KR20080110404A - Additive for non-aqueous electrolyte and secondary battery using the same - Google Patents

Abstract

An additive for non-aqueous electrolyte is provided to reduce or suppress the concentration of HX(X=F, Cl, Br, I) causing the performance degradation of a battery by using the electrolyte introduced with one or more silyl groups as an additive. An additive for non-aqueous electrolyte comprises an electrolyte salt and electrolytic solvent and further comprises a urea compound introduced with one or more silyl groups. The urea compound is a compound of the chemical formula 1 and reduces the concentration of HX(X=F, Cl, Br, I) existing within a battery. In the chemical formula 1, R1 - R8 are independently a hydrogen, C1~C6 arkenyl group of C2~C6 alkyl group. The content of the urea compound is 0.01 - 10 parts by weight based on the electrolyte 100.0 parts by weight.

Description

Non-aqueous electrolyte additive and secondary battery using same {ADDITIVE FOR NON-AQUEOUS ELECTROLYTE AND SECONDARY BATTERY USING THE SAME}

The present invention is provided with an electrolyte solution containing a urea compound in which one or more silyl groups are introduced, thereby reducing the concentration of HX (X = F, Cl, Br, I) in the battery, or suppressing the production, thereby improving the life performance and the high temperature performance. This improved secondary battery relates.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders and notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the field attracting the most attention in this respect, and among them, the development of a secondary battery capable of charging and discharging has become a focus of attention.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990's are chargeable and discharged cells with intercalation and disintercalation of lithium ions at the positive and negative electrodes. Energy can be converted into electrical energy. The lithium secondary battery generally has an average discharge voltage of about 3.6 to 3.7 V, and thus has a high operating voltage and a much higher energy density than conventional batteries such as Ni-MH and Ni-Cd.

On the other hand, the electrolyte of the lithium secondary battery is generally using a carbonate-based organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC) as the electrolyte solvent, lithium salts such as LiPF ₆ , LiBF ₄ as an electrolyte salt In order to have a high driving voltage as described above, an electrochemically stable electrolyte composition is required in the charge and discharge voltage range of 0 to 4.2 V.

However, fluorine-based lithium salts, such as LiPF ₆ and LiBF ₄ , which are mainly used as the electrolyte salts, have advantages in obtaining high capacity and high voltage, but have a problem in that they react very sensitively to moisture and cause a decrease in battery performance. That is, the fluorine-based lithium salt may react with moisture present in the battery manufacturing process or in the battery to form hydrofluoric acid (see Scheme 1 below), which may cause the following problems.

Scheme 1

LiPF ₆ + 4H ₂ O → LiF + 5HF + H ₃ PO ₄

First, the electrolyte is usually prepared in a glass container, in which the hydrofluoric acid may react with the silicon (Si) component of the glass container to form a silicon precipitate. When an electrolyte solution containing the silicon precipitate is used in the battery, the silicon precipitate is adsorbed on the surface of the battery to reduce the reaction area, resulting in a drastic decrease in the charge / discharge efficiency of the battery, or by side reaction with the electrode to reduce the life of the battery. You can.

Second, generally, during initial charging of a secondary battery, the carbonate-based organic solvent reacts with lithium ions in the electrolyte, and the solid electrolyte interface (SEI) film formed on the surface of the negative electrode passes only lithium ions. It can prevent it from being intercalated and can serve as a protective film which prevents destruction of the cathode structure. In addition, the contact of the electrolyte and the negative electrode is prevented by the SEI film, so that decomposition of the electrolyte and reduction of the amount of reversible lithium can be minimized. However, the SEI film can be easily destroyed due to the strong reactivity of the HX (X = F, Cl, Br, I) present in the battery, which leads to continuous regeneration of the SEI film, resulting in a decrease in battery capacity. Can be. In addition, gas, such as CO, CO ₂ , CH ₄ , and C ₂ H ₆ , may be continuously generated due to decomposition of the carbonate organic solvent during the regeneration of the SEI film, thereby reducing battery stability.

Conventionally, as a method for minimizing the collapse of the SEI film on the surface of the negative electrode, sulfide-based compounds (Japanese Patent Laid-Open Publication No. 07-176323), diphenyl picrylhydrazyl (DPPH: Japanese Patent Laid-Open Publication No. 09-73918) and the like. The method of changing the aspect of SEI film formation reaction using the compound of as an electrolyte additive was proposed. However, this method can reduce the degree of collapse of the SEI film due to thermal energy or electrochemical energy, but it is not a method of removing hydrofluoric acid in a highly reactive battery, and thus it is not possible to prevent deterioration of the electrode by hydrofluoric acid.

On the other hand, as a method of suppressing the reactivity of hydrofluoric acid, a method of adding a strong base such as KOH to a ppm concentration level has been proposed, but this has a short-term effect, but in long-life cycles, side reactions due to decomposition of water occur, resulting in a decrease in battery performance. Can cause.

In addition, Japanese Patent Application Laid-Open No. 07-211349 discloses a method of controlling hydrofluoric acid in an amount of 20 to 25 ppm by using a metal oxide such as MgO as a fluorine adsorbent, but water produced by the reaction of the metal oxide and hydrofluoric acid is again present. There was a problem of continuously forming hydrofluoric acid by reacting with the fluorine-based lithium salt.

As another method for suppressing the reactivity of hydrofluoric acid, a method of using a tetravalent alkyl ammonium salt as an electrolyte salt has been proposed. The tetravalent alkyl ammonium salt is widely used as a supporting electrolyte in a non-aqueous solution due to its high solubility, electrolyte conductivity, electrochemical stability, and ease of manufacture and purification, but is typically 4.1 to 4.5V because the potential window region is only 3.6V maximum. The lithium ion battery that requires the potential window region has a limit of being inefficient.

When the urea compound in which one or more silyl groups are introduced is used as an electrolyte additive, the present inventors reduce or reduce the concentration of HX (X = F, Cl, Br, I) that causes the degradation of the battery. By suppressing this, it has been found that the deterioration of the positive electrode and the resulting shortening of the battery life can be prevented, thereby improving the battery life performance and high temperature performance.

The present invention is based on this.

The present invention provides an electrolyte solution comprising an electrolyte salt and an electrolyte solvent, the electrolyte solution comprising an urea compound into which one or more silyl groups are introduced; And it provides a secondary battery comprising the electrolyte solution.

The present invention also provides a HX (X = F, Cl, Br, I) reducing agent for a secondary battery containing a urea compound having one or more silyl groups introduced therein.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is characterized by reducing the concentration of HX (X = F, Cl, Br, I) in the battery or suppressing production by using a urea compound having one or more silyl groups introduced as one component of the electrolyte.

HX (X = F, Cl, Br, I) is a strong acid produced by the reaction of lithium-containing halogen salts such as lithium-containing fluoride salts and lithium-containing chloride salts used as electrolyte salts with a small amount of water present in the battery. As an example, it is essentially accompanied by an undesirable side reaction when present in the battery. That is, as described above, the SEI film can be collapsed and continuous regeneration causes not only to decrease the capacity and stability of the battery, but also to abruptly oxidize and degenerate the positive electrode active material in the battery. . In addition, the internal resistance of the battery may be increased due to the increase in the thickness of the negative electrode due to the continuous regeneration of the SEI film and the adsorption of the positive electrode surface of lithium fluoride (LiF), a by-product of the formation of hydrofluoric acid, thereby reducing the electromotive force of the battery.

Accordingly, in the present invention, by using the urea compound in which one or more silyl groups are introduced as one component of the electrolyte solution, the concentration of HX present in the battery can be reduced, or the production can be suppressed, thereby improving the battery life performance and high temperature performance. Can be. The overall performance improvement of the battery can be estimated as follows, but is not limited thereto.

That is, the urea compound into which the at least one silyl group is introduced may have a nitrogen-silicon (Si—N) bond to easily react with water or hydrofluoric acid in the cell, as well as water (H ₂ O) or hydrofluoric acid (HF) and hydrogen. It can contain oxygen (O) and nitrogen (N) that can be bound to capture moisture or hydrofluoric acid in the cell. Therefore, the present invention can reduce the concentration of HX or suppress the production, and can prevent elution and degradation of the positive electrode active material by HX. In addition, the present invention can improve the overall performance of the battery, such as electromotive force, life characteristics of the battery by preventing the internal resistance of the electrode and the generation of gas. In particular, since the dissolution rate of the electrode by HX and the disintegration rate of the SEI film are increased at high temperatures, the conventional secondary battery has a great problem in battery cycle life and storage at high temperatures, whereas in the present invention, the concentration of HX is reduced. The above-mentioned problem is fundamentally solved, thereby improving the high temperature performance.

The compound to be used as the electrolyte additive of the present invention can be used without limitation as long as it is a urea compound having one or more silyl groups introduced therein. The compound may be represented by Formula 1, and non-limiting examples thereof include N, N'-bis (trimethylsilyl) urea (N, N'-Bis (trimethylsilyl) urea).

[Formula 1]

In Formula 1, R1 to R8 are each independently hydrogen, an alkyl group of C1 to C6, or an alkenyl group of C2 to C6.

The content of the urea compound in the electrolyte provided by the present invention can be adjusted according to the goal of improving the performance of the battery, the content of the urea compound is preferably 0.01 to 10 parts by weight per 100 parts by weight of the electrolyte. When the amount is less than 0.01 parts by weight, the desired effect of improving the overall performance is insignificant. When it exceeds 10 parts by weight, the performance of the battery may be reduced due to the increase in the viscosity of the electrolyte.

The secondary battery electrolyte to which the compound is to be added includes conventional electrolyte components known in the art, such as electrolyte salts and electrolyte solvents.

Electrolyte salts used in the secondary battery, the electrolytic solution provided by the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is a Li ^+, Na ^+, an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ It includes and B ^- is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 ^- , A salt containing an ion such as C (CF ₂ SO ₂ ) ₃ ^- or a combination thereof. In particular, it may be a lithium salt of LiN (C _x F _{2x +1} SO ₂ ) (C _y F _{2y +1} SO ₂ ), where x and y are natural water. In addition, the content of the electrolyte salt can be used in a conventional range known in the art, it is preferable that the concentration of the electrolyte salt is 0.8 to 2.0 M. When the concentration is less than 0.8 M, the lithium ion has a low concentration, resulting in poor battery life performance. When the concentration is higher than 2 M, an increase in the viscosity of the electrolyte may increase, thereby decreasing ion conductivity in the battery.

The electrolyte solvent may be a conventional organic solvent known in the art, such as cyclic or linear carbonates, esters, ethers, ketone organic solvents. Non-limiting examples of the solvent solvent is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), dimethyl sulfoxide Said, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), butyrolactone, gamma butyrolactone (GBL), valerian Rolactone, caprolactone, fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate or halogen derivatives thereof Etc. These electrolyte solvents can be used individually or in mixture of 2 or more types.

Furthermore, the present invention is a separator, an anode, a cathode; And it provides a secondary battery having an electrolyte solution containing a urea compound introduced at least one silyl group.

The secondary battery may be a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

The electrode to be applied to the secondary battery of the present invention is not particularly limited, and may be prepared by applying a positive electrode or a negative electrode active material to a current collector according to conventional methods known in the art.

The positive electrode active material may be a conventional positive electrode active material that can be used for the positive electrode of a conventional secondary battery, non-limiting examples of lithium such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) Transition metal composite oxides (for example, lithium manganese composite oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , lithium cobalt oxides such as LiCoO ₂ , and some of the manganese, nickel and cobalt oxides of these oxides And the like, or a vanadium oxide containing lithium) or a chalcogen compound (for example, manganese dioxide, titanium disulfide, molybdenum disulfide, and the like). Preferably LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-Y Co _Y O ₂ , LiCo _1-Y Mn _Y O ₂ , LiNi _1-Y Mn _Y O ₂ (where 0 ≦ Y <1), 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 ( Here, 0 <Z <2), LiCoPO ₄ , LiFePO _4, or a mixture thereof is mentioned. Non-limiting examples of the positive electrode current collector include a foil made of aluminum, nickel, or a combination thereof.

The negative electrode active material may be a conventional negative electrode active material that can be used in the negative electrode of a conventional secondary battery, non-limiting examples of lithium metal or lithium alloy, carbon, graphite, petroleum coke, activated carbon (activated carbon) ), Lithium adsorbents such as graphite or other carbons. Non-limiting examples of cathode current collectors include foils made of copper, gold, nickel or copper alloys or combinations thereof. In addition, the negative electrode may include a binder, and examples of the binder may include, but are not limited to, polyvinylidene fluoride (PVDF) or styrene butadiene rubber (SBR).

The separator is not particularly limited, but a porous separator may be used, for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator.

The secondary battery according to the present invention may be manufactured according to a conventional method known in the art, for example, an electrolyte prepared according to the present invention after assembling a separator between an anode and a cathode. It can be prepared by injecting.

The shape of the secondary battery is not limited, but cans are cylindrical, coin-shaped, square or pouch types.

Furthermore, the present invention provides an HX (X = F, Cl, Br, I) reducing agent for a secondary battery containing a urea compound having one or more silyl groups introduced therein.

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

Example 1

0.01 weight of N, N'-bis (trimethylsilyl) urea (N, N'-Bis (trimethylsilyl) urea) in 1M LiPF ₆ solution having a volume ratio of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) 1: 2 By addition was added to prepare an electrolyte solution.

A polymer cell was prepared using LiCoO ₂ as a positive electrode and MAG-E as a negative electrode, and the electrolyte prepared above was injected thereto to prepare a lithium polymer battery in a conventional manner, and then aged at room temperature (RT) for 2 days, and Formation was performed for 50 minutes under 0.2C-rate conditions.

Example 2

An electrolyte solution was prepared in the same manner as in Example 1, except that 0.5 parts by weight of N, N'-bis (trimethylsilyl) urea was added instead of 0.01 parts by weight.

Example 3

An electrolyte was prepared in the same manner as in Example 1, except that 1 part by weight of N, N'-bis (trimethylsilyl) urea was added instead of 0.01 part by weight to prepare an electrolyte.

Example 4

An electrolyte solution was prepared in the same manner as in Example 1, except that 5 parts by weight of N, N′-bis (trimethylsilyl) urea was added instead of 0.01 parts by weight.

Example 5

An electrolyte was prepared in the same manner as in Example 1, except that 10 parts by weight of N, N'-bis (trimethylsilyl) urea was added instead of 0.01 parts by weight.

Comparative Example 1

An electrolyte solution was prepared in the same manner as in Example 1, except that no compound was added to the electrolyte solution.

The present invention can use urea compound in which one or more silyl groups are introduced as an electrolyte additive to reduce the concentration of HX (X = F, Cl, Br, I) or to suppress the production of the battery, which causes performance degradation. . For this reason, the present invention can prevent the deterioration of the positive electrode and thereby shorten the life of the battery, thereby improving the battery life performance and high temperature performance.

Various modifications may be made without departing from the spirit and scope of the invention as set forth in the claims.

Claims (8)

An electrolyte solution for a secondary battery comprising an electrolyte salt and an electrolyte solvent, the electrolyte solution comprising a urea compound into which one or more silyl groups are introduced. The electrolyte of claim 1, wherein the urea compound is capable of reducing the concentration of HX (X = F, Cl, Br, I) present in the battery or inhibiting the production thereof. The electrolyte of claim 1, wherein the urea compound is a compound of Formula 1 below: [Formula 1]

In Formula 1, R1 to R8 are each independently hydrogen, an alkyl group of C1 to C6, or an alkenyl group of C2 to C6. The electrolyte of claim 1, wherein the content of the urea compound is 0.01 to 10 parts by weight per 100 parts by weight of the electrolyte. The secondary battery containing the electrolyte solution in any one of Claims 1-4. The secondary battery according to claim 5, which is a lithium secondary battery. An HX (X = F, Cl, Br, I) reducing agent for a secondary battery containing a urea compound having at least one silyl group introduced therein. The method of claim 7, wherein the urea compound is a compound of formula 1 HX (X = F, Cl, Br, I) reducing agent, characterized in that: [Formula 1]

In Formula 1, R1 to R8 are each independently hydrogen, an alkyl group of C1 to C6, or an alkenyl group of C2 to C6.