Positive electrode materials types

As mentioned above, the typical positive electrode material is LiCo02, and there are typically two types of negative electrode materials, such as coke and graphite. The characteristics of lithium-ion batteries constructed using these electrode materials are discussed below. 

In all primary lithium cells, the negative electrode is made of metallic lithium. Thus, different types of lithium cells differ in the positive electrode material and in the type of electrolyte. A variety of oxidant materials was offered as the active material of the positive electrode. These included different oxides, sulfides, selenides, oxysulfides, oxychlorides, and some other substances perfluorinated carbon and sulfur. However, only a small number of electrochemical systems in the cells actually reached the industrial production stage. The electrochemical systems of the cells produced industrially are given in Table 11.1. This Table also presents the values of open circuit voltage (OCV) of these cells and the theoretical values of their energy density. 

While the development of primary cells with a lithium anode has been crowned by relatively fast success and such cells have filled their secure rank as power sources for portable devices for public and special purposes, the history of development of lithium rechargeable batteries was full of drama. Generally, the chemistry of secondary batteries in aprotic electrolytes is very close to the chemistry of primary ones. The same processes occur under discharge in both types of batteries anodic dissolution of lithium on the negative electrode and cathodic lithium insertion into the crystalline lattice of the positive electrode material. Electrode processes must occur in the reverse direction under charge of the secondary battery with a negative electrode of metallic lithium. Already at the end of the 1970s, positive electrode materials were found, on which cathodic insertion and anodic extraction of lithium occur practically reversibly. Examples of such compounds are titanium and molybdenum disulfides. 

Let us consider an ideal battery of this type. Fig. 37.1. During dischaige, the negative electrode must supply protons to the solid electrolyte in which they are carried to the other electrode by a translocation/vehicular mechanism. Then they must penetrate into the positive electrode material. 

Carbon monofluoride (CFx) is one such fluoride compound that today is used as a positive electrode material in Li batteries for a number of different applications. For example, they are used in certain types of heart failure devices - implantable cardiac resynchronization therapy pacemakers (CRT-P). CRT-P devices can pace the right atrium and right ventricle, but they are also capable of pacing the left ventricle. Pacing three chambers requires more power than a cell can deliver, so a different battery type is needed. Li/CFx cells were developed in response to the increased power required by CRT-P devices. Vagal nerve stimulator devices also use a Li/CFx cells. 

Most positive electrode materials are solids. However, among the first lithium cell types to be developed used an inorganic liquid, SOQ2, as the positive electrode material. 

The design of a zinc-air cell is different than most other battery types. Nearly all cells store aU of the active materials required for the cell to function - negative and positive electrode materials, electrolyte - within a battery case or housing. 

Heat-treated Mn02 is often used as the positive electrode materials for a primary lithium cell. Spinel-type LiMn204 is applied as the positive electrode material in the rechargeable and large-scale lithium-ion cells. 

Lithium metal oxides such as LiCo02 and LiMn204 have also been considered as good candidates for positive electrode materials of hybrid ECs (HECs), which are composed of a battery-type electrode (faradaic reaction) and a capacitor-type electrode (nonfaradic reaction). HECs require both high rate capability and high capacity for positive electrode materials. 

Several types of batteries have been investigated using the SOj-based electrolyte cells (with L1A1C14 as a solute) and metallic lithium for the negative electrode. These use either carbon" or CuCl2 for the positive electrode material. 

A specialized type of Li-ion battery developed for semi-conductor and printed circuit board (PCB) applications are thin-film, solid-state devices. These batteries which employ ceramic negative, solid electrolyte and positive electrode materials, can sustain high temperatures (250°C), and can be fabricated by high volume manufacturing techniques on silicon wafers which are viable as on-chip or on-board power sources for microelectronics. Batteries of this type can be very small, 0.04 cm x 0.04 cm x 2.0 fjm. For microelectronics applications, all components must survive solder re-flow conditions, nominally 250°C in air or nitrogen for 10 minutes. Cells with liquid or polymer electrolytes cannot sustain these conditions because of the volatility or thermal stability of organic components. Further, cells that employ lithium metal also fail as solder re-flow conditions exceed the melting point of lithium (180.5°C). 

Polypyrrole (PPy) is another intensively studied conducting polymer used for energy storage applications. PPy has been synthesized from the polymerization of pyrrole by either electrochemical or chemical oxidation method [16, 19]. Since it is difficult to n-dope PPy, p-type PPy as positive electrode material is the common choice reported in lithium batteries. Typically, the specific energy of PPy falls in the range of 80-390 Wh kg with the open-circuit voltage of 3-4 V. One of ffie main drawbacks of PPy as cathode material is its relatively low theoretical capacity. 

The metal oxides used to make positive electrode materials for lithium-ion batteries commonly include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, vanadium oxide, and various others, such as iron oxides. Positive electrode materials of 5 V and polyanion-type positive electrode materials (so far mainly referring to lithium iron phosphate, LiFeP04) have also been investigated. Among the primary materials for these positive electrode materials, cobalt is the most expensive, followed by nickel and then manganese and vanadium. As a result, the prices of positive electrode materials are basically in line with the market prices of the primary materials. The structures of these positive electrode materials are mainly layered, spinel, and oliven. 

Cycling behavior of 30650-type lithium-ion batteries with nominal capacities of 3 Ah and 10 Wh based on a LiNio7Coo.302 positive electrode material and a mixture of graphite and coke (weight ratio, 4 1) as the negative electrode material The charge and discharge current is 1190 mA. (Adapted from Kida, Y. et al., Electmchim. Acta, 47,2002.)... 

For in situ x-ray diffraction measurements, the basic construction of an electrochemical cell is a cell-type enclosure of an airtight stainless steel body. A beryllium window, which has a good x-ray transmission profile, is fixed on an opening in the cell. The cathode material can be deposited directly on the beryllium window, itself acting as a positive-electrode contact. A glass fiber separator soaked in liquid electrolyte is then positioned in contact with the cathode followed by a metal anode (3). A number of variations and improvements have been introduced to protect the beryllium window, which is subject to corrosion when the high-voltage cathode is in direct contact with it. 

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