Atomic Layer Deposition of Textured Li4Ti5O12 A High Power and Long Cycle Life Anode for Lithium Ion Thin Film Batteries

The zero strain Li4Ti5O12 is an attractive anode material for 3D solid state thin film batteries TFB to power upcoming autonomous sensor systems. Herein, Li4Ti5O12 thin films fabricated by atomic layer deposition ALD are electrochemically evaluated for the first time. The developed ALD process with a growth per cycle of 0.6 cycle amp; 8722;1 at 300 C enables high quality and dense spinel films with superior adhesion after annealing. The short lithium ion diffusion pathways of the nanostructured 30 nm films result in excellent electrochemical properties. Planar films reveal 98 of the theoretical capacity with 588 mAh cm amp; 8722;3 at 1 C. Substrate dependent film texture is identified as a key tuning parameter for exceptional C rate performance. The highly parallel grains of a strong out of plane 111 texture allow capacities of 278 mAh cm amp; 8722;3 at extreme rates of 200 C. Outstanding cycle performance is demonstrated, resulting in 97.9 capacity retention of the initial 366 mAh cm amp; 8722;3 after 1000 cycles at 100 C. Compared to other deposition techniques, the superior performance of ALD Li4Ti5O12 is a breakthrough towards scalable high power 3D TFB

Formation of highly conformal spinel lithium titanate thin films based on a novel three-step atomic layer deposition process

Lithium titanate (Li4Ti5O12) (LTO) has several promising properties with regard to energy storage. The most important is its low volume expansion during lithium (de-) intercalation enabling the material for complex three-dimensional battery anode designs. To employ this property at a small scale, e.g., for micro batteries (<100 nm active layer thickness), a highly conformal deposition process like atomic layer deposition (ALD) is needed. However, the ALD of lithium containing layers is quite ambitious. Particularly, thermally activated deposition of lithium containing layers with water as a coreactant is challenging due to the high reactivity and hygroscopic nature of many lithium compounds, e.g., lithium hydroxide. That is why a novel ALD process regime has been developed, which allows the deposition of highly conformal and single phase LTO layers with excellent step coverage and composition. The process uses two metalorganic precursors: one acting as lithium and another as a titanium source. In contrast to usual ALD processes, these two precursors are subsequently applied. The reactive pulse with water is applied after the two metal precursor pulses. In this work, this novel ALD process sequence has been introduced and successfully demonstrated on 200 mm wafers using standard industrial ALD equipment. The layers are transformed to single phase Li4Ti5O12 by rapid thermal processing as proven by crystal phase analysis. Elemental composition has been analyzed by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy (XPS). Results show that the amounts of contaminants like carbon and chlorine are below the detection limits of XPS. Also, a uniform element distribution and stoichiometry in good agreement with theoretical expectations for lithium titanate could be shown