Anode active material for secondary battery, manufacturing method thereof, and lithium secondary battery including the same

Abstract

Provided are an anode active material for secondary battery which includes porous iron oxide nanoparticles, a manufacturing method thereof, and a secondary battery including the same. The anode active material for secondary battery of the present disclosure minimizes a volume change of iron oxide caused by intercalation and deintercalation of lithium even during consecutive charges and discharges and thus can improve the capacity and lifespan characteristics of a secondary battery employing the anode active material. Further, the manufacturing method of an anode active material for secondary battery makes it possible to manufacture an anode active material for secondary battery including iron oxide nanoparticles in an environmentally friendly and simple manner and thus makes it possible to mass-produce the anode active material.

Claims

1. A manufacturing method of an anode active material for secondary battery, the method comprising: mixing an iron compound, a metal salt, and a solvent to prepare an iron-mixed solution; and irradiating microwaves to the iron-mixed solution to form the anode active material through the self-assembly of spindle shaped iron oxide particles, wherein the iron-mixed solution has a concentration of from 0.01 M to 0.05 M; and wherein the microwaves are irradiated to the iron-mixed solution having a temperature range of from 100° C. to 300° C., output power range of from 100 W to 600 W for 10 to 30 minutes, and wherein the anode active material is formed into a porous structure and has a specific surface area of from 1 m2/g to 80 m2/g and an average particle diameter of from 400 nm to 800 nm.

2. The manufacturing method of an anode active material for secondary battery according to claim 1, wherein the iron compound includes a member selected from the group consisting of iron(II) nitrate, iron(III) nitrate, iron(II) sulfate, iron(III) sulfate, iron(II) acetylacetonate, iron(III) acetylacetonate, iron(II) trifluoroacetylacetonate, iron(III) trifluoroacetylacetonate, iron(II) acetate, iron(III) acetate, iron(II) chloride, iron(III) chloride (FeCl.sub.3), iron(II) bromide, iron(III) bromide, iron(II) iodide, iron(III) iodide, iron perchlorate, iron sulfamate, iron(II) stearate, iron(III) stearate, iron(II) oleate, iron(III) oleate, iron(II) laurate, iron(III) laurate, iron pentacarbonyl, iron enneacarbonyl, disodium tetracarbonyl ferrate, and mixtures thereof.

3. The manufacturing method of an anode active material for secondary battery according to claim 1, wherein the metal salt includes a member selected from the group consisting of nitrate, carbonate, chloride salt, phosphate, borate, oxide, sulfonate, sulfate, stearate, myristate, acetate, acetylacetonate, hydrates thereof, and mixtures thereof.

4. The manufacturing method of an anode active material for secondary battery according to claim 1, wherein the solvent includes a member selected from the group consisting of water, ethanol, isopropyl alcohol, propanol, butanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and mixtures thereof.

5. The manufacturing method of an anode active material for secondary battery according to claim 1, wherein the microwaves are irradiated at output power range of from 100 W to 600 W.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1A are electron microscopic images of an anode active material for secondary battery manufactured according to an example of the present disclosure;

(3) FIG. 1B are electron microscopic images of an anode active material for secondary battery manufactured according to an example of the present disclosure;

(4) FIG. 2 is a graph illustrating the BET specific surface area of an anode active material for secondary battery manufactured according to an example of the present disclosure;

(5) FIG. 3 is a charge/discharge curve illustrating a capacity depending on a voltage of a battery manufactured according to an example of the present disclosure; and

(6) FIG. 4 is a lifespan graph illustrating a capacity depending on the number of charge and discharge cycles of a battery manufactured according to an example of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(7) Hereinafter, the present disclosure will be described in more detail with reference to examples and the accompanying drawings.

(8) An anode active material for secondary battery according to the present disclosure includes porous iron oxide nanoparticles with a specific surface area of from 1 m.sup.2/g to 80 m.sup.2/g.

(9) Intercalation and deintercalation reactions of lithium ions vary depending on the surface characteristics of a material. A small specific surface area is unfavorable to these reactions.

(10) A large specific surface area means a large reaction active area and is favorable to intercalation and deintercalation of lithium ions.

(11) However, a specific surface area of a predetermined level or more may be disadvantageous to lifespan characteristics.

(12) An explosive reaction may cause destruction of a structure and may be disadvantageous to lifespan characteristics of the anode active material for secondary battery. Therefore, nanoparticles with an adequate specific surface area are favorable for the anode active material for secondary battery.

(13) Further, if the specific surface area is formed mostly due to a porous structure, the porous structure can serve as a channel when lithium ions or an electrolyte moves. Thus, it can be advantageous to operation of a battery.

(14) The anode active material including porous iron oxide nanoparticles have pores distributed uniformly within the particles and thus may have a large specific surface area.

(15) Further, the electrolyte can easily flow into the pores, and, thus, a resistance to movement of lithium ions can be decreased and a reaction active site for the electrolyte can be maximized. Therefore, the output characteristics can be improved.

(16) If the anode active material for secondary battery has a specific surface area of less than 1 m.sup.2/g or more than 80 m.sup.2/g, lithium ions may not be intercalated and deintercalated well during charges and discharges, which may result in degradation of cycle characteristics.

(17) Preferably, the porous iron oxide nanoparticles may be included in the amount of from 60 wt % to 90 wt % based on the total weight of the anode active material.

(18) The anode active material for secondary battery may further include a conductor and a binder.

(19) The conductor may include a member selected from the group consisting of natural graphite, synthetic graphite, carbon black, acetylene black, ketchen black, denka black, and carbon fibers.

(20) The conductor may be contained in a small amount for the purpose of improving electronic conductivity between active material particles and may employ any electronically conductive material that does not cause a chemical change without particular limitation.

(21) Preferably, the conductor may be contained in the amount of from 5 wt % to 15 wt % based on the total weight of the anode active material.

(22) The binder may include a member selected from the group consisting of polyacrylonitrile, 6,6-nylon, polyurethane, polybenzimidazole, polycarbonate, polyvinyl alcohol, polylacetic acid, polyethylene-co-vinylacetate, polymethylmethacrylate, polyaniline, polyethylene oxide, collagen, polystyrene, polyvinylcarbazole, polyethylene terephthalate, polyamide, polyamideimide, polyvinylphenol, polyvinylchloride, polyacrylamide, polycaprolactone, polyvinylidene fluoride, polyester amide, polyethylene glycol, polypyrrole, carboxymethyl cellulose, and combinations thereof.

(23) The binder needs to maintain binding of the anode active material even during charge and discharge cycles and may employ any material that enables the anode active material to be well bound to the current collector and thus contributes to the stability of a battery without particular limitation.

(24) Preferably, the binder may be contained in the amount of from 5 wt % to 15 wt % based on the total weight of the anode active material.

(25) A manufacturing method of an anode active material for secondary battery including porous iron oxide nanoparticles according to the present disclosure includes: preparing an iron-mixed solution by mixing an iron compound, a metal salt, and a solvent; and irradiating microwaves to the iron-mixed solution.

(26) Preferably, the irradiating of the microwaves to the iron-mixed solution may be performed when the temperature of the iron-mixed solution is in the range of from 100° C. to 300° C.

(27) Further, iron oxide can be obtained through oxidation of the iron-mixed solution. An additional process for adjusting a pH is not needed.

(28) Preferably, the irradiating of the microwaves may be performed for 10 minutes to 30 minutes.

(29) The manufacturing method of an anode active material including porous iron oxide nanoparticles makes it possible to obtain a large quantity of uniform nanoparticles of several hundred nanometers using a non-toxic metal salt as a source material.

(30) Further, the porous iron oxide nanoparticles are manufactured by irradiating the microwaves. Thus, a surfactant, a reductant, an oxidizer, and a co-precipitation agent which have been used in the conventional maturating method are not used. Therefore, no impurity remains even after the reaction and porous iron oxide nanoparticles can be manufactured in an environmentally friendly manner.

(31) Preferably, the iron-mixed solution has a concentration of from 0.01 M to 0.05 M.

(32) If the iron-mixed solution has a concentration of less than 0.01 M or more than 0.05 M, it is difficult to manufacture the anode active material including porous iron oxide nanoparticles to have a uniform particle diameter. Therefore, cracks may occur within an electrode due to volume expansion and contraction of the electrode during charges and discharges, which may result in a great loss of capacity and a sharp decrease in cycle efficiency.

(33) Particularly, as the particle diameter of the anode active material increases, an internal stress of particles caused by a volume change increases.

(34) Preferably, the anode active material including porous iron oxide nanoparticles has an average particle diameter of from 400 nm to 800 nm and has a spindle shape.

(35) The iron compound may include a member selected from the group consisting of iron(II) nitrate, iron(III) nitrate, iron(II) sulfate, iron(III) sulfate, iron(II) acetylacetonate, iron(III) acetylacetonate, iron(II) trifluoroacetylacetonate, iron(III) trifluoroacetylacetonate, iron(II) acetate, iron(III) acetate, iron(II) chloride, iron(III) chloride, iron(II) bromide, iron(III) bromide, iron(II) iodide, iron(III) iodide, iron perchlorate, iron sulfamate, iron(II) stearate, iron(III) stearate, iron(II) oleate, iron(III) oleate, iron(II) laurate, iron(III) laurate, iron pentacarbonyl, iron enneacarbonyl, disodium tetracarbonyl ferrate, and mixtures thereof, and may include preferably iron(II) chloride, but is not limited thereto.

(36) The metal salt may include a member selected from the group consisting of nitrate, carbonate, chloride salt, phosphate, borate, oxide, sulfonate, sulfate, stearate, myristate, acetate, acetylacetonate, hydrates thereof, and mixtures thereof, and may include preferably phosphate, but is not limited thereto.

(37) The phosphate may be preferably sodium dihydrogen phosphate, but is not limited thereto.

(38) The solvent may include a member selected from the group consisting of water, ethanol, isopropyl alcohol, propanol, butanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and mixtures thereof.

(39) Preferably, the microwaves may be irradiated at output power range of from 100 W to 600 W.

(40) If the microwaves are irradiated at output power of less than 100 W, a reaction may not be carried out sufficiently when the anode active material including porous iron oxide nanoparticles is manufactured. If the microwaves are irradiated at output power of more than 600 W, the temperature of a reaction solvent may be increased by excessive power output, which may cause a change in properties of the porous iron oxide nanoparticles.

(41) As described above, according to the present disclosure, it is possible to manufacture an anode active material for secondary battery including porous iron oxide nanoparticles with controlled particle diameter and particle shape through a simple manufacturing process, and the anode active material can be used to manufacture a secondary battery with reduced loss of capacity during numerous charges and discharges.

(42) A lithium secondary battery according to the present disclosure includes: an anode including an anode active material including porous iron oxide nanoparticles; a cathode including a cathode active material; a separator; and an electrolyte.

(43) The cathode active material may include at least one metal selected from the group consisting of lithium, cobalt, manganese, nickel, and combinations thereof as a compound suitable for reversible intercalation/deintercalation of lithium. For example, the cathode active material may include LiMn.sub.2O.sub.4, LiCoO.sub.2, LiNIO.sub.2, LiFeO.sub.2, V.sub.2O.sub.5, TiN, MoS.sub.2, etc., but is not limited thereto.

(44) The separator may include a member selected from the group consisting of polyethylene, polypropylene, polyvinylidene fluoride, or mixtures thereof, but is not limited thereto.

(45) Preferably, the electrolyte may be a non-aqueous electrolyte or a solid electrolyte.

(46) The non-aqueous electrolyte may employ a solution in which an electrolyte or a mixture of two or more electrolytes formed of a lithium salt such as LiCF.sub.3SO.sub.3,Li(CF.sub.3SO.sub.2).sub.2, LiPF.sub.6, LiBF.sub.4, LiClO.sub.4, LiN(SO.sub.2C.sub.2F.sub.5).sub.2 is dissolved in a non-proton solvent or a mixture of two or more non-proton solvents such as propylene carbonate (hereinafter, referred to as “PC”), ethylene carbonate (hereinafter, referred to as “EC”), butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate (hereinafter, referred to as “DMC”), ethyl methyl carbonate (hereinafter, referred to as “EMC”), diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether, etc., but is not limited thereto.

(47) Preferably, the solid electrolyte may employ a polymer with high ionic conductivity for lithium ions, such as polyethylene oxide, polypropylene oxide, polyethylene imine, etc., but is not limited thereto.

EXAMPLE

(48) Preparation of Anode Active Material for Secondary Battery

Example: 1

(49) An anode active material was prepared by mixing 0.04 M iron(II) chloride and 0.45 mM sodium dihydrogen phosphate in 40 ml of distilled water, stirring the mixture for 10 minutes, and irradiating microwaves to the mixture at 220° C. for 20 minutes.

(50) As illustrated in FIG. 1A, it can be seen that the anode active material has a particle diameter of 600 nm.

(51) Further, as illustrated in FIG. 1B, it can be seen that the anode active material is formed into a porous structure through self-assembly of spindle-shaped iron oxide particles with a diameter of about 50 nm.

(52) The specific surface area of the anode active material was measured using a BET specific surface area analyzer and illustrated in FIG. 2. It can be seen that the anode active material prepared according to Example 1 has a specific surface area of 70 m.sup.2/g.

Comparative Example 1

(53) An anode active material was prepared in the same manner as described in Example 1 except 0.04 M iron(II) chloride and 0.45 mM sodium dihydrogen phosphate.

(54) The anode active material prepared according to Comparative Example 1 includes primary fine nanoparticles with a diameter of 40 nm or less.

(55) Fabrication of Battery

Preparation Example 1

(56) The 70 wt % anode active material prepared in Example 1, a 15 wt % conductor (carbon black), and a 15 wt % binder (CMC) were mixed to prepare slurry. The slurry was applied to a copper current collector and then dried in a 100° C. vacuum oven for 12 or more hours. Lithium metal as a counter electrode, 1.0 M LiPF.sub.6/ethylene carbonate (EC): diethyl carbonate (DEC) (volume ratio of 1:1) as an electrolyte, and polyethylene as a separator were used to fabricate a coin-type half-cell.

Comparative Preparation Example 1

(57) A coin-type half-cell was fabricated in the same manner as described in Comparative Example 1 except the anode active material prepared in Example 2.

(58) In the battery fabricated in Comparative Preparation Example 1, the anode active material including fine particles prepared in Preparation Example 1 was used. Therefore, the particles underwent a volume change during charges and discharges, which resulted in a sharp decrease in capacity retention and cycle efficiency.

(59) [Evaluation Result]

(60) Battery Performance

(61) The performance of a secondary battery including the anode active material for secondary battery prepared according to Example 1 was evaluated. A charge and a discharge of the secondary battery were tested in a charge and discharge region ranging from 3.0 to 0.005 V (vs. Li/Li.sup.+), and the result was as illustrated in FIG. 3 and FIG. 4.

(62) As illustrated in FIG. 3 and FIG. 4, the battery including the anode active material prepared according to Example 1 had an initial charge and discharge efficiency (i.e. coulombic efficicency) of 86.5%, a discharge capacity of 1389.6 mAh/g, and a charge capacity of 1201.4 mAh/g, and the capacity was not much changed by intercalation and deintercalation of lithium ions during charges and discharges.

(63) Further, the capacity depending on the number of charge and discharge cycles was constantly maintained in the range of from 1150 mAh/g to 1250 mAh/g with high comlombic efficiency (more than 98%) even after repeated 100 charges and discharges, which shows the improvement in lifespan characteristics.