Cobalt-Free Core-Shell Structure with High Specific Capacity and Long Cycle Life as an Alternative to Li[Ni_0.8Mn_0.1Co_0.1]O₂

Abstract

Reduction of the Co content in Ni-rich positive electrode materials is an intense research area of great interest. Despite high specific capacity, Co-free Ni-rich materials normally suffer from poor cycling performance. In this work, a Co-free precursor with a 16 μm Ni(OH)2 core and 1 μm Ni0.8Mn0.2(OH)2 shell was reacted with LiOH · H2O at 750 °C (CS-750) or 800 °C (CS-800). CS-750 was found to retain the well-defined core–shell structure after heating, while CS-800 became homogeneous in composition due to Ni/Mn interdiffusion at the higher temperature. Although both of materials exhibit higher specific capacity than LiNi0.8Mn0.1Co0.1O2 (NMC811) the charge-discharge capacity retention shows a dramatic difference. The cycling performance of CS-750 is equivalent to NMC811 samples, whereas CS-800 experiences significant capacity fade, suggesting the importance of a core–shell structure for Ni-rich materials with no Co. The electrical resistivity of CS-750 and CS-800 materials are comparable to NCA and are slightly lower than single crystal NMC811 suggesting that Co may not be essential to maintain good electrical properties. The authors believe CS-750 and related materials represent excellent Co-free options for high energy density Li-ion cells.

Preventing Interdiffusion during Synthesis of Ni-Rich Core–Shell Cathode Materials

“…9−11 This is a good approach; however, these substituents are prone to interdiffusion to the core during the heat treatment with LiOH•H 2 O, making the surface passivation less effective. 12,13 It is challenging to prevent interdiffusion with Mg-and Albased shells even when using a considerable shell thickness. 14 Moreover, an increase in shell thickness compromises the energy density of these Ni-rich cathode materials.…”

“…One approach to increase the lifetime of Ni-rich cathode materials is to reduce the relative amount of Ni at the surface of the particles. Unwanted reactions such as surface reconstruction from layered to disordered rock-salt, electrolyte reactions with highly reactive surface Ni 4+ species at a high state of delithiation, gas generation, and safety limitations, etc., can all be directly correlated with high Ni content at the surface. − Core–shell or concentration gradient hydroxide precursors have been proposed where some Mg, Co, Mn, or Al is substituted for Ni near the surface of secondary particles while maintaining a Ni-rich core for high energy density. − This is a good approach; however, these substituents are prone to interdiffusion to the core during the heat treatment with LiOH·H 2 O, making the surface passivation less effective. , …”

NCA, NCM811, and the Route to Ni-Richer Lithium-Ion Batteries

“…A Co-free precursor with a 16 µm Ni(OH) 2 core and 1 µm Ni 0.8 Mn 0.2 (OH) 2 shell was reacted with LiOH.H 2 O at 750 • C to obtain retain a well-defined core-shell structured material. As a cathode, it exhibited higher specific capacity than NMC811, while the cycling performance was equivalent to NMC811 [299]. A cost-effective cobalt-free LiNi 0.9 Mn 0.1 O 2 was also synthesized by using a coprecipitation method; as a cathode, it delivered capacity of 190 mAhg −1 in the first cycle at a rate of 0.2 C, and a capacity retention of 93 % over 150 cycles at 2.7-4.…”

Understanding the Feasibility of Manganese Substitution for Cobalt in the Synthesis of Nickel-Rich and Cobalt-Free Cathode Materials

“…Synthesizing Ni-rich binary or ternary cobalt-free cathode materials is a significant breakthrough to get rid of the dependence on Co and get low-cost Ni-rich materials by replacing Co with other metals (such as Mn, Fe, Mg, Al, etc. ). − The proportion of Ni in these cobalt-free materials is almost all above 0.9, which makes the material have high capacity while also encountering the same unavoidable problems of poor rate performance and low capacity retention as LiNiO 2 . Compared with previous reports, we tried to avoid the abovementioned defects by reducing the content of Ni (0.8) in materials, employing Mn as a substitute element for Co and selecting oxalic acid as a precipitant to prepare the LiNi 0.8 Co 0.15– x Mn x Al 0.05 O 2 ( x = 0/0.05/0.1/0.15) materials via a coprecipitation route for the first time in this article.…”