Improving Li⁺ Kinetics and Structural Stability of Nickel-Rich Layered Cathodes by Heterogeneous Inactive-Al³⁺ Doping

Abstract

To improve the Li+ kinetics and structural stability of high-capacity nickel-rich layered oxides, but not at the cost of reducing reversible capacity, a heterogeneous inactive-Al3+ doping strategy is proposed to build an Al3+-rich surface within a low doping amount. As anticipated, the heterogeneous inactive-Al3+ doped nickel-rich LiNi0.7Co0.15Mn0.15O2 shows a large reversible capacity of ∼215 mAh g–1, corresponding to a high energy density of ∼850 Wh kg–1. Moreover, it also exhibits long-term cycle lifespan, capacity retention of ∼90% after 200 cycles even at a high upper cutoff voltage of 4.5 V (vs Li/Li+), and improved thermal stability. Surprisingly, the heterogeneous inactive-Al3+ doped electrode shows a high capacity of ∼145 mAh g–1 even at a high rate of 10C, which corresponds to ∼70% capacity retention at 0.1C, due to the enhanced Li+ kinetics. Also this heterogeneous inactive-ion doped approach is capable of being readily expanded to other types of layered, spinel and olivine cathodes to enhance their structural stability and Li+ kinetics.

Degradation and Aging Routes of Ni-Rich Cathode Based Li-Ion Batteries

“…Moreover, the considerations of cation doping and concentration gradients can be combined. Such a dopant concentration gradient is reported for aluminum [129]. Here, the inactive aluminum species stabilizes the surface of the Ni-rich NMC particle, whereas the capacity loss due to doping is diminished, since the overall amount of Al is smaller when compared to heterogeneous doping.…”

A Carbon‐Free Li2TiO3/Li2MTi3O8 (M═Zn1/3Co2/3) Nanocomposite as High‐Rate and Long‐Life Anode for Lithium‐Ion Batteries

“…In Figure b, the peak currents () have a good linear relation with the square root of scan rate ( υ 1/2 ), indicating the limited charge/discharge processes induced by Li + diffusion in this electrode. The diffusion coefficient of lithium ion ( D ) is extracted by the following equation where is the peak current value ( A ), n is the number of charge transfer in the redox, A is the total surface area of electrode (cm 2 ), υ is the scan rate (V s −1 ), D is the diffusion coefficient of Li + (cm 2 s −1 ), and C is molar concentration of Li + in the electrode (mol cm −3 ). The calculated Li + diffusion coefficients ( D ) are 1.24 × 10 −10 , 4.22 × 10 −11 , and 6.85 × 10 −12 cm 2 s −1 for peaks 1–3, respectively, indicating the improved Li + diffusion rate during redox reactions.…”

“…A reduction peak located at about 0.5 (vs Li/Li þ ) is also observed, corresponding to the different sites for Li þ insertion/extraction in such a Fd-3m spinel phase. [18] In Figure 6b, the peak currents (i p ) have a good linear is extracted by the following equation [46] i p ¼ 2:686 Â 10 5 n 3=2 AD 1=2 Cv 1=2 (1) where i p is the peak current value (A), n is the number of charge transfer in the redox, A is the total surface area of electrode (cm 2 ), υ is the scan rate (V s À1 ), D is the diffusion coefficient of Li þ (cm 2 s À1 ), and C is molar concentration of Li þ in the electrode (mol cm À3 ). The calculated Li þ diffusion coefficients (D) are 1.24 Â 10 À10 , 4.22 Â 10 À11 , and 6.85 Â 10 À12 cm 2 s À1 for peaks 1-3, respectively, indicating the improved Li þ diffusion rate during redox reactions.…”

The role of metal substitutions in the development of Li batteries, part I: cathodes

“…197 The protective effects at the surface can be improved through gradient substitution, where the more susceptible surface of the material has a higher Al content to protect from material degradation, while the less vulnerable centre maintains its pristine, or near-pristine composition, gaining the improved capacity of the unsubstituted material without compromising cycle life. 226 Al 3+ substitution also increases thermal stability and safety of Ni-rich NMC materials, offsetting the onset of exothermic reactions and making their onset more gradual. 197,226 Aluminum substitution has also been shown to decrease Li/Ni mixing in NMC 662 when substituted for Mn and in 811 which likely contributes to the increased stability seen in these compositions when substituted.…”