Suppress voltage decay of lithium-rich materials by coating layers with different crystalline states

Li-rich oxides are considered as the most commercial potential cathode materials due to the high theoretical specific discharge capacity. Here, ZrO_(2) in different crystalline states are applied as the coating layers to enhance the electrochemical performance of hollow Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_(2) materials.Meanwhile, a series of characterizations(XRD, SEM, TEM, EDX etc.) are conducted to compare the effects of ZrO_(2) coating layer with different crystalline states on the host material. The results elucidate that the Li-rich Mn-based material with the polycrystal ZrO_(2) coating layer has a slight advantage in rate performance, while the host material with the single crystal ZrO_(2)-coating layer has a better cycling performance and effectively suppresses voltage decay with the effect of excellently inhibiting layered to spinel-like phase transition and metal dissolution during charging and discharging process.

One-time sintering process to modify xLi2MnO3(1-x)LiMO2 hollow architecture and studying their enhanced electrochemical performances

To solve the critical problems of lithium rich cathode materials, e.g., structure instability and short cycle life, we have successfully prepared a ZrO2-coated and Zr-doping xLi2MnO3·(1–x)LiMO2 hollow architecture via one-time sintering process. The modified structural materials as lithium-ion cathodes present good structural stability and superior cycle performance in LIBs. The discharge capacity of the ZrO2-coated and Zr-doped hollow pristine is 220 mAh g-1 at the 20th cycle at 0.2 C(discharge capacity loss, 2.7%)and 150 m Ah g-1 at the 100 th cycle at 1 C(discharge capacity loss, 17.7%), respectively. However, hollow pristine electrode only delivers 203 m Ah g-1 at the 20 th cycle at 0.2 C and 124 mAh g-1 at the 100 th cycle at 1 C, respectively, and the corresponding to capacity retention is 92.2% and 72.8%, respectively.Diffusion coefficients of modified hollow pristine electrode are much higher than that of hollow pristine electrode after 100 cycles(approach to 1.4 times). In addition, we simulate the adsorption reaction of HF on the surface of ZrO2-coated layer by the first-principles theory. The calculations prove that the adsorption energy of HF on the surface of ZrO2-coated layer is about-1.699 e V, and the ZrO2-coated layer could protect the hollow spherical xLi2MnO3·(1–x)LiMO2 from erosion by HF. Our results would be applicable for systematic amelioration of high-performance lithium rich material for anode with the respect of practical application.

A novelty strategy induced pinning effect and defect structure in Ni-rich layered cathodes towards boosting its electrochemical performance

Layered Ni-rich transition metal oxide is treated as the most promising alternative cathode due to their high-capacity and flexible composition.However,the severe lattice strain and slow Li-ion migration kinetics severely restrict their practical application.Herein,a novelty strategy induced pinning effect and defect structure in layered Ni-rich transition metal oxide cathodes is proposed via a facile cation(iron ion)/anion(polyanion)co-doping method.Subsequently,the effects of pinning effect and defect structure on element valence state,crystal structure,morphology,lattice strain,and electrochemical performance during lithiation/delithiation are systematically explored.The detailed characterizations(soft X-ray absorption spectroscopy(sXAS),in-situ X-ray diffraction(XRD),etc.)and density functional theory(DFT)calculation demonstrate that the pinning effects built-in LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)materials by the dual-site occupation of iron ions on lithium and transition metal sites effectively alleviate the abrupt lattice strain caused by an unfavorable phase transition and the subsequent induction of defect structures in the Li layer can greatly reduce the lithium-ion diffusion barrier.Therefore,the modified LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)exhibits a high-capacity of 206.5 mAh g^(-1)and remarkably enhanced capacity retention of 93.9%after 100 cycles,far superior to~14.1%of the pristine cathodes.Besides,an excellent discharge capacity of 180.1 mAh g^(-1)at 10 C rate is maintained,illustrating its remarkable rate capability.This work reports a pinning effect and defect engineering method to suppress the lattice strain and alleviate lithium-ion kinetic barriers in the Ni-rich layered cathodes,providing a roadmap for understanding the fundamental mechanism of an intrinsic activity modulation and structural design of layered cathode materials.

Unveiling the impact of residual Li conversion and cation ordering on electrochemical performance of Co-free Ni-rich cathodes

The residual Li and Li^(+)/Ni_(2)+cation mixing play essential roles in the electrochemical properties of Ni-rich cathodes.However,a general relationship between the residual Li conversion,cation mixing,and their effects on the Li^(+)kinetics and structural stability has yet to be established,due to the presence of cobalt in the cathode.Here,we explore the synergistic impact of the residual Li conversion and cation ordering on a Co-free Ni-rich cathode(i.e.,LiNi0.95Mn0.05O_(2)).It discloses that the rate capability is mainly affected by residual Li contents and operating voltage.Specifically,residual Li can be electrochemically converted to cathode electrolyte interphase(CEI)below 4.3 V,thus inducing high interphase resistance,and decomposes to produce CO_(2)-dominated gas at 4.5 V,causing temporary enhancement of Li^(+)diffusivity but severe surface degradation during cycling.Moreover,the cycling performance of Co-free Ni-rich cathode is not only determined by Li^(+)/Ni_(2)+cation-ordered superlattice,which enhances the structural stability as it functions as the pillar to impede lattice collapse at a highly charged state,but also by the robust CEI layers which protect the bulk from electrolyte attack under 4.3 V.These findings promote an in-depth understanding of residual Li conversion and Li^(+)/Ni_(2)+cation ordering on Co-free Ni-rich cathode.

The Multiple Modification Road of Li-Rich Manganese-Based Cathode Materials

Li-rich manganese-based cathode materials(LR) are considered as excellent cathode materials for a new generation of lithium-ion batteries causes their outstanding electrochemical performance, friendly price, and environmental friendliness. But defects such as rapid voltage decay and loss of lattice oxygen limit their applications. The electrochemical performance of LR has to be improved by means of modification. The previous single modification methods like element doping, surface coating, structure design, etc. can only optimize the electrochemical performance of LR from one aspect. Recently, multiple modifications,which can combine the advantages of multiple modifications, have been favored by researchers. Here, we comprehensively review the recent progress of multiple modification of LR based on the combination of different modification means. The review and summary of the multiple modification of LR will play a guiding role in its development in the future.