CN1395332A - LiCoO2 type cathode material and its preparation method - Google Patents

Abstract

A LiCoO ₂ -type cathode material is characterized in that it is represented by the following structural formula: LiCo _1-x M _x O ₂ wherein, M is one or more of alkaline earth metal elements Be, Mg, Ca or Sr, and x=0.05- 0.10. The material is prepared according to the following steps: (1) according to LiCo _1-x M _x O ₂ (wherein x=0.05-0.10, M is one or more than one of Be, Mg, Ca or Sr) Li in the structural formula , Co, M molar ratio Weigh raw materials containing Li, Co, M, and mix them into ingredients; (2) Use a ball mill to pulverize the ingredients into fine powders with a particle size of less than 300 μm; (3) Roast at 600-800°C Micropowder for more than 1 hour to obtain oxides.

Description

A kind of LiCoO2 type cathode material and preparation method thereof

technical field

The invention relates to a cathode of a fuel cell, in particular to a cathode material for a molten carbonate fuel cell (MCFC) and a preparation method thereof.

Background technique

A fuel cell is a power generating device that directly converts the chemical energy in fuel and oxidant into electrical energy. It does not go through the heat engine process, so it is not limited by the Carnot cycle, and the energy conversion efficiency is very high. At the same time, it is a clean and pollution-free power generation device. Among them, the molten carbonate fuel cell (MCFC) is a high-temperature power generation device operating at 600-700 ° C. In addition to its characteristics of not being limited by the Carnot cycle, high energy utilization rate and environmental friendliness, it also has many other types of fuels. The incomparable advantages of batteries, such as a wide range of fuels, in addition to H ₂ and CO, can also directly use natural gas, coal gasification gas and other hydrocarbons as fuels, and at the same time do not need to use noble metal electrodes, which can greatly reduce the cost of batteries. However, due to the four major technical problems of diaphragm sintering, cathode corrosion and dissolution, anode creep and bipolar plate corrosion, MCFC has not been commercialized.

The MCFC cathode is mainly used to provide active sites for oxidant reduction reaction, catalyze the cathode reaction, provide reactant channels and transfer electrons, so a porous electronic conductor with catalytic effect is generally selected. Traditionally, MCFC cathodes have been porous nickel plates. After the battery is assembled with this porous nickel plate, it is oxidized to NiO in situ in the atmosphere of oxidizing agent, and becomes the cathode of MCFC. However, it is found that NiO is easily dissolved in molten carbonate, the cathode is consumed, the structure changes, and the cathode polarization continues to increase, resulting in battery performance degradation. What is more serious is that the dissolved Ni ⁺² diffuses to the anode side through the separator. , reductively deposited on the anode side, and finally connected to the cathode to form a nickel bridge, resulting in a short circuit of the battery. Therefore, the NiO dissolution of the cathode material is one of the main factors affecting the battery life. In order to eliminate this effect, people have been exploring new cathode materials and new preparation processes, modifying the surface of Ni (or NiO) or completely replacing NiO with other cathode materials. Alternative cathode materials include perovskite materials, Li/Mg/Fe(Mn)/O composite materials, etc. LiCoO ₂ and LiFeO ₂ are more suitable. Among them, LiCoO ₂ is most suitable. Since pure _LiCoO2 is used as the cathode, although the cathode dissolution problem is overcome to a certain extent, its conductance is too low and the performance of the battery deviates. Therefore, the modification of LiCoO ₂ has become a new starting point to improve its electrical conductivity.

In USP 5356731, 0.5 mol LiNO ₃ , 0.5 mol Co(NO ₃ ) ₂ , 1.5 mol citric acid and 2.25 mol ammonium nitrate were prepared into 1.5 liters of aqueous solution, stirred evenly, heated and evaporated, reacted at the ignition point, and roasted at 500°C for 8 The carbon is removed within hours, the film is formed by tape casting, and then sintered at 800-1000°C in an atmosphere of air and CO ₂ to prepare a LiCoO ₂ electrode.

USP 6063141 prepares LiCoO ₂ by anodic oxidation, uses Co ₂ O ₃ and Li ₂ CO ₃ as raw materials to prepare LiCoO ₂ , and prepares LiCoO ₂ and physical and chemical NiO double-layer cathode by anodic oxidation. Its polarization impedance is 0.2Ωcm ² , and its overpotential is 30mV at 150mA/cm ² .

WO 9728571 A1 uniformly mixes Li ₂ CO ₃ powder and metal Co powder to make a thin film, sinters, and treats it in an air flow at a temperature of 400-488 ° C for several hours until it is transformed into a LiCoO ₂ electrode plate with a large inner surface.

WO 9853513 A1 prepared a cathode with a double-layer structure, one layer is physical and chemical NiO, and the other layer is cerified LiCoO ₂ . The polarization resistance of the double-layer electrode has little influence with temperature and has a long active life. The preparation material of the second electrode layer is co-precipitation of activated cobalt oxide and cerium, which is treated with lithium carbonate to form a floating liquid. The suspension is applied to the first layer, dried and sintered at high temperature to form the second electrode layer.

WO 008702 A1 describes the direct production of electrode plates containing electrolytes. The cathode prepared in this way can consist of two or more layers, starting with a mixture of LiCoO ₂ and carbonate to make a membrane plate, which is heated in a furnace to melt the electrolyte.

Eur.Pat.Appl.EP 661767 A1 Mix the mixture of cobalt powder and Li ₂ CO ₃ , binder, defoamer and solvent, and use the tape casting technology to form a film on a flat plate, heat treatment to form LiCoO ₂ , and partially sinter The treatment produces a porosity that matches that required for the cathode in the MCFC.

However, the above-mentioned literatures have not yet proposed an effective method to enhance the cathode conductance of _LiCoO2 .

Contents of the invention

The purpose of the present invention is to overcome the low electrical conductivity of _LiCoO2 cathode in the above-mentioned known technology, and the problem of poor battery performance, to provide a _LiCoO2 type cathode electrode material, and the cathode energy prepared by using this electrode material can greatly reduce the negative energy of the cathode during melting. The solubility in carbonate improves the stability of the cathode and prolongs the battery life; it improves the conductance of the cathode itself (where the conductance is greater than or equal to the conductance of NiO).

To achieve the above object, the invention provides a _LiCoO2 type cathode material, characterized in that it is represented by the following structural formula:

LiCo _1-x M _x O ₂

Wherein, M is one or more of alkaline earth metal elements Be, Mg, Ca or Sr, and x=0.05-0.10.

In the above-mentioned LiCoO ₂ -type cathode material, it is characterized in that M is a Mg element.

In addition, in the above-mentioned LiCoO ₂ -type cathode material, it is characterized in that LiCo _1-x M _x O ₂ can also be doped with yttrium and/or rare earth elements, and the doping amount is LiCo _1-x M 10-40% of _{x O2} .

In addition, in the above-mentioned LiCoO ₂ -type cathode material, it is characterized in that the rare earth element is one or more of La, Ce, Pr, Na, Pm, Sm, Eu, Gd, Dy.

In addition, in the above-mentioned LiCoO ₂ -type cathode material, it is characterized in that the rare earth element is La and/or Ce.

The present invention also provides a kind of preparation method of _LiCoO2 type cathode material, it is characterized in that according to the following steps:

1). According to the molar ratio of Li, Co and M elements in the structural formula of LiCo _1-x M _x O ₂ (where x=0.05-0.10, M is one or more of Be, Mg, Ca or Sr) Take raw materials containing Li, Co, M and mix them into ingredients;

2). Use a ball mill to pulverize the ingredients into a fine powder with a particle size of less than 300 μm;

3). Calcining the fine powder at a high temperature of 600-800°C for more than 1 hour to obtain oxides.

In the above-mentioned ball milling, the ball milling is usually performed for more than 10 hours in order to achieve the desired particle size. In order to ensure better ingredients, it is best to carry out ball milling for 20-60 hours.

In the above preparation method, it is characterized in that the raw materials of Li, Co and M are nitrates, carbonates, acetates or oxides respectively.

In addition, in the above-mentioned preparation method, it is characterized in that in step 1) doping Y and/or rare earth elements in the amount of LiCo _1-x M _x O ₂ will contain Y and / or raw materials of rare earth elements are added and mixed into ingredients.

In addition, in the above preparation method, it is characterized in that the Y and/or rare earth elements are nitrates, carbonates, acetates or oxides.

In addition, in the above-mentioned preparation method, it is characterized in that after step 3), Y and/or rare earth elements are further doped with LiCo _1-x M _x O ₂ in an amount of 10-40% based on the oxide weight. Raw materials of Y and/or rare earth elements are added and mixed into ingredients.

In the above-mentioned present invention, since _LiCoO2 is used as the cathode matrix material, its dissolution rate is 8 times to an order of magnitude lower than that of the NiO cathode, but its electrical conductivity is low, and the electrode performance is low. Use semiconductor doping method to dope alkaline earth elements such as Mg, Ca, Be, Sr, etc., the content is 0.05-0.10 (molar ratio), after doping LiCo _1-x M _x O ₂ , the cathode conductance can be increased by about 1 to 5 times . At the same time, the chemical adsorption method is used to increase the electrode's adsorption of Li ⁺ ions, and the conductivity of the LiCo _1-x M _x O ₂ cathode that absorbs a large amount of Li ⁺ ions can be increased by about one to three times. In this way, the conductivity of the cathode is greatly improved, which improves the performance of the battery, and at the same time reduces the dissolution rate of the electrode, increases the stability of the battery performance, and prolongs the battery life.

In addition, in the present invention, in order to inject Li ⁺ into the LiCo _1-x M _x O ₂ crystal layer, and further increase its conductance, the LiC _1-x M _x O ₂ powder is heavily doped with rare earth elements such as La, Ca, Y, etc. . The doping amount is about 10-40% based on oxide. Its raw materials are carbonates, nitrates and acetates. Among them, nitrate has the best effect. The method is to mix evenly, decompose and sinter at high temperature. In order to increase its concentration on the surface of LiCoO ₂ , the sintering temperature is preferably 650 °C. Below 650 °C, the rare earth elements are not uniform on the surface of _LiCoO2 , and above 650 °C, the concentration of rare earth elements on the powder surface decreases due to the enhanced thermal diffusion.

In addition, in the present invention, the method of heavily doping rare earth elements is to mix LiCo _1-x M _x O ₂ to the molar ratio of rare earth elements, mix evenly, decompose and sinter at high temperature, and then prepare electrodes. It is also possible to mix the ingredients evenly first to prepare an electrode, and in-situ sintering in the battery to form an oxide. Since Ce(NO ₃ ) ₃ 6H ₂ O decomposes at 200°C, La(NO ₃ ) ₃ 6H ₂ O decomposes at 126°C Decomposition, so in-situ sintering in the battery not only makes it an oxide, but also creates pores in the electrode during this process. Using the above-mentioned cathode material prepared by the present invention to make an electrode, and then assemble it into a battery according to the conventional technology, good battery performance can be obtained. Specifically, if a porous sintered Ni-Cr plate is used as the anode, - _LiCoO2 type cathode assembled into a single cell with good battery performance. When LiCoO ₂ -doped with Mg is used as the cathode, at 0.9MPa, when discharged at 200mA/cm ² and 300mA/cm ² , the battery output voltages are 0.853V and 0.721V respectively, and the highest power density is 216.3mW/cm ² . When LiCoO ₂ -doped with Mg and La is used as the cathode, at 0.9MPa, when discharged at 200mA/cm ² and 372mA/cm ² , the battery output voltages are 0.944V and 0.781V respectively, and the highest power density is 291mW/cm ² . When LiCoO ₂ -doped with Mg, Ce, La is used as the cathode, at 0.9MPa, when discharged at 200mA/cm ² and 300mA/cm ² , the output voltage of the battery is 0.838V and 0.685V respectively, and the highest power density is 205.5mW/cm ² .

Description of drawings

Fig. 1 is a graph showing the performance curve of a battery assembled with electrodes made of the electrode material obtained in Example 1 of the present invention at the second start-up.

Fig. 2 is a graph showing the battery performance of the assembled battery using the electrode material prepared in Example 2 of the present invention at the ninth start-up.

Fig. 3 is a graph showing the performance curve of the battery assembled with electrodes made of the electrode material obtained in Example 3 of the present invention at the ninth start-up.

Detailed ways

The technology of the present invention will be further described below in conjunction with the accompanying drawings.

Example 1

In a 1 liter ball mill jar, add ceramic balls 1/3 of the volume of the ball mill jar. Weigh 30.03 grams of Co(NO ₃ ) ₃ 6H ₂ O, 4.15 grams of Li ₂ CO ₃ , and 0.36 grams of MgO, add them into a ball mill jar, and ball mill for 30 hours to make the ingredients particles smaller than 100 μm. Then it was dried in an oven at 120°C, mechanically crushed, ground, and gradually heated in a muffle furnace from 100°C to 800°C, and calcined for 20 hours to obtain LiCo _0.92 Mg _0.08 O ₂ powder.

Weigh 25.6 grams of LiCo _0.92 Mg _0.08 O _Powder , 12 grams of functional organic matter and 80 grams of ethanol-n-butanol solvent are ball-milled in a 1 liter ball mill jar, after filtering and degassing, the electrode is prepared by strip casting. Then it is dried, and after the thickness is matched, it is hot-pressed with a hot press to form an electrode for a battery.

The porous sintered Ni-Cr plate is selected as the anode, the γ-LiAlO ₂ is used as the diaphragm and the above-mentioned cathode is assembled into a single cell. Under the battery operating temperature of 650°C, after leak detection and channeling detection with N ₂ , the anode is supplied with H ₂ -CO ₂ mixed gas (H ₂ /CO ₂ =80/20, m/o), and the cathode is supplied with O ₂ -CO ₂ mixed gas (O ₂ /CO ₂ =40/60, m/o), the gas utilization rate is 20%. The battery performance was measured under the operating pressure of the system at 0.1MPa, 0.5MPa and 0.9MPa respectively. Table 1 shows the performance of multiple starts of the battery. Figure 1 shows the battery performance at the second startup. Under 0.9MPa, when discharged at 200mA/ ^cm2 and 300mA/ ^cm2 , the output voltage of the battery is 0.853V and 0.721V respectively, and the highest power density is 216.3mW/cm2 ² .

Table 1 ^* . The raw material gas utilization rate is 20%, and the 4th, 6th, and 8th times are empty starts.

Example 2

LiCo _0.92 Mg _0.08 O ₂ powder was prepared according to the method in Example 1. Weigh 14.2 grams of LiCo _0.92 Mg _0.08 O ₂ powder, 3.26 grams of La ₂ O ₃ , 8.2 grams of functional organic matter and 54.5 grams of ethanol-n-butanol solvent and ball mill in a 1 liter ball mill jar, after filtering and degassing, The electrode is prepared by the strip casting method, then dried, and after the thickness is matched, it is hot-pressed with a hot press to form an electrode for a battery. Table 2 shows the multiple starting performance of the battery. Figure 2 shows the battery performance at the ninth startup. Under 0.9MPa, when discharged at 200mA/cm ² and 372mA/cm ² , the output voltage of the battery is 0.944V and 0.781V respectively, and the highest power density is 291mW/cm ² .

^*.原料气利用率20％，其中第2、3、5、7次为空启动。Table 2

^* . The raw material gas utilization rate is 20%, and the 2nd, 3rd, 5th, and 7th times are empty starts.

Example 3

LiCo _0.92 Mg _0.08 O ₂ powder was prepared according to the method in Example 1. Weigh 20.4 grams of LiCo _0.92 Mg _0.08 O ₂ powder, 5.3 grams of Ce(NO ₃ ) ₃ 6H ₂ O, 10.5 grams of La(NO ₃ ) ₃ 6H ₂ O, 12 grams of functional organic matter and 80 grams of ethanol-n-butanol The solvent is ball-milled in a 1-liter ball-milling tank, filtered and degassed, and the electrode is prepared by a tape casting method, then dried, and after thickness matching, is hot-pressed with a hot-press machine to form an electrode for a battery.

Figure 3 shows the performance of the battery. When discharged at 200mA/cm ² and 300mA/cm ² at 0.9MPa, the output voltage of the battery is 0.838V and 0.685V respectively, and the highest power density is 205.5mW/cm ² . Comparative example 1

LiCoO ₂ was prepared by anodic oxidation as reported in USP 6063141, LiCoO ₂ was prepared by using CoO ₃ and Li ₂ CO ₃ as raw materials, and LiCoO ₂ and lithiated NiO double-layer cathode was prepared by anodic oxidation. Its polarization impedance is 0.2Ωcm ² , and its overpotential is 30mV at 150mA/cm ² .

Claims (10)

1. LiCoO ₂The type cathode material is characterized in that being represented by following structural formula:

LiCo _1-xM _xO ₂

Wherein, M be among alkali earth metal Be, Mg, Ca or the Sr one or more, x=0.05-0.10.

2. LiCoO according to claim 1 ₂The type cathode material is characterized in that M is the Mg element.

3. LiCoO according to claim 1 and 2 ₂The type cathode material is characterized in that LiCo _1-xM _xO ₂In can also doped with yttrium and/or rare earth element, its doping is counted LiCo by oxide weight _1-xM _xO ₂10-40%.

4. LiCoO according to claim 3 ₂The type cathode material, it is characterized in that described rare earth element be among La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, the Dy one or more.

5. LiCoO according to claim 4 ₂The type cathode material is characterized in that described rare earth element is La and/or Ce.

6. LiCoO ₂The preparation method of type cathode material is characterized in that by following step:

1). press LiCo _1-xM _xO ₂The mol ratio of Li, Co, M element takes by weighing the raw material that contains Li, Co, M in (x=0.05-0.10 in the formula, M are among Be, Mg, Ca or the Sr one or more) structural formula, and is mixed into batching;

2). prepare burden into the micro mist of particle diameter with the ball mill pulverizing less than 300 μ m;

3). the roasting micro mist obtained oxide more than 1 hour under 600-800 ℃ of high temperature.

7. preparation method according to claim 6 is characterized in that the raw material of Li, Co, M is respectively its nitrate, carbonate, acetate or oxide.

8. preparation method according to claim 6 is characterized in that in step 1) by LiCo _1-xM _xO ₂Amount doping Y and/or rare earth element are counted the 10-40% ratio with oxide weight and will be contained the raw material adding of Y and/or rare earth element and be mixed into batching.

9. preparation method according to claim 6 is characterized in that described Y and/or rare earth element are its nitrate, carbonate, acetate or oxide.

10. preparation method according to claim 6 is characterized in that after step 3) further by LiCo _1-xM _xO ₂Amount doping Y and/or rare earth element are counted the 10-40% ratio with oxide weight and will be contained the raw material adding of Y and/or rare earth element and be mixed into batching.

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