‘Cold expansion’ material could solve winter problems for lithium-ion batteries

Most solids expand when their temperature rises and contract when they cool. Some materials, on the other hand, expand in the cold. Lithium titanium phosphate is one such material and could provide a solution to the problem of rapid performance decline in lithium-ion batteries in low-temperature environments.

In an article published in the journal Angewandte Chemie International Edition, the Chinese team demonstrated its suitability for use in rechargeable battery electrodes.

Lithium-ion batteries and other rechargeable batteries based on metal ions power portable devices, power vehicles, and store solar and wind energy. As long as it’s warm, they work well. As temperatures drop, the performance of these batteries can decline rapidly, which is problematic for electric vehicles, aerospace, and military applications.

Measures such as built-in heaters, electrolyte modifications, and electrode coatings can increase the cost and complexity of battery manufacturing or reduce performance.

One cause of the low temperature problem is the slow diffusion of lithium ions within the electrode material. A team from Donghua University and Fudan University in Shanghai and Inner Mongolia University in Hohhot has proposed a new approach to tackle this problem. It is an electrode made of an electrochemical energy storage material with negative thermal expansion (NTE), such as lithium titanium phosphate. LiTi2(PO4)3 (LTP).

Using LTP as a model material, a team led by Liming Wu, Chunfu Lin, and Renchao Che demonstrated that electrode materials with NTE properties can exhibit excellent performance even at low temperatures.

Analysis of the crystal structure reveals that the three-dimensional lattice of TiO6 octahedrons and PO4 tetrahedra has an open, flexible structure containing both “cavities” and “channels” in which lithium ions can reside. Ta. Upon cooling, the structure stretches along one of the crystal axes.

Using spectroscopic and electron microscopy analysis combined with computer modeling, the research team determined that the vibrational modes of atoms change at low temperatures. This increases the occurrence of special transverse vibrations of certain oxygen atoms, increasing the distance between them and widening the cavities in the lattice. This facilitates the storage and transportation of lithium ions.

Even at -10°C, its diffusion rate is 84% ​​of the value obtained at 25°C. Electrochemical testing of carbon-coated LTP at -10 °C also showed good electrochemical performance with high capacity and high rate capability, and high capacity retention over 1,000 charge/discharge cycles.

Therefore, materials with negative thermal expansion are very promising as electrode materials for lithium-ion batteries in cold environments.