KR20080061692A - Nonaqueous electrolyte comprising trimethylsilyl phosphite for li-secondary battery and li secondary battery thereby - Google Patents

Abstract

A nonaqueous electrolyte is provided to improve life characteristic, high-rate characteristic, and charge and discharge characteristic of a lithium secondary battery. A nonaqueous electrolyte for a lithium secondary battery includes: a base electrolyte comprising a nonaqueous organic solvent and a lithium salt dissolved in the nonaqueous organic solvent; and trimethylsilyl phosphite represented by the following formula 1 to be added to the base electrolyte. A lithium secondary battery includes: the electrolyte; an electrode part comprising a positive electrode and a negative electrode between which the electrolyte is interposed and which are placed to face each other; and a separator which electrically separates the positive electrode from the negative electrode.

Description

Non-aqueous electrolyte solution for lithium secondary batteries containing trimethylsilyl phosphite and lithium secondary battery comprising same {Nonaqueous electrolyte comprising trimethylsilyl phosphite for Li-secondary battery and Li secondary battery Thus}

1 shows that aluminum (Al) is used as the positive electrode (100) metal, copper (Cu) is used as the negative electrode metal, LiCoO ₂ is used as the positive electrode active material, and carbon (C) is used as the negative electrode active material. It is a schematic diagram which shows the used lithium secondary battery.

2 is a graph showing the results of comparing the life characteristics at 1.0 C-rate with respect to Example 2 and Comparative Example.

<Explanation of symbols for the main parts of the drawings>

100: positive electrode 110: negative electrode

130: electrolyte solution 140: separator

The present invention relates to a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery comprising the same, and more particularly, to the conventional non-aqueous electrolyte (nonnaqueous electrolyte) for a lithium secondary battery without affecting the battery characteristics The present invention relates to a non-aqueous electrolyte lithium secondary battery comprising an additive capable of improving the discharge capacity at a high C-rate and the performance of a charge and discharge cycle, and a lithium secondary battery including the same.

Secondary battery is a chemical battery that can be used semi-permanently because it can be recharged unlike a primary battery, and its market size is growing exponentially due to the recent mass distribution of laptops, mobile communication devices, and digital cameras. Recently, it is rapidly growing as one of the three parts industries in the 21st century along with semiconductors and displays.

Secondary batteries include lead-acid batteries, nickel-cadmium (Ni-Cd) batteries, nickel-hydrogen (Ni-MH) batteries, and lithium batteries, depending on the cathode and anode materials. The potential and energy density are determined by Among them, especially lithium secondary batteries are used as a driving power source for portable electronic devices because of their high energy density due to the low redox potential and molecular weight of lithium.

Among these lithium secondary batteries, a lithium secondary battery using a nonaqueous electrolyte, in particular, is coated with a lithium metal mixed oxide as a cathode active material on a metal as an anode, and as a cathode active material on a metal as a cathode. A carbon material or a metal lithium is coated and used, and an electrolyte in which lithium salt is appropriately dissolved in an organic solvent is disposed between these anodes and cathodes.

In brief, the operation principle of the lithium secondary battery, lithium ions (Li +) present in the ionic state in the electrolyte is moved from the positive electrode to the negative electrode during charging, and from the negative electrode to the positive electrode during discharge. The electrons then move along the wire that connects the anode and cathode to the lithium ion.

As described above, in the state of charge of the lithium ion battery, lithium ions (Li ⁺ ) from the lithium metal oxide used as the positive electrode are moved to the carbon electrode used as the negative electrode and intercalated, where lithium ions are highly reactive. As a result, materials such as Li ₂ CO ₃ , LiO, LiOH, etc. are generated on the surface of the negative electrode by reacting with the carbon negative electrode, which forms a film on the surface of the negative electrode.

The film thus produced is called a solid electrolyte interface (SEI), and these SEI films serve as a kind of passivation to protect the cathode surface.

That is, the SEI film prevents the reaction between lithium ions and the negative electrode or other materials during charge and discharge, and serves to pass only lithium ions by acting as an ion tunnel.

The ion tunnel effect is characterized by co-intercalation of organic solvents (e.g. ethylene carbonate, dimethyl carbonate, diethyl carbonate, etc.) of high molecular weight electrolytes that solvate lithium ions and move together. This prevents the structure of the negative electrode from collapsing.

Once the SEI film is formed, the lithium ions do not react side-by-side with the negative electrode or any other material, thereby reversibly maintaining the amount of lithium ions.

That is, the carbon material of the negative electrode reacts with the electrolyte during overcharge to form a protective film SEI film on the surface of the negative electrode, thereby maintaining stable charge and discharge without further decomposition of the electrolyte.

As described above, the lithium secondary battery has a large performance change due to high current at high C-rate when applied to a portable electronic device such as a mobile phone.

Accordingly, it has been an important task to develop an electrolyte recipe that can improve the high rate characteristic of a battery and to prevent the degradation of the characteristic of the battery even when using a high current.

Despite these demands, most of the nonaqueous electrolyte solvents conventionally used in lithium secondary batteries have a low withstand voltage, and when the electrolytes using solvents having a low withstand voltage are used in the secondary batteries, charge and discharge are repeated. The solvent is decomposed and the resulting gas generates a phenomenon in which the internal pressure of the battery increases, a product causes a polymerization reaction, or adheres to the electrode surface.

For this reason, there arises a problem that the battery charge and discharge efficiency is lowered and the battery life is shortened due to the decrease in battery energy density.

Currently, in order to improve the high-rate characteristics, a part of attempting to form a stable solid electrolyte interface (SEI) on the surface of the electrode is mainly attempted, and the SEI thus formed has higher conductivity, and thus lithium ion ( Li ⁺ ) to improve the mobility (Mobility) and at the same time to improve the charging and discharging characteristics to improve the life and high rate characteristics.

As another attempt to solve the above problems, a study has been attempted to secure a high rate characteristic of a battery by adding a small amount of a compound as an additive to an electrolyte of a lithium secondary battery, for example, in Japanese Unexamined Patent Publication No. 8-22839. In the above, as the additive in the electrolytic solution, trimethyl phosphate and triethyl phosphate were used in combination to improve the withstand voltage and suppressed decomposition of the electrolytic solution solvent by oxidation.

In addition, Japanese Patent Application Laid-Open No. 2-10666 uses a carbonate ester solvent having a high withstand voltage instead of a solvent having a low withstand voltage, thereby suppressing a decrease in battery energy density after repeated charge and discharge, thereby improving life and high rate characteristics. It has been proposed as an electrolyte solution.

Japanese Laid-Open Patent Publication No. 2000-223152 has described an electrolyte solution containing a trialkyl silyl compound containing a lower alkyl group having a dehydrating effect, and has been reported to have an effect of suppressing deterioration of battery capacity.

In the embodiment, hexa methyl di silazane and N, O-bis trimethylsilyl trifluoro acetamide (vis) are used, but the effect of inhibiting capacity deterioration at high temperatures Esau failed to achieve satisfactory results.

In addition, Japanese Patent Laid-Open No. 2001-57237 has described an electrolyte solution containing a compound having a metal element, phosphorus or a boron-oxygen-silicon bond in order to improve battery life, charge / discharge characteristics, load characteristics and low temperature characteristics.

Although silyl esters, such as trimethylsilyl phosphate, are disclosed, they increase the viscosity of the electrolyte when added, thereby lowering the conductivity of the electrolyte, thereby increasing the internal resistance of the high density lithium ion secondary battery, and also increasing the internal resistance of the lithium ion secondary battery. In the above high temperature storage, there are disadvantages of generating a lot of decomposition gas and increasing battery thickness.

On the other hand, Japanese Patent Laid-Open No. 2001-342607 introduced an electrolyte solution used in parallel with LiBF ₄ simultaneously with a silyl ester compound as a method for solving this problem.

LiBF ₄ is used in combination to prevent the decomposition of the electrolyte on the negative electrode and to reduce the interfacial resistance between the negative electrode or the positive electrode and the electrolyte in a lithium ion secondary battery having a high packing density of the negative electrode active material, and thus has little deterioration in lithium ion conductivity due to thickening. It has been described as having an effect of improving low temperature and high temperature storage properties.

However, this also did not completely solve the high temperature safety which is a disadvantage of trimethylsilyl phosphate.

In order to solve the problems of the prior art, the inventors of the present invention, without affecting the basic performance of the lithium secondary battery, a non-aqueous lithium secondary battery that can bring an improved effect in high rate characteristics, life characteristics, other charge and discharge characteristics An electrolyte was developed.

The technical problem to be achieved by the present invention is to improve the life characteristics, high rate characteristics and charge and discharge characteristics of the battery by adding a certain additive to the non-aqueous electrolyte in the lithium secondary battery, especially the lithium secondary battery using the non-aqueous electrolyte. The present invention provides a nonaqueous electrolyte solution for lithium secondary batteries.

Another object of the present invention is to provide a lithium secondary battery including the non-aqueous electrolyte of the present invention.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A non-aqueous electrolyte lithium secondary battery according to an embodiment of the present invention for solving the above technical problem is a basic electrolyte containing a non-aqueous organic solvent and a lithium salt dissolved in the non-aqueous organic solvent; It is characterized in that trimethylsilyl phosphite represented by the following formula (1) is added to the basic electrolyte solution.

Lithium secondary battery according to an embodiment of the present invention for solving the above other technical problem is an electrolytic solution of the present invention, an electrode portion composed of a positive electrode and a negative electrode which are located opposite to each other with an electrolyte therebetween, and the positive electrode and the negative electrode electrically It includes a separator that separates it.

Specific details of other embodiments are included in the detailed description and the accompanying drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only the present embodiments to make the disclosure of the present invention complete, and common knowledge in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

A nonaqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention does not include water (H ₂ O) as it is, and only an organic solvent is used as a solvent, and a lithium salt is dissolved in such a non-aqueous organic solvent. To the basic electrolyte, additives for improving the life characteristics, high rate characteristics, and charge / discharge characteristics of the lithium secondary battery, which are the technical problem of the present invention, are added.

The basic electrolyte solution contains a non-aqueous organic solvent and a lithium salt.

Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reaction of a battery can move. It is recommended to use a material having a high dielectric constant (polarity) and a low viscosity to increase ion dissociation and facilitate ion conduction. In general, it is preferable to use two or more mixed solvents composed of a solvent having a high dielectric constant and a high viscosity and a solvent having a low dielectric constant and a low viscosity.

The non-aqueous organic solvent used in the present invention includes at least one solvent selected from the group consisting of carbonate-based, ester-based, ether-based, and ketone-based solvents.

Carbonate solvents include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate One or more of a cyclic carbonate organic solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate At least one chain carbonate organic solvent (EPC) is mixed.

In this case, the cyclic carbonate organic solvent and the chain carbonate organic solvent are mixed in a ratio of 1: 1 to 1: 9 based on the volume ratio, and preferably mixed in a volume ratio of 1: 1.5 to 1: 4. It is most preferable in view of the life characteristics and high rate characteristics of the battery.

In particular, in the cyclic carbonate organic solvent, ethylene carbonate and propylene carbonate having a high dielectric constant are used, and when artificial graphite is used as the negative electrode active material, ethylene carbonate is preferably used. In the chain carbonate organic solvent, Preference is given to using dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate having a low viscosity.

The ester organic solvent is methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, ε-capro One or more selected from the group consisting of lactones are used, and one or more selected from tetrahydrofuran, 2-methyltetrahydrofuran, and dibutyl ether is used as the ether organic solvent, and as the ketone organic solvent, Methylvinyl ketone is used.

The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent represented by Formula 3 below.

(R is a halogen or an alkyl group having 1 to 10 carbon atoms, q is an integer of 0 to 6)

Specifically, the aromatic hydrocarbon organic solvent may be one or more of benzene, fluorobenzene, bromobenzene, chlorobenzene, toluene, xylene, mesitylene, fluorotoluene, difluorotoluene, and trifluorotoluene. .

The amount of the aromatic hydrocarbon compound and the carbonate solvent is determined in the range of 1: 1 to 1:30 based on the volume ratio.

Lithium salt is dissolved in the non-aqueous organic solvent to form a basic electrolyte.

At this time, the lithium salt serves as a source of lithium ions in the battery to enable the operation of the basic lithium battery.

Lithium salts include LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ , wherein x and y are natural numbers), LiCl, and At least one selected from LiI is used.

The amount of lithium salt added is 0.6 to 2.0M in the total electrolyte, and considering the properties related to the electrical conductivity of the electrolyte and the viscosity related to the mobility of lithium ions, it is preferable to be in the range of 0.7 to 1.6M, and 0.7 to More preferably, it is in the range of 1.6M.

As described above, trimethylsilyl phosphite (Tris (trimethylsilyl) phosphite) represented by Chemical Formula 1 is added to the basic electrolyte in which lithium salt is dissolved in the non-aqueous organic solvent.

Trimethylsilyl phosphite is generally used as a cathode active material in lithium secondary batteries, such as LiCoO ₂ , LiNiO ₂ , or LiMn ₂ O ₄ , which have a large capacity per unit weight. Since it maintains an unstable state, it may cause rapid decomposition-heating reaction with electrolyte, or may precipitate lithium metal on the negative electrode and cause battery to rupture and ignite. Therefore, the additive may be added to the battery when used at high rate. It is added to ensure stability.

The trimethylsilyl phosphite is preferably added in an amount of 0.01 to 20 parts by weight based on 100 parts by weight of the basic electrolyte solution in consideration of the lifespan and high rate characteristics of the manufactured lithium secondary battery, and more preferably 0.2 to 5.0 parts by weight. .

Further, the non-aqueous electrolyte solution of the present invention may further contain propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, and the like, as necessary.

The electrolyte solution of the lithium secondary battery of the present invention is excellent in storage characteristics and can maintain a long life in the temperature range of -20 to 60 ℃, in particular, it improves the safety and reliability of the lithium secondary battery in a high rate state.

The electrolyte solution of the present invention can be applied to all lithium secondary batteries such as lithium ion batteries and lithium polymer batteries.

1 shows that aluminum (Al) is used as the positive electrode 100 metal, copper (Cu) is used as the negative electrode 110 metal, LiCoO ₂ is used as the positive electrode 100 active material, and carbon (C) is used as the negative electrode active material. It is a schematic diagram which shows the lithium secondary battery which used the nonaqueous electrolyte solution as electrolyte solution 130. FIG.

As shown in FIG. 1, a lithium secondary battery according to an exemplary embodiment of the present invention includes a positive electrode 100, a negative electrode 110, an electrolyte 130, and a separator 140.

However, since the electrolyte 130 used in the lithium secondary battery according to the embodiment of the present invention is used, the non-aqueous electrolyte according to the embodiment of the present invention has been described above. .

The positive electrode 100 and the negative electrode 110 are disposed to face each other with the electrolyte 130 interposed therebetween.

The positive electrode 100 is an active material in a metal, and the positive electrode is Li _x Mn _{1 - y} M _y A ₂ , Li _x Mn ₂ O _4-z X _z , Li _x Mn _{2 - y} M _y M ' _z A ₄ , Li _x Co _{1 - y} M _y A ₂ , Li _x Co _{1 - y} M _y O _{2 - z} X _z , Li _x Ni _{1 - y} M _y O _{2 - z} X _z , Li _x Ni _{1 - y} Co _{y O 2 -z x z, Li x} Ni 1 -y- z Co y M z A α, Li x Ni 1 -y- z Co y M z O 2 -α x α, Li x Ni 1 -y- z Mn _y M _z a _α, there are one or more active materials selected from _{Li x Ni 1 -y- z Mn y} M z O 2 -α x α is coated.

(Wherein 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2,

M and M 'are the same or different and include Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earths Selected from the group of elements,

A is selected from the group consisting of O, F, S and P,

X is selected from the group consisting of F, S and P)

The negative electrode 110 is coated with a carbon active material capable of inserting and detaching lithium ions into a metal (both crystalline carbon and amorphous carbon), but in addition, carbon composite, carbon fiber, lithium metal, lithium alloy, and lithium composite At least one active material selected from among may be coated.

For example, amorphous carbons include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or lower, mesophase pitch-based carbon fibers (MPCF), and the like.

Graphite-based materials are used as the crystalline carbon, and specific examples thereof include natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbonaceous material is preferably a material having an d002 interplanar distance of 3.35 to 3.38 kPa and an Lc (crystallite size) of at least 20 nm by X-ray diffraction. As the lithium alloy, an alloy of lithium with aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium may be used.

The positive electrode or the negative electrode may be prepared by dispersing an electrode active material, a binder and a conductive material, and, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector.

Aluminum or an aluminum alloy may be used as the positive electrode current collector, and copper or a copper alloy may be used as the negative electrode current collector. Examples of the positive electrode current collector and the negative electrode current collector include a foil, a film, a sheet, a punched one, a porous body, a foam, and the like.

The binder is a material that plays a role of pasting the active material, mutual adhesion of the active material, adhesion with the current collector, buffering effect on the expansion and contraction of the active material, and the like, for example, polyvinylidene fluoride and polyhexafluoropropylene-poly Copolymers of vinylidene fluoride (P (VdF / HFP)), poly (vinylacetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (methylmethacryl) Rate), poly (ethylacrylate), polytetrafluoroethylene, polyvinylchloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber and the like.

The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight based on the electrode active material. When the content of the binder is too small, the adhesion between the electrode active material and the current collector is insufficient, and when the content of the binder is too high, the adhesion is improved, but the content of the electrode active material decreases by that amount, which is disadvantageous in increasing battery capacity.

The conductive material may be at least one selected from the group consisting of a graphite-based conductive agent, a carbon black-based conductive agent, a metal or a metal compound-based conductive agent as a material for improving electronic conductivity. Examples of the graphite conductive agent include artificial graphite and natural graphite, and examples of the carbon black conductive agent include acetylene black, ketjen black, denka black, thermal black, Channel black and the like, and examples of the metal or metal compound conductive agent include perovskite such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ , and LaSrMnO _3. perovskite) substance.

However, it is not limited to the conductive agents listed above. The content of the conductive agent is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive agent is less than 0.1% by weight, the electrochemical properties are lowered, and when the content of the conductive agent is greater than 10% by weight, the energy density per weight decreases.

The thickener is not particularly limited as long as it can play a role of controlling the viscosity of the active material slurry. For example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, or the like may be used.

As a solvent in which an electrode active material, a binder, a conductive material, etc. are disperse | distributed, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

In this case, the metal used in the positive electrode 100 and the negative electrode 110 is a portion to which a voltage is applied from the outside during charging and supplies a voltage to the outside during discharge, and the positive electrode active materials are a collector and a negative electrode that collect positive charges. The active material serves as a current collector for collecting negative charges.

The separator 140 electrically separates the positive electrode 100 and the negative electrode 110 to prevent a short and serve as a movement path of lithium ions.

As the separator 140, one of a single layer separator made of polyethylene or polypropylene, a two layer separator laminated with polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, or a three layer separator laminated with polypropylene / polyethylene / polypropylene is used. It may be used in the form of a multi-layer, microporous film, woven fabric and nonwoven fabric. In addition, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

The electrode assembly manufactured as described above is accommodated in a can-shaped housing together with an electrolyte, and the upper end of the can is sealed with a cap assembly to complete a lithium secondary battery.

In this case, the cap assembly includes a cap plate, an insulating plate, a terminal plate, and an electrode terminal.

At this time, the cap assembly is combined with the insulating case serves to seal the can. In addition, a terminal through-hole having an electrode terminal inserted therein is formed at the center of the cap plate. When the electrode terminal is inserted into the terminal through-hole, a tubular gasket is coupled to the outer surface of the electrode terminal for insertion of the electrode terminal and the cap plate. .

After the cap assembly is assembled to the upper end of the can, the electrolyte is injected through the electrolyte injection hole and the electrolyte injection hole is closed by a cap. In this case, the electrode terminals are connected to the negative electrode tab of the negative electrode and the positive electrode tab of the positive electrode, respectively, to act as a negative electrode terminal or a positive electrode terminal.

Hereinafter, the life characteristics and the high rate characteristics of the lithium secondary battery may be improved by using the nonaqueous electrolyte solution for the lithium secondary battery according to the embodiments of the present invention with reference to specific examples and comparative examples. However, the content not described herein is omitted because it can be inferred technically sufficient by those skilled in the art.

One. Examples  And Comparative Examples

< Example  1>

The positive electrode used LiCoO ₂ as an active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black in slurry form as a conductive agent.

The slurry prepared as described above was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode.

The negative electrode was prepared by mixing natural graphite as an active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose as a thickener at a weight ratio of 96: 2: 2, and then dispersing it in water to prepare a negative electrode active material slurry. The slurry was coated on a copper foil having a thickness of 15 μm, dried, and rolled to prepare a negative electrode.

A film separator made of polyethylene (PE) having a thickness of 20 μm was inserted between the electrodes, and then wound and compressed to insert a cylindrical separator. An electrolyte was injected into the cylindrical can to prepare a lithium secondary battery.

The electrolyte solution is ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) mixed solvent was added to dissolved therein such that the 1.0M LiPF ₆ in (1: 1 volume ratio: 1), then, x trimethylsilyl phosphite Trimethylsilyl phosphite was added in an amount of 0.1% by weight of the organic solvent. Thereafter, a square battery was manufactured and discharge experiments were performed at different rates.

< Example  2>

It carried out similarly to Example 1 except adding 2 weight% of trimethylsilyl phosphites.

< Example  3>

The same procedure as in Example 1 was conducted except that 5 wt% of trimethylsilyl phosphite was added.

< Example  4>

It carried out similarly to Example 1 except adding 10 weight% of trimethylsilyl phosphites.

< Comparative example  1>

Trimethylsilyl phosphite was carried out in the same manner as in Example 1 except that only the basic electrolyte was used without addition.

< Comparative example  2>

The same procedure as in Example 1 was conducted except that 2 wt% of trimethylsilyl phosphate was added.

< Comparative example  3>

The LiBF ₄ was carried out the same as in Example 1 except that 0.2% by weight.

< Comparative example  4>

Tree was performed in the same manner as in Example 1 except that 2-methyl-silyl phosphate was added to 0.2% by weight LiBF _4% by weight.

2. High rate characteristic evaluation

The samples prepared by the above Examples and Comparative Examples were measured for a high rate characteristic in the range of 0.2 ~ 4.0 C-rate, and the discharge amount for each rate compared to 0.2 C-rate is shown in Table 1 as a% value.

Referring to Table 1, at 0.5 C-rate, the value of Comparative Example 1 has almost no difference compared to the Examples, but after 1.0 C-rate, the discharge amount of the sample of Comparative Example 1 gradually decreased to 4.0 C. In -rate, the embodiments had a discharge amount of approximately 70%, but in Comparative Example 1, the discharge amount dropped to less than 50%.

2 is a graph showing the results of comparing the life characteristics at 1.0 C-rate with respect to Example 2 and Comparative Example 1.

Referring to FIG. 2, in the case of Example 2, as the cycle is repeated, the capacity (mAh) gradually increases, and the capacitance decreases by about 10% even after 300 cycles. It can be seen that as the value is repeated, the capacitance decreases rapidly and the end of life is reached around 150 cycles.

Table 2 shows the viscosity and ions for Examples 1 to 4 using trimethylsilyl phosphite and Comparative Examples 1 to 4 without using trimethylsilyl phosphite or using trimethylsilyl phosphate. Conductivity, thickness after 30 days storage at 60 ° C (mm), storage capacity (mAh), recovery capacity after 30 days storage at 60 ° C (mAh), OCV (open circuit voltage) and IR (mW) A table comparing the results.

Referring to Table 2, the electrolytic solution (Trials 1 to 4) to which trimethyl silyl phosphite was added has a lower viscosity than the electrolytic solution (Comparative Examples 1 to 4) to which trimethylsilyl phosphate and LiBF ₄ were added, respectively, or at the same time. The thickness increase rate after 30 days at ℃ was about 8 to 28% improved, OCV 2 to 9% improved, IR was 13 to 29% improved.

In addition, trimethylsilyl phosphite, unlike trimethyl silyl phosphate, also has a feature that high-temperature characteristics are not deteriorated even if the amount of addition is increased.

This is because trimethyl silyl phosphite having no oxygen double bonds to P has superior viscosity characteristics compared to trimethyl silyl phosphate having oxygen double bonds to P, and the film formed at the cathode is more stable at high temperatures.

In addition, the trimethyl silyl phosphate has a characteristic that the viscosity increases as the amount of addition increases, because of the structure that oxygen is attached to the P atoms as a double bond. Therefore, the trimethyl silyl phosphite from which the oxygen bonded by the double bond is removed has the advantage that the viscosity does not increase even if a certain amount is added.

By using such a difference in physicochemical properties, the problem of high temperature standing that occurs when using conventional trimethyl silyl phosphate and a problem of increasing viscosity as the amount of addition increases are solved, thereby improving the characteristics of the lithium secondary battery.

As such, when trimethylsilyl phosphite is added to the non-aqueous electrolyte for lithium secondary batteries, the thickness increase rate is low even when left at a high temperature for a long time, and shows excellent characteristics in high temperature storage capacity and recovery capacity.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings and tables, the present invention is not limited to the above embodiments, but may be manufactured in various forms, and common knowledge in the art to which the present invention pertains. Those skilled in the art can understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

According to the non-aqueous electrolyte lithium secondary battery and the lithium secondary battery including the same according to an embodiment of the present invention it is possible to improve the high rate characteristics and life characteristics while maintaining the performance of the basic battery.

Claims (12)

A basic electrolyte solution containing a non-aqueous organic solvent and a lithium salt dissolved in the non-aqueous organic solvent; A non-aqueous electrolyte solution for lithium secondary batteries, characterized in that trimethylsilyl phosphite represented by the following formula (1) is added to the basic electrolyte solution.

The method of claim 1, A non-aqueous electrolyte solution for lithium secondary batteries, comprising 0.01 to 20 parts by weight of trimethylsilyl phosphite based on 100 parts by weight of the base electrolyte. The method of claim 1, A non-aqueous electrolyte solution for lithium secondary batteries comprising 0.2 to 5.0 parts by weight of trimethylsilyl phosphite based on 100 parts by weight of the basic electrolyte solution. The method of claim 1, The non-aqueous organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pen At least one cyclic carbonate-based organic solvent of thiylene carbonate; The chain carbonate organic solvent of at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) A non-aqueous electrolyte solution for lithium secondary batteries, which is mixed. The method of claim 4, wherein The cyclic carbonate organic solvent and the chain carbonate organic solvent are non-aqueous electrolyte solution for lithium secondary batteries, characterized in that they are mixed in a volume ratio of 1: 1 to 1: 9. The method of claim 1, As the non-aqueous organic solvent, the carbonate-based organic solvent further comprises an aromatic hydrocarbon-based compound represented by the following formula (2).

(Wherein R is a halogen or an alkyl group having 1 to 10 carbon atoms and q is an integer of 0 to 6) The method of claim 6, The aromatic hydrocarbon compound is lithium secondary, characterized in that one of benzene, fluorobenzene, bromobenzene, chlorobenzene, toluene, xylene, mesitylene, fluoro toluene, difluoro toluene, trifluoro toluene Non-aqueous electrolyte solution for batteries. The method of claim 6, The aromatic hydrocarbon compound and the carbonate solvent is a non-aqueous electrolyte solution for a lithium secondary battery, characterized in that mixed in a ratio of 1: 1 to 1:30. The method of claim 1, The lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ , wherein x and y are natural numbers), LiCl, and At least one selected from LiI, the concentration is 0.6 to 2.0M in the total electrolyte, characterized in that the non-aqueous electrolyte for lithium secondary battery. The electrolyte of any one of claims 1 to 9; An electrode unit including positive and negative electrodes positioned to face each other with the electrolyte interposed therebetween; And Lithium secondary battery comprising a separator for electrically separating the positive electrode and the negative electrode. The method of claim 10, The positive electrode is Li _x Mn _{1 - y} M _y A ₂ , Li _x Mn ₂ O _{4 - z} X _z , Li _x Mn _{2 - y} M _y M ' _z A ₄ , Li _x Co _{1 - y} M _y A ₂ , _{Li x Co 1 - y M y} O 2 - z X z, Li x Ni 1 - y M y O 2 - z X z, Li x Ni 1 - y Co y O 2 - z X z, Li x Ni 1 - _{y- z} Co _y M _z A _α , Li _x Ni _{1 -y- z} Co _y M _z O _{2 -α} X _α , Li _x Ni _{1 -y- z} Mn _y M _z A _α , Li _x Ni _{1 -y - z} Mn _y M _z O _{2 -α} X _α lithium secondary battery, characterized in that the coating is at least one active material selected from. (Wherein 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M 'are the same or different and include Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earths Selected from the group of elements, A is selected from the group consisting of O, F, S and P, X is selected from the group consisting of F, S and P) The method of claim 10, The negative electrode is a lithium secondary battery characterized in that the metal is coated with at least one active material selected from crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, lithium alloy, lithium composite.

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