KR102343230B1 - Lithium rechargeable battery - Google Patents

Abstract

The present substrate includes a positive electrode, a negative electrode, and an electrolyte solution including a lithium salt and an additive represented by Formula 4, wherein at least one of the positive electrode and the negative electrode is a current collector, an electrode tab extending from the current collector , an active material layer formed on the current collector, and a film formed on at least one of the current collector and the electrode tab, and including a film including a material represented by Formula 1, to a lithium secondary battery. Specific details regarding Formulas 1 and 4 are as defined in the specification.

Description

Lithium secondary battery {LITHIUM RECHARGEABLE BATTERY}

The present disclosure relates to a lithium secondary battery.

As a driving power source for mobile information terminals such as a mobile phone, a notebook computer, and a smart phone, a lithium secondary battery having a high energy density and being easy to carry is mainly used.

In general, a lithium secondary battery is manufactured by using a material capable of reversible intercalation and deintercalation of lithium ions as a positive electrode active material and a negative electrode active material, and charging an electrolyte between the positive electrode and the negative electrode.

In this case, a lithium-transition metal oxide is used as a cathode active material of a lithium secondary battery, various types of carbon-based materials are used as an anode active material, and a lithium salt dissolved in a non-aqueous organic solvent is used as an electrolyte.

In particular, in a lithium secondary battery, the use of an appropriate electrolyte is one of the important variables for improving the performance of a lithium secondary battery because the characteristics of the battery are displayed by a complex reaction between the positive electrode and the electrolyte, the negative electrode and the electrolyte.

Embodiments are intended to improve the characteristics of the lithium secondary battery.

A lithium secondary battery according to an embodiment includes a positive electrode, a negative electrode, and an electrolyte solution including a lithium salt and an additive represented by the following Chemical Formula 3, wherein at least one of the positive electrode and the negative electrode is a current collector, the current collector and an electrode tab extending from the entirety, an active material layer formed on the current collector, and a film formed on at least one of the current collector and the electrode tab, and including a material represented by the following Chemical Formula 1.

[Formula 1]

CuX(POF ₂ ) _n Y ₂ Z

In Formula 1,

X is a C1 to C10 alkylene group,

Y is represented by the following formula (2),

[Formula 2]

NC-R ¹ -CN, (In this case, R ¹ is a C1 to C10 alkylene group.)

Z is an anionic group of the lithium salt,

n is 1 or 2,

[Formula 4]

In Formula 4,

B is a C1 to C10 alkylene group, or (-C ₂ H ₄ -OC ₂ H ₄ -) _l (in this case, l is an integer from 1 to 10),

R ² is a C1 to C10 alkyl group.

According to embodiments, the lifespan characteristics and durability of the lithium secondary battery may be improved.

1 is a diagram schematically showing the structure of a lithium secondary battery according to an embodiment.
2 is a graph measuring the voltage change of the OCV state when the battery according to Comparative Example 1 is left at 100% SOC for 100 days after chemical charging/discharging.
3 is a graph measuring the voltage change in the OCV state when the battery according to Example 1 is left at 100% SOC for 100 days after chemical charging/discharging.
4 shows the LSV evaluation results for the three-electrode cell.
5 is an enlarged graph of a section in which a reduction peak appears among the LSV evaluation results.
6 and 7 are photographs confirming that a film is formed on the electrode of the three-electrode cell according to an embodiment of the present invention after LSV evaluation is performed.
8 is an SEM photograph of a cross-section of an electrode tab according to Example 2.
9 is an IR spectrum result obtained by analyzing the components of the coating film according to Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, in describing the present description, descriptions of already known functions or configurations will be omitted in order to clarify the gist of the present description.

In order to clearly explain the present description, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar elements throughout the specification. In addition, since the size and thickness of each component shown in the drawings are arbitrarily indicated for convenience of description, the present description is not necessarily limited to the illustrated bar.

Hereinafter, a lithium secondary battery according to an exemplary embodiment of the present disclosure will be described with reference to FIG. 1 . 1 schematically shows the structure of a lithium secondary battery according to an embodiment of the present disclosure.

Referring to FIG. 1 , a lithium secondary battery 100 according to an exemplary embodiment is disposed between a negative electrode 112 , a positive electrode 114 positioned to face the negative electrode 112 , and a negative electrode 112 and a positive electrode 114 , A battery cell including a separator 113 and a negative electrode 112, a positive electrode 114 and an electrolyte (not shown) impregnated with the separator 113, a battery container 120 containing the battery cell, and the battery and a sealing member 140 sealing the container 120 .

At least one of the positive electrode 114 and the negative electrode 112 is a current collector, an electrode tab extending from the current collector, an active material layer formed on the current collector, and at least one of the current collector and the electrode tab. It is formed and includes a film including a material represented by the following formula (1).

[Formula 1]

CuX(POF ₂ ) _n Y ₂ Z

In Formula 1,

X is a C1 to C10 alkylene group,

Y is represented by the following formula (2),

[Formula 2]

NC-R ¹ -CN, (In this case, R ¹ is a C1 to C10 alkylene group.)

Z is an anionic group of the lithium salt,

n is 1 or 2.

The current collector and the electrode tab according to an embodiment may include copper (Cu) metal. For example, the current collector and the electrode tab may be manufactured by including the same raw material.

On the other hand, the lithium salt contained in the electrolyte is dissolved in a solvent, serves as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and promotes movement of lithium ions between the positive electrode and the negative electrode is a substance that does

The lithium salt is LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers, for example, 1 to 20 integer), LiCl, LiI, and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate (LiBOB)), or combinations thereof.

The concentration of the lithium salt may be 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

Meanwhile, Z included in Formula 1 may correspond to an anionic group in which the lithium salt is dissociated into lithium ions and anionic groups in the electrolyte solution. For example, the lithium salt may be LiPF ₆ , and thus Z may be PF ₆ , but is not limited thereto.

Meanwhile, the electrolyte solution further includes an organic solvent for dissolving the lithium salt. As the organic solvent, a non-aqueous organic solvent having high ionic conductivity and dielectric constant and low viscosity may be used. The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the lithium secondary battery can move.

As such a non-aqueous organic solvent, for example, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent can be used.

Examples of the carbonate-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valero. Lactone, mevalonolactone, caprolactone, etc. may be used.

Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone etc. may be used as the ketone solvent. have.

As the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and the aprotic solvent is T-CN (T is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, nitriles such as nitriles (which may contain double bond aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used.

The non-aqueous organic solvent may be used alone or in combination of one or more. When one or more are mixed and used, the mixing ratio may be appropriately adjusted according to the desired battery performance.

In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the performance of the electrolyte may be excellent.

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

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following Chemical Formula 6 may be used.

[Formula 3]

(In Formula 3, R ₃ to R ₈ are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.)

Specific examples of the aromatic hydrocarbon-based organic solvent include 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-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rottoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3 ,5-triiodotoluene, xylene, and combinations thereof are selected from the group consisting of.

In a lithium secondary battery using such a non-aqueous organic solvent, irreversible side reactions may occur between the electrolyte and the positive electrode and between the electrolyte and the negative electrode at high temperature and high pressure. The decomposition products generated by these side reactions form a thick film acting as a resistance on the electrode surface, and reduce the cycle life and capacity of the lithium secondary battery. In addition, gas is generated inside the battery due to the decomposition of the non-aqueous organic solvent, thereby causing the battery to swell and swelling, which may lead to explosion of the battery.

The film according to an embodiment may be formed on one or more of the current collector and the electrode tab exposed to the electrolyte, thereby preventing irreversible side reactions between the electrolyte and the positive electrode and the electrolyte and the negative electrode at high temperature and high pressure.

The film may be formed on the current collector and the electrode tab through a separate process, but may be formed using a decomposition product generated by the side reaction. For example, the current collector and the electrode tab may include a copper (Cu) metal, and the copper component of the film represented by Formula 1 may include the current collector and the electrode tab from a copper (Cu) metal. may have been derived

The film according to an exemplary embodiment is formed to have an appropriate thickness, thereby preventing an additional side reaction without increasing electrical resistance on the electrode surface. For example, the film may be formed to a thickness of 25-50 μm. When the coating layer is formed to a thickness within the above range, it is possible to prevent additional side reactions without increasing the electrical resistance on the electrode surface.

As in one embodiment, in order to form a film capable of preventing an additional side reaction without increasing electrical resistance on the electrode surface, the electrolyte according to the embodiment may further include an additive.

The additive according to an embodiment may include a compound represented by the following Chemical Formula 3 or the following Chemical Formula 4.

[Formula 3]

In Formula 3,

A is a C1 to C10 alkylene group, or (-C ₂ H ₄ -OC ₂ H ₄ -) _m (in this case, m is an integer of 1 to 10),

[Formula 4]

In Formula 4,

B is a C1 to C10 alkylene group, or (-C ₂ H ₄ -OC ₂ H ₄ -) _l (in this case, l is an integer from 1 to 10),

R ² is a C1 to C10 alkyl group.

For example, in Formulas 3 and 4, A and B may each independently be a C1 to C5 alkylene group, and m and 1 may each independently be an integer of 1 to 5.

The compound represented by Formula 3 or Formula 4 includes a difluorophosphate (-PF ₂ ) group having excellent electrical and chemical reactivity at the terminal.

During the initial charging of the lithium secondary battery, lithium ions from the lithium-transition metal oxide as the positive electrode move to the carbon electrode as the negative electrode and are intercalated with carbon. At this time, since lithium has strong reactivity, it reacts with the carbon electrode to form Li ₂ CO ₃ , LiO, LiOH, etc. to form a film on the surface of the anode. Such a film is called a solid electrolyte interface (SEI) film. The film according to an embodiment may be the aforementioned SEI film.

The SEI film formed at the beginning of charging prevents the reaction between lithium ions and carbon anodes or other materials during charging and discharging. In addition, it acts as an ion tunnel, allowing only lithium ions to pass through. The ion tunnel serves to prevent the organic solvents of the electrolyte having a large molecular weight moving together by solvation of lithium ions from co-intercalating with the carbon anode, thereby collapsing the structure of the carbon anode. Once the SEI film is formed, lithium ions do not react with the carbon negative electrode or other materials again, and the amount of lithium ions is reversibly maintained. Therefore, in order to improve the high-temperature cycle characteristics and low-temperature output of the lithium secondary battery, a strong SEI film must be formed on the negative electrode of the lithium secondary battery.

However, when an additive including the compound represented by Formula 3 or Formula 4 is included in the electrolyte, such as the electrolyte for a lithium secondary battery according to the present disclosure, a SEI film having excellent ion conductivity while being strong is formed on the surface of the negative electrode to form a high temperature It is possible to suppress the decomposition of the anode surface that may occur during cycle operation and prevent the oxidation reaction of the electrolyte.

When the compound represented by Formula 3 or Formula 4 is decomposed, a difluorophosphate (-PF ₂ ) group and an alkylene dioxide fragment may be generated. For example, the alkylene dioxide fragment may be an ethylene dioxide fragment.

Since the difluorophosphate (-PF ₂ ) group has excellent electrical and chemical reactivity, it can form a donor-acceptor bond with the transition metal oxide exposed on the surface of the positive electrode active material, and thus a complex form of a protective layer may be formed.

_{In addition, since the difluorophosphate (-PF 2} ) attached to the transition metal oxide during initial charging of the lithium secondary battery can be oxidized to a large number of fluorophosphates, as a result, the positive electrode is more stable and has excellent ion conductivity. A film can be formed. Accordingly, the film may prevent oxidative decomposition of other components of the electrolyte, and as a result, the cycle life performance of the lithium secondary battery may be improved and the swelling phenomenon may be prevented from occurring.

In addition, the compound represented by Chemical Formula 3 or Chemical Formula 4 and its oxide participate in electrical and chemical reactions with components of the film corresponding to a kind of SEI film to make the film more robust, and other components included in the electrolyte through oxidative decomposition stability can also be improved.

In addition, since the compound represented by Formula 3 or Formula 4 _{can form a film by forming a complex with LiPF 6} , it prevents unwanted side reactions from occurring, thereby improving cycle life characteristics of the lithium secondary battery and lithium secondary battery By preventing the gas from being generated inside, it is possible to remarkably reduce the failure rate due to swelling.

The additive including the compound represented by Formula 3 or Formula 4 may be included in an amount of 0.1 wt% to 10 wt% based on the total weight of the electrolyte for a lithium secondary battery. More specifically, the content of the compound represented by Formula 3 may be 0.1 wt% to 5 wt% or 0.1 wt% to 1 wt%. When the content of the additive satisfies the above range, it is possible to prevent an increase in resistance to implement a lithium secondary battery having excellent lifespan characteristics.

For example, the additive may include a compound represented by the following Chemical Formula 3-1 or the following Chemical Formula 4-1.

[Formula 3-1]

[Formula 4-1]

However, this is only an example, and it goes without saying that additives according to various modifications may be included in addition to this.

Meanwhile, the additive may include a nitrile-based compound. For example, the nitrile-based compound may include succinonitrile, adiponitrile, glutaronitrile, or a combination thereof. When the film includes a nitrile component, it is effective in co-relation with the compound represented by Chemical Formula 3-1 or Chemical Formula 4-1 to facilitate formation of a film complex and to prevent additional Cu dissolution.

An active material layer is formed on the above-described current collector. According to one embodiment, active material layers are formed on both the positive electrode 114 and the negative electrode 112 , so that they may have the same external shape in terms of structure. However, since the functions and effects of each of the positive electrode 114 and the negative electrode 112 are different, the active material layer formed on each of the positive electrode 114 and the negative electrode 112 may include different materials. In this case, the active material layer formed on the positive electrode 114 is defined as a positive electrode active material layer, and the active material layer formed on the negative electrode 112 is defined as a negative electrode active material layer.

In the positive electrode active material layer, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used as the positive electrode active material, and specifically, cobalt, manganese, nickel, and these At least one of a complex oxide of a metal selected from a combination of lithium and lithium may be used. As a more specific example, a compound represented by any one of the following formulas may be used. Li _a A _1-b X _b D ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5); Li _a A _1-b X _b O _2-c D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤= 0.5, 0 ≤ c ≤ 0.05); Li _a E _1-b X _b O _2-c D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a E _2-b X _b O _4-c D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤ 2); Li _a Ni _1-bc Co _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn _1-b G _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn _1-g G _g PO ₄ (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _a FePO ₄ (0.90 ≤ a ≤ 1.8)

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X 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 the group consisting of Co, Mn, and combinations thereof; T 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; Z 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.

In addition, one having a coating layer on the surface of the lithium metal oxide may be used, or a mixture of lithium metal oxide and lithium metal oxide having a coating layer may be used. The coating layer may include at least one coating element compound selected from the group consisting of an oxide of a coating element, hydroxide of a coating element, oxyhydroxide of a coating element, oxycarbonate of a coating element, and hydroxycarbonate of a coating element. have.

The compound constituting the coating layer 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. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (eg, spray coating, immersion method, etc.). Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

In the positive electrode, the content of the positive active material may be 90 wt% to 98 wt% based on the total weight of the positive active material layer.

In one embodiment, the positive active material layer may further include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1 wt% to 5 wt%, respectively, based on the total weight of the positive electrode active material layer.

The binder serves to adhere the positive active material particles well to each other and also to the positive active material to the current collector, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl. Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electronically conductive material may be used without causing a chemical change. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber Metal powders such as copper, nickel, aluminum, silver, or metal-based materials such as metal fibers Conductivity such as polyphenylene derivatives and a conductive material containing a polymer or a mixture thereof.

Meanwhile, as the negative active material, a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide may be used.

As a material capable of reversibly intercalating/deintercalating lithium ions, for example, a carbon material, that is, a carbon-based negative active material generally used in lithium secondary batteries may be used. Representative examples of the carbon-based negative active material include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon ( hard carbon), mesophase pitch carbide, and calcined coke.

The lithium metal alloy includes lithium and a group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. An alloy of a metal selected from may be used.

Examples of materials capable of doping and dedoping lithium include Si, SiO _x (0 < x < 2), Si-Q alloy (wherein Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 element, 16 Group element, transition metal, rare earth element, and an element selected from the group consisting of a combination thereof, not Si), Si-carbon composite, Sn, SnO ₂ , Sn-R (wherein R is an alkali metal, alkaline earth metal, 13 an element selected from the group consisting of a group element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, but not Sn), Sn-carbon composite, and the like; At least one of SiO ₂ may be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, One selected from the group consisting of Se, Te, Po, and combinations thereof may be used.

Lithium titanium oxide may be used as the transition metal oxide.

The anode active material layer includes an anode active material and a binder, and may optionally further include a conductive material.

The content of the anode active material in the anode active material layer may be 95 wt% to 99 wt% based on the total weight of the anode active material layer. The content of the binder in the anode active material layer may be 1 wt% to 5 wt% based on the total weight of the anode active material layer. In addition, when the conductive material is further included, 90 wt% to 98 wt% of the negative active material, 1 to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material may be used.

The binder serves to well adhere the negative active material particles to each other and also to adhere the negative active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, and polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and an olefin copolymer having 2 to 8 carbon atoms, (meth)acrylic acid and (meth)acrylic acid alkyl ester. copolymers or combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electronically conductive material may be used without causing a chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, denka black, and carbon fiber; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or a metal fiber; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof.

The positive active material layer and the negative active material layer are formed by mixing an anode active material, a binder, and optionally a conductive material in a solvent to prepare an active material composition, and applying the active material composition to a current collector. Since such a method of forming an active material layer is widely known in the art, a detailed description thereof will be omitted herein. The solvent may include, but is not limited to, N-methylpyrrolidone. In addition, when a water-soluble binder is used for the anode active material layer, water may be used as a solvent used in preparing the anode active material composition.

Meanwhile, the electrolyte solution for a lithium secondary battery of the present disclosure may further include additional additives in addition to the above-described additives. The additional additive may be, for example, but not limited to, fluoroethylene carbonate, vinylethylene carbonate, hexane tricyanide, lithium tetrafluoroborate and propanesultone, or a combination thereof.

In this case, the content of the additional additive may be 0.1 wt% to 20 wt% based on the total content of the electrolyte for a lithium secondary battery. More specifically, the content of the additional additive may be 0.1 wt% to 15 wt%. When the content of the additional additive satisfies the above range, it is possible to more effectively suppress battery resistance and implement a lithium secondary battery having excellent cycle life characteristics.

Meanwhile, as described above, a separator 113 may be disposed between the positive electrode 114 and the negative electrode 112 . As the separator 113, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used. A polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and polypropylene/polyethylene It goes without saying that a mixed multilayer film such as a /polypropylene three-layer separator or the like can be used.

A method of manufacturing a lithium secondary battery according to another embodiment,

a positive electrode including a current collector, an electrode tab extending from the current collector, and an active material layer formed on the current collector; and an electrode assembly including a negative electrode including a current collector, an electrode tab extending from the current collector, and an active material layer formed on the current collector, and an electrolyte solution containing lithium salt into a battery container to form a battery cell to manufacture,

By initially charging the battery cell at 0.05 to 0.2C for 5 to 10 hours,

A film including a material represented by the following Chemical Formula 1 is formed on at least one of the current collector and the electrode tab.

[Formula 1]

CuX(POF ₂ ) _n Y ₂ Z

In Formula 1,

X is a C1 to C10 alkylene group,

Y is represented by the following formula (2),

[Formula 2]

NC-R ¹ -CN, (In this case, R ¹ is a C1 to C10 alkylene group.)

Z is an anionic group of the lithium salt,

n is 1 or 2.

The film according to an embodiment may be formed on one or more of the current collector and the electrode tab exposed to the electrolyte, thereby preventing irreversible side reactions between the electrolyte and the positive electrode and the electrolyte and the negative electrode at high temperature and high pressure.

The film may be formed on the current collector and the electrode tab by low-rate charging as described above.

The film according to an exemplary embodiment is formed to have an appropriate thickness, thereby preventing an additional side reaction without increasing electrical resistance on the electrode surface. For example, the film may be formed to a thickness of 25-50 μm. When the coating layer is formed to a thickness within the above range, it is possible to prevent additional side reactions without increasing the electrical resistance on the electrode surface.

As in one embodiment, in order to form a film capable of preventing an additional side reaction without increasing the electrical resistance on the electrode surface, the electrolyte according to an embodiment includes a compound represented by the following Chemical Formula 3 or the following Chemical Formula 4 as an additive may include

[Formula 3]

In Formula 3,

A is a C1 to C10 alkylene group, or (-C ₂ H ₄ -OC ₂ H ₄ -) _m (in this case, m is an integer of 1 to 10),

[Formula 4]

In Formula 4,

B is a C1 to C10 alkylene group, or (-C ₂ H ₄ -OC ₂ H ₄ -) _l (in this case, l is an integer from 1 to 10),

R ² is a C1 to C10 alkyl group.

For example, in Formulas 3 and 4, A and B may each independently be a C1 to C5 alkylene group, and m and 1 may each independently be an integer of 1 to 5.

The compound represented by Formula 3 or Formula 4 includes a difluorophosphate (-PF ₂ ) group having excellent electrical and chemical reactivity at the terminal.

During the initial charging of the lithium secondary battery, lithium ions from the lithium-transition metal oxide as the positive electrode move to the carbon electrode as the negative electrode and are intercalated with carbon. At this time, since lithium has strong reactivity, it reacts with the carbon electrode to form Li ₂ CO ₃ , LiO, LiOH, etc. to form a film on the surface of the anode. Such a film is called a solid electrolyte interface (SEI) film. The film according to an embodiment may be the aforementioned SEI film.

Meanwhile, the additive may further include a nitrile-based compound. For example, the nitrile-based compound may include succinonitrile, adiponitrile, glutaronitrile, or a combination thereof. When the film contains the nitrile component, it is co-related with the compound represented by Chemical Formula 3-1 or Chemical Formula 4-1 to facilitate formation of a film complex and to prevent additional Cu dissolution.

Meanwhile, the lithium secondary battery according to an embodiment may be provided in a device including one or more thereof. As such a device, for example, any one selected from the group consisting of a mobile phone, a tablet computer, a notebook computer, a power tool, a wearable electronic device, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage device can be As such devices to which the lithium secondary battery is applied are known in the art, a detailed description thereof will be omitted herein.

Hereinafter, the aspects of the present invention described above through examples will be described in more detail. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

(Manufacture of lithium secondary battery)

Comparative Example 1: Cu in 1.5M LiPF ₆ EC/EMC/DMC=2/2/6

_{LiNi 0.8} Co _0.15 Al _0.05 O ₂ as a positive electrode active material, polyvinylidene fluoride as a binder, and Ketjen Black as a conductive material were mixed in a weight ratio of 97.3:1.4:1.3, respectively, and dispersed in N-methyl pyrrolidone to slurry the positive electrode active material was prepared.

The cathode active material slurry was coated on Al foil having a thickness of 15 μm, dried at 100° C., and then pressed to prepare a cathode.

Graphite as an anode active material, polyvinylidene fluoride as a binder, and Ketjen Black as a conductive material were mixed in a weight ratio of 98:1:1, respectively, and dispersed in N-methyl pyrrolidone to prepare an anode active material slurry.

The negative electrode active material slurry was coated on a Cu foil having a thickness of 10 μm, dried at 100° C., and then pressed to prepare a negative electrode.

A lithium secondary battery was manufactured using the prepared positive electrode and negative electrode, a separator made of polyethylene having a thickness of 25 μm, and an electrolyte having the following composition.

(Electrolyte composition)

Salt: 1.5M LiPF ₆

Solvent: EC/EMC/DMC=2:2:6 volume ratio

Example 1

A lithium secondary battery was prepared in the same manner as in Comparative Example 1, except that the compound represented by the following Chemical Formula 3-1 was added to the electrolyte as an additive.

(Electrolyte composition)

Salt: 1.5M LiPF ₆

Solvent: EC/EMC/DMC=2:2:6 volume ratio

Additive: 1 wt% of a compound represented by the following formula 3-1

[Formula 3-1]

(However, in the above electrolyte composition, "wt%" is based on the total amount of electrolyte (lithium salt + solvent + additive).)

Example 2

A lithium secondary battery was prepared in the same manner as in Example 1, except that a compound represented by the following Chemical Formula 4-1 was added as an additive instead of Chemical Formula 3-1.

[Formula 4-1]

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the additive composition was changed as follows.

Additive: 1 wt% of a compound represented by the following Chemical Formula 3-1 and 1 wt% of succinonitrile

evaluation example

1. DC-internal resistance evaluation after cycle

For the lithium secondary batteries according to Example 1 and Comparative Example 1, the residual capacity (SOC) was set to 100%, then charged at 0.5C under 4.2V/0.05C cut-off conditions, and then discharged at 1C under 2.5V cut-off conditions. After repeating the charging/discharging process 250 times, DC-internal resistance was measured and the results are shown in Table 1 below.

Direct current resistance (DC-IR) was calculated from each current difference and voltage difference when different currents were applied.

A constant current of 10A was discharged for 10 seconds in a fully charged state.

Next, a constant current discharge of 1A was performed for 10 seconds, followed by a constant current discharge of 10A for 4 seconds.

The direct current resistance (DC-IR) was calculated by the equation ΔR =ΔV/ΔI from the data of 18 s and 23 s.

Referring to Table 1, in the case of Example 1, it can be seen that the DC-internal resistance after the cycle is small compared to Comparative Example 1.

2. Long-term neglect characteristic evaluation

For the batteries according to Comparative Example 1 and Example 1, chemical charge/discharge was performed twice at 0.2C/0.5C, the standard charge/discharge current density was 0.5C/0.2C, and the charge termination voltage was 4.2V (Li /graphite), after each charge/discharge test with a discharge termination voltage of 2.6 V (Li/graphite) was conducted once, left at the shipment SOC 100 for 100 days, and then the voltage drop was measured in OCV state, and the results are shown in Table 1 , are shown in FIGS. 2 and 3 .

2 and 3 are graphs measuring the voltage change in the OCV state when batteries according to Comparative Examples 1 and 1 were left at 100% SOC for 100 days after chemical charging/discharging.

Referring to FIG. 2 , in the case of the cell according to Comparative Example 1, samples showing a voltage drop after 40 days were identified.

On the other hand, referring to FIG. 3 , in the case of the cell according to Example 1, a sample showing a voltage drop was not observed.

In addition, referring to Table 1, it was confirmed that the defective rate of Comparative Example 1 was 0.6%, whereas that of Example 1 was 0.18%, which was relatively low.

From this, it can be seen that the cell in which the film is formed according to Example 1 has excellent long-term storage characteristics.

3. Evaluation of high temperature storage characteristics

Each of the lithium secondary batteries prepared according to Example 1 and Comparative Example 1 was left at 60° C. in a state of charge (SOC, state of charge = 100%) for 30 days, and the resistance increase rate at high temperature (60° C.) It was evaluated and the results are shown in Table 1 below.

The resistance increase rate (%) is the percentage value of DC-IR after 30 days of standing with respect to the initial DC-IR.

Referring to Table 1, in the case of Example 1, it can be seen that compared to Comparative Example 1, DC after being left for 30 days at 60 °C - internal resistance is small.

voltage drop characteristics
(Defective rate %) DC-IR after cycle DC-IR for high temperature storage Comparative Example 1 0.6% 26.1 mohm 35% Example 1 0.18% 25.4 mohm 27%

Therefore, in the case of the battery according to the embodiment, it can be confirmed that oxidation resistance and resistance according to charge/discharge, and high temperature oxidation resistance and resistance are improved.

4. Linear Sweep Voltammetry (LSV) evaluation of cells

A three-electrode cell was prepared for each metal as follows, and the oxidation electrode decomposition was evaluated using a linear sweep voltammetry (LSV) at 25° C. The results are shown in FIG. 4 .

(Preparation Example 1) Cathode metal: Cu

(Comparative Preparation Example 1) Anode metal: Ni

(Comparative Preparation Example 2) Anode metal: Fe

(Comparative Preparation Example 3) Cathode metal: Zn

A three-electrode electrochemical cell using each cathode metal as a working electrode and Li metal as a counter electrode and a reference electrode was used. At this time, the scan was performed at a scan rate of 1 mV/sec in the range of 2.5V to 7.0V.

4 shows the LSV evaluation results for the three-electrode cell.

5 is an enlarged graph of a section in which a reduction peak appears among the LSV evaluation results.

6 and 7 are photographs confirming that a film is formed on the electrode of the three-electrode cell according to an embodiment of the present invention after LSV evaluation is performed.

Referring to FIG. 5 , it can be confirmed that the three-electrode cell using the Cu anode according to Preparation Example 1 showed a reduction peak in the range of 2.5 to 3.5V in the electrolyte containing the additive. This means that a film is formed during initial charge/discharge, and referring to FIG. 4 , since the oxidation reaction between the electrode and the electrolyte is effectively suppressed due to the film, it can be expected that the effect of inhibiting metal elution from the electrode will be excellent.

In addition, referring to FIG. 6 , it was observed that a film was not formed on the electrode according to Preparation Example 1, whereas a film was formed on the electrode according to Preparation Example 1 with reference to FIG. 7 .

5. Confirmation of film formation and evaluation of components

The three-electrode cell used for the LSV evaluation was subjected to oxidation electrode decomposition in the electrolyte according to Example 3 to observe whether a film was formed.

8 is an SEM photograph of a cross-section of an electrode tab according to Example 3.

9 is an IR spectrum result obtained by analyzing the components of the coating film according to Example 3. FIG.

Referring to FIG. 8 , it can be confirmed that a film is formed on the cross-section of the electrode tab containing the copper component,

Referring to FIG. 9 , it can be confirmed that the film includes the component represented by Chemical Formula 1 above.

In the foregoing, specific embodiments of the present invention have been described and illustrated, but it is common knowledge in the art that the present invention is not limited to the described embodiments, and that various modifications and variations can be made without departing from the spirit and scope of the present invention. It is self-evident to those who have Accordingly, such modifications or variations should not be individually understood from the technical spirit or point of view of the present invention, and the modified embodiments should belong to the claims of the present invention.

100: lithium secondary battery
112: cathode
113: separator
114: positive electrode
120: battery container
140: sealing member

Claims (10)

anode;
cathode; and
Includes an electrolyte containing a lithium salt,
At least one of the positive electrode and the negative electrode,
current collector;
an electrode tab extending from the current collector;
an active material layer formed on the current collector; and
It is formed on at least one of the current collector and the electrode tab, and includes a film including a material represented by the following Chemical Formula 1,
The electrolyte solution further comprises an additive represented by the following formula (4), a lithium secondary battery:
[Formula 1]
CuX(POF ₂ ) _n Y ₂ Z
In Formula 1,
X is a C1 to C10 alkylene group,
Y is represented by the following formula (2),
[Formula 2]
NC-R ¹ -CN, (In this case, R ¹ is a C1 to C10 alkylene group.)
Z is an anionic group of the lithium salt,
n is 1 or 2,
[Formula 4]

In Formula 4,
B is a C1 to C10 alkylene group, or (-C ₂ H ₄ -OC ₂ H ₄ -) _l (in this case, l is an integer from 1 to 10),
R ² is a C1 to C10 alkyl group. According to claim 1,
The lithium salt is LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ), where x and y are integers from 1 to 20, LiCl, LiI and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate (LiBOB)), or a combination thereof. According to claim 1,
wherein Z is PF ₆ , a lithium secondary battery. According to claim 1,
The current collector and the electrode tab include a copper (Cu) metal, a lithium secondary battery. According to claim 1,
The additive is a lithium secondary battery comprising a compound represented by the following Chemical Formula 4-1:
[Formula 4-1]

. According to claim 1,
The additive comprises a nitrile-based compound, a lithium secondary battery. 7. The method of claim 6,
The nitrile-based compound is succinonitrile (succinonitrile), adiponitrile (adiponitrile), glutaronitrile (glutaronitrile), or a lithium secondary battery comprising a combination thereof. According to claim 1,
The additive is added in an amount of 0.1 wt% to 10 wt% based on the total weight of the electrolyte, a lithium secondary battery. According to claim 1,
The thickness of the film is 25㎛ to 50㎛, lithium secondary battery. a positive electrode including a current collector, an electrode tab extending from the current collector, and an active material layer formed on the current collector; and an electrode assembly including a current collector, an electrode tab extending from the current collector, and an anode including an active material layer formed on the current collector, and an electrolyte solution comprising a lithium salt and an additive represented by the following Chemical Formula 4 to prepare a battery cell by putting it in a battery container,
By initially charging the battery cell at 0.05 to 0.2C for 5 to 10 hours,
A method of manufacturing a lithium secondary battery for forming a film including a material represented by the following Chemical Formula 1 on at least one of the current collector and the electrode tab:
[Formula 1]
CuX(POF ₂ ) _n Y ₂ Z
In Formula 1,
X is a C1 to C10 alkylene group,
Y is represented by the following formula (2),
[Formula 2]
NC-R ¹ -CN, (In this case, R ¹ is a C1 to C10 alkylene group.)
Z is an anionic group of the lithium salt,
n is 1 or 2,
[Formula 4]

In Formula 4,
B is a C1 to C10 alkylene group, or (-C ₂ H ₄ -OC ₂ H ₄ -) _l (in this case, l is an integer from 1 to 10),
R ² is a C1 to C10 alkyl group.

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