Li thin films by ALD are being used to fabricate and enhance the performance of major components in Lithium-Ion batteries
Lithium-ion batteries (LIB’s) are being widely used in today’s consumer electronics especially in systems that need to be driven by an integral power supply with high energy density such as medical implants, self-powered integrated circuits and electric vehicles. Recent attention has been focused on all solid state LIB’s due to their flexibility in design, miniaturization for microelectronic devices and improved safety due to the absence of liquid electrolytes. Now, due to even greater power consumption needs, these two dimensional (2D) thin film batteries are being replaced by three dimensional (3D) microbatteries which offer significantly increased surface area of the active materials to provide higher battery capacity per unit area. New fabrication techniques have been developed to provided defect-free thin films onto 3D structures. Atomic Layer Deposition (ALD) which was used to prepare metal oxide films for LIB’s was also found as the ideal method to use to fabricate 3D microbattery components.1-3
Significant efforts have been dedicated recently to the development of ALD processes of lithium compounds for solid state electrolyte (SSE) materials. Several SSE materials such as lithium tantalite, lithium lanthanum tantalite and lithium niobium oxides have been reported.4-5 Glassy films have been preferred over crystalline systems due to the fact they do not require further annealing to obtain a pure phase SSE. Among the potential candidates, glassy lithium phosphorus oxynitride (LiPON) has become one of the most popular SSEs for thin film batteries. Conductivity of ALD LiPON thin films can reach as high as 10-7 S/cm at room temperature.6 Recently, as-grown lithium niobium oxide (LNO) ALD films have shown great promise for future SSE applications, delivering a room temperature Li+ conductivity of 6 x 10-8 S/cm.5
ALD lithium has also been used in the layer by layer synthesis of quaternary oxide lithium iron phosphate (LiFePO4) cathode materials in Li-ion batteries. LiFePO4 exhibits high power density, excellent rate capability and ultra-long lifetime making it a great candidate for both electric vehicle lithium batteries and microbatteries.7
The most common Li source for ALD thin films used in battery technology is lithium tert-butoxide (LiOtBu) and is available from the Strem catalog as #03-0780, Lithium t-butoxide, 98+%.
Catalog #03-0780 Lithium t-butoxide, 98+% (1907-33-1)
Strem also now offers a new, safer, non-flammable, amidinate based lithium precursor,(N,N-Di-i-propylacetamidinato)lithium, min. 97% (99.99+%-Li) PURATREM, catalog #03-8000, as an alternative to the spontaneously combustible Lithium t-butoxide for growing ALD films. Not only is this product safer to handle than the self-heating LiOtBu, but metal amidinates in general have good volatility and reactivity and are thermally stable at growth conditions making them ideal candidates for ALD processes.
Catalog #03-8000 (N,N-Di-i-propylacetamidinato)lithium, min. 97% (99.99+%-Li) PURATREM
Figure 1. Thermogravimetric analysis of 03-8000 under inert atmosphere. Sample held at 25oC for 2 minutes and ramped to 500C at a rate of 10C per minute. Weight loss onset at 268.7C, endset at 305.3C with 2.47% residue at 500C.
1. Mater. Horiz., 2017, 4, 133-154.
2. ECS Trans., 2009, 25, 333-344.
3. J. Mater. Chem., 2009, 19, 8767-8771.
4. J. Phys. Chem. C, 2013, 117, 20260-20267.
5. ACS Appl. Mater. Interfaces, 2018, 10, 1654-1661.
6. Chem. Mater., 2015, 27, 5324-2331.
7. Adv. Mater., 2014, vol. 26, issue 37, 6472-6477.
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