Jul 12, 2019 Pageview：95
First, the lightest metal
Lithium was discovered in 1817 by the student of the Swedish chemist Bezilius, Alfetson, who named it Lithium. By 1950, Nakamoto and Maggien used the method of electrolytic melting of lithium chloride to obtain metal lithium. The industrial lithium production was proposed by Gensa in 1893. Lithium lasted 76 years before it was identified as an element to industrial production. Now LiCl is made by electrolyzing LiCl, which still consumes a lot of electric energy. It consumes up to 6,000 to 70,000 kWh per ton of lithium.
Lithium has served the medical profession primarily as an anti-gout drug for more than 100 years after his birth. The National Aeronautics and Space Administration (NASA) was the first to conduct lithium primary battery research because their analysis showed that lithium batteries can provide the highest voltage in the smallest volume. According to P=UI, lithium has a high energy density, so a lithium battery is an efficient battery.
The battery voltage is closely related to the activity of the negative electrode metal. As a very active alkali metal, the lithium battery can provide a higher voltage. For example, a lithium battery can provide 3V, a 2 lead battery is only 2.1V, and a carbon zinc battery is only 1.5V. Another feature of lithium is "light". The density of lithium is 0.53 g/cm3, which is the lightest of all metals and can be as light as it is in kerosene. As element No. 3, lithium existing in nature consists of two stable isotopes, 6Li and 7Li, so the relative atomic mass of lithium is only 6.9. This means that metal lithium provides more electrons than other reactive metals at the same mass. In addition, lithium has another advantage. The lithium ion has a small ionic radius, so lithium ions move more easily in the electrolyte than other large ions.
Metal lithium has many advantages, but there are still many difficulties to overcome in manufacturing lithium batteries. First, lithium is a very active alkali metal element that reacts with water and oxygen, and it reacts with nitrogen at room temperature. For such a naughty guy, it is very difficult to save it. It will float up in both the water and the kerosene. The chemists finally forced it into the Vaseline oil or liquid paraffin. This results in the storage, use or processing of metallic lithium being much more complicated than other metals, and the environmental requirements are very high. Therefore, lithium batteries have not been used for a long time. With the development of science and technology, the technical obstacles of lithium batteries have been broken one by one. Lithium batteries have gradually entered the stage, and lithium batteries have entered a large-scale practical stage.
Second, the metal lithium battery
In 1958, Harris considered lithium as an alkali metal to react with water and air, and proposed the use of organic electrolytes as electrolytes for lithium metal batteries. According to the relevant working requirements of the battery, the organic electrolyte solvent needs to have three properties, 1 solvent is a polar solvent, the solubility of the lithium salt in the polar solvent is large, and the conductivity of the electrolyte is large; 2 the solvent must be aprotic A polar solvent because the proton-containing solvent readily reacts with lithium; 3 the solvent has a lower melting point and a higher boiling point, so that the electrolyte has the widest possible temperature range. The idea of this concept was immediately recognized by the scientific community and triggered a lot of research and development.
In the development of metal lithium primary batteries, the electrochemical properties of conventional cathode materials such as Ag, Cu, and Ni have not been met, and people have to find new cathode materials. In 1970, Sanyo Corporation of Japan used manganese dioxide as a positive electrode material to create the first commercial lithium battery. In 1973, Panasonic began mass production of a lithium primary battery with a positive electrode active material of a fluorinated carbon material as a positive electrode. In 1976, a lithium iodine primary battery with iodine as its positive electrode was introduced. Then some battery-specific batteries such as lithium-silver-vanadium oxide (Li/Ag2V4O11) batteries have emerged. These batteries are mainly used in implantable cardiac devices. After the 1980s, the cost of lithium mining was greatly reduced, and lithium batteries began to be commercialized.
Early metal lithium batteries were primary batteries that could only be used once and could not be charged. The success of lithium batteries has greatly stimulated the enthusiasm of people to continue to develop rechargeable batteries, and the prelude to the development of lithium secondary batteries has been opened. In 1972, Exxon developed titanium disulfide as a positive electrode material and lithium metal as a negative electrode material to develop the world's first metal lithium secondary battery. This rechargeable lithium battery has excellent performance for deep charge and discharge of 1000 times and no loss of more than 0.05% per cycle.
Lithium secondary battery research has been very deep, but the secondary batteries with metal lithium as the negative electrode have not been put into commercial production so far, because lithium secondary batteries have not solved the safety problem of charging. When the lithium battery is charged, lithium ions are precipitated as electrons in the negative electrode, but the deposition speed of lithium on the electrode is not the same, so the metal lithium does not uniformly cover the surface of the electrode, but is formed during the deposition process. Dendritic crystals these dendritic crystals undergo a charge-discharge cycle, and when the length of the branch is large enough, it can be connected from the positive electrode to the negative electrode, causing a short circuit inside the battery. This may cause a large amount of heat release from the battery, which may cause the battery to ignite or explode. After 1989, most companies stopped developing lithium secondary batteries.
Third, liquid lithium ion battery
In order to solve the dendritic crystals produced during the precipitation of metallic lithium, in 1980, Armand first proposed the concept of RCB. The metal poles are no longer using metallic lithium, but a lithium-based chimera. In the chimera, metallic lithium is not present in the form of crystals, but is present in the interstices between the chimeras in the form of ions and electrons. During charging, the current drives out the lithium ions in the positive electrode fitting, and these lithium ions "swim" through the electrolyte between the positive electrode and the negative electrode into the negative electrode fitting; while discharging, the lithium ions are embedded from the negative electrode the compound "swim" back into the positive electrode assembly through the electrolyte. Therefore, the process of charging and discharging is the process of intercalation and deintercalation of lithium ions. Lithium ions can oscillate at the poles of the battery, so it is also called "Rocking Chair Battery" (abbreviated as RCB).
The first negative-embedded material is what we are familiar with but graphite. As we all know, graphite has a layered structure with a layer spacing of 0.355 nm and a lithium ion of only 0.07 nm, so it is easy to insert into graphite to form a graphite intercalation compound having a composition of C6Li. In 1982, R.R. Agarwal and J.R. Selman of the Illinois Institute of Technology discovered that lithium ions have the property of being embedded in graphite. They found that the process of lithium ion intercalation into graphite is not only fast but also reversible.
The search for the positive electrode embedded material began as early as the lithium secondary battery period. In 1970, M.S. Whittingham discovered that lithium ions can be reversibly embedded in the layered material TiS2, which is suitable for lithium battery anodes, in 1980, American physics professor John Goodenough found a new substance, LiCoO2 which is also a graphite-like layered structure. In 1982, Goodenough discovered the spinel-structured LiMn2O4, which provides a three-dimensional lithium-ion deintercalation channel, while the common cathode material has only two-dimensional diffusion space. In addition, LiMn2O4 has a high decomposition temperature and is much less oxidizing than lithium cobaltate (LiCoO2), so it is safer. In 1996, Goodenough discovered LiFePO4 with an olive tree structure. This material has higher safety, especially high temperature resistance, and its overcharge resistance is far superior to that of traditional lithium ion battery materials.
In 1990, Sony Corporation of Japan took the lead in developing a successful lithium-ion battery. In 1992, the commercial rechargeable lithium cobalt oxide battery was introduced by Sony and renamed the technology "Li-ion". This logo can be found on many mobile phone batteries or laptop batteries. The "lithium battery" mentioned in many electronic products actually refers to a lithium ion battery. Its practicality has greatly reduced the weight and size of portable electronic devices such as mobile phones and notebook computers. The use time is greatly extended. Since the lithium ion battery does not contain heavy metal chromium, it greatly reduces environmental pollution compared with the nickel chromium battery.
At present, the most widely used lithium ion battery uses graphite as a negative electrode, lithium cobaltate as a positive electrode, and an organic solvent containing a lithium salt such as lithium hexafluorophosphate. During discharge, lithium embedded in the graphite negative electrode is oxidized into the electrolyte, and the positive electrode is inserted into the lattice gap of the cobalt oxide to form lithium cobaltate; when charging, lithium is deintercalated from the lithium cobaltate and slipped back into the graphite, so cycle back and forth. Such a battery can work at a voltage of 3.7 volts or more, and the energy density is greatly improved.
Fourth, polymer lithium ion battery
The main structure of a typical battery includes three elements: a positive electrode, a negative electrode, and an electrolyte. The so-called polymer lithium ion battery means that at least one or more of the three main structures use a polymer material as a main battery system. In the polymer lithium ion battery system currently developed, the main reason is that the polymer material mainly replaces the electrolyte solution. The lithium batteries that we use today are definitely divided into lithium-ion batteries (Li-ion) and lithium polymer batteries (Li-Po).
In 1973, Wright et al. found that polyoxyethylene-alkali metal salt complexes have high ionic conductivity, and since then, ion-conducting polymers have received much attention. In 1975, Feullade and Perche discovered that the alkali metal salt complexes of PEO, PAN, PVDF and other polymers have ionic conductivity and are made of PAN and PMMA-based ion-conducting membranes. In 1978, Dr. Armadnd of France predicted that such materials could be used as electrolytes for energy storage batteries, and the idea of solid electrolytes for batteries was proposed. Therefore, the development of polymer electrolytes has been carried out worldwide. The polymer electrolyte originally used in lithium secondary batteries has a complex system formed of PEO and a lithium salt, but the system has not been industrially applied because of its poor electrical conductivity at room temperature. It was later discovered that the addition of a plasticizer to the polymer electrolyte by blending can significantly increase the conductivity of the polymer electrolyte.
In a lithium-ion battery, the positive electrode and the negative electrode must not be in direct contact otherwise a short circuit may occur, causing a series of safety problems. The electrolyte of the polymer lithium ion battery exists in a solid or colloidal state, which can avoid the problem that the electrolyte of the liquid is liable to cause electrolyte leakage and large leakage current. Moreover, the polymer material is strong in plasticity, and can be made into a large-area ultra-thin film to ensure sufficient contact with the electrode. Since the electrolyte is trapped by the network in the polymer and uniformly dispersed in the molecular structure, the safety of the battery is greatly improved. In 1995, Sony Corporation of Japan invented a polymer lithium battery, and the electrolyte was a gel polymer. In 1999, polymer lithium ion batteries were commercialized.
The future trend of lithium ions makes lithium-ion batteries have higher energy density, power density, better cycle performance and reliable safety performance. At present, there are still some safety problems in lithium batteries. For example, some mobile phone manufacturers have poor control over the quality of diaphragm materials or process defects, resulting in partial thinning of the diaphragm, which cannot effectively isolate the positive and negative electrodes, thus causing battery safety problems. Secondly, the lithium battery is prone to short circuit during charging. Although most lithium-ion batteries now have anti-short-circuit protection circuits and explosion-proof lines, in many cases, this protection circuit does not necessarily work under various conditions, and the explosion-proof line can play a limited role.
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