Typically, solid materials tend to expand when heated and contract when cooled. However, there are exceptions, like lithium titanium phosphate, which actually expands in colder temperatures. This unique property may help alleviate the issue of significantly reduced performance of lithium-ion batteries in chilly conditions. A recent study published in the journal Angewandte Chemie by a team from China has confirmed its potential as a suitable material for electrodes in rechargeable batteries.
Lithium-ion and other metal-ion rechargeable batteries power our mobile devices, vehicles, and store renewable energy from sources like solar and wind. They function effectively in warmer conditions, but their performance often drops significantly in low temperatures, creating challenges for electric vehicles, aerospace applications, and military use. Strategies to combat this issue, such as adding integrated heating systems, improving electrolytes, or using specialized electrode coatings, often lead to increased costs and production complexity, or cause decreased performance.
A key factor contributing to the poor performance in the cold is the slowed movement of lithium ions within the electrode material. Researchers from Donghua University, Fudan University in Shanghai, and Inner Mongolia University in Hohhot have suggested a new solution: utilizing electrodes composed of electrochemical energy storage materials with negative thermal expansion (NTE) properties, such as lithium titanium phosphate (LiTi2(PO4)3, or LTP). The team, led by Liming Wu, Chunfu Lin, and Renchao Che, demonstrated that electrode materials with NTE characteristics can perform effectively even at low temperatures using LTP as a model material.
The research involved analyzing the crystal structure, which revealed a three-dimensional framework made up of TiO6 octahedra and PO4 tetrahedra that forms an open and flexible architecture, incorporating both “cavities” and “channels” for lithium ion accommodation. When cooled, this structure expands in one direction along a crystal axis. Through spectrometric and electron microscopic analysis, combined with computer modeling, the researchers discovered that low temperatures alter the vibrational modes of the atoms. This change enhances specific transverse vibrations of certain oxygen atoms, increasing their distance from each other and enlarging the cavities. This modification aids in both the storage and transport of lithium ions. The diffusion rate of lithium ions at −10 °C remains 84% of the rate observed at 25 °C, proving its effectiveness. Additionally, electrochemical tests on carbon-coated LTP at −10 °C exhibited impressive performance with high capacity, rapid rate capabilities, and a significant retention of capacity even after 1000 charge/discharge cycles.
Therefore, materials with negative thermal expansion show great promise for use as electrode materials in lithium-ion batteries, especially in cold environments.
