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Researchers discover new copolymer binder that can extend the life of lithium batteries

It is well known that the charge capacity of lithium batteries in smartphones decreases after more than a year of use, and the life of the phone may be reduced, which indirectly leads to economic losses and pollution. In addition, the short life of lithium batteries also hinders the development of renewable energy recycling and electric vehicle markets. Therefore, scientists have been working hard to find ways to increase the life of lithium batteries.

One of the key reasons why the capacity of lithium batteries decreases over time is the degradation of the widely used graphite anode (i.e., the negative electrode of the battery). The anode and electrolyte (the medium that carries the charge between the positive and negative electrodes of the battery) and the cathode (or the positive electrode of the battery) provide a good environment for the electrochemical reactions of the battery's charge and discharge cycles. However, in order to prevent fission when using graphite, a binder must be added to the graphite. The most widely used binder today is polyvinylidene fluoride (PVDF), but it has disadvantages and is far from an ideal material.

To solve the above problems, a research team at the Hokuriku Advanced Institute of Science and Technology (JAIST) reportedly invented a new binder made of a diimino-naphthoquinone-p-phenylene (BP) copolymer. First, the BP binder provides better adhesion and mechanical stability to the negative electrode than the PVDF binder. This is partly due to the supposed π-π interactions between graphite and the bis-imino-naphthoquinone groups, as well as the excellent adhesion between the copolymer ligands and the battery's copper current collector. Second, the BP copolymer is more conductive than PVD and provides a thinner, less resistive conductive solid electrolyte interface. Third, the BP copolymer does not react easily with the electrolyte, greatly preventing degradation.

As experiments have shown, the BP copolymer can also greatly enhance battery performance. JAIST Professor Noriyoshi Matsumi said: "The half-cell using PVDF as a binder was only 65% of the original capacity after about 500 charge and discharge cycles, while the half-cell using BP copolymer as a binder still showed 95% of the capacity after 1,700 charge and discharge cycles.

The half-cell using BP copolymer showed extremely high and stable coulombic efficiency, which also proves that the battery is long-lasting and durable. Coulombic efficiency refers to the ratio of the battery's discharge capacity to the charge capacity during the same cycle. The research team used electron microscopy to photograph the binder before and after the cycle. The photos show that only small cracks appeared on the BP copolymer, while large cracks appeared on the PVDF binder at less than one-third of the total number of cycles.

Both the experimental and theoretical results of this study will provide new methods for designing durable lithium batteries, which will have far-reaching environmental and economic effects. As Professor Matsumi said: The creation of durable batteries will help develop more reliable and long-lasting products, thereby encouraging consumers to buy expensive battery products such as electric vehicles that can be used for a long time.

Professor Matsumi also added that the development of long-lasting batteries will benefit many people, such as those with heart disease and others who rely on artificial organs. In addition, the general population will benefit from this as the number of daily charging devices such as laptops, tablets and smartphones increases. Other developments in electrode binders are also expected to enable scientists to produce longer-lasting battery products, thereby achieving a greener future.

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