Separators - Technology review: Ceramic based separators for secondary batteries

Abstract

Abstract. Besides a continuous increase of the worldwide use of electricity, the electric energy storage technology market is a growing sector. At the latest since the German energy transition ("Energiewende") was announced, technological solutions for the storage of renewable energy have been intensively studied. Storage technologies in various forms are commercially available. A widespread technology is the electrochemical cell. Here the cost per kWh, e. g. determined by energy density, production process and cycle life, is of main interest. Commonly, an electrochemical cell consists of an anode and a cathode that are separated by an ion permeable or ion conductive membranethe separator -as one of the main components. Many applications use polymeric separators whose pores are filled with liquid electrolyte, providing high power densities. However, problems arise from different failure mechanisms during cell operation, which can affect the integrity and functionality of these separators. In the case of excessive heating or mechanical damage, the polymeric separators become an incalculable security risk. Furthermore, the growth of metallic dendrites between the electrodes leads to unwanted short circuits. In order to minimize these risks, temperature stable and non-flammable ceramic particles can be added, forming so-called composite separators. Full ceramic separators, in turn, are currently commercially used only for high-temperature operation systems, due to their comparably low ion conductivity at room temperature. However, as security and lifetime demands increase, these materials turn into focus also for future room temperature applications. Hence, growing research effort is being spent on the improvement of the ion conductivity of these ceramic solid electrolyte materials, acting as separator and electrolyte at the same time. Starting with a short overview of available separator technologies and the separator market, this review focuses on ceramic-based separators. Two prominent examples, the lithium-ion and sodium-sulfur battery, are described to show the current stage of development. New routes are presented as promising technologies for safe and long-life electrochemical storage cells.

Lithium‐Ion Battery Separators for Ionic‐Liquid Electrolytes: A Review

“…Ceramic‐Filled Separators : Ceramic‐filled membranes are separators that contain ceramic particles . Ceramic‐filled membranes have increased wettability due to hydrophilic surface properties enhancing the electrolyte affinity . Ceramics are nonmetallic inorganic materials that have high thermal, chemical, and dimensional stability .…”

“…Ceramic‐filled membranes have increased wettability due to hydrophilic surface properties enhancing the electrolyte affinity . Ceramics are nonmetallic inorganic materials that have high thermal, chemical, and dimensional stability . Therefore, ceramic‐filled separators generally have good thermal stability and thermal conductivity compared to nonfilled polymer‐based separators .…”

“…Ceramics are nonmetallic inorganic materials that have high thermal, chemical, and dimensional stability . Therefore, ceramic‐filled separators generally have good thermal stability and thermal conductivity compared to nonfilled polymer‐based separators . Higher thermal stability and thermal conductivity of the separator, provided by the ceramic particles, can improve cell safety by decreasing the possibility of internal short circuits and hot‐spot formation, as well as improving heat dissipation in the cell …”

“…Polymer separators can be coated with ceramic particles to enhance their safety properties. Coating methods include spraying, casting, dip‐coating or roll coating of the polymer separator in a solution containing suspended ceramic particles along with a binder to ensure the particles bind to the polymer surface . Membranes that contain a ceramic filler have been manufactured with the ceramic particles dispersed in the polymer solution .…”

Identification of solid oxygen‐containing Na‐electrolytes: An assessment based on crystallographic and economic parameters

“…Temperatures of around 300 °C are necessary for normal operation of high‐temperature Na‐S batteries so that high thermal stability is required for the separator . Further favourable properties of ceramic separators/solid electrolytes can be found elsewhere . With regard to reported accidents and the expected strong growth of the separator and solid electrolyte market , such materials are of great importance, in particular to ensure safe battery systems.…”