KR20100112551A - Method and devices for producing air sensitive electrode materials for lithium ion battery applications - Google Patents

Abstract

Apparatus are provided for use in a furnace without a controlled atmosphere and performing a synthesis process for synthesizing precursors to form a synthesized product at elevated temperatures. The apparatus has at least one open hole and consists of a container for containing the material of the synthesis process, and a solid reducing material. The materials of the synthesis process are separated from the atmosphere of the furnace by vessels or reducing materials. The device is particularly suitable for synthesizing LiFePO ₄ from Fe ₂ O ₃ , Li ₂ O ₃ , carbon black, and phosphoric acid precursors.

Description

METHOD AND DEVICES FOR PRODUCING AIR SENSITIVE ELECTRODE MATERIALS FOR LITHIUM ION BATTERY APPLICATIONS

The invention relates, in particular, to reaction chambers used in the mass production of air sensitive materials for the synthesis of electrode materials for lithium batteries.

Oxidation and reduction reactions are commonly used for the synthesis of inorganic crystalline materials. This is especially true for the synthesis of electrode materials for lithium ion batteries, including cathode and anode materials. Typically, cathode materials such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide and mixed oxides are synthesized under an oxidizing environment. These materials can be obtained more easily since the control of the oxidative heat treatment environment (eg, heat treatment in an open air environment) is not difficult. In contrast, the reducing environment is less feasible because it is difficult to control the reducing heat treatment atmosphere. This difficulty stems from the fact that during the heat treatment phase of the synthesis, especially at elevated temperatures (eg above 500 ° C.), fine leakage of air during heat treatment may be detrimental to the reaction and thus degrade the quality of the synthesized material. do. Difficulties in controlling the reducing atmosphere make mass production difficult or expensive. One example is the synthesis of lithium iron phosphate, which is usually synthesized in a reducing or inert atmosphere. LiFePO ₄ type cathode materials have been discussed as a replacement for LiCoO ₂ in the field of lithium ion batteries due to the potential low cost of such materials (Co replacement Fe) and safer working properties (no decomposition of materials during charging). However, process issues such as high temperature heat treatments (above 600 ° C.) under inert or reducing atmospheres make these materials expensive and unacceptable. To date, maintaining a reducing or inert atmosphere at high temperatures is still a key factor in limiting good control of the quality of the synthesized material. It is very difficult to completely seal the furnace, especially at high temperature heat treatments.

U.S. Patent No. 5,910,382 No., 6.72347 million No., 6,730,281 No., 6,815,122 call, in the prior art, such as 6,884,544 No. and 6,913,855 arc generally for replacement of the stoichiometry (stoichiometric) form or a cation of iron of LiFePO ₄ (cation of iron) Disclosed are the methods and precursors used. The above patent shows only how the materials are synthesized. None of the prior art discloses a method for efficiently and cost effectively controlling a heat treatment environment.

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 to form electrode materials. Another object of the present invention is to provide a method and apparatus which is cost effective and ensures good quality of the synthesized material.

The present invention is an apparatus for use in a furnace without a controlled atmosphere in the synthesis process for synthesizing the precursor to form the synthesized material at elevated temperatures. The apparatus is a vessel having at least one open hole for receiving the material of the synthesis process and the solid reducing material, wherein the material of the synthesis process is separated from the atmosphere of the furnace by the container or reducing material.

According to the present invention, there is provided a method and apparatus for controlling a heat treatment environment that is widely applicable to the synthesis of materials to form electrode materials, which is cost effective and can ensure good quality of the synthesized materials.

The invention will be further clarified from the following description of the preferred embodiment, which is shown only by way of example in the accompanying drawings.
1 (a) and 1 (b) show a first embodiment of the device of the present invention.
1 (c) and 1 (d) show a second embodiment of the apparatus of the present invention.
1 (e) shows a third embodiment of the device of the present invention.
2 (a) shows the apparatus of the first and / or second embodiment in a furnace for carrying out the synthesis process.
2 (b) shows the apparatus of the third embodiment in a furnace for carrying out the synthesis process.
3 is a graph of x-ray diffraction patterns of a representative sample of synthesized electrode material provided using the apparatus of the present invention.
4 is a graph showing battery test data of a material as shown in FIG. 3.
5 is a graph of x-ray diffraction patterns of five similar synthesized electrode materials provided using the apparatus of the present invention.
6 is a graph showing battery test data of ten similar synthesized electrode materials provided using the device of the present invention.

1 (a) to 1 (e) are schematic views of an individually sealed device (ISU) comprising a material subjected to a synthetic heat treatment. The design of a furnace comprising different structures of the ISU is shown in FIGS. 2 (a) and 2 (b).

1 (a) and 1 (b), the ISU 1 is a container having one end 2 completely sealed and the other end 3 opened to the atmosphere. The precursor to be synthesized to form the electrode material is received at the position labeled 4. Precursors, intermediate products, and resultant materials of the synthetic process are referred to in the description as materials of the synthetic process. The material of the synthetic process accommodated in 4 is protected from the atmosphere of the furnace, in which the ISU is installed for heating, by means of a solid reducing material layer 5 which limits the penetration of air from the material of the vessel 1 or from the furnace atmosphere. do. It should be mentioned that since the reducing material (eg carbon black) is usually porous, the porosity of the reducing material layer will allow penetration of all gaseous by-products from the material being synthesized. In general, gaseous by-products and oxidation of the reducing material will produce gas and maintain the pressure inside the ISU compared to the atmosphere. However, if the material being synthesized does not produce a byproduct gas, a reduction in porosity of the reducing material layer (eg by tapping) will ensure 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 precursor synthesized to form the electrode material is received at four. The material of the synthesis process received at 4 is protected from the atmosphere of the furnace in which the ISU is placed for heating by a layer of solid reducing material 5 which limits the penetration of air from the furnace atmosphere. As mentioned above, the solid reducing material is usually porous to allow penetration of all gases due to the synthesis process.

In both embodiments, a divider 14 may be used to separate the reducing material 5 from the material 4 in the synthesis process. The divider is preferably inert to the material being separated and porous to all the gases produced. In addition, as shown in FIGS. 1A-1D, a high temperature resistant glass fiber packing can be used to hold all materials in the container.

Similar features can be observed in the third embodiment of the ISU shown in FIG. 1 (e). It can be seen from FIG. 1 (e) that the material to be synthesized is contained in a crucible 8. The bottom of the crucible separates the reducing material from the material of the synthesis process. The tray 12 facilitates the operation of the device. The vessel 9 is not tightly sealed to the tray 12 in order to allow the gas to flow freely to / from the reducing material as shown at 18.

2 (a) and 2 (b) illustrate various embodiments of the present invention as used in a furnace to perform a synthesis process.

In FIG. 2 (a), the first and / or second embodiment is shown in a furnace 13. The heating element of the furnace is shown at 14.

In FIG. 2 (b), four devices of the third embodiment of the present invention are shown 15 in the furnace 16. The heating element of the furnace is shown at 17. As mentioned above, the furnace need not be sealed and a controlled inert or reducing environment is not necessary.

The general structure of an ISU is as follows.

a. The ISU includes a space for receiving the material subjected to the synthetic heat treatment.

b. The ISU includes a space for receiving a reducing substance.

c. The reducing material is placed in the vessel in the following manner.

   Uncontrolled atmosphere / reducing material / synthetic material (FIGS. 1 (a) and 1 (b)) or

   Non-controlled atmosphere / reduced material / synthetic material / reduced material / non-controlled atmosphere

   1 (c) and 1 (d)

d. The reducing material may be selected from the synthesized materials as shown in FIGS. 1 (a) to 1 (d).

   Somewhere in contact with the outside atmosphere as shown above or in FIG. 1 (e).

   It can be located at.

e. ISU can dissipate the gas produced by the synthesis reaction.

In the embodiment of FIGS. 1 (b) and 1 (d), the gas flow is from the material of the synthesis process through the reducing material to the non-controlled atmosphere, or vice versa.

1 (a) and 1 (c), the gas flow is from the material of the synthesis process, through the separator, through the reducing material, to the non-controlled atmosphere, or vice versa.

In the embodiment of FIG. 1 (e), the gas flow is from the material of the synthesis process, through the separation between the crucible and the vessel, through the reducing material, to the non-controlled atmosphere, or vice versa.

Other advantages provided by the use of the ISU include the following.

A. There is no need for an inert atmosphere in the furnace, as a result,

  i. Easy to scale up for production.

  ii. Many reductions in furnace costs due to the need for gas-tight furnaces.

  iii. The cost of inert gas can be reduced.

  iv. Reduction of the overall cost of the synthesis protocol.

  v. Since one ISU can be considered as one furnace, the final synthesized material

    Easy control of the amount of.

B. Good performance of the synthesized material as illustrated in the following example.

C. Uniformity of performance of synthesized materials, which is very important in battery field.

Due to the advantages of the controlled heat treatment environment provided by the ISU, materials requiring heat treatment in an inert atmosphere can be obtained easily and cost effectively. The following are examples of materials synthesized within the ISU of the present invention to better illustrate the use of the present invention.

Example 1: Synthesis of LiFePO ₄ using the method and apparatus of the present invention

In order to illustrate the novelty of the ISU disclosed in this patent application, a large amount of prior art synthesis of LiFePO ₄ is used. 12 kg (75 moles) of Fe ₂ O ₃ , 5.55 kg (75 moles) of Li ₂ CO ₃ , and 1.8 kg (150 moles) of Super P (carbon black, available from MMM Carbon of Belgium) have a molar ratio (1: 1: 2), an appropriate amount of water was added and mixed with each other to form a paste. After complete mixing, the appropriate stoichiometric amount of phosphoric acid was added and mixing continued (6 hours). Finally, the slurry is dried in air at 150 ° C. for 10 hours and then further heat treated at 400 ° C. for 10 hours until a mass of material is obtained. The prepared material is then ground and ball milled for approximately 12 hours. The ground powder material was then loaded into several ISUs as shown in FIG. 1 (a) with the addition of carbonaceous material located directly above the ground powder material for heat treatment. Indeed, the carbonaceous material may be located directly above the synthesized material and separated by a thin layer of porous glass fiber fabric or other inert plate. The ISU was then placed in the furnace as shown in FIG. 2 (a).

The heat treatment was performed at 650 ° C. for 24 hours to form the synthesized material. After the heat treatment step, some grinding and sieving was performed on the synthesized material. The material after the heat treatment was then waited for further testing, as described below.

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

X-ray diffraction pattern data of the synthesized material is shown in FIG. 3. It can be seen that phase pure material has been obtained using the treatment methods and apparatus described in this example without the use and control of inert gases such as nitrogen or argon. Battery test data (obtained using a three-electrode design test battery and lithium is used as reference electrode) is shown in FIG. 4. It can be seen from FIG. 4 that the capacity is high during the first charge-discharge cycle (˜C / 5 rate, 0.23 mA / cm ² ). In this case the material to be synthesized is comparable or superior to the materials of the prior art disclosed in US Pat. No. 6,723,470 obtained using an inert atmosphere which is a heat treatment environment.

Example 2. Illustrative Uniformity of Synthesized LiFePO ₄ Using the Method and Apparatus of the Invention

In this example, 10 batches of materials synthesized using the ISU shown in FIG. 1 (a) were tested for quality uniformity. The precursor treatment procedure of each batch was the same as that described in Example 1. Ten different batches underwent ten identical heat treatment procedures within the ISU. From ten batches, five batches were subjected to x-ray diffraction pattern analysis and the results are shown in FIG. 5. Also, a stack of first cycle data of each batch is shown in FIG. 6. More accurate numeric data is provided in Table 1. It can be seen from FIG. 5 that all materials are essentially phase pure. The peak intensity and peak position of each sample are similar to each other as shown and indicated in FIG. 5. In Figure 6 the first charge and discharge plot of 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 uniformity of the materials synthesized using the ISU is ensured.

Detailed electrochemical data of 10 batches heat treated using ISU Batch name First charge capacity
(mAh / g) First discharge capacity
(mAh / g) First charge average
Voltage (V) First discharge average
Voltage (V) 1st cycle
Coulombic efficiency AE11021 133.97 118.69 3.5083 3.3800 0.8859 AE11031 132.15 118.64 3.5070 3.3805 0.8978 AE11041 137.30 124.11 3.5016 3.3845 0.9039 AE11051 135.29 118.60 3.5088 3.3778 0.8766 AE11061 133.03 119.06 3.5066 3.3810 0.8950 AE11121 132.14 118.75 3.5071 3.3608 0.8987 AE11131 133.19 120.19 3.5083 3.3791 0.9024 AE11141 135.69 122.59 3.5189 3.3794 0.9035 AE11151 136.43 122.55 3.5109 3.3776 0.8983 AE11161 134.71 120.52 3.5090 3.3778 0.8947

The apparatus of the present invention provides the following advantages. There is no need to use an inert gas in the furnace, such as nitrogen or argon, or forming gas (nitrogen plus hydrogen), and thus does not require a fully sealed furnace. The ISU is semi-open to the atmosphere of the furnace, so sealing of the ISU is not difficult. The heat diffusion distance from the heat source to the material synthesized is short. With the use of reducing materials such as carbon black or carbonaceous materials to prevent air penetration, even if a small amount of air penetration occurs during heat treatment, oxidation of the carbonaceous material prevents further oxidation of the material being synthesized. The reducing material is porous and may allow the dissipation of the gas produced by the material subjected to the heat treatment. The depths shown in Figures 1 (a) and 1 (b) are adjustable to prevent oxidation, for example, larger depths will provide a better isolation environment. In addition, the structure of the ISU is variable to accommodate the design of the furnace as shown in FIGS. 2 (a) and 2 (b).

Although specific materials, dimensional data, and the like are disclosed for the purpose of describing embodiments of the present invention, various modifications may be reclassified to the above-described guidelines without departing from the applicant's new contributions and, accordingly, the scope of the present invention. In determining this, reference is made to the appended claims.

1: ISU 2: one end
3: other end (3) 5: solid reducing material layer

Claims (14)

In an apparatus used in a furnace without a controlled atmosphere in a synthesis process for synthesizing precursors to form a synthesized product at elevated temperatures,
A container having at least one open hole for receiving a material of said synthesis process and
Including solid reducing materials,
The material of the synthesis process is separated from the atmosphere of the furnace by the vessel or the reducing material. The apparatus of claim 1 wherein the vessel and the reducing material are arranged such that the material of the synthesis process is in contact with the solid reducing material. The method of claim 1,
Further comprising a divider for separating the material of the synthesis process from the solid reducing material,
Wherein said divider consists of a material that is substantially inert to said material to be separated. The apparatus of claim 1 further comprising a crucible disposed within the vessel, the crucible holding the substance of the synthesis process and separating the substance of the synthesis process from the vessel and the reducing material. The device of claim 1, wherein the solid reducing material is porous to gas due to the synthesis process and to gas due to oxidation of the reducing material. 4. The apparatus of claim 3, wherein the reducing material is porous to gas due to the synthesis process and to gas due to oxidation of the reducing material, and the divider is porous to gas due to the synthesis process. 6. The apparatus of claim 5, wherein the combination of porosity and separation thickness of the solid reducing material substantially prevents the atmosphere of the furnace from entering the synthesis process. 8. The apparatus of claim 7, wherein the solid reducing material has a separation thickness of 5-10 cm. The apparatus of claim 1 wherein the solid reducing material is carbon black, coal, coke or metal powder. 10. The apparatus of claim 9, wherein the solid reducing material is carbon black. The apparatus of claim 1 wherein the vessel consists of a material that is substantially inert to the material of the synthesis process and the solid reducing material. The apparatus of claim 11, wherein the material of the container is stainless steel. A method used in the synthesis process for synthesizing precursors to form a synthesized product at elevated temperatures in a furnace without a controlled atmosphere,
Positioning a precursor in the vessel, having at least one open hole, for the synthesis process, with the precursor received in the vessel,
Placing a solid reducing material in association with the vessel such that the material of the synthesis process is separated from the atmosphere of the furnace by the vessel or the solid reducing substance,
Placing the received precursor into the furnace, and
Heating the received precursor to a synthesis temperature to form a synthesized article. The method of claim 13, wherein 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 synthesized product is LiFePO ₄ .

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