Lithium has a wide range of applications in our lives, most notably in the lithium batteries used in our indispensable mobile phones and computers. Therefore, we often hear terms like lithium battery, lithium metal battery, etc. Are they the same thing? If not, what is the relationship between them?
First, both lithium batteries and lithium metal batteries are types of lithium batteries. As the name suggests, lithium batteries primarily function by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li+ ions repeatedly insert and extract between the two electrodes, accompanied by the insertion and extraction of an equivalent number of electrons from the lithium ions. Graphite is typically used as the negative electrode (first generation), although silicon-carbon negative electrodes are now also used (second generation). Furthermore, lithium batteries have always been rechargeable batteries (secondary batteries).
Working principle of lithium batteries
Lithium is the lightest and most negatively charged metal in the periodic table, making it the ideal choice for the negative electrode. A lithium metal battery is a battery that uses metallic lithium as the negative electrode. However, the charging and discharging process of a lithium metal battery also involves the migration of Li+ ions in the electrolyte, so strictly speaking, a lithium metal battery is a special type of lithium battery. However, in scientific papers, it has become a common practice to refer to non-lithium metal lithium batteries when discussing lithium batteries; a lithium metal battery, specifically, is a battery that uses lithium metal as the electrode.
With this understanding, the difference between the two becomes clear: in lithium batteries, lithium exists only in the +1 valence form of Li+, and no electrons are gained or lost during charging and discharging, so it does not change from Li+ to elemental lithium; while in lithium metal batteries, lithium undergoes a corresponding valence change during charging and discharging.
When lithium metal batteries were first proposed in 1912, they were indeed primary batteries (i.e., non-rechargeable batteries), and lithium metal had very high reactivity, so they gradually disappeared and were replaced by lithium batteries. However, after a century of development, current technology can effectively achieve the dissolution and deposition of lithium metal during charging and discharging. Therefore, most lithium metal batteries reported in current research papers are secondary batteries, i.e., rechargeable batteries, such as the currently popular lithium-sulfur batteries, which use lithium metal.
Lithium-sulfur batteries
To clarify the relationship between memory batteries and lithium batteries, they are not the same type of battery. The memory effect refers to the phenomenon where a battery seems to remember the user's daily charging and discharging patterns and amplitudes, making it difficult to change these patterns over time and preventing significant charging or discharging. This is because older batteries used nickel-cadmium (NiCd) batteries, where the negative electrode was sintered, resulting in coarser cadmium grains. If NiCd batteries were recharged before being fully discharged, the cadmium grains tended to clump together, forming a secondary discharge plateau during discharge. The battery would store this plateau and use it as the endpoint for the next cycle. Lithium batteries, however, do not exhibit this effect, so users can use them with confidence.
