Department of Applied Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8552, Japan.
Phys Chem Chem Phys. 2012 Oct 28;14(40):13963-70. doi: 10.1039/c2cp42154b. Epub 2012 Sep 17.
The migration of lithium (Li) ions in electrode materials is an important factor affecting the rate performance of rechargeable Li ion batteries. We have examined Li migration in spinels LiMn(2)O(4), LiCo(2)O(4), and LiCo(1/16)Mn(15/16)O(4) by means of first-principles calculations based on density functional theory (DFT). The results showed that the trajectory of the Li jump was straight between the two adjacent Li ions for all of the three spinel compounds. However, there were significant differences in the energy profiles and the Li jump path for LiMn(2)O(4) and LiCo(2)O(4). For LiMn(2)O(4) the highest energy barrier was in the middle of the two tetrahedral sites, or in the octahedral vacancy (16c). For LiCo(2)O(4) the lowest energy was around the octahedral 16c site and the energy barrier was located at the bottleneck sites. The difference in the energy profile for LiCo(2)O(4) stemmed from the charge disproportion of Co(3.5+) to Co(3+)/Co(4+) caused by a Li vacancy forming and jumping, which was not observed for LiMn(2)O(4). Charge disproportion successfully accounted for the faster Li migration mechanism observed in LiCo(1/16)Mn(15/16)O(4). Our computational results demonstrate the importance of the effect of charge distribution on the ion jump.
锂离子在电极材料中的迁移是影响可充电锂离子电池倍率性能的一个重要因素。我们采用基于密度泛函理论（DFT）的第一性原理计算，研究了尖晶石 LiMn(2)O(4)、LiCo(2)O(4)和 LiCo(1/16)Mn(15/16)O(4)中锂离子的迁移。结果表明，对于所有三种尖晶石化合物，锂离子的跳跃轨迹在两个相邻的锂离子之间是直的。然而，LiMn(2)O(4)和 LiCo(2)O(4)在能量势垒和 Li 跳跃路径方面存在显著差异。对于 LiMn(2)O(4)，最高能量势垒位于两个四面体位置的中间，或者在八面体空位（16c）中。对于 LiCo(2)O(4)，最低能量位于八面体 16c 位置附近，而能量势垒位于瓶颈位置。LiCo(2)O(4)能量势垒的差异源于由于 Li 空位的形成和跳跃，Co(3.5+)的电荷不均匀分配导致 Co(3+)/Co(4+)，这在 LiMn(2)O(4)中没有观察到。电荷不均匀分配成功地解释了在 LiCo(1/16)Mn(15/16)O(4)中观察到的更快的 Li 迁移机制。我们的计算结果表明了电荷分布对离子跳跃的影响的重要性。
