Multivalent batteries, also known as multi-ion or multivalent-metal ion batteries, leverage elements with more than one valence electron to transfer. Commonly explored ions in this domain include Mg2+ (magnesium), Al3+ (aluminum), Ca2+ (calcium), and Zn2+ (zinc). By leveraging the multivalent nature of these ions, these batteries promise to significantly improve energy density.
✔️ Why Multivalent?
Lithium-ion batteries rely on the transfer of single lithium ions (Li+) between the anode and the cathode. In contrast, a multivalent ion can transfer multiple electrons per ion, potentially offering a substantial boost to energy storage capacity. For instance, a magnesium ion (Mg2+) can transfer two electrons, potentially doubling the energy storage capacity compared to lithium-ion batteries. The general design of a multivalent battery is similar to that of any other battery: an anode, a cathode, and an electrolyte connecting them. The key differentiator is the use of multivalent metal ions as charge carriers.
✔️Advantages of Multivalent Batteries
1. Higher Energy Density: Multivalent batteries can store more energy per unit volume than lithium-ion batteries due to the multivalence of their charge carriers.
2. Cost-effectiveness: The elements used in multivalent batteries, such as magnesium and calcium, are abundant and inexpensive compared to lithium.
3. Safety: Multivalent batteries are generally safer than lithium-ion batteries.
✔️ Challenges and Potential Solutions
While multivalent batteries offer several benefits, the path to their widespread adoption faces bigger challenges. The two key obstacles are the sluggish diffusion of multivalent ions through the electrolyte and cathode materials, and the difficulty in finding suitable materials that can intercalate (insert) these ions efficiently and reversibly.
1. Ion Mobility: Multivalent ions are larger and carry more charge, so they face stronger electrostatic interactions when moving through the electrolyte and entering/exiting the cathode lattice. This makes their diffusion slow, thereby limiting the battery's charge/discharge rates.
2. Cathode Materials: The search for suitable cathode materials that can reversibly intercalate multivalent ions is ongoing. Battery developers are investigating complex crystal structures and applying methods to predict and synthesize cathode materials suitable for multivalent batteries.
In light of the challenges, the future of multivalent batteries may seem uncertain, but the potential rewards are driving substantial research and development in this area.