A ceramic solid-state electrolyte of lithium aluminum titanium phosphate with the composition of Li[Formula: see text]Al[Formula: see text]Ti[Formula: see text](PO[Formula: see text] (LATP) was synthesized by a sol–gel method using a pre-dissolved Ti-source. The annealed LATP powders were subsequently processed in a binder-free dry forming method and sintered under air for the pellet preparation. Phase purity, density, microstructure as well as ionic conductivity of the specimen were characterized. The highest density (2.77[Formula: see text][Formula: see text] with an ionic conductivity of [Formula: see text] (at 30[Formula: see text]C) was reached at a sintering temperature of 1100[Formula: see text]C. Conductivity of LATP ceramic electrolyte is believed to be significantly affected by both, the AlPO4 secondary phase content and the ceramic electrolyte microstructure. It has been found that with increasing sintering temperature, the secondary-phase content of AlPO4 increased. For sintering temperatures above 1000[Formula: see text]C, the secondary phase has only a minor impact, and the ionic conductivity is predominantly determined by the microstructure of the pellet, i.e. the correlation between density, porosity and particle size. In that respect, it has been demonstrated, that the conductivity increases with increasing particle size in this temperature range and density.
Over the last two decades, several classes of highly ion-conductive SSEs have been developed which reach or surpass current liquid-state electrolyte conductivity. [5,6] Yet, no ASSB paying in on the above promises has been developed to date. This is mainly due to mechanochemical, chemical, and electrochemical stability issues and interfacial processes that have severely compromised any proposed cell's lifetime. [7][8][9][10][11] While many SSE material inherent (mechano-)chemical processing issues seem amenable to modern engineering approaches, [12][13][14][15][16][17][18][19] the situation is less bright regarding the control of interfacial chemical and electrochemical stability (especially when featuring a LMA), as well as ionic and electronic transport quantities across these interfaces. A hitherto missing deep understanding of the structural, chemical, and physical properties of the buried solid-solid interfaces inside ASSBs at the atomic level is required to overcome these performance limiting interfacial issues.The most studied interfacial properties so far are contact stability and dendrite nucleation and growth. [20][21][22] Both issues are accentuated for LMA/SSE interfaces. In a first approximation, interfacial stability can be traced back to the Dendrite formation and growth remains a major obstacle toward highperformance all solid-state batteries using Li metal anodes. The ceramic Li (1+x) Al (x) Ti (2−x) (PO 4 ) 3 (LATP) solid-state electrolyte shows a higher than expected stability against electrochemical decomposition despite a bulk electronic conductivity that exceeds a recently postulated threshold for dendrite-free operation. Here, transmission electron microscopy, atom probe tomography, and first-principles based simulations are combined to establish atomistic structural models of glass-amorphous LATP grain boundaries. These models reveal a nanometer-thin complexion layer that encapsulates the crystalline grains. The distinct composition of this complexion constitutes a sizable electronic impedance. Rather than fulfilling macroscopic bulk measures of ionic and electronic conduction, LATP might thus gain the capability to suppress dendrite nucleation by sufficient local separation of charge carriers at the nanoscale.
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