An international research team led by Hydro-Québec accessed the CNBC to obtain fundamental insights into how to make better materials for batteries.
Source: Canadian Neutron Beam Centre (CNBC)
Image: Kristoferb, CC BY-SA 3.0
Mobile phones, laptops and other portable devices widely use rechargeable lithium-ion batteries. These batteries require built-in safeguards against overheating, which could cause the battery cell to rupture or even catch fire in extreme cases.
Hydro-Québec is exploring the use of lithium iron phosphate (LiFePO4) as a cathode in these batteries. This material could eliminate concerns about overheating, while also increasing performance. One of the challenges in using lithium iron phosphate is to find an efficient method of producing these crystals to have high purity as well as uniform size and shape distribution.
One method involves crystallizing lithium iron phosphate out of solutions at high pressures and temperatures (around 180 °C). This hydrothermal method meets some of these criteria and is cheaper than most other methods. It takes many hours, however, and many of the crystals are formed with defects.
To understand how the hydrothermal synthesis of lithium iron phosphate can be improved, researchers from IREQ, Hydro-Québec’s research arm, accessed the Canadian Neutron Beam Centre to examine the crystal structures of intermediate materials created at various intervals during synthesis. They then repeated these studies while introducing calcium as a catalyst.
Using x‑rays and electron beams, the researchers determined that the calcium was having effects on the shapes of the crystals. Through a combination of neutron beam and electron beam methods, they were able to identify the intermediate materials and map out the development of lithium iron phosphate in each of the two synthesis methods (i.e., both with and without the calcium catalyst).
They found that the addition of calcium ions facilitates the elimination of the defects from the lithium iron phosphate crystals. The evidence led to the hypothesized mechanism illustrated in the schematic representation. According to this hypothesis, the antisite defects are eliminated by the cation exchange composed of the deintercalation of Fe2+ ions and the intercalation of Li+ ions. This study provides fundamental knowledge to support the development of the fast, low-cost production of high-quality lithium iron phosphate—a critical material for better, safer batteries for portable devices.
Schematic representation of the elimination mechanism of antisite defects in lithium iron phosphate (LiFePO4). The blue spheres represent iron ions and the green spheres represent lithium ions.