Fabrication of a Dendrite‐Free all Solid‐State Li Metal Battery via Polymer Composite/Garnet/Polymer Composite Layered Electrolyte

Abstract

densities among other known batteries making them highly suitable for application in portable electronics and electric vehicles. [3][4][5][6] The energy density of LIBs can be increased further by using Li metal as anode material as it offers several times higher specific capacity (≈3.8 Ah g −1 ) and the lowest electrochemical potential (−3.04 V vs SHE). However, practical use of Li metal is limited in conventional batteries due to its thermodynamic instability with organic liquid electrolytes, forming dendrites during Li cycling which pose threats of short circuits. Volatility, flammability, and leakage of the liquid electrolytes are additional issues demanding strict attention. [7] Further, the solid electrolyte interphase (SEI) layer formed at the interface cannot withstand mechanical deformation and continuously undergoes formation and dissolution resulting in low Coulombic efficiency (80%-90% for carbonate solvents and 90%-95% for ether solvents) and low cycle life. [8] Most of these issues can be addressed by replacing liquid electrolytes with solid-state electrolytes (SSEs) including organic polymer, or inorganic sulfide or oxide-type. [9][10][11] Among them, oxide SSEs in particular have shown improved electrochemical stability with Li metals. [12] Since the first discovery by Thangadurai et al., [11] garnet-type oxide SSEs (Li 5 La 3 M 2 O 12 (M = Nb, Ta)) have attracted considerable attention due to their highest stability with Li, [12] high Li + transference number (t Li+ ≈ 1), high room temperature ionic conductivities (10 −4 −10 −3 S cm −1 ), and thermal stability at higher temperatures. [12,13] However, with garnet SSEs major challenge lies in realizing intimate Li-SSE contact due to their brittle nature. A poor Li-SSE contact results in high charge-transfer resistance at the interface, which contributes towards high voltage polarizations in the cell. To tackle the issue, various approaches have been adopted such as pressing Li against SSEs at high pressures, [14][15][16] electrolyte surface modifications, [17][18][19] and tuning chemical composition of the SSEs. [20,21] Beside the high interfacial resistance, Li dendrite growth in garnet SSEs is also a cause of concern. In principle garnet SSEs should mechanically block Li dendrites due to their high shear While all-solid-state Li metal batteries based on ceramic solid-electrolytes offer higher energy density and better safety features over their liquid counterparts, critical challenges in their design such as high electrodeelectrolyte interface resistance and formation of Li-dendrites still remain unsolved. To address the issues, an intimate contact between Li and the solid-state electrolyte is necessary. Herein, a flexible and mechanically robust polymer membrane comprising of poly(ethylene oxide), lithium perchlorate, and garnet particles is used as an interlayer between Li metal and garnet ceramic electrolyte. The Li salt enhances the ionic conductivity of the membranes and ensures their flexible nature while garnet particles enhance their mech...

Overcoming the Interfacial Limitations Imposed by the Solid–Solid Interface in Solid‐State Batteries Using Ionic Liquid‐Based Interlayers

“…In this context the role of ILE is very important in homogenizing the Li flux through the interface, resulting in the suppression of Li dendritic growth as it was also demonstrated adopting other interface modification techniques. [ 13,22,41 ]…”

“…LLZO with nominal composition Li 6.5 La 2.5 Ba 0.5 ZrNbO 12 was prepared by the solid state reaction method. [ 22 ] In a typical synthesis, stoichiometric amounts of La 2 O 3 (99.99%, Alfa Aesar, pre‐heated at 900 °C for 12 h), Ba(NO 3 ) 2 (99%, Alfa Aesar), ZrO 2 (99%, Alfa Aesar), Nb 2 O 5 (99.5%, Alfa Aesar), and LiNO 3 (99%, Alfa Aesar, 10 wt% extra to make up for the Li loss during high temperature sintering), were properly milled in 2‐propanol with planetary ball mill (Pulverisette, Fritsch, Germany) at 200 rpm for 6 h. The metal salts were decomposed by heating the powder mixture at 700 °C for 6 h in air. The obtained powder was ball‐milled again to ensure homogenous mixing and then uniaxially pressed into pellets using a hydraulic press (Atlas manual hydraulic press, Specac, UK).…”

“…An interesting approach to tackle the issue of high interface resistance is to introduce ion conducting polymeric layers, gels and/or liquids as wetting agents at the interfaces. [ 21–25 ] In such designs, the Li ion conducting polymer or liquid fills the voids at the interface that ensures intimate electrode–electrolyte contact while the SE acts as a separator as well as single ion transfer medium (t Li + ≈ 1). Use of liquid ion conductors may prove more efficient, especially on the cathode side since liquids can penetrate through the pores of the composite electrode hence accessing a greater cathode surface area and providing interfacial paths for ionic transport at the interfaces.…”

Status and prospect of garnet/polymer solid composite electrolytes for all-solid-state lithium batteries

“…To solve these above-mentioned issues, especially for lithium dendrite growth and poor interfacial contact with electrodes, introducing interfacial layer has been considered as an effective strategy [16,111] . Inspired by the pioneer work of Goodenough's group on using a polymer/ceramic membrane/polymer sandwich electrolyte to construct an all-solid-state battery that can deliver a superb long term electrochemical stability and a high coulombic efficiency [112] , some LLZO-based/PEO layered SCEs, including "PEO/LLZO-based ceramics" bilayer electrolyte [113] , "PEO/LLZO-based ceramics/PEO" sandwich electrolyte [114] , "PEO-LLZO composite layer/LLZO/PEO-LLZO composite layer" sandwich electrolyte [115] and "PEO-LLZO composite thin layer/PEO-LLZO composite layer/PEO-LLZO composite thin layer" sandwich electrolyte (PEO-LLZO composite thin layer is"ceramic-in-polymers" and PEO-LLZO composite layer is "polymer-in-ceramics") [116] , have been developed. Within these layered SCEs, PEO polymer shows three significant roles: 1) PEO serving as a buffer layer to tolerate volume expansion of the electrode during cycling and thus maintain better contact with the electrolyte and electrodes; 2) PEO acting as a wetting layer to increase the contact area with electrodes and decrease interfacial impedance and 3) PEO as a buffer layer to suppress lithium dendrite growth due to its better mechanical strength and it can prevent the direct contact between Li metal anode and LLZO-based ceramics.…”

“…PEO filling with LLZO-based ceramics serving as the buffer layers to further improve the electrochemical performance and interfacial contact as well as suppress lithium dendrite growth have also been reported very recently. [115] . After detail investigation on the composite electrolytes from "ceramic-in-polymer" (CIP) to "polymer-in-ceramic" (PIC) with different sizes of garnet particles for dendrite suppression effect, Sun's group constructed a sandwich-type composite electrolyte (SCE) with hierarchical garnet particles (a PIC-5 μm interlayer sandwiched between two CIP-200 nm thin layers, where PIC-5 μm is a PEO-based composite electrolyte with 80 vol% 5 μm LLZTO and CIP-200 nm is PEO-based composite electrolyte with 20 vol% 200 nm LLZTO) in 2019, as shown in Fig.…”