For making wind and solar power usable on a grand scale there is a need for an efficient, durable, high-power, rechargeable battery to store large quantities of excess power generated. Conventionally lithium ion batteries are used in most applications.
Lithium ion batteries
The conventional lithium ion batteries have a high energy density so that they can hold a lot of charge for their size, making them great for portable electronics such as laptop computers. But energy density is not very important as for as storage on the power grid is concerned while cost is a greater concern. Some of the components in lithium ion batteries are so expensive that the batteries on a scale for use in the power grid will ever be economical. Also lithium ion battery can handle only about 400 charge/discharge cycles before it deteriorates too much to be of practical use.
Battery electrode
An electrode in an electrochemical cell is referred to as either an anode or a cathode (words that were by Faraday). The anode is the electrode at which electrons leave the cell and oxidation occurs, and the cathode is the electrode at which electrons enter the cell and reduction occurs. Each electrode may become either the anode or the cathode depending on the direction of current through the cell. When the battery is connected to an external load, or device to be powered, the negative electrode supplies a current of electrons that flow through the load and are accepted by the positive electrode. When the external load is removed the reaction ceases. Most batteries fail because of accumulated damage to an electrode's crystal structure.
New electrode
Stanford researchers have used nanoparticles of a copper compound to develop an efficient, durable, inexpensive and high-power battery electrode for making batteries big enough for economical large-scale energy storage on the electrical grid. The battery electrode is made of crystalline hexacyanoferrate nanoparticles of copper.
The batteries constructed using these electrodes could solve the problem of sharp drop-offs in the output of wind and solar systems due to minor changes in weather conditions. The electrode of the developed battery survived 40,000 cycles of charging and discharging, after which it could still be charged to more than 80 percent of its original charge capacity and it is predicted that this electrode may serve a life period of up to 30 years on the electrical grid.
The atomic structure of the crystalline copper of the new electrode has an open framework to allow ions which move en masse either to charge or discharge a battery without damaging the electrode. The right-sized ion turned out to be hydrated potassium is a much better fit compared with other hydrated ions such as sodium and lithium.
Because the ions can move so freely, the electrode's cycle of charging and discharging is extremely fast, which is important because the power output of a battery is proportional to how fast the electrodes are discharged.
The speed of the electrode is further enhanced due to a particles size of 100 atoms of electrode material which makes the ions travel very far into the electrode to react with active sites in a particle to charge the electrode to its maximum capacity, or to get back out during discharge.
The researchers chose to use a water-based electrolyte, which is claimed to be basically free compared to the cost of an organic electrolyte used in lithium ion batteries. They made the battery electric materials from readily available precursors such as iron, copper, carbon and nitrogen which is inexpensive compared with lithium.
Limitation
The limitation of the new electrode is that its chemical properties cause it to be usable only as a high voltage electrode. But the battery is made of two electrodes; a high voltage cathode and a low voltage anode in order to create the voltage difference to produces electricity. The researchers need to find another material to use for the anode before they can build an actual battery.