The status and progress toward solid‐state 3D thin‐film Li‐ion microbatteries is reviewed. Planar thin‐film batteries (TFBs) are commercially available. A major issue with planar TFBs, however, is that the total footprint capacity is limited, as only a relatively small electrode volume is available for energy storage. Coating of the complete battery thin‐film stack, i.e., cathode/solid electrolyte/anode, over a 3D microstructured current collector substrate can provide higher footprint capacity as a result of the surface area enhancement. However, thus far, no 3D TFB with footprint capacity exceeding the limit of ≈250 µAh cm−2 are achieved. The authors provide a status of the individual components: thin‐film cathodes, anodes, and thin‐film solid electrolyte conformally coated over 3D substrates with periodic microstructures. Guidance for designing a 3D TFB with optimum capacity is also provided.

The transition to solid-state Li-ion batteries will enable progress toward energy densities of 1000 W·hour/liter and beyond. Composites of a mesoporous oxide matrix filled with nonvolatile ionic liquid electrolyte fillers have been explored as a solid electrolyte option. However, the simple confinement of electrolyte solutions inside nanometersized pores leads to lower ion conductivity as viscosity increases. Here, we demonstrate that the Li-ion conductivity of nanocomposites consisting of a mesoporous silica monolith with an ionic liquid electrolyte filler can be several times higher than that of the pure ionic liquid electrolyte through the introduction of an interfacial ice layer. Strong adsorption and ordering of the ionic liquid molecules render them immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate mesophase layer results in solvation of the Li + ions for enhanced conduction. The demonstrated principle of ion conduction enhancement can be applied to different ion systems. Mees, P. M. Vereecken, Silica gel solid nanocomposite electrolytes with interfacial conductivity promotion exceeding the bulk Li-ion conductivity of the ionic liquid electrolyte filler. Sci. Adv. 6, eaav3400 (2020).

Ultrathin LiMn2O4 electrode layers with average crystal size of ∼15 nm were fabricated by means of radio frequency sputtering. Cycling behavior and rate performance was evaluated by galvanostatic charge and discharge measurements. The thinnest films show the highest volumetric capacity and best cycling stability, retaining the initial capacity over 70 (dis)charging cycles when manganese dissolution is prevented. The increased stability for film thicknesses below 50 nm allows cycling in both the 4 and 3 V potential regions, resulting in a high volumetric capacity of 1.2 Ah/cm3. It is shown that the thinnest films can be charged to 75% of their full capacity within 18 s (200 C), the best rate performance reported for LiMn2O4. This is explained by the short diffusion lengths inherent to thin films and the absence of phase transformation.

The deposition rate of polycrystalline silicon from a SiH4-H2 mixture is significantly influenced by the addition of ASH3, PH3, and B2H6. At a deposition temperature of 680~ AsH3 causes a decrease by a factor of 7, PH3 causes a decrease by a factor of 2.5, while a two times higher deposition rate is obtained with B2H6 addition. Out of these three dopant hydrides AsH~ and PH3 do not affect the activation energy of the deposition reaction compared to undoped growth (37 kcal/mole). The Arrhenius plot for the deposition of silicon from a B2H6-SiH4 mixture shows two activation energies: 20 kcal/mole at T = 620~176 and 7 kcal/mole below 620~ The experimentally found minimum values of the resistivity of doped polycrystalline silicon can be explained in terms of solid solubility and carrier mobility. At deposition temperatures below 700~ with and without addition of dopants the polycrystalline silicon surface is mirror-like. Significant differences have, however, been observed by electron microscopy. Compared to undoped growth boron was found to lower the etch rate of the polycrystalline silicon film markedly.Increasing interest is being shown in the use of polycrystalline silicon in silicon device technology. The application of polycrystalline silicon films is compatible with silicon device processing where polycrystalline silicon is mainly used as gate material in MOS structures (1) (self-aligned gate).Polycrystalline silicon can be deposited in different ways: by evaporating, by sputtering, and by chemical vapor deposition. Chemical vapor deposition is superior because it permits uniform deposition over oxide steps. To obtain a mirror-like surface, which enables very fine patterns to be etched in it, comparable with those in silicon oxide, the grain size of the polycrystalline silicon film should be as small as possible. DeLuca (2) has found that the grain size of the polycrystalline silicon film decreases with decreasing temperature. However, the deposition rate also decreases with decreasing temperature. At 650~176 an acceptable compromise between growth rate and grain size is realized. In this temperature region most polycrystalline silicon films suitable for high resolution I.C. processing are grown.In the case where polycrystalline silicon is used as the gate material for MOS structures, it may be deposited undoped and subsequently doped by impurity diffusion. In the case where design considerations prohibit high-temperature processing after polycrystalline silicon deposition, doping by codeposition becomes necessary.The present paper reports on the growth of doped polycrystalline silicon films by codeposition of silicon and either arsenic, phosphorus, and boron from the corresponding hydrides using hydrogen as a carrier gas. In particular the temperature dependence of the growth rate was studied. The effects of deposition temperature and dopant concentration on growth rate and resistivity are discussed. ExperimentalThe polycrystaUine silicon films were prepared in an uncooled vertical reactor. The substrates wer...

Ultrathin lithium phosphorus oxynitride glass (LiPON) films with thicknesses down to 15 nm, deposited by reactive sputtering in nitrogen plasma, were found to be electronically insulating. Such ultrathin electrolyte layers could lead to high power outputs and increased battery energy densities. The effects of stoichiometry, film thickness, and substrate material on the ionic conductivity were investigated. As the amount of nitrogen in the layers increased, the activation energy of the ionic conductivity decreased from 0.63 to 0.53 eV, leading to a maximum conductivity of 1 × 10(-6) S/cm. No dependence of the ionic conductivity on the film thickness or substrate material could be established. A detailed analysis of the equivalent circuit model used to fit the impedance data is provided. Polarization measurements were performed to determine the electronic leakage in these ultrathin films. A 15-nm LiPON layer on a TiN substrate showed electronically insulating properties with electronic resistivity values around 10(15) Ω·cm. To our knowledge, this is the thinnest RF-sputtered LiPON layer shown to be electronically insulating while retaining good ionic conductivity.