KR101429763B1 - Negative electrode active material for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

Disclosed is a negative electrode active material for a secondary battery comprising a metal-based or metal composite-based negative electrode active material, a solid electrolyte interface film-forming material, and a lithium secondary battery using the negative electrode active material.

The present invention reduces the loss of lithium ions released from an anode by doping a negative electrode active material with a solid electrolyte interface film-forming material doped with lithium to precharge it, thereby increasing the reversibility of lithium ions during initial charging and discharging, Can be increased.

A negative electrode active material, a solid electrolyte interface film forming material, a lithium ion

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a negative electrode active material for a secondary battery and a lithium secondary battery including the negative active material,

The present invention relates to a negative electrode active material, a method for producing the negative electrode active material, and a lithium secondary battery including the same.

It has been proposed to use a lithium metal having a very high energy density as a negative electrode active material of a lithium secondary battery. However, during charging, a dendrite is formed in the negative electrode, There is a risk of causing an internal short circuit by reaching the anode. The precipitated dendrites rapidly increase the reactivity of the lithium electrode as the specific surface area increases, and react with the electrolyte solution on the surface of the electrode to form a polymer film lacking electron conductivity. As a result, the cell resistance rapidly increases, or particles isolated from the network of electron conduction exist, which acts as an element to inhibit discharge.

For this reason, a method using a graphite material capable of absorbing / releasing lithium ions instead of lithium metal as the negative electrode active material has been proposed. Generally, since graphite anode active material does not precipitate metal lithium, an internal short circuit due to dendrite does not occur and no additional disadvantage is caused thereby. However, graphite has a theoretical capacity of 372 mAh / g, which is a very small capacity equivalent to 10% of the theoretical capacity of lithium metal.

In order to overcome such a problem, currently active materials are metal-based or intermetallic-based anode active materials. However, in the case of such a metal active material including metal, the theoretical discharge capacity is very high, but the reversibility of the electrochemical, the charging / discharging efficiency thereof, and the charge / discharge capacity of the electrochemical cycling are rapidly decreased.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a secondary battery capable of reducing the irreversible capacity of lithium ions during initial charging and discharging,

According to an aspect of the present invention,

Metal or metal composite anode active material; And

A negative electrode active material for a secondary battery comprising a solid electrolyte interface film-forming material containing lithium.

Generally, when a negative electrode active material of metal or metal complex type is used as a negative electrode active material of a secondary battery, the metal or metal composite negative electrode active material has the lowest unit electrode potential and can be used as a negative electrode to have the highest battery voltage. However, in practical use, the metal or metal composite system is eluted as lithium cations into the electrolyte during discharging and precipitates as lithium metal in the electrolyte during charging to form a resinous or particulate phase. It also falls off the dendrite and loses conductivity in reaction with the solvent, resulting in isolated lithium, resulting in poor current efficiency.

The negative electrode active material of the present invention is formed by doping a metal-based or metal-based composite negative electrode active material with a solid electrolyte interface film-forming material containing lithium, thereby minimizing the loss of lithium ions released from the positive electrode by forming a solid electrolyte interface coating on the negative electrode active material. Therefore, the reversibility of the lithium ion is increased due to the interfacial coating of the solid electrolyte which forms a compound between lithium and the metal during the initial charge / discharge, thereby increasing the charge / discharge efficiency and charge / discharge capacity of the secondary battery.

The metal-based anode active material may be at least one of a lithium-based, a silicon-based, and a tin-based, and may be preferably SiO ₂ , SnO _2, or Li ₂ O.

The metal composite anode active material may be a lithium metal composite or a silicon graphite composite wherein the matrix metal of the lithium metal composite may be at least one of Al, Si, Sn, Pb, In, Bi, Sb and Ag. Such a matrix metal may be accompanied by a structural change in the process of forming an alloy with lithium.

The solid electrolyte interface film-forming material may be a powdery compound including lithium (Li), and preferably has a melting point of 100 to 700 ° C. Also may be a solid electrolyte interface film-forming material is a lithium (Li) and -C, -O, -H is combined with the powder-type compound, alone or in _{combination, Li 2 CO 3, LiOH,} LiH, LiOOCCH 3, C 6 _{H 5 COOLi, CH 3 COCH 2} COOLi, CH 3 COCH = C (OLi) CH 3, (CH 3) 3 COLi, C 9 H 13 Li, C 6 H 11 (CH 2) 3 CO 2 Li, C 2 H ₅ LiO, HCO ₂ Li, (CH ₃ ) ₂ CHOLi, CH ₃ CH (OH) COOLi, C ₃ H ₅ O ₃ Li, CH ₃ LiO, C ₁₀ H ₁₅ Li, Li ₂ O ₂ And C ₆ H ₅ OLi.

The solid electrolyte interface film-forming material may be doped into the anode active material in the lithium ion form, and the lithium ion content may be 0.2 to 2.0 wt% with respect to the solid electrolyte interface film forming material. When the content of lithium ions is 0.2% by weight or less, the amount of lithium ions formed on the interface coat is decreased, so that the amount of lithium ions reversible at the time of initial charging and discharging is small and the charging and discharging efficiency can be reduced. The amount of the negative electrode active material decreases, and the capacity of the battery may decrease.

The weight ratio of the metal or metal composite anode active material to the solid electrolyte interface film forming material may be 7: 3 to 9: 1. When the weight ratio is 7: 3 or less, the amount of the negative electrode active material may be relatively decreased as compared with the solid electrolyte interface film-forming material, so that the battery capacity of the secondary battery is not easily increased. If the weight ratio is 9: 1 or more, the solid electrolyte interfacial film- The amount of reversible lithium ions is reduced, so that it is less likely to contribute to the charge-discharge efficiency.

The present invention also relates to a method for producing a solid electrolyte interfacial film forming material comprising a metal composite anode active material selected from the group consisting of a silicon-based or a tin-based metal, a lithium metal composite or a silicon graphite composite, and lithium in a weight ratio of 7: 3 to 9: Mixing them into a furnace; And

And the carbonaceous gas is injected at a temperature of 500 to 1000 ° C by increasing the mixture at 5 to 10 ° C / min for 5 to 20 hours in an argon gas atmosphere of the furnace.

In order to dope the lithium ion itself into the negative electrode active material of the metal or metal composite system, the solid electrolyte interface film-forming material containing lithium is mixed with the negative electrode active material at a weight ratio of 7: 3 to 9: 1, And heat treatment is carried out. This is to inject a carbon-based gas at a temperature of _{500 ~ 1000 ℃ Li 2 CO 3} , LiOH, LiH, LiOOCCH 3, C 6 H 5 COOLi, CH 3 COCH 2 COOLi, CH 3 COCH = C (OLi) CH 3, ( _{CH 3) 3 COLi, C 9} H 13 Li, C 6 H 11 (CH 2) 3 CO 2 Li, C 2 H 5 LiO, HCO 2 Li, (CH 3) 2 CHOLi, CH 3 CH (OH) COOLi, C ₃ H ₅ O ₃ Li, CH ₃ LiO, C ₁₀ H ₁₅ Li, Li ₂ O ₂ And C ₆ H ₅ OLi, and at least one of the solid electrolyte interface film-forming material and CO, CO ₂ , CH ₂ , CH ₄ And C ₂ H ₄ to ionize the lithium ions in the solid electrolyte interface film forming material to prevent the loss of lithium ions emitted from the positive electrode to increase the charge and discharge efficiency.

For example, by the following chemical reaction formula.

Li ₂ CO ₃ + CH ₂ ? 2Li ⁺ + 2CO + H ₂ O

The present invention also provides a negative electrode comprising a negative electrode active material doped with a solid electrolyte interface film-forming material;

A positive electrode capable of reversibly intercalating and deintercalating lithium; And

A lithium secondary battery characterized by comprising a separator.

As described in detail above, the present invention minimizes the loss of lithium ions released from the anode by pre-doping lithium ions contained in the solid electrolyte interface coating film-forming material with the metal or metal composite anode active material, And the charge / discharge efficiency can be increased.

Hereinafter, a secondary battery using the negative electrode active material according to the present invention will be described.

The negative electrode is composed of a negative electrode active material layer and a negative electrode collector. The negative electrode active material layer is formed by applying a negative electrode active material slurry obtained by mixing and dispersing a negative electrode active material binder in a solvent to an anode current collector, and drying and rolling the same. As the solvent used when mixing and dispersing the negative electrode active material and the binder or the like, a non-aqueous solvent or an aqueous solvent may be used.

As the non-aqueous solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, tetrahydrofuran and the like can be used. The binder may be a fluorine-containing binder or an SBR binder such as a copolymer of PVDF and vinylidene chloride. When the SBR binder is used, it may further include a thickener.

The content of the binder is preferably 0.8 to 5 wt%, more preferably 1 to 5 wt%, and most preferably 1 to 2 wt% based on the weight of the anode active material precursor. If the content of the SBR binder is less than 0.8% by weight, the binder content is too small and the adhesive force between the anode active material and the current collector is insufficient. If the content exceeds 5% by weight, the content of the anode active material decreases by an amount exceeding the battery capacity It is difficult to increase the capacity.

The thickening agent used for the viscosity control of the negative electrode active material according to the present invention may be selected from the group consisting of carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose. The content of the thickener is preferably 0.8 to 5 wt%, more preferably 1 to 5 wt%, and most preferably 1 to 2 wt% based on the total weight of the negative electrode active material.

When the content of the thickener is less than 0.8% by weight, there is a problem that the negative electrode active material flows down when the negative electrode active material is coated on the negative electrode collector. When the content of the thickener is more than 5% by weight, uniform spreadability is decreased when the negative electrode current collector is coated, So that it acts as a resistor.

As the negative electrode current collector, stainless steel, nickel, copper, titanium, an alloy thereof, or the like can be used. Of these, copper or a copper alloy is preferable.

The cathode active material may include one or more selected from the group consisting of LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiCrO ₂ , and LiMn ₂ O ₄ , and may include one or more selected from the group consisting of a binder and carbon black, acetylene black, ≪ / RTI > may be further included. The cathode current collector may be made of aluminum or an aluminum alloy.

The binder added to the positive electrode active material may be a fluorine-containing binder such as PVDF, a copolymer of vinylidene chloride and hexafluoropropylene, or the like.

The electrolyte solution of the present invention may include a non-aqueous organic solvent and a lithium salt. This non-aqueous organic solvent serves as an intermediary for ions to participate in the electrochemical reaction of the cell. The non-aqueous organic solvent may be a mixture of one or more selected from the group consisting of cyclic carbonates, non-cyclic carbonates, aliphatic carboxylic acid esters, acyclic ethers, cyclic ethers, alkyl phosphate esters or fluorides thereof .

The non-aqueous organic solvent may be a mixture of one or more selected from the group consisting of cyclic carbonates, non-cyclic carbonates, and aliphatic carboxylic acid esters.

The lithium salt according to the present invention acts as a source of lithium ions in the battery, thereby enabling operation of a basic lithium battery. To the lithium salt is the lithium salt is _{LiPF 6, LiBF 4, LiAsF 6} , LiClO 4, LiCF 3 SO 3, LiSbF 6, LiN (SO 2 CF 3) 2, LiC 4 F 9 SO 3, LiAlF 4, _{LiAlCl 4, LiN (SO 2 C} 2 F 5) 2, LiN (C X F 2X +1 SO 2) (C y F 2y +1 SO 2) ( where, x and y are natural numbers), LiCl and LiI, etc. Or a mixture of two or more of them may be used.

As the separator for preventing a short circuit between the positive electrode and the negative electrode, the separator according to the present invention may be a polymer membrane such as polyolefin, polypropylene, or polyethylene, or a multilayer thereof, a microporous film, a woven fabric, or a nonwoven fabric .

The lithium secondary battery includes an electrode assembly including a positive electrode including a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions and a negative electrode capable of reversibly intercalating and deintercalating lithium ions and a separator interposed therebetween, And a can containing an electrode assembly may be provided.

Hereinafter, the present invention will be described in more detail by way of examples, comparative examples and experimental examples.

Example 1

90% by weight of a silicon graphite anode active material and 10% by weight of lithium carbonate (Li ₂ CO ₃ ) powder solid electrolyte interface coating film forming material were mixed in a screw cone mixer (manufactured by Han River Engineering) and placed in a furnace in a crucible. The mixture was heated at a rate of 5 ° C / min for 5 hours in an argon gas atmosphere of the furnace, and CH ₂ gas was introduced at a temperature of 1000 ° C to prepare a lithium ion-doped anode active material.

Example 2

Except that the reaction was conducted for 10 hours in Example 1 described above.

Example 3

Except that the reaction was carried out for 20 hours in the above-described Example 1.

Comparative Example 1

In order to compare with Examples 1 to 3 described above, a negative electrode active material to which only silicon graphite was added without adding a solid electrolyte interface film-forming material was reacted for 1 hour.

Experimental Example 1: Lithium ion separated from the solid electrolyte interface film-forming material according to the reaction time

Each of the negative electrode active materials according to Examples 1 to 3 and Comparative Example 1 was measured for the content of lithium ion doped in the negative electrode active material by inductively coupled plasma (ICP).

The results of Experimental Example 1 are shown in Table 1 below.

Example (Reaction time) Lithium ion (wt%) Example 1 (5 hours) 0.165 wt% Example 2 (10 hours) 0.682 wt% Example 3 (20 hours) 1.109 wt% Comparative Example 1 (1 hour) 0.013 wt%

As shown in Table 1, the content of lithium ion doped in the negative electrode active material according to the present invention increases as the amount of lithium ions separated from the solid electrolyte interface film-forming material increases with time and is doped into the negative electrode active material Lithium ions increased. Therefore, the lithium ion is doped into the negative electrode active material, thereby minimizing the loss of lithium ions during the initial charge and discharge, thereby reducing the initial irreversible capacity and increasing the charge / discharge efficiency.

On the contrary, in the silicon graphite negative electrode active material performed according to the comparative example, the content of lithium ion was low. This result shows that the content of lithium ion is low in the negative electrode active material and is not precharged to the negative electrode active material. The loss of lithium ions may be increased due to the irreversible nature of the lithium ions, thereby reducing the charge and discharge efficiency.

Example 4

150 g of carboxymethylcellulose thickener powder was added to 1000 ml of pure water at a pH of 7 with stirring, and the mixture was stirred at room temperature until no precipitate was formed to prepare an aqueous solution having a concentration of about 1.5% by weight. The aqueous solution was allowed to stand at room temperature for about 3 hours, and then the negative electrode active material prepared in Example 1 was added while the 1.5% by weight aqueous solution of carboxymethylcellulose was stirred in a homogenizer. Thereafter, 3.87 g of a 40 wt% SBR binder aqueous emulsion was added to the mixture to prepare a negative electrode active material slurry.

Example 5

The negative electrode active material prepared in Example 2 was used in Example 4.

Example 6

The negative electrode active material prepared in Example 3 was used in Example 4.

Comparative Example 2

The negative electrode active material prepared in Comparative Example 1 was used in Example 4.

Example 7

LiCoO ₂ as a cathode active material, polyvinylidene fluoride (PVdF) as a binder and carbon as a conductive agent were mixed at a weight ratio of 92: 4: 4, and then dispersed in N-methyl-2-pyrrolidone to prepare a cathode slurry Respectively. This slurry was coated on an aluminum foil having a thickness of 20 mu m, followed by drying and rolling to prepare a positive electrode. The negative electrode active material used was a lithium-free pre-charged negative electrode active material slurry prepared according to Example 4 above. This slurry was coated on a lithium foil having a thickness of 15 mu m, followed by drying and rolling to prepare a negative electrode. A film separator made of polyethylene (PE) having a thickness of 20 탆 was inserted between the electrodes thus prepared, wound and compressed, and inserted into a square 463450 size can. An electrolyte was injected into the square can to prepare a lithium secondary battery. The electrolytic solution was prepared by adding 20% by weight of ethylene carbonate (EC) as a non-aqueous organic solvent and 70% by weight of diethyl carbonate (DEC) to 1.3M LiPF ₃ 10% by weight were added to prepare an electrolytic solution.

Example 8

Was prepared according to Example 7 using the negative electrode active material of Example 5 above.

Example 9

Was prepared according to Example 7 using the negative electrode active material of Example 6 above.

Comparative Example 3

The negative electrode active material of Comparative Example 2 was used in accordance with Example 7.

Experimental Example 2: Charging capacity

The batteries prepared in Examples 7 to 9 and Comparative Example 3 were charged at 0.2 C / 0.01 V and constant current-constant voltage for 3 hours, cut off at 0.01 C, and the charge capacity was measured.

Experimental Example 3: Discharge Capacity

Each battery was charged at 0.2 C / 0.01 V constant current-constant voltage for 3 hours, left for 2 hours, discharged at 0.2 C / 1.5 V constant current-constant voltage, and discharge capacity was measured.

Experimental Example 4: Charging / discharging efficiency

The secondary battery produced in the above example was charged at a current of 158 mA and a charging voltage of 4.2 V under the condition of constant current-constant voltage (CC-CV), left for 1 hour, discharged to 2.75 V at a current of 395 mA, Time left. This process was repeated three times and then charged at 4.2 V with a current of 395 mA for 3 hours.

Charging / discharging efficiency (%) = [(discharging capacity-charging capacity) / (charging capacity)] × 100 (%

The results of the experiments are shown in Table 2 below.

Example Charging capacity (mAh / g) Discharge capacity (mAh / g) Charging / discharging efficiency (%) Example 1 550 500 90.9 Example 2 538 500 92.9 Example 3 529 500 94.5 Comparative Example 1 562 500 88.9

The results of Table 2 are shown in Table 1. In the present invention, the lithium doping amount of the negative electrode active material increases with time, and the charging / discharging efficiency is increased corresponding to the result. Therefore, it can be deduced that the lithium ion is precharged to the negative electrode active material and the loss of lithium ion is reduced during the initial charge / discharge to reduce the irreversibility, thereby increasing the charge / discharge efficiency.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention . Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (21)

delete delete delete delete delete delete delete delete delete delete delete A solid electrolyte interface film-forming material comprising a metal composite anode active material selected from a lithium-based, silicon-based or tin-based metal, a lithium metal composite or a silicon graphite composite to lithium is mixed at a weight ratio of 9: 1, ); And And the carbonaceous gas is injected at a temperature of 500 to 1000 ° C by increasing the mixture at 5 to 10 ° C / min for 5 to 20 hours in the argon gas atmosphere of the furnace. The method of claim 12, wherein the gas is CO, CO _2, CH _2, CH _4, And C < ₂ > H < _{4 &} gt ;. _{5. A} method for producing a negative active material for a lithium secondary battery, delete 13. The method of claim 12, wherein the metal of the lithium metal composite is at least one of Al, Si, Sn, Pb, In, Bi, Sb and Ag. 13. The method of claim 12, wherein the solid electrolyte interface film-forming material is a powdery compound. 13. The method of claim 12, wherein the solid electrolyte interface coating material has a melting point of 100 to 700 ° C. 13. The method according to claim 12, wherein the solid electrolyte interface film-forming material is a powdery compound in which lithium (Li) and -C, -O, and -H are bonded singly or in combination. . The method of claim 12, wherein the solid electrolyte interface film-forming material is _{Li 2 CO 3, LiOH, LiH} , LiOOCCH 3, C 6 H 5 COOLi, CH 3 COCH 2 COOLi, CH 3 COCH = C (OLi) CH 3, ( _{CH 3) 3 COLi, C 9} H1 3 Li, C 6 H 11 (CH 2) 3 CO 2 Li, C 2 H 5 LiO, HCO 2 Li, (CH 3) 2 CHOLi, CH 3 CH (OH) COOLi, Wherein at least one selected from the group consisting of C ₃ H ₅ O ₃ Li, CH ₃ LiO, C ₁₀ H ₁₅ Li, Li ₂ O _2, and C ₆ H ₅ OLi is selected. 13. The method of claim 12, wherein the solid electrolyte interface film-forming material is doped into a negative electrode active material in a lithium ion form. 21. The method of claim 20, wherein the lithium ion content is 0.2 to 2.0 wt% based on the solid electrolyte interface film forming material.