Negative electrode film

Solid lithium-ion batteries are currently mainly manufactured in micro or mini capacity since they are mainly used for microelectronics. Large-capacity solid lithium-ion batteries are not yet in production, and they will not be discussed here. The positive electrode, electrolyte, and negative electrode for microelectronics should be prepared in multilayers. The manufacturing process for micro-lithium-ion batteries includes the preparation of the positive electrode film, the electrolyte film, and the negative electrode film. 

Four negative electrode films are currently known lithium metal, composite oxide, silicon, and alloys. Fithium metal is the most used negative electrode film since its preparation is simple, being carried out by direct evaporation of lithium metal. In this case, the battery should properly be called a microlithium metal rechargeable (secondary) battery. 

In the case of some microelectromechanical systems (MEMSs), a solder reflow step is used for their assembly processes, which requires all electronics to be heated above 250°C. At the moment, lithium metal cannot be used as the negative electrode film since its melting point is only 180°C. From the discussion in Chapters 7 and 8, it follows that carbon-based and non-carbon-based materials can be used as negative electrodes. Similarly, they can also act as negative electrode materials for the solid micro-lithium-ion battery. For example. 

Separator s a physical barrier between the positive and negative electrodes incorporated into most cell designs to prevent electrical shorting. The separator can be a gelled electrolyte or a microporous plastic film or other porous inert material filled with electrolyte. Separators must be permeable to ions and inert in the battery environment. 

The recent development of the convertible oxide materials at Fuji Photo Film Co. will surely cause much more attention to be given to alternative lithium alloy negative electrode materials in the near future from both scientific and technological standpoints. This work has shown that it may pay not only to consider different known materials, but also to think about various strategies that might be used to form attractive materials in situ inside the electrochemical cell. 

In our tests, we used pasted mixtures of carbon-carbon electrode components with KOH solution having a density of 1,26 g em"3. Positive and negative electrodes were pasted onto the conductive polymer film, separated by ionoconductive separator, made out of special paper, pressed between external collectors of nickel-plated copper with pressure of 8 kgf-ern 2. 

CAPABILITIES OF THIN TIN FILMS AS NEGATIVE ELECTRODE ACTIVE MATERIALS FOR LITHIUM-ION BATTERIES... 

The capabilities of thin tin films and tin-based alloys with different metals as active materials for lithium - ion battery negative electrodes are considered. Electrochemical characteristics of such films at different substrates and mechanisms of their functioning are discussed. 

A typical lithium-ion cell consists of a positive electrode composed of a thin layer of powdered metal oxide (e.g., LiCo02) mounted on aluminum foil and a negative electrode formed from a thin layer of powdered graphite, or certain other carbons, mounted on a copper foil. The two electrodes are separated by a porous plastic film soaked typically in LiPFe dissolved in a mixture of organic solvents such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC). In the charge/ discharge process, lithium ions are inserted or extracted from the interstitial space between atomic layers within the active materials. 

However, there are no known SB systems with Mg in aqueous solutions. The Mg anode s irreversibility in aqueous solutions is thought to be due, in part to the existence of monovalent Mg ions during the electrochemical discharge, in part to the selfcorrosion and film formation, and in part caused by other factors (136,140). All attempts to deposit this metal on the negative electrode from aqueous electrolytes have failed. It is claimed that the Mg cell with molten salt electrolyte, LiCl-KCl eut., is reversible (141) it operates at temperatures above the eutectic melting point, i.e. about 400°C. Small amounts of water might decrease the operating temperature. 

Intercalation of Cjq with lithium has been achieved by solid-state electrochemical doping [125]. In this technique, metallic lithium was used as the negative electrode and a polyethylene oxide lithium perchlorate (P(E0)8liCl04) polymer film served as electrolyte. The formation of stoichiometric phases Li Cgg (n = 0.5, 2, 3, 4, and 12) has been observed. 

Separators in lithium ion batteries must separate positive electrodes and negative electrodes to prevent short circuits, and must allow passage of electrolytes or ions. Porous films and nonwoven fabrics of resins are known separators. The lithium ion battery separators are also required to exhibit stable properties at high temperatures such as in charging, and therefore high heat resistance is desired (21). 

Among diverse alloys, amorphous Sn composite oxide (ATCO) reported by Fuji photo film has caused a great deal of renewed interests in Li alloys as an alternative for use in the negative electrode of Li-ion batteries [176,177]. The ATCO provides a gravimetric capacity of >600mAh/g for reversible Li adsorption and release, which corresponds to more than 2200mAh/cm3 in terms of reversible capacity per unit volume, that is, about twice that of the carbon materials. 

It was found in these experiments that corrosion of the negative electrode is less pronounced compared with lithium. This is partly because the alloys are less reactive and partly because a protective surface film is formed on the electrode surface [311,314,315],... 

These requirements hold for the films at both the positive and negative electrode surfaces. Thus, these surface films frequently comprise quite complex mixtures of reaction products and their presence affects the kinetic properties of charge transfer across the interface. It is the deviation of surface film s properties from meeting this set of ideal requirements that is the single most important cause of cell failure in a large fraction of cases. When the decomposition reactions occur, a small amount of active material must also be irreversibly consumed. 

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