Abstract
Lithium-ion batteries are the enabling technology for a variety of modern day devices, including cell phones, laptops and electric vehicles. To answer the energy and voltage demands of future applications, further materials engineering of the battery components is necessary. To that end, metal fluorides could provide interesting new conversion cathode and solid electrolyte materials for future batteries. To be applicable in thin film batteries, metal fluorides should be deposited with a method providing a high level of control over uniformity and conformality on various substrate materials and geometries. Atomic layer deposition (ALD), a method widely used in microelectronics, offers unrivalled film uniformity and conformality, in conjunction with strict control of film composition. In this review, the basics of lithium-ion batteries are shortly introduced, followed by a discussion of metal fluorides as potential lithium-ion battery materials. The basics of ALD are then covered, followed by a review of some conventional lithium-ion battery materials that have been deposited by ALD. Finally, metal fluoride ALD processes reported in the literature are comprehensively reviewed. It is clear that more research on the ALD of fluorides is needed, especially transition metal fluorides, to expand the number of potential battery materials available.
Highlights
The technological advancements that have taken place during the last few decades have created the need to store more energy in ever smaller volumes
This review briefly introduces the basic concept of lithium-ion batteries, some of the materials currently used in these batteries and the use of Atomic layer deposition (ALD) in depositing these materials
Liquid electrolytes are known to give rise to dissolution of the transition metal, decreasing the cathode capacity even further [18]. Thin film methods such as atomic layer deposition can be used to deposit thin layers (e.g., Al2O3 or AlF3) onto cathode materials to protect them from side reactions only half of the lithium-ions in LiCoO2 can be reversibly utilized [19]
Summary
The technological advancements that have taken place during the last few decades have created the need to store more energy in ever smaller volumes. Lithium-ion batteries can store large amounts of energy in small weights and volumes, making them the technology-of-choice for multiple applications. The most widely used lithium-ion battery materials include oxides and phosphates for cathodes [4,5] These materials are intercalation electrodes and have relatively low usable capacities of 100–150 mAh/g. The advantages of ALD, including high film uniformity and excellent conformality over high-aspect-ratio substrates, make it ideal for the deposition of materials for ever-smaller, more complicated batteries: strict conformality is especially important for integrated, all-solid-state batteries, in which the small electrode thin film thicknesses can still produce high energy densities per footprint area when deposited into deep trenches [8]. Fluoride materials are presented as a potential “new” class of battery materials with uses as both electrodes and solid electrolytes for lithium-ion batteries. To motivate further studies on fluoride deposition using ALD, the literature in this area is reviewed
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