WO2018097523A1 - Electrolyte solution for secondary battery and secondary battery comprising same - Google Patents

Abstract

The present invention relates to an electrolyte solution, which comprises glyoxal sulfate and difluorophosphate salts, for a secondary battery and a secondary battery comprising same. The secondary battery has excellent output properties and capacitive properties during high-temperature storage and shows enhanced high-temperature lifetime characteristics.

Description

Electrolyte for secondary battery and secondary battery comprising same

The present invention relates to a secondary battery electrolyte comprising a glyoxal sulfate and difluorophosphate and a secondary battery comprising the same, the secondary battery has excellent output characteristics and capacity characteristics at high temperature storage, and exhibits improved high temperature life characteristics. .

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among secondary batteries, lithium secondary batteries having high energy density, excellent lifespan characteristics, and low self discharge rate have been commercialized and widely used.

Recently, as interest in environmental problems increases, researches on electric vehicles and hybrid electric vehicles, which can replace vehicles using fossil fuel, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, are being conducted. . As a power source of such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries of high energy density, high discharge voltage, and output stability have been actively conducted, and some of them have been commercialized.

The lithium secondary battery is composed of a negative electrode such as a carbon material that occludes and releases lithium ions, a positive electrode made of a lithium-containing oxide, and the like, and a non-aqueous electrolyte solution in which lithium salt is dissolved in an appropriate amount. A number of additives and electrolyte composition techniques are added to improve the output stability of the non-aqueous electrolyte. In addition, a number of additives and electrolyte composition techniques are known that form a high quality film (solid electrolyte interface) on the positive electrode and the negative electrode to improve the capacity storage characteristics of the secondary battery.

For example, Japanese Patent No. 3439085 discloses an additive for a secondary battery including lithium fluorophosphate or lithium difluorophosphate. The registered patent discloses that a lithium fluorophosphate or lithium difluorophosphate additive reacts with lithium to form a good film at the interface between the positive electrode and the negative electrode, and the film inhibits direct contact between the active material and the organic solvent in a non-aqueous system. The effect which suppresses decomposition | disassembly of electrolyte solution is disclosed. In addition, the registered patent discloses that the storage characteristics are improved by suppressing self discharge of the battery when the secondary battery is stored for a predetermined period after charging of the secondary battery.

However, although lithium fluorophosphate or lithium difluorophosphate can improve the storage characteristics and lifespan characteristics of the secondary battery to some extent, there was a lack of long-term storage or lifetime characteristics of the battery at high temperatures. In addition, the registered patent does not disclose that the high output characteristics of the secondary battery including lithium fluorophosphate or lithium difluorophosphate is improved.

Therefore, there is a need for research and development of electrolytes that can significantly improve the high temperature characteristics of secondary batteries and at the same time satisfy high output characteristics.

Accordingly, an object of the present invention is to include an additive for forming a more dense coating on the negative electrode of the secondary battery, the secondary battery electrolyte excellent in the output characteristics and capacity characteristics during high temperature storage, and at the same time improve the high temperature life characteristics and It is to provide a secondary battery including the same.

The present invention to achieve the above object

Carbonate solvents;

Lithium salts;

A compound of Formula 1; And

There is provided an electrolyte solution for a secondary battery comprising lithium difluorophosphate (LiPO ₂ F ₂ ):

In addition, the present invention provides a secondary battery comprising the secondary battery electrolyte.

The electrolyte solution for a secondary battery of the present invention forms a stable film on the positive electrode and the negative electrode of the secondary battery, thereby improving output characteristics and capacity characteristics during high temperature storage of the secondary battery, and at the same time, improving the high temperature life characteristics of the battery.

The secondary battery electrolyte of the present invention is a carbonate solvent; Lithium salts; A compound of Formula 1; And lithium difluorophosphate (LiPO ₂ F ₂ ).

[Formula 1]

The compound of formula 1 is a known compound (CAS No. 496-45-7), bicyclo-glyoxal sulfate, glyoxal sulfate, or 3a, 6a-dihydro- [1,3,2] dioxathiolo [4,5-d] [1,3,2] dioxathiol 2,2,5,5-tetraoxide (3a, 6a-dihydro- [1,3, 2] dioxathiolo [4,5-d] [1,3,2] dioxathiole 2,2,5,5-tetraoxide), etc., and can be purchased commercially. In addition, the compound of Formula 1 may be prepared by a known synthesis method, for example, by reacting sulfuric acid with 1,1,2,2-tetrachloroethane as a starting material (US Patent No. 1,999,995 and US Patent Registration). 2,415,397).

In addition, lithium difluorophosphate (CAS No. 845910-47-6, difluorophosphate lithium) is a commercially available compound and can be purchased commercially or prepared by known synthetic methods.

The electrolyte may include 0.1 to 10% by weight of the compound of Formula 1 and 0.05 to 10% by weight of lithium difluorophosphate relative to the total weight. Specifically, the electrolyte solution is 0.1 to 8% by weight, 0.2 to 5% by weight, or 0.5 to 3% by weight of the compound of Formula 1; And 0.05-8%, 0.1-5%, or 0.2-2% by weight of lithium difluorophosphate. When the compound of Formula 1 is included in an amount within the content range, the secondary battery including the electrolyte of the present invention has an effect of suppressing an increase in resistance in a high temperature environment and an excessive improvement of initial resistance at room temperature. In addition, when the lithium difluorophosphate in an amount within the content range, the electrode surface of the secondary battery is coated with an appropriate thickness, it is possible to prevent an increase in the resistance of the secondary battery.

It is preferable that the carbonate solvent has high solubility in the lithium salt, the compound of Formula 1, and lithium difluorophosphate. Specifically, the carbonate solvent is diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (methylpropyl carbonate; MPC), ethylpropyl carbonate (EPC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), propyl propionate ( It may be at least one selected from the group consisting of propyl propionate (PP) and fluoroethylene carbonate (FEC). More specifically, the electrolyte is a carbonate solvent, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC At least one first carbonate-based solvent (linear carbonate) selected from the group consisting of; And at least one second carbonate solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), propyl propionate (PP) and fluoroethylene carbonate (FEC) Or cyclic carbonates).

The carbonate solvent may be dehydrated, and specifically, the carbonate solvent may include water of 30 ppm by weight or less.

The lithium salt is not particularly limited as long as it is commonly used in an electrolyte solution for secondary batteries. Specifically, the lithium salt is LiPF ₆ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiSO ₃ CF ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , It may be one or more selected from the group consisting of LiN (SO ₂ F) ₂ and LiC (CF ₃ SO ₂ ) ₃ .

The electrolyte may include 0.05 to 5.0 moles of lithium salt based on 1 liter of the carbonate solvent. Specifically, the electrolyte may include 0.1 to 5.0 mol, 0.1 to 3.0 mol, 0.1 to 2.5 mol, 0.5 to 3.0 mol or 0.5 to 2.5 mol lithium salt based on 1 liter of the carbonate solvent. When the lithium salt is included in the content within the above range, the ionic conductivity of the electrolyte is appropriately secured, and the effect of improving the ion conductivity of the electrolyte that can be obtained compared to the concentration of the added lithium salt is high and economical.

The secondary battery electrolyte according to the present invention can be prepared by simply mixing and stirring a carbonate solvent, a lithium salt, glyoxal sulfate and lithium difluorophosphate represented by the formula (1).

When the electrolyte solution for a secondary battery of the present invention is used in the manufacture of a secondary battery, it is possible to improve the output characteristics, capacity storage characteristics, and lifespan characteristics of the battery by lowering the interfacial resistance of the secondary battery and suppressing the increase in resistance over a wide temperature range.

The present invention provides a secondary battery including the secondary battery electrolyte. Specifically, the secondary battery includes a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; A separator disposed between the anode and the cathode; And it may include the secondary battery electrolyte.

The positive electrode includes a positive electrode active material capable of reversibly occluding and desorbing lithium ions. The positive electrode active material is at least one metal selected from the group consisting of cobalt, manganese and nickel; And a composite metal oxide including lithium. The solid solution ratio between the metals may be various, and the positive electrode active material may be Mg, Al, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Cr, Fe, in addition to the above-described metals. It may further include one or more elements selected from the group consisting of, Sr and rare earth elements.

The negative electrode includes a negative electrode active material capable of occluding and desorbing lithium ions. The negative electrode active material may be a crystalline or amorphous carbon, or a carbon-based negative electrode active material (thermally decomposed carbon, coke, graphite) of the carbon composite; Burnt organic polymer compound; Carbon fiber; Tin oxide compounds; Lithium metal; Or lithium alloys. For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbead (MCMB) fired at 1500 ° C. or lower, mesophase pitch-based carbon fiber (MPCF), or the like. Can be. The crystalline carbon may be a graphite material, and examples thereof include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. Other elements constituting the alloy with lithium of the lithium alloy may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

The separator is for preventing a short circuit due to direct contact between the positive electrode and the negative electrode, for example, a polymer membrane such as polyolefin, polypropylene, polyethylene, or a multilayer thereof; Microporous film; web; And nonwoven fabrics. The separator may be coated with a metal oxide or the like on one or both surfaces.

Hereinafter, the present invention will be described in more detail with reference to specific examples and comparative examples. The following examples are intended to illustrate the present invention in more detail, and the present invention is not limited by the following examples.

The compound of formula 1 and lithium difluorophosphate (LiPO ₂ F ₂ ) (Formula 2) used in the following Examples and Comparative Examples are all known compounds, and their structural formula, chemical name and CAS No. are as follows:

(1) Compound of formula 1: glyoxal sulfate, glyoxal sulfate, CAS No. 496-45-7.

[Formula 1]

(2) lithium difluorophosphate: difluorophosphate lithium, CAS No. 845910-47-6.

[Formula 2]

Preparation Example 1 Preparation of Glyoxal Sulfate

The compound of Formula 1 may be prepared according to known synthesis methods as follows.

First, a 1,000 mL three-necked flask and a condenser were mounted in an oil bath at 60 ° C. 70 g of 1,1,2,2-tetrachloroethane was added to the three neck flask, the temperature was stabilized at 60 ° C., and 320 g of sulfuric acid (60% fuming grade) was added to initiate a reaction. The reaction solution initially exhibited a clear to light brown viscosity, and a crystalline solid was formed after 4 hours from the start of the reaction. The oil bath was cooled to room temperature and stirred slowly for an additional 3 hours. It was then replaced with a cold water bath of 5 ~ 7 ℃ and stirred for an additional 2 hours at low speed. The reaction was terminated in the absence of further production of crystalline solids. The resulting slurry solution was solid-liquid separated with a filter, and then vacuum dried at 20 Torr for 12 hours. As a result, 72.8 g of glyoxal sulfate represented by Chemical Formula 1 was obtained (yield: 84.4%).

Example 1 Preparation of Electrolyte Solution

Ethylene carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) were mixed at a volume ratio of 20:40:40 to prepare a mixed solution, and LiPF ₆ was dissolved in the mixed solution at a concentration of 1 mol / l. To the total weight of the electrolyte, 1% by weight of glyoxal sulfate represented by Formula 1 and 1% by weight of lithium difluorophosphate were added and mixed to prepare an electrolyte solution (electrolyte solution) for a secondary battery.

Example 2.

An electrolyte solution was prepared in the same manner as in Example 1, except that glyoxal sulfate represented by Chemical Formula 1 was added in an amount of 2 wt% and lithium difluorophosphate in an amount of 1 wt%.

Comparative Example 1.

An electrolyte solution was prepared in the same manner as in Example 1, except that lithium difluorophosphate was not added.

Comparative Example 2.

An electrolyte solution was prepared in the same manner as in Example 2, except that lithium difluorophosphate was not added.

Comparative Example 3.

An electrolyte solution was prepared in the same manner as in Example 1, except that glyoxal sulfate represented by Chemical Formula 1 was not added.

Comparative Example 4.

An electrolyte solution was prepared in the same manner as in Example 1, except that glyoxal sulfate and lithium difluorophosphate represented by Chemical Formula 1 were not added.

Experimental Example 1. Output Characteristics at High Temperature Storage of Lithium Secondary Battery

Assembling a 1.4 Ah pouch cell by an ordinary method using the anode material used to 1 weight ratio of positive electrode active material of LiNi _1/3 Co _1/3 Mn cathode material with _1/3 and the negative electrode active material of artificial graphite and natural graphite 1 Then, 6.5 g of each of the electrolyte solutions of Examples 1 and 2 and Comparative Examples 1 to 4 were injected to complete a secondary battery. The 1.4 Ah pouch battery obtained through the chemical conversion process was discharged for 10 seconds at 3 ° C. (coulomb) while maintaining a 60% charge state voltage compared to full charge at 25 ° C., and the voltage difference generated at this time was PNE-0506 charger / discharger ( Manufacturer: PNE Solution Co., Ltd.), and calculated the initial resistance from it.

In addition, after the battery was fully charged, it was stored in a 60 ° C. high temperature oven for 6 weeks and the resistance after 6 weeks was measured and shown in Table 1 by the same method as described above.

Content of additive in electrolyte DC-IR (mΩ) 25 ℃ initial 6 weeks after 60 ℃ Example 1 Lithium Difluorophosphate of 1% by weight of Formula 1 + 1% by weight 35.7 41.7 Example 2 2% by weight of formula 1 + 1% by weight of lithium difluorophosphate 39.5 40.2 Comparative Example 1 1 weight% of formula 1 36.1 48.6 Comparative Example 2 2% by weight of formula 1 38.4 42.9 Comparative Example 3 1% by weight of lithium difluorophosphate 33.7 58.0 Comparative Example 4 No additives 36.1 74.6

As shown in Table 1, in the electrolyte solutions of Examples 1 and 2, the battery internal resistance was lower as compared with the case where no additives were added (Comparative Example 4) or one type of additive was used (Comparative Examples 1 to 3). . This is a result showing that the output characteristics of the battery is improved due to the low resistance characteristics of the electrode and the electrolyte interface during the discharge of the battery by using an electrolyte containing a combination of the compound of Formula 1 and lithium difluorophosphate. In particular, Examples 1 and 2 using lithium difluorophosphate and the compound of Formula 1 exhibited lower resistance than Comparative Example 3 using only lithium difluorophosphate, and thus the output characteristics of the battery were improved.

Experimental Example 2 Capacity Characteristics at High Temperature Storage of Lithium Secondary Battery

After the battery formation process in the same manner as in Experimental Example 1 to obtain a secondary battery (1.4 Ah pouch battery), and charged at 1 C to 4.2 V / 140 mA at 25 ° C constant current / constant voltage (CC / CV) conditions Next, the discharge capacity was discharged at 1 C up to 3 V under constant current (CC) conditions, and the initial discharge capacity was measured using a PNE-0506 charger.

In addition, after the battery was fully charged, the battery was stored in a 60 ° C. high temperature oven for 6 weeks, and the discharge capacity after 6 weeks was measured in the same manner as described above, and the capacity retention ratio with respect to the initial capacity was calculated and shown in Table 2.

Content of additive in electrolyte Capacity retention after 6 weeks at 60 ° C Example 1 Lithium Difluorophosphate of 1% by weight of Formula 1 + 1% by weight 93% Example 2 2% by weight of formula 1 + 1% by weight of lithium difluorophosphate 93% Comparative Example 1 1 weight% of formula 1 87% Comparative Example 2 2% by weight of formula 1 92% Comparative Example 3 1% by weight of lithium difluorophosphate 78% Comparative Example 4 No additives 71%

As shown in Table 2, the electrolyte solutions of Examples 1 and 2 were prepared by comparing the initial charge of the battery with no additives (Comparative Example 4) or one type of additives used (Comparative Examples 1 to 3). The discharge amount after high temperature (60 degreeC) storage was remarkably excellent. This is a result showing that the reduction of the electrochemical electrode capacity generated during the high temperature storage of the battery by using an electrolyte containing a combination of the compound of formula (1) and lithium difluorophosphate significantly reduced. As a result, it was confirmed that the secondary battery including the electrolyte solution of the present invention realized stable charge and discharge capacity even at a high temperature.

Experimental Example  3. High Temperature Life Characteristics of Lithium Secondary Battery

After carrying out the battery conversion process in the same manner as in Experimental Example 1 to obtain a secondary battery (1.4 Ah pouch battery), and charged at 1 C up to 4.2 V / 140 mA at a constant current / constant voltage (CC / CV) conditions at 45 ℃ Next, discharge was performed at 2 C up to 3 V under constant current (CC) conditions, and the initial discharge capacity was measured using a PNE-0506 charger. This was repeated 500 times, and the discharge capacity measured after 500 times was calculated as the capacity retention ratio compared to the initial capacity of the battery and is shown in Table 3.

Content of additive in electrolyte Capacity retention rate after 500 cycles of 45 ℃ life Example 1 Lithium Difluorophosphate of 1% by weight of Formula 1 + 1% by weight 97% Example 2 2% by weight of formula 1 + 1% by weight of lithium difluorophosphate 96% Comparative Example 1 1 weight% of formula 1 86% Comparative Example 2 2% by weight of formula 1 90% Comparative Example 3 1% by weight of lithium difluorophosphate 83% Comparative Example 4 No additives 6%

As shown in Table 3, the electrolyte solutions of Examples 1 and 2 did not add an additive (Comparative Example 4), or the high temperature life characteristics were improved compared with the case where one type of additive was used (Comparative Examples 1 to 3). It became. This is a result showing that by using an electrolyte containing a combination of the compound of formula (1) and lithium difluorophosphate significantly reduced side reactions occurring when the battery is used continuously at high temperatures. As a result, the secondary battery including the electrolyte solution of the present invention was able to realize stable life characteristics even at high temperature.

Claims (7)

Carbonate solvents; Lithium salts; A compound of Formula 1; And Phosphate, lithium secondary battery, an electrolyte containing (LiPO ₂ F ₂₎ difluoromethyl. [Formula 1]

The method of claim 1, The carbonate solvent is diethyl carbonate, diethyl carbonate, dimethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate ), Ethylene carbonate, propylene carbonate, butylene carbonate, propyl propionate and fluoroethylene carbonate. Electrolytic solution for secondary batteries containing. The method of claim 2, The carbonate solvent At least one first carbonate solvent selected from the group consisting of diethyl carbonate, ethylmethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, and An electrolyte solution for secondary batteries comprising at least one second carbonate solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, propyl propionate and fluoroethylene carbonate. The method of claim 1, The lithium salt is LiPF ₆ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiSO ₃ CF ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ and LiC (CF ₃ SO ₂ ) ₃ , at least one selected from the group consisting of electrolyte solution for secondary batteries. The method of claim 1, The electrolyte solution comprises 0.1 to 10% by weight of the compound of the formula (1) and 0.05 to 10% by weight of lithium difluorophosphate relative to the total weight, the secondary battery electrolyte. The method of claim 1, The electrolyte solution comprises a lithium salt of 0.05 to 5.0 moles of lithium salt based on 1 liter of the carbonate solvent. A secondary battery comprising the electrolyte solution for secondary batteries according to any one of claims 1 to 6.