KR101521646B1 - Secondary battery with high capacity and longevity comprising silazane-based compound - Google Patents

Abstract

The present invention relates to an electrolyte for a battery comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte is a compound capable of forming a passivation layer by electrochemically reacting in the battery, the electrolyte comprising at least one silane group and a silane A silazane-based compound, and a secondary battery comprising the electrolyte.

In the present invention, by using a silazane-based compound capable of forming an inactive film on both electrodes in the normal operating voltage range of a battery, side reactions between the both electrodes and the electrolyte are minimized to improve the capacity and lifetime performance Can be provided.

SEI layer, lifetime performance, capacity increase, lithium secondary battery

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a high-capacity and long-life secondary battery including a silazane-

1 is a cyclic voltammogram performed using the electrolytes of Example 1 and Comparative Example 1. FIG.

2A is a graph showing a relation between an initial formation charge amount and a voltage of a battery of Example 2 and Comparative Example 2. FIG.

FIG. 2B is a graph obtained by differentiating the charged amount according to the voltage increase in the graph of FIG. 2A.

3 is a graph of TPD-GC-MS-TIC of the negative electrode obtained after fully charging the batteries of Example 2 and Comparative Example 2, respectively.

FIG. 4 is a graph comparing the capacity and efficiency of the batteries according to the cycle progression of the batteries of Example 2 and Comparative Example 2. FIG.

5 is a graph showing life characteristics of the batteries of Example 2 and Comparative Example 2 after storage at full temperature (4.2 V) at 90 DEG C for 4 hours.

The present invention uses an electrolyte additive capable of forming an effective passivation layer on an anode and a cathode by an electrochemical oxidation-reduction reaction, thereby minimizing a side reaction between both electrodes and an electrolyte, Battery.

2. Description of the Related Art Recently, the importance of batteries as power sources for portable electronic devices such as cellular phones, video cameras, notebook personal computers and the like has been increasing. Accordingly, research and development have been actively made on a lithium secondary battery using a battery which is light in weight, high voltage, high capacity and high output as a driving power source for portable electronic devices, particularly, a non-aqueous electrolyte.

The lithium secondary battery generally uses a lithium-containing transition metal oxide as a positive electrode active material, and is capable of intercalating and deintercalating carbon, a lithium metal or an alloy thereof, and other lithium as an anode active material, and is capable of storing TiO ₂ , SnO ₂ Is used. The lithium secondary battery can be divided into lithium ion battery (LiLB), lithium ion polymer battery (LiPB) and lithium polymer battery (LPB) according to the electrolyte used. That is, LiLB is a liquid electrolyte, LiPB is a gel polymer electrolyte, LPB uses a solid polymer electrolyte.

(EC), propylene carbonate (PC), gamma-butylolactone (gamma -butyrolactone, hereinafter referred to as GBL), and the like are used as the non-aqueous solvent used in the battery electrolyte, Of cyclic carbonates are preferably used. In particular, when LiMn ₂ O ₄ is used as a cathode active material, HF, which is a strong acid, is generated due to a side reaction between a very small amount of water present in the battery and a lithium salt (Li salt), and this HF attacks an anode to dissolve Mn ). When manganese (Mn) is ionized into the electrolyte, it moves to the cathode and is reduced, thereby growing on the surface of the cathode, resulting in a decrease in capacity and an increase in internal resistance of the cell. Even when other cathode materials are used, the above phenomenon is not as severe as the manganese based active material, but it is very likely to occur in general.

On the other hand, in general, when the capacity of the battery is increased and the loading amount of the electrode active material is increased, lithium metal precipitates as the charge and discharge are repeated, thereby deteriorating battery capacity such as capacity and life. Further, in the case of some additives to be added as an electrolyte component in order to improve the capacity and lifetime characteristics, gas may be generated at a charge / discharge or a high temperature, which may cause problems such as cell shape deformation and cell performance. Therefore, H ₂ O scavenger is required to hold moisture, and it is necessary to protect the anode and the cathode to increase the capacity and to use the battery for a long time.

The present inventors have found that when a silazane-based compound containing a silane group and nitrogen is used as a constituent component of an electrolytic solution, the present inventors have found that an effective film is formed on both the positive electrode and the negative electrode through an oxidation- It is possible to suppress an additional reaction which causes deterioration of performance.

Accordingly, an object of the present invention is to provide an electrolyte containing the above-described silazane-based compound and a secondary battery comprising the electrolyte.

The present invention relates to an electrolyte for a battery comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte is a compound capable of forming a passivation layer by electrochemically reacting in the battery, the electrolyte comprising at least one silane group and a silane A silazane-based compound, and a secondary battery comprising the electrolyte.

The present invention also relates to a secondary battery comprising a passivation layer formed on a part or all of a surface of an electrode active material formed by electrically oxidizing or reducing a silazane-based compound having at least one silane group and nitrogen introduced thereinto, to provide.

Further, the present invention relates to an electrolyte additive for forming an SEI film, which is a compound capable of forming a solid electrolyte interface (SEI) film on a negative electrode of a secondary battery, which is a silazane type compound containing at least one silane group and nitrogen to provide.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by using a silazane-based compound capable of forming an effective passivation layer on both the positive electrode and the negative electrode by oxidation-reduction in an operating voltage range of a battery as an electrolyte component for a battery .

Due to the above characteristics, the secondary battery of the present invention can realize high capacity, high efficiency, excellent long life time characteristics and high temperature characteristics. The reason for exhibiting such excellent effects has not been clarified yet, but it can be estimated as follows.

1) The performance of the battery is greatly influenced by the basic electrolyte composition and the solid electrolyte interface (SEI) formed by the reaction between the electrolyte and the electrode. In the conventional rechargeable lithium battery, during the first charging process, the surface of the negative electrode active material such as carbon particles reacts with the electrolyte at the negative electrode of the battery to form a solid electrolyte interface (SEI) coating. Carbonic acid gas such as CO ₃ ^{2 -} which is a decomposition product of an organic solvent including a cyclic carbonyl group, is formed by reaction with saturated lithium ions in the electrolyte solution, and lithium is irreversibly consumed in forming the SEI film. Such an SEI film is a side reaction between an electrode active material and an electrolyte solvent; And collapse of the negative electrode material due to co-intercalation of the electrolyte solvent into the negative electrode material, as well as faithfully performing a role as a conventional lithium ion tunnel, thereby minimizing degradation of the battery. However, since the SEI film formed by the conventional organic carbonate-based solvent is weak, porous and dense, the lithium ion migration can not be smoothly performed, thereby reducing irreversible lithium amount, thereby increasing the irreversible reaction due to charge / Resulting in degraded characteristics.

Therefore, in the present invention, a silazane-based compound capable of forming a stable and dense inactive film on both electrodes by oxidation-reduction in an operating voltage range of a battery is used as an electrolyte component.

The silazane-based compound is superior to the solid-state interface (SEI) of fluorine or other inorganic components formed on the negative electrode active material due to the reaction between the carbonate-based electrolyte and the negative electrode, It is possible to improve the lifetime characteristics of the battery by reducing the reactivity between the electrolyte and the electrode by forming an SEI film of an organic component containing excellent ether species and N (see FIGS. 3 and 4). In addition, at the initial charging of the battery, a solid and dense SEI film is formed on the surface of the anode material before other components to increase initial charging / discharging efficiency, and the formed SEI film selectively stores and discharges only lithium ions (Li ⁺ ) Since it is a passivation layer with low chemical reactivity, it can exhibit high stability even in a long cycle.

2) In the conventional lithium secondary battery, the performance of the battery suddenly deteriorates under a high temperature environment. This is because the SEI film formed on the surface of the negative electrode is rapidly disintegrated, resulting in a side reaction between the electrode and the electrolyte, Gas generation, and electrode thickness (resistance) increase are also expected to occur rapidly.

In contrast, the SEI membrane of the present invention includes an ether and N which are superior in terms of consumption and regeneration of SEI. Therefore, the SEI membrane of the present invention not only rapidly regenerates upon collapse due to high temperature, The occurrence of side reactions can be reduced and the high temperature characteristics of the improved battery can be exhibited (see FIG. 5).

One of the elements constituting the electrolytic solution for a battery according to the present invention is a silazane-based compound containing at least one silane group and nitrogen.

The silazane-based compound has no particular limitation on the chemical structure, the number of silane groups, and the number of nitrogens, as long as it can oxidize-reduce in the normal operating voltage range of the battery to form an effective passivation layer on the anode and the cathode. The silazane-based compound may be represented by the following general formula (1), but is not limited thereto.

R ₁ R ₂ R ₃ Si-NR ₇ -SiR ₄ R ₅ R ₆

In this formula,

R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ are each independently hydrogen, a C 1 to C 6 alkyl group or an alkenyl group which is unsubstituted or substituted with a halogen atom.

The silazane-based compound of the present invention is preferably a disilazane-based compound in which two or more silane groups are present in the compound and are linked by nitrogen. For example, hexamethyldisilazane (HMDS) and the like are available.

Hexamethyldisilazane (HMDS) is reduced at the initial charging, and an SEI film of an organic component containing cyclic ethers and nitrogen (N) is firmly formed on the surface of the anode, thereby improving the initial capacity and long- In addition, a protective layer may be formed on the surface of the anode by oxidation in an operating voltage range of the battery, thereby suppressing a side reaction between the highly reactive anode and the electrolyte, thereby improving high temperature storage characteristics. In fact, the HMDS effectively oxidizes the anode coating through oxidation reaction at about 3.1 V near the lithium potential (Li / Li ⁺ ) and near 4 V, thereby suppressing side reactions of the anode and the electrolyte, And can contribute to property improvement (see Figs. 2A and 2B). As described above, since both electrodes, which are essential components in the battery, can be protected at the same time, the effect of improving the performance of the battery can be improved.

Also, the silazane-based compound is one of organic desiccants. As shown in the following reaction formula (1), the silazane-based compound reacts with water in an organic solvent to act as a scavenger, thereby suppressing side reactions by moisture.

_{(CH 3) 3 Si-NH} -Si (CH 3) 3 + H 2 O → (CH 3) 3 Si-O-Si (CH 3) 3 + NH 3

As a result of the above-described reaction, it is possible to suppress the reaction of reducing the battery performance by the halogen acid (HX, X = F, Cl, Br, I, etc.) generated by the reaction of water with the lithium salt. In case of using the active material (for example, LiMn ₂ O ₄ ), dissolution of the transition metal (for example, Mn) in the electrode active material can be suppressed.

The content of the silazane-based compound is preferably in the range of 0.01 to 10 parts by weight per 100% by weight of the nonaqueous electrolyte solution, depending on the goals of improving the performance of the battery, such as initial efficiency, capacity, cycle life characteristics and high- Do. When the amount is less than 0.01 part by weight, the effect of improving the performance of the desired battery is insignificant. If the amount is more than 10 parts by weight, degradation may occur due to an increase in irreversible capacity.

The battery electrolyte to which the compound is to be added includes conventional electrolyte components known in the art such as an electrolyte salt and an organic solvent.

Using the electrolyte salts is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, 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 -, C (CF 2 SO 2) 3 ^- < / RTI > or a combination thereof. In particular, a lithium salt is preferable. Nonlimiting examples of these include LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _2, and mixtures thereof.

The organic solvent may be a conventional solvent known to those skilled in the art, for example, a cyclic carbonate system with or without a halogen substituent; Linear carbonate system; Ester type, nitrile type, phosphate type or mixtures thereof can be used. Nonlimiting examples of these include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, formic acid Propyl acetate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, butyl propionate or mixtures thereof.

The present invention provides an electrode in which a passivation layer formed by electrically oxidizing or reducing a silazane-based compound to which at least one silane group and nitrogen are simultaneously introduced is formed on a part or all of the surface of the electrode active material.

When the electrode is charged and discharged using the above-described electrolyte, the silazane-based compound in the electrolyte can be automatically formed on the surface of the electrode active material together with the reversible lithium ion, or the compound can be coated on the surface of the electrode active material, Or may be formed by coating the surface of the produced electrode. At this time, the passivation layer may be a solid electrolyte interface coating formed on part or all of the surface of the electrode active material by polymerizing the silazane-based compound by electrical reduction.

As described above, the secondary battery in which the silazane type compound or the chemical reaction product thereof has electrodes formed on part or all of the surface of the electrode active material not only stabilizes the carbon materials, transition metals and transition metal oxides in the electrode, The exothermic reaction generated by the direct reaction can be effectively controlled and the breakdown of the structure of the electrode active material can be delayed, thereby preventing the ignition and rupture phenomenon caused by the temperature rise inside the battery. In addition, formation of a halogen acid (e.g., HF) by reaction with water present in the battery is suppressed, and the structural stability of the electrode active material can be fundamentally improved.

The electrode according to the present invention can be produced by binding an electrode active material to an electrode current collector according to a conventional method known in the art. One example of the electrode active material is an electrode slurry containing a cathode active material or a negative active material Coated on a current collector and dried. At this time, a small amount of conductive agent and / or binder may be optionally added.

As the cathode active material, a conventional cathode active material which can be used for a cathode of a conventional secondary battery can be used. Non-limiting examples of the cathode active material include LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) A transition metal complex oxide (for example, lithium manganese composite oxide such as LiMn ₂ O ₄ , lithium nickel oxide such as LiNiO ₂ , lithium cobalt oxide such as LiCoO ₂ , and manganese, nickel and cobalt of these oxides, Or vanadium oxide containing lithium), or a chalcogen compound (e.g., manganese dioxide, titanium disulfide, molybdenum disulfide, etc.). 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 ( here, 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), LiNi 1 - X Co X M Y O 2 ( here, M = Al, Ti, Mg , Zr, 0 <X ≤1, 0 ≤Y ≤0.2), LiNi X Co _y Mn _{1 -X- y} O ₂ (here, 0 <x ≤ 0.5, 0 <y ≤ 0.5) or _{LiM x M 'y Mn (2} -xy) O 4 (M, M' = V, Cr, Fe , Co, Ni, Cu, 0 <X? 1, 0 <Y? 1), LiCoPO ₄ , LiFePO ₄ or a mixture thereof.

The negative electrode active material may be a conventional negative electrode active material that can be used for a negative electrode of a secondary battery. Examples of the negative electrode active material include lithium metal or lithium alloy, carbonaceous material, petroleum coke, activated carbon, Graphite, Group 13 and Group 14 elements, solid solutions and alloys capable of lithium intercalation and deintercalation, and other TiO ₂ capable of intercalating and deintercalating lithium and having a potential for lithium of less than ₂ V, And metal oxides such as SnO ₂ and Li ₄ Ti ₅ O ₁₂ .

Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

As binders, conventional binders can be used, and non-limiting examples thereof include polyvinylidene fluoride (PVDF) or styrene butadiene rubber (SBR).

The conductive agent may be any electronic conductive material that does not cause a chemical change in the constructed battery. Carbon black such as acetylene black, ketjen black, fines black and thermal black; Natural graphite, artificial graphite, conductive piece fibers and the like can be used. Particularly, carbon black, graphite powder and carbon fiber are preferable.

As the binder, either a thermoplastic resin or a thermosetting resin may be used, or a combination thereof may be used. Of these, polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) is preferable, and PVdF is particularly preferable.

As the dispersion medium, an organic dispersion medium such as an aqueous dispersion medium or N-methyl-2-pyrrolidone can be used.

The present invention relates to a positive electrode; cathode; Electrolyte; And (d) a separator, wherein the electrolyte is an electrolyte solution containing the above-described electrolyte additive; Wherein the positive electrode, the negative electrode, or both electrodes are electrodes in which a passivation film containing the silazane type compound or a reduction (oxidation) product thereof is formed on part or all of the surface.

The secondary battery is preferably a lithium secondary battery, and examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

The secondary battery of the present invention may be manufactured by a conventional method known in the art, except that the electrolyte containing the silazane-based compound is used, a porous separator is interposed between the positive electrode and the negative electrode, . . In addition, the electrode into which the above-described compound is introduced may be used alone, or may be mixed with the electrolytic solution to which the above-mentioned electrolyte additive is added.

As the separation membrane, it is preferable to use a porous separation membrane. For example, a polypropylene-based, polyethylene-based, polyolefin-based porous separation membrane or a porous separation membrane into which inorganic particles are introduced may be used.

The outer shape of the secondary battery manufactured by the above method is not limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The present invention also provides an electrolyte additive for forming an SEI film, which is a compound capable of forming a solid electrolyte interface (SEI) film on a negative electrode of a secondary battery, which is a silazane-based thermal compound containing at least one silane group and nitrogen to provide.

The electrolyte additive for forming the SEI film is preferably a silazane-based compound of the above-mentioned formula (1), more preferably hexamethyldisilazane (HMDS).

In addition, the present invention provides a method of manufacturing a semiconductor device, comprising: (a) forming a protective film that oxidizes within an operating voltage range of an anode to increase the electrode resistance; And (b) a second compound which is oxidized at an operating voltage of the anode or higher to form at least one kind of action selected from the group consisting of heat generation, gas generation, and passivation film formation, 2 &lt; / RTI &gt; compound of the present invention is fluidly changed.

At this time, the second compound may have its own oxidation potential increased by the protective film formed by the oxidation of the first compound, and due to the increase of the oxidation potential of the second compound, the electrolyte can prevent overcharge voltage in the range of 4.2V to 5V have. That is, in the electrolyte containing HMDS as the first compound, the oxidation potential of the second compound (for example, CHB) due to HMDS is increased. Therefore, the reaction of CHB is suppressed within the practical range of the actual battery, It is possible to selectively operate in a non-ideal situation such as overcharging without affecting the overall performance.

The first compound may be hexamethyldisilazane (HMDS) or the like. Non-limiting examples of the second compound include toluene (TL), fluorotoluene (FT), t-butyl benzene ), Dibutylbenzene (DBB), t-amyl benzene (AB), cyclohexyl benzene (CHB), biphenyl (BP), fluorobiphenyl : FBP), anisol-based compounds, or mixtures thereof.

The present invention will be described in more detail based on the following examples and experimental examples. However, the examples and comparative examples are for illustrating the present invention and are not limited to the following examples and experimental examples.

Example 1

1-1. Electrolyte manufacture

EC: EMC = 1: 2 was mixed with 0.5 parts by weight of hexamethyldisilazane (HMDS) so that the LiPF ₆ concentration was 1 M in the electrolyte.

1-2. Battery Manufacturing

As the negative electrode active material, 97.5% by weight of MAG D / AGM, 1.5% by weight of a conductive agent and 1.0% by weight of CMC were added to prepare a negative electrode mixture slurry and then coated on a copper collector to prepare a negative electrode.

The positive electrode mixture slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) as a solvent to a composition of 96 wt% of LiCoO ₂ doped with Sn as a positive electrode active material, ₂ wt% of a conductive agent and 2 wt% of PVDF And then coated on an aluminum current collector to prepare a positive electrode.

After the porous separator was sandwiched between the anode and the cathode thus prepared, the electrolyte prepared in the above 1-1 was introduced to prepare a full cell.

Example 2

EC: electrolyte instead of EC having two composition:: EMC = 1 PC: DEC = 3: 2: 5 composition, and so that the electrolyte 1M of LiPF ₆ concentration and, the embodiment except that the mixed electrolyte HMDS 0.5 parts by weight The same procedure as in Example 1 was followed to prepare a battery having the electrolyte and the electrolyte.

Comparative Example 1

A lithium secondary battery was produced in the same manner as in Example 1 except that HMDS was not added to the electrolyte solution.

Comparative Example 2

A lithium secondary battery was produced in the same manner as in Example 2 except that HMDS was not added to the electrolyte solution.

Experimental Example 1. Evaluation of Cyclic Voltammetry of Electrolyte

Cyclic voltammetry was performed using the electrolyte of Example 1 in which HMDS was used as an electrolyte component and the electrolyte of Comparative Example 1 in which HMDS was not added. At this time, the working electrode was made of Pt, the auxiliary electrode was made of Pt, and the reference electrode was made of Li metal, and the voltage transfer rate was 20 mV / s.

As shown in FIG. 1, in the electrolyte solution of Example 1 in which HMDS was present in the electrolyte solution, a large oxidation current flowed around 4.0 V at a positive electrode potential of 3.15 V on the basis of Li metal. This means that the oxidation reaction is taking place by the HMDS contained in the electrolytic solution component. It can be expected that this oxidation reaction does not affect other performance and can act as a membrane or compound that can effectively protect the anode.

Experimental Example 2. Evaluation of performance of a battery

The performance evaluation of a lithium secondary battery in which a silazane-based compound was used as an electrolyte component according to the present invention was performed as follows.

2-1. Early formation  Cathode SEI layer  Difference

The lithium secondary battery of Comparative Example 2 including the lithium secondary battery of Example 2 and the HMDS-free electrolyte, in which HMDS was used as an electrolytic solution component, was formed as follows.

Each cell was subjected to a constant current (CC) at a rate of 0.2 C for 50 minutes. 2A, which is a result of the charging capacity and the voltage rise, is obtained, and a differential graph for the variation of the charging capacity per voltage rise by changing the X and Y axes is shown in FIG. 2B. 2A, it is difficult to gauge the difference in formation of the anode SEI layer during charging. Therefore, it is possible to confirm the change of the charged amount according to each voltage (that is, represented by the change of the charged amount according to the voltage change, differentiated). This is shown in FIG. 2B.

As a result, it was confirmed that the battery of Example 2 using HDMS significantly reduced the reaction peak between 3.0 and 3.2 V compared to the battery of Comparative Example 2 which did not use the electrolyte additive (see FIGS. 2A and 2B) . This shows that when HMDS is present in the electrolyte, it reacts with the electrolyte and lithium salt in the negative electrode to form a reduction product. In other words, it was found that the SEI layer which can influence the performance of the battery was formed differently.

In addition, the electrodes of Comparative Example 2 and Example 2 were decomposed in a fully charged state to perform TPD-GC-MS of the cathode. As a result of analysis through FIG. 3, in the cathode of Example 2 using HMDS, a cyclic ether stream was additionally detected at a temperature lower than 200 ° C, indicating that the SEI layer was decomposed. At high temperature (200 ~ 350degree), the structure is unknown except for the cyclic ether compound, but molecules containing nitrogen are also observed. That is, when HMDS is added as an electrolytic solution component, the formation of SEI layer is rapidly increased due to the reduction reaction. In addition, a salt component in which NH ₄ ⁺ is combined with various anions, It is believed that it acts as a protective film by precipitating on the cell surface.

2-2. Capacity characterization

The cells of Example 2 and Comparative Example 2 were subjected to a constant current to a voltage of 4.2 V at a constant current-constant voltage (CC-CV) at a rate of 0.92 C, and then a current was controlled at a constant voltage of 4.2 V. At the time of discharging, the cells were cut off at 3.0 V at a constant current (CC) at a rate of 1.0 C, repeated four times, and discharged at the rate of 0.2 C after charging in the same manner.

As a result of the experiment, it was confirmed that the capacity of the lithium secondary battery of Example 2 in which HMDS was added as an electrolyte component was improved by about 2% as compared with the comparative example (see Table 1). This is because the HMDS component participates in the consumption and regeneration of the SEI, so that the SEI coating containing the organic component lowers the negative reactivity of the electrolyte and the electrode, thereby suppressing the precipitation of Li on the surface of the negative electrode.

Discharge capacity (mAh) Example 2 (including HMDS) Comparative Example 2 (not containing HMDS) 1.0C discharge -1 times 887 874 1.0C discharge -2 times 894 885 1.0C discharge -3 times 890 880 1.0C discharge -4 times 887 874 0.2C discharge -1 times 918 899

2-3. Evaluation of life characteristics

Example 2 and Comparative Example 2 were subjected to a constant current-to-constant voltage (CC-CV) method at a rate of 0.92 C to 4.2 V, and then the current was controlled at a constant voltage of 4.2 V. In the discharge, the lifetime characteristics test was performed by the method of cut-off at 3.0V at a constant current of 1.0C.

As confirmed in the capacity confirmation experiment, the battery of Example 2 in which HMDS was present not only performed charging / discharging at a high initial capacity, but maintained the superiority of the discharging capacity in the subsequent charge / discharge cycle (see FIG. 4 ). That is, since the lifetime characteristics of the battery are closely related to the SEI layer of the cathode, it can be concluded that the use of the HMDS additive improves the quality of the SEI layer of the cathode.

EXPERIMENTAL EXAMPLE 3. Evaluation of High Temperature Storage Characteristics of Batteries

The high-temperature storage characteristics of the lithium secondary battery in which the silazane-based compound was used as an electrolytic solution component according to the present invention was evaluated as follows.

The lithium secondary battery of Comparative Example 2 including the lithium secondary battery of Example 2 in which HMDS was used as an electrolytic solution component and the electrolytic solution to which HMDS was not added was charged at a rate of 0.92 C in a constant current-constant voltage (CC-CV) V, and the current was controlled from 4.2V to the constant voltage. After the initial capacity was measured, the battery was stored at 90 ° C for 4 hours in a fully charged state and then subjected to 50 cycles to measure the high temperature storage characteristics of the battery.

As a result of the test, the battery of Example 2 exhibited an excellent initial discharge capacity as compared with the battery of Comparative Example 2, and also exhibited excellent high-temperature lifetime characteristics even after repeated charge-discharge cycles (see FIG. 5).

As a result, it has been found that the secondary battery of the present invention including the silazane-based compound has high efficiency, high capacity, long life, and excellent high-temperature storage characteristics.

Experimental Example 4. Comparative Evaluation of HF Concentration of Electrolyte

In order to evaluate the amount of increase in HF concentration in the electrolytic solution containing the electrolyte additive according to the present invention, the following experiment was conducted.

An experiment was conducted with an electrolyte HF meter (instrument 785 DMP Titrino) using the electrolyte of Example 1 in which HMDS was used as an electrolyte component and the electrolyte of Comparative Example 1 in which HMDS was not added. The initial pH (pH) of the electrolyte solution was measured, and the amount of HF remaining per 1 g of the electrolytic solution was measured by 0.01N NaOH titration.

As a result of the experiment, it was found that the electrolyte of Example 1 had an effect of reducing the initial pH (pH) and HF concentration compared with the electrolyte of Comparative Example 1 in which the electrolyte additive was not used (see Table 2). It was confirmed that HMDS plays a role of H ₂ O scavenger.

Example 1 Comparative Example 1 EC / EMC = 1/2, LiPF ₆ 1.0M EC / EMC = 1/2, LiPF ₆ 1.0M,
HDMS 0.02 parts by weight Initial pH (pH) 5.18 4.4 Remaining HF amount per unit weight of electrolyte (ppm / g) 17 ppm / g 42 ppm / g

In the present invention, by using a silazane-based compound as an electrolyte component, it is possible to suppress the additional reaction of reducing the battery performance by forming a stable film on the surface of both electrodes, thereby improving the capacity and life characteristics of the battery.

Claims (11)

The electrolyte for a battery comprising an electrolyte salt and an electrolyte solution, wherein the electrolyte is capable of forming a passivation layer by electrochemically reacting in a battery, wherein the electrolyte is a silazane-based compound represented by the following formula (1) / RTI &gt; Wherein the silazane-based compound is reduced by charge and discharge in an operating voltage range of a battery to form a passivation layer on the negative electrode. [Chemical Formula 1] R ₁ R ₂ R ₃ Si-NR ₇ -SiR ₄ R ₅ R ₆ Wherein R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ are each independently hydrogen or a C ₁ -C ₆ alkyl group which is unsubstituted or substituted with a halogen atom. The battery electrolyte according to claim 1, wherein the silazane-based compound has two or more silane groups in itself and they are connected by nitrogen. delete delete The battery electrolyte according to claim 1, wherein the content of the silazane-based compound ranges from 0.01 to 10 parts by weight per 100 parts by weight of the electrolyte solution. A passivation layer formed by electrically reducing the silazane-based compound represented by the following formula (1) is formed on a part or all of the surface of the negative electrode active material: [Chemical Formula 1] R ₁ R ₂ R ₃ Si-NR ₇ -SiR ₄ R ₅ R ₆ Wherein R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ are each independently hydrogen or a C ₁ -C ₆ alkyl group which is unsubstituted or substituted with a halogen atom. 7. The cathode of claim 6, wherein the passivation film comprises ether and nitrogen. delete A secondary battery comprising an anode, a cathode, an electrolyte and a separator, wherein the secondary battery includes the electrolyte according to any one of claims 1, 2, and 5. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the secondary battery comprises the negative electrode according to any one of claims 6 to 7. An electrolyte additive for forming an SEI film characterized by being a silazane system compound represented by the following formula (1) as a compound capable of being reduced on a negative electrode of a secondary battery to form a solid electrolyte interface (SEI) film: [Chemical Formula 1] R ₁ R ₂ R ₃ Si-NR ₇ -SiR ₄ R ₅ R ₆ Wherein R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ are each independently hydrogen or a C ₁ -C ₆ alkyl group which is unsubstituted or substituted with a halogen atom.

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