Performance lithium polymer batteries

However, some of the basic problems of polypyrrole and of the other heterocyclic polymers act to limit the performance of the lithium/polymer battery, and thus its wide applicability. These are essentially slow kinetics, self-discharge and low energy content. 

With the use of sohd to gelatinous, polymeric electrolyte layers that ensure electrical separation of the electrodes and the unity of the cell components combined with good conductivity for lithium ions, it is not necessary to employ hquid electrolytes in lithium batteries. This simplifies the production of lithium polymer batteries, which are also safer in operation because the electrolyte is polymeric, not liquid. This battery cell structure facilitates production of thin foil batteries, a favorable form for use in portable devices. The expected performance data correspond to what is obtained with other lithium ion systems. 

It is clear from the limited amount of development work performed over the past 10 years that the lithium polymer battery represents an exciting prospect for a wide range of applications. 

Arie et al. [116] investigated the electrochemical characteristics of phosphorus-and boron-doped silicon thin-film (n-type and p-type silicon) anodes integrated with a solid polymer electrolyte in lithium-polymer batteries. The doped silicon electrodes showed enhanced discharge capacity and coulombic efficiency over the un-doped silicon electrode, and the phosphorus-doped, n-type silicon electrode showed the most stable cyclic performance after 40 cycles with a reversible specific capacity of about 2,500 mAh/g. The improved electrochemical performance of the doped silicon electrode was mainly due to enhancement of its electrical and lithium-ion conductivities and stable SEI layer formation on the surface of the electrode. In the case of the un-doped silicon electrode, an unstable surface layer formed on the electrode surface, and the interfacial impedance was relatively high, resulting in high electrode polarization and poor cycling performance. 

Initially, lithium polymer battery electrolytes were in the form of a dry sohd polymer electrolyte but it was found that performance could be improved by introducing gelled electrolyte into the separator system. Described by some as a gehonic electrolyte which is not a genuine polymer, these critics maintain that the batteries should be described as being plastic hthium ion and not hthium polymer. 

Choi I, Ahn H, Park MJ (2011) Enhanced performance in lithium-polymer batteries using surface-functionalized Si nanoparticle anodes and self-assembled block copolymer electrolytes. Macromolecules 44 7327-7334... 

The polymer component in these batteries fulfills the function of a medium for ionic transport and a separator. The polymers are polyethers, PEO, or PPO. However, the lithium salts, dissolved in these polymers, have 100-fold lower conductivity than that of a lithium salt dissolved in water. The low conductivity below 70 °C, the reactivity of the interface with the lithium metal electrode, and the issues related to mechanical properties and electrochemical stability need to be resolved before the lithium polymer battery has acceptable performance. The use of inorganic composite membranes, described in a subsequent section, has been shown to result in improved ionic conductivity. 

These polymer electrol5rtes were exploited in the late 1990s for the fabrication of large-sized, laminated battery modules based on cells formed by a lithium foil anode and a vanadium oxide cathode, developed jointly by Hydro Quebec in Canada and 3M company in the United States [7,8]. The battery module had very good performance in terms of energy density (155 Wh kg ) and cycle life (600 cycles at 80% depth of discharge (DOD)), and it was proposed as a power source for EVs, a very futuristic concept back in 1996. However, despite this and other successful demonstration projects, the lithium polymer battery project was abandoned and only very recently reconsidered for use in an EV produced in France [9]. 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

The solid polymer electrolyte approach provides enhanced safety, but the poor ambient temperature conductivity excludes their use for battery applications. which require good ambient temperature performance. In contrast, the liquid lithium-ion technology provides better performance over a wider temperature range, but electrolyte leakage remains a constant risk. Midway between the solid polymer electrolyte and the liquid electrolyte is the hybrid polymer electrolyte concept leading to the so-called gel polymer lithium-ion batteries. Gel electrolyte is a two-component system, viz., a polymer matrix... 

Because of the importance of high-performance secondary batteries, the techniques of the secondary lithium batteries are still making rapid progresses. Lithium polymer secondary batteries, having gel-polymer electrolytes, are advantageous in that the rigid metal container is not essential. Thus, all-plastic thin lithium secondary batteries are now available. 

In modem commercial lithium-ion batteries, a variety of graphite powder and fibers, as well as carbon black, can be found as conductive additive in the positive electrode. Due to the variety of different battery formulations and chemistries which are applied, so far no standardization of materials has occurred. Every individual active electrode material and electrode formulation imposes special requirements on the conductive additive for an optimum battery performance. In addition, varying battery manufacturing processes implement differences in the electrode formulations. In this context, it is noteworthy that electrodes of lithium-ion batteries with a gelled or polymer electrolyte require the use of carbon black to attach the electrolyte to the active electrode materials.49-54 In the following, the characteristic material and battery-related properties of graphite, carbon black, and other specific carbon conductive additives are described. 

As mentioned above, a coin type Li polymer battery has high performance. In particular, the PMMA gel electrolyte is very stable toward lithium anodes. 

Carbon powder mixed with polymeric binder (PVdF, PTFE) has been widely used as anode material for lithium ion batteries and as the electrode material for EDLC with liquid electrolyte solutions. When such composite electrodes composed of carbon powder and polymer binder were used in all-solid-state EDLC, the performance was not good enough because of poor electrical contact between the electrode s active mass and the electrolyte. By having the electrolyte inside the composite electrode, the contact between the active mass in the electrode and the electrolyte can be considerably improved and hence the capacitance can... 

Liu, Y.T., Zhu, X.D., Duan, Z.Q., Xie, X.M., 2013c. Flexible and robust MoS2-graphene hybrid paper cross-linked by a polymer ligand a high-performance anode material for thin film lithium-ion batteries. Chem. Commun. 49,10305-10307. 

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