High-performance batteries require advanced materials that can provide electrodes with effective ionic and electronic transport. Lithium-ion batteries, which are rechargeable batteries that work by transporting lithium ions between an anode and a cathode during charging and discharging, are widely used in laptops, cell phones, and other personal electronic devices.
Typically, lithium-ion batteries contain a cathode made from lithium cobalt oxide, and an anode made from carbon. However, consumers continue to demand electronic devices that are smaller, lighter, charge faster, and last longer, than their predecessors. To keep up with these demands, there is extensive on-going research in the area of battery materials.
Anode and cathode materials for lithium ion batteries are the subject of extensive research worldwide. Microcrystalline Li4Ti5O12 (LTO) has long been considered a promising anode material for lithium-ion batteries due to its high stability and good cyclability, but its applications have been limited by low ionic and electronic conductivities.
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A new report published in Nature Communications describes work by a collaboration of researchers from France and Poland who have prepared a new hierarchically nanostructured LTO-type material with exceptional electrochemical performance and the potential to provide ultrafast charging lithium-ion batteries.
The nanostructured LTO reported by the team was prepared using a solvothermal method, which involved applying heat and pressure to a solution of lithium and titanium salts. Synthesis of nanostructured LTO materials have previously been reported in the literature, but most use complex synthesis routes that would be expensive or unsuitable for large scale synthesis. The team describes their synthesis method as “inexpensive and scalable,” meaning that their materials could be produced on a large scale for inclusion in commercial batteries.
Electron microscopy confirmed that the LTO material self-assembled into a hierarchical structure with 4-8 nm nanoparticles during synthesis (Figure 1). Nanostructuring LTO is thought to improve electrochemical performance by providing controlled porosity, enabling effective electrolyte penetration and minimal diffusion distances for the lithium ions during charging and discharging. The team tested the electrochemical performance of their LTO material, which exhibited excellent performance.
The LTO material demonstrated a stable capacity of 170 mAh g-1 after 1000 charge/discharge cycles at a 50C current rate, close to the theoretical capacity of LTO at 175 mAh g-1. Furthermore, a capacity of 99 mAh g-1 was achieved when the material was subjected to an extremely fast 500C charge current, followed by discharge at 50C. This suggests that LTO batteries may be capable of ultrafast charging
Although X-ray diffraction analyses showed the material was highly crystalline LTO, surface elemental analyses suggested that the material had fewer lithium ions than expected. The team attributed this to relaxation of the surface structure of the nanoparticles, resulting in increased exposure of the titanium ions at the surface, and decreased exposure of the lithium ions. The lithium deficient structure at the surface of the nanoparticles may aid insertion and extraction of lithium ions during charging and discharging.
The team suggests that the combination of nanostructure, microstructure, and non-stoichiometry resulted in the exceptional electrochemical performance of their LTO material.
To summarize, a new LTO-type material has been reported with a simple, scalable synthesis method resulting in a hierarchical nanostructured material with exceptional electrochemical performance. Further optimization could enable LTO batteries to find commercial applications and provide ultrafast charging for personal electronics.
Odziomek M, Chaput F, Rutkowska A, Świerczek K, Olszewska D, Sitarz M, Lerouge F, Parola S, “Hierarchically structured lithium titanate for ultrafast charging in long-life high capacity batteries.” Nat. Commun. 8:15636, 2017.
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