Lithium bis(oxalate)borate additive in the electrolyte to improve Li-rich layered oxide cathode materials

Abstract

Lithium-rich layered oxides (LLO), as the most attractive cathode materials for high-energy lithium-ion batteries (LIBs), are plagued by poor cyclability due to structural and electrode/electrolyte interface instability. Herein, we report the synthesis of a LLO and its performance enhancement by using boron-containing electrolyte additives. In a formulated 1.0 M LiPF₆ ethylene carbonate/ethyl methyl carbonate electrolyte with 0.1 M lithium bis(oxalato)borate (LiBOB), the battery assembled with Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ microspheres presents a stable specific capacity of 202 mA h g⁻¹ at 0.5C and a remarkable capacity retention of 96.4% after 100 cycles, significantly outperforming the cathode in the baseline electrolyte without LiBOB. The combination of voltammetry, impedance, microscopy, and spectroscopic analysis and density functional theory (DFT) calculations corroborates the beneficial effect of LiBOB in stabilizing the LLO/electrolyte interface. Reactions between LiBOB and activated oxygen radicals result in the formation of a dense cathode electrolyte interface (CEI) film (∼15 nm) containing oxalate, lithium fluoride and alkyl borate species, which contributes to suppression of the capacity/voltage decay of the LLO. These results would provide insight in understanding the effect of boron-containing electrolyte additives in upgrading high-capacity Li-rich cathode materials.