JP2011505536A - Method and apparatus for manufacturing an air sensitive electrode material for application in a lithium ion battery - Google Patents

Abstract

An apparatus for use in a heating furnace in an uncontrolled atmosphere to carry out a synthesis process for synthesizing a precursor for producing a synthesis product at a high temperature. The apparatus comprises a container having at least one opening for containing a synthetic processing material and a solid reducing material. The material of the synthesis process is separated from the furnace atmosphere by either a container or a reducing material. The apparatus is particularly suitable for the synthesis of LiFePO ₄ from Fe ₂ O ₃ , Li ₂ CO ₃ , carbon black and phosphoric acid precursor.

Description

  The present invention relates to a reaction chamber used for mass production of air sensitive materials, in particular for the synthesis of lithium battery electrode materials.

Redox reactions are commonly used for the synthesis of inorganic crystalline materials. In particular, this is the case for the synthesis of electrode materials for lithium ion batteries including cathode and anode materials. Conventionally, cathode materials such as lithium cobaltate, lithium nickelate, lithium manganate and mixed oxides are synthesized in an oxidizing environment. These materials are more readily available because it is not difficult to control the oxidative heat treatment environment (eg, heat treatment in an outside air environment). On the other hand, since it is difficult to control the reducing heat treatment atmosphere, the reducing environment is not so easy. This problem is due to the slight leakage of air during the heat treatment adversely affecting the reaction during the synthetic heat treatment process, especially at high temperatures (eg above 500 ° C.), thus reducing the quality of the synthetic material. To do. Problems in controlling the reducing atmosphere can eliminate the prospect of mass production or be very expensive. One example is the synthesis of lithium iron phosphate conventionally synthesized in a reducing or inert atmosphere. For applications in lithium ion batteries, LiFePO ₄ type cathode materials have been considered as an alternative to LiCoO ₂ , which is potentially lower cost (Fe replacing Co) and the safer operating characteristics of the material ( This is because the material does not decompose during charging. However, due to processing problems such as high temperature heat treatment in an inert or reducing atmosphere, the materials are expensive and not widely accepted. To date, maintaining a reducing or inert atmosphere at high temperatures has been a major factor limiting good control of synthetic material quality. In particular, it is extremely difficult to ensure complete sealing of the heating furnace during heat treatment at a high temperature.

Prior art such as US Pat. No. 5,910,382, US Pat. No. 6,723,470, US Pat. No. 6,730,281, US Pat. No. 6,815,122, US Pat. No. 6,884,544 and US Pat. The technology generally teaches methods and precursors that are utilized to produce stoichiometric LiFePO ₄ or to replace iron with a cation. The aforementioned patents only show how the materials are synthesized. None of the prior art teaches how to control the heat treatment environment efficiently and cost effectively.

  It is an object of the present invention to provide a method and apparatus for controlling a heat treatment environment that is widely applicable to the synthesis of materials for forming electrode materials. It is a further object of the present invention to provide a method and apparatus that is cost effective and ensures good quality of the synthetic material.

  The present invention is an apparatus for use in a heating furnace in an uncontrolled atmosphere in a synthesis process for synthesizing a precursor for producing a synthesis product at a high temperature. The apparatus includes a container having at least one opening for containing the synthetic processing material and a solid reducing material, the synthetic processing material being removed from the furnace atmosphere by either the container or the reducing material. Spaced apart.

  The invention will become more apparent from the following description of preferred embodiments, given by way of example only in the accompanying drawings, in which:

It is a figure which shows 1st Embodiment of the apparatus of this invention. It is a figure which shows 1st Embodiment of the apparatus of this invention. It is a figure which shows 2nd Embodiment of the apparatus of this invention. It is a figure which shows 2nd Embodiment of the apparatus of this invention. It is a figure which shows 3rd Embodiment of the apparatus of this invention. It is a figure which shows the apparatus of 1st and / or 2nd embodiment in a heating furnace for implementing a synthesis process. It is a figure which shows the apparatus of 3rd Embodiment in a heating furnace for implementing a synthetic | combination process. It is a graph of the X-ray-diffraction pattern of the representative sample of the synthetic electrode material prepared using the apparatus of this invention. It is a graph which shows the battery test data of the same material as the thing of FIG. 2 is a graph of X-ray diffraction patterns of five similar synthetic electrode materials prepared using the apparatus of the present invention. Figure 3 is a graph showing battery test data for 10 similar synthetic electrode materials prepared using the apparatus of the present invention.

  1 (a) -1 (e) are schematic diagrams of Individual Sealed Units (ISU) containing materials to be synthetically heat treated. A furnace design including differently shaped ISUs is shown in FIGS. 2 (a) and 2 (b).

  1 (a) and 1 (b), ISU 1 is a container having one end 2 that is completely sealed and the other end 3 that is open to the atmosphere. The precursors synthesized to produce the electrode material are included in 4. Synthetic processing precursors, intermediate products and resulting materials are referred to throughout this specification as synthetic processing materials. The synthetic processing material contained in the ISU is disposed inside for heating by either the material of the container 1 or the solid reducing substance layer 5 that restricts the permeation of air from the atmosphere of the heating furnace. Protected from the furnace atmosphere. Note that reducing materials (eg, carbon black) are typically porous, so the porosity of the reducing material layer allows the penetration of any gas by-products released from the material being synthesized into the atmosphere. Should. Typically, gas is generated either by gas by-products or by reducing substance oxidation, and the pressure in the ISU is maintained at a positive pressure compared to the atmosphere. However, if the material being synthesized does not generate gas as a byproduct, the reduced porosity of the reductant layer (eg, due to tapping) ensures separation from the atmosphere.

  1 (c) and 1 (d), each ISU of the second embodiment is a container 1 having both ends 6 open to the environment. The precursors synthesized to produce the electrode material are included in 4. 4 is protected from the atmosphere of the heating furnace in which the ISU is disposed for heating by the solid reducing substance layer 5 that restricts the permeation of air from the atmosphere of the heating furnace. As described above, since the solid reducing substance is usually porous, any gas generated from the synthesis process can be permeated.

  In both embodiments, the dividing portion 11 can be used to separate the reducing substance 5 from the material 4 for the synthesis process. The divider is preferably inert to the material being spaced and is permeable to any gas generated. Also, as shown in FIGS. 1 (a) -1 (d), in 7 a high temperature durable glass fiber wrap can be used to hold all the material in the container.

  Similar features can be observed in the third embodiment of the ISU shown in FIG. FIG. 1 (e) shows that the material 4 to be synthesized is contained in the crucible 8. The air flow path from any opening side of the container 9 is controlled by the presence of the reducing substance 10. The bottom of the crucible separates the reducing material from the material of the synthesis process. The pan 12 facilitates handling of the unit. As can be seen at 18, the container 9 is not airtight to the pan 12 so that the gas can flow freely into or out of the reducing material.

  Figures 2 (a) and 2 (b) show various forms of the present invention utilized in a furnace to perform the synthesis process.

  In Fig.2 (a), 1st Embodiment in the heating furnace 13 and / or 2nd Embodiment are shown. The heating element of the furnace is indicated at 14.

  In FIG. 2B, four units of the third embodiment of the present invention are indicated by 15 in the heating furnace 16. The heating element of the furnace is indicated at 17. As mentioned above, the furnace need not be sealed and a controlled inert or reducing environment is not required.

  The common structure of the ISU is as follows.

a. The ISU includes a space that contains the material to be synthetically heat treated.
b. The ISU includes a space that contains the reducing material.
c. The reducing material is placed in the container in the following manner.
Uncontrolled atmosphere / reducing substance / synthetic material (FIGS. 1 (a) and 1 (b)), or uncontrolled atmosphere / reducing substance / synthetic material / reducing substance / uncontrolled atmosphere (FIGS. 1 (c) and 1 (d)) ),
d. The reducing substance can be placed on top of the synthetic material as shown in FIGS. 1 (a) -1 (d) or elsewhere in contact with the outside air as shown in FIG. 1 (e).
e. The ISU can dissipate the gas generated by the synthesis reaction.

  In the embodiment of FIGS. 1 (b) and 1 (d), the gas flow flows from the material of the synthesis process through the reducing material to an uncontrolled atmosphere, and vice versa.

  In the embodiment of FIGS. 1 (a) and 1 (c), the gas flow flows from the material of the synthesis process through the split, through the reducing material to the uncontrolled atmosphere, and vice versa.

  In the embodiment of FIG. 1 (e), the gas flow flows from the material of the synthesis process through the split between the crucible and the vessel, through the reducing material to an uncontrolled atmosphere, and vice versa. is there.

  Other benefits afforded by the use of ISU include:

A. Since an inert atmosphere is not required in the furnace, the following results are obtained.
i. Easy to expand production.
ii. Since a gas tight heating furnace is not required, the heating furnace is further reduced in cost.
iii. The cost of the inert gas can be reduced.
iv. Reduces the overall cost of the synthesis procedure, and v. Since one ISU is considered as one heating furnace, it is easy to control the quality of the obtained synthetic material.
B. As shown in the examples below, it is a synthetic material with good performance.
C. It is a consistently performance synthetic material that is critical for battery applications.

  Because of the advantages of the controlled heat treatment environment provided by the ISU, materials that require heat treatment under an inert atmosphere are easily and cost-effectively obtained. The following are examples of materials synthesized with the ISU of the present invention to further illustrate the application of the present invention.

Example 1 Synthesis of LiFePO ₄ using the method and apparatus of the present invention To demonstrate the novelty of the ISU disclosed in this patent application, a conventional mass synthesis of LiFePO ₄ is used. 12 kg (75 mol) Fe ₂ O ₃ , 5.55 kg (75 mol) Li ₂ CO ₃ and 1.8 kg (150 mol) Super P (carbon black, manufactured by MMM Carbon, Belgium) In a molar ratio of (1: 1: 2), an appropriate amount of water was added and mixed to form a paste. After thorough mixing, the appropriate stoichiometric amount of phosphoric acid was added and extended mixed (6 hours). Finally, the slurry was dried at 150 ° C. for 10 hours and further heat treated at 400 ° C. for 10 hours until obtaining a mass of material. The material thus obtained was then comminuted and ball milled for about 12 hours. The pulverized powder material was loaded into several ISUs as shown in FIG. 1 (a), and a carbon substance was disposed just above the pulverized powder material for heat treatment. In practice, the carbon material can be placed directly over the synthetic material or separated by a thin layer of porous glass fiber cloth or other inert plate. Thereafter, the ISU was placed in a heating furnace as shown in FIG.

  The heat treatment was performed at 650 ° C. for 24 hours to obtain a synthetic material. After the heat treatment step, the synthetic material was lightly crushed and passed through a sieve. As a result, the heat treated material was ready for further testing as described below.

  The use of ISU is not limited to the synthesis of lithium iron phosphate or to the choice of starting materials and precursor processing steps described for the synthesis of lithium iron phosphate in this example.

The X-ray diffraction pattern data of the synthetic material is shown in FIG. It can be seen that the single phase material was obtained using the processing method and apparatus shown in this example without the use and control of an inert gas such as nitrogen or argon. Battery test data (obtained using a three-electrode design test battery and lithium was used as the reference electrode) is shown in FIG. FIG. 4 shows that the capacity is high during the first charge / discharge cycle (˜5 / C rate, 0.23 mA / cm ² ). The material synthesized in this example is comparable or superior to the prior art material disclosed in US Pat. No. 6,723,470 obtained using an inert atmosphere as the heat treatment environment.

Example 2 Demonstration of Consistency of LiFePO ₄ Synthesized Using the Method and Apparatus of the Present Invention In this example, ten batches synthesized using the ISU shown in FIG. The material was tested for quality consistency. The precursor processing procedure for each batch was the same as that described in Example 1. Ten different batches followed 10 identical heat treatment procedures at the ISU. From 10 batches to 5 batches were analyzed by X-ray diffraction pattern and the results are shown in FIG. Also shown in FIG. 6 is a stack of data for the first cycle for each batch. More accurate numerical data is provided in Table 1. From FIG. 5, it can be seen that all materials are virtually single phase. As shown and suggested in FIG. 5, the peak intensity and peak position of each sample are similar. In FIG. 6, the first charge / discharge plot for each sample is also very similar. The first charge capacity is in the range of 132 to 137 mAh / g, and the first discharge capacity is in the range of 118 to 124 mAh / g. All these data suggest that the consistency of materials synthesized using ISU is guaranteed.

  The apparatus of the present invention provides the following advantages. Because there is no need to use an inert gas such as nitrogen or argon in the furnace or to generate gas (hydrogen in addition to nitrogen), a completely enclosed furnace is not necessary. Since the ISU is half open with respect to the furnace atmosphere, it is not difficult to seal the ISU. The thermal diffusion distance from the heat source to the synthesized material is short. By using a reducing material such as carbon black or carbon material to prevent aeration, the oxidation of the carbon material prevents further oxidation of the synthetic material even if a small amount of aeration occurs during the heat treatment. The reducing material may be porous to allow the dissipation of gas generated from the material being heat treated. The depth of the ISU shown in FIGS. 1 (a) and 1 (b) can be adjusted to prevent oxidation, for example, longer depths provide additional isolation environments. Also, as shown in FIGS. 2 (a) and 2 (b), the shape of the ISU is flexible to adapt to the design of the furnace.

  While specific materials, dimensional data, etc. have been described for purposes of illustration of embodiments of the invention, various modifications can be made without departing from the applicant's novel contributions in light of the above teachings. Therefore, reference should be made to the appended claims in determining the scope of the invention.

Claims (14)

An apparatus for use in an uncontrolled atmosphere heating furnace in a synthesis process for synthesizing a precursor for producing a synthesis product at high temperatures,
A container having at least one opening for containing a synthetic processing material;
A solid reducing substance,
An apparatus in which the material for the synthesis process is separated from the atmosphere of the heating furnace by either a container or a reducing substance. The apparatus according to claim 1, wherein the container and the reducing substance are arranged so that the material for the synthesis process is in contact with the reducing substance. The apparatus according to claim 1, further comprising a dividing portion for separating the synthetic processing material from the solid reducing substance, wherein the dividing portion is made of a material that is substantially inert to the material to be separated. The apparatus of claim 1, further comprising a crucible disposed in the container for holding a material for the synthesis process and separating the material for the synthesis process from the container and the reducing material. The apparatus of claim 1, wherein the solid reducing material is permeable to a gas resulting from a synthesis process and a gas resulting from oxidation of the reducing material. The said reducing substance is permeable with respect to the gas resulting from the synthesis process and the gas resulting from the oxidation of the reducing substance, and the said division | segmentation part is permeable with respect to the gas resulting from the synthesis process. apparatus. 6. The apparatus of claim 5, wherein the combination of the permeability of the solid reducing material and the separation depth substantially prevents entry of the furnace atmosphere into the synthesis process. 8. The apparatus of claim 7, wherein the solid reducing material has a separation depth of 5 to 10 centimeters. The apparatus according to claim 1, wherein the solid reducing material is carbon black, coal, coke, or metal powder. The apparatus according to claim 9, wherein the solid reducing material is carbon black. The apparatus of claim 1, wherein the container is made of a material that is substantially inert to the synthetic processing material and the solid reducing material. The apparatus of claim 11, wherein the container material is stainless steel. A method used in a synthesis process for synthesizing a precursor for producing a synthesis product at a high temperature in a heating furnace in an uncontrolled atmosphere,
Disposing the precursor in a container to include the precursor in a container having at least one opening for the synthesis process;
Placing the solid reducing material in combination with the container such that the material of the synthetic material is separated from the furnace atmosphere by either the container or the solid reducing material;
Placing the included precursor in a furnace;
Heating the included precursor to a synthesis temperature to form a synthesis product. The precursor comprises Fe ₂ O ₃ , Li ₂ CO ₃ , carbon black and phosphoric acid, the precursor is heated to a temperature above 600 ° C., and the synthesis product is LiFePO _4. the method of.

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