Hi em!
Anh coi sơ sơ trên google, thấy cũng nhiều lắm mà, em coi thử cái này xem, nếu thích thì anh down về cho nhé
Thin film lithium batteries
Jean Louis Souquet, and Michel Duclot
Laboratoire d’Electrochimie et de Physicochimie des Matériaux et des Interfaces (LEPMI) (UMR CNRS, INPG, UIF, No. 5631, ENSEEG, B.P. 75, 38402 Saint Martin d’Hères, France
Available online 21 March 2002.
Abstract
New electrolyte materials, polymers or inorganic glasses, allow the design of flat lithium primary or secondary batteries for miniaturised devices from smart cards to CMOS back up. The so-called “hybrid plastic electrolytes” allow the design of thick film cells (1–3 mm) with a surface capacity of some mA h cm−2. For Li-ion secondary batteries, the number of cycles does not currently exceed 500.
All solid state thin film batteries are manufactured using sputtering and vacuum evaporation techniques. Their thickness and surface capacity are about one order of magnitude lower than for the polymer electrolyte batteries. In spite of metallic Li anodes, they offer a better cyclability and the solid state of all components guaranties no liquid leakage.
- Introduction
Many electronic devices result today in low current and power requirements. It is the case of energy storage associated to solar cells, smart cards, implantable medical devices, intelligent labels, micro-electromechanical systems (MEMS) or CMOS back up [1, 2, 3 and 4].
For all these systems, electrochemical requirements are better expressed by unit surface area. The expected power is in between 102 and 103 μW cm−2 in the temperature range −20 to 80 °C. A capacity of up to 103 μA h cm−2 with an operating voltage range of 2–3 V is required. The number of cycles depends on applications: primary batteries may be sufficient for smart cards whereas applications in aerospace require more than 104 cycles. The battery proximity to microelectronic components imposes the absence of any liquid leakage. The thickness of the battery should not exceed 0.3–3 mm including packaging. The battery surface obviously depends on the power requirement and may vary from 10−2 to 20 cm2.
Nowadays, two kinds of lithium batteries are complementing each other to satisfy these requirements. A first category regroups lithium batteries with polymer films as electrolytes or separators; the second ones, usually denominated as thin film microgenerators, are solid state cells with glassy electrolytes.
- Lithium batteries with polymer film electrolytes
These polymer films can be chosen in between two opposite types.
In the first type, the polymer is only an inactive separator made of polyolefins such as polypropylene (PP) or polyethylene (PE). Its main function is to separate the electrodes and trap the electrolyte consisting in a mixture of organic liquid solvents (ethylene, propylene or cyclic carbonates, etc.) and lithium salts (LiBF4, LiPF6, etc.) [5]. The porous volume of the polymer films ranges between 60% and 80% with pore size of the order of 1 μm. The thickness of this separator currently lies around 100 μm. Its conductivity depends of the pore tortuosity and a loss of one order of magnitude compared with the liquid electrolyte conductivity (10−3 S cm−1) is currently observed.
The second type regroups polymers (POP, POE, etc.) in which lithium salts (LiN(CF3SO3)2, LiCF3SO3, etc.) are dissolved [6]. In these electrolytes, the polymer acts simultaneously as solvent and separator. The ionic displacement involves the local movement of the macromolecular chains. Consequently, the operating temperature is over the glass transition temperature of the polymer. The major remaining difficulty lies in a too low conductivity which does not exceed 10−5 S cm−1 at room temperature and drops dramatically at subambiant temperatures.
In between these two extreme cases are the so-called “hybrid plastic electrolytes” [7, 8, 9, 10 and 11] which are either gels formed by polymers and organic solutions of lithium salts or plasticized polymer electrolytes in which the ionic transport simultaneously occurs in the liquid and polymeric phases.
The major difficulties remaining to solve with these polymer electrolytes are:
• the electrochemical stability (solvent, polymer and anion) versus the electrode materials;
• the low transport number of the Li+ cation (most of the polymer electrolytes, especially in case of the absence of organic liquid solvent, have a lithium transport number lower than 0.5);
• a limited number of cycles (<500) as a consequence of these two electrolytic characteristics [12];
• the electrolyte leakage when organic solvent are involved.
Several primary and secondary flat batteries with polymer films as electrolytes have been commercialised. Most of them use soft aluminium-laminated films as battery case in place of the traditional metal cans. Ten years ago, Mead (USA) has developed a lithium secondary battery using a cross-linked gelled PEO system [13]. A primary lithium battery (Li/LixMn2O4, 0.4 mm thick, capacity 2–4 mA h cm−2) for active smart cards is presently commercialised by Varta (Germany) [14]. A primary lithium polymer battery (Li/LixMnO2, 0.3 mm thick, 25 mA h capacity) was commercialised in 1996 by Yuasa (Japan) and a secondary version (LixC/LixCoO2) is today under development [10]. Using the same electrochemical couples, SANYO has recently developed a 3-mm-thick secondary battery with a cross-linked poly-alkylene oxide gel electrolyte [15]. In 1996, Bellcore (USA) announced the development of a lithium secondary battery (LixC/LixMn2O4) using a P(VDF-HFP) gelled polymer electrolyte [8]. Microporous PVDF membranes prepared by phase inversion with a thickness of about 40 μm and with a porosity close to 70% are presently developed by SAFT-Alcatel (France) [16]. These membranes are to be used in secondary batteries with a total thickness of less than 1 mm including packaging.
…
Thân!