Progress of research on cobalt-free nickel-rich cathodes for lithium-ion batteries
Since its development by Goodenough et al.in 1980,the cathode technology used in lithium-ion batteries has undergone numerous generational advancements.From the original LiCoO2 cathode to the current utilization of NMC cathodes,which include LiNi0.5Mn0.3Co0.2O2(NMC532),LiNi0.6Mn0.2Co0.2O2(NMC622),and LiNi0.8Mn0.1Co0.1O2(NMC811),cobalt has consistently been a crucial component.The centrality of cobalt in lithium-ion battery cathodes highlights its indispensable function.However,global cobalt resources are limited,and the concentration of cobalt mines in Africa has created a highly limited cobalt supply chain.Consequently,geopolitical instability and ethical concerns within the mining industry can significantly disrupt the stability of this crucial supply channel.The surge in demand for lithium-ion batteries fueled by the expanding electric vehicle sector has exacerbated the already pressing need for cobalt.This growing demand,combined with the scarcity and uneven distribution of cobalt resources,has resulted in a sharp rise in cobalt prices,leading to a substantial increase in battery costs.Additionally,it is widely acknowledged that current commercial battery systems offer an energy density of less than 200 Wh kg-1,which is insufficient to meet the growing requirements for battery capacity in diverse applications such as electric vehicles and portable devices.The specific capacity of commercial NCM ternary cathodes increases with increasing nickel content while simultaneously reducing the reliance on cobalt,thereby achieving the dual objectives of enhancing performance and lowering costs.Therefore,a high-capacity,high-nickel cathode system is a promising option that has the potential to boost battery capacity and simultaneously drive down costs.Therefore,this paper focuses on a cobalt-free high-nickel cathode system.Initially,we summarize the basic properties of LiNiO2 cathode materials.We discovered a significant Li/Ni mixing phenomenon in this cathode material.Furthermore,complex phase transitions occur during battery cycling,among which the H2↔H3 transition induces severe c-axis lattice contraction,resulting in lattice cracking.These two factors contribute to the poor structural stability of LiNiO2 cathodes.Additionally,the thermal stability is inadequate,with oxygen release at high temperatures causing irreversible oxygen loss.Due to their high nickel content,these cathodes often exhibit properties similar to those of LiNiO2 cathodes,exacerbating issues with their structural and thermal stability.By exploring the role of cobalt in nickel-containing cathodes,it was found that cobalt primarily alleviates magnetic resistance in the transition metal layer,thereby reducing Li/Ni mixing,enhancing the stability of the crystal structure,improving Li+ion diffusion kinetics,and optimizing rate performance.However,certain properties of cobalt-free high-nickel cathodes surpass those of their cobalt-containing counterparts.Doping with elements such as Mg and Al can compensate for the absence of cobalt,demonstrating the feasibility of cobalt-free high-nickel cathodes.Understanding the properties of LiNiO2 electrodes and the role of cobalt will inform research strategies aimed at eliminating the need for cobalt and the production of cobalt-free high-nickel cathode materials.These strategies involve element doping,surface coating,and single-crystal technology.Following a review of the relevant research strategies,the advantages and challenges of each approach are summarized in this article.The development and in-depth study of high-performance cobalt-free high-nickel cathode materials play a crucial role in the advancement of lithium-ion battery technology and utilization.It is essential to properly coordinate various performance aspects to achieve the best comprehensive optimization,thereby enabling the production of low-cost,high-energy-density lithium-ion battery cathode materials.This will meet the increasing demands for battery capacity and cost in the context of the development of electric vehicles and other fields,thereby promoting the robust development of new energy technologies.
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