A new lithium‐rich layer‐structured cathode material with improved electrochemical performance and voltage maintenance

Abstract

Summary Lithium‐rich layered oxides (LRLOs) are highly attractive cathode materials for next‐generation lithium‐ion batteries because of their high reversible capacity, but poor cycle performance and voltage decay are two main problems that strongly limit their practical applications. These challenges also apply to the Ru‐based LRLOs of Li2RuO3. The Li2RuO3 cathode material is highly attractive because of their high conductivity and favourable electrochemical reaction kinetics. To overcome the problems associated with Li2RuO3, in contrast to normal single atom doping, here, we propose a Na, Cr co‐doping strategy with the design of Li2−xNaxRu0.95Cr0.05O3 (x = 0, 0.02, 0.06, and 0.1) series materials. Cr doping increases capacity, and Na doping suppresses voltage decay. As a result, the discharge capacity of the optimal Li1.98Na0.02Ru0.95Cr0.05O3 sample over 240 mAh/g after 50 charge‐discharge cycles at 0.2 C is maintained, and the capacity retention reaches a value of 80.5% compared with 69.1% for the undoped Li2RuO3. The value of the voltage decay in the Li1.98Na0.02Ru0.95Cr0.05O3 sample is 125 mV after 100 cycles at a rate of 1 C, and the voltage decay is 188.4 mV for the undoped Li2RuO3. This finding will expand the scope for designing novel layered electrodes with excellent performance.

Dual Substitution Strategy in Co-Free Layered Cathode Materials for Superior Lithium Ion Batteries

“…Studies have shown that the layered materials will become more and more unstable at high delithium due to loss of Li + ion in lithium layer. , However, the cycle stability is significantly improved by Na–Al dual-substitution in this study, which could be attributed to following reasons. First of all, the substitution of Na + ions in the lithium layer could reduce the contraction of the spacing between the layers at a high-charge state, which stabilizes the crystal structure and inhibits the oxidation reaction of anions . Second, the substitution of Na + ions can provide a certain number of positive charge centers to stabilize the lattice oxygen and hinder the migration of TM ions in the cycling process, thus improving the cycling stability.…”

“…One is that a certain amount of Na ions play a “pillar” role in the lithium layer, which can effectively inhibit the structural transformation of the material. The other one is that, the path of TM ions in the LiM 2 layer to the tetrahedral position in the Li layer is squeezed by Na + , by substitution large ionic radius Na + for small ionic radius Li + , which prevents the irreversible transformation of the layered structure into the spinel structure …”

“…Finally, Na + ions will provide a certain number of positive charge centers to stabilize the structure, thus preventing the irreversible transformation of the layered structure into the spinel structure. 34,35 Particularly, the vacancy or defect of oxygen evolution is one of the driving forces for TM migration, and the stable lattice oxygen can reduce the cation disorder. We could infer that the Na−Al dualsubstitution could stabilize the layered crystal structure by inhibiting the oxygen evolution and cation disorder driven by electrochemical reactions.…”

Multiscale Investigation into the Co‐Doping Strategy on the Electrochemical Properties of Li2RuO3 Cathodes for Li‐Ion Batteries

“…Tian et al [26] . have shown that doping the oxide lattice is a more appropriate method to enhance the structural and electrochemical properties.…”

“…Tian et al [26] have shown that doping the oxide lattice is a more appropriate method to enhance the structural and electrochemical properties. Tarascon et al [27] studied a series of Li 2À x Ru y M 1À y O 3 (M=Sn, Ti) cathode materials and investigated the effect of dopants on the cationic and anionic electron transfers (redox mechanisms) at different charging and discharging states.…”