Tin-based materials applied to lithium anode

Due to the limited theoretical specific capacity of graphite anode materials, the mainstream has been unable to meet the needs of the development of lithium ion batteries, people are looking for higher energy density anode materials. Due to its high specific capacity, moderate lithium deposition voltage, abundant natural reserves, low price, high safety and environmental protection, tin-based materials have attracted the attention of researchers and are regarded as one of the next generation of ideal lithium anode materials.

Given a theory of tin base material is very high, pure tin theoretical specific capacity can reach 994 mah/g, but tin in the process of take off the intercalated-li volume will have change, will produce more than 300% of the volume expansion, the volume expansion caused by material deformation inside the battery causes a lot of impedance, leading to cell cycle performance, specific capacity attenuation too quickly. At present, a lot of progress has been made in the application of tin-based materials to lithium anode. Several tin-based anode materials are briefly introduced as follows.

Common tin-based anode materials introduction

Common tin-based anode materials are metal tin, tin-based alloy, tin-based oxide and tin-carbon composite materials, etc. :

①   Metallic tin material

Tin (Sn) belongs to the IVA group, which can react with lithium electrochemically to form various lithium tin alloys. Due to its high theoretical capacity, tin has attracted special attention as a cathode material for lithium-ion batteries. In the process of cycling, the volume of Sn has a great change, which seriously affects the cycling performance.

In the present research stage, the volume expansion of metal tin anode materials has been the core of the research. Because of the above problems, it is still a great challenge to use pure Sn as anode material. In the absence of buffer matrix, reducing Sn particle size to nanometer scale or creating porous Sn structure is an effective way to reduce the volume expansion effect.

At the same time, this method can effectively shorten the ion transport path while increasing the contact area between the material and the electrolyte, which is widely used in the preparation of materials.

②   tin-based alloy material

Some progress has been made in the research of tin-based alloy materials. At present, researchers have developed several methods for the synthesis of tin alloy anode materials, such as electroplating, electrolytic deposition, chemical reaction and mechanical ball milling. Generally, tin alloy anode materials consist of active phase (Sn) and inert phase (M). During the charging and discharging process, Sn acts as the active site to react with Li, while the inert phase (M) can act as a buffer matrix to alleviate the volume changes caused by tin alloying.

The experimental results show that the existence of both active and inert phases can significantly improve the cyclic stability of the material. Since the 1990s, the research of tin alloy based anode materials for lithium ion batteries has entered a stable development stage. The main strategy to improve the electrochemical performance of anode materials is to construct nanostructured alloy materials. To achieve better electrochemical performance, the researchers synthesized more refined and efficient structures. Nanowires or nanowire-like arrays show many advantages as anode materials for lithium-ion batteries.

③   Tin-based oxide material

Since 2000, tin-based oxides have become an important branch of tin-based anode materials and received wide attention. As one of the most typical representatives of tin-based oxides, SnO2 has the characteristics of N-type wide-band gap semiconductor and has been applied in many fields such as gas sensing and biotechnology. Meanwhile, SnO2 is considered as one of the most promising anode materials for lithium-ion batteries due to its abundant reserves and environmental protection.

Similar to SnO2, other tin-based oxides can also be used as anode materials for lithium-ion batteries. The theoretical capacities of SnSO4 and Sn2P2O7 are calculated to be 799mAh/g and 834mAh/g, respectively. The high theoretical capacity makes these tin-based oxides of interest. However, the inherent low conductivity and large volume expansion of tin-based oxides hinder their practical application. Therefore, the electrochemical performance of tin-based oxide anode materials can be improved by constructing nanostructures and supplementing with buffer substrates. Since 2010, researchers have been committed to the synthesis of hollow nanostructures, and a variety of hollow SnO2 nanomaterials have been prepared as anode materials for lithium-ion batteries, all of which have good electrochemical properties.

④   tin-carbon composite material

Tin-based materials are faced with the problems of large volume expansion and agglomeration in the process of charging and discharging. Compared with tin-based alloys and tin-based oxide anode materials, the origin of tin-carbon composites is relatively new. The wide application of carbon materials in the field of energy and the rapid development of nanotechnology promote the rapid development of tin-carbon composites. Among them, graphene, carbon nanotubes and amorphous carbon are the main carbonaceous materials, which are widely used as carbon substrates to mitigate the volume changes of tin-based materials. At the same time, the distribution of nanostructured tin-based materials on or in carbon matrix is the two mainstream strategies to obtain tin-carbon composites.

Tin-based materials are considered to be ideal anode materials to replace graphite, and there have been many achievements in the research of tin-based materials in lithium anode, but they are still far from real commercial applications. In particular, tin-based materials have problems such as huge volume expansion, easy structure damage, rapid capacity decay and poor cyclic performance, which need to be further studied. In the future, it is necessary to accelerate the practical application of this material by optimizing its performance in terms of first coulomb efficiency, reversible specific capacity, cyclic stability, and rate performance.