High‐Temperature Ultrafast Sintering: Exploiting a New Kinetic Region to Fabricate Porous Solid‐State Electrolyte Scaffolds

Abstract

issue has greatly hindered the development of these technologies for broader applications. [5,6] Solid-state electrolytes (SSEs) represent one promising solution to this problem as they offer better safety and potentially higher volumetric energy density. [7][8][9][10][11] A range of SSEs materials have been explored so far, with polymers [12,13] and ceramic Li-ion conductors [14] being the leading contenders. Among them, polymer SSEs show seamless interfacial contact and relatively larger production scale, [15] but suffer from low mechanical strength [16] and poor thermal stability. In addition, the organic backbone of these materials does not fundamentally address the flammability issue and is prone to thermal runaway. In comparison, ceramic Li-ion conductors such as garnet, [17,18] LISICON Li 10 GeP 2 S 12 , [19] and so on exhibit better mechanical strength and Li-ion conductivity, but comes with an expense of processability, poor interfacial contact, and flexibility. [20,21] Despite the high promise and broad research interest, these problems continue to limit the practicality of ceramic SSEs for broader applications. [22,23] It has been shown that integrating ceramic and polymer SSEs together promises a viable route to harvest the merits of the two while neutralizing each other's drawbacks. [6,[24][25][26] Such a "polymer in ceramic" strategy often requires the synthesis of 3D porous ceramic scaffold to form continuous Li-ion transport pathways with polymer SSEs. [27][28][29] On the other hand, the porous ceramic scaffold can also be used to decrease the interfacial resistance between the electrolyte and Li metal anode, [30] conventional intercalation cathode, [31] or conversion cathode such as sulfur. [32,33] To achieve desired porous structure with a pure crystalline phase, conventional sintering methods typically rely on poreforming agent [32] or freeze casting. [29,34,35] In particular, these conventional approaches to sinter porous ceramics can take advantage of prolonged sintering time at relatively low temperatures. In this low-temperature kinetic region, surface diffusion, which has a low activation energy, controls and leads to neck forming (bonding) without densification, yet surface diffusion also promotes grain growth (coarsening). The long sintering time also causes significant Li loss due to its highly volatile nature, which deteriorates the quality of the porous Solid-state batteries (SSBs) promise better safety and potentially higher energy density than the conventional liquid-or gel-based ones. In practice, the implementation of SSBs often necessitates 3D porous scaffolds made by ceramic solid-state electrolytes (SSEs). Herein, a general and facile method to sinter 3D porous scaffolds with a range of ceramic SSEs on various substrates at high temperature in seconds is reported. The high temperature enables rapid reactive sintering toward the desired crystalline phase and expedites the surface diffusion of grains for neck growth; meanwhile, the short sintering duration limits the coarsening, ...

Enabling High‐Voltage “Superconcentrated Ionogel‐in‐Ceramic” Hybrid Electrolyte with Ultrahigh Ionic Conductivity and Single Li+‐Ion Transference Number

“…[ 4 ] The OCEs have been shown to be very promising for the development of SSBs given their advantages of high ionic conductivity (10 −4 –10 −3 S cm −1 at 25 °C), wide electrochemical stability window (>5.0 V vs Li/Li + ), large ion transference number (≈1), high shear modulus (≈60 GPa), elevated thermal stability, nonflammability, good ambient stability, commercial cost‐effectiveness, and desirable chemical stability against Li metal. [ 5 ] Nevertheless, the OCEs have to be densified through high‐temperature treatment, which leads to uncontrollable volatilization of lithium and contamination from crucibles. Moreover, it is very difficult for these brittle and hard ceramics to be machined.…”

Developing Preparation Craft Platform for Solid Electrolytes Containing Volatile Components: Experimental Study of Competition between Lithium Loss and Densification in Li7La3Zr2O12

“…If the densification speed of LLZO is faster than that of Li loss in green bodies, ceramics can reach the final sintering stage without using the mother powder. Hu et al developed a flash sintering method for LLZO ceramic densification in seconds, − which can be realized without any external mother powder or Li source under ultrahigh heating speed and temperatures. However, the conductivity and relative density of the LLZO electrolyte by flash sintering require further optimization, compared to conventional solid-state reactions or hot pressing. − Wen et al provided a non-mother-powder sintering strategy using a small-volume MgO crucible and Pt support to decrease the serious Li loss and Pt loss .…”

CO2 Laser Sintering of Garnet-Type Solid-State Electrolytes

“…At a lab scale, hydraulic pressed LLZTO pellets with a relatively high initial packing density (∼65%) are generally densified via furnace sintering at elevated temperatures; however, LLZTO pellets are restricted to small sample sizes and ultrathick geometries (a centimeter size, hundreds of micrometers thick) in comparison with current ∼20-μm-thick polymer separators in typical LIBs, preventing them from practical large-scale ASSLB applications. ,, In order for the LLZTO SSE to be used in commercialized cells, it must be incorporated in a film configuration. However, only a handful of dense, thin garnet-type SSE films with ionic conductivities equivalent to those found in the highly dense bulk counterparts (∼0.1–1 mS·cm –1 ) have been reported to date, − likely due to the exceptional challenges involved in the synthesis of LLZTO films given their higher surface/volume ratios that lead to a faster Li loss. Tape casting − and spray coating ,, are some of methods that have been used to prepare garnet-type SSE thin films as well as thin ceramic layers (tens of micrometers thick) and are therefore a more attractive industrial approach.…”