Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Sun, Xueliang.

2nd Supervisor

Sham, Tsun-Kong.

Co-Supervisor

Abstract

Li-metal batteries are strongly considered to be one of the most promising candidates for high energy density energy storage devices in our modern society. However, the state-of-the-art Limetal batteries are still limited by several challenges including 1) low energy/power density; 2) Li dendrite growth; 3) low coulombic efficiency, and 4) safety concerns within the liquid electrolyte. This thesis mainly focuses on addressing these challenges by using a 3D printing technique to realize high energy/power density Li-metal batteries.

A self-standing high areal energy density cathode for Li-S battery was developed by the 3D printing method in the first part. The optimized porosity and conductivity of cathode design from macroscale to the nanoscale are beneficial for Li+/e- transport in a thick electrode. This work offers a new strategy to fabricate high sulfur loading cathodes and improve the electrochemical performance of advanced Li-S batteries.

However, Li+ transport is usually poor in thick cathodes, resulting in low capacity output, fast capacity decay, and large overpotential. To tackle the issue of thick sulfur cathodes, a thickness independent electrode structure is proposed in the second part which can transform a thick electrode into a combination of vertically aligned “thin electrodes”.

Apart from the cathode, Li anode also plays an important role in determining the Li-metal batteries performance. Herein, in the third part, a 3D-printed vertically aligned Li anode (3DP-VALi) is shown to efficiently guide Li deposition via a “nucleation within micro-channel walls” process, enabling a high-performance dendrite-free Li anode.

Issues like leakage, flammability, and electrochemical instability of liquid electrolytes have triggered safety issues as well as restrictions on the practical application of Li-metal batteries. Herein, in the fourth part, an ultra-high-energy/power density quasi-solid-state Li-Se battery was realized by combining a 3D-printed carbon nanotube interlayer with a high Se-loading gel polymer electrolyte-filled cathodes.

To achieve a high energy density all-solid-state Li metal battery, a dual vertically aligned electrodes structure with well-controlled microscale features is proposed in the fifth part to promote the development of fast charging all-solid-state Li metal battery.

In summary, these five parts in this thesis provide an important guide to achieve a high energy density Li metal battery by a 3D printing technique

Summary for Lay Audience

Li-metal batteries are concerned as one of the most promising energy storage systems because of their high energy density. However, their practical applications have long been hindered by some challenges, such as huge volume change during cycling, Li dendrite growth caused by uneven Li plating, and safety concern of flammable liquid electrolytes. This thesis is mainly dedicated to solving the challenges in Li-metal batteries and achieving high energy density Limetal batteries, including the cathode and anode part, from the liquid electrolyte to solid-state electrolyte.

At the cathode part, a 3D-printed freeze-dried S/C composite electrode was designed to realize a high energy density and high-power-density Li-S battery. And a high areal capacity was demonstrated by employing the designed cathode. However, Li-S battery still suffers from capacity decay during cycling, especially in high-S loading cathode with thick. Herein, in the second research work, a new strategy to apply 3D printing technique to carry out thickness independent Li-S cathode by converting the thick electrodes into a combination of numerous vertically aligned “thin electrodes” was demonstrated. This work opens a new opportunity for designing Li-S batteries with high sulfur loadings.

Besides the tremendous success made at the cathode part, enabling the stable Li metal is of great importance for high energy density Li-metal batteries. Therefore, in the third research work, we have developed a 3D printed vertically aligned Li anode with well-controlled microscale features for selective “nucleation within micro-channel walls”, which can successfully suppress Li dendrites.

The fourth and fifth research work was the 3D printing applied in quasi-solid-state and solid-state Li-metal batteries. To solve the safety concern of flammable liquid electrolyte, in the fourth part, a high energy density quasi-solid-state Li-Se battery with ultrahigh Se loading of 20 mg cm-2 and areal capacity of 12.99 mA h cm-2 under a high current density of 3 mA cm-2 was developed. Moreover, in the fifth work, a dual-vertically aligned electrode was employed to address the issues of poor Li+ kinetics and dendrite formation in fast charging all-solid-state Li-metal batteries.

In summary, the strategies developed in this thesis provide important guidance to realize high-energy-density Li-metal batteries.

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