![]() ![]() 13,14 The surface reconstruction and CEI build-up are also more detrimental when paired with particle cracking and exposure of fresh surfaces to the electrolyte leading to additional oxygen release, reduction of new surfaces, and electrolyte oxidation. 7,12 A second suggested mechanism for impedance increase across the surface is a build-up of a resistive cathode electrolyte interphase (CEI) due to chemical (released, reactive oxygen) and electrochemical oxidation of the electrolyte. 8–11 The oxygen release is also connected to surface reconstruction to spinel and rock salt-like phases (which are oxygen-deficient compared to layered NMC) that lead to hindrance of lithium (de)intercalation due to their lower ionic conductivity. 4,6,7 Oxygen release has been found to occur at similar high states of charge as the lattice collapse, leading to chemical oxidation of the electrolyte and transition metal dissolution. 5 The repetitive lattice expansion and contraction is thought to lead to particle degradation in the form of inter- and intra-granular cracking. It has been suggested that the lattice collapse at high states of charge (SOC) is the main driver of capacity loss for many layered transition metal oxides. However, higher Ni content CAMs negatively impact the cell longevity. 1 In particular, high nickel content (Ni-rich) layered transition metal oxides such as NMC811 (LiNi 0.8Mn 0.1Co 0.1O 2) are especially attractive, as they provide larger specific capacities compared to lower nickel alternatives and have lower costs and resource issues due to reduced Co content. 1,2 Among the CAMs, layered transition metal oxides, such as NMCs (LiNi xMn 圜o 1− x− yO 2) have been successfully applied commercially. Progress is limited by the cathode active material (CAM), as it tends to be the bottleneck of cost and performance. LIBs with better performance are urgently needed, as higher specific capacity, rate capability, lifetime, safety, and environmental impact are key parameters for longer driving range, safer, and more sustainable EVs. Introduction With hybrid and electric vehicle (EV) sales and market shares continuously rising, their most prevalent way of reversibly storing energy – the lithium-ion battery (LIB) – has become increasingly important. The present study provides insight into the leading causes for LIB performance fading, and highlights the defining role played by the evolving properties of the cathode particle surface layer. Scanning transmission electron microscopy electron energy loss spectroscopy reveals a correlation between impedance rise and the level of transition metal reduction at the surfaces of aged NMC811. Focused ion beam-scanning electron microscopy highlights that extensive microscale NMC particle cracking, caused by electrode manufacturing and calendering, is present prior to aging and not immediately detrimental to the gravimetric capacity and impedance. Using these protocols, impedance measurements, and differential voltage analysis, the primary drivers for capacity fade and impedance rise are shown to be large state of charge changes combined with high upper cut-off voltage. In this work, tailored aging protocols are employed to decouple the effect of electrochemical stimuli on the degradation mechanisms in graphite/NMC811 full cells. However, complex degradation mechanisms inhibit their use. ![]() Ni-rich layered transition metal oxides, such as NMC811 (LiNi 0.8Mn 0.1Co 0.1O 2), are promising cathode candidates for LIBs due to their higher specific capacity and lower cost compared with lower Ni content materials. The transition towards electric vehicles and more sustainable transportation is dependent on lithium-ion battery (LIB) performance. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |