ok thanks i found the answers
so means the polymer is better
lithium polymer cell
Lithium polymer batteries (Li-Poly or LiPo) are rechargeable batteries which have technologically evolved from lithium ion batteries. Ultimatively the lithium salt electrolyte is not held in an organic solvent, like in the proven lithium ion design, but in a solid polymer composite such as polyacrylonitrile. There are many advantages of this design over the classic lithium ion design. The solid polymer electrolyte is not flammable like the organic solvent that the Li-Ion cell uses. Thus these batteries are less hazardous if mistreated.
Cells sold today as polymer batteries are different from this ultimate design. Different from lithium ion cylindrical or prismatic cells which have a rigid metal case, polymer cells have a flexible, foil-type (polymer laminate) case, but they still contain organic solvent. The main difference between commercial polymer and to lithium ion cells is that in the latter cells, the rigid case presses the electrodes and the separator onto each other, whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.
Since no metal battery cell casing is needed, the battery can be lighter and it can be specifically shaped to fit the device it will power. Because of the denser packaging without the holes between cylindrical cells and the lack of metal casing, the energy density of Li-Poly batteries is over 20% higher than that of a classical Li-Ion battery and approximately three times better than NiCd and NiMH batteries.
The voltage of a Li-Poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-Poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination. During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a charge.
Early in its development, lithium polymer technology had problems with internal resistance. Other challenges include longer charge times and slower maximum discharge rates compared to more mature technologies. Li-Po batteries typically require more than an hour for a full charge. Recent design improvements have increased maximum discharge currents from two times the cell capacity to 15 or even 20 times it. In March 2005 Toshiba announced a new design offering a much faster (about 1-3 minutes) rate of charge. These cells have yet to reach the market but should have a dramatic effect on the power tool and electric vehicle industries, and a major effect on consumer electronics; especially electrically-powered model aeroplanes.
When compared to the lithium ion battery, Li-Poly had a greater life cycle degradation rate. However, in recent years, manufacturers are declaring upwards of 500 charge-discharge cycles before the capacity drops to 80% (see Sanyo). Another variant of Li-Poly cells, the "thin film rechargeable lithium battery" has been shown to provide more than 10,000 cycles.
The lithium in a Li-Poly cell is hazardous and will react violently with water. Cell disposal instructions usually suggest puncturing the cell and immersing it in salt water for several hours.
