energy storage technology
At present, lithium-ion batteries with specific energy from 110 W ∙ h / kg to 240 W ∙ h / kg can be found on the market. Most manufacturers produce batteries with specific energy from 150 W ∙ h / kg to 180 W ∙ h / kg. The optimistic forecast assumes that the annual increase in the specific energy of the battery will be about 50 W ∙ h / kg, and by 2035 will reach ≈ 500 W ∙ h / kg.
Important and the price of the battery. Usually the cost of one kilowatt-hour of the battery is estimated. The average price of a battery with an energy of 1 kWh is (195…250) $ / kWh. It is pl anned that by 2035 the price will fall to $ 100 / kWh. However, is it possible to reduce the cost of the battery, with a tenfold increase in demand by 2035?
Another desire for consumers is to quickly charge the battery. Half of the respondents want the charging time of the electric car battery not to exceed 15 minutes. The second half of the respondents agrees that the charging time of the battery should not exceed 30 minutes. Only 5% of respondents assume that the full charge time of the electric vehicle battery exceeds one hour. Optimists hope that by 2025 the time of the battery charge will be reduced to 10 minutes.
Increased battery safety is associated with replacing the liquid electrolyte with an ionic liquid or solid electrolyte. A detailed scenario of the thermal destruction and ignition of a battery with a liquid electrolyte is discussed in the article: “Materials for lithium-ion battery safety”.
In many countries of the world, studies are under way to create new electrolytes that meet the principles of “green chemistry”. Such electrolytes include ionic liquids with such unique properties as practically zero saturated vapor pressure, thermal stability, non-inflammability, etc.
Fluidic Energy planned to create a new power source with a stored energy density 11 times that of lithium-ion batteries, with a three times lower cost. The key point of development is the use of an ionic liquid as an electrolyte.
Solid electrolytes have gained wide popularity. For example, the development of NEI Corporation for solid electrolytes has shown that their conductivity can be comparable to the conductivity of liquid electrolyte – about 2.5 × 10‾² S / cm.
Toyota and Dyson both believe solid-state batteries could be in final products by 2020, but there’s no guarantee this will happen. As ever with technology, there’s a huge difference between a technology that works on a small scale and one that’s ready for mass-market production.
Solid electrolytes can be divided into three categories:
solid polymer electrolytes (SPE);
Inorganic electrolytes can be crystalline or amorphous (glass), or mixed phases (sitall).
The conductivity of solid electrolytes is (10 … 15) times less than the conductivity of liquid electrolytes, but they have a number of other advantages. A solid electrolyte can eliminate the formation of dendrites by using metallic lithium and obtain high energy of the lithium battery, without the risk of fires or degradation over time.
Most battery companies have patents and proprietary processes in the design and manufacture of solid-state batteries. Make a prediction, when their products will enter the broad market while it is very difficult.
In our opinion, the reason for the slow development of the battery capacity lies in the following.
The main cause of rapid degradation leading to thermal breakdown is the internal short circuit of the battery, which is very difficult to control. The reason may be the growth of dendrites with a high current density of the charge, the accumulation of conductive contaminants in the battery, an external shock, defective separators or poor-quality battery assembly.
Analysis of the causes leading to rapid degradation, a decrease in the specific energy of the battery and its ignition, can not yet be called complete and complete. There are reasons that are not given due attention. The main efforts of researchers are aimed at eliminating the consequences, which lead to already established causes.
Liquid electrolyte can ignite – it is changed to non-flammable – solid electrolyte or ionic liquid. A protective ceramic coating that slows their growth eliminates the growth of conductive dendrites. The separator with a low melting point is changed to a separator with a high melting point.
The reason for the increase in the internal temperature of the battery is its internal resistance. Moreover, the more internal resistance, the faster the battery temperature rises. From 20% to 50% of the internal resistance of the battery is the contact resistance between the metal foil and the active battery electrode. Poor adhesion of the active electrode to the foil further increases the contact resistance. A local increase in temperature at the contact resistance leads to an even greater separation of the active electrode from the foil, and hence an avalanche-like increase in the value of the contact resistance.
Measuring the contact resistance on a long-stored aluminum foil showed that the resistance can reach 8 ohm∙cm². The application of acetylene black can improve the adhesion of the active layer to the foil, but slightly changes the contact resistance. The application of acetylene black can improve the adhesion of the active layer to the foil, but slightly changes the contact resistance.
The situation changes radically, if a dense carbon coating is applied to the metal foil by magnetron sputtering. Vacuum technology allows to completely cleaning the surface of metal foil from dirt and oxide film. The carbon coating on the foil depleted from the oxide layer reduces the contact resistance to 0.3 mΩ ∙ cm² and improves the adhesion of the active electrode to the foil.