Nanorod and Nanoparticle Shells in Concentration Gradient Core–Shell Lithium Oxides for Rechargeable Lithium Batteries

Abstract

The structure, electrochemistry, and thermal stability of concentration gradient core-shell (CGCS) particles with different shell morphologies were evaluated and compared. We modified the shell morphology from nanoparticles to nanorods, because nanorods can result in a reduced surface area of the shell such that the outer shell would have less contact with the corrosive electrolyte, resulting in improved electrochemical properties. Electron microscopy studies coupled with electron probe X-ray micro-analysis revealed the presence of a concentration gradient shell consisting of nanoparticles and nanorods before and after thermal lithiation at high temperature. Rietveld refinement of the X-ray diffraction data and the chemical analysis results showed no variations of the lattice parameters and chemical compositions of both produced CGCS particles except for the degree of cation mixing (or exchange) in Li and transition metal layers. As anticipated, the dense nanorods present in the shell gave rise to a high tap density (2.5 g cm(-3) ) with a reduced pore volume and surface area. Intimate contact among the nanorods is likely to improve the resulting electric conductivity. As a result, the CGCS Li[Ni0.60 Co0.15 Mn0.25 ]O2 with the nanorod shell retained approximately 85.5% of its initial capacity over 150 cycles in the range of 2.7-4.5 V at 60 °C. The charged electrode consisting of Li0.16 [Ni0.60 Co0.15 Mn0.25 ]O2 CGCS particles with the nanorod shell also displayed a main exothermic reaction at 279.4 °C releasing 751.7 J g(-1) of heat. Due to the presence of the nanorod shell in the CGCS particles, the electrochemical and thermal properties are substantially superior to those of the CGCS particles with the nanoparticle shell.

Stabilization of a High-Capacity and High-Power Nickel-Based Cathode for Li-Ion Batteries

“…Meanwhile, the Mn content increases from 0.04 in the center to 0.2 on the surface, and the oxidation of electrolyte by the highly active Ni ions is effectively suppressed. The cathode can retain a capacity of 190 mAh/g after 100 cycles running in the voltage window of 2.7-4.5 V. 107,115 This improvement is obviously dramatic in comparison with the performance of the cathode material with the same inner high nickel composition: the capacity loss after 100 cycles is usually about 50% of its initial value as a result of the aggressively accelerated irreversible reactions on the cathode-electrolyte interphase at such a high cutoff voltage. Another superior property of the FCG structure over the CGS core shell, traditional core shell, and surface coating structure is the radial continuity of the composition as well as the crystal lattice structure.…”

“…The nanorod network also provides a short pathway for Li-ion diffusion from the surface to the bulk. 55,107,115 By maximizing the average Ni concentration at the center core as active redox species, as well as the Mn concentration near the particle outer surface, the FCG concept was extended to establish a new system with a two-sloped full concentration gradient (TSFCG) of Ni, Co, and Mn ions throughout a Li[Ni 0.65 Co 0.13 Mn 0.22 ]O 2 cathode particle. 116,117 The Ni-enriched core boosted even higher capacity and the Mn-enriched surface strengthened the safety protection with well-maintained rod-shaped primary particles during deep cycling.…”

Surface/Interfacial Structure and Chemistry of High‐Energy Nickel‐Rich Layered Oxide Cathodes: Advances and Perspectives

“…The origination of microcracks together with new resistance layer at the aged secondary particles created lack of connection among the primary grains and the fast rise of electrochemical impedance, respectively. Lately, Sun and co‐workers[93a,b] have designed and organized a series of compositionally graded nickel‐rich layered oxides with concentration‐gradient structure. In this structure, a single rod‐shaped primary grain with decreased nickel fraction was introduced for concentration‐gradient layer as demonstrated in Figure d.…”

“…The distinctive morphology assembled by radially aligned primary grains is anticipated to restrain microcracks in secondary particles by reducing anisotropic expansion and contraction during the continuous cycles. Liang and co‐workers[93c,d] noted that the aligned architectures had the following superiorities: (1) highly organized charger transfer and Li + migration pathways; and (2) tunable interspaces between architecture units. Additionally, as illustrated in Figure c, Cho and co‐workers also demonstrated the feasibility of utilizing a simplistic coating to develop a glue‐nanofiller layer (G‐layer), middle‐temperature Li x CoO 2 ( x < 1) with spinel‐like phase, between the primary grains of the nickel‐rich Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 secondary particles in mitigating the microcracks, specifically at high operating temperatures.…”

Synthesis and Electrochemical Performance of Nickel-Rich Layered-Structure LiNi0.65Co0.08Mn0.27O2Cathode Materials Comprising Particles with Ni and Mn Full Concentration Gradients

“…17 Circular, micro-sized secondary particles composed of nano-sized rod-shaped primary particles seem to confer the best particle morphology for both non-gradient, conventional cathode (CC) materials, as well as gradient materials. 33,34 These gradient materials are generally synthesized via a co-precipitation method, in which a manganese salt rich solution is slowly added to a nickel rich salt solution, with the salt concentration profiles over time controlling the composition of the precipitated particles. 24 For these studies, we chose to synthesize layered materials with roughly the composition of LiNi 0.65 Co 0.08 Mn 0.27 O 2 , which can deliver sufficiently high capacities, nearly 200 mAhr g −1 without resulting in Ni 2+ cation mixing in the Li layer.…”