Understanding the enhancement effect of boron doping on the electrochemical performance of single-crystalline Ni-rich cathode materials

A Molten‐Salt Method to Synthesize Ultrahigh‐Nickel Single‐Crystalline LiNi0.92Co0.06Mn0.02O2 with Superior Electrochemical Performance as Cathode Material for Lithium‐Ion Batteries

“…A slight expansion of $${I_{{\rm{Li}}{{\rm{O}}_2}}}$$ thickness is observed for SC‐780 compared with SC‐Ni92, which is contributed to the doping of B 3+ ion with smaller ionic radius that occupies the tetrahedral interstitial sites of the oxygen array and expands the interslab layers. [ 32,35 ] Meanwhile, the effect of B doping with the different amount on the single crystalline Ni‐rich oxides are investigated by our previous works, which also demonstrates that B doping will expand the interlayer distance with (003) peak slightly moving to a lower diffraction angle, as shown in Figure S1, Supporting Information. Besides, ultra‐high temperature calcination may create more Li/Ni cation mixing and damage the crystal structure of SC‐820, leading to the narrowest lithium migration layer thickness and the largest migration resistance.…”

“…[ 30 ] The sample SC‐780 (SC obtained at 780 °C) shows lower cation mixing in comparison with SC‐Ni92 (the powder was synthesized by a deprived molten‐salt method without the addition of boric acid, and the calcination process was set as same as SC‐780) for the enhanced covalent bonds B–O and the inhibition of oxygen release after boron doping. [ 31,32 ] Additionally, the diffraction peak intensity ratio I (003) / I (104) is capable of evaluating the cation mixing degree of layered oxides, and the higher intensity ratio means lower cation mixing. This indicator provides another evidence that the sample SC‐780 by novel molten‐salt synthesis method has a lower Li + /Ni 2+ ratio and less disordered structures.…”

“…Besides, two intense peaks of LiF and Li x PF y O z for F 1s spectra are attributed to the cathode electrolyte interface film, illustrating more LiPF 6 component decomposition in the PC‐Ni92. [ 32 ] Therefore, it is demonstrated that the single crystalline materials show enhanced mechanical integrity with avoided crack formation, which will significantly alleviate the undesired electrode/electrolyte interface parasitic reactions.…”

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

“…In addition, introducing the ions that possess strong covalent bonds with O could greatly inhibit lattice oxygen release and boost the chemical stability, further resulting in superior cycling durability. [63b,69,75] Liu et al [69] incorporated 0.6 mol% B in the TM layers to expand the unit cell volume and reduce the Li + /Ni 2+ mixing for singlecrystalline LiNi 0.83 Co 0.05 Mn 0.12 O 2 . As shown in Figure 7a, the surface energy was changed by the generation of robust BO covalent bonds, which substantially suppressed the formation of disordered rock salt phases, synergistically leading to the outstanding capacity retention of 91.35% after 500 cycles in pouch-type full-cells (Figure 7b) and an ultrahigh rate capacity of 170.6 mA h g −1 at 5 C. More greatly, co-doping with multiple elements has also been employed to simultaneously stabilize the bulk and surface chemistry of single-crystalline cathodes materials, which could further enhance their electrochemical performances benefiting from the synergistic modification effects.…”

Enhancing cycle life of nickel-rich LiNi0.9Co0.05Mn0.05O2 via a highly fluorinated electrolyte additive - pentafluoropyridine

“…Nickel-rich (Ni-rich) LiNixCoyMn1-x-yO2 (NCM, x ≥ 0.9) layered oxides have been considered one of the most promising cathode materials for next generation LIBs due to their high specific capacity and high achievable energy density, in comparison with LiCoO2 and NCM analogues with lower Ni content. [5][6][7] However, there are still some key problems unsolved for the Ni-rich cathode materials, especially the rapid capacity deterioration when operated with high charge cut-off voltages ≥ 4.3 V vs. Li/Li + . The reasons causing the rapid capacity deterioration of the Ni-rich NCM include (1) irreversible structure transformation from layered to disordered rock-salt phase during repeated charging and discharging process with excessive lithium utilization, [8] (2) the interfacial degradation resulted from the parasitic side reactions between Ni-rich NCM and electrolyte.…”