KR101130318B1 - Positive active material for lithium secondary battery, method of preparing the same, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same, and more particularly, a core including a compound capable of reversible intercalation / deintercalation of lithium; And a positive electrode active material including a surface treatment layer of an ammonium-containing fluoride compound on the surface of the core, a method of manufacturing the same, and a positive electrode including the positive electrode active material.

The ammonium cation in the ammonium-containing fluoride compound of the surface treatment layer removes hydrofluoric acid generated near the positive electrode active material to protect the positive electrode active material, and the surface treatment element-containing fluoride compound remaining on the surface of the positive electrode active material is obtained from the positive electrode active material. By suppressing or suppressing the reaction between the positive electrode active material and the electrolyte, the interfacial resistance between the positive electrode and the electrolyte is reduced, thereby improving charge / discharge characteristics, lifetime characteristics, high voltage characteristics, high rate characteristics, and thermal stability of the lithium secondary battery.

Cathode active material, ammonium-containing fluoride compound, high capacity, high rate characteristic, high voltage characteristic

Description

A positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same TECHNICAL FIELD

The present invention relates to a positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same. More particularly, the lithium secondary battery improves charge and discharge characteristics, life characteristics, high voltage characteristics, high rate characteristics, and thermal stability. The present invention relates to a cathode active material for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

The demand for secondary batteries, which are used for charging and discharging with portable electronic devices such as PDAs, mobile phones, notebook computers, and electric bicycles and electric vehicles, is rapidly increasing. In particular, since their product performance depends on secondary batteries, which are key components, the demand for high performance batteries is very large.

The characteristics required for the battery have various aspects such as charge and discharge characteristics, lifespan, high rate characteristics, and stability at high temperatures. Among them, lithium secondary batteries have the highest voltage and high energy density and are the most attracting attention.

Lithium secondary batteries are divided into lithium batteries using a negative electrode as a lithium metal and lithium ion batteries using an interlayer compound such as carbon, which lithium ions can insert and desorb. Alternatively, depending on the electrolyte used, it may be classified into a liquid battery using a liquid, a gel polymer battery using a mixture of a liquid and a polymer, and a solid polymer battery using purely a polymer.

Commercially available small lithium secondary batteries use LiCoO ₂ for the positive electrode and carbon for the negative electrode. Japan's Molly Energy Company uses LiMn ₂ O ₄ as its anode, but its use is negligible compared to LiCoO ₂ . LiNiO ₂ , LiCo _x Ni _1-x O ₂ and LiMn ₂ O ₄ are the positive electrode materials currently being actively researched and developed. More recently, the demand for Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ is replaced by LiCoO ₂ or composite electrode mixed with LiCoO ₂ .

However, the materials are poor in high rate and low temperature characteristics due to lower electronic conductivity than LiCoO ₂ , and the energy density of the battery is not improved despite the high capacity due to the low tap density. Especially in recent years _{Li [Ni 1/2 Mn 1} /2] O 2 spotlighted in the electron conductivity is very low, difficult to put to practical use (J. Power Sources , 112 (2002) 41-48). In particular, _{Li [Ni 1/2 Mn 1} /2] O 2 and _{Li [Ni 1/3 Co 1} /3 Mn 1/3] O , the output characteristics when used, the _second material as a hybrid (hybrid) power for an electric vehicle LiCoO ₂ or less than LiMn ₂ O ₄ . In order to solve this problem, a method of treating conductive carbon black on the surface (Japanese Patent Laid-Open No. 2003-59491) or a surface treatment method using a silane coupling agent (Japanese Patent Laid-Open No. 2002-367610, 2007-280830) has been proposed, but many improvements have been made. Is not reported yet.

Lithium secondary batteries have a problem in that their lifespan drops rapidly as they are repeatedly charged and discharged. This problem is particularly acute at high temperatures. This is due to a phenomenon in which the electrolyte is decomposed or the active material is deteriorated due to moisture or other effects in the battery, and thus the interface resistance between the electrode and the electrolyte including the active material is increased. Many efforts have been made to solve this problem.

Korean Patent Publication No. 10-277796 discloses a technique of coating a metal oxide by coating a metal such as Mg, Al, Co, K, Na, Ca on the surface of the positive electrode active material and heat-treating in an oxidizing atmosphere.

In addition, a technique for improving energy density and high rate characteristics by adding TiO ₂ to a LiCoO ₂ active material has been studied ( Electrochemical and Solid-State Letters , 4 (6) A65-A67 2001). Recently, a method of modifying the surface of a positive electrode active material with a lithium metal phosphate compound (Korean Patent Publication No. 2007-0119929) and a technique containing sulfur or phosphorus in the vicinity of the surface of a positive electrode active material particle (Japanese Patent Laid-Open No. 2007-335331) are known.

However, the problem of structural transition on the surface of the positive electrode active material due to the reaction between the electrolyte and the positive electrode active material or the attack of hydrofluoric acid has not been solved. In addition, a phenomenon in which an active material is dissolved by an acid generated by oxidation of an electrolyte during charging is introduced as a cause of a decrease in capacity of a battery ( Journal of Electrochemical Society , 143, 2204). 1996). Various electrolyte additives have been studied to suppress the reactivity between the electrolyte and the cathode active material. Recently, the Republic of Korea Patent Publication No. 2007-0120842 discloses the high temperature of the battery using benzoate, phthalate, malate, succinate and citrate, which are electrolyte additives that reduce the concentration of hydrofluoric acid which is present in the battery, resulting in performance degradation. Techniques for improving the preservation characteristics and long life characteristics are known. Another method of removing the hydrofluoric acid has been reported to significantly improve the life characteristics of the positive electrode active material at high temperature by coating zinc oxide (ZnO) which reacts well with the hydrofluoric acid to form a compound ( Electrochemical and Solid). State Letters, 5 ( 5), A99-A102 2002).

Recently, Korean Patent Publication No. 2003-32363 discloses a hydride containing a metal of Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, and Zr on the surface of a positive electrode active material. Techniques for coating the hydroxide, oxyhydroxide, oxycarbonate, hydroxycarbonate salts are known. However, this technique also does not solve the problem of reducing the lifetime of the cathode active material, especially LiCoO ₂ at high voltage.

More recently, AlF ₃ is coated on the surface of LiCoO ₂ and Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ active materials to improve the high rate characteristics without decreasing the capacity even at 4.5 V Li / Li ⁺ . ( Electrochem. Commun ., 8 (5), 821-826 2006, Journal of The Electrochemical Society, 154 (3) A168-A172 2007 ). This excellent increase in electrochemical properties is because the AlF ₃ present on the surface has a strong resistance from HF present in the electrolyte and maintains the crystal structure of the surface of the positive electrode active material so that the interface resistance with the electrolyte does not increase and remains constant. However, when AlF ₃ is stored in air, it reacts easily with moisture in the air to form AlF ₃ ㅇ H ₂ O. Therefore, when the AlF ₃ coated cathode active material is exposed to air for a long time, its electrochemical properties may be reduced. In addition, increasing the concentration of hydrofluoric acid in the battery reduces the life characteristics of the positive electrode active material.

One embodiment of the present invention is to reduce the concentration of the hydrofluoric acid generated near the positive electrode active material to protect the positive electrode active material, by suppressing the reaction between the positive electrode active material and the electrolyte, the positive electrode that can significantly improve the phenomenon of reducing the capacity of the battery It is to provide an active material and a method for producing the same.

Another embodiment of the present invention is to provide a lithium secondary battery having a positive electrode including the positive electrode active material and having improved charge / discharge characteristics, lifetime characteristics, high rate characteristics, and thermal stability at high potential.

According to one embodiment of the present invention, a core including a compound capable of reversible intercalation / deintercalation of lithium; And it provides a cathode active material comprising a surface treatment layer of the ammonium-containing fluoride compound containing a surface treatment element on the surface of the core.

According to another embodiment of the invention, the step of drying the ammonium-containing fluoride compound to remove water in the ammonium-containing fluoride compound; And dry mixing a core of a reversible intercalation / deintercalation compound of the ammonium-containing fluoride compound with lithium to coat an ammonium-containing fluoride compound on the surface of the positive electrode active material. It provides a manufacturing method.

Still another embodiment of the present invention comprises the steps of preparing a precursor solution by mixing a solution containing a surface-treated element-containing salt and a core of a compound capable of reversible intercalation / deintercalation of lithium; Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound; And forming a surface treatment layer comprising an ammonium-containing fluoride compound by filtration and drying the coprecipitation compound.

In another aspect, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte including the positive electrode active material.

The positive electrode active material coated with the ammonium-containing fluoride compound according to the present invention improves the life characteristics, high voltage characteristics, high rate characteristics, and thermal stability of the lithium secondary battery.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The positive electrode active material according to the present invention improves the charge and discharge characteristics, life characteristics, high voltage characteristics, high rate characteristics, and thermal stability of the lithium secondary battery.

The cathode active material uses a compound capable of reversible intercalation / deintercalation of lithium (hereinafter referred to as a 'core') as a core, and has a structure in which an ammonium-containing fluoride compound is formed as a surface treatment layer on its surface. Have

The core may be a compound capable of reversible intercalation / deintercalation of lithium used as a cathode active material known in the art, and is not particularly limited in the present invention.

Preferably, the core includes a compound having a structure of Formulas 1 to 7 or a mixture thereof.

Li _a Co _1-x M _x O _2-δ X _δ

(In Formula 1, M is Ni, Mn, Mg, Ca, Sr, B, Al, Ga, Si, Ge, Sn, Sb, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, and one of the elements selected from the group consisting of W, X is halogen or sulfur, 0.9≤a≤1.2, 0≤x≤0.2 and 0≤δ≤0.2)

Li _a Ni _1-xyz Co _x Mn _y M _z O _2-δ X _δ

(In Formula 2, M is in the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, and W) One element selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0.02 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.2, and 0 ≦ δ ≦ 0.2)

Li _a Ni _x Co _{1 -2 x} Mn _{x - y} M _y O _{2 -δ} X _δ

(In Formula 3, M is in the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, and W) One element selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.2, and 0 ≦ δ ≦ 0.2).

Li [M _{x / 2} N _{x / 2} Li _{(1 / 3-x / 2)} Mn _{(2 / 3-x / 2)} ] O _2-δ X _δ

(In Formula 4, M is a divalent element of alkaline earth metal (Mg, Ca), Zn, or transition metal (Ni, Co, Cu, Zn) and N is a group 13 element (B, Al, Ga), or transition A trivalent element of a metal (Ni, Co, Cr, Cu, Sc, V, Y), X is halogen or sulfur, and 0 ≦ x ≦ 2/3, 0 ≦ δ ≦ 0.2).

Li _a Mn _2-x M _x O _4-δ X _δ

(In Formula 5, M is M is B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Co, Ni, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, And W is one kind selected from the group consisting of, X is halogen or sulfur, 0.9≤a≤1.2, 0≤x≤0.5, and 0≤δ≤0.2)

Li _a M _x Fe _1-x PO _4-δ X _δ

(In Formula 6, M is in the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, and V One element selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 1 and 0 ≦ δ ≦ 0.2)

Li ₄ Ti ₅ O _12-δ X _δ

(In Formula 7, X is halogen or sulfur, and 0 ≦ δ ≦ 0.2)

In this case, the compounds of Formulas 1 to 4 have a layered crystal rock salt structure, the compounds of Formulas 5 and 7 are spinel compounds having a cubic crystal structure, and the compound of Formula 6 has an olivine (olivine) crystal structure.

The ammonium-containing fluoride compound surface-treated (or coated) on the surface of the core not only solves the problem of dissolving the positive electrode active material by hydrofluoric acid generated during the charge / discharge process of the conventional battery, but also reacts the reaction between the electrolyte solution and the positive electrode active material. Suppress The ammonium cation (NH ₄ ⁺ ) present in the ammonium-containing fluoride compound is easily decomposed due to the weak bonding force between the ammonium-containing fluoride compound. For example, ammonium hexanefluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) compounds are known to decompose into ammonium cations and ammonium tetrafluoroaluminate (NH ₄ AlF ₄ ) around 150 ° C. (Chem. Mater., 12, 1148 2000). This decomposed ammonium tetrafluoroaluminate (NH ₄ AlF ₄ ) compound is decomposed into ammonium cations and γ-AlF ₃ at about 320 ° C. This decomposition reaction is assumed to occur easily by electrochemical reaction at room temperature. Ammonium cations (NH ₄ ⁺ ) thus decomposed are reacted with fluorine anion (F ⁻ ) decomposed from the electrolyte salt LiPF ₆ to form ammonium fluoride (NH ₄ F). Therefore, ammonium-containing fluoride compounds with ammonium cations not only inhibit the formation of hydrofluoric acid in the battery but also exist on the surface of the positive electrode active material to inhibit the reaction between the electrolyte and the surface of the positive electrode active material, thereby maintaining a constant resistance value of the battery, thereby improving its life characteristics. Improves high rate characteristics, thermal stability, etc.

The ammonium-containing fluoride compound constituting the surface treatment layer is a compound represented by NH ₄ AF _x , wherein A is aluminum (Al), yttrium (Y), silicon (Si), germanium (Ge), and boron (B). , Phosphorus (P), titanium (Ti), zirconium (Zr), cerium (Ce), bismuth (Bi) and the like can be selected from, and x is determined according to the valence of A.

Specific examples of the ammonium-containing fluoride compound include ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ), ammonium decafluorotriumate (NH ₄ Y ₃ F ₁₀ ), ammonium hexafluorosilicate ((NH ₄ ) ₂ SiF ₆ ), ammonium hexafluorogermanate ((NH ₄ ) ₂ GeF ₆ ), ammonium tetrafluoroborate (NH ₄ BF ₄ ), ammonium hexafluorophosphate (NH ₄ PF ₆ ), ammonium hexafluoro titanate (( NH ₄ ) ₂ TiF ₆ ), ammonium hexafluorozirconate ((NH ₄ ) ₂ ZrF ₆ ), ammonium hexafluoroceriumate ((NH ₄ ) ₂ CeF ₆ ), ammonium decafluorobismusate (NH ₄ Bi ₃ F ₁₀ ), ammonium tetrafluoroaluminate (NH ₄ AlF ₄ ), or mixtures thereof.

The ammonium-containing fluoride compound to be surface treated at this time is contained in an amount of 0.005 to 10 mol, preferably 0.01 to 5 mol, more preferably 0.02 to 2 mol with respect to 100 mol of the core. If the content of the ammonium-containing fluoride compound is less than 0.01 mole, the coating effect is not sufficiently exhibited. On the contrary, if the content of the ammonium-containing fluoride compound exceeds 10 moles, the initial discharge capacity and the high rate characteristic of the lithium secondary battery may not be sufficiently increased.

The positive electrode active material in which the ammonium-containing fluoride layer present on the surface of the compound core capable of reversible intercalation / deintercalation of lithium is formed by the acid produced by oxidation of the electrolyte during the charging process of the conventional battery. Not only does it solve the problem of dissolving the active material, but also suppresses the reaction between the electrolyte and the positive electrode active material and keeps it constant without increasing the interface resistance according to the charge / discharge cycle.

A core as described above; And an ammonium-containing fluoride compound on the surface of the core may be prepared by a dry method and a wet method.

The drying method includes drying the ammonium-containing fluoride compound to remove water in the ammonium-containing fluoride compound (S11); And dry mixing the core of the ammonium-containing fluoride compound with a compound capable of reversible intercalation / deintercalation of lithium to coat an ammonium-containing fluoride compound on the surface of the positive electrode active material (S12).

Drying of the ammonium-containing fluoride compound (S11) is preferably vacuum dried at 100 to 150 ℃ for 1 hour to 24 hours, but is not limited thereto.

Dry mixing of the ammonium-containing fluoride compound and the core (S12) may be performed by a hybridization method, a mechano fusion, a speed mill, or a ball mill, but is not limited thereto. no. This mixing process causes the ammonium-containing fluoride compound to physically adhere to the surface of the core. The mixing ratio of the ammonium-containing fluoride compound and the core is adjusted to be 0.005 to 10 mol, preferably 0.01 to 5 mol, more preferably 0.02 to 2 mol relative to 100 mol of the core of lithium. In one example, the ammonium-containing fluoride compound and the core may be mixed in a molar ratio of 0.01: 99.99 to 10:90. When mixed by a ball mill process, the weight ratio of the ball and the mixture (mixture of core and ammonium-containing fluoride compound) may be 10:90 to 60:40. If the mixture is greater than 90 parts by weight, the compressive stress may not be sufficiently delivered to the mixture. If the mixture is less than 40 parts by weight, more than necessary balls are used to lower the yield. In addition, the ball may be a stainless ball or zirconia ball of 0.1 to 10mm in diameter.

The wet method includes preparing a precursor solution by mixing a solution containing a surface-treated element-containing salt and a core of a compound capable of reversible intercalation / deintercalation of lithium (S21); Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound (S22); And drying the co-precipitation compound after filtration (S23). The wet method is carried out using coprecipitation properties between the surface treatment element-containing salt and the fluoride compound. The process flowchart of the wet method is shown in FIG. 1.

Referring to FIG. 1, first, a solvent is injected into a reactor, a surface treatment element-containing salt is added, and then uniformly mixed to prepare a surface treatment element-containing salt solution, and then to the prepared surface treatment element-containing salt solution. As a core to be surface treated, a compound capable of reversible intercalation / deintercalation of lithium is added and uniformly mixed to prepare a precursor solution (S21).

It is also possible to prepare the precursor solution by simultaneously placing the surface treatment-element containing salt and the core in a reactor in which a solvent is injected.

The surface treatment element-containing salt is aluminum (Al), yttrium (Y), silicon (Si), germanium (Ge), boron (B), phosphorus (P), titanium (Ti), zirconium (Zr), cerium ( One compound selected from the group consisting of alkoxides, sulfates, nitrates, carbonates, acetates, chlorides, and phosphates comprising one element selected from the group consisting of Ce), bismuth (Bi) and combinations thereof is possible.

The solvent used is preferably a solvent in which the salt can be dissolved, and a solvent having good miscibility with a fluoride compound solution to be added later is possible. Typically, single or mixed solvents thereof selected from the group consisting of water, alcohols and ethers are used. At this time, the alcohol is preferably C1 to C4 lower alcohols selected from the group consisting of methanol, ethanol, isopropanol and combinations thereof. In addition, the ether is preferably ethylene glycol or butylene glycol.

In this case, the surface treatment element-containing salt is 0.005 to 10 mol based on 100 mol of the core, in which the ammonium-containing fluoride compound including the surface treatment element to be prepared is a compound capable of reversible intercalation / deintercalation of lithium. The content is adjusted to be preferably 0.01 to 5 moles, more preferably 0.02 to 2 moles.

The prepared precursor solution is adjusted so that the concentration of the precursor is 0.001 M to 0.1 M. If the concentration of the precursor is less than 0.001 M, it is difficult to form a sufficient amount of the surface treatment layer on the core due to insufficient reaction with the fluoride compound in a subsequent process. On the contrary, if the content exceeds 0.1 M, it is difficult to coat the surface of the core due to excessive reaction with the fluoride compound in the subsequent process to be coated, so that the coating is appropriately selected within the above range.

At this time, the preparation of the precursor is carried out by stirring at 50 to 1000 rpm for 2 to 48 hours at a temperature of 50 to 100 ℃. In this case, when the reaction temperature is less than 50 ° C., it is difficult to prepare a uniform precursor solution. On the contrary, when the reaction temperature is 100 ° C. or more, the solvent evaporates. In addition, the stirring is performed using a conventional stirring device, typically in a reactor to which an impeller is attached.

Next, after the fluoride compound solution is added to the precursor solution prepared above, a coprecipitation compound is obtained through reaction with a surface treatment element (S22).

The fluoride compound may be one containing fluorine (F), such as NH ₄ F, NH ₄ HF ₂ , HF, AHF (Anhydrous hydrogen fluoride) containing fluorine (F) may be selected from the group consisting of a combination thereof Provided is a method for producing a fine powder fluorine compound, which is at least one compound. At this time, the solvent used is the same as the solvent of the precursor solution, or a solvent having excellent miscibility.

This fluoride compound reacts with the surface treatment element present around the core in the precursor solution to form an ammonium fluoride complex compound and together with the core to form a fine powder of high dispersion. The high dispersion fine powder is not dissolved in a solvent to obtain a coprecipitation compound and precipitates as it is to the bottom of the reactor.

The coprecipitation compound may be obtained in the form of large particles due to the strong pulverization phenomenon due to the characteristics of the fine powder of high dispersion, wherein the larger the particle size, the lower the properties of the positive electrode active material. Therefore, to obtain co-precipitation compounds in the form of highly dispersed fine powders, it is necessary to control the concentration of the reactants, the dropping rate, the stirring speed and the reaction temperature.

This coprecipitation reaction is carried out for 3 to 48 hours by dropping the fluoride compound solution at a constant rate by stirring at a rate of 50 to 1000 rpm at a temperature of 50 to 100 ℃. If the reaction temperature is less than 50 ℃ coprecipitation does not occur well, if more than 100 ℃ reaction rate is increased to greatly increase the particles of the material forming the surface treatment layer to reduce the coating effect.

Moreover, the addition of the fluoride compound solution is slowly adding the fluoride compound solution at a constant rate while mixing well in a state in which the core alone in the precursor solution does not precipitate inside the reactor.

Next, when the coprecipitation compound obtained above is filtered and then dried to remove moisture, an ammonium-containing fluoride compound containing a surface treatment element present on the surface of the coprecipitation compound is present (S23). The filtration and drying may be carried out using a device commonly used in this field. At this time, the drying is performed for 15 to 30 hours at atmospheric pressure or vacuum at 120 to 200 ℃.

Through this step, a cathode active material having a surface treatment layer of an ammonium-containing fluoride compound containing a surface treatment element on the surface of the core is prepared (S24).

The positive electrode active material according to the present invention, prepared by the method described above, is preferably applied as a positive electrode active material of a positive electrode of a lithium secondary battery.

The lithium secondary battery may include a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material capable of intercalating and deintercalating lithium ions; And an electrolyte between the positive electrode and the negative electrode, wherein the core comprises a compound capable of reversible intercalation / deintercalation of lithium according to the present invention as the positive electrode active material; And a surface treatment layer of an ammonium-containing fluoride compound on the surface of the core.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, and the like, Depending on the size, it can be divided into bulk type and thin film type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

2 is a perspective view of a lithium secondary battery according to an embodiment of the present invention. FIG. 2 shows the preparation of the electrode assembly 9 by placing the separator 7 between the cathode 3, the anode 5, the cathode 3, and the anode 5 and placing it in the case 15. Injection is performed so that the cathode 3, the anode 5, and the separator 7 are impregnated with the electrolyte. The negative electrode 3 and the positive electrode 5 serve to collect current generated during battery operation, and conductive lead members are respectively attached to each other, and the lead members respectively induce positive and negative currents generated from the positive and negative terminals. Done. Although the pouch type secondary battery is illustrated in the drawings, the lithium secondary battery of the present invention is not limited to this shape, and any shape capable of operating as a battery is possible.

In this case, the positive electrode is manufactured using the positive electrode active material according to the present invention. The positive electrode may be prepared by mixing the positive electrode active material, the conductive material, and the binder to prepare a composition for forming a positive electrode active material layer, and then rolling the composition after applying the composition to a positive electrode current collector such as aluminum foil.

As the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or polypropylene may be used. It may be, but is not limited thereto.

In addition, in the battery constituted as the conductive material, any electronic conductive material can be used without causing chemical change. For example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel , Metal powders such as aluminum and silver, metal fibers, and the like can be used, and conductive materials such as polyphenylene derivatives can be mixed and used.

The negative electrode includes a negative electrode active material. As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material may be a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, or the like. In addition to the carbonaceous material, a metal compound capable of alloying with lithium, or a composite containing a metal compound and a carbonaceous material may also be used as the negative electrode active material. As a metal which can be alloyed with lithium, Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, Al alloy, etc. can be illustrated. Moreover, a metal lithium thin film can also be used as a negative electrode active material.

Like the positive electrode, the negative electrode may be prepared by mixing the negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then coating the negative electrode current collector such as copper foil.

As the electrolyte charged in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the non-aqueous organic solvent, a carbonate, ester, ether or ketone solvent may be used. As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, or the like may be used.

The separator may exist between the positive electrode and the negative electrode according to the type of the lithium secondary battery. 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 / It goes without saying that a mixed multilayer film such as a polypropylene three-layer separator can be used.

At this time, by using the positive electrode active material according to the present invention as a positive electrode not only solves the problem of dissolving the positive electrode active material by the acid generated by the oxidation of the electrolyte during the charging process of the conventional battery, but also suppresses the reaction between the electrolyte solution and the positive electrode active material. As a result, the charge and discharge characteristics, lifespan characteristics, high voltage characteristics, high rate characteristics, and thermal stability of the lithium secondary battery are improved. Especially when used at high voltage, the effect is increased.

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

Example 1 Ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) LiCoO including surface modification layer ₂  Preparation of Cathode Active Material

0.5 g of ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) from which moisture was removed by vacuum drying at 120 ° C. for 15 hours was added to a ball mill and 100 g of LiCoO ₂ (Japan Chemicals C5) was added and ball milled at room temperature for 1 hour. Ammonium hexafluoroaluminate was coated on the LiCoO ₂ active material powder to prepare a positive electrode active material. The coating amount of (NH ₄ ) ₃ AlF ₆ in the prepared cathode active material was 0.25 mol%.

(Example 2)

Except 0.25 g of ammonium hexafluoroaluminate coated on 100 g of LiCoO ₂ active material powder (1 mol of LiCoO ₂ : 0.00125 mol of (NH ₄ ) ₃ AlF ₆ ), and the surface treatment was carried out in the same manner as in Example 1 An active material was prepared.

(Example 3)

The same method as in Example 1, except that 0.15 g of ammonium hexafluoroaluminate was coated on 100 g of LiCoO ₂ active material powder (1 mol of LiCoO ₂ : 0.0008 mol of (NH ₄ ) ₃ AlF ₆ ). Surface treatment was carried out to prepare a cathode active material.

(Example 4)

Except for coating 1 g of ammonium hexafluoroaluminate on 100 g of LiCoO ₂ active material powder (1 mol of LiCoO ₂ : 0.005 mol of (NH ₄ ) ₃ AlF ₆ ), the surface treatment was carried out in the same manner as in Example 1 to obtain a positive electrode active material Was prepared.

(Example 5)

Except for coating ₂ g of ammonium hexafluoroaluminate on 100 g of LiCoO ₂ active material powder (1 mol of LiCoO ₂ : 0.01 mol of (NH ₄ ) ₃ AlF ₆ ), the surface treatment was carried out in the same manner as in Example 1 to prepare a cathode active material. Was prepared.

(Example 6)

A cathode active material was prepared by performing the same surface treatment as in Example 1 except that 0.5 g of ammonium tetrafluoroaluminate was coated on 100 g of LiCoO ₂ active material powder (1 mol of LiCoO ₂ : 0.0025 mol of NH ₄ AlF ₄ ). It was.

(Comparative Example 1)

LiCoO ₂ was used as a cathode active material (Japanese Chemical C5).

Experimental Example 1 Concentration Analysis of Hydrofluoric Acid

100 mg of the positive electrode active material prepared in Examples 1 to 6 and Comparative Example 1 was added to 10 ml of an electrolyte in which 1 M LiPF ₆ was dissolved in EC: DEC (1: 1 vol.%), And stored at 60 ° C. for 1 week. Table 1 shows the concentration of hydrofluoric acid contained in the electrolyte solution in which each sample was dissolved. The concentration of hydrofluoric acid was used for neutralization titration, and the indicator used was bromothylmol blue (BTB).

For comparison, the concentration of hydrofluoric acid was measured in the same manner as described above for the electrolyte solution of 1 M LiPF ₆ in EC: DEC (1: 1 vol%).

[Table 1]

sample Concentration of residual hydrofluoric acid (ppm) Example 1 LiCoO ₂ coated with 0.25 mol% (NH ₄ ) ₃ AlF ₆ 61 Example 2 LiCoO ₂ coated with 0.125 mol% (NH ₄ ) ₃ AlF ₆ 84 Example 3 LiCoO ₂ coated with 0.08 mol% (NH ₄ ) ₃ AlF ₆ 126 Example 4 LiCoO ₂ coated with 0.5 mol% (NH ₄ ) ₃ AlF ₆ 45 Example 5 LiCoO ₂ coated with 1 mol% (NH ₄ ) ₃ AlF ₆ 20 Example 6 LiCoO ₂ coated with 0.25 mol% NH ₄ AlF ₄ 97 Comparative Example 1 LiCoO ₂ 250 reference Electrolyte with 1M LiPF ₆ dissolved in EC: DEC 250

As can be seen from Table 1, the concentration of hydrofluoric acid remaining in the electrolyte decreased as the coating amount of ammonium hexafluoroaluminate increased. It was found that more Foshan remained. This is because the ammonium hexafluoroaluminate contains a greater amount of ammonium cation, so it reacts more with the fluorine anion to lower the concentration of hydrofluoric acid.

(Examples 7 to 13) Preparation of Half Cells

In order to evaluate the properties of the positive electrode active materials prepared in Examples 1 to 6 and Comparative Example 1, acetylene black, graphite (KS6, manufactured by Lonza), bonding as the positive electrode active materials and conductive materials of Examples 1 to 6 and Comparative Example 1 A slurry was prepared by mixing zero polyvinylidene fluoride (PVdF) in a weight ratio of 85: 3.75: 3.75: 7.5. The slurry was uniformly coated on an aluminum foil having a thickness of 20 μm, dried at 110 ° C., and pressed by a roll press to prepare a positive electrode.

Example 7 according to a conventional manufacturing process of a lithium battery using an electrolyte prepared by using a positive electrode and a lithium metal as a counter electrode, and an electrolyte solution in which 1 mol LiPF ₆ is dissolved in an ethylene carbonate: dimethyl carbonate (1: 1 volume ratio) mixed solvent. To 2032 standard coin cell (coin cell) of 13 to Comparative Example 2 were prepared.

(Experimental example 2) Life characteristic evaluation of the half coin battery

The cycle life characteristics were evaluated using half coin cells prepared according to Examples 7-13 and Comparative Example 2 above. Cycle life characteristics were evaluated at a current density of 0.5 C-rate (50 mA / g) in the voltage range of 3.0 to 4.5 V, and the evaluation temperature was 25 ° C. The life characteristics were obtained from the following equations and the results of Examples 7 to 10, 11 and Comparative Example 2 are shown in Table 2.

Life characteristics (%) = (discharge capacity at 50 cycles / 1 discharge capacity at cycles) x 100

TABLE 2

sample Initial capacity (mAh / g) Life Characteristics (%) Example 7 LiCoO ₂ coated with 0.25 mol% (NH ₄ ) ₃ AlF ₆ 182 97.5 Example 8 LiCoO ₂ coated with 0.125 mol% (NH ₄ ) ₃ AlF ₆ 181 96.8 Example 9 LiCoO ₂ coated with 0.08 mol% (NH ₄ ) ₃ AlF ₆ 183 94.3 Example 10 LiCoO ₂ coated with 0.5 mol% (NH ₄ ) ₃ AlF ₆ 180 89.7 Example 12 LiCoO ₂ coated with 0.25 mol% NH ₄ AlF ₄ 182 92.7 Comparative Example 2 LiCoO ₂ 179 60.6

As can be clearly seen in Table 2, Examples 7 to 10 including the positive electrode active material coated with ammonium hexafluoroaluminate were found to have a very good life characteristics as compared to Comparative Example 2 without coating, 0.25 mol% day The best time was 97.5%. In the case of the samples coated with ammonium hexafluoroaluminate, the initial dose decreased slightly as the coating amount increased, and the capacity retention rate increased to 0.25 mol%, and then decreased. In addition, in the case of ammonium tetrafluoroaluminate using the same coating amount, the initial capacity was the same as that of ammonium hexafluoroaluminate, but the life characteristics decreased slightly. This result is in good agreement with the decrease in the concentration of hydrofluoric acid in Table 1.

Experimental Example 3 Evaluation of Thermal Stability Characteristics

Using a half coin battery prepared according to Examples 7 to 12 and Comparative Example 2, constant current constant voltage charging was performed up to 4.5 V after 3-cycle charging and discharging at 0.2 C-rate (20 mA / g) in the range of 3.0 to 4.5 V. It was. At this time, the charging current was charged until the current reached 1/20 of the constant current charging current. The 4.5V rechargeable coin cell was disassembled in a dry room to obtain a positive electrode active material, and then placed in a differential scanning calorimeter (200 PC Netzs, Germany) and heated to 400 ° C. at 1 ° C. per minute at room temperature. Table 3 shows the thermal stability characteristics of the samples prepared in Example 7 and Comparative Example 2.

[Table 3]

sample Fever start temperature (℃) Maximum heat generation temperature (℃) Calorific Value (J / g) Example 7 LiCoO ₂ coated with 0.25 mol% (NH ₄ ) ₃ AlF ₆ 196 212.7 2102 Comparative Example 2 LiCoO ₂ 178 198.6 2985

As shown in Table 3, the exothermic onset temperature of the sample surface-treated with ammonium hexafluoroaluminate shifted to 18 ℃ and the maximum exothermic temperature to 14.1 ℃ above the untreated sample, and the calorific value also decreased by 883 J / g. It was. From this, it can be seen that the sample surface-treated with ammonium hexafluoroaluminate has excellent thermal stability characteristics.

Example 14 Ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) Li [Ni including surface modification layer _1/3 Co _1/3 Mn _1/3 ] O ₂  Preparation of Cathode Active Material

5 g of ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) removed from water by vacuum drying at 120 ° C. for 15 hours and Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ ) Ammonium hexafluoroaluminate was added to Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ active material powder by adding 1000g and processing at room temperature for 2 hours using a Mechano fusion device manufactured for this patent experiment. Coated on. In the prepared anode active material, (NH _{4) 3} AlF ₆ The coating amount of _{Li [Ni 1/3 Co 1} /3 Mn 1/3] O 2 was 0.25 mol% 1 mol contrast.

Experimental Example 4 Surface Characteristic Analysis

Scanning electron microscope (SEM, trade name: JSM 6400, company name) was prepared by scanning the surface of the Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ cathode active material surface treated with ammonium hexafluoroaluminate according to Example 14. : (JEOL, Japan) and the obtained result are shown in FIG.

3 is a scanning electron micrograph of the positive electrode active material prepared in Example 14, wherein (NH ₄ ) ₃ AlF ₆ of the fine powder is uniformly on the surface of Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ It can be seen that it is coated.

(Comparative Example 3)

Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ (manufactured by Grand _Chemical Co., Ltd.) was used as the positive electrode active material.

Example 15 and Comparative Example 4 Preparation of Half Cell

Half batteries were manufactured in the same manner as in Examples 7 to 13 and Comparative Example 2, using the positive electrode active materials according to Example 14 and Comparative Example 3.

Experimental Example 5 Evaluation of Life Characteristics of Half Coin Battery

The cycle life characteristics were evaluated using half coin cells prepared according to Example 15 and Comparative Example 3. Cycle life characteristics were evaluated at a current density of 0.5 C-rate (50 mA / g) in the voltage range of 3.0 to 4.3 V, the evaluation temperature was 25 ℃. The lifetime characteristics were obtained from the following equations and the results are shown in Table 4.

Life characteristics (%) = (discharge capacity at 90 cycles / 1 discharge capacity at cycles) x 100

Experimental Example 6 Evaluation of Load Characteristics of a Half Coin Battery

The load characteristics were evaluated using half coin cells prepared according to Example 15 and Comparative Example 3. The load characteristics were evaluated at a constant current of 0.2 C-rate (20 mA / g) at 25 ° C and a voltage range of 3.0 to 4.3 V, with a discharge current of 0.2, 0.5, 1, 2, and 3 C- Rate constant current was evaluated. According to Example 15 and Comparative Example 3, the load characteristics at each discharge current of the fms positive electrode active material are shown in Table 5 obtained from the following equation.

Load characteristic (%) = (discharge capacity at each current / discharge capacity at 0.2 C-rate) x 100

[Table 4]

sample Initial capacity (mAh / g) Life Characteristics (%) Example 15 0.25 mol% (NH ₄ ) ₃ Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ coated with AlF ₆ 154 91.3 Comparative Example 3 Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ 154 75.5

As shown in Table 4, it was found that the life characteristics of the samples surface-treated with ammonium hexafluoroaluminate were much superior.

TABLE 5

As shown in Table 5, the load characteristics of the samples treated with ammonium hexafluoroaluminate were excellent in the entire current range tested. In particular, as the discharge current increased, the difference in the load characteristics between the surface treated samples and the untreated samples increased. And it was found.

Example 16 Ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) Li [Ni including surface modification layer _0.8 Co _0.15 Al _0.05 ] O ₂  Preparation of Cathode Active Material

0.5 g of ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) dehydrated by vacuum drying at 120 ° C. for 15 hours was placed in a ball mill and 100 g of Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ (Toda) was added. Ammonium hexafluoroaluminate was coated on Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ active material powder by ball milling at room temperature for 10 hours. The coating amount of (NH ₄ ) ₃ AlF ₆ in the prepared cathode active material was 0.25 mol% compared to 1 mol of Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ .

(Comparative Example 4)

Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ (Toda) was used as the positive electrode active material.

Example 17 and Comparative Example 5 Preparation of Half Cell

Half batteries were manufactured in the same manner as in Examples 7 to 13 and Comparative Example 2, using the positive electrode active materials according to Example 16 and Comparative Example 4.

Experimental Example 7 Evaluation of Life Characteristics of Half Coin Battery

The cycle life characteristics were evaluated using half coin cells prepared according to Example 17 and Comparative Example 5. Cycle life characteristics were evaluated at a current density of 0.5 C-rate (50 mA / g) in the voltage range of 3.0 to 4.3 V, the evaluation temperature was 25 ℃. The life characteristics were obtained from the following equations and the results are shown in Table 6.

Life characteristics (%) = (discharge capacity at 50 cycles / 1 discharge capacity at cycles) x 100

TABLE 6

sample Initial capacity (mAh / g) Life Characteristics (%) Example 17 0.25 mol% (NH ₄ ) ₃ Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ coated with AlF ₆ 161 97.1 Comparative Example 5 Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ 160 92.0

As shown in Table 6, the initial capacity of the battery according to Example 17 including the positive electrode active material surface-treated with ammonium hexafluoroaluminate was similar to that of Comparative Example 5, but the lifespan characteristics increased by 5% or more.

Experimental Example 8 Evaluation of Thermal Stability Characteristics

Using a half coin battery prepared according to Example 17 and Comparative Example 5, constant current constant voltage charging was performed up to 4.3 V after 3-cycle charging and discharging at 0.2 C-rate (20 mA / g) in the range of 3.0 to 4.3 V. At this time, the charging current was charged until the current reached 1/20 of the constant current charging current. Only 4.3V charged coin battery was disassembled in a dry room to obtain a positive electrode active material and then placed in a differential scanning calorimeter 200 PC Netzs, Germany, and heated to 400 ° C. at 1 ° C. per minute at room temperature. The thermal stability characteristics of the samples prepared in Example 8 and Comparative Example 3 are shown in Table 7.

TABLE 7

sample Fever start temperature (℃) Maximum heat generation temperature (℃) Calorific Value (J / g) Example 17 0.25 mol% (NH ₄ ) ₃ Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ coated with AlF ₆ 235 255 1656 Comparative Example 5 Li [Ni _0.8 Co _0.15 Al _0.05 ] O ₂ 180 227 2152

As shown in Table 7, the exothermic onset temperature of the sample treated with ammonium hexafluoroaluminate was 55 ℃ and the maximum exothermic temperature was shifted to 28 ℃ higher than the untreated sample, and the calorific value also decreased by 496 J / g. . This shows that the sample surface-treated with ammonium hexafluoroaluminate has excellent thermal stability.

Example 18 Ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) Li including surface modification layer _1.05 [Al _0.08 Mn _1.87 ] O ₄  Preparation of Cathode Active Material

After vacuum drying at 120 ° C. for 15 hours, 0.25 g of ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ), from which moisture was removed, was added to a ball mill and 100 g of Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ (Toda) was added. Ammonium hexafluoroaluminate was coated onto Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ active material powder by ball milling for 10 hours at. The coating amount of (NH ₄ ) ₃ AlF ₆ in the prepared cathode active material was 0.22 mol% compared to 1 mol of Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ .

(Comparative Example 6)

Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ (Toda) was used as the positive electrode active material.

Example 19 and Comparative Example 7 Preparation of Half Cell

Half batteries were manufactured in the same manner as in Examples 7 to 13 and Comparative Example 2, using the positive electrode active materials according to Example 18 and Comparative Example 6.

Experimental Example 9 Evaluation of Life Characteristics of Half Coin Battery

The cycle life characteristics were evaluated using the prepared half coin cell. Cycle life characteristics were evaluated at a current density of 0.5 C-rate (50 mA / g) in the voltage range of 3.0 to 4.3 V, the evaluation temperature was 55 ℃. The lifetime characteristics were obtained from the following equations and the results are shown in Table 8.

Life time characteristic (%) = (discharge capacity at 100 cycles / 1 discharge capacity at cycles) x 100

[Table 8]

sample Initial capacity (mAh / g) Life Characteristics (%) Example 19 0.22 mol% (NH ₄ ) ₃ Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ coated with AlF ₆ 101.2 95.0 Comparative Example 7 Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ 100.8 82.8

As shown in Table 8, the battery according to Example 19 including the positive electrode active material surface-treated with ammonium hexafluoroaluminate was almost similar to the battery of Comparative Example 4, but the life characteristics were improved by 12.2%.

Example 20 Ammonium Decafluorobismuthate (NH ₄ Bi ₃ F ₁₀ ) Li including surface modification layer _1.05 [Al _0.08 Mn _1.87 ] O ₄  Preparation of Cathode Active Material

After vacuum drying at 120 ° C. for 15 hours, 0.25 g of ammonium decafluorobismusate (NH ₄ Bi ₃ F ₁₀ ), from which moisture was removed, was added to a ball mill and ₁₀₀ g of Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ (Toda) was added thereto at room temperature. Ammonium hexafluoroaluminate was coated on Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ active material powder by ball milling for 10 hours. The coating amount of (NH ₄ ) ₃ AlF ₆ in the prepared cathode active material was 0.10 mol% compared to 1 mol of Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ .

Using a half coin battery, cycle life characteristics were performed in the same manner as in Example 7. The lifetime characteristics were obtained from the following equations and the results are shown in Table 9.

Life time characteristic (%) = (discharge capacity at 100 cycles / 1 discharge capacity at cycles) x 100

TABLE 9

sample Initial capacity (mAh / g) Life characteristic (%) Example 20 Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ coated with 0.25 mol% NH ₄ Bi ₃ F ₁₀ 99.8 92.3 Comparative Example 6 Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ 100.8 82.8

As shown in Table 9, the initial capacity of the sample treated with ammonium hexafluoroaluminate was almost similar to that of Li _1.05 [Al _0.08 Mn _1.87 ] O ₄ of Comparative Example 4, but the lifespan was improved by 9.5%.

Example 21 Ammonium hexafluoroaluminate using the wet method ((NH ₄ ) ₃ AlF ₆ ) LiCoO including surface modification layer ₂  Preparation of Cathode Active Material

An aqueous 0.013 M Al (NO ₃ ) ₃ 9H ₂ O solution was injected into the reactor, and then 4 kg of LiCoO ₂ , a positive electrode active material, was added. At this time, the reactor was stirred at an impeller speed of 600 rpm while maintaining the temperature at 80 ° C for 2 hours. Subsequently, 2 L of 6 M NH ₄ F aqueous solution was slowly added to the reactor at a flow rate of 1 ml / min, and stirred for 24 hours to precipitate all unreacted materials to obtain a coprecipitation compound.

The coprecipitation compound was collected by filtration and dried in a 110 ° C. warm air thermostat for 12 hours. The dried compound was treated at 140 ° C. under vacuum for 12 hours to prepare a LiCoO ₂ positive electrode active material powder coated with (NH ₄ ) ₃ AlF ₆ . In this case, the prepared cathode active material powder was coated with 0.02 mol of (NH ₄ ) ₃ AlF ₆ per 1 mol of LiCoO ₂ .

Using a half coin battery, the cycle life characteristics were evaluated in the same manner as in Example 7. The lifetime characteristics of the positive electrode active materials prepared from Example 11 and Comparative Example 1 were obtained from the following equations and the results are shown in Table 10.

Life time characteristic (%) = (discharge capacity at 50 cycles / 1 discharge capacity at cycles) x 100

TABLE 10

sample Initial capacity (mAh / g) Life characteristic (%) Example 21 LiCoO ₂ coated with 0.2 mol% (NH ₄ ) ₃ AlF ₆ 181 93.7 Comparative Example 2 LiCoO ₂ 179 60.6

As shown in Table 10, the initial capacity of the battery according to Example 21 including the cathode active material surface-treated with ammonium hexafluoroaluminate was almost similar to that of LiCoO ₂ of Comparative Example 2, but the lifetime characteristics were improved by 33.1%.

Example 22 Ammonium Hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) Li [Ni including surface modification layer _1/3 Co _1/3 Mn _1/3 ] O ₂  High Temperature Life Evaluation of Cathode Active Material

0.5 g of ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) dehydrated by vacuum drying at 120 ° C. for 15 hours was placed in a ball mill and Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ ( 100 g of large purified gold) was added and ball milled at room temperature for 12 hours to coat ammonium hexafluoroaluminate on the powder of Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ active material. The coating amount of (NH ₄ ) ₃ AlF ₆ in the prepared cathode active material was 0.25 mol% compared to 1 mol of Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ .

Experimental Example 10 Evaluation of Life Characteristics of Half Coin Battery

The cycle life characteristics were evaluated using the prepared half coin cell. Cycle life characteristics were evaluated at a current density of 0.5 C-rate (50 mAh / g) in the voltage range of 3.0 to 4.5 V, the evaluation temperature was 55 ℃. The life characteristics are shown in Table 11 as a result from the following equation.

Life time characteristic (%) = (discharge capacity at 100 cycles / 1 discharge capacity at cycles) x 100

TABLE 11

sample Initial capacity (mAh / g) Life characteristic (%) Example 22 0.25 mol% (NH ₄ ) ₃ Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ coated with AlF ₆ 162.4 92.3 Comparative Example 3 Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ 157.4 52

As shown in Table 11, the initial capacity of a battery according to Example 22 including a cathode active material surface-treated with ammonium hexafluoroaluminate was Li [Ni _1/3 Co _1/3 Mn _1/3 ] O of Comparative Example 3. Not only is it better than ₂ , its lifespan is increased by more than 40%.

In general, the cycle characteristics of the battery are largely caused by the reaction between the surface of the positive electrode active material and the electrolyte and the structural change due to the dissolution of the positive electrode active material transition metal by hydrofluoric acid. On the other hand, as shown in Table 1, the positive electrode active material of Examples 1 to 6 surface-modified with ammonium hexafluoroaluminate compound reacted with the hydrofluoric acid in the electrolyte solution to significantly reduce the concentration of the hydrofluoric acid, Tables 2 to 11 As shown in FIG. 2, the cycle characteristics were significantly improved.

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 is within the scope of the present invention.

1 is a flow chart showing a wet manufacturing process of a positive electrode active material according to an embodiment according to the present invention.

2 is a perspective view of a lithium secondary battery according to one embodiment of the present invention.

3 is a scanning electron microscope photograph of the surface of a Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ positive electrode active material surface treated with ammonium hexafluoroaluminate prepared in Example 14 of the present invention.

Claims (21)

delete delete delete delete delete delete Drying the ammonium-containing fluoride compound to remove moisture in the ammonium-containing fluoride compound; And Dry mixing a core of the ammonium-containing fluoride compound and a compound capable of reversible intercalation / deintercalation of lithium to coat an ammonium-containing fluoride compound on the surface of the core to form a surface treatment layer Method for producing a positive electrode active material comprising. The method of claim 7, wherein The ammonium-containing fluoride compound of the surface treatment layer is ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ), ammonium decafluorotriumate (NH ₄ Y ₃ F ₁₀ ), ammonium hexafluorosilicate ((NH ₄ ) ₂ SiF ₆ ), ammonium hexafluorogernate ((NH ₄ ) ₂ GeF ₆ ), ammonium tetrafluoroborate (NH ₄ BF ₄ ), ammonium hexafluorophosphate (NH ₄ PF ₆ ), ammonium hexafluoro titanate ( (NH ₄ ) ₂ TiF ₆ ), ammonium hexafluorozirconate ((NH ₄ ) ₂ ZrF ₆ ), ammonium hexafluoroceriumate ((NH ₄ ) ₂ CeF ₆ ), ammonium decafluorobismusate (NH ₄ Bi ₃ F ₁₀ ), ammonium tetrafluoroaluminate (NH ₄ AlF ₄ ) and a method for producing a positive electrode active material for a lithium secondary battery which is one kind selected from the group consisting of these. The method of claim 7, wherein The dry mixing is a method for producing a cathode active material for a lithium secondary battery, which is carried out by a process selected from the group consisting of hybridization, mechano fusion, speed mill, ball mill, and combinations thereof. Preparing a precursor solution by mixing a surface treatment element-containing salt solution with a core of a reversible intercalation / deintercalation compound of lithium; Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound; And Filtering the dried coprecipitation compound and forming a surface treatment layer including an ammonium-containing fluoride compound on the surface of the core. The method of claim 10, The surface treatment element-containing salt is aluminum (Al), yttrium (Y), silicon (Si), germanium (Ge), boron (B), phosphorus (P), titanium (Ti), zirconium (Zr), cerium ( Lithium secondary selected from the group consisting of alkoxides, sulfates, nitrates, acetates, chlorides, phosphates and combinations thereof comprising one surface treatment element selected from the group consisting of Ce), bismuth (Bi) and combinations thereof Method for producing a positive electrode active material for batteries. The method of claim 10, The salt solution of the surface treatment element is a method for producing a positive electrode active material for a lithium secondary battery using one selected from the group consisting of water, alcohol, ether and combinations thereof as a solvent. The method of claim 10, The precursor solution is a method for producing a cathode active material for a lithium secondary battery that is used at a concentration of 0.005 M to 0.1 M. The method of claim 10, Preparation of the precursor solution is to be carried out at 50 to 100 ℃ a method for producing a positive electrode active material for a lithium secondary battery. The method of claim 10, The fluoride compound is a method for producing a positive electrode active material for a lithium secondary battery using one compound selected from the group consisting of NH ₄ F, NH ₄ HF ₂ , HF, AHF (Anhydrous hydrogen fluoride) and combinations thereof. The method of claim 10, The fluoride compound solution is a method of producing a positive electrode active material for a lithium secondary battery using one selected from the group consisting of water, alcohol, ether and combinations thereof as a solvent. The method of claim 10, The drying is a method of producing a positive electrode active material for a lithium secondary battery that is carried out at atmospheric pressure or vacuum at 120 to 200 ℃. delete The method of claim 7, wherein The core is a method of producing a positive electrode active material for a lithium secondary battery which is one selected from the group consisting of a compound represented by the formula 1 to 7 and mixtures thereof: [Formula 1] Li _a Co _1-x M _x O _2-δ X _δ (In Formula 1, M is Ni, Mn, Mg, Ca, Sr, B, Al, Ga, Si, Ge, Sn, Sb, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, and one of the elements selected from the group consisting of W, X is halogen or sulfur, 0.9≤a≤1.2, 0≤x≤0.2 and 0≤δ≤0.2) [Formula 2] Li _a Ni _1-xyz Co _x Mn _y M _z O _2-δ X _δ (In Formula 2, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0.02 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.2, and 0 ≦ δ ≦ 0.2) (3) Li _a Ni _x Co _1-2x Mn _xy M _y O _2-δ X _δ (In Formula 3, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.2, and 0 ≦ δ ≦ 0.2) [Formula 4] Li [M _{x / 2} N _{x / 2} Li _{(1 / 3-x / 2)} Mn _{(2 / 3-x / 2)} ] O _2-δ X _δ (In Formula 4, M is a divalent element of alkaline earth metal, Zn, or transition metal, N is a group 13 element, or a trivalent element of transition metal, X is halogen or sulfur, 0≤x≤2 / 3 , 0≤δ≤0.2) [Chemical Formula 5] Li _a Mn _2-x M _x O _4-δ X _δ (In Formula 5, M is M is B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W in the group consisting of 1 species selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, and 0 ≦ δ ≦ 0.2) [Formula 6] Li _a M _x Fe _1-x PO _4-δ X _δ (In Chemical Formula 6, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and V) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 1 and 0 ≦ δ ≦ 0.2) [Formula 7] Li ₄ Ti ₅ O _12-δ X _δ (In Formula 7, X is halogen or sulfur, and 0 ≦ δ ≦ 0.2). The method of claim 7, wherein In the dry mixing, the ammonium-containing fluoride compound is mixed in an amount of 0.005 to 10 mol with respect to 100 mol of the core. The method of claim 10, The core is a method of producing a positive electrode active material for a lithium secondary battery which is one selected from the group consisting of a compound represented by the formula 1 to 7 and mixtures thereof: [Formula 1] Li _a Co _1-x M _x O _2-δ X _δ (In Formula 1, M is Ni, Mn, Mg, Ca, Sr, B, Al, Ga, Si, Ge, Sn, Sb, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, and one of the elements selected from the group consisting of W, X is halogen or sulfur, 0.9≤a≤1.2, 0≤x≤0.2 and 0≤δ≤0.2) [Formula 2] Li _a Ni _1-xyz Co _x Mn _y M _z O _2-δ X _δ (In Formula 2, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0.02 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.2, and 0 ≦ δ ≦ 0.2) (3) Li _a Ni _x Co _1-2x Mn _xy M _y O _2-δ X _δ (In Formula 3, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.2, and 0 ≦ δ ≦ 0.2) [Formula 4] Li [M _{x / 2} N _{x / 2} Li _{(1 / 3-x / 2)} Mn _{(2 / 3-x / 2)} ] O _2-δ X _δ (In Formula 4, M is a divalent element of alkaline earth metal, Zn, or transition metal, N is a group 13 element, or a trivalent element of transition metal, X is halogen or sulfur, 0≤x≤2 / 3 , 0≤δ≤0.2) [Chemical Formula 5] Li _a Mn _2-x M _x O _4-δ X _δ (In Formula 5, M is M is B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W in the group consisting of 1 species selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, and 0 ≦ δ ≦ 0.2) [Formula 6] Li _a M _x Fe _1-x PO _4-δ X _δ (In Chemical Formula 6, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and V) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 1 and 0 ≦ δ ≦ 0.2) [Formula 7] Li ₄ Ti ₅ O _12-δ X _δ (In Formula 7, X is halogen or sulfur, and 0 ≦ δ ≦ 0.2).

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