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Study on hollow wrapped structure assisted silicon anode material

In recent years, with the country's strong support for new energy vehicles, sales of clean and pollution-free electric vehicles have achieved a spurt of growth. However, the current commercial lithium-ion battery anode material graphite can only reach a capacity of 300~340mAh/g in practical applications, and it has been difficult to improve, which is far from meeting the urgent demand for high-performance lithium-ion batteries in new market users.

Therefore, more and more people are working on the development of high energy density battery materials. Silicon anode materials are favored by researchers because of their high theoretical specific capacity (3752mAh/g), environmental friendliness and low cost, and are expected to become the main force of the next generation battery system.

However, there are still many problems in the development of silicon anode materials. For example, the volume expansion effect of elemental silicon during charging and discharging is as high as 300%, which causes structural collapse and pulverization, which seriously restricts the development of silicon as a negative electrode material for lithium ion batteries. application. To solve the above problems, the problem of suppressing the volume expansion effect in the electrode reaction and improving the conductivity of elemental silicon is the key to the research.

In view of this, Professor Wang Xianyou of Xiangtan University successfully prepared a double-coated hollow spherical Si@TiO2@C anode material by one-step method.

Figure 1 Schematic diagram of (a) preparation and (b) structure of Si@TiO2@C anode material

In this work, hollow Si spheres were prepared by template-free method and magnesium thermal reduction method, and then hollow spheres HN-Si were coated with butyl titanate and glucose to prepare Si@TiO2@ with rich pore structure and high stability. C negative electrode material.

Fig. 2 Electron micrograph of SiO2(a, d-f), HN-Si(b, g-i) and Si@TiO2@C(c, j-l)

Firstly, in the process of battery charge and discharge, Si nanospheres with hollow structure can self-adjust large volume expansion; secondly, TiO2 shell can increase lithium ion transmission rate (volume expansion rate is only 4%) due to its structural advantages, and Further, the volume expansion of the Si active material is transferred to the inner cavity instead of outward; finally, the outer C layer further improves the electrical conductivity and structural stability of the composite.

The results indicate that the traditional single-layer cladding strategy cannot meet the structural stability requirements of electrode materials in the face of the huge volume expansion effect of Si anode materials, and this new double-cladding-hollow strategy It can effectively improve the volume expansion effect of silicon and improve its conductivity.

The results show that the double-stabilized hollow Si@TiO2@C nanosphere anode material synthesized by magnesium thermal reduction method and sol-gel method is the first time at a current density of 0.2A/g and an operating voltage of 0.01-2.5V. The specific discharge capacity was 2557.1 mAh/g, and the coulombic efficiency was 86.06%. At a current density of 1 A/g, the reversible specific capacity of the Si@TiO2@C anode material after 250 cycles is still 1270.3 mAh/g. The uncoated HN-Si anode material has a first discharge specific capacity of 2264 mAh/g and a Coulomb efficiency of only 67.3%.

This double-layer cladding-hollow structure design can shorten the transmission path of Li+ and electrons. The rich pore structure can also promote the full wetting of the electrolyte and improve its rate performance. At the same time, the uniform TiO2 shell and C layer greatly improve Si. @TiO2@C Anode material structural stability and electrical conductivity.

Figure 3 Characterization of electrochemical properties of Si@TiO2@C anode material

Figure 4 Schematic diagram of Si@TiO2@C(a) working device, (b) structural change of charge and discharge under TEM, and (c) schematic diagram of lithiation (delithiation)

Figure 5 Cycle performance, rate performance and impedance analysis

In summary, the design of the bistable cavity structure in this study can promote the further research and development of silicon-based anode materials, and also provide reference for the study of anode materials with serious volume expansion and poor conductivity.

LuB, MaB, DengX, etal. Dual Stabilized Architecture of Hollow Si@TiO2@CNanospheres as Anode of High-Performance Li-IonBattery [J]. Chemical Engineering Journal, 2018.


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