KR20220000246A - Manufacturing method of positive electrode additives, positive electrode additives and positive electrode comprising the same - Google Patents

Abstract

The present invention relates to a method for producing a positive electrode additive, a positive electrode additive, and a positive electrode including the same, in which the method includes: mixing a lithium-citrated-based compound and an iron-containing raw material to form a mixture; and thermally treating the mixture to produce a compound represented by the following Chemical Formula 1, which has a carbon coating layer formed on a surface thereof, and the positive electrode additive includes a compound represented by the following Chemical Formula 1, which has a carbon coating layer formed on a surface thereof, wherein an initial irreversible capacity is 300 mAh/g or more. [Chemical Formula 1] Li_aFe_bO_c, wherein 2 <= a <= 7, 0.5 <= b <= 2, and 2 <= c <= 5. According to the present invention, a Fe-based sacrificial positive electrode material having a high initial irreversible capacity and improved electrical conductivity can be produced at a low cost.

Description

A positive electrode additive manufacturing method, a positive electrode additive, and a positive electrode comprising the same

The present invention relates to a method for manufacturing a positive electrode additive, a positive electrode additive, and a positive electrode comprising the same.

Recently, although the demand for lithium secondary batteries is increasing in various fields such as electric vehicles, smart phones, and wearable devices, the need for devices with higher energy in a limited space is continuously emerging.

In order to increase the electrochemical capacity of a lithium secondary battery, there is a method of improving the performance of the cathode material or minimizing the amount of lithium ions consumed by the formation of SEI generated in the anode.

On the other hand, various technologies such as lithium-pre-lithiation and lithium-alloying exist for compensating for lithium ions consumed in SEI formation, but industrial application is limited due to difficulties in the process. have. Accordingly, a method of compensating for consumed lithium ions by adding a lithium-based additive as a sacrificial cathode material to the cathode material has been studied and proposed.

On the other hand, an attempt is made to develop an inexpensive Fe-based sacrificial cathode material as the sacrificial cathode material, but there is a difficulty in development due to the low electrical conductivity of the Fe-based sacrificial cathode material, and there is a need to improve it. _{In addition, lithium oxide (Li 2} O), which is generally used in manufacturing the Fe-based sacrificial cathode material, has a very high unit price, so a raw material to replace it is required.

An object of the present invention is to provide a method for manufacturing a positive electrode additive, which is a Fe-based sacrificial positive electrode material having a high initial irreversible capacity and improved electrical conductivity, at a low manufacturing cost.

The present invention comprises the steps of forming a mixture by mixing a lithium citrate-based compound and an iron-containing raw material; and heat-treating the mixture to prepare a compound represented by the following Chemical Formula 1 having a carbon coating layer formed on the surface thereof. In addition, the present invention provides a positive electrode additive comprising a compound represented by the following Chemical Formula 1 having a carbon coating layer formed on its surface, and having an initial irreversible capacity of 300 mAh/g or more, and a positive electrode comprising the same.

[Formula 1]

Li _a Fe _b O _c

In Formula 1, 2≤a≤7, 0.5≤b≤2, and 2≤c≤5.

In the present invention, by using a lithium citrate-based compound as one of the raw materials when manufacturing a positive electrode additive, which is a Fe-based sacrificial positive electrode material, the production cost can be lowered, and a carbon coating layer can be formed without an additional carbon raw material material.

According to the present invention, a Fe-based sacrificial cathode material having a high initial irreversible capacity and improved electrical conductivity can be manufactured at a low manufacturing cost.

1 is a photograph taken with a camera of the positive electrode additive prepared in Example 1.
2 is a photograph taken with a camera of the positive electrode additive prepared in Comparative Example 1. Referring to FIG.
3 is a photograph taken with a camera of the positive electrode additive prepared in Comparative Example 2. Referring to FIG.
4 is a photograph taken with a camera of the positive electrode additive prepared in Comparative Example 3;

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the existence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof, is not precluded in advance.

Hereinafter, the present invention will be described in more detail.

Anode additive manufacturing method

The positive electrode additive manufacturing method of the present invention comprises the steps of mixing a lithium citrate-based compound and an iron-containing raw material to form a mixture; and heat-treating the mixture to prepare a compound represented by the following Chemical Formula 1 having a carbon coating layer formed on the surface thereof.

[Formula 1]

Li _a Fe _b O _c

In Formula 1, 2≤a≤7, 0.5≤b≤2, and 2≤c≤5.

Hereinafter, the method for manufacturing the positive electrode additive of the present invention will be described in detail step by step.

(1) forming a mixture by mixing a lithium citrate-based compound and an iron-containing raw material

The positive electrode additive manufacturing method of the present invention can realize cost reduction by using a lithium citrate-based compound instead of lithium _{oxide (Li 2} O), which is generally used in manufacturing a Fe-based sacrificial positive electrode material, as well as carbon without an additional carbon raw material. A coating layer may be formed.

According to the method for manufacturing a positive electrode additive of the present invention, the lithium citrate-based compound and the iron-containing raw material may be mixed in a molar ratio of 9:3 to 11:3. The lithium citrate-based compound and the iron-containing raw material may be mixed in a molar ratio of 9.5:3 to 10.5:3. When the molar ratio of the mixed lithium citrate-based compound and the iron-containing raw material is within the above range, there is an advantage in that the phase of the positive electrode additive produced due to the synthesis according to the correct stoichiometric ratio is a single phase.

According to the method for producing a positive electrode additive of the present invention, the lithium citrate-based compound is lithium citrate (Li ₃ C ₆ H ₅ O ₇ ) and lithium citrate hydrate (Li ₃ C ₆ H ₅ O ₇ -xH ₂ O, the x is an integer of 1 to 4) may include one or more selected from the group consisting of. The lithium citrate-based compound may be preferably lithium citrate hydrate.

According to the method for preparing a positive electrode additive of the present invention, the lithium citrate hydrate is Li ₃ C ₆ H ₅ O ₇ -4H ₂ O, Li ₃ C ₆ H ₅ O ₇ -2H ₂ O, and Li ₃ C ₆ H ₅ O ₇ It may be at least one selected from _{-H 2 O.} Preferably, the lithium citrate hydrate may be Li ₃ C ₆ H ₅ O ₇ -4H ₂ O.

When the above-mentioned material is used as the lithium citrate-based compound, when the mixture of the lithium citrate-based compound and the iron-containing raw material is heat-treated, the carbon-coated compound represented by Chemical Formula 1 may be easily formed.

According to the method for manufacturing a positive electrode additive of the present invention, the iron-containing raw material may include at least one selected _{from Fe 2} O ₃ , FeO, and Fe ₃ O _{4 .} Preferably, the iron-containing raw material may be _{Fe 2} O _{3 .} When the iron-containing raw material is Fe ₂ O ₃ , the compound represented by Formula 1 having a carbon coating layer formed on the surface without additional oxygen supply in stoichiometric terms, preferably Li ₅ FeO ₄ having a carbon coating layer formed on the surface It is possible to manufacture it, which may be the most preferable.

When mixing the above raw materials, a moisture scavenger may be optionally further added. The moisture scavenger may include citric acid, tartaric acid, glycolic acid or maleic acid, and a mixture of one or more of these may be used.

(2) heat-treating the mixture to prepare a compound represented by the following formula (1) having a carbon coating layer formed on the surface

Step (2) is a step of heat-treating a mixture of a lithium citrate-based compound and an iron-containing raw material to form a carbon-coated compound represented by Chemical Formula 1 below.

[Formula 1]

Li _a Fe _b O _c

In Formula 1, 2≤a≤7, 0.5≤b≤2, and 2≤c≤5.

For example, when the lithium citrate-based compound is Li ₃ C ₆ H ₅ O ₇ -4H ₂ O and the iron-containing raw material is Fe ₂ O ₃ , the reaction proceeds according to the following Reaction Formula 1 to form a carbon coating layer on the surface The formed Li ₅ FeO ₄ can be prepared.

[Scheme 1]

10 Li ₃ C ₆ H ₅ O ₇ -4H ₂ O + 3 Fe ₂ O ₃ → 6 Li ₅ FeO ₄ + 45 C + 15 CO ₂ + 29 H ₂ O

The present invention is to form a _{carbon-coated compound represented by Chemical Formula 1, specifically, carbon-coated Li 5} FeO ₄ , even without adding an additional carbon raw material by only heat-treating a mixture containing a lithium citrate-based compound. can Accordingly, according to the present invention, a Fe-based sacrificial cathode material having a high initial irreversible capacity and improved electrical conductivity can be manufactured at a low manufacturing cost.

According to the method for manufacturing the positive electrode additive of the present invention, the heat treatment may be performed at a temperature of 400°C to 900°C. Specifically, the heat treatment temperature may be 600 °C to 800 °C or 700 °C to 800 °C. When the heat treatment temperature is within the above range, the carbon coating layer may be uniformly formed on the surface of the compound represented by Formula 1 without causing decomposition of the compound represented by Formula 1 or the like.

According to the method for manufacturing the positive electrode additive of the present invention, the heat treatment may be performed for 5 to 25 hours. Specifically, the heat treatment time may be 6 hours to 15 hours. When the heat treatment time is within the above range, the crystalline phase of the compound represented by Formula 1 increases, thereby reducing side reactions and improving electrochemical capacity.

According to the method for manufacturing a positive electrode additive of the present invention, the heat treatment is performed after increasing the temperature from room temperature to 400° C. to 900° C., specifically, from 700° C. to 800° C. for 30 minutes to 2 hours, and then 400 for 10 hours to 20 hours. It may be carried out while maintaining a temperature of ℃ to 900 ℃, specifically, a temperature of 700 ℃ to 800 ℃. In this case, the crystalline phase of the compound represented by Formula 1 increases, thereby reducing side reactions and improving electrochemical capacity.

On the other hand, when the temperature is increased from room temperature to 700°C to 800°C, the temperature may be increased at a constant rate. In this case, the amount of gas (moisture, hydrocarbon, carbon monoxide, carbon dioxide, etc.) emitted while decomposing lithium citrate is constantly generated, thereby reducing variation for each reaction batch.

According to the method for manufacturing a positive electrode additive of the present invention, the heat treatment may be performed in a vacuum or in an inert atmosphere to increase reaction efficiency and suppress side reactions.

The positive electrode additive prepared according to the present invention is a compound represented by Formula 1 in which a carbon coating layer is formed on a surface with improved electrical conductivity, and may be included in the positive electrode active material layer together with the positive active material to be used in a secondary battery, and the initial irreversible of the battery capacity can be improved.

anode additive

The positive electrode additive of the present invention includes a compound represented by the following Chemical Formula 1 having a carbon coating layer formed on its surface, and has an initial irreversible capacity of 300 mAh/g or more.

In the present invention, the initial irreversible capacity is obtained by manufacturing an electrode assembly by interposing a separator between the positive electrode including the positive electrode additive, the conductive material, and the binder in a weight ratio of 90:5:5 and the lithium metal negative electrode, After placing it inside the case, the half-cell prepared by injecting electrolyte into the case was charged in CC mode at 25°C at 50mA/g to 1.25V, and then cut- at 5mA/g in CV mode. It means the value obtained by subtracting the discharge capacity value from the charge capacity value of the first cycle when charging with off and discharging in CC mode until it becomes 3.0V at 10mA/g as one cycle.

According to the present invention, the positive electrode additive may be prepared according to the method for preparing the positive electrode additive, and thus the initial irreversible capacity may be 300 mAh/g or more. Specifically, the initial irreversible capacity of the positive electrode additive may be 350 mAh/g or more. When the initial irreversible capacity of the positive electrode additive is within the above range, the initial irreversible capacity of the _{positive electrode active material such as LiCoO 2} (the positive electrode additive can compensate for lithium ions generated due to SEI formation, etc.) is reduced, thereby exhibiting an overall performance improvement effect. can

anode

The positive electrode of the present invention includes the positive electrode additive. The positive electrode may include a positive electrode additive and, as a result, improve the irreversible capacity of the battery when it is applied to the battery.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the current collector, and the positive electrode active material layer includes the positive electrode additive and the positive electrode active material.

The positive electrode additive and the positive electrode active material may be included in the positive electrode active material layer in a weight ratio of 1:97 to 10:90.

The positive active material may _{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; lithium iron oxides such as LiFe ₃ O _{4 ;} Lithium manganese oxide, such as Formula Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _{2 ;} lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} Formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3) Ni site-type lithium nickel oxide; Formula LiMn _2-c3 M _c3 O ₂ (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO ₈ (herein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.) lithium manganese composite oxide; It may be at least one selected _{from LiMn 2} O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , silver or the like surface-treated may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.

The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode additive and positive electrode active material prepared according to the present invention described above.

At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one or a mixture of two or more thereof may be used.

In addition, the positive electrode binder serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.

The secondary battery includes the positive electrode; cathode; a separator interposed between the anode and the cathode; and electrolytes.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the current collector, the negative electrode active material layer includes a negative electrode active material, and as the negative electrode active material, reversible intercalation and deintercalation of lithium is possible compounds may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0 < β < 2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The anode active material layer may include an anode conductive material and an anode binder together with the anode active material described above.

The negative electrode conductive material and the negative electrode binder may be the same as those described above for the positive electrode.

The separator separates the anode and the anode and provides a passage for lithium ions to move, and it can be used without any particular limitation as long as it is normally used as a separator in a secondary battery. Excellent is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

Examples of the electrolyte may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing a lithium secondary battery.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, 1,2-dime ethoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyropion An aprotic organic solvent such as methyl acid or ethyl propionate may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents and have a high dielectric constant and thus well dissociate lithium salts. If the same low-viscosity, low-dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, which can be more preferably used.

A lithium salt may be used as the metal salt, and the lithium salt is a material readily soluble in the non-aqueous electrolyte. For example, as an anion of the lithium salt ^{, F -} , Cl ^- , I ^- , NO ₃ ^- , N(CN ) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ At least one selected from the group consisting of _{CO 2} ^— , SCN ^— and (CF ₃ CF ₂ SO ₂ ) ₂ N ^{— may be used.}

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included.

As described above, since the lithium secondary battery containing the positive electrode additive manufactured according to the present invention is inhibited from deterioration of electrochemical performance, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles, HEV) and the like are useful in the field of electric vehicles.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Examples and Comparative Examples

Example 1

9.4 parts by weight of Li ₃ C ₆ H ₅ O ₇ -4H _{2 O and 1.6 parts by weight of Fe 2} O ₃ were mixed in a solid phase using a mortar. In this case, the _{molar ratio of Li 3} C ₆ H ₅ O ₇ -4H ₂ O to Fe ₂ O ₃ was 10:3. The mixture was prepared in the form of pellets through a press. The mixture in the form of pellets was heated from room temperature to 750° C. for 1 hour under an argon atmosphere, and then heat-treated while maintaining 750° C. for 12 hours _{to obtain a Li 5} FeO ₄ positive electrode additive having a carbon coating layer formed on the surface. .

1 is a photograph taken with a camera of the positive electrode additive prepared in Example 1. Referring to FIG. 1 , it was confirmed that the carbon coating layer was formed on the surface of _{Li 5} FeO ₄ because the color of the positive electrode additive prepared in Example 1 was black. _{For reference, Li 5} FeO ₄ on which a carbon coating layer is not formed has a light yellow color.

Comparative Example 1

1.5 parts by weight of Li _{2 O and 1.6 parts by weight of Fe 2} O ₃ were mixed in a solid phase using a mortar. In this case, the _{molar ratio of Li 2} O and Fe ₂ O ₃ was 5:1. 0.4 parts by weight of polyvinylpyrrolidone (PVP) was added to the mixture, and solid phase mixing was carried out through Malta. A mixture containing PVP was prepared in the form of pellets through a press. The mixture in the form of pellets was heated from room temperature to 750° C. for 6 hours under an argon atmosphere, and then heat-treated while maintaining 750° C. for 12 hours _{to obtain a Li 5} FeO ₄ positive electrode additive having a carbon coating layer formed on the surface. .

2 is a photograph taken with a camera of the positive electrode additive prepared in Comparative Example 1. Referring to FIG. Referring to FIG. 2 , it was confirmed that the carbon coating layer was formed on the surface of _{Li 5} FeO ₄ because the color of the positive electrode additive prepared in Comparative Example 1 was black.

Comparative Example 2

_{A Li 5} FeO ₄ positive electrode additive having a carbon coating layer formed on the surface was obtained in the same manner as in Comparative Example 1, except that 2 parts by weight of PVP was added.

3 is a photograph taken with a camera of the positive electrode additive prepared in Comparative Example 2. Referring to FIG. Referring to FIG. 3 , it was confirmed that the carbon coating layer was formed on the surface of _{Li 5} FeO ₄ because the color of the positive electrode additive prepared in Comparative Example 2 was black.

Comparative Example 3

1.5 parts by weight of Li _{2 O and 1.6 parts by weight of Fe 2} O ₃ were mixed in a solid phase using a mortar. In this case, the _{molar ratio of Li 2} O and Fe ₂ O ₃ was 5:1. The mixture was prepared in the form of pellets through a press. The mixture in the form of pellets was heated from room temperature to 950° C. for 3 hours under an argon atmosphere, and then heat-treated while maintaining 950° C. for 20 hours _{to obtain Li 5} FeO ₄ positive electrode additive without a carbon coating layer. .

4 is a photograph taken with a camera of the positive electrode additive prepared in Comparative Example 3; Referring to FIG. 4 , it was confirmed that the carbon coating layer was not formed on the surface of _{Li 5} FeO ₄ because the color of the positive electrode additive prepared in Comparative Example 3 was light yellow.

Experimental Example 1: Charge/discharge profile analysis

The positive electrode additive, carbon black conductive material, and PVdF binder prepared in Example 1, Comparative Example 1 and Comparative Example 3 were mixed in an N-methylpyrrolidone solvent in a weight ratio of 90:5:5 to prepare a composition for forming a positive electrode manufactured, coated on one side of an aluminum current collector, dried at 130° C., and then rolled to prepare a positive electrode.

A composition for forming a positive electrode was prepared by mixing the positive electrode additive, carbon black conductive material, CNT conductive material, and PVdF binder prepared in Comparative Example 2 in a weight ratio of 90:2.5:2.5:5 in N-methylpyrrolidone solvent. Except for that, a positive electrode was manufactured by the method and method described above.

An electrode assembly was prepared by interposing a porous polyethylene separator (W-scope, WL20C) between each positive electrode and the lithium metal negative electrode prepared as described above, and the electrode assembly was placed inside the case, and then the electrolyte was placed inside the case. By injection, half-cells were prepared. At this time, the electrolyte is ethylene carbonate / dimethyl carbonate / diethyl carbonate / (mixed volume ratio of EC / DMC / DEC = 1/2/1) in an organic solvent consisting of 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) by dissolving prepared.

Among the half-cells prepared as described above, half cells including the positive electrode additive of Example 1 and Comparative Example 1 as an active material were charged in CC mode at 25°C at 50mA/g to 1.25V, and then in CV mode at 5mA/g The charging and discharging capacities of the first and second cycles were measured as one cycle of charging by cut-off at g and discharging in CC mode at 10 mA/g until 3.0V, and the results are shown in Table 1 below. . The half-cell including the positive electrode additive of Comparative Example 2 as an active material was charged at 100 mA/g when charging in CC mode, except that the charging and discharging capacities of the first and second cycles were measured in the same manner as described above, and the result is shown in Table 1 below.

On the other hand, in the case of the half cell of Comparative Example 3, the electrical conductivity was too low to measure the charge/discharge capacity.

first cycle charging capacity
(mAh/g) discharge capacity
(mAh/g) irreversible capacity
(mAh/g) Example 1 413.4 20.8 392.6 Comparative Example 1 155.6 7.2 148.4 Comparative Example 2 295.5 28.8 266.7 Comparative Example 3 Measurable Measurable -

Referring to Table 1, it can be seen that the battery including the positive electrode additive of Example 1 has a higher charging capacity than the batteries including the positive electrode additive of Comparative Examples 1 and 2 and exhibits a significantly higher initial irreversible capacity. In the case of the positive electrode additive of Example 1 prepared using lithium citrate, the carbon coating was _{uniformly and appropriately distributed on the surface of Li 5} FeO ₄ , whereas the positive electrode additive of Comparative Examples 1 and 2 prepared using PVP was In this case, it is because the carbon coating was not done well on the surface of _{Li 5} FeO _{4 .}

Accordingly, it can be seen that the present invention uses a lithium citrate-based compound as one of the raw materials when manufacturing the positive electrode additive, thereby reducing the production cost and forming the carbon coating layer without an additional carbon raw material. In addition, it can be seen that the positive electrode additive prepared according to the manufacturing method of the present invention has a high initial irreversible capacity and excellent electrical conductivity.

Claims (11)

forming a mixture by mixing a lithium citrate-based compound and an iron-containing raw material; and
A positive electrode additive manufacturing method comprising a; heat-treating the mixture to prepare a compound represented by the following Chemical Formula 1 having a carbon coating layer formed on its surface:
[Formula 1]
Li _a Fe _b O _c
In Formula 1, 2≤a≤7, 0.5≤b≤2, and 2≤c≤5.
According to claim 1,
The method for manufacturing a positive electrode additive, wherein the lithium citrate-based compound and the iron-containing raw material are mixed in a molar ratio of 9:3 to 11:3.
According to claim 1,
The method for manufacturing a positive electrode additive, wherein the lithium citrate-based compound includes at least one selected from lithium citrate and lithium citrate hydrate.
4. The method of claim 3,
The lithium citrate hydrate is at least one positive electrode selected _{from Li 3} C ₆ H ₅ O ₇ -4H ₂ O, Li ₃ C ₆ H ₅ O ₇ -2H ₂ O, and Li ₃ C ₆ H ₅ O ₇ -H _{2 O} Additive manufacturing method.
According to claim 1,
The iron-containing raw material is Fe ₂ O ₃ , FeO, and Fe ₃ O _{4 The} positive electrode additive manufacturing method comprising at least one selected from the group consisting of.
According to claim 1,
The heat treatment is a positive electrode additive manufacturing method that is performed at a temperature of 400 ℃ to 900 ℃.
According to claim 1,
The method for producing a positive electrode additive wherein the heat treatment is performed for 5 to 25 hours.
According to claim 1,
The heat treatment is performed by increasing the temperature from room temperature to 400° C. to 900° C. for 30 minutes to 2 hours, and then maintaining the temperature at 400° C. to 900° C. for 10 hours to 20 hours.
According to claim 1,
The heat treatment is a positive electrode additive manufacturing method that is performed in a vacuum or an inert atmosphere.
Containing a compound represented by the following formula (1) formed on the surface of the carbon coating layer,
Anode additive with an initial irreversible capacity of 300 mAh/g or higher:
[Formula 1]
Li _a Fe _b O _c
In Formula 1, 2≤a≤7, 0.5≤b≤2, and 2≤c≤5.
A positive electrode comprising the positive electrode additive according to claim 10 .

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