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

Abstract

The layered nickel-rich materials have attracted extensive attention as a promising cathode candidate for high-energy density lithium-ion batteries (LIBs). However, they have been suffering from inherent structural and electrochemical degradation including severe capacity loss at high electrode loading density (>3.0 g cm ) and high temperature cycling (>60 °C). In this study, an effective and viable way of creating an artificial solid-electrolyte interphase (SEI) layer on the cathode surface by a simple, one-step approach is reported. It is found that the initial artificial SEI compounds on the cathode surface can electrochemically grow along grain boundaries by reacting with the by-products during battery cycling. The developed nickel-rich cathode demonstrates exceptional capacity retention and structural integrity under industrial electrode fabricating conditions with the electrode loading level of ≈12 mg cm and density of ≈3.3 g cm . This finding could be a breakthrough for the LIB technology, providing a rational approach for the development of advanced cathode materials.

Surface and Interfacial Chemistry in the Nickel‐Rich Cathode Materials

“…The acidic species such as the HF that was formed by the decompositions of the LiPF 6 salt and PVdF binder could dissolve the transition metal ions in the cathode structure. [25][26]51,[121][122] To date, it has been known that the trivalent manganese ions among the transition metal ions were preferentially dissolved from the cathode, which was attributed to the structural instability of the manganese ions. [17,[123][124][125][126][127][128] The Jahn-teller distortions of the trivalent manganese ions gave rise to the disproportionation reactions (2Mn 3 + !Mn 2 + + Mn 4 + ), and the divalent manganese ions were extracted from the cathode.…”

“…This limitation allowed the researchers to focus on the surface coating such as metal oxide, [46,48,55,133,[162][163] metal phosphate, [56,[164][165] and lithium reactive coating materials. [40][41][42]44,[51][52]54,122] In terms of the metal oxide, the metal oxide coating materials could mitigate the parasitic redox reaction with the electrolyte. [166] Furthermore, the metal phosphate such as AlPO 4 , [167] Ni 3 (PO 4 ) 2 , [168] Co 3 (PO 4 ) 2 [164] and MnPO 4 [169] suppressed the surface degradation because of the protection of the cathode materials by the metal phosphate coating layer.…”

“…Along with the surface coating layer, it has been reported that the surface protective layer combined with the doping could guarantee the interfacial stability in the nickel-rich cathode materials. [38,[40][41]44,[51][52] For example, the vanadiumbased surface treatment was performed in the Li-Ni 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathodes (Figure 7a). [41] Remarkably, the multi-valent vanadium ions reacted with the residual lithium compounds during the annealing process, ensuring the interfacial stability by mitigating the reactions with the HF.…”

“…To effectively stabilize the newly exposed primary particles, Kim et al incorporated the artificial SEI compounds, which could be electrochemically rearranged, in the LiNi 0.84 Co 0.14 Al 0.02 O 2 (NCA) cathode material. [51] In terms of the synthetic process, they mixed the NCA cathode with the cobalt phosphate as the coating precursor, which formed the artificial SEI compounds and transition metal concentration gradient at the surface (Figure 8a). The initial artificial SEI compounds consisting of the phosphorous locally existed with the thickness of~200 nm only at the surface of the NCA as shown in Figure 8b.…”

“…To mitigate the cathode reactivity with the electrolyte, there are five approaches for the development of high energy LIBs: (1) the incorporation of electrochemically inactive elements into the cathode structure, [30][31][32][33][34][35][36][37] (2) the introduction of the concentration gradient, (3) the introduction of surface coating layer on the cathode, [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] (4) the morphological changes to the porous structure, and (5) the crystallinity tuning from the polycrystalline to the single crystalline cathode. [57][58][59][60][61][62][63][64][65][66] With respect to the first approach, it could improve the interfacial stability by inhibiting the transition metal reductions.…”