Materials that expand in the cold might hold the key to improving lithium-ion battery performance in winter conditions. Typically, solids expand with heat and contract when cold, but lithium titanium phosphate does the opposite. This unique property could solve the problem of diminished performance in lithium-ion batteries under cold conditions, a common issue noted especially in electric cars and other applications.
In a study published in Angewandte Chemie International Edition, researchers from China demonstrated the effectiveness of lithium titanium phosphate for use in rechargeable battery electrodes. These batteries, vital for powering portable electronics, vehicles, and storing renewable energy, perform optimally in warmer temperatures. However, dropping temperatures can significantly impair their efficiency, posing challenges for industries like aerospace and the military.
Traditional solutions, such as incorporating heaters or enhancing electrolytes and coatings, often drive up costs and complexity or compromise the battery efficiency. The root of the cold weather problem is attributed to the reduced lithium ion diffusion within the electrode material. To address this, researchers from Donghua University, Fudan University, and Inner Mongolia University proposed using materials with negative thermal expansion properties in electrodes, such as lithium titanium phosphate LiTi2(PO4)3 (LTP).
Under the leadership of Liming Wu, Chunfu Lin, and Renchao Che, the research team showed that LTP, a model substance, provides consistent performance even at lower temperatures due to its negative thermal expansion characteristics. They found that the crystal structure comprises a lattice of TiO6 octahedra and PO4 tetrahedra, forming a flexible network with cavities and channels to accommodate lithium ions. Notably, as the temperature decreases, the structure expands along one axis.
Using spectrometric and electron microscopic tools combined with computer models, the team observed changes in atomic vibrational modes at low temperatures. These changes led to increased distances between oxygen atoms and widened cavities, facilitating lithium ion storage and transport. Remarkably, at -10°C, the diffusion rate of lithium ions was 84% of the rate at 25°C. Further electrochemical testing of carbon-coated LTP at the same low temperature revealed high capacity, excellent rate capability, and durability across 1,000 charge/discharge cycles.
Overall, materials with negative thermal expansion like lithium titanium phosphate present a promising advancement for lithium-ion battery electrodes, potentially overcoming performance issues in cold climates.
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