In recent years, lithium-ion batteries have become better at supplying energy but the current generation of batteries never reaches its highest energy potential. Researchers have developed a new electrolyte design for lithium-ion batteries that improves anode capacity by more than five times compared to traditional methods. The self-healing, protective layer in the battery significantly slows down the electrolyte and silicon anode degradation process, which could extend the lifespan of next-generation lithium-ion batteries.
A battery stores chemical energy and converts it into electrical energy. Batteries have three parts: an anode (-), a cathode (+), and the electrolyte. An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, through which current leaves an electrical device.
The electrolyte keeps the electrons from going straight from the anode to the cathode within the battery. In order to create better batteries, one can increase the capacity of the anode and the cathode but the electrolyte has to be compatible between them. Lithium-ion batteries generally use graphite anodes, which have a capacity of about 370 milliamp hours (mAh) per gram. But anodes made of silicon can offer about 1,500 to 2,800 mAh per gram, or at least four times as much capacity.
Silicon particle anodes, as opposed to traditional graphite anodes, provide excellent alternatives but they also degrade much faster. Unlike graphite, silicon expands and contracts during a battery’s operation. As the silicon nanoparticles within the anode get larger, they often crack the protective layer — called the solid electrolyte interphase — that surrounds the anode.
The solid electrolyte interphase forms naturally when anode particles make direct contact with the electrolyte. The resulting barrier prevents further reactions from occurring and separates the anode from the electrolyte. But when this protective layer becomes damaged, the newly exposed anode particles will react continuously with electrolyte until it runs out.
Instead of an elastic barrier, the researchers designed a rigid barrier that doesn’t break apart, even when the silicon nanoparticles expand. They developed a lithium-ion battery with an electrolyte that formed a rigid lithium-fluoride solid electrolyte interphase (SEI), when electrolyte interacts with the silicon anode particles and substantially reduced electrolyte degradation. The ceramic SEI has a low affinity to the lithiated silicon particles, so the lithiated silicon can relocate at the interface during volume change without damaging the SEI.
The battery design demonstrated a coulombic (the basic unit of electric charge) efficiency of 99.9%, which means that only 0.1 percent of the energy was lost to electrolyte degradation each cycle. This is a significant improvement over conventional designs for lithium-ion batteries with silicon anodes, which have a 99.5% efficiency. While seemingly small, this difference translates to a cycle life more than five times longer.
The battery’s higher capacity allowed the electrode to be markedly thinner, which made the charging time much faster and the battery itself much lighter. In addition, the battery could handle colder temperatures better than normal batteries.