Stanford team enhances ionic conductivity of solid electrolyte by 3 orders of magnitude; potential for high-energy Li-ion batteries
Stanford researchers led by Professor Yi Cui have used ceramic nanowire fillers to enhance the ionic conductivity of polymer-based solid electrolyte by three orders of magnitude. The ceramic-nanowire filled composite polymer electrolyte also shows an enlarged electrochemical stability window.
Solid-state electrolytes could provide substantial improvements to safety and electrochemical stability in next-generation high-energy Li-ion batteries when compared with conventional liquid electrolytes. However, the low mobility of lithium ions in solid electrolytes has limited their practical application. The Stanford researchers suggest that their discovery, described in the ACS journal Nano Letters, paves the way for the design of solid ion electrolytes with superior performance.
… because of their low ionic conductivities at room temperature (which is below their glass transition temperatures) and poor electrochemical stability, solid polymer electrolytes have not been widely used in commercial lithium-ion batteries.
To address these concerns, previous approaches including cross-linking, using diblock copolymer, or adding plasticizers have been investigated. Unfortunately, these modifications diminish performance by loss of ionic conductivity and compatibility with lithium electrodes, and by deterioration of mechanical properties and flame resistivity. In contrast, dispersing ceramic particles in polymer matrix increases ionic conductivity effectively, meanwhile improving electrochemical stability and mechanical strength. The addition of these ceramic particle fillers is believed to hinder the polymer crystallization or to contribute highly conductive interface layers between polymer and ceramic.
The ceramic fillers are generally divided into two categories: inactive fillers that are not involved in lithium ion conduction process (e.g., Al2O3 SiO2) and active ones that participate in lithium ion transport (e.g., Li3N and Li1.3Al0.3Ti1.7(PO4)3
Nanoscale ceramic fillers have large specific surface area and can enhance the ionic conductivity drastically. Most research has emphasized ceramic nanoparticles, whereas little attention has been given to one-dimensional ceramic fillers. Here we explore nanowire fillers and demonstrate significant improvement of ionic conductivity and electrochemical stability.—Liu et al.
The Stanford team fabricated Li0.33La0.557TiO3 (LLTO) nanowires and dispersed them into PAN-LiClO4 polymer without any other additive in concentrations ranging from 5−20 wt %.
They investigated the ionic conductivities of their solid electrolytes via AC impedance spectroscopy measurements with two stainless steel blocking electrodes.
The composite electrolyte with 15 wt % LLTO nanowires displayed the highest conductivity of 2.4 × 10−4 S cm−1 at room temperature—about three orders of magnitude higher than that of PAN-LiClO4 without fillers (2.1 × 10−7 S cm−1).
The researchers attributed the results to the fast ion transport on the surfaces of ceramic nanowires acting as a conductive network in the polymer matrix.
Our work opens the door for novel developments of one-dimensional Li+-conducting ceramic materials in solid electrolytes for lithium-ion batteries.—Liu et al.
Wei Liu, Nian Liu, Jie Sun, Po-Chun Hsu, Yuzhang Li, Hyun-Wook Lee, and Yi Cui (2015) “Ionic Conductivity Enhancement of Polymer Electrolytes with Ceramic Nanowire Fillers,” Nano Letters doi: 10.1021/acs.nanolett.5b00600