KR100785491B1 - Preparation method of active material for positive electrode of lithium secondary battery and lithium secondary battery thereby - Google Patents

Abstract

The present invention comprises the steps of mixing and grinding the LiFePO ₄ precursor and carbon; And it provides a method for producing an active material for lithium secondary battery cathode material comprising the step of microwave heating the pulverized product to prepare an electrode active material.

According to the present invention, it is possible to significantly shorten the manufacturing process time of the active material, and to provide an active material for a lithium secondary battery positive electrode material and a lithium secondary battery having a discharge capacity, a lifetime, and a high rate discharge characteristic.

Description

Preparation method of active material for lithium secondary battery positive electrode material and lithium secondary battery {Preparation method of active material for positive electrode of lithium secondary battery and lithium secondary battery

1 is a TEM photograph of an active material for positive electrode material (LiFePO ₄ / C composite) prepared according to the present invention.

2 is a graph showing the discharge capacity according to the discharge current density of the positive electrode material active material (LiFePO ₄ / C composite) prepared according to the present invention.

3 is a graph showing the electrode life of the active material for positive electrode material (LiFePO ₄ / C composite) prepared according to the present invention.

The present invention relates to a method for manufacturing an active material for a lithium secondary battery positive electrode material, and more particularly, to significantly shorten the manufacturing process time, active material for a lithium secondary battery positive electrode material having a discharge capacity and lifespan, high rate discharge characteristics It relates to a manufacturing method and a lithium secondary battery comprising the same.

As the demand for portable electric devices such as laptops, camcorders, mobile phones, and small recorders is rapidly increasing and miniaturizing, lithium secondary batteries, which are energy sources thereof, are developing toward increasing energy density and increasing lifespan. The most important part of the lithium secondary battery is the material constituting the negative electrode and the positive electrode, and in particular, the material used for the positive electrode of the lithium secondary battery has (1) high discharge capacity, (2) low price, and (3) cycle characteristics. It should be excellent and have long electrode life. (4) It should be excellent in thermal and structural stability, so there is no risk of explosion.

LiFePO ₄ has a theoretical capacity of 170mAh / g, which has a higher discharge capacity than LiCoO ₂ (120-150mAh / g), a cathode material of a lithium secondary battery, and is inexpensive because it uses cheap Fe without Co. It does not use heavy metal and has environmentally friendly advantages.

In addition, the material has excellent chemical and structural stability, and thus has a very good electrode life. In particular, the material has excellent thermal stability, which is very suitable as a cathode material of an automotive lithium secondary battery. However, since LiFePO ₄ has Fe ^{2+ as} the oxidation number of Fe, it is difficult to prevent the oxidation of Fe ²⁺ to Fe ³⁺ during the manufacturing process, and the difficulty of preparing single-phase LiFePO ₄ without any by-products and LiFePO _4. is a Li- this diffusion coefficient (10 ^-14 ㎠ / s) and electrical conductivity ^{(10 -8 ~ 10 -9 s /} cm) is very low, high-rate discharge characteristic has a considerably less drawbacks compared to LiCoO _2.

Succeeded in producing the single-phase LiFePO ₄ and that, but improved high-rate discharge characteristics are very rare and one research group reaching the level of commercialization in terms of performance, especially LiFePO ₄ has a high-performance processing time by several processes are many researchers to date There are very few groups that have been economically produced by shortening the time. Most research groups have reported that it takes at least 7 to 48 hours to produce LiFePO ₄ , including the mixing and heat treatment steps.

The present invention has been proposed to solve the problems of the prior art as described above, an object of the present invention is to significantly shorten the manufacturing process time, the lithium secondary battery positive electrode having a discharge capacity and life, high rate discharge characteristics The present invention provides a method for producing an active material for a material.

Another object of the present invention is lower cost than the conventional lithium secondary battery, high capacity, environmentally friendly, and particularly excellent thermal stability lithium can be commercialized as a next-generation secondary battery that can replace the conventional lithium secondary battery In providing a secondary battery.

In order to achieve the above object, the present invention comprises the steps of mixing and grinding the LiFePO ₄ precursor and carbon; And it provides a method for producing an active material for lithium secondary battery cathode material comprising the step of microwave heating the pulverized product to prepare an electrode active material.

The present invention preferably provides a method for producing an active material for a lithium secondary battery positive electrode material, wherein the grinding process includes a ball milling process.

The present invention preferably provides a method for producing an active material for a lithium secondary battery cathode material, wherein the microwave heating is performed in a reducing atmosphere.

The present invention preferably provides a method for producing an active material for a lithium secondary battery cathode material, wherein the reducing atmosphere is provided by covering the pulverized product with activated carbon.

The present invention preferably provides a method for producing an active material for a lithium secondary battery cathode material, wherein the reducing atmosphere is provided by supplying an argon-hydrogen mixed gas in which hydrogen is mixed with argon.

The present invention preferably provides a method for producing an active material for a lithium secondary battery positive electrode material, wherein the microwave heating is performed under an inert atmosphere.

The present invention preferably provides a method for producing an active material for a lithium secondary battery cathode material, wherein the inert atmosphere is provided by supplying argon gas or nitrogen gas.

The present invention also provides an active material for a lithium secondary battery cathode material containing a result obtained by microwave heating of a pulverized mixture of LiFePO ₄ precursor and carbon in a reducing atmosphere or an inert atmosphere.

The present invention also provides a lithium secondary battery using the active material as a cathode material.

Hereinafter, the content of the present invention will be described in detail.

The present invention relates to a method for producing an active material used for a positive electrode constituting a lithium secondary battery, an active material and a lithium secondary battery including a positive electrode composed of these active materials.

The active material for a positive electrode material according to the present invention has a short manufacturing time, can provide a discharge capacity and life, high rate discharge characteristics. Such an active material for a positive electrode material is manufactured by the following process.

LiFePO ₄ precursor and carbon are used as raw materials for the preparation of the positive electrode active material.

LiFePO ₄ precursor does not require special limitation as long as it can produce LiFePO ₄ by reaction, for example lithium phosphate (Li ₃ PO ₄ ), iron phosphate hydrate (Fe ₃ (PO ₄ ) ₂ ㆍ 8H ₂ O ). Although the theoretical molar ratio between these precursor materials is 1: 1, it is also possible to administer an excessive amount of either material depending on the conditions.

Carbon may be acetylene black, carbon black, or the like as a material having electrical conductivity.

The mixing ratio of the precursor of LiFePO ₄ and carbon is not particularly limited, and for example, 1 to 10% by weight of carbon may be mixed with respect to the weight of LiFePO ₄ .

The mixture of the precursor of LiFePO ₄ and carbon is ground to have a predetermined particle size, and may be preferably performed by a ball milling process. The particle size of the milled product is preferably in the size of submicron units, and preferably in the case of micron units does not exceed 10 microns.

The mixture pulverized through the above process is heated with microwaves to perform a thermal carbon reaction. The thermocarbon reaction includes a process of applying heat to the carbon contained in the mixture to oxidize it, and this process may be performed under a reducing atmosphere or an inert atmosphere.

The reducing atmosphere may be provided by placing a mixture obtained through the above process in a container through which microwave is well permeated, for example, a quartz container, and covering the surroundings of the mixture with activated carbon. In this case, in order to facilitate the separation and separation of the activated carbon and the mixture according to the present invention, it is preferable to pelletize the mixture. The pelletization process of the mixture can be carried out through known uniaxial press molding processes.

In addition, in addition to the activated carbon, a reducing atmosphere may also be provided through a process in which hydrogen, which is a reducing gas, flows through an argon-hydrogen mixed gas mixed with argon. In this case the mixture need not be molded into pellets.

An inert atmosphere may be provided through a process of supplying an inert gas to the mixture according to the present invention, for example, a process of supplying argon gas, nitrogen gas, and the like into a microwave oven. When the microwave is irradiated to the mixture under an inert atmosphere formed by this process, a desired active material may be prepared by thermal carbon reaction by activated carbon included in the mixture. As described above, even if the pellets are heated with microwaves in an argon atmosphere without filling the activated carbon, the carbon mixed in the pellets also causes a thermal carbon reaction, so that the process may be regarded as a reducing atmosphere as a whole. In this case also the mixture according to the invention need not be shaped into pellets.

The irradiation step of the microwave is required to be carried out under conditions sufficient to cause a thermal carbon reaction of the carbon used, for example, by irradiation for 1 to 20 minutes at about 0.5 ~ 5KW output.

After completion of the microwave heating step as described above, the reaction product is cooled to room temperature in a vacuum state, and if the pellet is made of pellets after cooling to perform a process of grinding using a mortar and the like.

The active material thus prepared is made of a slurry-like material by mixing with an electrically conductive material for improving electrical conductivity and a binder in an appropriate ratio, and applying the resulting slurry-like material onto the current collector, and then sufficiently dried and compressed in a vacuum oven. It is made into an electrode.

The composition ratio of the active material, the conductive material, and the binder used in the embodiment of the present invention is illustrated as 70 to 80: 10 to 20: 5 to 10 without weight, but is not limited thereto, and the conductive material is acetylene black or carbon. Conductive carbon, such as black, may be used, and as a binder, polyvinylidene fluoride, SBR aqueous binder, PTFE (no solvents are needed, and the active material and the conductive material are mixed with PTFE in a mud state without being a slurry process. Making an electrode and immediately compressing the current collector) may be used.

The slurry material may be prepared by mixing the active material and the conductive material in a solvent such as N-methylpyrrolidone (when polyvinylidene fluoride is a binder) and water (when SBR is a binder) as a binder. An aluminum foil or the like is used as the current collector to be applied, and the slurry may be applied to a thickness of about 20 to 60 μm on the current collector.

After the slurry containing the active material is applied, the drying process is not particularly limited, and for example, may be dried in a vacuum oven for 2 to 10 hours in the range of 100 to 140 ° C. The electrode obtained after the drying process is compressed to a pressure of 100 ~ 140kg / ㎠ to be manufactured as an electrode.

The process of manufacturing the lithium secondary battery using the prepared electrode may be performed according to a known manufacturing method. According to an embodiment of the present invention, the positive electrode manufactured according to the present invention includes a lithium foil as a counter electrode, an electrolyte in which lithium chloric acid is dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate, and a Celgard 2400 propylene separator 2016. A coin type battery was produced.

The manufacturing process of the active material according to the present invention takes less than 40 minutes considering the mixing process (approximately 30 minutes) and heat treatment (approximately several minutes) process of the raw material is significantly shorter than any of the known processes.

In addition, the result of the charge / discharge experiment using the battery manufactured through the above process showed a high discharge capacity of almost 100% higher than the theoretical capacity at a low current density, and also a high discharge capacity at a very high current density. It was confirmed to represent.

Electrode life according to the present invention with respect to the electrode life can be seen that the discharge capacity hardly decreases even if the charge and discharge cycle increases at various current densities.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are presented only for understanding of the present invention, and the scope of the present invention should not be construed as being limited thereto.

EXAMPLES Preparation of LiFePO ₄ -Carbon Composites Using Ball Milling and Microwave Heating

(1) Ball Milling of Precursor with Carbon

In this example, Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ .8H ₂ O were used as precursors for synthesizing LiFePO ₄ . Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ .8H ₂ O were mixed in a molar ratio of 1: 1, and then 5 parts by weight of acetylene black carbon was added. Afterwards, 30 minutes of vibrant-type ball milling was performed in an Ar atmosphere using stainless steel containers and balls. The ratio was 8.10: 1 and ball milling was performed according to the same ratio.

(2) microwave heating

The mixture prepared through ball milling was pelleted through uniaxial press molding and then heated for 2 minutes with microwave under a reducing atmosphere. At this time, the reducing atmosphere is a method in which a pellet is placed in a quartz crucible containing an appropriate amount of activated carbon and completely covered with activated carbon, and then provided by using a carbon thermal reaction of the activated carbon. It can be provided using only the hot carbon reaction of mixed acetylene black. In this embodiment, the thermal carbon reaction was carried out under the condition of irradiating the microwave for 2 to 4 minutes in a microwave oven of 750W using the method of putting the activated carbon together in the above method. After the microwave heating was completed, the pellet was immediately cooled to room temperature in a vacuum state and then ground using a mortar and pestle.

Tunneling electron microscopy (TEM) photographs of LiFePO ₄ / C composites prepared by using ball milling for 30 minutes and microwave heating for 2 minutes selected as the optimum conditions by the above process are shown in FIG. 1. According to the results, it can be seen that carbon and LiFePO ₄ having a very small and uniform particle size of 200 to 300 nm are uniformly mixed on the nanometer scale to form a composite.

(3) Preparation of the electrode

LiFePO ₄ -carbon composite as an active material, acetylene black as a conductive material to improve electrical conductivity, and PVDF (polyvinylidene fluoride) as a binder were used. The weight ratio (weight%) was 75: 17: 8. A slurry was prepared by mixing an active material and a conductive material in an NMP (N-methylpyrrolidone) solution in which a binder was dissolved, and then applying a slurry on Al foil, which is a current collector, and drying at 120 ° C. for 5 hours in a vacuum oven. Thereafter, the dried electrode was compressed to a pressure of 120 kg / cm 2 to prepare an electrode.

(4) assembly of batteries

In order to perform the charging and discharging experiment, the electrode manufactured through the process of (3) was used as a working electrode, a Li foil as a counter electrode, and EC (ethylene carbonate): DMC (dimethyl carbonate) was 1: 1. A coin-type cell was manufactured in 2016 by using an electrolyte in which 1 M LiClO ₄ was dissolved and a Celgard 2400 polypropylene separator. In manufacturing a coin type battery, a copper spacer was used for the miniaturization of the cell, and a coin type battery was assembled in a glove box filled with Ar.

(5) Charge / discharge experiment of battery

Charge / discharge tests of coin type batteries were conducted using a battery tester (Toscat-3100U) manufactured by Toyo system Co. (Japan). Cut-off voltage during charge and discharge is 2.5V-4.3V vs. Li / Li ⁺ and a charge / discharge rate were 0.02C-20C. And the rest time between charge and discharge was maintained for 10 minutes.

The experiment as a result also found in 2, LiFePO ₄ / in the discharge capacity results in accordance with the discharge current density of LiFePO ₄ / C composite of the C complex of C / in 30 166 mAh / g (theoretical capacity (170 mAh / g) It has a high discharge capacity of about 98%) and shows excellent high-rate discharge characteristics that maintain a discharge capacity of 107 mAh / g (about 65% of the capacity at C / 30) even at a very high current density of 20C.

In addition, as can be see in Figure 3 the results of measuring the electrode life, when charging and discharging the LiFePO ₄ / C composite electrode in a number of the current density in the LiFePO measuring electrode life of ₄ / C composite results produced in accordance with the present invention, the charge and discharge It can be seen that the discharge capacity hardly decreases even if the cycle increases.

According to the present invention, it is possible to significantly shorten the manufacturing process time of the electrode active material, and to provide an active material for a lithium secondary battery positive electrode material having discharge capacity, lifetime, and high rate discharge characteristics. Accordingly, the lithium secondary battery manufactured with the active material according to the present invention is cheaper than the existing lithium secondary battery, has a high capacity, is environmentally friendly, and has particularly excellent thermal stability, thereby replacing the existing lithium secondary battery. It can be commercialized as a next-generation secondary battery.

Claims (9)

Mixing and grinding LiFePO ₄ precursor and carbon; Pelletizing the mixed pulverized product of the LiFePO ₄ precursor and carbon; Heating the pelletized material with microwaves in a reducing atmosphere covered with activated carbon or an inert atmosphere in the presence of an inert gas, and Method of manufacturing an active material for a lithium secondary battery positive electrode material comprising the step of heating the pelletized material with a microwave and then pulverizing the pelletized material to produce an electrode active material. The method of claim 1, wherein the grinding process comprises a ball milling process. delete delete delete delete delete For a lithium secondary battery cathode material containing a result obtained by pelletizing a mixed powder of a LiFePO ₄ precursor and carbon and heating the pelletized material with microwaves in a reducing atmosphere covered with activated carbon or in an inert atmosphere in the presence of an inert gas. Active material. A lithium secondary battery using the active material of claim 8 as a positive electrode material.

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