Improving the Structural Stability of Li‐Rich Layered Cathode Materials by Constructing an Antisite Defect Nanolayer through Polyanion Doping

Abstract

To mitigate the gradual phase transition and improve the structural stability of Li‐rich layered cathode materials, an antisite defect nanolayer (transition‐metal ions replacing Li+ in a Li slab) with a thickness of approximately 2 nm was induced on the surface of Li1.16(Ni0.25Mn0.75)0.84O2 by doping with boracic polyanions. It is found that the 2 and 3 mol % BO33−‐doped samples show excellent cycling stability with capacity retentions of 91.2 and 93.7 %, respectively, after 300 cycles at 0.5 C. More importantly, the BO33− doping restrains the decay of discharge voltage upon cycling and has the prospect to overcome the fatal drawback of Li‐rich layered oxides. The results demonstrate that the BO33− doping contributes to the generation of an antisite defect nanolayer on the surface, which hinders the formation of Li‐ion vacancies and the continued migration of more transition‐metal ions to the Li slab in a deep charging state. The antisite defect nanolayer clearly improves surface structural stability and inhibits the appearance of the amorphous domain in the bulk, which are favorable to maintain the facile lithium‐diffusion pathways during cycling and improve the capacity retention and rate capability.

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

“…[58] Meanwhile, the reduction of the covalent TMÀ O (TM = Ni, Co, or Mn) bonds and the decrease of top O 2p band can mitigate the variation of the electronic structure of the O 2p band, which can suppress the layered-spinel phase transition, eliminate the formation of amorphous phase and enlarge Li-ion diffusion channel, thus ameliorating the cycling stability and achieving a capacity retention of 89% after 300 cycles. [58,64] The doping of F, as a common anion doping, can enlarge the interplanar spacing of OÀ Li-O configuration, which contributes to the elevated diffusion coefficient of Li-ion and abate the energy barrier of Liion diffusion. [34] Except for the monoatomic doping, the codopings, such as Ti 4 + , Nb 5 + and F À , Ni 2 + and SO 4 2À , are deemed as an important doping strategy to improve the structural stability and inhibit the voltage fading.…”

“…In the case of anion doping, the introduction of BO 3 3− can induce the surface nanolayer with antisite defects (Figure 2e), which can inhibit the migration of transition metal ions [58] . Meanwhile, the reduction of the covalent TM−O (TM=Ni, Co, or Mn) bonds and the decrease of top O 2p band can mitigate the variation of the electronic structure of the O 2p band, which can suppress the layered‐spinel phase transition, eliminate the formation of amorphous phase and enlarge Li‐ion diffusion channel, thus ameliorating the cycling stability and achieving a capacity retention of 89% after 300 cycles [58,64] . The doping of F, as a common anion doping, can enlarge the interplanar spacing of O−Li‐O configuration, which contributes to the elevated diffusion coefficient of Li‐ion and abate the energy barrier of Li‐ion diffusion [34] .…”

“…In addition, the formed W−O bonds have strong covalent bond property, which is conducive to reducing the migration of transition metal ions and the loss of surface oxygen. In the case of anion doping, the introduction of BO 3 3− can induce the surface nanolayer with antisite defects (Figure 2e), which can inhibit the migration of transition metal ions [58] . Meanwhile, the reduction of the covalent TM−O (TM=Ni, Co, or Mn) bonds and the decrease of top O 2p band can mitigate the variation of the electronic structure of the O 2p band, which can suppress the layered‐spinel phase transition, eliminate the formation of amorphous phase and enlarge Li‐ion diffusion channel, thus ameliorating the cycling stability and achieving a capacity retention of 89% after 300 cycles [58,64] .…”

“…(e) Schematic illustration of LRMC with an antisite defect layer on the surface. Reproduced with permission from Ref., [58] Copyright 2017, Wiley‐VCH.…”

Simply Constructing Li1.2Mn0.6Ni0.2O2/C Composites for Superior Electrochemical Performance and Thermal Stability in Li–Ion Battery

“…Among all kinds of reported novel cathode materials, Li‐rich oxides { x Li 2 MnO 3 ⋅(1‐ x )LiMO 2 , M=Mn, Co, Ni, Fe etc.} have grabbed enormous attentions because of their low cost and high capacity of over 250 mAh g −1 , almost twice higher than that of LiCoO 2 , which makes them as one of the promising alternatives as cathode for next generation lithium ion batteries . The high capacity of Li‐rich oxides is ascribed to the irreversible loss of Li 2 O from monoclinic phase Li 2 MnO 3 at high voltage (over 4.45 V vs .…”