Surface-modified concentration-gradient Ni-rich layered oxide cathodes for high-energy lithium-ion batteries

Abstract

Concentration-gradient layered Li[Ni 0.8 Co 0.2 ] 0.7 [Ni 0.2 Mn 0.8 ] 0.3 O 2 oxide with Ni-rich in the core and Mn-rich in the surface region has been synthesized through a condition-controlled tank reactor reaction. While the Ni-rich core facilitates high capacity, the Mn-rich surface enables good cyclability and thermal stability. The concentration-gradient sample exhibits a higher capacity of 204 mA h g-1 at C/5 rate with superior cyclability and thermal stability compared to the constant-concentration LiNi 0.62 Co 0.14 Mn 0.24 O 2 sample, which has the same net Ni, Co, and Mn contents as those present in the concentration-gradient sample. The concentration-gradient sample was also coated with a thin layer of Al 2 O 3 on the surface to stabilize the electrode/electrolyte interface and thereby further improve the electrochemical performance. Both the structural (gradient structure) and surface (Al 2 O 3 coating) modifications help suppress side reactions between electrode and electrolyte and reduce the decline in voltage during cycling. The Al 2 O 3-coated concentration-gradient sample exhibits improved long-term cyclability, rate capability, and thermal stability compared to the pristine uncoated sample.

Toward Low-Cost, High-Energy Density, and High-Power Density Lithium-Ion Batteries

“…102 Electrolyte decomposition products deposit on the cathode surface in the form of Li 2 CO 3 , LiOH, LiF, Li x POF y , polycarbonates, and species specific to electrolyte and cathode compositions. 103,104 Strategies to improve the surface properties include doping, 105 surface coatings, 106,107 and electrolyte additives. 108 These approaches typically result in trade-offs of maximum specific capacity and first cycle coulombic efficiency 109 for decreased impedance rise, thermal stability, and reduced CEI buildup to increase cell-cycle life.…”

“…110 One especially promising approach to reduce surface reactivity and prolong the cycle life of Nirich NMCs is the development of compositionally graded cathodes with less Ni at the surface. 96,106,107,112,113 These particles typically have a Mn-rich surface and a Ni-rich core. Mn 4+ is electrochemically inactive.…”

An Ostwald ripening route towards Ni-rich layered cathode material with cobalt-rich surface for lithium ion battery

“…To solve these problems, various approaches including structure tuning [34][35][36], substitution [37][38][39], and surface coating [40][41][42][43][44][45] have been proposed. Metal oxides such as Al 2 O 3 [46,47], ZrO 2 [48], MgO [49], have been studied as coating materials. The metal oxide layer is beneficial to protecting the cathode materials from being exposed to electrolyte directly, and thus reducing the side reactions.…”

“…Some lithium based materials have also been used to react with residual impurities on the surface of Ni-rich cathode materials and form a uniform coating layer on the bulk surface at the same time [54][55][56]. In addition, Co-shell and concentration-gradient Ni-rich cathodes have been designed to improve the cycle life, structural and thermal stability of the Ni-rich cathodes [46,[57][58][59][60]]. Sun's group first reported a novel high-capacity and safe cathode material with an average composition of Li[Ni 0.68 Co 0.18 Mn 0.18 ]O 2 , in which each particle consists of bulk material surrounded by a concentrationgradient outer layer [59].…”

Surface-modified Li[Ni0.8Co0.15Al0.05]O2Cathode Fabricated using Polyvinylidene Fluoride as a Novel Coating

“…Ni-rich compounds, e.g., Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 , are promising cathode materials with high specific discharge capacity. However, they exhibit several disadvantages such as insufficient cycling performance, rate capability, and thermal stability [16][17][18][19][20]. To address these issues, modification of cathode material surfaces with carbon has been studied [21][22][23][24][25].…”