TRANSITION METAL NIOBATES AS FAST-CHARGING ANODES FOR LITHIUM-ION BATTERIES
Abstract
With the existing environmental concerns and looming energy crisis, sustainability has become the main focus in many fields of research and development. Batteries have now emerged as a sustainable solution in decreasing the consumption of fossil fuels by powering electric vehicles and as a large-scale energy storage system for power grids and renewable energy sources. Conventional battery systems have become insufficient with current demands, especially in fast-charging applications and large-scale energy storage system. The immediate need for better alternatives to conventional anode materials in lithium-ion batteries requires exploring the diverse resources available. Transition metals have been one of the top groups of materials that have been investigated by researchers as the next best anode material with higher operating voltages that enhance safety and multiple oxidation states that can enable faster Li-ion kinetics. Niobium-based compounds have been a promising candidate as anodes for lithium-ion batteries due to their attractive properties and high theoretical capacities. However, their commercialization continues to be hindered due to insufficient capacities. Recently, mixed metal oxides have been gaining research interests as the unique combination of metals can offer synergistic effects and well-enhanced electrochemical performances. Niobate-based binary and ternary transition metal oxides were synthesized in this work through a scalable, solid-state mechanochemical synthesis method paired with calcination treatment. The transition metals explored were cobalt, nickel, and manganese in the binary compounds with niobium, whilst the ternary compound consisted of nickel, manganese, and niobium. The final products obtained were characterized by various analytical techniques, which revealed the formation of agglomerated/aggregated microparticles of orthorhombic niobate compounds with the general formula of MNb2O6 (M = Co, Ni, Mn) for the binary transition metal oxides and NiMnNb2O6 as the ternary transition metal oxide. These materials were tested as anode materials in half-cell and full-cell configurations through several electrochemical tests and results have shown that Co-Nb exhibited the highest specific capacities with initial discharge/charge capacities of 644/702 mAh g-1 at 2 A g-1 – the other niobates delivered capacities around 300-500 mAh g-1. Based on the GCD tests of half-cells, all niobate materials have an activation period of about 5 cycles or less in which rapid capacity loss is observed, followed by a period of capacity increase and stabilization. The ternary niobate material, Ni-Mn-Nb, delivered the most stable cycling performance with specific capacities >100 mAh g-1 in over 5000 cycles and minimal capacity loss after 7000 cycles at a fast-charging rate of 2 A g-1 (10C). The rate capability of the anode materials was evaluated by cycling up to a current density of 10 A g-1 (50C) to investigate their abilities for fast-charging applications. Interestingly, all anode materials still worked at a very high rate of 10C and after returning to a lower rate (0.2 A g-1 1C), demonstrating high-rate and fast-charging capabilities. XPS analysis with cycled anode materials revealed the formation of stable SEI layers with varying components across the niobate-based anode materials. Notably, the SEI components observed via XPS for Ni-Mn-Nb only consisted of LiF and Li2CO3, whilst the other niobates contained additional components (Li2O and ROCO2Li). The distinct composition of the SEI layer in Ni-Mn-Nb may be directly related to the material’s ultrastable cycling in the cyclability tests, which outperformed all three binary niobates. Furthermore, the mixture of Ni-Mn-Nb transition metals may have played an important role in structural and electrochemical stability in the anode material, which shows a promising approach to anode design for the next-generation lithium-ion batteries.
DOI/handle
http://hdl.handle.net/10576/62744Collections
- Materials Science & Technology [63 items ]