KR102594627B1 - Method for manufacturing positive electrode active material - Google Patents

Abstract

The present invention includes the steps of (a) preparing lithium iron phosphate-based particles, and (b) washing the lithium iron phosphate-based particles with a cleaning solution, wherein the cleaning solution includes a compound containing an epoxide functional group and a surfactant. A method for manufacturing a positive electrode active material comprising:

Description

Method for manufacturing positive electrode active material {METHOD FOR MANUFACTURING POSITIVE ELECTRODE ACTIVE MATERIAL}

The present invention relates to a method for producing a positive electrode active material.

As the electronics, communications, and space industries develop, the demand for secondary batteries as an energy power source is rapidly increasing. In particular, as the importance of global eco-friendly policies is emphasized, the electric vehicle market is growing rapidly, and research and development on secondary batteries is being actively conducted at home and abroad.

Among various secondary batteries, lithium secondary batteries with high discharge voltage and energy density are widely used as an energy source for various mobile devices and various electronic products.

Lithium transition metal composite oxide is used as a positive electrode active material for lithium secondary batteries, and among these, lithium cobalt composite metal oxide of LiCoO ₂ , which has a high operating voltage and excellent capacity characteristics, is mainly used. However, because LiCoO ₂ has low stability and is expensive, it is difficult to mass-produce lithium secondary batteries.

Accordingly, as materials to replace LiCoO ₂ , lithium manganese composite metal oxide, lithium iron phosphate, and lithium nickel composite metal oxide were developed. Among these, lithium iron phosphate (LiFePO ₄ ) with an olivine structure has a high volume density of 3.6 g/cm ³ and a theoretical capacity of about 170 mAh/g.

However, lithium impurities present on the surface of lithium iron phosphate (LiFePO ₄ ) cause surface defects in the lithium iron phosphate particles, which causes a problem of deterioration of lifespan characteristics. To solve this problem, a method of washing the surface of lithium iron phosphate (LiFePO ₄ ) with water was devised, but lithium impurities were not sufficiently removed, and the generally low electrical conductivity of lithium iron phosphate (LiFePO ₄ ) was considered. To compensate, a conductive layer is formed on the surface of lithium iron phosphate (LiFePO ₄ ), but the conductive layer is not formed uniformly on the surface of lithium iron phosphate (LiFePO ₄ ) due to the cleaning process, resulting in a decrease in electrical conductivity. A problem occurred.

As such, there is a need for a method in which lithium impurities formed in lithium iron phosphate (LiFePO ₄ ) can be sufficiently removed and electrical conductivity is not reduced.

The present invention provides a method for manufacturing a positive electrode active material with improved lifespan characteristics and electrical conductivity.

The method for producing a positive electrode active material according to the present invention includes the steps of (a) preparing lithium iron phosphate-based particles, and (b) washing the lithium iron phosphate-based particles with a cleaning solution, wherein the cleaning solution contains an epoxide functional group. Contains compounds and surfactants.

In one embodiment of the present invention, the lithium iron phosphate-based particles of step (a) may be a compound represented by Formula 1 below.

[Formula 1]

Li _1+a Fe _1-x M _x (PO _4-b )Y _b

In Formula 1, M is one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, and Zn, and Y is F, It is one or more elements selected from the group consisting of S and N, and a, b, and x are -0.5≤a≤0.5, 0≤b≤0.1, 0≤x≤0.5.

In one embodiment of the present invention, the lithium iron phosphate-based particles in step (a) may be LiFePO ₄ .

In one embodiment of the present invention, the compound containing an epoxide functional group in step (b) may be a compound represented by the following formula (2).

[Formula 2]

In Formula 2, R is a substituted or unsubstituted alkylene group having 2 to 6 carbon atoms, and n is an integer of 1 to 4.

In one embodiment of the present invention, the compound containing an epoxide functional group in step (b) may be a compound represented by the following formula (3).

[Formula 3]

In Formula 3, k is an integer of 1 to 2.

In one embodiment of the present invention, the compound containing an epoxide functional group in step (b) may be a compound represented by the following formula (4).

[Formula 4]

In Formula 4, p is an integer of 1 to 2.

In one embodiment of the present invention, the surfactant in step (b) may be a nonionic surfactant.

In one embodiment of the present invention, the content of the compound containing an epoxide functional group in step (b) may be 0.05% by weight to 3.00% by weight based on the total weight of the cleaning solution.

In one embodiment of the present invention, the content of the surfactant in step (b) may be 0.01% by weight to 1.00% by weight based on the total weight of the cleaning solution.

In one embodiment of the present invention, the cleaning solution of step (b) may include the compound containing the epoxide functional group and the surfactant in a weight ratio of 10:1 to 2:1.

In one embodiment of the present invention, after step (b), (c) heat treating the cleaned lithium iron phosphate-based particles at 90°C to 160°C for 1 hour to 20 hours, and (d) the heat treatment. It may further include forming a conductive layer on the surface of the lithium iron phosphate-based particles.

In one embodiment of the present invention, the content of residual lithium present on the surface of the positive electrode active material obtained in step (d) may be 0.1% by weight or less based on the total weight of the positive electrode active material.

The present invention has the effect of significantly reducing lithium impurities and improving the lifespan characteristics of secondary batteries by including a compound containing an epoxide functional group in the cleaning solution in the process of cleaning lithium iron phosphate-based particles.

In addition, the present invention has the effect of improving electrical conductivity by uniformly forming a conductive layer on the surface of the lithium iron phosphate-based particles by including a surfactant in the cleaning solution in the process of cleaning the lithium iron phosphate-based particles.

The structural or functional descriptions of the embodiments disclosed in the present specification or application are merely illustrative for the purpose of explaining embodiments according to the technical idea of the present invention, and the embodiments according to the technical idea of the present invention are described in this specification. Alternatively, it may be implemented in various forms other than the embodiments disclosed in the application, and the technical idea of the present invention is not to be construed as being limited to the embodiments described in this specification or application.

Below, a method for manufacturing a positive electrode active material according to the present invention will be described.

The method for producing a positive electrode active material according to the present invention is (a) lithium iron phosphate-based particles.

manufacturing, and (b) washing the lithium iron phosphate-based particles with a cleaning solution, wherein the cleaning solution includes a compound containing an epoxide functional group and a surfactant.

The production method according to the present invention includes the step of (a) producing lithium iron phosphate-based particles.

Lithium iron phosphate-based particles can be produced by adding a lithium (Li) precursor, a phosphorus (P) precursor, and an iron (Fe) precursor to a solvent, reacting the mixture, and then heat treating it in an inert gas atmosphere. The lithium (Li) precursor may include at least one selected from the group consisting of lithium carbonate, lithium nitrate, lithium hydroxide, and lithium chloride. The phosphorus (P) precursor may include at least one selected from the group consisting of ammonium phosphate and phosphoric acid. The iron (Fe) precursor may include at least one selected from the group consisting of iron sulfate, iron chloride, iron nitrate, and iron carbonate. In order to improve electrical conductivity as needed, metal-introduced lithium iron phosphate-based particles can be prepared by mixing a metal precursor with lithium iron phosphate.

The lithium iron phosphate-based particles prepared in step (a) may be a compound represented by Formula 1 below.

[Formula 1]

Li _1+a Fe _1-x M _x (PO _4-b )Y _b

In Formula 1, M is one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, and Zn, and Y is F, It is one or more elements selected from the group consisting of S and N, and a, b, and x are -0.5≤a≤0.5, 0≤b≤0.1, 0≤x≤0.5.

For example, the lithium iron phosphate-based particles prepared in step (a) may be LiFePO ₄ .

The manufacturing method according to the present invention includes the step of (b) washing the lithium iron phosphate-based particles with a cleaning solution, and the cleaning solution includes a compound containing an epoxide functional group and a surfactant.

Generally, in the process of manufacturing lithium iron phosphate-based particles, a cleaning process may be performed to remove lithium impurities remaining on the surface of the lithium iron phosphate particles. Remaining lithium impurities may include lithium salts in the form of lithium cations and anions such as hydroxide ions and carbonate ions, for example, lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and lithium oxide (Li ₂ O) etc. may be included. If a large amount of lithium impurities are present, defects may occur on the surface of the lithium iron phosphate-based particles, which may deteriorate the lifespan characteristics of the secondary battery. A cleaning process can be performed using water (H ₂ O) to remove lithium impurities, but the lithium impurities are not sufficiently removed, making it difficult to improve the lifespan characteristics of the secondary battery due to the remaining lithium impurities.

Accordingly, the production method according to the present invention can remove lithium impurities more effectively by including a compound containing an epoxide functional group in the cleaning solution. Specifically, the hydroxyl group of lithium hydroxide (LiOH) remaining on the surface of lithium phosphate can act as a nucleophile. The hydroxy group can react with the epoxide functional group, leading to a ring-opening reaction of the epoxide functional group, so that lithium hydroxide (LiOH) remaining on the surface of the lithium phosphate can be more effectively removed.

The compound containing an epoxide functional group may be a compound represented by the following formula (2).

[Formula 2]

In Formula 2, R is a substituted or unsubstituted alkylene group having 2 to 6 carbon atoms, and n is an integer of 1 to 4.

When n is an integer exceeding 4, the solubility of the compound containing the epoxide functional group in water (H ₂ 0) is reduced, resulting in a large amount of epoxide-based compounds remaining after manufacturing lithium iron phosphate-based particles, or The effectiveness of removing lithium impurities may be reduced.

Specifically, the compound containing an epoxide functional group may be a compound represented by the following formula (3).

[Formula 3]

In Formula 3, k is an integer of 1 to 2.

Additionally, the compound containing an epoxide functional group may be a compound represented by the following formula (4).

[Formula 4]

In Formula 4, p is an integer of 1 to 2.

The content of the compound containing an epoxide functional group may be 0.05% to 3.00% by weight, 0.10% to 3.00% by weight, or 0.30% to 1.00% by weight, based on the total weight of the cleaning liquid. When the above range is satisfied, the lifespan characteristics of the secondary battery can be improved by reducing lithium impurities without deteriorating electrical conductivity.

Meanwhile, in order to compensate for the low electrical conductivity of lithium iron phosphate due to its characteristics, a conductive layer can be formed on the surface of lithium iron phosphate. However, when a cleaning process is performed to remove lithium impurities remaining on the surface of the lithium iron phosphate, the adhesion between the lithium iron phosphate and the conductive layer forming material decreases after cleaning, making it difficult to form a uniform conductive layer. A problem occurred.

Accordingly, the manufacturing method according to the present invention improves the adhesion between lithium iron phosphate and the conductive layer forming material by including a surfactant as well as a compound containing an epoxide functional group in the cleaning solution, and the surface of the lithium iron phosphate-based particles Since the conductive layer is formed uniformly, electrical conductivity can be improved.

Surfactants can be classified into anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. Anionic surfactants, cationic surfactants, and amphoteric surfactants can cause corrosion of the positive electrode current collector due to remaining ionic substances when the manufactured positive electrode active material is formed on the positive electrode current collector. Preferably, the surfactant is It may be a nonionic surfactant.

The nonionic surfactant may include one or more selected from the group consisting of polyoxyethylene alkyl ether, polyoxyethylene acyl ester, polyoxyethylene sorbitan fatty acid ester, and tetraethylene glycol dodecyl ether.

The content of the surfactant may be 0.01% to 1.00% by weight, 0.05% to 1.00% by weight, or 0.05% to 0.50% by weight based on the total weight of the cleaning solution. When the above range is satisfied, electrical conductivity can be improved without reducing the capacity of the secondary battery.

The cleaning solution may include a compound containing an epoxide functional group and the surfactant in a ratio of 10:1 to 2:1, 9:1 to 2:1, or 7:1 to 2:1. When the above range is satisfied, the lifespan characteristics of the secondary battery can be significantly improved by improving electrical conductivity while minimizing the content of residual lithium.

The production method according to the present invention includes, after step (b), (c) heat treating the cleaned lithium iron phosphate-based particles at 90°C to 160°C for 1 to 20 hours, and (d) heat-treating the lithium iron phosphate-based particles. It may further include forming a conductive layer on the surface of the particle.

In step (c), the cleaned lithium iron phosphate-based particles may be heat treated at 90°C to 160°C, 90°C to 150°C, or 100°C to 150°C for 1 hour to 20 hours. Additionally, if necessary, step (c) may be performed by classifying the heat-treated lithium iron phosphate-based particles.

In step (d), electrical conductivity can be improved by forming a conductive layer on the surface of the heat-treated lithium iron phosphate-based particles. The conductive layer may include a carbon-based material. For example, carbon-based materials include carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal, activated carbon, polyphenylene derivative, natural graphite, artificial graphite, and Super-P. , acetylene black, Ketjen black, channel black, Phineas black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, gallium titanate, and titanium oxide.

The content of residual lithium present on the surface of the positive electrode active material obtained in step (d) may be 0.100% by weight or less, 0.080% by weight or less, or 0.062% by weight or less based on the total weight of the positive electrode active material. The content of residual lithium refers to the total content of materials present in the form of LiOH and Li ₂ CO ₃ present on the surface of the positive electrode active material. Residual lithium may react with the electrolyte in the secondary battery to generate gas or cause swelling, thereby reducing the high-temperature stability and lifespan characteristics of the secondary battery. The manufacturing method according to the present invention can significantly reduce the content of residual lithium by including a compound containing an epoxide functional group and a surfactant in the cleaning solution in the step of cleaning the lithium iron phosphate-based particles.

A secondary battery may include a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The positive electrode may include the above-described positive electrode active material, and the positive electrode active material may be mixed with a binder and a conductive material to form a positive electrode active material layer on the positive electrode current collector.

The binder can improve the bonding force between the positive electrode active material and the conductive material and the bonding force between the positive active material layer and the positive electrode current collector. The binder may be added in an amount of 1 to 30 parts by weight, 1 to 20 parts by weight, or 1 to 15 parts by weight based on 100 parts by weight of the positive electrode active material. The type of binder is not particularly limited, but for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, styrene butadiene rubber (SBR), cellulose resin, etc. can be used.

Conductive materials can improve the conductivity of the positive electrode active material. The conductive material may be added in an amount of 1 to 40 parts by weight, 1 to 20 parts by weight, or 1 to 10 parts by weight based on 100 parts by weight of the positive electrode active material. The type of conductive material is not particularly limited, but for example, Super-P, graphite, acetylene black, etc. can be used.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the secondary battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , those surface treated with nickel, titanium, silver, etc. can be used. The thickness of the positive electrode current collector may be adjusted depending on the required product, and may be, for example, 10 μm to 500 μm, 10 μm to 300 μm, or 20 μm to 300 μm.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the secondary battery. For example, it can be used on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding power of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The negative electrode active material layer may include a negative electrode active material.

The type of anode active material is not particularly limited, and usually a compound capable of reversible intercalation and deintercalation of lithium can be used. For example, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, and highly crystalline carbon; Metallic compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy, can be used. Low-crystalline carbon includes soft carbon and hard carbon, and high-crystalline carbon includes natural graphite, kish graphite, pyrolytic carbon, and liquid crystalline carbon. Examples include high-temperature calcined carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes. The negative electrode active material may be a composite containing a metallic compound and a carbonaceous material, if necessary.

A separator may be interposed between the cathode and the anode. The separator is designed to prevent electrical short-circuiting between the cathode and anode and to generate ion flow. The separator may include a porous polymer film or a porous non-woven fabric. Here, the porous polymer film is ethylene polymer, propylene polymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate. ) It may be composed of a single layer or multiple layers containing polyolefin-based polymers such as copolymers. The porous nonwoven fabric may include high melting point glass fibers and polyethylene terephthalate fibers. However, it is not limited to this, and depending on the embodiment, the separator may be a highly heat-resistant separator (CCS; Ceramic Coated Separator) containing ceramic.

The anode, cathode, and separator can be manufactured into an electrode assembly by winding, lamination, folding, or zigzag stacking processes. Additionally, the electrode assembly can be provided with an electrolyte to manufacture a secondary battery according to the present invention. The secondary battery may be any one of a cylindrical, square, pouch, or coin type using a can, but is not limited thereto.

The electrolyte may be a non-aqueous electrolyte. The electrolyte solution may include a lithium salt and an organic solvent. The organic solvent includes propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), dipropyl carbonate (DPC), Vinylene carbonate (VC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone ), propylene sulfide, or tetrahydrofuran.

Below, the present invention will be described in more detail based on examples and comparative examples. However, the following examples and comparative examples are only examples to explain the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

Example

Example 1

<Manufacture of positive electrode active material>

Add 0.5 mol of iron sulfate (FeSO ₄ ㆍ7H ₂ O), 0.5 mol of phosphoric acid (H ₃ PO ₄ ), and 2.0 mol of aqueous iron sulfate solution containing antioxidants and 2.0 mol of lithium aqueous solution (LiOH ㆍH ₂ O) to pH 6.4. A positive electrode slurry was prepared by adding ammonia water. Afterwards, the positive electrode slurry was added at a constant rate under the conditions of 500°C and 260 bar in a continuous process supercritical reactor to obtain LiFePO ₄ .

Afterwards, the LiFePO was added to a cleaning solution mixed with water (H ₂ O): ethylene glycol diglycidyl ether: tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1. After adding ₄ particles, the mixture was washed for 20 minutes and dried at 130°C to obtain LiFePO ₄ particles.

Afterwards, the LiFePO ₄ particles were mixed with amorphous carbon and then heat treated at 300°C for 3 hours to prepare a positive electrode active material in which a conductive layer was formed on the surface of the LiFePO ₄ particles.

<Anode manufacturing>

A positive electrode active material slurry was prepared by mixing the positive electrode active material, Super-P, and polyvinylidene fluoride binder in N-methyl pyrrolidone solvent at a weight ratio of 94.5:2.5:3.0. Afterwards, the positive electrode active material slurry was coated on a 20㎛ thick aluminum (Al) foil, dried at 100°C, and then pressed to produce a positive electrode.

<Cathode manufacturing>

A negative electrode active material slurry was prepared by mixing soft carbon negative electrode active material, which is amorphous carbon with an average particle diameter of 10㎛, acetylene black, and polyvinylidene fluoride binder, in N-methyl pyrrolidone solvent at a weight ratio of 85:5:10. Afterwards, the negative electrode active material slurry was coated on a 10㎛ thick copper (Cu) foil, dried at 100°C, and then pressed to produce a negative electrode.

<Secondary battery manufacturing>

After manufacturing the electrode assembly by interposing a separator made of polyethylene with a thickness of 20 μm between the cathode and the anode, the electrode assembly is stored in a case, and ethylene carbonate and methyl ethyl carbonate are mixed in a volume ratio of 2:1 inside the case. A secondary battery was manufactured by adding an electrolyte solution containing 1M LiPF ₆ and 3% by weight of vinyl carbonate to the solvent.

Example 2

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H ₂ O): Propylene glycol diglycidyl ether: A positive electrode active material is manufactured using a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1. A secondary battery was manufactured in the same manner as in Example 1 except that.

Example 3

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H ₂ O): Ethylene glycol diglycidyl ether: A positive electrode active material is manufactured using a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 96.2:3.5:0.3. A secondary battery was manufactured in the same manner as Example 1 except that.

Example 4

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H ₂ O): Ethylene glycol diglycidyl ether: Clean the positive electrode active material using a cleaning solution mixed with polyoxyethylene sorbitan fatty acid ester in a weight ratio of 99.4:0.5:0.1. A secondary battery was manufactured in the same manner as in Example 1, except that it was manufactured.

Example 5

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H ₂ O): Ethylene glycol diglycidyl ether: A positive electrode active material is manufactured using a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 96.8:2.0:1.2. A secondary battery was manufactured in the same manner as in Example 1 except that.

Example 6

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H ₂ O): Propylene glycol diglycidyl ether: Except that the positive electrode active material is manufactured using a cleaning solution mixed with Lauryl betaine at a weight ratio of 99.4:0.5:0.1. A secondary battery was manufactured in the same manner as Example 1.

Comparative Example 1

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was manufactured using only _2O ) as a cleaning solution.

Comparative Example 2

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H ₂ O): A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was prepared using a cleaning solution mixed with ethylene glycol diglycidyl ether at a weight ratio of 99.5:0.5. did.

Comparative Example 3

Water (H ₂ O): Ethylene glycol diglycidyl ether: Instead of a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.4:0.5:0.1, water (H ₂ O): A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was prepared using a cleaning solution mixed with tetraethylene glycol dodecyl ether at a weight ratio of 99.9:0.1. .

Experiment example

Experimental Example 1 - Measurement of residual lithium content

After dissolving 10 g of each positive electrode active material prepared in Examples 1 to 6 and Comparative Examples 1 to 3 in 100 ml of water (H ₂ 0), the change in pH value was measured while titrating with 0.1 M HCl, and a pH titration curve was used. Thus, the residual amount of LiOH and Li ₂ CO ₃ were calculated, and the sum thereof was evaluated as the total residual lithium content and is shown in Table 1 below.

LiOH residual amount Li ₂ CO ₃ residual amount Content of residual lithium Example 1 0.011% by weight 0.034% by weight 0.045% by weight Example 2 0.012% by weight 0.035% by weight 0.047% by weight Example 3 0.012% by weight 0.033% by weight 0.045% by weight Example 4 0.010% by weight 0.035% by weight 0.045% by weight Example 5 0.020% by weight 0.042% by weight 0.062% by weight Example 6 0.013% by weight 0.035% by weight 0.048% by weight Comparative Example 1 0.090% by weight 0.158% by weight 0.248% by weight Comparative Example 2 0.011% by weight 0.035% by weight 0.046% by weight Comparative Example 3 0.084% by weight 0.140% by weight 0.224% by weight

Experimental Example 2 - Electrical conductivity evaluation

10 g of each positive electrode active material prepared in Examples 1 to 6 and Comparative Examples 1 to 3 was placed in a holder and rolled with a force of 60 kN, and then applied to a powder-only 4-detection ring electrode (Mitsubishi Chemical, Powder Resistance System (MCP=PD51) )) was used to measure electrical conductivity, and the results are shown in Table 2 below.

electrical conductivity Example 1 0.0084 S/cm 49.34×10 ^-3 S/cm Example 2 0.0083 S/cm 49.35×10 ^-3 S/cm Example 3 0.0101 S/cm 42.33×10 ^-3 S/cm Example 4 0.0083 S/cm 49.33×10 ^-3 S/cm Example 5 0.0083 S/cm 49.34×10 ^-3 S/cm Example 6 0.0095 S/cm 43.12×10 ^-3 S/cm Comparative Example 1 0.0442 S/cm 11.23×10 ^-3 S/cm Comparative Example 2 0.0447 S/cm 12.32×10 ^-3 S/cm Comparative Example 3 0.0092 S/cm 49.35×10 ^-3 S/cm

Experimental Example 3 - Evaluation of lifespan characteristics

Each secondary battery prepared in Examples 1 to 6 and Comparative Examples 1 to 3 was charged and discharged at a constant current of 1C rate in a voltage range of 2.5V to 4.1V relative to lithium metal at room temperature, and the capacity retention rate and discharge at the 300th cycle were measured. The capacity was measured. The capacity retention rate at room temperature was calculated using Equation 1 below, and the results are shown in Table 3 below.

[Equation 1]

Capacity maintenance rate (%) = [discharge capacity in the 300th cycle/discharge capacity in the 1st cycle]Х100

Capacity maintenance rate Discharge capacity at 300th cycle Example 1 96.1% 137.3mAh/g Example 2 95.9% 137.1mAh/g Example 3 93.2% 132.3mAh/g Example 4 96.1% 137.3mAh/g Example 5 93.1% 132.1mAh/g Example 6 93.4% 132.4mAh/g Comparative Example 1 85.4% 118.7mAh/g Comparative Example 2 83.9% 115.3mAh/g Comparative Example 3 84.5% 116.6mAh/g

As can be seen in Tables 1 to 3, Examples 1 to 6, in which positive electrode active materials were prepared by washing lithium iron phosphate-based particles with a cleaning solution containing a compound containing an epoxide functional group and a surfactant, are Comparative Examples 1 and 6. It was confirmed that the content of residual lithium was significantly reduced compared to 3. In addition, it was confirmed that Examples 1 to 6 had significantly improved electrical conductivity compared to Comparative Examples 1 and 2. In addition, it was confirmed that the secondary batteries of Examples 1 to 6 containing the positive electrode active material manufactured according to the manufacturing process of the present invention had improved lifespan characteristics compared to Comparative Examples 1 to 3.

Claims (5)

(a) preparing LiFePO ₄ particles; and
(b) comprising the step of cleaning the LiFePO ₄ particles with a cleaning solution,
The cleaning liquid contains a compound containing an epoxide functional group and a surfactant.
Method for producing a positive electrode active material. delete According to paragraph 1,
A method for producing a positive electrode active material, wherein the compound containing an epoxide functional group in step (b) is a compound represented by the following formula (2):
[Formula 2]

In Formula 2,
R is a substituted or unsubstituted alkylene group having 2 to 6 carbon atoms,
n is an integer from 1 to 4. According to paragraph 1,
A method for producing a positive electrode active material, wherein the surfactant in step (b) is a nonionic surfactant. According to paragraph 1,
The cleaning solution of step (b) includes the compound containing the epoxide functional group and the surfactant in a weight ratio of 10:1 to 2:1.