Interlocking biphasic chemistry for high-voltage P2/O3 sodium layered oxide cathode

Sodium Composite Oxide Cathode Materials:Phase Regulation, Electrochemical Performance and Reaction Mechanism

“…Based on P2‐Na 2/3 Ni 1/3 Mn 2/3 O 2 , Sb‐substituted Na 0.62 Ni 0.33 Mn 0.62 Sb 0.05 O 2 consists of 68.78 % P2 phase and 31.22 % O3 phase, indicating the substitution of Sb 5+ can also lead to P2/O3 composite structure [69] . Another Ni/Mn based example is P2‐Na 0.85 Ni 0.34 Mn 0.66 O 2 [58] . As mentioned before, the substitution of Ti for Mn can facilitate the formation of O3‐type structure because Mn 4+ has a greater ionic potential than Ti 4+ , which is consistent with the evolution of crystal structure of Ti‐substituted Na 0.85 Ni 0.34 Mn 0.66− x Ti x O 2 (Figure 2c).…”

“…As for the regulation of TM composition, ion‐substitution (such as Ti 4+ , [58] Ni 2+ , [107] Sn 4+ , [56,57,68] Sb 5+ , [69] Mg 2+ , [59] Li + , [109,122,123] and Li + /Ti 4+[60] ) is an effective strategy to form P2/O3 composite structure. A series of Ti‐substituted Na 0.85 Ni 0.34 Mn 0.66− x Ti x O 2 ( x =0, 0.11, 0.22, 0.33, 0.44) were investigated to illustrate the synergistic effect of biphases [58] . Among them, composite P2/O3‐Na 0.85 Ni 0.34 Mn 0.33 Ti 0.33 O 2 (the ratio of P2 and O3 phase is 24.8 %: 75.2 %) exhibits the best electrochemical properties with a high discharge capacity of 126.6 mAh g −1 at 0.1 C and 82.4 mAh g −1 at 10 C as well as good capacity retention of 80.6 % after 200 cycles at 0.1 C. When assembling full cell with hard carbon, the good electrochemical properties demonstrate its application prospect.…”

“…Similarly, some studies have compared the performance of composite oxide cathode materials and single‐phase cathode materials [49,58,105,108,128,149] . For example, the single‐phase materials P2‐Na 2/3 Ni 1/3 Mn 0.57 Ti 0.1 O 2 and O3‐NaNi 1/3 Fe 1/3 Mn 1/3 O 2 were prepared by Wang et al .…”

“…An interface interlocking reaction mechanism to explain the excellent cycle stability and rate performance of P2/O3‐Na 0.85 Ni 0.34 Mn 0.33 Ti 0.33 O 2 (Figure 12d). [58] During the initial charge process, the O3 undergoes O3–P3 phase transformation while the crystal structure of P2 remains stable and plays a pillar role. As the charging process continues, the P2 and P3 structures hinder each other causing the stress in the opposite direction to the gliding, thus, inhibiting the gliding of the TMO 2 slabs.…”

“…For cathode materials, the leap from half‐cell to full cell is a key step towards commercialization. Some composite oxide cathode materials also show excellent performance in full batteries [49,58,68] . Moreover, the anode (e. g., hard carbon) of SIBs full cells in practical application often irreversibly consume part of sodium ions from the cathode materials.…”