In Situ Tuning Residual Lithium Compounds and Constructing TiO₂ Coating for Surface Modification of a Nickel-Rich Cathode toward High-Energy Lithium-Ion Batteries

Abstract

Nickel-rich layered oxides with excellent specific capacity and reasonable cost have extensively employed as cathode materials for higher energy density lithium-ion batteries (LIBs). However, side reactions caused by the surface contaminations and deterioration of the layered structure especially at high cutoff voltage lead to insufficient cycle life and poor electrochemical performance, which further hinder the commercial development of nickel-rich cathode materials. Herein, an optimized route combining acid treatment with titanium dioxide (TiO 2 ) coating successfully modifies the surface of the single-crystalline LiNi 0.6 Co 0.2 Mn 0.2 O 2 (SC-NCM) cathode material, which collaboratively eliminates surface residual contaminations and stabilizes the bulk structure. Furthermore, the evolution of the internal crack, phase transition, and host structure can be effectively mitigated via applying the TiO 2 coating on SC-NCM even after long-term cycling. Moreover, it is confirmed that such surface treatment significantly impedes the conversion of surface residual lithium after air exposure. As the cathode material for LIBs, as-optimized SC-NCM delivers a capacity retention of 87.4% at 1 C over 200 cycles at room temperature, higher than that of pristine SC-NCM (a capacity retention of 73.5%). This proposed method provides a simple and available strategy to obtain prolonged service life and safety characteristics of LIBs.

Nano-TiO2 coated single-crystal LiNi0.65Co0.15Mn0.2O2 for lithium-ion batteries with a stable structure and excellent cycling performance at a high cut-off voltage

“…The results of residual lithium titration showed that the amounts of residual lithium of S-NCM65 and 5TS-NCM65 were 5695 ppm and 3992 ppm, respectively, indicating that the TiO 2 coating had a signicant effect on the reduction of residual lithium, which may be due to the reaction of TiO 2 with partial residual lithium to form lithium titanate. 31 The decrease in Li 2 CO 3 and LiOH on the surface of the material is conducive to the suppression of the side reaction at the cathode/electrolyte interface. LiOH will react with LiPF 6 in the electrolyte to generate HF, further corroding the electrode material.…”

“…At such a high cut-off voltage and high current density, the 94.16% cycling retention rate for 200 cycles (97.16% for 100 cycles) of 5TS-NCM65 is the highest among nickel-rich materials in the literature. 27,30,31,[40][41][42][43][44][45][46] These results indicate that under high cut-off voltage and high current density, coating treatment is an effective method to improve the cycle performance of single crystal materials. Coating with 5000 ppm TiO 2 is the most signicant for improving the cycle performance of single crystal materials.…”

Simultaneously Constructing a TiO2–LiF Composite Coating Enhancing the Cycling Stability of LiCoO2 at 4.6 V High Voltage

“…The signal peaks of Ti 2p 3/2 and Ti 2p 1/2 were observed at 458.3 and 464.3 eV respectively, and both orbital peaks correspond to Ti 4+ in TiO 2 . 39 In the F 1s spectrum (Figure 2e), the signal peak of elemental F was also only detected on the surface of the LCO/ TF-1% sample. The peak at 685 eV is attributed to LiF formed on the LCO surface, which further proves that the gaseous fluorine compound decomposed by TiF 4 reacted with Li exposed on the surface layer during high-temperature heat treatment to generate LiF.…”

“…In the Ti 2p spectrum (Figure d), the signal of Ti was not detected on the surface of the pure LCO sample, but the standard Ti 2p orbital peak spectrum was detected on the surface of the coated LCO/TF-1% sample. The signal peaks of Ti 2p 3/2 and Ti 2p 1/2 were observed at 458.3 and 464.3 eV respectively, and both orbital peaks correspond to Ti 4+ in TiO 2 . In the F 1s spectrum (Figure e), the signal peak of elemental F was also only detected on the surface of the LCO/TF-1% sample.…”

Sr-Based Sub/Surface Integrated Layer and Bulk Doping to Enhance High-Voltage Cycling of a Ni-Rich Cathode Material

“…The popularity of consumer electronics and the rapid development of electric vehicles have put forward higher energy density and longer service life requirements for lithium-ion batteries (LIBs), which are mainly limited by cathode materials. − Among the various promising cathode materials, the nickel-rich layered oxides (LiNi x Co y Mn z O 2 , x ≥ 0.6, x + y + z = 1) attract widespread attention due to their extremely high reversible capacity that can even exceed 200 mAh g –1 when the charging voltage exceeds 4.5 V. Except for the contribution of cations, additional capacity is achieved by the redox reaction of anionic oxygen (O 2– /O 2 n – , where 1 < n < 2) during a high charging voltage. , However, Ni-rich materials suffer from severe phase transformation and surface side reactions that cause the capacity and voltage to fade during high-voltage cycling. − Therefore, many surface protectors, such as oxides (e.g., Al 2 O 3 , ZrO 2 , TiO 2 ), − phosphates (Li 3 PO 4 , FePO 4 , LiFePO 4 ), − and fluorides (AlF 3 , LiF, MgF 2 ), − were designed to mechanically restrain unwanted structural transformations and inhibit surface side reactions by avoiding direct contact between the cathode materials and the electrolyte.…”