Powder Aerosol Deposition as a Method to Produce Garnet‐Type Solid Ceramic Electrolytes: A Study on Electrochemical Film Properties and Industrial Applications

Abstract

Lithium metal batteries with solid-state electrolytes (SSEs) are promising as electrochemical storage devices for future stationary or mobile applications due to their potentially high specific energy density and increased safety compared with lithium-ion batteries with a liquid electrolyte. [1,2] Different types of polymer and ceramic solid electrolytes have recently been investigated regarding their chemical and electrochemical stability as well as their temperature-dependent ionic conductivity and processability. [3,4] One of the most promising ceramic electrolytes to meet all these requirements is Li 7 La 3 Zr 2 O 12 (LLZO) in the cubic garnet crystal structure. It shows a high thermodynamic and kinetic electrochemical stability to lithium metal electrodes, [5,6] combined with a high ionic transfer number close to 1 and a high ionic conductivity of up to 10 À3 S cm À1 at room temperature that makes it favorable over other electrolytes. [6] Usually, the cubic phase is stabilized by doping with Al 3þ or/and Ta 5þ . This also increases the conductivity and reduces the necessary sintering temperatures, yet also leads to a wide variety in reported compositions of Al y Li 7À3yÀz La 3 Zr 2Àz Ta z O 12 . [7,8] Although the production of sintered bulk samples produced by solid-state reaction with a high electrolyte thickness of several hundred micrometers allows remarkable current densities of up to 6 mA cm À2 at 60 C with high solid electrolyte conductivities of up to 10 À3 S cm À1 at room temperature, a commercial industrial large-scale production with high throughput rates in combination with moisture-free processing is challenging. [9][10][11] Ideally, the thickness of the electrolyte should be in the range of 5-20 μm to reduce the risk of short circuits on the one hand but, on the other hand, provide a low electrolyte mass for high cell energy densities. [12] Although much research has been conducted, the thickness range for LLZO films significantly below 50 μm could only rarely been realized yet due to the nonavailability of suitable ceramic production technologies. [13] Sintering of tape-casted ceramic electrolytes is an often reported method to produce tapes below 0.5 mm. [14][15][16][17][18][19][20][21][22][23][24] However, high sintering temperatures >1000 C in combination with dwell times of several hours lead to high investment and operating costs. Furthermore, an exact temperature control is necessary to achieve thin planar ceramic plates without deformation. [25][26][27] Alternative fabrication methods like metal organic chemical vapor deposition (MO-CVD), [28,29] pulsed laser deposition (PLD), [17,[30][31][32][33][34][35][36][37][38] radio frequency (RF) sputtering, [39][40][41][42][43][44][45] and atomic layer deposition (ALD) [46] have been investigated to produce films in a nanometer scale. However, all these coating techniques

Posttreatment of powder aerosol deposited oxide ceramic films by high power LED

“…In addition, the coating materials do not exhibit thermally induced phase transformations. Owing to the high coating rates of up to 2 μm min −1 , the industrial application of the technology, which has been under development since 1984, is becoming increasingly interesting 5,6 . Applications range from classic insulating protective films to functional films for sensor or photovoltaic applications to solid electrolytes for fuel cells or batteries 7,8 …”

“…Although a film formation at RT has distinct advantages, the Room Temperature Impact Consolidation (RTIC) of the particles leads to atomic‐scale lattice deformation, causes mechanical film stress, and reduces the charge carrier mobility and therefore lowers the electrical conductivity of functional films within the lattice 9,10 . Furthermore, the activation energy for charge carrier transport is increased in the as‐deposited state 5 . And due to the deposition method also the magnetic properties of functional PAD films can be reduced compared to sintered bulk samples 11 .…”

“…Owing to the high coating rates of up to 2 μm min −1 , the industrial application of the technology, which has been under development since 1984, is becoming increasingly interesting. 5,6 Applications range from classic insulating protective films to functional films for sensor or photovoltaic applications to solid electrolytes for fuel cells or batteries. 7,8 Although a film formation at RT has distinct advantages, the Room Temperature Impact Consolidation (RTIC) of the particles leads to atomic-scale lattice deformation, causes mechanical film stress, and reduces the charge carrier mobility and therefore lowers the electrical conductivity of functional films within the lattice.…”

“…9,10 Furthermore, the activation energy for charge carrier transport is increased in the as-deposited state. 5 And due to the deposition method also the magnetic properties of functional PAD films can be reduced compared to sintered bulk samples. 11 The nm-sized particles and pores can additionally influence the optical appearance of the films.…”

Making powder aerosol deposition accessible for small amounts: A novel and modular approach to produce dense ceramic films

“…An additional film densification emerges by subsequently impacting particles that consolidate the previously formed film. Already realized electrochemical applications are photocatalytic ceramics 11–17 like TiO 2 , GaN–ZnO, and BiVO 4 , as well as energy storage and conversion devices like fuel cells, 18–22 thermoelectric generators, 23,24 and batteries 25–32 . Furthermore, a variety of sensors was published using powder aerosol deposited functional films 33–38 .…”