Tuning (003) interplanar space by boric acid co-sintering to enhance Li+ storage and transfer in Li(Ni0.8Co0.1Mn0.1)O2 cathode

Abstract

High nickel layered oxides (LiNi0.8Co0.1Mn0.1O2, NMC811) demonstrate high capacity (≥ 200 mA h/g) and low cost, making them increasingly attractive as a high energy active cathode to replace LiCoO2 or LiFePO4 for lithium ion batteries. Nevertheless, their large scale practical applications are still inhibited by the low structural stability, insufficient rate capability and cyclability. In this work, a stable and safe LiNi0.8Co0.1Mn0.1O2 cathode was synthesized by facile oxalic acid assisted co-precipitation method. Boric acid has been chosen and utilized as a co-sintering agent to enhance the electrochemical performance via fine tuning internal interplanar space between transition metal oxide (003) layers. The B03 sample with 3.0 at% of boron doping exhibited a sustainable reversible capacity as high as 220 mA h g−1 with approximate 97% capacity retention after 100 cycles at 0.5 C charging/discharging rate. It also delivered 93 mA h/g under 10 C rate testing. In the long-term cycling test, this B03-NMC 811 cathode demonstrated 83% capacity retention after 300 cycles at 5 C cycling test. Appropriate adding of boron not only enhanced their C-rate capability and cyclability but also improved their structural stability during repetitive charging and discharging process through ex situ XRD measurement. The c axis variation of B03-NMC 811 cathode between 3.7 V and 4.3 V was reduced by 7.6% (0.014 Å) as compared to the pristine one. However, larger quantity (5.0 at%) of boron degrades the electrochemical performance induced by increased Li/Ni disorder. Thereafter, this enhancement in both electrochemical performance and structural stability benefits from the optimized interplanar space between transition metal oxide (003) layers, which can be tuned precisely by such a simple but novel co-sintering process with boric acid. This approach opens the door to structural modification and optimization of NMC811 cathode to satisfy the demanding performance and safety requirements of electric vehicles.