KR102094284B1 - Positive Electrode Active Material Particle Comprising Core Having Lithium Cobalt Oxide and Shell Having Composite metal Oxide Based Composition and Method of Manufacturing the Same - Google Patents

Abstract

The present invention is a core comprising a lithium cobalt oxide represented by the following formula (1); And a shell coated on the surface of the core and comprising a composite metal oxide of a metal having a +2 oxidation rate and a metal having a +3 oxidation rate: a positive electrode active material particle comprising:
Li _a Co _(1-x) M _x O _2-y A _y (1)
In the above formula, M is at least one selected from the group consisting of Ti, Mg, Zn, Si, Al, Zr, V, Mn, Nb and Ni,
A is an oxygen-substituted halogen,
1.00≤a≤1.05, 0≤x≤0.05, and 0≤y≤0.001.

Description

Positive Electrode Active Material Particle Comprising Core Having Lithium Cobalt Oxide and Shell Having Composite metal Oxide Based Composition and Method of Manufacturing the Same}

The present invention relates to a positive electrode active material particle comprising a core comprising a lithium cobalt oxide and a shell comprising a composite metal oxide, and a method for manufacturing the same.

As the technology development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, a lithium secondary battery exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate Has been commercialized and widely used.

In addition, as interest in environmental problems has increased, research into electric vehicles and hybrid electric vehicles capable of replacing fossil fuel vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, has been conducted. . As a power source for such electric vehicles and hybrid electric vehicles, nickel-metal hydride secondary batteries are mainly used, but studies using lithium secondary batteries having a high energy density and discharge voltage are actively being conducted, and are in some commercialization stages.

At present, LiCoO ₂ , Samsung branch (NMC / NCA), LiMnO ₄ , and LiFePO ₄ are used as cathode materials for lithium secondary batteries. Among them, in the case of LiCoO ₂ , the price of cobalt is expensive, and there is a problem that the capacity is low at the same voltage compared to the Samsung branch, and the usage of the Samsung branch etc. is gradually increasing to increase the capacity of the secondary battery.

However, in the case of LiCoO ₂ , there are obvious advantages such as high rolling density, and thus, LiCoO ₂ is still used a lot, and research is being conducted to increase the use voltage to develop a high-capacity secondary battery.

However, in the case of lithium cobalt oxide, when applying a high voltage for high capacity, and more specifically, when applying a high voltage of 4.5 V or more, as the amount of Li used in LiCoO ₂ increases, the surface becomes unstable and gas is generated due to side reaction with the electrolyte. , There is a problem that the safety decreases, such as a swelling phenomenon occurs, the possibility of structural instability increases, and the lifespan characteristics decrease rapidly.

To solve this, doping or coating a metal such as Al, Ti, Mg, or Zr on the surface of the LiCoO ₂ is a commonly used method. However, in the case of the coating layer made of the metal, there is a problem in that performance of the secondary battery may be deteriorated by interfering with the movement of Li ions between charge and discharge.

Therefore, there is a high need for the development of a positive electrode active material based on lithium cobalt oxide that can be used stably without deterioration even at high voltage.

The present invention aims to solve the problems of the prior art as described above and the technical problems requested from the past.

The inventors of the present application have undergone in-depth studies and various experiments, and as described later, the positive electrode active material particles include a core containing lithium cobalt oxide; And a shell coated on the surface of the core and comprising a composite metal oxide of a metal having a +2 oxidation rate and a metal +3 oxidation number, and confirming that a desired effect can be exhibited. The present invention has been completed.

The positive electrode active material particles according to the present invention for achieving this object,

Core comprising a lithium cobalt oxide represented by the formula (1); And

A shell coated on the surface of the core and comprising a composite metal oxide of a metal having +2 oxidation and +3 metal;

It is characterized by including:

Li _a Co _(1-x) M _x O _2-y A _y (1)

In the above formula, M is at least one selected from the group consisting of Ti, Mg, Zn, Si, Al, Zr, V, Mn, Nb and Ni,

A is an oxygen-substituted halogen,

1.00≤a≤1.05, 0≤x≤0.05, and 0≤y≤0.001.

In general, when a lithium cobalt oxide is used as a positive electrode active material at a high voltage, a large amount of lithium ions are released from the lithium cobalt oxide particles, resulting in a loss of crystal structure, destabilization of the unstable crystal structure, and a reversibility problem. In addition, when the lithium ion is Co ^{+ 3} or Co ⁴⁺ ions in the lithium cobalt oxide particle surface in the released state is to be reduced by the electrolyte, the oxygen is desorbed from the crystal structure of the above-described structure, the collapse is further promoted.

Therefore, in order to stably use lithium cobalt oxide under high voltage, even if a large amount of lithium ions is released, side reactions of the Co ions and the electrolyte must be suppressed while maintaining its crystal structure stably.

Accordingly, in the present invention, by forming a shell containing a metal oxide +2 and a metal +3 composite metal oxide on the surface of the lithium cobalt oxide, compared with the conventional positive electrode active material particles containing only lithium cobalt oxide, the electrolyte By significantly reducing the reactivity, it prevents the elution of Co, prevents problems of safety deterioration such as swelling due to gas generation, suppresses surface structure changes even under high voltage, improves the structural stability of the positive electrode active material particles, and at the same time, secondary battery By improving the lifespan characteristics of the shell, the shell also has a layered structure, so that the movement of lithium ions is relatively easy even in the shell, effectively preventing the degradation of the rate characteristic of the secondary battery.

In one specific example, the thickness of the shell formed on the surface of the core may be 5 nanometers to 100 nanometers, and specifically 10 nanometers to 30 nanometers.

If, outside the above range, the thickness of the shell is less than 5 nanometers, the proportion of the shell in the positive electrode active material particles may be too small to sufficiently exert the desired effect, and conversely, the thickness of the shell may be 100 nanometers. When it exceeds the meter, the ratio of the shell in the positive electrode active material particles is too high, the overall capacity of the positive electrode active material is relatively reduced, and the rolling density is lowered, so the energy density per volume in the actual cell is lowered and the output characteristics are lowered. It is undesirable because there is a problem of deterioration.

Further, in one specific example, the shell may be coated in an area of 50% to 100% with respect to the surface area of the core.

When the shell is coated in an area of less than 50% outside the above range with respect to the surface area of the core, the coating area of the shell is too small, which is not desirable because it does not sufficiently exhibit the desired effect.

The composite metal oxide of the shell thus formed is, in detail, in the form of a complex oxide of +2 and +3 metals, and may have a layered structure such as lithium cobalt oxide of the core.

Therefore, the shell containing the composite metal oxide suppresses a reaction that may occur by reaction with an electrolyte on the surface of lithium cobalt oxide to prevent elution of Co, secures structural stability of the surface, and has the same layered structure. Since it is coated, it can act as a conductor of Li ions, and more effectively, it can move Li ions from lithium cobalt oxide, thereby preventing deterioration of output characteristics.

The composite metal oxide may be represented by the following Chemical Formula 2 in one specific example.

M ' _t M'' _w O _u (2)

In the above formula, M 'is a metal having an oxidation number of +2, and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni,

M '' is a metal having an oxidation number of +3, and is one or more selected from the group consisting of Al, Co, Ni, and Fe,

0.125≤t / w≤1, and at 0.6≤ (t + w) /u≤0.8, u is determined according to the values of t and w.

More specifically, M 'may be Co, Zn, Ni, or Mg, and M' 'may be Al.

As described above, the oxide represented by Chemical Formula 2 is [M ' _t M'' _w (OH) ₂ ] ^{q +} (X ⁿ having a layered structure in the process in which the metal elements of the composite metal oxide are adsorbed on the surface of the lithium cobalt oxide particle. ^{_{-) q / n · zH 2}} O ( wherein, X is the anion ^{_{Cl-, CO 3 2-, OH -}} . ^{_{comprises, NO 3-, SO 4 2-,}} PO 4 3-) to be formed, Anions such as X may exist in the layered structure to balance charge valence and then be partially or completely removed as they are fired to form the composite metal oxide having a layered structure.

Meanwhile, the positive electrode active material particles may further include an outermost surface layer coated on the shell and including a complex metal oxide of a metal having +2 oxidation and +3 metal.

At this time, the composite metal oxide contained in the outermost surface layer may have the same composition as the composite metal oxide contained in the shell, but in detail, at least one of the metals forming the outermost surface layer is a metal not included in the shell, The composition of the shell and the outermost surface layer may be different.

That is, the positive electrode active material particles of the present invention may also include a structure in which a layered composite metal oxide layer is layered on the core of a lithium cobalt oxide in multiple layers.

On the other hand, the present invention provides a method for manufacturing the positive electrode active material particles, the manufacturing method,

(a) M'-containing metal salt (where M 'is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu, and Ni) and M' '-containing metal salt (where , M '' is a metal having an oxidation number of +3, and is a process of preparing a solution for preparing a shell containing Al, Co, Ni, and Fe.

(B) the process of dispersing the lithium cobalt oxide in a particle state in a solvent, and further mixing the solution for preparing the shell; And

(c) filtering and drying the mixed solution, followed by heat treatment;

It may include.

According to the above manufacturing method, the positive electrode active material particle of the present invention is prepared by forming a composite metal oxide due to the heat treatment of the process (c) in which the solution for shell production is first coated with lithium cobalt oxide on the particle.

Specifically, in the process (b) of the metal ions of M ' ^{2 +} , M'' ³⁺ is adsorbed on the surface of lithium cobalt oxide particles, having a layered structure, [M' _t M '' _w (OH) _{^{2] q + (X n -}} ) - and _{^{a, NO 3-, SO 4 2-,}} PO 4 3- q / n · zH 2 O ( wherein, X is the anion Cl-, CO ₃ ^2-, OH. ) Is formed, and the anions such as X are coated in a form existing between the layered structures in order to balance charges, and are partially or completely removed in the heat treatment process of step (c).

Therefore, the composite metal oxide forming the shell can be coated on the surface of the core in a layered structure by being coated on the surface of the lithium cobalt oxide particles forming the core in the precursor step, whereby the shell is By forming a continuous structure, a structurally more stable shell can be formed, and a chemically more stable shell layer can be formed with a structure in which M ' ^{2 +} and M'' ³⁺ metals are uniformly mixed.

At this time, the solvent of the process (b) is not limited, but in detail, it may be water, and the solvent used in the preparation of the solution for preparing the shell may be the same as or different from the solvent of the process (b), but the same It is more preferable.

In one specific example, the particle diameter (D50) of the lithium cobalt oxide in the particle state may be 5 micrometers to 25 micrometers.

Outside of the above range, if it is less than 5 micrometers, it is difficult to control lithium cobalt oxide particles, which is difficult in the process, and when it exceeds 25 micrometers, there is a loss in terms of rolling density and capacity. not.

Furthermore, the method for manufacturing the positive electrode active material particles when the positive electrode active material particles further include an outermost surface layer,

(d) M 'containing metal salt (where M' is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni) and M '' containing metal salt (where , M '' is a metal having an oxidation number of +3 and is a process of preparing a solution for preparing the outermost surface layer including Al, Co, Ni, and Fe.

(e) dispersing the lithium cobalt oxide in which the particle-like shell is formed in a solvent, and further mixing the solution for preparing the outermost surface layer; And

(f) filtering and drying the mixed solution, followed by heat treatment;

It may further include.

At this time, depending on whether the composition of the composite metal oxide contained in the outermost surface layer is the same as or different from the composition of the shell, the metal type of the metal salt included in the solution for manufacturing the outermost surface layer may be different.

Specifically, in the case of the same, the same solution as the solution for manufacturing the shell may be used, and when different, among the M'-containing metal salt and M ''-containing metal salt contained in the solution for preparing the outermost surface layer of the process (d) It can be produced by allowing at least one of the metals contained in the solution for manufacturing a shell to contain a metal different from the metal contained.

In the above manufacturing method, the pH of the mixed solution of the solution in which the lithium cobalt oxide is dispersed in a solvent and the solution for preparing a shell or outermost coating layer may be maintained at 7 to 12, specifically 8 to 11.

Outside the above range, when the pH of the solution is less than 7, the adsorption of metal ions in the solution for production may not be uniform, and the adsorbed metal ions are eluted back into the solution, and thus the coating layer is not well formed. It may not be able to form the desired layered structure, and when the pH is higher than 12, metal ions precipitate in the form of hydroxide, and thus may not be coated on the surface of lithium cobalt oxide.

On the other hand, the present invention provides another method for producing the positive electrode active material particles, the manufacturing method,

(a) M'-containing metal salt (where M 'is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu, and Ni) and M' '-containing metal salt (where , M '' is a metal having an oxidation number of +3, and is synthesized from a solution containing Al, Co, Ni, and Fe. process;

(b) a process of mixing the M'-M '' composite hydroxide in the particle state and the lithium cobalt oxide in the particle state; And

(c) heat treating the mixture;

It may include.

According to the above manufacturing method, the positive electrode active material particle of the present invention is a precursor of a composite metal oxide that will form a shell, and a composite metal hydroxide is prepared by coprecipitation reaction, mixed with lithium cobalt oxide particles, and heat treated to form lithium cobalt. It is produced by a method of forming a composite metal oxide on the oxide particle core.

Accordingly, the composite metal oxide forming the shell may be coated on the surface of the core in a layered structure while being attached to the surface of lithium cobalt oxide particles forming a core in the form of hydroxide and then turned into oxide by heat treatment.

The above method is easy to control the composition and structure of the complex oxide layer protecting the surface, and can form a complex layered complex oxide on the surface of the core without being sensitive to pH. There is an advantage to make the composition of the shell layer more uniform than the method using an aqueous solution.

In this case, the process (a) the M'-M '' complex hydroxide is a _{[M 't M''w} (OH) 2] synthesized in _{^{q + (X n -) q}} / n · zH 2 O ( wherein, X is anions Cl-, CO ₃ ^2-, OH ^{-, _{and, NO 3-, SO 4 2-,}} PO 4 3- included, and 0.125≤t / w≤1 the, determined according to the value of the q are t and w ).

The hydroxide-type shell-forming precursor may be more firmly attached to the surface of the lithium cobalt oxide particles while being changed to the oxide form.

Furthermore, on the continuous line in the manufacturing method, the method for manufacturing the positive electrode active material particles when the positive electrode active material particles further include an outermost surface layer,

(d) M 'containing metal salt (where M' is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni) and M '' containing metal salt (where , M '' is a metal having an oxidation number of +3, and is a second M'-M '' complex hydroxide through a coprecipitation reaction from a solution containing Al, Co, Ni, and Fe. Synthesis process;

(e) mixing a second M'-M '' composite hydroxide in a particle state and a lithium cobalt oxide in which a particle shell is formed; And

(f) heat treating the mixture;

It may further include.

At this time, depending on whether the composition of the composite metal oxide contained in the outermost surface layer is the same as or different from the composition of the shell, it is included in the solution of the process (d) for forming the second M'-M '' composite hydroxide. The metal type of the metal salt may vary.

Specifically, in the case of the same, the same solution as the solution for preparing the hydroxide for forming a shell may be used, and when different, the process (d) for forming the second M'-M '' composite hydroxide At least one of the M'-containing metal salt and the M ''-containing metal salt in the solution can be prepared by containing metals different from the metals contained in the metal salts included in the solution of step (a).

Here, the mixing ratio of the composite metal hydroxide formed by the co-precipitation reaction may be appropriately selected according to the coating thickness.

On the other hand, as described above, in order to prepare the positive electrode active material particles according to the present invention in each manufacturing method, M 'containing metal salt and M' 'containing metal salt are used to form a shell or outermost surface layer.

At this time, in the above solutions, the M'-containing metal salt and the M ''-containing metal salt may be mixed in a range in which M 'and M' 'satisfy the conditions of M' / M '' = 0.125 to 1 in a molar ratio.

Outside the above range, when the M '/ M' 'ratio is outside the above range and is less than 0.125 or higher than 1, a layered structure is not formed, and an M' containing metal salt or an M '' containing metal salt is formed to form a shell. It is not desirable.

In one specific example, the type of the metal salt is not limited, and may be one or more types selected from chloride, sulfate, carbonate, and nitrate.

In addition, the drying of the process (c) in each manufacturing process may be performed for 1 hour to 24 hours at 30 degrees Celsius to 130 degrees Celsius, and the heat treatment of the process (c) or (f) is 600 degrees Celsius. It may be performed for 1 hour to 10 hours in the range of 1 to 100 degrees, specifically 700 to 1000 degrees.

If, if the drying of the process (c) is performed at an excessively low temperature outside the above range, or is performed for an excessively short period of time, drying may not be properly performed, and conversely, when the drying is performed for an excessively long period or It is not desirable because reactions that lead to structural changes may occur.

In addition, when the heat treatment of the steps (c) and (f) is performed at an excessively low temperature outside the above range or for an extremely short time, the core-shell structure of the positive electrode active material particles may not be stably formed. On the contrary, when it is performed at an excessively high temperature or for an excessively long time, physical and chemical properties of the lithium cobalt oxide and the composite metal oxide constituting the positive electrode active material particles may be changed, thereby causing performance degradation. have.

In addition, the present invention provides a secondary battery including a positive electrode, a negative electrode, and an electrolyte containing the positive electrode active material particles. The secondary battery is not particularly limited in its kind, but as a specific example, high energy density, discharge It may be a lithium secondary battery such as a lithium ion battery, a lithium ion polymer battery, etc., which has advantages such as voltage and output stability.

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing lithium salt.

The positive electrode is prepared by, for example, coating a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector, followed by drying, and if necessary, further adding a filler to the mixture.

The conductive material is usually added in 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change 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 fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, 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 may be used.

The binder is a component that assists in bonding the active material and the conductive material and the like to the current collector, and is usually added at 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene styrene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component that inhibits the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery, and includes, for example, an olefinic polymer 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 a negative electrode active material on a negative electrode current collector, and if necessary, components as described above may be optionally further included.

Examples of the negative electrode active material include carbons such as non-graphitized carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Al, B, P, Si, group 1, group 2, group 3 elements of the periodic table, halogen; metal composite oxides such as 0 <x≤1;1≤y≤3;1≤z≤8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 separator and the separation film are 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 μm, and the thickness is generally 5 to 300 μm. Examples of the separator include olefin-based polymers such as polypropylene, which are chemically resistant and hydrophobic; Sheets or non-woven fabrics made of glass fiber or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

In addition, in one specific example, in order to improve the safety of a high energy density battery, the separator and / or the separation film may be an organic / inorganic composite porous safety-reinforcing separator (SRS) separator.

The SRS separator is manufactured by using inorganic particles and a binder polymer as an active layer component on a polyolefin-based separator substrate, wherein the pore structure included in the separator substrate itself and the interstitial volume between the inorganic particles as an active layer component are used. It has a uniform pore structure formed.

When using the organic / inorganic composite porous separator, there is an advantage that the increase in battery thickness due to swelling during chemical conversion (Formation) can be suppressed compared to the case where a conventional separator is used. When a gelable polymer is used when impregnating a liquid electrolyte, it can be used simultaneously as an electrolyte.

In addition, since the organic / inorganic composite porous separator can exhibit excellent adhesion properties by controlling the content of the inorganic particles and the binder polymer, which are the active layer components in the separator, the battery assembly process can be easily performed.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as there is no oxidation and / or reduction reaction in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). In particular, in the case of using the inorganic particles having the ion transport ability, it is preferable to increase the ion conductivity in the electrochemical device, thereby improving performance, and thus possible ion conductivity is high. In addition, when the inorganic particles have a high density, it is preferable that the density is as small as possible, as there is a problem in that it is difficult to disperse during coating and there is also a problem in weight increase during battery manufacturing. In addition, in the case of an inorganic material having a high dielectric constant, it is possible to improve the ionic conductivity of the electrolyte by contributing to an increase in dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte.

The lithium salt-containing non-aqueous electrolyte solution is composed of an organic electrolyte solution and a lithium salt. Non-aqueous liquid electrolyte, organic solid electrolyte, inorganic solid electrolyte, and the like are used as the organic electrolyte.

Examples of the non-aqueous liquid electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma. -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxol , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxon derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbohydrate Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, Polymers including ionic dissociative groups and the like can be used.

The inorganic solid electrolyte, for example, 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 , Li ₄ nitrides such as Li ₄ SiO _{4 -} LiI-LiOH, Li ₃ PO _{4 -} Li ₂ S-SiS ₂ , halides, sulfates, and the like can be used.

The lithium salt is a material 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.

Further, the lithium salt-containing non-aqueous electrolyte solution may include electrolyte additives, and the electrolyte additives may include ethylene carbonate, vinyl acetate, vinyl ethylene carbonate, thiophene, 1,3-propane sultone, succinic anhydride, and dinitrile. It includes at least one of the additives, and the dinitrile additive may be at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, and phthalonitrile.

In addition, for the purpose of improving charge / discharge characteristics, flame retardance, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative , Sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics.

The present invention also provides a battery pack including the secondary battery and a device including the battery pack. Since such battery packs and devices are known in the art, detailed descriptions thereof are omitted herein. do.

As described above, the positive electrode active material particles according to the present invention includes a core comprising lithium cobalt oxide; And a shell coated on the surface of the core and comprising a composite metal oxide of a metal having a +2 oxidation rate and a metal +3, compared to a conventional positive electrode active material particle containing only lithium cobalt oxide, Due to the surface protection effect of lithium cobalt oxide, the reactivity with the electrolyte is significantly reduced, thereby preventing problems of safety deterioration such as swelling due to gas generation, and suppressing surface structure changes even under high voltage. While improving the structural stability of the positive electrode active material particles, it is possible to improve the life characteristics of the secondary battery, and the shell also has a layered structure, so that the movement of lithium ions in the shell is relatively easy, so the rate of the secondary battery There is an effect that can effectively prevent the degradation of properties.

1 is a SEM photograph of the positive electrode active material particles according to Example 1 of the present invention;
2 is a SEM photograph of the positive electrode active material particles according to Example 2 of the present invention;
3 is a graph comparing life characteristics at 25 ° C according to Experimental Example 2 of the present invention;
Figure 4 is a graph comparing the life characteristics at 45 ℃ according to Experimental Example 2 of the present invention

Hereinafter, the present invention will be further described with reference to examples of the present invention, but the scope of the present invention is not limited thereto.

<Example 1>

LiCoO _{2 in the} form of particles with a particle size ranging from 10 to 20 micrometers 100 g of water is dispersed in 1000 ml, and a solution of CoCl ₂ and Al ₂ (SO ₄ ) ₃ mixed with water in a molar ratio of Co: Al = 1: 2 is added so that (Co + Al) is 5000 ppm compared to LiCoO ₂ Then, mix with a zirconia ball using a ball mill. The mixture (pH = 10) was filtered and dried at 130 ° C., followed by calcination at 1000 ° C. for 5 hours in an air atmosphere to synthesize a core-shell structured active material having a shell thickness of 10 nm. The SEM photograph of the synthesized active material is shown in FIG. 1.

Referring to Figure 1, it is shown that in CoAl ₂ O ₄ of the layered structure matches the layered structure and the structure of LiCoO ₂ is formed on the surface, it can be seen that attached to the surface.

<Example 2>

Co-Al hydroxide (CoAl ₂ (OH) ₈ ) by mixing and coprecipitating sodium hydroxide in a solution mixed with water such that Co: Al = 1: 2 in a molar ratio of CoCl ₂ and Al ₂ (SO ₄ ) ₃ in 500 ml ₈ ) Was synthesized.

100 parts by weight of LiCoO ₂ in the particle form with particle sizes distributed in the range of 10 to 20 micrometers, CoAl ₂ (OH) ₈ After dry mixing of 1 part by weight, firing was performed at 1000 ° C for 5 hours to synthesize an active material having a core-shell structure having a thickness of 10 nm in a shell containing CoAl ₂ O ₄ . The SEM photograph of the synthesized active material is shown in FIG. 2.

2, unlike Example 1, CoAl ₂ O ₄ coating is LiCoO ₂ It can be seen that while being evenly distributed over the entire surface, it exists as a coating layer of a continuous layered structure with the LiCoO ₂ matrix.

<Comparative Example 1>

LiCoO ₂ in the form of particles having a particle size of 10 to 20 micrometers was used as the positive electrode active material particles.

<Experimental Example 1>

After mixing the positive electrode active material particles, PVdF binder, and natural graphite conductive material prepared in Examples 1 to 2 and Comparative Example 1 in a weight ratio of 95: 2.5: 2.5 (positive electrode active material: binder: conductive material), mix well with NMP, and then 20 μm. After coating on a thick Al foil, it was dried at 130 ° C to prepare an anode. Lithium foil was used as the negative electrode, and a plurality of half coin cells were prepared using an electrolyte containing 1 M LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1.

A plurality of half coin cells manufactured as described above, at 25 degrees Celsius and 45 degrees, respectively, the CC / CV charging mode with the upper limit voltage of 4.55 V and the lower limit voltage of 2.5 V CC discharge mode after 0.1 C charging and discharging, then 0.5 C / 1C charging and discharging Life characteristics were evaluated, and the results are shown in FIGS. 3 and 4 below.

Referring to FIGS. 3 and 4, it can be confirmed that, in the case of embodiments, the stability of the surface is improved even under a high voltage of 4.55 V or more, and even up to 50 cycles, the capacity retention rate is 85% or more. On the other hand, in the case of Comparative Example 1, it can be seen that the lifespan characteristics were sharply dropped to 70% or less before 40 cycles, and structural stability was completely reduced.

Although described above with reference to the embodiments of the present invention, those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above.

Claims (24)

Core comprising a lithium cobalt oxide represented by the formula (1); And
A shell coated on the surface of the core and comprising a complex metal oxide of a metal having an oxidation number of +2 and a metal of +3 represented by the following Chemical Formula 2;
Cathode active material particles comprising:
Li _a Co _(1-x) M _x O _2-y A _y (1)
In the above formula, M is at least one selected from the group consisting of Ti, Mg, Zn, Si, Al, Zr, V, Mn, Nb and Ni,
A is an oxygen-substituted halogen,
1.00≤a≤1.05, 0≤x≤0.05, and 0≤y≤0.001,
M ' _t M'' _w O _u (2)
In the above formula, M 'is a metal having an oxidation number of +2, and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni,
M '' is a metal having an oxidation number of +3, and is one or more selected from the group consisting of Al, Co, Ni, and Fe,
0.125≤t / w≤1, and at 0.6≤ (t + w) /u≤0.8, u is determined according to the values of t and w. The positive electrode active material particles of claim 1, wherein the thickness of the shell is 5 nanometers to 100 nanometers. The positive electrode active material particles according to claim 1, wherein the shell is formed in an area of 50% to 100% of the surface area of the core. The cathode active material particle of claim 1, wherein the composite metal oxide of the shell has a layered structure. delete The cathode active material particle of claim 1, wherein M 'is Co, Zn, Ni or Mg, and M' 'is Al. The method of claim 1, wherein the positive electrode active material particles are coated on the shell, characterized in that it further comprises an outermost surface layer comprising a complex metal oxide of a metal having +2 and +3 metal oxides. Anodic active material particles. The cathode active material particle of claim 7, wherein at least one of the metals forming the outermost surface layer is a metal not included in the shell. As a method for producing the positive electrode active material particles according to claim 1,
(a) M'-containing metal salt (where M 'is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu, and Ni) and M''-containing metal salt (where , M '' is a metal having an oxidation number of +3, and is a process of preparing a solution for preparing a shell containing Al, Co, Ni, and Fe.
(B) the process of dispersing the lithium cobalt oxide in a particle state in a solvent, and further mixing the solution for preparing the shell; And
(c) filtering and drying the mixed solution prepared in step (b), followed by heat treatment;
Method for producing a positive electrode active material particles comprising a. The method according to claim 9, wherein the solvent of the process (b) is water. 10. The method of claim 9, wherein the particle diameter of the lithium cobalt oxide in the particle state (D50) is 5 to 25 micrometers. 10. The method of claim 9, The method for producing the positive electrode active material particles,
(d) M 'containing metal salt (where M' is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni) and M '' containing metal salt (where , M '' is a metal having an oxidation number of +3 and is a process of preparing a solution for preparing the outermost surface layer including Al, Co, Ni, and Fe.
(e) dispersing the lithium cobalt oxide in which the particle-like shell is formed in a solvent, and further mixing the solution for preparing the outermost surface layer; And
(f) filtering and drying the mixed solution prepared in step (e), followed by heat treatment;
Method for producing a positive electrode active material particles further comprising a. The method of claim 12, wherein at least one of the M'-containing metal salt and M ''-containing metal salt contained in the solution for manufacturing the outermost surface layer of the process (d) contains a metal different from the metal contained in the metal salts included in the solution for shell production Method for producing a positive electrode active material particles, characterized in that. As a method for producing the positive electrode active material particles according to claim 1,
(a) M'-containing metal salt (where M 'is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu, and Ni) and M''-containing metal salt (where , M '' is a metal having an oxidation number of +3, and is synthesized from a solution containing Al, Co, Ni, and Fe. process;
(b) a process of mixing the M'-M '' composite hydroxide in the particle state and the lithium cobalt oxide in the particle state; And
(c) heat-treating the mixture prepared in step (b);
Method for producing a positive electrode active material particles comprising a. 15. The method of claim 14, M'-M '' composite hydroxide synthesized in the process (a) is [M ' _t M'' _w (OH) ₂ ] ^{q +} (X ^n- ) _{q / n} zH ₂ O ( wherein, X is an anion as ^{_{Cl-, CO 3 2-, OH -}} , NO 3-, SO 4 2-, and includes PO ₄ ^3-, and 0.125≤t / w≤1, the value q is t and w It is determined according to.) Method for producing a positive electrode active material particles. 15. The method of claim 14, The method for producing the positive electrode active material particles,
(d) M 'containing metal salt (where M' is a metal having +2 oxidation number and is one or more selected from the group consisting of Co, Zn, Mg, Fe, Cu and Ni) and M '' containing metal salt (where , M '' is a metal having an oxidation number of +3, and is a second M'-M '' complex hydroxide through a coprecipitation reaction from a solution containing Al, Co, Ni, and Fe. Synthesis process;
(e) mixing a second M'-M '' composite hydroxide in a particle state and a lithium cobalt oxide in which a particle shell is formed; And
(f) heat-treating the mixture prepared in step (e);
Method for producing a positive electrode active material particles further comprising a. 17. The method of claim 16, wherein at least one of the M'-containing metal salt and the M ''-containing metal salt in the solution of process (d) for forming the second M'-M '' complex hydroxide is added to the solution of process (a). Method for producing a positive electrode active material particles, characterized in that it contains a metal and other metals contained in the metal salts contained. The method according to any one of claims 9, 12, 14, and 16, wherein the M'-containing metal salt and the M ''-containing metal salt have M '/ M' 'in a molar ratio of M' and M ''. = 0.125 ~ 1 method for producing a positive electrode active material particles, characterized in that mixed in a range that satisfies the conditions. The method according to any one of claims 9, 12, 14, and 16, wherein the metal salt is one or more kinds selected from chloride, sulfate, carbonate, and nitrate. . The method according to any one of claims 9, 12, 14, and 16, wherein the heat treatment of the process (c) or process (f) is performed for 1 hour to 10 hours in the range of 600 degrees Celsius to 1100 degrees Celsius. Method for producing a positive electrode active material particles, characterized in that. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte containing the positive electrode active material particles according to claim 1. 22. The method of claim 21, wherein the electrolytic solution comprises and contains electrolyte additives, the electrolyte additives are ethylene carbonate, vinyl acetate, vinyl ethylene carbonate, thiophene, 1,3-propane sultone, succinic anhydride and die A secondary battery comprising at least one of nitrile additives, and the dinitrile additive is at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, and phthalonitrile. A battery pack comprising the secondary battery according to claim 21. A device comprising the battery pack according to claim 23.

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