Abstract:

High-performance rechargeable lithium ion batteries have been widely applied in electrochemical energy storage fields, such as, energy storage grids, portable electronic devices, and electric vehicles (EVs). However, the energy density of lithium ion batteries needs to be increased, and the cost of battery materials could be further reduced for wider commercial applications. An Ni-rich cathode, LiNi_xMn_yCo_1-x-yO₂ (x > 0.8), with high specific capacity is the most promising material for next-generation Li-ion batteries. LiNi_xMn_yCo_1-x-yO₂ (x > 0.8) contains three transition metal elements, Ni, Mn, and Co, respectively. The role of Ni²⁺ is to provide high capacity for recharge The role of Mn⁴⁺ is to stabilize the lattice structure during charging-discharging cycling. Crucially, the role of Co³⁺ in Ni-rich materials is to improve the electrical conductivity and inhibit cation disorder in the lattice during electrochemical cycling. However, Co is both in shortage and expensive, which limits its worldwide commercial application. This work investigates substituting Co with other abundant and cheap transition metals. Transition metal ions Cr³⁺, Cd²⁺, and Zr⁴⁺ can replace Co³⁺ in Ni-rich cathode materials. LiNi_0.8Cr_0.1Mn_0.1O₂, LiNi_0.8Cd_0.1Mn_0.1O₂, and LiNi_0.8Zr_0.1Mn_0.1O₂ were synthesized by a co-precipitation method. Zr was found to be the best candidate for replacing Co in Ni-rich cathode materials. This study investigated Zr⁴⁺-doped Co-free Ni-rich materials. Initially, a carbonate co-precipitation process was used to synthesize Ni_0.8Zr_0.1Mn_0.1CO₃. This is due to that Zr³⁺/Zr⁴⁺ ions are not precipitated in the strong alkali solution, and the pH during hydroxide co-precipitation and carbonate co-precipitation processes are approximately 11 and 8, respectively. Therefore, the carbonate co-precipitation synthesis method was chosen. Ni_0.8Zr_0.1Mn_0.1CO₃ was synthesized by carbonate co-precipitation at pH = 7.6, 7.8, 8.0, and 8.2. After electrochemical analysis, pH = 7.8 was identified as the optimal value. The next stage of the research involved completing an electrochemical performance comparison on two lithium sources. The following lithium sources were added to the precursor; LiOH·₂O, and a 1:1 mixture of LiOH·₂O and Li₂CO₃. The lithium source with the 1:1 mixture, exhibited better performance for the Ni-rich cathode, LiNi_0.8Zr_0.1Mn_0.1O₂. In this study, the ideal doping amount of Zr in Ni-rich materials was 0.05. In conclusion, by careful control of co-precipitation pH and Li source, the Zr doped cobalt free Ni-rich cathode LiNi_0.85Mn_0.1Zr_0.05O₂ delivered a discharge capacity of 179.9 mAh·g^-1 at 0.2C. This was achieved between the voltage range of 2.75-4.3 V, with an 80 cycle capacity retention of 96.52%.

Key words: Lithium ion battery, Nickle-rich cathode material, Cobalt free, Cycling stability