The Influence of Ammonia Concentration on the Precipitation of Ni(OH)2 Precursor in the Synthesis of LiNiO2 Cathode Materials for Lithium-Ion Batteries
Authors: Kress Katja 
Published: February 2024

Lithium-ion batteries have been implemented in the energy storage market for many decades, used as rechargeable batteries in portable devices, electric vehicles and a wide range of other applications. Ni-rich layered oxides as cathode materials in Li-ion batteries are of great interest due to their higher energy density and theoretical capacity of 274 mAh/g. [1] To improve fast lithium-ion diffusion in lithium-ion battery cathodes, enhance the limited capacity due to oxygen release and phase changes, reduce cost and toxicity and most importantly, inhibit unethical mining of cobalt. Alternative compounds to replace LiCoO2 are investigated by substituting different transition metals, such as Ni, Mn, or Al on the Co site in the structure. The increase of the Ni content and decrease of the Co content increases the capacity and lowers the costs in $/kWh, as Ni provides higher performance and a high energy-density. To cope with the higher demand of volume constrained applications [2], the volumetric energy-density is to be considered and is achieved by a high tap density of the active material, which is related to particle size, particle size distribution and morphology. [3] However, for high-nickel content cathodes, degradation processes like Li/Ni mixing [4], surface layer deconstruction [5], particle cracking[6], decomposition reactions with the electrolyte [7] and slow Li+ diffusion kinetics [8] occur, leading to lower capacity retention, a loss of capacity in the first cycle and thus an overall insufficient cycling stability.

There are many research publications about optimising the calcination process of the Ni(OH)2 precursor and LiOH*H2O, [9][10][11], but currently, very little focus on the precursor material itself, it’s particle size and morphology, which affects the structural and electrochemical behaviour. The accumulation of mechanical strain due to repeated c-axis contraction and relaxation during charge/discharge processes lead to particle cracking, electrolyte infiltration, structural decay and results in a reduced electrochemical performance. To counter this, a large study regarding the morphology, particle size, and electrochemical behaviour of Ni(OH)2 precursor material produced in a highly controlled environment (batch stirred tank reactor BSTR) has been undertaken and the first results are presented here. A higher transition metal to ammonia ratio during synthesis leads to larger and more spherical secondary particles, a narrow particle size distribution, a higher tap density and also improved electrochemical cycling.

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