(Keynote) Lithium-Metal Anodes for Rechargeable Batteries: A Historical Perspective of Performance and Safety

Abstract

The first rechargeable Lithium battery used a Li-Al alloy anode and a TiS2-cathode, however, was never commercialized due to its limited cycle life (1). Lithium metal anodes were first commercially used by Moli Energy of Canada in a Li-MoS2 secondary battery with a liquid organic electrolyte (2). After a cycle life of about 300 cycles was demonstrated in cylindrical cells, production was started in the mid-1980ties. The cells were connected serially to larger batteries with an early version of a Battery Management System (BMS) to power cell phones and laptops. Later, the MoS2 cathode was replaced by a MnO2 based chemistry. About one million cells were produced. The products were recalled in 1989 due to battery fires caused most likely by internal shorts due to the formation of Li-dendrites (3). Seven catastrophic field failures were reported. These events could never be duplicated in the laboratory due to the Li-dendrites observed not being able to sustain a high short circuit current. A year later, Sony introduced the first Li-Ion product and no other Li-metal rechargeable battery with a liquid electrolyte was introduced to the market in significant numbers since then.The development of Li-batteries with solid electrolytes began at about the same time. In the late 1970ties, polyethylene oxide (PEO) hosting a Li-salt was proposed as an alternative to Li-ion conducting solids that were a subject of research already for some time (4). Its drawback compared to liquid electrolytes is the insufficient conductivity at room temperature which requires these batteries to be operated at about 80°C. The first commercial product was a power back-up battery for telecom systems produced by the Canadian company Avestor. Due to fires caused by the batteries, the company had to shut down in 2006. After improvements were made to the PEO based system, the French company Bolloré launched its “Blue Car” in 2011. The cells of these batteries use a Li-metal anode and an LFP cathode.Some of the learnings of the early effort of Moli Energy are still relevant today. Examples for this are the dependence of the cycled Li-metal anode morphology on charge and discharge rates, and other factors such as the pressure exerted on the anode. In turn, the morphology will determine cycle life and the risk of internal shorts due to dendrite formation (5). There were also some significant differences of the early cells compared to the efforts of most researchers today. The cells were built in the charged state with the lithium supplied by a Li-metal foil anode without a substrate like a copper foil. This allowed for a sufficiently large excess of Li to compensate for loss of active Li during cycling, however, it reduced the energy density. It was a manufacturing challenge both from the handling and safety point of view. Building the cell in the charged state also meant that the jelly roll as wound would be at its maximum volume enabling a rigid cylindrical cell.