CN100464907C - Preparation method of high specific capacity cobalt/antimony alloy material for negative electrode of lithium ion battery - Google Patents

Abstract

The invention discloses a method for preparing a high-capacity Co/Sb alloy lithium-ion battery negative electrode material, belonging to the field of lithium-ion batteries. The oxides of cobalt and antimony are measured and proportioned according to the ratio of Co and Sb in the alloy composite formed, and then appropriate activated carbon or carbon black is added as a reducing agent, and the formed mixture is mixed uniformly and placed in flowing argon, Under nitrogen or argon containing 5-10vol% H ₂ , nitrogen atmosphere, reach the required temperature of 750-1000°C at a heating rate of 2-30°C/min, keep warm for 1-6 hours, and then cool by program temperature control or furnace cooling to room temperature. The invention has the advantages of low raw material cost, simple process, less time-consuming and high yield, and the synthesized Co/Sb alloy particles are uniform and fine, with high crystallinity, and the prepared corresponding negative electrode material has high specific capacity, The cycle performance is stable.

Description

Preparation method of high specific capacity cobalt/antimony alloy material for negative electrode of lithium ion battery

technical field

The invention belongs to the technical field of lithium ion batteries, and in particular provides a preparation method for a cobalt/antimony alloy material used for negative electrodes of lithium ion batteries.

Background technique

Mobile communications, laptop computers and digital cameras are the three fastest-growing industries in the global electronic information industry. With the rapid development of these industries, lithium-ion batteries, one of the most important accessories of these three leading products, are undoubtedly It has also become a very promising sunrise industry. Compared with traditional Ni/Cd and Ni/MH batteries, lithium-ion batteries have the advantages of high energy density, high working voltage, good load characteristics, fast charging speed, safety and pollution-free, and are currently the fastest growing and brightest market prospect A secondary battery.

Lithium transition metal oxide/graphite system is mostly used in commercial lithium-ion batteries at present, but limited by the theoretical lithium storage capacity of the electrode itself (such as graphite, 372mAh/g, 855mAh/cm ³ ), it can be prepared simply by improving the battery It has been difficult to make breakthroughs in improving battery performance by technology. In order to meet the needs of high-capacity lithium-ion batteries, it is very urgent and necessary to research and develop high-capacity lithium-ion battery electrode materials.

In the study of negative electrode materials, it was found that certain alloy compounds may become new research ideas for lithium ion battery negative electrode materials. For example, Si, Ge, Sn, Pb, Al, Ga, Sb, etc. all have high lithium storage capacity. Therefore, alloy materials have become candidates for new lithium-ion battery anode materials. However, the alloy material has a big disadvantage. It will be accompanied by a very large volume change during the charging and discharging process. This huge volume change will easily lead to the powdering of the material, causing some particles to lose contact with each other, and even from the electrode matrix. If it falls off, it will eventually lead to a decrease in electrode capacity and a shortened lifespan. In order to increase and improve the lifetime of alloy anode materials, easing the volume change during lithium intercalation and deintercalation is the key. One of the feasible solutions is to introduce relatively less active or even inert components into metals that can be highly combined with lithium to act as a buffer "matrix" to buffer the volume change of the electrode during charge and discharge, thereby maintaining the material structural stability.

The theoretical lithium storage capacity of Sb is 660mAh/g, which is nearly twice that of carbon anode materials. However, the pure Sb negative electrode will be accompanied by a large volume change during the process of lithium intercalation and deintercalation, which will affect the cycle stability of the electrode. Studies have shown that the introduction of metal Co into other metals can improve the ductility of alloys (J.R.Dahn, S. Trussler, T.D. Hatchard, A. Bonakdarpour, Chem. Mater., 2002, 14:3519-3524). Alloying Co and Sb can improve the mechanical strain resistance of the alloy, so Co/Sb is a kind of good candidate material for alloy anode, which has broad development and application potential.

Literature (J.Xie, XBZhao, GSCao, YDZhong, MJZhao.Journal of ElectroanalyticalChemistry, 2003, 542:1-6) reports that pure Co and Sb are mixed and sealed in a crucible according to a certain metering ratio by a suspension melting method to evacuate, Afterwards, heat treatment under the protection of argon atmosphere until the metal mixture is completely melted, after natural cooling to room temperature, take out the alloy block and anneal at 600°C for a week, and grind it into a powder of 1-4 μm to obtain CoSb3 alloy material, the first reversible capacity is 420mAh /g, down to 243mAh/g during the 10th cycle, this kind of method takes a long time, the process is complicated, and the cost is high. Document (J.Xie, GSCao, YDZhong, XBZhao.Journal of Electroanalytical Chemistry, 2004, 568: 323-327) prepared CoSb ₃ alloy negative electrode by mechanical ball milling method, the first reversible capacity is 550mAh/g, and it is 350mAh/g in the 10th cycle. g. Although the preparation process of this method is simple and feasible, it is very easy to introduce abrasive media during the mechanical ball milling process, which will bring impurities to the product. The capacity decay of the Co/Sb alloy anode materials prepared by the above two methods is relatively fast, and the performance needs to be further improved. In the literature (J.Xie, XBZhao, GSCao, YDZhong, MJZhao, JPTu.Electrochimica Acta, 2005, 50:1903-1907), the liquid phase chemical reduction method is used to combine the reducing agent NaBH ₄ with CoCl ₂ 6H ₂ O and SbCl ₃ Mixing and reacting to obtain CoSb ₂ precipitates, and then repeated filtration, washing and vacuum drying to obtain nanopowder products. The particle size of the _CoSb synthesized by this method is below 20nm, and the uniformity is good, but the product has a large specific surface area, which is prone to agglomeration and surface oxidation, resulting in an increase in the irreversible capacity for the first time (up to about 600mAh/g), and the cost of raw materials is high. The process is complicated and the yield is low. In addition, the liquid phase chemical reduction method is also used, and the literature (J.Xie, XBZhao, GSCao, MJZhao, SFSu.Journal of Power Sources, 2005, 140:350-354) has produced a CoSb ₃ alloy anode material with better cycle performance , the first irreversible capacity is only 257mAh/g, the first reversible capacity is 521mAh/g, and it remains at 460mAh/g in the 10th cycle, indicating that Co/Sb materials can indeed become a good class of alloy negative electrode candidate materials, but this method Still can't avoid the high cost of raw materials, complicated technological process, and the shortcoming that productive rate is lower. Therefore, research and development of a synthesis method of Co/Sb alloy with low production cost, simple process, high yield and easy scale production is of great significance to promote the practical application of Co/Sb alloy in lithium-ion batteries.

Contents of the invention

The object of the present invention is to provide a method for preparing a Co/Sb alloy negative electrode material for a lithium ion battery. Low production cost, simple process and high yield are achieved; the synthesized Co/Sb alloy powder has uniform and fine particles, good crystallinity, high specific capacity and stable cycle performance.

The invention adopts a carbothermal reduction method to synthesize Co/Sb alloy negative electrode materials, uses carbon powder as a reducing agent to reduce cobalt and antimony oxides, and prepares alloy negative electrode materials with different Co/Sb ratios. Concrete preparation process is as follows:

Weigh micron, submicron or nanometer cobalt, antimony oxides and activated carbon or carbon black powders, and the amount of cobalt oxides and antimony oxides is based on the Co/Sb atomic ratio of 3:1~ 1:3 calculation, the amount of activated carbon or carbon black added is calculated according to the chemical equation (1) or (2), and the amount added is 95% to 105% of the theoretically calculated amount;

When Co ₃ O ₄ is used as Co source:

xCo ₃ O ₄ +ySb ₂ O ₃ +(4x+3y)C＝Co _3x Sb _2y +(4x+3y)CO where: 3x:2y＝3:1～1:3 (1)

When using CoO as the Co source:

xCoO+ySb ₂ O ₃ +(x+3y)C＝Co _x Sb _2y +(x+3y)CO where: x:2y＝3:1～1:3 (2)

Use mechanical dry mixing or wet mixing to mix them evenly. Place the mixture in flowing nitrogen, argon or argon or nitrogen atmosphere containing 5-10vol% _H2 , reach the required temperature of 750-1000°C at a heating rate of 2-30°C/min, and keep it warm for 1-6 hours . Then program the temperature control to cool down or cut off the power of the heating furnace, and naturally cool down to room temperature with the furnace. Controlling _the ratio of cobalt oxide and _Sb2O3 in the starting materials can effectively control the ratio of elements in the obtained Co/Sb alloy product.

According to thermodynamic calculations, the oxides of Co and Sb can be reduced to metals by C at relatively low temperatures (350-420°C), and due to the low melting point of Sb (631°C), at the reaction temperature, the reduced Sb will exist in liquid phase, and the liquid phase Sb will be easily alloyed with the reduced Co to form Co/Sb alloy or intermetallic compound. At the same time, in the process of carbothermal reduction, carbon dioxide gas is generated, and the continuous gas overflow process can prevent the agglomeration of alloy particles, and at the same time, pores may be generated inside the alloy particles, so that fine and uniform particles can be prepared. Microporous Co/Sb alloy powder. The present invention adopts carbothermal reduction technology, and uses carbon powder as a reducing agent to reduce the oxides of Co and Sb. Therefore, the final product Co /Sb alloy composites.

The invention has the advantages of low raw material cost, simple process, less time-consuming and high yield. The synthesized Co/Sb alloy has high crystallinity and forms micron-sized particles, so the specific surface area will not be too large, and it is not easy to cause serious agglomeration and surface oxidation, thereby reducing the first irreversible capacity of the negative electrode material; the synthesized alloy particles contain a certain amount of Inner micropores, micropores can buffer the volume expansion and contraction of the alloy during the process of lithium intercalation and deintercalation, thereby improving the structural stability of the alloy particles and improving the cycle stability of the alloy electrode.

Description of drawings

Figure 1 is the XRD pattern of the Co/Sb alloy powder synthesized by carbothermal reduction in the present invention, the atomic ratio of Co and Sb is 1:1, and the synthesis temperature is 1000°C.

Figure 2 is the XRD pattern of the Co/Sb alloy powder synthesized by carbothermal reduction in the present invention, the atomic ratio of Co and Sb is 1:3, and the synthesis temperature is 850°C.

Figure 3 is the specific capacity-cycle number curve of the Co/Sb alloy negative electrode synthesized by carbothermal reduction in the present invention, the atomic ratio of Co and Sb is 1:3, and the synthesis temperature is 850°C.

Detailed ways

Example 1:

Using Co ₃ O ₄ (≥98.5%), Sb ₂ O ₃ (≥99.0%) and activated carbon (>99.0%) as the initial raw materials, the molar ratio is 2:9:35 (equivalent to the atomic ratio of Co and Sb being 1:3) for batching, ball mill the mixture evenly, place it in a flowing argon atmosphere and raise the temperature to 850°C at a rate of 2°C/min, keep it warm for 2 hours, then turn off the power, and cool down to room temperature naturally. The XRD phase analysis results of the obtained sample show that the synthesized product is CoSb ₃ and a small amount of Sb, without the existence of other oxide impurity phases.

Add 10wt% conductive agent acetylene black and 10wt% binder PVDF to the synthesized material to make a slurry, evenly spread it on the copper foil, stick it into a circular pole piece after drying, and form an experimental battery with metal lithium for constant For current charge and discharge experiments, the charge and discharge current is 100mA/g, and the charge and discharge voltage range is controlled between 0.1-1.5V. The first irreversible capacity of the prepared CoSb ₃ anode material is 240mAh/g, and the reversible capacity is 549.8mAh/g.

Example 2:

Using CoO (≥98.5%), Sb ₂ O ₃ (≥99.0%) and activated carbon (>99.0%) as initial raw materials, the molar ratio is 2:1:5 (equivalent to the atomic ratio of Co and Sb being 1:1 ) for batching, the mixture was ball milled and mixed evenly, then placed in a flowing argon atmosphere and raised to 1000°C at a rate of 5°C/min, kept for 1 hour, then turned off and cooled to room temperature naturally. The XRD phase analysis results of the obtained sample showed that the synthesized product was CoSb. Add 10wt% conductive agent acetylene black and 10wt% binder PVDF to the synthesized material to make a slurry, evenly spread it on the copper foil, stick it into a circular pole piece after drying, and form an experimental battery with metal lithium for constant For current charge and discharge experiments, the charge and discharge current is 100mA/g, and the charge and discharge voltage range is controlled between 0.1-1.5V. The first irreversible capacity of the prepared CoSb anode material is 150mAh/g, and the reversible capacity is 450mAh/g.

Claims (2)

1, the preparation method of the alloy material of a kind of used as negative electrode of Li-ion battery height ratio capacity cobalt and antimony is characterized in that preparation process is as follows:

A, with cobalt/cobalt oxide, Sb ₂O ₃Carry out the weighing proportioning with carbon dust, powder is mixed, place flowing nitrogen, argon gas or contain 5～10vol%H ₂Argon gas or nitrogen atmosphere in, reach temperature required 750～1000 ℃ with the heating rate of 2～30 ℃/min, be incubated 1～6 hour; Wherein, cobalt/cobalt oxide and Sb ₂O ₃Addition calculate according to Co and Sb atomic ratio 3:1～1:3; Described cobalt/cobalt oxide is Co ₃O ₄Or CoO;

With Co ₃O ₄During for the Co source, the addition of carbon dust is according to chemical equation xCo ₃O ₄+ ySb ₂O ₃+ (4x+3y) C=Co _3xSb _2y+ (4x+3y) CO calculates; When being the Co source with CoO, the addition of carbon dust is according to chemical equation xCoO+ySb ₂O ₃+ (x+3y) C=Co _xSb _2y+ (x+3y) CO calculates;

Described carbon dust is activated carbon or carbon black, and the addition of activated carbon or carbon black is 95%～105% of a theoretical amount of calculation;

B, with heating furnace temperature programmed control cooling or cool to room temperature naturally with the furnace.

2,, it is characterized in that being mixed into wet mixing or doing and mix of described powder by the described method of claim 1.

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