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).

The lithium ion battery concept is a promising energy storage system, both for larger automotive systems and smaller mobile devices. The smallest of these, the microbatteries, are commonly based on the all‐solid state concept consisting of thin layers of electroactive materials separated by a solid state electrolyte. The fact that solid state electrolytes are required puts rather severe constraints on the materials in terms of electronic and ionic conductivity, as well as lack of pinholes otherwise leading to self‐discharge. The atomic layer deposition (ALD) technology is especially suitable for realization of such microbatteries for the Li‐ion technology. ALD has an inherent nature to deposit conformal and pinhole free layers on complex geometrical shapes, an architecture most commonly adopted for microbattery designs. The current paper gives an overview of ALD‐type deposition processes of functional battery materials, including cathodes, electrolytes, and anodes with the aim of developing all‐solid‐state batteries. Deposition of Li‐containing materials by the ALD technique appears challenging and the status of current efforts is discussed.

Atomic layer deposition (ALD) is an excellent tool for realisation of uniform coating of cathode materials on highly 3D-nanostructured microbatteries. We have developed an ALD-process for deposition of iron phosphate, FePO 4 , as a cathode material and characterised its electrochemical properties towards a lithium metal anode. Thin films were deposited between 196 and 376 C using the precursor pairs: trimethyl phosphate (TMP, Me 3 PO 4) with both H 2 O and ozone (O 3) as an oxygen source, and Fe(thd) 3 (Hthd ¼ 2,2,6,6-tetramethyl-3,5-heptanedionate) with O 3. The as-deposited films are amorphous and crystallize to trigonal FePO 4 after heat treatment in air at 600 C. The amorphous FePO 4 films were characterised electrochemically proving exceptional cyclability and capacities almost reaching the 100% theoretical value (178 mA h g À1) for 1 hour charge-discharge rates.

Atomic layer deposition (ALD) has been used to prepare nano-structured cathode films for Li-ion batteries of V2O5 from VO(thd)2 and ozone at 215 °C.

A nanocomposite electrolyte composed of a non-volatile ionic liquid, organic Li-salt and porous-inorganic material can be a promising option as a solid electrolyte material. We present a high-rate performance in solid-state lithium metal and Li-ion batteries using a silica-gel solid nanocomposite electrolyte (nano-SCE) made by the sol-gel method with a bis(fluorosulfonyl)imide (FSI)-based ionic liquid. The nano-SCE, composed of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMI-FSI) and Li-FSI confined in the mesoporous silica matrix, exhibits an ionic conductivity of 6.2 mS cm−1 at room temperature. The capacity of the Li-LiFePO4 cell using the EMI-FSI based nano-SCE reaches 150 mAh g−1 at 0.1C and 113 mAh g−1 at 1C, which is higher than that achieved by the other reported batteries that use a similar composite electrolyte. The C-rate performance of the prepared solid batteries is comparable to that of cells with the conventional lithium hexafluorophosphate (LiPF6) electrolyte. Our results show that impregnation of a liquid precursor is an efficient approach for an excellent electrode/electrolyte interface contact in the solid composite electrode as the reaction kinetics at the interface of the active mass and nano-SCE are sufficiently fast, and thus is advantageous compared with the other types of solid electrolytes.