 2 ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- A nonaqueous electrolyte solution for a lithium secondary battery.
The method according to claim 1,
Wherein the organic solvent is a mixture of two or more selected from the group consisting of ethylene carbonate, propylene carbonate, and ethyl propionate.
13. The method of claim 12,
Wherein said mixture is a mixture of ethylene carbonate, propylene carbonate and ethyl propionate in a weight ratio of 3: 1: 6 to 3: 2: 5.
14. A lithium secondary battery comprising an electrolyte solution according to any one of claims 1 to 12, and an anode, a cathode, and a separator interposed between the anode and the cathode.

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