Regulating the Grain Orientation and Surface Structure of Primary Particles through Tungsten Modification to Comprehensively Enhance the Performance of Nickel-Rich Cathode Materials

Abstract

Nickel-rich layered oxides, as the most promising commercial cathode material for high-energy density lithium-ion batteries, experience significant surface structural instabilities that lead to severe capacity deterioration and poor thermal stability. To address these issues, radially aligned grains and surface Li x Ni y W z O-like heterostructures are designed and obtained with a simple tungsten modification strategy in the LiNi0.91Co0.045Mn0.045O2 cathode. The formation of radially aligned grains, manipulated by the WO3 modifier during synthesis, provides a fast Li+ diffusion channel during the charge/discharge process. Moreover, the tungsten tends to enter into the lattice of the primary particle surface, and the armor-type tungsten-rich heterostructure protects the bulk material from microcracks, structural transformations, and surface side reactions. First-principles calculations indicate that oxygen is more stable in the surface tungsten-rich heterostructure than elsewhere, thus triggering an improved surface structural stability. Consequently, the 2 wt % WO3-modified LiNi0.91Co0.045Mn0.045O2 (NCM@2W) material shows outstanding prolonged cycling performance (capacity retention of 80.85% after 500 cycles) and excellent rate performance (5 C, 188.4 mA h g–1). In addition, its layered-to-rock salt phase transition temperature is increased by 80 °C compared with that of the pristine cathode. This work provides a novel surface modification approach and an in-depth understanding of the overall performance enhancement of nickel-rich layered cathodes.

Single step synthesis of W-modified LiNiO2 using an ammonium tungstate flux

“…Comparing the 1 mol% W samples, the particles at the surfaces of the 700 °C and 800 °C samples grow into a more elongated shape compared to the interior, which may be related to a gradient of tungsten concentration from the core to the surface of the secondary particles. 74 When the synthesis temperature is increased to 900 °C, a more uniform distribution of larger primary grains is found. Meanwhile, increasing the W content to 5% inhibits grain growth significantly, resulting in a morphology in which it is difficult to distinguish individual grains.…”

“…52,72,73 WO 3 -modied materials in particular were found to exhibit radially aligned grains. 74 While increasing the synthesis temperature to 750 C, the elongated grain-like morphology is retained. Further temperature increase results in a morphology more closely resembling the granular one of the reference sample, albeit with an increase of the primary particle size, which is pronounced signicantly in the 900 C sample.…”

Dual-Modified Compact Layer and Superficial Ti Doping for Reinforced Structural Integrity and Thermal Stability of Ni-Rich Cathodes

“…To determine the effect of titanium incorporation on the thermal stability of NCA materials, in situ time-resolved XRD (50–600 °C) is performed to investigate the phase transition during thermal decomposition of the delithiated cathode material. As shown in Figures a, b and S11–S13, there is phase transition from a layered structure ( R-3m ) to a spinel structure ( Fd3m ) at 230 °C for the delithiated LNCAT0, as evidenced by the weakening of the (003) R peak and merging of the (108) R and (110) R peaks. , Subsequently, at approximately 440 °C, the spinel phase is converted into the rock salt ( Fm3m ) phase, as indicated by the disappearance of the (311) S peak. , The temperature of R-3m → Fd3m phase transition for the delithiated LNCAT1 cathode is delayed to 240 °C, while that of the Fd3m → Fm3m transition temperature is delayed to 540 °C. These results imply that the phase transformation from the layered to rock salt structure is restrained after titanium modification because of the incorporation of steady Ti–O bonds and the ordered presence of Ni 2+ ions in the lithium layer that restricts TM migration (Figure c,d) .…”

“…The curves are consistent with the literature, and all electrodes have a semicircle at high frequencies, which reflects the impedance of Li + migrating through the surface film (R sf ), the second semicircle at the high-to-medium range corresponds to cathode interfacial film (CEI) resistance (R ct ), and the sloping line at the low frequencies refers to Li-ion diffusion (W 0 ). 39,40 The fitting results are listed in Table S7. At the initial cycle, LNCA0 has the smallest values of R sf and R ct .…”

“…As shown in Figures 7a, b and S11−S13, there is phase transition from a layered structure (R-3m) to a spinel structure (Fd3m) at 230 °C for the delithiated LNCAT0, as evidenced by the weakening of the (003) R peak and merging of the (108) R and (110) R peaks. 39,43 Subsequently, at approximately 440 °C, the spinel phase is converted into the rock salt (Fm3m) phase, as indicated by the disappearance of the (311) S peak. 43,44 The temperature of R-3m → Fd3m phase transition for the delithiated LNCAT1 cathode is delayed to 240 °C, while that of the Fd3m → Fm3m transition temperature is delayed to 540 °C.…”