Battery and energy materials
Which is a characteristic of the olivine LiFePO₄ cathode?
- ALi⁺ moves two-dimensionally between layers, and extracting more than half the Li on charge destabilizes the layered structure
- BIt has a spinel structure with three-dimensional Li⁺ pathways, and capacity loss from Mn dissolution is a challenge
- CStrong P–O bonds make it reluctant to release oxygen, but its electronic conductivity is low, so it is used as fine carbon-coated particles
Show answer and explanation
Answer: C. Strong P–O bonds make it reluctant to release oxygen, but its electronic conductivity is low, so it is used as fine carbon-coated particles
In LiFePO₄, oxygen is bound to P by strong covalent bonds in PO₄ tetrahedra, so it rarely releases oxygen even on overcharge or at high temperatures, giving it excellent thermal safety. On the other hand, Li⁺ diffusion is confined to one-dimensional tunnels and the electronic conductivity is extremely low, so the particles are made as small as about 100 nm and their surfaces are coated with carbon. Two-dimensional movement of Li⁺ between layers and structural instability when more than about half the Li is extracted are characteristics of layered rock salt LiCoO₂. Three-dimensional pathways with Mn dissolution as a challenge describe spinel LiMn₂O₄.