Rogier Adrianus Henrica Niessen

3D negative electrode stacks for integrated all-solid-state lithium-ion microbatteries

The deposition feasibility and electrochemical evaluation of highly structured negative electrode stacks for 3D-integrated batteries is demonstrated. The stacks comprise a TiN thin film, serving as both current collector and Li-barrier layer, covered by a polycrystalline Si (poly-Si) thin film as electrode material. In comparison with planar films, these poly-Si films present a storage capacity increase of about 5× for the highest pore aspect ratio electrodes. The step coverage of poly-Si can be considerably improved by growing TiN and poly-Si into wide trenches. This results in much smoother poly-Si films and significantly improved step coverage. Further optimization of the trench dimensions should result in poly-Si films with a Li-storage capacity increase of more than one order of magnitude with respect to planar films.

Tin Nitride Thin Films as Negative Electrode Material for Lithium-Ion Solid-State Batteries

eICG/AIME (UMR 5253 CNRS), Universite Montpellier II, 34095 Montpellier Cedex 5, France Tin nitride thin films have been reported as promising negative electrode materials for lithium-ion solid-state microbatteries. However, the reaction mechanism of this material has not been thoroughly investigated in the literature. To that purpose, a detailed electrochemical investigation of radio-frequency-sputtered tin nitride electrodes of two compositions 1:1 and 3:4 is presented for several layer thicknesses. The as-prepared thin films have been characterized by Rutherford backscattering spectrometry, inductively coupled plasma optical emission spectrometry, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical results point out that the conversion mechanism of tin nitride most probably differs from the conversion mechanism usually observed for other oxide and nitride conversion electrode materials. The electrochemical data show that more than 6 Li per Sn atom can be reversibly exchanged by this material, whereas only about 4 are expected. Moreover, the electrochemical performance of the material is discussed, such as electrode cycle life, and a method for improving the cycle life is presented. Finally, thicker films have been characterized by Mossbauer spectroscopy. This technique opens a new route toward

Low-Pressure Chemical Vapor Deposition of LiCoO2 Thin Films: A Systematic Investigation of the Deposition Parameters

The feasibility of volatile precursor low-pressure chemical vapor deposition (LPCVD) for the production of LiCoO2 cathodes for all solid-state microbatteries was examined. To test this feasibility, and gain insight into the deposition behavior, the influence of the deposition parameters on the properties of LPCVD grown thin-film LiCoO2 cathodes was systematically investigated. The deposition temperature, concentration of the various reactants, and duration of thin-film growth were varied. The resulting LiCoO2 layers were subjected to X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, Rutherford backscattering spectroscopy, and electrochemical analyses. Stoichiometry of the films could be controlled by varying the precursor flows. Samples deposited at high temperatures with the optimum stoichiometry showed a high crystallinity and a high electrochemical activity; a storage capacity corresponding to a reversible Li-content around the theoretical value of 0.55 per Co was reached, and a good cycling stability was obtained when using this electrode in combination with a solid-state electrolyte.

Low Pressure Chemical Vapor Deposition as a Tool for Deposition of Thin Film Battery Materials

Low Pressure Chemical Vapor Deposition was utilized for the deposition of LiCoO2 cathode materials for all-solid-state thin-film micro-batteries. To obtain insight in the deposition process, the most important process parameters were optimized for the deposition of crystalline electrode films on planar substrates. Also the electrochemical activity of the obtained LiCoO2 films was demonstrated.

Towards High Energy Density 3D-integrated Lithium-ion Micro-batteries

To investigate the feasibility of a 3D integrated all-solid-state micro-battery, the deposition of several battery materials was investigated. Deposition techniques where used that are in principle able to deposit step conformally in 3D structures: ALD was used to create a conductive Pt current collector, and LPCVD was applied for the deposition of poly-silicon anodes and LiCoO2 cathodes. The layers, initially deposited on planar substrates, showed the expected physical and electrochemical behavior and are in principle suitable for solid state micro-batteries.