Strain Engineering by Local Chemistry Manipulation of Triphase Heterostructured Oxide Cathodes to Facilitate Phase Transitions for High‐Performance Sodium‐Ion Batteries

Abstract

Sodium‐ion oxide cathodes with triphase heterostructures have attracted intensive attention, since the sodium‐storage performance can be enhanced by utilizing the synergistic effect of different phases. However, the composite structures generally suffer from multiple irreversible phase transitions and high lattice strain because of interlayer‐gliding during the charge/discharge process. Here, the concept of strain engineering via manipulating the local chemistry of heterostructured oxide cathode is proposed to regulate the relevant physical and chemical properties, resulting in highly reversible structural evolution (P2/P3/spinel → P2/P3″/spinel) and low intrinsic stress in the potential window of 1.5–4.0 V. Also, the simple structural evolution at a relatively high cut‐off potential of 4.3 V can be detected by in situ X‐ray diffraction and other electrochemical characterization techniques during Na+ extraction/insertion. Meanwhile, the electrode exhibits a high reversible capacity (169.4 mAh g−1 at 0.2 C) and excellent rate performance from 1.5 to 4.3 V. Overall, this study reveals the mechanisms of regulating local chemistry to realize strain engineering of the cathode materials and paves the way for the further improvement of high‐performance sodium‐ion batteries.

Layered oxide cathodes for sodium‐ion batteries: From air stability, interface chemistry to phase transition

“…Most recently, Chou's group reported a strain engineering strategy via local chemistry manipulation and designed a tri‐phase heterostructured cathode of Na 0.5 Ni 0.05 Co 0.15 Mn 0.65 Mg 0.15 O 2 (LLS‐NaNCMM15), which was confirmed by XRD and HR‐TEM (Figure 17C,D). 255 The content of P2, P3, and spinel in LLS‐NaNCMM15 are 46.5%, 48.8%, and 4.7%, respectively. The Mg substitution is beneficial to release intrinsic stress and elevate structural reversibility, leading to a simplified phase transition process.…”

“…(E) In situ XRD patterns and the corresponding evolution of the main characteristic diffraction peaks, and schematic illustration of the crystal structural evolution of P2/P3/spinel‐Na 0.5 Ni 0.05 Co 0.15 Mn 0.65 Mg 0.15 O 2 . Reproduced with permission 255 . Copyright 2022, John Wiley and Sons.…”

Accumulated Lattice Strain as an Intrinsic Trigger for the First-Cycle Voltage Decay in Li-Rich 3d Layered Oxides

“…Lithium-ion batteries (LIBs) have received considerable attention in the past decades because of their excellent rechargeability and high energy density. − Li- and Mn-rich layered oxide (LMLO) cathode materials are particularly attractive because they can deliver much higher specific capacities (exceeding 250 mA h g –1 ) than the most commonly used layered Li­(Ni, Co, Mn)­O 2 (NCM, R 3̅ m ) cathode materials (around 180 mA h g –1 ). − Such high specific capacity is attributable to the cationic and anionic redox processes in LMLOs, which are different from the transition-metal (TM) redox alone in NCM cathodes on cycling. − There is a high voltage plateau associated with the lattice oxygen oxidation in the first de-lithiation process, but it vanishes upon the lithiation process. − Furthermore, a continuous reduction of the average discharge voltage occurs during the subsequent cycles, which seriously restricts the commercial application of LMLOs. , These inspire tremendous research efforts to decipher the origin of the voltage decay in LMLOs.…”

Deciphering the degradation discrepancy in Ni‐rich cathodes with a diverse proportion of [003] crystallographic textures

“…Furthermore, the electrolyte will penetrate the cathode materials along the cracks, and then react with active substances to form a series of fluoride (LiF and (Co, Mn, Al, Ni) x F y etc.) with poor ionic/electronic conductivity, and so forth 24‐28 . Additionally, some Li + and O 2− ions on the surface of Ni‐rich cathodes will be lost, leading to the surface structure transformation from a layered structure ( R ‐3 m ) to a spinel ( Fd ‐3 m ) or a rock salt ( Fm ‐3 m ) phase during cycling 29,30 .…”

“…with poor ionic/electronic conductivity, and so forth. [24][25][26][27][28] Additionally, some Li + and O 2− ions on the surface of Ni-rich cathodes will be lost, leading to the surface structure transformation from a layered structure (R-3m) to a spinel (Fd-3m) or a rock salt (Fm-3m) phase during cycling. 29,30 The ionic conductivity of the structural reconstruction layer is very poor, which will markedly hinder the Li + extraction and insertion, causing capacity decay.…”