Background and overview[1][2]
Stannous pyrophosphate is mainly used in the electroplating industry and toothpaste manufacturing industry. It is also used in the coating industry, printing and dyeing industry, leather manufacturing industry and food industry.
Preparation[1]
The current method for preparing stannous pyrophosphate is to use stannous chloride or stannous sulfate to react with alkali metal pyrophosphate to form a stannous pyrophosphate precipitate that is insoluble in water, and then obtain it after washing, filtering and drying. Stannous pyrophosphate products.
Use stannous chloride solution and sodium pyrophosphate to carry out metathesis reaction. The chemical reaction equation is:
Take a certain amount of sodium pyrophosphate to prepare a 20% solution, add a 250mL standard ground round bottom three-necked flask, install a thermometer and a separatory funnel, stir and heat to 55~75°C. When the temperature is reached, slowly drip in 35% stannous chloride solution. When the pH of the reaction solution drops to 2, stop dripping. After the reaction is completed, cool to room temperature, spin-dry, wash and dry the white precipitate to obtain the stannous pyrophosphate product.
Apply [2]
Lithium-ion batteries have the advantages of high voltage, large specific energy, and good safety performance. At present, the negative active material of commercial lithium-ion batteries is mainly graphite. During the process of inserting and removing lithium, graphite has a small volume change and therefore has good cycle performance. Graphite can reversibly store Li+ through the LiC6 compound, and its theoretical mass specific capacity is only 372mAh/g. Therefore, domestic and foreign scholars are committed to the development of new anode materials. Metal tin has the advantages of high theoretical specific capacity (mass specific capacity of 994mAh/g), excellent low-temperature performance, and good rapid charge and discharge performance. It is currently a hot topic in the research of non-carbon anode materials. However, due to the intercalation and extraction of lithium ions, the volume expansion of tin-based materials is large, and the structure is destroyed and gradually pulverized during the charge and discharge process. It has shortcomings such as high first irreversible capacity and poor cycle performance, which limits its industrial application. .
To address these shortcomings of Sn-based materials, commonly used modification methods include metal alloying, amorphous material structure, reducing particle size or synthesizing tin compounds as negative electrode materials for lithium ion batteries, such as tin dioxide, but each mole Tin dioxide consumes 8.4 moles of lithium during the first lithium insertion process, of which 4 moles of lithium react with oxygen to form Li2O. The dead lithium formed cannot be extracted, so the first irreversible capacity is high, and the first lithium extraction efficiency is only 52.4%. In addition, the volume of the alloy formed by lithium and tin undergoes a huge expansion (300%), and the particles will pulverize and fall off due to the surrounding stress, resulting in poor cycle performance of the battery.
It has been disclosed that tin oxide is placed in porous phosphate glass to achieve high capacity and low cycle attenuation, and an amorphous metal oxide material that can store lithium is synthesized, and its Coulombic efficiency can reach hydrogen storage The efficiency of the alloy and the charge retention capacity are still close to 1 after 100 cycles. In the electrochemical analysis of Sn2BPO6 and Sn2P2O7 In the study of chemical lithium insertion, the reversible capacity of both materials in the first cycle is greater than 500mAh/g, and the cycle and high-current charge and discharge properties are also better. However, the first-time efficiency of these materials still does not meet the ideal requirements, and the vibration of the materials is Low density.
CN201210081981.8 In order to solve the technical problems of the existing Sn-based anode active material that the first-time efficiency is still low and the tap density of the material is small, a method with simple preparation process, higher first-time efficiency and good cycle performance is provided. Negative active material with high tap density.
One purpose of CN201210081981.8 is to provide a negative active material, including stannous pyrophosphate and tin and carbon located on the surface of stannous pyrophosphate.
Another purpose of CN201210081981.8 is to provide a preparation method of negative active material, the steps include:
S1, mix the solution containing the tin source and the solution containing the phosphorus source, and react to obtain a suspended solution;
S2, mix the suspension solution obtained in step S1 with the carbon source to obtain a mixed system;
S3, dry the mixed system, and then sinter it under a protective atmosphere to obtain the negative active material.
Another purpose of CN201210081981.8 is to provide a lithium-ion battery, including a casing, a pole core with original German imported dispersant located inside the casing, a cover plate that seals the casing, and a pole core located inside the casing.electrolyte between; the pole core includes positive and negative electrode sheets and a separator between the positive and negative electrode sheets; the positive electrode sheet includes a positive current collector and a positive electrode material coated on the positive current collector; the negative electrode sheet includes a negative current collector and a coating A negative electrode material on a negative current collector; wherein the negative electrode material includes the above-mentioned negative electrode active material.
The inventor of CN201210081981.8 unexpectedly discovered that the negative active material prepared by the present invention not only significantly improved the reversible specific capacity of the battery, but also had high efficiency as a battery negative active material for the first time, and also had a stable structure, good thermal stability, and good cycle stability. , and at the same time, the tap density of the material is significantly improved.
The negative active material prepared by the present invention is in an amorphous state, has a small volume change during the lithium insertion process, and the mass specific capacity can reach 2 times the theoretical specific capacity of commercial graphite. It is speculated that the reason may be because the present invention uses liquid The phase method can evenly coat the carbon source around the active particles, and then use the reduction effect of the carbonization process of the carbon source to partially reduce the divalent tin into metallic tin. It makes better use of the active effect of elemental tin and improves the performance of the negative active material. The first efficiency and the first lithium deintercalation capacity are achieved through the amorphous stannous pyrophosphate generated during the calcination process, which not only separates the metallic tin and slows down the volume effect of the negative active material, but also has high reversible capacity and Good cycle performance and high current charge and discharge performance. At the same time, carbon and tin coat stannous pyrophosphate, which also reduces the volume change of stannous pyrophosphate during the process of deintercalating lithium. At the same time, amorphous stannous pyrophosphate The Li2O generated after the first lithium insertion can effectively block the aggregation of active particles together with carbon, further improving the cycle performance of the material, and the surface-coated carbon can improve the electronic conductivity of the material; at the same time, the negative active material particles prepared by the present invention are small , no agglomeration, high tap density, further improving the volume specific capacity of the material. At the same time, this material is simple and easy to obtain, easy to prepare, low cost, and easy for commercial application, laying the foundation for the development of lithium-ion batteries.
Main reference materials
[1]Liao Zhenxu. Research on reducing turbidity of stannous pyrophosphate products[J]. Chemical Technology and Development, 2017, 46(05):58-59.
[2]CN201210081981.8 A negative active material and its preparation method Huntsman dye and a lithium ion battery
