Enabling Long‐Term Cycling Stability Within Layered Li‐Rich Cathode Materials by O2/O3‐Type Biphasic Design Strategy

Abstract

Typical Li-rich layered oxides are widely regarded as promising cathode candidates for high-energy-density Li-ion batteries because of additional output capacities boosted by oxygen redox activities. However, its commercialized applications are hindered by serious capacity loss and voltage decay related to structural degradation upon cycling. Herein, a Co/Ni-free biphasic O2/O3-type layered cathode material is proposed, Li 0.9 [Li 0.3 Mn 0.7 ]O 2 , which has been successfully prepared by the Li + /Na + ion-exchange strategy and characterized by the XRD Rietveld refinement and SAED as well as HRTEM analyses. O2/O3-type layered cathode material with an approximate composition of 81% O2 and 19% O3 phases are confirmed. Furthermore, the biphasic cathode exhibits a high discharge capacity of 232 mAh g −1 with capacity retention of 88.1% after 500 cycles at a current density of 200 mA g −1 . That is, volume changes of the O3-type phase are effectively restricted during Li + (de)intercalations, further enhancing the structural stability and suppressing the formation of spinel phase due to the biphasic structural design. Altogether, these findings prove the biphasic structural design is a feasible strategy to achieve Li-rich cathode materials with high capacity and long-term cycle stability.

Effects of cation superstructure ordering on oxygen redox stability in O2-type lithium-rich layered oxides

“…14,23,24,[26][27][28] Nevertheless, a slightly greater degree of the voltage decay was evidenced for the LLCMO electrode (93.8% retention) compared with the LLNMO (98.4%), even though they commonly shared the O2-type structure that is effective in suppressing the voltage decay. 14,[23][24][25][26][27][28][29] Considering that the voltage decay is primarily coupled with the irreversible transition metal migration, [13][14][15][16][17] it may be inferred that the LLCMO electrode has undergone the structural transition involving the irreversible transition metal migration during cycles, which will be verified in detail later.…”

“…And, these efforts have led to the identification of several O2-type lithium-rich layered oxides that could surpass their conventional O3-type counterparts. 14,[23][24][25][26][27][28][29] Nevertheless, studies also found that the degrees of voltage decay are slightly dependent on the species of substituents and the composition in the transition metal layer, even though they still could display a lower degree of voltage decay over O3-type electrodes. Moreover, some of the O2-type electrodes exhibited partially disordered structure with extended cycles, implying the presence of additional factors that trigger the irreversible transition metal migrations.…”

Fundamentals of Ion‐Exchange Synthesis and Its Implications in Layered Oxide Cathodes: Recent Advances and Perspective

“…[ 27–36 ] Compared with high‐temperature sintering, the ion‐exchange method reduces the energy consumption during the synthesis process and avoids the lithium loss caused by the volatilization of lithium salt. The reaction time required for molten‐slat ion exchange was further reduced for Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2+ δ −x F x materials [ 37 ] and Li 5/6 Li 1/4 (Mn 0.675 Co 0.325 ) 3/4 O 2 materials, [ 38 ] which was carried out in an argon‐filled tube furnace at 280 °C for 4 h. The Li 5/6 Li 1/4 (Mn 0.675 Co 0.1625 Ni 0.1625 ) 3/4 O x can also be synthesized by changing the atmosphere of the synthesis process to air, which can be completed at mild temperature of 280 °C for 4 h. [ 39 ] When using the ion‐exchange method for the synthesis of Li 0.66 [Li 0.12 Ni 0.15 Mn 0.73 ]O 2 [ 37 ] and Li 2/3 [Li 2/9 Mn 7/9 ]O 2 [ 40 ] materials, the researchers further reduced the reaction time to 1 h, while maintaining a mild temperature of 280 °C in air during ion exchange. Yang et al.…”

“…Later, Cao et al. [ 40 ] synthesized the layered composite materials with 81% O2 and 19% O3 via ion exchange. This Li 0.9 [Li 0.3 Mn 0.7 ]O 2 composite material achieves a good initial capacity of 232 mAh g −1 and a superior capacity retention of 88.1% after 500 cycles, due to the synergistic effect of dual‐phase structure (Figure 4c–e).…”

Low-Temperature Aged Synthesis of CeO₂-coated Li-rich Oxide as Cathode for Low Cost High Energy Density Li-ion Batteries

“…However, the poor cyclic stability of LLMOs prevents them from commercial applications. Dissolution of manganese from LLMOs and the electrolyte oxidation decomposition on LLMOs are the main reasons for the poor cyclic stability of LLMOs [7,[14][15][16][17][18][19][20][21][22][23] . Co-doping is effective for cyclic stability improvement of LLMOs [23] , but Co is expensive and toxic compared with Mn and Ni in LLMOs.…”