From cell phones to electric vehicles, lithium-ion batteries are the power pack of choice. They are capable of keeping large amounts of energy in a small space with relatively little weight, making them an efficient means of saving and delivering electricity. Researchers led by Maksym Kovalenko from the Laboratory of Inorganic Chemistry at ETH Zurich and Empa have developed a battery using tin nanocrystals for the anode that enable twice as much energy to be stored.
In lithium-ion batteries, energy is stored in the form of positively charged lithium atoms found at the anode (minus pole). When electricity is taken out, negatively charged electrons move to plus pole via an external circuit. To balance out the charge, positively charged lithium atoms flow from the plus pole to the minus pole in an electrolyte fluid found inside the battery. In a majority of lithium ion batteries currently on the market, the plus pole is made from oxides of nickel, cobalt, or manganese, and the minus pole is made of graphite. Now, researchers have developed a nanomaterial made of tin crystals for the anode.
Every tin atom can absorb at least four lithium ions. Scientists had to face the challenge of volume with the material, as the crystal becomes three times bigger upon absorption and then shrinks back down after discharging. By taking the tiniest tin crystals and placing them in a porous, permeable, conductive carbon matrix, they were able to created a sponge-like material that is able to suck up a large number ions and release them back again.
“The trick here was to separate the two basic steps in the formation of the crystals — the formation of as small as a crystal nucleus as possible on the one hand and its subsequent growth on the other,” says Kovalenko.
The uniform nanocrystals, carbon, and binding agents allowed the scientists to double the amount of energy they could store in the battery. They found that crystals with a diameter of ten nanometers to be the most efficient. For future prototypes, the researchers will focus on finding the best carbon matrix and binding agents for the electrode, most stable electrolyte liquid for ion movement, and the best materials to reduce production cost. The team is currently collaborating with a Swiss industrial partner to fabricate a battery with a higher storage capacity and longer life than what is presently on the market.
Second photo by Qurren