A Tale of Two Sites: On Defining the Carrier Concentration in Garnet-Based Ionic Conductors for Advanced Li Batteries
A Tale of Two Sites: On Defining the Carrier Concentration in Garnet-Based Ionic Conductors for Advanced Li Batteries
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DOI：
10.1002/aenm.201500096
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发表时间：
2015-06-03
影响因子：
27.8
通讯作者：
Sakamoto, Jeff
中科院分区：
文献类型：
--
作者：
Thompson, Travis;Sharafi, Asma;Sakamoto, Jeff
基于石榴石晶体结构的固体电解质最近被认为是一种有前途的材料，可以实现先进的锂电池化学性能，因为它前所未有地结合了高离子电导率和对金属锂的电化学稳定性。为了更好地理解产生高电导率的机制，这项工作的目标是将锂位点占用与锂离子传输联系起来。为了实现这一目标，我们研究了立方石榴石中锂位点占据率与组成范围内锂浓度的函数关系：Li7-xLa3Zr2-xTaxO12（x = 0.5、0.75 和 1.5）。使用中子和同步加速器衍射确定两个间隙位点（24d 和 96h）之间的 Li 分布。体积电导率是在相对密度 >97% 的多晶样品上测量的，以将锂离子传输与锂位点占用的函数相关联。确定电导率随着八面体（96h）Li位点的占据呈非线性变化。结果表明，有效载流子浓度取决于锂位点占用率，表明这是显着的载流子-载流子库仑相互作用的结果。此外，还解释了在 Li = 6.5 mol 附近观察到的最大电导率。
Solid electrolytes based on the garnet crystal structure have recently been identified as a promising material to enable advance Li battery cell chemistries because of the unprecedented combination of high ionic conductivity and electrochemical stability against metallic Li. To better understand the mechanisms that give rise to high conductivity, the goal of this work is to correlate Li site occupancy with Li-ion transport. Toward this goal, the Li site occupancy is studied in cubic garnet as a function of Li concentration over the compositions range: Li7-xLa3Zr2-xTaxO12 (x = 0.5, 0.75, and 1.5). The distribution of Li between the two interstitial sites (24d and 96h) is determined using neutron and synchrotron diffraction. The bulk conductivity is measured on >97% relative density polycrystalline specimens to correlate Li-ion transport as a function of Li site occupancy. It is determined that the conductivity changes nonlinearly with the occupancy of the octahedral (96h) Li site. It is shown that the effective carrier concentration is dependent on the Li site occupancy and suggests that this is a consequence of significant carrier-carrier coulombic interactions. Furthermore, the observation of maximum conductivity near Li = 6.5 mol is explained.