Surface modification of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ cathode materials with Li ₂ O‐B ₂ O ₃ ‐LiBr for lithium‐ion batteries

Abstract

Summary LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode material suffers from phase transformation and electrochemical performance degradation as its main drawbacks, which are strongly dependent on the surface state of NCM523. Herein, an effective surface modification approach was demonstrated; namely, the fast lithium‐ion conductor (Li2O‐B2O3‐LiBr) was coated on NCM523. The Li2O‐B2O3‐LiBr coating layer as a protecting shell can prevent NCM523 particles from corrosion by the acidic electrolyte, leading to a superior discharge capacity, rate capability, and cycling stability. At room temperature, the Li2O‐B2O3‐LiBr–coated NCM523 exhibited an excellent capacity retention of 87.7% after 100 cycles at the rate of 1 C, which is remarkably better than that (29.8%) without the uncoated layer. Furthermore, the coating layer also increased the discharge capacity of NCM523 cathode material from 68.7 to 117.0 mAh g−1 at 5 C. Those can be attributed to the reduction in the electrode polarization and improvement in the electrode conductivity, which was supported by electrochemical impedance spectroscopy and cyclic voltammetry measurements.

Borate‐Based Surface Coating of Li‐Rich Mn‐Based Disordered Rocksalt Cathode Materials

“…This demonstrates that the coating layer helps to maintain charge transfer. [ 17 ] This result is in agreement with the dQ/dV data that showed a sharper redox peak for coated samples. The uncoated sample (bare) suffered from a significant impedance growth after 50 cycles, indicative of unwanted chemical reactions that resulted in resistive CEI products, which were unfavorable for cell performance.…”

“…Furthermore, the absence of reflections from the phases LiOH·H 2 O or H 3 BO 3 suggests the completion of the surface‐coating reaction. [ 17 ] A slight shift of the diffractions peaks to higher angles was noticed after coating. The Rietveld refinement in Figure S1 (Supporting information) revealed a slight decrease of the cell parameter from the bare material (4.151 Å) to the coated samples (4.129–4.136 Å), which could result from the formation of under stoichiometric Li 2‐ x Mn 2/3 Ti 1/3 O 2 F 1‐ y materials at high temperature during the surface modification process.…”

Synthesis and Electrochemical Characterization of LiNi0.5Co0.2Mn0.3O2 Cathode Material by Solid-Phase Reaction

“…The diffraction patterns of all samples exhibit the typical characteristics of a layered α-NaFeO 2 structure with a group space of R m [ 23 , 24 ]. In addition, no peak of the impurity phase is observed in the patterns of samples synthesized at different temperatures.…”

Excellent electrochemical performance of LiNi0.5Co0.2Mn0.3O2 with good crystallinity and submicron primary dispersed particles

“…LIBs owing to their high discharge capacity, environmental friendliness, and low cost. [11][12][13][14][15] However, limited by preparation process, the ternary cathode materials are generally spherical or quasispherical secondary particles which are aggregated from small nanometer primary particles. These secondary particles are easily broken during the progress of preparation and cycling own to their poor mechanical properties.…”

“…The cathode materials, as an indispensable component of LIBs, determine the electrochemical performance of LIBs directly 6‐10 . Nickel‐cobalt‐manganese (NCM) ternary cathode materials are known as one of the most promising future cathode materials for LIBs owing to their high discharge capacity, environmental friendliness, and low cost 11‐15 …”