The use of a new polymer based on boron nitride can expand the scope of application of capacitors as batteries

While oil and gas companies spend a huge amount of energy and resources on exploring and developing new deposits of fossil fuels, scientists are working on another side of the “energy issue” : the storage and delivery of electricity in extreme conditions. Today, rechargeable batteries dominate the power supply market, but they have an alternative — capacitors that have several advantages over batteries: lightweight, fast charge-discharge cycles, do not lose capacity over time.

To ensure correct operation, when creating a capacitor, it is necessary to use dielectric materials that behave, in fact, as insulators, and provide charge storage. Polymeric dielectrics have a higher efficiency compared with classical materials and can operate in more intense electric fields without breakdowns, which ensures greater reliability of the product.

Now the main disadvantage of modern capacitors is their inability to operate at high temperatures, which does not meet the requirements of the scope of their possible application (extreme conditions). However, the developed composite polymer does not have these disadvantages and has a wider range of uses than previously used materials. The material was obtained by scientists by combining traditional polymer particles with hexagonal boron nitride nanosheets.

The new material (called BCB / BNNS) can be successfully used as a dielectric that can more effectively prevent current leakage and has a stable dielectric constant . The material consists of benzene-cyclobutane, combined with boron nitride nanosheets. Boron nitride used by scientists is similar in structure to graphene sheets one atom thick. The resulting material has excellent properties compared to previously available.

However, researchers are not pioneers. The properties of hexagonal boron nitride as a dielectric were previously known. For example, in 2010, following a joint study of scientists from universities in Houston, Tokyo and Krasnoyarsk, a paper was published in which boron nitride was considered in conjunction with graphene as an alternative to silicon in microelectronics.
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To test the dielectric properties, a team of scientists compared the polymer they obtained with other, best of the existing dielectrics on the market today. The first test for BCB / BNNS was the dielectric constant test at an ac frequency of 10 ⁴ Hz and temperatures up to 300 ° C.


Graph of dielectric constant (for vacuum = 1) materials at different temperatures.

As can be seen on the graph, unlike other materials, the dielectric properties of BCB / BNNS remain almost unchanged (a change in ε _r - relative dielectric constant at 300 ° C is only 1.7% versus 8% for the best dielectric used now). The tests were carried out with the use of direct current, during which scientists obtained the same results.

When using a dielectric as an insulating material, it is important to eliminate energy loss. For BCB / BNNS, the scattering coefficient does not change with increasing ambient temperature. But the new polymer is not perfect: scattering losses increase from 0.09% to 0.13% as the temperature rises from 25 to 300 ° C. Only one material has similar characteristics, when all others lose much more charge with increasing temperature.


Graph of the change in the scattering coefficient with increasing temperature.

The researchers also tested the new material in the charge-discharge cycle of a capacitor and measured the current density during discharge.


Current density during discharge at 200 ° C


The efficiency of the charge-discharge cycle at 200 ° C

The obtained results can be considered excellent, since for polymer dielectrics it is extremely important to hold the charge at high temperatures. With increasing leakage current with increasing temperature, the efficiency of the charge-discharge cycle decreases and heat is generated inside the capacitor itself, which reduces its parameters and service life.

Most of the capacitor failures are due to its overheating and the failure of the entire structure (an explosion and many familiar “swelling” of the capacitor). In some cases, an increase in the temperature of the structure leads to a so-called thermal breakdown. Despite the presence of effective dielectrics, many of them have poor thermal conductivity, which leads to the accumulation of heat inside the capacitor, which, in turn, increases the risk of thermal breakdown. The new material has a coefficient of thermal conductivity in the range from 300 to 2000 W / (m · K).


Thermal drawing of various materials during operation in comparison with BCB / BNNS

BCB / BNNS polymer has a coefficient of thermal conductivity from 300 to 2000 W / (m · K). Such a large range of values ​​of the coefficient of thermal conductivity tells us that this polymer can be used, among other things, as a radiator material as a passive cooling of elements in electronics.

Potentially, BCB / BNNS can also be used in the flexible electronics of the future, as it does not lose or change its properties under mechanical action (bending, twisting, etc.), including under mechanical action at high temperatures (up to 250 ° C)

Previously, another group of scientists from Rice University considered boron nitride and as an anticorrosive material that was proposed to be sprayed by chemical vapor-phase deposition with a layer several atoms thick, which protected materials from oxidation at temperatures up to 1100 ° C.

via ArsTechnica