KR20090053660A - Negative electrode and negative active material for rechargeable lithium battery, and rechargeable lithium battery comprising same - Google Patents

Abstract

The present invention relates to a lithium secondary battery negative electrode, a negative electrode active material and a lithium secondary battery comprising the same, the negative electrode is a non-carbon-based active material; Lithium salt containing an oxalato borate structure; And high strength polymer binders. In addition, the negative electrode active material of the present invention may include a non-carbon-based material and a coating layer formed on the non-carbon-based material. In this case, the coating layer includes a lithium salt and a high strength polymer including an oxalato borate structure.

The lithium secondary battery containing the negative electrode for lithium secondary batteries of this invention, or negative electrode active material is excellent in cycle life characteristics, and shows high capacity.

Lithium Secondary Battery, Cathode, Oxalate Borate, High Strength Polymer, Cathode Active Material

Description

A negative electrode and a negative electrode active material for a lithium secondary battery, and a lithium secondary battery comprising the same {NEGATIVE ELECTRODE AND NEGATIVE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERY, AND RECHARGEABLE LITHIUM BATTERY COMPRISING SAME}

The present invention relates to a negative electrode and a negative electrode active material for a lithium secondary battery, and a lithium secondary battery including the same, and more particularly, to a lithium secondary battery having excellent cycle life characteristics and a high capacity.

Lithium secondary batteries, which are in the spotlight as power sources of recent portable small electronic devices, exhibit high energy density by showing a discharge voltage that is twice as high as that of a battery using an alkaline aqueous solution using an organic electrolyte solution.

As a cathode active material of a lithium secondary battery, an oxide composed of lithium and a transition metal having a structure capable of intercalating lithium, such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNi _{1- x} Co _x O ₂ (0 <x <1) This is mainly used.

As the negative electrode active material, various types of carbon-based materials including artificial, natural graphite, and hard carbon capable of intercalating and deintercalating lithium have been applied. However, in recent years, due to stability and higher capacity requirements, non-carbon negative electrode active materials such as Si have been used. Research is being done.

The present invention provides a negative electrode and a negative electrode active material for a lithium secondary battery exhibiting improved cycle life characteristics and high capacity.

The present invention provides a lithium secondary battery including the negative electrode or the negative electrode active material.

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 first embodiment of the present invention is a non-carbon based active material; Lithium salt containing an oxalato borate structure; And to provide a negative electrode for a lithium secondary battery comprising a high-strength polymer binder.

A second embodiment of the invention also includes non-carbon based materials; And it provides a negative electrode active material for a lithium secondary battery comprising a coating layer formed on the non-carbon-based material. The coating layer includes a lithium salt and a high strength polymer binder containing an oxalato borate structure.

A third embodiment of the present invention is the negative electrode; A positive electrode including a positive electrode active material; And to provide a lithium secondary battery comprising an electrolyte containing a lithium salt and a non-aqueous solvent. The present invention also provides a lithium secondary battery comprising a negative electrode including the negative electrode active material, a positive electrode containing a positive electrode active material and an electrolyte containing a lithium salt and a nonaqueous solvent.

As a lithium salt containing the said oxalato borate structure, what is represented by following formula (1) can be used preferably.

[Formula 1]

Wherein R ₁ and R ₂ are the same or independently of each other a halogen or halogenated alkyl group, or R ₁ and R ₂ are equally OCO and R ₁ and R ₂ are cyclic rings comprising B together with B bonded . Examples of the halogen include F, Cl, I or Br. The alkyl group has 1 to 10 carbon atoms, and examples of the halogenated alkyl group include CF ₃ , CF ₂ CF ₃ , CH ₂ CF ₃ , and CFHCHF ₂ .

Representative examples of lithium salts comprising the oxalato borate structure include LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate, LiBOB), LiB (C ₂ O ₄ ) F ₂ (Lithium difluoro oxalato borate, LiFOB) and combinations thereof.

Examples of the non-carbonaceous materials include lithium vanadium oxide, Si, SiO _x (0 <x <2), Si-Y alloys (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and Are selected from the group consisting of combinations thereof, not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and these) It is an element selected from the group consisting of a combination of but not Sn) and those selected from the group consisting of a combination thereof can be used.

As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, It is preferable to select from the group which consists of Po, and its combination.

The lithium secondary battery containing the negative electrode for lithium secondary batteries of this invention, or negative electrode active material is excellent in cycle life characteristics, and shows high capacity.

The present invention relates to a negative electrode for a lithium secondary battery, and more particularly, to a negative electrode including a non-carbon-based negative electrode active material.

Recently, studies on non-carbon negative electrode active materials such as Si, which have a higher capacity than carbon-based negative electrode active materials, have been conducted. However, lithium secondary batteries including non-carbon negative electrode active materials such as Si have a negative electrode such as Si during charge and discharge. As the irreversible reaction in which the active material is dissolved occurs, there is a problem that the cycle life characteristics are significantly lowered.

The present invention solves the problem of deteriorating cycle life characteristics by using a lithium salt containing an oxalato borate structure in the negative electrode. In addition, when the lithium salt containing the oxalato borate structure is used for the positive electrode, the oxalato borate anion is low in oxidation resistance, and may cause oxidative decomposition at a low potential to generate a current, thereby causing a serious oxidative decomposition reaction. It is not preferable because there is a possibility that the life characteristics are significantly reduced.

In the present invention, the lithium salt including the oxalato borate structure may be used in addition to the composition for preparing the negative electrode, or may be directly coated on the negative electrode active material.

According to a first embodiment of the present invention in which a lithium salt including an oxalato borate structure is added to a composition for preparing a negative electrode, the negative electrode of the present invention includes a non-carbon-based negative electrode active material, a lithium salt comprising an oxalato borate structure, and High strength polymer binders.

As a lithium salt containing the said oxalato borate structure, what is represented by following formula (1) can be used preferably.

[Formula 1]

Wherein R ₁ and R ₂ are the same or independently of each other a halogen or halogenated alkyl group, or R ₁ and R ₂ are equally OCO and R ₁ and R ₂ are cyclic rings comprising B together with B bonded . Examples of the halogen include F, Cl, I and Br. 1-10 are preferable and, as for carbon number in the said alkyl group, 1-4 are more preferable. In addition, examples of the halogenated alkyl group include CF ₃ , CF ₂ CF ₃ , CH ₂ CF ₃ , CFHCHF ₂ .

Representative examples of lithium salts comprising the oxalato borate structure include LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate, LiBOB), LiB (C ₂ O ₄ ) F ₂ (Lithium difluoro oxalato borate, LiFOB) and combinations thereof.

Lithium salt containing such an oxalato borate structure is reduced and decomposed at about 1.7 V (vs. Li / Li ⁺ ) at the time of initial charging, and includes a carbonate group on the surface of the non-carbon-based negative electrode active material, and has a rigid and stable network structure. The film will be formed. A coating structure including a carbonate group formed when LIBOB was used as a lithium salt containing an oxalato borate structure was shown in Scheme 1 below.

Scheme 1

The film containing such a carbonate group has a high concentration of dissociated lithium ions freely movable in the film, thereby improving charge and discharge characteristics of the battery.

In addition, the film is a stable film having a network structure, so that the film does not break during charge and discharge. Therefore, the film formed during the initial charge forms a strong acid HF during the charge and discharge process of lithium salt used in an electrolyte such as LiPF _6, and the HF attacks the negative electrode active material to decompose the surface of the active material, that is, at room temperature, particularly at high temperatures. The non-carbon-based active material may be cracked and eluted into the electrolyte in the form of the following structure, thereby rapidly decreasing the electrode capacity and effectively preventing a problem of battery OCV failure.

[rescue]

In addition, when the lithium secondary battery is charged or discharged at room temperature, the reaction in which the organic solvent is decomposed excessively progresses, and a thick film is formed due to the growth of lithium carbonate (Li ₂ CO ₃ ) formed on the surface of the anode active material, thereby inhibiting the reaction of the anode active material. Can solve the problem.

Improving the cycle life characteristic effect of the lithium salts include the oxalate reyito borate structure can be obtained only when using a lithium salt having oxalate reyito borate structure can not be obtained from the lithium salt such as LiBF _4. This is because a lithium salt such as LiBF ₄ cannot form a film containing a carbonate group.

In addition, the cycle life characteristic improvement effect by the lithium salt containing the oxalato borate structure can be obtained only when the lithium salt containing the oxalato borate structure is used for the negative electrode, and when used for the positive electrode, the cycle life characteristic improvement effect is obtained. Not only can it be obtained, but also it may cause the problem that the thermal stability of a positive electrode active material falls.

In the present invention, the content of the lithium salt containing the oxalato borate structure is preferably 0.1 to 10 parts by weight, more preferably 1 to 5 parts by weight based on 100 parts by weight of the binder. When the content of the lithium salt containing the oxalato borate structure is less than 0.1 part by weight, the surface of the negative electrode active material may not be effectively covered with a stable coating, and thus, elution or cracking of the non-carbon-based active material may occur seriously, which is not preferable. Moreover, when it exceeds 10 weight part, the film formed by the reduction decomposition of the lithium salt containing an oxalato borate structure is formed thick, and it is unpreferable since it increases battery resistance and lowers a high-rate characteristic and a cycle life characteristic.

The high strength polymer is used as a binder, and for example, polyamideimide, polyimide, polyacrylonitrile, carboxymethyl cellulose, polyacrylic acid and cross-linked copolymer of carboxymethyl cellulose, and a combination thereof are preferably selected. Do. The cross-linked copolymer of polyacrylic acid and carboxymethyl cellulose means a matrix form formed by thermal crosslinking. As described above, an effective polymer in the present invention is a high strength polymer having rigidity, and when a polymer such as polyvinylidene fluoride having no rigidity is used, the effect of improving cycle life characteristics obtained in the present invention cannot be obtained, It is not possible to maintain a network to suppress the increase in electrical resistance and maximize electrode utilization.

The high strength polymer preferably has a weight average molecular weight of 10,000 to 1,000,000, more preferably has a weight average molecular weight of 50,000 to 500,000. If the weight average molecular weight of the high-strength polymer is too high, it is difficult to dissolve the polymer binder during the preparation of the binder solution, and if the molecular weight is too low, the mechanical strength of the binder decreases, making it difficult to control the electrode volume expansion, resulting in a drastic decrease in battery resistance. Cycle life characteristics are deteriorated, which is undesirable.

In the negative electrode of the present invention, the content of the high strength polymer binder is preferably 3 to 15% by weight, more preferably 5 to 10% by weight. When the content of the high-strength polymer binder is less than 3% by weight, it is difficult to form a negative electrode, and when the content of the high-strength polymer binder is more than 15% by weight, there is a problem that the loading capacity of the active material in the electrode is lowered, thereby lowering the battery capacity.

Examples of the non-carbon-based active material include lithium vanadium oxide, Si, SiO _x (0 <x <2), Si-Y alloy (Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, and Are selected from the group consisting of combinations thereof, not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and these) It is an element selected from the group consisting of a combination of (not Sn) and those selected from the group consisting of a combination thereof can be preferably used. As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, It is preferable to select from the group which consists of Po, and its combination.

The negative electrode of the present invention may optionally further include a conductive material. The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Metal powders, such as black, carbon fiber, copper, nickel, aluminum, silver, a metal fiber, etc. can be used, and also conductive materials, such as a polyphenylene derivative, can be mixed and used.

In addition, the negative electrode of the present invention includes a current collector for supporting the negative electrode active material layer. The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

According to a second embodiment of the present invention for coating a negative electrode active material with a lithium salt containing an oxalato borate structure, the negative electrode active material of the present invention includes a non-carbon based material and a coating layer formed on the non-carbon based material. The coating layer is formed on the surface of the non-carbonaceous material, and includes a lithium salt and a high strength polymer including an oxalato borate structure.

The non-carbon-based material is a non-carbon-based negative active material used in the first embodiment of the present invention, the lithium salt and the high-strength polymer is the same as in the first embodiment of the present invention will be omitted below.

The lithium salt containing the oxalato borate structure is preferably 0.005 to 1 parts by weight, more preferably 0.005 to 0.1 parts by weight, and most preferably 0.01 to 0.05 parts by weight based on 100 parts by weight of the non-carbonaceous material. When the content of the lithium salt containing the oxalato borate structure is less than 0.005 parts by weight, the surface of the negative electrode active material may not be effectively covered with a stable coating, and thus, elution or cracking of the non-carbon active material may occur seriously, which is not preferable. In addition, when the content of the lithium salt containing the oxalato borate structure exceeds 1 part by weight, a film formed by reduction decomposition of the lithium salt containing the oxalato borate structure is formed thick, thereby increasing battery resistance and deteriorating high rate characteristics and cycle life characteristics. It is not preferable because it is made.

The mixing ratio of the lithium salt and the high strength polymer including the oxalato borate structure is preferably 0.5: 100 to 10: 100 parts by weight, more preferably 1: 100 to 5: 100 parts by weight. When the content of the lithium salt containing the oxalato borate structure is less than 0.5 parts by weight, the surface of the negative electrode active material may not be effectively covered with a stable film, and thus, silicon dissolution and cracking problems may seriously occur, which is not preferable. In addition, when the content of the lithium salt containing the oxalato borate structure is more than 10 parts by weight, a film formed by reduction decomposition of the lithium salt containing the oxalato borate structure is formed thick, thereby increasing the battery resistance and deteriorating high rate characteristics and cycle life characteristics. It is not preferable because it is made.

The thickness of the coating layer is preferably 10nm to 50nm, more preferably 10nm to 30nm. If the thickness of the coating layer is less than 10nm, the electrode resistance is not increased, it is not preferable, if it exceeds 50nm, lithium salt containing oxalato borate and high-strength polymer can not effectively work, it is not preferable.

In the negative electrode including the negative electrode active material according to the second embodiment of the present invention, a high-strength polymer formed on the surface of the active material layer may serve as a binder. However, the negative electrode including the negative electrode active material according to the second embodiment of the present invention also includes the same binder as the negative electrode including the negative electrode active material according to the first embodiment, and may further include a conductive material. It also includes a current collector. Since the binder, the conductive material and the current collector are the same as described in the first embodiment, description thereof will be omitted.

As described above, in the present invention, the lithium salt including the oxalato borate structure is added to the negative electrode active material composition used in the manufacture of the negative electrode, or directly coated on the surface of the negative electrode active material, thereby using the cycle life of the lithium secondary battery including the non-carbon negative electrode. Properties can be improved. In particular, the effect of improving cycle life characteristics using the lithium salt of the present invention is hardly obtained when lithium salt is added to the electrolyte, as described in Japanese Patent Laid-Open No. 2005-26203 used by adding the lithium salt to the electrolyte. It can be maximized only when added to the negative electrode active material composition as described, or directly coated on the surface of the negative electrode active material.

The negative electrode according to the first embodiment of the present invention is the same as a conventional negative electrode manufacturing process. That is, a negative electrode active material composition may be prepared by mixing a non-carbon based negative electrode active material, a lithium salt containing an oxalato borate structure, a high strength polymer binder, and a solvent, and may be prepared by a conventional method of applying the negative electrode active material composition to a current collector. have.

In addition, the negative electrode active material according to the second embodiment may be prepared by the following method.

The non-carbon based material is coated with a coating solution. In this case, the coating solution includes a lithium salt, an high strength polymer, and a solvent including an oxalato borate structure. In this case, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), H ₂ O, or a combination thereof may be used, and the concentration of the coating solution may be 20 to 10% by weight. It is suitable. In other words, the coating solution is prepared by mixing 80 to 90% by weight of a solvent, a lithium salt containing an oxalato borate structure, and 20 to 10% by weight of a high strength polymer.

The coating process may be a screen printing method, a spray coating method, a dipping method or a coating method using a doctor blade according to the viscosity of the coating liquid, but is not limited thereto.

Subsequently, the non-carbon-based material coated with the coating solution is dried to prepare a negative electrode active material having a coating layer. It is preferable to perform the said drying process at 110-200 degreeC, and it is more preferable to carry out at 120-150 degreeC. Moreover, it is preferable to perform the said drying process in a vacuum atmosphere.

Since the solvent in the coating solution is removed by volatilization according to the drying process, only the lithium salt and the high strength polymer are present in the formed coating layer.

A negative electrode including the negative electrode according to the first embodiment of the present invention and the negative electrode active material according to the second embodiment is applied to a lithium secondary battery, and the lithium secondary battery includes a positive electrode and an electrolyte solution.

The positive electrode includes a current collector and a cathode active material layer formed on the current collector. As the cathode active material, a compound (lithiated intercalation compound) capable of reversible intercalation and deintercalation of lithium may be used. Specifically, at least one of a complex oxide of metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used, and more preferably, a compound represented by one of the following Chemical Formulas 2 to 24 may be used: Can be.

[Formula 2]

Li _a A _{1 - b} B _b D ₂

(Wherein 0.95 ≦ a ≦ 1.1, and 0 ≦ b ≦ 0.5)

[Formula 3]

Li _a E _{1 - b} B _b O _{2- c} F _c

(Wherein 0.95 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05)

[Formula 4]

LiE _{2 - b} B _b O _{4- c} F _c

(Wherein 0 ≦ b ≦ 0.5 and 0 ≦ c ≦ 0.05)

[Formula 5]

Li _a Ni _{1 -b- c} Co _b BcD _α

(Wherein 0.95 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2)

[Formula 6]

Li _a Ni _{1 -b- c} Co _b B _c O _{2 -α} F _α

(Wherein 0.95 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2)

[Formula 7]

Li _a Ni _{1 -b- c} Co _b B _c O _{2 -α} F ₂

(Wherein 0.95 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2)

[Formula 8]

Li _a Ni _{1 -b- c} Mn _b B _c D _α

(Wherein 0.95 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2)

[Formula 9]

Li _a Ni _{1 -b- c} Mn _b B _c O _{2 -α} F _α

(Wherein 0.95 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2)

[Formula 10]

Li _a Ni _{1 -b- c} Mn _b B _c O _{2 -α} F ₂

(Wherein 0.95 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2)

[Formula 11]

Li _a Ni _b E _c G _d O ₂

(Wherein 0.90 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, and 0.001 ≦ d ≦ 0.1.)

[Formula 12]

Li _a Ni _b Co _c Mn _d GeO ₂

(Wherein 0.90 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, and 0.001 ≦ e ≦ 0.1).

[Formula 13]

Li _a AG _b O ₂

(Wherein 0.90 ≦ a ≦ 1.1 and 0.001 ≦ b ≦ 0.1)

[Formula 14]

Li _a Mn ₂ G _b O ₄

(Wherein 0.90 ≦ a ≦ 1.1 and 0.001 ≦ b ≦ 0.1)

[Formula 15]

QO ₂

[Formula 16]

QS ₂

[Formula 17]

LiQS ₂

[Formula 18]

V ₂ O ₅

[Formula 19]

LiV ₂ O ₅

[Formula 20]

LiIO ₂

[Formula 21]

LiNiVO ₄

[Formula 22]

Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 3)

[Formula 23]

Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2)

[Formula 24]

LiFePO ₄

In Chemical Formulas 2 to 24, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof;

B is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof;

D is selected from the group consisting of O, F, S, P, and combinations thereof;

E is selected from Co, Mn, and combinations thereof;

F is selected from the group consisting of F, S, P, and combinations thereof;

G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof;

Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof;

I is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof;

J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Of course, what has a coating layer on the surface of this compound can also be used, or the compound and the compound which have a coating layer can also be used in mixture. The coating layer may include at least one coating element compound selected from the group consisting of oxides of the coating elements, hydroxides, oxyhydroxides of the coating elements, oxycarbonates of the coating elements and hydroxycarbonates of the coating elements. The compounds constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof may be used. The coating layer forming process may use any coating method as long as it does not adversely affect the physical properties of the positive electrode active material by using such elements in the compound (for example, spray coating, dipping, etc.). Detailed descriptions will be omitted since they can be understood by those in the field.

The positive electrode active material layer also includes a binder and a conductive material.

The binder adheres positively to the positive electrode active material particles, and also serves to adhere the positive electrode active material to the current collector well, and examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetylene cellulose, and polyvinyl. Chloride, carboxylated polyvinylchloride, polyvinyldifluoride, polymer comprising ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like can be used, but is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Metal powder, metal fiber, etc., such as black, carbon fiber, copper, nickel, aluminum, silver, etc. can be used, and 1 type (s) or 1 or more types can be mixed and conductive materials, such as a polyphenylene derivative, can be used.

Al may be used as the current collector, but is not limited thereto.

The positive electrode is prepared by mixing an active material, a conductive material and a binder in a solvent to prepare an active material composition, and applying the composition to a current collector. Since such an electrode manufacturing method is well known in the art, a detailed description thereof will be omitted. N-methylpyrrolidone may be used as the solvent, but is not limited thereto.

In the lithium secondary battery of the present invention, the electrolyte contains a nonaqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the cell can move.

As the non-aqueous organic solvent, a carbonate, ester, ether, ketone, alcohol or aprotic solvent can be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC) and the like can be used, and the ester solvent is n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, Ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like can be used. As the ether, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used, and cyclohexanone may be used as the ketone solvent. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol solvent, and the aprotic solvent may be R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms. Amides such as nitriles, dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like. .

The non-aqueous organic solvent may be used alone or in combination of one or more, and the mixing ratio in the case of mixing one or more may be appropriately adjusted according to the desired battery performance, which is widely understood by those skilled in the art. Can be.

In the case of the carbonate solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of 1: 1 to 1: 9, so that the performance of the electrolyte may be excellent.

The non-aqueous organic solvent of the present invention may further include an aromatic hydrocarbon organic solvent in the carbonate solvent. In this case, the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1: 1 to 30: 1.

As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound represented by the following Formula 25 may be used.

[Formula 25]

(In Formula 25, R ₃ to R ₈ are each independently selected from the group consisting of hydrogen, halogen, alkyl group having 1 to 10 carbon atoms, haloalkyl group, and combinations thereof.)

Preferably, the aromatic hydrocarbon organic solvent is benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 , 2,4-trichlorobenzene, iodobenzene, 1,2-dioodobenzene, 1,3-dioiobenzene, 1,4-dioiobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluor Rotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1, 2,4-trichlorotoluene, iodotoluene, 1,2-dioodotoluene, 1,3-diaodotoluene, 1,4- Iodo toluene, to which 1,2,3-tree-iodo toluene, 1,2,4-iodo toluene, xylene, and selected from the group consisting of.

The electrolyte may further include vinylene carbonate or an ethylene carbonate compound represented by Chemical Formula 26 to improve battery life.

[Formula 26]

(In the above formula, R ₉ and R ₁₀ are each independently selected from the group consisting of hydrogen, halogen group, cyano group (CN), nitro group (NO ₂ ) and fluoroalkyl group having 1 to 5 carbon atoms, wherein R ₉ And R ₁₀ At least one is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluoroalkyl group having 1 to 5 carbon atoms, provided that R ₉ and R ₁₀ are not all hydrogen.)

Representative examples of the ethylene carbonate-based compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. Can be. In the case of further using such life improving additives, the amount thereof can be properly adjusted.

The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (CyF _{2y +1} SO ₂ ), where x and y are natural numbers, LiCl, LiI and combinations thereof It includes one or more selected from the supporting electrolyte salt. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. If the concentration of the lithium salt is less than 0.1M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, if it exceeds 2.0M there is a problem that the mobility of the lithium ion is reduced by increasing the viscosity of the electrolyte.

Depending on the type of lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. As the separator, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / poly It goes without saying that a mixed multilayer film such as a propylene three-layer separator can be used.

1 schematically shows a typical structure of a lithium secondary battery of the present invention. As shown in FIG. 1, the lithium secondary battery 1 includes a positive electrode 3, a negative electrode 2, and an electrolyte solution impregnated in a separator 4 existing between the positive electrode 3 and the negative electrode 2. The container 5 and the sealing member 6 which encloses the said battery container 5 are included.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following embodiments are only preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

(Example 1)

A negative electrode active material, a lithium bis (oxalato) borate, a polyamideimide binder, and a carbon black conductive material were mixed in an N-methyl pyrrolidone solvent to prepare a negative electrode active material slurry composition. At this time, lithium bis (oxalato) borate was used to 1 part by weight based on 100 parts by weight of the polyamideimide binder. In addition, the mixing ratio of the Si negative electrode active material, the lithium bis (oxalato) borate, and the polyamide imide binder was 92.93: 0.07: 7 wt%. The weight average molecular weight of the said polyamide imide was 100,000.

The negative electrode active material slurry composition was applied to a copper current collector to prepare a negative electrode.

A positive electrode active material slurry composition was prepared by mixing a LiCoO ₂ positive electrode active material, a polyvinylidene fluoride binder, and an acetylene black conductive material in a 94: 3: 3 weight ratio in an N-methyl pyrrolidone solvent. The slurry composition was applied to an Al current collector to prepare a positive electrode.

A lithium secondary battery was manufactured using an electrolyte solution including a mixed nonaqueous solvent (50:50 by volume) of the negative electrode, the positive electrode, and 1M LiPF ₆ lithium salt in which ethylene carbonate and diethyl carbonate were dissolved.

(Example 2)

It carried out similarly to Example 1 except having changed the usage-amount of lithium bis (oxalato) borate into 5 weight part with respect to 100 weight part of polyamideimide binders.

(Example 3)

The same procedure as in Example 1 was carried out except that a polyamideimide polymer having a weight average molecular weight of 500,000 was used.

(Example 4)

Si was coated with a coating solution containing lithium bis (oxalato) borate, polyamideimide and N-methylpyrrolidone solvent. In this case, the amount of lithium bis (oxalato) borate was 1 part by weight based on 100 parts by weight of Si, and the mixing ratio of the lithium bis (oxalato) borate and polyamideimide was 0.9: 9.1 wt%. The weight average molecular weight of the said polyamide imide was 500,000.

Subsequently, Si coated with the coating liquid was dried at 120 ° C. to prepare a negative electrode active material having a coating layer.

The negative electrode active material, the polyamideimide binder, and the carbon black conductive material were mixed in an N-methyl pyrrolidone solvent to prepare a negative electrode active material slurry composition.

The negative electrode active material slurry composition was applied to a copper current collector to prepare a negative electrode.

A lithium secondary battery was manufactured using an electrolyte solution including the anode, a cathode including a LiCoO ₂ cathode active material, and an ethylene carbonate nonaqueous solvent in which 1M LiPF ₆ lithium salt was dissolved.

(Comparative Example 1)

The negative electrode active material and the polyamide imide were mixed in an N-methyl pyrrolidone solvent to prepare a negative electrode active material slurry composition. In addition, the mixing ratio of the Si anode active material and the polyamide imide binder was 93: 7 wt%. The weight average molecular weight of the said polyamide imide was 500,000.

The negative electrode active material slurry composition was applied to a copper current collector to prepare a negative electrode.

A lithium secondary battery was manufactured using the anode, a cathode including a LiCoO ₂ cathode active material, and an electrolyte solution. The electrolyte was prepared by adding lithium bis (oxalato) borate to an ethylene carbonate nonaqueous solvent in which 1M LiPF ₆ lithium salt was dissolved. At this time, the amount of lithium bis (oxalato) borate added was 2 parts by weight based on 100 parts by weight of the nonaqueous solvent.

(Comparative Example 2)

The same procedure as in Example 1 was carried out except that lithium bis (oxalato) borate was not added to the negative electrode active material composition.

(Comparative Example 3)

The same procedure as in Example 1 was carried out except that LiBF ₄ was used instead of lithium bis (oxalato) borate.

(Comparative Example 4)

The same procedure as in Example 1 was carried out except that polyvinylidene fluoride was used instead of polyamide imide.

(Comparative Example 5)

A positive electrode active material slurry composition was prepared by mixing a LiCoO ₂ positive electrode active material, a lithium bis (oxalato) borate, a polyvinylidene fluoride binder, and an acetylene black conductive material in an N-methyl pyrrolidone solvent. At this time, lithium bis (oxalato) borate was used to 5 parts by weight based on 100 parts by weight of the binder. In addition, the mixing ratio of LiCoO ₂ positive electrode active material, lithium bis (oxalato) borate, and polyvinylidene fluoride binder was 92.93: 0.07: 7 wt%. The weight average molecular weight of the polyvinylidene fluoride was 400,000.

The positive electrode active material slurry composition was applied to an Al current collector to prepare a positive electrode.

A negative electrode active material, a polyvinylidene fluoride binder, and an acetylene black conductive material were mixed in an N-methyl pyrrolidone solvent in a 94: 3: 3 weight ratio to prepare a negative electrode active material slurry composition. The negative electrode active material slurry composition was applied to a copper current collector to prepare a negative electrode.

A lithium secondary battery was manufactured using an electrolyte solution including a mixed nonaqueous solvent (50:50 by volume) of the positive electrode, the negative electrode, and 1M LiPF ₆ lithium salt in which ethylene carbonate and diethyl carbonate were dissolved.

The cathodes of Example 1 and Comparative Example 1 were measured by FT-IR, and the results are shown in FIG. 2. As shown in FIG. 2, the negative electrode of Example 1 containing lithium bis (oxalato) borate in the negative electrode had a weak Si-F bond peak, whereas Comparative Example 1 containing no lithium bis (oxalato) borate in the negative electrode The cathode of had a strong Si-F bond peak. As a result, it can be predicted that lithium bis (oxalato) borate effectively suppresses the silicon dissolution phenomenon due to Si-F formation.

In addition, the lithium secondary batteries prepared according to Examples 1 to 4 and Comparative Examples 1 to 5 were charged and discharged 200 times under 0.8C charging and 1.0C discharging conditions to measure capacity retention rate (cycle life characteristics). The results are shown in FIG. As shown in FIG. 3, it can be seen that the lithium secondary batteries of Examples 1 to 4 are superior in cycle life characteristics as compared to the lithium secondary batteries of Comparative Examples 1 to 5. In more detail, the lithium salt containing the oxalato borate structure and the comparative example 1 which does not contain the conductive material have a cycle life characteristic lower than those of Examples 1 to 4, and also a lithium salt containing the oxalato borate structure. When it does not contain, it turns out that when the electrically conductive material is added (comparative example 2), the cycle life characteristic falls rapidly and it is almost impossible to use.

Moreover, even if lithium salt was added to the negative electrode active material composition, in the case of Comparative Example 3 using LiBF ₄ , the cycle life characteristics were lower than those of Examples 1 to 4. In addition, even in the case of Comparative Example 4 using a non-rigid polyvinylidene fluoride as a binder, the cycle life characteristics were much lower than in Examples 1 to 4.

In addition, in Comparative Example 5 in which lithium bis (oxalato) borate was used for the positive electrode active material composition, cycle life characteristics were most poor. According to this result, when applying the lithium salt containing an oxalato borate structure to a positive electrode, it turns out that a desired cycle life improvement effect cannot be acquired.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

1 is a view schematically showing the structure of a lithium secondary battery of the present invention.

Figure 2 is a graph showing the measurement of the FT-IR of the negative electrode of Example 1 and Comparative Example 1 of the present invention.

Figure 3 is a graph showing the capacity retention rate of the lithium secondary battery prepared according to Examples 1 to 4 and Comparative Examples 1 to 5 of the present invention.

Claims (22)

Non-carbon-based active material; Lithium salt containing an oxalato borate structure; And High strength polymer binder A negative electrode for a lithium secondary battery comprising a. The method of claim 1, Lithium salt containing the oxalato borate structure is a lithium secondary battery negative electrode that is represented by the following formula (1). [Formula 1]

Wherein R ₁ and R ₂ are the same or independently halogen halogenated alkyl groups, or R ₁ and R ₂ are equally OCO and R ₁ and R ₂ are cyclic rings comprising B together with B bonded ) The method of claim 2, The lithium salt containing the oxalato borate structure is LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate, LiBOB), LiB (C ₂ O ₄ ) F ₂ (lithium Difluoro oxalato borate, LiFOB) and a combination thereof, the negative electrode for a lithium secondary battery. The method of claim 1, The high strength polymer is selected from the group consisting of polyamideimide, polyimide, polyacrylonitrile, carboxymethyl cellulose, cross-linked copolymer of polyacrylic acid and carboxymethyl cellulose, and a combination thereof. The method of claim 1, The high strength polymer is a lithium secondary battery negative electrode having a weight average molecular weight of 10,000 to 1,000,000. The method of claim 1, The lithium salt containing the oxalato borate structure is 0.1 to 10 parts by weight based on 100 parts by weight of the binder negative electrode for a lithium secondary battery. The method of claim 1, A content of the high strength polymer binder is 3 to 15% by weight of the negative electrode for a lithium secondary battery. The method of claim 1, The non-carbon-based active material is lithium vanadium oxide, Si, SiO _x (0 <x <2), Si-Y alloy (The Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element and these Is an element selected from the group consisting of, not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and their An element selected from the group consisting of a combination, not Sn) and a negative electrode for a lithium secondary battery that is selected from the group consisting of a combination thereof. The method of claim 8, The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and a negative electrode for a lithium secondary battery selected from the group consisting of a combination thereof. Non-carbon based materials; And It includes a coating layer formed on the non-carbon based material, The coating layer is a lithium secondary battery negative electrode active material comprising a lithium salt and a high strength polymer comprising an oxalato borate structure. The method of claim 10, The lithium salt containing the oxalato borate structure is represented by the following formula (1) negative electrode active material for a lithium secondary battery. [Formula 1]

Wherein R ₁ and R ₂ are the same or independently halogen halogenated alkyl groups, or R ₁ and R ₂ are equally OCO and R ₁ and R ₂ are cyclic rings comprising B together with B bonded ) The method of claim 10, The high strength polymer is selected from the group consisting of polyamideimide, polyimide, polyacrylonitrile, carboxymethyl cellulose, copolymers of polyacrylic acid and carboxymethyl cellulose, and combinations thereof. The method of claim 10, The high strength polymer is a lithium secondary battery negative electrode active material having a weight average molecular weight of 10,000 to 1,000,000. The method of claim 10, The lithium salt comprising the oxalato borate structure is included in an amount of 0.005 to 1 parts by weight based on 100 parts by weight of the non-carbonaceous material. The method of claim 10, The mixing ratio of the lithium salt and the high-strength polymer containing the oxalato borate structure is 0.5: 100 to 10: 100 parts by weight of the negative electrode active material for a lithium secondary battery. The method of claim 10, The coating layer is a negative active material for a lithium secondary battery having a thickness of 10nm to 50nm. The method of claim 10, The non-carbonaceous material is lithium vanadium oxide, Si, SiO _x (0 <x <2), Si-Y alloy (The Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element and Are selected from the group consisting of combinations thereof, not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and these) It is an element selected from the group consisting of a combination of, not Sn) and a negative electrode active material for a lithium secondary battery is selected from the group consisting of a combination thereof. The method of claim 17, The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and a negative electrode active material for a lithium secondary battery selected from the group consisting of a combination thereof. The cathode of any one of claims 1 to 9; A positive electrode including a positive electrode active material; And Electrolyte solution containing lithium salt and nonaqueous solvent Lithium secondary battery comprising a. The method of claim 19, The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (C _y F _{2y +1} SO ₂ ), where x and y are natural numbers, LiCl, LiI, and combinations thereof Lithium secondary battery that is selected from. A negative electrode comprising the negative electrode active material of any one of claims 10 to 18; A positive electrode including a positive electrode active material; And Electrolyte solution containing lithium salt and nonaqueous solvent Lithium secondary battery comprising a. The method of claim 21, The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (C _y F _{2y +1} SO ₂ ), where x and y are natural numbers, LiCl, LiI, and combinations thereof Lithium secondary battery that is selected from.

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