Revealing the Atomic Origin of Heterogeneous Li‐Ion Diffusion by Probing Na

Abstract

Tracing the dynamic process of Li‐ion transport at the atomic scale has long been attempted in solid state ionics and is essential for battery material engineering. Approaches via phase change, strain, and valence states of redox species have been developed to circumvent the technical challenge of direct imaging Li; however, all are limited by poor spatial resolution and weak correlation with state‐of‐charge (SOC). An ion‐exchange approach is adopted by sodiating the delithiated cathode and probing Na distribution to trace the Li deintercalation, which enables the visualization of heterogeneous Li‐ion diffusion down to the atomic level. In a model LiNi1/3Mn1/3Co1/3O2 cathode, dislocation‐mediated ion diffusion is kinetically favorable at low SOC and planar diffusion along (003) layers dominates at high SOC. These processes work synergistically to determine the overall ion‐diffusion dynamics. The heterogeneous nature of ion diffusion in battery materials is unveiled and the role of defect engineering in tailoring ion‐transport kinetics is stressed.

Lithium‐Substituted Tunnel/Spinel Heterostructured Cathode Material for High‐Performance Sodium‐Ion Batteries

“…Compared with the pure sample, the spinel structure undergoes slight dislocation during the first discharge to accommodate Na + with a larger atomic radius, which leads to the cathodic peak potential of [NL][ML]O shifting towards the negative direction. [ 39 ] The superior capacity at low current density and the slight shift in the voltage platforms correlate with the activation of the cathode product and the insertion/extraction of Na + into/from LiMn 2 O 4 . [ 37 ] The Na 0.44 MnO 2 /LiMn 2 O 4 heterostructure with directly connected 3D channels in the spinel phase and 1D channels in the tunnel phase shortens the Na + diffusion path, resulting in high redox reaction kinetics.…”

“…Moreover, the diffraction peak of (111), attributed to spinel LiMn 2 O 4 , shifts to a higher 2θ angle in the desodiated state and recovers its original state after discharge, revealing the favorable structural reversibility. Although the spinel phase undergoes slight dislocation, resulting in a decrease in peak intensity of spinel Li x Mn 2 O 4 , [ 37,39 ] the absence of impurity phases indicates that [NL][ML]O exhibits excellent structural stability. These results confirm that doping Li into the Mn site and forming a tunnel/spinel heterostructured can enhance the structural reversibility of [NL][ML]O and promote the extraction of Na + , thereby improving rate capability and cycling stability.…”

Charge distribution guided by grain crystallographic orientations in polycrystalline battery materials

“…The propagation of redox reactions governs the electrochemical properties of battery materials and their critical performance metrics in practical cells [3][4][5] . The recent research progress, especially aided by advanced analytical techniques 6 , has revealed that incomplete and heterogeneous redox reactions prevail in many electrode materials, such as olivine phosphates [7][8][9][10][11][12][13][14] , layered oxides [15][16][17][18][19][20] , spinel oxides 21,22 , and conversion materials 23,24 . Advanced highcapacity cathode materials for lithium (Li) ion and sodium (Na) ion batteries are mostly polycrystalline materials that exhibit complex charge distribution (the valence state distribution of the redox-active cations) due to the presence of numerous constituting grains and grain boundaries.…”

Intercalated water in aqueous batteries

“…In P‐type cathode, the Na + ions occupy two types of face‐sharing prismatic sites, whereas in O‐type cathode, the Na + ions occupy a single type of edge‐sharing octahedral site. The “2” and “3” in each acronym represent the number of repeating sequences in a unit cell 47 . In general, P‐type cathode shows higher voltage than O‐type cathode yet forms at Na‐deficient stoichiometry.…”