**Contents**


## **About the Special Issue Editors**

**Jian Liu** is an Assistant Professor at the University of British Columbia (UBC) Okanagan campus, Canada. Dr. Liu received his Ph.D. in materials science in 2013 from the University of Western Ontario (Canada), and worked as a NSERC Postdoctoral Fellow at Lawrence Berkeley National Laboratory and Pacific Northwest National Laboratory (USA) prior to joining UBC in January 2017. Dr. Liu is leading the Advanced Battery Facility at UBC (http://nesc.ok.ubc.ca/), and his current research interests focus on advanced nanofabrication techniques, materials design for Li-ion batteries and beyond, and interfacial control and understanding in energy storage systems. Dr. Liu has published over 70 research papers in high-quality peer-reviewed journals, such as *Nature Communication*, *Nature Energy*, *Advanced Materials*, *Nano Letters*, etc. Dr. Liu is the recipient of many prestigious awards, including the NSERC PDF Award, PNNL Alternated-Sponsored PDF, Mitacs Elevate PDF, and UBC Emerging Professor Award.

**Dongping Lu** is a materials scientist and the team leader of the Battery Materials Research team in the Battery Materials and Systems group at Pacific Northwest National Laboratory (PNNL). Dr. Lu's research interest is material and electrolyte development for energy storage as well as in-depth mechanism analysis through advanced in-situ/ex-situ techniques. Currently, he is focusing on the development of high energy lithium-sulfur and solid batteries including new materials, fundamental understanding, and pouch cell design and demonstration. He received his Ph.D. in Physical Chemistry (Electrochemistry) at Xiamen University, China in 2011. Dr. Lu has more than 40 papers published in peer-reviewed professional journals and holds 6 granted and pending U.S. Patents.

**Xiaolei Wang** is a tenure-track assistant professor of chemical engineering at the University of Alberta (UofA) with expertise in advanced materials, nanotechnology, and clean energy technologies. His research themes centre upon the design, development, and application of novel nanostructured materials for energy-related technologies including lithium-ion batteries, sodium (and other alkaline)-ion batteries, lithium-sulfur (Li-S) batteries, aqueous batteries, and electrocatalytic systems such as metal-air batteries, water electrolyzers, and systems for electrochemical CO2 reduction. Before joining UofA, he worked as a tenure-track assistant professor at Concordia University from 2017 to 2019, and postdoctoral fellow researcher at the University of Waterloo from 2014 to 2017. Dr. Wang received his Ph.D. in Chemical and Biomolecular Engineering at the University of California, Los Angeles (UCLA, 2013), M.Sc. in Chemical Engineering at Tianjin University (TJU, 2007), and B.Sc. in Polymer Chemical Engineering at Dalian University of Technology (DUT, 2004). Dr. Wang builds upon the knowledge from the fundamental studies and understanding of mechanisms by correlating the electrochemical performance of clean energy technologies with materials' morphologies and microstructures, aiming to develop next-generation high-performance clean energy technologies for practical applications. He has published more than 50 articles in peer-reviewed journals and received more than 3800 citations with an h-index of 31 (May 2020). His work is recognized by numerous awards, including NSERC Discovery Accelerator (2018), Petro-Canada Young Investigator Award (2018) and Concordia University Research Chair-Young Scholar (2019).

## **Preface to "Nanomaterials and Nanofabrication for Electrochemical Energy Storage"**

Electrochemical energy storage technologies play key roles for storing electricity harvested from renewable energy resources of an intermittent nature, such as solar and wind, and for utilizing electricity for a range of applications, such as electric vehicles and flights, wearable electronics, and medical implants. Several electrochemical systems, such as rechargeable batteries and supercapacitors, have shown grea<sup>t</sup> potential for these emerging applications. In these systems, nanostructured materials have been widely used for improving electrochemical performance, and for studying electrochemical reaction mechanisms due to their unique chemical and physical properties. For these applications, it is essential to design and synthesize novel multiscale nanomaterials with optimized structure and properties by using nanofabrication techniques.

The papers collected in this Special Issue include original research from controlled synthesis of various nanomaterials (porous carbon, graphene, solid electrolyte, thin film, one-dimensional nanowires and nanotubes); advanced characterizations; and applications in Li-ion batteries, supercapacitors, and Zn-ion batteries. The Guest Editors are thankful to all the authors who contributed their excellent works to this Special Issue. We hope researchers in the field will benefit from the results published herein for their future work.

> **Jian Liu, Dongping Lu, Xiaolei Wang** *Special Issue Editors*

## *Article* **Spark Plasma Sintering of Lithium Aluminum Germanium Phosphate Solid Electrolyte and Its Electrochemical Properties**

#### **Hongzheng Zhu, Anil Prasad, Somi Doja, Lukas Bichler and Jian Liu \***

School of Engineering, Faculty of Applied Science, The University of British Columbia, Kelowna, BC V1V 1V7, Canada

**\*** Correspondence: Jian.liu@ubc.ca

Received: 14 July 2019; Accepted: 26 July 2019; Published: 29 July 2019

**Abstract:** Sodium superionic conductor (NASICON)-type lithium aluminum germanium phosphate (LAGP) has attracted increasing attention as a solid electrolyte for all-solid-state lithium-ion batteries (ASSLIBs), due to the good ionic conductivity and highly stable interface with Li metal. However, it still remains challenging to achieve high density and good ionic conductivity in LAGP pellets by using conventional sintering methods, because they required high temperatures (>800 ◦C) and long sintering time (>6 h), which could cause the loss of lithium, the formation of impurity phases, and thus the reduction of ionic conductivity. Herein, we report the utilization of a spark plasma sintering (SPS) method to synthesize LAGP pellets with a density of 3.477 g cm<sup>−</sup>3, a relative high density up to 97.6%, and a good ionic conductivity of 3.29 × 10−<sup>4</sup> S cm<sup>−</sup>1. In contrast to the dry-pressing process followed with high-temperature annealing, the optimized SPS process only required a low operating temperature of 650 ◦C and short sintering time of 10 min. Despite the least energy and short time consumption, the SPS approach could still achieve LAGP pellets with high density, little voids and cracks, intimate grain–grain boundary, and high ionic conductivity. These advantages sugges<sup>t</sup> the grea<sup>t</sup> potential of SPS as a fabrication technique for preparing solid electrolytes and composite electrodes used in ASSLIBs.

**Keywords:** spark plasma sintering; NASICON-type; ionic conductivity; solid electrolyte; solid–solid interface; grain-boundary resistance
