Ji-Guang Zhang Wu Xu - Lithium Metal Anodes and Rechargeable Lithium Metal Batteries

Springer International Publishing Switzerland 2017

Ji-Guang Zhang 1 , Wu Xu 1 and Wesley A. Henderson 2

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mAh g1), the lowest negative electrochemical potential (3.040 V versus standard hydrogen electrode), and low density (0.534 g cm3); thus rechargeable Li metal batteries have been investigated extensively during the last 40 years (Whittingham c shows the typical morphology of a Li dendrite and the major problems associated with dendrites and low CE of the Li deposition/stripping processes.

With the urgent need for the next generation rechargeable batteries , such as LiS batteries (Bruce et al. ). These approaches rely on a strong mechanical barrier to prevent Li dendrite penetration through separator, but do not change the fundamental, self-amplifying behavior of the dendrite growth. In other words, these methods do not prevent Li dendrites from growing during long-term cycling, or barely improve the CE of Li deposition/stripping , thus they are not suitable for practical rechargeable Li batteries.

Although some factors that can suppress Li dendrite growth may also lead to high CE of Li cycling, in many experimental studies, they are not always directly correlated with each other. Overall, high CE is a more fundamental criterion required for stable cycling of a Li metal anode and the related Li metal batteries. To have a high CE, side reactions between native or freshly deposited Li and electrolyte have to be minimized. These side reactions are proportional to the chemical and electrochemical activity of native Li when it is in direct contact with the surrounding electrolyte. They are also proportional to the surface area of deposited Li. Therefore, a high CE of Li cycling is usually a direct result of low reactivity between freshly deposited Li and electrolyte as well as a low surface area of the deposited Li. On the one hand, a dendritic Li deposition always has a high surface area. This means that the high CE of Li deposition/stripping is always related to a low surface area Li deposition and a suppressed Li dendrite growth. A stable CE value during long-term cycling also means that an SEI layer formed during Li deposition is relatively stable and very minimal formation of new SEI layers occurs during each cycle. On the other hand, some electrolytes can lead to dendrite-free Li deposition, but exhibit a CE of only less than 80 % (Qian et al. ). This phenomenon often is related to a highly aligned nanoarray of Li structure that has no Li extrusion but still exhibits a high surface area, and freshly deposited Li is highly reactive with the surrounding electrolyte during the cycling process. Therefore, the enhancement of CE is a more fundamental factor controlling long-term, stable cycling of a Li metal anode .

In Chap..