Usage of conductive and flexible polymers in lithium batteries

Abstract

The present invention relates to a production method of a block copolymer (PFPEG) formed by PEG fluorenes and thiophene blocks. The block copolymer (PFPEG) increases the conductivity of the electrolyte active material. The binding of both the active material to itself and to the base material increase the flexibility of the copolymer when used in the electrodes of lithium batteries. The present invention also relates to a usage of the block copolymer (PFPEG) in lithium batteries.

Claims

1. A block copolymer for lithium ion batteries, represented by Formula 1: <Formula 1> ##STR00001## wherein A is selected from the group consisting of phenylene ##STR00002## pyrrole ##STR00003## and thiophene ##STR00004## R.sub.1 and R.sub.2 are each independently (CH.sub.2).sub.nCH.sub.3, and n is an integer selected from 0 to 8; x is 1 to 100; y is 1 to 100; and m is 1 to 100,000.

2. The block copolymer of claim 1, wherein A is phenylene ##STR00005##

3. The block copolymer of claim 1, wherein A is thiophene ##STR00006##

4. The block copolymer of claim 1, wherein the ratio of x:y is 1:2.

5. The block copolymer of claim 1, wherein the molecular weight of the polyethylene glycol (PEG) group is between 500 to 10,000.

6. A method for preparing the block copolymer of claim 1, comprising activating a 9,9-dihexylfluorene-2,7-diboronic acid bis (1,3-propanediol) ester and a monomer selected from a group consisting of ##STR00007## mixing the reactivated ester and monomer, wherein m is 1 to 100,000.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Specific capacity-conversion graphic, FIG. 1 shows a graphic in which charging and discharging have been carried out a 1000 times for an anode lithium ion battery that has been prepared with PEG addition polymer. As the electrode maintains its structural integrity for 1000 cycles the specific capacity has been maintained as an average of 700 mAh/g.

(2) FIG. 2: Schematic representation of the polymer synthesis (a) different monomers that are applicable (b)

DETAILED DESCRIPTION

(3) According to our invention, we have been producing electrodes using conductive and flexible polymers whose electrode active materials have been synthesized. The polymer we synthesized comprises conductive and flexible groups. Polymers used commercially in lithium batteries are however not conductive or flexible. By means of the conductivity we provided with our conductive polymer to our electrode, carbon based materials are not used as conductivity increasing agents in commercially used electrodes. Moreover, by means of the flexibility provided by our polymer the electrode structure preserves its integrity. The reason for this is that, according to the operating mechanism of the battery, while the Li.sup.+ ions move between anode and cathode electrodes, they position themselves into said electrode structures and in such a case the electrode structure swells up. Under the condition that the structure is not sufficiently flexible, then it breaks into pieces and disintegrates due to swelling. The flexible polymers synthesized according to our invention compensate this volumetric swelling. Thus, the active material is able to protect the structure of the battery during swelling and shrinkage in case of charge discharge. This ensures the electrode can withstand long cycles. Furthermore, since the pulverization of the structure is prevented, the capacity of the electrode shall be used significantly. In this case, the life span of the battery and its capacity shall be increased.

(4) In order to solve the problem, a polymer having a conductive and flexible structure has been developed. In this respect, the production of polymers is carried out using the Suzuki Coupling method, in the presence of 9,9-Dihexylfluorene-2,7-diboronic acid bis (1,3-propanediol) ester and 2,5-dibromothiophene (or pyrrole or phenylene) with the catalyst palladium, by mixing at 25-150 C. for 1-8 days (FIG. 1). The polymeric material obtained shall be a block copolymer made of PEG, fluorene and thiophene blocks. The contents of fluorene and thiophene in this block copolymer, play a significant role in the efficient operation of the material and therefore their usage ratios (equivalents) within the reaction are respectively 1:2. The reason for excessive usage of thiophene concentration is that it plays an important role in increasing the conductivity of the structure. Fluorene has been preferred as it presents high conjugation features. The aim of adding PEG groups to the polymer structure is to ensure flexibility to the polymer structure that is to be obtained. The addition of PEG groups has been obtained by addition reaction with acid catalyst using 2,5-dibromothiophene-3-carboxylic acid. The molecular weights of PEG groups vary between 500 to 10000.