KR20150044004A - Additive for non-aqueous liquid electrolyte, non-aqueous liquid electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

Provided are a non-aqueous electrolyte including a toluene sulfonyl isocyanate-based additive and a lithium secondary battery comprising the same. The lithium secondary battery including a non-aqueous electrolyte additive of the present invention can improve a high-rate discharge capacity maintenance rate and swelling property at high temperature.

Description

[0001] The present invention relates to an electrolyte additive for a lithium secondary battery, a non-aqueous electrolytic solution containing the electrolyte additive and a lithium secondary battery comprising the non-aqueous liquid electrolyte and a lithium secondary battery,

The present invention relates to an electrolyte additive for a lithium secondary battery including a toluene sulfonyl isocyanate system, a non-aqueous electrolyte containing the electrolyte additive, and a lithium secondary battery comprising the same.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used.

Lithium metal oxide is used as the positive electrode active material of the lithium secondary battery, and lithium metal, lithium alloy, crystalline or amorphous carbon or carbon composite material is used as the negative electrode active material. The active material is coated on the current collector with an appropriate thickness and length, or the active material itself is coated in a film form and wrapped or laminated with a separator as an insulator to form an electrode group. The electrode group is then placed in a can or similar container, Thereby manufacturing a secondary battery.

This lithium secondary battery is charged and discharged while repeating the process of intercalating lithium ions from the lithium metal oxide of the anode into the graphite electrode of the cathode and deintercalating the lithium ions. At this time, since lithium is highly reactive, it reacts with the carbon electrode to form Li ₂ CO ₃ , LiO, LiOH and the like to form a film on the surface of the cathode. This film is called a solid electrolyte interface (SEI) film,

The SEI film formed at the beginning of charging prevents the reaction between lithium ion and carbon anode or other materials during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. This ion tunnel serves to prevent the collapse of the structure of the carbon anode by co-intercalating the organic solvent of the electrolyte having a large molecular weight moving together by solvation of the lithium ion together with the carbon anode.

Therefore, in order to improve the high-temperature cycle characteristics and the low-temperature output of the lithium secondary battery, a solid SEI film must always be formed on the cathode of the lithium secondary battery. Once the SEI membrane is formed at the time of initial charging, it is used as an ion tunnel to prevent the reaction between the lithium ion and the negative electrode or other materials during repetition of charging and discharging by using the battery and passing only lithium ions between the electrolyte and the negative electrode .

It has been difficult to expect improvement in low-temperature output characteristics due to the formation of a non-uniform SEI film in the case of an electrolyte solution which does not contain an electrolyte additive or contains an electrolyte additive having poor characteristics. Further, even when the electrolyte additive is included, if the amount of the electrolyte additive can not be adjusted to the required amount, gas may be generated during the high temperature reaction due to the electrolyte additive, thereby causing a swelling phenomenon in which the thickness of the secondary battery is increased, There was a problem.

The present invention aims at solving the technical problems requested from the past as described above.

The inventors of the present application confirmed that when the electrolyte for a lithium secondary battery contains a toluene sulfonyl isocyanate-based additive, the high rate charge-discharge characteristics and the swelling characteristics are improved, and the present invention has been completed.

In order to solve the problems to be solved, the present invention relates to an electrolyte additive comprising a toluene sulfonyl isocyanate group compound; A non-aqueous organic solvent containing a kibonate-based compound and a propionate-based compound; And a non-aqueous electrolytic solution containing a lithium salt.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte solution.

According to the additive for lithium secondary battery of the present invention, the decomposition of PF ₆ ^{- on} the surface of the positive electrode, which may occur in a high temperature cycle operation of the lithium secondary battery, can be suppressed and the oxidation reaction of the electrolyte can be prevented, Ring characteristics and the like can be improved.

Fig. 1 is a graph showing the results of high-rate charge-discharge tests of Examples 1 and 2 and Comparative Example 1. Fig.

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.

One embodiment of the present invention may include a nonaqueous electrolytic solution containing a cyanate compound and a propionate compound of a lithium secondary battery, a lithium salt, and a toluene sulfonyl isocyanate system as an additive.

The toluene sulfonyl isocyanate-based additive is added to the non-aqueous electrolytic solution, and in the case of LiPF _{6 as} a lithium salt, the electrolyte solution having insufficient thermal stability is easily decomposed in the cell to form LiF and PF ₅ . At this time, the LiF salt decreases the conductivity and the number of free Li ⁺ ions, thereby increasing the resistance of the battery and consequently decreasing the capacity of the battery. That is, the decomposition of PF ₆ ^- ions on the surface of the anode, which may occur during the high temperature cycle operation, induces the isocyanate function as an anion receptor to form stable PF ₆ ^- , and Li ⁺ and PF ₆ ^- To thereby increase the ion-pair separation of the electrolyte, thereby improving the solubility of LiF in the electrolytic solution and lowering the interface resistance.

In addition, the toluene isocyanate-based additive can reduce the content of hydrogen and carbon dioxide generated in the battery after the battery activation process and reduce the content of carbon dioxide even after storage at a high temperature, thereby preventing the swelling phenomenon of the lithium secondary battery.

The toluenesulfonyl isocyanate-based additive may be stereochemically ortho, meta, para, preferably para-toluene sulfonyl isocyanate. .

Here, the toluenesulfonyl isocyanate-based additive may be contained in an amount of 0.1% by weight to 5.0% by weight, preferably 0.1% by weight to 1.0% by weight, based on the total weight of the electrolytic solution. When the content of the toluenesulfonyl isocyanate-based additive is less than 0.1 wt%, the effect of inhibiting decomposition as an anion receptor in a high-temperature cycle is insignificant. When the content of the toluenesulfonyl isocyanate-based additive exceeds 5.0 wt%, lithium ions The permeability is lowered to increase the impedance, and sufficient capacity and charge / discharge efficiency may not be obtained.

Meanwhile, the non-aqueous electrolytic solution according to an embodiment of the present invention may include the electrolyte additive, a non-aqueous organic solvent, and a lithium salt.

On the other hand, as the lithium salt that may be included in the non-aqueous electrolyte solution according to an embodiment of the present invention is _{LiPF 6, LiAsF 6, LiCF 3} SO 3, LiN (CF 3 SO 2) 2, LiBF 4, LiBF 6, LiSbF 6 , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF _3, LiClO ₄ , Li (CF 3 SO 2) (C ₂ F 5 SO ₂ ) N and Li (SO ₂ F) ₂ N, or a mixture of two or more thereof may be used, and LiPF ₆ may preferably be used.

The non-aqueous organic solvent that can be included in the non-aqueous electrolyte solution is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging of the battery, For example, carbonate-based or propionate-based. These may be used alone, or two or more of them may be used in combination.

Examples of the carbonate-based organic solvent in the non-aqueous organic solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC), or a mixture of two or more thereof. As the base compound, ethyl propionate (EP), propyl propionate (PP), n-propyl propionate, iso-propyl propionate, n-butyl propionate, iso-butyl propionate, Propionate, or a mixture of two or more thereof.

Preferably, a carbonate-based solvent and a propionate-based solvent can be used in parallel. The carbonate compound and the propionate compound may be contained in an amount of 10:90 to 50:50 based on the total weight of the electrolytic solution. In an embodiment of the present invention, diethyl carbonate (DEC) and ethyl propionate EP) can be used.

Additionally, in addition to the combined solvents, one or more carbonate-based solvents may be further included. The combination of the non-aqueous organic solvent used in one embodiment of the present invention may be ethylene carbonate (EC), propyl carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP).

When the carbonate compound and the propionate compound are combined in the weight ratio and used as a non-aqueous organic solvent, a large amount of gas generated in the high-temperature cycling process of the secondary battery can be efficiently generated by the toluene sulfonyl isocyanate- A lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a positive electrode disposed between the positive electrode and the negative electrode, and a negative electrode disposed between the positive electrode and the negative electrode, A separator and the non-aqueous electrolytic solution. The positive electrode and the negative electrode may include a positive electrode active material and a negative electrode active material, respectively.

Here, the cathode active material may include a manganese-based spinel active material, a lithium metal oxide, or a mixture thereof. Further, the lithium metal oxide may be selected from the group consisting of lithium-cobalt oxide, lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt oxide and lithium-nickel-manganese-cobalt oxide And more specifically LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1, 0 <b < (where 0 &lt; = _Y &lt; 1), LiNi _{1 - Y} Co _Y O ₂ , LiCo _{1 - Y} Mn _Y O ₂ , LiNi _{1 - Y} Mn _Y O ₂ , _{Li (Ni a Co b Mn c} ) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2-z Ni z O 4, LiMn 2 _-z Co _z O ₄ (where 0 <Z <2).

As the negative electrode active material, graphite based anode active materials such as carbonaceous, natural graphite and artificial graphite such as crystalline carbon, amorphous carbon or carbon composite may be used alone or in combination of two or more.

The separator may be a porous polymer film such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer Or may be a laminate of two or more kinds. In addition, nonwoven fabrics made of conventional porous nonwoven fabrics, for example, glass fibers having a high melting point, polyethylene terephthalate fibers, or the like can be used, but the present invention is not limited thereto.

The lithium secondary battery may be manufactured by a conventional method according to the present invention, and may be preferably a pouch type secondary battery.

Example

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

Example 1

[Preparation of electrolytic solution]

Aqueous organic solvent having a composition of ethylene carbonate (EC): propyl carbonate (PC): diethyl carbonate (DEC): ethyl propionate (EP) = 3: 1: 2: 4 (weight ratio) and 1.0M LiPF _6, and an electrolytic solution containing 0.5 wt% para-toluenesulfonyl isocyanate (p-TSI) relative to 100 parts by weight of the non-aqueous electrolyte was prepared.

[Production of lithium secondary battery]

(NMP) as a solvent, 96 wt% of LiCoO ₂ as a positive electrode active material, ₂ wt% of carbon black as a conductive agent, and 2 wt% of polyvinylidene fluoride (PVdF) To prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to produce a positive electrode, followed by a roll press to prepare a positive electrode.

The negative electrode mixture slurry was prepared by adding artificial graphite as a negative electrode active material, PVdF as a binder, and carbon black as a conductive agent to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to prepare a negative electrode, followed by roll pressing to produce a negative electrode.

The thus prepared positive electrode and negative electrode were fabricated by polymerizing a polymer type cell with a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), and then the prepared non-aqueous electrolyte was injected, The preparation of the battery was completed.

Example 2

A lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 wt% of para-toluenesulfonyl isocyanate (p-TSI) was added to 100 parts of the non-aqueous electrolyte.

Comparative Example 1

A lithium secondary battery was prepared in the same manner as in Example 1, except that para-toluenesulfonyl isocyanate (p-TSI) was not added.

<Experimental Example>

Initial capacity assessment

The lithium rechargeable battery in the factory-charged state manufactured in Examples 1 to 2 and Comparative Example 1 was discharged until a voltage of 3 V was reached at a current of 0.2 C, and the current was discharged at a constant current / constant voltage of 1.2 C / After charging to 1 / 20mA of current and discharging to 3V by 1C again 4 times, then the current reaches 1 / 20mA of 1C current at 1.2C / 4.2V constant current / constant voltage condition , And discharged to 3V at a current of 0.2C. At this time, the discharge capacity at the last stage was measured. The initial capacity is shown in Table 1.

Initial capacity (mAh) Example 1 1351.6 Example 2 1351.4 Comparative Example 1 1348.1

High rate Charging and discharging  Test

The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 that had undergone the initial capacity evaluation were charged at a room temperature (0.5 C charging / 0.2 C discharging), 0.5 C charging / 0.2 C discharging, (0.5 C charge / 1.0 C discharge), (0.5 C charge / 1.5 C discharge), (0.5 C charge / 2.0 C discharge) discharge capacity. The results are shown in FIG. 1 sequentially based on the discharge C-rate.

As can be seen from FIG. 1, the lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 had similar battery capacities up to the 0.5C rate stage, but the capacity of the battery was increased in the range of 1C to 2C, It was confirmed that the lithium secondary battery of Comparative Example 1 was superior to the lithium secondary battery of Comparative Example 1. That is, it was found that the lithium secondary battery including the toluene sulfonyl isocyanate additive according to an embodiment of the present invention has an effect of improving the high rate discharge capacity.

High temperature stability evaluation (cell thickness measurement)

The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 were heated from room temperature to 90 占 폚 for 1 hour and then stored at 90 占 폚 for 4 hours. Thereafter, after the temperature was further reduced to 90 ° C for 1 hour, the change in thickness of the battery was measured. The results are shown in Table 2.

Initial thickness (mm) Final thickness (mm) Thickness increase (mm) Example 1 4.44 6.00 1.56 Example 2 4.48 6.25 1.77 Comparative Example 1 4.43 6.38 1.95

As shown in Table 2, the lithium secondary battery of Comparative Example 1 containing no additive had a maximum increase rate of 25% (1.95 / 1.56 * 100%) than the lithium secondary batteries of Examples 1 and 2 including the toluene sulfonyl isocyanate- ). This confirms that the lithium secondary battery including the additive according to one embodiment of the present invention can effectively prevent the thickness increase at a high temperature.

Claims (15)

An electrolyte additive comprising a toluene sulfonyl isocyanate compound;
A non-aqueous organic solvent containing a kibonate-based compound and a propionate-based compound; And
A non-aqueous electrolytic solution comprising a lithium salt.
The method according to claim 1,
Wherein the toluene sulfonyl isocyanate compound is para-toluene sulfonyl isocyanate.
The method according to claim 1,
Wherein the content of the toluenesulfonyl isocyanate compound is 0.1 to 5 wt% based on the total amount of the electrolytic solution.
The method of claim 3,
Wherein the content of the toluenesulfonyl isocyanate compound is 0.5 to 1% by weight based on the total weight of the electrolytic solution.
The method according to claim 1,
Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , A non-aqueous electrolytic solution comprising any one selected from the group consisting of LiSO ₃ CF ₃ , LiClO ₄ , Li (CF ₃ SO 2) (C ₂ F 5 SO ₂ ) N and Li (SO ₂ F) ₂ N or a mixture of two or more thereof.
The method according to claim 1,
The carbonate compound may be selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) ), Propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC), or a mixture of two or more thereof.
The method according to claim 1,
Wherein said carbonate-based compound comprises diethyl carbonate (DEC).
The method according to claim 1,
The propionate compound may be at least one selected from the group consisting of ethyl propionate (EP), propyl propionate (PP), n-propyl propionate, isopropyl propionate, n-butyl propionate, And tert-butyl propionate, or a mixture of two or more thereof.
The method according to claim 1,
Wherein the propionate-based compound is ethyl propionate (EP).
The method according to claim 1,
Wherein the carbonate compound and the propionate compound are contained in an amount of 10:90 to 50:50 based on the total weight of the electrolytic solution.
The method according to claim 1,
Characterized in that the non-aqueous organic solvent comprises ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP)
anode; cathode; Separator and
A lithium secondary battery comprising the non-aqueous electrolyte according to any one of claims 1 to 11.
The method of claim 12,
Wherein the negative electrode is a carbon-based negative electrode active material selected from the group consisting of crystalline carbon, amorphous carbon, and carbon composite.
The method of claim 12,
Wherein the positive electrode is a manganese spinel-based active material or a lithium metal oxide.
The method of claim 12,
Wherein the lithium secondary battery is a lithium ion secondary battery or a lithium polymer secondary battery.

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