Self‐Induced Concentration Gradient in Nickel‐Rich Cathodes by Sacrificial Polymeric Bead Clusters for High‐Energy Lithium‐Ion Batteries

Abstract

along the grain boundaries. [12][13][14][15] Consequently, such structural instability causes rapid capacity fading and poor electrochemical performance, which are ascribed to the deteriorated ionic and electronic conduction. To date, many surface treatment and morphology control technologies have been suggested to prevent capacity fading and structure degradation during cycling. [3] For the surface treatment of nickel-based layered cathodes, this concept is considered as a very simple and viable way by introducing additional layers consisting of polymer, [16] metal phosphate, [17,18] metal fluoride, [19,20] metal oxide, [21,22] or core shell [23][24][25] on the surface of the secondary particle clusters. The point that is often overlooked, however, is that these approaches do not fully prevent the fundamental issues related to the grain boundaries among the primary particles. In this context, a novel concept of full concentration-gradient of manganeserich phase with long rod-shaped primary particles was reported and demon strated good structural stability. [26][27][28][29][30] More recently, Cho and co-workers introduced two approaches for the grain boundary coating including the nanoscale surface treatment by cobalt-rich cation mixing layer [31] and spinel-like Li x CoO 2 layer as a glue-nanofiller [32] for highly stable active materials, where an improved structural and thermal stability was achieved by suppressing the phase transition from layered to rock-salt phase of primary particles. However, these kinds of surface treatment methods accompanied a multistep coprecipitation process [29,30] or were carried out after coprecipitation process of active materials by using additional chemicals for surface coatings, [31][32][33] which can cause the increase of the process time and capital cost.Herein, we report a highly stable LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode with a TM concentration gradient in primary particles and inner pores in secondary particles via a simple, one-step coprecipitation method by exploiting polymeric-beads as a sacrificial template without any surface coating reagents. The prepared sample retains the self-induced TM concentration gradient with reduced nickel oxidation state in the primary particles, which significantly improved the structural stability by suppressing the evolution of microcracks in cathode particles at a high voltage cutoff of 4.45 V and even at a high temperature of 60 °C. Additionally, the internal pores in the secondary particles successfully provided a buffer effect against the volume change of the primary particles.The synthesis process for polystyrene beads (PSBs) incorporated LiNi 0.6 Co 0.2 Mn 0.2 O 2 , denoted as a PSB-NCM, is simple and highly scalable. Briefly, the cathode precursor, PSB-Ni 0.6 Co 0.2 Mn 0.2 (OH) 2 , was synthesized by the coprecipitation To meet the demand of electric vehicles and electrical energy storage systems, lithium-ion batteries with high energy density, high rate capability, and thermal stability have been required. [1][2][3] Among the man...

Prospect and Reality of Ni‐Rich Cathode for Commercialization

“…In order to overcome these challenges, our group synthesized a highly stable LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode exploiting polystyrene beads (PSBs) cluster incorporated coprecipitation method without the additional metal tank (Figure 9a). [136] Interestingly, during annealing process, the thermal decomposition of the PSBs located in the cathode core gave rise to the formation of pore space as well as the concentration gradient with reduced nickel oxidation state in the primary particles (Figure 9b,c). In terms of the reduction mechanism of the nickel ions, the carbonized PSBs were oxidized to the carbon dioxide gas during the annealing process, then the most unstable trivalent nickel ions among the transition metal ions were reduced to the stable divalent nickel ions.…”

Controllable Solid Electrolyte Interphase in Nickel‐Rich Cathodes by an Electrochemical Rearrangement for Stable Lithium‐Ion Batteries

“…In addition, the oxidation state of nickel ions was slightly different between two samples. The oxidation states of nickel can be characterized by the L 3 edge peak, for instance, L 3 edge peaks at 855 and 875 eV indicate divalent and trivalent nickel ions, respectively . The NCA exhibited constant nickel oxidation state, however, the ASL‐NCA showed larger amount of divalent nickel ions than trivalent nickel ions at the cathode surface (Figure S16c,f, Supporting Information).…”

Surface and Interfacial Chemistry in the Nickel‐Rich Cathode Materials

“…For example, Kim et al. synthesized the porous structured LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM) cathode using the polymeric bead clusters during the co‐precipitation . In terms of the synthetic procedure, they initially added the polystyrene bead (PSB) as the seed into the co‐precipitation reactor, then the transition metals hydroxide grew on the PSB.…”

“…[158][159][160] For example, Kim et al synthesized the porous structured LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM) cathode using the polymeric bead clusters during the coprecipitation. [161] In terms of the synthetic procedure, they initially added the polystyrene bead (PSB) as the seed into the co-precipitation reactor, then the transition metals hydroxide grew on the PSB. During the lithiation process, the PSB was carbonized, inducing the spontaneous reduction of the trivalent nickel ions to the divalent nickel ions.…”