KR20200033764A - positive material having surface coated positive active material for lithium secondary battery, preparation method thereof and lithium secondary battery comprising the same - Google Patents

Abstract

According to an embodiment of the present invention, provided is a positive electrode material for a secondary battery. The positive electrode material for a secondary battery includes a positive electrode active material particle and a surface coating layer positioned on a surface of the positive electrode active material particle and containing a material represented by chemical formula 1, Ca_5(PO_4)_3X_(1-x)Li_x. In the chemical formula 1, X is OH, F or Cl, and x is 0 to 1.

Description

A positive electrode material for a lithium secondary battery having a surface-coated positive electrode active material, a manufacturing method thereof, and a lithium secondary battery comprising the same {positive material having surface coated positive active material for lithium secondary battery, preparation method thereof and lithium secondary battery comprising the same}

The present invention relates to a secondary battery, and more particularly, to a lithium secondary battery.

A secondary battery refers to a battery that can be used repeatedly because it can be charged as well as discharged. The representative lithium secondary battery among the secondary batteries is the lithium ions contained in the positive electrode active material is transferred to the negative electrode through the electrolyte and then inserted into the layered structure of the negative electrode active material (charge), and then the lithium ions that were inserted into the layered structure of the negative electrode active material are again It works through the principle of returning to the anode (discharging). The lithium secondary battery is currently commercialized and used as a small power source for mobile phones and notebook computers, and is expected to be used as a large power source for hybrid vehicles, and the demand is expected to increase.

However, a composite metal oxide mainly used as a positive electrode active material in a lithium secondary battery exhibits somewhat insufficient reliability such as deterioration by reaction with an electrolyte.

The problem to be solved by the present invention is to provide an active material for a secondary battery having improved stability and a secondary battery comprising the same.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above technical problem, an embodiment of the present invention provides a positive electrode material for a secondary battery. The positive electrode material for a secondary battery includes a positive electrode active material particle and a surface coating layer on the surface of the positive electrode active material particle and containing a material represented by the following Chemical Formula 1, wherein in Formula 1, X is OH, F or Cl, x May be 0 to 1.

[Formula 1]

Ca ₅ (PO ₄ ) ₃ X _1- xLix

The positive electrode active material is represented by the formula Li _{1 + x} (Ni _1-yz Co _y M) _1-x O ₂ , in the formula, M is Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Al, Ga, In, Sn, Bi or Mn, -0.2 ≤ x ≤ 0.2, 0.01 ≤ y ≤ 0.5, 0.01 ≤ It may be z ≦ 0.5, 0 <y + z <1.

The thickness of the surface coating layer may be 0.1 to 100nm.

The surface coating layer represented by Chemical Formula 1 may be a layer containing at least one of Ca ₅ (PO ₄ ) ₃ (OH) _1-x Lix, and Ca ₅ (PO ₄ ) ₃ (F) _1-x Lix.

The surface coating layer is time of flight-secondary ion mass spectrometry (Time of Flight Secondary Ion Mass Spectrometry, ToF-SIMS) analysis in CaPOH _x ^- _(x = 3 or 4) peak and ^{_{LiCaPOH y - (y = 0,}} 1, 2, 3, or 4) may represent at least one of the peaks.

In order to achieve the above technical problem, another embodiment of the present invention provides a method for manufacturing a cathode material for a secondary battery. The method for manufacturing a cathode material for a secondary battery may include dissolving phosphoric acid and calcium salt in a solvent to prepare a coating solution, adding a cathode active material to the coating solution to obtain a precipitate, and heat treating the precipitate.

The solvent may include water, purified water, and distilled water.

The heat treatment may be performed at a temperature of 200 to 290 ℃.

After the step of obtaining a precipitate by adding a positive electrode active material to the coating solution, the step of drying the precipitate may be further included. The drying may be performed at a temperature of 50 to 100 ℃.

As described above, according to an embodiment of the present invention, it is possible to obtain a positive electrode active material with improved stability through surface treatment.

However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a schematic diagram showing a secondary battery according to an embodiment of the present invention.
2 is a flowchart illustrating a method for manufacturing a cathode material according to an embodiment of the present invention.
3 shows an XRD graph of a lithium compound according to comparative examples and a lithium compound having a surface coating layer formed according to an embodiment of the present invention.
4 is a graph showing the results of a thermogravimetric analyzer (TG) of a lithium compound having a surface coating layer according to a production example of the present invention.
Figure 5 is a graph showing the results of measuring the cyclic voltammetry (Cyclic Voltammetry, CV) of an electrode using a lithium compound having a surface coating layer according to an example of the present invention.
6A are graphs showing XRD results of pellets according to Chemical Stability Experimental Example 1 of the present invention.
Figure 6b is a graph showing the XRD results of the pellets according to Chemical Stability Experimental Example 2 of the present invention.
6C and 6D are schematic diagrams showing structures of hydroxyapatite and fluorine apatite used in Chemical Stability Experimental Examples 1 and 2, respectively.
7A and 7B are images showing SEM mapping of the positive electrode active material on which the surface coating layer is formed according to the manufacturing example of the present invention.
7C are images showing TEM mapping of the positive electrode active material on which the surface coating layer is formed according to the manufacturing example of the present invention.
8 is a graph showing the XRD results of the positive electrode active material (treated) and the positive electrode active material (bare) according to the comparative example, the surface coating layer is formed according to the manufacturing example of the present invention.
FIG. 9 shows the results of Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) analysis of the surface of the positive electrode active material (treated) on which the surface coating layer was formed and the positive electrode active material according to the comparative example according to the manufacturing example of the present invention. It is the graph shown.
10, 11, and 12 are graphs showing charging and discharging characteristics of batteries according to a battery manufacturing example (treated) and a battery comparison example (bare).
13 is an XRD graph of a positive electrode active material after a charge / discharge cycle of another battery in a battery manufacturing example.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms used in this specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “include” or “have” are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described on the specification exists, and that one or more other features are present. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

When the ranges for “X to Y” are described herein, all numbers between X and Y should also be construed as being described together. As an example, when a range of 1 to 10 is described, it should be interpreted that not only 1 and 10, but also numbers in between, ie, integers and decimals, are described.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

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

1 is a schematic diagram showing a secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, the secondary battery 100 includes a negative electrode having a negative electrode active material through which lithium can be de-inserted, a positive electrode containing the positive electrode active material described above, and an electrolyte 160 disposed between the negative electrode and the positive electrode. You can. The negative electrode active material layer 120 and the negative electrode current collector 110 may be referred to as a negative electrode, and the positive electrode active material layer 140 and the positive electrode current collector 150 may be referred to as a positive electrode. Specifically, the negative electrode active material layer 120, the positive electrode active material layer 140, and includes a separator 130 interposed therebetween, between the negative electrode active material layer 120 and the separator 130, and the positive electrode active material layer 140 ) And the separator 130 may be disposed or filled with the electrolyte 160. In addition, the negative electrode active material layer 120 may be disposed on the negative electrode current collector 110, and the positive electrode active material layer 140 may be disposed on the positive electrode current collector 150.

<Anode>

In order to obtain a positive electrode, a positive electrode active material may be prepared. The positive electrode active material is a particle that reversibly inserts and desorbs lithium, and may be a lithium-transition metal oxide. The lithium-transition metal oxide may be used as long as it is commonly used in the art, for example, LiCoO ₂ , LiNiO ₂ , Li (Co _x Ni _1-x ) O ₂ (0.5 ≤ x <1), LiMn ₂ O ₄ , LiMn ₅ O ₁₂ .

As an example, the positive electrode compound is represented by the formula Li _{1 + x} (Ni _1-yz Co _y M) _1-x O ₂ , where M is Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn , Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Al, Ga, In, Sn, Bi or Mn. In addition, it may be -0.2 ≤ x ≤ 0.2, 0.01 ≤ y ≤ 0.5, 0.01 ≤ z ≤ 0.5, 0 <y + z <1). In detail, the positive electrode active material may be [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ , Li [Ni _0.6 Co _0.2 Mn _0.2 ] O ₂ , Li [Ni _0.85 Co _0.1 Al _0.5 ] O ₂ , It is not limited thereto.

The surface coating layer may be on the surface of the positive electrode active material particles and may contain a phosphoric acid compound represented by Formula 1 below.

[Formula 1]

Ca ₅ (PO ₄ ) ₃ (X) _1-x Li _x

In Chemical Formula 1, X may be OH, F or Cl, and x may be 0 to 1.

Specifically, the surface coating layer is Ca ₅ (PO ₄ ) ₃ (OH) _1-x Lix, Ca ₅ (PO ₄ ) ₃ (Cl) _1-x Lix or Ca ₅ (PO ₄ ) ₃ (F) _1-x Lix In particular, it may be one containing at least one of Ca ₅ (PO ₄ ) ₃ (OH) _1-x Lix, and Ca ₅ (PO ₄ ) ₃ (F) _1-x Lix. Is 0 to 1). That is, the surface coating layer contains hydroxy apatite, fluoro apatite, or chloro apatite, and the apatite may be lithium doped.

In addition, the surface coating layer is time of flight-secondary ion mass spectrometry (Time of Flight Secondary Ion Mass Spectrometry, ToF-SIMS) analysis in CaPOH _x ^- _(x = 3 or 4) peak and ^{_{LiCaPOH y - (y = 0,}} 1, 2 , 3, or 4) at least one of the peaks.

The surface coating layer may be formed in a layered structure on the surface of the positive electrode active material particles, or may be attached in an island form. Here, the island shape may mean a shape in which hemispherical, non-spherical, or irregular shapes having a predetermined volume are discontinuously located.

The surface coating layer may serve to protect the positive electrode active material, thereby improving stability. In addition, the surface coating layer may be one that is doped with lithium and does not interfere with the movement of lithium metal ions.

The thickness of the surface coating layer may be 0.1 to 100 nm, for example, 1 to 80 nm, and more specifically, 5 to 20 nm. If the thickness of the surface coating layer is too thick, the amount of active lithium per unit volume of the electrode is reduced, which may cause a decrease in capacity of the secondary battery including the same. In addition, when the thickness of the surface coating layer is too thin, an effect of suppressing side reactions between the active material and the electrolyte may be insignificant. Therefore, it may be that the above-mentioned thickness range is satisfied.

2 is a flowchart illustrating a method for manufacturing a cathode material according to an embodiment of the present invention.

Referring to FIG. 2, a step (S10) of preparing a coating solution by dissolving phosphoric acid and calcium salt in a solvent may be included.

The solvent can be water. In detail, it may be distilled water or purified water, and preferably deionized water. Phosphoric acid may be H ₃ PO ₄ . The calcium salt may be calcium nitrate, calcium chloride, calcium acetate, calcium sulfide, or a combination of two or more of them. The calcium salt may be an acidic raw material capable of weakly acidifying such that the treatment solution exhibits weak acidity.

It may include the step of obtaining a precipitate by adding a positive electrode active material to the coating solution (S20).

As an example, the phosphoric acid and calcium salt in the coating solution may react with the residual lithium metal compound by the positive electrode active material to form calcium lithium phosphate as a precipitate through Reaction Schemes 1 and / or Reaction Scheme 2 below. However, it is not limited to the following reaction.

[Scheme 1]

[Scheme 2]

In detail, on the surface of the positive electrode active material, which is a lithium-transition metal oxide, there may be a lithium metal oxide remaining without forming a transition metal and an oxide. The residual lithium metal compound may be, for example, lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH), or the like. The residual lithium metal compound may react with a substance in an electrolyte in a secondary battery. The reaction product thus obtained may accumulate on the surface of the positive electrode active material, and may interfere with the movement of lithium metal ions. As an example, the residual lithium metal compound may react with hydrofluoric acid or the like in the electrolyte to produce lithium fluoride (LiF).

However, according to the present invention, as the residual lithium metal compound is consumed in the process of forming the surface coating layer, deterioration of the positive electrode active material due to side reaction with the electrolyte can be suppressed.

The precipitate obtained from the above may further perform a drying step (not shown). Drying may be performed at a temperature of 50 to 100 ° C, as an example, 60 to 95 ° C, and as another example, 70 to 90 ° C. The precipitate may further include drying at a temperature lower than the temperature at which the heat treatment is performed before heat treatment, thereby obtaining a surface coating layer containing the material according to the present invention.

It may include the step of heat-treating the precipitate (S30). A surface coating layer may be formed on the surface of the positive electrode active material particles through the heat treatment step, and the surface coating layer may contain hydroxy apatite, fluoro apatite, or chloro apatite, and the apatite may be doped with lithium.

As an example, calcium lithium phosphate, a precipitate obtained from Reaction Schemes 1 and / or 2, may be heat treated to form a material represented by Chemical Formula 1 through Reaction Scheme 3 below.

[Scheme 3]

The heat treatment may be performed at a temperature of 200 to 290 ° C, for example, 230 to 280 ° C. In detail, it may be performed at a temperature of 240 to 260 ° C for 1 hour to 3 hours. When the temperature range is satisfied, it may be to obtain a surface coating layer containing a material according to the present invention without containing a residual lithium metal compound.

The positive electrode material can be obtained by mixing the positive electrode active material, conductive material, and binder containing the thus obtained surface coating layer. At this time, the conductive material may be natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, carbon materials such as graphene. Binders include thermoplastic resins such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, vinylidene fluoride copolymers, fluorine resins such as propylene hexafluoride, and / or polyolefin resins such as polyethylene and polypropylene. It can contain.

The positive electrode material may be applied on the positive electrode current collector to form the positive electrode. The positive electrode current collector may be a conductor such as Al, Ni, and stainless steel. To apply the positive electrode material on the positive electrode current collector, a method of pressing the paste or making an paste using an organic solvent or the like and then applying the paste onto the current collector and pressing to fix it can be used. Organic solvents include amines such as N, N-dimethylaminopropylamine and diethyltriamine; Ether systems such as ethylene oxide and tetrahydrofuran; Ketone systems such as methyl ethyl ketone; Ester systems such as methyl acetate; Aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. Applying the paste on the positive electrode current collector may be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<Cathode>

The negative electrode active material is a metal, a metal alloy, a metal oxide, a metal fluoride, a metal sulfide, and natural graphite, artificial graphite, coke, carbon black, carbon nanotube, graphene that can deintercalate or convert lithium ions. It can also be formed using a carbon material such as a fin.

A negative electrode material can be obtained by mixing a negative electrode active material, a conductive material, and a binder. At this time, the conductive material may be natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, carbon materials such as graphene. Binders include thermoplastic resins such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, vinylidene fluoride copolymers, fluorine resins such as propylene hexafluoride, and / or polyolefin resins such as polyethylene and polypropylene. It can contain.

The anode material may be applied on the anode current collector to form an anode. The positive electrode current collector may be a conductor such as Al, Ni, and stainless steel. To apply the negative electrode material on the positive electrode current collector, a method of pressing the paste or making an paste using an organic solvent, etc., and then applying the paste onto the current collector and pressing to fix it can be used. Organic solvents include amines such as N, N-dimethylaminopropylamine and diethyltriamine; Ether systems such as ethylene oxide and tetrahydrofuran; Ketone systems such as methyl ethyl ketone; Ester systems such as methyl acetate; Aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. Applying the paste on the negative electrode current collector may be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<Electrolyte>

The electrolyte may be a lithium salt. Lithium salts include lithium perchloroate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanecellonate (LiCF ₃ SO ₃ ), lithium hexafluoroacetate (LiAsF) ₆ ), lithium trifluoromethanesulfonyl imide (Li (CF ₃ SO ₂ ) ₂ N), or a mixture of two or more thereof. Among them, an electrolyte containing fluorine can be used. Further, the electrolyte can be dissolved in an organic solvent and used as a non-aqueous electrolyte. As an organic solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, 4- Carbonates such as trifluoromethyl-1,3-dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, 2-methyltetrahydro Ethers such as furan; Esters such as methyl formate, methyl acetate, and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Carbamates such as 3-methyl-2-oxazolidon; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propanesultone; Alternatively, a fluorine substituent introduced into the above-described organic solvent may be used.

Alternatively, a solid electrolyte may be used. The solid electrolyte may be an organic solid electrolyte such as a polymer compound containing at least one of a polyethylene oxide-based polymer compound, a polyorganosiloxane chain or a polyoxyalkylene chain. Further, a so-called gel type electrolyte in which a nonaqueous electrolyte solution is supported on a polymer compound can also be used. Meanwhile, an inorganic solid electrolyte may be used. In some cases, the safety of the sodium secondary battery may be improved by using these solid electrolytes. In addition, the solid electrolyte may serve as a separator to be described later, and in that case, a separator may not be required.

<Separator>

A separator may be disposed between the anode and the cathode. The separator may be a material having a form of a porous film made of a material such as polyolefin resin such as polyethylene or polypropylene, a fluorine resin, or an aromatic polymer containing nitrogen, a nonwoven fabric or a woven fabric. The thickness of the separator is preferably as thin as possible as long as mechanical strength is maintained, in that the bulk energy density of the battery becomes high and the internal resistance becomes small. The thickness of the separator may generally be on the order of 5 to 200 μm, and more specifically 5 to 40 μm.

<Method for manufacturing alkali metal secondary battery>

A positive electrode, a separator, and a negative electrode may be stacked in order to form an electrode group, and then, if necessary, the electrode group may be rolled and stored in a battery can, and a secondary battery may be manufactured by impregnating the electrode group with a non-aqueous electrolyte. Alternatively, a positive electrode, a solid electrolyte, and a negative electrode may be stacked to form an electrode group, and then, if necessary, the electrode group may be rolled and stored in a battery can to produce a secondary battery.

Hereinafter, a preferred experimental example (example) is presented to help understanding of the present invention. However, the following experimental examples are only to aid the understanding of the present invention, and the present invention is not limited by the following experimental examples.

[Experimental Examples]

Preparation Example of Lithium Compound with Surface Coating Layer

Phosphoric acid and calcium nitrate, which are coating raw materials, were added to 100 ml of deionized water in a molar ratio of 1: 1, followed by stirring sufficiently to obtain a solution. Thereafter, lithium compound lithium carbonate (Li ₂ CO ₃ ) was put into the solution at a molar ratio of 1: 0.5 with the coating raw material, and the amount of the solution was set to the same weight as the positive electrode material. At this time, the obtained precipitate is sufficiently dried, and heat-treated at 250 ° C. for 2 hours to form a lithium compound with a surface coating layer, the surface coating layer containing hydroxyapatite (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ) The hydroxy apatite was obtained by lithium doping (Li-HAP).

Lithium compound comparative example 1

The precipitate was sufficiently dried, and was prepared in the same manner as in the lithium compound preparation example in which the surface coating layer was formed, except that the heat treatment was performed at 300 ° C for 2 hours.

Lithium compound comparative example 2

The precipitate was sufficiently dried, and was prepared in the same manner as in the lithium compound preparation example in which the surface coating layer was formed, except that the heat treatment was performed at 400 ° C. for 2 hours.

Lithium compound comparative example 3

The precipitate was sufficiently dried and was prepared in the same manner as in the lithium compound preparation example in which the surface coating layer was formed, except that the heat treatment was not performed.

3 shows an XRD graph of a lithium compound according to comparative examples and a lithium compound having a surface coating layer formed according to an embodiment of the present invention.

Referring to FIG. 3, in the lithium compound according to the comparative examples, a surface coating layer containing hydroxyapatite is not formed on the surface of the lithium compound, but the lithium compound according to the preparation example does not detect lithium carbonate on the surface. As a result, a surface coating layer containing hydroxyapatite was formed, and the hydroxyapatite was confirmed to be lithium doped (Li-HAP).

<Thermal stability>

FIG. 4 is a graph showing the results of thermogravimetric analyzer (TG) analysis of a lithium compound having a surface coating layer according to an exemplary embodiment of the present invention.

In detail, the weight loss rate was measured by raising the temperature from room temperature to 700 ° C in an argon atmosphere. Referring to FIG. 4, it can be seen that the weight loss rate at 700 ° C is less than 10% of the total compound at room temperature. Accordingly, it can be seen that the lithium compound having the surface coating layer (Li-HAP) formed according to the present invention has excellent thermal stability.

<Electrochemical stability>

Figure 5 is a graph showing the results of measuring the cyclic voltammetry (Cyclic Voltammetry, CV) of an electrode using a lithium compound having a surface coating layer according to an example of manufacture of the present invention.

In detail, the electrode active material slurry composition is formed by stirring the lithium compound, the super P carbon conductive material, and the PVdF binder formed with the surface coating layer according to the above preparation example in NMP in a weight ratio of 9: 0.5: 0.5. Was cast and dried on an aluminum foil current collector to form an electrode. The electrode was scanned at a voltage rate of 1 mV / s, and referring to FIG. 5, it can be seen that cycle driving is very stably performed in a voltage window of 2.5 to 4.5 V.

<Physical stability>

Table 1 below summarizes the mechanical properties of the hydroxyapatite contained in the surface coating layer of the present invention.

[Table 1]

<Chemical stability>

Chemical Stability Experimental Example 1-1

Pelletized 1 g of a lithium compound having a surface coating layer according to the preparation example, 1 M LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC), and vinylene carbonate in a weight ratio of 2 to the total weight of the electrolyte ( VC) was prepared. 0.1 g of water was added to 10 g of the solution obtained from the above, and it was stored for 1 week, and then the pellet was worked and dried.

Chemical Stability Experimental Example 1-2

A pellet was obtained in the same manner as in Chemical Experiment 1-1, except that 0.1 g of hydrofluoric acid (HF) was added instead of 0.1 g of water.

6A are graphs showing XRD results of pellets according to Chemical Stability Experimental Example 1 of the present invention.

The solution used in the Chemical Stability Experimental Example has the same composition as the electrolyte contained in the battery, and further includes water in the solution to implement an initial cycle state of the battery with this experiment. Referring to Figure 6a, it can be seen that the lithium compound having the surface coating layer has very similar peaks on the XRD compared to before adding water. This may mean that the lithium compound including the surface coating layer does not decompose even when reacted with water, that is, the surface coating layer may have stability against water by containing hydroxyapatite.

In addition, by further including hydrofluoric acid in the solution, the electrolyte salt is decomposed as the battery is driven in this experiment to realize a state in which hydrofluoric acid is formed in the electrolyte. Referring to Figure 6a, it can be seen that most of the hydroxyapatite contained in the surface coating layer is changed to fluorine apatite by reacting with hydrofluoric acid.

Chemical stability experiment example 2-1

A pellet was obtained in the same manner as in Chemical Stability Experimental Example 1-1, except that 1 g of a lithium compound having a surface coating layer containing fluorine apatite was used instead of hydroxy apatite.

Chemical stability experiment example 2-2

Instead of hydroxyapatite, pellets were prepared in the same manner as in Chemical Stability Experimental Example 1-1, except that 1 g of a lithium compound having a surface coating layer containing fluorine apatite was added, and 0.1 g of hydrofluoric acid was added instead of 0.1 g of water. Got

Figure 6b is a graph showing the XRD results of the pellets according to Chemical Stability Experimental Example 2 of the present invention.

Referring to FIG. 6B, when the surface coating layer contains a fluorine apatite as a lithium compound on which the surface coating layer is formed, it can be confirmed that even when exposed to water and hydrofluoric acid, there is no significant change in the structure of the lithium compound on the XRD compared to before exposure. have.

6C and 6D are schematic diagrams showing structures of hydroxyapatite and fluorine apatite used in Chemical Stability Experimental Examples 1 and 2, respectively.

That is, referring to FIGS. 6A and 6B, when the surface coating layer contains hydroxyapatite with a lithium compound having a surface coating layer, as the secondary battery is driven, it is exposed to hydrofluoric acid by decomposition of the electrolyte salt, thereby hydroxy in the surface coating layer. A portion of the apatite may be fluorinated to form fluorine apatite. At this time, even if fluorine apatite is included in the surface coating layer, it can be expected that the lithium compound on which the surface coating layer is still formed will be quite stable to water and acid components.

Preparation example of positive electrode active material with surface coating layer

Phosphoric acid and calcium nitrate, which are coating raw materials, were added to 100 ml of deionized water in a molar ratio of 1: 1, followed by stirring sufficiently to obtain a solution. Thereafter, the positive electrode active material Li [Ni _0.85 Co _0.1 Al _0.5 ] O ₂ was put into the solution in a weight ratio of 1: 0.5 with the coating raw material, and the amount of the solution was set to the same weight ratio as the positive electrode material. At this time, the obtained precipitate was sufficiently dried at 80 ° C, and heat-treated at 250 ° C for 2 hours to obtain a positive electrode active material having a surface coating layer.

Comparative example of positive electrode active material

Li [Ni _0.85 Co _0.1 Al _0.5 ] O ₂ was used as the positive electrode active material, and the surface treatment was not performed to form the surface coating layer.

7A and 7B are images showing SEM mapping of the positive electrode active material on which the surface coating layer is formed according to the manufacturing example of the present invention. 7C are images showing TEM mapping of the positive electrode active material on which the surface coating layer is formed according to the manufacturing example of the present invention.

8 is a graph showing the XRD results of the positive electrode active material (treated) and the positive electrode active material (bare) according to the comparative example, the surface coating layer is formed according to the manufacturing example of the present invention.

Referring to FIG. 8, it can be seen that the XRD phases of the comparative example before surface treatment and the preparation example after surface treatment show that the same peaks are identified, and that there is no structural difference between the active material itself before and after the surface treatment. On the other hand, the surface coating layer formed by the surface treatment is a very thin layer, so it may not appear in the XRD image.

FIG. 9 shows the results of Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) analysis of the surface of the positive electrode active material (treated) on which the surface coating layer was formed and the positive electrode active material according to the comparative example according to the manufacturing example of the present invention. It is the graph shown.

Referring to FIG. 9, it can be seen that the intensity of the LiOH _x ⁺ (x = 1 or 2) peak and the LiCO ₂ ⁺ peak decreases in the preparation example after the surface treatment compared to the comparative example before the surface treatment. LiOH _x ⁺ peak is related to LiOH on the lithium-transition metal oxide surface, LiCO ₂ ⁺ peak is related to Li ₂ CO ₃ on the lithium-transition metal oxide surface, and LiOH on the lithium-transition metal oxide surface through surface treatment. It can be estimated that the amount of Li ₂ CO _3, that is, the residual lithium metal compound is reduced.

On the other hand, CaPOH _x ^- _(x = 3 or 4) peak and LiCaPOH _y ^- intensity of the (y = 0, 1, 2 , 3, or 4), the peak can be seen that a detected new later than the surface-treated surface treated. It can be estimated that these CaPOH _x ^- peaks and LiCaPOH _y ^- peaks were detected from the surface coating layer formed on the surface of the active material obtained from the preparation example.

Battery manufacturing example

A positive electrode active material slurry composition was formed by stirring the positive electrode active material, super P carbon conductive material, and PVdF binder on which the surface coating layer according to the above Preparation Example was formed in a weight ratio of 94: 3: 3 in NMP. The positive electrode active material slurry composition was cast and dried on an aluminum foil current collector to form a positive electrode.

After that, 1M LiPF ₆ is dissolved in the obtained positive electrode, a negative electrode that is a lithium metal, a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC), and contains vinylene carbonate (VC) in a weight ratio of 2 to the total weight of the electrolyte. An electrolyte and a separator were prepared to prepare a 2032 type coin cell according to a typical manufacturing process of a secondary battery.

Battery Comparative Example

A battery was obtained in the same manner as the battery manufacturing example, except that the positive electrode active material according to the comparative example was used instead of the positive electrode active material having a surface coating layer according to the manufacturing example.

10, 11 and 12 are graphs showing charging and discharging characteristics of batteries according to a battery manufacturing example (treated) and a battery comparison example (bare), and FIG. 13 is a positive electrode active material after a charging and discharging cycle of another battery in a battery manufacturing example It is an XRD graph.

Referring to FIG. 10, the difference in the initial battery performance due to the battery comparison example before surface treatment and the battery manufacturing example after surface treatment is not very large, but the battery according to the production example compared to the comparative example shows somewhat high reversibility.

Referring to Figure 11, as a result of experiments while increasing the C-rate from 0.1C to 5C, it can be seen that the battery according to the manufacturing example has a superior discharge capacity even at a high rate compared to the battery according to the comparative example.

Referring to FIG. 12, as a result of performing a capacity evaluation experiment with a current density of 3C-rate (based on 1C = 200mAh / g), the battery according to the manufacturing example has a lower capacity reduction rate as the cycle proceeds than the battery according to the comparative example It can be seen that it is small, and it can be confirmed that the number of cycles that can be driven is much larger, thereby improving the life characteristics.

13 is, in detail, after the battery according to the comparative example and the manufacturing example was performed 300 cycles at 1C in a voltage range of 3 to 4.3V, the batteries were disassembled to measure the structure of the positive electrode active material. In the positive electrode active material of the electrode according to the comparative example, the structure of the initial active material is hardly found to remain at 1%, and the phase lacking lithium can be confirmed to be 99%. On the other hand, in the case of the electrode according to the manufacturing example, the positive electrode active material maintains the structure of the initial active material at 91% even after the above-described cycle, and 9% of the lithium-deficient phase, most of which are phases of the initial active material. You can confirm that it is found.

That is, since the surface coating layer can suppress the generation of by-products that interfere with the movement of lithium ions between charging and discharging, and can protect the surface of the positive electrode active material, the stability of the positive electrode active material is improved, and the secondary battery including the same has a longer life. It is interpreted that the electrochemical performance such as characteristics and capacity retention rate is improved.

Although it has been described with reference to the above embodiments, those skilled in the art can sufficiently modify or change the present invention in various ways without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand.

Claims (10)

Positive electrode active material particles; And
A positive electrode material for a secondary battery comprising a surface coating layer on the surface of the positive electrode active material particles and containing a material represented by Formula 1 below:
[Formula 1]
Ca ₅ (PO ₄ ) ₃ X _1- xLix
In Formula 1, X is OH, F or Cl, and x is 0 to 1. The method according to claim 1,
The positive electrode active material is a positive electrode material for a secondary battery represented by the formula Li _{1 + x} (Ni _1-yz Co _y M) _1-x O ₂ :
In the above formula, M is Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Al, Ga, In, Sn, Bi or Mn, and -0.2 ≤ x ≤ 0.2, 0.01 ≤ y ≤ 0.5, 0.01 ≤ z ≤ 0.5, 0 <y + z <1. The method according to claim 1,
The thickness of the surface coating layer is a positive electrode material for a secondary battery of 0.1 to 100nm. The method according to claim 1,
The surface coating layer represented by Chemical Formula 1 is a positive electrode material for a secondary battery which is a layer containing at least one of Ca ₅ (PO ₄ ) ₃ (OH) _1-x Lix, and Ca ₅ (PO ₄ ) ₃ (F) _1-x Lix. . The method according to claim 1,
The surface coating layer is time of flight-secondary ion mass spectrometry (Time of Flight Secondary Ion Mass Spectrometry, ToF-SIMS) analysis in CaPOH _x ^- _(x = 3 or 4) peak and ^{_{LiCaPOH y - (y = 0,}} 1, 2, 3 or 4) A positive electrode material for a secondary battery showing at least one of peaks. Preparing a coating solution by dissolving phosphoric acid and calcium salt in a solvent;
Obtaining a precipitate by adding a positive electrode active material to the coating solution; And
Method for manufacturing a cathode material for a secondary battery comprising the step of heat-treating the precipitate. The method according to claim 6,
The solvent is a method for producing a cathode material for a secondary battery including water, purified water, distilled water. The method according to claim 6,
The heat treatment is a method for manufacturing a cathode material for a secondary battery is performed at a temperature of 200 to 290 ℃. The method according to claim 6,
After the step of obtaining a precipitate by adding a positive electrode active material to the coating solution, the method of manufacturing a positive electrode material for a secondary battery further comprising the step of drying the precipitate. The method according to claim 6,
The drying is a method of manufacturing a cathode material for a secondary battery performed at a temperature of 50 to 100 ℃.

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