Oxygen Vacancies and Stacking Faults Introduced by Low-Temperature Reduction Improve the Electrochemical Properties of Li₂MnO₃ Nanobelts as Lithium-Ion Battery Cathodes

Abstract

Among the Li-rich layered oxides LiMnO has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine LiMnO generally has to be electrochemically activated in the first charge-discharge cycle which causes very low Coulombic efficiency and thus deteriorates its electrochemical properties. In this work, we show that low-temperature reduction can produce a large amount of structural defects such as oxygen vacancies, stacking faults, and orthorhombic LiMnO in LiMnO. The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine LiMnO changes into a LiMnO-LiMnO (0.71/0.29) composite, and the monoclinic LiMnO changes from LiMnO in the pristine LiMnO (P-LiMnO) to LiMnO in the reduced LiMnO (R-LiMnO), indicating the production of a large amount of oxygen vacancies in the R-LiMnO. High-resolution transmission electron microscope images show that a high density of stacking faults is also introduced by the low-temperature reduction. When measured as a cathode material for Li-ion batteries, R-LiMnO shows much better electrochemical properties than P-LiMnO. For example, when charged-discharged galvanostatically at 20 mA·g in a voltage window of 2.0-4.8 V, R-LiMnO has Coulombic efficiency of 77.1% in the first charge-discharge cycle, with discharge capacities of 213.8 and 200.5 mA·h·g in the 20th and 30th cycles, respectively. In contrast, under the same charge-discharge conditions, P-LiMnO has Coulombic efficiency of 33.6% in the first charge-discharge cycle, with small discharge capacities of 80.5 and 69.8 mA·h·g in the 20th and 30th cycles, respectively. These materials characterizations, and electrochemical measurements show that low-temperature reduction is one of the effective ways to enhance the performances of LiMnO as a cathode material for Li-ion batteries.

Role of polyvinylpyrrolidone in the electrochemical performance of Li2MnO3 cathode for lithium-ion batteries

“…Aer the activation process in the 1st cycle, no plateaus were shown in the curves and sloped curves appeared. [54][55][56] The coulombic efficiencies of OLO-only, OLO-PVP-400, OLO-PVP-500, and OLO-PVP-600 during the 1st cycling were 59.3%, 38.1%, 61.9%, and 73.4%, respectively. On the other hand, the samples showed relatively sloped discharge curves in the 1st cycles due to a layered structure with Mn atoms between the transition metal layers.…”

Function and Application of Defect Chemistry in High‐Capacity Electrode Materials for Li‐Based Batteries

“…In LRMC, the diffusion resistance of Li-ion can be reduced by expanding the crystal cell size, [46] and the spacing between crystal planes can be changed by stacking faults with high density. [47] A large number of nanoscale defects, such as twin-orderings and stacking faults, produce rich boundaries, which can be used as pins to alleviate structural transformation, suppress voltage attenuation, and improve cycling stability. [48] Also, the nanoporous structure can improve the contact between LRMC and electrolyte, which can effectively shorten the diffusion distance of Li-ion, and optimize the structural stability.…”

“…[46] High density of stacking faults can be introduced into the Li 2 MnO 3 nanobelts by a low-temperature reduction method to alter the interplanar distances. [47] Similarly, a great number of nanoscale defects, such as twin-orderings and stacking faults, can also be introduced into the lattice of LRMC by the treatment of in-depth chemical de-lithiation. [48] Nanoscale defects can create abundant boundaries which serve as the pins to mitigate the structure transformation and is beneficial to suppress voltage decay and ameliorate cycle stability.…”

“…also play important roles in maintaining the structure stability, promoting ionic/electronic transfer. In LRMC, the diffusion resistance of Li‐ion can be reduced by expanding the crystal cell size, [46] and the spacing between crystal planes can be changed by stacking faults with high density [47] . A large number of nanoscale defects, such as twin‐orderings and stacking faults, produce rich boundaries, which can be used as pins to alleviate structural transformation, suppress voltage attenuation, and improve cycling stability [48] .…”

Uniform Na+ Doping‐Induced Defects in Li‐ and Mn‐Rich Cathodes for High‐Performance Lithium‐Ion Batteries

“…[1][2][3][4] In response to this demand, enormous time and efforts have been invested in searching for satisficing solutions to achieve with an idea for designing Na + deep doping in LMR cathodes uniformly to avoid the formation of cracks, maintain the integrity of electrode particles during prolonged cycles, and utilize the Na + 's own intrinsically high bond strength with oxygen framework to inhibit the oxygen loss and preserve the layered structure. [38] In this work, we introduce abundant stacking faults in the as-prepared Na + -doped LMR to promote its electrochemical properties. [38] In this work, we introduce abundant stacking faults in the as-prepared Na + -doped LMR to promote its electrochemical properties.…”