KR101452950B1 - Lithium Nickel-based Oxide for Cathode Active Material of Secondary Battery and Method for Preparation of the Same - Google Patents

Abstract

The invention can be used as a cathode active material of a secondary battery, the general formula _{LiNi 1 - x M x O 2} ( wherein, x is in the range from 0≤x <0.3, M is Co, Mn, Zr, Si, Sn and Fe , And the particle type is a monolith structure. The lithium nickel-based oxide according to claim 1,

Accordingly, surface impurities such as Li ₂ CO ₃ and LiOH are minimized to prevent the reduction of the battery capacity and the swelling phenomenon, and the secondary battery including the secondary battery is excellent in high temperature stability, Can be improved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium nickel-based oxide for a cathode active material of a secondary battery, and a method of manufacturing the lithium nickel-

The present invention relates to a lithium nickel oxide for a cathode active material of a secondary battery, and more particularly to a lithium nickel oxide used as a cathode active material of a secondary battery, represented by the formula LiNi _{1 - x} M _x O ₂ , Structure, which minimizes surface impurities and prevents the reduction in battery capacity and the swelling phenomenon, thereby greatly improving the high-temperature stability, battery capacity, and charge-discharge characteristics of the secondary battery .

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It is commercialized and widely used.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of the lithium secondary battery. In addition, a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, (LiNiO ₂ ) is also being considered.

Of the above cathode active materials, LiCoO ₂ has excellent properties such as excellent cycle characteristics and is widely used at present. However, LiCoO ₂ has low safety, is expensive due to the resource limit of cobalt as a raw material, and is used as a power source for fields such as electric vehicles There is a limit.

Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have attracted much attention as a cathode active material capable of replacing LiCoO ₂ because they have the advantage of using manganese rich in resources and environment friendly as a raw material. However, these lithium manganese oxides have disadvantages such as small capacity and poor cycle characteristics.

On the other hand, lithium-nickel-based oxides such as LiNiO ₂ have a lower cost and a lower discharge capacity than the cobalt-based or manganese-based oxides. In recent years, studies on such nickel-based cathode active materials have been actively conducted .

However, since the lithium nickel-based positive electrode active material is in the form of secondary particles in which primary small particles are aggregated, lithium ions move to the surface of the active material and react with moisture or CO ₂ in the air to form Li ₂ CO ₃ , LiOH, and the like.

Therefore, when the lithium nickel oxide is used as the cathode active material, such surface impurities reduce the capacity of the battery or generate a gas by decomposition in the battery, thereby causing a swelling phenomenon of the battery. Therefore, Lt; / RTI &gt;

Therefore, there is a high need for a technique capable of achieving high-temperature safety by reducing the formation of surface impurities while using a lithium-nickel-based positive electrode active material suitable for high capacity.

In this connection, Korean Patent Application Laid-Open No. 2005-0052266 discloses a method in which a hydroxide containing nickel and cobalt and a lithium-containing compound are uniformly mixed and the mixture is subjected to a first heat treatment at 600 to 1,100 ° C for 2 to 30 hours , And a second heat treatment is performed at 700 to 900 ° C for 5 to 30 hours, whereby the amount of carbon present on the surface is 0.3% by weight or less based on the positive electrode active material.

However, since the above-described technique is subjected to a heat treatment process at a relatively high temperature for a long time, the manufacturing cost is increased and the production efficiency is lowered.

On the other hand, Japanese Patent No. 3008793 and No. 3232943 discloses a crystal structure is substantially a single phase (single phase) of the formula _{LiNi x Mn (1-x)} O 2 (0.70≤x≤0.95) or LiNi _x Co _{(1- x)} O ₂ (0.50? _x? 0.95), an alkali solution is added to a mixed solution of a nickel salt and a manganese salt or a cobalt salt, co-precipitating the mixed hydroxide is mixed with a lithium compound, And how to do it. Korean Patent Application Laid-Open No. 1999-014589 discloses a process for obtaining an aqueous metal salt solution of Li (M ₁ M ₂ ) Mn ₂ O ₄ in order to synthesize a single phase in which a secondary phase such as Mn ₂ O ₃ does not coexist , A method of adding a surfactant and a liquid film-strengthening agent to the aqueous solution to emulsify, and a method of drying and calcining the cathode active material powder.

However, in order to solve the problem that the capacity is drastically reduced due to the change of the crystal structure upon charging and discharging due to the unstable crystal structure of the lithium nickel-based oxide, the above-mentioned technologies are limited to manufacturing a lithium nickel oxide having a single- However, since the generation of surface impurities is not minimized in spite of the single crystal structure as described above, the problem of high temperature safety and capacity reduction can not be solved.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that when a lithium nickel oxide having a monolith structure is used as a cathode active material, surface impurities are minimized, It has been found that the high temperature stability, the battery capacity and the charge / discharge characteristics of the secondary battery can be greatly improved by preventing the swelling phenomenon, and the present invention has been accomplished.

Therefore, the lithium nickel oxide according to the present invention is a material which can be used as a cathode active material of a lithium secondary battery and has the formula LiNi _{1 - x} M _x O ₂ (where x is in the range of 0? X < 0.3, Is one or two or more selected from the group consisting of Co, Mn, Zr, Si, Sn and Fe) and has a monolith structure.

In the present invention, 'monolith particle structure' means a structure in which particles are present as independent phases in a morphology without mutual agglomeration. As compared with the monolithic structure, there is a structure in which small-sized particles ('primary particles') physically and / or chemically aggregate to form relatively large-sized particle shapes ('secondary particles') . Many conventional cathode active materials consist of such an agglomerated structure, which does not belong to the single particle structure of the present invention.

Thus, since the lithium nickel oxide according to the present invention has a monodisperse particle structure, the migration path for reaching the surface of the lithium ion to the oxide becomes long, and therefore, lithium ions migrated to the surface of the active material, Or CO ₂ to minimize formation of surface impurities such as Li ₂ CO ₃ and LiOH adsorbed on the oxide surface.

Therefore, there are many problems that can be caused by surface impurities, such as a reduction in cell capacity, an increase in interfacial resistance due to migration of lithium ions, generation of gas due to decomposition of impurities, and swelling of the resulting battery, As a result, the secondary battery including the secondary battery has excellent capacity, high temperature stability, and charge / discharge characteristics.

Furthermore, the lithium nickel oxide according to the present invention has a discharge capacity as high as 20% or more as compared with the case of using a conventional lithium cobalt oxide as a cathode active material, and thus can be more effectively used for a high capacity battery.

In the lithium nickel oxide according to the present invention, the surface BET is preferably 0.2 or less. Generally, it is known that the larger the surface BET is, the wider the ion contact area increases the output characteristics. However, since the lithium ions move to the surface of the active material and have a greater chance of reacting with moisture or CO ₂ in the air, There is a problem that the possibility of adsorption of impurities increases. In this connection, according to the experiments performed by the present inventors, when the surface BET of the lithium nickel-based oxide having a monodisperse particle structure is 0.2 or less, not only the adsorption of surface impurities can be significantly reduced, And the desired output characteristics can be exhibited.

The lower limit value of the surface BET is determined substantially by the outer shape of the particle, for example, the lowest value in the complete spherical form of a smoothly expressed state.

If the particle size of the lithium nickel oxide particles is too small, the crystals are not well developed and the reversibility of charging / discharging may be lowered, and a problem that an aggregated phase can be formed arises. However, there is a limit in increasing the particle size in the production process of the oxide, and when the average particle size is too large, the efficiency of the battery decreases with respect to weight, and a relatively small amount of the cathode active material is contained or the coating property , Which may degrade the capacity of the battery, which may be lost during the manufacturing process of the electrode.

As described above, the lithium nickel oxide according to the present invention is represented by the formula LiNi _{1 -x} M _x O ₂ , and when the content (x) of the dopant is 0.3 or more, it may cause distortion or collapse of the crystal structure The capacity of the battery can be lowered by interfering with the movement of lithium ions, so x should be in the range of 0? X <0.3.

The dopant may be selected from one or more of Co, Mn, Zr, Si, Sn and Fe, with Co and / or Mn being particularly preferable.

The lithium nickel based oxide may, for bars which may comprise all of the lithium nickel-based oxide with various compositions within the composition range, for _{example, LiNiO 2, LiNi 0 .5 Mn} 0 .5 O 2, LiNi 0.5 Co 0.5 O 2 And the like, but the present invention is not limited thereto.

The present invention also provides a process for producing the lithium nickel-based oxide. The manufacturing method according to the present invention, specifically,

i) preparing a nickel-containing precursor capable of achieving a monolithic particle structure after firing;

ii) mixing the nickel-containing precursor, the lithium-containing precursor, and optionally the dopant-containing precursor; And

iii) calcining the mixture;

As shown in FIG.

Thus, by conducting a series of reactions using a nickel-containing precursor capable of forming a monolithic particle form after firing, the desired lithium nickel-based oxide can be produced by a continuous process without any additional process .

The nickel-containing precursor should be capable of forming a monolithic particle structure in at least subsequent steps of mixing and firing, so as to achieve a monolithic particle structure after firing. Preferably, the precursor phase already has a monolithic particle structure, so that it can be converted into a lithium nickel-based oxide without any change in shape during mixing and firing.

One preferred example of such a nickel-containing precursor is Ni metal powder. Nickel metal powders are very economical since they can be made in a low cost process under relatively mild conditions. Further, according to the experiments performed by the present inventors, when the nickel metal powder is used as the precursor, the lithium particles can penetrate to the deep portion of the nickel metal powder within a relatively short period of time in the firing step, It was confirmed that low surface BET can be obtained by lowering the energy and facilitating the formation of monolithic structure.

Another example of a nickel-containing _{precursor, Ni (OH) 2, NiO} , NiOOH, NiCO 3 and 2Ni (OH) ₂ and 4H ₂ O, NiC ₂ O ₄ and _{2H 2 O, Ni (NO 3} ) 2 and 6H ₂ O, Ni 2 _{S 4} O ₄ , Ni _{2 S 4} O ₄ .6H ₂ O, nickel halide, and the like, but are not limited thereto.

The lithium-containing precursor is not particularly limited and includes, for example, lithium hydroxide, Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , Lithium acetate, dicarboxylic acid Li, citric acid Li, fatty acid Li, alkyl Li, lithium halide, and the like, preferably lithium hydroxide.

In the lithium nickel oxide according to the present invention, the dopant is selected from Co, Mn, Zr, Si, Sn and Fe, and the dopant-containing precursor may be a known precursor of a desired dopant. Or more.

When a metal dopant is used, the charge / discharge performance per unit mass of the active material can be improved, the electrochemical stability is enhanced, and the temperature performance is improved.

The nickel-containing precursor, lithium-containing precursor and optionally doped dopant are uniformly mixed and then subjected to a sintering process to form a monolithic particle.

If the temperature is too high in the step iii), it is difficult to form a monolithic particle structure due to nonuniform growth of the particles. On the contrary, if the temperature is too low, the bulk density and crystallinity are lowered and it may be difficult to maintain a stable shape. If the baking time is too short, it is difficult to obtain a highly crystalline lithium nickel oxide. On the other hand, if the baking time is too long, the grain size of the particles may become excessively large and the production efficiency may be lowered. Therefore, the firing process of step iii) may be performed for a suitable time in consideration of the temperature range. However, when nickel hydroxide is used as the nickel-containing precursor, it is preferable to carry out a firing process for a relatively long time in order to obtain a desired monolithic structure.

The present invention also provides a cathode active material for a secondary battery comprising the lithium nickel oxide.

The cathode active material according to the present invention may be composed only of the lithium nickel oxide of the monolithic structure, and may be constituted together with other lithium-containing transition metal oxides in some cases.

Examples of the lithium-containing transition metal oxide include a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; The formula Li _{1 + y} Mn _{2 - y} O ₄ (Where y is 0 to 0.33), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1 - y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2 - y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The present invention also provides a lithium secondary battery comprising the cathode active material. The lithium secondary battery generally comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt, and a method of manufacturing the lithium secondary battery is well known in the art, and thus a detailed description thereof will be omitted herein.

Hereinafter, the positive electrode, the negative electrode, the separator, the lithium salt-containing nonaqueous electrolyte and the like, which are components of the secondary battery according to the present invention, will be described.

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying and drying an anode active material on an anode current collector, and may further include the above-described components as needed.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li y Fe 2 O 3 (0≤y≤1} ), Li y WO 2 (0≤y≤1), Sn x Me 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

As described above, the lithium nickel oxide according to the present invention has a monolith structure, which minimizes surface impurities, thereby preventing battery capacity reduction and swelling phenomenon, The secondary battery has excellent high-temperature stability, battery capacity, and charge / discharge characteristics.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (7)

As a positive electrode active material of a secondary battery, Preparing a nickel-containing precursor capable of achieving a monolithic particle structure after firing; Mixing the nickel-containing precursor with a lithium-containing precursor and optionally a dopant-containing precursor; And firing said mixture, The nickel-containing precursor is a nickel metal powder, Wherein M is at least one element selected from the group consisting of Co, Mn, Zr, Si, and Sn), wherein the chemical formula is LiNi _1-x M _x O ₂ , And the particle shape is a monolith structure. The lithium nickel oxide according to claim 1, wherein the surface BET of the oxide is 0.2 or less. A process for producing the lithium nickel oxide according to claim 1, i) preparing a nickel-containing precursor capable of achieving a monolithic particle structure after firing; ii) mixing the nickel-containing precursor, the lithium-containing precursor, and optionally the dopant-containing precursor; And iii) calcining the mixture; &Lt; / RTI &gt; delete 4. The process according to claim 3, wherein the lithium-containing precursor is lithium hydroxide. A cathode active material for a secondary battery comprising the lithium nickel oxide according to claim 1. A lithium secondary battery comprising the cathode active material according to claim 6.