Revealing the Role of W-Doping in Enhancing the Electrochemical Performance of the LiNi_0.6Co_0.2Mn_0.2O₂ Cathode at 4.5 V

Abstract

More and more attention has been focused on Ni-rich ternary materials due to their superior specific capacity, but they still suffer inherent structural irreversibility and rapid capacity degradation under a high voltage. Oxidation of unstable oxygen will lead to the irreversible transformation of the structure. Taking into account the strong W–O bond, an appropriate amount of W-doping is studied to reinforce the thermal stability and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 (NCM622) at 4.5 V. Combining experiments and theoretical calculations, it can be found that W-doping is most preferred at Co sites, and the average charge around O in the NiO6 octahedron becomes more negative after W-doping, which can successfully restrain the release of oxygen, thereby improving the stability of the crystal structure during deep delithiation. In addition, W-doping decreases the energy barrier of the Li+ migration slightly and boosts the kinetic diffusion of lithium ions. As a result, NCM622 doped with 0.5% W boasts an outstanding capacity retention of 96.7% at 1 C after 100 cycles and a discharge specific capacity of up to 152.8 mA h g–1 at 5 C between 3.0 and 4.5 V. Furthermore, analysis of the cycled electrodes indicates that the lattice expansion and the formation of microcracks during long cycling are suppressed after W-doping, thereby elevating the structure and interface stability. Therefore, doping an appropriate amount of W via simple methods is helpful to obtain Ni-rich cathode materials with admirable performance.

Enhanced Electrochemical and Structural Stability of Ni‐rich Cathode Material by Lithium Metaborate Coating for Lithium‐Ion Batteries

“…Figure 4a and b are the Nyquist plots of NCMA88 and NCMA88@0.2B at different voltages. The curves contain one semicircle in the high‐frequency region representing the Li + diffusion through the CEI film ( R sf ), one semicircle in the high‐to‐medium‐frequency region is related to the charge‐transfer process ( R ct ), and a slope in the low‐frequency region representing Warburg impedance ( W ) resulting from the Li‐ion diffusion process [30,31] . The Li + diffusion coefficients ( D Li ) of the samples can be evaluated according to Equation (1) and [32] …”

Recent progress on the modification of high nickel content NCM: Coating, doping, and single crystallization

“…The capacity retention of 0.5 mol% W‐doped NCM622 (W‐0.5%) after 100 cycles was 96.7%, which was higher than that of pristine NCM622 at 90.6% (Figure 6G). [ 70 ] Besides, W‐doping also improved the thermal stability with the postponed thermal releasing temperature and shrunk thermal releasing amount, as shown in the DSC results (Figure 6H). [ 71 ] Because of the stronger W–O bond, W‐doping makes the average charge around O in the NiO 6 octahedron more negative, which suppressed the release of oxygen, thereby improving the stability of the crystal structure and the thermal stability of the high‐Ni NCM cathode.…”

“…Reproduced with permission. [ 70 ] Copyright 2021, American Chemical Society. (H) differential scanning calorimetry results of the pristine, W‐doped LiNi x Co y Mn 1− x − y O 2 ( x = 0.8, 0.9, and 1.0; y = 0.15, 0.05, and 0) and pristine cathode materials.…”

Challenges and Strategies towards Single‐Crystalline Ni‐Rich Layered Cathodes

“…[ 5a,62,63 ] In addition, different dopant sites, including Li site, TM site, and O site have also been shown to effectively tune the crystal lattice and redox properties. [ 63c,64 ] The doping effect can be summarized as follows: 1) enhance the cationic ordering by repressing TM migration; [ 58a,65 ] 2) increase the ion/electron conductivity by regulating lattice parameters, TM oxidation states, defects, and Li diffusion energy barrier; [ 3a,18b,47a,63a,66 ] 3) alleviate lattice distortion during deep charging by easing the H2‐H3 phase transition; [ 64b,66c,67 ] 4) mitigate the oxygen loss and structural degradation by tuning the bond strength and orbital hybridization between the TM and O ions. [ 3a,66a,b,68 ]…”