Optimized synthesis condition and mechanism for novel spherical cobalt-free 0.6Li2MnO3·0.4Li[Fe1/3Ni1/3Mn1/3]O2 cathode

Abstract

The spheroidization of cathode is extremely important for improving tap density and cycle stability. However, the spherical cobalt-free Li-rich and Mn-based cathode of xLi2MnO3·(1-x)LiMO2 (M = Fe, Ni, Mn, LFNMO) have not been successfully synthesized so far. For the first time, a spherical cobalt-free 0.6Li2MnO3·0.4Li [Fe1/3Ni1/3Mn1/3]O2 cathode is synthesized via co-precipitation approach in this work. It exhibits small Brunauer-Emmett-Teller (BET) specific surface area (2.56 m2 g−1) and high tap density (2.11 g cm−3). Meanwhile, an excellent cycle stability is also achieved, which delivers a high reversible capacity of 208 mAh g−1 at C/10 after 100 cycles. Further investigation demonstrates that the optimized sodium carbonate (Na2CO3) precipitant and suitable pH could adjust the solubility product (Ksp) of the precipitate and make the Fe2+, Ni2+ and Mn2+ precipitate simultaneously according to the designed stoichiometric ratio to form the spherical precursor, which is the key to forming the spherical LFNMO. The spherical LFNMO could reduce the side reactions between cathode and electrolyte, form thin cathode electrolyte interphase (CEI) and suppress the electrolyte corrosion to cathode, hence improving electrochemical performance. This work expatiates the synthesis condition and mechanism to prepare spherical LFNMO via co-precipitation, which might greatly advance the designing and development of cathode materials.