With the increasing prominence of energy crisis and environmental pollution, the demand for clean and renewable energy is more and more urgent, and in practical applications, renewable energy such as solar energy, wind energy and hydraulic power needs to be converted into secondary energy such as electricity to be widely used Is used by people.In order to solve the mismatch of space-time distribution of such natural renewable energy and electricity demand, the development of energy storage technology is indispensable.In many energy storage technologies, electrochemical energy storage technology, namely battery The use of battery has attracted more and more attentions.Efficient and scale-adjustable battery energy storage can be integrated into the power system as an energy storage unit to load the grid and improve the reliability of power grid operation And stability, but also can be used in mobile communications, new energy vehicles and other fields, to improve the quality of human life to provide a steady stream of energy support.
Figure 1 The main electrochemical energy storage battery than the energy and mileage for electric vehicles comparison
The development of secondary batteries has gone through from the early lead-acid batteries, to the later nickel-cadmium, nickel-metal hydride batteries, and now has been commercialized secondary lithium-ion batteries and sodium-sulfur batteries for grid energy storage. The cell uses lithium as the energy transport and storage medium. The lithium element is light (lithium metal has a molar mass of 6.94 g / mol, which is the lightest of the solid elements present in nature) and the redox potential is low (Li + / Li relative to the standard The typical redox potential of a hydrogen electrode is -3.04 V, the lowest of all standard redox couples, allowing lithium-ion batteries to achieve higher output voltages and energy densities than other types of cells (Figure 1) Since 1991, Sony introduced the first commercial rechargeable lithium-ion battery, Lithium battery has rapidly spread worldwide, becoming the preferred power supply type for many portable electronic products.In recent years, with the rise of electric vehicles, as well as renewable energy Generation of large-scale energy storage devices urgently needed, lithium battery research heating up again, the development of safe, high-capacity, high power and long-life secondary lithium battery become the focus.
Figure 2 secondary lithium-ion battery and lithium - air battery basic structure and working principle of the show
At present, commercial lithium batteries use graphite as the negative electrode and the positive electrode adopts an oxide material structure capable of inserting / extracting lithium ions, such as LiCoO2. The electrolyte is an organic solution containing lithium salt, and the lithium element exists in the form of ions in the whole battery, So called lithium ion battery (Figure 2 (a)). Lithium-ion battery significantly weakened the advantages of using lithium as the working medium can be considered as a transitional product.In order to further expand the energy density of lithium batteries, the current study:
On the one hand, it is trying to explore ways to inhibit the growth of lithium dendrites, making it possible to use lithium metal as a negative electrode.
On the other hand, it focuses on cathode materials with higher capacity or electrode potential, for example, using elemental sulfur or oxygen as the positive electrode and utilizing the ultra high unitary lithium storage capacity (1672 mA · h per gram of sulfur; 3862 mA · h), the capacity of the battery can be significantly improved, and the lithium batteries thus formed are respectively referred to as lithium-sulfur batteries and lithium-oxygen (air) batteries (Fig. 2 (b)).
In addition to meet the requirements of long-range mileage and high-power charge and discharge, the lithium-ion battery for vehicle use is particularly important for safety.At present, commercially available lithium-ion batteries release a large amount of heat in the event of a short circuit and cause the organic electrolyte to ignite Explosion hazards are clearly notoriously difficult to use.Even the most considered safest Tesla, using sophisticated battery management systems and protective measures, is still in its infancy within a few short years of occurrence. In addition, organic Problems with the electrolyte include:
Electrochemical window is limited, it is difficult to compatible with lithium metal anode and newly developed high-potential cathode material;
Lithium ion is not the only carrier. When the high current passes, the internal resistance of the battery will increase due to the ion concentration gradient (concentration polarization), and the battery performance will decrease.
Limited working temperature (safe working temperature 0 ~ 40 ℃);
Reacts with the negative electrode material to form a Solid Electrolyte Interphase (SEI) layer, resulting in a sustained consumption of two materials, resulting in a decrease in battery capacity.
Solid electrolyte instead of organic electrolyte, is expected to fundamentally solve the above problems, so the formation of lithium batteries called solid-state lithium batteries.This paper first describes the advantages of solid-state lithium batteries, and then solid-state lithium batteries, the key material - the development of solid electrolyte The situation is reviewed, and on this basis, the whole battery structure design, development history and current situation, as well as the current problems still exist.
